WO2022258520A1

WO2022258520A1 - Wind turbine with combined pitch and radial displacement coupling and control method

Info

Publication number: WO2022258520A1
Application number: PCT/EP2022/065187
Authority: WO
Inventors: Morten Fogtmann KRISTIANSEN
Original assignee: Aarhus Universitet
Priority date: 2021-06-07
Filing date: 2022-06-03
Publication date: 2022-12-15

Abstract

The invention relates to a wind turbine rotor comprising a rotor hub, aerodynamic blades radially extending away from the rotor hub and may be configured to generate lift, torque or lift that imposes a torque, to rotate the rotor upon being exposed to wind, said aerodynamic blades may each have a root and a tip, a connecting element connecting each aerodynamic blade with the rotor hub, said connecting element may be configured to enable a radial displacement of the whole of each aerodynamic blade between an innermost position and an outermost position of the whole of each aerodynamic blade, said connecting element may comprise a mechanical coupling between the radial displacement of the aerodynamic blade and the pitch of the aerodynamic blade so that a radial displacement of the aerodynamic blades may provide a change in pitch of the aerodynamic blade and/or so that a change in pitch of the aerodynamic blade provides a radial displacement of the aerodynamic blade.

Description

WIND TURBINE WITH COMBINED PITCH AND RADIAL DISPLACEMENT COUPLING AND CONTROL METHOD

FIELD OF THE INVENTION

The present invention relates to the general field of operation and/or general design of wind turbines.

BACKGROUND OF THE INVENTION

The efficiency, energy production and/or energy output of the wind turbine is/are dependent on a number of factors, such as the length of the blades, number of blades, aero dynamical shape of blade cross sections, pitch angle and rotational speed of the rotor. The location of the wind turbine and the wind speed impacting the blades of the wind turbine, often plays a secondary role with respect to the operation condition of the wind turbine.

A common way to increase the power production of wind turbines is to increase the length of the blades. The total power that can be extracted from the wind will therefore increase. However, this also results in added forces and strains on the wind turbine, which can damage the wind turbine. At high wind speed, the blades are typically pitched to control the production of electricity. Such a pitching is typically implemented as electrical components, such as generator, transformer, converter) of the wind turbine are designed to sense the electrical effect produced.. Thus, by pitching the blades, the forces and power output of the wind turbine can be controlled.

It is further possible to change the length of the blades to control the power and load strain, such as with a structure disclosed in WO 03/102414 or WO 03/026082. Such a solution allows for two control variables, the pitch and the length of the blade.

However, the structure disclosed in WO 03/036082, where the extension of the blade and pitch is separate mechanical mechanisms, results in a mechanically complex structure where multiple actuators and couplings are needed. The structure disclosed in WO 03/102414 consists of a fixed length part of the blade and a moveable outer part of the blade. The moveable blade in WO 03/102414 can further be pitched and moved radially in a slider track that can have a small amount of twist. However having a blade with two distinct sections, one section being pitchable and another non-pitchable, will create additional unbalanced forces on the blade and will restrict the operating range of the wind turbine leading to additional mechanical wear and tear. Further, it also limits the range of the pitch, as there can only be a small pitch difference between the two sections.

Hence, an improved wind turbine that allows for the control of the pitch and length of the blade would be advantageous, and in particular, a more structural sane and/or reliable control method would be advantageous.

OBJECT OF THE INVENTION

It is a further object of the present invention to provide an alternative to the prior art.

In particular, it may be seen as an object of the present invention to provide a wind turbine that solves the above-mentioned problems of the prior art of extracting the maximum amount of power from the wind.

SUMMARY OF THE INVENTION

Thus, the above described object and several other objects are intended to be obtained in a first aspect of the invention by providing a wind turbine rotor that may comprise

• a rotor hub,

• aerodynamic blades radially extending away from the rotor hub and may be configured to generate lift, torque or lift that imposes a torque, to rotate the rotor upon being exposed to wind, said aerodynamic blades may each have a root and a tip,

• a connecting element connecting each aerodynamic blade with the rotor hub, said connecting element may be configured to enable a radial displacement of the whole of each aerodynamic blade between an innermost position and an outermost position of the whole of each aerodynamic blade, said connecting element may comprise a mechanical coupling between the radial displacement of the aerodynamic blade and the pitch of the aerodynamic blade so that a radial displacement of the aerodynamic blades may provide a change in pitch of the aerodynamic blade and/or so that a change in pitch of the aerodynamic blade provides a radial displacement of the aerodynamic blade.

