DE102021100273A1 - Control device for a wind farm - Google Patents

Abstract

The application relates to a control device (102) for a wind farm (100) with an electrical wind farm network (132), in particular for an offshore wind farm (100), comprising at least one determination device (104), set up to determine at least one harmonic parameter from at least one provided electrical variable of the electrical wind farm grid (132), at least one evaluation device (106), set up to compare the at least one specific harmonic parameter with at least one predetermined harmonic parameter limit value in an evaluation step, at least one determination device (108), set up to adapt a for at least one converter (126 , 326) of the wind farm (100) set converter switching pattern if at least one minimum distance between the at least one specific harmonic parameter and the at least one predetermined harmonic parameter limit value is determined in the evaluation step, and at least one e control device (110), set up to control the at least one converter (126, 326) with the adapted converter switching pattern.

Description

The application relates to a control device (or regulating device) for a wind farm with an electrical wind farm network, in particular for an offshore wind farm with an electrical wind farm network. In addition, the application relates to a wind farm, a method for operating a wind farm and a computer program product.

Nowadays, electrical energy is increasingly being obtained from regenerative energy sources (e.g. solar energy or wind energy). Wind farms with at least one wind turbine are being installed more and more. A wind turbine converts the kinetic energy of the wind into electrical energy using a converter.

In addition to onshore wind farms, offshore wind farms in particular are being built. Offshore locations (compared to onshore locations) are usually characterized by relatively continuous wind conditions and high average wind speeds, so that so-called offshore wind farms are increasingly being installed.

As a rule, a wind farm has a plurality of wind power plants, for example at least one substation and an internal electrical wind farm network. The electrical energy/power generated by the wind turbines is fed into a (public) electrical distribution network and/or transport network at at least one feed point via the wind farm network. During the generation of the energy, harmonic emissions, such as voltage distortions and/or current distortions, can be generated by the components of the wind farm.

In order to avoid impermissible voltage distortions (in particular harmonics), it is known from the prior art that a control device controls the at least one converter of the at least one wind turbine of the wind farm with a converter switching pattern which is optimized with regard to minimizing the emissions of harmonics or voltage distortions . In this case, the converter switching pattern set on the named converter remains unchanged in the prior art.

In the prior art, the set converter switching pattern is only changed if the operating point of the wind turbine changes, i.e. a different target voltage and/or a different target current and/or a different target power is specified, or the network operator of the distribution and/or transport network or the feed-in point operator detects that a voltage distortion limit or harmonic limit has been exceeded by the at least one harmonic parameter (e.g. harmonic of a specific order) generated by the wind farm. In the latter case, it is then necessary in the prior art to calculate a new switching pattern.

A disadvantage of this control/regulation of a wind farm, however, is that switching losses can occur in the wind farm. These losses in turn reduce the electrical energy fed into the distribution and/or transport network.

The application is therefore based on the object of creating a possibility which reliably prevents impermissible voltage distortions or voltage loads and at the same time increases the electrical energy that can be fed into a distribution and/or transport network.

According to a first aspect of the application, the object is achieved by a control device according to claim 1 for a wind farm with an electrical wind farm network, in particular for an offshore wind farm. The control device includes at least one determination device, set up to determine at least one harmonic parameter from at least one provided electrical variable of the electrical wind farm network (in a determination step). The control device comprises at least one evaluation device set up to compare the at least one specific harmonic parameter with at least one predefined harmonic parameter limit value in an evaluation step. The control device comprises at least one determination device, set up to adapt a converter switching pattern set for at least one converter of the wind farm (for the set operating point of the converter) (in a determination step), if in the evaluation step at least one minimum distance between the at least one specific harmonic parameter and the at least one predetermined harmonic parameter limit is detected. The control device includes at least one control device set up to control the at least one converter with the adapted converter switching pattern (in one control step).

In contrast to the prior art, a possibility is created according to the application, which reliably prevents impermissible voltage distortions or voltage loads and at the same time increases the electrical energy that can be fed into a distribution and/or transport network by adapting at least one converter switching pattern if at least a minimum distance between the (instantaneous) harmonic parameter and the specified harmonic parameter limit value is determined and ascertained, i.e. a greater voltage load than is currently present is still permissible. By evaluating whether greater voltage distortion is still permissible, the at least one converter switching pattern can be changed in order to optimize the switching losses. A dynamic control of the at least one converter can take place.

According to the application, a harmonics parameter means in particular a harmonics level.

The control device is used to control at least one wind farm. The control device can be a central control device for the entire wind farm or a decentralized control device for a component of the wind farm, such as a converter of a wind turbine. A control device can be formed from a plurality of (decentralized) sub-control devices. In this case, a control device can also be arranged remotely from the wind farm, for example remotely from an offshore wind farm. The control device can in particular include software devices (executable code) that can be executed by a computer.

A wind farm according to the application comprises at least one electrical (internal) wind farm network, which is formed from at least one energy cable (e.g. medium-voltage or high-voltage cable). In addition, the wind farm includes at least one wind power plant connected to the wind farm network, set up to generate electrical energy from the wind energy. For this purpose, a wind turbine has at least one (power electronic) converter. It goes without saying that a wind turbine can include a large number of other components.

A wind farm preferably has a large number of wind turbines and, for example, at least one substation. The internal wind farm network is connected to an electrical distribution network and/or transport network via at least one feed point, in order in particular to feed the generated electrical energy into the distribution network and/or transport network. The wind farm and in particular the wind farm grid can include the feed-in point.

In a preferred embodiment, the wind farm is an offshore wind farm and the at least one wind turbine is an offshore wind turbine. The at least one power cable can be a submarine cable.

