EP4720507A1

EP4720507A1 - Wind turbine drivetrain control based on nacelle roll velocity

Info

Publication number: EP4720507A1
Application number: EP24733883.3A
Authority: EP
Inventors: Anders Druedahl THURLOW; Julio Xavier Vianna NETO
Original assignee: Vestas Wind Systems AS
Current assignee: Vestas Wind Systems AS
Priority date: 2023-05-31
Filing date: 2024-05-30
Publication date: 2026-04-08
Also published as: WO2024245515A1

Abstract

The invention relates to control of a wind turbine that includes a tower, a nacelle atop the tower, and a drivetrain that has drivetrain components housed in the nacelle. The invention includes receiving, from sensors of the wind turbine, sensor data indicative of movement of the nacelle. The invention includes determining, based on the received sensor data, a velocity of the nacelle in a roll direction defined relative to an axis of rotation of the drivetrain, where the velocity of the nacelle is determined in a fixed coordinate system. The invention then includes controlling the drivetrain of the wind turbine to dampen movement of the nacelle in the roll direction based on the determined nacelle roll velocity.

Description

WIND TURBINE DRIVETRAIN CONTROL BASED ON NACELLE ROLL VELOCITY

TECHNICAL FIELD

The invention relates to controlling a drivetrain of a wind turbine based on a velocity of a nacelle of the wind turbine in a roll direction.

BACKGROUND

Wind turbines as known in the art include a wind turbine tower supporting a nacelle and a rotor with a number of - typically, three - pitch-adjustable rotor blades mounted thereto. The nacelle houses different components of the wind turbine, including drivetrain components needed to convert wind energy captured by the rotor and rotor blades into electrical energy. The drivetrain components in a variable-speed wind turbine include a main or low-speed shaft connected to the rotor, a gearbox connected to the main shaft, a generator or high-speed shaft connected to the gearbox, and a generator connected to the generator shaft.

It is known to control components of the wind turbine drivetrain to maximise the production of electrical energy and/or minimise loading on certain components of the wind turbine in different operating conditions. In particular, it is known to adjust a pitch angle of the rotor blades relative to wind direction so as to change the aerodynamic torque on the rotor. Also, it is known to control electrical torque or power of the generator, e.g. by adjusting electrical current in the generator.

Accurate control of a wind turbine to maximise energy production while minimising component loading, or ensuring component loading is within acceptable bounds, relies on accurate monitoring of wind turbine operation and operating conditions. For instance, wind turbine generator torque may be controlled in accordance with a torque reference that has been determined to optimise wind turbine performance in some way, e.g. maximise energy production. In a similar manner, rotor blade pitch may be controlled in accordance with a (collective and/or individual) pitch reference that has been determined to optimise wind turbine performance in some way, e.g. minimise loading on the tower, rotor or rotor blades.

The torque reference and/or the pitch reference may be calculated based on a measured or estimated speed of the rotor or a drivetrain component, e.g. using an appropriate sensor of the wind turbine. However, the tower, nacelle and rotor of the wind turbine move in various ways during operation of the wind turbine. Such movement can influence measured sensor values, reducing the accuracy of monitored operational parameters. In turn, this can impact the calculated torque and/or pitch references, meaning that the wind turbine may not be operated in an optimal manner.

It is against this background to which the present invention is set.

SUMMARY OF THE INVENTION

According to an aspect of the invention there is provided a controller for a wind turbine. The wind turbine comprises a tower, a nacelle atop the tower, and a drivetrain comprising one or more drivetrain components housed in the nacelle. The controller is configured to receive, from one or more sensors of the wind turbine, sensor data indicative of movement of the nacelle. The controller is configured to determine, based on the received sensor data, a velocity of the nacelle in a roll direction defined relative to an axis of rotation of the drivetrain. The velocity of the nacelle is determined in a fixed coordinate system. The controller is configured to control the drivetrain of the wind turbine to dampen movement of the nacelle in the roll direction based on the determined nacelle roll velocity.

The controller may be configured to control the drivetrain to dampen movement of the nacelle in the roll direction only if a magnitude of the determined nacelle roll velocity is greater than a defined nacelle roll velocity threshold.

