WO2023088417A1

WO2023088417A1 - Controller for a wind turbine

Info

Publication number: WO2023088417A1
Application number: PCT/CN2022/132822
Authority: WO
Inventors: Fabio Caponetti; Jacob Deleuran GRUNNET; Ebbe Nielsen
Original assignee: Shanghai Electric Wind Power Group Co., Ltd.
Priority date: 2021-11-19
Filing date: 2022-11-18
Publication date: 2023-05-25
Also published as: DK181447B1; DK202170576A1

Abstract

A controller for a wind turbine configured to: receive acceleration information indicative of the acceleration experienced by a one or both of a tower and a nacelle of the wind turbine; determine in-band-acceleration information by application of at least one filter to the acceleration information, the at least one filter configured to filter at a predetermined frequency band, and wherein said in-band-acceleration information is indicative of the acceleration experienced by the tower at frequencies within said predetermined frequency band; perform a comparison based on said in-band-acceleration information with baseline acceleration information, wherein the baseline acceleration information is indicative of an average acceleration level experienced by the wind turbine; and determine an occurrence of at least a change in wind direction above a threshold level based on said comparison of the in-band-acceleration information to the baseline acceleration information.

Description

CONTROLLER FOR A WIND TURBINE

TECHNICAL FIELD

This invention relates to a controller for a wind turbine. In particular, it relates to a controller configured to detect rapid changes in wind direction from acceleration information indicative of the acceleration experienced by the wind turbine. The invention further relates to such a controller in combination with one or more acceleration sensors. The invention also relates to a wind turbine including such a controller; a method for detecting rapid changes in wind direction; and a computer program product and computer program code for implementing the method.

BACKGROUND

A wind turbine typically comprises a tower and a rotor mounted to the tower. The rotor comprises a hub and a plurality of blades configured to extend from the hub. The rotor typically comprises three blades, although other numbers of blades are possible. Each blade is operably coupled to the hub by a blade bearing which allows for rotation of the blades relative to the hub, such that the pitch of the blades is adjustable. The rotor is coupled to a generator, and may be coupled to the generator via a gearbox. The generator is configured to convert the rotational energy of the rotor to electrical energy. The generator and optional gearbox are housed within a nacelle. A main bearing supports the rotor and allows for rotation of the rotor relative to the nacelle and generator. In some examples, the wind turbine may include a brake to slow and stop the rotation of the rotor.

A wind turbine may, during operation, experience rapid changes in wind direction and/or rapid changes in wind speed. These rapid changes can cause extreme loading on the main bearing and other parts of the wind turbine and may introduce undesirable vibration. In order to manage the loading and vibration experienced during rapid changes in wind direction and/or speed, the controller of the wind turbine may provide a control action to mitigate the issue or shut down the wind turbine. It is a challenge to detect a rapid change in wind direction and/or wind speed event and provide a control action in a timely manner.

SUMMARY

According to a first aspect of the invention we provide a controller for a wind turbine configured to:

receive acceleration information, such as from one or more acceleration sensors, the acceleration information indicative of the acceleration experienced by a one or both of a tower and a nacelle of the wind turbine;

determine in-band-acceleration information by application of at least one filter to the acceleration information, the at least one filter configured to filter at a predetermined frequency band, and wherein said in-band-acceleration information is indicative of the acceleration experienced by the tower at frequencies within said predetermined frequency band;

perform a comparison based on said in-band-acceleration information with baseline acceleration information, wherein the baseline acceleration information is indicative of an average acceleration level experienced by the wind turbine;

determine an occurrence of at least a change in wind direction above a threshold level based on said comparison of the in-band-acceleration information to the baseline acceleration information.

In one or more examples, said determination of an occurrence of at least a change in wind direction above a threshold level is performed without information from a wind vane and/or ultrasonic wind sensor mounted on the wind turbine.

In one or more examples, said controller is configured to, based on the determination of the occurrence of at least the change in wind direction above the threshold level, provide one or more control signals to invoke a control action comprising one or both of:

control of the pitch of one or more blades of the wind turbine; and

control of a torque applied to the rotor by a generator of the wind turbine.

In one or more examples, said control action is configured to shut down the wind turbine. In one or more examples, said control action is configured to adjust a yaw of wind turbine to face the wind direction following said change in wind direction above the threshold level. In one or more examples, said control action is configured to restart said wind turbine.

In one or more examples, the controller is configured to determine an energy of said in-band-acceleration information at least including a determination of tower displacement from integration of the in-band-acceleration information and wherein said controller being configured to compare comprises a comparison between the energy derived from the in-band-acceleration information and an energy derived from the baseline acceleration information.

In one or more embodiments, said at least one filter comprises a band-pass filter or a quadrature filter and wherein said predetermined frequency band of the band-pass filter or quadrature filter includes one of a 1P, 2P, 3P, 4P, 6P or 9P excitation frequency of said wind turbine, wherein P represents the rotational speed of the rotor of the wind turbine.

In other examples, the band-pass filter or quadrature filter could be configured to extract one or more of, or two or more of, a 1P, 2P, 3P, 4P, 6P or 9P excitation frequency of said wind turbine.

In one or more embodiments, said filter comprises one of a quadrature filter and a bandpass filter, wherein the quadrature filter or bandpass filter is configured to provide said in-band-acceleration information at a 3P excitation frequency of said wind turbine, wherein P represents the rotational speed of the rotor of the wind turbine. In other examples, the 2P and/or 4P excitation frequency may be preferred.

In one or more embodiments, said baseline acceleration information comprises a dynamic baseline acceleration information. In one or more examples, said controller is configured to apply a low-pass filter to said acceleration information to obtain an approximated average of said acceleration information, wherein said dynamic baseline acceleration information is based on said approximated average of said acceleration information.

In one or more examples, the controller is configured to apply the low-pass filter having a cut off frequency which is a function of a rotational frequency of the rotor to determine said dynamic baseline acceleration information.

In one or more examples, said dynamic baseline acceleration information is determined by said controller being configured to determine a moving average of said acceleration information rather than by said application of the low-pass filter.

In one or more other examples, said baseline acceleration information is predetermined based on an average acceleration level experienced by the wind turbine obtained during a calibration procedure absent of an occurrence of said change in wind direction above the threshold level.

