METHOD FOR CONTROLLING AN ENERGY STORAGE SYSTEM

Abstract

The present invention relates to a method for controlling an energy storage system comprising the following steps: measuring (E01) the electrical parameters of the electrochemical element; implementing a degradation counter (E02) periodically updated according to a degradation increment determined from at least one predetermined table providing a degradation value based on profiles of electrical parameters measured at each counter update; and determining (E03) a limiting coefficient for the control parameter based on the value of the degradation counter to control a limitation (E04) of the operating range of the control parameter. The invention finds application in the field of electrified vehicles. Figure 3.

Description

Title of the invention: METHOD FOR CONTROLLING AN ENERGY STORAGE SYSTEM

[0001] The field of the invention relates to a method of controlling an electrochemical energy storage system for an extension of the duration of use of the storage system.

[0002] Conventionally, in electromobility applications, the electrochemical elements are lithium-ion type cells. These systems are controlled by a control unit whose function is to measure electrical parameters at all times, such as the voltage and temperature of the electrochemical elements, in order to maintain the operation of the storage system under safe conditions.

[0003] In the case of lithium-ion electrochemical cells, when constraints are exceeded relating to the internal gas pressure of their casing and the force between internal components, their use is considered risky. For a given design and a given field of use, these constraints can be deduced from a state of health on capacity aging control parameter, also designated by the acronym SOHc for "State of Health on Capacity", and from the state of charge, or SOC for "State of Charge".

[0004] An existing solution consists of ceasing the use of a storage system when a state of aging limit in storage capacity (SOHc) is reached, while having allowed the full state of charge (SOC) operating range to be used before reaching this limiting SOHc state. The two limiting phenomena, internal gas pressure and electrode expansion, will not evolve proportionally according to the operating conditions. Thus, monitoring the state of a storage system solely by the SOHc criterion leads to a compromise between false detection and non-detection cases that can be improved.

[0005] For other simplified strategies, the criterion determining when to stop use is based on the number of operating cycles (load / discharge) and not on actual monitoring of the SOHc. This presumed link between the number of cycles and the SOHc is valid only within the framework of controlled and reproducible aging profiles, which is not the case in real-world use.

[0006] Ultimately, these strategies can lead vehicle manufacturers to prematurely shut down a power storage system. This is all the more problematic because it would be possible to extend their use under safe conditions by limiting their performance, particularly the amount of energy stored.

[0007] To address this problem, the applicant filed patent application FR3126503A1 describing a method for extending the service life of a battery by determining a force applied to the wall of an electrochemical cell of the battery and determining a maximum permissible state of charge based on said force. According to this method, the force is determined from the battery's state of aging.

[0008] The applicant proposes a new solution to overcome the aforementioned problems. One objective of the invention is to improve the assessment of the aging state of an electrochemical element specifically with respect to one or more constraints. Another objective of the invention is to extend the service life of a power storage system under safe conditions.

[0009] More specifically, the invention relates to a method for controlling an energy storage system comprising an electrochemical element for extending the lifespan of the storage system, the method being implemented by a control unit of the storage system and comprising the following steps:

[0010] - the measurement of electrical parameters of the electrochemical element,

[0011] - limiting the range of use of at least one control parameter of the electrochemical element.

[0012] According to the invention, the process further comprises the following steps:

[0013] - the implementation of a degradation counter updated periodically in based on a degradation increment determined from at least one predetermined table providing a degradation value based on electrical parameter profiles measured at each meter update,

[0014] - the determination of a limiting coefficient of the control parameter as a function the value of the degradation counter to control the limitation of the operating range of the control parameter.

[0015] The method according to the invention may include the following additional features, alone or in combination:

[0016] - The degradation increment is calculated based on a first value and of a second value, the first value being delivered by a first predetermined table taking as input the current and voltage of the electrochemical element at each update of the counter, the second value being delivered by a second predetermined table taking as input the current and temperature of the electrochemical element.

[0017] - The control parameter is a maximum load state limit of the element electrochemical.

[0018] - The control parameter is a maximum limit of the load current or of discharge of the electrochemical element.

