Method of controlling a wind turbine and controller for a wind turbine

Abstract

A method for controlling a wind turbine (1) is described, wherein a minimum required hydraulic pressure represents the hydraulic pressure of at least one accumulator of the wind turbine (1), the hydraulic pressure of the at least one accumulator being required to pitch at least one blade (4) of the wind turbine (1) associated with the accumulator into a parked position (530, 630) of the wind turbine (1), and wherein a pitch angle represents the pitch angle of the normal of the at least one blade (4) of the wind turbine (1) relative to the incoming wind direction. The method comprises: (a) determining a minimum demand function (210) of the minimum required hydraulic pressure depending on the pitch angle; (b) detecting the current hydraulic pressure in the at least one accumulator at the current pitch angle of the at least one blade (4); and (c) controlling the wind turbine (1) such that the current hydraulic pressure is higher than the minimum required hydraulic pressure at the current pitch angle. Furthermore, a controller for the wind turbine (1) is described.

Description

Technical Field

[0001] The invention relates to a method of controlling a wind turbine. Furthermore, the invention relates to a controller for a wind turbine. Background Art

[0002] In the technical field of controlling wind turbines, it is generally known to use hydraulic accumulators and pumps to pitch the blades. The hydraulic accumulators and pumps are sized to deliver sufficient oil and pressure under almost all operating conditions. However, there may be situations in which this sizing is close to a limit or insufficient due to damaged hardware (such as, for example, a damaged accumulator or a damaged pump). This may result in a hydraulic pressure approaching a shutdown limit, which is continuously monitored by the turbine controller. The shutdown limit can be defined in each wind turbine by a pressure level at which the wind turbine can reach a safe stopping position (which may be during an emergency stop) and / or at which the wind turbine can have sufficient force and speed to pitch at least one blade during operation and during a normal stopping process.

[0003] When the hydraulic pressure drops below the shutdown level in current wind turbines, the wind turbine shuts down.While the minimum pressure to achieve the two above defined objectives varies with pitch angle, today the shutdown level is monitored by a single threshold for all pitch angles.

[0004] In today's wind turbines, hydraulic systems are optimized to require a minimum number of accumulators and pumps for operation. For rotor upgrade projects, the same hydraulic design is often used, pushing it even further toward the shutdown limit. Consequently, in some cases, insufficient pressure may be available for the startup sequence. Consequently, a lower pitch-in speed may be necessary during the startup sequence to maintain pressure above the shutdown limit. This can lead to increased startup times and an increased risk of shutdown during the startup sequence.

[0005] Furthermore, in today's wind turbines, if a hydraulic pump fails, the pressure may not remain above the shutdown limit, but may instead drop below it, due to, for example, only two of the three pumps being operational. Consequently, a failed pump can cause the turbine to shut down. Particularly in offshore installations, replacing a damaged component can be cost- and time-intensive, particularly due to weather conditions (e.g., high winds or rough seas).

[0006] Therefore, in current wind turbines, the wind turbine may have long downtime and low availability due to conventional methods.

[0007] Therefore, it may be desirable to provide a method of controlling a wind turbine such that low downtime of the wind turbine and at the same time high availability can be ensured. Summary of the Invention

[0008] This need may be met by the subject matter according to aspects of the present disclosure.Further aspects of the present disclosure describe advantageous embodiments of the invention.

[0009] According to a first aspect of the present invention, a method for controlling a wind turbine is provided, wherein a minimum required hydraulic pressure represents a hydraulic pressure in at least one accumulator of the wind turbine, the hydraulic pressure in the at least one accumulator being required to pitch at least one blade of the wind turbine associated with the accumulator into a parked position of the wind turbine, and wherein a pitch angle represents a pitch angle of a normal to the at least one blade of the wind turbine relative to an incoming wind direction. The method comprises: determining a minimum demand function for the minimum required hydraulic pressure depending on the pitch angle; detecting a current hydraulic pressure in the at least one accumulator at a current pitch angle of the at least one blade; and controlling the wind turbine such that the current hydraulic pressure is above the minimum required hydraulic pressure at the current pitch angle.

[0010] The described method is based on the idea of ​​using an active method for controlling a wind turbine, in which availability losses due to overly restrictive settings on the hydraulic system or due to damaged hydraulic pumps and / or accumulators can be reduced. Thus, active control of the wind turbine can be provided, resulting in increased availability times.

[0011] This can lead to an increase in the energy production of the wind turbine. Consequently, lower energy costs are possible. The increased overall power production within the wind farm, combined with lower fatigue loads due to higher turbulence levels, can lead to reduced fatigue loads, allowing for optimized structural design and, consequently, reduced costs.

[0012] Additionally, this can lead to the possibility of eliminating (costing out) a physical component (e.g., an accumulator or pump). This could result in, for example, two pumps instead of three, or two hydraulic accumulators instead of three. Consequently, the wind turbine design can be implemented closer to the shutdown limit. Any elimination of a component (e.g., a hydraulic accumulator or a hydraulic pump) can save on wind turbine production and maintenance costs.

