SINGLE BLADE ADJUSTMENT ON A WIND TURBINE

Description

[0001] The present invention relates to a method for controlling a wind turbine, and the invention also relates to a corresponding wind turbine. In particular, the invention relates to performing individual blade adjustment of rotor blades of a rotor of the wind turbine, which can also be referred to as individual blade adjustment.

[0002] Wind turbines are well known; they convert kinetic energy from wind into mechanical work using a rotor with multiple rotor blades and then into electrical energy using a generator. In any case, the present invention relates to wind turbines that operate according to this principle.

[0003] Modern wind turbines today have a rotor diameter of over 100 meters. The rotor blades thus cover a circular area with such a large diameter. Typically, three rotor blades are provided, arranged evenly offset by 120° from each other within the rotor, thus being located in different areas of the rotor surface at any given time. This means that the rotor blades can be exposed to different wind conditions at the same time. In particular, the wind speed and direction can vary.

[0004] In particular, these different wind conditions can result in different blade loads. To accommodate these, individual blade pitch control can be provided, which adapts the blade angle of each rotor blade to the specific load on the blade.

[0005] Such loads often occur in rotational cycles, so rotational cycle blade adjustment can be useful. To simplify and illustrate, the blade load may be greater in the upper area of ​​the rotor surface than in the lower area. Accordingly, the rotor blade can be rotated slightly out of the wind in the upper area of ​​the rotor surface and slightly into the wind in the lower area of ​​the rotor surface. A sinusoidal function can be provided for this purpose.

[0006] To control the wind turbine as a whole, a suitable operating point must also be set, which includes a collective blade angle. Such a collective blade angle can also be referred to as a collective pitch angle. In general, a blade angle can also be referred to as a pitch angle.

[0007] Such a collective blade angle is the same for all rotor blades and an individual offset angle is then superimposed or applied to it for each rotor blade.

[0008] In one case, this could mean superimposing an individual sinusoidal offset angle on the collective blade angle. Such a sinusoidal offset angle could, in principle, be the same for all rotor blades in terms of amplitude and frequency, but be phase-shifted. It could also have different amplitudes between the individual rotor blades, while the frequency should be the same for all rotor blades.

[0009] In a specific implementation, it may happen that the actual blade angle does not exactly correspond to the specified and / or assumed blade angle. Such deviations are usually individual and must therefore be considered for each blade individually. To account for such a deviation, a controller can be provided that compensates for any deviation between the detected blade angle and the intended blade angle. To achieve quasi-steady-state accuracy, an integral action can be provided.

[0010] It should be noted that modern wind turbines have such large rotor blades that their dynamics must be taken into account when adjusting the rotor blades. In other words, during blade adjustment, these rotor blades rotate around their own longitudinal axis, and this rotation cannot occur at any speed or with any degree of jerkiness, because such rotor blades, in addition to their enormous length, also have a considerable depth of several meters, at least in the area near the rotor hub. Therefore, it is often advantageous to specify blade angle adjustment rates for adjusting the blade angles via the higher-level control system rather than absolute values.

[0011] In the case of the described individual blade adjustment, this means that in addition to an adjustment rate for setting the collective blade angle, an adjustment rate must be provided to take into account the individual offset blade angle.

[0012] Overall, this can result in a complex system in which a collective blade angle must be specified and taken into account, an individual blade angle must be specified and taken into account for each rotor blade, various properties of the rotor, rotor blade, and adjustment device must be considered, in particular the dynamics or at least the moment of inertia of the respective rotor blade, and angular deviations must be considered as accurately as possible. An example from the prior art is disclosed in US2011 / 229300A1.

[0013] The present invention is therefore based on the object of addressing at least one of the problems mentioned. In particular, a solution is to be proposed in which individual blade adjustment is to be improved with regard to dynamics, accuracy and / or reliability, or at least a good solution is to be proposed. At least an alternative to previously known solutions is to be proposed. According to the invention, a method according to claim 1 is proposed. The method thus relates to the control of a wind turbine. The wind turbine is based on a rotor with a plurality of rotor blades, in particular with three rotor blades. The rotor blades are adjustable in their blade angle and each rotor blade is individually controllable and thus also individually adjustable, namely in its blade angle.For individual control, a total adjustment rate is specified, which indicates the intended rate of change of the respective blade angle. The adjustment rate thus describes a blade angle change per unit of time.

[0014] Furthermore, a collective blade angle that is the same for all rotor blades is provided. Such a collective blade angle can also be referred to synonymously as a collective pitch angle or as a common blade angle. The collective blade angle is therefore a blade angle that fundamentally does not take individual differences between the individual rotor blades into account. It primarily determines the current operating point. The collective blade angle can, for example, have a fixed value in the part-load range when the wind speed is still below a nominal wind speed. However, the collective blade angle can also be variable in the part-load range if the corresponding control concept allows for this. In particular, the collective blade angle is variable outside the part-load range, i.e. particularly in a full-load range or in a transition range from a part-load range to a full-load range.If the collective blade angle is variable, this variability is also the same for all rotor blades. The method of accounting for this is described below.

[0015] In addition, a collective pitch rate is provided that is the same for all rotor blades, which describes the intended rate of change of the collective blade angle. Accordingly, the collective pitch rate can also be referred to synonymously as the common pitch rate. The collective pitch rate is thus closely linked to the collective blade angle. It can be considered directly or via the collective blade angle. Likewise, the collective blade angle can be considered directly or via the collective pitch rate.

[0016] Furthermore, an individual offset angle is specified for each rotor blade, which indicates the value by which the blade angle should deviate from the collective blade angle. The collective blade angle, or collective pitch rate, thus ensures that all rotor blades have the same value. Individual differences can be accounted for for each rotor blade using the respective individual offset angle.

[0017] For example, each individual offset angle can be continuously recalculated and / or specified by a cyclic function, particularly rotational cyclic functions with the same frequency. The frequency can correspond to the rotational frequency of the rotor. For example, an individual offset angle for each rotor blade can be specified using a sine function. However, other functions are also possible, such as a triangular function. However, the sine function is preferred.

