Wind turbine damping in a wind park

Field of invention

The present invention relates to the technical field of damping wind turbine components such as tower and/or foundation within a wind park. In particular, the present invention relates to a method for operating a plurality of wind turbines in a wind park, to a wind park controller performing the method and to a system comprising such a wind park controller, with which mechanical oscillations and/or vibrations of wind turbine components are damped.

Art Background

For damping wind turbine movements it is known that each in dividual wind turbine in a wind park has an active damping component introduced by the generator that damps the tower and foundation frequencies by injecting torque and/or power which results in a reduced amplitude of the tower/foundation mode shapes and thereby significantly lowers the fatigue loading .

On a park level, these damping components in the active power are most of the time out of sync as the phase, frequency and amplitude differ over time per turbine due to different foun dation types, length of foundation (e.g. monopile), tempera ture and soil type and amount and input vibrations like wave and wind conditions. Soil also can accumulate or wash away over time, changing the frequency. However sometimes these damping components in the active power will align and create a significant amplitude on electrical signals on the park level - i.e. electrical signals of the power output at the point of coupling of the wind park to the grid -, potentially unwantedly exciting frequencies in the grid. These can be problematic as they can make the grid unstable, or overload electrical hardware on the substations.

So far, such effects have been accepted by grid authorities as they typically understand the essence of these tower damp ing components and the combined output is small compared to the total park output. With more recent turbines, these ac tive damping components in active power have been increased to optimize the foundation and tower design, making them less costly and achieve a better business case.

Therefore, there may be a need for improving these considera tions.

Summary of the Invention

This need may be met by the subject matter according to the independent claims. Advantageous embodiments of the present invention are described by the dependent claims.

According to a first aspect of the invention there is provided a method for operating a plurality of wind turbines in a wind park, wherein at least one component of a wind turbine is capable of being actively dampened, with the steps of (a) monitoring measurement values being indicative for acceleration, velocity or position of the at least one component of a subset of the plurality of wind turbines, wherein the subset comprises at least two wind turbines; (b) processing the monitored measurement values to a consolidated measurement value; (c) comparing the consolidated measurement value with a predefined threshold; and (d) changing a damping setpoint for a damping procedure for the components of the subset of the plurality of wind turbines such that fluctuations of the output power, particularly an amplitude of fluctuations of the output power, of the subset of the plurality of wind turbines are reduced. The described method is based on the idea that the total damping output can be effectively lowered by directly detecting and measuring the cause of unwanted exciting frequencies in electrical signals of the power output for instance at a point of coupling of the wind park to a utility grid.

Measuring on the total power output may be easier as one measures on the output and exactly that power output what could be problematic for the grid. However, according to the described method, by measuring the acceleration, velocity or position of the component that is to be actively dampened it can be estimated if they oscillate or vibrate in phase and thus if the output power on a park level can be problematic. By basing a proper control action on the described consolidated measurement value, e.g. the acceleration of the tower/foundation, instead of output power, advantage can be taken of the (roughly quarter period) phase-lead of the respective measurement value. This leads to a more precise control action and a response that suffers less from overshooting, delays etc. So, by measuring e.g. the accelerations of e.g. the tower on each wind turbine, this information can be sent to a central park controller which consolidates or combines all the received signals and computes if the amplitude of the consolidated / combined accelerations is above a certain threshold level.

The term "power on a park level" may have a reference to a measurement unit linked to the central wind park controller which outputs the total power output of the wind park to the grid (thereby also comprising of all damping components), i.e. to the plurality of wind turbines or at least to a subset (of two) thereof. At the respective wind turbine, an active damping electric signal component may be introduced by the electric generator that damps for example the tower and/or foundation oscillation by injecting electric signals that affect torque and/or power of the respective electric generator .

The predefined threshold may be defined by grid stability aspects or electric substation capacity limits to ensure save operation within the usual operation ranges.

According to an embodiment of the invention processing the monitored measurement values comprises taking into account a phase relation between the monitored measurement values. Preferably, it is taken into account whether the monitored measurement values are in phase. Accordingly, the phases of the monitored measurement values can be processed to a combined or consolidated phase value. It can be estimated to which extent the measurement values are in phase and/or if all measurement values of one type of component like e.g. the towers of the wind turbines are in phase. This approach provides the park control with detailed information about the overall oscillation behavior of the monitored components. Specifically, the criterion whether the measurement values are in phase may be a good rule for exciting proper frequencies with proper power amplitudes in the power output of the wind park.

