Thrust control for wind turbines using wind turbulence active sensing

Abstract

This invention provides a wind turbine and a method for defining multiple thrust limits for the wind turbine, the wind turbine being located in a field and having a rotor with rotor blades, wherein the thrust limit is defined as an aerodynamic thrust value on the rotor that will not be exceeded during operation. The method includes: providing a representative wind speed distribution for the field and defining one or more contour lines with constant turbulence probabilities, which represent turbulence parameters as a function of wind speed. The contour lines correspond to quantile levels of turbulence in the wind speed distribution, and the turbulence parameters indicate wind speed variations. The turbulence parameters are determined by continuously measuring the wind speed upstream of the rotor using an active sensing system and calculating wind speed variations based on the measured wind speeds. A turbulence range is defined with respect to the contour lines, and the thrust limit is defined with respect to the turbulence range.

Description

Technical Field

[0001] This invention relates to dynamic thrust control for wind turbine rotors, wherein wind turbulence is directly measured using an active sensing system such as a Doppler lidar system and is used as an input in the control process. Background Technology

[0002] Modern wind turbines are commonly used to supply power to the grid. This type of wind turbine typically consists of a tower and a rotor mounted on the tower. The rotor typically includes a hub and multiple blades, which begin to rotate under the influence of wind on the blades. This rotation generates torque, which is typically transmitted to a generator either directly through the rotor shaft (“direct drive”) or through a gearbox. In this way, the generator produces electricity that can be supplied to the grid.

[0003] Variable speed wind turbines (or variable speed wind turbines) are typically controlled by changing the generator torque and the blade pitch angle. Therefore, the aerodynamic torque, rotor speed, and electrical power will vary.

[0004] refer to Figure 3 Common existing technology control strategies for variable-speed wind turbines are described. Figure 3 In this context, the operation of a typical variable-speed wind turbine is described as a function of wind speed in terms of pitch angle (β), generated electrical power (P), generator torque (M), and rotor rotational speed (ω).

[0005] Within a first operating range from the cut-in wind speed to a first wind speed (e.g., approximately 5 or 6 m / s), the rotor can be controlled to rotate at a substantially constant speed, just high enough to allow for precise control. The cut-in wind speed could be, for example, approximately 3 m / s.

[0006] In the second operating range, from a first wind speed (e.g., approximately 5 or 6 m / s) to a second wind speed (e.g., approximately 8.5 m / s), the objective is typically to maximize power output while maintaining a constant blade pitch angle to capture maximum energy. To achieve this, generator torque and rotor speed can be varied to keep the tip speed ratio λ (the tangential velocity at the rotor blade tip divided by the prevailing wind speed) constant, thereby maximizing the power coefficient Cp.

[0007] To maximize power output and keep Cp constant at its maximum value, the rotor torque can be set according to the following equation: T = k.ω 2 , where k is a constant and ω is the generator speed. In direct-drive wind turbines, the generator speed is essentially equal to the rotor speed. In wind turbines that include a gearbox, there is typically a substantially constant ratio between the rotor speed and the generator speed.

[0008] Within a third operating range, starting from reaching the nominal rotor speed and increasing until reaching the nominal power, the rotor speed can remain constant, and the generator torque can be varied to achieve this effect. In terms of wind speed, this third operating range essentially increases from the second wind speed to the nominal wind speed, for example, from approximately 8.5 m / s to approximately 11 m / s.

[0009] Within a fourth operating range, which can increase from the nominal wind speed to the cut-out wind speed (e.g., from approximately 11 m / s to 25 m / s), the blades can rotate (“pitch”) to maintain a substantially constant aerodynamic torque delivered by the rotor. In effect, the pitch can be actuated to maintain a substantially constant rotor speed. At the cut-out wind speed, the operation of the wind turbine is interrupted.

[0010] Within the first, second, and third operating ranges—that is, at wind speeds below the nominal wind speed (below the nominal operating zone)—the blades typically maintain a constant pitch position, i.e., "below rated pitch position." This default pitch position can typically be close to 0° pitch angle. However, the exact pitch angle under "below rated" conditions depends on the overall design of the wind turbine.

[0011] The above operations can be transformed into a so-called power curve, such as Figure 3 The power curve shown is an example of a power curve that reflects the theoretically optimal operation of a wind turbine. However, in the wind speed range near the nominal wind speed, the aerodynamic thrust on the rotor can be very high, such as... Figure 4 As shown in the diagram, such high aerodynamic thrust results in high bending loads at the blade root. These high loads at the blade root, in turn, lead to high loads on the tower. If a wind turbine is repeatedly subjected to high loads, the fatigue life of wind turbine components such as the blades will be shortened.

[0012] In this regard, it is known that the rotor has a thrust limit, which is understood as the maximum level of aerodynamic thrust on the rotor that cannot be exceeded during operation. Therefore, the operation of the wind turbine is adjusted as necessary to avoid exceeding the thrust limit. Operation thus deviates from the theoretically optimal operation, and electrical output is negatively affected.

[0013] In some field applications, particularly at sea, it has been found that blades sometimes suffer high loads at the root and fatigue damage in highly turbulent winds, even with such thrust limits set.

[0014] Therefore, it will be beneficial to be able to reliably and accurately measure the wind turbulence upstream of the rotor, and to use this measurement to more precisely define the thrust limit on the rotor to accommodate this turbulence. This invention provides a solution to this need. Summary of the Invention

[0015] Aspects and advantages of the invention will be set forth in part in the description which follows, or may be apparent from the description or may be learned by practice of the invention.

[0016] In one aspect, this disclosure relates to a method for defining multiple thrust limits for a wind turbine located in a field and having a rotor with multiple blades, wherein the thrust limit is defined as an aerodynamic thrust value on the rotor that is not exceeded during operation. The method includes providing a representative wind speed distribution for the field and defining one or more contour lines with constant turbulence probabilities, which represent turbulence parameters as a function of wind speed, wherein the contour lines correspond to quantile levels of turbulence in the wind speed distribution and the turbulence parameters indicate wind speed variations. The turbulence parameters are determined by substantially continuously measuring the wind speed upstream of the rotor using an active sensing system and calculating wind speed variations based on the measured wind speeds. A turbulence range is defined with respect to the contour lines. A thrust limit is defined for each of the turbulence ranges.

[0017] In one embodiment of the method, the active sensing system uses a Doppler lidar system to generate multiple fixed measurement beams pointing upwind of the wind turbine to sample the incoming airflow. For example, in one embodiment, each of the fixed measurement beams can detect wind speeds at different angles relative to the rotor and at multiple different ranges from the rotor. For example, in one embodiment, the Doppler lidar system can generate five fixed measurement beams, each of which detects wind speeds at ten different ranges from the rotor.

