Estimation of inertial response power of wind turbines

Abstract

A method for estimating an additional power output (69, Pavail) for an inertial response (IR) is described, the additional power output being available for output over a preset inertial response time interval (65, #imgabs0#), the method comprising: obtaining current values ​​(77, 79; 43, 45) of at least a rotational speed (Ȧ) of a wind turbine rotor (13) and a power output (P) of the wind turbine (3); deriving the additional power output (69, Pavail) based on the obtained current values ​​(77, 79; 43, 45) and a remaining time interval (91) of the preset inertial response time interval (65, #imgabs1#), in particular such that the additional power is available for output over the entire predetermined time interval (65, #imgabs2#).

Description

Technical Field

[0001] The present invention relates to a method and an arrangement for estimating an additional power output of a wind turbine power output for an inertial response, in particular an additional power output over a current value of the power output, which additional power output will be available for output over a preset inertial response time interval. Furthermore, the present invention relates to a wind turbine comprising the arrangement and adapted to perform the method. Background Art

[0002] Traditionally, wind turbines provide electricity to a utility grid to which a plurality of consumers are connected. In the event of an electrical disturbance in the grid, in particular a decrease in the frequency of the AC power in the grid due to an imbalance in the power available within the utility grid and the power consumed by the consumers, a so-called "inertial response" of the wind turbines or the entire wind park may be required and may be requested, for example, by the operator of the utility grid. In such an inertial response, the wind park or individual wind turbines may be required to deliver more power than previously provided to the utility grid, or to deliver more power than the nominal power.

[0003] In particular, when an inertial response is performed at a wind turbine, the wind turbine may be required to deliver a specific amount of additional power within a specific time interval. The additional power may be obtained from the rotational energy stored in the rotor of the wind turbine. When the additional power is delivered within a specific time interval, the rotational speed of the rotor may be reduced in most cases. In other cases (e.g., high winds or reduced power operations), pitching can prevent or reduce the drop in the rotor speed. When the rotational speed of the rotor is reduced, the wind turbine may no longer be able to provide the required specific amount of additional power. If the power capacity (of the wind turbine) does not allow the required power to be delivered to the grid, the duration of the response may be a priority. That is, the required additional power may not be delivered in the required total amount. The problem is to estimate the maximum additional power that can be delivered within a specific number of seconds so that a constant power can be delivered during the inertial response.

[0004] Traditionally, the maximum additional power may have been determined as the difference between the maximum power available at a given rotational speed and the current power supplied to the utility grid. However, it has been observed that this solution is cumbersome because once the estimated additional power is delivered, the rotor speed decreases. This traditionally results in a limited response due to the maximum power curve.

[0005] Furthermore, conventionally, in case the acceleration of the rotor speed is lower / higher than expected, a function called a "kinetic drop estimator" may have been developed to compensate for the estimation. However, this also results in a response with high additional power at the beginning of the inertial response, but with reduced power during the inertial response, since the power is limited by the electrical capacity of the wind turbine. The kinetic drop estimator may be very sensitive due to the use of the rotor acceleration derived from the measured rotor speed, and may make the inertial response much less certain.

[0006] Therefore, there may be a need for a method and arrangement for estimating additional power output of a wind turbine for inertial response, which additional power output will be available for output over a preset inertial response time interval, with improved reliability and accuracy. Summary of the invention

[0007] This need is met by the subject matter according to the independent claims. The dependent claims describe advantageous embodiments of the invention.

[0008] According to an embodiment of the present invention, a method for estimating a (particularly maximum) additional power output (an additional power output of a wind turbine power output, particularly an additional power output exceeding a current value of the power output) for an inertia response is provided, the additional power output to be available for output over a preset inertia response time interval, the method comprising: obtaining current values ​​of at least a rotation speed of a wind turbine rotor and a power output of the wind turbine; deriving the additional power output based on the obtained current values ​​and a remaining time interval of a preset inertia response time interval (particularly a difference between a current time point and an end time point of the inertia response), particularly making the additional power available for output over the entire predetermined inertia response time interval.

[0009] The additional power output may in particular be an additional active power output of the wind turbine. The additional power output may be a maximum active power output by the wind turbine over the entire preset inertia response time interval that is higher or exceeds the active power currently output. The additional power output may be estimated such that the estimated additional power output may actually be output during the preset inertia response time interval.

[0010] The preset inertial response time interval may be set, for example, by a utility grid operator or by a wind farm operator, or at a park level or at a turbine level. The preset inertial response time interval may be, for example, between 1 second and several minutes, in particular between 5 seconds and 5 minutes, further in particular between 5 seconds and 20 seconds.

