DK201400518A1

DK201400518A1 - Wind turbine blade sensor device

Info

Publication number: DK201400518A1
Application number: DK201400518A
Authority: DK
Inventors: Knud Møller Andersen
Original assignee: Wind Solutions As Kk
Priority date: 2014-09-11
Filing date: 2014-09-11
Publication date: 2015-08-24

Abstract

The invention relates to a wind turbine blade sensor device which facilitates generation of information representing blade orientation wherein the blade sensor device comprising one or more sensors having in total at least three axis and wherein the blade sensor device is mounted on a rotatable blade component.

Description

Wind turbine blade sensor device

Field of the invention

The invention relates to a wind turbine blade sensor device and a method of generating information related to blade orientation.

Background of the invention

It is possible to adjust rotor speed of most modern wind turbines by pitching the blades of the wind turbine i.e. rotate the blades along a longitudinal axis of the blade. It is known to establish e.g. the pitch angle of a blade by means of e.g. an encoder or information from the pitch actuator. US patent application US2012139248 discloses a control system controlling the yaw of the nacelle of the wind turbine. This control system also includes pitch control where blade angle sensors are used to detect the blade angles. US patent US7972112 discloses to determine rotor blade position based on angular position of the wind turbine rotor which may be determined by measuring the tangential and radial acceleration at one or more locations on the rotor and by measuring the speed of the rotor.

Brief description of the invention

It is an object of the invention by means of a wind turbine blade sensor device to facilitate generation of information representing blade orientation wherein the blade sensor device comprising one or more sensors having in total at least three axis and wherein the blade sensor device is mounted on a rotatable blade component.

It is advantageous to be able to measure along three axis in that then information based on which it is possible to determine blade orientation is provided. The one or more sensors could be implemented as single or multi-axis sensors. Hence one three-axis sensor, three one axis sensors, two two-axis sensors multi-axis sensors having more than three axis, etc. could be used in order to obtain measurements along the three axis. A blade sensor device or at least the sensor(s) of the blade sensor device is advantageously rotatable mounted on a blade component such as the blade itself, joint between blade and hub, pitch actuator or other components rotating with the blade. In this way it is ensured that when the blade rotates along its longitudinal axis (i.e. is pitchedjthe blade sensor device or sensor(s) hereof are also rotating and thereby providing information based on which blade orientation could be determined.

Rotatable mounted on a blade component or mounted on a rotatable blade component is two ways of saying that the blade sensor device is mounted so as to rotate with the blade when the blade is rotated in its longitudinal direction i.e. when the blade is pitched and following the blade as the blade rotates in the rotor plane. Such rotation of the blade sensor device displaces the blade sensor device and sensors hereof e.g. in relation to gravity and this displacement is used to determine blade orientation.

In an embodiment of the invention the blade sensor device comprising a multi-axis sensor having at least three axis and wherein the blade sensor device is positioned in the root end of the interior of the blade.

Examples of information representing blade orientation could be acceleration or speed of movement of the blade sensor device and thereby of the blade. Further examples could be rotational position of the blade sensor device in relation to the earth gravity also simply referred to as gravity, etc.

The preferred examples of blade orientation are blade pitch angle and blade azimuth angle.

The blade azimuth angle is defined as the position of the blades in the rotor plane with reference to a predetermined reference point. The predetermined reference point could e.g. be when a blade referred to as blade A is in a vertical position. The position of the other blades e.g. blades B and C is then determined with reference to this predetermined reference point.

The blade pitch is defined as the rotation of a wind turbine blade around the longitudinal axis of the blade. The pitch angle is defining the angle of the blade with respect to the rotor plane typically in the range between 0° and 90°. Typically, when the pitch angle is 0° the blade is in line with the rotor plane and perpendicular to the direction of the wind and when the pitch angle is 90° the blade is in line with the direction of the wind and perpendicular to the rotor plane. Minimum rotor speed (also sometimes referred to as stop or idle) is obtained when the blades are positioned in a pitch angle of or close to 90°.

Preferably each blade have one blade sensor device in that it is then possible to generate information representing blade orientation for each blade.

