Abstract: With the high penetration of renewable energy, power system frequency stability is confronting growing challenges. In particular, under conditions of frequent dynamic load disturbances, system frequency exhibits rapid fluctuations and tends to experience instability. Conventional Virtual Synchronous Generator (VSG) adaptive control strategies often exhibits limited frequency regulation accuracy and delayed response under continuous load variations, while typically neglecting the constraints imposed by the state of charge (SOC) of the energy storage system on inertia support capability. To address these issues, this paper proposes a fuzzy adaptive VSG control strategy based on a variable universe approach, incorporating SOC feedback. This method utilizes a frequency deviation-based scaling factor to dynamically adjust the input and output universes of fuzzy rules, thus enabling real-time adaptation. Furthermore, the SOC of a vanadium redox flow battery (VRB) is introduced as a constraint to limit virtual inertia output. A PV-energy storage simulation model is developed in MATLAB/Simulink to evaluate the performance of the proposed strategy. Simulation results obtained under step and continuous load disturbances demonstrate that the proposed method can significantly enhance frequency stability and effectively suppress system instability induced by excessive virtual inertia.