Research On Low Voltage Ride Through Of DFIG For Wind Power Generation

Comparing with the conventional power plant capacity,when the installed wind capacity can not be ignored.If all the wind generation systems be disconnected from the grid on the condition of grid failure, and failure to provide support of frequency and voltage that like conventional energy for grid, it will affect the power system's safe operation adversely. Thus, with the continued expansion of wind power installed capacity, low voltage ride through (LVRT) has become a necessary requirement for wind farms.In this paper, with the support of "The National Eleventh Five-Year Research Programme of China" (2006BAA01A18,2006BAA01A20), when the gird dip happened,the dynamic process of DFIG was analyzed and how to achieve LVRT was investigated. This paper studies include:1)Through rigorous theoretical analysis, derived the values of the stator flux and rotor voltage of DFIG under all kind of grid failure, providing a theoretical basis for LVRT protection strategy.2)Analyze the dynamic process of the excitation system of the DFIG-back to back power converter, deduced the maximum fluctuant value of the DC side voltage under the grid failure.3)Analyze the transient process of DFIG when the grid recovery after three-phase fault occurs on the grid,derived the value of stator flux and rotor voltage at different grid voltage recovery time.4)Summarized the various existing LVRT control strategy of DFIG, analyse the active crowbar detailedly, proposed design rules for the crowbar resistance based on theoretical analysis of Chapterâ…¢.5) For the active crowbar's shortcomings, investigate a improved method based on the active crowbar-active crowbar associate with series resistance for rotor method.6)Establishing a LVRT for DFIG test platform,the active crowbar stratege LVRT strategy is preliminary experimented.