EP4173127A1

EP4173127A1 - Dc/dc voltage converter comprising an upper module and a lower module

Info

Publication number: EP4173127A1
Application number: EP21730929.3A
Authority: EP
Inventors: Juan David PAEZ ALVAREZ; Jose MANEIRO; Piotr DWORAKOWSKI; Seddik Bacha; Florent MOREL
Original assignee: Centre National de la Recherche Scientifique CNRS; Institut Polytechnique de Grenoble; Universite Grenoble Alpes; SuperGrid Institute SAS
Current assignee: Centre National de la Recherche Scientifique CNRS; Institut Polytechnique de Grenoble; Universite Grenoble Alpes; SuperGrid Institute SAS
Priority date: 2020-06-26
Filing date: 2021-06-08
Publication date: 2023-05-03
Also published as: FR3112037B1; FR3112037A1; WO2021259624A1

Abstract

The invention relates to a voltage converter (10) comprising an upper module (24) including at least one first upper arm (62) connected between first and third DC terminals and comprising a plurality of electrical conversion devices (33) connected in series in said at least one first upper arm, a lower module (26) comprising at least one first lower arm (30) connected between the third and fourth DC terminals and including a plurality of electrical conversion devices (32) connected in series in said at least one first lower arm and an electrical power exchange device (28) interconnecting the upper module and the lower module, at least one of the upper and lower modules comprising at least three electrical conversion devices (32) connected in series in said at least one corresponding upper or lower arm.

Description

DC / DC voltage converter consisting of an upper module and a lower module

Technical area

The present invention relates to the technical field of voltage converters making it possible to convert a first direct voltage into a second direct voltage. These converters are also called DC / DC voltage converters. This type of converter is particularly suitable for installation in high voltage direct current power supply installations (HVDC for "High Voltage Direct Current").

DC / DC voltage converters allow the connection of a first DC power supply network to a second DC power supply network.

Prior art

The most commonly used voltage converters in HVDC power supply installations are the Modular Multilevel Converter (MMC). These MMC converters offer excellent efficiency and numerous control possibilities. In addition, their modular structure makes it possible to build converters that can withstand very high voltages. A disadvantage of these converters is that they consist of a very large number of components. In particular, if it is known to produce a DC / DC converter from two MMC converters interconnected in their alternating parts, the resulting DC / DC converter comprises a very large number of components, is particularly bulky and has insufficient efficiency. - kept from two conversion floors.

DC / DC type converters are known such as the converter described in US 9748848. This converter comprises first and second DC terminals configured to be connected to a first DC power supply network and third and fourth DC terminals configured to be connected. to a second continuous electrical supply network. The converter includes an upper module connected between the first and third DC terminals and a lower module connected between the third and fourth DC terminals. Each of the upper and lower modules comprises at least one arm in which are connected in series two conversion devices comprising a plurality of controllable sub-modules connected in series in said arm. The upper module and the lower module are electrically connected to an electrical energy exchange device.

The ratio between the nominal voltage of the first DC power supply network and the voltage of the second DC power supply network, connected together by this converter, defines an overall transformation ratio of the converter. It can be seen that for a low overall transformation ratio, of the order of 1, the lower modulus is subjected to high tension while the upper modulus is subjected to low tension. The lower modulus is therefore subjected to a much higher voltage than that of the upper modulus. On the other hand, the lower module is subjected to a weak current while the upper module is subjected to a strong current. Conversely, for a large transformation ratio, greater than 2, the lower modulus is subjected to low tension while the upper modulus is subjected to high tension. The upper modulus is therefore subjected to a much lower voltage than that of the upper modulus. On the other hand, the lower module is subjected to a strong current while the upper module is subjected to a weak current. For the remainder of the present application, the terms “high current” and “high voltage” are to be interpreted relatively, in comparison with the terms “low current” and “low voltage”.

In order to allow one of the upper or lower modules subjected to a strong current to withstand said current, this document US Pat. No. 9748848 provides for connecting several arms in parallel in the corresponding module, so as to be able to distribute said current in each of said arms. The other module is subjected to a low current.

One drawback is that the structure of the converter of this prior art document necessarily imposes a ratio of 1 or 2 between the number of arms connected in parallel in the upper and lower modules. In other words, in this converter, either the upper and lower modules comprise an identical number of arms connected in parallel, or one of the upper or lower modules comprises twice as many arms connected in parallel as the other module. Also, when one of the upper or lower modules is subjected to a strong current and it is necessary to connect more than two arms in parallel in said module to withstand the strong current, this document also provides for increasing the number of arms. connected in parallel in the other module. When a module is required to withstand a high current, the number of arms connected in parallel is therefore increased in the upper module as well as in the lower module. However, this increase in the number of arms connected in parallel in the module subjected to a low current is not necessary. This module subjected to a low current is therefore oversized, which results in a significant increase in the number of submodules and therefore an undue increase in the cost and size of the converter. In addition, in this module subjected to a low current each of the arms connected in parallel is subjected to a high voltage. The increase in the number of arms connected in parallel in this module therefore implies a significant increase in the number of submodules necessary to withstand said high voltage in each of said arms connected in parallel.

Disclosure of the invention

An object of the present invention is to provide a voltage converter overcoming the aforementioned problems and in particular making it possible to reduce the number of submodules compared to the documents of the prior art.

To do this, the invention relates to a voltage converter making it possible to convert a first DC voltage into a second DC voltage and vice versa, the converter comprising first and second DC terminals configured to be electrically connected to a first electrical supply network. continued ; third and fourth DC terminals configured to be electrically connected to a second DC power supply network; an upper module configured to at least transform an AC voltage into a DC voltage and vice versa, the upper module being electrically connected between the first and third DC terminals, the upper module comprising at least a first upper arm connected between the first and third DC terminals , said at least one first arm comprising a plurality of electrical conversion devices connected in series in said at least one upper first arm; a lower module configured to at least transform an AC voltage into a DC voltage and vice versa, the lower module being electrically connected between the third and fourth DC terminals, the lower module comprising at least a first lower arm connected between the third and fourth DC terminals , said at least one first lower arm comprising a plurality of electrical conversion devices connected in series in said at least one first lower arm; and an electrical energy exchange device connecting the upper module and the lower module and being configured to allow an exchange of energy between said upper module and said lower module, said electrical conversion devices of the upper and lower modules each comprising an inductor connected in series with a chain of submodules, each of said chains of submodules comprising a plurality of submodules individually controllable by a control member specific to each submodule and each submodule comprising at least an energy storage device, the control member of each submodule being able to take at least a first state in which the energy storage device of the submodule is inserted into the chain of submodules and a second state in which the energy storage device is not inserted in said chain of submodules, at least one of the upper and lower modules comprising at least three electrical conversion devices connected in series in said at least one first upper arm or lower corresponding.

