METHOD FOR DETECTING DIFFERENT VIBRATIONS OF A WIND TURBINE

Abstract

A method for operating a wind turbine, and the wind turbine comprises a generator for generating electrical power from wind, the generator having a generator axis, a nacelle for supporting the generator, and a tower for supporting the nacelle, the tower having a tower axis, and the method comprises the steps sensing at least one tower vibration by means of a vibration sensor, sensing a mechanical generator vibration, caused by at least one electrical fault, by means of the same vibration sensor, and controlling the wind turbine in dependence on the sensed tower vibration and the sensed generator vibration.

Claims

1. A method comprising: operating a wind turbine, sensing at least one tower vibration of the wind turbine by a vibration sensor, sensing a mechanical generator vibration, caused by at least one electrical fault, by the vibration sensor, and controlling the operation of the wind turbine in dependence on the sensed tower vibration and the sensed generator vibration.

2. The method as claimed in claim 1, wherein the sensor is an acceleration sensor configured to sense vibration in at least two directions.

3. The method as claimed in claim 1, wherein the sensor is arranged on a stator of a generator of the wind turbine, a stator carrier of the wind turbine, a nacelle of the wind turbine, or a tower of the wind turbine.

4. The method as claimed in claim 1, wherein sensing at least one tower vibration comprises sensing a longitudinal vibration signal and a transverse vibration signal, wherein the longitudinal vibration signal is sensed from a force acting in a longitudinal direction of a generator axis, wherein the transverse vibration signal is sensed from a force acting in a direction transverse to the longitudinal direction.

5. The method as claimed in claim 1, separating at least one vibration signal sensed by the vibration sensor into a tower-vibration signal and a generator-vibration signal, wherein the separating is in dependence on frequency.

6. The method as claimed in claim 1, wherein sensing the at least one tower vibration of the wind turbine comprises sensing a tower longitudinal vibration and a tower transverse vibration.

7. The method as claimed in claim 1, wherein the controlling of the wind turbine is functionally divided into: a working-point control for controlling the wind turbine at a working point, and a protective control, which is hierarchically of a higher order than the working-point control, for checking protective functions of the wind turbine, wherein the protective control checks for disturbance criteria and, if a predetermined disturbance criterion is identified, take over the working-point control, and in dependence on the predetermined disturbance criterion that is sensed, moves to a safe working point, in particular reduces or stops a rotation of the rotor of the wind turbine.

8. The method as claimed in claim 7, wherein the protective control has a main and a secondary control, wherein the main control executes the protective control, and the secondary control takes over at least a portion of the protective control if the main control fails.

9. The method as claimed in claim 1, further comprising comparing the at least one tower vibration to a tower vibration limit value, wherein a disturbance is identified in response to the at least one sensed tower vibrations exceeding the predetermined tower-vibration limit value.

10. The method as claimed in claim 1, comprising: monitoring a vibration characteristic of at least one vibration chosen from the tower longitudinal vibration, the tower transverse vibration and the generator vibration, comparing the vibration characteristic in each case to a first vibration tolerance band, when the respective vibration characteristics depart from the first vibration tolerance band, summing or integrating each vibration characteristic to form an exceedance sum, comparing the exceedance sum to a predetermined maximum sum, and if the exceedance sum attains or exceeds the predetermined maximum sum in a predetermined first check period, stopping the wind turbine due to a disturbance, or outputting a first vibration warning and a stopping of the wind turbine depends on a subsequent variation of the vibration characteristic.

11. The method as claimed in claim 10, comprising obtaining the subsequent variation of the vibration characteristic, wherein obtaining the subsequent variation of the vibration characteristic comprises: in a first subsequent step, setting the exceedance sum to zero, and in a second subsequent step, summing or integrating each departure from the first vibration tolerance band to form the exceedance sum until a second vibration warning is output again, repeating the first and second subsequent steps, and counting the vibration warnings that occur during the first and second subsequent steps, and checking whether, in a predetermined second check period that is longer than the first check period, a number of vibration warnings has attained a predetermined warning number limit, and depending on this, the wind turbine is stopped due to a disturbance or continues to be operated, and checking whether the predetermined or a second warning number limit is attained, while the number of vibration warnings is in each case reduced by one counter following an expiration of a duration of a reduction interval, and depending on this, the wind turbine is stopped due to a disturbance or continues to be operated.

