Accurate determination of angular position of nacelle of wind turbine

Abstract

A method of determining the angular position of a nacelle (4) of a wind turbine (1) is described, said nacelle (4) being rotatably mounted at the upper end of a tower (3), the lower end of said tower (3) being supported by a foundation (2). The method comprises: obtaining and storing (21) a base angular position corresponding to a base reference point (13), the base angular position being relative to the true north, determining (22) a tower angular position based on the base angular position and information indicative of an angular relationship between the base and the tower, the tower angular position corresponding to a tower reference point (D), and determining (22) a tower angular position corresponding to the true north based on the base angular position and the information indicative of the angular relationship between the base and the tower. The method includes receiving (23) an encoder signal indicative of an angular position of the nacelle (4), detecting (24) until a sensor (15) mounted to the nacelle (4) is located near the tower reference point (D), and in response to the detecting: updating (25) the encoder signal such that the indicated angular position of the nacelle (4) corresponds to the tower angular position. Furthermore, a controller for a wind turbine, a wind turbine and a wind farm are described.

Description

Field of the Invention

[0001] The present invention relates to the field of wind turbine generators, and more particularly to a method for determining the angular position of a nacelle of a wind turbine. In addition, the present invention also relates to a controller for a wind turbine, a wind turbine, and a wind farm. Background Art

[0002] As part of the effort to optimize power production in modern wind farms, field-level control strategies involving so-called wake steering or wake adaptation methods have been developed. These control strategies aim to reduce the impact of the wake of certain wind turbines in a wind farm on other wind turbines. Briefly, the idea is that an upwind wind turbine can be slightly steered (yawed) off the wind direction in order to correspondingly change the wake direction and thus cause less or no wake to the downwind wind turbine behind it. Although this will also result in a slight reduction in power production at the upwind wind turbine, the corresponding increase in power production at the downwind wind turbine (compared to the case where the downwind wind turbine is directly in the wake of the upwind wind turbine) may more than compensate for this reduction and thus result in a net increase in total power production.

[0003] For wind farm control strategies involving wake steering or wake adaptation methods, a mandatory prerequisite is to have very precise information available on the position and orientation (angular position) of each individual wind turbine within the wind farm. For orientation, there must be a common reference between the wind turbines. In the absence of a common reference (e.g., true north), the wind turbines of a wind farm will not be able to know each other's positions and thus will not be able to act in accordance with field-level control strategies that utilize techniques such as wake steering.

[0004] If a wind farm uses wake steering in its field-level control strategy, but the turbines of a given field are not correctly calibrated northward, or if the calibration is too imprecise (e.g., ±2 degrees), then the expected increase in AEP (annual energy production) that may be obtained due to this control strategy may be significantly reduced and may even turn into a direct AEP reduction.

[0005] Existing wind turbines cannot directly determine their orientation relative to true north. This data can only be pushed to the turbines by using extensive, time-consuming, and somewhat uncertain data collection activities.

[0006] Currently, many wind turbines are calibrated towards magnetic north during commissioning using a simple compass. This process is highly inaccurate and does not provide the turbine with the required fixed position of true geographical north, but rather the fluctuating magnetic north. From this point in time, no further calibration is carried out, and due to so-called yaw slip, the yaw position signal of the turbine relative to the estimated magnetic north may drift into further uncertainty (it has been seen that the signals of some turbines show the turbine pointing west at 270 degrees while in reality it was pointing east at 90 degrees at that time).

[0007] One current method of operating a wind farm in an electric field level control strategy or implementing wake steering is to utilize intensive data collection to perform a three-month calibration campaign, in which the true north of the turbine is inferred by comparing the power production of a given turbine for all directions (360 degrees) and comparing it with simulation results. The wake of nearby wind turbines will appear as a dip in the power production curve. By applying a phase shift to this curve to fit it to a similar curve generated by simulation, the yaw offset of a given wind turbine relative to the known GPS position of nearby wind turbines will be equal to the degrees of the phase shift. Thus, the position of the wind turbine relative to true north can be determined. During this three-month data collection campaign, wake steering cannot be deployed, so the wind farm operator will miss out on potential AEP growth during this time period.

