Reluctance motor

A reluctance motor is an electric motor that induces non-permanent magnetic poles on a ferromagnetic rotor which carries no windings, and it produces torque through magnetic reluctance. Its subtypes include synchronous, variable, switched and variable stepping designs. The stator has several salient electromagnet poles like a wound-field brushed DC motor, and the rotor is made of soft magnetic material such as laminated silicon steel with salient poles of its own. Reluctance motors can offer high power density at low cost, but they show torque ripple at low speed, and the resulting noise. Their use was limited until the early twenty-first century by the difficulty of designing and controlling them, which advances in theory, computer design tools and low-cost embedded control then overcame.