METHOD FOR OPERATING A WIND TURBINE, WIND TURBINE, AND CONTROL MEANS FOR A WIND TURBINE

Abstract

In the case of wind turbines 10, deviations from the optimum operating state result in output losses. This applies, in particular, to angular deviations 62 in the alignment of the nacelle 14, and therefore of the rotor axis 28, relative to the wind direction 60. The invention relates to a wind turbine 10, and to a method for operating such a wind turbine, which wind turbine and method enable the nacelle 14 to be corrected, in respect of the wind direction, both on the basis of wind power and by motor.

Claims

1. A method for operating a wind turbine (10) having a rotor (20) on a rotor axis (28), wherein an angle of attack of each of the rotor blades (22, 24) is adjusted individually or continuously such that the nacelle (14) is made to rotate for the purpose of correcting a rotor axis (28) into the setpoint position by a yaw moment (68) effected by wind forces

Description

[0020] A preferred exemplary embodiment of the invention is described in greater detail on the basis of the figures of the drawing. In the latter:

[0021] FIG. 1 shows a representation of a wind turbine according to the invention, in a perspective representation,

[0022] FIG. 2 shows a view of the wind turbine of FIG. 1, in a top view from above,

[0023] FIG. 3 shows a portion of the nacelle bearing, with associated mechanism, and

[0024] FIG. 4 shows a lateral, partial representation of the mechanism relating to the rotation of the nacelle.

[0025] A wind turbine 10 comprises a support arrangement such as, in particular, a tower 12, disposed at the upper end of which there is a so-called nacelle 14. The nacelle 14 has a housing 16, inside which there are typically disposed various items of technical equipment such as, in particular, a gearbox, a generator, control means and the like.

[0026] An essential element carried by the nacelle 14 is the rotor 20, in this case having two rotor blades 22 and 24, which are attached on one side to a central rotor hub 26. The rotor 20 is designed to rotate in the wind, and thereby to drive a corresponding generator for the purpose of generating electrical energy. For this purpose, the rotor blades 22 and 24 in cross section have the shape of an aerofoil. In FIG. 1, the direction of rotation of the rotor 20 is indicated by corresponding arrows. The rotor 20 in this case rotates about the rotor axis 28, in the plane spanned by these rotor blades 22, 24 and a straight line that is simultaneously perpendicular both to the rotor blades 22 and 24, or to the blade axis 30, and to the rotor axis 28.

[0027] In the present case, the wind turbine 10 is a so-called two-bladed turbine. This means that the rotor 20 has just two rotor blades 22 and 24. In this case, for reasons of symmetry, the rotor blades 22 and 24 are each disposed such that they are substantially perpendicular to the rotor axis 28 and on a straight line, the so-called blade axis 30, which itself extends through the centre of the rotor hub 26. The rotor axis in this case extends, substantially in the longitudinal direction, through the housing 16 of the nacelle 14, and usually at least substantially horizontally.

[0028] The rotor blades 22 and 24 are disposed so as to be rotatable about the blade axis 30. For this purpose, corresponding blade bearings 32 are disposed in the region of the rotor hub 26. In the figures, the rotation capability is indicated by corresponding ring arrows.

[0029] The wind turbine 10 described here is a so-called downwind-rotor turbine. This means that the rotor 20 rotates on the side of the wind turbine 10 that faces away from the are, i.e. the wind first sweeps over the nacelle 14, in order then, as it were, to be incident upon the back side of the rotor 20. This is indicated with the case 34, which denotes the main wind direction. Basically, however, the described invention can also be applied in the case of so-called upwind-rotor turbines, i.e. wind turbines having a rotor that faces toward the wind.

[0030] The rotor blades 22 and 24 bend, in the region of their blade ends 36 and 38, according to the respective wind load, in the direction of the main wind direction, as indicated by the arrow 34. Usually, so-called strain gauges 40 are therefore disposed in the region of the surface of the rotor blades 22 and 24 to determine the deflection of the latter. Since the strain gauges 40 extend at least in the region of the blade ends 36 and 38, which are subjected to high loads, but usually substantially along the entire rotor blades 22 and 24, it is thus possible to measure the blade deflection. If necessary, strain gauges 40 may also be disposed on both sides of the rotor blades 22, 24 in order, for example, to enable oscillating motions of the blade to be picked up with greater precision.

