A METHOD FOR CONTROLLING A MULTIROTOR WIND TURBINE

Abstract

A method for controlling a multirotor wind turbine comprising two or more energy generating units is disclosed. At least one load carrying structure is connected to a foundation or to a tower via a yaw arrangement, and the load carrying structure carries the at least two energy generating units. A requirement to a change in operation of at least a first of the energy generating units is detected. Control commands for the first energy generating unit and for at least a second energy generating unit, mounted on the same load carrying structure, are generated. The control commands cause the required change in operation, and the control commands cause coordinated operation of at least the first energy generating unit and the second energy generating unit. The control commands are generated under the constraint that a yaw moment of the yaw arrangement is maintained below a predefined threshold level.

Claims

1. A method for controlling a multirotor wind turbine, the multirotor wind turbine comprising two or more energy generating units, each energy generating unit comprising a rotor comprising one or more wind turbine blades, and at least one load carrying structure, the load carrying structure being connected to a foundation or to a tower via a yaw arrangement, and the load carrying structure carrying the at least two energy generating units, the method comprising: detecting a requirement to a change in operation of at least a first of the energy generating units; generating control commands for the first energy generating unit and for at least a second energy generating unit, the first energy generating unit and the second energy generating unit being mounted to the same load carrying structure, the control commands causing the required change in operation, and the control commands causing coordinated operation of at least the first energy generating unit and the second energy generating unit; and controlling the energy generating units in accordance with the generated control commands, wherein the control commands are generated under the constraint that a yaw moment of the yaw arrangement is maintained below a predefined threshold level.

2. The method of claim 1, wherein the load carrying structure comprises two arm structures extending away from the yaw arrangement on opposing sides of a rotation axis of the yaw arrangement, and wherein the first energy generating unit is mounted to a first arm structure and the second energy generating unit is mounted to a second arm structure.

3. The method of claim 1, wherein detecting a requirement to a change in operation of at least the first energy generating unit comprises detecting a change in operational conditions of the first energy generating unit.

4. The method of claim 3, wherein generating control commands comprises setting identical thrust limits for the first energy generating unit and the second energy generating unit.

5. The method of claim 1, wherein detecting a requirement to a change in operation of at least the first energy generating unit is performed based on a command requesting a change in operation of the multirotor wind turbine.

6. The method of claim 1, wherein generating control commands comprises generating identical control commands for the first energy generating unit and for the second energy generating unit.

7. The method of claim 1, wherein generating control commands comprises generating a first control command for the first energy generating unit and a second control command for the second energy generating unit, the second control command differing from the first control command, and wherein the step of controlling the energy generating units comprises controlling the first energy generating unit and the second energy generating unit in accordance with different control commands in a coordinated manner.

8. The method of claim 7, wherein generating control commands comprises: generating a first control command for the first energy generating unit, the first control command causing the first energy generating unit to shut down; and generating a second control command for a second energy generating unit, the second control command causing the second energy generating unit to continue power production at a reduced load level.

9. The method of claim 1, wherein the coordinated operation of the first energy generating unit and the second energy generating unit is a time coordinated operation.

10. The method of claim 1, further comprising monitoring a yaw moment of the yaw arrangement, and wherein generating control commands is performed based on the yaw moment, and the control commands for the second energy generating unit provide instructions to control the second energy generating unit in accordance with the control commands when the yaw moment is below the predefined threshold level.

11. The method of claim 1, further comprising: monitoring operation of the energy generating units during operation in accordance with the generated control commands; and adjusting operation of at least one of the energy generating units in the case that time coordination of operation of the first energy generating unit and the second energy generating unit is lost.

12. The method of claim 1, wherein detecting a requirement to a change in operation is performed by one of the energy generating units.

13. The method of claim 1, wherein detecting a requirement to a change in operation is performed by the multirotor wind turbine.

14. The method of claim 1, wherein detecting a requirement to a change in operation comprises detecting that the first energy generating unit is to shut down.

15. The method of claim 14, wherein generating control commands comprises generating control commands causing the first energy generating unit as well as the second energy generating unit to shut down.

16. The method of claim 1, wherein detecting a requirement to a change in operation comprises detecting that the first energy generating unit is to start up.

17. The method of claim 16, wherein generating control commands comprises generating control commands causing the first energy generating unit as well as the second energy generating unit to start up.

18. The method of claim 16, wherein generating control commands comprises generating control commands causing the first energy generating unit as well as the second energy generating unit to start up in a load reduced operating mode.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0053] The invention will now be described in further detail with reference to the accompanying drawings in which

[0054] FIG. 1 is a diagrammatic view of a multirotor wind turbine being controlled in accordance with a method according to an embodiment of the invention,

[0055] FIGS. 2 and 3 illustrate control of a multirotor wind turbine during shut down in accordance with a prior art method and a method according to an embodiment of the invention, respectively,

[0056] FIGS. 4 and 5 illustrate control of a multirotor wind turbine following an event detection in accordance with a prior art method and a method according to an embodiment of the invention, respectively, and

[0057] FIGS. 6 and 7 illustrate control of a multirotor wind turbine during start up in accordance with a prior art method and a method according to an embodiment of the invention, respectively.

