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 $μ$m only increase AC loss by up to around 20 %. Therefore, motors with REBCO superconductors in the stator are feasible for aircraft propulsion.

Figures (17)

• Figure 1: Superconducting motor configuration in the present study with zooms in several parts (orange frame delimits the area of the next zoom). Modeling is from the scale of 1 m for the whole motor down to around 1 $\mu$m for the tape thickness. Wire frames in red, blue, and green are for the superconducting layers, iron yoke and permanent magnets, respectively.
• Figure 2: Simplified coupling configurations ("coupled", "coupled-at-ends", and "uncoupled" from top to bottom), where $y$ and $z$ are the directions of the tape width and length, respectively. Above, $I$ and $n$ are the coil current and number of parallel tapes, respectively. We assume that the metal presents zero resistivity.
• Figure 3: Coupling configurations considering finite resistances between the parallel tapes at the coil ends. Left: intermediate configuration between "ucoupled" and "coupled-at-ends" of figure \ref{['f.coupl']}. Right: Realistic coupling at the terminals.
• Figure 4: Dependence of the tape critical current, $I_c$, as a funcion of the applied magnetic field, $B$, and its angle with the tape normal at 40 K. Data for SuperOx YBCO 2021 from robinson_data (only curves for up to 1.5 T are shown). The critical current density is $J_c=I_c/(wd)$, where $w$ and $d$ are the superconductor width and thickenss, respectively
• Figure 5: Example of the solution of the magnetization, $\textbf{M}$, in the iron yoke and the permanent magnets for the radial component (top) and the angular component (bottom).