Magnetic Circuit Analysis/ IPM Motor

This section introduces the example of analysis applying rare earth magnets to IPM motors, which are motors with magnets embedded in them. Figure (a) shows the motor structure that is the subject of the analysis. The analysis used the integral element method to calculate the motor torque when 5A flowed through the stator. Figure (b) shows a comparison of the analysis results and the actual measured torque. As can be seen from the figure, the analysis values and the actually measured values match well.

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Figure (a) Motor structure

Figure (b) Comparison of the analysis results and the actual measured torque

Reference Literature:
K. Miyata and K. Ohashi, "Motor Simulation on IPM Motor", 16th International Workshop on Rare-Earth Magnets and their Applications, pp1031-1037 (2000)

Even for IPM motors, reducing the cogging torque and torque ripple are important themes for investigation. As measures for dealing with cogging torque and torque ripple, the effect of rotor skew was analyzed.

Figure (a) shows the structure without skew and Figure (b) shows the figure with the rotor skewed 7.5 degrees. The torque ripple and cogging torque with current of 5 A and current advance phase angle of 30 degrees were calculated. The results are shown in the figure below.

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Figure (a) Non-skew model

Figure (b) Skew model

Figure (c) Cogging torque of non-skew model

Figure (d) Cogging torque of skew model

For the structure without skew in Figure (a), the torque ripple is quite large, about 35% of the average drive torque and the cogging torque is also 7% of the average drive torque.
On the other hand, when the rotor is skewed as in Figure (b), the torque ripple and cogging torque are reduced more than 60%. Also, the reduction ratio for the average torque is a mere 1% or so. The analysis shows that skewing the rotor is extremely effective for reducing torque ripple and cogging torque.

Reference Literature:
K. Miyata and K. Ohashi, "Motor Simulation on IPM Motor", 16th International Workshop on Rare-Earth Magnets and their Applications, pp1031-1037 (2000)