FR3112042A1 - Three-phase AC / DC voltage converter including only two power converter modules - Google Patents

Abstract

Three-phase AC/DC voltage converter comprising only two electrical conversion modules A voltage converter (10) for converting an alternating voltage into a direct voltage and vice versa, the voltage converter comprising first and second electrical conversion modules (22, 24 ) connected in series in an arm (20); an electrical energy transformation device (40) comprising a first primary winding (41a) connected between first and second alternating terminals (30,32) and a second primary winding (42a) connected between second and third alternating terminals (32 ,34), as well as first and second secondary windings (41b,42b); and a control module (100) configured to control the first and second electrical conversion modules so that a first alternating current (I1) flowing in the first secondary winding and a second alternating current (I2) flowing in the second secondary winding are out of phase, the voltage converter comprising only two electrical conversion modules. Figure for abstract: Fig. 1.

Description

Three-phase AC/DC voltage converter comprising only two electrical conversion modules

The present invention relates to the technical field of AC to DC voltage converters and vice versa, also called AC/DC voltage converters. This type of converter is particularly suitable for installation in high voltage direct current (HVDC) power supply installations.

HVDC power supply installations generally comprise a continuous power supply network allowing the transmission of electricity over long distances by means of direct current lines of several hundred kilometers. They also include an alternative power supply network, for example connected to an offshore wind farm. AC/DC voltage converters allow the connection of such an alternating power supply network with a direct power supply network.

Three-phase AC/DC voltage converters are known, such as the converter described in EP 2 569 858 A1. This converter comprises an arm extending between first and second continuous terminals in which three electrical conversion modules are connected in series. This converter further comprises a transformer comprising three primary windings and three secondary windings. Each of the secondary windings of the transformer is electrically connected to one of the three electrical conversion modules.

A disadvantage of this three-phase converter is that it includes a very large number of components and that it turns out to be very bulky. Indeed, the high voltage application imposes minimum distances between the electrical conversion modules of this converter. This converter, equipped with three electrical conversion modules therefore has a large size and bulk.

Furthermore, each of the three electrical conversion modules of this converter comprises several tens of sub-modules connected in a phase branch. 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 expensive and complex.

An object of the present invention is to propose a voltage converter remedying the aforementioned problems and making it possible in particular to reduce the number of components of said voltage converter.

To do this, the invention relates to a voltage converter making it possible to convert an alternating voltage into a direct voltage and vice versa, the voltage converter comprising:
- First and second DC terminals configured to be electrically connected to a DC power supply network;
- First, second and third AC terminals configured to be electrically connected to an AC power supply network;
- an arm extending between the first and second continuous terminals and comprising a first electrical conversion module and a second electrical conversion module connected in series in said arm, the first and second electrical conversion modules each having a first continuous terminal and a second continuous terminal between which it extends, as well as a first alternating terminal and a second alternating terminal;
- an electric energy transformation device comprising a first primary winding connected between the first and second AC terminals and a second primary winding connected between the second and third AC terminals, the electric energy transformation device further comprising a first winding secondary connected between the first and second AC terminals of the first electrical conversion module and a second secondary winding connected between the first and second AC terminals of the second electrical conversion module, the first electrical conversion module being configured to generate a first controllable alternating current flowing in the first secondary winding, the second electrical conversion module being configured to generate a second controllable alternating current flowing in the second secondary winding;
- a control module configured to control the first and second electrical conversion modules so that the first alternating current flowing in the first secondary winding and the second alternating current flowing in the second secondary winding are out of phase,
the voltage converter comprising only two electrical conversion modules.

The voltage converter according to the invention can be easily connected in an HVDC electrical installation, between an AC power supply network and a DC power supply network. The voltage converter is advantageously reversible, so that it makes it possible to convert an alternating voltage into a direct voltage but also to convert a direct voltage into alternating voltage.

It is understood that each of the electrical conversion modules is connected in the arm via its first and second continuous terminals. Each secondary winding of the electrical transformation device is associated with an electrical conversion module.

Unlike the voltage converters of the prior art, in which the primary windings are coupled in star, and each have a terminal connected to neutral, or in triangle, each of the primary windings of the voltage converter according to the invention is connected between two AC terminals, and are therefore configured to be connected directly to the AC power supply network.

The first and second electrical conversion modules make it possible to respectively generate a first inserted DC voltage and a second inserted DC voltage that can be controlled in the arm between their respective first and second DC terminals. These first and second DC voltages inserted make it possible to control a DC current flowing in the arm.

The first and second electrical conversion modules also make it possible to respectively generate a first inserted AC voltage and a second inserted AC voltage that can be controlled between their respective first and second AC terminals.

These first and second inserted alternating voltages make it possible to respectively generate said first alternating current I ₁ flowing in the first secondary winding and said second alternating current I ₂ flowing in the second secondary winding.

The electrical energy transformation device has a transformation ratio r corresponding to the ratio between the number of turns of the first secondary winding and the number of turns of the first primary winding. As a first approximation, this transformation ratio is approximately equal to the ratio between the voltage across the terminals of the first secondary winding and the voltage across the terminals of the first primary winding.

From the first and second alternating currents circulating in the first and second secondary windings, the electrical energy transformation device supplies first and second alternating currents circulating in the first and second primary windings, which are images, at the transformation ratio close to said first and second alternating currents flowing in the first and second secondary windings.

From the first and second alternating currents circulating in the first and second primary windings, the voltage converter according to the invention makes it possible to construct a three-phase system of three alternating phase currents. This three-phase system comprises first, second and third AC phase currents I _a , I _b , I _c flowing respectively towards the first, second and third AC terminals of the voltage converter. These alternating phase currents are controllable in phase and amplitude, so that the active power and the reactive power of the voltage converter can also be controlled.

