Faculty Profiles - YAMAMOTO Masayoshi

Papers - YAMAMOTO Masayoshi

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Novel Vertical Shunt Resistor: Integration and Optimization in Power Modules Reviewed International coauthorship International journal

Choi, S; Warnakulasooriya, T; Choi, J; Yonezawa, Y; Imaoka, J; Yamamoto, M

IEEE TRANSACTIONS ON POWER ELECTRONICS Vol. 40 ( 1 ) page： 46 - 50 2025.1

Authorship：Last author Language：English Publisher：IEEE Transactions on Power Electronics

This paper proposes a novel vertical shunt resistor and its packaging method into power modules. The proposed shunt resistor has significantly lower equivalent series inductance and thermal resistance compared to lateral counterparts. It provides a higher maximum operating temperature and power rating using a NiCr-based resistor alloy. Integrating the shunt resistor into power modules does not compromise the size, layout, or manufacturability of the power module. Two types of shuntresistor-integrated power modules were prototyped, and guidelines to reduce variation of effective resistance and achieve a low temperature coefficient of resistance were provided.

DOI： 10.1109/TPEL.2024.3445388

Improved Packaging of Power Module with Low-Permittivity Material for Low Common-Mode Noise and High Reliability Invited Reviewed International coauthorship

Sihoon Choi, Jiyoon Choi, Thiyu Warnakulasooriya, Jong-Won Shin, Jun Imaoka, and Masayoshi Yamamoto

IEEE transactions on Power Electronics Vol. 39 ( 11 ) page： 14261 - 14270 2024.11

Power Module With Low Common-Mode Noise and High Reliability Reviewed International coauthorship International journal Open Access

Choi, S; Choi, J; Warnakulasooriya, T; Shin, JW; Imaoka, J; Yamamoto, M

IEEE ACCESS Vol. 12 page： 90929 - 90939 2024

Authorship：Last author Language：English Publishing type：Research paper (scientific journal) Publisher：IEEE Access

Silicon carbide devices provide higher switching speed and switching frequency than their silicon counterpart. However, these characteristics generate significant electromagnetic interference such as conducted common-mode (CM) noise. This paper proposes a novel power module to reduce CM noise without compromising size, thermal performance, and reliability of the power module. A specific part of the bottom copper layer of a directed-bonded copper is etched to reduce CM capacitance. Epoxy is used to increase mechanical reliability by supporting ceramic and top copper layers. This supporting epoxy also prevents an encapsulant from leaking into the etched area. Design methodologies for the proposed power module are provided in detail. Conventional and proposed power modules were prototyped and CM noise was experimentally measured with 400-V input, 200-V output, and 50-kHz switching frequency. The CM noise of the proposed power module was reduced by 5 dBμ V. Thermal cycling tests were conducted to confirm the degradation of the proposed power module. Cross-sections of the power modules and measured electrical characteristics verify the reliability of the proposed power module.

DOI： 10.1109/ACCESS.2024.3420393

Voltage-Controlled Variable Inductor for Fixed-Frequency Critical Conduction Mode Operation Reviewed

Choi S., Shin J.W., Imaoka J., Yamamoto M.

IEEE Transactions on Industrial Electronics Vol. 70 ( 6 ) page： 5707 - 5716 2023.6

Authorship：Corresponding author Language：English Publisher：IEEE Transactions on Industrial Electronics

This article proposes a novel voltage-controlled variable inductor (VI) for fixing the switching frequency of dc-dc converters in the critical conduction mode (CRM). It overcomes the limitations of conventional current-controlled VIs such as complex winding structures, difficulties in control, and high sensitivity to temperature. In the proposed voltage-controlled VI, the primary side inductance of a coupled inductor is regulated by an auxiliary voltage source on the secondary side. The auxiliary voltage source is implemented by an auxiliary dc-dc converter, which delivers power to the load in parallel with the main converter. The operating principle of the converter system for employing the proposed VI is presented, and a control loop is designed to fix the switching frequency, considering the small-signal model of the auxiliary converter. The validity of the proposed VI is experimentally verified using a prototype CRM boost converter with an output voltage of 400 V and a maximum power of 400 W. The switching frequency is fixed at 100 kHz and the soft switching of the main converter is maintained regardless of the input voltage and output power.

DOI： 10.1109/TIE.2022.3198235

A simple gate driver design for GaN-based switching devices with improved surge voltage and switching loss at 1 MHz operation Reviewed International coauthorship International journal

Jodo Shota, Iwaki Toshihiro, Uchiyama Kosuke, Islam Md. Zahidul, Kataoka Kensuke, Hayakasa Yuki, Imaoka Jun, Yamamoto Masayoshi, Niitsu Kiichi

JAPANESE JOURNAL OF APPLIED PHYSICS Vol. 60 ( SA ) 2021.1

Current and Voltage Hybrid Source Gate Driver for Maximizing the Switching Capability of SiC MOSFETs Reviewed International journal

Ishido Ryosuke, Okawauchi Yuta, Nakahara Ken, Shirai Shinya, Yamamoto Masayoshi

2020 IEEE WORKSHOP ON WIDE BANDGAP POWER DEVICES AND APPLICATIONS IN ASIA (WIPDA ASIA) 2020

Improved core loss calculation method considering the non-uniform distribution of magnetic flux density in powder cores Reviewed International coauthorship International journal

Ishikura Yuki, Imaoka Jun, Noah Mostafa, Yamamoto Masayoshi

IET POWER ELECTRONICS Vol. 12 ( 6 ) page： 1393 - 1399 2019.5

Bridgeless Power Factor Correction Flyback Rectifier Using a Novel Integrated Transformer Reviewed International journal

Hirasawa, H; Choi, S; Yonezawa, Y; Imaoka, J; Yamamoto, M

ELECTRICAL ENGINEERING IN JAPAN Vol. 218 ( 1 ) 2025.3

Authorship：Last author Language：English Publishing type：Research paper (scientific journal) Publisher：Electrical Engineering in Japan (English translation of Denki Gakkai Ronbunshi)

This study proposes a novel integrated transformer structure with simple circuit configuration and miniaturized magnetic components. In a bridgeless flyback rectifier, two flyback converters operate corresponding to the polarity of the AC input, requiring two transformers. This paper proposes a novel winding structure that realizes zero coupling co-efficient between two sets of windings. This enables the integration of two transformers into a single transformer, preventing their flyback operations from interfering with each other. The integrated transformer has approximately 16% lower volume compared to that of conventional transformers. The proposed integrated transformer was built, evaluated, and verified by designing a 75 W-bridgeless flyback rectifier with 100 kHz switching frequency.

DOI： 10.1002/eej.23485

Bridgeless Power Factor Correction Flyback Rectifier Using a Novel Integrated Transformer Invited Reviewed International coauthorship

H. Hirasawa, S. Choi, Y. Yonezawa, J. Imaoka, M. Yamamoto

ELECTRICAL ENGINEERING IN JAPAN 2025.1

Improved Packaging of Power Module With Low-Permittivity Material for Low Common-Mode Noise and High Reliability Reviewed International coauthorship International journal

Choi, S; Choi, J; Warnakulasooriya, T; Shin, JW; Imaoka, J; Yamamoto, M

IEEE TRANSACTIONS ON POWER ELECTRONICS Vol. 39 ( 11 ) page： 14261 - 14270 2024.11

Authorship：Last author Language：English Publishing type：Research paper (scientific journal) Publisher：IEEE Transactions on Power Electronics

This article proposes a novel power module configuration which replaces a part of the bottom copper layer of a direct-bonded copper by low-permittivity (low-ϵ) epoxy. The proposed power module reduced common-mode (CM) capacitance by 52.5% compared to that of the conventional counterpart. The CM noise measured from line impedance stabilization network was reduced by 4-5 dBμV in steady-state operation. The proposed power module does not sacrifice thermal performance which is proved by simulation and thermal resistance measurement. Thermal cycling tests confirmed high mechanical reliability with no cracks in the solder near the epoxy region. Less mechanical deformation of 5.80 μm was observed compared to the 9.48 μm of the power module that adopts air instead of low-ϵ epoxy.

DOI： 10.1109/TPEL.2024.3438831

Bridgeless Power Factor Correction Flyback Rectifier Using a Novel Integrated Transformer Reviewed

Hirasawa Haruki, Choi Sihoon, Yonezawa Yu, Imaoka Jun, Yamamoto Masayoshi

IEEJ Transactions on Industry Applications Vol. 144 ( 9 ) page： 645 - 653 2024.9

Authorship：Last author Language：Japanese Publishing type：Research paper (scientific journal) Publisher：The Institute of Electrical Engineers of Japan

<p>This study proposes a novel integrated transformer structure with simple circuit configuration and miniaturized magnetic components. In a bridgeless flyback rectifier, two flyback converters operate corresponding to the polarity of the AC input, requiring two transformers. This paper proposes a novel winding structure that realizes zero coupling coefficient between two sets of windings. This enables the integration of two transformers into a single transformer, preventing their flyback operations from interfering with each other. The integrated transformer has approximately 16% lower volume compared to that of conventional transformers. The proposed integrated transformer was built, evaluated, and verified by designing a 75W-bridgeless flyback rectifier with 100kHz switching frequency.</p>

DOI： 10.1541/ieejias.144.645

Analytical Model of Maximum Operating Frequency of Class-D ZVS inverter with Linearized Parasitic Capacitance and Any Duty Ratio Invited Reviewed

Y. Xiong, S. Thilak, Y. Yonezawa, J. Imaoka, and M. Yamamoto

IEICE Tran 2024.8

Technologies for e-Mobility Reviewed

Kato Takashi, Kuroda Hisashi, Matsumoto Kaori, Onaya Jun, Hosono Kenji, Kaneo Hidetsugu, Yamaguchi Koji, Morimoto Masayuki, Yoshimoto Kantaro, Yamamoto Masayoshi, Ota Yutaka

IEEJ Transactions on Industry Applications Vol. 144 ( 7 ) page： 513 - 522 2024.7

Language：Japanese Publishing type：Research paper (other academic) Publisher：The Institute of Electrical Engineers of Japan

<p>To reduce carbon dioxide emissions from mobility, electrified vehicles and mobility have been rapidly increasing in recent years. In this regard, this paper presents the latest trend of technologies supporting mobility electrification, such as electric motors, inverters, and related technologies including vehicle-to-everything, as social systems.</p>

DOI： 10.1541/ieejias.144.513

Efficient Multiphysics Circuit Simulation for Transformer Optimization Using Hybrid Dowell Artificial Neural Network Invited Reviewed International coauthorship

Yu-Hsin Wu, Koichi Shigematsu, Yasumichi Omoto, Yoshihiro Ikushima, Jun Imaoka, Masayoshi Yamamoto

IEEJ Journal of Industry Applications Vol. 13 ( 3 ) page： 327 - 337 2024.4

Design of Coupled Inductor Using Powder Core with Concentrated Air Gap in Multiphase Operation Reviewed International coauthorship International journal

Choi, S; Imaoka, J; Yamamoto, M

IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS Vol. 60 ( 2 ) page： 3449 - 3458 2024.3

Authorship：Last author Language：English Publishing type：Research paper (scientific journal) Publisher：IEEE Transactions on Industry Applications

Powder cores demonstrate soft saturation characteristics which shows gradual decrease of inductance with increase of winding current. Concentrated air gap has been utilized to suppress soft saturation by increasing effective magnetic reluctance and modifying flux cancellation in coupled inductors. However, the saturation characteristics has not been well elaborated due to the difficulty to estimate the varied saturation levels experienced by different segments of the coupled inductor. The proposed design scheme simplifies the magnetic design and presents the least number of turns with optimized air gap length, which satisfies the target inductances. The design method features good accuracy over a wide range of winding current even with large air gap. Five prototype coupled inductors with different air gap length were built to verify the proposed design scheme. They were implemented to an interleaved boost converter to prove the precision of the proposed scheme. The experimental results also revealed that the coupled inductor with the least number of turns and an optimal air gap length presents an efficiency gain of 0.7% at 1 kW and 1.36% at 1.5 kW, respectively, compared to the case with the highest number of turns.

DOI： 10.1109/TIA.2023.3344558

Efficient Multiphysics Circuit Simulation for Transformer Optimization Using Hybrid Dowell Artificial Neural Network Reviewed International journal Open Access

Wu Yu-Hsin, Shigematsu Koichi, Omoto Yasumichi, Ikushima Yoshihiro, Imaoka Jun, Yamamoto Masayoshi

IEEJ Journal of Industry Applications Vol. 13 ( 3 ) page： 327 - 337 2024

Authorship：Last author Language：English Publishing type：Research paper (scientific journal) Publisher：The Institute of Electrical Engineers of Japan

<p>This paper introduces a practical approach for transformer design optimization using a novel hybrid Dowell artificial neural network (HDANN) model. This model is a highly efficient and accurate method to estimate leakage inductance, which is an important parameter that affects the performance of transformers and power converters. The model combines the conventional hybrid Dowell's model, which uses analytical equations, and an artificial neural network, which uses machine learning techniques. It is integrated into an optimization program to optimize the design of a transformer in terms of its size and loss. We investigated the HDANN design scope by testing various transformer conditions. The results provided an in depth understanding of the capabilities and limitations of the HDANN model for transformer design. By understanding the HDANN design scope, the optimization program was implemented in a multidomain circuit simulation, which includes electric and magnetic circuits. This allows a high-speed co-simulation using the optimized transformer design that considers the geometry and material characteristics for the desired circuit specification. It showed that the HDANN offers significant advantages over existing design optimization methods, including improved ease of application, accuracy, and efficiency. The effectiveness of the optimization using the HDANN with the defined geometric parameters was demonstrated by the circuit analysis results of a phase-shift full-bridge converter. Summarizing, the proposed method can potentially revolutionize how transformers are designed and implemented for various applications, leading to increased design reliability as well as reduced power loss and size.</p>

DOI： 10.1541/ieejjia.23009691

Efficient Multi-physics Circuit Simulation with Transformer Optimization Using Hybrid Dowell Artificial Neural Network Reviewed International coauthorship

Y. -H. Wu, K. Shigematsu, Y. Omoto, Y. Ikushima, J. Imaoka and M. Yamamoto

IEEJ Journal of Industry Applications Vol. 13 ( 3 ) 2024

Maximum Output Power Design on an 85kHz Class-D Half-bridge ZVS Inverter with Power-MOSFETs Invited Reviewed

Vol. 144 ( 9 ) page： 645 - 653 2024

Maximum Output Power Design on an 85kHz Class-D Half-bridge ZVS Inverter with Power-MOSFETs Invited Reviewed International coauthorship

Yi Xiong, Senanayake Thilak, Daisuke Arai, Jun Imaoka and Yamamoto Masayoshi

IEICE Trans. Fundamentals 2024

Common-Mode Noise Reduction for Bridgeless Flyback PFC Rectifier with Balance Technique Reviewed International coauthorship International journal

Choi, S; Yin, Y; Shin, JW; Imaoka, J; Yamamoto, M

2024 IEEE APPLIED POWER ELECTRONICS CONFERENCE AND EXPOSITION, APEC page： 1478 - 1483 2024

Authorship：Last author Language：English Publishing type：Research paper (scientific journal) Publisher：Conference Proceedings - IEEE Applied Power Electronics Conference and Exposition - APEC

A novel bridgeless flyback power factor correction rectifier is proposed to reduce common-mode (CM) noise. The proposed rectifier realizes a symmetric configuration by placing a bidirectional switch between the equally split primary windings. To analyze CM noise propagation, highfrequency equivalent circuits with parasitic capacitances are derived. This study achieves the balance conditions in the equivalent circuit without additional inductors or capacitors. A 72-W prototype bridgeless flyback rectifier verifies a reduction in CM noise by maximum 35 dBμV at the frequency range of 150 kHz-30 MHz.

DOI： 10.1109/APEC48139.2024.10509297

A Novel Estimation Method for Equivalent Series Resistance of Film Capacitors Considering Frequency Characteristics Reviewed International journal

Sawada Y., Choi S., Yonezawa Y., Imaoka J., Yamamoto M., Tatsuki T., Ohkura M.

13th International Conference on Renewable Energy Research and Applications, ICRERA 2024 page： 852 - 856 2024

Language：English Publishing type：Research paper (scientific journal) Publisher：13th International Conference on Renewable Energy Research and Applications, ICRERA 2024

Capacitors have been widely utilized for power converters in renewable power generation. Their equivalent series resistance (ESR) is a critical parameter for estimating capacitor lifespan and aging. This study proposes a novel ESR estimation method specifically for low-ESR, low-capacitance capacitors such as film capacitors. Simulations and experimental results under various conditions demonstrate that the proposed method more accurately estimates ESR values, compared to the conventional methods. In addition, frequency characteristics of ESR are estimated under actual operating conditions, which has not been considered in previous literatures.

DOI： 10.1109/ICRERA62673.2024.10815499

Maximum Output Power Design on an 85kHz Class-D Half-bridge ZVS Inverter with Power-MOSFETs Reviewed International journal

XIONG Yi, THILAK Senanayake, ARAI Daisuke, IMAOKA Jun, YAMAMOTO Masayoshi

IEICE Transactions on Fundamentals of Electronics, Communications and Computer Sciences Vol. advpub ( 0 ) 2024

Authorship：Last author Language：English Publishing type：Research paper (scientific journal) Publisher：The Institute of Electronics, Information and Communication Engineers

<p>This paper analyzed and verified the condition for obtaining the maximum output power with an 85kHz class-D half-bridge zero-voltage-switching (ZVS) inverter. The shunt capacitance in the class-D half-bridge ZVS inverter is formed by nonlinear parasitic capacitance and linear external capacitors. The design equation of the shunt capacitance is derived. For verification, two class-D half-bridge inverters are designed with Si-MOSFETs and SiC-MOSFETs in four specifications. The simulated and experimental waveform verified the validity of the design procedure for achieving the ZVS operation, and the measured result verified the analysis of output power characteristics with good consistency. Furthermore, the relationship between the maximum output power and parasitic capacitance is analyzed. It is clarified that the power MOSFET with smaller parasitic capacitance can obtain higher maximum output power. By comparing the maximum output power between the Si-MOSFET and SiC-MOSFET, it is indicated that the SiC-MOSFET with smaller parasitic capacitance can obtain higher maximum output power than Si-MOSFET, verifying the condition for obtaining the maximum output power.</p>

DOI： 10.1587/transfun.2024eap1074

A Review of BMW iX3 Power Module - Part 1: Inner Configuration, Die Attachment, Busbar Connection and Encapsulation Reviewed International coauthorship International journal

Warnakulasooriya T., Choi J., Choi S., Kamiya A., Imaoka J., Yamamoto M.

13th IEEE CPMT Symposium Japan: Innovation of Packaging Technology for Advanced Heterogeneous Integration, ICSJ 2024 page： 216 - 219 2024

Authorship：Last author Language：English Publishing type：Research paper (scientific journal) Publisher：13th IEEE CPMT Symposium Japan: Innovation of Packaging Technology for Advanced Heterogeneous Integration, ICSJ 2024

The advancement of packaging of power modules is required to make improvements to electric vehicle drivetrains. This paper presents an independent review of the power module in a BMW iX3 inverter. The overall layout of the power module manufactured by Fuji Electric will be shown. Each half bridge uses two reverse conducting insulated gate bipolar transistors (RC-IGBTs) in parallel. The conventional wire bonding approach has been abandoned in favor of copper clip interconnections. The bonding mechanism of the bare dies, busbars and copper clips is also analyzed. The use of mold resin as encapsulation will also be discussed.

DOI： 10.1109/ICSJ62869.2024.10804738

A Review of BMW iX3 Power Module - Part 2: Stacked-Plate Fin Heatsink Structure Reviewed International coauthorship International journal

Choi J., Warnakulasooriya T., Choi S., Kamiya A., Imaoka J., Yamamoto M.

13th IEEE CPMT Symposium Japan: Innovation of Packaging Technology for Advanced Heterogeneous Integration, ICSJ 2024 page： 220 - 223 2024

Authorship：Last author Language：English Publishing type：Research paper (scientific journal) Publisher：13th IEEE CPMT Symposium Japan: Innovation of Packaging Technology for Advanced Heterogeneous Integration, ICSJ 2024

This paper introduces a heatsink structure employed in the power module of the BMW iX3 traction inverter. The heatsink features a stacked-plate configuration with single-sided cooling. Two distinct patterns of perforated plates are stacked alternately to direct coolant flow and enhance heat exchange performance. Geometric specifications are analyzed in detail and several related patents are reviewed to investigate heat exchange performance in a relation to various heatsink design parameters. Pressure loss is examined using Ansys Fluent simulation.

