Control yaw to reduce motor speed

Abstract

This invention relates to a method for controlling the yaw of a wind turbine system by controlling multiple yaw drive actuators. When the yaw drive actuators apply the same torque to all motors, if the motors are not engaged when the yaw system is activated, this can cause some motors to overspeed. Therefore, if the actual motor speed reference of a yaw drive actuator is higher than a specific motor speed reference, an output signal is applied to the yaw drive actuator whose actual motor speed reference is higher than the specific motor speed reference to reduce the actual motor speed reference.

Description

Technical Field

[0001] The present invention relates to a method for controlling the yaw of a wind turbine system, and more particularly to a method for controlling multiple yaw drive actuators to avoid overspeed of the motors of the yaw drive actuators. Background Technology

[0002] The yaw system's task is to determine the nacelle's orientation relative to the wind. Most of the time, the yaw system is inactive or stopped. It only activates when the orientation of the rotor and nacelle needs to be changed (usually due to a change in wind direction) to align the nacelle with the wind.

[0003] In normal operating mode, the deviation between the nacelle and the wind direction (yaw angle) should be as small as possible to avoid power generation losses and reduce load. However, at the same time, the yaw system should not be too sensitive to avoid continuous small yaw movements that would reduce the lifespan of mechanical components.

[0004] In modern wind turbine systems, the yaw system uses multiple yaw drive actuators to determine the orientation of the nacelle relative to the wind.

[0005] However, if all yaw drive actuators apply the same torque to all motors, this could cause some motors to overspeed if the motors are not engaged when the yaw system is activated.

[0006] Therefore, an improved method for controlling yaw systems would be advantageous, and in particular, a more efficient and / or reliable method for controlling multiple yaw drive actuators would be advantageous. Summary of the Invention

[0007] One object of the present invention is to provide a method for avoiding or at least reducing overspeed of the motor in the yaw drive actuator when the yaw system is in operation.

[0008] Another objective of this invention is to improve the control method for wind turbines, and in particular to improve the control method for increasing the service life of components in the yaw system.

[0009] Therefore, the above-mentioned and several other objectives are achieved in the first aspect of the invention by providing a method for controlling the yaw of a wind turbine system, the wind turbine system including a nacelle, a tower, a turbine controller, and a yaw system.

[0010] The yaw system can be activated to yaw the nacelle relative to the tower.

[0011] The yaw system includes a motor controller and multiple yaw drive actuators.

[0012] The motor controller receives the actual motor speed reference for each yaw drive actuator, and if the actual motor speed reference of the yaw drive actuator is higher than a specific motor speed reference, it applies an output signal to the yaw drive actuator whose actual motor speed reference is higher than the specific motor speed reference to reduce the actual motor speed reference.

[0013] To prevent the motor in the yaw drive actuator from overspeeding excessively or for extended periods, the motor controller sends an output signal to the yaw drive actuator to reduce the actual motor speed when overspeed is detected. The advantage of reducing overspeed is a lower load on the motor, thereby reducing the risk of overloading the motor and / or motor controller, which could lead to shutdown and stoppage. Furthermore, by avoiding overloading the motor and / or motor controller, their lifespan can be increased. Another advantage involves avoiding peak loads on the yaw drive system (pinion and yaw ring) caused by an overspeeding motor. Motor overspeed is typically set to a given speed at which continuous operation is not possible. Motor overspeed can, for example, be set to exceed the motor's specified design limits. However, motor overspeed can also be set as a function of design limits, such as being at a given speed above or below those limits.

[0014] The yaw system includes multiple yaw drive actuators, each comprising a motor and a pinion gear connected to the yaw drive actuator. The yaw system also includes a yaw ring, to which multiple actuators are connected. The yaw ring is located on the tower to allow nacelle rotation. Furthermore, the yaw drive actuators include a variable frequency drive (VFD). In this document, the VFD is generally considered part of the yaw drive actuator, even though the VFD can be configured separately from the other parts of the motor.

[0015] Yaw or rotation is understood, as is commonly understood in this field, as the rotation of the cabin.