[0019] -The degradation counter is a value representative of a force applied to a wall of the envelope of the electrochemical element.

[0020] - The degradation meter is a value representative of a gas pressure internal to the envelope of the electrochemical element.

[0021] - The degradation counter is a value representing a quantity of electrolyte forming a passivation layer on the surface of an electrode of the electrochemical element.

[0022] - The value of the degradation counter is multiplied by the value of a parameter state of aging in capacity to determine the limiting coefficient.

[0023] - The counter refresh period is between 0.5 seconds and 5 seconds.

[0024] The invention further provides an energy storage system comprising an electrochemical element and a control unit configured for implementing the control process according to any one of the preceding embodiments.

[0025] The invention further provides for an electrified vehicle comprising an electric drive machine and such an energy storage system.

[0026] A control unit for an energy storage system is also provided, comprising means specifically configured to implement the control method according to any one of the preceding embodiments.

[0027] A computer program is also provided comprising instructions which, when the program is executed by a control unit of an energy storage system, cause the latter to implement any one of the embodiments of the control method according to any one of the preceding embodiments.

[0028] It is further provided a computer-readable recording medium comprising instructions which, when executed by a computer, cause the computer to implement the control process according to any of the preceding embodiments.

[0029] The invention enables real-time monitoring of an electrochemical degradation phenomenon to adapt the operating range of a storage system and extend its service life. It offers the advantage of establishing a degradation counter related to a specific aging phenomenon, such as the expansion force, internal pressure, or the amount of electrolyte formed in the anode passivation layer. The invention allows for improved monitoring.

[0030] 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:

[0031] [Fig. 1] schematically represents an electrochemical element illustrating the aging phenomena in use which are observed in accordance with the control method according to the invention to extend the service life of an energy storage system.

[0032] [Fig.2] represents an electrical power system comprising an energy storage system capable of implementing the control method according to the invention.

[0033] [Fig.3] represents an embodiment of the control method according to the invention in the form of a block diagram.

[0034] [Fig.4] represents a functional block diagram of a first embodiment of the degradation counter according to the invention for estimating a degradation of the expansion of an electrochemical element.

[0035] [Fig.5] represents a functional block diagram of a second embodiment of the degradation meter according to the invention for estimating an internal gas pressure.

[0036] [Fig.6] represents a graph illustrating the evolution of the maximum limit in the state of charge as a function of the degradation counter of a dilation force.

[0037] The invention applies to electrified vehicles, that is, vehicles comprising an electric drive machine and power electronics, with fully or partially electric motors, preferably motor vehicles, but not exclusively, such as aircraft, trucks, tractors, bicycles, and ships. More generally, the invention applies to any autonomous electrical system such as drones, robots, or portable devices, computers, tablets, and mobile phones, which are cited as a non-exhaustive list of application examples. Electrified vehicles include an energy storage system designed to deliver electrical energy to the drive machine. These storage systems conventionally comprise a set of electrochemical elements connected in series and / or parallel.

[0038] In [Fig. 1], an electrochemical element 1 is represented by a diagram illustrating the aging phenomena occurring during its service life, in particular the expansion of the negative electrode through the formation of a passivation layer and the production of internal gas. The invention aims to implement a control method for estimating these degradations in order to extend the service life of a storage system.

[0039] The electrochemical element 1, also called the electrochemical cell, is an energy storage element having two electrical connection polarity terminals 2 and 3, and exhibiting a voltage of a few volts, most often between approximately 2.3V and 4.2V. The electrochemical element may be of the Lithium-ion type (lithiumized Nickel Manganese Cobalt oxide (NMC) or lithium iron phosphate (LFP) may be cited as examples of active materials for the positive electrode), Nickel Cadmium (Ni-cd), Nickel-Metal-Hydride (Ni-MH), Sodium-ion, Lead-based or even fuel cell for example.

[0040] More specifically, the electrochemical element 1 is primarily composed internally of a porous positive electrode 4 electrically connected to terminal 3, a porous negative electrode 5 electrically connected to terminal 2, a separator 7, and an electrolyte 8 (which may be liquid, polymeric, or solid). The operating principle of a lithium-ion electrochemical element is based on the reversible exchange of lithium ions between the two porous electrodes 4 and 5.

