Battery charger for an automotive vehicle, associated vehicle and method of implementation

Abstract

A battery charger (2) for a motor vehicle (1) comprises a primary circuit (5) configured to be connected to a power supply network (R1) and two secondary circuits (6, 7) connected to the primary circuit by a transformer (8). The transformer includes three high-voltage terminals (40, 41, 42) and one low-voltage terminal (43), the primary circuit and a first secondary circuit being connected to the high-voltage terminal and the second secondary circuit being connected to the low-voltage terminal, the high-voltage terminal and the low-voltage terminal being arranged within the transformer such that the mutual inductance between the windings (15, 16, 17) of the primary circuit is equal and the mutual inductance between each of the windings of the primary circuit and each of the windings of the second secondary circuit is equal, this condition being met by the high-voltage terminals being equidistant from each other and from the low-voltage terminal.

Description

[Technical field]

[0001] The present invention relates to battery chargers for motor vehicles.

[0002] More particularly, the present invention relates to a battery charger for charging batteries of different voltages, a vehicle equipped with such a charger, and a method of using such a charger. [Background technology]

[0003] The motor vehicle may be equipped with an electric powertrain including an electric motor, or a hybrid powertrain combining, for example, an internal combustion engine and an electric motor, a traction battery for storing energy to power the electric motor, and a charger for recharging the traction battery.

[0004] Battery chargers are typically designed to charge batteries from either a single-phase or a three-phase electrical grid, and therefore the same charger cannot be used to charge the traction battery from both types of electrical grids.

[0005] Depending on the type of powertrain, the voltage across the terminals of the traction battery varies greatly, typically ranging from 150 volts to 450 volts, or even 800 volts in some cases.

[0006] Auxiliary assemblies which consume significant power, typically greater than 1 kilowatt, and which are connected to the traction battery must be constructed to operate optimally with the voltage present across the terminals of the traction battery.

[0007] Such auxiliary assemblies include, for example, air conditioning compressors, heating elements and DC-DC power converters responsible for supplying power to the vehicle's low-voltage (12V) network.

[0008] However, adapting auxiliary assemblies to the various voltage ranges of the traction battery presents technical difficulties and involves significant additional costs, particularly related to development costs, the unit costs of auxiliary assemblies produced in smaller batches, and the costs of storing and managing the various types of auxiliary assemblies thus obtained.

[0009] Reference may be made to document WO2019 / 199964 which discloses three-phase or single-phase charging devices connected to an electrical grid and including a first output connected to a high-voltage battery and a second output connected to a low-voltage battery, these devices including multiple rectification stages.

[0010] Charging devices transfer electrical energy from the grid to the batteries and from one battery to another.

[0011] However, charging devices are designed to function on either a single-phase grid or a three-phase grid.

[0012] In addition, the topology of the charging device includes many inputs and outputs and complex magnetic circuits, making the device bulky, complex to manufacture, and poor in energy conversion efficiency.

[0013] Document CN110149053 discloses a charging device that allows the exchange of electrical energy flows between three DC power sources.

[0014] However, this device cannot be charged on a domestic power grid where one of the DC voltage sources supplies the AC voltage.

[0015] The document, titled "Analysis and design of multiport DC / DC converter for next generation hybrid vehicle subsystems" (Toyota R&D Review, Vol. 48, No. 2 (2017)), proposes a DC power converter that can power two circuits by one battery, where the voltages between the terminals of the two circuits are different and lower than the voltage between the terminals of the battery.

[0016] However, this power converter does not allow the battery to be charged by the electrical grid.

[0017] Reference may also be made to a document entitled "Consideration of PDM and power decoupling method in an isolated single-phase matrix converter for battery charger", Toyota R&D Review, Vol. 48, No. 2 (2017), which discloses a charging device including a primary circuit and a secondary circuit, the primary circuit including a single-phase input stage using direct matrix conversion.

