Modelling And Simulation Of Doubly-fed Variable-speed Pumped Storage Unit

With the increasingly severe environmental problems and energy crisis,the full development and utilization of renewable energy has become a global goal.However,with the increasing proportion of intermittent power sources such as wind power and photovoltaics in the power grid,the power fluctuation and the problem of wind and light abandoning when new energy is connected to the grid are also increasingly prominent,posing great challenges to the stable operation and frequency control of the power grid.Therefore,the power grid should be equipped with a large-capacity pumped-storage power station to participate in the power peak-shaking and frequency regulation to ensure stable operation of the power grid.However,traditional pumped-storage power stations mainly use synchronous motors,which have disadvantages of low operating efficiency and slow response speed.By contrast,the variable speed pumped storage unit in this paper adopts a doubly-fed induction motor,which can realize stepless variable speed operation within a certain range of rated speed,improve the operating efficiency of the unit,and participate in the power adjustment quickly to enhance the stability of the system.In this paper,the working principle of doubly-fed variable speed pumped storage unit is described firstly,and mathematical models are established for doubly-fed induction motor,reversible pump turbine,governor and frequency converter respectively.It focuses on the analysis of the static stability characteristics of the slip,the static stability characteristics of the power angle,the power factor characteristics and the flow direction of the capacity under different operating condition,which lays a theoretical foundation for the subsequent modeling.Secondly,the control strategy of grid side inverter and rotor side inverter of doubly-fed variable speed pumped storage unit is introduced.At the same time,in order to improve the operating efficiency of the unit,based on the optimal operating curve of the unit,according to the current measured power command and water head value,the optimal speed and vane opening of the unit are calculated,and aelectromechanical coordination control strategy of excitation system and speed regulation system is proposed to optimize the operating efficiency of the unit.Finally,in order to realize accurate observation and real-time tracking of rotor position of doubly-fed variable speed pumped storage unit,a rotor observation method based on electrical quantity is proposed.Considering the safety of the equipment,based on the power limit diagram of the doubly-fed induction motor,the excitation system network source coordinated control strategy is proposed,the excitation auxiliary limit control method is established,and the influence of PI parameters on the control stability of the controller is analyzed.