Patent Description:
Wind turbines convert kinetic energy from the wind into electrical energy, using a large rotor with a number of rotor blades. A typical Horizontal Axis Wind Turbine (HAWT) comprises a tower, a nacelle on top of the tower, a rotor hub mounted to the nacelle and a plurality of wind turbine rotor blades coupled to the rotor hub. Depending on the direction of the wind, the nacelle and rotor blades are turned and directed into an optimal direction by a yaw system for rotating the nacelle and a pitch system for rotating the blades.

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. So-called "direct drive" wind turbines that do not use gearboxes are also known. In a direct drive wind turbine, the generator is directly driven by a shaft connected to the rotor.

Ordinarily, the generator of a wind turbine is an IPM (interior permanent magnet) electric machine composed of an external stator assembly which surrounds an internal rotor assembly. The IPM internal rotor assembly is typically composed of multiple annular permanent magnetic packages, supported on a central shaft. The gearbox output shaft interfaces with the central shaft of the rotor assembly.

Like in other electric machines, the permanent magnetic packages are typically made of a stack of ring-shaped metal layers with aligned holes for receiving the permanent magnets that create the required magnetic field. For large generators, such as generators in large wind turbines, manufacturing the permanent magnet packages presents difficulties as the rings are simply too large to be manufactured in one piece. It is known to assemble the metal layers from a number of smaller segment sheets, all provided on a central hub to form a ring-shaped layer. Although the segmented layers may not have the same strength and structural integrity as layers made of a single piece of layer metal, the central hub provides for more than enough structural support for the rotor to withstand all centrifugal and other forces that act upon the rotor during use.

Another technical consideration for the design of wind turbine generators is that the generator becomes less effective as it heats up during use. This also applies to other key components of the wind turbine, such as the gearbox. Wind turbine performance and lifetime is therefore reliant upon efficient cooling of the generator.

Air-cooling is a cost-effective method of providing cooling of the generator. However, a megawatt-scale generator within the confined space of the generator housing produces too much heat for currently air-cooling methods to cool the generator effectively. The lack of efficient cooling of the generator results in a temperature rise in and around the generator components such as the rotor assembly.

The document <CIT> discloses a generator rotor assembly.

It is an object of the present invention to provide a solution to one or more of the problems mentioned above.

According to a first aspect of the invention, this object is achieved by providing a generator rotor assembly for a wind turbine, wherein the generator rotor assembly comprises a cylindrical ring structure defining a central hollow portion and arranged to rotate around a rotational axis. The cylindrical ring structure comprises a plurality of permanent magnet packages arranged coaxially around the rotational axis, the permanent magnet packages comprising a plurality of coaxially stacked ring-shaped segmented layers, a plurality of tie rod holes and a plurality of tie rods. The coaxially stacked ring-shaped segmented layers comprise a plurality of contiguous segment sheets arranged around the rotational axis to form the ring-shaped layer, the stacked layers being staggered such that segment breaks between two contiguous segment sheets in one of the layers are angularly offset with respect to segment breaks between two contiguous sheets in an adjacent layer. The tie rod holes extend axially through the layers of the permanent magnet packages, wherein the plurality of tie rod holes of adjacent permanent magnet packages are complementary in size and position, such that a plurality of tie rod bores is defined. The tie rods extend through respective ones of the plurality of tie rod bores.

The staggered configuration of the ring-shaped segmented layers leads to increased friction between the stacked layers of the permanent magnet packages. In addition thereto, axial tie-bolt preload forces add to the strength structural and structural integrity of the individual permanent magnet packages and the cylindrical ring structure as a whole. These advantages enable manufacturing large permanent magnet packages which have similar strength as solid rings and which can withstand centrifugal (and other) forces applied to it in a typical wind turbine generator. As a consequence, this allows large generator rotor assembly structures to be produced without needing to assemble the permanent magnet packages onto a central hub.

Not having a central hub in the rotor assembly results in a number of important benefits, such as reduced cost and weight and improved cooling airflow. Cooling air that is provided centrally to the generator can freely flow in axial and radial directions and effectively cool the rotor and any generator parts located in its direct vicinity. A further important advantage of the rotor structure according to the invention is the modular character of the rotor assembly. The technical specifications of the rotor assembly can easily be adapted to the required performance by selecting, e.g., the right number of permanent magnet packages and the number of layers per package.

