METHOD FOR DETECTING A BLOCKED CLOSED STATE OF AN ELECTRIC CIRCUIT BREAKER INSIDE AN ELECTRIC BATTERY OF A VEHICLE

Description

[0001] The invention relates to a method for detecting a blocked closed state of an intermediate electrical current interruption device arranged within a vehicle's electric battery. The vehicle is, in particular, an electric or hybrid vehicle. The method is implemented by a control unit of the electric battery. The electric battery (also called a battery pack) is a traction battery of the electric or hybrid vehicle, specifically a lithium-ion battery.

[0002] The invention relates to the field of electrical storage batteries for electric or hybrid vehicles. An electric battery typically comprises a set of electrical energy storage modules connected in series, each module containing several electrical energy storage cells. In the case of a vehicle traction battery, the battery also includes a positive conduction terminal and a negative conduction terminal connected to the vehicle's electric traction powertrain via a reversible voltage converter that combines a first battery voltage with a second voltage from the vehicle's electrical network. The battery also includes a first and a second electrical current interruption device.The first electrical current interruption device (typically an electromechanical relay) is connected in series between the positive conduction terminal of the electric battery and the first electrical energy storage module located at one end of the module assembly. The second electrical current interruption device (typically an electromechanical relay) is connected in series between the negative conduction terminal of the electric battery and the last electrical energy storage module located at the other end of the module assembly. These first and second electrical current interruption devices connect the electric battery to the vehicle's electric traction powertrain, thus supplying electrical power to the powertrain.

[0003] Thermal runaway in an electric battery, particularly a lithium-ion battery, is a well-known phenomenon in which a temperature rise within one or more battery cells triggers a series of chain reactions during which various internal components of the cell(s) are broken down. If the heat dissipated is less than the heat produced, these reactions continue, and the system becomes self-sustaining until a sudden and uncontrollable temperature rise occurs. Due to its sealed nature, the cell builds up pressure until it ruptures, releasing the electrolyte as very hot and flammable gases, generally leading to a fire with the emission of toxic fumes due to the presence of fluorinated compounds.

[0004] Systems exist that can detect the occurrence of such thermal runaway within an electrical storage battery, particularly within an electric vehicle battery. Some of these systems are configured to detect a sudden drop in the voltage of the current delivered by the electric battery.

[0005] Patent documents CN 110943261 A and JP 2013 076602 A describe, for example, such a detection system. The system comprises a first thermal runaway monitoring unit within a lithium-ion battery, where the conditions or risks of thermal runaway are monitored in real time using an algorithm tuned according to a temperature signal, an electrical voltage signal, and an electrical current signal from the battery. A second unit is also used to send an early warning signal of thermal runaway, and a third unit sends the information to a cloud-based computer network. Detection is performed by monitoring for any drop in electrical voltage during constant voltage and constant current charging of the battery.However, detecting such a voltage drop is not necessarily indicative of thermal runaway within the battery, as this voltage drop can be triggered by other reasons (such as the activation of certain electrically consuming devices within the vehicle). The detection provided by such a system is therefore unreliable.

[0006] Other systems are configured to detect a sudden increase in gas pressure at the battery. While the detection performed by these systems is relatively reliable, it occurs very late: by the time the system detects thermal runaway, the battery is already very close to catching fire. This poses problems in terms of battery protection and vehicle safety. Still other systems are based on measuring the temperature of the battery modules using one or more thermal sensors. However, the detection performed by these systems is unreliable because the thermal sensor is located on the outside of the module, while the battery's resistance and thermal capacity result in a much higher temperature inside the battery.However, the link between the measured temperature and the temperature inside the battery is unreliable due to the lack of thermal modeling of the battery. Other systems use fiber optic sensors embedded in the core of the electrical energy storage cells that make up the battery. However, such systems significantly impact battery manufacturing and are therefore not suitable for mass production.

