Diversity of Stator Teeth Modulation Effect on Radial Pressure in PM Machines

Recent literature has confirmed that a high-order radial pressure in airgap can induce significant low-order vibration due to the stator teeth modulation effect on radial pressure. The reported research on this modulation effect only focused on the conventional stator teeth topologies. However, for the permanent magnet (PM) machines, different stator teeth topologies lead to diverse paths for the transfer of pressure in airgap, resulting in varying vibration characteristics caused by the modulated radial pressures. It is plausible that dual or nonuniform modulation on radial pressure may be present. Therefore, to accurately predict and preferably reduce vibration, it is crucial to understand the diverse effects of different stator teeth modulation. In this article, first, the principle behind how the stator teeth modulate the radial pressure is explained. Second, the modulation effects of different stator teeth are detailedly analyzed, including single, dual, uniform, and nonuniform modulations. Lastly, taking a PM vernier machine as an example, its modulated radial pressures and resulting vibration are analyzed considering the nonuniform dual modulation. Results demonstrate that the stator teeth modulation effects on radial pressure are various and should be fully considered in accurate vibration prediction and low-vibration machine design.