Decentralized Unified Control for Inverter-Based AC Microgrids Subject to Voltage Constraints

The control law of electronically-interfaced distributed energy resources (DERs) must be able to maintain the stability and voltage regulation of the host microgrid in the two modes of operation. Ideally, this should be achieved by a decentralized primary control strategy that is independent of any communication infrastructure in order to increase the resilience of the microgrid. This is challenging as the primary control objectives in islanded and grid-connected modes of operation are conflicting. This paper proposes a decentralized control law for DER units based on state feedback and disturbance rejection. The controller provides an integral action which enables output current reference tracking. An ad-hoc partial input saturation technique is also proposed in order to prevent the integral action from having an adverse impact on the voltage amplitude and frequency regulation in the islanded mode of operation. The effectiveness of the proposed control strategy is demonstrated via a time-domain simulation of a medium-voltage distribution network with three embedded DER units, as well as through an experimental three-bus microgrid with two DER units. The results demonstrate the robustness of the proposed control strategy to transitions between the modes of operation and other network topological changes.