Electrical system comprising three electrical converters

Abstract

The invention relates to an electrical system (10) comprising three electrical converters (32, 34, 36) connected in series with respect to one another, by their DC terminals, between first and second DC terminals and an electrical power transformation device (40) comprising first, second and third primary windings (42a, 44a, 46a) connected to AC terminals of the electrical converters, the first electrical converter (32) comprising an electrical converter element (60) connected in cascade with a voltage level matching stage (50), the electrical system being capable of adopting a first operating mode in which the electrical converter element is configured to output an AC voltage from a DC voltage supplied by the voltage level matching stage and a second operating mode in which the voltage level matching stage is configured to output a DC voltage lower than a DC voltage supplied by the electrical converter element.

Description

[0001] ELECTRICAL SYSTEM COMPRISING THREE ELECTRICAL CONVERTERS

[0002] Technical Field

[0003] The present invention relates to the technical field of electrical systems for converting a direct voltage into an alternating voltage and / or vice versa. The present invention relates in particular to the field of electrical systems such as voltage converters, adapted to operate at low powers, preferably at powers lower than 1 Megawatt (MW), and for converting a medium direct voltage, for example between 3 kilovolts and 20 kilovolts, into an alternating voltage and / or vice versa. Such electrical systems are particularly useful in towns, in urban stations, for domestic current distribution. In the context of such an application, it is generally necessary to convert an input direct voltage of approximately 10 kilovolts into an alternating voltage of approximately 400 volts to be distributed.Furthermore, although today domestic electricity distribution is carried out in alternating current, it cannot be ruled out that in the future it will be distributed in direct current.

[0004] Prior art

[0005] Electrical systems are known for converting a direct voltage into an alternating voltage and / or vice versa, adapted to operate at high powers, preferably powers between 10 MW and 20 MW. For example, an electrical system for performing a DC / AC conversion 110 according to the prior art is known, illustrated in FIG. 1, comprising first and second direct terminals 112, 114 configured to be electrically connected to a direct electrical power supply network and first, second and third alternating terminals 116, 118, 120 configured to be electrically connected to an alternating electrical power supply network. This electrical system comprises three arms 122 connected in parallel with each other between the first and second direct terminals. Each of the arms 122 comprises an upper half-arm 122a and a lower half-arm 122b connected at a midpoint.Each half arm comprises a plurality of switching elements formed from an insulated gate bipolar transistor T (or IGBT for "Insulated Gate Bipolar Transistor" in English) associated with a parallel diode.

[0006] The midpoint of each of the arms is electrically connected to the primary winding 124a of a transformer 124. The secondary winding 124b of this transformer is electrically connected to the first, second and third DC terminals.

[0007] A disadvantage of this electrical system is that it is not suitable and is oversized for a low power and medium voltage application, in particular for urban applications for domestic power distribution. In particular, in order to deliver a three-phase alternating voltage of approximately 400 volts from a direct voltage of approximately 10 kilovolts, this electrical system necessarily comprises three arms, one per phase. In addition, in order to support the direct input voltage, this electrical system requires the series connection in each half-arm of numerous switching elements, in this case at least three IGBT transistors such as are commercially available, each capable of supporting a voltage of 3600 volts, so that the electrical system can support the direct input voltage of 10 kilovolts.

[0008] This electrical system therefore comprises a large number of components, in particular IGBT transistors, in this case at least eighteen IGBT transistors. This electrical system according to the prior art is therefore very heavy, it can weigh up to 10 tonnes, and is particularly bulky, with a very large footprint. This type of electrical system for converting voltage is also particularly expensive.

[0009] Furthermore, this type of electrical system uses commercially available high-voltage semiconductor components, including said IGBT transistors, which have large current ratings and are therefore sized to withstand high currents. However, given the three arms that this electrical system according to the prior art comprises, each IGBT transistor is only passed through by a low current and is therefore not fully utilized and is oversized.

[0010] Another disadvantage of this electrical system is that it is highly impacted by disturbances that may occur on the DC power supply network connected to the first and second DC terminals. In particular, a significant DC voltage drop at the input of this electrical system risks causing a loss of control of the power flow within the electrical system. In addition, a short circuit on the DC power supply network risks damaging the electrical system and being passed on to the AC power supply network connected to the AC terminals.

[0011] Statement of the invention

[0012] An aim of the present invention is to propose an electrical system that overcomes the aforementioned problems. To this end, the invention relates to an electrical system for converting a direct voltage into an alternating voltage and / or converting an alternating voltage into a direct voltage, the electrical system comprising: first and second direct terminals configured to be electrically connected to a direct electrical supply network; first, second and third alternating terminals configured to be electrically connected to an alternating electrical supply network; at least one conversion device comprising: a first electrical converter, a second electrical converter and a third electrical converter each comprising a first direct terminal and a second direct terminal, said first, second and third electrical converters being connected in series with respect to each other,by their first and second DC terminals, between the first and second DC terminals, said first, second and third electrical converters each further comprising at least a first AC terminal and a second AC terminal; an electrical energy transformation device comprising a first primary winding and a first secondary winding associated with the first primary winding, a second primary winding and a second secondary winding associated with the second primary winding, a third primary winding and a third secondary winding associated with the third primary winding, said first primary winding being connected to the first and second AC terminals of the first electrical converter, said second primary winding being connected to the first and second AC terminals of the second electrical converter,said third primary winding being connected to the first and second AC terminals of the third electrical converter, said first, second and third secondary windings each having at least one terminal connected respectively to the first AC terminal, to the second AC terminal and to the third AC terminal of the converter, characterized in that at least the first electrical converter comprises a voltage level adaptation stage, electrically connected to the first and second DC terminals of the first electrical converter, and an electrical converter element connected in cascade with the voltage level adaptation stage and electrically connected to the first and second AC terminals of said first electrical converter,the electrical system being able to adopt at least one operating mode chosen from: a first operating mode in which the voltage level adaptation stage is configured to deliver to the electrical converter element a direct voltage greater than the voltage between the first and second direct terminals of the first electrical converter, the electrical converter element being configured to generate, between the first and second alternating terminals of said first electrical converter, an alternating voltage from the direct voltage supplied by the voltage level adaptation stage; and a second operating mode in which the electrical converter element is configured to deliver to the voltage level adaptation stage a direct voltage from the alternating voltage between the first and second alternating terminals of said first electrical converter,the voltage level adaptation stage being configured to deliver, between the first and second DC terminals of said first electrical converter, a DC voltage lower than the DC voltage supplied by the electrical converter element.,

[0013] In a non-limiting manner, the electrical system according to the invention is particularly suitable for low power applications, preferably at powers of less than 1 Megawatt (MW). In a non-limiting manner, the electrical system according to the invention is particularly suitable for being connected to a direct current power supply network subject to a medium voltage, preferably between 3 kilovolts and 20 kilovolts. The alternating current power supply network is advantageously a three-phase network.

