Method for reducing rotor blade vibrations during wind turbine installation

Abstract

The invention provides a method for a wind turbine, having rotor assembly including a rotor hub and rotor blades, to be performed when the rotor assembly is in a partially installed state in which one or more of the rotor blades is finally installed in the rotor hub and one or more of the rotor blades is in a pre-installed state relative to the rotor hub. The method includes receiving sensor data indicative of vibrations of the rotor blade(s) finally installed in the rotor hub, and determining, based on the received sensor data, whether an amplitude of the vibrations of the rotor blade(s) finally installed in the rotor hub exceeds a defined threshold amplitude. If the vibrations amplitude exceeds the threshold amplitude, then the method includes outputting a signal for adjusting pitch of at least one of the finally installed rotor blades to reduce the vibrations amplitude.

Description

[0001] METHOD FOR REDUCING ROTOR BLADE VIBRATIONS DURING WIND TURBINE

[0002] INSTALLATION

[0003] TECHNICAL FIELD

[0004] The invention relates to a method for a wind turbine to reduce vibrations of rotor blades of the wind turbine during installation of the wind turbine. In particular, the method is to be performed when a rotor assembly of the wind turbine is in a partially installed state in which at least one of the rotor blades is finally installed in a rotor hub of the rotor assembly and at least one of the rotor blades is not finally installed relative to the rotor hub.

[0005] BACKGROUND

[0006] Wind turbines include a rotor and a number of rotor blades - typically, three rotor blades - connected to the rotor. Wind flowing past the wind turbine causes the rotor blades to rotate about a rotational axis of rotor, and a generator is used to generate electrical power from the energy captured from the wind by the rotor blades, e.g. to be supplied to an electrical grid.

[0007] The rotor has a rotor hub that receives and holds the rotor blades. During installation of some wind turbines, the rotor blades are lifted and secured to the rotor hub one at a time. Typically, when the rotor blades are being lifted and secured the wind turbine is in a completely still configuration. This means that features such as automatic yaw control of the wind turbine nacelle is disabled, and the rotor lock may be engaged to prevent rotation of the rotor.

[0008] In such a still configuration, a wind turbine may experience misalignment between the nacelle heading and the incoming wind (yaw error), which would normally be mitigated by turning the nacelle (yawing) into the incoming wind. Blade edge vibrations can happen in such conditions, even at relatively low wind speeds and even when only some of the blades have been secured to the rotor hub.

[0009] It is desired to mitigate or reduce blade vibrations in such cases. It is known to implement a so-called ‘fishnet solution’, in which a net is used to cover part of a blade before installation. This increases the roughness of the blade surface, which alters the aerodynamic profile of the blade to reduce a maximum lift of the blade, thereby reducing some modes of blade vibration.

[0010] US 2024 / 060473 A1 discloses that a fully or partially built wind turbine installation can take on variable operating conditions each characterised by a combination of settable installation conditions of the wind turbine and environment / wind conditions that may be captured. Operating conditions that are to be avoided, e.g. because they lead to large blade vibrations, are stored in memory. Environmental conditions are captured, and then installation settings are selected based on the captured environmental conditions to ensure that operating conditions to be avoided are not implemented.

[0011] US 12037984 B1 discloses an approach for reducing vibrations in wind turbine rotor blades when a rotor hub of the wind turbine is locked against rotation. When the rotor blades are detected to be vibrating above a threshold limit, an angle of attack of the rotor blades is determined based on wind parameters and blade orientation to reduce the vibrations. It is then determined whether loading at one or more wind turbine components will exceed a threshold limit at the angle of attack and, if it will, then the angle of attack is modified by pitching the rotor blades to implement the angle of attack, where the pitching is done using an auxiliary drive system.

[0012] There remains a need to provide improved approaches for mitigating undesirable loading conditions experienced by a wind turbine during installation. It is against this background to which the present invention is set.

[0013] SUMMARY OF THE INVENTION

[0014] According to an aspect of the invention there is provided a method for a wind turbine having a rotor hub and a plurality of rotor blades to be installed in the rotor hub to form a rotor assembly. The method is to be performed when the rotor assembly is in a partially installed state in which one or more of the rotor blades is finally installed in the rotor hub and one or more of the rotor blades is in a pre-installed state relative to the rotor hub. The method comprises receiving, from one or more sensors, sensor data indicative of vibrations of the one or more rotor blades finally installed in the rotor hub. The method comprises determining, based on the received sensor data, whether an amplitude of the vibrations of one or more of the rotor blades finally installed in the rotor hub exceeds a defined threshold amplitude. If the amplitude of the vibrations exceeds the defined threshold amplitude, then the method comprises outputting a signal for adjusting pitch of at least one of the one or more rotor blades finally installed in the rotor hub to reduce the amplitude of the vibrations.

