Wind turbine controls

Abstract

The invention describes a control device (2) for a variable speed wind turbine (3), the control device (2) comprising: a load analysis module (10) configured to analyze a plurality of environmental values ​​(10_1, ..., 10_n) to determine when the rotation speed of the aerodynamic rotor (30) has reached its rated value (ω rated ), whether the instantaneous wind turbine load (L) is lower than the load threshold (L max ); and a speed boost module (11) configured to increase the speed of the wind turbine when the wind turbine load (L) is below the load threshold (L max ), determine the speed increment (ω) of the rotation speed of the pneumatic rotor (30) inc ).

Description

Technical Field

[0001] The invention describes a wind turbine control device and a method of operating a variable speed wind turbine. Background Art

[0002] It is generally desirable to maximize the annual energy production (AEP) of a wind turbine. In practice, this means that the wind turbine should produce as much output power as possible. However, it is not always possible for a wind turbine to operate at its highest output power level. For example, it may be necessary to reduce the rotation speed of the aerodynamic rotor to avoid damaging the rotor blades, especially in the case of very long rotor blades.

[0003] Current conditions can vary greatly between wind farm sites. Therefore, to avoid overdesign, wind turbines are usually designed for specific wind classes. The most common "Wind Class II" wind turbines can handle average wind speeds up to 8.5m / s. "Wind Class III" wind turbines are designed for average wind speeds of less than 7.5m / s and may have long rotor blades and tall towers; and "Wind Class I" wind turbines are built for higher average wind speeds of more than 8.5m / s and must have shorter rotor blades and shorter towers to avoid excessive structural loads. Turbulence intensity (a measure of the extent to which the wind changes over a ten-minute period) is also taken into account by further refining the wind class. For example, "IIa" is used for sites with a turbulence intensity of 18%, while "Wind Class IIb" is used for sites with a turbulence intensity of 16%. These classes are defined by the IEC 61400-1 standard. Wind turbines with a particular turbine class are then particularly suitable for installation at sites where normal wind conditions are defined by particular values ​​of mean wind speed, extreme 50-year gusts and turbulence intensity.The AEP achievable by a wind turbine will depend largely on its wind class.

[0004] In general, the rotational speed of the aerodynamic rotor and the power output of the wind turbine are directly related to the wind speed. The fraction of the wind power that can be extracted by the wind turbine and converted into electrical power is called the power coefficient C. P The power coefficient is a function of the tip speed ratio and the rotor blade pitch angle, and the tip speed ratio is the ratio between the rotor blade tip speed and the wind speed. At a certain wind speed, the output power of the variable speed wind turbine is defined by a power / speed curve, which has a maximum value at a certain rotation speed of the aerodynamic rotor. The curve or trajectory defined by the power output maximum value within a certain range of wind speeds is its ideal trajectory T shown in Figure 6 ideal Any deviation from the ideal trajectory will reduce the power coefficient of the wind turbine.

[0005] The rated speed of a wind turbine will depend on its "wind class" and is essentially an upper limit for that type of wind turbine. Thus, as shown in Figure 6, the rated speed of a wind turbine ω rated is the maximum value of the power / speed curve corresponding to a specific upper wind speed C vmax As long as the wind speed is below this upper wind speed limit, the control algorithm will adjust the pitch and torque reference so that the rotation speed follows the ideal trajectory T ideal .

[0006] However, the rated rotor speed of a variable speed wind turbine is generally reached before the rated power, i.e., the wind turbine has the potential to produce more power even when its rotational speed has reached the maximum value of the power / speed curve at the upper wind speed limit. In prior art methods, the output power is increased by means of physical rotor blade additions such as trailing edge serrations, vortex generators, etc. The wind turbine is controlled to maintain the rated rotational speed while the output power can be increased. This region of the power / speed diagram may be referred to as the "constant speed region" and is represented in FIG6 as a vertical trajectory T CSZ When operating in this zone, the aerodynamic performance of the wind turbine is suboptimal.

[0007] There are a number of known control methods that can be applied in order to improve the AEP of a wind turbine. In one method, the wind turbine loads (the loads acting on the rotor blades, tower, etc.) are continuously monitored, and the rotational speed and / or output power are increased above their rated levels as long as the loads remain below an acceptable threshold. In another method, the wind turbine is operated at or above the rated level and is only curtailed when conditions (and therefore loads) become severe.

