FR3096849A1 - DC / DC voltage converter including a transformer - Google Patents

Abstract

DC/DC voltage converter comprising a transformer Voltage converter comprising an arm (20) and a second arm (30) each comprising a plurality of chains (21,22,23,31,32,33) of sub-modules connected in series in the arm, each of said chains of sub-modules having an upper point (21a, 22a, 23a) and a lower point (21b, 22b, 23b) between which it extends and comprising a plurality of individually controllable sub-modules by a control unit and at least one connectable energy storage device, and a transformer comprising a plurality of primary and secondary windings, each of the chains of sub-modules being connected in parallel with at least one capacitor (34, 36 ,38,44,46,48) and one of the windings of the transformer, at least one of the capacitors being electrically connected to one of the upper or lower points of one of the chains of sub-modules by a passive electrical connection. Figure for abstract: Fig. 1.

Description

DC/DC voltage converter comprising a transformer

The present invention relates to the technical field of voltage converters making it possible to convert a first DC voltage into a second DC 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 (HVCD for “High Voltage Direct Current”).

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

The voltage converters most commonly used in HVDC power supply installations are modular multilevel converters (MMC). These MMC converters offer excellent efficiency, are easily controllable and their properties do not deteriorate when subjected to very high voltages. A disadvantage of these converters is that they include very many components.

AC/DC type voltage converters having a reduced number of components are known, such as the converter described in EP 3 352 354. This converter comprises an arm extending between first and second continuous terminals in which are connected in series a a plurality of chains of vertical sub-modules, each of the chains of vertical sub-modules extending between an upper point and a lower point. This converter further comprises a transformer comprising a plurality of secondary windings, each of the chains of vertical sub-modules being connected in parallel with one of the secondary windings of the transformer and with a plurality of horizontal sub-modules. Said horizontal sub-modules and said secondary winding are connected in series with respect to each other in a branch.

Each of the branches of this converter comprises several tens of horizontal sub-modules. However, each horizontal sub-module comprises a plurality of control elements connected in parallel with an energy storage device. The control elements each comprise an IGBT (Insulated Gate Bipolar Transistor) type transistor connected in parallel with an antiparallel diode.

This converter is however of a different type than the converter according to the present invention and is therefore very far from the present invention. In particular, this converter according to the prior art does not allow two continuous power supply networks to be connected together.

Furthermore, a drawback of this converter is that the number of components remains very high. Also, this converter is very heavy, bulky and bulky. In addition, its manufacture is particularly difficult and expensive.

In addition, significant resources must be used to control all the control elements of this converter. The control of the converter is therefore particularly costly and complex.

An object of the present invention is to propose a voltage converter remedying the aforementioned problems.

To do this, the invention relates to a voltage converter making it possible to convert a first DC voltage into a second DC voltage, the converter comprising:
- First and second DC terminals configured to be electrically connected to a first DC power supply network;
- Third and fourth DC terminals configured to be electrically connected to a second DC power supply network;
- a first arm extending between the first and second continuous terminals;
- a second arm extending between the third and fourth continuous terminals,
the first and second arms each comprising a plurality of chains of sub-modules connected in series respectively in the first arm and in the second arm, each of said chains of sub-modules having an upper point and a lower point between which it extends , each of the chains of sub-modules comprising a plurality of individually controllable sub-modules by a control unit specific to each sub-module and each sub-module comprising at least one energy storage device connectable in series respectively in the first arm and in the second arm when the control member of the sub-module is in a controlled state,
the voltage converter further comprising a transformer comprising a plurality of primary windings and a plurality of secondary windings, each of the chains of sub-modules being connected in parallel with at least one capacitor and one of the primary or secondary windings of the transformer, said capacitor and said primary or secondary winding being connected in series relative to each other, at least one of the capacitors being electrically connected to one of the upper or lower points of one of the chains of sub-modules by an electrical connection passive.

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 converter according to the invention forms a high voltage DC/DC converter. The DC/DC converter according to the invention is also reversible. By high voltage, we mean a voltage greater than 1000 volts. The converter advantageously comprises at least two chains of sub-modules per arm.

The chains of sub-modules of the first arm are advantageously connected in parallel with the secondary windings of the transformer. The chains of sub-modules of the second arm are advantageously connected in parallel with the primary windings of the transformer.

Preferably, each of the primary and secondary windings of the transformer has a first terminal connected to a capacitor and a second terminal connected to a lower point of one of the chains of sub-modules. Without departing from the scope of the invention, the transformer can be formed from a single transformer having several phases or from a plurality of single-phase transformers each having a primary winding and a secondary winding.

The submodules of the submodule chains are connected in series with respect to each other.

According to a non-limiting variant, the voltage converter can comprise two chains of sub-modules per arm and the transformer can comprise two primary windings and two secondary windings. In this variant, the transformer can be formed by two single-phase transformers.

In a non-limiting manner, the control units of the sub-modules can comprise controllable switching elements of the IGBT switch type and an antiparallel diode. In a non-limiting way, the control devices can be placed in the controlled state in response to a control order, coming for example from a control module, or even according to the sign of the current flowing in the corresponding arm and crossing the chain of submodules. The energy storage device of the sub-modules may include a capacitor.

