On-board Direct-Drive Surface Permanent Magnet Synchronous Machine with Fractional-Slot Concentrated Windings for Electric Vehicles

Removal of the gear-box from an existing electric vehicle (EV) power-train incorporating direct-drive topology is expected to improve motor-to-wheel efficiency. Firstly, this paper discusses the need for a novel direct-drive scheme employing a single on-board motor in an EV. Electric machine and drive design targets for such a supermini EV with direct-drive scheme are fixed based on analytical equations, benchmark data obtained from commercially available EV motors, drives, transmissions and literature study. Employing a comprehensive vehicle dynamics model of the supermini EV, machine design targets previously fixed are further refined to yield desired dynamic and steady-state performance of the EV over an urban drive cycle. An on-board direct-drive surface permanent magnet synchronous machine with fractional slot concentrated windings in the stator is designed. The machine's performance is then analyzed using its electromagnetic model in conjunction with maximum-torque-per-ampere control scheme over the entire speed range of the motor. Results from finite element analysis are discussed in detail to show that that the proposed direct-drive scheme in EV is worth studying and the machine designed can be improved in order to obtain efficiency improvement in an EV drivetrain system and hence extend the driving range of EV.