Operating wind turbine to provide reactive power

Abstract

A method of operating a wind turbine is provided. A wind turbine (100) comprises a wind turbine rotor (101) and an electrical power system (103) comprising a doubly-fed induction generator (104) mechanically coupled to the wind turbine rotor, wherein the electrical power system is configured to exchange electrical power with an electrical grid (112). The method comprises obtaining a grid requirement for the wind turbine (100) to exchange reactive power with the grid (112), wherein providing reactive power by the power system (103) in accordance with the grid requirement requires the power system to consume an amount of active power. The method further includes consuming an amount of active power by the power system (103) providing reactive power to the grid (112) in accordance with the grid requirements. Providing reactive power includes supplying a required amount of active power to the electrical power system (103), in which the wind turbine (100) is operated such that the electrical power system does not deliver active power to the electrical grid (112), and the generator (104) is operated as a variable speed rotating phase modulator to provide at least a portion of the reactive power to the electrical grid (112).

Description

Technical Field

[0001] The present invention relates to a method of operating a wind turbine. It further relates to a computer program for performing such a method and a control system configured to implement such a method. Background Art

[0002] For efficient operation of the power grid, voltage stability is crucial and thus the grid voltage must be maintained at a suitable and stable level by voltage regulation. This is particularly important when grid-connected power plants are highly dispersed, when grid-connected power plants include renewable energy power plants, and / or in the case of a weak grid whose voltage and frequency are sensitive to distortion and load changes.

[0003] To maintain the grid voltage at a suitable and stable level, reactive power can be supplied by grid-connected power plants, such as wind power plants, which stabilize the voltage by providing reactive power. Reactive power is provided, for example, in response to a reactive power grid requirement received from a grid operator, such as a transmission system operator.

[0004] However, when the wind turbines of a wind power plant are idle or operating at low power output, such as during curtailment or in low wind conditions, the ability of the wind turbines of the wind power plant to provide reactive power may be unavailable or may be limited.

[0005] Therefore, reactive power compensation units, such as static classical compensators, like capacitor banks (e.g., for generating reactive power) or inductance banks (e.g., for consuming reactive power), and, for example, synchronous compensators / condensers, can be used to provide reactive power for grid stability. However, the use of static classical compensators has the disadvantage of discontinuous and rather low control capabilities. A synchronous condenser can be coupled to the grid as an independent system. However, since this implementation requires additional hardware, it is expensive and requires more effort.

[0006] According to another solution for providing reactive power, the grid-side connected converter of a wind turbine is used to provide reactive power by operating the converter in a static synchronous compensator (STATCOM) mode. However, based on the topology of the wind turbine, the reactive power capability of the wind turbine in STATCOM mode may be limited to a minority of the rated apparent power of the wind turbine.

[0007] In addition, a wind power plant may be equipped with an additional auxiliary power supply to provide reactive power in the case of low power output. However, such auxiliary systems may be expensive and their installation may require a high effort.

[0008] Document EP 2317135 A1 describes a method for controlling a wind turbine, in which the provision of reactive power is shared between a generator and a grid-side converter. The active power output is restricted depending on the reactive power to be provided.

[0009] Document EP 3896841 A1 describes a system in which, at low rotational speeds of a wind turbine generator, the reactive power output is increased by increasing the generator speed, which can be achieved by reducing the active power output of the wind turbine. SUMMARY OF THE INVENTION

[0010] Accordingly, there is a need to mitigate at least some of the above-mentioned disadvantages and to provide an efficient and increased reactive power capability of a wind turbine in low-wind situations, which provision is particularly associated with lower costs and / or effort.

[0011] The features of the independent claims meet this need. The dependent claims describe embodiments of the invention.

[0012] According to one aspect of the invention, there is provided a method of operating a wind turbine. The wind turbine includes a wind turbine rotor and an electrical power system including a doubly-fed induction generator mechanically coupled to the wind turbine rotor, wherein the electrical power system is configured to exchange electrical power with a grid. The method includes obtaining a grid requirement for the wind turbine to exchange reactive power with the grid, wherein providing the reactive power by the electrical power system requires the electrical power system to consume an amount of active power. The method further includes providing the reactive power to the grid by the electrical power system according to the grid requirement while consuming the amount of active power. Providing the reactive power includes supplying the required amount of active power to the electrical power system, wherein the wind turbine is operated such that the electrical power system does not deliver active power to the grid, and operating the generator as a variable-speed rotating phase shifter to provide at least a portion of the reactive power to the grid.

[0013] In low-wind situations, it is beneficial to operate the doubly-fed induction generator (DFIG) of a DFIG wind turbine as a variable-speed rotating phase shifter / compensator (also referred to as a doubly-fed induction (DFI) phase shifter / compensator or a doubly-fed induction reactive power compensator).

[0014] The topology of the DFIG wind turbine allows operation as a DFI phase regulator to provide the required reactive power without the need for additional hardware and without requiring modifications to the system topology using additional hardware before such operation can be performed. In contrast, for example, operating the electrically excited synchronous generator of a full converter wind turbine as a synchronous phase regulator requires additional hardware and modifications to the system topology before operation as a synchronous phase regulator can be performed. The additional hardware of the full converter wind turbine includes a clutch for decoupling the generator shaft from the drive train, a bypassing circuit to connect the stator of the synchronous generator directly to the grid, and a suitable automatic voltage controller for generator rotor excitation.

[0015] Furthermore, DFI phasers operate at variable speed (asynchronous or synchronous), whereas synchronous phasers operate only at synchronous speed. Hence, there is further no need to decouple the wind turbine rotor from the generator and thus a clutch for decoupling. Furthermore, no bypass power converter is required.

[0016] Thus, the hardware effort and the hardware implementation effort may be reduced. Reduced hardware may be accompanied by increased system reliability and thus reduced maintenance effort (this is particularly relevant for offshore wind turbines). Thus, costs may be reduced.

[0017] Furthermore, the reactive power capability of the wind turbine can be increased by approximately three times compared to the wind turbine's ability to provide negative or positive reactive power when only the converter is operated in STATCOM mode. Figure 6 A diagram illustrating the increased reactive power capability of a DFIG wind turbine when the generator is operated as a DFI phase regulator is exemplarily shown.

[0018] Since all DFIG wind turbines connected to the grid can be operated as DFI compensators and can be easily retrofitted (e.g., because no additional hardware is required), grid stability can be improved due to the highly increased number of reactive power sources. In contrast, only synchronous generators with an excitable rotor can be operated as synchronous condensers (permanent magnet synchronous generators are not suitable for synchronous condenser operation) and, as mentioned, for their operation as synchronous condensers, additional hardware is required. Therefore, the number of additional reactive power compensation units (e.g., static classical compensators or stand-alone synchronous compensators / synchronous condensers) can be reduced.

