WO2017182912A1

WO2017182912A1 - A generator having unlike magnetic poles radially aligned

Info

Publication number: WO2017182912A1
Application number: PCT/IB2017/052084
Authority: WO
Inventors: Kabu Walter MAKGERU
Original assignee: The Trustees For The Time-Being Of The Kmn Fulfilment Trust
Priority date: 2016-04-18
Filing date: 2017-04-11
Publication date: 2017-10-26
Also published as: ZA201702600B; AR108211A1

Abstract

An electric generator has magnetising and generating layers which are arranged coaxially and rotatable relative to each other. More specifically, the generator has at least two magnetising layers, namely an inner magnetising layer and an outer magnetising layer and the magnetising layers each include a plurality of circumferentially spaced magnetic poles. The poles of the inner magnetising layer are opposed and radially aligned with unlike poles in the outer magnetising layer, thereby creating a straight magnetic flux in a radial direction between the unlike poles of the respective magnetising layers. The generating layer is arranged between the magnetising layers.

Description

A generator having unlike magnetic poles radially aligned

FIELD OF INVENTION

The present invention finds application in the field of electric machines, particularly in power generation, and it relates specifically to an electric generator having at least one magnetising layer with opposed unlike (North-South), attracting poles.

BACKGROUND OF INVENTION

The primary object of this invention is to improve the efficiency of electrical energy generation. The invention is guided by the known theories in the fields of electricity and magnetism. A formula (1 ) is shown below, derived from Lorentz and Faraday's laws of induced EMF in a conductor. This formula forms the basis for calculating output voltage in a conventional generator.

EMF = vlBsin(0), (1 ) where v is the relative velocity between the conductor and the magnetic field,

/ is the length of the conductor exposed to the magnetic field,

B is the magnetic field density, and

Θ is the angle between the conductor and the magnetic field vector.

From this formula, it can be seen that by increasing v, I, and B, and, by keeping Θ at 90°, serve to maximise induced EMF. US7679249 discloses increases the EMF produced by increasing the relative velocity between the conductor and the magnetic field. This was achieved by using counter rotation between the conductor and the magnetic field thereby increasing the relative velocity whilst keeping the actual velocity low. Therefore, through counter rotation, the efficiency of the machine was increased due to the fact that the same output voltage was produced for a lower input speed. In the generator of US7679249 however, the magnetic field (B) was not, in the Applicant's opinion, optimally shaped or strengthens to yield higher results. The design of US7679249 has a hollow rotor filled with air which introduces massive reluctance to the magnetic path. This increased reluctance decreases the magnetic field strength within the machine leading to a lower induced EMF.

Increasing the relative velocity and the conductor length have physical design limitations and so the focus of the design is on increasing B and keeping Θ at 90° in order to optimise the induced EMF. These two variables were optimised by harnessing known theories in magnetism that have not yet been applied in generator design applications.

In patent EP 2736154 a dual stator permanent magnet generator for a wind turbine is described. In this design they place a hollow cylindrical rotor, containing permanent magnets, in between two concentric hollow cylindrical stators, containing coils. In this design they utilise both surfaces of the magnetising layer however they do not harness the use of diametrically opposite unlike poles to strengthen and straighten the magnetic field that intersects the conductors. In their design there are two factors that erode the magnetic field properties. Firstly, the inner stator is hollow thereby forcing the magnetic field to form around the air gap, due to its high reluctance, resulting in the coils within the inner stator not being cut at 90°. Secondly, the rotor contains three equidistantly spaced magnets. This causes the magnetic field shape to resemble that of a triangle which also ensures that the magnetic fields do not intersect the conductors at the optimal 90°. The Applicant wishes to overcome these drawbacks and create an improved generator. The Applicant wishes to provide for increased magnetic field properties and multiple generating and magnetising layers for increased utilisation.

SUMMARY OF INVENTION

Accordingly, the invention provides an electric generator as disclosed in the claims. Further aspects of the disclosure follow below.

There is disclosed an electric generator having at least one magnetising layer and at least one generating layer which are arranged coaxially and rotatable relative to each other, wherein: the magnetising layer is hollow, defining a coaxial inner cylindrical cavity; the magnetising layer includes a plurality of circumferentially spaced pairs of magnetic poles; unlike poles of different pairs are arranged diametrically opposite each other thereby creating a straight magnetic flux in a radial direction between the unlike poles within the cylindrical cavity; and the generating layer is provided inside the magnetising layer in the cylindrical cavity.

