Hierarchical microgrid paradigm for integration of distributed energy resources

This paper describes an approach to hierarchical integration of DC and AC microgrids containing distributed energy resources (DERs) into the existing electric power distribution infrastructure. Power electronic interfaces and controls permit the aggregated units at each level to represent themselves to a higher level as a single self-controlled entity (DC or AC, load or generator). At the top level of the hierarchy, the collection of all distributed energy resources within the microgrid appears to the utility grid as indistinguishable from many other currently legitimate customer sites. Maintaining this profile relies on the flexibility of advanced power electronics that control the interfaces among distributed energy resource units, DC links, AC links, and the surrounding power system. A decoupled control framework is then proposed for the hierarchical microgrid. Operational requirements and behavioral functions of the control systems are described in the paper. A case study demonstrates the operation of the microgrid paradigm.