NO20093412A1 - Method of turning a wind turbine in relation to the wind direction - Google Patents

Description

The present invention relates to a method for turning the rotor plane of a wind power plant when there is no wind or too little wind for the wind to generate a sufficient torque on the wind power plant to turn it.

Modern wind turbines usually have the rotor mounted upwind of the tower. Such turbines are equipped with an active direction system that turns the engine housing including the rotor against the wind when the average wind direction changes. Such a steering system normally consists of a turntable on the top of the tower. The slewing ring typically consists of a ball bearing or a slide bearing. Electric or hydraulic motors mounted against a gear wheel on the turntable turn the machine housing including the rotor on a signal from the wind power plant's control system. A counter is usually fitted which counts the number of complete revolutions of the machine housing in the same direction. After a certain number of revolutions in the same direction, for large wind turbines usually between 2-5, the rotor and energy production are stopped, and the turning motors turn the machine housing back to its original zero position so that tension on the electrical export cable is limited. Alternatively, drag rings can be used on the export cable so that you do not have to turn the machine housing back to the original zero position.

Wind turbines with the rotor mounted downwind of the tower also usually have a turning ring at the top of the tower. On floating wind turbines as shown in PCT/N02004/000119 (the applicant's own patent application), the slewing ring can be mounted at the bottom of the tower or floating undercarriage. It is also known that two or more wind turbines can be placed on one and the same floating chassis. Furthermore, it is known to align the rotor blades so that they are rotatable about their own longitudinal axis (blade pitching) in order to control the turbine's speed and power in that way. At high wind speeds, the blades twist in the pitch bearing so that the wind forces on each blade are reduced and power and rpm are also reduced. Optionally, the blade can be twisted using known methods such as piezoelectric fibers in the blades, or other mechanical methods to achieve the same effect without the entire blade being turned around its own axis at the pitch bearing. Another known alternative is to use adjustable spoilers or flaps on the blades to achieve the same effect. Another known alternative is that only parts of the blade are pitched by the pitch bearing being mounted anywhere between the root and tip of the blade. Another alternative is to use aerodynamic brakes according to known technology at the end of the blade.

If all the blades twist (pitches) the same amount at the same time, this is called collective pitch. If, according to known techniques, the blades are additionally twisted a small angle (+ or -) individually depending on where they are in the rotation path or which forces act on each blade, this is called individual pitch. By using individual pitch, the load on each individual blade can be controlled according to the wind speed locally where the blade is in the rotation path at all times, while the speed is still controlled. It is then possible to control the pitch angle of each individual blade so that the variation in the loads on the blades, which cause fatigue of the rotor blade and the rest of the construction, is reduced. This is particularly useful in reducing the effect of the wind usually varying with height since the wind hitting the rotor blade while upright is usually significantly stronger than when the rotor blade is pointing down. By using individual pitching, the fatigue loads on the rotor can therefore be reduced.

In the 3 patent applications EPO 05731806.5 - 2315 - NO2005000096 (applicant's own application), PCT/EP02/00898 and in US 4297076 it is further shown that individual pitch can also be used to let the wind create an active torque about the vertical axis through the turntable which can partially used as a replacement for the traditional motors in the turning system. The way this is done is that when a rotor blade is close to the horizontal position, e.g. near the horizontal position to the left, twists (pitches) the rotor blade with a small additional pitch angle so that the force of the wind on the blade in the direction of the wind is reduced or becomes negative (reversed). When the rotor blade comes into the opposite position, i.e. when the rotor blade in this example points to the right, the rotor blade twists (pitches) in the opposite direction so that the force of the wind on the rotor blade in the direction of the wind is increased. This can for example be done in practice by adding a sinusoidal additional signal to the control system for pitching or twisting of the rotor blades where the amplitude and phase angle are adjusted so that the desired torque about the vertical axis is achieved according to known principles.

This known form of directional control of a wind power plant by individual pitching cannot replace the conventional motors for the turning system during start-up of the wind power plant after a quiet period if the wind is too weak to turn the engine housing or if the direction of the engine housing is significantly different from the wind direction, e.g. if the wind direction is 90 degrees wrong on the machine housing and rotor plane.

In addition, individual pitch for directional control according to known techniques cannot be used as the only means of turning the machine housing back with repeated full rotations to reset the power cable's tension as described above.