[0013] Typically, energy generated above the committed availability level is shared between the wind turbine consumer and the wind turbine manufacturer. Availability losses below the committed availability level are paid for by the wind turbine manufacturer. Therefore, any availability above the committed availability level may be paid for by the wind turbine manufacturer.

[0014] The parked position of the wind turbine may denote a position of the at least one blade, in which position the wind turbine is unable to extract wind energy from the incoming wind because the at least one blade is pitched into the incoming wind.

[0015] The normal to the at least one blade of the wind turbine may denote a direction extending perpendicular to a chord of the blade of the wind turbine.A chord is defined as a straight line interconnecting a leading edge and a trailing edge of a blade.

[0016] The pitch angle can be defined as the angle between the normal of the blade and the incoming wind field. Thus, a pitch angle of 0° can indicate that the blades are pitched into the incoming wind and are in the operating position. In other words, the blades are in the active position or working position. In the operating position, the wind turbine can extract energy from the wind. Correspondingly, a pitch angle of 90° can indicate that the blades are pitched away from the incoming wind and are in the parked position. In the parked position, the wind turbine cannot extract energy from the incoming wind. Therefore, in the parked position, the blades of the wind turbine are not rotating or are idle (rotating at a low speed).

[0017] The wind direction may represent an average wind direction, which may be regarded as the main direction of the wind field hitting the wind turbine.

[0018] The minimum required hydraulic pressure may be based on a maximum pressure at which there is enough oil in the at least one accumulator to reach a safe stopping position of the wind turbine or sufficient force to pitch the at least one blade at a minimum pitch adjustment speed. The minimum required hydraulic pressure may be defined as representing (in other words, following) the maximum of the two pressures.

[0019] According to an exemplary embodiment of the present invention, the method further comprises: determining an offset minimum demand function, which is offset from the minimum demand function by a predetermined positive offset and represents a function of the offset minimum required hydraulic pressure depending on the pitch angle; detecting a current hydraulic pressure in the at least one accumulator at a current pitch angle of the at least one blade; determining whether the current hydraulic pressure is higher than the minimum required hydraulic pressure at the current pitch angle and lower than the offset minimum required hydraulic pressure at the current pitch angle, and controlling the wind turbine such that the current hydraulic pressure is higher than the offset minimum required hydraulic pressure at the current pitch angle.

[0020] Providing a predetermined positive offset allows the controller to have a buffer before the wind turbine's hydraulic system can meet the pressure of the minimum demand function. This can lead to a shutdown of the wind turbine, as there may not be sufficient hydraulic pressure in the hydraulic system. Consequently, the wind turbine is shut down to wait until the current pressure is higher than the pressure of the minimum demand function. The buffer provided by the predetermined positive offset allows for avoiding unnecessary shutdowns and thus increases the availability of the wind turbine.

[0021] If the detected current hydraulic pressure is higher than the minimum required hydraulic pressure at the current pitch angle and lower than the offset minimum required hydraulic pressure at the current pitch angle, a so-called low pressure situation may be detected. After detecting the low pressure situation, controlling the wind turbine so that the current hydraulic pressure is higher than the offset minimum hydraulic pressure at the current pitch angle may include two different actions.

[0022] According to a first action of an exemplary embodiment of the present invention, the at least one blade can be pitched from a current pitch angle to another pitch angle, the other pitch angle generally being toward a rest position of the at least one blade. In the rest position, the at least one blade is pitched away from the incoming wind. Thus, the at least one blade is pitched away from the wind. After pitching away, the controller controls the at least one blade so that the pitch angle does not change until the current pressure at the current pitch angle is again above the offset minimum demand function. Thereafter, the wind turbine can be set back to normal operation.

[0023] According to a second action of a further exemplary embodiment of the present invention, the pitch adjustment speed of the at least one blade of the wind turbine is adapted. For example, the pitch adjustment speed toward the operating position (at a pitch angle of 0°) is reduced to prevent stalling, while the pitch adjustment speed toward the idle position may be unaffected. This may allow the controller of the wind turbine to pitch the at least one blade away from the incoming wind at rated wind speed, for example, in situations where a gust of wind strikes the at least one blade. Consequently, rotor overspeed and high component loads may be prevented, since pitching the at least one blade away may reduce the hydraulic pressure required for the minimum deflection.

[0024] According to another example, the pitch adjustment speed towards the stop position (at a pitch angle of 90°) is reduced to enable the hydraulic system to increase the current hydraulic pressure.

[0025] According to an exemplary embodiment of the present invention, the minimum demand function is determined by segment-by-segment linear interpolation and / or segment-by-segment exponential interpolation.

[0026] The interpolation may be based on different scenarios that may occur at the at least one blade of the wind turbine and are illustrated as required hydraulic pressure in the at least one accumulator to enable the at least one blade to be pitched from a current pitch angle to a parked position pitch angle (90°).

[0027] According to an exemplary embodiment of the present invention, the distance between the minimum demand function and the offset minimum demand function is constant along the pitch angle.

