Method for detecting an electric arc fault for a battery system

Abstract

The present invention relates to a method for detecting an electric arc for a battery system (10) and comprising a step of determining a value of the operating voltage (VB) at the terminal terminals (2) of the battery system (10) and a value of the current (IB), further comprising the following steps of calculating a first ratio corresponding to a first voltage difference divided by the value of the operating voltage (VB) and a second ratio corresponding to a second difference divided by the value of the current (IB), monitoring a first detection criterion consisting of verifying whether the first ratio is equal to the second ratio and, a second detection criterion, whether the first voltage difference is greater than a first predetermined threshold, and generating an alert of an electric arc fault in the event of detection of the first and second criteria simultaneously. Figure 1.

Description

Title of the invention: Method for detecting an electric arc fault for a battery system

[0001] The field of the invention relates to the electrical protection of a battery system against electric arc faults.

[0002] Power battery systems, particularly for electrified vehicles, typically comprise a set of energy storage elements mounted in series and / or parallel in the system. The term energy storage element refers to an electrochemical cell or an assembly of cells forming a module. Typically, an electrical connection between two cells is made by means of screwed electrical connections whose function is to ensure that the connection is maintained in a vibration-constrained environment. A screwed connection is generally formed from a flexible or rigid conductive element (cable or busbar) and a coupling means by bolt or pressure tightening.

[0003] If a connection becomes partially loosened, this leads to an increase in resistance and an abnormal rise in temperature. If a complete loosening occurs while current is flowing through it, an electric arc may occur within the battery system, which would have the effect of generating a high heat dissipation, which could reach 4000 watts very locally, or even cause a projection of incandescent material. We seek to provide protection against these failures, in particular series electric arcs occurring in a high-voltage current line.

[0004] A solution is known which aims to integrate dedicated voltage measurements specific to the terminals of each targeted connection and the associated connector. In the presence of a current, the resistance of the connection is calculated in real time in order to detect an abnormal variation in its value. This solution, due to the high number of connections and sensors, increases the risk of failure. Another solution is the measurement of the temperature locally in a contact zone of a targeted connection at the level of an electrochemical cell. This solution is well suited to detecting a partial loosening, however the reactivity of the diagnosis is insufficient to stop an electric arc in the event of sudden complete loosening.

[0005] An alternative technique is known which consists of measuring the operating voltage at the terminal terminals of a battery system and, simultaneously, calculating the sum of the individual voltages measured for each storage cell or module. Detection is based on the comparison of these two values to signal a fault in the event of the presence of an abnormal voltage variation caused by an arc. electrical, identifiable by a voltage drop in the presence of a current in the module connection connectors and screw connections.

[0006] The signature of an electric arc corresponds to a voltage drop of the order of approximately 20 volts. However, for a consumer product comprising a battery system consisting of one or several hundred cells, the inaccuracy of the individual voltage measurements, which is of the order of approximately 5 millivolts per measurement, generates an uncertainty of the order of ten volts or more. In addition, the determination of the operating voltage at the terminals of a high-voltage battery system also has an inaccuracy of the order of approximately 10 volts to 20 volts for a 400-volt to 800-volt system. In addition to these measurements, there is also that of the current sensor which can have an inaccuracy of the order of approximately 0.1 ampere. The performance of the estimation of the voltage drop of the arc cannot therefore be better than approximately ±33 volts.To avoid false detections, it is therefore necessary to calibrate the detection thresholds to higher values, generally calibrated at around 40 volts or 50 volts. However, the detection performance is not satisfactory to trigger the relay opening protection quickly enough to prevent the creation of an arc.

[0007] Document WO2022152199A1 is known from the prior art and describes a method for detecting an electric arc for a battery system configured to implement a diagnosis based on the measurement of voltage and current signals of the battery system and the implementation of a time and frequency analysis of the signals, which is based on the search for eigenvalues in an equation system. The result of the analysis is then compared with a reference signature characteristic of an electric arc to determine the presence or absence of an electrical fault. This solution has the disadvantage of requiring significant and particularly energy-intensive computing resources, making it unsuitable for on-board electronic systems used for motor vehicles on the consumer market.

[0008] There is therefore a need to overcome the aforementioned problems. One objective of the invention is to improve the electrical protection of battery systems against electric arcs likely to occur in the event of failure of an internal electrical connection of a current line or connecting electrochemical cells. It is sought to propose a low-cost detection function for a battery system intended for a consumer market. Another objective is to design a sufficiently efficient electric arc fault diagnostic calibration while discriminating against cases of false detection.

