Method for determining a contribution to a measurement deviation of the state of charge of an electrochemical battery element and associated method and devices

Abstract

Method for determining a contribution to a measurement deviation of the state of charge of an electrochemical element of a battery and associated method and devices The present invention relates to a method for determining a contribution to the measurement deviation between a measurement of the state of charge of an electrochemical element of a battery and the actual value of the state of charge, the method comprising: - obtaining: - values ​​of the current and the capacity of the electrochemical element, - values ​​of the state of charge obtained by using an evaluation technique, - detecting two instants during which the value obtained is equal to a predefined value, - triggering a counter of the quantity of charge at the first instant, and - determining a contribution to the measurement deviation, each determined contribution depending on the value of the counter at the second instant and the time elapsed between the two instants. Figure for abstract: figure 3

Description

Title of the invention: Method for determining a contribution to a measurement deviation of the state of charge of an electrochemical battery element and associated method and devices

[0001] The present invention relates to a method for determining the difference between a measurement of the state of charge of at least one electrochemical element of a battery and the actual value of the state of charge of said at least one electrochemical element, the measurement being carried out on the basis of a counter of the quantity of charge accumulated. The present invention also relates to a control method using such a method. The invention also relates to an associated computer, management system and battery.

[0002] Typically a battery comprises one or more current accumulators also called electrochemical generators, cells or elements. An accumulator is an electricity production device in which chemical energy is converted into electrical energy. The chemical energy comes from the electrochemically active compounds deposited on at least one face of electrodes arranged in the accumulator. The electrical energy is produced by electrochemical reactions during a discharge of the accumulator. The electrodes, arranged in a container, are electrically connected to current output terminals which ensure electrical continuity between the electrodes and an electrical consumer with which the accumulator is associated.

[0003] In order to increase the electrical power delivered, several sealed accumulators can be combined together to form a battery. Thus, a battery can be divided into modules, each module being composed of one or more accumulators connected together in series and / or in parallel. Thus, a battery can for example comprise one or more parallel branches of accumulators connected in series and / or one or more parallel branches of modules connected in series.

[0004] A charging circuit is generally provided to which the battery can be connected to recharge the accumulators.

[0005] Furthermore, an electronic management system comprising measurement sensors and an electronic control circuit, more or less advanced depending on the applications, can be associated with the battery. Such a system makes it possible in particular to organize and control the charging and discharging of the battery, to balance the charging and discharging of the different accumulators of the battery with respect to each other.

[0006] The state of charge is useful information for the electronic battery management system to optimize its use and lifespan. The state of charge is often designated by the abbreviation SOC which refers to the English term “State of Charge”.

[0007] To obtain the state of charge SOC, it is known to use two calculation techniques using continuous measurements of the evolution of the voltage, the current and the temperature.

[0008] The first technique can be described as "coulometric" insofar as it uses the fact that the state of charge SOC depends on the charge (counting of Ampere-hours) and the capacity Q of the battery.

[0009] In fact, the following formulas come from expressing the quantities in percentages:

[0010] SOC = SOC0 +100

[0011] Where: SOCq is the initial value of the state of charge SOC at time t=0.

[0012] However, this first technique is very sensitive to the current measurement error as well as to the estimation of the capacity. Therefore, the use of this technique alone leads to the accumulation of the current measurement error, which induces an erroneous estimation of the state of charge.

[0013] The second technique is based on measurements of the open circuit voltage OCV and uses a pre-established look-up table to obtain the state of charge SOC as a function of the open circuit voltage. The open circuit voltage is often referred to by the abbreviation OCV which refers to the English term for “Open Circuit Voltage”.

[0014] Since the function that links the open circuit voltage OCV to the state of charge SOC is a function of the voltage from which the product of the resistance and the current is subtracted, the second technique is a technique sensitive to the estimation of the resistance. Also, it is appropriate to use the second technique under conditions that make it possible to minimize the error on the resistance, namely resting or low current conditions.

[0015] It is known to use the two aforementioned techniques by using the first technique as the usual technique and by regularly recalibrating the state of charge SOC using the second technique.

[0016] However, in some electrochemical elements, because the variation of the open circuit voltage as a function of the state of charge SOC has a plateau, the correspondence between the open circuit voltage OCV and the state of charge SOC may be false.

[0017] Thus, it is known to carry out a recalibration by carrying out a recharge with a state of charge SOC greater than the maximum state of charge SOC corresponding to the end of the plateau.

[0018] Such a technique then generally requires the interruption of the mission of the electrochemical element to carry out the recharge. This is particularly the case for frequency regulation missions which involve cycles on the plate. Such interruptions may be incompatible with the mission.

[0019] This means that knowledge of the contributions to the measurement deviation between a measurement of the state of charge SOC of an electrochemical element by a coulometric technique and the actual value of the state of charge of said electrochemical element can only be obtained by interrupting the mission.

[0020] There is therefore a need for a method making it possible to determine at least one contribution to such a difference, while remaining compatible with implementation by a battery calculator.

