Study On Transient Equivalent Model Of Doubly Fed Induction Generator Wind Farm Under Deep Voltage Drop Failure

With the penetration rate of wind power in power grids continuously increases,large-scale wind turbines have already affected the safety and the flexible operation of power systems,while the research on transient models of wind farms has received more and more attention.As the main model of wind farm,doubly fed Induction Generator(DFIG)has the characteristics of nonlinear,multivariable and high coupling.Influenced by the Crowbar resistance,the transient output current of the doubly fed wind turbine during the deep voltage drop fault contains a variety of attenuation sequence components,which complicates the transient modeling of large wind farms.Based on the coherence of unit failure performance in wind farms,this paper extracts the transient characteristics of the reaction unit and uses the unit aggregation method to perform transient equivalents on the wind farm.The mathematical model of each part of the double-fed wind power generator is studied.Taking the deep voltage drop fault as an example,the expression of the output fault current of the stator port of the DFIG is analyzed,and the resistance value of the Crowbar resistor during the fault is analyzed.Through the theoretical analysis and simulation,the feasibility of replacing the fault output current of the unit with the stator port fault current is verified.From the perspective of mechatronics,the influencing factors of the transient voltage variation of the DFIG stator port are analyzed.In the paper,the rotor speed trajectory is extracted as the coherence analysis index of the DFIG,the measurement method of rotor speed trajectory is studied,and the advantages and disadvantages of Dynamic Time Warping(DTW)in trajectory measurement are analyzed.From the perspective of morphological features of the trajectory,the role of time series derivatives in shape description is considered.The profile factor is added to the DTW algorithm to optimize the path matching,and the hierarchical agglomerative clustering is introduced to classify the time series samples.In the paper,the equivalent method of unit parameters of wind farm and collector network is studied.The relationship between power and input wind speed is analyzed,and an improved capacity weighting method for input wind speed and control parameter aggregation under different working wind speeds is proposed.Based on the principle of loss invariance,a convection network transformation method suitable for DFIG of arbitrary position aggregation in wind farms is proposed.The power system simulation model with wind farm is built in Matlab/Simulink and the calculation and verification are carried out.The simulation results show the correctness of the wind farm transient modeling method under the deep voltage drop fault in this paper.