| As a result of dual constraints of fossil energy depletion and environmentalprotection, wind power industry has a rapid development all over the world. With theaccess to grid of wind generation power centralized and on a large, the core controltechnology of doubly-fed induction generator (DFIG) which is one of the mainstreammodels of variable speed constant frequency wind power generation system, becomes theessential issue. Because of the structure difference of DFIG and traditional synchronousand asynchronous motors and its transient characteristics and fault mechanism has notbeen revealed thoroughly, it makes relay protection setting difficult, the safety ofelectrical equipment vulnerable and the stable operation of power grid out of safety.Based on DFIG wind power generation system, the in-depth study of controlstrategy in grid-side converter and machine side converter is conducted in this thesis.Firstly, stable operational model of DFIG is built on the RTDS simulation platform. Areasonable filter and control parameters is designed to satisfy the requirements of itsaccess to the grid a. Secondly, based on the space vector model of DFIG based derivationof symmetrical fault, the stator and rotor flux and current analytical expression undersymmetrical three-phase fault is derived. Analysis of the transient current mechanism ofaction is conducted and the correctness of the analytical results is verified by simulation.Finally, for the Low Voltage Ride-through (LVRT) of DFIG under symmetricalthree-phase fault, a rotor Crowbar adaptive control method which based on voltage dipdegree is proposed. The simulation results on the RTDS platform confirmed theeffectiveness of the proposed control strategies. |
