A METHOD FOR STARTING A WIND TURBINE WITH HINGED WIND TURBINE BLADES

Abstract

A method for starting a wind turbine with hinged wind turbine blades, the wind turbine further comprising an adjustable biasing mechanism arranged to apply an adjustable biasing force to each wind turbine blade which biases the wind turbine blade towards a position defining a minimum pivot angle. The biasing mechanism is adjusted to apply a predefined biasing force to each wind turbine blade, and the pivot angle of each wind turbine blade is monitored. The wind turbine is started in the case that the pivot angle of at least one wind turbine blade exceeds a predefined pivot angle threshold.

Claims

1. A method for starting a production of electrical energy of a wind turbine after a period of not producing electrical energy, the wind turbine comprising a tower, a nacelle mounted on the tower via a yaw system, a hub mounted rotatably on the nacelle, the hub comprising a blade carrying structure, and one or more wind turbine blades connected to the blade carrying structure via a hinge, each wind turbine blade thereby being arranged to perform pivot movements relative to the blade carrying structure between a minimum pivot angle and a maximum pivot angle, the wind turbine further comprising an adjustable biasing mechanism arranged to apply an adjustable biasing force to each wind turbine blade which biases the wind turbine blade towards a position defining a minimum pivot angle, the method comprising: adjusting the biasing mechanism to apply a predefined biasing force to each wind turbine blade; monitoring the pivot angle of each wind turbine blade; and starting the wind turbine in the case that the pivot angle of at least one wind turbine blade exceeds a predefined pivot angle threshold.

2. The method of claim 1, further comprising: monitoring the rotational speed of the hub; and starting the wind turbine in the case that the rotational speed of the hub exceeds a predefined rotational speed threshold.

3. The method of claim 1, wherein the starting the wind turbine comprises initially operating a generator of the wind turbine in motor mode.

4. The method of claim 1, wherein the predefined biasing force is selected to provide a predefined pivot angle at a predefined thrust force.

5. The method of claim 1, further comprising allowing a predefined time period to lapse between the step of adjusting the biasing mechanism and the step of monitoring the pivot angle.

6. The method of claim 1, further comprising, in the case that the pivot angle of at least one wind turbine blade exceeds the pivot angle threshold, adjusting the biasing force in order to maintain the wind turbine blades at the pivot angle of the wind turbine blades at the pivot angle threshold during start of the wind turbine.

7. The method of claim 1, further comprising, in the case that the pivot angle of at least one wind turbine blade exceeds the pivot angle threshold, adjusting the biasing force in order to move the wind turbine blades towards the position defining the minimum pivot angle.

8. The method of claim 1, wherein the starting the wind turbine is performed in the case that the pivot angle of each of the wind turbine blades exceeds the predefined pivot angle threshold.

9. The method of claim 1, further comprising detecting an azimuth position of each of the wind turbine blades, and wherein the starting the wind turbine is performed in the case that the pivot angle of at least one wind turbine blade exceeds a variable pivot angle threshold being dependent on the azimuth position.

10. The method of claim 1, wherein the starting the wind turbine comprises: connecting a generator to a rotating shaft of the wind turbine; ramping up the generator, while controlling the biasing force applied by the biasing mechanism to the wind turbine blades; and connecting the wind turbine to a power grid.

11. The method of claim 10, further comprising adjusting the biasing force in order to obtain a rotational acceleration of the generator which is substantially zero prior to connecting the generator to the rotating shaft of the wind turbine.

12. The method of claim 10, wherein the ramping up the generator comprises controlling the biasing force as a function of rotational speed of the hub and/or the generator, power output of the generator and pivot angle.

13. The method of claim 1, further comprising aligning the nacelle of the wind turbine in accordance with the direction of the wind, by means of the yaw system, prior to the step of adjusting the biasing mechanism.

14. A wind turbine, comprising: a tower; a nacelle disposed on the tower via a yaw system; a generator disposed in the nacelle; a rotor coupled to the generator; a hub mounted on the rotor and comprising a blade carrying structure; a plurality of wind turbine blades connected to the blade carrying structure via a hinge, each wind turbine blade thereby being arranged to perform pivot movements relative to the blade carrying structure between a minimum pivot angle and a maximum pivot angle; an adjustable biasing mechanism arranged to apply an adjustable biasing force to each wind turbine blade which biases the wind turbine blade towards a position defining a minimum pivot angle; one or more controllers configured to perform an operation starting a production of electrical energy of the wind turbine after a period of not producing electrical energy, the operation, comprising: adjusting the biasing mechanism to apply a predefined biasing force to each wind turbine blade; monitoring the pivot angle of each wind turbine blade; and starting the wind turbine when the pivot angle of at least one wind turbine blade exceeds a predefined pivot angle threshold.

