DC-DC CONVERSION DEVICE, ELECTRICAL SYSTEM WITH SUCH A DC-DC CONVERSION DEVICE AND MOBILITY VEHICLE

Abstract

This device comprises: - first and second DC-DC converters (112a, 112b), each comprising: an inverter (202a, 202b), a resonant circuit (204a, 204b) comprising a transformer (Ta, Tb), as well as a capacitor (Ca, Cb) and an inductor (La, Lb) in series with a primary coil (Pa, Pb) of the transformer (Ta, Tb), and a rectifier (206a, 206b), the secondary coil (S) of the transformer (T) having at least two terminals; - an output capacitor (COUT); and - for each of the transformers (Ta, Tb), a loop (B) extending from one terminal (S1a, S2a, Ma, S1b, S2b, Mb) to the other of the secondary coil (Sa, Sb) of the transformer (Ta, Tb) and passing through the output capacitor (COUT). The output capacitor (COUT) is positioned so that each of the two loops (B) has an inductance of at most 20 nH. Figure for the abbreviation: Fig. 8

Description

Title of the invention: DC-DC CONVERSION DEVICE, ELECTRICAL SYSTEM WITH SUCH A DC-DC CONVERSION DEVICE AND MOBILITY MACHINE Technical field of the invention

[0001] The present invention relates to a DC-DC conversion device, an electrical system with such a DC-DC conversion device and a mobility device.

[0002] A mobility device is, for example, a motorized land vehicle, a train, an aircraft or a drone. A motorized land vehicle is, for example, a motor vehicle, a motorcycle, a motorized bicycle or a motorized wheelchair. Technological background

[0003] A DC-DC conversion device is known from the state of the art, comprising: - first and second DC-DC converters, each comprising: • an inverter designed to convert an input voltage into a first intermediate AC voltage, • a resonant circuit comprising a transformer, as well as a capacitance and an inductance in series with a primary coil of the transformer and the first intermediate voltage, and • a rectifier designed to convert a second alternating intermediate voltage present at a secondary coil of the transformer into an output voltage, the secondary coil of the transformer having at least two terminals; - an output capacitance designed to present the output voltage; and - for each of the transformers, a loop extending from one terminal to the other of the secondary coil of the transformer and passing through the output capacitor.

[0004] For the proper operation of the DC-DC conversion device, it is necessary to prevent the output of the DC-DC converters from creating a resonance which would disturb that of the resonant circuits. For this, it is known to use a large capacity output capacitor, but which in return is expensive and bulky.

[0005] It may thus be desirable to provide a DC-DC conversion device which makes it possible to overcome at least some of the aforementioned problems and constraints. Summary of the invention

[0006] A DC-DC conversion device is therefore proposed, comprising: - first and second DC-DC converters, each comprising: • an inverter designed to convert an input voltage into a first intermediate AC voltage, • a resonant circuit comprising a transformer, as well as a capacitance and an inductance in series with a primary coil of the transformer and the first intermediate voltage, and • a rectifier designed to convert a second alternating intermediate voltage present at a secondary coil of the transformer into an output voltage, the secondary coil of the transformer having at least two terminals; - an output capacitance designed to present the output voltage; and - for each of the transformers, a loop extending from one terminal to the other of the secondary coil of the transformer and passing through the output capacitor; characterized in that the output capacitance is placed so that each of the two loops has an inductance of at most 20 nH.

[0007] Thus, thanks to the invention, it is possible to use a low value output capacitance, without disturbing the resonant circuits. In particular, the output capacitance can be placed sufficiently close to the two terminals of each of the transformers to obtain the desired inductance indicated above.

[0008] The invention may further comprise one or more of the following optional features, in any technically possible combination.

[0009] Optionally, the output capacitor is designed to present between two terminals the output voltage of the first and second DC-DC converters.

[0010] Also optionally, the secondary coil of each of the transformers has a first end terminal, a second end terminal and a middle terminal, and the loop passes through: - a first switching element and conductors for connecting the first switching element between a first terminal of the capacitor and the first end terminal; and / or - a second switching element and conductors for connecting the second switching element between the first terminal of the capacitor and the second end terminal.