12. The method as claimed in claim 10, wherein a disturbance is identified, and wherein the wind turbine is stopped if the vibration characteristic departs once from a second vibration tolerance band, wherein the second vibration tolerance band is broader than the first tolerance band.

13. A wind turbine, comprising: a generator having a generator axis for generating electrical power from wind, wherein the generator is configured to be driven by an aerodynamic rotor having one or more rotor blades, a nacelle, the generator coupled to the nacelle, a tower for supporting the nacelle, a vibration sensor for sensing a tower vibration, wherein the vibration sensor is configured to sense a mechanical generator vibration, and a controller configured to control the wind turbine in dependence on the sensed tower vibration and the sensed generator vibration.

14. (canceled)

15. The wind turbine as claimed in claim 13, wherein the wind turbine is a gearless wind turbine.

16. The wind turbine as claimed in claim 13, wherein the vibration sensor is an acceleration sensor configured to sense acceleration in at least two directions.

17. The wind turbine as claimed in claim 13, wherein the sensor is arranged on a stator of the generator, a generator carrier that supports the generator, or a front part of the nacelle.

18. The method as claimed in claim 4, further comprising: comparing the longitudinal vibration signal to a predetermined tower longitudinal-vibration limit value, comparing the transverse vibration signal to a predetermined exceeds a predetermined tower transverse-vibration limit value, and identifying a disturbance in response to at least one signal, chosen among the longitudinal vibration signal and the transverse vibration signal, exceeding the predetermined tower longitudinal-vibration limit value or the predetermined tower transverse-vibration limit value, respectively.

19. The method as claimed in claim 5, wherein separating in dependence on frequency comprises using a filter and wherein frequency components lying below a predefinable separation frequency are used as the tower-vibration signal and frequency components lying above the separation frequency are used as the generator-vibration signal.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0086] The invention is explained exemplarily in greater detail in the following on the basis of embodiments, with reference to the accompanying figures.

[0087] FIG. 1 shows a wind turbine in a perspective representation.

[0088] FIG. 2A shows, in schematic form, a side view of a part of a wind turbine.

[0089] FIG. 2B shows a close up of a portion of the wind turbine of FIG. 2A.

[0090] FIG. 3 shows, in schematic form, a measurement and control structure for operating a wind turbine, taking account of a vibration measurement.

[0091] FIG. 4 shows, in schematic form, a possible vibration characteristic to illustrate possible trigger criteria for identifying a disturbance.

DETAILED DESCRIPTION

[0092] FIG. 1 shows a wind turbine 100, having a tower 102 and a nacelle 104. Arranged on the nacelle 104 there is a rotor 106, which has three rotor blades 108 and a spinner 110. During operation, the wind causes the rotor 106 to rotate, thereby driving a generator in the nacelle 104.

[0093] FIG. 2A shows a schematic detail of a wind turbine 200, with a nacelle 202 and a generator 204. The generator 204 has a stator 206 and a rotor 208. The rotor 208 is directly coupled to three rotor blades 210, which are represented only partially and only in schematic form, and of which only two are represented, because in the position represented the third rotor blade is on the opposite side of the nacelle 202.

[0094] The generator 204 is thus realized as an internal rotor and, since this rotor 208 is directly connected to the rotor blades 210 and thus to the aerodynamic rotor 212, this a gearless wind turbine. During operation, the rotor 208 rotates relative to the stator 206, about a generator axis 214. The generator axis 214 is thus also simultaneously the axis of rotation of the rotor 212. For reasons of simplicity, any bearings are not represented in FIG. 2A.