[0019] The reactive power provided may include negative or positive reactive power. Negative reactive power may be generated, i.e., injected / supplied to the power grid. Positive reactive power may be absorbed from the power grid. Providing reactive power (to the power grid) may also be referred to as exchanging reactive power (with the power grid).

[0020] When the generator is synchronized with the power grid and, optionally, when the power system is energized, reactive power according to the power grid requirements may be provided.

[0021] The power system may include a power converter configured to convert the electric power exchanged with the power grid.

[0022] The power converter may include a grid-side converter and a rotor-side converter. The power converter may include a DC link. The power converter may be configured to convert alternating current to direct current and vice versa, or to convert AC to AC. An example of such a power converter may be a frequency changer, and in particular an AC / DC - DC / AC converter.

[0023] It should be clear that the power converter may be capable of bidirectionally transferring electric power from the rotor side to the grid side and from the grid side to the rotor side, and may further be capable of applying current and / or voltage to each phase on the rotor side and / or the stator side.

[0024] Operating the generator as a variable-speed rotating phase shifter to provide at least part of the reactive power may include controlling the rotor current of the generator (e.g., the rotor excitation current), in particular by setting at least one of the frequency, amplitude, and phase angle of the rotor current to control the (internal) stator voltage of the generator, e.g., by means of a power converter suitable for providing at least part of the reactive power (at the power grid voltage and frequency). Preferably, the stator voltage may further be suitable for providing at least part of the required active power.

[0025] The wind turbine may be operated such that the power system does not deliver active power to the power grid during the supply of the required amount of active power to the power system. In particular, during the supply of the required amount of active power to the power system, the wind turbine does not deliver active power to the power grid.

[0026] According to an alternative example, when the wind speed at the wind turbine is below or close to the cut-in wind speed of the wind turbine, reactive power according to the power grid requirements may be provided. Preferably, the wind speed may be close to the cut-in wind speed when the wind speed is different from the cut-in wind speed by 10%, 5%, or even 3%.

[0027] Additionally or alternatively, when the wind turbine generates active power in the near-zero region, reactive power can be provided according to grid requirements. Preferably, when the generated active power is below a (predetermined) threshold (e.g., in low wind conditions or in idle mode), the generated active power can be in the near-zero region, and the threshold is particularly below 10%, 5%, or even 3% of the rated apparent power of the wind turbine.

[0028] The method can include operating the wind turbine in an operating mode (e.g., the first or another (fourth) operating mode mentioned below), where operating in the operating mode includes receiving at least part of the amount of active power from the grid, and at least partially compensating for the losses associated with the power system by at least part of the amount of active power received from the grid (e.g., electrical losses at least due to generator operation and / or power converter operation, i.e., generator losses and / or power converter losses). Thus, even if there is not enough active power available from the generator to compensate for the losses of the wind turbine's power system, the generator can continue to operate as a synchronous condenser. The controller of the wind turbine can be configured to operate the wind turbine in the corresponding operating mode, and can particularly be configured to draw active power from the grid by the power system to at least partially compensate for the losses.

[0029] According to an example, the amount of active power can include the amount of active power required to compensate for the electrical power dissipated when providing the required reactive power. Preferably, the electrical power can be dissipated at least by the power system, particularly by the generator and / or by the converter of the power system, and / or during the rotation of the wind turbine rotor, particularly by the mechanical transmission system that mechanically couples the wind turbine rotor to the power system, and / or by one or more auxiliary systems of the wind turbine.

[0030] The mechanical transmission system can include or can not include a gearbox.

[0031] According to an example, the power system can include a power converter configured to convert the electrical power exchanged with the grid. The generator operating as a synchronous condenser can provide a part of the reactive power. The method can include operating at least a part of the power converter as a flexible alternating current transmission system (FACTS), particularly as a static synchronous compensator (STATCOM), to provide at least a part of the required reactive power to the grid, or to provide the remaining part of the reactive power to the grid. Preferably, the power converter can include a grid-side converter and a rotor-side converter. At least part of the power converter can include the grid-side converter.

[0032] By combining the operation of the generator as a variable-speed rotating phase modifier with the operation of the power converter as a STATCOM, the reactive power capability of the wind turbine is further increased. This is discussed in more detail below Figure 7 FIG. shows, by way of example, a diagram illustrating the further increased reactive power capability of a DFIG wind turbine that combines the STATCOM operation of the power converter and the DFI phase modifier operation of the generator. By combining, the reactive power capability can be further increased to approximately four times the capability of providing negative or positive reactive power when only the converter operates as a STATCOM

[0033] It should be clear that when the operation of the power converter as a STATCOM is described herein or when the STATCOM mode of the power converter is described herein, the converter can alternatively operate as a flexible alternating current transmission system different from a STATCOM

[0034] In an example, the (total) reactive power can be provided by the power converter and / or the generator

[0035] According to an example, the power system can include a power converter configured to convert the electrical power exchanged with the power grid. According to the corresponding maximum reactive power capability, the exchanged reactive power can be provided by both the generator and the power converter. Preferably, the corresponding maximum reactive power capability can be adjusted based on one or more operating conditions of the generator and / or the power converter

[0036] The operating conditions of the generator and / or the power converter can include, for example, at least one of temperature, voltage, in particular voltage amplitude, voltage frequency, and / or voltage phase angle, and current, in particular current amplitude, current frequency, and / or current phase angle

[0037] This adjustment can allow the provision of the required reactive power to be aligned with the current operating situation of the wind turbine. In this way, the adjustment can, for example, balance the load between both the generator and the power converter, and thus can reduce the fatigue, wear, and tear of the components and can extend their lifespan

[0038] According to an example, the method can include operating the wind turbine in an operating mode. Operating in the operating mode can include generating active power from the generator and from the rotational mechanical power provided by the wind turbine rotor to supply at least a portion of the required amount of active power to the power system. Preferably, the total amount of active power can be generated by the generator

[0039] In other words, the power system can consume the generated active power to provide reactive power according to grid requirements. Instead of decoupling the wind turbine rotor, the wind turbine generates at least part of the required amount of active power in low wind conditions. For example, using the active power generated from wind power generation, the losses of electrical components can be compensated and the active power consumed by the wind turbine auxiliary system can be supplied. Therefore, less or no required amount of active power must be consumed from an external active power source (e.g., from the grid), which can improve the efficiency of the wind turbine and can reduce costs.