In preferred embodiments, the generator rotor assembly is at least partially open at at least one of its end surfaces for allowing a cooling airflow to flow from an exterior of the generator rotor assembly into the central hollow portion. Cooling channels may be provided in between at least some of the plurality of permanent magnet packages in order to allow for a cooling airflow to flow from the central hollow portion, through the cooling channels towards an exterior of the generator rotor assembly.

Preferably, the generator rotor assembly further comprises a plurality of spacers arranged on the tie rods and between adjacent permanent magnet packages. Such spacers provide for air gaps between the subsequent permanent magnet packages, through which the cooling airflow can also reach the stator and any parts closer to the external housing of the generator.

In preferred embodiments, all segment sheets comprise a number of the tie rod holes, spaced apart over a tie rod separation angle, and an angular offset between two adjacent layers is a multiple of the tie rod separation angle. In order to ensure that the tie rods can extend through all the permanent magnet packages, it is important that the tie rod holes of adjacent layers are aligned, also when the layers are staggered and an angular offset between the layers is introduced. When all segment sheets have multiple tie rod holes, this allows for a higher number of different angular offsets that still allow for the necessary tie rod bores to be formed.

In an embodiment, the angular offset between any two adjacent layers in the permanent magnet packages is at least two tie rod separation angles. The larger distance between the segment breaks of adjacent layers, the larger the overlap of the respective segment sheets and the larger the friction between the two layers. The increased friction leads to improved strength and structural integrity for the magnet package as a whole.

In a special embodiment, for every layer in the permanent magnet package an angular offset with an adjacent layer is larger than an angular offset with the subsequent layer. The resulting zigzag arrangement further adds to the strength and structural integrity of the permanent magnet packages.

To further improve on these aspects, a number of layers between every two layers in the permanent magnet package that are not angularly offset with respect to each other may be equal to a total number of tie rod holes per segment sheet minus one. In such an embodiment, all available different angular offsets are in use.

An even more solid and strong permanent magnet package may be obtained by bonding the plurality of layers together, e.g. using an adhesive or bonding varnish such as backlack.

The cylindrical ring structure may further comprise a ring-shaped flange comprising a rotor connection portion that is securely attached to one of the end packages of the cylindrical ring structure. The flange further comprises a drive shaft connection portion that is configured for direct or indirect connection to a drive shaft. This flange enables connecting the hubless rotor to, e.g., an output shaft of the gearbox without impeding the flow of cooling air through the rotor centre and outwards to the permanent magnet packages and the stator.

The ring-shaped flange may be securely attached to the end package at the non-drive end of the rotor. The flange may be connected to the end package via the tie rods.

According to a further aspect of the invention, a wind turbine is provided comprising a generator with a generator rotor assembly as described above or below.

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

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 in to 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 <FIG>, 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 <NUM> comprises a tower <NUM>, a nacelle <NUM> rotatably coupled to the top of the tower <NUM> by a yaw system, a rotor hub <NUM> mounted to the nacelle <NUM> and a plurality of wind turbine rotor blades <NUM> coupled to the rotor hub <NUM>. The nacelle <NUM> and rotor blades <NUM> are turned and directed into the wind direction by the yaw system.

The nacelle <NUM> houses many functional components of the wind turbine, including the generator, gearbox, drive train and rotor brake assembly, as well as convertor equipment for converting the mechanical energy of the wind into electrical energy for provision to the grid. With reference to <FIG>, the nacelle <NUM> may include a shaft housing <NUM>, a gearbox <NUM> and a generator <NUM>. A main shaft <NUM> extends through the shaft housing <NUM>, and is supported on bearings (not shown). The main shaft <NUM> is connected to, and driven by, the rotor <NUM> and provides input drive to the gearbox <NUM>. The gearbox <NUM> 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 <NUM>, which converts the rotation of the gearbox output shaft into electricity. The electricity generated by the generator <NUM> 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 may therefore be considered optional.