The purpose of the present invention is thus to provide a method for turning a wind power plant's rotor plane when there is no wind or the wind is too weak to turn the wind power plant's rotor plane alone without having to equip the wind power plant with the traditional motors that drive the turning system.

It is also a purpose of the invention that the wind power plant should also be able to turn 360 degrees when there is little or no wind and more to remove disputes in the wind power plant's electrical export cable without having to equip the wind power plant with the traditional motors that drive the turning system.

This is achieved by means of a method for turning a wind turbine's rotor plane in relation to a wind direction or in relation to a dispute on an electric export cable as defined in independent claim 1 and an application of the method as defined in claim 14. Further embodiments of the invention are stated in the independent claims 2-13.

A method has been provided for turning a wind turbine's rotor plane in relation to a wind direction or in relation to tension on an electrical export cable. The wind power plant comprises at least one wind turbine which includes a rotor with at least one rotor blade which is arranged for rotation in the rotor plane. The method comprises the steps of adjusting at least a part of the at least one rotor blade, and of rotating the rotor with a motor on a signal from a control system in dependence on the wind direction or tension on the export cable so that the at least one wind turbine rotor is affected by a torque that turns the rotor plane in relation to the wind direction or the export cable's twist.

In one embodiment of the invention, the method includes adjusting at least one rotor blade and driving the generator or the engine on a signal from a control system depending on the wind power plant's azimuth deviation in relation to the direction of the wind or in relation to the export cable's twist. By azimuth deviation is meant the deviation between the average direction of the wind over a certain period of time and the direction of the wind power plant in relation to rotation about the vertical axis.

In a preferred embodiment of the invention, the method comprises adjusting at least one part of the at least one rotor blade and at the same time driving the rotor around by driving the wind power plant's generator as a motor on a signal from a control system depending on the wind power plant's azimuth deviation in relation to the direction of the wind or in relation to to the export cable dispute.

Preferably, the control system is continuously updated with values with respect to relevant data for wind (wind speeds, wind direction, etc.), rotor blade settings (e.g. pitch) and positions in the path of rotation and changes in the position of the rotor plane so that the rotor blades and/or the rotor or rotors' rotational speed can be adjusted as that the desired torque on the wind power plant is achieved.

This also involves adjusting the pitch setting of at least one rotor blade so that the rotor is affected by the desired torque when the rotor is rotated, or alternatively adjusting the pitch setting of only one or some of the rotor blades when the rotor comprises two or more rotor blades. It will also be possible to adjust the rotor blades individually as the rotor rotates when the rotor of the at least one wind turbine comprises a plurality of rotor blades.

Instead of, or in addition to, pitching one or more of the rotor blades, it is also an alternative to operate flaps or spoilers which in that case are arranged on one or more of the rotor blades so that the rotor is affected by the torque by reducing the lifting force in the wind direction of at least one rotor blade. You can also use all other known methods as mentioned earlier to influence the forces acting on a rotor blade from the surrounding air.

Alternatively, the wind power plant can also comprise two or more wind turbines mounted on a floating chassis, where at least one of the wind turbines includes a motor and a rotor with at least one rotor blade where at least part of the at least one rotor blade is adjustable, for example by rotatably mounted on the hub. The floating undercarriage is preferably arranged for rotation about an approximately vertical axis through the turntable when the wind turbine is installed and preferably connected to an electrical export cable. The method also includes in this embodiment of the invention adjusting at least a part of at least one rotor blade on one or more of the wind turbines, and rotating the rotor or rotors with the engine or engines on a signal from a control system depending on the wind direction or tension on the export cable so that at least one wind turbine's rotor is affected by a force or a torque that rotates the rotor plane in relation to the wind direction or the twist of the export cable. In this case, it is therefore possible to use collective pitch, i.e. all the rotor blades on one and the same rotor are pitched the same amount. The torque about the wind power plant's rotation system axis is then achieved by adjusting all the rotor blades on one rotor equally, but differently from the rotor blades on another of the wind power plant's, in this case at least two rotors. A different thrust force then arises between at least two of the wind turbine's rotors, which causes the entire wind turbine to rotate around the vertical axis.

In all embodiments, either the generator of the wind turbine or the wind turbines can be designed so that it is able to function as a motor by, for example, consuming electricity from the same electrical grid as the wind turbines or the wind turbines during normal operation supply electricity to, or alternatively that one or more of the wind turbines comprise a motor, and the motor or generator, when functioning as a motor, is arranged for rotation of the rotor of the wind turbine or wind turbines.

