Impact of Torque Ripple Induced Angular Oscillations on Maxwell Pressure Harmonics in Permanent-Magnet Synchronous Machines

Abstract

Torque ripple in electrical machines is a wellknown source of noise and vibration. While numerous studies focus on control strategies to mitigate this ripple, the feedback mechanism by which the resulting mechanical oscillations influence the electromagnetic forces remains less explored. This paper presents a detailed investigation into the impact of torque ripple on the rotor angular dynamics and the subsequent generation of new harmonics in the Maxwell pressure distribution. We first develop an analytical model for a rigid rotor subjected to a single torque harmonic, revealing the inherently non-linear nature of the angular response. This analysis demonstrates the creation of new harmonics in the rotor motion and a slight reduction in the mean rotational speed. The study is then extended to a flexible rotor model incorporating torsional modes, solved using the Finite Element Method. Finally, we introduce a strongly coupled magneto-mechanical model, based on the subdomain method, to quantify how these rotor oscillations modulate the air-gap magnetic field. The results show a new modulated spatio-temporal harmonic distribution in the Maxwell pressure spectrum, which is not predicted by conventional uncoupled models. These findings are crucial for high-fidelity Noise, Vibration, and Harshness (NVH) analysis, as these additional pressure waves can excite stator structural modes.