The relationships between the first and second alternating currents I ₁ , I ₂ flowing in the first and second secondary windings and the first, second and third alternating phase currents I _A , I _B , I _C are as follows:

The electrical energy transformation device of the voltage converter according to the invention makes it possible to obtain a three-phase distribution of three alternating phase currents from two alternating currents circulating in the secondary windings of the electrical energy transformation device.

These three alternating phase currents I _A , I _B , I _C define a three-phase system.

The phase and amplitude of the first alternating current flowing in the first secondary winding and the phase and amplitude of the second alternating current flowing in the second secondary winding of the electrical energy transformation device form four degrees of freedom of the given three-phase system above.

By applying a Fortescue transformation to this system, also known as the method of symmetric components, this three-phase system can be decomposed into a sum of three three-phase systems, namely a forward balanced system, an inverse balanced system and a zero sequence system.

The direct balanced system makes it possible to impose the active power and the reactive power of the voltage converter. For the three-phase system composed by the three alternating phase currents to be balanced, the inverse balanced system and the homopolar system must each have a real part and a zero imaginary part. Indeed, this makes it possible to keep only the direct system, which is a balanced three-phase system formed by the three alternating phase currents I_AT,I_B,I_VS, Who are then phase shifted by 120° and have the same amplitude. These three systems therefore impose six constraints to be satisfied, namely the control of the active power, the control of the reactive power, the cancellation of the real and imaginary parts of the inverse balanced system, the cancellation of the real and imaginary parts of the homopolar system .

The coupling of the primary windings of the energy transformation device of the voltage converter according to the invention, in which the first primary winding is connected between the first and second AC terminals and the second primary winding is connected between the second and third AC terminals, makes it possible to cancel the real part and the imaginary part of the homopolar system, by construction. Indeed, the zero sequence current is defined as the sum of the three alternating phase currents. Thanks to the three equations given above, it can be seen that the sum of the three alternating phase currents is zero. There is no zero sequence current, and therefore the real and imaginary parts of the zero sequence system are zero. Also, thanks to this coupling of the primary windings of the electrical transformation device according to the invention, only four constraints, namely the control of the active and reactive powers and the cancellation of the real and imaginary parts of the inverse system, must be satisfied by means of the four aforementioned degrees of freedom. The resolution of the three balanced systems is therefore permitted thanks to the particularly clever coupling of the primary windings of the voltage converter according to the invention. The control module is advantageously configured to adjust the phase difference between the first and second alternating currents flowing in the first and second secondary windings, so as to impose a phase difference of approximately 120° between each of the three alternating phase currents I _a , I _b ,I _c .

The voltage converter according to the invention therefore makes it possible to obtain a balanced three-phase distribution of three alternating phase currents I _a , I _b , I _c from two currents passing through the secondary windings of the electrical energy transformation device, at namely the first and second alternating currents flowing in the first and second secondary windings. Balanced means that the first, second and third alternating phase currents I _a , I _b , I _c have substantially the same amplitude and are out of phase by approximately 120° or 2π/3.

In other words, the voltage converter according to the invention makes it possible to obtain a balanced three-phase distribution of three alternating phase currents from two electrical conversion modules connected in series in the arm.

Thanks to the invention, the voltage converter comprises exactly two electrical conversion modules, and therefore strictly less than three electrical conversion modules, unlike the voltage converters of the prior art which include at least three electrical conversion modules.

Consequently, the voltage converter according to the invention comprises a reduced number of components, and in particular of electrical conversion modules. One interest is to reduce the size and the size of the voltage converter by reducing the number of electrical conversion modules.

In addition, it has a reduced number of sub-modules, when the conversion modules are provided with them. This also makes it possible to reduce the number of electrical connections between the various components, which can be costly and complex to make, and thus to simplify the layout of the voltage converter.

In addition, each of the electrical conversion modules of the voltage converter according to the invention is able to generate AC and DC voltages inserted greater than those generated by each of the conversion modules of the voltage converters provided with three conversion modules according to the prior art. Indeed, the total voltage to be produced is distributed over two electrical conversion modules instead of three. On the other hand, each of the electrical conversion modules is required to withstand lower currents than the electrical conversion modules of the prior art. Also, the size of these electrical conversion modules can be reduced.

The voltage converter according to the invention therefore has a much lower weight and bulk than the voltage converters of the prior art, as well as a reduced manufacturing cost.

Furthermore, the voltage converter according to the invention may be provided with only two primary windings and two secondary windings, which further reduces the size of the voltage converter.

Preferably, the control module is configured to control the first and second electrical conversion modules so that the first alternating current flowing in the first secondary winding and the second alternating current flowing in the second secondary winding are out of phase by an angle between between 55° and 65°, preferably by an angle substantially equal to 60°.

One interest is to improve the balance of the three-phase system formed by the first, second and third alternating phase currents, constructed from the first and second alternating currents circulating in the first and second secondary windings. This makes it possible to impose a phase shift of approximately 120° between the first and second alternating phase currents, as well as between the second and third alternating phase currents and between the third and first alternating phase currents.

Preferably, the control module controls the first and second electrical conversion modules so as to regulate the first and second alternating voltages inserted between the first and second alternating terminals of the first and second electrical conversion modules, which makes it possible to adjust the phase and amplitude of the first and second alternating currents flowing in the secondary windings of the electrical energy transformation device.

The first alternating current flowing in the first secondary winding is advantageously in phase with the first alternating phase current.

Advantageously, the first and second electrical conversion modules each comprise a main branch extending between the first and second continuous terminals of the corresponding electrical conversion module and in which is connected a chain of sub-modules, each of the chains of sub -modules comprising a plurality of sub-modules individually controllable by a control unit specific to each sub-module and each sub-module comprising a capacitor, the control unit of each sub-module being able to assume at least a first state in which the capacitor is inserted in the main branch and a second state in which the capacitor is not inserted in said main branch.

