WO2020259780A1

WO2020259780A1 - Generator rotor assembly for power generator of a wind turbine

Info

Publication number: WO2020259780A1
Application number: PCT/DK2020/050189
Authority: WO
Inventors: Peter Mongeau
Original assignee: Vestas Wind Systems A/S
Priority date: 2019-06-28
Filing date: 2020-06-24
Publication date: 2020-12-30

Abstract

A generator rotor assembly for a wind turbine comprising a permanent magnet structure arranged to rotate about a rotational axis within a stator. The permanent magnet structure has a first end and a second end and comprises a plurality of rotor laminations arranged along the rotational axis of the generator. A firs flux shield is located at the first end adjacent a first end of the plurality of rotor laminations, and a second flux shield is located at the second end adjacent a second end of the plurality of rotor laminations. The first and second flux shields are made from ferromagnetic material.

Description

GENERATOR ROTOR ASSEMBLY FOR

POWER GENERATOR OF A WIND TURBINE

TECHNICAL FIELD

The invention relates to a power generator for a wind turbine that is less affected by stray current paths generated by leakage flux.

BACKGROUND

As is well-known, wind turbines convert kinetic energy from the wind into electrical energy, using a rotor carrying a number of rotor blades. A typical Horizontal Axis Wind Turbine (HAWT) comprises a tower, a nacelle on top of the tower, a rotating hub or‘rotor’ mounted to the nacelle and a plurality of rotor blades coupled to the hub. The nacelle houses many functional components of the wind turbine, including for example a generator, gearbox, drive train and rotor brake assembly, as well as convertor equipment for converting the mechanical energy at the rotor into electrical energy for provision to the grid. The gearbox steps up the rotational speed of the low speed main shaft and drives a gearbox output shaft. The gearbox output shaft in turn drives the generator, which converts the rotation of the gearbox output shaft into electricity. The electricity generated by the generator may then be converted as required before being supplied to an appropriate consumer, for example an electrical grid distribution system.

A well-known challenge is that the magnetic fields generated by the generator can induce unintentional currents in other components of the generator and associated components. These so-called ‘stray currents’ can result in electrical arcing between adjacent components, and this can, in turn, cause damage such as pitting and welding. Bearings are particularly susceptible to this kind of damage. Stray currents are therefore a significant problem in high voltage generators such as those used in wind turbines. It is therefore desirable to prevent, or at least reduce the amplitude, of such stray currents as far as possible.

It is against this background that the invention has been devised. SUMMARY OF THE INVENTION

According to a first aspect of the invention, there is provided a generator rotor assembly for a wind turbine, comprising a permanent magnet structure arranged to rotate about a rotational axis within a stator, the permanent magnet structure having a first end and a second end, and comprising: a plurality of rotor laminations arranged along the rotational axis, a first flux shield located at the first end and adjacent a first end of the plurality of rotor laminations; and a second flux shield located at the second end and adjacent a second end of the plurality of rotor laminations, wherein the first and second flux shields are made from ferromagnetic material..

The flux shields prevent flux leakage from the ends of the rotor. Because the flux shields rotate with the rotor, there is no cyclical variation in the shielding that the shields provide as the rotor rotates in use.

Optionally, the permanent magnet structure comprises a cylindrical ring structure, wherein the a plurality of rotor laminations arranged co-axially around the rotational axis.

The first and/or second flux shield may optionally be ring-shaped.

Optionally, at least one of the first ring-shaped flux shield and the second ring shaped flux shield is arranged co-axially around the rotational axis to provide symmetry and reduce overall rotor envelope size. At least one of first ring-shaped flux shield and the second ring-shaped flux shield may optionally have the same radial cross-sectional profile as the plurality of rotor laminations to minimise weight.

The first flux shield may optionally be spaced from the first end of the plurality of rotor laminations by a gap created by a predetermined axial distance.

In an optional embodiment, an isolating spacer arrangement is provided in a gap created by a predetermined axial distance between the first flux shield and the first end of the plurality of rotor laminations. Optionally, the second flux shield is spaced from the second end of the plurality of rotor laminations by a gap created by a predetermined axial distance.

An isolating spacer arrangement may optionally be provided in a gap created by a predetermined axial distance between the second flux shield and the second end of the plurality of rotor laminations.