In one or more embodiments, said controller is configured to determine a current wind direction following said change in wind direction above a threshold level based on said acceleration information, wherein an indication of displacement of the tower and/or nacelle is derived from said acceleration information and the current wind direction is based thereon.

In one or more embodiments, said acceleration information is received from at least one acceleration sensor configured to provide acceleration information indicative of an acceleration along a fore-aft direction of said tower.

In one or more embodiments, said acceleration information is received from two or more acceleration sensors configured to provide acceleration information indicative of an acceleration along a fore-aft direction of said tower and a side-to-side direction of said tower.

In one or more embodiments, said controller being configured to perform a comparison comprises comparing an energy of said in-band-acceleration information with an energy of said baseline acceleration information, wherein said energy of said in-band-acceleration information is approximated by the controller being configured to apply a low-pass filter to said in-band-acceleration information, and wherein said energy of said baseline acceleration information is approximated by said controller being configured to apply a low-pass filter to said baseline acceleration information.

In one or more embodiments, said controller is configured to receive rotational speed information from a sensor indicative of the rotational speed of a rotor of the wind turbine, and wherein the controller is configured to dynamically control a cut-off frequency of said low-pass filter based on said rotational speed information.

In one or more embodiments, said low-pass filter applied to the in-band-acceleration information has a cut-off frequency at least one decade greater than the cut-off frequency of the low-pass filter applied to the baseline acceleration information

In one or more embodiments, said determination of the in-band-acceleration information by application of the at least one filter to the acceleration information comprises filtering such that said predetermined frequency band includes the 2P excitation frequency of said wind turbine, wherein P represents the rotational speed of the rotor of the wind turbine.

In one or more embodiments, said in-band-acceleration information comprises a first component frequency band comprising said predetermined frequency band that includes the 2P excitation frequency and a second component frequency band, wherein determination of the second component frequency band of the in-band-acceleration information comprises the controller being configured to apply a filter to said acceleration information at a second predetermined frequency band that includes the 4P and/or 6P excitation frequency of said wind turbine, wherein P represents the rotational speed of the rotor of the wind turbine.

In one or more embodiments, the controller being configured to determine the in-band-acceleration information includes application of a first weight to the acceleration information in the first component frequency band and application of a second weight to the acceleration information in the second component frequency band, wherein said first weight and second weight are configurable.

In one or more embodiments, said controller is configured to receive wind speed information, such as from a wind speed sensor configured to measure the current wind speed experienced by the wind turbine or derived from other information, and wherein determination of the occurrence of at least a change in wind direction above a threshold level is additionally based on said wind speed information being indicative of a wind speed above a threshold wind speed.

According to a second aspect of the invention we provide a wind turbine including the controller of the first aspect. In one or more embodiments, the wind turbine includes one or more acceleration sensors, such as accelerometers, configured to determine the acceleration information.

According to a third aspect of the invention we provide a method for a wind turbine, the method comprising:

receiving acceleration information from one or more acceleration sensors, the acceleration information indicative of the acceleration experienced by a one or both of a tower and a nacelle of the wind turbine;

determining in-band-acceleration information by application of at least one filter to the acceleration information, the at least one filter configured to filter at a predetermined frequency band, and wherein said in-band-acceleration information is indicative of the acceleration experienced by the tower at frequencies within said predetermined frequency band;

performing a comparison based on said in-band-acceleration information with baseline acceleration information, wherein the baseline acceleration information is indicative of an average acceleration level experienced by the wind turbine;

determining an occurrence of at least a change in wind direction above a threshold level based on said comparison of the in-band-acceleration information to the baseline acceleration information.

According to a fourth aspect, we provide a computer program or a computer program product comprising computer program code configured to cause a processor and memory to perform the method of the third aspect.

BRIEF DESCRIPTION OF THE DRAWINGS

There now follows, by way of example only, a detailed description of embodiments of the invention with reference to the following figures, in which:

Figures 1A and 1B show an example wind turbine and controller from a side view and a front view respectively;

Figure 2 shows an example controller, which may be provided in combination with one or more acceleration sensors;

Figure 3 shows an example flow chart illustrating an overview of a control scheme for use in detecting changes in wind direction above a threshold level and acting on said detection;

Figure 4 shows an example function block diagram of the controller according to a first example embodiment;

Figure 5 shows an example function block diagram of the controller according to a second example embodiment;

Figure 6 shows a flowchart illustrating a method performed by the controller of figure 2;

Figure 7 shows an example graph of side-to-side position derived from acceleration information measured by an acceleration sensor configured to measure the side-to-side acceleration the tower is subjected to relative to a long-term average over time; and

Figure 8 shows an example computer readable medium.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Example figures 1A and 1B show a side view and a front view of an example wind turbine 100 and a controller 101 for the wind turbine. The wind turbine 100 comprises a tower 102 and a rotor 103 which is operably coupled to a generator 104 mounted within a nacelle 105. The controller 101 is shown schematically within a base of the tower 102 but, in other examples, it could be mounted elsewhere. The rotor 103 may be coupled to the generator 104 via a gearbox 106, which is also mounted within the nacelle 105. A main bearing (not visible in Figures 1A and 1B) supports the rotor 103 and allows for its rotation. The rotor 103 comprises a hub 107 and three

blades

108A, 108B and 108C (shown collectively as 108 in Figure 1A) that extend from the hub 107. While this example wind turbine 100 has three blades, other numbers of blades are possible, such as two or more blades. Each blade is operably coupled to the hub 107 by a blade bearing which allows for rotation of the blades relative to the hub, such that the pitch, that is rotation around a longitudinal axis, of each of the blades is adjustable. The generator 104, and optional gearbox 106, is controllable and may, during operation, be controlled to efficiently extract energy from the wind. The generator 104 and optional gearbox 106 are also controllable such that a torque can be applied to the rotor 103, which can be used to control its rotational speed.

