Analysis of Vibration Characteristics Considering the Modulation Effect According to Rotor Bars of Induction Motor for EVs

The predominant method for mitigating vibrations in electric vehicle (EV) propulsion motors involves utilizing electromagnetic strategies to reduce air-gap electromagnetic force (AEMF) orders. This study investigates the origins of AEMFs that significantly induce vibrations in induction motor (IM) models with 6-poles and 54-slots. Initially, it is revealed through spatial harmonic analysis of winding distribution factors that harmonics of same magnitude to the fundamental component play a crucial role in the harmonics of the armature reaction (critical order). Subsequently, it analytically examines and compares the sources of vibration orders of AEMFs. The conditions for determining the rotor slot number are provided to avoid vibration orders that induce significant vibrations. To prove this, this paper utilizes 2D-FEA to calculate AEMFs at rated operating point for both the 44-bar and 70-bar models, confirming the substantial contribution of the critical order of MMF to lower vibration orders in the 44-bar model. Conversely, the 70-bar model exhibits significantly reduced forces due to the absence of correlation between lower vibration orders and the critical order of MMF. After that, considering the modulation effect of high vibration orders caused by rotor slots and slip effects, the forces are calculated by vector summation with lower vibration orders for all operating speeds. This comparison confirms that the 44-bar model generates larger AEMFs compared to the 70-bar model. Finally, through coupling analysis, it demonstrates that the 70-bar model is advantageous in terms of vibration compared to the 44-bar model.