Improvements related to the commissioning of wind turbines

Abstract

A method for commissioning a wind turbine, wherein the wind turbine comprises a tower extending along a tower axis (X), a tower top, and at least one connecting flange, and the wind turbine has a tower damping system that is operable to control the oscillating motion of the tower during operation. The method includes the step of controlling the tower damping system during the tower stabilization phase of operation to release residual stress in at least one connecting flange of the tower of the wind turbine by moving the tower top in a plurality of directions (F1 to F4) around at least a portion of the tower axis. An advantage of the present invention is that the stress accumulated during the manufacturing of the tower section of the wind turbine is released quickly, and a more efficient commissioning process is achieved.

Description

Technical Field

[0001] Technical Field The present disclosure relates to systems, devices, and methods for controlling the lateral and longitudinal vibration movements of a wind turbine during installation of the wind turbine. Aspects of the present invention relate to a wind turbine and a method for controlling the wind turbine, and a control device and a computer program product for the wind turbine.

Background Art

[0002] Background A wind turbine is a complex structure and requires regular maintenance and inspection to ensure safe and efficient operation. One important aspect of wind turbine maintenance is the inspection and maintenance of bolt connections used to join the various components of the wind turbine to each other. For example, in order to provide a secure connection of the wind turbine to its foundation, bolted connections are typically used at the flanged interface between the foundation of the wind turbine and the lowest tower section. Flanged interfaces also exist between adjacent tower sections that make up the wind turbine tower.

[0003] Flanged interfaces are generally highly stressed during use, and thus the establishment of bolted connections at flanged interfaces is an important part of the installation process to achieve the long operating life of a wind turbine. The bolts in bolted connections are typically pre-tensioned as part of an attachment process to improve the robustness of the flanged interface. However, after installation, the residual stress in the flanged connection can be released over time, reducing the pre-tension in the bolts. This effect can compromise the fatigue life of the bolts, which is undesirable. Bolt pre-tension can be measured and corrected, but this can only be done after a significant period of wind turbine operation. Furthermore, this is time-consuming and a physically demanding task.

[0004] The present invention aims to solve one or more drawbacks related to the prior art. [Overview of the project] [Means for solving the problem]

[0005] According to a first aspect of the present invention, a method for commissioning a wind turbine is provided. The wind turbine comprises a tower extending along a tower axis (X), a tower top, and at least one connecting flange, and has a tower damping system that is operable to control the oscillating motion of the tower during use. The method includes the step of controlling the tower damping system during the tower stabilization phase of operation to move the tower top in a plurality of directions (F1 to F4) around at least a portion of the tower axis to release residual stress in at least one connecting flange of the wind turbine tower. In this regard, the term “commissioning” can be understood as the process of setting up the wind turbine for operation. During commissioning, the wind turbine is operated to generate power and send that power to the power grid. However, the power output may fall below normal rated levels due to control functions implemented in the wind turbine system during such a commissioning process.

[0006] An advantage of the present invention is that stresses accumulated during the manufacturing and assembly of the wind turbine tower section can be rapidly released while applying conventional control algorithms used to control the damping of the vibration motion of the wind turbine. Therefore, any concerns regarding the subsequent release of such stresses, and their impact on the pre-tension of flange bolts, buckling, or fatigue strength of welds, can be eliminated in a short time and in a controlled manner.

[0007] In one example, by controlling the tower damping system, the top of the tower moves in multiple directions that completely surround the tower axis. Therefore, the damping system is adapted to vibrate or oscillate the tower in a specific selected direction to release residual stress in a controlled manner. Stress relaxation can be achieved uniformly by controlling the damping system so that the tower vibrates in many different directions around the tower axis. It is noteworthy that the damping system is used here in an unconventional way. While damping systems are conventionally used to reduce the vibrational motion of wind turbine towers, in this example, the damping system is used to increase, enhance, or amplify the vibrational tower motion to achieve stress relaxation. This effect can be enhanced by controlling the damping system so that the induced vibration of the tower has frequencies close to or substantially at the tower's natural frequency.

[0008] In another example, by controlling the tower damping system, the top of the tower follows a roughly circular path (F5) around the tower axis. This ensures that the load acts uniformly around the tower axis, but in a different way than the methods described so far.

[0009] In another embodiment, an example of the present invention provides a method for commissioning a wind turbine. The wind turbine comprises a tower extending along a tower axis (X), a tower top having a nacelle, and at least one connecting flange. The method includes controlling the wind turbine during the tower stabilization phase of operation, and includes the following steps: starting the wind turbine and controlling the yaw system of the wind turbine so that the nacelle is oriented in a first of a predetermined number of directions relative to the tower axis; performing an emergency stop of the wind turbine while the nacelle is oriented in the first of a predetermined number of directions; and repeating the steps of starting the wind turbine, controlling the yaw system, and performing an emergency stop of the wind turbine for each of the predetermined number of directions, thereby increasing the load applied to the tower in each of the predetermined number of directions and releasing residual stress in at least one connecting flange of the wind turbine tower.