By having, a single mechanical coupling that radially extends the whole of the blade as well as pitching the blade is advantageous since it can be implemented as only one mechanical structure and is thereby overall simpler. Further, it allows for a more dynamical control of the forces experienced by the wind turbine as well as the power extracted from the wind.

In preferred embodiments, the connecting element may comprise

• an elongate stub part connected at an end to the rotor hub and slideable engaged with the aerodynamic blade, such that the aerodynamic blade's inner and outermost positions may be obtained by sliding the blades along the stub part.

In an embodiment, the elongated stub part moves within a recess of the blade.

In preferred embodiments, the connecting element may comprise a stop element adapted to prevent the aerodynamic blade advancing beyond its outer most position.

In preferred embodiments, the mechanical coupling may comprise one of the stub part or the blades comprising a guiding element, such as a longitudinal extending groove or tongue and the other of the stub part or the blades comprising an engagement element, such as a protrusion adapted to fit within the groove or an opening in which the tongue fits, engaging with the guiding element to control the rotation of the blades around the stub part during sliding of the blade along the stub part.

Such an arrangement, where a guiding and engagement element are utilized as the mechanical coupling is advantageous since it allows for a change of the pitch as a result of a radial extension of the blade along the stub part. It further allows the pitch change pr. radial extension to be pre-defined by the shape of the guiding element, creating a simple robust mechanical coupling between the blade and the stub part.

In preferred embodiments, the guiding element may have at least a section forming at least a part of a screw thread.

In preferred embodiments, the section forming at least a part of a screw thread may have increasing pitch towards the root or towards the hub, so as to preferably form a telescopic helix.

In preferred embodiments, a sliding rod may be couple to the blade for facilitating the sliding of the blades on the stub part, such that the sliding rod contains either the groove or tongue and is adapted to facilitate the mechanical coupling.

Having a sliding rod couple to the blade will ensure that the blade remains sufficient stiff and will further ensure that the coupling forces between the blade and connecting member are preferable transferred through the sliding rod. This is advantageous since the sliding rod may be manufactured using a different material than material of the blades, such that the sliding rod could be manufactured from a more stiff material, which can handle higher loads than the blade. This will ensure that the blade will not deform at the connected point due to the load transfer.

In preferred embodiments, the sliding rod may be attached to the blade within a recess of the blade at the root end of the blade, the blades may be adapted to encase the elongated stub part of the connecting element within the recess when the sliding rod slides in connection with the stub part, wherein either the elongated stub part may be hollow and the sliding rod may be sliding within the stub part or the sliding rod is hollow and encasing the stub part.

In other preferred embodiments, the sliding rod may be attached to the root of the blades and adapted to slide in connection with the stub part, such that the either the elongated stub part may be hollow and the sliding rod may be sliding within the stub part or the sliding rod may be hollow and may encase the stub part.

In preferred embodiments, the wind turbine may comprise two blades, the two blades may be positioned across from each other with the connection elements of the blades may be adapted to slide within each other.

In preferred embodiments, a moving actuator may be configured for providing the radial displacement of each of the blades.

In preferred embodiments, the stub part may be hollow and the moving actuator may be configured for moving within the hollow stub part.

In other embodiments, the moving actuator may be attached to the rotor hub by a universal joint, such that the actuator may be able to move when the blades are pitching.

In preferred embodiments, a pitching actuator may be configured for providing a change in pitch of each of the blades.

In preferred embodiments, the moving actuator may be a hydraulic actuator, a pneumatic actuator and/or an electrical actuator.

In preferred embodiments, the relationship between pitch and radial displacement may be dynamical over the whole of the radial displacement, such as that the innermost extension range has a large pitch rotation per radial displacement and the outermost extension has a small or zero pitch rotation per radial displacement.

In preferred embodiments, the connecting element is configured to operate in a low wind mode and a high wind mode, wherein

• a rate of change of pitch is larger in high wind mode ( a_highwind ) than a rate of change in pitch in low wind mode ( a_lowwind ), preferably, the rate of change in pitch is changed continuously from the high speed rate to the low speed rate, and • a total displacement in high wind mode {AR_{high wind}) is smaller than the total displacement in low wind mode (AR,_0WWind).

In still further preferred embodiments, the connecting element (6) is configured to operate in a park mode wherein a rate of change of pitch (d_park) is larger than in high wind mode (a_{high wind}), and a total displacement in in park mode (Ar_park) is larger than in high wind mode ( AR_highwind ).