[0011] Also optionally, for each transformer, the loop passes through conductors to connect a second terminal of the output capacitance, different from the first terminal and the middle terminal of the transformer.

[0012] Also optionally, the second terminal of the output capacitor is connected to the middle terminal of each transformer.

[0013] Also optionally, the output capacitor comprises several capacitive elements.

[0014] Also optionally, the capacitive elements are in parallel.

[0015] Also optionally, the capacitive elements are distributed in at least two alignments, for example parallel.

[0016] Also optionally, at least one of the terminals of the secondary coil of a first of the transformers is separated by at most 3 cm from at least one of the terminals of the secondary coil of the other of the transformers.

[0017] Also optionally, there is a quadrilateral with four vertices located respectively on a pin of a first end terminal of the secondary coil of the first transformer, a pin of a second end terminal of the secondary coil of the first transformer, a pin of a first end terminal of the secondary coil of the second transformer and a pin of a second end terminal of the secondary coil of the second transformer, at least one capacitive element of the output capacitance extending in this quadrilateral.

[0018] Also optionally, the transformers are carried by the same electronic card, on the same side of the latter.

[0019] An electrical system is also proposed comprising: - a first and a second source of direct voltage; and - a DC-DC conversion device according to the invention in which the inverter of the first DC-DC converter is connected to the first DC voltage source to receive its input voltage and in which the inverter of the second DC-DC converter is connected to the second DC voltage source to receive its input voltage.

[0020] A mobility device comprising a DC-DC conversion device according to the invention or an electrical system according to the invention is also proposed. Brief description of the figures

[0021] The invention will be better understood with the aid of the following description, given solely by way of example and with reference to the appended drawings in which: - [Fig.l] is a very simplified view of a mobility device in which the invention can be implemented, - [Fig.2] is an electrical circuit of a DC-DC converter according to a first embodiment with an inverter, a resonant circuit and a rectifier, - [Fig.3] shows an example of a switching circuit and a rectifier of a DC-DC converter of [Fig.2], - [Fig.4] groups together timing diagrams of electrical quantities of the DC-DC converter of figures 2 and 3 when the control variable is a phase shift, - [Fig.5] groups together timing diagrams of electrical quantities of the DC-DC converter of figures 2 and 3 when the control variable is a phase shift in the absence of passage into the second mode according to the invention, - [Fig.6] is a circuit of another example of a rectifier for the DC-DC converter of Figures 2 and 3, - [Fig.7] is a functional view of a computer system that can be used in the DC-DC converter, - [Fig.8] is an electrical circuit of a DC-DC conversion device according to a second embodiment, - [Fig. 9] is an electrical circuit of a transformer and a rectifier of the DC-DC conversion device of the second embodiment, - [Fig. 10] is a top view of the DC-DC conversion device of [Fig. 9] when it is mounted on an electronic card, - [Fig. 11] is an enlargement of the view of [Fig. 10], illustrating in particular an arrangement of two transformers of the DC-DC conversion device, - [Fig. 12] is a simplified view of another example of transformer arrangement, and - [Fig. 13] is a simplified view of yet another example of transformer arrangement. Detailed description of the invention

[0022] With reference to [Fig. 1], a mobility device 100 in which the invention can be used will now be described.

[0023] The mobility device 100 comprises a propulsion system 102, for example drive wheels 104 and an electric motor 106 designed to drive the drive wheels 104. The mobility device 100 further comprises a battery 108 designed for example to electrically power the electric motor 106. The battery 108 is designed to provide a direct voltage, called battery voltage VBAt- The latter is a high voltage, i.e. greater than 100 V, preferably greater than 150 V.

[0024] The mobility device 100 further comprises a low voltage network 110 designed to be powered by a direct voltage, called VBT network voltage. A low voltage is a voltage less than or equal to 100 V, preferably less than or equal to 60 V.

[0025] To obtain the network voltage VBt from the battery voltage VBAT, the mobility device comprises a DC-DC converter 112 designed to convert the battery voltage VBAt into the network voltage VBT. The battery voltage VBAt and the network voltage VBT thus respectively form an input voltage and an output voltage of the DC-DC converter 112.

[0026] With reference to [Fig.2], an example of a DC-DC converter 112 will now be described.

