EP2655878A1

EP2655878A1 - A sliding yaw bearing with a rotor load dependent rotary stiffness

Info

Publication number: EP2655878A1
Application number: EP10799021.0A
Authority: EP
Inventors: Thomas Duffey
Original assignee: 3E
Current assignee: Xant NV
Priority date: 2010-12-21
Filing date: 2010-12-21
Publication date: 2013-10-30
Also published as: WO2012084016A9; WO2012084016A1

Abstract

A wind-speed dependent yaw damper for regulating the rotation of a nacelle of a wind turbine relative to a tower of said turbine comprising: - a first ring array (130) comprising two or more concentrically arranged rings (132), (134) arranged around a central (A-A') axis configured for attachment to the base of the nacelle (110), whereby each ring is flanked on one or both radial sides by an annular seating space (136), (138), - a second ring array (140) comprising two or more concentrically arranged rings (142), (144) arranged around a central (A-A') axis configured for attachment to the top of the tower 120 whereby each ring is flanked on one or both radial sides by an annular seating space (146), (148), wherein the two or more rings (132), (134) of the first array (130) are arranged to intercalate in the annular seating spaces (146, 148) in the second array (140) and vice versa, thereby revolutely coupling the first and second arrays around an axis of rotation (A-A'), such that the application of a force to the nacelle (110) divergent from the central axis of the first ring array (130) is transmitted through the rings,thereby increasing friction between the rings and regulating the torque required to rotate the nacelle relative to the tower.

Description

A SLIDING YAW BEARING WITH A ROTOR LOAD DEPENDENT ROTARY STIFFNESS

FIELD OF THE INVENTION

The present invention is in the field of wind turbines. More in particular, it is in the field of a yaw damper for a wind turbine

BACKGROUND TO THE INVENTION

In general, wind turbines are optimised to maximize their power output over the complete wind speed operating range. In order to guarantee a proper and safe operation at all available wind speeds, several servo mechanisms are incorporated in the design such as the pitch system and the yaw system. In older turbines these mechanisms are

mechanically or hydraulically actuated, and in the most recent designs they are electric- mechanically operated using electrical motors and gearboxes. One such a control mechanism is a wind orientation mechanism or yaw control. In upwind wind turbines such a mechanism orients the turbine rotor plane perpendicular to the wind stream.

In passive or free downwind yaw systems, the turbine follows the wind as the wind direction changes. In the latter case, the yaw system is usually very simple, and in many cases only includes a yaw bearing. However simple in design, passive yaw systems have to be designed in a way that the nacelle does respond to a sudden change in wind direction with a yaw movement that is too fast, otherwise high gyroscopic loads in the blade roots and oscillations of the nacelle can contribute to sources of structural stress. During operation in turbulent and gusty winds, a sudden change in wind direction or excessive turbulence or wind shear can also result in excessive teeter motion and the turbine can yaw unwieldy and hence cut performance.

To reduce or eliminate these problems, the free yaw system should include mechanisms to maintain the yaw rate below an acceptable value determined by the calculation of the gyroscopic loads. Hence, a yaw damper may be installed to reduce the yaw rate sufficiently and modulate the performance and dynamic response of the wind turbine. Hydraulic yaw damping systems have been described elsewhere for example, in US 4,674,954 J.A.C. Kenfield), in addition to electro-mechanical systems (e.g. used on the endurance E-3120; http://www.endurancewindpower.com/e3120.html ). Most of the free yaw systems on large wind turbine have a low friction joint between the nacelle and tower and add a damping device (electric motors, hydraulic pumps, etc). On small wind turbines, damping devices are usually not used but the structure itself is designed to withstand the gyroscopic loads.

Some yaw systems use friction in the rotational yawing motion to limit the yaw rate and dampen the oscillations, however, they suffer from inaccurate tracking at low wind speed as the aerodynamic yaw torque is insufficient to overcome the friction torque under these conditions. They, hence, they also use active yaw system.

The friction required to keep the yaw rate below an acceptable value with respect to the gyroscopic loads in the blade roots at high wind speed is usually very high. This value is determined by the maximal aerodynamic yaw produced at the highest wind speed. The friction required to overcome the aerodynamic yaw torque and effectively dampen the yaw rate at such speeds is higher than at low wind speed. Hence, using high friction leads to an inefficient behavior at low wind speeds because at these speeds, the nacelle cannot be aligned by the aerodynamic yaw torque. The nacelle will not track the wind or position itself at a large yaw angle as the aerodynamic yaw torque increase with the yaw angle. The present invention provides a new system for dampening the yaw rate according to wind speed at the top of the tower, while avoiding the requirement for active yaw systems.

