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Title:
WIND TURBINE WITH PASSIVE CONTROL
Document Type and Number:
WIPO Patent Application WO/1996/011337
Kind Code:
A1
Abstract:
In a wind turbine which is provided with a rotor having a number of rotor blades (1), each of which has a main part (2) situated near the rotary shaft of the rotor and a separate tip (3) which is rotatable relative to the main part about the longitudinal axis of the rotor blade (1). Each rotor blade (1) is provided with a control mechanism which is designed in such a way that the angular position (angle of attack) of the end part of the rotor blade is controlled depending on the speed of rotation of the rotor. The control mechanism comprises a tension-torsion element (11) made from a non-isotropic (anisotropic or othotropic) material, the longitudinal axis of which runs essentially in the same direction as the longitudinal axis (9) of the rotor blade, and which twists under the influence of an axial tensile force (centrifugal force on the end part of the rotor blade). The tension-torsion element (11) is expediently in the form of an elongated tube which is made up of layers of fibre-reinforced plastic, the fibres of the tension-torsion element being oriented in such a way that the tube twists under the influence of an axial tensile force.

Inventors:
VAN DEN BERG RENE MARCUS (NL)
JOOSSE PIETER ARIE (NL)
Application Number:
PCT/NL1995/000341
Publication Date:
April 18, 1996
Filing Date:
October 06, 1995
Export Citation:
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Assignee:
STORK PROD ENG (NL)
DEN BERG RENE MARCUS VAN (NL)
JOOSSE PIETER ARIE (NL)
International Classes:
F03D1/06; F03D7/02; (IPC1-7): F03D7/02; F03D1/06
Domestic Patent References:
WO1989002531A11989-03-23
Foreign References:
GB2216606A1989-10-11
US4273601A1981-06-16
US4374631A1983-02-22
US4797066A1989-01-10
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Claims:
C L I M S
1. Wind turbine, comprising a rotor with a number of rotor blades (1) , each of which has a main part (2) situated near the rotary shaft of the rotor and a separate tip (3) which is rotatable relative to the main part (2) about the longitudinal axis (9) of the rotor blade (1), each rotor blade being provided with a control mechanism which is connected to the tip (3) and is designed in such way that the angular position (angle of attack) of the tip (3) relative to the main part (2) is controlled depending on the speed of rotation of the rotor, characterized in that each control mechanism comprises an elongated tension torsion element (11) fitted in the rotor blade (1) and made from a nonisotropic material, such that the element twists under the influence of an axial tensile force, the central axis of the element running essentially in the same direction as the longitudinal axis (9) of the rotor blade, one end of the element being immovably connected to the tip (3) and the other end being immovably connected to the main part (2) of the rotor blade (1) .
2. Wind turbine according to claim l, characterized in that the tensiontorsion element is made of anisotropic material.
3. Wind turbine according to claim 1, characterized in that the tensiontorsion element is made of orthotropic material.
4. Wind turbine according to claim 1, characterized in that the tensiontorsion element is composed of layers of fibrereinforced plastic, the fibres of the tensiontorsion element being oriented in such a way that the element (11) twists under the influence of an axial tensile force.
5. Wind turbine according to claim 4, characterized in that the fibres are of glass, aramide or carbon, and in that the plastic is epoxy or polyester.
6. Wind turbine according to one of claims 1 to 5, characterized in that the tensiontorsion element (11) has the shape of a tube.
Description:
Wind turbine with passive control.

The invention relates to a wind turbine, comprising a rotor with a number of rotor blades, each of which has a main part situated near the rotary shaft of the rotor and a separate tip which is rotatable relative to the main part about the longitudinal axis of the rotor blade- each rotor blade being provided with a control mechanism which is connected to the tip and is designed in such away that the angular position (angle of attack) of the tip relative to the main part is controlled depending on the speed of rotation of the rotor.

Such a type of wind turbine is known. In the known wind turbine, the control mechanism comprises a screw mechanism and a spring whose longitudinal axis lies in the same direction as the longitudinal axis of the rotor blade. The tip is connected to the screw mechanism. As soon as the centrifugal force on the tip exceeds the pre-tension of the spring, the tip moves outwards and rotates simultaneously about its axis through the action of the screw mechanism. The aerodynamic power of the wind turbine is controlled by controlling the angular position of the tips of the rotor blades. The mechanism is passive and acts both as an output control system and as a safety system for preventing an excessively high speed of rotation.

