METHOD FOR CONTROLLING A WIND TURBINE

Abstract

A method for controlling a wind power installation, wherein the wind power installation has an aerodynamic rotor with rotor blades that are individually adjustable in their blade angle and the rotor can be operated with a variable rotational rotor speed, and the wind power installation has a generator coupled to the aerodynamic rotor, for generating a generator output, comprising the steps of: individually adjusting each blade angle in a way corresponding to an individual setpoint blade angle, wherein each setpoint blade angle is made up of a common basic angle, which is specified for all of the rotor blades, and an individual compensatory angle, to allow for individual load torques, detecting in each case at least one load torque on each of the rotor blades, or a variable that is representative of this, wherein for each rotor blade considered, there is a preceding rotor blade and the setpoint blade angle of each rotor blade considered is determined in dependence on the at least one load torque of its preceding rotor blade.

Claims

1. A method for controlling a wind power installation, wherein the wind power installation has an aerodynamic rotor with a plurality of rotor blades having individually adjustable blade angles, wherein the aerodynamic rotor is configured to be operated with a variable rotational rotor speed, and wherein the wind power installation has a generator coupled to the aerodynamic rotor for generating a generator output, the method comprising: individually adjusting each blade angle in a way that corresponds to an individual setpoint blade angle, wherein each setpoint blade angle depends on: a common basic angle, which is specified for all of the plurality of rotor blades, and an individual compensatory angle that compensates for individual load torques, detecting in each case at least one load torque or a variable indicative of the at least one load torque on each of the plurality of rotor blades, wherein for each rotor blade determining the setpoint blade angle in dependence on the at least one load torque of a preceding rotor blade.

2. The method as claimed in claim 1, further comprising determining the individual compensatory angle includes determining an angle trajectory, wherein each compensatory angle is an element of the angle trajectory, so that the angle trajectory respectively indicates a continuous progression of the respective compensatory angle.

3. The method as claimed in claim 2, wherein the angle trajectory is determined in at least first and second steps, wherein: in the first step, an optimum angle trajectory that is optimized with respect to at least one or more first design criteria is determined, and in the second step, the optimum angle trajectory determined in the first step is altered to an adapted angle trajectory, while making further allowance for one or more second design criteria.

4. The method as claimed in claim 2, wherein the angle trajectory is determined by way of a solution to an optimization problem on a basis of the at least one or more first design criteria.

5. The method as claimed in claim 1, wherein each setpoint blade angle is chosen in dependence on at least one: an initial blade angle, blade bending torques, operating state of pitch systems used, sector size of a sector considered for the at least one detected load torque, load torque of a rotor hub, rotor hub bending torque, rotational rotor speed, rotor position, or rotor acceleration.

6. The method as claimed in claim 3, wherein the at least one or more first design criteria is at least one of: reduction of the load, neutrality of yield, or preservation of a pitch drive, wherein the one or more second design criteria is at least one of: drive dynamics of the pitch drive, or limit values of the pitch drive.

7. The method as claimed in claim 6, wherein the at least one detected load torque or other variables are weighting factors or weighting functions.

8. The method as claimed in claim 7, wherein the weighting factors or weighting functions are chosen in dependence on a reduction of the load, neutrality of the yield, and preservation of the pitch drive.

9. The method as claimed in claim 1, wherein the compensatory angle is chosen such that at least one of: a mean value of the compensatory angles of all of the rotor blades is zero; or an absolute value of each compensatory angle does not exceed a predeterminable maximum angle.

10. The method as claimed in claim 1, wherein at least two loading measurements with different loading directions are detected on each rotor blade, and wherein the setpoint blade angles are determined such that a loading acting on the wind power installation is minimized such that at least one of: a pitching moment or a yawing moment are reduced.

11. The method as claimed in claim 1, wherein detecting the at least one load torque or a variable indicative of the at least one load torque on each of the plurality of rotor blades includes: dividing a rotor area passed over by the rotor blades into multiple sectors, and recording the load torques when a sector is passed over by a rotor blade, and using the recorded load torques to determine a partial trajectory for setpoint blade values of a following rotor blade.