The generator may include two generating layers respectively arranged radially inwardly of and radially outwardly of the magnetising layer.

There is disclosed an electric generator having at least one magnetising layer and at least one generating layer which are arranged coaxially and rotatable relative to each other, wherein: there are at least two magnetising layers, namely an inner magnetising layer and an outer magnetising layer; the magnetising layers each include a plurality of circumferentially spaced pairs of magnetic poles; one of the poles in a pair of the inner magnetising layer is opposed and radially aligned with an unlike pole in the outer magnetising layer, thereby creating a straight magnetic flux in a radial direction between the unlike poles of the respective magnetising layers; and the generating layer is arranged between the magnetising layers.

The generator may include a plural-layer generating member and a plural-layer magnetising member. The layers are in the form of prongs.

The generator may include a plurality of magnetising layers and a plurality of generating layers arranged alternatingly. The generator may include either one of:

N magnetising layers and N generating layers;

N magnetising layers and Λ/+1 generating layers; or

Λ/+1 magnetising layers and N generating layers, where N is 1 or more.

The generator may include two magnetising layers and three generating layers (e.g., N = 2). More specifically, the generator may include a two-prong magnetising rotor and a three-prong generating member (either a rotor or a stator).

The abovementioned aspects share a common feature in that each generator serves to provide a radially straight or constant portion of a magnetic field between two unlike magnetic poles, with coils on the generating layer being configured to pass transversely through the straightened magnetic field. Through experimental investigation and theoretical validation it was found that placing two opposing magnetic poles sufficiently close to each other causes the field lines between them to straighten. It was also found that the magnetic field density in the air between the two opposing pole magnets as well as on the outwards facing surfaces of the magnets was greater than the density of the magnetic field at the surface of the individual magnets when they were isolated from each other. It was also found that the magnetic field was directed towards the unlike pole thereby decreasing the unused tangential leakage flux. Therefore, conductors placed in between two sufficiently close magnets as well as on the outer surfaces may be penetrated by a denser magnetic field, thereby inducing a greater EMF, compared to a conductor placed next to the surface of an isolated magnet, with the latter being similar to that seen in the conventional generator design. A conductor placed in between two magnets will be penetrated perpendicularly by the magnetic field, which, according to the formula (1 ) above, will produce a maximum EMF. Thus a major design criterion for the current invention may be that there must be multiple magnets with unlike poles facing each other, as well as small air gaps (e.g., 5 mm) within the generator to ensure the magnets are sufficiently close together thereby inducing flux linkage between the two magnets, in order to harness the above described advantages.

By sandwiching a magnetising layer in between two generating layers, both surfaces of the magnetising layer will be used. By placing a generating layer in between two magnetising layers, the generating layer will be excited perpendicularly from both sides leading to the entirety of the generating layer being utilised.

The generating layer may include a plurality of coils, at least portions of which extend axially, wherein the axially extending portions of coils intersect the radial magnetic flux between the unlike poles orthogonally.

The or each generating layer may be provided by a stator. Instead, the or each generating layer may be provided by a rotor. Each magnetising layer may be provided by a rotor. In one embodiment, the generator may include two rotors, namely a magnetising rotor which carries the or each magnetising layer and a generating rotor which carries the or each generating layer, the rotors being counter-rotating.

The generating layer may define a plurality of radially extending coil structures about which coils may be wound, the coil structures being spaced circumferentially and being interspaced with coil slots, the coil structures having a laterally bulging shape such that the interspaced coil slots have an hourglass shape. The coils may be wound around the winding structures and urged by the bulge to respective radially inner and radially outer end of the coils structures, thus being urged towards adjacent respective inner and outer magnetising layers.

As described in the background to the invention, in order to optimise the induced EMF, and in turn increase the efficiency, the present invention is centred on increasing the magnetic field strength that intersects the conductors and ensuring that those conductors are intersected perpendicularly by the magnetic field lines. The efficiency can also be increased by maximizing the utilisation of the magnetising and generating layers. The just described design criteria form the basis for the multi-layered design.