According to the application, the control device comprises a determination device set up to determine at least one (instantaneous)

Harmonic parameter from at least one provided electrical variable of the electrical wind farm network. A harmonic parameter means in particular a voltage distortion or voltage load specification that is (currently) present in the wind farm network. As already described, a harmonics parameter is to be understood in particular as a harmonics level.

At least one electrical variable of the electrical wind farm network is made available to the determination device for the determination. As a rule, at least one current (measured in the wind farm grid) and one voltage (measured in the wind farm grid) can be provided. In the case of variants of the registration, further measured quantities can be provided, such as the mains frequency.

In one embodiment, at least one measuring device can be provided (in the wind farm). The control device can include the measuring device or can be connected to it. The at least one measuring device can be set up to measure the at least one electrical variable, preferably to measure current and voltage (in a conventional manner).

The measuring device can preferably detect and in particular measure the at least one electrical variable at the at least one feed point (or directly adjacent thereto). A feed-in point is in particular the place at which the internal wind farm grid is connected to an external distribution grid and/or transport grid that is not covered by the wind farm.

According to a preferred embodiment of the control device, the determination device can be a calculation device set up to calculate the at least one harmonic parameter (a plurality of harmonic parameters can preferably be calculated) based on a predetermined calculation rule. In particular, the calculation device can be set up to calculate the at least one harmonic parameter or at least one harmonic level by applying a Fourier transformation to the at least one electrical quantity provided (in particular current and voltage).

A DFT (Discrete Fourier Transformation) can preferably be specified as the calculation rule. This can be valid for a finite sequence of sampled and provided measured values. This can be ensured with a window function over the series of measurements.

bzw. $$X_k={\displaystyle \sum _{n=0}^{N-1}\left(\text{cos}\left(\frac{2\pi }{N}\ast k\ast n\right)-j\ast \text{sin}\left(\frac{2\pi }{N}\ast k\ast n\right)\right)}$$

Hierbei ist N die Anzahl der abgetasteten (Strom- oder Spannungs-) Messwerte und n die Nummer des jeweils abgetasteten Messwertes. _The complex Fourier _{coefficients X k =} X ₀ , _{X 1 ,} . .. X _N-1 can be determined. $$X_k={\displaystyle \sum _{n=0}^{N-1}{x}_n*e^{\frac{-\mathrm{<figure-callout\; id="2"\; label="j"\; filenames="DE102021100273A1\_0005.png,DE102021100273A1\_0006.png"\; state="\{\{state\}\}">j</figure-callout>}2\pi }{N}\ast k\ast n}}$$

or. $$X_k={\displaystyle \sum _{n=0}^{N-1}\left(\text{cos}\left(\frac{2\pi }{N}\ast k\ast n\right)-j\ast \text{sin}\left(\frac{2\pi }{N}\ast k\ast n\right)\right)}$$

Where N is the number of sampled readings (current or voltage) and n is the number of each sampled reading.

The at least one ascertained, in particular calculated, (instantaneous) harmonic parameter (value) is made available to the evaluation device. The evaluation device is set up to compare the ascertained harmonic parameter with at least one predetermined harmonic parameter limit value. For example, the at least one harmonic parameter limit value can be provided and in particular specified by the operator of the distribution and/or transport network and/or by the operator of the feed point.

If a plurality of different harmonic parameters are determined, an (individually determined) harmonic parameter limit value can preferably be provided for each of these harmonic parameters. It goes without saying that at least one harmonic parameter can be determined for each phase.

If at least one minimum distance between the at least one specific harmonic parameter and the at least one predetermined harmonic parameter limit value is determined in the evaluation step, this can be communicated to the determining device. A minimum distance is in particular the safety distance to be maintained between a harmonic parameter and the harmonic parameter limit value, at which it is (still) ensured that no impermissible interference/voltage distortions occur.

In one case, the minimum distance may be zero. A hysteresis value not equal to zero can preferably be defined as the minimum distance in order to prevent impermissible interference/voltage distortions in a particularly reliable manner.

Determining a minimum distance between the at least one specific harmonics parameter and the at least one predetermined harmonics parameter limit means in particular that the instantaneous voltage stress is still sufficiently far away from the harmonics parameter limit and a greater voltage stress is permissible (i.e. will still be below the harmonics parameter limit).

The at least one converter of the at least one wind turbine switches according to the set or specified converter switching pattern. A wind turbine can include at least one converter. As a rule, each wind turbine has two to three converters. Especially the converter includes a plurality of electronic power switches which switch depending on the set converter switching pattern. For example, IGBTs (insulated-gate bipolar transistors) and/or IGC thyristors (integrated gate-commutated thyristors), but also other technologies, can be used as electronic power switches. This ensures that the output electrical power (or current and/or voltage) corresponds to a specified target value. In particular, the setpoint specifies the operating point. It goes without saying that current regulation is generally provided in this case.

A converter switching pattern according to the present application specifies the switching behavior (in particular the individual switching times) in particular for the electronic power switches of the converter. A converter switching pattern contains in particular at least one switching time/switching angle and at least one binary signal for a gate driver. In particular, a converter switching pattern in the present case means an offline converter switching pattern.

A specific operating point (or desired value) can be set using a number of different converter switching patterns. According to the application, it has been recognized that the different converter switching patterns have an influence not only on the voltage distortions that are generated, but also on the switching losses. As a rule, the switching losses can be reduced all the more, the more the voltage distortions increase. In particular, it has been recognized that at least when there is a minimum distance, the currently set converter switching pattern can (still) be adapted in such a way that the switching losses are (even further) minimized.

