A system for protecting equipment with variable internal resistance.

Abstract

The present invention relates to a system for protecting a device (20) having variable internal resistance, the device comprising a fuse (25) capable of blowing when a current of strength greater than a strength threshold passes through it. According to the invention, the system further comprises an estimation device adapted to estimate the internal resistance of the device, and a protection device adapted to limit and / or prevent use of the device when the internal resistance is greater than a resistance threshold, and the fuse being ineffective when the resistance threshold is exceeded.

Description

Technical Field

[0001] This invention relates in general to the safety of storage batteries.

[0002] More specifically, the present invention relates to a protection system for protecting a device with variable internal resistance (e.g., an electrochemical cell of a storage battery), the protection system including a fuse capable of melting when a current of greater than a predefined strength threshold flows through it.

[0003] The present invention also relates to a method for protecting such a device.

[0004] This invention is particularly advantageous for use in the production of batteries for electric or hybrid vehicles. Background Technology

[0005] Electric and hybrid vehicles are equipped with batteries that supply current to electric motors to propel the vehicles.

[0006] As taught in document US2017005384, such batteries typically consist of multiple modules, each incorporating a large number of different electrochemical cell units.

[0007] These battery cells use chemical compounds to store electrical energy, and overcharging them can be dangerous.

[0008] A common system for protecting batteries involves individually monitoring the voltage across each battery cell and disconnecting the current in case of overcharging. Unfortunately, implementing this technical solution requires a large number of expensive components with redundant connections to achieve the desired level of safety.

[0009] Another solution described in document US2017005384 involves equipping each battery cell with its own integrated safety device. This safety device first includes a fuse connected between the chemical compound and the positive terminal of the battery cell, and secondly includes a pressure switch connected between the two terminals of the same battery cell.

[0010] Therefore, in the event of overvoltage within the battery cell, the switch closes, creating a short circuit within the battery cell and causing the fuse to blow, thus bringing the battery to a safe state.

[0011] The first drawback of this solution is that the fuse can cause a malfunction that renders the vehicle immobile.

[0012] The applicant has observed and found that the second defect is more serious than the first one. The second defect is that the fuse does not blow when the battery cell is short-circuited, which poses a risk of battery fire or explosion. Summary of the Invention

[0013] To overcome the aforementioned deficiencies in the prior art, this invention proposes to improve battery safety by adding computerized means for detecting battery aging.

[0014] More specifically, according to the present invention is a protection system as defined in the introduction, wherein an estimation device and a protection device are provided, the estimation device being designed to estimate the internal resistance of a device (e.g., the internal resistance of an electrochemical cell), and the protection device being designed to limit and / or prevent the use of the device once the internal resistance is greater than a selected resistance threshold, such that the device still has the ability to blow a fuse.

[0015] Specifically, the applicant has observed that when the electrochemical cell ages prematurely and therefore has excessive internal resistance, the power generated by the cell is not always sufficient to blow the fuse.

[0016] Instead of using smaller fuses (which can be problematic when the battery cell is under high load, as the fuse may blow unintentionally), the present invention proposes monitoring the aging condition of the battery cell so that the user can be (preferably, preventively) invited to have their battery serviced before the battery cell can no longer generate the power required to blow the fuse.

[0017] The following are other advantageous and non-limiting features of the protection system according to the invention, which can be considered individually or in any technically possible combination:

[0018] - The resistance threshold is equal to the internal resistance. If the internal resistance is exceeded, the device will no longer have the ability to blow the fuse within the safety margin.

[0019] - In the case where the device includes two electrical connection terminals, a switch is provided that is designed to automatically close the electrical circuit between the two terminals in the event of an overvoltage in the device;

[0020] - The estimation device is designed to estimate the internal resistance only if one or more of the following conditions are met:

[0021] The device is in the discharge phase.

[0022] The device delivers current within a predefined range.

[0023] ->The intensity of the current delivered by the device changes more than a predefined threshold over time.

[0024] The internal temperature of the device is within a predefined temperature range;

[0025] - The estimation device is designed to attempt to estimate the internal resistance periodically;

[0026] - The protection device is designed to warn the user that the protection device is about to limit and / or prevent the use of the device when the internal resistance is greater than the second resistance threshold;

[0027] -The protection device is designed to restrict the use of the device when the internal resistance is greater than a third threshold;

[0028] -The third threshold is strictly greater than the second threshold;

[0029] - The protection device is designed to prevent the use of the device when the internal resistance is greater than the resistance threshold (which is strictly greater than the third threshold).

[0030] The present invention also relates to a storage battery comprising an electrochemical battery cell equipped with the aforementioned protection system.