In one version of the invention, where N = 2, there may be five layers, achieved by interfacing a two pronged rotor with a three pronged stator. At the centre of the generator is the inner stator member which forms a stationary generating layer, consisting of copper coils. This is surrounded coaxially by the inner rotor member, forming a rotating magnetising layer, consisting of electromagnets and or permanent magnets. The third and fifth layers of the generator are the middle and outer stator members which form another set of stationary generating layers. The fourth layer in the generator is the outer rotor member forming another rotating magnetising layer. All the layers are arranged coaxially. It was decided to have less magnetising layers than generating layers as the magnetising layers are considered as inputs into the system with the generating layers acting as outputs from the system. Having more outputs than inputs may lead into an increased efficiency. An outermost layer of the generator may be a generating layer. The generator may include a sleeve of magnetic steel arranged around the outermost layer, to straighten magnetic flux. The outermost layer may have an outer surface wrapped with magnetising steel and its coil slots facing inwards the magnetising layer, thereby attracting flux to the outer surface and ensuring that the coil slots are penetrated by the straightened magnetic flux.

The generator may have an outer diameter of the active parts (comprising the generating and magnetising layers) is at least twice its length. Accordingly, the generator may be relatively short but fat. The generator may be 5-7 m long.

The generating layer may have two magnetising layers which are counter-rotating and in which the poles of the counter-rotating magnetising layers are electronically controlled and switched, thereby to maintain one of the poles in the inner magnetising layer in an opposed relationship with an unlike pole in the outer magnetising layer.

The generator may include at least two magnetising layers and a strength of the magnetic field between two adjacent magnetic layers may be greater than 1.2 T (Tesla).

A diameter of the generator may be twice or more as large as a length of the generator.

A generating surface of the generating layer the may be a quarter of that of a conventional design.

BRIEF DESCRIPTION OF DRAWINGS

The invention will now be further described, by way of example, with reference to the accompanying diagrammatic drawings. shows an axial-sectional view of a first embodiment of an electric generator in accordance with the invention; shows a cross-sectional view of the generator of FIG. 1 along line A-A; shows a schematic cross-sectional view of the generator of FIG. 1 including illustrative magnetic flux lines; shows a schematic cross-sectional view of a PRIOR ART generator (to be contrasted with FIG. 3); shows a cross-sectional view of a second embodiment of a generator in accordance with the invention; shows a schematic cross-sectional view of the generator of FIG. 5 including illustrative magnetic flux lines; shows an axial-sectional view of a third embodiment of a generator in accordance with the invention; shows an axial-sectional view of a fourth embodiment of a generator in accordance with the invention shows an axial-sectional view of a fifth embodiment of a generator in accordance with the invention; and shows an enlarged cross-sectional view of a including a generating layer of an electric generator in accordance with the invention.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENT

The following description of the invention is provided as an enabling teaching of the invention. Those skilled in the relevant art will recognise that many changes can be made to the embodiment described, while still attaining the beneficial results of the present invention. It will also be apparent that some of the desired benefits of the present invention can be attained by selecting some of the features of the present invention without utilising other features. Accordingly, those skilled in the art will recognise that modifications and adaptations to the present invention are possible and can even be desirable in certain circumstances, and are a part of the present invention. Thus, the following description is provided as illustrative of the principles of the present invention and not a limitation thereof.

In the example embodiments, various multi-layered electrical generators are described to provide a high efficiency in terms of electrical energy generation. The increased efficiency is achieved by utilising well known theories in magnetism as a guide in the physical design as well as maximising the utilisation of the magnetising and generating layers within the generator. These design criteria led to the development of the current embodiments.

Firstly, the design is structured around having unlike (North-South) poles facing each other. This leads to increased flux density as well as straighter magnetic field lines. Secondly, the design is multi-layered in order to increase the utilisation of layers within the generator. The multi-layered approach will ensure that inner and outer surfaces of magnetising layers are used to induce voltages in the generating layers and to ensure that inner and outer surface of the generating layers are intersected perpendicularly by magnetic field lines thereby increasing the percentage flux penetration within the layer.

