“SRF theory revisited” to control self supported dynamic voltage restorer (DVR) for unbalanced and nonlinear loads

The protection of the sensitive but unbalanced and/or non-linear loads from sag/swell, distortion and unbalance in supply voltage is achieved economically using a dynamic voltage restorer (DVR). A simple generalized algorithm for the generation of instantaneous reference compensating voltages for controlling DVR, based on basic SRF theory has been developed. This novel algorithm makes use of fundamental positive sequence phase voltages extracted by sensing only two unbalanced and/or distorted line voltages. The algorithm is general enough to handle linear as well as nonlinear loads. The compensating voltages when injected in series with a distribution feeder by a 3-single phase H-bridge voltage source converter (VSC) with constant switching frequency hysteresis band voltage controller, tightly regulate the voltage at load terminals against any power quality problem on the source side. A capacitor supported DVR does not need any active power during steady state operation because the injected voltage is in quadrature with the feeder current. The proposed control strategy is validated through extensive simulation studies in MATLAB.