Long Term Rotor Parking on a Wind Turbine

Abstract

A method for locking a rotor of a wind turbine in a long term parking state is disclosed. The method may include applying rotor brakes, enabling a long term parking configuration of the rotor and providing an emergency feather response for protecting the wind turbine against faults.

Description

CROSS-REFERENCE TO RELATED APPLICATION

This application is a Continuation-In-Part (CIP) Patent Application claiming priority under 35 U.S.C. §365(c) to International Application No. PCT/IB2009/006309 filed on Jul. 22, 2009, and also claims priority to Provisional Patent Application No. 61/206,207 filed on Jan. 28, 2009.

FIELD OF THE DISCLOSURE

The present disclosure generally relates to wind turbines and, more particularly, relates to stopping rotation of rotors of the wind turbines for extended periods of time.

BACKGROUND OF THE DISCLOSURE

A utility-scale wind turbine typically includes a set of two or three large rotor blades mounted to a hub. The rotor blades and the hub together are referred to as the rotor. The rotor blades aerodynamically interact with the wind and create lift or drag, which is then translated into a driving torque by the rotor. The rotor is attached to and drives a main shaft, which in turn is operatively connected via a drive train to a generator or a set of generators that produce electric power. The main shaft, the drive train and the generator(s) are all situated within a nacelle, which rests on a yaw system that continuously pivots along a vertical axis to keep the rotor blades facing in the direction of the prevailing wind current to generate maximum torque.

Various situations could necessitate stopping all rotation of the hub on a wind turbine and placing the rotor in a parked state for an extended period of time. For example, when performing maintenance on a wind turbine, for safety and/or practical reasons, it may be necessary to lock the rotor so that it does not rotate. Some storm and icing weather situations may also necessitate locking the rotor. Most wind turbines include a brake and/or a positive locking pin to stop rotation of the hub (and therefore the rotor) relative to the nacelle. The rotor can be locked with a locking pin that can be inserted from the nacelle into a mating receptacle on the hub. Other mechanisms for locking the rotor into a stationary position may be employed as well.

The wind turbine may remain in this rotor locked state for an extended period of time. Because of the large torques that a hub can generate during high wind velocities even in the locked state of the rotor, the brake or locking pin that is holding the hub must be able to provide a very large counter-rotational torque to prevent rotation and maintain the rotor in a stationary position. Specifically, even in the locked state, the wind continues to act on the rotor blades and produce lift. The continued lift of the rotor blades creates rotor torque and the brakes or the locking pin locking the rotor must be able to withstand and counteract this rotor generated torque.

Normally, the wind turbine would continue to yaw in the rotor locked state, to constantly change the orientation of the turbine into the wind. The loads and torque created by the wind when the rotor is locked are lowest and most predictable when the turbine is pointed into the wind. But, some situations and circumstances may require that the turbine cannot continue to yaw and adjust its orientation into the wind. In those situations where the turbine can no longer yaw, the loads and rotor torque may become a concern and it may be desirable to place the rotor in a long term parking state to protect the wind turbine from damaging winds and high loads.

Accordingly, it would be beneficial if a technique for a long term rotor parking were developed. It would additionally be beneficial if such a technique could be employed in addition to any braking or locking pins used to lock the rotor and to provide an additional factor of safety during conditions of high loading on the wind turbine when the rotor is in a locked state.

SUMMARY OF THE DISCLOSURE

In accordance with one aspect of the present disclosure, a method for locking a rotor of a wind turbine in a long term parking state is disclosed. The method may include providing a wind turbine having a rotor, the rotor having a hub and a plurality of blades radially extending therefrom. The method may further include locking the rotor to prevent rotation, enabling a long term parking configuration of the rotor and providing an emergency feather response for protecting the wind turbine against faults.

In accordance with another aspect of the present disclosure, a method of configuring a rotor of a wind turbine in a long term parking state is disclosed. The method may include providing a wind turbine having a rotor, the rotor having a hub and a plurality of blades radially extending therefrom. The method may further include locking the rotor against rotation and changing a pitch angle of each of the plurality of blades to zero degrees.