FIG. 1 illustrates a simplified schematic representation of the complex mechanical structure needed to achieve the multi-layered design. It should be noted that air gaps have been exaggerated for ease of differentiation between the multiple layers. A drive shaft 1 which can be connected to any source of rotational mechanical power is connected to a two pronged rotor 2. This rotor 2 consists of an inner cylindrical member 3 and an outer cylindrical member 4 (respectively, Layer 2 and Layer 4 of the multi-layered generator). This configuration allows for two jointly connected concentrically rotating layers, namely the inner rotor member 3 and the outer rotor member 4 which respectively function as inner and outer magnetising layers. A three-pronged stator 8 makes up a stationary part of the generator. The three- pronged stator consists of an inner stator member 5, a middle stator member 6 and an outer stator member 7, which respectively function as generating layers (respectively, Layer 1 , Layer 3, and Layer 5 of the multi-layered generator). The rotating and stationary parts of the generator are interfaced via a multitude of bearings 9 throughout the design. The top and bottom of the generator are supported and protected by casing members 24 which attach to the outer stator member 7.

Referring also to FIG. 2, the inner and outer rotor members 3, 4 contain electromagnets which supply the excitation field to the multi-layered generator. The electromagnets comprise: an electromagnet core 10 made from a highly magnetically permeable metal; dispersion layers 11 also made from a magnetically permeable metal; and coils of wire 12 which supply the excitation current to the electromagnets.

The electromagnets in the inner rotor member 3 and outer rotor member 4 comprise of the same components and general layout, however, due to the geometry of the design, the actual size of the electromagnets differs between the two rotors, as can be seen in FIG. 2. The excitation current direction within the electromagnet is chosen to ensure that dispersion layers of the inner and outer rotor members 3, 4 that face each other act as unlike poles (North-South) thereby guiding the magnetic flux throughout the generator as seen in FIG 3.

As can be seen in FIG. 3, the unlike pole configuration causes the magnetic field lines within the generator to straighten. This results in the magnetic field lines intersecting the conductors at the optimal angle of 90°. In contrast, FIG. 4 shows the magnetic field within a PRIOR ART generator design where the unlike pole configuration is not utilised resulting the field lines intersecting the conductors at sub optimal angles that are less than 90°. Through experimental investigation, it was found that the opposing pole configuration produces a greater flux density compared to the conventional design, hence the benefit in the multi-layered approach. Continuing with FIG.1 and FIG. 2, each stator member 5, 6, 7 comprises of two major components, namely, the support structure which connects the stator members within the three pronged design together, and the mild steel laminations, which hold the coils in place as well as guide the magnetic field lines in the directions shown in FIG. 3. Note that the coils within the stator coil slots have been left out of FIG. 2 to prevent congestion within the diagram. It will be understood that, in use, a stator coil slot will contain coils. Looking closer at the inner stator member 5, its supporting structure 14 is located at the centre of the lamination and forms the central supporting shaft for the generator. The laminations 15 of the inner stator member 5 wrap around the support shaft 14. There are twenty coil slots 16 spread evenly around the lamination 15.

The middle stator member 6 has a multitude of supporting beams 17 which are fed through its laminations 18. These support beams 17 attach to an end plate 19 thereby connecting the middle stator member to the three pronged stator 8. The middle stator's laminations 18 also contain twenty equally displaced coil slots 20 around its circumference. The outer stator member 7 has a similar structure to the middle stator member 6. It also has a multitude of support beams 21 which pass through its laminations 22. These support beams then connect to a back 13, thereby concluding the three pronged stator's make up. The outer stator member 7 also has twenty equally spaced coil slots 23.

FIG. 5 illustrates a second embodiment of the design, in which the inner and outer rotor members 3, 4 are made to hold four electromagnets thereby transforming the design into a four pole generator. The electromagnets consist of the same components as the two pole embodiment, namely, the electromagnet core 10, the dispersion layers 11 and exciter coils 12. The number of supporting structures 25 and coil slots 26 within the stator members for the four pole embodiment are identical to that seen in the two pole embodiment.

The direction of exciter currents within the electromagnet coils 12 are chosen in such a way as to emulate the poles seen in FIG. 6. As can be seen in FIG. 6, the unlike poles within the inner and outer rotor members 3, 4 straighten the magnetic fields entering the stator members 5, 6, 7. The highly magnetically reluctant coil slots 16, 20, 23 within the stator members guide the field entering the stator members into a straight line and prevent them from flaring out thereby ensuring that the conductors within the stator members are intersected perpendicularly by the field lines thereby maintaining the design objectives as stated at the beginning of the description.

