Yaw management

Abstract

The present invention relates to a method for monitoring a yaw fault event of a yaw system of a wind turbine. The yaw system comprises one or more actuators for driving the yaw system and a holding system for resisting a yaw rotation. The yaw system is arranged to provide a yaw rotation in response to a yaw control signal. According to the method, a monitored yaw angle is compared with the yaw control signal and based on the comparison, a correlation between a change in the monitored yaw angle and the yaw control signal is determined. A yaw fault event is determined based on the determined correlation.

Description

Technical Field

[0001] The present invention relates to yaw systems in wind turbines and, in particular, to monitoring the health of such yaw systems. Background Art

[0002] The function of a yaw system in a wind turbine is to yaw the rotor of the wind turbine into the wind and to keep it oriented into the wind.

[0003] The yaw system has a holding system such as a yaw friction bearing, a brake system or other holding mechanism responsible for holding the rotor of the wind turbine upwind during periods when the yaw angle is not adjusted.

[0004] A situation may arise where the holding torque of the holding system is unable to hold the nacelle and the wind turbine nacelle is forced out of the desired yaw orientation (e.g. due to gusts of wind). In this case, the yaw system will be activated to bring the nacelle and the rotor back into the upwind orientation. During the period when the yaw angle deviates from the correct yaw angle, there is a loss of energy production and a risk of mechanical overloading of the load-bearing components of the wind turbine.

[0005] Therefore, there is a need to reduce the occurrence of situations where a wind turbine nacelle is forced out of a desired yaw orientation.Therefore, there is a need for an improved yaw system or an improved yaw system management to increase the reliability of the yaw system's holding system. Summary of the invention

[0006] The object of the invention is to improve the reliability of a wind turbine, in particular of a yaw system and a holding system of the yaw system, to reduce the occurrence of situations where the wind turbine nacelle is forced out of its orientation. Another object of the invention is to increase energy production and reduce transient and fatigue loads.

[0007] In a first aspect of the invention, there is provided a method for monitoring a yaw fault event of a yaw system of a wind turbine, the wind turbine comprising a tower, a nacelle and a yaw system, the yaw system being arranged to provide a yaw rotation of the nacelle in response to a yaw control signal, wherein the yaw system comprises one or more actuators for driving the yaw system and a holding system for resisting the yaw rotation, the method comprising:

[0008] - monitoring the yaw angle of the yaw system,

[0009] - comparing the yaw angle with the yaw control signal,

[0010] - based on the comparison, determining a correlation between the monitored change in yaw angle and the yaw control signal,

[0011] - Logging of yaw fault events based on the correlation between the determined yaw angle and the yaw control signal.

[0012] Advantageously, by recording yaw fault events, the health of the yaw system, in particular the holding system, can be monitored so that problems with the holding system can be detected at an early stage so that maintenance and repair of the yaw system can be planned.

[0013] When using fixed maintenance intervals, the yaw system may be maintained either too early (ie unnecessarily) or too late (meaning unnecessary loss of energy production and / or mechanical load).

[0014] By monitoring the occurrence of yaw faults, maintenance can be performed immediately, or can be planned to be performed later together with other maintenance operations to reduce maintenance costs. Thus, maintenance of the yaw system can be planned, for example, depending on the number of accumulated yaw faults.

[0015] In this way, situations of unnecessary mechanical loads and unnecessary energy production losses can be reduced by appropriately handling yaw faults.

[0016] The purpose of determining a correlation between a monitored change in the yaw angle and the yaw control signal is generally to determine whether the change in the yaw angle is expected (i.e. generated in response to the control signal) or unexpected (i.e. not generated in response to the control signal or not generated solely in response to the control signal). Thus, the correlation may involve determining a relationship between the yaw angle and the yaw control signal, or conversely determining that there is no relationship or a strong relationship.

[0017] The yaw control signal may be any reference signal, error signal, controller output signal or other control related signal (such as a yaw enable / disable signal required to enable / disable a controlled yaw adjustment).

