Method for controlling a polyphase electrical system for DC fast charging

Abstract

The present invention relates to a method for controlling an electrical system comprising a battery (2) comprising a distributed multilevel inverter architecture formed by current lines (LT1, LT2, LT3) consisting of series-connected electrochemical modules comprising H-bridges. The method relates to DC fast charging. According to the invention, the method comprises controlling electrochemical modules of the battery (2) so as to generate a DC voltage wave across the terminals of each current line (LT1, LT2, LT3) based on a controlled selection of the series-connected modules, carrying out state-of-charge balancing of at least one line with respect to another line from among the three lines, configuring a set of power contactors so as to connect the three lines in parallel for connection to a charging interface (3), and carrying out parallel DC charging of the three lines using the source.

Description

[0001] DESCRIPTION

[0002] TITLE: METHOD FOR CONTROLLING A MULTIPHASE ELECTRICAL SYSTEM FOR RAPID CHARGING AT DIRECT VOLTAGE

[0003]

[0001] The present invention claims priority from French application No. 2407443 filed on 08.07.2024, the content of which (text, drawings and claims) is incorporated herein by reference.

[0004]

[0002] The field of the invention relates to a method of DC voltage charging of a power battery of a polyphase electrical system.

[0005]

[0003] In particular, the invention relates to fast charging solutions capable of reaching several hundred kilowatts, or even several gigawatts. Indeed, reducing charging time is a major challenge for electromobility applications.

[0006]

[0004] In this field, the voltages used by current commercial charging stations can be either 400 volts or 800 volts, with charging power reaching up to 400 kW. Currently, existing charging stations are designed to deliver a maximum current of up to 500 A and a maximum voltage of approximately 920 volts. Generally, vehicle batteries are configured to charge at one voltage type or the other. When a battery designed for 400 volts is connected to an 800-volt charging station, the latter is designed to reduce its voltage. Conversely, a battery designed for 800 volts is compatible with 400-volt charging stations but uses a power converter. These voltage conversions result in energy losses and are therefore not optimal.

[0007]

[0005] To solve this problem, prior art is known in US patent document US-A1-2022 / 126712 describing a multilevel voltage architecture for charging an electrified vehicle's traction battery from a charging station operating at 400 volts and 800 volts. This architecture includes battery interface contacts designed to reconfigure the electrochemical modules in series or parallel depending on the voltage detected by the charger. This system also includes a DC / DC converter designed to reduce the 800-volt voltage to a voltage compatible with the vehicle's electrical system.

[0006] This solution has a drawback if the electrochemical modules are unbalanced during charging. Indeed, when connected in parallel, there is a risk of discharge from one module to another, which could lead to an overcurrent during charging.

[0008]

[0007] To address this general problem, the applicants have developed a battery architecture with a distributed inverter in the battery which has the advantage, in addition to its optimal electrical efficiency, of allowing rapid charging in direct current voltage over a voltage range whose amplitude is determined by the number of electrochemical modules that can be connected in series in a line.

[0009]

[0008] The main advantage of this architecture is that it also allows for the direct AC power supply to an electric motor in an electrified vehicle, without the need for an external DC / AC converter. This type of architecture is applicable to all types of electromobility applications (e.g., motor vehicles, bicycles, trains, trucks, scooters, or even off-road vehicles such as aircraft or ships). In another stationary application, the battery can be connected directly to a three-phase network, for example, for grid compensation or to equip a renewable energy network.

[0010]

[0009] This architecture has been the subject of several patent applications. Examples include documents W0-A1-2017 / 153366, W0-A1-2021 / 048477, and W0-A1-2022 / 214745. They describe a polyphase electrical system comprising current lines formed by storage devices, each consisting of an electrochemical cell, or a cluster of cells, and a switching circuit forming an H-bridge. The storage devices are connected in series via the switching circuit to form the multilevel inverter structure integrated into the battery. This H-bridge arrangement improves electrical efficiency.

[0011]

[0010] There is a need to address the aforementioned problems in order to respond to the issue of fast charging operating at direct current voltage.

[0012]

[0011] The invention provides an optimized DC charging method for a battery with a distributed multilevel inverter. One objective is to maximize the DC charging power. Another objective of the invention is to provide a charging solution compatible with different voltage types. A further objective is to protect the electrochemical elements and power electronics against overcurrents when electrochemical modules are connected in parallel.

[0013]

[0012] More specifically, the invention relates to a method for controlling a polyphase electrical system for a DC voltage load comprising a power battery and a set of power contactors adapted to connect the battery to a charging interface intended to operate at DC voltage and intended to be connected to an external power source, the battery having at least three current lines in which each line has a plurality of electrochemical modules connected in series, each equipped with a cell or cluster of cells and a switching module comprising an H-bridge, forming a multilevel inverter distributed in the battery capable of generating a selected voltage waveform across each line.

