Comparative Study of Permanent Magnet Shapes in Outer Rotor PMSM for EC Fan in Data Center

초록

With the rapid growth of AI data centers, high-efficiency electrical machines have become increasingly important for HVAC applications. Outer-rotor surface permanent magnet synchronous motors (SPMSMs) with ferrite magnets are widely adopted for electrically commutated (EC) fans in AI data centers due to their low cost and high efficiency. Since the electromagnetic performance of SPMSMs is significantly influenced by the permanent magnet shape, extensive studies have been conducted to improve efficiency and reduce torque ripple. In this paper, a comparative study of outer-rotor PMSMs with four permanent magnet shapes—chamfer, linear chamfer, taper, and cycloid—is conducted for EC fan applications. For a fair comparison, all models are optimized under identical constraints using a multi-objective genetic algorithm (MOGA) based on finite element analysis (FEA). Electromagnetic characteristics, including back electromotive force (BEMF), torque, torque ripple, and efficiency, are evaluated. The results show that the chamfer-type magnet achieves the highest efficiency despite slightly higher harmonic components. To validate the FEA results, a prototype is manufactured and experimentally evaluated under both no-load and load conditions. The FEA results are validated through the comparison with the experimental results, demonstrating a BEMF error of 1.4% and an efficiency deviation of less than 1%. In addition, the efficiency of the prototype motor satisfies the IE5 efficiency class according to the IEC 60034-30-2.

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