However, the known wind turbine has the disadvantage that the control mechanism comprises different moving parts which interact with each other. Such a mechanism is expensive, takes up quite a lot of space and requires the necessary maintenance, which is very difficult to carry out in the case of wind turbines. The object of the invention is to provide a relatively cheap, compact, simple, reliable and maintenance-free control mechanism which can carry out the same output control and safety functions as the control mechanism in the known wind turbines. This object is achieved according to the invention through the fact that each control mechanism comprises an

elongated tension-torsion element fitted in the rotor blade and made from a non-isotropic material, such that the element twists under the influence of an axial tensile force, the central axis of the element running essentially in the same direction as the longitudinal axis of the rotor blade, one end of the element being immovably connected to the tip and the other end being immovably connected to the main part of the rotor blade.

The use of such a tension-torsion element provides a control mechanism which does not have any parts moving relative to each other, and which is therefore maintenance- free.

Expedient and preferred embodiments of the wind turbine according to the invention are claimed in the subclaims.

The invention is explained with reference to the following exemplary embodiment shown in the drawing, in which:

Fig. 1 shows diagrammatically a part of one of the rotor blades of a preferred embodiment of the wind turbine according to the invention,

Fig. 2 shows detail II of Fig. 1 in longitudinal section and on an enlarged seale,

Fig. 3 shows detail III of Fig. 1 in a longitudinal section and on an enlarged seale.

The rotor blade 1 of a wind turbine according to the invention, part of which is shown in Fig. 1, comprises a main part 2 which is immovably connected to the hub of the rotor of the wind turbine, and a tip 3 which is rotatable relative to the main part 2 of the rotor. The tip 3 is mounted by means of bearings 4 and 5 on a hollow shaft 6 (see also Fig. 2) , which is immovably connected at the position of the fixing points 7 and 8 to the main part 2 of the rotor blade 1. The central axis of the hollow shaft 6 coincides with the longitudinal axis 9 of the rotor blade. At the position of the fixing point 10, the tip 3, which is rotatable about the longitudinal axis 9, is immovably connected to one end of an elongated tension- torsion element 11, which is fitted inside the hollow shaft

6 and projects partially out of the hollow shaft (see also Fig. 2) . The other end of the tention-torsion element 11 is immovably connected to the inner end of the hollow shaft 6 (see also Fig. 3) . The tension-torsion element 11 is made of a non-isotropic material, such as an anisotropic or orthotropic material, in particular a fibre-reinforced plastic, and twists about the longitudinal axis when an axial tensile force is exerted thereon.

In this way a function separtation is made, through which the tension-torsion element 11 takes up the force in longitudinal direction and controls the angular position of the tip, while the hollow shaft 6 bears all other loads and provides the strength. The advantage of such a separation is that the separate parts can be optimally designed for their funtions.

In general, this construction will be designed in such a way that torsion of the element occurs only after a certain minimum value of the tensile f. se is exceeded.

When the speed of rotation of tne rotor of the wind turbine increases, the centrifugal force on the tip 3 of each rotor blade, and consequently the tensile force exerted on the tension-torsion element 11, will also increase. As a result of this, when the tensile force exceeds a certain value, the tension-torsion element 11 will undergo torsion, which causes the angular position of the tip 3 to change relative to the main part 2 of each rotor blade 1.

This means that, as in the case of known wind turbines, the output of the wind turbine can be controlled, and a safety function can be built into the wind turbine, in order to prevent the speed of rotation of the turbine from exceeding a certain maximum value.

It is known that a low torsion frequency of the tip about the longitudinal axis of the rotor can lead to aeroelastic instabilities (like flutter) . The risk of instabilities is further increased by the additional coupling introduced by the tension-torsion element. The position of the tension-torsion element relative to the centre of gravity of the tip, but also the stiffness and

the damping of the element are therefore of great importance.

The tension-torsion element 11 is preferably in the form of a tube made of fibre-reinforced plastic, the fibres being oriented in such a way that the tube twists under the influence of an axial tensile force. The relation between the axial tensile force and the torsion angle is determined by the dimensions of the tube, the plastic material, the material of the fibres, and the way in which the fibres are oriented in the tube.

Analyses and tests show that the angle of the fibres relative to the longitudinal axis of the tension- torsion element is optimally about 20°. It is important that the laminate structure is such that the influence of moisture and temperature on the deformation is minimal.

The plastic material of the tension-torsion element 11 is, for example, epoxy or polyester. The material of the fibres is, for example, glass, aramide or carbon. A particularly advantageous material combination for the tension-torsion element is epoxy with aramide fibres. In order to obtain a centrifugal force of sufficient magnitude acting upon the end part of each rotor blade, it will generally be necessary for additional mass to be applied to the end of the rotor blades. The magnitude of said mass is determined by the required relation between speed of rotation of the rotor and the torsion angle of the end part of the rotor blades.

The use of a tension-torsion element produces a wind turbine with a relatively cheap, compact, simple, reliable and maintenance-free control and safety system.