Controlling lateral oscillations of a wind turbine tower

Abstract

The invention provides a method of controlling operation of a wind turbine having a tower. The method comprises determining an overall control output comprising a lateral oscillation control for damping lateral oscillations of the tower, and using the overall control output to control operation of the wind turbine. The method further comprises receiving lateral oscillation sensor data indicative of a level of lateral oscillations of the tower, determining a nominal lateral oscillation control output in dependence on the received lateral oscillation data, and receiving an indication of a yaw error of the wind turbine. The lateral oscillation control output comprised in the overall control output is determined to be derated from the nominal lateral oscillation control output when the indicated yaw error is above a predetermined lower threshold level.

Description

Technical Field

[0001] This invention relates to controlling the operation of a wind turbine with a tower, particularly to de-rating the lateral tower oscillation control from its rated value when the yaw error of the wind turbine exceeds a predetermined lower threshold level. Background Technology

[0002] Wind turbine control technology is used to optimize power and minimize load. Many different loads, such as aerodynamic forces, gravity, centrifugal forces, and inertial loads, act on wind turbines. The load variations experienced by a wind turbine may be caused by wind conditions near the turbine (such as wind shear or turbulence) or by changes in the turbine's operation (such as grid losses).

[0003] Wind turbine control methods employ a combination of collective and cyclic control, such as controlling the collective and individual pitch of multiple blades of a wind turbine, or controlling the torque or power output of the wind turbine's generator. Cyclic or individual pitch is used to control factors such as lateral tower suppression, asymmetric rotor load control, and tower torsional suppression.

[0004] As more advanced control methods are implemented to control an increasing number of factors, there is a risk that some of the control methods or functions may, in fact, cancel each other out. That is, the implementation of one control method for one control objective may degrade the performance or effectiveness of another control method implemented simultaneously for a different control objective.

[0005] It is against this background that the present invention was proposed. Summary of the Invention

[0006] The inventors of this invention have recognized that different individual or cyclic pitch control methods or algorithms can adversely affect the effectiveness of each other's performance. In particular, control actions such as cyclic pitch control may not only fail to reduce structural loads but may actually have the opposite effect. Obviously, this is undesirable and may negatively impact the lifespan of certain structural components of the wind turbine. Therefore, it will be understood that it is necessary to ensure that specific control actions can consistently address the specific factors they are intended to address without negatively impacting other factors that need to be addressed.

[0007] According to one aspect of the invention, a method for controlling the operation of a wind turbine having a tower is provided. The method includes determining an overall control output based on a wind turbine control strategy and based on monitored wind turbine operation. The overall control output includes lateral oscillation control for suppressing or counteracting lateral oscillations of the tower. The method includes using the determined overall control output to control the operation of the wind turbine. The method further includes: receiving lateral oscillation sensor data indicating the level of lateral (lateral) oscillations of the tower; determining a rated lateral oscillation control output based on the received lateral oscillation data; and receiving an indication of yaw error of the wind turbine. When the indicated yaw error of the wind turbine is higher than a predetermined lower threshold level, it is determined that the lateral oscillation control output included in the overall control output will be derated from the rated lateral oscillation control output.

[0008] Control strategies can include any suitable or desired objectives for controlling the operation of a wind turbine, such as optimizing or limiting the turbine's power output. Monitored operation can include measurements and / or estimates of various operating parameters of the wind turbine or associated with it, such as rotor speed, power output, loads on various wind turbine components, wind conditions, etc. Yaw error refers to the misalignment of the wind turbine's rotor plane relative to the wind direction near the turbine, particularly misalignment in the yaw direction (which constitutes the rotation of the wind turbine nacelle about the axis defined by the wind turbine tower), but can also include misalignment in the turbine's tilt direction. The rated lateral oscillation control output can be considered the optimal control output for suppressing or counteracting lateral oscillations, while derating from the rated value can be considered a reduction in the effectiveness of the control output in suppressing or counteracting lateral oscillations.

[0009] When the indicated yaw error of the wind turbine is below a predetermined lower threshold level, the lateral oscillation control output can be determined as the rated lateral oscillation control output.

[0010] The lateral oscillation control output can be monotonically derated when the indicated yaw error of the wind turbine gradually increases above a predetermined lower threshold level.

[0011] Monotonically derating can be performed linearly from the rated transverse oscillation control output.

[0012] When the indicated yaw error of the wind turbine is higher than a predetermined upper threshold level greater than a predetermined lower threshold level, the lateral oscillation control output can be derated to essentially zero lateral oscillation control.