[0040] Providing reactive power, especially when operating in an operating mode, can include controlling the rotational speed of the wind turbine rotor or the generator rotor of the generator such that the wind turbine rotor or the generator rotor rotates at a speed within a predetermined speed range. Preferably, the power system can include a power converter configured to convert the electrical power exchanged with the grid, and the predetermined speed range can be set such that the voltage at the power converter is within the operating voltage range of the power converter. More preferably, the speed range can include a lower limit that causes the generator rotor to rotate higher than 50% or higher than 60% of the synchronous speed of the generator, and / or the speed range can include an upper limit that causes the generator rotor to rotate lower than 160% or lower than 150% or even lower than 130% of the synchronous speed of the generator.

[0041] The voltage at the power converter can be the voltage on the rotor side and / or the grid side of the power converter.

[0042] The speed within the predetermined speed range can be a fixed speed. In other words, the rotational speed of the wind turbine rotor or the generator rotor can be controlled such that the rotor rotates continuously at a fixed speed when operating in the operating mode.

[0043] In some examples, rotating the wind turbine rotor or the generator rotor at a speed within a predetermined range may require consuming active power from the grid (e.g., when the wind speed is not high enough).

[0044] According to an example, the operating mode can be a first operating mode in which the generator generates a part of the required amount of active power. Operating the wind turbine in the first operating mode can further include supplying the remaining part of the required amount of active power to the power system from the grid, especially only from the grid. Preferably, the wind turbine can further be operable in a second operating mode in which the generator generates the total required amount of active power.

[0045] Operating the wind turbine in a first operating mode can improve grid stability because the wind turbine can provide reactive power even in situations where the wind speed is so low that the generator cannot provide the total amount of active power. In other words, a continuous reactive power capability of the wind turbine can be provided, which has a higher independence from the wind speed. In addition, this can be achieved without additional hardware, such as an auxiliary active power source and / or a clutch, and thus, the hardware costs can be reduced.

[0046] Operating the wind turbine in a first operating mode can further include stopping the operation of the wind turbine in the first operating mode if the consumption of the remaining part of the required amount of active power from the grid rises above a corresponding, in particular predetermined, threshold and / or if a monitoring parameter indicating the wind speed at the wind turbine drops below a corresponding, in particular predetermined, threshold (e.g., when the wind speed is not high enough to maintain a controlled rotational speed of the wind turbine rotor).

[0047] For this and other purposes, the active power consumed from the grid (in addition to the reactive power exchanged with the grid) can be monitored, for example, by monitoring the voltage and / or current exchanged with the grid. In another example, the consumption of the active power can be derived from the difference between the required amount of active power and the active power provided by the power system. The active power provided by the power system can be monitored, for example, by monitoring at least one of the rotational speed of the wind turbine rotor, the rotational speed of the generator, the generator torque, the current of the generator, and the voltage of the generator.

[0048] For example, the monitoring can be performed - but is not limited to - by means of at least one of a sensor, a sensing system, a model, in particular a mathematical and / or physical model, implemented in software, and a filter-based monitoring system, such as a state observer, a Kalman filter, or the like. The result of the monitoring parameter can be a signal of the monitored parameter, such as a discrete or continuous signal indicating the progression of the monitored parameter by a plurality of values generated by the monitoring. The monitoring can further include signal preprocessing and postprocessing, such as filtering. In addition, the monitoring can utilize information obtained from hardware implemented for monitoring purposes, such as one or more sensors, and / or can utilize information obtained from hardware implemented for another purpose. The monitoring can further include estimation and / or prediction, preferably based on the obtained information.

[0049] For example, the threshold for the consumption of the remaining part of the required amount of active power from the grid can be higher than 60%, 70%, or even 80% of the required amount of active power, and / or the threshold for the wind speed can be lower than 50%, 40%, or 30% of the cut-in wind speed of the wind turbine.

[0050] In an example, stopping the operation of a wind turbine can include stopping providing reactive power in accordance with the grid requirements of at least a part of an electrical power system, in particular of a generator. Preferably, when the wind turbine stops, at least part of the operation of a power converter being a FACTS, in particular a STATCOM, can continue to provide at least part of the required reactive power.

[0051] Stopping can ensure that the wind turbine consumes only a limited amount of active power from the grid to provide the required amount of active power. For example, when the wind speed is low, stopping can prevent the wind turbine from operating / driving merely as a fan to maintain the rotational speed / rotor speed of the wind turbine. Thereby, the efficiency of reactive power provision in accordance with the grid requirements can be improved. Moreover, by stopping, the cost for operating the wind turbine can be reduced.

[0052] According to an example, a wind turbine can include a clutch that is configured to mechanically decouple the wind turbine rotor and / or a drivetrain arranged between the wind turbine rotor and a generator from the generator. Operating the wind turbine in a first operating mode can further include decoupling the wind turbine rotor and / or the drivetrain from the generator if the consumption of the remaining part of the required amount of active power from the grid rises above a corresponding, in particular predefined, threshold and / or if a monitoring parameter indicating the wind speed at the wind turbine drops below a corresponding, in particular predefined, threshold. Optionally, operating the wind turbine in the first operating mode can further include, after decoupling, continuing the operation of the wind turbine in a further different operating mode in which the grid supplies the total required amount of active power to the electrical power system.

[0053] For example, the threshold for the consumption of the remaining part of the required amount of active power from the grid can be higher than 60 percent, 70 percent or even 80 percent of the required amount of active power, and / or the threshold for the wind speed can be lower than 50 percent, 40 percent or 30 percent of the cut-in wind speed of the wind turbine.

[0054] The clutch can be arranged, for example, between the gearbox of a mechanical drivetrain and the generator.

[0055] Since the wind turbine rotor is decoupled, the required amount of active power for providing reactive power in accordance with the grid requirements and thus the amount of active power consumed from the grid can be reduced, while the provision of reactive power in accordance with the grid requirements can be maintained. Thereby, the efficiency and continuity of the reactive power capability of the wind turbine can be improved.

[0056] In an example, the wind turbine may include a corresponding clutch, and the method may include decoupling the wind turbine rotor and / or the drivetrain from the generator (e.g., if the consumption of the remaining part of the required active power amount from the grid rises above a corresponding, in particular predefined, threshold and / or if a monitoring parameter indicating the wind speed at the wind turbine drops below a corresponding, in particular predefined, threshold). The method may further include operating the wind turbine in a further (different) operating mode, wherein the operation in the further operating mode may include supplying the total required active power amount from the grid to the power system. Thus, a mode can be provided in which, in the case where the wind turbine rotor is not rotating, the reactive power requirement can be met by operating the generator as a rotating phase shifter.