[0010] It should be noted that a second aspect of the present invention can achieve the same or similar technical advantages as the first aspect of the present invention compared to known technologies.

[0011] This method may include stopping the operation of the wind turbine after the tower stabilization phase of operation, and re-tensioning bolts in one or more of the at least one flanged connections of the tower.

[0012] Examples of the present invention also include: i) a control device for a wind turbine control system comprising a processor and a memory module, wherein the memory module comprises a set of program code instructions that, when executed by the processor, implement the method defined in the above embodiment; ii) a computer program product stored on a machine-readable medium that is downloadable from a communication network and / or contains program code instructions for implementing the method according to the above embodiment; and iii) a wind turbine comprising a tower and the control device.

[0013] Within the scope of this application, the various aspects, embodiments, examples, and substitutes described in the preceding paragraphs, claims, and / or the following description and drawings, and in particular their individual features, are expressly intended to be adopted independently or in any combination. That is, all examples and / or features of any example can be combined in any way and / or combination, provided that such features do not conflict. The applicant reserves the right to amend any claim originally filed, or to file any new claim accordingly, including the right to modify any claim originally filed so as to depend on and / or incorporate any feature of any other claim, which was not originally claimed in this manner. [Brief explanation of the drawing]

[0014] The above and other aspects of the present invention are described merely as examples with reference to the accompanying drawings. [Figure 1] Figure 1 is a front view of a typical horizontal-axis wind turbine incorporating an embodiment of the present invention. [Figure 2] Figure 2 is a schematic diagram of a wind turbine illustrating the vibrational motion experienced by the wind turbine tower during operation. [Figure 3] Figure 3 is a schematic system diagram of the wind turbine shown in Figure 1. [Figure 4] Figure 4 is a more detailed schematic system diagram of the monitoring and control system of the wind turbine system shown in Figure 4. [Figure 5] Figure 5 is a flowchart illustrating an exemplary method for controlling a wind turbine. [Figure 6] Figure 6 is a diagram illustrating the principle applied according to an embodiment of the present invention. [Figure 7] Figure 7 is a diagram illustrating the principle applied by an embodiment of the present invention. [Figure 8] Figure 8 is a flowchart showing an example of another method for controlling a wind turbine. [Modes for carrying out the invention]

[0015] Detailed explanation Herein, specific embodiments of the present invention are described, and numerous features are discussed in detail to provide a complete understanding of the concept of the invention as defined in the claims. However, it will be apparent to those skilled in the art that the invention can be implemented without specific details, and that, in some cases, well-known methods, techniques, and structures are not described in detail to avoid unnecessarily obscuring the invention. Furthermore, it will be apparent to those skilled in the art that structural, logical, and electrical modifications can be made without departing from the scope of the invention as defined in the appended claims.

[0016] Broadly speaking, embodiments of the present invention described herein provide a system and corresponding method for improving the installation method of a wind turbine tower in order to make the "stabilization" process of newly installed flanged connections of a wind turbine tower more predictable. Because the stabilization process becomes more predictable, measures to address the results from the stabilization process, such as re-tensioning of bolted connections, can be taken earlier, which improves the long-term reliability of the flanged connections.

[0017] Figure 1 shows a wind turbine, generally designated as 10, comprising a tower 12. The tower 12 supports a nacelle 14 to which a rotor 16 is mounted. The rotor 16 is operably coupled to a generator (not shown) housed inside the nacelle 14. The rotor 16 is configured to rotate around a central axis to drive the generator and generate electrical energy. In addition to the generator, the nacelle 14 houses various components necessary for converting wind energy into electrical energy, along with various other components necessary for the operation, control, and performance optimization of the wind turbine 10.

[0018] The rotor 16 includes a plurality of rotor blades 18 that radially extend from a central hub 20. The blades 18 rotate within the rotor plane. In this example, the rotor 16 includes three rotor blades 18, although it will be apparent to those skilled in the art that other configurations are possible. The rotor blades 18 are pitch adjustable. That is, the pitch of the rotor blades 18 can be adjusted about their respective longitudinal axes 19 according to a collective pitch setting in which each rotor blade 18 is set to the same pitch value with respect to a collective pitch setting, and / or according to an individual pitch setting in which each rotor blade 18 can be set to a unique pitch value corresponding to an individual pitch setting. The nacelle 14 can yaw with respect to the tower 12 under the control of a yaw system (not shown) to ensure that the rotor 16 and the blades 18 face the wind flow during operation in order to optimize energy capture.

