中文摘要：

在电网发生严重故障情况下,双馈风电机组多采用Crowbar保护电路以实现低电压穿越（LVRT）,而Crowbar阻值和退出时间对LVRT效果有很大影响。文中从磁链角度推导给出了双馈感应发电机（DFIG）在并网运行情况下发生机端三相短路故障后的转子短路电流表达式及最大短路电流估算式,并给出了Crowbar阻值的整定方法。为了验证推导所得转子电流表达式的正确性,并分析Crowbar阻值与最大短路电流及其出现时间之间的关系和Crowbar阻值及退出时间对DFIG的LVRT效果的影响,针对1.5MWDFIG进行了一系列仿真分析,结果表明：推导所得转子短路电流表达式及最大短路电流估算式比较准确;随着Crowbar阻值的增大,最大转子电流逐渐减小,其出现时间在半同步周期内逐渐提前,但转子侧最大电压逐渐升高;在保证网侧变流器不过压的情况下,若Crowbar阻值在合理范围内偏大且Crowbar在故障切除前退出运行,则DFIG的LVRT效果更好。

英文摘要：

In the case of serious faults with the grid,the Crowbar protection circuit is frequently adopted to implement low voltage ride through（LVRT）of the grid-connected wind turbine driven doubly fed induction generator（DFIG）.The LVRT effect is greatly influenced by the resistance and quitting time of Crowbar.From the viewpoint of magnetic linkage in the case of a three-phase short-circuit fault occurring at the terminal of DFIG,the analytical expression of the short-circuit rotor current is deduced together with the estimated expression.The method for Crowbar resistance setting is proposed.To validate the rotor current expressions deduced,analyze the impact of Crowbar resistance on maximum short-circuit rotor current and its appearing time,and find the influence of resistance and quitting time of Crowbar on the LVRT effect,a series of simulations are conducted on a 1.5 MW DFIG.Simulation results show that：the analytical expression and the estimated expression presented in this paper can depict the rotor current correctly;with an increase of Crowbar resistance,the maximum short-circuit rotor current is gradually decreased and the appearing time is gradually advanced from the half grid-synchronized cycle to zero,but the maximum rotor voltage is gradually increased.On condition that the grid-side converter be not over-voltage,if the Crowbar resistance is fairly great at the rational level and the Crowbar quits before the fault is eliminated,the LVRT effect would be better.