In a second aspect of the present invention a method of operating a wind turbine having a rotor is provided, comprising acquiring an indication of the wind speeds experienced by the wind turbine, acquiring an indication of the power extracted from the wind by the wind turbine, controlling the radial displacement of the aerodynamic blades (3) based in part on the wind-speeds and the extracted power, wherein the controlling may comprise when the wind speed is below a cut-in velocity, contracting the blades to an idle position, when the wind speed is between the cut-in wind speed and a rated wind speed, operating the wind turbine in a variable rotational speed mode and radial extending the blades while keeping the power extracted under the rated power and obeying the operating constraints of the wind turbine, when the wind speed is above the rated wind speed, radial contracting the blades and when contracting the blades, the mechanism pitches the blade as well to contain the power to the rated power, and in an emergency brake situation, fully contracting the blades and pitching to stop position (90 degrees).

In preferred embodiments, the controlling may further comprise limiting the rotational speed of the wind blade. By effective cross-area is preferable meant the project surface area of the wind that can impact the blade and create lift or torque.

The first and second aspect of the present invention may each be combined with any of the other aspects. These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.

BRIEF DESCRIPTION OF THE FIGURES

The wind turbine rotor according to the invention will now be described in more detail with regard to the accompanying figures. The figures show one way of implementing the present invention and is not to be construed as being limiting to other possible embodiments falling within the scope of the attached claim set.

Figure la illustrates an embodiment of the wind turbine in connection with a wind turbine,

Figure lb illustrates an embodiment of the extension mechanism and relationship between extension and angle,

Figure lc i) and ii) illustrate the extension of the blades,

Figure 2a and 2b illustrate an embodiment of the mechanical coupling that is responsible for the rotation of the wind turbine blade,

Figure 3 is an embodiment of the power curve for different blade lengths,

Figure 4 is an embodiment of the pitch of the wind blades at different radial displacements,

Figure 5 is an embodiment of the relationship between radial displacement and pitch wherein figure 5A illustrates an idealized relationship and figure 5B illustrates simulations involving a coupling mechanism as disclosed herein,

Figure 6 illustrates the coupling mechanism, Figure 7 illustrates an embodiment of the sliding rod,

Figure 8 is a see-through version of the coupling mechanism,

Figures 9-10 show different views of the coupling mechanism of figure 8,

Figures 11 and 12 show a reversed embodiment of the coupling mechanics of figures 9-12,

Figure 13 shows some of the different embodiments of the mechanical coupling between the blade and the rotor hub.

DETAILED DESCRIPTION OF AN EMBODIMENT Referring to figure la, an embodiment of a wind turbine rotor according to the present invention is shown. The wind turbine rotor comprises a rotor hub 2, and aerodynamic blades 3 radially extending away from the rotor hub 2. The blades 3 are configured to generate lift, torque or lift that impose a torque to rotate the rotor upon being exposed to wind, said aerodynamic blades 3 each has a root 4 and a tip 5. As illustrated, the wind turbine comprises three aerodynamic blades, by rotors with other number of blades are considered to be within the scope of the invention.

As seen in figure lb the turbine further comprises a connecting element 6 connecting each aerodynamic blade 3 with the rotor hub 2, said connecting element 6 being configured to enable a radial displacement of the whole of each aerodynamic blade 3 between an innermost position and an outermost position of the whole of each aerodynamic blade, said connecting element 6 comprises a mechanical coupling between the radial displacement of the aerodynamic blade 3 and the pitch of the aerodynamic blade 3 so that a radial displacement of the aerodynamic blades provides a change in pitch of the aerodynamic blade 3 and/or so that a change in pitch of the aerodynamic blade 3 provides a radial displacement of the aerodynamic blade 3. The blade and rotation is therefore interlinked and mutual dependent on each other. The mechanical coupling is preferable a single mechanical arrangement. In figure lb, the radial displacement is indicated with respectively R1 and R2 and the pitch angle as Alpha 1 and 2. In some embodiments, the angles Alpha 1 and 2 are different and in some embodiments, they may be the same for an interval of the radial displacement. An embodiment of this mutual dependence could therefore contain a zero pitch change for some interval of the radial displacement and a high pitch change for a different interval of the radial displacement, see figure 5 for an embodiment of the relationship between radial displacement and pitch. As seen in figure 5, the relationship is preferable L-shape, but other shapes are envisioned, such as linear or exponential. In figure 5 is shown that three modes, low wind mode, where the pitch and extension should be as high as possible and the control of the effective cross area should be small incremental changes in order to extract as much power from the wind, a high wind mode, where the incremental changes should be higher and a parked mode, which should fully contract and pitch the wind turbine in a parked mode in a short interval with a high pitch change.

