This paper proposes an electromechanical transient method to build a battery energy storage system-based virtual synchronous generator model, suitable for a large-scale grid. This model consists of virtual synchronous generator control, system limitation and the model interface. The equations of a second-order synchronous machine, the characteristics of charging/discharging power, state of charge, operating efficiency, dead band and inverter limits are also considered. By equipping the energy storage converter into an approximate synchronous voltage source with an excitation system and speed regulation system, the necessary inertia and damping characteristics are provided for the renewable energy power system with low inertia and weak damping. Based on the node current injection method by the power system analysis software package (PSASP), the control model is built to study the influence of different energy storage systems. A study on the impact of renewable energy unit fluctuation on frequency and the active power of the IEEE 4-machine 2-area system is selected for simulation verification. Through reasonable control and flexible allocation of energy storage plants, a stable and friendly frequency environment can be created for power systems with high-penetration renewable energy.