A fully superconducting air-core machine for aircraft propulsion

Partial and fully superconducting (SC) machines promise high power density capabilities required for electric propulsion. These machines need to achieve high power densities while reducing electrical heat losses to minimize the required cryogenic power and subsequent additional weight. Hydrogen powered all-electric planes provide a design space where ac losses are manageable. However, the high electrical frequencies in high-speed fully superconducting machines pose a significant challenge to reducing armature ac losses. In high-speed applications, coupling loss in the SC armature coils dominates and becomes a barrier for practical application of these machines. In this paper a fully superconducting machine is proposed for a hydrogen powered regional all-electric plane. An air core design is considered utilizing low ac loss MgB2 wires. The design is targeted to achieve 50 kW/kg specific power while requiring ac losses to be less than 3 kW. This study explores the possibility of replacing a passive iron shield with active shielding coils to contain the magnetic flux inside the machine while reducing weight and increasing power density. The study focuses on minimizing weight as well as ac losses in the armature coils. An optimization algorithm is used to determine the trade-offs between iron shield and active shield coil designs. Results show that optimal designs for electric propulsion eliminate the passive shield in favor of active shielding coils - increasing the power density of the machine while maintaining the outside flux density below standard safety limits.