[0021] For this purpose, the description describes a method for determining at least one contribution to the measurement deviation between a measurement of the state of charge of at least one electrochemical element of a battery and the actual value of the state of charge of said at least one electrochemical element, the measurement being carried out on the basis of a counter of the quantity of charge accumulated by the at least one electrochemical element, the at least one contribution being chosen from the list consisting of a first contribution coming from a current sensor providing current values ​​of the at least one electrochemical element, a second contribution coming from the self-discharge of the at least one electrochemical element and a third contribution coming from errors in the estimation of the capacity of the at least one electrochemical element, the estimation method being implemented by a computer and comprising:

[0022] - a step of obtaining:

[0023] - values ​​of the current and the capacity of the at least one electrochemical element,

[0024] - values ​​of the state of charge of the at least one electrochemical element, the state of charge values ​​being obtained by using an evaluation technique having a deviation from the actual value of the state of charge of said at least one electrochemical element, the deviation of the evaluation technique being strictly less than the measurement deviation to be determined,

[0025] - a first step of detecting a first instant during which the value obtained of the state of charge is equal to a predefined value,

[0026] - a step of triggering a counter of the quantity of charge accumulated by the at least one electrochemical element at the first instant,

[0027] - a second step of detecting a second instant during which the value obtained from the state of charge is equal to the preset value, and

[0028] - a step of determining at least one contribution to the measurement deviation, each determined contribution depending on the value of the counter at the second instant and the time elapsed between the first instant and the second instant.

[0029] According to particular embodiments, the determination method has one or more of the following characteristics, taken in isolation or in all technically possible combinations:

[0030] - the determined contributions are the first contribution and the second contribution, the sum of the first contribution and the second contribution depending only on the value of the counter at the second instant and the time elapsed between the first instant and the second instant.

[0031] - the sum of the first contribution and the second contribution is equal to the opposite of the ratio of the counter value at the second instant and the time elapsed between the first instant and the second instant.

[0032] - the method is implemented for a plurality of electrochemical elements and during in the determining step, the second contribution of an electrochemical element is determined relative to the second lowest contribution of the plurality of electrochemical elements.

[0033] - the second contribution of the electrochemical element is obtained by subtraction between the sum of the first contribution and the second contribution determined for the electrochemical element considered and the sum of the first contribution and the second contribution determined for the electrochemical element presenting the second lowest contribution.

[0034] - a determined contribution is the third contribution, the third contribution also depending on the state of charge value at a third instant, the third instant being the instant during which the difference between the state of charge value obtained and the state of charge value deduced from the counter value is the greatest in absolute value.

[0035] - a determined contribution is the third contribution, the third contribution being given according to the following formula:

[0036] Q bias

[0037] Where: • Q denotes the estimation of the capacity of the electrochemical element 12 affected by capacity bias, • ASOC^^ denotes the difference between the obtained SOC state of charge value and the value of the state of charge SOC deduced from the value of the counter at the third instant and • I denotes the actual value of the current.

[0038] - the value of the sum of the first contribution and the second contribution for the evaluation technique is less than or equal to C / 30.

[0039] - the value of the third contribution for the evaluation technique is lower or equal to 3Q / 100, Q designating the value of the capacity of the electrochemical element.

[0040] - the at least one electrochemical element comprises at least one active material cathode selected from the following groups or their mixtures:

[0041] i) a compound of formula LixFei yMyPO4where M is selected from the group consisting of B, Mg, Al, Si, Ca, Ti, V, Cr, Mn, Co, Ni, Cu, Zn, Y, Zr, Nb and Mo; and 0.8 <x<l,2 ; 0<y<0,6,

[0042] ii) a compound of formula LiVPO4F.

[0043] The description also describes a method for controlling at least one electrochemical element of a battery, the control method comprising:

[0044] - a step of implementing the method for determining at least one contribution to the measurement difference between a measurement of the state of charge of the at least one electrochemical element and the actual value of the state of charge of said at least one electrochemical element, the determination method being as previously described, to obtain at least one determined contribution, and

[0045] - a step of implementing a corrective action depending on the value of the less a determined contribution.

[0046] Furthermore, the description relates to a method for obtaining a health status parameter of at least one electrochemical element of a battery, the method for obtaining comprising:

[0047] - a step of implementing the method for determining at least one contribution to the measurement difference between a measurement of the state of charge of the at least one electrochemical element and the actual value of the state of charge of said at least one electrochemical element, the determination method being as previously described and making it possible to obtain at least the third contribution,

[0048] - a step of estimating the capacity of the at least one electrochemical element, and

[0049] - a step of deducing a health status parameter of the at least one element electrochemical using the estimated capacity.

[0050] The description also proposes a calculator capable of determining the difference between a measurement of the state of charge of at least one electrochemical element of a battery and the actual value of the state of charge of said at least one electrochemical element, the measurement being carried out on the basis of a counter of the quantity of charge accumulated by the at least one electrochemical element, the difference taking into account at least one contribution chosen from the list consisting of a first contribution coming from a current sensor providing current values ​​of the at least one element electrochemical, a second contribution coming from the self-discharge of the at least one electrochemical element and a third contribution coming from errors in the estimation of the capacity of the at least one electrochemical element, the calculator being suitable for:

[0051] - obtain:

[0052] - values ​​of the current and the capacity of the at least one electrochemical element,

[0053] - values ​​of the state of charge of the at least one electrochemical element, the state of charge values ​​being obtained by using an evaluation technique having a deviation from the actual value of the state of charge of said at least one electrochemical element, the deviation of the evaluation technique being strictly less than the measurement deviation to be determined,

[0054] - detect a first instant during which the value obtained from the state of charge is equal to a predefined value,

[0055] - trigger a counter of the amount of charge accumulated by the at least one electrochemical element at the first instant,

[0056] - detect a second instant during which the obtained value of the state of charge is equal to the predefined value, and

[0057] - determine at least one contribution of the measurement deviation, each contribution determined depending on the value of the counter at the second instant and the time elapsed between the first instant and the second instant.