The determination device is (therefore) set up to adapt a converter switching pattern (currently) set for at least one converter of the wind farm (for the currently set operating point of the converter) if in the evaluation step at least a minimum distance between the at least one specific harmonic parameter and the at least one specified harmonic parameter limit value is detected.

As will be explained in more detail below, an adaptation preferably takes place by selecting a different (precalculated) converter switching pattern with at least better switching loss information than the currently set converter switching pattern. In other variants of the registration, individual switching times of the set converter switching pattern can also be adjusted.

Furthermore, the control device comprises at least one control device for controlling the at least one converter (or the converter controller) with the adapted, preferably determined or (re)selected converter switching pattern. For example, a (wireless and/or wired) communication network can be provided. The control device can transmit a pattern data record, containing the adapted converter switching pattern, to the converter via the communication network. The converter (or the converter controller) is set up to behave in accordance with the converter switching pattern.

In particular, it has been recognized according to the application that the voltage distortion changes (constantly) from the overall impedance (i.e. impedance of the wind farm network and impedance of the connected distribution and/or transport network). In particular, the configuration (in particular interconnection) of the internal wind farm network and/or the external distribution and/or transport network can (often) change, as a result of which the respective level of the voltage distortions can sometimes vary significantly. By (almost) continuously monitoring the electrical values and evaluating them as described, the circuit losses can (always) be kept to a minimum when the overall impedance changes. At the same time, it can be ensured that impermissible voltage distortions do not occur.

It goes without saying that if the at least one harmonic parameter limit value is exceeded and/or if the minimum distance is not maintained, the at least one converter switching pattern is also adjusted, in particular by determining a converter switching pattern with a reduced harmonic interference indication.

In one embodiment of the application, these steps can essentially be carried out sequentially in a (pre-described) evaluation process, comprising the determination step, the evaluation step, the determination step and the control step. The evaluation process can preferably be repeated, that is to say iteratively carried out, until the (specifiable and/or specified) minimum distance is (approximately) reached. If this is the case, in particular an optimal setting with regard to circuit losses and voltage distortions. As has already been described, (almost) continuous monitoring, evaluation and (if necessary) adaptation of the at least one converter switching pattern can take place in order in particular to (promptly) take account of changes in the overall impedance.

According to a further embodiment of the control device according to the application, the at least one ascertained harmonic parameter can be a total harmonic load. The overall harmonic load or the overall harmonic load level results in particular from the individual harmonics of different orders. The total harmonic load is also referred to as "Total Harmonic Distortion" (THD).

Alternatively and preferably additionally, the at least one harmonic parameter can be a harmonic of a specific order. In particular, a plurality of harmonics (levels) of different orders can be determined.

As already described, an (individual) harmonic parameter limit value can be specified for each of these harmonic parameters. Also, only a single limit value can be specified for all harmonic parameters. In this case, a converter switching pattern is adapted in such a way that all harmonic parameter limit values are complied with by the corresponding determined harmonic parameter (values). As has already been described, this can be achieved in particular by an evaluation process that is carried out iteratively.

• - mindestens eine Speichereinrichtung, eingerichtet zum Speichern, für mindestens einen Arbeitspunkt, eines ersten (vorberechneten) Umrichterschaltmusters und mindestens eines weiteren sich von dem ersten Umrichterschaltmuster zumindest teilweise unterscheidenden (vorberechneten) Umrichterschaltmusters.

According to a further embodiment of the control device according to the application, the control device can also include:

• - at least one storage device, set up for storing, for at least one operating point, a first (precalculated) converter switching pattern and at least one further (precalculated) converter switching pattern that differs at least partially from the first converter switching pattern.

A multiplicity of different converter switching patterns can preferably be calculated in advance (in particular optimized) and stored for a multiplicity of (potential) operating points of a converter. Depending on the evaluation result, the determining device can determine a converter switching pattern as an adapted converter switching pattern.

In the case of variants of the application, the memory device cannot be coupled with the control device. In this case, an external database (implemented in a backend system, cloud server and/or the like, for example) can be provided, which contains the storage device which the determination device can access via a (secured) communication connection.

According to a preferred embodiment of the control device according to the application, a first switching loss indication and a first harmonic interference indication can be assigned to at least the first converter switching pattern and a further switching loss indication and a further harmonic interference indication to the further converter switching pattern. A switching loss indication and a harmonic interference indication are preferably assigned to each stored converter switching pattern.

A switching loss specification enables the determining device in particular to estimate whether the switching losses increase or decrease when the corresponding converter switching pattern is selected, in particular compared to the currently set converter switching pattern. An indication of harmonic interference enables the determining device in particular to estimate whether the at least one harmonic parameter (value or level) increases or decreases when the corresponding converter switching pattern is selected, in particular compared to the currently set converter switching pattern. A harmonic interference indication and/or a switching loss indication may be an absolute or relative value, where the value may be explicitly stated or implicitly resulting from the converter switching pattern stored in some way.

The first harmonic interference indication may differ from the further harmonic interference indication. In particular, the first switching loss indication can additionally (but also alternatively) differ from the further switching loss indication.

According to a further preferred embodiment of the control device according to the application, at least the first converter switching pattern and the further converter switching pattern can be stored in a table form. In particular, all of the stored converter switching patterns can be stored in table form.

