Harmonic Impedance Modeling of DFIG Considering Dead Time Effect of Rotor Side Converter

This paper proposes a novel harmonic impedance modeling method of doubly fed induction generator (DFIG) considering the dead time effect. The dead time of the rotor side converter (RSC) will induce distorted voltage to the rotor side of DFIG. By obtaining the transfer function from stator voltage and rotor distorted voltage to stator current, the admittance of RSC+DFIG can be deduced. Considering that the harmonic currents caused by the dead time work as a current source, the Norton equivalent circuit of RSC+DFIG can be obtained. In this way, the harmonic currents not only caused by the grid harmonic voltages but also the dead time effect can be both accurately acquired, which is very useful for the harmonic currents analysis for wind farm. Furthermore, the impedance characteristic of RSC+DFIG is also obtained which is useful for harmonic resonance analysis. Finally, the correctness of the equivalent circuit and stator harmonic currents is validated by the simulation results.