[0008] However, known control strategies generally focus on how to operate the wind turbine to avoid damage caused by extreme operating conditions and can generally be viewed as preemptive curtailment strategies, but these known control strategies do not attempt to take advantage of other, less extreme operating conditions.

[0009] It is therefore an object of the present invention to provide an improved way of controlling a wind turbine. Summary of the invention

[0010] This object is achieved by a control device for a variable speed wind turbine, a variable speed wind turbine and a method of operating a variable speed wind turbine according to the invention.

[0011] According to the present invention, a wind turbine control device for a variable speed wind turbine configured to meet the requirements of wind classes as defined in IEC 61400-1 comprises a load analysis module configured to determine, while the rotational speed of the aerodynamic rotor is at or close to its rated value, whether the instantaneous wind turbine load is below a load threshold, the rated value being associated with an output power level that is less than the rated output power of the class of wind turbines. The control device further comprises a speed boost module configured to determine a speed increment for the rotational speed of the aerodynamic rotor if the load is less than the load threshold. The speed increment will allow the wind turbine to more closely follow its ideal power / speed trajectory T ideal .

[0012] The present invention is based on the recognition that the turbulence intensity level used in the IEC 61400-1 standard is the 90th percentile. This means that during 90% of its operating life, a wind turbine will be exposed to less severe turbulence and, during this time, will be subjected to loads lower than allowed by its specification. The present invention adopts a method of identifying "mild" conditions during which the rotor speed can be increased in a manner that follows the ideal power / speed trajectory. This is in contrast to the suboptimal "constant speed zone" approach known from the prior art, which is a strategy of keeping the rotational speed constant while allowing the output power to increase when the wind speed increases above the specification level.

[0013] In the context of the present invention, the purpose of the load analysis module is to identify "mild" environmental conditions, where the wind turbine is running at its rated speed, but is not being operated to extract the maximum amount of energy from the wind. Therefore, the load analysis module may be referred to as a "mild environmental condition analyzer" (MECA) hereinafter.

[0014] The method of the present invention for operating a variable speed wind turbine comprises the steps of determining whether the load is below a load threshold when the rotational speed is at or near the rated speed; and determining a speed increment for the rotational speed of the aerodynamic rotor based on a power / speed trajectory of the wind turbine if the observed load is below the load threshold.

[0015] Particularly advantageous embodiments and features of the invention are given by the preferred embodiments, as disclosed in the following description.Features of different embodiments may be combined as appropriate to give further embodiments not described herein.

[0016] In the following, it may be assumed that the wind turbine is a variable speed direct drive wind turbine. Such a wind turbine typically comprises a summing module for subtracting the instantaneous rotational speed of the aerodynamic rotor from a reference speed and transmitting the difference or error signal to a speed control block. To implement the method of the present invention, the summing module (typically implemented in the form of software) is configured to increase the speed increment such that the speed error signal is increased by the amount. Depending on the mildness of the ambient conditions, the speed increment may be an integer in radians per second or a fraction less than 1.

[0017] In the following, without limiting the invention in any way, it may be assumed that the wind turbine is constructed to meet the requirements of a wind class such as wind class IIa or wind class IIb as defined in IEC 61400-1.

[0018] These environmental values ​​may include any of the following: blade loading values, turbulence intensity values, tower acceleration values, yaw position values, or any other relevant values.

[0019] The turbulence intensity seen by a wind turbine is a highly relevant factor in assessing the transient loads on the wind turbine. The turbulence intensity may be estimated using a LIDAR device, and a suitable LIDAR device may be arranged to provide data to the load analysis module. The turbulence intensity may also be estimated or determined by analyzing various other parameters. Therefore, in another preferred embodiment of the present invention, the load analysis module is configured to receive rotor blade pitch position values, active power values ​​and rotor speed values, and the load analysis module may include a turbulence estimator unit configured to estimate the local turbulence intensity based on these parameters. For example, the standard deviation of the aerodynamic rotor speed may be used to estimate the turbulence intensity.

