Rotational speed control of a wind turbine based on rotor acceleration

1. A method for controlling the rotational speed of a rotor of a wind turbine during high wind speeds, the method comprising

determining a rotor acceleration value, wherein the rotor acceleration value is caused by a temporal change of the rotational speed of the rotor;

controlling the rotational speed of the rotor as a function of the determined internal speed limit;

measuring the rotational speed of the rotor,

calculating the rotor acceleration value by taking the derivative with respect to time of the measured rotational speed;

taking the absolute value of the calculated rotor acceleration value; and

determining an internal speed limit based on absolute value of the calculated rotor acceleration value.

2. The method as set forth in claim 1 , comrpsing providing an external speed limit and/or a nominal speed reference value, wherein

the rotational speed of the rotor is controlled by a speed reference value, and

the speed reference value is the minimum value taken

(a) from the internal speed limit, and

(b) from the external speed limit and/or the nominal speed reference value.

3. The method as set forth in claim 2 , wherein the controlling the rotational speed of the rotor comprises:

determining a power generation reference value and/or a blade pitch angle reference value based on the speed reference value, and

using the power generation reference value for operating the wind turbine and adapting the blade pitch angle of at least one blade of the rotor to the blade pitch angle reference value.

4. The method as set forth in claim 2 , wherein the controlling the rotational speed of the rotor comprises:

determining a power generation reference value and/or a blade pitch angle reference value based on the speed reference value, and

using the power generation reference value for operating the wind turbine.

5. The method as set forth in claim 2 , wherein the controlling the rotational speed of the rotor comprises:

determining a power generation reference value and/or a blade pitch angle reference value based on the speed reference value, and

using the power generation reference value for adapting the blade pitch angle of at least one blade of the rotor to the blade pitch angle reference value.

6. The method as set forth in claim 4 , wherein the determining the internal speed limit further comprises:

filtering the calculated rotor acceleration value.

7. The method as set forth in claim 4 , wherein the determining the internal speed limit further comprises

determining an acceleration limit, which represents a maximal allowable rotor acceleration, and

comparing the rotor acceleration value with the determined acceleration limit.

8. The method as set forth in claim 2 , wherein

the acceleration limit is determined based on

at least one of the following parameters characterizing the actual operational state of the wind turbine;

(a) the rotational speed of the rotor,

(b) the amount generated power, and

(c) the pitch angle of at least one blade of the rotor.

9. The method as set forth in claim 2 , wherein

the acceleration limit is determined based on

an estimated wind speed,

the actual wind speed and/or

a change of an estimated and/or actual wind speed.

10. The method as set forth in claim 2 , wherein the determining the internal speed limit further comprises:

integrating over time a result of comparing the rotor acceleration value with the determined acceleration limit.

11. A computer program for controlling the operation of a wind turbine at high wind speeds, the computer program, when being executed by a data processor, is adapted for controlling and carrying out the method as set forth in claim 1 .