Design and Performance of Electrical Propulsion System of Extended Range Electric Vehicle (EREV) Chevrolet Volt

This paper presents the design and performance details of the Chevrolet Volt electric propulsion system. The propulsion system has two machines: One machine is operating mostly as a motor while the other machine is operating mostly as a generator. Both machines of the Volt electric drive system are permanent-magnet ac synchronous machine types with the magnets buried inside the rotor. The motor has distributed windings. However, as opposed to a conventional stranded winding, the Chevrolet Volt motor has bar-wound construction to improve the motor performance, particularly in the low to medium speed range. At higher speed, the skin and proximity effects in the stator bars lead to increased stator winding losses but are addressed in the design. The bar-wound construction also has excellent thermal performance, in both the steady-state and transient conditions, necessary for full electric vehicle (EV) driving. The generator uses concentrated windings. The concentrated winding construction has good slot fill and short end-turn length. These features resulted in good performance in the intended operational region and were an enabler for machine packaging inside the transmission. Both the machines exhibit excellent efficiency and exceptionally smooth and quiet operation. The machine design and construction details, as well as the measured thermal, electromagnetic, and acoustic noise performances, are presented in this paper.