Preferably the multi-axis sensor is a MEMS type sensor or the individual parts together referred to as multi-axis sensor are of the MEMS type. A multi-axis sensor having three axis of accelerometer measurements may be able to provide information from a plurality of different locations of the blade in the rotor plane from which e.g. pitch angle and / or azimuth angle can be calculate or estimated.

Preferably the three axis is a mix of accelerometer and gyroscopic which may provide information from all locations of the blade in the rotor plane based on which e.g. pitch angle and / or azimuth angle can be calculate or estimated.

In an embodiment of the invention, the multi-axis sensor includes at least one accelerometer. Advantageously the multi-axis sensor comprises at least one accelerometer having three axis. Alternatively other accelerometer configurations ending up with measurements in three dimensions could also be used.

Having an accelerometer with three axis facilitates measurements along both the x, y and z axis thereby facilitating measurement both in-plane and out-of-plane also referred to as radial and tangential acceleration.

In an embodiment of the invention, the blade sensor device comprises at least one accelerometer and at least one gyroscope. Advantageously the gyroscope as well as the accelerometer comprises at least three axis together forming a multi-axis sensor having six axis. As with the accelerometer the gyroscopic axis could be obtained from one or more gyroscopes.

By adding gyroscopic measurements to the blade sensor device or preferably to the multi-axis sensor it becomes possible to obtain information of the orientation of the blade sensor device. This, together with information of acceleration from an accelerometer, makes it possible to calculate blade orientation as will be described below.

Preferably the six axis multi-axis sensor comprising both gyroscope and accelerometers are one device but the multi-axis sensor could also be implemented as a plurality of accelerometers and gyroscopes.

Preferably the multi-axis sensor is of a MEMS type.

In an embodiment of the invention, the blade sensor device facilitates generation of information while the wind turbine is in a power producing mode. By generating information while producing power, the information is provided real-time while force from the wind is acting on the blade and thereby any calculation of blade orientation are made with loaded blade.

In an embodiment of the invention, the blade sensor device is supplemented by a second sensor facilitating generation of information representing at least partly the same blade orientation information as the blade sensor device. This is advantageous in that such redundant sensor system minimizes the risk of missing information relating to blade orientation.

The wind turbine blade sensor and the second sensor are physically separated units preferably based on different measurement principles. The second sensor could be part of the pitch actuator set located in the hub or another separate hardware or software unit located in the hub. It could be implemented as an encoder or pitch actuator position determine means based e.g. on measurement of position of a hydraulic piston or revolutions of an electric motor.

In an embodiment of the invention, the information facilitates calculation of blade pitch angle and/or blade azimuth angle. The information facilitated by the blade sensor device is advantageously used to calculate the blade pitch angle which then could be used by a controller of the wind turbine to verify that the actual pitch angle is the same as the pitch angle reference provided by the controller of the wind turbine to the pitch actuator set. In case of difference, the controller then may facilitate correction of the pitch angle reference and in this way an adaptive pitch angle control may be created.

Alternatively blade orientation such as pitch angle calculated based on information from the blade sensor device is used to verify pitch angle measured or calculated based on information from a second sensor.

The blade pitch angle may be calculated by a data processor of the blade sensor device or a data processor located external to the blade sensor device in this case preferably in the hub, nacelle or tower. Such external data processor device could e.g. be a data processor of a main or sub controller of the wind turbine.

In an embodiment of the invention, the blade sensor device comprises a data processor, wherein the data processor facilitates calculation of the blade pitch angle of the blade at which the blade sensor device is positioned based on information provided by the multi-axis sensor. Preferably the calculation of pitch angle is a realtime calculation. Real-time is understood as the measurements from the multi-axis sensor are used to calculate the pitch angle continuously as the blade is pitched and/or as the blade rotates in the rotor plane.

In an embodiment of the invention, calculation of the pitch angle is made at least once per rotation of the blade in the rotor plane. The present invention facilitates that e.g. the pitch angle is calculated above 100 times per rotation of a blade in the rotor plane. If relevant, calculations could be done more than 300 times per blade revolution.