[0018] Furthermore, it is intended that an individual pilot control adjustment rate is determined for each rotor blade from the individual offset angle, which indicates the adjustment rate required to achieve the offset angle. In this respect, the pilot control adjustment rate is determined directly from the individual offset angle. In this respect, the implementation is similar to a control system, because the offset angle is directly transferred to the pilot control adjustment rate. Therefore, there is no comparison of the target / actual value between the specified individual offset angle and the actual or detected offset angle.

[0019] Nevertheless, it is also provided that an individual offset deviation is determined for each rotor blade depending on a comparison of the individual offset angle and a recorded, in particular measured, blade angle of the rotor blade. In particular, it is provided that an individual offset deviation is determined from the comparison of the individual offset angle and the recorded blade angle of the rotor blade, adjusted for the collective blade angle. The comparison is in particular a difference between the two values. Adjusting means in particular that the collective blade angle is subtracted from the recorded blade angle before the comparison, or the collective blade angle is added to the individual offset angle, or that the collective blade angle is subtracted after the comparison.Here, the offset deviation is intended to reflect the deviation between the specified offset angle and the individual offset angle set on the rotor blade in order to monitor the implementation. However, the offset angle is not applied to the rotor blade, but rather the sum of the collective blade angle and the individual offset; therefore, the collective blade angle is again adjusted for the comparison.

[0020] In this respect, a control system is also provided which carries out and uses this target-actual value comparison between the specified individual offset angle and the detected blade angle, as explained below.

[0021] The total pitch rate of each rotor blade is intended to be dependent on the collective blade angle and / or the collective pitch rate, the individual pilot control pitch rate and the individual offset deviation The total adjustment rate is therefore determined as a function of three variables. The collective blade angle determines the intended operating point of the wind turbine. The collective blade angle or the collective pitch rate can be considered here, or both variables together. The collective blade angle and the collective pitch rate are closely linked, and depending on the control concept, one of these two variables can be used directly, thereby establishing a relationship to the other variable. It is also possible to consider both variables directly.

[0022] From the individual pilot control pitch rate and the individual offset deviation, an individual pitch rate can be determined, which can be applied to the collective pitch rate to form the overall pitch rate for the respective rotor blade. The overall pitch rate of each rotor blade is thus composed of the collective pitch rate and the individual pitch rate. In particular, the sum of the collective pitch rate and the individual pitch rate forms the overall pitch rate.

[0023] The individual offset angle is used to determine the individual adjustment rate in two ways: firstly, via the individual pilot control adjustment rate and secondly, via the individual offset deviation. Thus, the individual offset angle is input via both a control and a closed-loop control. The control can also be referred to as the pilot control, and this therefore outputs the individual pilot control adjustment rate.

[0024] Through such a feedforward control, the individual adjustment rate can quickly and without dynamic influences that could otherwise result from a control feedback take into account the individual offset angle, which thereby immediately and directly influences the individual adjustment rate.

[0025] By taking the individual offset deviation into account, deviations can still be compensated for. However, due to the feedforward control used, such deviations are small, so a slow controller is preferable, which can achieve steady-state accuracy or at least improve quasi-steady-state accuracy with a slowly changing offset angle.

[0026] It should also be noted that in the control that takes the individual offset deviation into account, a blade angle or a blade angle deviation, namely the individual offset deviation, is converted into a pitch rate.

[0027] This allows any individual offset angle to be implemented immediately. The implementation is fast and, at the same time, achieves a high level of accuracy.

[0028] According to one aspect, it is proposed that the individual pilot control adjustment rate be determined from the individual offset angle by means of a pilot control, and that a controller adjustment rate be determined from the individual offset deviation by means of an offset controller in order to compensate for the individual offset deviation. The total adjustment rate is determined from the collective adjustment rate, the pilot control adjustment rate, and the controller adjustment rate, in particular from their sum. The individual adjustment rate is determined from the pilot control adjustment rate and the controller adjustment rate. The individual offset angle is thus taken into account in two ways.

[0029] Firstly, an individual pilot control adjustment rate is determined from the individual offset angle, namely in particular by deriving the individual offset angle. This is based in particular on the knowledge that the individual offset angle is a function that changes over time, in particular a cyclic function. A sine function is often considered. Such a time function can be derived with respect to time and, if necessary, modified with an amplification factor. The result is the individual pilot control adjustment rate. This individual pilot control adjustment rate thus indicates a planned adjustment speed of the blade angle. If the rotor blade angle is adjusted at this adjustment speed, the individual offset angle results as the rotor blade angle if the rotor blade angle would otherwise be zero.In other words, if such an individual pilot control rate is applied to a rotor blade angle with the value zero, the individual offset angle is ideally obtained.

[0030] During operation, however, the collective blade angle is added, and this can be configured as the collective pitch rate. The collective pitch rate and the individual pilot pitch rate can be added together, resulting in a pitch rate, i.e., a rate of change of the blade angle, at which the blade angle is adjusted. With ideal implementation, the result is that the rotor blade angle corresponds to the sum of the collective blade angle and the individual offset angle.

[0031] Such an approach, especially the use of feedforward control to determine the individual feedforward control rate, results in rapid implementation of both the collective blade angle and the individual offset angle. Because feedforward control is a control system, i.e., it does not involve feedback, any control oscillations can be eliminated. The individual offset angle can be specified directly and implemented using the individual feedforward control rate.

[0032] However, any deviations, especially stationary or quasi-stationary inaccuracies, cannot be taken into account by such feedforward control. A quasi-stationary inaccuracy is understood to be a tracking accuracy for a time-varying signal, particularly for a sinusoidal signal, which can be specified for the individual offset angle.

[0033] In order to achieve such steady-state or quasi-steady-state accuracy, an additional offset controller is provided, which determines a controller adjustment rate from the individual offset deviation. This allows deviations to be detected and corrected. However, it should be noted that such an offset controller is only intended to supplement the feedforward control. This still ensures fast and direct dynamic conversion of the individual offset angle into the aforementioned individual feedforward control adjustment rate, while also allowing compensation of - usually small - deviations. Accordingly, the controller gain of the offset controller can be selected so that the offset controller plays a subordinate dynamic role. In particular, controller-induced oscillation or even controller-induced instability can be avoided, while rapid conversion of the individual offset angle can still be achieved.