[0018] The charging device makes it possible to reduce second harmonics in the secondary circuit during charging from a single-phase electric grid.

[0019] However, this charger cannot charge batteries of different voltages.

[0020] Additionally, the charger operates on a single-phase electrical grid. Summary of the Invention

[0021] It is therefore proposed to overcome all or some of the drawbacks of prior art charging devices by providing a compact charger that is capable of charging batteries of different voltages, works on both single-phase and three-phase electrical grids, and has improved efficiency.

[0022] In view of the above, the present invention provides a battery charger for an automotive vehicle, the battery charger comprising: a primary circuit configured to be connected to a power grid, the primary circuit including three converters, each of which may be connected at an input side to one phase of a three-phase grid, and two secondary circuits connected to the primary circuit via a transformer.

[0023] A transformer includes three high voltage cores and a low voltage core, a primary circuit and a first secondary circuit are connected to the high voltage core, and a second secondary circuit is connected to the low voltage core, the high voltage cores and the low voltage cores are arranged in the transformer such that the mutual inductance between the windings of the primary circuit is equal and the mutual inductance between each of the windings of the primary circuit and the winding of the second secondary circuit is equal, this condition being met by arranging the high voltage cores equidistant from each other and by arranging each of the high voltage cores equidistant from the low voltage core.

[0024] According to one feature, each converter of the three-phase primary circuit is connected on the output side to a primary coil wound on a different high voltage core, and each converter is configured to be connected to a different phase of the three-phase grid.

[0025] Preferably, each converter of the three-phase primary circuit is connected on the output side to a primary coil wound on a different high-voltage core, the two converters of the two phases of the primary circuit are configured to be connected in parallel to a phase of a single-phase grid, and the two converters are configured to be driven in antiphase.

[0026] Advantageously, the first secondary circuit includes three secondary power converters each connected to a secondary coil wound on a different high voltage core, the secondary power converters being configured to be connected to the first battery.

[0027] According to another feature, the first secondary circuit includes three secondary coils connected in series with each other and each wound on a different high voltage core, and a secondary power converter connected to the secondary coils and configured to be connected to the first battery.

[0028] Advantageously, the second secondary circuit includes a low voltage coil wound on a low voltage core, and a low voltage power converter connected to the low voltage coil and configured to be connected to the second battery.

[0029] The invention also relates to a motor vehicle comprising two batteries and a charger such as defined above, wherein a first battery is connected to a first secondary circuit and a second battery is connected to a second secondary circuit, the voltage across the terminals of the first battery being higher than the voltage across the terminals of the second battery.

[0030] The present invention also relates to a method for charging a battery for a motor vehicle.

[0031] The method includes regulating the electrical energy delivered by a primary circuit to two secondary circuits, the primary circuit being connected to an electrical grid and to three high voltage cores of a transformer, a first secondary circuit being connected to the three high voltage cores and a first battery, and a second secondary circuit being connected to a low voltage core of the transformer and a second battery, the high voltage cores and the low voltage cores being arranged in the transformer such that a mutual inductance between each of the windings of the primary circuit is equal and a mutual inductance between each of the windings of the primary circuit and a winding of the second secondary circuit is equal, this condition being met by arranging the high voltage cores equidistant from each other and arranging each of the high voltage cores equidistant from the low voltage core, and regulating the power delivered to the first battery and the second battery is determined in response to a phase difference between the control signals of the primary circuits.

[0032] According to one feature, the method includes charging the second battery when a phase difference between control signals driving power converters of the primary circuit is less than π / 3.

[0033] Advantageously, the method further includes transferring electrical energy between the first battery and the second battery via a transformer, the transferring including correcting magnetic flux drift produced by transforming electrical energy from a source battery selected from the first battery and the second battery by modifying a duration of a voltage pulse produced from the source battery and provided to the transformer.