[0016] The motors are preferably electric drive motors (which are typically asynchronous induction motors), but can also be permanent magnet motors. Each motor is powered by a separate variable frequency drive (VFD), enabling individual motor control. The VFD is connected to and receives an output signal from the motor controller in the yaw system. This output signal is the desired motor torque reference from the motor controller, but in the event of motor overspeed, this output signal is reduced to a lower motor torque reference. Alternatively, these motors can be hydraulically driven motors.

[0017] The tower can be any support structure or construction on which one or more nacelles can be mounted and rotated relative to the tower. The tower may include support arms on which the nacelles are mounted; therefore, the phrase "rotate the nacelles relative to the tower" also covers the case where the nacelles placed on the support arms are rotated. Furthermore, embodiments are possible where the support arms are rotatable relative to the tower, so that when the support arms rotate relative to the tower, the nacelles simultaneously rotate relative to the tower; therefore, the phrase "rotate the nacelles relative to the tower" also covers this case.

[0018] According to one embodiment, the method includes: a motor controller receiving an average motor speed reference as a feedback signal. The average motor speed reference may be determined by a turbine controller or by the motor controller itself. If the motor controller determines the average motor speed reference, this is done in a separate computational block outside the computational block that handles feedback control.

[0019] The average motor speed reference is used to determine if the motor is overspeeding.

[0020] According to one embodiment, the method includes: a specific motor speed reference is an average motor speed reference to which a threshold has been added. Adding the threshold to the average motor speed reference to determine whether a motor is running faster than the average motor speed reference with the threshold added is used for early detection of whether the motor may be heading towards overspeed. All motors should preferably rotate at the same speed; therefore, if a motor moves faster than the average motor speed reference by more than the threshold, this is an indication that the motor is heading towards overspeed, and therefore measures should be taken to reduce the motor speed.

[0021] According to one embodiment, the method includes: a specific motor speed reference is a maximum motor speed reference.

[0022] The maximum motor speed reference is the maximum value that the motor should not exceed, even if it might run slightly faster. This is to avoid overloading the motor and preventing it from shutting down. Therefore, if the motor speed exceeds the maximum speed, measures must be taken to reduce it. The maximum motor speed reference is usually stored in the computer's memory as a parameter entered when setting up the system.

[0023] According to one embodiment, the method includes: the motor controller receiving from the turbine controller:

[0024] - The requested motor speed reference is used as the input signal, and

[0025] The motor controller provides:

[0026] - The required motor torque reference is used as an output signal, which is determined based on the requested motor speed reference and the average motor speed reference, to cause multiple yaw drive actuators to rotate the nacelle.

[0027] A control scheme with a virtual master drive, constructed based on the average motor speed reference as a feedback signal, is provided by using the required motor torque reference for multiple yaw actuators as the basis. The virtual master drive means that all yaw actuators receive the same required motor torque reference and act together as if there were only one yaw actuator. Therefore, the virtual master drive controls all normally operating yaw actuators, not those operating in overspeed or any other special mode. In this way, the load is distributed with respect to the virtual master drive, which is consistent with the drive operating at the average speed. As a result, the invention is particularly advantageous, but not exclusively advantageous, for achieving a uniform load distribution for multiple yaw actuators. Thus, each yaw actuator delivers essentially the same torque, performs uniform action to avoid imbalance, and avoids overloading of individual yaw actuators, thereby increasing the lifespan of the yaw system and improving the wind turbine's productivity by reducing downtime when the wind turbine is not producing electricity.

[0028] However, when a motor overspeeds (e.g., because the pinion is not engaged with the yaw ring), the motor overspeed requires special handling and is no longer part of the virtual drive, where all yaw drive actuators receive the same signal.

[0029] According to one embodiment, the method includes: an output signal for reducing the actual motor speed reference applied to a yaw drive actuator where the actual motor speed reference is higher than a specific motor speed reference is a reduced motor torque reference.

