Bang-bang controller and control method for variable speed wind turbines during abnormal frequency conditions

• US 8,219,256 B2
• Filed: 07/14/2009
• Issued: 07/10/2012
• Est. Priority Date: 07/14/2009
• Status: Active Grant

• Current Assignee: Siemens Gamesa Renewable Energy A/S (Siemens AG)
• Original Assignee: Siemens AG
• Inventors: Nelson, Robert J., Amos, John D., Ma, Hongtao
• Primary Examiner(s): JARRETT, RYAN A
• Application Number:
  US12/502,295
• Publication Number:
  US 20110012352A1
• Time in Patent Office: 1,092 Days
• Field of Search: 700/287, 290/44, 290/55
• US Class Current: 700/287
• CPC Class Codes: F03D 7/0272 by measures acting on the electrical generator
• CPC Class Codes: F03D 7/0284 in relation to the state of the electric grid
• CPC Class Codes: F03D 7/043 characterised by the type of control logic
• CPC Class Codes: F03D 7/048 controlling wind farms
• CPC Class Codes: F05B 2270/337 Electrical grid status parameters, e.g. voltage, frequency or power demand
• CPC Class Codes: Y02E 10/72 Wind turbines with rotation axis in wind direction

Abstract

A wind farm (10) may include a plurality of variable speed wind turbines (12, 14, 16). A centralized controller (50) may be configured to selectively adjust a respective electrical output power from each of the wind turbines at least during an underfrequency condition. The controller may include a monitor (52) configured to monitor a grid frequency value relative to at least a first threshold value. A deviation of the grid frequency value beyond the first threshold value is indicative of the underfrequency condition. The controller further includes a control unit (54) configured to effect a step response to the electrical output power of the wind turbine in a direction selected to counteract the underfrequency condition.

Claims

1. A wind farm comprising:

a plurality of variable speed wind turbines; and

a centralized controller configured to selectively adjust a respective electrical output power from each of the wind turbines at least during an underfrequency condition, the controller including a monitor configured to monitor a grid frequency value relative to at least a first threshold value, wherein a deviation of the grid frequency value beyond the first threshold value is indicative of the underfrequency condition, the controller further including a control unit configured to effect a step response to the electrical output power of the wind turbine from a baseline power level to a maximal power level in a direction selected to counteract the underfrequency condition, wherein the step response is effected by way of a singular step control function implemented by the controller from the baseline power level to the maximal power level so that kinetic energy stored in a rotating shaft of the wind turbine is instantaneously extracted to effect the step response to the electrical output power of the wind turbine.

2. The wind farm of claim 1, wherein the effected step response is performed by the control unit without evaluating at least one of the following:

a rate of change of the deviation, an integral of the deviation and/or a magnitude of the deviation.

3. The wind farm of claim 1, wherein the control unit is configured to perform an on-off control strategy, wherein an on-state of the control unit effects the step response to counteract the underfrequency condition.

4. The wind farm of claim 3, wherein the on-state is maintained to reach a predefined frequency value corresponding to a normal frequency condition.

5. The wind farm of claim 3, wherein an off-state of the control unit effects a step response to the electrical output power of the wind turbine in a direction to return to a wind turbine state corresponding to a normal frequency condition.

6. The wind farm of claim 1, wherein the controller is further configured to adjust the electrical output power from the variable speed wind turbine during an overfrequency condition, wherein the control unit is configured to effect a step response of the electrical output power of the wind turbine in a direction selected to counteract the overfrequency condition, whereby excess electrical energy generated during the overfrequency condition is converted to kinetic energy for storage by the rotating shaft in view of the effected step response to the electrical output power of the wind turbine during the overfrequency condition.

7. The wind farm of claim 6, wherein the effected step response during the overfrequency condition is performed without evaluating at least one of the following:

a rate of change of the deviation, an integral of the deviation and/or a magnitude of the deviation.

8. The wind farm of claim 1, wherein the controller further comprises a droop control unit configured to smooth the response of the electrical output power of the wind turbine as said output power returns from the underfrequency condition to a normal frequency condition.

9. A variable speed wind turbine comprising:

a controller coupled to the variable speed wind turbine, the controller configured to adjust an electrical output power from the wind turbine at least during an underfrequency condition, the controller including a monitor configured to monitor a grid frequency value relative to at least a first threshold value, wherein a deviation of the grid frequency value beyond the first threshold value is indicative of the underfrequency condition, the controller further including a control unit configured to effect a step response to the electrical output power of the wind turbine from a baseline power level to a maximal power value in a direction selected to counteract the underfrequency condition, wherein the step response is effected by way of a singular step control function implemented by the controller from the nominal power level to the maximal power level so that kinetic energy stored in a rotating shaft of the wind turbine is instantaneously extracted to effect the step response to the electrical output power of the wind turbine.