[0014] In a non-limiting manner, the electrical system may be configured solely to convert a direct voltage into an alternating voltage, in which case it adopts only the first operating mode. Alternatively, and in a non-limiting manner, the electrical system may be configured solely to convert an alternating voltage into a direct voltage, in which case it adopts only the second operating mode. Alternatively, and still in a non-limiting manner, the electrical system may be configured to allow the conversion of an alternating voltage into a direct voltage as well as the conversion of a direct voltage into an alternating voltage. In which case, the electrical system is then capable of adopting the first operating mode or the second operating mode. The transition from the first to the second operating mode is advantageously achieved by control.

[0015] When performing a DC / AC conversion, the electrical system according to the invention is advantageously configured to convert a medium DC voltage between its first and second DC terminals, for example of the order of 10 kilovolts, into a low voltage AC voltage, for example of the order of 400 volts in effective value. The electrical system then advantageously delivers a three-phase AC voltage that can be controlled in phase and amplitude.

[0016] Conversely, when it operates an AC / DC conversion, the electrical system according to the invention is advantageously configured to convert a low voltage alternating voltage, for example of the order of 400 volts in effective value, into a medium direct voltage between its first and second direct terminals, for example of the order of 10 kilovolts.

[0017] Advantageously, said conversion device comprises exactly three electrical converters. The electrical system advantageously comprises a number of electrical converters which is a multiple of three, more preferably exactly three electrical converters.

[0018] The first DC terminal of the first electrical converter is electrically connected to the first DC terminal. This first DC terminal may be connected directly to the first terminal. Alternatively, the first DC terminal may be connected indirectly to the first DC terminal, for example via a component such as an inductor connected between said first terminal and the first DC terminal. The second DC terminal of the first electrical converter is electrically connected to the first DC terminal of the second electrical converter. The second DC terminal of the second electrical converter is electrically connected to the first DC terminal of the third electrical converter. The second DC terminal of the third electrical converter is advantageously electrically connected to the second DC terminal or to the first DC terminal of the first electrical converter of a second conversion device.

[0019] Advantageously, the first, second and third electrical converters are identical. Alternatively, and without departing from the scope of the invention, the first, second and third electrical converters may have different configurations.

[0020] In a non-limiting manner, the electrical energy transformation device may comprise a single transformer, for example a single three-phase transformer, or a plurality of transformers, for example several single-phase transformers.

[0021] Each primary winding of the electrical energy transformation device is associated with one of the electrical converters.

[0022] The first secondary winding has a terminal connected to the first AC terminal. The second secondary winding has a terminal connected to the second AC terminal. The third secondary winding has a terminal connected to the third AC terminal. In a non-limiting manner, the secondary windings of the electrical energy transformation device may be coupled to the first, second and third AC terminals in a star connection, such that they each have a terminal connected to a neutral line.Alternatively, and in a non-limiting manner, the secondary windings of the electrical energy transformation device may be coupled in a delta coupling, such that the first secondary winding further has a terminal connected to one of the second and third AC terminals, the second secondary winding further has a terminal connected to one of the first and third AC terminals, and the third secondary winding further has a terminal connected to one of the first and second AC terminals.

[0023] The electrical energy transformation device is advantageously configured to operate at a frequency close to that of the alternating current power supply network.

[0024] The voltage between the first and second DC terminals of the electrical system is advantageously distributed between the first, second and third electrical converters and therefore at the input of the voltage level adaptation stages of said electrical converters.

[0025] The voltage level adaptation stage of the first electrical converter advantageously comprises a plurality of semiconductor components. It advantageously comprises one or more transistors, for example IGBT transistors, and one or more capacitors. The voltage level adaptation stage of the first electrical converter advantageously comprises less than two transistors, more preferably a single transistor. In a non-limiting manner, the voltage level adaptation stage may comprise one or more diodes.

[0026] The voltage level matching stage is advantageously configured to operate over a wide voltage range between its first and second DC terminals.

[0027] The first mode of operation involves using the electrical system to convert a direct voltage into an alternating voltage. The second mode of operation involves using the electrical system to convert an alternating voltage into a direct voltage.

[0028] In the first operating mode, the first electrical converter converts a DC voltage between its first and second DC terminals into an AC voltage between its first and second AC terminals. In this first operating mode, the voltage level adaptation stage of the first electrical converter behaves as a voltage boost stage. The voltage level adaptation stage is configured to provide the electrical converter element of the first electrical converter with a DC voltage of higher value than the DC voltage that it receives between its first and second DC terminals, and therefore higher than the voltage at the terminals of the DC electrical power supply network. Said voltage level adaptation stage delivers to the electrical converter element a voltage independent of the voltage of the DC electrical power supply network.

[0029] In this first operating mode, the electrical converter element of the first electrical converter behaves like an inverter. The electrical converter element of the first electrical converter makes it possible to convert the direct voltage supplied by the voltage level adaptation stage into a controlled alternating voltage. The electrical converter element advantageously comprises a plurality of semiconductor components. It preferably comprises a plurality of transistors, for example IGBT transistors, and one or more capacitors. The electrical converter element advantageously comprises two transistors or four transistors depending on its configuration.

[0030] The first electrical converter advantageously comprises a first connection point and a second connection point for the cascade connection of the voltage level adaptation stage and the electrical converter element of said first electrical converter. The DC voltage delivered by the voltage level adaptation stage to the electrical converter element then corresponds to the DC voltage between said first and second connection points.

