METHOD FOR CONTROLLING A BATTERY SYSTEM FOR BALANCING AND DETECTING A DEFECTIVE CELL

Abstract

The present invention relates to a method for controlling a battery system (1) comprising a plurality of energy storage elements (10a, 10b, 10c, 10d) and a control unit (11) configured to implement a balancing function (12) for the storage elements (10a, 10b, 10c, 10d). The method comprises the following successive steps: determining, for each storage element (10a), a value (DEQa) of a first parameter (P1) representing the difference in the quantity of electricity between the instantaneous state of charge (SOCt) and a target state of charge (SOC100); determining the maximum value of the first parameter (P1) among the plurality of storage elements (10a); determining, for each storage element (10a), a value of a second balancing parameter (P2) representing the quantity of electricity to be balanced; and determining a balancing setpoint for each storage element (10a) depending on the respective value of the second parameter (P2).Figure 1.

Description

Title of the invention: METHOD FOR CONTROLLING A BATTERY SYSTEM FOR BALANCING AND DETECTING A DEFECTIVE CELL

[0001] The field of the invention relates to a method for controlling a battery system, in particular for balancing and detecting a defective storage element.

[0002] Power battery systems, particularly for electrified vehicles, typically comprise a set of electrochemical cells connected in series and / or parallel within the system. The term energy storage element refers to an electrochemical cell or an assembly of cells that can be connected in series and / or parallel. Typically, in electromobility applications, energy storage elements are of the lithium-ion type.

[0003] During the service life of a battery, the storage elements tend to age unevenly, causing an imbalance in the state of charge. This imbalance is problematic because it leads to a decrease in the usable capacity of the battery system as a whole. Furthermore, excessive imbalance in a cell is a sign of electrochemical deterioration caused by lithium deposition, which can lead to the formation of a short circuit in the structure. To avoid this risk, battery systems implement monitoring and protection functions to warn the user.

[0004] Furthermore, to optimize the usable capacity of a battery, manufacturers also incorporate a balancing function for the storage elements. A balancing function relies on detecting a difference in the state of charge between the storage elements and controlling a balancing circuit to reduce the observed differences. Balancing functions use passive balancing circuits, implementing energy discharge circuits in a resistor, or more sophisticated so-called active balancing circuits that allow energy transfer between the storage elements. The latter improve energy efficiency.

[0005] Furthermore, to address these various protection and energy optimization issues, prior art document EP-B1-2171824 describes a solution for deactivating a defective battery cell. This solution also includes a method comprising a step of monitoring an electrical parameter of a group of electrochemical cells connected in parallel, which could be a self-discharge rate or the time required to perform an operation. resistive balancing or the amount of energy required during voltage balancing. Furthermore, US patent document US-A1-20210396817 is known, describing a method for detecting abnormal self-discharge of cells in a battery system based on monitoring energy quantities calculated for the needs of a balancing system against a monitoring criterion. Passive and active balancing techniques are described. This method aims to protect a battery system. EP-B1-2365352 is also known, describing a method for controlling a battery system implementing a function for detecting a defective cell by comparing the difference between the maximum state of charge of all cells and the state of charge of each cell against thresholds. When this difference exceeds one of the thresholds, a defective cell detection alert is generated.

[0006] This latter technique relies on measuring the state of charge of each storage element and implementing a balancing of the cell state of charge parameters. However, cells within the same battery system may exhibit capacity variations that can increase with age. These capacity variations lead to an imbalance in the states of charge as charge and discharge cycles occur, reducing the usable capacity of a battery. This phenomenon further increases the activity of the balancing function and consequently energy losses. In addition, these capacity variations can trigger false alarms indicating a defective state of the storage elements due to the state of charge variations that appear during charge and discharge cycles. However, an aging cell does not necessarily present an immediate risk of short circuit.

[0007] There is therefore a need to address the aforementioned problems. One objective of the invention is to provide a battery system that reduces the activation time of a balancing function. Another objective of the invention is to improve the protection function of a battery system against electrochemical cell failures, in particular against false alarms.

[0008] More specifically, the invention relates to a method for controlling a battery system comprising a plurality of energy storage elements and a control unit configured to implement a balancing function for the storage elements. According to the invention, the method comprises the following successive steps: - the determination, for each storage element, of a value for a first parameter representing the difference in the quantity of electricity between the instantaneous state of charge and a target state of charge, - determining the maximum value of the first parameter among the plurality of storage elements,

[0009] - determining for each storage element a value of a second balancing parameter of quantity of electricity to be balanced so that the value of the first parameter of each storage element is equal to the maximum value, - the determination of a balancing setpoint of each storage element as a function of the respective value of the second parameter.