[0008] Therefore, a simpler and less expensive (in terms of time, effort, and revenue loss) method may be needed to allow wind farms to effectively utilize wake steering technology. Summary of the Invention

[0009] This need can be met by the subject matter described in the independent claims. Advantageous embodiments of the invention are described by the dependent claims.

[0010] According to a first aspect of the present invention, there is provided a method of determining the angular position of a nacelle of a wind turbine, the nacelle being rotatably mounted at an upper end of a tower, the lower end of the tower being supported by a foundation. The method includes: (a) obtaining and storing a foundation angular position corresponding to a foundation reference point, the foundation angular position being relative to true north, (b) determining a tower angular position based on the foundation angular position and information indicating an angular relationship between the foundation and the tower, the tower angular position corresponding to a tower reference point, (c) receiving an encoder signal indicating the angular position of the nacelle, (d) detecting that a sensor mounted to the nacelle is located near the tower reference point, and (e) in response to the detection: updating the encoder signal such that the indicated angular position of the nacelle corresponds to the tower angular position.

[0011] This aspect of the invention is based on the idea that the base angular position (which is the angular position of a base reference point relative to true north) together with information about the angular relationship between the base and the tower is used to determine the tower angular position which is the angular position of a tower reference point. In other words, the obtained and stored base angular position together with said angular relationship is used to determine the tower angular position relative to true north. Then, the tower angular position (during operation of the wind turbine) is used to update an encoder signal indicating the angular position of the nacelle (also referred to as the yaw angle of the wind turbine) such that the angular position indicated by this encoder signal is correct. More specifically, this update is made each time it is determined that the nacelle is in a known position, i.e., when a sensor on the nacelle detects that it is near (or passing) the tower reference point. When this occurs, the encoder signal is updated to indicate the angular position of the nacelle corresponding to the (known) tower angular position. In other words, each time the nacelle is in a known angular position relative to the tower (corresponding to the tower angular position), the encoder signal is updated (corrected or recalibrated) such that any deviation in the encoder signal is minimized. As a result, the angular position of the nacelle relative to true north will be obtainable with high precision for use in wind turbine control (and other purposes).

[0012] In the present context, the term "angular position" may in particular represent an angle relative to a predetermined reference, in particular relative to true north. Thus, an angular position of 0° may correspond to true north, 90° may correspond to true east, 180° may correspond to true south, 270° may correspond to true west, etc.

[0013] In the present context, the term "angular position of the nacelle" may in particular represent the yaw angle of the wind turbine relative to a predetermined reference, in particular relative to true north. In other words, the "angular position of the nacelle" indicates the current direction of the nacelle which is typically aligned with the axial direction of the generator and the rotor.

[0014] In the present context, the term "base angular position" may in particular represent the orientation or direction of the base, in particular it may represent the angular position of a predetermined reference point (base reference point) on the base (e.g., on the side wall or surface of the base). Similarly, the term "tower angular position" in the present context may in particular represent the angular position of a predetermined reference point (tower reference point) on the tower (e.g., on the side wall or surface of the tower).

[0015] In the present context, the term "angular relationship" may specifically represent information about the differences in rotational angles (as a matter of construction and design) between different objects, parts or sections of a wind turbine, in particular between corresponding reference points on these objects. It should be noted that the angular relationship may include relative angular information of several (more than two) objects, parts or sections relative to each other, such that the angular relationship corresponds to the sum of the corresponding relative angular information of the entire construction.

[0016] In the present context, the term "encoder signal" may specifically represent a signal from an encoder that tracks the rotation (yaw) of the nacelle relative to the tower.

[0017] The method according to the first aspect of the invention allows the angular position (yaw angle) of the nacelle relative to true north to be determined in a simple but very precise manner. The method uses the base angular position and the angular relationship as preconditions to determine the tower angular position relative to true north. In the case where the tower angular position relative to true north is available, the method relies on encoders and sensors (which are usually already available in most wind turbines) to track the angular position of the nacelle relative to true north, which is done by updating the encoder signal each time a sensor on the nacelle passes a tower reference point.

[0018] According to an embodiment of the invention, obtaining the base angular position includes determining the angular position of the base reference point before, during and / or after the installation of the base.