The sub-modules can be controlled according to a sequence chosen to progressively vary the number of energy storage elements which are connected in series in the first arm and in the second arm of the voltage converter, so as to provide several levels tension in said arms.

By passive electrical connection is meant a connection without active components (diode, transistor, integrated circuit, switch). This means in particular that it cannot be controlled, for example to switch from a conductive state to a non-conductive state (which is the case when a switch is placed in an electrical connection, which is then active). The capacitor is therefore electrically connected to the upper or lower point of the chain of sub-modules permanently associated. No control means makes it possible to interrupt the electrical connection between the capacitor and said upper or lower point of the chain of sub-modules.

For example, the passive electrical connection may consist of electrical connectors and an electrical cable or wire, a conductive bar, a metallic track printed on a support, a bushing.

Preferably, the current flowing through the capacitor is substantially identical to the current at the level of the upper point, respectively of the lower point, of the chain of sub-modules.

Also, the branch in which the capacitor is electrically connected, passively, does not include a controllable sub-module.

The capacitor can be connected by a passive electrical connection to the upper point or to the lower point of the chain of associated sub-modules. In a non-limiting way, another capacitor can be connected in the branch, so that a first capacitor is connected by a passive electrical connection to the upper point of the chain of associated sub-modules while a second capacitor is connected by a passive electrical connection at the lower point of said chain of sub-modules.

Each of the chains of sub-modules makes it possible to generate a controllable voltage inserted in the arm between its upper and lower points. Said inserted voltage has a DC component and an AC component. The DC component of the inserted voltage makes it possible to control a DC current flowing in the corresponding arm. The alternating component of the inserted voltage, generated by a chain of sub-modules, makes it possible to control an alternating current passing through the capacitor and the primary or secondary winding of the transformer, connected in parallel to said chain of sub-modules. These alternating currents being controllable in phase and in amplitude, the active power and the reactive power of the converter can also be controlled.

Furthermore, the sum of the alternating components of the voltages inserted in the first arm, respectively in the second arm, generated by the sub-module chains, is zero, so that the circulation of an alternating current in the first arm, respectively in the second arm, is prevented.

The inventors have observed that it is possible to dispense with the use of horizontal sub-modules connected in parallel to the chains of sub-modules, as described in EP 3 352 354.

The use, according to the invention, of a capacitor electrically and passively connected to the upper or lower point of a chain of sub-modules makes it possible to block the circulation of a direct current in the corresponding winding of the transformer while by allowing the circulation of an alternating current. This alternating current is controllable thanks to the chains of sub-modules. This makes it possible to exchange power between the first and second arms and in particular between the chains of sub-modules of the first arm and the chains of sub-modules of the second arm.

In particular, the power exchanges between the first and second arms are controlled by controlling the chains of sub-modules in order to adjust the phase shift of the alternating components of the voltages inserted by the chains of sub-modules between the first arm and the second arm . Moreover, the frequency of said alternating voltages can be controlled, which makes it possible to reduce the size and weight of passive components, such as capacitors.

The voltage converter according to the invention therefore offers the degrees of control necessary to compensate for a potential difference between the first and third DC terminals and therefore between the connection points of the converter to the first and second DC power supply networks. The voltage converter according to the invention therefore makes it possible to connect together two DC power supply networks having different nominal voltages. In particular, the voltage adaptation between the first arm and the second arm is facilitated by the transformer and is not compromised by the use of a capacitor connected to the upper or lower point of a chain of sub-modules by a passive electrical connection.

An advantage of the invention, compared to the converters of the prior art, is therefore to reduce the weight and the size of the converter by dispensing with a large number of sub-modules and therefore of switching elements and storage elements in parallel chains of sub-modules. The insulation and cooling of the voltage converter are improved. Furthermore, the manufacture of the converter is facilitated and the manufacturing costs are reduced.

In addition, the voltage converter according to the invention makes it possible to connect together two DC power supply networks having different topologies. Preferably, the voltage converter is reversible so that it allows power exchanges from the first arm to the second arm and vice versa.

Furthermore, the number of controllable elements of the converter according to the invention being limited, the control of the converter is also facilitated.

Preferably, all the capacitors are electrically connected to the upper or lower points of the chains of sub-modules by passive electrical connections.

Preferably, said at least one of the capacitors is connected directly to said upper or lower point. Also, an electrical line devoid of electrical component or node connects an electrode of the capacitor and the upper or lower point of the chain of sub-modules. As an indication, this implies that there is no electrical node between the capacitor and the upper or lower point of the chain of sub-modules, and that the current which circulates in the passive electrical connection is not divided between two branches between the capacitor and the upper or lower point. The potential of the upper or lower point is therefore substantially equal to the potential of said electrode of the capacitor. Here again, there is an interest in reducing the number of components and therefore the weight and size of the voltage converter.

In a non-limiting way, said capacitor can form the only component connected between said secondary winding and the upper or lower point of the chain of sub-modules.

Advantageously, the first arm and the second arm each comprise three chains of sub-modules and the transformer comprises three primary windings and three secondary windings, each of the three chains of sub-modules of the first arm being connected in parallel with one of the three secondary windings of the transformer, each of the three chains of sub-modules of the second arm being connected in parallel with one of the three primary windings of the transformer.

