Control of Active and Reactive Power Ripple to Mitigate Unbalanced Grid Voltages

Managing power delivery from distributed generation systems is challenging when the grid voltages are unbalanced, since the negative sequence voltage causes power oscillations at twice the fundamental grid frequency. Current regulation using sequence components can be used to manage these real and reactive power oscillations, and thus help mitigate the unbalanced network voltages. This paper presents a consolidated control scheme using double sequence frame current regulators that can readily adjust between eliminating real or reactive power oscillations created by unbalanced grid voltages, or alternatively can simply balance the three-phase currents. The mitigation influence of these alternative control strategies on unbalanced grid voltages is then experimentally examined for a distribution feeder with a resistive and/or reactive series impedance.