WO2011131792A2

WO2011131792A2 - Wind turbine direction control

Info

Publication number: WO2011131792A2
Application number: PCT/EP2011/056554
Authority: WO
Inventors: Alain Van Ranst
Original assignee: EWF ENERGY GROUP Ltd; UG AVR Ltd
Current assignee: EWF ENERGY GROUP Ltd; UG AVR Ltd
Priority date: 2010-04-23
Filing date: 2011-04-26
Publication date: 2011-10-27
Anticipated expiration: 2012-10-23
Also published as: GB201006831D0; WO2011131792A3; GB201008096D0

Abstract

The present invention concerns a structure for converting the energy of a fluid flow into another form of energy, such as a windmill for generating current, said structure comprising: a base, and at least one turbine platform comprising: a ring structure (20) mounted on the base and configured to rotate about an axis with respect to the base, at least two fluid turbines (30, 40) mounted on the platform, each turbine comprising a rotor configured to rotate about an axis perpendicular to the axis of rotation of the ring structure in response to a fluid flow over the rotor, braking means controllable to individually impede rotation of the rotors, the fluid turbines being arranged so that, when rotation of a rotor is impeded by the braking means, the turbine platform is caused to rotate by the force resulting from a fluid flow over the impeded rotor.

Description

WIND TURBINE DIRECTION CONTROL

TECHNICAL FIELD

The present invention relates to an apparatus for controlling and adapting the direction of a fluid turbine with respect to the direction of the oncoming fluid flow.

BACKGROUND OF THE INVENTION

Most modern wind turbines are designed according to one of two mainstream paradigms. The 'Horizontal Axis' type wind turbine, as shown in figure 1 , has one or more rotors (each typically having 3 blades) and corresponding rotor shafts. When pointed into the wind, the rotor is driven to turn by the wind. The rotational force is then used to generate electricity or heat energy. The wind turbine is typically mounted at the top or part way down a tower structure (or wind tower).

The 'Vertical Axis' design has the main rotor and shaft arranged vertically, such that the rotor is driven to turn by the wind regardless of the direction from which the wind is coming. For the purposes of this document, a 'wind turbine' is a 'Horizontal Axis' type wind turbine.

For horizontal axis type wind turbines, the wind turbine is said to have 'yaw error' when the rotor is not perpendicular to the wind. In this case, wind energy is being lost relative to when no yaw error exists as the effective rotor cross section relative to the wind is reduced, i.e. a smaller portion of the wind energy is being applied to the rotor blades.

In order to allow the rotor to be turned to face into the wind and reduce yaw error to a minimum, many modern wind turbines mounted on wind towers are controllable to yaw. The yaw is achieved by means of a motor and pivoting component configured to cause the wind turbine, rotor and rotor shaft to move around the central vertical axis of the wind tower. By minimizing the yaw error, the amount of wind energy that can be converted by the wind turbine is maximized. Determination of wind direction is typically done by means of a wind vane situated on or around the wind turbine.

One problem with this arrangement is that the energy required to rotate the wind turbine to face the wind is not negligible. Given the weight of the rotor blades, many KWh/year are consumed by regularly modifying the direction in which the wind turbine is facing. Therefore, there is a need for a method of turning the rotors to face in an optimal direction with the use of little or no additional energy.

Another problem with this arrangement is that the determination of the wind direction is limited to instantaneous readings and does not take into account the variations and fluctuations in a fixed wind direction. The wind usually has a relatively stable average wind direction that changes only slowly over time. However, the instantaneous angle of the wind direction oscillates around that relatively stable average direction. The amplitude of this oscillation can sometimes be high enough to move the rotor to rotate in the opposite direction to that required. If the wind turbine is continually being moved to follow the instantaneous wind direction and reduce the yaw error, a significant amount of energy will be consumed by the motor used to move the wind turbine. Furthermore, wear and tear on the wind turbine yaw mechanism will increase. Therefore, there is a need for a better method for orienting a wind tower such that the rotors face the wind direction and are able to follow the corresponding oscillations, which reduces yaw error and reduces wear and tear.