It is pointed out that at least in some operational modes of the wind park the oscillation frequencies of the various wind turbine components may be different. Hence, there will be a phase difference between the corresponding component oscillations which will vary in time. In accordance with the described embodiment this time varying phase difference can be determined online or continuously and can be taken into account for the damping procedure for the respective component .

In this context it should be understood that depending on the phase differences the contributions of the oscillations of the various components to the overall output power of the wind park are combined differently. In case these oscillations are in phase, it should be clear that the effect of the respective in-phase oscillations to the total power will be amplified / increased. On the opposite, these oscillations may also be shifted in phase in such a manner that there is at least a certain compensation of the component oscillation effects towards a reduced fluctuation of the total output power.

Since in most application cases the subset of wind turbines comprises more than two wind turbines it may happen that at a certain point in time a first number of oscillating components have (approximately) a first phase and a second number of oscillating components have (approximately) a second phase being different from the first phase. In this case the step of processing the monitored measurement values may include a weighing of the difference phases with the respective number of wind turbine components.

According to a further embodiment of the invention processing the monitored measurement values comprises summing up the amplitudes of the monitored measurement values to a summation amplitude . Using the summation amplitude may provide the advantage that the described method can be realized with a simple but meaningful criterion which is used as the trigger for the described change of the damping setpoint for the damping procedure.

According to a further embodiment of the invention the damping procedure comprises a damping algorithm and changing the damping setpoint includes lowering at least one of a sensitivity, a gain, and a saturation value of the damping algorithm for the components of at least one wind turbine of the subset of the plurality of wind turbines. This approach may allow even for cases of high tower accelerations that the turbine will still be able to reach an unrestricted damping amplitude . Accordingly, even after lowering the respective parameter value, e.g. sensitivity, gain, saturation value, it is possible to keep the tower load under control. By reducing the gain, the damping level still can reach the maximum level. By contrast thereto, for standard approaches which introduce a restriction value to cap the damping level that maximum damping level cannot be achieved.

According to a further embodiment of the invention the at least one of the sensitivity, the gain, and the saturation value of the damping algorithm for the components of all wind turbines of the subset of the plurality of wind turbines is lowered . Damping all wind turbines by lowering e.g. their gains of damping action may increase the leverage as the whole park is included. Other approaches are to distinctly reduce e.g. the gain according to the individual measured acceleration, velocity and/or position values.

According to a further embodiment of the invention the step of changing the damping setpoint is performed by sending a signal to controllers of the subset of the plurality of wind turbines for lowering the fluctuations of the output power of the respective subset of the plurality wind turbines. In this case, the central park controller may send corresponding signals to the individual wind turbine controllers which then will control the damping algorithms / procedures of the respective wind turbine.

According to a further embodiment of the invention the at least one component includes a tower and/or a foundation of a wind turbine. This may provide a significant damping effect because these types of components have the biggest influence on wind turbine movement.

According to a further embodiment of the invention the output power of the subset of the plurality of wind turbines is an active power output. Although a reduction of the fluctuations of (also) the reactive power output may be of advantage for improving the power signal integrity of the utility grid, the described smoothening of the active power will typically be more relevant in most application cases. This is because the reactive power signal of a utility grid can be smoothened effectively also with other known measures for changing / adapting the power factor of the respective utility grid.

According to a further aspect of the invention there is provided a wind park controller for operating a wind park with a plurality of wind turbines, the wind park controller comprising a computation unit adapted for executing or controlling the method as described above, at least one input terminal adapted for receiving the measurement values, and at least one output terminal adapted for outputting the changed damping setpoint. The same advantages and modifications as described above for the method for operating a plurality of wind turbines apply mutatis mutandis for the wind park controller .

According to a further aspect of the invention there is provided a system comprising a wind park with a plurality of wind turbines and a wind park controller as described above. The same advantages and modifications as described above apply also for the described system.

According to a further embodiment of the invention acceleration, velocity and/or position sensors are provided at the at least one component of the wind turbines of the subset of the plurality of wind turbines. Such sensors may allow for a detailed picture of the wind turbines vibration and/or oscillation situation.

It has to be noted that embodiments of the invention have been described with reference to different subject matters.

In particular, some embodiments have been described with reference to apparatus type claims whereas other embodiments have been described with reference to method type claims. However, a person skilled in the art will gather from the above and the following description that, unless other notified, in addition to any combination of features belonging to one type of subject matter also any combination between features relating to different subject matters, in particular between features of the apparatus type claims and features of the method type claims is considered as to be disclosed with this document.

