A battery control method capable of controlling uniform current on battery cells in a current line

Abstract

The object of the present invention is to provide a control method for controlling a battery with integrated inverters, said battery comprising n elementary battery cell modules (MEk) delivering an elementary voltage Vcell, said n elementary battery cell modules being able to impose a uniform current on the combination of said battery cells. More precisely, said method comprises a regulation step for regulating the control signals (uik) of said elementary modules (MEk) so as to provide said voltage waveform (VM1) on the basis of a selection of a set of q elementary modules (MEk) made according to a reference voltage setpoint Vref, with Vref = qVcell, determining an arrangement of n elementary modules, the arrangement of said n plurality being processed according to a cyclic permutation of the positions of said elementary modules (MEk) so as to make each elementary module (MEk) of said n plurality participate in the implementation of said voltage waveform during an equal duration for each module. The invention applies to the field of electric vehicles and to the field of station-type energy storage.

Description

TECHNICAL FIELD

[0001] The present application claims priority from French application 1909868 filed on September 9, 2019, the content of which (text, drawings and claims) is hereby incorporated by reference.

[0002] The field of the present application relates to a control method for controlling electrochemical cells, said control method being able to balance the state of charge of a plurality of electrical cellules for electric vehicle and stationary energy storage applications. The present application does not exclusively apply to Li-ion. BACKGROUND

[0003] Nowadays, electrochemical cellules of lithium-ion technology are particularly suitable for electrical traction powertrains, as these electrochemical cellules have an advantageous energy density and kilowatt-hour cost ratio. As is known, the plurality of energy cellules that make up a battery have different self-discharge speeds, which leads to a natural deviation between these energy cellules. This is a slow phenomenon that, if not compensated, can limit the usable capacity of said battery over time. To correct this phenomenon, known operations aim at a balancing mechanism that aligns all the cellules of said battery at the same state of charge level. However, when said cellules are connected in series in order to increase the voltage of said battery, the same charging or discharging current passes through the combination of said cellules, which makes it impossible to adjust the state of charge of each cellule individually.

[0004] For these architectural cases, some specific balancing mechanisms are known to the person skilled in the art. A first balancing technique, the so-called passive balancing technique, aims at discharging the most charged cellules by temporarily connecting a resistor to the terminals of these cellules. This technique has several drawbacks. It leads to a loss of energy carried in said battery by the thermal dissipation in the balancing resistor. The balancing current is usually limited to low values (a few tens or even hundreds of milliamps) to avoid overheating of said resistor, which thus increases the balancing duration when said battery is very unbalanced. A second balancing technique, the so-called active balancing technique, aims at transferring the energy of the most charged cellules towards the least charged cellules by regulating the charge transfer current between said cellules. These balancing currents have values slightly greater than the passive solution and are of the order of a few amperes. The advantage of this technique is that it aims at preserving energy, however the cost of this technique is much greater than the passive balancing technique, as this active technique requires power electronics dedicated to operating the energy transfer (transformer, buffer capacitor). Furthermore, despite this, the implementation of the active technique has non-negligible transfer losses due to an energy efficiency of the order of 50% to 80%. Due to the much lower cost of the passive system, automobile manufacturers will generally choose this passive system.

[0005] In traditional battery modules (also known in English as "packs"), all the battery cells are connected in series and in parallel to form a high-voltage battery. This battery module is electrically connected to an external converter of the inverter type to deliver the sought voltage to the electric traction machine.

[0006] It is also known from the prior art that documents WO2012117110A2 and WO2014145756A1 describe a battery module architecture with integrated power control devices, comprising battery cell modules electrically connected in series and in parallel, and a management strategy for managing the battery that is able to balance the battery cells in the charging and discharging phases.

[0007] In addition, the patent applications WO2018193173A1 and WO2018154206A1 recently filed by the present applicant relate to an alternative battery architecture, the innovation of which lies in providing a control architecture integrated into the inverter that is in the high-voltage battery module itself, in which each electric battery cell presents a nominal base voltage between 2 V and 4 V at its own terminals (approximately 2.2 V, or 3.3 V to 3.7 V depending on the chosen technology, for example NMC / LTO or NMC / Graphite), and is associated with a monolithic power structure that is able to regulate the battery cell individually to provide a line output voltage equal to the base voltage generated by an amplitude step. The control principle of this battery architecture consists, at each instant, in connecting in series a number of q battery cells among a total of n battery cells to the current line, where q is a ratio between the reference voltage set value and the base voltage of the battery cell.

[0008] This architecture has the following, non-exhaustive, advantages. This architecture is promising in terms of performance and autonomy and is able to directly connect the battery module to the network, single-phase and three-phase, without the need to resort to an external inverter. This architecture is able to individually connect or bypass / circumvent (i.e. disconnect and add shunts) the battery cells in order to disconnect a defective battery cell when needed, without having to replace the entire battery module. The integrated control structure allows full-wave control, which causes less degradation in the windings of the electric machine, reduces common-mode currents, and eliminates current leakage that is usually present in traditional architectures. In the case of a motor vehicle, this architecture authorizes degraded operation without stopping the vehicle, and improves the recycling management or secondary management of the battery cells, since it is possible to know the state of health of each battery cell. In the application of a stationary energy store, it is possible to replace a defective battery cell without having to stop the operation of the station.

[0009] However, depending on the requested reference voltage, some battery cells of the system can be isolated during more or less long periods. This architecture thus tends naturally to unbalance the battery cells. In addition, some use cases of the motor vehicle, for example boarding a sidewalk, can require low voltage levels and strong current stresses at the same time. Thus, when implementing a reference voltage, most of the battery cells are bypassed. The battery cells can quickly become unbalanced over short periods. SUMMARY

[0010] The object of the present invention is to improve this latter battery architecture offered by the Applicant. More precisely, the object of the present invention is to prevent the unbalancing of the battery cells during the generation of the line voltage, more precisely, the object of the present invention is to provide a control method for guaranteeing the uniform charging and discharging of the battery cells. The object of the present invention is also to improve the control of the battery for electric vehicle applications and for stationary applications to readjust the balance of the battery cells at any operating instant of the battery in electrical charging and discharging when needed.

