EP2225815A2

EP2225815A2 - Axial flow electric rotary machine

Info

Publication number: EP2225815A2
Application number: EP08855782A
Authority: EP
Inventors: Bernard Claude Lhenry; Jean Marc Canini
Original assignee: DDIS SAS
Current assignee: DDIS SAS
Priority date: 2007-11-28
Filing date: 2008-11-27
Publication date: 2010-09-08
Also published as: WO2009071843A2; WO2009071843A3; FR2924285A1; FR2924285B1

Abstract

The invention relates to an axial-flow electric machine (1) for converting mechanical energy, in particular from a wind turbine, into electric energy, that comprises an outer rotor defining an inductor and symmetrically surrounding a stator defining the armature, the rotor and the stator being separated by two air gaps allowing the relative mobility of the rotor in an axial direction relative to the stator. The machine includes spacer means comprising, for each air gap, a so-called sliding layer made at least partially of a filler material for maintaining the distance of the air gaps.

Description

AXIAL FLUX ELECTRICAL ROTATING MACHINE

The present invention relates to an axial rotating electrical machine for converting a mechanical energy including a wind turbine into electrical energy.

In its main application, the electric machine will be an alternator of a wind turbine and in particular an alternator with axial flow.

However, although intended primarily for such an application, the electric machine may also be used for other applications and in particular be an integral part of power plants, as alternators or turboalternators, grouped to a steam turbine or a steam turbine. gas turbine, or used in hydraulic power plants, in naval propulsion applications or other motorization of large fans.

In the rest of the application, it will be detailed the advantages of the electric rotating machine in the form of an alternator with axial flow, component of a wind turbine.

However, this is a non-limiting example and one skilled in the art can easily derive from the structure described similar structures for the realization of the axial rotating electrical machine in other applications as mentioned above.

Different electrical machines adapted to equip wind turbines have already been proposed and are marketed on the market.

A first type of electric rotating machine is known that is arranged at the level of the nacelle of a horizontal axis wind turbine and connected via a multiplier to the transmission shaft which is fastened to the hub of the blades of the wind turbine.

This first type of rotating electrical machine has a disadvantage to know a large size at the head of the nacelle; major drawbacks in particular on the low reliability induced by the presence of an undersized multiplier because compliance with the rules of the art in force would lead to a cost and a mass incommensurate with what is required by designers wind turbines. On the other hand always in a concern for less cost these manufacturers specify for most cheap asynchronous electric chains powered by an IGBT converter but on the so-called "double fed" principle, electrical chain systems that can not meet the new standards of connection of wind turbines on the network . These major drawbacks are all the more important as the trend among wind turbine manufacturers is to make windings larger and larger so as to obtain very large electric powers without multiplying the number of wind turbines.

To overcome these major drawbacks, it has been proposed in particular in the patent application FR-2.810.374 an electric rotating machine axial flow direct attack, that is to say a machine does not require the use of a speed multiplier, the rotor of the generator being fixed directly on the transmission axis of the wind turbine.

In this second embodiment, the connection between the transmission axis and the rotor of the generator is extremely important since it ensures both the transmission of the rotational torque of the shaft and the maintenance of the air gap between the rotor. and the stator of the electric rotating machine.

In practice, the connection is provided by particularly heavy rigid elements increasing very significantly the weight of the nacelle.

For the production of large wind turbines with blade sizes greater than 100 meters, the manufacturers face a double limit, namely a weight limit and also a limit of resistance of the materials, since the effort on the connecting element is at its ends.

It is also known from document WO-2007/043894 describing a large-capacity wind turbine equipped with an axial flow alternator whose rotor is in direct engagement with the hub supporting the blades, said rotor being in the form of a jaw inside which is arranged the stator of the alternator. According to this document, the hub is in the form of a torus having a large diameter and section. The torus is connected to the axis of rotation by means of a plurality of uniformly distributed tension bars of radial way. The jaw has a diameter corresponding substantially to that of the torus and separates the rotor and the stator by two air gaps. According to such a design of the alternator of the wind turbine and in particular because of the inertia, the deformation of the material, or even the forces exerted on the blades of the wind turbine, the rotor is subjected to relative mobility relative to to the stator in the zone of the jaw both in the axial and radial direction, which has the major disadvantage of modifying the air gaps. The wind turbine according to this document WO-2007/043894 implements permanent magnets arranged between the rotor and the stator in the radial and axial direction in order to achieve a magnetic bearing between said rotor and said stator, in the radial direction and in the axial direction. This design is intended to guide the rotor vis-à-vis the stator.

The present invention aims to implement an axial rotating electrical machine to prevent contact between the rotor and the stator in the air gap areas. It also relates to a very large wind turbine equipped with an alternator consisting of such an axial rotating electrical machine.