[0027] The DC-DC converter 112 is an LLC converter and thus comprises first of all an inverter 202, a resonant circuit 204 and a rectifier 206.

[0028] The inverter 202 is designed to convert an input voltage (the battery voltage VBAT when used in the context of [Fig.l]) into a first intermediate alternating voltage Vl~.

[0029] More specifically, the inverter 202 comprises a switching circuit 208 and a control device 210 designed to control the switching circuit 208 in order to maintain an output voltage VOut (the voltage VBT when used in the context of [Fig.l]) at a desired setpoint Vout*, received by the control device 210.

[0030] The resonant circuit 204 comprises a transformer T, as well as a capacitor C and an inductance L in series with a primary coil P of the transformer T and the first intermediate voltage Vl~. The transformer T has a magnetizing inductance Lm. Thus, the capacitor C and the inductances L, Lm define a resonant frequency FR of the resonant circuit 204, for example between 80 and 120 kHz, for example 100 kHz.

[0031] The rectifier 206 is connected to a secondary coil S of the transformer T, designed to present a second alternating intermediate voltage V2~. The rectifier 206 is thus designed to convert this second intermediate voltage V2~ present at the secondary coil S of the transformer T into the output voltage VOut- In certain embodiments, the rectifier 206 may comprise one or more controllable switches (for example transistor switches), for example controlled by the control circuit 210.

[0032] The DC-DC converter 112 further comprises, for example, a voltage sensor 212 designed to measure the output voltage VOut and provide this measurement to the control device 210, so that the latter regulates the output voltage VOut to the setpoint V0UT*.

[0033] With reference to [Fig. 3], an example of a switching circuit 208 and a rectifier 206 will now be described.

[0034] In this example, the switching circuit 208 comprises a complete bridge of controllable switches G1A, G1B, G2A, G2B, for example controllable transistors. Thus, the switching circuit 208 comprises two switching arms. Each switching arm has two switches G1A, G1B and G2A, G2B connected to each other at a midpoint and together presenting the input voltage V 1N. The first intermediate voltage Vl~ is thus present between the two midpoints of the two switching arms.

[0035] For its part, still in this example, the rectifier 206 comprises a capacitor C yes, a first terminal of which is connected to a middle terminal M of the secondary coil S of the transformer T. The rectifier 206 further comprises two switches Ql, Q2, such as controllable transistors or diodes, connected between respectively one of the two end terminals SI, S2 of the secondary coil S of the transformer T, and a second terminal of the capacitor COut connected to an electrical ground. Furthermore, each of the two switches Ql and Q2 is connected to a different end terminal SI, S2.

[0036] The control device 210 is configured to control the switching circuit 208 selectively according to first and second modes.

[0037] In the first mode, the chopping circuit 208 is controlled at a chopping frequency FD fixed and substantially equal to the resonance frequency FR, for example equal to the resonance frequency FR to within 5%, preferably to within 1%, preferably below the resonance frequency FR.

[0038] For example, the switching circuit 208 is controlled by modifying a control variable. For example, in the case where the inverter 202 has two switching arms as illustrated in [Fig. 3], the first mode is a phase shift modulation mode where the control variable can be a phase shift PHI between the two switching arms, the duty cycle for each of the switching arms being for example fixed at 50%.

[0039] By using the switching frequency FD close to the resonant frequency FR, very high efficiency can be achieved. For example, a power efficiency greater than 90% can be achieved. However, this method is not possible below a certain input voltage level V^.

[0040] For example, in the case of using the PHI phase shift, the lower the input voltage V1N becomes, the more it is necessary to increase the PHI phase shift. However, the PHI phase shift can only be increased up to 180°.

[0041] In the second mode, the switching circuit 208 is controlled by modifying the switching frequency FD below the resonance frequency FR. The use of a switching frequency FD lower than the resonance frequency FR makes it possible to increase the gain between the input voltage Vin and the output voltage VOut, and therefore to reach the desired Vout* setpoint, even at input voltage levels VIN too low to continue to operate at the resonance frequency FR.

[0042] For example, in this second mode, the control variable, for example the phase shift PHI, is kept fixed.

