Design of HTS Axial Flux Motor for Aircraft Propulsion

Development of all-electric aircraft would enable more efficient, quieter and environmentally friendly vehicles and would contribute to the global reduction of greenhouse gas emissions. However, conventional electric motors do not achieve a power density high enough to be considered in airborne applications. Bulk high temperature superconducting (HTS) materials, such as YBCO pellets, have the capacity of trapping magnetic flux thus behaving as permanent magnets. Experimental data show that one single domain YBCO pellets could trap up to 17 T at 29 K, which enables the design of very high power density motors that could be used in aircraft propulsion. We designed a superconducting motor based on an axial flux configuration and composed of six YBCO plates magnetized by a superconducting coil wound on the outside of the motor. The six-pole homopolar machine uses a conventional air-gap resistive armature. Axial-flux configuration allows several rotors and stators to be stacked together and therefore enables the use of one or several conventional permanent magnet rotors to generate minimum safety torque in case of loss of superconductivity. All-electric aircraft are expected to be powered by fuel cells or turbo-generators fed with pure hydrogen cryogenically stored that would provide the motor with a convenient cooling system at 20 K. This paper presents the design and simulated performance of the motor for an application in aircraft propulsion.