[0041] The electrochemical element 1 is a prismatic cell in which the electrodes 4 and 5 are made of superimposed sheets separated by the separator. The sheets, arranged one on top of the other, are stacked or wound upon themselves to form a stack or coil, also known by the English term "Jelly Roll". The internal components of the electrochemical element 1 are placed inside a housing forming a rigid envelope 9 and are immersed in the electrolyte 8, which allows the passage of lithium ions between the two electrodes 4 and 5.

[0042] The electrochemical element 1 can be a cylindrical cell, or a flexible envelope cell (“Pouch Cell”) in which the electrodes can be stacked or wound.

[0043] The internal components of the electrochemical element 1 must be kept in contact within a positive pressure range. If the maximum value is exceeded, there is a risk in using the electrochemical element 1. During its service life, the active materials will expand during charging and discharging, but also due to aging, which will gradually generate a force exerted on the walls of the electrochemical element.

[0044] To this end, the electrochemical element 1 is housed within a rigid frame 10, generally made of aluminum, the function of which is to enclose the casing 9 of the electrochemical element 1 in order to counteract the internal pressure that tends to push against the walls of the casing. The frame 10 may contain at least one electrochemical element or a plurality of electrochemical elements forming a module. The frame 10 may be a housing or any other housing device that performs the function of enclosing the casing.

[0045] By way of non-limiting example, for a cell of format 28mm x 7mm x 14mm and for a frame dimensioned to contain a given force, the range of internal force in safe use resulting from the expansion force of the internal components (also called "Swelling Force" in the field of electrochemical energy storage elements) is respectively on the order of magnitude of 5kN at the beginning of life to 25kN at the end of life corresponding to a SOHc of the order of magnitude of 70%.

[0046] The variation of the expansion force can be estimated by testing and expressed in Newtons. Thus, tables of force variation can be established by testing or by models based on usage profiles and for a duration of application of the profile, for example, current / voltage and current / temperature parameter pairs in use of an electrochemical element.

[0047] Furthermore, the expansion of the negative electrode is an aging and degradation phenomenon resulting from the formation of a passivation layer 6 on the surface of the negative electrode, composed of electrolyte material. This layer is also designated by the English term SEI for "Solid Electrolyte Interphase". The quantity of electrolyte forming the passivation layer on the surface of the negative electrode can be estimated by testing and expressed in a unit of mass, for example, in grams. Thus, tables of the quantity of electrolyte consumed can be established by testing or by models based on usage profiles and for a duration of application of the profile, for example, current / voltage and current / temperature parameter pairs in use of an electrochemical element. The increase in the force exerted on the stack of electrodes and separators increases the risk of perforation of the latter in the presence of metallic particles and dendrites.

[0048] Furthermore, internal gas formation is another aging phenomenon causing degradation resulting from a reaction at the positive electrode and the formation of the passivation layer, illustrated by the bubbles in [Fig. 1]. The internal gas produces a pressure that pushes against the wall of the casing 9. For example, the maximum internal pressure at the end of life can be on the order of 6 to 8 bar, with a fluctuation due to breathing during charging and discharging, on the order of 0.35 bar during SOC variations. The gas pressure can be estimated by testing and expressed as force values ​​in Newtons. Thus, tables of gas pressure variations can be established by testing or by models based on usage profiles, for example, current / voltage and current / temperature parameter pairs in use of an electrochemical element.

[0049] In [Fig. 2], an electrical power system 20 comprising an energy storage system 21 intended for implementing the control method according to the invention is schematically represented. The storage system 21 is coupled to a power device 24 adapted to control the charging and discharging of the storage system 21. For an electrified vehicle application, the storage system 21 is a traction battery coupled to an electric drive machine 22. The electrical power system may further include a charging interface 23 adapted to be connected to an external power source such as the electrical distribution network operating at alternating voltage or a charging station operating at alternating or direct voltage. The power device 24 is electrically connected at the charging interface 23. It includes power electronics performing DC / DC and / or AC / DC voltage conversion, enabling energy transfer to / from the energy storage system 20. The power device 24 coordinates the charging / discharging of the storage system 21, such as managing the charging current setpoint to the interface 23 and the electric drive machine 22.

