Yasushi Nakayama

Two-dimensional observation of copper vapor in vacuum arcs by laser-induced fluorescence

The density distribution and the velocity of copper neutral atoms emitted from a single cathode spot in 40 A vacuum arc were measured by the two-dimensional (2-D) laser-induced fluorescence method. The density was calibrated from the two-dimensional fluorescence image observed by a CCD camera. The gap space was almost filled with the copper atoms, and the density reached 5/spl times/10/sup 19//m/sup 3/. We varied the wavelength of the laser light and measured the velocity of the copper atoms emitted from the cathode spot using the effect of Doppler shift. The velocity of the copper atoms was about 10 km/s.

A fast short-circuit protection method using gate charge characteristics of SiC MOSFETs

This paper describes a fast protection circuit for silicon carbide metal-oxide semiconductor field-effect transistors (SiC MOSFETs) subjected to hard-switching faults (HSFs). In terms of reliability of power converters, the protection of power semiconductors against short-circuit failures is of great concern. The reverse transfer capacitance increases with decreasing drain-source voltage during normal turn-on transient. Under HSF conditions, on the other hand, it hardly changes because the drain-source voltage remains high. As a consequence, quite a significant difference appears in gate charge characteristics between under HSF conditions and normal turn-on operation. Hence, an HSF can be detected by monitoring both the gate- source voltage and the amount of gate charge. The proposed protection circuit has high noise tolerance because it monitors not only the gate-source voltage but also the amount of gate charge. The validity of the protection circuit is verified by experiment. The proposed protection circuit can detect the HSF within only one microsecond.

Characterization and Modeling of a 1.2-kV 30-A Silicon-Carbide MOSFET

This paper describes a novel compact model for a SiC-MOSFET. The model is useful to achieve accurate simulation of output characteristics from a linear region to a saturation region, selecting both gate-source voltage and temperature as parameters. In order to construct the model systematically, attention is paid to a physics-based modeling procedure with channel mobility as an adjustable parameter. The model also features characterization and modeling of an internal drain-gate capacitor. The model shows fairly good agreement in the output characteristics and the dynamic behavior of both gate drive circuit and main power circuits between the experimental and simulated results. This successful validation indicates that this model offers a promising circuit-based simulation tool for designing whole power conversion systems using SiC-MOSFETs.

Investigations of parallel connected IGBT's using electromagnetic field analysis

Chip current imbalances caused by the structure and layout of main circuit and gate circuit in an insulated gate bipolar transistor (IGBT) module were analyzed using three-dimensional electromagnetic analysis. To confirm the results of the analysis, we also measured the current of each chip using a test module. A good agreement between the analytical result and the measurement result was achieved. Furthermore, we were able to specify the key factors of current imbalance and the effectiveness of the design using three-dimensional electromagnetic analysis was proven

Development of compact power control unit for HEVs

This paper presents a compact power control unit (PCU) for hybrid electric vehicles. The authors use silicon carbide (SiC) MOSFET power modules with insulated ceramic substrates, resulting in high thermal conductivity. In addition, direct connection of aluminum-made chassis of a reactor and a capacitor to the heat sink makes it possible to highly release heat generation of them. These two measures enable a size reduction of the PCU, and a power density of 86 kVA/L was achieved that is the most compact in the similar PCU class.

Modeling of a silicon-carbide MOSFET with focus on internal stray capacitances and inductances, and its verification

This paper describes a compact model for an SiC-MOSFET, which features characterization and modeling of a novel drain-gate capacitor. In addition, the inner gate resistance and stay inductances of the package are evaluated and modeled by a newly-proposal method. The gate drive circuit is also modeled and involved in this simulation study. The model shows excellent agreements in steady and transient states between simulated and experimental waveforms. The comparison shows accurate reproducibility of both the rate of drain-source-voltage change and that of drain-current-change with an error of 10 % for turn-on behavior, and with a maximum error of 20 % for turn-off behavior. This successful validation indicates that the developed model is expected to open up the possibilities of the simulation study for evaluating detailed performance of SiC-MOSFETs.