Diagnostic method for the storage cells of a traction battery in an electric or hybrid motor vehicle

Abstract

Diagnostic method (100) for the storage cells (210) of a traction battery (200) of an electric or hybrid motor vehicle (300). If the vehicle (300) is in an inactive state, the following steps are performed: A stop step (120) of the cell balancing method when it is active; For each cell (210) of said battery (200), a measurement step (130) of the change in open-circuit voltage across said cell (210) over a first predetermined period; When said predetermined period is reached, a detection step (140) of a faulty cell when a change in open-circuit voltage measured across its terminals during the first predetermined period exceeds a limit threshold; and If a faulty cell is detected, an alert emission step (150). Abbreviated figure: Figure 1

Description

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

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

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

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

[0004] Each cell is monitored for voltage in order to avoid overcharging or under-discharging.

[0005] Generally, the cells constituting an electric accumulator battery have similar characteristics. However, during the battery's lifetime, these cells may exhibit variations or differences.

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

[0007] The battery as a whole is directly affected by variations in the cells that constitute it, in particular by variations in state of charge. Indeed, the greater the difference in charge between the cells, the lower the total usable capacity of the battery.

[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 the charge states of cells by discharging the most charged cells in a re- assistance towards a target charge state.

[0011] In addition, monitoring of proper cell balancing is carried out. Indeed, the battery's operating range, maximum 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 prior art diagnostic method, as described in 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. Above this threshold, the least charged cell is then considered to be faulty.

[0014] However, this solution suffers from a lack of sensitivity, primarily because the effects of small leakage currents are masked by the stronger effects of balancing currents. Therefore, early detection of faulty cells is not possible. When the threshold is reached, it 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 triggered in the vehicle, and the customer is advised to go to the garage. Charging the electric vehicle is prohibited to ensure vehicle safety, which quickly leads to a breakdown immobilizing the vehicle.

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

[0016] To this end, a diagnostic method for the accumulation cells of a traction battery of an electric or hybrid motor vehicle is proposed, the motor vehicle including 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 for determining the state of activity of the motor vehicle between a state active and an inactive state;

[0019] If the vehicle is in an inactive state, the following steps should be implemented:

[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 across the terminals of said cell over a first predetermined period;

[0022] - When the said predetermined time is reached, a cell detection step faulty when a variation in the open-circuit voltage measured across its terminals during the first predetermined period exceeds a limit threshold, and

[0023] - If a faulty cell is detected, an alert is issued.

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

[0025] In particular, in parallel with the measurement step, the activity status of the motor vehicle is also monitored, and if the motor vehicle changes its activity status during the measurement step, the measurement step is interrupted.

[0026] Advantageously, if the measurement step is interrupted while it has been in progress for a duration less than a second predetermined duration, then the process is interrupted, and in that if the measurement step has been in progress for a duration greater than or equal to said second predetermined duration, then the following steps of the process 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 check of the consistency of the temperatures of all cells is carried out before the implementation of the step of measuring voltage variations.

[0029] Advantageously, the method includes a step of calculating a variation in the state of charge of each cell as a function of the open-circuit voltage variations 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 diagnostic assembly for the accumulation cells of a traction battery of an electric or hybrid motor vehicle, and the motor vehicle comprising a management unit for said battery adapted to implement a method for balancing the state of charge of said cells;

[0031] said diagnostic device comprising:

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

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

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

[0035] - A cell failure detection unit, adapted to detect, when a change in open-circuit voltage measured across its terminals during the first predetermined period exceeds a limit threshold, and

[0036] Means for issuing an alert if a faulty cell is detected. The invention also relates to an electric or hybrid motor vehicle comprising a battery of electric accumulators comprising a plurality of accumulation cells, the motor vehicle comprising a management unit for said battery adapted to implement a cell balancing process, and a diagnostic system 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 means of wireless telecommunication, said diagnostic set comprising a device for transmitting measurements, for each cell of said battery, of the variation of the charging voltage over a first predetermined period to said remote processing unit.

