WIND TURBINE CONTROL

Abstract

A controller is provided for a floating wind turbine including a rotor with a number of rotor blades connected to a generator. The controller includes an active damping controller for calculating one or more outputs for damping both a first motion of the floating wind turbine in a first frequency range and a second motion of the floating wind turbine in a second frequency range based on an input of the first motion and an input of the second motion, The controller is arranged to calculate an output for controlling a blade pitch of one or more of the rotor blades and/or for controlling a torque of the generator based on an actual rotor speed, a target rotor speed, and the one or more outputs from the active damping controller such that both the first motion and the second motion will be damped.

Claims

1. A controller for a floating wind turbine comprising a rotor with a plurality of rotor blades connected to a generator, wherein the controller comprises: an active damping controller for calculating one or more outputs for damping both a first motion of the floating wind turbine in a first frequency range and a second motion of the floating wind turbine in a second frequency range based on an input of the first motion and an input of the second motion; wherein the controller is arranged to calculate an output for controlling a blade pitch of one or more of the plurality of rotor blades and/or for controlling a torque of the generator based on an actual rotor speed, a target rotor speed, and the one or more outputs from the active damping controller such that both the first motion and the second motion will be damped.

2. A controller according to claim 1, wherein the first motion comprises pitch and/or surge motions in the first frequency range and the second motion comprises pitch and/or surge motions in the second frequency range, wherein the first frequency range is higher than the second frequency range.

3. A controller according to claim 1, wherein the input of the first motion is a measured or estimated velocity of the first motion and the input of the second motion is a measured or estimated velocity of the second motion.

4. A controller according to claim 1, wherein the input of the first motion is measured and/or estimated using the output from a first sensor and the input of the second motion is measured and/or estimated using the output from a second sensor.

5. A controller according to claim 4, wherein the first sensor is a motion sensor and/or the second sensor is a global positioning sensor.

6. A controller according to claim 1, wherein the active damping controller comprises a first control loop and a second control loop, wherein the first control loop receives the input of the first motion and the second control loop receives the input of the second motion.

7. A controller according to claim 6, wherein the first control loop and the second control loop include different filtering and/or parameter settings.

8. A controller according to claim 1, wherein the output for damping the first motion and/or second motion comprises one or more of an additional rotor speed reference signal, an additional blade pitch adjustment and/or an additional generator torque adjustment.

9. A controller according to claim 1, wherein the output for controlling a blade pitch of one or more of the plurality of rotor blades comprises a total blade pitch adjustment and/or wherein the output for controlling the torque of the generator comprises a total generator torque adjustment.

10. A floating wind turbine comprising a rotor with a plurality of rotor blades connected to a generator, and the controller of claim 1.

11. A method of controlling a blade pitch and/or a generator torque of a floating wind turbine, wherein the floating wind turbine comprises a rotor with a plurality of rotor blades, the method comprising: receiving an input of a first motion of the floating wind turbine in a first frequency range; receiving an input of a second motion of the floating wind turbine in a second frequency range; calculating one or more damping outputs for damping both the first motion and the second motion based on the input of the first motion and the input of the second motion; and calculating an output for controlling a blade pitch of one or more of the plurality of rotor blades and/or for controlling a torque of the generator based on an actual rotor speed, a target rotor speed, and the one or more damping outputs such that both the first motion and the second motion will be damped.

12. A method according to claim 11, wherein the first motion comprises pitch and/or surge motions in the first frequency range and the second motion comprises pitch and/or surge motions in the second frequency range, wherein the first frequency range is higher than the second frequency range.

13. A method according to claim 11, wherein the input of the first motion is a measured or estimated velocity of the first motion and the input of the second motion is a measured or estimated velocity of the second motion.

14. A method according to claim 11, wherein the input of the first motion is measured and/or estimated using the output from a first sensor and the input of the second motion is measured and/or estimated using the output from a second sensor.

15. A method according to claim 14, wherein the first sensor is a motion sensor and/or the second sensor is a global positioning sensor.

16. A method according to claim 11, wherein the one or more damping outputs comprise one or more of an additional rotor speed reference signal, an additional blade pitch adjustment and/or an additional generator torque adjustment.

17. A method according to claim 11, wherein the output for controlling a blade pitch of one or more of the plurality of rotor blades comprises a total blade pitch adjustment and/or wherein the output for controlling the torque of the generator comprises a total generator torque adjustment.

