Stopping a wind turbine rotor using a preset pitch rate

Abstract

The invention relates to control of a wind turbine during a stopping process, wherein a stopping controller is used to pitch the blades at a plurality of preset pitch rates including a first pitch rate and a second pitch rate. The stopping controller is arranged to obtain a desired pitch angle for the stopping process and to add an envelope band to the desired pitch angle. During the stopping process, pitching is performed at a pitch rate selected from the plurality of preset pitch rates, and the pitch rate is varied according to a criterion to keep the pitch value within the envelope band.

Description

Technical Field

[0001] The present invention relates to control of a wind turbine and, in particular, to pitching blades at a plurality of preset pitch rates including a first pitch rate and a second pitch rate using a stall controller. Background Art

[0002] In a pitch controlled wind turbine, the pitch of the wind turbine blades is adjusted in response to wind conditions in order to obtain the desired energy production. A variety of situations may arise that result in the need to stop the turbine rotor, either in a complete shutdown or in a situation where the rotor speed is reduced. Generally, the stopping process is accomplished by pitching out of the wind, i.e. feathering, to reduce the aerodynamic lift on the blades, thereby reducing the rotor speed. The stopping process may be a controlled shutdown, such as due to maintenance, high wind shutdown, fault shutdown, emergency shutdown, simple rotor speed reduction, or other reasons. In any case, there is no single stopping process that is suitable for all scenarios, and therefore many different stopping processes are described in the present technology.

[0003] WO 2006 / 007838 A1 (Vestas) discloses a solution in which the blade speed is initially controlled at a high speed and then dropped to a lower speed later in the process, further discussing embodiments in which independent pitch changes continue during the feathering process.

[0004] WO 2015 / 003710 A1 (Vestas) discloses a solution in which, after receiving a shutdown command, independent pitching is maintained to a certain extent. Here, the safety control system takes over the pitching of the blades and maintains the independent pitching in a manner that simulates independent pitching with a constant pitch rate, thereby also obtaining a certain degree of asymmetric load relief during the feathering process.

[0005] It is in this context that the present invention is designed. Summary of the invention

[0006] It is an object of embodiments of the present invention to improve the ability of a wind turbine to handle different rotor stopping processes in a generic manner.

[0007] Accordingly, in a first aspect, a method of controlling a wind turbine in response to a rotor stop signal is provided, the wind turbine comprising a rotor with one or more pitch-adjustable rotor blades; and wherein, upon receipt of the rotor stop signal, the rotor speed is reduced by a stop controller, the stop controller controlling the pitch-adjustable rotor blades towards a feathered position during the stop, and wherein the stop controller is arranged to pitch the blades at a plurality of preset pitch rates including a first pitch rate and a second pitch rate, the second pitch rate being lower than the first pitch rate;

[0008] The method comprises the following steps:

[0009] Obtaining the desired pitch angle of the stopping process;

[0010] adding envelope bands to the desired pitch angle by adding positive and negative values, thereby defining upper and lower band values; and

[0011] Among them, the stop controller is arranged as follows:

[0012] moving the pitch-adjustable rotor blade at a pitch rate selected from the plurality of preset pitch rates until the pitch angle signal is outside of a pitch angle value defined by an envelope band,

[0013] If the pitch angle signal is greater than the upper band value, changing the selected pitch rate to a lower pitch rate among the plurality of preset pitch rates, and

[0014] If the pitch angle signal is less than the lower band value, the selected pitch rate is changed to a higher pitch rate among the plurality of preset pitch rates.

[0015] In this way, a general control method is provided, which helps to follow an arbitrary pitch trajectory during the stopping process by a stop controller with reduced functionality in the sense of being limited to a plurality of preset pitch rates. Following means that the arbitrary pitch trajectory is approximated within the envelope band by the pitch trajectory generated. In this way, the stop controller simulates an approximate pitch stop trajectory by changing the pitch rate when the envelope band limit is reached. More options for stopping the rotor can be provided for the wind turbine. For example, rotor deceleration options, slow shutdown options, fast shutdown options, emergency shutdown options, etc. Embodiments of the present invention support such different shutdown options in a simple and general way, even for a stop controller with reduced pitch functionality. Using a stop controller with reduced functionality is advantageous because it facilitates building the stop controller in a robust and reliable manner. In particular for hydraulic pitch systems, a preset substantially constant pitch rate can be provided by controlling an on / off valve, thereby eliminating the need for a proportional valve.

