DUAL PURPOSE CONVERTER

Description

[0001] The present invention relates to a power converter, in particular of a wind turbine for feeding electrical power into an electrical supply network, as well as a central converter of a wind turbine and a wind turbine comprising such a power converter or central converter.

[0002] Generators of electrical energy, such as wind turbines, typically feed their generated electrical power into the electrical supply network using a power converter.

[0003] The power converter has the particular task of directing the electric current generated by the generator of electrical energy in such a way that the electric current meets any criteria of the electrical supply network, such as 50 Hz alternating current.

[0004] A power converter is therefore understood to be, in particular, a device that includes rectifiers and / or inverters and / or converters designed to handle and / or convert currents from several hundred amperes up to several kiloamperes. An example of such a power converter is the frequency inverter of a wind turbine, which, in the case of a full converter design, can also be referred to as a central converter.

[0005] As the power classes of electrical energy generators increase, so do the power classes of power converters and thus their dimensions.

[0006] In the field of wind turbines, this can lead to problems, for example, due to the limited nacelle sizes.

[0007] Furthermore, the increasing penetration of renewable energy sources into the electrical grid is leading to increasingly complex requirements being placed on all generators by grid operators. For example, grid operators require that generators be able to withstand voltage dips.

[0008] Such requirements are usually met by additional operating modes and / or components, which also leads to an increase in the size of the power electronics.

[0009] The German Patent and Trademark Office has searched the following prior art in the priority application for the present application: DE 10 2011 079 214 A1, DE 10 2014 219 909 A1 and DE 10 2017 120 298 A1.

[0010] Document Chen GEN et al.: "Reconfigurable Control for Fault-Tolerant of Parallel Converters in PMSG Wind Energy Conversion System", IEEE TRANSACTIONS ON SUSTAINABLE ENERGY, IEEE, USA, Vol. 10, No. 2, April 1, 2019 (2019-04-01), pages 604-614, XP011715495, ISSN: 1949-3029, DOI: 10.1109 / TSTE.2018.2841018 concerns a wind turbine with a permanent magnet synchronous machine.

[0011] US 2005 / 0201127 A1 concerns an uninterruptible power supply.

[0012] The object of the present invention is therefore to address at least one of the aforementioned problems, to improve the general state of the art, or to provide an alternative to what is currently known. In particular, a power converter is to be provided which meets a wide variety of operating conditions and / or requirements of network operators while requiring only a small form factor.

[0013] The present invention relates to a power converter according to claim 1 and a central converter of a wind turbine according to claim 2. Advantageous embodiments are defined in the dependent claims.

[0014] According to the invention, a power converter, in particular for a wind turbine for feeding electrical power into an electrical supply network, is proposed, comprising at least a plurality of rectifiers that can be connected to a first AC network to convert a first AC voltage into a DC voltage, a DC link connected to the plurality of rectifiers and configured to carry the DC voltage, and a plurality of inverters connected to the DC link and connectable to a second AC network to convert the DC voltage into a second AC voltage, and a switchable converter module, comprising at least: a converter connected to the DC link and a switching unit connected to the converter.which is connectable to the first and second AC networks and can be connected to the first AC network in such a way that the converter is configured as a rectifier, and - can be connected to the second AC network in such a way that the converter is configured as an inverter.

[0015] In particular, a power converter for a wind turbine in the form of a frequency converter or frequency inverter (English: AC-AC converter) is proposed.

[0016] In addition to the usual rectifiers, DC link and inverters, the power converter has a switchable converter module.

[0017] The switchable converter module comprises at least one converter connected to the DC link and a switching unit connected to the converter.

[0018] The converter is also designed to be operated as both a rectifier and an inverter.

[0019] It is therefore specifically proposed that the power converter should have at least one converter that can operate as both a rectifier and an inverter.

[0020] In a particularly preferred embodiment, the converter is further configured to switch between rectifying and inverter functions during operation. This can be achieved, for example, by means of a switching unit described below.

[0021] It is therefore specifically proposed to operate the converter as a rectifier or as an inverter during operation, depending on requirements.

[0022] For example, it may be that in an operating state of the power converter, more apparent power or current has to be converted from the first AC network than apparent power or current has to be converted from the DC link to the second AC network.

