Design, optimization and development of electric machine for traction application in GM battery electric vehicle

This paper presents the design optimization, development and performance details of the Chevrolet Spark battery electric vehicle (BEV) traction electric machine. The propulsion system has one electric machine inside an oild cooled drive unit operating as a motor or generator depending on the drive cycle demand. The machine is permanent magnet AC synchronous machine type with the magnets buried inside the rotor. Details of the motor design, such as; winding selection, efficiency optimization for given drive cycles and rotor geometry optimization are discussed. Absence of an engine and sound it brings to a conventional vehicle can underscore any noise from the drive unit in the battery electric vehicles. Hence, particular attention is given to the NVH performance and torque ripple optimization in this machine. A novel approach to torque ripple minimization, by shaping the rotor surface is presented and its contribution to the NVH characteristics of the motor are discussed in detail. Finally, measurement results of machine efficiency, thermal and NVH performance are presented in the context of the vehicle performance.