METHOD FOR RAPIDLY CHARGING A BATTERY SYSTEM

Abstract

The present invention relates to a method for charging a battery system (1) comprising a first charging phase including the determination of a first maximum charging current (IDC1) delivered by a first DC current table (151) providing applicable values ​​of the first current (IDC1) for a first fixed duration and charging the storage element to the value of the first DC current for the first fixed duration, and when the elapsed time (CT) of the charging operation is greater than the first fixed duration, the method includes controlling a second charging phase comprising the determination of a second maximum charging current delivered by a second DC current table (152) providing applicable values ​​of the second current (IDC2) until the storage element is fully charged, and charging the storage element to the value of the second DC current (IDC2). Figure 1.

Description

Title of the invention: METHOD FOR FAST CHARGING A BATTERY SYSTEM

[0001] The field of the invention relates to a method of charging a battery system for high power recharges.

[0002] The battery systems of electrified vehicles are currently mainly equipped with lithium-ion electrochemical cells. In operation, these cells are likely to deteriorate if they are not used under nominal operating conditions, i.e. within the thermal, current and voltage limits defined by the cell manufacturers. Indeed, in the event of excessively low temperatures or excessively high currents being driven, the electrodes of a cell can become saturated with lithium atoms on the surface, which can lead to the formation of dendrites causing internal short circuits. The management of the cell charge and discharge currents must be carried out under safe conditions while ensuring optimal energy management and the least restrictive use of the battery possible, particularly in terms of charging time and driving range.

[0003] Lithium transport in a negative graphite electrode is generally slower than in positive electrodes and, consequently, is the limiting phenomenon of the charging current. This phenomenon is called lithium deposition or lithium plating, also referred to as "Lithium Plating" in English. Too high a lithium concentration can lead to the formation of dendrites and cause an increase in internal resistance, or even a short circuit. During charging, lithium ions are reduced to lithium metal on the surface of the graphite structure during the exchange of electrons. The rate of reduction of lithium ions is proportional to the current and diffusion in the graphite structure follows the diffusion laws. The diffusion rate depends on the lithium metal concentration gradient and a diffusion coefficient, which depends on the state of charge, temperature and aging of a cell.Fick's law governs the diffusion of lithium ions in the various components of the battery, such as the electrolyte and the electrodes. This law is well known to those skilled in the art in the field of batteries. For example, the following bibliographic reference describing principles of application of Fick's law in the field of lithium-ion cells can be cited: "Wu Musheng, Xu Bo, Ouyang Chuying. Physics of electron and lithium-ion transport in electrode materials for Li-ion batteries. Chinese Physics B, 2016, 25(1): 018206".

[0004] Document CA-A1-3052382 is also known, describing a rapid charging method aimed at reducing the charging time and the degradation of electrocells. chemical processes by taking into account a modeling of the lithium concentration in the cell electrolyte. This method involves applying an input current at a first charge rate, the input current being applied at the first charge rate until a lithium ion concentration in an electrolyte at an anode current collector decreases below 500 mol / m3, then applying a second charge rate lower than the first charge rate which maintains a constant lithium ion concentration in the electrolyte at the anode current collector, and then applying the input current to the lithium ion battery at a decreasing charge rate, where the reduction in the charge rate decreases the lithium plating on the anode surface. The charge rates are determined from a simplified modeling of the lithium ion concentration in the form of a first-order equation.This technique requires significant computing resources to implement the concentration estimation function in real time. This solution is not optimal in terms of response time and energy consumption.

[0005] Patent document EP-A1-3358704 is also known, which describes a charging method using a multi-stage constant current charging scheme, in which a plurality of sequential stages are predefined during which the open circuit voltage (OCV) of an anode of the battery decreases over time, and in which for each stage there is a predefined constant current charging rate, these predefined sequential stages being defined as a function of the value of the slope dOCV / dSOC, namely the differential of the OCV with respect to the state of charge SOC (State of Charge) of the battery. The method comprises the operations of monitoring the SOC or the charging voltage of the battery and determining from the SOC or the charging voltage of the battery at which stage the battery is located and applying the respective predefined charging rate throughout the duration of the stage.According to this technique, the step change is achieved by controlling a potential difference (dphisl) between the potential of the battery anode and the potential of an electrolytic solution of the battery and that the charge rate change is controlled when this difference is less than a predefined value, less than 0.6 volts. Classically, a first known technique to determine this potential is the measurement by means of a reference electrode. However, this device is extremely fragile because it is in the form of a lithium strand and is used only in controlled experimental conditions. Its integration in a vehicle under real usage conditions would be too expensive to equip all the cells of a battery system and would have limited reliability over time.