15. The wind turbine of claim 14, wherein the operation further comprises: monitoring the rotational speed of the hub; and starting the wind turbine in the case that the rotational speed of the hub exceeds a predefined rotational speed threshold.

16. The wind turbine of claim 14, wherein the starting the wind turbine comprises initially operating the generator of the wind turbine in motor mode.

17. The wind turbine of claim 14, wherein the predefined biasing force is selected to provide a predefined pivot angle at a predefined thrust force.

18. The wind turbine of claim 14, wherein the operation further comprises allowing a predefined time period to lapse between the adjusting the biasing mechanism and the monitoring the pivot angle.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0070] The invention will now be described in further detail with reference to the accompanying drawings in which

[0071] FIGS. 1-3 illustrate a wind turbine being controlled in accordance with a method according to a first embodiment of the invention,

[0072] FIGS. 4-6 illustrate a wind turbine being controlled in accordance with a method according to a second embodiment of the invention,

[0073] FIGS. 7 and 8 show details of a biasing mechanism for use in a method according to an embodiment of the invention, and

[0074] FIG. 9 is a flow chart illustrating a method according to an embodiment of the invention.

DETAILED DESCRIPTION OF THE DRAWINGS

[0075] FIGS. 1-3 illustrate a wind turbine 1 being controlled in accordance with a method according to a first embodiment of the invention. FIG. 1 is a front view of the wind turbine 1, and FIGS. 2 and 3 are side views of the wind turbine 1.

[0076] The wind turbine 1 of FIGS. 1-3 comprises a tower 2 and a nacelle 7 mounted on the tower 2. A hub 3 is mounted rotatably on the nacelle 7, the hub 3 comprising a blade carrying structure 4 with three arms. A wind turbine blade 5 is connected to each of the arms of the blade carrying structure 4 via a hinge 6.

[0077] Thus, the wind turbine blades 5 rotate along with the hub 3, relative to the nacelle 7, and the wind turbine blades 5 can perform pivoting movements relative to the blade carrying structure 4, via the hinges 6.

[0078] Each wind turbine blade 5 defines an aerodynamic profile extending along the length of the wind turbine blade 5 between an inner tip end 5a and an outer tip end 5b. The hinge 6 is arranged at a hinge position of the wind turbine blade 5, the hinge position being at a distance from the inner tip end 5a as well as at a distance from the outer tip end 5b. The wind turbine blades 5 of the wind turbine 1 of FIGS. 1-3 are straight in the sense that an inner portion of the wind turbine blade 5, between the hinge 6 and the inner tip end 5a, and an outer portion of the wind turbine blade 5, between the hinge 6 and the outer tip end 5b, extend along the same direction, i.e. an angle is not formed between the inner and outer portions of the wind turbine blade 5.

[0079] A biasing mechanism comprising wires 8 attached to the wind turbine blades 5 at a position near the inner tip end 5a applies a biasing force to the wind turbine blades 5 which pulls the wind turbine blades 5 towards a position defining minimum pivot angle, and thereby maximum rotor diameter. This will be described in further detail below with reference to FIGS. 7 and 8.

[0080] In FIG. 2 the wind turbine blades 5 are positioned at the minimum pivot angle, i.e. at a pivot angle which results in a maximum rotor diameter of the wind turbine 1.

[0081] In FIG. 3 the wind turbine blades 5 are positioned at a larger pivot angle P than the minimum pivot angle illustrated in FIG. 2. Thereby the rotor diameter of the wind turbine 1 is smaller in the situation illustrated in FIG. 3 than in the situation illustrated in FIG. 2.

[0082] The wind turbine 1 of FIGS. 1-3 is a downwind wind turbine, i.e. the wind direction relative to the wind turbine 1 is illustrated by arrow 9 shown in FIGS. 2 and 3.

[0083] The wind turbine 1 of FIGS. 1-3 may be started up in the following manner. Initially the biasing mechanism 8 is adjusted to apply a predefined biasing force to each of the wind turbine blades 5. Thereby the wind turbine blades 5 are pulled towards the position shown in FIG. 2. However, the biasing force is selected in such a manner that when the wind 9 acts on the wind turbine blades 5, the wind turbine blades 5 start pivoting when the energy available in the wind exceeds a certain level.

[0084] The pivot angles of the wind turbine blades 5 are then monitored, and when the pivot angle of the wind turbine blades 5 exceeds a predefined pivot angle threshold, e.g. the pivot angle shown in FIG. 3, it can be assumed that the energy available in the wind is sufficient to ensure appropriate operation of the wind turbine 1. Accordingly, when this is detected the wind turbine 1 is started up.