DOI： 10.1109/ICSJ62869.2024.10804726

Analysis of eddy currents and thermal modeling of planar magnetic components with metal housing Reviewed International journal

Hasenuma, A; Imaoka, J; Yamamoto, M; Miyazaki, T; Okawauchi, Y; Kawano, A

2024 IEEE APPLIED POWER ELECTRONICS CONFERENCE AND EXPOSITION, APEC page： 3247 - 3254 2024

Language：English Publishing type：Research paper (scientific journal) Publisher：Conference Proceedings - IEEE Applied Power Electronics Conference and Exposition - APEC

In recent years, temperature rise due to high-frequency losses in magnetic components has become an important issue in power converters. One solution to this problem is to use a thin meander winding structure to increase the cooling area with the metal housing. However, the eddy current losses due to leakage flux from the magnetic core installed in the metal housing and the estimation of the maximum operating temperature of the core are not well discussed in the related literature. In this paper, the distribution of eddy currents due to leakage flux is analyzed by focusing on the relative permeability of the core and the thermal interface material between the core and the metal housing. The temperature characteristics were also experimentally confirmed. As a result, a trade-off between eddy current loss in the metal housing and core temperature was confirmed for the thickness of the thermal interface material. These insights offer valuable considerations for installation and operational reliability in the development of next-generation planar magnetic components.

DOI： 10.1109/APEC48139.2024.10509263

Common Mode Noise Reduction Methods Used for High Power Density DC/DC Converters Reviewed International journal

Imaoka J., Sasaki M., Omoto Y., Noah M., Shigematsu K., Yamamoto M.

2024 14th International Workshop on the Electromagnetic Compatibility of Integrated Circuits, EMC Compo 2024 2024

Authorship：Last author Language：English Publishing type：Research paper (scientific journal) Publisher：2024 14th International Workshop on the Electromagnetic Compatibility of Integrated Circuits, EMC Compo 2024

Compound power semiconductor devices such as Silicon Carbide (SiC) and Gallium Nitride (GaN), are increasingly being adapted into automotive, renewable energy, and energy management applications to advance carbon neutrality. These devices offer the advantage of operating at higher switching frequencies than their silicon-based devices, attributed to their superior switching speed and reduced on-resistance. The ability to operate at elevated switching frequencies also enables the realization of high-power density in DC/DC converters. However, with the widespread application of compound semiconductor devices capable of high-frequency operation, the importance of noise reduction generated from power converters is significantly increasing towards safe and secure societies. Consequently, this paper presents the latest advancements in noise reduction methods based on a comprehensive literature review. This paper introduces strategies for common-mode noise reduction in high-power and high-frequency applications without necessitating an increase in the converter’s volume.

DOI： 10.1109/EMCCompo61192.2024.10742027

Common Mode Noise Reduction with Balance Technique Considering Soft Saturation Characteristics Reviewed International journal

Omizu Y., Choi S., Imaoka J., Yamamoto M.

13th International Conference on Renewable Energy Research and Applications, ICRERA 2024 page： 736 - 741 2024

Authorship：Last author Language：English Publishing type：Research paper (scientific journal) Publisher：13th International Conference on Renewable Energy Research and Applications, ICRERA 2024

Balance techniques have been widely utilized to reduce common-mode (CM) noise. Powder cores, however, introduced soft saturation characteristics which disrupt balance conditions. This is because the leakage flux increases at heavy loads, resulting in decrease of coupling coefficient. In this study, the effect of the soft saturation characteristics of powder cores on the balance condition is investigated. Additionally, a winding structure minimizing the leakage flux by using foil winding is proposed. The proposed structure achieves a high coupling coefficient regardless of load conditions, confirmed by static magnetic field simulations. The CM noises of the conventional and proposed winding structures are compared in various load conditions from 0.5 kW to 4 kW and verified the effectiveness of the proposed structure.

DOI： 10.1109/ICRERA62673.2024.10815316

Optimising Electric Vehicle Wireless Charging Systems Using Neural Networks to Enable Free-Position Parking

Merrigan H., Wu Y.H., Shigematsu K., Yamamoto M., Imaoka J., Lesage-Landry A.

13th International Conference on Renewable Energy Research and Applications, ICRERA 2024 page： 1510 - 1514 2024

Publisher：13th International Conference on Renewable Energy Research and Applications, ICRERA 2024

This paper explores wireless power transfer (WPT) systems for public electric vehicle charging, focusing on optimising the transmitter design to enhance interoperability across various receiver coil geometries and alignment conditions. Due to the complex non-linear relationships inherent to WPT systems, traditional optimisation methods are computationally expensive. Therefore, this study proposes an approach using artificial neural networks (ANNs) trained on finite element method (FEM) data to develop a surrogate model of the WPT system. This model is integrated into a blackbox optimisation solver, enabling faster identification of improved transmitter designs. The proposed method achieves computational speeds 6,000 times faster than traditional FEM simulations, with post-validation on the final solutions verifying prediction errors below 0.6%. The results demonstrate a significant acceleration in the optimisation process, establishing this method as an effective framework for developing practical WPT systems for public charging applications.

DOI： 10.1109/ICRERA62673.2024.10815548

Research on Continuous Operation of Active Gate Driver Combining Current Source and Active Gate Resistor Reviewed International coauthorship International journal

Ono K., Choi S., Yonezawa Y., Imaoka J., Yamamoto M.

13th International Conference on Renewable Energy Research and Applications, ICRERA 2024 page： 730 - 735 2024

Authorship：Last author Language：English Publishing type：Research paper (scientific journal) Publisher：13th International Conference on Renewable Energy Research and Applications, ICRERA 2024

Active gate drivers (AGDs) improve the trade-off between switching losses and surge voltage by actively operating switching transitions. However, conventional AGDs, which actively change the gate resistance have limitations in achieving sufficiently high-speed drive. Therefore, a new AGD combining a current source and an active gate resistor was proposed. Double-pulse tests confirmed that the new AGD further reduces turn-on losses compared to conventional AGD. In this study, control of the new AGD with feedback of the load current was implemented. A six-pulse test verified the continuous operation of the new AGD and confirmed that the new AGD with the control reduces switching losses more than it without the control.

DOI： 10.1109/ICRERA62673.2024.10815482

SiC Power Module Design with a Low-Permittivity Material to Reduce Common-Mode Noise Reviewed International coauthorship International journal

Choi, S; Choi, J; Shin, JW; Yonezawa, Y; Imaoka, J; Yamamoto, M

2024 IEEE APPLIED POWER ELECTRONICS CONFERENCE AND EXPOSITION, APEC page： 1472 - 1477 2024

Authorship：Last author Language：English Publishing type：Research paper (scientific journal) Publisher：Conference Proceedings - IEEE Applied Power Electronics Conference and Exposition - APEC

This study proposes a silicon carbide (SiC) power module design to reduce common-mode (CM) noise. A low permittivity material replaces a part of the bottom copper layer of a direct-bonded copper (DBC) substrate, which decreases CM capacitance. The design scheme does not sacrifice thermal performance and the size of power module. The parasitic CM capacitance of the proposed module is reduced by 52.5% compared to that of the conventional module. Double pulse tests verified that the peak CM current was attenuated by 52% and 43% at turn-off and at turn-on instant, respectively. To examine the thermal performance and reliability of power modules, thermal simulations and thermal cycling tests were also conducted.

DOI： 10.1109/APEC48139.2024.10509406

Circuit Analysis of SiC Bare Die Embedded Prototype Board Reviewed

Proceedings of JIEP Annual Meeting Vol. 38 ( 0 ) page： 14A2-2 2024

Packaging and Manufacturability of Low Capacitive Coupling SiC Power Module with Low Permittivity Material Reviewed International coauthorship

Proceedings of JIEP Annual Meeting Vol. 38 ( 0 ) page： 13B1-4 2024

A current fed full bridge converter with auxiliary resonant capacitor Reviewed International journal Open Access

Yamada Tomoki, Yonezawa Yu, Yamamoto Masayoshi

IEICE Electronics Express Vol. 20 ( 21 ) page： 20230351 - 20230351 2023.11

Authorship：Last author Language：English Publishing type：Research paper (scientific journal) Publisher：The Institute of Electronics, Information and Communication Engineers

<p>This letter proposes a simpler and more efficient circuit scheme than the conventional current fed full bridge converter. In the proposed circuit, an auxiliary resonant capacitor is added to the conventional circuit to eliminate the adverse effects of leakage inductance of the transformer on the circuit operation, and at the same time, soft switching is achieved. As a result, switching losses were reduced and the efficiency was improved by approximately 4.7% compared to the conventional method, which was confirmed on LTspice. First, the basic structure of the proposed circuit is shown, followed by the principle of operation. Next, the advantages and disadvantages of the proposed method are presented. Finally, we compare the proposed method with the conventional method.</p>

DOI： 10.1587/elex.20.20230351

Conducted EMI Simulation for a DC-DC Converter : a DC Brush Motor System Considering Showering Arc at Mechanical Contacts Reviewed

Kodai Katagiri, Toru Ogawa, Masayoshi Yamamoto, Jun Imaoka, Mamoru Sasaki

IEEJ Journal of Industry Applications Vol. 12 ( 5 ) page： 933 - 944 2023.9

Analysis of the ratio of urinary beta-2-microglobulin to total protein concentration in children with isolated tubulointerstitial disease Reviewed International journal

Nishimura T., Uemura O., Hibino S., Tanaka K., Iwata N., Yamamoto M., Matsukuma E., Miyake Y., Gotoh Y., Fujita N.

Clinical and Experimental Nephrology Vol. 27 ( 8 ) page： 701 - 706 2023.8

Language：English Publishing type：Research paper (scientific journal) Publisher：Clinical and Experimental Nephrology

Background: Proteinuria is broadly classified into glomerular and tubular proteinuria. Urinary beta-2-microglobulin (β2-MG) is known as a marker for detecting tubulointerstitial diseases. However, tubulointerstitial damage can also lead to an increase in urinary β2-MG level in some patients with glomerular diseases. This study aimed to determine the ratio of urinary β2-MG to total protein (TP) concentration in patients with both isolated tubulointerstitial and glomerular disease. Methods: This multicenter, retrospective study included children with Dent disease or lupus nephritis in five facilities. Their urinary β2-MG levels were > 1000 µg/L. Urinary β2-MG and TP concentrations were obtained, and the ratio of urinary β2-MG to TP concentration (µg/mg) was calculated. The Mann–Whitney U test was performed to compare this ratio between these children. The optimal cutoff value of the ratio for considering the presence of glomerular disease was obtained from the receiver operating characteristic (ROC) curve. Results: We obtained information on 23 children with Dent disease and 14 children with lupus nephritis. The median ratios of urinary β2-MG to TP concentrations in children with Dent disease and lupus nephritis were 84.85 and 1.59, respectively. The ROC curve yielded the optimal cutoff value of this ratio for distinguishing between these diseases, and the cutoff value was found to be 22.3. Conclusion: In children with tubulointerstitial diseases, the urinary β2-MG concentration may be approximately 8.5% of the TP concentration. The possibility of presenting with glomerular disease should be considered in patients with a ratio of urinary β2-MG to TP concentration of < 22.3 (µg/mg).

DOI： 10.1007/s10157-023-02349-7

Balanced Two-phase Interleaved Boost Converter with Integrated Magnetics for Common-Mode Noise Reduction Reviewed

Tomotaka Nagai, Mamoru Sasaki, Jun Imaoka, Masayoshi Yamamoto, Akira Nakano

IEEJ Journal of Industry Applications Vol. 12 ( 4 ) page： 664 - 675 2023.7

Voltage-Controlled Variable Inductor for Fixed-Frequency Critical Conduction Mode Operation Reviewed

Sihoon Choi, Jong-Won Shin, Jun Imaoka, Masayoshi Yamamoto

IEEE Transactions on Industrial Electronics Vol. 70 ( 6 ) page： 5707 - 5716 2023.6

Common mode conductive noise cancellation formultiphase converter using auxiliary winding Reviewed

Electrical Engineering in Japan Vol. 143 ( 4 ) page： 263 - 272 2023.6

Common mode conductive noise cancellation for multiphase converter using auxiliary winding Reviewed International journal

Sasaki, M; Imaoka, J; Yamamoto, M; Nakano, A; Fuse, K

ELECTRICAL ENGINEERING IN JAPAN Vol. 216 ( 2 ) 2023.6

Language：English Publishing type：Research paper (scientific journal) Publisher：Electrical Engineering in Japan (English translation of Denki Gakkai Ronbunshi)

A multiphase DC-DC converter consisting of a coupled inductor and fast switching devices enables power electronics equipment to achieve a high-power density. However, with such devices, the fast voltage transition generates substantial common mode (CM) noise. However, there are very few studies on CM noise reduction for multiphase converters using a coupled inductor. Therefore, in this paper, a CM noise reduction method is proposed for a multiphase DC-DC converter that hardly lowers the power density.

DOI： 10.1002/eej.23439

Accurate Leakage Inductance Modeling Using Artificial Neural Network (ANN) Based on Dowell Model Reviewed International coauthorship

Yu-Hsin Wu, Koichi Shigematsu, Yasumichi Omoto, Jun Imaoka, Masayoshi Yamamoto

IEEJ Journal of Industry Applications Vol. 12 ( 3 ) page： 334 - 344 2023.5

Derivation of Resonant Period for Soft Switching Considering Nonlinear Characteristics of Output Capacitance in Switching Device Reviewed

Sihoon Choi, Ayato Suzuki, Jun Imaoka, Masayoshi Yamamoto

IEEJ Journal of Industry Applications Vol. 70 ( 6 ) page： 289 - 294 2023.5

Investigation on Relationship between Common Mode Noise and Distribution of Parasitic Capacitance Reviewed

Mamoru Sasaki, Jun Imaoka, Masayoshi Yamamoto

IEEJ Journal of Industry Applications Vol. 12 ( 3 ) page： 484 - 492 2023.5

Current Sharing Control of Multi-Input Modular DC-DC Converter Using Unregulated LLC Resonant Converter Reviewed International journal

Piao Qingyun, Imaoka Jun, Yamamoto Masayoshi

IEEJ Transactions on Industry Applications Vol. 143 ( 4 ) page： 337 - 348 2023.4

Authorship：Last author Language：Japanese Publishing type：Research paper (scientific journal) Publisher：The Institute of Electrical Engineers of Japan

<p>By applying an unregulated LLC resonant converter to a multi-input modular DC-DC converter (MIMC), the LLC converter can be operated at an optimal frequency while achieving power source flexibility. However, the output characteristics of an LLC converter are easily affected by the resonance parameter, and when connected in parallel, the output current is unbalanced. In this paper, we propose a current sharing control method to solve the current imbalance problem, and automatically balance the output current of each module. The effectiveness of the proposed current sharing control method is verified by simulations and experiments.</p>

DOI： 10.1541/ieejias.143.337

Common Mode Conductive Noise Cancellation for Multiphase Converter Using Auxiliary Winding Reviewed International journal

Sasaki Mamoru, Imaoka Jun, Yamamoto Masayoshi, Nakano Akira, Fuse Koji

IEEJ Transactions on Industry Applications Vol. 143 ( 4 ) page： 263 - 272 2023.4

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：The Institute of Electrical Engineers of Japan

<p>A multiphase DC-DC converter consisting of a coupled inductor and fast switching devices enables power electronics equipment to achieve a high power density. However, with such devices, the fast voltage transition generates substantial common mode (CM) noise. However, there are very few studies on CM noise reduction for multiphase converters using a coupled inductor. Therefore, in this paper, a CM noise reduction method is proposed for a multiphase DC-DC converter that hardly lowers the power density.</p>

DOI： 10.1541/ieejias.143.263

補助巻き線による結合インダクタ方式多相コンバータ用コモンモードノイズキャンセル Invited Reviewed

佐々木守, 今岡淳, 山本真義

電気学会論文誌Ｄ 2023.4

非制御 LLC共振形コンバータを用いたモジュラーDC-DCコンバータの電流分担制御 Reviewed

朴青云, 今岡　淳, 山本真義

電気学会論文誌D Vol. 143 ( 4 ) page： 337 - 348 2023.4

Gate Drive Circuit Suitable for a GaN Gate Injection Transistor Reviewed

Fumiya Hattori, Yuta Yanagisawa, Jun Imaoka, Masayoshi Yamamoto

IEEE Access Vol. 12 ( 3 ) page： 43169 - 43182 2023.4

補助巻き線による結合インダクタ方式多相コンバータ用コモンモードノイズキャンセル Invited Reviewed International journal

佐々木守, 今岡淳, 山本真義, 仲野陽, 布施浩司

電気学会論文誌D Vol. 143 ( 4 ) page： 263 - 272 2023.4

パワー半導体基板内蔵技術による SiC ハーフブリッジ回路の設計・試作・評価 Reviewed

中村和人, 今岡淳, 山本真義, 金山天, 韓榮建, 加藤義尚, 末次正, 服部篤典, 野北寛太, 稲田太朗, 浅井寛美, 小泉雄大

エレクトロニクス実装学術講演大会講演論文集 Vol. 37 ( 0 ) page： 15C4-2 2023.3

Novel measurement method to determine optimum reception frequency of electric field wireless power receiver Invited Reviewed

A. Oyane and M. Yamamoto

IEEJ Journal of Industry Applications Vol. 12 ( 1 ) page： 54 - 64 2023.1

Spike Surge and Conducted EMI Simulation of DC Brush Motor Considering Steady Arc at Mechanical Contacts Invited Reviewed

IEEJ Journal of Industry Applications Vol. 12 ( 1 ) page： 86 - 93 2023

Novel Measurement Method to Determine Optimum Reception Frequency of Electric Field Wireless Power Receiver Reviewed International journal

Oyane Aoi, Yamamoto Masayoshi

IEEJ Journal of Industry Applications Vol. 12 ( 1 ) page： 54 - 64 2023

Authorship：Last author Language：English Publishing type：Research paper (scientific journal) Publisher：The Institute of Electrical Engineers of Japan

<p>This paper proposes a novel method for measuring the characteristics of a wireless power receiver of an electric field wireless power transfer (eWPT) system. The proposed measurement method allows us to obtain the frequency response of the eWPT receiver's power-receiving characteristics with respect to the spatial electric field frequency. Conventionally, it was not possible to measure the reception characteristics of a single independent receiver. This is because a resonant eWPT transmitter has pronounced frequency dependent characteristics. As a result, frequency-dependent electric fields are emitted into space and act on the receiver. The proposed measurement method overcomes this obstacle by using the proposed device that generates a high-frequency electric field almost independently of the frequency. The proposed device generates high-frequency electric fields in space by using a terminating resistor instead of resonator circuits. Therefore, unlike resonant transmitters, the strength of the electric field generated by the proposed device does not exhibit a large frequency dependence. The proposed measurement method will also be useful for the prototyping, evaluation, and optimization of new advanced eWPT systems whose characteristics are not yet fully understood. Here, 85kHz series resonant eWPT receivers are evaluated using the proposed measurement method, and the details of this experimental device are also described.</p>

DOI： 10.1541/ieejjia.22004096

Accurate Leakage Inductance Modeling Using an Artificial Neural Network Based on the Dowell Model Reviewed

Wu Yu-Hsin, Shigematsu Koichi, Omoto Yasumichi, Ikushima Yoshihiro, Imaoka Jun, Yamamoto Masayoshi

IEEJ Journal of Industry Applications Vol. advpub ( 0 ) 2023

Authorship：Last author Language：English Publisher：The Institute of Electrical Engineers of Japan

<p>This study proposes strategies for improving the accuracy and usefulness of leakage inductance modeling using the Dowell model (DM). As the analytical method of modeling the leakage inductance model considers geometrical factors, it is vital for front-loading transformer design. DM is one such widely used one-dimensional magnetic field-based approach for analytically modeling both AC resistance and leakage inductance. It is more accurate and requires less computational work than other analytical approaches proposed in previous studies. However, some approximations may cause errors and eventually lead to inaccurate results. Therefore, this study aims to ascertain the conditions that result in inaccurate leakage inductance modeling. Additionally, a simple exponential-based model and an artificial neural network are developed to increase the accuracy of inaccurate modeling. The results clarify the conditions that result in a frequency-dependent and bias error. Moreover, the intended findings indicate that the proposed strategies effectively improve modeling accuracy while simultaneously providing some extra advantages for transformer design.</p>

DOI： 10.1541/ieejjia.22007452

Balanced Two-phase Interleaved Boost Converter with Integrated Magnetics for Common-Mode Noise Reduction Invited Reviewed

Nagai Tomotaka, Sasaki Mamoru, Imaoka Jun, Yamamoto Masayoshi, Nakano Akira

IEEJ Journal of Industry Applications Vol. advpub ( 0 ) 2023

Authorship：Corresponding author Language：English Publisher：The Institute of Electrical Engineers of Japan

<p>This paper presents an interleaved boost converter with integrated magnetics for common-mode (CM) noise reduction without introducing electromagnetic interference (EMI) filters. The noise reduction is realized using the balanced technique, which is an effective CM noise reduction technique from a circuit topology perspective. The application of this technique addresses the issue of the CM noise, while avoiding an increase in circuit volume due to EMI filters. Additionally, an interleaved circuit topology and integrated magnetics contribute to realizing the high-power density converter. The effectiveness of the proposed converter is discussed through theoretical analyses, simulations, and experiments.</p>

DOI： 10.1541/ieejjia.22007783

Fixed Frequency Operation in Critical Conduction Mode with Voltage-Controlled Variable Inductor Reviewed International coauthorship International journal

Choi S., Shin J.W., Imaoka J., Yamamoto M.

