Modified direct power control for PWM rectifier under unbalanced grid voltage conditions

Under the unbalanced power grid voltage conditions, three-phase voltage source PWM rectifier would produce non-sinusoidal and negative sequence current, fluctuations of active and reactive power. To deal with these problems, the mathematical model is established in the stationary αβ frame, then a dual power control scheme is presented to control the active and reactive power independently. By setting reference of power inner loop, the negative sequence current can be eliminated and grid current is sinusoidal. The proportional resonant controller in the outer loop suppresses the DC-link ripple. The PI repetitive control is applied in the inner loop to eliminate active and reactive power oscillation. Test results show the good performance of the proposed strategy.