[0014]

[0013] According to the invention, the process comprises the following steps:

[0015]

[0014] - the control of the electrochemical modules so as to generate a DC voltage wave across the terminals of each line from a controlled selection of said modules connected in series,

[0016]

[0015] - the configuration of all the power contactors so as to connect said three lines in parallel for a connection to the load interface,

[0017]

[0016] - the parallel charging of said three lines in direct voltage by the source.

[0018]

[0017] The method according to the invention may include the following additional features, alone or in combination:

[0019]

[0018] - A balancing step in the state of charge of at least one line with respect to another line among said three lines.

[0020]

[0019] - Load balancing comprises the following successive steps: determining the voltage across each line to identify a first current line with the lowest voltage; loading the first line solely from the source until the voltage of the first line reaches the voltage of a second line among the two remaining lines; and loading the first and second lines solely from the source until the voltages of the first and second lines reach the voltage of the third line.

[0020] - Load balancing further comprises a step of monitoring the maximum current of each line and a step of limiting the maximum current to a predetermined limit value.

[0021]

[0021] - A command to switch the electrochemical modules of at least one line among said three lines during the generation of the DC voltage wave to balance the state of charge of said electrochemical modules of the line.

[0022]

[0022] - A charging phase of said three lines configured in series comprising the following steps of configuring all the power contactors so as to connect said three lines in series for connection to the source and of simultaneously charging said three lines in series with DC voltage from the source.

[0023]

[0023] The invention provides for a polyphase electrical system comprising a power battery and a set of power contactors adapted to connect the battery to a charging interface intended to operate at direct voltage and intended to be connected to an external power source, the battery having three current lines in which each line has a plurality of electrochemical modules connected in series, each equipped 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 selected voltage waveform across the terminals of each current line, the set of contactors being arranged to connect said three lines in parallel to the charging interface.

[0024]

[0024] According to the invention, the system comprises a control unit configured for the implementation of the control method according to any one of the embodiments described above.

[0025]

[0025] According to one variant, the contactor assembly is arranged to connect each line of said three lines individually to a terminal of the charging interface to operate the charging phase in parallel.

[0026]

[0026] According to one variant, the contactor assembly is arranged to connect only one of said three lines to a terminal of the charging interface and to connect the other two lines in parallel to said line to operate the parallel charging phase.

[0027] The invention provides for an electrified vehicle comprising an electrical system according to any one of the preceding embodiments.

[0027]

[0028] The invention provides for a stationary energy system comprising an electrical system according to any one of the preceding embodiments.

[0028]

[0029] A control unit is provided comprising means specifically configured to implement the method of controlling a polyphase electrical system for a DC voltage load according to the invention.

[0029]

[0030] A computer program is planned comprising instructions which, when the program is executed by a control unit, lead the latter to implement any one of the embodiments of the control method of a polyphase electrical system for a DC voltage load according to the invention.

[0030]

[0031] It is further provided a computer-readable recording medium comprising instructions which, when executed by a computer, lead the computer to implement the method of controlling a polyphase electrical system for a DC voltage load according to the invention.

[0031]

[0032] The process optimizes DC charging power by connecting the three battery current lines in parallel.

[0032]

[0033] Other features and advantages of the present invention will become more apparent upon reading the following detailed description, which includes embodiments of the invention given by way of non-limiting examples and illustrated by the accompanying drawings, in which:

[0033]

[0034] [Fig.1] schematically represents a first embodiment of a polyphase electrical system according to the invention.

[0034]

[0035] [Fig.2] schematically represents a battery with a distributed multilevel inverter architecture.

[0035]

[0036] [Fig.3A] schematically represents a second embodiment of a polyphase electrical system according to the invention.

[0036]

[0037] [Fig.3B] schematically represents a third embodiment of a polyphase electrical system according to the invention.

[0038] [Fig.4] represents a block diagram of a first embodiment of the method for controlling the electrical system according to the invention.

[0037]

[0039] [Fig.5] represents graphs of a fast charging simulation in parallel configuration.

[0038]

[0040] [Fig.6] represents a block diagram of a second embodiment of the method for controlling the electrical system according to the invention.

[0039]

[0041] [Fig.7] represents an electrical architecture for an electrified vehicle comprising the system according to the invention.

[0040]

[0042] The invention applies to electrified vehicles comprising an electric drivetrain powered, at least partially, by an electric machine, i.e., with a fully electric or hybrid motor, preferably motor vehicles, but not exclusively, such as aircraft, trucks, tractors, bicycles, and ships. The invention also finds application in stationary energy storage systems, for example, for grid regulation. The field of application relates more specifically to DC fast charging solutions for power levels ranging from several hundred kilowatts to several gigawatts.