[0050] More specifically, the storage system 21 comprises a plurality of electrochemical elements 1a, 1b, and 1 connected in series and / or parallel depending on the required power. Three electrochemical elements are illustrated for the sake of simplicity in the figure. The storage system 21 comprises at least one electrochemical element. The storage system 21 further comprises a control unit 25 adapted to determine, estimate, or measure electrical parameters of each electrochemical element and to control the charging and discharging current.The control unit 25 is capable of measuring the voltage, temperature and current of each electrochemical element a, 1b and the in order to estimate the aging of the electrochemical elements periodically in accordance with the method according to the invention.

[0051] Furthermore, the control unit 25 is equipped with an integrated circuit computer and electronic memories, the computer and the memories being configured to execute the control method according to the invention. However, this is not mandatory. Indeed, the computer could be external to the control unit 25, 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.

[0052] In [Fig. 3], the control method is represented in the form of a flowchart. The control method aims to extend the service life of the storage system.

[0053] The method includes a measurement step E01 of electrical parameters of the electrochemical element or each electrochemical element, including parameters such as temperature T, expressed in degrees Celsius, voltage, expressed in volts, current, expressed in amperes, state of charge SOC expressed in points (%), and state of aging capacitance SOHc expressed in points. These parameters can be measured or estimated by models or algorithms. The electrical parameters can be obtained from measurements or estimates specific to an electrochemical element or a selection of electrochemical elements, or globally to all the electrochemical elements of the storage system. Alternatively, the electrical parameters can be voltage and current. at the terminals of the energy storage system, and a temperature of the storage system.

[0054] In this description, SOHc is a coefficient expressing the ratio between the maximum amount of electricity that can be stored at a given time and the amount of electricity that can be stored at full capacity. SOC is the ratio between the amount of energy stored at a given time and the maximum amount of electricity that can be stored at a given time. These dimensionless values ​​are generally expressed in points.

[0055] Furthermore, according to the invention, to periodically determine a state of degradation of one or each of the storage elements, the method includes the implementation of a degradation counter E02 updated periodically according to a degradation increment determined from at least one predetermined table delivering a degradation value according to profiles of electrical parameters measured at each update of the counter.

[0056] The refresh period corresponds to a duration between 0.5 seconds and 5 seconds, for example one, two, three, or four seconds. This duration has the advantage of being able to take into account the vehicle's usage history in order to differentiate between economical and sporty driving, under different temperature conditions, which affect the aging of electrochemical components differently.

[0057] The control method implements one or more degradation counters to monitor the progress of electrochemical degradation, including a first counter for monitoring the expansion force of the internal components, a second counter for monitoring the pressure of the internal gases, and a third counter for monitoring the amount of electrolyte formed in the passivation layer. For each counter, one or more predetermined tables stored in the memory of the storage system's control unit are used to estimate a degradation increment value based on specific electrical parameters: current, temperature, and voltage.

[0058] More specifically, each degradation counter aims to provide real-time aging status information, the purpose of which is to limit the operating range of the storage system in order to extend its lifespan. The operating range is determined by the maximum permissible state of charge or the maximum permissible charge and discharge current.

[0059] In [Fig.4], a first embodiment of the degradation counter 30 calculated during step E02 is described more precisely and is configured for monitoring the internal expansion force resulting from the increase in the thickness of the passivation layer.

[0060] The counter 30 includes a first increment module 31 implementing a first predetermined table delivering a degradation value INC_IV taking The measured current I, expressed in amperes, flowing through the electrochemical element and the voltage V across the electrochemical element, expressed in volts, are taken as input at each update of the counter 30. The counter 30 includes a second incrementing module 32 implementing a second predetermined table delivering a degradation value INC_IT taking as input the measured current I flowing through the electrochemical element and the temperature T across the electrochemical element at each update of the counter 30.

