Electromagnetic and Thermal Influence of Aspect Ratio on Flat-Type High Torque Density Dual-Rotor Permanent Magnet Motor for Aircraft Electric Propulsion

To achieve high torque density in direct-drive permanent magnet propulsion motors, flat-type motor topologies with large outer diameters and short stack lengths are generally preferred. However, such flat motor designs may also lead to performance degradation due to the negative impacts of end-winding weight, end-leakage magnetic flux, and temperature rise. This article investigates the influence of aspect ratio (stack length to outer diameter ratio) on both electromagnetic and thermal performances of high torque density dual-rotor permanent magnet synchronous machines (PMSMs) for aircraft electric propulsion. First, the design essentials of the compact high torque density dual-rotor PMSM are described. Then, the influences of aspect ratio on electromagnetic performances are analyzed considering end effects under different torque demands. The motors are optimized through a genetic algorithm based on 2-D and quasi-3-D models, respectively, to either neglect or account for end-leakage flux, elucidating the necessity of considering end effects during the optimization and analysis process. Furthermore, the influences of aspect ratio on loss and temperature distributions in heat pipe cooling systems attached to either active or end windings are comparatively analyzed, indicating that excessively flat topologies lead to higher temperature rise. Finally, by comprehensively considering effects on electromagnetic and thermal performances, an appropriate aspect ratio is selected. A 100-kW flat-type dual-rotor PMSM with end-winding heat pipes is developed and tested to confirm the analysis.