A wind turbine and a method for operating the same

Abstract

The invention relates to a control method and a wind turbine (1), comprising a vibration sensor (13) for measuring a vibration signal of the wind turbine (1) and a controller (15) for receiving the vibration signal. The controller (15) calculates a fatigue load parameter and determines an operating limit parameter (20) of a certain operating parameter (22) based on the fatigue load parameter. The controller (15) further determines a control signal based on the operating parameter (22). If the operating parameter (22) exceeds the operating limit, the operating mode of the wind turbine (1) is modified by the control signal so that the operating parameter (22) is within the safety limit again.

Description

Technical Field

[0001] The present invention relates to a wind turbine and a method for operating a wind turbine using a load control algorithm, wherein the wind turbine comprises a control system configured to control the operation of the wind turbine. The control system monitors the load level and changes the operating limit parameters when certain conditions are met. Background Art

[0002] It is known to continuously monitor and regulate the operation of a wind turbine to maximize power generation while maintaining the operation within operational safety limits. Load control algorithms are implemented in a control system to reduce the load in the wind turbine, wherein the control algorithm may generate pitch control parameters for adjusting the pitch angle of the wind turbine blades. These load control algorithms reduce the overall load on the wind turbine, but have a negative impact on power generation.

[0003] WO2015 / 192853A1 discloses a thrust-limiting control algorithm for reducing the maximum mechanical load on a wind turbine tower, wherein a wind estimator and a turbulence estimator generate multiple output signals input to a thrust limiter. The thrust limiter includes a safety switch that receives inputs from a turbulence detector and an external controller. The difference between the output signal from the safety switch and the estimated thrust is input to a post-processing module that generates another output signal. The output signal is then combined with a thrust limiter feedforward signal to generate a pitch control signal. The pitch angle of the wind turbine blades is adjusted according to the pitch control signal. The application records that the thrust limit control algorithm is efficient at average wind speeds. It also records that this control scheme still has a negative impact on power generation, although the impact is reduced.

[0004] WO2011 / 042369A1 discloses a load control algorithm for regulating the operation of a wind turbine, wherein the load control algorithm monitors a load signal representing the dynamic load of the rotor. The load control algorithm then estimates operating parameters based on the load signal and determines the changes in the operating parameters over time. These changes are then compared with a threshold, wherein if the change exceeds the threshold, the operation of the wind turbine will be derated or the operating parameters will be modified. If the change is below the threshold, the operation of the wind turbine remains unchanged. The application records that load control is activated if high turbulence is detected. The control scheme is based on wind speed measurement, however, the anemometer is usually located behind the rotor, so the measurement is disturbed by the passing wind turbine blades. In addition, LIDAR can be used for wind speed measurement, but this multi-point measurement still does not provide a reliable representation of the wind speed in the rotor area.

[0005] WO2017 / 036481A1 discloses a control scheme for operating a wind turbine, in which the control system uses a speed exclusion zone to control the speed of the rotor. The speed exclusion zone is aligned with a reference speed representing the eigenfrequency of the wind turbine tower. The speed of the rotor is then controlled so that the current speed moves out of the exclusion zone, thereby reducing the oscillatory motion in the wind turbine tower. The application states that the width of the speed exclusion zone is defined as a function of the measured vibration signal.

[0006] Therefore, there is a need for an improved load control method to reduce the load in a wind turbine while minimizing power losses. In addition, there is a need for an improved load control method that is activated only in critical situations and has minimal impact in other situations. Summary of the invention

[0007] An object of the present invention is to provide a method and a wind turbine which overcome the aforementioned problems of the cited prior art.

[0008] Another object of the present invention is to provide a method and a wind turbine for reducing mechanical loads in a wind turbine while maintaining power generation.

[0009] It is a further object of the present invention to provide a method and a wind turbine which allow increasing the blade tip to tower clearance under high blade loadings.

[0010] Yet another object of the present invention is to provide a method and a wind turbine for reducing the effects of extreme wind loading conditions.

[0011] One object of the present invention is achieved by a method for controlling a wind turbine, the wind turbine comprising: a wind turbine tower; a nacelle arranged at the top of the wind turbine tower; a rotor having at least two wind turbine blades rotatably arranged relative to the nacelle; and a wind turbine control system comprising a controller and a sensor unit, wherein the controller is configured to control the operation of the wind turbine, and the sensor unit is electrically connected to the controller and configured to measure a vibration signal of the wind turbine, wherein the method comprises the following steps:

[0012] -Measure vibration signatures of wind turbines that indicate turbulence;

[0013] - calculating a severity indicator based on the vibration signal;

[0014] - determining an operating limit parameter based on the severity indicator;

[0015] - determining a control signal based on the operating limit parameter;

[0016] - Controlling the operation of the wind turbine according to the control signal.

[0017] This provides a simple and reliable control method for reducing extreme loads in wind turbines without reducing the annual energy production (AEP). The control method eliminates the need for direct measurement of wind turbulence, which is usually associated with large uncertainties. This further reduces the need to perform constant peaking of thrust levels and / or derating of wind turbines, which in turn would have a negative impact on power generation.

[0018] The control method can indirectly reduce the maximum thrust under extreme load conditions. In addition, the control method also has a surprising effect on increasing the rated wind speed. This in turn allows increasing the tip-to-tower clearance under high blade loads. This can be achieved without increasing the blade stiffness and bending stiffness of the wind turbine tower, thereby saving weight and cost.

