Wind turbine and method for detecting and responding to loads acting thereon

Abstract

A method for operating a wind turbine for generating electrical power from wind, wherein the wind turbine has an aerodynamic rotor with a rotor hub and rotor blades of which the blade angle is adjustable, and the aerodynamic rotor can be operated with a variable rotation speed, and the wind turbine has a generator, which is coupled to the aerodynamic rotor, for the purpose of generating a generator power, wherein the generator can be operated with a variable generator torque, comprising the steps of: determining a loading variable which indicates a loading on the wind turbine by the wind, and reducing the rotation speed and/or the generator power in a loading mode depending on the loading variable, wherein at least one force variable that acts on the wind turbine is used for determining the loading variable or as the loading variable.

Claims

1. A method for operating a wind turbine for generating electrical power from wind, wherein: the wind turbine has an aerodynamic rotor with a rotor hub and a plurality of rotor blades, wherein blade angles of the plurality of rotor blades are adjustable, each rotor blade having a respective rotor blade root configured to couple the respective rotor blade to the rotor hub, wherein the aerodynamic rotor is configured to be operated at a variable rotation speed, the wind turbine has a generator, which is coupled to the aerodynamic rotor, and the generator is configured to be operated with a variable generator torque, wherein the method comprises: determining a loading acting on the wind turbine by the wind, wherein determining the loading comprises: determining a plurality of forces using a plurality of strain gauges, each of the plurality of strain gauges being coupled to a respective rotor blade root of the plurality of rotor blades, using the plurality of forces to calculate a plurality of hub bending moments acting on the rotor hub, wherein the plurality of hub bending moments vary between maximum and minimum hub bending moments depending on a position of the rotor, and using the maximum bending moment as the determined loading, comparing the determined loading to a predefined loading limit value, and reducing at least one of a rotation speed or a generator power of the wind turbine in response to the determined loading reaching or exceeding the predefined loading limit value.

2. The method as claimed in claim 1, wherein reducing the at least one of the rotation speed or the generator power of the wind turbine comprises reducing the rotation speed, and the rotation speed is reduced by adjusting the blade angle of each rotor blade of the plurality of rotor blades in a direction away from the wind, the method further comprising reducing the generator torque as wind speed increases.

3. A wind turbine configured to execute the method as claimed in claim 1.

4. The method as claimed in claim 1, wherein the reducing comprises reducing the rotation speed such that a rotation speed range of the aerodynamic rotor is between 10% to 90% of a nominal rotation speed of the aerodynamic rotor.

5. The method as claimed in claim 1, wherein the plurality of rotor blades are three rotor blades, and the plurality of strain gauges are three strain gauges.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

(1) The invention will be explained in more detail below by way of example using exemplary embodiments with reference to the accompanying figures, in which:

(2) FIG. 1 shows a perspective illustration of a wind turbine.

(3) FIG. 2 shows an illustrative structure for detecting a hub bending moment as the loading variable.

(4) FIG. 3 shows a structure for reducing the rotation speed and the generator power in a loading mode.

DETAILED DESCRIPTION

(5) FIG. 1 shows a wind turbine 100 having a tower 102 and a nacelle 104. A rotor 106 with three rotor blades 108 and a spinner 110 is arranged on the nacelle 104. The rotor 106 is caused to rotate by the wind during operation and in this way drives a generator in the nacelle 104.

(6) FIG. 2 symbolically shows a portion of a wind turbine 200. This wind turbine 200 has three rotor blades 201, 202 and 203. Said rotor blades are fastened to a hub which is arranged in the nacelle 206. The three rotor blades 201, 202 and 203 are each fastened to said nacelle by means of a blade root 211, 212 and, respectively, 213. A strain gauge 221, 222 and, respectively, 223 is arranged on each blade root 211 to 213 as a force-measuring means. FIG. 2 shows a respective strain gauge 221 to 223 for each blade root 211 to 213. However, at least two strain gauges, which are offset in relation to one another through 90°, are preferably to be provided for each blade root. In any case, in each case one force variable F.sub.1, F.sub.2 and, respectively, F.sub.3 is determined with each strain gauge 221 to 223. Here, these force variables can be bending moments which result from measurement values of a respective strain gauge. These three force variables F.sub.1 to F.sub.3 are input into the detection block 230. In this case, the force variables F.sub.1 to F.sub.3 can each also be vectorial variables which indicate the corresponding forces on the respective blade root 211 to 213 in respect of magnitude and direction. These force variables F.sub.1 to F.sub.3 that are detected in this way are therefore initially detected in the detection block 230.

