Faculty Profiles - YAMAMOTO Masayoshi

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

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

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

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.

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

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.

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

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.

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

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.

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

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%.

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