Comparative analysis of popular control schemes for parallel active power filter and experimental verification

Active power filter (APF) is an effective solution to the compensation of power quality problems, especially harmonics. To achieve better performance, the control method is crucial for APF. Currently, there are many control schemes available for APF, which may be classified as two types: one needs harmonics detection from load current, while the other does not need harmonics detection but does need detecting and controlling of the DC-link voltage. This paper presents a study on the popular control schemes comparatively, and leads to the conclusion that the latter type, the control scheme without harmonics detection, is just a reduced version of the broadly used regular load current harmonics detection control, and by nature has the similar essential control principles in the system point of view. The latter type is a simple feedback control, while the regular control scheme with load harmonics detection is a composite control, with both feedback of DC-link voltage and feedforward of the fundamental load current which results in better dynamic performance. This clear disclosure of the internal relationship between the two types of the control schemes would be very helpful to choose the most appropriate control scheme effectively. The above conclusion is illustrated with signal-flow graphs and corresponding analysis, and verified by both time-domain computer simulations and experimental tests on hardware prototypes