Faculty Profiles - YAMAMOTO Masayoshi

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

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

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.

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

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

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.

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

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

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.

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

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.

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

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.

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

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.

DOI： 10.1541/ieejjia.21012384