Voltage Sag Compensation Strategy Using Dynamic Voltage Restorer for Enhance the Power System Quality Ali M. Eltamaly 1 , Yehia Sayed 2 , Abou-Hashema M. El-Sayed 2 and Amer Nasr A. Elghaffar 2 1 Electrical Engineering Department, Mansoura University, Mansoura, Egypt 2 Electrical Engineering Department, Minia University, Minia, Egypt eltamaly@ksu.edu.sa, amernasr70@yahoo.com Abstract: Voltage sags associated with faults in transmission and distribution systems, energizing of transformers, and starting of large induction motor are considered as most important power quality disturbances (PQD). The most of the industries uses the power electronics conversion and switching for manufacturing and processing. These technologies are needs high quality and reliable power supply. Not only the industries, but also the electric power utilities and customers are becoming increasingly anxious about the electric power quality. Sensitive loads such as digital computers, programmable logic controllers (PLC), consumer electronics and variable frequency motor drives need high quality power supplies. Dynamic voltage restorer (DVR) is a series connected power electronic based device that can quickly mitigate the voltage sags in the system and restore the load voltage to the pre-fault value. DVR is recognized to be the best effective solution to overcome this problem. The primary advantage of the DVR is keeping the users always on-line with high quality constant voltage maintaining the continuity of production. This paper describes the DVR operation strategies and control. Results of simulation using MATLAB/Simulink are demonstrated to prove the usefulness of this DVR design and operation to enhance the power system quality. Keywords: Power System Quality, DVR, Voltage Sag and High Voltage. 1. Introduction Good quality of electric power is necessary for right functioning of industrial processes as well as protection to the industrial machines and its long usage. A voltage sag is a short-duration reduction in the RMS voltages and it is usually characterized by its magnitude and duration [1,4,6,7]. According to IEEE std. 1159/95, the magnitude of voltage sag ranges from 10 to 90 % of nominal voltage and duration from half cycles to one minute [8,9]. However, the short interruptions where the RMS voltage is below 0.1 pu of the nominal voltage can also be considered as voltage sag event. Despite its very short duration, it can cause serious problems to a wide range of industrial loads. Hence, the characterization, classification, and detection of the voltage sag have become essential requirements for PQ monitoring. In order to characterize the voltage sag through magnitude, several methods have been documented. Alternative methods have been also developed to characterize the voltage sag through one parameter [7–10]. These methods quantify the severity of the voltage sag through only one parameter resulting from either magnitude or combination of the magnitude and duration. Moreover, to quantify the magnitude of the voltage sag from recorded waveform or sample data, numbers of methods were documented in the paper. The magnitude of the voltage sag is accepted as one of the most important parameters for its characterization, classification, and the detection. Hence, the selection of most suitable method to quantify the magnitude of voltage sag is a basic requirement of the power quality (PQ) monitoring. DVR Its function is detecting the voltage sag and injecting the voltage difference between the pre-sag and post-sag voltage, so the voltage is maintained and reaches the load side as pre-sag voltage magnitude, however the phase angle is not crucial to return it back to the pre-sag condition. This is done by injecting the active and reactive power. Fig. 1 describes the power circuit of the DVR; it is small in size and best economical solution compared to other methods. This paper introduces the DVR control module that can to uses for voltage sag mitigation. Also, this paper uses MATLAB/Simulink are demonstrated to prove the usefulness of this DVR design and operation to enhance the power system quality.