[0016] In a further aspect, the invention relates to a wind turbine comprising a control system arranged to perform the method according to the first aspect, and to a computer program product comprising software code adapted to control the wind turbine when executed on a data processing system, the computer program product being adapted to perform the method of the first aspect.

[0017] The computer program product may be provided in a computer-readable storage medium or may be downloaded from a communication network. When loaded onto a data processing system, the computer program product includes instructions to cause the data processing system, for example in the form of a controller, to execute the instructions.

[0018] In general, a controller may be a unit or collection of functional units including one or more processors, one or more input / output interfaces, and a memory capable of storing instructions executable by the processors.

[0019] In general, the various aspects of the invention may be combined and coupled in any possible way within the scope of the invention. These and other aspects, features and / or advantages of the invention will become apparent from and elucidated with reference to the embodiments described hereinafter. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0021] Figure 1 An example of a wind turbine is shown schematically;

[0022] Figure 2 schematically illustrates a controller unit implemented to control a wind turbine in response to a rotor stop signal;

[0023] Figure 3 and Figure 4 An exemplary embodiment of a stopping process is shown, wherein a stopping controller controls the pitch-adjustable rotor blades toward a feathered position upon receiving a rotor stopping signal. Figure 3 The conventional pitch control is shown in Figure 4 The independent pitch is shown in ;

[0024] Figure 5 An embodiment is illustrated wherein the desired pitch angle is based on a superposition of a desired collective pitch angle setting and a desired individual pitch angle setting; and

[0025] Figure 6 and Figure 7 A further embodiment of the shutdown process is shown. DETAILED DESCRIPTION

[0026] Figure 1An example of a wind turbine 1 is shown in a schematic diagram. The wind turbine 1 includes a tower 2, a nacelle 3 placed at the apex of the tower, and a rotor 4 operatively coupled to a generator housed in the nacelle 3. In addition to the generator, the nacelle houses various components required to convert wind energy into electrical energy and various components required to operate, control and optimize the performance of the wind turbine 1. The rotor 4 of the wind turbine includes a central hub 5 and a plurality of blades 6 protruding outward from the central hub 5. In the embodiment shown, the rotor 4 includes three blades 6, but the number thereof may vary. In addition, the wind turbine includes a control system. The control system may be placed in the nacelle or distributed at multiple locations within (or outside) the turbine and is communicatively connected. The rotor blades are pitch adjustable, represented here by a pitch angle θ. The rotor blades may be adjusted according to a collective pitch setting, wherein each blade is arranged to the same pitch value. In addition, the rotor blades may be adjustable according to an independent pitch setting, wherein each blade may provide an independent pitch set point. The rotor blades move in the rotor plane, where the angular position of each blade in the rotor plane is determined by the azimuth angle Sure.

[0027] The rotor blades 6 may be mechanically connected to the generator via a gearbox. In direct drive systems and other systems, there may be no gearbox. The electrical energy generated by the generator is injected into the grid via a converter. The generator and converter may be based on a full-scale converter (FSC) architecture or a double-fed induction generator (DFIG) architecture, but other types may also be used.

[0028] The control system comprises a plurality of elements, including at least one main controller having a processor and a memory, so that the processor can perform computing tasks based on instructions stored in the memory. In general, the wind turbine controller ensures that the wind turbine generates the desired power output level during operation. This is achieved by adjusting the pitch angle and / or the power extraction of the converter. To this end, the control system comprises a pitch system, which includes a pitch controller using a pitch reference, and a power system, which includes a power controller using a power reference. The power controller controls various electronic components of the generator converter system in order to transmit the desired power, hereinafter controlling the torque of the generator, which is required to extract the desired power from the wind through the rotor. The control system or elements of the control system can be placed in an electric field controller (not shown) so that the turbine can operate based on instructions provided externally.

[0029] Figure 2Schematically shown are elements of a stop controller 20 arranged to respond to a rotor stop signal to control a wind turbine. The controller unit is implemented with a signal input 21 arranged to receive such a rotor stop signal. The stop process is obtained by controlling the pitch adjustable rotor blades, for example the pitch angle θ of the rotor blades, towards a feathered position based on pitch signals 22, 23 to be sent to actuators of the pitch adjustable rotor blades. It should be noted that the term stop the rotor should be interpreted broadly to include reducing the rotor speed to a lower speed, including a lower control speed and an idling speed, as well as reducing the rotor speed to a complete stop. The rotor stop signal may be a shutdown signal. The feathered position with respect to the wind turbine blades refers to a preset angle selected in the range of 85° to 120° depending on the mechanical design of the pitch system. The specific feathering position of the wind turbine is a design choice.