[0006] A second technique presented in document WO-A1-2022032460 teaches the use of a model embedded in a vehicle to determine this potential as a function of the charging current, state of charge and temperature. This document teaches a principle of charge current control aimed at reducing the current value according to this potential. The disadvantage of a real-time calculation model is that it is particularly energy-intensive.

[0007] There is therefore a need to overcome the aforementioned problems. One objective of the invention is to propose a method for charging an energy storage system making it possible to maximize the current value and thus reduce the charging time. Another objective of the invention is to propose a charging function that is economical in computing resources and in electrical consumption for its operation. Another objective of the invention is to propose a charging function that limits the risk of lithium deposition at the negative electrode of a lithium-ion type electrochemical cell with a graphite anode structure.

[0008] More specifically, the invention relates to a method for charging a battery system comprising an energy storage element, the method being implemented by a control unit of said battery system and comprising the following successive steps during a charging operation by a charger:

[0009] - a first charging phase comprising a first sub-step of measuring first electrical parameters of the storage element, a second sub-step of determining a first maximum charging current delivered by a first direct current table taking said measured electrical parameters as input, the first table delivering values ​​of the first current applicable during a first fixed duration, from a reference state of the storage element corresponding to the first measured electrical parameters, until reaching the lithium saturation level on the surface of a negative electrode of the storage element at the end time of the first fixed duration, and a third sub-step of charging the storage element to the value of the first direct current during the first fixed duration,

[0010] - when the elapsed time of the charging operation is greater than the first time fixed, the control of a second charging phase comprising a first sub-step of measuring second electrical parameters of the storage element, a second sub-step of determining a second maximum charging current delivered by a second direct current table taking as input the second measured electrical parameters, the second table delivering values ​​of the second current corresponding to the second measured electrical parameters and applicable until the storage element is fully charged, and a third sub-step of charging the storage element to the value of the second direct current.

[0011] The method according to the invention may include the following additional characteristics, alone or in combination:

[0012] - The first phase further comprises the following sub-steps of determination of a parameter representative of a real-time estimation of the lithium concentration on the surface of an electrode of the storage element, of determining a second controllable duration of the first phase as a function of said concentration parameter in relation to a limit of a permitted variation range of said parameter, of selecting the charge at the value of the first current if the elapsed duration is less than the second controllable duration, and when the elapsed duration is greater than the second controllable duration, the control of the second charging phase.

[0013] - The parameter representing the concentration is a first quantity of energy exchanged with the storage element during a calculation period prior to the first phase and the limit is a second quantity of energy corresponding to the energy charged by the first current during the first fixed duration.

[0014] - The second controllable duration is calculated according to the following relation: DPB = DI - (LhnH - Pcli), DPB being the second duration, DI being the fixed duration of application of the first current and LimH being the lithium saturation limit, Pcli being the parameter representative of the lithium concentration, LimH and Pcli being expressed by a ratio.

[0015] - The first phase further comprises the following sub-steps of determination of a third relaxation duration between a charging phase prior to the charging operation and the instant of commencement of the charging operation, of control of the first charging phase during the first fixed duration if the third duration is greater than a predetermined relaxation threshold, and when the third duration is less than the relaxation threshold, the immediate control of the second charging phase.

[0016] - Measurement of the instantaneous charging current of the storage element, calculation of a fourth duration during which the instantaneous current is greater than the first charging current during the first phase and the activation of a current protection of the battery system as a function of the fourth duration relative to a protection threshold.

[0017] - The first parameters are a state of charge and a temperature of the element of storage and the second parameters are a voltage and the temperature of the storage element.

[0018] Further contemplated is a battery system comprising an energy storage element and a control unit configured specifically for implementing any of the embodiments of the charging method according to the invention.

[0019] Further contemplated is an electrified vehicle comprising such a battery system and a charging interface intended to be electrically connected to a power source external to the vehicle for performing a charge of the battery system.

[0020] A computer program is provided comprising instructions which, when the program is executed by a control unit of a storage system energy, lead the latter to implement any of the embodiments of the method according to the invention.

[0021] A computer-readable recording medium is provided comprising instructions which, when executed by a computer, cause the computer to implement any one of the embodiments of the charging method according to the invention.

[0022] The invention accelerates a battery system recharge thanks to a phase of increasing the charging current according to a fixed duration and adapted according to the evaluation of a lithium concentration parameter at the surface of a negative electrode of an electrochemical cell. This phase also has the advantage of rapidly increasing the temperature of the electrolyte of the cells to promote the transport of lithium ions.

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

[0024] [Fig-1] schematically represents a battery system according to the invention.

[0025] [Fig.2] schematically represents a negative electrode structure illustrating the principle of diffusion of lithium atoms in a graphite particle structure.

