DK179140B1

DK179140B1 - Method of determining a rotor parameter

Info

Publication number: DK179140B1
Application number: DKPA201670402A
Authority: DK
Inventors: Knud Møller Andersen; Per Mølhave Christiansen
Original assignee: Kk Wind Solutions As
Priority date: 2016-06-06
Filing date: 2016-06-06
Publication date: 2017-12-04
Also published as: DK201670402A1

Abstract

The invention relates to a method of determining an operational parameter relating to the rotor of a wind turbine, wherein each blade of the wind turbine comprises a transducer, the method comprising the steps of: providing to a controller gravity related information from the transducers, by the controller from the gravity related information determining the size of the contribution from the gravity force, and by the controller determining at least one operational parameter based on the size of the contribution from the gravity force.

Description

Method of determining a rotor parameter Field of the invention

The invention relates to a method of determining an operational parameter related to the rotor of a wind turbine and to the control of the wind turbine based hereon

Background of the invention

During the last decade focus of retrieving information of the state or load of the blades of wind turbines has increased. Such information can be retrieved from placing sensor in the blades connected to a wind turbine controller.

Prior art therefore comprises a plurality of examples of different ways of monitoring the load, state, vibration, etc. As examples could be mentioned DE102007058054 describing fiber sensors such as strain gauges for measuring load, US20140278151A1 describing an audio measuring devices, US7883319 describing using an accelerometer to determine structural noise and EP1075600 describing accelerometers located in the blade used to monitor stress of the blade.

Further, the prior art document EP2339174 describes an accelerometer located in the hub or blade where acceleration values hereof are provided to an estimation unit estimating the rotor speed of the rotor of the wind turbine. The determined rotor speed is by a trigger unit evaluated and if considered necessary the trigger unit triggers the emergency system of the wind turbine.

The prior art and especially EP2339174 has the drawback that they require data acquisition from the accelerometer over a period of time to be able to estimate the rotor speed.

Prior art document W02009/001310 describes a method for determining an angular position of a rotor of a wind turbine. Blades of the wind turbine comprises acceleration sensors measuring acceleration and converting the measured accelerations to input signals based on which the angular positon of the rotor is calculated.

Prior art document GB2459726 describes a method for detecting formation of ice on the blades of a wind turbine by measuring mechanical strain of the blades by strain sensors mounted on the blades.

Brief description of the invention

It is an object of the present invention, to overcome the problem of the prior art. The present invention relates to a method of determining an operational parameter relating to the rotor of a wind turbine, wherein each blade of the wind turbine comprises a transducer, the method comprising the steps of: providing to a controller gravity related information from the transducers, by the controller from the gravity related information, determining the size of the contribution from the gravity force, and by the controller determining at least one operational parameter based on the size of the contribution from the gravity force.

According to an embodiment of the invention, the operational parameter is determined based on a change of the size of the contribution from the gravity force over time of the gravity related information from the transducer.

According to an embodiment of the invention, the controller from the gravity related information, is determining the size of the contribution from the centripetal force.

According to an embodiment of the invention, the transducer is positioned in the root portion of the blade.

The gravity related information at least comprises a contribution from the vertical gravity force Fg, a contribution which is referred to as Gr, and a contribution from the rotational centripetal force Fc.

The gravity related information is provided by at least one transducer of each of the blades of the rotor. The root portion is defined as the third of the blade closest to the root of the blade connected to the hub. The controller mentioned may by one and the same controller or different controllers depending on configuration of the control system of the wind turbine.

Being able to separate the different contribution forces in the gravity related information provided by the transducers facilitates determine different operational parameters such as rotor speed, azimuth angle, pitch angle of the blade, etc.

Further the present invention is advantageous in that within one or two revolutions of a blade in the rotor plan it is possible to determine the centripetal force (the gravity force is always present) and thereby operational parameters including at least pitch angle and, rotor speed. This is resulting in a safe control of the wind turbine from start of the operation of the wind turbine in contrary to the prior art which need time to gather data to estimate e.g. the rotor speed.