[0015] The outputted signal for adjusting pitch may be a warning signal output to one or more service personnel located at the wind turbine. The warning signal may be a signal instructing the service personnel to adjust pitch of at least one of the one or more rotor blades finally installed in the rotor hub. Optionally, the warning signal is an audio warning signal and / or visual warning signal.

[0016] The method may comprise, in response to the warning signal, one or more of the service personnel effecting manual adjustment of the pitch of at least one of the one or more rotor blades finally installed in the rotor hub.

[0017] The outputted signal for adjusting pitch may include an indication of a specific one of the one or more rotor blades finally installed in the rotor hub for which manual adjustment is to be effected.

[0018] The outputted signal for adjusting pitch may be a control signal configured to control a blade pitch adjustment system of the wind turbine to automatically adjust pitch of at least one of the one or more rotor blades finally installed in the rotor hub.

[0019] The outputted signal for adjusting pitch may include an indication that the pitch is to be adjusted within a defined range of pitching angles. Optionally, the pitch is adjusted by a defined value.

[0020] The method may comprise, prior to receiving sensor data from the one or more sensors, installing one or more of the rotor blades to be finally installed in the rotor hub. Installing the one or more rotor blades may comprise connecting a blade adjustment drive of each of the one or more rotor blades to a blade adjustment system of the wind turbine that is used when the rotor assembly is in a fully installed state. That is, a permanent pitch adjustment system of the wind turbine that is used to during normal operation of the wind turbine may beneficially be used to effect pitch adjustment of the finally installed rotor blades during installation.

[0021] The rotor hub may define a plurality of installation positions for installing each respective rotor blade thereto (at a root end of the blade). The method may comprise receiving a configuration signal indicating a current configuration of the wind turbine that defines which of the plurality of installation positions has a respective one of the rotor blades finally installed therein, thereby defining which one or more of the rotor blades is finally installed in the rotor hub.

[0022] The configuration signal may be received from a user input device configured to receive the current configuration of the wind turbine as input from one or more service personnel located at the wind turbine.

[0023] The method may comprise controlling, based on the received configuration signal, a pitch adjustment system of the wind turbine to permit pitch adjustment of only the one or more rotor blades finally installed in the rotor hub.

[0024] The current configuration of the wind turbine indicated in the configuration signal may indicate a current rotational position of the rotor hub. If the amplitude of the vibrations exceeds the defined threshold amplitude, then the method may comprise determining, based on the current rotational position of the rotor hub, a specific one of the one or more rotor blades finally installed in the rotor hub for which pitch adjustment is to be effected. The outputted signal for adjusting pitch may include an indication of the determined specific one of the rotor blades.

[0025] The method may comprise determining, based on the received sensor data, a vibration mode of the vibrations from a plurality of defined vibration modes. Optionally, the defined vibration modes include one or more of a stall-induced vibration mode and a vortex- induced vibration mode. If the amplitude of the vibrations exceeds the defined threshold amplitude, then the method may comprise determining, based on the determined vibration mode, a degree to which pitch of at least one of the one or more rotor blades finally installed in the rotor hub is to be adjusted. Optionally, the determined degree is a defined value or defined range of values. The outputted signal may include an indication of the determined degree of pitch adjustment.

[0026] The one or more sensors may be one or more blade load sensors of each of the one or more of rotor blades connected to the rotor hub. The sensor data may be edgewise and / or flapwise loading data of the respective rotor blade. The method may comprise, prior to the step of receiving sensor data from the one or more sensors, connecting the one or more sensors, e.g. blade load sensors of the finally installed rotor blade(s), to a controller / control system of the wind turbine.

[0027] The method may be performed when one or more service personnel are located at the wind turbine. Optionally, the one or more service personnel are at or in the rotor hub or a nacelle of the wind turbine. Optionally, the method is performed when one of the rotor blades in a pre-installed state relative to the rotor hub is being installed in the rotor hub.

[0028] According to another aspect of the invention there is provided a non-transitory, computer- readable storage medium storage instructions thereon that, when executed by one or more computer processors, cause the one or more computer processors to perform the method defined above.