[0034] Other objects, features and advantages of the present invention will become apparent on reading the following description, given purely by way of non-limiting example and with reference to the accompanying drawings, in which: [Brief description of the drawings]

[0035] [Figure 1] 1 shows a schematic diagram of a vehicle including a first embodiment of a charger according to the present invention; [Diagram 2] FIG. 2 is a schematic diagram of one embodiment of a power converter of the charger. [Diagram 3] FIG. 2 is a schematic diagram of one embodiment of a charger transformer according to the present invention. [Figure 4] FIG. 2 shows a schematic diagram of one embodiment of a magnetic half-element of a transformer according to the present invention. [Diagram 5] FIG. 4 is a diagram showing an example of a control signal of a charger according to the present invention. [Figure 6] FIG. 13 is a diagram showing an example of change in magnetic flux passing through a high-voltage core and a low-voltage core in the case of a phase difference of π / 3. [Figure 7] FIG. 13 is a diagram showing an example of change in magnetic flux passing through a high-voltage core and a low-voltage core for a phase difference smaller than π / 3. [Figure 8] FIG. 2 shows a schematic diagram of one part of a charger according to the present invention. [Figure 9] FIG. 2 shows a schematic diagram of a flux control circuit according to the present invention; [Figure 10] FIG. 2 illustrates a schematic diagram of voltage pulses generated by a power converter. [Figure 11]FIG. 2 illustrates a schematic diagram of voltage pulses generated by a power converter. [Figure 12] FIG. 2 shows a schematic diagram of a second embodiment of a charger according to the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0036] FIG. 1 shows, for example, a three-phase electrical grid R1 providing 16 amps per phase, and a hybrid or electric motor vehicle 1 including a first embodiment of a reversible battery charger 2 powered by the electrical grid R1 for the purpose of charging or discharging a first battery 3 and a second battery 4 connected to the charger 2.

[0037] The voltage across the terminals of the first battery 3 is higher than the voltage across the terminals of the second battery 4, the first battery 3 being, for example, a traction battery with a voltage across its terminals equal to 400 volts, and the voltage across the terminals of the second battery 4 being, for example, equal to 48 volts, the second battery being configured, for example, to power the most powerful electric auxiliary devices or a computer of the vehicle 1.

[0038] The charger 2 comprises a primary circuit 5 connected to a grid R1, two secondary circuits 6 and 7 connected to the primary circuit 5 via a transformer 8, and a processing unit UT.

[0039] The primary circuit 5 includes three primary power converters 12, 13 and 14, each connected on the input side to different phases L1, L2 and L3 of the grid R1 on the one hand and to the neutral point N of the grid R1 on the other hand.

[0040] Each primary converter 12, 13, 14 is connected on the output side to a respective primary coil 15, 16, and 17, which is energized by the respective primary power converter 12, 13, and 14 and forms the primary winding of the transformer 8.

[0041] The primary circuit 5 may further include a switch 18 connecting the two phases L1 and L2 of the primary circuit 5.

[0042] Switch 18 is open when charger 5 is connected to grid R1.

[0043] The first secondary circuit 6 includes three secondary power converters 25, 26, and 27 connected to secondary coils 22, 23, and 24, respectively, and each secondary power converter 25, 26, and 27 is further connected to the first battery 3. The secondary coils 22, 23, and 24 form a first portion of a secondary winding of the transformer 8.

[0044] The second secondary circuit 7 includes a low voltage coil 28 forming a second part of the secondary winding of the transformer 8 and a low voltage power converter 29 connected to the low voltage coil 28, the low voltage power converter being further connected to the second battery 4.

[0045] The charger 2 charges a first battery 3 and a second battery 4 from a grid R1.

[0046] Primary power converters 12, 13, and 14 are constructed from four-quadrant components including, among other things, diodes and transistors.

[0047] FIG. 2 shows an example of an embodiment of the power converter of the charger 2.

[0048] Since primary power converters 12, 13 and 14, secondary power converters 25, 26 and 27, and low voltage power converter 29 are identical in construction, only the construction of primary power converter 12 will be described in detail.

