Method for controlling the current balancing of the electrochemical cells of a battery and associated devices
Patent Information
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- Filing Date
- 2026-02-04
- Publication Date
- 2026-08-13
Smart Images
Figure EP2026052942_13082026_PF_FP_ABST
Abstract
Description
[0001] Method for controlling the current balancing of the electrochemical elements of a battery and associated devices
[0002] The present invention relates to a method for controlling the current balance of the electrochemical elements of a battery. The invention also relates to an associated computer, management system, and battery.
[0003] Typically, a battery comprises one or more current storage cells, also called electrochemical cells or elements. A battery is an electricity-producing device in which chemical energy is converted into electrical energy. The chemical energy comes from electrochemically active compounds deposited on at least one side of electrodes arranged within the battery. The electrical energy is produced by electrochemical reactions during the battery's discharge. The electrodes, arranged in a container, are electrically connected to current output terminals that ensure electrical continuity between the electrodes and the electrical load to which the battery is connected.
[0004] To increase the electrical power output, several sealed accumulators can be connected together to form a battery. A battery can thus be divided into modules, each module consisting of one or more accumulators connected in series and / or parallel. For example, a battery can have one or more parallel branches of accumulators connected in series and / or one or more parallel branches of modules connected in series.
[0005] A charging circuit is usually provided to which the battery can be connected to recharge the cells.
[0006] Furthermore, an electronic management system, including measurement sensors and an electronic control circuit of varying complexity depending on the application, can be connected to the battery. Such a system allows, in particular, for the organization and control of the battery's charging and discharging, balancing the charge and discharge of the battery's individual cells relative to one another.
[0007] Battery management systems thus enable the battery cells to be balanced to a predefined state of charge at the end of charging or discharging. The state of charge is often referred to by the abbreviation SOC, which stands for "State of Charge".
[0008] However, it is desirable to be able to balance the batteries at a first target state of charge (e.g., 50%) where the battery operates most of the time, and to balance the battery at a second target state of charge (e.g., 100%) for certain operations such as maintenance. For this purpose, balancing techniques based on voltage comparison are known.
[0009] However, these techniques do not work for batteries with a flat portion in the state of charge (SOC) open-circuit voltage (OCV) characteristic curve. The abbreviation OCV stands for "Open Circuit Voltage".
[0010] Furthermore, when the battery operates mostly around the first target state of charge, the cells are balanced around this value. Also, when the battery is fully charged, the cell with the lowest capacity will reach the second target state of charge first, and the battery will not be balanced at full charge.
[0011] Consequently, a certain amount of time is required to discharge the most charged batteries. During this discharge, the system is unavailable, which is inconvenient for the battery user.
[0012] There is a need for a method of controlling the balancing of a set of electrochemical elements to achieve balancing of the electrochemical elements mainly at a first target charge state and, for certain operations, at a second target charge state different from the first target charge state.
[0013] For this purpose, the description relates to a method for controlling the current balancing of a plurality of electrochemical cells in a battery, the battery being equipped with a balancing circuit allowing a respective balancing current to be applied to each electrochemical cell of the plurality of electrochemical cells, the control method being implemented by a computer, the control method comprising, for each electrochemical cell to be balanced:
[0014] - a step of obtaining measurement values, the measurement values including the capacitance of the electrochemical element, first measurement values and second measurement values, the first values including measurements or estimates of the current of the electrochemical element and the balancing current applied to the electrochemical element, the second values including measurements or estimates of the state of charge of the electrochemical element,
[0015] - a step for determining the amount of charge to be balanced for the electrochemical element, the determination step being implemented at a plurality of determination times, the determination step comprising, at each determination time:
[0016] - a sub-step for detecting the possible acquisition of at least one piece of information relating to the balancing to be carried out since the last moment of determination, the at least one piece of information being additional information compared to the measurement values obtained in the acquisition step, - a sub-step for calculating the quantity of charge to be balanced for the electrochemical element, the calculation sub-step being implemented by application:
[0017] - a first calculation technique based on the measured values obtained and at least one additional piece of information when at least one additional piece of information was detected during the detection sub-step,
[0018] the first technique involves calculating the amount of charge to be balanced for the electrochemical element as the difference between two terms, the first term being the maximum amount of charge to be supplied for an electrochemical element to reach a target charge state among the plurality of electrochemical elements, and the second term being the amount of charge to be supplied for the electrochemical element to reach the target charge state, and
[0019] - a second calculation technique on the measurement values obtained when no additional information was detected during the detection sub-step, the second technique comprising the calculation of a first contribution and a second contribution, the first contribution being the value of the quantity of charge supplied by the balancing circuit since the last instant of determination and the second contribution being the contribution related to the self-discharge differences between the electrochemical elements,
[0020] the amount of charge to be balanced for the electrochemical element calculated by the first or second technique being the amount of charge to be balanced determined, and
[0021] - a step of checking the balancing circuit according to the determined amount of load to be balanced.
[0022] The balancing process provides a solution to the problem of the fact that the state of charge will diverge between electrochemical elements due to the different self-discharges between the electrochemical elements as well as the differences in capacitance between the electrochemical elements.
[0023] As a simple example, if initially all electrochemical elements are fully charged to 100% and left at rest, since electrochemical elements 1 exhibit self-discharges that are often non-zero and different between electrochemical elements 1, then the difference in state of charge between the electrochemical elements will diverge until it reaches 100% if one of the electrochemical elements exhibits zero self-discharge.
