DESIGN AND IMPLEMENTATION OF FLC FOR INTERLINE UNIFIED POWER QUALITY CONDITIONER

This paper proposes anew connection for a unified power quality conditioner (UPQC) to improve the power quality of two feeders in a distribution system. The interline custom power devices named Interline Unified Power Quality Conditioner (IUPQC) is improved for various power quality disturbances and modeled in MATLAB/SIMULINK by using fuzzy logic controller. The developed topology can be used for simultaneous compensation of voltage and current imperfections in a multibus/multifeeder system. The proposed IUPQC is designed for medium voltage level (11 kV) and effective Enhanced Phase Locked Loop (EPLL) withFuzzy based control technique is used to detect and extract the PQ disturbances. The performance of Series Compensator of IUPQC is evaluated through extensivesimulations for mitigating unbalanced voltage sags with phase jumps and interruption. The performance of Shunt Compensator of IUPQC is also tested for harmonic and reactive power compensation that are not investigated before in literature. It is verified that IUPQC which is connected to two feeders, can compensate current and voltage distortions successfully in these feeders according to the results obtained using MATLAB/SIMULINK. INTRODUCTION Power quality has become an important factor in power systems, for consumer and household appliances with proliferation of various electric/ electronic equipment and computer systems. The main causes of a poor power quality are harmonic currents, poor power factor, supply voltage variations, etc. In recent years the demand for the quality of electric power has been increased rapidly. Power quality problems have received a great attention nowadays because of their impacts on both utilities and customers. Voltage sag, swell, momentary interruption, under voltages,overvoltages, noise and harmonics are the most common power quality disturbances. In recent years, the use of nonlinear and electrically switched devices that draw non-sinusoidal currents in to the power systems have increased in utility and thus contribute to the degradation of power quality. In recent studies, the concept of the multiconverter based Interline Custom Power Devices are introduced. In an interline custom power device, two or more VSCs are connected backtoback through a common dc capacitor to two neighboring feeders. These devices can be of series-series, shunt-shunt or series-shunt type [5]. The main advantage of multi-feeder devices is that if any power quality problem occurs in one feeder, other adjacent feeder supplies power for compensating power quality problem. Therefore the multi-feeder PQ devices assure superior performance than single feeder PQ devices. Unified Power Quality Conditioner (UPQC) consists of two IGBT based Voltage source converters (VSC), one shunt and one series cascaded by a common DC bus. The shunt converter is connected in parallel to the load. It provides VAR support to the load and supply harmonic currents. Whenever the supply voltage undergoes sag then series converter injects suitable voltage with supply[2]. Thus UPQC improves the power quality by preventing load current harmonics and by correcting the input power factor. This paper presents, a new concept named the Interline Unified Power Quality Conditioner (IUPQC) has been proposed in [3]. This concept can also be considered as the implementation of known Unified Power Quality Conditioner (UPQC) structure in two different feeders. The purpose of IUPQC is to regulate the bus voltage of one of the feeders, while regulating the voltage across a sensitive load in the other feeder. Multiconverter United Power Quality Conditioner (MC-UPQC) is the most recent interline custom power device which is proposed in [1]. In the basic configuration of MC-UPQC, one shunt and two series VSC exist. The MC-UPQC system can be applied to adjacent feeders to compensate for supply voltage and load current imperfections on the main feeder and full compensation of supply voltage imperfections on the other feeder [1]. This study mainly focuses on modeling of IUPQC in MATLAB/SIMULINKsimulation program. The proposed IUPQC is designed for medium voltage level (11 kV) and is developed for simultaneous compensation of voltage and current distortions in a multi-feeder system. An effective EPLL based control technique is used for IUPQC to INTERNATIONAL JOURNAL OF PROFESSIONAL ENGINEERING STUDIES Volume II/Issue4/JUL2014 IJPRES detect and extract the PQ disturbances. The performance of proposed IUPQC system is evaluated through extensive case studies for mitigating harmonics, unbalanced voltage sags with phase jumps and interruption. The paper is organized in the following manner: System description, power circuit configuration and control strategy of proposed IUPQC are presented in section 2. Simulation results for different case studies are provided and discussed in section 3. Finally, conclusions of the study are given in section 4.