## 5 Conclusions  
In this paper, four kinds of pole-slot ratio schemes were compared and the accuracies of six optimized surrogate models were analyzed for low-speed high-torque permanent magnet motors. The specific conclusions are summarized as follows:  
* The four pole-slot ratio schemes of 70P84S, 70P168S, 80P90S and 80P180S were compared. Since 70P84S and 80P90S are concentrated windings, the winding ends are shorter and the magnetic flux leakage is smaller, so the efficiency of the two is slightly higher and the power factor is also higher. However, the pole-slot ratio of the concentrated winding led to rich air gap harmonics, so the eddy current loss of the permanent magnet also increased significantly, and the torque ripple was also large. At the same time, the maximum output torque multiples of both were far less than four times. The power factor of the 80P180S motor was the highest, the torque ripple was 3.96%, and the maximum output torque multiple was slightly lower than four times. The efficiency of the 70P168 motor was slightly lower, and the power factor was much lower than the other three pole-slot ratios, but the minimum torque ripple was only 1.4%, and the maximum output torque multiple was far more than four times, reaching 4.48 times. * Six surrogate models were obtained by combining two sample point sampling methods (CCD, LHS) and three surrogate model fitting methods (GA, Kriging, ANN), and the \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Parameter Name** & **Measurement** & **Predicted** & **Calculation** \\ \hline Power (kW) & 37 & 37 & 37 \\ Phase current & 70 & 68.2 & 68.8 \\ Power factor & 0.92 & 0.93 & 0.925 \\ Efficiency (\%) & 95.48 & 95.7 & 95.68 \\ PM weight (kg) & 11.2 & 11.2 & 11.2 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Summary and comparison of simulation calculation and measured data. Figure 20: Test data and calculation data curve under rated load. (**a**) Line back EMF curves. (**b**) Rated current curves. accuracy of the six surrogate models was compared. It can be seen that the sample space obtained by CCD sampling was prone to normal concentration in distribution, and the samples sampled by LHS were evenly distributed in the sample space, which benefited from the hierarchical sampling strategy of LHS sampling. In addition, ANN required a large amount of sample data, which took a huge amount of calculation time, so the accuracy of the ANN fitting surrogate model was the worst, and the accuracy of the GA fitting surrogate model was worse than that of the Kriging fitting surrogate model. In summary, the LHS sampling method combined with the Kriging surrogate model fitting method was more suitable for motor optimization, and the finite element calculation results were very close to the optimization prediction results. * Low-speed and high-torque permanent magnet motors are mostly used in coal mining, transportation and other industries. At present, the low-speed high-torque permanent magnet motor is still a hot research topic. We believe that ultra-low-speed permanent magnet direct-drive motors and industrial and mining low-speed high-torque permanent magnet motors will have a broader prospect in the future. Ultra-low-speed permanent magnet direct drive can reduce the cooperation of low-speed motor in the first stage deceleration mechanism, giving full play to the advantages of direct drive motors. In addition, low-speed and high-torque permanent magnet direct-drive motors have been successfully applied in the fields of wind power generation and new energy vehicles. However, low-speed and high-torque permanent magnet motors for industrial and mining still need more research, which should mainly focus on exploring the relationship between the pole-slot ratio, winding form, and high starting torque and high overload capacity. In summary, we believe that ultra-low-speed permanent magnet direct-drive motors and high-performance industrial and mining low-speed high-torque permanent magnet motors have greater development prospects.