[0019] In other words, the angular position of the base reference point can, for example, be determined before the installation of the base, for example based on construction data that allows the (expected) angular position of the base reference point to be derived. Alternatively or additionally, the angular position of the base reference point can be obtained during the installation process, for example by means of measurements using high-precision GPS-based technology. Further alternatively or additionally, the angular position of the base reference point can be obtained after the installation of the base is complete, for example by means of GPS-based measurements. It should be emphasized that combinations are possible, where several values of the angular position of the base reference point obtained at different times or stages (for example, before, during and / or after the installation of the base) can be combined to form the final value of the base angular position.

[0020] According to another embodiment of the invention, the angular relationship between the base and the tower indicates the difference in the angular positions between the base reference point and the tower reference point.

[0021] In other words, the angular relationship indicates how many degrees would need to be moved on the circumferential circle around the tower axis in order to reach the position corresponding to the tower reference point from the position corresponding to the base reference point.

[0022] The angular relationship can in particular be determined on the basis of construction data and / or on the basis of one or more measurements.

[0023] According to a further embodiment of the invention, the angular relationship between the base and the tower comprises a plurality of angular relationships, each of which indicates the difference in angular position between predetermined reference points of adjacent sections of the tower.

[0024] In other words, the angular relationship comprises information on the respective differences in angular position between predetermined reference points of adjacent tower sections. More specifically, the angular relationship between the base and the tower can be formed by adding a plurality of angular differences corresponding to transition sections along the tower, for example a first angular difference corresponding to the transition section between the base and the lower tower section, a second angular difference corresponding to the transition section between the lower tower section and the middle tower section, and a third angular difference corresponding to the transition section between the middle tower section and the upper tower section. Each of these contributions can be derived with high precision on the basis of the construction and design data of the wind turbine structure.

[0025] According to a further embodiment of the invention, the encoder signal is provided by a yaw encoder.

[0026] The yaw encoder can in particular and as is generally known in the art comprise an encoder wheel of an encoder structure mounted on the nacelle such that it is coupled to a corresponding element (for example a flat or toothed structure along the perimeter of the tower) in such a way that the encoder wheel rotates when the yaw angle changes. The encoder signal can in particular be obtained (or derived) from the detection of a signed count of the rotation of the encoder wheel.

[0027] According to a further embodiment of the invention, the sensor is configured to detect a sensor activation element located at a reference point of the tower.

[0028] In other words, the sensor activation element is arranged in or on the tower surface in such a way that the sensor is activated (by detecting the sensor activation element) when the angular position of the nacelle brings the sensor into the vicinity of the tower reference point.

[0029] According to a further embodiment of the invention, the sensor is an inductive sensor.

[0030] Inductive sensors are preferred, especially because of their low cost and high robustness. However, depending on the circumstances, other types of sensors can also be considered, such as optical, electromagnetic or acoustic sensors.

[0031] According to another embodiment of the present invention, the step of updating the encoder signal includes: (a) determining a difference between an angular position indicated by the encoder signal and the tower angular position, and (b) updating the encoder signal based on the determined difference such that the angular position indicated by the updated encoder signal is equal to the tower angular position.

[0032] In other words, the update of the encoder signal utilizes the determined difference between the angular position indicated by the encoder signal (before update) and the known tower angular position, and makes the updated encoder signal (at least temporarily) consistent with the true angular position relative to true north.

[0033] According to another embodiment of the present invention, the step of updating the encoder signal includes adding an offset value to the encoder signal, wherein the offset value is based on the determined difference.

[0034] In other words, the difference is compensated by adding the offset value to the encoder signal.

[0035] According to a second aspect of the present invention, there is provided a controller for a wind turbine, the wind turbine including a nacelle rotatably mounted at an upper end of a tower, the lower end of the tower being supported by a foundation. The controller includes: (a) a storage unit that stores a foundation angular position corresponding to a foundation reference point, the foundation angular position being relative to true north, and (b) a processing unit configured to: (b1) determine a tower angular position corresponding to a tower reference point based on the foundation angular position and information indicating an angular relationship between the foundation and the tower, (b2) receive an encoder signal indicating an angular position of the nacelle, (b3) detect that a sensor mounted to the nacelle is located near the tower reference point, and (b4) in response to the detection: update the encoder signal such that the indicated angular position of the nacelle corresponds to the tower angular position.

