Method of operating a turbine

• US 20030185665A1
• Filed: 11/04/2002
• Published: 10/02/2003
• Est. Priority Date: 03/08/2000
• Status: Active Grant

• Current Assignee: Forskningscenter RISO
• Original Assignee: Forskningscenter RISO
• Inventors: Hansen, Lars H.
• Granted Patent: US 6,840,734 B2
• Time in Patent Office: Days
• US Class Current: 415/1
• CPC Class Codes: F03D 7/0224 Adjusting blade pitch
• CPC Class Codes: F03D 7/0256 Stall control adjusting the blades in stall position F03D7/0224
• CPC Class Codes: F03D 7/0276 controlling rotor speed, e.g. variable speed
• CPC Class Codes: F03D 7/044 with PID control
• CPC Class Codes: F03D 7/048 controlling wind farms
• CPC Class Codes: F05B 2270/20 to optimise the performance of a machine
• CPC Class Codes: F05B 2270/327 Rotor or generator speeds
• CPC Class Codes: F05B 2270/335 Output power or torque
• CPC Class Codes: Y02E 10/72 Wind turbines with rotation axis in wind direction

Abstract

A method of controlling a turbine, in particular a wind turbine, which improves the energy production from the turbine while ensuring that no damage or structural overload occurs. The turbine may be operated at or near the C_p,max trajectory at rotational speeds which exceed the nominal rotational speed of the rotor of the turbine. This provides an improved energy production.

Claims

1. A method of controlling the speed of rotation of a turbine, the turbine comprising a rotor, the method comprising the steps of

measuring or estimating power or torque related to the energy production of the turbine,

processing the measured or estimated power or torque so as to obtain a corresponding rotational speed,

comparing the obtained rotational speed to a first predefined threshold value and to a second predefined threshold value, the second predefined threshold value being larger than the first predefined threshold value, and

controlling the speed of rotation of the rotor according to the obtained rotational speed, so as to obtain a predetermined energy production from the turbine, and in such a way that

in case the obtained rotational speed does not exceed the first predefined threshold value, the predetermined energy production from the turbine is optimal,

in case the obtained rotational speed exceeds the first predefined threshold value, but does not exceed the second predefined threshold value, the predetermined energy production from the turbine is optimal,

in case the obtained rotational speed exceeds the second predefined threshold value, the speed of rotation of the rotor of the turbine is reduced in a predefined manner to a value corresponding to the first predefined threshold value.

2. A method according to claim 1, wherein the turbine is a wind turbine.

3. A method according to claim 1 or 2, wherein the processing step is performed electronically.

4. A method according to any of the preceding claims, wherein, in case the predetermined energy production from the turbine is optimal, the turbine is operated in such a way that the instantaneous C_p for the turbine is as close as possible or equal to the maximum C_p.

5. A method according to any of the preceding claims, wherein the processing is based on a predetermined set of data being values of pre-selected C_p'"'"'s and corresponding rotational speeds.

6. A method according to claim 5, the turbine being a wind turbine, wherein the pre-selected C_p'"'"'s are the maximum C_p'"'"'s obtained during stationary rational conditions of the wind turbine at varying wind speeds.

7. A method according to any of the preceding claims, further comprising the step of initially determining curves of mechanical power and/or C_p for the turbine rotor at different rotational speeds.

8. A method according to claim 7, the turbine being a wind turbine, wherein the step of processing the measured or estimated power or torque includes the steps of

for each rotational speed determining the wind speed which gives C_p,max, and

determining the mechanical and/or electrical power corresponding to said wind speed.

9. A method according to claim 7, the turbine being a wind turbine, wherein the step of processing the measured or estimated power or torque includes the steps of

subsequently determining curves of mechanical power and/or C_p for the turbine rotor at different rotational speeds,

for each rotational speed determining the wind speed which gives C_p,max, and

determining the mechanical and/or electrical power corresponding to said wind speed.

10. A method according to any of claims 7-9, wherein the wind speeds giving C_p,max for each rotational speed are predetermined from pre-recorded or theoretical data.

11. A method according to any of the preceding claims, wherein the first predefined threshold value corresponds to a nominal or a pseudo-nominal rotational speed of the rotor of the turbine, and wherein the second predefined threshold value corresponds to an upper limit of the rotor of the turbine.