[0049] Converter 12 includes four switching cells CEL1 to CEL4, and each switching cell includes a transistor T including a freewheeling diode D1, and a capacitor C1.

[0050] The input of the first cell CEL1 is connected to phase L1, to a first end of the capacitor C1 and to the input of the second cell CEL2.

[0051] The output of the cell CEL 1 is connected to the input of a third cell CEL 3 and to a first end of the winding 15 .

[0052] The output of the third cell CEL3 is connected to the neutral point N, to the second end of the capacitor C1, and to the output of the fourth cell CEL4.

[0053] The output of the second cell CEL 2 is connected to the input of the fourth cell CEL 4 and to a second end of the winding 15 .

[0054] The secondary power converters 25, 26 and 27 and the low voltage power converter 29 are, for example, reversible power converters and are created using diodes and transistors.

[0055] A first battery 3 and a second battery 4 can supply power to a grid R1 via a charger 2.

[0056] FIG. 3 shows one embodiment of transformer 8 including primary coils 15, 16, and 17, secondary coils 25, 26, and 27, and a low voltage coil .

[0057] Transformer 8 includes first and second magnetic half elements 30, 31 which are identical, overlapped and made, for example, from ferrite.

[0058] The half elements 30, 31 are for example circular.

[0059] FIG. 4 illustrates one embodiment of the magnetic half-element 30 .

[0060] The first magnetic half-element 30 includes three high voltage half-cores 32 , 33 , and 34 and one low voltage half-core 35 .

[0061] Similarly, the second half element 31 includes three high voltage half cores 36 , 37 , and 38 and one low voltage half core 39 .

[0062] The first half element 30 and the second half element 31 are overlapped with each other such that the high voltage half cores 32, 33, and 34 and the low voltage half core 35 of the first half element 30 contact the high voltage half cores 36, 37, and 38 and the low voltage half core 39 of the second half element 31, such that the half cores 32 and 36, 33 and 37, and 34 and 38, respectively, are in contact in this manner to form high voltage cores 40, 41, and 42, and the low voltage half cores 35 and 39 are in contact in this manner to form the low voltage core 43 (FIG. 2).

[0063] The primary coils 15 , 16 and 17 are wound, for example, on high voltage half cores 32 , 33 and 34 of the first half element 30 , and the secondary coils 22 , 23 and 24 are wound, for example, on high voltage half cores 36 , 37 and 38 of the second half element 31 .

[0064] The low voltage coil 28 is, for example, wound on a low voltage core 43 .

[0065] The high-voltage cores 40, 41, and 42 and the low-voltage core 43 are arranged in the transformer so that the mutual inductances M1, M2, M3 between the coils 15 and 16, 16 and 17, and 15 and 17 of the primary circuit are equal, as well as the mutual inductances M4, M5, and M6 between each pair of coils 15 and 22, 16 and 23, 17 and 24 between the primary circuit and the first secondary circuit 6. Similarly, the mutual inductances between each primary coil 15, 16, 17 on the one hand and the secondary coil 28 on the other hand are equal, and the mutual inductances between each secondary coil 22, 23, 24 on the one hand and the secondary coil 28 on the other hand are equal.

[0066] For example, as shown in FIG. 4, if the half elements 30, 31 are circular, the low voltage core 43 is placed at the center of the disk, the high voltage cores 40, 41, and 42 are placed equidistant from each other to obtain the same mutual inductance between the windings, and two adjacent high voltage cores are at an angle of 120° to the low voltage core.

[0067] The transformer 8 connects the primary circuit 5, the first secondary circuit 6 and the second secondary circuit 7 and makes it possible to reduce the complexity of the magnetic circuit (in particular by reducing the number of coils) and to reduce the bulk of the magnetic circuit (in particular by reducing the volume of the ferrite).

[0068] The reduction in the volume of the ferrite reduces the core losses and in fact reduces the copper length of the coil, reducing the copper losses and contributing to an improvement in the efficiency of the charger 2.

