Unified Power Quality Conditioner (UPQC) During Voltage Sag and Swell

This paper deals with conceptual study of unified power quality conditioner (UPQC) during voltage sag and swell on the power distribution network and researches profoundly on the coordinated control of UPQC (Unified Power Quality Conditioner). By analyzing the radical reasons of coupling effect between UPQC series unit and shunt unit, a simple and practical coordinated control strategy for UPQC series unit and shunt unit is proposed. Therefore, the complex degree of the whole UPQC control system is simplified greatly. The coordinated control between UPQC series unit and shunt unit is implemented by the proposed strategy. Finally, the unified power quality multi-function control of UPQC is achieved. Based on injected voltage phase angle with respect to the utility or PCC voltage phase angle, thus the UPQC can work in zero active power consumption mode, active power absorption mode and active power delivering mode. The series active power filter (APF) part of UPQC works in active power delivering mode and absorption mode during voltage sag and swell condition, respectively. The shunt APF part of UPQC during these conditions helps series APF by maintaining dc link voltage at constant level. This paper introduces a new concept of optimal utilization of a UPQC. The series inverter of UPQC is controlled to perform simultaneous 1) voltage sag/swell compensation and 2) load reactive power sharing with the shunt inverter. The active power control approach is used to compensate voltage sag/swell and is integrated with theory of power angle control (PAC) of UPQC to coordinate the load reactive power between the two inverters. The MATLAB / SIMULINK results are provided in order to verify the analysis. The author presents results with balanced, unbalanced and nonlinear loads at load bus.