[0009] More specifically, the invention relates to a method of detecting an electric arc for a battery system comprising a plurality of energy storage elements. electrically connected in series and comprising a step of determining at least two different times a value of the operating voltage at the terminal terminals of the battery system and a value of the current of the battery system to determine at least a first voltage difference and a second current difference between at least the two times.

[0010] According to the invention, the method further comprises the following steps of calculating a first ratio corresponding to the first voltage difference divided by the value of the operating voltage and a second ratio corresponding to the second difference divided by the value of the current, monitoring a first detection criterion consisting of verifying whether the first ratio is equal to the second ratio and, of a second detection criterion, whether the first voltage difference is greater than a first predetermined threshold and generating an alert of an electric arc fault in the event of detection of the first and second criteria simultaneously.

[0011] The method according to the invention may include the following additional characteristics, alone or in combination:

[0012] - Calculating a value of the sum of the voltages of each storage element of the battery system for determining a third voltage difference between the value of said sum of the voltages and the voltage value at the terminal terminals of the battery system, monitoring a third detection criterion consisting of checking whether the third difference is greater than a second predetermined threshold, and generating the alert only in the event of detection of the first, second and third criteria simultaneously.

[0013] - The second threshold is between 10 and 25 volts.

[0014] - The first threshold is between 10 and 25 volts.

[0015] - The duration between the two different instants is between 10 and 100 milli seconds.

[0016] There is further provided a battery system comprising a plurality of energy storage elements electrically connected in series comprising means configured to determine at at least two different times a value of the operating voltage at the terminal terminals of the battery system and a value of the current of the battery system and to determine at least a first voltage difference and a second current difference between at least the two times further comprising means configured to calculate a first ratio corresponding to the first voltage difference divided by the value of the operating voltage and a second ratio corresponding to the second difference divided by the value of the current, to monitor a first detection criterion consisting of verifying whether the first ratio is equal to the second ratio and, a second detection criterion, whether the first voltage difference is greater than a first predetermined threshold,and to generate an alert of an arc fault, electrical in case of detection of the first and second criteria simultaneously.

[0017] According to a variant, the system further comprises means configured to calculate a value of the sum of the voltages of each storage element of the battery system to determine a third voltage difference between the value of said sum of the voltages and the voltage value at the terminal terminals of the battery system, to monitor a third detection criterion consisting of verifying whether the third difference is greater than a second predetermined threshold, and to generate the alert only in the event of detection of the first, second and third criteria simultaneously.

[0018] An electrified vehicle comprising such a battery system is further provided.

[0019] Further provided is a control unit for a battery system comprising means specifically configured to implement any of the embodiments of the detection method according to the invention.

[0020] There is further provided a computer program product comprising instructions which, when the program is executed by a control unit of a battery system, cause the latter to implement any one of the embodiments of the detection method according to the invention.

[0021] Further provided is a computer-readable recording medium comprising instructions which, when executed by a computer, cause the computer to implement any one of the embodiments of the detection method according to the invention.

[0022] The invention provides a software solution adapted to sensors commonly used in automotive vehicle battery systems for detecting and protecting a vehicle against series arc faults that may occur in a vehicle power line. The invention avoids the need for precision metrological equipment while avoiding cases of false detection that may arise from measurement inaccuracies. The invention is a low-cost protection solution.

[0023] Other characteristics and advantages of the present invention will appear more clearly on reading the detailed description which follows, comprising embodiments of the invention given as non-limiting examples and illustrated by the appended drawings, in which:

[0024] [Fig.l] schematically represents a battery system according to the invention capable of implementing the series electric arc detection method.

[0025] [Fig.2] schematically represents by a functional block diagram an embodiment of the detection method.

[0026] [Fig.3] schematically represents an application of the invention for an electrified vehicle.

[0027] The invention applies to electrified vehicles, i.e. vehicles comprising a system battery, an electric motor machine and power electronics, 100% electric or hybrid, preferably motor vehicles, but not only such as aircraft, tractors, bicycles, ships. More generally, the invention applies to any autonomous electrical system in electromobility or stationary applications, such as drones, robots or portable devices, computers, tablets, mobile phones, consoles, cameras, scanners, photovoltaic stations or wind turbines which are cited as a non-exhaustive list of application examples.

[0028] The invention relates to a method for detecting an electric arc for a battery system. A preferred application relates to high-voltage battery systems for electromobility solutions, used in an operating range between 48 volts and 1000 volts, for example 400 volts or 800 volts, in which a series electric arc is likely to occur in the event of a failure of an inter-cell electrical connection or of an electrical element connected in the line between the battery and the electrical loads.