In accordance with yet another aspect of the present disclosure, a wind turbine is disclosed. The wind turbine may include a rotor having a hub and a plurality of blades radially extending from the hub and a control system in operable association with the rotor, the control system configured to put the rotor in a long term parking state.

Other advantages and features will be apparent from the following detailed description when read in conjunction with the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the disclosed methods and apparatuses, reference should be made to the embodiments illustrated in greater detail on the accompanying drawings, wherein:

FIG. 1 is a schematic illustration of a wind turbine, in accordance with at least some embodiments of the present disclosure;

FIG. 2 is an exemplary flowchart outlining steps in parking a rotor of the wind turbine in a long term parking state;

FIG. 3 is an exemplary wind rosette showing rotor torque produced from the wind relative to the wind turbine in every wind direction for different given blade pitch angles; and

FIG. 4 is an exemplary illustration of the rotor torque when blades of the wind turbine are pitched one at a time.

While the following detailed description has been given and will be provided with respect to certain specific embodiments, it is to be understood that the scope of the disclosure should not be limited to such embodiments, but that the same are provided simply for enablement and best mode purposes. The breadth and spirit of the present disclosure is broader than the embodiments specifically disclosed and encompassed within the claims eventually appended hereto.

DETAILED DESCRIPTION OF THE DISCLOSURE

Referring to FIG. 1, an exemplary wind turbine 2 is shown, in accordance with at least some embodiments of the present disclosure. While all the components of the wind turbine have not been shown and/or described, a typical wind turbine may include a tower section 4 and a rotor 6. The rotor 6 may include a plurality of blades 8 connected to a hub 10. The blades 8 may rotate with wind energy and the rotor 6 may transfer that energy to a main shaft 12 situated within a nacelle 14. The nacelle 14 may additionally include a drive train 16, which may connect the main shaft 12 on one end to one or more generators 18 on the other end. The generators 18 may generate power, which may be transmitted through the tower section 4 to a power distribution panel (PDP) 20 and a pad mount transformer (PMT) 22 for transmission to a grid (not shown). The nacelle 14 may be positioned on a yaw system 24, which may pivot about a vertical axis to orient the wind turbine 2 in the direction of the prevailing wind current or another preferred wind direction. In addition to the aforementioned components, the wind turbine 2 may also include a pitch control system (not visible) situated within the hub 10 for controlling the pitch (e.g., angle of the blades with respect to the wind direction) of the blades 8. The pitch control system may include servo motors, which drives the blades 8 relative to the hub 10 to change the pitch angle. The pitch control system may further include a pitch control unit (PCU) for controlling the servo motors, and a battery back-up system for providing power to the pitch control unit and the servo motors in the case of an emergency or in other situations. The wind turbine 2 may also include an anemometer 26 for measuring the speed and direction of the wind. A turbine control unit (TCU) 28 and control system 29 may be situated within the nacelle 14 for controlling the various components of the wind turbine 2.

Referring now to FIG. 2, an exemplary flowchart 30 outlining the procedure for parking the rotor 6 in a long term parking state are shown, in accordance with at least some embodiments of the present disclosure. As will be described further below, the long term parking state may be characterized by, in addition to locking the rotor, a rotor configuration with the hub 10 and/or blades 8 in a position which results in the lowest possible loads and/or torque on the wind turbine 2. Specifically, when the rotor 6 is locked against rotation, the blades 8 may still interact with the wind to produce varying amounts of lift. This lift may be translated by the blades 8 and the hub 10 into torque. The amount of lift and therefore torque generated from interaction with the wind may depend upon wind aerodynamics, which may be influenced largely by the wind direction, the azimuthal location of the rotor blades, and the pitch angle of the rotor blades. Thus, in order to park the rotor 6 in a long term parking state, the pitch angle of the blades 8 may be adjusted to be in an optimal state for any wind direction to minimize loads on the wind turbine 2, such as, by minimizing the rotor torque, thereby preventing any damage to the wind turbine. Also, the azimuthal position of the rotor 6 may be adjusted to be in an optimal state for any wind direction to minimize loads. Finally, the yaw orientation of the wind turbine 2 may be set to a particular position to minimize loads. Adjusting the pitch angle and the azimuthal position of the blades 8 and adjusting the yaw orientation of the wind turbine 2 are each described in greater detail below.