[0034] Preferably, a P-controller is used as the offset controller. It should be noted that this offset controller also outputs a displacement rate, i.e., a rate of change of the angle. A constant rate of change leads to a steady increase in the blade angle. The system thus exhibits integral behavior. Thus, the control loop as a whole, i.e., a P-controller with a system, also exhibits integral behavior. It has therefore been recognized that integral behavior can be achieved with an offset controller with P behavior if the controller outputs a displacement rate.

[0035] It is therefore preferably provided that the offset controller has a P controller or is designed as a P controller which converts the angle difference, i.e. the individual offset deviation, into an adjustment rate, namely the controller adjustment rate, using a corresponding P factor.

[0036] The individual pilot control adjustment rate and the controller adjustment rate can be added together and can thus together take into account or achieve the individual offset angle, i.e. its implementation.

[0037] The individual pilot control adjustment rate can then be added together with the controller adjustment rate to form the collective adjustment rate. The sum of the three adjustment rates can then be used to control the offset controller as a whole.

[0038] This can be done for each rotor blade, allowing for fast, vibration-free implementation of individual blade adjustment while maintaining high control quality.

[0039] According to one aspect, it is proposed that the pilot control adjustment rate be determined independently of the detected blade angle, in particular independently of the individual offset deviation. This embodiment emphasizes that no signal feedback from the detected blade angle is used to determine the pilot control adjustment rate. This is precisely what characterizes a control or pilot control. This allows for rapid conversion of the individual offset angle into the pilot control adjustment rate and eliminates control-related oscillation.

[0040] According to one aspect, it is proposed that the individual offset angle be specified as a temporal offset curve, in particular by a time-dependent and / or position- or rotation-dependent offset function. In this case, a rotational cyclic function is particularly suitable, which can be a sine function, particularly when the rotor rotates uniformly, i.e., when rotating at a constant speed. However, even when the rotor rotates less uniformly, assuming a sine function or specifying a sine function can be useful.

[0041] Especially with such a temporal offset curve of the individual offset angle, it is advantageous to provide and take into account the individual pre-control rate, namely in particular via the aforementioned pre-control, i.e., without feedback of the resulting blade angle. Dynamic feedback caused by feedback is avoided, and this also avoids design problems for a corresponding controller that would only take such consideration of the individual offset angle. It is particularly important to note here that the rotor speed can vary greatly depending on the situation. Accordingly, a controller design would require either a correspondingly robust controller or individual adaptation of the controller, particularly its gain, to the different speeds.

[0042] The individual offset angle can thus be specified as a temporal offset curve, but it can also be defined as a curve dependent on the rotor's rotational position. In this respect, a sine function can be defined as a function dependent on the rotor position, i.e., the rotational position of the rotor.

[0043] This is, of course, done individually for each rotor blade. For example, a 12 o'clock position, where the rotor blade points vertically upwards, can be assumed to be a rotational position with a value of 0° or 0π, which then continuously increases to 360° or 2π as the rotor rotates, once the rotor has rotated once and is back in the 12 o'clock position. This rotational position can be used as an input for a sine function for the individual offset angle. Further below, it is described to what extent the use of a sine function can be advantageous for further calculations or implementations in determining the individual pilot control rate.

[0044] According to one aspect, it is proposed that each individual offset angle is specified as a temporal offset curve with a pitch component for reducing a pitch moment and a yaw component for reducing a yaw moment.

[0045] By specifying the collective blade angle, the aim is to achieve the most optimal operating setting possible, which, together with the selected speed and generated power, should ideally form an optimal operating point. However, the wind speed is often not constant across the large rotor area swept by the rotor blades. In particular, the wind speed is often higher at higher altitudes than at lower altitudes, to put it simply and simply.

[0046] This results in cyclic load changes that must be taken into account and reduced by blade pitch adjustment. A distinction must be made between two load directions: one that leads to a pitching moment of the wind turbine nacelle and one that leads to a yaw moment of the wind turbine nacelle.

[0047] A pitching moment is a moment, or torque, that points in the nacelle's pitch direction. This movement causes the nacelle to move forward and backward, which also results in an upward and downward component in the rotor area, or the force points in this direction. The yaw moment is a moment in a direction about a vertical axis of rotation of the nacelle. An azimuth adjustment can also be made around this axis of rotation, and thus the yaw moment or the corresponding direction also points in the direction of an azimuth adjustment.

[0048] Depending on the position of the rotor blade during its rotation, the wind forces acting on the rotor blade have varying degrees of influence on the pitching moment or yaw moment. For rotor blades that are essentially vertical, the force acting in the direction of the pitching moment, and therefore the pitch component, is particularly large. If a rotor blade is essentially horizontal, the force acting on the rotor blade primarily acts as a yaw moment.

[0049] Thus, each rotor blade experiences a load in the pitch direction and a load in the yaw direction. Both loads can be cyclical with the rotation of the rotor, but with amplitudes at different rotor positions. In other words, the load in the pitch direction and the load in the yaw direction can have their own amplitude and phase. In other words, these two load functions are shifted relative to each other and exhibit different amplitudes.

[0050] To counteract every load in the pitch direction and every load in the yaw direction, each for a rotor blade, the temporal offset curve of the individual offset angle of the respective rotor blade has a component that counteracts the pitching moment, referred to as the pitch component, and a component that counteracts the yaw moment, referred to as the yaw component. The pitch component and the yaw component, which can thus be formed or viewed as a partial blade angle curve, can in turn also be formed in a rotational cycle with the rotation of the rotor, with their own amplitudes and phase angles or phase positions. The pitch component and the yaw component are themselves phase-shifted or phase-shifted with respect to each other.

[0051] The plan here is to provide each individual offset angle as a temporal curve that has a pitch component and a yaw component. The pitch component and the yaw component are superimposed in this single temporal offset curve.

