Implementation of redundancy control by degrading voltage level in modular multilevel converter

Modular Multilevel Converter (MMC) normally employs large number of sub-modules which increase the redundancy property of an MMC. This paper proposes a simple redundancy control to improve the reliability of an MMC. When power switches failures are identified, the proposed redundancy controller will automatically degrade the output voltage level. The proposed redundancy controller is fully described and validated experimentally. A small scale MMC prototype is used in this experiment. Capacitor voltage balancing control and Level-Shifted Pulse Width Modulation strategies will be implemented. Test results are presented to verify the feasibility of the proposed redundancy controller.