Method of handling gearbox vibrations in wind turbine

Abstract

A method of controlling operation of a generator (5) of a wind turbine is disclosed. A measured value of the rotational speed of the generator (5), a measured value of vibrations originating from the gear tooth engagement of the gearbox (3) of the wind turbine at the rotational speed of the generator (5), and at least one amplitude of harmonics in the gearbox vibrations are determined. The initial phase angle and the initial amplitude are selected based on the rotational speed of the generator (5), an initial characteristic of the wind turbine and at least one amplitude of a harmonic in the gearbox vibration. An optimization process is performed, the optimization process comprising adjusting the initial phase angle and the initial amplitude to obtain a minimum value of an amplitude of a resultant vibration of a vibration originating from the gearbox (3) and a vibration originating from the generator (5) corresponding to a harmonic in the gearbox vibration, thereby obtaining an adjusted phase angle and an adjusted amplitude. A torque modulation signal specifying the adjusted phase angle and the adjusted amplitude is generated for the generator (5) and injected into the generator (5). Information about the residual vibrations under the minimized resultant vibrations is derived.

Description

Technical Field

[0001] The invention relates to a method of controlling the operation of a generator of a wind turbine in such a way that noise originating from meshing of gear teeth of a gearbox of the wind turbine is reduced. Background Art

[0002] When operating a wind turbine, various movable parts of the wind turbine generate structure-borne vibrations and associated airborne noise, which may be amplified by various other structures of the wind turbine, such as the tower, wind turbine blades, etc. This is sometimes referred to as pitch. This may result in airborne noise levels near the wind turbine that annoy neighbors or interfere with animal life, and the noise may even approach or exceed permitted noise limits. Therefore, it is desirable to reduce this noise.

[0003] One source of wind turbine noise is vibrations from the operation of the generator. Another source is vibrations from the drive train (e.g., from the meshing of gear teeth in a gearbox). The vibrations from the generator and the vibrations from the drive train combine to constitute the vibrations of the power train of the wind turbine, and thus the noise of the entire wind turbine.

[0004] EP 2 485 388 B1 discloses a method for controlling the operation of an electromechanical transducer, such as a generator of a wind turbine. The method comprises determining a harmonic control signal indicative of a harmonic operating behavior of the electromechanical transducer. The determination of the harmonic control signal comprises observing at least one value of an operating parameter of the electromechanical transducer, and deriving the harmonic control signal from a database based on the observed value of the operating parameter of the electromechanical transducer. A modified drive signal is generated based on the determined harmonic control signal, and the generated modified drive signal is provided to an electromagnetic coil of a stator of the electromechanical transducer. Summary of the invention

[0005] It is an object of embodiments of the present invention to provide a method of controlling the operation of a generator of a wind turbine in such a way that noise originating from the operation of a gearbox of the wind turbine is reduced.

[0006] It is a further object of embodiments of the present invention to provide a method of controlling the operation of a generator of a wind turbine in such a way that noise originating from gear teeth of a gearbox of the wind turbine is reduced.

[0007] It is a further object of embodiments of the present invention to provide a method of controlling the operation of a generator of a wind turbine, which method allows easy monitoring of the condition of the wind turbine.

[0008] The present invention provides a method for controlling the operation of a generator of a wind turbine, the method comprising the following steps:

[0009] - obtaining a measurement of the rotational speed of the generator,

[0010] - obtaining, at said rotational speed of said generator, measured values ​​of vibrations originating from a gear tooth meshing of a gearbox of said wind turbine,

[0011] - determining at least one amplitude of a harmonic in the gearbox vibrations,

[0012] - generating a torque modulation signal for the generator by:

[0013] - selecting an initial phase angle and an initial amplitude based on the rotational speed of the generator, initial characteristics of the wind turbine and the at least one amplitude of a harmonic in the gearbox vibration,

[0014] - performing an optimization process, the optimization process comprising adjusting the initial phase angle and the initial amplitude to obtain a minimum value of the amplitude of a composite vibration of the vibration originating from the gearbox and the vibration originating from the generator, the composite vibration corresponding to the harmonics in the gearbox vibration, thereby obtaining an adjusted phase angle and an adjusted amplitude, and

[0015] - generating a torque modulation signal for the generator, the torque modulation signal specifying the adjusted phase angle and the adjusted amplitude,

[0016] - injecting the torque modulation signal into the generator so that the operation of the generator results in minimizing the resultant vibration of the gearbox vibration and the generator vibration, the resultant vibration corresponding to the harmonics in the gearbox vibration, and

[0017] - Derive information about the residual vibrations at the minimized combined vibrations.

[0018] Hence, the present invention provides a method of controlling the operation of a generator of a wind turbine.In the present context, the term "generator" is understood to mean an electromechanical transducer that converts the mechanical motion of the wind turbine into electrical energy.

[0019] In the method according to the first aspect of the invention, a measurement of the rotational speed of the generator is first obtained. The rotational speed may be the rotational speed of the low speed shaft or the high speed shaft. In any case, the obtained rotational speed provides information about how the rotating parts of the drive train rotate (including the rotation of the meshing gears of the gearbox). The rotational speed may be measured, for example, or may be provided by a controller of the generator.

[0020] Next, measurements of vibrations originating from the gear tooth meshing of a gearbox of the wind turbine are obtained at the rotational speed of the generator. The vibrations may be measured directly at the gearbox, for example by means of a suitable vibration sensor (such as an accelerometer) mounted on the gearbox. As an alternative, the vibrations may be measured in an indirect manner, for example by measuring vibrations of amplified components of the wind turbine (such as the tower and / or wind turbine blades) caused by the gearbox vibrations, and / or by measuring the noise level at a certain distance from the wind turbine.

[0021] Next, at least one amplitude of a harmonic in the gearbox vibration is determined.In this context, the term "harmonic" should be interpreted as referring to vibrations at a fundamental frequency (such as an eigenfrequency or a resonant frequency) of the gearbox system or a positive integer multiple of such a fundamental frequency.

[0022] The harmonics of a gearbox are closely related to the design of the gearbox, in particular to the design of the individual gear stages and the number of gear teeth on the meshing gears, and depend on the rotational speed of the gear system. For example, the vibrations originating from the gear tooth meshing define a fundamental frequency that is a non-integer multiple of the rotational speed of the input or output shaft of the gearbox, and according to standard practice, this non-integer ratio depends on the internal components of the gearbox.

