METHOD FOR BALANCING BETWEEN CURRENT LINES OF A BATTERY OF AN ELECTRICAL SYSTEM DURING CHARGING

Abstract

The present invention relates to a method for balancing an electrical system for recharging a power battery with electrochemical cells of said system, the battery (BAT) comprising at least three current lines (LT1, LT2, LT3) each comprising a plurality of elementary modules connected in series, forming a multi-level inverter distributed in the battery (BAT) comprising a first step (E10) of detecting an unbalanced state in the charging state between at least two lines of said three current lines (LT1, LT2, LT3), a second step (E11) of controlling a charge of said three current lines (LT1, LT2, LT3) from a charging line (25), a third step (E12) of controlling the voltage reference setpoints during which charging currents specific to each current line operate a rebalancing in the charging state between said three current lines. Figure 2.

Description

Title of the invention: METHOD FOR BALANCING BETWEEN CURRENT LINES OF A BATTERY OF AN ELECTRICAL SYSTEM DURING CHARGING

[0001] The field of the invention relates to a method for balancing a battery of an electrical system during alternating current or direct current charging.

[0002] Electrified vehicles include a high-power traction battery, typically operating in a voltage range of 260 volts to 450 volts.

[0003] The applicant has developed a disruptive architecture known as a distributed multilevel inverter which makes it possible to dispense with the voltage converters usually integrated between a battery with electrochemical cells and the power supply network operating at alternating voltage. This architecture has been the subject of several patent applications by the applicant. Examples include documents WO-A1-2017 / 153366 and WO-A1-2021 / 048477. They describe a cell architecture which comprises current lines formed by elementary modules each comprising an electrochemical cell, or a cluster of cells, and a switching module forming an H-bridge. These documents also describe innovative control methods for this architecture allowing the balancing of the cells in charge state and the generation of polyphase or direct electric current.

[0004] Such an architecture comprises three current lines each equipped with several clusters of cells connected in series via switching modules. The current lines are intended to directly power a three-phase electrical machine of a motor vehicle or in another use case to be linked to a three-phase network for example for network compensation or to equip a renewable energy network.

[0005] The battery lines can be charged from a single-phase current and can be connected in series or in parallel to the load line. As the battery is used or if the loads or network voltages are not balanced, the energy supplied or recovered by the three current lines will be different from each other. This situation leads to an imbalance between the three current lines. Passive balancing and active balancing techniques are known, but they have energy losses.

[0006] There is therefore a need to overcome the aforementioned problems. One objective of the invention is to propose a method for balancing the current lines of a battery having a distributed multi-level inverter architecture. Another objective is to control the balancing method during charging of the battery.

[0007] More specifically, the invention relates to a method for balancing an electrical system for recharging a power battery with electrochemical cells of said system, the battery comprising at least three current lines each comprising a plurality of elementary modules connected in series, each provided with a cell or a cluster of cells and a switching module comprising an H-bridge, forming a multi-level inverter distributed in the battery capable of generating a voltage waveform chosen at the terminals of each current line as a function of voltage reference setpoints specific to each current line.

[0008] According to the invention, the method comprises the following steps:

[0009] - a first step of detecting an unbalanced state in the state of charge between at least two lines of said three current lines,

[0010] - a second step of controlling a load of said three current lines to from a load line intended to deliver an alternating load current or a direct load current,

[0011] - a third step of controlling the voltage reference instructions for each current line determined as a function of a reference voltage of said load line and at least one reference current setpoint during which load currents specific to each current line operate a rebalancing in the state of charge between said three current lines.

[0012] The method according to the invention may include the following additional characteristics, alone or in combination:

[0013] - Said three current lines are connected in parallel to the load line and in which during the third control step the voltage reference setpoints are determined as a function of a single current reference setpoint and the reference voltage.

[0014] - Said three current lines are connected in parallel to the load line and in which during the third control step the voltage reference setpoints of each current line are determined as a function of three current reference setpoints, each current setpoint being specific to a current line and being determined as a function of the state of charge of each current line.

[0015] - The reference voltage of the load line is an alternating voltage.

[0016] - The reference voltage of the load line is a direct voltage.

[0017] It is further envisaged an electrical system comprising a power battery with electrochemical cells, the battery comprising at least three current lines each comprising a plurality of elementary modules connected in series, each provided with a cell or a cluster of cells and a switching module comprising an H-bridge, forming a multilevel inverter distributed in the battery capable of generating a voltage waveform chosen at the terminals of each current line. current according to voltage reference setpoints specific to each current line. According to the invention, the system comprises a control unit configured to implement the balancing method according to any of the preceding embodiments.

