METHOD FOR CONTROLLING A WIND POWER PLANT, WIND POWER PLANT AND WIND FARM

Description

[0001] The present invention relates to a method for operating a wind turbine, an associated wind turbine, and a wind farm. The present invention relates in particular to a method for operating a wind turbine comprising a tower with tower loads acting upon it and an aerodynamic rotor that generates rotor thrust. Methods for operating a wind turbine include, in particular, a step of reducing the rotor thrust.

[0002] In the control and operation of wind turbines, it is known that there are environmental and operating conditions in which it is advantageous to rapidly retract one or more of the rotor blades of the aerodynamic rotor, i.e., to increase the pitch angle of the rotor blades independently of the speed control. This is typically useful when mechanical stress, i.e., the loads on the wind turbine, needs to be reduced or overloading needs to be avoided. In such extreme situations, for example, to prevent extreme loads on the rotor blades, there are protective functions that generate instructions to reduce rotor thrust, for example, by retracting or pitching the rotor blades. As a result of the rapid retraction of the rotor blades, the rotor thrust will decrease abruptly.However, situations are conceivable in which the resulting reduction in rotor thrust is either unnecessary for reducing tower loads or even counterproductive. One such case is when an excessive reduction in rotor thrust occurs, which, depending on the situation, can have negative or even dangerous consequences.

[0003] Document EP 2 876 300 A1 describes a wind turbine system comprising a wind turbine including a plurality of blades and a tower, and a processing subsystem configured to shut down the wind turbine by nonlinearly unfolding the plurality of blades in the wind turbine towards a spring position at a tipping rate determined on the basis of a tower forward-backward velocity of an upper section of the tower during tower oscillations.

[0004] Document EP 2 746 576 A2 describes a method and a system for shutting down a wind turbine. The method includes determining one or more pitch angle positions for one or more rotor blades of the wind turbine, such that the sum of potential and kinetic energy in the wind turbine is minimized. The method further includes pitching the one or more rotor blades from an operating position to the determined pitch positions.

[0005] Document WO 2016 / 138647 A1 describes a method for mitigating wind turbine loads in response to the failure of one or more load sensors. The method involves operating the wind turbine in a standard operating mode via a controller and monitoring the turbine loads using one or more load sensors. The standard operating mode includes a predetermined thrust setpoint and a predetermined shutdown wind speed setpoint. Upon detection of a load sensor failure, the method includes activating a protective operating mode in the controller for a predetermined duration. Specifically, the protective operating mode involves reducing the predetermined thrust setpoint and the predetermined shutdown wind speed setpoint. A system for mitigating wind turbine loads is also described.

[0006] Document EP 2 963 283 A1 describes a wind turbine system. The wind turbine system comprises a tower, a plurality of blades, a rotor supported by the tower and rotatably coupled to the plurality of blades, a control unit programmed to predict the net energy of the tower at one or more future times, and if the predicted net energy is within a design limit, then proceeds with basic operational control models for the normal operation of the wind turbine system; if the predicted net energy exceeds the design limit, then uses a nonlinear tower damping model to generate tower damping commands to control the tower damping of the wind turbine system.

[0007] Against this background, one objective of the present invention was to enable improved operation of a wind energy plant.

[0008] The German Patent and Trademark Office has searched the following prior art in the priority application for the present PCT application: US 2017 / 0 152 835 A1 and CN 106 194 580 A.

[0009] According to the invention, the problem is solved by a method according to claim 1.

[0010] Accordingly, if, for example, a control system for a wind turbine typically generates a command to reduce rotor thrust, this command is not always followed, but only after verification. In other words, the function actually designed to protect the turbine—namely, reducing rotor thrust—is not implemented under all circumstances, but is adapted to the specific needs of the wind turbine. This can be understood as a protective function against the protective function.

[0011] In particular, by taking into account the effects on the tower loads according to the invention, a reduction of the rotor thrust can be avoided if, for example, a reduction is counterproductive or unnecessary for the tower loads.

