The increasing share of distributed generation (DG) units in the electrical power systems has a significant impact on the operation of the distribution networks which are increasingly being confronted with congestion and voltage problems. This demands for a coordinated approach for integrating DG in the network, allowing the DG units to actively contribute in the frequency and voltage regulation. Microgrids can provide such coordination by aggregating DG, (controllable) loads and storage in small-scale networks, that can operate both in grid-connected and islanded mode. Here, the islanded operating condition is considered. Analogous as in the conventional networks, a hierarchical control structure can be implemented in islanded microgrids. In recent years, many different concepts for primary, secondary and tertiary control of microgrids have been investigated. These controllers can be classified as either local or centralized. In this article, the hierarchical control for application in microgrids is discussed and an overview of the control strategies is given with respect to the reserve provision by the DG units, loads and storage equipment.
I E E E Industrial Electronics Magazine, 2013, Vol 7, Issue 4, p. 42-55