[0018] According to a variant, the electrical system further comprises a coupling device arranged to connect the three current lines in parallel to the load line in the event of detection of a single-phase alternating load current or a direct load current.

[0019] A motor vehicle is further provided comprising the electrical system according to the invention.

[0020] A stationary storage system comprising the electrical system according to the invention is further provided.

[0021] Further provided is a computer program product comprising instructions which, when the program is executed by a battery control unit, cause the latter to implement the balancing method according to any one of the preceding embodiments.

[0022] The balancing method makes it possible to achieve balancing between the current lines of the battery to preserve maximum exploitation of the battery capacity and therefore optimize the autonomy of a vehicle. It allows, in single-phase alternating current charging, to control specific charging currents for each current line. The balancing method avoids the energy losses usually observed for passive or active balancing systems in batteries. The method improves energy efficiency for the needs of balancing the current lines.

[0023] Other characteristics and advantages of the present invention will appear more clearly on reading the detailed description which follows, comprising embodiments of the invention given as non-limiting examples and illustrated by the appended drawings, in which:

[0024] [Fig. 1] represents an embodiment of a polyphase electrical system comprising a battery equipped with a multi-level inverter and designed to implement the balancing method according to the invention.

[0025] [Fig.2] represents a first embodiment of the system comprising a control unit configured for implementing a first balancing mode between the current lines.

[0026] [Fig.3] represents a first embodiment of the algorithm of the balancing method according to the invention.

[0027] [Fig.4] represents a second embodiment of the system comprising a control unit configured for implementing a second mode of balancing between the current lines.

[0028] [Fig.5] represents a second embodiment of the algorithm of the balancing method according to the invention.

[0029] [Fig.6] schematically represents an electric vehicle comprising the battery system according to the invention provided for the implementation of the balancing method according to the invention.

[0030] The invention relates to a polyphase electrical system for energy storage for electrified motor vehicles and stationary storage systems in electrical installations, for example for renewable energy or network regulation installations. The polyphase system comprises an electrochemical battery comprising elementary cell modules interconnected so as to form a distributed multi-level inverter structure in the battery making it possible to connect the battery to an electrical system operating at direct voltage and alternating voltage without the intermediary of an inverter. The battery system can be connected directly to an extended electrical supply network and to an electrical motive machine. The invention aims to provide a method for balancing the states of charge between the current lines of a battery comprising three current lines.

[0031] In the present description, the term distributed multilevel inverter means that the current line or each current line of the battery is formed by a plurality of elementary modules connected in series and each elementary module comprises a cell or a cluster of cells, as well as a switching module forming an H-bridge, the control unit comprises a means for controlling the elementary modules of the current line according to a reference setpoint and is capable of generating a chosen voltage waveform, alternating and direct, on each current line. This architecture is the subject of a more detailed description in [Fig.l].

[0032] With reference to [Fig.l], the power battery BAT comprises a plurality n of elementary modules MCLk forming the multi-level inverter structure distributed in the battery and comprises three current lines LT1, LT2 and LT3 connected to phase branches BPI, BP2 and BP3 and in which the elementary modules MCLk are arranged. The elementary modules MCLk are connected in series in each current line. The phase branches BPI, BP2 and BP3 make it possible to connect the battery to different systems intended to use an alternating or direct voltage. In this three-phase configuration, each current line comprises n / 3 elementary modules.

[0033] The BAT battery system has a voltage of several hundred volts at its terminals, for example 350 volts or 1000 volts. At 350 volts, each line LT1, LT2, LT3 is equipped, for example, with 24 elementary cell modules or cell clusters connected in series. However, depending on the electrical requirements, the system BAT battery has a nominal voltage of only several tens of volts (24V, 36V, 48V for example), particularly for automotive vehicle applications, or at a maximum voltage of 1500 Volts DC or even higher, particularly for stationary storage systems.

[0034] In a first set of branch connections of the phase branches BPI, BP2 and BP3, the battery system BAT comprises high-voltage switches Kres, also called high-voltage contactors, intended to electrically connect the battery BAT to an extended electrical supply network RES. Each current line LT1, LT2 and LT3 is connected, via these branch connections, on one side to a network connection switch, KR1, KR2 and KR3 respectively, and on the other side to a neutral terminal N of the battery. The extended supply network RES operates at 50Hz or 60Hz alternating voltage and comprises a three-phase line provided with three voltage lines PI, P2 and P3. The battery system BAT is adapted to generate three three-phase voltage waves offset by 2ir / 3. The control of each current line is similar, differing only by a 2ir / 3 offset between them.