The gearbox <NUM> and generator <NUM> may be coupled together in an integrated unit. <FIG> shows the generator <NUM> in more detail. In <FIG>, also the housing of the last stage of the gearbox <NUM> is shown as it is coupled to the housing of the generator <NUM>.

With reference firstly to the gearbox <NUM>, 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 <NUM> interfaces with a rotor <NUM> of the generator <NUM>. As such, the major axis of the gearbox output shaft defines the rotational axis of the generator <NUM>. In <FIG>, a cutaway view on the generator <NUM> only is provided. The generator <NUM> in the illustrated embodiment is an IPM (interior permanent magnet) electric machine having an external stator, which surrounds the rotor <NUM>. The stator includes stator windings <NUM> a stator core <NUM> and a stator frame which surrounds and supports the stator windings <NUM> and stator core <NUM>. 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 <NUM>, forming part of the rotor <NUM> of the generator <NUM>. Such a generator rotor assembly <NUM> is described below with reference to <FIG>. The generator rotor assembly <NUM> has a non-drive end, whereby the non-drive end faces away from the wind turbine driveline when the wind turbine is in use, and a drive end which faces toward the driveline when the turbine is in use. The non-drive end view of the generator rotor assembly <NUM> can be seen in <FIG>, and the drive end view of the generator rotor assembly <NUM> can be seen in <FIG>.

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

The cylindrical ring structure <NUM> is defined by two end packages and a plurality of permanent magnet packages <NUM> provided therebetween. The two end packages comprise a first end package <NUM> and a second end package arranged at opposite ends of the cylindrical ring structure <NUM>. Namely, as shown in <FIG>, the first end package <NUM> is located at the non-drive end of the cylindrical ring structure <NUM>, and the second end package is located at the drive end of the cylindrical ring structure <NUM>.

It is noted that an end package <NUM> is generally just a normal permanent magnet package, just like any other permanent magnet package <NUM> in the cylindrical ring structure <NUM>, with the sole exception that it is provided at an end of the cylindrical ring structure <NUM>. Alternatively, one or both of the end packages may have a greater thickness than the other permanent magnet packages <NUM>. The end packages <NUM> may further comprise additional features for allowing connection of the cylindrical ring structure <NUM> to other parts of the generator or a coating that covers the outer surfaces of the cylindrical ring structure <NUM>. An end ring <NUM> may be connected to one or both of the end packages <NUM>, which end ring <NUM> may not comprise any permanent magnets itself.

The permanent magnet packages <NUM> comprise a plurality of tie rod holes which extend axially through the permanent magnet packages <NUM>. The holes are located around the body of each of the permanent magnet packages <NUM>. The holes are preferably spaced apart by an equal distance, i.e. angle. The holes of adjacent permanent magnet packages <NUM> 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 packages <NUM> of the cylindrical ring structure <NUM> from the first end package <NUM> to the second end package, and possibly also through any additional end rings <NUM> or other structural elements that are directly connected to the cylindrical ring structure <NUM>.

A plurality of tie rods <NUM> extend through respective ones of the plurality of tie rod bores. There is a plurality of spacers or washers <NUM> arranged on the tie rods <NUM> and between adjacent permanent magnet packages <NUM>. Consequently, the tie rod bores are defined by a repeating pattern of inner surfaces of tie rod holes and washers <NUM>. It is noted that, in other embodiments, no washers <NUM> may be used at all, thereby providing a single permanent magnet package rotor that is also supported by a plurality of rods <NUM>.

The permanent magnet packages <NUM>, an embodiment whereof is shown in <FIG>, comprise a plurality of coaxially stacked ring-shaped segmented layers <NUM>, each comprising a plurality of contiguous segment sheets <NUM> arranged around the rotational axis to form the ring-shaped layer <NUM>. The tie rod holes <NUM> extend axially through the layers of the permanent magnet packages <NUM>, wherein the plurality of tie rod holes <NUM> of adjacent permanent magnet packages <NUM> are complementary in size and position, such that a plurality of tie rod bores is defined, and the tie rods <NUM> extend through respective ones of the plurality of tie rod bores.