[0043] To switch from the first mode to the second mode, the control device 210 is for example designed to detect when the control variable reaches a threshold, for example to detect when the phase shift PHI, when used, reaches 180°. To switch from the second mode to the first mode, the control device 210 is for example designed to detect when the switching frequency FD substantially reaches the resonance frequency FR, for example to within 5%, preferably to within 1%.

[0044] Alternatively, the control device 210 could be designed to switch from one mode to the other by comparing the input voltage V1N to a threshold: the control device 210 would be in the first mode when the input voltage was higher than this threshold, and in the second mode when the input voltage was lower than this threshold.

[0045] Thus, with reference to [Fig.4], an example of operation of the control device 210 will now be described, more particularly in the case where the control variable is the phase shift PHI.

[0046] Initially, in a phase 402, the control device 210 controls the chopping circuit 208 according to the first mode, that is to say with the chopping frequency FD substantially equal to the resonance frequency FR. The regulation of the output voltage VOut is obtained by modifying the phase shift PHI. In particular, when the input voltage decreases, the phase shift PHI is increased.

[0047] At a time 404, the phase shift reaches a predefined threshold S, for example 180°.

[0048] The control device 210 detects that this threshold S is reached by the shift of phase PHI and then controls, in a phase 406, the switching circuit 208 according to the second mode, that is to say by modifying the switching frequency FD below the resonant frequency FR. In particular, the more the input voltage decreases, the more the switching frequency FD is reduced. Conversely, when the input voltage V1N increases, the switching frequency FD is increased.

[0049] At a time 408, the switching frequency FD substantially reaches the resonance frequency FR.

[0050] The control device 210 detects that the resonant frequency FR has been reached and then controls again, in a phase 410, the chopping circuit 208 according to the first mode.

[0051] In the example of [Fig.4], the switch from one mode to the other takes place around 210 V. Thus, alternatively, the control device 210 could switch from one mode to the other depending on whether the input voltage Vin is higher or lower than this threshold of 210 V, as explained previously.

[0052] With reference to [Fig.5], in the absence of the transition to the second mode, when the input voltage V1N becomes too low (below approximately 210 V in the illustrated example) and it is no longer possible to play on the phase shift PHI because it is at its maximum of 180°, the output voltage VOut can no longer follow the setpoint VOut * and therefore drops at the same time as the input voltage V1N, until it reaches, in the illustrated example, an asymptote when the input voltage V1N stabilizes.

[0053] With reference to [Fig. 6], another example of rectifier 206 will now be described.

[0054] In this example, rectifier 206 comprises a complete bridge of switching elements, for example controllable transistors. Alternatively, the switching elements could be diodes.

[0055] The rectifier 206 of [Fig.6] operates in the manner previously described for the rectifier 206 of [Fig.3].

[0056] With reference to [Fig. 7], the control device 210 may be a computer system comprising a data processing unit 702 (such as a microprocessor) and a main memory 704 (such as a RAM memory, from the English "Random Access Memory") accessible by the processing unit 702. The computer system further comprises for example a network interface and / or a computer-readable medium, such as for example a local medium (such as a local hard disk 706) or a remote medium (such as a remote hard disk and accessible via the network interface through a communication network) or even a removable medium (such as a USB key, from the English "Universal Serial Bus", or a CD, from the English "Compact Disc" or a DVD, from the English "Digital Versatile Disc") readable by means of an appropriate reader of the computer system (such as a USB port or a CD and / or DVD disk reader).A computer program 708 containing instructions for the processing unit 702 is recorded on the medium 706 and / or downloadable via the network interface. This computer program 708 is for example intended to be loaded into the main memory 704, so that the processing unit 702 executes its instructions.

[0057] Alternatively, all or part of the computer program 708 could be implemented in the form of hardware modules, that is to say in the form of an electronic circuit, for example micro-wired, not involving a computer program.

[0058] With reference to [Fig. 8], a DC-DC converter device 800 will now be described. The device 800 may, for example, replace the converter 112 in the mobility device 100 of [Fig. 1].

[0059] The device 800 uses the voltage converter 112, doubling it to obtain redundancy. The device 800 therefore comprises two voltage converters 112a, 112b. Thus, the references used in the preceding figures will be repeated, adding the letter “a” for the elements of the voltage converter 112a and the letter “b” for the elements of the voltage converter 112b.

