Disclosed is an island-to-network switching method of a flexible direct-current transmission system. The flexible direct-current transmission system under an island operation state judges whether the flexible direct-current transmission system is in a networked state or not by detecting whether the converter valve side three-phase alternating current or the converter bridge arm current overflows and detecting the change of the alternating current side voltage; a control system switches from an island operation control mode to a networked control mode; the system switches to the networked control mode stably by means of power instruction changing and phase tracking of the current grid voltage at the switching moment, and the continuous operation of the system is kept.
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