Method and system for monitoring a battery by tracking its voltage and its 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 (U mes ) at the terminals of the storage element and a measurement of the current (I mes ) passing through the storage element; - determining a variation over time of the measured voltage; - determining a range of acceptability of the variation over time from the measured voltage, the measured current and an equivalent electrical model of the storage element; - verifying that the variation over time is within the range of acceptability; - when the variation over time is not within the range of acceptability, triggering a protection mode of the battery.

Description

[0001]DESCRIPTION Method and system for monitoring a battery by tracking its voltage and current TECHNICAL FIELD The field of the invention is that of monitoring an electric battery in order to detect a potential anomaly. PRIOR ART A storage battery, or more commonly a battery, is a set of electric accumulators connected together so as to create an electric 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 to be released in the form of direct current, in a controlled manner. The batteries are generally rechargeable. Rechargeable batteries contain flammable and reactive components, which can react violently in the event of overheating, short circuit, overload or physical damage.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. It is therefore important to be able to monitor any anomalies that may occur in the operation of a battery, in order to prevent any risk of fire, or even more simply to ensure the availability and good condition of the battery. In this context, battery management systems or BMS play a crucial role in the safety and performance of batteries. A BMS continuously monitors each cell of 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. 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 to ensure the safe and efficient use of rechargeable batteries in various applications, from electric vehicles to electronic devices. DISCLOSURE OF THE INVENTION The objective of the invention is to provide a battery monitoring solution that can quickly detect an anomaly that may occur in the operation of a battery and thus enable effective protection of installations and users.To this end, the invention proposes a method for monitoring an energy storage element consisting of one or more cells of a battery in order to detect a possible anomaly, 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 battery protection mode consisting of triggering an alert or interrupting the charging of the battery.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 capacitance and an equivalent resistance, 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;- the determination of the acceptability range comprises the determination of an upper bound ^^(^^ , ^^^^) from a minimum equivalent capacity of the storage element and the determination of a lower bound ^^(^^ , ^^^^) from a maximum equivalent capacity of the storage element;- the upper bound is determined according to ^^(^^ , ^^^^) = ^^^(^^ , ^^^^) ∗. + where ^^^(^^ , ^^^^) denotes the equivalent resistance function of the no-load ^ ^of the storage element and the temperature ^ ^^^ of the storage element, ^^^^ denotes the measured current, ^^^^(^^) denotes the minimum equivalent capacity for the no-load voltage ^^ and ^^ an upper admissible error; - the lower terminal is determined according to ^^(^ , ^^^^) = ^^^(^^ , ^^^^) ∗ where ^^^^(^^) denotes the maximum equivalent capacity for the no-load voltage ^^, ^^ a lower permissible error and ^^^ a maximum balancing current of the storage element; - determining the acceptability range comprises estimating the no-load voltage^^ according to ^^ = ^^^^ − ^^^(< ^^ >, ^^^^) ∗ ^^^^ , where ^^^^ denotes the measured voltage and where < ^^ > denotes a running average of the no-load voltage. BRIEF DESCRIPTION OF THE DRAWINGS Other aspects, aims, advantages and characteristics of the invention will become more apparent from the following detailed description of preferred embodiments thereof, given by way of non-limiting example, and with reference to the accompanying drawings in which Figure 1 is a diagram showing an example of an equivalent electrical model of the storage element that can be used in the context of the invention.DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS 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. 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). 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. The processor is more particularly configured to obtain a measurement of the voltage at the terminals of the storage element ^. ^^^ , a measurement of the current flowing through the storage element ^^^^ as well as a measurement of the temperature of the storage element ^ ^^^(for example an average temperature of the different cells constituting the storage element). The processor is further configured to determine a temporal variation of the measured voltage ^ ^^^ , for example in the form of a derivative with respect to time ^^ ^^^ ^^. The processor can notably calculate an average value de cette derived over a time window, for example a one-second time window. The processor is further configured to determine a temporal variation of the ^^ measured current ^ , for example in the form of a ^^^ ^^^ e derivative with respect to time ^^ . The processor can notably calculate an average value 〈^^ ^^^^^〉 of this derivative over a time window, for example a one-second time window. It can also calculate an average value of the measured current < ^^^^ >. The processor is further configured to determine an acceptability range of ^^ the time variation of the measured voltage ^^^ ^^ from the measured voltage ^ ^^^ , of the measured current ^ ^^^and an equivalent electrical model of the storage element. 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 storage element as a function of the value of these equivalent elements and the current flowing through the storage element. 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 storage element is bounded between a lower bound and an upper bound which define the range of acceptability. Let ^(^^, ^^^^) be a function based on the equivalent electrical model which relates the measured voltage ^^^ ^^^ ^^^ to the equivalent elements ^^ and to the current ^^^^, we then have^^ = ^^(^^,^ ^^^ ) ^^. ^^ being bounded between a minimum value ^^^^^ and a maximum value^^(^^ ,^ ^) ^^is found between ^^^ ^^ ^^^ , ^^ ^^ of anomaly of the storage element. In a possible embodiment, the equivalent electrical model is a quasi-static model in which the equivalent elements are not fixed but are likely to vary according to 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 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. An estimate of the no-load voltage of the battery (i.e. the voltage across the terminals of 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 across the terminals of the battery the cumulative number of coulombs stored at a given time in the battery. As shown in Figure 1, we can therefore consider ^^^(^^ , ^^^^) the equivalent resistance as a function of the no-load voltage ^ ^ and temperature ^ ^^^ and ^ ^^ (^ ^ ) the equivalent capacity as a function of the open-circuit voltage ^ ^ . In this case, the voltage measured across the storage element ^ ^^^ corresponds to the sum of the open-circuit voltage ^ ^and the voltage generated by the equivalent resistance ^^^ ∗ ^^^^, or ^^^^ = ^^ + ^^^(^^ , ^^^^) ∗ ^^^^.From To determine the acceptability range, the processor may be configured to determine an upper bound ^^(^^ , ^^^^) of the acceptability range from a minimum equivalent capacity of the storage element and determine a lower bound of the acceptability range ^^(^^ , ^^^^) from a maximum equivalent capacity of the storage element. The upper bound may thus be determined according to ^^(^^ , ^^^^) = ^^^(^^ , ^^^^) ∗ denotes the equivalent capacity of the minimum storage element for the open-circuit voltage ^ ^ and ^ ^ an upper admissible error. The lower bound can be determined according to ^^(^^ , ^^^^) = denotes the equivalent capacity of the maximum storage element for the open-circuit voltage ^ ^ , ^ ^an admissible lower error and ^^^ a maximum balancing current of the storage element. To calculate these lower and upper limits, the processor can be configured to interrogate a memory of the controller in which the values ​​^^^(^^ , ^^^^), ^^^^(^^) and ^^^^(^^) are stored. The equivalent capacities of the minimum and maximum storage element at the no-load voltage ^^ 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, thanks in particular to a set of measurements on battery samples. The admissible errors ^ ^ and ^ ^ may be dependent on the storage element voltage. The maximum balancing current ^ ^^can be taken into account or not. 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). In the previous equations, the values ​​^^^(^^ , ^^^^), can be replaced by the values ​​^^^(^^^, ^^^^ ), ^^^^(^^^) and ^^^^(^^^) when the state of charge ^^^ is known. This makes it possible to reduce the error and therefore to better monitor the evolution of the storage element. We can also consider the temperature as impacting the equivalent capacity, in the same way that we considered its impact on the equivalent resistance. We will then write ^^^(^^^, ^^^^)When the no-load voltage ^^ is used rather than the state of charge ^^^, the no-load voltage ^^ can be estimated according to ^^ = ^^^^ − ^^^(< ^^ >, ^^^^) ∗ ^^^^ , 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 typically lasting between 30s and 10min depending on the type of battery and the maximum permissible charging speed.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 respected. Finally, the processor is configured to trigger a battery protection mode when said time variation is not within the acceptability range. In one possible embodiment, different acceptability ranges are determined using different permissible error levels ^ ^ , ^ ^ . It thus turns out ^^ possible to have different levels of security alert (low level when ^^^ is not present in a range of acceptability with low permissible error but is present in a range of acceptability with higher permissible error; higher level when ^^^^^ is not present in a range of acceptability with a higher permissible error). In another embodiment, each of the permissible errors ^ ^ , ^ ^ can be broken down into several elements, typically in the form + is the image of the inductivity of the equivalent circuit, ^ is the image of the approximation error of the equivalent resistance, ^ is the image of the approximation error of the equivalent capacitance and ^ represents the measurement and sampling errors and approximation errors of the calculations. 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). It is also possible to follow the evolution over time of these parameters. It is thus possible to report an error in the event of too rapid deviation of one and / or the other of the parameters ^ ^^^ ^ ^^^ ^ ^^or in case of capacity becoming too low or resistance becoming too high (for example due to faulty connections, rust or altered chemistry). 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 ^^ ^ ^ ^^^(^^^^) ≅ ^^^^^(^^ ) ∗ ^^, where ^ ^^^ denotes the capacity of the storage element and ^^^^^ the capacity of a unit cell. It is then possible to take ^^^^(^^^^) = 1.1 *^^^^ and ^^^^(^^^^) = 0.9 *^^^^ . The equivalent resistance can be calculated in the same way: ^ (^^^^) ≅ ^^^^^ where ^ ^^^^ denotes the of a unit cell. It should be noted that 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 ^ ^and ^ ^ , 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. 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, lead the latter to implement the method previously described.