In another embodiment of the design, counter rotation between the generating layers (Layers 1 , 3, and 5) and the magnetising layers (Layers 2 and 4) within the generator can be achieved. This is accomplished by transforming the three pronged stator in the previous embodiment into a three pronged rotor, as can be seen in FIG. 7, thereby creating two independent rotors within the generator. Rotor one 27 forms a two pronged rotor containing electromagnets, with the same configuration as that shown in previous embodiments, on its inner and outer cylindrical members 28, 29 and driven by an external source via its own drive shaft 30. However, rotor two 31 forms a three- pronged rotor with its outer, middle and inner cylindrical members 32, 33, 34 having a similar configuration to the stator 8 of the previous embodiment. The support structure 40 forms the only stationary member within the design with a multitude of bearings 41 being used to interface the multiple rotating parts within the embodiment.

Looking at the cross section about line B-B would yield the same geometry as that seen in FIG. 2 for the two pole embodiment and FIG. 5 for the four pole embodiment of the counter rotating design. The reason for introducing the double rotor counter is that each of the rotors within the generator can be rotated in opposite directions at 1500 rpm. This would yield a relative speed of 3000 rpm between the magnetising and generating layers within the generator thereby producing the necessary 50Hz signal in the two pole design at half the normal rotational speed. In the four pole design the individual speeds of the independent rotors can be reduced even more to 750rpm each, in opposite directions, and still producing the required 50Hz signal. Lower rotational speed is mechanically advantageous as it decreases the centrifugal forces put on the generator by the square of the decrease in speed. Note that the alteration made to achieve counter rotation does not affect the magnetic field shape within the generator. The magnetic field will still look like that seen in FIG. 3 for the two pole design and FIG. 6 for the four pole design, thereby keeping with design objectives set out at the beginning of the description, namely, to increase the magnetic field strength and to straighten the magnetic field lines through the use of a multitude of unlike poles facing each other.

In another embodiment of the design, shown in FIG. 8, a two prong stator 35 is used in conjunction with a single hollow cylindrical rotor 36 attached to a drive shaft 37 thereby forming a three layer version of the previous embodiment. The generator is protected by a support structure 38 with a multitude of bearings 39 employed to interface the stationary and rotating parts of the generator, similar to that seen in previous embodiments. The structure of the stator and rotor members within this embodiment are similar to that seen in inner stator member 5, inner rotor member 3 and middle stator member 6 shown in FIG. 1 and FIG. 2. The outer generating layer of the stator 35 may be integrated with the support structure 38 to save weight. Optionally, all of the generating layers of the stator 35 may be integrated with the support structure 38.

The reasoning behind a three layer embodiment lies in the fact that for longer rotating generators, the multiple pronged rotors could prove difficult to manufacture and operate, hence the simpler three layer embodiment could be used in this case. The reason behind increasing the length of the generator is that this will increase the length of the conductors that are penetrated by the magnetic field thereby inducing a greater EMF, according to the formula presented in the background to the invention. Note that the straightening and strengthening effects on the magnetic fields as set out in the design objectives at the begging of the description are still achieved through the unlike pole configuration in the rotor 36.

In another embodiment of the design, shown in FIG. 9, a three layer generator is developed with counter rotation between its generating and magnetising layers, similar to that seen in previous embodiments. The generator has two independently driven rotors. The first rotor 42 represents a hollow cylindrical member containing electromagnets with the same structure as that seen in the inner rotor member 3 seen in FIG. 1 and FIG. 2 driven by its own drive shaft 43. The second rotor 44 is two pronged and is driven by its own drive shaft 45. The inner rotor member 46 and outer rotor member 47 have the same structure as the inner stator member 5 and middle stator member 6 as that seen in previous embodiments illustrated in FIG.1 and FIG. 2. The two rotors are interfaced via multitude of bearings 48 and the generator is protected by its support structure 49 which forms the only stationary part of the generator. The counter rotation between the magnetising and generating layers allows for the actual speed of the rotors to be decreased whilst maintaining the required relative speed between the magnetising and generating layers. Note that the straightening and strengthening effects on the magnetic fields as set out in the design objectives at the beginning of the description are still achieved through the unlike pole configuration in the first rotor 42.

