Abstract: This paper proposes a ripple-power decoupling based modular multilevel converter (RPD-MMC) motor governing system. Through the high frequency link based on the structure of half-bridge and transformer, the submodules (SM) are isolated and connected to realize the decoupling of three-phase ripple-power in SM capacitor, and thus eliminate the low-frequency fluctuation component of common-mode voltage (CMV). A pulse optimization control CPS-SPWM (POC-CPS-SPWM) strategy is proposed to control the number of SM on the upper and lower arms of the three-phase MMC at any time to maintain the same, so as to eliminate the high frequency fluctuation components of CMV. Finally, complete elimination of CMV can be achieved. Starting from the analysis of the mechanism and characteristics of CMV, this paper discusses the proposal, principle analysis and effect realization of low and high frequency suppression in detail. Finally, through simulation and experimental verification, the feasibility and effectiveness of the mechanism analysis of CMV and the two strategies to eliminate CMV are verified.