We have demonstrated a new analysis method using a precise equivalent circuit of 3.3 kV 400 A full SiC modules and showed that the calculated waveforms well agree with the measured waveforms. We have also examined the current distribution in the module by utilizing this equivalent circuit model.

Blocking characteristics of 2.2 kV and 3.3 kV -class 4H-SiC MOSFETs with various doping conditions for the edge termination region have been investigated. By optimizing the implanted dose into the edge termination structure consisting of junction termination extension (JTE) and field limiting ring (FLR), a breakdown voltage of 3,850 V for 3.3 kV -class MOSFET has been attained. This result corresponds to about 95% of the approximate parallel-plane breakdown voltage estimated from the doping concentration and the thickness of the epitaxial layer. Implanted doping for the JFET region is effective in reducing JFET resistance, resulting in the specific on-resistance of 14.2 mΩcm2 for 3.3 kV SiC MOSFETs. Switching characteristics at the high drain voltage of 2.0 kV are also discussed.

400V/2.5A 4H-SiC JFETs, having a reduced surface field (RESURF) structure have been fabricated. Measurements on the on-resistance, blocking, and switching characteristics were carried out. It was confirmed that the JFET has fast switching characteristics. A demonstration of a Pulse Width Modulation (PWM) decoder using JFETs was carried out. The input waveform, which is pulse width modulated 20.5MHz at 4.1MHz sine wave, as able to be decoded at 4.1MHz sine wave.

The authors have developed of partial discharge measurement techniques for underground transmission lines. However, confirmation of the occurrence of partial discharges still depends on the experience of the maintenance staff. The authors studied the characteristics of partial discharges caused by failures in exausion molded joints and investigated methods for distinguishing partial discharges from noises by evaluating the time, voltage and phase characteristics of the partial discharges. Tbe occurrence phase characteristics of partial discharges have been investigated and arc a useful index for distinguishing partial discharges from noises.

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