[0011] More precisely, the present invention relates to a control method for controlling a battery having a plurality of electrochemical battery cells, said control method being able to balance the average current passing through said electrochemical battery cells, said battery comprising at least one current line formed of n multiple basic battery cell modules connected in series, said at least one current line being able to deliver a voltage waveform, each basic module comprising two connection terminals, at least one battery cell delivering a basic voltage Vcell and a switching component able to regulate the basic module in the current line according to three different regulation states able to deliver respectively to said terminals said basic voltage Vcell, zero voltage and inverted voltage Vcell, in order to implement a voltage waveform, said method comprising a regulation step for regulating the control signals of said basic modules in order to provide said voltage waveform based on a selection of a set of q basic modules according to a reference voltage set value Vref, with Vref = qVcell. According to the invention, said method further comprises:

[0012] - determining a classification of n basic modules,

[0013] - processing the classification of said n multiple according to a circular permutation of the positions of said basic modules in order to make each basic module of said n multiple participate in the implementation of said voltage waveform.

[0014] According to a variant, the processing of the arrangement according to the cyclic permutation is performed in the case where it is also detected that the reference voltage setpoint Vref is less than a predetermined voltage threshold and in the case where it is simultaneously detected that the current setpoint of the current line is greater than a predetermined current threshold.

[0015] According to a variant, the cyclic permutation is performed with a permutation frequency greater than the frequency of the reference voltage setpoint.

[0016] According to a variant, the method further comprises determining the state of charge of each elementary module of the n plurality and determining the arrangement according to an order depending on the state of charge of each elementary module, and performing the processing of the arrangement according to the cyclic permutation only in the case where it is detected that each elementary module of the n plurality has a state of charge difference with respect to the other elementary modules less than a predetermined minimum threshold.

[0017] According to a variant, the method further comprises, in the case where it is detected that at least one elementary module of the n plurality has a state of charge difference with respect to the other elementary modules greater than a predetermined maximum threshold, stopping the processing of the arrangement according to the cyclic permutation.

[0018] According to a variant, the determination step for determining the arrangement is triggered according to a period whose value depends on the discharge and charge speed of the battery over a predetermined length of time.

[0019] According to a variant, the control method further comprises, in the case where it is detected that the remaining capacity of the battery is less than a predetermined minimum threshold, stopping the processing of the arrangement according to the cyclic permutation.

[0020] According to a variant of the method, in the case where it is detected that the processing of the arrangement according to the cyclic permutation is stopped, the regulation step aims to connect, in the case where a discharge line current is detected, the battery cells of a set of q elementary modules having the highest state of charge in the arrangement to the current line, and, in the case where a charge line current is detected, to connect the battery cells of a set of q elementary modules having the lowest state of charge in the arrangement to the current line.

[0021] According to a variant, the regulation step comprises the following substeps:

[0022] - when the current of the current line and the reference voltage setpoint Vref have the same sign, regulating the elementary modules so as to connect the battery cells of the elementary modules having a position nk between 1 and q to the current line,

[0023] - when the current of the current circuit and the reference voltage set value Vref have opposite signs, regulating the elementary modules so as to connect the battery cells of the elementary modules whose position nk is between n-q and n to the current circuit.

[0024] According to a variant, the determination of the state of charge of each elementary module is triggered at the switching instant for switching the regulation state of each elementary module, the determination aiming to estimate the variation of the state of charge of each module between the first switching instant and the second switching instant, based on the regulation state and the average current value of the current circuit of each module between the first switching instant and the second switching instant.

[0025] According to a variant, the method comprises a diagnostic step, for example for calibrating the state of charge values of the elementary modules and comprising the following sub-steps in succession:

[0026] - in the case where a diagnostic requirement is detected, assigning an exclusion position to the elementary module in the round so as to exclude the elementary module from the set of q modules during a predetermined exclusion duration,

[0027] - performing a diagnostic of the elementary module during the exclusion duration.

[0028] The application envisages a control unit for controlling an electrochemical battery comprising at least one current circuit formed of n elementary battery module cells connected in series, the at least one current circuit being able to deliver a voltage waveform, each elementary module comprising two connection terminals, at least one battery cell delivering an elementary voltage Vcell and a switching component able to regulate the elementary module in the current circuit according to three different regulation states able to deliver respectively to the terminals the elementary voltage Vcell, zero voltage and inverted voltage Vcell, so as to implement the voltage waveform. The control unit is configured to implement the control method according to any one of the above-described embodiments, the control method being able to balance the average current passing through the battery cells.

[0029] The application also provides an electrochemical battery system comprising the control unit.

[0030] The application provides a motor vehicle comprising an electrical traction module and a battery system electrically connected to the traction module.

[0031] The application also provides a station electrical energy storage unit comprising the battery system.

[0032] The present application also relates to a computer program product comprising instructions which, when the program is executed by a control unit of the battery system, direct the control unit to implement any one of the embodiments of the control method which enables balancing of the average current passing through the battery cells.

[0033] The regulation of the voltage wave on the current line according to the method is used to regulate uniform average charge and discharge currents on the combination of battery cells of the battery and also enables dynamic balancing of the battery cells individually when an unbalanced state is detected, during operation of the battery in charge and discharge, in the acceleration phase, in the regenerative braking phase and in the phases of charge and discharge on the electrical network sector when the vehicle is connected to external recharging terminals. The method also applies to stationary stations connected to an electrical network or operating in island mode, that is to say disconnected from the electricity distribution network.

[0034] Furthermore, the balancing is implemented under the effect of the charge and discharge currents of the battery, which improves the balancing dynamics compared to passive balancing solutions and active balancing solutions, while avoiding losses due to the Joule effect and reducing efficiency losses.

[0035] In addition, the electrical architecture of the battery with integrated inverter enables the coexistence of battery cells with different capacities in the battery, reduces switching losses, reduces common-mode currents in the electrical machines, eliminates current leaks and gear corrosion ("pitting") generated in traditional architectures of operating degradation mechanisms, regulates degraded operation without stopping the vehicle and regulates full control, which causes less degradation in the windings of the machines. Recharging implemented directly in connection with the network, single-phase and three-phase, with dynamic balancing of the battery cells and dynamic balancing implemented in hidden time, the architecture also has high efficiency in terms of low power and power components. Therefore, the use phase related to static balancing of the battery cells, which is usually implemented at the end of the charge of the battery, is no longer necessary. BRIEF DESCRIPTION OF DRAWINGS

[0036] Other characteristics and advantages of the application will become apparent on reading the detailed description of the application given as a non-limiting example, and on examining the attached drawings in which:

[0037] - Figure 1 A battery system enabling the implementation of the control method according to the application is schematically illustrated, the battery system comprising an integrated inverter architecture which enables individual regulation of the electrical battery cells.