The controller 101 is shown schematically within a base of the tower 102 but, in other examples, it could be mounted elsewhere. The controller is also shown separate from the wind turbine 100 that it controls in example Figure 2. The controller 101 is operably coupled to receive information at inputs 201 to 204 that may be derived from one or more sensors associated with the wind turbine 100. The controller 101 is configured to transmit one or more control signals to components of the wind turbine. Thus, the controller 101 may be configured to control the generator and, in particular, the torque applied to the rotor by providing one or more control signals, such as at a first output 205. The controller 101 may be configured to control the pitch of each of the plurality of blades 108 by providing one or more control signals, such as at a second output 206. It will be appreciated that the controller 101 may be configured to provide other control signals.

In one or more examples, the input 201 may be configured to receive acceleration information from a first acceleration sensor 207, such as an accelerometer, configured to measure acceleration along a fore-aft direction 110 of said tower. The first acceleration sensor being configured to measure in the fore-aft direction may therefore be measuring the acceleration of the sway of the tower forward in the direction the rotor is pointing and back. The input 202 may be configured to receive acceleration information from a second acceleration sensor 208, which may comprise an accelerometer, wherein the second acceleration sensor is configured to measure acceleration in a side-to-side direction 111 of said tower. The second acceleration sensor may therefore be configured to measure the acceleration of the sway of the tower side to side. The first and second acceleration sensors may be mounted at the top of the tower, such as within the nacelle 105. It will be appreciated that given the

sensors

207, 208 are configured to measure the acceleration experienced by the tower in terms of its sway in the fore-aft and side-to-side directions, then measurements of greater amplitude will be obtained with the sensors positioned at the top of the tower but viable information may still be obtainable with acceleration sensors mounted lower than the top of the tower provided they have the necessary sensitivity. It will further be appreciated that, while the sensors are described as being mounted to sense in the fore-aft direction and in the side-to-side direction respectively, the sensors may be physically mounted at any relatively perpendicular orientation around the tower in order to obtain viable directional acceleration information. For example, for an arbitrarily oriented acceleration sensor, the acceleration can be resolved to determine a component that act in one, or components that act in both, of the fore-aft and side-to-side directions, as will be known to those skilled in the art. Thus, the acceleration information may be considered to be indicative of fore-aft and/or side-to-side acceleration rather than the physical orientation of the sensors themselves.

The controller 101 may be configured to receive wind speed information at input 203 from a wind speed sensor configured to measure the current wind speed experienced by the wind turbine. The wind speed sensor is typically mounted on the wind turbine 100 but could be separate therefrom in the wind field that will be incident on the wind turbine. The controller 101 may be configured to receive rotational speed information at input 204 from a rotational speed sensor indicative of the rotational speed of the rotor 103 of the wind turbine 100.

The wind turbine 100 may experience rapid changes in wind direction and/or speed wherein these rapid changes induce undesirable loading on components of the wind turbine, such as the main bearing. The examples that follow relate to the operation of the controller 101 and, in particular, to the detection of changes in wind direction that may exceed a predetermined threshold and, optionally, to the detection of changes in wind direction and wind speed that may exceed predetermined thresholds. The predetermined threshold (s) may therefore define what is considered a rapid or “extreme” change in wind direction and/or wind speed event, which may be determined to cause undesirable damage, vibration or fatigue to the wind turbine. The detection of such above-threshold changes may be used by the controller 101 to trigger a control action to manage the operation of the wind turbine 100 during such events or in response to such events. The control action may include the issue of one or more control signals at

outputs

205, 206 for controlling one or both of generator torque and blade pitch.

What qualifies as a rapid change in wind direction and/or wind speed event to cause the controller 101 to issue a control action may differ between wind turbines. However, as an example, a change in wind direction greater than 30 degrees that occurs in less than 30 seconds may be consider a rapid change in wind direction and trigger the control action. Thus, the operation of the controller 101 may be calibrated to identify when such a change occurs. In other examples, the operation of the controller 101 may be calibrated to identify an extreme change in wind direction and/or speed as defined in the IEC standard 61400-1.

Traditionally, detecting wind direction changes is done using a wind vane or ultra-sonic wind sensor mounted behind the rotor 103 on the wind turbine 100. However, the examples described herein do not require or do not use information from a wind vane or ultrasonic wind sensor.

It has been identified that it is challenging to detect rapid or extreme wind direction changes quickly using wind direction measurements obtained from behind the rotor 103 because the rotor can significantly disturb the wind flow, which creates the need for heavy filtering of the measured wind direction. This, in turn, makes any wind direction detection method that uses the filtered measurement of wind direction slow.

Other methods have tried to use wind estimators and the fact that the estimated wind speed compared to the measured wind speed changes when the wind direction changes. Unfortunately, this method suffers from similar issues, wherein filtering, which is part of the wind estimator methodology, is too slow for rapidly detecting a wind direction change.

One or more examples herein provide a controller than implements an alternative method for determining the occurrence of an event in which there is a rapid or extreme change in wind direction.

Example figure 3 shows a flowchart illustrating a method the controller 101 may follow to mitigate against the effects of rapid changes in wind direction.

Block 301 represents the start of the method. Block 302 illustrates the provision of a control algorithm that detects the occurrence of at least a change in wind direction above a threshold level. The occurrence of a change in wind direction above a threshold level may be termed a “rapid change of direction” event or “ECD” event (standing for Extreme Change in Direction) , as will be known to those skilled in the art. In the examples that follow and that are described with reference to figure 3, the configuration of the controller 101 to provide the functionality of block 302 will be described.

If a rapid change of direction event or ECD event is detected, the method proceeds to block 303 which is termed “safe mode” in which a control action is taken to mitigate against the effects of the ECD.

If a rapid change of direction event or ECD event is not detected at block 302, the method proceeds to block 304 in which the controller determines if there is a high yaw error. In very general terms, a high yaw error is determined by calculation of the difference between the direction the wind turbine is pointing, i.e., the nacelle orientation, and the current wind direction and comparing the difference to a high-yaw-error-threshold. If a high yaw error is detected (by the high-yaw-error-threshold being exceeded) , the method may also proceed to block 303. If a high yaw error is not detected in this example the method ends at 305 and restarts at block 301.

