Suppression of Diode-induced Reverse Voltage Stress for the Asymmetric IGCT Device in the Hybrid MVDC Circuit Breaker

The asymmetric integrated gate commutated thyristor (IGCT) device is widely used in the hybrid medium-voltage direct current (MVDC) circuit breaker for current sharing and freewheeling, to improve the dielectric recovery of the vacuum interrupter. During freewheeling diode (FWD) conduction, the reverse voltage on the asymmetric IGCT device has to be suppressed to prevent device failure. Moreover, the absence of a di/dt limiting inductor in the hybrid circuit breaker results in rapidly rising freewheeling currents and high reverse voltage stress. Therefore, in this paper, reverse voltage suppression approaches are put forward to enhance the reliability of the asymmetric IGCT-based hybrid MVDC circuit breaker. First, an asymmetric IGCT circuit model is presented for the reverse voltage conditions, incorporating gate unit (GU) protection and the parasitic inductance Lpar in the FWD branch. Under various operation conditions, the experimental and simulation results show good consistency, which validate the IGCT circuit model. The proposed model reveals that Lpar in the FWD branch should be first optimized. Subsequently, it is suggested that the overcurrent protection in the GU should be deactivated in the hybrid MVDC circuit breaker application to further mitigate the reverse voltage stress on asymmetric IGCT devices.