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Dynamic Voltage Restorer (DVR) is a series connected power electronics based custom power device that is used to improve voltage disturbances in low voltage electrical power distribution network. Power quality requirement is one of the most important concerns for power system. The parts of the DVR is made up of voltage source inverter, injection/booster transformer, a harmonic filter, an energy storage device and a bypass switch. The DVR is used to inject three phase voltage in series and in synchronism with the network voltages in order to compensate voltage disturbances with a benefit of active /reactive power control. This paper presents a review of the researches on the dynamic voltage restorer application for power quality improvement in low voltage electrical power distribution networks. It describes power quality issues, principle of operation of DVR, basic components of DVR, DVRs control topologies in distribution network, DVR control strategies and compensation techniques.

With the ever increasing use of power semiconductor devices and information technology (ICT) equipment in the industries, homes and offices voltage quality are gaining meaningful attention to both industry and electric utility level. The lack of voltage quality causes unusually large economic losses all over the world, since voltage quality problem is one of the major power quality disturbances. This paper presents an investigative study on the 11/0.4 kV, low voltage electrical distribution network, aimed at analyzing voltage unbalance and variation problems and recommending an effective method of improving the voltage profile and reducing the voltage unbalance and variation to allowable standard. The network was modelled with the distribution network standard parameters for low voltage distribution network using MATLAB/Simulink Sim Power System tool box. The simulation results with distribution length 0.5 km for balanced three phase load is within the permissible voltage profile of ±5%, reaching the customers, meaning it is admissible for customers use also it was established that an inadmissible poor voltage profile reaching the customers at the network end of distribution network lengths 0.8 km to 5 km which is less than the standard minimum permissible limit of -5%, of nominal voltage value

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