[0019] The tower 12 can experience oscillations / vibrations along its entire length during operation of the wind turbine 10, particularly due to the vibration coupling between the rotor 16 and the tower 12, which can be a source of self-excitation. The oscillations of the tower 12 can also occur as a result of external forces. Self-excitation is typically caused by asymmetries or mass imbalances within the rotor 16. For example, an asymmetry of the rotor 16 can occur due to geometric errors or misalignments of the rotor blades 18, which results in an aerodynamic asymmetry. This causes an aerodynamic asymmetry. This asymmetry varies according to the rotational speed of the rotor 16.

[0020] Tower movement / vibration generates bending moments along tower 12 at both the flange between adjacent tower sections and the base of tower 12 where the free mass, i.e., the distance from nacelle 14 is maximum. The modes of tower vibration are schematically shown in FIG. 2. In this figure, wind turbine 10 is represented by beam structure 60, which is fixed to ground plane 62 at its lower end and is provided with a mass (i.e., nacelle 14) at its free end. When the top of beam structure 60 vibrates in direction X, i.e., in the lateral direction with respect to hub 20, it varies between two maximum values defined by the maximum deflection of the vibrating tower structure 60. The position representing the displacement of nacelle 14 in direction X may indicate the position of the center of gravity of nacelle 14, the position of the sensor housed within nacelle 14, or the position of other fixed points representing the movement of nacelle 14 in direction X.

[0021] Tower 12 is considered to have at least two degrees of freedom, i.e., vibration modes, in which it can bend in the lateral and longitudinal directions. Lateral bending is bending in the lateral direction parallel to the plane of rotor 16, as shown as direction X in FIG. 2. However, longitudinal vibration is bending in the front-back direction perpendicular to the plane of rotor 16, as shown by direction Y in FIG. 2.

[0022] The two-degree-of-freedom bending in the front-back and lateral directions can be quantified as the displacement or load received by tower 12 and can be mapped onto one or more horizontal planes arranged along the length of tower 12 through the tower. The averaged vibration motion and / or load along the length of tower 12 can also be mapped. The vibration of tower 12 in any direction can be considered to have a front-back component and a left-right lateral component since it can be expressed as the product of the front-back and lateral excitations.

[0023] Returning to Figure 1, further technical details of the present invention are shown. The tower 12 is connected to a foundation 22 buried underground. Foundation structures are well known in the art. As is also well known, foundation structures can be provided for onshore and offshore wind turbine facilities. In marine environments, foundation structures may include components known as transition pieces.

[0024] The tower 12 and the foundation 22 are secured by flanged connectors or "joints" 25. A portion of the flanged connector 25 between the tower 12 and the foundation 22 can be seen in the insert panel in Figure 1.

[0025] The flanged connector 25 comprises a tower flange 26 and a base flange 28 adjacent to each other, which fit together at a butt joint. In this example, the tower flange 26 is part of the tower, and the base flange 28 is part of the foundation 22. The tower flange 26 and the base flange 28 define their respective through holes, which are aligned to provide bolt holes 30 that pass through both flanges 26, 28. The bolt holes 30 accommodate the bolted connector 32.

[0026] The bolted connection 32 includes an anchor bolt 34 and a nut 36. In this example, the bolt 34 is a stud bolt having a shank 38. The shank 38 is provided with a threaded portion 39, and the nut 36 is screwed in conventionally so as to abut the washer 37. In other examples, the bolted connection 25 may include a headed bolt instead of a stud bolt.

[0027] At this point, although the bolted connection 32 shown in Figure 1 represents a single bolt, it should be noted that in reality, a bolted connection comprises a circular array of bolts arranged circumferentially around the base flange 28. To avoid misunderstanding, it should be noted that the term “bolted connection” should not be limited to the specific bolted connection shown in the illustrated example. The flanged connection shown in Figure 1 is merely one example of such a connection, and it should also be noted that, as is commonly known in the art, flanged connections can also be provided between adjacent tower sections in a wind turbine tower constructed from several tower sections.

[0028] Such bolted connections, as described herein, are typically pre-tensioned or pre-loaded to increase their effectiveness and resistance to periodic loads. While the contact surfaces of flanged connections can be assumed to be flat, small variations from ideal flatness may exist. These variations are more pronounced, for example, for large tower diameters of 7 meters or more, meaning that small gaps may exist between the contact surfaces, which is undesirable. By pre-tensioning the bolted connection around the connecting flange, these gaps can be reduced, improving the robustness of the flanged connection.