[0013] In some embodiments, the method includes determining a lateral oscillation activity level based on a received indication of yaw error, the lateral oscillation activity level indicating the extent to which a rated lateral oscillation control output will be derated, wherein the lateral oscillation control output is determined as a portion of the rated lateral oscillation control output using the determined lateral oscillation activity level.

[0014] The transverse oscillation control output can be included in the overall control output by at least one of the following: gain-scheduling the rated transverse oscillation control output; and reducing the amplitude of the rated transverse oscillation control output.

[0015] The indication of yaw error of a wind turbine can include data indicating wind conditions near the wind turbine.

[0016] Data indicating wind conditions may include data indicating the wind direction near the wind turbine relative to the rotor plane of the wind turbine. Optionally, this data is sensor data.

[0017] Data indicating wind conditions may include data indicating at least one of the following: positive wind shear; negative wind shear; and wind veer (wind direction as a function of altitude).

[0018] Indications of yaw error of a wind turbine may include data indicating asymmetrical loads experienced by one or more components of the wind turbine, optionally asymmetrical torques experienced by the one or more components, and further optionally yaw torques experienced by the one or more components.

[0019] The received yaw error indication may include data received from outside the wind turbine and indicating at least one of the following: the operation of one or more other wind turbines in the vicinity of the wind turbine; and the weather conditions near the wind turbine.

[0020] The indication of yaw error for a wind turbine may include an indication of the rotor load control level in the overall control output. Alternatively, this indication of the (implemented or required) rotor load control level may be separate from the indication of yaw error, but the derating of the rated lateral oscillation control output may be additionally or alternatively based on the indication of rotor load control, in particular, the derating of the rated lateral oscillation control output may be performed / determined when the indicated rotor load control level is above a predetermined lower threshold level.

[0021] In some embodiments, the lateral oscillation control output includes a pitch modulation value for each of a plurality of respective blades of the wind turbine, and wherein the overall control output includes a separate pitch reference value for each of the blades, including the respective pitch modulation value.

[0022] In some embodiments, the lateral oscillation control output includes a generator power offset value, and wherein the overall control output includes a generator power reference value for the generator of the wind turbine, including the generator power offset value.

[0023] According to another aspect of the invention, a non-transitory, computer-readable storage medium is provided having instructions stored thereon that, when executed by a processor, cause the processor to perform the methods described above.

[0024] According to another aspect of the invention, a controller is provided for controlling the operation of a wind turbine having a tower. The controller is configured to determine an overall control output based on a wind turbine control strategy and monitored wind turbine operation. The overall control output includes lateral oscillation control for suppressing lateral oscillations of the tower. The controller is configured to control the operation of the wind turbine using the determined overall control output. The controller is also configured to receive lateral oscillation sensor data indicating the level of lateral oscillations of the tower, determine a rated lateral oscillation control output based on the received lateral oscillation data, and receive an indication of the yaw error of the wind turbine. When the indicated yaw error of the wind turbine is higher than a predetermined lower threshold level, the lateral oscillation control output included in the overall control output is less than the rated lateral oscillation control output.

[0025] According to another aspect of the invention, a wind turbine is provided, which includes a controller as described above. Attached Figure Description

[0026] One or more examples of the invention will now be described by way of example only, with reference to the accompanying drawings, wherein:

[0027] Figure 1 This is a schematic diagram of a wind turbine according to an example of the present invention;

[0028] Figure 2 Showing Figure 1 The controller for the wind turbine, and the actuator system of the wind turbine controlled by the controller;

[0029] Figure 3 Showing Figure 2 The controller comprises a main controller for providing individual pitch and generator power control actions, and a tower lateral oscillation controller for adjusting the individual pitch and generator power control actions to provide overall control output.

[0030] Figure 4 The diagram shows... Figure 3 Examples of how the performance of a tower lateral oscillation controller can be derated under certain conditions; and

[0031] Figure 5 A summary of an example of the invention is provided. Figure 2 The method steps executed by the controller. Detailed Implementation

[0032] Figure 1 An example of the invention, a wind turbine 10, is shown that can be incorporated therein. The wind turbine 10 includes a tower 12 supporting a nacelle 14, to which a rotor 16 is mounted. The rotor 16 includes a plurality of wind turbine blades 18 extending radially from a hub 20. In this example, the rotor 16 includes three blades 18 and a single rotor 16, although other configurations including any suitable number of blades and rotors are possible.