The controller may be configured to control the drivetrain by controlling a speed of a generator of the wind turbine in accordance with an adjusted generator parameter reference for the generator. The adjusted generator parameter reference may be a generator parameter reference obtained from a generator parameter reference controller of the wind turbine that is adjusted based on the determined nacelle roll velocity.

The adjusted generator parameter reference may be an adjusted generator power reference. The generator parameter reference may be a generator power reference obtained from a generator power reference controller. The controller may be configured to determine a generator power reference correction based on the determined nacelle roll velocity. The determined generator power reference correction may be applied to the generator power reference from the generator power reference controller to obtain the adjusted generator power reference.

The adjusted generator power reference may be gain scheduled based on generator speed.

The adjusted generator parameter reference may be an adjusted generator torque reference. The generator parameter reference may be a generator torque reference obtained from a generator torque reference controller. The controller may be configured to determine a generator torque reference correction based on the determined nacelle roll velocity. The determined generator torque reference correction may be applied to the generator torque reference from the generator torque reference controller to obtain the adjusted generator torque reference.

The controller may be configured to convert the adjusted generator torque reference to a generator power reference using generator speed. The generator power reference may be used to control the drivetrain.

The controller may be configured to receive a measured velocity of the drivetrain from a velocity sensor of the wind turbine. The velocity sensor may be mechanically coupled to the nacelle. The controller may be configured to determine a corrected drivetrain velocity based on the measured drivetrain velocity and the nacelle roll velocity. The controller may be configured to control the drivetrain of the wind turbine based on the determined corrected drivetrain velocity.

The one or more drivetrain components may comprise a high-speed shaft of the drivetrain. The velocity sensor may be configured to measure a velocity of the high-speed shaft.

The controller may be configured to control the drivetrain by controlling a speed of the drivetrain of the wind turbine in accordance with a pitch reference for pitch-adjustable rotor blades connected to the rotor of the wind turbine. The pitch reference may be determined based on a speed reference obtained from a speed reference controller and on the determined corrected drivetrain velocity.

The controller may be configured to control the drivetrain based on the determined roll velocity when the wind turbine is in a full-load region of operation. The one or more sensors may include one or more accelerometers located in the nacelle or at a top of the tower. The nacelle roll velocity may be determined based on acceleration measurements in one or more mutually orthogonal directions received from each respective accelerometer.

The one or more sensors may include one or more gyroscopes located in the nacelle. The nacelle roll velocity may be determined based on angular velocity measurements from the one or more gyroscopes.

According to another aspect of the invention there is provided a wind turbine comprising a controller as defined above.

According to another aspect of the invention there is provided a method for a wind turbine. The wind turbine comprises a tower, a nacelle atop the tower, and a drivetrain comprising one or more drivetrain components housed in the nacelle. The method comprises receiving, from one or more sensors of the wind turbine, sensor data indicative of movement of the nacelle. The method comprises determining, based on the received sensor data, a velocity of the nacelle in a roll direction defined relative to an axis of rotation of the drivetrain. The velocity of the nacelle is determined in a fixed coordinate system. The method comprises controlling the drivetrain of the wind turbine to dampen movement of the nacelle in the roll direction based on the determined nacelle roll velocity.

According to another aspect of the invention there is provided a non-transitory, computer- readable storage medium storing instructions thereon that, when implemented on one or more computer processors, cause the one or more computer processors to perform the method defined above.

BRIEF DESCRIPTION OF THE DRAWINGS

Examples of the invention will now be described with reference to the accompanying drawings, in which:

Figure 1 is a schematic illustration of a wind turbine in accordance with an aspect of the invention; Figure 2 is a schematic sectional side view of the wind turbine of Figure 1 ;

Figure 3 schematically illustrates first and second tower mode shapes that may be exhibited by a tower of the wind turbine of Figure 1 ;

Figure 4 schematically illustrates a control scheme implemented by a controller of the wind turbine of Figure 1 in accordance with an aspect of the invention; and,

Figure 5 summarises the steps of a method implemented by a controller of the wind turbine of Figure 1 in accordance with an aspect of the invention.