[0069] Moreover, the geometry of the magnetic circuit of the transformer 8, including the first half-element 30 and the second half-element 31, balances the magnetic coupling within the magnetic circuit, thereby enabling each of the phases of the charger 2 to be controlled using a similar control strategy.

[0070] This control strategy may involve, for example, setting a phase difference between each winding 15, 16 and 17 of the primary circuit 5 and the neutral point N of the grid R1, or implementing a freewheeling phase.

[0071] In a first mode of embodiment of the charger 2 , the charger 2 charges the batteries 3 and 4 .

[0072] The power delivered by the charger 2 to the batteries 3, 4 is determined depending on the phase difference φ between the control signals S12, S13 and S14 of the primary power converters 12, 13 and 14, which drive the transistors of said power converters.

[0073] The phase difference φ between the control signals creates a zero-sequence component between the phases of the primary circuit 5 by unbalancing the phase differences between the magnetic fluxes Φ1, Φ2, and Φ3 generated by the primary coils 15, 16, and 17 at the switching frequencies of the power converters 12, 13, and 14.

[0074] The magnetic flux transferred by high voltage cores 40, 41, and 42 to low voltage core 43 is represented as Φ4, and magnetic flux Φ4 is transferred to low voltage coil 28.

[0075] The zero-sequence components associated with the control of the secondary converters 25, 26, 27, 29 allow differentiation of the flow of power passing from the grid R1 to the first battery 3 and the second battery 4.

[0076] The control signals S12, S13 and S14 are generated by the processing unit UT.

[0077] Furthermore, the processing unit UT controls the power converters 25 , 26 , 27 and 29 .

[0078] FIG. 5 shows an example of control signals S12, S13, and S14 out of phase with a phase difference φ as a function of time t.

[0079] The reader is further referred to FIG. 6 which shows the variation of magnetic fluxes Φ1, Φ2, Φ3 and Φ4 as a function of time when the phase difference Φ is equal to π / 3.

[0080] The amplitude of the magnetic flux Φ4 is small compared to the amplitudes of the magnetic fluxes Φ1, Φ2, and Φ3, and therefore the amplitude of the voltage induced in the coil 28 is small.

[0081] Since the voltage induced in the coil 28 is low, the transistors of the converter 29 can be turned off, so that no current is transferred to the battery 4 via the freewheeling diodes.

[0082] The power transferred by the charger 2 charges only the first battery 3 .

[0083] FIG. 7 shows the variation of the magnetic fluxes Φ1, Φ2, Φ3, and Φ4 as a function of time when the phase difference Φ is less than π / 3.

[0084] The magnetic flux Φ4 generated by the magnetic fluxes Φ1, Φ2, Φ3 is of sufficient amplitude to induce a voltage in the coil 28 large enough to charge the second battery 4 via the converter 29, and the magnetic fluxes Φ1, Φ2, Φ3 further generate induced voltages in the coils 22, 23, and 24 large enough to charge the first battery 3 via the first secondary circuit 6.

[0085] According to a second mode of embodiment, the charger 2 transfers electrical energy between the first battery 3 and the second battery 4 via the transformer 8, and the primary circuit 5 is not powered by the grid R1.

[0086] Since the various phases of the primary circuit 5 and secondary circuit 6 are identical, one example of transferring energy from one battery to the other through converters 12 and 25 is described in detail, and the method applies to other converters as well.

[0087] For simplicity, FIG. 8 shows a converter 12 of a primary circuit 5 connected to phase L1 and the neutral point of circuit R1, a converter 25 of a first secondary circuit 6 connected to a first battery 3, and a transformer 8 connecting circuits 5 and 6.

[0088] As a result of the exchange of energy between the two batteries, a voltage V1 is generated across the terminals of the coil 15 of the converter 12 and a voltage V2 is generated across the terminals of the coil 22 of the converter 25.