[0061] Each increment module 31 and 32 determines a degradation increment component, expressed in Newtons, as a function of electrical parameters characterizing a usage profile. In this example, the usage profile corresponds to the operating conditions in terms of voltage, temperature, and current. Alternatively, the voltage can be replaced by a state-of-charge estimate. Alternatively, a single increment module is implemented to evaluate the degradation increment. It is possible for a module to use a multidimensional mapping based on two or more electrical parameters. The degradation increment values ​​recorded in the first and second tables 31 and 32 are obtained through testing and depend on the counter's update time.

[0062] For example, an experimental protocol may involve measuring the expansion force exerted on the envelope of an electrochemical element using a suitable sensor or measuring device under various usage profiles in temperature, voltage, and current. The force increment values ​​measured over a given period are related to the update time and then recorded during control unit calibration. A person skilled in the art will be able to implement an experimental protocol for monitoring the expansion force.

[0063] In addition, the counter 30 includes a third calculation module 33 for the value of the expansion force SWF(t) configured to calculate the expansion force exerted on the wall of the enclosure periodically during the use of the storage system. The expansion force SWF(t) is equal to the value of the previous calculation step SWF(tl) plus the value of the degradation increment calculated for the current calculation step INC(t), according to the following relationship: SWF(t) = SWF(tl) + INC(t).

[0064] In this embodiment, INC(t)=INC_IV*INC_IT*[__K!---_], where Kl, K2 K2+SWF(t-\f' and K3 are unitless calibration factors determined in testing and SWF(tl) is the value of the expansion force from the previous calculation step and SWF(tO) is the value of the expansion force initialized at the time the counter was triggered.

[0065] The degradation increment function has a curve close to the logarithmic function, the square root function, or another order, obtained by reducing the degradation increment value created as a function of the value of the Cumulative degradation. The physical principle modeled by the increment function is that, for reactions at both the positive and negative electrodes, their rate can decrease depending on the amount of their own reaction product. This effect is obtained by dividing the increment by SWF(tl), the modulus of the parameterizable coefficients. To make this operation possible at each time step, the value of the preceding time step must be used. The precision of three factors, K1, K2, and K3, allows this dependence to be adjusted.

[0066] Finally, the control process determines at the output of the degradation counter 30 in step E02 a value of expansion force SWF(t) at each update.

[0067] Alternatively, a counter can be implemented to determine the state of degradation of the electrochemical element whose function is to establish a correction factor coupling the effect of the estimated degradation and the state of aging in SOHc capacity.

[0068] In [Fig. 5], a second embodiment of the degradation counter 40 calculated during step E02 is described in more detail and is configured for monitoring a gas pressure internal to the envelope of the electrochemical element. Identical to the first embodiment, the counter 40 includes a first increment module 41 implementing a first predetermined table delivering a degradation value IV_coef(t) taking as input the measured current I, expressed in amperes, flowing through the electrochemical element and the voltage V across the terminals of the electrochemical element, expressed in volts, at each update of the counter 40.The counter 40 includes a second increment module 42 implementing a second predetermined table that delivers a degradation value IT_coef(t) taking as input the measured current I flowing through the electrochemical element and the temperature T, expressed in degrees Celsius, across the terminals of the electrochemical element at each update of the counter 40. Each increment module 41 and 42 determines a coefficient of the degradation of the internal gas pressure, based on electrical parameters characterizing a usage profile. These coefficients are multiplied to determine a degradation increment IVT_coef(t) at each update. IVT_coef(t) is calculated according to the following relationship: IVT_coef(t) = IV_coef(t) * IT_coef(t).

[0069] In addition, the meter 40 includes a third calculation module 43 for the value of the internal gas pressure Gas_pres_(t), configured to calculate the internal gas pressure periodically during the use of the storage system. The value of the degradation increment IVT_coef(t) is iteratively recorded at each calculation step of the meter throughout the vehicle's life, and this increment value is averaged over the cumulative vehicle usage time Du(t) to obtain an average internal gas pressure coefficient Gas_moy_coef(t). Gas_moy_coef(t) is calculated according to the following relationship: Gas_moy_coef(t) = k^vt- coef(t) ■ Du(tl) is t the cumulative duration of vehicle use for the previous calculation step. The value of the duration Du(t) is updated every second, for example.

