METHOD FOR OPERATING A WIND TURBINE

Description

[0001] The invention relates to a method for operating a wind turbine and a wind turbine designed to carry out the method, as well as a corresponding computer program product.

[0002] In conventional wind turbines, a rotor rotating around a substantially horizontal axis with rotor blades arranged to adjust the blade angle can be rotated by the wind. The rotor is connected—possibly via a rotor shaft and / or a gearbox—to a generator for converting the rotor's rotational energy into electrical energy. The power-transmitting rotating components from the rotor to the generator are collectively referred to as the drive train and are usually arranged in a nacelle rotatably mounted on a tower.

[0003] The operation of such wind turbines can generally be divided into two operating ranges. In a partial load range, at wind speeds below the wind speed at which the wind turbine generates its rated power, the blades remain at a constant blade angle while the drive torque is increased according to the available wind until rated power is reached. Once the rated power has been reached, the drive torque is kept constant and the blade angles of the rotor blades are adjusted so that the permissible rotation speed of the rotor is not exceeded (full load range).

[0004] During operation of a wind turbine, the wind acting on the rotor not only generates the desired rotation of the rotor but also a thrust force that must be fully absorbed by the tower. Due to the turbulence that regularly occurs when the rotor interacts with the wind, the thrust force that must be absorbed fluctuates dynamically, which places a significant strain on the tower. Previously known methods for operating wind turbines, the objective of which is to achieve optimal energy yield while adhering to the operating limits of the drive train components, can temporarily experience very high thrust loads. The tower must be designed to withstand these high thrust loads so that their occurrence does not result in immediate damage to the tower or an undesirable reduction in its service life. However, towers designed for such high thrust loads are generally cost-intensive.

[0005] The document Enercon et al.: "Technical Description of the ENERCON E-115 3 MW Wind Turbine" provides a technical description of a wind turbine. Among other things, this wind turbine is designed for both full-load and partial-load operation. In full-load operation, in which the wind turbine operates at high wind speeds, the wind turbine operates at a maximum rotor speed of approximately 12.4 rpm and a rated power of 3000 kW. This speed is limited by blade pitch. At lower wind speeds, the wind turbine operates in partial-load operation, with the rotor speed and power output dependent on the current wind speed.

[0006] The document Pao LY et al: "Control of Wind Turbines" describes a control system for wind turbines in which the generator torque can be used to accelerate or decelerate the rotor.

[0007] Hau Erich's document "Passages from: Wind Turbines, Fundamentals, Technologies, Application, Economics, 2nd edition" is a textbook on wind turbines that describes, among other things, partial load operation of a wind turbine in light wind conditions. A fixed rotor blade angle is set, and as much power as possible is extracted from the wind based on the rotor's performance characteristics.

[0008] The object of the invention is to provide a method for operating a wind turbine and a correspondingly designed control device in which the disadvantages of the prior art no longer occur or only occur to a reduced extent.

[0009] This problem is solved by a method according to the main claim and a wind turbine according to the subordinate claim. Advantageous further developments are the subject of the dependent claims.

[0010] Accordingly, the invention relates to a method for operating a wind turbine comprising a rotor with angle-adjustable rotor blades and a generator with controllable torque connected thereto for rotation, wherein the torque of the generator is limited to a maximum value which is linked to the blade angle of the rotor blades in such a way that the maximum value at the switch-on blade angle value is smaller than the nominal torque value and the maximum value at a nominal blade angle deviating from the switch-on blade angle is equal to the nominal torque value.

[0011] Furthermore, the invention also relates to a wind turbine comprising a rotor with a plurality of rotor blades which are adjustable in terms of blade angle and which is rotatably arranged on a nacelle which is rotatably arranged on a tower and is connected via a drive train to a generator arranged in the nacelle for converting wind energy acting on the rotor into electrical energy, and a turbine control system for controlling the wind turbine and its components, wherein the turbine control system is designed to carry out one of the methods according to the invention.

[0012] The invention also relates to a computer program product comprising program parts which, when loaded into a computer, preferably the system control of a wind turbine, are designed to carry out one of the methods according to the invention.

[0013] First, some terms used in connection with the invention will be explained.

