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Against the backdrops that the large-scale DFIG-based wind generations are accessed to grid and requested to maintain grid-connected operation during faults, the short-circuit current contributed by the generation has become an unavoidable problem. However, the traditional calculation methods aimed at synchronous generator cannot apply to the grid contained the increasing DFIG-based wind generations. A new calculation method is urgently needed to solve the short-circuit current required by the planning, protection and control of the power grid. In the present paper, the transitions of DFIG under symmetrical and asymmetric short-circuit condition are mathematically deduced and the short-circuit characteristics of DFIG are analyzed. A controlled source is proposed to model DFIG during grid faults based on the derived expressions. Meanwhile, the equivalent circuit and the sequence networks of a single-machine infinite bus system is built to calculate the steady-state short-circuit current. The time-domain simulations are conducted to verify the accuracy of the proposed method.