Noble International Journal of Scientific Research ISSN(e): 2521-0246 ISSN(p): 2523-0573 Vol. 01, No. 11, pp: 112-121, 2017 Published by Noble Academic Publisher URL: http://napublisher.org/?ic=journals&id=2 Open Access 112 Voltage Sag Matigation in Distribution Network by Dynamic Voltage Restorer Aftab Ali Samejo a* , Zubair Ahmed Memon b , Mukhtiar Ahmed Mahar c , Abdul Sattar Larik d a* Department of Electrical Engineering, Mehran University of Engineering & Technology, Jamshoro, Pakistan b,c,d Department of Electrical Engineering, Faculty of Electrical, Electronics and Computer Engineering, Mehran University of Engineering & Technology, Jamshoro, Pakistan Abstract: Presently, most power quality issues in distribution networks are identified by voltage sags. Therefore, various solutions have been attempted to mitigate these voltage sags in the distribution network in order to avoid economic losses. Dynamic voltage restorers (DVRs) are being more recognized in distribution networks in reducing the effect of voltage sags to critical loads. The DVR, which is arranged in series with a critical load, must have capability to generate and absorb the active and reactive power from the system. In this paper, a dynamic voltage restorer is modelled based on Cascaded double-loop vector control method for voltage sag mitigation. The proposed approach is to illustrate these by an example of a real Pakistani distribution system. A feeder of Gulzar colony Hyderabad is modelled in Matlab/Simulink software for power quality analysis and simulations are carried out to verify the results. Keywords: Power Quality, Voltage Sag, Custom Power Devices, Dynamic Voltage Restorer (DVR), Vector Control Method. 1. Introduction Power quality is of significant importance in the electricity supply system due to its impacts on both industrial and commercial consumers as well as on domestic electrical consumers. In many ways, electricity consumers are gravely affected by problems of poor power quality. It results in malfunction or damage of electrical appliances, increased power losses, loss of production and interference with communication circuits, etc. [1, 2]. IEEE defines the power quality problem as "Any power disturbance that may appear as a change in the current, voltage or frequency waveform that results in malfunction or failure of sensitive equipment." Many power quality problems are currently being addressed to the distribution network, such as voltage spikes, surges, drops, momentary interruptions and harmonic distortions in which the most dangerous and frequent problem of power quality is the collapse of the voltage [3]. The voltage drop is a very serious disturbance that produces a sudden and unexpected reduction of the voltage but not a complete disruption of a power, it is a momentary drop of the nominal voltage value below 90%, plus most of the depths of the sag vary from 50% to 90% of the normal voltage value and for a duration of 10 ms to a few seconds or from 50 to 170 milliseconds [4]. Short circuits, sudden change of load, activation of the transformer and the starting of a larger motor are the main sources that cause the voltage sag. Towards voltage change, electrical and electronic equipment such as microprocessor based controllers, variable speed drives and computers are very sensitive [3]. Power electronic technology based custom power devices are found to be the most effective and economical as compared to other conventional devices. Hingorani was the first to propose the custom power concept in 1995. Custom power devices of different types are used to improve power quality issues such as Dynamic Voltage Restorer (DVR), Uninterruptible Power Supplies (UPS), Distribution Static Compensators (DSTATCOM), Static Var Compensator (SVC) and Unified Power Quality Capacitor (UPQC) are some of them [1, 5]. Each of them has its own advantages and limitations. Among them DVR is considered as the most effective and efficient, economical, results oriented, technically forward and