[0031] In the second operating mode, the first electrical converter converts an alternating voltage between its first and second alternating terminals into a direct voltage between its first and second direct terminals. In this second operating mode, the electrical converter element behaves as a rectifier element. The electrical converter element is configured to rectify the alternating voltage that it receives as input, at the first and second alternating terminals of the first electrical converter, and provide a generated direct voltage to the voltage level adaptation stage.

[0032] In this second operating mode, the voltage level adaptation stage of the first electrical converter behaves as a voltage step-down stage. The voltage level adaptation stage is configured to deliver between the first and second DC terminals of the first electrical converter a voltage having a value lower than the DC voltage supplied by the electrical converter element.

[0033] Advantageously, the first, second and third electrical converters are identical. The electrical converters advantageously comprise at least one semiconductor component. The electrical system according to the invention proposes an architecture in which the electrical converters are connected in series by their DC terminals, which makes it possible to distribute, between the different electrical converters, the voltage between the first and second DC terminals. The electrical system according to the invention also has a reduced number of arms compared to the electrical systems of the voltage converter type of the prior art.

[0034] The current flowing in each of the electrical converters of the electrical system according to the invention being greater than the current flowing in each of the electrical converters of the electrical systems according to the prior art, the components used in the electrical converters of the electrical system according to the invention are also crossed by currents of higher values. The invention then makes it possible to use commercially available semiconductor components, which have a high current rating, the electrical system according to the invention making it possible to better exploit these components compared to the electrical systems according to the prior art and not to oversize them.

[0035] As a result, the electrical system according to the invention makes it possible to better exploit the components, for example the IGBT transistors, constituting the electrical converters while making it possible to reduce the number of these components.

[0036] By way of example, in a particularly advantageous configuration of the electrical system according to the invention, in which it comprises three electrical converters in a basic configuration, said electrical converters each comprise three IGBT transistors, so that the electrical system comprises nine IGBT transistors. In this configuration, the electrical system according to the invention comprises half as many IGBT transistors as the electrical system according to the prior art in its simplest configuration, which comprises eighteen.

[0037] The electrical system according to the invention therefore has reduced weight, size and cost. It is particularly suitable for use at low power and medium voltage, for example in an urban domestic power distribution application.

[0038] Furthermore, the voltage level adaptation stage of the first electrical converter of the electrical system according to the invention makes it possible to limit the oscillation of the direct current between the first and second direct current terminals.

[0039] In addition, the voltage level adaptation stage of the first electrical converter has the advantage of not maintaining or amplifying a disturbance occurring on the direct current power supply network or at the direct current terminals of said first electrical converter. Such a voltage level adaptation stage also does not pass on a fault in the direct current power supply network to the alternating current power supply network.

[0040] Likewise, the electrical converter element of the first electrical converter of the electrical system according to the invention has the advantage of not maintaining or amplifying a disturbance occurring on the alternating current power supply network or at the alternating current terminals of said first electrical converter. Such an electrical converter element also does not pass on a fault in the alternating current power supply network to the direct current power supply network.

[0041] The electrical system according to the invention thus has better tolerance to faults and disturbances which may occur on the direct current power supply network and / or on the alternating current power supply network to which it is connected.

[0042] Preferably, each of the first, second and third electrical converters of the electrical system comprises a voltage level adaptation stage, electrically connected to the first and second DC terminals of the corresponding electrical converter, and an electrical converter element connected in cascade with the voltage level adaptation stage and electrically connected to the first and second AC terminals of said corresponding electrical converter.

[0043] Preferably, in the first operating mode, the voltage level adaptation stage of each of the first, second and third electrical converters is configured to deliver to the electrical converter element of the corresponding electrical converter a direct voltage greater than the voltage between the first and second direct terminals of this electrical converter, the electrical converter element being configured to generate, between the first and second alternating terminals of said corresponding electrical converter, an alternating voltage from the direct voltage supplied by the voltage level adaptation stage.

[0044] Preferably, in the second operating mode, the electrical converter element of each of the first, second and third electrical converters is configured to deliver to the voltage level adaptation stage of the corresponding electrical converter a direct voltage from the alternating voltage between the first and second alternating terminals of this electrical converter, the voltage level adaptation stage being configured to deliver, between the first and second direct terminals of said corresponding electrical converter, a direct voltage lower than the direct voltage supplied by the electrical converter element.Preferably, said voltage level adaptation stage of the first electrical converter comprises a main line extending between the first and second DC terminals of the first electrical converter and a secondary line extending between said first and second DC terminals, in parallel with said main line, said voltage level adaptation stage comprising at least a first capacitor and a second capacitor connected in series with each other in the secondary line and at least a first controllable switching element connected in the main line or in the secondary line.

[0045] Said controllable switching element advantageously comprises a transistor, for example an IGBT transistor. Said controllable switching element advantageously comprises a switch. Said switching element can advantageously take a controlled state in which it allows the flow of a current and a non-controlled state in which it prevents the flow of a current in the line to which it is connected.

[0046] Said first and second capacitors advantageously extend between the first connection point and the second connection point connecting the voltage level adaptation stage to the electrical converter element.

[0047] In the first operating mode, said voltage level adaptation stage is configured to deliver a DC voltage across the terminals of the two capacitors, or in other words, a DC voltage between said first and second connection points, which is greater than the DC voltage between the first and second DC terminals of the first electrical converter.

[0048] In the second operating mode, said electrical converter element is configured to deliver a direct voltage across the terminals of the two capacitors, or in other words, a direct voltage between said first and second connection points, from the alternating voltage between the first and second alternating terminals of the first electrical converter.

[0049] Advantageously, said voltage level adaptation stage of the first electrical converter further comprises a diode, said diode being connected in the main line of said voltage level adaptation stage when said first controllable switching element of said voltage level adaptation stage is connected in the secondary line, said diode being connected in the secondary line of the voltage level adaptation stage when said first controllable switching element of said voltage level adaptation stage is connected in the main line. Such a voltage level adaptation stage comprises commercially available and inexpensive components. Said voltage level adaptation stage advantageously comprises a single controllable switching element, whereby the control of said electrical converter is facilitated.

