Faculty Profiles - YAMAMOTO Masayoshi

Papers - YAMAMOTO Masayoshi

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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

Scopus

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

CiNii Research

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

Scopus

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

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

Scopus

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

Web of Science

Scopus

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

Scopus

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

Scopus

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

Scopus

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

Scopus

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

Web of Science

Scopus

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

Scopus

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

Web of Science

Scopus

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

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Papers - YAMAMOTO Masayoshi