[0057] The operation in the further different operating mode may include accelerating the rotor of the generator to a predefined rotational speed.

[0058] In another example, the operation of the wind turbine after a stop may be associated with a third operating mode, and operating the wind turbine in a further different operating mode may be associated with a fourth operating mode of the wind turbine. The method may include operating the wind turbine in the third and fourth operating modes.

[0059] The implementation of both the third and fourth operating modes may be beneficial because the benefits of the modes may be combined.

[0060] The active power threshold and / or the wind speed threshold associated with the third operating mode may be different from the active power threshold and / or the wind speed threshold associated with the fourth operating mode, respectively. For example, the thresholds may be set such that the fourth operating mode is executed before the third operating mode.

[0061] In this way, the operation of the generator in the DFI phase shifter mode can be extended, in which the wind turbine provides a larger amount of reactive power capacity.

[0062] The operation in the third and / or fourth operating modes may include stopping the wind turbine rotor.

[0063] In an example, the grid may be an island grid or a microgrid. Continuously supplying reactive power to this type of grid is particularly important for maintaining grid stability even in low wind conditions because only a relatively small number of wind turbines or other power sources are connected to such a grid, which may make its voltage and frequency sensitive to distortion and load changes, i.e., the grid voltage may be unstable (or prone to flicker) and / or the frequency may be unstable (e.g., due to high system impedance).

[0064] According to an example, an operation in an operating mode may include receiving at least a portion of an active power amount from the power grid. The method may further include switching from the operating mode to an additional operating mode when it is detected that an operation requirement of the wind turbine in a different additional operating mode is for less consumption of active power from the power grid in order to provide reactive power to the power grid. Preferably, the detection may be based on one or more monitoring parameters, which particularly include a parameter indicating a wind speed at the wind turbine. Additionally or alternatively, the detection may be based on an estimate of the consumption of the requirement of active power from the power grid in different additional operating modes, which estimate is particularly performed by employing a model that enables the operation of the wind turbine in different additional operating modes.

[0065] After switching from the operating mode to a different additional operating mode, an operation in the additional operating mode may include switching back from the different additional operating mode to the operating mode when it is detected that an operation requirement of the wind turbine in the operating mode is for less consumption of active power from the power grid in order to provide reactive power to the power grid. Preferably, the detection may be based on one or more monitoring parameters, which particularly include a parameter indicating a wind speed at the wind turbine. Additionally or alternatively, the detection may be based on an estimate of the consumption of the requirement of active power from the power grid in the operating mode, which estimate is particularly performed by employing a model that enables the operation of the wind turbine in the operating mode.

[0066] In this way, it can be ensured that the wind turbine operates in an operating mode that requires the least amount of active power to provide reactive power according to the power grid requirements, and thus the efficiency of the wind turbine can be improved.

[0067] According to an example, the method may include pitching one or more (particularly three or all) rotor blades of the wind turbine rotor when it is detected that the wind turbine provides or is capable of providing more active power than the required active power amount. Preferably, the detection may be based on a monitoring parameter that indicates at least one of a wind speed at the wind turbine, a rotational speed of the wind turbine rotor and / or a generator rotor, a voltage of the wind turbine, and a current of the wind turbine.

[0068] Pitching of one or more rotor blades may be performed synchronously in an example.

[0069] The method may further include obtaining a power grid requirement for the wind turbine not to output active power to the power grid before pitching.

[0070] By pitching, the rotational speed of the wind turbine rotor can be controlled such that the speed of the wind turbine rotor is within a predetermined speed range.

[0071] Pitch control can limit the amount of active power consumed from the grid in order to keep the rotational speed of the wind turbine rotor within a predetermined speed range, even at higher wind speeds, but without supplying active power from the wind turbine to the grid (e.g., in response to an obtained active power grid requirement). Thus, the efficiency of providing reactive power according to reactive power requirements can be further improved, and the cost of active power consumption from the grid can be reduced.

[0072] According to one aspect of the present invention, there is provided a control system for controlling the operation of a wind turbine. The wind turbine includes a wind turbine rotor and an electrical system, the electrical system including a doubly-fed induction generator mechanically coupled to the wind turbine rotor. The electrical system is configured to exchange electrical power with the grid. The control system can, for example, include a processing unit and a memory unit, the memory unit storing control instructions which, when executed by the processing unit of the control system, cause the control system to perform any of the methods described herein. The processing unit can, for example, include a digital signal processor, an application specific integrated circuit, a field programmable gate array, a microprocessor or the like. The memory unit can include RAM, ROM, flash memory, a hard disk drive and the like.

[0073] The wind turbine can include or can not include the control system, and / or the control system can be located at the site where the electrical system is located or at a site different from the site where the electrical system is located.

[0074] According to one aspect of the present invention, there is provided a wind turbine. The wind turbine includes a wind turbine rotor and an electrical system, the electrical system including a doubly-fed induction generator mechanically coupled to the wind turbine rotor. The wind turbine is configured to operate according to any of the methods described herein.

[0075] The wind turbine can include a mechanical drivetrain that mechanically couples the wind turbine rotor to the electrical system. Preferably, the drivetrain includes a gearbox and / or a clutch.

[0076] The wind turbine can be an offshore or onshore wind turbine.

[0077] According to one aspect of the present invention, there is provided a computer program for controlling the operation of a wind turbine. The computer program includes control instructions which, when executed by the processing unit of a control system for controlling the operation of the wind turbine, cause the processing unit to perform any of the methods described herein. The computer program can be provided on a volatile or non-volatile storage medium or data carrier.

[0078] It will be understood that, without departing from the scope of the present invention, the features mentioned above and those explained below can be used not only in the respective combinations indicated, but also in other combinations or alone. In particular, the features of the different aspects and embodiments of the present invention can be combined with each other, unless otherwise indicated.

[0079] It should be clear that all method features or functional features are applicable and thus disclosed, without limitation, individually as features, as combinations of features, or in any sub - combination in the devices or systems described herein. Similarly, all device or system features or structural features are applicable and thus disclosed, without limitation, individually as features, as combinations of features, or in any sub - combination to the methods described herein. BRIEF DESCRIPTION OF THE DRAWINGS

[0080] The foregoing and other features and advantages of the present invention will become further apparent from the following detailed description when read in conjunction with the accompanying drawings. In the drawings, like reference numerals refer to like elements.

[0081] Figure 1 is a schematic diagram that illustrates a DFIG wind turbine according to an exemplary implementation and the operation of the wind turbine in a first operating mode for providing reactive power to the power grid.

