The guiding principle behind the SRM drive is that when a magnetically salient rotor is subject to the flow of flux in the magnetic circuit, it tends to move toward the position of minimum reluctance. This phenomenon has been known ever
since the first experiments on electromagnetism. In the first half of the 19th century, scientists all over the world were experimenting with this effect to produce continuous electrical motion. A breakthrough came from W. H. Taylor in 1838, who obtained a patent for an electromagnetic engine in the United States. This machine was composed of a wooden wheel on the surface, on which was mounted seven pieces of soft iron equally spaced around the periphery. The wheel rotated freely in the framework in which four electromagnets were mounted. These magnets were connected to a battery through a mechanical switching arrangement on the shaft of the wheel such that excitation of an electromagnet would attract the nearest piece of soft iron, turning the wheel and energizing the next electromagnet in the sequence to continue the motion. However, the torque pulsations were the main drawback of this machine compared to DC and AC machines.

Improvement was noticed with the introduction of electronic parts that replaced the mechanical arrangements.

The trend moved toward reducing the mechanical arrangements and parts while increasing the electronic parts. Improved magnetic material and advances in machine design have brought the SRM into the variable-speed drive market. Presently demand for SRMs is increasing as they offer superior performance with lower price. Other than simplicity and low-cost machine manufacturing, the main motivation toward SRM use is the availability of low-cost power electronic switches, control electronic components, integrated circuits (ICs), microcontrollers, microprocessors, and digital signal processors (DSPs).

In the present global scenario,

SRM drives are one of the major emerging technologies in the field of adjustable-speed drives. They have many advantages in terms of machine efficiency, power density, torque density, weight, volume, robustness, and operational flexibility. SRM drives are finding applications in general-purpose industrial drives, traction, devices domestic appliances, and office and business equipment. The emerging markets in consumer and industrial products are very cost sensitive as well as demand high reliability and performance, equivalent to DC and induction motor drives.

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