In this example, the “safe mode” includes but is not limited to checking various conditions to determine if the turbine can be shut down (i.e., the rotor speed reduced, such as to a stop) . If the various “shut down” conditions are met, the method proceeds to block 306 in which the turbine is shutdown. In some examples, the checking of various “shut down” conditions is not performed and the method proceeds directly to block 306 from blocks 302 and/or 304. The method arrives at block 307 once the turbine is shutdown. Block 307 shows the step of controlling the yaw of the turbine such that it points in the current wind direction. Block 308 illustrates the restarting of the wind turbine. The method then proceeds to step 301. It will be appreciated that the method illustrated in Figure 3 is focussed on detecting rapid change of direction events or ECD events and various other control methods may be provided in parallel.

The example actions performed by the controller 101 in block 302 will now be described with reference to Figure 4. Figures 4 and 5 show a block diagram illustrating the functions performed by the controller 101. These functions may be implemented as hardware, software or a combination of hardware or software. Thus, the controller 101 may comprise a programmable logic controller comprising a processor and memory. Alternatively, the controller 101 may comprise a general purpose processor and memory and computer program code stored in the memory, which is configured to cause the processor, when executed, to provide a software-based implementation of the functions of the blocks of Figure 4 or 5. In other examples, the controller may comprise a combination of a processor and memory operably coupled with one or more of the following components: one or more signal processing filters; one or more signal combiners; one or more comparators and/or one or more logic gates.

The controller 101 is configured to receive acceleration information from one or more acceleration sensors. In the example of Figure 4, the input 201 is shown receiving acceleration information from the first acceleration sensor and input 202 is shown receiving acceleration information from the second acceleration sensor. Thus, in this example, the acceleration information may be considered to comprise the combined information from both acceleration sensors. The acceleration information may take the form of one or more analog signals representing the acceleration experience by the tower, which may be buffered. In one or more examples, the controller 101 is configured to sample the analog signal and includes an analog to digital convertor (not shown) to obtain a digital stream of samples of the analog signal (s) . In other examples, the acceleration information may take the form of stream of samples in digital form and thus the controller 101 may operate on the stream of samples in the digital domain.

In an alternate example, the controller receives acceleration information from only the fore-aft (first) acceleration sensor or the side-to-side (second) acceleration sensor. In one or more further examples, the controller may be configured to receive acceleration information from any number of acceleration sensors arranged to measure acceleration in a plurality of different directions which may not exactly correspond to fore-aft and side-to-side directions. In such examples, the acceleration information from the sensors may be used in combination such that the combined acceleration information allows for the determination of a substantially fore-aft acceleration and a substantially side-to-side acceleration.

In general terms, the controller 101 is configured to determine in-band-acceleration information by signal processing of the acceleration information by the functions in functional block 401. The controller 101 is configured to receive or determine baseline acceleration information by the functions in functional block 402. The controller is configured to perform a comparison based on said in-band-acceleration information with said baseline acceleration information at functional block 403. Further, in the present example, an optional second comparison is made at block 435. Thus, the controller is configured to determine an occurrence of at least a change in wind direction above a threshold level, such as an ECD event, based on said comparison at functional block 404. However, in other examples, the comparison at block 403 may yield the determination of the occurrence of at least a change in wind direction above the threshold level and block 404 may be absent.

The functionality will now be described in more detail.

Block 405 may be termed the “acceleration information receipt and processing block” and may provide the function of receiving the acceleration information at

inputs

201, 202. In the present example, as shown in functional block 405, the controller 101 is configured to combine the acceleration information received from the first acceleration sensor 207 at input 201 with the acceleration information received from the second acceleration sensor 208 at input 202. This is achieved in this example by taking a square of the acceleration information received from the first acceleration sensor at block 406. Thus, if the stream of acceleration information from the first sensor is designated x ₁ (k) wherein x is a function of samples, k, then block 406 calculates x ₁ ² (k) . Similarly, the controller 101 is configured to take the square of the acceleration information received from the second acceleration sensor at block 407. Thus, if the stream of acceleration information from the second sensor is designated x ₂ (k) wherein x is a function of samples, k, then block 407 calculates x ₂ ² (k) . A combiner 408 then combines the data streams from

blocks

406 and 407, thereby effectively adding the time-aligned samples together. A square root of the combined acceleration information may then be taken at block 409. The block 409 is optional and in other examples it may not be necessary. In other examples the “square” blocks 406 and 407 are optional and instead the magnitude of the acceleration information may be determined by blocks 406, 507, which is summed at block 408.

Block 405 may further include a first filter 410 and a second filter 411 configured to filter the acceleration information received from the first acceleration sensor and the acceleration information received from the second acceleration sensor respectively, prior to

blocks

406 and 407. The first filter 410 and second filter 411 may comprise notch filters configured to remove from the acceleration information signals or samples that occur at a resonant frequency of the tower 102. It has been found that removal of the tower’s resonant frequency may lead to improved detection of above-threshold changes of wind direction detection, in one or more examples. Without wishing to be bound by theory, it is perhaps because the tower resonant frequency can dominate the acceleration information in terms of its magnitude and thus the acceleration information without signals in said tower resonant frequency band are more representative of the occurrence of an above-threshold change of wind direction. The resonant frequency of the tower 102 may be predetermined information provided to the controller 101 or obtained during a installation or calibration procedure. Accordingly, the

notch filters

410 and 411 may be tuned accordingly.

Thus, to summarise, the controller 101, may be configured to filter the acceleration information from the one or more acceleration sensors to remove signals thereof that are present at or in a band centred on a resonant frequency of the tower 102 of the wind turbine 100. Further or alternately, in examples where the acceleration information is received from a plurality of acceleration sensors, the controller 101 may be configured to additively combine the square of the acceleration information from the plurality of acceleration sensors and the determination of the in-band-acceleration information (and optionally the baseline acceleration information) may be based on the combined acceleration information.

While figure 4 shows the acceleration information being combined in blocks 406-408 it will be appreciated that in other examples the processing of

blocks

401 and 402 could be performed in parallel on the acceleration information from the separate sensors received at

inputs

201 and 202 and a combination of the processed data could be used to determine the occurrence of at least a change in wind direction above a threshold level later in the process (not shown in the figures) .