In the same way the present invention is advantageous in that it is possible to determine the azimuth angle however to determine the azimuth angle it is not necessary to obtain information during rotation of the rotor. The azimuth angle can be determined also when the rotor is not rotating.

In a worst case scenario, the rotor of a wind turbine controlled according to the methods described in the prior art using accelerometer values to estimate rotor speed might reach over speed before the prior art methods has provided a rotor speed to the wind turbine controller. In such situation the wind turbine controller cannot react on such over speed unless an additional rotor speed monitoring device is used to monitor rotor speed. Such redundancy of rotor speed monitoring is not necessary to eliminate this risk by using the present invention in that almost instant the rotor speed can be determined according to the present invention. Thereby it is not necessary to buy a second monitoring unit nor to have one sensor for determining the azimuth angle and one sensor for determining the rotor speed and thereby reduction of cost is obtained as consequence of the present invention.

According to an embodiment of the invention, centripetal force is determined from the gravity related information by a summation of the gravity related information from each blade divided with the number of blades. The gravity related information is preferably the measurements from the transducers located in the individual blades hence by adding the raw measurements hereof to each other and dividing the result with the number of measurements a simple and reliable calculation of the centripetal force can be made.

The centripetal force is advantageous to determine in that from this it is possible to determine the rotor speed.

According to an embodiment of the invention, the contribution from the gravity force of each blade is determined from the gravity related information by subtracting centripetal force Fc from the gravity related information. The gravity force contribution from each blade is preferably found by subtracting the determined common centripetal force of the rotor from the gravity related information obtained from the transducers of the individual blades.

In this way the gravity force contribution of each of the blades are found which is advantageous in that from this value it is possible to determine at least the azimuth angle of the rotor.

Here it should be mentioned that preferably either the transducer / sensor in the blade or the controller facilitates a sin/con relation of the angle of the blade (phi) multiplied by the gravity force.

According to an embodiment of the invention, the operational parameter includes operational parameters of the list comprising: rotor speed, azimuth angle and pitch angle.

According to an embodiment of the invention, at least one of the operational parameters are used in the control of the wind turbine 1 during normal operation hereof. This is advantageous in that from the first or second revolution of a blade in the rotor plane the wind turbine controller is provided with reliable information of e.g. rotor speed and azimuth angle.

According to an embodiment of the invention, the operation parameter is determined by used of contribution from gravity force of two out of three blades, wherein the two blade contributions from gravity force are found by comparing the gradient of the contribution from gravity force from the three blades and selecting the two blades having the steepest gradient of the contribution of the gravity force. When using the present invention in relation to a wind turbine having a rotor comprising three blades, it is advantageous to use only gravity related information from the two of the blades having the fastest change of contribution of gravity force over time i.e. steepest gradient. This is because the information from these two blades 1) are less valuable to inaccurate measurements from the transducers and 2) the contribution to the calculations of the azimuth angle from these two blades are higher leading to a more precise result.

According to an embodiment of the invention, the operation parameter is determined by attaching importance to the measurements from the transducers wherein the level of importance attached to the individual measurement is determined by the contribution from gravity force of the individual measurement. It is especially advantageous if the level of importance attached to the measurement is dynamically i.e. changing over time. In this way it is possible to use the measurement providing the most information and thereby the most reliable determination of operation parameter. Preferably the level of importance is determined from the gradient of the measurement i.e. high gradient includes much information whereas low gradient includes less information.

According to an embodiment of the invention, the rotor plan is divided in a plurality of zones and wherein a unique equation for determining the azimuth angle is related to each individual zone. The zones are preferably defined so that each of the zones comprise a contribution from gravity force from one blade having the value of 1 [g] or -1 [g] i.e. having a rather flat gradient. Accordingly, equations for determining the azimuth angle are unique in that they are using the contribution from gravity force from different blades and different angles are added or subtracted in the equation.

The latter is determined based on the reference blade and angle which is selected.

According to an embodiment of the invention, the transducer is an accelerometer. An accelerometer is advantageous in that it per se provides gravity related information preferably forces.