In case the pitch angle should be used in controlling the blade e.g. to avoid the blade striking the tower, it is advantageous that the calculation of the pitch angle is initiated in time for the control system and the pitch actuator to be able to react and avoid such collision. Therefore the calculation should not be initiated after the blade has passed the position in which the blade is in a horizontal position. 90° should be understood as the position of the blade when the blade is in a horizontal position.

The result of the calculation may be compare to the actual pitch angle of the blade (e.g. in the form of the pitch reference sent from the pitch controller to the pitch actuator). I case the comparison indicates differences or risk of blade striking the tower the pitch angle of the blade is changed.

In an embodiment of the invention, the blade sensor device is positioned at a distance between 0 and 200 centimeters from the root of the wind turbine blade, preferably between 0 and 100 centimeters, most preferably between 0 and 50 centimeters. This is advantage in that requirements for protecting against lightning currents are reduced. Hence the optimal location of the blade sensor device is as close to the connection between the blade and the hub (also referred to as joint) as is technically and physically possible. This is because requirements to lightning protection may then be reduced and because this may reduce risk of damage of the blade sensor device from current induced if lightning strikes a blade.

In an embodiment of the invention, information from the blade sensor device facilitates validation of the pitch angle determined from the second pitch angle determine device. The second pitch angle determine device could e.g. be an encoder, similar senor as the blade sensor device, the second pitch angle sensor device may be implemented as a software application or as a hardware device e.g. as part of a pitch actuator set.

In an embodiment of the invention, the information from the blade sensor device is provided as input to a wind turbine controller. The wind turbine controller may be the main controller also referred to as wind turbine controller or a sub controller also referred to as pitch controller. The pitch angle may be calculated based in information generated from either the blade sensor device or the second sensor. A pitch actuator set which is pitching the blades could e.g. be a hydraulic system or en electric system facilitating pitch of the wind turbine blade.

In an embodiment of the invention, the blade sensor device is used for safety monitoring of the pitch angle. In relation to this invention safety may be obtained by having a redundant pitch angle measuring system including the blades sensor device. This is advantageous in that with a redundant system as describe it is possible to comply with industrial safety requirements such as ISO 13849-1:2006 safety of machinery

In an embodiment of the invention, information represents a change of position of the blade sensor device in time. Preferably information generated by the blade sensor device is time stamped. Hence from a comparison of information of a first position of the blade sensor device and from a second position of the same blade sensor device correlated with time of the measurements orientation, direction of movement, etc. could be calculated whereby information of rotor speed is obtained.

Because of the location of the blade sensor device in the blade, the location of the blade relative to gravity is indirectly part of the information generated by the blade sensor device.

Moreover the invention relates to a method of determining information representing blade orientation of a wind turbine blade, the method comprising the steps of: generating information representing blade orientation of a blade by means of one or more sensors having a total of three axis wherein the one or more sensors is rotating with the blade, and calculating blade orientation of the blade by means of a data processor based on information from the one or more sensors.

Rotation is understood both as rotation of the blade in the rotor plane and when the blade rotates around its longitudinal axis i.e. is pitching.

In an embodiment of the invention, the method further comprises calibrating the one or more sensors. Calibration is preferably done in relation to earth gravity.

Calibration may be relevant to ensure knowledge of the blade sensor device or sensors after they have been mounted. Furthermore it is advantage to perform realtime calibration to avoid measurements from the sensors especially the gyroscope sensor are drifting in time i.e. measurements becoming a bit inaccurate e.g. relative to earth gravity each time a blade have performed one rotation in the rotor planed.

In an embodiment of the invention, the one or more sensors is a multi-axis sensor having at least three axis and where in the multi-axis sensor is located in the root end of the blade.

Moreover the invention relates to a method of determining information representing blade orientation of a wind turbine blade during rotation of the blade in a rotor plane, the method comprising the steps of: by means of a multi-axis sensor located in the blade generating information representing blade orientation of a first blade, and calculating blade orientation of the first blade. This is advantages in that during rotation it is possible to calculate blade orientation i.e. real-time blade orientation is available. It should be mentioned that the calculation may be done either continuously or dis-continuously.

