Converter Recovery Strategy to Reduce the Commutation Failure Risk of Capacitor Commuted HVDC Transmission System

Commutation failure is an important factor affecting the grid-connected safety of LCC DC systems. The Capacitor Commutated Converter (CCC) is used to improve the ability of DC to resist commutation failure, but it also introduces new problems. In this paper, firstly, the recovery characteristics of the CCC converter in the AC asymmetric fault scenario is analyzed, based on which, a “capacitor bypass-parallel grounding” fault recovery strategy is proposed. This strategy can reduce the risk of commutation failure during AC fault period and accelerate the speed of the power recovery after the fault cleaning, so as to reduce the impact of the fault on the system. Base on Cigre_Benchmark electromagnetic transient model, CCC HVDC system has been verified in simulation experiments. The proposed strategy can effectively reduce the number of commutation failures, the duration of commutation failures and the loss of active power.