A coordinated AC-DC recovery strategy for suppressing continuous commutation failures in HVDC transmission

Summary

Addressing the low sensitivity of DC current regulation in traditional linear low-voltage current limit control schemes, this paper proposes a nonlinear AC/DC-VDCOL control strategy based on weighted averaging. This strategy adjusts system operating characteristics by using a weighted average of DC voltage and AC commutation voltage as input. Simulation results demonstrate that the designed control strategy can effectively limit DC current during fault conditions, shorten the recovery process from commutation failures, suppress consecutive commutation failures, maintain power transmission on system lines, and enhance the system's transient recovery characteristics. Based on the improved nonlinear VDCOL control strategy, a coordinated recovery strategy for dynamic amplitude-limited voltage support based on the receiving-end grid's Voltage Source Converter (VSC) is further designed. This strategy employs a reactive power priority control method to enhance the reactive power output capability of the VSC converter station. Simulation results indicate that the coordinated recovery strategy combining the improved nonlinear VDCOL on the DC side with the dynamic amplitude limitation of the VSC on the AC side can effectively suppress consecutive commutation failures, facilitate faster system recovery, provide voltage support to the system, and further enhance the stability of the HVDC system and the receiving-end grid.