[0028] Providing a constant distance along the pitch angle can make it possible to have a similar and sufficient offset buffer at each current pitch angle, so that the controller can control the wind turbine so that the current hydraulic pressure is above the minimum required hydraulic pressure at the current pitch angle. At the same time, the time required to determine whether the current hydraulic pressure is above the minimum required hydraulic pressure and below the offset minimum required hydraulic pressure at the current pitch angle can be kept short.

[0029] According to another exemplary embodiment of the present invention, the distance between the minimum demand function and the shifted minimum demand function may be line / limit calculated, in particular in order to fit the system.

[0030] According to a further embodiment of the invention the controlling comprises adapting a pitch adjustment speed of at least one blade of the wind turbine.

[0031] Adapting the pitch control speed can provide the possibility that the pitch control speed can depend on the remaining reaction time. Thus, on the one hand, if there is still enough time left for a reaction, for example if the current hydraulic pressure at the current pitch angle is still closer to the deviated minimum demand function than the minimum demand function, the pitch control speed can be kept low so that the hydraulic system can be refilled more slowly. On the other hand, if there is only a short time left for a reaction, for example if the current hydraulic pressure at the current pitch angle is closer to the minimum demand function than the deviated minimum demand function, the pitch control speed can be high so that the pressure in the hydraulic system drops more slowly and the hydraulic system has enough time to be refilled again.

[0032] According to a further exemplary embodiment, the adapting of the pitch adjustment speed comprises adapting the pitch adjustment speed towards a park position of the at least one blade of the wind turbine and / or adapting the pitch adjustment speed towards an operating position of the at least one blade of the wind turbine.

[0033] The park position of the at least one blade of the wind turbine may be a position in which the at least one blade is pitched out of the wind, eg a position in which the current pitch angle may be 90°.

[0034] The operating position of the at least one blade of the wind turbine may be a position in which the at least one blade is pitched into the wind, eg a position in which the current pitch angle may be 0°.

[0035] Adapting the pitch adjustment speed towards the park position or towards the operating position may provide the possibility to individually adapt the pitch adjustment speed that has to be adapted to maintain safe operation of the wind turbine.Thereby, non-mandatory control actions of the controller may be suppressed.

[0036] Adapting the pitch adjustment speed towards the operating position and towards the parked position may provide the possibility of reacting quickly to pressure losses occurring in the hydraulic system of the wind turbine. Thus, the availability of the wind turbine may be ensured.

[0037] According to a further exemplary embodiment of the present invention, the adaptation of the pitch adjustment speed defines a pitch adjustment speed that is dependent on the current hydraulic pressure.

[0038] Defining a pitch adjustment speed that depends on the current hydraulic pressure allows for the following: if the current hydraulic pressure approaches the minimum demand function, the pitch adjustment speed can be slowed down to minimize the pressure drop. This increases the availability of the wind turbine. If the current hydraulic pressure approaches a deviation from the minimum demand function, the pitch adjustment speed can be maintained. This allows for faster pitch control.

[0039] According to an exemplary embodiment of the present invention, the pitch adjustment speed is varied linearly or exponentially depending on the current hydraulic pressure.

[0040] Varying the pitch adjustment speed linearly may provide an adaptation of the pitch adjustment speed that is easy to implement and control.

[0041] Exponentially varying the pitch adjustment speed may provide an adaptation of the pitch adjustment speed, which provides an individually adapted pitch adjustment speed.

[0042] According to an exemplary embodiment, the pitch adjustment speed is changed stepwise depending on the current hydraulic pressure. This may provide the possibility of adapting the pitch adjustment speed in a fast manner.

[0043] According to an exemplary embodiment of the invention, towards the operating position of the at least one blade of the wind turbine the pitch adjustment speed is dependent on the current hydraulic pressure changing from 100% of the minimum required hydraulic pressure to 0% of the minimum required hydraulic pressure.

[0044] Changing the pitch adjustment speed from 100% of the minimum required hydraulic pressure to 0% of the minimum required pressure towards the operational position ensures that the hydraulic system can be recharged at a current hydraulic pressure close to the shutdown level before the pitch angle is further adapted. This prevents downtime of the wind turbine and increases its availability. At the same time, when the current hydraulic pressure is close to the minimum required pressure, the pitch angle can be adapted as quickly as possible. Consequently, the operational position of the at least one blade can be reached quickly, and the wind turbine's energy production can be increased.

[0045] In other words, when pitching towards the operational position, and when the current hydraulic pressure is below the minimum required hydraulic pressure for excursion at the current pitch angle, the pitch adjustment speed may be reduced (eg, linearly) from 100% of the nominal pitch adjustment speed to 0°.

[0046] According to an exemplary embodiment of the invention, towards a parking position of the at least one blade of the wind turbine the pitch adjustment speed is dependent on a current hydraulic pressure shifting from 50% of the minimum required hydraulic pressure to 0% of the minimum required hydraulic pressure.

[0047] In other words, when pitching towards the stop position and no hazardous situation is detected (eg, rotor speed approaching an overspeed limit), the pitch adjustment speed may be reduced (eg, linearly) from 50% of the nominal pitch adjustment speed to 0°.

