Method for controlling a wind turbine system in relation to braking of the yaw system

Abstract

The invention relates to a method for controlling a wind turbine system, more particular for a controlled sliding strategy to lower loads on the yaw system by controlling mechanical brakes and motor brakes in the yaw drive actuators. When the yaw system being in the non-yawing operational state, and the mechanical brake(s) being in an engaged state, and the yaw controller determines or receives a signal indicative of a yaw moment, and if the signal indicative of a yaw moment is above a signal threshold, then the yaw controller sends a braking signal to the yaw drive actuators to enter the motors into the brake state to apply a braking torque.

Claims

1. A method for controlling a wind turbine system, the wind turbine system comprising a nacelle, a tower and a yaw system, the yaw system comprising one or more yaw drive actuators and a yaw controller, the one or more yaw drive actuators comprising a motor and a mechanical brake: the yaw system being operable in a yawing operational state to rotate the nacelle with respect to the tower, and in a non-yawing operational state, and the mechanical brake being operable to be in an engaged state or in a dis-engaged state, and the motor being operable to be in a brake state in which a braking torque is applied to oppose movement of the nacelle; the method, comprising: when the yaw system is in the non-yawing operational state and the mechanical brake is in the engaged state: determining, by the yaw controller, a signal indicative of a yaw moment is above a signal threshold by detecting a movement of the nacelle, wherein detecting the movement of the nacelle comprises detecting a sliding of the mechanical brake; in response to the determining, sending, from the yaw controller, a braking signal to the yaw drive actuators causing the motor to enter the brake state and ramp up the braking torque over a period of time; and in response to determining the motor has ramped the braking torque up above a minimum braking torque, releasing the mechanical brake.

2. The method for controlling a wind turbine system according to claim 1, wherein the yaw controller determines the signal indicative of a yaw moment based on a determination of a probability of sliding of the mechanical brake.

3. The method for controlling a wind turbine system according to claim 1, wherein the one or more yaw drive actuators comprises an encoder for detecting sliding or a probability of sliding, and wherein the signal indicative of a yaw moment is based on a signal from the encoder.

4. The method for controlling the wind turbine system according to claim 1, wherein the signal indicative of a yaw moment is based on a yaw position signal obtained from a yaw position detector.

5. The method for controlling a wind turbine system according to claim 1, wherein, when sliding of the mechanical brake is detected and a sliding speed of the mechanical brake is higher than a threshold speed, the mechanical brake is released.

6. The method for controlling a wind turbine system according to claim 1, wherein, when sliding of the mechanical brake is detected, a sliding speed of the mechanical brake is determined, and wherein the applied braking torque is set in dependency of the sliding speed.

7. The method for controlling a wind turbine system according to claim 1, wherein, the yaw controller receives measurement values from a plurality of sensors and the yaw controller uses the measurement values to determine a probability of sliding.

8. The method for controlling a wind turbine system according to claim 1, wherein the signal indicative of a yaw moment is based on signals from a plurality of yaw drive actuators, and where signals from a sub-group of the yaw drive actuators are dis-regarded.

9. The method for controlling the wind turbine system according to claim 1, wherein the braking torque is applied until a stop criterion is fulfilled.

10. The method of claim 9, wherein the stop criterion comprises stopping the sliding of the mechanical brake.

11. The method of claim 10, wherein the stop criterion further comprises moving the nacelle back to a position the nacelle was in immediately prior to the sliding of the mechanical brake.

12. The method for controlling a wind turbine system according to claim 1, wherein the wind turbine system comprises a plurality of nacelles and the yaw system is arranged to rotate one or more of the plurality of nacelles, wherein the yaw system receives measured or estimated thrust on each of a plurality of rotors, and differences in the thrust for a plurality of rotors is used to determine the signal indicative of a yaw moment to detect a probability of sliding.

13. A wind turbine system comprising a mechanical brake and a control system for controlling the mechanical brake, wherein the control system is arranged to perform the method of claim 1.

14. A computer program product comprising software code adapted to control a wind turbine system when executed on a data processing system, the computer program product being adapted to perform the method of claim 1.

15. The method of claim 1, wherein the movement of the nacelle comprises a rotation of the nacelle.

16. The method of claim 15, wherein the signal indicative of the yaw moment indicates an amount the nacelle has rotated since the mechanical brake entered the engaged state.