The aspects defined above and further aspects of the present invention are apparent from the examples of embodiment to be described hereinafter and are explained with reference to the examples of embodiment. The invention will be described in more detail hereinafter with reference to examples of embodiment but to which the invention is not limited.

Brief Description of the Drawings

Figure 1 shows a schematic illustration of a wind park with a central park controller.

Figure 2 shows a block diagram of the central park controller of the wind park.

Figure 3 shows a flow diagram of a method for starting up a wind turbine having ice accretion on its blade.

Detailed Description

The illustration in the drawing is schematically. It is noted that in different figures, similar or identical elements are provided with the same reference signs.

Figure 1 shows a schematic illustration of a wind park 100 with a plurality of wind turbines 102 and a central park controller 104. Here, only three wind turbines 102 are depicted. The wind park 100 may for example include between ten and 100 wind turbines 102. The central park controller 104 is described with reference to Figure 2. The wind turbines 102 are connected to a point of common coupling like a substation which is connected to a utility grid. For better overview, the electrical connections are not depicted in Figure 1.

At each wind turbine 102, acceleration, velocity and/or position sensors 106 are provided. At least one component of the wind turbine 102 is equipped with such a sensor or such sensors 106. For example, the tower and the foundation of the wind turbine 102 are each equipped with acceleration, velocity and position sensors 106. In another example, only acceleration sensors 106 like accelerometers are provided at the tower and the foundation of each of the wind turbines 102.

Outputs of the sensors 106 are connected with inputs of the central park controller 104 via signal lines 108. The signal lines 108 may be distinct signal lines or part of a communication bus. The central park controller 104 may be connected directly to the sensors 106 or via a not depicted wind turbine controller.

At the central park controller 104, a method for operating a plurality of wind turbines 102 in a wind park 100 is executed . This method is described with reference to Figure 3.

Based on monitored measurement values of acceleration, velocity and/or position of the plurality of wind turbines 102 the central park controller 104 calculates or processes the monitored measurement values to a consolidated measurement combined value and changes a damping setpoint in case it is expected that excited frequency components having a significant amplitude are expected to be transmitted as disturbing power signal components into the grid.

To that end, output terminals of the central park controller 104 are connected with input terminals of active damping modules 112 of wind turbines 102 via signal lines 110. The signal lines 110 may be distinct signal lines or part of a communication bus.

The active damping module 112 is for example the generator of the wind turbine 102 that damps the tower and foundation frequency by injecting electric power signals that affect torque and/or power of the respective wind turbine. The central park controller 104 may be connected directly to the generator or via a not depicted wind turbine controller. Such wind turbine controller could also control the yaw angle adjustment and the blade pitch angle ad ustment of the rotor blades.

According to the exemplary embodiment described here a closed control loop is formed by the sensor 106, the central park controller 104 and the active damping module 112.

Figure 2 shows a block diagram of the central park controller 104 of the wind park 100.

The central park controller 104 includes input terminals 114 for receiving measurement values of acceleration, velocity and/or position of each of the wind turbines 102. The input terminals 114 are connected to respective signal lines 108.

In the depicted example, only one measurement value like acceleration is present. Thus, only one input terminal 114 is provided for each wind turbine 102.

For further sensors like for example velocity sensors additional input terminals may be provided. Alternatively, the outputs of several sensors may be sent over a single signal line 108. Necessary signal processing may be provided by a wind turbine controller. Accordingly, the input terminals 114 of the central park controller 104 are connected with the wind turbine controller in such case. The input terminals 114 are connected to a computation unit 115 like for example a microcontroller or the like. Units or subunits of the computation unit 115 can be implemented as a software routine or in hardware.

In detail, the input terminals 114 are connected to a summation unit 116 of the computation unit 115. In the summation unit 116, the measurement values are summed up. For example, amplitudes of the measurement values are summed up to a summation amplitude. In a broader sense, the measurement values are combined to a consolidated measurement value with an appropriate algorithm which may include summation.

The consolidated measurement value is fed into a level evaluation unit 118 which is connected with the summation unit 116. Here, the consolidated measurement value is compared with a predefined threshold. The predefined threshold is defined by grid stability aspects or substation capacity limits.

An output terminal of the level evaluation unit 118 is connected to an input of a mitigation unit 122. In the mitigation unit 122, the amount of changing a damping setpoint for a damping procedure performed for or within the respective wind turbine is calculated in case the threshold is met or exceeded.

