Method for operating a pitch-controlled wind turbine

A method for operating a pitch-controlled wind turbine having at least one rotor blade adjustable about its longitudinal axis to define a pitch angle (φ), and having a generator wherein a set-point for a generator torque (M) is specified in dependence upon a rotational speed (n) of the generator or of the rotor, and wherein a transition point (n3, M3) is provided whereat there is a switchover from a part-load operation to a full-load operation, the method comprising the steps of:

• determining a value for an air density (ρ);
• setting said pitch angle (φ) to a pre-pitch angle (φpre) starting at a pre-pitch rotational speed (n4) which is below the rotational speed (n3) at said transition point (n3, M3) with said value of said pre-pitch angle (φpre) being dependent on said value determined for said air density (ρ) so as to cause a larger pre-pitch angle to be set when said air density is lower than when said air density is higher;
• and,
• wherein φlim, φb and Δφ are constants for the pitch angles and the value of said pre-pitch angle (φpre) at a predetermined rotational speed results as:
• φ
• pre
• =
• max
• (
• φ
• lim
• ,
• φ
• b
• +
• Δ
• ⁢
• ⁢
• φ
• (
• 1
• -
• ρ
• ρ
• norm
• )
• )
• ,
• wherein:
• said φlim, φb and Δφ are constants for the pitch angle;
• ρnorm refers to an air density prevailing under normal conditions and ρ refers to the determined air density.