Method for performing a trip when the number of times for a flexible DC control system is temporarily locked and then unlocked again exceeds a threshold

A method for performing a trip, when the number of times that a flexible DC control system is temporarily locked and then unlocked again exceeds a threshold. When a short-time fault occurs to the grid side AC system of an interconnection transformer, after a valve control system determines that the current of a bridge arm is in an over-current state, the valve control system is triggered to be locked temporarily, and a pole control system is notified to be locked. When the current of the bridge arm is gradually attenuated, the temporary lock state disappears, and the pole control system is unlocked again after a fixed time. When a serious fault occurs to the grid side of the interconnection transformer, the valve control system and the pole control system may repeat the process of temporarily locking and unlocking. When the number of times for locking and unlocking exceeds a threshold, the pole control system implements the locking and tripping operation. The method not only improves the traversal success rate of the flexible DC control system during an AC fault, but also protects the flexible DC converter valve which is primary equipment.