Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
2000-04-18
2002-04-23
Mullins, Burton S. (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C310S154020, C310S154210, C310S154430, C310S154450, C310S168000, C310S012060, C318S701000
Reexamination Certificate
active
06376957
ABSTRACT:
TECHNICAL FIELD
This invention relates to alternating current machines such as motors and generators.
BACKGROUND OF THE INVENTION
A paper entitled “New permanent magnet excited synchronous machine with high efficiency at low speeds” by Weh. H; Hoffmann. H and Landreth. J, Technische Universitat Braunschweig, Germany presented at the International Conference on Electrical Machines; Pisa 1988 describes a transverse flux arrangement which offered specific torque values much higher than the traditional radial flux configuration. The transverse flux machines disclosed are excited by permanent magnets which are mounted in alternating order upon the flux-guiding iron elements of the rotor. The magnets and the flux-guiding elements are arranged in a circumferential array around the periphery of the rotor, that circumferential array being arranged to rotate between pairs of axially spaced windings which are mounted in the stator. In order to reduce the influence of the stray flux, the rotor has to be made of non-magnetic material in the pole region except for the active parts of the magnetic circuit.
The transverse flux configuration combines a permanent magnet system with pole number 2p (i.e. wavenumber p) with an iron circuit which provides a special distribution of reluctance which also has a wavenumber p. The flux generated, being the product of magnetomotive force (mmf) and reluctance has a prominent zero wavenumber component which is employed as the working flux for energy transfer.
The disclosed transverse flux arrangement has two main drawbacks. Firstly, the flux component with wavenumber zero pulsates and so the generated torque also pulsates. This calls for at least two machine elements to be combined on the rotor shaft if a net constant torque is required, which is the case in most applications. Secondly, the construction of the permanent magnet and variable-reluctance elements of the machine is difficult since the flux follows paths which are inherently three-dimensional.
In a known form of alternating current machine which is known as a vernier reluctance machine, excitation is provided by a polyphase ac winding. Both the rotor and the stator have high wavenumber reluctance distributions, there being a difference in wavenumber equal to the wavenumber of the winding.
U.S. Pat. Nos. 5,386,161 and 5,532,531 respectively disclose three-phase permanent magnet stepper or brushless motors wherein the permanent magnets are part of the rotor. The brushless motor disclosed by U.S. Pat. No. 5,532,531 has a circumferential array of electromagnetic poles spaced by a uniform pitch and alternately magnetised. The permanent magnets on the rotor are also alternately magnetised and uniformly spaced with a pitch which is different from the pitch of the spacing of the stator poles.
DE-A-19643791 describes and illustrates a two phase servomotor based on an electronically commutated synchronous motor for relatively high output torque operation, comprising a rotor rotatable within a cylindrical stator with an annular air gap therebetween, the rotor having a circumferential array of teeth projecting towards the stator, and at least one pair of main poles per motor phase carrying working windings, the main pole pairs carrying permanent magnet excitation pole pairs which are mounted on the face of the respective main pole that faces the rotor and which have a pole pair pitch corresponding to the pitch of the rotor teeth, the excitation pole pairs being offset identically with the main poles from one motor phase to the other by
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^
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H
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2
n
and
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^
p
H
=
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z
+
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where
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p
H is the main pole pitch
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z
=tooth pitch
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p
=excitation pole pair pitch
n=phase number
m=integer
EP-A-0373967 discloses an alternating current machine which includes two members of ferromagnetic material which form opposing boundaries of an air gap, one of which is movable relative to the other, one of the members having an armature winding arrangement and permanent magnets mounted on it, the magnets being arranged side by side in a line which follows the respective boundary of the air gap and being arranged to form a certain number of magnetic poles which are alternately north and south poles, the other member comprising a body portion and plurality of spaced projections which project from the body portion towards the one member in a direction which is transverse to the air gap, wherein each magnet is inserted into a respective groove which is formed in the surface of the one member that forms the respective boundary and which extends in a direction transverse to that boundary so that the surface of each magnet that faces the air gap is flush with the surface that forms that boundary.
One object of this invention is to provide novel configurations of alternating current machines which avoid the aforesaid main drawbacks of the disclosed transverse flux arrangement.
One subsidiary object of this invention is to avoid the need for electronic commutation.
Another subsidiary object of this invention is to provide an alternating current machine which offers high specific torque values.
SUMMARY OF THE INVENTION
According to one aspect of this invention there is provided an alternating current generator which is arranged to provide multipolar permanent magnet excitation in combination with multipolar reluctance distribution wherein different numbers of poles are used for the permanent magnet excitation on the one hand and for the reluctance distribution on the other hand so that the principal working flux has a finite waveform number which is equal to the difference in wavenumber between the mmf and permeance distributions.
According to another aspect of this invention, there is provided an alternating current motor which is arranged to provide multipolar permanent magnet excitation in combination with multipolar reluctance distribution wherein the motor has at least three phases whereby a traveling wave of mmf is produced substantially continuously and different numbers of poles are used for the permanent magnet excitation on the one hand and for the reluctance distribution on the other hand so that the principal working flux has a finite waveform number which is equal to the difference in wavenumber between the mmf and permeance distributions.
According to a further aspect of this invention there is provided an alternating current machine which is arranged to provide multipolar permanent magnet excitation in combination with multipolar reluctance distribution wherein different numbers of poles are used for the permanent magnet excitation on the one hand and for the reluctance distribution on the other hand so that the principal working flux has a finite waveform number which is equal to the difference in wavenumber between the mmf and permeance distributions, the machine including a cylindrical stator and a hollow cylindrical rotor which is mounted substantially coaxially with the cylindrical stator for rotation around the cylindrical stator with an annular air gap therebetween, the stator and the rotor being formed of ferromagnetic material, the stator having a winding arrangement and permanent magnets mounted on it, the magnets being arranged side by side in at least one circular line which follows the respective boundary of the air gap and being arranged to form a certain number of magnetic poles which are alternately north and south poles, the rotor being formed as a cylindrical body with a plurality of spaced projections which project radially from the body towards the stator, the number of projections being different from the magnetic waveform number that would be formed by a circular line of such alternately polarised magnets which were uniformly distributed along the whole of the respective boundary.
According to yet a further aspect of this invention there is provided an alternating current machine which is arranged to provide multipolar permanent magnet excitation in combination with
Haydock Lawrence
Spooner Edward
Gron Gary M.
Mullins Burton S.
Newage International Ltd.
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