[0024] According to other advantageous aspects of the invention, the control method comprises one or more of the following features, taken individually or in all technically possible combinations: - the quantity of charge calculated by the second technique is the sum of the two contributions.
[0025] - Additional information is a measurement of the state of charge of the electrochemical element.
[0026] - Additional information is a measure of the capacitance of the electrochemical element.
[0027] - Additional information is a new target charge state value for which current balancing of the electrochemical elements is to be performed. - The balancing circuit has an active state in which the balancing circuit applies a balancing current and an inactive state in which the balancing circuit does not apply the balancing current, the control step including putting the balancing circuit into the active state if the determined amount of charge to be balanced is greater than or equal to a threshold.
[0028] - each electrochemical element has a characteristic state of charge - open circuit voltage having a plane portion, a plane portion being a portion in which the open circuit voltage variation is less than 30 mV for a variation of at least 10% of the state of charge.
[0029] - at least one electrochemical element includes a cathodic active material comprising a lithium iron phosphate, a lithium manganese and iron phosphate or a lithium vanadium fluorophosphate.
[0030] The description also relates to a computer designed to control the current balancing of a plurality of electrochemical cells in a battery, the battery being equipped with a balancing circuit allowing a respective balancing current to be applied to each electrochemical cell of the plurality of electrochemical cells, the computer being designed to, for each electrochemical cell to be balanced:
[0031] - to obtain measurement values, the measurement values including the capacitance of the electrochemical element, first measurement values and second measurement values, the first values including measurements or estimates of the current of the electrochemical element and the balancing current applied to the electrochemical element, the second values including measurements or estimates of the state of charge of the electrochemical element,
[0032] - determine the amount of charge to be balanced for the electrochemical element at a plurality of determination times, the calculator being capable of performing the determination at each determination time by:
[0033] - detecting the possible acquisition of at least one piece of information relating to the balancing to be carried out since the last moment of determination, the at least one piece of information being additional information compared to the measurement values obtained at the acquisition stage,
[0034] - calculating the amount of charge to be balanced for the electrochemical element (12) by application:
[0035] - a first calculation technique based on the measured values obtained and at least one additional piece of information when at least one additional piece of information has been detected,
[0036] the first technique involves calculating the amount of charge to be balanced for the electrochemical element as the difference between two terms, the first term being the maximum amount of charge to be supplied for an electrochemical element to reach a target charge state among the plurality of electrochemical elements, and the second term being the amount of charge to be supplied for the electrochemical element to reach the target charge state, and
[0037] - a second calculation technique on the measurement values obtained when no additional information was detected, the second technique comprising the calculation of a first contribution and a second contribution, the first contribution being the value of the quantity of charge supplied by the balancing circuit since the last instant of determination and the second contribution being the contribution related to the self-discharge differences between the electrochemical elements,
[0038] the amount of charge to be balanced for the electrochemical element calculated by the first or second technique being the amount of charge to be balanced determined, and
[0039] - control the balancing circuit according to the determined amount of load to be balanced.
[0040] The description also relates to a management system for a plurality of electrochemical elements in a battery, the electrochemical elements having terminals, the management system comprising:
[0041] - a balancing circuit designed to apply a respective balancing current to each of the electrochemical elements in the plurality of electrochemical elements, - for each electrochemical element in the plurality of electrochemical elements:
[0042] - a sensor for the current delivered by the electrochemical element, - a unit for measuring the balancing current applied to the electrochemical element, and
[0043] - a voltage sensor suitable for measuring the voltage across the terminals of the electrochemical element, and - a calculator as previously described.
[0044] The description also includes a battery pack:
[0045] - electrochemical elements, and
[0046] - a management system as previously described.
[0047] In this description, the expression "specific to" means interchangeably "suited for", "adapted to" or "configured for".
[0048] The invention will become clearer upon reading the following description, given solely by way of non-limiting example, and made with reference to the drawings in which:
[0049] - Figure 1 is a schematic representation of an example of a battery containing an electrochemical element,
[0050] - Figure 2 is a graph illustrating an example of the open-circuit charge-voltage characteristic of the electrochemical element in Figure 1,
[0051] - Figure 3 is a block diagram representation of an example of the implementation of a process for controlling the balancing of an electrochemical element, and
[0052] - Figures 4 and 5 present experimental results obtained by the Applicant by implementing the process illustrated in Figure 3.
[0053] A battery 10 is shown in Figure 1.
[0054] The battery 10 is an arrangement of a plurality of electrochemical elements 12 and a management system 14 for each electrochemical element 12.
[0055] For the remainder of this text, we will denote / V as the number of electrochemical elements 12 in battery 10.
[0056] In addition, each electrochemical element 12 will be identified respectively by an index i.
[0057] However, for the sake of simplification, the representation in Figure 1 includes a single electrochemical element 12.
[0058] As explained previously, an electrochemical element 12 is an electricity-producing device in which chemical energy is converted into electrical energy.
[0059] The electrochemical element 12 therefore delivers a current and a voltage between two terminals.
[0060] The electrochemical element 12 can exhibit a state of charge SOC - open circuit voltage OCV characteristic as seen in Figure 2. This characteristic is referred to as the SOC / OCV characteristic hereafter.
[0061] The state of charge is useful information for the management system 14 to optimize the use and lifespan of the battery 10. In Figure 2, the state of charge is expressed as a percentage of a maximum state of charge.
