Ice detection method and system for a wind turbine

An ice detection method for a wind turbine, the wind turbine comprising a plurality of blades and a generator, wherein the method is carried out for a blade and including measuring ambient temperature and ambient humidity, the method comprising the following steps carried out in that order in a dynamic and cyclical manner:

• measuring an angular speed of the generator of the wind turbine;
• processing the angular speed to obtain a frequency spectrum thereof;
• identifying a frequency band associated with a frequency characteristic of the blade in the frequency spectrum;
• applying a Kalman filter on frequency band to identify an instantaneous vibration frequency of the blade;
• comparing the identified instantaneous frequency with a reference frequency that has been previously stored, and which corresponds with the natural frequency of the blade when there is no ice thereon;
• determining an electric power produced by the wind turbine;
• comparing the electric power which has been determined with an estimated electric power;
• and
• determining a presence of ice on the blade if the identified instantaneous frequency differs from the reference frequency, if it is detected that the electric power which has been determined is less than the estimated electric power, and if the measured temperature and humidity tend to cause icing.