In addition, said first upper or lower arm in which are connected in series at least three electrical conversion devices comprises at least a first terminal and a second terminal, each being electrically connected to at least one of the primary or secondary windings of the device. exchange of electrical energy.

The voltage converter according to the invention can be easily connected in an HVDC electrical installation, between a first DC power supply network and a second DC power supply network. The voltage converter according to the invention forms a high voltage DC / DC converter. The DC / DC converter according to the invention is further reversible, so that it allows energy to be transferred from the first DC power supply network to the second DC power supply network and vice versa. The term high voltage is preferably understood to mean a voltage greater than 1000 volts.

The voltage converter according to the invention makes it possible to connect two DC power supply networks with substantially equal nominal voltages to one another, in which case the overall transformation ratio of the voltage converter is approximately equal to 1. The voltage converter also allows to connect two DC power supply networks with very different nominal voltages to each other, in which case the overall transformation ratio of the voltage converter is greater than 1, preferably greater than 2.

In a nonlimiting manner, the second and fourth DC terminals can be electrically connected to each other. They can for example be connected to each other by a floating point or even by an earth line so that they both have a substantially zero potential. This configuration allows in particular to connect two DC networks with an asymmetric monopoly topology.

The voltage converter advantageously comprises a DC part connected to the DC terminals and an AC part including in particular the electrical energy exchange device. The upper module makes it possible in particular to convert at least part of a first DC power PDCI of a first DC power supply network, connected to the first and second DC terminals, into a first AC power PACI - The part of this first power DC PDCI which has not been converted into a first AC power PACI is transmitted directly to the third and fourth DC terminals and therefore to a second DC power supply network connected to these terminals. Compared to a DC / DC converter produced by interconnecting two MMC converters via their AC parts, an advantage is to reduce the quantity of DC power converted into AC power, in order to reduce the losses associated with said conversion.

The electrical energy exchange device allows an exchange of energy between the upper module and the lower module. It is preferably configured to transfer the AC power supplied by the upper module to the lower module. It also makes it possible to adapt the levels of the alternating voltages and of the currents, between said upper and lower modules, according to a transformation ratio of the device for exchanging electrical energy. The lower module advantageously transforms the alternating power transmitted by the electrical energy exchange device into a second direct power PDC ₂ , delivered to the third and fourth direct terminals.

In addition, the upper module is connected in series with the lower module, so that the total voltage at the terminals of the voltage converter is distributed between the upper module and the lower module, which makes it possible to reduce the number of submodules and therefore the cost and size of the converter.

Each electrical conversion device advantageously has an upper point and a lower point between which it extends. The submodules of an electrical conversion device make it possible to adjust the voltage between the upper and lower points of said electrical conversion device and therefore the voltage at the terminals of the corresponding upper or lower module.

In a nonlimiting manner, the submodules of the electrical conversion devices can be full bridge submodules, half bridge submodules or even a combination of these two types of submodules.

According to the invention, at least one of the upper or lower modules comprises three or more electrical conversion devices connected in series in its first arm. It is understood that according to a first nonlimiting variant, only the upper module comprises a first arm, forming a first upper arm, comprising at least three electrical conversion devices connected in series. According to a second non-limiting variant, only the lower module comprises a first arm, forming a first lower arm, comprising at least three electrical conversion devices connected in series. According to a third non-limiting variant, the upper module and the lower module each comprise a first arm comprising at least three electrical conversion devices connected in series. Without departing from the scope of the invention, the number of electrical conversion devices of the first arm of the upper module and of the first arm of the lower module may be equal or different.

Without departing from the scope of the invention, at least one of the upper and lower modules may include a plurality of arms each comprising at least three electrical conversion devices.

The upper and / or lower module, the first arm of which comprises at least three electrical conversion devices, and of which the first arm therefore comprises at least three chains of submodules, according to the invention, is particularly suitable for withstanding high voltage. In the voltage converter according to the invention, the first arm of this module, comprising at least three electrical conversion devices, comprises a sufficient number of controllable submodules connected in series between which the high voltage of said module can be distributed.

It is particularly advantageous to provide the first arm of the lower modulus with at least three conversion devices when the overall transformation ratio of the voltage converter is low, preferably approximately equal to 1. In fact, in this case, the lower modulus is subjected to low current and high voltage, in comparison with the current and voltage to which the upper module is subjected. Said first arm of said lower module, in which at least three chains of submodules are connected in series with one another, is then particularly suitable for withstanding this high voltage and this low current. In this scenario, where the overall transformation ratio is close to 1, it is particularly advantageous to provide the upper module with a plurality of arms connected in parallel, in order to withstand the high current and the low voltage to which this device is subjected. upper module.

It is particularly advantageous to provide the first arm of the upper modulus with at least three conversion devices when the overall transformation ratio of the voltage converter is much greater than 2, preferably greater than 3, and therefore when the upper modulus is subjected. at low current and high voltage. Indeed, in this case, said first arm of said upper module, in which at least three chains of submodules are connected in series with one another, is then particularly suitable for withstanding this high voltage and this low current.

Moreover, thanks to the invention, insofar as one of the upper and lower modules comprises a first arm in which at least three conversion devices are connected in series, it is possible to connect in parallel in the other module a number of arms at most equal to the number of conversion devices in said first arm, without increasing the number of arms connected in series in the module comprising said first arm provided with three electrical conversion devices. If the upper module comprises a first upper arm provided with three electrical conversion devices connected in series, it is for example possible to connect in the lower module up to three arms in parallel, in order to withstand a strong current, while maintaining a single first arm in the upper module. This is not possible with the devices of the prior art which impose a ratio of 1 or 2 between the number of arms connected in parallel in the upper and lower modules, and which therefore impose an increase in the number of arms connected in parallel. parallel in the two modules, when only one of these modules is required to withstand a strong current.

Thanks to the invention, the number of arms that can be connected in parallel in one upper or lower module is not limited by the number of arms connected in parallel in the other module. In other words, the presence of at least three electrical conversion devices in the first arm of one of the upper and lower modules offers greater freedom as to the ratio between the number of arms connected in parallel in the upper module and the lower module. This makes it possible in particular to limit the number of arms connected in parallel in the upper or lower module comprising a first arm provided with at least three electrical conversion devices, while having the possibility of having more than two arms connected in parallel in the other module, for example to withstand a strong current. An advantage and therefore to avoid oversizing one of the modules and therefore reducing the number of components, as well as the size and total cost of the converter.

