WO2009033484A2

WO2009033484A2 - A method of controlling a wind turbine, a wind turbine and use of a method

Info

Publication number: WO2009033484A2
Application number: PCT/DK2008/000322
Authority: WO
Inventors: Hans Henrik Lausen
Original assignee: Vestas Wind Systems A/S
Priority date: 2007-09-13
Filing date: 2008-09-12
Publication date: 2009-03-19
Also published as: WO2009033484A3

Abstract

The invention relates to a method for controlling a wind turbine comprising at least two rotor blades, comprising the steps of measuring one or more influence values of at least one of said rotor blades, and controlling the pitch of at least one blade in response to said one or more influence values of at least one of the other rotor blades. Furthermore the invention relates to a wind turbine and use of at method.

Description

A METHOD OF CONTROLLING A WIND TURBINE, A WIND TURBINE AND USE OF A METHOD

Background of the invention

The invention relates to a method of controlling a wind turbine, a wind turbine and use of a method.

Description of the related art

Pitch control of the rotor blades of various wind turbines are known in the art, either to control the speed of the rotor, torque control and/or power control.

For the example of variable speed wind turbines, problems may occur e.g. in the case of sudden wind gusts where the wind speed acting on the rotor may increase, as a related fast increase in the rotational speed of the rotor may follow e.g. due to a lag between the occurrence of a gust at the rotor plane and the actual pitching of the rotor blades. The amount of lag is related to the mechanical dynamic properties of the pitch and rotor system.

One problem related hereto is that said sudden wind gusts may increase loads on wind turbine components with the risk of reaching fatigue limits.

Furthermore e.g. for variable speed wind turbines, the rotational speed of the rotor may increase to near or to limits for the rotational speed.

It is an object of the present invention to provide solutions for wind turbines without the abovementioned disadvantages and for optimizing the control of wind turbines during various operational situations. The invention

The present invention provides a method for controlling a wind turbine comprising at least two rotor blades, comprising the steps of:

measuring one or more influence values of at least one of said rotor blades, and

controlling the pitch of at least one blade in response to said one or more influence values of at least one of the other rotor blades.

By using influence values of one or more rotor blades (B, C,...) for controlling the pitch of another rotor blade (A) it is ensured that a priori knowledge of e.g. wind loads that have been exposed on rotor blades (B, C,...) can be used in optimizing the pitch control of blade (A).

It is furthermore ensured that errors between desired and actual pitch angle of the rotor blades, e.g. due to parameters such as time delay in the pitch control and in the pitch actuator system as well as the mechanical dynamic behaviour of the rotor blades, can be minimized, as said pitch controlling means can bias the pitch control signal to a pitch actuator to obtain an optimum pitch angle at every specific angular position in the rotor plane.

In one aspect of the invention, said influence values comprises values from sensor means such as one or more pitch position sensors and/or one or more blade load sensors and/or one or more rotor azimuth sensors and/or one or more tower acceleration sensors. It is hereby ensured that values of primary parameters that have influences on the optimization of the rotor blade pitch angle are available and can be measured by measuring means and received by pitch controlling means.

In another aspect of the invention, said controlling means for one rotor blade receives influence values of the other rotor blade that most recently has taken the same angular position in the rotor plane. It is hereby ensured that the said a priori knowledge of e.g. wind loads at a certain angular position, measured at the other rotor blade is valid and that environmental parameters such as wind loads have not changed significantly from the time of measurement to the time that said one rotor blade takes the same angular position as the position of measurement.

In yet another aspect of the invention, the method further comprises the step of controlling the pitch of at least one blade in response to an overall pitch reference signal. Hereby it is ensured that the control signal for the pitch actuator of a first rotor blade can be a processed combination of said received influence values of at least one second rotor blade and an overall pitch reference signal. It is hereby achieved that e.g. in the case of loss of received influence values, the pitch controlling means can still operate due to the received overall pitch reference signal.

In yet another aspect of the invention, the method further comprises the step of controlling the pitch of at least one blade in response to influence values from the blade itself. It is hereby ensured that the said first rotor blade is pitch operated on the basis of actual instant measured influence values, depicting the load conditions that actually act on said first rotor blade.

In another aspect of the invention, said influence values are related to the angular position of the rotor blade in the rotor plane. It is hereby insured that measured influence values can be identified as to relate to specific angular positions providing a priori knowledge of actual conditions that can be used for the control of other rotor blades when they takes the same angular position.

