Robust Voltage Unbalance Control With Inherent Current Sharing in Grid-Connected Microgrids

Grid-connected ac microgrids (MG) are commonly exposed to voltage quality deterioration due to the presence of voltage imbalance. This article presents a control strategy that enables MG grid-feeding inverters (interfacing distributed generation units) to compensate for the voltage unbalance at a given remote node of the MG where for example a sensitive load is likely to be damaged. Each inverter is equipped with a new controller whose operation 1) allows to contribute in the control of the imbalance by only using a measure of the negative-sequence voltage at the remote node while 2) ensuring a fairly redistribution of the control effort among the participating inverters in terms of an inherent negative-sequence current sharing functionality. Since both control objectives are achieved without requiring the collaboration among the participating inverters, the presented solution offers an inherent robustness not found in previous state-of-the-art voltage unbalance control strategies. The new control strategy is accompanied by a controller parameter design receipt, and it is complemented by a formal analysis that permits evaluating how MG modeling errors and uncertainties affect stability and performance. Laboratory experimental results corroborate the properties of the presented control.