Optimisation and loss analyses of pulsed field magnetisation in a superconducting motor with cryocooled iron cores

Abstract Thanks to their compact size, reduced energy losses, and enhanced power density, superconducting motors utilising high-temperature superconducting (HTS) materials are particularly appealing for propulsion systems such as those used in electric aircraft. Upon magnetisation, stacked HTS coated conductors are transformed into trapped field stacks (TFSs), which represent a key variant of trapped field magnets. TFSs offer a promising alternative to traditional permanent magnets, providing rotor fields for motor operation, particularly in synchronous machines. To date, there has been a lack of comprehensive investigation into the interaction between HTS TFSs and cryocooled iron cores, as well as the losses generated in iron cores during pulsed field magnetisation (PFM). Furthermore, the optimal magnetisation strategy for achieving the maximum trapped field in TFSs through PFM for motor applications remains an unresolved issue. To address these challenges, a 2D electromagnetic-thermal coupled numerical model was built using the finite element method and validated against experimental data. This model was employed to analyse a superconducting machine featuring TFSs as rotor magnets and cryocooled iron cores. This study introduces two key novelties. The primary novelty lies in identifying the optimal combination of pulsed current amplitudes and TFS layer numbers required to achieve maximum magnetisation fields. The secondary novelty involves evaluating the overall losses in both superconducting and non-superconducting components of the machine during PFM. This includes heat generation in various layers of the TFS and losses in the motor’s active materials, such as copper windings and iron cores. Additionally, two practical motor configurations were proposed, and two calculation methods using linear interpolation of iron losses and steel grades were introduced to estimate the iron losses for the studied iron material, M270-35 A. This pioneering study is expected to serve as a valuable reference for loss analyses and structural design considerations in developing superconducting machines.