[0052] Because both components are superimposed in the temporal profile of the individual offset angle, only one such temporal profile of the individual offset angle is required. The individual pilot control rate of the rotor blade can thus be determined based solely on this single temporal offset profile. In particular, a corresponding pilot control requires only one temporal profile of the individual offset angle as an input variable.

[0053] According to one aspect, it is proposed that each individual offset angle be specified as a temporal offset curve by a time-dependent offset function in order to reduce a pitching moment and a yaw moment. The temporal curve of the time-dependent offset function is characterized by an amplitude parameter and a phase parameter. The amplitude parameter and the phase parameter take into account a reduction in both the pitching moment and the yaw moment, i.e., simultaneously. In particular, the amplitude parameter and the phase parameter each take into account a pitch component and a yaw component.

[0054] Considering the pitch component individually as a temporal, cyclical curve, particularly as a sinusoidal curve, can be described by a corresponding function of amplitude and phase, specifically depending on the rotor position. A rotor rotating evenly or approximately evenly, i.e., a constant or approximately constant speed, also results in a corresponding temporal function. A function can be provided for the yaw component in the same way. Both components differ in amplitude and phase, but not in frequency, because they both depend on the same rotating rotor position, i.e., the same speed.

[0055] Here, it was recognized that two such functions can be combined into a new function with amplitude and phase, which is referred to here as the amplitude parameter and the phase parameter, respectively. The amplitude parameter thus considers both amplitudes of the individual functions mentioned, and the phase parameter considers both phases of the individual functions mentioned. This joint function can be determined, especially when assuming two sine functions with the same frequency.

[0056] The pitch component and the yaw component can therefore be taken into account simultaneously by one function.

[0057] According to one aspect, it is proposed that at least one amplitude limit value be specified for the offset curve, a check is performed for each rotor blade to determine whether the offset curve reaches the amplitude limit value, and if it is reached, the switching of the individual pilot control adjustment rate to the collective adjustment rate is interrupted, in particular such that one or the controller adjustment rate continues to be switched to the collective adjustment rate. In particular, the controller adjustment rate continues to be switched to the collective adjustment rate, i.e., they are added together to form the total adjustment rate. The total adjustment rate is then the sum of the collective adjustment rate and the controller adjustment rate.

[0058] The pilot control adjustment rate is therefore no longer switched to the collective adjustment rate when it is detected that the offset curve reaches or exceeds the amplitude limit value.

[0059] An amplitude limit is thus a minimum angle for each individual offset angle that must not be undercut, or a maximum angle that must not be exceeded. It is possible to specify a minimum angle and a maximum angle for each individual offset angle, so that the offset angle should remain between the minimum and maximum angles, or to check for this.

[0060] Here, it is specifically assumed that the offset curve is cyclical, particularly sinusoidal, which is generally below the amplitude limit, but can reach or even exceed the amplitude limit at its maximum points. It can therefore exceed a maximum angle or fall below a minimum angle. In particular, the assumption here is that the offset curve is constantly determined depending on recorded loads or other operating conditions. Therefore, the offset curve can fluctuate in its amplitude.

[0061] If such a fluctuation causes the offset curve to temporarily reach, or would reach, the amplitude limit, it is now suggested not to limit the offset curve to this amplitude limit, i.e., to cut it off at the level, but rather to simply interrupt the activation of the pilot control adjustment rate. Thus, only the pilot control is deactivated. The control system that outputs the controller adjustment rate remains active.

[0062] This will, in particular, avoid the described truncation of a cyclic function. It was particularly recognized that the proposed feedforward control performs a derivation of the offset curve. If this offset is truncated, an unphysical break occurs, which can lead to undesirable effects during the derivation. Deactivating the feedforward control avoids this problem. However, because the controller remains active, the offset angle can still be taken into account, albeit not as well as with the feedforward control.

[0063] It was also recognized that the proposed individual blade adjustment, i.e. the specification of the individual adjustment rate, represents an improvement and relief of the wind turbine, and in particular can also extend the overall operating time, but it is acceptable that such individual blade adjustment is occasionally and temporarily weakened.

[0064] According to one aspect, it is proposed that the offset curve is specified using the following offset function f(t): f t = A*sin ω * t + ϕ where A denotes a predeterminable amplitude, ω describes a speed of the rotor and φ describes a predeterminable angular displacement relative to a reference angle.

[0065] Using such an offset function, the offset curve can be characterized by the amplitude A and the angular displacement φ. The amplitude A can also be referred to as the amplitude parameter, and the angular displacement φ as the phase parameter. This offset function allows both a pitch component and a yaw component to be considered simultaneously.

[0066] This offset function can also be easily and continuously derived. The derivative can be determined in advance, at least partially, resulting in a function dependent on the amplitude A and the angular displacement φ. This derivative, or a corresponding, particularly proportional, variable, can form the output of the feedforward control and / or the individual feedforward adjustment rate. The individual feedforward adjustment rate is then already permanently available as a function, of which only the parameterization needs to be adjusted, namely as a function of the specifiable amplitude A and the angular displacement φ, as well as the rotor speed ω.

[0067] This avoids a derivation in the feedforward control during operation. This simplifies the computational effort and also avoids any noise amplification that can occur when a noisy signal is derived during operation.

[0068] If the amplitude A and / or the angular displacement φ are time-dependent, only they would need to be derived. If they are constant, no further derivation is required.

[0069] According to one aspect, the method is characterized in that the pilot control adjustment rate is specified as a pilot control curve via the following pilot control function v(t): v t = A*cos ω *t + ϕ * ω + d ϕ / dt + dA / dt * sin ω * t + ϕ where A denotes a predeterminable amplitude, ω describes a speed of the rotor and φ describes a predeterminable angular displacement relative to a reference angle.

[0070] This feedforward control function v(t) is particularly derived from the offset function f(t)=A*sin(ω*t+φ) when the amplitude A and the angular displacement φ are time-dependent quantities or functions. Thus, the specified amplitude A and the specified angular displacement φ correspond to the corresponding values ​​of the aforementioned offset function f(t)=A*sin(ω*t+φ).