[0062] The SOC / OCV characteristic can, for example, have four zones: a first zone Z1, a second zone Z2, a third zone Z3, and a fourth zone Z4.
[0063] The first zone Z1 corresponds to the beginning of the charge and the fourth zone Z4 to the end of the charge.
[0064] For the two intermediate zones, insofar as the second zone Z2 and third zone Z3 correspond to a flat portion, the designation flat portion (Z23) will be used in the following.
[0065] The planar portion Z23 is a portion in which the open-circuit voltage variation OCV is less than 30 mV for a variation of at least 10% of the state of charge.
[0066] Such a type of SOC / OCV characteristic is found in particular when the electrochemical element 12 is an electrochemical element comprising a cathodic active material comprising a lithium iron phosphate (LFP).
[0067] According to one particular example, at least one electrochemical element 12 comprises a cathodic active material comprising a lithium iron phosphate (LFP), a lithium manganese iron phosphate (LMFP) or a lithium vanadium fluorophosphate (LVPF).
[0068] The anodic active material is not particularly limited. It is a material capable of incorporating lithium into its structure. It can be chosen from lithium compounds, carbonaceous materials such as graphite, coke, carbon black, and vitreous carbon. It can also be based on tin, silicon, carbon-silicon compounds, carbon-tin compounds, or carbon-tin-silicon compounds. It can also be a lithium titanium oxide such as Li4Ti5O 12 or a niobium titanium oxide such as TiNb2O7.
[0069] Of course, these examples are not exhaustive and the processes described later can be used for any type of electrochemical element 12.
[0070] Management system 14 is a system specifically designed to manage electrochemical element 12.
[0071] The management system 14 includes a balancing circuit 15 and, for each electrochemical element 12, a voltage sensor 16, a current sensor 18 of the electrochemical element 12 and a balancing current measuring unit 20.
[0072] The balancing circuit 15 is designed to apply a respective balancing current to each of the electrochemical elements 12 of the battery. The balancing circuit 15 has two states, namely an active state in which the balancing circuit 15 applies a balancing current and an inactive state in which the balancing circuit 15 does not apply the balancing current.
[0073] The voltage sensor 16 is suitable for measuring the voltage across the terminals of the electrochemical element 12.
[0074] The current sensor 18 is suitable for measuring the current delivered by the electrochemical element 12.
[0075] The measuring unit 20 is suitable for measuring the balancing current applied to the electrochemical element 12 by the balancing circuit 15.
[0076] For example, the unit of measurement 20 is suitable for measuring the current flowing through a resistor in which the electrochemical element will discharge.
[0077] Calculator 22 is designed to implement a balancing control method which will be described later.
[0078] The calculator 22 is an electronic circuit designed to manipulate and / or transform data represented by electronic or physical quantities in registers of the calculator and / or memories into other similar data corresponding to physical data in register memories or other types of display devices, transmission devices or storage devices.
[0079] As specific examples, the calculator 22 includes a single-core or multi-core processor (such as a central processing unit (CPU), a graphics processing unit (GPU), a microcontroller and a digital signal processor (DSP)), a programmable logic circuit, such as an application-specific integrated circuit (ASIC), a field-programmable gate array (FPGA), a programmable logic device (PLD) and programmable logic arrays (PLAs), a state machine, a logic gate and discrete hardware components.
[0080] An operation of the calculator 22 is now described with reference to Figure 3, which is a flowchart illustrating an example of the implementation of a process for controlling the current balancing of electrochemical elements 12.
[0081] The balancing process aims to balance all the electrochemical elements 12 at a balancing point.
[0082] More specifically, the balancing process seeks to balance electrochemical elements to a target state of charge SOC cible .
[0083] The balancing process includes a production step E50, a determination step E52 and a control step E54.
[0084] Each step of the balancing process is implemented for each electrochemical cell of the battery. An example of the implementation of the balancing process for an electrochemical cell is detailed below.
[0085] During the E50 acquisition step, the calculator 22 obtains a plurality of measurement values.
[0086] The measurement values include the capacitance of electrochemical element 12, first measurement values and second measurement values.
[0087] Capacity can be obtained by any means, including by implementing an estimation.
[0088] The first measurement values are the values of the current of the electrochemical element 12 and the balancing current applied to the electrochemical element 12.
[0089] According to the example described, the current sensor 18 and the measuring unit 20 measure these current values.
[0090] Alternatively, the first measured values are obtained by estimation. The second measured values are values of the charge state of electrochemical element 12.
[0091] As with the first measurement values, the second measurement values are obtained either through measurements or estimates.
[0092] For a measurement, it is necessary to perform a discharge or a charge (not necessarily complete).
[0093] Such an operation is often referred to as "taking a picture".
[0094] At the end of the acquisition step, the calculator 22 thus has a plurality of values for several physical quantities and will use these values during the determination step E52.
[0095] During the determination step E52, the calculator 22 determines the amount of charge to be balanced for the electrochemical element 12.
[0096] We will denote this quantity of charge to be balanced as ΔC →eq [i], this quantity of charge to be balanced varying over time and being specific to each electrochemical element 12.
[0097] The determination step E52 is implemented at a plurality of determination times t*.
[0098] The determination times t* are preferably separated by a constant time interval denoted At in the following.
[0099] Typically, this time interval At is between 50 ms and 4 h.
