Research and Analysis of an LLCL-Type Active Power Filter with Control Delay Compensation Mechanism

This paper presents a control delay compensation method for an LLCL-type active power filter (APF), aimed at improving performance in digital control systems. The proposed strategy is directly integrated into the inner-loop current controller, requiring no additional compensation modules, predictor structures, or capacitor current feedback, which simplifies the control structure and increases flexibility. The method uses real-time internal state responses of the controller to actively compensate for the phase lag caused by digital control delay, effectively maintaining current control accuracy and overall system dynamic stability. Simulation studies based on a 5.5 kW APF system are conducted to verify the effectiveness of the approach. The results show improved current tracking accuracy, stable dynamic behavior under various load conditions. The simulation-based results indicate the potential of the proposed method for improving control accuracy and stability in digitally controlled APF systems. Moreover, very few studies have addressed control delay compensation specifically for LLCL-based APF systems, making this work a valuable contribution to the field.