A coordinated hierarchical frequency control strategy for islanded microgrid using multiple flexibility resources

Abstract

To address the stringent dual requirements for frequency stability and operational economy in island microgrids under source-load uncertainties, this paper proposes a hierarchical coordinated frequency control strategy with incorporating economic dispatch. In the primary frequency control stage, a Sigmoid function-based adaptive Virtual Synchronous Generator (VSG) control is proposed. This method adjusts the virtual damping in real-time to enhance the dynamic response capability of renewable energy sources (RES). In the secondary frequency control stage, a Model Predictive Control (MPC) framework integrating an economic cost function is constructed to achieve the deep integration of frequency restoration and optimal power allocation. Simulation results in Matlab/Simulink demonstrate that the load response rate of RES in the primary control stage increases by over 280 %. In the secondary control stage, the RES response rate reaches approximately 34 %, and the comprehensive cumulative generation cost is reduced by about 73.9 %. Furthermore, the change rate of frequency deviation remains at the order of magnitude of $10^{-6}$ under system parameter perturbations, which verifying the robustness of the proposed strategy.