DETAILED DESCRIPTION

Figure 1 illustrates, in a schematic view, an example of a wind turbine 10. The wind turbine 10 includes a tower 102, a nacelle 103 disposed at the apex of, or atop, the tower 102, and a rotor 104 operatively coupled to a drivetrain including a generator housed inside the nacelle 103. The rotor 104 of the wind turbine 10 includes a central hub 105 and three rotor blades 106 that project outwardly from the central hub 105. The rotor blades 106 are pitch-adjustable. The rotor blades 106 can be adjusted in accordance with a collective pitch setting or reference, where each of the blades are set to the same pitch value. Optionally, the rotor blades 106 may be adjustable in accordance with individual pitch settings, where each blade 106 may be provided with an individual pitch setpoint or reference.

With additional reference to Figure 2, which schematically illustrates a sectional side view of the wind turbine 10 of Figure 1 , the nacelle 103 houses various components of the drivetrain 20. In particular, a low-speed shaft 201 (also referred to as a main shaft or rotor shaft) connects the rotor 104 with a gearbox 202 of the drivetrain 20. The gearbox 202 is connected to a high-speed shaft 203 (also referred to as a generator shaft), which in turn is connected to a generator 204 of the wind turbine 10.

Also shown in Figure 2 is a sensor 21 that is for measuring the velocity or rotational speed of one or more components of the drivetrain 20. In the described example, the sensor 21 is positioned in the nacelle 103, adjacent to the high-speed shaft 203, and is for measuring the velocity of the high-speed shaft 203. It will be understood, however, that in different examples the sensor 21 (or an additional sensor) may be positioned at a different location in the nacelle 103 or in the rotor 104, e.g. to measure the velocity of a different component such as the low-speed shaft 201 or the rotor 104. The sensor 21 may therefore be regarded more generally as being for measuring a drivetrain velocity. The sensor 21 may for instance be a resolver or (rotary) encoder as known in the art, such as a laser-based sensor or Hall sensor.

The sensor 21 is fixed to a frame 1031 of the nacelle 103, in particular via a connection element 211. In different examples, the sensor may be fixed to a different part of the nacelle 103 or to the rotor 104, for instance. The connection element 211 may be formed from a solid or relatively stiff material. Irrespective of this, as the sensor 21 is fixed to the nacelle frame 1031 , when the nacelle 103 moves the sensor 21 moves at the same time (and possibly by the same amount as the nacelle 103). In particular, during operation the nacelle 103 may move in tilt, yaw, and/or roll directions. Referring to Figure 2, the drivetrain 20 may be regarded as rotating about a certain axis of rotation 22. For instance, this may correspond to an axis of rotation of one or more components of the drivetrain 20, e.g. the low-speed shaft 201 or the high-speed shaft 203. When the nacelle 103 moves in a roll direction, such movement may be regarded as movement about the drivetrain axis or rotor axis 22, which may also be referred to as the (nacelle) roll axis 22. In this way, the nacelle 103 may roll around the same axis that the drivetrain rotates about.

The wind turbine 10 also includes a controller 23. The controller 23 may be in the form of any suitable computing device, for instance one or more functional units or modules implemented on one or more computer processors. Such functional units may be provided by suitable software running on any suitable computing substrate using conventional or custom processors and memory. The one or more functional units may use a common computing substrate (for example, they may run on the same server) or separate substrates, or one or both may themselves be distributed between multiple computing devices. A computer memory may store instructions for performing the methods performed by the controller, and the processor(s) may execute the stored instructions to perform the method.

In the example illustrated in Figure 2, the controller 23 is located in the nacelle 103; however, in different examples the controller - or some elements thereof - may be located elsewhere, e.g. in the tower 102 or remote from the wind turbine 10. The controller 23 is for controlling various aspects of wind turbine operation. For instance, the controller 23 is configured to output control signals to pitch actuators of the wind turbine 10 to adjust pitch angle of one or more of the rotor blades 106, e.g. to pitch the blades 106 into or out of the wind. Also, the controller 23 is configured to output control signals to control generator speed, torque or power, e.g. to maintain or maximise power output, to dampen oscillations of the drivetrain 20, etc. In the described example, the controller 23 is therefore a main controller of the wind turbine 10 (‘wind turbine controller’). However, in different examples the controller 23 may be a different controller of the wind turbine 10, such as a converter controller.

