Optimal Bore Diameter for Power Dense Traction Motor

The sine-wave permanent magnet brushless machine (PMSM) and Induction machine (IM) are the favorite motor types for traction applications. Modern permanent magnets (PM) are produced only in a few countries, and PM motors have higher efficiency. However, IM offers a robust, mature, rare-earth-material-free, and cost-effective. This study investigates the possibility of increasing IM efficiency by choosing an optimal bore diameter to reduce copper loss. Optimal bore diameter ensures that the motor operates at flux density levels that maintain a high power factor and give the possibility of increasing stator and rotor slot area to reduce copper loss. The investigation here is based on an experimentally verified FE model of the motor. This study illustrates that the rotor copper loss can be reduced by 25% with the choice of optimal bore diameter at rated voltage and frequency. A further 1% copper loss reduction is possible by introducing a sleeve over the stator slots to reduce air gap harmonics and, thus, surface losses on the rotor side.