Rotor Fatigue Life Calculation Using Constant-Amplitude Load Cycles for an Interior Permanent Magnet Synchronous Motor

Interior Permanent Magnet Synchronous Motors (IPMSM) are widely used as traction motors today because they can deliver high torque at low speeds, and high efficiency at low- and medium-speed ranges. Air flux barriers and bridges of an IPMSM have contradictory electromagnetic and structural requirements. The rotor undergoes a fluctuating load due to varying speeds in a drive cycle. Designing the rotor with the yield strength as a design criterion might not be sufficient. Fatigue life should be evaluated considering the mean value and amplitude of the fluctuating load profile, and the acceptance criteria should be derived based on field operations. This paper proposes a constant amplitude load cycle as an accelerated fatigue analysis approach for an IPMSM rotor and presents a fatigue analysis workflow considering the thermal and mechanical loads. It also presents the loads and boundary conditions for rotor stress analysis and the effect of elastic and elastic-plastic material properties on stress calculation.