Investigation of high-speed superconducting electric machines through time-space extrusion numerical modelling

Abstract

Featured by high power density and efficiency, high temperature superconducting (HTS) electric machines provide a promising solution to heavy-duty electric transport, e.g. electric aircraft. However, designing HTS machines, particularly high-speed HTS motors, presents significant challenges: (1) modelling is highly time-consuming due to the non-linear resistivity of superconductors and complex machine topology; (2) accurately estimating the AC loss of HTS windings remains an open aspiration due to the complicated AC environment. To reduce computational complexity, the thin film approximation (only considering the approximated 1-D HTS film) for HTS coated conductors (CCs) has been widely adopted in simulations, such as the T-formulation models; however, the thin film approximation becomes inadequate for HTS CCs under high-frequency magnetic fields, as encountered in high-speed motors for aerospace. To efficiently and accurately model the AC loss of HTS windings in high-speed superconducting machines, taking a 1 MW superconducting synchronous motor with HTS armature windings as an example, this paper has adopted a time-space extrusion (TSE) method, which demonstrates a >25-fold decrease in modelling time while maintaining comparable accuracy to two benchmark H-A models. The power dissipation in both normal-conducting and superconducting layers of HTS windings has been studied, the AC losses in different turns of the armature winding have been explored, and the slot leakage field harmonics have been illustrated. Results have shown that the losses in Cu and Ag layers for high-speed HTS machines operating at cryo-temperatures (e.g. liquid hydrogen temperature) are not neglectable, especially with a high residual resistance ratio and in the presence of harmonics. The HTS armature winding should be positioned away from the iron tooth and slot opening to minimise exposure to slot leakage fields. The adopted TSE modelling strategy and drawn conclusions have provided valuable insights for the efficient design of high-speed superconducting machines.