The control module advantageously controls the control members of the first and second electrical conversion modules.

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 members can be placed in the first state and in the second state in response to a command order, coming for example from the control module, or even according to the sign of the current flowing in the arm.

The sub-modules can be controlled according to a sequence chosen to gradually vary the number of capacitors which are connected in series in the main branch of the corresponding electrical conversion module and therefore in the arm of the voltage converter, so as to provide several levels Of voltage.

Advantageously, the control module is configured to control the control members of the sub-modules of the chains of sub-modules of the first and second electrical conversion modules, so as to regulate the voltages at the terminals of said chains of sub-modules. The control of the sub-modules of the electrical conversion modules makes it possible to adjust the direct voltages inserted in the arm but also the alternating voltages inserted between the alternating terminals of the electrical conversion modules, and therefore to regulate, in phase and in amplitude, the alternating currents circulating in the primary and secondary windings of the electrical energy transformation device. This makes it possible to regulate, in phase and in amplitude, the three alternating phase currents circulating towards the alternating terminals of the voltage converter.

Preferably, at least one of the first and second electrical conversion modules comprises an upper electrical connection, electrically connecting the first continuous terminal and the first alternating terminal of said electrical conversion module, and a lower electrical connection, electrically connecting the second continuous terminal and the second alternating terminal of said electrical conversion module, said electrical conversion module comprising at least one capacitor connected in said upper electrical connection and/or in said lower electrical connection. One interest is to block the circulation of a direct current in the secondary windings of the electrical transformation device while allowing the circulation of an alternating current.

Advantageously, the first electrical conversion module and the second electrical conversion module each comprise at least one capacitor connected in its upper electrical connection and/or in its lower electrical connection.

The first and/or the second electrical conversion module can comprise a single capacitor connected in its upper electrical connection or in its lower electrical connection. As a variant, the first and/or the second electrical conversion module can comprise a first capacitor connected in the upper electrical connection and a second capacitor connected in the lower electrical connection.

Advantageously, at least one of the first and second electrical conversion modules comprises a secondary branch, extending between the first and second continuous terminals of said electrical conversion module, and in which are connected in series a chain of sub-modules comprising a plurality of controllable sub-modules, and an H-bridge comprising a first sub-branch in which two switches are connected and a second sub-branch, connected in parallel with the first sub-branch, and in which two switches are connected, the first and second alternating terminals of said electrical conversion module being electrically connected respectively to the first sub-branch and to the second sub-branch.

The secondary branch is connected in parallel with the main branch of said electrical conversion module. The first sub-branch is connected to a first terminal of the corresponding secondary winding, while the second sub-branch is connected to a second terminal of said corresponding secondary winding.

Advantageously, the two switches of the first sub-branch are connected to each other at a first intermediate point, the first AC terminal of said electrical conversion module being electrically connected to said first intermediate point. Advantageously, the two switches of the second sub-branch are connected to each other at a second intermediate point, the second AC terminal of said electrical conversion module being electrically connected to said second intermediate point.

The switches of the H-bridge are advantageously controlled by the control module. The switches of the H-bridge are advantageously high-voltage switches. The H bridge makes it possible to adjust the direction of circulation of the first or second alternating current circulating in the corresponding secondary winding of the electrical energy transformation device.

Preferably, the sub-modules of the chains of sub-modules of the first and second electrical conversion modules 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. Each of the electrical conversion modules may include a combination of half-bridge sub-modules and full-bridge sub-modules.

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.

Preferably, the voltage converter further comprises a start-up module configured to charge the capacitors of the sub-modules of the first and second electrical conversion modules, when it is placed in a first state.

During the charging of said capacitors, the voltage at the terminals of the chains of sub-modules increases gradually until it reaches a nominal value.

The starter module is preferably connected between the AC terminals of the voltage converter and an AC power supply network to which said voltage converter is connected. Alternatively, the starter module can be connected between the DC terminals of the voltage converter and a DC power supply network to which said voltage converter is connected.

Preferably, the starter module comprises at least a first switch connected to one of the AC or DC terminals of the voltage 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.

Also, in the first state, an uncontrolled current appears in the arm. This uncontrolled current is limited by the limiting resistor and gradually charges the capacitors of the sub-modules of the first and second electrical conversion modules, up to a predefined pre-charge value.

This pre-charged pre-charge value is notably chosen so as to allow the control module to be supplied.

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 capacitors of the sub-modules of the electrical conversion modules reach the pre-set pre-charge value. The chains of sub-modules are then controllable and can be ordered to gradually increase the energy stored in their capacitors. When the voltage at the terminals of each chain of sub-modules reaches a final value substantially equal to the voltage of the DC power supply network, the starter module is placed in the second state.

All of the capacitors of the sub-modules of the first and second electrical conversion modules are then charged to a final charge value and the voltage converter then operates normally.

Preferably, said voltage converter comprises only two primary windings and two secondary windings. Here again, an advantage is to reduce the number of components of the converter and in particular the number of terminations called "bushings" forming external connections of said electrical energy transformation device. This further reduces the weight, size and manufacturing cost of the voltage converter, compared to the converters of the prior art which comprise at least three primary windings and three secondary windings. It is understood that the converter comprises exactly two primary windings and two secondary windings, each being associated with a single electrical conversion module.

In addition, the transformers of voltage converters are generally provided with termination called "bushings" which are particularly bulky. By reducing the number of primary and secondary windings, and therefore the number of transformers used, the voltage converter according to the invention also makes it possible to reduce the number of these terminations, which further reduces the size of the voltage converter.

Advantageously, the voltage converter according to the invention only comprises an electrical energy transformation device.

Advantageously, the voltage converter according to the invention comprises only two primary windings and two secondary windings.