2023 IEEE Energy Conversion Congress and Exposition, ECCE 2023 page： 6444 - 6449 2023

Authorship：Last author Language：English Publishing type：Research paper (scientific journal) Publisher：2023 IEEE Energy Conversion Congress and Exposition, ECCE 2023

This study introduces a novel voltage-controlled variable inductor (VI) that effectively fixes the switching frequency of DC-DC converters operating in the critical conduction mode (CRM). The proposed VI addresses the limitations encountered with conventional current-controlled VIs, such as complex winding structures, control challenges, and reliance on magnetic saturation. In the proposed voltage-controlled VI, the primary-side inductance of a coupled inductor is regulated by an auxiliary voltage source on the secondary side. The validity of the proposed VI is experimentally verified using a prototype CRM boost converter with an output voltage of 400 V. Experimental results demonstrate that the switching frequency remains fixed at 100 kHz, and the main converter maintains soft switching characteristics regardless of variations in output power.

DOI： 10.1109/ECCE53617.2023.10362859

Modeling of Lithium-Ion Batteries with Constant Phase Element and Butler-Volmer's Equation Reviewed International journal

Yamahigashi T., Shimura J., Shibuya K., Wu Y.H., Shigematsu K., Hosotani T., Kuromi J., Imaoka J., Yamamoto M.

ICPE 2023-ECCE Asia - 11th International Conference on Power Electronics - ECCE Asia: Green World with Power Electronics page： 697 - 702 2023

Authorship：Last author Language：English Publishing type：Research paper (scientific journal) Publisher：ICPE 2023-ECCE Asia - 11th International Conference on Power Electronics - ECCE Asia: Green World with Power Electronics

An equivalent circuit model of lithium-ion batteries which has a nonlinear resistor governed by Butler-Volmer's equation and a constant phase element was investigated. The current dependence of the real battery could be reproduced well by the contribution of the nonlinear resistor, and the transient response of voltage could be reproduced well by the contribution of the constant phase element.

DOI： 10.23919/ICPE2023-ECCEAsia54778.2023.10213775

Investigation on Relationship between Common Mode Noise and Distribution of Parasitic Capacitance Reviewed

Sasaki Mamoru, Imaoka Jun, Yamamoto Masayoshi

IEEJ Journal of Industry Applications Vol. 12 ( 3 ) page： 484 - 492 2023

Authorship：Last author Language：English Publishing type：Research paper (scientific journal) Publisher：The Institute of Electrical Engineers of Japan

<p>This study investigates the influence of parasitic capacitance on the common mode (CM) noise in a converter. A thermal pad on a switching device is necessary for sufficient heat dissipation. In addition, the thermal pad increases the CM capacitance between the printed circuit board and the ground plane. The parasitic capacitances form CM noise propagation paths. However, which node in the circuit and the corresponding parasitic capacitance influences the CM noise the most and the degree of the parasitic capacitance influence on the CM noise are unclear. In this study, the parasitic capacitance that influences the CM noise in a converter is identified, and the extent to which the parasitic capacitance affects the CM noise is investigated through simulations and experiments.</p>

DOI： 10.1541/ieejjia.22008018

High reliable transformer-less deadtime less Inverter for Grid-connected Applications Reviewed International coauthorship International journal

Senanayake S., Senanayake T., Imaoka J., Yamamoto M.

ICPE 2023-ECCE Asia - 11th International Conference on Power Electronics - ECCE Asia: Green World with Power Electronics page： 1788 - 1794 2023

Authorship：Last author Language：English Publishing type：Research paper (scientific journal) Publisher：ICPE 2023-ECCE Asia - 11th International Conference on Power Electronics - ECCE Asia: Green World with Power Electronics

This paper presents a transformer-less inverter topology that brings out the high-performance for grid connected inverters. The main advantages of this inverter eliminate the dead-time requirement, and allows both top and bottom switch from being on at same time, and thus shorting the DC bus supply to ground. This avoids the freewheeling diodes connected across the switches for loads other than purely resistive. Low output voltage distortion and low fundamental and common voltages losses result in high efficiency and high output power density. The input dc source and the output ac voltage share the same ground in proposed inverter, which effectively eliminates the leakage current caused by the DC source (PV panel, battery bank etc.). Analysis and simulation results are presented to demonstrate the effectiveness of the proposed inverter. Compared to the prior literature mentioned in this paper, 75- 86% reduction of semiconductor components is achieved with proposed inverter topology.

DOI： 10.23919/ICPE2023-ECCEAsia54778.2023.10213921

Gate Drive Circuit Suitable for a GaN Gate Injection Transistor Reviewed International journal

Hattori, F; Yanagisawa, Y; Imaoka, J; Yamamoto, M

IEEE ACCESS Vol. 11 page： 43169 - 43182 2023

Authorship：Last author Language：English Publishing type：Research paper (scientific journal) Publisher：IEEE Access

A GaN gate injection transistor (GIT) has great potential as a power semiconductor device. However, a GaN GIT has a diode characteristic at the gate-source, and a corresponding gate drive circuit is thus required. Several studies in the literature have proposed the gate drive circuits with the speed-up capacitors, but adding these capacitors complicates the gate drive circuit, and increases both the drive and reverse conduction losses. Moreover, driving a GaN GIT with such gate drive circuits becomes more susceptible to the false turn-on. In this paper, a gate drive circuit suitable for a GaN GIT without a speed-up capacitor is proposed. This type can provide the high-speed switching, and exhibit the low gate drive loss and reverse conduction loss. The proposed circuit also has high immunity against the false turn-on and stable gate-source voltage before and after startup. The drive loss of the proposed type is calculated and its validity is confirmed experimentally. Furthermore, the drive loss of the proposed type is compared with the conventional circuits. The result shows that the drive loss of the proposed type is improved by up to 50 %, compared with the conventional type. Finally, the proposed type is experimentally tested to drive a buck converter at the switching frequency of 150 kHz. The entire loss of the converter can be reduced by up to 9.2% at 250 W, compared with the conventional type.

DOI： 10.1109/ACCESS.2023.3270261

Design of Coupled Inductor Using Powder Core with Concentrated Air Gap in Multiphase Operation Reviewed International coauthorship

Sihoon Choi, Jun Imaoka and Masayoshi Yamamoto

IEEE Transactions on Industry Applications 2023

Butler–Volmer の式に従う非線形抵抗とCPEとを含むリチウムイオン電池の等価回路モデル Reviewed

南家憲史，渋谷賢佑，重松浩一，今岡淳，山本真義，細谷達也，黒見仁，志村重輔

第64回電池討論会 2023

Modeling of Lithium-Ion Batteries with Constant Phase Element and Butler-Volmer’s Equation Reviewed

T. Yamahigashi, J. Shimura, K. Shibuya, Y. ,K. Shigematsu, T. Hosotani, J. Kuromi, J. Imaoka, and M. Yamamoto

IEEE Energy Conversion Congress and Exposition Asia page： 667 - 702 2023

A current fed full bridge converter with auxiliary resonant capacitor Reviewed

Tomoki Yamada, Yu Yonezawa, Masayoshi Yamamoto

IEICE Electronics Express Vol. 20 ( 21 ) 2023

An Implementation of Dowell model with Neural Network to Foil Winding Transformer Reviewed International coauthorship International journal

Wu, YH; Shigematsu, K; Omoto, Y; Ikushima, Y; Imaoka, J; Yamamoto, M

2023 IEEE APPLIED POWER ELECTRONICS CONFERENCE AND EXPOSITION, APEC Vol. 2023-March page： 2684 - 2689 2023

Authorship：Last author Language：English Publishing type：Research paper (scientific journal) Publisher：Conference Proceedings - IEEE Applied Power Electronics Conference and Exposition - APEC

This research investigates the accuracy of Dowell model (DM) and builds an accurate and practically useful semi-analytical method for leakage inductance modeling of foil winding transformers. As a widely used model for AC resistance and leakage inductance, DM is well known for its high applicability and high accuracy compared to the other modeling methods. However, it is found that transformers with certain geometrical conditions are used in most works of literature for implementing DM. Although some analyses about the modeling accuracy were conducted, the applicability of DM for some geometry is still unclear. Therefore, in this research, the accuracy of the modeling is analyzed, focusing on the frequency and geometry dependency of foil winding. Some results show the modeling error of DM has frequency dependency. Furthermore, modeling using DM with Artificial Neural Network (ANN) is implemented to achieve more practically usable modeling. As a result, the utility could be proved with accurate modeling results of the transformer samples. Some advantages are also discussed to show more possibility of developing this method.

DOI： 10.1109/APEC43580.2023.10131441

Spike Surge and Conducted EMI Simulation of DC Brush Motor Considering Steady Arc at Mechanical Contacts Reviewed International journal Open Access

Katagiri Kodai, Ogawa Toru, Yamamoto Masayoshi, Imaoka Jun, Sasaki Mamoru

IEEJ Journal of Industry Applications Vol. 12 ( 1 ) page： 86 - 93 2023

Language：English Publishing type：Research paper (scientific journal) Publisher：The Institute of Electrical Engineers of Japan

<p>This study provides a circuit analysis model of a DC brush motor to predict spike surges at mechanical contacts and conducted EMI by considering the behavior of steady arc discharge. The mechanical contacts model comprises multiple variable resistors, constant voltage sources, ideal diodes, and stray capacitances. In the proposed model, spike surges with steady arc could be predicted with 90% accuracy. Moreover, simulated conducted EMI according to CISPR 25 standard is deviated from the measured value at a maximum of 25dB. Therefore, it is demonstrated that the quantitative prediction of conducted EMI requires consideration of a showering arc model at mechanical contacts.</p>

DOI： 10.1541/ieejjia.21011210

Overview of System Simulation Technology for Electric and Hybrid Aircraft Reviewed

Yamamoto Masayoshi, Shigematsu Koichi, Yamahigashi Takamitsu, Shibuya Kensuke, Maeda Mitsuyasu, Fujimori Mitsuaki

SYSTEMS, CONTROL AND INFORMATION Vol. 66 ( 12 ) page： 457 - 463 2022.12

A Study of Thermal and Electrical Multi-Domain Model of Aluminum Electrolytic Capacitors Reviewed

Mukaiyama Daisaku, Yamamoto Masayoshi

Journal of The Japan Institute of Electronics Packaging Vol. 25 ( 6 ) page： 527 - 534 2022.9

13.56MHz Half-Bridge GaN-HEMT Resonant Inverter Achieving High Power, Low Distortion, and High Efficiency by ‘L-S Network’ Invited Reviewed International journal Open Access

OYANE Aoi, SENANAYAKE Thilak, MASUDA Mitsuru, IMAOKA Jun, YAMAMOTO Masayoshi

IEICE Transactions on Electronics Vol. E105C ( 9 ) page： 407 - 418 2022.9

Authorship：Last author Language：English Publishing type：Research paper (scientific journal) Publisher：The Institute of Electronics, Information and Communication Engineers

<p>This paper proposes a topology of high power, MHz-frequency, half-bridge resonant inverter ideal for low-loss Gallium Nitride high electron mobility transistor (GaN-HEMT). General GaN-HEMTs have drawback of low drain-source breakdown voltage. This property has prevented conventional high-frequency series resonant inverters from delivering high power to high resistance loads such as 50Ω, which is typically used in radio frequency (RF) systems. High resistance load causes hard-switching also and reduction of power efficiency. The proposed topology overcomes these difficulties by utilizing a proposed ‘L-S network’. This network is effective combination of a simple impedance converter and a series resonator. The proposed topology provides not only high power for high resistance load but also arbitrary design of output wattage depending on impedance conversion design. In addition, the current through the series resonator is low in the L-S network. Hence, this series resonator can be designed specifically for harmonic suppression with relatively high quality-factor and zero reactance. Low-distortion sinusoidal 3kW output is verified in the proposed inverter at 13.56MHz by computer simulations. Further, 99.4% high efficiency is achieved in the power circuit in 471W experimental prototype.</p>

DOI： 10.1587/transele.2021ECP5048

Spike Surge and Conducted EMI Simulation of DC Brush Motor Considering Steady Arc at Mechanical Contacts Reviewed International journal

Katagiri Kodai, Ogawa Toru, Yamamoto Masayoshi, Imaoka Jun, Sasaki Mamoru

IEEJ Transactions on Industry Applications Vol. 142 ( 7 ) page： 490 - 497 2022.7

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：The Institute of Electrical Engineers of Japan

<p>This study provides a circuit analysis model of a DC brush motor to predict spike surges at mechanical contacts and conducted EMI by considering the behavior of steady arc discharge. The mechanical contacts model comprises multiple variable resistors, constant voltage sources, ideal diodes, and stray capacitances. In the proposed model, spike surges with steady arc could be predicted with 90% accuracy. Moreover, simulated conducted EMI according to CISPR 25 standard is deviated from the measured value at a maximum of 25dB. Therefore, it is demonstrated that the quantitative prediction of conducted EMI requires consideration of a showering arc model at mechanical contacts.</p>

DOI： 10.1541/ieejias.142.490

An Evaluation of a New Type of High Efficiency Hybrid Gate Drive Circuit for SiC-MOSFET Suitable for Automotive Power Electronics System Applications Invited Reviewed

YAMAMOTO Masayoshi, SHIRAI Shinya, THILAK Senanayake, IMAOKA Jun, ISHIDO Ryosuke, OKAWAUCHI Yuta, NAKAHARA Ken

IEICE Transactions on Fundamentals of Electronics, Communications and Computer Sciences Vol. E105A ( 5 ) page： 834 - 843 2022.5

Authorship：Corresponding author Language：English Publisher：The Institute of Electronics, Information and Communication Engineers

<p>In response to fast charging systems, Silicon Carbide (SiC) power semiconductor devices are of great interest of the automotive power electronics applications as the next generation of fast charging systems require high voltage batteries. For high voltage battery EVs (Electric Vehicles) over 800V, SiC power semiconductor devices are suitable for 3-phase inverters, battery chargers, and isolated DC-DC converters due to their high voltage rating and high efficiency performance. However, SiC-MOSFETs have two characteristics that interfere with high-speed switching and high efficiency performance operations for SiC MOS-FET applications in automotive power electronics systems. One characteristic is the low voltage rating of the gate-source terminal, and the other is the large internal gate-resistance of SiC MOS-FET. The purpose of this work was to evaluate a proposed hybrid gate drive circuit that could ignore the internal gate-resistance and maintain the gate-source terminal stability of the SiC-MOSFET applications. It has been found that the proposed hybrid gate drive circuit can achieve faster and lower loss switching performance than conventional gate drive circuits by using the current source gate drive characteristics. In addition, the proposed gate drive circuit can use the voltage source gate drive characteristics to protect the gate-source terminals despite the low voltage rating of the SiC MOS-FET gate-source terminals.</p>

DOI： 10.1587/transfun.2021GCI0001

Analysis of DC Brush Motor Spike Surge and Proposal of a Simulation Model Based on an Equivalent Circuit Reviewed International journal

Katagiri Kodai, Ogawa Toru, Yamamoto Masayoshi, Imaoka Jun, Sasaki Mamoru, Noda Kazuhiro

IEEJ Transactions on Industry Applications Vol. 142 ( 3 ) page： 167 - 176 2022.3

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：The Institute of Electrical Engineers of Japan

<p>This paper presents a circuit analysis model to predict spike surges at mechanical contacts of a DC brush motor. Measured spike surge waveforms are classified into four types depending on the existence of a steady arc and a showering arc. The directly open without arcs condition is clarified to be the maximum spike surge voltage condition. Additionally, an equivalent circuit model is developed to simulate spike surges. This model considers complex high-frequency characteristics and rotation angle dependence of impedances. A full-slot equivalent circuit model is represented by a combination of single-slot models. The spike surge simulation model considers induced voltage and variable resistors representing mechanical contact switching in addition to impedance characteristics. The simulated spike surges show good quantitative agreement with the measured values.</p>

DOI： 10.1541/ieejias.142.167

Improving DC superimposition characteristics of powder cores by applying coupled inductors in multi-phase boost converter Reviewed

Aoki Tatsuya, Imaoka Jun, Yamamoto Masayoshi, Yoshimoto Kosuke

IET POWER ELECTRONICS Vol. 15 ( 3 ) page： 237 - 250 2022.2

Authorship：Corresponding author Language：English Publisher：IET Power Electronics

In applications where DC current is superimposed, such as inductors for non-isolated DC-DC converters, powder core can be considered as an attractive solution owing to its superior features such as: high saturation flux density, high Curie temperature, and soft-saturation property. However, in powder cores, a drop of inductance appears prominently due to DC superimposition characteristics. This feature is not a desirable characteristic because it leads to an increase in the inductor ripple current under heavy load, which complicates the thermal design of power semiconductors and capacitors. This paper verifies the improvement of DC superimposition characteristics of powder cores by applying coupled inductors. First, the effect of coupled inductors on the improvement of DC superimposition characteristics is experimentally verified. Second, a measurement method for the DC superimposition characteristics of coupled inductor is proposed. Then, a magnetic circuit model is built using the measurement results. Finally, a coupled analysis of magnetic and electric circuits is performed, and it is confirmed that lower magnetic field operation can be realized by coupled inductors even under heavy load conditions. It has been proven that coupled inductors are effective in improving the DC superposition characteristics of the powder cores.

DOI： 10.1049/pel2.12226

Frequency Doubler Gate Drive Circuit Suitable for High-Frequency Applications Reviewed International coauthorship International journal

Hattori, F; Ushida, Y; Sumiya, K; Yanagisawa, Y; Imaoka, J; Noah, M; Yamamoto, M

IEEE JOURNAL OF EMERGING AND SELECTED TOPICS IN POWER ELECTRONICS Vol. 10 ( 1 ) page： 617 - 631 2022.2

Authorship：Last author Language：English Publishing type：Research paper (scientific journal) Publisher：IEEE Journal of Emerging and Selected Topics in Power Electronics

In megahertz (MHz) power converters, the gate drive loss becomes one of the main issues that should be addressed. In the relevant literature, several gate drive circuits had been proposed to reduce the gate drive losses. A literature survey is provided in the introduction section to summarize the merits and demerits of each circuit. These studies proposed innovative methods to reduce gate drive loss. Nonetheless, they did not propose any solution to reduce the loss of the buffer stage inside the drive IC. In this article, we present a frequency doubler gate drive circuit. The proposed gate drive circuit can double the frequency of the input PWM signal at the driver output stage, using the second harmonic of the input signal. Therefore, the loss of the buffer stage inside the drive IC can be significantly reduced, compared with the hard-switching, the inductive resonant, and multiresonant gate drive circuits. This article focuses on designing, simulating, and experimentally validating the frequency doubler gate drive circuit with a 6.78-MHz input frequency and 13.56-MHz driving frequency. The concept of a frequency tripler gate drive circuit is also introduced and discussed. For instance, the frequency tripler gate drive circuit can triple the frequency of the input PWM signal at the driver output stage using the third harmonic; in this scenario, a 20.34-MHz driving frequency can be obtained. The proposed frequency doubler gate drive circuit is experimentally tested in a 13.56-MHz class E inverter.