In an optional embodiment, the first flux shield may be associated with a drive coupling of the generator rotor assembly to provide a compact mounting arrangement.

Optionally, the drive coupling and the first flux shield are integral with one another to reduce part count.

The drive coupling may optionally comprise a radially extending flange that extends from a coupling hub at a radially inwards position to the first flux shield at a radially outwards position.

In an optional embodiment, the first flux shield and the second flux shield may form part of a clamping arrangement such that the plurality of magnet packages form an assembly that is clamped in compression between the first and second flux shields.

According to another aspect of the present invention, there is provided a wind turbine comprising the electrical power generating assembly substantially as described hereinabove. In particular, the wind turbine comprises a wind turbine tower, a nacelle rotatably coupled to the tower, a rotating hub mounted to the nacelle, and a plurality of wind turbine blades coupled to the hub. The nacelle comprises the electrical power generating assembly.

Within the scope of this application it is expressly intended that the various aspects, embodiments, examples and alternatives set out in the preceding paragraphs, in the claims and/or in the following description and drawings, and in particular the individual features thereof, may be taken independently or in any combination. That is, all embodiments and/or features of any embodiment can be combined in any way and/or combination, unless such features are incompatible. The applicant reserves the right to change any originally filed claim or file any new claim accordingly, including the right to amend any originally filed claim to depend from and/or incorporate any feature of any other claim although not originally claimed in that manner.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described, by way of example only, with reference to the attached drawings, in which:

Figure 1 is a front view schematic diagram showing a typical wind turbine;

Figure 2 is a schematic and perspective view of the main functional components housed within a nacelle of a typical wind turbine;

Figure 3 is an isometric view of the generator of the nacelle of Figure 2, coupled to a gearbox;

Figure 4 is a cutaway view of the generator of Figure 3;

Figure 5 is a non-drive end perspective view of a generator rotor, interfaced with a connector;

Figure 6 is a drive end perspective view of the generator rotor assembly shown in Figure 5;

Figure 7 is a front view of a ring-shaped layer which forms part of the generator rotor assembly shown in Figure 5 and Figure 6;

Figure 8 is a part cutaway view of the generator rotor assembly shown in Figures 5 and 6;

Figure 9 is a side cross-sectional view of the generator rotor assembly shown in Figures 5 and 6;

Figure 10 is a schematic side view of a cylindrical ring structure of the rotor with a superimposed representation of the associated magnetic field; and Figure 1 1 is a schematic side view of the cylindrical ring structure of Figure 10 with end rings in place with a superimposed representation of the associated magnetic field.

Note that features that are the same or similar in different drawings are denoted by like reference signs.

SPECIFIC DESCRIPTION

A specific embodiment of the present invention will now be described in which numerous features will be discussed in detail in order to provide a thorough understanding of the inventive concept as defined in the claims. However, it will be apparent to the skilled person that the invention may be put into effect without the specific details and that in some instances, well known methods, techniques and structures have not been described in detail in order not to obscure the invention unnecessarily.

In order to place the embodiments of the invention in a suitable context, reference will firstly be made to Figure 1 , which illustrates a typical Horizontal Axis Wind Turbine (HAWT) in which a generator rotor assembly according to an embodiment of the invention may be implemented. Although this particular image depicts an on-shore wind turbine, it will be understood that equivalent features will also be found on off-shore wind turbines. In addition, although the wind turbines are referred to as ‘horizontal axis’, it will be appreciated by the skilled person that for practical purposes, the axis is usually slightly inclined to prevent contact between the rotor blades and the wind turbine tower in the event of strong winds.

The wind turbine 1 comprises a tower 2, a nacelle 4 rotatably coupled to the top of the tower 2 by a yaw system, a rotor hub 8 mounted to the nacelle 4 and a plurality of wind turbine rotor blades 10 coupled to the rotor hub 8. The nacelle 4 and rotor blades 10 are turned and directed into the wind direction by the yaw system.