[0023] In such cases, it is now proposed to connect the converter to the first AC network using the switching unit in such a way that the converter is configured as a rectifier.

[0024] In other cases, depending on the operating conditions, it may happen that more apparent power or current has to be converted from the DC link to the second AC network than apparent power or current has to be converted from the first AC network to the DC link.

[0025] In such cases, it is now proposed that the converter be connected to the second AC network by means of the connected switching unit in such a way that the converter is configured as an inverter.

[0026] For example, the power converter has four rectifiers and four inverters, as well as a switchable converter module with two converters and two switching units.

[0027] According to the invention, it is possible to operate the power converter in such a way that the power converter has six rectifiers and four inverters, or five rectifiers and five inverters, or four rectifiers and six inverters.

[0028] In a particularly preferred embodiment, the rectifiers, inverters and converters of the switchable converter module have essentially the same power class.

[0029] Preferably, the power converter also includes a control unit which is configured to dynamically switch the switching unit and / or to operate the converter as a rectifier and as an inverter.

[0030] In particular, a control unit is proposed which is designed to dynamically switch the switching unit described above or below so that the converters of the switchable converter module operate as rectifiers or inverters as required during the operation of the power converter.

[0031] It is further specifically proposed that the switching unit be configured to operate the converter of the switchable converter module as a rectifier and / or as an inverter.

[0032] Preferably, the switchable converter module has, in particular, exactly two converters and two switching units, wherein the converters can be operated simultaneously as rectifiers and / or inverters.

[0033] The switchable inverter module therefore has exactly two inverters and two switching units, with each switching unit being assigned to one inverter.

[0034] Furthermore, the converters can be operated simultaneously as rectifiers and / or as inverters.

[0035] This also means, in particular, that both converters can be operated as rectifiers and both as inverters, and that each converter can also be operated as a rectifier and each as an inverter.

[0036] Preferably, the power converter comprises at least two switchable converter modules.

[0037] It is therefore also proposed that the power converter has several switchable converter modules as described above or below.

[0038] In a preferred embodiment, each of these switchable converter modules has exactly two converters and two switching units, wherein the converters can be operated simultaneously as rectifiers and / or as inverters.

[0039] Preferably, the power converter has a plurality of chokes that are essentially of the same size.

[0040] It is therefore also proposed that the power converter has a plurality of chokes arranged at the inputs of the rectifiers or at the outputs of the inverters and arranged at the inputs or outputs of the converters of the switchable converter modules.

[0041] In a particularly preferred embodiment, these chokes are essentially of the same size, preferably in the range between 100 and 1000 micro-henries, particularly preferably in the range between 200 and 800 micro-henries, and particularly preferably essentially 400 micro-henries.

[0042] According to the invention, a central converter for a wind turbine is also proposed, comprising a plurality of switchable converter modules, each switchable converter module comprising at least: a converter connected to a DC link and a switching unit connected to the converter, which can be connected to a first and a second AC network and can be connected to the first AC network in such a way that the converter is configured as a rectifier, and can be connected to the second AC network in such a way that the converter is configured as an inverter.

[0043] In particular, a central converter for a wind turbine is proposed, such as is used in full converter concepts for a wind turbine.

[0044] The central converter essentially comprises a large number of switchable converter modules, as described above or below.

[0045] Accordingly, it is specifically proposed that the individual converters of the central converter can each be operated as both rectifiers and inverters.

[0046] The difference between the central converter proposed herein and the power converter proposed herein lies in particular in the fact that all converter modules of the central converter can be dynamically adapted to the operating conditions, whereas the power converter has a large number of rectifiers and inverters, which have only this one function, namely to be designed as rectifiers or as inverters.

[0047] A particularly advantageous feature of such a central converter according to the invention for a wind turbine is that the central converter is designed to be able to traverse all operating states that may be required by an operator of an electrical supply network at any time, especially with a relatively small size of the central converter.

[0048] It was discovered according to the invention that up to 10% of the power electronics can be saved with such a design of a central converter.