A front view of a full ring-shaped layer <NUM> is shown in <FIG>. Close-ups of the segment sheets <NUM> are shown in <FIG>. The ring-shaped layer <NUM> comprises a plurality of segment sheets <NUM> arranged concentrically around the rotational axis. The ring-shaped layer <NUM> in this embodiment is made up of six segment sheets <NUM>, but other numbers of segment sheets <NUM> may be used in other embodiments. Effectively, the permanent magnet packages <NUM> of the generator rotor assembly are formed of stacked layers <NUM>, whereby each layer <NUM> is formed of a plurality of segment sheets <NUM> joined together at their segment edges to form a ring-shaped layer <NUM> with segment breaks. Preferably, all segment sheets <NUM> are identical and are dimensioned such that a whole number of segment sheets <NUM> makes up the <NUM> degrees of the complete ring-shaped layer <NUM>.

A segment sheet <NUM>, as shown in <FIG>, is an arc defined by an outer circumference <NUM>, an inner circumference <NUM> and an apex angle <NUM> (see <FIG>). The apex angle <NUM> is preferably equal to <NUM> degrees divided by the number of segment sheets <NUM> per layer <NUM>, such that all the segment sheets <NUM> used can be identical. A segment sheet <NUM> comprises two segment edges arranged at opposite ends of the segment sheet <NUM> and connecting the outer circumference <NUM> to the inner circumference <NUM>. The two segment edges are contiguous with the edges of adjacent segment sheets <NUM>.

The segment sheets <NUM> shown in <FIG>, comprises six magnet pairs <NUM> and an equal number of tie rod holes <NUM>. Together, six contiguous segment sheets <NUM> form a ring-shaped layer <NUM> with six segment breaks, <NUM> magnetic poles and <NUM> tie rod holes <NUM>. Here, magnetic poles are created by pairs of permanent magnets provided in magnet holes <NUM>. In this example, each segment sheet <NUM> has six tie rod holes <NUM> and provides for six magnetic North poles and six magnetic South poles. In alternative embodiments, the number of tie rod holes <NUM> per segment sheet <NUM> may differ from the amount of magnet pairs, which will lead to a different amount of tie rod holes <NUM> and/or magnet holes <NUM> per segment sheet <NUM>. Also the number of permanent magnets that is used for providing a magnetic pole may vary. Preferably, the number of magnetic holes <NUM> is a multiple of the number of tie rod holes <NUM>.

In the embodiment shown here, the positions of the tie rod holes <NUM> in the segment sheets <NUM> are such that partial tie rod holes <NUM> are arranged at the segment edges. When assembled into a full ring-shaped layer <NUM>, the partial tie rod holes <NUM> at each side of the segment breaks together form a full tie rod hole <NUM>. Alternative arrangements may result in segment sheets <NUM> with full tie rod holes <NUM> only. For example, the segment breaks may be provided in between the two magnet holes <NUM> of a magnet pair or even halfway one of the magnet holes <NUM>.

The ring-shaped layers <NUM>, formed of the segment sheets <NUM>, are stacked coaxially to form a permanent magnet package <NUM>, as shown in <FIG>. The layers <NUM> are stacked such that the segment sheets <NUM> of adjacent layers 80A-80F are angularly offset with respect to each other. As shown in <FIG>, this results in a staggering of layers <NUM> of the permanent magnet package <NUM>.

In order to allow for the forming of the tie rod bores through the permanent magnet packages <NUM>, the angular offset of two adjacent layers <NUM> needs to be equal to or a multiple of the tie rod separation angle, i.e. the angular distance between two adjacent tie rod holes <NUM>. In a symmetric setup, the tie rod separation angle is equal to <NUM> divided by the total amount of tie rods used in the cylindrical ring structure <NUM>, i.e. the segment sheet apex angle <NUM> divided by the number of tie rod holes <NUM> per segment sheet. In this example, with every segment sheet <NUM> comprising six tie rod holes <NUM>, five different angular offsets with respect to a first layer 80A are possible (i.e. six different possible orientations per layer 80A-80F).