[0060] Only the output capacity COut is not split, but common to the two converters 112a, 112b.

[0061] The device 800 is thus designed to receive two input voltages V1Na, V1Nb to provide an output voltage VOut- When used in the context of [Fig.l], the input voltages V^a, V^b are for example each half of the battery voltage VBAt- Alternatively, the input voltages could both be equal to the battery voltage VBAt-

[0062] With reference to [Fig.9], the device 800 comprises at least one loop B passing through the output capacitor COut and extending from one terminal to another of the secondary coil Sa of the transformer Ta.

[0063] In [Fig.9], loop B extends from the second end terminal S2b to the middle terminal Mb and further passes through the switch Q2a.

[0064] More precisely, each terminal Sla, S2a, Ma comprises at least one pin, four in the illustrated example, shown in dotted lines. Furthermore, the output capacitor C yes comprises one or more capacitive elements and each switch Q2a, Q2b comprises one or more switching elements. The capacitive elements are for example in parallel with each other. Furthermore, the capacitive elements can be distributed in at least two alignments, as in the illustrated example where they are distributed in two alignments, for example parallel. Preferably each alignment comprises at least three capacitive elements. More preferably, all the alignments comprise the same number of capacitive elements.

[0065] Thus, loop B extends from one of the pins of the middle terminal Ma to one of the pins of the second end terminal S2a, passing through one of the switching elements of the switch Q2a and through at least one of the capacitive elements.

[0066] It is further possible to define other loops such as loop B, depending on the connected pins, the switch Q2a or Q2b through which the loop passes, the switching element of this switch Q2a or Q2b through which the loop passes, and the capacitive element of the output capacitor COut through which the loop passes. For example, it is possible to define another loop extending from the middle terminal Ma to the first end terminal Sla and passing through the switching element Qla and one of the capacitive elements of the output capacitor COut-

[0067] Loops can be defined in a similar manner for transformer Tb.

[0068] To minimize the output parasitic inductance, the output capacitance Cour is placed sufficiently close to the secondary coils Sa, Sb of the two transformers Ta, Tb, so that, for each transformer Ta, Tb, at least one possible loop, preferably each of the possible loops, has an inductance of at most 20 nanohenry (nH).

[0069] With reference to [Fig. 10], the device 800 comprises an electronic card 1102 on the same face of which the transformers Ta, Tb, the capacitive elements of the output capacitor COut and the switching elements of the switches Qla, Q2a, Qlb, Q2b are mounted.

[0070] The electronic card 1102 comprises a high voltage input 1104 designed to receive the battery voltage VBat and divide it into the input voltages V1Na V^b, and a low voltage output 1106 designed to provide the output voltage VOut-

[0071] For each converter 112a, 112b, the electronic card 1102 carries a primary circuit CPa, CPb, a secondary circuit Csa, CSb and a control circuit CCA, CCb.

[0072] The primary circuit CPa, CPb is connected between the high voltage input 1104 and the primary coil Pa, Pb of the transformer Ta, Tb. This primary circuit CPa, CPb comprises in particular the switching circuit 202a, 202b and the resonant circuit 204a, 204b and is designed to operate at high voltage.

[0073] The secondary circuit CSa, CSb is connected between the secondary coil Sa, Sb of the transformer Ta, Tb and the low voltage output 1106. This secondary circuit CSa, CSb comprises in particular the rectifier 206a, 206b and is designed to operate at low voltage. The secondary circuit CSa, CSb thus comprises at least one switching element, namely that or those of the switches Qla, Q2a, Qlb, Q2b.

[0074] The control circuit CCa is designed to control the switching elements of the switches Qla, Q2a. For this purpose, it comprises, for example, a microcontroller uCa. Similarly, the control circuit CCb is designed to control the switching elements of the switches Qlb, Q2b. For this purpose, it comprises, for example, a microcontroller uCb.

[0075] The secondary circuits CSa, CSb are thus part of a low voltage circuit CBT carried by the electronic card 1102.

