Variable Flux Machines for Hybrid Electric Vehicles

The majority of hybrid electric vehicles and electric vehicles (HEV/EV) products use interior permanent magnet (IPM) synchronous machines for traction purpose due to the efficiency and power density consideration. IPM machines use high energy density rare earth based magnet materials such as neodymium and dysprosium. Variable flux (VF) machines using abundant and cheaper soft magnets such as AlNiCo feature better efficiency at moderate and high speed than IPM machines. Though a number of works have been published to demonstrate the benefits using VF machines versus IPM machines for vehicle application in lab environment, the mathematical modeling, control strategies, and design methodology for VF machines, very little work can be found to prove the reliability of VF machines from a real-world vehicle application point of view. Despite all the advantages of VF machines mentioned above, several major reliability-related application issues need to be solved before VF machines can be adopted for high volume HEV/EV production. In this Phase I STTR project, the potential technical and economic barriers and solutions to apply VF machines to the vehicle traction application will be investigated. Experimental methods will be used to understand the demagnetization and magnetization behavior of various grades of AlNiCo magnets under a wide range of operating temperature, how repeated demagnetization and magnetization process will affect reliability, how to implement online demagnetization and magnetization of the VF machine without interrupting the vehicle operation. A100-kW VF machine will be designed that uses multiple grades of AlNiCo magnets so both high power density and easy control of the demagnetization and magnetization of magnets can be achieved. Additionally, a silicon-carbide based power converter will be designed for the proposed VF machine. Finally, a cost analysis for a VF machine and drive system will be developed, a reliable supplier and manufacturer chain will be assembled to prepare for the 100-kW VF machine prototype construction in Phase II, and the proposed technology and research results will be disseminated to automotive OEMs.