[0058] The description also describes a system for managing at least one electrochemical element of a battery, the management system comprising:

[0059] - a voltage sensor capable of measuring the voltage across the terminals of said at least one electrochemical element,

[0060] - a current sensor capable of measuring the current delivered by said at least one electrochemical element,

[0061] - a temperature sensor capable of measuring the temperature of said at least one electrochemical element, and

[0062] - a calculator as previously described.

[0063] The description also provides a battery comprising:

[0064] - at least one electrochemical element, and

[0065] - a management system as previously described.

[0066] In the present description, the expression “suitable for” means indifferently “adapted for”, “adapted to” or “configured for”.

[0067] Characteristics and advantages of the invention will appear on reading the description which follows, given solely by way of non-limiting example, and made with reference to the appended drawings, in which:

[0068] - [Fig.l] [Fig.l] is a schematic representation of an example of a battery comprising an electrochemical element,

[0069] - [Fig.2] [Fig.2] is a graph illustrating an example of a characteristic state of charge - open circuit voltage of an electrochemical element comprising a cathodic active material based on lithium iron phosphate (LiFePO4),

[0070] - [Fig.3] [Fig.3] is a block diagram representation of an example of implementation implementation of a method for determining a contribution to the difference between a measurement of the state of charge of at least one electrochemical element of a battery and the actual value of the state of charge of said at least one electrochemical element, the measurement being carried out on the basis of a counter of the quantity of charge accumulated,

[0071] - [Fig.4] [Fig.4] is a graphical illustration of an example implementation of certain steps of the determination process described in [Fig.3],

[0072] - [Fig.5] [Fig.6] [Fig.7] Figures 5 to 7 are experimental curves involved in the implementation of the estimation method corresponding to figures 3 and 4,

[0073] - [Fig.8] [Fig.8] is a graphic illustration of another example of implementation implementation of certain steps of the determination process described in [Fig.3],

[0074] - [Fig.9] [Fig.9] is an experimental curve involved in the implementation of the estimation method corresponding to Figures 3 and 8, and

[0075] - [Fig. 10] [Fig. 10] is a graphic illustration of yet another example of implementation of certain steps of the determination method described in [Fig.3].

[0076] A battery 10 is shown in [Fig.l].

[0077] In a manner known per se, a battery is generally an arrangement of a plurality of electrochemical elements but for the sake of simplification of the subject, a case with a single electrochemical element is described in what follows, knowing that the transposition to other arrangements is immediate.

[0078] The battery 10 comprises an electrochemical element 12 and a management system 14 of the electrochemical element 12.

[0079] As explained previously, an electrochemical element 12 is an electricity generating device in which chemical energy is converted into electrical energy.

[0080] The electrochemical element 12 therefore delivers a current and a voltage between two terminals.

[0081] The electrochemical element 12 has a state of charge characteristic SOC - open circuit voltage OCV as seen in [Fig.2]. This characteristic is referred to as the SOC / OCV characteristic hereinafter.

[0082] In [Fig.2], the state of charge SOC is expressed as a percentage of a maximum state of charge.

[0083] The SOC / OCV characteristic has four zones, a first zone Z1, a second zone Z2, a third zone Z3 and a fourth zone Z4.

[0084] The first zone Z1 corresponds to the start of the charge and the fourth zone Z4 to the end of the charge.

[0085] For the two intermediate zones, since the second zone Z2 and third zone Z3 correspond to a flat portion, the term flat portion (Z23) will be used hereinafter.

[0086] 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 SOC.

[0087] 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 chosen from the following groups or their mixtures:

[0088] i) a compound of formula LixFei yMyPO4where M is selected from the group consisting of B, Mg, Al, Si, Ca, Ti, V, Cr, Mn, Co, Ni, Cu, Zn, Y, Zr, Nb and Mo; and 0.8 <x<l,2 ; 0<y<0,6, et

[0089] ii) a compound of formula LiVPO4F.

[0090] The anode active material is not particularly limited. It is a material capable of inserting lithium into its structure. It may be selected from lithium compounds, carbon materials such as graphite, coke, carbon black and glassy carbon. It may also be based on tin, silicon, carbon and silicon based compounds, carbon and tin based compounds or carbon, tin and silicon based compounds. It may also be a lithiated titanium oxide such as Li4Ti50i2 or a niobium titanium oxide such as TiNb2O7.

[0091] Of course, these examples are non-limiting and the method described later can be used for any type of electrochemical element 12.

[0092] The management system 14 is a system suitable for managing the electrochemical element 12.

[0093] The management system 14 comprises a voltage sensor 16, a current sensor 18, a temperature sensor 20 and a computer 22.

[0094] The voltage sensor 16 is suitable for measuring the voltage across the terminals of the electrochemical element 12.

[0095] The current sensor 18 is capable of measuring the current delivered by the electrochemical element 12.

[0096] The temperature sensor 20 is suitable for measuring the temperature of the electrochemical element 12.

[0097] The calculator 22 is capable of implementing a determination method described below.

[0098] The computer 22 is an electronic circuit designed to manipulate and / or transform data represented by electronic or physical quantities in registers of the computer and / or memories into other similar data corresponding to physical data in the memories of registers or other types of display devices, transmission devices or storage devices.

[0099] As specific examples, the computer 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.