[0019] The control method monitors the vibration level of the wind turbine instead of monitoring turbulence as in conventional control methods. This allows for more reliable measurements as there is no reliance on direct wind measurements. Vibration characteristics have been shown to provide very good correlation with turbulence characteristics. Therefore, existing sensor units in the wind turbine can be used to measure the vibration level, resulting in further cost savings. Alternatively, the vibration level can be measured by installing one or more sensor units in the wind turbine and electrically connecting it / them to the controller. The measured sensor signals are input to the controller and used to calculate or estimate the severity indicator.

[0020] Here, the term "severity indicator" is defined as a signal indicating the severity of the current vibration of the wind turbine. For example, but not limited to, the severity indicator can be a peak value, a peak-to-peak value, an average value, or a mean square (RMS) value. The severity indicator can also be a load value, such as a fatigue load value.

[0021] The vibrations may preferably be measured using one or more vibration sensors located on one or more components of the wind turbine such that they are able to measure vibrations.

[0022] According to one embodiment, the vibration signal is measured at a top part of the wind turbine.

[0023] The vibrations are preferably measured at the top part of the wind turbine, thus in a stationary reference frame. Alternatively, the vibrations may also be measured in a rotating reference frame and then converted to a stationary reference frame. For example, the vibrations may be measured on or in the rotor hub or the wind turbine blades. In another example, the vibrations may be measured on or in the nacelle or the wind turbine tower. This allows an indirect measurement of wind turbulence, since the sensor signal provides a representative measurement of the turbulence level.

[0024] The vibrations may advantageously be measured in one direction, for example along the axis of rotation of the rotor or an axis perpendicular to the axis of rotation. The axis of rotation may serve as the X-axis, the axis perpendicular to the axis of rotation may define the Y-axis, and the wind turbine tower may serve as the Z-axis. For example, the vibrations may be measured as acceleration, velocity and / or displacement. Thus, the vibrations may be measured as fore-aft vibrations of the wind turbine, for example acceleration. This allows reliable measurement of vibration levels.

[0025] According to an embodiment, the vibration measurements are measured in real time.

[0026] The vibration is preferably measured in real time or near real time to calculate the current severity level. This allows the control method to detect both extreme gust conditions and extreme load conditions. This increases the flexibility of the control method, while traditional load control methods can only detect extreme load conditions.

[0027] The vibration may be measured in the time domain, and a transform function is applied to the measured vibration signal to transform the vibration signal to the frequency domain. For example, the transform function may be a Fourier transform function, an impulse response algorithm, a Z-transform algorithm, a discrete algorithm, or other suitable transform algorithm. The Fourier transform algorithm may be a fast Fourier transform (FFT) function. The impulse response function may be a finite impulse response (FIR) filter algorithm. Alternatively, the vibration may be measured directly in the frequency domain. The transformed vibration signal may then be subjected to a spectral analysis to determine the severity indicator.

[0028] Alternatively, a spectral analysis can also be performed on the measured vibration signal.Depending on the type of sensor unit used, the severity indicator is determined in the time domain or in the frequency domain.

[0029] According to one embodiment, the severity indicator is calculated over a predetermined period of time.

[0030] The severity indicator may advantageously be a short-term value, such as a fatigue load parameter. The severity indicator, such as a fatigue load parameter, may be calculated over a predetermined time period, such as a few minutes. For example, the time period may be selected to be 30 seconds to 5 minutes, preferably 1 to 3 minutes. However, any time period in between may be selected depending on the rating and configuration of the wind turbine. Since the severity indicator may be determined as a short-term value, this enables it to characterize the wind turbulence well.

[0031] For example, a cycle counting algorithm may be applied to the measured or converted vibration signal for calculating the severity indicator. The severity indicator, such as a fatigue load parameter, may be accumulated over a time period to provide an accumulated value, such as an accumulated load parameter. The cycle counting algorithm may be, for example, but not limited to, a rainflow counting algorithm. However, a range pair algorithm or other cycle counting algorithms may be used to calculate the fatigue load parameter. This is a good representation of the fatigue load of the wind turbine.

[0032] Alternatively, a simple RMS or average function may be applied to the measured vibration signal for calculating the severity index. This also provides a good representation of the loading of the wind turbine.

[0033] According to one embodiment, the operating limit parameter is determined as a function of the severity indicator, or using a look-up table.

[0034] Here, the term "operation limit parameter" is defined as a threshold value for limiting the operation range of the operation parameter. For example, the operation limit parameter may indicate an upper limit value and / or a lower limit value of the operation range.

[0035] The operating limit parameters of a particular control signal can be simply determined using a lookup table implemented in the controller. The values ​​of the lookup table can be determined, for example, using wind turbine design parameters. Alternatively or additionally, the values ​​can be determined using a simulation of the dynamics and / or steady state of the wind turbine.

[0036] Alternatively, the operating limit parameter is determined as a function of the calculated severity index. The function may be a continuous function or a piecewise function comprising two or more sub-functions. For example, the continuous function or sub-function may be a step function, a ramp function, a sigmoid function or other suitable function. The function may define one or more end values, each of which indicates a predetermined operating limit parameter and / or a predetermined severity level. Therefore, the operating limit parameter may therefore be adapted to the current vibration level.

[0037] In addition, the values ​​of the lookup table and / or the parameters of the above functions (or sub-functions) can be adjusted using one or more adjustment methods that rely on statistical data. For example, the values / parameters can be adjusted based on first principle relationships, but other adjustment methods can also be used. Alternatively or additionally, one or more advanced adjustment methods including time series analysis can also be used to adjust the values ​​of the lookup table and / or the parameters of the above functions. This allows for more optimal operation and, in turn, improved performance of the wind turbine. This also allows the present control method to be adjusted so that it is only activated in critical situations and has minimal impact on other situations.