In another aspect of the invention, said measuring of influence values is done continuously. It is hereby ensured that the pitch control performance is optimized and follows any change in e.g. environmental conditions such as wind velocities. It is furthermore ensured that influence values related to substantially every angular position of the rotor plane are obtained. In another aspect of the invention, said measuring influence values are sampled influence values at a discrete number of angular positions in the rotor plane. It is hereby ensured that the amount of data showing the distributed influence values for angular positions of the rotor plane is minimized. This in turn ensures a faster data processing by measuring means and/or controlling means.

The invention also relates to a wind turbine comprising

at least two rotor blades including controlling means for controlling the pitch,

measuring means for measuring one or more influence values of at least one of said rotor blades, and

wherein at least one blade is controlled in response to said one or more influence values of at least one of the other rotor blades.

In another aspect of the invention said measuring means comprises sensor means such as one or more pitch position sensors and/or one or more blade load sensors and/or one or more rotor azimuth sensors and/or one or more tower acceleration sensors.

In another aspect of the invention said controlling means for one rotor blade receives influence values of the other rotor blade that most recently has taken the same angular position in the rotor plane.

In yet another aspect of the invention said controlling means further receives an overall pitch reference signal.

In another aspect of the invention said controlling means for said one rotor blade further receives influence values from the blade itself. In a further aspect of the invention, said influence values are related to the angular position of the rotor blade in the rotor plane.

In a further aspect of the invention, said measuring means is measuring said influence values continuously.

In an even further aspect of the invention, said measuring means is sampling said influence values at a discrete number of angular positions in the rotor plane.

In another aspect of the invention, said at least one blade is controlled in response to a weighted combination of said one or more influence values of at least one of the other rotor blades.

In yet another aspect of the invention, said at least one blade is controlled exclusively in response to said one or more influence values of at least one of the other rotor blades.

The invention also relates to use of method as outlined above in a wind turbine as a priori pitch control.

In one aspect of the invention, said a priori pitch control constitutes a part of a redundancy control for the wind turbine.

Figures

The invention will be described in the following with reference to the figures in which fig. 1 illustrates a large modern wind turbine including three wind turbine blades in the wind turbine rotor,

fig. 2 illustrates schematically a frontal view of a wind turbine,

fig. 3 illustrates schematically a side view of a wind turbine,

fig. 4 illustrates schematically a top view of a wind turbine,

fig. 5 illustrates schematically an example of load cells located near the root of wind turbine blades,

fig. 6 illustrates schematically blade root loads on the rotor blades of a 3 bladed wind turbine,

fig. 7 illustrates schematically transformed moment loads, ni_tu_t and m_yaw as a function of one full rotation of the rotor,

fig. 8 illustrates schematically an example of one preferred embodiment of a wind turbine with a control system for controlling the pitch angles of the wind turbine blades.

Detailed description

Fig. 1 illustrates a modern wind turbine 1 with a tower 2 and a wind turbine nacelle 3 positioned on top of the tower.

The wind turbine rotor, comprising at least one blade such as three wind turbine blades 5 as illustrated, is connected to the hub 4 through pitch mechanisms 6. Each pitch mechanism includes a blade bearing and pitch actuating means which allows the blade to pitch. The pitch process is controlled by a pitch controller.

As illustrated in the figure, wind over a certain level will activate the rotor and allow it to rotate in a plane at a perpendicular direction to the wind. The rotation movement is converted to electric power, which usually is supplied to the utility grid as will be known by skilled persons within the area.

One main task for pitch mechanisms 6 of a wind turbine is to turn the rotor blades 5 around their length and for various embodiments of wind turbines the pitch systems are hydraulic systems.

Fig. 2 illustrates schematically a frontal view of a wind turbine. The position of a reference rotor blade (blade 1) in the rotor plane (xz-plane) relative to a virtual vertical line through the centre of the rotor shaft is indicated by θ. For a wind turbine comprising 3 rotor blades, blade 2 will always have the position of θ -120 degrees and in a similar way blade 3 will have the position of θ - 240 degrees.

Fig. 3 illustrates schematically a side view of a wind turbine comprising a rotor connected to the nacelle 3 through the rotor shaft 9, which extends out of the nacelle front.

