Method for estimating the state of health of an electric or hybrid vehicle battery - Patents.com

Abstract

The present invention provides a method for estimating the state of health of an electric or hybrid vehicle battery, which may be performed while the vehicle is running, comprising: (a) a full charge step; (b) a first relaxation step; and (c) a state of charge SOC≦SOC performed for k vehicle driving cycles. target and discharging the battery to a capacity Q for each of those vehicle driving cycles. n (d) a second relaxation step at the end of cycle k, during which the state of charge SOC is determined; and (e) a function of the open circuit voltage (OCV). OCV (f) determining the SOC. OCV From the initial discharge capacity Q of a new battery, i (g) determining from the total capacity discharged by the battery during step (c), and Q i and estimating a state of health SOH of the battery from the

Description

[Technical field]

[0001] The present invention relates to a method for estimating the state of health of a battery, in particular a battery intended to power an electric or hybrid motor vehicle. [Background technology]

[0002] Determining the state of health, or aging, of a battery is an essential criterion for characterizing the condition of the battery in order to optimize the energy discharge / charge as well as the lifetime of the battery accumulator.

[0003] The state of health, or SOH, of a battery may be defined by the ratio of the capacity of the battery to store energy at a moment t to the nominal capacity of the battery to store energy (i.e. the capacity of a new battery before its use). The SOH is therefore an indicator of the state of health of a battery that takes into account the level of degradation of the autonomy of the battery, in particular due to the life of the battery and the conditions of its use.

[0004] Knowing the state of health of batteries, and especially of vehicle traction batteries, is important for technical, economic and legal reasons. Indeed, the state of health of a battery must be known precisely in order to avoid the risk of premature failure or unexpected deterioration of the performance capabilities of the system powered by said battery. In particular, an electronic system for managing and controlling the various parameters of a battery, called a BMS ("battery management system"), takes into account, for example, the estimated SOH in order to calculate the maximum available power and also to estimate the state of charge, or SOC, of ​​the battery. Moreover, the economic value of a battery is linked to the SOH of the battery, which allows the remaining useful life of the battery to be estimated. The economic value of an electric or hybrid vehicle is therefore also linked to the SOH of its traction battery. Finally, the regulations for electric and hybrid vehicles are changing and there are plans to stipulate that the state of health of the traction battery estimated by the BMS is determined with an accuracy of the order of 5%.

[0005] Currently, the state of charge of a traction battery is estimated by the BMS on the basis of physical or empirical models. Some models use electrochemical properties and / or performance capabilities that can be measured when the battery is used. This is then called an "online" estimation of the SOH. Thus, for example, document CN113296010 describes a method for the online assessment of the state of health of a battery based on the analysis of the differential voltage, which involves establishing a curve representing the voltage variation as a function of the capacity variation under given discharge conditions. The method described then establishes a model in which the slope of the tangent to this curve is correlated with the SOH. This model is used to estimate the SOH of a battery discharged under the same conditions as those used to establish the curve.

[0006] However, the accuracy of the SOH estimation may vary depending on the type of model and the quality of its calibration. For example, an empirical model of battery degradation may allow the SOH to be estimated with good accuracy up to a given SOH, for example 70% SOH. Beyond this, the estimation error may increase, as the degradation becomes more difficult to model.

[0007] The SOH of a battery can also be accurately determined by directly measuring the available capacity of the battery, however, this type of measurement requires removing the battery from the vehicle, which can prove difficult and expensive.

[0008] Thus, a need remains to reliably and accurately estimate the SOH of a battery, particularly online, and especially while the vehicle is moving, and without disturbing the operation of the vehicle. Summary of the Invention

[0009] To this end, the present invention relates to a method for estimating the state of health of a battery of an electric or hybrid vehicle, comprising: (a) Battery maximum state of charge (SOC) max charging the battery until (b) a first relaxation step, during which the battery is not used for a first duration; and (c) The battery is in a non-zero target state of charge (SOC) target and discharging the battery until it reaches a state of charge that is less than or equal to: n Discharging the battery, wherein: (d) a second relaxation step at the end of driving cycle k, during which the battery is not used for a second duration; (e) Battery state of charge SOC as a function of open circuit voltage when the battery is not in use. OCV determining (f) Initial discharge capacity Q of the battery in a new state i based on the state of charge determined in step (e) and a correlation previously established for the battery in a new state, and correlating the initial discharge capacity with the state of charge of the battery; (g) estimating a state of health (SOH) of the battery based on the total capacity discharged by the battery during the discharging step (c) and the initial discharge capacity determined in step (f); The present invention proposes a method including:

[0010] The method according to the invention allows for an accurate estimation of the vehicle's state of health without the need to remove the battery from the vehicle and without the driver having to modify how their vehicle is driven.

