Mitigation of voltage sag/swell using Dynamic voltage restorer (DVR)

The most noticeable topic for electrical engineering is power quality in recent year.Power quality problem is an occurrence manifested as a nonstandard voltage, current or frequency.Utility distribution networks, sensitive industrial load and critical commercial operation suffer from various types of outages and service interruption can cost significant financial losses.One of the major problems dealt here is the voltage sag.With the fast development in power electronics technology have made it possible to mitigate power quality problems.This work concentrates on the power quality problem such as voltage sag.Many of the devices such as STATCOM, tap changing transformer, UPFC and DVR are available to mitigate voltage sag problems.Among these, dynamic voltage restorer can provide the most commercial solution to mitigate voltage sag by injecting voltage as well as power in to the system.Dynamic Voltage Restorer is a series connected power electronics based device that can quickly mitigate the voltage sag in the system and restore the load voltage to the pre-fault value.This thesis first gives an introduction to relevant power quality problems for a DVR and power electronics controllers for voltage sag mitigation.Thereafter the operation and elements in DVR is described.In this thesis proposed utilizes the error signal to control the triggering of the switches of an inverter using Sinusoidal Pulse Width Modulation (SPWM) technique. Modeling and simulation of proposed DVR is implemented in MATLAB SIMULINK  Dynamic voltage restorer (DVR):It is a voltage source converter which is connected in series with supply through injection transformer where voltage sag or swell takes place.The DVR is most technically advanced and economical device for voltage sag mitigation in distribution system.Energy storage in DVR is responsible for supplying active power needed during voltage sag.If this energy is obtained from neighbour feeder than it is called interline dynamic voltage restorer. I.