[0031] For the purpose of rotating the two rotor blades 22 and 24, adjusting means are disposed in the region of the rotor blades 22 and 24, respectively, the rotor hub 26, or the nacelle 14, for the purpose of rotating the rotor blades 22 and 24 about the blade axis 30. This is usually an adjustment effected by motor, in particular a hydraulic and/or electric-motor adjustment. Furthermore, the rotor blades 20 and 24 can be adjusted separately, and independently of each other. For this purpose, both a common adjusting means and separate adjusting means may be provided.

[0032] The nacelle 14 is mounted so as to be rotatable, about the nacelle rotation axis 18, relative to the tower 12 of the wind turbine 10. Serving this purpose, on the one hand, is an inner bearing ring 42, which is surrounded by an outer bearing ring 44. The outer bearing ring 44 is connected to the upper end region of the tower 12. The inner bearing ring 42 is mounted on the nacelle 14. The inner bearing ring 42 is movable on the outer bearing ring 44 by means of corresponding bearing means, in particular as ball bearings or roller bearings, i.e. they are mounted, in particular, so as to be rotatable relative to each other. The inner bearing ring 42 in this case has been pressed into the inner circle of the outer bearing ring 44. Inserted between them are bearing means 56 such as, for example, balls or rollers, and, if necessary, spacers 58. Accordingly, the nacelle 14, together with the inner bearing ring 42 the outer bearing ring 44, is mounted so as to be rotatable, with little friction, on the tower 12.

[0033] A gear wheel 48 is connected, by means of an axle 52, to a drive unit 54, which is rotatably mounted on the nacelle 14. The drive unit 54 comprises a plurality of constituent parts that are not shown in detail here. On the one hand, the axle 52 is connected to a gearbox. This gearbox is connected to an electric motor, via a hydrodynamic clutch.

[0034] In the operating mode, for the purpose of driving the nacelle 14, the electric motor is operated while the hydrodynamic clutch is engaged. The power of the electric motor is thus transmitted to the ring gear 46 via the gearbox and the gear wheel 48. This results in the nacelle being rotated relative to the tower 12.

[0035] When operated as a damping element 50, the electric motor is stopped. The gear wheel 48 can thus only be rotated against the resistance of the hydrodynamic clutch. This results in the rotation of the nacelle 14 being damped by the braking force of the hydrodynamic clutch. The gear wheel 48 and the drive unit 54 are therefore also referred to jointly as a damping element 50.

[0036] The method according to the invention preferably proceeds as follows:

[0037] Since a deviation of the alignment of the rotor 20 from the optimum position in the wind direction causes output losses, this relative position, i.e. the so-called angular deviation, is determined. The rotor axis 28, which extends centrally through the rotor hub 26, and which is simultaneously the rotation axis of the rotor 20, is used as the relevant axis of the rotor 20.

[0038] A wind-direction measuring device, for example, may be used to determine the current relative position of the rotor 20, or nacelle 14, in relation to the wind direction. The measuring device may be attached to the nacelle 14, or to a stationary part of the wind turbine 10, or a part thereof that does not rotate concomitantly, such as, in particular, to the tower 12, or also to an external mounting. The measuring device may be, for example, a wind vane, possibly having an anemometer, a radar, a LIDAR (Light Detection And Ranging) or similar. Furthermore, the wind direction may be deduced by measuring the differences in wind load on the rotor blades 22, 24, and the resultant differences in blade deflection. This measurement method may be used separately or in combination with the known methods of measuring the wind direction.

[0039] Attachment to the concomitantly rotating nacelle 14 offers the advantage that the wind-direction measuring device already indicates a deviation without additional measurement of the nacelle position. In the case of a stationary measurement of wind direction, for example on the tower 12, it is also additionally necessary to determine the position of the nacelle 14 relative to the tower 12, in order that the deviation between the nacelle position and the wind direction can be calculated. The measured, or calculated, angle between the rotor axis 26 and the wind direction in this case is referred to as deviation. The deviation is preferably determined periodically, at short successive intervals, in order to have the current deviation available at any time, for example in the case of changes in the position of the rotor axis 46 or of the wind direction.

[0040] In a further method step, it is established whether the deviation is within predefined limits. This can then be used as a basis for decision concerning the means to be used for correction of the nacelle 14. On the one hand, correction may be effected by motor, but on the other hand correction may also be effected by wind force. If the deviation is below predefined limit values, correction by wind force is usually initiated, otherwise correction at least partially by motor.

