Microgrid design using folded P-f droop and new grid interface unit to minimize the need for communication 

A new control scheme is proposed for microgrids to enable seamless switching between islanded mode and grid-connected mode in this paper. Utilizing a specially designed interface unit as the interface device, a systematic control strategy is proposed to enable a smooth and autonomous transition from grid-connected to islanded and vice-versa. With the proposed scheme, the need for high-speed communication is eliminated despite of the change of operational mode. To make this happen, a folded droop scheme is proposed to enable autonomous frequency support for paralleled converters in the microgrid and a coordinating strategy is then proposed to enable autonomous re-synchronization with the main grid as well. The control scheme proposed are validated with a benchmark microgrid model of parallel- connected converters using MATLAB/SIMULINK. The results show that the proposed control can enable autonomous smooth transitions between modes with reduced power rating in the interface converter unit.