[0011] The method according to the invention may further comprise one or more of the following features. During the estimation step (g), the state of health SOH of the battery may be estimated using the following formula: TIFF2025507326000002.tif9170Here, Q n represents the capacity discharged by the battery during driving cycle n, where n is a non-zero integer ranging from 1 to k, and Q i represents the initial discharge capacity, - between the first relaxation step (b) and the discharge step (c), a checking step may be provided which involves checking that the state of charge of the battery in the relaxed state has reached a maximum state of charge; - during the discharging step (c), for each driving cycle, the capacity discharged by the battery can take into account the charge capacity received by the battery, - during the discharging step (c), the capacity discharged by the battery may be determined (i) by coulomb-counting the ampere-hours drawn from the battery, or (ii) by coulomb-counting the ampere-hours drawn from the battery and the ampere-hours supplied to the battery, and by subtracting the ampere-hours supplied to the battery from the ampere-hours drawn from the battery; - For each driving cycle n of the discharge step (c), the state of charge SOC of the battery n The value of the state of charge SOC can be estimated (i) by measuring the battery voltage while driving or (ii) by coulomb counting. n The value of the target state of charge value SOC target Compared with SOC n SOC target step (c) is considered complete when The correlation used during step (f) is set for a defined temperature range, so that during each driving cycle of the discharge step (c) (i) the battery can be maintained at a temperature within the defined temperature range, or (ii) the correction factor is a function of the capacity Q discharged by the battery as a function of the temperature of the battery. n can be applied to.

[0012] A further object of the invention is a computer program comprising instructions, which, when said instructions are executed by one or more processors, are for carrying out the steps of the estimation method according to the invention.

[0013] A further object of the invention is a computer readable medium storing the computer program of the invention.

[0014] The term "computer-readable medium" is understood to mean any memory, any storage device, any storage mechanism and any other storage and signaling mechanism, including interfaces and devices such as network interface cards and buffer memories therein, as well as any communication devices and any received and transmitted signals, and any other current and scalable technologies with which a computerized system can interpret, receive and / or transmit. This concept includes not only computer-readable media such as hard disks connected to a central unit and on which stored programs are directly executed, but also computer-readable media such as CD-ROMs that store programs that will be executed after being installed on the hard disk. Programs in this case include not only programs that can be executed directly, but also programs in source format, compressed programs and encrypted programs.

[0015] The estimation method according to the invention can in particular be executed by the inventive management system described below.

[0016] An object of the present invention is therefore also a system for managing a battery configured to estimate the state of charge of the battery by carrying out the steps of the estimation method according to the present invention.

[0017] Finally, an object of the invention is a motor vehicle equipped with a traction battery comprising a battery management system according to the invention. [Brief description of the drawings]

[0018] [Figure 1] 2 is a flow chart of an estimation method according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] The present invention is based on estimating the state of health SOH of a battery based on its capacity.

[0020] The first step (a) is to fully charge the battery, i.e., to ensure that the battery is within its SOC max This is the step of charging the battery until it reaches its maximum state of charge, denoted as maximum charge.

[0021] During this charging step (a), the state of charge of the battery can thus be monitored. It is therefore possible to (i) charge the battery, (ii) monitor the state of charge of the battery during this charging step, and (iii) continue charging as long as this state of charge does not reach the maximum state of charge. During this monitoring, it is possible to determine a value for the state of charge, for example based on measuring the voltage of the battery, and to compare this value with the value of the maximum state of charge.

[0022] For example, it is possible to proceed as follows: (i) The battery is charging, (ii) the value of the voltage at the terminals of the battery is measured; (iii) comparing the measured voltage value with a threshold voltage value corresponding to a maximum state of charge of the battery; (iv) If the value of the measured voltage reaches said threshold voltage value, charging of the battery is stopped, the battery is considered to be in a maximum state of charge and charging is stopped, otherwise charging of the battery is continued. The repetition frequency can be determined by a person skilled in the art depending on the type of battery. In this case, the value of the voltage measured at the terminals of the battery corresponds to the open circuit voltage, with the vehicle stationary. The threshold voltage value and the corresponding maximum state of charge can be determined by a person skilled in the art depending on the type of battery based on a curve of the state of charge as a function of the open circuit voltage. These threshold voltage and maximum state of charge values ​​can be stored in the management system, for example in the form of a map or a curve.

