EP2596238A2

EP2596238A2 - Method and device for determining a bending angle of a rotor blade of a wind turbine system

Info

Publication number: EP2596238A2
Application number: EP11730578.9A
Authority: EP
Inventors: Felix Hess; Martin Voss; Boris Buchtala; Christian Eitner
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2010-07-24
Filing date: 2011-07-02
Publication date: 2013-05-29
Also published as: DE102010032120A1; CN103003565A; WO2012019675A3; US20130272874A1; WO2012019675A2

Abstract

The present invention provides a method (900) for determining a bending angle of a rotor blade (300) of a wind turbine system (210). The method (900) comprises a step of reading in (910) at least one acceleration signal (a₁) which represents an acceleration of the rotor blade acting essentially perpendicularly with respect to a rotor plane (320). In addition, the method (900) comprises a step of determining (920) the bending angle of the rotor blade of the wind turbine using the acceleration signal.

Description

The present invention relates to a method and a device for determining a bending angle of a rotor blade of a wind turbine according to the independent patent claims.

Wind turbines are controlled by the adjustment of the rotor blades about their longitudinal axis and the Generatorrnoment. The controlled variable for the pitch control is the rotor speed and the manipulated variable is the pitch angle of the rotor blades. In conventional systems, the collective pitch control CPC (collective collective pitch control) is used. Here, the three rotor blades are all adjusted with the same pitch angle. In wind turbines with a horizontal axis and at least two rotor blades, the synchronous adjustment of the blade angle causes the rotational speed to be above the

Nominal wind speed regulated so that the change in the angle of attack, the aerodynamic lift and thus the drive torque is reduced in such a way that the system can be operated in the range of rated speed. At wind speeds above the shutdown speed, this blade pitch mechanism is also used as a brake by blowing the blades with the nose into the wind so that the rotor no longer delivers any significant drive torque. As a result of this asymmetric aerodynamic load, pitching and yawing moments on the nacelle result from this collective pitch adjustment. The asymmetric loads are caused, for example, by wind shears in the vertical direction (boundary layers), yaw angle errors, gusts and turbulences, impoundment of the flow at the tower, etc. One known approach to reducing these asymmetric aerodynamic loads is to adjust the pitch of the blades individually .: Individual Pitch Control = 1PC). For this control approach, it is necessary to determine the bending moments (in particular impact bending moments) prevailing at the rotor blade root. The bending moments then serve as a control variable for the individual blade adjustment. To determine the bending moments, strain gauge sensors (DMS = strain gauges), which are applied to the rotor blade root, can be used. The problem with the DMS sensors is the application and risk of breakage, as well as the short service life.

Other methods, as disclosed, for example, in WO 2008/041066 or DE 197 39 164 B4, determine the pitching and yawing moments by measuring the gondola acceleration via gyroscopes or by sensors which measure the deformation of system parts occurring by the loadings by means of distance measurements and thereby determine the loads. From the point of view of the IPC control, the sheet bending moments are very well suited as a controlled variable. However, it has not yet been possible to find suitable measuring technology for continuous use. Fiber Bragg sensors for measuring moments laminated to the blades can not be replaced in the event of a defect; glued-on strain gage sensors have a far too short service life. Both methods additionally have the problem that the measurement takes place only locally on the sheet. Local inhomogeneities in the laminate therefore lead to measurement errors, a conclusion about the global stress state in the leaf root, and thus the moment acting there is always subject to errors.

It is therefore the object of the present invention to provide a method and a device which enables an improved determination of the load of a rotor blade of a wind turbine.

This object is solved by the subject matter of the independent patent claims. Advantageous embodiments will become apparent from the subject matters of the dependent claims and the following description. The present invention provides a method for determining a bending angle of a rotor blade of a wind turbine, the method comprising the following steps:

Reading at least one acceleration signal representing an acceleration acting on the rotor blade; and

Determining the bending angle of the rotor blade of the wind turbine using the acceleration signal.

Furthermore, the present invention provides a device for determining a bending tendency of a rotor blade of a wind power plant, the device having the following features:

an interface for reading in an acceleration signal, one on the

Rotor blade acting acceleration represents; and

a unit for determining the bending angle of the rotor blade of the wind turbine using the acceleration signal.

Also of advantage is a computer program product with program code, which is stored on a machine-readable carrier such as a semiconductor memory, a hard disk memory or an optical memory and which is used to carry out the method according to one of the embodiments described above, when the program on a control device or a device is performed.