Another object of the present invention is to provide an electric machine for producing wind turbines of limited weight with respect to the electric power obtained. Another object of the present invention is to provide an electric machine for final assembly and reliable installation of the nacelle of the wind turbine in situ.

Another object of the present invention is to provide an electrical machine requiring reduced maintenance especially at the level of the connection between the rotor and the transmission axis of the wind turbine as well as between the rotor and the stator of the machine.

For this purpose, the rotating electric machine axial flow allows in particular the conversion of a mechanical energy into an electrical energy, the opposite being however possible. This machine comprises an outer rotor constituting an inductor and symmetrically surrounding a stator, constituting the armature, the rotor and the stator being separated in the axial direction by two air gaps allowing relative mobility of the rotor with respect to the stator in the axial direction. Such relative mobility of the rotor relative to the stator is due in particular to deformations of material due to the diameter of the elements, external forces and inertia during rotation of the rotor.

In addition, the machine comprises spacing means for maintaining the distance of the gaps. According to the invention, said spacing means comprise, for each air gap, a so-called sliding layer consisting at least mainly of a filling material.

This characteristic makes it possible to prevent any contact between the rotor and the stator both during the installation of the electric machine and during its operation.

According to another advantageous characteristic of the invention, the spacer means comprise means for blowing air under pressure through the sliding layer allowing the creation of an aerostatic film at each gap. This characteristic makes it possible in particular to limit the friction forces between the fixed part and the rotating part of the alternator, in the region of the sliding material, as well as the electromagnetic attraction forces between the said fixed and rotating parts, in order to limit the energy losses.

According to another characteristic of the invention, the sliding layer may completely or partially cover the interface between the stator and the rotor.

This characteristic makes it possible to adapt the shape of the sliding layer according to the applications of the electrical machine and in particular according to the interaction forces between the rotor and the stator.

According to another advantageous characteristic of the invention, the filling material is of porous type, advantageously with open cells.

This feature optimizes the distribution of air transmitted by the air blowing means at the gap.

According to a first embodiment, the thickness of the sliding layer corresponds substantially to that of the distance of the air gap. This feature allows the realization of an electrical machine that can use a large number of components already on the market. According to a second embodiment, a filler layer is provided which is smaller than the distance of the air gap leaving a clearance and a balancing system disposed on the rotor disk brake allowing axial control of the position of the rotor. This characteristic is particularly advantageous since it considerably limits the energy losses due to possible friction between the filler layer and the rotor or the stator, depending on the position of this filler layer respectively on the stator or on the rotor.

Another object of the present invention is the production of a wind turbine equipped with an axial rotating electrical machine according to the aforementioned characteristics.

Advantageously, the wind turbine comprises connecting means between the blade hub of the wind turbine and the rotor allowing a displacement in translation of said rotor. Furthermore, according to another characteristic of the invention, the connection means between the hub of the blades of the wind turbine and the rotor allow the transmission only torque between the transmission axis and the rotor.

This feature is particularly advantageous since it allows for connecting parts on which is exerted only a torque force, these parts can move in translation since the air gap is maintained by the particular structure of the electric machine.

This characteristic therefore makes it possible to produce large link elements and the realization of large-scale wind turbines that allow large electrical powers. Other features and advantages of the invention will appear more clearly on reading the following description of two preferred embodiments in which the description is given by way of non-limiting example and with reference to the drawings. annexed:

- Figure 1 shows a schematic view in transparency of an exemplary embodiment of a wind turbine nacelle according to the invention;

FIG. 2 represents a simplified sectional view of a first embodiment of the electrical machine and the connection between the machine. electric and transmission axis of the wind turbine according to the invention;

- Figure 3 shows an enlarged view of a detail of the embodiment of Figure 2; - Figure 4 shows a simplified sectional view of a second embodiment of the electric machine;

FIG. 5 represents a detail of embodiment of the second exemplary embodiment illustrated in FIG. 4.

Referring mainly to Figures 2,3 and 4, there is shown an electric machine 1 connected by connecting means 2 to the hub 3 of the blades 4 of a wind turbine 5.

The rotary electric machine 1 constituted in this application of an axial flux alternator is connected to the connecting means 2 by the outer rotor 6 constituting the inductor, said rotor 6 symmetrically surrounding a stator 7 constituting the armature, the free space on each side of the stator 7 being constituted by two gaps 8a, 8b.

Of course, what is necessary for the constitution of an alternator and as it could be described in the document FR-2.810.374, the side faces 6a, 6b of the rotor 6 in the form of a jaw consist of two permanent magnets, just as the stator 7 comprises two active surfaces 7a, 7b in the form of circular plates, said elements allowing the creation of the axial flow and the constitution of the two gaps 8a, 8b.

