A Unified Distributed Control in Networked Microgrids for Multiple Modes of Operation

In this paper, a unified distributed control framework is proposed for networked microgrids (NMGs), which designs to operate NMGs in islanded, grid-connected and transition modes. The control framework is divided into two layers, i.e. microgrid (MG) layer, and NMG layer. In the MG layer, the typical primary droop control and distributed secondary control for distributed generators (DGs) are designed. In the NMG layer, there are three control hierarchies: A droop based primary control for each MG; The distributed secondary control among MGs; A tertiary mode-supervisory control, which manages three control types for four operation conditions. The proposed control framework will achieve the following objectives: i) the frequency/voltage recovery and accurate power sharing in islanded (IS) mode; ii) flexible power exchange between main grid and NMG in grid-connected (GC) mode; iii) zero tie-line power flow from GC to IS mode; iv) active-synchronization from IS to GC mode. In addition, the proposed method only requires neighboring information exchange with sparse communication networks. The case studies validate the effectiveness of the proposed control in various operation conditions.