Method for monitoring the operation of a wind energy plant and wind energy plant

1. A method for monitoring operation of a wind energy plant that includes a tower, a nacelle arranged on the tower and a rotor having at least one blade angle adjustable rotor blade, wherein rotor blade vibrations of the at least one rotor blade are registered during the operation of the wind energy plant and at least one current natural frequency of the at least one rotor blade is established from the registered rotor blade vibrations, and wherein at least three parameters are registered that influence the at least one established current natural frequency of the at least one rotor blade, said at least three parameters registered being (1) temperature, (2) at least one parameter selected from rotor speed, generator speed and wind speed, and (3) at least one parameter selected from rotor blade angle and generated power, the method comprising:

calculating

at least one natural frequency expected value of the at least one rotor blade dependent on the at least three parameters registered, and

at least one confidence interval for the at least one natural frequency expected value of the at least one rotor blade;

monitoring whether the at least one established current natural frequency lies within, or outside of, the at least one confidence interval for the at least one natural frequency expected value; and

putting the wind energy plan into operation with reduced power or shutting down the wind energy plant when the established current natural frequency is determined in the monitoring step to lie outside of the at least one confidence interval for the at least one natural frequency expected value;

wherein the at least one natural frequency expected value is calculated as a result of at least one fit function in relation to

(A) simulated vibrational measurement data from a model of the wind energy plant dependent on the at least three parameters registered, or

(B) real measurement data of vibrations from the at least one rotor blade under regular operating conditions.

2. The method as claimed in claim 1 , wherein the vibrations of the at least one rotor blade are registered by a sensor system that is stationary in relation to the rotor.

3. The method according to claim 2 , wherein the sensor system is stationary in relation to the at least one rotor blade.

4. The method according to claim 2 , wherein the sensor system comprises acceleration sensors, deformation sensors and/or strain sensors.

5. The method as claimed in claim 1 , wherein a function underlying the at least one natural frequency expected value is adaptable to a current turbine configuration by statistical evaluation of measurement data.

6. The method as claimed in claim 1 , wherein the at least one depends linearly on the at least three parameters registered.

7. The method according to claim 6 , wherein the at least one fit function is a least-squares method.

8. The method as claimed in claim 6 , wherein the at least one fit function is adapted to an individual turbine configuration in a learning phase.

9. The method as claimed in claim 6 , wherein the at least one fit function is adapted automatically to an individual turbine configuration in a learning phase.

10. The method as claimed in claim 6 , wherein the at least one fit function is improved during ongoing operation by further real measurement data under regular operating conditions.

11. The method as claimed in claim 1 , wherein the at least one confidence interval is also calculated as a function of the at least three parameters registered.

12. The method as claimed in claim 1 , wherein a first blade pitch frequency is established as the natural frequency.

13. An operational control apparatus for use with a wind energy plant that includes a tower, a nacelle arranged on the tower and a rotor having at least one blade angle adjustable rotor blade, and which is configured to register rotor blade vibrations of the at least one rotor blade during operation of the wind energy plant and register at least three parameters that influence the at least one established current natural frequency of the at least one rotor blade, said at least three parameters registered being (1) temperature, (2) at least one parameter selected from rotor speed, generator speed and wind speed, and (3) at least one parameter selected from rotor blade angle and generated power, said operational control apparatus comprising an Operation Control System configured to:

establish at least one current natural frequency of the at least one rotor blade from the registered rotor blade vibrations:

calculate at least one natural frequency expected value dependent on the at least three parameters registered and at least one confidence interval for at least one natural frequency expected value of the at least one rotor blade;

monitor whether the at least one established current natural frequency lies within, or outside of, the at least one confidence interval for the at least one natural frequency expected value, and

put the wind energy plant into operation with reduced power or shuts down the wind energy plant when the established current natural frequency lies outside of the confidence interval for the natural frequency expected value;

wherein the at least one natural frequency expected value is calculated as a result of at least one fit function in relation to

(A) simulated vibrational measurement data from a model of the wind energy plant dependent on the at least three parameters registered, or

(B) real measurement data of vibrations from the at least one rotor blade under regular operating conditions.

14. The wind energy plant for use with the operational control apparatus according to claim 13 comprising the tower, the nacelle arranged on the tower, the rotor having the at least one blade angle adjustable rotor blade and which is configured to register the rotor blade vibrations of the said at least one rotor blade during the operation of the wind energy plant and to register at least three parameters that influence the at least one established current natural frequency of the at least one rotor blade, said at least three parameters registered being (1) temperature, (2) at least one parameter selected from rotor speed, generator speed and wind speed, and (3) at least one parameter selected from rotor blade angle and generated power.