The invention is based on the finding that the bending of the rotor blade of the wind turbine is in a predetermined relationship to a bending moment of this rotor blade at the blade root. To determine the bend, in particular an acceleration or an acceleration signal is used, which is measured substantially perpendicular to the rotor plane. As an additional acceleration signal, the acceleration in the blade longitudinal direction can also be used. In this case, a virtual plane or actual plane in which the rotor blades rotate about the rotor axis of the wind power plant is referred to as the rotor plane. This means that the acceleration used in the present approach represents an acceleration in the direction of the rotor axis. Knowing this predetermined relationship can in this case from the acceleration of the rotor blade or at least a part of the rotor blade, a conclusion can be drawn on the present bending moment at the blade root of this rotor blade, so that a conventional control unit for determining the pitch angle can be further used using slightly modified control parameters. In this case, it is not absolutely necessary to draw the conclusion on the present bending moment at the blade root, but rather, it is also possible to carry out a direct calculation of the setting angle to be set on the basis of the measured or read-in acceleration. In this case, the sheet deflection (ie a value beta) is determined from the determined acceleration, from which the IPC pitch angle or the angle of attack of the rotor blades is determined. The presented control can thus use the bending moment (or the bending angle) and then determines the so-called pitch angle of the rotor blade. In this case, the term "pitch angle" can also be used for the term "pitch angle". The angle of attack or the individual angle of attack for the rotor blade can therefore be determined from the bending angle.

The present invention has the advantage that conventional control units can continue to be used, so that no costly new development of a control unit for controlling the angle of attack of the rotor blades of Windkraftan- plant is required. At the same time sensors can be used to provide the sensor sizes used, which are significantly more robust against aging phenomena and measurement errors. After wind turbines are designed for a long term and in particular an exchange of rotor blades is very expensive, the above advantage gains even more weight. Even a simple and cost-effective retrofitting is possible with the approach presented here.

According to a favorable embodiment of the present invention, a course of the acceleration can be detected in the step of reading in, wherein in the step of determining from the course of acceleration, a spectrum is determined and the angle of attack is determined using the determined spectrum. Such an embodiment of the present invention offers the advantage that by using a spectrum which is determined over a certain period of time and subsequently transformed into the frequency domain, smaller measurement errors can be compensated. It can be exploited that occur by the circulation of the rotor blade or the rotor blades physical influences at certain positions in the flight circle of the rotor blade periodically, namely, exactly when the rotor blade reaches the specific position in the following circulation again.

It is particularly advantageous if, in the step of determining, a comparison of the determined spectrum with a provided spectrum is carried out, wherein the determination of the setting angle is determined using a comparison result between the determined spectrum and the provided spectrum. Such an embodiment of the present invention offers the advantage that a good and reliable determination of the provided spectrum is possible. In this case, for example, an average value can be determined from a multiplicity of recorded spectra, wherein such a provided spectrum can then also represent certain variations of the environmental conditions.

According to a particular embodiment of the present invention, in the step of reading a movement of the rotor blade substantially perpendicular to the rotor plane can be effected actively. Such an embodiment of the present invention offers the advantage that spectra already to be expected for specific, frequently occurring scenarios can be measured or calculated and stored in a memory. For example, in this case each spectrum stored in the memory can be assigned a specific bending angle. In practice, the numerical or circuit engineering very simple implementation of the determinations of the bending angle can be carried out in this way, since essentially a comparison of the determined

Spectrum must be carried out with one or more spectra from the memory to obtain from the comparison result an already quite accurate size for the bending angle, if the determined spectrum corresponds approximately to a certain spectrum to which this bending angle is assigned.

According to a further embodiment of the present invention, in the step of determining a low-pass filtering and / or a Kalman filtering of the acceleration Nigungssignals be performed. Such an embodiment of the present invention has the advantage that a smoothing of the read-in measured value is obtained by the filtering, which increases the stability of the control behavior for the angle of attack. In particular, high-frequency signal interference components are filtered away and the pure useful signal, which carries the desired information to be evaluated with regard to gravity and centrifugal force, is retained.

Furthermore, in a further embodiment of the invention, in the step of determining the bending angle, information about a bending stiffness or an approximation of the bending stiffness, information about a distance of an acceleration sensor providing the acceleration signal from a rotor axis, an inclination angle of the rotor axis relative to the Horizontal and / or an acceleration of a tower head of the wind turbine can be used. Such an embodiment of the present invention offers the advantage that this makes possible a very precise estimation of the bending moment occurring at the blade root, so that a small change in the parameterization of control units already in use is required. This is particularly relevant because the currently used control units determine the control of the angle of attack for a rotor blade on the basis of an occurring bending moment, so that an exchange of the control variable can be implemented very easily.

