WIND TURBINE OPERABLE IN A REVERSE MODE OF OPERATION AND CORRESPONDING METHOD OF OPERATING A WIND TURBINE

Abstract

A wind turbine is provided. The wind turbine includes a wind rotor and a generator, mechanically coupled to the wind rotor. The wind turbine is configured to operate in a first mode of operation and in a second mode of operation, wherein, in the second mode of operation, the wind rotor is oriented in an opposite direction relative to a wind direction compared with the first mode of operation. The generator of the wind turbine is configured to generate power both in the first mode of operation and in the second mode of operation. Furthermore, a corresponding method of operating a wind turbine is provided.

Claims

1. A wind turbine, comprising: a wind rotor; and a generator, mechanically coupled to the wind rotor; wherein the wind turbine is configured to operate in a first mode of operation and in a second mode of operation, wherein, in the second mode of operation, the wind rotor is oriented in an opposite direction relative to a wind direction compared with the first mode of operation; wherein the generator is configured to generate power both in the first mode of operation and in the second mode of operation.

2. The wind turbine according claim 1, wherein in the second mode of operation, the generator generates power for a supplementary power supply

3. The wind turbine according to claim 1, wherein the supplementary power supply is configured to provide power for at least one of adjusting a pitch angle of a blade of the wind turbine and adjusting a yaw angle.

4. The wind turbine according to claim 1, wherein in the first mode of operation, the generator generates power for a grid.

5. The wind turbine according to claim 1, wherein the second mode of operation is a reverse mode of operation, in which the wind rotor of the wind turbine and/or a shaft coupled with the generator turns in an opposite direction compared with the first mode of operation.

6. The wind turbine according to claim 1, wherein a torque of the wind rotor in the first mode of operation is larger than a further torque of the wind rotor in the second mode of operation at a given wind speed.

7. The wind turbine according to claim 1, wherein a power generated by the generator the first mode of operation is larger than, in particular at least twice as large as, a power generated by the generator in the second mode of operation at a given wind speed.

8. The wind turbine according to claim 1, wherein the first mode of operation is an upwind mode of operation and the second mode of operation is a downwind mode of operation.

9. The wind turbine according to claim 1, wherein the first mode of operation is a downwind mode of operation and the second mode of operation is an upwind mode of operation.

10. A method of operating a wind turbine, the method comprising: operating the wind turbine in a second mode of operation; and operating the wind turbine in a first mode of operation; wherein, in the second mode of operation, a wind rotor is oriented in an opposite direction relative to a wind direction compared with the first mode of operation; wherein a generator of the wind turbine, which is mechanically coupled to the wind rotor, is configured to generate power both in the first mode of operation and in the second mode of operation.

11. The method according to claim 10, further comprising: orienting the wind rotor by power generated in the second mode of operation.

12. The method according to claim 11, wherein orienting the wind rotor comprises orienting the wind rotor such that the wind turbine is operable in the first mode of operation

13. The method according to claim 11, wherein orienting the wind rotor comprises orienting the wind rotor such that the wind turbine remains operable in the second mode of operation.

14. The method according to claim 10, wherein the wind turbine is disconnected from a grid while in the second mode of operation.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0055] FIG. 1 shows a wind turbine operating in a first mode of operation according to an exemplary embodiment of the invention.

[0056] FIG. 2 shows the wind turbine of FIG. 1 operating in a second mode of operation.

[0057] FIG. 3 shows a rotor blade profile in an upwind mode of operation of a wind turbine according to an exemplary embodiment of the invention.

[0058] FIG. 4 shows the rotor blade profile of FIG. 3 operating in a downwind mode of operation.

DETAILED DESCRIPTION

[0059] The illustrations in the drawings are schematic. In different drawings, similar or identical elements are provided with the same reference signs. For the sake of clarity and comprehensibility, reference signs are sometimes omitted for those features, for which reference signs have already been provided in earlier figures.

[0060] Before, referring to the drawings, exemplary embodiments will be described in further detail, some basic considerations will be summarized based on which exemplary embodiments of the invention have been developed.

[0061] A horizontal axis wind turbine is normally configured for upwind operation. The wind turbine may either intentionally orient itself to the downwind orientation, in particular by yawing, or it may arrive at the downwind orientation due to changing wind direction while it is out of operation.

[0062] While in a downwind orientation the wind turbine will actively adjust the blade pitch orientation in order to rotate the rotor of the wind turbine in a rotational direction opposite of the normal rotational direction, i.e. reverse, as viewed from the frame of reference of the wind turbine itself.

[0063] It is possible to produce torque in this configuration, where the angle of attack of the aerodynamic profile of the wind turbine blades is greater than 180 degrees. The amount of torque produced at a given wind speed will be much lower than when in normal upwind operation at the same wind speed, but still sufficient for the production of a small amount of power.

[0064] The pitch control of the rotor blades is used to regulate the rotational speed of the rotor and to accommodate changes in the wind speed. Yawing of the turbine will take place to maintain the orientation of the rotor downwind in the event of changing wind direction.

[0065] The generator of the wind turbine will extract energy out of the rotating rotor. It may be that the phase sequence of power generated is reversed. The power produced by the generator will be conditioned by power electronics such that it may be used for export to a consumer, e.g. grid or otherwise.

[0066] In a preferred embodiment of this invention, the wind turbine is equipped with an energy storage system. This energy storage system may be used while the wind turbine is off grid to provide power for the turbine to maintain its communication systems, maintain its internal environment (e.g. operate de-humidifiers), provide power to maintenance equipment, safety lights and beacons and to control yaw orientation in the event of extreme weather.

