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As energy crisis and the increasingly serious environmental pollution, the development and utilization of new energy become a hot spot. Wind power, which was clean and has a rich reserves, got the attention of the world. Especially in recent years, wind power development is very quickly. Doubly-fed induction generator (DFIG) is a wind-power generator, which using variable speed constant frequency (VSCF) technology. It can achieve maximum wind capture, and it has small capacity converter, so it is excellent at economic characteristics, it was using very extensive now. But because of the small capacity converter, doubly-fed wind power system is very sensitive to grid failure. This paper does a research on the low voltage ride through (LVRT) of doubly-fed wind power systems, the main contents is as follows:Firstly, this paper established the mathematical models in synchronous reference frame of the grid side converter and wound rotor asynchronous motor respectively. On the basis of detailed models, we get the vector control strategy of the grid side converter based on grid voltage oriented and the vector control strategy of doubly-fed generator based on the rotor stator flux vector.Secondly, we did analysis of transient flux and rotor voltage from the rotor open model firstly, then, basing on the establishing of the transient model which considering rotor current, we get a conclusion that the transient flux of stator side is the reason of the over-current on rotor side. And the influence of some factors was analyzed.Then, based on the conclusion of the transient analysis, a new excitation control strategy was adopted in this paper. To guarantee the safety of the rotor side converter, the control strategy accelerate the attenuate of the transient stator flux through the control of the rotor current, it can expand the operating range of doubly-fed generator during the grid voltage drop. At last, simulation shows the effectiveness of the proposed scheme.
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