18. A method according to claim 11, wherein the method is performed using the controller of claim 1.

19. A computer program product comprising instructions that, when executed on processing circuitry for a floating wind turbine, will configure the processing circuitry to perform the method of claim 11.

20. A controller, computer program product or method as claimed in claim 1, wherein the damping takes place at or above the rated wind speed.

Description

[0132] Certain embodiments will now be described by way of example only and with reference to the accompanying drawings in which:

[0133] FIG. 1 is a graph of rotor thrust force as a function of wind speed for a 2.3 MW floating wind turbine using a conventional blade pitch control system;

[0134] FIG. 2 is a typical power spectrum of oscillations in a floating wind turbine installation;

[0135] FIG. 3 is a schematic diagram of a blade pitch control system with vibration control for a fixed-base wind turbine;

[0136] FIG. 4 is a block diagram of a controller for a floating wind turbine;

[0137] FIGS. 5A, 5B, and 5C are alternative controllers for a floating wind turbine;

[0138] FIGS. 6 and 7 are graphs showing results from a simulation comparing a floating wind turbine with a controller that accounted for motions within a first frequency range only with a floating wind turbine with a controller that accounted for motions in a first frequency range and motions in a second frequency range.

[0139] FIG. 4 illustrates a blade pitch controller 10 that can account for motions in different frequency ranges that may be experienced by a floating wind turbine. FIG. 4 illustrates a blade pitch controller that comprises an active damping controller 12 for calculating blade pitch adjustments β.sub.2 and β.sub.3 for damping a first motion (e.g. pitch and/or surge) in a first frequency range and a second motion (e.g. surge) in a second frequency range respectively. The active damping controller 12 is coupled to a standard blade pitch controller 14. The blade pitch controller 10 is operable in the manner described at or above rated wind speed.

[0140] The standard controller 14 subtracts an actual wind turbine rotor speed ω.sub.r from a reference wind turbine rotor speed ω.sub.ref0. The reference rotor speed ω.sub.ref0 is a target rotor speed at which the wind turbine may be at its most efficient operation when the floating wind turbine is not moving. Therefore, the standard pitch control means 14 attempts to continuously correct the pitch of turbine rotor blades to bring the actual rotor speed ω.sub.r as close to the target rotor speed ω.sub.ref0 as possible. The standard pitch control means 14 does not account for any motions of the wind turbine structure itself, however.

[0141] The active damping controller 12 in FIG. 4 comprises a first damping control loop 16 for calculating an output for damping rigid body motions of the wind turbine in a first frequency range (which may for example be, or comprise, pitch motions) and a second active damping control loop 18 for calculating a second output for damping rigid body motions of the wind turbine in a second frequency range (which may for example be, or comprise, surge motions).

[0142] In the first active damping control loop 16, a first measured or estimated velocity of the wind turbine v.sub.p (which may be referred to as {dot over (x)}.sub.1) is processed by the first signal processing means 20 and then operated on by the first active controller gain K.sub.p and the first active damper controller transfer function h.sub.p(s), which produces a first additional blade pitch adjustment signal β.sub.2. Similarly, in the second active damping control loop 18 a second measured or estimated velocity of the wind turbine v.sub.s (which may be referred to as {dot over (x)}.sub.2) is processed by the second signal processing means 22 and then operated on by the second active controller gain K.sub.s and the second controller transfer function h.sub.s(s), which produces a second additional blade pitch adjustment signal β.sub.3.

[0143] The first signal processing block 20 in the first damping control loop 16 for a floating turbine shown in FIG. 4 uses a sharp low pass filter with a filter frequency that is sufficiently below the wave frequency range (0.05 to 0.2 Hz) in order to avoid damping of wave induced motion, which would lead to bad performance with respect to key wind turbine parameters. The filter frequency may depend on the natural frequency in pitch of the floating wind turbine. It may be around 0.04 to 0.05 Hz.

[0144] The second signal processing block 22 in the second damping control loop 18 uses a similar sharp low pass filter with a filter frequency that is sufficiently below the first frequency range in order to minimise damping of motions in the first frequency range. The filter frequency may be around 0.01 to 0.02 Hz.

