Design Optimization and Comparison of PM-Assisted Synchronous Reluctance Machine using Different Magnet Combinations

The aim of this paper is to introduce motor topologies that combine different types of Permanent Magnets (PM) in order to reduce the expensive rare-earth PM content while maintaining the torque capability equivalent to the Chevy-Bolt traction motor, taken here as the baseline design, at a minimum risk of permanent demagnetization of magnets. For this purpose, five different magnet combinations are proposed, namely - (i) NdFeB and Ferrite, (ii) NdFeB and Iron-Nitride, (iii) Dysprosium (Dy) Free NdFeB and Ferrite, (iv) DyFree NdFeB and Iron-Nitride, and (v) Iron-Nitride and Ferrite. A Permanent Magnet assisted Synchronous Reluctance Machine (PMASynRM) utilizing each magnet combination is subjected to a multi-objective design optimization process to achieve the goal without pushing the magnets towards permanent demagnetization. The optimization results are obtained at 4 different speed operating points in order to cover the required torque-speed range. A detailed analysis of various performance characteristics of the best designs obtained from the optimization process of each magnet combination, in addition to their quantitative comparison is presented to highlight the various tradeoffs. All designs share the same stator and number of poles and the focus is on rotor designs with three layers of permanent magnets. A mechanical stress analysis is also conducted to optimize the rotor stress and ensure its structural integrity.