According to a first advantageous variant, the electrical energy transformation device comprises a single transformer comprising said first and second primary windings as well as said first and second secondary windings. One interest is to reduce the cost and size of the voltage converter by limiting the number of components it comprises.

According to a second advantageous variant, the electrical energy transformation device comprises: a first transformer comprising the first primary winding and the first secondary winding; and a second transformer including the second primary winding and the second secondary winding. These first and second transformers are single-phase transformers. One advantage is to allow better galvanic isolation between the windings of the first and second transformers. Also, for very high power applications, the size of a transformer with multiple primary and secondary windings can 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 transformation device and therefore of the voltage converter.

Preferably, the voltage converter comprises at least one filter module connected in series with the arm and configured to limit the AC component of a current flowing in said arm. The voltage resulting from the sum of the voltages inserted in the arm, generated by the first and second electrical conversion modules, has a residual alternating component so that an alternating current remains in the arm.

One advantage of the filtering module is to filter and therefore reduce, preferably eliminate, this alternating component of the total voltage in the arm so as to favor the circulation in the arm of a direct current. This makes it possible to have no alternating component in the current circulating in the DC power supply network and therefore to protect this network.

Advantageously, the filtering module comprises at least one passive component and/or one active component. By passive component, we mean a component whose state and/or behavior cannot be controlled. Such a passive component makes it possible to store or conserve energy. In a non-limiting manner, it may be a resistor or an inductor.

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.

By active component is meant a controllable component whose state and/or behavior can be controlled. 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. More preferably, the filter module consists of an inductor and a capacitor connected in parallel with each other.

The filtering module then forms a filter preventing the circulation of alternating current in the arm. Advantageously, said inductance and said capacitance are chosen so that the resonance frequency of the filtering module coincides with that of the AC power supply network.

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 a capacitor connectable in series with the arm when the control member of the sub-module is in a first state.

The invention also relates to a high voltage direct current transmission installation comprising a direct current power supply network, an alternating power supply network and a voltage converter as described above, said voltage converter being configured to electrically connect said AC and DC power supply networks between them.

The DC power supply network is electrically connected to the first and second DC terminals. The AC power supply network is electrically connected to the first, second and third AC terminals of the voltage converter.

The invention also relates to a method for controlling a voltage converter making it possible to convert an alternating voltage into a direct voltage and vice versa, the voltage converter comprising:
- First and second DC terminals configured to be electrically connected to a DC power supply network;
- First, second and third AC terminals configured to be electrically connected to an AC power supply network;
- an arm extending between the first and second continuous terminals and comprising a first electrical conversion module and a second electrical conversion module connected in series in said arm, the first and second electrical conversion modules each having a first continuous terminal and a second continuous terminal between which it extends, as well as a first alternating terminal and a second alternating terminal;
- an electric energy transformation device comprising a first primary winding connected between the first and second AC terminals and a second primary winding connected between the second and third AC terminals, the electric energy transformation device further comprising a first winding secondary connected between the first and second AC terminals of the first electrical conversion module and a second secondary winding connected between the first and second AC terminals of the second electrical conversion module, the voltage converter comprising only two electrical conversion modules,
the method comprising the steps according to which:
- Generating a first controllable alternating current flowing in the first secondary winding, using the first electrical conversion module;
- Generating a second controllable alternating current flowing in the second secondary winding, using the second electrical conversion module;
- The first and second electrical conversion modules are controlled so that the first alternating current flowing in the first secondary winding and the second alternating current flowing in the second secondary winding are out of phase.

Preferably, the first and second electrical conversion modules are controlled so that the first alternating current flowing in the first secondary winding and the second alternating current flowing in the second secondary winding are out of phase by an angle comprised between 55° and 65° , preferably at an angle substantially equal to 60°.

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 voltage converter according to the invention;

Figure 2 illustrates a first embodiment of the voltage converter of Figure 1;

Figure 3 illustrates a half-bridge topology sub-module;

Figure 4 illustrates a full-bridge topology sub-module;

FIG. 5 illustrates a reconstruction of the three-phase distribution of the three AC phase currents flowing towards the AC terminals of the converter of FIG. 2;

FIG. 6 illustrates a first variant of a filter module of the voltage converter of FIG. 2;

FIG. 7 illustrates a second variant of a filter module of the voltage converter of FIG. 2;

Figure 8 illustrates a second embodiment of the voltage converter of Figure 1.

The invention relates to a voltage converter for converting an alternating voltage into a direct voltage and vice versa and comprising only two electrical conversion modules.

The figure1illustrates an HVDC installation8comprising a first embodiment of a voltage converter10according to the invention, interconnecting a continuous power supply network12and an alternating power supply network14 of the facility. The alternating power supply network14is a three-phase network comprising three phases.

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 DC power supply network 12 . The voltage V _DC of the DC power supply network 12 is illustrated between the first DC terminal 16 and the second DC terminal 18 .

The converter includes an arm 20 extending between the first DC terminal 16 and the second DC terminal 18 . The arm 20 comprises a first electrical conversion module 22 and a second electrical conversion module 24 connected in series with each other in the arm 20 , between the first and second continuous terminals 16 , 18 .

The first electrical conversion module 22 comprises a first continuous terminal 22a and a second continuous terminal 22b between which it extends. It is connected in arm 20 via said first and second continuous terminals 22a , 22b . Similarly, the second electrical conversion module 24 comprises a first continuous terminal 24a and a second continuous terminal 24b between which it extends. It is connected in arm 20 via said first and second continuous terminals 24a , 24b .

Furthermore, the first electrical conversion module 22 comprises a first AC terminal 23a and a second AC terminal 23b . The second electrical conversion module 24 includes a first AC terminal 25a and a second AC terminal 25b .

According to the invention, the voltage converter 10 comprises only and exactly two conversion modules 22 , 24 , unlike the voltage converters of the prior art which comprise at least three electrical conversion modules.