[0018] According to one embodiment, comparing the yaw angle to the yaw control signal comprises determining whether a change in the yaw control signal has occurred within a time window preceding a moment in time when a change in the yaw angle is monitored.

[0019] Advantageously, by checking if the control signal is absent within a given period of time (i.e. within a time window), this means that a change in the yaw angle cannot be due to a control signal but indicates an undesired change in the yaw angle. In this case, a yaw fault may be set. The length of the time window may be set, for example, depending on the frequency of checking if a change in the yaw angle is required, e.g. such that the length of the time window is less than the time between checks of the yaw angle relative to the wind direction.

[0020] According to one embodiment, comparing the yaw angle to the yaw control signal comprises determining whether a magnitude of a monitored change in the yaw angle is due to a corresponding change in the yaw control signal.

[0021] For example, the resulting change in yaw angle may be too large or too small compared to the requested change (ie, the yaw angle reference), ie, where the yaw control signal requests a change, but the change is inconsistent with the control signal.

[0022] For example, the requested yaw change may be 1 degree, but the resulting yaw angle may have increased to, for example, 1.5 degrees due to the effect of the wind. This will require additional control effort to bring the yaw angle back to the desired 1 degree.

[0023] Therefore, even if there is a control signal in the time window before the moment when the change in yaw angle is monitored, if the resulting change in yaw angle does not match the change in the control signal, this may indicate the presence of a yaw fault event.

[0024] According to one embodiment, determining the correlation includes determining whether the change in the yaw angle is not generated in response to the yaw control signal. Thus, if the change in the yaw angle (whether a portion of the change or the entire change) is not correlated with or due to the control signal, this may indicate the presence of a yaw fault. That is, a portion of the change in the yaw angle may be a response to the control signal, but the remaining change may not be an expected change corresponding to the control signal.

[0025] According to one embodiment, the method further comprises:

[0026] - obtaining the wind conditions valid for the moment when the change in yaw angle is detected, and

[0027] - Logging of yaw fault events based on comparison of yaw angle with yaw control signal and based on wind conditions.

[0028] The wind condition may be wind speed, wind direction, wind turbulence or other wind condition valid for the location of the wind turbine. Advantageously, by logging a yaw fault event in dependence on a wind condition such as wind speed, a yaw fault event may be ignored even if there is no correlation between the yaw angle and the yaw control signal. This may be relevant, for example, in case of gusts at high wind speeds, where the holding system is configured to enable uncontrolled yaw rotations to avoid large loads on the wind turbine.

[0029] According to one embodiment, the recording of a yaw fault event is based on a comparison of a wind speed value of the wind condition with a wind speed threshold value. For example, if the wind speed is above the wind speed threshold value when a yaw rotation is detected without correlation with the control signal, no yaw fault is recorded.

[0030] A second aspect of the invention relates to a control system for monitoring a yaw fault event of a yaw system of a wind turbine (100), the wind turbine comprising a tower, a nacelle and a yaw system, the yaw system being arranged to provide a yaw rotation of the nacelle based on a yaw control signal, wherein the yaw system comprises one or more actuators for driving the yaw system and a holding system for resisting the yaw rotation, wherein the control system is arranged to perform the steps of the method according to the first aspect.

[0031] A third aspect of the invention relates to a monitoring system for monitoring a yaw fault event in a yaw system of a wind turbine, the wind turbine comprising a tower, a nacelle and a yaw system, the yaw system being arranged to provide a yaw rotation of the nacelle based on a yaw control signal, wherein the yaw system comprises one or more actuators for driving the yaw system and a holding system for resisting the yaw rotation, wherein the system comprises:

[0032] - a data communication unit arranged to receive data such as the yaw angle θm and the yaw control signal, and wherein the monitoring system is arranged to perform the steps of the method according to the first aspect.

[0033] The data communication unit may receive data from a wind turbine, a central data processing unit of a wind power plant, a weather data processing unit or other data source units. For example, the data communication unit may receive data in the form of or related to yaw angle values ​​and / or yaw control signal values.