Moreover, the invention relates to a system for determining an operational parameter relating to the rotor of a wind turbine according to any of the preceding claims wherein at least the transducers positioned in the blades are communicating with the wind turbine controller is protected from lightning currents. Protection of components in the wind turbine from lightning current is important and especially the transducer in the blade needs to be protected separately from the rest of the electric circuit in the wind turbine. Preferably lightning current should travel through a down conducted in the blades and the electronics including the transducer in the blade should be protected from flashover e.g. by transformers, optics or the like used for power and data communication.

Moreover, the invention relates to the use of a measurement from an accelerometer positioned in a blade of a wind turbine according to the method of any of the claims 1-12 for determining an operation parameter related to the rotor of the wind turbine.

Figures A few exemplary embodiments of the invention will be described in more detail in the following with reference to the figures, of which figure 1 illustrates a wind turbine, figure 2 illustrates the rotor of the wind turbine of figure 1, figure 3 illustrates a mathematic representation of the rotor plane of figure 2, and figure 4 illustrates a plot of the output of the transducers of the blades.

Detailed description of the invention

Figure 1 illustrates a 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 (from root to tip) is referred to as pitch by means of which the rotation of the rotor in the rotor plan can be controlled. 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 components (commonly denoted 9) such as generator, power converter, gear box etc. Rotational energy from the rotor is transferred to the generator by a main shaft 10 connecting the hub 4 with the generator. The generator transforms the rotational energy into electrical energy and the power converter “shapes” the electrical energy from the generator into a form, which complies with utility grid demands. The electrical energy is transported from the generator to the converter and further to the utility grid via high voltage cables.

Figure 2 illustrates the rotor i.e. the three blades 5a, 5b, 5c (commonly denoted 5) rotating in the rotor plane in a front view. The blades 5 are illustrated mounted to the hub 4 with an angle of 120 degrees between two of the blades 5. In the center of the hub the end of the main shaft 10 is illustrated. The tip of blade 5a is illustrated in position A (denoted Pos A) with its longitudinal axis in a vertical position substantially perpendicular to the horizontal main shaft 10. When the rotor rotates, the blades 5 change position. Hence as an example the tip of blade 5a is also illustrated (with stipulated lines) in a new position denoted Pos B in the rotor plane.

Throughout this document, the position of the blades 5 in the rotor plane is made with reference to blade 5a and it has been defined that when the azimuth angle is 0 [deg.] the tip of blade 5a is in position A pointing upwards.

It should be mentioned that the choice of blade 5a and position A as reference for the azimuth angle of the rotor is not essential to the invention, hence any of the blades 5 and any positon in the rotor plan could have been chosen as reference.

As mentioned figure 2 illustrates blade 5a in two positions, namely position A and position B. Accordingly, the azimuth angle of the rotor when the tip of blade 5a is in the upward direction in position A is 0 [deg.] and when the tip of blade 5a is in position B the azimuth angle is 90 [deg.].

As illustrated each of the blades 5 are equipped with at least one transducer preferably in the form of an accelerometer (also referred to as g-sensor) 1 la, 1 lb, lie (commonly denoted 11). The accelerometers 11 should be able to measure gravity related information Gx_BladeA, GxBladeB, Gx BladeC (commonly denoted Gx_Blade). The transducer 11 is preferably located in the root portion of the blade.

The gravity related information Gx_Blade comprises at least a contribution from the gravity force Gr_A, Gr_B, Gr_C (commonly denoted Gr and derived from the vertical gravity force Fg as will be described below) and from the rotational centripetal force Fc. The latter is the same for each of the blades 5 in that they are rotating with the same speed.

The acceleration arising from the change in direction of the velocity vector is called the centripetal acceleration and is determined mathematically by Fc = V2 / R (V = velocity and R = radius).

The gravity related information GxBlade is provided as a single value to one or more of the wind turbine controllers 6, 7. The gravity related information may also be referred to as acceleration or force in at least one direction i.e. along one axis. According to this invention the accelerometers 11 are preferably orientated and calibrated to measure g-force along the longitudinal axis of the blades 5.