Preferably the transformer is three-phase. Alternatively, and without departing from the scope of the invention, the three-phase transformer can be formed from three single-phase transformers each having a primary winding and a secondary winding.

Preferably, the sub-modules of the chains of sub-modules of the first and second arms have a half-bridge topology or a full-bridge topology. Without departing from the scope of the invention, other topologies of sub-modules can be envisaged.

The control member of a half-bridge sub-module comprises a first electronic switching element connected in series with the energy storage device and a second electronic switching element coupled between the input and output terminals of the submodule .

The control unit of a Full Bridge sub-module comprises four switching elements.

In these two topologies, the control unit advantageously comprises an antiparallel diode connected in parallel with each of the switching elements.

Advantageously, the sub-modules of the chains of sub-modules of the first arm have a half-bridge topology and the sub-modules of the chains of sub-modules of the second arm have a full-bridge topology.

One interest is to allow two heterogeneous DC power supply networks to be connected to each other. In particular, a DC power supply network comprising a voltage converter of the voltage source converter (VSC) type can be connected to the first and second DC terminals and a DC power supply network comprising a line commutated converter type voltage converter (LCC for "Line Commutated Converter" in English) can be connected to the third and fourth DC terminals.

Without departing from the scope of the invention, each of the arms may comprise a combination of full-bridge sub-modules and half-bridge sub-modules.

According to a particularly advantageous aspect of the invention, the voltage converter comprises at least one filter module connected in series with the first arm or the second arm and configured to prevent the circulation of an alternating current in said arm. A filter module is therefore connected in series with the first arm and/or with the second arm and is configured to prevent the circulation of an alternating current in said arm. A filter module can therefore be connected in the first arm, in the second arm or in both arms.

The chains of sub-modules of the first and second arms of the voltage converter effectively oppose the circulation of an alternating current in said arms. However, in the event of disturbance or imbalance on one of the DC power supply networks connected to the converter according to the invention, it happens that the voltage resulting from the sum of the voltages inserted in one of the arms, generated by the chains of sub-modules of said arm, has a residual alternating component so that an alternating current remains in the corresponding arm.

One interest of the filtering module is to filter and therefore to remove this alternating component from the total voltage in the corresponding arm, so as to guarantee the circulation in this arm of a single direct current.

The filter module is advantageously connected in series with the chains of sub-modules of the corresponding arm, between the first and second DC terminals or between the third and fourth DC terminals of the converter.

Preferably, the filtering module comprises at least one passive component and/or one active component.

By passive component, we mean a component that does not produce energy, voltage or current. Such a passive component makes it possible to store or conserve energy. In a non-limiting manner, it may be a resistor or a capacitor.

The filtering module may comprise only passive components so that it forms a passive filtering module. The passive components are then advantageously sized so that the filter module has a high impedance at its resonant frequency, in order to effectively filter the AC component of the current in the arm in which it is connected.

By active component is meant a controllable component capable of generating a controlled voltage or current. In a non-limiting way, it can be a switch, a semiconductor, such as a transistor or even a sub-module comprising at least one semiconductor.

The filtering module can comprise at least one active component, so that it forms an active filtering module.

Preferably, the filter module comprises an inductor and a capacitor connected in parallel with each other. Still preferably, the filtering module consists of an inductance and a capacitor connected in parallel to each other, in series with the corresponding arm.

The filtering module then forms a filter preventing the flow of alternating current in said arm.

Preferably, the filter module comprises a chain of additional sub-modules comprising a plurality of individually controllable sub-modules by a control unit specific to each sub-module and each sub-module of said chain of additional sub-modules comprising at least an energy storage device connectable in series with the first arm and/or the second arm when the control member of the sub-module is in a controlled state.

The chain of additional sub-modules makes it possible to generate an alternating voltage at its terminals having an amplitude equal to that of the alternating component of the total voltage at the terminals of all the chains of sub-modules of the arm in which the filter module is connected, and having opposite phase.

Advantageously, each of the chains of sub-modules of the first arm and of the second arm is also connected in parallel with an inductor, said inductor being connected in series with said capacitor and said primary or secondary winding of the transformer.

The inductor is preferably arranged between said primary or secondary winding and said capacitor.

Advantageously, the voltage converter comprises a start-up module configured to charge the energy storage devices of the sub-modules of at least one of the arms of the converter when it is placed in a first state. When charging the energy storage devices, the voltage at the terminals of the sub-module strings gradually increases until it reaches a nominal value.

The starter module is advantageously connected in series with one of the arms of the converter.

The starter module is preferably connected between one of the DC terminals of the voltage converter and a lower point of one of the chains of sub-modules.

Preferably, the starter module comprises at least a first switch connected to one of the DC terminals of the converter and a limiting resistor connected in parallel with said switch, said switch being open when the starter module is placed in the first state.

In the first state, an uncontrolled current appears in the series arm to which the starter module is connected. This uncontrolled current is limited by the limiting resistor and gradually charges the storage devices of the sub-modules of said arm, up to a predefined pre-charge value.

This pre-charged pre-charge value is chosen in particular so as to allow the supply of a control module.

Preferably, the starter module can be placed in a second state, in which said at least one switch is closed, so as to short-circuit said limiting resistor.