[0023] The amplitude of the harmonics in the gearbox vibrations represents the noise level originating from the gear tooth meshing of the gearbox.

[0024] Next, a torque modulation signal is generated for the generator. In this context, the term "torque modulation signal" should be interpreted as referring to a control signal that defines an AC torque sinusoid that can be added to the DC power production torque of the generator. Therefore, the torque modulation signal applied to the generator modulates the torque output of the generator.

[0025] The torque modulation signal is generated in the following manner. An initial phase angle and an initial amplitude are selected based on the rotational speed of the generator, initial characteristics of the wind turbine, and at least one amplitude of a harmonic in the gearbox vibration. The initial characteristics of the wind turbine may include, for example, design characteristics of the gearbox, such as a gear ratio, the number of teeth on the gears, etc.

[0026] Thus, the initial phase angle and the initial amplitude are selected in a manner that takes into account the rotational speed of the generator and the characteristics of the wind turbine related to the gearbox design. As described above, these two types of information can be used to derive information related to the gear tooth meshing, such as the vibration frequency originating from the gear tooth meshing. Furthermore, when selecting the initial phase angle and the initial amplitude, at least one amplitude of a harmonic in the gearbox vibration is taken into account. Thus, the initial phase angle and the initial amplitude are selected in a manner that is expected to match, at least to some extent, the vibration originating from the gear tooth meshing of the gearbox.

[0027] Next, an optimization process is performed. The optimization process includes adjusting the initial phase angle and the initial amplitude to obtain the minimum value of the amplitude of the composite vibration of the vibration originating from the gearbox and the vibration originating from the generator, the composite vibration corresponding to the harmonics in the gearbox vibration. In this context, the term "composite vibration" should be interpreted as referring to the total vibration of the power train, i.e. the combination of the vibration originating from the gearbox and the generator at the frequency corresponding to the harmonics in the gearbox vibration. Therefore, the composite vibration can be regarded as the superposition of the vibration originating from the gearbox and the vibration originating from the generator at the frequency corresponding to the harmonics in the gearbox vibration.

[0028] Thus, the result of the optimization process is to obtain an adjusted phase angle and an adjusted amplitude, which represent the minimum value of the amplitude of the composite vibration, and thus the minimum value of the total vibration of the powertrain. Furthermore, the amplitude of the composite vibration represents the noise level of the noise originating from the entire powertrain. Therefore, minimizing the amplitude of the composite vibration also minimizes the noise generated by the powertrain at the noise source. Therefore, in the optimization process, the best phase angle and amplitude that lead to the minimum noise are "sought".

[0029] A torque modulation signal is then generated for the generator, which specifies the adjusted phase angle and the adjusted amplitude. The torque modulation signal therefore also represents the minimum value of the amplitude of the resultant vibration. In other words, the torque modulation signal is "designed" in such a way as to match the vibrations originating from the gear tooth meshing of the gearbox, i.e. when the torque modulation signal is injected into the generator, the generator is caused to operate in such a way that the vibrations of the generator cancel the vibrations originating from the gear tooth meshing of the gearbox to the greatest possible extent.

[0030] For example, the torque modulation signal may define a frequency corresponding to harmonics in the gearbox vibrations, an amplitude corresponding to the amplitude of the harmonics in the gearbox vibrations, and a phase angle that ensures a match between the phase angle of the gearbox and the phase angle of the generator.

[0031] Next, the torque modulation signal generated in the above-described manner is injected into the generator. Thus, the generator operates based on the torque modulation signal, i.e., the torque of the generator is modulated in a manner specified by the adjusted phase angle and the adjusted amplitude. Thus, the generator operates in such a manner that the resultant vibrations of the vibrations of the gearbox and the vibrations of the generator (which correspond to the harmonics in the gearbox) are minimized because the vibrations originating from the generator cancel the vibrations originating from the meshing of the gear teeth of the gearbox to the greatest extent possible.

[0032] The overall noise generated by the wind turbine is thereby reduced.

[0033] Finally, information about the residual vibration under the minimized synthetic vibration is obtained.

[0034] Thus, in addition to optimizing the phase angle and amplitude of the torque modulation signal (i.e. minimizing the amplitude of the resultant vibration), information is derived about the residual vibration (i.e. the portion of the vibration signal that remains when the generator is operated according to the optimized torque modulation signal). This information may be valuable, for example, for evaluating the efficiency of noise reduction measures, benchmarking the wind turbine against other wind turbines and / or against a model or standard "ideal" wind turbine. Furthermore, by monitoring the residual vibration over time, valuable information about the condition or state of the wind turbine, in particular the power train, may be derived.

[0035] Specifically, the combination of residual vibration, optimized phase angle and optimized amplitude provides valuable information about the condition or state of the wind turbine. Therefore, monitoring these parameters over time can provide information about how the system ages, wears, plastic deformations in the drive train and changes in the connection of the gearbox to the hub, tower, etc.

[0036] The step of injecting the torque modulation signal into the generator may comprise injecting the torque modulation signal into an electronic generator controller. According to this embodiment, the torque modulation signal is provided to an electronic generator controller, i.e. a controller that controls the operation of the generator. This modulation signal is simply added to a DC quasi-static signal for the total generator torque command. This torque command signal is then converted to appropriate power switching devices using well-known motor control methods. This is applicable to generator control of induction or synchronous machines, but may also be applicable to motor control.

[0037] The steps of performing the optimization process may include the following steps:

[0038] - generating an initial torque modulation signal of a specified initial phase angle and initial amplitude for the generator,

[0039] - injecting an initial torque modulation signal into the generator and operating the generator based on the initial torque modulation signal while monitoring a composite vibration of the vibration originating from the gearbox and the vibration originating from the generator, the composite vibration corresponding to a harmonic in the gearbox vibration, and

[0040] -Based on the monitored synthetic vibration, the phase angle and amplitude of the torque modulation signal are adjusted to adapt to the actual position of the gearbox and the actual position of the generator until the minimum amplitude of the synthetic vibration is reached, thereby obtaining an adjusted torque modulation signal.