[0029] According to another aspect of the invention there is provided a controller for a wind turbine having a rotor hub and a plurality of rotor blades to be installed in the rotor hub to form a rotor assembly. The controller is configured to, when the rotor assembly is in a partially installed state in which one or more of the rotor blades is finally installed in the rotor hub and one or more of the rotor blades is in a pre-installed state relative to the rotor hub: receive, from one or more sensors, sensor data indicative of vibrations of the one or more rotor blades finally installed in the rotor hub; determine, based on the received sensor data, whether an amplitude of the vibrations of one or more of the rotor blades finally installed in the rotor hub exceeds a defined threshold amplitude; and if the amplitude of the vibrations exceeds the defined threshold amplitude, then output a signal for adjusting pitch of at least one of the one or more rotor blades finally installed in the rotor hub to reduce the amplitude of the vibrations.

[0030] According to another aspect of the invention there is provided a wind turbine comprising a controller as defined above.

[0031] BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Examples of the invention will now be described with reference to the accompanying drawings, in which:

[0033] Figure 1 schematically illustrates a wind turbine; Figure 2 shows the steps of a method, to be performed when a rotor assembly of the wind turbine of Figure 1 in a partially installed state, in accordance with an aspect of the invention;

[0034] Figure 3 is a simulated plot of edgewise loading of a finally installed rotor blade of the wind turbine of Figure 1 against time when the method of Figure 2 is implemented at a time t1; and

[0035] Figures 4(a)-4(d) schematically illustrate different configurations of the wind turbine of Figure 1 during installation.

[0036] DETAILED DESCRIPTION

[0037] Figure 1 illustrates, in a schematic view, an example of a wind turbine 10. The wind turbine 10 includes a tower 102, a nacelle 103 disposed at the top of the tower 102, and a rotor 104 operatively coupled to a generator housed inside the nacelle 103. In addition to the generator, the nacelle 103 houses other components required for converting wind energy into electrical energy, e.g. a gearbox, and various components needed to operate, control, and optimise the performance of the wind turbine 10. The rotor 104 of the wind turbine 10 includes a central hub 105 and three rotor blades 106 that project outwardly from the central hub 105. The rotor blades are pitch adjustable. The rotor 104, rotor hub 105 and rotor blades 106 may together be regarded as a rotor assembly (that may also include further components).

[0038] One or more blade load sensors may be placed at, or in the vicinity of, a root end of each blade 106 in a manner such that the sensor detects loading in the blade 106. Depending on the placement and the type of sensor, loading may be detected in the flap (flapwise) direction (in / out of plane) or in the edge (edgewise) direction (in-plane). Such sensors may be displacement sensors, strain gauge sensors or optical Bragg-sensors, for instance.

[0039] The wind turbine 10 may include other types of sensors for measuring various parameters, e.g. wind parameters, associated with wind turbine operation. The wind turbine 10 may include an accelerometer, e.g. for measuring vibrations (fore-aft and / or side-side) of the tower 102. One or more accelerometers may be placed at the top of the tower 102 or in / on the nacelle 103. During installation / erection of wind turbines, such as the wind turbine 10 in Figure 1 , the rotor blades 106 are typically lifted up and secured to the rotor hub 105 one-by-one. The blades 106 may be lifted by a crane. The wind turbine 10 may typically be in a (completely) still configuration in which movement of components is not permitted. For instance, a rotor lock may be engaged to prevent rotation of the rotor 104. Automatic control functions such as yaw control of the nacelle 103 and / or blade pitch actuation / adjustment may be disabled. This is to ensure the safety of service personnel located in / at the wind turbine during installation and to guard against collisions of wind turbine components with other equipment used in the installation process and in the vicinity of the wind turbine, e.g. cranes. Some manual pitching of the rotor blades may be permitted to align the blade bearing on the rotor hub with blade studs on the rotor blade for securing the blade to the hub.

[0040] In a still configuration, the wind turbine 10 is prone to inflow / wind conditions that may lead to blade vibrations. This would typically be avoided during normal operation of the fully installed turbine via the implementation of one or more wind turbine control functions. The control functions may include active yawing of the nacelle 103, rotating the rotor 104 and / or adjusting the pitch angle of the rotor blades 106 (as part of a collective and / or individual pitch control routine).

[0041] The inflow / wind conditions experienced by a wind turbine in a still configuration may result in excessive loading on different components of the wind turbine. In particular, relatively large vibrations - especially edgewise (or edge) vibrations - of the rotor blades may develop. Such vibrations can occur even at relatively low wind speeds and, indeed, below wind speeds at which erection of a wind turbine is expected to be performed. Furthermore, these vibrations can occur during installation when only some of the rotor blades have been secured to, or finally installed in, the rotor hub.

