A new method for calculating the rotor transient current is proposed，which deals with the electromagnetic transient progress of generators following a grid fault as the superposition of different states，and considers the stator voltage fault component，the rotor voltage fault component，and the transient impact of putting into a Crowbar.The relationship function of the rotor voltage peak value and Crowbar resistance is derived，so the appropriate Crowbar resistance can be set using the mapping method.Account for the control of generators during the grid fault after removing the Crowbar，a low voltage ride-through（LVRT）scheme is given，in which the active and reactive references adaptively adjusted according to the voltage sag depth.As a result，the doubly-fed wind turbine generator can give certain amount of reactive power support during the voltage sag.Finally，simulations of a 1.5 MW doubly-fed wind turbine generator case were carried out and the results show that the new method is correct and effective.