Research On Compoment Bifurcation Characteristics Of Doubly-fed Variable Speed Pumped Storage

With the large-scale integration of renewable energy such as wind power and photovoltaics into the power grid,the power grid’s demand for pumped storage power plants is increasing day by day.Therefore,the stability research of pumped storage units is particularly important.Because pumped-storage units are frequently started and stopped during operation and the stability of working condition conversion has become the key to restricting the development of pumped-storage power stations,doubly-fed variable-speed units have been widely used in pumped-storage power stations due to their good response characteristics.In this paper,the mathematical model of the doubly-fed variable-speed pumped storage unit under the operating conditions of the turbine and the pump is established,and the stability and regularity of it is studied and analyzed.The following three aspects are mainly completed:(1)Mathematical model.The doubly-fed motor is used as the generator/motor of the pumped storage unit.Based on the establishment of the water diversion system model,the governor model,the pump-turbine model,the doubly-fed motor and its control model respectively,a complete mathematical model of the variable-speed pumped storage unit under the operating conditions of the hydraulic turbine and the operating conditions of the pump is established.(2)Judgment of the bifurcation of the system under hydraulic turbine operating conditions and pump operating conditions.By using the Hopf bifurcation high-order judgment theorem,the bifurcation judgment of the doubly-fed variable-speed pumped storage unit is carried out.If the Jacobi matrix coefficients of the system meet the bifurcation judgment theorem,the system parameters will be bifurcated in a certain state.From the critical condition of the bifurcation theorem,the bifurcation critical value of the PID parameters of the system can be calculated,and the three-dimensional stability region of the PID parameters of the system can be obtained.And the accuracy of the calculation can be further verified through the time domain simulation and phase space image of the dynamic parameters of the unit.(3)Under the condition of fixed power controller parameters,consider the nonlinear characteristics of the pump-turbine,and compare and analyze the stability region of the linear.pump-turbine regulation system;consider the effect of elastic water hammer on the turbine operating conditions and pump operation.The influence of the stability domain under working conditions.In order to further improve the stability analysis of the doubly-fed variable-speed pumped-storage unit,the influence of the unit inertia time constant on the stability region of the system PID parameters is analyzed.The study found that when considering the nonlinear characteristic model of the pump-turbine,the stability region of the system with respect to the speed controller parameters is significantly smaller than that of the system with the linear model of the pump-turbine;considering the elastic water hammer effect for the double-fed variable speed In the stability region of the pumped storage unit,the system will be affected differently under the operating conditions of the hydraulic turbine and the operating conditions of the pump.The elastic water hammer effect will have a deteriorating effect on the stability region of the system under the operating conditions of the turbine.When running under pump conditions,the system will not be affected too much.At the same time,when considering and analyzing the influence of the unit inertia time constant change on the PID parameter stability domain,it is found that the larger the unit inertia time constant,the larger the speed controller parameter stability domain,indicating that the increase of Ta makes the system more stable.Adjusting the range has a positive effect on the stability of the system.