Wind turbine with gust compensating air deflector

An apparatus and system for counteracting wind gusts and other high load situations in a wind turbine includes the use of one or more gust counteracting devices configured to extend an air deflector outwardly from a surface of a turbine rotor blade. The air deflector may subsequently be retracted into the rotor blade once the wind gust has subsided or once the load falls below a certain threshold. Mechanisms for extending and retracting the air deflector may include pneumatic or hydraulic systems and/or electromechanical devices. Air deflectors are generally configured to normalize air flow around the rotor blade so that the risk of potential damage to components of the wind turbine is minimized. In one arrangement, the gust counteracting device may be located at a leading section of the turbine blade. Additionally or alternatively, the device may be modular in nature to facilitate the removal and replacement of the device.

TECHNICAL FIELD

The invention relates generally to the design and control of a wind turbine. More specifically, the invention relates to modifying the aerodynamics of a wind turbine blade.

BACKGROUND

Wind turbines create power proportional to the swept area of their blades. The choice of rotor attributes for a wind turbine, such as its diameter, is a design trade-off between longer blades for more energy production in low winds and shorter blades for load limitation in high winds. Thus, wind turbine having longer blades will increase the swept area, which in turn produces more power. However, at high wind speeds, a wind turbine having longer blades places greater demands on the components and creates more situations where the turbine must be shut down to avoid damaging components. Even in situations where the average wind speed is not high enough to cause damage, periodic wind gusts which change both the speed and direction of the wind, apply forces that may be strong enough to damage equipment.

Approaches with varying levels of success have been attempted in achieving higher power, fewer shut downs, and less instances of damage to components. For example, pitch control has been used to vary the pitch of the blade (i.e., the angle of the blade). On a pitch controlled wind turbine, an electronic controller on the turbine checks the power output of the turbine. When the power output exceeds a certain threshold, the blade pitch mechanism turns the rotor blades to reduce the loads on the rotor blades. The blades are later turned back when the wind drops again. However, pitch control can be fairly slow to respond to changes in the wind and is relatively ineffective to loads imparted by sudden wind gusts.

Stall control is another approach that has been used in an attempt to achieve higher power, and to reduce shut downs and damage to components. In passive-type stall controlled wind turbines, the rotor blades are mounted to the hub at a fixed angular orientation. The stall control is achieved passively by the shape of the blade being such that the blade goes into aerodynamic stall (destroying lift) when the wind speed exceeds a certain threshold. Active-type stall controlled wind turbines exist. In such systems, the rotor blades are adjusted in order to create stall along the blade. However, both types of stall control systems can be difficult to optimize and slow to respond, and may suffer from lower predictability of results than desired. These drawbacks are magnified in conditions with erratic winds and wind gusts.

Variable length rotor blade systems have also been used as an attempt to achieve higher power, and experience fewer shut downs and less damage to components. In such systems, the wind turbine rotor blades are telescopic so that their length can be adjusted based on the wind speed. Such provides advantages in that the rotor blades can be extended to provide higher output in low wind conditions and retracted to lower loads in high wind conditions. U.S. Pat. No. 6,902,370 discloses a wind turbine system having telescoping wind turbine rotor blades. While variable length rotor blade systems have certain advantages, they may suffer drawbacks in erratic wind conditions or may be too slow to respond when experiencing a wind gust.

As electricity continues to become a more valuable commodity, and as wind turbines present an environmentally-friendly solution to solve electricity shortage problems, a wind turbine design that overcomes the aforementioned drawbacks and provide increased power and decreased turbine shut downs and damage to components is thus desirable.

BRIEF SUMMARY

To overcome limitations in the prior art described above, and to overcome other limitations that will be apparent upon reading and understanding the present specification, the present invention is directed to a device and system for counteracting sudden increases in load or changes in operating environment such as when a gust suddenly increases the magnitude of the wind or changes the direction of the wind experienced by a wind turbine rotor.