Accordingly, after starting at a step 32, the process may proceed to a step 34, where it may be determined whether the rotor 6 needs to be parked in a long term parking state. In at least some embodiments, this determination may be made by a control signal generated manually (e.g., by maintenance personnel when maintenance is required) or automatically by the TCU 28 or the control system 29. The determination may be made automatically based upon several different factors, such as, severe weather conditions, or a damaged bearing or other component as detected by a condition monitoring system or the like. If the control signal at the step 34 for parking the rotor 6 in a long term parking state is, thus, ON, the process may proceed to a step 36. Otherwise, the process may end at a step 38.

At the step 36, it may be determined whether the brakes of the rotor 6 have already been applied or not, and/or whether the positive locking pin has engaged the hub 10 to positively lock it against rotation. If the brakes have not been applied or if the locking pin has not been engaged, then at a step 40, the brakes of the rotor and/or the locking pin may be automatically applied. In other embodiments, other types of braking mechanisms, whether manual or automatic, may be employed and implemented to lock the rotor 6.

On the other hand, if at the step 36, it is determined that the rotor 6 is already in a locked position, then the process may proceed directly to a step 42, where the rotor 6 is configured to a “fetal” or protective state. This protective state may be characterized by pitching the blades 8 to a specific pitch angle producing the least amount of torque, as described in FIGS. 3 and 4 below and, also by adjusting the azimuthal position of the blades to minimize loads on the wind turbine 2, as described further below.

Turning now to FIG. 3 in conjunction with FIG. 2, a wind rosette or graphical representation 44 showing the amount of rotor torque for several different blade pitch angle position settings generated from wind in any direction is illustrated, in accordance with at least some embodiments of the present disclosure. As will be described further below, it may be seen from the wind rosette 44 that when the blades 8 are pitched towards power (to at or near zero degrees from the plane of the rotor 6), the least amount of torque is produced irrespective of the wind direction relative to the wind turbine 2.

The wind rosette 44 plots rotor torque relative to the wind direction at various angles (such as 45°, 90°, 135°, 180°, 225°, 270°, 315°, and 360°). The torque generated at a given wind direction is proportional to the radial distance of the point from the center of the rosette. It should be noted that the typical convention for measuring pitch angles is that the pitch angle is the angular difference between the blade and the rotor plane of rotation, and that is the convention used herein. By determining the rotor torque for every wind direction for various pitch angles of the blades 8, the pitch angle that generates the minimum overall rotor torque may be observed. As shown, the graph 44 illustrates four different plots 46, 48, 50 and 52, each representing different pitch angles of the blades 8 and the corresponding rotor torque for every wind direction. In particular, the plots 46 and 48 shows the rotor torque when all of the three blades 8 are pitched at or near zero degrees)(0°. The plot 50 shows the rotor torque when each of the three blades 8 of the wind turbine 2 are pitched to different pitching angles, namely, a first blade may be pitched at ninety degrees)(90°, a second blade may be pitched at (or near) eighty seven and a half (87.5°) and a third blade may be pitched at (or near) ninety two and a half degrees (92.5°). The plot 52 shows the rotor torque when all of the blades 8 are pitched at or near ninety one degrees)(91°).

The plots 46, 50 and 52 indicate an instantaneous rotor torque value when the blades have been pitched to their specific pitching angles mentioned above. The plot 48 corresponds to the rotor blades 8 being pitched individually, one at a time, from a ninety degree)(90° position to a zero degree)(0°) position, which procedure is illustrated in greater detail in FIG. 4. The plot 48 indicates a maximum torque value that may be obtained over the entire time period (such as five to ten minutes) that it takes for all three blades to reach the final zero degree)(0°) pitch angle. It should be understood that all of the plots 46-52 may be for a given wind speed, for example, a wind speed of twenty two meters per second (22 m/sec), and an assumed rotor azimuth position, wind shear, etc. Similar results in terms of relative torque were observed at other wind speeds and conditions.