[0048] Changing the pitch adjustment speed from 50% of the minimum required hydraulic pressure to 0% of the minimum required pressure towards the stop position ensures that the hydraulic system can be recharged at the current hydraulic pressure close to the stop level before the pitch angle is further adapted. This prevents wind turbine shutdowns and increases wind turbine availability. At the same time, when the current hydraulic pressure approaches the minimum required pressure, the pitch angle can be adapted, ensuring additional energy production.

[0049] According to another aspect of the present invention, a controller for a wind turbine is provided, wherein a minimum required hydraulic pressure represents the hydraulic pressure of at least one accumulator of the wind turbine, the hydraulic pressure of the at least one accumulator being required to pitch at least one blade of the wind turbine associated with the accumulator to a parked position of the wind turbine, and wherein a pitch angle represents the pitch angle of a normal to the at least one blade of the wind turbine relative to the direction of the incoming wind. The controller comprises (a) determining means for determining a minimum demand function, the minimum demand function determining a minimum pressure value of the minimum required hydraulic pressure depending on the pitch angle; (b) detecting means for detecting a current hydraulic pressure in the at least one accumulator at a current pitch angle of the at least one blade; and (c) controlling means for controlling the wind turbine such that the current hydraulic pressure is higher than the minimum required hydraulic pressure at the current pitch angle.

[0050] Furthermore, the described controller is based on the concept of using an active method for controlling a wind turbine, in which availability losses due to overly stringent settings on the hydraulics or due to damaged hydraulic pumps and / or accumulators can be reduced. Thus, active control of the wind turbine can be provided, resulting in increased availability time.

[0051] This can lead to an increase in the energy production of the wind turbine. Consequently, lower energy costs are possible. The increased overall power production within the wind farm, combined with lower fatigue loads due to higher turbulence levels, can lead to reduced fatigue loads, allowing for optimized structural design and, consequently, reduced costs.

[0052] Additionally, this can lead to the possibility of eliminating a physical component (e.g., an accumulator or a pump). This could result in, for example, two pumps instead of three, or two hydraulic accumulators instead of three. Thus, a wind turbine design can be implemented closer to the shutdown limit.

[0053] In the following, some exemplary ideas of the present invention are described.

[0054] In the case where a wind turbine uses at least one blade sensor for individual pitch control (IPC), an additional component can be added to the collective pitch angle to reduce tilt or yaw loads. If IPC continues for too long, the hydraulic system of the wind turbine may be drained and the wind turbine may reach close to the minimum required hydraulic pressure. Therefore, the IPC amplitude can be reduced to prevent turbine shutdown. Therefore, by controlling the wind turbine so that the current hydraulic pressure is above the minimum required hydraulic pressure determined according to embodiments of the present invention, the wind turbine can have increased availability at the current pitch angle.

[0055] Furthermore, providing a method for controlling a wind turbine according to an embodiment of the present invention can make it possible to eliminate one of at least two hydraulic pumps in a wind turbine (e.g., one of three hydraulic pumps in a direct-drive wind turbine) for use only in startup, shutdown, gusty wind conditions, and / or redundancy. If the pitch adjustment speed is too fast for the hydraulic system to keep up, the pitch adjustment speed is adjusted instead of shutting down the wind turbine. Consequently, the robustness of the wind turbine can be increased, and thus the availability of the wind turbine can be increased.

[0056] Furthermore, the method of controlling a wind turbine may provide the possibility of a robust wind turbine configuration, in which the controller is less sensitive to configuration errors during startup situations and the wind turbine is designed closer to its limits which may result in a reduced cost of the wind turbine.

[0057] It should be noted that embodiments of the present invention have been described with reference to different subject matters. In particular, some embodiments have been described with reference to method-type solutions, while other embodiments have been described with reference to apparatus-type solutions. However, a person skilled in the art will appreciate from the above and following description that, unless otherwise indicated, any combination of features relating to different subject matters, in addition to any combination of features belonging to one type of subject matter, in particular any combination of features of method-type solutions and features of apparatus-type solutions, is also considered to be disclosed in the context of this document.

[0058] The aspects defined above and further aspects of the invention are apparent from the examples of embodiment to be described hereinafter and are explained with reference to the examples of embodiment.The invention will be described in more detail hereinafter with reference to examples of embodiment but to which the invention is not limited. BRIEF DESCRIPTION OF THE DRAWINGS

[0059] Figure 1 A schematic cross section of a wind turbine is shown, to which the control method and controller of the present invention may be applied to control the wind turbine.

[0060] Figure 2 A diagram illustrating how a wind turbine control according to an embodiment of the invention is operated is shown.

[0061] Figure 3 A diagram illustrating how wind turbine control according to an embodiment of the present invention may prevent a wind turbine shutdown is shown.

[0062] Figure 4 A diagram illustrating how a wind turbine control according to a further embodiment of the invention is operated is shown.

[0063] Figure 5Shown is a diagram illustrating how pitch regulation speed adaptation according to an embodiment of the invention is operated.