[0038] The function may simply be a peak shaving function which reduces local peaks in the operating parameter above a predetermined threshold. Such peak shaving functions are well known to those skilled in the art. Peak shaving may thus be applied or activated during the duration (i.e. the band) during which the operating parameter remains above the threshold, thereby limiting the operating parameter. Outside the band, peak shaving is not applied, and therefore the operating parameter is not limited. The function may advantageously be used to reduce local positive peaks as well as local negative peaks.

[0039] Conventional load control methods are activated by using power, pitch angle, wind speed or similar signals as input, which results in them being unable to differentiate between normal and abnormal vibration levels. This affects the AEP, as wind turbines are usually not operated in maximum power mode. The advantage of the control method of the present invention is that it is activated only when the vibration level is abnormal (detected by the severity indicator), so its impact on the AEP is negligible.

[0040] According to an embodiment of the present invention, the operating limit parameter indicates a minimum or maximum limit of an operating range of the operating parameter.

[0041] During operation, the operating parameter may vary within a preset operating range defined by a minimum operating limit and / or a maximum operating limit. The operating limit parameter may be a maximum operating limit, wherein the operating parameter may vary freely within a range below the maximum operating limit. For example, the maximum operating limit may be a maximum thrust value, a maximum speed value or a maximum power value. This allows the wind turbine to operate under safe conditions.

[0042] Alternatively or additionally, the operating limit parameter may be a minimum operating limit, wherein the operating parameter may vary freely within a range above the minimum operating limit. For example, the minimum operating limit may be a minimum pitch value. This limits the minimum pitch angle of the wind turbine blades.

[0043] In this configuration, the operating limit parameter can be used directly in the set point generator to generate a control signal for the operating parameter. For example, but not limited to, the operating limit parameter and the control signal can be the same, such as pitch angle, speed, thrust or other controllable parameters. Therefore, there is no need to generate another control signal (such as pitch angle) based on the operating limit parameter (such as thrust). This allows the control scheme of the present invention to act as an intelligent peak shaving function.

[0044] Preferably, the function may be a continuous function that allows for a smooth start and / or end of the peak shaving. Alternatively, the function may be a piecewise function that defines one or more transition bands at or near a threshold value, such that the peak shaving gradually fades in and / or out.

[0045] According to one embodiment of the present invention, the step of determining the operating limit parameter comprises:

[0046] - comparing the severity indicator or operating parameter to at least one threshold value;

[0047] - if the severity indicator or the operating parameter is above at least one threshold value, determining a first operating limit parameter; and

[0048] - If the severity indicator or the operating parameter is below at least one threshold value, a second operating limit parameter is determined.

[0049] The above-mentioned operating range and / or vibration range can be divided into a plurality of regions defined by one or more threshold values. Each threshold value can be associated with a corresponding operating value and / or severity level. For example, the threshold value can indicate one or more load regions of the wind turbine, wherein the operating limit parameters within each load region can define a dedicated activation level for the current load control. For example, the threshold value can indicate one or more operating regions, each region defining a dedicated sub-function or value of an operating limit parameter. This allows adaptive activation of the control method of the present invention.

[0050] For example, the severity indicator (e.g., fatigue load parameter) may include a first threshold value and a second threshold value. The first threshold value and the zero value may together define a low load zone where there is no turbulence or low turbulence. The first threshold value and the second threshold value may together define a normal operating zone where there is a normal level of turbulence. The second threshold value and a higher threshold value may together define a high load zone where there is extreme turbulence. Thus, the operation of the wind turbine may be adapted to different vibration levels.

[0051] For example, the low load region may define a first operating limit parameter or sub-function, the high load region may define a second operating parameter or sub-function, and the normal operating region may define a third operating limit parameter or sub-function. The first operating limit parameter or sub-function may be different from the second operating limit parameter or sub-function. Furthermore, the third operating limit parameter or sub-function may be different from the first and / or second operating limit parameter or sub-function. The operation of the wind turbine may further be adapted to different set point limits of the control signal.

[0052] Individual thresholds can be adapted or adjusted to the specific configuration of the wind turbine. Thus, the load control method can be fine-tuned so that it is only activated in critical situations and has a negligible impact in other situations.

[0053] According to an embodiment of the present invention, a first control signal is determined based on the first operation limit parameter, wherein the wind turbine operates in a first mode according to the first control signal.

[0054] The operating limit parameters may be input to a set point generator in the controller together with one or more other input signals. As explained later, the set point generator may be configured to generate a suitable control signal for a specific operating parameter of the wind turbine to be controlled during operation. The control signal may define a reference set point value for the operating parameter, wherein the operating limit parameters may define an upper or lower limit for the operating parameter. For example, the operating parameter may be the thrust acting on the wind turbine, the torque or rotational speed of the rotor, the common or individual pitch angles of the wind turbine blades, the generated electrical energy or other suitable operating parameters.

[0055] If the controller determines that the calculated severity indicator is between the first and second thresholds, the wind turbine may be operated in a normal operating mode. In the normal operating mode, the wind turbine may be operated to generate maximum electrical energy, and various control signals, such as reference set point values, are determined accordingly. In this normal operating mode, the operating parameters may be free to vary below an upper limit and / or above a lower limit, and thus, the control signals may remain unchanged.