[0100] In the following, the example is described with constant time intervals to simplify the notation, but the transposition to varying time intervals is immediate. At each determination time t*, the determination step E52 includes a detection substep SE521 and a calculation substep SE522.
[0101] During the SE521 detection substep, the calculator 22 detects whether additional information relating to the balancing to be carried out has been obtained since the last determination instant t*.
[0102] This information is additional information compared to the measurement values obtained in the E50 obtaining step.
[0103] According to a first example, additional information is a measurement of the state of charge of the electrochemical element 12.
[0104] This case corresponds to taking a photograph.
[0105] According to a second example, additional information is a capacitance measurement of electrochemical element 12.
[0106] According to a third example, additional information is a new target charge state value for which the current balancing of the electrochemical elements 12 is to be achieved.
[0107] These examples are preferably cumulative, so that the SE521 detection substep aims to detect whether additional information according to one of the previous examples has been obtained since the last determination instant t*.
[0108] The SE521 detection substep can be implemented by testing the value of a binary number.
[0109] This binary number is updated with each event, for example, taking a photo results in setting the value of the corresponding binary number to 1.
[0110] Thus, in the preferred embodiment, we test the value of each binary number corresponding to the previous examples of additional information and if one of these binary numbers is equal to 1, the computer 22 detects that additional information relating to balancing has been obtained since the last determination time t*.
[0111] During the SE522 calculation substep, calculator 22 calculates the amount of charge to be balanced for the electrochemical element 12.
[0112] The calculation technique applied by calculator 22 depends on the result of the detection substep.
[0113] More specifically, the computer 22 applies a first technique T1 when at least one additional piece of information has been detected during the detection substep SE521 (arrow 56 in Figure 3) while the computer 22 applies a second technique T2 otherwise (arrow 58 in Figure 3). According to the first technique T1, the computer 22 calculates the amount of charge to be balanced for the electrochemical element 12 as the difference between the largest amount of charge to be supplied for an electrochemical element 12 to reach a target charge state and the amount of charge to be supplied for the electrochemical element 12 to reach the target charge state.
[0114] This first technique, T1, stems from the considerations that will now be presented.
[0115] Before explaining these different considerations, it is necessary to introduce the notation that will be used subsequently. We will thus use the following notations:
[0116] • t n denotes the last moment a photo is taken, so it can be written that t* = t n + mast, where m is an integer,
[0117] • SOC is a vector of size N, each coordinate of which is the value of the state of charge of a respective electrochemical element 12, the value of the state of charge being the value measured or estimated at the time of determination t n , • Q is a vector of size N where each coordinate is the capacitance value of a respective electrochemical element 12, the capacitance value being the value measured at time t n or estimated at the time of determination t*,
[0118] • SOC min bat is the lowest state of charge among all the states of charge of each electrochemical cell 12 of the battery 10,
[0119] • SOC min ph is the minimum charge state of the area in which the photos are taken,
[0120] • SOCmax ph the maximum charge level of the area in which the photos are taken,
[0121] • Ibai is a vector of size N, each coordinate of which is the value of the balancing current applied by the balancing circuit 15 to a respective electrochemical element 12, and
[0122] • ï sd is a vector of size N whose coordinate is an estimate of the self-discharges of a respective electrochemical element 12, the self-discharge is estimated here using the receiver convention, so that the discharge current is negative and thus the self-discharge currents are negative currents.
[0123] In what follows, the units of each quantity are not specified to maintain generality. Depending on the unit chosen for each quantity, the following formulas would be modified by inserting a proportionality factor. For example, if the state of charge of an electrochemical element 12 is expressed as a percentage, this implies the presence in some formulas of a proportionality factor equal to 100.
[0124] At this moment n From a single photograph, the measured SOC charge states are necessarily included within an observation window corresponding to the segment [SOC min _p b , SOC max p].
[0125] Put another way, the measured SOC charge states undergo a phenomenon that can be likened to saturation at both the minimum and maximum values. Therefore, it is referred to hereafter as SOC satthe value of the state of charge thus limited by the observation window.
[0126] The minimum charge state of the electrochemical element is written as:
[0127] SOCfiin elX^n) 777-177. (TïllTL (tn), SOC min bat(tn) )
[0128]
[0129] \ L /
[0130] The minimum deviation of the state of charge to be balanced then satisfies:
[0131] S
[0132]
[0133] OC m unbalancing (^n) TnCLxÇSOC min _ e l(fn) > SOCmin _ph (fnS) From this, the saturated charge state SOC is deduced sat
[0134] SOC sat [i](t n ) = min(max (sOC[i^(t n ), SOC min
[0135]
[0136] equilibrage^J'rùj' > ^Qna>:
[0137] Next, the amount of AC charge^ cibie to reach the target state of charge SOC cible(possibly negative if there is a need to discharge) can be expressed as follows:
[0138] / 1 ^C^ cibie [j](t*) = \^SOC cible (t*) - SOC sat [i](t n ') - x J ^baiH(s)ds
[0139] - ç[i](t*) x / tn îsd ^ ds )
[0140]
[0141] x Assuming that the self-discharge estimates are constant between the two times t n and t*, we get the following relation 1:
[0142] 4 enable [i] (t*) = (S0C cibie (f) - SOC sat [i\(,t n ')) x Ç[i](t*) - I b ai[i](.s~)ds
[0143] tn
[0144]
[0145] - (t* - t n ) x / sd [j](t*) Now, the quantity of charge to be balanced AC^ eq for an electrochemical element i is written according to the following relation 2:
[0146]
[0147] Where j(t*) = argj max( 1C^ Cib ( e [j](t*)), this function giving the index i of the electrochemical element 12 whose quantity of charge AC^ cibie to reach the target charge state SOCdbie is the largest among all the electrochemical elements 12 at time t*.