The configuration of the voltage converter can therefore be adapted according to the DC power supply networks to which it is connected, so that the voltage converter according to the invention is particularly flexible.

In a nonlimiting manner, the voltage converter can be provided with a control module making it possible to control the energy storage devices of the electrical conversion devices of the upper and / or lower modules. In a nonlimiting manner, the first and second limits can be upper, lower or intermediate limits. For example, in a nonlimiting manner, said upper or lower arm in which three electrical conversion devices are connected in series can therefore comprise an upper terminal and a lower terminal, each being connected to a primary or secondary winding, or even an upper terminal. and an intermediate terminal, each connected to a primary or secondary winding.

The energy exchange device is connected to several terminals of said arm in which at least three electrical conversion devices are connected in series.

The connection of the windings of the energy exchange device to several terminals of the same arm makes it possible in particular to reduce the number of electrical conversion devices and therefore the number of submodules in the corresponding upper or lower module.

In a non-limiting manner, said first upper or lower arm in which at least three electrical conversion devices are connected in series can comprise two, three or four terminals, each being electrically connected to at least one of the primary or secondary windings of the device. exchange of electrical energy.

Preferably, said at least one of the upper and lower modules comprising at least three electrical conversion devices connected in series in the corresponding upper or lower first arm comprises a single arm.

Preferably, said upper module and said lower module comprise at least three electrical conversion devices connected in series in said at least one corresponding upper or lower first arm. One advantage of this configuration is that it allows each of the upper and lower modules to withstand a high voltage at their terminals and in particular a high voltage between the first and third DC terminals as well as a high voltage between the third and fourth DC terminals. In fact, in each of the upper and lower modules, the high voltage is distributed and balanced between said at least three electrical conversion devices.

Advantageously, said upper module comprises at least one second upper arm electrically connected in parallel with the first upper arm, between the first and third continuous terminals, said at least one second upper arm comprising a plurality of electrical conversion devices connected in series in said au at least a second upper arm and each comprising an inductor connected in series with a chain of submodules.

One advantage is to distribute the direct current flowing in the first direct terminal between the first and second upper arms. The upper module is then able to withstand a strong current passing through it. This configuration is particularly advantageous when the overall transformation ratio of the converter is close to 1. In fact, the upper modulus is then subjected to a high current. Preferably, the submodules of the second upper arm also include an energy storage device and are also individually controllable between a first state in which the energy storage device of the submodule is inserted in the chain of submodules. modules and a second state in which the energy storage device is not inserted in said chain of submodules.

Preferably, but in a nonlimiting manner, the upper module comprises as many upper arms as the number of electrical conversion devices of the first lower arm of the lower module.

Advantageously, said lower module comprises at least one second lower arm electrically connected in parallel with the first lower arm, between the third and fourth continuous terminals, said at least one second lower arm comprising a plurality of electrical conversion devices connected in series in said at least one second lower arm and each comprising an inductor connected in series with a chain of submodules.

An interest is to distribute the direct current flowing in the lower module, which is the difference between the current of the first and third direct terminals. The lower module is then able to withstand a strong current passing through it. This configuration is particularly advantageous when the overall transformation ratio of the converter is much greater than 2, preferably greater than 3. In fact, the lower modulus is then subjected to a high current.

Preferably, but in a nonlimiting manner, the lower module comprises as many lower arms as the number of electrical conversion devices of the first upper arm of the upper module.

Preferably, the electrical energy exchange device is an electrical transformation device comprising a plurality of primary windings and a plurality of secondary windings, the upper module being electrically connected to said primary windings while the lower module is electrically connected to said said windings. secondary windings. The electrical energy exchange device is configured to transmit a first AC power PAC-I, from the upper module to the lower module. The electrical energy exchange device also has a transformation ratio corresponding to the ratio between the number of turns of the secondary windings and the number of turns of the primary windings. The ratio between the alternating voltage, respectively the alternating current, at the output of the exchange device of electrical energy and the alternating voltage, respectively the alternating current, at the input of the electrical energy exchange device is substantially equal to the transformation ratio of the electrical energy exchange device.

The electrical energy exchange device preferably comprises at least three primary windings and three secondary windings.

Preferably, each of the electrical conversion devices of said at least one of the upper and lower modules comprising a first arm in which at least three electrical conversion devices are connected in series, has an upper point and a lower point between which it extends. , each of said electrical conversion devices having a primary, respectively secondary winding connected between said upper and lower points. Preferably, between the upper and lower points of each of the electrical conversion devices of said at least one of the upper and lower modules comprising at least three electrical conversion devices is connected a primary, respectively secondary, separate winding. By separate is meant that a single primary or secondary winding is connected between the upper and lower points of each of the electrical conversion devices and that each primary or secondary winding is connected between the upper points of a single electrical conversion device. In other words, each of said at least three electrical converting devices of said module has its own primary or secondary winding of the electrical energy exchange device associated with it. Without limitation, each of the primary and / or secondary windings of the electrical energy exchange device can be connected between two arms of the upper and / or lower module.

According to a first advantageous variant, the electrical energy exchange device comprises a single transformer having a plurality of primary windings and a plurality of secondary windings. One advantage is to reduce the cost and size of the converter by limiting the number of components it includes. The transformer advantageously comprises as many primary windings, respectively secondary, as the number of conversion devices connected in series in the first arm of said at least one of the upper and lower modules comprising at least three electrical conversion devices connected in said first arm. For example, if the lower module comprises a first arm provided with four electrical conversion devices connected in series, then the electrical energy exchange device advantageously comprises four primary windings and four secondary windings.

Again preferably, the transformer comprises as many primary windings, respectively secondary, as the number of conversion devices electrical connected in the first upper or lower arm comprising the most electrical conversion devices.

According to a second advantageous variant, the electrical energy exchange device comprises a plurality of transformers each having a single primary winding and a single secondary winding. These transformers are single phase transformers. One advantage is to allow better galvanic isolation between the windings of the different transformers. In addition, for very high power applications, the size of a transformer with multiple primary and secondary windings may be such that it will be difficult to manufacture and transport. The use of several single-phase transformers facilitates the manufacture and transport of the electrical energy exchange device and therefore of the converter.