[0026] [Fig.3] represents graphs illustrating the evolution of the lithium concentration on the surface of a graphite structure of a negative electrode for different constant charging currents at different states of charge of the storage element.

[0027] [Fig.4] represents a block diagram of an embodiment of the charging method according to the invention.

[0028] [Fig.5] represents graphs illustrating a controlled current profile according to the method according to the invention, the evolution of the state of charge and the lithium concentration according to this profile.

[0029] [Fig.6] represents an electrified vehicle intended for the implementation of the invention.

[0030] The invention applies to energy storage systems with electro-cells. chemical, in particular of the lithium-ion type. The charging method according to the invention aims to reduce the time of a charging operation of a battery system by a charger and to improve current control to avoid the risks of damage to the cells by lithium plating or by heating of the internal mechanical elements. The invention advantageously applies to electrified vehicles for a charging operation at a terminal. The invention relates to any type of electrified vehicle, that is to say comprising an electric motor machine and power electronics, 100% electric or hybrid, preferably motor vehicles, but not only, such as an airplane, tractor, electric bicycle, ships.

[0031] In the description, a charger is understood to be a power electronics device intended to deliver the charging current to the energy storage elements. The charger can be embedded in the electrical device powered by the storage system or can be remote. Typically for charging a motor vehicle, the charger can be an on-board AC / DC current conversion device or be integrated into a terminal remote from the vehicle. A charging operation is defined as a charging session between the instant of triggering the charging and the end instant determined by the charging stop condition, for example the reaching of a target state of charge, or the limit charging voltage of a cell.

[0032] [Fig.l] schematically represents an energy storage system 1 comprising an energy storage element 10 comprising at least one electrochemical cell 11 in accordance with the invention. The storage element 10 may comprise a plurality of cells 11 or group of cells (also called a cell cluster) electrically connected in parallel and / or in series.

[0033] An electrochemical cell is an electrical energy accumulator having two terminals, a positive electrode and a negative electrode, and having a voltage of a few volts, most often between 2.3V and 4.2V, approximately. The cells can be of the lithium-ion type. More precisely, a lithium-ion cell is composed mainly of a porous positive electrode, a porous negative electrode, a separator and an electrolyte (which can be liquid, polymeric or solid). A lithium Nickel Manganese Cobalt oxide NMC or a lithium iron phosphate LFP can be cited as examples of positive electrode active materials, Nickel Cadmium (Ni-cd), or Nickel-Metal-Hydride (Ni-MH) for example. The negative electrode can be a graphite structure or a metal alloy, for example. The operating principle of a lithium-ion cell is based on the reversible exchange of lithium ions between the two porous electrodes.

[0034] The storage system 1 further comprises means for measuring, estimating or sensing electrical parameters, including at least one current sensor 12 capable of measuring or estimating a current value passing through the storage element 10, a voltage sensor and a temperature sensor for cells 11 or each cell 11 of the energy storage element 10. The storage system 1 further comprises a control unit 13 (also called ECU for “Electronic Control Unit” or BMS for “Battery Management System”).

[0035] An objective of the invention is to control maximum currents in the charging phase at the terminal and to reduce the charging time. To this end, the control unit 13 is provided with an integrated circuit computer and electronic memories, the computer and the memories being configured to execute the charging method according to the invention. But this is not obligatory. Indeed, the computer could be external to the unit of battery control, while being coupled to the latter. The control unit 13, according to the invention, can be produced in the form of software modules (or computer modules (or even "software")), or electronic circuits (or "hardware"), or even a combination of electronic circuits and software modules.

[0036] In terminal charging, the lithium deposition phenomenon limits the value of the charging current. To illustrate the lithium deposition phenomenon, in [Fig.2], a negative graphite electrode structure is shown schematically for different charging rates. Diagram 2a represents the zero-current electrode where the surface concentration is uniform to the internal concentration of the graphite structure. Diagram 2b illustrates the electrode for a moderate charging current where the surface concentration is higher than the internal concentration but remains below a saturation level. Diagram 2c illustrates the electrode for a high charging current where lithium deposits form on the surface of the electrode. The reduced lithium is proportional to the current and cannot be inserted in its entirety. Lithium deposit appears, represented by oval-shaped patterns.