(7) In addition, a blade angle α, the rotation speed n and a rotor position β are input into the detection block 230. In the case of individual blade adjustment, that is to say when it is possible to adjust the rotor blades individually, specifically each individual rotor blade independently of the two other rotor blades, the three individual blade angles α.sub.1, α.sub.2 and α.sub.3 can also be recorded instead of the one blade angle α.

(8) An operating control block 232 is illustrated for recording these variables, specifically the one or more blade angles α, the rotor rotation speed n and the rotor position β. The use of this operating control block 232 is particularly also intended to illustrate that said variables are known in principle in the operational control arrangement of the wind turbine 200. In this respect, these variables need to be taken only from the operational control arrangement, for which the operating control block 232 is symbolically illustrated here. The operating control block 232 is illustrated in an upper region of the tower 234 only for reasons of illustration. However, the operational control arrangement, and therefore also an operating control block 232 of this kind, can usually be arranged in the nacelle 206, and these variables can be directly obtained from an overall operational control arrangement there.

(9) In any case, the detection block 230 calculates a respective hub bending moment component M.sub.B1, M.sub.B2 and M.sub.B3 from the variables which are input in said detection block. These hub bending moment components M.sub.B1, M.sub.B2 and M.sub.B3 are each based on the detected force variables F.sub.1, F.sub.2 and, respectively, F.sub.3. In other words, a hub bending moment component M.sub.B1, M.sub.B2 and, respectively, M.sub.B3, which can also be called blade root bending moments, is in each case calculated from a force variable F.sub.1, F.sub.2 or F.sub.3, and the variables α, n and β, that is to say the blade angle α, the rotor rotation speed n and the rotor position β, are also taken into consideration for this calculation. The first intermediate result of this detection block 230 is therefore these three hub bending moment components M.sub.B1 to M.sub.B3, which can each also be represented as vectors. Each of these hub bending moment components M.sub.B1 to M.sub.B3 is therefore preferably not only an individual scalar value, but rather a vector which indicates amplitude and direction. These three variables are then combined in the combination block 236 to form a single loading variable, specifically using the example of FIG. 2 to form a common hub bending moment M.sub.B. This common hub bending moment M.sub.B can be, for example, a vectorial sum of the three individual vectors M.sub.B1, M.sub.B2 and M.sub.B3 when these individual hub bending moment components M.sub.B1 to M.sub.B3 are each vectors. If this calculation is based only on the magnitudes, an average value can be calculated in the combination block 236 for example, just to mention a further example.

(10) In any case, FIG. 2 illustrates how an individual loading variable, here specifically the hub bending moment M.sub.B, can be determined from the force measurements at the blade roots 211 to 213 by means of the strain gauges 221 to 223.

(11) The hub bending moment M.sub.B that is determined as illustrated in FIG. 2 is then used, for example, according to a structure according to FIG. 3, for the purpose of controlling the wind turbine in a loading mode.

(12) Moreover, the strain can also be measured, and then conclusions can be drawn about blade root bending moments by means of weight-based calibration. As an alternative, this can also be carried out in the detection block 230.

(13) In the control structure according to FIG. 3, provision is made for the determined hub bending moment M.sub.B to be subtracted from a setpoint value for the hub bending moment M.sub.BS in the summing element 340. The result is a control error, which is called a control deviation, specifically a moment control deviation e.sub.M here. This moment control deviation e.sub.M is then input into a PI control block 342 and this PI control block 342 outputs a setpoint rotation speed n.sub.S as the result.

