The asymmetric faults occur on the AC side of flexible multi-state switch endangers the normal operation of the converter. To solve this problem, a fast decomposition algorithm of sequence components and an improved negative sequence current suppression strategy are proposed based on the four-terminal interconnected topology of flexible multi-state switch. The method can quickly and effectively suppress the negative sequence current at AC side, limit the amplitude of three-phase current, keep three-phase symmetrical operation, and control the power and the double fundamental frequency fluctuation of the DC voltage. PSCAD simulation software is applied to verify the effectiveness and accuracy of the proposed method.

Flexible multi-state switch, Asymmetric faults, Negative sequence current suppression strategy, fast decomposition algorithm of sequence components.