[0076] With reference to [Fig. 11], the secondary coils Sa, Sb of the transformers Ta, Tb are placed opposite each other, so that only the low voltage circuit CBT extends in the area of ​​the electronic card 1102 separating the secondary coils Sa, Sb. To define this area more precisely, it is likened to a quadrilateral Q, extending in particular in the plane of the electronic card 1102, with four vertices located respectively on a pin of the first end terminal Sla, a pin of the second end terminal S2a, a pin of the first end terminal Slb, and a pin of the second end terminal S2b. Thus, only the low voltage circuit CBT extends into the quadrilateral Q. In particular, the primary circuits CPa, CPb and the primary coils Pa, Pb of the transformers Ta, Tb extend outside the quadrilateral Q. For example, as in the example shown, this quadrilateral Q is a rectangle. “Extending into the quadrilateral” means that the orthogonal projection of the elements (components and conductors) of the low-voltage circuit CBT in the plane of the electronic card 1102 extends into the quadrilateral Q. Similarly, “Extending outside the quadrilateral” means that the orthogonal projection of the elements (components and conductors) of the primary circuits CPa, CPb operating at high voltage in the plane of the electronic card 1102 is outside the quadrilateral Q.

[0077] To obtain a low inductance in each loop, at least one capacitive element of the capacitor COut, preferably all the capacitive elements, is for example located in the quadrilateral Q. Thus, the capacitive elements are as close as possible to both secondary coils, and in particular to their pins, at the same time. Furthermore, at least one of the terminals Sla, S2a, Ma, Slb, S2b, Mb of the secondary coil Sa, Sb of a first of the transformers Ta, Tb is separated by at most 3 cm from at least one of the terminals Sla, S2a, Ma, Slb, S2b, Mb of the secondary coil Sa, Sb of the other of the transformers Ta, Tb. This ensures that the secondary coils Sa, Sb are sufficiently close to each other to allow the output capacitance Cour to be close to both at the same time.

[0078] Furthermore, the control circuits CCa, CCb both extend on one side outside the first and second lines L1, L2 forming sides of the quadrilateral Q extending from one transformer Ta, Tb to the other (the control circuits CCa, CCb extend below the line L2 in the illustrated example). However, each control circuit CCa, CCb may need to be connected to a component located outside the quadrilateral Q on another side of the lines L1, L2 than the control circuit CCa, CCb (above the line L1 in the illustrated example).

[0079] For example, each control circuit CCa, CCb may need to be connected to the switching elements of the switch Qla, Qlb or to drivers (not shown) of these switching elements, in order to control these switching elements.

[0080] Alternatively, each control circuit CCb, CCb may need to be connected to a current sensor 1108 (for example, to measure a current passing through the low voltage output 1106) or a temperature sensor 1110 (for example, to measure a temperature of the low voltage output 1106), to receive the measurements from the sensor 1108, 1110.

[0081] To avoid having to pass a connection under the transformers Ta, Tb or through the secondary circuits operating at high voltage, a connection 1202a, 1202b is provided between the control circuit CCa, CCb and each component to which this control circuit CCa, CCb must be connected, this connection 1202a, 1202b crossing the quadrilateral Q through the two lines L1, L2. "Crossing the quadrilateral” means that the orthogonal projection of the connection 1202a, 1202b in the plane of the electronic card 1102 passes through the quadrilateral Q. In practice, the connection 1202a, 1202b may be formed at least in part from an internal layer in the electronic card to pass above or below the tracks and / or components of the low voltage circuit CBT extending in the quadrilateral Q, such as the capacitive elements of the output capacitor COut-

[0082] The connection 1202a, 1202b connects for example the microcontroller uCa, uCb to the desired component.

[0083] Thus the connection 1202a, 1202b crosses the low voltage circuit CBT and not the primary circuits CPa, CPb which would have required insulation or a large distance as they operate at high voltage.

[0084] [Fig. 12] and [Fig. 13] show two other possible arrangements of transformers Ta, Tb and the quadrilaterals Q that can be defined in this case.

[0085] In conclusion, it will be noted that the invention is not limited to the embodiments described above. It will indeed appear to those skilled in the art that various modifications can be made to the embodiments described above, in light of the teaching which has just been disclosed to them.