[0011] The inertial response may involve operation of the wind turbine during which additional (e.g., active) power output is provided to the utility grid. The inertial response may be requested, for example, from a utility grid operator or a wind turbine operator or controller. For example, in the event of a frequency drop in the utility grid, an inertial response may be initiated or requested. The frequency of the AC power within the utility grid may decrease when, for example, the amount of generated power provided to the utility grid is less than the power consumed by consumers. In this case, the wind turbine may be required to provide additional power output to the utility grid in order to restore the balance between generated power and consumed power and thereby restore the nominal frequency (e.g., 50 Hz or 60 Hz) of the utility grid.

[0012] The method may be applied to a single wind turbine, or may be applied to a plurality of wind turbines of a wind park, for example in parallel.

[0013] The current values ​​of the rotational speed of the wind turbine rotor and the power output of the wind turbine may be related to actual measured or derived values ​​and may be continuously updated.The rotational speed of the wind turbine rotor may be related to the electrical rotational speed or the mechanical rotational speed of the wind turbine rotor.

[0014] The power output of the wind turbine may in particular be related to the active power output of the wind turbine, which active power output may be determined, for example, by measuring electrical quantities, such as voltage and current at the output terminals of the wind turbine. The wind turbine may in particular comprise a permanent magnet synchronous motor as a generator, which is coupled to a rotor, at which a plurality of rotor blades are connected. Furthermore, a converter may be connected to the output terminals of the generator, the converter in particular comprising an AC-DC part, a DC link and a DC-AC part, the converter being capable of converting a variable frequency AC power flow into a substantially fixed frequency AC power flow. Furthermore, downstream of the converter, a wind turbine transformer may be provided for transforming the output power flow to a higher voltage.

[0015] The method may be started (immediately) before the initiation of the inertial response and may continue throughout the inertial response duration, i.e. throughout a preset inertial response time interval. The method may, for example, be run all the time during the operation of the wind turbine. The inertial response may, for example, be started at a starting time point of the inertial response and may be terminated at an ending time point of the inertial response. The remaining time interval may be the difference between the ending time point of the inertial response and a current time point, which is in particular after the inertial response has started. Thus, the method may continuously and repeatedly derive the additional power output based on a continuously updated current value and a continuously updated remaining time interval. Thus, changes in external or environmental conditions may be taken into account, in particular for improving the reliability and / or accuracy of the derived additional power output.

[0016] In particular, the method is designed to derive the additional power output so that the derived additional power output is actually available for output to the utility grid during the entire predetermined inertia response time interval. Therefore, in an ideal case, the additional power actually output during the entire predetermined inertia response time interval does not need to vary by more than 10%, in particular more than 5%, and can therefore be substantially constant. Therefore, stabilizing the electrical properties of the utility grid can be achieved in an improved manner. According to an embodiment of the present invention, the method uses a starting prior-value corresponding to the operating state before or when the inertia response is initiated as the current value, and uses the preset inertia response time interval as the remaining time interval.

[0017] The previous value of the power output may be related to a previous value of the active power output of the wind turbine, which may in particular be lower than the maximum power that the wind turbine can output according to a power curve related to the rotational speed and the maximum power. Furthermore, the previous value of the rotational speed may be higher than a lower limit of the rotational speed. The operating state may be defined by at least the rotational speed value and the power output value. Furthermore, other operating parameters may be included, such as a pitch angle, etc.

[0018] According to an embodiment of the present invention, the current value and the remaining time interval are updated throughout the preset inertia response time interval, and the additional power output is repeatedly derived based on the updated values.

[0019] The current value of the rotational speed and / or the power output may vary due to changes in environmental conditions, such as changes in wind speed, but may also vary due to the additional output power. While executing the method, the remaining time interval may be continuously reduced.

[0020] The estimated additional power output may be transmitted to the wind farm controller and in particular also to the utility grid operator. When the utility grid operator receives information about the additional power output by a plurality of wind turbines, the utility grid operator may advantageously assign different power references to the wind turbines depending on the estimated additional power output of all wind turbines of the wind farm. Thus, stabilization actions for stabilizing the electrical properties of the utility grid may be improved.

[0021] Furthermore, when the additional power output is repeatedly and continuously derived and transmitted to the utility grid operator, the utility grid may in turn continuously and repeatedly provide a (new or updated) power reference to the wind turbine for reliably supporting the utility grid.

