Universal Journal of Electrical and Electronic Engineering 1(2): 11-15, 2013 http://www.hrpub.org DOI: 10.13189/ujeee.2013.010201 Application of Distribution Static Compensator (D-STATCOM) to Voltage Sag Mitigation H. Molavi 1,* , M. M. Ardehali 2 1 Institute of technology, Sharif University, Tehran, Iran 2 Electrical Department, Amirkabir University, Tehran, Iran *Corresponding Author: hmolavi@aut.ac.ir Copyright © 2013 Horizon Research Publishing All rights reserved. Abstract This paper presents a study of a D-STATCOM (Distribution Static Compensator) used for mitigating voltage sag. The basic idea of the voltage sag mitigation, using a D-STATCOM is to dynamically inject a current of desired amplitude, frequency and phase into the grid line. The proposed method extracts the active and reactive parts of the positive- and negative-sequence component for generating reference values of current that need to be injected into the point of connection D-STATCOM in order to compensate the voltage errors. The proposed method offers structural simplicity and less calculation complexity. Simulation results indicate that this method is effective and D-STATCOM has good performance to mitigate the voltage sag. Keywords Voltage Sag, D-STATCOM, D-Q Controller 1. Introduction Voltage sag is a reduction between 10 and 90%in rms voltage with a duration between 0.5 cycles and 1 min (although voltage sag depth and duration typically range from 80 to 90% and 0.5 to 30 cycles, respectively) [1]. Voltage sags are the most important power quality (PQ) problems that many industries and utilities face it. Among different types of disturbances occurring in power system, voltage sag is known to produce the most devastating impact on the loads [2]. Studies show that 92% of all disturbances in the electrical power distribution systems are voltage sags, transients, and momentary interruptions [3, 4]. Voltage sags are not tolerated by sensitive equipment used in modern industrial plants such as process controllers; programmable logic controllers (PLC), adjustable speed drive (ASD) and robotics [5]. Various methods have been applied to reduce or mitigate voltage sags. The conventional methods are by using capacitor banks, introduction of new parallel feeders and by installing uninterruptible power supplies (UPS). Recently D-STATCOM has emerged as a promising device to provide not only for voltage sag mitigation but also for a host of other power quality solutions such as voltage stabilization, flicker suppression, power factor correction, and harmonic control [6]. D-STATCOM is a shunt connected device that generates a balanced set of three sinusoidal voltage or current at the fundamental frequency [7]. DSTATCOM configuration consists of a VSC that converts voltage across the storage device into a set of three-phase ac output voltages. These voltages are in phase and coupled with the ac system of network through the reactance of the coupling transformer [8]. In [9], a repetitive- based controller for a D- STATCOM is presented that compensate reactive power, but it offers more calculation complexity. [10], presented a D-STATCOM control algorithm which enables seperate positive and negative sequence currents, but the presented method needs more time than the control method that perenetd in this paper. This paper presents a study of a D-STATCOM (Distribution Static Compensator) used for mitigating voltage sag. The control object of D-STATCOM is that the line voltages at the normal operation only include positive sequence. The control method is made up of DC voltage controller and current controller. The rest of the paper is organized as follows: section II present the D-STATCOM description. Section III explains the control method. The obtain simulation results are discussed in section IV and finally, section V concludes the paper. 2. Description of the D-STATCOM Figure.1 shows the schematic representation of D-STATCOM. The basic electronic block of the D-STATCOM is the voltage source inverter that converts an input dc voltage into a three-phase output voltage at fundamental frequency and the dc link voltage is provided by capacitor.