Method for Rotating the Rotor of a Wind Turbine

Abstract

A method for rotating the rotor of a wind turbine, in particular in still air conditions. The rotor rotates about a rotor axis and comprises at least three rotor blades, each having a center of gravity located outside of the respective axes of rotation. To create an imbalance in the rotor, the blade pitch angle of a first rotor blade is systematically set to be different from the blade pitch angle of a second rotor blade in such a way that a gravitational torque about the rotor axis is generated as a result of the change in the position of the center of gravity of the first rotor blade. The invention also relates to a computer program product and a wind turbine, which are designed to carry out this method.

Claims

1. A method for rotating the rotor of a wind turbine having a rotor that is rotatable about a rotor axis said rotor comprising at least three rotor blades, the center of gravity of each of which lies outside a rotary axis for adjusting a blade pitch angle of the individual rotor blades wherein the blade pitch angle of a first rotor blade for creating an imbalance in the rotor is systematically set differently from the blade pitch angle of a second rotor blade so that a gravitational torque about the rotor axis is generated by changing the position of the center of gravity of the first rotor blade.

2. The method of claim 1, wherein the gravitational torque generated about the rotor axis is sufficient to overcome a breakaway torque existing in the drive train due to the frictional forces.

3. The method of claim 1, wherein the blade pitch angle of at least the first rotor blade is changed as a function of a rotor angle so that the imbalance resulting from the torque acts in a predetermined direction about the rotor axis.

4. The method of claim 1, wherein the axis of rotation for adjusting the blade pitch angle of the first rotor blade for generating an imbalance deviates from the horizontal by at least 5, preferably by at least 10, more preferably by at least 20.

5. The method of claim 3, wherein the blade pitch angles of at least two, preferably of all rotor blades are changed as a function of the rotor angle so that the imbalance of the rotor is increased compared to the change in the angle of attack of only the first rotor blade.

6. The method of claim 3, wherein for moving the rotor to a predetermined angular position the rotor angle is monitored and the imbalance in the rotor is reduced or eliminated before or on reaching the predetermined angular position and/or the rotor is stopped in the specified angular position by a brake.

7. The method of claim 1, wherein before and/or during the execution of the method the wind speed at the wind turbine is monitored, and the method is terminated at wind speeds of more than 3 m/s, preferably more than 2 m/s, more preferably more than 1 m/s.

8. The method of claim 1, wherein before and/or during the execution of the method the rotational speed of the rotor is monitored and the method is terminated on exceeding a predetermined maximum speed.

9. The method of claim 1, wherein for eliminating the imbalance in the rotor and/or on terminating the process method, the blade pitch angle of the rotor blades are set as identical, preferably in the feathered position.

10. The method of claim 1, wherein electric blade adjustment actuators are provided for the adjustment of the blade pitch angle of the individual rotor blades.

11. The method of claim 1, wherein the rotor blades are pre-curved rotor blades.

12. A computer program product comprising program parts that are designed to perform the method claim 1 when loaded in a computer, preferably the control unit of a wind turbine.

13. A wind turbine with a rotor that is rotatable about a rotor axis, comprising at least three rotor blades, the center of gravity of each of which lies outside the axes of rotation for adjusting the blade pitch angles of the individual rotor blades, and a control unit, wherein the control unit is designed to carry out the method of claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The invention is now further explained on the basis of an advantageous embodiment with reference to the attached drawings. In the figures:

[0028] FIG. 1: shows a schematic representation of a wind turbine according to the invention;

[0029] FIG. 2: shows a schematic representation of the gondola of the wind turbine from FIG. 1;

[0030] FIG. 3: shows a front view of the rotor of the wind turbine according to FIGS. 1 and 2 in the balanced state;

[0031] FIG. 4: shows a front view of the rotor of the wind turbine according to FIGS. 1 and 2 with an imbalance produced according to the invention;

[0032] FIG. 5: shows a schematic representation of the dependence of the torque induced by a rotor blade on the blade pitch angle using the example of the wind turbine from FIGS. 1 and 2;

[0033] FIG. 6: shows a schematic representation of the dependence of the blade pitch angle of a rotor blade on the rotor angle using the example of the wind turbine from FIGS. 1 and 2; and

[0034] FIG. 7: shows a diagram of the generation according to the invention of a gravitational torque using the example of the wind turbine from FIGS. 1 and 2.

DETAILED DESCRIPTION

[0035] A wind turbine 1 and its gondola 5 according to the invention and thus designed for carrying out the method according to the invention are schematically represented in FIGS. 1 and 2. The wind turbine 1 comprises a rotor 2 with a total of three rotor blades 4 attached to a rotor hub 3. The rotor 2 is disposed on the gondola 5 so as to be rotatable about a rotor axis 20, wherein the gondola 5 is in turn disposed on a tower 6 so as to be rotatable about a vertical axis by means of an azimuth drive 11.

