## 3 PMSM Design Process  
The design process of an electrical machine usually starts from the constitutive equation given in (15), where S is the apparent motor power in VA, Bm is the magnetic charge, a\({}_{\text{c}}\) is the specific electric charge in A/m, D is the inner diameter of the stator, L is the active length of the motor, k\({}_{\text{w}}\) is the fundamental winding factor, and n is the rated speed in rpm. By initializing the above quantities, except those related to the motor dimensions, product D\({}^{2}\)L is calculated. Then, following common practices, the designer accepts a specific value for the ratio of these two quantities and finally calculates the values of D and L. The problem with this approach is that on the one hand, the directions provided in the various scientific literature are empirical and, on the other hand, they relate to classic modern machines. As there are no guidelines relating to permanent magnet machines and, in particular, those with high-power motors, it was decided to take a different approach in this case. \[\text{S}=11\text{k}_{\text{w}}\text{B}_{\text{m}}\text{a}_{\text{c}}\text{D}^ {2}\text{Ln} \tag{15}\] \begin{table}
\begin{tabular}{c c c} \hline \hline
**Feature** & **SCIM** & **WRIM** \\ \hline Slip Control & Fixed, determined by load & Adjustable via external \\  & & resistance \\ Starting Torque & Moderate & High, tunable via external \\  & & resistance \\ Efficiency & Higher at nominal load & Lower due to rotor \\  & & resistance losses \\ Cooling Requirements & Passive (air/liquid) & Higher due to rotor \\  & & windings \\ Inverter Complexity & High (FOC or DTC) & Lower (simple speed \\  & & control via resistance) \\ Magnetic Field Stability & Moderate & High, tunable via rotor \\  & & resistance \\ Maintenance & Low (no brushes/slip & Higher (requires \\  & rings) & brush/slip ring \\  & & maintenance) \\ Rotor Material & Aluminum or copper bars & Copper windings \\  & & 15–20\% higher due to slip \\  & & construction & rings and external resistors \\ Operational Cost & Lower maintenance, but & Higher due to brush/slip \\  & & ring wear and cooling \\ Maintenance Cost & Minimal (only stator & Higher (slip rings and \\  & & brushes require periodic \\  & & replacement) \\  & & 10–15\% higher lifecycle \\  & & years) with minimal & cost due to frequent \\  & & intervention & maintenance \\ Overall Cost & Lower initial cost, higher & Higher maintenance cost \\  & & inverter cost \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Comparison between SCIMs and WRIMs for 10 MW Ship Propulsion. In the case under study, the design process started by calculating the DL product again, but this time using (16):  
\[\mathrm{E}=\frac{4\pi}{\sqrt{2}}\frac{\mathrm{fN_{s}K_{w}B_{g}\big{(}D-L_{g}\big{)} L}}{2\mathrm{p}} \tag{16}\]  
where \(\mathrm{E}\) is the induced voltage, \(\mathrm{f}\) is the motor supply frequency, \(\mathrm{N_{s}}\) is the number of winding coils per phase, \(\mathrm{B_{g}}\) is the desired average value of the magnetic flux density in the gap, \(\mathrm{L_{g}}\) is the gap length, and \(\mathrm{p}\) is the number of poles of the motor. The number of coils per phase was calculated as a function of the number of stator slots \(\mathrm{Q_{s}}\) and the number of conductors per slot \(\mathrm{n_{s}}\) using Equation (17). Value \(\mathrm{B_{g}}\) requires initialization. In the considered case, this value was set to 0.8 T. At the same time, the induced voltage should be set to equal the phase supply voltage so that during its operation, the motor would absorb the minimum possible current. Therefore, \(\mathrm{E}=U_{ph}=U_{L}/\sqrt{3}\), where \(U_{ph}\) and \(U_{L}\) are the phase and pole voltage, respectively. Having chosen the number of poles, slots of the stator, and the supply frequency and having determined the fundamental winding factor, it was easily understood that there were a large number of possible products \(\mathrm{N_{s}}\)(D-Lg)L that could lead to the desired value for induced voltage.