12. The method as claimed in claim 11, wherein dividing the rotor area into multiple sectors takes place in dependence on a detected wind field in a region of the rotor area, such that at least one of: a size or number of the sectors is chosen in a manner dependent on the detected wind field, or a number of interpolation points of the partial trajectory depends on the detected wind field.

13. The method as claimed in claim 11, wherein dividing the rotor area into sectors is performed adaptively during of operation of the wind power installation.

14. The method as claimed in claim 1, wherein multiple virtual rotor areas are defined, wherein each virtual rotor area corresponds to the actual rotor area and is additionally comprising at least one time value and/or an associated rotor revolution.

15. The method as claimed in claim 1, wherein a loading detection takes place over a plurality of revolutions of the aerodynamic rotor, and wherein the setpoint blade angle additionally depends on the loading that occurs during at least one previous revolution.

16. The method as claimed in claim 1, wherein each rotor blade is readjusted to its setpoint blade value with specifiable setting dynamics, the setting dynamics having at least one of: PTn behavior with n being equal to or greater than 1 or a different asymptotically damped behavior.

17. The method as claimed in claim 1, wherein individually adjusting each blade angle takes place without feedback of a loading of the respective rotor blade.

18. The method as claimed in claim 1, wherein values of the setpoint blade angle are specified such that a pitching moment and a yawing moment are reduced in comparison with a setpoint angle without a compensatory angle, permitting an increase in a loading of the rotor blades.

19. The method as claimed in claim 1, wherein: the rotor has a rotor area that is passed over by the rotor blades and has a center point of rotation, which forms a geometrical center point of the rotor area and about which the rotor rotates, and the rotor has in its rotor area a load center point, which forms a center point of all of the loads acting on the rotor, and wherein the method further comprises such that when the load center point deviates from the center point of rotation, the setpoint blade angles are determined such that the load center point substantially remains constant with respect to its oscillating amplitude and is not brought to the center point of rotation.

20. A wind power installation, comprising an aerodynamic rotor configured to be operated with a variable rotational rotor speed; a plurality of rotor blades coupled to the aerodynamic rotor, wherein the plurality of rotor blades have individually adjustable blade angles; and a generator coupled to the aerodynamic rotor, the generator being configured to generate a generator output, a load detecting unit for detecting at least one load torque on each of the rotor blades; a blade control device for individually adjusting each blade angle in a way corresponding to an individual setpoint blade angle, wherein each setpoint blade angle is determined based on: a common basic angle, which is specified for all of the rotor blades, an individual compensatory angle, to allow for individual load torques, and at least one load torque of a preceding rotor blade.

21. A wind power installation performing the method as claimed in claim 1.

22. The wind power installation as claimed in claim 20, wherein the load detecting unit includes at least one blade sensor on each of the rotor blades.

23. The method as claimed in claim 11, wherein the partial trajectory is made up of a plurality of interpolation points, wherein between the interpolation points, values of the partial trajectory are interpolated.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0071] The invention is explained in more detail below by way of example on the basis of embodiments with reference to the accompanying figures.

[0072] FIG. 1 shows a wind power installation in a perspective view.

[0073] FIG. 2 shows a structural diagram on which the invention is based.

[0074] FIG. 3 shows a structural diagram of a proposed individual blade adjustment.

[0075] FIG. 4 shows a schematic representation of a load center point in a rotor area.

[0076] FIG. 5 shows part of a control structure, which may be part of the control structure according to FIG. 3.

[0077] FIG. 6 illustrates a partial aspect of a proposed method.

[0078] FIG. 7 illustrates possible loads acting on a wind power installation that may be influenced by a blade adjustment.

DETAILED DESCRIPTION

[0079] FIG. 1 shows a wind power installation 100 with a tower 102 and a nacelle 104.

[0080] Arranged on the nacelle 104 is a rotor 106 with three rotor blades 108 and a spinner 110. During operation, the rotor 106 is set in a rotary motion by the wind, and thereby drives a generator in the nacelle 104.

[0081] In the nacelle 104, a central control unit 103 may be provided. Adjusting drives 105, one of which is shown by way of example, are provided in the spinner 110 respectively in the region of each rotor blade 108 and, together with the central control unit 103, can form a blade adjusting device. Provided on the rotor blades 108 are three blade sensors 107 for determining loadings at the rotor blades 108, to be specific one on each rotor blade 108. The three blade sensors 107 can together form a load detection device or unit. The central control unit 103 may also be located on a rotor blade and rotate along with the rotor.

