A Dynamic Series Voltage Compensator for the Mitigation of LCC-HVDC Commutation Failure

To effectively mitigate the commutation failure (CF) of the LCC-HVDC transmission system, a dynamic series voltage compensator (DSVC) scheme is proposed. The DSVC consists of three IGCT-based FBSM chains to match the bulk power transmission of the LCC-HVDC. Inserted between the transformer and the AC port of the inverter, the DSVC assists the commutation process by superposing the transient voltage to the line voltage and increasing the commutation margin of the inverter valve. Operation and control strategies are critical techniques for the DSVC. It is designed based on the working states of the FBSMs, assisting the commutation and balancing the DSVC capacitor dynamic voltages. CF detection, another critical technique, is improved considering the reverse time of the LCC-HVDC thyristors. Compared with the topologies in the existing literature, the DSVC has better performances for safe and stable operation due to the urgent control strategy considering a situation beyond its ability. A detailed EMT simulation shows that the DSVC can respond quickly to mitigate CFs and validate the effectiveness of the overall design and key techniques. Furthermore, the operation and control can limit the current stress once it is beyond the capability of the DSVC, which guarantees its feasibility and practicability.