[0022] According to an embodiment of the invention, deriving the additional power is further based on prior values ​​of the wind speed, in particular used over a preset inertial response time interval, and / or a continuously updated current value of the wind speed, wherein the prior value of the wind speed is in particular estimated from prior values ​​of the power output and the rotational speed.

[0023] When also taking into account the previous value of the wind speed, it is enabled to set the blade pitch angle to a power optimal value for further allowing to increase the power output of the wind turbine. According to an embodiment of the invention, it is assumed that the wind speed does not change during the entire preset inertial response time interval. In this case, the previous value of the wind speed can be utilized throughout the execution of the method. In other embodiments, the wind speed value can be continuously derived and taken into account, thereby also taking into account the possibly changing wind conditions.

[0024] According to embodiments of the present invention, wind speed values ​​may be estimated from power output and rotation speed, or in still other embodiments, may be measured using one or more anemometers mounted at the respective wind turbine or at a mast close to or far from the wind turbine.

[0025] According to an embodiment of the invention, deriving the additional power output is further based on a relationship of a power optimum value of the pitch angle depending on the rotation speed value and the power output value.

[0026] The power optimal value of the pitch angle may be a specific value of the pitch angle for which the power output may be maximum under current environmental conditions (including wind speed, rotational speed). In particular, before initiating the inertial response, the pitch angle may not be adjusted to the power optimal value of the pitch angle, for example because the nominal power has been reached and / or the nominal rotational speed has also been reached. In addition, the nominal wind speed may have been reached. If, for example, the wind speed is greater than the nominal wind speed, and the wind turbine may be operated so that the power output is at the nominal power output (e.g., less than the maximum power) and the rotational speed is at the nominal rotational speed. In this case, as the wind speed increases, the pitch angle may be continuously increased toward a feather position so as to maintain the rotational speed and the power output at the respective nominal values. In this case, when it is necessary to activate the inertial response, the wind turbine may be adjusted to a power optimized pitch angle for still increasing the power output beyond the nominal power output.

[0027] According to an embodiment of the invention, deriving the additional power output comprises solving an optimization problem in which a post-value of the rotational speed is an optimization variable, wherein the post-value of the rotational speed is determined such that the additional power output is maximized, wherein in particular a simplex method is used to solve the optimization problem.

[0028] The optimization problem may in particular be a nonlinear optimization problem. Other methods for solving linear optimization problems may be applied.

[0029] In an optimization problem, the additional power output may be maximized, which may require finding a specific subsequent value of the rotational speed. Thus, the subsequent value of the rotational speed may not be a pre-given quantity, but may be found or determined when performing the method. The subsequent value of the rotational speed may be a rotational speed reached after terminating the inertial response, i.e. after a preset inertial response time interval has passed after the start time point of the inertial response. Thus, the subsequent value of the rotational speed may be a rotational speed value as present at or after the end time point of the inertial response.

[0030] The simplex algorithm or simplex method is a traditional algorithm for linear programming. In particular, the downhill simplex method (also known as the Nelder-Mead method) for nonlinear optimization can be applied. During or in this method, simplex cones are utilized, and these cones become appropriate simplexes with additional constraints. Simplex cones are corners (i.e., neighborhoods of vertices) of a geometric object called a polyhedron. The shape of the polyhedron can be defined by constraints applied to the objective function. A system of linear inequalities defines the polyhedron as a feasible region. The simplex algorithm can start from a starting vertex and can move along the edges of the polyhedron until it reaches the vertex of the optimal solution. By adopting the simplex method, a simple implementation can be provided.

[0031] According to one embodiment, the available additional power is maximized with the rear rotor speed as a free variable. It is subject to the following constraints:

[0032] The prior power + the estimated additional power should be less than or equal to the maximum power envelope at the subsequent speed,

[0033] The power at the following speed and optimum pitch should be greater than the preceding power − the maximum permissible dip,

[0034] The latter speed should be greater than the minimum limit on the rotor speed.

[0035] According to an embodiment of the present invention, at least one of the following constraints is satisfied: the rotational speed value, in particular throughout the method, is higher than a preset rotational speed lower limit; the power reduction from a power output preceding value to a power output succeeding value after an inertial response is higher than a preset power reduction limit; the preset power curve specifies a maximum power output depending on the rotational speed.

[0036] The preset lower rotation speed limit may have been set by the wind park operator or the utility grid operator. If the rotation speed value is above the preset lower rotation speed limit (in particular, throughout the method), a reacceleration of the rotor may be performed to reach the nominal rotation speed within a reasonably short time interval. If the power reduction is above the preset power reduction limit, the restoration of the power output to the nominal power output may also be accelerated.