[0056] If the operating parameter exceeds an upper limit or falls below a lower limit, the load control may be activated and the setpoint generator may modify the control signal to reduce the load. As soon as the operating parameter crosses an upper limit or falls below a lower limit again, the current load control may be deactivated and the setpoint generator may freely determine the control signal. This allows the control method to detect extreme gusts, such as extremely coherent gusts (ECD) with a change of direction.

[0057] According to an embodiment of the present invention, a second control signal is determined based on the second operation limit parameter, wherein the wind turbine operates in a second mode according to the second control signal.

[0058] The controller may further determine that the calculated severity indicator is below the first threshold value, then the wind turbine may be operated in an alarm mode. In the alarm mode, the wind turbine may be placed in a reduced operation mode to detect any extreme wind gusts. Accordingly, the set point generator may modify the control signal such that the operating parameter is reduced below an upper limit defined by the first operating limit parameter. The current load control is then activated or deactivated as previously described.

[0059] The controller may further determine that the calculated severity indicator is above a second threshold value, then the wind turbine is operated in a reduced load mode. In the reduced load mode, the operation of the wind turbine may be reduced to reduce the extreme load. Therefore, the set point generator may modify the control signal such that the operating parameter is reduced below an upper limit defined by the second operating limit parameter. The current load control is then activated or deactivated as previously described.

[0060] Optionally, the parameters of the control scheme of the present invention may be selected so that the wind turbine can be operated in a boost operation mode with an increased power set point. Optionally, the parameters of the control scheme of the present invention may be selected so that the wind turbine can be operated in a derated operation mode with a decreased power set point. Optionally, the parameters of the control scheme of the present invention may be selected so that the control signal may be used to perform individual pitch control of the wind turbine blades, thereby reducing the blade root bending moment.

[0061] Another object of the present invention is achieved by a wind turbine, the wind turbine comprising:

[0062] - Wind turbine towers;

[0063] - a nacelle arranged at the top of the wind turbine tower;

[0064] - a rotor having at least two wind turbine blades rotatably arranged relative to the nacelle;

[0065] - A wind turbine control system, comprising a controller and a sensor unit, wherein the controller is configured to control the operation of the wind turbine, and the sensor unit is electrically connected to the controller and configured to measure a vibration signal of the wind turbine;

[0066] - wherein the controller is further configured to calculate a severity index based on the vibration signal, determine an operating limit parameter based on the severity index, and determine a control signal based on the operating limit parameter, and the controller uses the control signal to control the operation of the wind turbine.

[0067] This provides a simple and reliable control solution for reducing extreme loads in wind turbines without reducing the annual energy production (AEP). Here, there is no need to measure the turbulence of the wind, which is usually associated with large uncertainties. Therefore, the tip-to-tower clearance under high blade loads can be increased without having to increase the stiffness of the wind turbine blades and thereby increase the weight of the wind turbine blades. This in turn allows reducing raceway fatigue in blade bearings, hub bearings and main bearings.

[0068] The control scheme of the present invention monitors the severity level of the wind turbine through vibration sensors that provide a reliable representation of turbulence. Conventional control schemes use turbulence sensors to directly measure turbulence, however such measurements are not reliable because the wind field is measured at a limited number of points. The vibration level is used to determine the operating limit parameters of specific control signals used to control the operation of the wind turbine. This allows the control scheme of the present invention to be implemented in the wind turbine control system of a new wind turbine.

[0069] The wind turbine generator comprises a wind turbine tower, a nacelle arranged at the top of the wind turbine tower, and a rotor arranged relative to the nacelle. The rotor comprises two or more wind turbine blades connected to a rotor hub. The rotor is connected to a generator via a rotating shaft. The rotor, the nacelle and the upper part of the wind turbine tower together define the top of the wind turbine generator. A pitch bearing system is arranged between the hub and the blade root or between two blade segments to enable at least an outer portion of the wind turbine blade to be pitched. A yaw bearing system is arranged between the wind turbine tower and the nacelle to enable the nacelle and the rotor to yaw relative to the wind direction.

[0070] A wind turbine control system is installed in the wind turbine for controlling and monitoring the operation of the wind turbine. The wind turbine control system includes a controller electrically connected to one or more vibration sensors located at the top of the wind turbine. Additional sensors may be arranged on or in the wind turbine and electrically connected to the controller for monitoring other operating parameters. For example, the wind turbine may include a pitch angle sensor, a torque sensor, a rotation speed sensor, a thrust sensor and / or other suitable sensors.

[0071] According to an embodiment of the present invention, the sensor unit is arranged on top of the wind turbine, wherein the sensor unit is configured to measure at least one of acceleration, velocity or displacement in at least one direction.

[0072] The vibration sensor may be, for example, but not limited to, a strain gauge, a displacement sensor, an accelerometer, a velocity sensor or an optical fiber sensor unit. The optical fiber sensor unit may include an optical light source that transmits an optical signal into an optical fiber, wherein a detector receives the optical signal reflected back from the optical fiber. This allows the vibration to be measured using any suitable vibration sensor.

[0073] Preferably, the vibration sensor is an accelerometer configured to measure acceleration in at least one direction. Alternatively, the accelerometer may be configured to measure acceleration in multiple directions, such as the X-axis, the Y-axis and / or the Z-axis. The vibration sensor, such as an accelerometer, may be an existing sensor in the wind turbine, so that no new sensor needs to be installed. Alternatively, the wind turbine may be equipped with a vibration sensor, such as an accelerometer, to measure acceleration. This allows the control scheme of the present invention to be retrofitted into a wind turbine control system of an existing wind turbine, thereby enabling the existing wind turbine to be upgraded.

