Abstract: Variable speed pump storage is very likely become the effective measure for the control of power grid load frequency and for balancing fluctuation caused by renewable energy resources. Based on the principle introduction of variable frequency pump storage, the topology and configuration of frequency conversion and field excitation unit of typical converters used for variable speed pump storage are mainly described. Analysis indicates that the AC-AC cycle-converter has few devices and high reliability, however with limited range of frequency change and low response speed. Meanwhile the AC-DC-AC converter possesses the large range of frequency adjustment and high response speed, its cost performance rapidly raising, and would become the leading topology in the future development. The speed change principle and adjustment process are analyzed for the generator set operating in both generator mode and pump mode. Based on the characteristic curve of electric output power and rotating speed in generator mode, the optimum output power is able to be achieved by speed control. According to the relationship between the input power and speed in pump mode, the power extracting from electric grid is able to be controlled through speed control. The reference power could be calculated by combining the energy balance with fluctuating load, tracing power output generated by renewable energy resources, and the voltage stability control. By adopting a d-q decoupling strategy, the control of active power and reactive power for variable speed unit is able to be realized. Finally, by taking electric fence power adjustment, voltage fluctuation control, and wind generation power balance as example, the control function of variable speed unit to electric fence operation is addressed.