Transient Current Balancing of Parallel IGCTs in 10-kV/10-kA Hybrid DC Circuit Breaker

Integrated gate-commutated thyristor (IGCT) is an emerging alternative for hybrid dc breaker (HDCB) to achieve fault current clearance in dc systems. However, the maximum controllable current of present IGCT products cannot cope with high-capacity interruption and IGCTs often need to be paralleled. Unlike insulated gate bipolar transistor whose parallel methods have been widely studied, there lacks intensive study on the transient current balancing and optimization methods for parallel IGCTs, especially in critical current breaking applications. This article proposes a practical solution to the transient current balancing of parallel IGCTs in HDCB. Theoretical and mathematical analysis shows that current spike occurs due to anode voltage discrepancy. Although self-balancing effect and delayed gate signals can help relieve the current spike, IGCT is still possible to exceed the safe operation area. An improved topology of parallel IGCTs with bypass capacitors is used to deal with this problem, which is verified by 10-kA turn- off experiment. Successful 10-kA current breaking tests of 10-kV HDCB prototype demonstrate the feasibility and validity of the improved parallel IGCT switch.