[0042] Different phenomena may give rise to blade vibrations when a wind turbine is subject to certain wind conditions in a still configuration. One such phenomenon is dynamic stall. For pitch regulated wind turbines, the aerodynamic profile of the rotor blades is typically constructed such that there exists a relatively high maximum lift value for an angle of attack (AoA) of the wind turbine around 10-15 degrees. This high lift is typically followed by a sudden drop, if the AoA exceeds the value at which stall occurs, namely, the 'stall angle'. If the wind direction is such that the AoA is constantly in the vicinity of the stall angle, then there is a risk that negative aerodynamic damping occurs, as the blade movement will result in changing AoA. In this case, large blade edge vibrations can occur in resonance with various structural modes of the wind turbine, hereunder eigenmodes in the edgewise direction of the blade.

[0043] Another such phenomenon is vortex shredding. This is well known from many different structures, such as high rise buildings, bridge decks and chimneys. In the context of wind turbines, periodic shedding of vortices on the blades - as well as the tower and nacelle - may at certain inflow conditions match the eigenfrequency of different vibration modes of the wind turbine.

[0044] It has previously been considered that performing installation of a wind turbine in a still configuration is beneficial because this minimises the risk of service personnel / technicians being harmed by moving parts / components of the wind turbine. However, an excessive build-up of vibrations in rotor blades of a wind turbine in a still configuration during installation can pose safety risks for service personnel at the wind turbine, e.g. in the wind turbine rotor.

[0045] It is noted that yawing of a wind turbine during its installation is typically not permitted as this risks already-installed rotor blades colliding with installation equipment, such as cranes and installation vessels, which can cause damage to the various components. Also, a rotor lock of the wind turbine rotor may need to be engaged to prevent rotation of the rotor during at least part of the installation process.

[0046] The present invention is advantageous in that it provides for an approach to mitigate or prevent excessive build-up of rotor blade vibrations during installation of a wind turbine. In particular, the invention benefits from being appropriate / safe to implement when one or more service / installation personnel / crew are on / in the wind turbine during installation, e.g. in the wind turbine rotor as one of the rotor blades is being installed in I secured to the rotor hub. The invention beneficially allows for wind turbine installation to be performed in a greater variety of wind conditions, e.g. higher wind speeds.

[0047] The advantageous effects of the invention are achieved by detecting / measuring the onset of vibrations of one or more rotor blades that are already installed in the rotor hub, e.g. using blade load sensors, and generating / outputting a signal for adjusting the pitch angle of one or more already-installed blades in order to alleviate the vibrations. The signal may beneficially be a warning signal to alert installation / service crew of the excessive vibrations and to instruct them to manually pitch the one or more installed rotor blades to a different pitch angle. Indeed, this may be performed while another one of the rotor blades is in the process of being installed (such that installation crew are present in / at the wind turbine rotor). The output signal may additionally / alternatively be a control signal to effect automatic pitch adjustment of one or more rotor blades that have already been installed. The invention may beneficially provide for permitting adjustment - manual and / or automatic - of only those rotor blades that have been installed in the rotor hub. Further advantageous effects of examples of the invention will be described, or will otherwise become apparent, in the following description.

[0048] Figure 2 shows the steps of a method 20 in accordance with examples of the invention. The method 20 is performed during installation of the wind turbine 10 when the wind turbine rotor assembly is in a partially installed state, or at another time when the rotor assembly is in a partially installed state, such as during maintenance of the wind turbine 10, e.g. when one or more components of the rotor assembly are being replaced.

[0049] In a partially installed state of the rotor assembly, at least one of the rotor blades 106 is finally installed in the rotor hub 105 and at least one of the rotor blades is in a pre-installed state relative to the rotor hub 105. For a wind turbine with three rotor blades, this means that in the partially installed state of the rotor assembly, either: one blade is finally installed, and the other two blades are in a pre-installed state; or two blades are finally installed, and the other one blade is in a pre-installed state.

[0050] By ‘finally installed’ is meant that a rotor blade has been fully secured to the rotor hub 105 and that any installation / configuration processes to complete installation of the rotor blade have been performed. For instance, after a rotor blade is secured to the rotor hub, some configuration of the rotor blade may be needed to ensure mechanical completion. This can involve rotating the rotor 104 such that the installed rotor blade 106 is pointing directly downwards, and then adjusting the pitch angle of the rotor blade 106 to reach all of the bolts of the blade 106.

[0051] By ‘pre-installed state’ is meant that a rotor blade is not yet finally installed. This includes both: situations where installation of the rotor blade has not yet commenced; and situations where installation of the rotor blade has been only partially completed. Indeed, the pre- installed state includes a situation when a rotor blade has been secured to the rotor hub, but any required installation / configuration processes have not yet been completed.