DOI： 10.1109/JESTPE.2021.3089506

非制御 LLC共振形コンバータを用いたモジュラーDC-DCコンバータの電流分担制御 Invited Reviewed

電気学会論文誌Ｄ 2022

Reducing Transformer Losses with Adjustable Path-Core Type Inductance in 1.4-MHz LLC Resonant Converters Invited Reviewed

Ou Tengfei, Noah Mostafa, Tsuruya Mamoru, Namiki Seiji, Morita Koichi, Imaoka Jun, Yamamoto Masayoshi

IEEJ Journal of Industry Applications, vol Vol. 11 ( 5 ) page： 664 - 673 2022

Voltage-Controlled Variable Inductor for Fixed-Frequency Critical Conduction Mode Operation Invited Reviewed

S. Choi, J. -W. Shin, J. Imaoka and M. Yamamoto

IEEE Transactions on Industrial Electronics 2022

Transformer with Adjustable Path-Core Type Inductance for Use in GaN-HEMT LLC Resonant Converter Invited Reviewed

Ou Tengfei, Noah Mostafa, Tsuruya Mamoru, Namiki Seiji, Morita Koichi, Imaoka Jun, Yamamoto Masayoshi

IEEJ Journal of Industry Applications Vol. 11 ( 1 ) page： 41 - 48 2022

Authorship：Last author Language：English Publisher：The Institute of Electrical Engineers of Japan

<p>A novel magnetic structure for use in LLC resonant converters is proposed in this paper. It is known as a Path-core type Resonant Inductance Adjustable (PRIA) transformer, which is a type of transformer with adjustable resonant inductance. In the proposed transformer, the resonant inductance and magnetizing inductance can be designed separately; therefore, it becomes less challenging to realize the required resonant frequency. Moreover, the magnetizing inductance is not affected by any variation in the resonant inductance. The proposed PRIA transformer is found to improve the efficiency of the LLC converters. In this paper, the design of a resonant inductance of a PRIA transformer is presented. In addition, the application of PRIA transformers to a 1-MHz LLC resonant converter and 1kW 1.4-MHz LLC resonant converter is presented.</p>

DOI： 10.1541/ieejjia.21002488

An Investigation and Proposal for Accurate Leakage Inductance Modeling Based on Dowell Model Reviewed

Wu Y.H., Shigematsu K., Omoto Y., Imaoka J., Yamamoto M.

2022 International Power Electronics Conference, IPEC-Himeji 2022-ECCE Asia page： 1964 - 1969 2022

Authorship：Last author Language：English Publisher：2022 International Power Electronics Conference, IPEC-Himeji 2022-ECCE Asia

The aim of this research is to build a highly applicable, accurate, and fast leakage inductance modeling method based on Dowell model. Which is a widely used analytical modeling method to estimate AC resistance and leakage inductance. Since most of the literatures use Dowell model basically with the limited condition achieving ac-curate modeling of leakage inductance, in this research, an accuracy investigation is conducted with the samples of EE-core transformers by finite element method (FEM) simulation and practical transformers to find the inaccurate modeling related to the geometrical characteristic. After that, a proposed hybrid modeling using artificial neural network (ANN) is conducted to create a black box error correction model of conventional Dowell model with FEM results. As the result, the modeling shows high accuracy by Dowell with ANN error correction model. It carries out the future to develop a modified Dowell model by analyzing the ANN error correction model. Which can describe the geometrical characteristic of transformer accurately.

DOI： 10.23919/IPEC-Himeji2022-ECCE53331.2022.9807009

Common Mode Noise Reduction of Two-Phase Interleaved Boost Converters with Integrated Magnetics Utilizing Balanced Technique Reviewed

Nagai T., Sasaki M., Imaoka J., Yamamoto M., Nakano A.

2022 International Power Electronics Conference, IPEC-Himeji 2022-ECCE Asia page： 746 - 752 2022

Authorship：Corresponding author Language：Japanese Publisher：2022 International Power Electronics Conference, IPEC-Himeji 2022-ECCE Asia

High-power density and high efficiency in boost converters are required in several applications such as motor drive systems in eco-friendly vehicles and power conditioning systems used in renewable energy systems. To realize these requirements, applying compound semiconductor devices such as GaN and SiC are attractive options because they can drive at high-switching frequency with low power losses, and it is known to contribute to the miniaturization of passive devices. However, when driving power devices with high switching speed at high-switching frequency, EMI (Electro-Magnetic Interference) noise with a wide spectrum is produced. To attenuate EMI noise, large EMI filters have to be equipped. When using large EMI filters, the downsizing effect of power converters is reduced. To countermeasure the above problem, this paper proposes interleaved boost converter with integrated magnetics capable of Common-Mode (CM) noise reduction without adding EMI filters. The noise reduction is realized by the balanced technique, which is known as an effective noise reduction technique from a circuit topology perspective. In addition, interleaved circuit topology and integrated magnetics are contributed to realizing high-power density converters. The effectiveness of the proposed converters is discussed from simulation and experimental viewpoints.

DOI： 10.23919/IPEC-Himeji2022-ECCE53331.2022.9806834

Reducing Transformer Losses with Adjustable Path-Core Type Inductance in 1.4-MHz LLC Resonant Converters Invited Reviewed

Ou Tengfei, Noah Mostafa, Tsuruya Mamoru, Namiki Seiji, Morita Koichi, Imaoka Jun, Yamamoto Masayoshi

IEEJ Journal of Industry Applications Vol. 11 ( 5 ) page： 664 - 673 2022

Authorship：Corresponding author Language：English Publisher：The Institute of Electrical Engineers of Japan

<p>Path-core type resonant inductance adjustable (PRIA) transformer usage in high-frequency LLC resonant converters is proposed herein to reduce transformer losses. The proposed magnetic structure is a type of transformer with adjustable resonant inductance combined with a path core for LLC resonant converters. In the proposed transformer, the flux density of the magnetizing inductance can be reduced with a path core. Therefore, fewer core losses are generated when using the proposed transformer. Moreover, the flux of leakage inductance that can be set with the path core has been previously proven by researchers at the Nagoya University laboratory. Consequently, the coil losses, which are one of the largest components of transformer losses, can be reduced effectively by controlling the path of the leakage flux. The proposed PRIA transformer has been reported to improve the efficiency of LLC converters. In this study, a conventional transformer with a magnetic structure is compared with a PRIA transformer through experiments. The core losses were obtained through finite-element simulations, and the coil losses not generated by the magnetic structures were estimated via calculations. The advantage of reducing transformer losses in high-frequency LLC resonant converters with PRIA-structure transformers is presented in this work.</p>

DOI： 10.1541/ieejjia.21012384

An Investigation and Proposal for Accurate Leakage Inductance Modeling Based on Dowell Model Reviewed

Wu Yu-Hsin, Shigematsu Koichi, Omoto Yasumichi, Imaoka Jun, Yamamoto Masayoshi

2022 INTERNATIONAL POWER ELECTRONICS CONFERENCE (IPEC-HIMEJI 2022- ECCE ASIA) page： 1964 - 1969 2022

An Investigation on the Relationship between CM Noise and Distribution of Parasitic Capacitance Reviewed

Sasaki Mamoru, Imaoka Jun, Yamamoto Masayoshi

2022 INTERNATIONAL POWER ELECTRONICS CONFERENCE (IPEC-HIMEJI 2022- ECCE ASIA) page： 753 - 758 2022

Analytical Model of Class-D Inverter for High-frequency Operation Reviewed

Xiong Y., Thilak S., Arai D., Yonezawa Y., Imaoka J., Yamamoto M.

IECON Proceedings (Industrial Electronics Conference) Vol. 2022-October 2022

Authorship：Corresponding author Language：English Publisher：IECON Proceedings (Industrial Electronics Conference)

This paper proposed an approach to transferring nonlinear parasitic drain-source capacitance of MOSFET to a linear model by charge-related equivalent conversion. It is applied to a previously researched analytical model of the class-D inverter to add its feasibility in high frequency. Based on the proposed approach, the relationship between maximum operation frequency, the nonlinear capacitance, and the input voltage are inferred and verified by spice simulation, resulting in good consistency.

DOI： 10.1109/IECON49645.2022.9968760

Common Mode Noise Reduction of Two-Phase Interleaved Boost Converters with Integrated Magnetics Utilizing Balanced Technique Reviewed

Nagai Tomotaka, Sasaki Mamoru, Imaoka Jun, Yamamoto Masayoshi, Nakano Akira

2022 INTERNATIONAL POWER ELECTRONICS CONFERENCE (IPEC-HIMEJI 2022- ECCE ASIA) page： 746 - 752 2022

Derivation of Resonant Period for Soft Switching by Linearizing Output Capacitance of Switching Device Reviewed

Choi Sihoon, Suzuki Ayato, Imaoka Jun, Yamamoto Masayoshi

2022 INTERNATIONAL POWER ELECTRONICS CONFERENCE (IPEC-HIMEJI 2022- ECCE ASIA) page： 2236 - 2241 2022

Derivation of Resonant Period for Soft Switching by Linearizing Output Capacitance of Switching Device Reviewed

Choi S., Suzuki A., Imaoka J., Yamamoto M.

2022 International Power Electronics Conference, IPEC-Himeji 2022-ECCE Asia page： 2236 - 2241 2022

Authorship：Last author Language：English Publisher：2022 International Power Electronics Conference, IPEC-Himeji 2022-ECCE Asia

Many soft switching techniques utilize the resonance between an inductor and parasitic output capacitor of switching device. However, output capacitance has nonlinear characteristics depending on drain-source voltage which obscure the resonant period. The proposed method estimates the resonant period by linearizing output capacitance. The method can be applied to the bridge-type converter which utilizes resonance for soft switching. Simulation and experiment with a 3-kVA prototype half bridge auxiliary resonant commutated pole inverter were implemented to verify the proposed method.

DOI： 10.23919/IPEC-Himeji2022-ECCE53331.2022.9806865

Derivation of Resonant Period for Soft Switching Considering Nonlinear Characteristics of Output Capacitance in Switching Device Reviewed

Choi Sihoon, Suzuki Ayato, Imaoka Jun, Yamamoto Masayoshi

IEEJ Journal of Industry Applications Vol. advpub ( 0 ) 2022

Authorship：Last author Language：English Publisher：The Institute of Electrical Engineers of Japan

<p>Many soft switching techniques utilize a resonance between an inductor and parasitic output capacitors of switching devices. However, output capacitance has nonlinear characteristics, which obscures the resonant period for soft switching. In this paper, a new method is proposed to derive the resonant period by considering nonlinear characteristics of the output capacitance. The method can be applied to a bridge-type converter which utilizes resonance for soft switching. Other parasitic capacitances which affect the resonant period, are also considered. To verify the proposed method, simulations and experiments were performed with a 3-kVA prototype half bridge auxiliary resonant commutated pole inverter.</p>

DOI： 10.1541/ieejjia.22006987

Feasible Evaluations of Low Profile Magnetic Structure Based on Meander Winding and Split-Magnetic Cores with High-Cooling Capability Used in Power Converters Reviewed International coauthorship International journal

Imaoka, J; Kazuya, M; Ochiai, H; Shigematsu, K; Noah, M; Yamamoto, M

2022 IEEE ENERGY CONVERSION CONGRESS AND EXPOSITION (ECCE) 2022

Authorship：Last author Language：English Publishing type：Research paper (scientific journal) Publisher：2022 IEEE Energy Conversion Congress and Exposition, ECCE 2022

It is well-known that wide-bandgap power semiconductor devices such as GaN and SiC have attractive features such as low on-resistance and capability of high switching speed, which results in realizing high power density converters. Therefore, power converters using GaN (Gallium Nitride) or SiC (Silicon Carbide) power devices have usually high efficiency, smaller passive components can be adopted than Si-based power converters by driving the converter at high switching frequency. However, driving at high switching frequency may result in a temperature rise of magnetic components, which can be one of the critical issues due to a downsized small surface area of magnetic cores and increasing power loss density per unit volume. Therefore, this paper proposes and evaluates a low-profile magnetic structure based on split-magnetic cores and meander winding capable of high cooling performance. The effectiveness of the proposed magnetic structure used in power converters is confirmed by experimental tests.

DOI： 10.1109/ECCE50734.2022.9947805

Finite Element Method based Thermal Magnetic Core Characteristics Modeling and Thermal Simulation Reviewed International journal

Ochiai, H; Shigematsu, K; Imaoka, J; Yamamoto, M

2022 IEEE 31ST INTERNATIONAL SYMPOSIUM ON INDUSTRIAL ELECTRONICS (ISIE) Vol. 2022-June page： 320 - 324 2022

Authorship：Last author Language：English Publishing type：Research paper (scientific journal) Publisher：IEEE International Symposium on Industrial Electronics

Electric vehicles and electric aircraft are being developed for decarbonization, and their power converters need to be miniaturized. High-frequency switching of semiconductors using GaN or SiC materials is an attracting attention as one of the options to reduce the size of the inductor core. On the other hand, reducing the core size leads to an increase in core temperature. Therefore, Design methods that take heat into consideration are desired, and the use of simulation is expected. Although FEM is an accurate simulation method, it takes a lot of calculation time when used as a thermal simulation during the circuit operation for several hours. Thus, accurate core loss modeling is necessary. In this study, we used accurate FEM-based modeling to perform thermal simulation of inductors in high-frequency switching.

DOI： 10.1109/ISIE51582.2022.9831609

Modeling and Design Method of Coupled Inductor Using Powder Core with Concentrated Air Gap Reviewed International coauthorship International journal

Choi, S; Imaoka, J; Yamamoto, M

2022 IEEE ENERGY CONVERSION CONGRESS AND EXPOSITION (ECCE) 2022

Authorship：Last author Language：English Publishing type：Research paper (scientific journal) Publisher：2022 IEEE Energy Conversion Congress and Exposition, ECCE 2022

Concentrated air gap is utilized to suppress soft saturation characteristics of powder cores by increasing effective magnetic reluctance. This paper proposes a high-precision magnetic circuit model for powder core in coupled inductors. The proposed model, considering soft saturation and flux cancellation, can be utilized even with large air gap, and simplifies the magnetic design. The model features good accuracy of inductance variation in a wide range of winding current. Five prototype coupled inductors were built using the proposed model and applied to a 1-kW interleaved boost converter to prove the precision of the proposed magnetic circuit.

DOI： 10.1109/ECCE50734.2022.9947578

A Magnetic Design Method for Powder Core Inductor with Concentrated Airgap Considering DC Superposition Characteristics Used for High Current Applications Reviewed International coauthorship International journal

Imaoka J., Yu-Hsin W., Shigematsu K., Noah M., Yamamoto M., Martinez W.

2021 23rd European Conference on Power Electronics and Applications, EPE 2021 ECCE Europe 2021.9

Language：English Publishing type：Research paper (scientific journal) Publisher：2021 23rd European Conference on Power Electronics and Applications, EPE 2021 ECCE Europe

Powder cores are attractive magnetic cores for high current applications such as bidirectional dc/dc converters used in power trains of eco-friendly automotive because of their high saturation flux density, high Curie temperature, and soft saturation characteristics. However, powder cores have nonlinear relative permeability characteristics dependent on the magnetic field intensity which results in a drop in the inductance value at high current values. There are two key solutions to keep constant inductance value at maximum power rating of circuit specifications: (1) inserting a concentrated airgap (2) reducing the number of turns to tackle the drop of relative permeability due to dc-bias. Therefore, this paper proposes a novel magnetic design method for powder core inductors with concentrated airgap which to keep the desired inductance constant under dc-bias conditions. The feature of the proposed design methodology is based on considering non-linear relative permeability directly based on the magnetic characteristics modeling. The validity of the proposed method is confirmed by experimental tests using EE core.

Cooperative Control of Multi-Input Modular DC/DC Converter for Electric Off-Highway Vehicles Reviewed International coauthorship International journal

Piao Qingyun, Kakisaka Tasuku, Imaoka Jun, Yamamoto Masayoshi, Konoto Masaaki

IEEJ Transactions on Industry Applications Vol. 141 ( 4 ) page： 304 - 312 2021.4

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：The Institute of Electrical Engineers of Japan

<p>A cooperative control scheme for a power conversion system having several energy sources and modular dc/dc converters is proposed in this paper. The proposed cooperative control approach has the advantage of realizing constant dynamic characteristics even when the different input voltages fluctuate or when the output power of each input voltage source is limited. The effectiveness of the proposed cooperative control method is verified via simulation and experiment.</p>

DOI： 10.1541/ieejias.141.304

Improvement of the Transmission Efficiency in the Electric Field Resonance Wireless Power Transmission by Utilizing Helical Resonators

OYANE Aoi, YAMAMOTO Masayoshi

Vol. J104-B ( 3 ) page： 309 - 311 2021.3

Authorship：Last author Language：Japanese

The efficiency of electric field resonance wireless power transmission (WPT) is low in long distances. However, the proposed system realizes high efficiency in long distances by utilizing high-Q helical resonators. The transmission efficiency of the proposed system is increased by at most 69.4% compared with the conventional system at 27.12MHz.

DOI： 10.14923/transcomj.2020gwl0001

A Novel Power Loss Calculation Method for Power Magnetic Components in Power Converters Reviewed

Ishikura Yuki, Hosotani Tatsuya, Yamamoto Masayoshi

IEEJ Transactions on Fundamentals and Materials Vol. 141 ( 1 ) page： 69 - 75 2021.1

Authorship：Last author Language：Japanese Publisher：The Institute of Electrical Engineers of Japan

<p>This paper reports a power loss calculation method for magnetic components in power converters. The differences in B-H loop areas are analyzed and discussed in case of sinusoidal waveform and square wave voltage excitation. Relying on the output results, iron loss calculation method based on square wave excitation is proposed. Experimental results show that the proposed iron loss calculation method is accurate compared with the traditional method using Steinmetz's equation. In addition, the proposed method reduces the calculation procedure compared with the method using Steinmetz's equation. The proposed iron loss calculation method is very practical and beneficial for converter designers.</p>

DOI： 10.1541/ieejfms.141.69

Effect of Tunnel Pits Radius Variation on the Electric Characteristics of Aluminum Electrolytic Capacitor Reviewed International journal

MUKAIYAMA Daisaku, YAMAMOTO Masayoshi

IEICE Transactions on Electronics Vol. E104C ( 1 ) page： 22 - 33 2021.1

Authorship：Last author Language：English Publishing type：Research paper (scientific journal) Publisher：The Institute of Electronics, Information and Communication Engineers

<p>Aluminum Electrolytic Capacitors are widely used as the smoothing capacitors in power converter circuits. Recently, there are a lot of studies to detect the residual life of the smoothing Aluminum Electrolytic Capacitors from the information of the operational circuit, such as the ripple voltage and the ripple current of the smoothing capacitor. To develop this kind of technology, more precise impedance models of Aluminum Electrolytic Capacitors become desired. In the case of the low-temperature operation of the power converters, e.g., photovoltaic inverters, the impedance of the smoothing Aluminum Electrolytic Capacitor is the key to avoid the switching element failure due to the switching surge. In this paper, we introduce the impedance calculation model of Aluminum Electrolytic Capacitors, which provides accurate impedance values in wide temperature and frequency ranges.</p>

DOI： 10.1587/transele.2020ECP5009

A simple gate driver design for GaN-based switching devices with improved surge voltage and switching loss at 1 MHz operation Reviewed

Jodo S., Iwaki T., Uchiyama K., Islam M.Z., Kataoka K., Hayakasa Y., Imaoka J., Yamamoto M., Niitsu K.

Japanese Journal of Applied Physics Vol. 60 ( SA ) 2021.1

Authorship：Corresponding author Language：English Publisher：Japanese Journal of Applied Physics

In power electronics, the impedance of reactance components increases proportionally with frequency; therefore, the sizes of reactance components can be reduced by increasing the switching frequency. Gallium nitride (GaN)-based devices have received significant attention in high-frequency applications because the figure-of-merit of GaN is superior to that of silicon (Si). However, for high-frequency operation, a trade-off relationship between the surge voltage induced by parasitic inductances, and the switching loss becomes significant. Therefore, in this study, we propose a gate driver that improves the trade-off relationship. This gate driver was obtained via the addition of simple logic circuits and capacitors to a conventional gate driver. The effectiveness of our proposed circuit was verified via SPICE simulations with Cadence Spectre using 180 nm CMOS technology. The simulation results show that by operating at 1 MHz, this circuit can help reduce the surge voltage by 12.2% and the switching loss by 14.3%.