[0030] The motor controller sends the required motor torque reference to all yaw drive actuators. However, if it is determined that the motor is overspeeding or operating at least faster than a specific motor speed reference, the required motor torque reference sent to the specific yaw drive actuator with the overspeeding motor is a reduced motor torque reference. This reduces the speed of the overspeeding motor, thereby decreasing the risk of motor shutdown.

[0031] According to one embodiment, the method includes: the reduced motor torque reference is a desired motor torque reference reduced by a coefficient or percentage.

[0032] Different strategies for reducing motor speed can be applied by using a reduced motor torque reference. The reduced motor torque reference can be a percentage subtracted from the desired motor torque reference, or the desired motor torque reference can be divided by a coefficient.

[0033] According to one embodiment, the method includes: reducing the motor torque reference proportionally from the desired motor torque reference relative to the detected speed.

[0034] The reduced motor torque reference can be a proportional reduction of the desired motor torque reference, calculated based on the average motor speed reference from a normally operating motor. For example, if the motor is running 30% faster, the reduced motor torque reference is set to 30% lower.

[0035] According to one embodiment, the method includes: if an output signal for reducing the actual motor speed reference is applied to a yaw drive actuator, then the remaining yaw drive actuators receive an output signal for increasing the actual motor speed reference.

[0036] If a motor is overspeeding, it does so because the yaw drive actuator is not engaged with the yaw ring and therefore is not participating in actual yaw, thus placing a higher load on the motors of the other yaw drive actuators. Therefore, it is advantageous to increase the speed of the motors of the normally operating yaw drive actuators (by increasing the required motor torque reference of these motors so that they can compensate for the motors not engaged with the yaw ring).

[0037] According to one embodiment, the method includes: an average motor speed reference being calculated as the average of the actual motor speed references of all motors.

[0038] According to one embodiment, the method includes: each yaw drive actuator includes a motor, and an average motor speed reference is calculated as the average of actual motor speed references of a selected subgroup of motors.

[0039] According to one embodiment, the method includes: in the calculation of the average motor speed reference, the selected motor subgroup does not include motors whose actual motor speed reference is higher than a high-speed threshold speed and / or motors whose actual motor speed reference is lower than a low-speed threshold speed.

[0040] If some motors are not running or are running at significantly different speeds than other motors, it is advantageous to exclude those motors from the calculation of the average motor speed reference. This typically occurs when initiating yaw, if the actuator must rotate a greater distance than other actuators to engage the pinion with the yaw ring gear. This can happen, for example, if there are broken teeth on the yaw ring. Therefore, overspeed motors are excluded from the calculation of the average motor speed reference, and thus from the calculation of the required motor torque reference for normal operation.

[0041] According to one embodiment, the method includes: a wind turbine system comprising multiple nacelles, and a yaw system arranged to rotate one or more of the multiple nacelles. Therefore, the method of the present invention can also be applied to multi-rotor wind turbines.

[0042] In multi-rotor turbines, nacelles can be mounted on support arms or on other support structures that allow for the installation of more nacelles on the same wind turbine system. The method of this invention can be used individually for multiple nacelles, such that a single nacelle placed on a support arm can rotate while other nacelles remain stationary. The method can also be used to rotate all nacelles by rotating the entire structure on which multiple nacelles are mounted, causing multiple nacelles to rotate simultaneously. The multiple nacelles then rotate relative to the tower, thus each individual nacelle also rotates relative to the tower.

[0043] The second aspect of the invention relates to a control system for controlling the yaw of a wind turbine, wherein the control system is arranged to perform the steps of the method according to the first aspect.

[0044] A third aspect of the invention relates to a wind turbine, wherein the wind turbine further includes a control system according to the second aspect for controlling the yaw of the wind turbine system.

[0045] The fourth aspect of the invention relates to a computer program product comprising software code adapted to control a wind turbine when executed on a data processing system, the computer program product being adapted to perform the method of the first aspect.

[0046] Different parts of a motor controller, dynamic speed limiter, speed controller, torque limiter, etc., can be implemented in separate computer programs, or as different functional blocks within the same computer program running on the same or different microprocessors. Similarly, motor controllers and turbine controllers can be implemented in different software programs running on separate computers or microprocessors, in the same software program running on the same computer or microprocessor, or in any combination thereof.

