Demagnetization prevention using optimization of PM machine operation with integrated multi speed transmission.

This paper presents a comprehensive methodology for optimizing electric bike powertrains to address the operational challenges of permanent magnet (PM) machines in electric vehicles (EVs), particularly under wide speed ranges and high-temperature conditions that can induce irreversible demagnetization. To mitigate risks in the field weakening region, a multi-speed transmission (MST) system is proposed to confine the machine's operation to targeted speed and torque intervals. The PM machine's design parameters and transmission gear ratios are jointly optimized to minimize demagnetization risk across all driving scenarios. Comparative analysis indicates that the adoption of multi-speed transmission architecture significantly enhances system reliability by reducing the time spent in the field weakening region from 57 to 10%. Furthermore, energy assessments based on the WLTP Class 3 drive cycle demonstrate that any additional losses due to gearbox weight depend on the drive cycle and driver behavior. This study delivers a holistic solution to prolong the service life and economic viability of PM machines in EV applications by leveraging advanced powertrain design to suppress demagnetization phenomena.