Surround control of distributed energy resources in micro-grids

Smart micro-grids offer a new and wide application domain for power electronics. In fact, every distributed energy resource (DER) includes an electronic power processor (EPP) to control the power exchange with the grid. If such distributed EPPs perform cooperatively, they have the capability to fully exploit all renewable power sources and energy storage units while improving the power quality and transmission efficiency. In fact, EPPs control phase and shape of the currents injected into the grid, thus they can provide, in addition to dynamic control of the power flow between DERs and grid, also voltage stabilization and harmonic damping. This is of particular relevance in low-voltage residential micro-grids, where number of active DERs and generated power are unpredictable and may vary during the daytime. A simple and effective solution to achieve cooperative operation of EPPs is described in the paper. It is based on a control approach which requires communication between neighbor units only (surround control) and holds even in presence of multiple feeding points from the utility. Moreover, it allows independent and stable operation of the EPPs while providing voltage support and reduction of distribution losses. Accordingly, residential micro-grids may perform efficiently, adapt to supply and load variations and switch automatically from grid-connected to islanded operation.