In this paper, a nonlinear control method is proposed to improve the primary frequency control for doubly fed induction generator (DFIG) wind turbine system. Individual wind turbines in wind power plant are controlled in deloaded operation to provide the frequency support during depressed frequency conditions. By considering of nonlinearity of the system, input-output linearization method is applied to improve the performance of primary frequency response. It can be guaranteed that the system is exponentially stable with the proposed method. The proposed method is validated by using a simple microgrid, consisting of one wind power plant, one diesel generator, and a load, through MATLAB/Simulink. The simulation results show that the proposed method has an improvement of primary frequency control when the load increases.