University of Leicester

Department of Engineering

Department of Engineering

Centre for Advanced Electronically Controlled Drives

This centre and these projects have mostly moved to the Company Technelec Ltd,[Globe Graphic] that was set up
by Professor Pollock to exploit this technology



1.1 History of the Switched Reluctance Motor

The reluctance motor operates on the principle that a magnetically salient rotor is free to move to a position of minimum reluctance to the flow of flux in a magnetic circuit.  The phenomena 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.  In 1838, W. H. Taylor obtained a patent for an electromagnetic engine  in the United States and subsequently on 2nd May 1840 he was granted a patent [1] in England for the same engine.  The engine was composed of a wooden wheel on the surface of which were mounted seven pieces of soft iron equally spaced around the periphery.  The wheel rotated freely in a framework in which four electromagnets were mounted.  The electromagnets 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 energising the next electromagnet in the sequence to continue the motion.  However  this motor and other subsequent inventions all suffered from torque pulsations and were soon superseded by the invention of the d.c. machine and the a.c. induction machine.

Over 140 years after these early experiments, the advent of suitable power electronic switches has meant that the mechanical commutator of the early reluctance motors can be replaced by an electronic one.  Improved magnetic materials and advances in machine design have brought the switched reluctance motor into the variable speed drive market [2,3].  The simple brushless construction of the motor makes it cheap to build and very reliable in operation.  The unipolar current requirements of the phase windings results in a simple and very reliable power converter circuit.

In this tutorial Prof. Pollock will explain why research is now focusing on switched reluctance motors and drives with only one or two phase windings so that applications for the technology are being created in low cost, high volume markets such as domestic appliances, heating ventilation and air conditioning and automotive auxiliaries.  The tutorial will go on to show that through innovative design, new classes of electronically controlled motors have been invented which have an exciting future in the cost competitive world of high volume manufacturing.

Whilst the initial thrust of most of the current research is into these high volume applications the next ten years will see a dramatic increase in the number of switched reluctance drives and they will also start to be employed in more routine applications including the marine industry.  With a current trend in the variable speed drive market to package motors with electronics there is a tremendous opportunity for switched reluctance technology to be used in place of other electronically controlled motors since it will almost always be able to offer superior performance at a lower price.




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Author: Ewan Goodier, last updated 17/10/2000.
This document has been approved by the Head of Department.