[0038] - Figure 2An example of a voltage waveform is shown, which can be generated by the battery system, in particular for powering an electrical machine with an alternating voltage in sinusoidal form.

[0039] - Figure 3 An operating module of the control unit of the battery system is schematically shown, the function of which is to ensure the balancing of the battery cells in the case of charging and discharging of the battery.

[0040] - Figure 4 An embodiment of the battery control algorithm is shown, which enables the operation of the balancing of the battery cells in the current line and the maintenance of this state of balance by means of the control method according to the invention.

[0041] - Figure 5 is a graph showing the instantaneous current obtained by the battery cells in the elementary module during the implementation of the balancing control method.

[0042] - Figure 6 is a graph showing the instantaneous current obtained by the battery cells in the elementary module when the cyclic processing by cyclic permutation according to the invention is activated.

[0043] - Figure 7 An example system of an electrical traction powertrain of a motor vehicle is shown, comprising a battery system with integrated inverter and more precisely a control chain of a battery system implementing the method according to the invention.

[0044] - Figure 8 An example system of an electrical energy storage site for a high-voltage network is shown, comprising a battery system with integrated inverter and more precisely a control chain of a battery system implementing the method according to the invention. DETAILED DESCRIPTION

[0045] The present invention applies to a battery system consisting of electrochemical cells of the lithium-ion type, for example, where each battery cell can be individually regulated according to the architecture set out in the international patent applications WO2018193173A1 and WO2018154206A1 of the present applicant mentioned above. This architecture enables the generation of complex output voltages that can take on multiple types of form without the need to resort to supplementary voltage converters external to the battery system, for example, an alternating voltage in sinusoidal form, which is electrically connected to an asynchronous or synchronous electrical machine, or to a single-phase or three-phase electrical network, or a constant voltage, which is electrically connected to a direct-current electrical machine, a voltage converter of the DC / DC type or a recharging interface.

[0046] Figure 1An embodiment of a battery system configured for applying the control method according to the application is schematically shown. The battery system comprises a battery module BAT having at least one current circuit LT1 and a control unit UMI whose function at least consists in regulating the voltage waveform of the circuit LT1 as a function of a reference set value Vref. According to Figure 1 the embodiment, the battery BAT comprises three current circuits LT1, LT2, LT3 which can generate three three-phase voltages with a deviation of 2π / 3. The regulation of each current circuit is similar, distinguished only by a deviation of 2π / 3 from one another. The purpose of the control method according to the application is to be able to balance the electrical cells in the same current circuit LT1, LT2 or LT3.

[0047] As known to the person skilled in the art, a basic electrical cell in a battery is an electrical energy accumulator having two terminals, i.e. a positive electrode and a negative electrode, and having a voltage of a few volts, more generally between 2 and 4 V, usually of the order of 2.2 or 3.7 V. More precisely, a lithium-ion cell additionally consists of a separator, an electrolyte and a current collector deposited on the electrodes. The operating principle of a lithium-ion cell is based on the reversible exchange of lithium ions between the two electrodes. At discharge, the cell supplies electrical energy, lithium ions disengage from the negative electrode while releasing an electron, which then migrates and is transported through the electrolyte towards the positive electrode. The electrons generated at the negative electrode and consumed at the positive electrode circulate from an external circuit external to the cell, while generating a current that powers a load connected to the terminals of the cell. This process is reversed during charging. The control method applies to other technologies, such as lithium-polymer type cells, nickel-cadmium type cells or nickel-metal hydride type cells.

[0048] A battery system (or pack) is constituted by a plurality of basic cells configured to have a voltage at the terminals of the current circuit greater than that of the basic cell. According to Figure 1 the battery system BAT has a voltage at its own terminals of a few hundred volts, preferably 250 V or more, but this voltage can have only a few tens of volts, for example 24 V, 36 V, 48 V, according to the electrical needs, especially for applications for powering electrical traction machines of vehicles, especially motor vehicles equipped with asynchronous, synchronous or direct-current electrical machines, and for applications of stationary energy storage sites required for high-voltage electrical networks.

[0049] In the case of a vehicle powertrain, the output of each current circuit is used to connect directly (without a voltage converter) to the current circuit of one or more electric machines and to the current circuit of a recharging interface of the vehicle, which can operate at constant voltage or alternating voltage.

[0050] The battery system BAT also comprises n multiple elementary electrical battery cell modules ME1, MEk-1, MEk, MEn, assembled in series between two terminals B1, B2 to form each current circuit LT1, LT2, LT3. The n elementary modules are indexed by the index k, where k is a natural integer between 1 and n. For example, n can be equal to 80 to form a line voltage (which can reach an average peak of about 290 V on each current circuit LT1, LT2, LT3) or a lower voltage (which is for example about 240 V based on a set of q elementary modules, with q being less than n). For simplicity, only one elementary module is detailed.

[0051] More precisely, each elementary module MEk comprises two connection terminals Bk1, Bk2, at least one elementary electrical battery cell CEk coupled between said terminals delivering a basic voltage Vcell, and switching means comk1, comk2 able to configure the elementary module MEk in three different states delivering respectively to the connection terminals Bk1, Bk2 the basic voltage Vcell, a zero voltage and an inverted voltage Vcell. Each elementary module MEk comprises a single elementary battery cell.

[0052] In a variant, two or more elementary battery cells are directly and permanently electrically connected in parallel and / or in series between them in the same elementary module. In this way, such a set of elementary battery cells has two connection terminals electrically connected to the switching means cmk1, comk2 in order to deliver at the terminals of the set of elementary battery cells a voltage, a zero voltage and an inverted voltage at the connection terminals Bk1, Bk2 of the elementary module. In a possible implementation in which a plurality of elementary battery cells is connected in series in a single elementary module MEk, the elementary module also comprises conventional balancing means of the series battery cells of the elementary module.