[0064] Figure 6 Shown is a diagram illustrating how pitch regulation speed adaptation according to a further embodiment of the invention is operated.

[0065] Figure 7 A diagram illustrating how wind turbine control according to a further embodiment of the invention may prevent a wind turbine shutdown is shown.

[0066] Figure 8 A diagram illustrating how wind turbine control according to a further embodiment of the invention may prevent a wind turbine shutdown is shown. DETAILED DESCRIPTION

[0067] The illustrations in the accompanying drawings are schematic. It should be noted that in different figures, similar or identical elements or features are provided with the same reference symbols or with reference symbols that differ from the corresponding reference symbols only within the first digit. To avoid unnecessary repetition, elements or features that have already been explained with reference to previously described embodiments will not be explained again at a later point in this description.

[0068] Figure 1 A wind turbine 1 according to the invention is shown. The wind turbine 1 comprises a tower 2 mounted on a foundation (not depicted). A nacelle 3 is arranged on top of the tower 2. The wind turbine 1 further comprises a wind rotor 5 (at Figure 1 In the embodiment of FIG. 5 , the wind rotor comprises three blades 4 , of which only two blades 4 are visible. The wind rotor 5 is rotatable about an axis of rotation Y. The blades 4 extend substantially radially with respect to the axis of rotation Y and along a respective longitudinal axis X.

[0069] The wind turbine 1 comprises a generator 11 comprising a stator 20 and a rotor 30. The rotor 30 is rotatable relative to the stator 20 about an axis of rotation Y. The wind rotor 5 is driven either directly (e.g., directly) or by means of a rotatable main shaft 9 and / or through a gearbox ( Figure 1 The main shaft 9 is rotatably coupled to the generator 11 (not shown). A schematically depicted bearing assembly 8 is provided to hold the main shaft 9 and the rotor 5 in place. The rotatable main shaft 9 extends along an axis of rotation Y.

[0070] Wind rotor 5 includes three flanges 15 for connecting respective blades 4 to wind rotor 5. A pitch bearing is interposed between each blade flange 15 and the respective blade 4. A hydraulic pitch actuation circuit is associated with the pitch bearings of blades 4 for adjusting the pitch angle of each blade, i.e., the angular position of each blade about the respective blade longitudinal axis X. The hydraulic pitch actuation circuit can adjust all pitch angles on all rotor blades 4 simultaneously, and / or individual pitch adjustment of rotor blades 4 may be possible.

[0071] Wind turbine 1 includes a controller (not shown) having a processor and memory. The processor performs computational tasks based on instructions stored in the memory. Based on these tasks, the wind turbine generates a requested power output level during operation. Furthermore, the wind turbine avoids emergency shutdowns during operation and maintains the current hydraulic pressure above the minimum required hydraulic pressure, particularly above the offset minimum hydraulic pressure.

[0072] Figure 2 A minimum demand function 210 is shown, which can be generated by a controller for controlling the wind turbine 1. All functions are illustrated as functions of pressure p depending on the pitch angle α. The dashed line illustrates a first pressure function 220 based on simulated blade forces, which the hydraulic system of the wind turbine 1 needs to overcome in order to be able to pitch at least one blade 4 at a minimum speed. The dashed line shows a second pressure function 230, which the hydraulic system of the wind turbine 1 needs to be able to reach a safe stop position. According to Figure 2 In the embodiment shown in , the second pressure function 230 represents a lower pressure value than the first pressure function 220, because in the case of reaching a safety stop position, the safety accumulator can help so that the required pressure is lower. Figure 2 In the present embodiment shown in , the minimum demand function 210 is determined by segment-by-segment linear interpolation of the first pressure function 220 .

[0073] The minimum demand function 210 includes a first section 211 that is constant at a third pressure p3 within a pitch angle range extending from a first pitch angle α1 to a second pitch angle α2. The first pitch angle α1 is 0° and represents the operating position of the at least one blade 4. In the operating position, the normal to the chord of the at least one blade 4 and the incoming wind direction enclose a pitch angle α1 of 0°. The minimum demand function 210 further includes a second section 212 and a third section 213, wherein the second section 212 extends between the first section 211 and the third section 213. The second section 212 is determined by linear interpolation from the third pressure p3 at the second pitch angle α2 to the second pressure p2 at the third pitch angle α3, wherein the second pressure p2 is lower than the third pressure p3 and the second pitch angle α2 is less than the third pitch angle α3. In the exemplary embodiment, the third pitch angle α3 is equal to 20°. Third section 213 is defined by linear interpolation extending from second pressure p2 at a third pitch angle α3 to first pressure p1 at a fourth pitch angle α4, where first pressure p1 is lower than second pressure p2 and third pitch angle α3 is less than fourth pitch angle α4, which in the exemplary embodiment is 90°. When fourth pitch angle α4 is 90°, at least one blade 4 is in a stopped position. In the stopped position, where fourth pitch angle α4 is 90°, the normal to at least one blade 4 and the incoming wind direction enclose a fourth pitch angle 4 of 90°. In other words, at least one blade 4 is turned into the wind, and at least one blade 4 of wind turbine 1 stops rotating.

