A New Control for Series Compensation of UPQC to Improve Voltage Sag/Swell

Voltage sag/swell is one of the most frequent power quality problems affecting power systems with sensitive loads. The unified power quality conditioner (UPQC) is capable of mitigating the effect of voltage sag/swell at the load or point of common coupling (PCC). In this paper, a new UPQC control based on combining the sag detection and voltage injection established on a d-q frame is proposed. Based on a vector control which can immediately discover all the voltage sag in different directions, the voltage sag is detected. This method employs the phase-locked loop and positive-negative sequence to detect the sags and the injected voltage produced by the series converter. The proposed UPQC is investigated in two case studies, including different sags/swells in the main Bus and forward-backward sags in the main and load Buses. Also, the proposed control can improve other power quality phenomena, such as voltage and current harmonics and the power factor in the main Bus. The simulation results show the accuracy of the proposed method.