Active Power Sharing and Frequency Regulation in Droop-Free Control for Islanded Microgrids Under Electrical and Communication Failures

The droop-free control for ac microgrids achieves active power sharing and frequency regulation by replacing the centralized secondary control and the primary-level droop mechanism by a cooperative distributed control strategy. This article analyses the performance of the droop-free control when an islanded microgrid suffers electrical and communication failures. The microgrid is modeled by two connected graphs corresponding to the electrical and communication networks. The considered failures leads to partitioned electrical/communication subgraphs that coexist within the microgrid. A closed-loop model integrating the power flow equations, the droop-free control, and the electrical and communication graphs is derived. The stability analysis identifies critical partitions where the microgrid is driven to the instability, and the steady-state analysis characterizes the equilibrium points when the partitioned microgrid remains stable. This article also provides a control strategy that is able to avoid the instability scenario. Selected experimental results on a low-scale laboratory microgrid illustrate the impact that failures have in system performance and the ability of the proposed control for confining the microgrid operation into a safe region.