[0053] The switching means are constituted, for example, by two elementary switching modules comk1, comk2 forming an H-bridge, which can be regulated by control signals uik of a control unit UMI of the battery BAT in three different states to implement the "DRIVER" function according to the English terminology. The states are illustrated by the control variable uik, which can take, for example, the values 1, 0, -1, which represent the three different states to control the elementary voltage Vcell, zero voltage and inverted voltage -Vcell at the connection terminals Bk1, Bk2 of the elementary module of index k, respectively. As Figure 1 illustrated, each elementary switching module comprises two electronic components, which are, for example, power transistors of the optional MOSFET or HEMT (English for "High Electron Mobility Transistor") type, and are regulated by signals ui1 to uin of the control unit UMI. Thus, the voltage vik at the terminals Bk1, Bk2 of each elementary module MEk can be regulated according to the control signal uik according to the following relationships:

[0054] [Equation 1]

[0055]

[0056] In Figure 2 the above, an example of a voltage waveform is illustrated, which can be delivered by the battery BAT on the current line LT1. In this non-limiting example, the reference voltage set value Vref has a sinusoidal form, and the phase voltage VM1 of the current line LT1 is formed by amplitude steps equal to the elementary voltage Vcell. Any voltage waveform can be regulated by the control unit, for example, a sinusoid or a constant voltage of 50hz frequency.

[0057] The operating means of the control unit UMI will now be described, which are able to implement the control method according to the application to ensure the balancing of the state of charge of the battery cells in the same current line. This embodiment can be implemented by means of a control unit UMI of the battery BAT, which can be integrated into or constitute a battery management computer BMS (English for "Battery Management System") in a decentralized architecture, as Figure 1The above is not limiting. This is not mandatory. In fact, the method can be implanted in an external module of the BMS, for example, even in a base module MEk according to a decentralized architecture, coupled with this decentralized architecture. In this latter case, the external module itself can be configured in the form of a dedicated computer, comprising possible dedicated programs. Therefore, the implementation module for implementing the battery control method according to the present application can be implemented in the form of software (or computer (or "software") module, or electronic circuit (or "hardware"), or a combination of electronic circuit and software module.

[0058] In Figure 3 More precisely, the operating module of the control unit UMI of the battery BAT is shown, the function of which is to regulate the control signals uik for controlling each base module MEk.

[0059] The control unit UMI is able to receive as input parameters the reference voltage set value Vref and the current value la (set value or measured value) of the current line. In response to the voltage set value Vref, the line current is generated that passes through each base module connected to the current line. The line current can be a charging and discharging current (with active and / or reactive component). In the case of an alternating reference voltage, the line current can be in phase with the reference voltage or have a phase difference with the reference voltage (with a phase difference value between -90° and 90° according to the electrical behavior (resistive induction) of the electrical network (grid section or on-board network of the vehicle) to which one or each current line of the battery is connected).

[0060] The first module 11 is able to determine at each instant the number q of base modules required among the n plurality to implement the voltage waveform according to the following relationship for each quantized voltage phase ViM required by the set value Vref (where all the base battery cells have the same base voltage Vcell):

[0061] [Equation 2]

[0062] where

[0063] The second module 12 is able to assign to each base module MEk a position nk in an arrangement 13 (table, list or index) recorded in the memory of the control unit UMI. The arrangement 13 is dynamic and modifiable by the control unit UMI and records at each instant the position nk of each of the base modules MEk. Thus, thanks to the dynamic arrangement, it is possible to obtain the same voltage based on different control combinations uik of the base modules.

[0064] The object of the application is to implement a modification of the schedule 13 of the current line during the charging and discharging of the battery, in order to maintain the balance of the state of charge of the battery cells.

[0065] To this end, the control unit comprises a module 16, the function of which is to operate the processing of the schedule for the n multiple, according to a cyclic permutation of the positions nk of the elementary modules MEk, in order to involve each elementary module of the n multiple in the implementation of the voltage waveform. The permutation aims to move the positions of the elementary modules in the schedule. Since the number q of elementary modules required for the implementation of the waveform is less than the total number n of available modules, at each instant, modules are shunted while other modules are crossed by the line current. The cyclic operation of the schedule is an action of pulsing the current passing through each unshunted battery cell. The cycle is particularly advantageous when the battery cells reach a balance of state of charge between them over a given period of time to equalize the average current passing through the battery cells over the period of the reference voltage. Likewise, the cycle can reduce the effects of strong current stress, especially in the case of a motor vehicle mounting a sidewalk, when few battery cells are subjected to stress to implement the voltage waveform (q is low relative to n). In this way, an aggravation of an optional imbalance already present is avoided.

[0066] In all cases, when q is less than n, the module 16 is intelligently activated to form a voltage wave that is likely to be generated over a long period of time (several tens of minutes, or even several hours).

[0067] In this way, the triggering of the cycle by the module 16 according to the cyclic permutation can depend on the difference in state of charge between the elementary modules MEk relative to a predetermined threshold, or on the ratio of the current set value relative to the value of the voltage level requested.

[0068] More precisely, the module 16 modifies the schedule table 13 according to the following algorithmic relationship:

[0069] [Equation 3]

[0070] n k ←(n k +1)mod n

[0071] When q is less than n, the cycle of the position nk in the total list of n elementary modules is performed at an arrangement frequency greater than the frequency of the signal Vref (for example, for a reference voltage Vref with a frequency of 50 Hz, the arrangement frequency is about 1 kHz). The ratio between the arrangement frequency and the frequency of the voltage signal can be different and is chosen as a function of the Joule losses in switching related to the drop in internal impedance of the battery. The arrangement frequency is configured to ensure a complete arrangement of the n modules over a predetermined time duration, that is to say that each module has been positioned in the position in the arrangement in turn over the time duration. The predetermined time duration is equal to or less than the period of the electrical voltage of the current line.

[0072] It is observed that, for batteries of lithium iron phosphate technology, the cycle is able to reduce the internal impedance value of the electrical battery cell by about 30%. Thereby, it is possible to adapt the arrangement frequency to the technology of the selected battery cell. Thereby, in a variant, the arrangement frequency of the cycle arrangement can depend on the value of the internal impedance of the battery cell in each elementary module.

[0073] In addition, another purpose of the control unit is to implement the dynamic balancing of the battery cells before, simultaneously or after the cycle of the cycle arrangement of the battery cells. When the battery cells in the current line are unbalanced, or to guarantee a level of balancing before operating the cycle, the control unit UMI comprises means for operating the balancing of the battery cells.

