SRMs

SRMs stands for reluctance-based electric machines and refers to two main families that generate torque primarily from magnetic reluctance rather than from permanent magnets. The two principal types are Switched Reluctance Motors (SRMs) and Synchronous Reluctance Motors (SynRMs). Both rely on rotor saliency—the variation of magnetic reluctance with rotor position—to produce torque as the rotor tends to align with the stator field.

Switched Reluctance Motors have a simple, robust rotor with salient poles and stator windings that are energized in a predetermined sequence. Control is typically achieved with position feedback and electronic commutation, which allows torque to be developed without magnets. Benefits include low rotor copper loss, potential for high overload capability, and reduced magnet material costs. Drawbacks commonly include torque ripple and acoustic noise, and a drive system that requires careful control design and reliable rotor position sensing.

Synchronous Reluctance Motors use a salient-geometry rotor without magnets and operate synchronously with the stator magnetic field. They aim to maximize reluctance torque while providing smooth torque and good efficiency. SynRMs offer high efficiency and favorable thermal and power-density characteristics, making them attractive for variable-speed applications. Control strategies often involve advanced vector control or direct torque control, and rotor position sensing or sensorless techniques are employed to ensure precise synchronization.

Compared with magnet-based machines, SRMs and SynRMs avoid permanent magnets, reducing material risk and supply-chain exposure while delivering competitive efficiency in many operating ranges. Typical applications include industrial drives, pumps, fans, and HVAC equipment, with increasing adoption in automotive traction and other energy-efficient systems as control methods and power electronics advance.