[0012] In a preferred embodiment, taking into account the effect of reducing rotor thrust on tower loads includes omitting or mitigating the reduction of rotor thrust if reducing rotor thrust causes an increase in tower loads.

[0013] Particularly when the tower swings forward, that is, in the direction of the wind or the direction from which the wind is coming, the rotor thrust generates a braking force on the tower's oscillation. If the rotor thrust is reduced in this situation, the braking force acting on the tower decreases, and consequently, the tower will swing forward faster and further than it would have with full rotor thrust. Therefore, reducing the rotor thrust will, especially in this case, lead to an increase in the tower loads. By recognizing this situation and, for example, refraining from reducing the rotor thrust, the extreme loads acting on the tower can be reduced, according to the invention.

[0014] In an extreme situation, a protective function of the wind turbine, for example, issues a command to reduce the rotor thrust. According to the invention, the effects of this protective function can be mitigated or omitted entirely if reducing the rotor thrust is not practical or even dangerous for other reasons, particularly when considering the effects on the tower. The present invention is therefore a type of protective function for the protective function, which can prevent the intervention of the first protective function from being too severe. The first protective function is, for example, a load control system that intervenes when loads on the rotor blades or the rate of change of the blade loads is too high. It is particularly preferred if, according to the invention, the effects on the tower loads are taken into account depending on the power output and / or the rotational speed.

[0015] In a preferred embodiment, taking into account the effect of reducing rotor thrust on tower loads includes omitting or mitigating the reduction of rotor thrust if reducing rotor thrust results in an unnecessary reduction of the loads acting on the tower.

[0016] For example, if an instruction to reduce rotor thrust is generated, this method determines whether reducing the rotor thrust is necessary, taking into account the impact on the tower loads. If, regardless of the reduction in rotor thrust, no extreme loads are expected on the tower, then, considering the loads, there is no need for a reduction. Reducing the rotor thrust nonetheless could lead to an unnecessary loss of yield. By refraining from reducing the rotor thrust in this case, as described in this method, the energy yield of the wind turbine can be optimized.

[0017] In a preferred embodiment, the method further comprises a step of determining the tower loads, wherein taking into account the effect of reducing the rotor thrust on the tower loads involves comparing a change in the tower loads with a threshold value.

[0018] Determining the change in tower loads is preferably done by direct or indirect measurement. Various methods for determining tower loads are known to experts. Changes can be understood as the gradient of the tower loads. The direction of the change is preferably indicative of a backward or forward oscillation of the tower. Thus, by determining the tower loads and / or the change in tower loads, the current position of the tower can be determined, and depending on whether the change exceeds a threshold value, the rotor thrust can then be reduced or not.

[0019] In a preferred embodiment, taking into account the effect of reducing rotor thrust on tower loads includes determining a tower head velocity or a nacelle oscillation velocity.

[0020] In this design, the tower loads are not determined by direct measurement, but indirectly by determining the tower head velocity. The prevailing loads, and in particular the effect of reducing rotor thrust, can then be deduced from the tower head velocity.

[0021] In a preferred embodiment, the tower head velocity is determined based on the acceleration of the tower head. Accordingly, the tower head velocity is not determined directly, but rather derived from the acceleration acting on the tower head. This is particularly simple, for example, by installing accelerometers in the tower head or in the nacelle area. Thus, a simple measurement of accelerations, by simply reformulating the results, provides an indication of the expected effects on the tower loads.

[0022] In this context, the term "tower head" preferably refers to the upper 50% of the height of the wind turbine tower. More preferably, the tower head refers to the upper 20%, and particularly the upper 10%, of the tower. Specifically, within the context of load / load transfer velocity and nacelle / tower head velocity, this disclosure primarily considers longitudinal movements of the tower head perpendicular to a vertical direction of the tower. Longitudinal movements parallel to the wind direction are of particular relevance.

[0023] In a preferred embodiment, the reduction of the rotor thrust is omitted as long as the tower head speed in the wind direction falls below a predetermined threshold.

