Method for operating a pitch-controlled wind turbine
Method for operating a pitch-controlled wind turbine, in which a set-point value for the generator torque (M) is prescribed in dependence upon a rotational speed (n) of the generator or of the rotor. A transition point (n 3 , M 3 ) is provided at which a transition from a partial-load operation to a nominal-load operation occurs. A control of the rotational speed takes place by adjusting the blade pitch angle for a set-point value (M 3 ) from the transition point. The values (n 3 , M 3 ) of the transition point are determined in dependence upon a current value of the air density. With falling air density, the rotational speed (n 3 ) is increased and/or the set-point value for the generator torque (M 3 ) is reduced.
1. A method for operating a pitch-controlled wind turbine having a rotor blade, a rotor and a generator, the method comprising the steps of:
prescribing a set-point value for the generator torque (M) in dependence upon a rotational speed (n) of the generator or of the rotor;
providing a transition point (n 3 , M 3 ) whereat a transition occurs from a partial-load operation into a nominal-load operation wherein said rotational speed (n) is controlled by adjusting the pitch angle of said rotor blade;
determining the values (n 3 , M 3 ) of said transition point in dependence upon a current value of the air density (ρ);
with falling air density, increasing the rotational speed (n 3 ) and/or reducing said set-point value (M 3 ) for the generator torque;
determining a change (Δρ) in said air density (ρ) and comparing said change (Δρ) to a maximum allowable change (Δρ 2 ) in air density; and,
if said change (Δρ) in air density (ρ) exceeds said maximum allowable change (Δρ 2 ), then changing said transition point.
2. The method of claim 1 , wherein the blade pitch angle is already adjusted to a minimum blade pitch angle in the partial-load operation.
3. The method of claim 2 , wherein the value of the minimum blade pitch angle is selected in dependence upon the air density.
4. The method of claim 1 , wherein the current air density (ρ) is determined in dependence upon a measured air temperature (T) and a measured air pressure (p) taking into account a value for the humidity (ψ).
5. The method of claim 1 , wherein a value (Ψ) for humidity is provided in dependence upon a time of day and/or a season.
6. The method of claim 4 , wherein said value for the humidity (ψ) is measured.
7. The method of claim 1 , wherein a characteristic curve of generator torque (M Gen ) as a function of generator rotational speed (n Gen ) is provided and said characteristic curve has a predetermined point (n 2 , M 2 ), starting from which the set-point value for the generator torque increases linearly up to a nominal-load operation.
8. The method of claim 7 , wherein the set-point value (M 2 ) for the generator torque is reduced given constant rotational speed (n 2 ) with falling air density.