[0070] Next, the value of the average internal gas pressure coefficient, Gas_moy_coef(t), is multiplied by the value of the aging state parameter, SOHc, to determine the internal pressure degradation state, Gas_pres_(t). Gas_pres_(t) is calculated according to the following relationship: Gas_pres_(t) = Gas_moy_coef(t) * SOHc. This embodiment applies an aging state correction using the internal pressure meter, which takes into account the actual use of the storage system.

[0071] Alternatively, according to the second embodiment of the counter 40, the control process determines at the output of the degradation counter 40 at step E02 a value of internal gas pressure force Gas_pres(t) at each update.

[0072] In return, in [Fig. 3], the control method further includes a step E03 for determining a limiting coefficient Ksoc of the control parameter as a function of the degradation counter value to control a limitation of the operating range of the control parameter. The control parameter can be the maximum limit of the state of charge SOC of an electrochemical element or the storage system, or the maximum limit of the charge or discharge current.

[0073] More specifically, the limiting coefficient Ksoc is determined from a predetermined table and stored in the memory of the control unit delivering a value of coefficient Ksoc as a function of the expansion force SWF(t) or the internal gas pressure Gas_pres_(t).

[0074] By way of non-limiting example, for expansion force values ​​between 5 kN and 25 kN, the table provides values ​​between 1 and 0 (100% and 0%). For 5 kN, the limiting coefficient, 1 or 100%, allows the electrochemical element to be charged up to the maximum SOC (State of Charge). For 25 kN, corresponding to the maximum permissible degradation, the table provides a coefficient value of 0 or 0%, thus ending the use of the storage system. In other words, for the lowest expansion force, the operating range under load is the largest, and this range decreases as the expansion force increases. In a calibration example, for expansion force values ​​of 5kN, 10KN, 15kN, 20kN and 25kN, the respective limiting coefficient values ​​correspond to 1, 1.1, 0.8 and 0.Other calibrations are possible depending on the electrochemical technology and the dimensions of the frame enclosing the electrochemical element.

[0075] Next, the process includes a step E04 limiting the operating range of at least one control parameter of the electrochemical element. The parameter of The control value is the maximum state load limit SOCmax. The limitation is applied according to the following relationship: SOCmax(t) = SOCmaxO * Ksoc, where SOCmaxO is the maximum limit in the new state and Ksoc is the limiting coefficient provided by the limiting coefficient table. The table can also directly provide values ​​for the maximum SOC limit.

[0076] Alternatively or in addition, the control parameter is the maximum charge and discharge current limit. For expansion force values ​​between 5 kN and 25 kN, the table provides KImax limiting coefficient values ​​for the maximum charge and discharge current ranging from 1 to 0 (100% to 0%). The current limitation is applied according to the following relationship: Imax(t) = Imax * KImax, where Imax is the maximum current under normal operating conditions and KImax is the limiting coefficient provided by the limiting coefficient table at the current calculation step. The maximum current is determined based on the operating conditions of the storage system, including state of charge and temperature.

[0077] Other counters can be implemented alternatively or in addition to limit the operating range of the control parameters. For example, the method is adapted to implement a degradation counter that determines representative values ​​of the internal gas pressure of the electrochemical element's casing, expressed in bar, the degradation increment values ​​of which are determined from pressure-specific tables, predetermined and stored in the control unit's memory. Based on the degradation counter associated with the internal gas pressure, the method applies, similarly to the expansion force counter, a limitation to the maximum state of charge (SOC) limit or the charge and discharge current.

[0078] The method is adapted to implement a degradation counter that determines representative values ​​of the quantity of electrolyte forming a passivation layer on the surface of the negative electrode of the electrochemical element. The degradation increment values ​​are determined from specific, predetermined tables stored in the control unit's memory. For each counter, the increments are determined according to the same principle as the expansion force, using tables established through testing based on usage profiles of voltage, current, and temperature. Based on the degradation counter associated with the quantity of electrolyte, the method applies, similarly to the expansion force counter, a limitation to the maximum state of charge (SOC) or the charge and discharge current.