In FIG. 1 , it can be seen that the voltage converter 10 also comprises a first AC terminal 30 , a second AC terminal 32 and a third AC terminal 34 . Each of the first, second and third AC terminals 30 , 32 , 34 is configured to be electrically connected to one of the three phases of the AC power supply network 14 .

The voltage converter 10 further comprises an electrical energy transformation device 40 comprising, in this non-limiting example, a single two-phase transformer comprising first 4 1a and second 4 2a primary windings respectively associated with first 4 1b and second 4 2b secondary windings. The electrical energy transformation device 40 comprises only and exactly two primary windings 41a , 42a and only and exactly two secondary windings 41b , 42b . The voltage converter 10 comprises only and exactly two primary windings 41a , 42a and only and exactly two secondary windings 41b , 42b

As can be seen in the figure1, the first secondary winding41bis connected between the first and second AC terminals23a,23bof the first electrical conversion module22. The second secondary winding42bis connected between the first and second AC terminals25a,25b of the second electrical conversion module24.

According to the invention, the first primary winding 41a is connected between the first and second AC terminals 30 , 32 of the voltage converter 10 . In other words, the first primary winding 41a comprises a first terminal 43 electrically connected to the first AC terminal 30 and a second terminal 45 electrically connected to the second AC terminal 32 . The second primary winding 4 2 a is connected between the second and third alternating terminals 3 2 , 3 4 of the voltage converter 10 . In other words, the second primary winding 4 2 a comprises a first terminal 47 electrically connected to the second AC terminal 3 2 and a second terminal 49 electrically connected to the third AC terminal 34 .

FIG. 2 illustrates a first embodiment of the voltage converter of FIG. 1 provided with a first variant of electrical conversion modules. In this embodiment, the first electrical conversion module 22 and the second electrical conversion module 24 are substantially identical. The first electrical conversion module 22 comprises a main branch 46 connected between the first and second continuous terminals 22a , 22b of the first electrical conversion module 22 . The first electrical conversion module 22 comprises a chain of sub-modules SM connected in said main branch 46 . Similarly, the second electrical conversion module 24 comprises a main branch 48 connected between the first and second continuous terminals 24a , 24b of the second electrical conversion module 24 and in which is also connected a chain of sub- SM- modules.

Each of the sub-module chains comprises a plurality of SM sub-modules connected in series with each other in the corresponding main branch and which can be controlled according to a desired sequence. In FIG. 2 , only two sub-modules per chain are shown. However, each chain of sub-modules can comprise from two to several tens of sub-modules SM .

As illustrated in Figures 3 and 4 , 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. 3 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 FIGS. 3 and 4 .

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

In a first state called the “on” or inserted state, the first switching element T1 and the second switching element T2 are configured so as to insert the capacitor C _SM into the main branch 46 , 48 , in series with the other sub- modules of the chain of submodules. In a second state called the "off" or non-inserted state, the first switching element T1 and the second switching element T2 are configured so as to bypass the capacitor C _SM and not insert it into the main branch 46 , 48 .

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 arm 20 of the voltage converter 10 , so as to provide several voltage levels.

FIG. 4 illustrates a variant of the sub-module of FIG. 3 , 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.

Referring again to FIG. 2 , it can be seen that the first electrical conversion module 22 comprises an upper electrical connection 50 electrically connecting the first continuous terminal 22a and the first alternating terminal 23a of said first electrical conversion module 22 . The first electrical conversion module 22 also comprises a lower electrical connection 52 , electrically connecting the second DC terminal 22b and the second AC terminal 23b of said first electrical conversion module 22 . In this non-limiting example, the upper electrical connection 50 is provided with a first capacitor 54 . The capacitor makes it possible to block the circulation of a direct current in said upper electrical connection 50 and in the first secondary winding 41b .

Similarly, the second electrical conversion module 24 comprises an upper electrical connection 56 electrically connecting the first continuous terminal 24a and the first alternating terminal 25a of said second electrical conversion module . The second electrical conversion module 2 4 also comprises a lower electrical connection 5 8 , electrically connecting the second continuous terminal 2 4 b and the second alternating terminal 2 5 b of said second electrical conversion module 2 4 . In this non -limiting example, the upper electrical connection 56 is equipped with a second capacitor 60 . Capacitor 60 makes it possible to block the circulation of a direct current in said upper electrical connection 56 and in second secondary winding 4 2 b .

The chain of sub-modules SM of the first electrical conversion module 22 makes it possible to generate a first DC voltage inserted V _{C 1} that can be controlled in the arm between the first and second DC terminals 22a , 22b of the first electrical conversion module 22 . The chain of sub-modules SM of the second electrical conversion module 24 makes it possible to generate a second DC voltage inserted V _{C 2} which can be controlled in the arm between the first and second DC terminals 24a , 24b of the second electrical conversion module 24 . A total voltage V _sum appears in the arm 20 , between the first DC terminal 22a of the first electrical conversion module 22 and the second DC terminal 24b of the second electrical conversion module 24 .

Said first and second inserted DC voltages V _{C 1} , V _{C 2} make it possible to control a DC current I _DC flowing in the arm.

The chain of sub-modules SM of the first electrical conversion module 22 also makes it possible to generate a first inserted AC voltage V ₁ controllable between the first and second AC terminals 23a , 23b of the first electrical conversion module 22 . The chain of sub-modules SM of the second electrical conversion module 24 makes it possible to generate a second inserted alternating voltage V ₂ controllable between the first and second alternating terminals 25a , 25b of the second electrical conversion module 2 4 .

Said first inserted alternating voltage V ₁ makes it possible to generate a first alternating current I ₁ flowing in the upper electrical connection 50 and therefore in the capacitor 54 and in the first secondary winding 41b . Said second inserted alternating voltage V ₂ also makes it possible to generate a second alternating current I ₂ flowing in the upper electrical connection 5 6 and therefore in the capacitor 60 and in the first secondary winding 4 2 b .