Preferably each of the blades of the wind turbine comprises a blade sensor device comprising a multi-axis sensor or at least a solely multi-axis sensor. Preferably the blade sensor device comprises a data processor or data processing means facilitating calculating of the blade orientation.

In an embodiment of the invention, the method further comprises the following calibration step which is performed real-time: calibrating the multi-axis sensor of the first blade according to earth gravity. The calibration may be done in a plurality of locations of the blade in the rotor plane as the blade rotates in the rotor plane therefore the calibration step is referred to as performed real-time.

Preferably the calibration steps are performed before the multi-axis sensor starts to generate information which is used to derive the blade orientation, in control or safety control.

The method may include the calibration steps at predefined time intervals, predefined number of resolutions of the blade in the rotor plane, etc.

It is advantageously if each of the steps mentioned above is carried out for each of the blades of the wind turbine.

In an embodiment of the invention, the blade orientation is pitch angle and/or azimuth angle.

In an embodiment of the invention, the multi-axis sensor is supplemented by a second sensor also generating information representing blade orientation.

In an embodiment of the invention, the multi-axis sensor is positioned at a distance between 0 and 200 centimetres from the root of the wind turbine blade, preferably between 0 and 100 centimetres, most preferably between 0 and 50 centimetres.

In an embodiment of the invention, the multi-axis sensor preferably comprises 3 accelerometers and 3 gyroscopes.

In an embodiment of the invention, the multi-axis sensor is part of a blade sensor device, wherein the blade sensor device facilitates continuously calculation of the pitch angle.

It is advantageous if the blade sensor device calculates the pitch angle of the blade to which it belongs. Further it might be advantageous to have an additional second sensor or pitch angle determine unit per blade in order to make the calculation of the pitch angle redundant.

It case the blade sensor device is calculating the pitch angle, the blade sensor device is preferably equipped with a data processor. Alternatively information from the multi-axis is communicated to a wind turbine controller.

In an embodiment of the invention, the multi-axis sensor is calibrated when the wind turbine is in a non-power producing mode. This is advantageous in that there is sufficient time to calibrate in that no production is lost e.g. this could be in situation with low wind.

In an embodiment of the invention, calibration of the multi-axis sensor is done when the blade in which the multi-axis sensor is positioned is perpendicular or parallel to the earth gravity. Preferably the calibration is done when the blade is in a substantial horizontal orientation. In the horizontal position one force (earth gravity) is known and based on this information it is possible to calibrate the multi-axis sensor and use information from the multi-axis sensor to calculate e.g. pitch angle.

Figures A few exemplary embodiments of the invention will be described in more detail in the following with reference to the figures, of which fig. 1 illustrates a wind turbine according to an embodiment of the invention, fig. 2 illustrates part of a blade and hub of a wind turbine, and fig. 3 illustrates steps of a method according to the invention.

Detailed description of the invention

Fig. 1 illustrates an electrical power generating system in the form of a variable speed wind turbine 1 according to an embodiment of the invention. The wind turbine 1 comprises a tower 2, a nacelle 3, a hub 4 and two or more blades 5. The blades 5 of the wind turbine 1 are rotatably mounted on the hub 4, together with which they are referred to as the rotor. The rotation of a blade 5 along its longitudinal axial is referred to as pitch. The wind turbine 1 is controlled by a control system comprising a wind turbine controller 6, sub controllers 7 for controlling different parts of the wind turbine 1 and communication lines 8.

The wind turbine 1 further comprises a generator 9 and a power converter 10. The generator 9 transforms rotational energy from the rotor into electrical energy and the power converter 10 “shapes” the electrical energy from the generator 9 into a form, which complies with grid codes of the utility grid. The electrical energy may be transported from the generator 9 to the converter 10 and further to the utility grid 16 via high voltage cables 11.

Fig. 2 illustrates part of a rotor in the form of one wind turbine blade 5 which is connected to the hub 4 at a joint 14. In the blade 5 a blade sensor device 12 according to the invention is located. The blade sensor device 12 comprises a multi-axis sensor 13 preferably having at least three axis x, y, z. The blade sensor device 13 is located in the root end of the blade 5. The location in the blade as close to the joint 14 between the blade 5 and the hub 4 is preferred in that the closer to the hub 4 the blade sensor device 12 is located the less problems with lightning currents are expected. This is due to the less or shorter cables necessary in the blade 5 which lightning currents in case a lightning strike the blade could damage.