[0029] The process of applying pre-tension to bolted connections is a known technique in this regard. Furthermore, it is known that pre-pressure or pre-load introduced to such bolted connections can decrease or "stabilize" over time. This may be due to the release of residual stress present in the tower material, usually steel, after the manufacturing process. Conventionally, post-installation protocols have been observed that involve operating the wind turbine for a predetermined period of 3 to 12 months, during which time the wind turbine is exposed to various wind and load conditions. These various load conditions have the effect of releasing residual stress in the tower structure near the flanged connections, which can cause a certain degree of tension reduction in the bolted connections. After this predetermined period, the bolts in the flanged connections can be inspected and tension can be reapplied if necessary. However, this is a considerable maintenance task, and the period during which the wind turbine must be operated during this "post-installation protocol" is significant, leading to delays in possible maintenance activities and uncertainty regarding the integrity of the flanged connections.

[0030] The object of the present invention is to address the technical challenge of performing the aforementioned post-installation process, currently carried out as part of the commissioning process of wind turbines, in a more efficient manner. Commissioning a wind turbine can be a redundant task, which can delay the process of handing over the wind turbine to the operator / owner's control. Therefore, any means that can shorten the commissioning time is desirable.

[0031] In one embodiment, the objective is to intentionally increase the load applied to the wind turbine tower during the "stabilization phase" of operation during commissioning, thereby promoting the release of residual stress in the tower near or at the flanged connections, by applying a load to the flanged connections of the wind turbine tower through a range of directions. This technical effect can be achieved by operating the tower damping system of the wind turbine to induce vibrational motion at the top of the wind turbine tower, causing the tower top to move in multiple directions around the tower axis to achieve the desired load profile at one or more flanged connections of the tower. The multiple directions may involve the tower damping system being controlled so that the tower top vibrates reciprocatingly with longitudinal and lateral motion components. This effect involves vibrating the tower top in multiple selected radial directions around the tower axis, and since the tower top preferably covers an angular range surrounding the tower axis, the reduction of residual stress at the flanged connections is appropriately uniform around its circumference.

[0032] Next, an exemplary control system for a wind turbine to achieve this technical function will be described with reference to Figures 3 and 4.

[0033] In Figure 3, the wind turbine 10 is equipped with control means 50 that can be operated to monitor the operation of the wind turbine 10 and issue commands to it in order to achieve a series of control objectives. The control means 50 is shown in Figure 3 as a simplified schematic diagram of a plurality of control units and modules, and in Figure 4, a more detailed example is shown of how certain units and modules may be arranged to facilitate data exchange between them.

[0034] The wind turbine 10 also includes a gearbox 52 and a power generation system 54, which includes a generator 56 and a power conversion system 58. The gearbox 52 increases the rotational speed of the rotor 16, drives the generator 56, and supplies the generated power to the power conversion system 58. Typically, such a system is based on three-phase power, but this is not mandatory. Other wind turbine designs are known, such as "gearless" types, also known as "direct drive," and "belt-driven" transmission systems.

[0035] The generator 56 and the power conversion system 58 may, for example, be based on a full-scale converter (FSC) architecture or a dual-fed induction generator (DFIG) architecture, but other architectures will also be known to those skilled in the art.

[0036] In the illustrated embodiment, the power output of the power conversion system 58 is transmitted to a load 60, which may be a power grid. Those skilled in the art will understand that different power conversion and transmission options exist, and that the system schematic diagram in Figure 3 merely provides an example of a system architecture suitable for implementing the functionality discussed herein.

[0037] Returning to the control means 50 in Figures 3 and 4, the control means 50 comprises a processor 62 configured to execute instructions stored in an external data store that forms part of a memory module 64 and / or an external network 66, and read from there. Measurement data can also be stored in the memory module 64 and retrieved to execute a process according to instructions executed by the processor 62.

[0038] Commands and data may also be received from external control devices or sensors that form part of the external network 66, and recorded data and / or warnings may be issued via the external network 66 and stored / displayed at external sources for analysis and remote monitoring.

[0039] Furthermore, the processor 62 communicates with a plurality of sensors 68 located within the wind turbine 10. For example, as shown in Figure 4, the plurality of sensors 68 may include a tower accelerometer 72, a rotor speed sensor 74, a blade pitch angle sensor 76, a nacelle yaw angle sensor 78, and a rotor position sensor 79.

