Hierarchical Delay-Dependent Distributed Coordinated Control for DC Ring-Bus Microgrids

In this paper, a hierarchical distributed coordinated control method is proposed based on the multi-agent system for dc ring-bus microgrids to improve the bus voltage performance. First, a two-level multi-agent system is built, where each first-level unit control agent is associated with a distributed energy resource to implement local decentralized control, and the second-level control agent is associated with the first-level agent to implement distributed coordination control together with the first-level agent. Afterward, the assessment index of each distributed energy resource subsystem is established. By the assessment index, the multi-agent system can judge whether the subsystem should implement the local decentralized control or the distributed coordinated control. Furthermore, by means of the assessment index, both the local controller and distributed coordinated controller are designed, respectively, based on two kinds of dynamic models of DER unit. To reduce the communication pressure, the distributed coordinated controller is built by local controller combined with the coordinated control laws. The coordinated control laws are synthesized by using the states from only neighboring subsystems. Considering the effect of communication delays on control performance, a delay-dependent H∞ robust control method is proposed to design the distributed coordinated controller. Finally, the validity of the proposed control scheme is testified by simulation results.