[0007] Other known systems exist to protect the electric battery and its environment from such thermal runaway. In particular, within the framework of new standards relating to the detection of thermal runaway in an electric storage battery (such standards requiring that the vehicle user be warned of the onset of thermal runaway five minutes before the first smoke appears in the passenger compartment – ​​for example, via a warning on the vehicle's dashboard), it is known to add an intermediate electrical current interruption device between the first and second electrical current interruption devices (depending on the configuration of the electric battery), in order to more effectively interrupt the propagation of thermal runaway and thus meet or even exceed the relevant regulatory requirements.

[0008] A safe solution involves using an electromechanical relay to perform this function as an intermediate electrical current interruption device. The electromechanical relay is connected in series between two battery energy storage modules, and its operation is monitored by a battery management system (also known as a BMS). This solution ensures a degree of safety (because the relay is in a naturally open position to guarantee compliance with regulatory requirements, even when the battery management system is in sleep mode). The BMS is connected to the first and second electrical current interruption devices, the intermediate electrical current interruption device, and the reversible voltage converter.There is therefore a need to be able to reliably diagnose the "relay closed blocked" state for the intermediate electrical current interruption device, because such a configuration represents a direct loss of safety barrier for the system, and therefore a high risk of uncontrolled propagation of thermal runaway.

[0009] For the first and second electrical current interruption devices, the diagnoses of "relay open stuck" and "relay closed stuck" failure cases are usually carried out as follows: For the first electrical current interruption device: a comparison of the electrical voltages upstream and downstream of the relay. This solution involves two voltage measurements by the BMS system; for the second electrical current interruption device: a re-reading of the relay's state via the injection of an electrical current and the re-reading of the information to determine the relay's state.

[0010] However, the solutions mentioned above for diagnosing the relays of the first and second electrical current interruption devices are unsatisfactory for diagnosing the "closed blocked" state of the intermediate electrical current interruption device, for the following reasons: The solution of adding a voltage measurement downstream of the relay cannot work because the equivalent voltage will be seen in the same way whether the relay is open or closed: this voltage "passes" in fact through a device measuring the electrical voltages at the terminals of the electrical energy storage cells (belonging for example to a cell management controller component CMC, from the English "Cell Monitoring Controller"); the solution by injecting an electrical current, while it could work technically, requires the installation of new components in the BMS system management unit, implying an increase in the production costs of the system, and also requiring the passage of a wire carrying low voltage (therefore dangerous to humans) from the middle of the electric battery to the BMS system management unit, which represents a very strong constraint for the safety of the assembly.

[0011] The aim of the invention is to overcome the disadvantages of the prior art by proposing a method for detecting a blocked closed state of an intermediate electrical current interruption device arranged within an electric battery of an electric or hybrid vehicle, which is simple, safe and reliable, and which does not require the use of one or more additional component(s) or the addition of any safety constraints whatsoever on the assembly.

[0012] To this end, the invention relates, in its broadest sense, to a method for detecting a blocked closed state of an intermediate electrical current cut-off device of an electric vehicle battery, the electric battery comprising: the intermediate electrical current interruption device, a positive terminal and a negative terminal connected to a reversible voltage converter of the vehicle coupling a first voltage from the battery with a second voltage from a vehicle electrical network, a set of electrical energy storage modules connected in series, each electrical energy storage module comprising several electrical energy storage cells, the intermediate electrical current interruption device being connected in series between two intermediate electrical energy storage modules, a first electrical current interruption device connected in series between all the modules and the positive terminal, and a second electrical current interruption device connected in series between all the modules and the negative terminal, the vehicle further comprising an electric battery control unit and switching devices suitable for implementing the process and comprising a device for measuring the electrical voltages at the terminals of the electrical energy storage cells, the intermediate electrical current switching device and the first electrical current switching device being initially closed, the process performing the following successive steps: a converter operating command raising the electrical network voltage to a value slightly higher than that of the electric battery, for a predetermined voltage setpoint and for a predetermined duration, then during this duration: o a measurement of an electrical voltage value across the terminals of the intermediate electrical current interruption device, then o a comparison between the measured electrical voltage value on the one hand, and a predetermined voltage value on the other; then o depending on the result of the comparison, a determination of a blocked closed state of the intermediate electrical current interruption device, the predetermined voltage setpoint value being decomposed as a sum of a first predetermined voltage setpoint value and a second predetermined voltage setpoint value, the first predetermined voltage setpoint value being equal to the nominal voltage value of the electric battery, and the predetermined voltage value used during the comparison step is equal to the second predetermined voltage setpoint value, the electric battery control unit detecting a blocked closed state of the intermediate electric current cutting device if the electric voltage value measured across the terminals of the intermediate electric current cutting device is less than the predetermined voltage value, in particular if the electric voltage value measured across the terminals of the intermediate electric current cutting device is zero.

