System for dynamic pitch control

Abstract

The present invention relates to a system for dynamic pitch control primarily for wind turbine blades, which system calculates the pitch position of the wind turbine blades independently, which control system performs feedback regulation. The object of the pending patent application is to perform effective pitch regulation and hereby to reduce thrust on the tower and the rotor. This can be achieved if the system performs feed forward regulation of the pitch of the blades, based on the load of the previous blade in substantially the same position. Hereby it can be achieved that the actual load on the previous blade has passed the same position in relation to the wind blowing around the wind turbine. Hereby it can be achieved that measured parameters are used after a short delay to perform a very precise and highly efficient adjustment of the next wind turbine blade passing the same position. The feed forward regulation can be combined with already existing control parameters for pitch control of wind turbine blades.

Claims

1. A method comprising: providing a wind driven generator by independently controlling pitch of wind turbine generator blades, providing a tower, providing an electric generator rotationally mounted atop the tower, providing a rotor connected to the electric generator, providing at least first, second and third wind driven blades rotationally connected to the rotor for changing pitch of the wind driven blades relative to the tower, providing a control system, providing a power and pitch control in the control system, connecting the rotor to the power and pitch control, connecting the generator to the power and pitch control, connecting the first, second and third wind driven blades to the power and pitch control, providing measurements of speed and thrust from the rotor to the power and pitch control, providing measurements of individual rotational pitch position of the first, second and third wind driven blades from the rotor to the power and pitch control, providing measurements of first, second and third individual wind loads from the rotor to the power and pitch control, individually controlling pitch of a next blade according to actual measured load of a preceding blade, providing a short delay before the individually controlling pitch of the next blade, and using the short delay for performing a precise and efficient adjusting of the controlling the pitch of the next blade.

2. The method of claim 1, further comprising using pitch demand from the preceding blade as well as the actual load of the preceding blade for individually controlling the pitch of the next blade.

3. The method of claim 1, further comprising providing a variable delay depending on rotor velocity before the individually controlling the pitch of the next blade.

4. The method of claim 1, further comprising providing a scaling factor to the individually controlling the pitch of the next blade.

5. A method comprising providing individually controlling pitch of rotor blades in a wind turbine generator by: providing a power and pitch control, inputting actual load level of each blade to the power and pitch control, inputting power production of the entire wind turbine generator power and pitch control, inputting rotor speed power and pitch control, regulating blade pitch of individual blades by power and pitch control based on load on a preceding blade in relation to angular velocity of the rotor, dynamically regulating pitch on a next blade, providing a short delay before the individually controlling pitch of the next blade, and using the short delay for performing a precise and efficient adjusting of the controlling the pitch of the next blade.

6. The method of claim 5, further comprising using pitch demand from the preceding blade as well as the actual load of the preceding blade for individually controlling the pitch of the next blade.

7. The method of claim 5, further comprising providing a variable delay depending on rotor velocity before the individually controlling the pitch of the next blade.

8. The method of claim 5, further comprising providing a scaling factor to the individually controlling the pitch of the next blade.

Description

DESCRIPTION OF THE DRAWING

(1) FIG. 1 shows a wind turbine, and

(2) FIG. 2 shows a possible conceptual integration of IPC algorithms.

DETAILED DESCRIPTION OF THE INVENTION

(3) FIG. 1 shows a wind turbine 4 comprising a tower 6, a nacelle 8, and a rotor with blades 12. Further, a power and pitch control system 14 are indicated.

(4) By the present invention it is possible to reduce the maximum thrust, both at the tower 6 and at the blades 12. The advantage of the present invention is that this reduction of thrust can be performed, and maybe the power production can be increased.

(5) FIG. 2 shows a possible conceptual integration of IPC algorithms. The figure shows the integration point of the pitch offsets and thus the relevant signals. The two sets of vectors are named IPCA and IPCB for the two IPC algorithms.

(6) Below there are described relevant concerns/challenges when superimposing the individual pitch references with a pitch offset. The integration concerns are of a general character for many IPC algorithms. It is preferred to avoid cross-coupling to collective pitch control (speed control).

(7) A contribution to the pitch angle reference has the potential for disturbing collective pitch control (i.e. speed control). Other types of IPC algorithms, such as the existing cyclic pitch control, have guaranteed a mean=0 across the three blades at all times whereby the risk of disturbing the collective pitch control is reduced. The IPC is not designed to ensure that the mean=0 across the three blades, hence a disturbance of the speed control may be present. However, IPC is designed to react only to changes in blade load, i.e. not mean level whereby it is expected that the mean=0 for each blade over time. For the collective pitch control to be influenced by IPC, the external conditions must be such that all three blades are exposed to the same load change e.g. coherent gust which would cause the IPC for all blades to go positive. It is important to notice that the IPC will unload the blades in such a situation and thereby actually aid speed control.

(8) The IPC is intended to co-exist with the existing cyclic pitch control. In short, the differences between the two algorithms is that cyclic pitch control attempts to minimize the nacelle tilt/yaw loads via cyclic pitch offset to the three blades, whereas the IPC attempts to minimize load variations in the local blade coordinate system by the previously described feed forward and feedback algorithms. There is nothing added specifically to the design of the IPC which eliminates unwanted interference between IPC and cyclic pitch control.

(9) Another option for minimizing the risk of cross-coupling effects between the two controllers is to simply include a filter on the blade load measurement. The motivation for this is that loads are static tilt/yaw loads which are the scope of cyclic pitch control. However, such a solution is not included in the design as it introduces a phase delay in the response time of IPC for all frequencies within the range of which to react. Thereby the ability to handle extreme loads may be compromised.

(10) Avoiding Stalling Resulting Pitch

(11) The collective pitch control has some level of protection against driving the blade pitch into stall through minimum pitch constraint. The design of the IPC has some level of stall protection as it is not allowed to go below a minimum contribution, e.g. 0:5 deg. Again, the IPC reacts only to changes which eliminated a static operation in stall due to the IPC