At Fig. 2 the blade sensor device 12 is located a distance R from the joint 14. The distance R is as mentioned preferably short and as close to the root end of the blade 5 as technically and physically possible. Since the purpose of the blade sensor device 12 is obtaining information of blade orientation and not e.g. blade stress or vibrations a location close to the root of the blade is advantages. Examples of suitable values of R could be less than 200 centimetres from the joint 14 preferably between 50 and 100 centimetres or even below.

It should be mentioned that the blade sensor device 12 is fully functional at distances of R exceeding 200 centimetres, but as mentioned then it is more exposed to damage from lightning currents. Furthermore the longer distance R the more naturally occurring physical impact is present in form e.g. twist and bending of the blade.

Further it should be mentioned that the blade sensor device 12 or sensor(s) 13 hereof could also be located at a blade components 17 which are physically located inside the hub 4. As examples of blade components rotating with the blade 5 could be mentioned part of the pitch actuator 18 such as an axis, a motor, piston etc. Only requirement to a location in the hub 4 is that the blade sensor device 12 or sensor(s) hereof 13 have to be mounted on a blade component 17 so as to rotate with the blade 5 when the blade 5 is pitched.

In the simplest embodiment, the blade sensor device 12 comprises only the multiaxis sensor 13 which communicates with a wind turbine control 6 or a sub-controller 7 located e.g. in the hub 4 of the wind turbine 1. Such communication is preferably through communication lines 8 cable, fiber or wireless. In addition the blade sensor device 12 is preferably supplied by power from a power supply cable 19 from a power source e.g. in the hub (not illustrated). The supply from a cable is preferred in that the blade sensor device 12 preferably comprises a multi-axis sensor 13, data processor 15 and also other power consuming elements may be located at the blade sensor device 12. Therefore supplying the blade sensor device 12 solely from e.g. batteries charged by solar cells or energy generated from movements of a charging device is not sufficient.

The power supply cable 19 and data communication cable 8 are vulnerable to lightning current, but is preferably protection against such by galvanic separation of the power supply interface of the of the blade sensor device 12 from the rest of the components of the blade sensor device 12. The data communication cable could be of an optical type to make it less vulnerable to lightning currents.

In other embodiments additional data processing means 15 could also be part of the blade sensor device 12. Hence the blade sensor device 12 is defined as a device comprising at least the multi-axis sensor 13 which as part of the blade sensor device 12 could be one of a plurality of different components including one or more data processing means 15. Such data processing means 15 could e.g. be a digital signal processor, various types of microprocessors, converter (analogue to digital / digital to analogue, electric / optic), etc. capable of processing data obtained from the multiaxis sensor 13. In such embodiments not only information relating to blade orientation but the actual blade orientation may be provided from the blade sensor device 12 to wind turbine controllers 6 or sub-controllers 7. As mentioned the preferred blade orientation is the pitch angle followed by the azimuth angle of the blade 5.

In any embodiment the output from the multi-axis sensor 13 (preferably from both an accelerometer and a gyroscope) i.e. the information representing blade orientation is aggregated by the data processing means 15 such as e.g. a data processor located in a sub-controller 7. The result of this aggregation (also referred to as processing of data) of information from the accelerometer and the gyroscope is preferably pitch angle and / or azimuth angle of the wind turbine blade 5 in which the blade sensor device 12 is positioned.

The multi-axis sensor 13 preferably comprises an accelerometer preferably with three axis. A range of different types of accelerometers are possible to use and the specific type depends on design choice of the multi-axis sensor 13. From the three axis of the accelerometer information relating to relative position and direction of movement of the multi-axis sensor 13 with reference to gravity is obtained. This information could be used to calculate e.g. the pitch angle at least at some locations of the blade 5 in the rotor plane. In addition this information together with information from a gyroscope may be used to find e.g. the pitch angle at locations of the blade in the rotor plane where information solely from the accelerometer is not sufficient to find e.g. the pitch angle.