[0037] The lithium concentration at the electrode surface can be expressed by a first-order differential equation that indicates the evolution of the concentration curve for a constant current profile of a fixed duration as a function of time. In [Fig.3] are illustrated concentration curves Cx on the upper curves for three different current profiles on the lower curves starting from a state of charge of 0% (SOC) of the total capacity of a lithium-ion cell for graph 3a and a state of charge of 70% of the total capacity of a lithium-ion cell for graph 3b. The concentration level is expressed on a scale of 0% and 100% of the saturation level. The abscissa axis is the duration. Three constant current profiles are shown for fixed durations of 10 seconds, 30 seconds and 180 seconds.It is observed that for durations of 10 seconds and 30 seconds, current values ​​of 350A and 180A are applicable respectively until reaching the saturation level at the end time of the fixed duration. It is further observed that the concentration value at the start time of the pulse is dependent on the state of charge of the cell. For example, for 0% of the capacity, the concentration of the core and electrode surface is at 0% of the saturation level and for a state of 70% of the capacity, the concentration level of the surface and the structure corresponds to 70% of the saturation level. The assumption is that the concentration expressed as a ratio of the saturation level is proportional to the state of charge of a cell.

[0038] From these observations, calibration information for constant current tables for a fixed duration is obtained either by numerical modeling or by experimental means, taking as input electrical parameters including the state of charge (SOC) and the temperature of an energy storage element, a cell or a cell group. These constant current tables provide current values ​​applicable during the fixed duration and beyond which the saturation level is exceeded. An experimental protocol carried out on cells under controlled conditions can be a numerical modeling from the lithium concentration equations described above. Another experimental protocol can be the measurement of a reference potential of the negative electrode corresponding to a voltage measured between the negative electrode and a so-called reference electrode, generally made of lithium, connected to the electrolyte. During a charge, when this voltage reaches 0 volts, this condition indicates that the saturation level has been reached.

[0039] A first table delivers values ​​of a first constant charging current applicable for the first duration at most as a function of measured electrical parameters. The current values ​​are applicable until a saturation level of lithium deposition is reached on the surface of a negative electrode of said storage element at the end of the first duration. The measured parameters include the state of charge SOC and the temperature of a storage element, for a range of [0%, 100%] in SOC and for a temperature range [-20°C, 60°C] for example. It is envisaged to obtain several first tables for different applicable durations, for example durations between 1 second and 180 seconds, for example a table for a duration of 10 seconds, another table for a duration of 30 seconds and another table for a duration of 180 seconds.

[0040] A second table, for controlling a constant current, differs from the first table in that the applicable duration of the current is greater than that of the first table or tables, i.e. greater than several minutes, possibly between several minutes and several hours. The constant current value delivered by the second table corresponds to a lithium reduction rate close to that of the diffusion of atoms in the core of the electrode structure. This second current can be controlled until the voltage limit of a cell corresponding to the so-called “Cut-off voltage” voltage, close to 4.2V, is reached, without the lithium deposition phenomenon appearing. These are current values ​​suitable for charging at a terminal.The second table provides current values ​​applicable without risk of lithium deposition as a function of state of charge parameters SOC and temperature of a storage element, for a range of [0%, 100%] in SOC and for a range of [-20°C, 60°C] for example. Alternatively, the second table provides current values ​​applicable as a function of the voltage in volts and the temperature of a storage element, for a range of [3.2V, 4.2V] in voltage and for a range of [-20°C, 60°C] for example. It is envisaged to obtain several second tables for durations of 180 seconds or more.

[0041] With reference to [Fig.l], the control unit 13 comprises an estimator 15 of the lithium concentration on the surface of the graphite structure of an electrode. The estimator 15 comprises, stored in memory, at least a first constant current table 151 and a second constant current table 152. The control unit may comprise a plurality of tables 151 for different durations. For example, first tables 151 are stored for constant currents of duration 10 seconds, 30 seconds and 180 seconds. First tables and second tables specific to charging currents or discharging currents may also be provided. The control unit 13 is configured to deliver maximum current values ​​applicable during the first durations specific to each first table as a function of instantaneous electrical parameters including the state of charge and the temperature of the storage element.

[0042] Conventionally, the control unit 13 of the battery system further comprises an estimator of the aging state of the cells providing an SOH parameter representative of the aging state. The estimator 15 further comprises a table delivering a current correction factor as a function of the SOH aging parameter. The current correction factor is provided to correct a value of the current delivered by the first and second tables 151 and 152.

[0043] Furthermore, the estimator 15 comprises a calculation module 153 receiving in real time the current value I(t) passing through the storage element 10 of the battery system 1. This calculation module has the function of calculating a quantity of energy exchanged EQ(t) with the storage element during a calculation period. The calculation period is initiated for example at the start-up of the storage system, in particular when starting an electrified vehicle. The quantity of energy EQ(t) is delimited in a variation range by a first limit LimH and a second limit LimB. The quantity of energy EQ(t) is a parameter representative of the surface concentration level of the graphite structure. The quantity EQ(t) is a parameter expressed in Ah taking positive values ​​to account for the charged energy and negative values ​​for the discharged energy. EQ(t) as a function of time is calculated according to the following relationship: [00441 W =

[0045] Where by convention, a charge current is of negative value and a discharge current of positive value.

