Variable-Pole Induction Machine Drive for Electric Vehicles

High power density, high efficiency, and inexpensive drivetrains operating over wide speed and torque ranges are critical for electric vehicles (EVs). The induction machine (IM) offers a cost-effective and reliable alternative to permanent magnet-based solutions. A fixed pole IM's high torque requirement at low speed sacrifices its performance at partial loads and high speeds. A variable-pole IM has an additional degree of freedom which is the pole count. This paper uses a variable pole count to improve IM performance over a wide torque and speed range. An approach to select the best pole configuration for a given operation strategy is presented. For illustration, a maximum torque per ampere (MTPA) strategy is used on a 36-slot toroidally wound IM. Variable-pole operation increases the torque capability of the machine and enlarges its high efficiency region to a wide speed range. The analytical results provide guidelines for designing and operating a variable-pole machine tailored for this application.