[0071] A particular advantage of this is that parts of the feedforward function v(t), i.e., parts of the derivative, can be predetermined or precalculated. For operational use, it is sufficient to insert the corresponding variables into the feedforward function v(t) or to derive the predefined amplitude A and the predefined angular displacement φ. This predefined amplitude can also form the previously described amplitude parameter, and the predefined angular displacement φ can form the previously described phase parameter, especially if these are constant values.

[0072] The predeterminable amplitude A and / or the predeterminable angular displacement φ can be determined, in particular, as a function of load detection. Such load detection can be performed directly on the rotor blade in question, in particular at its blade root or near the blade root, or can be determined in another way, for example, by observing blade bending. When determining both the amplitude A and the angular displacement φ, there may still be some design freedom, such as filtering as described below, so that neither the amplitude A nor the angular displacement φ necessarily have to be clearly determined from the loads. Therefore, they can at least be specified by selecting their calculation method.

[0073] According to one aspect, it is proposed that the amplitude A and the angular displacement φ of the offset function f(t)=A*sin(ω*t+φ) be determined as a function of a load detection. Such a determination as a function of the load detection has already been explained above. In particular, it is considered that a pitching moment and a yaw moment are detected, or that a pitching moment component of the respective rotor blade and a yaw moment component of the respective rotor blade are detected. These can each be characterized by a sinusoidal function with amplitude and phase angle, i.e. angular displacement, with the frequency being the same. From this, a sinusoidal function can be derived for both loads, i.e. for the pitching moment and the yaw moment, so that an amplitude and an angular displacement for both together result for each rotor blade.

[0074] In particular, it is proposed that the amplitude A and / or the angular displacement φ form filtered variables. Here, particular consideration is given to the fact that, during further calculations to determine the pilot control adjustment rate, a derivation is performed, which may also include a derivation of the amplitude A and the angular displacement φ. A higher-frequency disturbance variable, especially noise, superimposed on the amplitude or angular displacement can be detrimental to the derivation. Filtering can solve, or at least reduce, the problem.

[0075] In particular, it is proposed that a pre-amplitude Av and / or a pre-angular shift φv be determined depending on the load recording. Basically, the pre-amplitude Av corresponds to the unfiltered amplitude A and the pre-angular shift φv to the unfiltered angular shift φ. Accordingly, the amplitude A or the angular shift φ is determined from the pre-amplitude Av and / or the pre-angular shift φv by filtering the pre-amplitude Av or the pre-angular shift φv. It is also possible to specify a ramp as the maximum rate of change for the pre-amplitude Av and / or for the pre-angular shift φv, or instead of a filter. This avoids excessive increases and thus specifies the maximum amplitude of the time-derived signal.

[0076] Alternatively, it is proposed to specify the amplitude A and the angular displacement φ as constant values ​​depending on a load measurement, thus allowing a simplified feedforward control function vs(t) to be specified from a derivative of the offset function f(t)=A*sin(ω*t+φ). This results in the following simplified feedforward control function vs(t): vs t = A*cos ω * t + ϕ * ω

[0077] Such a simplified feedforward control function vs(t) is particularly easy to predict and, in online applications, avoids the need for a continuous derivation of the amplitude A and the angular displacement φ. Instead, only these simplified constant values ​​need to be determined, in particular from the load acquisition described above—in particular from a pitch moment component and a yaw moment component. These values ​​can then simply be entered into this simplified feedforward control function vs(t), along with the rotor speed ω. This also avoids the problems associated with deriving noisy signals.

[0078] However, it is specifically suggested that these two quantities, namely the amplitude A and the angular displacement φ, be assumed to be constant only for the purpose of derivation. For simplicity, it is thus assumed that these quantities are constant. However, it has been shown that such an assumption is often permissible. In particular, it can often be assumed that these two quantities change only slowly.

[0079] Here, it was particularly recognized that although the offset function has a time-varying curve, namely a sinusoidal function, the amplitude A and the angular displacement φ, as characteristic quantities of this function, change much more slowly. Thus, this simplified pre-control function can be specified while still taking into account a changing amplitude A and a changing angular displacement Φ.

[0080] According to the invention, a wind turbine is also proposed. The wind turbine has a rotor with multiple rotor blades. The rotor blades are adjustable in their blade angle, and each rotor blade is individually controllable. Furthermore, the wind turbine has a control device and is configured to perform individual blade adjustment. The wind turbine, in particular its control device, is configured to perform a method according to one of the aspects described above. For this purpose, the method can be implemented in the wind turbine, in particular in the control device.

[0081] According to one aspect, the wind turbine is provided with a detection device for detecting a load on a wind turbine. This can particularly be load-measuring devices such as strain gauges on the rotor blade in the area of ​​its blade root.

[0082] In particular, the detection device is configured to detect a pitch moment component and a yaw moment component for each rotor blade. The wind turbine, in particular the control device, is configured to determine an individual offset angle for the respective rotor blade from the detected pitch moment component and the detected yaw moment component. Furthermore, the wind turbine or its control device is configured to determine an individual pre-control adjustment rate for the respective rotor blade from the individual offset angle.

[0083] The details of this can be found in the description of the relevant procedural aspects, as explained above.

[0084] For the wind turbine, but also for the process as a whole, it is also possible that the pre-control adjustment rate is determined directly from recorded loads, in that an explicit output of the individual offset angle as an intermediate value may be dispensable.

[0085] The individual offset deviation can be derived from the pilot control adjustment rate, or an individual offset angle can be determined for the offset deviation, for example from the recorded loads, but without being used for the pilot control adjustment rate.

[0086] The invention is explained in more detail below using exemplary embodiments with reference to the accompanying figures. Figure 1 shows a wind turbine in a perspective view. Figure 2 shows a schematic control structure of a conventional single-blade adjustment. Figure 3shows a schematic diagram of a single-blade control via an adjustment rate specification. Figure 4 shows a schematic control structure of a single blade adjustment via a pitch rate with feedforward control and offset controller for controlling the single blade angle to be applied. Figure 5 shows schematically an overall structure of a single-blade adjustment with feedforward control and offset controller for the offset angle to be applied. Figure 6 shows a simplified diagram of a possible offset angle curve of a rotor blade.

