To ensure the proper operation of power system, some independent system operators have specified that wind power plants should be able to participate in frequency control. This paper presents a combined control scheme exploiting the self-capability of PMSG based wind turbine to provide primary frequency response. In this scheme, the wind turbine operates in de-loading mode to obtain the power reserve under normal condition.On detecting frequency deviation, the proposed control strategy can not only utilize the power reserve and the kinetic energy of rotor for frequency regulation by adjusting the rotor speed, but employ the energy stored in DC capacitor to provide additional frequency support by slightly changing the DC-link voltage as well. The simulation results reveal that the wind turbines with the proposed method can improve frequency performance under both constant wind speed condition and variable wind speed condition.