[0074] To this end, the position nk of each elementary module MEk is preferably dependent on the state of charge level SOC of each elementary module, to allow the balancing of the battery cells at any operating instant of the battery. However, it is not excluded that the arrangement is obtained on the basis of a value representative of the state of aging of the battery cell, or more generally on the basis of any parameter representative of the operating state specific to the battery cell which defines the battery cell interference for forming the voltage wave.

[0075] In a preferred embodiment, the function of the arrangement 13 is to record the list of the elementary modules in ascending order or descending order of the state of charge SOC. For an arrangement implemented in descending order, the module 12 is assigned the position nk = 1 when the elementary module MEk has the highest state of charge, and so on until the position nk = n is assigned for the elementary module with the lowest state of charge.

[0076] Moreover, each elementary module MEk can be individually regulated by the module 14 in three different states (+1, 0, -1 ), and, in compliance with the method, the module 14 is configured for regulating the elementary modules so as to connect, in the event of detection of a discharge current passing through the current circuit LT1, a set of q elementary modules MEk having the highest state of charge SOC in the arrangement 13 to the current circuit, and, in the event of detection of a charge current passing through the current circuit LT1, a set of q elementary modules MEk having the lowest state of charge in the arrangement to the current circuit. The q modules have successive positions in the arrangement 13.

[0077] Conventionally, the following concepts are defined:

[0078] The line current is a discharge current when the current and the voltage have the same sign, that is, at a given instant, both the reference voltage and the line current have a positive sign or a negative sign.

[0079] The line current is a charge current when the current and the voltage have opposite signs, that is, at a given instant, the reference voltage has a positive sign and the line current is negative, or the reference voltage has a negative sign and the line current is positive.

[0080] The line current is positive when the current is output towards the electrical circuit, and negative when the current is input towards the battery.

[0081] The sign of the voltage is referenced with respect to the terminals B1, B2 of the current circuit of the battery, in which the terminal B1 is coupled to the phase terminal of the electrical circuit (electrical machine winding terminal or electrical network phase terminal) and the terminal B2 is coupled to the neutral terminal. In the case of a direct voltage circuit, the terminal B1 is the positive terminal of the battery and the terminal B2 is the negative terminal or the ground terminal.

[0082] This regulation mode of the voltage wave on the current circuit enables, during operation of the battery, to individually operate the dynamic balancing of the battery cells by regulating the charge and discharge currents passing through the current circuit. Moreover, the balancing is implemented under the action of charge and discharge currents of the battery of the order of tens or even hundreds of amperes, which improves the balancing dynamics compared to known passive and active balancing solutions in which the balancing currents are only a few amperes, the balancing currents have Joule effect losses and therefore efficiency losses. The charge / discharge currents are the currents passing through the current circuit of the battery when the current circuit is connected to the electrical network of the vehicle or of the grid section.

[0083] According to a control variant of the battery, the module 14 is configured so that the ordering aims to assign to each elementary module MEk a position nk between 1 and n in a list implemented in descending order of state of charge, and, at each instant, the regulation step of the elementary modules comprises the following sub-steps:

[0084] - determining the line current la of the current line LT1,

[0085] - when the line current la and the reference voltage setpoint Vref have the same sign, regulating the elementary module MEk so as to connect the elementary module MEk having a position nk between 1 and q to the current line,

[0086] - when the line current and the reference voltage setpoint have opposite signs, regulating the elementary module MEk so as to connect the elementary module having a position nk between n-q and n to the current line.

[0087] It is noted that, at each instant, the control unit UMI connects q elementary cells (q < n), where q is the ratio between the reference voltage Vref expected at the line output and the elementary cell voltage Vcell at this instant.

[0088] Thus, the state of each control variable of the elementary modules can be regulated by the module 14 according to the following algorithmic relationship, where the ordering is indexed in descending order of state of charge:

[0089] [Equation 4]

[0090] if nk < q

[0091] else if nk > n-q

[0092] where nk is the position of each module in the ordering, Vcell is the elementary voltage of the cell, and V refi and i i are the reference voltage setpoint and the line current (in amperes) of each current line referenced i, where i is between 1 and 3, for example, for each current line of a three-phase voltage, respectively.

[0093] The person skilled in the art will of course be able to configure the ordering in ascending order of state of charge and thus modify the algorithmic relationship allowing the regulation of each elementary module MEk.

[0094] In addition, it is conceivable that the module 12 is able to distribute the positions nk depending on a criterion (depending on the aging state of each elementary module or on the residual capacity of each elementary module) in addition to the state of charge SOC. For example, for modules having the same state of charge, it is conceivable that the sorting is operated by taking into account the aging state in order to preferentially activate the modules that are newer or that have a higher total residual capacity with respect to the modules that have a higher degree of fatigue.

[0095] Furthermore, the module 15 is able to determine at each instant the state of charge SOCk of each elementary module MEk. The state of charge SOCk corresponds to the electrical capacity (expressed in A.s, A.h (ampere seconds or ampere hours)) contained in the battery cell of the elementary module MEk or further generally to the percentage of charge with respect to the actual total capacity at the instant t.

[0096] The determination of the state of charge SOCk is calculated by a first Coulomb method. As is well known to the person skilled in the art, the estimation is operated by a Coulomb measurement based on a known initial reference state of charge (for example, a full state of charge corresponding to 100% SOC, i.e. a total capacity known at the instant of estimation for a known aging state) and on the charge variation measured by the current sensor of the current line. Estimation algorithms for estimating the state of health of electrochemical battery cells are well known to the person skilled in the art and can be implemented by the control unit of the battery system BAT.

[0097] Advantageously, the module 14 is configured for determining the state of charge SOC of each elementary module MEk at the switching instant of the regulation state of each elementary module. To this end, the module 14 estimates the variation of the state of charge of each module MEk between a first switching instant and a second switching instant based on the regulation state uik of each module MEk and the average current value of the current line. Thanks to this first Coulomb method, it is thus not necessary to equip the battery with a current sensor for each battery cell. The control logic variable uik is known at any instant and it is thus possible to estimate the state of charge by integration calculation over the period between the two switching instants based only on the current measurement value of the line. This period can be fixed or variable. The "regulation state switching" is understood to correspond to a regulation control corresponding to a refresh of the regulation state of the elementary module MEk and covers the case of changing a first regulation state among the states +1, 0, -1 into a second different state among these same states or changing a regulation state among the states +1, 0, -1 into this same state.

