Overvoltage Suppression and Energy Balancing for Sequential Tripping of Hybrid DC Circuit Breakers

During sequential tripping of dc hybrid circuit breakers (HCBs), the energy-absorbing metal-oxide varistors (MOVs) are inserted one after the other rather than simultaneously. This tripping scheme has been demonstrated to be effective in reducing the peak fault current and fault interruption time. However, the voltage overshoots during the sequential tripping process need to be suppressed and the fault energy among the MOVs needs to be balanced. Therefore, this article proposes, first, a simple overvoltage suppression method and second, a modified sequential tripping algorithm for HCBs. The former method is realized by increasing the turn-off gate resistance of the semiconductor devices, for which an analytical expression relating the HCB peak overvoltage and the semiconductor switch's gate resistance is provided. The latter algorithm is able to evenly distribute the MOV energy absorption under different grid conditions with the least number of switching events via a predefined tripping scheme and an energy feedback loop. Verification results from both time-domain simulation and a 1.2 kV circuit breaker hardware corroborate the efficacies of the proposed strategies, which will improve the performance of the sequentially tripped HCBs.