AC loss modelling in a 2 MW-class REBCO high temperature superconducting motor for hydrogen-electric aircraft

Abstract

High temperature superconducting motors are very promising for hydrogen-electric aircraft thanks to their high specific power, specific torque, and efficiency. High temperature superconductor REBCO offer high cryogenic flexibility, but a stator made of REBCO tapes could present high AC loss. Although stacking effect reduce AC loss, it could be compromised by imperfections, such as winding misalignment and tape inhomogeneity. Therefore, it is needed to know whether the AC loss is acceptable in realistic REBCO stators. This article analyses the AC loss in a REBCO propulsion motor for aviation that takes these imperfections into account. For this purpose, we developed our own fast and accurate numerical model, which considers the highly nonlinear screening currents in the superconductor into account. This work studies a motor of around 2 MW power with REBCO stator coils with 27 parallel tapes as conductor and a permanent-magnet rotor. We consider several electric coupling scenarios of the multi-tape conductor. We also analyze the effect of finite tape-to-tape resistances at the terminals. We have found that the AC loss for the whole motor in the most realistic coupling scenario represents less than 0.018 % of the rated power. Misalignments and tape degradation at the edges of up to 100 $\mu$m only increase AC loss by up to around 20 %. Therefore, motors with REBCO superconductors in the stator are feasible for aircraft propulsion.