[0046] The variation range is correlated to the variation of the lithium concentration around a reference level corresponding to the concentration of the core of the electrode structure and is delimited by the quantities of energy exchanged during the application of the currents defined by the tables during the fixed duration associated with the tables. The energy quantity parameter has the advantage of taking into account the evolution of the electrical stresses in charge and discharge applied to the storage element thus improving the estimation of the surface condition. This makes it possible to take into account during driving a braking situation which has led to an increase in the lithium concentration on the surface. It is usual that before charging at a terminal, particularly on the motorway, the recharging phase takes place immediately following braking, which could possibly cause regenerative braking and saturation of the surface with lithium. Estimator 15 makes it possible to detect this situation.

[0047] It is conceivable that the calculation module 153 implements other types of real-time estimator of the lithium concentration at the surface of an electrode of the storage element, for example by measuring a reference voltage between the negative electrode and a reference electrode of the electrolyte or by modeling the reference voltage.

[0048] A module 154 calculates the first limit of the variation range LimH from the first table 151 determining the maximum applicable current IDC1 and the first associated duration Dl, LimH=IDCl*Dl. This information is obtained as a function of the instantaneous electrical parameters P including the state of charge SOC and temperature during the current control of the battery system. The limit LimH corresponds to the quantity of energy charged from the reference state of the storage element to reach the saturation level. For example, for a constant charging current of 350A for a fixed duration of 10 seconds, the first limit LimH is equal to approximately 1 Ah, for a constant charging current of 150A for a fixed duration of 30 seconds, the first limit is equal to 1.25 Ah

[0049] The control unit 13 comprises a current controller 16 comprising a control function 161 delivering current control information CCI. The function 161 takes as input information comprising at least the current values ​​delivered by the first and second constant current tables 151 and 152, and the value of the elapsed charging time CT since the instant of generation of a charging current, either IDC1 or IDC2. The information CCI is delivered via communication means to other electrical systems consuming and / or generating energy, for example a voltage converter, an electric motor. In the context of the invention, the information CCI is intended for a charger of the battery system, for example the on-board charger of an electrified vehicle or a charging terminal external to an electrified vehicle.The CCI information can be maximum allowed charging current information, or maximum allowed charging power.

[0050] The current controller 16 comprises a protection function 162 configured to monitor the current I(t) flowing through the storage element with respect to the current control information CCI. The function 162 detects whether the current I(t) is greater than the information CCI and calculates a new maximum current information taking into account takes into account a correction coefficient to reduce the value of the maximum authorized current or alternatively delivers the correction coefficient to the control function 161. The protection function 162 can calculate several protection variables, in particular a duration of excess of the current. The protection function aims to detect situations where the charger or the terminal delivers, by failure, a current greater than the CCI current information. The protection function 162 makes it possible to reduce the maximum current information CCI and consequently to reduce the current actually controlled. This strategy has the advantage of avoiding the immediate actuation of disconnection switches (protection relay or MOSFET) of the storage element 10. This function can be activated in a non-critical range of values ​​around the CCI information and can provide different levels of correction depending on the difference between the CCI information and the measurement of I(t).It is further provided that if a current I(t) is detected which is greater than a critical threshold, the control unit actuates the current cut-off switches.

[0051] Furthermore, it is envisaged that the CCI information delivered by the current controller 16 may be information on the maximum electrical power that can be exchanged with the storage element at a given instant or a remaining electrical power from a given instant.

[0052] Furthermore, the control unit 13 comprises a means 14 for measuring or determining the elapsed time CT of a charging operation, typically for an electrified vehicle the charging time during a charging session by connection to a terminal. The elapsed time CT is calculated from an on-board stopwatch, clock or counter for example which is triggered at the instant of detection of a charging current.

[0053] Furthermore, the control unit 16 may comprise a means 163 for estimating a controllable duration DPB of the first accelerated charging phase. In a first variant, the controllable duration DPB is determined as a function of the parameter for estimating the lithium concentration at the surface of the electrode. In a second variant, the controllable duration is determined as a function of the measurement of a relaxation duration between the last charging phase while driving, for example in regenerative braking, and the instant of initialization of the first charging phase at the terminal. The controllable duration DPB conditions the selection of the first current or the second current during current control.

[0054] In [Fig. 4], the charging method according to the invention is shown. The current control method is implemented by the control unit of the energy storage system as described in detail in [Fig. 1]. This method is applied during the recharging phase on an external charging station, a domestic terminal or a public use terminal. The charging station may be a so-called mode 4 fast charging station capable to deliver a continuous charging current to the storage system. The charging according to the invention provides a first phase of acceleration of the charging, called “Boost”, controlled at a high power, i.e. greater than 22kW, greater than 50kW or greater than 150kW, during the first fixed duration Dl, then a second charging phase at the value of a current determined by a second table specific to the charging on the terminal at a power lower than that of the first phase.

