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 battery cells, comprising the following steps: obtaining a voltage measurement (V) across the storage element and a current measurement (C) through the storage element; determining a time variation of the measured voltage; determining an acceptable range for said time variation from the measured voltage, the measured current, and an equivalent electrical model of the storage element; verifying that said time variation is within the acceptable range; and, when said time variation is not within the acceptable range, triggering a battery protection mode. 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. Previous technique

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

[0003] Rechargeable batteries contain flammable and reactive components that can react violently in the event of overheating, short circuit, overcharging, or physical damage. When a battery cell is damaged, it can release heat and potentially ignite surrounding materials, leading to 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 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 (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 preventive measures such as power cutoff in the event of overheating, overvoltage, or overcurrent, thus minimizing the risk of fire or explosion. Furthermore, the BMS optimizes 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. Description of the invention

[0006] The invention aims to provide a battery monitoring solution that can quickly detect any anomaly that may occur during operation of a battery and thus allow 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 battery cells, comprising the following steps: - obtaining a measurement of the voltage across the terminals of 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 for said temporal variation based on the measured voltage, the measured current and an equivalent electrical model of the storage element; - verification that the said temporal variation is within the range of acceptability; - when said temporal variation is not within the acceptable range, a battery protection mode is triggered.

[0008] Some preferred but not limiting aspects of this process are as follows: - the equivalent electrical model is a quasi-static model; - the quasi-static model consists of the series association of an equivalent capacitance and an equivalent resistance, the equivalent capacitance 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 bound TH[Uc Tbat) from a minimum equivalent capacity of the storage element and the determination of a lower bound TL( Un T^) from a maximum equivalent capacity of the storage element; - the upper limit is determined according to Req(Uc, T but) denotes the equivalent resistance as a function of the open-circuit voltage Uc of the storage element and the temperature Tl)at of the storage element, Imes denotes the measured current, Cmin( Uc) denotes the minimum equivalent capacitance for the open-circuit voltage Uc and £p an upper permissible error; - the lower limit is determined according TI ( II T \ — R (II T \ ' °ùCmax(Uc) designates. 1^) -Keq\Uc, I but) \ dt! + +en the maximum equivalent capacitance for the open-circuit voltage Uc, £n an error lower permissible and leq a maximum balancing current of the storage element; - the determination of the acceptability range includes the estimation of the open-circuit voltage Uc according to Vc-Umes-Req( < Uc>, T b(tt)*Jmes, where Ufnes denotes the measured voltage and where < Uc > denotes a moving average of the open-circuit voltage. Brief description of the drawings

[0009] Other aspects, objectives, advantages and features of the invention will become more apparent from the following detailed description of preferred embodiments thereof, given by way of non-limiting example, and made with reference to the accompanying drawings in which [Fig.1] is a diagram representing an example of an equivalent electrical model of the storage element that can be used within the scope of the invention.

[0010] DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

[0011] The invention relates to a method for monitoring an energy storage element consisting of one or more battery cells. The invention also relates to a controller for a battery monitoring system that includes a processor configured to implement this monitoring method. The monitoring system may be a BMS (Battery Management 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 various measured values ​​and is configured to process these measured values ​​in order to detect a possible anomaly in the storage element and, if necessary, trigger a battery protection mode. Triggering a protection mode may consist of issuing an alert (for example, in the case of a battery charger) or of interrupting the battery charging (for example, in the case of a BMS).

[0013] In general, the processor is capable of detecting a possible anomaly of the storage element by monitoring the variation of the voltage across the terminals of the storage element using the measured values ​​and by verifying that this variation conforms to 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 terminals of the storage element Ume^ a measurement of the current 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 dumes. The processor can, in particular, calculate an average value dt of this derivative over a time window, for example a one-second time window.

[0016] The processor is further configured to determine a time variation of the measured current Imes, for example in the form of a derivative with respect to time. 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. It can also calculate an average value of the measured current <Imes>.