[0041] According to this embodiment, the optimization process, and thereby the "search" for the optimal phase angle and amplitude of the torque modulation signal, is performed by initially generating an initial torque modulation signal for the generator that specifies an initial phase angle and an initial amplitude. The initial torque modulation signal is injected into the generator, and the generator operates based on the initial torque modulation signal. Therefore, the torque of the generator is modulated in a manner specified by the initial phase angle and the initial amplitude, so as to at least to some extent reflect or match the vibrations originating from the gear tooth meshing of the gearbox.

[0042] When the generator is operated based on the initial torque modulation signal, the composite vibration of the vibration originating from the gearbox and the vibration originating from the generator (which corresponds to the harmonics in the gearbox vibration) is monitored.

[0043] Finally, based on the monitored synthetic vibration, the phase angle and the amplitude of the torque modulation signal are adjusted to adapt them to the actual position of the gearbox and to the actual position of the generator. This is achieved by adjusting or regulating the phase angle and the amplitude while monitoring the synthetic vibration and in such a way that a minimum value of the amplitude of the synthetic vibration is achieved. Thus, the optimal phase angle and amplitude of the torque modulation signal are "sought". This results in an adjusted torque modulation signal that specifies an adjusted phase angle and an adjusted amplitude.

[0044] The step of deriving information about the residual vibration at the minimized combined vibration may include generating a residual vibration map that specifies related values ​​of a phase angle of the torque modulation signal, an amplitude of the torque modulation signal, and an amplitude of the combined vibration.

[0045] According to this embodiment, the derived information about the residual vibration is in the form of, or comprises, a residual vibration map. The residual vibration map specifies relevant values ​​of at least the following three entities, namely:

[0046] 1. Phase angle of torque modulation signal

[0047] 2. Amplitude of torque modulation signal

[0048] 3. Amplitude of synthetic vibration

[0049] Thus, the residual vibration diagram may be viewed as a three-dimensional graph or table that specifies in what manner the above three entities are related or dependent upon each other. For example, the residual vibration diagram may specify the amplitude of the resultant vibration measured at a given combination of phase angle and amplitude of the applied torque modulation signal corresponding to a particular operating point (operating point) of the wind turbine. Thus, the residual vibration diagram may be viewed as a response function to a given torque modulation input.

[0050] The combination of the three entities identified above provides more information than any one entity alone. For example, achieving the same resultant vibration amplitude, but requiring, for example, 50% of the torque modulation signal amplitude to achieve this, indicates that a change has occurred in the system mechanical structure.

[0051] Similarly, changes in the phase angle of the torque modulation signal itself indicate changes in certain key positional elements within the overall drive train structure. For example, the stretching of the generator mount is different from the original new manufacturing condition.

[0052] The method may further comprise the step of transmitting information about the residual vibrations at the minimized combined vibrations to an external monitoring system and / or control system.

[0053] According to this embodiment, the derived information about the residual vibrations is not only applied locally on the wind turbine, but is also shared with an external monitoring system and / or control system. In the present context, the term "external system" should be interpreted as referring to a system which does not form part of the wind turbine controlled according to the method according to the invention. Thus, the external monitoring system and / or control system may form part of a central monitoring or control facility, a power plant controller (PPC) for controlling the wind turbines of a wind farm, a controller of another wind turbine, etc.

[0054] By transmitting the derived information about residual vibrations to an external monitoring system and / or control system, this information obtained during operation of the wind turbine in question can be used on a wider scale, for example for optimizing the operation of other wind turbines, coordinated operation of wind turbines within a wind park, central or remote condition monitoring or performance monitoring, for the purposes of wind turbine fleet management, for statistical purposes, etc.

[0055] Furthermore, information about the optimized phase angle, the optimized amplitude, the rotational speed of the generator and / or the DC torque of the generator can be transmitted to an external monitoring system and / or a control system.

[0056] It should be noted that the above communication may be bidirectional, ie a wind turbine may transmit information about the wind turbine to an external monitoring and / or control system and receive similar information about other wind turbines from the external monitoring and / or control system.

[0057] The method may further comprise the step of controlling one or more further wind turbines based on the information about the residual vibrations at the minimized resultant vibrations.

[0058] This can be achieved, for example, by transmitting the information about the residual vibrations directly to a controller of at least one further wind turbine (e.g. a wind turbine arranged nearby, such as a wind turbine arranged within the same wind farm). Thus, the information about the residual vibrations can be directly taken into account when controlling the at least one further wind turbine. For example, the information about the residual vibrations can be used as a baseline and deviations from the baseline can be regarded as a sign of degradation or impending failure of the at least one further wind turbine or one or more components thereof.

[0059] As an alternative, the information about the residual vibrations may be transmitted to a power plant controller (PPC) of the wind farm where the wind turbines are arranged. In this case, the PPC may apply the received information about the residual vibrations to the coordinated control of the wind turbines of the wind farm.

[0060] As another alternative, the information about the residual vibrations may be transmitted to a central facility, such as a monitoring and / or control facility for monitoring and / or controlling a plurality of wind farms (i.e., a wind farm group), a data collection facility (such as a SCADA system), or any other suitable type of central facility. In this case, the information about the residual vibrations may be used for statistical purposes and / or to exploit experience from certain wind turbines when controlling other wind turbines within the group. Furthermore, the information about the residual vibrations received from several wind turbines may be used to derive baseline vibration characteristics or standard vibration characteristics, which may be applied, for example, when new similar wind turbines are put into operation.

[0061] The method may further comprise the step of transmitting the torque modulation signal and / or the adjusted phase angle and / or the adjusted amplitude to a monitoring system and / or a control system.

[0062] According to this embodiment, the torque modulation signal finally injected into the generator and / or at least the phase angle and / or the amplitude of the torque modulation signal are further transmitted to a monitoring system and / or a control system, i.e. to a system for monitoring and / or controlling the wind turbine and possibly one or more further wind turbines.

[0063] In case the torque modulation signal is transmitted to a monitoring system, the monitoring system can, for example, be used to monitor the condition of the wind turbine. For example, the monitoring system can be used to detect any signs of impending wear, failure, fatigue, etc. of various components or sensors of the wind turbine. Alternatively or additionally, the monitoring system can be used to monitor the performance of the wind turbine.

