Low Torque Ripple Spoke-Type Permanent Magnet Motor for Electric Vehicle

We have designed a rotor for a spoke-type interior permanent magnet synchronous machine (IPMSM) with rare-earth-free permanent magnets (RE-free PM) to lower torque ripple while maintaining reasonable torque. Three kinds of RE-free PMs, SrFe
₁₂
O
₁₉
(SrM ferrite), Nd
₂
Fe
₁₄
B (NdFeB), and low-temperature phase (LTP)-MnBi, were used for the designed rotor to evaluate motor performance at 20°C and 125°C. The proposed motor with LTP-MnBi for the rotor-core magnet and SrM for the flux-directing magnet shows the increased torque by 7.1% and 12.5% at 20°C and 125°C, respectively, and decreased torque ripple by 50% and 62.9% at 20°C and 125°C, respectively, as compared to the conventional rotor. According to the demagnetization analysis, the proposed motor is far less vulnerable to irreversible demagnetization than the conventional motor. This work opens a new avenue in the design of rare-earth-free permanent magnet synchronous motor for electric vehicle applications.