[0100] An example of implementation of the determination method is now described with reference to the flowchart of [Fig.3] and to the schematic representation of [Fig.4],

[0101] According to the example of [Fig.3], the computer 22 seeks to determine the current bias in measuring the state of charge of the electrochemical element 12 on the basis of a counter of the quantity of charge accumulated by the electrochemical element 12.

[0102] Such a technique can be described as coulometric and is based on the fact that the state of charge SOC of an electrochemical element 12 depends directly on the ratio between the quantity of charge accumulated (or counting of Ampere-hours with reference to the unit often used for this quantity) and the capacity of the electrochemical element 12.

[0103] More precisely, the following relationship is used between the current values ​​and the capacitance value:

[0104] F Ixdt SOC{t)=SOC^lMx-^^

[0105] Where: * tinit designates the instant during which the technique is triggered, • SOC^t. denotes the value of the state of charge SOC at the initial instant and • SOC^ denotes the value of the state of charge SOC obtained at time t.

[0106] In this formula, it appears that the determination of the state of charge SOC depends on the value of the current used for the calculation.

[0107] If the current value used in the calculation has a bias, the estimated state of charge SOC value will also have a bias.

[0108] Such a corresponding current bias may in particular come from imperfections in the current sensor 18 providing the current values ​​and / or from the self-discharge of the electrochemical element 12.

[0109] It is this current bias noted in the remainder of the description that the calculator 22 seeks to determine.

[0110] The proposed determination method comprises an obtaining step E30, a first detection step E32, a triggering step E34, a second detection step E36 and a determination step E38.

[0111] During the obtaining step E30, the calculator 22 obtains a plurality of values.

[0112] For example, the calculator 22 obtains measurements (values) of the voltage U, of the current I of temperature T and capacity Q of electrochemical element 12.

[0113] This means that the computer 22 is capable of interacting with the sensors 16, 18 and 20 to obtain the values ​​measured by these sensors.

[0114] During the obtaining step E30, the computer 22 also obtains values ​​of the state of charge of the at least one electrochemical element 12.

[0115] The calculator 22 can, depending on the case, receive the values ​​or calculate them.

[0116] For example, it is assumed that the calculator 22 calculates the values ​​using an evaluation technique.

[0117] The evaluation technique is an accurate technique in the sense that it gives a better evaluation of the state of charge than that obtained with the coulometric technique.

[0118] Preferably, the current bias of the evaluation technique is 10 times smaller than the current bias of the coulometric technique.

[0119] In the example described, the current bias of the evaluation technique is less than or equal to C / 30.

[0120] For example, the evaluation technique is a resting voltage measurement.

[0121] As a result, such an evaluation technique is completely insensitive to current and capacity biases and can be carried out in one go (no iteration). This technique is restrictive because it requires a rest phase generally involving a shutdown of the application for several hours.

[0122] Also, alternatively, the evaluation technique is a technique involving neural networks.

[0123] The neural network takes, as input, the measured values ​​to evaluate the value of the state of charge.

[0124] In such a case, the technique involves an iteration to gradually eliminate the current and capacitance biases. This elimination is based on a feedback loop that can involve an observer or a proportional corrector based on a simple law which only reinjects 50% of the value of the detected biases into the input in order to avoid any wave phenomenon in the results.

[0125] This makes it possible to obtain a bias-robust technique, a robust technique corresponding to a current bias of the evaluation technique less than or equal to C / 30 and a capacity bias less than or equal to 3Q / 100.

[0126] It can thus be considered with regard to the precision of a coulometric technique that the evaluation technique makes it possible to obtain the value of the state of charge of the electrochemical element 12.

[0127] The value of the SOC obtained by the evaluation technique at a time t is noted SOC( t ) in the remainder of the description.

[0128] According to the example described, the obtaining step E30 is implemented continuously, so that the solid line curve in FIG. 4 is obtained which represents the temporal variation of the evaluation of the state of charge SOC(t) by the evaluation technique.

[0129] In this case, the state of charge of the electrochemical element 12 decreases from a maximum value to a minimum value and then rises towards the same maximum value.

[0130] Other profiles of temporal variations of the state of charge SOC(t) are conceivable depending on the intended use of the electrochemical element 12.

[0131] It may also be noted that the measurement values ​​obtained may differ depending on the needs of the evaluation technique.

[0132] For example, if the evaluation technique does not require the temperature, it is not necessary for the computer 22 to obtain the temperature measurement values.

[0133] At a minimum, the calculator 22 will obtain the measurement values used in the coulometric counter, namely the current and capacitance values.

[0134] During the first detection step E32, the calculator 22 detects a first instant during which the obtained state-of-charge value is equal to a predefined value.

[0135] The predefined value is chosen according to the use of the electrochemical element 12 so that the state of charge definitely passes twice through the same value.

[0136] By way of example, it may be chosen as the value half of the maximum extension in the variation of the state of charge of the electrochemical element 12 during typical use. This is especially the case for a frequency regulation application.

[0137] Such a choice allows the method to be implemented without stopping the operation of the electrochemical element 12.

[0138] The first instant is noted tinit in the rest of the description.

