Method for diagnosing the storage cells of a traction battery of an electric or hybrid motor vehicle

Abstract

The invention relates to a method for diagnosing (100) the storage cells (210) of a traction battery (200) of an electric or hybrid motor vehicle (300), wherein, if the vehicle (300) is in an inactive state, the following steps are implemented: - a step (120) of stopping the cell-balancing process if it is active; - for each cell (210) of the battery (200), a step (130) of measuring the variation in the open-circuit voltage across the terminals of the cell (210) over a first predetermined time; - once the predetermined time has elapsed, a step of detecting (140) a faulty cell when a variation in the open-circuit voltage measured across its terminals during the first predetermined time is greater than a limit threshold; and - if a faulty cell is detected, a step of issuing (150) an alert.

Description

Title of the invention: Method for diagnosing the storage cells of a traction battery of an electric or hybrid motor vehicle

[0001] The invention relates to a method for diagnosing the storage cells of a traction battery of an electric or hybrid motor vehicle.

[0002] Such vehicles are equipped with a battery comprising a large number of electric accumulators of the electrochemical cell type, Lithium-ion cells for example, which will be referred to indifferently hereinafter using the expressions "electric accumulators" or "accumulation cells" or simply "cells". These cells can be connected in series and / or in parallel.

[0003] For example, in an automobile traction battery, it is common to have a nominal voltage varying between 288V and 400V, which requires putting around a hundred cells in series, generally 96 to 100 cells.

[0004] Each cell is voltage monitored to prevent overcharging or underdischarging.

[0005] Generally speaking, the cells that make up an electric storage battery have similar characteristics. However, during the life of the battery, these cells may exhibit dispersions or differences.

[0006] For example, there may be a dispersion of cell capacity, a dispersion of cell resistance, or even, temporarily, a dispersion of the state of charge of the cells or a dispersion of the temperature of the cells. These dispersions result in different aging for each cell of an electric storage battery and a dispersion of the state of health of the cells.

[0007] The electric storage battery as a whole is directly impacted by the relative dispersions of the cells that constitute it, in particular by the dispersions of state of charge. Indeed, the greater the difference in charge between the cells, the more the total usable capacity of the battery decreases.

[0008] To overcome this drawback, the charge states of the cells are generally balanced regularly, also called balancing in English.

[0009] This balancing can be ensured by a battery management system, also known as BMS, from the English Battery Management System, directly and autonomously.

[0010] For example, cell balancing can be dissipative, consisting of balancing cell charge states by discharging the most charged cells through a resistor to a target charge state.

[0011] In addition, monitoring of the correct cell balancing is carried out. In fact, the battery's operating range, maximum state of charge and minimum state of charge, is defined by the minimum and maximum voltage thresholds of each cell.

[0012] Another need is to check the integrity of the battery cells.

[0013] A diagnosis known from the prior art, as described by document FR1756838, consists of verifying during the balancing procedure that the voltage difference between the most charged cell and the least charged cell is less than a threshold, for example a difference of 200mV. Beyond this threshold, the least charged cell is then considered to be faulty.

[0014] However, this solution lacks sensitivity, particularly due to the fact that the effects of small leakage currents are masked by the effects of the balancing currents, which are stronger. Thus, it is not possible to detect faulty cells early. When the threshold is reached, this means that the leakage currents of the least charged cell are already significant, at least of the same order of magnitude as the balancing current. An alert is then raised in the vehicle, and the customer is asked to go to the garage. Charging the electric vehicle is prohibited to ensure the safety of the vehicle, which quickly leads the customer to a breakdown immobilizing the vehicle.

[0015] There is therefore a need for a method for diagnosing the storage cells of a traction battery early and capable of detecting low leakage currents.

[0016] To this end, a method is proposed for diagnosing the storage cells of a traction battery of an electric or hybrid motor vehicle, the motor vehicle comprising a management unit for said battery adapted to implement a method for balancing the state of charge of said cells.