The controller 23 controls the wind turbine 10 based on current operating conditions. In particular, the controller 23 controls various aspects of operation of the drivetrain 20 based on the (current) drivetrain velocity, e.g. as measured by the sensor 21. In order to control the wind turbine 10 in an optimal manner, such as to optimise wind turbine performance (e.g. maximise power production), an accurate measurement or estimation of the drivetrain velocity is needed.

As mentioned above, during wind turbine operation the nacelle 103 may move in tilt, yaw and/or roll directions. In particular, as the wind turbine tower 102 is not of infinite stiffness, but is fixed to the ground (or floating platform in the case of an offshore wind turbine arrangement), then the tower 102 - and so the nacelle 103 - may move as the rotor 104 and rotor blades 106 rotate about the rotor axis. Specifically, the tower 102 may move according to certain mode shapes. With reference to Figure 3, the tower 102 may for instance move according to a first tower mode shape 31 or a second tower mode shape

32. As illustrated schematically in Figure 3, for both tower modes 31 , 32, a top of the tower 102 bends such that an angle a that the nacelle 103 makes with a horizontal plane/axis

33, e.g. relative to the ground 34, changes. This change may for instance be relative to when the wind turbine 10 is not operational and (a lower surface of) the nacelle 103 is substantially horizonal relative to the ground 34, i.e. a = 0. When the tower 102 moves according to the first or second tower mode shapes 31 , 32, the nacelle 103 rolls about the roll axis 22 to form the angle a.

As the sensor 21 is fixed to the nacelle 103, the sensor 21 therefore measures drivetrain velocity relative to the nacelle 103 rather than relative to the ground or other fixed reference frame. The motion of the nacelle 103 in the roll direction will cause the sensor 21 itself to rotate, which from a point of view of the sensor 21 is interpreted to be a rotation of the drivetrain 20 (e.g. shaft 23) rather than of the nacelle 103. The nacelle movement will in particular be interpreted as drivetrain rotation in an opposite direction to the change of angle a at the tower top. The measured drivetrain velocity is therefore a combination of the (actual) drivetrain velocity and the change in angle a at the tower top.

The present invention beneficially takes the movement of the nacelle into account when controlling various aspects of wind turbine operation. In particular, the invention beneficially determines a velocity of the nacelle in the roll direction and determines control actions for controlling the drivetrain based on the determined roll velocity, e.g. as a correction to a measured drivetrain velocity. Advantageously, wind turbine operation can therefore be improved as performance of different control features is improved, including maintaining stability of control features. The improved performance can reduce drivetrain oscillations, reduce nacelle oscillations in the roll direction, increase power production, etc., as will become apparent from the following description.

In order to be able to take nacelle roll velocity into account when determining control actions for controlling the drivetrain 20, the nacelle roll velocity needs to be determined. This may be performed in any suitable manner. For instance, the nacelle roll velocity may be determined using signals from existing hardware on the wind turbine 10. The wind turbine 10 may include one or more accelerometers located in - or on top of - the nacelle

103. An example of one such accelerometer 24 is illustrated schematically in Figure 2. Each accelerometer may be a three-axis accelerometer that measures acceleration in three mutually orthogonal directions. Typically, the positioning and orientation of accelerometers in a wind turbine is known. With this known information, the rotational velocity of the nacelle in the roll direction may then readily be calculated using the measured acceleration signals obtained by one or more of the accelerometers. The wind turbine 10 may include one or more gyroscopes, e.g. positioned in the nacelle 103 or rotor

104, which may also be used to measure orientation and velocity of the nacelle 103, and therefore determine the velocity of the nacelle 103 in the roll direction.

