Frequency and voltage coordinated control of a grid of AC/DC microgrids

This paper proposes a hierarchical control scheme based on a distributed controller design for a multi-microgrid system. Thus, a proposed control approach of ac and dc microgrid interfaces is presented, based on virtual synchronous generators to control the power exchange of the interconnected microgrids, and provide frequency support, voltage regulation, and virtual inertia for the individual microgrids and ac host grid. A hierarchical distributed control technique is proposed, with primary controls of interfacing virtual synchronous generators providing adaptive inertia for all ac systems, while a secondary distributed control regulates the frequency and the voltages of the ac host grid and the interconnected ac and dc microgrids, based on a consensus technique with limited information about the overall system. The proposed controller shares the total system load among the grid and microgrids, while minimizing the overall frequency and dc-voltage deviations in all interconnected systems. The presented interface and the controller are implemented, tested, and validated using time-domain simulations for a multi-microgrid test system, which is based on a CIGRE benchmark medium voltage system and consists of both ac and dc microgrids.