[0052] Referring back to Figure 2, at step 201 the method 20 involves receiving sensor data indicative of vibrations of the one or more of the rotor blades 106 that are finally installed in the rotor hub 105. The sensor data is received from one or more sensors that are part of the wind turbine 10 or located in the vicinity of the wind turbine 10. The sensor data may in some examples be received from different types of sensor. The sensors may be permanent sensors in the sense that they are present after installation of the wind turbine is complete. The sensor data may in some examples be received from sensors that are present in / at the wind turbine 10 only during installation of the wind turbine 10 (temporary sensors).

[0053] In some examples, the sensor data is received from one more of the blade load sensors of the wind turbine 10. In particular, the sensor data is received from the or each blade load sensor of each rotor blade 106 that is finally installed in the rotor hub 105. During installation of a rotor blade, the or each blade load sensor of the rotor blade may be connected I plugged in to a controller or control system of the wind turbine 10. The loading measured by the blade load sensors may typically be loading in an edgewise direction, that is then used to detect vibrations of the rotor blade in the edgewise direction. However, loading in the flapwise direction may additionally or alternatively be monitored.

[0054] Typically, once a wind turbine rotor is fully installed a calibration routine is performed to properly calibrate blade load sensors of each of the rotor blades to map strain measurements to load signal outputs. To allow blade load sensors of finally installed rotor blades to be used prior to the calibration routine having been performed - in particular, for the above purpose of monitoring vibrations during installation of the rotor - the blade load sensors may be provided / loaded with a default calibration for mapping strain measurements to load signal outputs. This default calibration is sufficient to allow a controller of the wind turbine to detect blade vibrations, based on the blade load sensor measurements, during installation of the wind turbine rotor.

[0055] In some examples, other types of sensor may be used to obtain sensor data indicative of rotor blade vibrations. This may include one or more of a tower top accelerometer, wind speed sensor, wind direction sensor, etc. The other types of sensor may in some examples be used where measurements from blade load sensors are not available, e.g. if the blade load sensors are not connected or present.

[0056] Referring back to Figure 2, at step 202 the method 20 involves determining, based on the sensor data received at step 201 , whether an amplitude of the vibrations of one or more of the rotor blades 106 finally installed in the rotor hub 105 exceeds a defined threshold amplitude. The defined threshold amplitude may be any suitable value. Figure 3 is a simulated plot 30 of edgewise loading measured by a blade load sensor of a finally installed rotor blade against time. It is observed that the amplitude of the measured signal increases over time - indicating the onset of edgewise vibrations - and the amplitude reaches a threshold value at a time t1.

[0057] At step 203, the method 20 involves outputting a signal for adjusting pitch of at least one of the one or more rotor blades 106 finally installed in the rotor hub 106 to reduce the amplitude of the vibrations. This step is performed if the amplitude of the vibrations exceeds the defined threshold amplitude.

[0058] The outputted signal can take different forms. In some examples, the outputted signal is a warning signal to inform service personnel present at the wind turbine 10 that vibrations of the already-installed rotor blade(s) has exceeded a certain level. The warning signal may for instance be an audio and / or visual warning signal, e.g. a warning tone, audio announcement, illuminated light (e.g. flashing LED), etc.

[0059] The warning signal indicates that pitch adjustment of one or more of the finally installed rotor blades 106 is needed to dampen the blade vibrations. In response to the outputted warning signal, one or more service personnel present at the wind turbine 10 may effect manual adjustment of the pitch angle of one or more of the finally installed rotor blades, e.g. using a pitch adjustment system of the wind turbine 10. For instance, service personnel may be present in the rotor hub 105 to install one of the rotor blades 106 into the rotor hub 105 and, upon becoming aware of the warning signal, may effect manual adjustment of a different one (or more) of the rotor blades 106 that is finally installed (and so for which pitch adjustment is possible / permitted). As service personnel working to install a rotor blade may be in close proximity to a different, finally installed rotor blade (in the rotor hub), then manual pitch adjustment of the finally installed blade may be preferred in some examples for a personnel safety point of view. The warning signal may provide an indication to the service personnel which of the (finally installed) rotor blades 106 to move. In one example, the warning signal may simply indicate each of the rotor blades 106 that are finally installed, and the service personnel can adjust the pitch angle of one or more of these. In other examples, a specific one of the finally installed rotor blades 106 may be indicated in the warning signal. This may be based on the rotational position of the one or more finally installed rotor blades 106 when the blade vibrations exceed the threshold level. Alternatively, this may be based on the detected level of vibrations of each of the finally installed rotor blades.