[0064] The vibration characteristics of the gearbox, in particular changes in the vibration characteristics of the gearbox, can provide information about the condition of the wind turbine. For example, if a component of the wind turbine is degrading, this may result in changes in the vibrations generated by the wind turbine, for example, resulting in changes in the vibrations originating from the meshing of the gear teeth of the gearbox. For example, the position of any pitch-sensitive resonances may change. Such vibration changes will further result in changes in the phase angle and / or amplitude of the torque modulation signal injected into the generator to maintain the resultant vibrations at a minimum. By transmitting the torque modulation signal, the phase angle and / or the amplitude of the adjusted torque modulation signal to the monitoring system, the monitoring system is able to detect such changes in the vibration characteristics of the gearbox and thus react to it. Similar changes in the vibration characteristics of the gearbox may be caused by changes in seasonal conditions.

[0065] In particular, the combination of information about the residual vibrations, in particular the amplitude of the minimum residual vibration, the amplitude and phase angle of the torque modulation signal providing the minimum residual vibration, and the DC operating point of the wind turbine provides valuable information about the condition, health or performance of the system.

[0066] The monitoring system may be internal, i.e. it is adapted to monitor only this wind turbine. As an alternative, it may be external, i.e. it is arranged externally with respect to the wind turbine, for example at a power plant controller (PPC) or at a central facility. In the latter case, the torque modulation signal may be used for group monitoring and / or statistical purposes.

[0067] In case the torque modulation signal is transmitted to a control system, the control system may be the control system of the wind turbine, or may be an external control system, such as a power plant controller (PPC) or a central control facility as described above. In the latter case, the torque modulation signal may be further taken into account during control of one or more further wind turbines, similar to the case described above.

[0068] The method may further comprise the steps of providing information about the residual vibration under minimized combined vibration to a continuous monitoring system of the wind turbine and monitoring a condition of the wind turbine by means of the continuous monitoring system and at least partly based on the information about the residual vibration under minimized combined vibration.

[0069] According to this embodiment, the residual vibrations are continuously monitored so that a possible development of the residual vibrations over time can be derived. Such information may be valuable for monitoring the condition of the wind turbine.

[0070] For example, if the residual vibration changes over time, such as in such a way that the amplitude of the residual vibration increases, this may indicate that the vibration characteristics of the gearbox are changing, and this may be a sign that one or more components of the wind turbine may be degrading, as described above. Thus, monitoring the residual vibration can provide an early warning of a component of the wind turbine that may be about to degrade or fail.

[0071] The step of selecting an initial phase angle and an initial amplitude may comprise selecting at least one amplitude from a lookup table. According to this embodiment, the lookup table may be generated, for example, empirically and / or by means of theoretical calculations. The lookup table may specify a suitable amplitude of the torque modulation signal for a suitable combination of design details of the wind turbine (in particular design details of the gearbox), the rotational speed of the generator and the amplitudes of the harmonics in the gearbox vibrations. Thus, the initial amplitude is a qualified guess at the optimal amplitude, resulting in an amplitude that minimizes the resultant vibration. This makes the above-mentioned "search process" faster and more accurate.

[0072] Furthermore, the initial phase angle may also be selected from a look-up table. Alternatively, the initial phase angle may be selected arbitrarily and the "correct" phase angle may be identified with the aid of the "finding process" described above.

[0073] The method may further comprise the step of updating the look-up table based on the adjusted phase angle and / or the adjusted amplitude of the adjusted torque modulation signal.

[0074] According to this embodiment, the lookup table is continuously adjusted and improved based on the adjusted phase angle and / or the adjusted amplitude, and thus based on the values ​​of the phase angle and amplitude that actually result in the amplitude of the composite vibration being minimized. Thus, the initial phase angle and / or initial amplitude selected on future occasions will be more accurate. This is sometimes referred to as feedforward control with self-regulation.

[0075] As an alternative to selecting the initial phase angle and / or the initial amplitude from a lookup table, the initial phase angle and / or the initial amplitude may be selected in any other suitable manner, such as based on calculations performed in real time or near real time.

[0076] The step of acquiring measurements of vibrations originating from a gear tooth mesh of the gearbox may comprise measuring vibrations of the gearbox by means of at least one sensor.

[0077] According to this embodiment, the gearbox vibration can be measured directly, for example, by means of one or more suitable sensors mounted on or connected to the gearbox. Suitable sensors include, but are not limited to, accelerometers, high-fidelity strain gauges, displacement sensors, or any other suitable type of sensor from which the amplitude of the harmonics in the gearbox vibration can be derived or isolated.

[0078] Alternatively or additionally, measurements of vibrations from the gear tooth meshes of the gearbox may be obtained in an indirect manner, for example by measuring vibrations of large wind turbine components (e.g., the tower and / or wind turbine blades) that are affected by the gearbox vibrations, or by measuring the noise level and its associated frequency spectrum at a specific distance from the wind turbine.

[0079] The measured inputs related to the synthetic vibration may originate from two or more sensors, for example, located at different locations and / or of different types. In this case, the measured inputs may be processed separately, i.e. each measured input forms part of a separate processing channel for performing the above-mentioned "finding" process. Thus, the separate processing channels may run in parallel, i.e. independently of each other and based on their respective measured inputs. This results in the generation of two or more torque modulation signals, one torque modulation signal for each processing channel. The two or more torque modulation signals may then be added to obtain a synthetic torque modulation signal, which is then injected into the generator.

[0080] The individual "seeking" processes may occur in the frequency domain, while the addition of the torque modulated signals may occur in the time domain.

[0081] Each torque modulation signal may be multiplied by an appropriate weight before being added to each other. Each weight may, for example, reflect the importance, significance, reliability, etc. of each corresponding sensor. Therefore, a more important or more reliable sensor may be set with a higher weight than a less important or considered less reliable sensor.

[0082] The weights may be in the form of a weighting function that depends, for example, on the frequency level, average torque and / or power level of the wind turbine. For example, for measurements within a first frequency range, average torque and / or power level, a first sensor may be assigned a higher weight than a second sensor, while within a second frequency range, average torque and / or power level the opposite may be true. This may reflect that certain sensors are most important or reliable within certain frequency ranges, average torque and / or power levels, while other sensors are most important or reliable within other frequency ranges, average torque and / or power levels. Thus, when forming the synthetic torque modulation signal, the most important or reliable sensor at the relevant frequency, average torque and / or power level will be assigned the highest weight.

[0083] The method may further comprise the step of continuously performing the optimization process so as to maintain the amplitude of the synthesized vibration at a minimum value.

[0084] According to this embodiment, a "search process" for the optimum phase angle and amplitude is continuously performed while the wind turbine is operating, thereby ensuring that the minimum amplitude of the resultant vibration is maintained even if something in the system drifts or changes.