[0082] FIG. 2 illustrates in the simplified structure a wind power installation 200, on which a schematically indicated wind field 202 acts. Initially, this wind field 202 acts particularly on the rotor 204 of the wind power installation 200.

[0083] Particularly forces acting on the rotor blades 206, particularly also loads acting on them, can be detected by corresponding sensors. Such detection is subject to sensor dynamics, which are illustrated here by the sensor dynamics block 208.

[0084] The result of the detected forces, loads or other influences that are detected in the sensor dynamics block 208 is passed to a calculation block 210 of the central control unit 103, which calculates from it specification values, such as angle specifications, and among them particularly angle trajectory specifications. Such values can then be output as setpoint values. The calculation block 210 is only shown here as a block by way of representation, and concerns in particular any algorithms that are used for such a calculation.

[0085] Setpoint values calculated in the calculation block 210, particularly for blade angles to be set, are passed on to corresponding pitch drive systems. This is illustrated as a transfer to the pitch dynamics block 212, in order to illustrate that pitch dynamics exist between such setpoint blade angle values and the blade angles that are then actually established.

[0086] The output of this pitch dynamics block 212 then acts again on the wind power installation, particularly on the rotor 204 and its rotor blades 206. As a result, consequently these values for the blade angles that are generated by the pitch dynamics block 212 and the wind according to the wind field 202 act on the rotor 204 and its rotor blades 206. All of this then produces a load behavior, which for the sake of simplicity is depicted here for purposes of illustration as a load behavior block 214. Other variables also result of course, but the resultant loads or the resultant load behavior is/are of significance, so that this is illustrated here in the load behavior block 214.

[0087] FIG. 3 shows details of an embodiment of a proposed control for individual blade adjustment in the overall structure 300, which forms the central control unit. The essential elements of this overall structure 300 are the controlled system 302, the sensor dynamics 304, the individual blade algorithm block 306, the pitch dynamics 308 and, in addition, the general blade adjustment 310.

[0088] The controlled system 302 stands for the behavior of the wind power installation that is relevant to the present consideration. This includes particularly the command behavior 312, which indicates how the wind power installation reacts to a command variable. This relates here particularly to the behavior of the wind power installation or its reaction to blade angle adjustments. The dynamics of the blade angle adjustment, that is to say the pitch dynamics 308, are allowed for here separately from the command behavior. Here, the output variable of the pitch dynamics 308 forms the input variable for the command behavior 312.

[0089] Furthermore, disturbances 314 also act on the wind power installation, to be specific particularly changes in speed or differences in speed in the wind speed, which are referred to here as v.sub.1, v.sub.2 and v.sub.3. These disturbances 314 are not measured directly. However, the disturbance behavior 316 is known, or at least partially known, and if appropriate can be allowed for. The disturbances 314 therefore act by way of the disturbance behavior 316 on the controlled system, that is to say on the behavior of the wind power installation.

[0090] The result can be detected with the aid of sensors and is in this case changed by way of the sensor dynamics 304.

[0091] This output behavior of the controlled system 302, that is to say of the wind power installation, that is changed by the sensor dynamics 304 is sent or fed back to the individual blade algorithm block 306. Building on this, an individual blade adjustment can be specified or preplanned in the individual blade algorithm block 306. Preplanned should be understood here as meaning very short-term planning, to be specific in particular for a planning time period which is shorter than the time that the rotor 204 of the wind power installation requires to rotate further by one blade 206.

[0092] Furthermore, the individual blade algorithm block 306 makes allowance for properties of the pitch dynamics 308, the sensor dynamics 304 and the disturbance behavior 316, which is combined in the property group 336. The arrow indicated from this property group 336 to the individual blade algorithm block 306 is intended merely to indicate that allowance can be made specifically for these properties mentioned. It does not mean that they are always fed back there. Rather, they may be stored, and if appropriate updated, in the individual blade algorithm block 306.