It is now described how the determined nacelle roll velocity may be used to control the wind turbine drivetrain 20. Figure 4 schematically illustrates a control scheme 40 that may be implemented by the controller 23 in examples of the invention. Figure 4 schematically shows the drivetrain 20. Operation of the drivetrain 20 results in a torque 401 at the top of the tower 102, which may be regarded as a combined reaction of the generator 204 and gearbox 202 of the drivetrain 20. This tower top torque 401 can result in movement of the tower top as described above, e.g. in accordance with a first or second tower mode 31 , 32. This tower top movement is in conjunction with movement of the nacelle 103 in the roll direction, schematically represented in Figure 4 as the nacelle roll 402. The nacelle roll

402 will have a velocity 403 associated therewith. The nacelle roll velocity 403 may be determined as described above, i.e. based on received signals from one or more accelerometers or gyroscopes of the wind turbine 10. In particular, the nacelle roll velocity

403 refers to the velocity of movement of the nacelle 103 about the drivetrain axis 22 relative to a fixed coordinate system, e.g. relative to the ground.

In one example, the obtained nacelle roll velocity 403 is used to correct a measured velocity 404 of the drivetrain 20. The measured drivetrain velocity 404 may for instance be a velocity signal obtained from the velocity or speed sensor 21 as described above. That is, the measured drivetrain velocity 403 may be a measured rotational speed of the generator shaft 203 or other drivetrain component.

In this example, the measured drivetrain velocity 404 is combined with the determined nacelle roll velocity 403, e.g. via a summation block I operator 405, to obtain a corrected or true drivetrain velocity 406. The corrected drivetrain velocity 406 is in particular the measured drivetrain velocity 404, corrected to account for movement of the nacelle 103 in the roll direction (i.e. about the roll axis 22).

This corrected drivetrain velocity 406 is then used as input to a control module for controlling operation of the wind turbine 10. In particular, the controller 23 may include a speed control module 407 (or speed controller) for controlling wind turbine rotor speed. The speed control module 407 typically takes as input a speed reference 408, with the wind turbine 10 then controlled so that the (actual) rotor speed is in accordance with the speed reference 408. The speed reference 408 may be determined as an error or difference between a desired rotor speed and a (current) measured rotor speed, e.g. as measured by an appropriate sensor measuring the rotational speed of the rotor 104 or rotor shaft 201 , for instance.

As the rotor 104 is connected to the drivetrain 20, then movement of the nacelle 103 (including the drivetrain 20) also results in movement of the rotor 104. As the sensor that is used to obtain the measured rotor speed will be attached or fixed to the rotor 104 or nacelle 103, then movement of the nacelle 103 and rotor 104 will influence the received measurement signal. That is, the measured rotor speed that is obtained will be the rotor speed relative to the rotor 104 or nacelle 103, rather than relative to a fixed coordinate system, such as relative to the ground. This means that the speed reference 408 is influenced in an undesirable manner by nacelle and rotor movement that occurs during wind turbine operation.

The corrected drivetrain velocity 406 can therefore be used to correct the speed reference 408 to account for movement of the nacelle 103 and rotor 104 in the roll direction. In particular, the corrected drivetrain velocity 406 is applied to the speed reference 408 at a summation block I operator 409 to obtain an error term 410. Depending on the sign of the corrected drivetrain velocity 406 (i.e. the direction of nacelle movement about the roll axis), the operation at block 409 may be addition or subtraction. The error term 410 is then provided as input to the speed control module 407 (instead of the speed reference 408).

The speed control module 407 determines a pitch reference 411 for controlling I adjusting pitch of the rotor blades 106 based on the speed error term 410. The pitch reference 411 may include collective and/or individual pitch control signals. The pitch angle adjustment changes the aerodynamic torque 412 experienced by the rotor 104 and rotor blades 106. For instance, changing the blade pitch to pitch the rotor blades 106 into the wind (i.e. into the oncoming wind direction) typically increases the energy being captured from the wind flowing past the wind turbine 10, which increases the aerodynamic torque experienced by the rotor 104 and rotor blades 106. The wind speed 413 and (actual) rotor speed 414 also influence the aerodynamic torque 412 experienced by the rotor 104, which in turn is experienced by the drivetrain 20 (as it is connected to the rotor 104).

