## 3 Analysis of Results for Optimal Model
### Fault-Tolerant Operation Modes  
Torque characteristics were analyzed for two fault states using FEM. The analysis was performed at 480 r/min with the UVW2 phase opened, as shown in Figure 1. The first was constant-current (CC) mode; since the magnitude of the phase current did not change, it was a control mode in which the output torque decreased when switching from six to three phases. The second was constant-torque (CT) mode, which was a control mode that maintained the output torque by doubling the phase current when switching from six to three phases. Therefore, 5 A, which is half the rated current of 10 A, was selected for the load current when switching to three-phase winding in the constant-torque mode, and the simulation was also conducted under 4 A to confirm the variation in torque ripple. In constant-torque mode, there is a risk of exceeding the rated current of the system, and therefore appropriate control scenarios and safeguards must be built in. Table 7 shows an \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multicolumn{2}{c}{**Parameters**} & **2 A** & **4 A** & **5 A** & **6 A** & **8 A** & **10 A** \\ \hline \multirow{8}{*}{Six-phase} & Max. torque [Nm] & 3.4 & 6.8 & 8.5 & 10.4 & 14.2 & 18.1 \\  & Min. torque [Nm] & 2.9 & 6.1 & 7.7 & 9.5 & 13.1 & 17.0 \\  & Mean torque [Nm] & 3.1 & 6.4 & 8.1 & 9.9 & 13.6 & 17.5 \\  & Difference of min/max [Nm] & 0.5 & 0.7 & 0.8 & 0.9 & 1.1 & 1.1 \\  & Ripple factor [\%] & 16.1 & 10.9 & 9.9 & 9.1 & 8.1 & 6.3 \\  & Power factor & 0.992 & 0.965 & 0.951 & 0.934 & 0.903 & 0.869 \\  & Efficiency [\%] & 95.0 & 95.9 & 92.0 & 90.9 & 88.9 & 87.0 \\ \hline \multirow{8}{*}{Three-phase} & Max. torque [Nm] & 1.8 & 3.5 & 4.3 & 5.2 & 6.9 & 8.7 \\  & Min. torque [Nm] & 1.4 & 2.8 & 3.6 & 4.4 & 6.1 & 7.8 \\  & Mean torque [Nm] & 1.6 & 3.2 & 4.0 & 4.8 & 6.5 & 8.2 \\  & Difference of min/max [Nm] & 0.4 & 0.7 & 0.7 & 0.8 & 0.8 & 0.9 \\  & Ripple factor [\%] & 25.0 & 21.9 & 17.5 & 16.7 & 12.3 & 11.0 \\  & Power factor & 0.997 & 0.983 & 0.974 & 0.963 & 0.969 & 0.924 \\  & Efficiency [\%] & 90.7 & 87.0 & 84.9 & 82.8 & 79.2 & 75.9 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Torque characteristic according to currents in FEM at 480 r/min. Figure 9: Torque curves of six and three phases from FEM analysis at 480 r/min and 10 A.  
example of the operation of a six-phase motor that can be converted into a three-phases motor within a rated phase current of 10 A, and analysis was performed assuming that a phase current of 5 A flowed through the six-phase motor. Here, when comparing the average torque of 6 PH_5A and 3 PH_10A, which generated MMF of the same magnitude, differences as large as 0.1 Nm were found in the three-phase condition, but this value is within the analytical margin of error. When comparing RF, the RF in the three-phase condition was interpreted as a 1.1% larger value, which represents a significant increase. This increase in torque ripple appears to be influenced by the 5 th and 7 th harmonics analyzed through Figure 7b during three-phase operation. If the constant-current mode was applied at 6 PH_5A, the state was converted into 3 PH_5A, and the average torque was reduced to 49% of the original level. In this case, since the torque was small, it could only be applied in a light-load situation. However, if the constant-torque mode was applied within a limit that did not exceed the rated current range, operation with 3 PH_10A became possible, and an average torque similar to that of 6 PH_5A operation could be obtained. The conditions for this situation to be possible are either when the system is operated with a load less than half the maximal allowable phase current in the system or when the maximal current of the system is forcibly limited within the rated current.