## 4 Experimental Result
The waveform of the line-to-line EMFs under the no-load condition and with the speed of 3000 rpm is shown in Figure 23.  
The three-phase per-phase resistance is 0.01565 \(\Omega\) and 0.017 \(\Omega\), respectively, in the experiment and simulation. The effective value of the line-to-line EMFs in Figure 23 is 134.4 V, and then the value of the phase EMFs is 77.6 V. In the same operating condition, the value of the original motor is 123.5 V and 71.3 V, respectively. Comparing the experiment data and simulation results, the consistency between the simulations and experimental data can be easily seen in Table 12.  
Figure 23: The waveform of line-to-line EMFs of optimized motor under no-load condition. Figure 22: The experiment test of the prototype motor: (**a**) prototype motor; and (**b**) controller. The average output torque and output active power of the motor at different rotor speeds were recorded and the characteristic curves are illustrated in Figure 24 when the driving current of the stator is kept at 250 A. From Figure 24, it can be seen that the constant output torque of 205 N-m can be achieved under the rotor speed of 3000 rpm and the constant output power of 65 kW can be fulfilled between the rotor speed of 3000 rpm and 9000 rpm, which means the optimized motor can satisfy the output requirements of the original motor in Table 1. And the maximum values of the constant output torque and power are both higher than the original one; the output performance has been improved by the new structures. The efficiencies of the prototype motor at different speed and load conditions were computed by measuring the output power from the rotor shaft and the active power in the grids. The test speed range is between 1000 rpm and 9000 rpm, and the output power range is between 10 kW and 60 kW. The efficiencies data are calculated at a stable operating temperature when the output power is under 40 kW. For 60 kW, the efficiencies data are calculated when the operation time is 180 s. Selecting the efficiencies data corresponding to real operating conditions from 20 to 60 kW, at intervals of 1000 rpm, the results are listed in Table 13.  
The maximum efficiency of the prototype motor is 97.8% at the rotor speed of 4000 rpm and output power of 60 kW, while the maximum efficiency of the original motor is 96.7%. Furthermore, from the calculation and analysis, the efficiency area above 90% is around 79.5% of the whole test area, and the area proportion, for which the efficiency is over 80%, \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \multirow{2}{*}{**Output Power**} & \multicolumn{8}{c}{**The Efficiencies at Different Rotor Speeds**} \\ \cline{2-9}  & **1000 rpm** & **2000 rpm** & **3000 rpm** & **4000 rpm** & **5000 rpm** & **6000 rpm** & **7000 rpm** & **8000 rpm** \\ \hline
20 kW & 0.959 & 0.948 & 0.952 & 0.958 & 0.940 & 0.860 & 0.778 & 0.908 \\
40 kW & 0.970 & 0.952 & 0.968 & 0.971 & 0.959 & 0.902 & 0.907 & 0.926 \\
60 kW & 0.969 & 0.949 & 0.963 & 0.978 & 0.965 & 0.960 & 0.927 & 0.871 \\ \hline \hline \end{tabular}
\end{table} 
Table 13: The efficiencies at different speeds and load conditions. Figure 24: Average output torque and active power performance of the optimized motor at different rotor speeds. \begin{table}
\begin{tabular}{c c c c} \hline \hline \multicolumn{1}{c}{**Parameter**} & **Value** & **The Original** & **The Optimized** \\ \hline \multirow{2}{*}{Simulation result} & Line EMFs & 132.2 V & 142.0 V \\  & Phase EMFs & 76.4 V & 82.0 V \\ \hline \multirow{2}{*}{Experiment data} & Line EMFs & 123.5 V & 134.4 V \\  & Phase EMFs & 71.3 V & 77.6 V \\ \hline \hline \end{tabular}
\end{table} 
Table 12: The comparison of the experiment data and simulation results of EMFs. is about 96.58%. Compared with the original motor, the high-efficiency area is expanded, and the maximum efficiency is also improved by the optimization.