POWER QUALITY IMPROVEMENT BY DYNAMIC VOLTAGE RESTORER

Abstract

Power quality is one of the major concerns in the present era. It has become important, especially, with the introduction of sophisticated devices, as their performance is very sensitive to the quality of power supply. Power quality problem is an occurrence manifested as a nonstandard voltage, current or frequency that results in inefficient performance of end use equipments. The major problems related with power quality are the voltage sags, swells and harmonics. To solve power quality problems, custom power devices are used. One such device is the Dynamic Voltage Restorer (DVR), which is the most efficient and effective modern custom power device used in power distribution networks. The Dynamic Voltage Restorer (DVR) provides an advanced and economical solution for both voltage sag and swell problems. Its appeal includes lower cost, smaller size, and its fast dynamic response to the disturbance. Voltage sags and swells are an important power quality problem and the dynamic voltage restorer is an effective device to mitigate them. To improve the performance of the distribution system and to improve the load voltage profile DVRs are used. The output voltage can be regulated using two schemes viz. open loop voltage control and closed loop voltage control. In open loop scheme the load voltage is maintained according to the reference voltage set but it is distorted. Load voltage is shown to be improved if the closed loop voltage control scheme is used. Furthermore, the closed loop voltage control scheme permits a closer tracking of the reference load voltage. In this work the open loop voltage control and closed loop voltage control schemes are simulated and the performance both the schemes are compared. Dynamic voltage restorer is then controlled by using two control strategies, one is control of DVR using self generated PWM technique and other is control of DVR using SRF (synchronous reference frame) method. In first method controlling is done by analyzing the load side voltage and thus setting parameters of DVR to maintain the load voltage but this strategy could not work for variable load. Whereas, in SRF control method load voltage can be maintained under variable load conditions also. In this work both PWM technique and SRF method are used for DVR control. The analysis is done using MATLAB / SIMULINK and results obtained from both the methods.