## 6 Comparison of SHG Characteristics without Magnets and with Ferrite Magnets
\begin{table}
\begin{tabular}{c c c} \hline
**Characteristics** & **SHG without Magnets** & **SHG with Ferrite Magnets** \\ \hline Stator laminated steel weight, kg & 34.2 & 28.0 \\ \hline Rotor laminated steel weight, kg & 15.6 & 17.1 \\ \hline Copper weight of armature winding, kg & 17.8 & 14.7 \\ \hline Copper weight of excitation winding, kg & 2.44 & 2.62 \\ \hline Weight of ferrite magnets, kg & - & 7.88 \\ \hline Weight of structural steel of the rotor sleeve and stator housing, kg & 53.2 & 29.2 \\ \hline Total weight of the active materials and the structural steel, kg & 123.24 & 99.5 \\ \hline Stator laminated steel cost, USD & 34.2 & 28.0 \\ \hline Rotor laminated steel cost, USD & 15.6 & 17.1 \\ \hline Copper cost of armature winding, USD & 124.6 & 102.9 \\ \hline Copper cost of excitation winding, USD & 17.1 & 18.3 \\ \hline Cost of ferrite magnets, USD & - & 145.5 \\ \hline Cost of the structural steel, USD & 53.2 & 29.2 \\ \hline The total cost of the active materials (permanent magnets, copper, electrical steel) & 244.7 & 341.0 \\ and low carbon steel of the stator housing of the rotor sleeve, USD \({}^{*}\) & 152.7 & 128.3 \\ \hline Length of all stacks of the stator laminated steel, mm & 152.7 & 128.3 \\ \hline Length of all laminated stacks plus the axial clearances between them for & 180 & 150 \\ \hline Laminated stator external diameter, mm & 370 & 370 \\ \hline Air gap, mm & 0.88 & 0.91 \\ \hline \end{tabular} \({}^{*}\) Note: when calculating the cost of materials, it is assumed that the price of copper is $? per kilogram; the price of electrical steel and the price of the structural steel are $1 per kilogram; the price of ferrite magnets of Y30H-2 grade is $18.46 per kilogram [38].  
\end{table} 
Table 5: Comparison of the cost and geometric characteristics of the considered configurations. According to the results of comparative analysis of the characteristics of the SHG with ferrite magnets and without magnets, shown in Tables 4 and 5, the following conclusions can be drawn:  
1. The average losses for the generator with ferrite magnets have been reduced, in comparison with the generator without magnets, by 100% (5.97 - 4.58)/5.97 = 23.4%;
2. The maximum armature current for the SHG with ferrite magnets is slightly higher than that for the SHG without magnets, by 100%(700 - 676.2)/676.2 = 3.5%. This is due to the fact that the optimization result is a compromise between the minimum losses and the minimum current, and the losses <\(P_{loss}\)> in the objective function (6) have a larger weight coefficient;
3. The output torque ripple at maximum speed for a generator with ferrite magnets is reduced by 100% (11.3 - 8.6)/11.3 = 23.9% compared to a generator without magnets;
4. Due to the addition of ferrite magnets, the length of the magnetic core of the generator, taking into account the axial clearance for installing excitation coils, can be reduced by 100% (180 - 150)/150 = 16.7%;
5. Due to the contribution of the ferrite magnets to the resulting excitation flux, the MMF of the excitation winding can be reduced; in addition, the MMF generated by the excitation winding and the magnets in the non-laminated parts are opposite. All of these factors make it possible to significantly reduce the cross-section of non-laminated parts and reduce their weight by about two times;
6. When adding ferrite magnets, the total mass of the materials of the electromagnetic core of the generator is reduced by 100% (123.24 - 99.5)/23.24 = 19.3%;
7. An SHM without magnets allows the control technique in which the current ratio is equal throughout the entire constant mechanical power speed range (CPSR). In an SHM with (ferrite) magnets, the magnets' contribution in the machine excitation does not reduce at high speed. Therefore, the excitation current must decrease more rapidly than armature current does with an increase of speed. In the considered SHG with ferrite magnets, the current ratio at 3450 rms is 1.5 times less than that at 750 rpm;
8.