WO2021089700A1 - Arrangement and method for detecting malfunction in a battery - Google Patents

Arrangement and method for detecting malfunction in a battery Download PDF

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Publication number
WO2021089700A1
WO2021089700A1 PCT/EP2020/081137 EP2020081137W WO2021089700A1 WO 2021089700 A1 WO2021089700 A1 WO 2021089700A1 EP 2020081137 W EP2020081137 W EP 2020081137W WO 2021089700 A1 WO2021089700 A1 WO 2021089700A1
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Prior art keywords
battery assembly
flight
time
enclosure
sensor arrangement
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Application number
PCT/EP2020/081137
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French (fr)
Inventor
Erik Cardelius
Original Assignee
Northvolt Ab
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Publication of WO2021089700A1 publication Critical patent/WO2021089700A1/en

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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
    • G01N29/44—Processing the detected response signal, e.g. electronic circuits specially adapted therefor
    • G01N29/4409—Processing the detected response signal, e.g. electronic circuits specially adapted therefor by comparison
    • G01N29/4436—Processing the detected response signal, e.g. electronic circuits specially adapted therefor by comparison with a reference signal
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
    • G01R31/36—Arrangements for testing, measuring or monitoring the electrical condition of accumulators or electric batteries, e.g. capacity or state of charge [SoC]
    • G01R31/367—Software therefor, e.g. for battery testing using modelling or look-up tables
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N25/00—Investigating or analyzing materials by the use of thermal means
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
    • G01N29/02—Analysing fluids
    • G01N29/024—Analysing fluids by measuring propagation velocity or propagation time of acoustic waves
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
    • G01N29/22—Details, e.g. general constructional or apparatus details
    • G01N29/222—Constructional or flow details for analysing fluids
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
    • G01N29/22—Details, e.g. general constructional or apparatus details
    • G01N29/24—Probes
    • G01N29/2406—Electrostatic or capacitive probes, e.g. electret or cMUT-probes
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
    • G01N29/22—Details, e.g. general constructional or apparatus details
    • G01N29/24—Probes
    • G01N29/2437—Piezoelectric probes
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
    • G01N29/22—Details, e.g. general constructional or apparatus details
    • G01N29/32—Arrangements for suppressing undesired influences, e.g. temperature or pressure variations, compensating for signal noise
    • G01N29/326—Arrangements for suppressing undesired influences, e.g. temperature or pressure variations, compensating for signal noise compensating for temperature variations
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
    • G01N29/44—Processing the detected response signal, e.g. electronic circuits specially adapted therefor
    • G01N29/4409—Processing the detected response signal, e.g. electronic circuits specially adapted therefor by comparison
    • G01N29/4427—Processing the detected response signal, e.g. electronic circuits specially adapted therefor by comparison with stored values, e.g. threshold values
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
    • G01N29/44—Processing the detected response signal, e.g. electronic circuits specially adapted therefor
    • G01N29/449—Statistical methods not provided for in G01N29/4409, e.g. averaging, smoothing and interpolation
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/42—Methods or arrangements for servicing or maintenance of secondary cells or secondary half-cells
    • H01M10/4228—Leak testing of cells or batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/42—Methods or arrangements for servicing or maintenance of secondary cells or secondary half-cells
    • H01M10/425—Structural combination with electronic components, e.g. electronic circuits integrated to the outside of the casing
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/42—Methods or arrangements for servicing or maintenance of secondary cells or secondary half-cells
    • H01M10/48—Accumulators combined with arrangements for measuring, testing or indicating the condition of cells, e.g. the level or density of the electrolyte
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/42—Methods or arrangements for servicing or maintenance of secondary cells or secondary half-cells
    • H01M10/48—Accumulators combined with arrangements for measuring, testing or indicating the condition of cells, e.g. the level or density of the electrolyte
    • H01M10/486—Accumulators combined with arrangements for measuring, testing or indicating the condition of cells, e.g. the level or density of the electrolyte for measuring temperature
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/42—Methods or arrangements for servicing or maintenance of secondary cells or secondary half-cells
    • H01M10/48—Accumulators combined with arrangements for measuring, testing or indicating the condition of cells, e.g. the level or density of the electrolyte
    • H01M10/488—Cells or batteries combined with indicating means for external visualization of the condition, e.g. by change of colour or of light density
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2291/00—Indexing codes associated with group G01N29/00
    • G01N2291/01—Indexing codes associated with the measuring variable
    • G01N2291/011—Velocity or travel time
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2291/00—Indexing codes associated with group G01N29/00
    • G01N2291/02—Indexing codes associated with the analysed material
    • G01N2291/021—Gases
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2291/00—Indexing codes associated with group G01N29/00
    • G01N2291/02—Indexing codes associated with the analysed material
    • G01N2291/025—Change of phase or condition
    • G01N2291/0258—Structural degradation, e.g. fatigue of composites, ageing of oils
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2291/00—Indexing codes associated with group G01N29/00
    • G01N2291/02—Indexing codes associated with the analysed material
    • G01N2291/028—Material parameters
    • G01N2291/02809—Concentration of a compound, e.g. measured by a surface mass change
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2291/00—Indexing codes associated with group G01N29/00
    • G01N2291/04—Wave modes and trajectories
    • G01N2291/045—External reflections, e.g. on reflectors
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2291/00—Indexing codes associated with group G01N29/00
    • G01N2291/10—Number of transducers
    • G01N2291/101—Number of transducers one transducer
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2291/00—Indexing codes associated with group G01N29/00
    • G01N2291/10—Number of transducers
    • G01N2291/102—Number of transducers one emitter, one receiver
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2291/00—Indexing codes associated with group G01N29/00
    • G01N2291/26—Scanned objects
    • G01N2291/269—Various geometry objects
    • G01N2291/2697—Wafer or (micro)electronic parts
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Definitions

  • the present invention relates generally to a sensor arrangement and method for detecting gas in a battery assembly, more specifically for the purpose of detecting malfunction in the battery assembly.
