A state machine is proposed in the energy management system (EMS) of a microgrid as the solution for smooth microgrid's transition operation. This state machine includes six “states” that cover all the operating modes during the microgrid's transition operation: two basic modes (grid-connected and islanded) and four temporary modes (preparing for disconnection, transition to islanding, preparing for resynchronization, and transition to grid-connected). Temporary modes are designed to fine-tune the control references for the microgrid assets to avoid harmful transients during microgrid transitions, therefore achieving smooth transition operation. The developed state machine is validated by simulation in MATLAB with a sample microgrid, and the test results show excellent performance of the state machine and smooth microgrid transition operation.
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