In order to obtain the most accurate possible determination of the bending angle of the rotor blade, a time profile of the acceleration at a position of the rotor blade can be determined in the step of determining from the acceleration signal and the bending angle or blade deflection of the rotor blade can be determined using the determined course. The time course can extend over a rotor blade circulation around the rotor axis. Such an embodiment of the present invention determines the bending of the rotor blade in that the position is determined relative to the acceleration of gravity, which in the measurement of the acceleration of the rotor blade periodically amplifying once and once reducing acting on the measured sensor signal. According to another embodiment of the present invention, in the read-in step, a further acceleration signal can be read in, which is measured in the direction of the longitudinal axis of the rotor blade. In this case, in the step of determining the bending angle of the rotor blade of the wind turbine is determined using the further acceleration signal.

The invention will now be described by way of example with reference to the accompanying drawings. Show it:

1 shows a representation for the uniform definition of designations of the possibilities of movement on a wind energy plant;

2 is a block diagram of a control unit for the individual angle of attack of a rotor blade of a wind power plant, in which an embodiment of the present invention can be used;

3 is a schematic representation of the relevant variables in a positioning of

Sensors on a rotor blade;

4 shows a diagram for clarifying the relationship between a blade deflection and a root bending moment over time;

5 shows an illustration of a sensor coordinate system on a rotor blade;

6 is an illustration for illustrating the measuring principle and the processing of the obtained sensor signal;

Fig. 7 is a diagram showing a low-pass filtered sensor signal and a reference signal;

8 shows a diagram in which the relationship between a sheet deflection and a useful signal of the acceleration measurement of a sensor is shown, which is positioned at a distance of r = 10 m from the rotor hub; and

9 is a flowchart according to an embodiment of the present invention

Invention as a method.

The same or similar elements may be provided in the following figures by the same or similar reference numerals. Furthermore, the figures of the drawings, the description and the claims contain numerous features in bination. It is clear to a person skilled in the art that these features are also considered individually or that they can be combined to form further combinations which are not explicitly described here. Furthermore, in the following description, the invention may be explained using different dimensions and dimensions, the invention not being restricted to these dimensions and dimensions. Furthermore, method steps according to the invention can be repeated as well as carried out in a sequence other than that described. If an embodiment includes an "and / or" link between a first feature / step and a second feature / step, this may be read such that the embodiment according to one embodiment includes both the first feature / the first feature and the second feature The second step and, according to another embodiment, either only the first feature / step, or only the second feature / step 2. A particular object of the invention is to provide a way to adjust the yawing and pitching moments through a closed-loop control process The manipulated variables are favorably the individual angles of incidence of the blades of the wind turbine.An important aspect is that the controlled variables are determined according to the approach presented here via acceleration sensors on the rotor blades in at least one Rotor blade at least one acceleration sensor installed, the accelerations in the direction of impact (ie perpendicular to the rotor plane) can measure. This offers the advantage that in this case point sensors can be used which are easy to apply in the leaves, are easy to replace and static errors such as tensions due to temperature differences and the inhomogeneous sheet material does not capture. In addition, the sensors may already be present if condition monitoring of the blades is installed.

In order to uniformly define the variables of the possibilities of movement of a wind power plant used below, reference is made to the representation according to FIG. In this case, a wind turbine means a system with a tower on which a nacelle is mounted. This gondola contains a generator that with is coupled to a rotor, wherein the rotor in the example shown in FIG. 1 has two rotor blades. The tower can thereby run at a flow of wind and a transmission of forces from the rotor to the nacelle and the tower a tower longitudinal bend 100 and a Turmquerbiegung 1 10. The tower can also perform a tower twist 120 about its vertical axis. A movement of the tower about its vertical axis is also referred to as yawing 130 of the wind turbine. Furthermore, forces can act on the tower or the wind turbine, which leads to a roll 140, that is, a rolling motion about the rotor axis of the wind turbine. If a movement is induced by the action of wind on the wind turbine, which acts both perpendicular to the vertical axis of the tower and to the rotor axis, it is spoken of a pitch 150 of the wind turbine. On the one hand, the rotor blades can execute a pivoting movement 160 or a striking movement 170 or twist inwardly, which is also referred to as torsion 180, now relative to the rotor blades. The pivoting movement 160 corresponds to a desired movement of the rotor blades about the rotor axis, wherein the striking movement 170 denotes a movement, in particular of the tips of the rotor blades, out of the rotor plane, that is to say in the direction of extension of the rotor axis. Such a definition of movements of a wind turbine is modeled on the definition in the book "Wind turbines" by E. Hau, in which corresponding control parameters for the yaw and pitching moment of the nacelle are called.The impact movement leads to bending moments at the blade root and is cause for greed and pitching moments of the gondola.

An important aspect of the present invention can be seen in that the use of acceleration signals from sensors on the blade and the processing of these signals can be done within a control method to reduce the yawing and pitching moments on the nacelle via the individual adjustment of blade pitch angles.