SUMMARY OF THE INVENTION

The present invention is a wind-speed dependent yaw damper for regulating the resistance to rotation of a nacelle of a wind turbine relative to a tower of said turbine on which the nacelle is attached. The nacelle is preferably a horizontal axis system i.e. the axle of the turbine blades is aligned essentially horizontally. The wind turbine tower is preferably longitudinal, and vertically mounted. The wind turbine nacelle is attached to a wind turbine tower using a revolute (rotatable or yawing) mounting. The tower may be fixed to the ground or to the seabed, or be floating on water.

In general the tower is not able to rotate around its longitudinal axis, while the nacelle is able to rotate around the longitudinal axis of the tower in order to track the wind direction and keep the rotor perpendicular to the dominating wind flow. The relative motion between the nacelle and the tower is known as the yawing or yaw motion, and is in most cases facilitated by a yaw bearing. One aspect provides a yaw damper comprising:

- a first ring array comprising two or more concentrically arranged rings arranged around a central (Α-Α') axis configured for attachment to the base of the nacelle, the rings are flanked on one or both radial sides by an annular seating space, - a second ring array comprising two or more concentrically arranged rings arranged around a central (Α-Α') axis configured for attachment to the top of the tower whereby the rings are flanked on one or both radial sides by an annular seating space,

wherein the two or more rings of the first array are arranged to intercalate in the annular seating spaces in the second array, and the two or more rings of the second array are arranged to intercalate in the annular seating spaces in the first array.

Two or more rings of the first array are arranged to intercalate (insert or couple) in the annular seating space of the second array. Similarly, two or more rings of the second array are arranged to intercalate (insert or couple) in the annular seating space of the first array. By virtue of intercalating, the first and second arrays are revolutely coupled around an axis of rotation. The application of a force divergent from the axis of rotation of the coupling is transmitter through the rings, which increases friction between the rings. The force is wind-speed dependent. As a consequence, the torque required to rotate the nacelle relative to the tower changes responsive to the wind speed.

At least one ring (134) of the first array (130) and at least one ring (142) of the second array (140) may be rigid, and

a circumferential surface of at least one of the other rings, a deformable ring (144), of the second array (140) may be deformable in a radial plane centred around the central axis (Α-Α') of the second array (140).

At least one ring (134) of the first array (130) and at least one ring (142) of the second array (140) may be rigid, and the attachment is rigid, and

a circumferential surface of at least one of the other rings, a deformable ring (144), of the second array (140) may be deformable relative to the rigid ring (142) of the second array (140), said deformity being in a radial plane centred around the central axis (Α-Α') of the second array (140). Said rigid rings (134, 142) may be the outermost ring of the first array (130) and innermost ring of the second array (140), or vice versa. A deformable ring may be segmented (132a, 132b, 132c, 144a, 144b, 144c), and the majority of segments (132b, 132c, 144b, 144c) are adapted for displacement, in a radial plane centred around the central axis (Α-Α') of the array to which the deformable ring is attached.

A deformable ring may be segmented (132a, 132b, 132c, 144a, 144b, 144c), and the majority of segments (132b, 132c, 144b, 144c) adapted for displacement, relative to the rigid ring (134, 142) of the array to which the deformable ring is, in a radial plane centred around the central axis (Α-Α') of the array to which the deformable ring is attached.

The minority of segments (132a, 144a), preferably one segment, may be held in fixed alignment with the rigid rings (134, 142).

Each adjacent segment of a ring may be connected using one or more compliant members, such as a spring.

One ring (134) of the first array (130) and one ring (142) of the second array (140) may be rigid, and

- the circumferential surfaces of all the other rings (132) of the first array (130) and of all the other rings (144) of the second array (140) may each be deformable in a radial direction.

All the rings (134) of the first array (130) and one ring (142) of the second array (140) may be rigid, and

- the circumferential surface of all the other rings (144) of the second array (140) may each be deformable in a radial direction.

The rings (134, 138) of the first array (130) may be attached to a mounting, adapted for attachment to the nacelle (1 10), and/or,

the rings (142, 144) of the second array (140) may be attached to a mounting, adapted for attachment to the tower (120).

The first-array mounting may comprise a plurality of radial slots for guidance of the ring segments (132a, 132b, 132c) in a radial plane centred on the central axis of the first array, and/or - the second-array mounting may comprise a plurality of radial slots for guidance of the ring segments (144a, 144b, 144c) in a radial plane centred on the central axis of the second array, and/or The deformable ring may be adapted for local or global radial expansion and/or contraction.

Another aspect of the invention provides a horizontal-axis wind turbine comprising a turbine tower (120) and a nacelle (1 10) in revolute attachment to the tower (120), incorporating a yaw damper (100) as described herein.

FIGURE LEGENDS

FIG. 1 is a schematic illustration of a cross-sectional view of a first and second array of a yaw damper, whereby the arrays are separated. The cross-sectional view is taken through a plane parallel to and touching the central (Α-Α') axis.

