This conference paper was submitted for presentation at the NAFEMS World Congress 2025, held in Salzburg, Austria from May 19–22, 2025.

Abstract

Rotor notching is an established machine-design procedure for mitigating electrical machine noise and vibrations. The air-gap forces are shaped by introducing rotor notches to reduce specific temporal harmonics that excite the machine structure and create mechanical vibration orders. This method has the same effects as the skewing technique. Additionally, the rotor notches can reduce permanent-magnet synchronous machine (PMSM) torque ripple by acting on the tangential air-gap force harmonics responsible for the torque fluctuations. This paper focuses on the radial-flux PMSM for the electrical machine type due to its overwhelming market share in traction and auxiliary systems vehicle applications. The traditional simulation methodology for rotor notching involves a 2-dimensional (2D) finite element (FE) electromagnetic analysis of the machine cross-section to extract the air-gap forces for a specific notch configuration for a few operation conditions, usually the maximum torque operation across the whole speed range. Afterward, the vibroacoustic response is computed. Two main methods are usually employed in the industry. In the first method, an analytical vibroacoustic model (usually of the stator only) is used to compute the response. This represents a trade-off between speed and accuracy, with a penalty applied to the accuracy metric because complex housing, local flexibility, and anisotropic material properties cannot be considered. The second method involves a mesh-mapping operation from the 2D (or 2.5D if skewing is present) electromagnetic mesh to a 3D FE vibroacoustic model of the machine assembly and computation of 3D frequency-domain vibroacoustic responses. This method is accurate (if attention is paid to the conservation of energy and force spectra during the mesh-mapping procedure) but is more time- and data-intensive. In this paper, the air gap forces coming from Simcenter e-Machine Design are computed and tabulated under the Maximum Torque per Ampere (MTPA) operation conditions. The electromagnetic-vibro-acoustic coupling method employs the fast and accurate 3D vibroacoustic reduced-order modeling (ROM) technique in Simcenter 3D using the vibration-synthesis approach. In this way, the vibroacoustic response across the full machine torque and speed range can be determined quickly. This method retains the computational speed advantages of the analytical solution, along with the accuracy of the mesh-mapping approach. Finally, a design of experiments (DOE) using Simcenter HEEDS is conducted for different notch configurations. Different noise maps (vibroacoustic mechanical order responses for the whole operation range) are used to identify key regions of improvement and degradation in terms of NVH using specific KPIs and results are discussed.