Design and implementation of a microgrid controller for bumpless transitions between grid-connected and island operation

The transition between a grid-connected and an islanded microgrid has been examined in this paper with particular emphasis on bumpless transition between these two modes so that the power delivery to the load can be maintained. The proposed control strategy is composed of a voltage controller and a current controller. The roles of these controllers are examined to achieve a bumpless transition through coordination. The developed scheme has been validated through extensive simulation studies. Finally, a physical experimental microgrid with a 1.2 kW fuel cell power module is constructed to validate the performance of the proposed scheme in a physical environment. A grid connection interface has been designed and constructed to allow the microgrid to be connected to the utility grid (university campus grid). Experimental studies have demonstrated the effectiveness of the proposed scheme in achieving bumpless transitions between the grid-connected and the islanded modes of operation under a variety of conditions.