[0087] Fig. 1shows a schematic representation of a wind turbine according to the invention. The wind turbine 100 has a tower 102 and a nacelle 104 on the tower 102. An aerodynamic rotor 106 with three rotor blades 108 and a spinner 110 is provided on the nacelle 104. During operation of the wind turbine, the aerodynamic rotor 106 is set in rotation by the wind and thus also rotates an electrodynamic rotor or rotor of a generator, which is directly or indirectly coupled to the aerodynamic rotor 106. The electrical generator is arranged in the nacelle 104 and generates electrical energy. The pitch angles of the rotor blades 108 can be changed by pitch motors at the rotor blade roots 109 of the respective rotor blades 108.

[0088] Fig. 2shows a control structure 200 relating to a conventional blade pitch control with individual blade adjustment. The structure shows an operating control block 202 that specifies a collective blade angle α C . This operating control block 202 contains, for example, a known speed control that outputs the blade angle as a manipulated variable to control the speed. This operating control thus relates to a blade angle that is the same for all rotor blades, which is referred to as the collective blade angle. It can also be synonymously referred to as the common blade angle.

[0089] In addition, a single-blade control 204 is provided, which provides an offset angle α of for each rotor blade. Fig. 2 the structure for a single blade. Typically, a wind turbine has three rotor blades, and therefore three such control structures would be required.

[0090] The offset angle α of and the collective blade angle α C are added at the first summing point 206 to form the nominal blade angle α S . Therefore, with three rotor blades and correspondingly three structures, three nominal blade angles result. However, since only the structure for one rotor blade is shown here for illustrative purposes, any indices indicating a specific rotor blade are omitted. The presented structure is therefore identical for all rotor blades.

[0091] The desired blade angle α S is then compared with a detected actual angle α i at the second summing point 208. The result is a control deviation, which is further processed in the blade control according to the blade control block 210 to control the schematically illustrated wind turbine 212 or the corresponding pitch motor of the rotor blade. This results in the detected blade angle α i , which is fed back as described.

[0092] Such a structure according to Fig. 2 Thus, individual blade pitch control is feasible, but the control dynamics can be unfavorable due to the specification of the absolute blade angle for the collective blade angle. In particular, it has been shown that a collective pitch rate, also known as the collective pitch rate, can be advantageously specified via the operating control block instead of a collective blade angle.

[0093] Such a structure is in Fig. 3 The control structure 300 of the Figure 3 thus also has an operating control block 302, which can also include speed control and other operating controls and can thereby generate a collective blade angle. However, in this structure, the operating control block 302 outputs a collective blade rate Rc.

[0094] A single-blade control 304 is also provided, which outputs an offset angle α of . This is compared with a detected blade angle α' i at a third summing point 314. The detected blade angle α' i can thus be an actual blade angle adjusted for the collective blade angle. However, it is also possible for the actual blade angle to be fed to the third summing point 314, while the offset angle α of is adjusted for the collective blade angle. In any case, the difference formation at the third summing point 314 results in a control deviation that indicates how far the offset angle α of has been successfully applied.

[0095] The blade angle deviation is then fed to the offset controller 316, which determines an individual pitch rate R of . This individual pitch rate R of and the collective pitch rate Rc are summed in the first summing point 306 and result in the desired pitch rate for the respective rotor blade.

[0096] In the second summing point 308, a comparison of the setpoint actual value with the actual adjustment rate or actual pitch rate R i , which was recorded at the wind turbine 312, is carried out. This control deviation, as the output of the second summing point 308, is then implemented in the adjustment rate control 310 and leads to a control of the wind turbine, in particular a corresponding pitch drive system.

[0097] The problem with this structure of Figure 3is that the offset angle is compared with a detected blade angle and the deviation is corrected using the offset controller 316. While such correction is desirable, control behavior with good steady-state accuracy can lead to poor, particularly slow, dynamics. In particular, the offset controller 316 can have a proportional or integral behavior and / or sluggish dynamics to avoid excessive control excursions when the reference variable changes. In other words, a controller for steady-state accuracy is designed to correct even small deviations. It can do this slowly, so that it is then sluggish overall, or quickly, which can, however, lead to strong control activities when the reference variable changes.

[0098] Fig. 4 shows a control structure 400, which in this respect corresponds to the control structure 300 of the Fig. 3is intended to achieve an improvement and explains the solution according to the invention. First, a collective adjustment rate Rc is output in an operating control block 402. Operating control blocks 402 and 302 can be identical.

[0099] A single-blade control 404 is also provided, which outputs an offset angle α of . To better explain the functionality, the control structure 400 shows that the single-blade control 404 outputs the offset angle α of twice. However, this is for illustrative purposes, and it could just as easily be provided to output the offset angle α of only at one point, or another structural implementation could be considered, in which, for example, the pilot control adjustment rate is derived directly from load data.

[0100] In any case, it is intended that the offset angle α of is input, among other things, to the pilot control 418. The pilot control 418 determines an individual pilot control adjustment rate R v from the individual offset angle α of . This pilot control adjustment rate R v is intended to essentially implement the offset angle α of and should be added to the collective adjustment rate Rc to obtain a total target adjustment rate.

[0101] For this purpose, the feedforward control 418 can calculate a derivative of the offset angle α of , possibly providing it with a gain factor, in order to directly determine a corresponding adjustment rate. However, equivalent implementations can also be carried out, such as performing a simplified derivation, performing a preliminary filtering, and / or calculating part of the derivation in advance. It is also possible to simplify the derivation to such an extent that the derivation can be fully calculated in advance, requiring only specific parameters to be used depending on the situation.

[0102] Such feedforward control allows a corresponding adjustment rate to be implemented quickly and precisely for the offset angle. A stationary or quasi-stationary deviation can neither be detected nor corrected.

[0103] Therefore, it is additionally provided to compare the offset angle α of in the third summing point 414 with a detected blade angle α' i. As in the control structure of the Fig. 3 The detected blade angle can be a modified blade angle, namely a measured blade angle modified by a collective blade angle. Here, too, a modification by the collective blade angle can be made instead in the offset angle α of . In this case, however, such a modification would only be performed for the offset angle α of , which is input to the third summing point 414. The value input to the feedforward control 418 should not be modified.