[0085] The method may further comprise the following steps:

[0086] - determining at least one amplitude of at least one further harmonic of the gearbox vibrations,

[0087] - selecting an initial phase angle and an initial amplitude based on a rotational speed of the generator, an initial characteristic of the wind turbine and at least one amplitude of at least one further harmonic in the gearbox vibrations,

[0088] - performing an optimization process, the optimization process comprising adjusting an initial phase angle and an initial amplitude to obtain a minimum value of the amplitude of a composite vibration of the vibration originating from the gearbox and the vibration originating from the generator, the composite vibration corresponding to at least one further harmonic of the gearbox vibration, thereby obtaining an adjusted phase angle and an adjusted amplitude, and

[0089] - generating a further torque modulation signal for the generator, the further torque modulation signal specifying an adjusted phase angle and an adjusted amplitude,

[0090] The step of injecting the torque modulation signal into the generator includes adding the adjusted torque modulation signal to another torque modulation signal to obtain a composite torque modulation signal, and injecting the composite torque modulation signal into the generator.

[0091] According to this embodiment, by injecting an appropriate torque modulation signal into the generator in the manner described above, at least one additional harmonic in the gearbox vibration is made the subject of a process of reducing the noise originating from the gear tooth meshing of the gearbox. Thus, two or more harmonics in the gearbox vibration can be addressed and processed simultaneously.

[0092] The harmonics are processed individually, i.e. an individual torque modulation signal is generated for each harmonic, in such a way that the resultant vibrations corresponding to the individual harmonics are minimized. The torque modulation signals generated in this way are then added to each other, thereby obtaining a resultant torque modulation signal, which is then injected into the generator. The resultant torque modulation signal thus ensures that the resultant vibrations corresponding to all processed harmonics are minimized. Furthermore, processing the harmonics individually and then adding the generated torque modulation signals is a simple way to achieve this.

[0093] The step of obtaining measurements of vibrations originating from gear tooth meshes of the gearbox may comprise obtaining measurements from at least two sensors, and each sensor may provide measurements relating to a separate harmonic in the gearbox vibrations.

[0094] According to this embodiment, the harmonics are processed by two completely independent channels, since each of the torque modulation signals is generated based on the measurements provided by a separate sensor. Therefore, the measurements related to one harmonic do not interfere with the measurements related to any other harmonic. Therefore, it is easy to ensure that the true minimum of the composite vibration corresponding to each harmonic is achieved.

[0095] Alternatively, measurements from a given sensor may be related to two or more harmonics. BRIEF DESCRIPTION OF THE DRAWINGS

[0096] The present invention will now be described in further detail with reference to the accompanying drawings, in which:

[0097] Figure 1 is a cross-sectional view of a power train of a wind turbine controlled according to a method according to an embodiment of the present invention,

[0098] Figure 2 and Figure 3 is a diagram illustrating a wind turbine controlled according to a method according to an embodiment of the present invention,

[0099] Figure 4 is a block diagram illustrating a method according to an embodiment of the present invention,

[0100] Figure 5 1 shows a power generation part of a wind turbine controlled according to a method according to another embodiment of the invention,

[0101] Figure 6 and Figure 7 is a block diagram illustrating a method according to two embodiments of the present invention,

[0102] Figure 8 is a table illustrating optimal values ​​of the phase angle and amplitude of the torque modulation signal at various operating points of the wind turbine, and

[0103] Fig. 9 is a block diagram illustrating a method according to another embodiment of the present invention. DETAILED DESCRIPTION

[0104] Figure 1 1 is a cross-sectional view of a power train 1 of a wind turbine controlled according to a method according to an embodiment of the invention. The power train 1 comprises a main shaft 2 connected to a rotor (not shown) of the wind turbine, a gearbox 3 connected to the main shaft 2 via an input shaft 4, and a generator 5 connected to the gearbox 3 via an output shaft 6.

[0105] The generator 5 is controlled in such a way that the amplitude of the total vibration of the powertrain 1 in the form of a composite vibration of the vibration originating from the meshing of the gear teeth of the gearbox 3 and the vibration originating from the generator 5 is minimized.

[0106] This is achieved by taking a measurement of the rotational speed of the generator 5, for example in the form of the rotational speed of the input shaft 4 or in the form of the rotational speed of the output shaft 6. In addition, the vibrations originating from the gear tooth meshing of the gearbox 3 at this rotational speed are measured and the frequency and amplitude of at least one harmonic in the gearbox vibrations are determined.

[0107] The torque modulation signal of the generator 5 is then generated in the following manner. First, an initial phase angle and an initial amplitude are selected, which are expected to match the vibration of the gearbox 3. For example, at least the initial amplitude can be selected from a lookup table. An optimization process is then performed, for example, in the following manner. An initial torque modulation signal of the generator 5 (which specifies the initial phase angle and the initial amplitude) is generated and injected into the generator 5.

[0108] Therefore, the generator 5 operates based on the initial torque modulation signal, and thus operates according to the initial phase angle and the initial amplitude. During this period, the synthetic vibration of the powertrain 1 is monitored, which corresponds to the harmonics in the gearbox vibration. In addition, based on the monitored synthetic vibration, the phase angle and amplitude of the torque modulation signal are adjusted to adapt to the actual position of the gearbox 3 and the actual position of the generator 5 until the minimum value of the amplitude of the synthetic vibration is reached. Thereby, an adjusted torque modulation signal of the generator 5 is obtained, which specifies the adjusted phase angle and the adjusted amplitude.

[0109] The adjusted torque modulation signal is then injected into the generator 5. Thus, the generator 5 operates in such a way that the resultant vibration of the powertrain 1 (which corresponds to the harmonics of the gearbox vibration) has a minimum amplitude. In this way, the noise generated by the powertrain 1 is also minimized.

[0110] Furthermore, information about the residual vibrations at the minimized resultant vibrations is obtained in the above-described manner.

[0111] Figure 2 is a schematic diagram of a power generating portion of a wind turbine controlled according to a method according to an embodiment of the invention. Figure 2 The diagram shows a power train 1 of a wind turbine, comprising a drive train with a main shaft 2 and a gearbox 3, and a generator 5. The power train 1 is mechanically connected to large structures of the wind turbine in the form of a tower 7, a hub 8 and wind turbine blades 9. These large structures amplify vibrations of the power train 1, thereby emitting airborne noise to the surroundings.

