Analysis of Axial Flux Permanent Magnet Synchronous Motors Based on Aspect Ratio and Stator-Rotor Topologies

초록

Axial flux permanent magnet synchronous motor (AFPMSM) is attracting attention in various industrial fields with spatial constraints, such as robotic joints and urban air mobility (UAM), due to its advantage of achieving high power density in a thin structure where the axial length is short relative to the diameter. The design flexibility of the AFPMSM stems from various combinations of topologies. For rotors, they are classified into single rotor and dual rotor types. For stators, they are broadly divided into the slotted type, where copper windings are directly wound onto conventional iron core teeth, and the slotless type, which replaces copper windings with printed circuit board (PCB) patterns and eliminates the iron core. Stator topologies exhibit markedly different electromagnetic performance depending on the specific geometry of the stator core or the PCB winding patterns, and the Aspect Ratio range that achieves optimal performance varies significantly when combined with different rotor topologies. Furthermore, the electromagnetic performance of AFPMSMs is strongly affected by the Aspect Ratio. As the outer diameter increases, higher torque and output power can be achieved due to the larger effective torque arm. However, rotor mass, permanent magnet eddy-current loss, and mechanical stress also increase, resulting in different power, efficiency, and torque density characteristics depending on the Aspect Ratio and topology combination. Currently, there is a lack of systematic design guidelines for determining which topology combination is efficient for the specific Aspect Ratio required by various applications, making efficient initial design difficult in practice. In this paper, major stator-rotor topology combinations were selected considering practical feasibility, and their power, efficiency, and torque density were comparatively analyzed using finite element analysis (FEA) to present design indices. Subsequently, a prototype model for a specific Aspect Ratio range was fabricated, and performance tests were conducted to verify the validity of the analysis results.

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