[0018] In a particular embodiment, the wind turbine includes a nacelle, and the Doppler lidar system is mounted on top of the nacelle. The fixed measurement beam may include a central axial beam and multiple other beams projected at an angle away from the central axial beam and equidistantly spaced around a circular circumference. For example, four fixed beams may be spaced 90 degrees apart on the circular circumference. In another embodiment, the beams do not need to be fixed in space but can be used in a scanning configuration.

[0019] In one embodiment of the method, wind measurements from multiple different ranges for each fixed measurement beam are used to calculate the average wind speed of the incoming airflow and the standard deviation of the wind speed across the entire sampling field, where the standard deviation of the wind speed corresponds to the turbulence parameter. The wind speed measurements and the calculation of the standard deviation can be performed at a rate of at least 4 Hz, and the standard deviation calculation can be smoothed using a low-pass filter. The filter time constant for the low-pass filter can be adjustable and can be selected to approximate the typical wind speed of the incoming airflow.

[0020] In one embodiment, the method may include: contour lines defining the standard deviation as a linear function of wind speed within a wind speed range.

[0021] The wind speed distribution at this site can be based on wind measurements taken at the wind turbine site.

[0022] The method may also include selecting one of the thrust limits based on the determined turbulence parameters and the determined wind speed, and operating the wind turbine such that the thrust on the rotor is lower than the selected thrust limit. For example, the thrust on the rotor may be compared with the selected thrust limit, and if the thrust is higher than the selected thrust limit, the method includes sending a collective pitch signal to the rotor blades to pitch the blades and reduce the thrust on the rotor.

[0023] This disclosure also includes a wind turbine comprising a rotor with multiple blades and a pitch system configured to rotate the blades about a longitudinal axis. The wind turbine includes an active sensing system mounted on it, such as a Doppler lidar system, which generates multiple fixed measurement beams upwind of the wind turbine to detect the wind speed of the incoming airflow. The wind turbine includes a control system that communicates with the Doppler lidar system and is configured to measure the wind speed of the incoming airflow substantially continuously and calculate turbulence parameters corresponding to variations in the measured wind speed. The control system is also configured to select a thrust level based on the turbulence parameters and the measured wind speed, wherein the thrust level is selected from multiple thrust limits for different turbulence ranges, the multiple thrust limits being determined by a wind speed distribution and a quantile-based regression of the turbulence parameters. The control system sends a signal to the pitch system to collectively pitch the blades such that the aerodynamic thrust on the rotor is lower than the selected thrust level.

[0024] In a particular embodiment, the Doppler lidar system is configured to generate multiple fixed measurement beams upwind of the wind turbine to sample the incoming airflow, wherein each of the fixed measurement beams measures wind speed at different angles relative to the rotor axis and at multiple different ranges from the rotor.

[0025] In one embodiment, the Doppler lidar system is mounted on the top of the nacelle of a wind turbine, and the fixed measurement beam includes a central axial beam and multiple beams projected at an angle away from the central axial beam and equidistantly spaced around the circumference.

[0026] The control system can be configured to use wind measurements from multiple different ranges for each fixed measurement beam to calculate the average wind speed and standard deviation of the incoming airflow, where the standard deviation of the wind speed corresponds to the turbulence parameter.

[0027] The control system can perform wind speed measurement and standard deviation calculation at a rate of at least 4 Hz, and smooth the standard deviation calculation with a low-pass filter. The control system can set the filter time constant for the low-pass filter to take into account the typical wind speed of the incoming airflow and the average range of wind speed measurements from the rotor, for example, in 10 seconds, to reflect a typical wind speed of 10 m / s and a travel distance of 100 meters.

[0028] The invention will be further supported and described with reference to the following description and the appended claims. The accompanying drawings, which are included in and form part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.

[0029] Technical Solution 1. A method for defining multiple thrust limits for a wind turbine located in the field and having a rotor with multiple blades, wherein the thrust limits are defined as aerodynamic thrust values ​​on the rotor that will not be exceeded during operation, the method comprising:

[0030] A representative wind speed distribution is provided for the aforementioned site.

[0031] Define one or more contour lines with constant turbulence probabilities, the contour lines representing turbulence parameters as a function of wind speed, wherein the contour lines correspond to the quantile level of turbulence in the wind speed distribution, and the turbulence parameters indicate wind speed variations;

[0032] The turbulence parameters are determined by measuring the wind speed upstream of the rotor substantially continuously using an active sensing system and calculating the wind speed change based on the measured wind speed.

[0033] Regarding the contour lines defining the turbulence range; and

[0034] The thrust limit is defined for the turbulence range.

[0035] Technical Solution 2. The method according to Technical Solution 1, wherein the active sensing system uses a Doppler lidar system to generate multiple measurement beams pointing upwind of the wind turbine to sample the incoming airflow.

[0036] Technical Solution 3. The method according to Technical Solution 2, wherein the measuring beam is a fixed measuring beam that points at different angles relative to the axis of the rotor to define an increasing sample field as the distance from the rotor increases, and each of the fixed measuring beams measures wind speed at different angles relative to the axis of the rotor and at multiple different ranges from the rotor.

[0037] Technical Solution 4. The method according to Technical Solution 3, wherein the Doppler lidar system generates five fixed measurement beams, and each fixed measurement beam detects the wind speed at ten different distances from the rotor.

[0038] Technical Solution 5. The method according to Technical Solution 4, wherein the wind turbine includes a nacelle, the Doppler lidar system is installed on the top of the nacelle, the fixed measurement beam includes a central axial beam and multiple additional beams, the multiple additional beams being projected at a certain angle away from the central axial beam and equidistantly spaced around a circular circumference.

[0039] Technical Solution 6. The method according to Technical Solution 3, wherein multiple wind measurements from different ranges for each fixed measurement beam are used to calculate the average wind speed of the incoming airflow and the standard deviation of the wind speed, wherein the standard deviation of the wind speed corresponds to the turbulence parameter.

[0040] Technical Solution 7. The method according to Technical Solution 6, wherein the wind speed measurement and the calculation of the standard deviation are performed at a rate of at least 4 Hz, and the standard deviation calculation is smoothed by a low-pass filter.

[0041] Technical Solution 8. The method according to Technical Solution 7, wherein the filter time constant for the low-pass filter is adjustable and is selected to approximate the typical wind speed of the incoming airflow and the average range of wind speed measurements from the rotor.