[0060] The rotor hub 105 includes a defined position to hold / receive each of the blades 106. The warning signal may indicate which of the rotor blades 106 to be moved (or can be moved) by indicating in the rotor hub 105 which of the defined positions of the rotor hub 105 has a rotor blade 105 finally installed therein, e.g. a warning light adjacent the relevant defined position(s). For instance, if two of the rotor blades 106 of the wind turbine 10 are finally installed, then it may only be needed or desired to adjust the pitch angle of one of these finally installed blades to break the onset of vibrations in one or more of the blades.

[0061] The pitch angle of the or each finally installed rotor blade to be moved can be adjusted by any suitable value. Service personnel may be permitted to move a finally installed rotor blade by any desired amount. In some examples, the service personnel may move, or be permitted to move, a finally installed rotor blade within a defined range of pitch angles. Even relatively small adjustments of rotor blade pitch angle can break / disrupt the build-up of blade vibrations, and so relatively small adjustments may be sufficient (and indeed preferable) in examples of the described method. The defined range of pitch angles may therefore be relatively small compared to a complete range of pitch angles achievable for the rotor blade(s). For instance, the defined range may be less than 30 degrees, less than 20 degrees, less than 10 degrees, or any other suitable limited range of pitch angles.

[0062] The outputted warning signal may indicate to what degree service personnel are to move one or more of the finally installed rotor blades 106. For instance, the warning signal may include an indication of the desirable or permitted range of pitch angle values (e.g. in degrees) that the rotor blade(s) 106 may be moved within. The warning signal may include an instruction or recommendation of a defined amount (and optionally, a direction) that service personnel are to adjust rotor blade pitch, such as a prescribed number of degrees, e.g. 5 degrees, 10 degrees, etc. The defined amount may be a fixed amount or may be determined based on, for instance, the level of blade vibrations being experienced. The rotor blades 106 may be installed into the rotor hub 105 at a default pitch angle. This default pitch angle may be at, or close to, a stall angle of the wind turbine. Adjustments to the pitch angle in response to the onset of blade vibrations may typically be to reduce pitch angle from the default pitch angle. In some examples, it may be desired to pitch the rotor blade(s) to angle relatively close to the default pitch angle (which may be close to the stall angle). The desired degree of which pitch angle adjustment may depend on factors such as wind direction. In general, it is desired to adjust blade pitch in a manner that guards against relatively high loading being experienced while the wind turbine 10 is in a still configuration, e.g. with the rotor lock engaged.

[0063] Referring back to Figure 3, at time t1 the warning signal is output and manual adjustment of one of the finally installed rotor blades 106 is implemented. In this example, the pitch angle of said rotor blades is reduced slightly from a default pitch angle. It is observed that the blade vibrations then reduce after time t1.

[0064] The manual pitch adjustment may be performed by service personnel using a permanent pitch adjustment system of the wind turbine 10, i.e. the same pitch adjustment system used during normal operation of the (fully installed) wind turbine. The process of fully installing a rotor blade into the rotor hub may therefore include attaching a hydraulic drive of a pitch adjustment drive of the rotor blade to a hydraulic system of the wind turbine 10, and attaching an electric pitch drive to a power source of the wind turbine 10 that is used in the fully installed state, i.e. used during normal wind turbine operation. In order to use the pitch adjustment system during installation, service personnel may need to pressurise the system, e.g. by actuating a switch or button, and select which rotor blade to pitch, e.g. by actuating another switch or button.

[0065] Referring again to step 203 of Figure 2, in some examples the outputted signal for adjusting blade pitch may be a control signal configured to automatically effect pitch adjustment of one or more of the finally installed rotor blades 106. In particular, the control signal may control the pitch adjustment system of the wind turbine 10 to adjust the pitch angle of the relevant finally installed blade(s). Similarly to above, the degree to which the pitch angle is adjusted may be a prescribed value or a value within a defined range of pitch angles. The amount by which the pitch angle is adjusted automatically may be preset or may be determined (automatically) based on factors such as the level of blade vibrations being experienced, wind speed, wind direction, etc. As mentioned above, the rotor hub 105 includes a defined position to hold / receive each of the blades 106. When automatic adjustment of blade pitch angle is to be implemented, a controller determining when to instruct automatic pitch adjustment may receive an input signal indicative of which of the defined rotor hub positions have a rotor blade 106 finally installed thereto. This input signal may be generated automatically upon a rotor blade 106 being finally installed in the rotor hub 105 at one of the defined positions. Alternatively, this input signal may be generated manually by a service person interacting with an input device (e.g. switch) to indicate that a rotor blade 106 has been finally installed in a defined position of the rotor hub 105. Based on the indication provided to the controller as to which rotor hub positions have rotor blades finally installed thereto, a control signal that effects automatic blade pitch adjustment only at the identified rotor hub positions is generated and output.