[0029] In [Fig. 1], a battery system 10 is shown schematically and is provided for implementing the detection method according to the invention. The battery system 10 comprises a storage assembly 1 comprising a plurality of energy storage elements electrically arranged in several storage modules Ml to Mn connected by electrical connections 4. The electrical connections 4 are for example busbars associated with screwed connections of the bolt type. Their function is to maintain the conductive elements in contact forming the electrical connection with sufficient mechanical pressure to minimize resistance and guarantee this contact over time in a stressful vibration environment, in particular. The electrical connections may be of another type, for example by pressure or magnetically. The storage modules Ml to Mn may be connected in series and / or parallel. The storage assembly 1 may comprise at least one storage element.More precisely, each storage module Ml to Mn has a voltage VM1 to VMn respectively which can be measured and determined in real time at any time by one or more dedicated sensors.

[0030] In the present description, an electrochemical cell is an electrical energy accumulator having two terminals and having a voltage of a few volts, most often between 2.3V and 4.2V, approximately. The cells can be of the Lithium-ion type (a lithium Nickel Manganese Cobalt oxide NMC or a lithium iron phosphate LFP can be cited as examples of positive electrode active materials), Nickel Cadmium (Ni-cd), Nickel-Metal-Hydride (Ni-MH) for example. More precisely, a Lithium-ion cell is composed mainly of a porous positive electrode, a porous negative electrode, a separator and an electrolyte (which can be liquid, polymeric or solid).

[0031] Furthermore, the storage assembly 1 is electrically connected to a current line of a voltage bus by terminal terminals 2 of the battery system delivering the operating voltage VB of the storage assembly 1 of the battery system 10. The terminal terminals 2 are the voltage interfaces with the high voltage bus connected to an electrical load. One or more electrical interfaces are provided to connect the battery system 10 to one or more voltage buses. The voltage VB is in this example between 48 volts and 1000 volts depending on the desired electrical specifications. The voltage VB is designated as the operating voltage of the battery system 10 delivered by the storage assembly 1 to the terminals 2 and can be determined in real time at any time by the battery system 10, for example by voltage sensor measurement or indirectly by the voltage difference measured on each terminal 2.

[0032] A current branch 6 of the battery system 10 connected to the terminals 2 comprises a current sensor 5 whose function is to measure and determine in real time at each instant a charging and discharging current value IB during operation of the battery system 10. The current branch 6 further comprises at least one controllable switch 7, for example of the high-voltage relay or contactor type, whose function is to connect / disconnect the storage assembly 1 to the terminals 2. Conventionally, the current line 6 further comprises one or more electrical protection elements 9, such as for example a fuse or relay, where each element 9 is connected to the current line by a screwed electrical connection.

[0033] Furthermore, the battery system 10 comprises a control unit 3 (commonly designated by the acronym ECU for “Electronic Control Unit”, BMS for “Battery Management System” or TBCU for “Traction Battery Control Unit” for an electrified vehicle) provided to supervise the parameters specific to the battery in cooperation with the current and voltage sensors, such as the operating voltage VB, the charge and discharge current IB and the individual voltages VM1 to VMn. The control unit 3 is further provided to control the opening and closing of the switch(es) 7 by means of an electric arc detection function 8 implementing the method according to the invention, in particular. Furthermore, the control unit 3 is adapted for the supervision of the battery system 10 and the cooperation with the external electrical systems.

[0034] More specifically, the detection function 8 controls one or more control signals CR intended to open and close each switch 7 in order to isolate the battery system from the electrical systems. The detection function 8 is further capable of delivering to other external computers a signal or information of an alert of an electric arc fault, in particular. The detection function 8 is intended to determine, by a digital measurement or calculation of analog measurements, at at least two instants different a value of the operating voltage at the terminal terminals of the battery system and a value of the current of the battery system to determine at least a first voltage difference and a second current difference between at least the two instants. This makes it possible to detect a characteristic signature of an electrical series arc occurring at the level of the internal targeted electrical connections of the storage element 1. For this purpose, the detection function 8 is able to calculate a first ratio corresponding to the first voltage difference divided by the value of the operating voltage and a second ratio corresponding to the second difference divided by the value of the current. The detection function 8 is able to implement monitoring of a first detection criterion consisting of verifying whether the first ratio is equal to the second ratio and, of a second detection criterion, whether the first voltage difference is greater than a first predetermined threshold.Finally, the detection function is able to generate an alert of an electric arc fault depending on the monitoring result.

[0035] The ratio comparison is based on a fully software-based and therefore low-cost detection solution, and is also capable of being implemented by a computer used in a consumer product, such as an electrified motor vehicle.