[0010] The method according to the invention may include the following additional features, alone or in combination:

[0011] - The target state of charge is the value of a target state of charge setpoint of a battery system charging control function.

[0012] - The target state of charge is within a range between 50% and 100% of the capacity total of a storage element.

[0013] - The balancing setpoint is a discharge time in a discharge circuit calculated based on the value of the second parameter.

[0014] - the control unit is further configured for the implementation of a function for detecting a defective storage element comprising the following steps: - determining for each storage element a value of a third parameter representative of a difference between the value of the first parameter of each said storage element and the average value of the first parameter values ​​for the plurality of storage elements,

[0015] - the determination for each storage element of a first current corresponding to the variation in the value of the third parameter over an observation period, - the determination, for each storage element, of a value for a fourth parameter representing the difference between the value of the balancing setpoint of each said storage element and the average value of the balancing setpoints for the plurality of storage elements,

[0016] - the determination for each storage element of a second current corresponding to the variation in the value of the fourth parameter over the observation period, - the determination of a fifth parameter representing the self-discharge current for each storage element over the observation period, depending on the first and second currents,

[0017] - the generation of an alert when the fifth parameter exceeds a first threshold.

[0018] - The detection function further includes generating an alert when the derivative of the fifth parameter with respect to time over the observation period exceeds a second threshold.

[0019] - The detection function further includes generating an alert when the derivative of the fifth parameter with respect to the amount of electricity discharged over the observation period exceeds a third threshold.

[0020] A battery system is further provided comprising a plurality of energy storage elements and a control unit configured for the implementation of a function for balancing the storage elements and a function for detecting a defective storage element, wherein the control unit is configured to implement the control method according to any one of the preceding embodiments.

[0021] An electrified motor vehicle comprising such a battery system is also planned.

[0022] The invention provides a battery system control unit comprising means specifically configured to implement the control method according to any one of the preceding embodiments.

[0023] The invention provides for a computer program comprising instructions which, when the program is executed by a control unit of a battery system, cause the latter to implement any one of the embodiments of the control method.

[0024] It is further provided a computer-readable recording medium comprising instructions which, when executed by a computer, cause the computer to implement any one of the embodiments of the control method.

[0025] The invention reduces energy losses in a battery system due to the shorter activation time of the balancing device. The invention also improves the detection of defective storage cells and prevents the generation of false alarms.

[0026] Other features and advantages of the present invention will become more apparent upon reading the following detailed description, which includes embodiments of the invention given by way of non-limiting examples and illustrated by the accompanying drawings, in which:

[0027] [Fig. 1] schematically represents a battery system configured for the implementation of the control method according to the invention.

[0028] [Fig.2] represents a block diagram of an embodiment of the control method during the execution of a balancing function.

[0029] [Fig.3] schematically represents a battery system and the parameters calculated during the execution of the process according to the invention for the balancing function.

[0030] [Fig.4] schematically represents a battery system and the parameters calculated during the execution of the process according to the invention for the balancing function.

[0031] [Fig.5] represents a block diagram of an embodiment of the control method during the execution of a function for detecting a defective storage element.

[0032] The invention applies to electrified vehicles, that is, vehicles comprising an electric motor and power electronics, whether 100% electric or hybrid, preferably motor vehicles, but not exclusively, such as aircraft, tractors, bicycles, and ships. More generally, the invention applies to any autonomous electrical system such as drones, robots, or portable devices, computers, tablets, mobile phones, consoles, cameras, and scanners, which are cited as a non-exhaustive list of application examples.

[0033] In [Fig. 1], a battery system 1 intended to implement the control method according to the invention is schematically represented. The battery system 1 comprises a plurality of energy storage elements, at least two, illustrated by way of non-limiting example by four elements 10a, 10b, 10c, 10d, and a control unit 11 configured for implementing the control method, including a balancing function 12 for the energy storage elements, as well as a detection function 13 for a defective storage element. The storage elements are electrically arranged in series so as to deliver an electrical voltage at connection terminals. Each storage element may comprise at least one electrochemical energy storage cell or may consist of a group of cells connected in series and / or in parallel according to the electrical specifications of the system.