[0041]

[0043] Figure 1 schematically represents a polyphase electrical system 1 according to the invention, comprising a power battery 2 with three current lines LT1, LT2, and LT3, in which each line comprises a plurality of electrochemical modules connected in series, each equipped with a cell or cluster of cells and a switching module comprising an H-bridge, forming a multilevel inverter distributed throughout the battery 2 capable of generating a selected voltage waveform across each line LT1, LT2, and LT3. A detailed description of the battery architecture will be provided later. The three current lines LT1, LT2, and LT3 are electrically connected to three phase branches 6, 7, and 8 of the electrical system 1, respectively, by first terminals, and to a neutral terminal N of the electrical system 1 by second terminals at the other end of the lines LT1, LT2, and LT3.

[0042]

[0044] The electrical system 1 further comprises a set of power contactors K1 to K8, also referred to as relays or power switches. The contactors can be operated in both the closed and open positions. Contactors K1, K2, K3, K4, and K5 are arranged to connect the battery 2 to a charging interface 3, which is intended to be connected to an external power source designed to operate at a direct current voltage, in high-voltage ranges such as 400 volts, 800 volts, or 1200 volts. The external power source is, for example, a fast-charging station equipped with a charging cable that can be connected to interface 3.

[0043]

[0045] More specifically, the charging interface 3 has two terminals. The first terminal is electrically connected to the phase branch 6 via contactor K1. The second terminal is connected to the neutral terminal N of the electrical system via contactor K2. In addition, interface 3 has a socket adapted for use with a DC charging cable. The charging interface, for example, conforms to CCS (Combined Charging System) and CHAdeMO standards based on the international standards IEC 61851-1 and IEC 61851-23. It can also conform to an MCS (Megawatt Charging System) connector.In addition to the power circuit lines, the charging interface 3 includes communication and detection signal lines adapted to implement the communication intended to operate DC voltage charging, in particular to communicate the voltage level used and a charging current setpoint.

[0044]

[0046] The electrical system 1 also includes an interface 4 for supplying a DC voltage bus, for example, 400 volts or 800 volts. Power electronics systems are connected to the bus, for example, a DC / DC voltage converter, a compressor, or refrigeration equipment. The voltage bus can also be configured to supply a DC / DC power converter, for example, to supply a low-voltage network operating at 12 volts.

[0045]

[0047] Furthermore, the electrical system 1 includes an interface 5 designed for supplying power to an electrical machine. The term "electrical machine" generally refers to any electrical machine, whether direct current or alternating current, preferably with a polyphase stator, of the permanent magnet synchronous or asynchronous type. An electrical machine can be used to generate torque for a traction system or to produce electrical power. Examples include, but are not limited to, an electric traction machine for an electrified vehicle, an alternator, or a starter-alternator. In this example, the electrical machine is three-phase, and the three phase lines of interface 5 are connected to the LT1, LT2, and LT3 lines of battery 2, respectively.

[0046]

[0048] An additional branch (not shown in Figure 1) is provided for phase branches 6, 7, and 8 to connect each LT1, LT2, and LT3 line of battery 2 to a phase branch of an external power distribution network operating at alternating current, either 110 volts or 230 volts at frequencies of 50 Hz or 60 Hz. This additional branch is suitable for charging battery 2 with alternating current. Optionally, the same connection socket can be shared with the charging interface 3.

[0047]

[0049] In this embodiment, the contactor assembly includes a contactor K3 electrically connecting the first terminal of line LT1 to the first terminal of line LT2, and a second contactor K4 electrically connecting the first terminal of line LT2 to the first terminal of line LT3. Contactors K3 and K4 are adapted to connect the three battery lines LT1, LT2, and LT3 in parallel when contactors K3, K4, and one contactor K5 are closed. K5 electrically connects the second terminal of line LT2 to the second terminal of line LT3. Only line LT1 is connected to the charging interface 3. Note that the three lines can be connected in series to interface 3 when contactors K3 and K5 are open and contactor K4 is closed.

[0048]

[0050] The contactor assembly also includes contactors K6, K7 and K8 electrically connected respectively to a phase branch of interface 5 and to a phase branch 6, 7 and 8 of electrical system 1. These contactors have the function of connecting and disconnecting the electrical machine from the phase branches.

[0049]

[0051] Figure 2 shows a detailed diagram of the LT1 current line of battery 2 with a distributed multilevel inverter. The two other current lines, LT2 and LT3, not shown for simplicity in the description, are identically constructed to line LT1. The term "distributed multilevel inverter" means that each current line of battery 2 is formed by a plurality of electrochemical modules MCLk connected in series by two connection terminals S1 and S2. Each electrochemical module MCLk comprises a cell CLk or a cluster of cells, as well as a switching module COMk forming an H-bridge. Battery 2 includes the control unit 21, which has a means for controlling the electrochemical modules of each current line LT1, LT2, and LT3 according to a reference setpoint and is capable of generating a chosen AC and DC voltage waveform on each current line.