[0014] "Blade angle" refers to the angle of the rotor blades around their longitudinal axis relative to a defined zero position. Often, all rotor blades of a wind turbine have essentially identical blade angles. However, it is also possible for the rotor blades of a wind turbine to be set to individual, different blade angles. For reasons of clarity, this application assumes that all rotor blades of the wind turbine have the same blade angle or are set to this angle, without, however, precluding the possibility of individual blade angle adjustment.

[0015] The "switch-on blade angle" refers to the blade angle to which the rotor blades are set at the switch-on wind speed sufficient to start the rotor from rest into rotation and connect the generator to the grid for feeding in electrical power. The switch-on blade angle can be maintained throughout the entire partial load range of a wind turbine, or the blade angle can be varied by a few degrees from the switch-on blade angle throughout the partial load range.

[0016] "Rated torque" refers to the torque of the generator that occurs at the rated power of the wind turbine. The "rated power" of the wind turbine is the electrical power of the wind turbine for which the wind turbine and its components are designed, i.e., the maximum continuous power that can be fed into the power grid during normal operation without causing damage or similar to the wind turbine or any of its components.

[0017] The "nominal blade angle" is the blade angle at which the nominal torque is achieved. The nominal blade angle is generally not a constant value but can vary depending on the operating mode of the wind turbine and / or the load dynamics described below. It is, of course, also possible for the nominal blade angle to vary depending on other operating parameters. Starting from the switch-on blade angle, the nominal blade angle is usually in the direction of the feathering position.

[0018] The invention recognizes that for the operation of a wind turbine, particularly with regard to the shear load on the tower of a wind turbine, it is advantageous to be able to change the blade angle of the rotor as dynamically as possible even in the partial load range, in order to be able to react to gusts at short notice, for example. According to the invention, this is achieved by limiting the torque of the generator to a maximum value that can be changed across the partial load range between the switch-on blade angle and the nominal blade angle. If this maximum value is reached, the rotational speed of the rotor of the wind turbine would generally increase without any control intervention as the wind continues to increase due to the generator torque not increasing any further.To prevent this, the rotor blade angle can be changed - usually increased - using state-of-the-art, usually very dynamic speed controls for the full load range.

[0019] According to the invention, the maximum torque value at the switch-on blade angle is lower than the nominal torque value. Since the maximum value in question is linked to the rotor blade angle according to the invention, the maximum torque corresponds to the nominal torque value at the latest when the rotor blade angle assumes a predetermined nominal blade angle that deviates from the switch-on blade angle due to other controls, such as the blade angle control depending on the rotation speed. As soon as the maximum torque value subsequently equals the nominal torque value, the wind turbine can, in principle, deliver rated power if there is sufficient wind.With the method according to the invention, the rotor blades already have a blade angle deviating from the starting blade angle, preferably the rated blade angle, when the rated power is reached, which is preferably selected such that the thrust load is reduced at least at rated power compared to a blade position with the starting blade angle.

[0020] It is understood that in a wind energy installation delivering rated power according to the method according to the invention, when the wind decreases, the maximum value for the torque is reduced according to the blade angle changed in the direction of the starting blade angle - for example due to the decreasing rotational speed.

[0021] As already mentioned, the blade angle of wind turbines can already be changed depending on the rotation speed using a control system that is basically known from the state of the art, if the rotation speed can no longer be limited by increasing the generator torque because this already corresponds to the current maximum value. Accordingly, with a torque corresponding to the maximum value and a decreasing rotation speed, the blade angle is first changed to the switch-on blade angle before the generator torque is reduced to maintain rotor rotation.

[0022] Alternatively, it is also possible to change the blade angle, for example, by a predetermined step or according to a predetermined pattern, as soon as the generator torque reaches the maximum value resulting from the previously changed blade angle. By directly coupling the blade angle to the reaching of the maximum value, a rapid adjustment of the blade angle can be achieved without having to wait for a detectable change in the rotation speed of the rotor, which is sluggish in this respect.

[0023] The maximum torque value and the blade angle can be linked using a characteristic curve, which is preferably parameterized. The characteristic curve can be represented by one or more mathematical functions, whereby, for example, different functions can apply to different blade angle ranges. However, it is also possible for the characteristic curve to be stored in the form of a characteristic value table, with linear interpolation between any two adjacent characteristic values ​​if necessary.

