Frequency-Adaptive Virtual Variable Sampling-Based Repetitive Control for Active Power Filter

Abstract

To compensate for the harmonics in the grid, repetitive controllers are widely applied as current controllers for active power filters (APF). In the actual situation, fractional delay filters appear in repetitive controllers when the grid frequency varies. As a result, the controller can't compensate for harmonics well. To solve this problem, a frequency adaptive repetitive controller based on virtual variable sampling (VVS-FARC) for APF is adopted in this paper. The ratio is kept as an integer by replacing the actual sampling filter with the virtual sampling filter. Compared with conventional repetitive controller (CRC), the adopted scheme can compensate for harmonics exactly for APF when frequency varies. Furthermore, a low-pass filter is introduced to enhance the system stability margin. Experiments have verified the effectiveness of the scheme adopted for APF.