With the present invention, without using rotary motors on the turntable, it is possible to turn the machine housing with rotor even in little or no wind, or if the direction of the wind is significantly wrong on the machine housing and rotor plane. One can also make repeated full 360-degree rotations of the machine housing including the rotor to remove the twist from the power cable as needed. The same applies to wind power plants where a majority of wind turbines are mounted on a floating and rotatable undercarriage. It is thus possible to omit the slewing motors which are connected to the slewing ring, and which with current technology is necessary to use in addition to individual pitch for direction control for the cases described above.

In particular, it would be beneficial to be able to completely omit turning motors connected to the turning ring if the turning system of a floating wind turbine is mounted underwater.

When there is no wind, or in those cases where the component of the wind along the axis of rotation of the rotor, i.e. "incoming wind" or "wind" as shown in Figures 2, 5 and 6, is not strong enough, the wind turbine's generator is run as a motor to increase the rotor's rotational speed. Alternatively, a motor can be fitted to drive the rotor to achieve the same effect. In that case, the engine is preferably arranged in the machine housing of at least one wind turbine. This further causes the relative wind to increase and sufficient forces on the blades are mobilized either by means of individual pitching of the blades or by blade tipping or in another known way so that the rotor plane is affected by a torque and the machine housing turns in the desired direction. In little or no wind, the rotor will then, in principle, temporarily act in whole or in part as a propeller that applies energy to the surrounding air instead of as a wind rotor that only absorbs energy from the air. The auxiliary motor is preferably mounted in the wind power plant's machine room.

In an embodiment where the wind power plant comprises two or more wind turbines which are arranged on a floating and rotatable chassis, the blades of the wind turbines are adjusted so that the wind turbines are exposed to different thrust forces which cause the chassis to be affected by a torque about a vertical axis through the turntable so that the wind turbine rotates in desired direction. In little or no wind, or if the wind direction is significantly wrong at start-up or one wants to make full 360-degree rotations to remove tension from the electrical export cable, at least one wind turbine is run with the rotor in motor mode to increase the rotor speed so that the wind power plant is affected by the desired torque. The motor that drives the rotor or rotors can, as before, in a preferred embodiment consist of either the turbine's generator run in motor mode, or you can mount a motor that drives the rotor.

An alternative to having the generator or motor rotate the rotor continuously while rotating the rotor plane would be to have the motor rotate the rotor periodically or intermittently while rotating the rotor plane. That is that the rotor or rotors are set into rotation and then disengage the engine(s) or generator(s) (i.e. run it(s) at idle), then start individual pitching of the rotor blades or other adjustment of the blades so that the forces on the blades are changed , to turn the machine housing and rotor, possibly the floating undercarriage, before the speed of the rotor or rotors again becomes too low. The generator is therefore only run as a motor first and then only individual pitching of the rotor blades is used, or other adjustment of the blades so that the forces on the blades change, to turn the machine housing while the rotor is still in motion. This procedure can be repeated several times until the machine housing is in the desired position. As already mentioned, an engine can be used instead of the generator in engine operation to rotate the rotor of a wind turbine. Although this procedure is not the preferred one, it is considered to be one of several possible embodiments of the present invention.

In what follows, some preferred embodiments of the present invention will be described with reference to the figures where

Figure 1 shows a wind power plant with an upwind rotor that includes three rotor blades. Figure 2 shows the wind power plant in Figure 1 seen from above when the rotor is rotated at least partially by the generator in engine operation or a separate engine and the rotor blades are adjusted so that the rotor is affected by a torque about a vertical axis. Figure 3 shows section A-A as indicated in Figure 1 and the forces acting on the rotor blade at this section. Figure 4 shows section B-B as indicated in Figure 1 and the forces acting on the rotor blade at this section. Figure 5 shows an alternative embodiment of the invention where the wind power plant comprises two wind turbines arranged on a floating, rotatable undercarriage. Figure 6 shows the wind power plant in Figure 5 seen from above with a desired direction of rotation in relation to the direction of the wind.

