Combined with the actual engineering needs

a fault current suppression and starting-up control method is proposed in view of the problem of over-current tripping after the AC side fault for the flexible DC transmission system operating in islanded mode. The method can satisfy the requirement of suppressing fault current under all kinds of AC faults in the islanded state

provide the preset fault current to AC system within its own capacity of the flexible DC device

and realize the normal startup procedure in the islanded operation state. Based on the real control and protection devices and the real-time closed-loop simulation system constructed by RTLAB

the proposed control strategy is verified. The results demonstrate that the proposed control strategy can improve the fault ride-through capability in contrast to the conventional control strategy

such as the amplitude frequency open-loop island control or the normal closed-loop current control strategy. Meanwhile

the starting-up control realizes the startup without impact in islanded operation mode.