17. A wind turbine system, comprising: a tower; a nacelle disposed on the tower; and a yaw system operable in a yawing operational state to rotate the nacelle with respect to the tower, and in a non-yawing operational state; the yaw system, comprising: a yaw controller; one or more yaw drive actuators; a mechanical brake operable in an engaged state or in a dis-engaged state; and a motor operable to be in a brake state in which a braking torque is applied to oppose movement of the nacelle; wherein the yaw system is arranged to perform an operation, comprising: when the yaw system is in the non-yawing operational state and the mechanical brake is in the engaged state: determining, by the yaw controller, a signal indicative of a yaw moment is above a signal threshold by detecting a movement of the nacelle, wherein detecting the movement of the nacelle comprises detecting a sliding of the mechanical brake; in response to the determining, sending, from the yaw controller, a braking signal to the yaw drive actuators causing the motor to enter the brake state and ramp up the braking torque over a period of time; and in response to determining the motor has ramped the braking torque up above a minimum braking torque, releasing the mechanical brake.

18. A non-transient computer readable medium comprising computer executable instructions to be executed by a data processing system to perform a method for controlling a wind turbine system; wherein the wind turbine system comprises: a tower; a nacelle disposed on the tower; and a yaw system operable in a yawing operational state to rotate the nacelle with respect to the tower, and in a non-yawing operational state; the yaw system, comprising: a yaw controller; one or more yaw drive actuators; a mechanical brake operable in an engaged state or in a dis-engaged state; a motor operable to be in a brake state in which a braking torque is applied to oppose movement of the nacelle; and wherein the method, comprises: when the yaw system is in the non-yawing operational state and the mechanical brake is in the engaged state: determining, by the yaw controller, a signal indicative of a yaw moment is above a signal threshold by detecting a movement of the nacelle, wherein detecting the movement of the nacelle comprises detecting a sliding of the mechanical brake; in response to the determining, sending, from the yaw controller, a braking signal to the yaw drive actuators causing the motor to enter the brake state and ramping up the braking torque over a period of time; and in response to determining the motor has ramped the braking torque up above a minimum braking torque, releasing the mechanical brake.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) Embodiments of the invention will be described, by way of example only, with reference to the drawings, in which

(2) FIG. 1 illustrates a wind turbine,

(3) FIG. 2 illustrates wind turbines configured as multi-rotor wind turbines,

(4) FIG. 3 illustrates the yaw system,

(5) FIG. 4 is a schematic illustration of a yaw motor,

(6) FIG. 5 illustrates an embodiment of a procedure to determine when to disengage the mechanical brakes and engage motor braking.

(7) FIG. 6 illustrates an embodiment of a procedure to determine when to engage the mechanical brakes and disengage motor braking.

(8) FIG. 7 illustrates an embodiment where the signal indicative of a yaw moment is based on a yaw position signal obtained from a yaw position detector.

(9) The figures show one way of implementing the present invention and is not to be construed as being limiting to other possible embodiments falling within the scope of the attached claim set.

DETAILED DESCRIPTION OF AN EMBODIMENT

(10) FIG. 1 shows a wind turbine 100 (also commonly referred to as a wind turbine generator, WTG) comprising a tower 101 and a rotor 102 with at least one rotor blade 103. Typically, three blades are used, but a different number of blades can also be used. The blades 103 are connected with the hub 105, which is arranged to rotate with the blades. The rotor is connected to a nacelle 104, which is mounted on top of the tower 101 and being adapted to drive a generator situated inside the nacelle 104 via a drive train. The rotor 102 is rotatable by action of the wind. The wind induced rotational energy of the rotor blades 103 is transferred via a shaft to the generator. Thus, the wind turbine 100 is capable of converting kinetic energy of the wind into mechanical energy by means of the rotor blades and, subsequently, into electric power by means of the generator. The generator is connected with a power converter for injection the generated power into the utility.

(11) FIG. 2 shows alternative wind turbines 100 configured as multi-rotor wind turbines. Multi-rotor wind turbines comprise a plurality of nacelles 104. The nacelles 104 can be supported, as illustrated in the upper drawing, via a tower 101 and support arms 106 extending outwardly from the tower 101 so that the nacelles are placed away from the tower and on opposite sides of the tower. Here two arm levels are shown, however also embodiments with a single arm level, as well as three or more levels is possible. Alternatively, as illustrated in the lower drawing, the nacelles 104 can be supported by angled towers 101 extending from a foundation 130, e.g. a ground or floating foundation, so that two or more nacelles 104 are sufficiently separated from each other at a given height. Embodiments of the present invention may be used with multi-rotor wind turbines or single-rotor wind turbines.

(12) FIG. 3 shows an embodiment of a yaw system 300 in accordance with the present invention. In the illustrated example, the yaw system 300 comprises a number of yaw drive actuators 301 of which ten are shown on FIG. 3. In other configurations, more or less yaw drive actuators 301 may be used. Each yaw drive actuator 301 comprises a motor 302, in this embodiment an electrical drive motor, and a pinion 304. The pinion 304 is connecting the yaw drive actuator 301 and the yaw ring 305. In the illustrated embodiment, the yaw drive actuator 301 comprises a variable frequency drive (VFD) 306. However, the VFD need not be present and can be replaced by a power supply, possibly with a soft starter.