The mitigation unit 122 is connected with output terminals 124 to output the changed damping setpoint to respectively one of the wind turbines. In order to realize this "distribution" of the changed damping setpoint the output terminals 124 are connected to respective signal lines 110.

In the depicted example, only one measurement value like acceleration is used. Thus, only one output terminal 124 is provided for each wind turbine 102.

Only one active damping module 112 like the generator of the wind turbine 102 may be utilized for the wind turbine 102. This is viable even for a plurality of sensors and/or components as the inputs are processed together and can be output by the central park controller 104 in a single output value for the active damping module 112 or the respective wind turbine.

For further active damping modules additional output terminals may be provided. Alternatively, the output terminals for several active damping modules may be sent over a single signal line 110. Necessary signal processing may be provided by the central park controller 104. Accordingly, the output terminals 124 of the central park controller 104 may be connected with the respective wind turbine controller in such case.

Figure 3 shows a flow diagram of a method for operating a plurality of wind turbines 102 in a wind park 100, wherein at least one component of a wind turbine 102 is capable of being actively dampened. The method can be executed by or implemented in the central park controller 104 as described before.

In a first step 300, measurement values of acceleration, velocity or position of the at least one component of a subset of the plurality of wind turbines 102 are monitored. This monitoring may be achieved by the sensors 106 and the central park controller 104. The subset comprises at least two wind turbines 102.

In a second step 310, the monitored measurement values are processed to a consolidated measurement value. As a first approach, it may be taken into account whether the monitored measurement values of the subset of the plurality of wind turbines 102 are in phase. As a second approach, amplitudes of the monitored measurement values may be summed up to a summation amplitude. Both approaches may be combined. For example, the approaches may be calculated in parallel and the outcome which exceeds a threshold is set as the result for the consolidated measurement value.

In a third step 320, the consolidated measurement value is compared with a predefined threshold. The predefined threshold is defined by grid stability aspects or substation capacity limits to ensure save operation within the usual operation ranges.

In a fourth step 330, a damping setpoint for a damping procedure for the components of the subset of the plurality of wind turbines 102 is changed in case the predefined threshold is met or exceeded. Thereby, the damping setpoint is changed in such a manner that fluctuations of the output power, particularly an amplitude of fluctuations of the output power, of the subset of the plurality of wind turbines are reduced.

The preceding steps may be iterated in a loop so that the method is iterative and takes changes over time into account.

Further, it may be proposed, at the park controller of the wind park, to monitor the total contribution of tower damping (so the sum of each turbine's active power damping component) . If the frequency of interest, related to grid stability or substation capacity limits, has reached a certain threshold, then the total active tower damping component in power can be lowered, by lowering the tower damping on each individual turbine. This can be done by either lowering the gain used for active tower damping and/or by lowering the saturation of the active tower damping on each individual wind turbine.

This method guarantees a total power limit on the oscillations fed to the substation (usually the point of common coupling) or the grid. In events where all tower damping contributions align, the individual tower damping procedures can temporarily be disabled (at one, several, or all turbines of the wind park), like grid fault ride through procedures or large/extensive changes to the power reference, etc.

Some embodiments of the invention comprise a method for operating a plurality of wind turbines in a wind park, with the steps of:

- monitoring, via a central park controller of the wind park, active power frequency signal at an output of active power of the wind park, wherein the active power frequency behavior is affected by tower damping methods performed at at least a subset of the plurality of wind turbines,

- selecting a frequency information from the monitored active power frequency signal, preferably the frequency information being related to grid stability or substation capacity limits;

- comparing the selected frequency signal with a predefined threshold;

- and in case the threshold is met or exceeded, lowering the total active tower damping setpoint.

In some embodiments the method is characterized in that the step of lowering the total active tower damping setpoint is performed by sending a signal to controllers of at least a subset of the plurality wind turbines for lowering the tower damping on the respective subset of the plurality wind tur bines.

Some embodiments of the invention comprise a system comprising a wind park controller, in which the wind park controller performs the steps of the previous claims.

It should be noted that the term "comprising" does not exclude other elements or steps and "a" or "an" does not exclude a plurality. Also, elements described in association with different embodiments may be combined. It should also be noted that reference signs in the claims should not be construed as limiting the scope of the claims.

List of reference signs:

100 wind park 102 wind turbine 104 wind park controller

106 sensor 108 signal lines 110 signal lines 112 active damping module 114 input terminals

115 computation unit

116 summation unit

118 level evaluation unit 122 mitigation unit 124 output terminals

300 first step 310 second step 320 third step 330 fourth step