  • One way of detecting a malfunctioning battery cell is to analyze the gas released from the cell to identify certain types of gas which are indicative of thermal runaway or even fire, such as hydrogen, carbon monoxide, carbon dioxide etc., by means of gas sensors based on e.g. solid oxide fuel cells. Examples of such devices are disclosed e.g. in US 2018/003685.
  • the known sensors are sensitive to specific gases, some of which are normally present in the ambient surrounding.
  • a reference sensor outside of the battery pack is used to compensate for the effect.
  • this could be problematic since the mine truck could be exposed to rapidly varying surrounding gas compositions when going in and out of a mine. This could lead to nuisance alarm events.
  • the known sensors are prohibitively expensive for many applications.
  • An object of the present invention is to provide a solution which achieves these advantages.
  • This object is achieved in a first aspect of the invention, in which there is provided a sensor arrangement for detecting malfunction in a battery assembly, the sensor arrangement comprising: an enclosure delimiting a space and arranged to receive gas released from the battery assembly; means for measuring the time-of-flight of an acoustic wave in gas present in the enclosure; and processing means configured to receive the time- of-flight measurements and compare the measured time-of-flight with at least one reference value for the time-of-flight corresponding to a normal operating condition of the battery assembly, wherein the processing means is further configured to generate a signal indicating malfunction of the battery assembly if the measured time-of-flight deviates from the at least one reference value for the time-of-flight.
  • the present invention uses the relation between the speed of sound in a gas on the one hand, and the temperature and composition of the gas on the other hand. Changes in either the temperature or composition of the gas emanating from the battery assembly, which indicate possible thermal runaway, may thereby be detected and used to generate a signal indicating malfunction of the battery assembly.
  • the present invention provides reliable, accurate and early detection of malfunction of a battery assembly, using a simple and inexpensive sensor arrangement. In the case of multiple battery assemblies in a larger module, pack or system, one sensor arrangement could be provided for each battery assembly of the system to enable accurate pinpointing of battery malfunction at low cost and low complexity.
  • a further advantage is that the sensor arrangement according to the present invention is sensitive to any gas which differs in molar mass from the normally present gas, as well as temperature changes independent of changes in gas composition. Hence, a battery malfunction which does not generate off- gassing but only heat could be detected by the sensor arrangement according to the present invention.
  • the processing means is configured to use a predetermined time-of-flight interval corresponding to a normal operating condition of the battery assembly as the at least one reference value for the time-of-flight, and wherein the processing means is further configured to generate the signal indicating malfunction of the battery assembly if the measured time-of-flight falls outside the predetermined interval.
  • the sensor arrangement comprises a temperature sensor arranged to measure the temperature within the enclosure, wherein the processing means is further configured to adjust the predetermined time-of-flight interval based on the measured temperature to compensate for changes in temperature.
  • the processing means is further configured to adjust the predetermined time-of-flight interval based on the measured temperature to compensate for changes in temperature.
  • the processing means is further configured to low-pass filter the measured time-of-flight at a first cut-off to establish a baseline value corresponding to a normal operating condition of the battery assembly, and to low-pass filter the measured time-of-flight at a second cut-off higher than the first cut-off to establish a filtered measurement value and wherein the processing means is further configured to generate the signal indicating malfunction of the battery assembly if the filtered measurement value exceeds or falls below the baseline value by more than a first predetermined threshold.
  • the processing means is further configured to calculate the derivative of the measured time-of-flight, and wherein the processing means is further configured to generate the signal indicating malfunction of the battery assembly if the calculated derivative of the measured time-of-flight exceeds or falls below a second predetermined threshold.
  • the means for measuring the time-of-flight of the acoustic wave comprises an ultrasonic transducer arranged in the enclosure and configured to transmit and receive an ultrasonic wave along an acoustic path within the enclosure.
  • the ultrasonic transducer comprises a piezoelectric element or a capacitive micromachined ultrasonic transducer, CMUT. The use of an ultrasonic transducer achieves a reliable and inexpensive sensor arrangement.
  • the enclosure comprises a casing arranged to be mounted on or near the battery assembly, wherein the ultrasonic transducer is arranged in the casing such that the acoustic path of the ultrasonic wave is disposed between two opposing surfaces separated by a predetermined distance.
  • a fixed surface of the battery assembly is used as one of the opposing surfaces.
  • the sensor arrangement may be used to detect changes in the measured time-of-flight caused by changes of the acoustic path, e.g. rising liquid level, opening of a hatch or lid, any moving object blocking the acoustic path etc.
  • the sensor arrangement further comprises a structure arranged to be positioned on or near the battery assembly in order to direct gas released from the battery assembly towards the enclosure.
  • the gas directing structure ensures that any gas emanating from the battery assembly, e.g. as a result of cell venting, enters into the enclosure for measurement.
  • the sensor arrangement further comprises a temperature sensor arranged to measure the temperature within the enclosure, wherein the processing means is further configured to determine whether the measured temperature lies within a predetermined temperature range corresponding to a normal operating condition of the battery assembly, and to generate a signal indicating malfunction of the battery assembly if the measured temperature falls outside the predetermined temperature range.
  • a temperature sensor By using a temperature sensor, changes in the ambient temperature may be accounted for to adjust the predetermined interval corresponding to normal operating conditions of the battery assembly.
  • a battery management system comprising at least one battery assembly connected thereto, and at least one sensor arrangement for detecting malfunction in a battery assembly according to any one of the preceding claims arranged in the vicinity of the respective at least one battery assembly in such a way that gas released from the at least one battery assembly enters into the enclosure of the at least one sensor arrangement.
  • the BMS is configured to shut down the at least one connected battery assembly in response to receiving a signal indicating malfunction of the at least one battery assembly.