FIG. 2 is a schematic illustration of a cross-sectional view of a first and second array of a yaw damper, whereby the arrays are coupled. The cross-sectional view is taken through a plane parallel to and touching the central (Α-Α') axis.

FIG. 3 is a schematic illustration a transverse cross-sectional view of the first array of FIG. 1. The cross-sectional view is taken through a plane perpendicular to and touching the central (Α-Α') axis.

FIG. 4 is a schematic illustration a transverse cross-sectional view of second array of FIG. 1. The cross-sectional view is taken through a plane perpendicular to and touching the central (Α-Α') axis.

FIG. 5 is a schematic illustration a transverse cross-sectional view of a first and second array of a yaw damper which are coupled as shown in FIG. 2. The cross-sectional view is taken through a plane perpendicular to and touching the central (Α-Α') axis.

FIG. 6 is a schematic illustration a transverse cross-sectional view of a first array of a yaw damper as shown in FIG. 3, in which one ring is deformable i.e. segmented. The cross- sectional view is taken through a plane perpendicular to and touching the central (Α-Α') axis.

FIG. 7 is a schematic illustration a transverse cross-sectional view of a second array of a yaw damper as shown in FIG. 4, in which one ring is deformable i.e. segmented. The cross-sectional view is taken through a plane perpendicular to and touching the central (A- A') axis. FIG. 8 is a schematic illustration a transverse cross-sectional view of a first array of FIG. 6 and the second array of FIG. 7 are coupled. The cross-sectional view is taken through a plane perpendicular to and touching the central (Α-Α') axis.

FIG. 9 is a schematic illustration a transverse cross-sectional view of a first array of FIG. 3 and the second array of FIG. 8 are coupled. The cross-sectional view is taken through a plane perpendicular to and touching the central (Α-Α') axis.

FIG. 10 is a schematic illustration a transverse cross-sectional view of a first and second array of a yaw damper which are coupled as shown in FIG. 8, highlighting transmission of forces between the rings in light wind/no wind conditions. The cross-sectional view is taken through a plane perpendicular to and touching the central (Α-Α') axis.

FIG. 11 is a schematic illustration a transverse cross-sectional view of a first and second array of a yaw damper which are coupled as shown in FIG. 8, highlighting transmission of forces between the rings in moderate conditions. The cross-sectional view is taken through a plane perpendicular to and touching the central (Α-Α') axis.

FIG. 12 is a schematic illustration a transverse cross-sectional view of a first and second array of a yaw damper which are coupled as shown in FIG. 2, highlighting transmission of forces between the rings in high wind conditions. The cross-sectional view is taken through a plane perpendicular to and touching the central (Α-Α') axis.

FIG. 13 is a plan view of a mounting for rings of an array, which mounting is disposed with a plurality of radial slots.

FIG. 14 is a graph depicting the result of a simulation of the yaw angle of a nacelle when the wind speed is 5m/s and the wind direction is 20° and the yaw friction is 2000 Nm. FIG. 15 is a graph depicting the result of a simulation of the yaw angle of a nacelle when the wind speed is 5m/s and the wind direction is 20° and the yaw friction is 4000 Nm. FIG. 16 is a graph depicting the result of a simulation of the yaw angle of a nacelle when the wind speed is 9m/s and the wind direction is 20° and the yaw friction is 5000 Nm. FIG. 17 is a graph depicting the result of a simulation of the yaw angle of a nacelle when the wind speed is 9m/s and the wind direction is 20° and the yaw friction is 20000 Nm. DETAILED DESCRIPTION OF THE INVENTION

Before the present device of the invention is described, it is to be understood that this invention is not limited to the particular device or combinations therewith, since such device may, of course, vary. It is also to be understood that the terminology used herein is not intended to be limiting, since the scope of the present invention will be limited only by the appended claims. As used herein, the singular forms "a", "an", and "the" include both singular and plural referents unless the context clearly dictates otherwise.

The terms "comprising", "comprises" and "comprised of" as used herein are synonymous with "including", "includes" or "containing", "contains", and are inclusive or open-ended and do not exclude additional, non-recited members, elements or method steps. It will be appreciated that the terms "comprising", "comprises" and "comprised of" as used herein comprise the terms "consisting of", "consists" and "consists of". The recitation of numerical ranges by endpoints includes all numbers and fractions subsumed within the respective ranges, as well as the recited endpoints.

Unless otherwise defined, all terms used in disclosing the invention, including technical and scientific terms, have the meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. By means of further guidance, term definitions are included to better appreciate the teaching of the present invention.

In the following passages, different aspects of the invention are defined in more detail. Each aspect so defined may be combined with any other aspect or aspects unless clearly indicated to the contrary. In particular, any feature indicated as being preferred or advantageous may be combined with any other feature or features indicated as being preferred or advantageous.