[0036] Optionally, to improve the robustness of the monitoring, the detection function 8 is capable of calculating the sum of voltages VM1 to VMn of each energy storage element of the plurality of storage elements of the battery system to determine a third voltage difference between the value of said sum of the voltages and the voltage value VB at the terminal terminals 2 of the battery system and to check whether the third difference is greater than a second predetermined threshold. The values of the first and second thresholds are recorded in memories of the control unit 3 of the battery system.

[0037] In [Fig.2], the detection method according to the invention is described. The detection method is implemented by the control unit of a battery system, which is equipped with an integrated circuit computer and electronic memories. But this is not obligatory. Indeed, the computer could be external to the control unit, while being coupled to the latter. In the latter case, it can itself be arranged in the form of a dedicated computer including a possible dedicated program, for example. Consequently, the control unit, according to the invention, can be produced in the form of software modules (or computer software), or electronic circuits (or hardware), or a combination of electronic circuits and software modules.

[0038] In an initial phase 20, the battery system is started, in an operating state and connected to a current line. The battery system is in a state in which a charging or discharging current flows in the cells of storage.

[0039] The detection method comprises a first step 21 of determining at least two different times a value of the operating voltage VB at the terminal terminals of the battery system and a value of the current IB of the battery system to determine at least a first voltage difference AVB and a second current difference AIB between at least the two times. The voltage values VB and IB are measured or determined digitally from analog measurements and are recorded in the memory of the control unit. The sampling period between two times is between 10 milliseconds and 100 milliseconds, for example is equal to 10 milliseconds, 20 milliseconds, 50 milliseconds, 80 milliseconds or 100 milliseconds. The period has a duration adapted so that the electrical protection is sufficiently reactive to prevent an electric arc early.

[0040] In addition, the detection method comprises a second step 22 of calculating a first ratio AVB / VB corresponding to the first voltage difference divided by the value of the operating voltage VB and a second ratio AIB / IB corresponding to the second difference divided by the value of the current IB. VB and IB are one or the other value of the last samples VB and IB or of the penultimate samples recorded in the memory of the control unit. These two ratios make it possible to identify a characteristic signature of an electric arc which corresponds to an equal variation of the two ratios between two samples.

[0041] Indeed, it is considered that a series arc in a battery system behaves in a simplified manner as a counter-electromotive force of approximately 20 volts. It is further considered that between two sampling instants the voltages of the storage elements over a period of between 10 milliseconds and 100 milliseconds do not vary before and after the instant of creation of an electric arc. Similarly, the load resistance of the voltage network does not vary greatly over this duration. This implies that only when an electric arc is created, the relative variation of the current of the battery system is equal to the relative variation of the operating voltage of the battery system. Monitoring these two ratios and comparing them thus makes it possible to identify the creation of a series electric arc in a battery system current line.

[0042] Alternatively, the detection method comprises a third step 23 of calculating a value of the sum of the voltages of each storage element of the battery system, expressed by the following formula r), where VMk is the individual voltage of a storage element of index k among the plurality N of elements connected in series in the battery system, to determine a third voltage difference between the value of said sum of the voltages and the voltage value at the terminal terminals of the battery systems. The third gap is expressed by the following formula: (

[0043] This variable improves the robustness of the detection function, because it allows the creation of the counter-electromotive force to be verified. The third step 23 remains optional.

[0044] Furthermore, the detection method comprises a fourth monitoring step 24 consisting of verifying at least two detection criteria C1 and C2. The first criterion C1 consists of verifying whether the first ratio AVB / VB is equal to the second ratio AIB / IB, at least substantially equal within a margin of less than 10%. The second criterion C2 consists of verifying whether the first voltage difference AVB is greater than a first predetermined threshold SI whose value is between 10 volts and 25 volts, for example approximately 15 volts or 20 volts preferably. If these two criteria are observed simultaneously, this event is characteristic and solely attributable to the creation of a series electric arc. In the event of the occurrence of such an event, the method controls a fifth step 25 of generating an alert for an electric arc fault.

[0045] Alternatively, the monitoring 24 further verifies whether the current is a discharge or charge current. The detection is validated only in a battery system discharge situation or in a charge situation only. This optional criterion makes it possible to customize the activation of the detection function in a specific situation with detection thresholds adapted to each situation.

[0046] As a variant, the monitoring 24 further verifies a third criterion C3, consisting of verifying whether the third deviation (yA VMk is greater than a second pre-determined threshold S2, where S2 is between 10 volts and 25 volts. The generation of the alert 25 is triggered only in the event of detection of the first, second and third criteria simultaneously.