[0042] Technical Solution 9. The method according to Technical Solution 6, wherein the contour lines define the standard deviation as a linear function of the wind speed within the wind speed range.

[0043] Technical Solution 10. The method according to Technical Solution 1, wherein the wind speed distribution at the site is based on wind measurements at the wind turbine site.

[0044] Technical Solution 11. The method according to Technical Solution 1 further includes: selecting one of the thrust limits based on the determined turbulence parameters and the determined wind speed, and operating the wind turbine such that the thrust on the rotor is lower than the selected thrust limit.

[0045] Technical Solution 12. The method according to Technical Solution 11, wherein operating the wind turbine to cause the thrust on the rotor to be lower than a predetermined thrust limit includes comparing the thrust on the rotor with the selected thrust limit, and if the thrust is higher than the selected thrust limit, sending a collective pitch signal to the blades of the rotor to pitch the blades and reduce the thrust on the rotor.

[0046] Technical Solution 13. A wind turbine, comprising:

[0047] A rotor having multiple blades;

[0048] A pitch system equipped with blades to rotate the blades about the longitudinal axis of the blades;

[0049] An active sensing system, installed on the wind turbine, includes a Doppler lidar system that generates a measurement beam upwind of the wind turbine to detect the wind speed of the incoming airflow.

[0050] The control system communicates with the Doppler lidar system and is configured to:

[0051] Basically, the wind speed of the incoming airflow is continuously measured, and turbulence parameters corresponding to the wind speed changes are calculated based on the measured wind speed.

[0052] The thrust level is selected based on the turbulence parameters and the measured wind speed, wherein the thrust level is selected from multiple thrust limits for different turbulence ranges, the multiple thrust limits being determined by wind speed distribution and quantile-based regression of the turbulence parameters; and

[0053] A signal is sent to the pitch system to cause the blades to pitch collectively, such that the aerodynamic thrust on the rotor is lower than the selected thrust level.

[0054] Technical Solution 14. The wind turbine according to Technical Solution 13, wherein the Doppler lidar system is configured to generate a plurality of fixed measurement beams in the upwind direction of the wind turbine to sample the incoming airflow, wherein each of the fixed measurement beams detects wind speed at different angles relative to the axis of the rotor and at multiple different ranges from the rotor.

[0055] Technical Solution 15. The wind turbine according to Technical Solution 14 further includes a nacelle, the Doppler lidar system is installed on the top of the nacelle, and the fixed measurement beam includes a central axial beam and a plurality of beams projected at a certain angle away from the central axial beam and equidistantly spaced around the circular circumference.

[0056] Technical Solution 16. The wind turbine according to Technical Solution 15, wherein the control system is configured to calculate the average wind speed and the standard deviation of the incoming wind flow using wind measurements from multiple different ranges for each fixed measurement beam, wherein the standard deviation of the wind speed corresponds to the turbulence parameter.

[0057] Technical Solution 17. The wind turbine according to Technical Solution 16, wherein the wind speed measurement and the calculation of the standard deviation are performed by the control system at a rate of at least 4 Hz, and the standard deviation calculation is smoothed by a low-pass filter.

[0058] Technical Solution 18. The wind turbine according to Technical Solution 17, wherein the control system sets the filter time constant for the low-pass filter to approximate the average range of the typical wind speed of the incoming airflow and the wind speed measurement from the rotor. Attached Figure Description

[0059] The complete and feasible disclosure of the invention, including its preferred mode, is set forth in the description with reference to the accompanying drawings, for those skilled in the art, wherein:

[0060] Figure 1 A perspective view of a wind turbine based on an example is shown;

[0061] Figure 2 A simplified interior view of a wind turbine nacelle, based on an example, is shown.

[0062] Figure 3 The power curve of a wind turbine according to the prior art is shown;

[0063] Figure 4 The diagram schematically illustrates the aerodynamic thrust as a function of wind speed when a wind turbine operates according to its theoretical power curve.

[0064] Figure 5 An example of contour lines for determining constant turbulence is illustrated schematically;

[0065] Figure 6 An example of a method for operating a wind turbine is illustrated schematically;

[0066] Figure 7-9 The effect of dynamic thrust levels on different wind distributions is illustrated schematically;

[0067] Figure 10-11 The effect of varying thrust levels on annual energy output and blade root bending moment is illustrated schematically.

[0068] Figure 12 This schematically illustrates another example of a method for operating a wind turbine;

[0069] Figure 13 It is a side view of a wind turbine, wherein the active sensing system according to an embodiment is mounted on the top of the nacelle;

[0070] Figure 14 yes Figure 13A front view of a wind turbine rotor, depicting multiple stationary measurement beams from an active sensing system; and

[0071] Figure 15 It is a schematic diagram of multiple fixed beams arranged around a central axial beam, and a representative range of fixed distances used to detect the wind speed along each of the beams. Detailed Implementation

[0072] Reference will now be made in detail to embodiments of the invention, one or more of which are illustrated in the accompanying drawings. The various examples are provided by way of explanation, not limitation, of the invention. Indeed, it will be apparent to those skilled in the art that various modifications and variations can be made to the invention without departing from its scope or spirit. For example, features shown or described as part of one embodiment may be used with another embodiment to produce yet another embodiment. Therefore, it is intended that the invention cover these modifications and variations falling within the scope of the appended claims and their equivalents.

[0073] Figure 1 A perspective view of an example wind turbine 1 is shown. As shown, the wind turbine 1 includes a tower 2 extending from a support surface 3, a nacelle 4 mounted on the tower 2, and a rotor 5 coupled to the nacelle 4. The rotor 5 includes a rotatable hub 6 and at least one rotor blade 7 coupled to and extending outward from the hub 6. For example, in the illustrated example, the rotor 5 includes three rotor blades 7. However, in alternative embodiments, the rotor 5 may include more or fewer than three rotor blades 7. Each rotor blade 7 may be spaced apart from the hub 6 to facilitate rotation of the rotor 5, thereby enabling kinetic energy to be converted from wind into usable mechanical energy, and subsequently into electrical energy. For example, the hub 6 may be rotatably coupled to a generator 10 located within or forming part of the nacelle 4. Figure 2 This allows for the generation of electrical energy. The rotation of the rotor can be transmitted directly to the generator, for example, in a direct-drive wind turbine, or through a gearbox.

[0074] Figure 2 A simplified internal view of an example of the gear train and power generation components within the nacelle 4 is shown. The rotor 5 may include a main rotor shaft 8, which is coupled to a hub 6 for rotation therewith. A generator 10 may then be coupled to the rotor shaft 8 such that rotation of the rotor shaft 8 drives the generator 10. For example, in the illustrated embodiment, the generator 10 includes a generator shaft 11, which is rotatably coupled to the rotor shaft 8 via a gearbox 9.

