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

Voltage sag/swell is one of the most frequently power quality problems which affects the 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 control of UPQC is proposed based on combining the sag detection and voltage injection established on d-q frame. The voltage sag is detected based on vector control which can immediately discover all of voltage sag in different directions. This method is used the phase-locked loop and positive-negative sequence to detect the sags and the injected voltage in produced by series converter. The proposed UPQC is investigate in two case studies including the different sags/swells in main bus and forward and backward sags in main and load buses. Also proposed control can improve the other power quality phenomena such as voltage and current harmonics and power factor in the main bus. The simulation results show the accuracy the proposed method.