Improvement of unified power quality conditioner performance with enhanced resonant control strategy

This study proposes an enhanced resonant control strategy for the unified power quality conditioner (UPQC) to simultaneously tackle voltage sags, unbalance and distortions on the supply side as well as current harmonics on the load side. The proposed control strategy is developed in both the series and shunt active power filters (APFs) of the UPQC. In the series APF, a proportional-resonant controller and a resonant controller are employed to mitigate voltage sags, unbalance and distortions, whereas a proportional-integral (PI) controller and three vector PI controllers are used in the shunt APF to compensate harmonic currents. The performance of the proposed UPQC control scheme is significantly improved compared with the conventional control strategy owing to the superiority of the resonant controllers. In addition, voltage sag/harmonic and current harmonic detectors are not required in the proposed control scheme, which helps to simplify the control strategy and to improve the control accuracy. The proposed control strategy is theoretically analysed and its feasibility is validated through experiments.