The Research Of Doubly Fed Induction Wind Generator System

Wind power is one of the most promising energy among all kinds of renewable energy.The world has witnessed a huge increase of installed capacity of wind power year by year.Doubly Fed Induction Generator(DFIG)system has become a hot spot among wind power research due to its friendly response to grid and relatively high efficiency of power transformation.This dissertation first analyzes the model of wind turbine,and establishes mathematical models of DFIG in stationary coordinate system and two-phase synchronous coordinate system.Then the constant power grid voltage oriented vector control strategy containing dual loop of RSC and vector control strategy in stand-alone mode are carried out in Matlab/Simulink environment.In case that the loads are unbalanced,a control strategy of rotor side converter with PIR controller is designed to minimize the twice order components in stator voltage and to reduce the asymmetry factor of stator voltage.In order to improve the low voltage ride through(LVRT)ability of the system,the DFIG system implemented with Crowbar device is investigated in this dissertation.First,the analytical expression of shortcut current and voltage are calculated and tested,then the simulation model of DFIG implemented with Crowbar during three phases symmetrical voltage dip is established.The ripples of active power,reactive power and electro-magnetic torque and maximum current are measured and applied to evaluate the transient character of the system.The influences of grid voltage dip extent and Crowbar resistance on the transient response are discussed.Lastly,the resistance of Crowbar is optimized.Furthermore,this dissertation tested the impedance model of DFIG system.The impacts of key characters such as parameters of PLL,parameters of current regulator,rotor speed and power setting on the output impedance are investigated.The stability of DFIG inductive-grid system when different control parameters applied is tested and the stable areas of proportional coefficient of current loop are calculated.Finally,this dissertation designs a micro 100W DFIG system,and provides the theme of hardware and flowchart of the software in detail.Experiments such as constant voltage output in standalone mode,loaded-grid connection and constant power regulation in grid-connected mode are designed and tested.The experiment results verified the proposed control strategy of DFIG.