[0036] This aspect of the present invention is based on the same concept as the above first aspect, and thus, can provide at least the same advantageous technical effects in the architecture of a wind turbine controller, that is, a controller capable of performing the method according to the first aspect and the methods of its various embodiments as described above.

[0037] In the current context, the term "storage unit" may particularly represent any form of data storage known in the art. In particular, the "storage unit" may correspond to or be part of a larger controller memory. The storage unit may include volatile memory and / or non-volatile memory. Additionally, the storage unit may be or may include a cache memory that temporarily stores data provided by the controller or received from an external source (e.g., a central database in a wind farm). Thus, the base angular position may be permanently stored in the storage unit, or it may be received from the central database and temporarily stored in the storage unit.

[0038] In the current context, the term "processing unit" may particularly represent a data processing unit, such as a CPU or a similar unit, or a part of such a data processing unit, which is capable of performing computational and logical operations as needed to, for example, execute the steps of determination, reception, detection, and update mentioned above.

[0039] According to a third aspect of the present invention, there is provided a wind turbine comprising a controller according to the second aspect above.

[0040] Thus, the third aspect of the present invention utilizes this controller to provide the aforementioned technical effects and advantages in a wind turbine.

[0041] According to a fourth aspect of the present invention, there is provided a wind farm comprising: (a) a plurality of wind turbines according to the third aspect; and (b) a wind farm controller in communication with the controller of each wind turbine.

[0042] Furthermore, this fourth aspect of the present invention also utilizes the general principles of the first and second aspects above in order to provide corresponding advantages at the wind farm level here.

[0043] According to another embodiment of the present invention, the wind farm controller is configured to apply a wake steering control algorithm.

[0044] By utilizing very precise data regarding the angular position of each wind turbine in the wind farm relative to a fixed reference (e.g., true north), the yaw control of each individual wind turbine can be modified in such a way that the negative impact of the wake between adjacent wind turbines is reduced, and correspondingly, the total energy production of the wind farm is increased.

[0045] 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 claims, while other embodiments have been described with reference to apparatus-type claims. However, those skilled in the art will learn from the foregoing and the following description that, unless otherwise indicated, any combination of features related to different subject matters, in particular the combination of features of method-type claims and apparatus-type claims, is also part of the disclosure of this document, in addition to any combination of features belonging to one type of subject matter.

[0046] The aspects of the present invention defined above, as well as additional aspects, will be apparent from and will be elucidated with reference to the examples of embodiments described hereinafter. The present invention will be described in more detail hereinafter with reference to the examples of embodiments. However, it should be expressly noted that the present invention is not limited to the described exemplary embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 A wind turbine according to an exemplary embodiment of the present invention is shown.

[0048] Figure 2 A flowchart of a method according to an exemplary embodiment of the present invention is shown.

[0049] Figure 3 A top view of a wind turbine according to an exemplary embodiment of the present invention is shown.

[0050] Figure 4 An encoder and sensors on a wind turbine according to an exemplary embodiment of the present invention are shown. DETAILED DESCRIPTION

[0051] The illustrations in the drawings are schematic. It should be noted that in different drawings, similar or identical elements are provided with the same reference numerals or reference numerals that differ only in the first digit.

[0052] Figure 1Shows a wind turbine 1 according to an exemplary embodiment of the present invention. The wind turbine 1 is part of an offshore installation and includes (in a known configuration) a foundation 2, a tower 3, and a nacelle 4 with a hub 5 and rotor blades 6. The foundation 2 has an elongated structure and extends into the seabed 7 at its lower end. The foundation 2 is coupled to the tower 3 above the waterline 8 by an interface flange 14. The nacelle 4 is rotatably mounted at the upper end of the tower 3. More specifically, as shown in the enlarged view, a yaw motor (stepper motor) 9 is provided to rotate the nacelle about the tower axis by engaging with a toothed rim 10 that extends around a circumferential section of the tower 3. Thus, the yaw motor 9 can rotate the nacelle 4 to point in any desired direction, such as directly into the wind. An encoder 11 is mounted to the nacelle 4 and is configured to track the yaw rotation, as is known in the art. More specifically, the yaw encoder 11 includes an encoder wheel 16 that engages with the toothed rim 10. By detecting the corresponding rotation of the encoder wheel by means of a suitable sensor (not shown), an encoder signal is provided. Thus, this encoder signal indicates the angular position of the nacelle 4, i.e., the yaw angle. The yaw encoder 11 also includes a sensor (not shown) that is configured to detect a sensor activation element 12 mounted at a tower reference point (not shown). In other words, when the nacelle rotates (yaws) to a corresponding angular position, this sensor is able to detect the sensor activation element 12. This sensor is typically provided to allow counting of the complete rotation of the nacelle around the tower, which is important information in wind turbine control to avoid damaging the cables inside the wind turbine that rotate with the nacelle. Finally, a foundation reference point 13 is shown on the surface of the foundation 2. The angular position of the foundation reference point 13 relative to true north (or another fixed reference) can be determined and stored for subsequent use when installing the foundation and / or the rest of the wind turbine 1.