[0013] The method according to the invention offers a simple, safe, and reliable means of detection. Furthermore, by using a reversible voltage converter (in its boost or inverted mode) already present in any electric or hybrid vehicle's power supply system, the method according to the invention does not require the use of one or more additional components for detection, nor does it add any safety constraints to the assembly. This reduces manufacturing and development costs, while ensuring compliance with standards for detecting thermal runaway within the battery. This also improves the reliability of detecting the blocked closed state of the intermediate electrical current-cutting device.Indeed, the electrical voltage measured by the electrical voltage measuring device across the terminals of the intermediate electrical current-interrupting device is equal to the second predetermined voltage setpoint if and only if the intermediate electrical current-interrupting device is open. Otherwise, the process detects that the intermediate electrical current-interrupting device is in the closed, blocked state.

[0014] According to a particular technical feature of the invention, the second predetermined voltage setpoint value and / or the predetermined duration are calibrable by a user.

[0015] Preferably, the second predetermined voltage setpoint is +5V. This +5V value allows for optimal calibration of the closed-state detection of the intermediate current-cutting device, based on the accuracy of the voltage measurement on each current distribution bar connecting two battery modules (to ensure clear distinction between the open and closed states). Since the intermediate current-cutting device is connected between two battery modules on one of the current distribution bars, this +5V value, which corresponds to the maximum voltage on each current distribution bar, effectively maximizes the difference between the measured voltage for the open state and the measured voltage for the closed state. This further improves the reliability of the detection.

[0016] According to a particular technical feature of the invention, the method further comprises a sleep stage for the control unit, said sleep stage being performed based on the result of the comparison. This sleep stage is implemented, for example, if the electrical voltage measured across the terminals of the intermediate current-cutting device is equal to the predetermined voltage value. In this case, no fault of the type "intermediate relay in the closed, blocked state" is detected by the electric battery control unit.

[0017] According to another particular technical feature of the invention, the intermediate electrical current interruption element and the first and second electrical current interruption elements are electromechanical relays.

[0018] The following are examples of embodiments of the present invention, by way of non-limiting illustration, with reference to the accompanying figures in which: [ Fig.1 ] schematically illustrates an assembly comprising an electric battery of an electric or hybrid vehicle, the electric battery comprising a first electrical current interruption device, a second electrical current interruption device and an intermediate electrical current interruption device; Fig.2 ] is a flowchart representing a method for detecting a blocked closed state of the intermediate electrical current interruption device of the figure 1 according to the present invention; and [ Fig.3 ] is a set of four diagrams, three of these diagrams representing respectively the evolution, as a function of time, of the open or closed state of the first and second electrical current interruption devices and the intermediate electrical current interruption device, according to different phases of the process of the figure 2 The fourth diagram represents the evolution, as a function of time, of an electrical voltage measured across the terminals of the intermediate electrical current interruption device, according to different phases of the process. figure 2 .

[0019] By referring to the figure 2 The present invention relates to a method for detecting a blocked closed state of an intermediate electrical current interruption device arranged within an electric vehicle battery (particularly an electric or hybrid vehicle). The electric battery is a traction battery of the electric or hybrid vehicle, in particular a lithium-ion battery. On the figure 1 An electric battery 2 and an assembly 4 installed in a vehicle (not shown) are depicted. The assembly 4 includes a converter 6 that transforms a first DC voltage into a second DC voltage, and a control unit 8 for the electric battery 2. The control unit 8 includes a device 10 for measuring the electrical voltages across the terminals of the electrical energy storage cells of the electric battery 2.