[0037] In this optimization, the minimum power limit may also be used to predict additional power so that additional power can be delivered without violating the minimum power limit. When the turbine reaches this power limit during recovery, it can maintain output to the minimum power limit until the rotor speed recovers, or if the rotor speed drops below a certain limit (relative to the rotor speed) when it reaches the minimum power limit, the turbine can be further reduced in power.

[0038] The preset power curve may be a relationship between rotational speed and maximum power output, in particular maximum active power output of the wind turbine.The maximum power output may relate to the power output which is maximally provideable to the utility grid depending on the rotational speed.

[0039] If these constraints are met individually or in any combination, restoring the nominal operating behavior of the wind turbine after the inertial response can be simplified. According to an embodiment of the invention, the derived additional power output is smaller than the difference between the maximum power output according to the preset power curve, in particular for a previous value of the rotation speed, and the previous value of the power output.

[0040] Conventionally, the power output may have been increased from the previous value of the power output to the maximum possible power output, i.e. to the power output on the preset power curve for the previous value of the rotational speed. In contrast, according to this embodiment of the invention, the derived additional power output is less than the difference between the maximum power output for the subsequent value of the rotational speed and the previous value of the power output. Thus, it is enabled to provide the derived additional power output during the entire preset inertia response time interval without requiring significant changes to the utility grid. In conventional approaches, the additional power output would vary, in particular, would drop significantly during the preset inertia response time interval. When the additional power actually output is substantially constant, the control for stabilizing the grid may be more efficient and / or simplified.

[0041] According to an embodiment of the present invention, in order to derive the additional power output, at least one, in particular all, of the following items are taken into account: a power gain related to rotor deceleration, which in particular depends on the difference between the square of the current value of the rotation speed and the square of the subsequent value of the rotation speed; a power gain related to pitch optimization, which in particular is obtained as the difference between the power output at an optimal pitch angle, in particular a pitch angle set to optimize the power output for the current value of (power output and) rotation speed, and a previous value of the power output; a power loss related to rotor efficiency, which in particular is obtained as half of the difference between the previous value of the power output and the subsequent value of the power output, the latter value of the power output being the subsequent value of the power output that can be output at the subsequent value of the rotation speed without losing the rotation speed after the inertial response.

[0042] The power gain associated with rotor deceleration can be determined as the difference between the current rotational energy in the rotor and the rotational energy after the inertial response is terminated, where the difference can be divided by twice the preset inertial response time interval. Therefore, the power gain associated with rotor deceleration can be related to energy conservation.

[0043] If the pitch angle of the rotor blades is also adjusted during the method, the pitch optimization-related power gain can be particularly taken into account. When the pitch angle is set to a power-optimal value depending on the current operating conditions, additional power is available for increasing the amount of additional power output.

[0044] The power loss related to the rotor efficiency can be related to the compensation for handling the change of the rotor efficiency when the rotor speed decreases. The purpose of the rotor efficiency compensation can be: given a constant wind speed, to compensate for the reduced efficiency of the rotor at a lower rotor speed. Therefore, the previous value of the power output is the power output before the inertial response is initiated (the power that the rotor can generate at the speed before the inertial response without losing the rotation speed). The subsequent value of the power is the power that the rotor can generate at the subsequent value of the rotation speed without losing speed (for example, in a lookup table based on the subsequent value of the rotation speed, the wind speed, in particular the previous value of the wind speed, and the optimal pitch angle). It takes a preset inertial response time interval to go from the previous value of the rotation speed to the subsequent value of the rotation speed. Then, the energy loss is approximated by half of the energy balance between the two rotor speeds.

[0045] This approximation assumes that during the inertia response, ie during the preset inertia response time interval, the rotor speed decreases at a constant rotor speed decrease rate. Therefore, efficiency changes can be accounted for in a simple manner.

[0046] According to an embodiment of the present invention, the additional power output is obtained as the sum of the power gain related to rotor deceleration and the power gain related to pitch optimization minus the power loss related to rotor efficiency. Therefore, the most important factors for deriving the additional power output can be considered in a simple combination.

[0047] According to an embodiment of the invention, during a preset inertial response time interval, the pitch angle is changed, in particular optimized with respect to the power output for the respective current values ​​of the power output and the rotational speed. When the pitch angle is changed, the power that can be additionally output can be increased still further. In another embodiment, the pitch angle is maintained at a fixed (e.g., power optimal) value.