[0024] This design avoids the particularly unfavorable situation where the tower head velocity has a component in the direction of the wind, such that reducing the rotor thrust would increase the forward deflection of the tower. The predetermined threshold can also be negative, allowing even small vibration components in the direction against the wind to lead to a reduction in rotor thrust. However, this design specifically ensures that precisely those situations in which the tower swings forward at high speed are excluded from a reduction in rotor thrust.

[0025] In a preferred embodiment, reducing the rotor thrust comprises increasing the pitch angle of at least one rotor blade of the aerodynamic rotor.

[0026] Increasing the pitch angle of one or more rotor blades directly reduces rotor thrust, as is widely known. The rotor blades can be subjected to the same pitch angle increase, or they can be controlled individually or in groups. Additionally or alternatively, a change in the shape of the rotor blade(s), for example, through dynamic surface features or attachments such as flaps, can also be controlled to achieve a reduction in rotor thrust. Other suitable control methods that result in a reduction of rotor thrust can be used in the same way.

[0027] In a preferred embodiment, reducing the rotor thrust includes raising a minimum pitch angle.

[0028] It is known that a so-called minimum pitch angle is required. a minute -The control system monitors a minimum pitch angle applied to the blade. This ensures that the pitch angle(s) of the rotor blade(s) is not set below a certain threshold, which could lead to excessively high loads on the rotor. Reducing rotor thrust can therefore be easily and efficiently integrated into the existing system. a minute - The control system is integrated or superimposed on top of it. This design is therefore characterized by minimal additional effort for setup and control.

[0029] In a preferred embodiment, reducing the rotor thrust involves lowering the target rotational speed. Lowering the target rotational speed can be achieved either as an alternative or in addition to raising the minimum pitch angle. Further control interventions that result in a reduction of rotor thrust are also conceivable.

[0030] In a preferred embodiment, the reduction of rotor thrust, taking into account the effect of the reduction of rotor thrust on the tower loads, is achieved by implementing a maximum permissible change in the pitch angle of at least one of the rotor blades of the aerodynamic rotor as a complex function of the tower loads, in particular as a function of a tower head velocity.

[0031] Implementing the system according to this design enables particularly precise control. Although this implementation is more complex than comparing it to a threshold value, it results in significantly more efficient control. In particular, the reduction of rotor thrust can then be precisely tailored to ambient conditions.

[0032] The greater the change in pitch angle, the greater its effect on reducing or increasing rotor thrust. Therefore, in this design, a maximum permissible change can be determined for a given tower head speed. For example, the change in pitch angle may not be restricted if the tower head swings backward, but may be significantly restricted if it moves forward. Both the rate and magnitude of the change are relevant here. Significant effects on the loads are only to be expected with a sufficiently large absolute change in pitch angle. The effects on the loads are greater the faster the change occurs, i.e., the higher the rate of change.

[0033] According to a further aspect, the problem is solved according to the invention by a wind turbine comprising a tower with tower loads acting upon it, an aerodynamic rotor that generates rotor thrust, and a control system. The control system is configured to operate the wind turbine according to at least one embodiment of the method according to the invention.

[0034] Compared to known wind turbines, the wind turbine according to the invention can be designed with lower expected loads on the tower, for example, because the control method is designed to avoid extreme loads, such as those occurring when the tower swings forward. Furthermore, the wind turbine according to the invention enables optimal energy yield, as unnecessary reduction of rotor thrust and the associated power losses are avoided. The wind turbine according to the invention, along with its associated advantages, can be combined with all of the embodiments of the method described as preferred.

[0035] According to another aspect, the problem is solved according to the invention by a wind farm with several wind turbines according to the invention.

[0036] Further advantages and exemplary designs are described below with reference to the attached figures. These show: Fig. 1 schematically and by way of example a wind turbine and Fig. 2 schematically and by way of example the process of a method according to the invention for operating a wind turbine.