A system in which the present invention according to an exemplary embodiment can be used is shown in simplified form in FIG. 2 as a block diagram. The system 200 for controlling the wind power plant 210 comprises a unit 220 for operation management and a unit 230 for controlling the individual angle of attack 235 (ßipci, 2,3) for each of the rotor blades of the wind turbine 210. The unit 220 for operation management (also known as CPC, Collective Pitch Control) receives for its task a signal from a sensor of the wind turbine 210, in particular a signal with respect The rotation speed ω of the rotor of the wind turbine 210. From this signal, the unit 220 for operation now on the one hand determine a generator torque 240 to be set and make this available to control the wind turbine 210 and on the other hand a common angle of attack 242 (ßcpc) for all rotor blades determine at the wind turbine has an optimal power output. The unit 230 (also referred to as IPC controller) for controlling the individual angle of attack 235 receives from at least one sensor in or on a rotor blade of the wind turbine 210 a signal relating to an acceleration a of this rotor blade at the position at which the sensor is mounted. In particular, the unit 230 for controlling the individual angle of attack 235 can receive signals via accelerations ai _>2> 3 from a plurality of, for example, all rotor blades and in this case a corresponding signal βipci, ₂ , 3 for each rotor blade for which it receives a sensor signal provide for adjusting the individual angle of attack 235 of the relevant rotor blade. In this way, the common angle of attack signal for each individual rotor blade can be corrected to account for local wind inhomogeneities. Furthermore, the shear of the wind leads to asymmetric loads. The signal with respect to the common angle of attack 242 can then be linked, for example, additively with the different signals with respect to the individual angle of attack 235 for the respective rotor blades, resulting in a control signal 250 for the individual rotor blades of the wind turbine 210 concerned. This adjustment of the angle of attack of the individual rotor blades of the wind turbine 210 in accordance with the desired angles of attack is subsequently set by an actuator 255. Under the influence of changing wind conditions 260, the rotor blades are then deflected differently in the direction of impact, said deflection or the acceleration occurring in turn measured by the corresponding sensors and the sensor signals 265 of the unit 220 for operation and the unit 230 for controlling the individual pitch is supplied. In this way, the control loop is closed to control the individual angles of attack. Through the use of acceleration signals, which represent an acceleration of the individual rotor blades in the direction of impact, a very simple modification of already existing control systems for the individual angles of incidence of the rotor blades of a wind turbine can be implemented. Conventional wind turbines usually use the bending moments at the blade root of the rotor blades for adjusting the individual angles of attack of the respective rotor blades. However, since usually a simple relationship between a bending moment on the blade root of a rotor blade and an associated bending of the rotor blades in strike direction is recognizable or known, a signal of a substantially more robust acceleration sensor can be used to adequately utilize a signal for controlling the angle of attack of the rotor blade representing the acceleration of the rotor blade or of a part of the rotor blade in the direction of impact, by determining the bending angle of the rotor blade according to the invention from this signal. In order to obtain and process a signal which is easy to process and as low as possible in terms of a bending angle of a rotor blade, two variants are conceivable.

In a first variant, a natural frequency analysis of the specific accelerations or the acceleration signals derived therefrom can be carried out. For this, the natural vibrations of the (rotor) blade are used. The excitation during operation of the system is carried out by aerodynamically induced vibrations or an additionally mounted shaker, ie a unit that actively sets the rotor blade in vibration. In this case, the acceleration sensors continuously record and store signals and determine the amplitude spectrum of the natural oscillations after a certain measuring time (maximum 1 sec.). This frequency spectrum is compared for example with desired spectra, which are stored in the control device and belong to certain load conditions of the sheet. By adjusting the blade angle, the load on the blade is reduced, which is controlled by comparison with the target spectra. The desired spectra are determined beforehand by measurements on the blade with and without loads, or determined by natural frequency analysis from calculations. The advantage of this variant is that the measurement technology already available for condition monitoring can be used, which has already integrated the sensors, measured value acquisition, processing and evaluation of the acceleration signals. This also includes already stored target spectra. In addition, nominal spectra for load cases stored in the control device should be included for such an application scenario. These can be determined by measurements on blade test stands. It is more probable to perform reference measurements before mounting on the blade and to carry out analog measurements after mounting at wind speeds below the start-up speed on the rotor blade. On the basis of these spectra and the sheet data, the deviations from these spectra under load are calculated by simulation and stored as nominal spectra.