  • a method of detecting malfunction in a battery assembly comprising the steps of:
  • a predetermined interval corresponding to a normal operating condition of the battery assembly is used as the at least one reference value for the time-of-flight, and wherein the signal indicating malfunction of the battery assembly is generated if the measured time-of-flight falls outside the predetermined interval.
  • the method further comprises measuring the temperature within the enclosure and adjusting the predetermined time-of-flight interval based on the measured temperature to compensate for changes in temperature.
  • the method further comprises low-pass filtering the measured time-of-flight to establish a baseline value corresponding to a normal operating condition of the battery assembly, and wherein the signal indicating malfunction of the battery assembly is generated if the measured time-of-flight exceeds or falls below the baseline value by more than a first predetermined threshold.
  • the method further comprises calculating the derivative of the measured time-of-flight, and wherein the signal indicating malfunction of the battery assembly is generated if the calculated derivative of the measured time-of-flight exceeds or falls below a second predetermined threshold.
  • the method further comprises measuring the temperature in the enclosure, determining whether the measured temperature lies within a predetermined temperature range corresponding to a normal operating condition of the battery assembly, and generating a signal indicating malfunction of the battery assembly if the measured temperature falls outside the predetermined temperature range.
  • the method further comprises shutting down the battery assembly in response to generation of the signal indicating malfunction of the battery assembly.
  • the time-of-flight is measured continuously or intermittently.
  • Continuous measurement i.e. the ‘sing-around’ method
  • the intermittent measurement at regular time intervals may be used in order to reduce energy consumption whilst maintaining efficient detection.
  • the intermittent method achieves substantially continuous measurement since the repetition frequency may be set high in relation to the expected changes in time-of-flight.
  • Fig. 1 shows a schematic view of a sensor arrangement according to one embodiment of the present invention.
  • Fig. 2 shows a graph of measured and processed time-of-flight values vs. time to illustrate the principles underlying the present invention.
  • the present invention utilizes the premise that any gas released from the cells can be detected by analyzing the speed of sound in the gas.
  • the speed of sound in a gas is dependent on both the gas composition and the temperature of the gas.
  • the speed of sound ci deai is given by the equation: where y is the adiabatic index also known as the isentropic expansion factor, is the pressure and p is the density of the gas.
  • g is actually measured over a range from 1.399 to 1.403 at 0 °C, for air.
  • the mean molar mass for dry air is about 0.0289645 kg/mol.
  • the speed of sound in a gas is calculated with the above formula. As can be seen, the speed of sound is in practice only dependent on the temperature and the molar mass of the gas. In the context of the present invention, the distance travelled by an acoustic wave transmitted through the gas may be unknown but constant, hence time-of- flight may be used as a relative measurement of the speed of sound.
  • the gases that may be released from a lithium-ion cell differs in terms of molar mass compared to the air normally present on the outside of the battery cell.
  • the detection of the off-gas can be done without knowing exactly what specific gas to look for. Any deviation in the speed of sound compared to the normal surrounding air can be considered to be caused by an off-gassing event in a cell.
  • the off-gases are normally hot when released from the cell. A sudden change of the temperature of the analyzed gas will also be detected as a sudden change of the measured time-of-flight.
  • a sensor arrangement 10 for detecting malfunction in a battery assembly 20 according to one exemplary embodiment of the present invention.
  • the sensor arrangement 10 may of course be different from the one shown, comprising fewer or more components.
  • the battery assembly 20 may comprise any type, number and/or arrangement of individual or multiple battery cells 25, modules or packs.
  • the sensor arrangement 10 comprises an enclosure 100 delimiting a space 110 and is arranged to receive gas from a battery assembly 20.
  • the enclosure 100 comprises one or more walls and at least one opening which is arranged in the exhaust path of the battery assembly 20, i.e. facing towards the battery assembly 20 such that any off gas released from the battery cells 25 in case of cell venting enters into the enclosure 100, as shown by the dashed arrow.
  • the enclosure 100 is shown as a separate structure arranged above the battery assembly 20.
  • the enclosure 100 may be integrally formed with or mounted directly on the battery assembly 20 and even use a fixed surface of the battery assembly 20 as one of the walls of the enclosure 100, as will be further explained below.
  • An alternative placement would be in a battery pack enclosure which contains multiple battery modules. In both cases the enclosure 100 is exposed to any gases vented from the cells in the pack.
  • the enclosure 100 is formed by means of a casing or bracket including fittings or holes for mounting additional components of the sensor arrangement 10.
  • the means 200 for measuring the time-of-flight comprises an ultrasonic transducer 200 configured to transmit and receive an ultrasonic wave or pulse along an acoustic path within the enclosure 100, as shown by the solid arrows in Fig. 1.
  • the term ‘transducer 200’ is understood to include both transmitters and receivers as separate components, as well as transceivers which both transmit and receive ultrasound.
  • the transmitter and receiver are arranged on opposite walls of the enclosure 100 to define the acoustic path between them, whereas in the latter case, the transceiver is arranged on one wall of the enclosure 100 and the transmitted ultrasonic wave or pulse is reflected off an opposite surface 120 of the enclosure 100 and back towards the transceiver, as shown in Fig. 1.
  • the speed of sound can be measured with high resolution through the proxy of time-of-flight measurement.
  • the ultrasonic transducer 200 comprises a piezoelectric element or a capacitive micromachined ultrasonic transducer, CMUT, and the sensor arrangement 10 comprises a drive circuit 310 for generating a burst of ultrasonic pulses which travels to the other side of enclosure 100 and bounces back to the ultrasonic transducer 200.
  • the sensor arrangement 10 further comprises processing means, e.g. a central processing unit, CPU 300, which receives or performs the time-of-flight measurements by communicating with or controlling the ultrasonic transducer 200.