[0075] exist Figure 2In this configuration, the wind turbine rotor 5 can be rotatably mounted on the support frame 12 via two rotor bearings at the connection area. In other examples, the support frame 12 may not extend through the hub 6, and thus the rotor may be supported by a single rotor bearing, typically referred to as the main bearing.

[0076] The generator 10 can be electrically connected to a converter that adapts the generator's output power to the grid requirements. In some examples, the converter can be housed within the nacelle 4; however, in other examples, it can be placed elsewhere on the wind turbine.

[0077] It should be understood that the rotor 5 of the wind turbine and the generator 10 can be supported by the base plate or support frame 12 located on top of the wind turbine tower 2.

[0078] The nacelle 4 is rotatably connected to the tower 2 via a yaw system 20. The yaw system includes a yaw bearing (in... Figure 2 (Not visible in the image), the yaw bearing has two bearing components configured to rotate relative to the other. The tower 2 is coupled to the first bearing component, and the nacelle 4 (e.g., a base plate or support frame 12) is coupled to the second bearing component. The yaw system 20 includes a ring gear 21 and a plurality of yaw actuators 22, each actuator having a motor 23, a gearbox 24, and a pinion 25 for meshing with the ring gear to rotate one of the bearing components relative to the other.

[0079] Figure 3 The conventional power curve of a wind turbine according to existing technology is shown. The operation of a variable-speed wind turbine as a function of wind speed has already been explained above. It can be noted that the operation of a wind turbine is not necessarily based on an actual direct measurement of wind speed. Rather, the wind speed can be derived or estimated from the rotor speed. Typically, the generator speed is measured within the wind turbine. The rotor speed can be easily derived from the generator speed.

[0080] Figure 4 This schematically illustrates aerodynamic thrust as a function of wind speed when a wind turbine operates according to its theoretical power curve. (For example, it can be...) Figure 4 As seen in the diagram, the aerodynamic thrust on the rotor peaks near the nominal wind speed. According to aspects of this disclosure, multiple thrust levels can be introduced to avoid peak aerodynamic thrust and thereby limit structural loads.

[0081] exist Figure 4 The system describes multiple thrust limits (TLs), including minimum, average, and maximum thrust limits. One of these thrust limits can be selected based on the turbulence level at a given moment. The wind turbine is then operated to ensure that the aerodynamic thrust on the rotor remains below the selected thrust limit.

[0082] Figure 5 An example of contour lines for determining a constant turbulence probability is schematically illustrated. In methods for defining multiple thrust limits for wind turbines, where the thrust limit is defined as the aerodynamic thrust value on the rotor that is not exceeded during operation, the following can be used: Figure 5 An example is provided. A representative wind speed distribution for this site is given. In this specific example, a wind range from 10 m / s to 20 m / s has been provided. Typically, the thrust limit will operate within a wind speed range near the nominal wind speed, for example, from 1-3 m / s below the nominal wind speed to 1-3 m / s above the nominal wind speed.

[0083] Wind speed distribution can be obtained through wind speed measurements, such as using a wind tower, before the installation of wind turbines or wind farms. Wind speed distribution can also be obtained from similar field wind speed measurements or from computer simulations.

[0084] exist Figure 5 The diagram contains multiple contour lines defining a constant turbulence probability. These contour lines represent turbulence parameters, indicating wind speed variation as a function of wind speed. In this particular example, the turbulence parameter is the standard deviation of wind speed relative to the mean wind speed. In further examples, other turbulence parameters can be used, such as turbulence intensity or wind speed variance. Turbulence intensity can be defined as the standard deviation divided by the mean wind speed. The standard deviation is the square root of the variance.

[0085] exist Figure 5 In the specific example depicted, the turbulence parameters are assumed to be a linear function of wind speed.

[0086] Figure 5 The contour lines in the diagram correspond to the quantile levels of the turbulence probability of the wind speed distribution. These three lines correspond to the 5%, 50%, and 95% quantiles, respectively (i.e., quantile-based regression has been used). The standard deviation in this example is assumed to be a linear function of wind speed.

[0087]

[0088] Here, σ lim It is the standard deviation of one of the contour lines as a function of wind speed V. Parameter a σ and b σ It is the parameter of a linear function. V on and V off It is a linear function that will be used to determine the wind speed at the lower and upper ends of the wind speed range.

[0089] Different parameters 'a' can be assigned to each contour line. σ and bσ.

[0090] Wind speed distribution can be viewed as a set of data points combining wind speed and its standard deviation.

[0091] In quantile-based regression, the cost function Jσ to be minimized for a constant quantile level is given in the following equation:

[0092]

[0093] The 95% contour line indicates that the turbulence in the wind speed distribution is below the 95% confidence level of the indicated level; that is, in this example, the standard deviation of the wind speed for a given wind speed is below this line.

[0094] In this specific example, a range of 10 m / s to 20 m / s is chosen, but it should be clear that different ranges of wind speeds can be used. In some examples, the wind speed range can be divided into smaller parts, such as 10–12 m / s, 12–14 m / s, etc. For each of these smaller ranges, quantile-based regression can be performed to find the isoline portions. In this case, using the equation above, the isolines can include several linear portions.

[0095] Once contour lines are defined, the turbulent region can be defined about these contour lines. The turbulent region can be defined above, below, or between the contour lines. One or more of the edges or ends of the turbulent region are therefore defined by the contour lines.

[0096] In this specific example, the turbulence range can be defined as below the 5% isoline, the second turbulence range increases from the 5% isoline to the 95% isoline, and the third turbulence range can be defined for turbulence above the 95% isoline. It should be clear that the values ​​of 5%, 50%, and 95% are merely illustrative and other values ​​can be used. It should also be clear that more isolines (and more turbulence ranges) can be defined than in the example shown.

[0097] Finally, for each of these ranges, the thrust limit can be defined such that the (peak) load remains at a predefined acceptable level even in highly turbulent winds. On the other hand, if the wind turbulence is less, a higher limit can be used, since the peak load will remain below an acceptable level.

[0098] Figure 6 An example of how to operate a wind turbine is illustrated. Once multiple thrust limits have been defined for different turbulence ranges, as just mentioned... Figure 5 As shown, a method for operating a wind turbine may include: estimating wind speed and turbulence parameters, and selecting a thrust limit based on the estimated turbulence parameters and the estimated wind speed. The wind turbine can then be operated such that the thrust on the rotor is lower than the selected thrust limit.