[0035] It should be noted that, thanks to this architecture of multi-level inverter distributed in the battery, the electrical system does not include an AC / DC voltage converter between the current lines LT1, LT2 and LT3 and the phase branches BPI, BP2 and BP3 operating in alternating current.

[0036] Furthermore, in the case of an embodiment for an electrified vehicle, the battery system BAT is the traction battery of the vehicle and further comprises high voltage switches Kmel intended to electrically connect the battery BAT to an electric motor machine MEL. Each current line LT1, LT2 and LT3 is connected, via a second set of derivations of the phase branches BPI, BP2 and BP3, on a first side to a connection switch of the electric machine, KM1, KM2 and KM3 respectively, and on the other side to a neutral terminal N of the battery. The electric motor machine can be an asynchronous or synchronous machine, possibly a direct current machine because the battery system is capable of generating any voltage waveform, alternating or direct.

[0037] Alternatively, for an embodiment of a renewable energy installation, the second phase branch branch assembly may be connected to a photovoltaic installation or a wind turbine installation. Alternatively, the battery is connected to the power supply network for network regulation purposes.

[0038] Furthermore, another set of branches is provided for connecting the battery to a DC direct voltage bus.

[0039] The BAT battery system further comprises a BMS control unit, one of the functions of which is to control the voltage waveform of each line LT1, LT2, LT3 as a function of a reference setpoint Vref from the modules ele MCLk units. Each MCLk elementary module may comprise a single CLk cell, or a cluster of CLk cells which may be two, three, four, five, six or more cells, forming the elementary voltage Vclk. The MCLk elementary module further comprises a COMk switching module capable of configuring the MCLk elementary module in three different states to deliver the voltage Vmclk which is respectively said elementary voltage Vclk, a zero voltage and the inverted Vclk voltage to said connection terminals of the MCLk module.

[0040] The switching module COMk is for example made up of two switching parts forming an H-bridge controllable in the three different states by a control signal from the BMS control unit of the battery BAT specifically addressing the module MCLk. The states are represented by a control variable uik which can take for example the values ​​1, 0, -1 representing the three different states respectively controlling said elementary voltage Vclk, a zero voltage and said inverted voltage - Vclk at said connection terminals of the elementary module k addressed by the control signal uik. Each switching module COMk comprises electronic components, such as power transistors, possibly of the MOSFET or HEMT type ("High Electron Mobility Transistor" in English), controlled by the control signals from the BMS control unit.Thus, the voltage Vmclk at the terminals of each elementary module MCLk among the set of a totality n of modules can be controlled according to a control signal uik according to the following relation: .

[0041] M siV„fM>nt-VM -1 if VrefJ(t)<-nil-Vak ■ 0 otherwise

[0042] Thus, the BMS control unit can control on each voltage line LT1, LT2 and LT3, any voltage waveform formed by steps of amplitude equal to the elementary voltage Vclk as a function of a reference voltage setpoint Vref by connecting the cells in series via the switching modules COMk. The reference voltage setpoint Vref can be of sinusoidal form with a frequency of 50 Hz, any alternating form, for example square, or can be of constant voltage for example.

[0043] It is recalled that an electrochemical cell is an electrical energy accumulator having two terminals, a positive electrode and a negative electrode, and having a voltage of a few volts, most often between 2.3V and 4.2V, approximately. The cells can be of the Lithium-ion type (a lithium Nickel Manganese Cobalt oxide NMC or a lithium iron phosphate LFP can be cited as examples of positive electrode active materials), Nickel Cadmium (Ni-cd), Nickel-Metal-Hydride (Ni-MH) for example. More precisely, a Lithium-ion cell is composed mainly of a porous positive electrode, a porous negative electrode, a separator and an electrolyte (which can be liquid, polymeric or solid). The operating principle of a Lithium-ion cell is based on the reversible exchange of lithium ions between the two porous electrodes.

