High Saliency Ratio Segmented Rotor Wound Field Synchronous Machine for Traction Applications

Wound Field Synchronous Machines present an attractive alternative to PMSMs in EV traction applications as they do not require expensive rare-earth magnets for rotor excitation. However, in high torque density designs, the saliency ratio of these machines tend to be poor due to the increased field excitation, which translates to saturation along the rotor d-axis. Therefore, the contribution of reluctance torque is small at rated torque, and the copper losses on the rotor field are high, which leads to higher cost and thermal issues. In this paper, a high saliency ratio segmented rotor wound field synchronous machine is presented with high reluctance torque, low copper loss, and low rotor mass. Details on the rotor design and optimization are presented, along with the structural analysis at the maximum speed. A detailed comparison of the proposed rotor to an optimized conventional rotor is provided. Drive cycle-based analysis has been used to demonstrate the suitability of the proposed design in EV traction applications.