Evaluation of Torque Ripple and Tooth Forces of a Skewed PMSM by 2D and 3D FE Simulations

TL;DR

The paper addresses torque ripple and tooth-force concerns in skewed PMSMs for automotive NVH by comparing 2D and 3D FE simulations using the Maxwell stress tensor across skewing configurations. It analyzes an 8-pole, 48-slot PMSM with step, V, and continuous skewing, detailing modeling approaches and the computed optimal skew angle from pole-slot relations. The findings show that skewing reduces torque harmonics and radial force disturbances, with 2D FE generally aligning with 3D results for many operation points, though 3D modeling is necessary to capture axial forces at magnet-transition points. The work highlights that while 2D simulations suffice for many torque/Radial analyses, 3D simulations are essential for accurate NVH predictions and bearing-related considerations due to axial force components.

Abstract

In this paper, various skewing configurations for a permanent magnet synchronous machine are evaluated by comparing torque ripple amplitudes and tooth forces. Since high-frequency pure tones emitted by an electrical machine significantly impact a vehicle's noise, vibration, and harshness (NVH) behavior, it is crucial to analyze radial forces. These forces are examined and compared across different skewing configurations and angles using the Maxwell stress tensor in 2D and 3D finite-element (FE) simulations. In addition to conventional investigations in 2D FE simulations, 3D FE simulations are executed. These 3D FE simulations show that axial forces occur at the transition points between the magnetic segments of a linear step skewed rotor.

Figures (10)

• Figure 1: Visualisation of the RFM in 2D FE simulations (left) and 3D FE simulations (right)
• Figure 2: Diagram of different rotor-skewing configurations (a) Step Skewing, (b) V-Skewing, (c) Continuous Skewing
• Figure 3: Torque over mechanical rotor angle for different rotor skewing configurations at load condition (left) and corresponding Fourier transform of the torque (right)
• Figure 4: Ratio between 2D and 3D simulation results for the magnitude of the 48th torque harmonic, shown for all operation points in the motor map
• Figure 5: Calculation of radial and azimuthal force density by one section (left) or by three sections (right)