Thus, it can be seen that a pitch angle at or near zero degrees (0°) generates significantly less torque than the other simulated pitch angles. Therefore, to minimize rotor torque during long term rotor parking, the blades 8 may be pitched at or near zero degrees (0°). The zero degree (0°) pitch position is somewhat counter-intuitive. This position may generate the most lift and torque (and hence maximum power) during operation when the rotor 6 is turning at a certain RPM, but when the rotor is stationary and not turning, the zero degree)(0°) pitch position may also produce the least amount of torque.

Notwithstanding the fact that in the present embodiment, a zero (or near zero) degree pitch position of the blades 8 has been determined to minimize rotor torque, the pitch angle corresponding to minimum torque may vary for other wind turbines. Also, it may be desirable to optimize the rotor position to minimize other loads in addition to rotor torque. In that case, the pitch position of the blades 8 may also be different.

Furthermore, the blades 8 may be pitched all together at the same time or, alternatively, each blade may be pitched individually. If all the blades 8 are moved simultaneously from or near the ninety degree position to the zero degree position, for example, all three blades may at the same time reach a pitch position where, despite the lack of rotation of the hub 10, they may produce a lot of lift and, therefore, torque. In order to avoid this, the blades 8 may be pitched from or near ninety degrees to at or near zero degrees one at a time, the next blade not beginning to pitch until the previous blade has finished pitching to zero degrees. The rotor torque that may be produced when the blades 8 are pitched one at a time is shown in FIG. 4 below.

Referring now to FIG. 4 in conjunction with FIGS. 2 and 3, an exemplary time domain graph 54 showing rotor torque values as the blades 8 are pitched from or near ninety degrees to near or at zero degrees is depicted, in accordance with at least some embodiments of the present disclosure. The time domain graph 54 plots degrees on the left side Y-axis of the table against time in seconds on the X-axis and the torque on the right side Y-axis. The time domain graph 54 corresponds to a wind speed of eighteen meters per second (18 m/sec) and an assumed wind shear value and wind direction. Similar results are observed at other wind speeds and conditions. It can be reaches the zero degree pitch angle does a blade 62 begin pitching. Similarly, blade 64 starts pitching only after the blade 62 has reached its pitch angle of zero degrees. By virtue of pitching the blades 8 one by one, it can be seen that the rotor torque remains relatively stable, and avoids the sharp spike in torque that may be generated due to pitching all of the blades simultaneously.

Thus, in order to park the rotor 6 in a long term parking state, the pitch angles of each of the blades 8 may be pitched to at or near zero degrees, and the blades may be moved to that position either simultaneously or one by one as described above. The process of moving the blades 8 one by one from their current blade position to the at or near zero degree position may be accomplished manually in the step 42, or automatically with appropriate commands from the control system 29. In a preferred embodiment, the positioning of the blades 8 may happen automatically through commands from the control system 29. The control system 29 could even control the pitch rate of individual blades 8 to minimize the amount of time the rotor 6 might spend in a particular position where a large or maximum torque is generated, in other words, the control system may be programmed to move through such a large or maximum torque position as quickly as possible.

In addition to optimizing the pitch angle position of the blades 8, in at least some circumstances, the azimuthal position of the blades 8 may be optimized as well. Specifically, the blades 8 in their stationary position may be placed at an azimuthal position which may result in a lowest rotor torque, or lowest loads, or some combination of lowest loads and lowest torque. In at least some embodiments, an optimal azimuthal position may correspond to a “Y” position of the blades 8 in which the blades may be positioned at two o'clock, six o'clock and ten o'clock, respectively. The optimal azimuthal position may vary in other embodiments. As with pitch positioning, this azimuthal positioning of the rotor 6 may occur in the step 42 manually, or automatically with appropriate commands from the control system 29. The control system 29 may disengage the brakes and/or the positive locking pin and the hub 10 may be permitted to rotate a few degrees to obtain the desired azimuthal position of the blades 8 for long term rotor parking before the brakes and/or locking pin are re-engaged.