[0034] An electrochemical cell is an electrical energy storage device with two terminals and a voltage of a few volts, most often between approximately 2.3V and 4.2V. Cells can be of the Lithium-ion type (lithiumized Nickel Manganese Cobalt Oxide (NMC) or lithium iron phosphate (LFP) can be cited as examples of active materials for the positive electrode), Nickel Cadmium (Ni-Cd), or Nickel Metal Hydride (Ni-MH), for example. More precisely, a lithium-ion cell is mainly composed of a porous positive electrode, a porous negative electrode, a separator, and an electrolyte (which can be liquid, polymeric, or solid). The operating principle of a lithium-ion cell is based on the reversible exchange of lithium ions between the two porous electrodes.

[0035] Furthermore, the control unit 11 (designated by the acronym BMS for "Battery Management System" or TBCU for "Traction Battery Control Unit") is adapted to monitor the electrical parameters specific to the battery and each energy storage element 10a, 10b, 10c, 10d by means of current, voltage, and temperature sensors, such as the state of charge (SOC), which designates the level of charge state of the battery expressed as a ratio between the quantity The state of charge is measured by the amount of electricity stored at a given moment and the maximum amount of electricity that can be stored at a given moment, the open-circuit voltage (OCV) expressed in volts, the charging current expressed in amperes, the state of health (SOH), which refers to the battery's aging level parameter, representing the ratio between the maximum amount of electricity that can be stored at a given moment and the maximum amount of electricity that could be stored when the battery was new, or the amount of electricity or energy, expressed in Ah or Wh, stored at a given moment by each storage cell. A technique known to those skilled in the art for estimating the state of charge is to measure the open-circuit voltage of a storage cell after a relaxation phase, for example, when the vehicle is woken up, and to determine an estimate of the state of charge from a map.The stored electricity quantity parameter EQ_10a for an energy storage element 10a can be determined at any time from the product of the values ​​of the state of charge parameters SOCt and the total capacity in Ah.

[0036] The balancing function 12 cooperates with a storage element balancing device comprising a balancing circuit 14a for each cell or group of cells of the plurality of storage elements 10a to 10d. Balancing consists of transferring energy to reduce the dispersion of the state of charge of the storage elements. The balancing device may be passive and include circuits of controllable switches and resistors. Alternatively, the balancing device may be active and include circuits of switches and capacitors arranged to control energy transfers between adjacent cells or groups of cells. The control method according to the invention provides improved control of the balancing function, making it possible to reduce the activation time of the balancing circuit in order to limit electrothermal losses.

[0037] More specifically, for the implementation of the control method according to the invention, the balancing function 12 includes means for determining and storing in the memory of the control unit, for each storage element 10a at lOd, a first parameter PI having the value of a difference in the quantity of electricity DEQa between the instantaneous state of charge SOCt and a target state of charge SOC100, for example, the full charge of the storage elements. The parameter PI can be expressed in Ah or Wh. The target state of charge SOC100 can be between 50% and 100% of the state of charge, between 80% and 100%, or preferably be equal to 100% of the state of charge. Unlike known balancing solutions, the target state of charge SOC100 is a fixed value in the calibration of the balancing function.This parameter is the cell balancing reference in the state of charge and ensures that balancing is achieved when the battery is charged to this target value, for example during charging at a charging station.

[0038] The balancing function 12 further includes means for determining the maximum or minimum value stored in the control unit's memory of the first PI parameter among the plurality of storage elements. The maximum value of the PI parameter is used by the control method to balance the storage elements in terms of the quantity of electricity so as to finalize the balancing during charging to the target state of charge. Thus, balancing is partially implemented during charging at the terminal, which reduces energy losses compared to conventional solutions where all the energy is lost in a discharge circuit.

[0039] Furthermore, the balancing function 12 includes means for determining and storing in the control unit's memory, for each storage element, a second parameter P2 whose value is a quantity of electricity to be balanced such that the value of the first parameter PI of each storage element is equal to the maximum value DEQmax of the difference in the quantity of electricity between the instantaneous state of charge SOCt and a target state of charge SOC100. The parameter P2 is used to determine the balancing setpoint for each storage element. The balancing setpoint is, for example, an activation time of the discharge circuit determined as a function of the quantity of electricity to be balanced.

[0040] Furthermore, the detection function 13 for a defective storage element is designed to estimate, at any given time, a self-discharge parameter for each storage element in order to generate or not trigger an alert. The detection function is based on the observation, over a given period, of a first component corresponding to the electricity requirements for a variation in the amount of stored electricity relative to an average for all storage elements, and a second component corresponding to the activation requirements of the balancing function relative to an average for all storage elements. An abnormal deviation in self-discharge from the average behavior suggests a defective state of an electrochemical cell, in particular lithium deposition that could cause a short circuit. The detection may implement at least one or more detection criteria relative to at least one self-discharge threshold.