[0086] In the detailed presentation of the invention which is made above, the terms used must not be interpreted as limiting the invention to the embodiments set out in the present description, but must be interpreted to include all equivalents whose prediction is within the reach of those skilled in the art by applying their general knowledge to the implementation of the teaching which has just been disclosed to them.

Claims

Claims

1. DC-DC conversion device (800), comprising: - first and second DC-DC converters (112a, 112b), each comprising: • an inverter (202a, 202b) designed to convert an input voltage (ViNa, ViNb) into a first alternating intermediate voltage (Vl~a, Vl~b), • a resonant circuit (204a, 204b) comprising a transformer (Ta, Tb), as well as a capacitance (Ca, Cb) and an inductance (La, Lb) in series with a primary coil (Pa, Pb) of the transformer (Ta, Tb) and the first intermediate voltage (Vl~a, Vl~b), and • a rectifier (206a, 206b) designed to convert a second alternating intermediate voltage (V2~a, V2~b) present at a secondary coil (Sa, Sb) of the transformer (Ta, Tb) into an output voltage (VOut), the secondary coil (Sa, Sb) of the transformer (Ta, Tb) having at least two terminals (Sla, S2a, Ma, Slb, S2b, Mb); - an output capacitance (COut) designed to present the output voltage (VOut); and - for each of the transformers (Ta, Tb), a loop (B) extending from one terminal (Sla, S2a, Ma, Slb, S2b, Mb) to the other of the secondary coil (Sa, Sb) of the transformer (Ta, Tb) and passing through the output capacitance (Cour); characterized in that the output capacitance (Cour) is placed so that each of the two loops (B) has an inductance of at most 20 nH.

2. A DC-DC conversion device (800) according to claim 1, wherein the secondary coil (Sa, Sb) of each of the transformers (Ta, Tb) has a first end terminal (Sla, Slb), a second end terminal (S2a, S2b) and a middle terminal (Ma, Mb), and wherein the loop (B) passes through: - a first switching element and conductors for connecting the first switching element between a first terminal of the capacitor (COut) and the first terminal end terminal (Sla, Slb); and / or - a second switching element and conductors for connecting the second switching element between the first terminal of the capacitor (Cour) and the second end terminal (S2a, S2b).

3. A DC-DC conversion device (800) according to claim 1 or 2, wherein the output capacitance (Cour) comprises a plurality of capacitive elements.

4. A DC-DC conversion device (800) according to claim 3, wherein the capacitive elements are in parallel and / or distributed in at least two alignments.

5. A DC-DC conversion device (800) according to any one of claims 1 to 4, wherein at least one of the terminals (Sla, S2a, Ma, Slb, S2b, Mb) of the secondary coil (Sa, Sb) of a first of the transformers (Ta, Tb) is separated by at most 3 cm from at least one of the terminals (Sla, S2a, Ma, Slb, S2b, Mb) of the secondary coil (Sa, Sb) of the other of the transformers (Ta, Tb).

6. A DC-DC conversion device (800) according to any one of claims 1 to 5, wherein there is a quadrilateral (Q) with four vertices located respectively on a pin of a first end terminal (Sla) of the secondary coil (Sa) of the first transformer (Ta), a pin of a second end terminal (S2a) of the secondary coil (Sa) of the first transformer (Ta), a pin of a first end terminal (Slb) of the secondary coil (Sb) of the second transformer (Tb) and a pin of a second end terminal (S2b) of the secondary coil (Sb) of the second transformer (Tb), at least one capacitive element of the output capacitance (COut) extending in this quadrilateral (Q).

7. DC-DC conversion device (800) according to any one of claims 1 to 6, in which the transformers (Ta, Tb) are carried by the same electronic card (1102), on the same side of the latter.

8. Electrical system comprising: - a first and a second direct voltage source; and - a direct-direct conversion device (800) according to any one of claims 1 to 7, in which the inverter of the first DC-DC converter (112a) is connected to the first DC voltage source to receive its input voltage (ViNa) and wherein the inverter of the second DC-DC converter (112b) is connected to the second DC voltage source to receive its input voltage (ViNb).

9. Mobility device (100) comprising a DC-DC conversion device (800) according to any one of claims 1 to 7 or an electrical system according to claim 8.

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