A first aspect of the invention provides a wind turbine including an airfoil rotor blade having an air deflector. The air deflector may be configured to extend from an exterior surface of the airfoil rotor blade when a change in load or wind gust magnitude or angle is detected. In this way, the air deflector acts to counteract such changes. In one arrangement, the air deflector may be located on a leading side of the airfoil rotor blade as defined by a leading edge and a trailing edge of the blade. For example, the leading edge and surface may correspond to an edge or surface of the airfoil rotor blade closest to an origin of the wind. The air deflector may further be moved to a retracted position in normal operating conditions (e.g., when a load is not excessive) such that the air deflector does not extend outwardly from the surface of the airfoil rotor blade.

A second aspect of the invention provides a wind turbine including an airfoil rotor blade that is telescopically extendable and having at least one air deflector. To counteract excessive loads and other environmental factors, the airfoil rotor blade may be extended or retracted in conjunction with the extension or retraction of at least one air deflector. For example, when a sudden change occurs, the air deflector may be activated since the air deflector may be extended very quickly. For more gradual changes, extension or retraction of the blade may be used since quick compensation is not as critical. In other arrangements, the air deflector may be extended to further reduce loads in cases where the airfoil rotor blade has been retracted as much as possible.

A third aspect of the invention provides a wind gust or load counteracting module connected to an airfoil blade. The counteracting module may include an air deflector, a controller for controlling the extension and retraction of the air deflector and a sensor configured to sense various conditions. In one or more configurations, an airfoil blade may include multiple counteracting modules, each including an air deflector, a controller and a sensor. Use of modules may facilitate the removal, insertion or replacement of air deflectors or other components associated therewith out having to modify the entire airfoil blade.

DETAILED DESCRIPTION

Aspects of the present invention are directed to a deployable device and combinations of its attributes that may be mounted to a rotor blade in various applications to quickly assist in counteracting wind gusts. In addition, aspects of the present invention are directed to a rotor blade having the deployable device, and to a wind turbine with a rotor blade having the deployable device.

FIG. 1shows a wind turbine2on a foundation4with a tower6supporting a nacelle8. One or more blades10are attached to a hub12via a bolt flange14. In the depicted embodiment, the wind turbine includes three blades10. The hub12is connected to a gear box, a generator, and other components within the nacelle8. The blades10may have a fixed length or may be of the variable length-type, i.e., telescopic, such as shown inFIG. 1. As shown inFIG. 1, each variable length blade10includes a root or base portion16and a tip portion18. The tip portion18is movable with respect to the root portion16so as to controllably increase and decrease the length of the rotor blade10, and in turn, respectively increase and decrease the swept area of the rotor blades10. Any desirable drive system, such as a screw drive, a piston/cylinder, or a pulley/winch arrangement may be used to move the tip portion18with respect to the root portion16. Such drive systems are described in U.S. Pat. No. 6,902,370, which is hereby incorporated by reference. The wind turbine2further includes a yaw drive and a yaw motor, not shown.

FIGS. 2-5show a cross section of a wind turbine blade10containing at least one gust counteracting device30. The blade10has a leading edge20, a trailing edge22, a high pressure side24and a low pressure side26. A chord line c can be defined as a line between the leading edge20and trailing edge22of the blade10. It is recognized that the leading side of the rotor blade10corresponds to the leading half of the rotor blade10and the trailing side of the rotor blade10to the trailing half of the rotor blade10.

The blade10depicted in the figures is merely one illustrative cross-sectional design and it is recognized that infinite cross-sectional variations can be used as part of the present invention. The airfoil rotor blade may be made of any suitable construction and materials, such as fiberglass and/or carbon fiber.