A second variant for the use of the approach presented here is to be seen in the use of data from a direct acceleration measurement and its extension. The bending angle of the rotor blade is determined from the measured accelerations. The main goal then is to set the same bending angles on all rotor blades. In turn, manipulated variables are the blade angles. Due to aerodynamic effects such as turbulence and vortex shedding vibrations of the blade are always excited, but which are higher-frequency than the vibrations to be corrected in the range of the first natural frequencies of blade and tower. Therefore, for the control, the measured acceleration should be filtered by a low-pass filter. For the position of the first (acceleration) sensor, the lower half of the rotor blade is favorable, since the blade tip due to the taper and prevailing there cross flows, which also drive the tip vortex, can be excited to strong vibrations. As advantages of the two variants described above, the following aspects can be introduced. Firstly, the use of known and possibly already existing measuring devices as well as data possibly determined by the condition monitoring of the sheets can take place. Furthermore, there is no need to apply strain gauges or the like where the current state of the art does not know where and how to attach them accurately. In addition, the temperature compensation of these sensors is technically not satisfactorily solved. In addition, an acceleration sensor can be easily replaced in the event of a defect. This is included laminated strain sensors impossible. The signals provided by strain sensors may not be meaningful because they only detect local strain. Also occur in the use of the approach described above, no errors by static loads such as temperature stresses, local stress peaks by the inhomogeneous material, ice accumulation (with simultaneous use of the

Condition monitoring), etc., which significantly increases the reliability of the control using the magnitude of bend angle calculated from the blade acceleration. In other words, this means that the approach presented here represents a use as an additional control function in the pitch drives of the Applicant. Future drives should be able to adjust the blades individually based on current market trends. Another important aspect of the present invention is based on an acceleration sensor (DCU) to enable an improved IPC-suitable measurement method, in which the sensor has a longer life, easy replacement of the sensor is ensured and possibly one to global stress state in the leaf root equivalent size is recorded.

In the approach presented below, an essential aspect is the use of a signal of an acceleration sensor, which measures the acceleration of the rotor blade in the direction of the rotor axis. The acceleration sensor should be able to measure stationary acceleration. The measurement of the acceleration in the sheet is known in the current state of the art and is among other things to

Condition Monitoring used. A twofold integration of this measured acceleration would give the current blade displacement. However, this method has a drift, which falsifies the calculated results for a long time. This parameter is therefore unsuitable for IPC control.

According to one embodiment, a measuring concept is presented with the invention presented here, which is a suitable signal evaluation for the IPC control allows. On the basis of sensor data of a single-axis acceleration sensor, an online signal evaluation can take place. One possible application is, for example, in the field of IPC control or in experimental measurements on wind turbines. For the regulation of the blade angle of the rotor blades of a wind turbine, the

Sheet deflection in the direction of impact (i.e., perpendicular to the rotor plane at 0 degrees

Pitch position) needed. To determine this size, the blade deflection can be measured directly via strain gauges on the rotor blade root. An alternative sensor concept for the measurement of blade deflection is the use of acceleration sensors, whose measurement equation is described by the so-called navigation equation (3), which reads as follows: where a corresponds to the measured acceleration and g corresponds to the acceleration due to gravity.

With appropriate low-pass filtering of the local acceleration, the projection of the gravitational vector and thus the pitch angle of the sensor coordinate system can be estimated via the sensor signal. Based on the orientation of the sensor, it is possible to conclude on the deflection of the rotor blade and thus on the corresponding impact bending moment. A measured relationship for the deflection of the rotor blade and the corresponding impact moment is shown in the diagram of Fig. 4, in which the abscissa represents the time and the ordinate the course of the blade deflection (dashed line) and the blade root bending moment (solid line) are shown , It can be seen from FIG. 4 that the curves for the measured blade deflection and the measured blade root bending moment correspond, so that the blade deflection and consequently also the acceleration which can be used for the control of the individual pitch angle of the rotor blade can be used Leaf deflection leads.

For the determination of the sheet deflection, it is sufficient to consider the x-component of the sensor signal, assuming negligible torsion. The x component points in the direction of the normal vector on the leaf surface and is, insofar as there is no leaking twist, in the bending direction. For this purpose, it is assumed that a sensor coordinate system 500 in the rotor blade, as shown in FIG. 5. The z-component in the direction of the rotor blade end, the x-component oriented in a normal to the rotor plane and the y-component in the pivoting direction of the rotor blade. Furthermore, a coordinate system 510 in the hub of the rotor and a coordinate system 520 in the rotor shaft can be used for the conversion of the sensor acceleration values, as will be described in more detail below.

