Method and system for monitoring a battery by tracking its voltage and current

Abstract

The invention relates to a method for monitoring an energy storage element consisting of one or more cells of a battery, comprising the following steps: obtaining a measurement of the voltage () at the terminals of the storage element and a measurement of the current () flowing through the storage element; determining a temporal variation of the measured voltage; determining a range of acceptability of said temporal variation from the measured voltage, the measured current and an equivalent electrical model of the storage element; verifying that said temporal variation is within the range of acceptability; when said temporal variation is not within the range of acceptability, triggering a protection mode of the battery. Figure for abstract: Figure 1

Description

Title of the invention: Method and system for monitoring a battery by tracking its voltage and current Technical field

[0001] The field of the invention is that of monitoring an electric battery in order to detect a potential anomaly. Prior art

[0002] A storage battery, or more commonly a battery, is a set of electrical accumulators connected together to create an electrical generator of desired voltage and capacity. These accumulators are commonly referred to as cells. The storage battery allows electrical energy to be stored in chemical form and released in the form of direct current, in a controlled manner. Batteries are generally rechargeable.

[0003] Rechargeable batteries contain flammable and reactive components, which can react violently if overheated, short-circuited, overcharged, or physically damaged. When a battery cell is damaged, it can release heat and potentially ignite surrounding materials, resulting in a fire that is difficult to control and can cause property damage and endanger lives.

[0004] It is therefore necessary to be able to monitor any anomaly that may occur in the operation of a battery, in order to be able to prevent any risk of fire, or even more simply to guarantee the availability and good condition of the battery.

[0005] In this context, battery management systems, or BMS, play a crucial role in battery safety and performance. A BMS continuously monitors each cell in a battery, controls incoming and outgoing currents, balances charges, and reacts to potential anomalies. It can trigger preventative measures such as shutting off power in the event of overheating, overvoltage, or overcurrent, thereby minimizing the risk of fire or explosion. In addition, the BMS helps optimize battery efficiency and lifespan by ensuring that each cell operates within predefined safety limits. In short, BMSs are essential for ensuring the safe and efficient use of rechargeable batteries in various applications, from electric vehicles to electronic devices. Statement of the invention

[0006] The invention aims to propose a solution for monitoring a battery which can quickly detect an anomaly which may occur in the operation. of a battery and thus enable effective protection of installations and users.

[0007] To this end, the invention proposes a method for monitoring an energy storage element consisting of one or more cells of a battery, comprising the following steps: - obtaining a measurement of the voltage across the storage element and a measurement of the current flowing through the storage element; - determination of a temporal variation of the measured voltage; - determination of a range of acceptability of said temporal variation at from the measured voltage, the measured current and an equivalent electrical model of the storage element; - verification that said temporal variation is within the range of acceptability; - when said temporal variation is not within the acceptable range, triggering of a battery protection mode.

[0008] Some preferred but non-limiting aspects of this method are as follows: - the equivalent electrical model is a quasi-static model; - the quasi-static model is constituted by the series association of an equivalent capacity and an equivalent resistance, the equivalent capacity varying according to the state of charge of the storage element and the equivalent resistance varying according to the temperature of the storage element and the state of charge of the storage element; - the determination of the acceptability range includes the determination of an upper limit TH(U„ Th t) from a minimum equivalent capacity of the storage element and the determination of a lower limit TL(Tbat) from a maximum equivalent capacity of the storage element; - the upper limit is determined according to TH(U„Tlx„) = Rai(UaTb,„)*(^) Req( U& Tbat ) denotes the equivalent resistance as a function of the no-load voltage Uc of the storage element and the temperature of the storage element, Imes denotes the measured current, Cmin{ U denotes the minimum equivalent capacitance for the no-load voltage Uc and an upper permissible error; - the lower limit is determined according to TL( U„ T= R„,( Ub where V,) denotes the maximum equivalent capacity for the no-load voltage Uc, a lower permissible error and leq a maximum balancing current of the storage element; - the determination of the acceptability range includes the estimation of the open-circuit voltage U c according to Uc = Umes-Req( < Uc >, ThaT) *Imes, where Umex denotes the measured voltage and where < Uc > denotes a running average of the open-circuit voltage. Brief description of the drawings

[0009] Other aspects, aims, advantages and characteristics of the invention will appear better on reading the following detailed description of preferred embodiments thereof, given by way of non-limiting example, and made with reference to the appended drawings in which [Fig.l] is a diagram representing an example of an equivalent electrical model of the storage element which can be used within the framework of the invention.

