Impact of Mixed Magnets and Their Placement on Traction IPMSM Performance

Interior permanent magnet synchronous motors (IPMSMs) with mixed-magnet configurations that combine rare-earth (RE) and non-rare-earth (NRE) magnets within a rotor offer promising, cost-effective alternatives that reduce RE material dependency. However, when placed alongside magnetically stronger RE magnets, NRE permanent magnets (PMs) are susceptible to a higher risk of demagnetization, often making it an inadequate approach for traction motors. To address this issue, this paper proposes double layer V-type mixed-magnet IPMSM variants that avoid direct physical contact between RE and NRE PMs and eliminate the risk of demagnetization using a comparative analysis of electromagnetic performances. With a focus on balancing torque production, torque ripple, and magnetic stability, the study explores different PMs and their placements and provides a general approach for selecting optimal RE-to-NRE PM ratios for mixed-magnet designs. Effects of PM length, thickness, and location on machine performance are examined with maximum average torque with minimal ripple at peak operating conditions at the base speed of each valid design combination through parametric analysis using three different rotor modifications. Lastly, torque-ripple trade-off charts and performance metrics are used to compare and identify the best configuration and PM mass ratio.