## 3 Initial Design Parameters of HSPMM
### Multi-Objective Optimization of Electromagnetic Performance and Losses
From the Pareto front surface of the important parameter subspace X2, it can be found that the minimum eddy current loss of permanent magnet is 10 W, the maximum output torque is 20.6 Nm, the maximum efficiency of motor is 97.26%, and the minimum thermal load of motor is 106 A\({}^{2}\)/mm\({}^{3}\). However, when the eddy current loss of permanent magnet and the thermal load of motor are minimal, the motor efficiency is low and the output  
Figure 11: The Pareto solutions of stator parameters subspace. (**a**) The Pareto solutions of PM eddy current loss, efficiency and motor thermal load. (**b**) The Pareto solutions of torque, PM eddy current loss and motor thermal load. (**c**) The Pareto solutions of torque, PM eddy current loss and efficiency. (**d**) The Pareto solutions of torque, efficiency and motor thermal load. torque cannot reach the rated torque requirement. When the output torque is maximum and the motor efficiency is maximum, the eddy current loss of permanent magnet is large and the thermal load of motor is large. From the Pareto front, the motor efficiency, output torque and permanent magnet eddy current loss after stator important parameter subspace optimization is not as good as those after rotor important subspace optimization. Although these three performances decrease slightly, they fully meet the design requirements of the motor. At the same time, it makes the motor thermal load reduction effect obvious, which is very worthwhile. It can be seen from this that the multi-objective optimization design of motor is a compromise selection of optimization objectives on the Pareto front surface composed of all non-inferior optimal solutions rather than all optimization objectives reaching optimization. According to the Pareto front surface of the multi-objective optimization design of the important stator parameter subspace X2, the design requirements of the HSPMM are synthesized, and three non-inferior optimal solutions are selected as the candidate values of the final optimization results, as shown in Table 5. The candidate values and the key motor performance parameters corresponding to the initial design are shown in Table 6.  
From the three candidate values of stator important parameter optimization subspace X2, it can be seen that the motor performance of the three candidate values greatly reduces the thermal load of the motor under the condition of ensuring that the other optimization objectives are basically unchanged. In order to ensure that the subsequent motor temperature field verification meets the design requirements and the low temperature operation of the high-speed permanent magnet motor, the three candidate values of motor efficiency and winding thermal load are basically consistent, so the minimum eddy current loss of the permanent magnet becomes the priority objective. Therefore, candidate value 2 of the three schemes is selected as the final optimization design scheme of stator important parameter subspace. After multi-objective genetic optimization of rotor important parameter subspace X1 and stator important parameter subspace X2, and Pareto frontier screening of optimization objectives, the optimized optimization scheme is obtained, as shown in Table 7. \begin{table}
\begin{tabular}{c c c c c} \hline \hline  & **Back EMF** & **Torque (Nm)** & **PM Loss (W)** & **Efficiency (\%)** &
\begin{tabular}{c} **Thermal** \\ **Load(A2/mm3)** \\ \end{tabular} \\ \hline Initial design & 364 & 19.1 & 31.2 & 96.1 & 180 \\ Candidate 1 & 367 & 19.1 & 14 & 97.18 & 168 \\ Candidate 2 & 376 & 19.3 & 11 & 97.27 & 169 \\ Candidate 3 & 378 & 19.7 & 21 & 97.09 & 169 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Key performance by the optimized X2.