10. The wind turbine of claim 9, wherein the effected step response is performed by the control unit without evaluating at least one of the following:

a rate of change of the deviation, an integral of the deviation and/or a magnitude of the deviation.

11. The wind turbine, of claim 9, wherein the control unit is configured to perform an on-off control strategy, wherein an on-state of the control unit effects the step response to counteract the underfrequency condition.

12. The wind turbine of claim 11, wherein the on-state is maintained to reach a predefined frequency value corresponding to a normal frequency condition.

13. The wind turbine of claim 11, wherein an off-state of the control unit effects a step response to the electrical output power of the wind turbine in a direction to return to a wind turbine state corresponding to a normal frequency condition.

14. The wind turbine of claim 9, wherein the controller is further configured to adjust the electrical output power from the variable speed wind turbine during an overfrequency condition, wherein the control unit is configured to effect a step response of the electrical output power of the wind turbine in a direction selected to counteract the overfrequency condition, whereby excess electrical energy generated during the overfrequency condition is converted to kinetic energy for storage by the rotating shaft in view of the effected step response to the electrical output power of the wind turbine during the overfrequency condition.

15. The wind turbine of claim 14, wherein the effected step response during the overfrequency condition is performed without evaluating at least one of the following:

a rate of change of the deviation, an integral of the deviation and/or a magnitude of the deviation.

16. The wind turbine of claim 9, wherein the controller further comprises a droop control unit configured to smooth the response of the electrical output power of the wind turbine as said output power returns from the undefrequency condition to a normal frequency condition.

17. A method for controlling a variable speed wind turbine, the method comprising:

monitoring a grid frequency value relative to at least one threshold value, wherein a deviation of the grid frequency value beyond the at least one threshold value is indicative of an underfrequency condition; and

adjusting an electrical output power from the wind turbine at least during the underfrequency condition, the adjusting configured to cause a step response to the electrical output power of the wind turbine from a baseline power level to a maximal power value in a direction selected to counteract the underfrequency condition;

implementing the step response by way of a singular step control function from the baseline power level to the maximal power level so that kinetic energy stored in a rotating shaft of the wind turbine is instantaneously extracted to provide the step response to the electrical output power of the wind turbine.

18. The method of claim 17, wherein the step response is effected without evaluating at least one of the following:

a rate of change of the deviation, an integral of the deviation and/or a magnitude of the deviation.

19. The method of claim 17, wherein the adjusting of the output power of the wind turbine is based on an on-off control strategy, wherein the effected step response occurs during an on-state of the control strategy.

20. The method of claim 19, maintaining the on-state to reach a predefined frequency value corresponding to a normal frequency condition.

21. The method of claim 19, wherein, during an off-state of the control strategy effecting a step response to the electrical output power of the wind turbine in a direction to return to a wind turbine state corresponding to a normal frequency condition.

22. The method of claim 17, further comprising adjusting the electrical output power from the variable speed wind turbine during an overfrequency condition, the adjusting configured to effect a step response of the electrical output power of the wind turbine in a direction selected to counteract the overfrequency condition, whereby excess electrical energy generated during the overfrequency condition is converted to kinetic energy for storage by the rotating shaft in view of the effected step response to the electrical output power of the wind turbine during the overfrequency condition.

23. The method of claim 22, wherein the step response during the overfrequency condition is effected without evaluating at least one of the following:

a rate of change of the deviation, an integral of the deviation and/or a magnitude of the deviation.

24. The method of claim 17, further comprising smoothing the response of the electrical output power of the wind turbine as said output power returns to a normal frequency condition.

25. A bang-bang controller stored on a non-transitory computer-readable storage medium and configured to adjust an electrical output power from a variable speed wind turbine at least during an underfrequency condition, the controller comprising:

a monitor configured to monitor a grid frequency value relative to at least a first threshold value, wherein a deviation of the grid frequency value beyond the first threshold value is indicative of the underfrequency condition; and

a control unit configured to effect a step response to the electrical output power of the wind turbine from a baseline power level to a maximal power level in a direction selected to counteract the underfrequency condition, wherein the effected step response is performed by the control unit without evaluating at least one of the following;

a rate of change of the deviation, an integral of the deviation and/or a magnitude of the deviation, wherein the step response is effected by way of a singular step control function implemented by the controller from the baseline power level to the maximal power level so that kinetic energy stored in a rotating shaft of the wind turbine is instantaneously extracted to effect the step response to the electrical output power of the wind turbine.