Core loss and torque ripple in IPM machines: dedicated modeling and design trade off

The proper combination of stator and rotor slot numbers is pursued in the design of Interior Permanent Magnet (IPM) motors with wide speed range. At high speed, in the flux-weakening region, the arising of the stator and rotor iron losses due to MMF spatial harmonics limits the IPM motor performance. Torque ripple is another problem for this kind of machines, both at low and high speed. The numbers of stator slots and rotor equivalent slots have a major impact on both the loss and ripple aspects. A simplified model is proposed here, in order to evaluate both the problems with a general approach and point out the possible design trade-off. Respect to previous models in the literature, both stator and rotor losses are included, and a more comprehensive approach is followed in the description of the rotor MMF harmonics. The model effectiveness is tested by means of FEA simulations. The proposed approach is useful for the selection of the IPM machine structure according to the specific requirements of the application.