(13) The motors 302 may be of the asynchronous induction motor type, possibly enabled for individual motor control, either via on/off control or via VFD control. In the embodiment with VFD control, the motors 302 may be operated in accordance with a 4-quadrant control scheme. The frequency drives 306 are seen in FIG. 3 to be clustered in a cabinet in the centre and being connected to the motor controller 307, however the frequency drives 306 can be placed in other locations as well.

(14) The motor 302 comprises an encoder, which is a position meter, detecting the position of the motor, and from the angular changes in the position, the motor speed can be derived. The encoder is used to detect the speed of the motor 302 and return the speed to the frequency drive 306.

(15) The encoder may be used for every motor 302 to detect the position and speed of the motor 302 and to ensure great load sharing, while avoiding overloading any of the motors 302.

(16) The motor controller 307 may be arranged to output a torque reference to the variable frequency drives 306, and the motor controller 307 receives information about the motor speed either through communication with the encoder, the individual variable frequency drives 306 or through communication with the yaw controller 308. Further, the motor controller 307 receives signals from the yaw controller 308 about when to yaw and in which direction based on input from the wind direction device 309. However, the yaw controller 308, wind direction device 309 and cables for input power and communication are not a part of the yaw system 300.

(17) The yaw controller 308 may control the yaw system 300, and the yaw controller 308 activates the motor controller 307 when yawing is needed.

(18) The yaw controller 308 may be part of the turbine controller, e.g. a control module of the turbine controller, or may be a dedicated controller connected to the turbine controller.

(19) As an addition or alternative to applying an encoder at the motors, a yaw position sensor 310 may be present. The yaw position sensor may be an optical sensor which detect the position of the nacelle, e.g. from detecting the position of the yaw ring. Another example includes a GPS mounted at the back of the nacelle which can detect the absolute nacelle position.

(20) FIG. 4 is a schematic illustration of an electrical yaw drive actuator 301 including a mechanical brake 400. The mechanical brake 400 is connected to the motor 302 and the pinion 304 by a motor shaft 416. The mechanical brake 400 can be designed in different ways, but the one illustrated in FIG. 4 comprises a friction surface 414, forming the interface between the stationary part 410 and the rotating part, specifically the brake disk 412, of the motor. Further, the mechanical brake 400 comprises springs and coils (not shown). The mechanical brakes 400 are often normally closed meaning that if the coils are not energized the springs creates a force onto the friction surfaces 414 which prevents the rotation of the motor 302 by the friction surfaces 414 engaging the brake disk 412. When the coils are energized, they create a force counteracting the spring pressure, which releases the mechanical brakes 400, and thereby hinder the rotation or the motor 302 and the pinion 304. The pinion 304 is engaged with the yaw ring 305, and when the mechanical brakes 400 brake the pinion 303, the pinion 304 is hindering the nacelle 104 from rotating.

(21) In an embodiment, the yaw system may be implemented to comprise three operation states:

(22) a) Parked by brake, wherein the mechanical brakes 400 are engaged. In this state detection of sliding in the mechanical brakes 400 may be set to be active. In an embodiment, if sliding in mechanical brakes 400 is detected above a signal threshold, the state changes to state Parked by motor.

(23) b) Parked by motor, wherein the motors 302 are actively controlled to apply a braking torque to oppose movement of the nacelle 104, meaning that the electrical motor brakes are activated. In embodiments, the mechanical brakes 400 are disengaged in this state; however, the parked by motor state may also be selected before disengaging the mechanical brakes 400 in certain situations.

(24) c) Yawing, either clockwise or counterclockwise, wherein there is active yaw. The direction of the rotation of the nacelle 104 as well as the speed and torque may be set by an input signal. The yawing state is controlled by the commands from the yaw controller 308.

(25) The yaw system 300 may be arranged for changing state from parked by brake to parked by motor, when the angle of sliding is higher than a threshold value.

(26) The yaw system 300 may be arranged for changing state from parked by motor to parked by brake, when a signal is received from the turbine controller that the yaw moment has been below a given threshold for a time period, or when the moment applied by the motor 302 have been lower than a threshold value for a time period.

(27) FIG. 5 illustrates an example of a procedure to determine when to disengage the mechanical brakes 400 and utilize motor braking, going from Parked by brake to Parked by motor. Initially the yaw system 300 is in the state parked by brake. .sub.trig is the triggering state depending on the motor shaft angle, which triggers the mode switching to parked by motor. The state changes to parked by motor if .sub.trig is above the signal threshold .sub.unlock. .sub.trig is the angle the motor shaft 416 has moved from an initial position. .sub.unlock is the signal threshold that triggers the mode switching. If |.sub.trig|>.sub.unlock the status changes to parked by motor.