[0112] The generator 5 is also connected to a power generation system 10, which includes a turbine-side AC / DC converter 11 and a grid-side DC / AC converter 12, which are interconnected via a DC link 13. The AC output of the grid-side converter 12 is connected to a grid 14.

[0113] The power train 1 and the power generation system 10 are controlled by means of a generator controller 15. The vibrations originating from the gear tooth meshing of the gearbox 3 are measured and based on this the generator controller 15 controls the power train 1 and the power generation system 10 by means of a generator controller 15, for example as described above with reference to FIG. Figure 1 The torque modulation signal for the generator 5 is generated in the manner described. The generator controller 15 then controls the power production system 10 in accordance with the torque modulation signal, thereby controlling the torque of the generator 5 in a manner that minimizes the amplitude of the resultant vibration of the power train 1. Thereby, the airborne noise emitted by the tower 7, the hub 8 and the wind turbine blades 9 is also minimized.

[0114] Figure 3 is a wind turbine (similar to Figure 2 Schematic diagram of wind turbine components shown in FIG. Figure 3 The diagram shows a power train 1, a gearbox 3, a generator 5, a tower 7 and a wind turbine blade 9. More specifically, Figure 3 The generator 5 is illustrated as operating in such a way that vibrations originating from the gear teeth meshing of the gearbox 3 and vibrations originating from the generator 5 are cancelled to the greatest possible extent, resulting in minimization of airborne noise emanating from the tower 7 and the wind turbine blades 9 .

[0115] Figure 4 is a block diagram illustrating a method according to an embodiment of the present invention.

[0116] Measurements of the rotational speed of the generator 5 are taken by means of a torque / speed sensor 16 and a high speed shaft encoder 17. Furthermore, measurements of the vibrations originating from the gear tooth meshing of the gearbox 3 are taken by means of a noise sensor 18 and a vibration sensor 19 mounted on the drive train. The amplitudes 20 of the harmonics in the gearbox vibrations are determined and provided to a table adjuster 21 which updates a lookup table 22 based thereon.

[0117] Based on the outputs from the torque / speed sensor 16 and the high-speed shaft encoder 17, the phase angle and amplitude are selected using a lookup table 22 and a gear angle estimator 23. The phase angle and amplitude are provided to a modulator 24, which generates a torque modulation signal specifying the selected phase angle and the selected amplitude, and injects the torque modulation signal into the generator 5. Therefore, the generator 5 operates in accordance with the torque modulation signal, thereby operating in accordance with the specified phase angle and amplitude. This allows the generator 5 to operate in a manner that matches the operation of the gearbox 3, that is, the vibrations originating from the gear tooth meshing of the gearbox 3 and the vibrations originating from the generator 5 are offset to the greatest extent, thereby minimizing the amplitude of the resultant vibrations of the powertrain.

[0118] The phase angle and amplitude of the torque modulation signal can be continuously adjusted based on the measurement results of the noise sensor 18 and / or the vibration sensor 19 until a minimum value of the amplitude of the synthetic vibration is obtained, for example, as described above with reference to Figure 1 The method described.

[0119] Figure 5 The diagram illustrates a power generating part of a wind turbine controlled according to a method according to another embodiment of the invention. Figure 5 A gearbox 3 is shown connected to a hub 8 and wind turbine blades 9 via a low speed input shaft 4 and to a generator 5 via a high speed output shaft 6. The gearbox 3 is also structurally connected to a tower 7 via a support frame 26. The wind turbine blades 9 and tower 7 amplify vibrations of the gearbox 3, thereby generating airborne noise, as described above.

[0120] Figure 5 The wind turbine shown in FIG. 1 is substantially as described above with reference to FIG. Figure 1-4 Control is performed as described in order to minimize the noise (originating from the meshing of the gear teeth) emitted by the tower and the wind turbine blades 9. Therefore, the comments made in this regard also apply here.

[0121] The shaft angle sensor 27 measures the shaft angle of the high-speed shaft 6, thereby tracking the phase angle of the high-speed shaft 6 over time. The output of the shaft angle sensor 27 is provided to the gear angle estimator 23. Based on this, the gear angle estimator 23 estimates the phase angle and provides it to the generator controller 15. The generator controller 15 generates a torque modulation signal for the generator 5, which specifies the estimated phase angle. The gear angle estimator 23 repeatedly adjusts the estimated phase angle based on the input from the shaft angle sensor 27 so as to minimize the phase angle offset between the phase angle of the high-speed shaft 6 and the phase angle of the gear teeth of the gearbox 3 meshing, thereby minimizing the resultant vibration.

[0122] The ratio between the low speed shaft 4, high speed shaft 6 and the gear tooth meshing frequency is fixed and determined by the mechanical design of the gearbox 3. However, the ratio between the high speed shaft 6 and the gear tooth meshing is a non-integer. Therefore, the gear angle estimator 23 needs to synthesize an angle that requires several full rotations of the high speed shaft 6 before the gear tooth profile repeats and is aligned with the observable shaft angle of the gearbox 3.

[0123] This is achieved with the aid of a phase locked loop which periodically realigns the shaft angle of the output shaft 6 with the phase angle of the gear tooth meshing to prevent loss of synchronism. According to the invention, this is done without knowing or measuring the phase angle of the gear tooth meshing, but only by observing the resultant vibration.

[0124] Instead, the shaft angle sensor 27 tracks the phase angle starting position of the high speed shaft 6, and the gear angle estimator 23 and generator controller 15 generate a torque modulation signal that is synchronized with the phase angle of the gear teeth meshing. The phase angle offset is unknown, but synchronization is achieved by adjusting the internal offset until the observed resultant vibration reaches a minimum.

[0125] Furthermore, in the above-described manner, information about the residual vibration under the minimized combined vibration is obtained.

[0126] Figure 6 2 is a block diagram illustrating a method according to an embodiment of the present invention. The vibration of the wind turbine (e.g. in the form of a composite vibration of the gearbox vibration and the generator vibration) is measured by means of a suitable sensor 28, and the measurement signal is provided to the torque modulation optimizer module 29. More specifically, the measurement signal is provided to a first digital bandpass filter 30a and a second digital bandpass filter 30b. The digital bandpass filters 30a, 30b are designed to allow two different frequency bands to pass, which correspond to two different harmonics in the gearbox vibration.

