Analysis and Improvement of Torque Characteristics in Dual-Airgap Permanent Magnet Motor for Aircraft Propulsion

In this article, the torque characteristics of a dual-airgap yokeless-stator permanent magnet synchronous motor (PMSM) for aircraft propulsion are analyzed and improved. The motor topology and mechanical structure are first introduced, and both the dual-airgap PMSM (DM) and a conventional outer-rotor PMSM (OM) are optimized. Through theoretical analysis and finite-element analysis (FEA), the flux density distributions and torque characteristics of the DM and OM are comparatively investigated considering dual-airgap electromagnetic effects. The results indicate that the DM achieves higher torque density than the OM; however, its torque ripple may increase due to its specialized topology and mechanical structure. To mitigate torque ripple in dual-airgap PMSMs, two approaches are proposed and analyzed. First, the dual-rotor phase displacement method effectively suppresses torque ripple by properly adjusting the phase displacement angle. Second, an alternative stator mechanical structure employing stator holders at the slot openings is introduced, which provides higher output torque and lower torque ripple, albeit at the expense of increased eddy current losses in the stator holders. Finally, a prototype dual-airgap yokeless-stator PMSM is fabricated and experimentally tested. The measured results show good agreement with the simulation results, thereby validating the analysis and the proposed methodology.