[0066] During an installation phase, the wind turbine 10 is typically moved through a number of different configurations or positions. Figures 4(a)-4(d) schematically illustrate configurations 41-44 that are cycled through in one example in which rotor blades 106 are installed in the wind turbine 10 one at a time. At the start of the installation phase, the wind turbine 10 is in a first configuration 41 - illustrated in Figure 4(a) - in which none of the rotor blades have yet been installed in the rotor hub 105. Figure 4(a) also illustrates a first one A of the rotor blades 106 being lifted and secured to the rotor hub 105. The rotor 104 may be rotated to a different position and a second one B of the rotor blades 106 is lifted and secured to the rotor hub 105 in a second configuration 42, as illustrated in Figure 4(b). The rotor 104 may be rotated to a further different position and a third one C of the rotor blades 106 is lifted and secured to the rotor hub 105 in a third configuration 43, as illustrated in Figure 4(c). Figure 4(d) illustrates a fourth configuration 44 in which each of the rotor blades 106 is finally installed. A rotor lock may be engaged or disengaged in some of these configurations 41-44.

[0067] The specific configuration that the wind turbine 10 is in during installation may inform which finally installed rotor blade(s) 106 to move, and by how much. This may also inform which rotor blades 106 it is permitted to move, either manually or automatically.

[0068] A current configuration of the wind turbine 10 may be input manually by service personnel at the wind turbine 10. For instance, a dedicated input device may be provided in the rotor hub 105, nacelle 103 or tower 102 of the wind turbine 10 that is accessible by service personnel during wind turbine installation. A service person may input a specific configuration from a list of defined configurations, e.g. the configurations illustrated in Figure 4. Alternatively, a service person may individually input which of the rotor blades 106 is finally installed, and so can be moved, and which of the rotor blades 106 is not yet finally installed, and so cannot be moved. Based on this manual selection, a rotor hub position where the corresponding rotor blade is not yet finally installed may be controlled to prevent pitch adjustment, e.g. prevent pitch adjustment of a blade that has been secured to the rotor hub but is not yet finally installed. This may be achieved via a lock being engaged, for instance.

[0069] A current of the wind turbine 10 may alternatively be detected automatically by a controller implementing the described method. In particular, it may be detected which positions of the rotor hub 105 have a rotor blade 106 secured thereto and it may be detected once any configuration processes, e.g. to ensure mechanical completion, have been completed such that a rotor hub 106 is finally installed. The controller may then automatically control a pitch adjustment system, or other components, of the wind turbine 10 to permit movement of only those blades that are finally installed.

[0070] A controller of the wind turbine 10 for performing at least some steps of the described method 20 (including steps 201 , 202, 203) may be in the form of any suitable computing device, for instance one or more functional units or modules implemented on one or more computer processors. Such functional units may be provided by suitable software running on any suitable computing substrate using conventional or custom processors and memory. The one or more functional units may use a common computing substrate (for example, they may run on the same server) or separate substrates, or one or both may themselves be distributed between multiple computing devices. A computer memory may store instructions for performing the methods performed by the controller, and the processor(s) may execute the stored instructions to perform the method. The controller may be located in one or more locations of the wind turbine 10. The controller may be a controller that is to be implemented during normal operation of the wind turbine (i.e. after installation is completed), e.g. a main controller of the wind turbine, or the controller may be a (dedicated) controller to be used to implement this method (and optionally other functions) during installation of the wind turbine.

[0071] Many modifications may be made to the described examples without departing from the scope of the appended claims. Although the described examples relate to methods performed during installation of a wind turbine, it will be understood that the methods are applicable to different scenarios in which the wind turbine rotor assembly is in a partially installed state. For instance, this could be during maintenance of the wind turbine where one or more rotor blades are not fully installed / secured to the wind turbine rotor hub, or during the replacement of a different component of the wind turbine where service personnel are present in the wind turbine.