[0148] By replacing the different terms, relation 2 becomes:= ( r' il? f * ) p[î hr* i ) «. SCH~, [ri> .11* ii [ / if “ i|ir,, j.% P [hr* j|k *! — £> ( it,, j. [• iz r ,ipp ] ifi h- / , f P ] Î ti — f,r! [hf ] ii f " ij * i ' — £,is - 1" I | r'ilf.ç
[0149]
[0150] The discretized version of relation 2 is therefore:
[0151] - {yl / S ff]u ' 1 ■” J ; ri 1 WC. J / sr Htr,, I * tflMî ■ 1h t' I ~ Mb, -| lf [r]( j., J - fj|rp f ' i H ( / 1? [îjlf * ) - | L / < i' 'B 1 ' I (A-.iuPP ht tûr j t| iir ' 1J ( r„ I târj )
[0152]
[0153] Àlsd
[0154] It can be noted here that the previous expression simplifies when the time of determination t* corresponds to a photo being taken, that is, t* = t n or that the integer m is zero.
[0155] Equation 2 then simplifies and becomes:
[0156] AC-^. [?]( t* i - ( y [;i " ip t * i - [r 'i £ ' 11 5OL 1S ', lt , 1.1 " i
[0157]
[0158] + ir" ip (,, ) (J [ji r ' )]( £ * i
[0159]
[0160] hr f , i ppji t' i
[0161] When no additional information has been detected during the SE522 detection substep, the calculator 22 applies the second technique T2.
[0162] The second technique T2 consists of calculating two contributions to the quantity of charge to be balanced C^ eq [i] for the electrochemical element 12 considered.
[0163] The first contribution is the value of the quantity of charge supplied by the balancing circuit 15 since the last instant of determination.
[0164] The second calculated contribution is the contribution related to the differences in self-discharge between the electrochemical elements 12.
[0165] More precisely, the second contribution corresponds to the contribution related to the difference between the self-discharge of the electrochemical element 12 considered and the self-discharge of the electrochemical element 12 with index j, that is to say the maximum of the quantity of charge AC^ cibie to reach the target state of charge SOC cible for an electrochemical element 12 among the set of electrochemical elements 12.
[0166] The second technique, T2, can thus be expressed as follows:
[0167] HAS
[0168]
[0169] C^ eq [i](tp + ( / c + l)At) = AC cl [j](tp + (k + l)At) + AC C2 [i](Ç + (k + l)At)
[0170] Where: • t* here denotes the last moment of determination during which the first technique T1 was implemented,
[0171] • (c + l)At expresses the time elapsed since the instant of determination t*, • C cl [i] denotes the first contribution, and
[0172] • 4lC C 2 [i] denotes the second contribution.
[0173] As previously stated, the first contribution C cl [i] is related to the value of the quantity of charge supplied by the balancing circuit 15, such that:
[0174] 4
[0175]
[0176] lC Ci [i] (tp + (k + l)At) — AC cl[j](tp + / cAt) = &tl ba i[i](tp + / cAt)
[0177] According to the example described, the second contribution C C2 [i] corresponds to the difference in charge quantity gain related to self-discharge for the electrochemical element 12 considered and that of the self-discharge of the electrochemical element 12 having index j.
[0178] This leads to the following expression:
[0179] AQ - f (k II )Ar}
[0180] = IU' I 1 lAr). W' n 4dU,-J ç t 'k I HAR)
[0181]
[0182] h AG I Where:
[0183] • AC ad [j](t) denotes the amount of charge related to self-discharge for the electrochemical element i, and
[0184] • AC ad [ / (t)](t) denotes the quantity of charge related to self-discharge for the electrochemical element j.
[0185] By introducing self-discharge estimates, the previous relationship becomes:
[0186] AC4 e(? [j](t* + ( / c + l)At) = AC e(? U i[j](t* + ( / c + l)At) + ( / c + l)At s l d - î s J d
[0187] Or:
[0188] • AC equi [i](tp + ( / c + l)At) = AC equi [i](tp + / cAt) + &tl ba i[i](tp + / cAt)
[0189]
[0190] At the end of the E52 determination step, a specific quantity of charge to be balanced, C^, is thus obtained. eq [iJ.
[0191] During the E54 control step, the control unit 22 checks the balancing circuit 15 according to the quantity of charge to be balanced determined C^ eq [iJ.
[0192] According to the example described, the calculator 22 puts the balancing circuit 15 into the active state of the balancing circuit 15 if the quantity of charge to be balanced determined C^ eq[i] is greater than or equal to a threshold. The threshold is non-zero, for example between 0.5% and 10%. Indeed, a zero threshold should be avoided to prevent the balancing circuit 15 from being activated and immediately deactivated.
[0193] Otherwise, the calculator 22 puts the balancing circuit 15 into the inactive state.
[0194] Advantageously, an additional test is added.
[0195] This test consists of verifying if the quantity of charge to be balanced is determined AC^ eq [i] is greater than or equal to a threshold reduced by a hysteresis threshold.
