Research On Frequency Response Technology Of Wind Farm For Adapting To Large Power Grid With Weak Inertial

With the development of large-scale wind power generation,the high-penetration wind power grid-connected operation is the future trend of power grid development.High penetration wind power will weaken the equivalent inertia of the system if it replaces the traditional synchronous generator gradually,which has a profound impact on the frequency dynamic characteristics of the power grid and poses a threat to the security and stable operation of the system.Therefore,the frequency stability of wind power integration has become a key factor affecting the development of high-penetration wind power,especially the frequency response technology for adapting to the high-penetration wind power integration needs further study.Aiming at the problem of frequency transient stability of power grid with high-penetration wind power integration,this thesis presents the performance of an in-depth study of research on frequency response technology of wind farm for adapting to large power grid with weak inertial.The main content and innovative contribution of this thesis are as follows: the impact of high-penetration wind power integration on the transient frequency of the power grid is analyzed,and a fast evaluation method for the maximum wind power penetration level of power grid is proposed;in order to improve the frequency stability of high-penetration wind power integrated grid,the frequency coordination control strategy of the wind farm is proposed considering the difference of reserve capacity among units;considering the wind turbine generation(WTG)operating area and wind speed disturbance,the WTG frequency response equivalent model is established,and the multi-machine frequency response model of wind farm is aggregated and equivalent;combined with the traditional system frequency response(SFR)model and the wind farm frequency response equivalent model,the power grid frequency dynamic security quantitative evaluation including wind power participating in frequency regulation is realized.The specific work is as follows:The operation characteristics of the mainstream variable speed constant frequency WTG are analyzed.Aiming at the problem of power grid inertia weakening caused by decoupling of WTG active power and power grid frequency,the impact of wind power integration on key parameters of power grid such as integrated inertia,static frequency characteristic coefficient and damping coefficient was analyzed from the mechanism level.Combined with the equivalent single machine SFR model aggregated by the multi machine SFR model,the SFR model of power grid considering wind power integration is established,and the quantitative analysis of frequency response characteristics is realized.On this basis,an evaluation method of maximum wind power penetration considering the cumulative effect of frequency deviation is proposed,the frequency response trajectory characteristics of power grid under power disturbance are calculated by SFR model,and combines the transient frequency security index based on the cumulative effect of frequency deviation,the quantitative function relationship between the wind power penetration level and the transient frequency security index is established,which can quickly and effectively predict the frequency security state and the maximum penetration level of the power grid.In order to improve the frequency stability of power grid with wind power,combined with the advantages of traditional frequency control methods such as simulated inertial control,rotor over-speed control and pitch angle control,a frequency control method for WTG considering the operating range under full wind condition is proposed,the simulated inertia and rotor overspeed coordinated control are used in the maximum power tracking range,while the simulated inertia and pitch angle coordinated control are used in the constant speed and the constant active power range.Furthermore,the impact of the wake effect on the active power output of the wind farm is analyzed,that is,the wake effect will cause the rotor kinetic energy and the deloading power under the same deloading level for different WTGs to be different.To make full use of the reserve capacity such as rotor kinetic energy and deloading power of the wind farm,so as to ensure the security and stable operation and maximize the inertial support and primary frequency regulation capability,a frequency coordination control strategy of wind farm considering the releasable reserve capacity is proposed,the gains of integrated inertial control are adjusted adaptively according to the current rotor kinetic energy of the WTGs,while the gains of primary frequency control such as rotor over-speed control and pitch angle control are adjusted adaptively according to the current deloading power of the WTGs.Consider that the wind farm frequency response characteristic analysis method based on the full time domain state simulation has the disadvantage of large amount of calculation and long time-consuming,the application requirement for analyzing the dynamic response characteristics of wind farms using a simplified frequency control system equivalent model is analyzed.Combine with the idea of the traditional synchronous generator frequency response equivalent modeling,and the additional integrated inertia and the primary frequency regulation control for WTG under all wind conditions,the frequency response equivalent model is established by using small signal analysis method,and the mathematical analytical description method of the dynamic frequency response characteristics after active power disturbance is constructed.Due to the difference in operating parameters and frequency control parameters of different WTGs,the frequency response equivalent model parameters of different WTGs are also different.To further quantitatively characterize the dynamic response characteristics of wind farms,the multi-machine frequency response model is aggregated into a single-machine frequency response equivalent model by system identification analysis method,and the hypothesis of solving the equivalent parameters of the aggregate model is verified by mathematical proof method.Based on the traditional SFR model and the equivalent frequency response model of wind farm,a frequency response model of power grid with wind power participating in frequency regulation is proposed,then the system stability with wind power participating in frequency regulation is analyzed by establishing the closed-loop transfer function of the model.Furthermore,by decomposing the frequency-domain expression of the grid frequency response model,and using Laplace Inverse transform,the time-domain expression of the grid frequency response model with wind power participating in frequency regulation is derived,it shows that the grid frequency dynamics after power disturbance is a sinusoidal damping expression related to wind power frequency control parameters.On this basis,the impact of frequency control parameters and wind turbine inertia time constant on grid frequency dynamics is analyzed.Based on the in-depth analysis of the frequency dynamic response process of power grid with wind power participating in frequency regulation,combined with the transient frequency security index considering the cumulative effect of frequency deviation,a quantitative evaluation method for the frequency dynamic security of power grid with high penetration wind power is proposed,this method calculates the value of the transient frequency security index by estimating the system power shortage,so that the frequency dynamic security state of the power grid under power disturbance can be effectively evaluated.