[0020] The electric battery 2, for example, comprises a housing (not shown) containing a set of electrical energy storage modules 12 connected in series. Each electrical energy storage module 12 typically comprises several electrical energy storage cells (such cells are not shown in the figures for clarity). The electric battery 2 also comprises a positive conduction terminal 14A, a negative conduction terminal 14B, a first electrical current interruption device 16A, a second electrical current interruption device 16B, and an intermediate electrical current interruption device 18. Preferably, as illustrated in the figure 1 , the electric battery also includes an electromechanical relay 19 for pre-charging the first electrical current cutting device 16A.

[0021] The positive and negative conduction terminals 14A and 14B are connected to the vehicle's electric traction powertrain (not shown) via the converter 6, which converts a first DC voltage to a second DC voltage. The electric battery 2 provides a power supply circuit to the electric powertrain, with a nominal voltage, for example, of 300 V. The first electrical current-cutting device 16A is connected in series between the positive conduction terminal 14A and a first electrical energy storage module 12A located at one end of the module assembly 12. The second electrical current-cutting device 16B is connected in series between the negative conduction terminal 14B and a second electrical energy storage module 12B located at the other end of the module assembly 12.The first and second electrical current-cutting devices 16A, 16B allow the electric battery 2 to be electrically connected to the vehicle's electric traction powertrain, thus supplying electrical power to the electric powertrain. The intermediate electrical current-cutting device 18 is connected in series between two electrical energy storage modules 12, preferably between two intermediate electrical energy storage modules 12C, 12D. The first and second electrical current-cutting devices 16A, 16B and the intermediate electrical current-cutting device 18 each have two states: an open state and a closed state. In the particular embodiment illustrated in Figure 1. figure 1 The first and second electrical current-cutting devices 16A, 16B and the intermediate electrical current-cutting device 18 are electromechanical relays. The electromechanical pre-charge relay 19 is connected in parallel with the first electrical current-cutting device 16A.

[0022] Converter 6 is a reversible voltage converter that combines a first voltage from battery 2 with a second voltage from the vehicle's electrical network. Converter 6 is capable of operating alternately in step-down or step-up mode. In its step-down mode, converter 6 reduces the voltage of a direct current from battery 2 (for powering the electric drivetrain), and in its step-up mode, it increases the voltage of a direct current intended to recharge battery 2 (such a current being, for example, from a low-voltage auxiliary battery in the vehicle, typically a battery with a nominal voltage of approximately 12 V or 48 V).

[0023] The control unit 8 for the electric battery 2 is also capable of controlling the switching devices 16A, 16B, and 18. The control unit 8 is, for example, a BMS (Battery Management System) for the electric battery 2. The control unit 8 is connected to the intermediate switching device 18 and to the first and second switching devices 16A and 16B, for their opening and closing control. The control unit 8 is also connected to the converter 6, which converts a first DC voltage to a second voltage. The control unit 8 is further configured to directly measure the voltage between the first switching device 16A and the second switching device 16B. The control unit 8 is, for example, in the form of a dedicated integrated circuit.

[0024] The voltage measurement device 10, which measures the electrical voltages across the electrical energy storage cells of the battery 2, is specifically configured to measure (or approximate) the electrical voltage U1 across the intermediate electrical current interruption device 18, by measuring the voltage difference between the two electrical energy storage cells closest to the intermediate electrical current interruption device 18. These two cells belong to separate electrical energy storage intermediate modules 12C-12D. The measurement of the electrical voltage U1 across the intermediate electrical current interruption device 18, performed by the voltage measurement device 10, is therefore an indirect voltage measurement.The electrical voltage measurement unit 10 belongs, for example, to one or more cell monitoring controller (CMC) components. Each CMC component (not shown in the figures) enables balancing of the modules 12 of the electrical battery 2, as well as temperature regulation of the modules 12. Each CMC component is, for example, in the form of a dedicated integrated circuit.