The limiting module is first maintained in the first state until the storage organs of the sub-modules reach the pre-set pre-charge value. The chains of sub-modules are then controllable and can be controlled to gradually increase the energy stored in their storage devices. When the voltage at the terminals of each chain of sub-modules reaches a final value substantially equal to the voltage of the associated DC power supply network, the starter module is placed in the second state.

All of the energy storage devices of the sub-modules of the arm in series to which the starter module is connected are charged to a final charge value. Control of the direct current flowing in said arm and of the alternating currents flowing in the branches of the converter is then restored and the voltage converter then operates normally.

In a non-limiting way, the converter can comprise a first starting module and a second starting module connected respectively in series with the first arm and with the second arm.

Preferably, the voltage converter comprises a control module configured to control the control members of the sub-modules of the chains of sub-modules of the first arm and of the second arm, so as to regulate the voltages at the terminals of said chains of sub-modules .

The control module is configured to regulate the energy stored in the capacitors of the sub-modules of the chains of sub-modules of the first arm and of the second arm and, preferably, of the chain of additional sub-modules, by controlling the organs control of the sub-modules.

The control module makes it possible in particular to regulate the DC and AC components of the voltages inserted in the first and second arms, generated by the chains of sub-modules.

Consequently, the control module makes it possible to regulate the direct current circulating in the first and second arms and therefore the alternating current circulating in the capacitors and the primary and secondary windings connected in parallel to the chains of sub-modules.

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

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 appended drawings, in which:

FIG. 1 illustrates an HVDC installation comprising a first embodiment of a voltage converter according to the invention;

Figure 2 illustrates a half-bridge sub-module of the voltage converter of Figure 1;

Figure 3 illustrates a full-bridge sub-module of the voltage converter of Figure 1;

FIG. 4 illustrates an HVDC installation comprising a second embodiment of a voltage converter according to the invention;

FIG. 5 illustrates an HVDC installation comprising a third embodiment of a voltage converter according to the invention;

FIG. 6 illustrates a first variant of a filter module of the voltage converter of FIG. 4;

FIG. 7 illustrates a second variant of a filter module of the voltage converter of FIG. 4; And

FIG. 8 illustrates an HVDC installation comprising a fourth embodiment of a voltage converter according to the invention.

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

The figure1illustrates an HVDC installation8comprising a first embodiment of a voltage converter10according to the invention, interconnecting a first DC power supply network12and a second DC power supply network14 of the facility. The voltage converter10according to the invention therefore forms a DC/DC converter.

As can be seen in FIG. 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 voltage V _{DC 1} of the first DC power supply network 12 is illustrated between the first DC terminal 16 and the second DC terminal 18 .

The voltage converter comprises a first arm 20 extending between the first DC terminal 16 and the second DC terminal 18 . The first arm 20 comprises first 21 , second 22 and third 23 chains of sub-modules SM . The first, second and third chains 21 , 22 , 23 of sub-modules are connected in series in the first arm 20 .

The first chain 21 of sub-modules extends between a first upper point 21a and a first lower point 21b . The second chain 22 of sub-modules extends between a second upper point 22a and a second lower point 22b . The third chain 23 of sub-modules extends between a third upper point 23a and a third lower point 23b .

Furthermore, the voltage converter 10 comprises a third DC terminal 24 and a fourth DC terminal 26 configured to be electrically connected to the second DC power supply network 14 . The voltage V _{DC 2} of the second DC power supply network 14 is illustrated between the third DC terminal 24 and the fourth DC terminal 26 .

The voltage converter comprises a second arm 30 extending between the first DC terminal 24 and the second DC terminal 26 . The second arm 30 comprises fourth 31 , fifth 32 and sixth 33 chains of sub-modules SM . The fourth, fifth and sixth chains 3 1 , 3 2 , 3 3 of sub-modules are connected in series in the second arm 30 .

The fourth chain 31 of sub-modules extends between a fourth upper point 31a and a fourth lower point 31b . The fifth chain 32 of sub-modules extends between a fifth upper point 32a and a fifth lower point 32b . The sixth chain 33 of sub-modules extends between a sixth upper point 33a and a sixth lower point 33b .

Each of the chains of sub-modules of the first and second arms 20 , 30 comprises a plurality of sub-modules SM which can be controlled according to a desired sequence. Each chain of sub-modules can comprise from two to several tens of SM sub-modules.

As illustrated in Figures 2 and 3 , each SM sub-module comprises an energy storage device comprising in this example a capacitor C _SM , and a control device for selectively connecting this capacitor in series between the terminals of the SM sub-module or to circumvent it.

FIG. 2 illustrates a sub-module having a half-bridge topology. In this half-bridge sub-module, the control device comprises a first electronic switching element T1 such as an insulated gate bipolar transistor ("IGBT: Insulated Gate Bipolar Transistor" in English) connected in series with the capacitor C _SM . This first switching element T1 and this capacitor C _SM are mounted in parallel with a second electronic switching element T2 , also an insulated-gate bipolar transistor (IGBT). This second electronic switching element T2 is coupled between the input and output terminals of the sub-module SM . The first and second switching elements T1 and T2 are both associated with an antiparallel diode D represented in FIG .

