Voltage unbalance in a three-phase system causes double line frequency ripples in the dc link. In this paper, an instantaneous power method is adopted to analysis PWM converter under unbalanced condition. Based on this method, a lossless concept is proposed to reduce the double line voltage ripples in the dc link. Instead of using the conventional control strategy, the coupled energy of line impedance from positive and negative sequences which affect the output voltage is considered. Then, based on a lossless concept, a current control method is presented. Finally, simulation results are given to illustrate the significance of the proposed lossless concept and as a verification of the validity of the derived control scheme.