Determining a wind turbine tower inclination angle

Abstract

Provided is a method of determining an inclination angle of a wind turbine tower at which a nacelle is mounted, the method including measuring plural acceleration values of an acceleration of the nacelle in a predetermined direction relative to the nacelle for plural yawing positions of the nacelle; deriving the inclination angle based on the plural acceleration values.

Claims

1. A method of operating a wind turbine, including determining an inclination angle of a wind turbine tower at which a nacelle is mounted, the method comprising: rotating the nacelle around a yawing axis, wherein the rotating comprises multiple rotations around the yawing axis; measuring plural acceleration values of an acceleration of the nacelle in a predetermined direction relative to the nacelle for plural yawing positions of the nacelle, wherein the measuring occurs during the rotating of the nacelle around the yawing axis and without stopping the nacelle at any yawing position of the nacelle during the multiple rotations around the yawing axis; deriving the inclination angle based on the plural acceleration values, the deriving the inclination angle comprising: averaging acceleration values in each yawing position bin of a plurality of yawing position bins to obtain for each yawing position bin an associated averaged acceleration value in which noise and oscillations have been filtered out; deriving the inclination angle based on the averaged acceleration values in which noise and oscillations have been filtered out, and shutting down the wind turbine if the determined inclination angle exceeds a threshold.

2. The method according to claim 1, further comprising: measuring further plural acceleration values of an acceleration of the nacelle in a further predetermined direction relative to the nacelle for the plural yawing positions of the nacelle; deriving the inclination angle further based on the further plural acceleration values.

3. The method according to claim 1, further comprising: deriving an at least one of an orientation and a direction of the inclination of the wind turbine tower based on the plural acceleration values.

4. The method according to claim 1, wherein the deriving the inclination angle comprises: deriving a mean acceleration value by averaging the plural acceleration values over all yawing positions; calculating plural acceleration differences between the averaged acceleration values and the mean acceleration value; determining a maximum and a minimum of the acceleration differences; determining a difference between maximum and minimum and deriving an inverse of a trigonometric function using a quantity proportional to the difference as an argument, to obtain the inclination angle.

5. The method according to claim 1, wherein the deriving the inclination angle comprises: fitting a trigonometric function, including a cosine function or a sine function, on the plural acceleration values; deriving the inclination angle based on an amplitude of the trigonometric function.

6. The method according to claim 1, wherein the different yawing positions cover samples of one or more circumferences, including at least 360°, of a rotation of the nacelle around an axis running along a longitudinal direction of the wind turbine tower.

7. The method according to claim 1, performed during a cable untwist operation.

8. The method according to claim 2, wherein the predetermined direction is substantially parallel to a longitudinal direction of the nacelle, the further predetermined direction is substantially orthogonal to the longitudinal direction of the nacelle.

9. The method according to claim 1, wherein the measuring of the plural acceleration values is performed using an accelerometer installed at the nacelle.

10. An arrangement for operating a wind turbine and determining an inclination angle relative to a vertical direction of a wind turbine tower at which a nacelle is mounted, the arrangement comprising: an accelerometer adapted to measure plural acceleration values of an acceleration of the nacelle in a predetermined direction relative to the nacelle for plural yawing positions of the nacelle, wherein the accelerometer measures the plural acceleration values during a continuous rotation of the nacelle around a yawing axis, the continuous rotation of the nacelle comprising multiple rotations around the yawing axis, wherein the nacelle is not stopped at any of the plural yawing positions of the nacelle during measuring; a processor adapted to derive the inclination angle based on the plural acceleration values, the derivation comprising: averaging acceleration values in each yawing position bin of a plurality of yawing position bins to obtain for each yawing position bin an associated averaged acceleration value in which noise and oscillations have been filtered out; and deriving the inclination angle based on the averaged acceleration values.

11. A wind turbine, including: a nacelle; a wind turbine tower having rotatable supported the nacelle on top; and an arrangement for operating the wind turbine and determining an inclination angle relative to a vertical direction of the wind turbine tower at which the nacelle is mounted, the arrangement comprising: an accelerometer adapted to measure plural acceleration values of an acceleration of the nacelle in a predetermined direction relative to the nacelle for plural yawing positions of the nacelle, wherein the accelerometer measures the plural acceleration values during a continuous rotation of the nacelle around a yawing axis, the continuous rotation of the nacelle comprising multiple rotations around the yawing axis, wherein the nacelle is not stopped at any of the plural yawing positions of the nacelle during measuring; a processor adapted to derive the inclination angle based on the plural acceleration values, the derivation comprising: averaging acceleration values in each yawing position bin of a plurality of yawing position bins to obtain for each yawing position bin an associated averaged acceleration value in which noise and oscillations have been filtered out; and deriving the inclination angle based on the averaged acceleration values.

Description

BRIEF DESCRIPTION

(1) Some of the embodiments will be described in detail, with reference to the following figures, wherein like designations denote like members, wherein:

(2) FIG. 1 schematically illustrates a wind turbine including a nacelle with an arrangement for determining an inclination angle according to an embodiment of the present invention; and

(3) FIG. 2 illustrates a graph as considered in a method of determining an inclination angle of a wind turbine tower according to an embodiment of the present invention which may for example be performed by the arrangement illustrated in FIG. 1.

DETAILED DESCRIPTION

(4) The illustration in the drawings is in schematic form.

(5) Illustrated in FIG. 1 is a wind turbine 100 according to an embodiment of the present invention including a nacelle 105 with an arrangement 101 for determining an inclination angle (relative to a vertical direction 104) of a wind turbine tower 103 according to an embodiment of the present invention. The wind turbine 100 comprises a nacelle 105, the wind turbine tower 103, the foundation 102, and rotor blades 107 connected to a not illustrated rotation shaft which drives a generator to generate electric energy.