In the following detailed description of the invention, reference is made to the accompanying drawings that form a part hereof, and in which are shown by way of illustration only of specific embodiments in which the invention may be practiced. It is to be understood that other embodiments may be utilised and structural or logical changes may be made without departing from the scope of the present invention. The following detailed description, therefore, is not to be taken in a limiting sense, and the scope of the present invention is defined by the appended claims.

The friction acting between the tower and nacelle that provides resistance to rotation may theoretically be split in two separate elements - basic friction and added friction. The basic friction is that between surfaces in the axial direction and depends upon parameters such as the weight of the nacelle, the fabrication materials of both the nacelle and tower at the axial contact surfaces, and the lubrication of these surfaces. The added (or kinetic) friction is that between surfaces in the radial direction, and is mainly dependent of the fabrication material in contact at the radial contact surfaces, their lubrication, and the wind speed. The value of the basic friction is essentially constant in a given wind turbine setting, and is at a level to assure that the nacelle can yaw at acceptable angles and acceptable rates at relative low wind speeds. The value of this basic friction is usually much higher than the value of the added friction value, and hence in classical turbines the effect of the wind speed is masked.

One way to control the value of the torque acting between the nacelle and the tower, is to increase the relative importance of the added friction value relative to basic friction responsive to the wind speed. The present invention achieves this by the yaw damper 100 which increases friction in the radial direction only, while maintaining a constant basic friction, hence increasing the ratio added friction to basic friction.

With reference to FIGs. 1 to 5, the present invention relates to a wind-speed dependent yaw damper 100 for regulating resistance to rotation of a nacelle 110 of a wind turbine relative to a tower 120 of said turbine. In FIG. 1 the nacelle 110 and tower 120 are only partly shown. The yaw damper 100 comprises:

- a first ring array 130 comprising two or more concentrically arranged rings 132, 134 arranged around a central (Α-Α') axis configured for attachment to the base of the nacelle 110, the rings are flanked on one or both radial sides by an annular seating space 136, 138,

- a second ring array 140 comprising two or more concentrically arranged rings

142, 144 arranged around a central (Α-Α') axis configured for attachment to the top of the tower 120 whereby the rings are flanked on one or both radial sides by an annular seating space 146, 148,

wherein the two or more rings 132, 134 of the first array 130 are arranged to intercalate in the annular seating spaces 146, 148 in the second array 140, and the two or more rings 142, 144 of the second array 140 are arranged to intercalate in the annular seating spaces 136, 138 in the first array 130 (FIG. 5).

By virtue the intercalated array 180 so formed, the first 130 and second 140 arrays are revolutely coupled around an axis of rotation (Α-Α'), which is the yawing axis of the nacelle. The application of a force to the nacelle 110 divergent from the central axis of the

■p:— + . - A nr : ~ + _™ :++— ι + — . . ~ + — . , : : — ι— +.. , — rings and regulating the torque required to rotate the nacelle relative to the tower. It is noted that one axis (Α-Α') is drawn in the figures since the axis of rotation, the central axes of the first and second arrays are essentially coaxial. At least one ring of the first array 130 (preferably the outermost or innermost ring 134) and at least one ring of the second array 140 (preferably the innermost or outermost ring 142) are preferably rigid. In other words, they are not radially deformable, at least under the normal working conditions of the wind turbine. One or more of the other rings 132, 144 of either or both arrays 130, 140 may be deformable, locally or globally, in a radial direction (e.g. can expand or contract in a radial direction), such that a force applied to the nacelle in a direction divergent from the axis of rotation, is transmitted via the deformable rings radially across the intercalated array 180, thereby increasing friction between the surfaces of the rings 132, 134, 142, 144 and providing increased resistance to rotation. A deformable ring may be achieved using a ring made from a plurality of rigid but radially slidable ring segments. By employing a combination of rigid and deformable rings in an intercalated array 180, force of wind applied to the nacelle is transmitted radially through the rings, increasing the contact force between all adjacent rings, thereby frictionally increasing the resistance to rotation of the nacelle responsive to the force of the wind. In the absence of a force divergent to the central axis of the rings of the first array, i.e. in lighter wind conditions 152 (FIG. 10) there is no or less force between the axial (curved) surfaces of the rings 132, 134 of the first array and of the rings 142, 144 of the second array, consequently, the nacelle can revolve relative to the tower with relatively little resistance.

When a light force divergent to the central axis of the rings of the first array is applied, i.e. in moderate wind conditions 154 (FIG. 11 ), an external force applied to the outermost nacelle ring 134 is transmitted via translatable, segmented rings 144, 132 to the innermost tower ring 142. The effect is an increase in frictional pressure between the axial surfaces of rings 134, 144, 132, 142. Consequently, the nacelle revolves relative to the tower under resistance, due to the application of friction. The principal frictional contact surfaces 158, 160 and 162 are highlighted in FIG. 11.