[0047] More specifically, the fifth step 25 comprises the opening of relays of the battery system thus allowing the current to be cut off and the storage elements to be protected. The fifth step further comprises the creation of a fault alert for recording in the memory of the battery system control unit and / or in an external diagnostic log.

[0048] If the fault detection criteria are not recognized, then the detection method returns to the first step 21 in order to carry out a new voltage and current measurement.

[0049] In [Fig. 3], a preferred application of the invention for an electrified motor vehicle 30 is shown schematically. The vehicle may have a fully electric or hybrid engine. The vehicle comprises a battery system of traction 31 according to the invention, an electric motor machine 32, power electronics 34 and, not necessarily, an on-board charging device 35. A high-voltage voltage bus 33 electrically connects the power electronics and the battery system 31. The battery system 31 is configured to implement the series electric arc detection method according to the invention. Other applications are conceivable, such as for example a stationary electrical system comprising a battery system according to the invention.

[0050] The invention is described in the above by way of example. It is understood that the person skilled in the art is able to produce different variant embodiments of the invention by associating, for example, the different characteristics above taken alone or in combination, without departing from the scope of the invention.

Claims

Claims

1. Method for detecting an electric arc for a battery system (10) comprising a plurality of energy storage elements (1) electrically connected in series and comprising a step of determining (21) at at least two different times a value of the operating voltage (VB) at the terminal terminals (2) of the battery system and a value of the current (IB) of the battery system (10) to determine at least a first voltage difference and a second current difference between at least the two times, characterized in that it further comprises the following steps: - calculating (22) a first ratio corresponding to the first voltage difference divided by the value of the operating voltage (VB) and a second ratio corresponding to the second difference divided by the value of the current (IB), - monitoring (24) a first detection criterion (Cl) consisting of verifying whether the first ratio is equal to the second ratio and,of a second detection criterion (C2), if the first voltage difference is greater than a first predetermined threshold (SI), - the generation (25) of an alert of an electric arc fault in the event of detection of the first and second criteria (Cl, C2) simultaneously.,

2. Method according to claim 1 further comprising: - calculating (23) a value of the sum of the voltages of each storage element (Ml, Mn) of the battery system (10) to determine a third voltage difference between the value of said sum of the voltages and the voltage value (VB) at the terminal terminals (2) of the battery system (10), - monitoring (24) a third detection criterion (C3) consisting of checking whether the third difference is greater than a second predetermined threshold (S2), - generating (25) the alert only in the event of detection of the first, second and third criteria simultaneously.

3. The method of claim 2, wherein the second threshold (S2) is between 10 and 25 volts.

4. Method according to any one of claims 1 to 3, in which the first threshold (SI) is between 10 and 25 volts.

5. A method according to any one of claims 1 to 4, wherein the duration between the two different times is between 10 and 100 mil- seconds.

6. Battery system (10) comprising a plurality of energy storage elements (1) electrically connected in series comprising configured means (8) for determining at least two different times a value of the operating voltage (VB) at the terminal terminals (2) of the battery system and a value of the current (IB) of the battery system and for determining at least a first voltage difference and a second current difference between at least the two times, characterized in that it further comprises configured means (8): - for calculating a first ratio corresponding to the first voltage difference divided by the value of the operating voltage (VB) and a second ratio corresponding to the second difference divided by the value of the current (IB), - for monitoring a first detection criterion (Cl) consisting of verifying whether the first ratio is equal to the second ratio and, a second detection criterion (C2),if the first voltage difference is greater than a first predetermined threshold (SI), - and to generate an alert of an electric arc fault in the event of detection of the first and second criteria (Cl, C2) simultaneously.,

7. Battery system according to claim 6, further comprising configured means (8): - to calculate a value of the sum of the voltages of each storage element (Ml, Mn) of the battery system (10) to determine a third voltage difference between the value of said sum of the voltages and the voltage value (VB) at the terminal terminals (2) of the battery system (10), - to monitor a third detection criterion (C3) consisting of checking whether the third difference is greater than a second predetermined threshold (S2), - and to generate the alert only in the event of detection of the first, second and third criteria (Cl, C2, C3) simultaneously.

8. An electrified vehicle (30) comprising a battery system (31) according to claim 6 or 7.

9. Control unit (3) of a battery system (10) comprising means (8) specifically configured to implement the detection method according to any one of claims 1 to 5.

10. A computer program product comprising instructions which, when the program is executed by a control unit (3) of a battery system (10), causing the latter to implement the detection method according to any one of claims 1 to 5.

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