Power-based droop control in DC microgrids enabling seamless disconnection from AC grids

This paper proposes a unified power-based droop control method for distributed energy resources in dc microgrids that can operate both in grid-connected and islanded mode. When the main grid is available, the bus voltage is regulated by the grid-interface ac/dc converter, while distributed energy resources operate as power controlled sources. During abnormal operation of the main grid (e.g., due to faults), the grid-interface converter loses the capability of regulating the bus voltage and the proposed controller inherently converts from a power controller to a droop controller, without any need of communication with other microgrid components, enabling the seamless transition between the two operating modes. The proposed solution is experimentally verified by a testbed having one grid-interface converter and four distributed energy resource converters, 5kW of rated power each.