A repetitive control scheme to improve performance of UPQC under distorted source and nonlinear load conditions

This paper proposes an enhanced control strategy for three-phase unified power quality conditioners (UPQCs) under the distorted source and nonlinear load conditions. The proposed controller consists of a proportional-integral and a repetitive controller (RC), which is developed on both the series and the shunt APFs of the UPQC to compensate (6n±1) (n=1, 2, 3...) harmonic voltages in distorted source voltage and those harmonic currents produced by nonlinear loads. As a result, the load voltage and the supply current are compensated to be sinusoidal. In the proposed RC, the delay time is reduced to be one-sixth of the fundamental period which is much shorter than that of the traditional RC, i.e., one fundamental period. Hence, the proposed RC provides a much faster dynamic response compared to the traditional RC. The proposed control strategy is analyzed and design of the RC for the UPQC is presented in detail. The feasibility of the proposed control strategy is verified through simulations.