Improvement of grid-connected inverter systems with PR controllers under the unbalanced and distorted grid voltage

This paper proposes a control method for grid-connected inverter systems under unbalanced and distorted grid voltage. The proposed method can reduce the power ripple caused by the unbalanced condition as well as it can compensate the low-order harmonics of the output currents due to the distortion of grid voltage. To reduce the power ripple, the proposed method replaces the four conventional PI controllers with two PR controllers in the stationary frame. PR controllers can implement the compensation of selective harmonic without excessive computational requirements; the use of these controllers simplifies the method. The simulation results agree well with the theoretical analysis.