The most interesting issue for electrical engineers is power quality/power quality improvement in modern era. Power quality is the most noticeable trouble for electrical engineering students. This problem occurs due to occurrence of substandard voltage, may be substandard current, and of frequency which contain harmonics which may damage to power system equipments. Many power supplying companies, responsive industrial load, serious commercial operation experience from various type of problem occurred due to power quality issues and providers can cost large financial losses. So one of the most important problem is voltage sag/swell. DVR is a power electronics based device that can easily alleviate these power quality issues like voltage sag in the system. In this thesis firstly give the introduction of all major power quality issues for this controller. After that the operation and the elements of this controller is discussed. In this paper, DVR uses the error signal to adjust the triggering of the control of an inverter using SPWM technique. All the simulation work are done in MATLAB software version 7.13. So modeling and simulation work is unique. On seeing the performances, we conclude that DVR is the best device for alleviating such problems.