The existence of redundant submodules (SMs) is an important guarantee of reliability of modular multilevel converters (MMCs) to avoid the risk of abnormal operation and even outage. A novel redundant protection strategy based on carrier phaseshifted sinusoidal pulse width modulation (CPSSPWM) is proposed

which includes carrier dynamic allocation

additional carrier control and optimization of capacitor voltage. The carrier dynamic allocation rearranges the carriers of SMs without additional records. The additional carrier control adjusts the state of the redundant SMs to retain their priority to be charged. The optimization of capacitor voltage is capable of maintaining slight fluctuation of the capacitor voltage as well as reducing the circulating current. Simulation results of a 7level and a 101level MMC system by PSCAD/EMTDC show that the proposed strategy is effective and generic for various voltagelevel MMC systems to ensure successful converter operation when a SM fault occurs. This work is supported by National Natural Science Foundation of China (No. 51277068)

Program for New Century Excellent Talents in Universities (No. NCET120846) and Program of Introducing Talents of Discipline to Universities (“111” Program) (No. B08013).