When a stronger force divergent to the central axis of the rings of the first array is applied, i.e. in high wind conditions 156 (FIG. 12), more frictional pressure is applied as the rings 132, 134 of the first array and the rings 142, 144 of the second array are subject to greater

The. roc i fi i r 11 relative to the tower. Frictional contact surfaces 158, 160 and 162 are highlighted are highlighted in FIG. 11.

There are preferably no discernable air gaps present between the curved surfaces of the rings. Even when no wind is present, rotation between the first and second arrays is under a constant force of friction. In all wind conditions, the central axes of the first and second arrays remain essentially co-axial (FIG. 10, 11 , 12) with each other, and essential co-axial with the axis of rotation or yawing. Thus, while the rings are capable of deformation, as the material used in the rings is non-compressible and no air gaps are present in the intercalated array, the deformable rings essentially retain their circular shape, even under high wind conditions.

The yaw damper 100 is able to provide a high friction at high wind speeds, which friction is released at lower wind speeds. There is no requirement for other mechanisms which rely on hydraulics or motorised systems. In view of the lack of additional systems which add expenditure and must be maintained, the instant invention provides a mechanically simple design for dampening excessive yawing that is economical to implement.

A ring 132, 134, 142, 144 as provided in the arrays 130, 140 has an essentially circular transverse (i.e. perpendicular to the central axis) profile. Typically it has a cylindrical form that is hollow. The ring 132, 134, 142, 144 has an axial (Α-Α') direction, and a central axis which is preferably coaxial with the central (Α-Α') axes of the other concentric rings of the array 130, 140. The cylindrical ring wall may be circumferentially intact for example in the case of an anchoring ring, or may be segmented. By segmented, it is meant divided into a plurality of separate arc-shaped elements, thereby allowing the ring 132, 144 to deform (e.g. expand or contract, locally or globally). The number of segments may be 2, 3, 4, 5, 6, 7, 8, 9, 10, 1 1 , 12, 13, 14, 15, 16, 17, 18, 19, 20, 21 , 22, 23, 24 or more, or a value in the range between any two of the aforementioned values. One axial end of an array ring 132, 134, 142, 144 is attached or configured for attachment to a structure (nacelle or tower), while the other axial end is open to receive one or more reciprocally coupling rings of the other array.

A ring may be made from any suitable material having the requisite stiffness and strength such as steel, or a polymer having the requisite friction coefficient. The suitable material may have a high coefficient of friction, or be at least partly coated or lined with a material having a high coefficient of friction. Example of a material having a high coefficient of friction is sintered steel. The dimensions of each ring and the number of rings 132, 134, 142, 144 will depend on the size and weight of the installation, and on the requisite friction required. The skilled person will understand that the length and diameter of the ring will increase the frictional effect. As a general guidance, for a nacelle having a weight of 5500 kg, the maximum outer diameter of a ring be 50 cm 100 cm, 200, cm, 300 cm 400 cm, or more, or a value in the range between any two of the aforementioned values, preferably 200 cm.

A ring may have an axial (Α-Α') length of 50 cm 100 cm, 200, cm, 300 cm 400 cm, or more, or a value in the range between any two of the aforementioned values, preferably 200 cm.

A ring may have a wall width (thickness in the radial direction) of 1 cm, 2 cm, 3 cm, or a value in the range between any two of the aforementioned values.

The rings in an array may each have an equal wall width. The annular seating spaces in an array may each have an equal radial width i.e. when the radial distance between two adjacent concentric rings is measured. Alternatively, at least two rings in an array may have different wall widths. Accordingly, the annular seating spaces in the reciprocating array may have different radial widths.

At least one ring 134 of the first array 130, preferably one ring, a first array anchoring ring 134, is configured for rigid attachment to the nacelle 110. As such, it can both rotate around the axis of rotation and displace in concert or unison with the nacelle 110 (FIGs. 3 and 6). It also has a rigid structure. In other words, it is not radially deformable, at least under the normal working conditions of the wind turbine. Preferably the first array anchoring ring 134 is the innermost or outermost ring of the array, preferably the innermost ring. Preferably, is it is circumferentially intact

Some, or all of the remainder of the rings 132 of the first array 130, may be configured for rigid attachment to the nacelle 110 such that they can both rotate around the axis of rntotinn onH H ic lo o in pnnport r»r i i nicrtn /ith tho firct o rro\/ anphnrinn ri nn 1 "ΧΛ f tnr hence the nacelle 110) (FIG. 3). This implies they also have a rigid structure. In other words, they are not radially deformable, at least under the normal working conditions of the wind turbine. Preferably they are circumferentially intact Alternatively, at least one, preferably all of the remainder of the rings 132 of the first array 130 may be deformable in a radial plane centred around the central axis of the first array. In other words, a part or all of the circumference of the ring 132 may be (locally) displaced in a radial plane centred around the central axis of the first array 130. A radially deformable ring 132 may be achieved using a segmented ring, wherein at least some of the segments are slidably displaceable in a radial plane centred around the central axis of the first array.