[0089] It is assumed that the energy of the first battery 3 is transferred to the second battery 4 via a second secondary circuit 7 (not shown).

[0090] As a variant, energy is transferred from the second battery 4 to the first battery 3 .

[0091] During the energy transfer, there generally appears a magnetic flux drift which is produced by the conversion of electrical energy.

[0092] To correct the flux drift, the processing unit UT uses a flux control circuit 44 shown in FIG.

[0093] The processing unit UT corrects the magnetic flux drift generated by converting the electrical energy from a source battery selected from the batteries 3, 4 by modifying the duration of the positive or negative part of a voltage pulse 50 generated using the source battery, which pulse energizes the transformer 8.

[0094] Flux control circuit 44 includes an amplifier 45 which receives voltage V 1 as an input, and an integrator 46 which has an input connected to the output of amplifier 45 and an output connected to an input of a low pass filter 47 .

[0095] The control circuit 44 further includes a time determination module 48 for generating a correction time Tc and a module 49 for determining the sign of the signal for generating a signal representative of the sign SELEC, the inputs of the time determination module 48 and the sign determination module 49 being connected to the output of the filter 47.

[0096] Processing of voltage V1 by control circuit 44 makes it possible to detect flux drifts and to correct them by lengthening or shortening the duration of the positive or negative part of the voltage pulse 50 generated by coil 22, by adding or subtracting a correction time Tc depending on the value of sign SELEC, which voltage pulse is applied to transformer 8.

[0097] The symbol SELEC is the image of the average value of the magnetic flux of the transformer 8, which indicates the direction of the correction to be applied, and which is ideally zero.

[0098] 10 and 11 respectively show a reduction in the positive portion of pulse 50 (dashed line) achieved by subtracting time Tc from the time to the falling edge, and an increase in the negative portion of pulse 50 (dashed line) achieved by adding time Tc to the time to the rising edge.

[0099] By transferring energy from one battery to the other, it is possible to ensure redundancy in energy storage, which is particularly required when powering safety-critical equipment such as sensors and computers used when the vehicle 1 is driven autonomously.

[0100] The transfer of energy from one battery to the other further makes it possible to pre-charge the “high voltage” first secondary circuit 6 using the second battery 4 without an additional pre-charging device inside the first battery 3.

[0101] Hereinafter, elements that are identical to those described above are designated by the same references.

[0102] FIG. 12 shows a single-phase electrical grid R2 including a phase L supplying, for example, 32 amps, and a hybrid or electric motor vehicle 1 powered by the electrical grid R2, the vehicle 1 including a second embodiment of a charger 2.

[0103] The charger 2 differs from the first embodiment of the charger 2 shown in FIG. 1 in that switch 18 is closed so that phase L of grid R2 supplies power to converters 12 and 13 of the primary circuit 5, and converter 14 is not powered.

[0104] The converters 12 and 13 are controlled in anti-phase to minimize the current spectrum conducted by the two phases L1, L2.

[0105] Depending on the state of switch 18, the charger 2 can be powered by a single-phase grid R2 (switch closed) or a three-phase grid R1 (switch open) without any structural modifications to the charger 2 and without oversizing the charger 2 electrically or magnetically.

[0106] Moreover, since the two converters 12 and 13 are arranged in parallel, the current supplied by phase L of grid R2 can be twice the current supplied by one of the phases of the three-phase grid R1.

[0107] In addition, the first secondary circuit 6 differs from the secondary circuit of the first embodiment of the charger 2 shown in FIG. 1 in that it includes a single reversible power converter 51 connected to three secondary coils 52, 53, and 54 connected in series with each other.

[0108] The converter 51 is further connected to the first battery 3 .

[0109] Each secondary coil 52 , 53 , and 54 is wound on a different primary half-core 36 , 37 , and 38 of the second half-element 31 .