Another problem with this arrangement is that maintenance performed by an engineer on such a turbine can be awkward and dangerous. An unprotected engineer performing maintenance to the external components of the turbine may be required to make use of a harness to allow his body to be positioned in the appropriate position. In this case, the engineer may be exposed to high winds which may prevent or hamper maintenance work from being done as well as putting the engineer in a potentially difficult position. Furthermore, the moving rotors are extremely hazardous to engineers performing maintenance on a turbine and so the rotor on the wind tower must be prevented from rotating during maintenance. On a wind tower with multiple rotors, all the rotors will be stopped during maintenance. This reduces the danger, as well as limiting the noise and vibration in the tower during the period that the engineer is at work. However, stopping the turbines prevents the generation of electricity for the entire wind tower for the duration of the maintenance work. What is needed is a means to allow the engineer to operate on a single wind turbine without exposure to wind or rotating blades, and without requiring that the remaining turbines be prevented from operating.

SUMMARY OF THE INVENTION

According to a first aspect of the invention, there is provided a structure for converting the energy of a fluid flow into another form of energy— typically a windmill for converting wind energy into electrical current— said structure comprising a base, and at least one turbine platform which comprises:

• a ring structure mounted on the base and configured to rotate about an axis with respect to the base,

• at least two fluid turbines mounted on the platform, each turbine comprising a rotor configured to rotate about an axis perpendicular to the axis of rotation of the ring structure in response to a fluid flow over the rotor,

• braking means controllable to individually impede rotation of the rotors,

the fluid turbines being arranged so that, when rotation of a rotor is impeded or stopped by the braking means, the turbine platform is caused to rotate by the force resulting from a fluid flow over the impeded rotor.

According to a second aspect of the invention, there is provided a hollow body suitable for being fixed to a ring structure as defined above and having an external geometry nesting at least part of each wind turbine and enhancing the hydrodynamic properties of the structure. Such hollow body comprises preferably one or more apertures arranged to provide maintenance access to the fluid turbines.

BRIEF DESCRIPTION OF THE FIGURES

Aspects of the present invention will now be described by way of example with reference to the accompanying drawing. In the drawings:

Figure 1 shows a Horizontal Axis type wind turbine as known in the art.

Figure 2 shows a (a) a side view and (b) a top down view of a wind tower according an embodiment of the present invention.

Figure 3 shows a top down view of the wind tower of figure 2: (a) with a yaw error and (b) after yaw correction..

Figure 4 shows a wind tower according to Figure 2, comprising a protective structure improving the hydrodynamic properties of the structure.

Figure 5 shows a hollow protective structure and maintenance aperture according to the present invention.

Figure 6: shows a vertical stack of several turbine platforms of Figure 5.

DETAILED DESCRIPTION OF THE INVENTION

The structure of the present invention can serve in several environments wherein the energy of a fluid flow of varying directions can be converted into another form of energy such as electrical current or heat. For example, the structure can be a wind tower, converting wind energy into electricity or heat. Such structure can also be used to convert liquid flows into another form of energy, such as for example offshore, under water applications in locations where the currents may change direction or for converting tidal energy, Figure 2 shows (a) a side perspective and (b) a top down view of a wind tower according to a preferred embodiment of the invention. Figure 3 shows a top down perspective of the same embodiment. The preferred embodiment comprises the following components:

- A surface 80, which may be the ground, the roof of a building or a similar surface capable of supporting the wind tower. - A central shaft 10, rising from the surface.

- At least one pivoting ring structure 20, mounted to the central shaft 10 and configured to rotate about the axis of the central shaft. The ring structure 20 is supported by the central shaft and may freely rotate with respect to the shaft.

- Two wind turbines 30 and 40, each fixedly mounted to the pivoting ring structure 20. It is preferred that the two wind turbines be positioned diametrically opposed to one another on a circle centred on the point of rotation of said ring structure and with their respective rotor axes being tangential to said circle and preferably both turbines (30, 40) are mounted on a peripheral edge of the ring structure..