[0139] During the triggering step E34, the computer 22 triggers a counter of the quantity of charge accumulated by the electrochemical element 12 at the first instant {■mit-

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[0159] The dotted curve in [Fig.4] shows the time evolution of the state of charge of the electrochemical element 12 deduced from the meter of the quantity of charge accumulated according to the previous formula, namely: SOC{t)= SOC(tinit}+ lOOx-^ The variations observed between the solid curve and the dotted curve in [Fig.4] correspond to the effect of the biases that controller 22 seeks to determine. During the second detection step E36, the computer 22 detects a second instant during which the value obtained from the state of charge is equal to a predefined value. The second instant is distinct from the first instant tinit and is noted tf in the following. With the introduced notations, the following relation is verified: SOC(tinit) = SOC(tf) During the determination step E38, the calculator 22 determines the value of the current bias by applying a calculation function. The calculation function here is as follows: = 1 bias 'trtinit' Where Ahÿ ) denotes the value of the Ampere hour count at the final instant tf as obtained by the counter. This makes it possible to obtain the value of the current bias I easily since the method can be implemented without stopping the electrochemical element 12 and the computational load associated with the implementation of the method is sufficiently reduced to be able to be carried out on board by the controller 22. In other words, the determination process allows the current bias to be measured in real time. This determination also allows good precision to be obtained as can be demonstrated by calculation and experimentally. A computational proof corresponds to the following reasoning. Noting Ah^ the value of the Ampere hour count at the final instant tf, from the initial instant tinit, based on the real current, a first relation RI comes: = A^-Â^ Moreover, the quantity Ahÿ} verifies a second relation R2: The magnitude ) verifies a third relation R3: C 1 Ah(tinit)+ ff. Jsys.dt

[0161] Where: • Ahy y denotes the balance of the Ampere hour count starting at the initial instant and • Isys denotes the measured current of the electrochemical element 12.

[0162] In addition, the quantity Isys verifies a fourth relation R4:

[0163] I Sys = 1 + 1

[0164] Where I denotes the actual current.

[0165] In these four previous relations, the quantities I and ^ are unknown.

[0166] Using relations R3 and R4, there comes a fifth relation R5: 101671 A^+ f' ï.dt +

[0168] By using the relations R2 and R5 in the first relation RI, it comes: [01691 = fi Ldt. (^,,+ fi IM+ fi = -fi I^dt

[0170] Due to its definition, the value can be considered constant over the period [ t^f, tf], so that:

[0171] AA^-I^tf-t^t)

[0172] That is to say the following sixth relation R6:

[0173] = AAh(t{} I bias " trtjnit

[0174] Now, the definition of the actual state of charge SOC at the second instant tf is as follows: 101751 SOC^=

[0176] With the equality SOC^ = SOQtf), it comes: S OC^ - SOC(t.ait) = 100 [tf T fit

[0177] From which a seventh relation R7 emerges: 101781 0=C I.dt I finish

[0179] This seventh relation R7 corresponds to the fact that the value of the Ampere hour count at the second instant tf, Ahÿ j, is zero since the actual state of charge returns to the same predefined value.

[0180] Now, the coulometric counter Ah^ is started at the first instant tjnit, which implies Ah^ = 0.

[0181] Using the relations R2 and R3, in the first relation RI, it comes as follows: [°182] AA^-Ah(t.[i.è+ ff^JsysXlt}

[0183] The seventh relation R7 thus leads to: 101841 ^tf)= Sllsy.dt

[0185] From which results the relation:

[0186] T. Linit 1 bias “trtin[t

[0187] Experimental proof of the accuracy also results from experiments conducted by the Applicant, the results of which are shown in Figures 5 to 7.

[0188] In this implementation, an evaluation technique based on neural networks is used.

[0189] The use of this technique on an electrochemical element based on LiFePO4 type chemistry leads to the current profile visible in [Fig.5] which represents the temporal evolution of the state of charge of this electrochemical element.

[0190] In the experiment, the electrochemical element has a capacity of 195.9 Ah.

[0191] In addition, a current bias of 235 mA and a capacity bias of - 4000 mAh are artificially added. The concept of capacity bias will be detailed later, in particular with reference to Figures 8 and 9.

[0192] [Fig.6] represents the time evolution of the estimation of the current bias implemented by a proportional corrector.

[0193] The result of implementing the method in this case is shown in [Fig.7] which shows the value for the current bias obtained as a function of the time interval elapsed between the two values ​​of equality of the state of charge SOC.

[0194] As expected, the longer the time interval, the better the accuracy.

[0195] In the experiment conducted, this leads to a value for the current bias equal to 236.2 mA. This value is very precise since it corresponds to the actual value within almost 1 mA.

[0196] Additionally, it can be observed that after 2 weeks, the current bias is almost detected at 90%, as illustrated in [Fig.7].

[0197] The results obtained by the determination method are thus satisfactory.

[0198] Another example of implementing the determination method is now described with reference to the flowchart of [Fig.3] and the schematic representation of [Fig.8].

[0199] In this example, the computer 22 seeks to determine the capacity bias in measuring the state of charge of the electrochemical element 12 based on the counter of the amount of charge accumulated by the electrochemical element 12.

