Automated Testing of Rotor Faults in Wound Field Synchronous Motors for EV Applications

Wound field synchronous motors (WFSM) are being considered as a viable alternative to permanent magnet synchronous motors (PMSM) by leading electric vehicle (EV) manufacturers. With WFSMs, the risk related to the instability of rare-earth PM supply can be averted, and it is possible to improve the motor performance across a wide operating range with flexible control of the rotor field. However, reliability concerns arise from harsh operating conditions with fluctuating load and speed. Given the historical predominance of PMSMs in EVs, industry lacks experience with WFSM rotor testing and failure analysis. In this paper, a new concept for automated detection of WFSM rotor faults such as field winding turn faults and eccentricity is proposed. The main idea is to use the dc-dc converter available for field control, as the test equipment for detecting rotor faults, whenever the EV is stopped. The change in the field winding impedance under optimal excitation conditions is used for detection and classification of field winding turn faults and eccentricity. An experimental study on 20 and 30 kVA WFSMs shows that the proposed method can provide automated detection and classification of WFSM rotor faults using existing hardware.