A resonant current regulator based microgrid control strategy with smooth transition between islanded and grid-connected modes

Microgrids consisting of distributed generators (DGs) have the ability to operate connected to the utility grid and also in stand-alone (island) mode. In both cases, frequency and voltage regulation across the microgrid must be ensured, and the DGs should share their generation equally. The transition of the microgrid between the two operating modes also needs to be seamless, which is conventionally achieved by switching between current or voltage based control, depending on the system context. This paper presents a new microgrid control strategy that exploits the intrinsic droop characteristics of a PR current regulator to achieve these objectives for both modes of microgrid operation. The strategy incorporates a predictive regulator to achieve dynamic voltage control within one fundamental cycle, a frequency adaptation strategy for islanded mode, and ensures DG power sharing. Simulation and experimental results obtained for a microgrid transitioning between both modes are used to verify the performance of the proposed strategy.