# Adoption of Multiphase and Variable Flux Motors in Automotive Applications
## 4 Results and Discussion
### Power Losses and Efficiency  
As well as torque ripple, power losses were calculated at the four working points, where the copper, stator iron, rotor iron, and magnet losses were distinguished. Other losses, such as mechanical ones, were not analysed as they were equal for all motors. The losses are represented in Figure 12 and Table 4.  
In WP1, where the torque level is high and the speed is 1/3 of its maximum value, the copper losses were dominant due to the high current. As mentioned in Section 4.1, the DTP motor has more torque capability and needs less current to generate a certain torque level. Thus, the copper losses of the DTP motors were reduced by 7.66% compared to the 3-phase ones. The stator iron losses exhibited minimal variation across the different motor topologies and were the second-highest losses. The rotor iron and magnet losses constituted less than 1% of the total losses in all motors. Notably, the DTP motor demonstrated lower rotor iron and magnet losses compared to the 3-phase motors, which can be attributed to the reduced harmonic content in its airgap field. In WP2, copper losses had relatively small values due to the low torque at this point, and the stator iron losses were greater than them. When comparing the losses in different motors, they behaved as in WP1: copper, rotor iron, and magnet losses were smaller in the DTP motors for the same reason, whereas there was practically no change in stator iron losses. Figure 11: Torque ripple at different working points in 1/6 of the electrical period. (**a**) WP1. (**b**) WP2. (**c**) WP3. (**d**) WP4. \begin{table}
\begin{tabular}{c c c c c} \hline  & **3-Phase** & **DTP** & **3-Phase VF** & **DTP VF** \\ \hline WP1 & 3.4\% & 1.7\% & 3.4\% & 1.7\% \\ WP2 & 7.1\% & 2.8\% & 7.1\% & 2.8\% \\ WP3 & 16.5\% & 9.9\% & 12.4\% & 4.6\% \\ WP4 & 37.3\% & 18.2\% & 21.4\% & 11.8\% \\ \hline \end{tabular}
\end{table} 
Table 3: Torque ripple values at different motors and working points. In WP3, characterised by high torque and speed, copper losses remained predominant. However, there was a notable increase in stator iron, rotor iron, and magnet losses, particularly in the stator iron losses. This increase is attributed to the higher frequency, which elevates iron losses and magnet eddy currents. Compared to the 3-phase motor, the DTP motor exhibited higher copper losses due to the increased current required in the flux-weakening region. Conversely, both VF motors experienced a significant reduction in copper losses (over 25%) because the flux-weakening current requirement is diminished in the FW-MS. Stator iron losses were similar again, but rotor iron and magnet losses were different in the four motors. On the one hand, losses were lower in the DTP topologies due to the more sinusoidal airgap field. On the other hand, as a lower current was required in the two-phase motor, the higher  
the VF topologies, the stator magnetic field was reduced, which lowered the losses in the rotor elements. Last, in the WP4, torque level is low and the speed is high. The high speed requires a high current to work in the flux-weakening region. In the variable flux motors, this flux-weakening current requirement was lower than in the constant flux motors, reducing copper losses to around 50%. Stator iron losses did not vary significantly, although the VF motors exhibit around 9% lower loss, probably due to the weaker magnetic fields. Rotor iron losses were reduced in both DTP and VF configurations, and the VF modification achieved a higher reduction. Regarding magnet losses, the DTP motor had slightly higher losses than the 3-phase motor. Although the DTP motor produces a field with less harmonic content, which should reduce magnet losses, it seems that the higher stator current used for field-weakening counters this advantage, generating even more losses than in the 3-phase motor.