Influence of Magnetization Nonlinearity and Non-Sinusoidal MMF Spatial Distribution on Harmonic Content of Current and Electromagnetic Torque in Three-Phase Induction Machine

In recent years, improving the energy efficiency of induction machines (IM) has become a key research focus, with particular attention to loss reduction. Losses in IM are significantly influenced by two design-related factors: the nonlinear magnetization characteristic and the non-sinusoidal distribution of the magnetomotive force (MMF) in stator slots. These effects lead to harmonic distortions in stator and rotor currents as well as pulsations of the electromagnetic torque. This paper presents a comprehensive harmonic analysis of the interaction between the nonlinear magnetization curve and the non-sinusoidal MMF distribution in induction machines. A mathematical model in phase coordinates was developed, incorporating both effects through the introduction of harmonic components into the magnetizing inductance. The proposed model enables the evaluation of the impact of these phenomena on stator and rotor currents, as well as on the electromagnetic torque. The validity of the model is verified by experimental results, which show close agreement with simulations. The analysis demonstrates that the nonlinearity of the magnetization curve results in the appearance of the third harmonic in stator currents and the second harmonic in torque, while the non-sinusoidal MMF distribution produces the fifth and seventh harmonics in stator currents and the sixth harmonic in torque. Additionally, the study reveals that in no-load conditions, the third harmonics are dominant, whereas with increasing load, their magnitudes decrease, and the amplitudes of the fifth and seventh harmonics increase due to the interaction between stator and rotor currents. The proposed modeling approach provides an effective tool for accurate performance evaluation and design optimization of induction motor drives.