[0017] Said diagnostic method comprising:

[0018] - A step of determining the activity state of the motor vehicle between an active state and an inactive state;

[0019] If the vehicle is in an inactive state, implement the following steps:

[0020] - A step to stop the cell balancing process when it is active;

[0021] - For each cell of said battery, a step of measuring the variation of the open circuit voltage at the terminals of said cell over a first predetermined duration;

[0022] - When said predetermined duration is reached, a step of detecting a faulty cell when a variation in the open-circuit voltage measured at its terminals during the first predetermined duration is greater than a limit threshold, and

[0023] - If a faulty cell is detected, a step of issuing an alert.

[0024] In particular, said predetermined duration is between 5 and 7 days, preferably 6 days.

[0025] In particular, in parallel with the measuring step, the activity state of the motor vehicle is further monitored, and if the motor vehicle changes activity state during the measuring step, the measuring step is interrupted.

[0026] Advantageously, if the measuring step is interrupted while it has been in progress for a duration less than a second predetermined duration, then the method is interrupted, and in that if the measuring step has been in progress for a duration greater than or equal to said second predetermined duration, then the following steps of the method are implemented.

[0027] In particular, said second predetermined duration is between 2 and 4 days, preferably 3 days.

[0028] Advantageously, the step of detecting a faulty cell depends on one or more temperature measurements of each cell. In particular, a verification of the consistency of the temperatures of all the cells is implemented before implementing the step of measuring the voltage variations.

[0029] Advantageously, the method comprises a step of calculating a variation in the state of charge of each cell as a function of the variations in open circuit voltage measured during the measurement step, said step of detecting a faulty cell then being a function of the variation in the state of charge.

[0030] The invention also relates to a cell diagnostic kit for accumulating a traction battery of an electric or hybrid motor vehicle, and the motor vehicle comprising a management member for said battery adapted to implement a method for balancing the state of charge of said cells;

[0031] said diagnostic device comprising:

[0032] - Means for determining the activity state of the motor vehicle between an active state and an inactive state;

[0033] - Means for controlling the stopping of the cell balancing process when it is active;

[0034] - Means for measuring, for each cell of said battery, the variation in the open circuit voltage at the terminals of said cell over a first predetermined duration;

[0035] - A cell failure detection unit, adapted to detect when a variation in the open-circuit voltage measured at its terminals during the first predetermined duration is greater than a limit threshold, and

[0036] Means of issuing an alert if a faulty cell is detected. The invention also relates to an electric or hybrid motor vehicle comprising an electric accumulator battery comprising a plurality of accumulation cells, the motor vehicle comprising a management member for said battery adapted to implement a method for balancing said cells, and a diagnostic assembly as described previously.

[0037] The invention also relates to a diagnostic system comprising a motor vehicle as described above and a remote processing unit, said motor vehicle and the remote processing unit being adapted to communicate by wireless telecommunication means, said diagnostic assembly comprising a member for transmitting measurements, for each cell of said battery, of the variation in the charging voltage over a first predetermined duration to said remote processing unit.

[0038] Other features and advantages of the invention will emerge from reading the description given below of a particular embodiment of the invention, given for informational purposes but not as a limitation, with reference to the appended drawings in which:

[0039] [Fig. 1] represents a general flowchart of the method according to the invention;

[0040] [Fig. 2] graphically represents the link between variation of the tension of a cell and state of charge variation.

[0041] [Fig. 3] represents the voltage variations over time over three days of a plurality of battery cells;

[0042] [Fig. 4] represents the calculation of the slopes, by linear interpolation, of the discharge voltage of each cell;

[0043] [Fig. 5] represents two examples of the voltage discharge curves of two cells, a healthy cell and a faulty cell;

[0044] [Fig. 6] represents additional steps of a particular embodiment of the invention;

[0045] [Fig. 7] represents a diagnostic assembly according to the invention.

[0046] In the main embodiment of the invention, an electric or hybrid motor vehicle 300 comprises an electric storage battery 200 comprising a plurality of storage cells 210.

[0047] The motor vehicle 300 comprises a management unit 310, such as a battery management device 310, also known by the English abbreviation BMS, adapted in particular to implement a method of balancing the cells 210.

[0048] The battery management device 310, also called BMS 310, implements a diagnostic method 100 as set out below.

[0049] It should be noted that the battery management device 310 is not necessarily composed of a single BMS type computer.