[0041] More specifically, function 13 is configured to determine, for each storage element, a value of a third parameter P3 representative of a difference between the value DEQa of the first parameter PI of each said storage element 10a and the average value DEQm for the plurality of storage elements 10a at 10d, and to determine a first current corresponding to the variation of the value of the third parameter P3 over an observation period. The control unit stores in memory at least two, or more, values ​​of the parameter P3 and the dates of recording said values ​​for the purposes of the detection function. Conventionally, a table A sliding value system is implemented for recording; for example, one hundred values ​​of parameter P3 are stored in the control unit's memory. The resolution of the array allows for the calibration of different detection thresholds.

[0042] Furthermore, function 13 is configured to determine, for each storage element, a value of a fourth parameter P4 representative of the difference between the balancing setpoint value of each storage element 10a and the average value of the balancing setpoints for the plurality of storage elements 10a at lOd, and to determine a second current corresponding to the variation of the value of the fourth parameter P4 over the observation period. The control unit stores in memory at least two, or more, values ​​of parameter P4 and the dates of recording said values ​​for the purposes of the detection function. Conventionally, a sliding table of values ​​is implemented for recording; for example, one hundred values ​​of parameter P4 are stored.

[0043] Finally, function 13 is configured to determine a fifth parameter P5 representing the self-discharge current for each storage element 10a over the chosen observation period. This fifth parameter P5 consists of the contribution of the first current and the second current. Function 13 is configured to generate or not generate an alert based on the fifth parameter P5 relative to at least a first threshold, or based on the variation of parameter P5 during the chosen observation period relative to a second or third threshold.

[0044] In [Fig. 2], the control method implemented by the battery system control unit is schematically represented by a functional block diagram. The control unit is equipped with an integrated circuit computer and electronic memory, the computer and memory being configured to execute the control method. However, this is not mandatory. Indeed, the computer could be external to the control unit, while still being coupled to it. In this latter case, it could itself be arranged as a dedicated computer including, for example, a dedicated program. Consequently, the control unit, according to the invention, can be implemented in the form of software modules, electronic circuits, or hardware, or a combination of electronic circuits and software modules.

[0045] The parameters calculated for implementing the control method are illustrated in Figures 3 and 4, alongside the description of the method. In these figures, the storage element 10b has a lower electrical capacity than the other elements 10a, 10c, and 10d. Furthermore, the storage elements are in a state of charge imbalance.

[0046] More specifically, the control method implements the balancing function, which comprises the following successive steps, among which a first step 20 consists of determining, for each storage element 10a, a DEQa value of the first parameter PI corresponding to the difference in the quantity of electricity between the instantaneous state of charge SOCt and a target state of charge SOC 100, for example 100%. The values ​​of the first parameter PI are calculated from the product of the state of charge, expressed as a ratio with respect to the total capacity, and the value of the total capacity at a given instant expressed in Ah, where Pl = SOCt * CTOT, CTOT being the total capacity determinable at each instant, either by an on-board estimator or possibly by a remote estimator connected to the control unit.

[0047] Next, the process includes a second step 21 consisting of determining the maximum value DEQmax of the first parameter PI among the plurality of storage elements 10a at lOd. In this example, element 10b exhibits the maximum difference in the quantity of electricity.

[0048] Next, the process includes a third step 22 consisting of determining, for each storage element 10a, a value EBa of the second balancing parameter P2, as illustrated in [Fig. 3] by the hatched bands. P2 corresponds to the quantity of electricity to be balanced so that the value of the first parameter PI of each storage element is equal to the maximum value DEQmax, where P2 = DEQmax - DEQa, DEQmax being the maximum deviation among the storage elements and DEQa being the deviation of the quantity of electricity from SOC 100. In this step, it is determined that the elements 10a, 10c, and 1Od have values ​​EBa, EBc, and EBd, respectively, of the parameter P2 of the quantity of electricity to be discharged such that the deviation from SOC 100 is identical for the plurality of storage elements in the battery.

[0049] Next, the method includes a fourth step 23 of determining a balancing setpoint CSBa, CSBc, and CSBd for each storage element 10a, 10c, and lOd, respectively, as a function of the respective value of the second parameter P2. The balancing setpoint is an activation time for the individual discharge circuit 14a, 14c, and 14d. This setpoint is illustrated in [Fig. 4], and the controlled discharge is shown by a solid arrow for the storage elements 10a, 10c, and lOd for which the control unit has determined a quantity of electricity to be discharged. Once the balancing device has performed its action, all the battery storage elements exhibit an identical deviation in the quantity of electricity from the target state of charge SOC100.