[0074] from Figure 2 As can be seen in FIG. 2 , the minimum demand function 210 is always at least on or above the first pressure function 220 of the wind turbine 1 .

[0075] Figure 3 As shown above, Figure 2 Described is a minimum demand function 210 , and a hydraulic function 340 of the wind turbine 1 , which represents the required hydraulic pressure p in the at least one accumulator depending on the pitch angle α of the wind turbine.

[0076] The minimum demand function 210 is obtained by combining the above Figure 2 The segment-by-segment linear interpolation is described. Figure 3 The hydraulic function 340 illustrated in illustrates the hydraulic pressure p in dependence on the pitch angle α of the wind turbine 1. When a gust of wind hits the wind turbine 1, a large number of pitch activities from the controller of the wind turbine 1 may be required.

[0077] At a first system state 341, a gust of wind hits the wind turbine. The actual pressure when the gust hits the wind turbine 1 is p7 at a pitch angle α7. Due to the gust of wind, at least one blade 4 is pitched away, and the hydraulic pressure drops from pressure p7 to a pressure p5 which is lower than pressure p7. At the same time, due to this pitching away, the pitch angle α5 at a second system state 342 is greater than the pitch angle α7. Due to the detection of the lower pressure p5, at least one pump of the wind turbine 1 is activated and starts adding hydraulic pressure to at least one accumulator. This Figure 3 This is illustrated in third system state 343. During the reaction of wind turbine 1, which takes time, pressure p8 in third system state 343 at pitch angle α8 is lower than pressure p5 in second system state 342. At the same time, the pitch shift continues from second system state 342 to third system state 343.

[0078] When the gust of wind has passed and / or sufficient pressure has been added to the hydraulic accumulator of wind turbine 1, the pressure increases again from pressure p8 in third system state 343 to pressure p9 in fourth system state 344. Due to the reaction time of wind turbine 1, pitch angle α9 in fourth system state 344 is greater than pitch angle α8 in third system state 343. Thereafter, the pressure increases further, reaching pressure p6 in fifth system state 345. Additionally, at least one blade 4 of wind turbine 1 is pitched in again. Consequently, pitch angle α6 of at least one blade 4 is less than pitch angle α9 in fourth system state 344.

[0079] All hydraulic pressure values ​​of the first, second, third, fourth, and fifth system states 341 , 342 , 343 , 344 , and 345 are above the minimum demand function 210 , so that a shutdown due to too low available hydraulic pressure of the wind turbine 1 can be prevented.

[0080] Figure 4 A shifted minimum demand function 410 is shown, which may be generated by a controller for controlling the wind turbine 1 .

[0081] In combination with the above Figure 2 After the minimum demand function 210 is generated by the controller as described, the minimum demand function 410 is offset by a predetermined positive offset 420 that is constant and has a value of, for example, 10 bar. The minimum demand function 210 may be a shutdown level at which the wind turbine is shut down. The offset minimum demand function may be defined as the predetermined positive offset 420 from the minimum demand function 210.

[0082] Minimum demand function 210 is linear segment by segment and correspondingly offset minimum demand function 410 is linear segment by segment. Additionally, predetermined positive offset 420 is constant and thus the distance between minimum demand function 210 and offset minimum demand function 410 is constant along pitch angle α.

[0083] like Figure 4 , at a first pitch angle α1, the minimum demand function includes a first pressure pi, and the offset minimum demand function 410 includes a second pressure p2 that is offset from the minimum demand function 210 by a predetermined positive offset 420. The same is true for a second pitch angle α2, where at the second pitch angle α2, the minimum demand function 210 includes a third pressure p3 that is lower than the first pressure pi and the second pressure p2, and the offset minimum demand function 410 includes a fourth pressure p4 that is offset from the minimum demand function 210 by a predetermined positive offset 420. The predetermined positive offset 420 is the same at the first pitch angle α1 and the second pitch angle α2.

[0084] Figure 5 As shown above, Figure 4 The minimum demand function 210 and the offset minimum demand function 410 are described. Additionally, Figure 5 , the pitch adjustment speed towards the stop position 530 and the pitch adjustment speed towards the operating position 560 are depicted.

[0085] The pitch adjustment speed toward the stop position 530 does not change depending on the hydraulic pressure and is set to 100%. The pitch adjustment speed toward the operating position 560 changes / scales linearly from 100% at the second pressure p2, which is the minimum required hydraulic pressure for the offset, to 0% at the first pressure p1, which is the minimum required pressure.

[0086] Figure 6 As shown above, Figure 4 The minimum demand function 210 and the offset minimum demand function 410 are described. Additionally, Figure 6 , the pitch adjustment speed towards the stop position 630 and the pitch adjustment speed towards the operating position 560 are depicted.

