Modeling, Analysis and Validation of Controller Signal Interharmonic Effects in DFIG Drives

This paper presents the development of a doubly fed induction machine (DFIG) harmonic model in MATLAB/Simulink, which is used to examine the spectral content of DFIG controller signals and improve the understanding of their behavior and spectral nature. The reported DFIG harmonic model has the capability of representing the effects of higher order time and space harmonics and thus, allows detailed analysis of the controller signals embedded spectral effects. The model consists of a wound rotor induction machine (WRIM) harmonic model coupled with a stator flux oriented controller (SFOC) model. The WRIM space harmonic effects are represented using the conductor distribution function approach to enable the calculation of winding inductances as harmonic series. In addition, analytical expressions are derived to define the possible spectral content in the controller signals of DFIGs. Both the reported DFIG harmonic model and the analytical equations are validated by comparison with measurements taken from a purpose built vector controlled DFIG laboratory test rig. The findings confirm the capability of the developed DFIG harmonic model in representing the controller signals embedded spectral effects, as well as the accuracy of the reported analytical expressions, and enable a much improved understanding of the spectral nature of the DFIG controller signals.