[0082] Figure 2 is a schematic diagram that illustrates a DFIG wind turbine according to an exemplary implementation and the operation of the wind turbine in a second operating mode for providing reactive power to the power grid.

[0083] Figure 3 is a schematic diagram that illustrates a DFIG wind turbine according to an exemplary implementation and the operation of the wind turbine in an additional operating mode for providing reactive power to the power grid.

[0084] Figure 4 is a schematic diagram that illustrates a state diagram representing transitions between operating modes in which a DFIG wind turbine operates to provide reactive power according to an exemplary implementation.

[0085] Figure 5 is a schematic flowchart diagram that illustrates a method of operating a wind turbine according to an exemplary implementation.

[0086] Figure 6 is a schematic diagram that illustrates the respective reactive power capabilities of a DFIG wind turbine when the generator of the DFIG wind turbine operates as a variable - speed rotating phase shifter and when the power converter of the DFIG wind turbine operates as a static synchronous compensator (STATCOM).

[0087] Figure 7is a schematic diagram showing the reactive power capabilities of a DFIG wind turbine when the generator of the DFIG wind turbine operates as a variable-speed rotating phase shifter and when the power converter of the DFIG wind turbine operates as a static synchronous compensator (STATCOM) in combination. DETAILED DESCRIPTION

[0088] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. It will be understood that the following description of the embodiments is given for illustrative purposes only and is not to be construed in a limiting sense. It should be noted that the drawings are only regarded as schematic representations, and the elements in the drawings are not necessarily in proportion to each other. Instead, the representations of the various elements are chosen such that their functions and general purpose become clear to those skilled in the art. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. Unless otherwise indicated, the terms "comprising", "having", "including" and "containing" will be construed as open-ended terms (i.e., meaning "including, but not limited to").

[0089] Figure 1 is a schematic diagram showing the operation of a DFIG wind turbine 100 according to an exemplary implementation and the operation of the wind turbine in a first operating mode 401 to provide (negative or positive) reactive power Qtot to the power grid 112.

[0090] When the wind turbine 100 is in a low active power generation operation, for example, when the wind speed at the wind turbine 100 is below the cut-in wind speed and / or when the wind turbine is idle, the operation of the wind turbine 100 in the operating modes described herein for providing reactive power can be performed. A control system 120 can control the operation of the wind turbine 100 in each of the operating modes described herein, and the control system 120 can include a processing unit 121 and a memory unit 122.

[0091] The wind turbine 100 can be controlled in each of the operating modes described herein such that active power is not delivered to the power grid 112, for example, by setting the active power output reference of the power control of the wind turbine 100 to zero. In other words, in each of the operating modes described herein, active power can be consumed from the power grid 112 (e.g., in the first operating mode 401 shown in Figure 1 and in the third operating mode 403 (when the operation of a part of the power system 103 of the wind turbine 100 continues to provide reactive power after being stopped), and in Figure 3 the different additional (fourth) operating mode 404 shown in Figure 2in the second operating mode 402 and the third operating mode 403 shown in (when the power system does not continue to provide reactive power after stopping).

[0092] This is in contrast to the conventional operation of a DFIG wind turbine, in which when the wind turbine is not idle and not in low-power generation operation, for example when the wind speed at the wind turbine is higher than the cut-in wind speed, the generator is used to supply active power and reactive power to the grid. In conventional operation, the active power is fed / delivered to the grid.

[0093] The wind turbine 100 can exchange reactive power with the grid 112 when receiving / obtaining a grid requirement to supply reactive power Qtot to the grid. The power system 103 exchanging / supplying reactive power according to the grid requirement may require the power system 103 to consume an amount of active power. As described herein, the required amount of active power can be provided differently in the operating modes 401, 402, 403, 404.

[0094] Referring again to Figure 1 , the wind turbine 100 can be electrically coupled to the grid 112 via a transformer 111. The wind turbine 100 can include a wind turbine rotor 101, which can be mechanically coupled to the power system 103 via a drivetrain 102 including a gearbox 113 (and an optional clutch 314). The gearbox 113 can convert the rotational speed and torque of the wind turbine rotor 101. The power system 103 can include a power converter 107 and a doubly-fed induction generator 104. The generator 104 can include a stator 105 and a rotor 106.

[0095] The power converter 107 can include a rotor-side converter 108, a DC link 109, and a grid-side converter 110. The grid-side converter 110 can be electrically coupled to the rotor-side converter 108 via the DC link 109, and the rotor-side converter 108 can be electrically coupled to the rotor 105. The power converter 107 may be capable of bidirectionally transmitting electrical power from the rotor side to the grid side and from the grid side to the rotor side, and may further be capable of applying a voltage-controlled rotor current Ir on each phase of the rotor 105, and the rotor current in each phase is preferably defined by a corresponding current value, frequency, and phase angle. An example of such a power converter 107 can be a frequency converter and particularly an AC / DC-DC / AC converter.

[0096] The reactive power Qtot, which consists of the reactive power Qs provided by the stator 105 and the reactive power Qgsc provided by the grid-side converter 110, can be provided to the grid 112, for example, in response to a grid requirement for the wind turbine 100 to exchange reactive power with the grid 112. The grid requirement can be received from the grid operator. During the provision of the reactive power Qtot, the power system 103 can be synchronized with the grid 112 and can be energized.

[0097] The reactive power Qtot can be provided by operating the doubly-fed induction generator 104 as a variable-speed rotating phase shifter (DFI phase shifter), and optionally by operating at least part of the converter 107, in particular the grid-side converter 110 and the DC link 109, as a static synchronous compensator (STATCOM). The variable-speed rotating phase shifter (DFI phase shifter) is a reactive power compensator / dynamic phase shifter. If the operation includes both the DFI phase shifter and the STATCOM, the provision of the reactive power Qtot can be shared between the two according to their respective maximum reactive power capabilities. Preferably, the respective maximum reactive power capabilities can be adjusted based on one or more operating conditions of the power converter and / or the generator.

[0098] Depending on the rotational speed of the generator rotor 106 and the frequency of the rotor current Ir, the phase shifter / compensator operation of the generator 104 can be synchronized or asynchronous (i.e., variable speed) with the grid 112. Since the DFI phase shifter operates at variable speed, a clutch 314 (indicated by a dashed line as optional) for decoupling the wind turbine rotor 101 may not be required, for example, to reduce mechanical stress or reduce drivetrain and rotor aerodynamic losses.

