Dynamic Voltage Restorer is a series connected device that injects voltage into the system in order to regulate the load side voltage. The DVR was first installed in 1996. It is normally installed in a distribution system between the supply and the critical load feeder. Its primary function is to rapidly boost up the load side voltage in the event of a disturbance in order to avoid any power disruption to that load there are various circuit topologies and control schemes that can be used to implement a DVR. In addition to its main task which is voltage sags and swells compensation, DVR can also added other features such as: voltage harmonics compensation, voltage transients’ Reduction and fault current limitations The general configuration of the DVR consists of a voltage injection transformer, an output filter, an energy storage device, Voltage Source Inverter (VSI), and a Control system as shown in Figure.
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| Figure: Structure of DVR |
1) VOLTAGE INJECTION TRANSFORMER:
The basic function of this transformer is to connect the DVR to the distribution network via the HV-windings and couples the injected compensating voltages generated by the voltage source converters to the incoming supply voltage. The design of this transformer is very crucial because, it faces saturation, overrating, overheating, cost and performance. The injected voltage may consist of fundamental, desired harmonics, Switching harmonics and dc voltage components. If the transformer is not designed properly, the injected voltage May saturate the transformer and result in improper operation of the DVR.
2) OUTPUT FILTER:
The main task of the output filter is to keep the harmonic voltage content generated by the voltage source inverter to the permissible level (i.e. eliminate high frequency switching harmonics).It has a small rating approximately 2% of the load VA.
3) VOLTAGE SOURCE INVERTER:
A VSI is a power electronic system consists of a storage device and switching devices, which can generate a sinusoidal voltage at any required frequency, Magnitude, and phase angle. In the DVR application, the VSI is used to temporarily replace the supply voltage or to generate the part of the supply voltage which is missing.
4) DC ENERGY STORAGE DEVICE:
The DC energy storage device provides the real power requirement of the DVR during compensation. Various storage technologies have been proposed including flywheel Energy storage, super-conducting magnetic energy storage (SMES) and Super capacitors these have the advantage of fast response. An alternative is the use of lead-acid battery, Batteries were until now considered of limited suitability for DVR applications since it takes considerable time to remove energy from them. Finally, conventional capacitors also can be used.
5) CONTROL SYSTEM:
The aim of the control system is to maintain constant voltage magnitude at the point where a sensitive load is connected, under system disturbances
