Detecting a pitch angle adjustment fault

Abstract

A method for detecting a rotor blade pitch angle adjustment fault of a rotor blade of a wind turbine is provided, the method includes measuring a rotor blade pitch angle speed; predicting, based on an actual rotor speed, a rotor blade pitch angle speed; indicating a fault, if a first criterion is satisfied, wherein the first criterion is satisfied, if deviation between the measured rotor blade pitch angle speed and the predicted rotor blade pitch angle speed exceeds a speed threshold.

Claims

1. A method for detecting a rotor blade pitch angle adjustment fault of a rotor blade of a wind turbine, the method comprising: measuring a rotor blade pitch angle speed during operation of the wind turbine wherein the rotor blade pitch angle speed is a speed or velocity with which a rotor blade pitch angle changes with time; predicting, based on an actual rotor speed, a predicted rotor blade pitch angle speed; and indicating a fault, if a first criterion is satisfied, wherein the first criterion is satisfied, if deviation between the measured rotor blade pitch angle speed and the predicted rotor blade pitch angle speed exceeds a speed threshold wherein indicating the fault further comprises activating a safety system which increases the rotor blade pitch angle.

2. The method according to claim 1, wherein the measured rotor blade pitch angle speed is taken as an average rotor blade pitch angle speed or a maximum rotor blade pitch angle speed among at least two rotor blades of the wind turbine.

3. The method according to claim 1, wherein predicting the predicted rotor blade pitch angle speed is further based on a rotor acceleration and/or the rotor blade pitch angle of a respective rotor blade.

4. The method according to claim 1, wherein predicting the predicted rotor blade pitch angle speed includes computing a derivative of a predicted rotor blade pitch angle.

5. The method according to claim 1, wherein the predicted rotor blade pitch angle speed is derived based on a deviation between a reference rotor speed and the actual rotor speed.

6. The method according to claim 1, wherein the predicted rotor blade pitch angle speed is derived based on an instantaneous and a time integrated deviation between a reference rotor speed and the actual rotor speed.

7. The method according to claim 1, wherein the predicted rotor blade angle speed is derived based on a predicted rotor blade pitch angle (.sub.ref) defined according to: ${}_{\mathrm{ref}}=G\left(\right).Math.\left(K_p+{}_0^t{K}_{i}dt\right)$ wherein G() is a gain function depending on a filtered blade pitch angle , is a deviation between a reference rotor speed and the actual rotor speed, K.sub.p is a proportional gain, and K.sub.i is an integrative gain.

8. The method according to claim 1, wherein, if the predicted rotor blade pitch angle speed is greater than a maximum controller pitch angle speed, the predicted rotor blade pitch angle speed is reset to the maximum controller pitch angle speed, the maximum controller pitch angle speed being a maximum speed the controller is able to change the pitch angle.

9. The method according to claim 1, wherein a fault is not indicated, if the measured rotor blade pitch angle speed, that is in a direction to increase the rotor blade pitch angle, is greater than a minimum rotor blade pitch angle speed threshold.

10. The method according to claim 1, wherein a fault is not indicated, if the rotor speed is smaller than a minimal rotor speed threshold.

11. The method according to claim 1, wherein the fault is indicated, if at least one of the first criterion and a second criterion is satisfied, wherein the second criterion is satisfied, if the rotor speed is greater than a maximum rotor speed threshold.

12. The method according to claim 1, wherein the fault is indicated, if at least one of the first criterion and a second criterion and a third criterion is satisfied, wherein the second criterion is satisfied, if the rotor speed is greater than a maximum rotor speed threshold, wherein the third criterion is satisfied, if the following holds: rotor speed>PitchRunAwayEnableSpeed AND (ABS(Pitch_A_Pitch_B)>MaxPitchDeviation) OR ABS(Pitch_B_Pitch_C)>MaxPitchDeviation) OR ABS(Pitch_A_Pitch_C)>MaxPitchDeviation)) wherein the PitchRunAwayEnableSpeed is a rotor speed threshold, the Pitch_A is the rotor pitch angle of a first rotor blade, the Pitch_B is the rotor pitch angle of a second rotor blade, the Pitch_C is the rotor pitch angle of a third rotor blade, the first, second and third rotor blades being connected to a shaft of the wind turbine, and the MaxPitchDeviation is a pitch angle deviation threshold.

