Optimize the series LC design of a quasi proportional-resonant controlled hybrid active power filter for harmonic compensation

The LC hybrid active power filter (LC-HAPF) is able to compensate reactive power and harmonics with operating voltage lower than the grid voltage. The quasi proportional-resonant (PR) controller could reduce the current tracking error by increasing the open loop gain at the selected frequency. Multiple PR controllers have been adopted for improving harmonic compensation in LCL filter coupled grid-connected inverter. In this paper, the system response of the LC-HAPF is analyzed. Results indicate that the series LC coupling branch could increase the open loop gain at its resonant frequency, which has almost the same effect as a PR controller. Therefore, only one quasi-PR controller is used to reduce fundamental frequency current tracking error of the LC-HAPF. Furthermore, a LC coupling impedance selection method is proposed, in which both low order harmonic compensation and switching frequency ripples suppression are considered. Simulation and experimental results are provided to show the validity of the proposed LC design method. It can be concluded that the LC-HAPF is able to compensate harmonics without adding multiple PR controllers. The switching frequency ripples are also attenuated without using a LC or a LCL filter.