双馈感应发电机(DFIG)的暂态过程是研究其低电压穿越(LVRT)的基础和关键.常规研究大多只针对故障发生期间的电磁暂态过程,而未涉及故障清除这一过程,对DFIG的暂态过程分析不全面,导致对转子最大短路电流计算不准确,进而导致Crowbar阻值选取不合理.本文从DFIG数学模型出发,给出了电网电压对称跌落及电网电压恢复时的定子磁链暂态表达式,以转子侧等效电路为基础分析推导转子电流的解析表达式,并据此修正了Crowbar阻值.在PSCAD/EMTDC中建立1.5MW并网DFIG仿真模型,验证了理论分析推导的正确性;并揭示不同故障持续时间将导致电网电压恢复时DFIG不同的暂态过程,忽略故障清除时刻的暂态过程将导致Crowbar阻值选取过大,Crowbar阻值选取需同时考虑故障发生和清除时刻的暂态过程.%Transient characteristics analysis is the foundation and the key for low voltage ride through (LVRT) of doubly fed induction generator (DFIG). Conventional studies usually focus on the transient processes during gird faults and ignore the transient process of fault clearing. Thus, the transient process analyses are incomplete. It will result in the inaccurate calculation of the maximum rotor short-circuit current, further leading to Crowbar resistance selection unreasonable. In this paper, the expressions of the stator flux during the grid fault and fault clearing were proposed based on the mathematical model of DFIG. Then the expression of the rotor current was derived from the view point of the rotor equivalent circuit. Accordingly, the Crowbar resistance was amended. The results of simulations on a 1.5MW DFIG in PSCAD/EMTDC verify the correctness of the derivation. What's more, different fault durations will lead to the different transient processes during fault clearing, where ignoring the process of fault clearing will lead to the excessive crowbar resistance. The resistance optimization of Crowbar needs to consider the processes of grid fault and fault clearing.
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