[0098] However, this first Coulomb method has drawbacks, since it is likely to lead to an estimation error of the SOC which increases over time as the calculation proceeds. Therefore, the control unit UMI also comprises a module 18 which is able to perform a readjustment or calibration of the estimation of the state of charge for each of the elementary modules, or else further perform any other type of diagnosis (for example an estimation of the state of ageing).

[0099] According to a variant aiming at calibrating the state of charge, when the precision is no longer guaranteed by the Coulomb method, the module 18 is able to estimate the open-circuit voltage of the battery cell during a discharge phase of the battery cell (based on the principle of a Kalman filter or optionally tabulated values). The estimation techniques for estimating the open-circuit voltage are well known to those skilled in the art and are not exactly the object of the application. It is known that some approaches require several tens of minutes to observe the stabilisation of the static voltage and to obtain a reliable value of the open-circuit voltage and therefore of the state of charge SOC of the battery cell. Other modelling approaches can be performed in a shorter time but require more calculation resources.

[0100] Whatever the estimation approach for estimating the open-circuit voltage, the control unit UMI comprises a module 17 which is configured to assign to each elementary module MEk in the inventory 13 at any instant an exclusion position so as to exclude the elementary module from the set of q modules during a predetermined exclusion duration. Thus, thanks to the module 17, it is possible to temporarily bypass electrically the battery cell (whatever the value of the state of charge of this battery cell) to operate a diagnosis or calibration in hidden time without affecting the normal operation of the battery. It is envisaged, for example, that the exclusion action of the module 17 is triggered for any type of diagnosis requiring the deactivation of the elementary module concerned, whether for a calibration of the state of charge or for an estimation of the state of ageing of the battery cell.

[0101] It is noted that the exclusion duration depends on the duration required to operate the diagnosis. Once the exclusion position is assigned, the module 18 is authorised to perform the estimation approach for estimating the open-circuit voltage for the associated elementary module during discharge when nk is greater than q and during charge when nk is less than n-q. It is noted that the action of the module 17 depends on the state of a flag or index which is activated when the precision of the state of charge is not guaranteed by the control unit. The index is activated, for example in the high state, to require a readjustment of the SOC. When the readjustment is performed, the index is deactivated, i.e. in the low state.

[0102] It is added that the sorting 13 of the elementary modules in order of state of charge is active at any instant of operation (charge, discharge) of the battery, in order to guarantee the balancing of the cells in the current line, without the need for dedicated monitoring protocols. The frequency of implementation of the sorting in order of state of charge is configured according to a predetermined time length or according to the discharge / charge speed of the battery, for example in the range between 1 second and 5 minutes, or for a predetermined proportion of the total capacity of the battery, for example every 1% of discharged / charged SOC (that is to say, every one hundredth of the capacity with respect to the total capacity of the battery).

[0103] In Figure 4 , an algorithmic diagram is described which describes an embodiment of a battery control method which is able to balance and maintain the balancing of the cells in the current line. The balancing step of the method is preferably operated before the loop process, in order to ensure an initial balancing state. However, this order is not mandatory and the loop relating to step 36 can be activated as soon as the control unit detects a sufficient balancing state of the cells (for example, detecting that the state of charge difference between the cells is less than a predetermined threshold).

[0104] Preferably, the method first comprises the following steps for ensuring the balancing of the cells:

[0105] - a determining step 31 for determining the state of charge of each elementary module MEk of the n plurality,

[0106] - then, a determining step 32 for determining a sorting of the n elementary modules according to an order which depends on the state of charge of each elementary module,

[0107] - then, a regulating step 33 for regulating the control signal of the elementary module MEk, in order to provide the voltage waveform of the current line at any instant t based on the selection of a set of q elementary modules according to a reference voltage set value Vref, where Vref = qVcell.

[0108] The determining step 31 is not limited to the state of charge of the cells. It is noted that the sorting 13 can be obtained based on the value of any operating parameter specific to the cells (for example, state of aging, residual capacity) or further by the electrical position in the current line.

[0109] More precisely, according to a variant of the method, preferably, the regulating step 33 aims at connecting to the current line the set of q elementary modules having the highest state of charge in the ordering, in the case of detection of a discharge current, and the set of q elementary modules having the lowest state of charge in the ordering, in the case of detection of a charge current.

[0110] Thanks to the application, this step is performed during the charge and discharge operating phases of the battery under the effect of charge and discharge currents, thus guaranteeing a balanced dynamic which is superior to the passive and active solutions described in the prior art. The line current and the voltage set value are alternating signals in sinusoidal form, which take positive and negative values over time periods. Thus, the method maintains the balance of the battery cells at any operating instant of the vehicle, since the direction of the current is taken into account to detect charge and discharge phases over at least one phase period, in particular during successive acceleration and regenerative braking phases. The control of the balance can of course be applied equally to a vehicle battery connected to an electrical network via a recharging terminal, or to a stationary application, in particular in the case of a so-called "Smart Grid" control process for managing a network in which charge and discharge phases are controlled.

[0111] Thus, over the periods of the reference voltage, the elementary charge modules which are relatively large with respect to the other modules (for example nk = 1) are subjected only to a discharge current, while the charge modules which are relatively small with respect to the other modules (for example nk = n) are subjected only to a charge current.

[0112] To illustrate this example, in Figure 5 the instantaneous current Ia of the battery cells in the elementary module in position nk = 10 is shown for the example of a battery architecture during the execution of the control method. The values of the charge current are shown in amperes on the ordinate axis and the time t in milliseconds on the abscissa axis.

[0113] In this example, the current line is equipped with 80 elementary modules assembled in series, the unit voltage Vcell is equal to 3.3 V, the sinusoidal reference voltage has an amplitude of 264 V, and the sinusoidal current is equal to 100 A. By taking into account the inductive behavior of the machine winding and its operating point, the voltage and the current have a phase difference of 45°. As can be seen on this figure, the current obtained by the battery cell has a partial sinusoidal form and remains positive over the same period, since the battery cell in the elementary module is only connected to the line when the line current is a discharge current. Indeed, the relatively low position of this battery cell in the list (high state of charge) places this battery cell only in a discharge current. It is noted that the current obtained by an elementary module thus depends on the state of charge value of the battery cell in the elementary module and on the phase difference between the voltage setpoint and the line current. In the case where the phase difference is zero, the current has a continuous value without discontinuity.