[0030] The invention relates to the case where the stopping process is handled by a stopping controller with reduced functionality, i.e. the stopping controller cannot control the pitch at an arbitrary pitch rate, but the stopping controller is arranged to pitch the blades at a plurality of preset pitch rates including a first pitch rate and a second pitch rate, the second pitch rate being lower than the first pitch rate. In the figure, this aspect is illustrated by the pitch signals 22, 23, each representing a pitch signal with a given pitch rate. The precise implementation of the interaction between the controller and the pitch actuator of the blade may vary depending on the specific system.

[0031] The pitch rate is generally set to be constant. Depending on the system, this can be achieved in different ways, including constant degrees per second, i.e. related to the movement of an angle, and constant displacement per second, i.e. related to the movement of a piston. For hydraulic systems, the pitch rate may vary slightly with pressure drop, and this variation is understood to be classified under the term constant.

[0032] Figure 3 An exemplary embodiment of a stop process is shown, wherein a stop controller controls the pitch-adjustable rotor blades toward a feathered position upon receiving a rotor stop signal. In the illustrated example, the turbines are operated following a common pitch θcom, a reference during operation. At time t0, the stop controller receives the stop signal and thereafter during the stop process instructs the turbines to follow a common pitch trajectory defined by a desired common pitch angle for the stop process. Figure 4 Another embodiment is shown, in which the turbines are instructed to follow individual pitch trajectories defined by desired individual pitch angles for the stopping process.

[0033] exist Figure 3 In the example of , the desired pitch angle defines a pitch trajectory 30 , with a first phase having a high average pitch rate and a second phase having a lower average pitch rate.

[0034] The figure further shows the rotor speed, showing the turbine operating at rated speed until a rotor stop signal is received at t0, after which the rotor speed decreases towards zero. The rotor speed merely represents a general characteristic of the rotor speed, not the exact rotor speed that matches the pitch angle shown.

[0035] The stop controller 20 comprises a calculation module 24 which is implemented to obtain a desired pitch angle 25 (at Figure 3 30), and by adding positive and negative values, an envelope band 26 is added to the desired pitch angle, thereby defining an upper band value 31 and a lower band value 32. After defining the band, the stop controller is arranged as:

[0036] moving the pitch-adjustable rotor blade at a pitch rate 22, 23 selected from said plurality of preset pitch rates until the pitch angle signal is outside a pitch angle value defined by an envelope band,

[0037] If the pitch angle signal is greater than the upper band value, changing the selected pitch rate to a lower pitch rate among the plurality of preset pitch rates, and

[0038] If the pitch angle signal is less than the lower band value, the selected pitch rate is changed to a higher pitch rate among the plurality of preset pitch rates.

[0039] exist Figure 3 In the example of , the stop controller is arranged to pitch the blades at two preset pitch rates, a first high pitch rate 22 and a second low pitch rate 23. The pitch rates may be set according to a given design. The first pitch rate may be between 3 and 15° / s, while the second low pitch rate may be between 0 and 5° / s. Other pitch rates may also be set, including negative pitch rates.

[0040] After receiving the rotor stop signal at t0, all pitch blades are moved at a high pitch rate 22. When moving the blades, Figure 2 As shown, the pitch angle signal is compared to the envelope band 26, and once it is detected that the pitch angle signal is higher than 33 the upper band value, the selected pitch rate is changed to a low pitch rate 23. The comparison is maintained during the stopping process, and once it is detected that the pitch angle signal is less than 34 the lower band value, the low pitch rate 23 is changed to a high pitch rate 22. This logic remains operational during the stopping process. At this point, it should be noted that this logic allows the stopping controller to follow (in an approximate manner) any desired pitch trajectory.

[0041] Figure 4 An illustrative general implementation is shown. Figure 3 , which shows an example of a stopping process in which a stopping controller moves the pitch-adjustable rotor blades toward a feathered position upon receiving a rotor stop signal. Figure 3By contrast, before and after the time t0 at which the stop controller receives the stop signal, the turbine is operated to follow the independent (possibly cyclic) pitching of the pitch-adjustable rotor blades. Thus, during the stop, the turbine is instructed to follow an independent pitching trajectory defined by the desired pitch angle of each of the pitch-adjustable rotor blades.

