Research On Dynamic Behavior Of Doubly Fed Induction Generator During Low Voltage Ride-Though

With the rapid development of wind energy and the high market share of doubly fed induction generator(DFIG), the low voltage ride through ability(LVRT)of the DFIG is getting more and more attention. At present, there are a lot of researches on the dynamic behavior of DFIG under gird fault,but its physical properties are still not clear. Under this background, the paper makes a thorough study on the dynamic behavior and the transient characteristics of DFIG under low voltage ride through. In order to clarify the electromagnetic characteristics of DFIG under voltage dips and the impact of the power grid fault on the mechanical performance of the motor, a combined simulation platform was built. The mutual influence of stator flux and rotor flux linkage and the change of the electric quantity in the generator under four kinds of classical voltage sag are all analyzed.Firstly, based on the mathematical model of the steady-state operation of the DFIG, the change of the external current voltage, internal flux and mechanical properties of the DFIG in three-phase symmetrical fault, single-phase-to-ground,phase-to-phase fault,and two-phase-to-ground fault are deduced, and the motion trajectory of stator flux linkage is simulated.Secondly, according to the actual data of a DFIG wind farm, a 1.5MW DFIG is built and its initial angle is debugged, the simulation waveform data of the model in no-load and load is proved that this model is reasonable; Comparing the different types of voltage sag generator(VSG) and selecting an appropriate one, and the circuit parameters are computed, the circuit model including the grid, transformers,back-to-back converter, DC link, voltage sag generator, grid side converter with LCL filter, and the rotor side converter du/dt filter is built in Simplorer. On the basis of the principle of stator voltage oriented vector control strategy, back-to-back converter controller is built in MATLAB Simulink,and the data exchange between Matlab and Simplorer is realized by S-Function module.Finally, the three softwares is coupled with each other through the external interface of the Simplorer interface, and the data is exchanged between the three models. So the joint simulation system is built. The different faults which are set up by the VSG are run,and the results of the combined simulation are presented. The waveforms of the typical faults are analyzed in detail, and the results are in complete agreement with the theoretical analysis.