[0095] The stator 206 is attached to a main carrier 218 via a stator carrier 216. The main carrier 218 is rotatably mounted on the tower 222 via a yaw bearing 220.

[0096] FIG. 2B also shows an enlarged detail 224. In addition to a circumferential brush seal 226, a vibration sensor 228 is shown, which may be realized as an acceleration sensor. This vibration sensor 228 is arranged on and attached to the stator 206, and thus to the generator 204. The vibration sensor 228 is also at the same time arranged on the stator carrier 216.

[0097] It can also be seen from the general view in FIG. 2A that the vibration sensor 228 is arranged in a front part of the nacelle 202. It should be noted that in this FIG. 2A the rotating part, namely the so-called spinner 230, is drawn significantly longer than usual. Usually, the distance between the rotor blades 210, or the hub 232 to which they are attached, and the rotor 208 is much shorter. The front part 234 may be referred to as the nacelle part that adjoins the main carrier 218 and in which the generator 204, including stator carrier 216, is arranged. On the other hand, the rear part 236 of the nacelle extends approximately from the connection region between main carrier 218 and the stator carrier 216, rearward to the ventilation outlet 238.

[0098] In FIG. 2A it can be seen, in particular, that the generator 204 extends far beyond the tower 222. The vibration sensor 228 also extends far beyond this tower 222. In particular, it is not arranged on the tower 222 and also not in the region above the tower 220, in particular there also not in the region of an extension of the tower axis 240.

[0099] The vibration sensor 228 is configured to detect two directions of vibration, namely, on the one hand, in the longitudinal direction of the generator axis 214 and, on the other hand, in a direction transverse to it, namely into the plane of the drawing as shown in FIG. 2A. Thus, two informative directions of vibration can be sensed, for both a tower vibration of the tower 222 and for a generator vibration of the generator 204. A possible evaluation, together with further processing, is illustrated in FIG. 3.

[0100] Thus, a measurement and control structure 300 is shown schematically in FIG. 3. This measurement and control structure 300 begins, on the left-hand side represented there, with the schematic representation of a vibration sensor 328, which may correspond to the vibration sensor 228 of FIG. 2A. This vibration sensor 328, which is preferably realized as an acceleration sensor, can sense two mutually orthogonal directions of vibration, denoted here as X and Y. Preferably and/or in the case of a preferred vibration sensor 228 according to FIG. 2A, these two directions X and Y lie in a horizontal plane. The X-direction may denote a direction of vibration in the direction of the longitudinal axis of the generator, and the Y-direction a direction transverse thereto.

[0101] Accordingly, this vibration sensor 328 outputs two measurement signals, namely one for each of the two directions X and Y. These two vibration signals may be referred to as a longitudinal-vibration signal S.sub.X and transverse-vibration signal S.sub.Y. These two signals are then given to a separation block 302, in which there may be an integrated separation circuit, or in which a signal separation, described below, is performed by a corresponding microprocessor, or a corresponding evaluation program. Thus, both signals, i.e., the longitudinal-vibration signal S.sub.X and the transverse-vibration signal S.sub.Y, are separated, respectively, into a tower-vibration signal and a generator-vibration signal. For this purpose, it is symbolically represented in the separation block 302 that a total signal S is separated into a tower signal T and a generator signal G.

[0102] The separation block 302 then outputs, as a result, three individual signals, namely, a tower longitudinal-vibration signal S.sub.TX, a tower transverse-vibration signal S.sub.TY, and a generator-vibration signal S.sub.G.

[0103] As a next step, this exemplary measurement and control structure 300 proposes to take into account, in a protective control that is included in the protective function block 306, these three signals, namely here the tower longitudinal-vibration signal S.sub.TX, the tower transverse-vibration signal S.sub.TY, and the generator-vibration signal S.sub.G.