For the determination of the sheet deflection, a transformation of the coordinates from the tower into the rotor axis, from the rotor axis into the rotor blade and from the rotor blade into the bent rotor blade is first carried out for this purpose. The following transformation matrices can be used for this:

sin A 0 cos A / 0 _

Rotor axis in Rotorbaltt- I 0 COS Ω Sin Ω I - M _BS ,

\ 0 sin Ω cos Ω /

M rotor blade in a bent rotor blade ^- I

where Λ represents the angle of inclination of the rotor axis with respect to a horizontal, Ω represents the rotor azimuth angle about the rotor axis, and β represents the angle of rotation of the rotor blade at the location of the sensor from the rotor plane. In this case, a projection of the gravitational acceleration

* ^■ (·.).

be described as follows: (cos β · sin Λ + sin β · cos Ω · cos Λ

- sin Ω · cos Λ

sin β · sin Λ cos β · cos Ω · cos Λ

Furthermore, a measurement equation of the acceleration sensors can be specified as follows: From which follows:

^ Senson

ω ² · cos ß ß · sin · rs + r + g _s ß ^■ (cos + sin ß · sinA · ß cosfl

0 - 5 · (sinfl · cosA)

-ω ² · (cos β) ² · r _s · (sin β · sinA-cos β · cosβ

wherein the first column of the above matrix represents the centripetal acceleration, the second column of the above formula represents the measured accelerations due to the rotation of the sensor coordinate system, and the third column of the formula given above represents the gravitational acceleration.

If the tower head acceleration is not to be neglected, the sensor alignment must be extended by ajurmkopf, whereby

+ a _x (cos β · cos Λ-sin β · sin Λ · sin Ω) + a _y · sin β · sin Ω aTunnkopf ~ + a _x · sin Λ · sin Ω + a _y · cos Ω

+ a _x (sin β · cos Λ + cos β · sin Λ · cos Ω) - a _y · cos β · sin Ω,

Thus then applies to the total measured acceleration as _s sor of the sensor:

^Q sensor ~ ^Q -Senson ^Q tower head

The proportions due to the rotation of the sensor coordinate system can be filtered by a low-pass filter and thus eliminated. According to the embodiment of the present invention presented here, two measuring concepts or methods can be realized. For the first method, a single-axis accelerometer is used on the rotor blade. In this case, the acceleration is measured, which is directed, for example, normally to the rotor blade surface. This acceleration is referred to as a _X s _e sor and, ignoring the tower head acceleration, can be expressed as follows: X _tSensor = ω ² · cos β · sin β · r _s + r _s · β + g · (cos β · sin Λ + sin ß · cos Ω · cos Λ), The term ^ · (cos ß · sin Λ -I-sin ß · cos Ω · cos Λ) is repeated periodically with the angle Ω. Further, if β is none and thus tends to 0, the trajectory of gravity acceleration can be used unambiguously for the determination of β.

Without leaf deflection ß = 0 applies. It follows = +9 'Sin A = COUSt.

With ß ^ O results in a circulating frequency component (sin ß · cos il · cos A), wherein the bending angle can be determined from the following context:

The change in the projection trajectory of the acceleration due to gravity is thus due to the deflection of the rotor blade φ) and can be used for the determination of β. This first measuring method of sheet deflection on the basis of a single-axis measuring acceleration sensor offers advantages in terms of a cost-effective sensor and a simpler evaluation of the sensor signals than in the utilization of multiple sensor signals. However, a disadvantage of this measuring method for the bending angle is that a smaller useful signal is available, since only the signal amplitude can be used for the determination of β. For the second method for determining the bending angle, sizes can be used, as they are explained in more detail with reference to FIG. Here, the acceleration of the rotor blade 300 in the direction of the rotor axis 310 is considered, wherein the acceleration sensor is arranged at the distance r from the latter. The local acceleration of the rotor blade at the location of the acceleration sensor by the angle β due to the deflection of the rotor blade from the rotor plane (320) _{causes the} following accelerations to be measured: a _XiSensor = ω ² · cos β · sin β · r _s + r _s · β + g · (cos β · sin Λ + sin β · cos Ω · cos Λ)

+ a _x (cos ß · cos Λ- sin ß · sin Λ · sin Ω) + a _y · sin ß · sin Ω and ^a zsensor = ~ <*> ² '( ^cos ß) ² ' ^r s ^{- r} s ^* β ² + 9 '( ^sin β "Sin Λ -COS β * COS Ω * COS Λ) + a _x (sin β * cos Λ + cos β * sin Λ * cos Ω) -a _y * cos β * sin The first term (ie, the first product) of the two equations is constant with respect to the angle β. The second term (ie, the second product) is negligible when the acceleration sensor signal is low-pass filtered For example, at an angular velocity of ω = 1.7 rad / s (which corresponds to an installation speed of 15 rpm) and a distance of the sensor r _s = 20 m, a constant proportion of co ² -r _s = be obtained 58m / s ^2. the umlauffrequente proportion amounts to g = 9.81 m / s .Somit vary the acceleration in the z-direction, for example from 68m / s ² to 48 m / s ² within one rotation of the rotor blade to the rotor axis ,

In the filtered equation for a ^ sensor (i.e., the second term is filtered away), all sizes except β are now known. The equation can thus be solved numerically according to the desired twist angle ß.

