  The increasing diffusion of distributed energy generation systems requires
the development of new control paradigms for the coordination of
micro-generators, storage systems, and loads aimed at maintaining the
efficiency and the safe operability of the electricity network. MicroGrids
(MGs) are an interesting way to locally manage groups of generation devices,
but they cannot singularly provide a significant contribution to sustain the
main electricity grid in terms of ancillary services, such as the availability
of a minimum amount of power reserve for the frequency regulation. For these
reasons, in this paper we propose a framework for the aggregation and
coordination of interconnected MGs to provide ancillary services to the main
utility. The proposed framework is structured in three main phases. In the
first one, a distributed optimization algorithm computes the day-ahead profile
of the active power production of the MGs based on the available forecasts of
the renewable sources production and the loads absorption. In this phase,
scalability of the optimization problem and confidentiality requirements are
guaranteed. In the second phase, reactive power flows are scheduled and it is
ensured that the active power trends planned in the first phase do not
compromise the voltage/current limitations. A final third phase is used to
schedule the active and reactive power profiles of the generation units of each
MG to make them consistent with the requirements and results of the previous
two phases. The developed method is used for control of the IEEE 13-bus system
network and the results achieved are thoroughly discussed in terms of
performance and scalability properties.