[0042] Figure 4 Three pitch trajectories 40, 41 and 42 are shown, but for simplicity, only one of the pitch trajectories 40 is discussed according to an embodiment. It should be understood that the same aspects are also relevant to the other two pitch trajectories 41, 42.

[0043] Combination Figure 4 In the embodiment shown, the stop controller 20 is implemented to follow the Figure 3 The same general steps are followed as in the embodiment of the stopping process, namely obtaining the desired pitch angle 25 for the stopping process and adding an envelope band 26 to the desired pitch angle by adding positive and negative values, thereby defining an upper band value 43 and a lower band value 44. After defining the bands, the stopping controller is arranged as follows:

[0044] moving the pitch-adjustable rotor blade at a pitch rate selected from the plurality of preset pitch rates until the pitch angle signal is outside a pitch angle value defined by an envelope band,

[0045] If the pitch angle signal is greater than the upper band value, changing the selected pitch rate to a lower pitch rate among the plurality of preset pitch rates, and

[0046] If the pitch angle signal is less than the lower band value, the selected pitch rate is changed to a higher pitch rate among the plurality of preset pitch rates.

[0047] exist Figure 4 In the example, stop the controller with Figure 3 Similarly, the arrangement is to pitch the blades at two preset pitch rates, a first high pitch rate 22 and a second low pitch rate 23. The desired pitch angle is as defined by curve 45, shown as an increasing oscillation trajectory. Figure 5 An embodiment is shown how such desired independent pitch trajectories may be determined.

[0048] After receiving the rotor stop signal at t0, the pitch blades move at a high pitch rate 22. Figure 2 and Figure 3 As described in the embodiment of the present invention, when moving the blade towards feathering, the pitch angle signal is compared with the envelope band, and once it is detected that the pitch angle signal is higher than the upper band value 46, the selected pitch rate is changed to a low pitch rate 23. The comparison is maintained during the stopping process, and once it is detected that the pitch angle signal is less than the lower band value 47, the low pitch rate 23 is changed to a high pitch rate 22. This logic remains operational during the stopping process.

[0049] Although not shown, similar to the shown band defined by the boundaries 43 , 44 , there are two further bands, one for each of the two pitch trajectories 41 , 42 . Figure 4 Thus an exemplary embodiment is shown, wherein a stop controller is arranged to independently move each of the one or more pitch-adjustable rotor blades according to a pitch angle defined by an envelope band.

[0050] The desired pitch angle for the stopping process, ie the pitch trajectory for the stopping process, can be generated in different ways.

[0051] Figure 5 An advantageous embodiment is shown, in which the stop controller is implemented in such a way that the desired pitch angle is based on a desired collective pitch angle setting and a desired individual pitch angle setting.

[0052] like Figure 5 Schematically, the desired pitch angle is divided into a desired collective pitch angle setting as shown in box 50, and a desired individual pitch angle setting as shown in box 51. Pitch angle settings based on a combination of collective parts and individual parts are common practices for setting pitch angles. During the stopping process, the common pitch angle setting can be used to control rotor deceleration and thrust problems, while the individual pitch angle settings can be used to mitigate asymmetric loads on the rotor and tower vibrations during the stopping process.

[0053] This embodiment can be used to determine Figure 3 and Figure 4 The desired pitch angle for any example of Figure 3 In an embodiment of the invention, the desired pitch angle may be determined by setting the desired independent pitch angle to zero. Figure 4 In an embodiment, the desired pitch angle may be achieved by setting the desired set pitch angle to zero.

[0054] like Figure 5 As shown, the aggregate pitch angle setting and the individual pitch angle settings are added to produce a desired pitch trajectory 52, as shown in box 53, showing the superimposed pitch trajectory 52. ​​An aggregate pitch trajectory 54 is also shown for illustrative purposes.

[0055] Finally, the envelope band 56 is determined to follow the desired pitch angle of the superimposed trajectory.

[0056] Figure 3 and Figure 4 An example of defining the desired pitch angle for the entire stop process, i.e. the entire stop pitch trajectory, is shown. In one embodiment, the desired pitch angle is predefined for the entire duration of the stop process. That is, the stop controller obtains or generates the desired pitch angle upon receiving the stop signal and generates the desired pitch angle for the entire stop process.