FIG. 6 depicts an embodiment wherein a ring 132 of the first array 130 is segmented 132a, 132b, 132c. By segmented, it is meant divided into separate arc-shaped elements, thereby allowing the ring 132 to deform (e.g. radially expand or contract locally or globally). The majority, preferably all but one, of the segments 132b, 132a of a segmented ring 132 may be configured for slidable attachment to the nacelle 110 so that they rotate around the axis of rotation in concert or unison with the anchoring ring 134 (and hence the nacelle 110), but can slidably displace in a radial plane around the axis of rotation, relative to the anchoring ring 134 (and hence nacelle 110). The minority, preferably one, of the segments 132a of said ring 132 may be configured for immovable attachment to the nacelle 110 so that it can rotate around the axis of rotation and displace in concert or unison with the first array anchoring ring 134 (and hence the nacelle 110). In other words, the minority segment 132a is in fixed relation with the first array anchoring ring 134. Each segment 132a, 132b, 132c may be attached to an adjacent segment using one or more deformable members such as a spring.

At least one ring 142 of the second array 140, preferably only one ring, a second array anchoring ring 142, is configured for rigid attachment to the tower 120. As such, it can both rotate around the axis of rotation and displace in concert or unison with the tower 120 (FIGs. 4 and 7). The second array anchoring ring 142 also has a rigid structure. In other words, it is not radially deformable, at least under the normal working conditions of the wind turbine. Preferably the second array anchoring ring 142 is the innermost or outermost ring of the array, preferably the innermost ring. Preferably is it is circumferentially intact At least one, preferably all of the remainder of the rings 144 of the second array 140 may be deformable in a radial plane centred around the central axis of the second array 140. In other words, a part of the circumference of the remaining ring 140 may be (locally) displaced in a radial plane centred around the central axis of the second array 140. A radially deformable ring may be achieved using a segmented ring, wherein at least some of the segments are slidably displaceable in a radial plane centred around the central axis of the array.

FIG. 7 depicts an embodiment wherein a ring 144 of the second array 140 is segmented 144a, 144b, 144c. By segmented, it is meant divided into separate arc-shaped elements, thereby allowing the ring 144 to deform (e.g. radially expand or contract, locally or globally). The majority, preferably all but one, of the segments 144b, 144c of a segmented ring 144 are configured for slidable attachment to the tower 120 such that they are capable of rotating around the axis of rotation in concert or unison with the anchoring ring 142 (and hence tower 120), but can slidably displace in a plane radial to the axis of rotation, relative to the anchoring ring 142 (and hence tower 120). The minority, preferably one, of the segments 144a of said segmented ring 144 is configured for rigid attachment to the tower 120; as such it can both rotate around the axis of rotation and displace in concert or unison with the tower 120. In other words, the minority segment 144a is in fixed relation with the second array anchoring ring 142. The segments 144a, 144b, 144c may be adjacently attached to each other using a deformable member such as a spring.

The application of a force to the nacelle 110 divergent from the central axis of the first ring array 130 applies a force that is transmitted through the between the anchoring ring 134 of the first array 130 and the anchoring ring 142 of the second array 140 via the ring segments 132a, 132b, 132b, 144a, 144b, 144c, reinforcing the friction between the rings 142, 144 of the second array 142, 144, thereby regulating the torque required to rotate the nacelle 110 relative to the tower 120. As explained elsewhere herein, an array 130, 140 as used in the yaw damper 100 comprises two or more concentrically arranged rings 132, 134, 142, 144 arranged around a central axis. In the first array 130, the rings configured for or are in fixed attachment to the base of the nacelle 110. In the second array 140, the rings are configured for or are in fixed attachment to the top of the tower 120. Each ring of the array 130, 140 may be fixed at one axial end to a mounting, such as a circular disc, which mounting is attached or configured for attachment to the nacelle or tower, preferably in fixed relation. The other axial end of a ring is preferably open to receive a reciprocally coupling ring present on the other array.

The mounting 190 (FIG. 13) may have a plurality of radial slots 192, 194, 196 for slidable attachment of at least some of the ring segments. As such, the segments can be guided for radial displacement within the slots 192, 194, 196.

In each array 130, 140, the two or more rings 132, 134, 142, 144 are arranged concentrically. In other words, when two or more rings are present, their central axes are essentially coaxial, and are arranged one inside the other.

