A Coordinated Hierarchical Control Strategy for Hybrid AC/DC Microgrids with Supervisory Mode Transition

The increasing integration of power electronic converters in hybrid AC/DC microgrids introduces significant challenges in maintaining DC-link voltage stability during mode transitions, where uncoordinated actions cause large voltage deviations. This paper proposes a coordinated hierarchical control strategy incorporating a supervisory finite state machine (FSM) and a slew-rate-limited reference shaping mechanism to ensure smooth transitions in a microgrid interfaced through a bidirectional DC–DC converter and a three-level T-type inverter. The supervisory layer coordinates the sequencing of subsystem activation and routes all mode changes through a dedicated transition state in which the power reference is gradually shaped to suppress DC-link disturbances, while a dedicated resynchronization state manages reconnection to the grid after a sustained outage. The strategy is validated through detailed switching-level simulations across five operating scenarios, including islanded load energization, grid blackout, discharging-to-charging transitions, state-of-charge limit management, and grid restoration through reclosing and resynchronization, and is further compared against a droop-based coordination scheme. Simulation results demonstrate that the proposed approach reduces the transient DC-link voltage deviation from approximately 18–20% to below 7%, and to as low as 2.6%, without introducing steady-state error, confirming its effectiveness in enhancing the dynamic stability of the system during mode transitions.