[0033] The wind turbine 10 includes several different sensors used to measure various characteristics of the turbine 10's operation, as well as various characteristics of the conditions near the turbine 10. An optional blade load sensor 181 is shown within each blade 18 (in other examples, there may be multiple blade load sensors, allowing the blade load to be represented by more than one variable). This sensing element can be a fiber optic strain gauge, a resistance strain gauge, or any other suitable detector. A rotor wind speed and / or wind direction detector 182 is also shown—again, this measurement can be performed in several ways that a person skilled in the art will understand, one being via a wind vane and anemometer, and another via lidar, as a person skilled in the art will understand from the literature on wind turbine design and control. A rotational speed sensor 183 is also shown—this could be, for example, in the form of a rotary encoder on the generator shaft of the turbine 10; however, the rotor speed can be determined in any suitable manner. An accelerometer 184 for measuring lateral or sideways oscillations or vibrations of the tower 12 is also included in a suitable location. It may also include further sensors for measuring data indicating misalignment of the turbine in one or both of the yaw and tilt directions, and / or for measuring asymmetric (tilt / yaw) load torques on components of the wind turbine 10.

[0034] Figure 2 An example of a wind turbine control system 22 according to the present invention is shown, which can be used in... Figure 1This is implemented in the wind turbine 10. Here, the control system 22 includes an actuator system 24 controlled by a control unit or (overall) controller 26. In this particular example, the actuator system 24 may be or may include a pitch system for controlling the pitch of one or more of the wind turbine blades 18, which may include a hydraulic actuator 28 arranged to adjust the blade pitch in a known manner. The actual position of the actuator 28 may be controlled by an actuator position control unit 30 that provides positioning command signals to the hydraulic actuator 28. The controller 26 and the actuator system 24 may be replicated for each of the blades 18 of the wind turbine 10 so that the position of each blade 18 can be controlled independently.

[0035] The pitch system of wind turbine 10 is just one example of a controllable wind turbine system. Controller 26 can also be used to control other wind turbine systems and / or components. For example, actuator system 24 could be an electric or hydraulic yaw drive for the nacelle 14 of wind turbine 10, providing rotational position control of the nacelle 14 relative to the tower 12. Another example is a converter control system, where actuator system 24 could be a power converter for the power generation system of wind turbine 10, which, in a process known as “full power conversion,” converts the alternating current supplied by the generator via a DC link into a variable-frequency alternating current output, i.e., the generator’s synchronous speed is changed independently of the grid voltage and frequency variations.

[0036] In one example method of the invention, the pitch of individual blades 18 of a wind turbine 10 can be controlled according to a control strategy to maximize energy production and minimize load based on monitored wind turbine operation. Specifically, individual blade pitch can be controlled to mitigate fatigue loads on the turbine tower 12 caused by lateral (or sideways) oscillations of the tower 12. That is, the pitch is controlled to create lateral or sideways forces to counteract these forces, thereby suppressing lateral tower oscillations. Individual blade pitch can also be controlled to reduce loads on one or more components of the turbine 10 caused by misalignment of the planes of the turbine rotor 16 and blades 18 relative to the wind direction in the tilt and / or yaw directions, or by excessive tilt and / or yaw moments.

[0037] Figure 3A specific example of implementing this method in a controller or control system 26 is illustrated schematically. Several functional elements are shown: the main controller 40 determines and generates control actions or outputs 42a, 42b based on a specified control strategy and on monitored—e.g., measured and / or estimated—operation of the wind turbine relative to the control strategy. Control actions 42a, 42b from the main controller 40 include actions that provide rotor load control to reduce asymmetrical loads on the rotor 16 of the wind turbine 10. In particular, control output 42a includes collective and individual pitch control, and control output 42b controls the wind turbine power output through, for example, generator torque control.

[0038] It also includes functional elements for determining and generating control actions or modifications to provide lateral (lateral) oscillation control for suppressing lateral oscillations of the tower 12. Specifically, control elements 44a and 44b are provided to determine (rated) control actions for suppressing lateral tower oscillations based on acquired signals indicating the lateral acceleration of the tower 12. Different elements 46a and 46b are provided to determine the activity level for lateral tower oscillation control based on various acquired information. The activity level is combined with the (rated) control actions from control elements 44a and 44b to provide lateral oscillation control outputs 48a and 48b, which are combined with control actions 42a and 42b from the main controller 40 to determine overall control outputs 50a and 50b for controlling the operation of the wind turbine 10. This is discussed in more detail below.