[0040] The control means 50 of the wind turbine 10 also includes at least one control unit 70. In the configuration shown in Figure 4, five control units are shown. These are a blade pitch angle control unit 82, a nacelle yaw angle control unit 84, a speed control unit 86, a longitudinal tower damping (FATD) control unit 85, and a transverse tower damping (SSTD) control unit 87. The blade pitch angle control unit 82 and the nacelle yaw angle control unit 84 are configured to change the pitch angle of the rotor blades 18 and the yaw angle of the nacelle 14, respectively, while the speed control unit 86 functions to control the rotational speed of the rotor 16 by converter control and pitch control.

[0041] The functions of the FATD and SSTD control units 85 and 87 will be discussed in more detail below. In the illustrated embodiment, the blade pitch angle control unit 82 and the FATD and SSTD control units 85 and 87 are separate control units. However, those skilled in the art will understand that the functions of each of these separate control units 82, 85, and 87 may be delivered by a single control unit or two control units.

[0042] Network 88 forms a central connection between each of the modules (according to an appropriate protocol), thereby enabling the exchange of relevant commands and data between each of the modules. However, it will be understood that appropriate wiring may be provided to interconnect the units. It will also be understood that the wind turbine 10 may include more control units 70, and Figure 4 is provided only to illustrate an example of a system configuration in which the present invention can be implemented.

[0043] The primary function of the control means 50 is to control the power generation of the wind turbine 10 to optimize power generation under current ambient wind conditions and in accordance with the power generation requirements of the power grid operator. However, in addition to its primary power control task, the control means 50 may also be capable of performing a series of other functions. In embodiments of the present invention, one of these functions is to operate the wind turbine during commissioning to prepare it for handover to the end user of the wind turbine or the wind power facility in which the wind turbine is a component. As part of this, the control means 70 may be configured to control the FATD control unit 85 and the SSTD control unit 87 to influence the movement of the tower, particularly the vibrational motion of the tower top. Increasing the load applied to one or more connecting flanges of the tower is intended to release residual stress in the tower in the connecting flange area at an accelerated rate. In this way, the bolts of the connecting flanges stabilize at a more predictable and accelerated rate, which allows for more accurate planning of follow-up maintenance and faster completion of commissioning.

[0044] It should be noted here that the functions of the active tower damping system, namely the FATD control unit 85 and the SSTD control unit 87, are generally known in the art as means implemented in wind turbines to reduce tower vibration motion. Since such systems are well known to those skilled in the art, a detailed description is omitted here to avoid obscuring the present invention. However, it should be noted that at a high level, the lateral vibration motion of the tower can be influenced primarily by changing the individual pitch of each blade 18 of the wind turbine 10, i.e., by changing the turbine's power generation by adjusting the generator torque, known as "generator speed control" or "generator torque control". In any case, this function involves using the electrical characteristics of the generator to control the torque on the main rotor shaft that generates a lateral force on the nacelle. The application of this lateral force can conventionally be used to counteract the lateral movement of the tower. In this example, the periodic blade pitch control and generator torque control in the active damping system are managed by the SSTD control unit 87. In some embodiments, the SSTD control unit 87 may receive control signals and control the blade pitch angle control unit 82 and / or the speed control unit 86 to perform the associated changes or operations. Other control units may be used, as will be understood by those skilled in the art.

[0045] Unlike adjusting the lateral load, the longitudinal load is changed by adjusting the aggregate pitch of the blades 18. This can be achieved by the operation of a FATD control unit 85 configured to adjust the aggregate pitch of the blades 18 to perform active damping in the longitudinal direction in response to an appropriate control signal. The FATD control unit 85 may achieve this function by communicating with a blade pitch angle control unit 82. However, in some examples, the aggregate pitch may be controlled directly by the FATD control unit 85. In summary, the FATD control unit 85 and the SSTD control unit 87 can be considered to constitute an active tower damping system for the wind turbine 10.

[0046] To perform the functions described above, the control means 50 operates according to a control protocol. A typical protocol is shown by method 100 in Figure 5.

[0047] This method begins in step 102, which is when the tower stabilization phase of operation begins. It should be noted that the tower stabilization phase of operation may be a typical operating state in which the wind turbine is connected to the power grid and generates electricity. However, as will be described later, the control of the wind turbine during the initial stabilization phase is adjusted so that the motion of the tower is strengthened or amplified in a controlled manner in order to achieve material stress relaxation at the flanged connections of the tower.

[0048] Once the tower stabilization phase of operation begins, the method determines, in step 104, a target load profile that should be satisfied to allow for the relaxation of residual stress in the steel at one or more tower flange connections.

[0049] The load profile can be determined in various ways. One example is that the load profile can be stored in a memory module 64 ready to be recalled by the processor 62 of the control means 50. Thus, the load profile can be expressed in appropriate form as an array of force values ​​or bending moments that need to be applied to the individual flanged connections of the wind turbine tower. Such force values ​​or bending moments may be directly convertible into displacement / velocity / acceleration components that should be achieved at the top of the tower to achieve the desired force values.