As can be seen in cross sections ofFIGS. 2 and 3, the rotor blade10further includes at least one gust counteracting device, generically referenced to as reference number30, but specifically referred to as reference number30aand30bwith reference to a specific side of the rotor blade10.FIG. 2depicts a placement of a first wind gust counteracting device30ato affect the airflow on the low pressure side26of the rotor blade10.FIG. 3depicts a placement of a second wind gust counteracting device30bto affect the airflow on the high pressure side24of the rotor blade10. It is recognized that in use, the more curved surface26aand the opposing less curved surface24acreate the dynamics of the low pressure side26and the high pressure side24due to well known principles of aerodynamics. This, in combination with the airflow over the rotor blade10, creates an effect known as “lift” that assists in the rotation of the rotor.

In one embodiment, each rotor blade10includes at least one first wind gust counteracting device30ato affect the airflow on the low pressure side26and at least one second wind gust counteracting device30bto affect the airflow on the high pressure side24. That is, it includes wind gust counteracting devices30aand30b, and these devices30a,30bmay be longitudinally spaced along the rotor blade10. Any desired number of these devices30a,30bmay be used. In another embodiment, each rotor blade10includes at least one wind gust counteracting device30ato affect the airflow on the low pressure side26and no wind gust counteracting devices on the high pressure side24. Any desired number of the devices30amay be used on the low pressure side26. In yet another embodiment, each rotor blade10includes at least one wind gust counteracting device30bon the high pressure side24and no wind gust counteracting devices on the low pressure side26. Any desired number of the devices30bmay be used on the high pressure side24.

Each wind gust counteracting device30a,30bincludes an air deflector32. The air deflector32is movable between an extended position in which the air deflector32extends from an exterior surface of the airfoil rotor blade10and a retracted position in which the air deflector32is substantially flush with, recessed, or otherwise does not materially extend from the exterior surface of the airfoil rotor blade10.FIGS. 2 and 3both show the air deflector32in an extended position wherein the air deflector32extends from the exterior surface of the rotor blade10.FIG. 4is an isometric sectional view through the rotor blade10depicting the wind gust counteracting device30a.

In a first arrangement, the location of the air deflectors32with respect to the leading edge20and the trailing edge22of the airfoil rotor blade10is in the leading half, i.e., is between 0%-50% of the length of the chord c when measured perpendicularly thereto from the leading edge20to the trailing edge22. In another arrangement, the location of the air deflectors32with respect to the leading edge20and the trailing edge22of the airfoil rotor blade10is between 5%-25% of the length of the chord c when measured perpendicularly thereto from the leading edge20to the trailing edge22. In yet another arrangement, the location of the air deflectors32with respect to the leading edge20and the trailing edge22of the airfoil rotor blade10is between 5%-15% of the length of the chord c when measured perpendicularly thereto from the leading edge20to the trailing edge22.

The air deflector32may be sized based on the desired wind turbine condition parameter and further in view of the number of gust counteracting devices used. The air deflector may be made from any suitable material, such as fiberglass, carbon fiber, stainless steel, and/or aluminum. The air deflector32may be of any desired width, for example from a few inches to a foot. Additionally, air deflector32may extend from the airfoil surface to any desired height, e.g., from less than a percent to a few percent of the chord c (FIG. 3), and they may have any suitable thickness based on the material chosen, typically less than one inch.

FIGS. 4 and 5are isometric sectional views through the rotor blade10depicting the low pressure side wind gust counteracting device30with the air deflector32in a retracted position (FIG. 4) and in an extended position (FIG. 5). The wind gust counteracting device30is suitably mounted by an interface to substantially maintain the surface contour the rotor blade10. This may be accomplished by the use of one or more contoured cover plates34that fixedly attach to both the gust counteracting device30and the blade structure. Alternatively, the leading face of the wind gust counteracting device30may be suitably contoured and fixed to the blade structure. In another arrangement, the leading face of the wind gust counteracting device30may be mounted to the underside of the blade. Suitable fastening arrangements such as hardware and adhesives may be used.

