Analysis and optimization of permanent magnet and dc-excited ironless superconducting synchronous machines for electric aircraft

Abstract

Superconducting motors have high power densities and thus have a high potential to be used for the propulsion of large electric aircraft. However, superconductors also dissipate ac loss when they are subject to a time-varying magnetic field or when they are carrying ac current. Refining an analytical machine evaluation model in the literature, this paper provides a fast analytical model that incorporates new ac loss formulae to model machines with a superconducting MgB2 armature, and rotor excitation via either permanent magnets (PMs) or superconducting coils. Machines with and without an iron yoke are modeled. In addition, the machine models are used in multiobjective optimization to explore the trade-off between minimizing the active mass and minimizing the armature ac loss, using the optimization package 'pymoo' in Python. The machines are rated at 3 MW, 4,500 rpm, based on NASA's N3-X concept aircraft. Results suggest that the lighter, yokeless machines do not have much higher armature ac loss than the machines with yoke (difference less than 0.1% of machine power), which may be contrary to expectation.