[0196] If so, the calculator 22 keeps the balancing circuit 15 in the active state of balancing circuit 15.
[0197] Otherwise, the calculator 22 puts the balancing circuit 15 into the inactive state.
[0198] Such an additional test helps to prevent the balancing circuit 15 from blocking in active mode.
[0199] Examples of concrete implementation by the Applicant are schematically illustrated by figures 4 and 5, which are now described.
[0200] Figure 4 illustrates the time variation of the state of charge of two electrochemical elements 12, a first electrochemical element 12 corresponding to curve C1 with a capacity of 190 Ah and a second electrochemical element 12 corresponding to curve C2 with a capacity of 185 Ah.
[0201] The target state of charge (SOC) cible is set at 60%, which is represented by a line in figure 4.
[0202] Using the previous notation, the first photo taken at time ti leads to measuring a charge state SOC^t^ of the first electrochemical element 12 at time equal to 30% as well as a charge state SOC2(.t1) of the second electrochemical element 12 at time equal to 28%.
[0203] Applying relation 2 above leads to determining that the charge states SOC1 and SOC2 of the two electrochemical elements 12 should be balanced at 1.16% and 0% respectively.
[0204] This corresponds, for the first electrochemical element 12 to 2.2 Ah and, for the second electrochemical element to 0 Ah.
[0205] This means that the balancing circuit 15 switches to the active state for the second electrochemical element 12.
[0206] Curves C3 and C4 schematically illustrate the charge balance for the first electrochemical element 12 and the second electrochemical element 12, respectively. On the first portion located between the instant
[0207]
[0208] At the time of taking the photo and at a specific instant (corresponding to the start of charging), curve C3 is zero to indicate that the balancing circuit 15 is inactive for the second electrochemical element 12, while curve C4 shows a linear variation to illustrate that the balancing circuit 15 causes the discharge of a quantity of charge to the first electrochemical element 12 to ensure balancing.
[0209] On the second portion located between the toc instant of the start of charging and the tpc instant of the end of charging, a charge of 59.2Ah is achieved for the two electrochemical elements 12.
[0210] At the time tpc of the end of charging, it is observed that the two electrochemical elements 12 do indeed have the same state of charge, which is equal to 60%, that is to say, the target state of charge S0C cibie .
[0211] A second example is illustrated by Figure 5, which shows the variation over time of the dispersion of the charge state to be balanced with respect to the limiting electrochemical element.
[0212] In this simulation scenario, a five-electrochemical element example is considered, including a cathodic active material comprising lithium iron phosphate (LFP). These electrochemical elements exhibit a flat chemistry, and it is assumed here that the calibration zone lies within the first zone, Z1, corresponding to a charge state range between 0% and 6%.
[0213] The state of charge estimation zone is assumed to be located at the end of discharge ([0%, 15%]). In the first part of the scenario, the target state of charge (SOC) cible is set at 50% and the operational state of charge is set at 60%. At certain times, the elements are brought back to the target state of charge (SOC). cibleto measure their effective dispersion and thus quantify the efficiency of the process. At the end of the scenario, the target state of charge (SOC) cible is modified to the value 95%. Finally, the threshold triggering the activation of the balancing circuit 15 is set at 5% and the threshold determining the hysteresis at 2%.
[0214] The capacitance and self-discharge values of the five electrochemical elements in series are shown in the following table:
[0215] [Table 1]
[0216] Element
[0217] electrochemical 1 2 3 4 5
[0218] [number]
[0219] Capacity [Ah] 180 186 182 190 185
[0220]
[0221] Self-discharge
[0222] 2.5 1 2 6.5 5.5
[0223] [my]
[0224]
[0225] However, to complicate matters, it is assumed that the initial values are incorrect. The capacitance and self-discharge values of the five selected electrochemical elements are shown in the following table:
[0226] [Table 2]
[0227] Element
[0228] electrochemical 1 2 3 4 5
[0229] [number]
[0230] Capacity [Ah] 185 180 190 185 187 Self-discharge
[0231] 0 0 0 0 0
[0232] [my]
[0233]
[0234] The simulated procedure is as follows:
[0235] • first instant (indicated 1 in figure 5): insertion of erroneous capacities and incorrect self-discharge values;
[0236] • second moment: go to the target charge state of 50% and rest at the charge state of 60% for 400 hours;
[0237] • third moment: go to the calibration zone;
[0238] • fourth moment: setting the correct capacities (after measurement) and rest at the state of charge at 60% for 200 hours;
[0239] • fifth instant (indicated 5 in figure 5): sending the command to reset capabilities;
[0240] • sixth instant (indicated 6 in figure 5): go to the target charge state of 50% to perform a check and rest at the charge state of 60% for 400 hours;
[0241] • seventh instant (indicated 7 in figure 5): go to the target charge state of 50% and rest at the charge state at 50% for 400 hours;
[0242] • eighth moment (indicated 8 in figure 5): go to calibration zone 1;
[0243] • ninth instant: setting the correct capacities (after measurement) and rest at the 60% load state for 200 hours; tenth instant (indicated 10 on figure 5): going to the target 50% load state and rest at the 60% load state for 400 hours;
[0244] eleventh instant (indicated 11 in figure 5): sending of the order to change self-discharges and then rest in the state of charge at 60% for 200 hours;
[0245] twelfth instant (indicated 12 in figure 5): go to the target charge state of 50% and rest at the charge state of 60% for 400 hours;
[0246] Thirteenth moment (indicated 13 in Figure 5): go to the calibration area and change the target charge state to 95% and then rest at the 60% charge state for 200 hours, and
[0247] fourteenth instant (indicated 14 in figure 5): go to the target charge state of 95%.
