Figure 14 shows cogging torque numerical results when movable stator position is at 9.3 and 14.3 deg position measured according to Figure 12. According to the proposed motor design (18-slot 30-pole), the cycles per mechanical revolution [17] of cogging torque components are 90. In order to observe easily, the cogging torque numerical results are shown from 0 to 120 mechanical angle. Hence, one-third of the CPMR can be observed in both Figures 14(a) and 14(b). Back-EMF waveforms are shown in Figure 15, and both movable stator positions are sinusoidal waves. The back-EMF waveform is in red dotted line when the movable stator is at 14.3 deg position with blue line when the movable stator is at 9.3 deg position. Obviously, the red dotted line is higher than the blue line, which means that different movable stator positions can generate different back-EMF waveforms.

Figure 13. Computational results by using ANSYS Maxwell software with phases U, V , and W windings. (a) Flux distribution when the movable stator is at 9.3 deg position measured according to Figure 12. (b) Flux density when the movable stator is at 9.3 deg position measured according to Figure 12. (c) Flux distribution when the movable stator is at 14.3 deg position measured according to Figure 12. (d) Flux density when the movable stator is at 14.3 deg position measured according to Figure 12.

Figure 14. (a) Cogging torque when the movable stator is at 9.3 deg position measured according to Figure 10. (b) Cogging torque when the movable stator is at 14.3 deg position measured according to Figure 10.