\ ω ² · r _s · cos ² ß \

The equation for a _x sensor given above indicates how the acceleration measured in the x-direction is composed of the known and unknown quantities. If this acceleration is additionally measured, then the accuracy of the determination of β can be increased. In particular, the use of a Kalman filter can lead to better results. In this case, a model of the rotor blade is simulated in the Kalman filter and the deflection determined therefrom. The simulation is updated or corrected in each time step with the aid of the two measurements (a _x , a _z ) (for example by means of a predictor, corrector method). From the sheet pitch, the sheet deflection can be determined directly by means of a model for the sheet bending (ie the bending line). From the model for sheet bending, the blade root bending moment follows. For this, in addition, the bending stiffness EI must be known. Since the known IPC controllers only use the differences in the leaf root bending moments of the blades for regulation, an absolutely accurate value is not required and an approximate value is sufficient for the bending stiffness El. Such a measurement concept mentioned above would also be detectable simply by the presence of an acceleration sensor in the rotor blade, which is arranged to measure the acceleration in the z-direction. This application of the equations described above can then be deduced from the acceleration signals on the bending angle of the rotor blade, which is then used to control the angle of attack of the rotor blade. In particular, the use of the second method has the advantage that over a rotor revolution there is a constant useful signal due to a constant centrifugal force, from which the g-projection can then be calculated or used to determine β.

In order to be able to determine the sheet deflection, the projection component of the fall acceleration, which is purely due to the impact bending of the rotor blade, should be determined. For this purpose, the projection change of the fall acceleration, which results from the rigid body movement of the system, can be filtered out. Two degrees of freedom determine the rigid body movement: the rotation around the rotor axis and the Blade angle adjustment about the pitch axis. In addition, the rotation of the azimuth bearing could still be considered, but this is neglected in this consideration.

The projection component responsible for the leaf deflection thus results from:

9size ⁼ dmeasure ~ URBFilter (4)

Where g RBFiiter corresponds to the calculated on the basis of rigid body motion projection vector of gravity acceleration. gMess is the acceleration component measured by the sensor. Bending is the correspondingly filtered signal which is due solely to the elastic deformation of the rotor blade (i.e., corresponds to the bend in the direction of impact). By equation (4) it is possible to filter out the projection component of the gravitational vector, which is not due to the deflection. The calculation of the case acceleration acceleration resulting from the rigid body movement can be seen from the following equation (5).

§RBFilter ~ Tßladejiub 'T _z (ß ^' T _{Stroke Rotor} · T _x (a) · §R ₀ torCOS (5) where

Tßiade Hub corresponds to a transformation matrix for transformation into leaf segment COS;

Tz (β corresponds to a rotation about β (i.e., a pitch angle of the rotor blade) with respect to the Z-axis of the sheet-bearing COS;

^ HubjRotor corresponds to a transformation matrix for transformation into leaf-bearing COS; and

Γ () corresponds to a rotation about a (ie, an azimuth angle of the rotor) with respect to the x-axis of the rotor COS. 9Rotorcos denotes the gravitational vector expressed in the inertial rotor axis coordinate system. The rotor axis is tilted by about 5 ° up to the so-called Shaft angle. The measuring principle according to the first method is shown in the two subfigures of FIG. In this case, a measuring principle and an associated measurement signal is shown in the left part of the figure, in which the wind turbine or the rotor blades are bent. In the right-hand part of FIG. 7, by contrast, a measuring principle and an associated measuring signal are shown when this measuring principle is used, it being possible to infer the elastic deformation of the rotor blade from the change in the amplitude. In the graphs of FIGS. 7 and 8, the sensor signal (dashed line 700) at the blade tip (ie, at a distance of r = 36m from the blade root) and the low pass filtered sensor signal (solid line 710) are shown over time, while FIG. 8 shows the course of a low-pass filtered sensor signal. The reference signal corresponds in each case to the projection of the gravitational acceleration into the sensor coordinate system. It can be seen that the low-pass filtering makes it possible to determine the amplitude of the projection of the gravitational vector. For the evaluation of the sheet deflection, the amplitude size of the projection is relevant.