The “in-band-acceleration” block 401 receives the acceleration information, which may comprise, as in this example, a combination of acceleration information from a plurality of sensors, at 420. In general, the block 401 represents the controller 101 being configured to determine in-band-acceleration information by application of at least one

filter

421, 422 to the acceleration information. The one or

more filters

421, 422 are, in this example, band-pass filters to obtain acceleration information that is in a predetermined frequency band. In the example of figure 4, two

filters

421, 422 are used such that the in-band-acceleration information is indicative of the acceleration experienced by the tower at frequencies within two different predetermined frequency bands. It will be appreciated that in other examples the in-band-acceleration information may comprise data in a single predetermined frequency band or one or more predetermined frequency bands or two or more predetermined frequency bands. In some examples, low pass or high pass filters may be acceptable to extract the desired tones.

It has been found by the inventors that focussing on the 1P, 2P, 3P, 4P or 6P excitation frequency of said wind turbine, wherein P represents the rotational speed of the rotor of the wind turbine, can be used as an effective indicator of the occurrence of an above-threshold change in wind direction. In particular, in the case of the acceleration information being indicative of acceleration along a single axis, the controller may be configured to focus on the 1P and 3P excitation frequencies, which may provide for effective indicators of the occurrence of an above-threshold change in wind direction. In the case of the acceleration information being indicative of acceleration along two axes, the controller may be configured to focus on one or more of the 2P, 4P and 6P excitation frequencies, which may provide for effective indicators of the occurrence of an above-threshold change in wind direction.

In the example of Figure 4, the first band-pass filter 421 is centred on the 2P excitation frequency. Accordingly, the first band-pass filter may comprise a dynamic or tuneable band-pass filter such that the controller, which receives the rotation speed information at input 204, may control the first band-pass filter 421 to set the predetermined frequency band to include the 2P excitation frequency, such as centred on the 2P excitation frequency.

In the example of Figure 4, the second band-pass filter 422 is centred on the 4P excitation frequency. Accordingly, the second band-pass filter may comprise a dynamic or tuneable band-pass filter such that the controller, which receives the rotation speed information at input 204, may control the second band-pass filter 422 to set the predetermined frequency band to include the 4P excitation frequency, such as centred on the 4P excitation frequency. In other examples, the band-

pass filters

421, 422 may not be tuneable and may instead have a pass band that is pre-set to include said 2P, 4P or any other predetermined excitation frequency at a range of rotation speeds that it is desired for the controller to detect rapid change in wind direction events.

Thus, the in-band-acceleration information comprises a first component frequency band comprising said predetermined frequency band that includes the 2P excitation frequency and a second component frequency band comprising a predetermined frequency band that includes the 4P excitation frequency.

In other examples the second band-pass filter 422 may be centred on or include the 6P excitation frequency rather than the 4P excitation frequency. In other examples, a third band-pass filter may be included in block 401 such that the in-band-acceleration information includes frequency bands that include the 2P, 4P and 6P excitation frequencies respectively. In other examples, a single band-pass filter 421 may be provided centred on or including the 2P excitation frequency.

The Q-factor of the one or more band-pass filters may be between 0.1 and 2. In other examples, the Q-factor may be between 0.5 and 1.5. The selection of the Q-factor may be configurable. It has been found that a reduced Q may reduce the detection time of an occurrence of an above-threshold change of direction but could, in some examples, increase false detections. However, an increased Q may increase detection times but reduce false detections. Accordingly, the selection of Q may be customizable such that an appropriate trade-off can be reached for whatever the environmental conditions at the site of the wind turbine 100.

In one or more examples, said

filter

421 or 422 may comprise a bandpass filter wherein the bandpass filter only allows frequencies in a predefined frequency band pass therethrough and frequencies outside of said predetermined frequencies are attenuated or excluded entirely. In one or more alternative examples, not shown in the figures, said

filter

421 or 422 may comprise a quadrature filter configured to provide said in-band-acceleration information at a 3P excitation frequency (for example) of said wind turbine, wherein P represents the rotational speed of the rotor of the wind turbine. A quadrature filter configured such has been found to be effective at removing the resonant frequency of the tower (such that

notch filters

410 and 411 may not be required) . A quadrature filter may provide for increased selectiveness, thus making it more resilient in efficiently extracting only desired frequencies or a single desired tone, i.e., nP, where n is an arbitrary multiple of the rotational frequency P. It will be appreciated that a quadrature filter may replace any of the band pass filters presented herein.

The block 401 may further include the controller being configured to determine the square of the in-band-acceleration information in the first predetermined frequency band, that is the 2P band in this example, at block 423. The block 401 may further include the controller being configured to determine the square of the in-band-acceleration information in the second predetermined frequency band, that is the 4P band in this example, at block 424. The

blocks

423 and 424 thereby determine a signal indicative of the energy of the in-band acceleration information. Accordingly, blocks 423 and 424 may be considered more generally as energy detectors with block 428 described below.

The controller 101 is configured to perform a comparison based on said in-band-acceleration information with baseline acceleration information. The comparison may comprise a function such that a function of the in-band-acceleration information is compared to a function of the baseline acceleration information. The square applied at

blocks

423 and 424 may be part of said function.

In this example, such a function of the in-band-acceleration information is implemented by application of different weightings comprising a first weight and a second weight to the in-band-acceleration information in the first component (2P) band relative to the second component (4P) band. The implementation of the different first and second weights may be implemented by

amplifiers

425 and 426. The weightings may be implemented by virtue of the

amplifiers

425 and 426 being configured to apply different gains, K ₁ and K ₂, by the

amplifiers

425 and 426 respectively.

The first weight and second weight are configurable in this example and may be set when the controller 101 is installed in the wind turbine 100.

The weighted in-band-acceleration information in the first component (2P) band is combined with the weighted in-band-acceleration information in the second component (4P) band by a combiner 427. Thus, the controller 101 may be configured to additively combine the in-band-acceleration information in the different component frequency bands.

As mentioned above, the controller 101 is configured to perform a comparison based on said in-band-acceleration information with baseline acceleration information at block 403. In this example the comparison is based on the energy content of the in-band-acceleration information and the energy content of the baseline acceleration information. In other examples, the amplitude of the respective acceleration may be compared but in this example it is the energy content. The determination of energy content will be known to those skilled in the art and it may require the controller being configured to integrate the in-band-acceleration information over a first time period and integrate the baseline acceleration information over a second time period.

