Power Quality improvement of a three phase four wire system using UPQC

---------------------------------------------------------------------***--------------------------------------------------------------------Abstract This paper presents two different control strategies applied to Unified Power Quality Conditioner (UPQC) to improve power quality in a three-phase, four-wire distribution system. The two control techniques are Unit Vector Template Generation (UVTG) technique and Synchronous Reference Frame (SRF). Generally, some topologies applied for three-phase, four-wire UPQC use active compensation for the mitigation of source neutral current along with other power quality (PQ) problems, while the uses of passive elements for the mitigation of source neutral current are advantageous over the active compensation due to ruggedness and less complexity of control. Hence, in this paper a star-delta transformer is connected in shunt near the load for mitigation of source neutral current, while three-leg voltage source inverters (VSIs) based shunt and series active power filters (APFs) of three-phase UPQC mitigate the current and voltage based distortions, respectively. Here two control techniques are compared in terms of Total Harmonic Distortion (THD).This is done by using MATLAB/ Simulink.