From the first and second alternating currents I ₁ , I ₂ circulating in the first and second secondary windings 41b , 42b _, the electrical energy transformation device 40 supplies first and second alternating currents I _{p 1} , I _{p 2} circulating in the first and second primary windings 41a , 42a . From these two alternating currents, the voltage converter according to the invention makes it possible to reconstruct first I _A , second I _B and third I _C alternating phase currents flowing towards the alternating terminals 30 , 32 , 34 of the voltage converter, and therefore to the AC power supply network 14 .

Specifically, the first alternating phase currentI _AT circulates from the first terminal43of the first primary winding41a to the first alternative terminal30. The third alternating phase currentI _VS circulates from the second terminal4 9of the second primary winding4 2 To to the third alternative terminal3 4. The second alternating phase currentI _B is a current resulting from the difference between the second alternating currentI _{p 2} circulating in the second primary winding42aand the first alternating currentI _{p 1} circulating in the first primary winding41a. The second alternating phase currentI _B circulates from an electrical node51to the second alternative terminal32. The electrical node extends between the second terminal45of the first primary winding and the first terminal47of the second primary winding42a.

The relationships linking the first and second alternating currents flowing in the first and second primary windings 41a , 42a are as follows:

Said first and second alternating currents I ₁ , I ₂ , and consequently the first, second and third alternating phase currents I _A , I _B , I _C are controllable in phase and in amplitude.

The voltage converter10includes control module100configured in particular to control the first and second conversion modules22,24, and more precisely the switching elements of the control units of the sub-modulesSMof said conversion modules to adjust the first and second DC voltages insertedV _{VS 1} ,V _{VS 2} , said first and second alternating voltages insertedV ₁ ,V ₂ and therefore the first and second alternating currentsI ₁ ,I ₂ , as well as the first, second and third alternating phase currentsI _AT ,I _B ,I _VS .

The relationships between the first and second alternating currents I ₁ , I ₂ circulating in the first and second secondary windings and the first, second and third alternating phase currents I _A , I _B , I _C are as follows:

In these relations, r is the transformation ratio of the electrical energy transformation device.

The three alternating phase currents I _A , I _B , I _C make it possible to define a three-phase system. Applying a Fortescue transformation to this system, also known as the method of symmetric components, allows this system to be decomposed into a sum of three three-phase systems, namely a forward balanced system, an inverse balanced system and a zero sequence system.

The coupling of the first and second primary windings 41a , 42a of the electrical energy transformation device 40 to the alternating terminals 30 , 32 , 34 of the voltage converter according to the invention, in which the first primary winding 41a is connected between the first and second alternating terminals 30 , 32 and the second primary winding 42a is connected between the second and third alternating terminals 32 , 34 , makes it possible to cancel the real part and the imaginary part of the homopolar system.

The phase and the amplitude of the first alternating current I ₁ and of the second alternating current I ₂ circulating in the secondary windings 41b , 42b form four degrees of freedom of the three-phase system. To provide a balanced three-phase system, these degrees of freedom must satisfy four system constraints, which are the control of the active and reactive powers and the cancellation of the real and imaginary parts of the inverse system.

The electrical energy transformation device 40 of the voltage converter 10 according to the invention makes it possible to obtain a three-phase distribution of three alternating phase currents from two alternating currents circulating in the secondary windings. The coupling of the primary windings 41a , 42a of the voltage converter 10 according to the invention makes it possible to obtain a balanced three-phase distribution of three alternating phase currents I _A , I _B , I _C .

The control module 100 is configured to control the control member of the sub-modules of the first and second electrical conversion modules 20 , 24 so as to impose a chosen phase shift between the first and second alternating currents I ₁ , I ₂ . In a non-limiting way, this phase shift is preferably by an angle between 55° and 65°, preferably by an angle substantially equal to 60°. This makes it possible to obtain a phase shift of about 120° between the first, second and third alternating phase currents I _A , I _B , I _C and therefore to obtain a balanced three-phase current system.

The reconstruction of the three-phase distribution of the three alternating phase currents I _A , I _B , I _C from the first and second alternating currents I ₁ , I ₂ is illustrated in FIG . It can be seen in this figure 5 that a phase shift of approximately 60° between the first and second alternating currents I ₁ , I ₂ improves the balance of the three-phase system obtained and makes it possible to obtain a phase shift of approximately 120° between the first and second alternating phase currents I _A , I _B , between the second and third alternating phase currents I _B , I _C and between the third and first alternating phase currents I _C , I _A . In a non-limiting manner, the control module controls the electrical conversion modules so that the first alternating current I ₁ flowing in the first secondary winding 41b is in phase with the first alternating phase current I _A .

In FIG. 2 , it is noted that the voltage converter 10 also comprises a filter module 80 connected in series with the arm 20 , between the first and second DC terminals 16 , 18 , and more precisely between the first DC terminal 16 and the first continuous terminal 22a of the first electrical conversion module 22 . The filtering module 80 is configured to filter the alternating component of the first and second DC voltages V _{C 1} , V _{C 2} inserted into the arm 20 , so as to prevent the circulation of an alternating current in the arm and to guarantee the circulation in the arm of a single direct current I _DC .

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 making it possible to reduce, preferably eliminate, the AC component circulating in arm 20 . They are dimensioned so that the resonant frequency of the filter module 80 coincides with that of the AC power supply network 14 and so that the filter module 80 has a high impedance at said resonant frequency.

FIG . 7 illustrates a second variant of a filter module 80 . In this example, the filter module 80 comprises a chain of additional sub-modules comprising a plurality of sub-modules SM individually controllable by a control unit specific to each sub-module. Each sub-module of said chain of additional sub-modules comprises at least one capacitor connectable in series with the arm 20 when the control member of the sub-module is in a first state.