For example, the energy in the 2P predetermined frequency band may be determined by the controller being configured to calculate E _2P, wherein

where x is the 2P frequency information from block 421 and Z is an example amplitude thereof. However, in this example, it has been found that an effective approximation of the definite integral used to calculate the energy content can be obtained by use of a low-pass filter 428. The low pass filter 428 has been found to yield information that is indicative of the energy content of the in-band-acceleration information in a first recent time period, wherein the first recent time period is a function of the rotational frequency of the rotor. For example, in simple case where the filtering time is not dynamic, the first recent time period may be on the order of a single revolution of the wind turbine which may be, for example, between 3 and 6 seconds. The output of the low-pass filter is provided to the block 403, which comprises the comparator at 429.

The controller 101, as mentioned above, is configured to receive rotational speed information indicative of the rotational speed of a rotor of the wind turbine. The controller may be configured to dynamically control a cut-off frequency of said low-pass filter 428 based on said rotational speed information. The cut-off frequency may thus comprise a function of the rotational speed such as B*1P frequency, where B=0.25. It will be appreciated that other values of B may be used.

Block 402 shows the determination of the baseline acceleration information upon which the comparison at the comparator 403 is based. In some examples, the baseline acceleration information is predetermined or static. Thus, in one or more examples (not shown) the baseline acceleration information is based on an average acceleration level experienced by the wind turbine obtained during a calibration procedure absent of an occurrence of said change in wind direction above the threshold level. It should be appreciated that following this approach may lead to an increase of false alarms as operating at different turbulence intensities leads to increased oscillations levels at 3P. Thus, the use of dynamic baseline acceleration information may be preferred.

In this example of figure 4, said baseline acceleration information comprises dynamic baseline acceleration information. Thus, the dynamic baseline acceleration information is based on the acceleration information received at

inputs

201 and 202 over a second recent time period, which is longer than the first recent time period described in relation to block 428.

The controller 201 is configured to apply a low-pass filter 430 to said acceleration information to obtain an approximated average of said acceleration information, wherein said dynamic baseline acceleration information is based on said approximated average of said acceleration information. The cut-off frequency of the low-pass filter 430 may be set to less than 0.1Hz or less than 0.05 Hz or less than 0.03 Hz. In one or more examples, the dynamic baseline acceleration information is effectively indicative of the DC level of the acceleration information.

The controller 101, as mentioned above, is configured to receive rotational speed information indicative of the rotational speed of the rotor of the wind turbine. The controller may be configured to dynamically control a cut-off frequency of said low-pass filter 430 based on said rotational speed information. The cut-off frequency of the low-pass filter 430 is thus set as a function of the rotational frequency of the rotor, such as less than 0.2P or less than 0.1P where P is the rotation speed of the rotor. Accordingly, the cut-off frequency may be around 0.005 to 0.03 Hz.

The controller 201 is configured to determine the square of the output from the low-pass filter 430 (i.e., that is the average of the DC component of the acceleration information) at block 431. It will be appreciated that the square at block 431 is used to compute the energy at approximately DC acceleration levels. The output from block 431 is provided to the comparator 403. The DC energy (E _DC) can be calculated by the controller by way of the following equation:

where Z is an example amplitude function over time, T is a time period over which the DC component or baseline is determined.

The low-pass filter 430 has been found to provide an effective approximation of the integral function used to compute the energy of said baseline acceleration information. It will be appreciated that, alternatively, the controller may be configured to calculate the energy content rather than approximate it by use of the low-pass filter 430.

It will also be appreciated that the low pass filter 430 is intended to establish an average or baseline acceleration level over a long time period. It can then be determined, by said comparator 403, whether the in-band-acceleration information as represented by the energy content over a short time period from filter 428 is indicative of above-threshold changes in wind direction. Accordingly, said low-pass filter 428 applied to the in-band-acceleration information may have a cut-off frequency at least one decade or at least half a decade greater than the cut-off frequency of the low-pass filter 430 applied to the baseline acceleration information. This difference in cut-off frequency implements the averaging over the long and short time period. However, it will be appreciated that, in general, the averaging provided by block 430 may be over a longer time period than the averaging provided by block 428.

Accordingly, in this example, the comparator 403, implemented by the controller 101, is configured to perform a comparison of the energy content of said in-band-acceleration information with the energy content of the baseline acceleration information (or at least an effective approximation thereof) .

If the energy content of said in-band-acceleration information (weighted by 425 and 426) is greater than the energy content of the baseline acceleration information, then the comparator 403 provides an output indicative of the occurrence of at least a change in wind direction above a threshold level at output 432. If the energy content of said in-band-acceleration information is less than the energy content of the baseline acceleration information, then the comparator 403 provides an output indicative of the non-occurrence of at least a change in wind direction above a threshold level at output 432.

As described above in relation to figure 3, blocks 303 and 306, the controller may be configured to, based on the determination of the occurrence of at least the change in wind direction above the threshold level, provide one or more control signals to invoke a control action comprising one or both of:

control of the pitch of one or more blades 108 of the wind turbine 100; and

control of a torque applied to the rotor 103 by a generator 104 of the wind turbine 100.

The control action may be configured to shut down the wind turbine, as shown at block 306.

In the example of Figure 4 however, there is an additional, optional, condition to be met before there is a determination of the occurrence of at least a change in wind direction above a threshold level. Functional block 404 comprises a logic AND gate and receives the output 432 from the comparator 403. In order for the AND gate to output the determination of the occurrence of at least a change in wind direction above a threshold level, its second input 433 must also be true.

The controller 101 is configured to receive wind speed information at input 203 from the wind speed sensor configured to measure the current wind speed experienced by the wind turbine 100. The controller 101 is configured to apply a low-pass filter to said wind speed information at 434. This effectively determines the average wind speed in a recent time period. The controller then implements a comparator 435 to determine if the wind speed information or average thereof is above a threshold wind speed. The threshold wind speed may be at least 6 m/s. Thus, the determination of the occurrence of at least a change in wind direction above a threshold level is additionally based on said wind speed information being indicative of a wind speed above a threshold wind speed, which is provided at 433 when the comparator 435 determines that the average wind speed information from the low pass filter 434 is greater than the threshold wind speed.