Particularly preferably, the respective harmonic interference information and the respective switching loss information of the (respectively) stored converter switching pattern can at least be derived from the table position of the respective converter switching pattern. In particular, the converter switching patterns can be stored, in particular positioned, in a table in accordance with a predetermined storage rule. From the table position of a first converter switching pattern, in particular in comparison to the table position of the at least one further converter switching pattern in the table, it can be derived how the switching losses and/or the at least one harmonic parameter are influenced by the first converter switching pattern in comparison to the at least one further converter switching pattern. An example table is shown below: Table 1 m S S S S S S m _{1 S1.1 S1.2 S1.3 S1.4 S1.5 S1.6} m _{2 2.1 S2.2 2.3 2.4 S2.5 2.6}

In this case _, m _n designates the various operating points with _n =1 _, 2 distinguish from each other. In the present example, the at least one harmonic parameter (value) (ie the voltage distortion) increases as k increases, while the switching losses decrease as k increases.

If, for example, the converter switching pattern S _1.3 is currently set for the at least one converter for the operating point mi and it is determined in the evaluation step that a safety distance (based on the limit value) is above the specified minimum distance between the at least one specific harmonic parameter and the at least one predetermined harmonic parameter limit value (ie at least a minimum distance is determined), the determination device can preferably determine the (adjacent) converter switching pattern S _1.4 . Then the at least one harmonic parameter can be determined again (etc., as previously described).

It should be understood that Table 1 is just an example and a table may be organized differently, may include a variety of different or additional entries, may be multi-dimensional, may be formed for a plurality of converters, and/or the like. As an alternative to a table form, a functional connection between the stored patterns is also conceivable.

According to a further preferred embodiment of the control device according to the application, the evaluation device can be set up to determine a (current) harmonic safety distance between the at least one determined harmonic parameter and the at least one harmonic parameter limit value. If the determined harmonic safety distance is greater than the minimum distance (based on the harmonics parameter limit and is below the harmonics parameter limit), the determining means may be arranged to determine the converter switching pattern from the stored converter switching patterns (e.g. Table 1). In other words, it can be determined whether even higher voltage distortions are possible to (even further) reduce the switching losses.

Preferably, the distance between the determined harmonic safety distance and the minimum distance (and/or the harmonic parameter limit) can be determined and a converter switching pattern determined depending on the size of the distance. For example, if the distance is small, the immediately adjacent pattern can be selected in the table above. If, on the other hand, the distance is large, the next but one pattern can be determined, for example. A corresponding rule can be implemented in the determination device.

In addition, according to a further embodiment of the control device according to the application, the determination device can be set up to determine the converter switching pattern at least at least from the first converter switching pattern and the at least one further converter switching pattern, based on (the determined harmonic safety margin and) the respective harmonic interference data and switching loss data assigned to the converter switching patterns (as was explained in particular). As a result, a more optimal converter switching pattern can be determined in a particularly simple and at the same time reliable manner.

Preferably, at least one shift pattern determination rule can be specified. The switching pattern determination rule can stipulate that if the minimum distance is exceeded by the harmonic safety margin, a converter switching pattern is determined based on the associated harmonic interference information, which causes a reduction in the harmonic safety margin (i.e. increases the interference (but at the same time minimizes the switching losses). The switching pattern determination rule can in particular specify the determination of a converter switching pattern from a table (e.g. table 1).

In a further embodiment of the control device according to the application, the control device can be a central control device (of the entire wind farm). The determination device of this control device can be set up to adapt a plurality of converter switching patterns for a corresponding plurality of converters of the wind farm, for example based on a predefined determination rule (if at least one minimum distance between the at least one specific harmonic parameter and the at least one predefined harmonic parameter limit value is determined in the evaluation step ).

The control device of the central control device can be set up to control the plurality of converters of the wind farm with the adapted converter switching patterns. Depending on the at least one determination rule, in particular only the converter switching pattern of a single converter (e.g. strong) can be changed, the converter switching pattern of a part (> 1) of the converters of the wind farm or all converter switching patterns of all converters of the wind farm can be adjusted (as described above). For example, the determination rule can be mapped in the table itself.

• - mindestens eine Windkraftanlage mit mindestens einem Umrichter, und
• - mindestens eine zuvor beschriebene Steuervorrichtung.

Another aspect of the application is a wind farm, in particular an offshore wind farm, comprising:

• - at least one wind turbine with at least one converter, and
• - at least one control device as described above.

As has already been described, the wind farm can have an internal electrical wind farm grid which is electrically connected to at least one distribution grid and/or transport grid at at least one feed point. The at least one wind power plant is connected to the wind farm network and can, in particular, feed the generated electrical energy into this network.

The wind farm network can include at least one measuring device as described above, in particular set up for detecting current and voltage at the feed-in point. With other variants of the registration, the recording can also take place at a different point, for example before or after the feed-in point (from the point of view of the wind farm network). In addition, the wind farm can include at least one previously described communication network.

In a preferred embodiment, the wind farm may be an offshore wind farm. As a rule, an offshore wind farm has a large number of offshore wind energy structures, such as a large number of offshore wind power plants, measuring masts and/or at least one offshore transformer station. The offshore wind farm can be electrically connected via the offshore substation to an onshore substation or another offshore substation or offshore converter station, for example. An onshore substation, in turn, can be connected to the distribution network and/or transport network and form the feed-in point, for example.

• - Ermitteln mindestens eines Oberwellenparameters aus mindestens einer bereitgestellten elektrischen Größe des elektrischen Windparknetzes in einem Ermittlungsschritt,
• - Vergleichen des mindestens einen bestimmten Oberwellenparameters mit mindestens einem vorgegebenen Oberwellenparametergrenzwert in einem Auswerteschritt,
• - Anpassen eines für mindestens einen Umrichter des Windparks eingestellten Umrichterschaltmusters (für den eingestellten Arbeitspunkt des Umrichters) in einem Bestimmungsschritt, wenn in dem Auswerteschritt zumindest eine Mindestdistanz zwischen dem mindestens einen bestimmten Oberwellenparameter und dem mindestens einen vorgegebenen Oberwellenparametergrenzwert festgestellt wird, und
• - Ansteuern des mindestens einen Umrichters mit dem angepassten Umrichterschaltmuster in einem Steuerschritt.

