Design procedure for brushless PM traction machines for electric vehicle applications

Brushless permanent magnet machines are ideally suited for traction applications, since they are energy efficient and have a high specific torque and a high peak to continuous torque capability. Further, they can be field-weakened to facilitate constant power operation over an extended speed range without compromising the VA rating of the drive. However, they must be design optimised with due regard to their duty cycle, their thermal management, the volt-ampere constraint of the drive and any space envelope constraints. Additionally, the selection of gear-stage ratio and implementation can significantly the complete drive package. A design methodology that accommodates these aspects into the electromagnetic design synthesis process has been developed and employed to design a traction drive for a typical urban electric vehicle. The methodology is general and could be applied to other vehicle formats.