## 5 Comparative Evaluation of the Two Motors for Electric Ship Propulsion  
Regarding the functional characteristics of the two motors, a detailed comparison is made in Table 8, where the percentage of change (increase or decrease) is also noted, taking as a reference the elements of the induction motor. From the data listed in this table, the following can be easily understood:  
(i) The PMSM presented a significantly lower current during its nominal operation and therefore lower copper losses compared to the inductive one. This feature was particularly attractive in the case of electric propulsion where the energy available to power the motors was limited. In addition, lower copper losses would result in lower temperatures during engine operation. Therefore, the PMSM was expected to show better thermal behavior and, at the same time, the lifetime of the insulation of the windings would be enhanced. In addition, the lower current requirements were also beneficial for the inverter used to power the motor, as its cooling requirements were reduced and it was less stressed. It was noted that the requirements of this application were particularly high. Propulsion motors exhibit long continuous operation while being supplied with high currents. (ii) The induction motor showed lower core losses compared to the PMSM counterparts. This was due to the fact that the supply frequency of the induction motor was equal to 60 Hz. In the case of PMSM, it was equal to 250 Hz. The higher supply frequency (almost 4.2 times that of the induction motor) may explain the higher core losses. This was also reflected in the density of core losses. For the induction motor, the specific magnitude was equal to 2.57 W/kg, while for the PMSM, it was equal to 9.96 W/kg. \begin{table}
\begin{tabular}{c c} \hline \hline
**Load per Nominal (\%)** & **Efficiency \(\eta\) (\%)** \\ \hline
25 & 93.97 \\
50 & 96.78 \\
75 & 97.69 \\
100 & 98.16 \\
125 & 98.23 \\
150 & 98.05 \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Efficiency of the PMSM Under Various Loading Conditions. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Quantity/Symbol** & **Induction Motor** & **PMSM** & **Percentage Difference** \\ \hline Output Power/Pout & 10,000.00 kW & 10,235.00 kW & +2.35\% \\ Electromagnetic Torque/Tout & 189.51 kNm & 198.4124 kNm & +4.70\% \\ Frequency/\(f\) & 60 Hz & 250 Hz & +316.67\% \\ Nominal Phase Current/Tph & 1150.00 A & 1101.94 A & \(-\)4.18\% \\ Power Factor & 0.80 & 0.83 & +3.75 \\ Nominal Speed/n\({}_{\mathrm{m}}\) & 504 rpm & 500 rpm & \(-\)0.79\% \\ Stator Winding Density/\(l_{s}\) & 5.85 A/mm\({}^{2}\) & 2.75 A/mm\({}^{2}\) & \(-\)52.99\% \\ Core Loss Density/Pdcor & 2.57 W/kg & 9.96 W/kg & +287.55\% \\ Copper Losses stator/Pscu & 132.30 kW & 38.083 kW & \(-\)71.21\% \\ Core Losses/Pcor & 50.00 kW & 100.209 kW & +100.42\% \\ Total Mass of Motor/\(M_{total}\) & 34,118 kg & 13,088.7 kg & \(-\)61.64\% \\ Total Magnet Mass/\(M_{mag}\) & — & 882 kg & \\ Efficiency/\(\eta\) (\%) & 95.20\% & 98.16\% & +3.11\% \\ \hline \hline \end{tabular}
\end{table} 
Table 8: Comparison of Operational Characteristics between Induction Motor and PMSM. (iii) The performance of the two engines showed a noticeable difference. The efficiency of the PMSM was higher by 3.11%, compared to the equivalent of the induction motor, and mainly quite stable in a large load range that did not depend on the operating conditions and the slip. In contrast, the induction motor performance was highly dependent on its loading conditions, which increased slip and reduced its efficiency (Figure 2). (iv) The mass of the PMSM was 61.64% less than the mass of the induction motor. The masses of the stator core and the rotor for the PMSM were significantly smaller than the induction motor counterparts. This could also be explained by the fact that PMSM had a larger number of poles. The greater number of poles favored the reduction of the length of the zygoma in the stator as the magnetic flux that had to be produced was divided among a greater number of poles.