Optimal Rotor Design for Reducing Electromagnetic Force Harmonics in Wound Field Synchronous Motor for EV Propulsion

The electromagnetic radial force is the main source of the vibration in wound field synchronous motor (WFSM). When the radial electromagnetic force of a specific harmonic order matches the stator’s natural frequency at any operating point, the vibration acceleration become significant that is so-called resonance. This paper proposes an optimal design process to reduce vibration acceleration through rotor geometry optimization. First, the natural frequency is identified through the modal analysis, and the order of electromagnetic force to be reduced is specified through the comparison with the natural frequency. Finally, an optimal rotor design is performed to reduce the target harmonic components of the radial force. The proposed model is then validated by analyzing the vibration acceleration based on the results of the forced vibration analysis.