[0087] The pitch adjustment speed toward the operating position 560 changes / scales linearly from 100% at the second pressure p2, which is the minimum required hydraulic pressure for the offset, to 0% at the first pressure p1, which is the minimum required pressure. Additionally, the pitch adjustment speed toward the stop position 630 can be reduced to 50% of the nominal pitch adjustment speed as long as the operating conditions are considered safe. Thus, the pitch adjustment speed toward the stop position 630 represents the pitch departure speed and changes / scales linearly from 100% at the second pressure p2, which is the minimum required hydraulic pressure for the offset, to 50% at the first pressure p1, which is the minimum required pressure. Thus, in a situation where the rotor is approaching an overspeed limit, the limit on the pitch adjustment speed can be removed.

[0088] Figure 7 As shown above, Figure 2 The minimum demand function 210 described above is combined with Figure 4 The depicted offset minimum demand function 410 and a hydraulic function 740 of the wind turbine 1 , which represents the required hydraulic pressure in the at least one accumulator depending on the pitch angle α of the wind turbine 1 .

[0089] During startup, wind turbine 1 starts in a first system state 741 defined by a first pitch angle α1 of 86° and a first pressure p1 comprising a nominal pressure. In subsequent steps, at least one blade 4 is pitched until a second system state 742 can be reached. Second system state 742 is defined by a second pressure p2 and a second pitch angle α2 of, for example, 60°, the second pressure p2 comprising a lower pressure than the first pressure p1. In second system state 742, pitching is stopped, and hydraulic pressure is added to at least one accumulator via at least one hydraulic pump until a third system state 743 is reached, defined by the second pitch angle α2 and the first pressure p1. Only when third system state 743 is reached will at least one blade 4 continue to be pitched toward the operating position.

[0090] In the event of a damaged pump, or if the hydraulic system (either the at least one accumulator or the at least one hydraulic pump) is slightly undersized, the at least one hydraulic pump may not maintain a pressure above the minimum required pressure for the offset defined by the offset minimum demand function 410. Consequently, a fourth system state 744 is reached, defined by a fourth pressure p4 and a fourth pitch angle α4, which is equal to the minimum required pressure for the offset at the fourth pitch angle α4. In the next step, the controller controls wind turbine 1 so that the pitch adjustment speed is slowed down so that the current hydraulic pressure remains above the minimum required hydraulic pressure defined by the minimum demand function 210. Consequently, a fifth system state 745 is reached, defined by a fifth pressure p5 and a fifth pitch angle α5. The fifth pressure p5 is below the offset minimum demand function 410 and above the minimum demand function 210. Consequently, wind turbine 1 continues to operate without shutting down.

[0091] The pitch adjustment speed then follows the maximum hydraulic pump capacity present in the wind turbine 1 and is pitched further towards the production position. Figure 7 , which is represented by a sixth system state 746 in FIG. 7 , which is defined by a sixth pressure p6 and a sixth pitch angle α6, wherein the sixth pressure p6 is higher than the fifth pressure p5 and still lower than the minimum required pressure for the excursion at the sixth pitch angle α6. In the operating position, a seventh system state 747 is reached, which is defined by a seventh pressure p7 and a seventh pitch angle α7, wherein the seventh pressure p7 is higher than the sixth pressure p6 and higher than the minimum required pressure for the excursion function 410, and the seventh pitch angle α7 is equal to the nominal pitch angle (e.g., 1°) at the generation position.

[0092] Figure 8 As shown above, Figure 2 The minimum demand function 210 described above is combined with Figure 4 The depicted offset minimum demand function 410 and a hydraulic function 840 of the wind turbine 1 , which represents the required hydraulic pressure in the at least one accumulator depending on the pitch angle α of the wind turbine.

[0093] In the event of a damaged hydraulic pump, the wind turbine 1 can generate power in limp mode to ensure higher availability than in a complete shutdown. Similarly, in the event of severe gusts in which at least one blade 4 requires a greater pitching distance than is accounted for in the design of the wind turbine 1, a shutdown can be suppressed.

[0094] In a first system state 841, wind turbine 1 is operating in an operational position at a first pressure p1 and a first pitch angle α1 during normal operation. Subsequently, when a severe gust of wind strikes at least one blade 4 during normal operation or a small gust of wind strikes at least one blade 4 during limp home mode, at least one blade 4 is pitched away, and wind turbine 1 reaches a second system state 842 defined by a second pressure p2 and a second pitch angle α2. The second pressure p2 is less than the minimum required hydraulic pressure for deflection defined by the minimum required hydraulic pressure function 410 and greater than the minimum required hydraulic pressure defined by the minimum required hydraulic pressure function 210. The pitch adjustment speed toward the stop position is unaffected, and the pressure continues to decrease during the pitching activity of the at least one blade 4. Consequently, a third system state 843 is reached, defined by a third pressure p3, which is less than the second pressure p2 and the minimum required hydraulic pressure for deflection, but still greater than the minimum required hydraulic pressure, and a third pitch angle α3, which is greater than the second pitch angle α2.

