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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

Sleeve Material

  • 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