1.Power Dispatching and Control Center of China Southern Power Grid, Guangzhou 510663, China;2.Electric Power Research Institute, EHV Power Transmission Company of China Southern Power Grid Co., Ltd., Guangzhou 510623, China;3.Electric Power Research Institute of China Southern Power Grid Co., Ltd., Guangzhou 510663, China

Regarding the incident on August 19th, 2023, where the Luxi back-to-back conventional high voltage direct current (HVDC) project of China experienced a prolonged DC current breaking due to an external AC fault, causing a bipolar block, the current establishment mechanism of the back-to-back conventional HVDC project is analyzed. The reasons for the unsuccessful establishment of DC current in the Luxi back-to-back conventional HVDC project are identified. The valved-controlled compensated pulse optimization strategy in low DC current scenarios is proposed. The simulation results of the real-time digital simulator (RTDS) platform fully verified its effectiveness and the measures are successfully implemented on site. The practical application results show that the proposed optimization strategy effectively eliminates the prolonged DC current breaking in the Luxi back-to-back conventional HVDC project caused by the external AC fault and further prevents the bipolar block risk, significantly improving the operational reliability and stability of the back-to-back conventional HVDC project.