DOI： 10.35848/1347-4065/abbdc7

Bidirectional Converter with Multi-stage FETs Featuring Voltage Balance Control Function Using Variable Capacitors

Ishikura Yuki, Hosotani Tatsuya, Yamamoto Masayoshi

IEEJ Journal of Industry Applications Vol. 10 ( 1 ) page： 100 - 106 2021

Authorship：Corresponding author Language：English Publisher：The Institute of Electrical Engineers of Japan

<p>This paper presents a bidirectional converter with multi-stage FETs featuring voltage balance control function using variable capacitors. The proposed converter is constructed using low-voltage Si-FETs in a series connection, and it improves the voltage balance between the drain-source voltages of the series connected FETs in the OFF period. Using the converter figure of merit (FOM), which can estimate the converter losses from the specifications of the FETs, the effectiveness of the proposed converter is compared to that of a converter using SiC-FETs. The factors of the voltage unbalance are analytically clarified using the equivalent circuit. The principle of voltage balance control function using the variable capacitor is discussed. The experimental results show that the proposed converter can achieve a maximum power conversion efficiency of 99.2%.</p>

DOI： 10.1541/ieejjia.19003873

Reversed Configuration Boost Converter to Reduce Effective CM Capacitance Reviewed

Sasaki Mamoru, Imaoka Jun, Yamamoto Masayoshi

2021 IEEE INTERNATIONAL FUTURE ENERGY ELECTRONICS CONFERENCE (IFEEC) 2021

Authorship：Last author Language：English Publisher：2021 IEEE International Future Energy Electronics Conference, IFEEC 2021

More and more wide band gap power devices are used in switching converters to achieve high power density and high efficiency. However,those devices increase electromagnetic interference (EMI),especially common mode (CM) noise propagates through parasitic capacitance. A noise filter is a popular way to decrease EMI. But a filter decreases the power density of the converter because of the bulk components. Therefore,a noise reduction method with small increase in volume and weight is necessary. In this paper,a novel but simple circuit configuration for high power application to reduce CM noise is investigated in simulation and experiment.

DOI： 10.1109/IFEEC53238.2021.9662002

Time-Shifted Control of Self-Synchronous Rectifier For MHz Wireless Power Transfer Systems

Sasaki Masato, Sakuno Keiichi, Yamamoto Masayoshi

PROCEEDINGS OF 2021 IEEE 30TH INTERNATIONAL SYMPOSIUM ON INDUSTRIAL ELECTRONICS (ISIE) Vol. 2021-June 2021

Language：Japanese Publisher：IEEE International Symposium on Industrial Electronics

Recently wireless power transfer systems via resonant magnetic coupling (MRC-WPT) is the promising wireless power supply method to mobile applications. 13.56MHz highly resonant wireless power receivers experience high rectifier losses when using Schottky diodes and can fail to meet the thermal limit requirements for many products such as laptops. Therefore, the synchronous rectification is one of the effective solutions. However, the increased occupancy of the control signal propagation delay in switching cycle, tend to make the introduction of the synchronous rectification difficult. This novel synchronous rectifier can operate under any propagation delay of gate drivers. The analysis successfully verified the operating principle and clarified the usefulness of the proposed control for MHz WPT systems.

DOI： 10.1109/ISIE45552.2021.9576180

A Magnetic Design Method for Powder Core Inductor with Concentrated Airgap Considering DC Superposition Characteristics Used for High Current Applications Reviewed International coauthorship International journal

Imaoka, J; Yu-Hsin, W; Shigematsu, K; Noah, M; Yamamoto, M; Martinez, W

2021 23RD EUROPEAN CONFERENCE ON POWER ELECTRONICS AND APPLICATIONS (EPE'21 ECCE EUROPE) 2021

EMI Analysis and Suppression Method Using Ferrite Beads Applied to LLC Converter Reviewed International journal

Okochi, R; Takatsuji, H; Imaoka, J; Yamamoto, M

2021 IEEE INTERNATIONAL FUTURE ENERGY ELECTRONICS CONFERENCE (IFEEC) 2021

Authorship：Last author Language：English Publishing type：Research paper (scientific journal) Publisher：2021 IEEE International Future Energy Electronics Conference, IFEEC 2021

To operate the LLC converter at high switching frequency,the excitation current flowing through the transformer is increased,which generates a large conducted noise. The peaks in the noise spectrum are caused by the ringing of the switching node voltage and the resonance of the CM equivalent circuit. In this paper,a method using ferrite beads and additional resistors in combination with the input filter is proposed to suppress the ringing. Its effectiveness in reducing the high-frequency noise while maintaining the fast-switching speed is confirmed by simulation and experiment.

DOI： 10.1109/IFEEC53238.2021.9661804

Analysis on Parasitic Capacitance to Prevent False Turn-on in GaN HEMT

Iwaki Toshihiro, Sawada Takashi, Imaoka Jun, Yamamoto Masayoshi

2021 IEEE ENERGY CONVERSION CONGRESS AND EXPOSITION (ECCE) page： 5616 - 5621 2021

Language：Japanese Publisher：2021 IEEE Energy Conversion Congress and Exposition, ECCE 2021 - Proceedings

Driving power devices such as GaN HEMTs at high-frequency is one of the successful solutions to miniaturize the magnetic components of circuits. On the other hand, GaN HEMTs have drawbacks in high-speed switching. For example, in a full-bridge inverter configuration, a fast turn-on of one power device can cause a false turn-on of the complementary power device. Therefore, the GaN HEMT might be destroyed by the overcurrent and transient heat caused by the short circuit. The most important factor for the false turn-on of GaN HEMTs is its reverse transfer capacitance (Crss), but other parasitic components such as inductances in PCB should be considered to analyze the false turn-on phenomena. In this paper the theoretical analysis of the capacitance components that may cause the false turn-on is conducted. Based on the theoretical analysis, we propose the conditions of the parasitic component of the gate drive circuit to prevent false turn-on.

DOI： 10.1109/ECCE47101.2021.9595846

A Novel Measurement Method for DC Superimposition Characteristics of Three-Phase Coupled Inductors with Powder Cores

Mishima Yamato, Aoki Tatsuya, Matsuta Kazuya, Imaoka Jun, Yamamoto Masayoshi, Yoshimoto Kosuke

2021 IEEE ENERGY CONVERSION CONGRESS AND EXPOSITION (ECCE) page： 5334 - 5341 2021

Language：Japanese Publisher：2021 IEEE Energy Conversion Congress and Exposition, ECCE 2021 - Proceedings

the objective of this research is to build the measurement method of DC superimposition of multiphase coupled inductors with powder cores. From a perspective of magnetic material, powder cores are usually applied to inductor core in high current applications such as E-mobility due to their attractive features. In addition, multiphase DC/DC converters with coupled inductors can effectively downsize passive components that occupy significant space in power converters. However, when applying coupled inductor with powder cores under the dc current superimposed condition, self-inductance and mutual inductance values of coupled inductors are varied depending on dc current values. Furthermore, measurement methods of the dc superimposition characteristics of multiphase coupled inductor have not been discussed in the relevant literature. Therefore, this paper proposes two measurement methods for DC superimposition characteristics of three-phase coupled inductors with powder cores used in three-phase DC-DC converters. The first method is for three-phase coupled inductors with an asymmetric magnetic core structure, and the values of each self-inductance and mutual inductance can be measured separately. The second method is a simplified measurement method limited to multiphase coupled inductors with symmetric magnetic core structures. DC superimposition characteristics of coupled inductors can be measured with a smaller number of measurements than the first method, and it can be extended to N phase coupled inductors. The verification of the two methods has been evaluated through simulation and experiment.

DOI： 10.1109/ECCE47101.2021.9595692

Effects of High-frequency Operation on Magnetic Components in Power Converters Reviewed International coauthorship International journal

Imaoka, J; Yu-Hsin, W; Shigematsu, K; Aoki, T; Noah, M; Yamamoto, M

2021 IEEE 12TH ENERGY CONVERSION CONGRESS AND EXPOSITION - ASIA (ECCE ASIA) page： 978 - 984 2021

Authorship：Last author Language：English Publishing type：Research paper (scientific journal) Publisher：Proceedings of the Energy Conversion Congress and Exposition - Asia, ECCE Asia 2021

Compound semiconductor devices such as Gallium Nitride (GaN) and Silicon Carbide (SiC) are actively adopted in power converters to improve power conversion efficiency, downsize passive components and miniaturize cooling systems. However, in the power converters, magnetic components often become bottlenecks in power converters from size, power losses, and temperature rise perspective. Therefore, in some cases, the attractive performance of GaN and SiC cannot be fully utilized due to the limits imposed by magnetic components. To indicate this matter from an experimental perspective, this paper conducts a fundamental investigation of the downsizing effect of magnetic components and temperature rise when varying switching frequency (85 kHz, 150 kHz, 350 kHz, 1 MHz) of a 1 kW boost converter as a case study. As results of experiments, although high-switching frequency operation contributes to downsizing magnetic component effectively, the thermal runaway of the magnetic core while driving at high frequency is confirmed due to downsized small surface area and increasing iron loss due to temperature dependency of Mn-Zn ferrite magnetic cores. For a fair comparison, the area product approach is used in the design procedure for selecting core size. The effect of the high-frequency drive is discussed from theoretical and experimental viewpoints.

DOI： 10.1109/ECCE-Asia49820.2021.9479365

13.56MHz high power half-bridge GaN-HEMT resonant inverter achieving 99% power efficiency Reviewed International journal

Oyane A., Senanayake T., Hattori F., Imaoka J., Yamamoto M., Masuda M.

9th IEEE International Conference on Power Electronics, Drives and Energy Systems, PEDES 2020 2020.12

Language：English Publishing type：Research paper (scientific journal) Publisher：9th IEEE International Conference on Power Electronics, Drives and Energy Systems, PEDES 2020

High-power inverters with high frequency have been required for progressing technologies such as wireless power transfer (WPT) and plasma processing. Recently, gallium nitride high electron mobility transistor (GaN-HEMT) is getting lots of attention from the viewpoint of fast switching ability and low power consumption. However, GaN-HEMT inverters are difficult to be operated in over several kW because of its low drain-source breakdown voltage. In other words, the conventional half-bridge GaN-HEMT inverter can output high power only for the small load resistance less than several-O. This paper overcomes this difficulty by implementing an impedance conversion network in the prior stage of the series resonator. The proposed topology realizes not only high-power from low drain-source voltage but also the sine wave output with very low harmonics. 3kW output to 50O load at 13.56MHz is theoretically designed, and verified by computer simulations. And also, the experimental prototype using GaN-HEMTs achieves the high efficiency of 99.43% at 13.56MHz and 471W.

DOI： 10.1109/PEDES49360.2020.9379451

Magnetic Design Method for Multi-Material Inductor to Flatten Efficiency Curve of Power Converters within Wide Load Ranges Invited Reviewed

Ishikura Y, Imaoka J., Noah M., Aoki T, Ito K, Yamamoto M

IEEE Transactions on Magnetics Vol. 56 ( 10 ) page： 1 - 8 2020.10

Magnetic Design Method for Multi-Material Inductor to Flatten Efficiency Curve of Power Converters Within Wide Load Ranges Reviewed International coauthorship International journal

Ishikura Yuki, Imaoka Jun, Noah Mostafa, Aoki Tatsuya, Ito Koichiro, Yamamoto Masayoshi

IEEE TRANSACTIONS ON MAGNETICS Vol. 56 ( 10 ) 2020.10

Output Power Pulsation Suppressed with an Activity Smoothen Buck-Boost Converter to Achieve Electrolytic Capacitor-less AC/DC Converter

Ou T., Namiki S., Tsuruya M., Noah M., Morita K., Mukaiyama D., Imaoka J., Yamamoto M.

12th AEIT International Annual Conference, AEIT 2020 2020.9

Language：Japanese Publisher：12th AEIT International Annual Conference, AEIT 2020

An Activity Smoothen Circuit with bidirectional Buck-Boost Converter (AS-BBC) was approached to smoothen the output power of a power factor correction (PFC) converter, which is an AC/DC converter, without using any electrolytic capacitors in this paper. In order to smoothen the output pulsation current of the PFC converter, electrolytic capacitors have been used generally, since electrolytic capacitors have a large magnitude capacity. However, there is a lifespan to electrolytic capacitors. On the other hand, film capacitors have a semi-permanent lifespan with so much less magnitude capacity than electrolytic capacitors. A way of using the AS-BBC to make a small capacitor work like a large capacitor as a smoothing capacitor to handle the output power is presented in this paper. Approximately 47% of the pulsation output is suppressed with a 4.4μ F film capacitor with the AS-BBC. Since there is no electrolytic capacitor adapted, a semi-permanent lifespan PFC converter is achieved successfully.

DOI： 10.23919/AEIT50178.2020.9241166

Temperature Dependency Modeling, Simulation and Experimental Validations of DC Superimposition Characteristics for Gapped-Ferrite Inductor Including Saturation Region

Imaoka J., Aoki T., Shigematsu K., Yamamoto M.

IEEE International Symposium on Industrial Electronics Vol. 2020-June page： 1466 - 1473 2020.6

Language：Japanese Publisher：IEEE International Symposium on Industrial Electronics

To realize the early development of power converters, research on the front-loading design in which the efficiency, control characteristics, converter size, thermal management, and Electromagnetic Compatibility (EMC) are carefully considered before making a prototype, has been attracting. To carefully design and predict these design factors before prototyping, making accurate models of active/passive components operated on simulation of the multi-physical domain such as thermal, magnetic, and electrical is indispensable. This is because these characteristics of active/passive components on power converters are affected by each other. In this background, this paper proposes a nonlinear relative permeability modeling method with a temperature dependency of gapped-ferrite cores. The temperature dependency of the effective relative permeability of the gapped-ferrite core is investigated under core temperature within-50°C-+ 150°C. As features of the proposed modeling method and simulation model, a simple mathematical equation and lookup tables are utilized for simple implementation to the simulator. The validity of the proposed modeling method is confirmed by both simulation and experimental tests under operating conditions including the magnetic saturation regions.

DOI： 10.1109/ISIE45063.2020.9152521

Analysis of Common Mode Noise Reduction Mechanism in A Shielded Inductor

Sasaki M., Imaoka J., Yamamoto M., Nakano A., Fuse K.

IEEE International Symposium on Industrial Electronics Vol. 2020-June page： 660 - 665 2020.6

Language：Japanese Publisher：IEEE International Symposium on Industrial Electronics

To achieve high power density, a power converter circuit is often operated at high frequency, and fast switching devices are also combined to reduce switching loss. On the other hand, both high frequency and fast switching greatly increases conductive noise amplitude at frequency over several megahertz. Therefore, electromagnetic compatibility (EMC) is necessary for a high power density converter. However, an additional filter, which consists of large and heavy passive elements, greatly degrades power density. Thus, in this paper, a noise reduction method for noise at frequency band over 10 MHz with small volume increase is presented and investigated. Consequently, the simulation and experimental result verifies that the proposed method decreases MHz-band noise with small volume increase.

DOI： 10.1109/ISIE45063.2020.9152408

Comparison of switching performance between GaN and SiC MOSFET via 13. 56MHz Half-bridge Inverter

Xiong Y., Oyane A., Ou T., Thilak S., Imaoka J., Yamamoto M.

IEEE International Symposium on Industrial Electronics Vol. 2020-June page： 672 - 676 2020.6

Language：Japanese Publisher：IEEE International Symposium on Industrial Electronics

Both silicon-carbide (SiC) and gallium-nitride (GaN) are wide bandgap power transistor which are developing rapidly. They are able to be used as the main switches in the high-frequency power conversion systems successfully. These high-frequency switches just meet the high demand of low-size power electronics device in recent years. As the high-frequency system always relies on the switches, we designed and made evaluation boards for both SiC and GaN switches by 13. 56MHz half-bridge inverter. Both simulation and experimental results show that GaN achieved more successfully switching, which made good output waveform with very short dead-time. And in simulation, lower switching loss of GaN is also confirmed. As all above, it is obvious that GaN device is more suitable for high-frequency application.

DOI： 10.1109/ISIE45063.2020.9152253

Technical Trend of Power Electronics Systems for Automotive Applications Invited Reviewed

Yamamoto M., Kakisaka T, Imaoka J

Japanese Journal of Applied Physics Vol. 59 ( SG ) page： 0805-1 - 0805-13 2020.4

多段FET駆動技術を用いた双方向コンバータ Invited Reviewed

石倉祐樹 ,細谷達也, 山本真義

電子情報通信学会論文誌 B Vol. J103-B ( No.4 ) page： .154 - 161 2020.4

Technical trend of power electronics systems for automotive applications Reviewed International journal

JAPANESE JOURNAL OF APPLIED PHYSICS Vol. 59 2020.4

Bidirectional Converter Using Multi-stage FET Driving Technique

ISHIKURA Yuki, HOSOTANI Tatsuya, YAMAMOTO Masayoshi

Vol. J103-B ( 4 ) page： 154 - 161 2020.4

Language：Japanese

This paper presents a bidirectional converter using by multi-stage FET driving technique. The proposed converter is constructed by implementing series connected low voltage Si-FETs in multi-stage. A driving circuit using multi-stage driving technique can drive series connected FETs from the one power supply without any isolated power supplies and high voltage process ICs. In addition, the balancing capacitors which constructed the converter have voltage averaging function in drain-source voltage to tackle the voltage unbalance between the series connected FETs. Using the figure of merit which can estimate converter losses from the specification of power devices, the usefulness of the circuit configuration which using low voltage Si-FETs instead of SiC-FETs is shown. The effect of the voltage averaging function by the balancing capacitors, the operating principle of the driving circuit and the power conversion mechanism are clarified and presented using the circuit simulator and a converter equivalent circuit. The experimental results show that the proposed driving technique allows the bidirectional converter to achieve a maximum power conversion efficiency of 99.2%.

DOI： 10.14923/transcomj.2019jbp3022

Bidirectional Converter with Multi-stage FETs Featuring Voltage Balance Control Function Using Variable Capacitors

Ishikura Yuki, Hosotani Tatsuya, Yamamoto Masayoshi

IEEJ Transactions on Industry Applications Vol. 140 ( 3 ) page： 168 - 174 2020.3

Language：Japanese Publisher：The Institute of Electrical Engineers of Japan

<p>This paper presents a bidirectional converter with multi-stage FETs featuring voltage balance control function using variable capacitors. The proposed converter is constructed using low-voltage Si-FETs in a series connection, and it improves the voltage balance between the drain-source voltages of the series connected FETs in the OFF period. Using the converter figure of merit (FOM), which can estimate the converter losses from the specifications of the FETs, the effectiveness of the proposed converter is compared to that of a converter using SiC-FETs. The factors of the voltage unbalance are analytically clarified using the equivalent circuit. The principle of voltage balance control function using the variable capacitor is discussed. The experimental results show that the proposed converter can achieve a maximum power conversion efficiency of 99.2%.</p>

DOI： 10.1541/ieejias.140.168

Voltage Balancing Control Method Using Variable Capacitors with Simple Turn-on Adjusting Function for Multi-Stage FET Bidirectional Converter

Ishikura Y., Hosotani T., Noah M., Imaoka J., Yamamoto M.

Conference Proceedings - IEEE Applied Power Electronics Conference and Exposition - APEC Vol. 2020-March page： 2944 - 2949 2020.3

Language：Japanese Publisher：Conference Proceedings - IEEE Applied Power Electronics Conference and Exposition - APEC

This paper proposes a voltage balancing control method using variable capacitors with simple turn-on adjusting function for multi-stage FET bidirectional converter. The proposed voltage balancing control circuit is composed of a feedback circuit using photocouplers and a delay circuit using variable capacitors with turn-on adjusting diodes. The proposed voltage balancing circuit can reduce the drain-source voltage unbalance which occur during the turn-on and turn-off period of series-connected FETs. The theoretical discussion includes analyzing the unbalanced drain-source voltage in seriesconnected FETs using a simplified converter. Also, the principal of the proposed voltage balancing control method is clarified. The experimental results show that the proposed voltage balancing control method can reduce the drain-source voltage difference Δvds of series-connected FETs from 36 V to 11 V (69% reduction in Δvds) during the turn-off and from 22 V to 11 V (50% reduction in Δvds) during the turn-on period. The multistage FET bidirectional converter can achieve a maximum power conversion efficiency of 99.2%.

DOI： 10.1109/APEC39645.2020.9124221

Effects of Secondary Leakage Inductance on the LLC Resonant Converter Reviewed International coauthorship International journal

Noah Mostafa, Shirakawa Tomohide, Umetani Kazuhiro, Imaoka Jun, Yamamoto Masayoshi, Hiraki Eiji

IEEE TRANSACTIONS ON POWER ELECTRONICS Vol. 35 ( 1 ) page： 835 - 852 2020.1

Acute Pain Intensity After Collagenase Clostridium histolyticum Injection in Patients With Dupuytren Contracture

Noto K., Yamamoto M., Iwatsuki K., Kurimoto S., Tatebe M., Hirata H.