[0104] At the same time, an operation control block 308 is also provided, which includes a working-point control and also receives all information about the vibration, namely the three signals, i.e., the tower longitudinal-vibration signal Six, the tower transverse-vibration signal S.sub.TY, and the generator-vibration signal S.sub.G.

[0105] A working point, specified by the working-point control of the operation control block 308 in order to control the wind turbine at this working point, may thus be adapted, altered or set depending on vibration information, or it may also be determined that an alteration of the working point is not necessary. To this extent, the operation control block 308, or the working-point control therein, performs a control of the wind turbine, namely at least to the extent that it outputs a setpoint power P.sub.S and a setpoint rotational speed n.sub.S.

[0106] These two variables may substantially define the working point of the wind turbine, which may also be referred to as the operating point. This may be effected, in particular, in dependence on a sensed rotational speed n.sub.i and a sensed power P.sub.i.

[0107] The sensed power P.sub.i, and then correspondingly also the setpoint power PS, denotes in particular an output power of the wind turbine, which is represented schematically as the wind turbine 310. The representation of the wind turbine 310 in FIG. 3 is also to be understood as being purely schematic, in that the measurement and control structure 300 shown may in principle be completely contained in the wind turbine 310.

[0108] In any case, this operating point is entered into the main control means 312 by specification of the setpoint rotational speed n.sub.S and the setpoint power P.sub.S. The main control means 312 is also to be understood to this extent as being merely schematic, because in a main control means of a wind turbine basically everything can be performed that is explained in the measurement and control structure 300. In any case, the main control means 312 can then, in particular, generate correcting variables that are used to adjust the wind turbine 312, or its components.

[0109] To this extent also represented only illustratively, the main control means 312 of the measurement and control structure 300 of FIG. 3 outputs a torque for respectively one pitch motor, and a setpoint power P.sub.S. The torque for the pitch motor is denoted here as Ma. It is specified by the main control means 312, and may relate to various other aspects that are not elaborated here, such as, for example, a consideration of the load on the respective pitch drives, and a consideration of a required adjustment speed, to name just two examples.

[0110] The setpoint power P.sub.S is also given for illustrative purposes only and may be implemented, for example, in such a manner that, in the case of an externally excited synchronous generator, a corresponding excitation current is set for this external excitation. In addition or alternatively, the setting of the setpoint power P.sub.S may be achieved or influenced by controlling the stator currents.

[0111] In any case, these two values shown by way of example, namely the drive torque M.sub.α of a pitch motor in each case, and the intended output power P.sub.S, are given to the wind turbine 310. By this it is meant that these values are given to the corresponding actuating means. According to the aforementioned examples, these would be the respective pitch motor, the respective excitation controller and/or a controllable rectifier connected downstream of the stator.

[0112] The wind turbine 310 is normally operated in this manner, i.e., via the working-point control in the operating control block 308 and the further implementation in the main control means 312. If a disturbance occurs, however, a protective control, as contained in the protective-control function block 306, can become active. Such a protective control function in this case monitors the vibrations, namely the tower longitudinal-vibration signal Six, the tower transverse-vibration signal S.sub.TY, and the generator-vibration signal S.sub.G.

[0113] If one of these signals exceeds a corresponding limit value, the protective control is activated and this initially results in the normal control being overridden. This is illustrated by the deactivation block 314. This is because, in this case, the protective control block 306 can trigger the deactivation block 413 and deactivate the normal control according to the operation control block 308 and the main control means 312. This is indicated by the symbolically represented open switch in the deactivation block 314.

[0114] At the same time, the protective control of the protective function block 306 performs its own control of the wind turbine 310 in order to bring it to a safe working point. In the simplest case, which is also illustrated here, the wind turbine is stopped for this purpose, i.e., thus brought as rapidly as possible to zero rotational speed. In the illustrative example, it is also necessary for this purpose to turn the blade angle to the feathered position, which in FIG. 3 is shown illustratively as 90 degrees. Usually, the feathered position is not exactly 90 degrees, but is close to it, such the value of α=90 degrees is illustratively a reasonable value. Other controls may of course be performed, such as also reducing the output power. For reasons of clarity, however, this is not elaborated here.