[0010] DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS

[0011] The invention relates to a method for monitoring an energy storage element consisting of one or more cells of a battery. The invention also relates to a controller of a battery monitoring system which comprises a processor configured to implement this monitoring method. The monitoring system may be a BMS system. Alternatively, the monitoring system may be integrated within a battery charger, such as an electric vehicle charger.

[0012] According to the invention, the processor is capable of receiving different measured values ​​and is configured to process these measured values ​​in order to detect a possible anomaly of the storage element and to trigger, if necessary, a battery protection mode. Triggering a protection mode may consist of triggering an alert (for example in the case of a battery charger) or consist of interrupting the charging of the battery (for example in the case of a BMS).

[0013] Generally speaking, the processor is able to detect a possible anomaly of the storage element by monitoring the variation of the voltage at the terminals of the storage element using the measured values ​​and by verifying that this variation is consistent with an expected behavior derived from an equivalent electrical model of the storage element.

[0014] The processor is more particularly configured to obtain a measurement of the voltage across the storage element Umes, a measurement of the current flowing through the storage element Imes as well as a measurement of the temperature of the storage element Tbat (for example an average temperature of the different cells constituting the storage element).

[0015] The processor is further configured to determine a temporal variation of the measured voltage Umes, for example in the form of a derivative with respect to time dU^. The processor can in particular calculate an average value / \ of this dt \ dt / derived over a time window, for example a one-second time window.

[0016] The processor is further configured to determine a temporal variation of the measured current Imes, for example in the form of a derivative with respect to time dI^. The processor can in particular calculate an average value dl^ of this derivative over a time window, for example a time window of one second. It can also calculate an average value of the measured current < Imes >.

[0017] The processor is further configured to determine a range of acceptability of the temporal variation of the measured voltage from the measured voltage Umex, dt of the measured current Imes and an equivalent electrical model of the storage element.

[0018] The equivalent electrical model makes it possible to represent the behavior of the storage element by a network of equivalent elements. In particular, it makes it possible to describe by an equation the voltage at the terminals of the storage element as a function of the value of these equivalent elements and the current flowing through the storage element.

[0019] The equivalent element(s) may take a value bounded between a minimum value and a maximum value so that the derivative of the equation of the voltage across the storage element is bounded between a lower bound and an upper bound which define the range of acceptability.

[0020] Let F(Eq, Im(C) be a function based on the equivalent electrical model which links the measured voltage Umes to the equivalent elements Eq and to the current we then have dUmes _ dF(Eq <lmO ' Eq étant borné entre une valeur minimale Eq . et une valeur dt “ dt m“l maximum Eq dullies is found between dF^Eq^ imex} and dEfa^ 1IM^ in dt 'dt dt absence of anomaly of the storage element.

[0021] In one possible embodiment, the equivalent electrical model is a quasi-static model in which the equivalent elements are not fixed but are likely to vary depending on the state of charge of the storage element, its temperature, the direction of the electrical stress (charge or discharge) and its state of health.

[0022] The quasi-static model can be constituted by the series association of an equivalent capacitance Ceq{ SOC) and an equivalent resistance Ree^SOC, the equivalent capacitance varying as a function of the state of charge SOC of the storage element and the equivalent resistance varying as a function of the temperature Tha{ of the storage element and the state of charge SOC of the storage element.

