Hierarchical Robustness Strategy Combining Model-Free Prediction and Fixed-Time Control for Islanded AC Microgrids

Addressing the issue of power quality degradation caused by parameter uncertainty and the problem of voltage and frequency deviation due to disturbance in islanded AC microgrids (MGs) in harsh environments, this article proposes a hierarchical robustness strategy combining model-free prediction and fixed-time control (CMFP-FTC). Firstly, an ultra-local model (ULM) of an LC-filter is established, and the unknown disturbances in the ULM are observed using the designed fixed-time sliding model observer to enhance the robustness and dynamic performance of the system. Additionally, the Artstein transform theory is employed to convert the model with communication delay into a delay-free model. Furthermore, a distributed fixed time secondary controller (DFTSC) based on saturation function is designed to avoid the control signal from exceeding the physical limitations of the actuator, and the deviations in frequency and voltage are corrected by DFTSC for accurate power sharing. Finally, the simulation and experimental results demonstrate that the proposed CMFP-FTC strategy exhibits strong robustness and has the ability to rapidly and accurately restore frequency and average voltage to rated values, as well as achieve active and reactive power sharing.1