The number of rings 132, 134, 142, 144 in an array 130, 140 may be 1 , 2, 3, 4, 5, 6, 7, 8, 9, 10 or more, preferably 2. The number of rings in the first array may be less than, equal to or more than the number of rings in the second array, preferably equal.

A ring 132, 134, 142, 144, preferably each and every ring, is flanked on one or both radial sides by an annular seating space 146, 148. In other words, it is flanked on its inner or outer or both ring surfaces by an annular seating space 136, 138, 146, 148. The annular seating space of an (e.g. first) array is configured to receive a ring of the other (e.g. second) intercalating array. It provides a space into which a reciprocating (inserting) ring of the other array can be seated. The annular seating space may be confined to a gap between two adjacent concentric rings of an array, in which case an annular space is evident. In the case of an innermost ring (e.g. 132) of an array, it may extend towards the central axis of the ring, thereby having a cylindrical form that incorporates said annular shape. In the case of an outermost ring (e.g. 144) of an array, it may extend away from central axis of the ring, thereby having a volumetric form that incorporates said annular shape. It will be appreciated that the space defined herein incorporates said annular space. In general, but not necessarily, the outermost ring (e.g. 134) may be flanked on its inner ring surface by an annular seating space (e.g. 138); the innermost ring (e.g. 142) may be flanked on its outer ring surface by an annular seating space (e.g. 146); an intervening ring may be flanked on both its outer and inner ring surfaces by an annular seating space. A ring may be separated from a neighbouring ring by an annular seating space.

An annular seating space 136, 138, 146, 148 of an array may have a minimum radial rings. In the case of the innermost receiving ring (e.g. 132), it is the radial distance between the inner surface of the ring to the central axis. In the case of an outer most receiving ring (e.g. 144), it is the radial distance between the outer surface of the ring to edge of the array structure.

The annular seating space 136, 138, 146, 148 of an array has a minimum axial depth that is the minimum axial distance between one axial end of the space and the other i.e. from an open end to a closed end of the space. An annular seating space present in a first array 130 is dimensioned to receive a reciprocating ring of the second array 140. Similarly, an annular seating space present in a second array 140 is dimensioned to receive the reciprocating ring of the first array 130. More in particular, the radial width of an annular seating space is the same size or slightly greater than the radial width of the reciprocating ring wall, so that there are no substantial air gaps. The radial width of an annular seating space may be 1 % or 2 % or more greater than width of the ring wall for insertion into the annular seating space.

The skilled person will appreciate that selection of the radial width of the annular seating space and intercalating ring wall will have an effect on the friction at low and high wind speeds, as will the axial length of the ring wall.

The two or more rings 132, 134 of the first array 130 are arranged to intercalate in the annular seating spaces 146, 148 of the second array 140. The two or more rings 142, 144 of the second array 140 are arranged to intercalate in the annular seating spaces 136, 138 in the first array 130. Once intercalated, the first and second arrays are revolutely coupled, as shown, for instance, in FIGs. 5 and 9. The first array 130 is able to rotate relative to the second array 140. Preferably, there is no limit to the rotation i.e. it may rotate in either direction, and in multiple turns. In a preferred arrangement (FIG. 8), one ring (134) of the first array (130) and one ring (142) of the second array (140) is rigid and rigidly attached to the nacelle, and

all the other rings (132) of the first array (130) and of all the other rings (144) are each deformable, preferably segmenetd. In another preferred arrangement (FIG. 9), all the rings (134) of the first array (130) and one ring (142) of the second array (140) is rigid, and all the other rings (144) of the second o rro\/ ( Λ AC\\ a ra aorh rlc_fnrmo lc- nrafarohK/ The yaw damper 100 of the invention provides frictional resistance to the revolute motion between the nacelle and tower. It is preferable that it has no bearing function, more in particular that the arrangement of concentric rings do not act as bearings. In such case the weight of the nacelle is borne by a separate bearing (ball bearing or sliding bearing) disposed, for example, around the outside of the yaw damper 100. While a bearing function of the yaw damper is not preferred, however, it is not necessarily excluded from the scope of the invention.

Another aspect described is a horizontal-axis wind turbine described herein comprising the turbine tower 120 and a nacelle 110 in revolute attachment to the tower 120, comprising the yaw damper 100 as described herein. The turbine tower 120 may be at least partially hollow. The nacelle 110 may be dismountably attached to the tower 120.

Although the preferred embodiments of the invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.