FIGS. 6 and 7depict isometric views of an illustrative embodiment of a gust counteracting device30, in isolation, with the air deflector32shown in a retracted position (FIG. 6) and in an extended position (FIG. 7). In a first arrangement, the gust counteracting device30includes frame33made from first and second portions34aand34b. The portions34aand34binterface so as to define a slot35in which the air deflector32travels. If desired, the facing edges of the first and second portions34aand34binclude air exhausts36. Air exhausts36are generally used in pneumatic configurations (i.e., where the air deflector32is actuated by pressurized air) to release retained pressurized air, thereby allowing the air deflector32to return to an alternate position (e.g., retracted or extended). The operation of air exhausts like air exhausts36is discussed in further detail below with respect toFIGS. 18aand18b.

According to one aspect, gust counteracting device30may include guide notches (not shown) that act as a track for the air deflector32. For example, the lower portion of the air deflector32may include projections (not shown) that are sized, spaced, and shaped complimentary to the guide notches. The projections may then follow the track corresponding to the notches when the air deflector32is extended or retracted. Such an arrangement provides increased alignment and additional structural support. Any desired arrangement, such as screws and other hardware38, may be used to affix the first and second portions34aand34bof the gust counteracting device30together. If openings in the rotor blade10are accommodated to be the same size, the air deflector30and its separate modular characteristic, facilitate easy replacement from potential damage, such as if hit by lightning, or selected replacement for customization purposes. Additionally or alternatively, port40may be provided as a fluid conduit coupling, e.g., to connect to a pressurized air source via an air tube or the like.

As described above, if more than one gust counteracting device30is used on each rotor blade10, they may be longitudinally spaced along the length of the rotor blade10as desired.FIG. 8depicts an illustrative spacing arrangement for a series of gust counteracting devices30with the air deflectors32.FIG. 9depicts a longitudinally-telescopic rotor blade10showing a series of longitudinally-spaced gust counteracting devices30with air deflectors32on both the base portion16of the rotor10and the tip portion18of the rotor10. For each arrangement, and based on space constraints within the rotor blade10, it may be desirable to longitudinally space the gust counteracting devices30at wider intervals so that they may alternate between locations on the high pressure side24(FIG. 2) and the low pressure side26(FIG. 2).

The functionality of the gust counteracting device30aand30bis generally described herein with respect toFIGS. 10-14.FIG. 10shows a rotor blade10being subjected to airflow under normal wind conditions where the angle of attack of the wind, i.e., the angle between the chord line c and the direction of the relative wind, is within normal desired operating conditions. Such conditions are reflected in the graph ofFIG. 14where the angle of attack is between the lines represented by α1and α2. In this range, the air deflectors would preferably remain in a retracted position as the wind conditions are achieving the desired lift with low drag. The boundary layer of the air flow on the low pressure side26is completely attached. Such may achieve desired operating results under normal wind conditions.

FIG. 11shows the rotor blade10being subjected to airflow under a gust condition that quickly increases the angle of attack of the wind in excess of α1. This creates increased lift and may exceed desired loads. As described above, this can damage components and force a shut down. The lift and drag characteristics on the rotor blade10under these conditions are shown on the graph inFIG. 14by the line segments to the right of α1containing point G1.

Operation of the gust counteracting device30aon the low pressure side26under these conditions counteracts the negative effects of such a gust. Such effects are shown inFIG. 12.FIG. 12depicts similar wind conditions relative to the rotor blade as shown inFIG. 11. InFIG. 12, the gust counteracting device30a(e.g., the load control device) is deployed to move the air deflector32to the extended position. This induces upper flow separation adjacent or at a minimum closer to the leading edge20. This creates a significant increase in drag and a large reduction in lift. Since the gust counteracting device30acan move the air deflector32from the retracted position to the extended position in a fraction of a second, the load on the rotor blade and the other components can likewise be reduced in a fraction of a second to better preserve the equipment and prevent failures.