In operation, the sub-module can be placed in two distinct states.

In a first state called the "on" or controlled state, the first switching element T1 and the second switching element T2 are configured so as to connect the capacitor C _SM in series with the other sub-modules of the chain of sub-modules . In a second state called the “off” or non-controlled state, the first switching element T1 and the second switching element T2 are configured so as to bypass the capacitor C _SM .

The sub-modules are controlled according to a sequence chosen to gradually vary the number of energy storage elements, and therefore the number of capacitors, which are connected in series in the chain of corresponding sub-modules and therefore in the first arm 20 and in the second arm 30 of the voltage converter 10 , so as to provide several voltage levels in these arms.

FIG. 3 illustrates a variant of the sub-module of FIG. 2 , in which the sub-module has a full-bridge topology. In this topology, the sub-module comprises four switching elements T′1 , T′2 , T′3 , T′4 , each being associated in parallel with an antiparallel diode D.

In a non-limiting way, the sub-modules of the chains of sub-modules of the first arm can have a half-bridge topology and the sub-modules of the chains of sub-modules of the second arm can have a full-bridge topology. This allows to connect between them two heterogeneous continuous power supply networks. In particular, the first DC power supply network 12 may comprise a voltage converter of the voltage source converter (VSC) type. The second DC power supply network 14 may comprise a voltage converter of the line-commutated converter (LCC) type.

In this non-limiting example , the voltage converter 10 further comprises a transformer 40 comprising first 41a , second 42a and third 43a primary windings respectively associated with first 41b , second 42b and third 43b secondary windings .

Voltage converter 10 further includes first capacitor 34 , second capacitor 36 , third capacitor 38 , fourth capacitor 44, fifth capacitor 46 , and sixth capacitor 48 .

The first capacitor34and the first secondary winding4 1 bare connected in series with respect to each other in a first branch60extending between the first upper point21 Toand the first lower point21 b of the first chain of submodules21. The first capacitor34and the first secondary winding4 1bare therefore connected in parallel to the first chain21of sub-modules.

According to the invention, the first capacitor 34 is electrically connected to the first upper point 21a of the first chain 21 of sub-modules by a first electrical connection 35 forming a passive electrical connection, devoid of controllable means and active components.

One benefit is to dispense with the use of sub-modules in said first branch 60 , in order to reduce the number of components of the voltage converter 10 and thus reduce its weight, its size and its manufacturing cost .

The first capacitor 34 is also connected directly to the first upper point, so that no component or node is placed between the first capacitor 34 and the first upper point 21a .

The second capacitor 36 and the second secondary winding 42b are connected in series with respect to each other in a second branch 62 extending between the second upper point 22a and the second lower point 22b of the second chain of sub-modules 22 . The second capacitor 36 and the second secondary winding 4 2 b are therefore connected in parallel with the second chain of sub-modules 22 .

According to the invention, the second capacitor 36 is electrically connected to the second upper point 22a by a second electrical connection 37 forming a passive electrical connection, devoid of controllable means. The second capacitor 36 is connected directly to the second upper point 22a of the second chain of sub-modules.

The third capacitor38and the third secondary winding4 3 bare connected in series with respect to each other in a third branch6 4extending between the upper third point23 Toand the third lower point23 b of the third chain of submodules. The third capacitor38and the third secondary winding4 3 bare therefore connected in parallel with the third chain of sub-modules23.

According to the invention, the third capacitor 38 is electrically connected to the third upper point 23a by a third electrical connection 39 forming a passive electrical connection, devoid of controllable means. The third capacitor is connected directly to the third upper point.

The fourth capacitor 44 and the first primary winding 41a are connected in series with respect to each other in a fourth branch 66 extending between the fourth upper point 31a and the fourth lower point 31b of the fourth chain of sub-modules 31 . The fourth capacitor 44 and the first primary winding 41a are therefore connected in parallel with the fourth chain of sub-modules 31 .

According to the invention, the fourth capacitor 44 is electrically connected to the fourth upper point 31 a by a fourth electrical connection 45 forming a passive electrical connection, devoid of controllable means. The fourth capacitor is connected directly to the fourth upper point.

The fifth capacitor 46 and the second primary winding 42a are connected in series with respect to each other in a fifth branch 68 extending between the fifth upper point 32a and the fifth lower point 32b of the fifth chain of sub-modules 32 . The fifth capacitor 46 and the second primary winding 42a are therefore connected in parallel with the fifth chain of sub-modules 32 .

According to the invention, the fifth capacitor 46 is electrically connected to the fifth upper point 32a by a fifth electrical connection 47 forming a passive electrical connection, devoid of controllable means. The fifth capacitor is connected directly to the fifth upper point.

The sixth capacitor 48 and the third secondary winding 43a are connected in series with respect to each other in a sixth branch 70 extending between the sixth upper point 33a and the sixth lower point 33b of the sixth chain . of sub-modules. The sixth capacitor 48 and the third primary winding 43a are therefore connected in parallel with the sixth chain of sub-modules 33 .

According to the invention, the sixth capacitor 48 is electrically connected to the sixth upper point 33a by a sixth electrical connection 49 forming a passive electrical connection, devoid of controllable means. The sixth capacitor is connected directly to the sixth upper point.

