A zero-sequence voltage injection control scheme for modular multilevel converter under submodule failure

In this paper, a modulation strategy based on zero-sequence voltage injection is proposed for module multilevel converter (MMC). By the proposed method, the remaining capacitor voltages not vary and the line-to-line voltages are balanced. This method is easy to be implemented by adjusting the voltage injection coefficient when SM fault occurs. The coefficient of injected zero-sequence voltage is designed by the number and position of the fault submodules (SMs) and the fault-tolerant capability of this method are also discussed. The effectiveness and advantages of proposed method are confirmed with simulation and experiment.