[0038] Other features and advantages of the invention will become apparent from the following description of a particular embodiment of the invention, given by way of example but not limitation, with reference to the accompanying drawings in which:

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

[0040] [Fig.2] graphically represents the relationship between variation in the voltage of a cell and variation in the state of charge.

[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 discharge in voltage of each cell;

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

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

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

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

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

[0048] The battery management device 310, also called BMS 310, implements a diagnostic process 100 as described 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 Wireless BMS.

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

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

[0053] A step 110 is first 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 switched off or in standby mode; this is also referred to as the sleep state. It is important to understand that when the vehicle is inactive or in sleep mode, the battery is neither charged by driving nor discharged by connecting to a charging station.

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

[0055] In a preferred embodiment, the diagnostic process is only implemented if, in addition to the inactive state, the process 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 objective is indeed not to carry out this diagnostic procedure too frequently, but only at a relevant time interval, here every month.

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

[0059] In addition, a preliminary, but not mandatory, first step 170 of battery balancing is implemented. 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 process is stopped 171, with a fault alert being triggered immediately.

[0060] This preliminary step 170 may in particular implement any prior art detection method, including the one stated above.

[0061] Next, a stop step 120 of the cell balancing process is implemented 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, particularly under the effect of balancing voltages. cells.

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

[0064] In the main embodiment of the invention, the measurement of variation for each cell is carried out at 10-minute intervals; however, the invention is not limited to this value and may, for example, be within a range from 1 minute to 1 hour per acquisition.

[0065] In the main embodiment of the invention, this first predetermined period 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 shows in particular an example of voltage measurements of 96 cells over 3 days. By linear interpolation, the decay slopes of each cell can be obtained, as shown in Figure 4, and we note, in particular by the example of Figure 5, the evolution of a healthy cell, cell 19, from a faulty cell, cell 80, which has a much steeper slope.

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

[0069] Once the first predetermined duration has elapsed, a detection step 140 of 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 charge voltage measured during the first predetermined time is greater than a limit threshold.

[0071] In the main embodiment, but not in a limiting manner, the failure of a cell is detected by calculating, through linear interpolation, a decay slope of the cell voltage over a predetermined initial time period. 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.lmV over a 3-day measurement.

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

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

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

[0076] Thus, if we know how to detect a variation of 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 0.02 AH. Also, for a leakage current of 35mA, this requires a time of 0.57 hours.

[0078] Conversely, a current leak can therefore be detected 10 times weaker by increasing the observation time by a factor of 10, i.e. 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 about 3 days or more, and beyond 3 days, it is preferable to reactivate the battery balancing.

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

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

[0083] The diagnostic process 100 also includes monitoring 160 of the activity status of the vehicle 300 during the measurement step 130. Thus, if the activity status of the vehicle 300 changes during this measurement step 130, the measurement step 163 is interrupted. 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 process is interrupted without the diagnosis being carried out.

[0085] However, if the measurement step 130 of the variation of the load voltage has been 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 process, the diagnostic process 100 may also include a step of detecting a faulty cell further comprising one or more temperature measurements of each cell 210.

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

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

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

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

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

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

[0094] The vehicle includes an electric accumulator battery 200 comprising a plurality of accumulation cells 210. These accumulation cells 210 are intended to store the electrical energy required for the operation of the vehicle.

[0095] The motor vehicle 300 also includes a battery management unit 310 adapted to implement a cell balancing method 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 includes a diagnostic set for the accumulation cells of the traction battery 400.

[0098] This diagnostic set 400 is suitable for diagnosing the condition of each storage cell 210 of the battery 200 and for issuing an alert if a faulty cell is detected.

[0099] In addition, 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 enable 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, for example a screen or a mobile application, for displaying alerts and other diagnostic information relevant to the driver or other users.

Claims

Claims

1. A method (100) for diagnosing 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 (110) of determining the state of activity 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 (120) of stopping the method for balancing the cells 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 than (161) 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 to (162) 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 for controlling (420) the stopping of the cell balancing process when it is active; - Means for measuring (430), for each cell of said battery, the variation of the open-circuit voltage at the terminals of said cell (210) over a first predetermined duration;- A unit (440) for detecting the failure of a cell, 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 (450) for transmitting 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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