Flexible DC Circuit Breaker With Pre-limiting Current Capability

The DC circuit breaker (DCCB) is an indispensable part of a flexible DC transmission and distribution system, the function of which is to quickly remove the fault current in the system and ensure the safe and stable operation of the grid. In response to the inability of the high-voltage DCCB to suppress the fault currents when large capacities break, a flexible DC circuit breaker topology with pre-limiting current capability is proposed in this paper, which has the capability of pre-charged capacitor self-charging and adaptive reclosing. The main branch of this topology consists of the ultra-fast mechanical switches only, and the fault handling branch includes the commutation circuit, the oscillation circuit, the current limiting circuit and the breaking circuit. This topology achieves the fault current commutation by using an oscillation circuit, and pre-limits the fault current before breaking it. The structure and operation process of the proposed topology are introduced in detail, and the theoretical analysis and derivation of the fault current transfer and pre-limiting process are presented. Finally, a single-ended equivalent system is built in the PSCAD/EMTDC to simulate and verify the results of the theoretical analysis. Compared with the simulation model of a four-terminal DC power grid of the ABB hybrid DC circuit breaker, the fault current amplitude of the proposed topology is reduced by 43.04%, which proves the feasibility and economy of the proposed topology. © 2023 Power System Technology Press. All rights reserved.