[0050] This conceptual diagram is shown in Figure 6, but please note that the force values ​​represented here are contained within an appropriate data structure.

[0051] In Figure 6, for clarity, the base tower section 90 is shown with a solid line, and the further tower section 92 above it is shown with a dotted line. The flanged connection between the base tower section 90 and the adjacent tower section 92 is indicated by 94. Note that the dimensions of the tower sections shown in Figure 5 are not to scale.

[0052] As can be seen in Figure 6, there are four pairs of force vectors labeled F1 to F4 in the horizontal plane P1 above the flanged connection 94. Note that plane P1 may coincide with the flanged connection 94.

[0053] Here, the force vector pairs F1 to F4 are equally distributed around the tower axis X to provide a 360-degree coverage. Thus, the force vector pairs +F1 and -F1 extend substantially in the longitudinal direction of the tower top, and the force vector pairs +F3 and -F3 extend substantially in the lateral direction of the tower top. The force vector pairs + / -F2 and + / -F4 are in the intermediate position. Thus, overall, the eight force vectors extending around the tower axis X are arranged in 45-degree angular increments. Note that this is merely an example, and there may be more or fewer force vectors than those shown in Figure 6. Each force vector represents the minimum target load or force to be applied to the tower in the horizontal plane P1, and therefore also in the associated flanged connection 94. Note that the target load profile may be stored in the memory module 64 as part of the wind turbine commissioning process. The download of the target load profile may be performed on the wind turbine body, or it may be achieved by wireless download over a suitable communication network, as will be understood by those skilled in the art.

[0054] The control means 50 is configured to interpret the data contained in the target load profile in order to operate the wind turbine to release residual stress in the tower. Thus, once the load profile is determined in step 104, the control means starts operating the wind turbine in step 106. In order to apply the increased load indicated by the desired load profile, the control means calculates control signal components based on the target load profile in step 108.

[0055] In step 108, the control means 50 uses the determined target load profile to operate the tower damping system, in particular the FATD control unit 85 and the SSTD control unit 87, in order to control the vibration of the top of the tower and thereby achieve the increased load required by the desired load profile determined in step 104.

[0056] The control signal components determined in step 108 are configured to increase the vibrational motion of the tower 12, and the lateral and longitudinal components of the vibrational motion satisfy or exceed the determined load profile.

[0057] In Figure 6, it will be understood that the load profile is represented by eight force vectors spaced at equal angular increments around the tower axis. Thus, the control means 50 can be configured to operate the tower damping system so that the top of the tower, i.e., the wind turbine nacelle, vibrates sequentially along each of the vector pairs F1 to F4. For example, the control means 50 may be configured to control the FATD control unit 85 to move the top of the tower only substantially in the longitudinal direction along the vector pair + / -F1 for a predetermined period of time. The predetermined period can be any period suitable for releasing residual stress in the tower, for example, 1 hour, 5 hours, or 10 hours.

[0058] Once the predetermined period has ended, the control means 50 can select another vector pair, for example, + / -F2, and operate the tower damping system to vibrate the top of the tower in the direction of that vector pair. Since the vector pair + / -F2 lies between the longitudinal vector pair + / -F1 and the transverse vector pair + / -F3, the control means 50 is configured to generate appropriate control signals for each of the FATD control unit 85 and the SSTD control unit 87 so that the two control units operate synchronously to vibrate the top of the tower in the desired intermediate direction.

[0059] A similar consideration applies to the vector pair + / -F4.

[0060] Once the control means 50 calculates appropriate control signal components in step 108, in step 110, those control signal components are applied to the relevant control units 85 and 87 of the tower damping system.

[0061] The FATD control unit 85 and the SSTD control unit 87 can be operated for an appropriate period and in an appropriate manner to achieve the desired load on the connecting flange of the tower 12. As shown in Figure 5, this can be achieved by operating the FATD control unit 85 and the SSTD control unit 87 according to the determined control signals calculated in step 108 for a predetermined time calculated to bring about sufficient release of residual stress in the tower, as shown in step 112.

[0062] Alternatively, step 114 demonstrates a feedback method in which the load applied to the connecting flange of the tower 12 can be appropriately monitored. In this way, the tower damping system can operate until the required load, indicated by the load profile, is achieved. The load applied to the tower 12 can be determined in various ways. One way this can be achieved is by providing a suitable load cell on the connecting flange that provides a load indicator to the control means. The load cell can form part of a plurality of sensors 68, as shown in Figures 3 and 4.

