Experimental Demonstration of an IGCT/SiC PiN Diode Switching Cell Operating Without Any Turn-On Snubber

IGCTs are attractive for high power, low-frequency converters such as HVdc MMCs because of their lower losses compared to IGBTs. However, a drawback of IGCTs is that they typically require an additional and bulky turn-on snubber circuit to limit their turn-on <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$dI/dt$</tex-math></inline-formula>. This limitation in current dynamics prevents destructive recovery from occurring in the diode of an IGCT/diode switching cell. Previous studies have shown the possibility of removing the snubber by setting strict limits to the operating range of the IGCT/Si-diode pair, which in practice strongly restrain the application of a snubberless IGCT submodule or switching cell. In this article, high-voltage, high-current, SiC PiN diodes are used successfully with IGCTs in a snubberless configuration up to 4 kV/500 A, and a comparison is made with IGCTs operating with Si PiN diodes. The IGCT turn-on behavior is analyzed, through the evaluation of the IGCT equivalent resistance during turn-on. The impact of very short reverse recovery (RR) is also investigated, with the observation and analysis of the shared voltage between the IGCT and the diode and its impact. It is found that SiC PiN diodes can operate with IGCTs without the limitations encountered with Si diodes and without requiring a turn-on snubber.