[0023] This charging step (a) is followed by a first relaxation step (b) during which the battery is not used for a first duration t_relax_1. This rest period ensures in particular a temperature stabilization of the battery at the completion of charging and thus improves the accuracy of estimating its state of charge. This first duration of the relaxation step can be predetermined by a person skilled in the art. The first duration is, for example, from 15 minutes to 6 hours, typically from 30 minutes to 1 hour.

[0024] In order to improve the accuracy of determining the state of charge, the method according to the invention comprises determining, after the first relaxation step (b) and before the discharge step (c), that the state of charge of the battery in the relaxed state is equal to or less than the maximum state of charge SOC max The method may include a step of checking that the state of charge of the battery in the relaxed state has reached a maximum state of charge SOC. max If so, the method proceeds to step (c), otherwise the method may be interrupted or steps (a) and (b) may be repeated until a checking step confirms that the battery in the relaxed state has reached the maximum state of charge.

[0025] During this inspection step, e.g. (i) The state of charge (SOC) of the battery in the relaxed state, for example by measuring the open circuit voltage at the terminals of the battery. relax Determine the value of (ii) The state of charge (SOC) of the battery in the relaxed state relax The value of the maximum state of charge SOC max Compared with the value of (iii) SOC relax The value of SOC max If so, determine that charging is complete and proceed to step (c); otherwise, repeat steps (a) and (b). It is possible.

[0026] It is also possible to proceed as follows: (i) measuring the value of the voltage at the terminals of the battery in a relaxed state; (ii) comparing the measured voltage value with a threshold voltage value corresponding to a maximum state of charge of the battery; (iii) if the measured voltage value is equal to the threshold voltage value, determine that charging is complete and proceed to step (c), otherwise repeat steps (a) and (b).

[0027] The driver then uses the vehicle as normal during a discharging step (c), which is performed until the battery reaches the target state of charge SOC target The discharge lasts until a state of charge equal to or less than 0 is reached, which may occur over one or more driving cycles. Note that when this discharging step (c) is performed over several driving cycles, the battery is not recharged. In other words, this step is performed without charging the battery between two consecutive driving cycles.

[0028] This target state of charge SOC target is a non-zero state of charge, which is generally greater than the minimum state of charge required for the vehicle to operate during a driving cycle. This target state of charge SOC target For example, the maximum state of charge SOC max It can handle a charge state of 10 to 15%.

[0029] Step (c) determines whether the battery is at this target state of charge SOC target This is carried out until a state of charge smaller than or equal to is reached. For this purpose, it is possible, for example, to monitor the value of the state of charge.

[0030] For example, it is possible to proceed as follows: for each driving cycle of the discharge step: - State of charge SOC n The value of is estimated by (i) measuring the battery voltage while driving, or (ii) by coulomb counting, and then - State of charge SOC n The value of is the target state of charge value SOC target Compared to, - Step c) is the SOC n SOC target It is considered complete when it is less than or equal to

[0031] State of charge SOC by measuring the battery voltage n When estimating the value of , the measured voltage does not correspond to the open circuit voltage at the terminals of the battery. In that case, it is necessary to determine the open circuit voltage based on the measured voltage, for example by Kalman filtering type modeling, and then to calculate the state of charge SOC based on the open circuit voltage thus determined. n It is possible to estimate

[0032] During this step (c), for each driving cycle n (where n is a non-zero integer), the capacity Q discharged by the battery is n is determined, which may take into account, in particular, the charge capacity received by the battery, for example during braking.

[0033] This discharged capacity Q n may be determined, for example, (i) by coulomb-counting the ampere-hours drawn from the battery, or (ii) by coulomb-counting the ampere-hours drawn from the battery and the ampere-hours supplied to the battery and by subtracting the ampere-hours supplied to the battery from the ampere-hours drawn from the battery.

[0034] Therefore, this discharged capacitance Q n can be written as: Q n =Ah disch-running n -Ah ch-running n (Formula 2) Where: Ah disch-running nis the capacity in ampere-hours discharged during driving cycle n and is written as: TIFF2025507326000003.tif8170Where I is the current drawn from the battery in amperes and t is time, Ah ch-running n is the capacity in ampere-hours charged during driving cycle n and is written as: TIFF2025507326000004.tif8170Where I is the current flowing in the battery in amperes and t is time.

[0035] In particular, for each driving cycle, the estimated state of charge SOC n and the discharged capacity Q n The device may be arranged to store values ​​of

[0036] Upon completion of step (c), i.e. at the end of the last driving cycle, denoted k, a second relaxation step (d) is performed during which the battery is not used for a second duration t_relax_2. This rest period ensures that the open circuit voltage of the battery returns to an equilibrium state. The longer this rest period, the closer the measurement of the open circuit voltage is to reality. The duration of this second relaxation step can be predetermined by a person skilled in the art. Its duration is, for example, from 15 minutes to 6 hours, typically from 30 minutes to 1 hour.

