Design and Comparison of Power-Dense Surface Inset Permanent Magnet Machine and Surface Permanent Magnet Machine without Heavy Rare Earth Magnets for Traction Applications

This paper presents two machine designs: a surface inset permanent magnet (SIPM) machine and a surface permanent magnet (SPM) machine, both without heavy rare-earth magnets, that achieve 50 kW/L active power density and a constant-power speed ratio of 3 for EV traction applications. Compared to SPM machines, SIPM machines do not require a special containment sleeve to hold the magnets in place at high speeds, provided that the rotor laminations are carefully designed together with the magnet mounting configuration to ensure the rotor's structural integrity. Comparisons between the SPM and SIPM machines sharing the same stator, same current level, and same power speed envelope are presented. Both deliver very similar performance characteristics, but the SIPM machine's simpler magnet containment configuration may give it an advantage in terms of reduced use of material and manufacturing costs. Testing of the SIPM machine shows good agreement with FEA-predicted performance. Measured back EMF is within 3% difference from the FEA predicted performance. The difference between the measured and FEA-predicted torque values is usually less than 5%. Thermal testing is conducted to evaluate the steady-state performance of the machine under various current levels. The results confirm that effective cooling is achieved, supporting the machine's reliability in continuous operation.