Further in addition to the accelerometer, the multi-axis sensor 13 preferably comprises a gyroscope preferably with three axis. A range of different types of gyroscopes are possible to use and the specific type depends on design choice of the multi-axis sensor 13. From the three axis of the gyroscope information relating to the movement of the multi-axis sensor 13 is obtained. Together with information from the accelerometer find e.g. pitch angle e.g. where it may not be possible or difficult solely based on information from the accelerometer.

Hence a multi-axis sensor 13 comprising both accelerometer and gyroscopes is able to provide information for determine e.g. the pitch angle of a blade 5 in any location of this blade 5 in the rotor plane.

It should be mentioned that the accelerometer and gyroscope of the multi-axis sensor 13 could be any combination of n-axis accelerometers / gyroscopes e.g. depending of design requirements or requirements to the output of the multi-axis sensor 13.

The principles of accelerometers and gyroscopes are known by the person skilled in the art and will not be discussed further

Both the accelerometer and the gyroscope may be small Micro Electro Mechanical Systems (MEMS; Micro Electro Mechanical Systems) and thereby very small in size. It should be mentioned that size or integration of multiple sensors or axis are a matter of design and thus the multi-axis sensor 13 are not limited to any special configuration.

Fig. 3 illustrates a method of obtaining information representing blade orientation and determine blade orientation based hereon.

Step 1 SI is an initial step which when performed for the first time may not be necessary to include in the method each time the remaining steps S2-S4 of the method are executed. This is indicated by the dashed line in the figure.

Step 1 SI is optional in that rotation of the blade 5 may not necessary to obtain the desired information related to blade orientation. But in case the rotor of the wind turbine 1 starts rotation after it has been stopped for some reason this is referred to as step 1 SI. Hence in step 1 SI rotation of the blades 5 in the rotor plane is initiated. Typically this is controlled by setting a pitch angle reference based on the wind speed to the pitch actuator set controlling the orientation of the blade i.e. pitch angle.

One way of defining the pitch angle is to define a reference point such as 0° e.g. when the trailing edge of the blade is in line with the rotor plane. Since pitch angle is well known by the skilled person no further definitions are needed.

It should be mentioned that if the rotor rotates, this step may not be necessary.

In step 2 S2 the multi-axis sensor 13 is calibrated. The calibration is not necessarily performed in a specific position but is rather performed real-time as the blade rotates in the rotor plane. It is at least the accelerometer(s) of the multi-axis sensor 13 which is calibrated and preferably according to gravity.

The multi-axis sensor 13 is calibrated and as mentioned it is at least the axis of the accelerometer(s) which is calibrated according to the gravity of earth. This calibration is preferably done when the wind turbine 1 is in a power production mode but could of course also be done e.g. when the wind turbine is idling.

No matter if the calibration is made in a preferred calibration position or not the calibration includes at least alignment of at least one axis of the accelerometer with the axis of the force of earth gravity.

Hence the calibration of the multi-axis sensor 13 ensures that the information from the accelerometer and especially from the gyroscope do not drift in time. Thereby if not calibration is present a risk occurs that aggregation of this information does not found basis for a result (such as pitch or azimuth angle) which is as precise as required in some contexts.

As mentioned calibration could be done at any blade position in the rotor plane even though the horizontal position of the blade 5 is preferred. Followed by this it is possible to calibrate the multi-axis sensor 13 as often as required. Preferably calibration of each multi-axis sensor 12 in each blade is performed once in each revolution of the blade 5 in the rotor plane.

It should be mentioned that calibration may be performed at different levels in that a so called initial calibration may be done once or twice per revolution of a blade in the rotor plane based on information obtained from this revolution. Alternative calibration may be more accurate in that calibration may be done more than hundred times per revolution and may not comprise information not only from the last revolution of the blade 5.

In step 3 S3 the multi-axis sensor 13 generates the information representing the blade orientation. This information is as mentioned obtained by an accelerometer and / or by a gyroscope of the multi-axis sensor 13. It should be mentioned that the multi-axis sensor 13 could be either digital or analogue in terms of measurements and / or output.