[0074] Characteristics of vibrations, such as acceleration, have been shown to correlate well with characteristics of wind turbulence. Turbulence can therefore be measured indirectly by vibration sensors, such as accelerometers, which provide reliable measurements. No turbulence sensor is required.

[0075] According to an embodiment of the present invention, the severity indicator is a short-term value.

[0076] The controller is configured to calculate a severity indicator, such as a fatigue load parameter, based on the measured vibration signal. Alternatively, the measured vibration signal may be transformed into the frequency domain before calculating the severity indicator. The severity indicator or fatigue load parameter is preferably a short-term value, such as a short-term fatigue load parameter. The vibration signal may be input to a severity indicator module of the controller, which is configured to calculate the severity indicator. This allows for optimal detection of vibration levels.

[0077] According to an embodiment of the present invention, the controller is configured to calculate the severity indicator using at least one of a cycle counter, an RMS algorithm or an averaging algorithm.

[0078] Preferably, the severity indicator module may use a cycle counting algorithm to calculate the cumulative fatigue load parameter in real time. For example, the cycle counter may be a rainflow counter. However, another type of cycle counter may also be used. This allows for an optimal calculation of the severity level.

[0079] However, the severity module may also use an RMS or averaging algorithm to calculate the RMS value or average value in real time. This allows for optimal calculation of the severity level.

[0080] According to an embodiment of the present invention, the operating limit parameter is determined by the controller using a lookup table or a function implemented in the controller.

[0081] The controller may use a lookup table to determine the operating limit parameters for a particular control signal. The lookup table may be implemented in the controller, or in a database connected to the controller. The operating limit parameters may be input to a set point generator of the controller together with the current value of the operating parameter. The operating parameter may be determined by an operating parameter module of the controller. Alternatively, the operating parameter may be determined by the set point generator. The set point generator may then determine the control signal based on the operating limit parameters and the current value. This allows for a simple and effective control of the operation of the wind turbine.

[0082] Instead of using a lookup table, the controller may also apply a predetermined function to the calculated severity index to determine the operating limit parameter. As previously described, the function may be a continuous function or a piecewise function. This allows the operating limit parameter to be adapted to the current load level.

[0083] When the operating parameter is below an upper limit and / or above a lower limit, the corresponding control signal remains unchanged. When the operating parameter exceeds an upper limit and / or falls below a lower limit, the control signal is modified to bring the operating parameter within safe operating limits again.

[0084] The control scheme of the present invention may use a separate lookup table or function to determine operating limit parameters for multiple operating parameters. The separate operating limit parameters may be input to one or more set point generators along with the operating parameters. This may allow the control scheme of the present invention to adapt the operation of the wind turbine if more than one condition is met. For example, if two or more operating parameters are both below the corresponding operating limit parameters within the same load range, the set point generator may increase the power set point.

[0085] According to one embodiment of the present invention, the control signal is at least one of a pitch control signal, a thrust control signal, a torque control signal or a speed control signal.

[0086] Preferably, the control signal may be a thrust control signal for controlling the thrust level acting on the wind turbine. This is particularly advantageous because the thrust does not affect the power calculation. Furthermore, this increases the tip-to-tower clearance under high loads.

[0087] The control signal may also be a pitch set point, which is used to control the common pitch angle or the individual pitch angles of the wind turbine blades. The control signal may also be a torque set point or a rotational speed set point, which is used to control the torque or the rotational speed of the rotor. This allows the control scheme of the present invention to adapt to the operation of the wind turbine when activated.

[0088] Alternatively, the control signal may be a power set point, which is used to control the power generation of the wind turbine.Thus, the control scheme of the present invention may be used to increase or decrease power generation depending on the current severity level.

[0089] According to an embodiment of the invention, the controller is configured to operate the wind turbine in a first mode if the severity indicator is above at least one threshold, and to operate the wind turbine in a second mode if the severity indicator is below at least one threshold.

[0090] As previously mentioned, the control scheme of the present invention can adjust the operating limit parameter according to the current severity level. The range of the severity index can be divided into two or more load zones by a threshold. In addition, the range of the operating parameter can be divided into two or more operating zones by a threshold. Therefore, the limit of the operating parameter and therefore the control signal can be adjusted according to the current severity level, such as the load level.

[0091] For example, if the severity level increases or decreases to cross a threshold, and the operating parameter remains below an upper limit and / or above a lower limit, the control signal and thus the operating mode may remain unchanged. For example, if the severity level increases or decreases to cross a threshold, and the operating parameter thereby exceeds an upper limit and / or drops below a lower limit, the control signal and thus the operating mode may be modified.

