Recent findings in microgrids control confirm that the current definition for hierarchical control structure (primary, secondary, and tertiary controls), which was initially inspired by the hierarchical frequency control levels in power systems is inadequate for classifying different control tasks and covering all possible control loops. This paper presents a critical review of the existing three-level control structure and proposes an updated generalized four-level hierarchical control scheme consisting of local, supplementary, central, and global controls to cover the shortcomings. The increasing deployment of microgrids in real-world power grids and the growing body of research in this field highlight the significance of this updated control framework for low/medium voltage energy networks.