Figure 1 shows a wind turbine 10 seen from the front with the rotor's direction of rotation to the right, i.e. clockwise, as indicated by arrow A. The wind turbine 10 comprises a tower 12 with an engine house 13 mounted on top of the tower 12. The wind turbine 10 can be mounted on land or fixed or floating at sea. The wind power plant 10 further comprises a wind turbine 11 with a rotor 14, comprising three rotor blades 15 which are mounted on a rotor shaft which drives a generator (not shown in the figures). The generator is designed so that it can be run as a motor and drive the rotor when necessary. The generator can be connected to a gear or be direct driven. Alternatively, a motor (not shown in the figures) can be arranged which is arranged to be able to rotate the rotor 14. The rotor blades 15 are preferably rotatably arranged on the rotor shaft so that they can be pitched about a longitudinal axis. During normal operation of the wind turbine 11, the rotor blades 15 are pitched so that the desired speed of the rotor 14 and/or torque of the generator is achieved. Alternatively, as described above, the rotor blades 15 can be designed so that only an (outer) part of the rotor blades 15 is pitchable. Another alternative is to arrange the rotor blades 15 with flaps, spoilers or similar devices to influence the torque so that the lifting force is reduced in the wind direction on one or more of the rotor blades. A third alternative is to align the blade with devices, for example piezoelectric fibers cast into the blades, so that the blade is twisted about its own longitudinal axis in parts of or the entire length of the blade.

Figure 2 shows the same wind power plant 10 as in Figure 1, but seen from above. The wind comes in from the front as shown, but slightly from the right. In this case, it is desirable to turn the machine housing 13 and the rotor plane, i.e. the plane in which the rotor 14 rotates, to the right or anti-clockwise as indicated by arrow B. If the wind is not strong enough in relation to the frictional forces in the turning ring that the machine housing 13 is mounted on, it will not be possible to mobilize enough rotational speed and forces on the rotor 14 to turn the machine housing 13 and the rotor plane to the right by means of individual pitching of the rotor blades 15. The wind power plant's 10 main generator, which can for example consist of a permanent magnet generator with a frequency converter , is then run as a motor by drawing electricity from the grid to which the wind power plant is connected. In this way, the rotational speed of the rotor 14 is brought up to a sufficient level so that the resultant forces LI and L2 from the relative wind against the blades become large enough to turn the machine housing 13 and the rotor plane in the desired clockwise direction as indicated by arrow B.

In Figures 3 and 4, sections A-A and B-B are of the rotor blades 15, respectively to the left and right of a vertical axis through the tower 12. When a rotor blade 15 is in a position to the right of the tower axis, as shown in Figure 4 (section B-B), the rotor blade or blade tip will be set with a small pitch angle »2, or even a small negative pitch angle »2 as shown in this example. It is common for the rotor blades to be pitched to a negative pitch angle of 2-4 degrees. It will also be possible to align the blades so that larger negative pitch angles can be achieved if this is desired. In section B-B, it is thus shown that the rotor blade is set with minimum pitch so that the most positive lifting forces L2 are mobilized.

When the blade is in position to the left of the tower axis, the rotor blade 15 or blade tip is pitched out to a large angle, for example • i = 30° as shown in figure 3 (section A-A). Then the lifting forces LI on the rotor blade or blade tip will be reduced or, as in the example shown, become negative. The result is that a torque occurs which tries to turn the rotor about the vertical axis in the direction indicated by arrow B in Figure 2.

Figure 5 shows another embodiment of the present invention. This embodiment comprises a floating wind power plant 20 comprising two wind turbines, a first wind turbine 21 and a second wind turbine 31, mounted on a rotatable, floating undercarriage 17. In this case, as indicated in Figure 5, the wind enters from behind. The wind turbines 21, 31 are mounted on respective towers 22, 32 which are arranged on the chassis 17. The chassis 17 shown in Figure 5 has a triangular shape seen from above, but it is of course possible to make the chassis 17 with other types of geometric shapes. The undercarriage 17 is further anchored to the bottom by means of one or more anchoring lines 19 which are preferably attached to a turning device 18 on the undercarriage 17. The turning device 18 preferably comprises a turning ring around which the undercarriage 17 can turn.

As for the first embodiment, which is described above, the wind turbines 21, 31 comprise machine housings 23, 33 which are arranged on the respective towers 22, 32. The wind turbines 21, 31 further comprise respective rotors 24, 34 comprising respective rotor blades 25, 35. The rotor blades 25, 35 are attached to respective rotor shafts which, during normal operation of the wind turbines 21, 31, drive generators which are arranged in machine housing one 23, 33. Alternatively, the generators can be directly driven with a fixed or rotating shaft.