[0044] In [Fig. 2], the electrical system for a first balancing mode is shown schematically and comprises the battery BAT connected to a power supply network 23 for single-phase alternating current charging to a load line 25. The battery BAT comprises the control unit 21 and an alternating current charge controller 22. The current lines LT1, LT2 and LT3 of the battery BAT can be connected to the load line 25 in series or in parallel by means of controllable switches arranged in the electrical system. For example, two switches controllable in open and closed positions can be arranged in the electrical system, a first switch connecting on the load line 25 side one end of the first line LT1 to one end of the second line LT2 and a second switch connecting on the load line 25 side one end of the second line LT2 to one end of the third line LT3.

[0045] As an alternative to controllable switches integrated into the battery system, a connection device 24 may be provided integrated into a power supply interface connecting the current lines to the network 23 having means for connecting the lines LT1, LT2 and LT3 in parallel and powered by the charging line operating at single-phase alternating voltage. Typically, the power supply interface 24 may be a connection socket, charging cable or any power supply interface means comprising a coupling device arranged to connect the three current lines in parallel to the single-phase power supply line operating at alternating voltage. For example, two switches controllable in the open and closed position may be arranged in a charging cable connector, for example type 2 in accordance with standard IEC 62196.A first switch connects on the side of the load line 25 one end of the first line LT1 to one end of the second line LT2 and a second switch connects on the side of the load line 25 one end of the second line LT2 to one end of the third line LT3.

[0046] For the sake of clarity, the bypass assembly of the electric motor machine is no longer shown in [Fig. 2]. It should be noted that one or more bypass assemblies may be powered by the battery 20, in particular for powering a DC direct voltage bus, or energy generation systems.

[0047] For this first balancing mode, the single-phase alternating current charge controller 22 comprises a current regulator 221 receiving as input a reference current setpoint Iref for the three current lines of the battery, and a measurement of the current Iltl, Ilt2 and Ilt3 of each line LT1, LT2 and LT3 for the control of the load current. The current regulator 221 is configured to operate a current control of each current line by controlling the voltage reference setpoint of each current line.

[0048] Furthermore, the load controller comprises a synchronizer 222 configured to synchronize the voltage waves of each line LT1, LT2 and LT3 with the load line 25 of the network 23. The control unit 21 comprises three allocation units 211, 212 and 213 for controlling the elementary modules of the three current lines LT1, LT2 and LT3 respectively during the execution of the balancing method. These allocation units have the function of activating the elementary modules of each current line to form the reference voltage wave, the setpoint Vrefl determining the control of the line LT1, the setpoint Vref2 for the line LT2 and the setpoint Vref3 for the line LT3.

[0049] The principle of synchronization during charging is to synchronize the phase and the voltage amplitude of each line LT1, LT2 and LT3 with the charging line 25, then to electrically connect these lines when the control unit 21 of the battery BAT detects that the voltage amplitude is less than a predetermined difference. The charging method then provides for controlling a differential voltage lower than the voltage of the charging line 25 by current regulation in order to generate the circulation of a charging current to the battery.

[0050] The control unit 21 comprises sensors and functional modules making it possible to determine the electrical operating parameters of the battery 20, such as the voltage of each elementary module, the current flowing through the current lines, the state of charge of the elementary modules or of a set of elementary modules forming each line, the state of aging, in particular. In addition, the control unit 21 is provided with an integrated circuit computer and electronic memories, the computer and the memories being configured to execute the balancing method according to the invention. But this is not obligatory. Indeed, the computer could be external to the control unit 21, while being coupled to the latter 21. In the latter case, it can itself be arranged in the form of a dedicated computer comprising a possible dedicated program, for example.Consequently, the control unit, according to the invention, can be produced in the form of software modules (or computer modules (or even "software")), or electronic circuits (or "hardware"), or even a combination of electronic circuits and software modules.

[0051] In [Fig.3] we describe by a block diagram the first balancing mode of the method according to the invention during which the voltages of each current line of the battery are controlled from the same voltage reference Ures and a single setpoint of current Iref, the voltage Ures can be a single-phase alternating voltage or a direct voltage.

[0052] In a first initial step E10, it is assumed that the three current lines are unbalanced with each other in the charging state, and that they are all three connected in parallel to the same potential of the network for example, that is to say that the voltages Vltl=Vlt2=Vlt3=Ures, 230V effective direct or alternating current for example. In this initial step E10, the battery control unit detects the unbalanced state in the charging state between at least two current lines, for example from an estimation of the charging state of an elementary module or from a measurement of the charging voltage of an elementary module.

