An Enhanced Control Strategy for Three-phase ZVR Grid-Connected Inverter Under Unbalanced and Distorted Grid Voltage Conditions

The unbalanced and distorted grid voltage is a common fault in practical power system. The effects of unbalanced and distorted grid voltage on the current control of three-phase ZVR grid-connected inverter are analyzed in detail. To solve the problem of distorted output currents, an enhanced control strategy based on PI + multi-resonant controller is proposed, and controller parameters are designed by the system model. This control strategy does not need the extraction of positive-sequence and negative-sequence component, and it is convenient to realize. The simulation model and experimental platform are constructed, and simulation and experimental studies have been carried out. The obtained results validate the correctness of the theoretical analyses and the effectiveness of the proposed control strategy. It is demonstrated that the proposed control strategy can reduce the output current THD under unbalanced and distorted grid voltage conditions, and the current quality is significantly improved.