## 4 FEM Verification and Analysis
### Comparative Analysis with Six-Phase CSW-6/2-BPMSM  
To verify the performance advantages of the six-phase DSW-12/2-BPMSM in terms of the amplitude and fluctuation of electromagnetic torque and radial magnetic levitation force waveforms, as well as the electromagnetic coupling rate between them, a detailed comparison was conducted with a six-phase centralized-winding BPMSM with 6 slots and 2 poles (six-phase CSW-6/2-BPMSM), which is frequently used in the field of low power. Since the slot number of the six-phase CSW-6/2-BPMSM is half of that of the six-phase DSW-12/2-BPMSM, the number of turns for each tooth coil in the CSW-6/2-BPMSM was set to twice that of the six-phase DSW-12/2-BPMSM. The selected slot type is a flat-bottomed groove with a larger area, and the other parameters are the same as those of the six-phase DSW-12/2-BPMSM. In the case of zero radial displacement, Figure 13 gives the dynamic waveforms of the torque and radial magnetic levitation force in the \(y\)-axis direction when a 4.5 A torque current and a 1.0 A levitation current are applied to the stator winding of the six-phase CSW-6/2-BPMSM. Based on Figure 13, combined with Figures 6-9, the following comparison result were obtained:  
(1) When a 4.5 A torque current is applied, the average torque of the six-phase CSW-6/2-BPMSM is 0.7351 N\(\cdot\)m, and the peak-to-peak fluctuation rate is about 13.72%, while the average torque of the six-phase DSW-12/2-BPMSM is 0.9503 N\(\cdot\)m, and the peak-to-peak fluctuation rate is about 6.73% (refer to Figure 6). Thus, compared with the commonly used six-phase CSW-6/2-BPMSM, the generated torque of the six-phase DSW-12/2-BPMSM increased by 0.2152 N\(\cdot\)m, i.e., the steady-state torque generated by the unit torque current of the six-phase DSW-12/2-BPMSM increased by 0.0478 N\(\cdot\)m (about 22.63%). At the same time, the torque pulsation rate was reduced by about 6.99%. (2) When a 1.0A levitation current is fed, the average value of the radial magnetic levitation force of the six-phase CSW-6/2-BPMSM is 30.5838 N, and the peak-to-peak fluctuation rate of the magnetic levitation force waveform is about 28.2%. Meanwhile, the average value of the radial magnetic levitation force of the six-phase DSW-12/2-BPMSM is 28.8302 N, and the peak-to-peak fluctuation rate is about 14.58% (refer to Figure 8). Therefore, compared with the commonly used six-phase CSW-6/2-BPMSM, the average value of the magnetic levitation force per unit of levitation current of the six-phase DSW-12/2-BPMSM reduced by 1.7536N (about 5.73%). However, the main advantage of the six-phase DSW-12/2-BPMSM is that the peak-to-peak pulsation rate of the radial magnetic levitation force is about 28.2%. Figure 13: Torque and magnetic levitation force waveforms of the six-phase CSW-6/2-BPMSM used for comparison. levitation force is reduced by about 13.62%, which is more conducive to the stable levitation control of the bearingslest rotor. In order to verify the electromagnetic coupling situation inside the six-phase DSW-12/2-BPMSM, the levitation current was kept at 1A, and the torque current was set to vary in the range of zero to 6A. Figures 14 and 15 show the dynamic waveforms of the magnetic levitation force of the six-phase CSW-6/2-BPMSM and the six-phase DSW-12/2-BPMSM, respectively. Under the same excitation conditions, including zero eccentric displacement, 4.5 A torque current, and 1 A levitation current, Figure 16 shows a comprehensive numerical comparison between the six-phase DSW-12/2-BPMSM and the six-phase CSW-6/2-BPMSM in terms of electromagnetic torque, radial magnetic levitation force, coupling degree, etc. Here, Figure 16a gives the numerical comparison chart of steady-state torque and radial magnetic levitation force, and Figure 16b gives the numerical comparison charts of the peak-to-peak fluctuation rate for torque and radial magnetic levitation force and that of the coupling degree of the torque current to the magnetic levitation force.