- Each wind turbine comprises a rotor 50, a rotor shaft 60, a braking component and an energy conversion component for converting the rotational force of the rotor shaft driven by the wind flowing therethrough to another form of energy. The energy conversion component typically comprises an electrical generator, but may also comprise, for example, a heat generator, or a combination of the two. The braking component may be an electrical or mechanical brake. The braking means are preferably regenerative braking means able to recover and transform at least part of the kinetic energy released by the system by slowing down or stopping the rotation of a rotor (for more general information on the principle of regenerative braking means, cf. e.g., http://en.wikipedia.org/wiki/Regenerative_braking). Each rotor 50 is connected to the respective rotor shaft 60, such that the rotor shaft rotates as the rotor is driven to rotate by the wind. Both wind turbines are mounted to the ring structure 20 such that their rotor faces point in the same direction (i.e. have parallel axes). Preferably, each turbine is mounted on an edge of the ring structure 20 and their respective axes of rotation are tangential to a circle centred in the point of rotation of the ring structure. Here forth, each ring structure and its corresponding wind turbines shall be known as a "turbine platform." - A wind direction determination device 70, configured to produce a continuous or regular sequence of readings measuring the direction of the wind at or near the wind tower.

- A control unit 90 configured to receive the output of the wind direction determination device, determine the orientation of the at least one turbine platform, and to control the braking component of each turbine.

By applying braking/resistance to the rotating rotor of the turbines in appropriately windy conditions, the control unit can advantageously control each turbine platform to rotate about the axis of the central shaft. If regenerative braking means are used, at least part of the kinetic energy released by the impeded rotor is converted into current.

Yaw error is defined as the angle between the optimal orientation for harnessing the maximum amount of wind energy and the actual orientation of the turbine rotors, i.e. the angular difference between the rotational axes of the wind turbines and a determined wind direction. As shown in figure 3(a), the yaw error is defined by this document as being negative when the wind direction 100 is in the range marked with a '-' with respect to the orientation 1 10 of the turbine rotors (i.e. to the left of the orientation 1 10 or from the perspective of central shaft 10) and positive when the wind direction 100 is in the range marked with a '+' in figure 3(a) with respect to the orientation 1 10 of the turbine rotors (i.e. to the right of the orientation 1 10 or from the perspective of central shaft 10).

As illustrated in Figure 3(b), in one embodiment of the invention, the control system 90 is configured to receive the output of the wind direction determination device 70 and, when the wind direction is determined to be 'positive' relative to the orientation 1 10 of the turbine rotors, the control unit controls the braking means to reduce the rotational speed of the rotor of turbine 40. The relative slow rotational speed of the rotor of turbine 40 compared with the rotor of turbine 30 causes the turbine platform to rotate in an clockwise manner, reducing the yaw error. When the control system detects that the yaw error is zero or close to zero, the braking means is controlled to reduce or stop braking of the rotor of turbine 40, so that the rotors of turbines 40 and 30 may rotate at the same speed. At this point the platform will stop rotating.

Similarly, when the wind direction is determined to be 'negative' relative to the orientation 1 10 of the turbine rotors, the control unit controls the braking means to reduce the rotational speed of the rotor of turbine 30. The relative slow rotational speed of the rotor of turbine 30 compared with the rotor of turbine 40 causes the turbine platform to rotate in an anti-clockwise manner, reducing the yaw error. When the control system detects that the yaw error is zero or close to zero, the braking means is controlled to reduce or stop braking of the rotor of turbine 30, so that the rotors of turbines 30 and 40 may rotate at the same speed. At this point the platform will stop rotating.

When the yaw error is determined to be within a particular range either side of zero, the control unit controls the braking means to allow the rotational speed of the rotors of turbines 30 and 40 to be equal. This range may be configurable to account for different wind conditions. Where wind direction is fluctuating rapidly over of a range of e.g., 30 degrees, a suitable range may be 30 degrees (i.e. 15 degrees either side of orientation of the platform).

The rotation of the turbine platform by means of reducing the speed of, or stopping altogether the rotation of one of the turbine rotors is achieved in the following manner. As the rotor of one of the turbines is slowed by the braking action controlled by the control unit, a greater degree of drag results from the wind flowing over the blades of that rotor and a greater degree of force is applied to the rotor in the direction of the wind flow. If the force being applied by the wind to one rotor is greater than the force being applied to the other rotor, the turbine platform will be moved to rotate about the central shaft such that the braked rotor is dragged around by the wind.

The advantages of this technique are as follows. Unlike existing wind tower designs which require complex, expensive and heavy driving means for turning the wind turbines to face the oncoming wind, this technique requires no additional driving means at all. Furthermore, the rotation of the wind platform is driven by the wind, and so no auxiliary energy (i.e. electrical energy generated or stored by the wind tower) is consumed by the process. On the contrary, if regenerative braking means are used, the rotation of the turbine platform contributes to the generation of additional current.