If the outermost layer is a generating layer (as is the case with most of the embodiments illustrated), then the generator may include a sleeve of magnetic steel arranged around the outer layer. The sleeve of magnetic steel may assist in straightening the magnetic field further, particularly as it traverses the outer generating layer.

FIG. 10 illustrates another embodiment of the design, in which the coil slots 50 within the generating layer 51 are shaped in order to maximise the amount of coils placed close to the magnetising layers 52. This design utilises the fact that the magnetic field density is greater at the surface of the magnetising layers 52, hence placing conductors closer to them will result in a greater induced voltage. This coil slot configuration can be used in all the above discussed embodiments.

Claims

1. An electric generator having magnetising and generating layers which are arranged coaxially and rotatable relative to each other, wherein: there are at least two magnetising layers, namely an inner magnetising layer and an outer magnetising layer; the magnetising layers each include a plurality of circumferentially spaced magnetic poles; the poles of the inner magnetising layer are opposed and radially aligned with unlike poles in the outer magnetising layer, thereby creating a straight magnetic flux in a radial direction between the unlike poles of the respective magnetising layers; and the generating layer is arranged between the magnetising layers.

2. The electric generator as claimed in claim 1 , which includes a plurality of magnetising layers and a plurality of generating layers arranged alternatingly.

3. The electric generator as claimed in claim 2, which includes a plural-layer generating member and a plural-layer magnetising member.

4. The electric generator as claimed in any one of claims 2-3, in which the layers are in the form of prongs.

5. The electric generator as claimed in any one of claims 2-4, which includes any one of:

N magnetising layers and N generating layers; or N magnetising layers and AM generating layers; or N magnetising layers and Λ/+1 generating layers, where N is 2 or more.

6. The electric generator as claimed in claim 5, which includes two magnetising layers and three generating layers.

7. The electric generator of any one of claims 2-6, which has a support structure or enclosure and in which at least one of the generating layers is integrated with the support structure, to save weight.

8. The electric generator of any one of claims 1 -7, in which the or each generating layer is provided by a stator.

9. The electric generator of any one of claims 1 -7, in which the or each magnetising layer is provided by a stator.

10. The electric generator of any one of claims 1 -7, in which the or each generating layer is provided by a rotor.

11. The electric generator of any one of claims 1 -7, in which the or each magnetising layer is provided by a rotor.

12. The electric generator as claimed in claim 10 and 1 1 , which includes two rotors, namely a magnetising rotor which carries the or each magnetising layer and a generating rotor which carries the or each generating layer, the rotors being counter-rotating.

13. The electric generator of any one of claims 1 -12, in which the generating layer defines a plurality of radially extending coil structures about which coils may be wound, the coil structures being spaced circumferentially and being interspaced with coil slots, the coil structures having a laterally bulging shape such that the interspaced coil slots have an hourglass shape.

14. The electric generator as claimed in claim 13, in which the coils are wound around the winding structures and are urged by the bulge to respective radially inner and radially outer end of the coils structures, thus being urged towards adjacent respective inner and outer magnetising layers.

15. The electric generator as claimed in any one of claims 1 -14, in which an air gap between adjacent magnetising and generating layers 0-5 mm.

16. The electric generator as claimed in any one of claims 1 -15, in which an outer diameter of active parts (comprising the generating and magnetising layers) is at least twice its length.

17. The electric generator as claimed in any one of claims 1 -16, in which an outermost layer is a generating layer, the generator including a sleeve of magnetic steel arranged around the outermost layer, to straighten magnetic flux.

18. The electric generator as claimed in claim 17, in which the outermost layer has an outer surface wrapped with magnetising steel and its coil slots facing inwards the magnetising layer, thereby attracting flux to the outer surface and ensuring that the coil slots are penetrated by the straightened magnetic flux.

19. The electric generator of claim 1 1 , which has two magnetising layers which are counter-rotating and in which the poles of the counter-rotating magnetising layers are electronically controlled, thereby to maintain one of the poles in the inner magnetising layer in an opposed relationship with an unlike pole in the outer magnetising layer.

20. The electric generator as claimed in any one of claims 1 -19, which includes at least two magnetising layers and in which a strength of the magnetic field between two adjacent magnetic layers is greater than 1 .2 T (Tesla).