[0017] The processor is further configured to determine an acceptability range of the temporal variation of the measured voltage from the measured voltage Umes, dt of the measured current 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 across 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) can take a bounded value between a minimum value and a maximum value so that the derivative of the equation of the voltage across the terminals of the storage element is bounded between a lower bound and an upper bound which define the range of acceptability.

[0020] Let F(Eq. Inie^ be a function based on the equivalent electrical model which relates The measured voltage Utnes at the equivalent elements Eq and the current, we then have dümes _ dFEg. lms). Eq being bounded between a minimum value Eq and a value dt ~ dt >nm maximum Eq^, is found to be between d^Eq^l^} and dF^Eq^ Ime^ in

[0021]

[0022] absence of storage element anomaly. In one possible realization, 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. The quasi-static model can be constituted by the series association of an equivalent capacitance Ceq(SOC) and an equivalent resistance Re^O(^ ​​'a equivalent capacitance varying according to the state of charge SOC of the storage element and the equivalent resistance varying according to the temperature Tbat of the storage element and the state of charge SOC of the storage element.

[0023] An estimate of the battery's open-circuit 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 coulomb counting, which involves calculating the cumulative number of coulombs stored in the battery at a given moment from the current measurement taken across the battery terminals.

[0024] As shown in Figure 1, Tba^ 'a can therefore be considered equivalent resistance function of open-circuit voltage U c and temperature Tbat and ^e / üc) 'a equivalent capacitance function of open-circuit voltage Uc.

[0025] In this case, the voltage measured across the storage element Umes corresponds to the sum of the open-circuit voltage Uc and the voltage generated by the equivalent resistance Req*lmes, i.e., = UC + Req, Tbat)*Imes-

[0026] From then on, dUmes dLc p ijj rp Imes C . dt - dt 1 balj dt - + 1 bat) dt

[0027] To determine the acceptability range, the processor can be configured to determine an upper bound TH)UcTbat) of the acceptability range from a minimum equivalent capacity of the storage element and to determine a lower bound of the acceptability range TL( Uc,Tbat') from a maximum equivalent capacity of the storage element.

[0028] The upper limit can thus be determined according to T TJ t TT T \ t tt T tithes \ (Imes) , where Uc) denotes the 1 {U c 1 bat ) - c J ) \ dt / + Cmjlt(Uc) + 8P equivalent capacity of the minimum storage element for the open-circuit voltage Uc and sp an upper permissible error.

[0029] The lower limit can, for its part, be determined according to TT (TT T \ — TT (TT T 1 \, where Uc) designates the bat ) "-eqx.'do bat) \ dl equivalent capacity of the maximum storage element for the open-circuit voltage Uc, 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 query a memory of the controller in which the values ​​Req(Uc, Tbat), Cmin(Vc) and Cmax(Uc) 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 charge as a function of the voltage of the storage element, thanks in particular to a set of measurements on battery samples.

[0032] The permissible errors eP and Sn 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 load is too low, for example less than 80% of a maximum state of load).

[0034] In the preceding equations, the values ​​Req( Uc TbatC Cmin( l / c) and Cmax( Uc) can be replaced by the values ​​Rei^SOC )' ^min(SOC') and Cmax{SOC} when the state of charge SOC is known. This reduces the error and thus allows for better monitoring of the storage element's evolution.

[0035] Temperature can also be considered as impacting the equivalent capacitance, in the same way that its impact on the equivalent resistance has been considered. We will then write Ceq(SOC, T^)

[0036] When the open-circuit voltage Uc is used rather than the state of charge SOC, the open-circuit voltage Uc can be estimated according to UC=Umes-Req( <uc>where <Uc> denotes A moving average of the open-circuit voltage. This moving average calculates the average of a set of previous open-circuit voltage estimates. It covers a time window typically ranging from 30 seconds to 10 minutes, depending on the battery type and the maximum permissible charging speed.

