Design considerations for permanent magnet machine drives for direct-drive electric vehicles

Understanding the need for improvement in efficiency of an electric vehicle drivetrain system, this paper exclusively discusses various design aspects of a permanent magnet machine drive for direct-drive electric vehicles (EV). Firstly, the motivation to employ a direct-drive configuration in EV is discussed. Thereafter, initial electric machine rating design considerations for a typical Supermini or B-segment EV employing a direct-drive configuration is discussed. Furthermore, employing an existing stator, investigations are performed through analytical equations and designed machines to understand different permanent magnet machine design aspects with regards to selection of: number of poles, type of permanent magnet rotor, stator winding configuration and number of phases. The study performed here will assist in providing decision points on various structural design indices of the machine before venturing into the FEA based permanent magnet machine design and assessment for the direct-drive EV application.