Connection and disconnection transients for micro-grids under unbalance load condition

The recent grid integration of Distributed Energy Resources (DER) possibility the formation of intentional islands in the case of a grid fault conditions. For such island formation is required an active agent capable of governing the micro-grid connection state in a safe mode, especially in connection and disconnection transients. This paper focuses on the design of a method oriented to carry out a stable intentional disconnection, and later re-connection, of local grids from the main distribution grid in an intentional way; also under unbalance load condition. Seamless transfer between grid-connected and isolated mode has been achieved in an alpha-beta stationary reference frame with a frequency based synchronization control loop. Simulation and experimental results are provided to verify the proper performance of the proposed solution.