Therefore, if there is no rotation of the rotor and blade 5 a is in a horizontal position (pointing to one of the sides e.g. is in position B) the output of accelerometer 11a will be 0 [g] (the unit “g” in this document refers to g-force). If the blade 5a is in a vertical position e.g. Pos A the output of the accelerometer 1 la will be 1 [g].

It should be mentioned that when the blade points upward in position A the g-force value is positive and when the blade points downward in positon C the g-force is negative. Again this is not essential and the operational sign could be determined to be opposite and accounted for in the below calculations.

The g-force measured from the sensors 11 would therefore vary in a sinusoidal waveform between 1 and -1 [g] if the rotation of the rotor was infinitely slow as illustrated in figure 4. However, when speed is added and the rotor rotates the forces created by the rotation is displacing the sinusoidal curves 12 this force is also referred to as the centripetal force Fc. As an example, the rotation may displace the curves to vary between e.g. -0,9 and 1,1 [g] (not illustrated).

Figure 3 illustrated a mathematic representation of the rotor plane with blades a-c represented by lines 5a-5c. As mentioned there is 120[°] between each of the blades 5. The rotor plane is in an embodiment of the invention divided in 6 zones Z1-Z6 as illustrated on figure 3

The zones Z1-Z6 are also illustrated in figure 4 facilitating evaluating the angles of the blades 5 with respect to the zone Z1-Z6 in which the blade in question is located. The representation of the position of the blades in the rotor plane illustrated in figure 4 is made with reference to blade A 5a (curve 12a) and the curves 12b, 12c representing blades B and C 5a, 5c may simply be plotted with a horizontal displacement of ±120[°] from curve 12a.

The zones Z1-Z6 may be defined either by equally splitting the rotor plane i.e. each zone representing 60[°] of the rotor plane. Preferably the zones Z1-Z6 are defined so that each zone covers an area of the rotor plan in which one of the blades 5 are in a vertical position. When the blades 5 are in a vertical positon i.e. represent by 1 or -1 [g] in figure 4 the gradient of the sinusoidal curve 12 hereof is 0 or close to this value.

Each of the blades 5 are in a vertical position 2 times during one rotation therefore the rotor plan is preferably divided in 6 zones.

When one blade 5 is in a vertical position, the other two blades are between horizontal and vertical position leading to a gradient of the sinusoidal curves which is steep (a gradient is always present). The gradient of the two non-vertical positioned blades are always steep in their intersection point as illustrated in figure 4.

Based on information of gravity force (Fg) experienced by the sensors 11 of the blades 5 and on the knowledge of the 120[°] between each of the blades it is possible to determine in which zone the blades 5 are in. Further, based on the gradients of the three sinusoidal curves the position of the blades in the rotor plane can be determined based on sinus relations.

The sinus relations used are different from zone to zone. The sinus relations used are determined based on the determined reference blade and the determined position of the reference angle (0[°]). The equations are the same only the angles used in the equations changes depending on the determined reference blade and reference angle (0[0])·

It should be mentioned that it is preferred to only use gradient information from the two blades with the steepest gradient in that the contribution to the calculations are largest from these. In fact, if the sensor 11 providing information of the gravity force in its angle phi experienced by the (most) vertical blade is not calibrated correctly an error from measurements hereof can have relative large effect on the calculated angle.

Therefore, it is preferred that the gradients of the curves 12 are compared and the calculation / determination of the angle is based on information from the two sensors 11 based on which the curves 12 having the two steepest gradients are plotted. It is preferred that it is the numeric value of a gradients which are used and it should be mentioned that a plot is only mentioned to better explain the idea. The controllers) performing the calculation are preferably only using / comparing the numeric values the determine the two steepest gradients.

When it has been determined which two of the sensors (and thereby blades) have provided information to the two curves 12 having the steepest gradients, information from these sensors are used in sinus relations to determine the azimuth angle.

The gravity related information Gx_BladeC from blade C 5c is illustrated in figure 3. It is seen that the measurement from the transducer 11c provides gravity related information GxBladeC which comprises contributions from the gravity force Fg pointing downwards (vertical force) and from the centripetal force Fc pointing towards the blade root (rotational force).