[0099] The input for box 30 includes parameter a for each of the n defined contour lines. σiand b σi , where n is the total number of contour lines, and i is the number of individual contour lines. The output of box 30 is for a given average wind speed V. w Standard deviation σ i One or more values. In this specific case, two standard deviation values ​​are defined for each wind speed, σ. 5% and σ 95% .

[0100] During operation, the wind speed V can be determined substantially continuously. In this paper, substantially continuous means that the wind speed is determined at a sufficiently high frequency so that it can be meaningfully taken into account in the operation of the wind turbine.

[0101] Wind turbines may include remote sensing systems, such as SODAR (sonic detection and ranging) or LIDAR (light detection and ranging), to measure wind conditions upstream of the rotor. The wind turbine's control system may be configured to receive wind conditions from the remote sensing system and determine the wind speed and turbulence impacting the rotor based on the upstream wind measurements.

[0102] Alternatively, the wind turbine may include a nacelle anemometer, and the control system is configured to determine wind speed and turbulence based on measurements from the nacelle anemometer (i.e., the nacelle anemometer provides continuous measurements of wind speed V). For a given interval (the most recent interval), the average wind speed V... w and wind speed variation (standard deviation σ in this example) w The wind speed can be calculated from the data of the naval anemometer. However, it is known that the reliability of using a naval anemometer to measure wind speed is limited because the wind can be interfered with when it reaches the anemometer.

[0103] In yet another example, wind speed can be estimated by determining the power output, the blade pitch angle, and the rotor speed. Based on the power output, blade pitch angle, and rotor speed, a Kalman filter can be used to estimate the wind speed. Typically, suitable sensors and systems are provided on the wind turbine to measure the power output, the blade pitch angle (which should be used for appropriate pitch control), and the rotor speed (typically, the generator rotor speed can be measured). The use of Kalman filters has been found to be reliable for estimating wind speed.

[0104] At box 40, the average wind speed V can be derived from the time series of wind speed measurements V. w And turbulence parameters indicating wind speed changes. One of the outputs of box 40 is the selected turbulence parameter, in this case, the standard deviation of wind speed σ. w The output of box 40 is provided as input to boxes 30 and 50.

[0105] Within box 50, multiple turbulence ranges are defined, for example, below the lowest quantile level, above the highest quantile level, and between the lowest and highest quantile levels. For each of these turbulence ranges, a thrust limit is defined. In this particular example, T max It is the maximum thrust limit, T min It is the minimum thrust limit, T mean It is the average thrust limit. When T min When enabled, higher priority tends to keep the load at an acceptable level and sacrifice potential electrical power output to the greatest extent possible.

[0106] If, at a given moment, the turbulence level (output from box 40) and wind speed (output from box 40) are known, then it is also known in which turbulence range the wind turbine operates.

[0107] If this is known, then at box 50, a suitable thrust limit T can be selected from the previously defined thrust limits. sel Then, the wind turbine can be operated to ensure that the aerodynamic thrust on the rotor remains below the selected limit.

[0108] Therefore, the aerodynamic thrust on the rotor can be measured directly, for example, by using appropriate strain or deformation sensors on the blades. Alternatively, the thrust on the rotor can be estimated by calculating the thrust based on the estimated wind speed, rotor speed, and blade pitch angle.

[0109] Then, during operation, the estimated thrust on the rotor can be compared with the selected thrust limit, and if the estimated thrust is higher than the selected thrust limit, a collective pitch signal can be sent (from the wind turbine control) to the rotor blades (or the pitch control system) to pitch the blades and reduce the thrust on the rotor.

[0110] exist Figure 12-15 The text broadly describes alternative embodiments of methods and systems for detecting and measuring actual turbulence entering an airflow. These methods and systems utilize an active sensing system 60 mounted on the wind turbine 1, for example, on top of the nacelle 4, to detect wind speeds in the airflow at multiple distances / ranges 66 upstream of the rotor 5, as explained in more detail below. The wind speed measurements are then used to derive a measure of turbulence intensity (wind speed variation), which is provided to the thrust limit control process. Figure 12 ).

[0111] Compared to measuring wind speed from an anemometer installed in the nacelle or estimating wind speed from power output, blade pitch angle, and rotor speed, Figure 12-15The implementation of these methods can offer significant advantages. For example, using either method, to estimate turbulence intensity, the standard deviation of wind speed within a sliding data window is calculated, where the data window can be relatively long, such as up to 60 seconds. This can be undesirable because the turbulence intensity estimate may respond slowly to actual turbulence changes. Moreover, relatively large wind offsets in the measured wind speeds can unduly influence the wind turbulence estimate for extended periods. Therefore, in certain environments, it may be necessary to... Figure 12-15 The embodiments address these potential drawbacks.

[0112] Overall reference Figure 13-15 The active sensing system 60 can be implemented by a Doppler lidar system 62, which generates multiple fixed measurement beams 64 pointing upwind of the wind turbine rotor 5 to sample the incoming airflow. In the embodiment shown in the figure, the fixed measurement beams 64 can be pointed outward from the Doppler lidar system 62 at an angle relative to the axis 70 of the rotor 5, so as to define an increasing sample field with increasing distance from the rotor 5, such as from... Figure 13 and 15 That's understandable.

[0113] Each of the fixed measuring beams 64 can detect and measure wind speed at multiple distances from the system 62. For example, in Figure 15 In this embodiment, each beam 64 detects and measures wind speed at ten separate distances or ranges 66 from the system 62, wherein the range points 66 are spaced twenty meters apart. It should be understood that the number of fixed measuring beams 64, the number of range points 66 along each beam 64, and the distance between the range points 66 may vary for different embodiments, including embodiments using a configuration that uses scanning beams instead of fixed beams.

[0114] In the depicted embodiment, the Doppler lidar system 60 generates five fixed measurement beams 64, one of which is a central beam 68 oriented substantially parallel to the rotor axis 70. The other beams 72 are equidistantly spaced around the circular circumference 74. For example, the four fixed beams 72 may be spaced 90 degrees apart on the circular circumference 70.