Claims

CLAIMS1. Method for monitoring an energy storage element consisting of one or more cells of a battery in order to detect a possible anomaly, 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 battery protection mode consisting of triggering an alert or interrupting the charging of the battery.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 consists of the series association of an equivalent capacitance. )) and an equivalent resistance (^^^(^^ , ^^^^)), the equivalent capacity 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 ^^(^^ , ^^^^) from a minimum equivalent capacity of the storage element and determining a lower bound ^^(^^ , ^^^^) from a maximum equivalent capacity of the storage element.

5. The method of claim 4, wherein:- the upper bound is determined according to ^^(^^ , ^^^^) = + 〈^ ^^^ 〉 ^ ^^^ (^ ^ )+ ^^, where ^^^(^^ , ^^^^) denotes the equivalent resistance as a function of the open-circuit voltage ^ ^ of the storage element and the temperature ^ ^^^of the storage element, ^^^^ denotes the measured current, ^^^^(^^) denotes the minimum equivalent capacity for the no-load voltage ^ ^ and ^ ^ an upper admissible error; and- the lower bound is determined according to ^^(^ , ^^^^) = ^^^(^^ , ^^^^) ∗ where ^^^^(^^) denotes the maximum equivalent capacity for no-load voltage ^^, ^^ a lower permissible error and ^^^ a maximum balancing current of the storage element.

6. Method according to claim 5, wherein the determination of the acceptability range comprises estimating the no-load voltage ^^ according to ^^ = ^^^^ −^^^(< ^^ >, ^^^^) ∗ ^^^^, where ^^^^ denotes the measured voltage and where < ^^ > denotes a running average of the no-load 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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