Research On Low Voltage Ride-Through Of Doubly-Fed Wind Power Generators Of Wind Farm In Inner Mongolia

At present,the problem of energy consumption has become the major problem in the development of the global economy,and the lack of energy is particularly prominent.Renewable energy will play a more important role in the future and the application prospect of the wind power technology is the most promising.With the installed capacity of wind turbines increasing,the influence of wind turbines on the local power grid is becoming more and more obvious when faults happen especially when the power grid voltage collapse happens.Therefore,the research on the maintenance of the grid connected operation of the wind turbines has received more and more attention.This thesis summarizes the development of the wind power industry at home and abroad and analyzes the recent situation of wind power generation in Inner Mongolia.And the research on the low voltage ride through(LVRT)of the doubly fed induction generators(DFIG)which occupy larger installed capacity is done.The thesis summarizes the research status of the control method of the LVRT.Based on the magnetic and circuit structure of the DFIG,the mathematical model of the DFIG in three-phase static coordinate system and two-phase rotating coordinate system is established.The typical Crowbar protection circuit of the rotor side is studied,and the value of the resistance and the switching strategy of the Crowbar protection circuit are introduced.An offline accident of the DFIG in the M wind farm which is located in the W city,Inner Mongolia region,happened in 2013.Through the study on wind farm using the passive crowbar circuit,combining with the fault recorded wave,fault process and the actual situation of the M wind farm,the thesis summarizes the possible reasons for the occurrence of the accident.Aiming at the existing problems of the passive crowbar protection circuit used in the DFIG,a novel active Crowbar protection circuit in which the resistance is in series with inductance is proposed and the appropriate switching control method for the Crowbar circuit is designed.Due to the low voltage ride through(LVRT)test has certain risks and the field experiment is difficult to achieve,the simulation which is based on the electrical system construction and the equipment parameters of the M wind farm is done in this thesis.The simulation results show that the novel Crowbar protection circuit in the DFIG can well achieve the LVRT,which has a certain engineering guidance and provides reference for the improvement of the Crowbar circuit of the M wind farm in the future.