[0053] In a second step E11, a single-phase alternating current load or a direct current load is controlled by the control unit. It should be noted that the second step E11 may be triggered prior to the time of detection of the unbalance state.

[0054] In a first variant E12, the controlled voltages of each line are equal and controlled from the same setpoint, Vrefl=Vref2=Vref3=Ures, where Vrefl is the voltage setpoint of the first current line LT1, Vref2 of the second current line LT2 and Vref3 of the third current line LT3. For this purpose, the battery control unit electrically connects in series at each instant the same number of elementary modules on each of the lines with a current control established with respect to a single reference current setpoint Iref.

[0055] Due to an imbalance in the state of charge between modules of two current lines involving a lower voltage for one line for the same number of modules connected in series, i.e. the voltages Vltl, Vlt2 and Vlt3 are of different values, then the line with the lowest voltage will be assigned the highest current. The greater the difference between Vltl, Vlt2 and Vlt3, the greater the differences in charging current will be, thus accelerating the rebalancing between the lines.

[0056] In [Fig. 4], the electrical system for a second balancing mode is shown schematically. The functional modules 221, 222, 211, 212 and 213 remain identical to the system described in [Fig. 2]. For this second balancing mode, the control unit 21 independently and individually controls the reference voltages Vrefl, Vref2 and Vref3 as a function of the state of charge of each current line LT1, LT2 and LT3 to accelerate the rebalancing between each line so as to control higher currents on the least loaded branch and lower currents on the most loaded branch.

[0057] The system therefore further comprises a module for calculating the three reference currents Iref1, Iref2 and Iref3, specific for each current line LT1, LT2 and LT3, configured to calculate using a Coulomb law or a regulation dynamic based on an estimate of the state of charge of each current line. For example, if it is detected that the state of charge of the first line LT1 is lower than the state of charge of lines LT2 and LT3, the value of the current setpoint Irefl is higher than the value of the current setpoints Iref2 and Iref3. This embodiment variant has the advantage that balancing is faster, of the order of a few minutes. The sum of the three currents Iltl, Ilt2 and Ilt3 is equal to the current value supplied by the load line 25.

[0058] In [Fig.5], a block diagram describes this second mode of balancing of the method according to the invention during which the voltages of each current line of the battery are controlled from specific reference setpoints, which may be different. Indeed, each setpoint Vrefl, Vref2 and Vref3 results from the current regulation as a function of the reference currents Irefl, Iref2 and Iref3, specific to each current line.

[0059] This second balancing mode comprises, identically to the first mode, a first initial step E20, during which it is assumed that the three current lines are unbalanced with each other in the charging state, and that they are all three connected in parallel to the same network potential, i.e. the voltages Vltl=Vlt2=Vlt3=Ures, 230V effective direct or alternating current for example. At this initial step E20, the battery control unit detects the unbalanced state in the charging state between at least two current lines, for example from an estimation of the state of charge of the elementary module or from a voltage measurement of each elementary module.

[0060] The method also comprises a second step E21 during which a single-phase load or a direct current load is controlled by the control unit. It should be noted that the second step E21 can be triggered prior to the time of detection of the unbalance state.

[0061] In a third step E22, reference currents Irefl, Iref2 and Iref3, specific for each current line LT1, LT2 and LT3, are calculated using a Coulomb law or dynamic regulation depending on the state of charge of each current line. The current regulation determines the reference setpoint Vrefl, Vref2 and Vref3 specifically for each current line depending on each reference current Irefl, Iref2 and Iref3.

[0062] In one embodiment, step E12 or E22 can be triggered at the end of charging, for example, if a state of unbalance in charge between the current lines is also detected.

[0063] In [Fig.6], an embodiment of the electrical system is shown for an electrified vehicle with a fully electric motor or hybrid motor. The vehicle comprises an electric motor 64 capable of transmitting torque to the drive wheels 62 of the vehicle through a transmission 61. The electric machine 64 can be three-phase. The vehicle comprises an electrical system comprising the battery 60 according to the architecture with a multi-level inverter distributed in the battery in accordance with the description given in [Fig. 1]. The battery comprises three current lines capable of generating three-phase or single-phase voltage waves. The vehicle further comprises an interface for recharging the battery 68 from a power supply network operating in alternating voltage. The recharging interface 68 is a recharging box electrically connecting the terminals of the battery 60 to the terminal for recharging. The recharging interface 68 is also capable of rapid recharging in direct voltage. The battery system 60 is advantageous in that its control unit 65 adapts the voltage wave into alternating form or direct wave form without resorting to a voltage converter.The vehicle further comprises a supervision system 66 cooperating with the control unit 65 of the battery system 60. The battery system 60 can be directly electrically connected to the electric motor 64, thus improving its energy efficiency in traction.