[0047] Generally speaking, aspects and embodiments of the present invention can be combined and coupled in any possible manner within the scope of the invention. These and other aspects, features, and / or advantages of the invention will become apparent and will be elucidated with reference to the embodiments described below. Attached Figure Description

[0048] Embodiments of the present invention will be described by way of example only with reference to the accompanying drawings, wherein:

[0049] Figure 1 The illustration shows a wind turbine.

[0050] Figure 2The illustration shows a wind turbine configured as a multi-rotor wind turbine.

[0051] Figure 3 The diagram illustrates the yaw system.

[0052] Figure 4 The diagram illustrates the yaw controller.

[0053] Figure 5 The diagram illustrates the running envelope.

[0054] Figure 6 The diagram illustrates the motor controller for each drive.

[0055] Figure 7 illustrates the difference between operation with and without overspeed protection.

[0056] The accompanying drawings illustrate one mode of carrying out the invention and should not be construed as limiting other possible embodiments falling within the scope of the appended claims. Detailed Implementation

[0057] Figure 1 A wind turbine 100 (WTG) is shown, comprising a tower 101 and a rotor 102 with at least one rotor blade 103. Three blades are typically used, but a different number can also be used. The blade 103 is connected to a hub 105, which is arranged to rotate together with the blade. The rotor is connected to a nacelle 104, which is mounted on top of the tower 101 and adapted to drive a generator located within the nacelle via a drivetrain. The rotor 102 rotates under the influence of wind. The rotational energy of the rotor blades 103 caused by the wind is transferred to the generator via a shaft. Thus, the wind turbine 100 is able to convert the kinetic energy of the wind into mechanical energy by means of the rotor blades, and subsequently into electrical energy by means of the generator. The generator is connected to a power converter.

[0058] Figure 2An alternative wind turbine 100 configured as a multi-rotor wind turbine is shown. The multi-rotor wind turbine includes multiple nacelles 104. An example of four nacelles is shown here, but in general, two or more nacelles can be used in a multi-rotor turbine. As shown in the figure above, the nacelles 104 can be supported via a tower 101 and support arms 106 extending outward from the tower 101, thereby positioning the nacelles away from the tower and on opposite sides of the tower. In a multi-rotor wind turbine, a yaw system can be placed at the tower for collective rotation of the arm structure and / or as a separate yaw system for each nacelle. Another example of a multi-rotor structure is shown in the figure below, where the nacelles 104 are supported by an inclined tower 101 extending from a base 130 (e.g., ground or floating base), thereby sufficiently separating two or more nacelles 104 from each other at a given height. Embodiments of the invention can be used with multi-rotor wind turbines or single-rotor wind turbines.

[0059] Figure 3 An embodiment of a yaw system according to the present invention is shown. In the illustrated example, the yaw system includes a plurality of yaw drive actuators 301. In other configurations, more or fewer yaw drive actuators may be used. Each yaw drive actuator 301 includes a motor 302 (an electric drive motor in this embodiment) and a pinion 304. Additionally, a transmission may be included. The pinion 304 connects the yaw drive actuator 301 and the yaw ring 305. Furthermore, the yaw drive actuator 301 includes a variable frequency drive (VFD) 306.

[0060] Motor 302 can be an asynchronous induction motor, each powered by a separate variable frequency drive 306, thus enabling individual motor control. Figure 3 As can be seen, the frequency converter drive 306 is clustered in the central cabinet and connected to the motor controller 307, but the frequency converter drive 306 can also be placed in other locations.

[0061] Motor 302 includes an encoder for detecting the motor's position. This encoder is a position gauge, and the motor speed can be derived from changes in position. The encoder is used to detect the speed of motor 302 and return the speed to the frequency converter drive 306.

[0062] An encoder can be used for each motor 302 to detect the position and speed of the motor 302 and ensure large load sharing while avoiding overloading any of the motors 302.