The chain of additional sub-modules makes it possible to generate an alternating voltage v _supp 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 20 , and having an opposite phase. The sub-modules of this chain of additional sub-modules are advantageously of the full-bridge type.

It can be seen in FIG. 2 that the voltage converter 10 also comprises a start-up module 90 . In this non-limiting example, the starter module 90 comprises a switch 92 connected to the second DC terminal 18 of the voltage converter and a limiting resistor 94 connected in parallel with said switch 92 . The starting module 90 is configured to charge the capacitors of the SM sub-modules of the first and second electrical conversion modules 22 , 24 in order to allow the starting of the voltage converter 10 and the control of the direct and alternating currents circulating in the converter of tension.

When the starter module is placed in a first state, said switch 92 is open so that an uncontrolled current appears and circulates in arm 20 .

The capacitors C _SM of the sub-modules of the arm are charged and the voltage across the terminals of the first and second electrical conversion modules 22 , 24 gradually increases until it reaches its nominal value. The sub-modules are then commanded to gradually increase the energy stored in their capacitors. When the voltage at the terminals of each chain of sub-modules reaches a predetermined final value, switch 92 is then closed so as to short-circuit and thus bypass said limiting resistor 94 . The start-up module is then placed in a second state.

Control of the direct current flowing in the arm and of the alternating currents flowing in the windings of the electrical energy transformation device40 is then restored and the voltage converter then operates normally.

Alternatively, the starter module 90 could be connected between the AC power supply network and the AC terminals of the converter.

FIG. 8 illustrates a second embodiment of the voltage converter of FIG. 1 comprising a second variant of electrical conversion modules 2 2 , 24 . In this embodiment, the first and second electrical conversion modules 22 , 24 also each comprise a main branch 46 , 48 in which a chain of sub-modules SM is connected.

The first electrical conversion module 22 further comprises a secondary branch 62 , connected between the first and second continuous terminals 22a , 23a , in parallel with the main branch 46 . The second electrical conversion module 24 also comprises a secondary branch 64 , connected between the first and second continuous terminals 22a , 23a , in parallel with the main branch 46 .

In the secondary branch 62 of the first electric conversion module 22 , a chain of sub-modules SM and an H bridge 6 6 are connected in series. Similarly, in the secondary branch 64 of the second electrical conversion module 24 are connected in series a chain of sub-modules SM and an H bridge 68 . Said H-bridges 66 , 68 each comprise a first sub-branch 66a , 68a and a second sub-branch 66b , 68b , connected in parallel to each other. Said sub-branches 66a , 66b , 68a , 68b each comprise two switches 70 electrically connected to each other in said sub-branches.

The two switches 70 of the first sub-branch 66a of the first electrical conversion module 22 are connected together at a first intermediate point 72 . The two switches 70 of the second sub-branch 66 b of the first electrical conversion module 22 are connected to each other at a second intermediate point 7 4 . The first intermediate point 72 is electrically connected to the first AC terminal 23a of the first electrical conversion module 22 and to a first terminal of the first secondary winding 41b . The second intermediate point 74 is electrically connected to the second AC terminal 23b of the first electrical conversion module 22 , and to a second terminal of the first secondary winding 41b .

Similarly, the two switches 70 of the first sub-branch 68a of the second electrical conversion module 24 are connected together at a first intermediate point 72 . The two switches 70 of the second sub -branch 68b of the second electrical conversion module 24 are connected together at a second intermediate point 74 . The first intermediate point 72 is electrically connected to the first AC terminal 25a of the second electrical conversion module 24 and to a first terminal of the second secondary winding 42b . The second intermediate point 74 is electrically connected to the second AC terminal 25b of the second electrical conversion module 22 and to a second terminal of the second secondary winding 42b .

The switches of the two H-bridges 66 , 68 are controlled by the control module 100 . Said H-bridges 66 , 68 make it possible to adjust the direction of circulation of the first or second alternating current flowing in the corresponding secondary winding of the electrical energy transformation device.

Claims (17)