  • the CPU 300 is further configured to determine whether there is a malfunction in the battery assembly 20 by comparing the measured time-of-flight with at least one reference value for the time-of- flight corresponding to a normal operating condition of the battery assembly 20. Any large and/or sudden changes of the measured time-of-flight can be considered an indication of cell venting, which in turn may be evidence of battery malfunction. Hence, if the measured time-of-flight deviates from the at least one reference value for the time-of-flight, the CPU 300 interprets this as an indication of battery malfunction and generates a signal indicating malfunction of the battery assembly 20.
  • processing means e.g. a central processing unit, CPU 300, which receives or performs the time-of-flight measurements by communicating with or controlling the ultrasonic transducer 200.
  • the reference value for the time-of-flight may be predetermined based on expected parameters which determine the speed of sound, i.e. the gas composition and temperature within the enclosure 100 and the environment surrounding the battery assembly 20. In other embodiments, the reference value for the time-of-flight may be updated or adjusted in response to changes which do not stem from battery malfunction but are caused by changes in the surrounding environment.
  • the raw value of the measured time-of-flight over time is shown as a dashed line.
  • the reference value for the time-of-flight is defined as an interval with fixed limits represented by the horizontal dashed lines in Fig. 2. If the measured time-of-flight falls outside the predetermined time-of-flight interval, this is interpreted as a cell venting event and in response, the CPU 300 generates the battery malfunction signal.
  • the raw value of the measured time-of-flight is seen to increase over time which indicates that the speed of sound in the gas within the enclosure 100 decreases, presumably caused by a change in the gas composition and/or temperature. After a certain amount of time, the measured time-of-flight exceeds the upper fixed limit of the predetermined interval, which triggers the battery malfunction signal from the CPU 300 as explained above.
  • the time-of-flight measurement is low-pass filtered to establish a baseline value A, shown as a solid line in Fig. 2, to be used as a reference value for the time-of-flight.
  • the low-pass filter provides a smooth signal, removing short-term fluctuations and leaving a longer-term trend. Any normal changes in ambient temperature or changes in gas composition in the environment where the sensor is situated are considered to be slow changes that would change the baseline value A, whereas rapid changes are attenuated.
  • the baseline value A is then compared to a second low-pass filtered measurement value B, shown as a dash-dotted line in Fig. 2.
  • the second cut-off is chosen higher than the first cut-off for the baseline value A, such that more rapid changes of the time-of-flight measurement are included in the filtered measurement value B. Any difference between values A and B above a first predetermined threshold C would indicate venting or off-gassing. In Fig. 2, it may be seen that the filtered measurement value B increases more rapidly than the baseline value A over time, even as both values rise due to changes in the gas composition and/or temperature within the enclosure 100. After a certain amount of time, the difference between values B and A exceeds the first predetermined threshold C, which triggers the battery malfunction signal from the CPU 300 as explained above.
  • the second cut-off may be chosen so high that the filtered measurement value B effectively equals the raw measurement value of the time-of-flight measurement, i.e. substantially all changes of the time-of-flight measurement are included.
  • a temperature sensor 400 could be added to compensate for any changes in gas temperature, e.g. due to changes in the surrounding environment.
  • a temperature sensor 400 is provided in or near the enclosure 100 to measure the temperature therein. The temperature measurements is received by the CPU 300 and used to adjust the predetermined time-of-flight interval in order to account for temperature changes not deriving from the battery assembly 20. The sensor arrangement 10 would then only be sensitive to changes in gas composition.
  • the temperature sensor 400 could be used to directly detect any large and/or rapid temperature changes indicative of battery malfunction independently or together with the time-of-flight measurement and trigger generation of the signal.
  • the sensor arrangement 10 further comprises a structure 130 arranged to guide or direct any gas released from the battery assembly 20, in case of venting or normal operation, towards the enclosure 100.
  • the gas directing structure 130 may include fins or panels in the exhaust path on or near the battery assembly 20, as shown in Fig. 1. Thereby, it is assured that the gases released from the battery assembly 20 reaches the enclosure 100 for detection instead of leaking out undetected.
  • the ultrasonic wave or pulse is transmitted through the gas in the enclosure 100 and reflected back off an opposing surface 120.
  • the reflecting surface 120 of the enclosure 100 could be any fixed surface in the mechanical structure of the battery assembly 20, module or pack. It could be possible to define a second function of the sensor arrangement 10, for example:
  • any opening of it could be detected.
  • Any moving object blocking the path of the acoustic wave could be detected.
  • a battery management system, BMS, 30 for monitoring one or more battery assemblies 20 connected thereto.
  • the BMS 30 comprises at least one sensor arrangement 10 arranged in the vicinity of the respective at least one battery assembly 20 in such a way that gas released from the at least one battery assembly 20 enters into the enclosure 100 of the at least one sensor arrangement.
  • one sensor arrangement 10 could be provided for each battery assembly 20 or for groups of battery assemblies 20, or a combination thereof.
  • the BMS 30 is shown in Fig. 1 as being connected to and communicating with the CPU 300 to receive the signal indicating malfunction of the at least one battery assembly 20.
  • the CPU 300 is incorporated in the electronic circuitry of the BMS 30 to control the sensor arrangement 10 directly.
  • the BMS 30 is further configured to shut down the at least one connected battery assembly 20.
  • the sensor arrangement 10 provides the possibility of preventing potential damage caused by thermal runaway in one or more battery cells 25 in one or more battery assemblies 20.
  • Preferred embodiments of a sensor arrangement and method for detecting malfunction in a battery assembly have been disclosed above. However, the person skilled in the art realises that this can be varied within the scope of the appended claims without departing from the inventive idea.

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Abstract

A sensor arrangement (10) for detecting malfunction in a battery assembly (20), the sensor arrangement (10) comprising: an enclosure (100) delimiting a space (110) and arranged to receive gas released from the battery assembly (20); means (200) for measuring the time-of-flight of an acoustic wave in gas present in the enclosure (100); and processing means (300) configured to receive the time-of-flight measurements and compare the measured time-of-flight with at least one reference value for the time-of-flight corresponding to a normal operating condition of the battery assembly (20), wherein the processing means (300) is further configured to generate a signal indicating malfunction of the battery assembly (20) if the measured time-of-flight deviates from the at least one reference value for the time-of-flight. In a second aspect, a method for detecting malfunction in a battery assembly is provided.