The nacelle 4 houses a shaft housing 20, a gearbox 22 and a generator 24 as illustrated in Figure 2. A main shaft 26 extends through the shaft housing 20, and is supported on bearings (not shown). The main shaft 26 is connected to, and driven by, the rotor 8 and provides input drive to the gearbox 22. The gearbox 22 steps up the rotational speed of the low speed main shaft via internal gears (not shown) and drives a gearbox output shaft. The gearbox output shaft in turn drives the generator 24, which converts the rotation of the gearbox output shaft into electricity. The electricity generated by the generator 24 may then be converted by other components (not shown) as required before being supplied to an appropriate consumer, for example an electrical grid distribution system. So-called “direct drive” wind turbines that do not use gearboxes are also known. The gearbox 22 may therefore be considered optional.

The gearbox 22 and generator 24 may be coupled together in an integrated unit. Figure 3 shows the generator 24 in more detail. In Figure 3, also the housing of the last stage of the gearbox 22 is shown as it is coupled to the housing of the generator 24.

With reference firstly to the gearbox 22, a gearbox housing is generally cylindrical in form and is oriented such that its major rotational axis is horizontal, in the orientation of the drawings. The cylindrical configuration of the gearbox housing is due to the specific type of gearbox that is used in the illustrated embodiment, which is an epicyclic gearbox. As the skilled person would know, an epicyclic gearbox comprises a series of planet gears that are arranged about a central sun gear, and which collectively are arranged within an encircling ring gear. The ratio of the number of teeth between the ring gear, the planet gear and the sun gears determines the gear ratio of the gearbox. For clarity, fine detail of the gearbox will not be described in further detail here as the gearbox is not the principal subject of the invention. Suffice to say that other gearbox configuration could also be used, although it is currently envisaged that an epicyclic gearbox provides an elegant solution fit for the confines of a wind turbine nacelle.

The output shaft of the gearbox 22 interfaces with a rotor 32 of the generator 24. As such, the major axis of the gearbox output shaft defines the rotational axis of the generator 24. In Figure 4, a cutaway view on the generator 24 only is provided. The generator 24 in the illustrated embodiment is an IPM (interior permanent magnet) electric machine having an external stator 36, which surrounds the rotor 32. The stator 36 includes stator windings 38 a stator core 40 and a stator frame which surrounds and supports the stator windings 38 and stator core 40. It is however noted that the invention is not limited to a specific type of stator.

In accordance with an embodiment of the invention, there is provided a generator rotor assembly 42, forming part of the rotor 32 of the generator 24. Such a generator rotor assembly 42 is described below with reference to Figures 6 to 1 1. The generator rotor assembly 42 has a non-drive end 70, whereby the non-drive end 70 faces away from the wind turbine driveline when the wind turbine 1 is in use, and a drive end 71 which faces toward the driveline when the turbine 1 is in use. The non-drive end 70 view of the generator rotor assembly 42 can be seen in Figure 5, and the drive end 71 view of the generator rotor assembly 42 can be seen in Figure 6.

The generator rotor assembly 42 is made up of a cylindrical ring structure 46 defining a central hollow portion and arranged to rotate around a rotational axis. The cylindrical ring structure 46 comprises a plurality of permanent magnet packages 48. In the present embodiment, the permanent magnet packages 48 are all of equal circumference and thickness. In some embodiments, the thickness of the permanent magnet packages 48 may vary with respect to one another. For example, the rotor may comprise permanent magnet packages 48 of two different thicknesses, where the permanent magnet packages 48 of different thicknesses are arranged alternately. The permanent magnet packages 48 are arranged coaxially around the rotational axis, such that when assembled the arrangement of permanent magnet packages 48 defines a cylindrical structure with a central hollow portion. The permanent magnet packages 48 are spaced apart by an equal distance such that a gap 41 is defined in between each pair of permanent magnet packages 48. These gaps 41 allow air that is provided centrally to the generator 24 to flow through the rotor structure 32 and cool the generator rotor assembly 42 as well as other parts of the generator 24, including parts that are located radially outside the rotor assembly 42. This airflow is further enhanced by the fact that no central hub is needed for providing structure and support for the rotor assembly 42.

The cylindrical ring structure 46 is defined by two end permanent magnetic packages 50 and a plurality of permanent magnet packages 48 provided therebetween. The two end packages 50 comprise a first end package 50 and a second end package 50 arranged at opposite ends of the cylindrical ring structure 46. Namely, as shown in Figure 5, the first end package 50 is located towards the non-drive end 70 of the cylindrical ring structure 46, and the second end package 50 is located towards the drive end 71 of the cylindrical ring structure 46. An end ring 52 is connected to the magnetic package located at the drive end 71 of the cylindrical ring structure 46, which end ring 52 does not comprise any permanent magnets itself.