[0145] The value of the active damping gains will be tailored depending on the motions being damped. The exact value that is used for this parameter may be found by conventional controller tuning. Indeed, the first and second active damping gains K.sub.p and K.sub.s shown in FIG. 4 will also normally have different values to account for the different levels of damping that may be required for motions in the first and second frequency ranges.

[0146] FIG. 5A shows an example of a blade pitch controller 30 for a floating wind turbine using converters in the form of proportional integral (PI) controllers 31, 33 and 35. This blade pitch controller 30 also comprises a standard controller 34 and an active damping controller 32 similar to the controller 10 of FIG. 4.

[0147] This particular controller 30 uses a PI controller for each of the first and second damping control loops 36, 38 and a PI controller 35 for the standard blade pitch control means 34. Similarly to the controller of FIG. 4, the first damping control loop 36 uses a first active damping gain K.sub.p, represented as a first active damping gain block 37, which operates on a signal processed from the first measured or estimated velocity v.sub.p of the wind turbine before being operated on by a first PI controller 31. The first PI controller 31 comprises processing circuitry that is capable of converting an output from the first active damping gain block 37 in order to produce a first additional blade pitch adjustment ref.sub.2.

[0148] Similarly, the second damping control loop 38 uses a second active damping gain K.sub.s, represented as a second active damping gain block 39, which operates on a signal processed from the second measured or estimated velocity v.sub.s of the wind turbine before being operated on by a second PI controller 33. The second PI controller 38 comprises processing circuitry that is capable of converting an output from the second active damping gain block 39 in order to produce a second additional blade pitch adjustment β.sub.3.

[0149] The additional blade pitch adjustments β.sub.2 and β.sub.3 are combined with the blade pitch adjustment β.sub.1 from the standard controller 34 to provide a total blade pitch adjustment β.sub.ref that is used to control the wind turbine so as to damp the first and second motions and cause the rotor speed co, to tend towards the target rotor speed ω.sub.ref0. This is so as to reduce the forces on the wind turbine structure and mooring system whilst maximising power output for the given wind speed. The controller 30 is operable in the manner described at or above rated wind speed. An alternate controller 40 is shown in FIG. 5B. This is similar to the controller 30 shown in FIG. 5A except it uses a single PI controller 41 for the first and second control loops of the active damping controller 42 rather than two as shown in FIG. 5A. FIG. 5B shows a standard controller 44 and an active damping controller 42, wherein the active damping controller 42 comprises the single PI controller 41, a first and second signal processing blocks 46, 48 and a first and second active damping gain blocks 47, 49. The standard controller 44 is configured to combine the standard blade pitch adjustment β.sub.1 with a combined additional blade pitch adjustment β.sub.4, where the combined additional blade pitch adjustment β.sub.4 is the sum of the first additional blade pitch adjustment β.sub.2 and the second additional blade pitch adjustment β.sub.3. The combination of the standard blade pitch adjustment and the combined additional blade pitch adjustment β.sub.4 provides the total blade pitch adjustment β.sub.ref. The alternate controller 40 is operable in the manner described at or above the rated wind speed.

[0150] Whilst the controllers 10, 30, and 40 of FIGS. 4, 5A, and 5B are illustrated as blade pitch controllers they may additionally or alternatively calculate a generator torque adjustment that can be used to control the wind turbine so as to tend the actual rotor speed ω.sub.r towards the target rotor speed ω.sub.ref0 whilst damping the first and second motions. This can also have the effect of reducing the forces on the wind turbine structure and mooring system whilst maximising power output for the given wind speed.

[0151] Another floating wind turbine controller 50 for damping a first motion and a second motion of different frequencies is shown in FIG. 5C. This also comprises a standard controller 54 and an active damping controller 52.

[0152] This controller 50 receives an input of the first motion v.sub.p (which may be a measured or estimated velocity of the wind turbine in a first frequency range) and processes this using the signal processing 56 and active damping gain K.sub.p 57 to convert it to a first additional rotor speed signal ω.sub.ref1. The controller 50 also receives an input of the second motion v.sub.s (which may be a measured or estimated velocity of the wind turbine in a second frequency range) and processes this using the signal processing 58 and active damping gain K.sub.s 59 to convert it to a second additional rotor speed signal to ω.sub.ref2. ω.sub.ref1 and ω.sub.ref2 are outputs that are for damping the first motion and the second motion respectively. The signal processing 56 and 58 may each be tailored to the frequency range of concern for that control loop. The controller 50 is operable in the manner described at or above the rated wind speed.