[0099] The supply of (positive or negative) reactive power of the DFI phase shifter can be controlled by the rotor current Ir. For example, based on the underexcitation or overexcitation of the generator rotor 106. Controlling the rotor current Ir in the generator rotor 106 can apply a stator voltage at the stator 105, in response to which a current that lags (i.e., inductive reactive power) or leads (i.e., capacitive power) the grid voltage can be output to the grid 112.

[0100] Since the operation of the generator 104 as a phase shifter can be controlled by the power converter 107, in particular by the rotor-side converter 108, the operating limitations of the power converter 107 must be considered.

[0101] For this purpose, the wind turbine rotor 101 can be controlled to rotate within a predetermined speed range, in particular at a predetermined fixed speed. The controlled speed of the wind turbine rotor 101 can be set to a value at which the generator rotor 104 rotates at such a high speed that the voltage at the rotor side of the power converter 107, in particular the induced voltage, is within the operating voltage limit of the power converter 107.

[0102] The power system 103 providing the reactive power Qtot according to grid requirements may require the power system 103 to consume an amount of active power. The amount of active power consumed can include the active power that compensates for the losses occurring during the operation of the wind turbine 100 for reactive power provision, such as losses associated with the power system 103, in particular losses associated with the generator 104 and / or the power converter 107, and / or losses associated with the drivetrain 102. Additionally or alternatively, the amount of active power consumed can include the active power required to control the rotational speed of the wind turbine rotor 101 / generator rotor 106 within a predetermined range and / or the active power required to operate one or more auxiliary systems of the wind turbine 100 / wind turbine generator 104.

[0103] In a first operating mode 401, active power Pin can be consumed from the grid 112, as indicated by the arrow pointing to the wind turbine 100. Consumption of active power Pin is required in the first operating mode because the power system 103 generates less active power than the amount of active power that the power system 103 must consume to provide reactive power according to grid requirements. This can be the case when the wind turbine rotor 101 is driven by a wind speed that is not so high that the wind turbine rotor 101 supplies sufficient mechanical power Pm to the generator 104. In other words, in the first operating mode 401, the generator 104 can provide a part of the required amount of active power and the grid 112 can provide the remaining part of the required amount of active power.

[0104] When the remaining part of the required amount of active power from the grid 112 rises above a threshold, for example, when the wind turbine 101 consumes a large amount of active power from the grid 112 to maintain the rotational speed of the wind turbine rotor 101 within a predetermined speed range, the wind turbine 100 can be stopped. However, it should be clear that after the stop, the operation of the wind turbine 100 can continue in a third operating mode 403. The third operating mode can include providing at least a part of the reactive power according to grid requirements by operating the power converter 107 as a STATCOM.

[0105] In an example, when the wind turbine 100 supplies or is capable of supplying more active power than the required amount of active power and upon receiving / obtaining a grid requirement not to supply active power to the grid 112, one or more rotor blades of the wind turbine 100 can be pitched (e.g., all rotor blades can be pitched synchronously or simultaneously to reduce the mechanical power Pm) by means of pitch control. In this way, the amount of active power consumed from the grid 112 can be reduced, e.g., to control the wind turbine not to supply an excessive amount of active power to the grid.

[0106] Figure 2 is a schematic diagram that illustrates a DFIG wind turbine 100 according to an exemplary implementation and the operation of the wind turbine 100 in a second operating mode 402 for supplying reactive power Qtot to the grid 112.

[0107] The second operating mode 402 differs from the first operating mode 401 in that the generator 104 can generate the total required amount of active power to supply reactive power according to the grid requirement. In other words, when the wind turbine is operating in the second operating mode 402, due to a sufficiently high wind speed at the wind turbine 100, the wind turbine rotor 101 can provide sufficient mechanical power Pm for supplying the amount of active power to the generator. Therefore, no active power Pin is consumed (Pin = 0).

[0108] Figure 3 is a schematic diagram that illustrates a DFIG wind turbine 100 according to an exemplary implementation and the operation of the wind turbine 100 in a further operating mode 404 (fourth operating mode) for supplying reactive power Qtot to the grid 112. The fourth operating mode can be executed, for example, during a complete lack of wind speed at the wind turbine 101. Figure 3 The wind turbine 100 shown in Figure 1 and Figure 2 differs from the wind turbine 100 shown in that the clutch 310 is no longer optional. When the wind turbine is operating in the fourth operating mode 404, the generator 104 is mechanically decoupled from the wind turbine rotor 101 and the drivetrain 102 (gearbox), and mechanical power Pm is not supplied from the wind turbine rotor 101 to the generator 104. The rotation of the wind turbine rotor 101 can be stopped, for example, by an interruption (parking). The operation of the wind turbine 100 in the fourth operating mode 404 can further differ from the operating modes 401 and 402 in that the total required amount of active power for supplying reactive power can be consumed from the grid 112 by operating the generator 104 as a variable-speed rotating phase shifter and optionally by operating the converter 107 as a STATCOM. In other words, the amount of active power Pin consumed from the grid 112 can be equal to the required amount of active power.

[0109] It should be clear that since the wind turbine rotor 101 and the drivetrain 102 are decoupled, the amount of active power required for reactive power provision in the fourth operating mode 404 may be less than the amount of active power required for reactive power provision in the first or second operating modes 401, 402. In the fourth operating mode 404, the required active power can be reduced because only the rotation of the generator rotor 106 is controlled to rotate within a predetermined speed range and because the losses associated with the wind turbine rotor 101 and the losses associated with the drivetrain 102 are no longer relevant.

[0110] After decoupling, operation in the fourth operating mode 404 may include accelerating the generator rotor 106 to a desired rotational speed within a predetermined speed range in order to limit the connection current. The acceleration can be performed as follows: by a motor drive connected to the shaft of the generator 104 or by a voltage variator connected to the stator 105 and the generator rotor 106 is short-circuited by the rotor-side converter 108 or by the rotor-side converter 108 acting as a voltage regulator connected to the rotor 104 and the generator stator 105 is short-circuited.

[0111] Figure 4 is a schematic diagram showing a state diagram that represents the transitions between the operating modes 401, 402, 403, 404 according to an exemplary implementation, where the DFIG wind turbine 100 operates to provide reactive power. Operation of the wind turbine 100 in each of the operating modes 401, 402, 403, 404 and the transitions between the operating modes 401, 402, 403, 404 can be controlled by the control unit 120. In the operating modes 401, 402, 404, the generator 104 can operate as a variable-speed rotating phase shifter, and optionally, the power converter 107 can operate as a STATCOM, as described herein. In the operating mode 403, the wind turbine 100 can be stopped, but the power converter 107 can operate as a STATCOM. Operating the wind turbine 100 in the fourth operating mode 404 requires that the wind turbine 100 include a clutch 314, while operation in the remaining operating modes 401, 402, 403 is independent of the presence of the clutch 314.