[0037] Then, during a determining step (e), the state of charge SOC of the battery as a function of the open circuit voltage while the battery is not in use. OCV is determined.

[0038] Upon completion of the discharge step, the estimation of the SOC may be associated with a rather large error due to the increase in the internal resistance of the battery resulting from the aging of the battery. When the battery is fully discharged (0% SOC), an accurate estimate of the SOC can be obtained. This solution would involve performing the discharge step until the vehicle is no longer able to run, which is not practical for the driver. The second relaxation step allows the SOC to be accurately estimated without the need to reach a minimum state of charge at which the vehicle can no longer run. In fact, based on the measurement of the open circuit voltage (OCV) (SOC OCV Estimating the SOC (denoted as SOC) is not affected by the increase in the battery's internal resistance due to battery aging.

[0039] Then, the initial discharge capacity Q of the battery in a new state i the state of charge SOC determined in step (e) OCV and a correlation previously established for the battery in a new state, and it is possible to correlate the initial discharge capacity with the state of charge of the battery (f).

[0040] Therefore, this initial discharge capacity Q i is the maximum state of charge and the state of charge SOC determined in step (e). OCV corresponds to the capacity that would have been discharged by the battery in its new state during the discharging step (c).

[0041] It is then possible to estimate (g) the state of health SOH of the battery based on the total capacity discharged by the battery during the discharging step (c) and the initial discharge capacity determined in step (f).

[0042] In particular, the battery state of health SOH may be estimated by the above equation, Equation 1.

[0043] The capacity measurement depends on the temperature of the battery. Also, to get a more accurate estimate of the SOH, we measure the capacity Q when the battery is in the same temperature range. n and Q i It is therefore preferred that, when carrying out the method according to the invention, when the correlation used in step (f) has been established for a defined temperature range, during each driving cycle n of the discharging step (c) (i) the battery is maintained at a temperature within this defined temperature range, or (ii) a correction factor, which is a function of the temperature of the battery, is determined to be a function of the capacity discharged by the battery Q n applies to.

[0044] In case (i), the temperature of the battery may be maintained in this temperature range by appropriately controlling a system for cooling / heating the battery, in case (ii), the temperature of the battery may be measured by a probe and a model may be used that expresses the correction factor as a function of temperature, the model being empirically or otherwise pre-established.

[0045] The estimation method according to the invention is executed by a management system. This management system generally comprises one or more processors (for example microprocessors, microcontrollers, etc.), specifically programmed to execute the method according to the invention. This management system may also comprise communication means, optionally bidirectional means, for communicating with the battery, and means for measuring the voltage and also the temperature of the battery. The one or more processors may comprise storage means, which may be a random access memory (RAM), an electrically erasable programmable read-only memory (EEPROM), a flash memory, an external memory, etc. These storage means may in particular store the received data, the control model, one or more maps, and one or more computer programs. The management system belongs to or for example forms part of the battery management system of the vehicle, also called BMS.

[0046] The estimation method according to the invention can be triggered at any time, either by the driver of the vehicle containing the battery, or by a technician in the context of a maintenance operation. This triggering can occur at any time throughout the life of the vehicle, for example, when the vehicle is resold, or in case of autonomy issues, or for simple information purposes.

[0047] It should be noted that one may provide for interrupting the estimation method or for continuing the estimation method in a degraded mode if the relaxation step is not followed, e.g. if the relaxation step is interrupted before the end of the specified duration and / or if the temperature of the battery during the discharge step is not within a defined temperature range. The state of health estimated in this way will in fact be less accurate than if the state of health had been determined subject to the conditions of the specified duration of the relaxation step and / or the temperature of the battery during the discharge step.

[0048] When the evaluation process is underway, (i) At the end of each driving cycle n, the capacity Q discharged during driving cycle n n and the state of charge SOC for driving cycle n n and (ii) the state of charge SOC determined during the last driving cycle n the next time the management system is switched on, in other words the next time the vehicle is started n Target State of Charge SOC target Compare with

[0033] a. This state of charge SOC n is the target state of charge SOC target and if the battery has not been used for the duration specified by the second relaxation step, steps (e)-(g) are performed; b. If this state of charge is greater than the target state of charge, the number of driving cycles is incremented by one (equals n+1) and step (e) continues, i.e., the capacity discharged for this driving cycle is determined and the SOC n+1 , then the method returns to step (i) for this cycle (n+1).