The lift and drag characteristics on the rotor blade10under these conditions are shown on the graph inFIG. 14by the line segments to the right of α1containing point G2. Specifically, the decrease in lift with the extended air deflector32is represented by the difference between the line segments to the right of α1containing point G1and G2, respectively. Additionally, the increase in drag with the extended air deflector32is represented by the difference between the line segments to the right of α1containing point G2and G1, respectively. When the angle of attack moves back into normal conditions, the air deflector32may be moved back into its retracted position.

FIG. 13is a schematic sectional view of a rotor blade representing airflow under an alternative gust or wind turbine rotor emergency stop conditions and schematically depicting a high pressure side air deflector32in an extended position and the effect on air flow. In the conditions as depicted inFIG. 13, the angle of attack has fallen below α2(seeFIG. 14). Without the deployment of the high pressure side air deflector32, the lift would continue to decrease as depicted inFIG. 14.

However, when the air deflector32on the high pressure side is moved to an extended position, lower surface flow separation is immediately induced. This in turn, increases the drag, but has the effect of reducing the unwanted negative lift. The lift and drag characteristics on the rotor blade10under these conditions are shown on the graph inFIG. 14by the line segments to the left of α2containing point G3. This offset of the unwanted negative lift reduces the aerodynamic loads on the wind turbine during undesirable wind gust conditions or wind turbine rotor emergency stop conditions. When the angle of attack moves back into normal conditions, the air deflector32may be moved back into its retracted position.

The air deflector32is beneficial under other gust conditions, such as a sudden increase in wind speed without a change in the angle of attack. By quickly moving the air deflector32from the retracted position to the extended position, on either or both the low pressure side26(as shown inFIG. 2) or on the high pressure side24, it alters the shape of the rotor blade10around or near the leading edge20. This in turn drastically changes the lift and drag properties of the blade10. Thus, a strong wind gust that increases wind velocity and imparts an increased load on the equipment, can be counteracted in a fraction of a second by the deployment of one or more air deflectors32. Thus, it effectively acts as instantaneous increase of drag, akin to functioning as an air brake.

Any desired drive may be used to move the wind gust counteracting devices30can move their respective the air deflector32between its extended and retracted position. In an illustrative arrangement in which a fluid such as air is used to control the movement of the air deflectors32, a centralized source of pressurized air is operatively coupled to a port of the wind gust counteracting devices30(e.g., port40ofFIGS. 6 and 7) via a conduit (e.g., conduit58ofFIG. 15). Within the wind gust counteracting devices30, an air pressure actuated solenoid or piston/cylinder and a valve is used to drive the air deflector32between its extended and retracted positions. A valve for controlling the flow of pressurized air, e.g., valve73ofFIGS. 18aand18b, may be electronically controlled if desired. In one arrangement, the signal to operate the valve and move the air deflector32travels via an optical fiber. If desired, a spring may be used to bias the air deflector32into either position as a fail safe. While some small amount of electricity may be needed to operate this system, and the power may be from a local source such as a battery or remotely from a conductive wire, this arrangement has advantageous attributes in that it minimizes power consumption and minimizes the likelihood of a lightning strike. It is recognized that alternative drive systems may be used. For example, a spring may be used to bias air deflector32into an extended position. To subsequently retract the air deflector32, a motor may be used. Other electromechanical mechanisms and systems may also be used.

FIGS. 18aand18billustrate a piston/cylinder arrangement76/78, a valve73and a controller for extending and retracting an air deflector79. In the extended position shown inFIG. 18a, air deflector79(i.e., a top portion of piston76) extends past a surface of the gust counteracting module in which the piston/cylinder arrangement76/78is housed and an exterior surface81of a corresponding airfoil rotor blade (not shown). Stoppers77are configured and placed to prevent air deflector79and piston76from extending past a certain point, thereby controlling an amount by which air deflector79may protrude from surface81. InFIG. 18b, the air deflector79is in a retracted position and stoppers77prevent piston76and deflector79from retracting past a certain point. In the retracted position, the top of air deflector79may be flush with an exterior surface81of the airfoil rotor blade.

