This paper proposes an efficient control scheme for unified power quality conditioner (UPQC) system based on three-level neutral point clamped (NPC) inverter capable to compensate all voltage disturbances. The proposed UPQC is designed by the integration of series and shunt active power filters (APFs) sharing a common dc bus capacitor. The dc voltage is maintained constant using proportional integral (PI) voltage controller. To get the reference signals for shunt and series APFs, synchronous reference frame (SRF) and instantaneous reactive power (PQ) strategies are adopted. These reference signals are derived from the control algorithm and injected in PWM controllers to generate the switching signals. The performance of proposed UPQC system is evaluated using MATLAB-Simulink software and SimPowerSystem Toolbox for all voltage disturbances compensation. The simulation results demonstrate that the proposed UPQC system can improve the power quality at the common connection point of the non-linear load.

Keywords: Unified power quality conditioner (UPQC), Three-level inverter, Voltage disturbance compensation, Synchronous reference frame strategies, Instantaneous reactive power strategies