Repetitive control is extensively employed for harmonic suppression in active power filters. However, its performance degrades under power supply frequency variations. This paper proposes a fractional order repetitive controller based on Newton interpolation with fixed int(N) and a fractional order repetitive controller with adjustable duty cycle to solve this problem from different perspectives. The fractional order repetitive controller based on Newton interpolation with fixed int(N) yields the most rapid convergence and minimal current overshoot. In contrast, the fractional order repetitive controller with adjustable duty cycle is highly effective in compensating for large frequency deviations. This paper, therefore, introduces a fractional-order repetitive control strategy incorporating a mode-switching mechanism based on these two methods. The proposed approach maintains the advantages of fast convergence and low overshoot while simultaneously ensuring a rapid response to significant frequency variations.
Zheng et al. (Mon,) studied this question.