Due to the complex dynamic characteristics of pumped storage units, ultra-low frequency oscillation is prone to occur when a high proportion of pumped storage energy is involved in grid frequency regulation, which poses a threat to the safe and stable operation of the grid. To effectively address this issue, this paper proposes a new method for pumped storage units to participate in grid frequency regulation based on small signal modeling analysis. Firstly, in order to more accurately reflect the dynamic characteristics of pumped storage units under actual working conditions, a mathematical model for their participation in power grid frequency regulation was constructed using the method of small signal analysis. Furthermore, considering that the small signal model can reveal potential risks such as ultra-low frequency oscillation in the system, the nonlinear characteristics of the system are further highlighted, and a Fractional Order PID (FOPID) controller with strong robustness is designed to achieve precise control of pumped storage units. Finally, through simulation analysis and verification, the established small signal model of pumped storage units can not only accurately describe the dynamic characteristics of water turbines, but also provide effective technical support for power grid frequency regulation. The proposal of this method not only helps to improve the performance of pumped storage units in power grid frequency regulation, but also provides a new solution for the safe and stable operation of the power grid.