The steps of determination of the azimuth angle of the rotor i.e. the positon of the reference blade here blade A 5a will now be describe according to a preferred embodiment of the invention. Other embodiments may facilitate deriving the azimuth angle e.g. without one of the steps below.

The numbers given in relation to this embodiment are only for the purpose of explanation of the embodiment. The numbers may change according to position of sensor 11, rotor speed, length of blade, etc.

Step 1

Measurements (Gx_bladeA, GxbladeB, GxbladeC) from each of the sensors 11 are received a controller 6, 7. The measurements from the sensors 11 will over time form three sinusoidal curves which as mentioned in the infinitely slow rotation will vary between 1 and -1 [g].

An example of the measured signals could be: GxbladeA = 0,8495, GxbladeB = -0,8785 and Gx bladeC = 0,0403

Step 2

The displacement of one blade due to the rotation is calculated assuming that this force Fc (sometimes referred to as the centripetal force) is the same of each of the individual blades 5. As mentioned this force Fc is the force with which the sinusoidal curves are displaced from the interval 1 to -1 [g] (the displacement is vertical up or down).

The centripetal force Fc may be found from the blow equation:

Fc = (GxBladeA + GxBladeB + Gx_BladeC)/3 Fc = (0,8495 + -0,8785 + 0,0403)/3 = 0,0037

Step 3

Moving or displacing the sinusoidal curves back in the interval between 1 and -l[g], the force Fc calculated in step 2 is subtracted the measurements from the sensors 11.

Gr_A = Gx BladeA - Fc = 0,8495 - 0,0037 = 0,8458 Gr_B = Gx BladeB - Fc = -0,8785 - 0,0037 = 0,8748 Gr_C = GxBladeC - Fc = 0,0403 - 0,0037 = 0,0366

Hence now the values Gr_A, Gr_B and Gr_C represents the gravity force of the blades 5 experienced by the sensors 11 measured in the longitudinal direction of the blade.

As the force Gx blade measured by the sensor 11 is in the longitudinal direction of the blade the raw measurement may comprise a contribution from the centripetal force Fc and gravity force Fg. The contribution of the gravity force Fg in the measurement Gr can be found either at the sensor 11 or at a controller 6, 7 e.g. from a sin/cons to the angle between the gravity force Fg and the positon of the blade e.g. cos(phi) x Fg where phi is the angle between gravity force Fg and blade position.

According to alternative embodiments steps 2 and 3 may not be necessary to include in the calculation of the azimuth angle. The centripetal force Fc may be accounted for in step 4 below, however this may complicate the calculations of step 4.

Step 4

When the values Gr_A, Gr_B and Gr_C are found the values plotted over time can be illustrated as three sinusoidal curves varying between 1 and -1 [g] as illustrated on figure 4. On figure 4 the curve 12a represents blade A 5 a, curve 12b represents blade B 5b and curve 12c represents blade C 5c.

It should be mentioned that it is not necessary to actually plot the curves 12 to determine the gradients of the curves 12. Figure 4 therefore may only serve as illustration and assist in the description of the principles of the present invention.

The angles of figure 4 represents the position of blade A 5a in the rotor plane and thereby the azimuth angle of the rotor can be made in relation hereto. From figure 4 the relationship between the azimuth angle and the gravity force experienced by the sensors 11 can be read off. Accordingly, it is found that blade A 5a points downwards (-l[g]) at an angle of 180[°].

Now based on comparison of the absolute value of the gravity force Gr experienced by the sensors 11 it is possible to determine in which of the zone Z1-Z6 blade A 5a is positions in the rotor plane. This may be done by the following equations: IF ABS(Gr A) > ABS(Gr B) & ABS(Gr A) > ABS(Gr_C) & (Gr_A) > 0 = Z1 IF ABS(Gr C) > ABS(Gr A) & ABS(Gr C) > ABS(Gr B) & (Gr_C) < 0 = Z2 IF ABS(Gr B) > ABS(Gr A) & ABS(Gr B) > ABS(Gr C) & (Gr_B) > 0 = Z3 IF ABS(Gr A) > ABS(Gr B) & ABS(Gr A) > ABS(Gr_C) & (Gr_A) < 0 = Z4 IF ABS(Gr C) > ABS(Gr A) & ABS(Gr C) > ABS(Gr B) & (Gr_C) > 0 = Z5 IF ABS(Gr B) > ABS(Gr A) & ABS(Gr B) > ABS(Gr C) & (Gr B) < 0 = Z6

Now the curves / sensor measurements / blades having the two steepest gradients within the determined zone are easily found by simple comparison. The gravity force of from the sensors 11 is now used to calculate the position of blade A and thereby the azimuth angle of the rotor Az.

