Loss Minimization and Maximum Torque-Per-Ampere Operation for Variable-Pole Induction Machines

High power density, high efficiency, inexpensive drivetrains operating over a wide torque/speed range are critical for traction applications. An induction machine (IM) offers a cost-effective, rugged, and reliable alternative to permanent magnet solutions. Varying the IM's pole count on-the-fly overcomes the finite inverter voltage constraint and extends the machine's speed range. To date, the operating pole count of variable-pole IMs has been determined based on the operating speed irrespective of the torque requirement, utilizing a high pole count at low speeds and a low pole count at high speeds. This article expands the pole-selection strategy of variable-pole IMs to both torque and speed. The pole count is used to improve the machine efficiency and minimize the stator current over the entire operating torque-speed range. An experimental 36-slot toroidally wound IM driven by an 18-leg inverter validates the proposed pole-selection method for variable-pole IMs. Stator current and machine losses are reduced at partial loading conditions by utilizing lower pole counts rather than selecting the pole with the highest rated torque capability. The average loss reduction by 1/3 and torque-per-ampere improvement of 2x are experimentally achieved at partial loading by using the proposed pole-selection method compared to linking the pole count solely to the operating speed.