[0034] A monitoring system (which may be an external monitoring system) may comprise the control system of the second aspect and the data communications unit.

[0035] A fourth aspect of the invention relates to a wind turbine comprising a tower, a nacelle and a yaw system, the yaw system being arranged to provide a yaw rotation of the nacelle based on a yaw control signal, wherein the yaw system comprises one or more actuators for driving the yaw system and a holding system for resisting the yaw rotation, wherein the wind turbine is arranged to perform the steps of the method according to the first aspect.

[0036] A fifth aspect of the present invention relates to a computer program product, the computer program product comprising instructions which, when the program is executed by a computer, cause the computer to perform the steps of the method of the first aspect.

[0037] In general, the various aspects and embodiments of the present invention may be combined and coupled in any possible manner within the scope of the present invention. These and other aspects, features and / or advantages of the present invention will become apparent from and be elucidated with reference to the embodiments described hereinafter. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0039] Figure 1A shows a wind turbine,

[0040] Figure 1B A cross-section of the yaw system is shown.

[0041] Figure 2 shows a wind turbine configured as a multi-rotor wind turbine,

[0042] Figure 3A The control system used to control the yaw system is shown.

[0043] Figure 3B shows an example of controlling the yaw angle in response to changes in the yaw reference,

[0044] Figure 4A A control system for monitoring a wind turbine for a yaw fault event based on a yaw angle is shown, and

[0045] Figure 4B An external monitoring system for monitoring a wind turbine for yaw fault events is shown. DETAILED DESCRIPTION

[0046] Figure 1A A wind turbine 100 (WTG) is shown comprising a tower 101 and a rotor 102 having at least one rotor blade 103, such as three blades. The blades 103 are connected to a hub 105 arranged to rotate with the blades. The rotor is connected to a nacelle 104, which is mounted on the top of the tower 101 and is suitable for driving a generator located inside the nacelle via a transmission system. The rotor 102 can be rotated by the action of the wind. The rotational energy of the rotor blades 103 caused by the wind is transmitted to the generator via a shaft. Therefore, the wind turbine 100 is able to convert the kinetic energy of the wind into mechanical energy by means of the rotor blades, and then convert it into electrical energy by means of the generator. The generator is connected to a power converter, which includes a generator side converter and a grid side converter. The generator side converter converts the generator AC power into DC power, and the grid side converter converts the DC power into AC power to be injected into the utility grid via the output inductor of the wind turbine 100.

[0047] The nacelle 104 is guided by the yaw system 130 (only Figure 1A 101 ), the yaw system 130 being mounted on top of the tower 101 , the yaw system 130 being arranged to enable the nacelle to rotate around the longitudinal axis of the tower 101 .

[0048] Figure 1BMainly illustrated is a cross-sectional view of a yaw system 130 with a yaw holding system 131 and a yaw actuator 132 .

[0049] The purpose of the yaw system is to rotate the nacelle 104 according to the wind direction so that the rotor 102 is oriented against the wind, that is, the rotor plane is vertical or substantially vertical to the wind direction. The rotation of the yaw system is achieved by using one or more drive actuators 132 included in the yaw system 130 for driving the yaw system. One or more drive actuators 132 (referred to as actuators 132) may include electric motors, hydraulic actuators or others.

[0050] Uneven wind distribution on the blades 103 in the rotor plane inevitably results in an uneven load distribution on the rotor plane, which results in the formation of a yaw moment acting in a direction around the tower 101. The yaw system is configured to resist the yaw rotation due to the uneven wind distribution, at least for yaw moments below a given threshold.

[0051] Therefore, the yaw system 130 is configured with a holding system 131, which is arranged to provide a holding moment to prevent yaw rotation or to prevent yaw rotation for yaw moments below a yaw moment threshold. Very high yaw moments can damage components of the wind turbine, so the yaw system 130 can be configured to provide yaw slip for yaw moments above a given maximum yaw moment threshold.