[0024] The characteristic curve can, for example, provide a first maximum value for a first blade angle, e.g., corresponding to the switch-on blade angle, and a second constant blade angle for a range greater than or equal to a second blade angle, with the maximum value in the range between the first and second blade angles varying proportionally, preferably linearly, depending on the blade angle. The initial maximum torque value therefore remains constant until it is reached by the actual torque, whereupon it then increases as the torque continues to rise, depending on the blade angle, until the maximum value equals the nominal torque. However, any other characteristic curve progressions are also conceivable.

[0025] It is preferred if the characteristic curve and / or the nominal blade angle are changed depending on the operating state of the wind turbine and / or the ambient conditions. For this purpose, the parameters of the characteristic curve can be changed, if available. However, it is also possible to provide different characteristic curves for different operating states and / or ambient conditions, which are used according to the current operating state. For safe minimum operation of the wind turbine, for example, a characteristic curve with a constant maximum torque value for all blade angles can be provided. Changing the characteristic curve regularly also changes the nominal blade angle.

[0026] One possible factor that can be used to change the characteristic curve is the rotor power dynamics, as described in DE 10 2017 011 318.1. The load dynamics of a wind turbine in interaction with the wind are calculated as the gradient of the sum of the instantaneous acceleration power leading to the acceleration of the drive train of a wind turbine ( P acceleration ) from the measured rotational speed ( ω ) of the drive train and determining the power currently transmitted by the drive train (10) ( P U transfer ). The currently transmitted power ( P U transfer ) can be calculated from a current torque setpoint ( M Should ) or a measured torque ( M Mess ) or can be calculated with the measured electrical power ( P electric) of the wind turbine. The dynamic load can be interpreted as the feedback effect of the dynamic load on the wind turbine caused by the wind acting on the rotor. If the dynamic load is low, a steady wind can be assumed, while high dynamic load indicates gusty wind. In the former case, the maximum value in the method according to the invention can be increased due to the lower expected fluctuations in the thrust load, for example, whereas in the latter case, a reduction is more appropriate to avoid excessive thrust loads.

[0027] For the method, the actual torque of the generator, measured using a suitable measuring device, and / or the actual blade angle, measured in a suitable manner, can generally be used. The generator torque can also be limited directly, for example, by intervening in the corresponding control system of the wind turbine. However, it is preferred if, instead of a measured actual torque and / or a measured actual blade angle, the setpoint value(s) regularly required for control and therefore available in the turbine control system are used for these variables. The control systems of wind turbines are generally designed to regulate the actual torque to the torque setpoint, whereby, at least in modern turbines, only extremely small, negligible deviations between the actual and setpoint torque values ​​occur.The same applies to the actual blade angle and the blade angle setpoint. Since any deviations between the setpoint and actual values ​​– however small – nevertheless fluctuate regularly, it has been shown that directly accessing the torque setpoint and / or the blade angle setpoint leads to more robust operation of the wind turbine, as this also avoids any inaccuracies in the recording of the actual values.

[0028] In particular, if the method according to the invention uses setpoints for blade angle and torque, and the blade angle is changed upon reaching the instantaneous maximum torque value depending on the rotor rotation speed, it is sufficient if the method according to the invention influences exclusively the torque setpoint. By temporarily increasing or reducing the torque setpoint ultimately implemented by the generator or the associated converter by an offset, the rotor can be accelerated or decelerated, which, with corresponding wind turbine control systems, then results in a predictable change in the blade pitch angle, without the blade angle setting having to be directly influenced for the method according to the invention.

[0029] For an explanation of the wind turbine according to the invention and the computer program product according to the invention, reference is made to the above explanations.

[0030] The invention will now be described by way of example using a preferred embodiment with reference to the accompanying drawings. Figure 1: a schematic representation of the nacelle of a wind turbine according to the invention designed to carry out the method according to the invention; and Figure 2: the schematic diagram of a possible implementation of the method according to the invention; and Figure 3: a possible characteristic curve for linking the blade angle and the maximum value for the torque.

[0031] In Figure 1The nacelle 2 of a wind turbine 1 according to the invention and thus designed to carry out the method according to the invention is shown schematically. The wind turbine 1 comprises a rotor 3 with a total of three rotor blades 5 rotatably attached to a rotor hub 4 via blade angle adjustment devices (not shown). The rotor 3 is rotatably arranged on the nacelle 2, which in turn is arranged on a tower 6 rotatably about a vertical axis via an azimuth drive 14.