[0039] The various functional elements or units of controller 26 may be provided by suitable software running on any suitable computing substrate using conventional or custom processors and memory. These various functional elements may use a common computing substrate (e.g., they may run on a single server) or separate substrates, or one or each may be distributed independently among multiple computing devices.

[0040] exist Figure 3In the example shown, the overall control outputs 50a, 50b include: individual and collective pitch references 50a for each of the plurality of blades 18; and a power setpoint or reference 50b for the wind turbine generator, such as torque or speed. However, it is possible that at any given time, only one of the collective pitch or generator torque is controlled according to the appropriate reference point (by means of an appropriate actuator). For example, it is common practice to control the collective pitch during the rated operation (“full load”) of the wind turbine 10 and to control the generator torque during the sub-rated operation (“partial load”) of the turbine 10. Note that individual pitch is typically controlled during both full load and partial load operations of the wind turbine 10. Operation is described below primarily with the individual pitch SSTD control system 44a active, but it will be understood that the power SSTD control system 44b may be used additionally or alternatively.

[0041] The main controller 40 generates blade pitch control output 42a, which includes both collective and individual pitch control outputs. As previously described, the individual pitch control output 42a includes rotor load control for reducing the asymmetric load experienced by the turbine 10. This is combined with individual pitch modulation 48a to generate an overall individual pitch reference 50a, which also includes tower lateral oscillation control.

[0042] In some cases, when the control outputs from each algorithm are included in a single overall pitch reference, the respective individual pitch control algorithms for rotor load control and tower lateral oscillation control can degrade each other's performance. This could mean that asymmetrical loads are not reduced as expected by the corresponding control algorithms and / or lateral tower oscillations are not suppressed as expected by the corresponding control algorithms.

[0043] It is important to note that the performance degradation of the load shedding cycle pitch algorithm is particularly pronounced under conditions of large yaw errors (i.e., significant misalignment between the rotor plane of turbine 10, defined by rotor 16 and blade 18, and the wind direction) or excessive moments experienced by wind turbine components in the tilt and / or yaw directions. Large yaw errors may imply that the asymmetric rotor load controller needs to be active to reduce the asymmetric load caused by the yaw error. However, in such cases, it has been recognized that operation of the SSTD controller to suppress lateral tower oscillations degrades the performance of the asymmetric rotor load controller.

[0044] This disclosure addresses the problem by recognizing that, under these conditions, the SSTD controller can be derating to mitigate the performance degradation of the asymmetric rotor load controller without significantly negatively impacting its own objectives. Specifically, it recognizes that under these conditions, asymmetric rotor load control can take precedence over tower lateral oscillation control, since tower lateral oscillation control is designed to reduce fatigue loads, which are less sensitive to the (relatively rare) derating of its contribution to individual pitch control compared to those of rotor load control. That is, under conditions of significant tilt / yaw misalignment and / or moment, the performance of tower lateral oscillation control is derating from its established rated or optimal performance.

[0045] Control element 44a—or Lateral Tower Suppression (SSTD) control system 44a—receives data 56 indicating the lateral (sideways) oscillations experienced by the wind turbine tower 12. In the example described, this data is in the form of sensor data received from an accelerometer measuring the lateral acceleration of the tower 12.

[0046] Based on the received tower acceleration data, control element 44a then determines the control output required to suppress the lateral oscillations of tower 12. In particular, this determination can be considered the optimal control output in terms of the effectiveness of suppressing the lateral oscillations being experienced by tower 12. That is, control element 44a determines the control output for the rated performance of the tower lateral oscillation controller for the delivery turbine 10.

[0047] The rated control output from control element 44a is then combined with the output from control element 46a. Control element 46a—or SSTD active level unit 46—receives an indication of the yaw error of the wind turbine 10. This indication may take different forms.

[0048] In the example described, the indication includes sensor data or signals 58 indicating the level of tilt and / or yaw misalignment of turbine 10. For example, sensor data 58 may indicate wind conditions near wind turbine 10. Specifically, sensor data 58 may indicate the level of yaw misalignment or error of turbine 10, i.e., the error or difference between the wind direction and the axis of rotor 16. Alternatively, yaw misalignment may be determined based on the wind direction relative to the plane defined by the swept areas of turbine rotor 16 and blades 18 of turbine 10, where ideal yaw alignment is when the wind direction is perpendicular to the rotor plane. Tilt misalignment may be determined in the same manner. In this case, the received data 58 may include measurements of the relative and / or absolute wind direction at the yaw position of nacelle 14.

