Wind turbine and method for controlling the same

Abstract

A method is for controlling a wind turbine. The wind turbine has a tower, a nacelle, a rotor with at least two rotor blades and a yaw system with at least one yaw drive configured to rotate the nacelle about a vertical axis of the tower (yaw axis). A control signal for the at least one yaw drive depends on at least one signal indicative of the wind direction. The control signal for the at least one yaw drive further depends on at least one value indicative of a vibration mode of the rotor blades.

Claims

1. A method for controlling a wind turbine including a tower defining a vertical axis, a nacelle, a rotor having at least two rotor blades defining a rotor plane, and also a yaw system having at least one yaw drive for rotating the nacelle about the vertical axis, the method comprising the steps of: providing at least one signal indicative of wind direction; providing at least one value indicative of an edgewise vibration mode of the at least two rotor blades in the rotor plane; and, applying the at least one signal to a yaw control for the at least one yaw drive to control the position of the nacelle according to the at least one signal and wherein the yaw control further depends upon the at least one value indicative of the edgewise vibration mode of the at least two rotor blades in the rotor plane; wherein: a change in a rotational position of the nacelle is the at least one value indicative of the edgewise vibration mode of the at least two rotor blades; a rotational speed of the at least one yaw drive is controlled such that an amplitude of the change in the rotational position of the nacelle at a predetermined frequency (f) is dampened; and, the predetermined frequency (f) corresponds to the edgewise vibration mode of the at least two rotor blades in the rotor plane.

2. The method of claim 1, wherein the predetermined frequency (f) is determined in dependence upon a rotor frequency in an operational state of the wind turbine.

3. The method of claim 1, wherein the predetermined frequency (f) is determined by a whirling mode frequency of the at least two rotor blades in the rotor plane; and, the whirling mode frequency is determined by a first edgewise backward whirling mode frequency.

4. A wind turbine comprising: a tower defining a vertical axis; a nacelle mounted on said tower; a rotor having at least two rotor blades defining a rotor plane; a yaw system including at least one yaw drive for rotating said nacelle about said vertical axis; a yaw control for said at least one yaw drive; said yaw control being configured to receive at least one signal indicative of wind direction and to control a position of said nacelle in accordance with said at least one signal; and, said yaw control being further dependent on at least one value indicative of an edgewise vibration mode of said at least two rotor blades in said rotor plane; wherein: said yaw control receives a change in the rotational position of the nacelle as said at least one value indicative of the edgewise vibration mode of the at least two rotor blades; said yaw control is configured to control the rotational position of said nacelle such that an amplitude of the change in the rotational position of said nacelle at a predetermined frequency (f) is dampened; and, the predetermined frequency (f) corresponds to the edgewise vibration mode of said at least two rotor blades in said rotor plane.

5. The wind turbine of claim 4, wherein: said yaw control comprises a first-level rotational position control for said at least one yaw drive; and, said first-level rotational position control specifies a target value for a rotational speed that is converted by a second-level rotational speed control for said at least one yaw drive into a target value for a torque.

6. The wind turbine of claim 5, wherein said second-level rotational speed control comprises a PI (Proportional and Integral) controller.

7. The wind turbine of claim 6, wherein said second-level rotational speed control comprises a notch filter which dampens the amplitude of the change in the rotational position of the nacelle at the predetermined frequency (f).

8. The wind turbine of claim 7, wherein a negative feedback loop is provided, which generates a correction value (M.sub.corr) for the torque in dependence upon an actual value of a rotational speed (n.sub.actual) that is subtracted from the target value for the torque.

9. The wind turbine of claim 8, wherein said correction value (M.sub.corr) for the torque is determined by a bandpass filter having a passing range containing said predetermined frequency (f).

10. The wind turbine of claim 8, wherein said negative feedback loop has an amplification (K) of said correction value (M.sub.corr) for the torque.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) The invention will now be described with reference to the drawings wherein:

(2) FIG. 1 shows a schematic of a yaw system having several yaw drives for a wind turbine;

(3) FIG. 2 shows a schematic of the yaw control incorporating a PI controller for active damping;

(4) FIG. 3 shows a schematic of incorporating the controller for active damping in the yaw control; and,

(5) FIG. 4 shows a schematic of incorporating the controller for active damping in the yaw control by using a notch filter.

DETAILED DESCRIPTION

(6) FIG. 1 shows a yaw system for a wind turbine. The rotary connection 10, typically located between the tower and the nacelle is shown, wherein it has external teeth 12 in which the particular drive pinions 14a-c of the individual yaw drives 16a-f mesh. In FIG. 1, a machine frame 18 can furthermore be seen which is supporting the nacelle (not shown) including the drive train (not shown) and other components (not shown).

(7) The several yaw drives 16a-f which work independent of each other effectuate a rotation of the nacelle about the vertical axis of the tower and adjust the alignment of the nacelle in a horizontal direction. The yaw drive assembly 112 shown in FIG. 1 is represented schematically in FIG. 2 by block 112. The yaw control shown in FIG. 2 receives a signal 132 corresponding to a change in the rotational position of the nacelle as the at least one value indicative of the vibration mode of the rotor blades.