[0063] The motor controller 307 outputs the required motor torque reference 403 to the variable frequency drive 306. The motor controller 307 receives information about the motor speed through communication with the encoder, each variable frequency drive 306, or with the turbine controller 308 which calculates the average motor speed reference 402. Furthermore, based on input from the wind direction device 309, the motor controller 307 receives signals from the main turbine controller 308 regarding when and in which direction to yaw.

[0064] The turbine controller 308 can control the yaw system 300, and the turbine controller 308 activates the motor controller 307 when yaw is required.

[0065] Figure 4 This is a schematic diagram of one embodiment of a yaw control scheme. The yaw controller includes a centralized control structure in which a single motor controller 307 operates all yaw drive actuators 301 based on a requested motor speed reference 401 and an average motor speed reference 402 of all motors 302 or a selected subgroup of motors 302.

[0066] The selected motor 302 subgroup may exclude the fastest and / or slowest motor 302 to increase robustness, or the selected motor 302 subgroup may exclude motors 302 that operate faster than the high-speed threshold speed and / or slower than the low-speed threshold speed.

[0067] Under normal operation, the same torque, the required motor torque reference 403, is requested for all yaw drive actuators 301 to ensure uniform load distribution. However, the required motor torque reference 403 can be distributed unevenly for each individual yaw drive actuator, if requested. For example, when passing through a segmented yaw section, it may be desirable to reduce torque, or each drive may be tested individually during self-test. Moreover, if the motor 302 overspeeds, the required motor torque reference 403 can differ for the yaw drive actuator 301 with the overspeed motor 302 from the other yaw drive actuators 302.

[0068] The required motor torque reference 403 sent from the motor controller 307 to the yaw drive actuator is received by the frequency converter drive 306. Then, the frequency converter drive 306 sends a motor signal 420 to the motor 302, and the motor 302 applies the motor shaft torque 421 to the yaw system 300 and the pinion 304 to transmit the torque to the yaw ring 305.

[0069] Based on the motor speed 422 from each motor 302, the turbine controller 308 or the motor controller 307 calculates an average motor speed reference 402 as a feedback signal. The motor controller can calculate its own feedback signal in a separate calculation block from the control loop calculation block. Furthermore, the motor speed of each motor 302 is sent back to the frequency converter drive 306 as a feedback signal via the internal torque control loop 423.

[0070] Figure 5 An example of the operating envelope 501 for 4-quadrant control of a motor is shown. The operating envelope 501 is a coordinate system: where the X-axis is the average motor speed reference 402, and the Y-axis is the desired motor torque reference 403 applied to motor 302.

[0071] Finite motor speed reference 407 calculated by motor controller 307 Figure 6 The speed must not exceed the maximum motor speed 506. The maximum motor speed 506 is illustrated by the vertical curve portion in the first quadrant 502.

[0072] The required motor torque reference 403 calculated by the motor controller 307 must not exceed the maximum torque 507. The maximum torque 507 is illustrated by the horizontal curve portion in the first quadrant 502.

[0073] The curved portion 508 of the curve in the first quadrant 502 illustrates the relationship between speed and torque, taking into account the maximum power usage reference 405. When the motor is running at high speed, the applicable torque is limited by the maximum power usage reference 405.

[0074] The third quadrant 503 is equivalent to the first quadrant 502, except that the motor 302 is rotated in the opposite direction.

[0075] Figure 6 The illustration shows a graphical representation of an embodiment of the motor controller 307.

[0076] The goal of motor controller 307 is to determine the required motor torque reference 403 that generates the requested motor speed reference 401.

[0077] The control strategy comprises two feedback control loops in a cascaded structure, where both torque and speed control are used. These two feedback loops consist of an inner loop and an outer loop. The inner loop... Figure 4 The diagram shows an internal torque control loop, which is illustrated as being processed by a frequency converter drive 306, which receives the required motor torque reference 403 from the motor controller 307. Figure 6 The variable frequency drive 306, not shown in the diagram, is placed between the motor controller 307 and the motor 302, as follows: Figure 4 As shown in the image.

[0078] The internal torque control loop 423 is processed by the frequency converter drive 306 so that the output is a torque reference for obtaining the desired motor torque. Ideally, the motor shaft torque 421 is equal to the required motor torque 403.

