Background: Conventional micro-grids operate autonomously in islanded mode but they
always rely on the utility grid for BUS voltage support and power balance in the grid-connected
mode. This results in non-seamless mode switching, alternating operation strategy and power exchange
Methods: An AC/DC/AC converter is utilized as the interface between the micro-grid and the utility
grid. This enables the two entities to have different voltages in the grid-connected mode. The microgrid
exchanges predefined amount of power with the utility grid in the grid-connected mode. The
power amount is estimated based on power forecasting of local generations and loads with the consideration
of the Sate of Charge (SOC) of the battery, and is updated and broadcasted every 15
Results: A 100kVA AC micro-grid with a rotating generator, battery storage and solar arrays is built
on Matlab/Simulink for investigation. Results indicate that the battery can effectively balance the
power flow and mode switching hardly causes distortions.
Conclusion: The proposed micro-grid can operate autonomously in both grid-connected and islanded
mode without relying on the utility grid. Seamless switching between operation modes can be
achieved naturally. Constant power is exchanged with the power grid, which benefits the powerdispatching
algorithm of the power system.