For high performance and high efficiency, rare earth magnets have been widely used in recent motors. Rare earth is very unstable as a future industry due to limited resources and monopoly of some countries. For this reason, as the price of rare earth magnets and overall materials has increased recently, the issues of cost reduction and weight reduction are increasing. In this paper, iron usage and weight were reduced by changing the existing EPS motor to the STM model 1. However, the STM model showed low performance compared to the amount of magnet used because large leakage occurred in the lips. To compensate for these shortcomings and to reduce the amount of magnet used, consequent poles were applied. When Consequent pole is applied, the usage of rare earth magnet is greatly reduced. Therefore, the weight and price are greatly reduced. In general, the consequent pole reduces the use of magnets by half, so the performance is also reduced by half. However, in the STM model, the magnetic flux leakage from the lips is greatly reduced by removing the poles. Therefore, the performance is reduced by about 35%, not by half. Therefore, even though the use of magnets has been reduced by half, by applying STM as a consequent pole rather than a general consequent pole with the same performance, many advantages such as weight reduction and reduced use of magnets can be brought. The application of this motor is EPS. For EPS, cogging torque is the most important performance factor. However, when the Consequent pole is applied, only the N pole or the S pole exists and the rest is made of iron, so a lot of cogging torque and torque ripple occurs. In this paper, after applying the consequent pole to the STM model, various methods are applied to reduce the cogging torque. Finally, it can be seen that the weight and magnet usage are reduced with the same performance, and the cogging torque is similarly generated.
References:
1 S. -W. Song, I. -J. Yang, S. -H. Lee, D. -H. Kim, K. S. Kim and W. -H. Kim, "A Study on New High-Speed Motor That Has Stator Decreased in Weight and Coreloss," in IEEE Transactions on Magnetics, vol. 57, no. 2, pp. 1-5, Feb. 2021, Art no. 8201105, doi: 10.1109/TMAG.2020.3012482.

Fig. 1 Consequent pole applied to STM structure

Fig. 2 STM structure magnetic flux line