[0127] The first digital bandpass filter 30a can receive measurements only from the first sensor 28a or the first group of sensors 28a, while the second digital bandpass filter 30b can receive measurements only from the second sensor 28b or the second group of sensors 28b. In this case, the processing of the two harmonics is completely separated in two different and parallel channels. As an alternative, both digital bandpass filters 30a, 30b can receive measurements from the same sensor 28c or the same group of sensors 28c.

[0128] The bandpass filtered signal is provided to the corresponding torque modulation optimizer 31a, 31b, wherein the corresponding torque modulation signal specifying the corresponding phase angle and amplitude is generated in the above-mentioned manner, that is, the corresponding torque modulation signal is generated in a manner to minimize the combined vibration of the gearbox vibration and the generator vibration (which corresponds to the corresponding harmonic).

[0129] The two torque modulation signals are added to each other at the adder 32, thereby obtaining a resultant torque modulation signal, which is provided to the generator controller 15 for injection into the generator. In addition, corresponding torque modulation optimizer maps 33a, 33b are also generated.

[0130] Therefore, in Figure 6 In the embodiment shown, the two harmonics are processed simultaneously and through two separate channels represented by separate digital bandpass filters 30a, 30b and torque modulation optimizers 31a, 31b, and the resultant torque modulation signal ensures minimized resultant vibrations corresponding to the two harmonics. It should be noted that Figure 6 The concept shown can be expanded to include more channels representing more harmonics in the gearbox vibration, thereby allowing three or more harmonics in the gearbox vibration to be processed simultaneously.

[0131] Furthermore, information about the residual vibrations at the minimized resultant vibrations is derived, for example, from the torque modulation optimizer maps 33 a , 33 b .

[0132] Figure 7 is a block diagram illustrating a method according to an alternative embodiment of the present invention. Figure 6 Similar to the embodiment shown in , the vibrations of the wind turbine are measured by means of appropriate sensors 28d, 28e and the measured signals are provided to the torque modulation optimizer module 29.

[0133] More specifically, the measurement signal from sensor 28d is provided to digital bandpass filter 30d, and the measurement signal from sensor 28e is provided to digital bandpass filter 30e. Figure 6 In contrast to the embodiment shown in Figure 7 The digital bandpass filters 30d, 30e shown in FIG. 3 are designed to allow the same frequency band to pass, ie the bandpass filters 30d, 30e process the same harmonics, but process the harmonics based on measurements from different sensors 28d, 28e.

[0134] and Figure 6 Similar to the embodiment shown in , the bandpass filtered signals are provided to respective torque modulation optimizers 31d, 31e, where respective torque modulation signals specifying respective phase angles and amplitudes are generated in the manner described above. The torque modulation signals are multiplied by appropriate weighting factors 34d, 34e and then added to each other at adder 32 to obtain a resultant torque modulation signal to be provided to generator controller 15, as described above.

[0135] The weighting factors 34d, 34e may be selected in such a way that they reflect the importance, significance, reliability, etc. of the respective corresponding sensor 28d, 28e.

[0136] Therefore, in Figure 7 In the embodiment shown in , one harmonic is processed by two independent and parallel channels, each channel relying on measurements from a separate sensor 28d, 28e.

[0137] Furthermore, information about the residual vibrations at the minimized resultant vibrations is obtained, for example, from the torque modulation optimizer maps 33 d , 33 e .

[0138] Figure 8 is a table illustrating optimal values ​​of the phase angle and amplitude of the torque modulation signal at various operating points of the wind turbine. More specifically, Figure 8 The table lists the wind turbine torque Ti and the generator speed ω i For each operating point, the optimal amplitude Tm is listed. ij and the optimal phase angle θ ij The optimal torque modulation signal is represented by the amplitude Tm ij and phase angle θ ij have been identified (determined) during the optimization process according to the invention, as described above. They therefore represent torque modulation signals that, when injected into the generator, will minimize the resultant vibrations of the gearbox vibrations and the generator vibrations.

[0139] Figure 8 The table may be used as a look-up table for selecting an appropriate torque modulation signal during operation of the wind turbine. Figure 8 The table can also be viewed as an example of a lookup table that is provided to a newly installed wind turbine, where the model-specific lookup table is used as the initial table. The turbine-specific table will evolve over time as the table is adjusted and turbine components are exposed to wear.

[0140] Figure 8 The table shown may also include amplitude values ​​of the residual vibrations and / or values ​​of the order of the gear tooth mesh vibrations that are mitigated for each entry in the table. For example, the tonal performance of a wind turbine may depend on which order of the gear tooth mesh or planet gear carrier is most significant. Even if the gear tooth mesh, number of planet gears, etc. are fixed numbers, the specific eigenfrequency order that is most significant may be a function of the torque and speed of the operating point of the wind turbine. However, the order of the gear tooth mesh defines the multiplier to be applied when deriving the frequency from the speed of the generator.

[0141] Fig. 9 is a block diagram illustrating a method according to another embodiment of the present invention. Figure 6 and Figure 7Similar to the embodiment shown in , vibrations originating from the power train 1 of the wind turbine are measured by means of suitable sensors 28. The measured vibrations may include a composite vibration of vibrations originating from the gearbox 3 and vibrations originating from the generator 5. Furthermore, vibrations originating from the gear tooth meshing of the gearbox 3 may be measured.

[0142] The measured signal is provided to a digital bandpass filter 30 which is designed to allow a specific frequency band to pass corresponding to the harmonics in the gearbox vibrations.

[0143] The bandpass filtered signal is provided to the torque modulation optimizer 31, wherein a torque modulation signal of a specified phase angle and amplitude is generated using the optimization process as described above, i.e., the torque modulation signal is generated in a manner that minimizes the amplitude of the combined vibration of the gearbox 3 and the generator 5 (which corresponds to the harmonics).

[0144] The torque modulation signal is provided to the generator controller 15 for injection into the generator 5, and the generator controller 15 controls the generator 5 in accordance with the signal. Thus, the wind turbine operates in a manner that minimizes the resultant vibrations, thereby minimizing the noise originating from the power train 1 of the wind turbine.

