Assessment of commutation failure under asymmetric fault in the HVDC inverter side

Abstract

The short-circuit fault of the AC system on the inverter side is the main cause of the commutation failure of the HVDC transmission system. Among them, the asymmetric short-circuit fault not only causes the amplitude of the commutation voltage to drop, but also causes the phase shift of the commutation voltage. Valves face different risks of commutation failure. In order to evaluate the risk of commutation failure during asymmetric faults, this paper proposes the concept of maximum commutation current from the perspective of the DC control system. Based on the method of power system analysis, the calculation formula of the maximum commutation current of the 12-pulse converter valve is derived, and the risk of commutation failure of each valve is evaluated by comparing the maximum commutation current and the VDCOL current command. Based on PSCAD/EMTDC electromagnetic transient simulation, the correctness of the maximum commutation current mentioned in the article on the risk assessment of commutation failure of different valves is verified. The maximum commutation current can provide guidance for the DC control system's measures to suppress commutation failure.