Claims

1. A battery charger (2) for a motor vehicle (1), the battery charger comprising a primary circuit (5) configured to be connected to a power grid (R1, R2), the primary circuit including three converters, each of which may be connected at its input side to one phase of a three-phase grid, and two secondary circuits (6, 7) connected to the primary circuit via a transformer (8), the transformer including three high voltage cores (40, 41, 42) and one low voltage core (43), the primary circuit and 1. A battery charger (2) comprising: a first secondary circuit connected to the high voltage core; and a second secondary circuit connected to the low voltage core; the high voltage core and the low voltage core arranged in the transformer such that mutual inductances between windings (15, 16, 17) of the primary circuit are equal, and mutual inductances between each of the windings of the primary circuit and each of the windings of the second secondary circuit are equal, the conditions being met by arranging the high voltage cores equidistant from each other and by arranging each of the high voltage cores equidistant from the low voltage core.

2. 2. The charger of claim 1, wherein each converter (12, 13, 14) of the three-phase primary circuit is connected on the output side to a primary coil (15, 16, 17) wound on a different high voltage core (40, 41, 42), each converter being configured to be connected to a different phase of the three-phase grid (R1).

3. 2. A charger as claimed in claim 1, wherein each converter (12, 13, 14) of a three-phase primary circuit is connected on the output side to a primary coil (15, 16, 17) wound on a different high-voltage core (40, 41, 42), and the two converters (12, 13) of the primary circuit are arranged to be connected in parallel to a phase of a single-phase grid (R2), the two converters being arranged to be driven in antiphase.

4. 4. The charger of claim 1, wherein the first secondary circuit (6) includes three secondary power converters (25, 26, 27) each connected to a secondary coil (22, 23, 24) wound on a different high voltage core (40, 41, 42), the secondary power converters being configured to be connected to a first battery (3).

5. 4. The charger of claim 1, wherein the first secondary circuit (6) includes three secondary coils (52, 53, 54) connected in series with each other and each wound on a different high voltage core (40, 41, 42), and a secondary power converter (51) connected to the secondary coils and configured to be connected to the first battery (3).

6. 6. The charger of claim 1, wherein the second secondary circuit (7) includes a low-voltage coil (28) wound around the low-voltage core (43) and a low-voltage power converter (29) connected to the low-voltage coil and configured to be connected to a second battery (4).

7. A motor vehicle (1) comprising two batteries (3, 4) and a charger (2) according to any one of claims 1 to 6, wherein a first battery (3) is connected to the first secondary circuit (6) and a second battery (4) is connected to the second secondary circuit (7), and the voltage across the terminals of the first battery is higher than the voltage across the terminals of the second battery.

8. A method for charging a battery (3, 4) for a motor vehicle (1), the method comprising regulating the electrical energy delivered by a primary circuit (5) to two secondary circuits, the primary circuit being connected to an electrical grid and to three high voltage cores (40, 41, 42) of a transformer (8), a first secondary circuit being connected to the three high voltage cores and to a first battery (3), and a second secondary circuit being connected to a low voltage core (43) of the transformer and to a second battery (4), the high voltage core and the low voltage core being connected to the windings of the primary circuit. the mutual inductance between each of the windings of the primary circuit and the winding of the second secondary circuit are equal, this condition being met by placing the high voltage cores equidistant from each other and placing each of the high voltage cores equidistant from the low voltage core, and adjusting the power delivered to the first battery and the second battery is determined in response to a phase difference (φ) between the control signals (S12, S13, S14) of the primary circuit.

9. 9. The method of claim 8, comprising charging the second battery when the phase difference (φ) between the control signals (S12, S13, S14) driving the power converters of the primary circuit (5) is less than π / 3.

10. 10. The method according to claim 8 or 9, further comprising transferring electrical energy between the first battery (3) and the second battery (4) via the transformer (8), said transferring comprising correcting magnetic flux drift produced by converting electrical energy from a source battery selected from the first battery and the second battery by modifying the duration of a voltage pulse (50) produced from the source battery and supplied to the transformer (8).

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