A Novel Topology With the Combination of Superconducting Magnet and Permanent Magnet for the Propulsion Motor of eVTOL Aircraft

The high-temperature superconducting (HTS) tape can bring significant improvement to the performance of electric vertical take-off and landing (eVTOL) aircraft's propulsion motor. However, it requires cryogenic environment to function normally, which causes a huge amount of cryogenic loss. Meanwhile, the motor outputs different levels of torque during a flight mission and the difference can be up to tens of time. In this paper, permanent magnet auxiliary excitation structure (PMAES) is investigated for eVTOL aircraft's propulsion motor. In the proposed design, superconducting magnet (SM) is utilized as main excitation unit to achieve a higher torque density while permanent magnet (PM) is adopted to form PMAES. SM and PMAES operate during machine's high-load condition, and SM is shut off during the low-load condition to eliminate loss caused by the operation of SM's current lead. With such a structure, the HTS material can be utilized to extract the optimal performance of the machine while reducing the cryogenic losses when possible. Four topologies with PMAES are studied, and it is found axial flux superconducting machine (AFSCM) with radial permanent magnet auxiliary excitation structure (RPMAES) has the best performance and ability to significantly reduces the energy consumption of the motor during a complete flight mission.