The rotor blades 5 are influenced by airflow with wind velocities

at different positions on the rotor plane (xz-plane). The airflow produces a wind force Fi_oad(t) dependent of e.g. the wind direction relative to the rotor blades, the area of the rotor blades, the pitch of the rotor blade etc.

As airflow is predominantly non-symmetric e.g. due to wind shear, local turbulence etc. a torque M_tn_t around the rotor x-axis is produced. Fig. 4 illustrates schematically a top view of a wind turbine comprising a rotor connected to the nacelle 3 trough the rotor shaft 9 which extends out of the nacelle front.

The rotor blades 5 are influenced by airflow with wind velocities V_5j6j7,8(t) at different positions on the rotor plane (xz-plane). The airflow produces a wind force Fi_oad(t) dependent of e.g. the wind direction relative to the rotor blades, the area of the rotor blades, the pitch of the rotor blade etc.

As airflow is predominantly non-symmetric e.g. due to yaw error, local turbulence etc. a torque M_yaw around the rotor z-axis is produced.

Fig. 5 schematically illustrates for one embodiment of a wind turbine, sensor means 10 installed at or near the root of each rotor blade 5 in order to measure e.g. load moment values mi, m₂, m₃ on blade 1, 2, 3 respectively.

By continuously measuring the present load moments values on the rotor-blades, calculating an desired optimum pitch angle setting and feeding this information to the pitch control system in a closed feedback loop, it is possible to optimize control values e.g. to (substantially) control the rotor at the design limits of the wind turbine and especially the design limits of the wind turbine blades.

As an example of prior art for controlling out of plane moment loads on wind turbine blades of a wind turbine, fig. 6 schematically illustrates the blade root loads M_R = [mi m₂ m₃]^τ on the rotor blades of a 3 bladed wind turbine are defined as a result of a given linear wind shear distribution between a rotor blade top position (θ = 0 degrees) and down-ward position (θ = 180 degrees) corresponding closely to an idealized free wind inflow situation.

Transforming MR into a coordinate system defined by the tilt, yaw and thrust equivalent directions, the respective moments loads m_tiit, m_yaW3 m_SUm become: m_tilt = Hi₁ • cos(<9)+ m₂ • cos(<9 + 24θ)+ m₃ • cos(<9 + 120) m_yaw = -nii -Sm(^)- Hi₂ ^(0 + 24O)-In₃ - sin^ + ^O) m_s«m ^{= m}i +m₂ +m₃

For the loads illustrated in figure 6, the said transformed moment loads, ni_tπ_t, m_yaw, are illustrated in fig. 7 as a function of one full rotation of the rotor. For this idealized example of a prior art, m_tu_t and m_yaw are constant.

For other examples of controlling said loads where said blade root loads MR are under influence of e.g. non-linear, time varying wind shear comprising turbulent influences, said m_tϋt and m_yaw are not constant.

Parameters such as delay in the pitch control, the pitch actuator system and the mechanical dynamic behaviour of the rotor blades produces an error between desired and actual pitch angle of the rotor blades.

In order to minimize said error and to optimize wind turbine performance, the present invention provides a learning pitch system, where measured influences on one rotor blade at positions around the rotor plane, is used for control of the following rotor blade that moves into the same angular position in the rotor plane under influence of substantially the same relatively slowly varying wind parameters i.e. blade X measures one or more parameters in one position of the rotor plane. Based on these measurements it is calculated how the next blade that passes the same position is to react.

Fig. 8 illustrates schematically an example of one preferred embodiment of a wind turbine with a control system for controlling the pitch angles of the wind turbine blades 5. Influence values of one wind turbine rotor blade e.g. blade 3 are measured with measuring means 11 preferably comprising sensor means 10 such as pitch position sensors, blade load sensors, rotor azimuth sensors, tower acceleration sensors etc. The measured values are related to the blade angular position. The measured sensor data are supplied to measuring means for preprocessing.

Preprocessed sensor data of blade 3 is supplied to the pitch controlling means of blade 1 which will be the next rotor blade that takes the same angular position as blade 3 in the rotor plane.

The controlling means preferably includes a microprocessor and computer storage means for continuous control and/or processing of the said sensor data.

