Study On The Control Technology Of Doubly Fed Induction Generators Low Voltage Ride Through

As environmental pollution and Energy shortage are growing, renewable greenenergy development and utilization of wind energy has great significance. In recentyears, the development of wind power is very fast. Due to different structures andproperties between wind turbine and the traditional synchronous generators, with theincreasing proportion of wind generator in the grid, wind power system has moreobvious effects to maintain the stable operation of power system. More and morecountries have introduced the operation specifications, and require the wind turbineshould have a certain low voltage ride through capability. Therefore the study of windturbine low voltage ride through capability has important theoretical and practicalsignificance.This paper firstly reviews the current research on LVRT of doubly fed windgenerators at home and abroad, and make a comparison between advantages anddisadvantages. Then the paper establishes a complete dynamic mathematical modelsof DFIGs for all parts.Based on such models, a control strategy using vector control strategy isemployed. This control strategy contains power decoupling control strategy usingstator flux oriented for rotor converter and voltage decoupling control strategy usingstator voltage oriented for grid converter. A simulation system is established usingDIgSILENT platform to verify the validity.For the server fault, the Crowbar circuit has great influence on LVRT especiallythe resistance value and swith strategy. This chapter makes a lot work on theresistance value and swith strategy, and gets some conclusion which could be used asreference by the engineering project.Applying nonlinear control method of input-output feedback linearization, wedesign a LVRT control strategy. This method firstly form a affine input-output nonlinear system, and than transform it to linear controllable system by state feedbacklinearization. Finally, the design of system control strategy can be obtained by linearoptimal control method. Such control strategy is only related to its parameters ofwind turbine, which also improves parameters robustness of system. Simulationanalysises are carried out, and the results show that those control strategy has goodperformance and enhances the LVRT capability of DFIGs.