[0020] The individual contribution of each monitored parameter is preferably determined taking into account the nature of that parameter. To this end, the processing of the parameter preferably involves passing it through a filter and / or subjecting it to an operator and / or comparing it to a threshold and / or multiplying it by a gain factor, whereby these stages may be applied in any suitable order.

[0021] In this way, the load analysis module calculates the partial contribution of each environmental value and sums them together. The value of the resulting sum will be an indication as to whether the rotational speed may be increased above the rated speed of the wind turbine. For example, if the MECA concludes that the rated speed load of the wind turbine is actually lower than allowed by the wind turbine specification, it may issue a permit to increase the rotor speed. As a result, the controller may respond by increasing or boosting the rotor speed by a predetermined increment, such as by 0.5 rad / s, 2 rad / s, etc. The speed boost increment may be determined based on the turbulence level of the wind turbine and / or its wind level.

[0022] The size of the speed increment may decrease as the deviation from rated speed increases, for example the first speed increment may increase the rated speed by 2 rad / s; but if the rotor speed is already 5 rad / s above rated speed, any further speed increments may be in steps of 0.1 rad / s.

[0023] The size of the speed increment may be proportional to the difference between the actual load and the load threshold, e.g., if the actual load is only 80% of the load threshold, the speed increment may increase the rated speed by 2 rad / s; but if the actual load is 95% of the load threshold, any further speed increment may be limited to a smaller value, e.g., 0.1 rad / s.

[0024] In a particularly preferred embodiment of the invention, the wake exposure of the wind turbine is preferably also taken into account. To this end, the load analysis module is configured to determine the wake exposure of the wind turbine. The wake exposure can be determined from a lookup table using knowledge of the location of the wind turbine in the wind farm, its yaw attitude and various other relevant parameters. Based on the determined wake exposure, the load analysis module can deny the above-mentioned speed increase permission if the wake exposure is considered to be critical, or grant the speed increase permission if the wake exposure is considered to be non-critical. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Other objects and features of the present invention will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed for illustration purposes only and not as a definition of the limits of the present invention.

[0026] Figure 1 A block diagram showing an embodiment of a control device of the present invention;

[0027] Figure 2 Shows Figure 1 A block diagram of an embodiment of a load analysis module;

[0028] Figure 3 shows a speed / power diagram of a wind turbine controlled using the method of the present invention;

[0029] Figure 4 The incremental speed improvement of the method of the present invention is illustrated;

[0030] Figure 5 An exemplary wind farm is shown;

[0031] Fig. 6 shows a speed / power diagram of a wind turbine controlled using a prior art method.

[0032] In the drawings, like reference numerals refer to like objects throughout. Objects in the drawings are not necessarily drawn to scale. DETAILED DESCRIPTION

[0033] Figure 1 The block diagram of an embodiment of the control device 2 of the present invention is shown. The aerodynamic rotor and the generator are considered together as a power generation unit 21, and the power output of the generator is mainly determined by the pitch reference 21 pitch (to the rotor blades) and torque (or power reference) reference 21 torque (To generator) OK.

[0034] The control device 1 of the invention comprises a load analysis module 10 or "mild environmental condition analyzer" (MECA) 10, which receives various inputs providing it with relevant data 10_1, ..., 10_n, such as flap bending moment data 10_1 (e.g. from sensors of blade load limiter modules 22), turbulence intensity data (e.g. from a LIDAR unit), tower load data, yaw position data, etc. Based on this information, the MECA 10 can evaluate the current environmental conditions of the wind turbine and can decide whether a speed increase is allowed. This decision is sent as a speed increase approval signal SB OK Output to the speed boost module 11. The speed boost module 11 is provided with a boost level 11_in, i.e. the extent to which the rotor speed can be increased. The boost level 11_in may be a predetermined parameter or setting and may set a limit on the maximum allowable boost. The speed boost module 11 may then set one or more speed increments ω within the constraints of this maximum allowable boost. inc , in order to approach the maximum value 11_in. For example, the continuous speed increment ω inc The maximum value 11_in can be approached gradually in several small steps. Then, the expected speed increment ω inc Added to the speed reference 20ω. The speed reference 20ω may originate from a park controller (not shown).