[0067] The wind turbine is capable of maintaining the energy content of the energy storage system, by operating in either the normal upwind orientation or in the downwind orientation.

[0068] Thus, a wind turbine designed for normal upwind operation can also be used for downwind operation. It is well known that turbines may be designed for either upwind or downwind operation, however, horizontal-axis wind turbines designed for operation in a certain orientation, so far, only operate in that one orientation.

[0069] It is only possible to produce small amounts of power when operating the rotor backwards in the downwind orientation. This is due to the very poor aerodynamic performance of the rotor when rotating backwards. However, with the growing use of energy storage systems in wind turbines it is useful to produce even a small amount of power for the purpose of maintaining the energy content of these systems.

[0070] Furthermore, the increased use of power electronics in wind turbines enables conditioning of power produced by the wind turbines generator. This allows the wind turbine to be able to export power to either the grid or an energy storage system with the correct phase sequence, even if operating in a direction which is reverse from normal.

[0071] Finally, reverse operation of a wind turbine may cause stress on the wind turbine's drivetrain components, i.e. bearings, gears, etc. However, this may be avoided if the amount of torque extracted from the rotor by the generator is very low, e.g. 10's to 100's of kWs for a turbine designed for multiple MW's of power, and so the impact on the drive train components would be negligible.

[0072] As opposed to operating a “normally upwind” turbine in the downwind orientation, the same solution could be applied to allow a “normally downwind” turbine to be operated in the upwind orientation. This would be beneficial for such a turbine for example in the case of a situation similar to the first problem described in the background section above.

[0073] FIG. 1 shows a wind turbine 100 according to an exemplary embodiment of the invention. The wind turbine 100 comprises a wind rotor 101 with blades that turn in a rotation direction 107 within a rotor plane 105. A surface normal 106 of the rotor plane 105 points from the wind rotor 101 towards the nacelle 106 of the wind turbine 100. The wind turbine 100 is configured to operate in a first mode of operation and a second mode of operation. In this case, the first mode of operation is an upwind mode of operation, in which the rotor is arranged upwind from a tower 103 of the wind turbine 100 and in which the surface normal 106 is aligned with and points in the same direction as the incoming wind 104.

[0074] A generator of the wind turbine 100, which is mechanically coupled to the wind rotor 101 and may be arranged in the nacelle 102, is configured to generate power both in the first mode of operation and in the second mode of operation. In the second mode of operation, the wind rotor 101 is oriented in an opposite direction relative to the wind direction 104 compared with the first mode of operation. Thus, the second mode of operation may be a downwind mode of operation as shown in FIG. 2.

[0075] FIG. 2 shows the wind turbine of FIG. 1 operating in a second mode of operation. In this case, the second mode of operation is a downwind mode of operation, in which the rotor is arranged downwind from the tower 103 of the wind turbine 100 and in which the surface normal 106 is aligned with and points in a direction opposite to the incoming wind 104. Compared with the upwind mode of operation depicted in FIG. 1, in the downwind mode of operation, the rotation direction 107 in the rotor plane 105 is opposite with respect to a frame of reference determined by the nacelle 102 and the generator 108 positioned in the nacelle 102.

[0076] FIG. 3 shows the aerodynamic performance of a rotor blade profile 306 in an upwind mode of operation. The x.sub.1 axis is oriented perpendicular to the rotor plane 105 in direction of the surface normal 106 and x.sub.2 is along the rotor plane 105. V.sub.1 represents the combined velocity of the incoming and induced wind speed 104 and V.sub.2 is the linear velocity of the blade profile through the wind field. V.sub.e is therefore the resultant relative wind velocity that acts at an angle φ (phi) relative to the rotor plane.

[0077] β (beta) represents the pitch angle of the rotor blade 306 while κ (kappa) represents the “pre-twist” of the blade 306 at the location of the profile cross-section. α (alpha) is the angle-of-attack of the blade profile 306 relative to the relative wind direction. The resultant forces p.sub.L and p.sub.D created by the wind and the motion of the blade profile are the lift force and drag force, respectively.

[0078] In normal operation the blade profile 306 creates sufficient lift such that the resultant force in the direction of the rotation V.sub.2 is positive. This creates a rotor torque useful for generating electricity.

[0079] FIG. 4 shows the aerodynamic performance of the rotor blade profile 306 of FIG. 3 in a downwind mode of operation. In the downwind mode of operation, it is similarly possible as in the upwind mode of operation to create and control rotor torque. Compared with the upwind mode of operation depicted in FIG. 3, for a similar velocity V.sub.1, the velocity V.sub.2 will be much lower and the pitch angle β will need to be larger. Also, the angle of attack α is now greater than 180 degree.

[0080] In this configuration the drag force p.sub.D will be large relative to the lift force p.sub.L, but it will be predominately in a direction perpendicular to the rotor plane 105, whereas the small lift force p.sub.L will be more aligned with the rotor plane 105 and therefore generating a small amount of rotational torque on the rotor.

[0081] Finally, the direction of rotation, V.sub.2, is now opposite in the downwind operation orientation compared with the upwind orientation relative to the wind turbine's coordinate axes. For this reason, the rotation of the rotor is considered to be in reverse during this mode.

[0082] The rotational speed of the rotor can be controlled by actively adjusting the pitch angle β to produce more or less torque, as desired.

[0083] It should be noted that the term “comprising” does not exclude other elements or steps and the use of articles “a” or “an” does not exclude a plurality. Also, elements described for different embodiments may be combined. It should also be noted that reference signs in the claims should not be construed as limiting the scope of the claims.