In a preferred embodiment of the invention, each wind turbine further comprises the means to drive the rotor to turn. The means to drive the rotor to turn may constitute using an electrical generator, otherwise used to convert the rotation of the rotor shaft to electrical energy, to drive the rotor by means of an electrical current. Alternatively, an auxiliary motor maybe used. In this embodiment, the means to drive the rotor to turn is used to generate a directional force with the rotor and consequently rotate the turbine platform in a desired direction. This may be used when, for example, the turbine platform is in a position in which the rotor axes are perpendicular to the direction of the oncoming wind and the rotors are not being turned by the wind. In this scenario, the method for rotating the turbine platform by braking the respective rotor is not available, and so the ability to drive at least one rotor to turn allows the turbine platform to be driven to an orientation with respect to the wind such that the tower can be turned by impeding one of the rotors.

In an alternative embodiment, one or more stops are provided to prevent the turbine platform from turning further than a particular angular distance from a fixed central point.

In one embodiment, a rotor may be slowed by means of a friction brake, applied either to the rotor or the rotor shaft to which the rotor is connected. Alternatively, the rotor may be slowed by means of an electrical field applied to the electrical generator connected to the rotor. The electrical field would act as a braking force on the generator. Alternatively, the individual blades of a rotor may be rotated, such that the incline of the surface of the blade relative to the wind is reduced. This would decrease the amount of wind energy converted to rotational energy by the rotor, and would increase the drag of the rotor in the wind. The blades of a rotor for a structure according to the present invention are preferably made of fibre reinforced composites for their excellent mechanical properties to weight ratio. Alternatively, the blades can be made of metal, such as aluminium or in wood. The nature of the fluid and environmental conditions of use of the structure may determine a specific choice for a material, such as e.g., if the fluid is sea water.

In a preferred embodiment of the invention, the structure further comprises a shaped structure (200) rigidly attached to the ring structure (20), The shaped structure may advantageously direct wind energy from an area larger than the turbine rotors onto the relatively small face surface area of the turbine rotors. This results in an improved energy output of the turbines. An example of such embodiment is illustrated in Figure 4. In a preferred embodiment, the shaped structure (200) has an external geometry nesting at least part of each wind turbine (30, 40) and enhancing the hydrodynamic properties of the structure. For example, as illustrated in Figure 5, the external geometry may be generated by revolving around the rotating axis of the ring structure (20) a curve substantially complementary to at least a portion of the turbines outer structure. In another embodiment, the turbines can be enclosed into wind tunnels comprising an inlet opening 201 and an outlet opening 202 as depicted in Figure 4.

If the body of the shaped structure (200) is hollow, it may be accessed by an operator as shown in Figure 5. By providing one or more apertures or "windows" 210 arranged at the level of the wind turbines 30, 40, maintenance access to the turbines from the inside of the hollow body is ensured. This advantageously allows an engineer, by means of a ladder or other access means within the central shaft of the wind tower, to rise to the level of the turbine platform and then perform maintenance on the wind turbine whilst keeping his body substantially within the shaped structure 200 and without being exposed to the wind or risk of being struck by the rotor blades. By reducing risk of an engineer being struck, such a means of maintenance can dramatically improve safety, and any remaining operational turbine platforms in the tower would consequently be allowed to continue operating whilst an engineer is performing the maintenance. Many current wind tower designs require that the rotors of the turbines are prevented from moving during maintenance. The maintenance panels are preferably mounted immediately above or below the turbine, such that there is sufficient space within the hollow body shape for the engineer to occupy whilst performing the maintenance tasks.

The access panels may consist of sliding, hinged or pivoting, windows or doors. The access panels are preferably non-detachable from the shaped structure, such that the panels cannot be completely detached during normal maintenance work. This reduces the risk, especially during high wind environments, of the panel from being dropped by the engineer, and potentially colliding with a rotating rotor below.

