Dynamic Motor Drive Propels Externally Excited Synchronous Motor to even Higher Efficiency

The electrification of the automotive industry is a transition being mandated by regulators and embraced by manufacturers. This electrification has resulted in increased use of electric motors which, in many cases, require rare earth elements. As the demand for these rare earth elements increase, the electrification of the automotive industry will be hindered by increasing cost and supply limitations.

Recent developments in externally excited synchronous motors have resulted in powertrains that do not use rare earth elements and yet are comparable in cycle-average efficiency to industry default motors using internal permanent magnets. Unfortunately, at light loads both wound rotor and internal permanent magnet motors are challenged in providing optimal efficiency.

To address this challenge, Tula has developed Dynamic Motor Drive, a strategy that uses intermittent operation at optimal efficiency to deliver superior performance at low loads. Furthermore, Tula has implemented Dynamic Motor Drive on a production vehicle, demonstrating a reduction of 2.5% in energy consumption with no perceived change in drivability and ride quality. This work details the rare-earth free motor design used, the control methodology, and the energy consumption results of this new motor operation which is now among the most efficient EV powertrains in the industry.