The electrical energy exchange device advantageously comprises as many transformers as the number of electrical conversion devices connected in series in the first arm of the upper and / or lower module, said first arm of which comprises at least three electrical conversion devices. For example, if the lower module comprises a first arm provided with four electrical conversion devices connected in series, then the electrical energy exchange device advantageously comprises four primary windings and four secondary windings.

Advantageously, at least one of the upper and lower modules comprises at least one intermediate terminal interconnecting two adjacent electrical conversion devices of said upper or lower module, said at least one intermediate terminal being electrically connected to at least one of the primary windings or secondary of the electrical energy exchange device by an intermediate branch.

In a nonlimiting manner, each intermediate terminal can be electrically connected to two separate primary or secondary windings by said intermediate branch.

Preferably, the first upper or lower arm of said at least one of the upper or lower modules comprising at least three electrical conversion devices connected in series in its first upper or lower arm comprises at least one intermediate terminal interconnecting two electrical conversion devices. adjacent to said upper or lower module, said at least one intermediate terminal being electrically connected to at least one of the primary or secondary windings of the electrical energy exchange device by an intermediate branch. It will then be understood that at least one of the first and second terminals is an intermediate terminal.

Said at least one of the upper and lower modules comprising at least three electrical conversion devices advantageously comprises at least two intermediate terminals, each being connected to a separate primary or secondary winding by an intermediate branch specific to said primary or secondary winding.

Advantageously, the first upper or lower arm of said at least one of the upper or lower modules comprising at least three electrical conversion devices connected in series in its first upper or lower arm comprises said two intermediate terminals.

Preferably, the electrical energy exchange device comprises an intermediate filter configured to limit the passage of a direct electric current, the intermediate filter being connected in said intermediate branch between said intermediate terminal and said at least one of the primary windings or secondary. Said intermediate filter forms a decoupling member configured to prevent the passage of a direct electric current. It avoids the saturation of the electrical energy exchange device, especially when the latter includes one or more transformers. The intermediate filter can include a capacitor. In a nonlimiting manner, the intermediate filter can consist of a capacitor.

Advantageously, said intermediate filter comprises a chain of submodules comprising a plurality of submodules connected in series in the intermediate branch and individually controllable by a control member specific to each submodule and each submodule comprising at least an energy storage device, the control member of each submodule being able to take at least a first state in which the energy storage device of the submodule is inserted in the chain of submodules and a second state in which the energy storage device is not inserted in said chain of submodules. One benefit is to allow the current flowing to the windings of the electrical energy exchange device to be more efficiently regulated.

Preferably, at least one of the upper or lower modules comprises an upper terminal electrically connected to at least one of the primary or secondary windings of the electrical energy exchange device by an upper branch.

It will be understood that in the case of an upper module, the upper terminal is connected to a primary winding of the device for exchanging electrical energy by the upper branch. In the case of a lower module, the upper terminal is connected to a secondary winding of the device for exchanging electrical energy via the upper branch.

Preferably, said at least one upper or lower module comprising an arm comprising at least three electrical conversion devices connected in series comprises an upper terminal electrically connected to at least one of the primary or secondary windings of the device for exchanging electrical energy by an upper branch.

Preferably, the first upper or lower arm of said at least one of the upper or lower modules comprising at least three electrical conversion devices connected in series in its first upper or lower arm comprises an upper terminal electrically connected to at least one of the primary windings or secondary of the electrical energy exchange device by an upper branch.

It is then understood that at least one of the first and second bounds is an upper bound.

Advantageously, at least one of the upper or lower modules comprises a lower terminal electrically connected to at least one of the primary or secondary windings of the electrical energy exchange device by a lower branch.

It is understood that in the case of a lower module, the lower terminal is connected to a primary winding of the electrical energy exchange device via the lower branch. In the case of a lower module, the lower terminal is connected to a secondary winding of the electrical energy exchange device through the lower branch.

Preferably, said at least one upper or lower module comprising a first arm comprising at least three electrical conversion devices connected in series comprises a lower terminal electrically connected to at least one of the primary or secondary windings of the device for exchanging electrical energy. by a lower branch.

Preferably, the first upper or lower arm of said at least one of the upper or lower modules comprising at least three electrical conversion devices connected in series in its first upper or lower arm comprises a lower terminal electrically connected to at least one of the primary windings or secondary of the electrical energy exchange device by a lower branch.

It is then understood that at least one of the first and second limits is a lower limit. Advantageously, at least one of the upper or lower modules comprises an upper terminal electrically connected to at least one of the primary or secondary windings of the energy exchange device by an upper branch and a lower terminal electrically connected to at least one of the primary or secondary windings of the device for exchanging electrical energy via a lower branch, and in which said upper and lower branches are electrically connected to two separate windings. Preferably, said at least one upper or lower module comprising a first arm comprising at least three electrical conversion devices connected in series has such a configuration.

Preferably, the electrical energy exchange device comprises at least one upper or lower filter, connected in said upper branch or in said lower branch and configured to limit the passage of a direct electric current to said at least one of the primary windings. or secondary to which said upper or lower branch is connected.

Preferably, said upper or lower filter blocks the flow of a direct electric current to the windings of the electric energy exchange device.

Preferably, the first upper or lower arm of said at least one of the upper or lower modules comprising at least three electrical conversion devices connected in series in its first upper or lower arm comprises at least a first intermediate terminal and a second intermediate terminal, each being electrically connected to at least one of the primary or secondary windings of the device for exchanging electrical energy by an intermediate branch.

The invention also relates to a high-voltage direct current transmission installation comprising a first direct electrical power supply network, a second direct electrical power supply network and at least one voltage converter as described above, said voltage converter being configured to electrically connect said first and second DC power supply networks to each other.

The installation is an HVDC installation.

The first DC power supply network is preferably connected between the first and second DC power terminals. The second DC power supply network is preferably connected between the third and fourth DC power terminals.

According to an advantageous variant, the high voltage direct current transmission installation comprises first and second voltage converters such as previously described, the first DC terminal of the first voltage converter and the fourth DC terminal of the second voltage converter being electrically connected to the first DC power supply network, the third DC terminals of the first and second voltage converters being electrically connected to the second DC power supply network, and the fourth terminal of the first voltage converter being electrically connected to the first DC terminal of the second voltage converter.

Such an installation makes it possible to connect two DC power supply networks with different topologies, for example a "bipole" type network and a "symmetrical monopoly" type network.