[0049] Sensor data 58 may optionally include data indicating extreme, coherent gusts with directional changes and / or other extreme wind conditions (such as extreme positive or negative wind shear or wind direction) that cause extreme rotor loads. For example, sensor data indicating such wind conditions may be acquired from one or more lidar sensors of the wind turbine 10.

[0050] Indication of yaw error of wind turbine 10 may optionally include sensor data or signals indicating asymmetric (yaw) loads experienced by one or more components of wind turbine 10. For example, this may include measured and / or estimated (significant) asymmetric torques experienced by one or more turbine components. In particular, these may compensate for the cyclic pitch control amplitude implemented by controller 26. Alternatively, or additionally, this may include a combination of measured and / or estimated (significant) asymmetric torques with the rotor load control amplitude at the rotational frequency. Furthermore, asymmetric load data may include data from blade sensor 181 indicating extreme blade flapping torques.

[0051] Data indicating wind conditions and / or the load on turbine components caused by wind conditions may optionally be obtained from outside the wind turbine 10. For example, controller 26—specifically control element 46a—may receive data indicating that neighboring turbines in the wind farm of wind turbine 10 have experienced or are experiencing any of the aforementioned wind conditions or loads. Furthermore, the external data received by controller 26 may include meteorological information from a central server indicating wind conditions near wind turbine 10.

[0052] It will be understood that any suitable combination of the above examples, or any other suitable data, can be used to provide an indication of the yaw (and / or tilt) error of the wind turbine 10.

[0053] Based on the received yaw error indication, control element 46a determines the activity level for the tower lateral oscillation controller. The activity level is an indication of the level of tower lateral oscillation control to be utilized relative to its optimal or rated performance level. Generally, the higher the yaw error level of the wind turbine, the lower the determined activity level. This is to ensure that tower lateral oscillation control does not degrade the performance of the rotor load controller, while still ensuring that the goal of tower lateral oscillation control—namely, suppressing the lateral oscillation or vibration of tower 12—is being addressed.

[0054] Figure 4An illustrative graph showing how a defined activity level changes according to an indication of yaw error, in the example described, where the yaw error is provided by sensor signal 58. The SSTD activity level in this example can be considered as a scaling factor for the rated lateral oscillation control output, determined by control element 44a. Therefore, the SSTD activity level can vary on a scale between zero and one.

[0055] Three illustrative examples 60, 62, and 64 show how the activity level can change with variations in sensor signal 58. In the described examples, an increase in the amplitude of sensor signal 58 indicates an increase in yaw misalignment or error; however, for example, this could also mean an increase in tilt misalignment or asymmetric moment.

[0056] In each of the three examples 60, 62, and 64, the activity level is equal to one for the case where the sensor signal level is below the trigger lower limit level 66. That is, in the examples described, the activity level is one for the case where the yaw misalignment error is less than the lower threshold level, so that, in effect, no scaling is applied to the rated lateral oscillation control output used to modulate the overall control output. Expressed differently, the tower lateral oscillation (SSTD) controller is fully operational up to a certain yaw misalignment level. This ensures that SSTD operation is not shut down or derated without significantly affecting the operation of the rotor load controller. In a non-limiting example, the lower trigger level 66 could correspond to approximately 20 degrees of rotor yaw misalignment; however, any suitable value can be used.

[0057] In each of Examples 60, 62, and 64, the activity level monotonically decreases from 1 at the lower trigger level 66 of the sensor signal 58 to zero at the higher trigger level 68. In the first Example 60, the activity level decreases linearly from the lower trigger level 66 to the higher trigger level 68. In each of the other two Examples 62 and 64, the activity level decreases according to a quadratic curve, with the curvature of 62 downwards and the curvature of 64 upwards.

[0058] In each of the three examples 60, 62, and 64, the activity level is zero for sensor signal levels higher than the trigger's higher level 68. That is, in the examples described, the activity level is zero for yaw misalignment errors greater than the upper threshold level, so there is no lateral oscillation control output to modulate the overall control output; i.e., tower lateral oscillation control is not present in the overall individual pitch control output 50a. In other words, when rotor yaw misalignment is, for example, particularly severe, the lateral oscillation controller will not contribute to controlling individual blade pitch.

[0059] The lower and upper trigger levels 66 and 68 are tuning parameters that can be set according to the desired operation of the wind turbine 10. In some examples, only the lower trigger level may exist, while the activity level may asymptotically approach zero with increasing sensor signal 58.

[0060] The relationship between the activity level and sensor signal 58 can be continuous and optionally smooth to ensure predictable, consistent and smooth operation of the tower lateral oscillation controller and wind turbine 10.