The permanent magnet packages 48 comprise a plurality of tie rod holes 86 which extend axially through the permanent magnet packages 48. The holes 86 are located around the body of each of the permanent magnet packages 48. The holes 86 are preferably spaced apart by an equal distance, i.e. angle. The holes 86 of adjacent permanent magnet packages 48 are complementary in size and position, such that a plurality of tie rod bores is defined. The tie rod bores are arranged concentrically around the rotational axis. The tie rod bores extend through the end ring 52 and packages 48 of the cylindrical ring structure 46 from the first, or non-drive, end 70 to the second, or drive, end 71. A plurality of tie rods 54 extend through respective ones of the plurality of tie rod bores. There is a plurality of spacers or washers 56 arranged on the tie rods 54 and between adjacent permanent magnet packages 48. Consequently, the tie rod bores are defined by a repeating pattern of inner surfaces of tie rod holes and washers 56.

The permanent magnet packages 48 comprise a plurality of coaxially stacked ring-shaped segmented layers 80 (Figure 7), each comprising a plurality of contiguous segment sheets 82 arranged around the rotational axis to form the ring-shaped layer 80. The ring-shaped layers 80, formed of the segment sheets 82, are stacked coaxially to form a permanent magnet package 48.

The rods 54 and the permanent magnet packages 48, preferably together with the washers 56 provide for the main structure of the rotor. In order to allow the hub-less rotor to be connected to a drive shaft, e.g. the output shaft of the gearbox, the cylindrical ring structure 46 comprises a ring-shaped flange 57, as can be seen in Figure 5, which is securely attached to the first end package 50 which is towards the non-drive end 70. The ring- shaped flange 57 comprises a rotor connection portion 58 that is securely attached to the first end package 50 at the non-drive end 70 of the cylindrical ring structure 46, and a drive shaft connection portion 60, configured for indirect connection to the gearbox output shaft, which is also known as the drive shaft. The generator rotor assembly 42 is interfaced with a connector 44 (see Figure 5) for further parts, for example a brake disc.

The rotor connection portion 58 of the ring-shaped flange 57 is attached to the first end package 50 using the tie rods 54 which hold the permanent magnetic packages 48 together to form the cylindrical ring structure 46. The circumference of the rotor connection portion 58 of the ring-shaped flange 57 is substantially equal to the circumference of the first end package 50. The rotor connection portion 58 comprises a plurality of holes which extend axially through the rotor connection portion 58. The plurality of holes of the rotor connection portion 58 are arranged for receiving the plurality of tie rods 54 and attaching the ring-shaped flange 57 to the first end package 50. The drive shaft connection portion 60 of the ring-shaped flange 57, which can be seen clearly in Figure 8 and Figure 9, extends in a plane that is parallel to the rotor connection portion 58. The circumference of the drive shaft connection portion 60 is smaller than the circumference of the rotor connection portion 58. The drive shaft connection portion 60 is located within the central hollow portion defined by the cylindrical ring structure 46.

The ring-shaped flange 57 may be just a single ring of which a radially outer portion forms the rotor connection portion 58 and a radially inner portion the drive shaft connection portion 60. Alternatively, the ring-shaped flange 57 may further comprise an intermediary portion 62 (see Figure 8) connecting the rotor connection portion 58 to the drive shaft connection portion 60. This intermediary portion 62 may be angled relative to the two connection portions 58, 60, such that the ring-shaped flange 57 partially projects into the hollow portion of the generator rotor assembly 42. In the embodiment of Figure 8, the angle between the intermediary portion 62 and the rotor connection portion 58 around their common point (the vertex) is approximately 135 degrees. The angle between the intermediary portion 62 and the drive shaft connection portion 60 around their common point is approximately 135 degrees.

A drive shaft connection frame 68 is joined to the drive shaft connection portion 60 of the ring shaped flange 57. The drive shaft connection frame 68 extends into the central hollow portion of the cylindrical ring structure 46. The ring-shaped flange 57 and the drive shaft connection frame 68 provide a stable and space saving structure for joining the cylindrical ring structure 46 of the generator rotor assembly 42 to the drive shaft.

