Reluctance Motors (SynRM, SRM, and PM-Assisted)
Reluctance motors are electric motors that produce torque because the rotor tends to align with the lowest-reluctance magnetic path created by the stator.
Main forms
Reluctance is magnetic opposition, loosely comparable to resistance in an electrical circuit. The family name covers machines that share this torque principle but use different rotor geometry, excitation, and control.
- Synchronous reluctance motor (SynRM): a rotating stator field pulls a magnet-free, salient rotor at synchronous speed. Flux barriers create different magnetic reluctance along the rotor axes.
- Switched reluctance motor (SRM): the controller energizes stator phases in sequence so a toothed rotor moves toward successive aligned positions. Its construction can be simple and magnet-free, while torque ripple and acoustic noise require careful design and control.
- Permanent-magnet-assisted reluctance motor: magnets add magnetic flux while rotor saliency also produces reluctance torque. The boundary overlaps with some interior permanent-magnet synchronous motor descriptions. Permanent-Magnet Synchronous Motor (PMSM)
How the terms differ
SynRM and SRM are not interchangeable. A SynRM is supplied with a rotating multiphase field and operates synchronously; an SRM uses position-dependent phase switching around discrete salient poles. A PM-assisted design adds magnets, so it is not a fully magnet-free reluctance motor even when reluctance torque is important.
For rotor designs, control, strengths, and limitations, see Reluctance Motors.