[0061] It will be understood that any suitable relationship can be defined or used between the SSTD activity level and the data indicating yaw error (in this case, sensor signal 58).

[0062] Back Figure 3 The activity level scaling factor determined in the SSTD activity level module 46a is applied to the rated control output determined by the SSTD control system 44a in the processing element 70a, thereby derating the rated control output (when the activity level is less than 1). The controller 26 includes a lateral pitch modulation element 72 that receives the drated control output and determines an individual pitch modulation 48a to be included in the overall individual pitch control output 50a, so as to include a certain amount of tower lateral oscillation suppression in the overall individual pitch reference 50a used to control the operation of the wind turbine 10. A lower activity level may mean that a lower amplitude modulation—i.e., less tower lateral oscillation control—is included in the overall control output 50a. Alternatively, or additionally, a lower activity level may mean that gain scheduling is applied to the amplitude modulation of the rated control output.

[0063] It will be understood that the functions of the control elements described above for determining the individual pitch output of tower lateral oscillation control are equally applicable to the control elements 44b and 46b for determining the adjusted power offset, in order to provide tower lateral oscillation control, thereby determining the overall power setpoint for controlling the operation of the turbine generator.

[0064] Figure 5 The steps of a method 80, executed by controller 26, to determine and output an overall control output 50a for controlling the operation of wind turbine 10 (particularly individual pitch control), are summarized. At step 82, controller 26—particularly the SSTD control system 44a—receives data 56 indicating the lateral or sideways oscillations experienced by tower 12. In the example described, this data is in the form of lateral acceleration measured from accelerometer 184.

[0065] At step 84, controller 26—specifically SSTD control system 44a—determines a rated lateral oscillation control output based on the received lateral oscillation data 56. In the described example, this is in the form of individual blade pitch adjustment, but in different examples, this may alternatively, or additionally, be in the form of generator torque (power) offset. This rated lateral oscillation control output will, in a sense, be the optimally determined control output for suppressing tower oscillations, for example, in the absence of other control considerations related to controlling rotor load (cyclic load).

[0066] At step 86, controller 26—specifically SSTD active level unit 46a—receives an indication of the yaw (and / or tilt) error of wind turbine 10. That is, this indication may indicate the rotor / asymmetric load experienced or likely to be experienced by wind turbine 10, thereby incorporating a level of rotor load control into the control output of the asymmetric rotor load controller (included in the main controller 40 in this example). The yaw (and / or tilt) error may indicate the misalignment of rotor 16 relative to the wind direction in the yaw (and / or tilt) direction. The yaw error may additionally, or alternatively, indicate a significant torque experienced by the wind turbine. In the example described, the indication of the yaw error of wind turbine 10 is in the form of a sensor signal 58 indicating a measured yaw ( / tilt) misalignment and / or torque. This may include measurements of wind conditions such as wind direction, positive wind shear, negative wind shear, and / or wind direction. Additionally or alternatively, estimates of these variables / parameters may be used. The received indication of yaw error may additionally or alternatively include data received from outside the wind turbine 10. For example, this may include information about the operation of one or more other wind turbines in the wind farm adjacent to the wind turbine 10, and / or meteorological conditions near the wind turbine 10 from a central server.

[0067] At step 88, controller 26 determines the lateral oscillation control output 48a to be included in the overall control output 50a. Specifically, the lateral oscillation control output 48a is determined to be derated from the rated lateral oscillation control output (determined in step 86) when the indicated yaw error 58 of the wind turbine 10 is greater than a predetermined threshold level. In this example, the threshold level corresponds to the sensor signal trigger lower limit level 66. In this example, SSTD activity level unit 46a determines activity levels 60, 62, and 64 based on sensor signal 58, which are used to scale the rated lateral oscillation control output in unit / module 70a. If this scaling factor is less than 1, the lateral oscillation control output used to control the turbine 10 is derated from the rated lateral oscillation control output. In this example, the lateral oscillation control output is in the form of a separate pitch modulation value 48a determined using the output from scaling / derating unit 70a in SSTD pitch modulation unit 72.

[0068] At step 90, controller 26—specifically main controller 40—determines and outputs control output 42a for controlling wind turbine 10 in a known manner, based on the wind turbine control strategy and the monitored operation of wind turbine 10. This control output from main controller 40 also includes asymmetrical rotor load control for reducing asymmetrical loads on wind turbine 10.