A further aspect of the application is a method for controlling a wind farm (with at least one wind power plant), in particular a wind farm as described above. The procedure includes:

• - Determination of at least one harmonic parameter from at least one provided electrical variable of the electrical wind farm network in a determination step,
• - Comparing the at least one specific harmonic parameter with at least one predefined harmonic parameter limit value in an evaluation step,
• - Adaptation of a converter switching pattern set for at least one converter of the wind farm (for the set operating point of the converter) in a determination step if at least one minimum distance between the at least one specific harmonic parameter and the at least one specified harmonic parameter limit value is determined in the evaluation step, and
• - Driving the at least one converter with the adapted converter switching pattern in one control step.

The method can be carried out in particular by a previously described control device.

Yet another aspect of the application is a computer program product (or computer program) comprising instructions which, when the computer program is executed by a computer (in particular the control device), cause the latter to execute the method described above.

The computer program product, in particular the instructions or program instructions, can be stored in a computer program memory, in particular a program memory. For example, program memory is non-volatile memory such as flash memory, magnetic memory, EEPROM memory (Electrically Erasable Programmable Read Only Memory), and/or optical memory.

In addition, a control device may have a main memory, for example a volatile or non-volatile memory, in particular a random access memory (RAM) such as a static random access memory (SRAM), a dynamic random access memory (DRAM), a ferroelectric RAM memory (FeRAM) and/or magnetic random access memory (MRAM). The processor of the control device can, for example, store intermediate results or the like in the main memory.

In the present case, a facility or a device can be formed at least partially from software and/or at least partially from hardware. In particular, a device/element may include appropriate computing elements (e.g., processor, memory, etc.).

The features of the control devices, wind farms, methods and computer program products can be freely combined with one another. In particular, features of the description and/or the dependent claims, even if features of the independent claims are completely or partially bypassed, can be independently inventive on their own or freely combined with one another.

• 1 eine schematische Ansicht eines Ausführungsbeispiels eines Windparks gemäß der vorliegenden Anmeldung mit einem Ausführungsbeispiels einer Steuervorrichtung gemäß der vorliegenden Anmeldung,
• 2 ein Diagramm eines Ausführungsbeispiels eines Verfahrens gemäß der vorliegenden Anmeldung,
• 3 eine schematische Ansicht eines Ausführungsbeispiels einer Umrichterregelung,
• 4 ein Diagramm mit einem beispielhaften Pegelverlauf,
• 5a ein Diagramm mit einer beispielhaft gemessenen Oberschwingung 5. Ordnung (Spannungs- und Stromverlauf) bei einer ersten Gesamt-Impedanz, und
• 5b ein Diagramm mit einer beispielhaft gemessenen Oberschwingung 5. Ordnung (Spannungs- und Stromverlauf) bei einer weiteren Gesamt-Impedanz.

There are now a large number of possibilities for designing and further developing the control device according to the application, the wind farm according to the application, the method according to the application and the computer program product according to the application. In this regard, reference is made on the one hand to the claims subordinate to the independent claims and on the other hand to the description of exemplary embodiments in conjunction with the drawing. In the drawing shows:

• 1 a schematic view of an embodiment of a wind farm according to the present application with an embodiment of a control device according to the present application,
• 2 a diagram of an embodiment of a method according to the present application,
• 3 a schematic view of an embodiment of a converter control,
• 4 a diagram with an example level curve,
• 5a a diagram with an exemplary measured 5th order harmonic (voltage and current profile) at a first total impedance, and
• 5b a diagram with an example of a measured 5th order harmonic (voltage and current curve) with a further total impedance.

The same reference symbols are used below for the same elements.

the 1 shows a schematic view of an embodiment of a wind farm 100 according to the present application with an embodiment of a control device 102 according to the present application.

As can be seen, the wind farm 100 comprises at least one wind turbine 120 and an electrical internal wind farm network 132, which is formed from at least one energy cable (in particular medium-voltage cable and/or high-voltage cable). In preferred variants, a wind farm can include a plurality of wind power plants. In particular, the wind farm 100 can be an offshore wind farm 100 .

The wind power plant 120 is in particular a conventional wind power plant 120. The wind power plant 120 has a tower 122 and a nacelle 126 arranged on the tower 122. The wind energy is converted into electrical energy with the aid of a converter 126. This is fed into the internal wind farm network 132 via a transformer 128 and an electrical connection 130 . In other variants, the transformer can also be omitted.

The electrical energy generated is transmitted to a feed point 134 via the wind farm network 132 . The electrical energy is fed into an external distribution and/or transport network 136 at the feed point 134 . As can be seen, the wind farm 100 in the present exemplary embodiment includes at least one measuring device 138.

The measuring device 138 is presently set up to measure the current and the voltage of the wind farm network 132 at the feed point 134. These measured electrical variables can be transmitted to a receiving module 116 of the control device (via a (wireless and/or wired) communication network). In particular, the measuring device 138 can be set up for (almost) continuous monitoring, that is to say in particular measuring almost continuously.

In the present case, the control device 102 can in particular be a central control device 102 for controlling the entire wind farm 100 .