[0055] In a first step 60, the control unit 13 is started and initialized. The battery system is electrically connected to a battery charger. In the case of an electrified vehicle, the vehicle is connected by a charging cable to a terminal. The value of the parameter representing the lithium concentration on the surface of the negative electrode is initialized to the last value calculated during the last driving.

[0056] The method then comprises a first charging phase 61 for accelerating the charging. This first phase is designed to be controlled for a fixed duration D1 determined by the first table 151 at the value of the current IDC1 delivered by this first table.

[0057] For this purpose, the first phase 61 comprises a first sub-step 611 of measuring or estimating first electrical parameters P of the storage element of the battery, the first parameters being the temperature T and the state of charge SOC of each storage element of the battery, an aging state parameter SOH of the cells, and the exchanged current I(t) in particular. The measurement is carried out periodically during operation of the battery.

[0058] Then, the method comprises a second sub-step 612 of determining the first maximum current IDC1 delivered by the first direct current table 151 taking said measured electrical parameters as input. The first table 151 delivers values ​​of the first current IDC1 applicable during the first fixed duration D1 from a reference state of the storage element corresponding to the measured electrical parameters. The reference electrical parameters are the state of charge SOC and the temperature T of the storage element. This sub-step further provides for correcting the value of the current by a coefficient dependent on the aging state parameter SOH.

[0059] The method further comprises a third sub-step 613 of charging the storage element to the value of the first direct current IDC1 during the first fixed duration DL. This is the so-called “Boost” phase. The first phase 61 is controlled as long as the charging duration CT is less than the first duration DL. The profile of the charging current IDC1 is in the form of a single constant current slot.

[0060] Alternatively, the first phase 61 may further comprise the following sub-steps to take into account the lithium concentration of the surface of a negative electrode. For example, when driving on a motorway, the preceding regenerative braking arrival at a charging station may result in a state of saturation of the surface. The method advantageously makes it possible to control the first phase of charging acceleration according to the concentration. More precisely, the first phase may comprise the following sub-steps:

[0061] - the determination of a parameter representative of a real-time estimation of the lithium concentration on the surface of an electrode of the storage element,

[0062] - the determination of a second controllable duration DPB of the first phase 61 in function of said concentration parameter relative to a limit of a permitted range of variation of said parameter,

[0063] - the selection of the load at the value of the first current IDC1 if the elapsed time CT is less than the second DPB controllable duration,

[0064] - and when the elapsed duration CT is greater than the second controllable duration DPB, the second charging phase control 62.

[0065] More precisely, the controllable duration DPB is calculated according to the following relationship dependent on the concentration parameter: DPB=Dl*(LimH-Pcli), where DPB is the second controllable duration, DI is the fixed duration of the charging current IDC1, LimH is the lithium saturation limit and Pcli is the parameter representative of the concentration. LimH and Pcli are expressed by a percentage ratio (%) or a parameter expressed between the range [0,1]. LimH=100% for the maximum saturation level and Pcli is between [0% and 100%]. According to a variant, Pcli is a quantity of energy exchanged during a vehicle driving cycle preceding the charging operation and LimH is a quantity of energy corresponding to the quantity of energy charged by the first current during the duration DI.

[0066] In another variant, the first phase 61 may further comprise the following sub-steps to take into account a relaxation time of the cells between the last charge, for example regenerative braking while the vehicle is running, and the time of commencement of the first phase 61 while charging on a terminal. More specifically, the first phase 61 further comprises the following sub-steps:

[0067] - the determination of a third relaxation time between a prior charge and the charging operation and the time of commencement of the charging operation,

[0068] - the control of the first charging phase 61 during the first fixed duration DI if the third duration is greater than a predetermined relaxation threshold,

[0069] - and when the third duration is less than the relaxation threshold, the command immediate start of the second charging phase 62 when charging is triggered. Immediate means that the first phase is not carried out and that the second phase begins at the second current value IDC2.

[0070] The predetermined relaxation threshold is a parameter configured in the memory of the control unit of the storage system. The third relaxation time is measured at by means of a counter, clock or stopwatch of the control unit adapted to measure a duration between two events.

[0071] Then, when the second charging phase 62 is controlled, this is operated at current values ​​IDC2 lower than those IDC1 delivered by the first table 151 so that the lithium saturation level at the surface of an electrode cannot be reached.

[0072] For this purpose, the second phase 62 comprises a first sub-step 621 comprising the measurement of second electrical parameters P of the storage element. These parameters are the voltage expressed in volts and the temperature expressed in degrees Celsius of the storage element. The voltage parameter is a measurement obtained by a sensor which makes it possible to dispense with the calculation of the state of charge and makes it possible to take into account in part the necessary reduction in currents with aging. It is envisaged that the second parameters comprise the state of charge (SOC) and the temperature.