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[0210] For this purpose, it can be used that when the deviation between the measurement of the state of charge of the electrochemical element 12 based on the counter of the amount of charge accumulated by the electrochemical element 12 and the actual value of the state of charge of the electrochemical element 12 is maximum, this deviation is linked to the sum of the current bias / / nais ct ^hiis of capacity Q . . jJIIaI J This difference is observed at a third instant during which the difference between the obtained SOC state of charge value and the SOC state of charge value deduced from the counter value is the greatest in absolute value. This third moment is tD0D in reference to the fact that the acronym DOD stands for depth of discharge. The difference at the third instant tD0D is visible in Figure 8 which represents the temporal evolution between the first instant tD0D and the third instant tD0D of three quantities: the actual or evaluated state of charge SOC (solid curve), the state of charge SOC deduced from the meter (dash-and-dash curve) and the state of charge SOC deduced from the meter and corrected for the current bias (dotted curve). Knowing the current bias it is therefore possible to determine the capacity bias O, . . . bias Advantageously, knowledge of the current bias comes from the implementation of the determination method as previously described. It is therefore sufficient to detect a third instant during which the difference between the obtained SOC state of charge value and the SOC state of charge value deduced from the counter value is the greatest in absolute value. At this third instant tDOD, the calculator 22 obtains the value of the state of charge soc{tDOD). By expressing the capacity bias Qj^ as a fraction of the initial capacity, it is sufficient to apply the following calculation function during the determination step: bias Or: • Q denotes the estimation of the capacity of the electrochemical element 12 affected by the capacity bias, ASOC(tD( ,D) denotes the difference between the obtained SOC state of charge value and the SOC state of charge value deduced from the counter value at the third instant and

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[0218] • I the actual value of the current, which corresponds to the measured current corrected for the current bias As previously, this makes it possible to obtain the value of the capacity bias easily since the method can be implemented without stopping the electrochemical element 12 and the computational load associated with the implementation of the method is sufficiently reduced to be able to be carried out on board by the controller 22. In other words, the determination method allows the capacity bias to be measured in real time, separately from the current bias. This determination also allows good precision to be obtained as can be demonstrated by calculation and experimentally. A computational proof corresponds to the following reasoning. The notations used in the following are: • SOC^jnjt) the state of charge of the electrochemical element 12 evaluated by the evaluation technique at the first instant • SOC^) the state of charge of the electrochemical element 12 evaluated by the evaluation technique at the third instant • Ibias 'c current bias of the electrochemical element 12, * Qbias 'C b'a's of capacity of the electrochemical element 12, SÔCir, the state of charge of the electrochemical element 12 in the third instant deduced from the coulometric counter affected by the biases of current and capacity Q^-a^s • SOCt \ the state of charge of the electrochemical element 12 at the third instant based on the coulometric counter affected only by the capacity bias Q^^i because compensated for the current bias • 'Q the estimation of the capacity of the electrochemical element 12 affected by capacity bias O, . . , bias • Q the actual capacity of the electrochemical element 12, • Isys denotes the measured current of the electrochemical element 12, and • I denotes the actual current delivered by the electrochemical element 12. It is recalled that the relation SOCÿ j = SOC^ is verified. From the above definitions, the following relationships Rll to R15 are known: ASOC(t \= SOCtt sÔCa JR11)

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[0239] SOC(t )= SOC(t .)+ (R12) SOC ig „ = SOC^ ^.^ xm I sys .dt (R13) Q=Q+Q (R14) bias Isys = J + In these different relationships, O, ■ and Q are the unknowns here. bias Substituting relation R15 into relation R13 gives: SOCiq = SOCft .}+ QV tjnit silly- I tinit (R16) The current bias being known thanks to relation R15, relation RI6 can be rewritten and becomes: SÔCtt )= SOC,t. .)+ f' l.dl (R17) In fact, the current is freed from its average current bias, that is, the integration is carried out on the actual current directly. This estimate, however, is still affected by the capacitance bias. The substitution of relations R12 and R17 in relation RI 1 then leads to the following relation: SOC(t„„)+ ^“^-(sOC^ Either : ASOC, = Wt- Solving then for Q, it comes ASOC(t ) = 1 OQj^Lddi ) J tîllit \QQ} That's to say : dgQQtccp) _ ii lOOj^ / .dt ~ Q'Q your inn From where: ASOC^^ i _ i lOO.f^Ldt Q ç Which is rewritten as the following RI8 relation:

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[0255] 1 (RI 8) ASOCltn^ J WüJ^l.dt Q The capacity bias O, . . is then obtained using relation R14 and the bias relation RI8 and verifies the following relationship: Qbias Experimental proof of accuracy also results from experiments conducted by the Applicant corresponding to [Fig.9]. The conditions of the experiment are the same as those carried out for the cases in figures 5 to 7. Implementing the previous procedure allows us to obtain an assessment of the bias of capacity O, . ■ bias The result of implementing the method in this case is shown in [Fig.9] which shows the value for the capacity bias obtained as a function of the time interval elapsed between the two values ​​of equality of the state of charge SOC. As expected, the larger the time interval, the better the accuracy. In the experiment performed, this leads to a value for the capacity bias equal to - 4002.58 mAh. This value is very precise since it corresponds to the actual value almost to within 2 mAh. Furthermore, it can be seen that after 3 weeks the capacity bias is almost 80% detected. The results obtained by the determination process are therefore satisfactory. Such a determination of the capacity bias Q . is useful for determining the state aging of the electrochemical element 12. It can also improve the accuracy of the estimation of the state of charge of the electrochemical element 12 when this is obtained from a coulometric counter. Yet another example of implementing the determination method is now described with reference to the flowchart of [Fig.3] and to the representation schematic of [Fig. 10]. The current bias corresponds to the sum of two contributions A first contribution to the current bias / ^ïais Comes from imperfections in the current sensor 18 providing the current values. This first contribution is noted Ibiais_captem'-

[0256] A second contribution to the current bias Ij^g comes from a physical phenomenon, it is the self-discharge of the electrochemical element 12. This second contribution is noted I self-discharge-

[0257] This is written mathematically as:

[0258] ^bias~ Ibias_sensor+1 self-discharge

[0259] This relationship is valid considering a receiver convention that is I positive in charge. Thus, Iself-discharge is less than or equal to zero.