[0050] When said diode is connected in the secondary line and the first controllable switching element is connected in the main line of the voltage level adaptation stage, the voltage level adaptation stage is configured to provide the electrical converter element with a DC voltage greater than the voltage between the DC terminals of the electrical converter. In other words, this configuration corresponds to the first operating mode, or to a DC / AC conversion, in which the first electrical converter is configured to convert a DC voltage between its DC terminals into an AC voltage between its AC terminals. In other words, the voltage level adaptation stage then behaves like a voltage booster.

[0051] When said diode is connected in the main line and the first controllable switching element is connected in the secondary line, the voltage level adaptation stage, the voltage level adaptation stage is configured to deliver between the DC terminals of the first electrical converter a DC voltage lower than the voltage supplied by the electrical converter element. In other words, this configuration corresponds to the second operating mode, or to an AC / DC conversion, in which the first electrical converter is configured to convert an AC voltage between its AC terminals into a DC voltage between its DC terminals. In other words, the voltage level adaptation stage then behaves like a voltage step-down.

[0052] Preferably, said voltage level adaptation stage of the first electrical converter comprises a parallel chopper. A parallel chopper is also called a boost converter. The voltage level adaptation stage then behaves like a voltage booster.

[0053] According to an advantageous variant, the first controllable switching element of the voltage level adaptation stage of the first electrical converter is connected in the main line, said voltage level adaptation stage of the first electrical converter further comprising a second controllable switching element connected in the secondary line of said voltage level adaptation stage. In this variant, the voltage level adaptation stage is power reversible. The voltage level adaptation stage can then behave as a voltage booster, capable of providing the electrical converter element with a voltage greater than the voltage between the DC terminals of the first electrical converter, which corresponds to the first operating mode.In this variant, the voltage level adaptation stage can also behave as a voltage step-down device, capable of delivering between the first and second DC terminals of the first electrical converter a voltage lower than the voltage supplied by the electrical converter element, which corresponds to the second operating mode. An advantage is also to allow more efficient control of the voltage level adaptation stage by having an additional switching element.

[0054] Preferably, the electrical converter element of the first electrical converter has a half-bridge or full-bridge topology. In the half-bridge configuration, the electrical converter element advantageously comprises two controllable switching elements. In the full-bridge configuration, the electrical converter element advantageously comprises four controllable switching elements.

[0055] The half-bridge topology has the advantage of being inexpensive due to the reduced number of controllable switching elements. In addition, this topology allows the capacities of the semiconductor elements constituting the controllable switching elements to be efficiently exploited. In this topology, the electrical converter element allows a relatively low voltage to be delivered to the first primary winding of the electrical energy transformation device.

[0056] The full-bridge topology has the advantage of being able to deliver significant output power, in particular twice that of a half-bridge electrical converter element. In addition, this topology makes it possible to efficiently exploit the capacities of the semiconductor elements constituting the controllable switching elements. In this topology, the electrical converter element makes it possible to deliver a relatively low current to the first primary winding of the electrical energy transformation device.

[0057] Advantageously, the electrical converter element of the first electrical converter comprises at least a first loop comprising at least a first capacitor, a second capacitor, a first controllable switching element and a second controllable switching element connected in said first loop, said first and second controllable switching elements being connected to each other at a connection point forming said first AC terminal of the first electrical converter.

[0058] Said first and second capacitors advantageously extend between said first and second connection points connecting the voltage level adaptation stage and the electrical converter element. Preferably, the first capacitor and the second capacitor of the electrical converter element of the first electrical converter are connected together at an intermediate point forming the second AC terminal of said first electrical converter. This configuration corresponds to a half-bridge topology.

[0059] Preferably, the electrical converter element of the first electrical converter further comprises a third controllable switching element and a fourth controllable switching element connected in series with each other and in parallel with the first and second controllable switching elements, the third and fourth controllable switching elements being connected together at a connection point forming said second AC terminal of the first electrical converter. This configuration corresponds to a full bridge topology.

[0060] According to a particularly advantageous variant, the first electrical converter further comprises a third AC terminal connected to the first primary winding of the electrical energy transformation device, the first capacitor and the second capacitor of the electrical converter element of the first electrical converter being connected to each other at an intermediate point forming said third AC terminal of the first electrical converter. This configuration corresponds to a variant of the full bridge topology of the electrical converter element. This configuration makes it possible to reduce the caliber and therefore the size and cost of the capacitors used. The first and second controllable switching elements then extend in a first arm while the third and fourth controllable switching elements extend in a second arm.In this variant, adapted control of the voltages generated in each of the first and second arms makes it possible to adjust the current flowing in these arms, further reducing the ripple of the voltage delivered to the voltage level adaptation stage.

[0061] The first primary winding of the electrical energy transformation device advantageously comprises a midpoint to which said intermediate point of the electrical converter element is electrically connected and therefore the third alternating terminal of the first electrical converter.

[0062] Particularly advantageously, the first and second capacitors of the electrical converter element of the first electrical converter form the first and second capacitors of the voltage level adaptation stage of said first electrical converter, so that these first and second capacitors are common to said electrical converter element and to said voltage level adaptation stage. It is understood that the first electrical converter then comprises only two capacitors.

[0063] The first electrical converter advantageously comprises a common line extending between the first and second connection points between the voltage level adaptation stage and the electrical converter element, said capacitors being connected in series in said common line.

[0064] The voltage between said first and second connection points corresponds, in the first operating mode, to the direct voltage delivered by the voltage level adaptation stage and from which the electrical converter element generates an alternating voltage intended for the electrical energy transformation device. In the second operating mode, the voltage between said first and second connection points corresponds to the direct voltage delivered by the electrical converter element which is then lowered by the voltage level adaptation stage.

[0065] Preferably, at least one inductor is connected between said conversion device and the first DC terminal and / or between said conversion device and the second DC terminal. An advantage is to limit the circulation of an alternating current in the voltage level adaptation stage or in the DC power supply circuit.

[0066] Advantageously, the electrical energy transformation device of said at least one conversion device comprises a first single-phase transformer comprising said first primary winding and said first secondary winding, a second single-phase transformer comprising said second primary winding and said second secondary winding, and a third single-phase transformer comprising said third primary winding and said third secondary winding. The use of a plurality of single-phase transformers reduces the insulation constraints compared to a three-phase transformer.

