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, $\text{SrFe}_{12}\mathrm{O}_{19}$ (SrM ferrite), $\text{Nd}_{2}\text{Fe}_{14}\mathrm{B}$ (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.