According to the preferred embodiment shown in <FIG>, the angular offset of any two adjacent layers 80A-80F in the permanent magnet packages <NUM> is at least twice the tie rod separation angle. Compared to offsets that would only correspond to tie rod separation angle, this arrangement provides for added friction between adjacent layers <NUM> and improved strength and structural integrity for the magnet package <NUM> as a whole. Starting from the left hand side, the angular offset of the second layer 80B with respect to the first layer 80A is two tie rod separation angles. The angular offset of the third layer 80C with respect to the first layer 80A is five tie rod separation angles. The angular offset of the fourth layer 80D with respect to the first layer 80A is three tie rod separation angles. The angular offset of the fifth layer 80E with respect to the first layer 80A is one tie rod separation angle. The angular offset of the sixth layer 80F with respect to the first layer 80A is four tie rod separation angles. This translates in a layer-to-layer offset between the six consecutive layers 80A-80F of two, three, two, two and three tie rod separation angles, while still using all six available orientations. After six layers 80A-80F, the same pattern may be repeated until the package <NUM> is completed. Consequently, there will always be five layers <NUM> in between two layers with equal orientation, thereby again increasing the strength and structural integrity for the magnet package <NUM> as a whole. More generally, the number of layers between every two layers in the permanent magnet packages <NUM> that are not angularly offset with respect to each other equals the total number of tie rod holes <NUM> per segment sheet <NUM> minus one.

For further added friction between the layers 80A-80F and improved strength and structural integrity of the whole permanent magnet package <NUM>, every offset in one direction is followed by an offset in the other direction. In other words, for every layer 80A-80F in the permanent magnet package <NUM>, an angular offset with an adjacent layer 80A-80F is larger than an angular offset with the subsequent layer 80A-80F. Adding directions to the already listed layer-to-layer offset (measured in tie rod separation angles) between the six consecutive layers 80A-80F is {+<NUM>, +<NUM>, -<NUM>, -<NUM>, +<NUM>, +<NUM>}, whereby +<NUM> and -<NUM> leads to the same offset in a symmetric setup with six tie rod holes <NUM> per layer <NUM>. This zigzag arrangement provides for a much stronger friction bond between the different layers <NUM> of the permanent magnet package <NUM> than when all offsets would be in the same direction.

In the present embodiments, the number of available angular orientations (six, equal to the number of tie rod holes <NUM>) is lower than the number of layers in the permanent magnet package (twelve). Consequently, the angular offset between adjacent layers <NUM> can be different up to the sixth layer. Starting from the seventh layer, the pattern of rotation is repeated for the remaining layers <NUM> of the permanent magnet package <NUM>. It is noted that the permanent magnet package <NUM> may comprise any number of layers <NUM>, which number is not necessarily a multiple of the number of tie rod holes <NUM> per segment sheet <NUM>. Alternatively, in a thinner permanent magnet package <NUM>, when using thicker layers <NUM> or when using larger segment sheets <NUM> with more tie rod holes <NUM> per segment sheet, the total number of possible orientations may be equal to (or even lower than) the number of layers <NUM> in the permanent magnet package <NUM>. In this case, all layers <NUM> in the permanent magnet package <NUM> can be angularly offset with respect to each other.

The increased friction force between the ring-shaped layers <NUM> caused by staggering and further increased by the special staggering patterns results in the stack of layers <NUM> having a strength and structural integrity similar to that of a single solid ring of the same dimensions. For further improve structural integrity, the stacked ring-shaped layers <NUM> may be bonded together by an adhesive or bonding varnish such as backlack.

This staggered configuration enables manufacture of large permanent magnet packages <NUM> which have similar strength as solid rings and which can withstand centrifugal (and other) forces applied to it in a typical wind turbine generator. Therefore, it allows large generator rotor assembly structures, whereby manufacturing generator rotor assemblies from solid rings is not feasible, to be produced without needing to assemble the permanent magnet packages <NUM> onto a central hub. Not having a central hub in the rotor assembly results in a number of important benefits, such as reduced cost and weight and improved cooling airflow. The absence of a central hub means that air that is provided centrally to the generator is allowed to flow freely in axial and radial directions and cool the generator rotor assembly <NUM> and other parts of the generator that are located in its direct vicinity. In combination with the staggered arrangement of segmented ring-shaped layers <NUM>, the tie rods <NUM> and washers <NUM> may serve as shear pins which further prevent the layers from slipping relative to one another.

