High Frequency Operation of Series-Connected IGCTs for Resonant Converters

Series connected IGCTs find application in hard-switched commercial power converters at the MW power levels. Expanding the application of these devices to medium voltage dc-dc resonant converters is of great interest due to the IGCTs low conduction losses. This requires a deeper understanding of the devices behaviour in series connection and under switching conditions different than those in hard switched converters. In particular, the voltage sharing between series connected IGCTs must be achieved with significantly reduced turn-off currents, typical for resonant converters. Relying on a versatile IGCT test setup, this paper explores the operational performances of series connected IGCT operation at very low turn-off current and with snubber capacitance in the range of a few tens of nF. The results presented in the paper are obtained from commercially available 4:5 kV 68mm reverse conducting IGCTs (with standard irradiation), as well as two customized engineering samples (high irradiated variants), optimized on their technology curve for high switching frequencies. The IGCTs are successfully operated in series connection at 5 kHz, with device voltage being effectively shared in resonant converter operation.