[0115] Figure 12 Depicting Figure 6 The thrust limit control process is specifically modified to utilize information from the Doppler lidar system 60. In process step 55, multiple signals from the fixed measurement beam 64 are input to the controller. Wind speed measurements from different range points 66 for each beam 64 are used to calculate the average wind speed V of the incoming airflow. w and the standard deviation of wind speed σ w Standard deviation σ wIt is input into process box 50 (as a turbulence intensity parameter), and as described above regarding... Figure 6 It is used as discussed in box 50. Therefore, the standard deviation σ of the mean wind speed w The estimate is in Figure 6 Process block 40 was eliminated. Furthermore, the average wind speed V of the incoming airflow calculated in process block 55 was also eliminated. w It can be used as an input for process box 30 (e.g.) Figure 12 (As shown by the dashed line in the image), where the above information can also be eliminated. Figure 6 The discussion process is based on the average wind speed V at point 40 in the process frame. w The estimate. Alternatively, the standard deviation σ of wind speed from process box 55. w It can be entered into process box 40 and used as a check on the estimated value exported at process box 40.

[0116] At process frame 55, wind speed measurement and average wind speed V w and the standard deviation of wind speed σ w The calculations are determined substantially continuously, meaning that the wind speed is determined at a sufficiently high frequency so that it can be meaningfully taken into account in wind turbine operation. For example, measurements and calculations can be performed at a rate of at least 4 Hz. Furthermore, the standard deviation can be smoothed using a low-pass filter with an adjustable filter time constant selected to consider the typical wind speed of the incoming airflow and the average range of wind speed measurements from the rotor, for example, over 10 seconds, to reflect a typical wind speed of 10 m / s and a travel distance of 100 meters.

[0117] The above discussion Figure 6 Other aspects of the thrust limit control process also apply to Figure 12 The process. For example, the method may include: contour lines defining the standard deviation as a linear function of wind speed within a given wind speed range.

[0118] Moreover, the wind speed distribution at the site can be based on wind measurements taken at the wind turbine site.

[0119] Figure 12-15 The method may also include: selecting one of the thrust limits based on the determined turbulence parameters and the determined wind speed, and operating the wind turbine such that the thrust on the rotor is lower than the selected thrust limit. For example, the thrust on the rotor may be compared with the selected thrust limit, and if the thrust is higher than the selected thrust limit, the method includes sending a collective pitch signal to the rotor blades to pitch the blades and reduce the thrust on the rotor.

[0120] In another aspect of this disclosure, and according to the example shown, a wind turbine is provided. The wind turbine includes a rotor having multiple blades, one or more pitch systems for rotating the blades about a longitudinal axis of the blades, a generator, and a control system. The control system is configured to estimate wind speed and turbulence, and select a thrust level based on the turbulence and the estimated wind speed, wherein the thrust level is selected from multiple thrust limits for different turbulence ranges, and to send a signal to the pitch systems to collectively pitch the blades such that the aerodynamic thrust on the rotor is lower than the selected thrust level. The multiple thrust levels have been determined by quantile-based regression of the wind speed distribution and parameters indicative of turbulence.

[0121] In the example, the control system can use Kalman filtering to estimate wind speed, with the Kalman filter being fed variables such as power output, blade pitch angle, and rotor speed.

[0122] In other embodiments, the control system and Figure 12-15 The active sensing system 60 communicates and is configured to measure the wind speed of the incoming airflow substantially continuously and calculate turbulence parameters corresponding to the wind speed changes, as discussed above.

[0123] In a particular embodiment, the wind turbine may utilize the Doppler lidar system 62 discussed above to generate multiple fixed measurement beams 64 pointing upwind of the wind turbine to sample the incoming airflow, wherein each of the fixed measurement beams detects the wind speed at different angles relative to the axis 70 of the rotor 5 and at multiple different ranges 66 from the rotor 5.

[0124] In one embodiment, the Doppler lidar system 62 is mounted on top of the nacelle 4 of the wind turbine 1. The fixed measurement beam 64 may include a central axial beam 68 and a plurality of other beams 72 projected at an angle away from the central axial beam to define an increasing sample field as the distance from the rotor 5 increases, wherein the beams 72 are equidistantly spaced around the circular circumference 74.

[0125] Figure 7-9 The effect of dynamic thrust levels on different wind distributions is illustrated schematically. Figure 7-9 This illustrates different wind speed distributions for the same wind turbine at a given site. Based on the example above, the quantile level of the turbulence probability has been defined according to the specific wind speed distribution. Figure 7 In the same location, the wind exhibits relatively low turbulence intensity. Figure 8 In this case, the wind speed distribution is uniform, or essentially the same as the theoretical wind speed distribution. Finally, in Figure 9 The figure shows the wind speed distribution with relatively high turbulence.

[0126] exist Figure 7 In such cases, the thrust limit is usually chosen as the high limit, thus prioritizing energy production. However, in Figure 9 In such cases, a relatively low thrust limit is more often chosen, thus sacrificing power output but ensuring that the load remains below the predefined limits.

[0127] In all cases, wind turbines can incorporate some form of control to avoid rapidly changing thrust limits. This can happen, for example, when turbulence approaches isopleths. To avoid such rapid changes, hysteresis control can be incorporated. One way to implement this control might be to introduce a time delay between the thrust range and the thrust limit selection. Another approach is to have a separation between turbulent ranges and (linearly) change the thrust limit between the defined thrust ranges.

[0128] In one operational example, for each of the predefined contour lines, one or more check levels are defined, wherein the thrust limit remains unchanged until the wind turbulence parameters reach one of the check levels. The check levels may define small bands around the contour lines.

[0129] Figure 10 and 11 The effect of varying thrust levels on annual energy output and blade root bending moment is schematically illustrated. Figure 10 The figure shows the AEP (Annual Energy Production) of wind turbines with three different settings in three different scenarios. The three different settings include a single high-thrust limit T mean Single low thrust limit T min and multiple thrust limits T var The variable thrust limit includes T. min T mean and as defined by the examples in this disclosure, higher than T mean T max These three scenarios include wind speed simulations with different levels of turbulence intensity, denoted by the letters A, B, and C. Scenario A corresponds to a scenario with relatively low or little turbulence, Scenario B corresponds to "average" turbulence, and Scenario A corresponds to highly turbulent winds.

[0130] exist Figure 11 The diagram shows three settings (T) for the same purpose. mean T min T var The bending moment at the leaf root under the same three simulation scenarios (A, B, and C). Figure 10 As can be seen, in scenarios A and B, dynamically changing the thrust limit leads to an increase in annual energy production. From... Figure 11As can be seen, dynamically changing the thrust limit also ensures that the load is controlled. In the scenario with the strongest turbulence (C), the blade root moment reaches its limit in order to be controlled in conjunction with the single high thrust limit. In scenario C, the single thrust limit produces a slightly higher annual energy output, but at a significant cost: high loads. These high loads can lead to fatigue damage, which may result in future performance degradation or premature replacement or scrapping of the wind turbine or its components.