[0048] According to an embodiment of the present invention, a method for controlling a wind farm comprising a plurality of wind turbines during an inertial response is provided, the method comprising: performing a method according to one of the preceding embodiments for at least one wind turbine of the plurality of wind turbines; controlling the at least one wind turbine based on an estimated additional power output, the estimated additional power output being in particular used as an upper limit to an actual output power.

[0049] When additional power output is estimated for one or all of the wind turbines, the respective wind turbines may be individually controlled using different power references while ensuring that the respective wind turbines are actually capable of providing the estimated additional power output. Thus, stabilizing the utility grid may be improved.

[0050] The method may further comprise allocating different power references to the wind turbines, the power references being dependent on the estimated additional power output of all wind turbines such that a sum of the power references is constant to a preset total power value over a preset inertial response time interval.

[0051] The preset total power value may be derived and calculated, for example, by a utility grid operator, such that grid stabilization may be achieved when the preset total power value is actually provided to the utility grid. Depending on different power references, different wind turbines may provide different additional power outputs depending on the estimated respective power outputs.

[0052] It should be understood that features disclosed, described or applied to the method of estimating additional power output for inertial response (alone or in any combination) may also be applied, alone or in any combination, to an arrangement for estimating additional power output for inertial response according to embodiments of the invention, and vice versa.

[0053] According to an embodiment of the invention, an arrangement for estimating a (particularly maximum) additional power output (additional power output of a wind turbine power output) for an inertial response, which additional power output will be available for output throughout a preset inertial response time interval, is provided, the arrangement comprising: an input module adapted to obtain current values ​​of at least a rotational speed of a wind turbine rotor and a power output of the wind turbine; a processor adapted to derive the additional power output based on the obtained current values ​​and a remaining time interval of the preset inertial response time interval, in particular such that the additional power is available for output during the entire predetermined time interval.

[0054] Furthermore, according to an embodiment, there is provided a wind turbine comprising: a rotor having a plurality of rotor blades mounted thereon, the rotor blades being adjustable with respect to a pitch angle; a generator coupled to the rotor; and an arrangement according to the preceding embodiments.

[0055] Furthermore, a wind farm is provided, comprising a plurality of wind turbines as defined in the preceding embodiments.

[0056] The aspects defined above and further aspects of the 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

[0057] Embodiments of the present invention will now be described with reference to the accompanying drawings. The present invention is not limited to the embodiments shown or described.

[0058] Figure 1 schematically illustrates a wind farm comprising a wind turbine according to an embodiment of the invention, the wind turbine comprising an arrangement for estimating additional power output according to an embodiment of the invention;

[0059] Figure 2 A graph is shown for explaining an embodiment of the present invention;

[0060] Figure 3 illustrates a graph for explaining an embodiment of the present invention; and

[0061] Figure 4 A curve according to the prior art is shown. DETAILED DESCRIPTION

[0062] Figure 1The wind farm 1 schematically illustrated in comprises a plurality of wind turbines 3 which are connected at their output terminals 5 to a point of common coupling 7 which is connected to a utility grid 11, in particular via a wind farm transformer 9. The wind turbines 3 comprise a rotor 13 at which a hub 15 is mounted to which a plurality of rotor blades 17 are mounted. The rotor blades 17 are configured to be adjustable with respect to a pitch angle, i.e. a rotational adjustment angle about a pitch angle axis 19. Therefore, a pitch adjustment system 21 is provided which comprises respective actuators for rotating the blades 17 about the longitudinal axis 19 in order to adjust a specific pitch angle.

[0063] The wind turbine 3 further comprises a generator 23 coupled to the rotor 13. The three-phase output terminals of the generator 23 are coupled to a converter 25, which comprises an AC-DC part 27, a DC link 29 and a DC-AC part 31 and is configured for converting a variable frequency AC power flow into a substantially fixed frequency power flow 32. The fixed frequency power flow 32 is provided to a wind turbine transformer 33, which transforms the power flow to a higher voltage and provides it as a power flow 34 to the point of common coupling 7.

[0064] The wind turbine 3 further comprises an arrangement 35 according to an embodiment of the invention for estimating the additional power output of the wind turbine for the inertial response. The arrangement 35 comprises an input module 37 comprising input terminals 39 and 41 for receiving current values ​​of at least a rotational speed 43 and a power output 45 of the wind turbine 3.

[0065] The power output is therefore represented by a measurement signal 45 derived by a measurement module 47 which is connected to the output terminals of the transformer 33 and which is able to measure the voltage and / or the current of the output power flow 34 .