[0104] In any case, a setpoint-actual value comparison is carried out in the third summing point 414 and, depending on this, a controller adjustment rate R r is determined. This is done by means of the offset controller 416, which can now be parameterized differently than the offset controller 316 of the Fig. 3, because the offset controller 416 of the Fig. 4 A fast, dynamic conversion of the offset angle α of into a pilot control adjustment rate is not required. The offset controller 416 can be specifically designed to simply compensate for or otherwise take into account a controller deviation.

[0105] The pilot control adjustment rate R v and the controller adjustment rate R r are added at the fourth summing point 420 to form the individual adjustment rate R of. This individual adjustment rate R of is thus the total adjustment rate for the offset angle generated by the pilot control 418 and the offset controller 416. It is added to the collective adjustment rate Rc at the first summing point 406, resulting in the total target adjustment rate Rs. This can then be calculated similarly to Fig. 3in the second summing point 408, the measured actual pitch rate R i is compared, resulting in a control error. This error is implemented in the blade rate control 410, which then controls the wind turbine 412, in particular the corresponding blade pitch system.

[0106] Fig. 5 illustrates a general overview of the underlying method. A wind turbine 512 is indicated. This wind turbine 512 has three rotor blades 552, of which only two are visible in the schematic representation. Each of these rotor blades 552 has several load sensors 554. These can be provided as strain gauges on the respective rotor blade 552 in the area of ​​a rotor blade root, to name one example.

[0107] It is schematically indicated that corresponding load signals L are passed to an evaluation block 556. This evaluation block evaluates these measured values ​​and can also take into account other operating data, such as the rotor speed ω and the respective rotor position Φ.

[0108] Depending on this, the evaluation block 556 can calculate a pitch moment component m N and a yaw moment component m G. This is illustrated by the pitch moment block 558 and the yaw moment block 560. The pitch moment component m N and the yaw moment component m G therefore do not constitute the entire pitch moment or yaw moment, but only the portion that can be assigned to the respective rotor blade being evaluated. Fig. 5 only the evaluation for one rotor blade.

[0109] In the pitching moment block 558 and the yaw moment block 560, an offset function is then calculated, f N (t) for the pitching moment and f G (t) for the yaw moment. This offset function specifies how an offset angle curve could be selected as a function of the rotational speed ω of the rotor 551 in order to compensate for the pitching moment component mr or the yaw moment component m G as much as possible. This is illustrated by the first and second individual offset blocks 561 and 562, respectively. The partial offset functions shown in these two blocks are combined in the overall offset block 564 into a common offset function f(t).

[0110] This offset function f(t) thus represents a time function for the offset angle α of. Accordingly, the total offset block 564 outputs the offset angle α of. This is also done here in the representation of the Fig. 5illustratively so that two offset angles α of are output, which can be identical. The total offset block 564 can thus be assigned to the single sheet control 404 of the Fig. 4 The further processing of the offset angle α of thus also corresponds to the Figure 4 depicted.

[0111] Thus, a pre-control 518 is provided, in which Fig. 5 It is made clear that it is essentially a derivative. This feedforward control 518 also does not necessarily have to be an exact derivative; simplifications and / or additional functions such as filtering or the provision of a gain factor can also be considered. The result is thus a feedforward control adjustment rate R v .

[0112] In addition, an offset controller 516 is provided, which receives a control deviation as the difference between the offset angle α of and a detected blade angle α' i . Here, too, it should be noted that the detected blade angle α' i can be modified by the collective α C . Alternatively, the offset angle α of entering this third summing point 514 can be modified.

[0113] The offset controller 516 thus outputs a controller adjustment rate R r and this is added to the individual adjustment rate R of at the fourth summing point 520.

[0114] The individual pitch rate R of is finally added to the collective pitch rate Rc at the first summing point 506, resulting in the target pitch rate Rs, i.e., the total target pitch rate. This target pitch rate Rs is then input to the operating control block 502, which previously also generated the collective pitch rate Rc. This operating control block 502 thus performs several functions, i.e., more functions than the operating control block 402 of the Figure 4 . The second summing point 408 of the Fig. 4 can be analogously in the operation control block 502 of the structure of the Figure 5 In any case, the operating control block 502 interacts with the wind turbine 512, or rather, it is also part of the wind turbine 512, and can thus intervene in a controlling manner as well as receive, evaluate, and forward measured values.

[0115] Thus, loads are recorded, the pitch and yaw moments are taken into account, a total offset function is generated to determine the offset angle, and the individual blade pitch adjustment is performed based on this. The individual blade pitch adjustment is performed by specifying an individual pitch rate R of , which depends on the feedforward control 518 and the offset controller 516. This is then added to the collective pitch rate Rc to obtain a target pitch rate Rs. This target pitch rate Rs then takes into account both the blade setting for general system control and the individual load reduction.

[0116] Fig. 6 illustrates such an offset function f(t). It is plotted here as a function of the rotor angle Φ and is obviously cyclical over 360°. It can be viewed as a sine function.

[0117] It does not pass through the origin but intersects the abscissa at the angular displacement φ. The angular displacement is relative to a reference angle and can be considered zero here.

[0118] In this respect, the Figure 6 the offset function as the course of the offset angle α of . An amplitude limit value α max can be provided for the offset angle α of . A horizontal dashed line is also drawn for this. If the offset function f(t), i.e. the offset angle α of , reaches this amplitude limit value α max , the offset function f(t) would have to be truncated, which is illustrated in the diagram by the function section α S . The dashed course of the offset function f(t), α S ', must not be implemented.

[0119] However, it is suggested not to truncate the offset function, as illustrated by section α S, but to temporarily interrupt the feedforward control. During the interruption, measured value acquisition and evaluation can continue, thus continuing normally. Control of the offset angle can also remain active, but the feedforward control and thus the activation of the feedforward adjustment rate are temporarily deactivated.

