| This thesis deals with the control scheme of doubly-fed induction generator (DFIG) in wind power conversion system, which can make power generation in Variable Speed Constant Frequency (VSCF) mode. Furthermore, the operation mode of DFIG system in low voltage ride through (LVRT) condition is investigated and simulated in detail.The structure characteristic of DFIG system is described by comparing with other kinds of wind generators. The power characteristic of DFIG is analyzed by using the T- type equivalent circuit, which means the stator-side output power of DFIG can be controlled by adjusting the rotor-side slid power. Also the principle of VSCF mode on DFIG is described, and the other parts of DFIG system is introduced briefly.The control scheme of DFIG system is designed based on its mathematical model, which is a kind of rotor current vector control in stator-voltage-oriented frame, and can control active and reactive output power of DFIG independently. Compared to the stator-flux-oriented frame, this control method doesn't need stator-flux measurement. The control system is simulated by Matlab/Simulink for 1.5MW DFIG. The simulation results show the effectiveness of the control scheme during variations of active power and reactive power.LVRT is a new and necessary request to wind turbines, which means the generator should keep connecting to the grid when grid voltage sag happens. There are many problems to DFIG system in LVRT operation, and the general answer to these problems is active crowbar circuit, which can protect rotor-side converter and keep generator connecting to the grid during LVRT. The different types of active crowbar circuit are investigated in this thesis, and the operation effect is simulated based on the control scheme mentioned above.
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