The AC voltage supplied by VSI is stepped up by using injection transformer to the desired voltage level.
The winding connection of injection transformer depends on step down transformer connected in distribution line. It is either connected in star/open star winding or delta/open star winding. The former connection allows injection of zero sequence components as well whereas the latter connection does not allow it. Here three phase single transformer is used. The amount of voltage sag/swell compensated by DVR depends upon the rating of injection transformer and inverterThe 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