[0093] First, a first evaluation of the values entered, that is to say the values that are obtained from the sensor dynamics 304, takes place in the process block 320. Among other things, bending torques can be extracted in the process block 320 and transferred to the estimating block 322. The estimating block 322 can estimate from the measured bending torques disturbances that are not measured. Also coming into consideration for this is to use a state observer. In this case, allowance can also be made for the disturbance behavior 316. Such disturbances that are not measured, which by way of illustration enter the disturbance behavior block 316 as disturbances 314, may particularly be wind variations, to be specific particularly changes of the wind speed and wind direction.

[0094] Particularly, in the estimating block 322 the disturbances that are not measured are estimated for each individual blade, that is to say are thereby detected. These results for the individual blades, such as for example the blades 206 according to FIG. 2, are fed to the shift block 324. The shift block 324 ensures that the disturbances of individual blades detected in this way are in each case provided or used for a following blade. Proposed for this are shift and assignment operations, which may be implemented as a linked sequence of mathematical transformations. One result is a torque block 326, which in each case contains a differential torque, to be specific a differential bending torque for each rotor blade. Such a differential bending torque is the difference between the estimated bending torque of the respective rotor blade and a mean value of the estimated bending torques of all three rotor blades.

[0095] In the torque block there are consequently different torque vectors, which to be specific respectively comprise three elements, that is to say one element for each rotor blade. Multiple vectors are provided here, because these torque values are not constant and change over the rotor area, particularly as a result of the movement of the rotor blades due to rotation of the rotor. In principle, a continuous torque vector with continuously changing differential bending torques may also be used, but in terms of control technology this is scarcely implementable, particularly when using a digital computer. It has also been found that such a theoretical continuous implementation is not required.

[0096] The output of the torque block 326 is then passed to the precontrol block 328. The precontrol block 328 can consequently specify part of a blade angle or a change of a blade angle or a blade angle difference for each blade in the sense of a feedforward compensation. This corresponds in principle to the individual compensatory angle, apart from the fact that the latter can still be changed further.

[0097] This precontrol block 328 alone can in this case specify for each rotor blade an angle trajectory for a phase of movement of the rotor blade over the rotor area, for this part of the angle, differential angle or change of angle. For example, an angle trajectory may be specified for a rotor blade for its movement from a 12 o'clock position to a 2 o'clock position, while this is specified for a further blade for a region from the 4 o'clock position to the 6 o'clock position. In this example, both angle trajectories respectively concern a region of 60. However, other regions, that is to say other sectors of the rotor area, may also be taken as a basis. In this case, these sectors may also respectively differ in their size from one blade to the other.

[0098] The result of the precontrol according to the precontrol block 328 is then fed to the nonlinear optimization block 330. In the nonlinear optimization block 330, the angles that the precontrol block 328 has created and produced can be further adapted while still making allowance for constraints. Such constraints are fed to the nonlinear optimization block 330 from the constraint block 332. Such constraints may be for example the dynamics of the pitch drive, limits of the pitch drive or a blade synchronicity. The blade synchronicity makes allowance as a constraint for the fact that the rotor blades 206, though individually adjusted, are nevertheless coordinated with one another overall in their adjustment. Particularly, the mean value of the blade angles is intended to correspond to the basic angle. In this case, it is sufficient that this is satisfied in the long term. It does not have to be satisfied at every sampling time, but instead the intention is simply to prevent that the blade angles diverge permanently, which could happen for example as a result of rounding errors.

[0099] The constraints for which allowance is made in the constraint block 332 are consequently particularly drive dynamics and limits of the pitch drives and the blade synchronicity mentioned. Allowance may be made for other constraints.

[0100] With this adaptation of the blade angles or blade angle trajectories in the nonlinear optimization block 330, they can be fed to the postprocessing block 334. In the postprocessing block 334, if appropriate still further adaptations may be performed. Particularly, a trajectory may be finally checked in the postprocessing block 334, particularly for plausibility and implementing practicality. It may be checked whether the respective trajectory can be valid, for example whether it lies within predetermined limits and/or can be put together with a previous trajectory, to name just two examples. Also or alternatively, angle values to be set in actual fact at the specific time can be derived in the postprocessing block in dependence on the rotational speed or rotor position. Each angle trajectory is an angle progression in dependence on the rotational angle, and consequently the angle to be set in each case at a particular moment and/or the portion of a trajectory to be used at a particular moment depends on the actual position of the rotating rotor. The actual angle values can consequently be determined while making allowance for the rotor position at the specific time, and consequently the rotor blade position at the specific time. Alternatively or in addition, this may be determined by making allowance for the rotational rotor speed. This can be performed in the postprocessing block 334. In this case, the postprocessing block 334 may output actual angles, that is to say setpoint angles, instead of angle trajectories. Finally, these compensatory angles are added to a basic angle 339 in the summing element 338. This basic angle 339 can be specified in the usual way.