Referring mainly to Figure 3, we see that the electric machine 1 comprises spacing means 9 having for each air gap 8a, 8b a sliding layer 10 at least partially formed of a filler material.

In the examples of Figures 1 to 5, the sliding layer 9 is secured to the rotor 6. However, other embodiments could provide that the sliding layer 9 is secured to the stator 7. Advantageously, this sliding layer 9 will be fixed by gluing; however, other modes of subjection within the scope of those skilled in the art are also possible and in particular a subjection by rivets. The sliding layer 10 is made at least partially by a filling material; the latter advantageously has characteristics to prevent direct contact between the rotor 6 and the stator 7. This filling material 10 also has sufficient strength to prevent crushing or premature wear.

For this purpose, it is advantageously provided that the filling material is a material with a low coefficient of friction.

Advantageously, this material will be a foam, especially extruded polyethylene.

Furthermore, it is expected that the foam has a density of between 30 and 40 kg / m ³ and preferably 35 kg / m ³ .

Also in order to avoid or limit friction, it is provided that the spacer means 9 comprise air blowing means 11. These air blowing means 11 allow air to be sent under pressure through the layer sliding member 10 allowing the creation of an aerostatic film at each gap 8a, 8b, in order to maintain an equilibrium of each gap 8a, 8b and to avoid as much as possible the friction of the filling material on the stator. Advantageously, these air blowing means 11 are arranged at the level of the stator 7.

Advantageously, it is expected that the pressure exerted by the air blowing means 11 is between 0.1 and 0.5 bar.

These air blowing means 11 may be constituted in a conventional manner by compressors.

It is important at this level to emphasize that in order to homogeneously distribute the air at the air gaps 8a, 8b, it is advantageously provided that the filling material used to form the sliding layer 10 is a porous type material . Advantageously, this porous material will be made from open cells, increasing the diffusion of air under pressure in said material. Another possibility for promoting the flow of air may also constitute a particular distribution of the sliding layer 10.

It will be possible in particular to provide that this sliding layer 10 completely or partially overlaps the interface between the rotor 6 and the stator 7. This particular arrangement can also meet other technical constraints and in particular is defined according to the interaction forces. existing between the rotor 6 and the stator 7 or depending on the dimensions of the electric machine.

Referring this time mainly to FIGS. 2 and 3, a first embodiment of the electric machine 1 will be described.

In this embodiment, each sliding layer 10 substantially corresponds to the thickness of the gap 8a, 8b.

This embodiment allows while allowing a displacement between translation of the rotor assembly 6 and stator 7 along the axis XX 'at the same time to prevent the reduction of the gap distance 8a, 8b.

When the connecting means 2 drive the rotor 6 in a given direction along the axis XX ', the sliding layer 10 situated on the side opposite to the direction of movement prevents any contact between the rotor 6 and the stator 7 and thus allows the maintenance a first gap. When the connecting means 2 drive the rotor in the other direction, it is the opposite sliding layer that prevents any contact between the rotor 6 and the stator 7 at the second gap.

This structure of electric generator 1 thus allows a translation along the axis XX 'and therefore allows the use of connecting means 2 between the hub 3 of the blades of the wind turbine and the rotor 6 allowing this movement.

This characteristic thus makes it possible to dispense with rigid connection means and consequently allows the use of a wind turbine with flexible connecting means 2 allowing transmission only of the torque between the transmission axis 20 and the rotor 6. Referring again to FIGS. 4 and 5, there is shown a second embodiment of the electric machine 1. In this second embodiment, the sliding layer 10 is smaller than the distance of the gap 8a, 8b leaving a gap of between 0.5 and 1 mm.

This characteristic makes it possible to limit friction during operation of the electric generator 1.

In this embodiment, it can also be seen that the spacing means 9 comprise a balancing system 12 disposed on the disk brake 13 of the rotor 6.

This balancing system 12 allows an axial control of the position of the rotor 6. In this way, the sliding layer 10 makes it possible to avoid any contact between the rotor 6 and the stator 7 and the balancing system 12 makes it possible to to limit friction during operation of the electric machine 1.

For this purpose, the balancing system 12 comprises at the level of the disc brake 13 in addition to the conventional braking jaws at least one positioning jaw 14 and means 15 for controlling the position of said at least one jaw relative to the brake disc 13.

