Determination of a state of a wind turbine blade

A method for detecting a state of a wind turbine blade, the method comprising:

• receiving a load signal from a sensor configured to measure loads on the wind turbine blade;
• determining an energy of the load signal at a first frequency, and determining an energy of the load signal at a second frequency, wherein the first frequency corresponds to a natural frequency of the blade in a default state;
• comparing the energy of the load signal at the first frequency to the energy of the load signals at the second frequency;
• and
• generating a flag signal when the energy of the load signal at the first frequency is smaller than the energy of the load signal at the second frequency.

A wind turbine, comprising:

• one or more blades;
• a control system, the control system configured to perform the following operations:
• receive a load signal from one or more sensors configured to measure loads on the blades;
• determine an energy of the load signal in a first frequency, and determine an energy of the load signal in a second frequency, wherein the first frequency is a frequency substantially corresponds to a natural frequency of the blade in a default state;
• compare the energy of the load signal in the first frequency to the energy of the load signal in the second frequency;
• and
• generate a flag signal when the energy of the load signal in the first frequency is smaller than the energy of the load signal in the second frequency.

A method for detecting a state of a wind turbine blade, the method comprising:

• receiving one or more edgewise load signals from one or more sensors configured to measure edgewise loads on the wind turbine blade;
• filtering out of the edgewise load signals a frequency corresponding to a rotor rotational speed frequency;
• determining an energy of the filtered edgewise load signals at a first frequency, wherein the first frequency corresponds to a natural frequency of the blade in a default state;
• determining an energy of the filtered edgewise load signals at a second frequency;
• comparing the energy of the load signals at the first frequency to the energy of the load signals at the second frequency;
• and
• generating a flag signal when the energy of the load signals at the first frequency is smaller than the energy of the load signals at the second frequency band.