Dc-dc converter, mobility machine comprising such a dc-dc converter, method for controlling a dc-dc converter, and corresponding computer program

Abstract

This converter (112) comprises: - an inverter (202) comprising a chopping circuit (208) and a control device (210) designed to control the chopping circuit (208); - a resonant circuit (204) having a resonant frequency (FR); and - a rectifier (206). The control device (210) is designed to control the chopping circuit (208) selectively in two modes: - a first mode in which the chopping circuit (208) is controlled at a fixed chopping frequency (FD) substantially equal to the resonant frequency (FR); and - a second mode in which the chopping circuit (208) is controlled by modifying the chopping frequency (FD) to below the resonant frequency (FR).

Description

DC-DC CONVERTER, MOBILITY MACHINE COMPRISING SUCH A DC-DC CONVERTER, METHOD FOR CONTROLLING A DC-DC CONVERTER AND CORRESPONDING COMPUTER PROGRAM Technical field of the invention

[0001] The present invention relates to a DC-DC converter, a mobility device comprising such a DC-DC converter, a method for controlling a DC-DC converter and a corresponding computer program.

[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] Known in the prior art is a DC-DC converter between an input voltage and an output voltage, comprising:an inverter designed to convert the input voltage into a first alternating intermediate voltage, the inverter comprising a chopping circuit and a control device designed to control the chopping circuit in order to maintain the output voltage at a setpoint;a resonant circuit having a resonant frequency, the 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; anda rectifier connected to a secondary coil of the transformer and designed to convert a second alternating intermediate voltage present at the secondary coil of the transformer into the output voltage.

[0004] It is known that the control device implements one of several known control techniques. In particular, it is known to control the switching circuit at a switching frequency equal to the resonant frequency, and to modify another variable to regulate the output voltage. For example, when the switching circuit has two switching arms, it is possible to play on a phase shift between these two switching arms. Using a switching frequency equal to the resonant frequency is advantageous because it allows the best power efficiency to be obtained. However, like all control techniques, it is only possible to carry out the conversion over a certain input voltage range. Outside this range, the output voltage may become too low to power sensitive elements.

[0005] However, with the rise of autonomous mobility devices and Stearing by Wire systems, the reliability of the power supply to sensitive elements must increase. It is therefore desirable to expand the range of use of the DC-DC converter.

[0006] It may therefore be desirable to provide a DC-DC converter which makes it possible to overcome at least some of the aforementioned problems and constraints.

[0007] There is therefore provided a DC-DC converter between an input voltage and an output voltage, comprising:an inverter designed to convert the input voltage into a first AC intermediate voltage, the inverter comprising a chopping circuit and a control device designed to control the chopping circuit in order to maintain the output voltage at a setpoint;a resonant circuit having a resonant frequency, the 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; anda rectifier connected to a secondary coil of the transformer and designed to convert a second AC intermediate voltage present at the secondary coil of the transformer into the output voltage;characterized in that the control device is designed to control the chopping circuit selectively according to two modes: a first mode in which the chopping circuit is controlled at a fixed chopping frequency and substantially equal to the resonant frequency; and a second mode in which the chopping circuit is controlled by modifying the chopping frequency below the resonant frequency.;

[0008] Thus, when the input voltage becomes too low to perform, according to the first mode, chopping at the resonant frequency, the control device can switch to the second mode which is compatible with low input voltages.

[0009] The invention may further comprise one or more of the following optional features, in any technically possible combination.

[0010] Optionally, in the first mode, the switching circuit is controlled by modifying a control variable.

[0011] Also optionally, the control device is designed to switch from the first mode to the second mode when the control variable reaches a threshold.

[0012] Optionally also, in the second mode, the control variable is kept fixed.

[0013] Optionally also, in the second mode, the control variable is kept fixed at its threshold.

[0014] Also optionally, the inverter has two switching arms and the first mode is a phase shift modulation mode where the control variable is a phase shift between the two switching arms.

[0015] Also optionally, the control device is designed to switch from the second mode to the first mode when the switching frequency substantially reaches the resonant frequency.