[0041] Moreover, correction is effected by motor if a plurality of complete rotations of the nacelle 14 about the nacelle rotation axis 18 in only one direction of rotation has in the meantime resulted in the cables, going out from the nacelle, having become twisted inside the tower 12. In order to undo this twist, rotation may then be effected by motor, if necessary, in the opposite direction.

[0042] Typically, angular deviations of between 5 and 90, typically of less than approximately 60, on both sides are defined as limit values for wind-operated correction. Below this, correction by wind force alone can be achieved without difficulty. Above this, correction may be effected entirely by motor. Alternatively, it is possible to effect a downward adjustment into the range defined for wind-operated correction, i.e. until the deviation is less than the defined maximum angular deviation. At least, however, correction by motor is normally effected above an angular deviation of approximately 90, since the rotor 20, rotating perpendicularly in relation to the wind direction, can virtually no longer be driven. Consequently, in this position, correction based on wind force usually can no longer function.

[0043] Here, correction by motor is effected by means of an electric motor. For this purpose, such an electric motor may already be built-in as part of the damping element 50. The motor is operated, as a drive, in such a manner that, via the gear wheel 48, the nacelle 14 is rotated relative to the ring gear 46 on the outer bearing ring 44, and is thereby rotated relative to the tower 12. This rotation is maintained until the angular deviation of the nacelle 14 relative to the wind direction either becomes less than the defined limit value or even is reduced virtually to zero.

[0044] A wind-operated correction is produced by individual adjustment of the angles of attack of the rotor blades 22 and 24, so-called individual pitch control (IPC). For this purpose, the angles of attack of the two rotor blades 22 and 24 are altered, independently of each other, in such a manner that, overall, a resultant yaw moment, i.e. a torque, acts upon the nacelle 14. This is effected by rotation of the rotor blades 22, 24 about their blade axis 30. In order to exert opposing forces, it is necessary for the rotor blades 22, 24 to be rotated in exactly opposite directions, in particular by the same, but opposite, angle of rotation. The resultant yaw moment caused by the wind forces then effects a rotation of the nacelle 14, and thereby effects a correction to reduce the angular deviation. The damping element 50 in this case additionally serves to retard a rotation of the nacelle 14, which can rotate freely relative to the tower 12.

[0045] In detail, the individual pitch control (IPC) proceeds as follows:

[0046] Firstly, the current position of the nacelle 14 relative to the current wind direction 60, i.e. a possible angular deviation 62, is determined. This may be effected in the ways described above, i.e. for example by measurement of wind direction or by means of blade loads. If it is accordingly found that there is an angular deviation between the current wind direction 60 and the rotor axis 28, the control means initiates a correction by blade pitch control. For this purpose, as described above, the rotor blades 22 and 24 are mounted so as to be rotatable about their own longitudinal axis, i.e. the blade axis 30, for the purpose of adjustment of the so-called blade pitch.

[0047] In this case, the rotor blades 22 and 24 are turned in opposing directions of rotation, in such a manner that the two blades 22 and 24 exert opposing resultant wind forces 64 and 66, respectively, via the rotor axis 28, upon the nacelle 14. A torque, or a so-called yaw moment 68, is thereby exerted upon the nacelle 14. The nacelle 14 thus rotates in the direction of the exerted yaw moment 68, such that the current angular deviation 62 is reduced as a result of this correction.

[0048] The control system performs the measurement and correction almost continuously, or at a high repetition rate, i.e., in particular, several times to many times per second. The control system can thus react at any time to changes in wind conditions.

LIST OF REFERENCES

[0049] 10 wind turbine [0050] 12 tower [0051] 14 nacelle [0052] 16 housing [0053] 18 nacelle rotation axis [0054] 20 rotor [0055] 22 rotor blade [0056] 24 rotor blade [0057] 26 rotor hub [0058] 28 rotor axis [0059] 30 blade axis [0060] 32 blade bearing [0061] 34 arrow [0062] 36 blade end [0063] 38 blade end [0064] 40 strain gauge [0065] 42 inner bearing ring [0066] 44 outer bearing ring [0067] 46 ring gear [0068] 48 gear wheel [0069] 50 damping element [0070] 52 axle [0071] 54 drive unit [0072] 56 bearing means [0073] 58 spacer [0074] 60 wind direction [0075] 62 angular deviation [0076] 64 wind force [0077] 66 wind force [0078] 68 yaw moment