Multi-physics evaluation of radial- and axial-flux YASA high-torque-density PMSMs for aircraft electric propulsion considering size constraint effects

This paper presents a comparative study of radial- and axial-flux Yokeless and Segmented Armature (YASA) Permanent Magnet Synchronous Motors (PMSMs) from a multi-physics perspective, addressing the requirements for high torque density and compact design in aircraft electric propulsion systems. First, the configurations and requirements of aircraft electric propulsion systems and propulsion radial- and axial-flux YASA PMSMs are introduced. Then, to ensure a fair comparison, radial- and axial-flux YASA PMSMs are optimized respectively under different size constraints, with conventional radial-flux outer-rotor PMSMs included as a comparison benchmark. The electromagnetic characteristics of the optimized topologies are compared for high mass torque density, volume torque density and efficiency. Furthermore, given the extreme weight sensitivity and limited installation space in propulsion systems, as well as the greater mechanical challenges of YASA PMSMs, the structural layouts of radial- and axial-flux YASA PMSMs are presented and examined. The impact of structural components on motor mass, volume, and output capability is quantified across varying motor sizes. In addition, considering the high loss density and escalating cooling requirements of propulsion PMSMs, temperature rise characteristics of PMSMs with a specific end-embedded heat pipe cooling method are investigated, and the maximum output capacity of motor under thermal limitations is evaluated. Finally, a radial-flux dual-rotor YASA PMSM is developed and tested, which confirms the validity of analysis.