[0067] Preferably, the electrical system comprises at least a first conversion device and a second conversion device, the first, second and third electrical converters of the second conversion device being connected in series with the first, second and third electrical converters of the first conversion device by their first and second DC terminals, between said first and second DC terminals, the first secondary windings of the first and second conversion devices each having at least one terminal connected to the first AC terminal of the converter, the second secondary windings of the first and second conversion devices each having at least one terminal connected to the second AC terminal of the converter,the third secondary windings of the first and second conversion devices each having at least one terminal connected to the third AC terminal of the converter.,

[0068] In other words, the first and second conversion devices are connected in series by their continuous parts and in parallel with each other by their alternating parts.

[0069] The use of a second conversion device allows the conversion of a voltage between the first and second DC terminals of the electrical system greater, preferably up to twice as great, than the voltage that can be supported with a single conversion device.

[0070] The invention also relates to an electrical installation comprising a direct current power supply network, an alternating current power supply network and an electrical system as described above, said electrical system being configured to electrically connect said direct current power supply network and said alternating current power supply network to each other.

[0071] The invention further relates to a method of controlling an electrical system as described above, in which each of the first, second and third electrical converters is controlled according to a pulse width modulation technique.

[0072] According to this method, the pulse width of the control signals of the electrical converters and in particular of the controllable switching elements is modulated. These control signals are associated with a duty cycle. This duty cycle corresponds to the proportion, considered over time, in which the controllable switching element is placed in the controlled state.

[0073] Advantageously, when a first and a second controllable switching elements are connected in series in one of the electrical converters, for example two controllable switching elements of an electrical converter element, they are controlled in a complementary manner. Also, the first controllable switching element is placed in the controlled state while the second switching element is kept in the uncontrolled state, and vice versa.

[0074] Advantageously, the control signals of the voltage level adaptation stages of the first, second and third electrical converters are modulated from phase-shifted carrier signals. One advantage is to reduce the voltage ripple seen by the DC power supply network.

[0075] Preferably, the duty cycle of the control signals of each of said voltage level adaptation stages of the first, second and third electrical converters is adjusted so as to maintain constant the voltages between the first and second DC terminals of the first, second and third electrical converters.

[0076] Brief description of the drawings

[0077] The invention will be better understood on reading the following description of embodiments of the invention given as non-limiting examples, with reference to the appended drawings, in which:

[0078] [Fig. 1]Figure 1 illustrates a DC / AC conversion electrical system according to the prior art;

[0079] [Fig. 2]Figure 2 is a block diagram of an electrical installation comprising an electrical system according to the invention;

[0080] [Fig. 3]Figure 3 illustrates an embodiment of the electrical system according to the invention;

[0081] [Fig. 4]Figure 4 illustrates an electrical converter of the electrical system of Figure 3;

[0082] [Fig. 5]Figure 5 illustrates a first variant of the voltage level adaptation stage of the electrical converter of Figure 4;

[0083] [Fig. 6]Figure 6 illustrates a second variant of the voltage level adaptation stage of the electrical converter of Figure 4;

[0084] [Fig. 7]Figure 7 illustrates a first variant of the electrical converter element of the electrical converter of Figure 4;

[0085] [Fig. 8]Figure 8 illustrates a second variant of the electrical converter element of the electrical converter of Figure 4; and

[0086] [Fig. 9]Figure 9 illustrates the control signals of the electrical converters of the electrical system of Figure 3.

[0087] Description of the embodiments

[0088] The invention relates to an electrical system for converting a direct voltage into an alternating voltage and / or for converting an alternating voltage into a direct voltage. The invention also relates to an electrical installation comprising such an electrical system and to a method for controlling such an electrical system.

[0089] Figure 2 is a block diagram of an electrical installation 8 comprising an electrical system 10 according to the invention. This electrical system 10 comprises a first DC terminal 12 and a second DC terminal 14 connected to a first DC power supply network 100. The electrical system 10 further comprises a first AC terminal 16, a second AC terminal 18 and a third AC terminal 20 connected to an AC power supply network 102.

[0090] In this non-limiting example, the electrical system 10 comprises a first conversion device 30 and a second conversion device 30'. Without departing from the scope of the invention, the electrical system could comprise only one conversion device. The second conversion device 30' is identical to the first electrical conversion device 30 so that only said first conversion device 30 will be described in detail.

[0091] The first conversion device 30 comprises a first electrical converter 32, a second electrical converter 34 and a third electrical converter 36. The first electrical converter 32 comprises a first DC terminal 32a and a second DC terminal 32b. Similarly, the second electrical converter 34 comprises a first DC terminal 34a and a second DC terminal 34b and the third electrical converter 36 comprises a first DC terminal 36a and a second DC terminal 36b.

[0092] The first, second and third electrical converters 32, 34, 36 are connected in series with respect to each other by their DC terminals 32a, 32b, 34a, 34b, 36a, 36b between said first and second DC terminals 12, 14. More precisely, the first DC terminal 32a of the first electrical converter 32 is electrically connected to the first DC terminal indirectly, via an inductor 33. The second DC terminal 32b of the first electrical converter 32 is electrically connected to the first DC terminal 34a of the second electrical converter 34. The second DC terminal 34b of the second electrical converter 34 is electrically connected to the first DC terminal 36a of the third electrical converter 36.In this non-limiting example, the second DC terminal 36b of the third electrical converter 36 is connected to the second conversion device 30' and more precisely to a first DC terminal of a first electrical converter of the second conversion device 30'. The second DC terminal of a third electrical converter of the second conversion device is indirectly connected to the second DC terminal 14 via an inductor 33.

[0093] Alternatively, in the case where the electrical system 10 only comprises a single conversion device 30, the second DC terminal 36b of the third electrical converter 36 can be indirectly connected to the second DC terminal 14 via an inductance 33.

[0094] The first conversion device 30 and the second conversion device 30' are connected in series on the DC side, between the first and second DC terminals 12, 14. In this non-limiting example, the first, second and third electrical converters 32, 34, 36 are identical. They each comprise a voltage level adaptation stage 50 and an electrical converter element 60 connected in cascade with the voltage level adaptation stage 50.

