Method for operating a pitch-controlled wind turbine
The invention is directed to a method for operating a pitch-controlled wind turbine having a rotor blade adjustable about its longitudinal axis 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. A transition point (n 3 , M 3 ) is provided whereat a switchover occurs from a part-load operation to a full-load operation. In the method, a value for air density (ρ) is determined and a pre-pitch angle (φ pre ) is set starting at a pre-pitch rotational speed (n 4 ) less than the rotational speed (n 3 ) at the transition point (n 3 , M 3 ). The value of the pre-pitch angle (φ pre ) is dependent on the value determined for the air density (ρ) so that a larger pre-pitch angle is set when the air density is lower than when the air density is higher.
1. 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 (n 3 , M 3 ) 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); and,
setting said pitch angle (φ) to a pre-pitch angle (φ pre ) starting at a pre-pitch rotational speed (n 4 ) which is below the rotational speed (n 3 ) at said transition point (n 3 , M 3 ) with said value of said pre-pitch angle (φ pre ) 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.
2. The method of claim 1 , wherein said pitch angle (φ) is constant starting at a minimal rotational speed (n 1 ) up to reaching said pre-pitch rotational speed (n 4 ).
3. The method of claim 2 , wherein the constant value of the pitch angle (φ) is zero.
4. The method of claim 1 , wherein the pitch angle (φ) is increased starting at the pre-pitch rotational speed (n 4 ) up to reaching a maximum pre-pitch rotational speed (n 5 ) wherein the maximum pre-pitch rotational speed (n 5 ) is greater than or equal to the rotational speed (n 3 ) at said transition point (n 3 , M 3 ).
5. The method of claim 4 , wherein the pitch angle (φ) is increased linearly.
6. The method of claim 1 , wherein the air density (ρ) is determined dependent on a measured air temperature (T), a measured air pressure (p) and a value for the humidity (ψ).
7. The method of claim 6 , wherein the value for the humidity (ψ) is pregiven in dependence upon a time of day and/or time of year.
8. The method of claim 6 , wherein the value for the humidity (ψ) is measured.
9. 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 (n 3 , M 3 ) 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 (φ pre ) starting at a pre-pitch rotational speed (n 4 ) which is below the rotational speed (n 3 ) at said transition point (n 3 , M 3 ) with said value of said pre-pitch angle (φ pre ) 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 φ lim , φ b and Δφ are constants for the pitch angles and the value of said pre-pitch angle (φ pre ) at a predetermined rotational speed results as:
φ
pre
=
max
(
φ
lim
,
φ
b
+
Δ
φ
(
1
-
ρ
ρ
norm
)
)
,
wherein: said φ lim , φ b and Δφ are constants for the pitch angle; ρ norm refers to an air density prevailing under normal conditions and ρ refers to the determined air density.
10. The method of claim 9 , wherein the pre-pitch angle (φ pre ) is determined for the rotational speed (n 3 ) at said transition point (n 3 , M 3 ).