Abstract: In view of problem that capacitor voltage balance control strategy of common modular multilevel converter has a large fluctuation of capacitance voltage, a composite capacitor voltage control strategy was proposed on the basis of analysis of mechanism of influence of changing capacitance value of sub-modules on its capacitor voltage. The strategy combines control strategy of modifying modulation wave with control strategy of changing capacitance value of sub-modules, so as to control balance of the capacitor voltage. It uses CPS-SPWM to modulate modular multilevel converter, adopts accurate feedback linearization to decouple input active and reactive current of PWM rectifier, so as to control rectifier power factor and DC voltage after rectification. The Matlab simulation results show that the control strategy effectively reduces fluctuations of capacitance voltage and reaches prospective effect.