[0079] External feedback loop in Figure 6 The diagram shows a speed control loop 612, which returns an average motor speed reference 402 to a speed control unit 408. The speed control unit receives a finite motor speed reference 407 as an input signal and an average motor speed reference 402 as a feedback signal, and sends the desired motor torque reference 403 as an output to the motor 302.

[0080] The speed control unit consists of a PI controller 409, an overspeed damping function block 450, and a torque limiter 404.

[0081] The PI controller 409 is a proportional-integral controller for speed control because it produces a uniform DC gain and excellent noise suppression. The speed control loop 612 returns an average motor speed reference 402 to the speed control unit 408. Subtracting the average motor speed reference 402 from a finite motor speed reference 407 yields an error signal 424, which serves as the input to the PI controller 409, which provides a calculated motor torque reference 410 as its output. The PI controller could also be a PID controller, but in the described embodiment, the derivative (D) portion of the PID is zero.

[0082] The overspeed damping function block 450 receives the calculated motor torque reference 410 as input from the PI controller 409 and the actual motor speed reference 451 from each motor 302. If overspeed is detected in a motor 302, the overspeed damping function block 450 lowers the torque reference and sends the lowered motor torque reference as an output signal to the torque limiter 404 for the specific motor that is overspeeding. If the motor is not overspeeding, the output signal is the calculated motor torque reference 410 received from the PI controller.

[0083] Torque limiter 404 Figure 5 During operation in the first and third quadrants, the torque is limited to a maximum torque of 507. The torque limiter 404 receives an output signal 452 from the overspeed damping function block 450 and outputs the desired motor torque reference 403 as an output signal. Preferably, the torque limiter 404 sends the same desired motor speed reference 403 to all yaw drive actuators 301, but in cases of motor overspeed or other special circumstances, it can send different desired motor speed references 403 to each yaw drive actuator 301.

[0084] Dynamic speed limiter 406 is used to limit a speed reference 407 that defines a finite motor speed reference. The requested speed reference 401 is received from turbine controller 308, but can be reduced due to power limitations based on maximum power usage reference 405. Furthermore, the speed can be reduced in speed saturation routine 615 to not exceed the maximum power speed, and speed ramp routine 616 ensures that the motor is not accelerated beyond the maximum rate of speed change.

[0085] After passing through the low-pass filter 618 and the directional saturation filter 617 (which ensures that the feedback signal has a minimum value, rather than zero), the feedback of the motor torque reference 403 required for normal operation of the yaw drive actuator is also used by the dynamic speed limiter 406.

[0086] Figure 7 illustrates the advantages of using overspeed protection. Figure 7a -b illustrates the method of using overspeed protection. Figure 7a The diagram illustrates the motor speed when overspeed protection is applied. Figure 7b The diagram illustrates the resulting motor torque.

[0087] Figure 7c The -d option indicates that overspeed protection is not used. Figure 7c The diagram illustrates the motor speed without overspeed protection. Figure 7d The diagram illustrates the resulting motor torque.

[0088] Figure 7a and Figure 7c The diagram illustrates a speed reference 701 received as input by the motor and a speed 702 of the motor engaged with the yaw ring. Speeds 703 and 704 originate from two motors not engaged with the yaw ring. Therefore, the speeds of these two motors are rapidly increasing. Figure 7c The diagram illustrates the increase in speed without overspeed protection, while... Figure 7a The diagram shows the overspeed protection tripping. Figure 7d The diagram illustrates that when overspeed protection is not used, all motors apply the same torque of 705, while... Figure 7b The diagram illustrates that when overspeed protection is used, the two motors not engaged with the yaw ring apply reduced torque 707, 708, while the motor engaged with the yaw ring applies the requested torque 706.

[0089] Although the invention has been described in conjunction with specific embodiments, it should not be construed as being limited in any way to the presented examples. The scope of the invention is defined by the appended set of claims. In the context of the claims, the terms "comprising" or "including" do not exclude other possible elements or steps. Furthermore, references to words such as "a" or "an" should not be construed as excluding multiples. The use of reference numerals for elements shown in the figures in the claims should also not be construed as limiting the scope of the invention. Moreover, individual features mentioned in different claims may be advantageously combined, and mentioning these features in different claims does not preclude the possibility and advantage of combining features.