[0031] The present invention also proposes a method for protecting a device with variable internal resistance (e.g., an electrochemical battery cell equipped with a protective fuse), the method comprising:

[0032] - The step of estimating the internal resistance of the device.

[0033] - The step of comparing the internal resistance with at least one resistance threshold (beyond which the protective fuse will not function) and determining whether the internal resistance is greater than the resistance threshold.

[0034] - Protective steps to prevent or restrict the use of the device while still allowing it to blow the fuse.

[0035] Of course, the various features, variations and embodiments of the present invention can be combined with each other in various combinations, as long as they are not incompatible or mutually exclusive. Detailed Implementation

[0036] The description given with reference to the accompanying drawings, by way of non-limiting examples, will make it easy to understand what the invention includes and how it can be practiced.

[0037] In the attached diagram:

[0038] [ Figure 1 [Illustration] is a schematic diagram of a motor vehicle equipped with a battery according to the present invention;

[0039] [ Figure 2 ]yes Figure 1 A schematic diagram of the electrochemical cell unit of a storage battery;

[0040] [ Figure 3 ]yes Figure 2 Circuit diagram of an electrochemical battery cell;

[0041] [ Figure 4 [This is to showcase when] Figure 2 A graph showing the voltage change across the two ends of an electrochemical cell when it receives a step current.

[0042] [ Figure 5 [This is a graph showing the step current;]

[0043] [ Figure 6 ] is shown in the form of points. Figure 2 The graph shows the test results of the electrochemical cell unit, with the vertical axis representing the measured voltage difference and the horizontal axis representing the current difference delivered by the cell unit.

[0044] [ Figure 7 ] is shown to be the result of these tests by Figure 2 A graph showing the change in current delivered by the electrochemical cell unit over time;

[0045] [ Figure 8 ] is shown to be the result of these tests by Figure 2 A graph showing the rate of change of the current delivered by the electrochemical cell unit over time.

[0046] [ Figure 9 ] is to show Figure 2 The graph shows the measured internal resistance of an electrochemical cell unit as a function of its charge level.

[0047] Figure 1 A motor vehicle 10 comprising two drive wheels 16 is shown schematically.

[0048] In this case, the vehicle is an electric vehicle. As a variation, the vehicle could also be a hybrid vehicle.

[0049] Figure 1 The illustrated motor vehicle 10 therefore includes at least one electric motor 15 for driving two drive wheels 16 to rotate. The motor vehicle also includes a battery 11 that allows current to be supplied to the electric motor 15 via an inverter 14.

[0050] The battery 11 includes a storage casing that houses a large number of electrochemical battery cells 20.

[0051] The motor vehicle 1 also includes a measuring device 18 for measuring the temperature of the battery 11 (e.g., in the form of a temperature probe installed inside the storage casing of the battery 11).

[0052] The vehicle also includes an acquisition device 19 for acquiring the voltage U across each electrochemical cell 20. batt and the current I delivered or received by each of these electrochemical cell units 20batt .

[0053] In order to manage the various units of the motor vehicle, the motor vehicle 1 includes a computer 12, which includes a processor and a memory, and is equipped with various input and output interfaces 13.

[0054] Through its input interface, the computer 10 is designed to receive input signals from the measuring device 18 and the acquiring device 19, respectively. Therefore, the computer is designed to acquire the internal temperature T of the battery 11 and the voltage U across each electrochemical cell 20. batt and the current I delivered or received by each of these battery cells batt .

[0055] The computer 12 stores computerized application programs consisting of computer programs including instructions that, when executed by the processor, allow the computer 12 to perform the methods described below.

[0056] Finally, through the computer's output interface, the computer 12 is designed to communicate with the safety system 17 to protect the battery 11. Here, the safety system 17 specifically includes a display screen 17' arranged on the vehicle's dashboard, and a control element 17" for controlling the charging of the battery.

[0057] Figure 2 It shows Figure 1 One of the electrochemical cell units 20 of the storage battery.

[0058] This disclosure will assume that these battery cells all have the same reference and are connected in series with each other. More specifically, this disclosure will focus on only one of these battery cells.

[0059] like Figure 2 As shown, the electrochemical battery cell 20 includes a housing 29 that houses the electrochemical components 21 (here, two electrodes immersed in a lithium-ion-based electrolyte) and two terminals 22 (negative electrode) and 23 (positive electrode) respectively connected to the two electrodes.

[0060] Here, the electrochemical cell unit 20 is equipped with a partially integrated and partially remote protection system.

[0061] The remote portion of the protection system includes the aforementioned security system 17.

