Distributed Secondary Frequency Cooperation and Power Allocation in Cyber-Physical Microgrids With Multiple Operational Constraints

For the frequency regulation and power allocation problem for ac microgrids, the multiple constraints of load frequency restrictions, nodal active power injections, and power-flow balance that guarantee transient stability are as crucial as the final consistent steady-state results. This article investigates a class of droop-controlled ac microgrids with the abovementioned constraints, and it presents sufficient and necessary conditions to improve system robustness and reliability under load fluctuations. By integrating the Kuramoto oscillator model into the primary control law, cyber-physical coupling dynamics for ac microgrids are established. A novel communication-network-based secondary distributed control approach is presented, which considers physical nodes with different characteristics of power generation and load units. By using invariant theory and nonquadratic Lyapunov techniques, the bounded input-output stability of microgrids can be guaranteed under certain conditions, which is especially pertinent in active power allocation. The theoretical results are verified through numerical case studies of both public and self-built power test systems, demonstrating the obvious improvement in robustness and reliability against variable power generation and load demand.