Journal of Hand Surgery Global Online Vol. 2 ( 1 ) page： 16 - 20 2020.1

Language：English Publisher：Journal of Hand Surgery Global Online

Purpose: To investigate multidimensional pain intensity and quality after collagenase Clostridium histolyticum (CCH) injection in patients with Dupuytren contracture using a pain visual analog scale (VAS) and the revised version of the Short-Form McGill Pain Questionnaire (SF-MPQ-2). Methods: This prospective observational study was carried out from 2015 to 2017. As a primary end point, patients completed the pain VAS (range, 0 [no pain] to 100) and SF-MPQ-2 before and after CCH injection; 3, 9, and 24 hours after CCH injection; after the extension procedure; and 3 and 7 days after CCH injection. In addition, they reported the dose and duration of supplementary analgesic use during this period. Results: A total of 41 patients were enrolled in this study (51 joints). Mean pain VAS score (mean ± SD, 34 ± 21) was maximal 9 hours after CCH injection and decreased within the following 7 days. The total score of the SF-MPQ-2 significantly increased after CCH treatment and decreased in the 7 days after the injection. Among the SF-MPQ-2 subscales, the highest and lowest scores after CCH injection were recorded for continuous pain and affected descriptors, respectively. Nonsteroidal anti-inflammatory drugs were most frequently self-administered during 7 days after the extension procedure compared with any other study period. Conclusions: The pain VAS and SF-MPQ-2 revealed acute pain after CCH injection. However, all examined pain aspects dramatically improved within 7 days after injection. Pain after CCH injection is characterized by low scores in the Affective Descriptors subscale of the SF-MPQ-2. Type of study/level of evidence: Prognostic Ⅳ.

DOI： 10.1016/j.jhsg.2019.10.004

A simple gate driver design for GaN-based switching devices with improved surge voltage and switching loss at 1-MHz operation Invited Reviewed

Shota Jodo, Toshihiro Iwaki, Kosuke Uchiyama, Md. Islam, Kensuke Kataoka, Yuki Hayasaka, Jun Imaoka, Masayoshi Yamamoto, Kiichi Niitsu

Japanese Journal of Applied Physics Vol. No. 60 ( SADD02 ) page： SAAD02-1 - SAAD02 2020

Analysis of Common Mode Noise Reduction Mechanism in A Shielded Inductor

Sasaki Mamoru, Imaoka Jun, Yamamoto Masayoshi, Nakano Akira, Fuse Koji

2020 IEEE 29TH INTERNATIONAL SYMPOSIUM ON INDUSTRIAL ELECTRONICS (ISIE) page： 660 - 665 2020

Comparison of switching performance between GaN and SiC MOSFET via 13.56MHz Half-bridge Inverter

Xiong Yi, Oyane Aoi, Ou Tengfei, Thilak Senanayake, Imaoka Jun, Yamamoto Masayoshi

2020 IEEE 29TH INTERNATIONAL SYMPOSIUM ON INDUSTRIAL ELECTRONICS (ISIE) page： 672 - 676 2020

Temperature Dependency Modeling, Simulation and Experimental Validations of DC Superimposition Characteristics for Gapped-Ferrite Inductor Including Saturation Region

Imaoka Jun, Aoki Tatsuya, Shigematsu Koichi, Yamamoto Masayoshi

2020 IEEE 29TH INTERNATIONAL SYMPOSIUM ON INDUSTRIAL ELECTRONICS (ISIE) page： 1466 - 1473 2020

Voltage Balancing Control Method Using Variable Capacitors with Simple Turn-on Adjusting Function for Multi-Stage FET Bidirectional Converter

Ishikura Yuki, Hosotani Tatsuya, Noah Mostafa, Imaoka Jun, Yamamoto Masayoshi

2020 THIRTY-FIFTH ANNUAL IEEE APPLIED POWER ELECTRONICS CONFERENCE AND EXPOSITION (APEC 2020) page： 2944 - 2949 2020

Energy Management Storage System with a Multi-stage FET Bidirectional Converter

Ishikura Yuki, Hosotani Tatsuya, Yamamoto Masayoshi

Journal of the Japan Institute of Power Electronics Vol. 46 ( 0 ) page： 44 - 50 2020

Language：Japanese Publisher：The Japan Institute of Power Electronics

This paper presents an energy management storage system with a multi-stage FET bidirectional converter. The
proposed system is constructed by a bidirectional converter using series connected FETs, and it realizes highly energy management that maximizes battery performance. By calculating the power loss using the converter performance index FOM (Figure of merit), it is shown that the proposed configuration can be possible to reduce the power loss 70% compared to the conventional configuration. In the proposed system, using a power control method that reduces the charging current, the battery charging losses can be reduced 60%. The analysis results show that the proposed system can achieve a charging energy efficiency of 96.9%, and reduce the yearly CO2 emission of 33%.

DOI： 10.5416/jipe.46.44

Dielectric Characteristics Analysis of Aluminum Electrolytic Capacitors Based on Linear Response Function Reviewed International journal

Mukaiyama Daisaku, Yamamoto Masayoshi

JOURNAL OF THE ELECTROCHEMICAL SOCIETY Vol. 166 ( 16 ) page： E554 - E563 2019.12

Modeling, Magnetic Design, Simulation Methods, and Experimental Evaluation of Various Powder Cores Used in Power Converters Considering Their DC Superimposition Characteristics Reviewed International coauthorship International journal

Imaoka Jun, Okamoto Kenkichiro, Shoyama Masahito, Ishikura Yuki, Noah Mostafa, Yamamoto Masayoshi

IEEE TRANSACTIONS ON POWER ELECTRONICS Vol. 34 ( 9 ) page： 9033 - 9051 2019.9

Comprehensive Analysis of Coupled Inductors with Powder Cores Used in Interleaved Converter: Measurement, Modeling, Design Methods, and Experimental Evaluation

Aoki T., Imaoka J., Yamamoto M., Yoshimoto K.

Proceedings of the International Conference on Power Electronics and Drive Systems Vol. 2019-July 2019.7

Language：Japanese Publisher：Proceedings of the International Conference on Power Electronics and Drive Systems

One of the best techniques for downsizing power converters is to use coupled inductors in multiphase circuits. Meanwhile, from a magnetic material perspective, powder core material is well known as an attractive magnetic material with superior features such as high saturation flux density. However, since the relative permeability of power cores depends on the magnetic field intensity, designing coupled inductors is difficult, and the modeling method is not well discussed in the relevant literature. The purpose of this research is to model coupled inductors with powder cores and present a simple magnetic design method. A model of coupled inductors is created by a novel measurement method of the dc superimposition characteristic unique to the coupled inductor of two-phase interleaved circuits. Furthermore, a design method based on a theoretical analysis using a magnetic circuit model had been established. The validity and effectiveness of the proposed methods are confirmed from simulation and experimental tests. This research is helpful in the field of the model-based development of coupled inductors.

DOI： 10.1109/PEDS44367.2019.8998883

Effects of secondary leakage inductance on the LLC resonant converter - Part II: Frequency control bandwidth with respect to load variation

Noah M., Shirakawa T., Umetani K., Imaoka J., Yamamoto M., Hiraki E.

Conference Proceedings - IEEE Applied Power Electronics Conference and Exposition - APEC Vol. 2019-March page： 1408 - 1414 2019.5

Publisher：Conference Proceedings - IEEE Applied Power Electronics Conference and Exposition - APEC

Resonant converters rely on a precise knowledge of leakage inductance of the equipped transformers. Resonant circuit topologies such as LLC usually utilize the transformer leakage as an inductive component in the resonant tank, allowing for a drastic reduction in the converter weight, size and volume. The existence of the secondary leakage inductance affects the whole operation of the LLC resonant converter. This paper reveals that placing the secondary winding near the air gap would increase the resonant tank input impedance, vertically shrink the voltage-gain curve of the converter, and consequently minimize the frequency range (i.e frequency bandwidth with respect to load variation). On contrary, placing the secondary winding in a close contact with the magnetic core would decrease the resonant tank input impedance, vertically stretches the voltage-gain curve of the converter, and widen the frequency variation range. It has been reported that the winding location with respect to the air gap has an impact on the leakage inductance value. In other words, placing the secondary winding in a close contact with the magnetic core (zero mmf position) would maximize the leakage energy storage originated from the secondary winding, and hence maximize the secondary leakage inductance and vice versa. The theoretical discussion is presented which is merely based on Ampere's law and Dowell's model. Furthermore, transformer prototypes had been constructed and tested in a 390V/12V-220W LLC converter prototype to evaluate the proposed analysis.

DOI： 10.1109/APEC.2019.8722190

Effects of secondary leakage inductance on the LLC resonant converter - Part i: Transformer voltage gain and efficiency

Noah M., Shirakawa T., Umetani K., Imaoka J., Yamamoto M., Hiraki E.

Conference Proceedings - IEEE Applied Power Electronics Conference and Exposition - APEC Vol. 2019-March page： 780 - 786 2019.5

Publisher：Conference Proceedings - IEEE Applied Power Electronics Conference and Exposition - APEC

Minimizing the transformer magnetizing inductance is essential for the soft switching operation of the LLC resonant converter, despite the fact that it results in higher values of magnetizing current, which deteriorates the converter efficiency. Furthermore, it is a well-known practice to utilize the transformer leakage as an inductive component in the resonant tank to improve the power destiny. This paper reveals that the transformer voltage gain can be improved when the transformer leakage inductance in concentrated on the secondary side to avoid the voltage drop inflicted by the relatively large value of the magnetizing current (im), especially at light load condition. The theoretical discussion relies on the asymmetry of the EI core by placing the secondary winding in a close contact with the magnetic core and placing the primary winding in the vicinity of the air gap. Moreover, noise absorber had been utilized to control the leakage inductance value. The proposed transformer design maximizes the value of the secondary leakage inductance and minimizes the primary leakage inductance. Alongside with the theoretical discussion, experimental tests had been conducted to evaluate the proposed method using a 390V-12V, 220W LLC resonant converter.

DOI： 10.1109/APEC.2019.8721980

Bidirectional Converter with Balancing Capacitor using Multi-stage FET Driving Technique

Ishikura Y., Imaoka J., Noah M., Yamamoto M.

2019 IEEE 3rd International Conference on DC Microgrids, ICDCM 2019 2019.5

Language：Japanese Publisher：2019 IEEE 3rd International Conference on DC Microgrids, ICDCM 2019

This paper proposes a bidirectional converter with balancing capacitor using multi-stage FET driving technique. The proposed converter is constructed by implementing series-connected low voltage Si-FETs in multi-stages. The balancing capacitor can average the applied voltage on FETs in the transient state of the switching operation and tackle the voltage unbalance between the series-connected FETs. The proposed driving circuit is using multi-stage FET driving technique and can drive all the series-connected FETs using only one power supply. The effect of the balancing capacitor and the proposed driving technique are clarified and presented using the circuit simulator and the converter equivalent circuit. The proposed topology improves the converter power conversion efficiency. The experimental results show that the proposed driving technique allows the bidirectional converter to achieve a maximum power conversion efficiency of 99.2%.

DOI： 10.1109/ICDCM45535.2019.9232896

Cooperative Control of Multi-Input Modular DC/DC Converter for Electric Off-Highway Vehicles

Piao Q., Konoto M., Kakisaka T., Imaoka J., Yamamoto M.

2019 IEEE 3rd International Conference on DC Microgrids, ICDCM 2019 2019.5

Language：Japanese Publisher：2019 IEEE 3rd International Conference on DC Microgrids, ICDCM 2019

This paper proposes a cooperative control used in a power conversion system consists of several energy sources and modular DC/DC converters. The proposed cooperative control method has attractive features of realizing constant dynamic characteristics even when each input voltage fluctuates or in case of the output power of each input voltage source is limited. The proposed cooperative control method has dual control loops with current control as an inner loop and voltage control as the outer loop. In addition, feed-forward control of the input voltage and the compensators for each control loop are implemented to suppress the influence of input voltage fluctuation or power capacity limit on dynamic characteristics. The effectiveness of the proposed control is validated by simulation test.

DOI： 10.1109/ICDCM45535.2019.9232868

Magnetic Design Method for Multi-Material Powder Core Inductor to Improve Efficiency of Bidirectional DC/DC Converter within Wide Load Range

Imaoka J., Ishikura Y., Ito K., Aoki T., Noah M., Yamamoto M.

ICPE 2019 - ECCE Asia - 10th International Conference on Power Electronics - ECCE Asia 2019.5

Publisher：ICPE 2019 - ECCE Asia - 10th International Conference on Power Electronics - ECCE Asia

Utilizing powder cores in many power electronics applications have been gaining much attention due to their attractive magnetic properties. However, it is quite challenging for the circuit designer to choose the proper core, as there are many kinds of magnetic powder cores available in the market. Therefore, due to the limitation of a single magnetic material property, it is often difficult to realize high power conversion efficiency within wide load ranges, including light and heavy load conditions. This paper proposes a novel design method of the multi-material inductor which combines multiple powder cores having different material properties. The aim of this work is to provide improved efficiency over the entire load range of power converters. The experimental results have proven that the inductor with multi-material powder cores can improve the efficiency over wide load range. The validity and effectiveness of the proposed magnetic design method are confirmed from theoretical analysis, simulation and experimental tests.

東海支部における地域貢献活動紹介

山本真義

電気学会誌 Vol. 139 ( 4 ) page： 244 - 244 2019.4

Introduction: Applications Roadmap of GaN Power Semiconductor Devices

YAMAMOTO Masayoshi

The Journal of The Institute of Electrical Engineers of Japan Vol. 139 ( 2 ) page： 76 - 79 2019.2

Comparative Evaluation of Electrical and Calorimetric Methods to Estimate Core Loss in Powder Cores

Ishikura Yuki, Imaoka Jun, Noah Mostafa, Yamamoto Masayoshi

IEEJ Journal of Industry Applications Vol. 8 ( 3 ) page： 386 - 393 2019

Language：Japanese Publisher：The Institute of Electrical Engineers of Japan

<p>The utilization of powder cores for many power electronic applications has drawn a significant amount of attention owing to their attractive magnetic properties. However, because of their low relative permeability characteristics, a precise measurement of the core loss is very difficult to obtain. Imprecise estimation of the core loss may lead to an inaccurate thermal design of power converters. Measuring and calculating the accurate value of the core loss allows the circuit designer to design a more efficient system. This paper discusses the revalidation of electrical measurement by comparing the electrical method with the calorimetric method in powder cores. The calorimetric method is one of the most promising methods to accurately measure the core loss; however, it is time consuming. A difference less than 10% has been reported for the core loss measurement error while comparing the electrical method and the calorimetric method in various conditions. These results indicate that the electrical method using the B-H analyzer is effective for measuring the core losses in some conditions for powder cores. Along with the theoretical discussion, simulation and experimental tests are also conducted.</p>

DOI： 10.1541/ieejjia.8.386

Magnetic Design Method for Multi-Material Powder Core Inductor to Improve Efficiency of Bidirectional DC/DC Converter within Wide Load Range Reviewed International coauthorship International journal

Imaoka J., Ishikura Y., Ito K., Aoki T., Noah M., Yamamoto M.

2019 10TH INTERNATIONAL CONFERENCE ON POWER ELECTRONICS AND ECCE ASIA (ICPE 2019 - ECCE ASIA) 2019

Effects of Secondary Leakage Inductance on the LLC Resonant Converter-Part II: Frequency Control Bandwidth with respect to Load Variation Reviewed International coauthorship International journal

Noah Mostafa, Shirakawa Tomohide, Umetani Kazuhiro, Imaoka Jun, Yamamoto Masayoshi, Hiraki Eiji

THIRTY-FOURTH ANNUAL IEEE APPLIED POWER ELECTRONICS CONFERENCE AND EXPOSITION (APEC 2019) page： 1408 - 1414 2019

Effects of Secondary Leakage Inductance on the LLC Resonant Converter-Part I: Transformer Voltage Gain and Efficiency Reviewed International coauthorship International journal

Noah Mostafa, Shirakawa Tomohide, Umetani Kazuhiro, Imaoka Jun, Yamamoto Masayoshi, Hiraki Eiji

THIRTY-FOURTH ANNUAL IEEE APPLIED POWER ELECTRONICS CONFERENCE AND EXPOSITION (APEC 2019) page： 780 - 786 2019

Comprehensive Analysis of Coupled Inductors with Powder Cores Used in Interleaved Converter: Measurement, Modeling, Design Methods, and Experimental Evaluation

Aoki Tatsuya, Imaoka Jun, Yamamoto Masayoshi, Yoshimoto Kosuke

2019 IEEE 13TH INTERNATIONAL CONFERENCE ON POWER ELECTRONICS AND DRIVE SYSTEMS (PEDS) 2019

Study on the Imbalanced Voltage of Series-connected Active Power Semiconductor Devices in Power Conversion Systems

Zhang Hongjing, Imaoka Jun, Noah Mostafa, Ishikura Yuki, Yamamoto Masayoshi

2019 IEEE WORKSHOP ON WIDE BANDGAP POWER DEVICES AND APPLICATIONS IN ASIA (WIPDA ASIA 2 2019

Bidirectional Converter with Balancing Capacitor using Multi-stage FET Driving Technique

Ishikura Yiki, Imaoka Jun, Noah Mostafa, Yamamoto Masayoshi

2019 IEEE THIRD INTERNATIONAL CONFERENCE ON DC MICROGRIDS (ICDCM) 2019

Cooperative Control of Multi-Input Modular DC/DC Converter for Electric Off-Highway Vehicles

Piao Qingyun, Konoto Masaaki, Kakisaka Tasuku, Imaoka Jun, Yamamoto Masayoshi

2019 IEEE THIRD INTERNATIONAL CONFERENCE ON DC MICROGRIDS (ICDCM) 2019

Common Mode Conductive Noise Cancellation for Multiphase Converter Using Auxiliary Winding

Sasaki Mamoru, Imaoka Jun, Yamamoto Masayoshi, Nakano Akira, Fuse Koji

2019 IEEE THIRD INTERNATIONAL CONFERENCE ON DC MICROGRIDS (ICDCM) 2019

A Novel Transformer Structure Used in a 1.4 MHz LLC Resonant Converter with GaNFETs

Ou T., Noah M., Morita K., Tsuruya M., Namiki S., Imaoka J., Yamamoto M.

Proceedings - 2018 IEEE International Power Electronics and Application Conference and Exposition, PEAC 2018 2018.12

Publisher：Proceedings - 2018 IEEE International Power Electronics and Application Conference and Exposition, PEAC 2018

A novel integrated magnetic structure suitable for a high-frequency switching current resonant converter (LLC) with GaNFETs is proposed in this paper. Creating a leakage inductance to resonate with a capacitor, and the mutual inductance in an LLC resonant converter is the most common solution. However, the volume of leakage inductance is very difficult to be controlled or adjusted. Furthermore, the losses may increase when the leakage fluxes cross the patterns on the PCB board or the primary and secondary coils. In order to tackle this problem, a new magnetic structure core is proposed in this paper. The proposed magnetic structure can decrease the losses of the core, which means the magnetic structure proposed in this paper can improve the efficiency of the converter. A power density of approximately 2.6 W/cm 3 has been realized for the 1.4-MHz LLC resonant converter with the proposed magnetic structure with a maximum efficiency of 96.4%. Along with the theoretical discussion, finite element analysis (FEA) electromagnetic simulation and experimental results are also presented.

DOI： 10.1109/PEAC.2018.8590446

Fundamental Experiment of 3-phase Electric Resonant Coupling Wireless Power Transfer Reviewed International journal

Hattori F., Imaoka J., Yamamoto M., Masuda M.

7th International IEEE Conference on Renewable Energy Research and Applications, ICRERA 2018 page： 1417 - 1422 2018.12

Language：English Publishing type：Research paper (scientific journal) Publisher：7th International IEEE Conference on Renewable Energy Research and Applications, ICRERA 2018

Lots of researches of electric coupling is performed for wireless power transfer system. For achieving high power transfer, electric resonant coupling is used. A 3-phase electric resonant coupling is one option for higher power wireless transfer. However, as far as the author knows, much less work has been done for a 3-phase electric resonant coupling. In this paper, fundamental experiment of a 3-phase electric resonant coupling wireless power transfer is performed. From experiment results, the possibility that 3-phase electric resonant coupling can be used for wireless power transfer has been found.

DOI： 10.1109/ICRERA.2018.8566938

Magnetic Design and Experimental Evaluation of a Commercially Available Single Integrated Transformer in Three-Phase LLC Resonant Converter Reviewed International coauthorship International journal

Noah Mostafa, Kimura Shota, Imaoka Jun, Martinez Wilmar, Endo Shun, Yamamoto Masayoshi, Umetani Kazuhiro

IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS Vol. 54 ( 6 ) page： 6190 - 6204 2018.11

Core Loss Evaluation in Powder Cores: A Comparative Comparison between Electrical and Calorimetric Methods

Ishikura Y., Imaoka J., Noah M., Yamamoto M.

