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HOME / Applications / Cogging Torque reduction in Surface-Mounted Permanent Magnet Motors

Permanent Magnet Synchronous machines (PMSMs) are widely used in traction applications and electric vehicles, where steady-state operation, high efficiency, and torque density are needed, such as Toyota Prius, etc.

In this application note, the cogging torque of a Surface-Mounted PMSM in [1] is computed and validated using EMWorks2D software inside SOLIDWORKS. Figure 1 illustrates a 2D model of the studied motor designed using SOLIDWORKS. Then, the impact of PMs’ segmentation on the cogging torque is investigated using the “multi-configuration” feature of SOLIDWORKS.

**Magnetic field mappings of the original PMSM: **The magnetic field mapping of the original surface mounted PMSM motor is simulated for an initial angular position of 0 degrees using EMWorks2D inside SOLIDWORKS, as presented in Figure 2.

Considering the above figures, one can notice that the magnetic field is maximum when the stator tooth is facing the totality of the pole.

**Cogging torque of the original PMSM: **The cogging torque versus the angle position of the angle over one period is computed using EMWorks2D inside SOLIDWORKS. This result has been validated, as shown in Figure 4.

The cogging torque of the original PMSM has a peak-to-peak value of 5.58N.m and an average value of -0.0185N.m.

Two case studies were performed to investigate the impact of magnet segmentation on no-load torque, using EMWorks2D inside SOLIDWORKS, where the PMs are first segmented into two then three blocks each, as indicated in Figure 5.

Magnetic field mappings of the segmented PMSMs:The magnetic field mappings of the PMSMs having one and two segmentations of the PMs are illustrated in Figures 6 and 7, respectively.

Cogging torque of the segmented PMSMs:The cogging torque is computed using EMWorks2D for different segmentation cases, as shown in Figure 8. To better highlight, the effect of the PMs’ segmentation on the cogging torque, its peak-to-peak, and average values are given in table 1.

Cogging torque |
1 PM per pole | 2 PMs per pole | 3 PMs per pole |

Peak-to-peak value (N.m) | 5.4629 | 3.355 | 3.99478 |

Average value (N.m) | 0.01486 | 0.011802 | 0.029759 |

Considering table 1, one can deduce that the average value of the cogging torque is almost null. The differences between the three configurations could be explained by computation errors.

Considering the second configuration with 2 PMs per pole, the peak-to-peak value of the cogging torque is significantly reduced. Whereas, it has slightly increased for the third configurations.

The magnet segmentation technique can be used to reduce the peak-to-peak value of the cogging torque, as can be seen in Table 1. However, this technique can possibly lead to its increase instead of decreasing it, if performed randomly. Therefore, an optimization of the segmentation angle is needed to minimize the cogging torque peak-to-peak value.

[1] A. Frikha, “Contribution to the Multiphysics Modelling of Permanent Magnet Synchronous Machines”, Master Thesis, National Engineering School of Sfax, Tunisia, 2019.