A Power and Unbalanced-Current Inverter Controller for Three-Phase Microgrids capable of Islanded Operation

A power and unbalanced-currents controller for three-phase inverters in microgrids is presented herein. Based on symmetric sequences, it allows tracking positive-sequence active and reactive power setpoints and negative-sequence currents setpoints during grid-tied operation. Moreover, if islanded operation occurs, the controller can seamlessly transition into this mode of operation without the need for data exchange (i.e., communication) among the units. Islanded operation with other inverters connected in parallel is fully supported. The control principle and design guidelines are discussed, and experimental results are reported. The controller is useful to provide i) active and reactive power tracking to support demand-response and reactive power compensation, ii) unbalanced current compensation, iii) balanced power injection also in case of unbalanced grid voltages, iv) uninterrupted operation in case of islanding.