Suppression of LCC-HVDC Inverter Commutation Failure Caused by Sending End Faults

AC fault disturbance can cause commutation failure (CF) in LCC-HVDC, potentially threatening the secure and stabile operation of sending and receiving AC systems. Previous studies have focused on commutation failures in inverters resulting from receiving-end AC system faults. Different from previous studies, this paper comprehensively analyzes the commutation failure mechanism of the inverter caused by a three-phase symmetrical grounding fault at different HVDC sending terminals. First, based on actual HVDC transmission system parameters, a simulation model is established in the electromagnetic transient simulation platform Hypersim, and the phenomenon of inverter commutation failure due to a sending-end fault is simulated and verified. Second, unlike the qualitative analysis used in the past to explain reasons for CF, the quantitative analysis investigates dominant factors that lead to inverter CF under different control modes. In control mode 1, the main reason for CF is that the inverter commutation voltage drops beyond the critical value. In control mode 2, the decrease in the inverter advance angle increases the risk of inverter CF. At the same time, through analysis of the relevant electrical quantities before CF, excessive DC current in the system recovery stage is the root cause of the above phenomenon. On these bases, a control strategy is proposed to suppress commutation failures caused by the fault at the sending end by adjusting the rectifier's trigger angle. Electromagnetic transient simulation results show that the proposed control strategy can effectively inhibit CF.