[0049] According to the invention, a wind turbine is also proposed comprising at least a generator for generating an alternating voltage, a power converter or a central converter as described above or below, which is connected to the generator, and a control system which is configured to dynamically switch the switchable converter module during the operation of the wind turbine so that the converter is operated as a rectifier and / or as an inverter.

[0050] In the case of a central converter as described above or below, it is therefore also possible for the wind turbine to switch all converters on the grid side in order to operate in STATCOM mode, i.e., with double the reactive power control range. The wind turbine is then essentially configured as a STATCOM.

[0051] Preferably, the wind turbine has different operating modes, with the control system switching the switchable converter module depending on these operating modes.

[0052] It is therefore specifically proposed that the wind turbine be designed to have different operating modes, such as: sound-optimized operation, power boost, extended Q-adjustment range, mains undervoltage, etc.

[0053] Noise-optimized operation describes a mode in which the wind turbine is operated at a reduced rotational speed to minimize noise emissions from the rotor blades. This also reduces the induced voltage at the generator terminals, which can only be partially compensated for by increasing the electrical excitation of the rotor. To still feed as much power as possible into the grid, a correspondingly higher current is required on the rectifier side. The grid-side inverter, however, is unaffected, as normal conditions prevail from the DC link onward. Such operation typically necessitates increased inverter capacity on the rectifier side.

[0054] Power boost describes an operating mode in which the wind turbine briefly feeds in active power beyond its rated power. This is achieved in part by utilizing thermal time constants (e.g., in the generator). This is not possible with inverters, especially semiconductor ones, as their time constants are in the lower millisecond range. As a compromise, reactive power feed-in can be reduced on the grid side. This option is not available on the generator side. Such operation requires more inverter capacity on the rectifier side.

[0055] The extended Q-control range describes an operating mode in which the wind turbine is operated with an extended reactive power control range, for example, to compensate for the reactive power demand of industrial plants (e.g., with induction heating systems) and can be understood as an alternative to STATCOM systems. The provision of grid-side reactive power has no influence on the rectifier. Such operation requires more converter capacity on the inverter side.

[0056] Grid undervoltage describes an operation in which the grid voltage falls below the nominal grid voltage by a certain amount. This prevents the wind turbine from delivering its full apparent power, as the current limits of the grid-side inverters are reached. To reduce yield losses or the reduced reactive power control range, a higher rated current is therefore necessary on the grid side. The grid voltage has no effect on the rectifiers. Such operation requires more converter capacity on the inverter side.

[0057] It was also recognized according to the invention that, depending on the operation of the wind turbine, the required capacities of rectifiers and inverters can be distributed differently. The switchable converter module can be used precisely for these purposes, both as a rectifier and as an inverter, and in particular, as needed.

[0058] It is therefore specifically proposed that switchable converter modules be switched during the operation of the wind turbine depending on the operating modes; for example, the following assignments are conceivable for a configuration with twelve rectifiers, twelve inverters and one switchable converter module with two inverters: 14 rectifiers, 12 inverters; 13 rectifiers, 13 inverters; 12 rectifiers, 14 inverters.

[0059] Preferably, the operating modes include at least one noise-optimized operation and / or one mains fault operation.

[0060] It is therefore specifically proposed that the wind turbine should have at least a noise-optimized operation and / or a grid fault operation.

[0061] These can, for example, be implemented in the control system of the wind turbine, which preferentially acts on the switching units of the switchable converter modules.

[0062] Noise-optimized operation describes a mode in which the wind turbine is operated at a reduced rotational speed to minimize noise emissions from the rotor blades. This also reduces the induced voltage at the generator terminals, which can only be partially compensated for by increasing the rotor's electrical excitation. To still feed as much power as possible into the grid, a correspondingly higher current is required on the rectifier side. The grid-side inverter, however, is unaffected, as normal conditions prevail from the DC link onward. Such operation typically necessitates increased inverter capacity on the rectifier side.

[0063] Preferably, the wind energy plant further comprises a plant transformer that is connected to the second AC power grid and is configured to be connected to an electrical supply network and / or an electrical wind farm network.

[0064] According to the invention, a wind farm is further proposed comprising a plurality of wind turbines according to one of the preceding claims and an electrical wind farm network connecting the wind turbines to each other.

