Switched reluctance motor

Unlike brushed DC motors, power is delivered to windings in the stator (case) rather than the rotor.

However it complicates the electrical design, because a switching system must deliver power to the different windings and limit torque ripple.

Industrial motors may have some cost reduction due to the lack of rotor windings or permanent magnets.

Common uses include applications where the rotor must remain stationary for long periods, and in potentially explosive environments such as mining, because no commutation is involved.

The windings in an SRM are electrically isolated from each other, producing higher fault tolerance than induction motors.

The optimal drive waveform is not a pure sinusoid, due to the non-linear torque relative to rotor displacement, and the windings' highly position-dependent inductance.

Rather than using a mechanical commutator to switch the winding current as in traditional motors, the switched-reluctance motor uses an electronic position sensor to determine the angle of the rotor shaft and solid state electronics to switch the stator windings, which enables dynamic control of pulse timing and shaping.

SRM's absence of slip makes it possible to know the rotor position exactly, allowing the motor to be stepped slowly, even to the point of being stopped completely.

It also enables a soft start function in software form, in order to reduce the amount of required hardware.

A capacitor, in either configuration, is used for storing BEMF for re-use and to suppress electrical and acoustic noise by limiting fluctuations in the supply voltage.

[5][11] SRMs are used in some appliances,[12] in linear form for wave energy conversion,[13] magnetic levitation trains,[14] or industrial sewing machines.

Such generators can be run at much higher speeds than conventional types as the armature can be made as one piece of magnetisable material, as a slotted cylinder.