[0053] It should be noted that the principles and functions of the present invention described below apply not only to the offshore wind turbine as depicted in Figure 1 but also to any other wind turbine having a tower supported on a foundation. However, for ease of understanding, the present invention will now be further explained in detail with reference to the structure shown in Figure 1 below.

[0054] Figure 2 Shows a flow chart of a method 20 according to an exemplary embodiment of the present invention. More specifically, the method 20 starts at 21 with obtaining and storing a foundation angular position corresponding to the foundation reference point 13. This foundation angular position is determined relative to true north, for example by using a GPS device.

[0055] Then, at 22, the method continues as follows: based on the base angular position and information indicating the angular relationship between the base 2 and the tower 3, the tower angular position is determined. This tower angular position corresponds to the tower reference point. This will be described in further detail below with reference to Figure 3 At this stage, based on the tower angular position and this angular relationship, the tower angular position relative to true north (i.e., the angular position of the tower reference point) can be obtained.

[0056] Then, method 20 continues at 23 as follows: receiving an encoder signal from the yaw encoder 11. This encoder signal indicates the current angular position of the nacelle 4, i.e., the yaw angle.

[0057] At step 24, method 20 detects that a sensor (described in further detail below in conjunction with Figure 4 is located near the tower reference point. Therefore, at this stage, it is determined that the nacelle is yawed to the direction corresponding to the tower angular position. Thus, at this moment, the yaw angle relative to true north is known with high precision.

[0058] Finally, at step 25, the method responds to the detection in step 24 as follows: updating the encoder signal such that the indicated angular position of the nacelle 4 corresponds to the tower angular position. In other words, if the angular position indicated by the encoder signal deviates from the tower angular position, the encoder signal is adjusted to indicate the correct angular position. By repeating this process each time the detection of the sensor (step 24) occurs, the encoder signal can provide accurate and reliable information about the actual angular position of the nacelle relative to true north. This is obtained only by having the available base angular position and angular relationship and does not require new hardware.

[0059] Figure 3 A top view of a wind turbine 1 according to an exemplary embodiment of the present invention is shown. For ease of understanding, Figure 3 the nacelle and rotor structure are not shown, and only the perimeter of the wind turbine tower 3 is shown. The geographical location of the wind turbine 1 is represented as point P by three-dimensional GPS coordinates (X, Y, Z). Reference points A, B, C, D are shown along the perimeter of the tower 3. More specifically, reference point A corresponds to the Figure 1 expected position of the base reference point 13 shown in Figure 1The points at the interface flange 14 as shown. As can be seen, the reference point C is offset from the reference point B by an amount BC of approximately 30°. Finally, the reference point D corresponds to the tower angle position where the sensor activation element 12 is located. The offset CD from the reference point C is approximately 50°. The sum of these offsets, i.e., AB + BC + CD = 82.5°, forms the angular relationship between the foundation and the tower mentioned elsewhere in this application and corresponds to the difference in the angular positions between the foundation reference point 13 and the tower reference point 12.