13. A software program stored on a non-transitory computer-readable medium, adapted, when executed on a computing system, to carry out a method according to claim 1.

14. The method according to claim 1, wherein the measured rotor blade pitch angle speed is taken as an average rotor blade pitch angle speed or a maximum rotor blade pitch angle speed among all rotor blades of the wind turbine.

15. The method according to claim 1, wherein the measured rotor blade pitch angle speed is continuously measured or continuously sampled during the operation of the wind turbine.

16. A wind turbine controller comprising: an arrangement including a processor for detecting a rotor blade pitch angle adjustment fault of a rotor blade of a wind turbine, the arrangement of the wind turbine controller configured to: receive a measured rotor blade pitch angle speed and to receive an actual rotor speed wherein the measured rotor blade pitch angle speed is a speed or velocity with which a rotor blade pitch angle changes with time: predict, based on the actual rotor speed, a predicted rotor blade pitch angle speed and determine that a first criterion is satisfied, if a deviation between the measured rotor blade pitch angle speed and the predicted rotor blade pitch angle speed exceeds a speed threshold; and transmit a signal to a safety system which indicates a fault, if the first criterion is satisfied wherein the safety system causes a change in the rotor blade pitch angle of the rotor blade.

17. The wind turbine controller according to claim 16, wherein the predicted rotor blade angle speed is derived based on a predicted rotor blade pitch angle (.sub.ref) defined according to: ${}_{\mathrm{ref}}=G\left(\right).Math.\left(K_p+{}_0^t{K}_{i}dt\right)$ wherein G() is a gain function depending on a filtered blade pitch angle , is a deviation between a reference rotor speed and the actual rotor speed, K.sub.p is a proportional gain, and K.sub.i is an integrative gain.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 schematically illustrates a top view of a wind turbine comprising an arrangement for detecting a rotor blade pitch angle adjustment fault according to an embodiment of the present invention;

(2) FIG. 2 schematically illustrates an arrangement for detecting a rotor blade pitch angle adjustment fault according to an embodiment of the present invention which is adapted to carry out a method for detecting a rotor blade pitch angle adjustment fault according to an embodiment of the present invention; and

(3) FIG. 3 illustrates a schematic diagram of an arrangement for detecting a rotor blade pitch angle adjustment fault according to an alternative embodiment of the present invention.

DETAILED DESCRIPTION

(4) The illustration in the drawings is in schematic form. It is noted that in different figures, similar or identical elements are provided with the same reference signs or with reference signs, which are different from the corresponding reference signs only within the first digit.

(5) The wind turbine 100 illustrated in a top view in FIG. 1 comprises a nacelle 101 in which a rotor shaft 103 is supported in a not illustrated bearing and can rotate within the nacelle 101. To the rotor shaft 103, a hub 105 is connected to which one or more rotor blades 107 are attached, wherein only one rotor blade 107 is illustrated in FIG. 1. The rotor blade 107 rotates in a rotation plane 109 which is perpendicular to an axis 111 of the rotor shaft 103. The rotor blade 107 has a particular cross sectional profile or airfoil having a, relative to a chord line 113, thinner side 115 facing the wind 117 and having a thicker side 119 directed away from the wind 117. The rotor blade 107 can be rotated around a longitudinal axis 121 of the rotor blade 107, in order to adjust a rotor blade pitch angle which is the angle between the rotation plane 109 and the chord line 113.

(6) The partially illustrated wind turbine 100 further comprises an arrangement 123 for detecting a rotor blade pitch angle adjustment fault. The arrangement 123 receives input signals 125, 127 which may comprise a measured rotor blade pitch angle speed 125, i.e. the velocity or speed with which the rotor blade pitch angle of the rotor blade 107 changes with time. The rotor blade pitch angle speed 125 may for example be measured using an encoder which basically measures the rotor blade pitch angle and forms a derivative of this measured rotor blade pitch angle . The arrangement 123 further receives an actual rotor speed 127.