[0069] At step 92, the control output 42a from the main controller 40 is combined with individual and cyclic pitch modulation 48a to determine the overall control output 50a. For example, the control output 42a can be amplitude modulated using the control output 48a to determine the overall control output 50a. That is, the overall control output 50a includes a dated level of tower lateral oscillation control where rated—or at least a higher level—total tower lateral oscillation control would negatively affect the effectiveness of rotor load control also included in the overall control output 50a. At step 94, the wind turbine 10 is controlled using the determined overall control output 50a.

[0070] Many modifications may be made to the above examples without departing from the scope of the appended claims.

[0071] In the example described above, derating of the defined rated tower lateral oscillation control output is achieved by applying a scaling factor in the form of a defined activity level to the rated control output. However, it will be understood that in different examples, derating can be achieved in any suitable manner, such as by subtracting an appropriate / defined amount from the rated control output. In some examples, the rated control output can be determined directly without explicitly defining it.

[0072] In the example described above, the rated lateral oscillation control output is dated based on a signal indicating the yaw error of the wind turbine. The determination of the derating—e.g., the determination of the activity level—can also be based on additional factors. For example, when the detected tower lateral oscillation reaches a predetermined level, the controller can be configured to issue an alarm or alert for large oscillations. Therefore, the derating of the tower lateral oscillation controller can be based on how close the tower is to this predetermined oscillation level. For example, the closer the tower is to the predetermined level, the less the lateral tower level controller is dated to ensure that it does not exceed the predetermined level, thereby avoiding an alarm. As another example, the wind turbine may have certain thresholds for asymmetric load moments (associated with one or more wind turbine components), exceeding which would trigger an alarm or even require turbine shutdown. Therefore, the derating of the tower lateral oscillation controller can be based on how close the measured and / or estimated asymmetric load moments are to these thresholds. For example, the closer the measured and / or estimated values ​​are to these threshold torques, the more the tower lateral oscillation control can be derated to ensure that the tower lateral oscillation control does not degrade the performance of the rotor load controller that is attempting to reduce these torques.

[0073] In the example described above, the rated lateral oscillation control output is derated based on a signal indicating yaw error. In this example, yaw error may indicate the inclusion of a certain level of asymmetric rotor load control in the overall control output; however, yaw error does not necessarily indicate this. In different examples, the rated lateral oscillation control output may be additionally or alternatively derated based on an indication of the implemented or required level of asymmetric rotor load control. In particular, lateral oscillation control included in the overall control output may be derated when the indication of the required or included amount of asymmetric rotor load control in the overall control output is higher than a threshold level. For example, the indication of the rotor load control amount may be based on a blade root load measurement or on a reading of a resulting gain factor used to scale the signal from the asymmetric rotor load controller superimposed on a separate pitch or power reference signal.

[0074] Examples of the present invention are advantageous because they prevent different controllers designed to reduce cyclic loads on wind turbines from degrading each other's performance, while still not allowing fatigue loads to increase in a way that affects component life. In particular, the invention is advantageous in that individual pitch (or generator torque control) used to suppress lateral oscillations of the wind turbine tower can be dated (e.g., as a function of wind direction relative to the rotor plane or via a measurement of yaw moment) so that controls used to reduce other asymmetric loads on the rotor are not degraded in performance. This is because controls used to suppress tower lateral oscillations are not as sensitive as (relatively rare) derating of their individual pitch contribution (or generator torque offset) to other cyclic load controls. That is, reducing other asymmetric or cyclic loads can be prioritized because these other loads, if not reduced, could lead to a larger / faster life reduction compared to the tower lateral oscillation load. As previously stated, derating of tower lateral oscillation control can be achieved using one or more interpolations between one or more parameters to allow for smooth derating of periodic pitch.

Claims

1. A method (80) for controlling the operation of a wind turbine (10) having a tower (12). The method (80) includes: Based on the wind turbine control strategy and the monitored operation of the wind turbine (10), an overall control output (50a, 50b) is determined (92), which includes rotor load control for reducing asymmetrical loads on the rotor (16) of the wind turbine (10) and lateral oscillation control for suppressing lateral oscillations of the tower; and the operation of the wind turbine (10) is controlled using the overall control output (50a, 50b) determined (94). The method (80) further includes: Receive (82) lateral oscillation sensor data (56) indicating the lateral oscillation level of the tower (12); The rated transverse oscillation control output (84) is determined based on the received transverse oscillation data; and Receive (86) an indication (58) of the yaw error of the wind turbine (10). Wherein, the yaw error is the misalignment of the rotor plane of the wind turbine (10) relative to the wind direction near the wind turbine (10), and When the indicated yaw error (58) of the wind turbine (10) is higher than a predetermined lower threshold level (66), the lateral oscillation control output (48a, 48b) included in the overall control output (50a, 50b) is determined to be derated from the rated lateral oscillation control output so that the rotor load control takes precedence over the lateral oscillation control.

