PIR-R Control for Three-Phase Grid-Connected Inverter with Unbalanced Grid Current Correction

Proposed in this paper a proportional-integral-resonant-resonant (PIR-R) control method for a three-phase grid-connected inverter. Unbalanced loads at the point of common coupling (PCC) can disrupt grid current balance and adversely impact other PCC connections, impairing the inverter’s ability to accurately track active and reactive power commands. The PIR-R control integrates PI and PR components for fundamental reference current tracking and second-order harmonic rejection. The first resonant controller component targets the grid frequency, while the second addresses the double-frequency oscillations caused by unbalanced grid currents. Without the need for additional correction devices such as shunt active power filters at the PCC, the PIR-R method ensures effective reference command tracking and corrects unbalanced grid currents. Simulation and experimental results confirm that the PIR-R control provides improved transient response and reduced steady-state error compared to conventional methods.