[0085] Additionally, a rotational speed of the hub 3 may be monitored, and the wind turbine 1 may be started up when the rotational speed of the hub 3 exceeds a predefined rotational speed threshold, also indicating that the energy available in the wind is sufficient to ensure appropriate operation of the wind turbine 1.

[0086] FIGS. 4-6 illustrate a wind turbine 1 being controlled in accordance with a method according to a second embodiment of the invention. The wind turbine 1 of FIGS. 4-6 is very similar and will therefore not be described in detail here. FIGS. 4-6 are all side views of the wind turbine 1 with the wind turbine blades 5 arranged at three different pivot angles. FIG. 4 shows the wind turbine blades 5 at minimum pivot angle, FIG. 6 shows the wind turbine blades 5 at maximum pivot angle, or barrel mode, and FIG. 5 shows the wind turbine blades 5 at an intermediate pivot angle.

[0087] The wind turbine blades 5 of the wind turbine 1 of FIGS. 4-6 are angled in the sense that the inner portion and the outer portion of the wind turbine blade 5 extend from the hinge 6 along different directions, forming an angle there between.

[0088] FIGS. 7 and 8 show details of a biasing mechanism for applying a biasing force to wind turbine blades 5 of a wind turbine, e.g. the wind turbine 1 of FIGS. 1-3 or the wind turbine 1 of FIGS. 4-6.

[0089] FIG. 7 shows a portion of a blade carrying structure 4 and a portion of a wind turbine blade 5. The wind turbine blade 5 is pivotally mounted on the blade carrying structure 4 via a hinge (not shown). A wire 8 is connected to the wind turbine blade 5 at a position between an inner tip end 5a of the wind turbine blade 5 and the position of the hinge. The wire 8 extends from the connecting position at the wind turbine blade 5, via a pulley 10 and along the blade carrying structure 4 towards a hub (not shown).

[0090] A biasing force applied by means of the wire 8 pulls the wind turbine blade 5 towards a position defining a minimum pivot angle. In FIG. 7 the wind turbine blade 5 is arranged at the minimum pivot angle. Reducing the biasing force applied by means of the wire 8 will allow the wind turbine blade 5 to more easily pivot towards larger pivot angles.

[0091] FIG. 8 is a cross sectional view of part of a hub 3 and part of a nacelle 7. Arms of a blade carrying structure 4 are mounted on the hub 3. The wires 8 which are also illustrated in FIG. 7 are connected to a winch mechanisms 11 arranged in the hub 3. Thereby the biasing force applied by means of the wires 8 can be adjusted by rotating the winch mechanisms 11, thereby adjusting the length of the wires 8.

[0092] FIG. 9 is a flow chart illustrating a method according to an embodiment of the invention. The process is started at step 12. At step 13 a biasing force applied to the wind turbine blades of a wind turbine is adjusted to a predefined biasing force.

[0093] At step 14 the pivot angle of the wind turbine blades and the rotational speed of the hub and/or of the generator of the wind turbine are monitored. Wind acting on the wind turbine blades acts against the biasing force, and will therefore attempt to move the wind turbine blades towards larger pivot angles. Therefore, when the force provided by the wind exceeds the biasing force, the wind turbine blades will start moving towards larger pivot angles. Furthermore, the wind acting on the wind turbine blades may cause the hub to rotate.

[0094] Thus, at step 15 the pivot angles of the wind turbine blades are compared to a predefined pivot angle threshold. In the case that this comparison reveals that the pivot angle of at least one of the wind turbine blades exceeds the predefined pivot angle threshold, this is an indication that the energy available in the wind is sufficient to ensure appropriate operation of the wind turbine. Therefore the process is forwarded to step 16, and the wind turbine is started.

[0095] In the case that step 15 reveals that none of the pivot angles of the wind turbine blades exceeds the predefined pivot angle threshold, the process is forwarded to step 17, where it is investigated whether or not the rotational speed of the hub and/or of the generator exceeds a predefined rotational speed threshold. If this is the case, this is an indication that the energy available in the wind is sufficient to ensure appropriate operation of the wind turbine, even though the pivot angles of the wind turbine blades were not above the predefined pivot angle threshold. Therefore the process is forwarded to step 16, and the wind turbine is started.

[0096] In the case that step 17 reveals that the rotational speed of the hub and/or of the generator does not exceed the predefined rotational speed threshold, it can be assumed that the energy available in the wind is insufficient to ensure appropriate operation of the wind turbine, and the wind turbine should therefore not be started. Accordingly, the process is, in this case, returned to step 14 for continued monitoring of the pivot angles and the rotational speed.