The general concept of the invention can therefore be seen in fig. lc i) and ii), wherein the wind turbine can be extended and thus the radius and diameter of the wind turbine will increase while a pitch change further occurs. This is advantageous since a bigger rotor will be able to harvest more energy from the wind, while a small rotor will protect the wind turbine against power overloads. A further advantageous feature of the current invention is that the connecting element is a single mechanical coupling, which is responsible for both the pitch modulation and the radial length modulation.

In some embodiments, as seen in figure lc ii), the connecting element 6 can comprises an elongate stub part 7 connected at an end to the rotor hub 2, and is slideable engaged with the aerodynamic blade 3, such that the aerodynamic blade's 3 inner and outermost positions are obtained by sliding the blade 3 along the stub part 7. In the embodiment of figure 2a the aerodynamic blades 3 encases the stub part 7. However, the stub part could also encase the aerodynamic blades. By having the blade moveable engaged with the stub part 7, the wind turbine blades can be radially extended with the length of the stub part. The stub part will therefore, in an embodiment, provide the possible extension interval of the blades.

As the stub part provides the extension mechanism it is necessary in some embodiments for the stub part and/or connecting element to comprise a stop element 12 adapted to prevent the aerodynamic blade 3 advancing beyond its outermost position. This stop element could be a single element on the stub part, such as a protrusion or elements on the stub part or blades designed to mutual engage to limit the extension. An embodiment of this stop element 12 can be seen in figure 7, where the stop element 12 is located on a sliding rod 19.

In some embodiments, the mechanical coupling is facilitated by one of the stub part 7 or the blades 3 comprising a guiding element 16, such as a longitudinal extending groove 12 or tongue 13 and the other of the stub part 7 or the blades 3 comprising an engagement element 17, such as a protrusion adapted to fit within the groove or an opening 18, as seen in figure 7, in which the tongue fits, engaging with the guiding element 16 to control the rotation of the blade 3 around the stub part 7 during sliding of the blade 3 along the stub part 7, as seen in figure 2a.

In figures 2a and 2b, is shown an embodiment wherein the stub part comprises a groove on its outer surface, which is adapted to contain a tongue of the blade 3 which is located on a sliding rod 19, the sliding rod 19 is connected to the blade 3 within a recess of the blade. However, the functionality of the sliding rod 19 could also be manufactured as part of the blade. The sliding rod will therein facilitate the connection between the blade and the connecting member. In such embodiments, when the blade is moved along the stub part the tongue will be guided by the groove and rotate, thereby pitching the blade. A detailed view of this is also illustrated in fig. 6 and 7.

The shape of the groove can take a variety of forms, such as a telescope spiral as seen in figure 2b. However, the exact shape of the tongue will depend on the application and wind turbine at hand. The shape of such a tongue will determine the relationship between radial displacement and pitch. Some applications may require a section with low pitch change per radial displacement and a section with high pitch change per radial displacement while others applications may need a constant pitch change per radial displacement. The length, transition between sections, and pitch per radial displacement can change based on the application requirements, type of wind turbine and control strategy. A possible shape could be one that ensures the characteristics of figure 5.

In some embodiments, the mechanical coupling could be accomplished by other arrangements. In some embodiments, it is envisioned that more than one groove or tongue is present on either the stub part or the blades, such that the characteristics of the mechanical coupling can be changed. The changing between mechanical couplings could be accomplished by turning the whole of the wind blade at specific points while keeping the radial displacement fixed. In such an arrangement, different mechanical couplings with different characteristics can be accomplished.

The engagement of a groove and a tongue results in only one mechanical movement/coupling being needed in order to both radial displace and pitch the blades. In some embodiments, the longitudinal extending groove 12 has at least a section forming at least a part of a screw thread. This screw thread will define the rotation, pitch, of the blade as a function of the extension of the blade and, in some embodiments, the section forming at least a part of a screw thread has increasing pitch towards the root 4 or towards the hub, so as to preferably form a telescopic helix 9.

A number of different embodiments of the connection between the sliding rod 19, the blade 3 and the elongated stub 7 are envisioned. As seen in figures 13, 1A,

IB, 2A, 2B, where A denote extended and B contracted, the sliding rod 19 can be connected to the root of the blade and either the stub 7 is hollow or the sliding rod is hollow, so the sliding rod and stub can move within and along each other.

In another embodiment, as shown in figures 13, 3A, 3B, 4A, 4B and 5A, 5B, the sliding rod is attached to the blade within a recess 21 of the blade and either the stub 7 is hollow or the sliding rod is hollow, so the sliding rod and stub can move within each other. Further, the sliding rod 19 can be attached at the root of the blade or within the recess, as shown in 4A where the sliding rod is attached within the recess and 5B were the sliding rod is attached at the root of the blade, as indicated by the attachment point 23.

