The Influence of Excitation Inrush Current on the Second Harmonic Characteristics of Doubly Fed Induction Generator

ABSTRACT When large scale doubly fed induction generators (DFIGs) are connected to a power grid, the harmonic characteristics of the power grid appear to be considerably different from those of a conventional synchronous motor. Although no load closing of a transformer is a common scenario that causes harmonic currents in the power grid, the harmonic characteristics of DFIGs have not been analysed in detail in such scenarios. Therefore, considering the no load closing of a transformer in the adjacent substation of a wind farm as the research background, this study investigated the harmonic distortion in the voltage at the point of common coupling caused by the inrush current. By quantitatively analysing the transient response of the stator and rotor flux linkage of the wind turbine under the control of the converter, the generation mechanism of the second harmonic current of the DFIG stator is revealed. Then, the generation mechanism of the second harmonic component of the grid side converter (GSC) output current is analysed by constructing the transfer function of the GSC control. Next, considering the influence of voltage distortion on the phase locked loop, the mechanism of the influence of phase locking deviation on the second harmonic current is analysed. Finally, the accuracy of the theoretical analysis is verified through time‐domain simulations.