The measured (and sampled) measured values are provided in particular to a determination device 104 of the control device 102 . The determination device 104 is set up to determine at least one harmonic parameter (preferably a plurality of harmonic parameters) from the provided electrical variables current and voltage of the electrical wind farm network 132 in a determination step. As previously described, this can be done using a DFT.

The at least one ascertained harmonic parameter is made available to an evaluation device 106 of control device 102 . The evaluation device 106 evaluates the ascertained harmonic parameter and the associated (specified) harmonic parameter limit value. The evaluation device 106 is set up to compare the at least one specific harmonic parameter with at least one predefined harmonic parameter limit value in an evaluation step.

The evaluation device 106 is preferably set up to determine a harmonic safety margin between the at least one ascertained (instantaneous) harmonic parameter and the at least one harmonic parameter limit value. In particular, the determined harmonic safety distance is compared with the minimum distance and it is checked whether the minimum distance is reached or not (yet). It is therefore checked in particular whether there is at least a (specified) minimum distance between the harmonic parameter and the at least one harmonic parameter limit value.

The evaluation result is made available to determination device 108 of the control device. If at least one minimum distance between the at least one specific harmonics parameter and the at least one specified harmonics parameter limit value is determined in the evaluation step, i.e. the specific harmonics safety distance (based on the harmonics parameter limit value) is greater than the minimum distance (based on the harmonics parameter limit value), determination device 108 an adjustment of a converter switching pattern set for at least one converter 126 of the wind farm 100 for the set operating point of the converter 126 in a determination step.

In particular, a multiplicity of precalculated converter switching patterns for preferably a multiplicity of potential operating points, ie operating points which may be set on the converter 126, can be stored in a memory device 112 in the form of a data memory 112. The precalculated converter switching patterns can particularly preferably be stored in tabular form.

A respective harmonic interference indication and a respective switching loss indication of a respective stored converter switching pattern can in particular from the table position of the respective converter switching pattern can at least be derived. Depending on the evaluation result, the converter switching pattern is adapted by determination device 108.

1. 1. Der OberwellenSicherheitsabstand ist größer als die Mindestdistanz, also der Oberwellenparameter ist kleiner als der Oberwellenparametergrenzwert (d.h. insbesondere: In dem Auswerteschritt wird zumindest eine Mindestdistanz zwischen dem mindestens einen bestimmten Oberwellenparameter und dem mindestens einen vorgegebenen Oberwellenparametergrenzwert festgestellt).
2. 2. Der OberwellenSicherheitsabstand ist ungefähr gleich der Mindestdistanz, also der Oberwellenparameter ist insbesondere ungefähr gleich oder nahe an dem Oberwellenparametergrenzwert, aber noch im zulässigen Bereich.
3. 3. Der OberwellenSicherheitsabstand ist kleiner als die Mindestdistanz, also der Oberwellenparameter ist insbesondere größer als der Oberwellenparametergrenzwert, also nicht mehr im zulässigen Bereich.

In particular, the evaluation can lead to the following three evaluation results:

1. 1. The harmonics safety distance is greater than the minimum distance, i.e. the harmonics parameter is smaller than the harmonics parameter limit value (ie in particular: In the evaluation step, at least one minimum distance between the at least one specific harmonics parameter and the at least one specified harmonics parameter limit value is determined).
2. 2. The harmonic safety distance is approximately equal to the minimum distance, so in particular the harmonic parameter is approximately equal to or close to the harmonic parameter limit but still within the allowable range.
3. 3. The harmonics safety distance is smaller than the minimum distance, that is, the harmonics parameter is in particular greater than the harmonics parameter limit value, that is, no longer in the permissible range.

1. 1. Wenn beispielsweise für den mindestens einen Umrichter 126 für den Arbeitspunkt mi derzeit das Umrichterschaltmuster S_1,3 eingestellt ist, kann die Bestimmungseinrichtung 108 vorzugsweise das (benachbarte) Umrichterschaltmuster S_1,4 bestimmen, welches vorzugsweise eine im Vergleich zum eingestellten Umrichterschaltmuster S_1,3 geringere Schaltverlustangabe aufweist (die Oberwellenstörangabe kann im Vergleich zum eingestellten Umrichterschaltmuster S_1,3 höher sein).
2. 2. Das derzeit eingestellte Umrichterschaltmuster, z.B. S_1,3, bleibt eingestellt.
3. 3. Wenn beispielsweise für den mindestens einen Umrichter 126 für den Arbeitspunkt mi derzeit das Umrichterschaltmuster S_1,3 eingestellt ist, kann die Bestimmungseinrichtung 108 vorzugsweise das (benachbarte) Umrichterschaltmuster S_1,2 bestimmen, welches vorzugsweise eine im Vergleich zum eingestellten Umrichterschaltmuster S_1,3 geringere Oberwellenstörangabe aufweist (die Schaltverlustangabe kann im Vergleich zum eingestellten Umrichterschaltmuster S_1,3 höher sein).

According to the example in Table 1, the following occurs in particular in the three cases:

1. 1. If, for example, the converter switching pattern S _1.3 is currently set for the at least one converter 126 for the operating point mi, the determination device 108 can preferably determine the (neighboring) converter switching pattern S _1.4 , which is preferably one in comparison to the set converter switching pattern S _{1 .3} has lower switching loss information (the harmonic interference information can be higher compared to the set converter switching pattern S _1.3 ).
2. 2. The converter switching pattern currently set, eg S _1.3 , remains set.
3. 3. If, for example, the converter switching pattern S _1.3 is currently set for the at least one converter 126 for the operating point mi, the determination device 108 can preferably determine the (neighboring) converter switching pattern S _1.2 , which is preferably one in comparison to the set converter switching pattern S _{1 .3} has lower harmonic interference information (the switching loss information can be higher compared to the set converter switching pattern S _1.3 ).

