Research On Transient Characteristics And Experiment Based On Double-Fed Induction Wind Generator During Frequency And Voltage Changes

In order to study ride-through characteristics of doubly-fed wind generators at thecase of frequency and voltage faults in the grid, it is necessary to analyze transientcharacteristics of doubly-fed wind generators. The ideal analytical method is to conductfield test, however, field test of wind power system could not to be conducted at any timedue to constrain conditions. Therefore, it is necessary to build wind power test platform inthe laboratory. In view of this situation, the study object is1.5MW double-fed windgenerators. Doubly-fed wind generator experiment platform was established and thefrequency and voltage characteristic of wind generators were analyzed.Firstly, the mathematical models for wind, turbine, pitch system, drive chain anddouble-fed wind generator were established. The working principle of doubly-fed windgenerator was analyzed, double-fed wind generators simulate experiment platform wasbuilt. Wind turbine was simulated by induction motor. Drive system was controlled bySiemens controllers. Test platform has the function of pitch system and safety chain. Thewind speed and wind power were simulated at the experiment platform according to themathematical model. The results of experiment show that wind speed can be simulatedcorrectly via setting man-machine interface and simulating wind parameters at the testplatform. In addition, voltage drop generator was used in the experimental platform tostudy low voltage ride through (LVRT) and high voltage ride through (HVRT),Experimental results when the voltage dips50%were compared and analyzed with themeasured data. The result shows that the experimental platform can be used to analyze thevoltage characteristics of the doubly-fed wind generator well.Secondly, to research the characteristics of doubly-fed wind generators duringfrequency change, mathematical models for doubly-fed wind power generator wereestablished according to the park transformation. The control strategy for the doubly-fedinduction wind power generators was analyzed. Current feed-forward compensation of stator flux linkage oriented vector control was applied to motor side converter to achievethe decoupling control between active power and reactive power. Grid voltage orientedvector control was applied to grid side converter to maintain the DC and currentdecoupling control.Finally, MATLAB software was used to simulate and analyze the outputcharacteristics of wind power generators in the condition of increasing or dropping the gridfrequency. The measured data were contrasted with experimental data, which confirms thefeasibility of the model and the validity of the control method. Against the over-currentphenomenon of double-fed wind generator during the frequency cross-over, a low passfilter of Butter Worth was proposed to prevent rotor over-current caused by frequencychange. Thus the ride-through capability of DFIG in the case of grid frequency changeswas enhanced.