[0016] Alternatively, the control device is designed to switch from one mode to the other by comparing the input voltage to a single predetermined threshold: the device being in the first mode when the input voltage is above this threshold and in the second mode when the input voltage is below this threshold.

[0017] This is an advantageous embodiment due to the simplicity of controlling the input voltage value, making it easier to implement the converter control system.

[0018] A mobility device comprising a DC-DC converter according to the invention is also proposed.

[0019] There is also provided a method for controlling a DC-DC converter between an input voltage and an output voltage, the DC-DC converter comprising: - an inverter designed to convert the input voltage into a first AC intermediate voltage, the inverter comprising a chopping circuit; - a resonant circuit having a resonant frequency, the 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 connected to a secondary coil of the transformer and designed to convert a second AC intermediate voltage present at the secondary coil of the transformer into the output voltage;the method being characterized in that it comprises, in order to maintain the output voltage at a setpoint: a first control mode in which the chopping circuit is controlled at a fixed chopping frequency substantially equal to the resonant frequency; and a second control mode in which the chopping circuit is controlled by modifying the chopping frequency below the resonant frequency.;

[0020] Optionally, the DC-DC converter controlled by the control method comprises a control device adapted to control the switching circuit.

[0021] There is also provided a computer program downloadable from a communication network and / or recorded on a computer-readable medium, characterized in that it comprises instructions for executing the steps of a method according to the invention, when said program is executed on a computer. Brief description of the figures

[0022] 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:is a very simplified view of a mobility device in which the invention can be implemented,is an electrical circuit of a DC-DC converter according to a first embodiment with an inverter, a resonant circuit and a rectifier,is an example of a chopping circuit and a rectifier of a DC-DC converter of the,is a group of timing diagrams of electrical quantities of the DC-DC converter of Figures 2 and 3 when the control variable is a phase shift,is a group of 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,is a circuit of another example of a rectifier for the DC-DC converter of Figures 2 and 3,is a functional view of a computer system that can be used in the DC-DC converter,is an electrical circuit of a DC-DC converter device according to a second embodiment,is an electrical circuit of a transformer and a rectifier of the DC-DC converter device of the second embodiment,is a top view of the DC-DC converter device of when mounted on an electronic card,is an enlargement of the view of, illustrating in particular an arrangement of two transformers of the DC-DC converter device,is a simplified view of another example of arrangement of the transformers, andis a simplified view of yet another example of arrangement of the transformers., Detailed description of the invention

[0023] With reference to the, a mobility device 100 in which the invention can be used will now be described.

[0024] 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 V BAT The latter is a high voltage, i.e. greater than 100 V, preferably greater than 150 V.

[0025] The mobility device 100 further comprises a low voltage network 110 designed to be powered by a direct voltage, called network voltage V BT . Low voltage is a voltage less than or equal to 100 V, preferably less than or equal to 60 V.

[0026] To obtain the network voltage V BT from battery voltage V BAT , the mobility device includes a DC-DC converter 112 designed to convert the battery voltage V BAT in the network voltage V BT . Battery voltage V BAT and the network voltage V BT thus respectively form an input voltage and an output voltage of the DC-DC converter 112.

[0027] With reference to the, an example of a DC-DC converter 112 will now be described.

[0028] 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.

[0029] The 202 inverter designed to convert an input voltage V IN (battery voltage V BAT when used in the context of the) in a first intermediate voltage V1~ alternating.

[0030] More specifically, the inverter 202 includes a switching circuit 208 and a control device 210 configured to control the switching circuit 208 to maintain an output voltage V OUT (the voltage V BT when used in the context of the) to a V instruction OUT * desired, received by the control device 210.

[0031] 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 V1~. The transformer T has a magnetizing inductance Lm. Thus, the capacitor C and the inductances L, Lm define a resonant frequency F R of the resonant circuit 204, for example between 80 and 120 kHz, for example 100 kHz.

[0032] 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 V OUT . In some embodiments, the rectifier 206 may comprise one or more controllable switches (e.g., transistor switches), for example controlled by the control circuit 210.

