Overview of Electric Vehicle Machines - From Tesla to Tesla, and Beyond

Starting from the rotating magnetic field theory developed by Nikola Tesla in 1882, the induction machine has become the most popular electric machine for over a century. Actually, the Tesla's AC Induction Motor is dubbed one of the ten greatest discoveries of all time. This popularity has been extended to the latest Tesla Motors which has set a new world speed record for production electric vehicles (EVs). Meanwhile, the permanent-magnet (PM) brushless machines are superseding the induction machine because of their high efficiency and high power density. In order to fulfill the ever increasing demand on electric propulsion, innovation of electric machines accelerates. For instance, the stator-PM machines combine the merits of both PM brushless and switched-reluctance machines to offer energy-efficient robust operation; the vernier PM in-wheel machines incorporate the vernier effect into the PM brushless machines to provide low-speed high-torque direct-drive operation; and the advanced magnetless machines adopt innovative topologies to compensate the reduction of torque and power densities due to the absence of PM material. Increasingly, the development of electric machines has been expanded to incorporate the heat engine for hybrid propulsion. Rather than using the planetary-geared machine system to perform power split for electronic continuously variable transmission (ECVT), the double-rotor machine system is developed to achieve gearless ECVT, and the magnetic-geared machine system is proposed to achieve ECVT without physical gearing or brushes. In this paper, various electric machines and machine systems for electric and hybrid vehicles will be discussed, with emphasis on the challenges and opportunities of those emerging machine topologies.