[0131] The thrust limit constraint based on quantile regression disclosed in this paper allows for site-specific adjustments based on the turbulence intensity distribution of the relevant site. Both the confidence level (quantile) and the threshold can be adjusted to maximize wind power extraction for sites with relatively low turbulence, while for sites with high turbulence, a better balance can be achieved between structural safety (in terms of load) and power extraction by appropriately constraining the confidence level and relative thrust threshold.

[0132] Based on the examples disclosed herein, a method for operating a wind turbine comprising a rotor having multiple blades has been disclosed. The method may include determining a time series of wind speeds and deriving an average wind speed and turbulence parameters indicating wind speed variability from the time series. A thrust limit can then be selected from multiple thrust limits based on the derived turbulence parameters and the wind speed. Based on the selected thrust limit, the wind turbine can be operated to ensure that the thrust on the rotor is below the selected thrust limit.

[0133] Multiple thrust limits can be defined for the range of turbulence parameters for each possible wind speed (within the wind speed range). The range of turbulence parameters at a given average wind speed is defined by the confidence interval of the turbulence parameters at the average wind speed being lower than a given value in the wind data representation for the wind turbine location.

[0134] In some examples, wind data at the turbine location represents data including wind speed bands, which include the turbine's nominal wind speed. For wind speeds near the nominal wind speed, the aerodynamic thrust and corresponding load on the rotor can be high. For wind speeds close to the cut-in speed, and wind speeds significantly higher than the nominal wind speed, the aerodynamic thrust is relatively low. In the former case, this is because the wind energy is low, while in the latter case, this is because the turbine blades have been pitched high enough to maintain the rotor torque at the nominal level. Wind speeds close to the cut-in speed and close to the cut-out speed, or significantly higher than the nominal wind speed, can be safely excluded from this probabilistic analysis.

[0135] Other aspects of the invention are provided by the subject matter of the following provisions:

[0136] Clause 1: A method for defining multiple thrust limits for a wind turbine located in the field and having a rotor with multiple blades, wherein the thrust limit is defined as an aerodynamic thrust value on the rotor that will not be exceeded during operation, the method comprising:

[0137] Provide a representative wind speed distribution for this site.

[0138] Define one or more contour lines with constant turbulence probabilities, which represent turbulence parameters as a function of wind speed, where the contour lines correspond to the quantile levels of turbulence in the wind speed distribution, and the turbulence parameters indicate wind speed variations;

[0139] Among them, turbulence parameters are determined by measuring the wind speed upstream of the rotor almost continuously using an active sensing system and calculating the wind speed change based on the measured wind speed.

[0140] Regarding the contour lines defining the extent of turbulence; and

[0141] The thrust limit is defined for the turbulence range.

[0142] Clause 2: The method described in Clause 1, wherein the active sensing system uses a Doppler lidar system to generate multiple measurement beams directed upwind of the wind turbine to sample the incoming airflow.

[0143] Clause 3: The method according to Clause 2, wherein the measuring beam is fixed and points at different angles relative to the axis of the rotor to define an increasing sample field as the distance from the rotor increases, and each of the fixed measuring beams measures wind speed at different angles relative to the axis of the rotor and at multiple different ranges of the rotor.

[0144] Clause 4: According to the method of Clause 3, wherein the Doppler lidar system generates five fixed measurement beams, and each fixed measurement beam detects the wind speed at ten different distances from the rotor.

[0145] Clause 5: The method according to Clause 4, wherein the wind turbine includes a nacelle, the Doppler lidar system is mounted on top of the nacelle, and the fixed measuring beam includes a central axial beam and a plurality of additional beams, the plurality of additional beams being projected at an angle away from the central axial beam and equidistantly spaced around a circular circumference.

[0146] Clause 6: According to the method of Clause 3, wind measurements from multiple different ranges for each fixed measurement beam are used to calculate the average wind speed and standard deviation of the incoming wind flow, wherein the standard deviation of the wind speed corresponds to the turbulence parameter.

[0147] Clause 7: The method of Clause 6, wherein wind speed measurement and standard deviation calculation are performed at a rate of at least 4 Hz, and the standard deviation calculation is smoothed by a low-pass filter.

[0148] Clause 8: The method according to Clause 7, wherein the filter time constant for the low-pass filter is adjustable and is selected to approximate the typical wind speed of the incoming airflow and the average range of wind speed measurements from the rotor.

[0149] Clause 9: In accordance with the method of Clause 6, wherein the contour lines limit the standard deviation to a linear function of wind speed over the wind speed range.

[0150] Clause 10: The method described in Clause 1, wherein the wind speed distribution at the site is based on wind measurements at the wind turbine site.

[0151] Clause 11: The method described in Clause 1 further includes selecting one of the thrust limits based on the determined turbulence parameters and the determined wind speed, and operating the wind turbine such that the thrust on the rotor is lower than the selected thrust limit.

[0152] Clause 12: The method according to Clause 11, wherein operating the wind turbine to reduce the thrust on the rotor to a predetermined thrust limit includes comparing the thrust on the rotor to a selected thrust limit, and if the thrust is higher than the selected thrust limit, sending a collective pitch signal to the rotor blades to pitch the blades and reduce the thrust on the rotor.

[0153] Clause 13: A wind turbine comprising:

[0154] A rotor with multiple blades;

[0155] A pitch system equipped with blades to allow the blades to rotate about the longitudinal axis of the blades;

[0156] An active sensing system, installed on a wind turbine, includes a Doppler lidar system that generates multiple measurement beams upwind of the wind turbine to detect the wind speed of the incoming airflow.

[0157] The control system, which communicates with the Doppler lidar system, is configured as follows:

[0158] Basically, the wind speed of the incoming airflow is continuously measured, and the turbulence parameters corresponding to the wind speed changes are calculated based on the measured wind speed.

[0159] The thrust level is selected based on turbulence parameters and measured wind speed, wherein the thrust level is chosen from multiple thrust limits for different turbulence ranges, and the multiple thrust limits are determined by wind speed distribution and quantile-based regression of turbulence parameters; and

[0160] A signal is sent to the pitch system to cause the blades to pitch collectively, so that the aerodynamic thrust on the rotor is lower than the selected thrust level.

[0161] Clause 14: The wind turbine according to Clause 13, wherein the Doppler lidar system is configured to generate a plurality of fixed measurement beams upwind of the wind turbine to sample incoming airflow, wherein each of the fixed measurement beams measures wind speed at a different angle relative to the axis of the rotor and at a plurality of different ranges from the rotor.