The rods <NUM> and the permanent magnet packages <NUM>, preferably together with the washers <NUM> provide for the main structure of the rotor. In order to allow the hubless rotor to be connected to a drive shaft, e.g. the output shaft of the gearbox, the cylindrical ring structure <NUM> comprises a ring-shaped flange <NUM>, as can be seen in <FIG>, which is securely attached to the first end package <NUM> which is at the non-drive end. In some embodiments, the ring-shaped flange may be securely attached to the second end package which is at the drive end. An end ring <NUM> may be provided in between the end package and the ring-shaped flange <NUM>.

The ring-shaped flange <NUM> comprises a rotor connection portion <NUM> that is securely attached to the first end package <NUM>, and a drive shaft connection portion <NUM>, configured for indirect connection to the gearbox output shaft, which is also known as the drive shaft. The generator rotor assembly <NUM> is interfaced with a connector <NUM> (see <FIG>) for further parts, for example a brake disc.

The rotor connection portion <NUM> of the ring-shaped flange <NUM> is attached to the first end package <NUM> using the tie rods <NUM> which hold the permanent magnetic packages <NUM> together to form the cylindrical ring structure <NUM>. The circumference of the rotor connection portion <NUM> of the ring-shaped flange <NUM> is substantially equal to the circumference of the first end package <NUM>. The rotor connection portion <NUM> comprises a plurality of holes which extend axially through the rotor connection portion <NUM>. The plurality of holes of the rotor connection portion <NUM> are arranged for receiving the plurality of tie rods <NUM> and attaching the ring-shaped flange <NUM> to the first end package <NUM>. The rotor connection portion <NUM> is attached parallel to and in direct contact with the first end package <NUM>. This can be seen particularly clearly in the part cutaway view and the side cross-section view of the generator rotor assembly shown <FIG> and <FIG>, respectively.

The drive shaft connection portion <NUM> of the ring-shaped flange <NUM>, which can be seen clearly in <FIG> and <FIG>, extends in a plane that is parallel to the rotor connection portion <NUM>. The circumference of the drive shaft connection portion <NUM> is smaller than the circumference of the rotor connection portion <NUM>. The drive shaft connection portion <NUM> comprises a ring-shaped element. In addition, the drive shaft connection portion <NUM> is located within the central hollow portion defined by the cylindrical ring structure <NUM>.

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

The intermediary portion <NUM> comprises a plurality of bridge portions <NUM> arranged at predetermined intervals along the rotor connection portion <NUM> and concentrically around the rotational axis, such that bridge gaps <NUM> are defined between adjacent bridge portions <NUM>. The bridge gaps <NUM> allow for cooling airflow passing through the ring-shaped flange <NUM> and into the internal structure of the generator.

The ring-shaped flange <NUM> also has a drive shaft connection frame <NUM> joined to the drive shaft connection portion <NUM>. The drive shaft connection frame <NUM> extends into the central hollow portion. In this example, the connection frame <NUM> has a frustoconical shape with an outer surface that may be approximately parallel to the intermediary portion <NUM> of the ring shaped flange <NUM>. The outer surface preferably comprises openings for allowing a cooling airflow to flow through and reach the internal structure of the generator. The drive shaft connection frame <NUM> is configured to connect the ring-shaped flange <NUM> to the drive shaft. The ring-shaped flange <NUM> and the drive shaft connection frame <NUM> provide a stable and space saving structure for joining the cylindrical ring structure <NUM> of the generator rotor assembly <NUM> to the drive shaft.

The drive shaft connection frame <NUM> can be seen more clearly in <FIG>, which is a non-drive end perspective view of the generator rotor assembly of <FIG>, with the connector <NUM> removed. The drive shaft connection frame <NUM> has a generally frustro-conical shape whereby the circular outer edge <NUM> of the base of the frame <NUM> is joined to the circular outer edge <NUM> of the drive shaft connection portion <NUM>. The frame <NUM> extends from the drive shaft connection portion <NUM> into the hollow portion defined by the cylindrical ring structure <NUM>. The frame <NUM> comprises a circular channel <NUM> arranged to rotate around the rotational axis with the cylindrical ring structure <NUM> of the generator rotor assembly <NUM>. The circular channel <NUM> is for receiving the gearbox output shaft. The frame <NUM> also comprises a perforated wall <NUM> which extends from the circular outer edge <NUM> of the base of the frame <NUM> to the circular channel <NUM>. The perforations in the perforated wall <NUM> facilitate airflow through the generator rotor assembly.

