Shinichi Kinouchi

Power-Loss Breakdown of a 750-V 100-kW 20-kHz Bidirectional Isolated DC–DC Converter Using SiC-MOSFET/SBD Dual Modules

This paper describes the design, construction, and testing of a 750-V 100-kW 20-kHz bidirectional isolated dual-active-bridge dc-dc converter using four 1.2-kV 400-A SiC-MOSFET/SBD dual modules. The maximum conversion efficiency from the dc-input to the dc-output terminals is accurately measured to be as high as 98.7% at 42-kW operation. The overall power loss at the rated-power (100 kW) operation, excluding the gate-drive and control circuit losses, is divided into the conduction and switching losses produced by the SiC modules, the iron and copper losses due to magnetic devices, and the other unknown loss. The power-loss breakdown concludes that the sum of the conduction and switching losses is about 60% of the overall power loss and that the conduction loss is nearly equal to the switching loss at the 100-kW and 20-kHz operation.

A short circuit protection method based on a gate charge characteristic

This paper describes a high-speed circuit to protect IGBTs against short-circuit faults. The reverse transfer capacitance depends on a collector-emitter voltage and it produces a significant effect on a switching behavior under short-circuit fault conditions as well as under normal conditions. A gate charge characteristic under short-circuit fault conditions differs from that under normal turn-on conditions. Hence, hard-switching fault (HSF) can be detected by monitoring both a gate-emitter voltage and an amount of gate charge. IGBTs can be rapidly protected from destruction because the protection circuit based on a gate charge characteristic does not require any blanking time. Fault under load can be also detected by almost the same circuit configuration. Simulation and experiment verify the validity of the novel protection circuit based on a gate charge characteristic.

A High-Speed Protection Circuit for IGBTs Subjected to Hard-Switching Faults

This paper describes a high-speed protection circuit for IGBTs subjected to hard-switching faults (HSF). The reverse transfer capacitance depends on a collector-emitter voltage and it produces a significant effect on a switching behavior not only under normal conditions but also under HSF conditions. A gate charge characteristic under HSF conditions differs from that under normal turn-on conditions. Hence, a hard-switching fault can be detected by monitoring both a gate-emitter voltage and an amount of gate charge during the turn-on transient period. IGBTs can be rapidly protected from destruction because a blanking time is unnecessary. Simulation and experiment verify the validity of the proposed high-speed protection circuit.

Microstructure and superconducting properties of Bi-Sr-Ca-Cu-O system prepared by a melt process

The microstructure and superconducting properties for samples with the nominal composition of Bi2Sr2Ca1+2xCu2+xOy (x=0, 0.2, 1.0) prepared by a melt process have been examined. The magnetic field dependence of the intragrain critical current density was improved by enriching the Ca and Cu contents. Such samples included two kinds of precipitates, (Ca, Sr)2CuOy and Sr-Pt-O compounds. The latter precipitates were much smaller in size than the former, and this suggests that they may be more effective in enhancing the pinning force.

A high-speed protection circuit for IGBTs subjected to hard-switching faults

This paper describes a high-speed protection circuit for IGBTs subjected to hard-switching faults (HSF). The reverse transfer capacitance depends on a collector-emitter voltage and it produces a significant effect on a switching behavior not only under normal conditions but also under HSF conditions. A gate charge characteristic under HSF conditions differs from that under normal turn-on conditions. Hence, a hard-switching fault can be detected by monitoring both a gate-emitter voltage and an amount of gate charge during the turn-on transient period. IGBTs can be rapidly protected from destruction because a blanking time is unnecessary. Simulation and experiment verify the validity of the proposed high-speed protection circuit.

Bidirectional Isolated Dual-Active-Bridge (DAB) DC-DC Converters Using 1.2-kV 400-A SiC-MOSFET Dual Modules

This paper describes the 750-Vdc, 100-kW, 20kHz bidirectional isolated dual-active-bridge (DAB) dcdc converters using four 1.2-kV 400-A SiC-MOSFET dual modules with or without Schottky barrier diodes (SBDs). When no SBD is integrated into each dual module, the conversion efficiency from the dc-input to the dc-output terminals is accurately measured to be 98.0% at the rated-power (100 kW) operation, and the maximum conversion efficiency is as high as 98.8% at 41-kW operation, excluding the gatedrive and control-circuit losses from the total power loss. The bidirectional isolated DAB dc-dc converters are so flexible that series and/or parallel connections of their individual input and output terminals make it easy to expand the voltage and current ratings for various applications such as the so-called “solid-state transformer” or “power electronic transformer.”

YBa2Cu3O7 growth on metal substrates with SrTiO3 buffer layer by metal-organic chemical vapor deposition

We prepared oxide superconducting YBa2Cu3O7-x thin films on Hastelloy substrates with a SrTiO3 buffer layer by metal-organic chemical vapor deposition (MOCVD) using a single source of tetrahydrofuran solution. To clarify the cause of poor superconducting properties, the cross section of YBa2Cu3O7-x/SrTiO3/Hastelloy was examined by TEM. The YBa2Cu3O7-x and SrTiO3 layers grew perpendicular to the Hastelloy surface, which was columnar. The orientation of the YBa2Cu3O7-x layer seems to depend on that of the SrTiO3 layer. As a result, it is considered that the deposition of a good single-crystalline buffer layer on Hastelloy is the most important factor for obtaining excellent YBa2Cu3O7-x films.