[0037] Fig. 1Figure 1 shows a schematic representation of a wind turbine according to the invention. The wind turbine 100 has a tower 102 and a nacelle 104 on the tower 102. An aerodynamic rotor 106 with three rotor blades 108 and a spinner 110 is provided on the nacelle 104. During operation of the wind turbine, the aerodynamic rotor 106 is set into rotation by the wind and thus also rotates an electrodynamic rotor or rotor of a generator, which is directly or indirectly coupled to the aerodynamic rotor 106. The electric generator is arranged in the nacelle 104 and generates electrical energy. The pitch angles of the rotor blades 108 can be changed by pitch motors at the rotor blade roots of the respective rotor blades 108.

[0038] The thrust generated by the aerodynamic rotor 106 causes the tower 102 to vibrate. A primary direction of this vibration is in the direction of the oncoming wind or the azimuth setting of the nacelle 104. This vibration exerts considerable loads on the tower 102. These loads are crucial for the design of the tower 102. The present invention enables the wind turbine to be controlled in such a way as to reduce extreme loads on the tower 102, thereby allowing the tower 102 to be designed to be lighter and therefore more cost-effective.

[0039] In this example, to estimate the loads acting on tower 102, an acceleration sensor 112 is arranged in an upper area of ​​tower 102, called the tower head. Alternatively, the acceleration sensor 112 could also be arranged in other areas of tower 102 or even in the area of ​​the nacelle 104, as long as the acceleration measurements allow conclusions to be drawn about the acceleration acting on tower 102. Multiple acceleration sensors 112 can also be provided.

[0040] The determination of the tower loads using the acceleration sensor 112 is carried out by determining or estimating the speed of the tower head from the measured acceleration values, thus a position within the periodic oscillation, and from this the loads acting on the tower 102.

[0041] The inventive method 200 for operating a wind turbine 100 is described below with reference to Figure 2described. The procedure 200 includes a step 210 of considering the effect of reducing rotor thrust on the tower loads and, based on this, a step 220 of reducing the rotor thrust.

[0042] The core principle of this method is the understanding that reducing rotor thrust, as is typically implemented in wind turbine control systems under certain conditions, is either counterproductive or unnecessary in some situations. Regardless of speed control, there are environmental conditions, or conditions of the wind turbine itself, where reducing rotor thrust is advantageous. This can be achieved, for example, by rapidly retracting the rotor blades (108), i.e., by significantly and rapidly increasing the pitch angle of the rotor blades (108). This is the case, for instance, when the mechanical stress on the wind turbine, i.e., the loads, needs to be reduced, or when overloading needs to be prevented. Possible implementations for reducing rotor thrust include raising a minimum blade angle for one or more of the rotor blades or reducing the target rotational speed of the wind turbine.This leads to an abrupt decrease in rotor thrust, which is not always desirable. The present disclosure serves to mitigate or prevent the reduction in rotor thrust potentially required by other protective functions, thus ensuring it does not exceed a level that is healthy for all components of the wind turbine.

[0043] For example, if the rotor blades are rapidly retracted, meaning the pitch angle of the rotor blades increases rapidly, and the tower 102 simultaneously swings forward, essentially into the wind, the decrease in thrust from the rotor 106 causes the tower 102 to swing even faster and, more importantly, further forward. This can lead to extreme stresses on the tower 102. In another situation, however, the rotor blades 108 are also rapidly retracted to protect the tower 102 itself from overload. The aim here is to prevent the tower 102 from being pushed too far backward, i.e., into the wind, by the thrust of the rotor 106. However, the risk of overloading the tower 102 does not exist if the tower 102 is swinging directly forward, i.e., into the wind. If the rotor thrust of the rotor 106 were reduced in this case, potential energy loss would be unnecessarily incurred.

[0044] For this reason, step 210 first checks whether reducing the rotor thrust is beneficial and necessary. Only if this condition is met will the inventive method 200 actually reduce the rotor thrust in step 220, for example by increasing the minimum pitch angle of the rotor blades 108 or by reducing the target rotational speed. Other methods for reducing rotor thrust are, of course, also possible.