By controlling rotor blade pitch based on accurate measurements of the speed of the wind turbine 10 (e.g. rotor 104 and drivetrain 20), the wind turbine 10 can be controlled in a manner such that the actual rotor speed more closely matches a desired rotor speed.

In another example, the obtained nacelle roll velocity 403 is used to dampen oscillations of the nacelle 103 in the roll direction. As described above, operation of the wind turbine 10 can cause the tower 102 to move according to the tower first mode 31 and/or the tower second mode 32, which yields a change of angle a at the tower top. Movement of the nacelle 103 in the roll direction occurs with this change in angle. As such, the nacelle roll velocity 403 can be used as a proxy for the change in angle a resulting from the flexible tower 102.

It may be desired to dampen oscillations of the wind turbine components that are moving according to the first or second tower mode shape. For instance, if the nacelle roll velocity 403 is greater than a defined threshold, then this may correspond to the tower top bending angle a increasing above an acceptable level, which in turn corresponds to oscillatory motion of undesirably large magnitude.

In the described example, a nacelle roll damper control module or controller 415 (or simply, nacelle roll damper 415) is provided to output control signals to dampen oscillations according to the first or second tower mode shape based on the determined nacelle roll velocity 403. This control damper feature may be active continuously or, as mentioned above, may activate if the nacelle roll velocity 403 increases above a threshold value, for instance.

In the illustrated example, the nacelle roll damper 415 is implemented as a modification to a torque reference signal 416 that is used to control generator torque of the generator 204. In particular, the controller 23 may include a torque control module or torque controller for controlling generator torque of the generator 204. The torque reference 416 may be determined based on a rotor speed or drivetrain speed signal.

In this example, the output of the nacelle roll damper 415 is therefore a torque (modification) signal which is then combined with the torque reference 416, e.g. via summation at the summation block I operator 417. The generator torque 418 is therefore controlled in accordance with a modified or adjusted torque reference such that oscillations of the drivetrain 20 are damped, e.g. oscillations according to the tower first or second mode 31 , 32 (or other vibration modes) are damped such that nacelle roll velocity is reduced.

In some examples, the adjusted torque reference is converted to a power reference, with the power reference instead being used to control the drivetrain 20. In particular, the power reference may be obtained from the adjusted torque reference using the generator speed. The generator output power is then controlled in accordance with the power reference.

The nacelle roll damper 415 may therefore be regarded as first or second tower mode damper. The second tower mode frequency is close to the drivetrain frequency. The nacelle roll damper 415 may therefore be particularly useful for damping oscillations according to the second tower mode 32. In the illustrated example, the nacelle roll damper 415 outputs a torque modification signal to modify a torque reference 415. However, in different examples the nacelle roll damper 415 may instead output a power modification signal to modify a power reference used to control operation of the generator 204. In particular, a generator power reference may be obtained from a power controller of the wind turbine 10, which may determine the power reference based on rotor speed or drivetrain speed. The modified or adjusted power reference signal may be further adjusted based on generator speed, e.g. via an applied gain. The gain may be higher for higher generator speeds, for instance. While the torque experienced by the nacelle 103 will be in sync with movement of the nacelle 103, fluctuations in power may be exhibited.

The nacelle roll velocity 403 may also be used to ensure proper or desired operation of a drivetrain damper of the controller 23, i.e. for damping oscillations of the drivetrain 20. In particular, the drivetrain damper may monitor oscillations of the drivetrain and output control signals, e.g. to control generator speed, to reduce the detected oscillations, for instance if the detected oscillations become too large. There is a risk that such a drivetrain damper could interpret the nacelle 103 (including the drivetrain 20) moving around the roll axis 22 as oscillations of the drivetrain 20, and output control signals to try to reduce the detected movement. However, this could in fact result in the drivetrain damper exciting the second tower mode 32. As such, in an example the drivetrain damper may be configured to receive the determined nacelle roll velocity 403 as an input. This means that nacelle movement in the roll direction can be removed from detected movement of the drivetrain 20, meaning that the drivetrain damper acts on the remaining signal to reduce drivetrain oscillations. In particular, this means that the drivetrain damper advantageously does not react to nacelle movement in the roll direction.