In one embodiment, multiple maintenance panels are present in the hollow body shape for each turbine, allowing convenient access to the different components, such as the rotor blades, the rotor shaft and the generator. In one embodiment of the invention illustrated in Figure 6, the tower comprises multiple such turbine platforms arranged in a vertical stack. It is preferred that all the turbine platforms be rigidly fixed to one another so that it is ensured that all the turbines are always facing a single direction. In some cases, however, each turbine platform may be free to rotate with respect to one another. This could be useful in case the flow direction depends on the altitude from the base, as could happen with underwater currents.

As shown in figure 6, a vertical stack of turbine platforms may comprise a hollow body 200 which geometry enhances the hydrodynamic properties of the structure, directing air flow to each turbine. The shaped structure may be made of several elements rigidly fixed to each ring structure 20 and in combination forming the desired geometry. As discussed above, the hollow body can be provided with maintenance panels which may be removed or opened, in order to allow access from within the revolution shaped structure to the various wind turbines.

The applicant hereby discloses in isolation each individual feature described herein and any combination of two or more such features, to the extent that such features or combinations are capable of being carried out based on the present specification as a whole in the light of the common general knowledge of a person skilled in the art, irrespective of whether such features or combinations of features solve any problems disclosed herein, and without limitation to the scope of the claims. The applicant indicates that aspects of the present invention may consist of any such individual feature or combination of features. In view of the foregoing description it will be evident to a person skilled in the art that various modifications may be made within the scope of the invention.

Claims

1 . A structure for converting the energy of a fluid flow into another form of energy, said structure comprising:

a base, and

at least one turbine platform comprising:

a ring structure (20) mounted on the base and configured to rotate about an axis with respect to the base,

at least two fluid turbines (30, 40) mounted on the platform, each turbine comprising a rotor configured to rotate about an axis perpendicular to the axis of rotation of the ring structure in response to a fluid flow over the rotor,

braking means controllable to individually impede or stop rotation of the rotors,

the fluid turbines being arranged so that, when rotation of a rotor is impeded by the braking means, the turbine platform is caused to rotate by the force resulting from a fluid flow over the impeded rotor.

2. The structure of claim 1 , wherein each rotor is configured to drive a generator.

3. The structure of claim 2, wherein at least one of the generators is an electrical generator.

4. The structure of any preceding claim wherein the rotational axes of the rotors are mutually parallel.

5. The structure of any preceding claim, further comprising,

a fluid direction sensor configured to determine the angular difference between the direction of the fluid flow and the orientation of the rotors, and a control unit configured to, in dependence on the determined angular difference, control the braking means to impede rotation of one or more of the rotors so as to rotate the platform and reduce the angular difference between the direction of the fluid flow and the orientation of the rotors.

6. The structure of any preceding claim, wherein the fluid is air and the fluid flow is caused by wind or the fluid is water and the fluid flow is caused by currents or tide.

7. The structure of any preceding claim wherein the pair of fluid turbines (30, 40) are mounted on the ring structure (20), such that they are positioned diametrically opposed to one another on a circle centred on the point of rotation of said ring structure and with their respective rotor axes being tangential to said circle and preferably both turbines (30, 40) are mounted on a peripheral edge of the ring structure..

8. The structure of any preceding claim wherein the braking means are regenerative braking means.

9. The structure of any preceding claim, further comprising at least one mechanical stop to limit the range of angular rotation of the platform.

10. The structure of any preceding claim, further comprising at least one rotor driver controllable to rotate a rotor, wherein the control unit is further configured to rotate the platform by controlling the rotor driver to rotate a rotor, thereby generating a thrust capable of rotating the platform.

1 1 . The structure of any preceding claim, wherein a hollow body (200) is rigidly attached to the ring structure (20), said body having an external geometry nesting at least part of each wind turbine (30, 40) and enhancing the hydrodynamic properties of the structure.

12. The structure of the preceding claim, wherein the external geometry of the hollow body (200) is generated by revolving around the rotating axis of the ring structure (20) a curve substantially complementary to at least a portion of the turbines outer structure.

13. The structure of claims 1 1 or 12, wherein the hollow body comprises one or more apertures arranged to provide maintenance access to the fluid turbines (30, 40).

14. The structure of any preceding claim, wherein the tower comprises multiple such turbine platforms arranged in a vertical stack.

15. The structure of the preceding claim, wherein each turbine platform is provided with a rigidly attached hollow body (200) as defined in any of claims 1 1 to 13.