[0052] In this context, a moment applied to, for example, a wind turbine or a yaw system is understood to be equivalent to a torque. Similarly, a holding moment of the holding system 131 is understood to be equivalent to a holding torque.

[0053] The holding system 131 may be a passive or active friction brake or holding mechanism that may utilize frictional contact between contacting components 131a, 131b of the yaw system 130 to provide desired holding characteristics. For example, a contact force 133 established between the brake components of the yaw system, where relative motion or rotation is generated between the components during a yaw rotation, generates the holding torque required to resist the yaw rotation. The contact force may be established by a system arranged to press the brake components together, such as a passive system in which the contact force is generated, for example, by a compression spring, or an active system in which the contact force is generated by an actuator such as a hydraulic linear actuator that presses the components together when required. Specific examples of brakes of the holding system 131 include hydraulic yaw brakes, yaw friction bearings with passive or active braking friction systems, and yaw drives with brake and clutch systems, or combinations thereof. The holding system 131 does not have to be a separate system (i.e., a system separate from the drive system including one or more actuators 132 and / or a yaw gear). That is, the holding system 131 may be comprised by such a drive system, or a separate holding system (eg a friction brake) may be supplemented by another holding system comprised by the drive system.The yaw system need not be configured with a yaw friction bearing, but may be configured with a roller bearing.

[0054] In order to keep the contact force and holding torque within desired limits, the system used to provide the contact force may require maintenance periodically or when the holding torque exceeds limits.

[0055] The holding system may also be configured as an electric brake, where the torque generated by the motor is controlled via the power supplied to the motor to generate the desired holding torque.

[0056] exist Figure 1B In the embodiment, the contact parts 131a, 131b of the yaw system 130 include flanges connected to the tower 101 and the nacelle 104, respectively, and are arranged with friction surfaces arranged adjacent to each other. The holding system can also be configured similarly to a caliper brake with a hydraulically actuated brake piston.

[0057] Obviously, the retention system can be configured as a combination of the above examples or other retention systems.

[0058] Figure 2An alternative wind turbine 100 configured as a multi-rotor wind turbine is shown. The multi-rotor wind turbine includes a plurality of nacelles 104. As shown in the upper figure, the nacelles 104 can be supported via a tower 101 and a support arm extending outward from the tower 101, so that the nacelles are away from the tower and placed on the opposite side of the tower. Alternatively, as shown in the lower figure, the nacelles 104 can be supported by an inclined tower 101 extending from a base 230 (e.g., the ground or a floating base) so that two or more nacelles 104 are sufficiently separated from each other at a given height. The multi-rotor wind turbine can be configured with a yaw system 130 similar to the wind turbine 100. For example, the yaw system 130 can be arranged for each of the nacelles. Alternatively or additionally, the yaw system 130 can be arranged as a common yaw mechanism arranged between the tower and the support arm or between the base 230 and the inclined tower 101. Embodiments of the present invention can be used with a multi-rotor wind turbine or a single-rotor wind turbine.

[0059] Figure 3A A possible control system 300 for controlling the yaw system 130 is shown, which is illustrated for the purpose of explaining an embodiment of the present invention. Other differently configured control systems providing the same or similar functionality are also possible for the purpose of controlling the yaw angle of the yaw system 130. A desired yaw angle θref and a monitored yaw angle θm are provided as inputs to the control system 300. An error e=θref-θm is determined and used to determine a yaw actuator signal y. The yaw actuator signal y is provided to the yaw system 130, which uses the yaw actuator signal y to control the yaw actuator 132. In the case where the yaw system uses active or maneuvering brakes, the control system may also determine a yaw braking signal for the brake (not shown). The yaw actuator signal y is determined so that the controlled actuation of the yaw system minimizes the error e. Control of the yaw actuator based on the yaw actuator signal y may be performed continuously or periodically. When the actuator is not controlled via the yaw actuator signal y, for example when the error e is below a certain threshold, the yaw angle is maintained by means of the holding system 131 .