The control scheme 40 may be implemented when the wind turbine 10 is in a full-load region of operation, e.g. operating at rated power. The speed controller 407 may be activated to adjust pitch angle, e.g. to limit component loading, only when the wind turbine 10 is in the full-load region. Also, the wind turbine 10 exhibiting first or second tower mode oscillations, and/or the drivetrain components exhibiting more problematic oscillations, may be more likely to occur at the higher wind speeds associated with the full-load region of operation (i.e. above a rated wind speed).

In the example illustrated in Figure 4, the determined nacelle roll velocity is used for both: damping nacelle movement in the roll direction; and, correcting a measured drivetrain velocity used as input to a speed controller. It will be understood, however, that these use cases need not be in combination and can be implemented individually. In addition, it will be understood that these use cases may be used in combination with other control features of the wind turbine 10 that makes use of the determined roll velocity, e.g. ensuring that a drivetrain damper does not react to nacelle roll movement as described above.

Figure 5 summarises the steps of a method 50 performed by the controller 23 in examples of the invention. At step 501 , the method involves receiving sensor data indicative of movement of the nacelle 103. The sensor data is received from one or more sensors of the wind turbine 10. For instance, this may include one or more accelerometers 24 and or gyroscopes positioned in the nacelle 103, rotor 104 or tower 102 of the wind turbine 10. As such, the sensor data may be in the form acceleration and/or orientation signals.

At step 502, the method 50 involves using the received sensor data to determine a velocity of the nacelle 103 in a roll direction. The roll direction is defined relative to an axis 22 of rotation of the drivetrain 20 or the rotor 104. For instance, the roll axis 22 may be defined as the rotor axis or an axis of rotation of one of the shafts 201 , 203 of the drivetrain 20. The velocity of the nacelle 103 is determined in a fixed coordinate system. For instance, the nacelle velocity may be determined relative to the ground.

At step 503, the method 50 involves controlling the drivetrain 20 of the wind turbine 10 based on the determined nacelle roll velocity. In one example, the determined nacelle roll velocity is used to correct a measured drivetrain velocity, e.g. as obtained from a drivetrain sensor 21 such as an encoder, with the corrected drivetrain velocity being used to control the drivetrain 20. This may involve adjusting a speed reference for a speed controller of the wind turbine 10 using the corrected drivetrain velocity, with the speed controller controlling adjusting rotor blade pitch angle, thereby varying the aerodynamic torque experienced by the rotor 104 and drivetrain 20.

In another example, the determined nacelle roll velocity is used as part of a control feature to reduce or dampen oscillations of the nacelle 103 about the roll axis 22. In particular, a nacelle roll damper 415 may determine an adjustment to a generator parameter reference used to control a speed of the generator 204, where the adjustment is determined based on the nacelle roll velocity. The form of the output of the nacelle roll damper 415 depends on the reference signal that is to be adjusted or modified. The generator parameter may be generator torque, in which case the nacelle roll damper 415 is a torque adjustment signal. Alternatively, the generator parameter may be generator output power, in which case the nacelle roll damper 415 is a power adjustment signal. The nacelle roll damper 415 may be activated only if the nacelle roll velocity is above a certain thresholds level, indicative of nacelle oscillations in the roll direction that are considered to be too high.

In a further example, the determined nacelle roll velocity is used by a drivetrain damper control feature. In particular, monitored oscillations of the drivetrain 20 may be adjusted or corrected to remove content relating to movement of the nacelle 103 in the roll direction, specifically using the determined nacelle roll velocity. The drivetrain damper then acts to reduce the adjusted or corrected drivetrain oscillations (rather than the original oscillation signal). In this way, the drivetrain damper therefore does not react to movement of the nacelle 103 in the roll direction, and so does not excite the second tower mode 32.

Many modifications may be made to the described examples without departing from the scope of the appended claims.