[0092] For example, if the operating parameter remains below an upper limit and / or above a lower limit while remaining in a load region, the control signal and thus the operating mode may remain unchanged. For example, if the operating parameter exceeds an upper limit and / or falls below a lower limit while remaining in a load region, the control signal and thus the operating mode may be modified. BRIEF DESCRIPTION OF THE DRAWINGS

[0093] The present invention is described by way of example only and with reference to the accompanying drawings, in which:

[0094] Figure 1 An exemplary embodiment of a wind turbine is shown;

[0095] Figure 2 A first embodiment of a load control scheme according to the present invention is shown;

[0096] Figure 3A second embodiment of the load control scheme of the present invention is shown;

[0097] Figure 4 An example diagram showing peak shaving of operating parameters;

[0098] Figure 5 An example graph of operating limit parameters with threshold values ​​is shown;

[0099] Figure 6 An example diagram showing adjustment thresholds for operating limit parameters using a rapid adjustment technique;

[0100] Figure 7 Four example graphs showing adjustment thresholds for operating limit parameters using different adjustment techniques;

[0101] Figure 8 Graphs showing measured operating parameters of an exemplary on-site wind turbine implementing the load scheme of the present invention;

[0102] Fig. 9 Five operating parameters of an exemplary wind turbine with and without implementation of the load scheme of the present invention during low turbulence are shown;

[0103] Fig.10 shows five operating parameters of an exemplary wind turbine with and without implementation of the load scheme of the present invention during normal operation; and

[0104] Fig.11 Five operating parameters of an exemplary wind turbine are shown with and without implementation of the inventive load scheme during high turbulence.

[0105] In the following, the drawings will be described one by one, and different parts and positions seen in the drawings will be numbered with the same numbers in different drawings. Not all parts and positions indicated in a particular drawing must be the same as those in that drawing. Figure 1 Start a discussion.

[0106] List of Reference Numerals

[0107] 1. Wind turbines

[0108] 2. Wind turbine tower

[0109] 3. Cabin

[0110] 4. Yaw mechanism

[0111] 5. Wind turbine blades

[0112] 6. Rotor hub

[0113] 7. Pitch mechanism

[0114] 8. Cutting Edge

[0115] 9. Leaf root

[0116] 10. Leading Edge

[0117] 11. Trailing Edge

[0118] 12. Wind turbine control system

[0119] 13. Vibration sensor

[0120] 14. Sensor unit

[0121] 15. Controller

[0122] 16. Braking mechanism

[0123] 17. Severity Indicator Module

[0124] 18. Severity Indicator

[0125] 19. Lookup Table

[0126] 20. Operation limit parameters

[0127] 21. Set point generator

[0128] 22. Operation parameters

[0129] 23. Operation signal

[0130] 24. Run Level

[0131] 25. Threshold

[0132] 26. Belt

[0133] 27. First Threshold

[0134] 28. Second Threshold DETAILED DESCRIPTION

[0135] Figure 1 A wind turbine is shown, which comprises a wind turbine tower 2 and a nacelle 3 arranged on top of the wind turbine tower 2. A yaw mechanism 4 is arranged between the nacelle 3 and the wind turbine tower 2 and is configured to yaw the nacelle 3 to a yaw angle around a yaw axis. A rotor and a hub comprising at least two wind turbine blades 5 are rotatably arranged relative to the nacelle 3 and connected to a transmission system in the wind turbine 1 via a rotor shaft. The wind turbine blades 5 are connected to a rotor hub 6 via a pitch mechanism 7. The pitch mechanism 7 is configured to pitch each wind turbine blade 5 to a pitch angle around a pitch axis.

[0136] Each aerogenerator blade 5 extends from a tip 8 to a blade root 9 and further from a leading edge 10 to a trailing edge 11. The aerogenerator blade 5 has a blade shell having an aerodynamic profile defining a pressure side and a suction side.

[0137] The wind turbine 1 includes a wind turbine control system 12, which includes a controller 15 configured to control the operation of the wind turbine 1, and a plurality of sensor units 14 configured to measure a plurality of operating parameters. Each sensor unit 14 communicates with the controller 15 via a wired or wireless connection. The sensor unit 14 includes at least one of a pitch angle sensor, a torque sensor, a rotation speed sensor, a thrust sensor, a wind speed sensor or a suitable sensor. In addition, a vibration sensor unit 13 is disposed at the top of the wind turbine and is configured to measure the vibration of the wind turbine 1. Here, the vibration sensor 13 is disposed on the wind turbine tower 2, but it can be placed at any position on the top of the wind turbine 1.

[0138] The braking system is arranged relative to the rotor or the rotating shaft and comprises a braking mechanism 16 configured to brake the rotational speed of the rotor. The braking system is connected to the controller 15, wherein the controller 15 controls the operation of the braking system. In addition, the controller 15 is connected to and controls the operation of a pitch system for pitching the wind turbine blades 5, wherein the pitch mechanism 7 forms part of the pitch system.

[0139] Figure 2 A first embodiment of a load control scheme according to the present invention is shown, which is implemented in the controller 15 of the wind turbine control system 12 .

[0140] The vibrations are measured in real time and the signal from the vibration sensor 113 is input to a severity indicator module 17 which calculates a severity indicator 18 based on the vibration signal. A transformation function, such as an FFT function, is applied to the measured vibration signal before performing a spectral analysis to determine the severity indicator 18. Here, the severity indicator 18 is calculated as a fatigue load parameter. This allows reliable indirect measurement of turbulence without the use of a turbulence sensor.

[0141] The controller 15 uses a lookup table 19 to determine an operating limit parameter 20 for a specific operating parameter of the wind turbine 1. The operating limit parameter 20 is input to a set point generator 21, which generates a control signal based on the output from the lookup table 19. Here, the control signal is a pitch angle control signal θ. The controller 15 uses the control signal to control the operation of the wind turbine 1. This allows the load scheme of the present invention to be activated only in critical situations without affecting the AEP.

[0142] Figure 3 A second embodiment of the load control scheme of the present invention is shown, wherein the severity indicator 18 is used to determine a plurality of control signals. Here, the controller 15 uses the severity indicator 18 to determine a first operating limit parameter 20' using a first lookup table 19'. The first operating limit parameter 20' is input to a first set point generator 21', which generates a first control signal, such as a pitch control signal θ.