As shown in figures 13, 6A and 6B, it is also possible to have a configuration wherein the wind turbine comprises two blades, the two blades are positioned across from each other with the connection elements of the blades being adapted to slide within each other.

As shown in figure 10, the extension or radial displacement of the blades could be accomplished by a moving actuator 14 configured for providing a radial displacement of each of the blades 3. This actuator is preferable attached to the root of the wind turbine and connected to the blade or sliding rod. In some embodiments, the stub part 7 and/or sliding rod 19 is hollow and the moving actuator is configured for moving within the hollow stub part 7 and hollow sliding rod 19, the moving actuator being connected to the blade or the sliding rod that is connected to the blade. This is seen in figure 2a, wherein the actuator is placed within the hollow stub part 7 and adapted to extend or contract the blade.

Optionally a separate pitching actuator 15 configured for providing a change in pitch of each of the blades 3 can be provided in the wind turbine.

In some embodiments, the moving actuator 14 and/or the pitching actuator 15 is a hydraulic actuator, a pneumatic actuator and/or an electrical actuator. However, other actuators are envisioned.

For most embodiments, the mechanical coupling provides a decrease in pitch in response to moving the aerodynamic blades 3 towards its outermost position.

Such an arrangement minimise the forces acted on the blade when it is contracted, by virtue of the reduced blade length and the pitch. The mechanical coupling could be adapted to provide a pitch between than 0 and 10 degree, such as zero degree, when the aerodynamic blades 3 are in their outermost positions, and a pitch between 80 and 90 degrees, such as 90 degrees, when the aerodynamic blades 3 are in their innermost position. The higher the pitch of the blade, the smaller the effective cross-section of the blade is. This results in an arrangement where the blade will generate the least amount of power, both due to its length and pitch, when it is retracted and the most when the blade is fully extracted, e.g. in the outermost position. This will in some embodiments help in the optimization of the extraction of power from the wind, as will be detailed later.

As the mechanical coupling may have different shapes according to the application, the relationship between pitch and radial displacement is in some embodiment non-linear, preferable such that the innermost extension range has a large pitch rotation per extension length and the outermost extension has a small or zero pitch rotation per extension length.

In order to extract the most power during the operation of the wind turbine, the method should maximize the extracted power of the wind, while keeping the local load levels under an acceptable level for the wind turbine. In figure 3, left hand side, power curves of wind turbines with different length blades are shown.

In figure 3 left graph, power curves are shown for rotor diameters of 160 m, 170 m and 180 m. Further, and for comparison, a power curve for a wind turbine with a medium sized rotor is shown. A graph for a generic small rotor and a generic relatively larger rotor is shown in figure 3 right hand side to illustrate the effect of the rotor size. A figurative wind turbine is defined by three parameters; rated power 8MW, maximal tip speed 90 m/s, power coefficient Cp=0.50, trust coefficient Ct=0.85. Taking a 170m rotor as the default rotor, the required torque (to produce the rated power at a rotational speed corresponding to the maximum tip speed) is calculated and used a design constraint. Furthermore, the trust force on the rotor plane is calculated and used a design constraint.

Increasing the rotor diameter and maintaining the tip speed implied a reduced rotational speed. This implies that a larger torque is required for a larger rotor in order to produce the same power as the reference rotor.

As shown in the graphs, the longer blades can extract more power from the wind than the small ones, but will also reach the maximum operating conditions at lower wind speeds. The longer blades have therefore a need for power optimization, which in the current invention is achieve by a combination of regulating the length of the blades and the controlling the rotational speed of the blades, which can at least assume a fixed speed mode and variable speed mode. To optimize the effect the wind turbine will operate with a variable speed mode under rated power.

Figure 3, right graph side illustrates a baseline power curve for a small rotor, which shows the power produced by the wind turbine as function of wind speed and a power curve for at variable rotor. Both curves have the same rated power level, which is restricted by the electrical systems (generator, converter, transformer).

The benefit of the variable rotor is that is can achieve larger power outputs at low wind speeds, and operate at high wind speeds at low loads levels. At low wind speeds (below the rated power) the turbine can operate with a large rotor area, which increase the power output. At high wind speeds (above rated power) the turbine can operate with a reduced rotor area, which can regulate the power levels, and reduce the loads on the turbine.