[0260] The calculator 22 here seeks to determine at least relatively the value of the second contribution I self-discharge-

[0261] By implementing the method for several electrochemical elements 12 (three in the example of [Fig. 10]), the computer 22 can obtain the second contribution of the electrochemical element 12 by subtraction between the sum Ibiais of the first contribution and the second contribution determined for the electrochemical element considered and the sum Ibiais of the first contribution and the second contribution determined for the electrochemical element 12 having the second lowest contribution.

[0262] This is based on the fact that a priori the first contribution is relatively similar from one electrochemical element 12 to another.

[0263] [Fig. 10] represents in solid lines the temporal evolution of the real value of the state of charge SOC (that obtained by the evaluation technique) and the temporal evolutions of the values ​​of the state of charge affected by the current bias for a first electrochemical element (long dotted curve), affected by the current bias for a second electrochemical element (short dotted curve) and affected by the current bias for a third electrochemical element (dash-and-dash curve). In this representation, the capacity bias Qbiais is ignored to simplify the representation.

[0264] Here the second weakest contribution is that of the second electrochemical element 12 which can thus serve as a reference.

[0265] Such relative knowledge of the self-discharge value makes it possible to envisage the implementation of a balancing method, the correction to be applied to each electrochemical element being the value determined for the second contribution of the electrochemical element.

[0266] Such balancing is proactive balancing since rather than undergoing the self-discharge differences of the electrochemical elements 12 and compensating for the differences observed at the a posteriori level, knowledge of the self-discharge differences between the electrochemical elements 12 makes it possible to control the balancing circuit so that there is no longer any difference between the electrochemical elements 12 permanently.

[0267] This is particularly interesting for electrochemical elements with an active cathode material based on lithium iron phosphate which must be completely or partially disconnected in order to be able to estimate the differences in charge state between the electrochemicals 12 in order to then be able to rebalance them.

[0268] More generally, the described determination method makes it possible to determine at least one contribution to the measurement deviation between a measurement of the state of charge SOC of the electrochemical element 12 and the actual value of the state of charge SOC of the electrochemical element 12, the measurement being carried out on the basis of the counter, the at least one contribution being chosen from the list consisting of a first contribution from the current sensor providing current values of the electrochemical element 12, a second contribution from the self-discharge of the electrochemical element 12 and a third contribution Qbiais from errors in the estimation of the capacity of the electrochemical element 12.

[0269] This determination is based on a clever use of the usage profile and a technique for evaluating the state of charge SOC of the electrochemical element 12 that is precise enough to be able to evaluate the values of the contributions.

[0270] In each case, the determination depends on the value of the counter at the second instant tf and the time elapsed between the first instant tinit and the second instant tf.

[0271] Refinements of the determination may be considered.

[0272] For example, it would be possible to collect over a long period pairs {Ibiais; (tf - tinit)} and estimate the current bias by applying a weighted average or other filtering techniques.

[0273] Knowledge of the value of the contributions given by the determination method is useful in implementing a method for controlling the electrochemical element 12.

[0274] Such a method firstly comprises a step of implementing the determination method as previously described, then a step of implementing a corrective action depending on the value of the at least one determined contribution.

[0275] An example given was the correction of the balance by applying a current opposite to the determined self-discharge current.

[0276] It may also be considered to correct the evaluation of a coulometric counter.

[0277] Knowledge of the third contribution may also be useful in implementing a method for obtaining a health status parameter of the electrochemical element 12.

[0278] Such a method firstly comprises a step of implementing the determination method as previously described to obtain at least the value of the capacity bias Q^as-

[0279] The method then comprises estimating the capacity of the electrochemical element 12 using this value and deducing a health parameter according to techniques known to those skilled in the art, using the estimated capacity.

Claims

1. Claims Method for determining at least one contribution to the measurement deviation between a measurement of the state of charge (SOC) of at least one electrochemical element (12) of a battery (10) and the actual value of the state of charge (SOC) of said at least one electrochemical element (12), the measurement being carried out on the basis of a counter of the quantity of charge accumulated by the at least one electrochemical element (12), the at least one contribution being chosen from the list consisting of a first contribution coming from a current sensor providing current values of the at least one electrochemical element (12), a second contribution coming from the self-discharge of the at least one electrochemical element (12) and a third contribution (QbiaiS) coming from errors in the estimation of the capacity of the at least one electrochemical element (12), the estimation method being implemented by a computer (22) and comprising: - a step of obtaining: - values of the current and the capacity of the at least one electrochemical element (12), - values of the state of charge (SOC) of the at least one electrochemical element (12), the state of charge (SOC) values being obtained by using an evaluation technique having a deviation from the actual value of the state of charge (SOC) of said at least one electrochemical element (12), the deviation of the evaluation technique being strictly less than the measurement deviation to be determined, - a first step of detecting a first instant (tinit) during which the obtained value of the state of charge (SOC) is equal to a predefined value, - a step of triggering a counter of the quantity of charge accumulated by the at least one electrochemical element (12) at the first instant (tinit), - a second step of detecting a second instant (tf) during which the value obtained from the state of charge (SOC) is equal to the predefined value, and - a step of determining at least one contribution to the measurement deviation, each determined contribution depending on the value of the counter at the second instant (tf) and the time elapsed between the first instant (tinit) and the second instant (tf).

2. A determination method according to claim 1, wherein the determined contributions are the first contribution and the second contribution, the sum (IbiaiS) of the first contribution and the second contribution depending only on the value of the counter at the second instant (tf) and the time elapsed between the first instant (tinit) and the second instant (tf).

