ORNL’s SR motor
One of the ideas pursued at the Oak Ridge National Lab is the synchronous reluctance motor, attractive because it is energy efficient and can be fabricated without the use of rare earth magnets. There were few details available about the SR motor on display — it seemed to be a traction motor for an EV. SR motors have have an equal number of stator and rotor poles. The rotor operates at synchronous speed and there are no current-conducting parts in the rotor, so rotor losses are minimal compared to those of an induction motor. The motors induce non-permanent magnetic poles on the ferromagnetic rotor and generate torque through magnetic reluctance. They deliver high power density but are notorious for having a high torque ripple (the difference between maximum and minimum torque during one revolution) when operated at low speed, and noise that arises because of the torque ripple.
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