[0025] During an initial phase 20 (visible on the figure 3 ), the intermediate electrical current-cutting device 18 and the first electrical current-cutting device 16A are closed. This initial phase 20 of the intermediate electrical current-cutting device 18 and the first electrical current-cutting device 16A is illustrated on curves C1 and C2 of the figure 3 (which represent the closed state "1" or open state "0" of the intermediate electrical current-cutting device 18 and the first electrical current-cutting device 16A, as a function of time). At the end of the initial phase 20, the intermediate electrical current-cutting device 18 and the first electrical current-cutting device 16A are triggered to open by the control unit 8. The first electrical current-cutting device 16A then opens (and the pre-charge relay 19 closes), which is illustrated on curve C2 of the figure 3 (and on a C3 curve representing the closed state "1" or open state "0" of the pre-charge relay 19).

[0026] As illustrated on the figure 2 The detection method preferably includes a first step 22 in which the control unit 8 detects a predefined voltage value between the first electrical current-interrupting device 16A and the second electrical current-interrupting device 18A. The predefined voltage value is, for example, zero (i.e., equal to 0 V). This first detection step 22 initializes the method.

[0027] The method includes a subsequent step 24 in which the control unit 8 transmits to the converter 6 a command to operate the converter 6 in its boost mode, at a predetermined voltage setpoint and for a predetermined duration. The converter 6 then increases, for the predetermined duration, the voltage of a direct current intended to electrically recharge the electric battery 2 (such current being, for example, from a low-voltage auxiliary battery of the vehicle, typically a battery with a nominal voltage of approximately 12 V or 48 V), the voltage being increased to the predetermined voltage setpoint. According to a preferred embodiment of the invention, the predetermined voltage setpoint is decomposed as a sum of a first predetermined voltage setpoint and a second predetermined voltage setpoint.The first predetermined voltage setpoint is equal to the nominal voltage of the electric battery (e.g., 300 V). Preferably, the second predetermined voltage setpoint is +5 V. The second predetermined voltage setpoint and / or the predetermined duration are advantageously user-configurable.

[0028] The process executes steps 26, 28, 30, 32 during the predetermined duration.

[0029] More specifically, the method includes a subsequent step 26 in which the voltage measuring device 10 measures the voltage value U1 across the intermediate current-interrupting device 18 by measuring the voltage difference between the two electrical energy storage cells closest to the intermediate current-interrupting device 18, the two cells belonging to separate electrical energy storage intermediate modules 12C-12D. Following step 26, the voltage measuring device 10 transmits the measured voltage value U1 to the control unit 8.

[0030] The method includes a subsequent step 28 in which the control unit 8 compares the electrical voltage value U1 measured across the terminals of the intermediate electrical current-interrupting device 18 to a predetermined voltage value. According to the preferred embodiment of the invention mentioned above, the predetermined voltage value is equal to the second predetermined voltage setpoint value. Therefore, the predetermined voltage value is preferably +5V in the preferred embodiment.

[0031] According to the preferred embodiment of the invention mentioned above, if the electrical voltage value U1 measured across the terminals of the intermediate electrical current-cutting device 18 is less than the predetermined voltage value (in other words, the second predetermined voltage setpoint value), in particular if this measured voltage value U1 is zero, then the method includes a subsequent step 30 in which the control unit 8 detects a blocked closed state of the intermediate electrical current-cutting device 18. A "fault" alert is then, for example, sent by the control unit 8 to a monitoring system for the vehicle's electronic components (not shown).