Description

DESCRIPTION
Title of Invention:
ARRANGEMENT AND METHOD FOR DETECTING MALFUNCTION IN A BATTERY
Technical field
[0001] The present invention relates generally to a sensor arrangement and method for detecting gas in a battery assembly, more specifically for the purpose of detecting malfunction in the battery assembly.
Background Art
[0002] When handled improperly, or if manufactured defectively, some types of rechargeable batteries can malfunction and experience thermal runaway, resulting in overheating. Gas is then released from the battery cell as it heats up, also known as off gassing or venting. Sealed battery cells will sometimes explode violently if safety vents are overwhelmed or nonfunctional. Especially prone to thermal runaway are lithium-ion batteries.
[0003] However, if the gas is detected in time, a shutdown of the battery cell can be carried out. If the shutdown is done early, this may prevent the battery cell from going into full thermal runaway. When a cell failure has been detected, the battery pack module containing the cell should be permanently shut off and replaced because of the risk of degraded adjacent cells.
[0004] One way of detecting a malfunctioning battery cell is to analyze the gas released from the cell to identify certain types of gas which are indicative of thermal runaway or even fire, such as hydrogen, carbon monoxide, carbon dioxide etc., by means of gas sensors based on e.g. solid oxide fuel cells. Examples of such devices are disclosed e.g. in US 2018/003685.
[0005] However, the known sensors are sensitive to specific gases, some of which are normally present in the ambient surrounding. A reference sensor outside of the battery pack is used to compensate for the effect. In an underground mining application this could be problematic since the mine truck could be exposed to rapidly varying surrounding gas compositions when going in and out of a mine. This could lead to nuisance alarm events. Furthermore, the known sensors are prohibitively expensive for many applications.
[0006] Thus, there is a need for improved devices and methods for detecting malfunction in a battery which are less expensive and may be applied in a broad range of situations.
Summary of Invention
[0007] An object of the present invention is to provide a solution which achieves these advantages. This object is achieved in a first aspect of the invention, in which there is provided a sensor arrangement for detecting malfunction in a battery assembly, the sensor arrangement comprising: an enclosure delimiting a space and arranged to receive gas released from the battery assembly; means for measuring the time-of-flight of an acoustic wave in gas present in the enclosure; and processing means configured to receive the time- of-flight measurements and compare the measured time-of-flight with at least one reference value for the time-of-flight corresponding to a normal operating condition of the battery assembly, wherein the processing means is further configured to generate a signal indicating malfunction of the battery assembly if the measured time-of-flight deviates from the at least one reference value for the time-of-flight.
[0008] By measuring the time-of-flight of an acoustic wave in the gas present in the enclosure, the present invention uses the relation between the speed of sound in a gas on the one hand, and the temperature and composition of the gas on the other hand. Changes in either the temperature or composition of the gas emanating from the battery assembly, which indicate possible thermal runaway, may thereby be detected and used to generate a signal indicating malfunction of the battery assembly. Advantageously, the present invention provides reliable, accurate and early detection of malfunction of a battery assembly, using a simple and inexpensive sensor arrangement. In the case of multiple battery assemblies in a larger module, pack or system, one sensor arrangement could be provided for each battery assembly of the system to enable accurate pinpointing of battery malfunction at low cost and low complexity. A further advantage is that the sensor arrangement according to the present invention is sensitive to any gas which differs in molar mass from the normally present gas, as well as temperature changes independent of changes in gas composition. Hence, a battery malfunction which does not generate off- gassing but only heat could be detected by the sensor arrangement according to the present invention.
[0009] In a preferred embodiment, the processing means is configured to use a predetermined time-of-flight interval corresponding to a normal operating condition of the battery assembly as the at least one reference value for the time-of-flight, and wherein the processing means is further configured to generate the signal indicating malfunction of the battery assembly if the measured time-of-flight falls outside the predetermined interval. By comparing the measured time-of-flight to a predetermined interval, a large deviation of the measured time-of-flight outside the expected reference value defined by the predetermined interval can easily and quickly be ascertained to indicate malfunction of the battery assembly.
[0010] In a further preferred embodiment, the sensor arrangement comprises a temperature sensor arranged to measure the temperature within the enclosure, wherein the processing means is further configured to adjust the predetermined time-of-flight interval based on the measured temperature to compensate for changes in temperature. By using a temperature sensor, changes in the ambient temperature may be accounted for to adjust the predetermined interval corresponding to normal operating conditions of the battery assembly.
[0011] In an alternative embodiment, the processing means is further configured to low-pass filter the measured time-of-flight at a first cut-off to establish a baseline value corresponding to a normal operating condition of the battery assembly, and to low-pass filter the measured time-of-flight at a second cut-off higher than the first cut-off to establish a filtered measurement value and wherein the processing means is further configured to generate the signal indicating malfunction of the battery assembly if the filtered measurement value exceeds or falls below the baseline value by more than a first predetermined threshold. By low-pass filtering the measured time-of-flight, only slow changes in ambient temperature or gas composition in the environment where the sensor arrangement is placed affects the baseline value, whereas rapid changes are filtered out. The resulting effect is that the reference value for the time-of-flight used in comparison is adjusted to account for normal changes in ambient temperature and gas composition, thus making the detection more robust and adaptable to actual conditions in the environment of the battery assembly. [0012] In an advantageous embodiment, the processing means is further configured to calculate the derivative of the measured time-of-flight, and wherein the processing means is further configured to generate the signal indicating malfunction of the battery assembly if the calculated derivative of the measured time-of-flight exceeds or falls below a second predetermined threshold. By using the derivative of the measured time-of-flight, rapid or sudden changes of the time-of-flight, which may be considered to indicate battery cell venting, are quickly detected even if the measure time-of-flight lies within an interval corresponding to normal operating conditions of the battery assembly.