In step 4 S4 the information is used by a data processing means 15 to establish blade orientation such as pitch angle, azimuth angle, etc. The blade orientation is preferably established by an algorithm of the data processing means 15 which aggregates information of the accelerometer with information from the gyroscope both of the multi-axis sensor 13.

It should be mentioned that the multi-axis sensor 13 could also comprise a plurality of different sensors together referred to as a multi-axis sensor 13.

It should be mentioned that data from the multi-axis sensor 13 of the blade sensor device 12 is preferably communicated to the data processing means 15 either in step S3 or step S4.

Preferably the aggregation of data is performed by data processing means 15 which is part of the blade sensor device 12. The output of this aggregation of data is preferably a pitch angle or azimuth angle which is sent a controller 6, 7 in the hub, nacelle or tower of the wind turbine. Alternatively the aggregation of data is performed by data processing means 15 not located in the blade based on information received from the multi-axis sensor 13.

From step 4 S4 if calibration of the multi-axis sensor 13 is necessary which is preferred step 2 S2 is initiated. Calibration is not necessary step S3 is initiated (indicated by dashed line) for obtaining information related to blade orientation in a new position of the blade 5 in the rotor plane and thereby continuously establishment of the blade orientation is facilitated.

Finally it should be mentioned that in case the calibration is performed real-time, the calibration step S2, the blade information generation step S3 and the blade orientation step S4 may follow each other. With the rotation step SI only used if the blades are not rotating (indicated with dashed line).

The method may be carried out simultaneous and preferably continuously in relation to each of the blades 5 of the wind turbine 1.

In general calibration of the sensors or multi-axis sensor described in this document is necessary in that mounting of the sensors or the blade sensor device 100% aligned with reference points such as e.g. main shaft, blade angle to main shaft, and / or gravity is difficult. Hence to be sure to be aligned e.g. with a offset to one or more of the mentioned reference points such so-called initial calibration is preferably initially made.

As mentioned a continuously (also referred to as real-time) calibration is preferably made. This is to ensure alignment of the sensors or multi-axis sensor to one or mreo the reference point over time are the same.

It should be mentioned that information relating to e.g. the main axis and blade angle relative to main axis could be part of the calibration in the form of parameter or be adjusted. Calibration could include using marking points e.g. at 0° and 90°. Upon pitch of a blade to these positions a visual inspection is made if the blade is at the marking points. Further calibration could include information from other relevant sensors or parameters relating to wind turbine design or control. Further calibration could include auto tuning which should be understood as the blade is pitched e.g. from 0° to 90° a plurality of times and in this way blade control (e.g. data processor of be blade sensor device 12 or sub-controller 7) could learn positions and angles relative to gravity. Further calibration could include positioning the blade in a horizontal poistin where sensors or multi-axis sensor is calibrated according to earth gravity.

It should be mentioned that the data processing means 15 may comprise a plurality of different algorithms. Hence a first algorithm may be used to aggregate information from the multi-axis sensor 13 resulting in blade orientation in the form of a pitch angle. A second algorithm may aggregate information resulting in blade orientation in the form of azimuth angle of the blade, etc. It should be mentioned that the algorithms of the data processing means 15 each may contribute to the resulting blade orientation. Thus the data processing means 15 may be used to process other data than data received from the multi-axis sensor 13. A blade sensor device 12 as describe above located in the blade 5 should preferably be protected from current induced be lightning striking the blade 5. If the blade sensor device 12 is not protected a risk of serious damage of the blade sensor device 12 is present. Therefore means for protecting the blade sensor device 5 from such currents are preferred. Such means could be chosen from various known lightning protection strategies.

List of reference numbers 1. Wind turbine 2. Tower 3. Nacelle 4. Hub 5. Blade 6. Wind turbine controller 7. Sub controller 8. Communication line 9. Generator 10. Power converter 11. High voltage cables 12. Blade sensor device 13. Multi-axis sensor 14. Joint between blade and hub 15. Data processing means 16. Utility grid 17. Blade component 18. Pitch actuator 19. Power supply cable

Claims

1. A wind turbine blade sensor device facilitates generation of information representing blade orientation wherein the blade sensor device comprising one or more sensors having in total at least three axis and wherein the blade sensor device is mounted on a rotatable blade component.