(7) The arrangement 123 is in further detail illustrated in FIG. 2. The arrangement 123 for detecting a rotor blade pitch angle adjustment fault of the rotor blade 107 (or also one or more other rotor blades connected to the wind turbine hub 105) comprises a reception section 129 which is adapted to receive a measured rotor blade pitch angle speed 125 and also adapted to receive an actual rotor speed 127 being the rotational speed with which the rotor 103 rotates around its rotation axis 111. Further, the arrangement 123 comprises a computing section 131 which is adapted to predict, based on the actual rotor speed 127, a rotor blade pitch angle speed and to determine that a first criterion is satisfied, if a deviation between the measured rotor blade pitch angle speed 125 and the predicted rotor blade pitch angle speed 133 (calculated within the computing section 131) exceeds a speed threshold. Furthermore, the arrangement 123 comprises an output section 135 which is adapted to indicate a fault (comprising signals 137) if the first criterion is satisfied.

(8) The signal 137 may thereby comprise a control signal for activating or controlling a safety system 139 which is then adapted to increase the rotor blade pitch angle such that the driving force caused by the impacting wind 117 decreases or even vanishes.

(9) The predicted rotor blade pitch angle speed may be derived from a predicted or referenced rotor blade pitch angle, as defined in the equation below:

(10) $\begin{array}{cc}{}_{\mathrm{ref}}=G\left(\right).Math.\left(K_p+{}_0^t{K}_{i}dt\right)& \left(\mathrm{eq}.1\right)\end{array}$

(11) wherein G() is a gain function depending on a filtered blade pitch angle is the deviation between the reference rotor speed and the actual rotor speed K.sub.p is a proportional gain K.sub.i is an integrative gain.

(12) Thereby, .sub.ref is the reference pitch angle, K.sub.p is the proportional gain, K.sub.i=K.sub.p/T.sub.i is the integral gain and =.sub.ref, wherein is the rotor speed of the rotor 103 and .sub.ref is the rated rotor speed or the reference rotor speed or nominal rotor speed, being the rotor speed of the normal energy production operation of the wind turbine 100. Thereby further, G=G() is a gain scheduling function based on the pitch angle .

(13) The gain scheduling function is defined as: if >.sub.2
G=K.sub.1/(.sub.2+.sub.offset) else if .sub.2>>.sub.1
G=K.sub.1/(+.sub.offset) else
G=1 where
=(K.sub.2K.sub.1)/(.sub.2.sub.1)
.sub.offset=K.sub.1.sub.1

(14) All parameters K.sub.1, K.sub.2, .sub.1 and .sub.2 can be based on controller input parameters or tuned based on parameter studies.

(15) From the reference rotor blade pitch angle .sub.ref, the rotor blade pitch angle speed may be predicted by differentiation, as shown below and assuming that

(16) $\begin{array}{cc}\begin{array}{c}dG\\ dt\end{array}0\text{:}\frac{d}{dt}=G\left(K_p\frac{d}{dt}+K_1\left(-{}_{\mathrm{ref}}\right)\right)& \left(\mathrm{eq}.2\right)\end{array}$

(17) To ensure that the predicted pitch speed is not exceeding the maximum controller pitch speed, a check may be made if d/dt>pitch_speed_max
pitch_speed_predict=pitch_speed_max else
pitch_speed_predict=d/dt

(18) According to an embodiment of the present invention, the detection method comprises a pitch run away monitor which compares the pitch speed predicted by the above equation (eq. 1) based on rotor speed, acceleration and pitch position and compares this predicted pitch speed to the actual measured pitch speed, which may for example be based on a measured position, such as using a hydraulic system, or an encoder.

(19) Thereby, the following is calculated:
Pitch_Speed_Error=Pitch_Speed_PredictedPitch_Speed_Measured

(20) The measured pitch speed can be taken as the average pitch speed of the blades or as the maximum pitch speed among the blade 107 connected to the hub 105 of the wind turbine 100 illustrated in FIG. 1. If the Pitch_Speed_Error becomes larger than some threshold, a safety system, such as safety system 139 illustrated in FIG. 1, may be activated.

(21) If Pitch_Speed_Error>Pitch_Speed_Error_Max (first criterion) activate safety system

(22) To ensure that the pitch runaway monitor is not triggered, if the wind turbine is currently in the process of slowing down or stopping the rotor, the following check is performed:

(23) If Pitch_Speed_Measured Pitch_Speed_Min Pitch_Speed_Error=1

(24) That is, if the turbine is pitching towards stop with a certain pitch speed Pitch_Speed_Min, the pitch speed monitor is deactivated.