[0079] In [Fig. 6], a graph schematically illustrates the evolution of the degradation counter S WF, representative of the expansion force exerted on the wall of an electrochemical element of the energy storage system, as well as the control of the maximum charge state limit parameter SOCmax of the electrochemical element. These parameters are represented as a function of the evolution of an aging state parameter in capacitance SOHc on the x-axis.

[0080] It is understood that the degradation counter representing an internal gas pressure in the envelope of the electrochemical element or the counter representing an amount of electrolyte forming a passivation layer can be represented in a similar graph illustrating the control of the maximum limit of the state of charge SOCmax as a function of the value of the counter, and the evolution of aging in capacity SOHc.

[0081] In this example, the SWF counter increases progressively according to the use made of the storage system, depending on the charge and discharge current profiles, temperature, and voltage or state of charge. When the degradation counter representing the SWF reaches a value of approximately 20 kN, the maximum state of charge limit begins to decrease progressively in order to maintain the expansion force below the hatched risk zone. In other words, this action keeps the expansion force below a critical threshold, thus allowing the use of an electrochemical element in a safe operating range up to a SOHc of 50%. Without the action of the SOCmax limitation, the SWF force, illustrated by the dashed line, would exceed the critical threshold, which would necessitate terminating the use of the storage system at an SOHc of approximately 30 to 35%.

[0082] Thus, the control method according to the invention makes it possible to extend the duration of use of the storage system by progressively reducing the maximum limit of state of charge SOCmax.

[0083] The invention is described above by way of example. It is understood that a person skilled in the art is able to carry out different variant embodiments of the invention by combining, for example, the different features above taken alone or in combination, without departing from the scope of the invention.

Claims

Demands

1. A method for controlling an energy storage system (21) comprising an electrochemical element (la, 1b, le) to extend the service life of the storage system (21), the method being implemented by a control unit (25) of the storage system and comprising the following steps: - measuring (E01) electrical parameters of the electrochemical element (la, 1b le), - limiting (E04) the operating range of at least one control parameter (SOCmax) of the electrochemical element (la, 1b le), the method being characterized in that it further comprises the following steps: - implementing (E02) a degradation counter (30) periodically updated according to a degradation increment determined from at least one predetermined table (31, 32) providing a degradation value based on profiles of electrical parameters measured at each update of the counter (30),- the determination (E03) of a limiting coefficient for the control parameter (SOCmax) as a function of the degradation counter value to control the limitation (E04) of the operating range of the control parameter.

2. A control method according to claim 1 in which the degradation increment is calculated as a function of a first value and a second value, the first value (INC_IV) being delivered by a first predetermined table (31) taking as input the current and voltage of the electrochemical element at each update of the counter (30), the second value (INC_IT) being delivered by a second predetermined table (32) taking as input the current and temperature of the electrochemical element.

3. A control method according to claim 1 or 2 wherein the control parameter is a maximum state of charge limit (SOCmax) of the electrochemical element.

4. A control method according to claim 1 or 2 wherein the control parameter is a maximum limit of the charging or discharging current of the electrochemical element.

5. A control method according to any one of claims 1 to 4 wherein the degradation counter (30) is a value representative of a force applied to a wall of the envelope of the electrochemical element.

6. A control method according to any one of claims 1 to 4 wherein the degradation counter (30) is a value representative of a gas pressure internal to the envelope of the electrochemical element.

7. A control method according to any one of claims 1 to 4 wherein the degradation counter (30) is a value representative of an amount of electrolyte forming a passivation layer on the surface of an electrode of the electrochemical element.

8. A control method according to any one of claims 1 to 7 wherein the value of the degradation counter is multiplied by the value of a capacity aging state parameter (SOHc) to determine the limiting coefficient (Ksoc).

9. Energy storage system (21) comprising an electrochemical element (la, 1b, le) and a control unit (25) configured for implementing the control method according to any one of claims 1 to 8.

10. Electrified vehicle comprising an electric drive machine (22) and an energy storage system (21) according to claim 9.

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