Design Optimization of a Surface-Mounted Permanent-Magnet Motor With Concentrated Windings for Electric Vehicle Applications

This paper describes design techniques for electric vehicle (EV) traction machines to achieve high efficiency against a defined driving cycle such as the New European Drive Cycle (NEDC) while satisfying the required torque-speed operating range. A fractional-slot concentrated-winding (FSCW) surface-mounted permanent-magnet (SPM) machine has been identified as a suitable candidate for EV applications due to its high power/torque density, high efficiency, and good flux-weakening capability compared with other competing machine topologies. Based on the vehicle characteristics and the reference driving cycle, the motor specifications are established, and the design constraints for the SPM machine to satisfy the peak torque and flux-weakening capabilities are derived. Furthermore, the influence of the key parameters, such as slot-pole number combination, machine inductance, axial length, and number of turns, on the machine copper and iron losses over the NEDC is evaluated. Optimizations were carried for these parameters to minimize the total energy losses over the driving cycle. It has been shown that conventional design methodologies that aim to maximize efficiency in the region close to the rated operating condition may lead to less optimal designs and higher energy losses over the NEDC. A prototype motor for a front- and rear-wheel-driven EV has been designed, manufactured, and tested. The experimental results validate the proposed design methodology.