[0073] Then, the second phase comprises a second sub-step 622 comprising the determination of the second maximum charging current IDC2 delivered by the second direct current table 152 taking as input the second measured electrical parameters P which are the temperature and the voltage of the storage element, or alternatively the temperature and the state of charge. This sub-step further provides for correcting the value of the current by a coefficient dependent on the aging state parameter SOH. Unlike the first current IDC1, the values ​​of the second current IDC2 are applicable until the storage element is fully charged. These values ​​are defined experimentally and are configured so that the diffusion rate of the lithium atoms in the electrode is less than or equal to the reduction rate of the lithium ions. The values ​​of the second tables are therefore strictly lower than those of the first table.

[0074] The second phase 62 further comprises the third sub-step 623 of charging the storage element to the value of the second direct current IDC2. Throughout the second phase 62, the value of the second current varies as a function of the temperature and the voltage of the storage element, until the charging stop condition is reached, i.e. the target state of charge or the cut-off voltage, corresponding to the so-called “Cut-off Voltage” value. The second phase 62 is controlled until the charging stop condition is reached. For example, for a charge from 30% of the SOC to 100% of the SOC, the profile of the charging current IDC2 will be in the form of successive constant current steps until the charging end time. The charging current profile does not include a relaxation period.

[0075] The charging method further provides protection functions that are permanently active during the charging operation. A protection function is a function overcurrent detection which aims to detect whether the measured current I(t) is greater than the commanded current setpoint IDC1 or IDC2 during the first phase or the second phase respectively. The protection function further provides for the measurement of a fourth duration during which the measured current is greater than the current I(t). In the event of detection of an overcurrent, and the fourth duration is greater than a protection threshold, the method provides for the control of a reduction of the current setpoint or the control of an opening of a protection relay or switch electrically connecting the storage element to the charger. The method may comprise several current reduction stages depending on the fourth measured duration.

[0076] In [Fig.5], graphs 5a, 5b and 5c represent an initialization sequence of a charging operation in accordance with the method according to the invention comprising the first phase 61 of acceleration of the charging then the second phase 62. Graph 5A illustrates the evolution of the parameter Pcli representative of the lithium concentration at the surface of a negative electrode of the storage element. The concentration is expressed as a percentage of lithium saturation, where 100% is equivalent to a maximum concentration in the electrode structure, for 100% of the SOC and 0% the minimum concentration corresponding to 0% of SOC. CHG1 represents the concentration profile during the control of the charging method according to the invention. CHG2 is the concentration profile for a conventional charge without control of the first acceleration phase.

[0077] Graph 5b represents the current profile II controlled during a charging operation according to the invention comprising the first phase 61. Profile 12 illustrates a conventional charge. Graph 5C represents the evolution of the state of charge during the first 180 seconds. The first phase of acceleration of the charge makes it possible to quickly increase the charging time and has the additional advantage of quickly heating the cells to bring them into the optimal thermal conditions to then control the constant charging currents delivered by the charging tables taking into account the voltage and temperature parameters of the cells. This method is particularly advantageous in low temperature charging conditions.

[0078] In [Fig. 6], an electrified vehicle 80 having a battery system 83 according to the invention is shown schematically. The vehicle may be a hybrid or fully electric vehicle. The vehicle 80 has an electric prime mover 81 for moving the vehicle and powered by the battery system 83. Some or all of the functions of the vehicle 80 are controlled by a control unit 82. The control unit 82 may include at least one processor that executes instructions stored in a computer-readable medium such as non-volatile memory. The control unit 82 may also be multiple computing devices that control individual components or vehicle subsystems 80 in a distributed manner. The processor may be any conventional processor, such as a commercially available central processing unit. Alternatively, the processor may be a dedicated device such as an application-specific integrated circuit (ASIC) or other hardware processor.

[0079] The prime mover 81 and the battery system 83 can be controlled in regenerative braking operation. The battery system comprises a control unit 84 comprising a computer and memories configured for implementing the current control method according to the invention. In particular, the memories have a recorded program comprising instructions which, when the program is executed by the control unit of the battery system, cause the latter to implement any one of the embodiments of the charging method according to the invention. Furthermore, the control unit 84 is connected in communication with computers of the vehicle by means of an on-board communication bus 88, for example of the CAN (Control Area Network) type, to deliver the current control information determined from the method according to the invention.The control unit 84 informs, for example, the powertrain of a maximum permitted current determined as a function of the estimation of the lithium concentration. The current value is a constant current which is associated with a maximum permitted fixed duration. The vehicle further comprises a voltage converter 85 of the DC / DC or AC / DC type. The vehicle further comprises an electrical relay or switch 86 provided for selectively disconnecting and connecting the battery system 83 from the vehicle's electrical systems and a charging box 87. The charging box is an interface allowing the connection of a charging cable 89 to an external energy source 90 connected to an extended electrical supply network 91 operating at alternating voltage. Alternatively, the charging interface is suitable for wireless charging.