[0050] In particular, the invention preferably implements a wireless BMS also called BMS Wireless.

[0051] Such a Wireless BMS generally comprises a master computer 420, 450, called Master BMS and slave BMS 430, 440, called Slave BMS. The slave BMS communicates via wireless links with the master BMS, and each BMS is independent of the other BMS.

[0052] Consequently, the slave BMS dedicated to implementing the diagnostic method 100 according to the invention will be able in particular to implement the method while the master BMS is on standby, and transmit the information and data to it when it wakes up.

[0053] First of all, a step 110 is implemented to determine the activity state of the vehicle 300. This state is either active, when the vehicle is running, or inactive, when the vehicle is off or on standby, we then also speak of a sleeping state. It is important to understand that, when the vehicle is inactive or asleep, the battery is neither charged due to driving, nor discharged due to connection to a terminal.

[0054] When the vehicle 300 is in an inactive state, the diagnostic method 100 continues.

[0055] In a preferred embodiment the diagnostic method is only implemented if, in addition to the inactive state, the method has not been implemented less than one month before the present implementation.

[0056] For this purpose, a verification step 180 of the age of the last diagnosis carried out is implemented.

[0057] The aim is not to carry out this diagnostic procedure too frequently, but only at a relevant time interval, in this case every month.

[0058] However, the invention is not limited to a monthly implementation of this method, and can be freely adapted, for example every week, every three months, or at any predetermined frequency. Furthermore, the frequency of implementation can vary, for example to take into account the conditions of use of the vehicle, its frequency of use or the age of the batteries.

[0059] In addition, a first verification step 170 of the balancing of the battery is implemented in a preliminary, but not mandatory, manner. Thus, if too large a variation is detected between the maximum and minimum charge states of the cells, for example a difference greater than 10%, a significant fault in at least one cell is immediately detected, and the method is stopped 171, a fault alert being able to be triggered immediately.

[0060] This preliminary step 170 can in particular implement any detection method of the prior art, in particular that stated previously.

[0061] Then, a step 120 is implemented to stop the cell balancing process if it is active.

[0062] Indeed, cell balancing is a necessary maintenance operation to optimize the performance and lifespan of the 200 battery. However, for battery diagnostics, it is important to ensure that cell balancing does not interfere with measurements, especially under the effect of cell balancing voltages.

[0063] Then, for each storage cell 210 of the battery 200, a step measuring 130 of the variation in the charging voltage is carried out over a first predetermined duration.

[0064] In the main embodiment of the invention, the variation measurement for each cell is carried out at intervals of 10 minutes, however the invention is not limited to this value and can, for example, be included in a range from 1 min to 1 hour per acquisition.

[0065] In the main embodiment of the invention, this first predetermined duration can be between 5 and 7 days, preferably 6 days.

[0066] After this first predetermined duration, the measurement step 130 is interrupted 131.

[0067] Figure 3 represents in particular an example of measurement of the voltages of 96 cells over 3 days. By linear interpolation we can obtain the decrease slopes of each cell, as represented in figures 4, and we note, in particular by the example of figure 5 the evolution of a healthy cell, cell 19, of a faulty cell, cell 80, which presents a much more significant slope.

[0068] However, preferably but not obligatorily, if a significant variation in the state of charge of at least one cell is detected 190 during this first predetermined duration, for example a variation greater than 10% of its maximum capacity, a significant fault in at least one cell is immediately detected, and the method according to the invention is stopped 191, a fault alert being able to be triggered immediately.

[0069] Once the first predetermined duration has elapsed, a step 140 of detecting a faulty cell is then implemented.

[0070] This detection step 140 detects that a cell 210 of the battery 200 is faulty if a variation in its charging voltage measured during the first predetermined duration is greater than a limit threshold.

[0071] In the main embodiment, but in a non-limiting manner, the failure of a cell is detected by calculating, by linear interpolation, a decreasing slope of the cell voltage over the first predetermined duration. The slope is then compared to a maximum slope corresponding to the limit threshold.

[0072] Here the limit threshold is defined in a range between 0.01 mV and 0.2 mV, for example 0.1mV over a 3-day measurement.