The permanent magnet packages <NUM> in the generator rotor assembly are connectable in a modular structure to alter the number of permanent magnetic rings comprised within the cylindrical ring structure. The structure of the generator rotor assembly of the present invention therefore enables a modular approach wherein rotors of any desirable number and type of permanent magnet packages <NUM> can be used.

When the generator is assembled, the generator rotor assembly <NUM> is surrounded by the external stator assembly <NUM>, whereby the external stator assembly <NUM> includes the stator core <NUM> and the stator frame which surrounds and supports the stator core <NUM>. Both the generator rotor assembly <NUM> and the generator stator assembly <NUM> are surrounded by a generator housing <NUM>, which can be seen in the exploded view of the generator housing <NUM>, the generator rotor assembly <NUM>, and the generator stator assembly <NUM> in <FIG>.

The generator rotor assembly <NUM> and the connection to the drive shaft allow for a cooling airflow through the central hollow portion, which is defined by the cylindrical ring structure <NUM>, and between the adjacent permanent magnet packages <NUM>.

Many modifications may be made to the specific examples described above without departing from the scope of the invention as defined in the accompanying claims. Features of one embodiment may also be used in other embodiments, either as an addition to such embodiment or as a replacement thereof.

For example, some of the permanent magnet packages <NUM> in the cylindrical ring structure <NUM> may have a different circumference to others within the cylindrical ring structure <NUM>. Some of the permanent magnet packages <NUM> in the cylindrical ring structure <NUM> may have a different thickness to others within the cylindrical ring structure <NUM>.

For example, the cylindrical ring structure <NUM> of the generator rotor assembly may comprise a ring-shaped flange with a rotor connection portion that is securely attached to the second end ring, which is at the drive end of the rotor assembly. The drive shaft connection portion may be configured for direct connection to the drive shaft.

The ring-shaped flange may be attached to either one of the end packages by other means than the tie rods <NUM> that are used for that purpose in the embodiment described above.

The drive shaft connection portion may extend in a plane coinciding with, rather than simply parallel to, the rotor connection portion.

The intermediary portion, which is defined between the rotor connection portion and the drive shaft connection portion, may be at an angle of <NUM>-<NUM>, preferably <NUM>-<NUM>, and even more preferably <NUM>-<NUM> degrees with respect to the rotor connection portion and a similar angle with respect to the drive shaft connection portion. When both angles are the same, but in different directions, the rotor connection portion and the drive shaft connection portion will be in parallel planes, which may be practical in view of connecting the gearbox output shaft to the rotor assembly. It is, however, noted that both angles are not necessarily equal and may differ where that would be desired.

Claim 1:
A generator rotor assembly (<NUM>) for a wind turbine, wherein the generator rotor assembly (<NUM>) comprises a cylindrical ring structure (<NUM>) defining a central hollow portion and arranged to rotate around a rotational axis, the cylindrical ring structure (<NUM>) comprising:
a plurality of permanent magnet packages (<NUM>) arranged coaxially around the rotational axis, the permanent magnet packages (<NUM>) comprising:
a plurality of coaxially stacked ring-shaped segmented layers (<NUM>) comprising a plurality of contiguous segment sheets (<NUM>) arranged around the rotational axis to form the ring-shaped layer, the stacked layers (<NUM>) being staggered such that segment breaks between two contiguous segment sheets (<NUM>) in one of the layers are angularly offset with respect to segment breaks between two contiguous segment sheets (<NUM>) in an adjacent layer,
a plurality of tie rod holes (<NUM>) which extend axially through the layers of the permanent magnet packages (<NUM>), wherein the plurality of tie rod holes (<NUM>) of adjacent permanent magnet packages (<NUM>) are complementary in size and position, such that a plurality of tie rod bores is defined, and
a plurality of tie rods (<NUM>) extending through respective ones of the plurality of tie rod bores.