Simulation And Study Of Three-phase Four-wire Unified Power Quality Conditioner Based On Direct Control Strategy

ABSTRACT:With the development of power electronic technology, non-linear loads bring much harmonic current to distribution system. In this case, power quality has been more and more deterioration. Meanwhile, much sensitive loads and high-tech products have higher requirements on power quality. The improvement of power quality is the necessary trend of the times development, therefore the research which how to improve power quality has the significant meaning.Unified Power Quality Conditioner (UPQC) is a equipment which can compensate multiple power quality problem. UPQC integrates the characters of series compensation devices and shunt compensation devices. It can restrain current harmonics; meanwhile compensate voltage fluctuations and reactive current. It is based on power electronic technology.UPQC can solve voltage controlling, active power filtering, uninterrupted power supply and so on. Therefore, it has important significance to study UPQC system.A three-phase four-wire of Unified Power Quality Conditioner is introduced. Compared all kinds of topologies, and then a new topology of UPQC in three-phase four-line is presented. In this topology, the series part of UPQC is a three-phase full-bridge voltage-source inverter, while the shunt part is a four-leg voltage-source inverter. The mathematic model of UPQC is set up in the ABC coordinate and dq0 coordinate, and the parameter design methods also presented. Meanwhile, the power balance principle is used to analyze load flow of UPQC system in the different conditions.This paper introduces two control strategies and compares them, on the basic of the effect which is wanted to be. Finally the direct control strategy is presented, and it is used to compensate power quality utilizing UPQC. The series part of UPQC is controlled as a sinusoidal current source, while the shunt part is controlled as a sinusoidal voltage source. This UPQC system can solve the power quality which includes voltage fluctuation, reactive power and harmonic currents and so on. Three-phase four-line system simulation model of UPQC is constructed with MATLAB/Simulink software in the power distribution system. And simulation results demonstrated that the proposed structure and control strategy is effectiveness and feasibility.