[0035] The difference between the target speed and the actual speed 21ω or the speed reference error 20 err is input to the speed control module 20 which then calculates the target pitch reference and torque reference 21 torque .

[0036] In the exemplary embodiment, the target pitch reference is modified by the load limit deviation provided by the blade load limiter 22. The corrected pitch reference 21 is then used pitch and torque reference 21 torque To control the pneumatic rotor and generator to achieve the target rotation speed (speed reference 20ω plus speed increment ω inc ) and target output power.

[0037] Figure 2 Shows Figure 1 Here, each input signal 10_1, ..., 10_n is processed in various stages SF, SO, ST, SG to determine its contribution to the final "boost speed" decision SB OK contribution. Depending on the type of input signal 10_1, ..., 10_n, it may be processed by a filter stage SF and / or an operator stage SO and / or a threshold stage ST and / or a gain stage SG. Depending on the nature of the input signal 10_1, ..., 10_n, the filter type of the filter stage SF may be any of low pass, band pass, high pass, etc.; the operator of the operator stage SO may be any of the calculations of standard deviation, absolute value, maximum value, etc.; the threshold stage ST may determine whether its input reaches the required threshold to include it in the final decision; the gain stage may determine the weights of the partial contributions C1, ..., C5. These considerations apply to input signals, such as LIDAR input 10_2, blade load sensor input 10_1, sensor input 10_3, such as a wind speed sensor, etc.

[0038] The pitch position 10_5, active power 10_6 and actual rotor speed value 21ω are fed to a lookup table 100 which returns a wind speed estimate which is then used by a turbulence estimator module 101 to obtain an estimate of the local turbulence intensity. The lookup table 100 may also deliver a thrust estimate which is processed in conjunction with the tower acceleration input 10_4.

[0039] The partial contributions C1, ..., C5 from the processing stages are summed to obtain the total load value 10 total , and then set the total load value to 10 total With the sum threshold SB thold Compare. If the total load is 10 total Less than the threshold SB thold , then in principle the rotation speed can be increased, and this possibility is increased by the preparation speed SB pre Signal indication.

[0040] In this exemplary embodiment, the decision to increase or boost the rotational speed also depends on the "wake position" of the wind turbine, i.e., whether the wind turbine is in the wake of another wind turbine, because when the wind turbine is in the wake of another wind turbine, the possibility of excessive loading increases significantly. To this end, the yaw attitude 10_7 of the wind turbine is fed to the wake module 102, which can use the electric field layout lookup table. The wake module 102 can also be informed of the yaw position of other related wind turbines in the wind farm. Using this information, the wake module 102 can determine whether the wind turbine is in the wake or outside the wake. For example, the wake state WS can be "true" (the wind turbine is in the wake) or "false" (the wind turbine is outside the wake). The boost approval module 103 receives the wake state WS and the initial speed boost SB pre The speed boost approval module 103 prevents speed boost when the wind turbine is "in the wake" and enables speed boost once the wind turbine is "outside the wake". Effectively, a positive speed boost SB enabling rotor speed boost is issued only when the wind turbine is outside the wake, i.e. the wind turbine is not currently affected by the wake of the upstream wind turbine. OK Signal.

[0041] Figure 3 Speed / power curves for several wind turbine types are shown, with power P (in Watts) along the Y axis and rotational speed ω (in radians per second) along the X axis. It should be understood that there are an infinite number of speed / power curves and that for clarity, the figure shows only a few.

[0042] Each curve shown in the figure is associated with a specific integer wind speed ν and has a maximum power output value at a specific rotation speed. νmax Corresponding to the wind turbine being able to reach its rated speed ω rated Wind speed ν max The figure also shows the ideal trajectory T for this wind turbine type. ideal Along this ideal trajectory T ideal Each point of is the maximum value of the speed / power curve. vmax , rated speed ω rated is associated with the output power P0. When the wind turbine is at its rated speed ω rated The achievable output power P0 during operation is less than the achievable rated output power P of the wind turbine of this category rated .