[0032] The rotor hub 4 is connected to a generator 9 via a rotor shaft 7 with an intermediate gear 8 for converting wind energy acting on the rotor 3 into electrical energy. The power-transmitting components from the rotor 3 to the generator 9—in particular the rotor shaft 7 and the gear 8—form the drive train 10.

[0033] In the illustrated embodiment, the generator 9 is a double-fed asynchronous generator in which part of the generated power is fed directly, another part of the power is fed via a converter 11 and a switching element 12 to a transformer (not shown) located at the base of the tower 6 and from there into a public supply network.

[0034] A brake 13 is also provided between the gearbox 7 and the generator 9, with which the rotational movement of the drive train 10 can be slowed down and the rotor 3 can be locked if necessary. Furthermore, sensors 14 are provided between the gearbox 8 and the generator 9 to determine the rotor speed or the speed of the shaft 7.

[0035] The wind turbine 1 and all of its components are controlled by the computer-based turbine control system 20. For this purpose, all measured values ​​recorded in the wind turbine 1 as well as setpoints, e.g., from a grid operator, are fed to the turbine control system 20 via a data line 21 and converted into control signals using control algorithms stored in a memory 22 and generally known to those skilled in the art. These control signals are then transmitted to the various components of the wind turbine 1. In a first part, the turbine control system 20 determines setpoints for individual controllable parameters of the operation of the wind turbine 1 based on the available information. These setpoints are then implemented by other parts of the turbine control system 20 such that the corresponding actual values ​​correspond to the setpoints.

[0036] According to the invention, the system control 20 is designed to carry out the method according to the invention described in more detail below, for which purpose a computer program product designed for this purpose is stored in the memory 22 and executed by the system control 20.

[0037] In Figure 2 A schematic diagram for implementing the method according to the invention in the system control 20 is shown. The illustration is limited to the part of the system control 20 that is essential for carrying out the method.

[0038] As already explained, the turbine control system 20 determines target values ​​for the individual operating parameters of the wind turbine 1 based on the recorded measured values ​​and other control specifications. These also include target values ​​for the blade angle α Should and for the generator torque M Should , which are from other, in Figure 2parts of the system control 20 (not shown in detail) into control commands for the individual components of the wind turbine 1, so that the actual blade angle α and the actual generator torque M correspond to the target values. In addition, the system control 20 determines a standardized load dynamic according to DE 10 2017 011 318.1 q Yours , which takes values ​​between 0 and 1 and provides information about the turbulence occurring at the wind turbine. Last but not least, the turbine control 20 and thus also the wind turbine 1 have various operating modes, e.g., a normal operation and a safety mode, in which the power generation is reduced in order to avoid having to shut down the wind turbine 1 completely in the event of any malfunctions. The currently active operating mode of the turbine control 20 is reflected in the value in mode again.

[0039] The torque setpoint determined in a known manner M Should is fed to a setpoint limiter 23, which sets the setpoint M Should to a value between 0 and a maximum value for the torque M Should ; Max limited.

[0040] The maximum value M Should ; Max is determined by the calculation module 24, which uses as input variables the blade angle setpoint α Should , the setpoint for the torque M Should , the load dynamics q Yours and the signal for the current operating mode Mode receives.

[0041] To determine the maximum value M Should ; Max the calculation module 24 accesses a characteristic curve 30 as shown in Figure 3 The characteristic curve 30 represents a direct link between the blade angle and the blade angle setpoint α Shouldand the maximum value for the torque or its setpoint M Should ; Max In the calculation module 24, several different characteristic curves are stored, which, depending on the current operating mode, are calculated according to the input signal in mode selected and used. Some of these characteristics are further parameterized, with at least one parameter being dependent on the load dynamics q Yours is changed.

[0042] The characteristic curve 30 in Figure 3 is designed for normal operation of wind turbine 1 and depending on the load dynamics q Yours changeable.