The ring-shaped flange 57 and the end ring 52 may be attached to either one of the end packages 50 by other means than the tie rods 54 that are used for that purpose in the embodiment described above.

Figure 10 shows a schematic side view of the cylindrical ring structure 46 without the end ring 52 and ring-shaped flange 57 in place. A schematic representation of the associated magnetic field produced by the stack of permanent magnetic packages 48, 50 is also shown. It is to be understood that the representation of the magnetic field is schematic and for the purposes of explanation only.

The arrangement of the stack of permanent magnetic packages 48, 50 results in a permanent magnetic field that can be thought of as field lines 90 which emerge from the north poles 92 of the permanent magnetic packages 48, 50 and which re-enter the south poles 93 of the permanent magnetic packages 48, 50. As is well known it the art, the magnetic field extends beyond the physical boundary of the cylindrical ring structure 46. This is represented by field lines 90 which extend beyond the edges of the cylindrical ring structure 46. It will be understood that the field lines 90 shown contained within the boundary of the magnetic packages 48, 50 actually project out from the page in a similar manner to the field lines 91 shown at either axial end of the cylindrical ring structure 46. There is a logarithmic decrease in magnetic field strength with increasing distance from the cylindrical ring structure 46.

Figure 1 1 shows a schematic side view of the cylindrical ring structure 46 with the end ring 52 and ring-shaped flange 57 in place and a schematic representation of the associated magnetic field 90. The end ring 52 and the ring-shaped flange 57 are made of a ferromagnetic material such that the field lines 90 generated by the stack of permanent magnetic packages 48, 50 preferentially pass through the end ring 52 and ring-shaped flange 57 due to their low reluctance. The magnetic field 90 is therefore substantially contained in the axial direction within the axial extent of the cylindrical ring structure 46.

As best illustrated by Figure 4, when assembled, the rotor 32 of the generator 24 is mounted within the stator 36 with an air gap 85 separating the stator 36 from the rotor 32. The air gap 85 is ideally as small as possible to minimise reluctance and flux leakage. However, the air gap 85 must be set to allow sufficient clearance between the rotor 32 and the stator 36 so that these components do not come into contact whilst the rotor 36 rotates in use. An example air gap size in a generator 24 for use in a wind turbine might be 1 to 5mm.

When the rotor 32 (comprising the cylindrical ring structure 46) is mounted within the stator 36, the magnetic field interacts with components of the generator 24; namely, the stator 36. The magnetic field lines 90 preferentially pass through the stator core 40 due to the low reluctance of the core material. This is beneficial as the core 40 serves to concentrate the magnetic field in the vicinity of the windings 38 so that the field 90 interacts with the windings 38 in the most efficient manner as the rotor 32 rotates within the stator 36.

It is important that the magnetic field 90 does not interact with any other components of the generator 24, as such interaction has the potential to cause stray currents within the systems and mounts of the generator 24 and other connected components. Much of the generator 24, gearbox 22, housing 20 and main shaft 26 etc. are metallic, and potentially ferromagnetic in their own right, and therefore there are a number of closed galvanic paths which have the potential to become electrically excited if they interact with the rotating magnetic field 90 of the rotor 32. If the cylindrical ring structure 46 did not include the end ring 52 and ring-shaped flange 57, the magnetic field at each axial end of the cylindrical ring structure 46 (illustrated by magnetic field lines 91) would extend beyond the axial extent of the rotor 32 and would therefore be able to interact with unintended components at either end of the rotor 32, thereby potentially causing damaging stray currents. It can therefore be seen that the end ring 52 and ring-shaped flange 57 act as flux shields which substantially prevent the magnetic field produced by the stack of permanent magnets 48, 50 from interacting with unintended parts of the generator 24 or any of the attached systems.

The gap 72 between the end permanent magnetic packages 50 and the end ring 52 and ring-shaped flange 57 is ideally in the range of 10mm to 40mm, for example approximately 20mm. Ideally the gap 72 is at least twice the size of the air gap 85 separating the rotor 32 from the stator 36. The gap 72 is ideally at least 5mm, however any suitable gap size may be used.