[0060] Figure 4 An encoder 11 and a sensor 15 on a wind turbine 1 according to an exemplary embodiment of the present invention are shown. More specifically, Figure 4 The detailed view of shows the encoder unit 11, which is mounted to the nacelle 4 ( Figure 4 not shown in ) and includes a sensor 15 (preferably an inductive sensor 15) and an encoder wheel 16. The encoder wheel 16 engages with the toothed rim 10 on the tower 3 to count the corresponding rotational movement of the nacelle 3 relative to the tower 3, as is known in the art. Below the toothed rim 10 and at the tower reference point D, a sensor activation element 12, preferably a magnetic material block, is shown. Thus, as also described above, when the nacelle yaws to the angular position where the sensor 15 detects the sensor activation element 12, the angular position of the nacelle 4 relative to true north is considered to be the same as the tower angular position. By continuously updating, in particular by correspondingly adjusting or recalibrating the encoder signal each time the sensor 15 detects the activation element 12, it is possible to obtain very precise information about the angular position of the nacelle 4 relative to true north in a simple and very reliable manner, which only requires two pieces of information (i.e., the foundation angular position and the angular relationship between the foundation and the tower) and the corresponding processing, as described above.

[0061] In a wind farm where the so-called wake steering control algorithm is applied to avoid a significant drop in power production at a wind turbine directly downwind of other wind turbines, precise information about the angular position is particularly useful and necessary.

[0062] It should be noted that the term "comprising" does not exclude other elements or steps, and the use of the words "a", "an", or "one" does not exclude a plurality. In addition, elements described in connection with different embodiments may be combined. It should also be noted that the reference signs in the claims should not be construed as limiting the scope of the claims.

Claims

1. A method for determining the angular position of a nacelle (4) of a wind turbine (1), the nacelle (4) being rotatably mounted at the upper end of a tower (3), the lower end of the tower (3) being supported by a foundation (2), the method comprises: obtaining and storing (21) a foundation angular position corresponding to a foundation reference point (13), the foundation angular position being relative to true north, determining (22) a tower angular position based on the foundation angular position and information indicating the angular relationship between the foundation and the tower, the tower angular position corresponding to a tower reference point (D), receiving (23) an encoder signal indicating the angular position of the nacelle (4), detecting (24) that a sensor (15) mounted to the nacelle (4) is located near the tower reference point (D), and in response to the detection: updating (25) the encoder signal such that the indicated angular position of the nacelle (4) corresponds to the tower angular position.

2. The method according to the preceding claim, wherein, obtaining the foundation angular position includes determining the angular position of the foundation reference point before, during and / or after installation of the foundation.

3. The method according to any one of the preceding claims, wherein, the angular relationship between the foundation and the tower indicates the difference in angular position between the foundation reference point and the tower reference point.

4. The method according to the preceding claim, wherein, the angular relationship between the foundation and the tower includes a plurality of angular relationships, each of which indicates the difference in angular position between predetermined reference points of adjacent sections of the tower.

5. The method according to any one of the preceding claims, wherein, the encoder signal is provided by a yaw encoder (11).

6. The method according to any one of the preceding claims, wherein, the sensor is configured to detect a sensor activation element (12) located at the tower reference point.

7. The method according to the preceding claim, wherein, the sensor is an inductive sensor.

8. The method according to any one of the preceding claims, wherein, updating the encoder signal includes: determining the difference between the angular position indicated by the encoder signal and the tower angular position, and updating the encoder signal based on the determined difference such that the angular position indicated by the updated encoder signal is equal to the tower angular position.

9. The method according to the preceding claim, wherein, updating the encoder signal includes adding an offset value to the encoder signal, wherein the offset value is based on the determined difference.

10. A controller for a wind turbine, the wind turbine including a nacelle rotatably mounted at the upper end of a tower, the lower end of the tower being supported by a foundation, the controller comprises: a storage unit that stores a foundation angular position corresponding to a foundation reference point, the foundation angular position being relative to true north, and a processing unit configured to: determine a tower angular position based on the foundation angular position and information indicating the angular relationship between the foundation and the tower, the tower angular position corresponding to a tower reference point, Receiving encoder signals indicative of the angular position of the nacelle, Detecting that a sensor mounted to the nacelle is near the tower reference point, and In response to the detection: updating the encoder signals such that the indicated angular position of the nacelle corresponds to the tower angular position.

11. A wind turbine comprising a controller according to the preceding claim.

12. A wind farm, Comprising: A plurality of wind turbines according to the preceding claim, and A wind farm controller in communication with the controller of each wind turbine.

13. The wind farm according to the preceding claim, Wherein, The wind farm controller is configured to apply a wake steering control algorithm.

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