(8) FIG. 2 shows a schematic view of the rotational speed control. A target value for the rotational speed .sub.tar is applied to a rotational speed controller. This is adjusted by a PI controller to a target value for a torque applied to the yaw drive. The rotational speed control can assume various tasks through the yaw system. On the one hand, the yaw drives of the yaw system can be rotated into a specific horizontal direction, for example when the wind direction changes and the rotor of the wind turbine is to be aligned corresponding to the wind direction. A yaw control for the at least one yaw drive receives at least one signal 130 indicative of the wind direction and controls the position of the nacelle according to the received signal. An adjustment of the rotational speed of the yaw drive also occurs when the rotor of the wind turbine is fixed in a specific horizontal direction (hold state). In this case, different yaw drives can be controlled in opposite rotational directions in order to apply tension between the yaw drives and thereby maintain the alignment of the rotor of the wind turbine in a specific horizontal direction. In the hold state, several external forces may act on the wind turbine which can cause a rotational motion of the nacelle. To this extent, the cascaded control of the yaw drives always actively works with changing rotational speed values even when it attempts to maintain a specific alignment of the rotor of the wind turbine. The applied target value for the rotational speed 100 is converted by a PI controller 102 into a target value for the torque M.sub.tar 104 to be generated. A correction value for the torque M.sub.corr 108 originates from a negative feedback loop 106. Both values are subtracted from each other and sent to the yaw drive assembly 112 as a corrected target value for the torque 110. By controlling the yaw drive assembly 112 with the corrected target value for the torque 110 together with the external effects consisting of forces and torques that arise during the operation of the wind turbine an actual value of the rotational speed n.sub.actual 114 is produced. This actual value of the rotational speed n.sub.actual 114 is subtracted through closed feedback loop 116 from the target value for the rotational speed 100 in order to form the control variable 118 for the PI controller 102. Likewise, the actual value of the rotational speed n.sub.actual 114 is applied to a bandpass filter 126. The bandpass filter 126 includes a passing range for frequencies around the predetermined frequency (f) at which vibration modes of the rotor blades have to be dampened. Consequently, those frequencies are suppressed by the bandpass filter 126 that do not correspond to the passing range for frequencies around the predetermined frequency (f) and consequently those frequencies are allowed to pass which correspond to the frequency of the resonant blade vibrations to be dampened. The bandpass-filtered rotational speed 122 is recalculated by an amplification element K 124 into the correction value for the torque M.sub.corr108. A resonant vibration mode of the rotor blade is thereby dampened.

(9) FIG. 3 shows a schematic overall view of the position control of the yaw drive, wherein the position of the yaw drive is expressed by a yaw angle. A first-level rotational position control 20 specifies a target value for the yaw angle 22 that is converted by a profile generator 24 into a generated target value for the yaw angle 26. The actual value of the yaw angle 28 is also applied to the profile generator 24 so that the generated target value for the yaw angle 26 can be determined not only depending on the target value for the yaw angle 22, but also depending on the actual value of the yaw angle 28.

(10) The profile generator 24 simultaneously also produces a generated angular velocity 30 by a forward control loop. A position controller 32 converts the difference between the generated target value for the yaw angle 26 and the actual value of the yaw angle 28 into a rotational speed that is distributed together with the generated angular velocity 30 from the forward control loop to the individual yaw drives. The generated target value from the forward control loop together with the target value from the position controller 32 form the overall target value for the rotational speed 36. The yaw drive assembly 112 is operated by a rotational speed controller 34 to which the difference between the actual value of the rotational speed 114 and the overall target value of the rotational speed 36 is applied as a control difference. The corresponding yaw drive is controlled by the controller structure from FIG. 2 and so defines the yaw control. The actual value of the yaw angle 28 is detected at the rotary connection 10 and reported back to the first-level rotational position control 20.

(11) FIG. 4 shows a schematic overview using a notch filter 50 for the target value for the rotational speed.sub.tar 100. Just as in the embodiment with a negative feedback loop shown in FIG. 2, the target value for the rotational speed.sub.tar 100 is applied to the PI controller 102 and converted into a target value for the torque M.sub.tar 104. The target value for the torque M.sub.tar 104 is applied to the notch filter 50 which calculates a final target value for the torque M.sub.tar. This final target value for the torque M.sub.tar is applied to the current controller of the yaw drive assembly 112. The way of using the notch filter 50 in a forward line avoids an additional control loop which could bring control interferences and control instability. The notch filter 50 is used for filtering the target value for the torque M.sub.tar 104 having filter settings which provide a specific frequency rejection range, the specific frequency rejection range including the predetermined frequency (f). In an embodiment the yaw system includes a first-level rotational position control and a second-level rotational speed control for the at least one yaw drive. The second-level rotational speed control converts a target value for the rotational speed into a target value for a torque. The second-level rotational speed control may include a PI controller. Preferable the second-level rotational speed control includes the notch filter 50 shown in FIG. 4 which supports the control in dampening blade vibrations at the predetermined frequency (f).

(12) It is understood that the foregoing description is that of the preferred embodiments of the invention and that various changes and modifications may be made thereto without departing from the spirit and scope of the invention as defined in the appended claims.

REFERENCES (PART OF THE DESCRIPTION)

(13) 10 rotary connection 12 external teeth 14a-c drive pinions 16a-f yaw drives 20 first-level rotational position control 22 target value for the yaw angle 24 profile generator 26 a generated target value for the yaw angle 28 actual value of the yaw angle 30 generated angular velocity 32 position controller 34 rotational speed controller 36 overall target value for the rotational speed 50 notch filter 100 target value for the rotational speed 102 PI controller 104 target value for the torque 106 negative feedback loop 108 correction value for the torque 110 corrected target value for the torque 112 yaw drive assembly 114 actual value of the rotational speed 116 closed feedback loop 118 control variable 126 bandpass filter 122 bandpass-filtered rotational speed 124 amplification element 130 signal indicating wind direction 132 signal indicating change in rotational position of nacelle .sub.tar target value for the rotational speed M.sub.tar target value for the torque M.sub.tar final target value for the torque M.sub.corr correction value for the torque K amplification element BP-Filter bandpass filter n.sub.actual actual value of the rotational speed