In this variant, the second and fourth DC terminals of the first voltage converter are interconnected, for example by a common electric line. Likewise, the second and fourth DC terminals of the second voltage converter are interconnected, for example by a common electric line.

The fourth terminal of the first voltage converter is advantageously electrically connected to the first DC terminal of the second voltage converter at a point of connection of the first and second voltage converters. This connection point is preferably connected to earth.

Preferably, the HVDC installation further comprises an additional energy exchange device connected between one of the upper or lower modules of the first voltage converter and one of the upper or lower modules of the second voltage converter.

Brief description of the drawings

The invention will be better understood on reading the following description of embodiments of the invention given by way of non-limiting examples, with reference to the accompanying drawings, in which:

[Fig. 1] Figure 1 illustrates a first embodiment of an HVDC installation comprising a voltage converter according to the invention;

[Fig. 2] Figure 2 illustrates a first embodiment of a voltage converter according to the invention;

[Fig. 3] Figure 3 illustrates a second embodiment of a voltage converter according to the invention;

[Fig. 4] Figure 4 illustrates a third embodiment of a voltage converter according to the invention;

[Fig. 5] FIG. 5 illustrates a fourth embodiment of a voltage converter according to the invention; and [Fig. 6] FIG. 6 illustrates a second embodiment of an HVDC installation comprising a voltage converter according to the invention.

Description of the embodiments

The invention relates to a voltage converter for converting a first DC voltage into a second DC voltage.

FIG. 1 illustrates a first embodiment of an HVDC installation 8 comprising a schematic representation of a voltage converter 10 according to the invention, connecting between them a first DC power supply network 12 and a second power supply network DC electric 14 of the installation 8. The voltage converter 10 according to the invention therefore forms a DC / DC converter.

As can be seen in Figure 1, the voltage converter 10 comprises a first DC terminal 16 and a second DC terminal 18 configured to be electrically connected to the first DC power supply network 12. The nominal voltage VDCI of the first DC network. DC power supply 12 is shown between the first DC terminal 16 and the second DC terminal 18.

The voltage converter 10 also comprises a third DC terminal 20 and a fourth DC terminal 22 configured to be electrically connected to the second DC power supply network 14. The nominal voltage VDC2 of the second DC power supply network 14 is illustrated between the third DC terminal 20 and the fourth DC terminal 22. The ratio between the nominal voltage VDCI of the first DC power supply network 12 and the nominal voltage VDC2 of the second DC power supply network 14 defines an overall transformation ratio of the converter Of voltage.

In this non-limiting example, the voltage converter 10 comprises a ground line connecting the second and fourth DC terminals 18, 22. The first and second continuous terminals therefore have the same zero potential. This voltage converter 10 is suitable for connecting two DC power supply networks with asymmetric monopoly topologies.

The voltage converter 10 comprises an upper module 24 connected between the first DC terminal 16 and the third DC terminal 20. The upper module 24 comprises a continuous part 24a connected between said first and third DC terminals. The voltage converter further comprises a lower module 26 connected between the third DC terminal 20 and the fourth DC terminal 22. The lower module 26 comprises a continuous portion 26a connected between said third and fourth DC terminals 20,22. The upper 24 and lower 26 modules are connected in cascade with one another, between the first continuous terminal 16 and the fourth continuous terminal 22, and therefore the ground line.

The voltage converter further comprises an electrical energy exchange device 28 connecting the upper module 24 and the lower module 26 and being configured to allow energy exchange between said upper module and said lower module. More specifically, the upper module 24 includes an alternating part 24b electrically connected to the electrical energy exchange device 28. Likewise, the lower module 26 includes an alternating part 26b electrically connected to the electrical energy exchange device 28.

Figure 2 illustrates a first embodiment of a voltage converter 10 according to the invention. In this embodiment, in a nonlimiting manner, the lower module 26 comprises a single arm forming a first lower arm 30. According to the invention, this first lower arm 30 comprises three electrical conversion devices 32, 32 ', 32 ”connected. in series in said first lower arm 30. The voltage of the first lower arm is therefore distributed between the three electrical conversion devices. More specifically, it comprises a first electrical conversion device 32, a second electrical conversion device 32 "and a third electrical conversion device 32". Each of the electrical conversion devices includes an upper point and a lower point between which it extends. Without departing from the scope of the invention, the lower module could include more electrical conversion devices.

The first electrical conversion device 32 extends between an upper terminal 34, forming an upper point of said first electrical conversion device, and a first intermediate terminal 36 of the lower module 26, forming a lower point of said electrical conversion device. The first upper terminal 34 has a potential equal to the potential of the second DC terminal 20. The second electrical conversion device 32 'extends between the first intermediate terminal 36, forming an upper point of said second electrical conversion device, and a second terminal intermediate 38 of the lower module 26, forming a lower point of said second electrical conversion device. The third electrical conversion device 32 "extends between the second intermediate terminal 38, forming an upper point of said third electrical conversion device, and a lower terminal 40 of the lower module 26, forming a lower point of said third electrical conversion device.

Each of the electrical conversion devices of the lower module 26 comprises a plurality of submodules 42 connected in series in the first lower arm 30, so as to form a chain of submodules. The submodules 42 can be ordered in a desired sequence. Each string of sub- modules 42 can comprise from two to several hundred submodules. Each submodule 42 comprises an energy storage device comprising in this example a capacitor, and a control member for selectively connecting this capacitor in series between the terminals of the submodule or for bypassing it. More precisely, the control member of each submodule 42 can take at least a first state in which the energy storage device of the submodule is inserted in the chain of submodules and a second state in which the energy storage device is not inserted in said chain of submodules. The submodules can be of the half-bridge or full-bridge type.

Furthermore, each electrical conversion device 32, 32 ’, 32” of the lower module 26 comprises an inductor 44 connected in series with the chain of submodules 42 of said electrical conversion device, in the first lower arm 30.

In this non-limiting example, the electrical energy exchange device 28 comprises three single-phase transformers separate from each other, and therefore forms an electrical transformation device. More precisely, the energy exchange device 28 comprises a first transformer 46, a second transformer 48 and a third transformer 50. These transformers 46,48,50 are of the single-phase type and each include a single primary winding 46a, 48a, 50a and a single secondary winding 46b, 48b, 50b.

Alternatively, the electrical energy exchange device 28 could include only a single three-phase transformer comprising three primary windings and three secondary windings.