Voltage converter (10) for converting an alternating voltage into a direct voltage and vice versa, the voltage converter comprising:
- first and second DC terminals (16,18) configured to be electrically connected to a DC power supply network (12);
- first, second and third AC terminals (30,32,34) configured to be electrically connected to an AC power supply network;
- an arm (20) extending between the first and second continuous terminals and comprising a first electrical conversion module (22) and a second electrical conversion module (24) connected in series in said arm, the first and second electrical converter each having a first continuous terminal (22a, 24a) and a second continuous terminal (22b, 24b) between which it extends, as well as a first alternating terminal (23a, 25a) and a second alternating terminal (23b, 25b);
- an electrical energy transformation device (40) comprising a first primary winding (41a) connected between the first and second AC terminals and a second primary winding (42a) connected between the second and third AC terminals, the energy transformation device electrical energy further comprising a first secondary winding (41b) connected between the first and second AC terminals of the first electrical conversion module and a second secondary winding (42b) connected between the first and second AC terminals of the second electrical conversion module, the first electrical conversion module being configured to generate a first controllable alternating current (I ₁ ) flowing in the first secondary winding, the second electrical conversion module being configured to generate a second controllable alternating current (I ₂ ) flowing in the second winding secondary;
- a control module (100) configured to control the first and second electrical conversion modules so that the first alternating current flowing in the first secondary winding and the second alternating current flowing in the second secondary winding are out of phase,
the voltage converter comprising only two electrical conversion modules. Voltage converter according to claim 1, in which the control module (100) is configured to control the first and second electrical conversion modules (22,24) so that the first alternating current (I ₁ ) flowing in the first winding secondary (41b) and the second alternating current (I ₂ ) flowing in the second secondary winding (42b) are phase shifted by an angle comprised between 55° and 65°, preferably by an angle substantially equal to 60°. Voltage converter according to claim 1 or 2, in which the first and second electrical conversion modules (22,24) each comprise a main branch (46,48) extending between the first (22a,24a) and second (22b , 24b) continuous terminals of the corresponding electrical conversion module and in which is connected a chain of sub-modules (SM), each of the chains of sub-modules comprising a plurality of sub-modules individually controllable by a control device (T1, T2) specific to each sub-module and each sub-module comprising a capacitor (C _SM ), the control unit of each sub-module being able to assume at least a first state in which the capacitor is inserted in the main branch and a second state in which the capacitor is not inserted in said main branch. Voltage converter according to Claim 3, in which the control module (100) is configured to control the control members (T1, T2) of the sub-modules (SM) of the chains of sub-modules of the first and second conversion modules electric (22,24), so as to regulate the voltages at the terminals of said chains of sub-modules. Voltage converter according to any one of claims 1 to 4, in which at least one of the first and second electrical conversion modules (22, 24) comprises an upper electrical connection (50), electrically connecting the first continuous terminal (22a, 24a) and the first AC terminal (23a, 25a) of said electrical conversion module, and a lower electrical connection (52), electrically connecting the second DC terminal (22b, 24b) and the second AC terminal (23b, 25b) of said module electrical conversion module, said electrical conversion module comprising at least one capacitor (54,60) connected in said upper electrical connection or in said lower electrical connection. Voltage converter according to any one of claims 1 to 4, in which at least one of the first and second electrical conversion modules (22,24) comprises a secondary branch (62,64), extending between the first (22a , 24a) and second (22b, 24b) continuous terminals of said electrical conversion module, and in which are connected in series a chain of sub-modules (SM) comprising a plurality of controllable sub-modules, and an H-bridge (66 ,68) comprising a first sub-branch (66a,68a) in which two switches (70) are connected and a second sub-branch (66b,68b), connected in parallel with the first sub-branch, and in which are connected two switches (70), the first (23a, 25a) and second (23b, 25b) alternating terminals of said electrical conversion module being electrically connected respectively to the first sub-branch and to the second sub-branch. Voltage converter according to any one of Claims 1 to 6, in which the sub-modules (SM) of the chains of sub-modules of the first and second electrical conversion modules (22, 24) have a half-bridge topology or a full-bridge topology. Voltage converter according to any one of claims 3 to 7, further comprising a start module (90) configured to charge the capacitors (C _SM ) of the sub-modules (SM) of the first and second electrical conversion modules (22 ,24), when placed in a first state. A voltage converter according to any of claims 1 to 8, wherein said voltage converter (10) comprises only two primary windings (41a,42a) and two secondary windings (41b,42b). Voltage converter according to any one of claims 1 to 9, in which the electrical energy transformation device (40) comprises a single transformer comprising said first and second primary windings (41a, 42a) as well as said first and second primary windings secondary (41b,42b). A voltage converter according to any one of claims 1 to 9, wherein the electric power transformation device (40) comprises: a first transformer comprising the first primary winding (41a) and the first secondary winding (41b); and a second transformer comprising the second primary winding (42a) and the second secondary winding (42b). Voltage converter according to any one of Claims 1 to 11, comprising at least one filtering module (80) connected in series with the arm (20) and configured to limit the AC component of a current (I _DC ) flowing in said arm. Voltage converter according to Claim 12, in which the filter module (80) comprises at least one passive component and/or one active component. Voltage converter according to Claim 12 or 13, in which the filtering module (80) comprises a chain of additional sub-modules 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 capacitor connectable in series with the arm (20) when the control member of the sub-module is in a first state. High-voltage direct current transmission installation (8) comprising a direct current power supply network (12), an alternating power supply network (14) and a voltage converter (10) according to any one of claims 1 to 14, said voltage converter being configured to electrically connect said AC and DC power supply networks to each other. Method for controlling a voltage converter (10) making it possible to convert an alternating voltage into a direct voltage and vice versa, the voltage converter comprising:
- first and second DC terminals (16,18) configured to be electrically connected to a DC power supply network (12);
- first, second and third AC terminals (30,32,34) configured to be electrically connected to an AC power supply network (14);
- an arm (20) extending between the first and second continuous terminals and comprising a first electrical conversion module (22) and a second electrical conversion module (24) connected in series in said arm, the first and second electrical converter each having a first continuous terminal (22a, 24a) and a second continuous terminal (22b, 24b) between which it extends, as well as a first alternating terminal (23a, 25a) and a second alternating terminal (23b, 25b);
- an electrical energy transformation device (40) comprising a first primary winding (41a) connected between the first and second AC terminals and a second primary winding (42a) connected between the second and third AC terminals, the energy transformation device electrical energy further comprising a first secondary winding (41a) connected between the first and second AC terminals (23a, 23b) of the first electric conversion module and a second secondary winding (42b) connected between the first and second AC terminals (25a 25b) of the second electrical conversion module, the voltage converter comprising only two electrical conversion modules,
the method comprising the steps according to which:
- Generating a first controllable alternating current (I ₁ ) flowing in the first secondary winding, using the first electrical conversion module;
- Generating a second controllable alternating current (I ₂ ) flowing in the second secondary winding, using the second electrical conversion module;
- The first and second electrical conversion modules are controlled so that the first alternating current flowing in the first secondary winding and the second alternating current flowing in the second secondary winding are out of phase. Control method according to Claim 16, in which the first and second electrical conversion modules (22, 24) are controlled so that the first alternating current (I ₁ ) flowing in the first secondary winding (41b) and the second alternating current (I ₂ ) circulating in the second secondary winding (42b) are out of phase by an angle of between 55° and 65°, preferably by an angle substantially equal to 60°.