[0065] Further advantages and advantageous embodiments of the invention are described in more detail below with reference to the accompanying figures, whereby the same reference numerals are used for identical or similar components or assemblies. These figures show: Fig. 1 schematically and by way of example a perspective view of a wind turbine; Fig. 2 schematically and by way of example a preferred embodiment of a power converter according to the invention; Fig. 3 schematically and by way of example a preferred embodiment of a central converter. Fig. 1 shows a perspective view of a wind turbine 100.

[0066] The wind turbine 100 comprises a tower 102 and a nacelle 104. An aerodynamic rotor 106 with three rotor blades 108 and a spinner 110 is mounted on the nacelle 104. During operation, the wind sets the rotor 106 into rotation, thereby driving a generator in the nacelle. The generator produces electricity, which is fed into an electrical grid via an inverter.

[0067] Fig. 2 Figure 1 schematically and exemplarily shows a preferred embodiment of a power converter 200 according to the invention, in particular of a wind turbine as shown in Figure 2. Fig. 1 shown, which is controlled by means of a control unit 160.

[0068] The power converter 200 is connected on the generator side to a generator 120 of a wind turbine and on the grid side to a wind turbine transformer 150 of a wind turbine, which connects the wind turbine to an electrical supply network or a wind farm network.

[0069] The power converter 200 comprises a variety of rectifiers 210, a DC link 220, a variety of inverters 230, a switchable converter module 240 and a control unit 250.

[0070] For example, the rectifier 210 has a power rating between approximately 350 kVA and approximately 700 kVA. The DC link has a nominal voltage between approximately 950 V and approximately 1200 V. Similarly, the inverter 230 has a power rating between approximately 350 kVA and approximately 700 kVA. The switchable converter module 240 also has a power rating between approximately 350 kVA and approximately 700 kVA. Preferably, the rectifier 210, the inverter 230, and the switchable converter module 240 have essentially the same power rating.

[0071] The multiple rectifiers 210 are connected to the generator 120 via a first AC voltage network 125 and are designed to convert an AC voltage into a DC voltage.

[0072] The DC link 220 is arranged between the rectifiers 210 and the inverters 230 and is configured to carry the DC voltage. The DC link 220 also connects the plurality of rectifiers 210 to the plurality of inverters 230.

[0073] The multiple inverters 230 are also connected to the wind turbine transformer 150 via a second AC network 126. Furthermore, the inverters 230 are configured to convert direct current into alternating current.

[0074] The switchable converter module 240 comprises two converters 242 connected to the DC link and one switching unit 244 connected to each converter 242, which can be connected to the first and second AC networks 125,125 and can be connected to the first AC network 125 in such a way that the converter 242 is configured as a rectifier, and can be connected to the second AC network 126 in such a way that the converter 242 is configured as an inverter.

[0075] The converter module 240 therefore essentially has two converters that have a dual function, namely that of a rectifier as well as that of an inverter.

[0076] Depending on requirements, one of the two functions can therefore be selected using the wind turbine control unit 160 or a corresponding control unit 250, preferably also during the ongoing operation of the wind turbine.

[0077] The control unit 250 is at least configured to dynamically switch the switching unit 244 and / or to operate the converter 242 as a rectifier and / or as an inverter.

[0078] In a particularly preferred embodiment, the converter module, preferably comprising two converters 242 and two switching units 244, is installed in a power cabinet. This is indicated by the dashed lines.

[0079] In another preferred embodiment, a rectifier 210 and an inverter 230 are also designed as a functional unit and / or installed in a power cabinet. This is also indicated by the dashed lines.

[0080] In further embodiments, the power converter 200 also has several switchable converter modules 240.

[0081] In a particularly preferred embodiment, the control unit 160 is configured to dynamically switch the switchable converter module during the operation of the wind turbine so that the converter is operated as a rectifier and / or as an inverter, in particular depending on the operating modes described above.

[0082] Fig. 3 Figure 1 schematically and exemplarily shows a preferred embodiment of a central converter 300 according to the invention, in particular of a wind turbine as shown in Figure 2. Fig. 1 shown, which is controlled by means of a control unit 160.