In this non-limiting example, a secondary winding 46b, 48b, 50b of a separate transformer 46,48,50 is connected between the upper and lower points of each of the electrical conversion devices 32, 32 ’, 32”. A single secondary winding is associated with each of the electrical conversion devices. Each of these secondary windings is connected in parallel with one of the electrical conversion devices via branches comprising, without limitation, capacitors.

More precisely, the upper terminal 34 of the lower module 26 is electrically connected to a first terminal of the secondary winding 46b of the first transformer 46 by an upper branch 52. The first intermediate terminal 36 of the lower module 26 is electrically connected to a second terminal of the secondary winding 46b of the first transformer 46 by a first intermediate branch 54. Furthermore, the first intermediate terminal 36 of the lower module 26 is also electrically connected to a first terminal of the secondary winding 48b of the second transformer 48 by the first intermediate branch 54. The second intermediate terminal 38 of the lower module 26 is electrically connected to a second terminal of the secondary winding 48b of the second transformer 48, as well as at a first terminal of the secondary winding 50b of the third transformer 50, by a second intermediate branch 56. In addition, the lower terminal 40 of the lower module 26 is electrically connected to a second terminal of the secondary winding 50b of the third transformer 50 by a lower branch 58.

The secondary winding 46b of the first transformer 46 is therefore connected between the upper and lower points of the first electrical conversion device 32, in parallel with said first electrical conversion device via the upper branch 52 and the first intermediate branch 54, in each of which is connected a capacitor 60. The secondary winding 48b of the second transformer 48 is connected between the upper and lower points of the second electrical conversion device 32 ', in parallel with said second electrical conversion device via the first and second intermediate branches 54,56, each comprising a capacitor 60. The secondary winding 50b of the third transformer 50 is connected between the upper and lower points of the third electrical conversion device 32 ”, in parallel with said third electrical conversion device via the second intermediate branch 56 and the lower branch 58, including each a a capacitor 60.

The first arm 30 of the lower module 26 therefore comprises an upper terminal 34, a first intermediate terminal 36, a second intermediate terminal 38 and a lower terminal 40, each of which is electrically connected to a secondary winding. These terminals respectively form first, second, third and fourth terminals of said arm, each being connected to a secondary winding.

The capacitors 60 of the electric energy exchange device 28 form filters 60, configured to prevent the passage of a direct electric current, to the secondary windings of the transformers. In this non-limiting example, the filters 60 each consist of a capacitor 60 but could include other electrical components. Each of the capacitors 60 is connected in one of the upper, intermediate or lower branches 52,54,56,58 of the lower module, between one of the secondary windings of the electrical energy exchange device and the first lower arm 30. These capacitors allow to limit, preferably block, the flow of a direct electric current in the windings of the transformers. The filters 60 connected in the upper, intermediate and lower branches respectively form upper, intermediate and lower filters.

As a variant, the filters 60 can comprise a plurality of submodules connected in series in the corresponding intermediate, upper or lower branch. These submodules are advantageously controllable individually by a control member specific to each submodule and each submodule comprises at least one energy storage device which may or may not be inserted into the submodule chain by the member. control.

Each secondary winding 46b, 48b, 50b is therefore connected in series with two capacitors 60 and in parallel with an electrical conversion device 32, 32 ’, 32” which is specific to it.

Furthermore, in this non-limiting example, the upper module 24 comprises a first upper arm 62, a second upper arm 64 and a third upper arm 66, connected in parallel with each other in the upper module 24. Each of the first, second and third upper arm 62,64,66 comprises an upper half-arm 62a, 64a, 66a and a lower half-arm 62b, 64b, 66b interconnected at intermediate points 67. Each of the half-arms comprises a conversion device 33.33 ′ comprising a chain of submodules 42 connected in series with an inductor 44.

The first arm 62 is connected to a first terminal of the primary winding 46a of the first transformer 46 via a first intermediate branch 68. The second arm 64 is connected to a first terminal of the primary winding 48a of the second. transformer 48 via a second intermediate branch 70. The third arm 66 is connected to a first terminal of the primary winding 50a of the third transformer 50 via a third intermediate branch 72.

The second terminals of the primary windings 46a, 48a, 50a of the first, second and third transformers 46,48,50, which are not connected to one of the upper arms 62,64,66, are connected together, for example at a common point floating, or interconnected to the earth.

This first embodiment of the voltage converter 10 according to the invention is particularly suitable for connecting between them a first DC power supply network 12 and a second DC power supply network 14 having nominal voltages whose ratio, defining a overall transformation ratio of the voltage converter is close to 1, and therefore when the lower module 26 is subjected to a low current and to a high voltage. Indeed, in this case, the first lower arm 30 of said lower module, in which three electrical conversion devices 32, 32 ', 32 ”are connected in series with one another, is then particularly suitable for withstanding this high voltage and this weak current.

With each of the secondary windings 46b, 48b, 50b of the electrical energy exchange device 28 is associated an electrical conversion device 32, 32 ', 32 ”of the lower module 26 and with each of the primary windings 46a, 48a, 50a is associated an arm 62,64,66 of the upper module 24. Also, thanks to the invention, it is possible to connect up to three arms in parallel in the upper module 24, in order to withstand a strong current, while maintaining a single first arm 30 in the lower module 26. The ratio between the number of arms of the upper module and the number of arms of the lower module is therefore 3. This is not possible with the devices of the prior art which impose a ratio of 1 or 2 between the number of arms connected in parallel in the upper and lower modules. One advantage is therefore to allow the upper module to withstand a high current while limiting the number of components of the voltage converter 10 and consequently its weight, its size and its manufacturing cost.

Figure 3 illustrates a second embodiment of a voltage converter 100 according to the invention. In this embodiment, in a nonlimiting manner, the upper module 124 is substantially identical to the lower module 26 of the first embodiment. Also, the upper module 124 here comprises a single arm forming a first upper arm 130. According to the invention, this first upper arm 130 comprises three electrical conversion devices 132, 132 ', 132 ”connected in series in said first upper arm 130. More specifically, it comprises a first electrical conversion device 132, a second electrical conversion device 132 'and a third electrical conversion device 132 ”.

Each of the electrical conversion devices of the upper module 124 comprises a plurality of sub-modules 142 connected in series in the first upper arm 130 so as to form a chain of sub-modules, and an inductor 44 connected in series with the sub-chain. -modules 142 of said electrical conversion device, in the first upper arm 130.