In an alternative example (not shown) the end ring 52 and/or ring-shaped flange 57 may be separated from the stack of permanent magnetic packages 48, 50 by a nonferromagnetic material such as a non-ferrous metal, a classic insulator, or any other suitable non-ferromagnetic material. In a further alternative example (not shown), the end ring 52 and/or ring-shaped flange 57 may be made of any suitable ferromagnetic material or composite material. For example, the end ring 52 and/or ring-shaped flange 57 may comprise a non-ferromagnetic composite material outer shell which contains a ferromagnetic core. Alternatively, the composite material may comprise ferromagnetic elements embedded in the fibre weave or ferromagnetic particles contained within the matrix.

The ring-shaped flange 57 may comprise a ferromagnetic rotor connection portion 58 and/or intermediary portion 62.

In one example (not shown), the end ring 52 and/or the ring-shaped flange 57 do not have the same circumference as the permanent magnetic packages 48, 50.

Claims

CLAIMS 1. A generator rotor assembly (32) for a wind turbine (1), comprising a permanent magnet structure (46) arranged to rotate about a rotational axis within a stator (36), the permanent magnet structure (46) having a first end (70) and a second end (71), and comprising:

a plurality of rotor laminations (48, 50) arranged along the rotational axis, a first flux shield (57) located at the first end (70) and adjacent a first end of the plurality of rotor laminations (48, 50); and

a second flux shield (52) located at the second end (71) and adjacent a second end of the plurality of rotor laminations (48, 50), wherein the first (57) and second (52) flux shields are made from ferromagnetic material.

2. The generator rotor assembly (32) of Claim 1 , wherein the permanent magnet structure (46) comprises a cylindrical ring structure, wherein the plurality of rotor laminations (48, 50) are arranged co-axially around the rotational axis.

3. The generator rotor assembly (32) of Claim 1 or 2, wherein the first (57) and/or second (52) flux shield is ring-shaped.

4. The generator rotor assembly (32) of Claim 3, wherein at least one of the first flux shield (57) and the second flux shield (52) is arranged co-axially around the rotational axis.

5. The generator rotor assembly (32) of Claims 3 or 4, when dependent on claim 2, wherein at least one of first flux shield (57) and the second flux shield (52) has the same radial cross-sectional profile as the plurality of rotor laminations (48, 50).

6. The generator rotor assembly (32) of any of the preceding Claims, wherein the first flux shield (57) is spaced from the first end (70) of the plurality of rotor laminations (48, 50) by a gap created by a predetermined axial distance (72).

7. The generator rotor assembly (32) of Claim 6, wherein an isolating spacer arrangement is provided in a gap created by a predetermined axial distance (72) between the first flux shield (57) and the first end (70) of the plurality of rotor laminations (48, 50).

8. The generator rotor assembly (32) of any of the preceding Claims, wherein the second flux shield (52) is spaced from the second end (71) of the plurality of rotor laminations (48, 50) by a gap created by a predetermined axial distance (72).

9. The generator rotor assembly (32) of Claim 8, wherein an isolating spacer arrangement is provided in a gap created by a predetermined axial distance (72) between the second flux shield (52) and the second end (71) of the plurality of rotor laminations (48, 50).

10. The generator rotor assembly (32) of any of the preceding Claims, wherein the first flux shield (57) is associated with a drive coupling (60) of the generator rotor assembly (32).

1 1. The generator rotor assembly (32) of Claim 10, wherein the drive coupling (60) and the first flux shield (57) are integral with one another.

12. The generator rotor assembly (32) of Claim 1 1 , wherein the drive coupling (60) comprises a radially extending flange (62) that extends from a coupling hub at a radially inwards position to the first flux shield (58) at a radially outwards position.

13. The generator rotor assembly (32) of any preceding claim, wherein the first flux shield (57) and the second flux shield (52) form part of a clamping arrangement such that the plurality of magnet packages (48, 50) form an assembly that is clamped in compression between the first (57) and second (52) flux shields.

14. A wind turbine comprising the generator rotor assembly (32) as claimed in any one of Claims 1 to 13, the wind turbine comprising a wind turbine tower (2), a nacelle (4) rotatably coupled to the tower (2), a rotating hub (8) mounted to the nacelle (4), and a plurality of wind turbine blades (10) coupled to the hub (8), wherein the nacelle (4) comprises the generator rotor assembly (32).