Claims

CLAIMS1. A method for a wind turbine having a rotor hub and a plurality of rotor blades to be installed in the rotor hub to form a rotor assembly, the method to be performed when the rotor assembly is in a partially installed state in which one or more of the rotor blades is finally installed in the rotor hub and one or more of the rotor blades is in a pre-installed state relative to the rotor hub, the method comprising, at one or more processors: receiving, from one or more sensors, sensor data indicative of vibrations of the one or more rotor blades finally installed in the rotor hub; determining, based on the received sensor data, whether an amplitude of the vibrations of one or more of the rotor blades finally installed in the rotor hub exceeds a defined threshold amplitude; and if the amplitude of the vibrations exceeds the defined threshold amplitude, then outputting a signal for adjusting pitch of at least one of the one or more rotor blades finally installed in the rotor hub to reduce the amplitude of the vibrations.

2. A method according to Claim 1 , wherein the outputted signal for adjusting pitch is a warning signal output to one or more service personnel located at the wind turbine.

3. A method according to Claim 2, the method comprising, in response to the warning signal, one or more of the service personnel effecting manual adjustment of the pitch of at least one of the one or more rotor blades finally installed in the rotor hub.

4. A method according to Claim 3, wherein the outputted signal for adjusting pitch includes an indication of a specific one of the one or more rotor blades finally installed in the rotor hub for which manual adjustment is to be effected.

5. A method according to any previous claim, wherein the outputted signal for adjusting pitch is a control signal configured to control a blade pitch adjustment system of the wind turbine to automatically adjust pitch of at least one of the one or more rotor blades finally installed in the rotor hub.

6. A method according to any previous claim, wherein the outputted signal for adjusting pitch includes an indication that the pitch is to be adjusted within a defined range of pitching angles.

7. A method according to any previous claim, the method comprising, prior to receiving sensor data from the one or more sensors, installing one or more of the rotor blades to be finally installed in the rotor hub, wherein installing the one or more rotor blades comprises connecting a blade adjustment drive of each of the one or more rotor blades to a blade adjustment system of the wind turbine that is used when the rotor assembly is in a fully installed state.

8. A method according to any previous claim, wherein the rotor hub defines a plurality of installation positions for installing each respective rotor blade thereto, and the method comprising, at the one or more processors, receiving a configuration signal indicating a current configuration of the wind turbine that defines which of the plurality of installation positions has a respective one of the rotor blades finally installed therein, thereby defining which one or more of the rotor blades is finally installed in the rotor hub.

9. A method according to Claim 8, wherein the configuration signal is received from a user input device configured to receive the current configuration of the wind turbine as input from one or more service personnel located at the wind turbine.

10. A method according to Claim 8 or Claim 9, the method comprising, at the one or more processors, controlling, based on the received configuration signal, a pitch adjustment system of the wind turbine to permit pitch adjustment of only the one or more rotor blades finally installed in the rotor hub.11 . A method according to any of Claims 8 to 10, wherein the current configuration of the wind turbine indicated in the configuration signal indicates a current rotational position of the rotor hub, and the method comprising, at the one or more processors: if the amplitude of the vibrations exceeds the defined threshold amplitude, determining, based on the current rotational position of the rotor hub, a specific one of the one or more rotor blades finally installed in the rotor hub for which pitch adjustment is to be effected, wherein the outputted signal for adjusting pitch includes an indication of the determined specific one of the rotor blades.

12. A method according to any previous claim, the method comprising, at the one or more processors:determining, based on the received sensor data, a vibration mode of the vibrations from a plurality of defined vibration modes; if the amplitude of the vibrations exceeds the defined threshold amplitude, then determining, based on the determined vibration mode, a degree to which pitch of at least one of the one or more rotor blades finally installed in the rotor hub is to be adjusted, wherein the outputted signal includes an indication of the determined degree of pitch adjustment.

13. A method according to any previous claim, wherein the one or more sensors is one or more blade load sensors of each of the one or more of rotor blades connected to the rotor hub, and wherein the sensor data is edgewise and / or flapwise loading data of the respective rotor blade.

14. A controller for a wind turbine having a rotor hub and a plurality of rotor blades to be installed in the rotor hub to form a rotor assembly, the controller being configured to, when the rotor assembly is in a partially installed state in which one or more of the rotor blades is finally installed in the rotor hub and one or more of the rotor blades is in a pre-installed state relative to the rotor hub: receive, from one or more sensors, sensor data indicative of vibrations of the one or more rotor blades finally installed in the rotor hub; determine, based on the received sensor data, whether an amplitude of the vibrations of one or more of the rotor blades finally installed in the rotor hub exceeds a defined threshold amplitude; and if the amplitude of the vibrations exceeds the defined threshold amplitude, then output a signal for adjusting pitch of at least one of the one or more rotor blades finally installed in the rotor hub to reduce the amplitude of the vibrations.

15. A wind turbine comprising a controller according to Claim 14.

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