[0043] For the switch-on blade angle, which the rotor blades 5 of the wind energy 1 have, so that the rotor is set into rotation from rest with sufficient wind (regularly 0°), a maximum value for the torque M Should ; Max below the nominal torque M nominalIn addition, a blade angle is specified at which the maximum value for the torque M Should ; Max constant to the nominal torque M nominal In the range between the switch-on blade angle and the nominal blade angle, from which the maximum value M Should ; Max to the nominal torque M nominal is set, there is a linear relationship between the blade angle setpoint α Should and maximum value for the torque M Should ; Max . Likewise, additional characteristic curves may be specified for other reasons, for example to comply with sound parameters.

[0044] The nominal blade angle changes depending on the load dynamics q Yours. With low load dynamics q Yours the nominal blade angle in question is shifted towards the switch-on blade angle, with a high load dynamic q Yoursin the opposite direction. This is indicated Figure 3 by the dashed characteristic curves.

[0045] In addition to the characteristic curve 30 for normal operation shown Figure 3 in, there is also another characteristic curve for safe minimum operation stored in the calculation module 24. For this characteristic curve 30, the maximum value for the torque M Should ; Max is set to a constant value for all blade angles.

[0046] The calculation module 24 calculates the maximum value for the torque M Should ; Max based on the characteristic curve valid for the current operating mode and provides this to the setpoint limiter 23 as an input value for limiting the setpoint M Should from which the setpoint M Should ; Max limited to the maximum value I should results. This setpoint I shouldcan already be used in principle for the final control of the generator torque.

[0047] In the Figure 2 In the embodiment shown, the calculation module 24 is further designed to, in certain operating modes in mode and / or from a certain load dynamic q Yours , by temporarily increasing and reducing the setpoint determined by the setpoint limiter 23 I should to the target value M"Sol To influence the rotational speed of the rotor 3 of the wind turbine 1, which, with a corresponding design of the turbine control 20, results in a change in the blade angle of the rotor blades 5 in a known manner.

Claims

1. Method for operating a wind power plant (1) comprising a rotor (3) with angle-adjustable rotor blades (5) and a generator (9) rotationally connected thereto and having a controllable torque, characterized in that the torque of the generator (9) is limited to a maximum value that is linked to the blade pitch angle of the rotor blades (5) in such a way that the maximum value at the switch-on blade pitch angle value is less than the nominal torque value (MNenn) and the maximum value at a nominal blade pitch angle that differs from the switch-on blade pitch angle is equal to the nominal torque value (MNenn).

2. Method according to Claim 1, characterized in that the blade pitch angle on reaching the maximum value is changed by the torque.

3. Method according to Claim 1, characterized in that the link between the maximum value for the torque and the blade pitch angle is made on the basis of a preferably parameterized characteristic curve (30).

4. Method according to Claim 1, characterized in that the characteristic curve and / or the rated blade pitch angle is changed depending on the operating state of the wind power plant (Modus) and / or on the ambient conditions.

5. Method according to Claim 1, characterized in that the change to the characteristic curve (30) takes the loading dynamic (BDyn) of the wind power plant (1) into consideration.

6. Method according to one of the preceding claims, characterized in that the blade pitch angle of the rotor blades (5) and the torque of the generator (9) are regulated toward a blade pitch angle setpoint value (αSoll) and a torque setpoint value (MSoll), wherein the maximum value (MSoll;Max) limits the torque setpoint value (MSoll), and is linked to the blade pitch angle setpoint value (αSoll).

7. Wind power plant (1) comprising a rotor (3) with a plurality of rotor blades (5) whose blade pitch angle is adjustable that is arranged rotatably at a nacelle (2) that is arranged rotatably on a tower (6) and is connected via a drivetrain (10) to a generator (9) arranged in the nacelle (2) for the conversion of wind energy acting on the rotor (3) into electrical energy, and a plant controller (20) for controlling the wind power plant (1) and its components, characterized in that the plant controller (20) is designed to carry out the method according to one of the preceding claims.

8. Wind power plant (1) according to Claim 7, characterized in that the plant controller (20) is designed, on reaching the maximum value for the torque (MSoll;Max), to control the blade pitch angle of the rotor blades depending on the rotation speed of the rotor (3).

9. Wind power plant (1) according to Claim 8, characterized in that the plant controller (20) is designed to increase or reduce the torque and / or the torque setpoint value (MSoll) for a period of time in order to influence the rotation speed of the rotor (3).

10. Computer program product comprising program segments which, if loaded into a computer, preferably the plant controller (20) of a wind power plant (1), are designed to carry out the method according to one of Claims 1 to 6.