EXAMPLES

The improvement of the wind dependent friction on the yaw system behaviour has been confirmed by simulations performed on an aero-elastic code. The simulations have been performed with a defined wind turbine at different wind speed (3-5-7-9-1 1 -13-15-17-19- 21 m/s) and different friction value on the yaw system. Each time the wind turbine has been released with an initial yaw angle of 20°. Two different wind conditions have been simulated with deterministic wind (steady conditions) or with turbulent wind. The major outputs of these simulations are the yaw angle, the stability of the wind turbine and the yaw rate. These simulations show the need to have a large friction value on the yaw system at high wind speed to decrease the oscillations and keep the yaw rate below an acceptable value. At the same time, it shows that at low wind speed, the friction value must be lowered for decreasing the yaw error (remaining yaw angle). In FIGs. 14 and 15, the wind speed is 5m/s and the wind direction is 20°. With 2000Nm of yaw friction, the final yaw error (angle remaining angle between wind direction and nacelle cv c\ ic ¾ R° /Elfi 1 A\ anH with innflMm it ic Λ Α° ^PIft 1 \ In FIGs. 16 and 17, the wind speed is 9m/s and the wind direction is 20°. With 5000Nm of yaw friction, the final yaw error is 4° (FIG. 16) and with 20000Nm it is 14° (FIG. 17).

Claims

1 . A wind-speed dependent yaw damper for regulating the rotation of a nacelle of a wind turbine relative to a tower of said turbine comprising:

- a first ring array (130) comprising two or more concentrically arranged rings (132), (134) arranged around a central (Α-Α') axis configured for attachment to the base of the nacelle (1 10), whereby each ring is flanked on one or both radial sides by an annular seating space (136), (138),

- a second ring array (140) comprising two or more concentrically arranged rings (142), (144) arranged around a central (Α-Α') axis configured for attachment to the top of the tower 120 whereby each ring is flanked on one or both radial sides by an annular seating space (146), (148),

wherein the two or more rings (132), (134) of the first array (130) are arranged to intercalate in the annular seating spaces (146, 148) in the second array (140) and vice versa, thereby revolutely coupling the first and second arrays around an axis of rotation (Α-Α'), such that the application of a force to the nacelle (1 10) divergent from the central axis of the first ring array (130) is transmitted through the rings, thereby increasing friction between the rings and regulating the torque required to rotate the nacelle relative to the tower.

2. Yaw damper (100) according to claim 1 , wherein

- at least one ring (134) of the first array (130) and at least one ring (142) of the second array (140) is rigid, and

- a circumferential surface of at least one of the other rings, a deformable ring (144), of the second array (140) is deformable in a radial plane centred around the central axis (Α-Α') of the second array (140).

3. Yaw damper (100) according to claim 1 or 2, wherein said rigid rings (134, 142) are the outermost ring of the first array (130) and innermost ring of the second array (140), or vice versa.

4. Yaw damper (100) according to any of claims 1 to 3, wherein a deformable ring is segmented (132a, 132b, 132c, 144a, 144b, 144c), and the majority of segments (132b, 132c, 144b, 144c) are adapted for displacement, in a radial plane centred around the central axis (Α-Α') of the array to which the deformable ring is attached.

5. Yaw damper (100) according to any of claims 1 to 4, the minority of segments (132a,

1 ΑΑα 1 A \

6. Yaw damper (100) according to claims 4 or 5, where each adjacent segment of a ring is connected using one or more compliant members.

7. Yaw damper (100) according to any of claims 1 to 6, wherein

- one ring (134) of the first array (130) and one ring (142) of the second array (140) is rigid, and

- the circumferential surfaces of all the other rings (132) of the first array (130) and of all the other rings (144) of the second array (140) are each deformable in a radial direction.

8. Yaw damper (100) according to any of claims 1 to 7, wherein

- all the rings (134) of the first array (130) and one ring (142) of the second array (140) is rigid, and

- the circumferential surface of all the other rings (144) of the second array (140) is each deformable in a radial direction.

9. Yaw damper (100) according to any of claims 1 to 8, wherein:

- the rings (134, 138) of the first array (130) are attached to a mounting, adapted for attachment to the nacelle (1 10), and/or,

- the rings (142, 144) of the second array (140) are attached to a mounting, adapted for attachment to the tower (120).

10. Yaw damper (100) according to any of claims 4 to 9, wherein:

- the first-array mounting comprising a plurality of radial slots for guidance of the ring segments (132a, 132b, 132c) in a radial plane centred on the central axis of the first array, and/or

- the second-array mounting comprising a plurality of radial slots for guidance of the ring segments (144a, 144b, 144c) in a radial plane centred on the central axis of the second array, and/or

1 1 . Yaw damper (100) according to any of claims 2 to 10, wherein the deformity is radial expansion and/or contraction.

12. Yaw damper (100) according to any of claims 2 to 1 1 , wherein attachment of the at least one ring (134) of the first array (130) and at least one ring (142) of the second array (140) is rigid.

13. A horizontal-axis wind turbine comprising a turbine tower (120) and a nacelle (1 10) in revolute attachment to the tower (120), incorporating a yaw damper (100) according to any of claims 1 to 12.