Controller71is configured to control valve73(e.g., a five way valve) to allow the flow of pressurized air into an upper chamber (i.e., a region above the base of the piston76) or a lower chamber (i.e., a region below the base of the piston76) of the cylinder78. By injecting pressurized air into the upper chamber, for example, the piston76may be forced down into a retracted position (as shown inFIG. 18b). Injecting air into the lower chamber, on the other hand, forces the deflector79and piston76upward into an extended position (as shown inFIG. 18a). In one arrangement, pressurized air may be retained in either the lower or the upper chamber to hold deflector79and piston76in a corresponding position. Accordingly, pressurized air does not need to be continuously injected into a particular chamber to hold the deflector79in a particular position in such an arrangement. To subsequently move deflector79and piston76from an extended to a retracted position, or vice versa, the pressurized air currently retained in either the lower or upper chamber may be evacuated from cylinder78through one or more air release valves75(or other air release mechanism) and further released from the gust counteracting module through exhaust channel85. According to one aspect, exhaust channel85may allow air to escape into the atmosphere. The air release valves75may be electronically controlled, e.g., by controller71and/or include mechanical control systems.

The wind gust counteracting devices such as devices30may be activated based on readings from one or more of various sensors and/or controller that used sense values to determine whether predetermined thresholds have been exceeded or when an air deflector should be moved based on an algorithm. Such sensors can include one or more of the following: accelerometers, strain gauges, absolute and differential pressure gauges, wind vanes, and wind speed detectors.

As can be seen inFIG. 15, the gust counteracting devices30may each be locally-controlled. According to this arrangement, each of gust counteracting devices30would have a controller50and one or more sensors52coupled to the controller50. Upon determining that a predetermined threshold has been exceeded (e.g., based on a reading from sensor52), the controller50would send a signal to operate the valve54to control the flow of pressurized air and move the air deflector32. According to this arrangement, each of gust counteracting devices30may be coupled to a common pressurized air source56via a fluid conduit58.

As can be seen inFIG. 16, the gust counteracting devices30may also be centrally-controlled. According to this arrangement, each gust counteracting device30would be functionally coupled to a common controller60. Controller60could send signals to individually or commonly control the gust counteracting devices30. Signals may be sent by controller60to each gust counteracting device30via an optical fiber62and/or other wired or wireless signaling mechanisms. Similar to the embodiment ofFIG. 15, each of gust counteracting devices30may be coupled to a common pressurized air source56via a fluid conduit58. In this centrally-controlled embodiment, there is more flexibility to use additional sensors52such as sensors spaced from the gust counteracting device30. Additionally, the controller60may be coupled to the blade rotor drive system64to telescopically control the effective length of the rotor blades10.

Additionally, in another arrangement, the gust counteracting devices30are controlled according to a system containing substantially the details ofFIGS. 15 and 16. As illustrated inFIG. 17, the gust counteracting devices30may each be controlled in a distributed manner. According to this arrangement, each of gust counteracting devices30would have a local controller50and one or more sensors52coupled to the local controller50. Thus, each local controller50may independently control the extension and retraction of its corresponding deflector32based on detected conditions local to each controller50. Additionally, the local controllers50are coupled to a central controller60. Central controller60may send signals to the local controllers50to individually or commonly control the gust counteracting devices30. Each local controller50may further send signals to the central controller60to inform the central controller60of a status of each of the gust counteracting devices30. The collected status information may then be used by central controller60to determine an overall manner or scheme in which to control the local controllers50and deflectors32(e.g., to reduce load and/or optimize power capture). In this distributed control embodiment, there may also be flexibility to use additional sensors52such as sensors spaced from the gust counteracting device30. Additionally, the controller60may be coupled to the blade rotor drive system64to telescopically control the effective length of the rotor blades10. Such a distributed system may also provide redundancy. In each control arrangement, the controllers50,60may be any desired or known control circuitry including but not limited to microprocessors.