2018 International Power Electronics Conference, IPEC-Niigata - ECCE Asia 2018 page： 1087 - 1094 2018.10

Language：Japanese Publisher：2018 International Power Electronics Conference, IPEC-Niigata - ECCE Asia 2018

Utilizing powder cores in many power electronics applications have gained interest due to the attractive magnetic properties of powder core materials. For instance, powder cores have soft saturation characteristics and high saturation flux density compared to gapped ferrites. However, due to their low relative-permeability and the low loss characteristics, a precise measurement of the core losses is very difficult to be obtained. One of the common approaches to measure core losses is by measuring the electrical signals of the winding terminals, we hereafter refer it as electrical methods. Another alternative approach is calorimetric methods, which rely on measuring the core temperature rise. Nonetheless, these methods may have huge measurement error in case of powder cores. This paper evaluates the accuracy of measuring core losses in powder cores, and a comparison between the electrical and calorimetrical methods is presented. Along with the theoretical discussion, simulation and experimental tests are conducted.

DOI： 10.23919/IPEC.2018.8508012

Multiple Exciting Voltage Control for Maximization of Multi-hop Wireless Power Transfer Efficiency

Sasaki M., Yamamoto M.

2018 International Power Electronics Conference, IPEC-Niigata - ECCE Asia 2018 page： 3344 - 3348 2018.10

Publisher：2018 International Power Electronics Conference, IPEC-Niigata - ECCE Asia 2018

Recently multi-hop wireless power transfer (WPT) systems for the area extension of a wireless battery charging have been addressed by several research groups. This paper describes a discrete exciting voltage control technique for the multi-hop WPT system via magnetic resonant coupling which can maximize the power transfer efficiency in response to the change of coupling status. The theory allows the equations of the wireless power transfer efficiency of the system to be determined at all the ratio of the mutual inductance. The calculated results are included to confirm the advantage to single transmitting multi-hop WPT systems.

DOI： 10.23919/IPEC.2018.8508026

Modeling, Magnetic Design, and Simulation Methods Considering DC Superimposition Characteristic of Powder Cores Used in Power Converters

Imaoka J., Okamoto K., Shoyama M., Ishikura Y., Noah M., Yamamoto M.

2018 International Power Electronics Conference, IPEC-Niigata - ECCE Asia 2018 page： 1095 - 1102 2018.10

Publisher：2018 International Power Electronics Conference, IPEC-Niigata - ECCE Asia 2018

Powder cores have been gained much attention as one of the attractive magnetic cores used in power converters due to their superior features such as high saturation flux density or distributed air gaps. However, powder cores have a unique feature that the relative permeability of the magnetic core varies depending on the magnetic field intensity. However, modeling the variable relative permeability, the design method for powder cores, and computer simulation methods of non-linear inductance are well not discussed in the related literature. Therefore, this paper proposes a novel modeling, magnetic design methods, and simulation technique considering dc superimposition characteristics of powder cores. The modeling method uses a novel model equation representing the behavior of relative permeability under the dc current superimposition condition, which is helpful to evaluate the performance of powder cores and to properly design various magnetic components. Theoretical analysis has been presented and the effectiveness and the validity of the proposed methods are evaluated through simulation and experimental tests.

DOI： 10.23919/IPEC.2018.8507874

Parasitic Inductance Design Considerations to Suppress Gate Voltage Oscillation of Fast Switching Power Semiconductor Devices Reviewed International journal

Sugihara Y., Nanamori K., Yamamoto M., Kanazawa Y.

2018 International Power Electronics Conference, IPEC-Niigata - ECCE Asia 2018 page： 2789 - 2795 2018.10

Language：English Publishing type：Research paper (scientific journal) Publisher：2018 International Power Electronics Conference, IPEC-Niigata - ECCE Asia 2018

Fast switching power semiconductor devices such as SiC MOSFET and GaN FET have attracting increasing attention because of superior switching capability which contributes to high efficiency and high power density of power converters. However, fast switching capability generates large switching noise. Particularly, parasitic oscillation observed in the gate voltage is a severe problem due to the gate-source breakdown. This paper hypothesized that the gate resonator selectively takes in parasitic oscillation caused by a power circuit because of its frequency characteristic and analyzed the gate voltage oscillation. As a result, the phenomenon is characterized by an oscillation susceptibility which indicates susceptibility of the gate voltage to a drain voltage oscillation. Moreover, the oscillation susceptibility predicts the parasitic inductance dependency of the gate voltage oscillation. Therefore, the parasitic inductance should be designed to suppress this oscillation considering the oscillation susceptibility. Results obtained by simulation and experiment indicated appropriateness of analysis results.

DOI： 10.23919/IPEC.2018.8507433

GaN半導体研究拠点としての名古屋における活動紹介

山本真義

電気学会誌 Vol. 138 ( 10 ) page： 695 - 695 2018.10

Effect of inductor parasitic resistances on the voltage gain of high step-up DC-DC converters for electric vehicle applications

Martinez Wilmer, Cortes Camilo, Yamamoto Masayoshi, Imaoka Jun

IET POWER ELECTRONICS Vol. 11 ( 10 ) page： 1628 - 1639 2018.8

Review of Current Balance Mechanism in Multiphase LLC Resonant Converters

Noah M., Imaoka J., Ishikura Y., Umetani K., Yamamoto M.

IEEE International Symposium on Industrial Electronics Vol. 2018-June page： 1030 - 1036 2018.8

Language：Japanese Publisher：IEEE International Symposium on Industrial Electronics

In multi-phase power conversion circuits, achieving an equalized current sharing between the paralleled modules is a challenge. Especially, in the LLC resonant converter topology, where the voltage gain is very sensitive to a minor change in the resonant tank parameters. In practical applications, the resonant tank parameters are never exactly identical among the phases, leading to unbalanced current sharing between the paralleled modules. This paper reviews the state of the art of current balance mechanisms proposed previously in the literature and revisits a newly proposed method to improve the current balance, which relies on a single balancing transformer connected in series with the paralleled resonant tanks. A comparison between the proposed method and connecting the three transformers in star is conducted. While evaluating the current balancing methods, the following sources of unbalance have been considered: a) resonant and magnetizing inductances b) resonant capacitors. c) on-resistances of the switching devices. d) propagation delay of the gate drivers.

DOI： 10.1109/ISIE.2018.8433827

Oscillation analysis and current peak reduction in paralleled SiC MOSFETs

Nanamori Kimihiro, Sugihara Yusuke, Yamamoto Masayoshi

IET CIRCUITS DEVICES & SYSTEMS Vol. 12 ( 4 ) 2018.7

Ankle–brachial pressure index as a predictor of the 2-year outcome after transcatheter aortic valve replacement: data from the Japanese OCEAN-TAVI Registry

Yamawaki M., Araki M., Ito T., Honda Y., Tokuda T., Ito Y., Ueno H., Mizutani K., Tabata M., Higashimori A., Tada N., Takagi K., Yamanaka F., Naganuma T., Watanabe Y., Yamamoto M., Shirai S., Hayashida K.

Heart and Vessels Vol. 33 ( 6 ) page： 640 - 650 2018.6

Language：Japanese Publisher：Heart and Vessels

Peripheral artery disease plays a pivotal role for access site selection in transcatheter aortic valve replacement (TAVR). Abnormal ankle–brachial index (ABI) is a generalized mortality marker in many cardiovascular scenarios. However, the long-term outcomes in high-risk TAVR populations remain unclear. We investigated the association between low ABI and 2-year outcome after TAVR. Of 1613 patients enrolled in the OCEAN-TAVI registry, 1458 (90.4%) who underwent ABI before TAVR were divided into groups: patients with (1) ABI ≥ 0.9 in both legs and (2) ABI < 0.9 in either leg. Primary endpoint was all-cause death within 2 years. ABI < 0.9 was noted in 304 patients (20.8%). ABI < 0.9-group had more frequent and severe comorbidities. Primary endpoint in ABI < 0.9-group was significantly higher than that in ABI ≥ 0.9-group (15.8 vs. 8.7%, p < 0.001). This trend continued in the transfemoral (TF)-approach (14.9 vs. 7.5%, p < 0.001), but not in the alternative approach (17.2 vs. 15.8%, p = 0.815). Within 30 days, ABI < 0.9-group had a higher cardiac death rate (3.1 vs. 1.0%, p = 0.033), whereas between 31 days and 2 years, non-cardiovascular death was more frequently observed (9.2 vs. 5.1%, p = 0.003). In ABI < 0.9-group, in-hospital vascular complications (11.9 vs. 4.9%, p < 0.001) and acute kidney injury (10.8 vs, 5.7%, p = 0.009) were more frequently found when using the transfemoral-approach. In multivariate analysis, ABI < 0.9 was an independent predictor of 2-year mortality (adjusted hazard ratio 1.495, 95% CI 1.007–2.220, p = 0.046). Pre-procedure ABI < 0.9 is a useful prognostic marker for all-cause mortality, even in high-risk TAVR populations.

DOI： 10.1007/s00380-017-1096-y

A Current Sharing Method Utilizing Single Balancing Transformer for a Multiphase LLC Resonant Converter With Integrated Magnetics Reviewed International journal

Noah, M; Endo, S; Ishibashi, H; Nanamori, K; Imaoka, J; Umetani, K; Yamamoto, M

IEEE JOURNAL OF EMERGING AND SELECTED TOPICS IN POWER ELECTRONICS Vol. 6 ( 2 ) page： 977 - 992 2018.6

Authorship：Last author Language：English Publishing type：Research paper (scientific journal) Publisher：IEEE Journal of Emerging and Selected Topics in Power Electronics

Integrated magnetics is applied to replace the three-discrete transformers by a single core transformer in a three-phase LLC resonant converter. The magnetic circuit of the integrated transformer is analyzed to derive coupling factors between the phases; these coupling factors are intentionally minimized to realize the magnetic behavior of the three-discrete transformers, with the benefit of eliminating the dead space between them. However, in a practical design, the transformer parameters in a multiphase LLC resonant converter are never exactly identical among the phases, leading to unbalanced current sharing between the paralleled modules. In this regard, a current balancing method is proposed in this paper. The proposed method can improve the current sharing between the paralleled phases relying on a single balancing transformer, and its theory is based on Ampere's law, by forcing the sum of the three resonant currents to zero. Theoretically, if an ideal balancing transformer has been utilized, it would impose the same effect of connecting the integrated transformer in a solid star connection. However, as the core permeability of the balancing transformer is finite, the unbalanced current cannot be completely suppressed. Nonetheless, utilizing a single balancing transformer has an advantage over the star connection, as it keeps the interleaving structure simple which allows for traditional phase-shedding techniques, and it can be a solution for the other multiphase topologies where realizing a star connection is not feasible. Along with the theoretical discussion, simulation and experimental results are also presented to evaluate the proposed method considering various sources of the unbalance such as a mismatch in: 1) resonant and magnetizing inductances; 2) resonant capacitors; 3) transistor on-resistances of the MOSFETS; and 4) propagation delay of the gate drivers.

DOI： 10.1109/JESTPE.2017.2777508

A Magnetic Design Method Considering DC-Biased Magnetization for Integrated Magnetic Components Used in Multiphase Boost Converters Reviewed International journal Open Access

Imaoka, J; Okamoto, K; Kimura, S; Noah, M; Martinez, W; Yamamoto, M; Shoyama, M

IEEE TRANSACTIONS ON POWER ELECTRONICS Vol. 33 ( 4 ) page： 3346 - 3362 2018.4

Language：English Publishing type：Research paper (scientific journal) Publisher：IEEE Transactions on Power Electronics

High power density and high efficiency in dc/dc converters are required in various applications such as the automotive application. Interleaved multiphase circuits with integrated magnetic components can fulfill these requirements because passive components occupying significant space in power converters can be downsized without high-switching frequency driving of power devices. However, dc-biased magnetization is a drawback of integrated magnetic components because of unbalanced inductor average currents. This imbalance arises from the tolerance among the phase components. To overcome this problem, inductor average current control is implemented in interleaved multiphase dc/dc converters. Nevertheless, the imbalance cannot be completely eliminated because the current sensors inserted into each phase have gain errors. The purpose of this paper is to present a magnetic design method to improve the immunity to unbalanced currents. A comprehensive analysis is carried out with two main objectives: to prevent magnetic saturation, which may arise due to the current unbalance and to downsize the magnetic components by selecting the optimal coupling coefficient taking into consideration the maximum permissible percentage of unbalanced currents. Simulation case studies are presented to support the analysis. Finally, a 1-kW prototype of the interleaved boost converter is built to validate the accuracy of the design method.

DOI： 10.1109/TPEL.2017.2707385

Lagrangian dynamics model and practical implementation of an integrated transformer in multi-phase LLC resonant converter Reviewed International coauthorship International journal

Noah Mostafa, Umetani Kazuhiro, Imaoka Jun, Yamamoto Masayoshi

IET POWER ELECTRONICS Vol. 11 ( 2 ) page： 339 - 347 2018.2

Winding orientation method to minimise the secondary leakage of a gapped transformer utilised in LLC resonant converter

Noah M., Umetani K., Yamamoto M., Imaoka J.

ELECTRONICS LETTERS Vol. 54 ( 3 ) page： 157 - 159 2018.2

A Novel Transformer Structure Used in a 1.4 MHz LLC Resonant Converter with GaNFETs

Ou Tengfei, Noah Mostafa, Morita Koichi, Tsuruya Mamoru, Namiki Seiji, Imaoka Jun, Yamamoto Masayoshi

2018 IEEE INTERNATIONAL POWER ELECTRONICS AND APPLICATION CONFERENCE AND EXPOSITION (PEAC) page： 1562 - 1566 2018

Multiple Exciting Voltage Control for Maximization of Multi-hop Wireless Power Transfer Efficiency Reviewed International journal

Sasaki Masato, Yamamoto Masayoshi

2018 INTERNATIONAL POWER ELECTRONICS CONFERENCE (IPEC-NIIGATA 2018 -ECCE ASIA) page： 3344 - 3348 2018

Modeling, Magnetic Design, and Simulation Methods Considering DC Superimposition Characteristic of Powder Cores Used in Power Converters Reviewed International coauthorship International journal

Imaoka Jun, Okamoto Kenkichiro, Shoyama Masahito, Ishikura Yuki, Noah Mostafa, Yamamoto Masayoshi

2018 INTERNATIONAL POWER ELECTRONICS CONFERENCE (IPEC-NIIGATA 2018 -ECCE ASIA page： 1095 - 1102 2018

Fundamental Experiment of 3-phase Electric Resonant Coupling Wireless Power Transfer Reviewed International journal

Hattori Fumiya, Imaoka Jun, Yamamoto Masayoshi, Masuda Mitsuru

2018 7TH INTERNATIONAL CONFERENCE ON RENEWABLE ENERGY RESEARCH AND APPLICATIONS (ICRERA) page： 1417 - 1422 2018

Experimental Evaluation of Inverter System Consisting of 4-parallel GaN Devices Unit

Ohnuma Yoshiya, Miyawaki Satoshi, Hattori Fumiya, Yamamoto Masayoshi

2018 INTERNATIONAL POWER ELECTRONICS CONFERENCE (IPEC-NIIGATA 2018 -ECCE ASIA) page： 2738 - 2742 2018

Core Loss Evaluation in Powder Cores: A Comparative Comparison between Electrical and Calorimetric Methods

Ishikura Yuki, Imaoka Jun, Noah Mostafa, Yamamoto Masayoshi

2018 INTERNATIONAL POWER ELECTRONICS CONFERENCE (IPEC-NIIGATA 2018 -ECCE ASIA) page： 1087 - 1094 2018

Parasitic Inductance Design Considerations to Suppress Gate Voltage Oscillation of Fast Switching Power Semiconductor Devices

Sugihara Yusuke, Nanamori Kimihiro, Yamamoto Masayoshi, Kanazawa Yasuki

2018 INTERNATIONAL POWER ELECTRONICS CONFERENCE (IPEC-NIIGATA 2018 -ECCE ASIA) page： 2789 - 2795 2018

Review of Current Balance Mechanism in Multiphase LLC Resonant Converters

Noah Mostafa, Imaoka Jun, Ishikura Yuki, Umetani Kazuhiro, Yamamoto Masayoshi

2018 IEEE 27TH INTERNATIONAL SYMPOSIUM ON INDUSTRIAL ELECTRONICS (ISIE) page： 1030 - 1036 2018

Proposal for the New Control Method Having High Responsiveness and Robustness for the Boost-Type DC-DC Converter Reviewed

Kawakami Taichi, Harada Toshikazu, Yamamoto Masayoshi, Umetani Kazuhiro

IEEJ Transactions on Electronics, Information and Systems Vol. 138 ( 4 ) page： 395 - 404 2018

Language：Japanese Publishing type：Research paper (conference, symposium, etc.) Publisher：The Institute of Electrical Engineers of Japan

<p>This paper proposes a novel control method to improve the responsiveness and the robustness of the boost DC-DC converter. The proposed control method is a feedback control incorporating a minor control that works to balance the input and output power. Experiment was carried out to verify the responsiveness and the robustness of the proposed control in comparison with the conventional voltage-mode and current-mode control. As a result, the proposed method revealed both of the fast response and the robust output voltage regulation against the load change.</p>

DOI： 10.1541/ieejeiss.138.395

Bidirectional Converter Using Multistage FET Driving technique with voltage balance function Reviewed

Ishikura Yuki, Hosotani Tatsuya, Yamamoto Masayoshi

Journal of the Japan Institute of Power Electronics Vol. 44 ( 0 ) page： 128 - 134 2018

Authorship：Corresponding author Language：Japanese Publishing type：Research paper (other academic) Publisher：The Japan Institute of Power Electronics

This paper presents a bidirectional convert using by multistage FET driving technique with voltage balance function. The voltage balance function can reduce influence of the voltage unbalance phenomenon which drain voltage fluctuation depending on output current. The voltage unbalance phenomenon is clarified by using an equivalent circuit of FETs connected in series. The necessity of voltage balance function is discussed, and verified in experiment. The experimental results have proven that the bidirectional converter by using the driving technique can achieve 98% or more power conversion efficiency from 170 W to 1000 W of power range, and a maximum power conversion efficiency of 99.2%.

DOI： 10.5416/jipe.44.128

An mathematical analysis of false turn-on phenomenon of GaN HEMT

Iwaki T., Sawada T., Yamamoto M.

2017 IEEE CPMT Symposium Japan, ICSJ 2017 Vol. 2017-January page： 189 - 190 2017.12

Language：Japanese Publisher：2017 IEEE CPMT Symposium Japan, ICSJ 2017

GaN-HEMT achieves the reduction in size and weight of power conversion circuits, thanks to its high frequency switching characteristics. However, the switching speed and low threshold voltage may cause a false turn-on phenomenon, which is a fatal effect for the applications. It is urgent issue to tackle and avoid this problem by modifying the circuit conditions. In this letter, the theoretical analysis of a full bridge inverter is developed to figure out the behavior of the gate voltage, which is the keyfactor parameter of false turn-on. Based on the analysis, the circuit conditions which minimize the gate voltage spike are derived.

DOI： 10.1109/ICSJ.2017.8240113

An analysis of false turn-on phenomenon of GaN HEMT with parasitic components

Iwaki T., Ishiwaki S., Sawada T., Yamamoto M.

INTELEC, International Telecommunications Energy Conference (Proceedings) Vol. 2017-October page： 347 - 350 2017.12

Language：Japanese Publisher：INTELEC, International Telecommunications Energy Conference (Proceedings)

Wide band gap power semiconductor devices are now replacing the Si-MOSFET or IGBT. GaN-HEMT achieves the reduction in size and weight, thanks to its high frequency switching behavior. However, its high-speed switching characteristics and low threshold voltage may cause a false turn-on phenomenon, which is a fatal effect for the applications. It is urgent issue to tackle and avoid this problem by modifying the circuit conditions. We described differential equations from simplified equivalent circuit of inverter, and algebraically solved with some assumptions. At the same time, drain voltage equation is also developed. As a result, the gate voltage fluctuation was described as a composite waveform including two LC resonance phenomenon, which occur on gate drive circuit and main power flow.

DOI： 10.1109/INTLEC.2017.8214160

Analytical investigation of interleaved DC-DC converter using closed-coupled inductor with phase drive control

Ebisumoto D., Kimura S., Nanamori K., Noah M., Ishihara M., Imaoka J., Yamamoto M.

