To improve the reliability of the active power filter (APF) in face of the DC voltage fluctuation too large to properly compensate for harmonics during load current fluctuation and load sudden stop

a selective harmonic direct detection method based on multiple synchronous rotating coordinates is proposed. And the DC-side voltage control effects are analyzed and compared for d-q harmonic currents detection method or the direct detection method used. A control strategy combining the direct detection method with composite repetitive control is proposed. This strategy not only has direct harmonic detection to ensure system reliability

but also combines the composite repetitive control to ensure dynamic performance and steady-state precision of the system

plus its ability to complete selective harmonic compensation that is flexible. Both simulation and experimental results verify the effectiveness of the research contents.