Research on the Suppression Strategy of Commutation Failure Caused by AC Fault at the Sending End

It is generally believed that the commutation failure (CF) of LCC-HVdc is caused by ac fault at the receiving end, but the engineering practice suggests that ac fault at the sending end may also cause the CF. Hence, this article firstly summarizes the characteristic difference between the CF caused by ac fault at the sending end and that caused by ac fault at the receiving end by analyzing the response of ac system and dc system. Then, the phase advance characteristics of the bus voltage at the receiving end after the fault and the accompanying commutation risk are analyzed. In addition, this article also deeply investigates the limitations of inverter control strategy under different working conditions. Based on the above analyses, the article proposes preventive control strategy for the CFs caused by ac fault at the sending end. Finally, the simulation results verify the correctness of the theoretical analyses and the effectiveness of the proposed strategy.