[0026] FIG. 1 is a plan view on to a wind power installation with the machine housing 10 and rotor blades 11, 12. The centre of rotation of the machine housing 10 is marked by a point 20 while the main axis of the horizontal-axis rotor is indicated by a central line 14.

[0027] Now, as soon as there is a deviation between the main axis 14 of the rotor and the wind direction which is indicated in this Figure by inclinedly extending arrows, a check is made to ascertain whether a predeterminable threshold value in respect of the magnitude of the change in wind direction and the duration thereof is reached or exceeded. If that is the case, the angle of incidence of the rotor blade 11 shown at the left in the Figure is altered in such a way that the air resistance is reduced. That results in an imbalance of forces between the two rotor blades 11, 12 and the air resistance, which is now higher, at the right rotor blade 12, gives rise to a force F which acts on the machine housing 10 with a torque in the direction of the arrow illustrated above the centre of rotation 20. In that way the rotor is adjusted to track to the wind without the azimuthal drive having to be switched on.

[0028] If the difference between the main axis 14 of the rotor and the wind direction exceeds a predeterminable threshold value, an existing azimuthal drive can be switched on to assist with the rotary movement and to reduce the asymmetric loading. That azimuthal drive is also required if the wind has completely died away and, after a period when there is no wind, blows from a different direction which excludes tracking adjustment of the rotor by the adjustment of the angle of incidence in the above-described manner.

[0029] It will be appreciated that, in an alternative embodiment of the invention, it is possible, in the situation shown in FIG. 1, to increase the air resistance of the right rotor blade 12, instead of reducing the air resistance of the left rotor blade 11. It will be noted that this increase in the air resistance of the right rotor blade 12 would result in a higher level of loading on that rotor blade 12 and would thus detrimentally affect the service life thereof. For that reason a reduction in the air resistance of the left rotor blade 11 and therewith a reduction in the loading on that rotor blade 11 is to be preferred.

[0030] FIG. 2 shows a wind power installation on a platform 30 which is floating in the water and which is held in its predetermined position for example by at least two anchor chains 32.

[0031] In this case the platform 30 is below the surface 2 of the water while the pylon 8 of the wind power installation sticks up out of the water and carries the machine housing 10 with the rotor blades 12.

[0032] As long as the wind is impinging on the wind power installation in precisely frontal relationship, a nodding moment will occur which deflects the wind power installation rearwardly in the perspective shown in FIG. 2. It will be noted that as soon as the wind direction is inclined, a lateral component is also added to the frontal component. That lateral component will cause a laterally directed deflection, in addition to the rearwardly directed deflection. That is manifested on the one hand in an inclination of the surface of the platform 30 out of the horizontal or by an inclination of the pylon 8 of the wind power installation out of the vertical by a predetermined amount which is indicated in the Figure by the angle α on the one hand at the pylon 8 of the wind power installation and on the other hand at the surface of the platform 30.

[0033] While the deflection at the surface of the platform is still relatively slight, the deflection out of the perpendicular at the top of the pylon 8 can already be of a clearly detectable magnitude so that detection at the top of the pylon 8 can provide for the embodiment of a very sensitive device for detecting a change in wind direction and a deflection arising therefrom.

[0034] It will be appreciated that, in terms of detecting the deflection, it is to be noted that only a deflection due to the lateral wind component is relevant for the control action according to the invention.

[0035] FIG. 3 shows an embodiment for the control of the wind power installation in accordance with the invention. A device 40 ascertains the wind direction. That device 40 can be for example a simple weather vane, for example with an incremental sender, as is provided in any case on any wind power installation. A further device 42 ascertains the azimuthal position. Those two devices 40, 42 communicate their measurement results or data to a control 44 which in turn evaluates the two values from the wind direction detection device 40 and the azimuthal position detection device 42 and compares them and if necessary, on the basis of predeterminable characteristic values, implements suitable adaptation of the angle of incidence of the rotor blades, by way of an adjusting device 46.