(14) The current rotation speed of the wind turbine 300 is then subtracted from this setpoint rotation speed n.sub.S, that is determined in this way, in the rotation speed summing element 344. The result is the rotation speed control deviation e.sub.n. Said rotation speed control deviation is input into an angle determining block 346 which determines a blade angle α.sub.S, that is to be set, from said rotation speed control deviation. In this respect, this blade angle α.sub.S is a setpoint value and is input into the wind turbine 300 for corresponding conversion for blade adjustment.

(15) Here, the wind turbine 300 is depicted only highly schematically as a corresponding block which is subdivided into a blade angle range B, a generator region G and the rest of the wind turbine W. The setpoint angle α.sub.S therefore acts on the blade region 348.

(16) At the same time, the rotation speed n is input into the power block 350 which determines a setpoint power P.sub.S from said rotation speed, which setpoint power is input into the generator region 352.

(17) In particular, these two values, specifically the blade setpoint angle α.sub.S and the setpoint power P.sub.S, now form the input variables for the wind turbine 300 for this consideration. By way of precaution, it should be noted that this is based on only one blade angle α.sub.S. It goes without saying that it is also possible to set individual blade angles. In this case, the blade angle α.sub.S, which forms the output of the angle determining block 346 here, can be considered to be the main angle to which any individual adjustments of the individual angle can be correspondingly added in each case.

(18) In any case, the result of the wind turbine 300 is at least one force variable F, which can be made up of the three individual forces F.sub.1, F.sub.2 and F.sub.3 according to the illustration of FIG. 2 here. This force variable F is then entered into the detection device 354. The detection device 354 can, for example, be made up of the detection block 230 and the combination block 236 according to FIG. 2. In this respect, the two blocks, specifically the detection block 230 and the combination block 236, can also be called the detection device 238.

(19) In any case, the structure of FIG. 3 functions in combination as follows. In the loading mode, this structure initially operates according to FIG. 3. Then, load-dependent correction takes place in principle such that the hub bending moment M.sub.B is corrected to the setpoint value of the hub bending moment M.sub.BS. This takes place such that the moment control deviation e.sub.M by the PI controller according to the PI control block 342 leads to a setpoint rotation speed. Therefore, if the hub bending moment M.sub.B has precisely reached its setpoint value M.sub.BS, the control deviation is zero and the setpoint rotation speed is then kept at its last value on account of the integral component in the PI control block 342.

(20) The conversion of this setpoint rotation speed into an actual rotation speed takes place by the control loop which begins with the setpoint/actual value comparison in the rotation speed summing element 344. The result of this setpoint/actual value comparison, specifically the rotation speed control deviation e.sub.n, is then converted via the angle control block 346 into a corresponding angle, specifically initially as a setpoint value which is then actually converted in the blade region 348.

(21) However, at the same time, a power, specifically a generator power, is prespecified in accordance with a characteristic curve depending on the rotation speed. Accordingly, a rotation speed-dependent power characteristic curve is stored in the power block 350. Accordingly, the power block 350 outputs a setpoint value for the power and this setpoint value P.sub.S is converted in the generator region 352. If this leads to a change in power, the rotation speed can also change and the power is then adjusted in accordance with the characteristic curve and therefore by the power block 350.

(22) If the power is reduced as a result, the generator torque is therefore also reduced, and this can, in turn, lead to an increase in rotation speed. This is counteracted in the rotation speed control arrangement particularly by the angle determining block 346 by way of the blade angle then being reduced. However, this can, in turn, also lead to a change in the loading and therefore to a change in the force variable F. Accordingly, the hub bending moment M.sub.B can then change and this can lead to a change in the setpoint rotation speed by means of the moment control deviation e.sub.M and the PI control block 342.

(23) In any case, this structure leads, in the case of an increase in the hub bending moment which is to be countered as a result, to initially the rotation speed being lowered and, depending on this, the power also being adjusted, specifically reduced, on account of a characteristic curve in the power block 350.