The frequency regulation of pumped storage unit represents an important approach to improve the frequency security of power system. However

the frequency regulation performance of the fixed-speed pumped storage unit in generating operation mode is seriously affected by the water hammer effect. In addition

the fixed-speed pumped storage unit in pumping operation mode cannot adjust its input power. To solve these problems

we carried out research on frequency regulation control strategy of the fixed-speed pumped storage unit based on flexible DC excitation system with energy storage. Firstly

we analyzed the control theory of flexible DC excitation system with energy storage and the frequency regulation mechanism of pumped storage unit. Then

the frequency regulation strategy of the unit was designed. When the unit is in generating operation mode

the active inertia support of the excitation system energy storage device is used to compensate and reduce the negative output adjustment of the pump turbine

which weakens the impact of the water hammer effect. In pumping operation condition

the unit participates in inertia response and primary frequency regulation by the energy storage device of the excitation system. Further

the influence of the proposed strategy on the pumped storage unit and the system frequency is analyzed theoretically. The simulation results show that the proposed control strategy can effectively take the advantage of flexible DC excitation system with energy storage to improve the frequency regulation performance of fixed-speed pumped storage unit

and maintain the frequency stability of the power grid.