Method and apparatus for damping tower oscillation in a wind turbine

1. A method of damping tower oscillation in a wind turbine, comprising:

determining a rotor rotational speed of the wind turbine;

selecting an input comprising an avoid frequency input parameter, the avoid frequency input parameter being a null value or a critical frequency value; and

selecting, according to the input parameter value, an operation mode adapted to control the rotor rotational speed of the wind turbine,

when the avoid frequency input parameter is the null value:

the selecting of the operation mode is of an auto tuner operation mode,

detecting a tower oscillation frequency,

calculating a critical rotor speed based on the detected tower oscillation frequency to avoid the calculated critical rotor speed corresponding to the critical frequency value comprised in the avoid frequency input parameter, and

controlling the rotor rotational speed to avoid the calculated critical rotor speed; and

when the avoid frequency input parameter is not null value:

the selecting of the operation mode is of an static frequency mode, and

controlling the rotor speed to avoid the avoid frequency input parameter.

2. The method according to claim 1 , wherein the selecting the auto tune operation as the operation mode comprises verifying that the detected tower oscillation frequency matches a stored reference frequency.

3. The method according to claim 1 , a disable operation mode, which is an operation mode for disabling the tower damping, is selected when the avoid range input parameter is a Null value or a value smaller than a Null value.

4. The method according to claim 1 , wherein the critical rotor speed is calculated based on the triple of the detected tower oscillation frequency on the condition of the detected tower oscillation frequency being larger than and/or equal to a rotor speed corresponding to the maximum number or revolutions per minute of the generator of the wind turbine.

5. The method according to claim 1 , wherein the controlling the rotor rotational speed comprises:

increasing a power reference by an additional amount to exceed an optimum power curve of the wind turbine when the rotor speed is below the calculated critical rotor speed and within an outer range encompassing a range specified by the avoid range input parameter;

decreasing the power reference when the rotor speed is within the range specified by the avoid range input parameter; and

increasing the power reference up to an optimum power reference of the optimum power curve when the rotor speed exceeds the range specified by the avoid range input parameter.

6. The method according to claim 1 , wherein the controlling the rotor rotational speed comprises:

decreasing a power reference by an additional amount to go below an optimum power curve of the wind turbine when the rotor speed is above the calculated critical rotor speed and within an outer range encompassing a range specified by the avoid range input parameter;

increasing the power reference when the rotor speed is within the range specified by the avoid range input parameter; and

decreasing the power reference down to an optimum power reference of the optimum power curve when the rotor speed goes below the range specified by the avoid range input parameter.

7. A wind turbine control apparatus, comprising:

a speed detector that determines a rotational speed of a rotor of a wind turbine;

an acceleration sensor that determines a tower oscillation frequency of a tower of the wind turbine;

a memory that comprises an input parameter value;

a processing unit:

controls the rotor rotational speed such that a critical rotor speed is avoided

selects an auto tune operation mode when the input parameter is null and selects a static operation mode when the input parameter is not null,

when the selected operation mode is the auto tune operation mode the processing unit:

detects the tower oscillation frequency, and

calculates the critical rotor speed based on the detected tower oscillation frequency and controlling the rotor rotational speed to avoid the calculated critical rotor speed,

when the selected operation mode is the static operation mode the processing unit;

does not detect the tower oscillation frequency, and

sets the critical rotor speed based on the input parameter.

8. The wind turbine control apparatus according to claim 7 , wherein the auto tune operation mode is selected as the operation mode when the input parameter value comprises an avoid range input parameter with a positive value and when the input parameter value comprises a. avoid frequency parameter with a value of 0.

9. The wind turbine control apparatus according to claim 7 , wherein in order to control the rotor rotational speed, the processing unit:

increases a power reference by an additional amount to exceed an optimum power curve of the wind turbine when the rotor speed is below the calculated critical rotor speed and within an outer range encompassing a range specified by the avoid range input parameter,

decreases the power reference when the rotor speed is within the range specified by the avoid range input parameter, and

increases the power reference up to an optimum power reference of the optimum power curve when the rotor speed exceeds the range specified by the avoid range input parameter.

10. The wind turbine control apparatus according to claim 7 , wherein in order to control the rotor rotational speed, the processing unit:

decreases a power reference by an additional amount to go below an optimum power curve of the wind turbine when the rotor speed is above the calculated critical rotor speed and within an outer range encompassing a range specified by the avoid range input parameter;

increases the power reference when the rotor speed is within the range specified by the avoid range input parameter; and

decreases the power reference down to an optimum power reference of the optimum power curve when the rotor speed goes below the range specified by the avoid range input parameter.

11. A computer program product stored on a computer-readable medium comprising computer-readable instructions for carrying out the method of claim 1 .