As mentioned this is done by sinus relations having different angles. The formulas for zones Z1-Z6 with blade A as reference blade and 0[°] upwards could be as follows:

Zl: Az = mod(180 + (180 + asin(Gr_B)*l 80/pi + 180 - asin(GR_B)*180/pi)/2); Z2: Az = ((90 - asin(GrA)* 180/pi) + (30 + asin(Gr_B)*180/pi))/2 Z3: Az = ((90 - asin(Gr A)* 180/pi) + (150 + asin(Gr C)*180/pi))/2 Z4: Az = ((210 - asin(Gr_B)* 180/pi) + (150 + asin(Gr C)*180/pi))/2 Z5:Az = ((210 + asin(Gr_A)*l80/pi) + (270 - asin(Gr_B)*180/pi))/2 Z6: Az = ((270 + asin(Gr_A)*180/pi) + (330 - asin(Gr_C)*180/pi))/2

As can be seen from the equations only values Gr A, Gr_B, Gr_C from two sensors 11 are used in each equation. When looking into the equations and figure 4 it is found that the used values in the equations of the different zones are the values of the zone having the steepest gradient.

According to an embodiment, the displacement due to the rotation of the rotor is included in the calculations described above hence the step of subtracting the centripetal force is mainly made to simplify the calculation of the azimuth angle.

According to yet an embodiment all three measured values Gr_A, Gr_B, Gr_C could be used in the equations in step 4, however in this situation, it would be relevant to attach importance to the two values contributing the most to the calculations i.e. if not leaving the measured value closest to l[g] (or -l[g]) out of the calculations then it should be given less impotence in the calculation. The main result of including all three values is a more ungraduated shift in the results of the calculations made in two different zones.

According to yet an embodiment the raw measurements Gxblade from the sensors 11 can be used for determining the azimuth angle (and the rotor RPM). Preferably the centripetal force Fc should be found and subtracted the measurements Gx blade to arrive at the gravity force Fg contribution Gr. However, this step may not be necessary if accounted for in the calculations of the azimuth angle.

In the same way, the definitions of zones to determine position of a blade in the rotor plane may not be necessary although it simplifies the calculations significantly. If the raw measurements Gx blade is used different importance is attached to each of these measurements in the calculations of the azimuth angle and rotor RPM. The determining factor of which measurement to attach importance to and how much differ during one revolution. Preferably, the measurements used are the once with the most information i.e. as described above e.g. having the steepest gradient.

One particular advantage of the above method of determine the azimuth angle is that it may be determined even when the rotor is standing still e.g. in a situation where there is no wind to facilitate rotation of the rotor in the rotor plane.

Further, from the above method of determining the azimuth angle it is possible to determine when the rotor rotates e.g. by monitoring if blades are changing zones Zl-Z6. Therefore, the above method may initiate calculation of the rotor speed referred to as rotor RPM (RPM: Revolutions Per Minute).

Hence, according to a preferred embodiment of the invention, the present invention may also be used to determine or calculate the rotor RPM. The rotor RPM can be calculated based on information from one of the blades in the following steps where step 1 and step 2 are identical to step 1 and step 2 described above (i.e. the values determined during step 1 or step 2 above may be used).