Particularly in cases 1 and 3, the specific converter switching pattern is made available to the control device 110 or the control device 110 is informed about it. The control device 110 is set up to control the at least one converter 126 with the adapted converter switching pattern in one control step. Especially with the newly selected converter switching pattern from the table.

For this purpose, a transmitting device 114 of control device 102, prompted by control device 110, can transmit the specific converter switching pattern via a (wireless and/or wired) communication network 140 to a receiving device 142 of converter 126. Then the converter 126, in particular the circuit breakers, can be operated according to the converter switching pattern.

the 2 shows a diagram of a method according to the present application, in particular for operating a wind farm, as exemplified in FIG 1 was described. The method can in particular by the control device according to the 1 be performed. To avoid repetition, therefore, in the explanations for 2 in addition to the remarks on 1 referred.

In a first step 201, at least one harmonic parameter is determined from at least one provided electrical variable of the electrical wind farm network in a determination step.

In a (subsequent) step 202, the at least one specific harmonic parameter is compared with at least one predefined harmonic parameter limit value in an evaluation step.

Then, in step 203, an adjustment (as described above) of a converter switching pattern set for at least one converter of the wind farm (for the set operating point of the converter) takes place in a determination step if at least one minimum distance between the at least one specific harmonic parameter and the at least one predetermined harmonics parameter limit value is determined, ie in particular when the certain harmonics safety distance is greater than the minimum distance (each based on the harmonics parameter limit value).

Then, in step 204, the at least one converter is controlled with the adapted converter switching pattern in a control step. The method then continues with step 201. In particular, the method, ie in particular the evaluation process, is carried out iteratively. The evaluation process can preferably be repeated until it is determined in step 202 that the minimum distance has (approximately) been reached, ie in particular the harmonic safety distance is (almost) identical to the minimum distance.

3 shows an example of a schematic view of an embodiment of a converter control with an embodiment of a converter according to the application 326.

How from the 3 As can be seen, a setpoint current i setpoint _is specified as the setpoint value and _is compared with the actual current i actual at comparator 350 . The determined control difference 351 or deviation 351 is fed to the controller 352 of the converter 326 .

This determines the manipulated variable 354 (in particular degree of modulation m and phase angle δ) and feeds it to the modulator 358 . In addition, the modulator 358 is supplied with the adapted, in particular determined, converter switching pattern 356 (as previously described).

The modulator 358 generates switching signals 362 from the supplied manipulated variable 354 and the supplied converter switching pattern 356, which are supplied to the power electronics 360, in particular the IGBTs 360 and/or IGCTs 360. This minimizes the droop 351 while optimizing the overall switching losses and voltage distortion as previously described. It goes without saying that both parameters are optimized in that one parameter improves and the other parameter deteriorates, but overall an optimization takes place for the wind farm.

the 4 shows a diagram with an exemplary level profile P of a plurality of different harmonic parameters 484, 486, 488 in the form of harmonic levels 484, 486, 488 of three phase voltages. The three harmonic levels 484, 486, 488 were measured at three different points in time 1, 2 and 3 or determined using DFT. Numeral 482 indicates the harmonics parameter limit. This is constant for the times 1, 2 and 3 shown, but can also change over time with other variants of the registration.

Reference number 480 indicates the minimum distance. In variants, this distance may also be zero (or approximately zero) based on the harmonic parameter limit. The reference symbols 478.1, 478.2, 478.3 designate the respective harmonic signal-to-noise ratios determined in the evaluation step, starting from the harmonic parameter limit value.

As can be seen from point in time 2, a converter switching pattern was determined after point in time 1 in particular, which entails lower switching losses but higher harmonic interference.

Since in the present exemplary embodiment at point in time 2 or for point in time 2 (still) at least one minimum distance between the at least one specific harmonic parameter and the at least one predetermined harmonic parameter limit value is determined (in other words, the harmonic safety distance 478.2 is greater than the minimum distance 480), a new converter switching pattern is determined again, which compared to the converter switching pattern set at time 2 has lower switching losses but higher harmonic interference.

In the present example, this results in an optimal converter switching pattern being set at time 3, in which the harmonic safety distance 478.3 essentially corresponds to the minimum distance 480, but (in any case) is still below the harmonic parameter limit value 482, i.e. in the permissible range. Here, the switching losses (not shown in the figure) are minimized.

the 5a and 5b each show a diagram with an exemplary measured 5th order harmonic (voltage and current curve) at a first total impedance ( 5a) and one will be total impedance ( 5b) . The explanations can be transferred to harmonics of other orders or the THD.

The voltage level P _u is plotted against the time t in each case in the upper diagram and the current i is plotted against the time t in the respective lower diagram. As you can see, the current amplitudes are the same in both cases, because the converter sometimes makes them, sometimes more, sometimes less, depending on the operating point.

As can also be seen, the voltage distortion is significantly higher in the first case than in the second case. This is due in particular to the different overall impedance that occurs at the network connection point. If the current of a certain order meets an impedance of this order, a high distortion occurs according to U = R * I.

It should be noted that as part of the permanent measurement and calculation of the harmonics at the feed point, it is determined according to the application in particular how far the harmonics (parameters) are below the maximum permissible values of the harmonic load/harmonic parameter limit value. An off-line converter switching pattern or pulse pattern (for the respective operating point) optimized in terms of switching losses can then be sequentially loaded into the individual wind turbines or converters. Furthermore, the harmonic load at the feed point can be monitored.