DETAILED DESCRIPTION OF THE DRAWINGS

[0058] FIG. 1 is a diagrammatic view of a multirotor wind turbine 1 being controlled in accordance with a method according to an embodiment of the invention. The wind turbine 1 comprises a tower 2 and a load carrying structure comprising two arms 3. The load carrying structure 3 is connected to the tower 2 via a yaw arrangement 4, and thereby the load carrying structure 3 is capable of performing yawing movements relative to the tower 2.

[0059] Each of the arms carries an energy generating unit 5, each energy generating unit 5 comprising a rotor 6 and a number of wind turbine blades 7. The arms 3 extend away from the yaw arrangement 4 on opposite sides of a rotation axis 8 of the yaw arrangement 4. Thereby differences in operation of the two energy generating units 5 may result in different forces being applied to the load carrying structure 3 on opposing sides of the rotation axis 8 of the yaw arrangement 4, This may introduce a yaw moment 9 in the yaw arrangement 4.

[0060] The multirotor wind turbine 1 of FIG. 1 may be controlled in the following manner. During operation, the energy generating units 5 provide operational data to a multirotor wind turbine controller 10. In the case that it is detected that a change in operation of at least one of the energy generating units 5 is required, the multirotor wind turbine controller 10 generates control commands for both of the energy generating units, and provides the generated control commands to the respective energy generating units 5.

[0061] The change in operation may be required due to events or conditions occurring or being detected at the energy generating units 5. In this case the multirotor wind turbine controller 10 may react based on the operational data received from the energy generating units 5. Alternatively or additionally, the change in operation may be required due to events or conditions applying at wind turbine level. In this case the multirotor wind turbine controller 10 may react based on other input and/or measurements performed by the multirotor wind turbine controller 10 itself.

[0062] The control commands are generated in such a manner that it is ensured that the required change in operation is in fact obtained. Furthermore, the control commands are generated in a coordinated manner, i.e. in such a way that the two energy generating units 5 are caused to operate in a coordinated manner, in order to ensure that the yaw moment 9 of the yaw arrangement 4 is maintained below a predefined threshold level.

[0063] FIGS. 2 and 3 illustrate control of a multirotor wind turbine during shut down in accordance with a prior art method and a method according to an embodiment of the invention, respectively. The multirotor wind turbine being controlled could, e.g., be the multirotor wind turbine of FIG. 1. In any event, the multirotor wind turbine comprises two energy generating units, illustrated by a solid line and a dashed line, respectively.

[0064] The upper graph illustrates operating states of the energy generating units as a function of time. It can be seen that the energy generating units can be in a ‘Run’ state, in which the energy generating units operate, or in a ‘Stop’ state, in which the energy generating units have been shut down.

[0065] The lower graph illustrates a yaw moment of the yaw arrangement of the multirotor wind turbine as a function of time, and during the operation of the energy generating units illustrated in the upper graph.

[0066] At time t.sub.0, it is detected that a first one of the energy generating units is required to shut down. In the prior art method illustrated in FIG. 2, the first energy generating unit, illustrated by the solid line, is switched from the ‘Run’ state to the ‘Stop’ state in order to shut down the energy generating unit, and thereby fulfil the requirement. However, the second energy generating unit, illustrated by the dashed line, remains in the ‘Run’ state, and thereby continues to operate as before the requirement to shut down the first energy generating unit was detected. It can be seen that this results in a high yaw moment on the yaw arrangement, as well as in large variations in the yaw moment.

[0067] In the method according to an embodiment of the invention illustrated in FIG. 3, the first energy generating unit is also switched from the ‘Run’ state to the ‘Stop’ state, in order to shut down the first energy generating unit as required. However, in this case the control commands generated for the two energy generating units are coordinated, and therefore the second energy generating unit is also switched from the ‘Run’ state to the ‘Stop’ state, simultaneously with the first energy generating unit. It can be seen from the lower graph of FIG. 3 that this results in a much lower yaw moment, as well as in much smaller variations in the yaw moment. Thereby the loads on the wind turbine, in particular on the yaw arrangement, are significantly reduced as compared to the prior art case illustrated in FIG. 2.

[0068] FIGS. 4 and 5 illustrate control of a multirotor wind turbine following an event detection in accordance with a prior art method and a method according to an embodiment of the invention, respectively. Similarly to the situation described above with reference to FIGS. 2 and 3, the multirotor wind turbine comprises two energy generating units, i.e. a first energy generating unit illustrated by a solid line and a second energy generating unit illustrated by a dashed line.

[0069] The upper graph illustrates operating states of the energy generating units as a function of time. The energy generating units can be in a ‘Normal’ state, in which the energy generating units operate normally, and in a ‘Load reduced’ state, in which the energy generating units are operated in a cautious manner which limits the loads introduced on the energy generating units, and thereby on the multirotor wind turbine.

