| Achieving the carbon neutralization target of "3060" is an important demand for the sustainable development of energy in our country and even the world.With the increasing scale of wind power grid connection,tradition al thermal power generation has been replaced by a large number.The f orm and operation characteristics of the power grid have changed significantly.The power system presents high power electronics characteristics,which leads to wide-band oscillation when large-scale wind farms are connected to the weak power grid,which seriously affects the power grid integration and elimination,and threat ens the safe and stable operation of the power grid.Therefore,it is urgent to study the wide-band oscillation mechanism of wind farms connected to the weak power grid and its strategies.In this thesis,the modeling of sequential impedance of SVG and doubly-fed wind turbines and the mechanism of wide-band oscillation and its suppression strategy for parallel operation of doubly-fed wind farms with SVG in weak power network are studied in Gansu province.This thesis analyses the impedance characteristics of SVG and doubly-fed wind turbines in a wide-band range,solves the key technical problem of wide-band oscillation mechanism analysis of doubly-fed wind farms with SVG in a weak power network,and puts forward a wide-band oscillation suppression strategy for wind farms with impedance remodeling from the SVG side in a weak power network,which is of great significance to improve the parallel absorption of doubly-fed wind farms in a weak power network and improve the safe and stable operation of the power system.The main research content includes:1)Considering the influence of phase-locked loop,current loop and voltage outer loop of SVG,a positive sequence wide-band oscillation impedance model of SVG and DFW wind turbines under different operation modes is established.The validity of the established sequence impedance model is verified by frequency scanning method.The impedance model established is the foundation for further analysis of the wide-band oscillation mechanism of incorporating SVG doubly-fed wind farms into the weak power grid.2)Based on the established impedance model,the effects of phase-locked loop,current loop and AC voltage outer ring on the impedance characteristics of SVG are analyzed.The effects of slip ratio,phase-locked loop and current-measured inner ring on the impedance characteristics of doubly-fed wind turbines are analyzed.A network aggregated positive sequence impedance modeling and stability analysis method for large scale wind farms connected to the grid is presented,and the feasibility of this method is verified by an application example of a double-fed wind farm with SVG in Gansu Province.The mechanism of wide-band oscillation easily occurring when large-scale wind farms are merged into weak p ower networks is also explained:weakening of power grid and operation mode of SVG will cause insufficient phase margin at the intersection of the aggregated output impedance of wind farm and the amplitude of power grid impedance,which will lead to poor s tability of wind farm,and then cause wide-band oscillation.The simulation verifies the correctness of the theoretical analysis.3)An impedance remodeling strategy based on SVG end is proposed,which remodels the impedance of SVG by adding a vir tual impedance controller to the S VG end.SVG after impedance remodeling can meet the requirements of SVG-network impedance amplitude/phase margin under different grid SCRs and can operate stably.When the SVG with remodeled impedance is connected to the w ind farm,the field-network impedance amplitude/phase margin can meet the requirements of stable operation,and can suppress the wide-band oscillation of the wind farm with double-feed SVG in weak power grid.The experimental results verify the effectiveness of the proposed wide-band oscillation suppression strategy based on SVG end impedance reshaping.The simulation results verify the effectivenes s of the proposed wide-band oscillation suppression strategy based on SVG end impedance reshaping. |
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