12. A method according to any of the preceding claims, wherein the speed of rotation of the rotor of the turbine, in case the obtained rotational speed exceeds the second predefined threshold value, is reduced by:

maintaining the speed of rotation on a value corresponding to the second predefined threshold value, while the energy production of the turbine increases until it reaches an energy threshold value, and

subsequently reducing the speed of rotation to a value corresponding to the first predefined threshold value in case the energy production continues to increase.

13. A method according to any of claims 1-11, wherein the speed of rotation of the rotor of the turbine, in case the obtained rotational speed exceeds the second predefined threshold value, is reduced by:

reducing the speed of rotation linearly with respect to the energy production of the turbine until a predefined energy production as well as the speed of rotation corresponding to the first predefined threshold value is obtained.

14. A method according to any of the preceding claims, further comprising the step of measuring the speed of rotation of the rotor.

15. A method according to claim 14, further comprising the steps of

comparing the measured speed of rotation of the rotor and the rotational speed obtained by processing the measured or estimated power or torque,

producing a signal being significant for said comparison, and

controlling the speed of rotation of the rotor according to said signal.

16. A method according to claim 15, wherein the produced signal indicates the difference between the measured speed of rotation and the rotational speed obtained by processing the measured or estimated power or torque.

17. A method according to any of the preceding claims, the turbine being a wind turbine, the method further comprising the step of adjusting the power generated by the turbine by adjusting the pitch angle of the turbine.

18. A turbine comprising

a rotor,

a generator,

means for measuring or estimating power or torque related to the energy production of the turbine,

processing means for processing the power or torque measured or estimated by the measuring or estimating means, so as to obtain a corresponding rotational speed,

comparing means for comparing the obtained rotational speed to a first predefined threshold value and to a second predefined threshold value, the second predefined threshold value being larger than the first predefined threshold value, and

control means for controlling the speed of rotation of the rotor according to the obtained rotational speed, the control means being adapted to control the speed of rotation in such a way that a predetermined energy production is obtained from the turbine, and in such a way that

in case the obtained rotational speed does not exceed the first predefined threshold value, the predetermined energy production from the turbine is optimal,

in case the obtained rotational speed exceeds the first predefined threshold value, but does not exceed the second predefined threshold value, the predetermined energy production from the turbine is optimal,

in case the obtained rotational speed exceeds the second predefined threshold value, the speed of rotation of the rotor of the turbine is reduced in a predefined manner to a value corresponding to the first predefined threshold value.

19. A turbine according to claim 18, wherein the turbine is a wind turbine.

20. A turbine according to claim 18 or 19, wherein the processing means is electronically processing means.

21. A turbine according to claim 19 or 20, further comprising means for determining curves of mechanical power and/or C_p for the turbine.

22. A turbine according to claim 21, further comprising

means for determining, for each rotational speed, the wind speed which gives C_p,max, and

means for determining the mechanical and/or electrical power corresponding to said wind speed.

23. A turbine according to claim 21 or 22, wherein the means for determining wind speed comprises tables containing pre-recorded or theoretical data.

24. A turbine according to any of claims 21-23, wherein the means for determining wind speed comprises curves of pre-recorded or theoretical data.

25. A turbine according to any of claims 18-24, further comprising means for measuring the speed of rotation of the rotor.

26. A turbine according to claim 25, further comprising means for comparing the measured speed of rotation and the rotational speed obtained by processing the measured or estimated power or momentum.

27. A turbine according to claim 26, wherein the control means comprises means for receiving a signal, said signal being produced by the means for comparing the measured speed of rotation and the obtained rotational speed, and wherein the control means controls the speed of rotation of the rotor according to said signal.

28. A turbine according to any of claims 19-27, wherein the turbine is a gear-less wind turbine.

29. A turbine according to any of claims 18-28, further comprising means for, in case the obtained rotational speed exceeds the second predefined threshold value, reducing the speed of rotation of the rotor of the turbine, the reducing means being adapted to

maintain the speed of rotation on a value corresponding to the second predefined threshold value, while the energy production of the turbine increases until it reaches an energy threshold value, and

subsequently reduce the speed of rotation to a value corresponding to the first predefined threshold value in case the energy production continues to increase.

30. A turbine according to any of claims 18-28, further comprising means for, in case the obtained rotational speed exceeds the second predefined threshold value, reducing the speed of rotation of the rotor of the turbine, the reducing means being adapted to

reduce the speed of rotation linearly with respect to the energy production of the turbine until a predefined energy production as well as the speed of rotation corresponding to the first predefined threshold value is obtained.