[0112] When the total amount of active power required to provide reactive power according to the obtained grid requirements is generable / generated by the rotational mechanical power provided by the generator 104 from the wind turbine rotor 101 (i.e., when the wind speed at the wind turbine 100 is high enough), the wind turbine 100 can operate in the operating mode 402. When at least a part of the amount of active power must be consumed from / drawn from the power grid 112, the wind turbine 100 can operate in the operating mode 401 or 403, or when the wind turbine 100 includes a clutch 314, depending on the active power that must be consumed from / drawn from the power grid 112 and / or depending on the wind speed at the wind turbine 100, operate in the operating mode 404. For example, when the active power that must be consumed from / drawn from the power grid 112 and / or the wind speed exceeds the corresponding threshold, the operation of the wind turbine 100 can be switched between the operating modes 401, 403, 404.

[0113] In an example, the power efficiency and / or cost optimization unit 407 can adjust / modify the transition between operating modes such that the wind turbine 100 operates in one of the operating modes in which the wind turbine 100 operates with maximum power efficiency and minimum cost. For this purpose, the unit 407 can, for example, consider the amount of active power that must be consumed from / drawn from the power grid 112 and / or the potential fines that must be paid when the obtained grid requirements are not met, by means of a corresponding model that implements the operation of the wind turbine 100 in the operating mode.

[0114] Figure 5 is a schematic flowchart illustrating a method 500 for operating a wind turbine, such as the wind turbine 100, according to an exemplary implementation. The method can be executed by a control system such as the control system 120.

[0115] Figure 5 The sequence of method steps in is not limited to the sequence shown. The method is further not limited to the number of steps shown. Some steps of the method may not be implemented, may be replaced or extended. Additional steps may be added.

[0116] The wind turbine can include a wind turbine rotor and an electrical system that includes a doubly-fed induction generator mechanically coupled to the wind turbine rotor, wherein the electrical system is configured to exchange electrical power with the power grid. The wind turbine rotor can be mechanically coupled to the generator via a drivetrain that includes a gearbox. The electrical system can include a power converter that is configured to convert the electrical power exchanged with the power grid.

[0117] According to step S02 of the method 500, the method can include obtaining grid requirements for the wind turbine to exchange reactive power with the power grid, wherein providing reactive power by the electrical system according to the grid requirements can require the electrical system to consume an amount of active power.

[0118] In step S04 of method 500, the method may include providing reactive power to the power grid by the power system according to grid requirements while consuming an amount of active power, wherein providing reactive power may include supplying the required amount of active power to the power system, and wherein the wind turbine may be operated such that the power system does not deliver active power to the grid. In particular, (at least) during the supply of the required amount of active power to the power system, the wind turbine or the power system does not deliver active power to the grid. Providing reactive power may further include operating the generator as a variable speed rotating phase shifter (doubly-fed induction compensator) to provide at least a portion of the reactive power to the grid.

[0119] In step S06 of method 500, the method may include operating the wind turbine in an operating mode, wherein the operation in the operating mode may include generating active power by the generator and from the rotational mechanical power provided by the wind turbine rotor to supply a portion of the required amount of active power to the power system.

[0120] In step S08 of method 500, the method may include operating at least a portion of the power converter as a flexible alternating current transmission system, in particular as a static synchronous compensator (STATCOM), to provide the remaining portion of the required reactive power to the grid.

[0121] Figure 6 is a schematic diagram that illustrates the respective reactive power capabilities of a DFIG wind turbine when the generator of the DFIG wind turbine is operated as a variable speed rotating phase shifter and when the power converter of the DFIG wind turbine is operated as a static synchronous compensator (STATCOM).

[0122] The illustration includes a first graph 601 (solid line) that depicts the ability of the stator of the generator to provide reactive power depending on the active power generated by the power system when the generator is operated as a variable speed rotating phase shifter / DFI phase shifter. The graph further includes a second graph 602 (dashed line) that depicts the ability of the (grid-side) converter included in the power system to provide reactive power depending on the active power generated by the power system when the converter is operated in STATCOM mode. In Figure 6 it, the dashed circles indicate the reactive power capabilities of each of the generator and the converter in the case of low generated active power (e.g., due to low wind conditions), i.e., close to the abscissa of the graph. It can be seen that in the region of the dashed circles, the ability of the generator to provide negative (inductive) or positive (capacitive) reactive power in DFI phase shifter operation is approximately three times the ability of the converter to provide negative or positive reactive power in STATCOM operation.

[0123] Figure 7is a schematic diagram that illustrates the reactive power capabilities of a DFIG wind turbine when the generator of the DFIG wind turbine operates as a variable speed rotating phase shifter / DFI phase shifter and when the power converter of the DFIG wind turbine operates as a static synchronous compensator (STATCOM) in combination.

[0124] The figure includes Figure 701, which illustrates the ability to provide reactive power depending on the active power generated by the power system during such operation. From Figure 7 it can be seen that in the region of the dashed circle, the ability of the wind turbine to provide negative or positive reactive power increases from approximately three times the ability to provide negative or positive reactive power when only the converter operates as a STATCOM (as Figure 6 shown) to approximately four times.

[0125] While specific embodiments are disclosed herein, various changes and modifications can be made without departing from the scope of the invention. The embodiments are considered illustrative and non - limiting in all respects, and all changes within the meaning and equivalence of the appended claims are intended to be included therein.

Claims

1. A method of operating a wind turbine, wherein the wind turbine (100) comprises a wind turbine rotor (101) and an electrical system (103), the electrical system (103) comprising a doubly-fed induction generator (104) mechanically coupled to the wind turbine rotor, wherein the electrical system is configured to exchange electrical power with a power grid (112), and wherein the method comprises: - obtaining a grid requirement for the wind turbine (100) to exchange reactive power with the power grid (112), wherein the electrical system (103) provides the reactive power according to the grid requirement and the electrical system consumes an amount of active power; and - providing, by the electrical system (103), the reactive power to the power grid (112) according to the grid requirement while consuming the amount of active power, wherein providing the reactive power comprises supplying the required amount of active power to the electrical system (103), operating the wind turbine (100) such that the electrical system does not deliver active power to the power grid (112), and operating the doubly-fed induction generator (104) as a variable-speed rotating phase shifter to provide at least a part of the reactive power to the power grid (112), wherein the reactive power according to the grid requirement is provided when the wind speed at the wind turbine (100) is lower than or close to the cut-in wind speed of the wind turbine (100), and wherein the wind speed is close to the cut-in wind speed when the wind speed is different from the cut-in wind speed by less than 10%, 5% or 3% of the cut-in wind speed.