[0248] Curve A in Figure 5 illustrates the measured balancing dispersion, and its analysis shows that balancing is correctly performed at the target load state. Figure 5 shows that the significant dispersion present at the beginning of the scenario is reduced to within the permissible tolerance of 5% (see time points 13 and 14).
[0249] A third example is now finally described.
[0250] In this example, we consider the case of three electrochemical elements with capacities of 180 Ah, 190 Ah and 185 Ah respectively.
[0251] We assume that the state of charge of each electrochemical element measured at the time of taking the photo is respectively 50% (first electrochemical element), 56% (second electrochemical element) and 51% (third electrochemical element).
[0252] It is also assumed that the target state of charge SOC cible is equal to 10%.
[0253] Calculating the quantities of charge to be balanced C^ cibie Therefore, it gives:
[0254] • for the first electrochemical element,
[0255] 1
[0256] AC^ C ible = — x ( 10 - 5°) X 180000 = -72000 mAh
[0257]
[0258] • for the second electrochemical element,
[0259] 1
[0260] Target AC = — x ( 10 - 56 ) x 190000 = -87400 mAh
[0261]
[0262] • for the third electrochemical element,
[0263] 1
[0264] Target AC = — X ( 10 - 51) x 185000 = -75850 mAh
[0265]
[0266] From this point, it is possible to calculate the state of charge to be balanced ASOC^ cibie according to the following generic formula
[0267] ASOC^ bie [i](t*) = 100 x q
[0268]
[0269] X' UJk*' )• for the first electrochemical element,
[0270] -72 + 72
[0271] ASOC^ cible = 100 x = 0 [%]
[0272] batch)
[0273] • for the second electrochemical element,
[0274] -72 + 87.4
[0275] ASOC^ cible = 100 x - — - = 8.1053 [%]
[0276]
[0277] • for the third electrochemical element,
[0278] -72 + 75.85
[0279] ASOC^ cible = 100 x - — - = 2.0811 [%]
[0280] 185
[0281] Now we can consider the situation where the target state of charge SOC cible changes during operation to be fixed at 100%.
[0282] At the time of this modification, 7% of the 8.1053% were balanced for the second electrochemical element and the entire state of charge to be balanced for the third electrochemical element was discharged.
[0283] With this assumption, the calculation of the quantities of charge to be balanced AC^ cibie becomes:
[0284] • for the first electrochemical element,
[0285] 1
[0286] Target AC = — x (100 - 50) x 180000 = 90000 mAh
[0287]
[0288] • for the second electrochemical element,
[0289] 1
[0290] Alible = — x (10° - 56 + 7) x 190000 = 96900 mAh
[0291] • for the third electrochemical element,
[0292] 1
[0293] Alible = — x (100 - 51 + 2.0811) x 185000 = 94500 mAh
[0294]
[0295] From this point, it is possible to calculate the state of charge to be balanced ASOC^ cibLe :
[0296] • for the first electrochemical element,
[0297] 96.9 - 90
[0298] ASOC^ cible = 100 x = 3.8333 [%]
[0299] 180
[0300] • for the second electrochemical element,
[0301] 96.9 - 96.9
[0302] ASOC^ cible = 100 x - — - = 0 [%]
[0303]
[0304] • for the third electrochemical element,
[0305] 96.9 - 94.5
[0306] ASOC^ cible = 100 x - — - = 1.2973 [%]
[0307] 185
[0308] In the first simulation step following this update of the charge states to be balanced, applying equation 2, once converted to a percentage, gives 0% for the second electrochemical element, meaning that this electrochemical element will not need to be balanced using the described process. Indeed, only electrochemical elements whose charge state to be balanced is S0C^ cibie If a concentration is positive and greater than a given threshold, it will be considered unbalanced with respect to the other electrochemical elements.
[0309] Furthermore, it is important to keep a record of the balancing operations performed in order to calculate the quantities of charge to be balanced AC^ cibie used for calculating the load state vector to be balanced ASOC^ ciMe at a time of reset of the target state of charge SOC cible .
[0310] The described process therefore makes it possible to reach a given state of charge, which represents a saving of time, for example, on maintenance operations.
[0311] The process therefore constitutes a proactive balancing process with a balancing point that can be modified by a simple change in the target charge state.
[0312] The control process just described makes it possible to obtain a balancing of the electrochemical elements mainly at a first target charge state and, for certain operations, at a second target charge state different from the first target charge state.