[0013] In a preferred embodiment, the means for measuring the time-of-flight of the acoustic wave comprises an ultrasonic transducer arranged in the enclosure and configured to transmit and receive an ultrasonic wave along an acoustic path within the enclosure. Preferably, the ultrasonic transducer comprises a piezoelectric element or a capacitive micromachined ultrasonic transducer, CMUT. The use of an ultrasonic transducer achieves a reliable and inexpensive sensor arrangement.
[0014] In a further preferred embodiment, the enclosure comprises a casing arranged to be mounted on or near the battery assembly, wherein the ultrasonic transducer is arranged in the casing such that the acoustic path of the ultrasonic wave is disposed between two opposing surfaces separated by a predetermined distance. Preferably, a fixed surface of the battery assembly is used as one of the opposing surfaces. By using a fixed surface in the mechanical structure of the battery assembly, for instance as a reflecting surface for the acoustic wave, the sensor arrangement may be used to detect changes in the measured time-of-flight caused by changes of the acoustic path, e.g. rising liquid level, opening of a hatch or lid, any moving object blocking the acoustic path etc.
[0015] In an advantageous embodiment, the sensor arrangement, further comprises a structure arranged to be positioned on or near the battery assembly in order to direct gas released from the battery assembly towards the enclosure. The gas directing structure ensures that any gas emanating from the battery assembly, e.g. as a result of cell venting, enters into the enclosure for measurement.
[0016] In an alternative embodiment, the sensor arrangement further comprises a temperature sensor arranged to measure the temperature within the enclosure, wherein the processing means is further configured to determine whether the measured temperature lies within a predetermined temperature range corresponding to a normal operating condition of the battery assembly, and to generate a signal indicating malfunction of the battery assembly if the measured temperature falls outside the predetermined temperature range. By using a temperature sensor, changes in the ambient temperature may be accounted for to adjust the predetermined interval corresponding to normal operating conditions of the battery assembly.
[0017] In a second aspect of the present invention, there is provided a battery management system, BMS, comprising at least one battery assembly connected thereto, and at least one sensor arrangement for detecting malfunction in a battery assembly according to any one of the preceding claims arranged in the vicinity of the respective at least one battery assembly in such a way that gas released from the at least one battery assembly enters into the enclosure of the at least one sensor arrangement. Preferably, the BMS is configured to shut down the at least one connected battery assembly in response to receiving a signal indicating malfunction of the at least one battery assembly.
[0018] In a third aspect of the present invention, there is provided a method of detecting malfunction in a battery assembly, the method comprising the steps of:
(i) providing an enclosure delimiting a space and arranging the enclosure in the vicinity of the battery assembly in such a way that gas released from the battery assembly enters into the enclosure;
(ii) measuring the time-of-flight of an acoustic wave in gas present within the enclosure by means of an acoustic velocity meter;
(iii) comparing the measured time-of-flight with at least one reference value for the time-of-flight corresponding to a normal operating condition of the battery assembly; and
(iv) generating a signal indicating malfunction of the battery assembly if the measured time-of-flight deviates from the at least one reference value for the time-of-flight.
[0019] In a preferred embodiment, a predetermined interval corresponding to a normal operating condition of the battery assembly is used as the at least one reference value for the time-of-flight, and wherein the signal indicating malfunction of the battery assembly is generated if the measured time-of-flight falls outside the predetermined interval. Preferably, the method further comprises measuring the temperature within the enclosure and adjusting the predetermined time-of-flight interval based on the measured temperature to compensate for changes in temperature.
[0020] In an advantageous embodiment, the method further comprises low-pass filtering the measured time-of-flight to establish a baseline value corresponding to a normal operating condition of the battery assembly, and wherein the signal indicating malfunction of the battery assembly is generated if the measured time-of-flight exceeds or falls below the baseline value by more than a first predetermined threshold.
[0021] In an alternative embodiment, the method further comprises calculating the derivative of the measured time-of-flight, and wherein the signal indicating malfunction of the battery assembly is generated if the calculated derivative of the measured time-of-flight exceeds or falls below a second predetermined threshold.
[0022] In a preferred embodiment, the method further comprises measuring the temperature in the enclosure, determining whether the measured temperature lies within a predetermined temperature range corresponding to a normal operating condition of the battery assembly, and generating a signal indicating malfunction of the battery assembly if the measured temperature falls outside the predetermined temperature range.
[0023] In an advantageous embodiment, the method further comprises shutting down the battery assembly in response to generation of the signal indicating malfunction of the battery assembly.
[0024] In an alternative embodiment, the time-of-flight is measured continuously or intermittently. Continuous measurement (i.e. the ‘sing-around’ method) is preferably used for the case with separate transmitter and receiver for the acoustic wave and ensures that any changes in time-of-flight are detected quickly. Furthermore, the requirements on the components are lower since attenuation of the transmission signal before reception of the reflected signal at the transceiver is not needed. Alternatively, intermittent measurement at regular time intervals may be used in order to reduce energy consumption whilst maintaining efficient detection. In practice, the intermittent method achieves substantially continuous measurement since the repetition frequency may be set high in relation to the expected changes in time-of-flight. Brief Description of Drawings
[0025] The invention is now described, by way of example, with reference to the accompanying drawings, in which:
Fig. 1 shows a schematic view of a sensor arrangement according to one embodiment of the present invention; and
Fig. 2 shows a graph of measured and processed time-of-flight values vs. time to illustrate the principles underlying the present invention.
Description of Embodiments
[0026] In the following, a detailed description of a sensor arrangement and method for detecting malfunction in a battery according to the present invention is presented. In the drawing figures, like reference numerals designate identical or corresponding elements throughout the several figures. It will be appreciated that these figures are for illustration only and are not in any way restricting the scope of the invention.
