Electrical generator or motor structure – Dynamoelectric – Rotary
Patent
1994-06-09
1996-08-13
Dougherty, Thomas M.
Electrical generator or motor structure
Dynamoelectric
Rotary
310162, 310166, H02K 1910
Patent
active
055459382
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND TO THE INVENTION
The present invention relates to the general group of doubly salient reluctance machines (DSRMs), including switched reluctance machines (SRMs), also known as variable reluctance machines, stepping motors and hybrid stepping motors producing linear or rotary motion.
Doubly salient reluctance motors have received increasing attention over the past few years, with a large number of publications reviewing their relevant merits with regard to other machine types. The DSRM has been shown to produce a high specific output, despite rather poor utilisation of both the electrical and magnetic circuits, because of the introduction of a magnetic gearing ratio, which arises from the doubly salient nature of the geometry. The magnetic circuit of the machine is poorly utilised because each stator tooth can only be excited to produce positive torque for half of each rotation cycle.
It is to be understood that the term `saliency`, when applied to reluctance machines, implies magnetic saliency, which may or may not involve actual physical saliency.
A doubly salient reluctance machine has a stator and a rotor, both of which exhibit saliency. Magnetic saliency is used here as generally understood in the art, that is, a component of a reluctance machine (either its stator or rotor) is said to be salient if, in operation, changes in the reluctance of the magnetic circuit of the machine occur due to the construction of that component as the relative position of the rotor and the stator changes during operation of the machine.
For example a conventional switched reluctance stepping motor is doubly salient since when a winding in energised and the rotor rotates towards a new position, the main portion of the cross-sectional areas of the active magnetic path in the both rotor and the stator increase and the reluctance of the magnetic circuit decreases due to the construction of both rotor and stator. In operation, energising different windings selects different active magnetic circuits but the topography of a selected circuit varies as the rotor rotates.
A fuller description of switched reluctance motors and their principles and applications can be found in the IEEE Industry Applications Society Tutorial Course Publication "Switched Reluctance Drives" by J. M. Stephenson, S. R. MacMinn and J. R. Hendershot, Jr., as presented on Oct. 12, 1990 at the IEEE IAS Conference In Seattle, Wash. The book "Stepping Motors: a guide to modern theory and practice" by P. P. Acarnley, published by Peter Peregrinus Ltd. on behalf of the Institution of Electrical Engineers, provides an equally useful publication on stepping motors in general.
A related machine which Is not a stepping motor is the synchronous reluctance motor. Such a motor has saliency on the rotor only, the stator being similar to that of an induction motor. A device of this type is disclosed in U.S. Pat. No. 5010267, which describes a variable speed synchronous reluctance machine with a multiphase stator and a rotor divided into segments which constitute flux guides. This machine has a salient rotor, according to the definition of saliency as given above, but the stator has semi-closed slots and is not salient. The topography of the active magnetic path is determined by the flux guides and as the rotor rotates the reluctance of this path changes due to the construction of the rotor only. The stator of the machine of U.S. Pat. No. 5010267 is fully pitched, a fairly common winding arrangement for such machines. Further mention of the significance of fully pitched windings will be made later on in this specification. The specific design of this machine is intended to reduce any effect of mutual inductance between phases as much as possible, as it is recognised that in a machine of this sort mutual inductance will not produce torque which will add to that resulting from the changing self-inductance of each phase.
A further type of related machine is the hybrid stepping motor. Essentially, a permanent magnet provides a component of the magnetic flux in this
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British Technology Group Ltd
Dougherty Thomas M.
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