Advantageously, the positioning jaws 14 will be three or more in number and homogeneously arranged on the surface of the disc brake 13. Referring mainly to FIG. 5, a balancing system 12 according to FIG. the invention with a positioning jaw 14 disposed on a disk brake 13, the jaw 14 having two additional sliding layers 15 in contact with the two surfaces 16 of the brake disk 13. The control means 15 of the brake disk 13 are also seen. position of the jaw 14, these control means 15 being disposed on either side of each jaw 14 and advantageously comprising a processing unit 17 controlling a jack 18 according to pressure data recovered at a sensor 19. The operation of the device is as follows: in case of axial displacement of the rotor 6 due to a displacement of the connection means 2, the disc brake 13 subject to the roto r 6 also moves axially and exerts pressure on one of the additional slip layers causing a change in pressure.

This modification of the pressure is transmitted via the sensors 19 to the processing units 17 so that the positioning jaws 14 are always in contact with the surfaces 16 of the brake disc 13.

This displacement of the balancing system 12 connected directly or indirectly to the rotor 6 allows the displacement of the latter which consequently follows the movements of the stator 7 in one or other of the directions of the axis XX '. Consequently, the spacer means 9 combining the balancing system 12 and the sliding layer 10 make it possible to maintain the two air gaps 8a, 8b preventing any contact between the rotor 6 and the stator 7.

In this second embodiment, it is therefore like the first possible embodiment to use for the connection between the transmission axis 20 of the blades of the wind turbine and the electrical machine 1 connecting means 2 flexible allowing the transmission only torque between the transmission axis 20 and the rotor 6 since the connecting means 2 can, thanks to the particular structure of the machine 1, admit a displacement in translation of the rotor 6. Therefore, both embodiments considerably limit the technical constraints of design and manufacture of connecting elements 2 for the design of large wind turbines for the realization of wind turbines with significant electrical power.

Of course, other embodiments within the reach of those skilled in the art could also be envisaged without departing from the scope of the invention defined by the claims below.

Claims

1. An axial flow electric machine (1) for converting a mechanical energy, in particular a wind turbine, into electrical energy comprising an external rotor (6) constituting an inductor and symmetrically surrounding a stator (7) constituting the induced, the rotor (6) and the stator (7) being separated axially by two air gaps (8a, 8b) allowing the relative mobility of the rotor (6) vis-à-vis the stator (7) in the axial direction, means spacing device for maintaining the distance of air gaps (8a, 8b) CHARACTERIZED in that these spacing means (9) comprise, for each gap (8a, 8b) a so-called sliding layer (10) constituted at least partially of a filling material.

2. Electrical machine according to claim 1, wherein the spacing means (9) comprise means for blowing air (11) under pressure through the sliding layer (10) allowing the creation of an aerostatic film. at each gap (8a, 8b).

3. Electrical machine according to claim 2 wherein the pressure exerted by the air blowing means (11) is between 0.1 and 0.5 bar.

An electrical machine as claimed in any one of the preceding claims, wherein the slip layer (10) completely or partially covers the interface between the stator (7) and the rotor (6).

An electrical machine as claimed in any one of the preceding claims wherein the filler material is a porous-type material preferably with open cells.

Electric machine according to any one of the preceding claims, wherein the sliding layer (10) is fixed on the stator (7).

Electric machine according to one of the preceding claims 1 to 6, wherein the sliding layer (10) is fixed on the rotor (6).

An electric machine according to any one of the preceding claims, wherein the slip layer (10) is bonded to either the rotor (6) or the stator (7).

Electric machine according to any of the preceding claims, wherein the slip layer (10) is an extruded polyethylene foam.

Electrical machine according to any one of the preceding claims, wherein the slip layer (10) is a density foam of between 30 and 40 kg / m ³ .

11. Electrical machine according to any one of the preceding claims, wherein the thickness of the sliding layer (10) substantially corresponds to the thickness of the air gap (8a, 8b).

Electric machine according to any one of the preceding claims 1 to 10, in which the spacing means comprise a balancing system (12) arranged on the disk brake (13) of the rotor (6) enabling control. axial position of the rotor (6).

Electric machine according to claim 12, in which the balancing system comprises, on the one hand, at least one positioning jaw (14) arranged on the disc brake (13) and, on the other hand, control means (15) for the position of said at least one jaw with respect to the brake disc (13).

An electric machine according to claim 12, wherein said at least one jaw (14) comprises two additional slip layers.

(15) in contact with both surfaces (16) of the brake disc (13).

15. Electrical machine according to any one of claims 10 to 13 above, wherein the thickness of the sliding layer (10) is less than the distance of the gap (8a, 8b), leaving a gap between 0.5 and 1 mm.

16. Wind turbine equipped with an electric machine according to any one of the preceding claims.

17. A wind turbine according to claim 16, wherein the connecting means (2) between the hub (3) of the blades (4) of the wind turbine and the rotor (6) allow a translational movement of said rotor (6).

Wind turbine according to claim 16 or 17, wherein the connecting means

(2) are flexible allowing transmission only torque between the transmission shaft (20) and the rotor (6).