Suppression of DC Power Ripple for Single-phase Non-isolated UPQC in Islanding Mode

Due to the inherent double-line(2ω) frequency ripple caused by the instantaneous power unbalance between dc-and ac-side, dc source damage and ac-side power quality deterioration become a challenge to the unified power quality conditioner (UPQC) operating in the island mode. In this paper, a novel active power decoupling method is proposed for a single-phase half-bridge non-isolated UPQC in islanding mode. By utilizing the spare series-side half-bridge as the power decoupling circuit and coordinately working with dc capacitors, the double-line frequency voltage ripple at the DC side can be reduced effectively without any extra circuit. Moreover, by adopting the proposed method, the power ripple reduction performance still can be maintained with smaller dc capacitance, which could further improve the power density of the UPQC system. Simulation and experimental results show the correctness and effectiveness of the proposed method. More than 75% of DC voltage ripple is cut down, while 64% capacitance can be reduced with acceptable voltage ripple.