[0153] The additional rotor speed signals to ω.sub.ref1 and ω.sub.ref2 for damping the first and second motions are combined with the target rotor speed signal ω.sub.ref0 and the actual rotor speed ω.sub.r is subtracted to provide a rotor speed error ω.sub.error. The rotor speed error ω.sub.error is converted using the convertor 51 to a blade pitch adjustment signal β.sub.ref and/or a generator torque adjustment signal τ.sub.gref that is/are for controlling the floating wind turbine. The convertor 51 may be any known means for converting a rotor speed signal to a blade pitch adjustment signal and/or generator torque signal such as a PI controller, a PID controller, a transfer function, a non-linear equation and/or some other wind turbine control system.

[0154] As with the other controllers 10, 30, and 40 of FIGS. 4, 5A, and 5B, the blade pitch adjustment signal β.sub.ref and/or the generator torque adjustment signal τ.sub.ref can be used to control the wind turbine so as to tend the actual rotor speed ω.sub.r towards the target rotor speed ω.sub.ref0, whilst also damping the first and second motions. This can lead to reducing the forces on the wind turbine structure and mooring system whilst maximising power output for the given wind speed.

[0155] The controller 50 of FIG. 5C uses one converter 51 with inputs from the active damping controller 52 and the standard controller 54.

[0156] The order in which contributions from each of the active damping controller and standard controller are added together or whether they have been processed by a PI controller (or some other converter) may vary between different implementations of the controller.

[0157] The common features between the various exemplary controllers for a floating wind turbine are that the controller comprises an active damping controller and a standard controller. The active damping controller receives an input of the first motion and a separate input of the second motion which have different frequencies. These motions may be rigid body motions, in particular axial motions such as pitch and/or surge. The inputs may be measurements and/or estimates of the velocity of the motions. The inputs may be based on the outputs from different sensors. For example, the velocity of a first, higher frequency motion may be based on the output from a motion sensor provided on the floating wind turbine. The velocity of a second, lower frequency motion may be based on the output from a differential global positioning system.

[0158] The active damping controller calculates one or more outputs (e.g. either two separate outputs or a combined output) that are for causing the damping of the first and second motions. The outputs may be one or more additional rotor speed signals, blade pitch adjustment signals and/or generator torque adjustment signals.

[0159] These outputs from the active damping controller are combined with the actual rotor speed and target rotor speed to provide an output for controlling the actual blade pitch and/or generator torque of the floating wind turbine. This output is for effectively damping the first motion and the second motion. This can reduce loads on both the wind turbine structure and the mooring structure which may be caused by the different types of motion of different frequencies.

[0160] Because separate control loops and/or inputs are provided in respect of the first motion and the second motion of different frequencies they can be tailored to the different frequencies so that effective damping of both types of motions can be achieved.

[0161] FIGS. 6 and 7 show the results of a simulation to help illustrate the benefits of wind turbine control that accounts for motions of different frequencies. FIG. 6 shows the surge motions for a floating wind turbine with a known controller and with a controller that accounts for motions of two different frequencies (in this case higher frequency pitch motions and lower frequency surge motions). FIG. 7 shows the mooring line tension in the highest loaded mooring line from the same simulation. The simulation compares scenarios where the floating wind turbine uses a blade pitch controller with active damping for pitch motions only with a floating wind turbine having a controller with active damping for higher frequency pitch motions and lower frequency surge motions.

[0162] In this simulation, an 8 MW spar buoy-type floating wind turbine with three mooring lines was modelled. FIGS. 6 and 7 depict a snapshot of the simulation between 700 and 1700 seconds, where the total length of the simulation was 2700 seconds. Parameters of the simulation included that the mean wind speed was 14 ms.sup.−1, there was a turbulence intensity of 8.9%, significant wave heights were set to 1.8m, and the characteristic peak period was 13.8 s.

[0163] For the extent of the 2700 second simulation for this particular set of parameter values, it was found that the mooring line fatigue life is increased with a factor of 3.68 in the case of combined active damping for pitch motions and for surge motions (i.e. accounting for motions of two different frequency ranges), compared to that of active damping for pitch motions only (i.e. accounting for motions within one frequency range).