[0095] Subsequently, the pitch adjustment speed toward the operating position decreases, allowing the at least one hydraulic pump to be filled with hydraulic pressure again. A fourth system state 844 is reached, defined by a fourth pressure p4 and a fourth pitch angle α4. The fourth pressure p4 is greater than the minimum required hydraulic pressure for the excursion defined by the minimum required excursion function 410, and the fourth pitch angle α4 is less than the third pitch angle α3 and greater than the second pitch angle α2. The at least one hydraulic pump continues to be filled with hydraulic pressure, reaching a fifth system state 845 defined by a fifth pressure p5 and a fifth pitch angle α5 of, for example, 1°.

[0096] It should be noted that the term "comprising" does not exclude other elements or steps, and the use of the article "a" or "an" does not exclude a plurality. Elements described in conjunction with different embodiments may also be combined. It should also be noted that reference signs in the claims should not be construed as limiting the scope of the claims.

Claims

1. A method of controlling a wind turbine (1), wherein the minimum required hydraulic pressure represents the hydraulic pressure of at least one accumulator of the wind turbine (1) which is required to pitch at least one blade (4) of the wind turbine (1) associated with the accumulator into a parked position (530, 630) of the wind turbine (1), wherein the pitch angle denotes the pitch angle of the normal of the at least one blade (4) of the wind turbine (1) relative to the direction of the incoming wind, The method comprises: a minimum demand function (210) for determining a minimum required hydraulic pressure depending on the pitch angle, detecting a current hydraulic pressure in the at least one accumulator at a current pitch angle of the at least one blade (4), controlling the wind turbine (1) so that the current hydraulic pressure is higher than the minimum required hydraulic pressure at the current pitch angle; wherein the method further comprises: determining a shift minimum demand function (410) which is offset from the minimum demand function (210) by a predetermined positive offset (420) and represents a function of the shift minimum required hydraulic pressure as a function of the pitch angle, detecting a current hydraulic pressure in the at least one accumulator at a current pitch angle of the at least one blade (4), determining whether the current hydraulic pressure is above the minimum required hydraulic pressure at the current pitch angle and below the offset minimum required hydraulic pressure at the current pitch angle, The wind turbine (1) is controlled so that the current hydraulic pressure is higher than the hydraulic pressure required for the minimum deflection at the current pitch angle.

2. The method according to claim 1, The minimum demand function (210) is determined by segment-by-segment linear interpolation and / or segment-by-segment exponential interpolation.

3. The method according to claim 1, Wherein a distance between the minimum demand function (210) and the offset minimum demand function (410) is constant along the pitch angle.

4. The method according to claim 1, The control includes: The pitch adjustment speed of at least one blade (4) of a wind turbine (1) is adapted.

5. The method according to claim 4, The adaptation of pitch adjustment speed includes: A pitch adjustment speed is adapted towards a park position (530, 630) of at least one blade (4) of a wind turbine (1) and / or towards an operating position (560) of the at least one blade (4) of the wind turbine (1).

6. The method according to claim 4 or 5, The adaptation of the pitch adjustment speed defines a pitch adjustment speed that depends on the current hydraulic pressure.

7. The method according to claim 6, In this case, the pitch control speed is varied linearly or exponentially depending on the current hydraulic pressure.

8. The method according to claim 4, wherein towards the operating position (560) of the at least one blade (4) of the wind turbine (1), the pitch adjustment speed is dependent on the current hydraulic pressure changing from 100% of the minimum required hydraulic pressure to 0% of the minimum required hydraulic pressure.

9. The method according to claim 4, wherein towards a stop position (530, 630) of the at least one blade (4) of the wind turbine (1), the pitch adjustment speed is dependent on a change in the current hydraulic pressure from 50% of the minimum required hydraulic pressure to 0% of the minimum required hydraulic pressure.

10. A controller for a wind turbine (1), wherein the minimum required hydraulic pressure represents the hydraulic pressure of at least one accumulator of the wind turbine (1) which is required to pitch at least one blade (4) of the wind turbine (1) associated with the accumulator into a parked position (530, 630) of the wind turbine (1), wherein the pitch angle denotes the pitch angle of the normal of at least one blade (4) of the wind turbine (1) relative to the direction of the incoming wind, The controller comprises: determining means for determining a minimum demand function (210), said minimum demand function (210) determining a minimum required hydraulic pressure depending on said pitch angle, Detection means for detecting a current hydraulic pressure in the at least one accumulator at a current pitch angle of the at least one blade (4), A control device for controlling the wind turbine (1) so that the current hydraulic pressure is higher than the minimum required hydraulic pressure at the current pitch angle; Further including: determining means for determining a deviation minimum demand function (410), said deviation minimum demand function (410) being offset from the minimum demand function (210) by a predetermined positive offset (420) and representing a function of the deviation minimum required hydraulic pressure depending on said pitch angle, Detection means for detecting a current hydraulic pressure in the at least one accumulator at a current pitch angle of the at least one blade (4), determining means for determining whether the current hydraulic pressure is higher than the minimum required hydraulic pressure at the current pitch angle and lower than the minimum required hydraulic pressure for offset at the current pitch angle, A control device is provided for controlling the wind turbine (1) so that the current hydraulic pressure is higher than the hydraulic pressure required for minimum deflection at the current pitch angle.

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