Study of Power Quality Improvement Using UPQC

This paper describes role of UPQC as applied to a 3P4W system to improve PQ. The Forth wire of 3P4W system is developed by means of neutral of series transformer. Neutral current which flows through neutral terminal of transformer is removed with the help of 4 leg voltage source inverter (VSI) topology for shunt part. The series transformer neutral will have 0 potential in all conditions of operation. Simulation is carried out by considering the major PQ issues like voltage, current, harmonic by connecting load which is nonlinear in nature to 3P4W scheme with UPQC. A novel control strategy of unit vector template is implemented here for designing series APF. By extending the principle of single phase PQ theory, series APF can be used for balancing the unbalanced voltage present at the load side. The PQ theory as applied to the 3 phase balanced system can even be independently used for unbalanced system.