For a given wind speed below rated power the variable turbine will produce more power. The wind speed at which the turbine reaches it rated power level is lower for variable rotor, which implies more full load hours and thereby increases the capacity factor, and reduces power fluctuations in the electrical grid.

This is accomplish by acquiring an indication of the wind speeds experienced by the wind turbine, acquiring an indication of the power extracted from the wind by the wind turbine, acquiring the rotational speed of the blades and/or torque on generator, since the torque is correlated with the rotational speed, and controlling the radial displacement of the aerodynamic blades 3 based in part on the wind- speeds and the extracted power. It is noted, that an advantageous way of controlling the rotational speed of the rotor is to control the torque on the generator.

In order to maximise the extracted power the controlling will comprise contracting the blades to an idle position when the wind speed is below a cut-in velocity. This idle position is preferable the innermost position of the blades. When the wind speed exceeds the cut-in velocity and is able to generate power, the blades are extended in order to maximise the extracted power. This is preferable done in a variable rotational speed mode of the turbine, meaning that the rotational speed of the wind turbine depends on the wind speed and is not restricted, except restricted to a maximum speed to prevent the turbine from running loose. In most situations for wind speeds above the cut-in speed and below rated power, the blades will be extended to its outermost position.

In figure 3 the power curve for different size blades can be seen. From figure 3 it is seen that the longer the blade is the more power can be extracted from the same wind speed. However, the load on the wind turbine and the generator will equally increase and as such, it may be necessary to contract the blades in order to obey and maintain the operating constraints of the wind turbine. The expanding and contracting of the wind turbine can therefore be seen as a way of decreasing or increasing the power produced and load. The control strategy is therefore to extend the blades to the outermost position possible while keeping the power extracted under the rated power and obeying the operating constraints of the wind turbine.

When the wind speed is over the rated wind speed, meaning that energy produced by the wind exceeds the operating range of the wind turbine, the blades are contracted in order to contain the power to the rated power. In figure 3 this is seen as the plateau. The power could also be constrained by fixing the rotational speed of the blades. In the situation where the wind speed is much higher than the rated wind speed the blades is fully contracted. Further, in an emergency brake situation the blades are fully contracted to minimise the forces of the wind on the blades.

In figure 4 an example of the control method is shown. In this example, the outermost range has a small radial displacement per pitch and the innermost range has a high radial displacement per pitch. When the wind speed is below the rated power the blade is preferable in the outermost position, as seen in figure 4a, and generally the blade has the largest length that is possible when factoring in the loads on the turbine. When the load on the turbine increases if might be necessary to contract the blades. The first range of the contracting of the blades will not or only slightly pitch the blade, as seen in figure 4a.

In figure 4b is shown that when operating near or above rated power, it may be necessary to contract the blades in order to contain the load and power within the operating conditions. However, it may not be advantageous in such scenarios to also pitch the blades to further limit the load. The mechanical coupling would therefore preferable assure that first range of contraction from the outermost position only results in a small or zero pitch change.

When a large change in power and loads occurs, such as in high wind situations, The blade will contract and pitch to limit the power, as shown in figure 4C, where the last range of the contracting to the innermost radial displacement would provide a large pitch change, such that the blade is in a parked position generating minimal loads on the wind turbine as seen in figure 4D. This may also be used as a safety measure to park the wind turbine in prevailing high wind situations.

In figure 5, an example of the relationship between pitch and radial displacement is shown. However, other relationships are envisioned. It is envisioned that the general shape is L-shaped, such that a discrete transition from operating with maximum rotor size to operating as a normal pitch regulated turbine with minimum rotor size. Figure 5A illustrates an idealized relationship and figure 5B illustrates simulation involving a coupling mechanism as disclosed herein.

With reference to fig. 5A, it can be seen that beside a parked mode, the wind turbine is operated in two modes, which are referred to as "high wind mode" and "low wind mode". It is noted that high wind mode may preferably be defined as the wind speeds at which the wind turbine can reach rated power and low wind mode may be defined as the wind speeds at which the rated power cannot be reached. The park mode may be defined as the occurring when the wind speed exceed a maximum operating wind speed for the wind turbine and which requires stand still of the rotor. Based on fig. 5 it can be realized that a rate of change in pitch, ά, can be defined as change in pitch per meter radial displacement e.g. as da ά = — where r is the radial direction dr

In the low wind mode, it is preferred that no pitch (ά = 0) is introduced as a consequence of a radial displacement of the wing. However due to mechanical constraints it is often preferred to keep ά as small as possible. Accordingly, the low wind mode may be characterized in that the main contribution to changes on produced power comes from the change in rotor area.