[0045] In this example, the consideration in step 210 is implemented by having a suitable control unit of the wind turbine preferably check that the reduction of the rotor thrust 106 is neither counterproductive nor unnecessary. The acceleration sensors 112 are used for this purpose, calculating or estimating the velocity of the tower head or nacelle 104 in this example. The velocity can be determined from the acceleration of the tower head measured in this example. Alternatively, instead of using the acceleration sensor 112, a load measurement can also be used to obtain the tower head velocity. In further examples, a change in the determined load itself can also be used to assess the effect of reducing the rotor thrust.

[0046] In the simplest example, threshold values, such as tower head velocity, nacelle oscillation velocity, or load changes, are used to determine whether or not rotor thrust should be reduced. In this case, rotor thrust would only be reduced if the threshold values ​​are reached. In alternative implementations, a maximum value for the pitch speed, or alternatively, any other control parameters for reducing rotor thrust, can be defined as a function of parameters indicative of their effect, such as tower head velocity, nacelle oscillation velocity, or load change rate. Variations and combinations of threshold values ​​and complex functions, such as staggered threshold values, are also conceivable. Furthermore, more than one input variable, such as several measured or estimated velocities, can be used.

Claims

1. A method for operating a wind turbine, wherein the wind turbine (100) has a tower (102) with tower loads acting thereon and an aerodynamic rotor (106) which generates a rotor thrust, wherein the method (200) has a step of reducing (220) the rotor thrust, characterized in that the reduction of the rotor thrust is not performed in any case but only after checking (210) the effect of the reduction of the rotor thrust on the tower loads, wherein the checking (210) the effect of the reduction of the rotor thrust on the tower loads occurs after a step of issuing an instruction to perform the step of reducing (220) the rotor thrust.

2. The method as claimed in claim 1, wherein the checking (210) of the effect of the reduction of the rotor thrust on the tower loads comprises the suppression or attenuation of the reduction (220) of rotor thrust if the reduction of rotor thrust leads to an increase in tower loads, in particular causes extreme loads on the tower.

3. The method as claimed in one of the preceding claims, wherein the checking (210) of the effect of the reduction of the rotor thrust on the tower loads comprises the suppression or attenuation of the reduction (220) of rotor thrust if the reduction of rotor thrust leads to an unnecessary reduction in loads acting on the tower.

4. The method as claimed in one of the preceding claims, furthermore comprising a step of determining the tower loads, wherein the checking (210) of the effect of the reduction of the rotor thrust on the tower loads comprises a comparison of a change in tower loads with a threshold value.

5. The method as claimed in one of the preceding claims, wherein the checking (210) of the effect of the reduction of the rotor thrust on the tower loads comprises a determination of a tower head speed or a gondola oscillation speed.

6. The method as claimed in claim 5, wherein the tower head speed and / or the gondola oscillation speed is determined from an acceleration of the tower head or gondola of the wind turbine.

7. The method as claimed in claim 5 or 6, wherein the reduction (220) of the rotor thrust is suppressed as long as the tower head speed in the wind direction lies below a predefined threshold value.

8. The method as claimed in one of the preceding claims, wherein the reduction (220) of rotor thrust comprises an increase in a pitch angle of at least one rotor blade (108) of the aerodynamic rotor (106).

9. The method as claimed in claim 8, wherein the reduction (220) of rotor thrust comprises an increase in a minimum pitch angle.

10. The method as claimed in one of the preceding claims, wherein the reduction (220) of rotor thrust comprises a lowering of the nominal rotation speed.

11. The method as claimed in one of the preceding claims, wherein the reduction (220) of rotor thrust is performed while considering the effect of the reduction of rotor thrust on the tower loads, in that a maximum permitted change of pitch angle of at least one of the rotor blades (108) of the aerodynamic rotor (106) is implemented as a complex function of the tower loads, in particular as a function of a tower head speed.

12. A wind turbine (100) having a tower (102) with tower loads acting thereon, an aerodynamic rotor (106) which generates a rotor thrust, and a controller, characterized in that the wind turbine (100) is operated using the method as claimed in at least one of claims 1 to 11.

13. A wind park with a plurality of wind turbines (100) as claimed in claim 12.