[0027] The present invention utilizes the premise that any gas released from the cells can be detected by analyzing the speed of sound in the gas. The speed of sound in a gas is dependent on both the gas composition and the temperature of the gas. For an ideal gas, the speed of sound cideai is given by the equation:
Figure imgf000009_0001
where y is the adiabatic index also known as the isentropic expansion factor, is the pressure and p is the density of the gas. Using the ideal gas law to replace p with nRT/V , and replacing p with nM/V , the equation for an ideal gas becomes:
Figure imgf000009_0002
where R is the molar gas constant (approximately 8.314,5 J · mol-1 · K_1), k is the Boltzmann constant, T s the absolute temperature, Mis the molar mass of the gas, n is the number of moles and m is the mass of a single molecule. [0028] At room temperature, where thermal energy is fully partitioned into rotation (rotations are fully excited) but quantum effects prevent excitation of vibrational modes, the value of g is 7/5 = 1.400 for diatomic molecules, according to kinetic theory. Experimentally, g is actually measured over a range from 1.399 to 1.403 at 0 °C, for air. g is exactly 5/3 = 1.6667 for monatomic gases such as noble gases and it is approximately 1.3 for triatomic molecule gases. The mean molar mass for dry air is about 0.0289645 kg/mol.
[0029] The speed of sound in a gas is calculated with the above formula. As can be seen, the speed of sound is in practice only dependent on the temperature and the molar mass of the gas. In the context of the present invention, the distance travelled by an acoustic wave transmitted through the gas may be unknown but constant, hence time-of- flight may be used as a relative measurement of the speed of sound.
[0030] The gases that may be released from a lithium-ion cell differs in terms of molar mass compared to the air normally present on the outside of the battery cell. The detection of the off-gas can be done without knowing exactly what specific gas to look for. Any deviation in the speed of sound compared to the normal surrounding air can be considered to be caused by an off-gassing event in a cell.
[0031] The off-gases are normally hot when released from the cell. A sudden change of the temperature of the analyzed gas will also be detected as a sudden change of the measured time-of-flight.
[0032] Referring now to Fig. 1, there is shown a sensor arrangement 10 for detecting malfunction in a battery assembly 20 according to one exemplary embodiment of the present invention. The sensor arrangement 10 may of course be different from the one shown, comprising fewer or more components. The battery assembly 20 may comprise any type, number and/or arrangement of individual or multiple battery cells 25, modules or packs. The sensor arrangement 10 comprises an enclosure 100 delimiting a space 110 and is arranged to receive gas from a battery assembly 20. To that end, the enclosure 100 comprises one or more walls and at least one opening which is arranged in the exhaust path of the battery assembly 20, i.e. facing towards the battery assembly 20 such that any off gas released from the battery cells 25 in case of cell venting enters into the enclosure 100, as shown by the dashed arrow. In Fig. 1, the enclosure 100 is shown as a separate structure arranged above the battery assembly 20. Alternatively, the enclosure 100 may be integrally formed with or mounted directly on the battery assembly 20 and even use a fixed surface of the battery assembly 20 as one of the walls of the enclosure 100, as will be further explained below. An alternative placement would be in a battery pack enclosure which contains multiple battery modules. In both cases the enclosure 100 is exposed to any gases vented from the cells in the pack. In one embodiment, the enclosure 100 is formed by means of a casing or bracket including fittings or holes for mounting additional components of the sensor arrangement 10.
[0033] Arranged within the enclosure 100, there is provided means 200 for measuring the time-of-flight of an acoustic wave or pulse in the gas present in the enclosure 100. In one embodiment, the means 200 for measuring the time-of-flight comprises an ultrasonic transducer 200 configured to transmit and receive an ultrasonic wave or pulse along an acoustic path within the enclosure 100, as shown by the solid arrows in Fig. 1. In the context of the present invention, the term ‘transducer 200’ is understood to include both transmitters and receivers as separate components, as well as transceivers which both transmit and receive ultrasound. In the former case, the transmitter and receiver are arranged on opposite walls of the enclosure 100 to define the acoustic path between them, whereas in the latter case, the transceiver is arranged on one wall of the enclosure 100 and the transmitted ultrasonic wave or pulse is reflected off an opposite surface 120 of the enclosure 100 and back towards the transceiver, as shown in Fig. 1. By using ultrasound, the speed of sound can be measured with high resolution through the proxy of time-of-flight measurement. In one embodiment, the ultrasonic transducer 200 comprises a piezoelectric element or a capacitive micromachined ultrasonic transducer, CMUT, and the sensor arrangement 10 comprises a drive circuit 310 for generating a burst of ultrasonic pulses which travels to the other side of enclosure 100 and bounces back to the ultrasonic transducer 200.
[0034] The sensor arrangement 10 further comprises processing means, e.g. a central processing unit, CPU 300, which receives or performs the time-of-flight measurements by communicating with or controlling the ultrasonic transducer 200. The CPU 300 is further configured to determine whether there is a malfunction in the battery assembly 20 by comparing the measured time-of-flight with at least one reference value for the time-of- flight corresponding to a normal operating condition of the battery assembly 20. Any large and/or sudden changes of the measured time-of-flight can be considered an indication of cell venting, which in turn may be evidence of battery malfunction. Hence, if the measured time-of-flight deviates from the at least one reference value for the time-of-flight, the CPU 300 interprets this as an indication of battery malfunction and generates a signal indicating malfunction of the battery assembly 20.
[0035] The reference value for the time-of-flight may be predetermined based on expected parameters which determine the speed of sound, i.e. the gas composition and temperature within the enclosure 100 and the environment surrounding the battery assembly 20. In other embodiments, the reference value for the time-of-flight may be updated or adjusted in response to changes which do not stem from battery malfunction but are caused by changes in the surrounding environment.
