**6. Conclusions**

An AFPM machine with an arc hexagonal magne<sup>t</sup> shape is proposed to decrease cogging torque. In the proposed model, cogging torque is reduced, and output torque has been reduced due to an increase in air-gap length as compared to the conventional model. The VTHD of the conventional hexagonal-shaped model is 1.33%, and the VTHD of the proposed model is 0.789%; hence, the VTHD is reduced in the proposed model. The arc hexagonal-shaped proposed model is then further optimized to achieve reduced cogging torque and increased output torque. In the optimized model, cogging torque and torque ripples are reduced, the output torque is improved, and power is also increased as compared with the proposed hexagonal model. The performance characteristics of the optimized model exhibit improved results relative to the proposed and conventional models.

**Author Contributions:** Conceptualization, J.I.; software, H.U. and M.Y.; formal analysis, H.U., M.Y., and K.S.A.; writing—original draft preparation, S.S.H.B.; funding acquisition, J.-S.R. All authors have read and agreed to the published version of the manuscript.

**Funding:** National Research Foundation of Korea, 2016R1D1A1B01008058; the Brain Pool (BP) Program, 2019H1D3A1A01102988.

**Acknowledgments:** This work was supported in part by the Brain Pool (BP) Program, funded by the Ministry of Science and ICT through the National Research Foundation of Korea under Grant 2019H1D3A1A01102988, and in part by the Basic Science Research Program through the National Research Foundation of Korea, funded by the Ministry of Education under Grant 2016R1D1A1B01008058.

**Conflicts of Interest:** The authors declare no conflict of interest.