[0062] The integrated portion of the protection system includes a fuse 25 and a switch 26 housed in a housing 29.

[0063] Switch 26 is connected between the two terminals 22 and 23 of the battery cell. The switch is supplied in the open state and is designed to automatically close in the event of an overpressure within the housing 29. For this purpose, the switch includes a pressure-sensitive membrane.

[0064] Therefore, it is possible to short-circuit the electrochemical battery cell 20, especially in cases where overcharging may cause a fire.

[0065] Fuse 25 itself connects the positive terminal 23 of the electrochemical cell unit 20 to the corresponding electrode. This fuse is designed to withstand strength I... batt The circuit will melt and disconnect when a current exceeding a certain intensity threshold flows through it.

[0066] Therefore, specifically, the fuse is designed to blow when the switch 26 short-circuits the electrochemical cell 20.

[0067] The combination of the fuse 25 and the switch 26 thus protects the battery 11 from the risk of explosion and fire.

[0068] As is well known, the aging of electrochemical cell 20 is consistent with the charge and discharge cycles it undergoes.

[0069] As the electrochemical cell ages, its internal resistance Ri increases. Then, there may be a situation where the electrochemical component 21 of the electrochemical cell is no longer able to generate enough power to blow the fuse 25.

[0070] This is why one particularly advantageous feature according to the invention is:

[0071] - The protection system for protecting the storage battery 11 includes an estimation device (formed herein by computer 12) designed to estimate the internal resistance Ri of each electrochemical cell 20, and

[0072] -Safety system 17 is designed to prevent the internal resistance Ri from exceeding the first resistance threshold S when the internal resistance Ri is greater than the first resistance threshold S. R1 The threshold for limiting and / or preventing the use of battery 11 is selected such that each electrochemical cell 20 only needs its internal resistance Ri to be below the first resistance threshold S. R1 It has the ability to blow its fuse 25.

[0073] The following describes how to calculate the internal resistance Ri of each electrochemical cell 20.

[0074] To understand these calculations, we can first use... Figure 3 The electrochemical cell unit 20 is modeled in the form of electrical circuit 41.

[0075] In this figure, electrical circuit 41 includes an ideal voltage source 30, a resistor 31, and a parallel RC circuit connected in series with each other.

[0076] The ideal voltage source 30 has a voltage value that depends on the charge level BSOC of the electrochemical cell 20. It will also be recalled that the charge level BSOC represents the amount of electrical energy remaining in the cell as a percentage. Therefore, when the cell is fully charged, its value is 100%, and when the cell is fully discharged, its value is 0%.

[0077] Resistor 31 represents the internal resistance Ri of the electrochemical cell 20. This depends specifically on the aging condition of the cell.

[0078] The parallel RC circuit includes a resistor 32 and a capacitor 33 connected in parallel. This illustrates the fact that the battery cell has a non-zero response time during charging and discharging. The resistor and capacitor values ​​are selected based on the measurable response time of the battery cell.

[0079] Then, Figure 4 and Figure 5 This shows the voltage U across the electrochemical cell 20 when the cell receives a charging current in the form of a step current with a value of ΔI. batt and the current I flowing through the electrochemical cell unit batt During this charging process, a transient change in voltage, ΔV, is observed, and this change continues gradually until a threshold is reached.

[0080] Given the modeling of the electrochemical cell 20, the internal resistance Ri of the cell can be obtained using the following equation:

[0081] [Math.1]

[0082] Ri=ΔV / ΔI

[0083] Computer 12 is then programmed to periodically calculate the internal resistance Ri, with a sampling frequency that is neither too high nor too low (typically about one second).

[0084] Preferably, the computer is programmed to calculate the estimated value of the internal resistance Ri only when specific usage conditions of the electrochemical cell 20 are met.

[0085] Specifically, the reliability of the estimated internal resistance Ri has been observed to depend on the operating conditions of the battery cell.

[0086] Then, in order to determine the conditions required to achieve a good estimate of the internal resistance Ri, a series of tests were conducted, the results of which are presented in point form. Figure 6 It is displayed in the middle.

[0087] In these tests, values ​​ΔI and ΔV were measured under various operating conditions of the electrochemical cell 20. If these conditions do not affect the results, all points should be aligned along an affine line whose slope is equal to the internal resistance Ri of the cell.

[0088] However, this is not the case.

[0089] Then Figure 7 and Figure 8 The current I delivered by the electrochemical cell unit 20 is shown. batt The change over time and the rate of change of the current.

