Compensation for asymmetric load moment experienced by wind turbine rotor

Patent metadata

Field	Value
Publication number	US-9835137-B2
Application number	US-201314406409-A
Country	US
Kind code	B2
Filing date	Jun 7, 2013
Priority date	Jun 8, 2012
Publication date	Dec 5, 2017
Grant date	Dec 5, 2017

Abstract

A method of operating a wind turbine is provided. The wind turbine comprises a turbine rotor with at least two blades, each blade having a variable pitch angle. The method comprises determining mechanical loads on the blades, determining an asymmetric load moment experienced by the turbine rotor based on the mechanical loads on the blades, determining high order harmonics from the asymmetric load moment, and determining an individual pitch control signal for each of the blades for varying the pitch angle of each blade to compensate for the asymmetric load moment. The individual pitch control signal for each blade is determined at least based on the high order harmonics.

First claim

What is claimed is:

1. A method of operating a wind turbine comprising a turbine rotor with at least two blades, each blade of the at least two blades having a variable pitch angle, the method comprising:
determining, using one or more sensors of the wind turbine that are communicatively coupled with one or more computer processors of the wind turbine, mechanical loads on the at least two blades:
frequency modulating a signal that is based on the asymmetric load moment to produce a frequency-modulated signal: and
notch filtering the frequency-modulated signal to identify the high order harmonics; and
determining, using the high order harmonics, an individual pitch control signal for each blade of the at least two blades for varying a pitch angle of each blade to compensate for the asymmetric load moment; and
controlling, using a pitch controller, the pitch angle of each blade based on the corresponding individual pitch control signal.

2. The method of claim 1 , wherein determining the asymmetric load moment comprises determining at least one of tilt moment and yaw moment.

3. The method of claim 1 , wherein determining the individual pitch control signal comprises:
subtracting the high order harmonics from a reference value to generate a modified reference value;
determining high order harmonics components based on the modified reference value;
generating a cyclic pitch value based on the high order harmonics components for each blade; and
summing the cyclic pitch value with a collective pitch value to generate the individual pitch control signal for each blade.

4. The method of claim 1 , further comprising:
filtering the asymmetric load moment to remove low frequency components to produce the signal before frequency modulating the signal.

5. The method of claim 1 , wherein determining an asymmetric load moment comprises determining the tilt moment and the yaw moment,
wherein frequency modulating the asymmetric load moment comprises:
determining a first plurality of frequency-modulated signals using the tilt moment; and
determining a second plurality of frequency-modulated signals using the yaw moment, and

wherein notch filtering the frequency-modulated asymmetric load moment comprises:
notch filtering each of the first plurality of frequency-modulated signals to identify a plurality of tilt moment frequency components; and
notch filtering each of the second plurality of frequency-modulated signals to identify a plurality of yaw moment frequency components.

6. The method of claim 5 , further comprising:
transforming the plurality of tilt moment frequency components and the plurality of yaw moment frequency components to produce an x-moment frequency component and a z-moment frequency component,
wherein the individual pitch control signal for each blade of the at least two blades is determined using the x-moment frequency component and the z-moment frequency component.

7. The method of claim 6 , wherein the plurality of tilt moment frequency components and the plurality of yaw moment frequency components are transformed using a predefined weighting factor that is selected from a predefined range from zero to one.

8. The method of claim 7 , wherein the x-moment frequency component is produced by summing (1) a product of the predefined weighting factor and a first tilt moment frequency component and (2) a product of a first yaw moment frequency component and (one minus the predefined weighting factor), and
wherein the z-moment frequency component is produced by summing (3) a product of the predefined weighting factor and a second tilt moment frequency component and (4) a product of a negative second yaw moment frequency component and (one minus the predefined weighting factor).

9. The method of claim 5 , wherein determining the first plurality of frequency-modulated signals comprises applying each of a first carrier signal and a second carrier signal to a first signal that is based on the tilt moment, and
wherein determining the second plurality of frequency-modulated signals comprises applying each of the first carrier signal and the second carrier signal to a second signal that is based on the yaw moment.

10. The method of claim 9 , wherein the first signal is produced by passing the tilt moment through a first high-pass filter, and wherein the second signal is produced by passing the yaw moment through a second high-pass filter.

11. The method of claim 10 , wherein a cutoff frequency of the first high-pass filter and the second high-pass filter corresponds to a rotor speed of the turbine rotor.

12. The method of claim 9 , wherein the first carrier signal and the second carrier signal are each based on an azimuth angle of the turbine rotor.

13. A wind turbine comprising: a turbine rotor with at least two blades, each blade of the at least two blades having a variable pitch angle; and a load control system comprising one or more computer processors, wherein the load control system is configured to:
determine, using one or more sensors, mechanical loads on the at least two blades;
determine, using the mechanical loads, an asymmetric load moment experienced by the turbine rotor;
determine high order harmonics from the asymmetric load moment by:
frequency modulating a signal that is based on the asymmetric load moment to produce a frequency-modulated signal; and
notch filtering the frequency-modulated signal to identify the high order harmonics;
determine, using the high order harmonics, an individual pitch control signal for each blade of the at least two blades for varying a pitch angle of each
blade to compensate for the asymmetric load moment; and control, using a pitch controller, the pitch angle of each blade based on the corresponding individual pitch control signal.

14. The wind turbine of claim 13 , wherein the load control system is configured to determine at least one of tilt moment and yaw moment as the asymmetric load moment.

15. The wind turbine of claim 13 , wherein the load control system comprises: a first summing unit to subtract the high order harmonics from a reference value to generate a modified reference value;
a Proportional Integral (PI) controller for determining high order harmonics components based on the modified reference value;
a cyclic pitch actuator for generating a cyclic pitch value based on the high order harmonics components for each blade; and
a second summing unit for summing the cyclic pitch value with a collective pitch value to generate the individual pitch control signal for each blade.

16. The wind turbine of claim 13 , wherein the load control system further comprises:
a frequency modulator for frequency modulating the signal; and
a notch filter for filtering the frequency-modulated signal to produce the high order harmonics.

17. The wind turbine of claim 13 , wherein the load control system further comprises a high pass filter for filtering off low frequency components from the asymmetric load moment to produce the signal before frequency modulating the signal.

18. A load control system for use in a wind turbine having a turbine rotor with at least two blades, each blade of the at least two blades having a variable pitch angle, the load control system comprising one or more computer processors, wherein the load control system is configured to:
determine, using one or more sensors physically coupled with the wind turbine, mechanical loads on the at least two blades;
determine, using the mechanical loads, an asymmetric load moment experienced by the turbine rotor, wherein

Assignees

• Vestas Wind Sys As

Inventors

• Atzler Martin
• Brath Per
• Krüger Thomas
• Zaib Ali

Classifications

• F03D7/043

  characterised by the type of control logic · CPC title

• F03D7/0224 Primary

  Adjusting blade pitch · CPC title

• F03D7/044 Primary

  with PID control · CPC title

• F05B2260/966

  by correcting static or dynamic imbalance · CPC title

• Y02E10/723

  Cross-Sectional Technologies · mapped topic