Claims

1. A controller for a wind turbine, the wind turbine comprising: a tower; a nacelle atop the tower; and, a drivetrain comprising one or more drivetrain components housed in the nacelle, the controller being configured to: receive, from one or more sensors of the wind turbine, sensor data indicative of movement of the nacelle; determine, based on the received sensor data, a velocity of the nacelle in a roll direction defined relative to an axis of rotation of the drivetrain, wherein the velocity of the nacelle is determined in a fixed coordinate system; and, control the drivetrain of the wind turbine to dampen movement of the nacelle in the roll direction based on the determined nacelle roll velocity.

2. A controller according to Claim 1 , wherein the controller is configured to control the drivetrain to dampen movement of the nacelle in the roll direction only if a magnitude of the determined nacelle roll velocity is greater than a defined nacelle roll velocity threshold.

3. A controller according to any previous claim, wherein the controller is configured to control the drivetrain by controlling a speed of a generator of the wind turbine in accordance with an adjusted generator parameter reference for the generator, wherein the adjusted generator parameter reference is a generator parameter reference obtained from a generator parameter reference controller of the wind turbine that is adjusted based on the determined nacelle roll velocity.

4. A controller according to Claim 3, wherein the adjusted generator parameter reference is an adjusted generator power reference, wherein the generator parameter reference is a generator power reference obtained from a generator power reference controller, wherein the controller is configured to determine a generator power reference correction based on the determined nacelle roll velocity, wherein the determined generator power reference correction is applied to the generator power reference from the generator power reference controller to obtain the adjusted generator power reference.

5. A controller according to Claim 4, wherein the adjusted generator power reference is gain scheduled based on generator speed.

6. A controller according to Claim 5, wherein the adjusted generator parameter reference is an adjusted generator torque reference, wherein the generator parameter reference is a generator torque reference obtained from a generator torque reference controller, wherein the controller is configured to determine a generator torque reference correction based on the determined nacelle roll velocity, wherein the determined generator torque reference correction is applied to the generator torque reference from the generator torque reference controller to obtain the adjusted generator torque reference.

7. A controller according to Claim 6, wherein the controller is configured to convert the adjusted generator torque reference to a generator power reference using generator speed, the generator power reference being used to control the drivetrain.

8. A controller according to any previous claim, wherein the controller is configured to: receive a measured velocity of the drivetrain from a velocity sensor of the wind turbine, the velocity sensor being mechanically coupled to the nacelle; determine a corrected drivetrain velocity based on the measured drivetrain velocity and the nacelle roll velocity; and, control the drivetrain of the wind turbine based on the determined corrected drivetrain velocity.

9. A controller according to Claim 8, wherein the one or more drivetrain components comprises a high-speed shaft of the drivetrain, and wherein the velocity sensor is configured to measure a velocity of the high-speed shaft.

10. A controller according to Claim 8 or Claim 9, wherein the controller is configured to control the drivetrain by controlling a speed of the drivetrain of the wind turbine in accordance with a pitch reference for pitch-adjustable rotor blades connected to the rotor of the wind turbine, wherein the pitch reference is determined based on a speed reference obtained from a speed reference controller and on the determined corrected drivetrain velocity.

11. A controller according to any previous claim, wherein the controller is configured to control the drivetrain based on the determined roll velocity when the wind turbine is in a full-load region of operation.

12. A controller according to any previous claim, wherein the one or more sensors include: one or more accelerometers located in the nacelle or at a top of the tower, the nacelle roll velocity being determined based on acceleration measurements in one or more mutually orthogonal directions received from each respective accelerometer; or, one or more gyroscopes located in the nacelle, the nacelle roll velocity being determined based on angular velocity measurements from the one or more gyroscopes.

13. A wind turbine comprising a controller according to any previous claim.

14. A method for a wind turbine, the wind turbine comprising: a tower; a nacelle atop the tower; and, a drivetrain comprising one or more drivetrain components housed in the nacelle, the method comprising: receiving, from one or more sensors of the wind turbine, sensor data indicative of movement of the nacelle; determining, based on the received sensor data, a velocity of the nacelle in a roll direction defined relative to an axis of rotation of the drivetrain, wherein the velocity of the nacelle is determined in a fixed coordinate system; and, controlling the drivetrain of the wind turbine to dampen movement of the nacelle in the roll direction based on the determined nacelle roll velocity.