1884 | International Journal of Current Engineering and Technology, Vol.4, No.3 (June 2014) Research Article International Journal of Current Engineering and Technology E-ISSN 2277 – 4106, P-ISSN 2347 - 5161 ©2014 INPRESSCO ® , All Rights Reserved Available at http://inpressco.com/category/ijcet Enhancement of Voltage Quality using D-STATCOM Arathi Sunkara Ȧ* , S. B. Karajgi Ȧ , Rashmi Kannur Ȧ and Sandeep S Mudakannavar Ȧ Ȧ Department of EEE, SDMCET, Dharwad, India Accepted 02 May 2014, Available online 01 June 2014, Vol.4, No.3 (June 2014) Abstract This paper presents the mitigation of voltage sags and harmonic distortion using Distribution Static Compensator (D- STATCOM) in existing 11kV/440v distribution system. The D-STATCOM is controlled using decoupled theory using the PI controller. This model is based on voltage source converter (VSC) principle. The D-STATCOM injects a current into the system to improve the voltage profile and also to reduce the harmonic distortion in the system. The simulations are carried out using Matlab/simulink. The results are presented. Keywords: Distribution system, voltage sag, D-STATCOM, optimal allocation, total harmonic distortion (THD). 1. Introduction 1 Power quality is one of the most important topics that electrical engineers have been noticed in recent years. Voltage sag is one of the problems related to power quality. This phenomenon happens continuously in transmission and distribution systems. During a voltage sag event, amplitude of the effective load voltage decrease from 0.9 of the nominal load voltage to 0.1 in very short time (less than one minute). Short circuit, transformer energizing, capacitor bank charging etc are causes of voltage sag (H. Nasiraghdam et al, 2007). 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). However, the PQ problems are not solved completely due to uncontrollable reactive power compensation and high costs of new feeders and UPS. The 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 (G. F. Reed et al, 1999). D-STATCOM is a shunt device that generates a balanced three-phase voltage or current with ability to control the magnitude and the phase angle (S. Aizam et al, 2006). Among the vast literature about the D-STATCOM, only a few of them explore its performance when connected to a realistic and complex distribution system. The aim of this work is to contribute in the assessment of the D-STATCOM performance in realistic distribution system. A 11kV/440V distribution system is considered for analysis. The role of D-STATCOM in voltage sag *Corresponding author: Arathi Sunkara mitigation has been analyzed through computer simulation in Matlab/Simulink. 2. Distribution Static Compensator (D-STATCOM) A D-STATCOM (Distribution Static Compensator), which is schematically depicted in Figure1, consists of a two-level Voltage Source Converter (VSC), a dc energy storage device, a coupling transformer connected in shunt to the distribution network through a coupling transformer. The VSC converts the dc 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 through the reactance of the coupling transformer. Suitable adjustment of the phase and magnitude of the D-STATCOM output voltages allows effective control of active and reactive power exchanges between the D-STATCOM and the ac system. Such configuration allows the device to absorb or generate controllable active and reactive power. Fig.1 Schematic representation of D-STATCOM as a custom power controller The VSC connected in shunt with the ac system provides a multifunctional topology which can be used for up to three quite distinct purposes: