GB2493149A

GB2493149A - An electrical generator with a one piece magnet support yoke

Info

Publication number: GB2493149A
Application number: GB1112710.7A
Authority: GB
Inventors: Giles Henry Rodway
Original assignee: Individual
Current assignee: Individual
Priority date: 2011-07-24
Filing date: 2011-07-24
Publication date: 2013-01-30
Anticipated expiration: 2031-07-24
Also published as: GB201112710D0; GB2493149B

Abstract

A radial flux electrical generator employs a hollow cylindrical array of electrical coils1 electrical power being generated by rotating an array of concentric rings of magnets 2a, mounted on a one-piece magnetic flux conducting mounting/yoke 5, relative to said array of electrical coils. The yoke may comprise a plurality of cantilevered elements carrying the magnets which extend from a ring. The permanent magnet assembly may form the rotor and be mounted to the rotor shaft via spokes (figs 8,9 not shown) and the cantilever elements may be associated with reinforcing wires passing around or within the yoke structure (figs 10,11 not shown). Alternatively the yoke may be formed with a continuous circular channel by deep drawing an initially planar ring of material to form a â àâ or â Câ shaped section.

Description

I

Improved Electrical Generator

FIELD AND BACKGROUND OF THE INVENTION

Electrical generators are in widespread use, with those generators employing permanent magnets being increasingly used as the means of generating electrical power in small and medium sized wind turbine systems. When equipped with high strength permanent magnets, such as the commonly used neodymium iron, boron (NdFeB) magnets and manufactured to the necessary tolerances, permanent magnet generators are capable of generating significant electrical power outputs at the relatively low generator rotation speeds used in direct drive wind turbine systems, and require only moderate amounts of the key raw materials, namely the magnets themselves and the electrically conductive (usually lacquered copper or aluminium wire) coils in which electric current is induced by the relative motion of the magnets with respect to the coils.

Typically, the coils are arranged around a rotation axis in a circular array which is static with respect to that axis (i.e. it does not rotate), whilst the magnets are arranged in an array which rotates about the same axis (powered by, for example, air flowing through the wind turbine, itself coupled to the generator), the magnets being in close proximity to the coils, such that the magnetic flux lines emanating from each magnet repeatedly cut the electrically conductive wires as the magnets move, generating a voltage in the wires.

Some designs use magnets on only one side of the coils, whereas other designs employ magnets on both sides of the coils, the latter arrangement having the advantage of increasing the density of the magnetic flux passing through tile coils.

Designs for such electrical generators must comprise some means of mounting the magnets which supply the magnetic fields such that the magnets are able to move in a co-ordinated manner as a rotating array, typically, as indicated above, in a continuous circular path adjacent to the circular array of electrical coils.

Said circular array of electrical coils is typically a flat, planar array in the case of axial flux generators (electrical generators in which the flux lines of the magnetic fields from the magnets run substantially perpendicular to the plane of the coils, and parallel to the rotation axis of the array of magnets). The array of coils is typically cylindrical, though, in the case of radial flux generators (electrical generators in which the flux lines of the magnetic fields from the magnets run substantially perpendicular to, and radially towards or away from, the rotation axis of the array of magnets, said rotation axis being coincident with the central axis of said cylindrical array of electrical coils). Radial flux electrical generators are generally considered more difficult to manufacture than axial flux generators, requiring more complex shaping of magnets, coils and mountings, but possess some advantages in ease of assembly and disassembly once the components are manufactured (facilitating, for instance, access to bearings), especially for designs in which magnets are placed on both sides of the electrical coils.

The cores of the above described electrical coils may optionally contain a magnetic flux conducting (typically ferromagnetic) material to assist with the channelling of magnetic flux through the coil, however in many modem electrical generators, especially permanent magnet electrical generators, air-cored coils are preferred, that is coils with air, or another non-ferromagnetic material, in the centre, as they eliminate or minimise some constructional and operational problems, such as cogging and excessive vibration, which may be associated with the attraction between rotating an'ays of magnets and ferromagnetic coil cores.

Even with air-cored generators it is advantageous, though, that the magnetic flux generated by the magnets should pass through magnetic flux conducting material to the greatest extent possible, except where it 15 intended to pass through the electrically conductive coils themselves, so as to channel the magnetic flux efficiently, and thus maximise the net flux density and linearity passing through the coils themselves, and hence the electrical power generated for a given rotation rate. Various such configurations of magnets and magnetic flux conducting materials, either stationary or rotating with the magnets, have been proposed.

US7525230, for example, describes inner and outer ferromagnetic cylinders to which arrays of magnets are attached to pass either side of electrical coils, and EP2005562 describes arrays of individual C or U-shaped flux conducting elements on which opposed pairs of magnets are mounted, also to pass either side of electrical coils Designs based on lame numbers of individual flux conducting elements, however, as in the latter example, suffer drawbacks in manufacturing and assembly complexity in forming arrays from the large number of parts concerned and, potentially, weight penalties in ensuring that the individual elements are reliably secured in position for rotation.

Designs based on complete cylinders of flux conducting material as in the former example may suffer weight and cost penalties due to an excess of flux conducting material in the cylinders themselves, over and above what is needed to accommodate the magnetic flux from the magnets, and also from manufacturing complexities in producing cylinders to the precise dimensions required, and from the additional cost incurred in manufacturing the relatively expensive magnets with curved surfaces required to fit the internal and external cowed surfaces of said flux conducting cylinders.

SUMMARY OF THE INVENTION

Embodiments of the present invention address the above shortcomings of the manufacturing complexity, weight and cost of existing electrical generatordesigns by the provision of a radial flux electrical generator in which electrical power is generated by the rotation of an array of pairs of magnets, preferably permanent magnets, arranged in concentric rings, relative to a hollow cylindrical array of electrical coils wherein the entire array of pairs of magnets is mounted on a one-piece mounting comprising a single piece of magnetic flux conducting (preferably ferromagnetic) material, shaped so asto define a space, between the rings of magnets, wherein is placed the hollow cylinder of electrical coils.

In some advantageous embodiments of the present invention said one-piece mounting comprises a ring or spoked wheel, from the inside and outside edges of which extend a plurality of cantilevered elongate elements, in directions parallel to a rotation axis coincident with the central longitudinal axis of the hollow cylindrical array of electrical coils, such that inner and outer cantilevered elements lie opposite one another and on opposite sides of said electrical coils during rotation of said mounting and attached magnets about said rotation axis.

In other advantageous embodiments of the present invention, the one-piece magnetic flux conducting mounting comprises a disc or ring or spoked wheel and a plurality of cantilevered elongate portions, extending from the outer edge of said disc or ring or spoked wheel wherein said cantilevered portions are C or U-shaped and oriented so as to define a hole to receive said hollow cylindrical array of electrical coils Said cantilevered elements or portions of the one-piece magnetic flux conducting mounting may optionally have flat faces for the mounting of magnets, such that commercially available standard magnets with flat faces may readily be attached thereto.

Reinforcement of the cantilevered elements of said one-piece magnetic flux conducting mountings against bending moments due to the effects of high rotation speeds may conveniently be achieved by using radial or circumferential tensile members such as wire, fibre, straps or hoops, advantageously constructed from materials (either ferromagnetic or non-ferromagnetic) possessing a high ratio of tensile strength to weight.

Rotation of said one-piece magnetic flux conducting mounting and attached magnets may be achieved via spokes, disc or other apparatus connecting said one-piece magnetic flux conducting mounting to a central drive shaft, said drive shaft itself being driven by an external source of mechanical power such as a wind turbine. Said spokes, disc or other connecting apparatus may be part of the one-piece magnetic flux conducting mounting, or may be a separate article or articles attached thereto.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. I is a perspective view of a radial flux electrical generator, comprising an array of electrical coils which are curved so as to fit a cylindrical surface, said array being hollow and comprising magnets on both sides of said electrical coils.

Fig. 2 is a perspective view of a planar one-piece blank (made from a magnetic flux conducting material) prior to shaping, suitable for shaping into a one-piece magnetic flux conducting mounting to support an array of magnets according to the present invention.

Fig. 3 is a perspective view of the magnetic flux conducting blank of Fig. 2. after pressing to form a one-piece magnetic flux conducting mounting for an array of magnets according to a preferred embodiment of the present invention.

Fig. 4 is a perspective view of the magnetic flux conducting mounting piece of Fig. 3. after an away of magnets has been mounted on it.

Fig. 5 is a perspective view of an electrical generator constructed in accordance with a preferred embodiment of the present invention.

Fig. 6 is a perspective view of an altemate style of one-piece magnetic flux conducting mounting for an array of magnets.

Fig. 7 is a perspective view of the alternate style of one-piece magnetic flux conducting mounting as illustrated in Fig. 6. after the array of magnets has been mounted on it.

Fig. 8 isa plan view of a blank for producing a one-piece magnetic flux conducting mounting for magnets, additionally comprising integral central spokes for direct mounting of said one-piece magnetic flux conducting mounting to a central drive shaft.

Fig. 9 is a plan view of a blank for producing an alternate style of one-piece magnetic flux conducting mounting, also comprising central spokes for direct mounting onto a central drive shaft.

Fig. 10 Is a perspective view of a one-piece magnetic flux conducting mounting with attached magnets, as in Fig. 4, but with the addition of circumferential reinforcing members constraining the inner and outer cantilevered elements so as to resist the bending moments generated during high speed rotation.

Fig. 11 Is a perspective view of a one-piece magnetic flux conducting mounting with attached magnets and with the addition of reinforcing members as in Fig. 10, but wherein the inner reinforcing members lie in approximately radial directions rather than in circumferential ones.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the present invention provide a radial flux electrical generator comprising a plurality of pairs of magnets supported on a one-piece magnetic flux conducting mounting, said one-piece magnetic flux conducting mounting being shaped so as to mount said plurality of pairs of magnets as two concentric circular rings of magnets, such that a first magnet in each pair lies on an inner circular ring of magnets, and a second magnet in each pair lies on an outer circular ring of magnets opposite said first magnet, said first and second magnets in each pair being oriented with opposite magnetic poles facing one another so as to drive magnetic flux in radial directions between them, and said concentric rings of magnets defining an annular space in which is housed a plurality of electrical coils, said plurality of electrical coils being arranged to form a hollow cylindrical array, said hollow cylindrical array being concentric with, and having its central axis perpendicular to the plane of, said cimular rings of magnets, such that relative rotation of the mounted array of magnets and said hollow cylindrical array of electrical coils about said central axis induces a voltage in said electrical coils.

Advantageous and preferred embodiments of the present invention employ high strength permanent magnets, such as NdFeB magnets, to provide the required magnetic flux.

Fig. 1 shows an array of electrical coils 1 and magnets 2 in a radial flux arrangement, wherein a voltage is induced in the electrical coils due to their being cut by the movement of magnetic flux lines lying in radial directions. The radial magnetic flux in the example illustrated is provided by magnets 2, arranged in pairs, with opposite magnetic poles facing one another, on either side of said electrical coils, and caused to rotate as an array in circumferential directions 4 (shown arbitrarily as anticlockwise, when viewed from above, in Fig. 1, but which could equally well be clockwise within the scope of the present invention) around the central longitudinal axis of the cylindrical array of coils.

For clarity, the mounting mechanism for the magnets is omitted in Fig. 1. Fig. 2, however illustrates how a mounting mechanism for the whole array of magnets, according to the present invention, could be fabricated from a single piece of material. Fig. 2 is a perspective view of a single, planar, piece of magnetic flux conducting material such as iron or steel, shaped so as to comprise a plurality of elongate elements 5, emanating in pairs from the inside and outside edges of a ring 6, to form a blank suitable for a subsequent pressing operation Such a blank could conveniently be stamped, laser cut, or otherwise fabricated. The arrows 7 in Fig. 2 illustrate how a pressing operation might be used to press the elongate elements 5 in a downward direction relative to ring 6 to form an article suitable for mounting the array of magnets illustrated in Fig. 1.

Fig. 3 illustrates how the blank of Fig. 2 would appear after the pressing operation, with the elongate elements 5 being cantilevered beams in the embodiment illustrated, emanating in pairs perpendicular to their original directions in the blank, to form a one-piece magnetic flux conducting mounting for an array of magnets, according to an advantageous embodiment of the present invention.

Fig. 4 illustrates the appearance of the array of magnets once attached to the one-piece magnetic flux conducting mounting The magnets are arranged opposite each other in pairs, a first magnet being attached to the outside of an inner cantilevered magnetic flux conducting element, and a second magnet being attached to the inside of the corresponding outer cantilevered magnetic flux conducting element, the magnets in each pair having opposite magnetic poles facing one another so that the north pole of a first magnet in any pair faces the south pole of a second magnet in the pair, such that magnetic flux from those poles is directed radially between each magnet in the pair, directly through the air gap between them, thus passing through any electrical coils placed in that space. Magnetic flux lines emanating from the side of each magnet directly attached to the elongate magnetic flux conducting elements are, however, channelled through said elongate magnetic flux conducting elements to other magnets in the array of coils, thus bypassing any electrical coils placed in the space between pairs of magnets. This channelling of the flux is advantageous for the efficiency of the generator as some of the magnetic flux would otherwise pass instead through said electrical coils and would tend to partially cancel out the voltage generating effect, during operation of the generator, of the radial magnetic flux passing directly between the magnetic poles which face each other. The array of concentric rings of magnets is. by means of attachment to the one-piece magnetic flux conducting mounting, arranged so as to rotate together about a common axis at a common rotation rate. In some advantageous and preferred embodiments of the invention, the elongate structural elements 5 of the one-piece magnetic flux conducting mounting have substantially planar faces over a substantial part of their length, and the magnets attached thereto also have a substantially planar face on at least their north or south pole, or preferably on both poles, facilitating the secure attachment of the magnets to the elongate structural elements, thus facilitating the selection of cost-effective standard flat disc or bar magnets for the application, and minimising any air gap for the magnetic flux to cross between the magnets and the one-piece magnetic flux conducting mounting. The magnets may conveniently be attached to the one-piece magnetic flux conducting mounting using their own magnetic attraction force, in the case of permanent magnets, augmented where required by adhesive, locating lugs. tapes, overmoulding, or any other appropriate attachment mechanism. Where adhesive or other material is interposed between the magnets and the one-piece magnetic flux conducting mounting, the adhesive or other material may optionally comprise magnetic flux conducting material thus facilitating the conducting of magnetic flux between the magnets and the one-piece magnetic flux conducting mounbng Fig. 5 illustrates a radial flux electrical generator constructed in accordance with a preferred embodiment of the present invention, said electrical generator comprising electrical coils arrayed in a hollow cylindrical stator (the coils being preferably embedded in a polymeric matrix or enclosed in a casing to form the walls of the cylinder), contained within a rotor, said rotor itself compñsing a one-piece magnetic flux conducting mounting holding an array of petmanent magnets 2a, said rotor and attached array of permanent magnets being arranged so as to rotate as indicated by arrows 4, about the central axis of the hollow cylindrical array of stator coils, and to drive magnetic flux in radial directions (substantially perpendicular to said rotation axis, and to the surface of the hollow cylindrical array of stator coils) through said stator coils. It is noted that although for simplicity of illustration the example shown is a single phase design (in which the number of electrical coils equals the number of pairs of magnets), nevertheless three phase and other designs, where the ratio of number of pairs of magnets to number of coils would not normally be 1:1, are also within the scope of the present invention.

Fig. 6 illustrates an alternate embodiment of the one-piece magnetic flux conducting mounting for an array of magnets, according to another advantageous embodiment the present invention, and Fig. 7 illustrateS the same mounting, populated with an array of pairs of magnets. This design differs in that there are no cantilevered elongate elements extending inwards 1mm the inner edge of ring 6a, and the cantilevered elongate elements 5a which extend outwards and upwards from the ring are shaped so as to form C or U-shaped elements, each such element comprising two flat intemal surfaces for the mounting of magnets suitable for providing magnetic flux in radial directions through a cylindrical array of electrical coils.

The configurations for the one-piece magnetic flux conducting mounting illustrated in Fig. 3 and Fig. 6 have slightly different relative advantages and disadvantages. Whilst the embodiment of Fig. 3 may be simpler to press into the correct shape in a single operation, the embodiment illustrated in Fig. Gallows for the ring 6a to be substituted for a disc, or more readily to contain internal spokes as part of the same one-piece magnetic flux conducting mounting, for attachment to a central spindle or drive shaft. Nevertheless, variants of the types illustrated In both Fig. 3 and Fig. 6 may optionally comprise such internal spokes, even when they also comprise a relatively large number of cantilevered elongate elements for the mounting of magnets.

This possibility for the two variants is illustrated in the plan views of blanks in Fig. 8 and Fig. 9, each indicating integral spokes 8 and an integral central ring 9 for attachment to a central spindle or drive shaft.

Although the examples of the one-piece magnetic flux conducting mounting illustrated may conveniently be pressed from initially flat blanks, other fabrication methods are also possible within the scope of the present invention. For example, a one-piece magnetic flux conducting mounting could be cast, or fabricated by powder metallurgical techniques, or by other known fabrication methods, however pressing from initially flat blanks is generally preferred on the grounds of speed of fabrication and cost.

In service, it is anticipated that substantial bending moments in the cantilevered elongate elements of the one-piece magnetic flwc conducting mountings may occur at high rotation speeds due to centrifugal effects.

Distortion of the cantilevered elongate elements due to these bending moments may be reduced by shaping of the one-piece magnetic flux conducting mountings to give the cantilevered elements, for example U-shaped or other stiffer cross-sections. Such distortion may, however, be minimised conveniently and with a relatively low weight penalty by adding reinforcing wires, hoops, spokes or other tensile members, made from either ferromagnetic or non-ferromagnetic materials, advantageously oriented in substantially circumferential or radial directions. Fig. 10 illustrates circumferential structural members ba and lob, reinforcing outer and inner arrays of cantilevered magnetic flux conducting elements 5a of a one-piece magnetic flux conducting mounting for magnets. Fig. Ii illustrates an alternative reinforcing arrangement in which the inner reinforcing structural elements lOb have been replaced with substantially radial structural elements lOc.

It will be understood that design variations within the scope of the present invention, include, but are not limited to, variations in the numbers and shapes of the electrical coils and magnets, the detailed design of the support mechanisms for the coils and magnets, and the materials, thicknesses and dimensions for the coils, magnets and insulation and support mechanisms. For example, a single magnetic flux conducting mounting could be formed without discrete elongate structural elements, by deep-drawing an initially planar ring of material, to form a continuous circular channel with, for example, a U-shaped cross section, to the insides of which pairs of magnets could be attached for operation, within the scope of the present invention.

Further, electrical generator designs in which the relative movement of coils and magnets is achieved by rotation of the array of coils instead of, or in addition to, rotation of the array of magnets, are also within the scope of the present invention.