A repetitive-based controller for a hybrid filter with high quality grid current waveform

Hybrid filters could restrain harmonic current in distribution power-line effectively and their compensation precision relies heavily on the design of current loop controllers. Since the reference and feedback signals of the current loop controller are composed by different harmonic components and the bandwidth of conventional proportional controller is limited, this controller cannot control the output current waveform without any steady-state error. In this paper, the limitation of conventional proportional controller in the application of a parallel hybrid active power filter is analyzed. Then this paper proposes a repetitive-based composite controller composed by a proportional controller inner loop and repetitive controller external loop to improve the output current waveform with the control object of the seventh-tuned LC filter, and the design method is given in detail. The proposed controller could acquire high quality power-line current waveform when used to suppress odd harmonic as well as even harmonic current, and guarantee excellent dynamic performances. Experimental results obtained from a 380 V, 20 kVA experimental prototype system validate the feasibility of the proposed control strategy.