Power Quality Compensation Using Universal Power Quality Conditioning System

Author Affiliation: Institute for Power, Electronics and Telecommunications Engineering, Faculty of Engineering, University of Novi Sad, Novi Sad, Yugoslavia. Abstract: The aim of this letter is to present a universal power quality conditioning system (UPQS) named after unified power quality conditioner (UPQC), which is extended by adding a shunt active filter at the load side. Its main purpose is to compensate for supply voltage and load current imperfections, such as sags, swells, interruptions, imbalance, flicker, harmonics, reactive currents, and current unbalance. Converter and control analysis is presented together with results showing the UPQS modes of operation. Introduction: Power electronics loads inject harmonic currents in the ac system and increase overall reactive power demanded by the equivalent load. On the other hand, development in the digital electronics/communications and in process control have increased the number of sensitive loads that require ideal sinusoidal supply voltages for their proper operation [1]. The load/supply and supply/load influence is listed in Figure 1. In order for power quality to meet limits proposed by standards it is necessary to include some sort of compensation. Modern solutions for active power factor correction can be found [2] in forms of active rectification (active wave shaping) or active filtering. Such solutions are suited for elimination of negative load influence to the supply network. If there are supply voltage imperfections, none of them can provide proper compensation. In last few years solutions based on flexible ac transmission systems (FACTS) have appeared. FACTS converters have been modified to serve in distribution networks and through a modification of a unified power flow controller (UPFC). Unified power quality conditioners (UPQC) were presented during 1998 [3]. Topology of UPQS: As known, elimination of supply voltage imperfections can be done using a series filter [4]. Also, the series filter can compensate load current harmonics in the case of voltage-type harmonic producing loads (capacitively loaded diode rectifier). If such a solution is implemented, voltage regulation demands dc bus capacitor charging. If a diode rectifier is used for charging, then only voltage sags can be compensated. If a voltage swell compensation is desired, then an active rectifier should be used, leading to solution known as UPQC [5].