[0090] and Figure 6 The time corresponding to the point located along the affine line has been marked with points. Therefore, it can be observed that the current and the rate of change of the current must meet specific operating conditions to make the estimation of the internal resistance Ri reliable.

[0091] Therefore, it can be observed that if the battery cell is in the discharge phase, if the battery cell delivers a current between 5A and 40A, and if the change in current between two consecutive sampling times is sufficiently large (here, if the rate of change of current δI), then... batt If δt is greater than 1A / s, then the estimated value of the internal resistance Ri is reliable.

[0092] Figure 9 The test results were also plotted to observe the effects of the battery charge level BSOC and the internal temperature of the battery cell on the estimated internal resistance Ri.

[0093] Therefore, it can be observed that if the internal temperature T of the battery cell is not high enough (25 degrees on curve C1), slight temperature changes may affect the estimated internal resistance Ri. Therefore, it is preferable to operate between 45°C (curve C2) and 55°C (curve C3).

[0094] It can also be observed that as long as the charge level BSOC of the electrochemical cell 20 is between 40% and 75%, this charge level has almost no effect on the estimation of the internal resistance Ri.

[0095] Therefore, various operating conditions of the electrochemical cell 20 can be found and selected as needed to obtain a reliable estimate of the internal resistance Ri.

[0096] These data have now been explained in detail, and can describe how the computer 12 of the motor vehicle 10 protects the use of each electrochemical battery cell 20 in the storage battery 11.

[0097] For this purpose, computer 12 iteratively repeats the steps described below. These steps are performed in the same manner for each electrochemical cell 20. For the sake of simplicity in this disclosure, only one of these cell units will be considered below.

[0098] In the first step, the computer obtains the internal temperature T of the battery 11.

[0099] The computer also acquires the voltage U of the electrochemical cell unit 20. batt and current I batt The value of .

[0100] In the second step, the computer 12 determines whether the operating conditions of the electrochemical cell 20 are met in order to estimate the internal resistance Ri of the cell.

[0101] For this purpose, the computer determines whether the electrochemical cell 20 is in the discharge phase, and the intensity I of the current delivered by the cell. batt Whether the intensity I of the current delivered by device 20 is within a predefined range (in this case, between 5A and 40A) batt Whether the rate of change is greater than a predefined change threshold (1A / s in this case), and whether the internal temperature of the battery 11 is within a predefined temperature range (45°C to 55°C in this case).

[0102] Of course, the above ranges can vary as variations. Many different usage conditions for the battery cell can also be considered.

[0103] Here, if these conditions are met, the computer measures the values ​​ΔU and ΔI, and then derives an estimate of the internal resistance Ri based on the above equation "Math.1". If these conditions are not met, the method is reset.

[0104] At this stage, computer 12 can directly consider the estimated value to be a good approximation of the internal resistance Ri of electrochemical cell 20.

[0105] However, this estimate will be combined with several other estimates previously made to obtain a better estimate of the internal resistance Ri. Thus, for example, the average can be taken over a sliding window covering hundreds (e.g., 500 or 1000) of previous results, and the internal resistance Ri can be considered equal to that average, which will avoid any erroneous measurements.

[0106] Once an estimate of the internal resistance Ri is obtained, the computer 12 compares the internal resistance with at least one resistance threshold.

[0107] In practice, this internal resistance Ri is compared with three resistance thresholds S. R1 S R2 S R3Compare them.

[0108] These three resistance thresholds S R1 S R2 S R3 The value is equal to the internal resistance Ri within three safety margins. If the value is exceeded, it is considered that the user can no longer be assured that the electrochemical battery cell 20 will still have the power required to blow the fuse 25.

[0109] The safety margins considered are different.

[0110] First resistance threshold S R1 It has the smallest safety margin, while the second threshold S R2 Having the largest safety margin means that it can be written as:

[0111] [Math.2]

[0112] S R1 >S R3 >S R2

[0113] Four scenarios can then be envisioned, depending on whether the internal resistance is contained within one or another of the four intervals defined by these thresholds.

[0114] Therefore, if the internal resistance Ri is less than or equal to these three thresholds, the method is reset. This corresponds to the case where the internal resistance Ri indicates that the electrochemical cell 20 is in good condition and that the cell will have the power required to blow the fuse 25 when the switch 26 is closed.

[0115] If the internal resistance Ri is at the second threshold S R2 With the third threshold S R3 If, between these points (meaning the electrochemical battery cell 20 is in a state of premature aging, but the cell is still capable of blowing fuse 25), the computer 12 is programmed to command a message to be displayed to the driver on the display screen 17'. This message is then intended to warn the driver that his battery 11 will be unusable within a limited number of charging cycles. The message could, for example, indicate that the battery 11 will no longer be usable after five charging cycles and should be replaced or repaired accordingly.