[0050] This strategy reduces the activation time of the balancing device during discharge because the discharge in the individual discharge circuit represents only the first phase of the entire balancing process. Balancing will ultimately be achieved during a second phase during a charging operation. from an external charging station. The balancing process therefore comprises a first phase during which the storage cells to be balanced are discharged until the energy difference from the target state of charge is identical for all storage cells in the battery, and then a second phase during which the storage cells are charged until they reach the target state of charge. The target state of charge can be the value at which a charging operation is terminated at a charging station external to the battery system. The target state of charge information can be provided by an onboard charge controller of the battery system.

[0051] In addition, the control method includes, for the implementation of a function for detecting a defective storage element, the following steps described in [Fig.5].

[0052] The method includes a fifth step 50, for each storage element in the battery system, of determining a value of the third parameter P3 representative of a difference between the DEQa value of the first parameter PI of each said storage element 10a and the average value DEQm of the values ​​of the first parameter PI for the plurality of storage elements. The values ​​of P3 are calculated according to the following relationship: P3 = DEQm - DEQa, expressed in terms of electricity. The values ​​of P3 make it possible to identify abnormal self-discharge behavior of a storage element relative to the other elements. The values ​​of P3 are recorded in the memory of the control unit and time-stamped in a table. At least two values, or more, are recorded to define an observation period for the variation of the parameter P3. P3 makes it possible to calculate an initial current contribution to assess the self-discharge of a storage element.Preferably, a P3 value is recorded at each battery system start-up or is recorded periodically at a predetermined frequency.

[0053] The method further comprises a sixth step 51 consisting of determining, for each storage element, a first current corresponding to the variation in the value of the third parameter P3 over an observation period, for example, the last two values ​​of P3 recorded in the table created for this purpose. The first current is calculated according to the following relationship, Ivl = [P3(tl) - P3(t2)] / (tl-t2), Ivl being the first current expressed in Amperes, where tl and t2 are two time-stamped times of calculation of the parameter P3.

[0054] Furthermore, the method also includes a seventh step 52 consisting of determining for each storage element a value of a fourth parameter P4 representative of the difference between the value of the balancing setpoint of each storage element and the average value of the balancing setpoints for the plurality storage elements. The balancing setpoint is, for example, an activation time of the discharge circuit and is expressed in seconds.

[0055] The values ​​of P4 are calculated according to the following relationship: P4 = CSBa - CSBm, expressed in time units, where CSBa is the balancing setpoint for a particular storage element, for example, element 10a, and CSBm is the average value of the balancing setpoints for the plurality of storage elements in the battery system. The P4 values ​​make it possible to identify abnormal balancing behavior of a storage element relative to the other elements. The P4 values ​​are stored in the control unit's memory and time-stamped in a table. At least two or more values ​​are recorded to define an observation period for the variation of the P4 parameter. P4 allows for the calculation of a second current contribution for balancing purposes. Preferably, a P4 value is recorded at each battery system startup or is recorded periodically at a predetermined frequency.

[0056] Next, the control method includes an eighth step 53 consisting of determining, for each storage element, a second current corresponding to the variation in the value of the fourth parameter P4 over the observation period. The values ​​of the second current are calculated according to the following relationship, Iv2 = [P4(tl) - P4(t2)] * Ibal / (tl-t2), Iv2 being the second current expressed in Amperes, where tl and t2 are two time-stamped times of calculation of the parameter P4 corresponding to differences in the balancing activation time and Ibal being the balancing current value imposed by a discharge circuit of the storage element.

[0057] Finally, the control method includes a ninth step 54 consisting of determining a fifth parameter P5 representative of the self-discharge current for each storage element over the observation period, the fifth parameter P5 being dependent on the first current and the second current, where P5 = Ivl + Iv2, expressed in amperes.

[0058] Next, the method includes a tenth step of generating an alert when the fifth parameter P5 exceeds a first threshold. Several strategies for monitoring the self-discharge of a storage element based on the fifth parameter P5 are envisaged.

[0059] A first strategy consists of comparing the value of P5 with a first current threshold SI and when P5 is greater than SI, an alert is generated and identifies the storage element at risk.

