Effect of Rotor Eccentricity on the Vibration and Noise of External-Rotor SPM Machine

The electromagnetic vibration and noise of external-rotor (ER) surface-mounted permanent magnet (SPM) machines are significantly affected by rotor eccentricity (RE). The RE is often inevitable due to the single-sided support structure, manufacturing tolerances, and fluctuating operational load. However, its impact on vibration and noise remains unclear, owing to complex interactions among the magnetomotive force (MMF), permeance variations, modulation effect in SPMs, and the harmonics of the structural modal shapes. To address this challenge, this paper proposed an analytical model (AM) based on circular convolution in the spatial domain. The proposed AM reveals a spectral multiplication property in the frequency domain, which can be utilized to identify the dominant harmonics in airgap permeance that contribute to electromagnetic vibration under RE conditions. A 24-slot 22-pole ER-SPM machine is employed as a case study to validate the proposed AM. The effects of both static and dynamic eccentricity on the vibration are discussed and clarified by applying the spectral multiplication property. The results indicate that the harmonic orders of electromagnetic vibration predicted by the AM are consistent with those obtained from both simulation and experiments.