With the rapid development of wind power industry and the continuous growth of capacity of power electronic devices

the middle-frequency band(MFB)harmonics problem that results from the widespread usage of doubly-fed induction generator(DFIG)based wind turbines has become much outstanding. To precisely reflect the harmonic interactions between DFIGs and a power grid

the equivalent harmonic model that can be used to evaluate the MFB harmonic current of DFIG needs to be developed. Based on the typical vector-controlled DFIG

the mechanism of influence of power grid background harmonics and pulse width modulation(PWM)dead time on the stator-side MFB current of DFIG is studied. A mathematical model that can be used to assess the stator side MFB current of DFIG is also developed with consideration of power grid background harmonics and PWM dead time. The accuracy of the proposed equivalent harmonic model of DFIG is verified by comparative analysis of simulation results

calculation results and field test data of a 3. 0 MW DFIG.