[0064] The battery can further be connected to a high voltage DC bus 63, for example operating at a nominal voltage of between 350 and 800 volts, for example 450 volts, and to a low voltage on-board network 67 operating at a nominal voltage of 12 volts. In addition, the power electronics 69 comprises a DC / DC converter connecting the voltage bus to the on-board network 67 (450 volts / 12 volts) comprising a service battery.

[0065] A stationary electrical system is further envisaged, for example for network regulation or for a photovoltaic or wind renewable energy system. This electrical system comprises the battery according to the invention and a control unit configured to implement the current line balancing method according to the invention.

[0066] The invention is described in the above by way of example. It is understood that the person skilled in the art is able to produce different variant embodiments of the invention by associating, for example, the different characteristics above taken alone or in combination, without departing from the scope of the invention.

Claims

Claims

1. Method for balancing an electrical system for recharging a power battery (BAT) with electrochemical cells of said system, the battery (BAT) comprising at least three current lines (LT1, LT2, LT3) each comprising a plurality of elementary modules (MCLk) connected in series, each provided with a cell (CLk) or a cluster of cells and a switching module (COMk) comprising an H-bridge, forming a multilevel inverter distributed in the battery (BAT) capable of generating a voltage waveform (Vltl, Vlt2, Vlt3) chosen at the terminals of each current line (LT1, LT2, LT3) as a function of voltage reference setpoints (Vrefl, Vref2, Vref3) specific to each current line, the method being characterized in that it comprises the following steps: - a first step (E10) of detecting an unbalanced state in the charging state between at least two lines of said three current lines (LT1, LT2, LT3),- a second step (El 1) of controlling a charge of said three current lines (LT1, LT2, LT3) from a load line (25) provided to deliver an alternating load current or a direct load current, - a third step (E12) of controlling the voltage reference setpoints (Vrefl, Vref2, Vref3) for each current line determined as a function of a reference voltage (Ures) of said load line (25) and of at least one reference current setpoint (Iref) during which load currents specific to each current line operate a rebalancing in the state of charge between said three current lines.,

2. Balancing method according to claim 1 wherein said three current lines (LT1, LT2, LT3) are connected in parallel to the load line (25) and wherein during the third control step (E12) the voltage reference setpoints (Vrefl, Vref2, Vref3) are determined as a function of a single current reference setpoint (Iref) and the reference voltage (Ures).

3. Balancing method according to claim 1 wherein said three current lines (LT1, LT2, LT3) are connected in parallel to the load line (E25) and wherein during the third control step (E22) the voltage reference setpoints (Vrefl, Vref2, Vref3) of each current line (LT1, LT2, LT3) are determined according to three current reference setpoints (Irefl, Iref2, Iref3), each current setpoint being specific to a current line and being determined according to the state of charge of each current line.

4. A method according to claim 2 or 3 wherein the reference voltage of the load line is an alternating voltage.

5. A method according to claim 2 or 3 wherein the reference voltage of the load line is a DC voltage.

6. Electrical system comprising a power battery (BAT) with electrochemical cells (CLk), the battery (BAT) comprising at least three current lines (LT1, LT2, LT3) each comprising a plurality of elementary modules (MCLk) connected in series, each provided with a cell (CLk) or a cluster of cells and a switching module (COMk) comprising an H-bridge, forming a multilevel inverter distributed in the battery (BAT) capable of generating a voltage waveform (Vltl, VLT2, VLT3) chosen at the terminals of each current line (LT1, LT2, LT3) as a function of voltage reference setpoints (Vrefl, Vref2, Vref3) specific to each current line, characterized in that it comprises a control unit (BMS) configured to implement the balancing method according to any one of claims 1 to 5.

7. Electrical system according to claim 6 comprising a connection device (24) arranged to connect the three current lines (LT1, LT2, LT3) in parallel to the load line (25) in case of detection of a single-phase alternating load current or a direct load current.

8. Motor vehicle comprising an electrical system according to claim 6 or 7.

9. A stationary storage system comprising an electrical system according to claim 6 or 7.

10. A computer program product comprising instructions which, when the program is executed by a battery control unit, cause the latter to implement the balancing method according to any one of claims 1 to 5.

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