[0101] FIG. 5 shows a detail of FIG. 3, to be specific of the controlled system 302 with upstream pitch dynamics 308 and downstream sensor dynamics 304. The controlled system 302 comprises the command behavior 312 and the disturbance behavior 316, by way of which the disturbances 314 act on the controlled system 302.

[0102] In FIG. 5 it is particularly intended to illustrate that the pitch dynamics 308, the sensor dynamics 304 and the disturbance behavior 316 are relevant properties for the control structure. The respective dynamics are illustrated here.

[0103] For the pitch dynamics 308, a schematic Bode plot 508 is used to show that the pitch dynamics have essentially second-order low-pass characteristics.

[0104] For the disturbance behavior, it is illustrated by a disturbance diagram 516 that there is an angle-dependent sensitivity. The disturbance diagram shows here a sensitivity factor, which is plotted in a normalized form on the y axis over a collective pitch angle of 0-40, the characteristic curve extending from 2-37. The sensitivity factor indicates here by how many degrees () the blade must be turned out of the wind in order to counteract a bending torque as loading. With a blade angle of 6, the blade must therefore be turned further out of the wind by over 10 in order to reduce a flexural loading of approximately 0.9 pu. This flexural loading can be reduced in the case of a blade angle of 35 by a further turning movement out of the wind by less than 7.

[0105] The collective pitch angle is the average pitch angle for which allowance is made.

[0106] It is consequently evident that the sensitivity essentially decreases with increasing blade angles. With greater blade angles, the blade is therefore less susceptible to disturbances. In the example shown, the maximum value is obtained however at 6. What is decisive here however is that such a disturbance behavior does exist and allowance can be made for it, particularly for the individual blade algorithm, particularly in the individual blade algorithm block 306. This is so because the disturbances cannot be measured, or are not measured, but it is nevertheless known how strong their influence can be in dependence on the blade angle. Consequently, on the one hand the disturbance can be inferred on the basis of the blade angle and a detected bending torque, on the other hand the bending torque for the following blade can be better inferred on the basis of the detected disturbance, to put it clearly at least as an estimate.

[0107] Therefore, while making allowance for the disturbance sensitivity, particularly the sensitivity factor, which relates to the blade load or a flexural loading, the disturbance can be estimated from the flexural loading of the preceding blade. Then, while making allowance for the disturbance sensitivity, particularly the sensitivity factor, this estimated disturbance can be used to derive the flexural loading of the following rotor blade that runs after this preceding rotor blade.

[0108] For the sensor dynamics 404, a sensor diagram 504 that is intended particularly to illustrate the complexity of the sensors is presented. Particularly indicated is a part-diagram 505, which particularly illustrates the variance of such a sensor or of such sensors.

[0109] Furthermore, FIG. 6 schematically illustrates that there is a relationship between the rotor 604 with its rotor blades 606 and the illustrated wind field 602. Moreover, the rotor area 605 is also depicted as a circle.

[0110] It is illustrated in the main block 616 that this is influenced by the rotor 606 or that, overall, control actions for the wind power installation can be derived from it. By way of example, it should be pointed out that this main block 616 may comprise sensors, in order to detect states of the rotor such as for example the rotational rotor speed. A main control, which can control the wind power installation, is also operated in a manner dependent on these states. In particular, it may also depend on the rotational speed of the rotor. It may, however, also make allowance for blade angles, to mention a further example. The generator may also be controlled in manner that is also dependent on the rotor or its behavior, such as for example dependent on the detected rotational rotor speed.

[0111] A resultant control measure is to activate a pitch system 620 from this main block 616. For this purpose, the pitch control 620, shown by way of example, provides a main input 622. Furthermore, the wind field 602 acts on the pitch control 620, which is illustrated by way of the load input 624. Particularly this feedback of the wind field 602 should be understood as an illustration of individual loads that are not homogeneous in the rotor field 605.