[0115] In any case, the protective control of the protective function block 306 causes the rotor blades to be moved into the feathered position, and for this purpose, via the main block 316, causes a torque to be generated for each pitch motor. For this purpose, the main block 316 may generate, or specify, for the respective pitch motor a torque that, for example, initially increases and then decreases over time. This is illustrated accordingly in the main block 316.

[0116] Preferably, however, this protective control is also realized as a fail-safe control and for this purpose may have a main control and a secondary control. The main block 316 may be regarded as the main control by way of illustration, or it may be representative of other main control functions that the protective control may have to perform. If this main control, or the main block 316 shown as representative of it, cannot perform the desired control, i.e., the desired generation of the torque for the pitch motor, a secondary block 318 is available as an illustrative element for a secondary control, which then takes over the activity that the main control can no longer perform due to the failure.

[0117] The secondary control, and thus illustratively the auxiliary block 318, may in this case be configured to execute in a more simple manner the control that is to be performed. This is illustrated here by the fact that the secondary block 318 also generates, or specifies, a torque M.sub.α in order to control a pitch motor, but that this torque specification is effected less explicitly. By way of illustration, for this purpose the auxiliary block 318 has a symbolic diagram to indicate here that the torque M.sub.α is simply set to a fixed value. The respective rotor blade can then rotate into its feathered position and this control, i.e., the generation or specification of the torque for the pitch motor, ends when the rotor blade has attained its feathered position and thereby actuates a limit switch. This limit switch then has the effect that no further torque is applied to the respective pitch motor.

[0118] The main control and the secondary control, illustrated here by the main block 316 and the secondary block 318 respectively, may also, however, be of the same design and work simultaneously and in parallel in that, for example, both issue a torque request to the pitch motors or a pitch motor control in the event of a disturbance, or only issue a switch-off signal that the pitch control can execute independently because, for example, this is pre-programmed accordingly.

[0119] FIG. 4 shows a schematic characteristic of a vibration a over time. This illustratively represented vibration a may in each case represent a time-related characteristic of an acceleration, and may be illustrative for a tower vibration as well as illustrative for a generator vibration. In particular, they may relate to the tower longitudinal-vibration signal S.sub.TX, the tower transverse-vibration signal S.sub.TY, and the generator-vibration signal S.sub.G and for this purpose show, for example, the respective acceleration. These three vibrations may differ in many characteristics, but in the diagram of FIG. 4 two possible criteria in particular are to be explained, which can result in the identification of a disturbance. These criteria are proposed in the same way for the three vibration types.

[0120] It should also be noted, not only for this illustrative FIG. 4, but in general, that the vibration under consideration may be a tower vibration, both transverse and longitudinal, or a generator vibration. In particular in this case, the value of the respective criterion, or criteria, in particular the limit values, may be adapted accordingly.

[0121] FIG. 4 now shows the vibration characteristic a, which initially shows a vibration having a small amplitude, which then increases. At the time-point t.sub.1 this vibration attains a first upper vibration limit value A.sub.o1. This is indicated by a horizontal dashed line, and there is also a first lower vibration limit value A.sub.u1, which preferably corresponds to the negative value of the first upper vibration limit value A.sub.o1. It is thus preferably the case that A.sub.u1=−A.sub.o1. These two first vibration limit values may thus form a first vibration tolerance band. They may each form a first generator-vibration limit value or a first tower-vibration limit value, or a first tower longitudinal-vibration limit value or a first tower transverse-vibration limit value.