[0143] Similarly, the controller 15 uses the severity indicator 18 to determine a second operating limit parameter 20 ″ using a second lookup table 19 ″. The second operating limit parameter 20 ″ is input to a second set point generator 21 ″, which generates a second control signal, such as a speed control signal ω.

[0144] In addition, the controller 15 uses the severity indicator 18 to determine a third operating limit parameter 20'' using a third lookup table 19''. The third operating limit parameter 20''' is input to a third set point generator 21'' which generates a second control signal, such as a torque control signal τ.

[0145] Instead of using a look-up table 19 , 19 ′, 19 ″, 19 ′″, the controller 15 may determine the operating limit parameter 20 , 20 ′, 20 ″, 20 ′″ as a function of the signal of the severity indicator 18 .

[0146] Figure 4 An example diagram of peak shaving of an operating parameter 22 of a wind turbine 1 measured using one of the sensor units 14 is shown. The X-axis indicates an operating signal 23 of the wind turbine 1 and the Y-axis indicates an operating level 24 or a magnitude of the operating parameter 22.

[0147] Here, the above function applied to the severity indicator 18 acts as a peaker which is activated when the operating parameter 22 exceeds a predetermined threshold 25. The peaking is applied within a band 26 defined by the duration that the operating parameter remains above the threshold 25.

[0148] The band width may vary depending on the selected threshold. For example, the threshold may be determined as a percentage of the maximum amplitude of the operating parameter 22.

[0149] Figure 5 An example graph of an operating limit parameter 19 divided into a plurality of regions defined by a set of threshold values ​​is shown. The X-axis indicates the severity index 18 and the Y-axis indicates the severity level or magnitude. Figure 5 As shown, the range of the severity indicator 18 is divided into three areas by a first threshold 27 and a second threshold 28 .

[0150] The first threshold value 27 and the zero value define a low load zone in which the upper limit of the operating parameter 22 is reduced to the second operating limit parameter 19". In this mode, the wind turbine 1 operates in an alarm mode, enabling the wind turbine 1 to detect and react to extreme gust conditions.

[0151] The first and second threshold values ​​27, 28 define a normal operating region in which the operating limit parameter 19' is set to a first operating limit parameter indicating a maximum upper limit. In this mode, the wind turbine 1 operates to generate maximum power.

[0152] The second threshold 28 and above define a high load zone in which the upper limit of the operating parameter 22 is reduced to a second operating limit parameter 19". In this mode, the wind turbine 1 is operated in a load reduction mode in which extreme loads are reduced to safe operating conditions.

[0153] Figure 6 An example diagram of an adjustment threshold value for an operating limit parameter 20 using a rapid adjustment technique is shown. In this case, previous or simulated measured values ​​of the wind turbine 1 are used to adjust the threshold value.

[0154] like Figure 7 As shown, the first and second thresholds and different levels of the operating limit parameter 20 in different regions are adjusted so that the load scheme of the present invention is activated only in critical situations and has minimal impact in other situations.

[0155] exist Figure 6 In the embodiment, only statistical data are used to adjust different values ​​of the operating limit parameter 20. However, the value of the operating limit parameter 20 can also be adjusted using advanced adjustment techniques, such as Figure 7 shown.

[0156] Figure 7 Four example graphs of adjustment thresholds for operating limit parameters 20 using different adjustment techniques are shown. Figure 7 As shown, the upper limit values ​​of the operating limit parameters 20 in different areas are adjusted so that the load scheme of the present invention is activated only in critical situations. Similarly, the first and second thresholds 27 and 28 are adjusted so that the bandwidth of each area can be adapted to the setting and configuration of the wind turbine 1.

[0157] Figure 8 A diagram showing measured operating parameters 22' of an exemplary on-site wind turbine 1' implementing the load scenario of the present invention is shown. Here, the dashed lines indicate operating limit parameters 20' implemented in said wind turbine 1'.

[0158] Here, the X-axis indicates the severity indicator 18 and the Y-axis indicates the level or magnitude of the operating parameter 22 ′.

[0159] As shown, the operating parameter 22' follows the value of the operating limit parameter 20'. This indicates that the load scheme of the present invention does not affect the AEP when activated.

[0160] Fig. 9 Five operating parameters of an exemplary wind turbine 1 ″ are shown with and without implementing the load scheme of the present invention during low turbulence. In this case, the wind turbine 1 ″ is operated in a low load mode.

[0161] Graph 30 shows the operating parameters of the wind turbine 1 ″ implementing the load scheme of the present invention. Graph 31 shows the operating parameters of the wind turbine 1 ″ not implementing the load scheme of the present invention.

[0162] like Fig. 9 As shown in the bottom Figures 30 and 31, using the load side of the present invention, the clearance from the blade tip to the tower is increased (marked by arrow 29). Therefore, the weight and cost of the wind turbine blade 5 can be reduced without requiring additional structural strength.

[0163] Fig.10 Five operating parameters of a wind turbine 1 ″ are shown with and without the implementation of the load scheme of the present invention during normal operation. As shown in graph 30 , in this mode, the wind turbine 1 ″ is subject to extreme gusty wind conditions.

[0164] These extreme gust conditions are detected by the inventive loading scheme (marked by arrows 32) and the operating parameters 22 of the wind turbine 1" are limited according to the operating limit parameters 20. Thus, the inventive loading scheme also acts as a safety feature for the wind turbine operation.

