CHAPTER

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The name switched reluctance has now become the popular term for this class of electric machine. The first reference to the term switched-reluctance was made by Nasar in a paper in the IEE Proceedings in 1969.

The machines are alternatively known as variable reluctance motors, reflecting the origins of the technology being derived from VR stepper motors.

A reluctance motor can be defined as an electric motor in which torque is produced by the tendency of its moveable part to move to the position where the inductance of the excited winding is maximized.

The earliest recorded switched reluctance motor was the one built by Davidson in Scotland in 1838 and used to propel a locomotive on the Glasgow-Edinburgh railway near Falkirk.

Electrical machine can be broadly classified into two categories on the basis of how they produce torque electro magnetically or variable reluctance.

The performance and inherently low manufacturing cost of the switched reluctance motor make it a vigorous challenger to the ac and dc drives.

There are some disadvantages which still restrict its area of applications and constitute a rich field for research studies.

As control techniques developed, applications of SRMs include:

Application-specific drives: compressors, fans, pumps, centrifuges.Domestic drives: food processors, washing machines.Used as a generator for wind energy conversionGeneral purpose industrial drives.Electric vehicle application.aircraft applications.Servo-drives.

The switched reluctance motor is topologically and electromagnetically identical to the variable reluctance stepper motor. The differences are in the engineering design, in the control method and in the performance and the application characteristics.

Switched reluctance motor VR stepper motor

Normally operated with

shaft position feedback to

synchronize the

commutation of phase

currents with precise

rotor position

Normally runs open loop

with out shaft-position

feedback

Normally designed for

efficient conversion of

powerup to at least

300KW.

Normally designed to

maintain step-integrity

rather than to achieve

efficient power

conversion.

Conventional electric rotating machines (synchronous, induction and d.c machines) have been intensively studied for many years. The design of these machines is, in broad terms, well understood and well documented .

In this approach the inductance parameters at extreme rotor positions are approximated by linear values.It is well represented by the work of Miller , and further papers following his work is by Krishnan .

The phenomenon of saturation in SRM is both inherit and important. It also complex, with both local and bulk saturation effects being in evidence.

When the switched reluctance motor first became widely known in 1960, as mentioned before, the technology was shrouded in mystery. Claims were made for its performance and operating characteristics that seemed hardly believable at the time.