[0023] An estimate of the battery's no-load voltage (i.e. the voltage across the equivalent capacity) indicates its state of charge. It should be noted that the state of charge can also be determined by other methods such as coulombic counting, consisting of deducing from the current measurement made at the terminals of the battery the cumulative number of coulombs stored at a given time in the battery.

[0024] As shown in Figure 1, we can therefore consider R^U c. the re equivalent resistance as a function of the open-circuit voltage Uc and the temperature T bat and Ce^U^ the equivalent capacitance as a function of the open-circuit voltage Uc.

[0025] In this case, the voltage measured at the terminals of the storage element Umes corresponds to the sum of the no-load voltage Uc and the voltage generated by the equivalent resistance Refîmes,^umes= Uc + ReiUc T

[0026] From then on, dVmes _ düc _ \*dlmes _ lmt!S „ ( T j j- \^dlmes. dt ” dt 1 bat) dt “ C^Uc) + O 1 bat) dt

[0027] To determine the acceptability range, the processor may be configured to determine an upper bound TH(UC, Tbaf) of the acceptability range from a minimum equivalent capacity of the storage element and determine a lower bound of the acceptability range TL(U„ Tbat) from a maximum equivalent capacity of the storage element.

[0028] The upper limit can thus be determined according to ™( U„ T,m) = U„ Tu)'{fy ) + V where C^,(Ur) the equivalent capacity of the minimum storage element for the open-circuit voltage Uc and £p an upper admissible error.

[0029] The lower limit can be determined according to TL(U„ T») = Red U„ Tha + e,; where G»(U„) denotes the maximum equivalent storage element capacity for the open-circuit voltage Uc, £r, a lower permissible error and leq a maximum balancing current of the storage element.

[0030] To calculate these lower and upper bounds, the processor can be configured to interrogate a memory of the controller in which the values ​​Req(U„ T, CmiÀUc) ^Cmax{U^ are stored.

[0031] The equivalent capacities of the minimum and maximum storage element at the open-circuit voltage Uc may have been determined by incremental capacity analysis, namely by analysis of the derivative dQ / dV of the quantity of charges as a function of the voltage of the storage element, in particular thanks to a set of measurements on battery samples.

[0032] The admissible errors sp and £" may be dependent on the voltage of the storage element.

[0033] The maximum balancing current leq may or may not be taken into account. In particular, it is not taken into account when data relating to the state of balancing is not available or when this balancing is not implemented (for example because the state of charge is too low, for example less than 80% of a maximum state of charge).

[0034] In the preceding equations, the values ​​U„ T^t), Cmin( Uc) and Cma^ Ue) can be replaced by the values ​​Re(^SOC, That ), Cmin(SOC) and Cmax(SOC) when the state of charge SOC is known. This makes it possible to reduce the error and therefore to better monitor the evolution of the storage element.

[0035] We can also consider the temperature as impacting the equivalent capacitance, in the same way that we considered its impact on the equivalent resistance. We will then write Cecj(SOC, That)

[0036] When the no-load voltage Uc is used rather than the state of charge SOC, the no-load voltage Uc can be estimated according to Uc = U mes - Req{ < Uc>, That} where denotes a running average of the no-load voltage. This running average is used to average a set of previous estimates of the no-load voltage. It covers a time window whose duration is typically between 30s and 10min depending on the type of battery and the maximum permissible charging speed.

[0037] After determining the acceptability range, the processor is configured to verify that the temporal variation of the voltage across the storage element is within the acceptability range. The processor thus verifies that the following inequalities are respected: TL(UT{ S <th(u t} ^)-

[0038] Finally, the processor is configured to trigger a battery protection mode when said temporal variation is not within the acceptability range.

[0039] In one possible embodiment, different acceptability ranges are determined using different permissible error levels £p, en. It is thus possible to have different security alert levels (low level when dU^ is not present in a low permissible error acceptability range but dt is present in a range of acceptability with higher admissible error; higher level when is not present in a range of acceptability with higher dt permissible error).