Alternatively, and without departing from the scope of the invention, said capacitors could be electrically connected to the lower points of the chains of associated sub-modules by passive electrical connections.

According to another variant, in a non-limiting manner, each of the branches could comprise two capacitors, namely a first capacitor connected to the upper point of the chain of associated sub-modules by a passive electrical connection and a second capacitor connected to the lower point of the chain of sub-modules associated by a passive electrical connection.

In a non-limiting manner, each of the primary 41a , 42a , 43a and secondary 41b , 42b , 43b windings has an upper terminal connected directly to the corresponding capacitor and a lower terminal connected to the lower point of the chain of sub-modules associated in parallel.

The converter further comprises a control module 72 configured to control the control members of the sub-modules SM of the chains of sub-modules 21 , 22 , 23 , 31 , 32 , 33 of the first arm and of the second arm, so as to regulating the voltages at the terminals of said chains of sub-modules.

The operation of the voltage converter 10 of FIG. 1 , according to the invention will now be detailed.

Each of the first, second, third, fourth, fifth and sixth chains 21 , 22 , 23 , 31 , 32 , 33 of SM sub-modules behaves like a voltage source and makes it possible to generate respectively in the first arm 20 and in the second arm 30 an inserted voltage. Also, the first, second and third chains of sub-modules are configured to respectively generate a first inserted voltage v _m1 , a second inserted voltage v _m2 and a third inserted voltage v _m3 in the first arm 20 , each depending on the number of sub -modules ordered.

Similarly, the fourth, fifth and sixth chains of sub-modules are configured to respectively generate a fourth inserted voltage v _m4 , a fifth inserted voltage v _m5 and a sixth inserted voltage v _m6 in the second arm 30 , each depending on the number of sub-modules ordered.

Said voltagesv _m1 ,v _m2 ,v _{m3 ,} v _m4 ,v _m5 ,v _m6 respectively inserted into the first arm 20 and in the second arm30are controllable thanks to the control module72which allows to control the sub-modules of the chains of sub-modules. Said inserted voltages have a DC component and an AC component that can be controlled independently of each other.

The DC components of the first, second and third inserted voltagesv _m1 , v _m2 , v _m3 have the consequence of generating a first direct currentI _{DC 1} flowing in the first arm20 and crossing the chains of sub-modules of this first arm. The DC components of the fourth, fifth and sixth inserted voltagesv _m4 ,v _m5 ,v _m6 result in the generation of a second direct currentI _{DC 2} flowing in the second arm3 0and crossing the chains of sub-modules of this second arm.

The alternating component of each of the voltages inserted in the first arm and in the second arm, generated by each of the chains of sub-modules, makes it possible to generate an alternating current circulating in the associated branch.

Also, a first alternating current i _{AC 1} flows in the first branch 60 and crosses the first capacitor 34 and the first secondary winding 41 b . Similarly, a second alternating current i _{AC 2} flows in the second branch 6 2 and passes through the second capacitor 36 and the second secondary winding 4 2b . In addition, a third alternating current i _{AC 3} flows in the third branch 6 4 and crosses the third capacitor 38 and the third secondary winding 4 3b .

This results in a fourth alternating current i _{AC 4} flowing in the fourth branch 66 and crossing the fourth capacitor 44 and the first primary winding 41a . The fourth alternating current i _{AC 4} is proportional to the first alternating current i _{AC 1} by a factor equal to the transformation ratio of the transformer between the first primary and secondary windings. In addition, a fifth alternating current i _{AC 5} flows in the fifth branch 68 and passes through the fifth capacitor 46 and the second primary winding 42a . Finally, a sixth alternating current i _{AC 6} flows in the sixth branch 70 and passes through the sixth capacitor 48 and the third primary winding 43a .

The power flow between the first and second arms is adjusted by controlling the magnitude of the inserted voltages. The power flow is more particularly adjusted by controlling the phase shift respectively between the alternating components of the first and fourth voltages inserted v _m1 , v _m4 , second and fifth voltages insertedv _m2 , v _m5 and third and sixth voltages inserted v _m3 , v _m6 . This in fact makes it possible to control the first, second, third and alternating currentsI _AC1 ,I _AC2 And I _AC3 and consequently the fourth, fifth and sixth alternating currentsI _{AC 4} ,I _{AC 5} And I _{AC 6 .}

The first capacitor 34 being connected directly and by a passive connection to the first upper point 21a , the potential of the electrode of the capacitor connected to the first connection 35 is substantially equal to the potential of the first upper point 21a . It is the same for the second, third, fourth, fifth and sixth capacitors 36 , 38 , 44 , 46 , 48 .

Furthermore, the first, second and third capacitors34,36,38make it possible to block the passage of a direct electric current respectively in the first, second and third branches6 0,6 2,6 4. Similarly, the fourth, fifth and sixth capacitors44,4 6,4 8make it possible to block the passage of a direct electric current respectively in the fourth, fifth and sixth branches66,68,70. Also, said capacitors make it possible to decouple the DC component from the AC component of the inserted voltages, generated by the chains of sub-modules.