[0060] Figure 3B An example of controlling the yaw angle θm in response to a change in the yaw reference θref, or equivalently in response to a change in the error e, is shown. Figure 3B Also shown is an example of recording a yaw fault event based on a comparison of the determined yaw angle θm with a yaw control signal 351 (such as a yaw actuator signal y or a yaw error signal e). All signals are shown as a function of time, not to scale, and are displayed along the same ordinate axis despite their different units.

[0061] At t0, the reference signal θref increases to a new value. The change in the reference signal θref may be due to a change in wind direction, which requires a corresponding change in the yaw angle. The error signal e=θref-θm increases immediately and causes a change in the yaw actuator signal y, which causes an increase in the monitored yaw angle θm. At t1, the monitored yaw angle θm has reached a level that matches the yaw reference θref, and the error signal e has returned to a value of zero.

[0062] Depending on the configuration of the yaw system 130, the yaw actuator signal y may be set to zero, may be unchanged, or may be set to another inactive state 361, as shown by the dashed line. The inactive state 361 of the actuator signal y means that adjustment of the yaw angle by using the actuator 132 is effectively disabled. During the period from t1 to t2 or other periods during which the actuator is disabled, the holding system 131 may be responsible for maintaining the yaw angle unchanged.

[0063] At t2, a new change in the reference signal θref is generated, which results in a non-zero value for the error signal e. The actuator signal y changes (e.g. from a previous value before t2 or from another value) to result in a change in the yaw angle θm. At t3, the desired value of the yaw angle θm has been reached.

[0064] At t4, the yaw reference θref has not changed, but the yaw angle has changed anyway as observed by the monitored yaw angle θm. This may be due to the gusts generating a moment that exceeds the holding moment of the holding system 131. The error signal e shows the change due to the deviation between the yaw angle θm and the reference θref.

[0065] At t5, the control signal is determined based on the error signal e, and thus changes to bring the yaw signal θm back to the yaw reference θref. If not already enabled, the actuator 132 will be enabled, for example, via an enable signal, the value of the actuator signal y, or otherwise. At t6, the rotor 102 has rotated back to the desired yaw angle θm.

[0066] A change in the yaw angle θm that occurs without a change in the yaw reference θref is generally undesirable because there is a loss of energy production and a risk of mechanical overloading of load-bearing components of the wind turbine 100, such as the yaw gear and actuator 132, during the time that the nacelle 104 is forced from its upwind position to the time that the nacelle returns to the upwind direction. Such an unintended change in the yaw angle θm is referred to as a yaw fault event.

[0067] In order to avoid or limit future occurrences of such undesired yaw misalignment, it is necessary to maintain the yaw system 130 including its retaining system 131. Embodiments of the present invention disclose a yaw management method capable of detecting yaw fault events so that maintenance can be planned and related spare parts ordered before maintenance.

[0068] In the above example, the actuator signal y is determined in response to the reference signal θref or the error signal e or in response to a change in the reference signal θref or the error signal e. Thus, a change in the desired, i.e., planned, yaw angle θm occurs in response to a change in the state (such as a change in value) of the reference signal θref, the error signal e, the actuator signal y, or other yaw control signals 350 of the yaw system 130 or the control system 300. Such other yaw control signals 350 may be any input signal (such as the reference θref) of the control system 300 or any signal generated in response to the input signal.

[0069] According to one embodiment, a method for monitoring a yaw fault event is to monitor the yaw angle θm of the yaw system. The yaw angle θm may be monitored by monitoring a sensor output related to the yaw angle. For example, an encoder or other position sensor may be arranged with a rotatable component of the yaw system 130 to measure the yaw angle θm.

[0070] The monitored yaw angle θm is compared to the yaw control signal 350 to determine whether the change in yaw angle is a response to the yaw control signal 350 .

[0071] In order to avoid reacting to small changes in the yaw angle θm, only changes in θm above a threshold may be considered.

[0072] Thus, if a change in the yaw angle θm is detected and the yaw control signal 350 has not changed, the change in yaw angle is unexpected and indicates a yaw fault event.

