Improving Grid Power Quality by Harmonic Compensation in Three-Phase PV Inverters with Active Filtering

This paper presents a control strategy for a threephase inverter system that functions as an Active Power Filter (APF) to improve grid current quality and enable photovoltaic (PV) power injection as an auxiliary function. The proposed system employs a cascaded control structure combining a Proportional-Integral (PI) controller for fundamental current regulation and a Multi-Resonant (MR) controller to compensate for specific harmonic orders, including the 5th, 7th, 11th, 13th, 17th and 19th orders. The system performance is experimentally validated under four scenarios: 1) harmonic compensation performance with and without HC, where the grid current total harmonic distortion (THD) is reduced from <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathbf{7 2. 8 2 \%}$</tex> to <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathbf{1 7. 1 8 \%}$</tex>, and further to 6.15% with HC enabled 2) control stability under step load variations, where the DC bus voltage is regulated with fast dynamic response 3) simultaneous harmonic compensation and PV power injection, demonstrating the inverter's ability to maintain power quality while contributing active power to the grid; and 4) analysis of inverter efficiency. The results confirm that the proposed PI+MR control system effectively enhances power quality while utilizing PV power injection as a supplemental feature to support energy flow into the grid.