[0112] The pitch control 620 then has a pitch outlet 626, which acts on the rotor blades 606 and consequently on the rotor 604, to be specific provides individual blade adjustments, at least specifies for them corresponding setpoint blade angles. These setpoint blade angles are preferably specified as angle trajectories.

[0113] The pitch control 620 is also shown enlarged with its main input 622, its load input 624 and its pitch output 626.

[0114] The pitch control 620 shows in its enlargement a pitch control block 630, which obtains both variables from the main control, that is to say the main block 616, and load variables by way of the load input 624. This is used to determine a basic angle in the basic angle block 632 and an individual compensatory angle for each rotor blade in the individual angle block 634. These two angles can be added in the summing element 638 to form a setpoint blade angle.

[0115] With the switch 636, the pitch control 620 provides the possibility that the compensatory angle that is determined in the individual angle block 634 is not provided as feedforward compensation. In this case, the basic angle determined by the basic angle block 632 then already corresponds to the setpoint angle. In this case, the angles of all three rotor blades 606 are also the same. Consequently, this switch 636 provides an easy way of deactivating an individual blade adjustment when it is evident that it is likely to have little effect. Particularly in situations where the wind is weak, it may be envisaged to open this switch 636, as represented in FIG. 6, in order thereby to deactivate the individual blade adjustment.

[0116] It should in this case be remembered that, in a situation with weak wind, the optimization calculations nevertheless calculate compensatory angles or compensatory angle trajectories. Although these are likely to be only small as a result of the solution to an optimization problem while making allowance for boundary conditions, they would nevertheless lead to an unnecessary activation of the pitch drives. This can be prevented by the switch 636. The switch can be switched in a manner dependent on wind speeds or else in a manner dependent on other states of the wind power installation, such as for example the rotational rotor speed. It also comes into consideration to use a result of the individual blade algorithm, for example the size of calculated compensatory angles, as a criterion for the switch 636.

[0117] FIG. 7 particularly shows various loadings, which can occur particularly also due to a non-homogeneous wind field. Initially, blade bending torques may be produced in the chordwise direction, illustrated by the reference sign 702 or the blade bending torque arrow in the chordwise direction 702. Blade bending torques may also occur in the flapwise direction 704.

[0118] It is illustrated in the representation on the left that particularly blade bending torques in the chordwise direction 702 may lead to a chordwise movement 708 of the nacelle 706 about its horizontal axis. A torsional movement 710 of the tower 712 also comes into consideration.

[0119] Particularly the bending torques in the flapwise direction 704 may lead to a pitching moment 714, which is illustrated in the right-hand part of FIG. 7. A tower bending torque 716 may also occur here, and also a rotor torsion 718.

[0120] In the middle diagram of FIG. 7, it is also illustrated that a torque 720 can act on the rotor 722. Furthermore, a yawing moment 724 may occur, which is a torque that acts on the nacelle 706 about its perpendicular axis. Lastly, a rotor thrust 726 may also occur, which represents an axial loading on the rotor.

[0121] Otherwise indicated for purposes of illustration and orientation are the three Cartesian force directions X.sub.R, Y.sub.R and Z.sub.R possibly acting on the rotor. Likewise for orientation, the three Cartesian directions X.sub.T, Y.sub.T and Z.sub.T are indicated.

[0122] FIG. 4 shows a schematic representation of a load center point 801 in a rotor area 803. The rotor area 803 is the area that is passed over by the rotor blades 805 of the rotor 809. The rotor 809 has a center point of rotation 811, which is also the geometrical center point of the rotor 809. The load center point 801 deviates in FIG. 8 from the center point of rotation 811. Although it could be regarded as optimum when the load center point 801 always coincides with the center point of rotation 811, it has been recognized that it is often better to operate the wind power installation such that the load center point remains as constant as possible in terms of its amplitude. This is so because it has been recognized that this avoids alternating loads, which can sometimes represent a greater loading than absolute loading caused by the load center point 801 deviating from the center point of rotation 811. It has in this respect also been recognized that a corresponding individual blade adjustment can be used to achieve the effect of keeping the load center point 801 substantially constant with respect to the center point of rotation.