ConclusionThis paper presents a new solution for microgrid inverters interms of circuit topology and control structure. The combinedthree-phase four-wire inverter, which is composed of three single-phase full-bridge inverter circuits, is adopted. The control structureis divided into three main parts: the islanding detection unit, thegrid-connected controller, and the islanding controller. The inver-ters automatically operate in the grid-connected or the islandingmode using the islanding detection unit. In the grid-connectedmode, the controller is composed of the sliding-mode currentinner loop and the constant power control outer loop. The invertereffectively rejects the grid voltage disturbances and the param-eter uncertainties. Moreover, the inverter also provides constantcurrents to the grid. In the islanding mode, the controller isbased on the sliding-mode voltage inner loop, the virtual resis-tive output-impedance loop, and the improved P/Q sharing controlloop. The controller guarantees the parallel operation of the micro-grid inverters with robustness performance and a good powersharing accuracy. The dynamic characteristics and the high disturb-ance rejection performance during the transition is ensured. Thetheoretical analysis and test results validate the proposed controlstrategy effectiveness.