Salient Features for High Speed Motor Design – Part 2
Soft Iron Material
- Eddy current loss occurs in the stator and rotor iron parts
- The high operating speed of motor will cause higher switching frequency. The stator teeth sees high frequency for flux density, leads to higher losses.
- Thinner lamination reduces eddy current loop, enhancing resistance to eddy current. This lowers the eddy current loss
- For magnet with typical mechanical strength, higher speed of rotation of the rotor results in higher centrifugal forces on the rotating magnet
- Need of sleeve (0.3 to 0.5 mm thick) on magnet prevent magnet breakage
- Presence of sleeve leads to
- Increased effective airgap lowers magnet operating point. This increase the need for higher magnet volume for desired flux which increase magnet cost.
- Increased cost due to additional component and assembly complexity.
- High motor speed causes high frequency of flux direction change in sleeve. Hence, increase the eddy current loss in sleeve
- Sleeve material with high resistivity lower the eddy current loss
- Use of high strength MQ1TM magnet can eliminate the need for sleeve