[0037] After determining the acceptability range, the processor is configured to verify that the time variation of the voltage across the storage element is within the acceptability range. The processor thus verifies that the following inequalities are indeed satisfied: TL ( U» ) < TH ( U„ T M '

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

[0039] In one possible embodiment, different acceptability ranges are determined using different levels of permissible errors sp, Sn. It is thus possible to have different levels of safety alerts (low level when dumes is not present in an acceptability range with low permissible error but dt is present within an acceptability range with the highest permissible error; higher level when not present within an acceptability range with the highest dt permissible error).

[0040] In another embodiment, each of the permissible errors sp, e" can be decomposed into several elements, typically in the form A ( ) + B( Vc.} + C( Vc, ) <lm)+ d(    rm)• où a est l'image of the inductance 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 B represents the measurement and sampling errors and approximation errors of the calculations.

[0041] It should be noted that a typical cycling of the storage element can be carried out to recognize its 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 detect an error in the event of an excessively rapid deviation of one or both of the parameters Cmax Cmin Req or in the event of a capacitance that has become too low or a resistance that has become too high (for example, due to faulty connections, rust or chemical alteration).

[0043] The following is 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 s (rr, where Cbat denotes the capacity of the storage element and Cceü the capacity of a single cell. It is then possible to take Cmax( U^) = 1.1 *Cbat and Cmin( Uhat) = 0.9 *Cbat ■ The equivalent resistance can be calculated in the same way: » z tt i *70 where Rceu denotes the resistance of a single cell. (JJ bat) = Kcell V 70 J 2

[0044] It should be noted that approximations at the storage element level can be distorted in the case of an unbalanced storage element. This imbalance can, however, be taken into account in the permissible errors εp and ε' by adding a variable dependent on the state of charge and the battery's health. This health status can be automatically taken into account by tracking, as previously discussed, the evolution over time of the various parameters.

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

Claims

Demands

1. A method for monitoring an energy storage element consisting of one or more battery cells in order to detect a possible anomaly, comprising the following steps: - obtaining a measurement of the voltage (Unies) across the terminals of the storage element and a measurement of the current (Imes) through the storage element; - determining a time variation of the measured voltage; - determining an acceptability range for said time variation from the measured voltage, the measured current and an equivalent electrical model of the storage element; - verifying that said time variation is within the acceptability range; - when said time variation is not within the acceptability range, triggering a battery protection mode consisting of triggering an alert or interrupting the battery charging.

2. A method according to claim 1, wherein the equivalent electrical model is a quasi-static model.

3. A method according to claim 2, wherein the quasi-static model is constituted by the series association of an equivalent capacitance (Ceq(Uc )) and an equivalent resistance ( Req{Uc, Tbat)\ 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. A method according to claim 3, wherein the determination of the acceptability range includes the determination of an upper bound TH (U&Tbat) from a minimum equivalent capacity of the storage element and the determination of a lower bound TL{Uc,Tbai) from a maximum equivalent capacity of the storage element.

5. The method according to claim 4, wherein: the upper limit is determined according

6.

7.

8. TH(U a T^) = + where Req( Uc, Tbat) denotes the equivalent resistance as a function of the open-circuit voltage Uc of the storage element and the temperature Tbat of the storage element, I„ws denotes the measured current, and denotes the equivalent capacitance minimum for the open-circuit voltage Uc and eP an upper permissible error; and - the lower limit is determined according TL( Uo Tu U, Tu) * ( ) + Cmax( Ue) denotes the maximum equivalent capacity for the open-circuit voltage Uc, £n a lower permissible error and leq a maximum balancing current of the storage element. Method according to claim 5, wherein the determination of the acceptability range includes the estimation of the open-circuit voltage Uc according to Uc - Umes-Req( <uc>, where U mes denotes the tension measured and where <vc>denotes a moving average of the open-circuit voltage. Controller of a battery monitoring system, comprising a processor configured to implement the method according to any one of claims 1 to 6. Product computer program comprising instructions which, when the program is executed by a computer, cause the computer to carry out the method according to any one of claims 1 to 6.< / vc> < / uc>

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