| With the rapid development of wind power and large-scale centralized access,the frequent occurrence of wind turbine off-grid accidents due to the sudden change of grid voltage and abnormal frequency,which makes the grid face severe stability problems.Therefore,studying the voltage ride-through control and frequency response control strategies of wind turbines has important practical significance for improving the stable operation capability.At the same time,in order to study the problem of safe and stable operation of wind farms after being connected to the grid at the domain level,it is necessary to conduct research on equivalent modeling of wind farms to provide a model basis.Based on the above background,this paper studies the grid-connected stable operation control of the doubly-fed induction generator(DFIG)and the equivalent modeling of wind farm from voltage ride-through control,frequency response control and dynamic equivalent modeling of wind farm.Aiming at the rotor overcurrent problem of DFIG during the sag/swell of the grid voltage,the voltage ride-through control strategy that takes into account the dynamic changes of the stator flux linkage is proposed.Based on the analysis of the changes in the stator flux linkage during the sag/swell of the grid voltage and recovery process,the influence of the dynamic change of the stator flux linkage on the control effect of the rotor-side converter is considered,the power outer loop feed-forward compensation and the current inner loop feed-forward compensation are added to optimize the suppression effect of rotor overcurrent during the sag/swell of the grid voltage.The simulation results show that the proposed control strategy can significantly reduce the impact amplitude of the rotor current.Aiming at the problem that it is difficult for wind turbines to provide inertial support under high-speed-high-frequency and low-speed-low-frequency conditions,the frequency response control strategy based on the coordination of rotor kinetic energy and DC-side capacitor storage energy is proposed.First,the frequency response link of DC capacitor is added to the virtual inertia control of the rotor kinetic energy to establish the coupling relationship between the DC capacitor voltage and the system frequency.Then,the participation coefficients of the rotor kinetic energy and the DC capacitor storage energy are dynamically adjusted according to the rotor speed.The inertia response capability of the DFIG is fully explored,and the inertia support under full wind speed conditions is realized.The simulation results show that the proposed control strategy can effectively improve the inertia support capability of DFIG under full wind speed conditions.Aiming at the uncertainty of the selection of clustering index and clustering number in the process of wind farm equivalence,a DFIG wind farm equivalence method based on principal component analysis is proposed.Three dominant variables are selected as clustering indicators from all state variables by principal component analysis.The adaptive K-means clustering algorithm is used to obtain the optimal clustering value,and the wind farms are clustered according to the dom inant clustering index.The simulation results show that the established equivalent model can more accurately reflect the dynamic response characteristics of the large-scale DFIG wind farm and greatly reduce the simulation calculation time.In summary,the voltage ride-through control strategy considering the change of stator flux linkage,the frequency response control strategy based on the coordination of rotor kinetic energy and DC capacitor storage energy,and the wind farm equivalent method based on principal component analysis are proposed in this paper,which improves the grid-connected stable operation ability of DFIG and the accuracy of wind farm equivalent model. |
