Abstract: The mathematical model of Pulse Width Modulation (PWM) inverter was established. According to the symmetrical components theory, the phenomena of 2nd ripple in the DC side voltage of PWM inverter fed by imbalanced grid voltage was analyzed. The control performance degradation of traditional control methods was caused by the presence of negative sequence components. The Proportional Resonant (PR) control algorithm was proposed in detail in this paper. The improved PR control algorithm was applied to control PWM inverter fed by imbalanced grid voltage. The improved PR controller could effectively reduce the 2nd ripple in PWM inverter DC side voltage and could reduce harmonic content of PWM inverter AC side current. Thereby the PR controller proposed could improve the control performance of the PWM inverter. The effectiveness of the proportional resonant control algorithm proposed was demonstrated by the simulation results in MATLAB.