[0122] At this time-point t.sub.1, when the vibration exceeds the first upper limit value, i.e., departs from the first vibration tolerance band, a disturbance is not yet identified, but the exceeding of this limit value is integrated, as is the under-running of the first lower vibration limit value, which is a further departure from the first vibration tolerance band. This is illustrated in FIG. 4 as the hatched integral area IF.sub.1. Such an integration is then continued over a predetermined integration period t.sub.1, which can also be referred to synonymously as the first check period. Within this integration period t.sub.1, the vibration continues and then falls below the first lower vibration limit value A.sub.u1, thus again departing from the first vibration tolerance band. Upon this under-run, there is then likewise a value to be integrated, which is illustrated as the second integration area IF.sub.2. This is also added to the integrated value of the first integration area IF.sub.1. The vibration then continues and, in the example shown, again exceeds the first upper vibration limit value, such that the integration is continued, namely with the content of the third integration area IF.sub.3.

[0123] This integration is also illustrated in a partial diagram in FIG. 4, which shows the characteristic of the exceedance integral value I, which may also be referred to synonymously as the exceedance sum, as the result of this integration, namely in the diagram directly beneath the integration period t.sub.1 under consideration. If this excess integral value I were to attain the reference integral value IM indicated as a horizontal dashed line, which may also be referred to synonymously as the maximum sum, the protective control would identify a disturbance and, in particular, trigger the stopping of the wind turbine with an emergency blade pitching. In the example shown, however, the exceedance integral value I does not attain the reference integral value IM. A disturbance is therefore not identified, because the vibration in the example shown subsides somewhat and then, within the integration period t.sub.1, no longer falls below the first lower vibration limit value A.sub.u1 and also no longer exceeds the first upper vibration limit value A.sub.o1, i.e., it remains in the first vibration tolerance band.

[0124] Instead of the integration shown, a summation, i.e., counting, may also be considered. Transferred to the situation in FIG. 4, the reference integral value, i.e., the maximum sum, could have, for example, the value 4. In this case, departure from the first vibration tolerance band occurred only three times, such that the value of the exceedance sum is 3, and thus a disturbance has not yet been identified.

[0125] If the vibration characteristic, i.e., the considered acceleration a, later exceeds the first upper vibration limit value A.sub.o1 or falls below the first lower vibration limit value A.sub.u1, an integration would then start again from zero, and thus also a new integration period t.sub.1 would start. Alternatively, the exceedance integral value, or the exceedance sum, may be reduced gradually. For example, if the departure from the first tolerance band is only counted, the exceedance sum may be reduced by the value 1 per day.

[0126] Furthermore, a second upper vibration limit value A.sub.o2 is provided. This is also indicated by a dashed horizontal line and there is also a counterpart, namely the second lower vibration limit value A.sub.u2. Here, too, it is preferably proposed that the second lower vibration limit value A.sub.u2 corresponds to the negative value of the second upper vibration limit value A.sub.u2 (A.sub.u2=−A.sub.o2). These two second vibration limit values may thus form a second vibration tolerance band. They may respectively form a second generator-vibration limit value or a second tower-vibration limit value, or a second tower longitudinal-vibration limit value or a second tower transverse-vibration limit value.

[0127] In FIG. 4, for example, the second upper vibration limit value A.sub.o2 is exceeded at the time-point t.sub.2. This results immediately in the identification of a disturbance, without any integration being performed. Then, i.e., at time-point t.sub.2, the wind turbine is stopped, in particular by emergency pitching of the rotor blades to the feathered position. Shortly before the second upper vibration limit value A.sub.o2 is attained, the considered acceleration a of the vibration also initially exceeds the first upper vibration limit value A.sub.u1, which results in a renewed starting of the integration. For reasons of simplicity, this integration is not represented here, because the second criterion is attained shortly afterwards, at time-point t.sub.2, and this is to be explained here.

[0128] The switching-off of the wind turbine then also causes the vibration to subside, which is also indicated in FIG. 4.

[0129] In the same way, under-running of the second lower vibration limit value A.sub.u2 would also result in the identification of a disturbance and in the triggering of stopping of the wind turbine, in particular by means of an emergency pitching of the rotor blades.