[0083] The central converter 300 is, like the power converter from Fig. 2 , between a generator 120 of a wind turbine, preferably as in Fig. 1 shown, and arranged in a wind turbine transformer 150.

[0084] In a particularly preferred embodiment, the central converter 300 is designed as a full converter of a wind turbine.

[0085] The central converter comprises a large number of switchable converter modules 240, as described above.

[0086] Each switchable converter module 240 comprises two converters 242 connected to a DC intermediate circuit 220 and one switching unit 244 connected to each converter 242, which can be connected to a first and a second AC network 125, 126 and can be connected to the first AC network 125 in such a way that the converter 242 is configured as a rectifier, and can be connected to the second AC network 126 in such a way that the converter 242 is configured as an inverter.

Claims

1. A power converter (200), in particular of a wind power installation (100) for feeding electrical power into an electrical supply network, at least comprising: - a multiplicity of rectifiers (210) which can be connected to a first alternating voltage network (125), in order to convert a first alternating voltage into a direct voltage, - a direct voltage intermediate circuit (220) which is connected to the multiplicity of rectifiers (210) and which is set up to carry the direct voltage and - a plurality of inverters (230) which are connected to the direct voltage intermediate circuit (220) and can be connected to a second alternating voltage network (126), in order to convert the direct voltage into second alternating voltage (126), characterized in that the power converter (200) further comprises: - a switchable converter module (240), at least comprising: - a converter (242) which is connected to the direct voltage intermediate circuit (220) and - a switching unit (244) which is connected to the converter (242) and which - can be connected to the first and the second alternating voltage network (126) and - can be connected to the first alternating voltage network (125) in such a manner that the converter (242) is designed as a rectifier (210), and - can be connected to the second alternating voltage network (126) in such a manner that the converter (242) is designed as an inverter (230).

2. The power converter (200) as claimed in claim 1, further comprising: - a control unit (250) which is set up to dynamically switch the switching unit (244) and / or to operate the converter (242) as a rectifier (210) and as an inverter (230).

3. The power converter (200) as claimed in claim 1 or 2, wherein - the switchable converter module (240) has, in particular precisely, two converters (242) and two switching units (244), wherein the converters (242) can be operated simultaneously as rectifiers (210) and / or inverters (230).

4. The power converter (200) as claimed in one of the preceding claims, wherein - the power converter (200) comprises at least one further switchable converter module (240).

5. The power converter (200) as claimed in one of the preceding claims, further comprising: - a multiplicity of chokes which are the same order of magnitude.

6. A central converter (300) of a wind power installation (100), comprising - a multiplicity of switchable converter modules (240), characterized in that, that each switchable converter module (240) at least comprises: - a converter (242) which is connected to a direct voltage intermediate circuit (220) and - a switching unit (244) which is connected to the converter (242) and which - can be connected to a first and a second alternating voltage network (126) and - can be connected to the first alternating voltage network (125) in such a manner that the converter (242) is designed as a rectifier (210), and - can be connected to the second alternating voltage network (126) in such a manner that the converter (242) is designed as an inverter (230).

7. A wind power installation (100), at least comprising: - a generator (120) for generating an alternating voltage, - a power converter (200) or a central converter (300) as claimed in one of the preceding claims which is connected to the generator (120), and - a control system (160) which is set up to dynamically switch the switchable converter module (240) during ongoing operation of the wind power installation (100) in such a manner that the converter (242) is operated as a rectifier (210) and / or as an inverter (230).

8. The wind power installation (100) as claimed in claim 7, wherein - the wind power installation (100) has different operating modes, and wherein the control system (160) switches the switchable converter module depending on these operating modes (240).

9. The wind power installation (100) as claimed in claim 8, wherein - the operating modes comprise at least sound-optimized operation and / or network error operation.

10. The wind power installation (100) as claimed in claims 7 to 9, further comprising: - an installation transformer which is connected to the second alternating voltage network (126) and is set up to be connected to an electrical supply network and / or an electrical wind farm network.

11. A wind farm comprising a multiplicity of wind power installations (100) as claimed in claims 7 to 10 and an electrical wind farm network which connects the wind power installations (100) to one another.