Control Strategy Reseach Of Wind Power System With Doubly Fed Induction Generator In Symmetrical Grid Fault

With the development of wind power technology, doubly-fed induction generator hasbecome popular in wind power generation around the world. Based on different gridvoltage dip, two strategies are proposed separately aiming at solving low voltageride-through problems for DFIG wind power system in this paper. By controlling rotorside voltage value with the designed controller, the rotor side current can be adjusted totrack the expectation of current value, so that the whole wind power system can operatesteadily. Specific research contents are as follows:Firstly transient electromagnetic dynamics is analysed. Generally traditional controlstrategies are based on the premise of ideal grid condition without involving the impact ofgrid fault on DFIG system. So the transient dynamics of stator flux for DFIG wind powersystem is given in this paper, based on which the mathematic model of DFIG under gridvoltage dip is also proposed, laying groundwork for research to be continued.Secondly small symmetric voltage dip for DFIG ride through is mainly discussed inthis paper. Control strategy without adopting hardware device is preferred aiming at smalldepth of voltage drop. In consideration of parameter uncertainty and external interference,a robust controller is designed to track the expected rotor side current value and at thesame time suppress interference, guaranteeing low voltage ride through operation forDFIG. At last, effectiveness of the designed robust controller is validated with simulationresults.Finally large symmetric voltage dip for DFIG ride through is mainly studied in thispaper. The above control strategy is no use for severe grid voltage drop due to capabilityof the converter. So hardware device becomes an necessity in order to restrain the faultcurrent. Considering nonlinearity of DFIG and uncertainty of parameters, an adaptivecontroller is designed, which ensures rotor current can track the desired current value, sothat DFIG can operate steadily disconnecting from the grid. At last, a simulationexperiment is conducted to test effectiveness of the controller, which indicates that thedesigned adaptive controller meets all the requirements.