## 6 Discussion  
A comparative analysis between permanent magnet synchronous motors (PMSMs) and induction motors (IMs) revealed critical insights into their suitability for ship electrification applications. The study demonstrates that PMSMs offer significant advantages in terms of efficiency, power density, and reduced current requirements, which are crucial for applications with high-energy demands and constrained space, such as maritime propulsion. Specifically, PMSMs exhibit approximately 3.11% higher efficiency compared to IMs, \begin{table}
\begin{tabular}{c c c} \hline \hline
**Parameter** & **Induction Motor** & **PMSM** \\ \hline Initial Cost & Lower & High (\(\sim\)30\% higher than IM) \\ Efficiency & 93–95\% & 97–98\% \\ Maintenance Cost & Higher & Lower (\(\sim\)30\% less) \\ Cooling System & Simpler and cost-effective & Complex and costly \\ Control System & Simpler, lower cost & Advanced, expensive \\ Lifespan & 15–20 years & 20–25 years \\ Total Lifecycle Cost & Higher due to energy & \\  & losses & Lower long-term costs \\ Payback Period & — & \(\sim\)7 years (Based on fuel and \\  & — & maintenance savings) \\ \hline \hline \end{tabular}
\end{table} 
Table 9: Comparison of Selection Criteria between Induction Motor and PMSM. largely due to lower copper losses, which translate to less heat generation and improved thermal performance. This not only supports better system reliability but also extends the lifespan of motor components, especially the insulation in windings, which is highly susceptible to thermal degradation. On the other hand, IMs, while exhibiting lower efficiency and higher mass, operate at a lower frequency, which limits core losses in the stator and rotor. This characteristic is particularly beneficial in settings where efficiency is less of a concern and the initial cost and maintenance simplicity take priority. However, for advanced electric propulsion systems, PMSMs appear to be the superior choice, given their higher performance, especially when efficiency, weight reduction, and fuel savings are critical factors. Our comparative analysis highlighted several key factors relevant to ship electrification. PMSMs, with their higher efficiency and power density, are particularly suited for applications where weight and space are critical constraints. However, their increased core losses at high frequencies necessitate advanced cooling strategies to ensure long-term reliability. On the other hand, IMs offer a proven and cost-effective solution with lower core losses and simpler cooling requirements, making them suitable for applications where initial investment costs are a primary concern. Additionally, WRIMs offer benefits in applications where high starting torque and precise slip control are essential. The external rotor resistance adjustment capability provides flexibility in regulating torque and speed, eliminating the need for complex inverter systems. However, this comes at the expense of increased maintenance due to the wear of slip rings and brushes, as well as higher rotor copper losses. Our FEM-based sensitivity analysis revealed that fine-tuning the rotor slot depth and stator design can improve WRIM efficiency by up to 94.5%, but this remains slightly lower than PMSMs due to additional slip ring losses. Moreover, WRIMs are heavier due to the presence of additional rotor components, increasing the mass by 10-12% compared to PMSMs, while SCIMs remain the lightest among the three configurations. PMSMs benefit from higher power density and reduced volume, which is advantageous in marine applications where spatial constraints are critical. However, the high-frequency operation of PMSMs leads to elevated core losses, necessitating advanced cooling solutions. Furthermore, the high-frequency operation of PMSMs introduces electromagnetic interference (EMI) challenges that require careful system integration within the ship's electrical infrastructure.