Analysis and suppression of LCC-HVDC inverter commutation failure caused by sending end faults

AC fault disturbance will lead to commutation failure (CF) of LCC-HVDC, which may threaten the security and stability operation of the sending and receiving AC systems. Previous studies have focused on the commutation failure of inverters caused by voltage sags caused by receiving-end AC system faults. Different from the 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. Firstly, based on the actual HVDC transmission system parameters, a simulation model is established in the electromagnetic transient simulation platform Hypersim, and the phenomenon of inverter commutation failure caused by sending-end fault is simulated and verified. Secondly, different from the qualitative analysis method used in the past to explain the reasons for CF, the dominant factors that lead to inverter CF under different control modes are investigated by quantitative analysis. In the case of control mode 1, the main reason for CF is that the inverter commutation voltage drops beyond the critical value. In the case of control mode 2, the decrease of the inverter advance angle will increase the risk of inverter CF. At the same time, through the analysis of the relevant electrical quantities before CF, the 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 the commutation failure caused by the fault at the sending end by adjusting the trigger angle of the rectifier. Electromagnetic transient simulation results show that the proposed control strategy can effectively inhibit CF.