[0063] Another way to implement load monitoring is to estimate the load based on the tower acceleration signal obtainable from the tower accelerometer 72. Since acceleration is directly related to the force applied to the tower, load data can be easily determined from the accelerometer data.

[0064] Furthermore, a combination of operating the tower damping system for a specified period, as in step 112, and monitoring the applied load, as in step 114, can be performed.

[0065] Following the operation of the tower damping system to achieve the desired load profile for one or more connection flanges of the tower, the process ends as shown in step 116.

[0066] The completion of Method 100 can trigger an inspection event to check the tension of bolts in one or more connecting flanges of the tower 12. This can be achieved by appropriate techniques, for example, by observing whether the nuts of the bolted connections have moved from their reference positions, and / or by non-destructive testing techniques known in the art. One known system for determining the tension of bolted connections is commercially available from R&D Test Systems A / S as the "Bolt-Check" product.

[0067] Any bolt in which a decrease in tension is detected may be immediately re-tensioned or scheduled to be re-tensioned during the next maintenance work.

[0068] Various modifications can be made to the specific embodiments described above with reference to the attached drawings. While some variations have already been described, other variations will be obvious to those skilled in the art. Therefore, the scope of the present invention should be determined from the appended claims rather than by referring to the specific embodiments described herein.

[0069] In the above explanation, it has been assumed that the control means 50 implements a load profile as shown in Figure 6 so that the tower damping system causes the tower to vibrate separately and sequentially in each direction of force vectors F1 to F4. However, other options are possible. One possible option is shown in Figure 7, which is similar to Figure 6 but shows a different load profile.

[0070] In Figure 7, it can be observed that the load profile includes a force vector F5. This force vector F5 is configured to cause the top of the tower to follow a circular movement path above the tower axis X when implemented by the control means 50 in the method 100 described above.

[0071] Next, a further example of the present invention will be described with reference to Figure 8, which discloses Method 200. In common with Method 100 shown in Figure 5, Method 200 aims to increase the load applied to one or more connecting flanges of a tower in multiple directions in order to release residual stress in the tower in the region of the connecting flanges at an accelerated rate. In this way, the bolts in the connecting flanges stabilize at a more predictable and accelerated rate, which means that follow-up maintenance can be planned more accurately and commissioning can be completed more quickly.

[0072] However, in contrast to method 100, method 200 achieves the release of residual stress in a different way, and more specifically, utilizes an emergency stop function of the wind turbine 10 that can be performed when the nacelle 14 of the wind turbine 10 is oriented in each of a given number of directions. During an emergency stop, typically the blades 18 of the rotor 16 are aggressively pitch-adjusted to reduce aerodynamic lift, and the generator is operated to increase generator torque. Combined, these means act to apply a torque brake to the rotor, which rapidly decelerates the rotor, at which point a parking brake may be applied to the rotor. When performing this function, the tower will bend substantially in the direction the nacelle is oriented, and a large bending moment is applied to the tower's connecting flange. By repeatedly performing the emergency stop function in multiple different yaw directions of the nacelle, a predictable and consistent load can be applied to the tower's connecting flange extending above the yaw axis.

[0073] Method 200 begins in step 202, at which point the tower stabilization phase of operation is initiated as described above. Once the tower stabilization phase of operation is initiated, in step 204, the method determines a target load profile that should be satisfied in order to allow for the relaxation of residual stress in the steel at one or more tower flange connections.

[0074] In the context of applying emergency response procedures, the determined load profile may consist of multiple yaw directions to be applied to the wind turbine and, optionally, the number of cases in which an emergency stop procedure should be applied. Similar to the previous method, the load profile may be stored in a memory module 64 ready to be called by the processor 62 of the control unit 50, or it may be downloaded from a remote location.

[0075] Once the target load profile is determined, method 200 proceeds to step 206, at which point, provided there is sufficient wind, the wind turbine is started and appropriate control signals for activating the emergency stop procedure are calculated in step 208. Such control signals may take into account wind speed, rotor speed, yaw direction, etc., in order to execute the emergency stop function at which sufficient load is generated on the tower in a desired yaw direction among several yaw directions. Note that the multiple yaw directions may be selected to map the load around the tower axis X in an appropriate manner. Thus, a given set of multiple yaw directions may be an angular increment suitable for providing sufficient release of residual stress in the tower. The incremental angular interval may be, for example, 10 degrees, 20 degrees, or 45 degrees. Note that a balance must be struck between the time required to perform the emergency stop under desired wind conditions in many different nacelle yaw directions and the magnitude of residual stress release.