[0036] The rotor hub 3 is connected by means of a gearbox 7 to a generator 8 for the conversion of wind energy acting on the rotor 2 into electrical energy. The generator 8 is a dual-fed asynchronous generator in which one part of the generated power is passed directly and another part of the power is passed via an inverter 9 and a switching element 10 to a transformer located at the base of the tower 6 (not shown) and from there is fed into a public supply network.

[0037] Furthermore, between the gearbox 7 and the generator 8, a brake 12 is provided with which a rotational movement of the rotor 2 about the rotor axis 20 can be braked and the rotor 2 can be locked. In addition, there is a device 13 for determining the current rotor angle, a device 14 for determining the rotor speed (or the speed of the shaft between the gearbox 7 and the generator 8, which directly correlates with the rotor speed), and a device 15 for determining the wind speed in the vicinity of the gondola 5 and the rotor 2.

[0038] The components 7-11 disposed in the gondola 5 of the wind turbine 1 that can be controlled or monitored, as well as all sensors 13, 14, 15, are connected to a control unit 16 that controls the operation of the wind turbine 1. The control unit 16 is programmable and includes a memory 17 in which control programs can be stored.

[0039] As can be seen in FIG. 1, the rotor blades 4 of the rotor 2 are pre-curved, so that even in strong winds free passage of the rotor blades 4 in front of the turret 6 is guaranteed. Furthermore, the rotor blades 4 are each adjustable about an axis of rotation 40 with respect to their respective angles of attack. To adjust the blade pitch angle, an electric blade adjustment actuator 41 is disposed in the rotor hub 3. Said blade adjustment actuators 41 are also controlled by the control device 16 via control lines that are not shown for reasons of clarity. From the state of the art, sufficient methods for operating the wind turbine are known, in which the angle of attack of the rotor blades is changed in order to obtain the best possible power generation in different wind conditions.

[0040] In FIG. 3 a front view of the rotor 2 of the wind turbine 1 from FIGS. 1 and 2 is shown, wherein the representation of the gondola 5 and the tower 6 was omitted for reasons of clarity. The three rotor blades 4 all have a blade pitch angle of 90, so they are in the feathered position. A rotor blade 4namely the first rotor blade 4points vertically upwards, which corresponds here to a rotor angle of 0. As a result, the other rotor blades 4 are at 120 and 240.

[0041] The rotor blades 4 each have a mass of 8000 kg, wherein the center of gravity 42 of each of the rotor blades 4 is 20 cm outside the respective axis of rotation 40. In the 90 position shown in FIG. 3, the distance between the center of gravity 42 and the axis of rotation 40 in the plane relevant to the rotor axis 20 running perpendicularly to the plane of the bladenamely the plane of the bladeis just 20 cm. As a result, respective torques act due to the mass of the rotor blades 4, but are always in equilibrium if the three rotor blades 4 are at the same blade angle setting. Thus, the counterclockwise torques of the first rotor blade 4 and the rotor blade 4 at 120 are compensated by the torque of the rotor blade 4 at 240. The rotor 2 is therefore balanced. It should be noted that the rotor 2 is balanced independently of the rotor angle if all rotor blades 4 have the same blade pitch angle.

[0042] The rotor 2 from FIG. 3 is shown in FIG. 4, but the blade pitch angle of the first rotor blade 4 is set differently compared to the blade pitch angle of a second rotor bladethat is, one of the other two rotor blades 4. The blade pitch angle of the first rotor blade 4 is 90 in this case (the so-called negative feathered position), so that the center of gravity 42 of the first rotor blade 40 is now at a distance of 20 cm on the other side of the axis of rotation 40.

[0043] Due to the adjustment of the blade angle of the first rotor blade 4 shown in FIG. 4, the torque applied to the rotor 2 by said rotor blade 4 changes, while the torques caused by the other rotor blades 4 have remained unchanged compared to FIG. 3. In particular, the direction of rotation of the torque induced by the first rotor blade 4 changes. This torque no longer works counterclockwise (cf. FIG. 3), but rather in the clockwise sense. As a result, the rotor is no longer in torque equilibrium and a resulting gravitational torque that acts clockwise is produced. As a result, the rotor 2 is set in rotational motion about the rotor axis. Again, it is pointed out that it is not mandatory to change the direction of the torque due to the first rotor blade 4; a reduction of this torque starting from the situation according to FIG. 3 is usually sufficient to produce a sufficient gravitational torque to rotate the rotor 2.

[0044] FIG. 5 shows schematically how the torque exerted on the rotor 2 by a rotor blade 4 can change as a function of the blade pitch angle. This torque results from the horizontal distance between the rotor axis 20 and the center of gravity 42, 42 of the rotor blade 4. The horizontal distance or lever arm results initially from the angular position of the axis of rotation 40 of the rotor blade 4 relative to the 0 rotor angle, but is influenced by the relative position of the center of gravity 42, 42 relative to the axis of rotation 40.