2. A wind turbine blade sensor device according to claim 1, wherein the blade sensor device comprising a multi-axis sensor having at least three axis and wherein the blade sensor device is positioned in the root end of the interior of the blade.

3. A wind turbine blade sensor device according to any of the preceding claims 2, wherein the multi-axis sensor includes at least one accelerometer.

4. A wind turbine blade sensor device according to any of the preceding claims, wherein the blade sensor device comprises at least one accelerometer and at least one gyroscope.

5. A wind turbine blade sensor device according to any of the preceding claims, wherein the blade sensor device facilitates generation of information while the wind turbine is in a power producing mode.

6. A wind turbine blade sensor device according to any of the preceding claims, wherein the blade sensor device is supplemented by a second sensor facilitating generation of information representing at least partly the same blade orientation information as the blade sensor device.

7. A wind turbine blade sensor device according to any of the preceding claims, wherein the information facilitates calculation of blade pitch angle and/or blade azimuth angle.

8. A wind turbine blade sensor device according to any of the preceding claims, wherein the blade sensor device comprises a data processor, wherein the data processor facilitates calculation of the blade pitch angle of the blade at which the blade sensor device is positioned based on information provided by the multi-axis sensor.

9. A wind turbine blade sensor device according to any of the preceding claims, wherein calculation of the pitch angle is made at least once per rotation of the blade in the rotor plane.

10. A wind turbine blade sensor device according to any of the preceding claims, wherein the blade sensor device is positioned at a distance between 0 and 200 centimeters from the root of the wind turbine blade, preferably between 0 and 100 centimeters, most preferably between 0 and 50 centimeters.

11. A wind turbine blade sensor device according to any of the preceding claims, wherein information from the blade sensor device facilitates validation of the pitch angle determined from the second pitch angle determine device.

12. A wind turbine blade sensor device according to any of the preceding claims, wherein the information from the blade sensor device is provided as input to a wind turbine controller.

13. A wind turbine blade sensor device according to any of the preceding claims, wherein the blade sensor device is used for safety monitoring of the pitch angle.

14. A wind turbine blade sensor device according to claim 1, wherein the generated information represents a change of position of the blade sensor device in time.

15. A method of determining information representing blade orientation of a wind turbine blade, the method comprising the steps of: - generating information representing blade orientation of a blade by means of one or more sensors having a total of three axis wherein the one or more sensors is rotating with the blade, and - calculating blade orientation of the blade by means of a data processor based on information from the one or more sensors.

16. A method according to claim 15, wherein the method further comprises calibrating the one or more sensors.

17. A method according to any of the claims 15- 16, wherein the one or more sensors is a multi-axis sensor having at least three axis and where in the multi-axis sensor is located in the root end of the blade.

18. A method according to any of the claims 15- 17, wherein the blade orientation is the pitch angle and/or azimuth angle.

19. A method according to any of the claims 15-18, wherein the multi-axis sensor is supplemented by a second sensor also generating information representing blade orientation.

20. A method according to any of the claims 15-18, wherein the multi-axis sensor is positioned at a distance between 0 and 200 centimeters from the root of the wind turbine blade, preferably between 0 and 100 centimeters, most preferably between 0 and 50 centimeters.

21. A method according to any of the claims 15-20, wherein the multi-axis sensor, preferably having 3 accelerometers and 3 gyroscopes.

22. A method according to any of the claims 15-21, wherein the multi-axis sensor 13 is part of a blade sensor device 12, wherein the blade sensor device 12 facilitates continuously calculation of the pitch angle.

23. A method according to any of the claims 15-22, wherein the multi-axis sensor is calibrated when the wind turbine is in a non-power producing mode.

24. A method according to any of the claims 15-23, wherein calibration of the multi-axis sensor is done when the blade in which the multi-axis sensor is positioned is perpendicular or parallel to the earth gravity.