As mentioned, rotor RPM step 1 and step 2 is equal to step 1 and step 2 above in relation to determining the azimuth angle. Hence the centripetal force Fc is found from measurements Gx blade from the sensors 11 by the following equation

Fc = (Gx BladeA + Gx BladeB + Gx BladeC) / 3

Rotor RPM step 3

The centripetal force Fc is then used used to calculate of the rotor RPM from the following equation:

Fc= 1.12 x R x (RPM/1000)2

Where R is Radius of the rotor in [mm]

RPM is the rotor RPM 1,12 is a constant RPM is then isolated as follows: (RPM/1000)A2 = Fc / (1.12 * R) RPM = 1000 * sqrt(Fc/(1.12 * R)) RPM = 1000 * sqrt(Fc / (1.12 * R))

Accordingly, the present invention describes a method of calculating the rotor RPM and a method of calculating the azimuth angle of the rotor. The methods are based on the location of at least one one-axis accelerometer positioned in the root end (e.g. within 5 meters) of each of the blades. Measurements from these sensors relating to gravity is provided to a wind turbine controller 6, 7.

It should be mentioned that when providing electronics in a blade it should always be protected from currents induced by lightning’s. Therefore, data communication and power to and from transducers or controllers in a blade should be galvanic separated from the rest of the wind turbine as far as possible. Such galvanic separation or other ways of lightning protection could be made from using optical fibers, wireless communication including radio communication, electrical coils of e.g. a transformer, etc.

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. Components 10. Main shaft 11. Transducers 12. Plot of transducer measurements Gr. Contribution from gravity froce Fc. Centripetal force

Gx Blade. Gravity related information measured by sensor 11 Az. Azimuth angle

Claims

A method for determining an operating parameter related to the rotor of a wind turbine (1), wherein each vane (5) of the wind turbine (1) comprises a transducer (11), the method comprising the steps of: - providing a control unit ( 6, 7) of gravity-related information Gxblade ffa transducers (11), - determination made by the control unit (6, 7) from the gravity-related information Gx_blade, of the magnitude of the contribution of gravity Gr, and - determination made by the control unit (6, 7), of at least one operating parameter based on the magnitude of the contribution of gravity Gr, where the operating parameter is determined using the contribution of gravity Gr from two out of three blades, the two wing contributions of gravity Gr being found by comparing the gradient of the contribution of gravity Gr from the three blades and select the two blades which have the steepest gradient for the contribution of gravity Gr.

A method according to claim 1, wherein the operating parameter is determined on the basis of a change in the magnitude of the contribution ffa gravity Gr over time for the gravity-related information Gx leaves the ffa transducer (11).

The method of any one of claims 1 or 2, wherein the controller (6, 7), apart from the gravity-related information Gx_blade, determines the magnitude of the contribution of the centripetal force Fc.

Method according to any one of the preceding claims, wherein the transducer (11) is arranged in the root part of the blade.

A method according to any one of the preceding claims, wherein the centripetal force Fc is determined from the gravity-related information Gxblade by summing the gravity-related information Gx_blade from each wing (5) divided by the number of wings (5).

A method according to any of the preceding claims, wherein the contribution of gravity Gr for each wing (5) is determined from the gravity-related information Gx_blade by subtracting the centripetal force Fe from the gravity-related information Gx_blade.

A method according to any one of the preceding claims, wherein the operating parameter includes operating parameters from the list which include: rotor speed, azimuth angle and pitch angle.

A method according to any one of the preceding claims, wherein at least one of the operating parameters is used to control the wind turbine (1) during normal operation thereof.

Method according to any one of the preceding claims, wherein the operating parameter is determined by weighting the measurements Gx blade from the transducers (11), wherein the weighting of the individual measurement Gx blade is determined by the contribution of gravity Gr for the individual measurement.

A method according to any one of the preceding claims, wherein the rotor plane is divided into a plurality of zones and wherein a unique equation for determining the azimuth angle is associated with each zone.

A method according to any one of the preceding claims, wherein the transducer (11) is an accelerometer.

A system for determining an operating parameter related to the rotor of a wind turbine (1) according to any of the preceding claims, wherein at least the transducers (11) disposed in the blades (5) and which communicates with the wind turbine control unit (6, 7) is protected against lightning current.

Use of a measurement Gx blade from an accelerometer (11) arranged in a wing (5) of a wind turbine (1) according to the method according to any one of claims 1-11, for determining an operating parameter which is related to the wind turbine rotor.