Faculty Profiles - YAMAMOTO Masayoshi

Papers - YAMAMOTO Masayoshi

Division display 1 - 20 of about 197 ／ All the affair displays >>

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

Web of Science

Scopus

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

Open Access

Web of Science

Scopus

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

Scopus

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

Web of Science

Scopus

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

Web of Science

Scopus

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

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.

DOI： 10.1541/ieejias.144.645

Scopus

CiNii Research

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

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.

DOI： 10.1541/ieejias.144.513

Scopus

CiNii Research

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

Web of Science

Scopus

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

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.

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

Web of Science

Scopus

　 PREV - NEXT 　

<YAMAMOTO Masayoshi>

Papers - YAMAMOTO Masayoshi