[0066] The rotational speed value is represented by a measurement signal 43 obtained by a rotational speed sensor 49 which measures the rotational speed of the rotor 13 .

[0067] The arrangement 35 comprises a processor 51 adapted to derive the additional power output based on the obtained current values ​​43, 45 of rotational speed and power output and the remaining time interval of the preset inertia response time interval such that the additional power is available for output during the entire predetermined time interval.

[0068] During the inertial response, the arrangement 35 (which may for example be comprised in a wind turbine controller (in particular incrementally in software and / or hardware)) may provide control signals 53, 55 to the pitch regulation system 21 and the converter 25, respectively, in order to control these components for actually enabling an additional power output to be output as power flow 34 above the previously output power output.

[0069] Figure 2 A graph is shown with an abscissa 57 indicating time and an ordinate 59 indicating additional power output, i.e., in addition to Figure 1 The inertial response starts at a start time point 61 and ends at an end time point 63 of the inertial response. The difference between the end time point 63 of the inertial response and the start time point 61 corresponds to a preset inertial response time interval 65 (also referred to as Δt), as shown in FIG. Figure 2 As shown in the figure.

[0070] Curve 67 indicates the Figure 1 The additional power output of the wind turbine 3 shown in FIG. Figure 2 It can be appreciated that after the start time point 61 of the inertial response, the additional power 67 increases sharply to above zero, i.e. the wind turbine 3 outputs an active power which is greater than the previous value of the output power before the inertial response and thus before the start time point 61. The additional output power 67 is substantially constant during the preset inertial response time interval 65. In particular, it increases rapidly from zero at the start time point 61 and quickly reaches a value 69. The additional output power 67 drops rapidly from the value 69 to zero at the end time point 63 of the inertial response.

[0071] After the inertial response, the additional power is negative, reaches a value 71 (representing the preset power reduction limit), which value 71 lasts until a time point 73, at which the additional power is zero again, i.e. the wind turbine has output the same amount of power as it had output before the inertial response. Thus, according to curve 67, the drop in power output (from the previous value) after the inertial response is above or equal to the preset power reduction limit 71. Figure 2 The curve 67 in is obtained according to a method for estimating the additional power output 69 according to an embodiment of the invention, which the arrangement 35 is adapted to perform.

[0072] Figure 2A curve 75 of additional power output according to a conventional method is also illustrated. It can be seen that the power output 75 decreases during the preset inertial response time interval, making it more difficult to properly control or properly restore the stability of the utility grid. In addition, after the IR, i.e., after the time point 63, according to the conventional curve 75, the power drops below the preset power reduction limit 71, for example until the nominal rotation speed is restored.

[0073] Figure 3 The curve considered in an embodiment according to the invention is illustrated, wherein the abscissa 77 indicates the rotation speed ω of the rotor 13 and the ordinate 79 indicates the total power output of the wind turbine 3 .

[0074] Curve 81 indicates a preset power curve defining a maximum power output in dependence on the rotation speed ω. Curve 83 indicates a speed-power trajectory according to normal operation of a wind turbine.

[0075] Point 85 (ωprior, Pprior) indicates the operating point of the wind turbine 3 before the inertial response, i.e. where the rotation speed and power output have prior values. According to an embodiment of the present invention, during the inertial response, i.e. during the Figure 2 During the preset inertial response time interval 65 illustrated in FIG. 8 , a trajectory 87 is traversed according to curve 67 . In particular, considering the previous values ​​of rotational speed and power output, i.e. Figure 3 point 85 in the example, based on the current values ​​of the rotational speed and power output of the wind turbine rotor and the Figure 2 The additional power output 69 is derived from the remaining time interval 91 illustrated in FIG. The remaining time interval 91 is the difference between the end time point 63 of the inertial response and the current time point t.

[0076] In the vertical portion of trace 87, the power output increases from Pprior to Pprior plus the additional power 69 to point 93, at which the power P_IR is output. Figure 3 Starting at point 93 in , the trajectory 87 follows a horizontal path, ie a path with constant additional power output, until encountering the preset power curve 81. The preset power curve 81 is encountered at a rotational speed ωpost which has been determined so that the additional power output 69 is maximum.

[0077] After the trajectory 87 hits the preset power curve 81, the inertial response is completed at the end time point 63 of the inertial response. Ideally, this is when the curve 81 is hit, i.e. at point 95. However, in reality, it may either never reach it or be limited by it for a short time due to overestimation / underestimation.