Furthermore, in addition to adjusting the pitch angle position of the blades 8 and the azimuthal position thereof, in at least some embodiments, a particular yaw orientation of the wind turbine 2 may also be desirable to line up the wind turbine most favorably with the average or prevailing wind direction at a particular wind turbine site. Some wind turbines may experience the lowest rotor torque or other loads when those wind turbines are facing directly into the wind. For other wind turbines, or for particular loads that need to be minimized, a yaw angle other than facing directly into the wind may be the most desirable. For example, if the wind direction for the strongest or most prevalent wind patterns for a particular wind turbine site is known, then the wind turbine may be yawed to face that direction in order to orient the wind turbine directly into the wind to minimize loads thereon during a long term rotor parking state or it may be determined that for a given turbine or a particular load to be minimized the most optimal yaw position is ninety degrees) (90°) out of the prevailing wind direction or some other yaw orientation relative to the wind. Similar to the pitch angle of the blades 8 and the azimuthal position thereof, the desired yaw orientation for minimal loads may be achieved manually at the step 42 or automatically according to appropriate commands from the control system 29.

Now returning to FIG. 2, thus, at the step 42, the rotor 6 may be adjusted into a “fetal” or protective state to achieve a long term parking state (in addition to locking the rotor at the step 40) by (1) changing the pitch angle position of the blades 8 to at or near zero degrees or any other desirable pitching angle, and/or (2) adjusting the azimuthal position of the blades, and/or (3) adjusting the yaw orientation to a particular position where it is expected to generate minimal loads.

When this long term parking state is enabled, an additional safety factor to ensure that the rotor 6 safely stays in this position may be provided. Specifically, extra caution may be necessary to ensure that in this long term parking position, the rotor 6 does not begin to turn (or rotate), due to a broken locking pin or failed brake, for example, which might possibly occur when power to the wind turbine 2 is lost or when there is some other type of fault or failure. If the rotor 6 does begin to turn, it may eventually reach a speed where a lot of torque may be produced, given especially that the blades 8 have been pitched to the zero degree position for maximum power, at which point the rotor may over-speed. So, in this long term parking state, special controls may be implemented to take action if any rotor rotation begins and is detected. Accordingly, at a step 66, the rotor 6 may be monitored (by the control system 29 within the wind turbine 2) for any faults, such as those described above. If a fault is indeed detected, then the process may proceed to a step 68, where an emergency feather response may be taken to prevent damage to the wind turbine 2. If no faults at the step 66 are detected, then the control system 29 may continue to monitor the rotor 6 for any faults and the process may end at the step 38.

At the step 68, in order to take protective action, if any rotation of the hub is detected during the long term parking state of the rotor, or if any other fault is detected such as loss of power, or if the loss of power is sustained for longer than a set period of time, the PCU may fault and go into an emergency feather response. During this emergency feather response, the PCU may instruct and pitch the blades 8 back to the ninety degrees in a position of least power generation. The PCU may also be programmed such that if there is any detection of loss of braking hydraulic pressure or other brake failure, or if the locking pin is retracted (e.g., broken off) from the hub 10, the PCU may instruct the blades 8 back to the ninety degrees pitching angle. Furthermore, if power to the wind turbine 2 is lost, in those situations, the PCU may employ its battery bank to power the pitch motors to pitch the blades 8 to the ninety degrees pitching position and prevent any damage to the wind turbine and enter the emergency feather condition. In at least some embodiments, the PCU may pitch the blades 8 to the zero degrees position only when power is supplied to the wind turbine 2. As soon as the power goes off, the PCU may command the blades 8 to return to the ninety degree position.

Notwithstanding the fact that in the present embodiment, certain types of protective actions have been described, other types of actions to prevent damage to the wind turbine 2 or any component thereof may be taken in other embodiments. Subsequent to activating the emergency feather condition, the process may end at the step 38.