[0114] Next, according to the method, steps 31 and 32 are re-executed in the event of detection of the activation of a rearrangement condition of the grooming, in step 34, i.e. a time duration from the previous arrangement greater than a predetermined time duration, or optionally a state of charge variation from the previous arrangement greater than a predetermined threshold. The predetermined time duration can be between, for example, one or more minutes, in order to reduce the energy losses related to the switching action of the transistors.

[0115] According to a variant of the method (illustrated in Figure 4 , the grooming step 32 aims, in a sub-step 320, to assign to each elementary module a position nk between 1 and n in a list implemented in decreasing order of state of charge, and the regulation step 33 comprises, in succession:

[0116] - determining 330 the sign of the current of the current line, to compare the sign of the current with the sign of the reference voltage in step 331 next, in order to detect whether the line has a charging or a discharging current.

[0117] - when the current and the reference voltage setpoint have the same sign (i.e. a discharging current), regulating 332 the elementary modules so as to connect to the current line the elementary modules whose position nk is between 1 and q.

[0118] - when the current and the reference voltage setpoint have opposite signs (i.e. a charging current), regulating 333 the elementary modules so as to connect to the current line the elementary modules whose position nk is between n-q and n.

[0119] It is also envisaged that the whole of the conditioning performed in charge state order by the module 12 can be deactivated when the control unit UMI detects that the battery cells are balanced, that is, when the difference in state of charge between each battery cell is less than a predetermined minimization threshold.

[0120] It is specified that the steps 31, 32, 33, 34 of the control method are not mandatory. The balancing of the battery cells can be obtained by means of any type of balancing approach, in particular by means of a passive approach or an active approach, for example described in the prior art.

[0121] In step 35, in compliance with the control method according to the present application, when the control unit detects that the battery cells are balanced, the module 16 is activated to operate, in step 36, a cyclic permutation of the conditioning so as to make each elementary module of the n plurality participate in implementing the voltage waveform. On the period of the reference voltage, the cyclic permutation guarantees the same stress in terms of average current for all the battery cells. The permutation is performed when q is less than n. The cyclic permutation is activated as long as the battery cells are balanced and is implemented with a permutation frequency greater than the frequency of the reference voltage set value Vref, for example 1 kHz for a reference voltage of 50 Hz.

[0122] In a variant of step 35, the module 16 is activated also in the case in which it is detected that the reference voltage set value is less than a predetermined voltage threshold, and simultaneously in the case in which it is detected that the current set value is greater than a predetermined current threshold. This strategy aims to respond specifically to a strong current stress when a small number of battery cells is subjected to stress to implement the voltage waveform. This activation aims to prevent the unbalancing of the battery cells.

[0123] The conditioning 32 performed in charge state order can be activated simultaneously with the cyclic permutation process 36, or one after the other only during a given period.

[0124] In Figure 6 In Fig. 6, a graph is shown which shows, for an example of battery architecture, the instantaneous current Ia of a battery cell in an elementary module in position nk = 10 during the execution of the cycle. The values of the charging current are shown in amperes on the ordinate axis and the time t in milliseconds on the abscissa axis.

[0125] In this example, as in the example of Figure 5 The current circuit is equipped, as in the example of

[0126] As can be seen on this figure, the current drawn by the battery cells has a partial sinusoidal form, since the battery cells are activated at the level of the reference voltage whose absolute value is ten times the base voltage Vceii. The pulsation of the current caused by the cyclically positioned battery cells in the unrequested position of the regiment (position controlling the addition of the shunt state) during the generation of the voltage wave is observed. The cycling implemented by the cyclic permutation of the battery cells can minimize the thermal energy losses, reduce the internal resistance of each battery cell and equalize the average current values of all battery cells during the period of the cycle.

[0127] Finally, in step 35 of the method, in the event of detection of an imbalance of the state of charge and of a requirement for deactivation of the cyclic permutation, the method returns to step 31 to operate the balancing of the battery cells. This event is detected when the difference in state of charge between at least one of the other battery cells is greater than a predetermined maximum threshold value.

[0128] In a variant, the regiment by order of state of charge is activated when the residual capacity of the battery (or for example the residual range of the vehicle) is less than a predetermined threshold value. In this case, the regiment by order of state of charge and the associated balancing regulation remain activated until the residual capacity of the battery reaches a minimum limit value, for example less than 10% or a few percentage points of the total capacity, even further to zero capacity. In this way, all the battery cells reach an authorized minimum state of charge at the same instant.

[0129] Moreover, as mentioned above, the regiment can temporarily add a shunt to one or more battery cells, the purpose of which is to diagnose or calibrate the state of charge while maintaining the normal operation of the battery system. In Figure 4 In a variant, the steps 40, 41, 42 are also shown to be carried out, in which:

[0130] In the event of detection 40 of a diagnostic requirement (for example calibration of the state of charge), the method comprises an allocation step 41 for allocating an excluded position to a base module in the regiment in order to exclude the base module from the set of q modules during a predetermined exclusion duration, then an execution step 42 for executing a diagnosis for the base module during the exclusion duration.

[0131] In a variant, the steps 40, 41, 42 are also shown to be carried out, in which: Figure 6 In a variant, a first application of the control method according to the application in the field of electric vehicles is shown for a motor vehicle powertrain comprising an architecture with an integrated inverter (as in Figure 1The battery system is described in the description. The vehicle may be a hybrid or electric vehicle equipped with one or more (asynchronous, synchronous, or DC) electric traction machines, wherein said or each machine is electrically connected to the battery system. The powertrain 500 includes a generation module 50 for generating a current setpoint 51, which is sent to a current servo loop. The generation module 50 transmits the current setpoint based on torque requirements from the vehicle's accelerator pedal or from an automated control module (e.g., an automated speed adjustment function based on measurements of the speed and torque of the drive wheel axles). Typically, the current servo loop receives the setpoint 51 and a measurement 58 of the current generated on at least one of the current lines of the battery 56. The battery 56 is directly (without an electrical insertion voltage converter) electrically connected to at least one electric traction machine 57 for driving the wheel axles 59 of the vehicle, and via a recharge interface (not shown) connected to an external electrical network of the vehicle, in this three-phase voltage example. The battery architecture does not require the use of an inverter at the battery's line output.

[0132] The servo loop also includes a calibrator 52, which transmits a reference voltage setting 53 to the control unit 54 of the battery 56 based on a setpoint 51 and a measured value 58. The control unit 54 transmits a control setting 55 to regulate each basic module of the battery according to the voltage setting in accordance with the control method described above, in order to maintain the balance of the battery cells, thanks to the cycling of the battery cells.