[0073] As an example, figure 2 represents in its lower part, the variation of charge, abbreviated SOC, from the English State Of Charge, which can be detected by the variation of the voltage

[0074] This charge variation depends on the OCV-SOC curve, shown in the upper part, with OCE the open circuit voltage, and SOC the state of charge.

[0075] As an example, for a state of charge of 60%, Figure 2 shows that a BSOC% voltage variation of 1 mV corresponds to a DSoc% charge variation of 0.125%.

[0076] Thus, if we know how to detect a variation in O.lmV, we can detect a charge variation of the order of 0.0125%.

[0077] For a battery with a capacity of 157AH, for example, this gives 0.02AH. Also for a leakage current of 35mA, this requires a time of 0.57 hours.

[0078] Conversely, we can therefore detect a current leak 10 times weaker by increasing the observation time by a factor of 10, or here 5.7 hours.

[0079] In the main embodiment of the invention, an observation horizon of 3 days is set, which makes it possible to observe a leak of 35*0.57 / 72=0.27 mA

[0080] Indeed, 3 days is a relevant duration: we regularly have parking stops of around 3 days or more, and beyond 3 days, it is preferable to put the battery balancing back into service.

[0081] If a faulty cell is detected, an alert step 150 is then implemented to warn of the fault in the battery 200.

[0082] This alert may be displayed on the vehicle's dashboard 300, sent to a driver communication device, or transmitted to a remote processing unit for further intervention.

[0083] The diagnostic method 100 also comprises monitoring 160 of the activity state of the vehicle 300 during the measurement step 130. Thus, if the activity state of the vehicle 300 changes during this measurement step 130, the measurement step is interrupted 163. Indeed, starting the vehicle does not allow the measurement step 130 to be maintained.

[0084] If the measurement step 130 is interrupted while it has been in progress for a duration less than a second predetermined duration, then the method is interrupted without carrying out the diagnosis.

[0085] However, if the measurement step 130 of the variation of the load voltage is in progress for a duration greater than or equal to this second predetermined duration, the following steps of the process are then implemented.

[0086] The second predetermined duration, in the main embodiment of the invention, is between 2 and 4 days, here 3 days.

[0087] According to a particular embodiment of the method, the diagnostic method 100 may also include a step of detecting a faulty cell further comprising one or more temperature measurements of each cell 210.

[0088] For example, before implementing the measurement step 130, a step of verifying the uniformity of the temperatures between the cells can be implemented, in order to ensure that the measurements will be independent of temperature differences.

[0089] According to another example, the temperature consideration can further be monitored throughout the measurement step 130, so that if a significant cell deviation appears, the process is interrupted, the data being potentially non-compliant.

[0090] According to another variant of implementation of the method according to the invention, the detection 140 of the faulty cell can be carried out as a function of the variation in the state of charge, rather than the variation in the voltage, as shown in figure 6.

[0091] Thus, with reference to Figure 6, the method comprises, after the measurement step 61, an intermediate step 62 of calculating the variation of SOC 62, then a step 63 of calculating the slope of evolution of the SOC of each cell. If the slope is greater 64 than a predetermined target value, then it is detected that the cell is faulty.

[0092] The invention also relates to a diagnostic assembly 400 for the storage cells of a traction battery of an electric or hybrid motor vehicle.

[0093] The invention also relates to the electric or hybrid motor vehicle 300 and diagnostic assembly for the storage cells of the traction battery 400 adapted to implement the method according to the invention.

[0094] The vehicle comprises an electric storage battery 200 comprising a plurality of storage cells 210. These storage cells 210 are intended to store the electrical energy necessary for the operation of the vehicle.

[0095] The motor vehicle 300 also comprises a battery management unit 310 adapted to implement a method for balancing the cells 210.

[0096] This balancing process is designed to maintain an optimal charge balance among all the storage cells 210 of the battery 200, in order to optimize the performance of the battery 200 and increase its lifespan.

[0097] According to the invention, the motor vehicle 300 also comprises a diagnostic assembly for the storage cells of the traction battery 400.