In this second embodiment, the electrical energy exchange device 28 is substantially identical to that of the first embodiment, and comprises three single-phase transformers 46,48,50 distinct from each other, and consequently forms a device of electrical transformation. More precisely, the electrical energy exchange device 28 comprises a first transformer 46, a second transformer 48 and a third transformer 50. In this non-limiting example, each of the primary windings 46a, 48a, 50a is connected between the upper and lower points of an electrical conversion device 132, 132 ', 132 ”of the upper module 124 which is specific to it.

More precisely, the primary winding 46a of the first transformer 46 is therefore connected between the upper and lower points of the first electrical conversion device 132, via a lower branch 158 and a first intermediate branch 156. The primary winding 48a of the second transformer 48 is connected between the upper and lower points of the second electrical conversion device 132 ', via the first intermediate branch 156 and a second intermediate branch 154. The primary winding 50a of the third transformer 50 is therefore connected between the upper and lower points of the third electrical conversion device 132 ”, via the second intermediate branch 154 and an upper branch 152.

The electrical energy exchange device 28 further comprises a plurality of capacitors 160, connected in the upper, middle or lower branches 152,154,156,158 of the upper module.

Furthermore, in this second embodiment, the lower module 126 is substantially identical to the upper module 24 of the voltage converter 10 of the first embodiment. The lower module 126 includes a first lower arm 162, a second lower arm 164, and a third lower arm 166, connected in parallel with each other in the lower module 126. Each of the first, second and third lower arms 162,164,166 includes a half. upper arm and a lower half-arm each comprising a chain of submodules connected in series with an inductor.

This second embodiment of the voltage converter 100 according to the invention is particularly suitable for connecting between them a first DC power supply network 12 and a second DC power supply network 14 having nominal voltages whose ratio, defining a The overall transformation ratio of the voltage converter 100 is high, greater than 2, preferably greater than 3. In fact, in this case, the upper modulus is subjected to a low current and to a high voltage. The first upper arm 130 of said upper module 124, in which three electrical conversion devices 132, 132 ’, 132” are connected in series with each other, is particularly suited to withstand this high voltage and low current.

Each of the primary windings 46a, 48a, 50a of the electrical energy exchange device 28 is associated with an electrical conversion device 132, 132 ', 132 ”of the upper module 124. Thanks to the invention, it is possible to connect up to 'with three arms in parallel in the lower module 126, in order to support a strong current, while retaining a single first arm 130 in the upper module 124. The ratio between the number of arms of the upper module and the number of arms of the lower module is therefore 3. There is again an interest in allowing the lower module to withstand a high current while limiting the number of components of the voltage converter 100 and consequently its weight, its size and its manufacturing cost.

Figure 4 illustrates a third embodiment of a voltage converter 200 according to the invention. In this embodiment, in a nonlimiting manner, the upper module 224 and the lower module 226 are substantially identical. They each comprise a single arm respectively forming a first upper arm and a first lower arm. According to the invention, the upper module 224 comprises three electrical conversion devices 233, 233 ’, 233” connected in series in said first upper arm. The lower module 226 includes three electrical conversion devices 232, 232 ’, 232” connected in series in said first lower arm.

In this third embodiment, the electrical energy exchange device 28 is substantially identical to that of the first and second embodiments of the voltage converter, and comprises three single phase transformers 46,48,50 distinct from each other. In this third embodiment, the connection between the lower module 226 and the transformers is identical to the connection between the lower module 26 and the transformers of the converter of the first embodiment described above. Likewise, in this third embodiment, the connection between the upper module 224 and the transformers is identical to the connection between the upper module 124 and the transformers of the converter of the second embodiment described above.

Figure 5 illustrates a fourth embodiment of a voltage converter 300 according to the invention. In this embodiment, in a nonlimiting manner, the upper module 324 comprises a single first upper arm. According to the invention, said upper module 324 comprises first, second, third, fourth, fifth and sixth electrical conversion devices 331,332,333,334,335,336 connected in series in said first upper arm and each having an upper point and a lower point between which it s' extends. The electrical conversion devices each comprise a chain of submodules 342.

The lower module 326 includes a first lower arm 362, a second lower arm 364 and a third lower arm 366 connected in parallel in the lower module. Each of said arms comprises an upper half-arm and a half-arm. lower arm each comprising an electrical conversion device 340 comprising a chain of submodules 342.

In this fourth embodiment, the electrical energy exchange device 28 comprises three single-phase transformers 46,48,50 distinct from each other each comprising a primary winding 46a, 48a, 50a and a secondary winding 46b, 48b, 50b .

The first primary winding 46a is connected between the lower and upper points of the fifth electrical conversion device 335 and between the upper and lower points of the sixth electrical conversion device 336. The second primary winding 48a is connected between the lower and upper points of the third. electrical converting device 333 and between the upper and lower points of the fourth electrical converting device 334. The third primary winding 50a is connected between the lower and upper points of the first electrical converting device 331 and between the upper and lower points of the second device electric converter 332.

In this fourth embodiment, the secondary windings 46b, 48b, 50b are coupled in a triangle. Further, the second secondary winding 48b is connected between the first and second lower arms 362,364 of the lower module. The first secondary winding 46b is connected between the second and third lower arms 364,366 of the lower module. The third secondary winding 50b is connected between the first and third lower arms 362,366 of the lower module.

FIG. 6 illustrates a second non-limiting embodiment of an HVDC installation 80 comprising a first voltage converter 10 according to the invention and a second voltage converter 10 ’according to the invention. This HVDC installation 80 makes it possible to connect between them a first DC power supply network 12 and a second DC power supply network 14. These two DC power supply networks may have different topologies. For example, the first DC power supply network 12 may be of the "bipole" type and the second DC power supply network 14 may be of the "symmetrical monopoly" type.

The first voltage converter 10 comprises an upper module 24 and a lower module 26 interconnected by an electrical energy exchange device 28. The second voltage converter 10 'comprises an upper module 24' and a lower module 26 '. interconnected by an electrical energy exchange device

28 ’.

The HVDC installation 80 is connected to the first DC power supply network 12 via the first DC terminal 16 of the first voltage converter 10 and the second DC terminal 18 'of the second voltage converter 10'. The HVDC installation 80 is connected to the second DC power supply network 14 via the third DC terminal 20 of the first voltage converter 10 and the third DC terminal 20 'of the second voltage converter 10'. The second and fourth DC terminals 18, 22 of the first voltage converter are electrically connected to each other and are connected to the first DC terminal 16 'of the second voltage converter 10'.