Furthermore, there is a correlation between the amplitude size of the sheet bend and the filtered sensor signal. Here, the change in the g-projection is taken into account, which can be attributed to the deflection of the rotor blade. This means that even with greater distance of the sensor from the blade root, a larger amplitude signal is expected. This information can also be obtained from the amplitudes of the variable bend. With a corresponding calibration, the blade root (impact) bending moments can thus be determined directly on the basis of the blade acceleration sensors. It can be shown that with a distance of r = 20 meters of the acceleration sensor compared with the rotor hub, a better evaluation is possible due to the larger sheet bending. The same applies a distance of r = 36 meters of the acceleration sensor with respect to the rotor hub, the simulation results are not shown here. A problem, however, is that the useful signal, ie the change in the inclination of the gravitational vector due to the sheet bending, is relatively small in relation to the interfering signal, the closer to the blade root of the sensor is applied. Accordingly, it is more advantageous to measure further outward on the blade at, for example, a position of r = 36 meters from the blade hub, because of the greater deflection in comparison to the measuring points located relatively close to the blade bearing, for example where r = 10 and r = 20 meters , Important for the application of the measuring concept presented here is also the measurement of the rotor rotational speed and the pitch angle. However, this is currently the state of the art in wind turbines and is used for conventional control methods.

The approach presented here also makes it possible to use an already well-developed acceleration sensor system (for example MM3, DCU) of the applicant for the sensor signal evaluation described here and can be used on a larger scale in the area of regulating wind turbines in the future.

According to a further embodiment, the present invention comprises a method 900 for determining a pitch angle of a rotor blade of a wind turbine, as shown as a flow chart in FIG. 9. The method 900 includes a step of reading in 910 an acceleration signal representing an acceleration of the rotor blade acting substantially perpendicular to a rotor plane of the wind turbine. Further, the method 900 includes a step of determining 920 the angle of attack of the rotor blade of the wind turbine using the acceleration signal.

26

LIST OF REFERENCE NUMBERS

100 tower bend

1 10 Tower Crossing

120 tower twist

130 yaw

140 rolls

150 nods

160 pivoting movement

170 beat movement

180 twist

200 system for controlling the wind turbine

210 wind turbine

220 Plant management unit

230 unit for controlling the individual angle of attack 235 individual angle of attack (ßwcw)

240 generator torque

242 common angle of attack (ßcpc)

250 control signal

255 actuator

260 local wind conditions

265 sensor signals

300 rotor blade

310 rotor axis

320 rotor level

500 coordinate system in the rotor blade 27

510 coordinate system in the rotor hub

520 coordinate system in the rotor shaft

700 reference signal

710 filtered sensor signal

900 Method of determining a bending angle of a rotor blade 910 Reading in an acceleration signal

920 Determining the bending angle of the rotor blade of the wind turbine

Claims

23

claims

A method (900) for determining a bending angle of a rotor blade (300) of a wind turbine (210), the method comprising the following steps:

Reading (910) at least one acceleration signal (ai) representing an acceleration acting on the rotor blade substantially perpendicular to the rotor plane (320); and

Determining (920) the bending angle of the rotor blade of the wind turbine using the acceleration signal.

A method (900) according to claim 1, characterized in that in the step of reading (910) a course of the acceleration is detected, wherein in the step of determining (920) from the course of acceleration, a spectrum is determined and the bending angle using the determined Spectrum is determined.

Method (900) according to claim 2, characterized in that in the step of determining (920) a comparison of the determined spectrum with a provided spectrum is performed, wherein the determination of the bending angle is determined using a comparison result between the determined spectrum and the provided spectrum ,

Method (900) according to claim 2 or 3, characterized in that in the step of read-in (910) a vibration excitation of the rotor blade is actively effected. 24

5. The method (900) according to claim 1, characterized in that in the step of determining (920) a low-pass filtering and / or a Kalman filtering of the acceleration signal is performed.

Method (900) according to one of the preceding claims, characterized in that in the step of determining (920) for determining the bending angle, information about a distance of an acceleration sensor providing the acceleration signal from a rotor axis, an inclination angle of the rotor axis (310) relative to the horizontal and / or an acceleration of a tower head of the wind turbine is used as well as information about the rotational speed and the rotational position of the rotor.

Method (900) according to one of the preceding claims, characterized ge indicates that the bending angle is determined in the step of determining (920) from the time profile of the acceleration at a position of the rotor blade.

Method (900) according to one of the preceding claims, characterized in that in the read-in step (910) a further acceleration signal is read in which represents an acceleration acting essentially in the longitudinal direction of the rotor blade at the location of the first acceleration sensor and wherein in the step of determining Bending angle of the rotor blade of the wind turbine is determined using the further acceleration signal.

Method for determining individual angles of incidence of the rotor blades on the basis of a bending angle calculated according to claims 1 to 8 or a load of the rotor blade or of the rotor blades determined from the calculated bending angle. 25

Device (200) for determining a bending angle of a rotor blade of a wind turbine (210), the device having the following features:

- An interface (230) for reading at least one acceleration signal (ai), which represents an acceleration acting on the rotor blade; and

- A unit (230, 220, 255) for determining the bending angle of the rotor blade of the wind turbine using the acceleration signal.

Computer program product with program code for carrying out a method (900) according to one of claims 1 to 9, when the program is executed on a control device (230) or a device.