[0098] This diagnostic assembly 400 is adapted to diagnose the state of each storage cell 210 of the battery 200 and to issue an alert if a faulty cell is detected.

[0099] Further, the motor vehicle 300 may include wireless communication means 320 for communicating with a remote processing unit 500.

[0100] These wireless communication means 320 can allow the transmission of diagnostic data collected by the diagnostic assembly 400 to the remote processing unit 500 for further analysis.

[0101] In an alternative embodiment, the motor vehicle 300 may also include a user interface 330, e.g., a screen or mobile application, for displaying alerts and other relevant diagnostic information to the driver or other users.

Claims

Claims

1. Method for diagnosing (100) the storage cells (210) of a traction battery (200) of an electric or hybrid motor vehicle (300), the motor vehicle (300) comprising a management member for said battery (420, 430, 440, 450) adapted to implement a method for balancing the state of charge of said cells (210), said diagnostic method (100) comprising: - A step of determining (110) the activity state of the motor vehicle (300) between an active state and an inactive state; If the vehicle (300) is in an inactive state, implementing the following steps: - A step of stopping (120) the cell balancing process when it is active; - For each cell (210) of said battery (200), a step of measuring (130) the variation of the open circuit voltage at the terminals of said cell (210) over a first predetermined duration; - When said predetermined duration is reached, a step of detecting (140) a faulty cell when a variation in the open-circuit voltage measured at its terminals during the first predetermined duration is greater than a limit threshold, and - If a faulty cell is detected, a step of transmitting (150) an alert.

2. Method (100) according to claim 1, characterized in that said predetermined duration is between 5 and 7 days, preferably 6 days.

3. Method (100) according to claim 1 or 2, characterized in that in parallel with the measuring step (130), the activity state of the motor vehicle is further monitored (160), and if the motor vehicle changes activity state during the measuring step, the measuring step (130) is interrupted.

4. Method (100) according to claim 3, characterized in that, if the measuring step (130) is interrupted while it has been in progress for a duration less (161) than a second predetermined duration, then the method (100) is interrupted, and in that if the measuring step (130) has been in progress for a duration greater than or equal (162) to said second predetermined duration, then the following steps of the method are implemented.

5. Method (100) according to claim 4, characterized in that said second predetermined duration is between 2 and 4 days, preferably 3 days.

6. Method (100) according to any one of claims 1 to 5, characterized in that the detection of a faulty cell depends on one or more temperature measurements of each cell.

7. Method (100) according to any one of claims 1 to 6, characterized in that the method comprises a step of calculating a variation in the state of charge of each cell as a function of the variations in open circuit voltage measured during the measurement step (130), said step of detecting (140) a faulty cell then being a function of the variation in the state of charge.

8. Diagnostic assembly (400) for the storage cells (210) of a traction battery (200) of an electric or hybrid motor vehicle (300), and the motor vehicle (300) comprising a management member (420, 430, 440, 450) of said battery adapted to implement a method for balancing the state of charge of said cells; said diagnostic device (400) comprising: - Means for determining (410) the state of activity of the motor vehicle between an active state and an inactive state; - Means (420) for controlling the stopping of the cell balancing process when it is active; - Measuring means (430), for each cell of said battery, of the variation of the open circuit voltage at the terminals of said cell (210) over a first predetermined duration; - A cell failure detection unit (440), adapted to detect, when a variation in the open-circuit voltage measured at its terminals during the first predetermined duration is greater than a limit threshold, and - Means for transmitting (450) an alert, if a faulty cell is detected.

9. Electric (300) or hybrid motor vehicle comprising an electric accumulator battery (200) comprising a plurality of accumulation cells (210), the motor vehicle (300) comprising a management member (420, 430, 440, 450) of said battery adapted to implement a method of balancing said cells, and a diagnostic assembly (400) according to claim 8.

10. Diagnostic system comprising a motor vehicle (300) according to claim 9 and a remote processing unit (500), said motor vehicle (300) and the remote processing unit (500) being adapted to communicate by wireless telecommunication means (510), said diagnostic assembly comprising a member for transmitting measurements (320), for each cell of said battery, of the variation in the charging voltage over a first predetermined duration to said remote processing unit (500)

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