(28) The angle .sub.trig is checked every T.sub.c seconds and .sub.trig is reset, if the change since last check is below a minimum threshold .sub.reset: |.sub.trig(T.sub.c(k).sub.trig(T.sub.c(k1)|<.sub.reset. This ensures minor sliding during a longer period do not initiate changing the state to parked by motor.

(29) The angle movement of the motor shaft 416 is monitored continuously during Parked by brake. The triggering state .sub.trig is changing in accordance with the measured motor shaft angle. Every time period of T.sub.c, the state .sub.trig is compared to the lower threshold level .sub.reset and reset if .sub.trig<.sub.reset. The angle movement should be above the low angle threshold .sub.reset in order to not reset after a short time period, T.sub.c.

(30) This ensures that the motor control is not activated, if there is neglectable sliding in the mechanical brakes 400 or movement in reality is integrated noise on the speed signal over a longer period. If .sub.trig>.sub.reset, the triggering state continuous to change in accordance with the motor shaft angle. If .sub.trig>.sub.unlock the mechanical brakes 400 are released and parked by motor control is enabled.

(31) FIG. 6 illustrates an example of a procedure to determine when to engage the mechanical brakes 400 and disengage motor braking, going from Parked by motor to Parked by brake.

(32) .sub.motor is the motor braking torque; the motor 302 must apply to counter the yaw moment, when parked by motor. .sub.brake is the braking torque the mechanical brakes 400 must apply to counter the yaw moment, when parked by brake.

(33) At T.sub.unlock the mode changes to parked by motor, the mechanical brakes 400 are released and the .sub.brake goes to zero, instead the motors 302 takes over going into brake state and applies a motor braking torque .sub.motor which goes to .sub.capacity.

(34) When .sub.motor goes below .sub.lock, .sub.lock is a certain level below the nominal sliding level .sub.capacity, a timer T.sub.trig starts. When the timer T.sub.trig has run for a time T.sub.lock, indicating that the motor torque needed to keep the yaw system 300 from sliding has been below .sub.lock for the time T.sub.lock, the mode is changed to Parked by brake. Now the mechanical brakes 400, at the time T.sub.B, are engaged and they take over braking from the motors 402. The motor torque .sub.motor is ramped down by lowing .sub.motor to zero and .sub.brake increases.

(35) FIG. 7 illustrates an embodiment where the signal indicative of a yaw moment is based on a yaw position signal obtained from a yaw position detector. The yaw position signal may be expressed in different ways. For example, the yaw position may be an angle, that is the nacelle angle. The angle may e.g. be expressed in relation to an absolute zero angle or relative to the last stop position. Use of a yaw position detector may e.g. be in a situation where the yaw motors are not equipped with a VFD.

(36) In FIG. 7A, the nacelle position in the form of the angular position is shown as a function of time, while FIG. 7B shows the counteracting motor torque as a function of time. The motor torque is in the illustrated embodiment applied in an on/off fashion. In a first period, P.sub.1, the nacelle is positioned at angle .sub.0, and as the angle is constant the motors are in the brake state. At time t.sub.1, the nacelle starts to slide (period P.sub.12). Once it has been detected that the nacelle position has moved a predetermined amount to .sub.s, a braking signal is provided to the yaw drive actuators so that the motor applies a motor braking torque. The nacelle keeps sliding until the applied motor braking torque is enough overcome the loads that makes the nacelle slide and thereby bring the nacelle sliding to a stop. This happens in period P.sub.2 and stops at t.sub.3 where the yaw angle is .sub.m.

(37) In the illustrated embodiment, the wind direction has changed during the sliding, and to place the nacelle in the upwind direction, the motor braking torque is applied until a stop criterion is fulfilled, i.e. including P.sub.3. At time t.sub.4, the nacelle position matches the wind direction, and the motors are stopped.

(38) Although the present invention has been described in connection with the specified embodiments, it should not be construed as being in any way limited to the presented examples. The scope of the present invention is set out by the accompanying claim set. In the context of the claims, the terms comprising or comprises do not exclude other possible elements or steps. Also, the mentioning of references such as a or an etc. should not be construed as excluding a plurality. The use of reference signs in the claims with respect to elements indicated in the figures shall also not be construed as limiting the scope of the invention. Furthermore, individual features mentioned in different claims, may possibly be advantageously combined, and the mentioning of these features in different claims does not exclude that a combination of features is not possible and advantageous.