Thus, in the embodiment of example figure 4, the controller 101 determines the occurrence of at least a change in wind direction above a threshold level without information from a wind vane or ultrasonic wind sensor mounted on the wind turbine to determine wind direction. Thus, rotor speed information and wind speed information may be used to control the settings of the various filters, but the determination of the occurrence of change in wind direction above a threshold level is based on said acceleration information. This is advantages because it has been found that a determination of the occurrence of change in wind direction above a threshold level can be made more quickly using acceleration information, which can be critical in the effective control of the wind turbine. Thus, by being able to make a mitigating control action sooner, the wind turbine 100 can be operated more effectively.

Figure 5 shows an alternative embodiment. Many of the functional blocks are the same as the example figure 4 and the same reference numerals have been used where this is the case.

The acceleration information receipt and processing block 405 is replaced with block 505. In this second example, block 505 performs the functions of squaring

blocks

406, 407 and combiner 408 and square root block 409, but does not include said

notch filters

410, 411.

In the “in-band-acceleration” block 501 of figure 5, the in-band-acceleration information comprises data in a single predetermined excitation frequency band, namely including the 3P excitation frequency. Thus, the block 501 comprises a band-pass filter block 521 centred on or including the 3P excitation frequency.

Rather than low pass filter 428 and amplifier 425, the controller of the example of figure 5 is configured to determine a moving average of said in-band-acceleration information. The moving average may be an average over the most recent 3 –5 seconds, although other recent time periods may be used. The moving average calculation performed at block 540 may be expressed as follows:

wherein

Wherein 1/1P is the time required for one rotor revolution; Ts is the sampling time of the controller or the sample time used to provide the acceleration information; and m is the number of rotor revolutions over which the average is taken. Thus, N is the number of samples over which the moving average is taken.

Further, considering the baseline acceleration information block 502 (comparable to 402 in the example of Figure 4) , the low pass filter 430 is replaced with a block 541 which is configured to determine a moving average of the acceleration information as the baseline acceleration information. The moving average calculation performed at block 541 may be expressed as follows:

wherein

Wherein 1/1P is the time required for one rotor revolution; T _s is the sampling time of the controller used to sample the incoming acceleration information or the sample time used to provide a stream of digital samples that comprise the acceleration information; and t is the number of rotor revolutions over which the average is taken. Thus, T is the number of samples over which the moving average is taken.

The moving average calculation for the baseline acceleration information is performed over a longer time period than the moving average calculation for said in-band-acceleration information. That is, T is significantly greater than N (T >> N)

Otherwise, the operation of the example of figure 5 is the same as that described for example figure 4.

In one or more examples, the present controller has been found to effectively provide an indication of a rapid change in wind direction. In some examples, this is achieved more quickly than other prior methods.

It may be advantageous for the controller 101 not only to output the occurrence of at least a change in wind direction above a threshold level. In some examples, the control action (s) that may be initiated in response to occurrence of at least a change in wind direction above a threshold level may depend on the direction from which the wind is incident on the wind turbine following the rapid change. Accordingly, the controller may be configured to advantageously “launch” control actions based on an output of (a) the occurrence of at least a change in wind direction above a threshold level and (b) the new wind direction.

The controller may be configured to determine said new wind direction based on the acceleration information. The example graph of Figure 7 shows two

traces

701 and 702 of acceleration information derived from an acceleration sensor configured to measure the side-to-side acceleration the tower is subjected to relative to a long-term average. It will be appreciated by those skilled in the art that a long-term average of the acceleration information provides a reference point because it can be assumed that over the long term the tower will be subject to acceleration in all directions and an average of this acceleration information will be indicative of a neutral tower acceleration. In other examples the controller may be configured to use a reference point determined in a different way, such as from position sensors determining a neutral position of the tower. Trace 1201 shows the acceleration information relative to the average acceleration information when the wind direction is from the first side. Trace 1202 shows the acceleration information relative to the average acceleration information when the wind direction is from the second side. It can be readily appreciated that there is a strong correlation between the sign of the acceleration information relative to the average acceleration information. It has been found that there are several effective methods that may be used to derive the wind direction from the acceleration information. Thus, in summary and in one or more examples, we provide a controller configured to determine a side of the wind turbine upon which the wind is incident based on acceleration information indicative of the side-to-side acceleration experienced by the wind turbine. In a first example, the controller may be configured to low pass filter the acceleration information at a frequency lower than the resonant frequency of the tower (e.g., less than 0.5 of the resonant frequency of the tower) and integrate the acceleration information over time and then further integrate the result over time to obtain a displacement. The displacement may be compared to a reference point derived from averaging of the acceleration information or from information from other sensors. The direction of the displacement has been found to be indicative of the wind direction as the force of the wind against the wind turbine displaces it in the direction of the wind flow. In other examples, rather than a low-pass filter, a notch filter tuned to the resonant frequency of the tower may be used. In a further example, the controller may be configured to provide the tower side-to-side acceleration information to a cumulative sum block, such that the input to the block is long-term de-trended to provide the reference point. The cumulative sum block may be configured to provide the CUSUM (or cumulative sum control chart) sequential analysis technique. Such a cumulative sum block may be used to determine if the current acceleration information is positive or negative and thereby from which side of the wind turbine the wind is incident, while being robust to noise. Thus, whichever technique is used the controller may determine an indication of displacement from the acceleration information and derive the side of the tower from which the wind is incident therefrom.

In one or more examples and with reference to figure 2, we provide a controller 101 for a wind turbine 100 in combination with one or

more acceleration sensors

207, 208 the controller configured to detect rapid changes in wind direction based on acceleration information from said one or

more acceleration sensors

207, 208.

In one or more examples and with reference to figure 1 and figure 2, we provide a wind turbine 100 in combination with the controller 101.