(6) The arrangement 101 (here installed in the nacelle 105) comprises an accelerometer 109 and further a processor 111. The accelerometer 109 is adapted to measure plural acceleration values of an acceleration of the nacelle 105 in a predetermined direction 113 (in the illustrated embodiment the longitudinal direction of the nacelle) relative to the nacelle for plural yawing position of the nacelle. The processor 111 is adapted to derive the inclination angle ‘Inc’ based on the plural acceleration values.

(7) For adjusting the nacelle in the plural different yawing directions or yawing positions, the nacelle 105 is turned around (yawed around) the yawing axis 115 which substantially runs along a longitudinal axis of the wind turbine tower 103. The arrangement 101 is adapted to perform a method of determining an inclination angle ‘Inc’ of the wind turbine tower 103 by measuring plural acceleration values of an acceleration of the nacelle 105 in a predetermined direction 113 relative to the nacelle 105 for plural yawing positions Nac_pos of the nacelle 105 and by deriving the inclination angle ‘Inc’ based on the plural acceleration values.

(8) In FIG. 1, ‘Ag’ denotes the gravity acceleration (9.82 m/s.sup.2, and ‘Ay’ is the acceleration measured by the accelerometer 111 in the direction 113 which is fixed relative to the nacelle 105. ‘Inc’ is the maximum inclination in all nacelle positions. ‘Nac_pos’ is the nacelle position (also called yaw position) relative to North, i.e. an arbitrary direction.

(9) The acceleration Ay is measured by the accelerometer 111 and according to the method for determining the inclination angle, the inclination is extracted from nacelle acceleration measurements, while the turbine is performing for example a cable untwist operation. The accelerometer 101 is for example placed within or at the nacelle 105 to measure Ay according to FIG. 1. The measured nacelle acceleration Ay can be expressed by:
Ay=Ag*sin(Inc)*sin(Nac_pos+k)+offset+vibrations

(10) Therein, ‘offset’ is the sensor offset which is steady over a shorter time and ‘vibrations’ are representing accelerations caused by movements of the tower. These vibrations have a zero mean value. While the turbine is performing a cable untwist, it may yaw more than one round which will give data points for Nac_pos from 0 to 360°.

(11) According to an embodiment of the present invention, a binning method is utilized to reduce noise and vibrations and scatter in the measured acceleration data. By averaging A y in bins of nacelle positions, the vibrations will be filtered out, as indicated by the next equation.
Ay_filtered=BinData(Nac_pos,Ay,0:360)=˜Ag*sin(Inc)*sin(Nac_pos+k)+offset

(12) The offset can be subtracted as it is the mean value of the binned data:
Ay_UnBiased=Ay_filtered mean(Ay_filtered)=˜Ag*sin(Inc)*sin(Nac_pos+k)

(13) The inclination can then be calculated by applying an inverse of the sine function to the relation between the amplitude of this signal and the gravity acceleration:

(14) FIG. 2 illustrates a graph in a coordinate system having an ordinate 201 indicating the nacelle positions in degree and having an ordinate 203 indicating the nacelle acceleration as measured by the accelerometer 111. The scatter points 205 represent the raw measured acceleration values of the nacelle 105 along the direction 113. The scattered data 205 comprise noise and vibrations and are filtered according to the embodiments of the present invention to derive filtered acceleration values or averaged acceleration values 207. As can be appreciated from FIG. 2, the curve 207 resembles a sine curve shifted by a particular phase-shift. The phase-shift k in the equation above comprises information regarding the direction/orientation of the inclination angle. The amplitude A of the curve 207, i.e. half of the difference 2A between the maximum 209 and the minimum 211, is related to the inclination angle. By taking the inverse of half the difference 2A between the maximum 209 and the minimum 211 of the curve 207, the inclination angle Inc can be determined. The measured inclination can then be compared to a defined threshold and an alarm can be raised if the inclination exceeds this threshold. The accuracy of the method may be in the range of 0.01°.

(15) Embodiments of the present invention may enable to monitor the inclination of the wind turbine tower and foundations without any manual operations. This may have the advantage during the takeover process after commissioning, where it has to be verified that the inclination is within the tolerance limits. It has also an advantage relative to continuously monitoring the inclination where an early warning can be set before for example a scaur projection on the foundation needs repair.

(16) Compared to the manual methods which are conventionally employed with for example spirit levels, the embodiments of the present invention may save efforts and maintenance personnel and may not be dependent on the actual weather conditions.

(17) The inclination monitoring function may be placed in the turbine controller or it can be done offline from a central workstation or in a park controller.

(18) The signal processing by the for example processor 111 may also comprise a fitting procedure to fit a sine function to the raw or filter data instead of employing the binning method as detailed above.

(19) A dual axis accelerometer (e.g. for measuring accelerations Ax and Ay in directions x and y) placed in the nacelle may provide even higher accuracy. In this case, the data may be fitted to a model for example
Ay=Ag*sin(Inc)*sin(Nac_pos+k)
Ax=Ag*sin(Inc)*cos(Nac_pos+k)

(20) The orientation of the inclination relative to North may by be extracted by finding the best fit of the parameter k to the data set. This might be useful for the foundation inspection planning.

(21) The cable untwist may be forced so it is not necessary to wait for an untwisting event.

(22) A monitoring function may check the inclination during every cable untwist event and set a warning in the turbine lock in case of excessive inclination.

(23) Although the present invention has been disclosed in the form of preferred embodiments and variations thereon, it will be understood that numerous additional modifications and variations could be made thereto without departing from the scope of the invention.

(24) For the sake of clarity, it is to be understood that the use of “a” or “an” throughout this application does not exclude a plurality, and “comprising” does not exclude other steps or elements.