3. A determination method according to claim 1 and 2, wherein the sum (Ibiais) of the first contribution and the second contribution is equal to the opposite of the ratio of the value of the counter at the second instant (tf) and the time elapsed between the first instant (tinit) and the second instant (tf).

4. A determination method according to claim 2 and 3, wherein the method is carried out for a plurality of electrochemical elements (12) and in the determining step, the second contribution of an electrochemical element (12) is determined relative to the second lowest contribution of the plurality of electrochemical elements (12).

5. Determination method according to claim 4, in which the second contribution of the electrochemical element (12) is obtained by subtraction between the sum (Ibiais) of the first contribution and the second contribution determined for the electrochemical element considered and the sum (Ibiais) of the first contribution and the second contribution determined for the electrochemical element (12) having the second lowest contribution.

6. A determination method according to any one of claims 1 to 5, wherein a determined contribution is the third contribution (Qbiais), the third contribution (Qbiais) also depending on the value of the state of charge (SOC) at a third instant (tDoo), the third instant (tD0D) being the instant during which the difference between the state of charge value (SOC) obtained and the state of charge value (SOC) deduced from the value of the counter is the greatest in absolute value.

7. A determination method according to any one of claims 1 to 6, wherein a determined contribution is the third contribution (QbiaiS), the third contribution (QbiaiS) being given according to the following formula: bias । Where: • Q denotes the estimate of the capacity of the electrochemical element 12 affected by the capacity bias, • AS denotes the difference between the obtained SOC state of charge value and the SOC state of charge value deduced from the counter value at the third instant ^DOD' and • I denotes the actual value of the current.

8. A determination method according to any one of claims 1 to 7, wherein the value of the third contribution (Qbias) for the evaluation technique is less than or equal to 3Q / 100, Q denoting the value of the capacity of the electrochemical element (12).

9. A determination method according to any one of claims 1 to 8, wherein the at least one electrochemical element (12) comprises at least one cathodic active material selected from the following groups or mixtures thereof: i) a compound of formula LixFei yMyPO4where M is selected from the group consisting of B, Mg, Al, Si, Ca, Ti, V, Cr, Mn, Co, Ni, Cu, Zn, Y, Zr, Nb and Mo; and 0.8 <x<l,2 ; 0<y<0,6, ii) un composé de formule LiVPO4F.

10. Method for controlling at least one electrochemical element (12) of a battery (10), the control method comprising: - a step of implementing a method for determining at least one contribution to the measurement deviation between a measurement of the state of charge (SOC) of the at least one electrochemical element (12) and the actual value of the state of charge (SOC) of said at least one electrochemical element (12), the determination method being according to any one of claims 1 to 9, to obtain at least one determined contribution, and - a step of implementing a corrective action depending on the value of the at least one determined contribution.

11. Method for obtaining a state of health parameter of at least one electrochemical element (12) of a battery (10), the obtaining method comprising: - a step of implementing a method for determining at least one contribution to the measurement deviation between a measurement of the state of charge (SOC) of the at least one electrochemical element (12) and the actual value of the state of charge (SOC) of said at least one electrochemical element (12), the determining method being according to any one of claims 1 to 9 and making it possible to obtain at least the third contribution (Qbiais), - a step of estimating the capacity of the at least one electrochemical element (12), and - a step of deducing a state of health parameter of the at least one electrochemical element (12) using the estimated capacity.

12. A calculator (22) capable of determining the difference between a measurement of the state of charge (SOC) of at least one electrochemical element (12) of a battery (10) and the actual value of the state of charge (SOC) of said at least one electrochemical element (12), the measurement being carried out on the basis of a counter of the quantity of charge accumulated by the at least one electrochemical element (12), the difference taking into account at least one contribution chosen from the list consisting of a first contribution coming from a current sensor (18) providing current values of the at least one electrochemical element (12), a second contribution coming from the self-discharge of the at least one electrochemical element (12) and a third contribution (Qbiais) coming from errors in the estimation of the capacity of the at least one electrochemical element (12),the calculator (22) being capable of: - obtaining: - values of the current and the capacity of the at least one electrochemical element (12), - values of the state of charge (SOC) of the at least one electrochemical element (12), the state of charge (SOC) values being obtained by using an evaluation technique having a deviation from the actual value of the state of charge (SOC) of said at least one electrochemical element (12), the deviation of the evaluation technique being strictly less than the measurement deviation to be determined, - detecting a first instant (tinit) during which the obtained value of the state of charge (SOC) is equal to a predefined value, - triggering a counter of the quantity of charge accumulated by the at least one electrochemical element (12) at the first instant (tinit), - detecting a second instant (tf) during which the obtained value of the state of charge (SOC) is equal to the predefined value, and - determining at least one contribution of the measurement deviation, each determined contribution depending on the value of the counter at the second instant (tf) and the time elapsed between the first instant (tinit) and the second instant (tf).

13. Management system (14) of at least one electrochemical element (12) of a battery (10), the management system (14) comprising: - a voltage sensor (16) capable of measuring the voltage across the terminals of said at least one electrochemical element (12), - a current sensor (18) capable of measuring the current delivered by said at least one electrochemical element (12), - a temperature sensor (20) capable of measuring the temperature of said at least one electrochemical element (12), and - a computer (22) according to claim 12.

14. Battery (10) comprising: - at least one electrochemical element (12), and - a management system (14) according to claim 13.

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