Effects Of Doubly-fed Variable-speed Pumped Storage Units On Frequency Stability Of Power System

With the increasing installed capacity of new energy generation,the power system shows the characteristics with high proportion of new energy and high proportion of power electronic equipment,and the system rotational inertia is reduced,damping is weakened,and the frequency regulation capability is insufficient,which seriously affect the stability of the power system.Therefore,it is important to analyze the influence of doubly-fed variable-speed pumped storage units on the stability and damping property of power system and the frequency response of power system.In this dissertation,the static stability and damping property of the power system with doubly-fed variable-speed pumped storage units are studied by using the eigenvalue analysis method,and the frequency response of the new SFR model with doubly-fed variable-speed pumped storage units are studied by using the simplified model method,the details are as follows:(1)Mathematical model of reheat turbine units,fixed-speed hydropower units,fixed-speed pumped storage units,doubly-fed variable-speed pumped storage units and power system are established.The frequency response controller with PD control is designed for doubly-fed variable-speed pumped storage units to improve the ability of doubly-fed variable-speed pumped storage units to participate in power system frequency regulation.(2)Stability and damping property of the power system with doubly-fed variable-speed pumped storage units are analyzed.The state-space equations of the power system with fixed-speed pumped storage units and doubly-fed variable-speed pumped storage units are established separately,and in the comparison analysis with the eigenvalue analysis method we obtained:the doubly-fed variable-speed pumped storage units and their participation in frequency regulation influence the eigenvalues of the system to the left,which improves the static stability of the power system,and increases the damping of the system,which improves the damping property of the system;the participation factors affecting different oscillation the damping property of the system;the participation factors affecting different oscillation modes are analyzed to reflect the degree of correlation between oscillation modes and state variables.The damping property of the power system of doubly-fed variable-speed pumped storage unit are investigated,and the conclusions are as follows:the larger the proportional link coefficient 1/ep,the larger the differential link coefficient Kdf,and the smaller the differential link time constant Td,the larger the damping of the power system and the more stable of the system,and the reasonableness of the conclusions is verified by simulation.(3)Frequency response of the power system with doubly-fed variable-speed pumped storage units are analyzed.In order to use the simplified model method to analyze the frequency response of the system,the first order inertia simplified model of the doubly-fed variable speed pumped storage unit is proposed based on the simplified active power model of the unit,and a new SFR model including the doubly-fed variable speed pumped storage unit is proposed based on the traditional system frequency response(SFR)model.The time-domain expression of frequency response of the system under load disturbance is analyzed and the dynamic frequency response curve of the system is obtained.By comparing the curve drawn by the time-domain expression of the system frequency response obtained from the theoretical analysis with the frequency response curve obtained from the system simulation,the correctness of the proposed new SFR model with doubly-fed variable speed pumped storage unit is proved.Through the new SFR model,the change of the transfer function root locus of the system is obtained to determine the optimal range of frequency response controller parameters.