[0095] The voltage level adaptation stage 50 is connected to the first and second DC terminals of the corresponding electrical converter. The electrical converter element 60 is connected to the first and second AC terminals of the corresponding electrical converter. The electrical converter element 60 is therefore connected between the voltage level adaptation stage 50 and the AC terminals of the corresponding electrical converter.

[0096] The electrical system 10 further comprises an electrical energy transformation device 40 comprising in this non-limiting example a first single-phase transformer 42, a second single-phase transformer 44 and a third single-phase transformer 46. The first single-phase transformer 42 comprises a first primary winding 42a and a first secondary winding 42b. The second single-phase transformer 44 comprises a second primary winding 44a and a second secondary winding 44b. The third single-phase transformer 46 comprises a third primary winding 46a and a third secondary winding 46b.

[0097] The first electrical converter 32 comprises a first AC terminal 32c and a second AC terminal 32d connected to the first primary winding 42a. The second electrical converter 34 comprises a first AC terminal 34c and a second AC terminal 34d connected to the second primary winding 44a. The third electrical converter 36 comprises a first AC terminal 36c and a second AC terminal 36d connected to the third primary winding 46a.

[0098] In this non-limiting example, the secondary windings 42b, 44b, 46b of the electrical energy transformation device 40 are coupled in star to the alternating terminals 16, 18, 20 of the electrical system 10. More precisely, the first secondary winding 42b has a first terminal connected to the first alternating terminal 16 and a second terminal connected to a neutral line N. The second secondary winding 44b has a first terminal connected to the second alternating terminal 18 and a second terminal connected to said neutral line N. The third secondary winding 46b has a first terminal connected to the third alternating terminal 20 and a second terminal connected to said neutral line N.

[0099] The secondary windings of the electrical energy transformation device of the second conversion device 30' are connected in a similar manner to the AC terminals 16, 18, 20 of the electrical system 10. The second conversion device is connected in parallel with the first conversion device, on the AC side.

[0100] Figure 3 shows a first non-limiting embodiment of an electrical system 10 according to the invention. In this first embodiment of Figure 3, the electrical system comprises only a single conversion device 30. In this embodiment, the electrical system 10 is configured to convert a DC voltage between its first and second DC terminals 12, 14 into an AC voltage at its AC terminals 16, 18, 20. The electrical system 10 adopts a first operating mode. The voltage level adaptation stage 50 of each of the voltage converters behaves as a voltage booster. Each of the voltage level adaptation stages 50 is configured to deliver to the electrical converter element 60 a DC voltage greater than the voltage between the first and second DC terminals of the corresponding electrical converter 32, 34, 36.The electrical converter element 60 of each of the voltage converters behaves like an inverter. It is configured to generate, between the first and second alternating terminals of said corresponding electrical converter, an alternating voltage from the direct voltage supplied by the voltage level adaptation stage.

[0101] The voltage level adaptation stages 50 of the first, second and third electrical converters 32, 34, 36 comprise a parallel chopper 51 and the voltage type conversion stages 60 have a half-bridge topology.

[0102] The first electrical converter 32 of the converter of Figure 3 is illustrated in Figure 4. The second and third electrical converters 34, 36 of the converter of Figure 3 are identical to this first electrical converter 32 and are therefore not described in detail.

[0103] As can be seen in Figure 4, the voltage level adaptation stage 50 and the electrical converter element 60 of this first electrical converter 32 are connected in cascade with respect to each other by a first connection point 59 and a second connection point 61.

[0104] The voltage level adaptation stage 50 of this first electrical converter 32 comprises a main line 52 extending between the first and second continuous terminals 32a, 32b as well as a secondary line 53 extending between said first and second continuous terminals 32a, 32b, in parallel with the main line 52.

[0105] The main line 52 of the voltage level adaptation stage 50 comprises a controllable switching element T1 formed by an IGBT transistor associated with a freewheel diode. The secondary line 53 comprises a passing diode DI, as well as a first capacitor C1 and a second capacitor C2. The first and second capacitors C1 and C2 are connected between the first and second connection points 59, 61 of the voltage level adaptation stage 50 to the electrical converter element 60.

[0106] In the embodiment of Figure 4, the electrical converter element 60 has a half-bridge topology. The electrical converter element 60 comprises a loop 62 in which the first and second capacitors C1, C2 are connected. These two capacitors C1, C2 are therefore common to the voltage level adaptation stage 50 and to the electrical converter element 60. They are connected in a branch 63 common to the voltage level adaptation stage 50 and to the electrical converter element 60. The electrical converter element further comprises two controllable switching elements, namely a first controllable switching element T1' and a second controllable switching element T2'.

[0107] In this non-limiting embodiment, the first capacitor C1 and the second capacitor C2 of the electrical converter element 60 are connected to each other at an intermediate point 64 forming the second alternating terminal 32d of the first electrical converter 32.

[0108] Furthermore, said first and second controllable switching elements T1', T2' of the electrical converter element 60 are connected to each other at a connection point 66 forming said first alternating terminal 32c of the first electrical converter.

[0109] Referring again to Figure 3, it can be seen that in this non-limiting example, the electrical system 10 is connected to a DC power supply network 100 having a voltage of 10 kilovolts. The electrical system therefore has an input voltage between its first and second DC terminals 12, 14 of 10 kilovolts. In a non-limiting manner, this input voltage is distributed substantially equally to the DC terminals 32a, 32b, 34a, 34b, 36a, 36b of the first, second and third electrical converters 32, 34, 36. Also, each of these first, second and third electrical converters has between its first and second DC terminals a DC voltage of 3.33 kilovolts, corresponding substantially to one third of the input voltage of 10 kilovolts. Each of the voltage level adaptation stages 50 of the electrical converters receives this direct voltage of 3.33 kilovolts as input.

[0110] Said voltage level adaptation stages 50 deliver to the associated voltage type conversion stages 60 a direct voltage of 3.6 kilovolts which is greater than the direct voltage of 3.33 kilovolts received at the input of said voltage level adaptation stages. This direct voltage of 3.6 kilovolts is considered between the first and second connection points 59, 61, at the terminals of the first and second capacitors C1, C2.