[0050]

[0052] It is worth recalling that a cell is an electrochemical storage device with two electrical connection terminals and a voltage of a few volts, most often between 2.3V and 4.2V. Cells can be of the lithium-ion type (lithiumized nickel manganese cobalt oxide (NMC) or lithium iron phosphate (LFP) are examples of active materials for the positive electrode), nickel cadmium (Ni-Cd), nickel metal hydride (Ni-MH), or sodium-ion, for example. More specifically, a lithium-ion cell is primarily composed 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.

[0051]

[0053] Battery 2 can present a maximum voltage of several hundred volts across each line, for example, approximately 400 volts, 600 volts, 800 volts, or more. In a non-limiting embodiment, for a voltage of 400 volts, each line LT1, LT2, LT3 consists of 96 cells, which can be distributed into 16 electrochemical modules, each comprising a cluster of 6 cells connected in series within the cluster. More generally, each electrochemical module MCLk can comprise a single cell CLk, or a cluster of CLk cells of two, three, four, five, six, or more, forming an elementary voltage Vclk.

[0052]

[0054] However, depending on the electrical requirements, other voltage levels are configurable and will be determined by the number of cells and the number of electrochemical modules connected in a line. Battery 2 can have a nominal voltage of only a few tens of volts (24V, 36V, 48V for example), particularly for automotive applications, several hundred volts for the needs of electric traction and on-board power equipment, or even higher, particularly for stationary storage systems.

[0053]

[0055] Furthermore, the control unit 21 has the function of controlling the voltage waveform of each line LT1, LT2, LT3 according to a reference setpoint Vref from the electrochemical modules MCLk. The switching module COMk is capable of configuring the electrochemical module MCLk in three different states to deliver the voltage Vmclk, which is respectively the said elementary voltage Vclk, a zero voltage, and the inverted voltage Vclk at the said connection terminals of the MCLk module.

[0054]

[0056] The COMk switching module, for example, consists of two switching sections forming an H-bridge that can be controlled in three different states by a control signal from the battery 2 control unit 21, specifically addressing the MCLk module. These states are represented by a control variable uik, which can take, for example, the values ​​1, 0, and -1, representing the three different states that respectively control the elementary voltage Vclk, a zero voltage, and the inverted voltage -Vclk at the connection terminals of the electrochemical module k addressed by the control signal uik. Each COMk switching module includes electronic components, such as power transistors, possibly of the MOSFET or HEMT (High Electron Mobility Transistor) type, driven by the control signals from the control unit 21.Thus, the voltage Vmclk across each electrochemical module MCLk among a set n of modules can be controlled according to a control signal uik according to the following relationship:.

[0055]

[0058] Thus, the control unit 21 can control, on each voltage line LT1, LT2, and LT3, any voltage waveform formed in amplitude steps equal to the elementary voltage Vclk, according to a reference voltage setpoint Vref, by connecting the cells in series via the switching modules COMk. The reference voltage setpoint Vref can be a sinusoidal waveform with a frequency of 50 Hz, any alternating waveform, for example a square wave, or a constant voltage, particularly used in a DC voltage charging operation.

[0056]

[0059] Optionally, each MCLk electrochemical module may include a CCK bypass circuit adapted to implement a redundant bypass function constituting a fourth bypass state. The CCK circuit comprises two power MOSFETs mounted back-to-back in a common-source configuration, electrically connected to the two connection terminals S1 and S2 of the electrochemical module, respectively, to ensure that the CCLk bypass circuit is open regardless of the sign of the voltage across its terminals.

[0057]

[0060] In addition, the battery 2 includes sensors 22, 23 and 24 coupled respectively to the lines LT1, LT2 and LT3 so that the control unit 21 is able to determine the voltage across each current line LT1, LT2 and LT3, as well as the current of each line.

[0058]

[0061] It should be noted that battery 2 is capable of delivering a 400-volt load voltage when lines LT1, LT2, and LT3 are connected in parallel or in series and when the electrochemical modules of each line are driven to generate said maximum 400-volt voltage. Furthermore, battery 2 is capable of delivering a compatible 800-volt load voltage when lines LT1, LT2, and LT3 are connected in series and when the electrochemical modules of each line are driven to generate said maximum 800-volt voltage.

