Investigations on the Role of Dynamic Voltage Restorer for Power Quality Improvement of Distribution Networks

Abstract

Modem power systems comprises of complex networks, where many generating stations and load centres are interconnected through long power transmission and distribution networks. Utility distribution networks, critical commercial operations and sensitive industrial loads all suffer from various types of outages and interruptions which can lead to significant financial loss, loss of production, idle work forces etc. Today due the changing trends and restructuring of power systems, the consumers are looking forward to the quality and reliability of power supply at the load centres. A power quality problem is an occurrence manifested as a nonstandard voltage, current or frequency that results in a failure or a mis-operation of end use equipments. With shifting trend towards distributed and dispersed generation, the issue of power quality is taking new dimensions. The concept of custom power was introduced to distribution systems for improving the system performance. The aim therefore, in this work, is to identify the prominent concerns in the area and thereby to recommend measures that can enhance the quality of the power, keeping in mind their economic viability and technical consequences. The Dynamic Voltage Restorer (DVR) is an effective custom power device for the enhancement of power quality due to its quick response, high reliability and nominal cost. A dynamic voltage restorer is used to compensate deep voltage sags, voltage unbalances and harmonics. It is efficiently capable of protecting sensitive loads against the voltage variations or disturbances. DVR is a forced commutated voltage source converter that injects a dynamically controlled voltage in series with the supply voltage through injection transformer or three single-phase transformers for correcting the load voltage. The modeling and simulation of a DVR using Matlab Simulink has been presented. A control system based on dqo technique, which is a scaled error between source side of the DVR and its reference for sags/swell correction is used. The system based on this control technique is developed and the results have been analysed for the cases of static load and adjustable speed drive load. The simulation results show that the DVR performance is satisfactory in mitigating unbalanced voltages and faulted conditions in the system.