In the high wind mode, the wind turbine operates at its rated power. In this mode, the rotor area is generally smaller than in the low wind mode and the main contribution to maintain the wind turbine's power production at rated power may be characterized as pitch control, since the rotor area relatively to ά plays a limited role.

In the park mode, the aim is to bring the wind turbine into standstill as fast as possible. This is accomplished by designing ά to be large relatively to the values of the low wind mode and high wind mode. This may be summarised as:

&low wind ^ ^high wind ^ ^park

While fig. 5A discloses the rate of change as constant in the various modes (depicted by straight lines), the rate of change may be depending on the displacement, that which symbolically may be written as d(r). In such situation, the above ordered magnitudes may be considered as an averaged rate of change, e.g. the difference between maximum rate of change and minimum rate of change divided by two, averaged based on ron other averaging procedures.

It is noted that in fig. 5A, the change of mode is illustrated as discontinuous changes and that in that such discontinuous changes may be not be implemented in a mechanical construction. Thus, in preferred embodiments, the changes in mode includes a transition mode during which the changes in ά occurs in a continuous manner. It is also noted that ά do not as such gives a total radial displacement. However, and as indicated in fig. 5A the total radial displacement, Ar, within each of the three modes may be summarized as:

A Tiow wind '^> ^high wind '^> ^ ark

The actual choices of ά and AR is typically made in accordance with a specific design of a wind turbine. Non-limiting examples of ά and AR

It is furthermore noted, that the park mode may be left out e.g. in case the wind turbine can be brought to standstill in another manner than be pitching. Reference is now made to fig. 5B. Kindly observe that the axis have been reverted in the left hand side of fig. 5B relatively to fig. 5A. The right hand side of fig. 5B illustrates the pitch in a polar coordinate system together with the colour grading used to indicate wind speed. The right hand side of fig. 5A shows that the aerodynamic blade is pitched 90 degrees and the rate of change of pitch can be deduced from the (most clearly from left hand side figure).

In figure 8 is shown a transparent view of an embodiment of the invention. As seen in figure 8 the wind turbine rotor comprises a hollow connecting element, which has a guiding element 16 in the form of a tongue. A blade 3 is adapted to slide over the connecting element 6 by a sliding rod 19 containing an engagement element 17, which is adapted to be contained in the guiding element. This arrangement will ensure that pitching of the blades will occur together with the extension/contraction of the blades. The blade contains in some embodiment a recess 21 that is adapted to contain the sliding rod, which can slide within the hollow connecting element. Figures 9 and 10 show different views of the embodiment. Figure 10 shows the moving actuators, which is connected to the hub with a universal joint, such that they are not impeded when the blades pitch.

Figures 11 and 12 show an embodiment wherein guiding element is located on the blades and the engagement element 17 is located on the stub part.

Although the present invention has been described in connection with the specified embodiments, it should not be construed as being in any way limited to the presented examples. The scope of the present invention is set out by the accompanying claim set. In the context of the claims, the terms "comprising" or "comprises" do not exclude other possible elements or steps. Also, the mentioning of references such as "a" or "an" etc. should not be construed as excluding a plurality. The use of reference signs in the claims with respect to elements indicated in the figures shall also not be construed as limiting the scope of the invention. Furthermore, individual features mentioned in different claims, may possibly be advantageously combined, and the mentioning of these features in different claims does not exclude that a combination of features is not possible and advantageous.

List of reference symbols used

1 Wind turbine rotor

2 Rotor hub

3 Aerodynamic blade

4 Root

5 Tip

6 Connecting element

7 Stub part

9 Telescope spiral

10 Internal cavity 11 Stop element

12 Groove

13 Tongue

14 Moving actuator (radial displacement) 15 Pitching actuator (pitching)

16 Guiding element

17 Engagement element

18 Opening

19 Sliding rod 20 Tower

21 Recess

22 Universal joint

23 Attachment point

R1 Radius of rotor at inner most position R2 Radius of rotor at outermost position

Claims

1. A wind turbine rotor (1) comprising · a rotor hub (2),

• aerodynamic blades (3) radially extending away from the rotor hub (2) and configured to generate lift, torque or lift that imposes a torque, to rotate the rotor upon being exposed to wind, said aerodynamic blades (3) each has a root (4) and a tip (5), · a connecting element (6) connecting each aerodynamic blade (3) with the rotor hub (2), said connecting element (6) being configured to enable a radial displacement of the whole of each aerodynamic blade (3) between an innermost position and an outermost position of the whole of each aerodynamic blade, said connecting element (6) comprising a mechanical coupling between the radial displacement of the aerodynamic blade (3) and the pitch of the aerodynamic blade (3) so that a radial displacement of the aerodynamic blades provides a change in pitch of the aerodynamic blade (3) and/or so that a change in pitch of the aerodynamic blade (3) provides a radial displacement of the aerodynamic blade (3).