(25) To ensure that the pitch speed monitor is only active, when the turbine is running, the following check of rotor speed may be performed:

(26) If Rotor_Speed<Rotor_Speed_Min Pitch_Speed_Error=1

(27) The above criterion regarding the Pitch_Speed_Error may also be referred to as a first criterion.

(28) Furthermore, additionally to the first criterion, a second criterion may be defined and may be monitored within the method for detecting the fault:

(29) Rotor_Speed>Over_Speed_Limit (second criterion)

(30) If the rotor speed is above a threshold, the safety system may be activated.

(31) Furthermore, additionally, a third criterion may be evaluated, as follows according to a Pitch position deviation monitor (third criterion): rotor speed>PitchRunAwayEnableSpeed AND (ABS(Pitch_APitch_B)>MaxPitchDeviation) OR ABS(Pitch_BPitch_C)>MaxPitchDeviation) OR ABS(Pitch_APitch_C)>MaxPitchDeviation))

(32) wherein PitchRunAwayEnableSpeed is a rotor speed threshold Pitch_A is the rotor pitch angle of a first rotor blade Pitch_B is the rotor pitch angle of a second rotor blade Pitch_C is the rotor pitch angle of a third rotor blade, the first, the second and the third rotor blade being connected to the shaft of the wind turbine, MaxPitchDeviation is a pitch angle deviation threshold

(33) If the rotor speed is above a threshold and the deviation between the pitch angle of the blade exceeds a threshold, the safety system may be activated.

(34) The detecting method, which may be carried out by the arrangement 123 illustrated in FIGS. 1 and 2 may be more robust, may offer earlier detection and less faults false positive activations of the safety system compared to conventional methods.

(35) The arrangement 123 may further comprise a program reader 141 which may be adapted to read program code (compiled or not compiled) comprising instructions which, when carried out by the arrangement 123 causes performing or performs the detection method according to embodiments of the present invention described above.

(36) FIG. 3 illustrates a schematic diagram of an arrangement for detecting a rotor blade pitch angle adjustment fault according to an alternative embodiment of the present invention.

(37) The arrangement 323 comprises a speed sensor 343 which senses the rotational speed of the rotor 103. The measurement signals 345 are transmitted to a speed sensor diagnostic 347 and also to a monitoring matrix 349. From the rotational speed measurement values 345, a block 351 calculates the acceleration 353 of the rotational speed of the rotor 103. The acceleration of the rotor speed is also input into the monitoring matrix 349. Failsafe pitch sensors 355 sense or detect rotor blade pitch angles and output the rotor blade pitch angles 357 to a pitch signal diagnostic 359 and also to a block 361 which calculates the rotor blade pitch angle speed 363 from the pitch angles 357.

(38) Thereby, the monitoring matrix 349 may indicate a fault 365 under the following conditions:

(39) Speed monitoring: Rotor speed<rotor speed_1

(40) Pitch runaway:

(41) TABLE-US-00001 ( Rotor speed > rotor speed_2 AND Rotor acceleration > rotor acceleration_1 AND piston speed < piston speed_1 ) OR ABS (piston speed) > piston speed_2

(42) The fault signal is transmitted to a contactor 367 which then sends a control signal to the emergency pitch function 369.

(43) The diagnostic monitoring according to this embodiment of the present invention monitors the piston speed and may be done in a failsafe manner, as the interface is based on pulsed signal on a balanced transmission line (RS485 hardware). The length between the start and the stop pulse is giving the position of the piston. If too many or too few pulses are received within the cycle time, the sensor will be seen as faulty.

(44) By detecting the fault situation or the pitch action related to the condition of the rotor speed and rotor acceleration instead of a rotor overspeed detection may make is possible to react much earlier and before the rotor speed reaches a critical limit. Thereby, the controller fault situation is not giving design driving loads and hereby material cost may be saved. Another advantage of the control method may be that a control failure mode may be precisely detected. Other detection methods, e.g. acceleration as a function of speed may not be able to distinguish between a pitch runaway and a grid drop situation, in contrast to the method according to this embodiment of the present invention.

(45) It should be noted that the term comprising does not exclude other elements or steps and a or an does not exclude a plurality. Also elements described in association with different embodiments may be combined. It should also be noted that reference signs in the claims should not be construed as limiting the scope of the claims.