[0145] Furthermore, a torque modulation optimizer map 33 is generated and provided to a continuous monitoring system 35 of the wind turbine. Thus, the torque modulation optimizer map 33 is applied during condition monitoring of the wind turbine, for example, in order to allow early warning in case of a possible imminent degradation or failure of one or more components of the wind turbine, as described above.

[0146] Furthermore, information about the residual vibrations at the minimized composite vibrations is derived in the form of a residual vibration map 36. The residual vibration map 36 specifies the relative values ​​of the phase angle of the torque modulation signal, the amplitude of the torque modulation signal and the amplitude of the composite vibration. Thus, the residual vibration map 36 can be viewed as a three-dimensional graph or table, which specifies in what way the above three entities are related or dependent on each other. For example, the residual vibration map 36 can specify the amplitude of the composite vibration measured at a given combination of phase angle and amplitude of the applied torque modulation signal (which corresponds to a specific operating point of the wind turbine) and can be extended to all relevant operating points of the wind turbine. Thus, the residual vibration map 36 can be viewed as a response function for a given torque modulation input.

[0147] The torque modulation optimizer map 33 and the residual vibration map 36 are transmitted to an external monitoring system 37. The external monitoring system 37 may, for example, take the form of a power plant controller (PPC) for controlling the wind turbines within a wind farm, or a central facility that collects data from a large number of wind turbines (e.g. from multiple wind farms). The external monitoring system 37 may, for example, monitor the wind turbines of an entire wind farm or even an entire group of wind farms over time.

[0148] Thereby, the torque modulation optimizer map 33 and the residual vibration map 36 may be obtained externally, for example, in order to provide optimized operation of wind turbines on a wind farm level or even a cluster level. Furthermore, this information may be used for statistical purposes.

Claims

1. A method for controlling the operation of a generator (5) of a wind turbine, the method comprising the following steps: - obtaining a measured value of the rotation speed of the generator (5), - obtaining, at said rotational speed of said generator (5), measured values ​​of vibrations originating from the meshing of the gear teeth of a gearbox (3) of said wind turbine, - determining at least one amplitude of a harmonic in the gearbox vibrations, - generating a torque modulation signal for the generator (5) by: - selecting an initial phase angle and an initial amplitude based on the rotational speed of the generator (5), the initial characteristics of the wind turbine and the at least one amplitude of the harmonics in the gearbox vibrations, - performing an optimization process, the optimization process comprising adjusting the initial phase angle and the initial amplitude in order to obtain a minimum value of the amplitude of a composite vibration of the vibration originating from the gearbox (3) and the vibration originating from the generator (5), the composite vibration corresponding to the harmonic in the gearbox vibration, thereby obtaining an adjusted phase angle and an adjusted amplitude, and - generating a torque modulation signal for the generator (5) specifying the adjusted phase angle and the adjusted amplitude, - injecting the torque modulation signal into the generator (5) so that the operation of the generator (5) results in minimizing the resultant vibration of the gearbox (3) and the generator (5), the resultant vibration corresponding to the harmonic in the gearbox vibration, and - Derive information about the residual vibrations at the minimized combined vibrations.

2. The method according to claim 1, wherein: The steps to perform the optimization process include the following steps: - generating an initial torque modulation signal for the generator (5) specifying the initial phase angle and the initial amplitude, - injecting the initial torque modulation signal into the generator (5) and operating the generator (5) based on the initial torque modulation signal while monitoring a composite vibration of the vibration originating from the gearbox (3) and the vibration originating from the generator (5), the composite vibration corresponding to the harmonic in the gearbox vibration, and - Based on the monitored synthetic vibration, the phase angle and amplitude of the torque modulation signal are adjusted to adapt to the actual position of the gearbox (3) and the actual position of the generator (5) until the minimum amplitude of the synthetic vibration is reached, thereby obtaining an adjusted torque modulation signal.

3. The method according to claim 1 or 2, wherein: The step of deriving information about residual vibrations at the minimized combined vibration includes generating a residual vibration map (36) that specifies relative values ​​of a phase angle of the torque modulation signal, an amplitude of the torque modulation signal, and an amplitude of the combined vibration.

4. The method according to any one of the preceding claims, further comprising the steps of: Information about the residual vibrations at the minimized combined vibrations is transmitted to an external monitoring system and / or control system (37).

5. The method according to claim 4, further comprising the steps of: One or more further wind turbines are controlled based on the information about the residual vibration at the minimized resultant vibration.

6. The method according to any one of the preceding claims, further comprising the steps of: The torque modulation signal and / or the adjusted phase angle and / or the adjusted amplitude are transmitted to a monitoring system and / or a control system (35, 37).

7. The method according to any one of the preceding claims, further comprising the steps of: Information about the residual vibrations under the minimized combined vibrations is provided to a continuous monitoring system of the wind turbine (35), and a condition of the wind turbine is monitored by means of the continuous monitoring system (35) and at least partly based on the information about the residual vibrations under the minimized combined vibrations.

8. A method according to any one of the preceding claims, wherein: The step of selecting an initial phase angle and an initial amplitude includes selecting at least one amplitude from a look-up table (22).

9. A method according to any one of the preceding claims, wherein: The step of acquiring a measurement of vibrations originating from the meshing of gear teeth of the gearbox (3) comprises measuring the vibrations of the gearbox (3) by means of at least one sensor (28).

10. The method according to any one of the preceding claims, further comprising the steps of: The optimization process is continuously performed so as to maintain the amplitude of the synthetic vibration at a minimum value.

11. The method according to any one of the preceding claims, further comprising the steps of: - determining at least one amplitude of at least one further harmonic of the gearbox vibrations, - selecting an initial phase angle and an initial amplitude based on the rotational speed of the generator (5), initial characteristics of the wind turbine and at least one amplitude of the at least one further harmonic in the gearbox vibration, - performing an optimization process, the optimization process comprising adjusting the initial phase angle and the initial amplitude to obtain a minimum value of the amplitude of a composite vibration of the vibration originating from the gearbox (3) and the vibration originating from the generator (5), the composite vibration corresponding to the at least one further harmonic in the gearbox vibration, thereby obtaining an adjusted phase angle and an adjusted amplitude, and - generating a further torque modulation signal for the generator (5) specifying the adjusted phase angle and the adjusted amplitude, The step of injecting the torque modulation signal into the generator (5) comprises adding the adjusted torque modulation signal to the other torque modulation signal to obtain a composite torque modulation signal, and injecting the composite torque modulation signal into the generator (5).

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