[0073] It is also possible that the yaw angle θm is detected, but the magnitude of the change in the yaw angle does not match the expected change in the yaw angle θm, i.e., the change in the yaw angle θm does not correspond to the yaw control signal 350. For example, the change in the yaw angle θm may be less than or greater than the expected change in the yaw angle θm. Such a monitored change in the yaw angle θm that deviates from the expected change in the yaw angle may similarly indicate a yaw fault event.

[0074] Therefore, the monitored yaw angle θm is compared to the yaw control signal 350 to determine the correlation between the changes in the monitored yaw angle θm and the yaw control signal 350 .

[0075] The correlation may include determining whether the change in yaw angle θm is not generated in response to the yaw control signal 350 and / or the magnitude of the change in yaw angle θm does not correspond to the expected magnitude of the change in yaw angle θm, i.e., the yaw angle that should be generated by the yaw control signal 350, such as the reference θref.

[0076] For example, Figure 3B As shown, the unexpected change in yaw angle θm at t4 is not generated in response to the yaw control signal 350 because there is no change in the yaw control signal 350 within the time window ΔT prior to the time t4 at which the change in yaw angle is monitored.

[0077] Figure 3B The yaw fault that starts at t4 in Figure 1 results in the formation of the error signal, but the change in the error signal starts after the first change in the yaw angle θm at t4. Therefore, in the time window ΔT before t4 indicating the presence of a yaw fault event, there is no change in any of the actuator signal y, the error signal e, or the yaw reference θref.

[0078] The length of the time window ΔT may be a few seconds, possibly a minute or so. The yaw system 130 may be configured such that any change in the yaw reference θref or monitoring of the yaw angle θm occurs within a given control period. Therefore, the time window ΔT may be selected to be smaller than the control period.

[0079] Depending on the correlation between the determined yaw angle θm and the yaw control signal 350 , a yaw fault event may be recorded.

[0080] Figure 4A A control system 400 is shown for monitoring a wind turbine 100 for a yaw fault event based on a yaw angle θm, a yaw control signal 350 and optionally a wind condition signal 401 provided to the control system 400 via an input. The yaw fault event may be recorded by the control system 400 and available via an output 402. The control system 400 is configured to perform the method steps of various embodiments described herein, for example by means of a digital processor comprised by the control system and a computer program. Thus, based on the input, the control system 400 may be configured to compare the yaw angle θm with the yaw control signal 350, thereby determining a correlation between a monitored change in the yaw angle θm and the yaw control signal 350 based on the comparison, and determining a yaw fault event based on the determined correlation.

[0081] Control system 400 may be included in wind turbine 100 or may be a system external to the wind turbine.

[0082] Figure 4BSuch an external control system 400 is shown in the form of a monitoring system 450 for monitoring a wind turbine 100 for a yaw fault event. The monitoring system 450 receives data necessary for determining whether a yaw fault event exists based on the received data, such as the yaw angle θm, the yaw control signal 350, and optionally the wind condition signal 401. The monitoring system 450 may include a data communication unit 451, which is arranged to receive data such as the above data, for example via a wired or wireless connection. The data may be provided from one or more wind turbines 100. For example, the yaw angle θm and the yaw control signal 350 may be provided from one or more wind turbines, while the wind condition data 401 may be provided from another system such as a wind monitoring system. Similarly, the yaw reference θref may be provided from another system other than the wind turbine. The monitoring system 450 is arranged to perform the same method steps as the control system, and may therefore include the control system 400 or a digital processor arranged to perform the method steps of the embodiments described herein.

[0083] As described above, for high yaw moments above a given maximum yaw moment threshold, yaw system 130 may be configured to provide yaw slip to prevent potentially damaging yaw moments.Such high yaw moments may be generated under special wind conditions (eg, at high wind speeds or turbulent winds).