[0033] The DC-DC converter 112 further comprises, for example, a voltage sensor 212 designed to measure the output voltage V OUT and provide this measurement to the control device 210, so that the latter regulates the output voltage V OUT to the V instruction OUT *.

[0034] With reference to the, an example of a switching circuit 208 and a rectifier 206 will now be described.

[0035] 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 comprises two switches G1A, G1B and G2A, G2B connected to each other at a midpoint and together having the input voltage V IN The first intermediate voltage V1~ is thus present between the two midpoints of the two switching arms.

[0036] For its part, still in this example, the rectifier 206 has a capacitor C OUTa 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 Q1, Q2, such as controllable transistors or diodes, connected between respectively one of the two end terminals S1, S2 of the secondary coil S of the transformer T, and a second terminal of the capacitor C OUT connected to an electrical ground. In addition, each of the two switches Q1 and Q2 is connected to a different end terminal S1, S2.

[0037] The controller 210 is configured to control the switching circuit 208 selectively in first and second modes.

[0038] In the first mode, the switching circuit 208 is controlled at a switching frequency F D fixed and substantially equal to the resonance frequency F R , for example equal to the resonance frequency F Rto within 5%, preferably to within 1%, preferably below the resonance frequency F R .

[0039] 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 the, the first mode is a phase shift modulation mode where the control variable may be a phase shift PHI between the two switching arms, the duty cycle for each of the switching arms being for example set to 50%.

[0040] Using the switching frequency F D close to the resonance frequency F R , very high efficiency can be achieved. For example, a power efficiency of over 90% can be achieved. However, this method is not possible below a certain input voltage level V IN .

[0041] For example, in the case of using the phase shift PHI, the higher the input voltage V IN decrease, the more it is necessary to increase the PHI phase shift. However, the PHI phase shift can only be increased up to 180°.

[0042] In the second mode, the switching circuit 208 is controlled by modifying the switching frequency F D below the resonance frequency F R . The use of a switching frequency F D lower than the resonance frequency F R allows to increase the gain between the input voltage V IN and the output voltage V OUT , and therefore reach the setpoint V OUT * desired, even at input voltage levels V IN too weak to continue operating at the resonant frequency F R .

[0043] For example, in this second mode, the control variable, for example the phase shift PHI, is kept fixed.

[0044] 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 F D substantially reaches the resonance frequency F R , for example to within 5%, preferably to within 1%.

[0045] Alternatively, the controller 210 could be designed to switch between the modes by comparing the input voltage V IN at 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.

[0046] Thus, with reference to the, 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.

[0047] 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 F D substantially equal to the resonance frequency F R . Regulation of the output voltage V OUT is obtained by modifying the phase shift PHI. In particular, when the input voltage V IN decreases, the PHI phase shift is increased.

[0048] At time 404, the phase shift reaches a predefined threshold S, for example 180°.

[0049] The control device 210 detects that this threshold S is reached by the phase shift PHI and then controls, in a phase 406, the chopping circuit 208 according to the second mode, that is to say by modifying the chopping frequency F D below the resonance frequency F R . In particular, the higher the input voltage V IN decreases, the more the switching frequency F D is decreased. Conversely, when the input voltage V IN increases, the switching frequency F D is increased.

[0050] At time 408, the switching frequency F D substantially reaches the resonance frequency F R .

[0051] The controller 210 detects that the resonant frequency F R is reached and then controls again, in a phase 410, the cutting circuit 208 according to the first mode.

[0052] In the example of the, 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 the input voltage V IN is higher or lower than this threshold of 210 V, as explained previously.

[0053] With reference to the, in the absence of the transition to the second mode, when the input voltage V IN becomes too low (below approximately 210 V in the example illustrated) and it is no longer possible to play on the phase shift PHI because it is at its maximum of 180°, the output voltage V OUT can no longer follow the instructions V OUT * and therefore drops at the same time as the input voltage V IN , until reaching, in the illustrated example, an asymptote when the input voltage V IN stabilizes.

[0054] With reference to the, another example of rectifier 206 will now be described.

