Distributed Secondary Frequency Restoration Control Based on Virtual Asynchronous Machines for Virtual Energy Storage Systems

Although virtual asynchronous machine (VAM) control has been proposed for virtual energy storage systems (VESSs), research into its secondary control applications is still limited. Thus, a distributed secondary frequency restoration control strategy based on VAMs is presented for VESSs. First, the VAM control is introduced, and a detailed electro-thermal coupling model of the VESS is developed. This model includes indoor-outdoor temperature differences, heat transfer through building envelope (walls, windows, and roof), solar radiations, ventilation losses, and electric boiler dynamics. It effectively captures the coupling between indoor temperature regulation and grid power balancing. Next, a distributed secondary frequency restoration control strategy based on VAM is proposed. It addresses parameter heterogeneity within a nonlinear multi-agent framework among VESSs. The nonlinear dynamics are converted into a linear reference model, which simplifies controller design and stability analysis. Using only local and neighboring information, the proposed strategy restores frequency and ensures active power sharing. Furthermore, the proposed strategy coordinates thermal power regulation to maintain indoor temperature balancing across VESSs within seasonal thermal comfort ranges. This improves thermal comfort without compromising dynamic response. Finally, the stability of the proposed strategy is verified using Lyapunov method, and simulation results from an islanded microgrid (MG) test system under parameter variations, communication imperfections, and winter/summer operating scenarios validate the effectiveness and robustness of the proposed strategy.