[0059]

[0062] To this end, the control unit 21 is capable of controlling the set of contactors in order to manage the connection configurations of the LT1, LT2, and LT3 power lines in series or parallel to charge the battery 2 using a desired voltage level. The control unit 21 is adapted to cooperate with other systems interacting with the electrical system 1, for example, an external charging station or a vehicle supervisor. The control unit 21 is capable of receiving the information necessary for initiating the electrical charging of the battery, including the charging voltage and a charging setpoint.

[0060]

[0063] Furthermore, the control unit 21 of battery 2 is capable of implementing a function for balancing the state of charge of the electrochemical modules MCLk of each line LT1, LT2, LT3. This function takes as input measurements or estimates of the state of charge of each module MCLk and performs a periodic permutation of the modules participating in the generation of the voltage waves based on a state of charge criterion. When the number of electrochemical modules selected to generate the voltage wave is less than the quantity available in a line, the permutation principle consists of selecting a rotating set from the available quantity according to a predetermined rotation cycle. The permutation thus ensures the balancing of the state of charge of the modules.

[0061]

[0064] Furthermore, the control unit 21 of battery 2 is capable of implementing a current limiting function for each line LT1, LT2, LT3. This function provides electrical protection in the event that the current intensity exceeds a protection threshold. This protection threshold may be higher than the maximum current setting.

[0062]

[0065] Figure 3A shows a second embodiment of the electrical system 1. The reference numerals from Figure 1 are retained to designate the same elements and are not described again. This second embodiment is distinguished by the arrangement of all the contactors K1 to K10. The contactor K3 of the first embodiment is absent, and contactors K9 and K10 are added. The first terminal of the load interface 3 is electrically connected to the phase branch 7 via contactor K9, and the first terminal of interface 3 is electrically connected to the phase branch 8 via contactor K10. This variant of the contactor arrangement has the advantage that each line can be individually connected to the terminal of the load interface 3 to operate the charging phase in parallel.This alternative arrangement allows for a preliminary line balancing phase during a DC voltage charging operation. This phase will be described in more detail later in the description.

[0063]

[0066] Furthermore, the electrical system 1 also includes a diode module 9 comprising three diodes. A first diode d1 connects the first terminal of the first line LT1 to one polarity of the DC voltage bus of interface 4, a second diode d2 connects the first terminal of the second line LT2 to said polarity of the DC voltage bus of interface 4, and a third diode d3 connects the first terminal of the third voltage line LT3 to said polarity of the DC voltage bus of interface 4. The diode module 9 allows the supply of a DC voltage regardless of which current line is loaded.

[0064]

[0067] It is further envisaged that the load balancing phase occurs naturally between the lines when they are connected in parallel, always under the control of the current limiting function.

[0068] Figure 3B shows a third embodiment of the electrical system 1. The reference numerals from Figure 3A are retained to designate the same elements and are not described again. This third embodiment differs from the second embodiment described in Figure 3A by the arrangement of all the contactors K1 to K10. Contactors K4 and K5, whose main function is to connect the lines in series, are absent. Contactor K5 is replaced by a permanent electrical connection. In this variant, only the fast charging mode in parallel configuration is implemented.

[0065]

[0069] Figures 4 and 6 schematically represent block diagrams of embodiments of the control method for the polyphase electrical system according to the invention, the function of which is to charge the power battery in parallel configuration. The method is implemented by the battery control unit. The control unit is equipped with an integrated circuit computer and electronic memory, the computer and memory being configured to execute the control method. However, this is not mandatory. The computer can be configured as a dedicated computer including optional dedicated software, for example. Consequently, the control unit, according to the invention, can be implemented in the form of software modules, electronic circuits, or hardware, or a combination of electronic circuits and software modules.

[0066]

[0070] In Figure 4, a first embodiment of the control method can be implemented by the three embodiments described in Figure 1, Figure 3A, and Figure 3B for charging in a parallel configuration. In the example described below, the implementation uses the electrical system described in Figure 1.

[0067]

[0071] According to this first embodiment, the method includes an initial step E40 for triggering a fast charging operation. This event corresponds to the connection of a charging cable to the charging interface of the electrical system. The information exchange steps between the battery and the power source to initiate charging are implemented. These steps are known to those skilled in the art and conform to standard charging protocols.

[0068]

[0072] The method further includes a control step E41 of the electrochemical modules so as to generate a DC voltage wave across each line from a controlled selection of said modules connected in series. This step aims to configure the battery voltage to a voltage compatible with the external charging terminal. The voltage value of each line is determined by the number of modules connected in series and is communicated to the terminal prior to initiating charging so that it delivers a compatible voltage.

[0069]

[0073] The method then includes configuring all the power contactors E42 so as to connect said three lines in parallel for connection to the load interface. Contactors K3, K4, and K5 are closed. Then contactors K1 and K2 are closed to allow energy transfer between the battery and the external source. Contactors K6, K7, and K8 are opened to isolate the electrical machine.