[0078] From that point on, the power output decreases from P_IR to a point 97 corresponding to a power output that is lower than the power output prior value Pprior by an amount 71. From point 97 onwards, the rotation speed increases again until the horizontal line touches the curve 83.

[0079] Thus, the wind turbine is controlled to reach point 85 starting from the end of the inertial response at point 95 via trajectory 99. In other embodiments, trajectory 101 is traversed to return to normal operation again. For example, during the transition between 95 and 97, the rotor speed may change. Thus, point 97 is not necessarily at ωpost, but may have a lower or higher rotation speed.

[0080] Embodiments of the present invention estimate the available inertial response power that can be constantly delivered during the inertial response, also referred to as P avail The estimated maximum available power P avail Based on the rotor performance data table, ie, power as a function of rotor speed, pitch angle and wind speed given by P(ω,ν,β).

[0081] Therefore, considering the current rotor speed ω, the optimal pitch curve β opt 、Wind speed when IR is activated ν pre , the power Pprior when the IR is activated, and the inertial response duration (ie, the time with additional power) Δt (also referred to as the preset inertial response time interval 65).

[0082] According to one embodiment, the above content can be formulated as an optimization problem subject to the following constraints:

[0083] • Maximum power curves (e.g. Figure 3 Curve 81 in Fig.

[0084] • Regarding the lower limit of rotor speed, e.g. Figure 3 The ω indicated in low ,

[0085] • Maximum power reduction after inertial response, e.g. Figure 3 P dip or Figure 2 The amount is 71.

[0086] The available inertial response power can be approximated by the amount of power that can be generated from the rotor decelerating and pitching to the optimum pitch. This can be expressed by:

[0087]

[0088] Therefore, P_RotExtract is the power balance from rotor deceleration

[0089]

[0090] POptPitch is the power obtained by changing the pitch to the optimum pitch (for example, the power obtained from the Cp power table)

[0091]

[0092] PEffComp is a compensation used to account for changes in rotor efficiency as rotor speed decreases.

[0093] The estimate (available power or additional power output P) can be updated throughout the response. avail , reference symbol 69), thereby estimating how much additional power is available within the remaining time 91 of the response.

[0094] Embodiments of the present invention provide several advantages:

[0095] • Provides a more deterministic IR,

[0096] • Maximize constant power output during IR,

[0097] • Provides available IR power estimates for field level control and consumer use,

[0098] • Eliminates tuning,

[0099] • Make IR function meet grid requirements,

[0100] ○ delivered x kW of additional power for y seconds,

[0101] ○ During the recovery period (after overproduction), the power must not drop by more than z kW.

[0102] Further features may contribute to the above advantages:

[0103] • The estimated available IR power can be used as an upper limit on the additional power actually provided during IR.

[0104] • This estimation can be formulated as an optimization problem, maximizing the amount of additional power that can be delivered for the entire response,

[0105] • Since the estimate takes into account rotor speed and rotor efficiency degradation, it may be accurate enough to be used in closed loop control at the field level and for reporting to consumers,

[0106] • The estimator can utilize rotor performance data from the APE, which eliminates the need for many tuning handles,

[0107] • Since this estimate can be used in closed loop control, it enables the IR function to deliver a constant power output over the entire duration of the response required by the grid. dip The lower bound is implemented as a constraint in the optimization. The estimate is also used in field level control and reference assignment to turbulence, enabling the field to provide an even better overall response.

[0108] Figure 4 The trajectory 103 traversed according to the conventional method is illustrated. The previous value of power output at point 105 is retained and the power is increased until the optimal power curve 81 is encountered. Then, during the inertial response, additional power output (according to Figure 2 75 in FIG. 1 ) decreases along trajectory 103 (eg, due to reduced rotor speed and limitations imposed by the maximum power curve) until reaching point 107. Thus, according to conventional methods, it may not be possible to provide a constant additional power output to the utility grid, thereby complicating the stabilization of the utility grid.

[0109] It should be noted that the term "comprising" does not exclude other elements or steps, and "a" or "an" does not exclude a plurality. Moreover, elements described in connection with different embodiments may be combined. It should also be noted that reference signs in the claims should not be interpreted as limiting the scope of the claims.

Claims

1. A method for estimating an additional power output (69) for an inertial response, the additional power output to be available for output over a preset inertial response time interval (65), the method comprising: Obtaining at least a current value of a rotation speed of a wind turbine rotor (13) and a power output (P) of the wind turbine (3) (77, 79; 43,45)； deriving the additional power output (69) based on the obtained current value (77, 79; 43, 45) and the remaining time interval (91) of the preset inertial response time interval (65), so that the additional power output is available for output during the entire preset time interval (65), wherein deriving the additional power output (69) comprises solving an optimization problem in which the subsequent value of the rotational speed is an optimization variable, wherein the subsequent value of the rotation speed is a rotation speed reached after the preset inertia response time interval has passed after the start time point of the inertia response; and wherein the subsequent value of the rotational speed is determined to maximize the additional power output.