[0040] In another embodiment, each of the admissible errors eP, can be decomposed into several elements, typically in the form 4^») +B(Uc + the image of the inductivity of the equivalent circuit, B is the image of the approximation error of the equivalent resistance, C is the image of the approximation error of the equivalent capacitance and D represents the measurement errors and sampling and approximation of calculations.

[0041] It should be noted that a typical cycling of the storage element can be carried out to recognize the different parameters (capacitance, inductance and resistance).

[0042] It is also possible to monitor the evolution of these parameters over time. It is thus possible to report an error in the event of too rapid deviation of one and / or the other of the CmaxCminReq parameters or in the event of capacity becoming too low or resistance becoming too high (for example due to faulty connections, rust or alteration of the chemistry).

[0043] We consider in the following an example of possible values ​​for a storage element composed of 70 blocks of two cells in parallel connected in series. This storage element has a capacity qj = C j* 2, where Cbat denotes the capacity of the storage element and Ccell the capacity of a unit cell. It is then possible to take Ubat) = 1.1 *Cbat and Cmin(Ubat) = 0.9 *Cbat. The equivalent resistance can be calculated in the same way: ) = R.- / / (¾) °where Rcel1 denotes the resistance of a unit cell.

[0044] It should be noted that the approximations at the scale of the storage element can be distorted in the case of an unbalanced storage element. This imbalance can however be taken into account in the admissible errors sp and sn, by adding a variable dependent on the state of charge and the state of health of the battery. This state of health can be automatically taken into account by following, as previously discussed, the evolution over time of the different parameters.

[0045] The invention is not limited to the processor and the method previously described, but also extends to a computer program product comprising instructions which, when the program is executed by a computer, cause the latter to implement the method previously described.

Claims

Claims

1. Method for monitoring an energy storage element consisting of one or more cells of a battery, comprising the following steps: - obtaining a measurement of the voltage (UfWS) at the terminals of the storage element and a measurement of the current (Imes) flowing through the storage element; - determining a temporal variation of the measured voltage; - determining a range of acceptability of said temporal variation from the measured voltage, the measured current and an equivalent electrical model of the storage element; - verifying that said temporal variation is within the range of acceptability; - when said temporal variation is not within the range of acceptability, triggering a battery protection mode.

2. The method of claim 1, wherein the equivalent electrical model is a quasi-static model.

3. The method of claim 2, wherein the quasi-static model is constituted by the series association of an equivalent capacitance ( C^( Uc ) ) and an equivalent resistance (Req( Uc That ) ), the equivalent capacitance varying as a function of the state of charge of the storage element and the equivalent resistance varying as a function of the temperature of the storage element and the state of charge of the storage element.

4. The method of claim 3, wherein determining the acceptability range comprises determining an upper bound TH(Uc, T} from a minimum equivalent capacity of the storage element and determining a lower bound TL(Tbat) from a maximum equivalent capacity of the storage element.

5. Method according to claim 4, in which: - the upper limit is determined according to TH (U„ r +v cJ where Req( U„ Tbat] denotes the equivalent resistance as a function of the open-circuit voltage Ue of the storage element and the temperature That of the storage element, lmes denotes the measured current, Cmil( Uc) denotes the minimum equivalent capacitance for the open-circuit voltage Uc and £p an upper permissible error; and - the lower limit is determined according to TT t TT T \ _ » ( TT 'T > * / \ । „ , 1 L ( Uv 1 ba{ ) - Keq [ U 1 bal J where Cmax( Uc) denotes the maximum equivalent capacitance for the open-circuit voltage Uc, £n an upper permissible error and leq a maximum balancing current of the storage element.

6. The method of claim 5, wherein determining the acceptability range comprises estimating the open-circuit voltage Uc according to Uc = U!nes-Req{ < Uc >, That) *1 mes, where denotes the measured voltage and where < Uc > denotes a running average of the open-circuit voltage.

7. Controller of a battery monitoring system, comprising a processor configured to implement the method according to one of claims 1 to 6.

8. Computer program product comprising instructions which, when the program is executed by a computer, cause the latter to implement the method according to one of claims 1 to 6.

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