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Research on the hybrid topology of unified power quality conditioner based on direct control philosophy

Research on the hybrid topology of unified power quality conditioner based on direct control philosophy,10.1109/DRPT.2011.5993897,FANG Fang,Gao Qin-Xi

Research on the hybrid topology of unified power quality conditioner based on direct control philosophy  
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This paper presents the direct control philosophy to compensate the power quality problems utilizing unified power quality conditioner (UPQC). The series part of UPQC is controlled as a sinusoidal current source by using a three-phase full-bridge voltage-source inverter, while the shunt part is controlled as a sinusoidal voltage source by using a four-leg voltage-source inverter. The mathematic model of UPQC is set up. The performance of proposed UPQC system was analyzed under non-ideal and unbalanced load conditions. The simulation results based on Matlab/Simulink are presented to show the effectiveness and feasibility of the topology structure and control philosophy. Keywords-unified power quality conditioner (UPQC); four-leg voltage-source inverter; direct control philosophy; Matlab/Simulink I. INTRODUCTION Due to the extensive use of power electronic equipments, non-linear and unbalanced loads bring harmonic current in the distribution system. These characteristics cause the decline of power quality. In addition, increasingly sensitive loads and high-tech products have high requirements to make sure of operating properly. Therefore, it has important significance to study UPQC which can improve multiple power quality in the distribution system. A three-phase four-wire system utilizing UPQC provides a zero sequence pathway, which can compensate the neutral current caused by three-phase unbalanced loads. Therefore the three-phase four-wire system can compensate the unbalanced load current and the excessive neutral current. At present, there are two control strategies, which are indirect control and direct control. The former is needed to detect the distortion of the source voltage and load current, and to compensate power quality by eliminating the disturbance. In addition, the shunt inverter is needed to change operating modes when power off or power restoration, which is harmful to control inverters (1). Because of these disadvantages of the former method, the latter is used in this paper. The paper presents a hybrid topology of UPQC for a three- phase four-wire distribution system based on direct control. The simulation results based on Matlab/Simulink validate the effectiveness and feasibility of the structure and control strategy. In a word, the proposed UPQC system can improve multiple power quality in the distribution system.
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