As the measured sensor data are related to the blade angular position in the rotor plane, a priori knowledge of e.g. the loads at every angular position is present. Thereby the measured data of blade 3 that is received by controlling means of blade 1 can be used as a priori data in the process of calculating an optimum pitch angle of blade 1 when it takes the same angular positions as blade 3.

The pitch controlling means establishes a pitch angle command signal that further is provided to a pitch actuator system connected to the rotor blade as illustrated in fig. 8.

For various embodiments of the invention, the pitch controlling means further receives an overall pitch reference input as indicated on fig. 8.

For further embodiments of the invention, a pitch controller for a first rotor blade can receive influence values from more than one second rotor blade.

For preferred embodiments of the invention the measured sensor data are used in parallel processes, where influence values of sensor means 10 of blade X are used as feedback to immediate pitch control of blade X itself as well as a priori data for pitch control of one or more blades Y.

Faulty situations can occur where sensor means 10 for one rotor blade - e.g. blade 1 of fig. 8 - is non-operational e.g. due to break down of the sensor.

According to various embodiments of the present invention the pitch controlling means of blade 1 can still be operational as it receives influence values from sensor means 10 of blade 3.

As a result of this it is not necessary to terminate energy production and close down the wind turbine if one of said sensor means 10 is non-operational.

List

1. Wind turbine

2. Tower

3. Nacelle

4. Hub

5. Blade

6. Pitch mechanism

7. Virtual centre line of rotor blade

8. Virtual vertical line of wind turbine

9. Rotor shaft

10. Sensor means

11. Measuring means

Claims

1. Method for controlling a wind turbine comprising at least two rotor blades, comprising the steps of

- measuring one or more influence values of at least one of said rotor blades, and

- controlling the pitch of at least one blade in response to said one or more influence values of at least one of the other rotor blades.

2. Method according to claim 1, wherein said influence values comprises values from sensor means such as one or more pitch position sensors and/or one or more blade load sensors and/or one or more rotor azimuth sensors and/or one or more tower acceleration sensors.

3. Method according to claim 1, wherein said controlling means for one rotor blade receives influence values of the other rotor blade that most recently has taken the same angular position in the rotor plane.

4. Method according to claim 1, further comprising the step of controlling the pitch of at least one blade in response to an overall pitch reference signal.

5. Method according to any of the preceding claims, further comprising the step of controlling the pitch of at least one blade in response to influence values from the blade itself.

6. Method according to any of the preceding claims, wherein said influence values are related to the angular position of the rotor blade in the rotor plane.

7. Method according to any of the preceding claims, wherein said measuring of influence values is done continuously.

8. Method according to any of the preceding claims, wherein said measuring influence values are sampled influence values at a discrete number of angular positions in the rotor plane.

9. A wind turbine comprising

- at least two rotor blades including controlling means for controlling the pitch,

- measuring means for measuring one or more influence values of at least one of said rotor blades, and

10. A wind turbine according to claim 9, wherein said measuring means comprises sensor means such as one or more pitch position sensors and/or one or more blade load sensors and/or one or more rotor azimuth sensors and/or one or more tower acceleration sensors.

11. A wind turbine according to claim 9, wherein said controlling means for one rotor blade receives influence values of the other rotor blade that most recently has taken the same angular position in the rotor plane.

12. A wind turbine according to any of claims 9 to 11, wherein said controlling means further receives an overall pitch reference signal.

13. A wind turbine according to claim 9, wherein said controlling means for said one rotor blade (5) further receives influence values from the blade itself.

14. A wind turbine according to any of claims 9 to 13, wherein said influence values are related to the angular position of the rotor blade in the rotor plane.

15. A wind turbine according to claim 9, wherein said measuring means is measuring said influence values continuously.

16. A wind turbine according to claim 9, wherein said measuring means is sampling said influence values at a discrete number of angular positions in the rotor plane.

17. A wind turbine according to any of claims 9 to 16, wherein said at least one blade is controlled in response to a weighted combination of said one or more influence values of at least one of the other rotor blades.

18. A wind turbine according to any of claims 9 to 17, wherein said at least one blade is controlled exclusively in response to said one or more influence values of at least one of the other rotor blades.

19. Use of method according to claims 1 to 8 in a wind turbine as a priori pitch control.

20. Use of a method according to claim 19, wherein said a priori pitch control constitutes a part of a redundancy control for the wind turbine.