[0060] A second strategy consists of calculating the derivative of the fifth parameter P5 over an observation period, and when the time derivative of the fifth parameter P5 over the observation period exceeds a second threshold S2, an alert is generated and identifies the storage element at risk. Indeed, a short circuit can evolve faster than the variation of the self-discharge current and it is then preferable to switch off the battery system before the P5 parameter reaches the value of the first SI threshold.

[0061] A third strategy consists of calculating the derivative of the fifth parameter P5 over an observation period, and when the derivative with respect to the quantity of electricity discharged over the observation period exceeds a third threshold S3 an alert is generated and identifies the storage element at risk.

[0062] The monitoring method has the advantage that it allows the detection of abnormal self-discharge during a prolonged relaxation phase of the cells, by monitoring the parameter P3 corresponding to a first self-discharge current, but also during activation phases of the balancing device by monitoring the parameter P4 corresponding to a second current dependent on the balancing activity.

[0063] The control method applies to the battery system of electrified vehicles, in particular vehicles equipped with means of recharging from an energy source external to the vehicle.

[0064] The invention is described above by way of example. It is understood that a person skilled in the art is able to carry out different variant embodiments of the invention by combining, for example, the different features above taken alone or in combination, without departing from the scope of the invention.

Claims

1. Demands Method for controlling a battery system (1) comprising a plurality of energy storage elements (10a, 10b, 10c, lOd) and a control unit (11) configured for implementing a balancing function (12) of the storage elements (10a, 10b, 10c, lOd), the method being characterized in that it comprises the following successive steps: - the determination (20) for each storage element (10a) of a value (DEQa) of a first parameter (PI) of the difference in quantity of electricity between the instantaneous state of charge (SOCt) and a target state of charge (S OC 100), - the determination (21) of the maximum value (DEQmax) of the first parameter (PI) among the plurality of storage elements (10a), - the determination (22) for each storage element (10a) of a value (EBa) of a second balancing parameter (P2) of the quantity of electricity to be balanced so that the value of the first parameter (PI) of each storage element is equal to the maximum value (DEQmax), - the determination (23) of a balancing setpoint (CSBa) for each storage element (10a) as a function of the respective value of the second parameter (P2), and in that The control unit (11) is configured to implement a function for detecting (13) a defective storage element comprising the following steps: - the determination (50) for each storage element (10a) of a value of a third parameter (P3) representative of a difference between the value (DEQa) of the first parameter (PI) of each said storage element and the average value of the values ​​of the first parameter (PI) for the plurality of storage elements (10a, 10b, 10c, 1Od), - the determination (51) for each storage element (10a) of a first current corresponding to the variation of the value of the third parameter (P3) over an observation period, - the determination (52) for each storage element of a value of a fourth parameter (P4) representative of the difference between the value of the balancing setpoint (CSBa) of each said storage element (10a) and the average value of the balancing setpoints for the plurality of storage elements (10a, 10b, 10c, 1Od), - the determination (53) for each storage element (10a) of a second current corresponding to the variation of the value of the fourth parameter (P4) over the observation period, - the determination of a fifth parameter (P5) representative of the self-discharge current for each storage element (10a) over the observation period depending on the first current and the second current, - the generation of an alert when the fifth parameter (P5) exceeds a first threshold (SI).

2. A control method according to claim 1, wherein the target state of charge (SOC100) is the value of a target state of charge setpoint of a battery system charging control function (1).

3. A control method according to claim 1 or 2, wherein the target state of charge (SOC100) is within a range between 50% and 100% of the total capacity of a storage element (10a).

4. A control method according to any one of claims 1 to 3, wherein the balancing setpoint (CSBa) is a discharge time in a discharge circuit (14a) calculated as a function of the value (EBa) of the second parameter (P2).

5. Control method according to claim 1, wherein the detection function (13) further comprises the generation of an alert when the derivative of the fifth parameter (P5) with respect to time over the observation period exceeds a second threshold (S2).

6. Control method according to claim 1 or 5, wherein the detection function (13) further comprises generating an alert when the derivative of the fifth parameter (P5) with respect to the quantity of electricity discharged over the observation period exceeds a third threshold (S3).

7. Battery system (1) comprising a plurality of energy storage elements (10a, 10b, 10c, 10d) and a control unit (1) configured for the implementation of a balancing function (12) of the storage elements and a detection function (13) of a defective storage element, characterized in that the control unit (11) is configured to implement the control method according to any one of claims 1 to 6.

8. Electrified motor vehicle comprising a battery system (1) according to claim 7.