[0036] In this respect it is possible to predetermine for example three threshold values for the magnitude of the difference between the wind direction and the azimuthal position. If the deviation between the two values reaches the first of those threshold values for a given period of time, the angle of incidence of a rotor blade 12 is adjusted by an adjusting device 46 by way of a control line 48, for example to a pitch motor (not shown), in a given segment of the circle of the rotor, in such a way that the air resistance thereof is reduced so that the machine housing 10 with the rotor is adjusted in tracking relationship with the wind until the wind direction and the azimuthal position are again coincident within also predeterminable tolerance limits. The control 44 then again provides for the setting of the rotor blades 11, 12, which is appropriate for optimum energy output.

[0037] If in evaluation of the data the second threshold value in respect of the deviation between azimuthal position and wind direction occurs, the control 44 can switch on the azimuthal drive 22 for example by way of a separate control line 49 and thus support the wind direction tracking effect. The third threshold value can be so determined that then a wind direction tracking action is no longer possible by virtue of the change in the angle of incidence of a rotor blade so that here the azimuthal drive 22 is definitely required.

[0038] FIG. 4 shows an active wind direction tracking device by means of a motor azimuthal drive. That motor drive rotates the machine head of the wind power installation in such a way that the rotor of the wind power installation is optimally aligned in the direction of the wind. Such an active drive for the wind direction tracking action can be an azimuthal drive 51 with an associated azimuthal bearing 52. That azimuthal bearing is disposed between the pylon head and the machine housing. One azimuthal drive is sufficient in small wind power installations, larger wind power installations are generally equipped with a plurality of azimuthal drives, for example four azimuthal drives, as shown in FIG. 4. The four drives 51 are distributed uniformly around the periphery of the pylon head (a non-uniform distribution is also possible).

[0039] The illustrated azimuthal drives are three-phase current asynchronous motors which are used as asynchronous drive machines. For adjustment purposes, for active azimuthal adjustment, those three-phase current asynchronous motors are supplied with corresponding three-phase current, in which case they produce a corresponding torque. After the machine housing adjustment procedure (after it has assumed the desired azimuthal position) the four three-phase current asynchronous motors (ASM) are switched off and thus no longer produce any torque. In order to uniformly retard the motors and also thereafter still to produce a braking torque, the motors are supplied with a direct current immediately after separation from the three-phase current network, as far as possible immediately thereafter. That direct current produces a stationary magnetic field in the motors which are immediately braked therewith. The direct current supply continues as far as possible throughout the entire stoppage time and can be regulated in respect of amplitude.

[0040] After the adjusting operation the ASM-drives are supplied with a regulated direct current by means of a regulating device (see FIG. 5). Slow rotary movements of the pylon head which are caused by asymmetrical gusts of wind are only damped by a low direct current (about 10% of the minimum current), but are admitted. Faster rotary movements are avoided by an adapted higher direct current and thus a higher braking torque. In the case of very fast rotary movements the direct current is raised to the nominal current of the motor.

[0041] The asynchronous motor does not produce any torque with the direct current magnetisation in the stopped condition. However with a rising rotary speed—up to about 6% of the nominal rotary speed—the torque produced rises linearly, symmetrically in both directions of rotation.

[0042] It is also appropriate for the individual motors of the azimuthal drives to be coupled by means of a current transformer. Simple counter-coupling of the asynchronous motors stabilises the individual drives in that respect.

[0043] If therefore—as described—azimuthal adjustment is not to be effected by means of active supply of three-phase current to the asynchronous motors, the direct current of the asynchronous azimuthal drives is set to zero or is made so low that controlled adjustment of the azimuth can still be effected by means of rotor blade angle adjustment. In order for example to maintain a low braking counter-moment, it may also be advantageous to limit the direct current of the asynchronous motors to a value of between 1% and 10% of the nominal current so that a motor braking moment is also afforded, over and above the braking action of the plain bearings, and that braking moment makes it possible for the azimuthal change to be effected in the desired manner and without excessive swing deflection.