[0120] Illustrated by the flow chart of the Fig. 5 Thus, only the precontrol 518 is deactivated. The entire offset block 564 can continue to calculate the offset function f(t) despite the interruption of the individual blade adjustment, and it can then be determined whether the amplitude limit value α max is still being reached or would be reached. The precontrol 518 can then be reactivated accordingly.

Claims

1. A method for controlling a wind power installation (100), wherein - the wind power installation has a rotor (106) with a plurality of rotor blades (108), - the rotor blades (108) are adjustable in their blade angle, - each rotor blade (108) is activatable individually, - for the individual activation, in each case a total adjustment rate Rof which indicates an intended speed of change of the respective blade angle is predetermined, - a collective blade angle identical for all of the rotor blades (108) is provided, - a collective adjustment rate (Rc) identical for all of the rotor blades describes an intended speed of change of the collective blade angle, - an individual offset angle (αof) which indicates a value by which the blade angle is intended to deviate from the collective blade angle (αc) is predetermined for each rotor blade, - an individual feed forward control adjustment rate which indicates an adjustment rate which is provided for reaching the offset angle is determined for each rotor blade (108) from the individual offset angle, - an individual offset deviation is determined for each rotor blade depending on a comparison of the individual offset angle (αof) and a detected blade angle of the rotor blade, and - the total adjustment rate of each rotor blade is determined depending on - the collective blade angle and / or the collective adjustment rate, - the individual feed forward control adjustment rate, and - the individual offset deviation.

2. The method as claimed in claim 1, characterized in that - the individual feed forward control adjustment rate is determined from the individual offset angle by means of a feed forward control (414), and - a feedback controller adjustment rate is determined from the individual offset deviation by means of an offset feedback controller (416) in order to adjust the individual offset deviation, wherein - the total adjustment rate is determined from the collective adjustment rate, the feed forward control adjustment rate and the feedback controller adjustment rate, in particular from the sum thereof.

3. The method as claimed in claim 1 or 2, characterized in that the feed forward control adjustment rate is determined independently of the detected blade angle, in particular independently of the individual offset deviation.

4. The method as claimed in one of the preceding claims, characterized in that the individual offset angle is predetermined as a temporal offset profile, in particular by an offset function which is time-dependent and / or dependent on a position or rotation of the rotor.

5. The method as claimed in one of the preceding claims, characterized in that each individual offset angle is predetermined as a temporal offset profile having - a pitching component for reducing a pitching moment, and - a yaw component for reducing a yaw moment, in particular in that - the pitching component and the yaw component are combined in the temporal profile of the individual offset angle.

6. The method as claimed in one of the preceding claims, characterized in that each individual offset angle is predetermined as a temporal offset profile by a time-dependent offset function, in particular cyclic offset function, in order - to reduce a pitching moment and a yaw moment, wherein - the temporal profile is characterized by an amplitude parameter (A) and a phase parameter (φ) and - the amplitude parameter (A) and the phase parameter (φ) take into consideration a reduction in the pitching moment and the yaw moment, in particular in that - the amplitude parameter and the phase parameter each take into consideration a pitching component and a yaw component.

7. The method as claimed in one of the preceding claims, characterized in that - at least one amplitude limit value is predetermined for a or the offset profile, - it is checked for each rotor blade whether the offset profile reaches the amplitude limit value, and - if it is reached, connection of the individual feed forward control adjustment rate to the collective adjustment rate is interrupted, in particular such that a or the feedback controller adjustment rate continues to be connected to the collective adjustment rate.

8. The method as claimed in one of the preceding claims, characterized in that a or the offset profile is predetermined via the following offset function f(t): f t = A*sin ω * t + ϕ wherein A denotes a predeterminable amplitude, ω describes a rotational speed of the rotor, and φ describes a predeterminable angular displacement relative to a reference angle.

9. The method as claimed in one of the preceding claims, characterized in that the feed forward control adjustment rate is predetermined as a feed forward control profile via the following feed forward control function v(t): v t = A*cos ω * t + ϕ * ω + d ϕ / dt + dA / dt*sin ω * t + ϕ wherein A denotes a or the predeterminable amplitude, ω describes a or the rotational speed of the rotor, and φ describes a or the predeterminable angular displacement relative to a reference angle.

10. The method as claimed in one of the preceding claims, characterized in that - a or the amplitude A and a or the angular displacement φ of a or the offset function f(t) = A*sin(ω*t+φ) are determined depending on detection of a loading, and in particular - the amplitude A and / or the angular displacement φ form filtered variables, in particular such that - depending on the detection of a load, a preliminary amplitude Av and / or a preliminary angular displacement φv are ascertained, and - the amplitude A and / or the angular displacement φ are each determined from the preliminary amplitude Av and / or the preliminary angular displacement φv by filtering of the preliminary amplitude Av and / or the preliminary angular displacement φv, and / or in each case by predetermining a ramp as the maximum speed of change for the preliminary amplitude Av and / or for the preliminary angular displacement φv, or depending on detection of a load, the amplitude A and the angular displacement φ are predetermined as constant values and therefore a simplified feed forward control function vs(t) is predetermined from a derivation of the offset function f(t) = A*sin(ω*t+φ) as: vs t = A*cos ω * t + ϕ * ω .

11. A wind power installation (100), wherein - the wind power installation (100) has a rotor (106) with a plurality of rotor blades (108), - the rotor blades (108) are adjustable in their blade angle, - each rotor blade (108) is activatable individually, and - the wind power installation (100) has a control device (502) and is set up for carrying out an individual blade adjustment, and wherein - the wind power installation, in particular the control device (502), is designed to carry out a method as claimed in one of claims 1 to 10.

12. The wind power installation as claimed in claim 11, characterized in that - the wind power installation (100) has a detection device (554) for detecting a loading of the wind power installation, in particular - for detecting a pitching moment component and a yaw moment component for each rotor blade (108), and wherein the wind power installation (100), in particular the control device (502) is set up so as to determine, from the detected pitching moment component and the detected yaw moment component, an offset angle individual to the rotor blade (108) concerned, and to determine an individual feed forward control adjustment rate therefrom for the rotor blade concerned.