[0133] exist Figure 7 The diagram illustrates a second application of the control method according to the invention in the field of site-type batteries, wherein it conforms to an architecture with an integrated inverter (such as in...). Figure 1 The battery system 600 (described in the text) is connected to a (high-voltage, ultra-high-voltage) electrical network. The battery system 600 receives a power setpoint 60 derived from requirements for active power (P) and reactive power (Q) to be injected into the electrical network 70. The system also includes a determination module 61 for determining a current setpoint 62 in amplitude and phase based on the setpoint 60 and a voltage measurement 69 on the current line at the output of the battery 67, and a current servo loop including a corrector 63 that transmits a reference voltage setpoint 64 based on a current measurement 68 on the (here, three-phase) current line at the output of the battery 67 and the current setpoint 62. The control unit 65 of the battery 67 transmits control setpoints for each basic module of the battery according to the reference voltage setpoint, conforming to the control method described above, to maintain the balance of the battery cells through cell cycling.

[0134] In this type of application, the system 600 can be regulated for charging and discharging the battery based on the electrical network.

[0135] The following different technical advantages of the control method are now summarized:

[0136] - dynamic balancing of the battery units during the use phase of the vehicle: traction, recharging and discharging on the electrical network of the grid section,

[0137] - balancing of battery units possibly having different states of aging,

[0138] - balancing of battery units having different capacities,

[0139] - dynamic balancing without resorting to means specific to the balancing, but by reusing the local inverters of each elementary module,

[0140] - high balancing efficiency (> 90%),

[0141] - balancing current equal to the cycling current of the battery (charge and discharge current of the battery in operation).

Claims

1. A control method for controlling a battery (BAT) having multiple electrochemical cell units (CEk), the control method being capable of balancing the average current flowing through the electrochemical cell units (CEk), the battery (BAT) comprising at least one current line (LT1) formed by n basic cell unit modules (MEk) connected in series, the at least one current line being capable of transmitting a voltage waveform, each basic cell unit module (MEk) comprising two connection terminals (Bk1, Bk2), at least one cell unit (CEk) transmitting a basic voltage Vcell, and switching components (comk1, comk2), the switching... The switching component can regulate the basic battery cell modules (MEk) in the current line (LT1) according to three different regulation states, which can respectively transmit the basic voltage Vcell, zero voltage, and reverse voltage Vcell to the connection terminal to implement a voltage waveform (VM1). The control method includes a regulation step (33) for regulating the control signal (uik) of the basic battery cell modules (MEk) to provide the voltage waveform (VM1) based on the selection of a set of q basic battery cell modules (MEk) according to a reference voltage setpoint Vref. Vref = qVcell, characterized in that the control method further includes: - Determine (32) the arrangement of n basic battery cell modules (13), - The arrangement of the n or more basic battery cell modules (MEk) is processed (36) according to the cyclic arrangement of their positions nk, so that each of the n or more basic battery cell modules (MEk) participates in implementing the voltage waveform (VM1). If the reference voltage setting value Vref is detected to be less than a predetermined voltage threshold and the current setting value of the current line is detected to be greater than a predetermined current threshold, the sorting (13) according to the cyclic arrangement process (36) is performed.

2. The control method according to claim 1, characterized in that, The cyclic arrangement is performed at an arrangement frequency greater than the reference voltage setting value.

3. The control method according to claim 1 or 2, characterized in that, The control method further includes: - Determine the state of charge of each of the n basic battery cell modules in (31), and determine the arrangement (13) according to the order depending on the state of charge of each basic battery cell module (MEk). - Furthermore, the sorting process according to the cyclic arrangement is performed only if each of the n basic battery cell modules detected (35) has a charge state difference less than a predetermined minimum threshold relative to the other basic battery cell modules.

4. The control method according to claim 3, characterized in that, The determination step for determining the conditioning (13) is triggered according to a time period, the value of which depends on the discharge and charging rate of the battery (BAT) over a predetermined duration.

5. The control method according to claim 3, characterized in that, The control method further includes stopping the sorting according to the cyclic arrangement process (36) when it is detected that at least one of the n basic battery cell modules has a charging state difference greater than a predetermined maximum threshold relative to other basic battery cell modules.

6. The control method according to any one of claims 1, 2, 4 and 5, characterized in that, The control method further includes stopping the sorting (13) according to the cyclic arrangement process (36) when the remaining capacity of the battery (BAT) is detected to be less than a predetermined minimum threshold.

7. The control method according to claim 5, characterized in that, If the tidying process is stopped according to the cyclic arrangement, the control step (33) is intended to: connect the battery cells of the set of q basic battery cell modules (MEk) with the highest state of charge in the tidying (13) to the current line (LT1) if a discharge line current is detected, and connect the battery cells of the set of q basic battery cell modules (MEk) with the lowest state of charge in the tidying (13) to the current line if a charging line current is detected.

8. The control method according to claim 7, characterized in that, The regulation step (33) includes the following sub-steps: When the current (Ia) in the current line (LT1) and the reference voltage setting value Vref have the same sign, the basic battery cell module (MEk) is adjusted so that the battery cells in the basic battery cell module with position nk between 1 and q are connected to the current line (LT1). - When the current (Ia) of the current line (LT1) and the reference voltage setting value Vref have opposite signs, the basic battery cell module (MEk) is adjusted so that the battery cells of the basic battery cell module (MEk) with position nk between nq and n are connected to the current line (LT1).

9. A control unit (UMI) for controlling an electrochemical cell (BAT), the electrochemical cell comprising at least one current line (LT1) formed by n basic cell modules (MEk) connected in series, the at least one current line capable of transmitting a voltage waveform (VM1), each basic cell module (MEk) comprising two connection terminals (Bk1, Bk2), at least one cell (CEk) transmitting a basic voltage Vcell, and switching components (comk1, comk2), the switching components capable of controlling the basic cell modules (MEk) in the current line (LT1) according to three different control states, the three different control states being capable of transmitting the basic voltage Vcell, zero voltage, and reversed voltage Vcell to the connection terminals respectively, so as to implement the voltage waveform (VM1), characterized in that, The control unit (UMI) is configured to implement the control method according to any one of the preceding claims, the control method being capable of balancing the average current passing through the battery cell (CEk).

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