Dynamic Direct Voltage Controller (D2VC) for grids with intermittent sources

Abstract

This work proposes a voltage regulator to solve quality issues at the point of common coupling (PCC) of distribution grids affected by the intermittency of renewable energy sources. The proposed solution is a voltage compensator based on single-phase voltage source converter (VSC) units, called Dynamic Direct Voltage Controller (D2VC). The three-phase D2VC topology comprises three single-phase VSC back-to-back units. For each unit, one converter is connected in series with the grid at the PCC and the other converter is connected in shunt similar to an UPFC (Unified Power Flow Controller). To avoid coupling transformer, the series converter is directly connected in series to the existing distribution transformer thus no extra transformer is necessary. The D2VC can regulate the three-phase voltage profile at the PCC and balance all phases independently. The control strategy for each series converter is based on the estimation of the instantaneous symmetrical components of the voltage. Simulation results using PSCAD/EMTDC and an experimental platform of the D2VC are shown to confirm all the D2VC advantages in grids with resistive lines (R >> X). The proposed solution is much lighter and effective than the conventional indirect voltage control (reactive power control) and more robust than on load tap changer transformer.