[0057] In one embodiment, the desired pitch angle is determined during the stopping process. That is, the desired pitch angle is determined when the rotor stops. The determination may be based on a duration or sensor input. Such sensor input may be related to parameters such as rotor acceleration, rotor speed, tower top motion, blade loading, thrust, wind speed, wind direction, etc.

[0058] For example, refer to Figure 3 , the specific slope of the linear segment of the pitch trajectory 30 for the desired pitch angle can be determined based on the input. In addition, the timing of switching between the first high average pitch rate and the second lower average pitch rate can be based on the input. As an example, such switching can be done in view of the rotor acceleration angle. In an embodiment, a high average pitch rate can be used until the rotor acceleration is zero, at which time the switch to the lower average pitch rate is completed. Another example may involve the thrust acting on the rotor. For example, based on the rotor speed and blade loading, the thrust value can be determined and used to set the average pitch rate. At this point, even a negative pitch rate can be applied to temporarily increase the thrust on the rotor. This temporary thrust increase can alleviate undesirable forward bending of the tower.

[0059] The purpose of stopping the rotor is to (naturally) reduce the rotor speed. The rotor speed is reduced by pitching the blades outwards towards the feathered position. Different independent pitching activities are applied during the stopping process generally for the purpose of load relief, for example, to relieve asymmetric loads on the rotor or to relieve tower vibrations. In an embodiment, independent pitching activities during the stopping process are only performed when they are strong enough. By using independent pitching only when necessary, wear on the pitch actuator can be reduced. In an embodiment, the desired independent pitch angle setting is only applied when the required amplitude is above a threshold. The required amplitude can be calculated based on the blade load signal or the tower acceleration signal. The amplitude can be the amplitude of the oscillation signal on which the independent pitch is based.

[0060] from Figure 4 It can be seen that when the individual pitch angles are applied during the period until the stop signal is received, the specific pitch angles of the individual blades will be different at time t0.

[0061] In an embodiment, the desired pitch angles of the stopping process may be selected for each pitch-adjustable blade, but they may also be selected to be the same for all pitch-adjustable blades. If the same is selected, the pitch angles of each blade may still be different during the stopping process because the starting angles may be different. In an embodiment where the desired pitch angles of all blades are selected to be the same, some pitch angles at t0 may fall outside the resulting envelope, while some may fall within the resulting envelope, depending on the specific pitch angles of the blades at t0. Figure 6 An illustrative example is shown in FIG. 60 .

[0062] In one embodiment, when a stop signal is received, the pitch-adjustable rotor blades having a pitch angle within the envelope band or a pitch angle below the lower band value are set to move at the highest pitch rate of a plurality of preset approximately constant pitch rates, and the pitch-adjustable rotor blades having a pitch angle greater than the upper band value are set to move at the lowest pitch rate of a plurality of preset pitch rates. In this way, it can be ensured that when the pitch angle is initially outside the envelope band, the pitch angle will fall into the band after a short time. This embodiment can also be used for systems that select the desired pitch angle for each pitch-adjustable blade, since it will result in such blades always being initially pitched at the highest pitch rate.

[0063] Figure 6 Another pitch trajectory is shown to illustrate a further embodiment of the invention.

[0064] In the figure, three different pitch trajectories are shown in the time period before t0. In the time period 61-63 after t0, only a single pitch trajectory and a single envelope band are shown. This is for illustrative reasons, as there may be more envelope bands consistent with various embodiments.

[0065] When the rotor stop signal is received, the desired pitch angle 65 is obtained and the envelope band 66 is determined. In the illustrated embodiment, the bandwidth of the envelope band changes during the stopping process. The change in bandwidth can be performed in different ways, examples including gradually changing at a specific point in the stopping process or as the stopping process proceeds. In the illustrated embodiment, the bandwidth gradually widens as the stopping process proceeds. It is also conceivable to apply a first bandwidth in a first stage 61 with a high average pitch rate and a larger bandwidth in a later stage 62 with a lower average pitch rate. In general, the bandwidth may widen as the rotor speed decreases, because for a slowly rotating rotor, the need for strict control of the stopping process may be less. In addition to the rotor speed, parameters such as pitch angle, pitch speed and pitch acceleration may also be used.

[0066] Figure 6 An embodiment is further shown in which, when the termination criteria are reached, the pitch angle is controlled so that the blades are pitched at one of the preset pitch rates, regardless of the envelope. Here, a low pitch rate is used, and only a single pitch rate is shown in the period 63 after the termination criteria are reached. The termination criteria include rotor speed, pitch angle, pitch velocity and pitch acceleration.