[0070]

[0074] The method then includes a charging step E43 in parallel of said three DC voltage lines via the external charging terminal. The three current lines are traversed by a charging current simultaneously.

[0071]

[0075] An example of a model for the charging power obtained at a 400-volt voltage is described in this paragraph. For cells with a capacity of 60 ampere-hours, a maximum charging current of 120 amperes, i.e., a charge rate of 2C, and for 100 cells per current line, the charging power at a low state of charge (between 5 and 20%) reaches 118 kW, and the charging power at approximately 80% state of charge reaches approximately 150 kW. This result shows that parallel charging makes it possible to achieve a higher charging power compared to series charging, for a voltage of 950 volts permitted by current fast charging stations at a current of 120 amperes. Indeed, the power would be limited to approximately 114 kW. The parallel configuration of the current lines has the advantage of increasing the number of cells that can be charged simultaneously.

[0072]

[0076] Furthermore, at the start of this charging process, if the battery's current lines exhibit an imbalance in their state of charge, an initial balancing phase occurs, resulting from a higher charging current in the line with the lower state of charge. The current difference between the lines depends on the difference in open-circuit voltage and the line resistance. This balancing is considered natural because it does not actively involve a specific current control for the charging operation. However, charging step 43 is carried out under the control of the current limiting function to prevent any overcurrent delivered by the charging terminal.

[0077] Charging step 43 is operated according to a protocol comprising a constant current charging phase, followed by a final DC voltage charging phase, also referred to as the CC-CV protocol for "Constant Current - Constant Voltage".Other charging protocols are conceivable without departing from the scope of the invention.

[0073]

[0078] Once the target charge state is reached, the charging operation is finalized at step E44.

[0074]

[0079] Figure 5 shows a load simulation describing a line balancing phase at the start of charging. This simulation corresponds to a rapid charge at 400 volts DC. The configuration consists of three parallel current lines, each made up of 96 Li-ion cells.

[0075]

[0080] The charging procedure is a CC-CV protocol operating over a duration represented on the x-axis for a duration t of approximately 1200 seconds. The graph in the upper left shows the current curves of the three battery lines. The graph in the upper right shows the voltage of the battery lines. The graph in the lower left shows the state of charge of the lines exhibiting an initial imbalance, with respective state charges of 5%, 10%, and 20%. Finally, the graph in the lower right shows the charging power.

[0076]

[0081] A high current is observed in the branch with the lowest state of charge: between 125A and 130A for a specified maximum current of 120A. The maximum voltage, reached from 80% SOC, is 393.6V, corresponding to the 96 cells multiplied by 4.1V. The maximum power reached at an 80% SOC is approximately 142kW, corresponding to 3 x 120A x 393.6V. Between 0 and 80% SOC, the power is between 125 and 142kW.

[0077]

[0082] The observed overcurrent is not critical for the cells and ensures rebalancing of the lines. However, it is envisaged that the current limiting function could intervene to prevent this overcurrent at startup.

[0078]

[0083] Furthermore, during the closing of the contactors, a current exchange may occur between the lines due to a voltage imbalance in the lines. This current will be stronger the greater the voltage imbalance, and its intensity is related to the relatively low resistance of each current line.

[0084] In Figure 6, a second embodiment of the control method is implemented by the second or third architecture of the electrical system 1 described in Figure 3A and Figure 3B for charging in a parallel configuration. Unlike the first mode, it includes a line balancing phase in controlled mode.

[0079]

[0085] More specifically, the method includes an initial step E50 for triggering a fast charging operation. This event corresponds to the connection of a charging cable to the electrical system's charging interface. The information exchange steps between the battery and the power source to initiate charging are implemented. These steps are known to those skilled in the art and conform to standard charging protocols.

[0080]

[0086] The method further comprises a control step E51 of the electrochemical modules so as to generate a DC voltage wave across each line from a controlled selection of said modules connected in series. This step aims to configure the battery voltage to a voltage compatible with the external charging terminal. The voltage value of each line is determined by the number of modules connected in series.

[0081]

[0087] The method then includes a controlled balancing phase E52 of the battery current lines in case a voltage difference is detected between the lines. The voltage difference may result from a difference in state of charge for the same number of connected electrochemical modules. If the control unit does not detect an imbalance, the method directly controls the charging step E53 in parallel configuration of the three current lines.

[0082]

[0088] More specifically, during the controlled balancing phase E52, the method includes, in a step E520, determining the voltage of each current line to identify a first current line with the lowest voltage. In this step, the method further includes communicating the value of the lowest voltage to the terminal so that it delivers a voltage set at the voltage of this first current line.