The control of the amplitude and the phase difference between the AC components of the inserted voltages of the first arm and the second arm makes it possible to control the exchanges of power between the first and second arms and in particular between the chains of sub-modules of the first arm and the chains of sub-modules of the second arm.

Additionally, the frequency of AC voltages flowing through the branches can be controlled, reducing the size and weight of passive components, such as branch capacitors and transformers.

Further, transformer 40 facilitates voltage matching between the first arm and the second arm.

The voltage converter 10 therefore makes it possible to connect together two DC power supply networks having different nominal voltages. In particular, the use of capacitors connected to the upper points of the chains of sub-modules by passive electrical connections makes it possible to reduce the weight and the size of the converter by dispensing with a large number of sub-modules. Furthermore, the manufacture of the converter is facilitated, the control hardware is simplified and the manufacturing costs are reduced.

FIG. 4 illustrates an HVDC installation 8 comprising a second embodiment of the voltage converter 10 according to the invention. This second embodiment is a variant of the voltage converter 10 of FIG .

In this variant, the voltage converter 10 is further provided with a filter module 80 connected in series with the first arm 20 , between the first and second DC terminals 16 , 18 , and more precisely between the first DC terminal 16 and the first upper point 21a of the first chain 21 of sub-modules. The filter module 80 is configured to filter the alternating component of the total voltage resulting from the sum of the voltages v _m1 , v _m2 , v _m3 inserted into the first arm 20 , so as to prevent the circulation of an alternating current in the first arm and to guarantee the circulation in the first arm of a single direct current i _{DC 1} .

In a non-limiting way, a second filter module could be connected in series with the second arm 30 .

A first variant of a filtering module is illustrated in FIG . In this example, the filtering module 80 comprises an inductor 82 and a capacitor 84 connected in parallel to each other. These two components are passive so that the filter module 80 is also passive. Said inductance 8 2 and said capacitor 8 4 form a filter.

FIG . 7 illustrates a second variant of a filter module 80 . In this example, the filtering module 80 comprises a chain of additional sub-modules 86 comprising a plurality of sub-modules SM individually controllable by a control unit specific to each sub-module and each sub-module of said chain of additional sub-modules comprising at least one energy storage device connectable in series with the first arm or in the second arm when the control member of the sub-module is in a controlled state. Said chain of sub-modules is substantially identical to the first, second and third chains 21 , 22 , 23 of sub-modules. Without departing from the scope of the invention, the filter module could comprise Full Bridge type sub-modules while the chains of sub-modules of the first arm could be of the Half-Bridge type.

The additional sub-module chain 86 makes it possible to generate an alternating voltage v _m at its terminals having an amplitude equal to that of the alternating component of the total voltage at the terminals of all the sub-module chains of the arm in which the filter module is connected, and having an opposite phase

Referring again to Figure 4 , it can be seen that the voltage converter 10 further comprises, in a non-limiting manner, a first inductor 74 connected in series with the first arm 20 and a second inductor 76 connected in series with the second. arm 30 . The first inductor 74 is connected between the filter module 50 and the first chain of sub-modules 21 .

Still in FIG. 4 , it can be seen that the voltage converter 10 also comprises a starter module 88 . In this non-limiting example, the starter module comprises a switch 90 connected to the second DC terminal 18 of the voltage converter and a limiting resistor 92 connected in parallel with said switch 90 . The starting module 88 is configured to charge the energy storage devices C _SM of the sub-modules SM of the chains of sub-modules in order to allow the starting of the voltage converter 10 and the control of the direct and alternating currents circulating in the voltage converter.

When the starter module is placed in a first state, said switch 90 is open so that an uncontrolled current appears and flows in the first arm 20 .

The energy storage devices of the sub-modules of the arm are charging and the voltage at the terminals of the chains of sub-modules increases progressively. The sub-modules are then controlled to gradually increase the energy stored in their storage elements. When the voltage across the terminals of each chain of sub-modules reaches a final value substantially equal to the voltage of the associated DC power supply network, switch 90 is then closed so as to bypass said limiting resistor 92 . The start-up module is then placed in a second state.

Control of the direct current circulating in the arms and of the alternating currents circulating in the branches of the converter is then restored and the voltage converter then operates normally.

Alternatively, the start module88could be connected between the first continuous terminal16and the first upper point21a. The starter module88could also be connected between the second DC power supply network14and the converter, and more precisely between the fourth DC terminal26and the lower sixth point33b or between the third continuous terminal24and the fourth upper point31a.

FIG. 5 illustrates an HVDC installation 8 comprising a third embodiment of the voltage converter 10 according to the invention. This third embodiment is a variant of the voltage converter 10 of FIG .

In this variant, the capacitors are connected, via passive electrical connections, to the lower points of the chains of associated sub-modules.

Alternatively, each of the branches may include two capacitors, so that a first capacitor is connected by a passive electrical connection to the top point of the associated chain of sub-modules while a second capacitor is connected by an electrical connection passive at the lower point of said chain of sub-modules.

The figure8illustrates an installation8comprising a fourth embodiment of a voltage converter10according to the invention. In this non-limiting example, each of the arms of the voltage converter comprises only two chains of sub-modules. Also, the first arm20 'of the converter comprises a first and a second chain of sub-modules21',22'respectively connected between upper and lower first points21a',21b'and between upper and lower second points22a',22b'. The second arm 30 'includes third and fourth chains of submodules31',32'respectively connected between upper and lower third points31a',31b'and between upper and lower fourth points32a',32b'.