2. The method according to claim 1, wherein The method comprises operating the wind turbine in an operating mode (401, 404), wherein operating in the operating mode (401, 404) comprises receiving at least a part of the amount of active power from the power grid (112) and at least partially compensating for losses associated with the electrical system (103) by at least a part of the amount of active power received from the power grid (112).

3. The method according to claim 1 or 2, wherein The amount of active power comprises the amount of active power required to compensate for the electrical power dissipated when providing the required reactive power, and wherein, preferably, the electrical power is dissipated at least by the electrical system (103), in particular by the generator (104) and / or by a power converter (107) of the electrical system, and / or during rotation of the wind turbine rotor (101), in particular by a mechanical drivetrain (102) mechanically coupling the wind turbine rotor to the electrical system, and / or by one or more auxiliary systems of the wind turbine (100).

4. The method according to any one of the preceding claims, wherein, The electrical system (103) comprises a power converter (107) configured to convert the electrical power exchanged with the power grid (112), and wherein the generator (104) operating as the phase shifter provides a part of the reactive power, and wherein the method comprises Operate at least a part of the power converter (104) as a flexible alternating current transmission system, in particular as a static synchronous compensator STATCOM, to supply at least a part of the reactive power to the power grid (112) or to supply the remaining part of the required reactive power to the power grid (112).

5. The method according to any one of the preceding claims, wherein, The power system (103) includes a power converter (107) configured to convert the electrical power exchanged with the power grid (112), and wherein the reactive power exchanged is provided by both the generator (104) and the power converter (107) according to their respective maximum reactive power capabilities, where preferably, the respective maximum reactive power capabilities are adjusted based on one or more operating conditions of the generator (104) and / or the power converter (107).

6. The method according to any one of the preceding claims, wherein, The method includes operating the wind turbine (100) in operating modes (401, 402), wherein operating in the operating modes includes: - Generating active power from the generator (104) and from the rotational mechanical power provided by the wind turbine rotor (101) to supply at least a part of the required amount of active power to the power system (103).

7. The method according to claim 6, wherein, Operating in the operating modes (401, 402) includes controlling the rotational speed of the wind turbine rotor (101) or the generator rotor (106) of the generator (104) such that the wind turbine rotor or the generator rotor (106) rotates at a speed within a predetermined speed range, where preferably, the power system (103) includes a power converter (107) configured to convert the electrical power exchanged with the power grid (112), and wherein the predetermined speed range is set such that the voltage at the power converter (107) is within the operating voltage range of the power converter, where more preferably, the speed range includes a lower limit such that the generator rotor (106) rotates at more than 50% of the synchronous speed of the generator (104) and / or the speed range can include an upper limit such that the generator rotor rotates at less than 160% of the synchronous speed of the generator.

8. The method according to claim 6 or 7, wherein The operating mode is a first operating mode (401), wherein the generator (104) generates a part of the required amount of active power, and wherein operating the wind turbine (100) in the first operating mode further includes Supplying the remaining part of the required amount of active power from the power grid (112) to the power system (103), wherein the wind turbine (100) is preferably further operable in a second operating mode (402), in which the generator (104) generates the total required amount of active power.

9. The method according to claim 8, wherein, Operating the wind turbine (100) in the first operating mode (401) further includes: If the consumption of the remaining part of the required active power amount from the power grid (112) rises above a corresponding threshold and / or if a monitoring parameter indicating the wind speed at the wind turbine (100) drops below a corresponding threshold, the operation of the wind turbine (100) in the first operation mode (401) is stopped.

10. The method according to claim 8 or 9, wherein, The wind turbine (100) includes a clutch (314) configured to mechanically decouple the wind turbine rotor (101) and / or a drivetrain (102) arranged between the wind turbine rotor (101) and the generator (104) from the generator, wherein operating the wind turbine in the first operation mode (401) further includes: If the consumption of the remaining part of the required active power amount from the power grid (112) rises above a corresponding threshold and / or if a monitoring parameter indicating the wind speed at the wind turbine (100) drops below a corresponding threshold, decouple the wind turbine rotor (101) and / or the drivetrain (102) from the generator.

11. The method according to any one of claims 6-10, wherein, Operating in the operation mode includes receiving at least a part of the active power amount from the power grid, wherein the method further includes: When it is detected that the operation requirement of the wind turbine (100) in a different additional operation mode (404) requires less consumption of active power from the power grid (112) in order to supply the reactive power to the power grid, switch from the operation mode (401) to the additional operation mode (404), wherein preferably, the detection is based on one or more monitoring parameters, wherein in particular, the one or more parameters include a parameter indicating the wind speed at the wind turbine (100), and / or wherein the detection is based on an estimate of the consumption of the required active power from the power grid (112) in the different additional operation mode (404), and the estimate is particularly performed by using a model that enables the operation of the wind turbine (100) in the different additional operation mode (404).

12. The method according to any one of the preceding claims, wherein, The wind turbine (100) includes a clutch (314) configured to mechanically decouple the wind turbine rotor (101) and / or a drivetrain (102) arranged between the wind turbine rotor (101) and the generator (104) from the generator, wherein the method includes: Decouple the wind turbine rotor (101) and / or the drivetrain (102) from the generator; and After the decoupling, operate the wind turbine (100) in an additional operation mode (404), wherein operating in the additional operation mode (404) includes supplying the total required active power amount from the power grid (112) to the power system (113).

13. The method according to any one of the preceding claims, wherein, The method includes pitching one or more rotor blades of the wind turbine rotor (101) when it is detected that the wind turbine (100) is providing or capable of providing more active power than the required amount of active power. Preferably, the detection is based on a monitoring parameter that indicates at least one of the wind speed at the wind turbine (100), the rotational speed of the wind turbine rotor and / or the generator rotor of the generator, the voltage of the wind turbine (100), and the current of the wind turbine (100).

14. A control system for controlling the operation of a wind turbine, wherein, The wind turbine (100) includes a wind turbine rotor (101) and an electrical system (103), the electrical system (103) includes a doubly-fed induction generator (104) mechanically coupled to the wind turbine rotor (101), wherein the electrical system (103) is configured to exchange electrical power with the power grid (112), and wherein the control system (120) is configured to perform the method according to any one of claims 1-13.

15. A computer program for controlling the operation of a wind turbine, wherein, The computer program includes control instructions that, when executed by a processing unit (121) of a control system (120) that controls the operation of the wind turbine (100), cause the processing unit to perform the method according to any one of claims 1-13.

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