Reluctance motors can have very high power density at low-cost, making them ideal for many applications. Disadvantages are high torque ripple when operated at low speed, and noise caused by torque ripple. Until recently, their use has been limited by the complexity inherent in both designing the motors and controlling them. These challenges are being overcome by advances in the theory, by the use of sophisticated computer design tools, and by the use of low-cost embedded systems for motor control. These control systems are typically based on microcontrollers using control algorithms and real-time computing to tailor drive waveforms according to rotor position and current or voltage feedback.
When a rotor pole is equidistant from the two adjacent stator poles, the rotor pole is said to be in the "fully unaligned position". This is the position of maximum magnetic reluctance for the rotor pole. In the "aligned position", two (or more) rotor poles are fully aligned with two (or more) stator poles, (which means the rotor poles completely face the stator poles) and is a position of minimum reluctance.
When a stator pole is energized, the rotor torque is in the direction that will reduce reluctance. Thus the nearest rotor pole is pulled from the unaligned position into alignment with the stator field (a position of less reluctance). (This is the same effect used by a solenoid, or when picking up ferromagnetic metal with a magnet.) In order to sustain rotation, the stator field must rotate in advance of the rotor poles, thus constantly "pulling" the rotor along. Some motor variants will run on 3-phase AC power (see the synchronous reluctance variant below). Most modern designs are of the switched reluctance type, because electronic commutation gives significant control advantages for motor starting, speed control, and smooth operation (low torque ripple).
Dual-rotor layouts provide more torque at lower price per volume or per mass.
The phase windings in a SRM are electrically isolated from each other, resulting in higher fault tolerance compared to inverter driven AC motors. The optimal drive waveform is not a pure sinusoid, due to the non-linear torque relative to rotor displacement, and the highly position dependent inductance of the stator phase windings.
"Torque Generator Using Full-Pitch Winding Reluctance Motor and Control Unit Therefor" in Patent Application Approval Process
Jan 10, 2013; By a News Reporter-Staff News Editor at Politics & Government Week -- A patent application by the inventors ISHIKAWA, Tomokazu...