[0032] If the electrical voltage value U1 measured across the terminals of the intermediate electrical current-interrupting device 18 is equal to the predetermined voltage value (in other words, the second predetermined voltage setpoint), then no fault is detected by the control unit 8 (which means that the intermediate electrical current-interrupting device 18 is indeed in its "open" state, in accordance with the initial command issued during phase 20 by the control unit 8). The process then includes a step 32 during which the control unit 8 puts itself into sleep mode. This situation is illustrated on curve C1 of the figure 3This shows that the intermediate current-interrupting device 18 is indeed in its "open" state at the time of step 28. Curve C4 represents the evolution, as a function of time, of the electrical voltage U1 measured across the terminals of the intermediate current-interrupting device 18. On this curve C4, it can be seen that, during the comparison step 28 of the process, the electrical voltage U1 measured across the terminals of the intermediate current-interrupting device 18 is equal to +5V (in other words, the predetermined voltage value). This allows the control unit 8 to detect that the intermediate current-interrupting device 18 is indeed in its "open" state. Otherwise (not shown), curve C4 is flat and located at the 0V level, which indicates that the intermediate current-interrupting device 18 is in the closed, blocked state.

[0033] The method according to the invention is simple, safe and reliable, reduces costs and does not require the use of one or more additional component(s) or adding any safety constraints to the assembly.

Claims

1. Method for detecting a stuck closed state of an intermediate electric current interruption device (18) of an electric battery (2) of a vehicle, the electric battery (2) comprising: - the intermediate electric current interruption device (18), - a positive terminal (14A) and a negative terminal (14B) connected to a reversible voltage converter (6) of the vehicle coupling a first voltage of the battery with a second voltage of an electrical network of the vehicle, - a set of electrical energy storage modules (12, 12A-12D) connected in series, each electrical energy storage module (12, 12A-12D) comprising a plurality of electrical energy storage cells, the intermediate electric current interruption device (18) being connected in series between two intermediate electrical energy storage modules (12C-12D), a first electric current interruption device (16A) connected in series between the set of modules and the positive terminal (14A), and - a second electric current interruption device (16B) connected in series between the set of modules and the negative terminal (14B), the vehicle further comprising a control unit (8) of the electric battery (2) and of the interruption devices (18, 16A) suitable for implementing the method and comprising a device (10) for measuring the electrical voltages at the terminals of the electrical energy storage cells, the intermediate electric current interruption device (18) and the first electric current interruption device (16A) being initially closed during an initial phase (20) of the method, the intermediate electric current interruption device (18) and the first electric current interruption device (16A) being controlled to open by the control unit (8) at the end of the initial phase (20), characterized in that the method executes the following successive steps: - a control of operation of the converter (6) increasing the voltage of the electric battery (2) to a predetermined voltage setpoint value and for a predetermined duration, then during this duration: ∘ a measurement (26) of an electrical voltage value (U1) at the terminals of the intermediate electric current interruption device (18), then ∘ a comparison (28) between the measured electrical voltage value (U1) on the one hand, and a predetermined voltage value on the other hand; then depending on the result of the comparison (28), a determination (30) of a stuck closed state of the intermediate electric current interruption device (18), the predetermined voltage setpoint value being decomposed as a sum of a first predetermined voltage setpoint value and a second predetermined voltage setpoint value, the first predetermined voltage setpoint value being equal to the nominal voltage value of the electric battery (2), and in that the predetermined voltage value used during the comparison step (28) is equal to the second predetermined voltage setpoint value, the control unit (8) detecting (30) a stuck closed state of the intermediate electric current interruption device (18) if the electrical voltage value (U1) measured at the terminals of the intermediate electric current interruption device (18) is lower than the predetermined voltage value, in particular if the electrical voltage value (U1) measured at the terminals of the intermediate electric current interruption device (18) is zero.

2. Method according to claim 1, characterized in that the second predetermined voltage setpoint value and / or the predetermined duration are calibratable by a user.

3. Method according to claim 1 or 2, characterized in that the second predetermined voltage setpoint value is equal to +5 V.

4. Method according to any one of claims 1 to 3, characterized in that the method further comprises a step (32) of putting the control unit (8) into sleep mode, said sleep step (32) being carried out depending on the result of the comparison (28).

5. Method according to any one of claims 1 to 4, characterized in that the intermediate electric current interruption device (18) and the first and second electric current interruption devices (16A, 16B) are electromechanical relays.