[0080] The energy source 90 is for example a charging terminal capable of operating in so-called mode 4 fast charging, capable of delivering an electrical power greater than 50 kW, 150 kW or 350 kW. In the case of a charging operation implemented by the invention, the battery system 83 is provided to communicate with the on-board charger 85 and / or the charging terminal 90 in order to communicate information on the maximum authorized current, delivered by the first table during the first phase and by the second table during the second phase.

[0081] The invention is described in the above by way of example. It is understood that the person skilled in the art is able to produce different variant embodiments of the invention by associating, for example, the different characteristics above taken alone or in combination, without departing from the scope of the invention.

Claims

Claims

1. Method for charging a battery system (1) comprising an energy storage element (10), the method being implemented by a control unit (13) of said battery system (1) and being characterized in that it comprises the following successive steps during a charging operation by a charger: - a first charging phase (61) comprising the following sub-steps: - the measurement (611) of first electrical parameters (P) of the storage element (10), - determining (612) a first maximum charging current (IDC1) delivered by a first direct current table (151) taking as input said measured electrical parameters (P), the first table (151) delivering values ​​of the first applicable current (IDC1) for a first fixed duration (Dl), from a reference state of the storage element (10) corresponding to the first measured electrical parameters (P), until reaching the lithium saturation level at the surface of a negative electrode of the storage element at the end time of the first fixed duration (Dl), - charging (613) the storage element to the value of the first direct current during the first fixed duration (Dl), - when an elapsed duration (CT) of the charging operation is greater than the first fixed duration (Dl), the control of a second charging phase (62) comprising the following sub-steps: - the measurement (621) of second electrical parameters (P) of the storage element (10), - determining (622) a second maximum charging current (IDC2) delivered by a second direct current table (152) taking as input the second measured electrical parameters (P), the second table (152) delivering values ​​of the second current (IDC2) corresponding to the second measured electrical parameters (P) and applicable until the storage element is fully charged, - charging (623) the storage element to the value of the second direct current (IDC2).

2. The method of claim 1, wherein the first phase further comprises the following substeps: - the determination of a parameter (Pcli) representative of an estimate in real time of the lithium concentration on the surface of an electrode of the storage element, - the determination of a second controllable duration (DPB) of the first phase as a function of said concentration parameter in relation to a limit (LimH) of a permitted variation range of said parameter, - the selection of the charge at the value of the first current if the elapsed duration (CT) is less than the second controllable duration, - and when the elapsed duration is greater than the second controllable duration, the control of the second charging phase.

3. Method according to claim 2, in which the parameter representative of the concentration is a first quantity of energy (EQ(t)) exchanged with the storage element during a calculation period prior to the first phase (61) and the limit (LimH) is a second quantity of energy corresponding to the energy charged by the first current (IDC1) during the first fixed duration (Dl).

4. Method according to claim 2 or 3, in which the second controllable duration (DPB) is calculated according to the following relation: DPB = Dl -(LimH - Pcli), DPB being the second duration, Dl being the fixed duration of application of the first current (IDC1) and LimH being the lithium saturation limit, Pcli being the parameter representative of the lithium concentration, LimH and Pcli being expressed by a ratio.

5. Method according to any one of claims 2 to 4, in which the first phase further comprises the following sub-steps: - determining a third relaxation duration between a charging phase prior to the charging operation and the instant of commencement of the charging operation, - controlling the first charging phase (61) during the first fixed duration (D1) if the third duration is greater than a predetermined relaxation threshold, - and when the third duration is less than the relaxation threshold, immediately controlling the second charging phase (62).

6. The method of claim 5, further comprising measuring the instantaneous charging current of the storage element (10), calculating a fourth duration during which the instantaneous current is greater than the first charging current during the first phase and activating a current protection of the battery system (1) as a function of the fourth duration relative to a protection threshold.

7. Battery system (1) comprising an energy storage element (10) and a control unit (13) configured specifically for implementing the charging method according to any one of claims 1 to 6.

8. An electrified vehicle (80) comprising a battery system (83) and a charging interface (87) adapted to be electrically connected to an external power source (90) to the vehicle (80) for performing charging of the battery system (83) and wherein the battery system is according to claim 7.

9. A computer program comprising instructions which, when the program is executed by a control unit of an energy storage system, cause the latter to implement the method according to any one of claims 1 to 6.

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