High-Torque-Density Composite-Cooled Axial Flux Electrically Excited Synchronous Motor

Shumei Cui, Yuqi Zhang, Beibei Song (), Kexin Xu, Can Feng and Shaoshuan Qi
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Shumei Cui: School of Electrical Engineering and Automation, Harbin Institute of Technology, Harbin 150001, China
Yuqi Zhang: School of Electrical Engineering and Automation, Harbin Institute of Technology, Harbin 150001, China
Beibei Song: School of Electrical Engineering and Automation, Harbin Institute of Technology, Harbin 150001, China
Kexin Xu: School of Electrical Engineering and Automation, Harbin Institute of Technology, Harbin 150001, China
Can Feng: School of Electrical Engineering and Automation, Harbin Institute of Technology, Harbin 150001, China
Shaoshuan Qi: Zhengzhou Research Institute of Harbin Institute of Technology, Zhengzhou 450001, China

Energies, 2025, vol. 18, issue 17, 1-20

Abstract: Axial flux motors, characterized by compact axial dimensions and high torque density, are well-suited for space-constrained applications such as in-wheel drives and flying vehicles. However, conventional axial flux permanent magnet synchronous motors (AFPMSMs) face challenges such as high-temperature demagnetization, reduced efficiency at high speeds, and elevated manufacturing costs. Electrically excited synchronous motors (EESMs) offer a promising alternative, providing high-temperature reliability and superior high-speed capability while maintaining high torque density. In this paper, a novel composite-cooled axial flux electrically excited synchronous motor (AFEESM) is proposed. From an electromagnetic design perspective, the effects of key parameters such as shaft-to-outer-diameter ratio, inner-to-outer-diameter ratio, slot depth, and yoke thickness on output performance are systematically investigated, and a dedicated design procedure is established. Through multi-objective optimization, the motor’s torque output is increased by 19.6%. Comparative simulations are conducted to evaluate differences in torque density, efficiency, and cost between the proposed AFEESM, a conventional radial flux EESM, and an AFPMSM. To address the cooling requirements of double-sided windings on both the stator and rotor, a dual-channel composite cooling structure is developed, integrating internal–external double-loop water cooling for the stator and axial through-hole air cooling for the rotor, reducing the peak temperature by over 36%. Finally, a prototype is manufactured, and no-load characteristics and load efficiency validate the effectiveness of the electromagnetic design and the structural reliability of the motor.

Keywords: electrically excited synchronous motor; axial flux; parameter design; high torque density; composite cooling structure (search for similar items in EconPapers)
JEL-codes: Q Q0 Q4 Q40 Q41 Q42 Q43 Q47 Q48 Q49 (search for similar items in EconPapers)
Date: 2025
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