[0111] From these direct voltages of 3.6 kilovolts supplied by the voltage level adaptation stages 50, the voltage type conversion stages 60 generate between the first and second alternating terminals 32c, 32d, 34c, 34d, 36c, 36d of each of the electrical converters an alternating voltage of 1.1 kilovolts in effective value. The electrical energy transformation device 40 is configured to supply, at the terminals of its secondary windings 42b, 44b, 46b, three alternating voltages of approximately 400 volts each in effective value, from these alternating voltages supplied by the voltage type conversion stages 60.

[0112] With the aid of figures 5 to 8, we will now describe variants of the voltage level adaptation stage 50 and of the electrical converter element 60 of the electrical converter of figure 4. Each of the variants of the voltage level adaptation stage 50 illustrated in figures 4, 5 and 6 can be combined and connected in cascade indifferently with one or other of the variants of the electrical converter element 60 illustrated in figures 4, 7 and 8.

[0113] Figure 5 illustrates a first variant of the voltage level adaptation stage 50 of the first electrical converter of Figure 4 in which the diode DI is connected in the main line 52 while the first controllable switching element T1 is connected in the secondary line 53.

[0114] This variant corresponds to a use of the electrical system 10 to convert an alternating voltage at its alternating terminals 16, 18, 20 into a direct voltage between its first and second direct terminals 12, 14. The electrical system 10 then adopts a second operating mode in which the electrical converter element 60 of each of the electrical converters behaves as a rectifier. The electrical converter element 60 is configured to deliver to the voltage level adaptation stage 50 a direct voltage from the alternating voltage between the first and second alternating terminals of the corresponding electrical converter. The voltage level adaptation stage 50 behaves as a voltage step-down.It is configured to deliver, between the first and second DC terminals of said corresponding electrical converter, a DC voltage lower than the DC voltage supplied by the electrical converter element 60.

[0115] Figure 6 illustrates a second variant of the voltage level adaptation stage 50 of the first electrical converter of Figure 4 in which said voltage level adaptation stage 50 comprises a first controllable switching element T1 connected in the main line 52 and a second controllable switching element T2 connected in the secondary line 53. This voltage level adaptation stage 50 allows better control of the voltage conversion carried out. The voltage level adaptation stage 50 is here reversible in power, so that it can behave as a voltage booster or as a voltage step-down.

[0116] This variant corresponds to a configuration of the electrical system 10 in which it makes it possible to convert an alternating voltage into a direct voltage but also to convert a direct voltage into an alternating voltage. The electrical system 10 can therefore alternately adopt the first operating mode or the second operating mode described above. The selection of the operating mode is preferably carried out by control.

[0117] Figure 7 illustrates a first variant of the electrical converter element 60 of the first electrical converter 32 of Figure 4. In this non-limiting variant, the electrical converter element 60 has a full-bridge topology. The electrical converter element 60 of the first electrical converter 32 comprises, in addition to the first and second controllable switching elements T1', T2', a third controllable switching element T3' and a fourth controllable switching element T4'. Said third and fourth controllable switching elements T3', T4' are connected in series with each other and in parallel with the first and second controllable switching elements T1', T2'.

[0118] The first and second controllable switching elements T1', T2' are connected to each other at a first connection point 66 forming the first AC terminal 32c of the first electrical converter 32. The third and fourth controllable switching elements T3', T4' are connected to each other at a second connection point 68 forming said second AC terminal 32d of the first electrical converter.

[0119] Figure 8 illustrates a second variant of the electrical converter element 60 of the first electrical converter 32 of Figure 4. In this non-limiting variant, the electrical converter element 60 also has a full bridge topology. The first electrical converter comprises a third AC terminal 32e configured to be connected to a midpoint of the first primary winding of the electrical energy transformation device 40. The first capacitor C1 and the second capacitor C2 of the electrical converter element 60 of the first electrical converter 32 are connected to each other at an intermediate point 70 forming said third AC terminal 32e of the first electrical converter. This variant of the electrical converter element is called “Power Pulsation Buffer” in English.

[0120] The first controllable switching elements T1 of the voltage level adaptation stages 50 of the first, second and third electrical converters 32, 34, 36 of the electrical system 10 according to the invention are preferably controlled according to a pulse width modulation technique. These controllable switching elements are controlled by means of modulated control signals associated with a duty cycle. Figure 9 illustrates first, second and third voltage control signals VIN 1 , WINE 2 ,VI N 3 applied to the first controllable switching elements T1 of the voltage level adaptation stages 50 of the first, second and third electrical converters 32, 34, 36 respectively. In this non-limiting example, the duty cycles of each of the first, second and third control signals are substantially equal.

[0121] Wine totis the total voltage resulting from the sum of the VIN voltages 1 , WINE 2 and WINE 3 .

[0122] These first, second and third control signals are modulated respectively from first, second and third P1,P2,P3 illustrated in figure 9. These carrier signals P1,P2,P3 are phase shifted.

