## 4 Conclusions  
In this paper, the induction motor, synchronous reluctance motor, permanent-magnet-assisted synchronous reluctance motor and interior permanent-magnet motor are comprehensively compared. Firstly, the volume and stator structure of the four motors are guaranteed to be the same. Then, the influence of the rotor parameters on electromagnetic performance is analyzed, and the motors are optimized using a genetic algorithm (GA). Finally, the electromagnetic performance, material cost and temperature of the four motors are compared. The comparison results are as follows:  
* In terms of the electromagnetic performance, the efficiencies of the IPM, SynRM and ferrite-assisted SynRM are equivalent, at about 2.5% higher than that of the IM. The power factor of the SynRM is lower than that of the other three motors. The power factor of the ferrite-assisted SynRM is higher than that of the IM, and lower than that of the IPM. The torque ripples of the SynRM and the IPM are close, at about 14.6%. The torque ripple of the ferrite-assisted SynRM is 11.4%. The torque ripple of the IM is the smallest, at about 11.23%. * For the motor temperature: the stator copper loss and core loss of the IM are much higher than those of the other three motors. Regarding the comparison of the SynRM, ferrite-assisted SynRM and IPM, the iron loss of the SynRM is the highest, and the copper loss of the IPM is the highest, but the total losses of the three motors are equivalent. Under the same cooling method, the temperature of the IM can be up to 126.1 \({}^{\circ}\)C. The temperatures of the ferrite-assisted SynRM and the IPM are equivalent, at about 20 \({}^{\circ}\)C lower than that of the IM. * In terms of the motor material cost and weight: the weight of the SynRM and the ferrite-assisted SynRM is about 50% lower than that of the IM. The weight of the IPM is about 30 kg heavier than that of the SynRM and the ferrite-assisted SynRM. The costs of the SynRM and the ferrite-assisted SynRM are very close, at about 33% lower than the cost of the IPM and 23% lower than the IM. * The manufacturing process and control system of the IM are very mature, but its electromagnetic performance needs to be further improved. The power factor, efficiency and torque density of the IPM are excellent, but the cost of the motor needs to be considered. The structure of the SynRM is simple and the cost is very low, but its low torque density and low power factor limit its development. The electromagnetic performance of some of the ferrite-assisted SynRMs are better than that of the IM and the SynRM, and its cost is much lower than that of the IPM. However, it is necessary to pay attention to the torque ripple of the ferrite-assisted synchronous reluctance motor and the demagnetization of the ferrites. It is very important to select the appropriate motor type for different applications. This paper comprehensively compares the four common motors, and provides a certain reference significance for the selection and application of motors. \begin{table}
\begin{tabular}{c c c c c} \hline \hline  & **Induction** & **SynRM** & **Ferrite-Assisted** & **IPM** \\  & **Machine** & **SynRM** & **SynRM** & **IBM** \\ \hline Iron mass (kg) & 194.4 & 103.92 & 103.92 & 137 \\ PM mass (kg) & - & - & 5.96 & 3.32 \\ Cooper mass (kg) & 24.1 & 26.23 & 26.23 & 26.23 \\ Aluminum mass & 6.02 & - & - & - \\ Total mass (kg) & 224.52 & 130.15 & 136.11 & 166.64 \\ Iron (USD) & 412.13 & 220.31 & 220.31 & 290.44 \\ PM (USD) & - & - & 1.01 & 258.86 \\ Copper cost (USD) & 357.89 & 389.52 & 389.52 & 389.52 \\ Aluminum cost (USD) & 25.55 & - & - & - \\ Total (USD) & 795.57 & 609.83 & 610.84 & 938.82 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Material costs of the SynRM, ferrite-assisted SynRM, IPM and induction machine. **Author Contributions:** Conceptualization, G.D.; Data curation, G.D. and G.Z. ; Formal analysis, G.Z. ; Funding acquisition, G.D.; Investigation, G.D. and G.Z. ; Methodology, G.D. and G.Z. ; Project administration, G.D.; Resources, G.D.; Software, G.Z.