[0043] When the wind turbine is running at its rated speed ω ratedDuring operation, the load analysis module continuously monitors the load to assess whether it is safe to increase the rotor speed. If the speed increase is authorized, the rotor speed can be temporarily increased, allowing the wind turbine to follow the ideal trajectory T ideal From curve C vmax Starting from the maximum value, the output power can increase from the initial level P0 to its rated output power P rated , while following the ideal trajectory T ideal In this way, the wind turbine can be controlled to extract the maximum possible amount of energy from the wind when the wind has increased (within safe levels) above the rated wind speed for the wind turbine class. As a result, the AEP of the wind turbine can be significantly increased.

[0044] With the control method of the invention, the power coefficient of a wind turbine type can be maximized by identifying mild ambient conditions that allow a careful increase in the rotation speed. max , and also sends out to keep the rotation speed at the rated value ω rated The rotation speed is allowed to increase gradually so that the power / speed relationship T SB Can follow the ideal trajectory T ideal Of course, as soon as the load is deemed too great, the rotational speed is reduced again towards its rated speed (or below rated speed, as the case may be), thereby again following the optimum power / speed trajectory T SB .

[0045] Figure 4 The diagram illustrates the incremental speed increase performed by the method of the present invention during operation of a wind turbine. The diagram shows the cumulative wind load L on the wind turbine. prior , the wind turbine is controlled by prior art control techniques to operate at or near its rated speed. The accumulated wind load L prior Fluctuates according to collective changes in environmental conditions, such as changes in turbulence, tower load, wind speed, etc. The load threshold L of the wind turbine max is represented as a constant value.

[0046] The invention is based on the premise that the load on a wind turbine is usually less than a specified load threshold L max The present invention aims to fill the gap G between the load threshold and the actual load. prior The efficiency loss caused by these “gaps” G prior This indicates that the wind turbine is not extracting maximum energy from the wind. Figure 2 The total load is estimated as explained in , and compared to a load threshold (e.g., the total load is 10 total and Figure 2 The threshold SB tholdCompare). If the wind turbine is not in the wake, the rotor speed can be increased to follow the ideal trajectory, as explained above.

[0047] The figure shows an exemplary speed boost increment ω that is added to the speed reference 20ω inc (in rad / s), such as Figure 1 The speed increase increment ω inc is determined by the MECA 10 and the speed boost module 11 based on the observed load on the wind turbine, as explained above. As long as the actual load does not exceed the load threshold, the speed of the aerodynamic rotor can be increased carefully. This diagram shows a more optimal cumulative load L SB The results of the control method of the present invention are shown in the form of , which shows that the wind turbine is able to always extract maximum energy from the wind.

[0048] Figure 5 An exemplary wind farm is shown, in which a plurality of wind turbines 3 are arranged in a suitable formation. The farm controller 5 issues speed references 20ω_1, ..., 20ω_n to the wind turbines 3 based on input data 50_1, ..., 50_n, such as power demand input, turbine capacity, meteorological data, etc. The upstream wind turbine is not exposed to the wake of any other wind turbine and can give its aerodynamic rotor 30 a high speed reference.

[0049] As explained in the introduction, FIG6 shows speed / power curves for several wind turbine types, with power P (in Watts) along the Y axis and rotational speed ω (in radians / second) along the X axis. It should be understood that there are an infinite number of speed / power curves, and for the sake of clarity, the figure shows only three curves. Curve C vmax Corresponding to the wind turbine being able to reach its rated speed ω rated Wind speed ν max The figure also shows the ideal trajectory T for this wind turbine type. ideal Along this ideal trajectory T ideal Each point of is the maximum value of the speed / power curve. vmax , rated speed ω rated Associated with output power P0.

[0050] Using the existing control technology, only for less than ν max The wind speed follows the ideal trajectory T ideal If the wind speed increases beyond ν max , the rotation speed is maintained at the rated value ω rated , and any increase in power output must follow the vertical trajectory T CSZ, and can only be achieved by equipping the rotor blades with physical additions such as serrations, vortex generators, etc. vmax Starting from the maximum value, the output power can theoretically increase from the initial level P0 to its rated output power P rated . In the bounds P0–P rated In this “constant speed region” defined, the output power follows a suboptimal vertical trajectory T CSZ If the wind turbine is not configured to achieve this power boost, the difference between the actual output power and the achievable output power can result in an unnecessary reduction in the AEP.

[0051] Although the present invention has been disclosed in the form of preferred embodiments and variations thereon, it will be understood that numerous additional modifications and variations could be made thereto without departing from the scope of the invention.

