Research On Control Method And Control Characteristics Of Variable-Speed Pumped Storage Units

The pumped storage power stations have multiple functions such as peak regulation and valley filling,which is one of the important means to smooth the fluctuation of renewable energy output and solve the current problem that the large-scale development of new energy power generation brings to the safe and stable operation of the power grid.Using the mature technology of variable speed constant frequency to achieve variable speed of pumped storage units,compared with the conventional constant speed pumped storage units,it is possible to adjust the speed according to the changes of operation condition under generating mode to improve the operation efficiency.Under pump mode,it can adjust the power,improve the frequency modulation performance.And it also have a variety of functions such as improving power quality and improving power system stability.This paper first introduces the composition of the double-fed variable-speed pumped storage units and the mathematical model of each component.Then introduces two control strategies of the unit,including the power priority control strategy and the speed priority control strategy,and then establishes the control block diagram of two control strategies when they are adopted for generating mode and pump mode.The influence of the internal parameters of the unit on the control characteristics is analyzed,and the control parameters of the control system are designed by analyzing the stability,steady state characteristics,and step signal response characteristics,etc.The control characteristics of the two control strategies used in generating mode and pump mode are compared,and the applicable conditions for each control strategy are obtained.Secondly,the phenomenon of different power response speeds in the fast dynamic adjustment process is analyzed.The active power,including the stator side active power of the double-fed motor,the rotor side active power,the released power of the kinetic energy from the shaft,the mechanical output power of the pump turbine,the output active power by the unit to the grid,in the fast dynamic adjustment process under generating mode and pump mode,and various reactive powers,including the stator-side reactive power and rotor-side reactive power of the doubly-fed motor,are modeled respectively.Relationship between different powers and flow direction in different operating stages are analyzed.Finally,the compensation effect of variable-speed pumped storage units in grid power regulation is studied,and a piecewise linearized pump-turbine model is established.The piecewise linearized pump-turbine model is applied to the unit model and the control parameters of the control system are designed when each linearized model was used.The output power model of the unit during the whole process of operation condition switching is established and applied to simulation example.The smoothing and compensating effects of variable speed pumped storage units on the power regulation of power grid are studied.