Claims
DEMANDS 1. A method for controlling the current balancing of a plurality of electrochemical cells (12) of a battery (10), the battery (10) being provided with a balancing circuit (15) for applying a respective balancing current to each electrochemical cell (12) of the plurality of electrochemical cells (12), the control method being implemented by a computer (22), the control method comprising, for each electrochemical cell (12) to be balanced: - a step of obtaining measurement values, the measurement values comprising the capacitance of the electrochemical element (12), first measurement values and second measurement values, the first values comprising measurements or estimates of the current of the electrochemical element (12) and the balancing current applied to the electrochemical element (12), the second values comprising measurements or estimates of the state of charge of the electrochemical element (12), - a step of determining the amount of charge to be balanced for the electrochemical element (12), the determination step being carried out at a plurality of determination times, the determination step comprising, at each determination time: - a sub-step for detecting the possible acquisition of at least one piece of information relating to the balancing to be carried out since the last moment of determination, the at least one piece of information being additional information compared to the measurement values obtained in the acquisition step, - a sub-step for calculating the amount of charge to be balanced for the electrochemical element (12), the calculation sub-step being implemented by application: - a first calculation technique based on the measured values obtained and at least one additional piece of information when at least one additional piece of information was detected during the detection sub-step, the first technique comprising a calculation of the amount of charge to be balanced for the electrochemical element (12) as the difference between two terms, the first term being the maximum amount of charge to be supplied for an electrochemical element (12) to reach a target charge state among the plurality of electrochemical elements (12) and the second term being the amount of charge to be supplied for the electrochemical element (12) to reach the target charge state, and - a second calculation technique on the measurement values obtained when no additional information was detected during the detection substep, the second technique comprising the calculation of a first contribution and a second contribution, the first contribution being the value of the quantity of charge supplied by the balancing circuit (15) since the last instant of determination and the second contribution being the contribution related to the self-discharge differences between the electrochemical elements (12), the amount of charge to be balanced for the electrochemical element (12) calculated by the first technique or second technique being the amount of charge to be balanced determined, and - a balancing circuit control step (15) according to the determined quantity of charge to be balanced.
2. Control method according to claim 1, wherein the quantity of charge calculated by the second technique is the sum of the two contributions.
3. Control method according to any one of claims 1 or 2, wherein additional information is a measurement of the state of charge of the electrochemical element (12).
4. Control method according to any one of claims 1 to 3, wherein additional information is a measurement of the capacitance of the electrochemical element (12).
5. Control method according to any one of claims 1 to 4, wherein additional information is a new target charge state value for which current balancing of the electrochemical elements (12) is to be achieved.
6. A control method according to any one of claims 1 to 5, wherein the balancing circuit (15) has an active state in which the balancing circuit (15) applies a balancing current and an inactive state in which the balancing circuit (15) does not apply the balancing current, the control step comprising putting the balancing circuit (15) into the active state if the determined amount of charge to be balanced is greater than or equal to a threshold.
7. Control method according to any one of claims 1 to 6, wherein each electrochemical element (12) has a charge state-open circuit voltage characteristic having a planar portion, a planar portion being a portion in which the open circuit voltage variation is less than 30 mV for a variation of at least 10% of the charge state.
8. A method according to any one of claims 1 to 7, wherein at least one electrochemical element (12) comprises a cathodic active material comprising a lithium iron phosphate, a lithium manganese iron phosphate, or a lithium vanadium fluorophosphate.
9. Calculator (22) suitable for controlling the current balancing of a plurality of electrochemical elements (12) of a battery (10), the battery (10) being provided with a balancing circuit (15) allowing a respective balancing current to be applied in each electrochemical element (12) of the plurality of electrochemical elements (12), the calculator (22) being suitable for, for each electrochemical element (12) to be balanced: - obtaining measurement values, the measurement values including the capacitance of the electrochemical element (12), first measurement values and second measurement values, the first values including measurements or estimates of the current of the electrochemical element (12) and of the balancing current applied to the electrochemical element (12), the second values including measurements or estimates of the state of charge of the electrochemical element (12), - determine the quantity of charge to be balanced for the electrochemical element (12) at a plurality of determination times, the calculator (22) being capable of performing the determination at each determination time by: - detecting the possible acquisition of at least one piece of information relating to the balancing to be carried out since the last moment of determination, the at least one piece of information being additional information compared to the measured values obtained, - calculating the amount of charge to be balanced for the electrochemical element (12) by application: - a first calculation technique based on the measured values obtained and at least one additional piece of information when at least one additional piece of information has been detected, the first technique comprising a calculation of the amount of charge to be balanced for the electrochemical element (12) as the difference between two terms, the first term being the maximum amount of charge to be supplied for an electrochemical element (12) to reach a target charge state among the plurality of electrochemical elements (12) and the second term being the amount of charge to be supplied for the electrochemical element (12) to reach the target charge state, and- a second calculation technique on the measurement values obtained when no additional information has been detected, the second technique comprising the calculation of a first contribution and a second contribution, the first contribution being the value of the amount of charge supplied by the balancing circuit (15) since the last instant of determination and the second contribution being the contribution related to the self-discharge differences between the electrochemical elements (12), the amount of charge to be balanced for the electrochemical element (12) calculated by the first technique or second technique being the amount of charge to be balanced determined, and - check the balancing circuit (12) according to the amount of charge to be balanced determined.
10. Management system (14) for a plurality of electrochemical elements (12) of a battery (10), the electrochemical elements (12) having terminals, the management system (14) comprising: - a balancing circuit (15) suitable for applying a respective balancing current to each of the electrochemical elements (12) of the plurality of electrochemical elements (12), - for each electrochemical element (12) of the plurality of electrochemical elements (12): - a sensor for the current (18) delivered by the electrochemical element (12), - a unit for measuring the balancing current applied to the electrochemical element (12), and - a voltage sensor (16) suitable for measuring the voltage across the terminals of the electrochemical element (12), and - a calculator (22) according to claim 9.
11. Battery (10) including: - electrochemical elements (12), and - a management system (14) according to claim 10.