[0055] In this example, rectifier 206 comprises a full bridge of switching elements, e.g., controllable transistors. Alternatively, the switching elements could be diodes.

[0056] The rectifier 206 of the operates in the manner previously described for the rectifier 206 of the.

[0057] With reference to the, 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.

[0058] 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.

[0059] With reference to the, 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 the.

[0060] 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 previous figures will be used again, adding the letter “a” for the elements of the voltage converter 112a and the letter “b” for the elements of the voltage converter 112b.

[0061] Only output capacity C OUT is not split, but common to both converters 112a, 112b.

[0062] The device 800 is thus designed to receive two input voltages V IN a, V IN b to provide an output voltage V OUT . When used in the context of the, the input voltages V IN a, V IN b are each worth, for example, half the battery voltage V BAT . Alternatively, the input voltages could both be equal to the battery voltage VBAT .

[0063] With reference to the, the device 800 comprises at least one loop B passing through the output capacitor C OUT and extending from one terminal to another of the secondary coil Sa of the transformer Ta.

[0064] On the, loop B extends from the second end terminal S2b to the middle terminal Mb and further passes through the switch Q2a.

[0065] More precisely, each terminal S1a, S2a, Ma has at least one pin, four in the illustrated example, shown in dotted lines. Furthermore, the output capacitance C OUTcomprises 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 example illustrated 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.

[0066] 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.

[0067] It is further possible to define other loops like loop B, depending on the pins connected, 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 C OUT 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 S1a and passing through the switching element Q1a and one of the capacitive elements of the output capacitor C OUT .

[0068] Loops can be defined similarly for transformer Tb.

[0069] To minimize the output parasitic inductance, the output capacitance C OUTis 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 nanohenries (nH).

[0070] With reference to the, the device 800 comprises an electronic card 1102 on the same face of which the transformers Ta, Tb, the capacitive elements of the output capacity C OUT and the switching elements of switches Q1a, Q2a, Q1b, Q2b are mounted.

[0071] The electronic board 1102 has a high voltage input 1104 designed to receive the battery voltage V BAT and divide it into the input voltages V IN has , V IN b, and a low voltage output 1106 designed to provide the output voltage V OUT .

[0072] 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.

[0073] 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.

[0074] 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 Q1a, Q2a, Q1b, Q2b.

[0075] The control circuit CCa is designed to control the switching elements of switches Q1a, Q2a. For this purpose, it includes, for example, a microcontroller uCa. Similarly, the control circuit CCb is designed to control the switching elements of switches Q1b, Q2b. For this purpose, it includes, for example, a microcontroller uCb.

[0076] The secondary circuits CSa, CSb are thus part of a low voltage circuit CBT carried by the electronic card 1102.

[0077] With reference to the, 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 S1a, a pin of the second end terminal S2a, a pin of the first end terminal S1b, 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 illustrated, this quadrilateral Q is a rectangle.“Extend 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, “Extend 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.

[0078] To obtain low inductance in each loop, at least one capacitive element of the capacitance C OUT, 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 a time. Furthermore, at least one of the terminals S1a, S2a, Ma, S1b, 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 S1a, S2a, Ma, S1b, 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 close enough to each other to allow the output capacitance C OUT to be close to both at the same time.

[0079] 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 a different side of the lines L1, L2 than the control circuit CCa, CCb (above the line L1 in the illustrated example).

[0080] For example, each control circuit CCa, CCb may need to be connected to the switching elements of the switch Q1a, Q1b or to drivers (not shown) of these switching elements, in order to control these switching elements

[0081] Alternatively, each control circuit CCb, CCb may need to be connected to a current sensor 1108 (for example, to measure a current flowing in 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.

[0082] 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 is to 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 into the quadrilateral Q, such as the capacitive elements of the output capacitor C OUT .

[0083] Connection 1202a, 1202b connects for example the microcontroller uCa, uCb to the desired component.

[0084] Thus 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.

[0085] Laet show two other possible arrangements of transformers Ta, Tb and the quadrilaterals Q that can be defined in this case.

[0086] 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.