[0067] Figure 7 Another embodiment of the stopping process is shown. Figure 6 In addition, two further embodiments are shown. Independently pitched blades generally do not follow the same pitch trajectory, so at different times the blades will have different pitch angles. Figure 7An embodiment is shown in which the pitch angles are controlled to align 70 all pitch angles in a first process and to pitch at the same pitch rate 71 in a second process when the termination criterion is reached at time tT. Figure 7 It is further shown that after reaching the termination criteria, the pitch rate of the blades may be changed. For example, the pitch rate 71 may be selected to ensure a rapid reduction in the rotation rate to bring the rotor to an almost complete stop as quickly as possible, but as the pitch angle approaches the end stop, a slow pitch rate 72 may be applied to reduce the mechanical shock when the blade reaches the end stop.

[0068] In the illustrated embodiment, only two pitch rates are shown, and the possibility of negative pitch rates has been mentioned. In general, it is understood that more pitch rates can be realized. Naturally, the fewer pitch rates, the simpler the pitch actuation system is required. However, with more pitch rates available, a given pitch trajectory can be followed more precisely, and there may be situations where 3, 4, 5 or even more pitch rates are available.

[0069] The stop controller may be based on a general or standard industrial computing device, but it may advantageously be based on a safety computing device instead; that is, on a safety controller. Although the safety controller in the embodiment may be a safety certified controller, it does not need to be safety certified, but is a controller based on rigorously tested software and hardware that meets the same or similar requirements as required for certification. This type of controller may also be referred to as a safety certifiable controller. Often, the safety-related parts of the control system may be constructed according to the principles given in recognized functional safety standards. Such standards include, for example, ISO13849, IEC61508, and IEC62061. In addition to meeting specific, quantitative requirements for reliability and diagnostic coverage, systems built according to these standards are assumed to be free of system failures, such as software defects. The control system can therefore be divided into a normal control domain that uses standard computing devices to perform computing tasks and a safety control domain that uses safety-related computing devices to perform computing tasks.

[0070] In an advantageous embodiment, the rotor stop signal is generated by a safety controller. In this way, a high reliability of the safety controller for controlling the stop of the rotor can be ensured.

[0071] In an advantageous embodiment, the generation of the rotor stop signal is triggered by the safety controller when a fault signal occurs. The fault signal may originate from a sensor also located in the safety domain, but this is not necessary.

[0072] In an embodiment, a desired pitch angle for the stopping process is determined based on the stored pitch angle signal. The stored pitch angle signal is generated by storing the pitch angle signal for each of the pitch-adjustable rotor blades for at least a portion of a full rotor rotation, for example between 0.5 and 1.5 revolutions, before receiving the rotor stop signal. It may be advantageous to obtain the IP signal component using at least one rotation. In an embodiment, the at least portion of a full rotor rotation is substantially one full rotor rotation.

[0073] In this embodiment, before or upon receiving the rotor stop signal, at least one periodic component of the stored signal is determined. The periodic component may advantageously be determined using a Fourier transform routine including a discrete Fourier transform.

[0074] In this way, upon receiving the rotor stop signal, controlling the pitch-adjustable rotor blades towards the feathered position is accomplished using the pitch control signal including the at least one periodic component.

[0075] In one embodiment, the stored pitch signal may be based on a function of the rotor azimuth angle. Using a pitch signal as a function of the azimuth angle is advantageous because the signal synthesis is independent of the rotor speed while still being able to correctly synthesize the nP component.

[0076] Basing the desired pitch angle of the stopping process on the stored pitch angle signal according to this embodiment is advantageous because the independent pitch activated before receiving the rotor stop signal can be maintained at least to some extent during the stopping period of moving the pitch-adjustable rotor blades towards the feathered position.

[0077] Example embodiments of the present invention are described for illustrative purposes only, and not to limit the scope of the invention as defined in the appended claims.

