磁极径向组合式定子无磁轭模块化轴向磁通电机磁热特性分析

doi:10.19595/j.cnki.1000-6753.tces.241230

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Abstract The Yokeless and segmented armature (YASA) axial flux machine has a wide range of applications in electric vehicles, aerospace, and industrial robotics due to its flat and compact structure, high operating efficiency, and high power density. However, the yokeless structure of its stator core leads to high cogging torque and torque pulsations. Additionally, the high power density and poor heat dissipation conditions at the stator end of such machines hinder further improvement of electromagnetic performance. The choice of the rotor topology, cooling method, and design of the cooling structure directly affect the electromagnetic performance of the machine.
Firstly, the rotor topology directly affects the harmonic content in the air gap magnetic field. The equivalent magnetic circuit of the magnetic pole radial combined YASA machine is analyzed, the power equation under the rotor topology is derived, and the weakening mechanism of the cogging torque is studied. Then, based on the three-dimensional finite element electromagnetic simulation calculation, the effects of three rotor topologies— surface-mounted, Halbach array, and magnetic pole radial combination—are compared in terms of magnetic field distribution, air gap flux density, no-load back EMF, and torque characteristics.
To further enhance the electromagnetic performance of the YASA machine, a double-ring water-cooling structure is proposed to be embedded in the stator support. Based on the accurate calculation of machine loss, the temperature rise characteristics of the machine under natural cooling and double-ring water-cooling conditions are calculated using the computational fluid dynamics (CFD) method. The temperature field and fluid field of the machine under different current conditions are then analyzed.
Finally, the electromagnetic and thermal characteristics analysis results, along with the effectiveness of the proposed cooling structure, are verified through experiments. The following conclusions can be drawn.
(1) When the auxiliary magnetic pole angle is 0<γ<T, the waveform of the cogging torque in the first half cycle is negative. When T<γ<2T, the waveform of cogging torque in the first half cycle is positive. The magnetic pole radial combined YASA machine utilizes the superposition of cogging torque to mitigate it by adjusting the main and auxiliary magnetic pole angles in the inner and outer layers.
(2) The electromagnetic performance of the traditional surface-mounted type is the worst. The performance of the magnetic pole radial combined type and the Halbach array YASA machine is basically the same in terms of magnetic field distribution, air gap flux density, and no-load back EMF. Compared with the Halbach array, the pole radial combined YASA machine significantly reduces the cogging torque and torque ripple at the expense of some electromagnetic torque.
(3) The double-ring water-cooling structure embedded in the stator support can significantly reduce the temperature rise of the stator core and windings. At the same time, the problem of excessive temperature rise at the inner and outer ends of the windings has been effectively solved. When the maximum temperature of the windings under water-cooling and naturally cooling conditions is kept the same, the current density can reach 16.2 A/mm², which is 2.9 times that of naturally cooling conditions. Consequently, the torque density and power density of the machine can be significantly increased.

Key words： Yokeless and segmented armature (YASA) machine Halbach arrays torque pulsation cogging torque water-cooling structure

Received: 11 July 2024

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TM351

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	Gao Peng
	Ren Hongxing
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Gao Peng,Ren Hongxing,Wang Xiaoyuan等. Magnetic and Thermal Characteristics Analysis of Magnetic Pole Radial Combination Yokeless and Segmented Armature Axial Flux Machine[J]. Transactions of China Electrotechnical Society, 2025, 40(24): 7969-7983.

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