[0070] The middle graph illustrates a mean pitch angle of the wind turbine blades of the energy generating units as a function of time, and during the operation of the energy generating units illustrated in the upper graph.

[0071] The lower graph illustrates a yaw moment of the yaw arrangement of the multirotor wind turbine as a function of time, and during the operation of the energy generating units illustrated in the upper graph.

[0072] At time t.sub.0 it is detected that an event has occurred which requires that the first energy generating unit operates in a load reducing manner. In the prior art method, illustrated in FIG. 4, the first energy generating unit is switched from the ‘Normal’ state to the ‘Load reduced’ state as required. In consequence thereof, the mean pitch angle of the first energy generating unit is increased. However, the second energy generating unit remains in the ‘Normal’ state, and continues to operate without taking the operation of the first energy generating unit into account. Accordingly, the mean pitch angle of the second energy generating unit remains at the level which it was at prior to t.sub.0. It can be seen from the lower graph of FIG. 4 that this results in a high yaw moment being introduced in the yaw arrangement, as well as in large variations in the yaw moment, caused by a rapid change in yaw moment.

[0073] In the method according to an embodiment of the invention illustrated in FIG. 5, the first energy generating unit is also switched from the ‘Normal’ state to the ‘Load reduced’ state at time t.sub.0. However, in this case, the second energy generating unit is also switched from the ‘Normal’ state to the ‘Load reduced’ state at time t.sub.0. Therefore, the mean pitch angle of the second energy generating unit is increased to a level which is comparable to the mean pitch angle of the first energy generating unit.

[0074] It can be seen from the lower graph of FIG. 5 that this results in a much lower yaw moment, as well as in much smaller variations in the yaw moment. Thereby the loads on the wind turbine, in particular on the yaw arrangement, are significantly reduced as compared to the prior art case illustrated in FIG. 4.

[0075] FIGS. 6 and 7 illustrate control of a multirotor wind turbine during start up in accordance with a prior art method and a method according to an embodiment of the invention, respectively. Similarly to the situation described above with reference to FIGS. 2 and 3, the multirotor wind turbine comprises two energy generating units, i.e. a first energy generating unit illustrated by a solid line and a second energy generating unit illustrated by a dashed line.

[0076] The upper graph illustrates operating states of the energy generating units as a function of time. The energy generating units can be in a ‘Load reduced’ state, in which the energy generating units are operated in a cautious manner, a ‘Normal’ state, in which the energy generating units are operating in a normal manner, a ‘Start up’ state, in which the energy generating units are being started up, and an ‘Idling’ state, in which the energy generating units are not producing power.

[0077] The lower graph illustrates a yaw moment of the yaw arrangement of the multirotor wind turbine as a function of time, and during the operation of the energy generating units illustrated in the upper graph.

[0078] Initially both of the energy generating units are in the ‘Idling’ state, i.e. none of the energy generating units is producing power. At time t.sub.0, it is detected that the energy generating units should start up. Accordingly, both of the energy generating units are switched from the ‘Idling’ state to the ‘Start up’ state. At time t.sub.1 the first energy generating unit has completed its start up process, and it is therefore ready to start operating normally. However, the second energy generating unit has not yet completed its start up process.

[0079] In the prior art method, illustrated in FIG. 6, the first energy generating unit is switched from the ‘Start up’ state to the‘Normal’ state at time t.sub.1, while the second energy generating unit simply remains in the ‘Start up’ state until it has completed its start up process. This is obtained at time t.sub.2, where the second energy generating unit is switched from the ‘Start up’ state to the ‘Normal’ state, after which both of the energy generating units operate normally.

[0080] It can be seen from the lower graph of FIG. 6 that this results in a high yaw moment in the yaw system during the time where the first energy generating unit is operating normally, while the second energy generating unit is still in the process of starting up, i.e. from time t.sub.1 to time t.sub.2.

[0081] In the method according to an embodiment of the invention illustrated in FIG. 7, the operation of the two energy generating units is coordinated. Accordingly, when the first energy generating unit has completed its start up process at time t.sub.1, it is taken into account that the second energy generating unit has not yet completed its start up process. Therefore, instead of switching the first energy generating unit to the ‘Normal’ state it is switched to the ‘Load reduced’ state, where the loads acting on the energy generating unit are lower. Thereby the difference in forces acting on the two energy generating units is reduced.

[0082] When the second energy generating unit has completed its start up process, at time t.sub.3, it is also switched from the ‘Start up’ state to the ‘Load reduced’ state, and both of the energy generating units are now operating in a cautious manner.

[0083] When operation of both energy generating units is stable, they are both switched from the ‘Load reduced’ state to the ‘Normal’ state, in a coordinated manner, at time t.sub.4.

[0084] It can be seen from the lower graph of FIG. 7, that this results in a low yaw moment on the yaw arrangement throughout the entire start up process of the multirotor wind turbine.