Effect of Changing Magnet Material on Cogging Torque and Torque Ripple of Brushless DC Motor

Abstract

Brushless DC motors (BLDC)are extensively used for high-control applications because of their small size, high efficiency, and high-performance qualities. It gained popularity since the permanent magnetic materials were improved, so the drive system must have precise positioning and smooth electromagnetic torque for high performance and precision. Numerous elements contribute to torque ripples in this motor; one of them is the type of permanent magnet material. In this paper, a 3-phase, four-pole, 1500 W BLDC motor was modeled based on RMxprt and Maxwell 2D software. Four magnet materials: alnico 5, ceramic 5, SmCo 28, and NdFe 35, were studied to show the effect of each magnet on motor performance. The finite element analysis (FEA) results showed that the motor's average torque and cogging torque are directly proportional to the magnet strength. Also, the torque ripple exists with using a lower magnet strength magnet. Ndfe35 and SmCo28 have strong mechanical properties, are relatively expensive, and have higher cogging torque and torque ripple. The other materials, Alnico 5 and ceramic 5, are less costly and have less cogging torque and torque ripple. The full load simulations demonstrate that weaker magnets can also provide lower torque. Due to the results presented, while choosing the magnet materials, the trade-off between nominal torque, torque ripple, and price should be taken into account. The methodology adopted in this research will allow motor designers to select the best magnet material,and leading to excellent motor performance without the requirement to construct and test several prototype motors.