Claims

1. Voltage converter (10) for converting a first DC voltage into a second DC voltage and vice versa, the converter comprising: first and second DC terminals (16,18) configured to be electrically connected to a first power supply network continuous electric (12); third and fourth DC terminals (20,22) configured to be electrically connected to a second DC power supply network (14); an upper module (24,124,224) configured to at least transform an AC voltage into a DC voltage and vice versa, the upper module being electrically connected between the first and third DC terminals, the upper module comprising at least a first upper arm (62,130) connected between first and third continuous terminals, said at least one first arm comprising a plurality of electrical conversion devices (33,33 ', 132,132', 132 ”) connected in series in said at least one upper first arm; a lower module (26,126,226) configured to at least transform an AC voltage into a DC voltage and vice versa, the lower module being electrically connected between the third and fourth DC terminals, the lower module comprising at least a first lower arm (30,162) connected between the third and fourth continuous terminals, said at least one first lower arm comprising a plurality of electrical conversion devices (32, 32 ', 32 ”) connected in series in said at least one first lower arm; and an electrical energy exchange device (28) connecting the upper module and the lower module and being configured to allow an exchange of energy between said upper module and said lower module, said electrical conversion devices of the upper and lower modules each comprising an inductor (44) connected in series with a chain of submodules, each of said chains of submodules comprising a plurality of submodules (42, 142) individually controllable by a control member specific to each submodule and each submodule comprising at least one energy storage device, the control member of each submodule being able to take at least a first state in which the energy storage device of the submodule is inserted in the chain of submodules and a second state in which the energy storage device is not inserted in said chain of submodules, at least one of the upper and lower modules comprising at least three electrical conversion devices ( 32,32 ', 32 ”, 132,132', 132”) connected in series in said at least one corresponding upper or lower first arm, said first upper or lower arm in which are connected in series at least three electrical conversion devices comprising at least at least a first terminal and a second terminal, each being electrically connected to at least one of the primary or secondary windings of the device for exchanging electrical energy.

2. Voltage converter according to claim 1, wherein said upper module (224) and said lower module (226) comprise at least three electrical conversion devices (232, 232 ', 232 ”, 233, 233', 233”). connected in series in said at least one corresponding upper or lower first arm.

3. Voltage converter according to claim 1 or 2, wherein said upper module comprises at least one second upper arm (64) electrically connected in parallel with the first upper arm (62), between the first and third DC terminals (16,20 ), said at least one second upper arm comprising a plurality of electrical conversion devices (33,33 ') connected in series in said at least one second upper arm and each comprising an inductor (44) connected in series with a sub string -modules (42).

4. Voltage converter according to any one of claims 1 to 3, wherein said lower module (126) comprises at least a second lower arm (164) electrically connected in parallel with the first lower arm (162), between the third ( 20) and fourth (22) continuous terminals, said at least one second lower arm comprising a plurality of electrical conversion devices connected in series in said at least one second lower arm and each comprising an inductor connected in series with a chain of sub- modules.

5. Voltage converter according to any one of claims 1 to 4, wherein the electrical energy exchange device (28) is an electrical transformation device comprising a plurality of windings. primary (46a, 48a, 50a) and a plurality of secondary windings (46b, 48b, 50b), the upper module (24,124,224) being electrically connected to said primary windings while the lower module (26,126,226) is electrically connected to said secondary windings.

The voltage converter of claim 5, wherein the electrical energy exchange device (28) comprises a single transformer having a plurality of primary windings (46a, 48a, 50a) and a plurality of secondary windings ( 46b, 48b, 50b).

7. A voltage converter according to claim 5, wherein the electrical energy exchange device comprises a plurality of transformers each having a single primary winding (46a, 48a, 50a) and a single secondary winding (46b, 48b, 50b. ).

8. Converter according to any one of claims 5 to 7, wherein at least one of the upper and lower modules comprises at least one intermediate terminal (36,38) interconnecting two adjacent electrical conversion devices (32, 32 ', 32 ”) of said upper or lower module, said at least one intermediate terminal being electrically connected to at least one of the primary or secondary windings of the device for exchanging electrical energy by an intermediate branch (54,56, 154,156).

9. Converter according to claim 8, wherein the electric energy exchange device comprises an intermediate filter (60,160) configured to limit the passage of a direct electric current, the intermediate filter being connected in said intermediate branch (54, 56,154,156) between said intermediate terminal and said at least one of the primary or secondary windings.

10. Voltage converter according to claim 9, wherein said intermediate filter (60,160) comprises a chain of submodules comprising a plurality of submodules connected in series in the intermediate branch and individually controllable by a control member specific to each. submodule and each submodule comprising at least one energy storage device, the control member of each submodule being able to take at least a first state in which the energy storage device of the submodule is inserted in the sub string modules and a second state in which the energy storage device is not inserted in said chain of submodules.

11. A converter according to any one of claims 5 to 10, wherein at least one of the upper or lower modules comprises an upper terminal (34) electrically connected to at least one of the primary or secondary windings of the exchange device. electrical energy by an upper branch (52).

12. Converter according to any one of claims 5 to 11, wherein at least one of the upper or lower modules comprises a lower terminal (40) electrically connected to at least one of the primary or secondary windings of the exchange device. electrical energy by a lower branch (58).

13. Converter according to claims 11 or 12, wherein at least one of the upper or lower modules comprises an upper terminal (34) electrically connected to at least one of the primary or secondary windings of the device for exchanging electrical energy by an upper branch (52) and a lower terminal (40) electrically connected to at least one of the primary or secondary windings of the device for exchanging electrical energy by a lower branch (58), and in which said upper and lower branches are electrically connected to two separate windings.

14. Converter according to any one of claims 11 to 13, wherein the electrical energy exchange device (28) comprises at least one upper or lower filter (60) connected in said upper branch or in said lower branch and configured to limit the passage of a direct electric current to said at least one of the primary or secondary windings to which said upper or lower branch is connected.

15. High voltage direct current transmission installation comprising a first direct electric power supply network, a second direct electric power supply network and at least one voltage converter according to any one of claims 1 to 14, said voltage converter. being configured to electrically connect said first and second DC power supply networks to each other.

16. High voltage direct current transmission installation according to claim 15, comprising first and second voltage converters according to any one of claims 1 to 14, wherein the first direct current terminal of the first voltage converter and the fourth direct current terminal. of the second voltage converter are electrically connected to the first DC power supply network, wherein the third DC terminals of the first and second voltage converters are electrically connected to the second DC power supply network, and wherein the fourth terminal of the first voltage converter is electrically connected to the first DC terminal of the second voltage converter.