The traditional half bridge sub-module (HBSM) cannot clear the DC side fault by itself. On the other hand, the clamp double sub-module (CDSM) has the ability to self-clear the fault current, but it can only output the negative level of the single capacitive voltage during reverse locking, which will affect the speed of fault removal. To address this issue, a three-level bidirectional switch sub-module (TLBSSM) based on the bidirectional switch and CDSM is proposed in this paper. The sub-module can output 3 levels when working normally and twice the negative level of the capacitive voltage when reverse locking, which greatly accelerates the fault current removal. In addition, compared with other common sub-module, TLBSSM has certain economic advantages and stronger DC fault clearing capability. Simulation results based on MATLAB/Simulink show that TLBSSM can quickly remove DC faults, and the sub-module capacitance voltage is stably near the rated voltage after the fault, which is conducive to the rapid restart of MMC. Finally, the effectiveness of TLBSSM and its DC fault clearing capability are validated by the experiment results.