2. The method according to claim 1, wherein the method uses a starting previous value corresponding to an operating state before or when an inertial response is initiated as the current value, and uses a preset inertial response time interval (65) as the remaining time interval.

3. A method according to any one of claims 1, wherein the current value (77, 79; 43, 45) and the remaining time interval (91) are updated over a preset inertial response time interval, and the additional power output (69) is repeatedly derived based on the updated values.

4. The method according to any one of claims 1-3, wherein deriving the additional power output (69) is further based on previous values ​​of wind speed used over a preset inertial response time interval, and / or a continuously updated current value of wind speed, wherein the previous value of wind speed is estimated from previous values ​​of power output and rotational speed.

5. The method according to any one of claims 1-3, wherein deriving the additional power output (69) is further based on a relationship of a power optimum value of a pitch angle depending on a rotational speed value and a power output value.

6. The method according to any one of claims 1 to 3, wherein the simplex method is used to solve the optimization problem.

7. The method according to any one of claims 1 to 3, wherein at least one of the following constraints is satisfied: The rotation speed value throughout the method is higher than a preset rotation speed lower limit; A power reduction from a prior power output value to a subsequent power output value after an inertial response is greater than or equal to a preset power reduction limit (71); A preset power curve (81) specifies a maximum power output dependent on the rotational speed.

8. A method according to any one of claims 1 to 3, wherein the derived additional power output (69) is less than the difference between the maximum power output (94) according to the preset power curve (81) for the subsequent value of rotational speed and the previous value of the power output.

9. The method according to any one of claims 1 to 3, wherein to derive the additional power output (69), at least one of the following is taken into account: the power gain associated with rotor deceleration, which depends on the difference between the square of the current value of the rotational speed and the square of the subsequent value of the rotational speed; a pitch optimization-related power gain obtained as the difference between the power output at the pitch angle set in order to optimize the power output for the current value of the rotational speed and a previous value of the power output; The power loss related to the rotor efficiency is obtained as half of the difference between the previous value of the power output and the subsequent value of the power output, wherein the subsequent value of the power output is the subsequent value of the power output after the inertial response and can be output at the subsequent value of the rotational speed without losing the rotational speed.

10. The method of claim 9, wherein the additional power output (69) is obtained as the sum of a rotor deceleration related power gain and a pitch optimization related power gain minus a rotor efficiency related power loss.

11. A method according to any of claims 1-3, wherein during a preset inertia response time interval the pitch angle is optimized with respect to the power output for respective current values ​​of the power output and the rotational speed.

12. A method for controlling a wind farm (1) comprising a plurality of wind turbines (3) during an inertial response, the method comprising: performing a method according to any one of the preceding claims for at least one wind turbine of the plurality of wind turbines; At least one wind turbine (3) is controlled based on the estimated additional power output, the estimated additional power output serving as an upper limit on the actual output power.

13. The method according to claim 12, further comprising: Different power references are assigned to the wind turbines, the power references being dependent on the estimated additional power output of all wind turbines such that the sum of the power references is constant to a preset total power value over a preset inertia response time interval.

14. An arrangement (35) for estimating an additional power output (69) for an inertial response, the additional power output to be available for output over a preset inertial response time interval (65), the arrangement comprising: an input module (37) adapted to obtain at least a rotational speed of a rotor of the wind turbine (3) and a current value (43, 45) of a power output of the wind turbine; a processor (51) adapted to derive the additional power output (69) based on the obtained current value (43, 45) and the remaining time interval (91) of the preset inertial response time interval, so that the additional power output is available for output during the entire predetermined time interval, wherein deriving the additional power output (69) comprises solving an optimization problem in which the subsequent value of the rotational speed is an optimization variable, wherein the subsequent value of the rotation speed is a rotation speed reached after the preset inertia response time interval has passed after the start time point of the inertia response; and wherein the subsequent value of the rotational speed is determined to maximize the additional power output.

15. A wind turbine (3), comprising: a rotor (13) on which a plurality of rotor blades (17) are mounted, said rotor blades being adjustable with respect to a pitch angle (β); a generator (23) coupled to the rotor; as well as An arrangement (35) as claimed in claim 14.

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