Furthermore, the transformer 40 comprises only a first and a second primary windings 41a ' , 42a ' and a first and a second secondary windings 41b ' , 42b ' .

Each of the capacitors is connected in series with a corresponding winding of the transformer in a leg 60' , 64' , 66' , 70' and connected to the corresponding upper point via a passive electrical connection 35' , 37' , 45' , 47' .

Each of the first, second, third and fourth chains of sub-modules makes it possible to generate an inserted voltage v _m1 , v _m2 , v _m3 , v _m4 .

Claims (14)

A voltage converter (10) for converting a first DC voltage to a second DC voltage, the converter comprising:
- first and second DC terminals (16,18) configured to be electrically connected to a first DC power supply network (12);
- third and fourth DC terminals (24,26) configured to be electrically connected to a second DC power supply network (14);
- a first arm (20) extending between the first and second continuous terminals;
- a second arm (30) extending between the third and fourth continuous terminals,
the first and second arms each comprising a plurality of chains (21,22,23,31,32,33) of sub-modules connected in series respectively in the first arm and in the second arm, each of the said chains of sub-modules having an upper point (21a,22a,23a,31a,32a,33a) and a lower point (21b,22b,23b,31b,32b,33b) between which it extends, each of the chains of sub-modules comprising a plurality sub-modules (SM) individually controllable by a control unit (T1, T2) specific to each sub-module and each sub-module comprising at least one energy storage device (C _SM ) connectable in series respectively in the first arm and in the second arm when the control member of the sub-module is in a controlled state,
the voltage converter further comprising a transformer (40) having a plurality of primary windings (41a,42a,43a) and a plurality of secondary windings (41b,42b,43b), each of the chains of sub-modules being connected in parallel with at least one capacitor (34,36,38,44,46,48) and one of the primary or secondary windings of the transformer, said capacitor and said primary or secondary winding being connected in series with respect to each other other, at least one of the capacitors being electrically connected to one of the upper or lower points of one of the chains of sub-modules by a passive electrical connection (35,37,39,45,47,49). A voltage converter according to claim 1, wherein said at least one of the capacitors (34,36,38,44,46,48) is connected directly to said upper (21a,22a,23a,31a,32a,33a) or lower point . Voltage converter according to claim 1 or 2, in which the first arm (20) and the second arm (30) each comprise three chains (21,22,23,31,32,33) of sub-modules and in which the transformer (40) comprises three primary windings (41a,42a,43a) and three secondary windings (41b,42b,43b), each of the three chains of sub-modules of the first arm being connected in parallel with one of the three secondary windings of the transformer , each of the three chains of sub-modules of the second arm being connected in parallel with one of the three primary windings of the transformer. Voltage converter according to any one of Claims 1 to 3, in which the submodules of the chains (21,22,23,31,32,33) of submodules of the first and second arms (20,30) have a half-bridge topology or a full-bridge topology. Voltage converter according to claim 4, in which the sub-modules of the chains of sub-modules (21,22,23) of the first arm (20) have a half-bridge topology and in which the sub-modules of the chains of sub-modules (31,32,33) of the second arm (30) have a full-bridge topology. Voltage converter according to any one of claims 1 to 5, comprising at least one filter module (80) connected in series with the first arm (20) or the second arm (30) and configured to prevent the circulation of a alternating current in said arm. Voltage converter according to claim 6, in which the filter module (80) comprises at least one passive component and/or one active component. A voltage converter according to claim 6 or 7, wherein the filter module (80) comprises an inductance (82) and a capacitor (84) connected in parallel with each other. Voltage converter according to any one of Claims 6 to 8, in which the filtering module (80) comprises a chain of additional sub-modules (86) comprising a plurality of sub-modules (SM) individually controllable by a control specific to each sub-module and each sub-module of said chain of additional sub-modules comprising at least one energy storage device connectable in series with the first arm (20) and/or the second arm (30) when the control member of the sub-module is in a controlled state. Voltage converter according to any one of claims 1 to 9, comprising a start-up module (88) configured to charge the energy storage devices (C _SM ) of the sub-modules of at least one of the arms of the converter when he is placed in a first state. A voltage converter according to claim 10, wherein the start module (88) comprises at least a first switch (90) connected to one of the DC terminals of the converter and a limiting resistor (92) connected in parallel with said switch, said switch being open when the start module is placed in the first state. Voltage converter according to claim 11, wherein the start module (88) can be placed in a second state, in which said at least one switch (90) is closed, so as to short-circuit said limiting resistor (92 ). A voltage converter according to any one of claims 1 to 12, further comprising a control module (72) configured to control the controllers of the sub-modules of the strings (21,22,23,31,32,33) of sub-modules of the first arm (20) and of the second arm (30), so as to regulate the voltages at the terminals of said chains of sub-modules. High voltage direct current transmission installation (8) comprising a first direct current power supply network (12), a second direct current power supply network (14) and a voltage converter (10) according to any one of the claims 1 to 13, said voltage converter being configured to electrically connect said DC power supply networks to each other.