Research On Dynamic Stability Of Variable Speed Pumped Storage Units

With a large number of new energy sources such as wind power and photovolta-ics connected to the power grid,their inherent intermittency and volatility have brought a lot of threats to the safe and stable operation of the power grid.By excavating and giving full play to the functions of pumped storage power stations in peak shaving and valley filling,smoothing the fluctuation of renewable energy output,etc.,promote the absorption of new energy and ensure the safe and stable operation of the power system.Compared with the traditional synchronous motor pumped storage unit,the variable speed pumped storage unit using doubly-fed motor has the characteristics of variable speed,high efficiency and energy saving and high reliability.In this paper,the dynamic regulation characteristics of doubly-fed variable speed pumped storage units are studied,and the dynamic stability of grid-connected units is analyzed and simulated to be verified.Firstly,the basic structure and operation principle of the variable speed pumped storage unit are expounded,mathematical models are established for doubly-fed motor,pump turbine speed regulation system,converter and its control system,and two different control schemes of power priority and speed priority are proposed,focusing on the analysis of the dynamic adjustment characteristics of doubly-fed motor and reversible pump turbine under different working conditions.Secondly,a small signal model of the variable speed pumped storage unit is established,and the dynamic response process of the unit under different step disturbances is analyzed by using the linearized small signal model.The influence of controller parameters,unit operating status and power level,AC system strength and other factors on the stability of small disturbances of the unit is studied,and a parameter optimization method based on feasible domain is proposed.Based on the PSCAD simulation platform,it is verified that the proposed method has a certain degree of optimization for improving the stability of small disturbances of the unit.Finally,the stator mode of the variable speed pumped storage unit is extracted by modal analysis,and the influence of the closedloop control bandwidth and rotor current active damping on these modes and the dynamic performance of the unit under large voltage dip disturbance are studied,and the simulation verifies that increasing the closed-loop control bandwidth and active damping can improve the rotor current dynamics,reduce the tracking error,and limit the rotor current transients,but it will lead to poor stator mode and deterioration of the dynamic performance of the unit.