In general, the present disclosure sets forth a mechanism for parking the rotor in a long term parking state. The long term parking state of the rotor may be characterized by locking the rotor, changing the pitch angle of the blades to at or near zero degrees, adjusting the azimuthal position of the blades and aligning the yaw system to face the direction of wind. An emergency feather condition to provide any protective measures during conditions of faults, such as, rotor rotation and power loss, may be programmed within a control system that controls the long term parking state of the rotor.

By virtue of parking the rotor in a long term parking state, the amount of torque that the rotor produces while it is locked may be minimized, thereby relieving at least some of the requirement of the brake or pin to provide a very large counter-rotational force. The size and structure of the locking pin may also be reduced or simplified, and implementation of the long term parking state may provide an extra factor of safety by reducing the torque of the locked rotor.

While only certain embodiments have been set forth, alternatives and modifications will be apparent from the above description to those skilled in the art. These and other alternatives are considered equivalents and within the spirit and scope of this disclosure and the appended claims.

Claims

1. A method for locking a rotor of a wind turbine in a long term parking state, the method comprising:

providing a wind turbine having a rotor, the rotor having a hub and a plurality of blades radially extending therefrom;

locking the rotor to prevent rotation;

enabling a long term parking configuration of the rotor; and

providing an emergency feather response for protecting the wind turbine against faults.

2. The method of claim 1, wherein locking the rotor to prevent rotation comprises inserting a locking pin into a receptacle on the hub of the wind turbine.

3. The method of claim 1, wherein enabling a long term parking configuration comprises minimizing rotor torque generated by the rotor in a locked state.

4. The method of claim 1, wherein enabling a long term parking configuration comprises adjusting a pitch angle of the plurality of blades to produce a least amount of torque.

5. The method of claim 4, wherein each of the plurality of blades are pitched from a standby position near feather towards a power position near zero degrees.

6. The method of claim 4, wherein a pitching angle of zero degrees produces the least amount of torque when the rotor is in a locked state in every wind direction.

7. The method of claim 1, wherein enabling a long term parking configuration comprises optimizing an azimuthal position of the plurality of blades.

8. The method of claim 7, wherein an optimal azimuthal position of the plurality of blades comprises positioning a first blade at a two o'clock position, a second blade at a six o'clock position and a third blade at a ten o'clock position.

9. The method of claim 1, wherein enabling a long term parking configuration comprises adjusting a yaw orientation of the wind turbine relative to the prevailing wind direction.

10. The method of claim 1, wherein providing an emergency feather response comprises pitching the plurality of blades to a ninety degree pitch angle upon the detection of a fault.

11. The method of claim 1, wherein the emergency feather response is invoked when the rotor begins rotation in the long term parking configuration.

12. The method of claim 1, wherein the emergency feather condition is invoked when power to the wind turbine is lost.

13. A method of configuring a rotor of a wind turbine in a long term parking state, the method comprising:

providing a wind turbine having a rotor, the rotor having a hub and a plurality of blades radially extending therefrom;

locking the rotor against rotation; and

changing a pitch angle of each of the plurality of blades to at or near zero degrees.

14. The method of claim 13, wherein the pitch angle of each of the plurality of blades is changed one at a time, a second blade starting pitching after a first blade has reached zero degree pitch angle.

15. The method of claim 13, wherein each of the plurality of blades is pitched simultaneously to zero degrees.

16. The method of claim 13, further comprising:

optimizing the yaw orientation of the wind turbine; and

optimizing an azimuthal position of the plurality of blades.

17. A wind turbine, comprising:

a rotor having a hub and a plurality of blades radially extending from the hub; and

a control system in operable association with the rotor, the control system configured to put the rotor in a long term parking state.

18. The wind turbine of claim 17, wherein the long term parking state of the rotor comprises locking the rotor.

19. The wind turbine of claim 17, wherein the long term parking state of the rotor is characterized by one or more of changing a pitch angle of the plurality of blades, adjusting an azimuthal position of the plurality of blades and yawing the wind turbine to at least substantially face in to the wind.

20. The wind turbine of claim 17, wherein the control system further controls an emergency feather condition of the long term parking state of the rotor.