**7. Conclusions**

The aim of this study was to theoretically compare the PMFSG with a conventional IPMSG in a direct-driven low-power wind application. To ensure a fair comparison, both machines were first optimized using the Nelder–Mead algorithm. The optimization objective functions were selected so as to take into account the required power of frequency converter, the evaluation of the active materials cost, and losses in generators averaged over the working profile of the wind turbine. Additionally, the torque ripple was included in the optimization function of the IPMSG, since this parameter was significantly higher in the IPMSG than in the PMFSG. To reduce the computational time, the substituting profile method was applied. As a result, the strengths and weaknesses of the machines were revealed.

This study shows that the PMFSG requires 1.4 times less rare earth-earth magne<sup>t</sup> material than the IPMSG. Considering that the mining of rare-earth materials and their manufacturing have a harmful effect on the environment, this advantage of the PMFSG is highly valuable for mass production. In addition, the PMFSG torque ripple is less. However, the PMFSG requires a slightly higher power rating of the semiconductor inverter, and the average losses in the IPMSG are 1.2 times lower than in the PMFSG.

The results of this comparative study can be used by developers of direct-driven wind generators when selecting the type of electric machine suitable for a specific wind power application.

**Author Contributions:** Conceptual approach, V.P. and V.D.; data curation E.A. and V.K.; software V.D. and V.P.; calculations and modeling, V.P and V.D. and V.K.; writing of original draft, E.A., V.P., V.D. and V.K.; visualization, E.A., V.D. and V.K.; review and editing, E.A., V.P., V.D. and V.K. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** Data is contained within the article.

**Acknowledgments:** The authors thank the editors and reviewers for careful reading, and constructive comments.

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