Conference: 2025 한국자동차공학회 춘계학술대회
Authors: 김재현, 배예나, 홍영진, 곽병길, 김일우, 임명섭
DOI:
Permanent magnet synchronous motors (PMSMs) such as interior permanent magnet synchronous motors (IPMSMs) and surface-mounted permanent magnet synchronous motors (SPMSMs) are being widely studied as motors for driving urban air mobility (UAM). This is because permanent magnet synchronous motors can achieve higher torque density, specific torque, and specific power than induction motors, and this is further maximized when rare earth permanent magnets such as NeFeB and SmCo are used. Among PMSMs, SPMSMs are mainstream for driving UAM, and this is because the load increases with speed due to the load characteristics. For electric vehicle (EV) drive motors with reduction gears, the small, high-speed, low-torque IPMSM type is suitable, but for UAMs with relatively low speeds even when directly driven, the SPMSM is considered a suitable type. In addition, research on axial flux motors (AFMs) has also been actively conducted recently to increase torque density. AFMs are motors in which the main flux path is axial, and the rotor and stator face each other axially. Accordingly, since the rotor in the shape of a disk rotates, the axial length can be designed shorter than that of RFMs, and it is attracting attention as a motor with high torque density. Since the AFM has a rotor and stator facing each other, it has a high degree of freedom in the number and arrangement of the same rotor and stator. Therefore, it is easy to select various topologies. Basically, it can be broadly classified into the single-stator single-rotor (SSSR) type with one rotor and stator, the double-stator single-rotor (DSSR) type with an internal rotor and stator on both sides, the single-stator double-rotor (SSDR) type with an internal stator and rotors on both sides, and the multi-disc type with multiple types connected. Next, in the case of double rotors or double stators, it can be subdivided into NN type and NS type according to the magnetic flux path. In the case of SSDR-NS type, there is a Yokeless and segmented armature (YASA) type that removes the stator yoke that is not used as a magnetic flux path. In the case of the YASA type, additional weight reduction is possible because there is no stator yoke. It is true that AFM can reduce the volume because the axial length is small, but a comparison of the specific torque is also necessary. Therefore, in this paper, we compare the maximum torque and specific torque of various topologies of outer rotor SPMSM and AFM according to the number of poles, axial length, and outer diameter as motors for urban air mobility. As a result, through the comparison of maximum torque and specific torque, we confirm the common features of RFM and AFM and the differences in geometric features for performance improvement.