[0162] Clause 15: The wind turbine as described in Clause 14 also includes a nacelle, a Doppler lidar system mounted on the top of the nacelle, and a fixed measuring beam comprising a central axial beam and a plurality of beams projected at an angle away from the central axial beam and equidistantly spaced around a circular circumference.

[0163] Clause 16: The wind turbine as described in Clause 15, wherein the control system is configured to calculate the average wind speed and standard deviation of the incoming wind flow using wind measurements from multiple different ranges for each fixed measurement beam, wherein the standard deviation of the wind speed corresponds to turbulence parameters.

[0164] Clause 17: Wind turbines according to Clause 16, wherein wind speed measurement and standard deviation calculation are performed by the control system at a rate of at least 4 Hz, and the standard deviation calculation is smoothed by a low-pass filter.

[0165] Clause 18: The wind turbine as described in Clause 17, wherein the control system sets the filter time constant for the low-pass filter to approximate the typical wind speed of the incoming airflow and the average range of wind speed measurements from the rotor.

[0166] This written description uses examples to disclose the invention, including the best mode, and also enables any person skilled in the art to practice the invention, including making and using any device or system and performing any incorporated methods. The patentable scope of the invention is defined by the claims, but may include other examples that would occur to a person skilled in the art. Such other examples are intended to be within the scope of the claims if they include structural elements that are not different from the literal language of the claims, or if they include equivalent structural elements that are not substantially different from the literal language of the claims.

Claims

1. A method for defining multiple thrust limits for a wind turbine, the wind turbine being located in the field and having a rotor with multiple blades, wherein, The thrust limit is defined as the aerodynamic thrust value on the rotor that will not be exceeded during operation, and the method includes: A representative wind speed distribution is provided for the aforementioned site. Define one or more contour lines with constant turbulence probabilities, the contour lines representing turbulence parameters as a function of wind speed, wherein the contour lines correspond to the quantile level of turbulence in the wind speed distribution, and the turbulence parameters indicate wind speed variations; The turbulence parameters are determined by measuring the wind speed upstream of the rotor substantially continuously using an active sensing system and calculating the wind speed change based on the measured wind speed. Regarding the contour lines defining the turbulence range; and The thrust limit is defined for the aforementioned turbulence range; The active sensing system uses a Doppler lidar system to generate multiple measurement beams pointing upwind of the wind turbine to sample the incoming airflow. The measuring beams are fixed measuring beams that point at different angles relative to the axis of the rotor to define an increasing sample field with increasing distance from the rotor. Each of the fixed measuring beams measures wind speed at different angles relative to the axis of the rotor and at multiple different ranges from the rotor. Among them, wind measurements from multiple different ranges for each fixed measurement beam are used to calculate the average wind speed and the standard deviation of the incoming airflow, wherein the standard deviation of the wind speed corresponds to the turbulence parameter, wherein the wind speed measurements and the calculation of the standard deviation are performed at a rate of at least 4 Hz, and the standard deviation calculation is smoothed by a low-pass filter; and Specifically, the standard deviation estimate of the average wind speed is derived from the time series of wind speed measurements based on the wind speed distribution, and the standard deviation estimate is checked relative to the standard deviation of the wind speed.

2. The method according to claim 1, wherein, The Doppler lidar system generates five fixed measurement beams, and each fixed measurement beam detects the wind speed at ten different distances from the rotor.

3. The method according to claim 2, wherein, The wind turbine includes a nacelle, the Doppler lidar system is mounted on the top of the nacelle, and the fixed measurement beam includes a central axial beam and multiple auxiliary beams, which are projected at an angle away from the central axial beam and are equidistantly spaced around a circular circumference.

4. The method according to claim 1, wherein, The filter time constant for the low-pass filter is adjustable and is selected to approximate the typical wind speed of the incoming airflow and the average range of wind speed measurements from the rotor.

5. The method according to claim 1, wherein, The contour lines define the standard deviation as a linear function of the wind speed within the wind speed range.

6. The method according to claim 1, wherein, The wind speed distribution at the site is based on wind measurements taken at the wind turbine site.

7. The method according to claim 1, further comprising: One of the thrust limits is selected based on the determined turbulence parameters and the determined wind speed, and the wind turbine is operated such that the thrust on the rotor is lower than the selected thrust limit.

8. The method according to claim 7, wherein, Operating the wind turbine to reduce the thrust on the rotor below a predetermined thrust limit includes comparing the thrust on the rotor with the selected thrust limit, and if the thrust is higher than the selected thrust limit, sending a collective pitch signal to the rotor blades to pitch the blades and reduce the thrust on the rotor.

9. A wind turbine, comprising: A rotor having multiple blades; A pitch system equipped with blades to rotate the blades about the longitudinal axis of the blades; An active sensing system, mounted on the wind turbine, includes a Doppler lidar system that generates a measurement beam upwind of the wind turbine to detect the wind speed of incoming airflow. The Doppler lidar system is configured to generate multiple fixed measurement beams upwind of the wind turbine to sample the incoming airflow. Each of the fixed measurement beams detects the wind speed at different angles relative to the axis of the rotor and at multiple different distances from the rotor. The control system communicates with the Doppler lidar system and is configured to: Basically, the wind speed of the incoming airflow is continuously measured, and turbulence parameters corresponding to the wind speed changes are calculated based on the measured wind speed. The thrust level is selected based on the turbulence parameters and the measured wind speed, wherein the thrust level is selected from multiple thrust limits for different turbulence ranges, the multiple thrust limits being determined by wind speed distribution and quantile-based regression of the turbulence parameters; and A signal is sent to the pitch system to cause the blades to pitch collectively, such that the aerodynamic thrust on the rotor is lower than the selected thrust level; The wind speed measurement and standard deviation calculation are performed by the control system at a rate of at least 4 Hz, and the standard deviation calculation is smoothed by a low-pass filter; wherein the control system is configured to calculate the average wind speed and the standard deviation of the incoming airflow using wind measurements from multiple different ranges for each fixed measurement beam, wherein the standard deviation of the wind speed corresponds to the turbulence parameter; and Specifically, the standard deviation estimate of the average wind speed is derived from the time series of wind speed measurements based on the wind speed distribution, and the standard deviation estimate is checked relative to the standard deviation of the wind speed.

10. The wind turbine of claim 9 further includes a nacelle, wherein the Doppler lidar system is mounted on the top of the nacelle, and the fixed measuring beam includes a central axial beam and a plurality of beams projected at an angle away from the central axial beam and equidistantly spaced around a circular circumference.

11. The wind turbine according to claim 9, wherein, The control system sets the filter time constant for the low-pass filter to approximate the average range of the typical wind speed of the incoming airflow and the wind speed measurement from the rotor.

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