[0083]

[0089] The method then includes a charging step E521 of the first line only through the terminal until the voltage of the first line reaches the voltage of a second line among the two remaining lines. With reference to Figures 3A and 3B, the contactor of the line with the lowest voltage is closed: K1 for line LT1, K9 for line LT2, and K10 for line LT3. Contactor K2 is also closed.

[0084]

[0090] Next, the method includes a charging step E522 of the first and second lines solely from the source until the voltages of the first and second lines reach the voltage of the third line. The contactor of the second line is then closed. At the end of this step, the three current lines are voltage-balanced, and the method controls the charging step of the three current lines in parallel configuration.

[0085]

[0091] The method comprises the configuration E53 of all the power contactors so as to close the third contactor connecting the battery to the charging interface to connect said three lines in parallel, and then, finally, the charge E54 in parallel of said three lines with direct current from the source. The charge is therefore carried out at the maximum power allowed by connecting the three current lines in parallel. The charge is carried out according to the CC-CV protocol. Other protocols are conceivable without departing from the scope of the invention. Finally, once the target state of charge is reached, the charging operation is completed in step E55.

[0086]

[0092] Finally, both embodiments of DC battery charging may include a balancing phase, either executed naturally upon activation of the parallel charging, corresponding to step E43 of the first embodiment, or executed in a controlled manner prior to the parallel charging, corresponding to step E52 of the second embodiment. However, it is understood that the balancing phase is not mandatory, particularly in a situation where the lines are not unbalanced.

[0087]

[0093] To enhance electrical protection when connecting lines in parallel, the method includes a step of monitoring the maximum current of each line and a step of limiting the maximum current to a predetermined limit value. This limitation aims to improve protection in the event of current transfer from one line to another that could add to the load current supplied by the external source.

[0088]

[0094] Furthermore, the electrical system provides a control method comprising a charging phase for said three lines configured in series, including the following steps: configuring all the power contactors so as to connect said three lines in series for connection to the charging terminal, and then simultaneously charging said three lines in series with direct current via the terminal. The series charging mode is suitable, for example, if the battery has current lines where the maximum voltage of each line reaches 400 volts and if the charging terminal is compatible with an 800-volt mode.

[0089]

[0095] If the terminal is adapted to deliver a voltage of type 400 volts and 800 volts, the control method may provide for switching from a charging mode in parallel configuration to a mode in series configuration, or vice versa.

[0090]

[0096] Regardless of the charging mode in parallel or series configuration, the control method may include a balancing control of the electrochemical modules of the same current line by permuting the modules of the selection participating in the generation of the voltage wave.

[0091]

[0097] The invention provides a method for controlling the discharge of a DC battery to an external load connected to the charging interface or to an extended distribution network. The discharge is operable by the first, second, and third embodiments of the architecture described in Figure 1, Figure 3A, and Figure 3B, respectively. The discharge is operable in a configurable parallel configuration of the current lines or in a series configuration of the current lines.

[0092]

[0098] Furthermore, if a balancing phase is required before triggering the discharge in parallel configuration, the discharge will first be carried out using only the current line with the highest voltage, until it reaches the voltage of a second line. Then, a discharge will be carried out using the two current lines with their voltages aligned, and finally, the discharge will be performed using all three parallel lines simultaneously once the three current lines are balanced. This discharge mode is implemented by the architecture described in Figure 3A or Figure 3B.

[0093]

[0099] Figure 7 shows an embodiment of the electrical system for an electrified vehicle comprising at least partially electrified traction. The vehicle includes an electric drive machine 64 capable of transmitting torque to the drive wheels 62 of the vehicle via a transmission 61. The electric drive machine 64 may be three-phase. The vehicle includes an electrical system comprising the battery 60 according to the multilevel inverter architecture distributed within the battery as described in Figure 1 and Figure 2. The battery has three current lines capable of generating alternating and direct current voltage waves. The vehicle further includes a battery charging interface 68 for charging from an external power source operating at direct voltage. The charging interface 68 is a charging unit that electrically connects the terminals of the battery 60 to the external source for charging at direct voltage.Alternatively, the charging interface 68 can also be adapted for single-phase or three-phase alternating current. The battery system 60 is advantageous in that its control unit 65 is configured to control the fast charging process according to the invention in parallel or series configuration. It is further configured to control a discharge process to an external load or an external DC distribution network according to the invention. The charging interface can therefore operate in bidirectional mode.

[0094]

[0100] The vehicle further comprises a supervisory system 66 cooperating with the control unit 65 of the battery system 60. The battery system 60 can be directly connected electrically to the electric drive machine 64, thus improving its energy efficiency in traction.