INTELEC, International Telecommunications Energy Conference (Proceedings) Vol. 2017-October page： 526 - 529 2017.12

Language：Japanese Publisher：INTELEC, International Telecommunications Energy Conference (Proceedings)

Interleaved techniques and magnetic integration in a boost converter have gained attention in electric powertrains system for electric, hybrid and fuel cell vehicles in order to achieve high power density or to improve power conversion efficiency. Furthermore, the proposed multi-phase boost converter is equipped with a phase drive control to improve the efficiency at all load ranges. Furthermore, a design method of a coupled-inductor for an interleaved boost converter with phase drive control is also proposed. However, the interleaved DC-DC converter using coupled method with phase drive control has many problems. In this paper, this problem of interleaved DC-DC converter using coupled inductor with phase drive control (PDC) is analyzed. In addition, defensive method of this method.

DOI： 10.1109/INTLEC.2017.8214190

A novel LLC resonant DC-DC converter with integrated transformer

Kimura S., Nanamori K., Noah M., Yamamoto M.

INTELEC, International Telecommunications Energy Conference (Proceedings) Vol. 2017-October page： 506 - 510 2017.12

Publisher：INTELEC, International Telecommunications Energy Conference (Proceedings)

DC-DC converters in electric vehicle (EVs) and hybrid electric vehicles (HEVs) have required higher power density and high efficiency. This paper proposes a novel LLC resonant DC-DC converter with integrated transformer. This circuit is composed of three LLC converter cells which are connected in series on the primary side and in parallel on the secondary side with interleaved control scheme. The Series Input Parallel Output (SIPO) structure enables the converter cells to share the input voltage and output current. The interleaved operation diminishes the ripple current of the output capacitor, and can reduce the size of the output capacitor. Also a reduction effect of the transformers is obtained by using the integrated transformer which independent transformers are combined into a single core. All these features make the proposed converter suitable for especially high input voltage and high output current applications to realize higher power and higher efficiency. The steady state operating principle of the converter was demonstrated. The theoretical analysis, the equivalent model and voltage gain of the converter are presented based on fundamental harmonic analysis of the converter. A prototype with 330V input and 500W output was built-up to validate the theoretical analysis.

DOI： 10.1109/INTLEC.2017.8214186

Modeling and design of interleaved multi-phase DC-DC converter with 2-phase coupled inductor cell for high power density

Kimura S., Nanamori K., Yamamoto M.

2017 6th International Conference on Renewable Energy Research and Applications, ICRERA 2017 Vol. 2017-January page： 416 - 422 2017.12

Publisher：2017 6th International Conference on Renewable Energy Research and Applications, ICRERA 2017

An interleaved multi-phase converter with coupled inductor can achieve high power density and high efficiency, and is an effective approach for high power applications. However, a number of phases also results in the fact that component counts are increased. In this paper, the downsizing performances when the number of phase change in a multi-phase DC-DC converter with 2-phase coupled inductor cell are investigated to make the full performance. The volume and the loss modeling of each component at n-phases are provided. Also some comparison results are derived and discussed.

DOI： 10.1109/ICRERA.2017.8191096

Total volume evaluation of high-power density non-isolated DC-DC converters with integrated magnetics for electric vehicles Reviewed International coauthorship International journal

Martinez Wilmar, Cortes Camilo, Yamamoto Masayoshi, Imaoka Jun, Umetani Kazuhiro

IET POWER ELECTRONICS Vol. 10 ( 14 ) page： 2010 - 2020 2017.11

Language：Japanese Publisher：IET Power Electronics

One of the main problems in electric vehicles is the volume of their electrical systems because their bulky components carry additional mass and high cost to the total system. On this topic, interleaving-phases and magnetic coupling techniques have been reported as effective methods for increasing the power density of the DC-DC converters that work between the storage unit and the motor inverter. In that sense, a volume assessment of these topologies would provide a better understanding of the problems to be faced when an electric power train is designed. In this paper, a volume modelling methodology is introduced with the purpose of comparing four different DC-DC converters: Single-Phase Boost, Two-Phase Interleaved with non-coupled inductors, Loosely Coupled Inductor (LCI), and Integrated Winding Coupled Inductor (IWCI). The analysis considers the volume of magnetic components, power devices (conventional and next-generation), cooling devices and capacitors. The methodology can be used as a part of an optimization procedure to minimize the volume of DC-DC converters. Conclusively, LCI and IWCI were found effective to miniaturize power converters with a power density of 8.4 W/cc and 9.66 W/cc, respectively. Moreover, a maximum efficiency of 98.04% and 97.61% was obtained for a 1kW LCI and IWCI prototypes, respectively.

DOI： 10.1049/iet-pel.2017.0157

An investigation into a slight-variation of the transformer effective permeability in LLC resonant converter

Noah M., Endo S., Kimura S., Yamamoto M., Imaoka J., Umetani K., Hiraki E.

2017 19th European Conference on Power Electronics and Applications, EPE 2017 ECCE Europe Vol. 2017-January 2017.11

Language：Japanese Publisher：2017 19th European Conference on Power Electronics and Applications, EPE 2017 ECCE Europe

In the LLC resonant converter,the transformer core is usually gapped to realize the designed value of magnetizing inductance that allows for soft switching. The air gap length which is in a scale of millimeters may be affected by the humidity and long working hours of the ferrite material, resulting into a variation of the core permeability. Moreover, a slight variation of the transformer core permeability may be encountered with any possible change in the core temperature. In a proper transformer design, the transformer shall operate with an optimum value of effective permeability where the sum of both copper and core losses is minimal. In this paper, the transformer optimal design is presented. Moreover, the influence of the permeability on the transformer's copper and core losses is revealed. Furthermore, with the help of newly derived equations, the effect of the transformer's effective permeability on the LLC converter conduction turn-on and turn-off losses is reported. Along with the theoretical discussion,the analysis is supported with simulation and experimental results utilizing a 250W 200kHz prototype.

DOI： 10.23919/EPE17ECCEEurope.2017.8099301

Power flow interactive sharing between two dc nanogrids photovoltaic local branch dynamic systems at island operation Reviewed International coauthorship International journal

Bauomy M.F., Gamal H., Shaltout A.A., Noah M., Yamamoto M.

2017 19th European Conference on Power Electronics and Applications, EPE 2017 ECCE Europe Vol. 2017-January 2017.11

Authorship：Last author Language：English Publishing type：Research paper (scientific journal) Publisher：2017 19th European Conference on Power Electronics and Applications, EPE 2017 ECCE Europe

Nowadays DC nanogrid topologies are going spread with the deployment of distributed generation. Therefore, the investigation of interactive sharing between DC nanogrid branches is mandatory to realize a continuous operation of the photovoltaic considering: Maximum power tracking, Off-maximum power point tracking, load sharing, and battery charge sharing. This paper discusses the power flow interaction among two DC nanogrids in island mode. To demonstrate that, a detailed dynamic branch modeling systems is proposed. The IVIPPT and Off-MPPT control are tested on this nanogrid dynamic model; the IVIPPT is working continuously unless the two BSS are fully charged which is known by the reference indicator state of charge (SOC) value. If the BSS reaches SOC 100 %, the Off-MPPT control will be operated to stop extraction of more power. The objective of interactive sharing is proposed by a control approach for the bidirectional converter utilized in charging and discharging of BSS. This control approach with the support of simple nanogrid controller transfers power via transmission line to performs load sharing and B SS charging of the nanogrid. The power transfer between the two buses will be performed by rising the sending bus voltage above the receiving bus.

DOI： 10.23919/EPE17ECCEEurope.2017.8099348

A Lagrangian dynamics model of integrated transformer incorporated in a multi-phase LLC resonant converter Reviewed International journal

Noah M., Umetani K., Endo S., Ishibashi H., Imaoka J., Yamamoto M.

2017 IEEE Energy Conversion Congress and Exposition, ECCE 2017 Vol. 2017-January page： 3781 - 3787 2017.11

Authorship：Last author Language：English Publishing type：Research paper (scientific journal) Publisher：2017 IEEE Energy Conversion Congress and Exposition, ECCE 2017

In conventional arrangements of three-phase LLC converters, there are at least three magnetic components that occupy a considerable volume and mass of the power converter. Although, the three-phase LLC topology has many advantages over the single-phase one, circuit designers tend to select the singlephase topology because it has a minimal number of magnetic components. In this paper, with the purpose of promoting the industrial applications of the three-phase topology, Lagrangian dynamics is applied to theoretically prove that it is possible to replace the three-discrete transformers by a single integrated transformer. The Lagrangian dynamics theory allowed us to derive a physically motivated model for the integrated transformer, in which each component of the integrated transformer has its own Lagrangian parameter. The remarkable result to emerge from the Lagrangian model is that in a symmetrical design, there is no interphase coupling; this is regardless of the value of the coupling coefficient between the phases. This means that there is no return path for the three ac fluxes, and as a result the magnetic components can be downsized. Therefore, the major advantages of using integrated magnetics in the LLC converter can be concluded as: cost-reduction, reduced weight, and realizing higher power density. Along with the theoretical discussion, experimental validation is provided utilizing a 500W - 390V/12V - 200kHz prototype.

DOI： 10.1109/ECCE.2017.8096668

Analytical investigation on design instruction to avoid oscillatory false triggering of fast switching SiC-MOSFETs

Sugihara Y., Nanamori K., Ishiwaki S., Hayashi Y., Aikawa K., Umetani K., Hiraki E., Yamamoto M.

2017 IEEE Energy Conversion Congress and Exposition, ECCE 2017 Vol. 2017-January page： 5113 - 5118 2017.11

Language：Japanese Publisher：2017 IEEE Energy Conversion Congress and Exposition, ECCE 2017

SiC-MOSFETs have attracting increasing attention because of their outstanding characteristics that contributes to high efficiency and high power density of power converters. However, compared to conventional Si-IGBTs, SiC-MOSFETs are susceptible to false triggering, because they tend to generate large switching noise due to ultrafast switching capability and have a lower threshold voltage in high temperature operation. Particularly, disastrous oscillation of repetitive false triggering can occur after a fast turn-off, which is the severe issue for practical application of SiC-MOSFETs. The purpose of this paper is to give an instruction to avoid this phenomenon. This paper hypothesized that the repetitive false triggering is the parasitic oscillation caused by parasitic capacitance of SiC-MOSFET, and parasitic inductance of wiring. Based on this hypothesis, this paper analyzed the oscillatory condition of the parasitic oscillator to propose a design instruction to avoid the oscillatory false triggering. The result revealed that the parasitic inductance of the gate, drain, and source wiring should be designed so that the resonance frequency of the parasitic LC resonator in the gating circuit is far apart from that of the power circuit. This paper also presents experimental results that support appropriateness of the proposed design instruction.

DOI： 10.1109/ECCE.2017.8096861

Analysis of false turn-on phenomenon of GaN HEMT with parasitic inductances for propose novel design method focusing on peak gate voltage

Ishiwaki S., Iwaki T., Sugihara Y., Nanamori K., Yamamoto M.

2017 IEEE Energy Conversion Congress and Exposition, ECCE 2017 Vol. 2017-January page： 1395 - 1401 2017.11

Language：Japanese Publisher：2017 IEEE Energy Conversion Congress and Exposition, ECCE 2017

GaN HEMT is generally characterized as fast switching and expected to achieve a power converter with high efficiency and high power density as a next-generation power semiconductor. However, the fast switching generates large switching noise, causing gate voltage fluctuation. Therefore, GaN HEMT can suffer from false triggering such as a false turn-on phenomenon due to its own low threshold voltage. The phenomenon is problematic especially for practical applications such as a half-bridge circuit. In order to elucidate this phenomenon, we derived the equation expressing gate voltage fluctuation. As a result, the gate voltage fluctuation was described as a composite waveform including two resonance frequencies. Additionally, the appropriateness of the analysis result was supported by comparing theoretical peak gate voltage of the simulation and experimental results. On the other hand analytical results indicated likelihood that balancing factors included in an analytical expression suppress false turn-on phenomenon. Although analytical treatment elucidated gate voltage fluctuation comprehensively, theoretical equation is complicated as design guideline to avoid the false turnon phenomenon. Therefore, this paper analyzed the gate voltage fluctuation mathematically based on L'Hopital's Rule and derived the minimum condition of the peak gate voltage. As a result, mathematical treatment proposes a design method focusing on a peak gate voltage that can achieve the safe operation of a halfbridge circuit.

DOI： 10.1109/ECCE.2017.8095953

Magnetic structure of Close-coupled inductors to improve the thermal handling capability in interleaved DC-DC converter Reviewed International coauthorship International journal

Chuong T.H., Kimura S., Ebisumoto D., Noah M., Ishihara M., Yamamoto M., Imaoka J., Martinez W.

2017 IEEE Energy Conversion Congress and Exposition, ECCE 2017 Vol. 2017-January page： 205 - 210 2017.11

Language：English Publishing type：Research paper (scientific journal) Publisher：2017 IEEE Energy Conversion Congress and Exposition, ECCE 2017

Interleaved DC-DC converter employing closecoupled inductors is a popular topology among other power converters topologies. Close-coupled inductors allow the power converter to achieve high power density and high efficiency. This paper proposes a novel magnetic structure of close-coupled inductors suitable for increasing the thermal handling capability. The proposed magnetic structure is combined of different magnetic materials, namely, ferrite and powder cores. The design method of the integrated close-coupled inductors are presented. Furthermore, this design method is considering the DC bias superposition characteristics, and the iron and copper losses as well. A 300W prototype is built to validate the proposed analysis. Finally, excellent heat dissipation of the proposed magnetic structure of the integrated close-coupled inductors is also reported.

DOI： 10.1109/ECCE.2017.8095782

Mathematical analysis of GaN high electron mobility transistor false turn-on phenomenon Reviewed International coauthorship International journal

Iwaki T., Ishiwaki S., Sawada T., Yamamoto M.

ELECTRONICS LETTERS Vol. 53 ( 19 ) page： 1327 - 1329 2017.9

A Lagrangian Dynamics Model of Integrated Transformer Incorporated in a Multi-phase LLC Resonant Converter Reviewed International journal

Noah Mostafa, Umetani Kazuhiro, Endo Shun, Ishibashi Hiraki, Imaoka Jun, Yamamoto Masayoshi

2017 IEEE ENERGY CONVERSION CONGRESS AND EXPOSITION (ECCE) page： 3781 - 3787 2017

Modeling and Design of Interleaved Multi-phase DC-DC Converter with 2-phase Coupled Inductor Cell for High Power Density Reviewed International journal

Kimura Shota, Nanamori Kimihiro, Yamamoto Masayoshi

2017 IEEE 6TH INTERNATIONAL CONFERENCE ON RENEWABLE ENERGY RESEARCH AND APPLICATIONS (ICRERA) page： 416 - 422 2017

Analytical Investigation on Design Instruction to Avoid Oscillatory False Triggering of Fast Switching SiC-MOSFETs

Sugihara Yusuke, Nanamori Kimihiro, Ishiwaki Seiya, Hayashi Yuma, Aikawa Kyota, Umetani Kazuhiro, Hiraki Eiji, Yamamoto Masayoshi

2017 IEEE ENERGY CONVERSION CONGRESS AND EXPOSITION (ECCE) page： 5113 - 5118 2017

Analytical Investigation of Interleaved DC-DC Converter using Closed-Coupled Inductor with Phase Drive Control

Ebisumoto Daigoro, Kimura Shota, Nanamori Kimihiro, Noah Mostafa, Ishihara Masataka, Imaoka Jun, Yamamoto Masayoshi

2017 IEEE INTERNATIONAL TELECOMMUNICATIONS ENERGY CONFERENCE (INTELEC) page： 526 - 529 2017

Analysis of False Turn-On Phenomenon of GaN HEMT with Parasitic Inductances for Propose Novel Design Method Focusing on Peak Gate Voltage

Ishiwaki Seiya, Iwaki Toshihiro, Sugihara Yusuke, Nanamori Kimihiro, Yamamoto Masayoshi

2017 IEEE ENERGY CONVERSION CONGRESS AND EXPOSITION (ECCE) page： 1395 - 1401 2017

An Mathematical Analysis of False Turn-On Phenomenon of GaN HEMT

Iwaki Toshihiro, Sawada Takashi, Yamamoto Masayoshi

2017 IEEE CPMT SYMPOSIUM JAPAN (ICSJ) page： 189 - 190 2017

An Investigation into a Slight-Variation of the Transformer Effective Permeability in LLC Resonant Converter

Noah Mostafa, Endo Shun, Kimura Shota, Yamamoto Masayoshi, Imaoka Jun, Umetani Kazuhiro, Hiraki Eiji

2017 19TH EUROPEAN CONFERENCE ON POWER ELECTRONICS AND APPLICATIONS (EPE'17 ECCE EUROPE 2017

An Analysis of False Turn-On Phenomenon of GaN HEMT with Parasitic Components

Iwaki Toshihiro, Ishiwaki Seiya, Sawada Takashi, Yamamoto Masayoshi

2017 IEEE INTERNATIONAL TELECOMMUNICATIONS ENERGY CONFERENCE (INTELEC) page： 347 - 350 2017

Allowable Power Analysis and Comparison of High Power Density DC-DC Converters with Integrated Magnetic Components

Kimura Shota, Nanamori Kimihiro, Kawakami Taichi, Imaoka Jun, Yamamoto Masayoshi

IEEJ Journal of Industry Applications Vol. 6 ( 6 ) page： 463 - 472 2017

Language：Japanese Publisher：The Institute of Electrical Engineers of Japan

<p>Interleaved dc-dc converters with integrated magnetic components are popular as converters capable to achieve high efficiency with less of volume and mass. There are three methods for integrated magnetic components: loosely-coupled inductors, closed-coupled inductors and integrated-winding-coupled inductors. This paper presents a method to calculate the allowable power in various circuit topologies. It is useful for measuring the allowable power without magnetic saturation of an inductor based on its size. Following the analysis of allowable power for each coupled inductor, the allowable power of the integrated magnetic components is compared to that of the conventional interleaved converter. This comparison is realized under the same conditions. As a result, the interleaved converter with loosely-coupled and integrated winding coupled inductors were found to be effective for the downsizing of the magnetic components under continuous conduction mode operation. On the other hand, the interleaved converter with close-coupled inductors is effective for the downsizing of the magnetic components under critical conduction mode operation. This comparative data is discussed from both theoretical and experimental points of view.</p>

DOI： 10.1541/ieejjia.6.463

A Novel LLC Resonant DC-DC Converter with Integrated Transformer Reviewed International coauthorship International journal

Kimura Shota, Nanamori Kimihiro, Noah Mostafa, Yamamoto Masayoshi

2017 IEEE INTERNATIONAL TELECOMMUNICATIONS ENERGY CONFERENCE (INTELEC) page： 506 - 510 2017

Power Flow Interactive Sharing between Two DC Nanogrids Photovoltaic Local Branch Dynamic System at Island Operation

Bauomy Maged F., Gamal Haytham, Shaltout Adel A., Noah Mostafa, Yamamoto Masayoshi

2017 19TH EUROPEAN CONFERENCE ON POWER ELECTRONICS AND APPLICATIONS (EPE'17 ECCE EUROPE) 2017

Magnetic Structure of Close-Coupled Inductors to Improve the Thermal Handling Capability in Interleaved DC-DC Converter Reviewed International coauthorship International journal

Chuong, TH; Kimura, S; Ebisumoto, D; Noah, M; Ishihara, M; Yamamoto, M; Imaoka, J; Martinez, W

2017 IEEE ENERGY CONVERSION CONGRESS AND EXPOSITION (ECCE) page： 205 - 210 2017

Analysis of Self Turn-ON Phenomenon for the Application of Power Semiconductor Devices

Proceedings of Microelectronics Symposium Vol. 27 ( 0 ) page： 15 - 16 2017

Analyzing visitors' characteristics in tourist areas based on mobile phone users' location data

Yamamoto M.

Conference Proceedings - 23rd ISSAT International Conference on Reliability and Quality in Design page： 1 - 5 2017

Language：Japanese Publisher：Conference Proceedings - 23rd ISSAT International Conference on Reliability and Quality in Design

In recent years, so-called "big data" have been attracting the attention of companies and researchers. This study aims to identify the number of visitors of each period and their characteristics based on the location data of mobile phone users collected by the mobile phone company. The study sites of this survey are tourist destinations in Ishikawa Prefecture and Toyama city, including Kanazawa city, which became nationally popular after the Hokuriku Shinkansen opened in 2015. The opening of the Hokuriku Shinkansen brought more visitors to many areas. However, it also led to fewer visitors in some areas. The positive effect was remarkable in Kanazawa.

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