Claims

Claims Electrical system (10) for converting a direct current voltage into an alternating current voltage and / or for converting an alternating current voltage into a direct current voltage, the electrical system comprising: first and second direct current terminals (12, 14) configured to be electrically connected to a direct current power supply network (100); first, second and third alternating current terminals (16, 18, 20) configured to be electrically connected to an alternating current power supply network (102); at least one conversion device (30) comprising: a first electrical converter (32), a second electrical converter (34) and a third electrical converter (36) each comprising a first direct current terminal (32a, 34a, 36a) and a second direct current terminal (32b, 34b, 36b), said first, second and third electrical converters being connected in series with respect to each other, by their first and second direct current terminals,between the first and second continuous terminals, said first, second and third electrical converters further comprising each at least one first AC terminal (32c, 34c, 36c) and one second AC terminal (32d, 34d, 36d); an electrical power transformation device (40) comprising a first primary winding (42a) and a first secondary winding (42b) associated with the first primary winding, a second primary winding (44a) and a second secondary winding (44b) associated with the second primary winding, a third primary winding (46a) and a third secondary winding (46b) associated with the third primary winding, said first primary winding being connected to the first and second AC terminals of the first electrical converter, said second primary winding being connected to the first and second AC terminals of the second electrical converter,said third primary winding being connected to the first and second AC terminals of the third electrical converter, said first, second and third secondary windings each having at least one terminal connected respectively to the first AC terminal, the second AC terminal and the third AC terminal of the converter, characterized in that at least the first electrical converter comprises a voltage level adaptation stage (50), electrically connected to the first and second DC terminals of the first electrical converter, and, an electrical converter element (60) connected in cascade with the voltage level adaptation stage and electrically connected to the first and second AC terminals of said first electrical converter, the electrical system being able to adopt at least one mode of operation chosen from: a first mode of operation in which the voltage level adaptation stage is configured to deliver to the electrical converter element a DC voltage greater than the voltage between the first and second DC terminals of the first electrical converter, the electrical converter element being configured to generate, between the first and second AC terminals of said first electrical converter, an AC voltage from the DC voltage supplied by the voltage level adaptation stage;and a second mode of operation in which the electrical converter element is configured to deliver to the voltage level adaptation stage a DC voltage from the AC voltage between the first and second AC terminals of said first electrical converter, the voltage level adaptation stage being configured to deliver, between the first and second DC terminals of said first electrical converter, a DC voltage lower than the DC voltage supplied by the electrical converter element.

2. Electrical system according to claim 1, wherein said voltage level adaptation stage (50) of the first electrical converter (32) comprises a main line (52) extending between the first and second DC terminals (32a, 32b) of the first electrical converter and a secondary line (53) extending between said first and second DC terminals, in parallel with said main line, said voltage level adaptation stage (50) comprising at least one first capacitor (C1) and a second capacitor (C2) connected in series with respect to each other in the secondary line and at least one first controllable switching element (T1) connected in the main line or in the secondary line.

3. An electrical system according to claim 2, wherein said voltage level adaptation stage (50) of the first electrical converter (32) further comprises a diode (D1), said diode being connected in the main line (52) of said voltage level adaptation stage when said first The controllable switching element (Tl) of said voltage level adaptation stage is connected in the secondary line (53), said diode being connected in the secondary line of the voltage level adaptation stage (50) when said first controllable switching element of said voltage level adaptation stage is connected in the main line. Electrical system according to claim 3, wherein said voltage level adaptation stage (50) of the first electrical converter (32) comprises a parallel chopper (51).An electrical system according to claim 3, wherein the first controllable switching element (T1) of the voltage level adaptation stage (50) of the first power converter is connected in the main line (52), said voltage level adaptation stage of the first power converter (32) further comprising a second controllable switching element (T2) connected in the secondary line (53) of said voltage level adaptation stage. An electrical system according to any one of claims 1 to 5, wherein the power converter element (60) of the first power converter (32) has a half-bridge or full-bridge topology.An electrical system according to claim 6, wherein the electrical converter element (60) of the first electrical converter (32) comprises at least one first loop (62) including at least one first capacitor (C1), a second capacitor (C2), a first controllable switching element (T1'), and a second controllable switching element (T2') connected in said first loop, said first and second controllable switching elements being connected to each other at a connection point (66) forming said first AC terminal (32c) of the first electrical converter. An electrical system according to claim 6, wherein the first capacitor (C1) and the second capacitor (C2) of the electrical converter element (60) of the first electrical converter (32) are connected to each other at an intermediate point (64) forming the second AC terminal (32d) of said first electrical converter. The electrical system according to claim 6, wherein the electrical converter element (60) of the first electrical converter (32) further comprises a third controllable switching element (T3') and a fourth controllable switching element (T4') connected in series with respect to each other and in parallel with the first and second controllable switching elements (T1', T2'), the third and fourth controllable switching elements being connected together at a connection point (68) forming said second alternative terminal (32d) of the first electrical converter.An electrical system according to claim 9, wherein the first electrical converter (32) further comprises a third alternative terminal (32e) connected to the first primary winding (42a) of the electrical power transformation device (40), the first capacitor (C1) and the second capacitor (C2) of the electrical converter element (60) of the first electrical converter being connected together at an intermediate point (70) forming said third alternative terminal (32e) of the first electrical converter.An electrical system according to claim 3 in combination with any one of claims 7 to 10, wherein the first and second capacitors (C1, C2) of the electrical converter element (60) of the first electrical converter (32) form the first and second capacitors (C1, C2) of the voltage level adaptation stage (50) of said first electrical converter, such that these first and second capacitors are common to said electrical converter element and said voltage level adaptation stage. An electrical system according to any one of claims 1 to 11, wherein at least one inductor (33) is connected between said conversion device (30) and the first DC terminal (12) and / or between said conversion device and the second DC terminal (14).Electrical system according to any one of claims 1 to 12, wherein the electrical energy transformation device (40) of said at least one conversion device (30) comprises a first single-phase transformer (42) comprising said first primary winding (42a) and said first secondary winding (42b), a second single-phase transformer (44). comprising said second primary winding (44a) and said second secondary winding (44b), and a third single-phase transformer (46) comprising said third primary winding (46a) and said third secondary winding (46b). Electrical system according to any one of claims 1 to 13, comprising at least a first conversion device (30) and a second conversion device (309), the first, second, and third electrical converters of the second conversion device being connected in series with the first, second, and third electrical converters (32, 34, 36) of the first conversion device by their first and second DC terminals, between said first and second DC terminals (12, 14), the first secondary windings (42b) of the first and second conversion devices each having at least one terminal connected to the first AC terminal of the converter,the second secondary windings (44b) of the first and second conversion devices, each having at least one terminal connected to the second AC terminal of the converter, the third secondary windings (46b) of the first and second conversion devices, each having at least one terminal connected to the third AC terminal of the converter. . Electrical installation (8) comprising a DC power supply network (100), an AC power supply network (102) and an electrical system (10) according to any one of claims 1 to 14, said electrical system being configured to electrically connect said DC power supply network and said AC power supply network. . Method for controlling an electrical system according to any one of claims 1 to 14, wherein each of the first, second and third electrical converters (32, 34,36) is controlled using a pulse-width modulation technique.

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