This study deals with non-linear interaction problems of DFIG (doubly fed induction generator) based wind farm in a stressed power system. The study is performed on an IEEE modified test system using the non-linear analysis based on the modal series (MS) method. As the installed capacity of renewable energy, especially the wind-energy increases, the wind farm connection to the grid should be studied from different viewpoints. The dynamic performance of this composite power system is an important issue and should be investigated carefully especially in stressed conditions and different operating points of system controllers. The non-linear interactions will complicate the dynamic behaviour of power systems. If such interaction exists between wind farm and other system controllers and is quantitatively significant, the stability of wind plant is jeopardised. To verify the analytical results of MS method, the necessary comparisons have been made with the results of the non-linear simulation and approximate linear methods

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