[0049] Moreover, the management system may be configured (programmed) to perform tests each time the management system is powered on in order to check the status of the estimation method according to the invention. The management system may, for example, perform the following tests: - Test T1: Is the battery fully charged (has it reached maximum charge state)? (i) if the answer is yes, a reset of the stored variables may be provided, thus - Discharge capacity Q n and the value SOC n and an index n for counting the number of discharge driving cycles is reset to 0; - The amount of time used to record the absolute start time of each of the driving phases, and the initial SOC amount at the beginning of each driving cycle, are reset to 0 and these amounts are calculated by subtracting the SOC amount from the maximum state of charge (100%). target This allows the effect of the number of driving cycles to be examined for transitioning to a lower state of charge. The system is then ready to start the estimation method according to the invention. (ii) If the answer is no, the system transitions to test T2. - Test T2: The vehicle starts running, and SOC>SOC target and when the determination method according to the invention is in progress, the index n is incremented by 1 and Q n and state of charge SOC n is determined. If not, the system transitions to test T3. - Test T3: Battery is in relaxed state and SOC <SOC target (corresponding to the completion of step (d) of the method according to the invention), the state of charge SOC of the batteryOCV (step (e) of the method) and the initial discharge capacity Q i (step (f) of the method) and the state of health SOH (step (g)) is determined. If not, the system transitions to test T4. - Test T4: Is the battery charging? If yes, the estimation method according to the invention is interrupted.

Claims

1. 1. A method for estimating the state of health of a battery in an electric or hybrid vehicle, comprising: (a) the battery has a maximum state of charge (SOC) ｍａｘ charging the battery until (b) a first relaxation step, during which the battery is not used for a first duration; (c) the battery has a non-zero target state of charge SOC ｔａｒｇｅｔ wherein the discharging step is performed for k driving cycles of the vehicle, k being a non-zero integer, and 1≦n≦k, and for each driving cycle n, a capacity Q discharged by the battery is ｎ Discharging the battery, wherein: (d) a second relaxation step at the end of the driving cycle k, during which the battery is not used for a second duration; (e) the state of charge (SOC) of the battery as a function of open circuit voltage when the battery is not in use; ＯＣＶ determining a (f) the initial discharge capacity Q of the battery in a new state ｉ based on the state of charge determined in step (e) and a correlation previously established for the battery in a fresh state, and correlating the initial discharge capacity with the state of charge of the battery; (g) estimating a state of health (SOH) of the battery based on the total capacity discharged by the battery during the discharging step (c) and the initial discharge capacity determined in step (f); A method comprising:

2. During the estimation step (g), the state of health SOH of the battery is estimated using the following equation: Here, Q ｎ represents the capacity discharged by the battery during driving cycle n, where n is a non-zero integer ranging from 1 to k; and Q ｉ The estimation method of claim 1 , wherein: represents the initial discharge capacity.

3. 3. The method of claim 1, further comprising a checking step between the first relaxation step (b) and the discharging step (c), which involves checking that the state of charge of the battery in a relaxed state has reached the maximum state of charge.

4. 3. The estimation method of claim 1 or 2, wherein during the discharging step (c), for each driving cycle, the capacity discharged by the battery takes into account the charge capacity received by the battery.

5. 3. The method of claim 1 or 2, wherein the capacity discharged by the battery during the discharging step (c) is determined by (i) coulomb-counting ampere-hours drawn from the battery, or (ii) coulomb-counting ampere-hours drawn from the battery and ampere-hours supplied to the battery and subtracting the ampere-hours supplied to the battery from the ampere-hours drawn from the battery.

6. For each driving cycle n of the discharging step (c), the state of charge SOC of the battery ｎ is estimated by (i) measuring the voltage of the battery while it is running, or (ii) by coulomb counting, and then calculating the state of charge SOC ｎ The value of the target state of charge value SOC ｔａｒｇｅｔ is compared with SOC ｎ is SOC ｔａｒｇｅｔ 3. The method of claim 1, wherein step (c) is considered complete when .times. ...

7. The correlation used during step (f) is established for a defined temperature range, and during each driving cycle of the discharging step (c), either (i) the battery is maintained at a temperature within the defined temperature range, or (ii) a correction factor is added to the capacity Q discharged by the battery as a function of the temperature of the battery. ｎ The estimation method according to claim 1 or 2, which is applied to

8. A computer program comprising instructions, which when executed by one or more processors, are for carrying out the steps of the estimation method according to claim 1 or 2.

9. A battery management system configured to estimate the state of charge of a battery by performing the steps of the estimation method according to claim 1 or 2.

10. A motor vehicle equipped with a traction battery comprising the battery management system of claim 9.

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