2. The method (80) according to claim 1, wherein, When the indicated yaw error (58) of the wind turbine (10) is below the predetermined lower threshold level (66), the lateral oscillation control output (48a, 48b) is determined as the rated lateral oscillation control output.

3. The method (80) according to claim 1 or claim 2, wherein, The lateral oscillation control outputs (48a, 48b) monotonically derate as the indicated yaw error (58) of the wind turbine (10) gradually increases above the predetermined lower threshold level (66).

4. The method (80) according to claim 3, wherein, The derating is performed monotonically and linearly from the rated transverse oscillation control output (60).

5. The method (80) according to claim 1 or 2, wherein, When the indicated yaw error (58) of the wind turbine (10) is higher than the predetermined upper threshold level (68) of the predetermined lower threshold level (66), the lateral oscillation control output (48a, 48b) is derated to a substantially zero lateral oscillation control.

6. The method (80) according to claim 1 or 2, the method (80) comprising determining a lateral oscillation activity level based on a received indication (58) of yaw error, the lateral oscillation activity level indicating the extent to which the rated lateral oscillation control output will be derated, wherein the lateral oscillation control output (48a, 48b) is determined as a part of the rated lateral oscillation control output using the determined lateral oscillation activity level.

7. The method (80) according to claim 1 or 2, wherein, The transverse oscillation control outputs (48a, 48b) are included in the overall control outputs (50a, 50b) by at least one of the following: Gain-controlled regulation of the rated transverse oscillation control output; and Reduce the amplitude of the rated transverse oscillation control output.

8. The method (80) according to claim 1 or 2, wherein, The indication (58) of the yaw error of the wind turbine (10) includes data indicating the wind conditions near the wind turbine (10).

9. The method (80) according to claim 8, wherein, The data indicating wind conditions includes data indicating the wind direction near the wind turbine (10) relative to the rotor plane of the wind turbine (10).

10. The method (80) according to claim 8, wherein, Data indicating wind conditions include data indicating at least one of the following: positive wind shear; negative wind shear; and wind direction.

11. The method (80) according to claim 1 or 2, wherein, The indication (58) of the yaw error of the wind turbine (10) includes one or more of the following: Data indicating the asymmetric load experienced by one or more components of the wind turbine (10); Data indicating the asymmetric torque experienced by one or more components of the wind turbine (10); as well as Data indicating the yaw moment experienced by one or more components of the wind turbine (10).

12. The method (80) according to claim 1 or 2, wherein, The lateral oscillation control output (48a) includes a pitch modulation value for each of the plurality of corresponding blades (18) of the wind turbine (10), and the overall control output (50a) includes a separate pitch reference value for each of the blades (18), including the corresponding pitch modulation value.

13. The method (80) according to claim 1 or 2, wherein, The lateral oscillation control output (48b) includes a generator power offset value, and the overall control output (50b) includes a generator power reference value for the generator of the wind turbine (10), including the generator power offset value.

14. A controller (26) for controlling the operation of a wind turbine (10) having a tower (12). The controller (26) is configured to: determine an overall control output (50a, 50b) based on a wind turbine control strategy and the monitored operation of the wind turbine (10), the overall control output (50a, 50b) including rotor load control for reducing asymmetrical loads on the rotor (16) of the wind turbine (10) and lateral oscillation control for suppressing lateral oscillations of the tower (12); and use the determined overall control output (50a, 50b) to control the operation of the wind turbine (10). The controller (26) is also configured to: Receive lateral oscillation sensor data (56) indicating the lateral oscillation level of the tower (12); The rated transverse oscillation control output is determined based on the received transverse oscillation sensor data (56); and Receive an indication (58) of the yaw error of the wind turbine (10). in, The yaw error is the misalignment of the rotor plane of the wind turbine (10) relative to the wind direction near the wind turbine (10), and wherein, when the indicated yaw error (58) of the wind turbine (10) is higher than a predetermined lower threshold level (66), the lateral oscillation control outputs (48a, 48b) included in the overall control outputs (50a, 50b) are determined to be derated from the rated lateral oscillation control outputs, such that the rotor load control takes precedence over the lateral oscillation control.

15. A wind turbine (10) comprising a controller (26) according to claim 14.

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