Claims

1. A method for controlling the yaw of a wind turbine system, the wind turbine system comprising a nacelle (104), a tower (101), a turbine controller (308), and a yaw system (300). The yaw system (300) can be operated to rotate the nacelle (104) relative to the tower (101). The yaw system (300) includes a motor controller (307) and a plurality of yaw drive actuators (301), wherein, The method includes: The actual motor speed reference (451) of each yaw drive actuator (301) is received by the motor controller (307). The motor controller (307) calculates an average motor speed reference (402) for the plurality of yaw drive actuators or subgroups of the plurality of yaw drive actuators (301), and When it is determined that the actual motor speed reference (451) of one or more of the plurality of yaw drive actuators (301) is higher than a specific motor overspeed reference corresponding to the sum of a threshold and the average motor speed reference, an output signal (452) for reducing the actual motor speed reference (451) of the one or more yaw drive actuators is applied to the one or more yaw drive actuators.

2. The method for controlling the yaw of a wind turbine system according to claim 1, wherein, The specific motor overspeed reference is the maximum motor speed reference.

3. The method for controlling the yaw of a wind turbine system according to claim 1 or 2, wherein, The motor controller (307) receives from the turbine controller (308): - The requested motor speed reference (401) is used as the input signal, and The motor controller (307) provides: - A required motor torque reference (403) is output as an output signal, which is determined based on the requested motor speed reference (401) and the average motor speed reference (402) for causing the plurality of yaw drive actuators (301) to rotate the nacelle (104).

4. The method for controlling the yaw of a wind turbine system according to claim 3, wherein, The output signal (452) for reducing the actual motor speed reference (451) applied to the yaw drive actuator (301) where the actual motor speed reference (451) is higher than the specific motor overspeed reference is a reduced motor torque reference provided to the corresponding torque limiter of the one or more yaw drive actuators.

5. The method for controlling the yaw of a wind turbine system according to claim 4, wherein, The reduced motor torque reference is the desired motor torque reference reduced by a coefficient or percentage (403).

6. The method for controlling the yaw of a wind turbine system according to claim 4, wherein, The reduced motor torque reference is proportionally reduced from the desired motor torque reference (403) relative to the detected overspeed.

7. The method for controlling the yaw of a wind turbine system according to claim 1 or 2, wherein, If an output signal for reducing the actual motor speed reference (451) is applied to one yaw drive actuator (301), the remaining yaw drive actuators (301) receive an output signal for increasing the actual motor speed reference (451).

8. The method for controlling the yaw of a wind turbine system according to claim 1 or 2, wherein, Each yaw drive actuator (301) includes a motor (302), and the average motor speed reference (402) is calculated as the average of the actual motor speed reference (451) of all motors in the plurality of yaw drive actuators or motors (302) in a subgroup of the plurality of yaw drive actuators.

9. The method for controlling the yaw of a wind turbine system according to claim 8, wherein, In the calculation of the average motor speed reference (402), the motors (302) in the subgroup of the plurality of yaw drive actuators do not include motors (302) whose actual motor speed reference (451) is higher than the high speed threshold speed and / or motors (302) whose actual motor speed reference (451) is lower than the low speed threshold speed.

10. The method for controlling the yaw of a wind turbine system according to claim 1 or 2, wherein, The wind turbine system includes multiple nacelles (104), and the yaw system (300) is arranged to rotate one or more of the multiple nacelles (104).

11. A control system for controlling the yaw of a wind turbine system, wherein, The control system is configured to perform the steps of the method according to any one of claims 1-10.

12. A wind turbine system comprising a control system for controlling the yaw of the wind turbine system as described in claim 11.

13. A computer program product comprising software code adapted to control a wind turbine system when executed on a data processing system, said computer program product being adapted to perform the method of any one of claims 1-10.

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