[0095]

[0101] The battery can further be connected to a DC voltage bus to which one or more high-voltage power devices 63 can be connected, for example operating at a nominal voltage between 100 and 800 volts, for example 450 volts, and to a low-voltage on-board network 67 operating at a nominal voltage of the 12-volt type. In addition, the power electronics 69 includes a DC / DC converter connecting the voltage bus to the on-board network 67 (450 volts / 12 volts) which includes a service battery.

[0096]

[0102] The method according to the invention optimizes charging power by controlling a parallel configuration of the battery's current lines. This configuration offers superior performance in terms of power and charging time compared to a series configuration of the three lines. Furthermore, it is understood that the voltage and cell count values ​​described earlier in the description for common 400-volt or 950-volt fast-charging solutions on the market are in no way limiting to the invention. The architectures of the polyphase electrical system and the control method according to the invention can be adapted for power solutions exceeding one megawatt, particularly those designed to operate at voltages of approximately 1200 volts and currents of 3000 amperes in fast-charging applications for freight vehicles.

[0097]

[0103] The invention is described above by way of example. It is understood that a person skilled in the art is able to carry out different variant embodiments of the invention by combining, for example, the different features above taken alone or in combination, without departing from the scope of the invention.

Claims

DEMANDS 1. A method for controlling a polyphase electrical system for a DC voltage load comprising a power battery (2) and a set of power contactors (K1-K10) adapted to connect the battery to a load interface (3) intended to operate at DC voltage and to be connected to an external power source, the battery (2) having at least three current lines (LT1, LT2, LT3) in which each line has a plurality of electrochemical modules (MCLk) connected in series, each equipped 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 (2) capable of generating a selected voltage waveform across each line (LT1, LT2, LT3), the method being characterized in that it comprises the following steps: - the control (E41; E51) of the electrochemical modules so as to generate a DC voltage wave across each line from a controlled selection of said modules connected in series, - the configuration (E42; E53) of all the power contactors (K1 - K10) so as to connect said three lines in parallel for a connection to the load interface (3), - the load (E43; E54) in parallel with the said three lines in direct voltage by the source.

2. Method according to claim 1 further comprising a balancing step (E43; E52) in charge state of at least one line with respect to another line among said three lines (LT1, LT2, LT3).

3. A method according to claim 2 in which the balancing (E52) under load comprises the following successive steps: - the determination (E520) of the voltage across each line (LT1, LT2, LT3) to identify a first current line with the lowest voltage, - the load (E521) of the first line only by the source until the voltage of the first line reaches the voltage of a second line among the two remaining lines, - the load (E422) of the first and second lines only by the source until the voltages of the first and second lines reach the voltage of the third line.

4. Method according to claim 2 or 3 wherein the balancing (E43; E52) in the state of charge further comprises a step of monitoring the maximum current of each line (LT1, LT2, LT3) and a step of limiting the maximum current to a predetermined limit value.

5. Method according to any one of claims 1 to 4 further comprising a control for switching the electrochemical modules of at least one line among said three lines (LT1, LT2, LT3) during the generation of the DC voltage wave to balance the state of charge of said electrochemical modules (MCLk) of the line.

6. A method according to any one of claims 1 to 5 further comprising a charging phase of said three lines (LT1, LT2, LT3) configured in series, comprising the following steps: - the configuration of all power contactors (K1-K10) so as to connect said three lines in series for connection to the source, - the series loading of the said three lines (LT1, LT2, LT3) simultaneously with direct voltage from the source.

7. A polyphase electrical system (1) comprising a power battery (2) and a set of power contactors (K1-K10) adapted to connect the battery (2) to a load interface (3) designed to operate at direct current and intended to be connected to an external power source, the battery having three current lines (LT1, LT2, LT3) in which each line has a plurality of electrochemical modules (MCLk) connected in series, each equipped with a cell (CLk) or a cluster of cells and a switching module (COMk) comprising an H-bridge, forming a multilevel inverter distributed throughout the battery (BAT) capable of generating a selected voltage waveform across each current line (LT1, LT2, LT3), the set of contactors (K1-K10) being arranged to connect said three lines in parallel to the load interface (3), the system being characterized in this that it includes a control unit (21) configured for the implementation of the control method according to any one of claims 1 to 6.

8. System according to claim 7 in which the set of contactors (K1-K10) is arranged to connect each line of said three lines (LT1, LT2, LT3) individually to a terminal of the load interface (3) to operate the charging phase in parallel.

9. System (1) according to claim 7 in which the set of contactors is arranged to connect a single line among said three lines (LT1, LT2, LT3) to a terminal of the charging interface and to connect the other two lines in parallel to said line to operate the parallel charging phase.

10. Electrified vehicle comprising an electrical system (1) according to any one of claims 7 to 9.

11. Stationary power system comprising an electrical system (1) according to any one of claims 7 to 9.

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