[0084] In order to avoid recording a fault event in case a yaw slip is expected, the control system 400 may be arranged to obtain a wind condition 401 via an input. The wind condition 401 may be provided regularly so that a wind condition valid for the moment when a change in the yaw angle is monitored or valid for determining a potential yaw fault event is available. The recording of a yaw fault event may then be determined based on a comparison of the yaw angle θm with the yaw control signal 350 and based on the wind condition 401. For example, the control system 400 may be configured to record a yaw fault event based on a comparison of a wind speed value of the wind condition 401 with a wind speed threshold, so that a potential yaw fault event is not recorded as a yaw fault event even if the actual wind speed value is higher than the wind speed threshold.

[0085] Although the present invention has been described in conjunction with specific embodiments, it should not be interpreted as being limited in any way to the examples presented. The scope of the present invention should be interpreted in accordance with the appended claims. In the context of the claims, the terms "comprise" or "comprising" do not exclude other possible elements or steps. Furthermore, references such as "one" or "an" should not be interpreted as excluding a plurality. The use of reference numerals in the claims with respect to elements shown in the drawings should also not be interpreted as limiting the scope of the present invention. Furthermore, individual features mentioned in different claims may be advantageously combined, and the mention of these features in different claims does not exclude that a combination of these features is impossible and advantageous.

Claims

1. A method for monitoring a yaw fault event of a yaw system (130) of a wind turbine (100), the wind turbine comprising a tower, a nacelle and a yaw system (130), the yaw system (130) being arranged to provide a yaw rotation of the nacelle in response to a yaw control signal (350), wherein: The yaw system comprises one or more actuators (132) for driving the yaw system and a holding system (131) for resisting yaw rotation, the method comprising: - monitoring the yaw angle (θm) of the yaw system, - comparing the yaw angle with the yaw control signal (350), wherein comparing the yaw angle with the yaw control signal comprises: determining whether a change in the yaw control signal (350) occurred within a time window (ΔT) preceding the moment when the change in the yaw angle was monitored; and determining whether the magnitude of the monitored change in the yaw angle is due to a corresponding change in the yaw control signal, - based on the comparison, determining a correlation between the monitored change in yaw angle and the yaw control signal (350), and - recording a yaw fault event based on a correlation between the determined yaw angle and the yaw control signal (350).

2. The method according to claim 1, wherein: Determining the correlation includes determining whether the change in the yaw angle is not generated in response to the yaw control signal.

3. The method according to claim 1 or 2, further comprising: - obtaining the wind conditions valid for the moment when the change in yaw angle is detected (401), and - registering a yaw fault event based on a comparison of the yaw angle with the yaw control signal and based on the wind condition.

4. The method according to claim 3, wherein: The recording of the yaw fault event is based on a comparison of a wind speed value of the wind condition with a wind speed threshold.

5. A control system (400) for monitoring a yaw fault event of a yaw system of a wind turbine (100), the wind turbine comprising a tower, a nacelle and a yaw system, the yaw system being arranged to provide a yaw rotation of the nacelle based on a yaw control signal, wherein: The yaw system comprises one or more actuators for driving the yaw system and a holding system for resisting yaw rotation, wherein the control system is arranged to perform the steps of the method according to claim 1 .

6. A monitoring system (450) for monitoring a yaw fault event of a yaw system of a wind turbine (100), the wind turbine comprising a tower, a nacelle and a yaw system, the yaw system being arranged to provide a yaw rotation of the nacelle based on a yaw control signal, wherein: The yaw system comprises one or more actuators for driving the yaw system and a holding system for resisting yaw rotation, wherein the system comprises: - a data communication unit (451) arranged to receive data such as the yaw angle θm and the yaw control signal (350), and wherein the monitoring system is arranged to perform the steps of the method according to claim 1.

7. A wind turbine (100) comprising a tower, a nacelle and a yaw system, the yaw system being arranged to provide a yaw rotation of the nacelle based on a yaw control signal, wherein: The yaw system comprises one or more actuators for driving the yaw system and a holding system for resisting yaw rotation, wherein the wind turbine is arranged to perform the steps of the method according to claim 1 .

8. A computer program product comprising instructions which, when the program is executed by a computer, cause the computer to perform the steps of the method of claim 1.

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