[0165] Fig.11 Five operating parameters of a wind turbine 1 ″ implementing the load scheme of the present invention during high turbulence are shown. As shown in graph 30 , the load scheme of the present invention is activated only in critical load conditions.

Claims

1. A method for controlling a wind turbine (1), the wind turbine (1) comprising a wind turbine tower (2), a nacelle (3) arranged on top of the wind turbine tower (2), a rotor having at least two wind turbine blades (5) rotatably arranged relative to the nacelle (3), and a wind turbine control system (12) comprising a controller (15) and a sensor unit (13, 14), wherein the controller (15) is configured to control the operation of the wind turbine (1), and the sensor unit (13, 14) is electrically connected to the controller (15) and configured to measure vibration signals of the wind turbine (1), wherein the method comprises the steps of: - measuring a vibration signal of the wind turbine (1) indicative of turbulence; - calculating a severity indicator (18) based on the vibration signal; Performing a spectral analysis on the measured vibration signal to determine the severity indicator in the time domain or in the frequency domain, depending on the type of sensor unit used; - determining a plurality of operating limit parameters (20', 20", 20'") based on the severity indicator (18): The steps to determine the operating limit parameters include: - comparing the severity indicator or operating parameter to at least one threshold value; - if the severity indicator or the operating parameter is above at least one threshold value, determining a first operating limit parameter; as well as - if the severity indicator or the operating parameter is below at least one threshold value, determining a second operating limit parameter; - determining a plurality of control signals based on the plurality of operating limit parameters (20, 20", 20"'), wherein the control signals include a first control signal, a second control signal and a third control signal, wherein the first control signal is a pitch control signal (θ), the second control signal is a speed control signal (ω), and the third control signal is a torque control signal (τ); when the severity indicator is below said second operating limit parameter, the wind turbine operates in an alarm mode in which the wind turbine is placed in a reduced operating mode to detect any extreme wind gusts; When the severity indicator is higher than the first operating limit parameter, the wind turbine is operated in a reduced load mode, in which the operation of the wind turbine is reduced to reduce the extreme load; When the severity indicator is between the second operating limit parameter and the first operating limit parameter, the wind turbine generator operates in a normal operating mode, in which the wind turbine generator operates to generate maximum electrical energy; - Controlling the operation of the wind turbine (1) according to the plurality of control signals.

2. The method according to claim 1, characterized in that The vibration signal is measured at the top of the wind turbine (1).

3. The method according to claim 1, characterized in that Measure vibrations in real time.

4. The method according to claim 1, characterized in that The severity indicator (18) is calculated over a predetermined period of time.

5. The method according to any one of claims 1 to 4, characterized in that: The operating limit parameter (20, 20", 20"') is determined as a function of the severity indicator (18) or using a look-up table (19, 19", 19"'), the operating limit parameter (20, 20", 20"') indicating a minimum or maximum limit of an operating range of the operating parameter (22).

6. A wind turbine (1), comprising: - Wind turbine tower (2); - a nacelle (3) arranged on the top of the wind turbine tower (2); - a rotor having at least two wind turbine blades (5) rotatably arranged relative to the nacelle (3); - A wind turbine control system (12), comprising a controller (15) and sensor units (13, 14), wherein the controller (15) is configured to control the operation of the wind turbine (1), and the sensor units (13, 14) are electrically connected to the controller (15) and configured to measure vibration signals of the wind turbine (1); - wherein the controller (15) is further configured to: calculate a severity index (18) based on the vibration signal; determine a plurality of operating limit parameters (20, 20", 20"') based on the severity index (18); and determine a plurality of control signals based on the plurality of operating limit parameters (20, 20", 20"'), wherein the control signals include a first control signal, a second control signal and a third control signal, wherein the first control signal is a pitch control signal (θ), the second control signal is a speed control signal (ω), and the third control signal is a torque control signal (τ), and the controller (15) uses the control signals to control the operation of the wind turbine (1); Performing a spectral analysis on the measured vibration signal to determine the severity indicator in the time domain or in the frequency domain, depending on the type of sensor unit used; The steps to determine the operating limit parameters include: - comparing the severity indicator or operating parameter to at least one threshold value; - if the severity indicator or the operating parameter is above at least one threshold value, determining a first operating limit parameter; and - if the severity indicator or the operating parameter is below at least one threshold value, determining a second operating limit parameter; when the severity indicator is below said second operating limit parameter, the wind turbine operates in an alarm mode in which the wind turbine is placed in a reduced operating mode to detect any extreme wind gusts; When the severity indicator is higher than the first operating limit parameter, the wind turbine generator is operated in a reduced load mode, in which the operation of the wind turbine generator is reduced to reduce the extreme load; When the severity indicator is between the second operating limit parameter and the first operating limit parameter, the wind turbine generator operates in a normal operating mode, in which the wind turbine generator operates to generate maximum electrical energy.

7. The wind turbine generator according to claim 6, characterized in that: The sensor unit (13) is arranged on the top of the wind turbine (1), wherein the sensor unit (13) is configured to measure at least one of acceleration, velocity or displacement in at least one direction.

8. The wind turbine generator according to claim 6, characterized in that: The severity indicators are short-term values.

9. The wind turbine generator according to claim 8, characterized in that: The controller (15) is configured to calculate the severity indicator using at least one of a cycle counter, an RMS algorithm, or an averaging algorithm.

10. The wind turbine generator according to claim 6, characterized in that: The operating limit parameters (20, 20", 20'") are determined by the controller (15) using a lookup table (19, 19", 19'") or a function implemented in the controller (15).

Images