[0087] In the detailed presentation of the invention given above, the terms used should not be interpreted as limiting the invention to the embodiments set forth in this description, but should be interpreted to include all equivalents the prediction of which is within the reach of those skilled in the art by applying their general knowledge to the implementation of the teaching just disclosed to them.

Claims

DC-DC converter (112) between an input voltage (V IN ) and an output voltage (V OUT ), comprising: an inverter (202) designed to convert the input voltage (V IN ) into a first alternating intermediate voltage (V1~), the inverter (202) comprising a chopping circuit (208) and a control device (210) designed to control the chopping circuit (208) in order to maintain the output voltage (V OUT ) to an instruction (V OUT *); a resonant circuit (204) having a resonant frequency (F R), the resonant circuit (204) comprising a transformer (T), as well as a capacitance (C) and an inductance (L) in series with a primary coil (P) of the transformer (T) and the first intermediate voltage (V1~); and a rectifier (206) connected to a secondary coil (S) of the transformer (T) and designed to convert a second alternating intermediate voltage (V2~) present at the secondary coil (S) of the transformer (T) into the output voltage (V OUT ); characterized in that the control device (210) is designed to control the chopping circuit (208) selectively according to two modes: a first mode in which the chopping circuit (208) is controlled at a chopping frequency (F D ) fixed and substantially equal to the resonance frequency (F R ); and a second mode in which the chopping circuit (208) is controlled by modifying the chopping frequency (F D ) below the resonant frequency (F R ). The DC-DC converter (112) of claim 1, wherein in the first mode the switching circuit (208) is controlled by modifying a control variable (PHI). The DC-DC converter (112) of claim 2, wherein the controller (210) is configured to transition from the first mode to the second mode when the control variable (PHI) reaches a threshold. DC-DC converter (112) according to claim 2 or 3, wherein, in the second mode, the control variable (PHI) is kept fixed. DC-DC converter (112) according to claims 3 and 4, wherein, in the second mode, the control variable (PHI) is kept fixed at its threshold. A DC-DC converter (112) according to any one of claims 2 to 5, wherein the inverter (202) comprises two switching arms and wherein the first mode is a phase shift modulation mode where the control variable (PHI) is a phase shift (PHI) between the two switching arms. A DC-DC converter (112) according to any one of claims 2 to 6, wherein the controller (210) is adapted to switch from the second mode to the first mode when the switching frequency (F D ) substantially reaches the resonance frequency (F R ). A DC-DC converter (112) according to any one of claims 2 to 6, wherein the controller (210) is adapted to switch from one mode to the other by comparing the input voltage (V IN ) to a single predetermined: the device being in the first mode when the input voltage (V IN) is greater than this threshold and in the second mode when the input voltage (V IN ) is lower than this threshold Mobility device (100) comprising a DC-DC converter (112) according to any one of claims 1 to 8. A method of controlling a DC-DC converter (112) between an input voltage (V IN ) and an output voltage (V OUT ), the DC-DC converter (112) comprising: - an inverter (202) designed to convert the input voltage (V IN ) into a first intermediate alternating voltage (V1~), the inverter (202) comprising a chopping circuit (208); - a resonant circuit (204) having a resonant frequency (F R), the resonant circuit (204) comprising a transformer (T), as well as a capacitance (C) and an inductance (L) in series with a primary coil (P) of the transformer (T) and the first intermediate voltage (V1~); and - a rectifier (206) connected to a secondary coil (S) of the transformer (T) and designed to convert a second alternating intermediate voltage (V2~) present at the secondary coil (S) of the transformer (T) into the output voltage (V OUT ); the method being characterized in that it comprises, in order to maintain the output voltage (V OUT ) to an instruction (V OUT *): a first control mode in which the switching circuit (208) is controlled at a switching frequency (F D ) fixed and substantially equal to the resonance frequency (F R ); and a second control mode in which the switching circuit (208) is controlled by changing the switching frequency (F D ) below the resonant frequency (FR ). Computer program downloadable from a communications network and / or recorded on a computer-readable medium, characterized in that it comprises instructions for executing the steps of a method according to claim 10, when said program is executed on a computer.

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