In particular, off-line converter switching patterns or pulse patterns can be loaded into the individual wind turbines until they are below a previously defined hysteresis value or a previously defined minimum distance (and below the maximum permissible values of the harmonic load).

As a further option, a finite number of off-line converter switching patterns or pulse patterns (so-called weighted off-line converter switching patterns or pulse patterns, which represent a compromise between harmonic load and switching losses) can be pre-calculated depending on the level of permissible voltage distortion and per limit level simultaneously in all wind turbines or only a part of the wind turbines can be charged.

The present method has the advantage that a wind farm can be operated in a switching-loss-optimized manner with very little effort, and a higher yield can thus be generated.

As an alternative to a central control device, as in 1 shown, the selection of the off-line pulse pattern can also be performed at the wind turbine level.

In an offline method, as is used in particular here, the precalculated pulse patterns can be generated quasi “offline”, ie outside of the converter, then imported into the converter and subsequently used by it. In contrast to this, with an online method, the converter considers how it should switch “live” during operation. In an offline method, an optimization can take place, which requires a high computing power. The converter cannot do this “online” itself, since the control in the FPGA of the converter runs in the nanosecond range. In the case of variants of the registration, an (external) additional system can be provided, set up to carry out the calculations.

With this optimization, i.e. the pre-calculation of the pulse pattern for a specific ratio between switching losses and harmonics, the slow regulation/control of the wind farm at the grid connection point can preferably be taken into account, i.e. in particular there where the harmonics are also determined using DFT/FFT.

Claims (12)

Control device (102) for a wind farm (100) with an electrical wind farm network (132), in particular for an offshore wind farm (100), comprising: - at least one determination device (104), set up to determine at least one harmonic parameter from at least one electrical variable provided of the electrical wind farm grid (132), - at least one evaluation device (106), set up to compare the at least one specific harmonic parameter with at least one predetermined harmonic parameter limit value in an evaluation step, - at least one determination device (108), set up to adapt a for at least one converter (126 , 326) of the wind farm (100) set converter switching pattern if at least one minimum distance between the at least one specific harmonic parameter and the at least one specified harmonic parameter limit value is determined in the evaluation step, and - At least one control device (110), set up to control the at least one converter (126, 326) with the adapted converter switching pattern. Control device (102) after claim 1 , characterized in that - the at least one determined harmonic parameter is a total harmonic load, and/or - the at least one harmonic parameter is a harmonic of a specific order. Control device (102) after claim 1 or 2 , characterized in that the control device (102) further comprises: - at least one storage device (112), set up for storing, for at least one operating point of the converter (126, 326), a first converter switching pattern and at least one further converter switching pattern that differs from the first converter switching pattern at least partially differing converter switching pattern. Control device (102) after claim 3 , characterized in that - at least the first converter switching pattern is assigned a first switching loss indication and a first harmonic interference indication and the further converter switching pattern is assigned a further switching loss indication and a further harmonic interference indication, - the first harmonic interference indication differs from the further harmonic interference indication, and/or - the first switching loss indication differs from the further switching loss indication. Control device (102) after claim 4 , characterized in that - at least the first converter switching pattern and the further converter switching pattern are stored in a table form, - the respective harmonic interference data and the respective switching loss data of the stored converter switching patterns being at least derivable from the table position of the respective converter switching pattern. Control device (102) according to any one of the preceding claims 3 until 5 , characterized in that - the evaluation device (106) is set up to determine a harmonic safety margin between the at least one determined harmonic parameter and the at least one harmonic parameter limit value, and - the determination device (108) is set up to determine the converter switching pattern from the stored converter switching patterns if the specific Harmonic safety distance is greater than the minimum distance. Control device (102) after claim 4 or 5 and 6 , characterized in that - the determination device (108) is set up to determine the converter switching pattern at least from the first converter switching pattern and the at least one further converter switching pattern, based on the respective converter switching patterns associated harmonic interference data and switching loss data. Control device (102) according to one of the preceding claims, characterized in that - at least one switching pattern determination rule is specified, - the switching pattern determination rule specifying that when the minimum distance is exceeded by the harmonic safety distance, a converter switching pattern is determined based on the associated harmonic interference information, which causes a reduction in the harmonic safety margin. Control device (102) according to one of the preceding claims, characterized in that - the control device (102) is a central control device (102) of the wind farm (100), - the determination device (108) is set up to adapt a plurality of converter switching patterns for a corresponding Multiple converters (126, 326) of the wind farm (100), and - the control device (110) of the central control device (102) is set up to control the plurality of converters (126, 326) of the wind farm (100) with the adapted converter switching patterns. Wind farm (100), in particular offshore wind farm (100), comprising: - At least one wind turbine (120) with at least one converter (126, 326), and - At least one control device (102) according to any one of the preceding claims. Method for controlling a wind farm (100), in particular a wind farm (100). claim 10 , comprising: - determining at least one harmonic parameter from at least one provided electrical quantity of the electrical wind farm network (132) in a determination step, - comparing the at least one determined harmonic parameter with at least one predetermined harmonic parameter limit value in an evaluation step, - adapting a converter for at least one converter (126, 326) of the wind farm (100) set converter switching pattern in a determination step if at least one minimum distance between the at least one specific harmonic parameter and the at least one specified harmonic parameter limit value is determined in the evaluation step, and - activating the at least one converter (126, 326) with the adapted one Inverter switching pattern in one control step. Computer program product, comprising instructions which, when the program is executed by a computer, cause it to carry out the method according to claim 11 to execute.

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