[0045] For illustrative purposes, two exemplary center of gravity positions are shown in FIG. 5, wherein the center of gravity 42 represents the position at a 90 blade pitch angle (i.e. in the feathered position), the center of gravity 42 represents the position at a 90 blade pitch angle (i.e. in the negative feathered position). The two center of gravity positions are spaced apart from each other by a distance d of 40 cmi.e. twice the distance between the centers of gravity 42, 42 and the axis of rotation 40, which with a difference l of the lever arm leads to the calculation of the torque of dcos . Due to this possible change of the lever arm by the length l, a gravitational torque about the rotor axis 20 can be generatedif the change of the lever arm is not carried out similarly with the other rotor blades.

[0046] From the relationships shown in FIG. 5 it is further apparent that the influence of the blade pitch angle on the lever arm is very small for the torque in the region of the horizontal. In the embodiment shown, the change in torque due to adjusting the blade pitch angle in a range of +/20 around the horizontal is very small, so that it has little or no influence on the gravitational torque.

[0047] In order to ensure that the gravitational torque generated on the rotor 2 by adjusting the different blade pitch angle of the first rotor blade 4 always points in the same direction, even when the rotor 2 is rotating, the blade pitch angle must be different for a position of the rotor blade 4 above the horizontal than if the rotor blade 4 is below the horizontal.

[0048] In FIG. 6, this situation is shown by way of example. For a constant clockwise rotation of the rotor 2, the blade pitch angle of the first rotor blade 4 in the sector designated with A can be 90, while in the sector designated with B it can then be +90. Those sectors in the range of +/20 around the horizontal that can be used to move the rotor blade 4 between the +/90 positions, in which, as explained, the blade pitch angle of a rotor blade 4 has only a small influence on the torque applied to the rotor axis 20, are designated with C in FIG. 6.

[0049] In FIG. 6 it can also be seen that not only the blade pitch angle of the first rotor blade 4 is systematically changed, but also those of the other rotor blades 4. If the other rotor blades 4 are also adjusted according to the stated specifications in the individual sectors A, B and C, the gravitational torque can be increased compared to the adjustment of only a single rotor blade 4.

[0050] FIG. 7 shows by way of example the gravitational torque M.sub.ges that can be achieved in the wind turbine 1 according to FIGS. 1 and 2 depending on the rotor angle if all the rotor blades 4, 4 of a wind turbine 1 according to the sectors shown in FIG. 6 can be adjusted to blade angles of +/90. Here, the first rotor blade (designated with index 1 in FIG. 7) points perpendicularly upwards at a rotor blade angle of 0, while the second rotor blade (index 2) is at 120 and the third rotor blade (index 3) is at 240 (cf. FIG. 3). At 0, the blade pitch angle of the first rotor blade .sub.1 is therefore +90, while the blade pitch angles .sub.2, .sub.3 of the other two rotor blades are 90. With the rotor 2 rotating, the rotor angle must change and the blade pitch angles .sub.1, .sub.2, .sub.3 are adjusted according to FIG. 6 in order to always obtain the maximum gravitational torque M.sub.ges.

[0051] FIG. 7 shows the torque components M.sub.1, M.sub.2, M.sub.3 that the individual rotor blades 4, 4 contribute to the gravitational torque M.sub.ges. It can be seen from these components M.sub.1,M.sub.2,M.sub.3 that the influence of a rotor blade 4, 4 on the gravitational torque M.sub.ges decreases whenever a rotor blade 4, 4 approaches the horizontal. In just these areas (sector C in FIG. 6) the blade pitch angle is moved from +90 to 90 or vice versa in each case.

[0052] With the method according to the invention, the rotor 2 of the wind turbine 1 can be moved in particular in still wind conditions. Also due to the different blade pitch angles of the individual rotor blades 4, 4 during the process, which can lead to undesirable loads on the wind turbine, it is preferred if the control unit 16 only begins the process according to the invention when the device 15 for determining the wind speed measures a wind speed of less than 3 m/s, preferably of less than 2 m/s. The control unit 16 also terminates the process if the wind speed increases during said process to more than 3 m/s, preferably to more than 2 m/s. The control unit 16 also terminates the process if the rotor speed determined by the device 14 exceeds a predetermined maximum value. In both cases, the rotor blades 4, 4 are moved to the feathered position, i.e. the 90 position.

[0053] The method according to the invention is particularly suitable for moving the rotor 2 to a desired angular position, for example to be able to carry out maintenance on the wind turbine 1. For this purpose, the current rotor angle detected by the device 13 is compared with the desired angular position and the rotor 2 is braked with the help of the brake 12 so that the rotor 2 comes to a standstill in the desired position. At the same time, the rotor blades 4 are placed in a low-load position, for example in the feathered position, in order to avoid an unnecessary load on the brake 12.

[0054] In practice, it has been shown that the deformation of the rotor blades due to their own weight in the gravitational field also has a non-negligible influence on the center of gravity displacements. In this respect, it is particularly preferable to take into account these elastic deformations when adjusting the blade angles. This can be done empirically or by computational simulation with a computational model that takes into account the gravitational deformation of the rotor blades in the gravitational field.