[0076] Once an appropriate control signal is calculated, the control means 50 controls the wind turbine in step 210 to perform an emergency stop from a plurality of predetermined yaw directions of the nacelle to a first yaw direction.

[0077] Once the first emergency stop is successfully completed, the control means 50 restarts the wind turbine 10 in step 212 and activates the nacelle yaw angle control unit 84 (see Figure 4) to yaw the nacelle in the yaw direction that matches the next direction among a plurality of directions indicated by a predetermined load profile. This process can be completed until an emergency stop is performed in each of the plurality of predetermined directions indicated by the load profile.

[0078] Following the completion of emergency stops in each of the predetermined directions, in step 214, it is verified that the load applied to the connecting flange is sufficient, at which point the method may be terminated in step 216.

[0079] In the context of the emergency shutdown procedure described above, it should be noted that the flange stabilization operation of Method 200 may be interrupted by the normal operation of the wind turbine. For example, if an emergency shutdown is performed in one direction (see Step 210), the wind turbine may return to normal operation until sufficient time has passed for the wind direction to change, as monitored by the yaw system. Appropriate monitoring yaw direction functions may be appropriately configured for this task. The wind turbine then resumes tower flange stabilization and performs an emergency shutdown in the new direction before returning to normal operation. This is repeated until the target load profile is met.

Claims

1. A method (100) for commissioning a wind turbine (10), The wind turbine comprises a tower (12) extending along a tower axis (X), a tower top, and at least one connecting flange (25), and the wind turbine has a tower damping system (85, 87) that can be operated to control the vibrational motion of the tower during use. The method is characterized by including the step of controlling the tower damping system during the tower stabilization phase of operation such that the top of the tower is moved in a plurality of directions (F1 to F4) around at least a portion of the tower axis to release residual stress in the at least one connecting flange (25) of the tower of the wind turbine.

2. The method according to claim 1, characterized in that the step of controlling the tower damping system includes the step of moving the top of the tower in a plurality of directions that completely surround the tower axis.

3. The method according to the previous version, characterized in that the step of controlling the tower damping system includes moving the top of the tower to follow a substantially circular path (F5) around the tower axis.

4. The step of controlling the tower damping system is: Step (104) of determining a minimum load profile of the at least one flange connection of the tower, which represents the minimum load to be applied to at least one flange connection in multiple directions extending around the tower axis, The steps include determining a first control signal component relating to the lateral component of the vibration tower motion based on the required load profile (108), The steps (108) include determining a second control signal component relating to the forward and backward components of the vibration tower motion based on the required load profile, The method according to any one of claims 1 to 3, further comprising the first and second control signal components being configured such that the tower damping system causes an increase in the horizontal vibration tower motion such that the load applied to the at least one flanged connection exceeds the determined minimum load profile.

5. The method according to 4, characterized in that the control signal component is configured such that the load applied to the at least one flanged connection satisfies a target magnitude that exceeds the determined load profile.

6. The method according to 4 or 5, characterized in that the determined load profile corresponds to a predetermined operating load limit of the tower.

7. The method according to any one of claims 1 to 6, characterized in that the tower stabilization stage of the operation is remotely controlled from the wind turbine.

8. A method (200) for commissioning a wind turbine, The wind turbine comprises a tower (12) extending along a tower axis (X), a tower top having a nacelle (14), and at least one connecting flange (25), the method includes the step of controlling the wind turbine during the tower stabilization phase of operation, the method The steps include starting the wind turbine and controlling the yaw system of the wind turbine so that the nacelle faces a first direction among a predetermined number of directions with respect to the tower axis, Step (210) of performing an emergency shutdown of the wind turbine while the nacelle is facing the first of the predetermined plurality of directions, A method characterized by having the steps of: starting the wind turbine in order to increase the load applied to the tower in each of the predetermined plurality of directions, thereby releasing residual stress in the at least one connecting flange of the tower of the wind turbine; controlling the yaw system; and repeating the step of performing an emergency stop of the wind turbine in each of the predetermined plurality of directions (212).

9. The steps include stopping the operation of the wind turbine following the tower stabilization stage of the operation, The method according to any one of claims 1 to 8, further comprising the step of re-tensioning a bolt in one or more of the at least one flanged connection portion of the tower.

10. A control device (50) for a wind turbine control system, comprising a processor (62) and a memory module (64), wherein the memory module includes a set of program code instructions that, when executed by the processor, perform the method according to any one of claims 1 to 8.

11. A wind turbine (10) comprising a tower (12) and a control device (50) as described in claim 10.

12. A computer program product stored on a machine-readable medium and downloadable from a communication network, comprising program code instructions for carrying out the method according to any one of claims 1 to 8.

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