Figure 6 shows an example method. The method comprises:

receiving 601 acceleration information from one or more acceleration sensors, the acceleration information indicative of the acceleration experienced by a tower of the wind turbine;

determining 602 in-band-acceleration information by application of at least one filter to the acceleration information, the at least one filter configured to filter at a predetermined frequency band, and wherein said in-band-acceleration information is indicative of the acceleration experienced by the tower at frequencies within said predetermined frequency band;

performing 603 a comparison based on said in-band-acceleration information with baseline acceleration information, wherein the baseline acceleration information is indicative of an average acceleration level experienced by the wind turbine; and

determining 604 an occurrence of at least a change in wind direction above a threshold level based on said comparison of the in-band-acceleration information to the baseline acceleration information.

Figure 8 shows a computer program product 800 comprising computer program code for implementing the method of figure 6. The computer program product 800 may comprise a USB mass storage device or other media for use in updating software or firmware of a controller 101 of a wind turbine 100.

Claims

A controller for a wind turbine configured to:

receive acceleration information, the acceleration information indicative of the acceleration experienced by a one or both of a tower and a nacelle of the wind turbine;

determine in-band-acceleration information by application of at least one filter to the acceleration information, the at least one filter configured to filter at a predetermined frequency band, and wherein said in-band-acceleration information is indicative of the acceleration experienced by the tower at frequencies within said predetermined frequency band;

perform a comparison based on said in-band-acceleration information with baseline acceleration information, wherein the baseline acceleration information is indicative of an average acceleration level experienced by the wind turbine;

determine an occurrence of at least a change in wind direction above a threshold level based on said comparison of the in-band-acceleration information to the baseline acceleration information.
The controller of claim 1, wherein said controller is configured to, based on the determination of the occurrence of at least the change in wind direction above the threshold level, provide one or more control signals to invoke a control action comprising one or both of:

control of the pitch of one or more blades of the wind turbine; and

control of a torque applied to the rotor by a generator of the wind turbine.
The controller of claim 1 or 2, wherein said at least one filter comprises a band-pass filter or a quadrature filter and wherein said predetermined frequency band of the band-pass filter or quadrature filter includes one of a 1P, 2P, 3P, 4P, 6P or 9P excitation frequency of said wind turbine, wherein P represents the rotational speed of the rotor of the wind turbine.
The controller of claim 1 or 2, wherein said filter comprises one of a quadrature filter and a bandpass filter, wherein the quadrature filter or bandpass filter is configured to provide said in-band-acceleration information at a 3P excitation frequency of said wind turbine, wherein P represents the rotational speed of the rotor of the wind turbine.
The controller of any preceding claim, wherein said baseline acceleration information comprises a dynamic baseline acceleration information, wherein said controller is configured to apply a low-pass filter to said acceleration information to obtain an approximated average of said acceleration information, wherein said dynamic baseline acceleration information is based on said approximated average of said acceleration information.
The controller of any preceding claim, wherein said controller is configured to determine a current wind direction following said change in wind direction above a threshold level based on said acceleration information, wherein an indication of displacement of one or both of the tower and nacelle is derived from said acceleration information and the current wind direction is based thereon.
The controller of any preceding claim, wherein said acceleration information is received from at least one acceleration sensor configured to provide acceleration information indicative of an acceleration along a fore-aft direction of said tower.
The controller of any preceding claim, wherein said acceleration information is received from two or more acceleration sensors configured to provide acceleration information indicative of an acceleration along a fore-aft direction of said tower and a side-to-side direction of said tower.
The controller of any preceding claim, wherein said controller being configured to perform a comparison comprises comparing an energy of said in-band-acceleration information with an energy of said baseline acceleration information, wherein said energy of said in-band-acceleration information is approximated by the controller being configured to apply a low-pass filter to said in-band-acceleration information, and wherein said energy of said baseline acceleration information is approximated by said controller being configured to apply a low-pass filter to said baseline acceleration information.
The controller of claim 9, wherein said controller is configured to receive rotational speed information from a sensor indicative of the rotational speed of a rotor of the wind turbine, and wherein the controller is configured to dynamically control a cut-off frequency of said low-pass filter based on said rotational speed information.
The controller of claim 9 or claim 10, wherein said low-pass filter applied to the in-band-acceleration information has a cut-off frequency at least one decade greater than the cut-off frequency of the low-pass filter applied to the baseline acceleration information.
The controller of any preceding claim, wherein said determination of the in-band-acceleration information by application of the at least one filter to the acceleration information comprises filtering such that said predetermined frequency band includes the 2P excitation frequency of said wind turbine, wherein P represents the rotational speed of the rotor of the wind turbine.
The controller of claim 12, wherein said in-band-acceleration information comprises a first component frequency band comprising said predetermined frequency band that includes the 2P excitation frequency and a second component frequency band, wherein determination of the second component frequency band of the in-band-acceleration information comprises the controller being configured to apply a filter to said acceleration information at a second predetermined frequency band that includes the 4P and/or 6P excitation frequency of said wind turbine, wherein P represents the rotational speed of the rotor of the wind turbine.
The controller of claim 13, wherein the controller being configured to determine the in-band-acceleration information includes application of a first weight to the acceleration information in the first component frequency band and application of a second weight to the acceleration information in the second component frequency band, wherein said first weight and second weight are configurable.
The controller of any preceding claim wherein said controller is configured to receive wind speed information from a wind speed sensor configured to measure the current wind speed experienced by the wind turbine, and wherein determination of the occurrence of at least a change in wind direction above a threshold level is additionally based on said wind speed information being indicative of a wind speed above a threshold wind speed.
A wind turbine including the controller of any preceding claim.
A method for a wind turbine, the method comprising:

receiving acceleration information from one or more acceleration sensors, the acceleration information indicative of the acceleration experienced by a one or both of a tower and a nacelle of the wind turbine;

determining in-band-acceleration information by application of at least one filter to the acceleration information, the at least one filter configured to filter at a predetermined frequency band, and wherein said in-band-acceleration information is indicative of the acceleration experienced by the tower at frequencies within said predetermined frequency band;

performing a comparison based on said in-band-acceleration information with baseline acceleration information, wherein the baseline acceleration information is indicative of an average acceleration level experienced by the wind turbine;

determining an occurrence of at least a change in wind direction above a threshold level based on said comparison of the in-band-acceleration information to the baseline acceleration information.
A computer program or a computer program product comprising computer program code configured to cause a processor and memory to perform the method of claim 17.