2. A wind turbine rotor according to claim 1, wherein the connecting element (6) comprising

• an elongate stub part (7) connected at an end to the rotor hub (2) and slidable engaged with the aerodynamic blade (3), such that the aerodynamic blade's (3) inner and outermost positions are obtained by sliding the blades (3) along the stub part (7).

3. A wind turbine rotor according to claim 2, wherein the connecting element (6) comprising a stop element (12) adapted to prevent the aerodynamic blade (3) advancing beyond its outer most position.

4. A wind turbine rotor according to claim 2 or 3, wherein the mechanical coupling is comprised by one of the stub part (7) or the blades (3) comprising a guiding element (16), such as a longitudinal extending groove (12) or tongue (13) and the other of the stub part (7) or the blades (3) comprising an engagement element (17), such as a protrusion adapted to fit within the groove or an opening (18) to in which the tongue fits, engaging with the guiding element (16) to control the rotation of the blades (3) around the stub part (7) during sliding of the blade (3) along the stub part (7).

5. A wind turbine rotor according to claim 4, wherein the guiding element (16) has at least a section forming at least a part of a screw thread.

6. A wind turbine rotor according to any of the preceding claims, wherein a sliding rod (19) is coupled to the blade for facilitating the sliding of the blades on the stub part (7), such that the sliding rod contains either the groove or tongue and is adapted to facilitate the mechanical coupling.

7. A wind turbine rotor according to claim 6, wherein the sliding rod (19) is attached to the blade within a recess (21) of the blade at the root end of the blade, the blades are adapted to encase the elongated stub part of the connecting element (6) within the recess when the sliding rod (19) slides in connection with the stub part (7), wherein either the elongated stub part (7) is hollow and the sliding rod (19) is sliding within the stub part (7) or the sliding rod is hollow and encasing the stub part.

8. A wind turbine rotor according to claim 6, wherein the sliding rod (19) is attached to root of the blades (3) and adapted to slide in connection with the stub part (7), such that the either the elongated stub part is hollow and the sliding rod is sliding within the stub part or the sliding rod is hollow and encasing the stub part.

9. A wind turbine rotor according to any of the preceding claims, further comprising a moving actuator (14) configured for providing the radial displacement of each of the blades (3).

10. A wind turbine rotor according to claim 9, wherein the moving actuator is attached to the rotor hub by a universal joint (22), such that the actuator is able to move when the blades are pitching.

11. A wind turbine rotor according to claim 9 or 10, wherein the moving actuator (14) is a hydraulic actuator, a pneumatic actuator and/or an electrical actuator.

12. A wind turbine rotor according to any of the preceding claims, wherein the relationship between pitch and radial displacement is dynamical over the whole of the radial displacement, such as that the innermost extension range has a large pitch rotation per radial displacement and the outermost extension has a small or zero pitch rotation per radial displacement.

13. A wind turbine according to any of the preceding claims, wherein the connecting element (6) is configured to operate in a low wind mode and a high wind mode, wherein

• a rate of change of pitch is larger in high wind mode ( a_highwind ) than a rate of change in pitch in low wind mode (di_owwind), preferably, the rate of change in pitch is changed continuously from the high speed rate to the low speed rate, and

• a total displacement in high wind mode ( AR_hig_{h wind} ) is smaller than the total displacement in low wind mode (A¾_owwind).

14. A method of operating a wind turbine having a rotor according to any of the preceding claims, comprising acquiring an indication of the wind speeds experienced by the wind turbine, - acquiring an indication of the power extracted from the wind by the wind turbine,

Rod controlling the radial displacement of the aerodynamic blades (3) based in part on the wind-speeds and the extracted power, wherein the controlling comprises when the wind speed is below a cut-in velocity, contracting the blades to an idle position, when the wind speed is between the cut-in wind speed and a rated wind speed, operating the wind turbine in a variable rotational speed mode and radial extending the blades while keeping the power extracted under the rated power and obeying the operating constraints of the wind turbine, when the wind speed is above the rated wind speed, radial contracting the blades and when contracting the blades, the mechanism pitches the blade as well to contain the power to the rated power, and in an emergency brake situation, fully contracting the blades and pitching to stop position (90 degrees).

15. A method according to claim 14, wherein the controlling further comprises limiting the rotational speed of the wind blade.