Sub-module fault types of modular multilevel converters（MMCs）are explained，including insulated gate bipolar translator（IGBT）module fault，fault of capacitor in DC link and control signal.Advantages and disadvantages of three redundancy fault-tolerated schemes of sub-module are analyzed.One scheme with sub-modules in hot standby is adopted，which has small impact on MMC.The drawback of this scheme is DC currents fluctuation presenting when MMC operates under unsymmetrical condition.Thus，based on derived basic math model of MMC under redundancy operation condition and yielded arm-energy math expressions，a redundancy fault-tolerated control strategy based on energy balance of arms is proposed to suppress the fluctuation of DC currents.A61voltage-level MMC simulation model is set up in PSCAD/EMTDC.Simulation results verify the validation of the proposed redundancy fault-tolerated control strategy.