Faculty Profiles - YAMAMOTO Masayoshi

Papers - YAMAMOTO Masayoshi

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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

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

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

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

Scopus

CiNii Research

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

CiNii Research

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

Scopus

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

Scopus

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

Scopus

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

Scopus

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

Scopus

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

Web of Science

Scopus

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

Scopus

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

Scopus

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

Scopus

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

Scopus

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Papers - YAMAMOTO Masayoshi