[0052] For the sake of clarity, it is to be understood that the use of "a", "an" or "an" throughout this application does not exclude a plurality, and "comprising" does not exclude other steps or elements. References to a "unit" or "module" do not exclude the use of more than one unit or module.

Claims

1. A control device (2) for a variable speed wind turbine (3), the variable speed wind turbine (3) being configured to meet the requirements of wind levels defined by IEC 61400-1, the control device (2) comprising: - a load analysis module (10) configured to analyze a plurality of environmental values ​​(10_1, . . . , 10_n) to determine when the rotation speed of the pneumatic rotor (30) has reached its rated speed (ω rated ), whether the instantaneous wind turbine load (L) is lower than the load threshold (L max ), the rated speed (ω rated ) is less than the rated output power (P rated ) is associated with an output power level (P0); and a speed boost module (11) configured to increase the speed of the wind turbine when the wind turbine load (L) is below the load threshold (L max ), the speed increment (ω inc ) is applied to the rotational speed of the pneumatic rotor (30), and wherein the power / speed relationship (T SB ) follows the ideal trajectory of the wind turbine (T ideal ), the ideal trajectory (T ideal ) is the curve defined by the maximum value of the speed / power curve.

2. The control device according to claim 1, wherein: The environmental values ​​(10_1, . . . , 10_n) include any one of the following: a blade load value, a turbulence intensity value, a tower acceleration value, and a yaw position value.

3. The control device according to claim 1 or 2, wherein: The load analysis module (10) is configured to receive a pitch position value (10_5), an active power value (10_6) and a rotor speed value (10_7).

4. The control device according to claim 3, wherein: The load analysis module (10) comprises a turbulence estimator unit (101) configured to estimate the local turbulence intensity based on the pitch position value (10_5), the active power value (10_6) and the rotor speed value (10_7).

5. The control device according to claim 1 or 2, wherein: The load analysis module (10) is configured to process environmental values ​​(10_1, . . . , 10_n) according to relevant threshold values ​​(ST).

6. The control device according to claim 1 or 2, wherein: The load analysis module (10) is configured to calculate a partial contribution (C1, ..., C5) of each environmental value (10_1, ..., 10_n), and based on the sum (10 total ), so that through the speed increment (ω inc ) to increase the rotation speed.

7. The control device according to claim 1 or 2, wherein: The load analysis module (10) is configured to determine the wake exposure (10) of the wind turbine (3) WE ), and based on the wake exposure (10 WE ), so that through the speed increment (ω inc ) to increase the rotation speed.

8. The control device according to claim 1 or 2, wherein: The speed increase module (11) is configured to determine a speed increment (ω) based on an estimated turbulence level and / or an estimated load level. inc ) size.

9. A variable speed wind turbine (3), comprising: A control device (2) according to any one of claims 1 to 8; and a summing module (20S) configured to increase the speed reference (20ω) by a speed increment (ω inc ).

10. A variable speed wind turbine (3) according to claim 9, configured to meet the requirements of turbulence levels and / or wind levels defined by IEC 61400-1.

11. A method of operating a variable speed wind turbine (3), the method comprising the steps of: - Determine when the rotation speed of the pneumatic rotor (30) has reached its rated speed (ω rated ), whether the instantaneous wind turbine load (L) is lower than the load threshold (L max ), the rated speed (ω rated ) is less than the rated output power (P rated ) is associated with an output power level (P0); and - If the wind turbine load (L) is below the load threshold (L max ), then based on the ideal trajectory (T ideal ), to determine the speed increment (ω) of the rotation speed of the pneumatic rotor (30) inc ), the ideal trajectory (T ideal ) is the curve defined by the maximum value of the speed / power curve; as well as - through the speed increment (ω inc ) to increase the rotor speed.

12. The method according to claim 11, comprising increasing the speed reference (20ω) by the speed increment (ω inc ) steps.

13. The method according to claim 11 or 12, comprising identifying a wake exposure (10 WE ) steps.

14. The method according to claim 13, wherein: The rotational speed of the aerodynamic rotor (30) is increased only when the wind turbine (3) is not in the wake of another wind turbine.

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