Figure 6 shows the same wind power plant 10 as in Figure 5, but seen from above. The desired direction of rotation of the wind power plant 10 is in this case clockwise as indicated by arrow C.

If the first rotor 24 and the second rotor 34 rotate clockwise, the wind power plant's desired direction of rotation C can be achieved by running the generator of the second wind turbine 31 in motor mode, i.e. the generator is run as a motor. Thus, the rotational speed of the rotor 34 on the second wind turbine 31 is increased so that the relative thrust of the wind on the second wind turbine 31 is greater than on the first wind turbine 21. The rotor blades 25 on the first wind turbine 21 are set with a large pitch angle, while the rotor blades 35 on the second wind turbine 31 is set with a small pitch angle. Alternatively, the rotation of the first wind turbine 21 can also be stopped completely. The result is that the floating wind turbine 10 rotates in the desired direction even in little or no wind. The setting of the pitch angle on the rotor blades 25 and on the rotor blades 35 takes place in a similar way as shown in figures 3 and 4, except that the pitch angles of the rotor blades for a given turbine can here be changed collectively, i.e. that they do not need to be changed individually in that the rotors 24, 34 rotates.

Claims (14)

1. Method for rotating the rotor plane of a wind power plant (10, 20) in relation to a wind direction or in relation to a dispute on an electrical export cable, which wind power plant (10, 20) comprises at least one wind turbine (11, 21, 31) including a rotor (14, 24, 34) with at least one rotor blade (15, 25, 35) which is arranged for rotation in the rotor plane, where the method comprises adjusting at least a part of the at least one rotor blade (15, 25, 35), characterized in that the method further comprises rotating the rotor (14, 24, 34) with a motor on a signal from a control system depending on the wind direction or tension on the export cable so that the at least one wind turbine's rotor (14, 24, 34) is affected by a torque, or a force if the wind power plant includes two or more wind turbines, which turn the rotor plane in relation to the wind direction or the export cable's twist. 2. Procedure according to claim 1, characterized by adjusting at least one rotor blade (14, 24, 34) and driving the generator or engine on a signal from a control system depending on the wind power plant's (10, 20) azimuth deviation in relation to the direction of the wind or in relation to the export cable's twist. 3. Method according to one of claims 1-2, characterized by rotating the rotor (14, 24, 34) depending on the strength of the wind. 4. Method according to one of claims 1-3, characterized by adjusting the pitch setting of the at least one rotor blade (15, 25, 35) so that the rotor (14, 24, 34) is affected by the torque when the rotor (14, 24, 34) is rotated. 5. Method according to one of claims 1-4, characterized by adjusting the pitch setting of only one or some of the rotor blades (15, 25, 35) when the rotor (14, 24, 34) comprises two or more rotor blades (15, 25, 35). 6. Method according to one of claims 1-3, characterized by operating flaps or spoilers which are arranged on one or more rotor blades (15, 25, 35), so that the rotor (14, 24, 34) is affected by the torque by reducing the lifting force in the wind direction on at least one rotor blade (15, 25, 35). 7. Method according to one of claims 1-6, characterized by adjusting the rotor blades (15, 25, 35) individually when the rotor (14, 24, 34) of the at least one wind turbine (11, 21, 31) comprises a plurality of rotor blades (15, 25, 35). 8. Method according to one of claims 1-7, characterized by allowing the motor to rotate the rotor (14, 24, 34) continuously while rotating the rotor plane. 9. Method according to one of claims 1-7, characterized by allowing the motor to rotate the rotor (14, 24, 34) periodically or intermittently while rotating the rotor plane. 10. Method according to one of claims 1-9, characterized by adjusting the at least one rotor blade (15, 25, 35) as the rotor (14, 24, 34) rotates so that the wind power plant (10, 20) is at any time affected by the desired torque. 11. Method according to one of claims 1-10, characterized by using a separate motor to rotate the rotor (14, 24, 34). 12. Method according to one of claims 1-11, characterized by arranging the motor in the machine housing (13, 23, 33) of the at least one wind turbine (11, 21, 31). 13. Method according to one of claims 1-10, characterized by using the smallest one wind turbine's (11,21, 31) generator as a motor to rotate the rotor (14, 24, 34). 14. Application of a method according to any one of claims 1-13 where the wind power plant (10, 20) is placed in a body of water.