[0116] If the internal resistance Ri is at the first threshold S R1 With the third threshold S R3Between (meaning that the electrochemical battery cell 20 is in a highly premature state of aging and the cell is still close to blowing fuse 25), computer 12 is programmed to command a message to be displayed on display 17' to warn the driver that his battery will be unusable for a very short number of charge cycles. Computer 12 is also programmed to send a signal to control element 17" telling it that it should only allow a small number (e.g., one or two) of battery recharge cycles before blocking any further recharging of the battery.

[0117] Finally, if the internal resistance Ri is greater than the first threshold S R1 (This means that the electrochemical battery cell 20 is in an aging state, which is premature and it cannot be determined whether the electrochemical battery cell can still blow the fuse 25.) The computer 12 is then programmed to command a message to be displayed on the screen 17', warning the driver that his battery cannot be recharged. The computer 12 is also programmed to send a signal to the control element 17" instructing it to prevent any new recharging of the battery.

[0118] This invention is by no means limited to the embodiments already described and shown, but those skilled in the art will know how to add any variations according to the invention to these embodiments.

[0119] Therefore, this protection system can be used in devices other than the electrochemical battery cells of a storage battery.

Claims

1. A protection system for a device (20) having a variable internal resistance (Ri), the protection system comprising a fuse (25) capable of withstanding a strength (Ri). batt The fuse melts when a current exceeding the strength threshold flows through it. Its features are, The protection system also includes: - An estimation device (12) designed to estimate the internal resistance (Ri) of the device (20), and - Protection device (17), which is designed to activate once the internal resistance (Ri) is greater than a selected first threshold (S) R1 This restricts and / or prevents the use of the device (20) so that the device (20) still has the ability to blow the fuse (25). Wherein, when the internal resistance (Ri) is greater than the first threshold (S) R1 When the device (12) is in use, the estimation device (12) is programmed to send a signal to the control element (17") of the device (20) to prevent the device (20) from being recharged.

2. The protection system as described in the preceding claim, wherein, In the case where the device (20) includes two electrical connection terminals (22, 23), a switch (26) is provided, which is designed to automatically close the electrical circuit between the two terminals (22, 23) in the event of an overvoltage in the device (20).

3. The protection system as described in any one of the preceding claims, wherein, The estimation device (12) is designed to estimate the internal resistance (Ri) only when one or more of the following conditions are met: -The device (20) is in the discharge phase. - The intensity of the current delivered by the device (20) (I batt Within the predefined value range, - The intensity of the current delivered by the device (20) (I batt The change over time exceeds a predefined threshold. - The internal temperature of the device (20) is within a predefined temperature range.

4. The protection system as described in claim 1 or 2, wherein, The estimation device (12) is designed to attempt to estimate the internal resistance (Ri) periodically.

5. The protection system as described in claim 1 or 2, wherein, The protection device (17) is designed to activate when the internal resistance (Ri) is greater than the second threshold (S). R2 The device (17) warns the user that it will soon restrict and / or prevent the use of the device (20).

6. The protection system as described in claim 5, wherein, The protection device (17) is designed to activate when the internal resistance (Ri) is greater than the third threshold (S). R3 The use of this device is restricted when (20).

7. The protection system as described in claim 6, wherein, The third threshold (S) R3 Strictly greater than the second threshold (S) R2 ).

8. The protection system as described in claim 1 or 2, wherein, The protection device (17) is designed to respond when the internal resistance (Ri) is greater than the first threshold (S). R1 (20) Prevent the use of the device when it is used.

9. The protection system as claimed in claim 1, wherein, The device is an electrochemical battery unit of a storage battery (11).

10. A storage battery (11) comprising at least one electrochemical battery cell equipped with a protection system as described in any one of the preceding claims.

11. A method for protecting a device (20) having a variable internal resistance (Ri), the device (20) being equipped with a fuse (25), characterized in that, The method includes: - The step of estimating (12) the internal resistance (Ri) of the device (20), - The step of comparing the internal resistance (Ri) with at least one resistance threshold, and then determining whether the internal resistance (Ri) is greater than the resistance threshold. -A protective step to prevent or restrict the use of the device (20) so that the device (20) still has the ability to blow the fuse (25). The method further includes the following step: when the internal resistance (Ri) is greater than a first threshold (S) R1 When the device (20) is recharged, a signal is sent to the control element (17") of the device (20) to prevent the device (20) from being recharged.

12. The method of claim 11, wherein, This device is an electrochemical battery unit.

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