Claims

1. A method for controlling a wind turbine in response to a rotor stop signal, the wind turbine comprising a rotor with one or more pitch-adjustable rotor blades; and wherein, upon receiving the rotor stop signal, reducing the rotor speed by a stop controller, the stop controller controlling the pitch-adjustable rotor blades towards a feathered position during the stop, and wherein the stop controller is arranged to pitch the blades at a plurality of preset pitch rates including a first pitch rate and a second pitch rate, the second pitch rate being lower than the first pitch rate; Wherein, the method comprises the following steps: Obtaining the desired pitch angle of the stopping process; adding envelope bands to the desired pitch angle by adding positive and negative values, thereby defining upper and lower band values; and Among them, the stop controller is arranged as follows: moving the pitch-adjustable rotor blade at a pitch rate selected from the plurality of preset pitch rates until the pitch angle signal is outside of a pitch angle value defined by an envelope band, If the pitch angle signal is greater than the upper band value, changing the selected pitch rate to a lower pitch rate among the plurality of preset pitch rates, and If the pitch angle signal is less than the lower band value, the selected pitch rate is changed to a higher pitch rate among the plurality of preset pitch rates.

2. The method according to claim 1, wherein: The stop controller is arranged to independently move each of the one or more pitch-adjustable rotor blades according to a pitch angle defined by the envelope band.

3. The method according to claim 1, wherein: The desired pitch angle is based on the desired collective pitch angle setting and the desired individual pitch angle settings.

4. The method according to claim 3, wherein: Only if the required amplitude is above a threshold value, the desired individual pitch angle setting is applied.

5. The method according to any one of claims 1 to 4, wherein: The desired pitch angle is predefined for the entire duration of the stopping process.

6. The method according to any one of claims 1 to 4, wherein: A desired pitch angle is determined during the stopping process.

7. The method according to claim 6, wherein: Based on the duration or sensor input, a desired pitch angle is determined.

8. The method according to any one of claims 1 to 4, wherein: When a stop signal is received, the pitch-adjustable rotor blades having a pitch angle within the envelope band or a pitch angle below a lower band value are set to move at a highest pitch rate among the plurality of preset pitch rates, and the pitch-adjustable rotor blades having a pitch angle greater than an upper band value are set to move at a lowest pitch rate among the plurality of preset pitch rates.

9. The method according to any one of claims 1 to 4, wherein: The bandwidth of the envelope band changes at a specific point in the stopping process or changes gradually as the stopping process proceeds.

10. The method according to any one of claims 1 to 4, wherein: When the termination criterion is reached, the pitch angle is controlled so that the blades are pitched at one of the preset pitch rates without regard to the envelope.

11. The method according to claim 10, wherein: The pitch angles are controlled to align all pitch angles in the first process, and are controlled to pitch at the same pitch rate in the second process.

12. The method according to any one of claims 1 to 4, wherein: The stop controller is implemented as a safety controller.

13. The method according to any one of claims 1 to 4, wherein: The desired pitch angle for the stopping process is determined based on the stored pitch angle signal, where: generating a stored pitch angle signal by storing the pitch angle signal for each of the pitch-adjustable rotor blades for at least a portion of a full rotation of the rotor prior to receiving the rotor stop signal; determining at least one periodic component of the stored signal before or upon receiving the rotor stop signal; Upon receiving the rotor stop signal, controlling the pitch adjustable rotor blades toward a feathered position using the pitch control signal including the at least one periodic component.

14. Computer program products, including: A computer program product adapted as software code for controlling a wind turbine when executed on a data processing system, the computer program product being adapted to perform the method of any of the preceding claims.

15. A wind turbine comprising a control system, the wind turbine comprising a rotor with one or more pitch-adjustable rotor blades, and the control system being arranged to control the wind turbine in response to a rotor stop signal, the control system comprising a stop controller arranged to control the pitch-adjustable rotor blades towards a feathered position during a stop, and wherein, the stop controller being arranged to pitch the blades at a plurality of preset pitch rates including a first pitch rate and a second pitch rate, the second pitch rate being lower than the first pitch rate; Wherein, the stop controller comprises one or more controller units, and the controller units are arranged as follows: Obtaining the desired pitch angle of the stopping process; adding envelope bands to the desired pitch angle by adding positive and negative values, thereby defining upper and lower band values; and Among them, the stop controller is arranged as follows: moving the pitch-adjustable rotor blade at a pitch rate selected from the plurality of preset pitch rates until the pitch angle signal is outside of a pitch angle value defined by an envelope band, If the pitch angle signal is greater than the upper band value, changing the selected pitch rate to a lower pitch rate among the plurality of preset pitch rates, and If the pitch angle signal is less than the lower band value, the selected pitch rate is changed to a higher pitch rate among the plurality of preset pitch rates.

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