Internal Model Repetitive Control for an Active Power Filter

Power quality is a major issue for power distribution systems, especially in microgrids, where the voltage is not as stiff as in large interconnected networks. Distribution efficiency is highly influenced by the power factor value, where larger-than-necessary currents cause larger ohmic losses on the transmission lines. Harmonic currents also cause unwanted EMI which can shorten the lifetime or cause degraded performance for some sensible equipment. These problems can be successfully alleviated by employing Active Power Filters (APFs). An APF current control system is designed by employing the Internal Model Principle and the dq transform, to obtain a closed-loop control which offers good stability margins and adequate performance in the face of various tasks/use-cases that an APF must accomplish. The proposed APF performance for harmonic compensation and active/reactive power flow is assessed through practical experiments.