[0036] Referring now to Fig. 2, the raw value of the measured time-of-flight over time is shown as a dashed line. In a first example, the reference value for the time-of-flight is defined as an interval with fixed limits represented by the horizontal dashed lines in Fig. 2. If the measured time-of-flight falls outside the predetermined time-of-flight interval, this is interpreted as a cell venting event and in response, the CPU 300 generates the battery malfunction signal. In Fig. 2, the raw value of the measured time-of-flight is seen to increase over time which indicates that the speed of sound in the gas within the enclosure 100 decreases, presumably caused by a change in the gas composition and/or temperature. After a certain amount of time, the measured time-of-flight exceeds the upper fixed limit of the predetermined interval, which triggers the battery malfunction signal from the CPU 300 as explained above.
[0037] In a second example, the time-of-flight measurement is low-pass filtered to establish a baseline value A, shown as a solid line in Fig. 2, to be used as a reference value for the time-of-flight. The low-pass filter provides a smooth signal, removing short-term fluctuations and leaving a longer-term trend. Any normal changes in ambient temperature or changes in gas composition in the environment where the sensor is situated are considered to be slow changes that would change the baseline value A, whereas rapid changes are attenuated. The baseline value A is then compared to a second low-pass filtered measurement value B, shown as a dash-dotted line in Fig. 2. The second cut-off is chosen higher than the first cut-off for the baseline value A, such that more rapid changes of the time-of-flight measurement are included in the filtered measurement value B. Any difference between values A and B above a first predetermined threshold C would indicate venting or off-gassing. In Fig. 2, it may be seen that the filtered measurement value B increases more rapidly than the baseline value A over time, even as both values rise due to changes in the gas composition and/or temperature within the enclosure 100. After a certain amount of time, the difference between values B and A exceeds the first predetermined threshold C, which triggers the battery malfunction signal from the CPU 300 as explained above. In one embodiment, the second cut-off may be chosen so high that the filtered measurement value B effectively equals the raw measurement value of the time-of-flight measurement, i.e. substantially all changes of the time-of-flight measurement are included.
[0038] Variants of the above algorithm are possible. For example, if the derivative of the raw value of the measured time-of-flight and/or of the low-pass filtered measurement value B is larger than a second predetermined threshold value it would indicate a venting event and trigger the battery malfunction signal from the CPU 300 as explained above.
[0039] In an alternative configuration a temperature sensor 400 could be added to compensate for any changes in gas temperature, e.g. due to changes in the surrounding environment. In Fig. 1, a temperature sensor 400 is provided in or near the enclosure 100 to measure the temperature therein. The temperature measurements is received by the CPU 300 and used to adjust the predetermined time-of-flight interval in order to account for temperature changes not deriving from the battery assembly 20. The sensor arrangement 10 would then only be sensitive to changes in gas composition. Alternatively, the temperature sensor 400 could be used to directly detect any large and/or rapid temperature changes indicative of battery malfunction independently or together with the time-of-flight measurement and trigger generation of the signal.
[0040] In one embodiment, the sensor arrangement 10 further comprises a structure 130 arranged to guide or direct any gas released from the battery assembly 20, in case of venting or normal operation, towards the enclosure 100. The gas directing structure 130 may include fins or panels in the exhaust path on or near the battery assembly 20, as shown in Fig. 1. Thereby, it is assured that the gases released from the battery assembly 20 reaches the enclosure 100 for detection instead of leaking out undetected. [0041] As mentioned above, in the case of an ultrasonic transducer 200 in a single component (i.e. a transceiver), the ultrasonic wave or pulse is transmitted through the gas in the enclosure 100 and reflected back off an opposing surface 120. The reflecting surface 120 of the enclosure 100 could be any fixed surface in the mechanical structure of the battery assembly 20, module or pack. It could be possible to define a second function of the sensor arrangement 10, for example:
If the bottom surface of a liquid cooled battery assembly is used as a reflecting surface, a detection of a liquid leakage could be done. A rising liquid level would then decrease the fixed length of the acoustic path in the enclosure 100, changing the measured time-of-flight.
If a lid or hatch is used as a reflecting structure, any opening of it could be detected.
Any moving object blocking the path of the acoustic wave could be detected.
[0042] In a further aspect of the present invention, there is provided a battery management system, BMS, 30 for monitoring one or more battery assemblies 20 connected thereto. To that end, the BMS 30 comprises at least one sensor arrangement 10 arranged in the vicinity of the respective at least one battery assembly 20 in such a way that gas released from the at least one battery assembly 20 enters into the enclosure 100 of the at least one sensor arrangement. In the case of the BMS 30 being connected to and controlling a plurality of battery assemblies 20, one sensor arrangement 10 could be provided for each battery assembly 20 or for groups of battery assemblies 20, or a combination thereof. The BMS 30 is shown in Fig. 1 as being connected to and communicating with the CPU 300 to receive the signal indicating malfunction of the at least one battery assembly 20. Alternatively, the CPU 300 is incorporated in the electronic circuitry of the BMS 30 to control the sensor arrangement 10 directly.
[0043] In case of battery malfunction being indicated by means of the sensor arrangement, the BMS 30 is further configured to shut down the at least one connected battery assembly 20. Thereby the sensor arrangement 10 provides the possibility of preventing potential damage caused by thermal runaway in one or more battery cells 25 in one or more battery assemblies 20. [0044] Preferred embodiments of a sensor arrangement and method for detecting malfunction in a battery assembly have been disclosed above. However, the person skilled in the art realises that this can be varied within the scope of the appended claims without departing from the inventive idea.
[0045] All the described alternative embodiments above or parts of an embodiment can be freely combined or employed separately from each other without departing from the inventive idea as long as the combination is not contradictory.

Claims

1. A sensor arrangement (10) for detecting malfunction in a battery assembly (20), the sensor arrangement (10) comprising:
(i) an enclosure (100) delimiting a space (110) and arranged to receive gas released from the battery assembly (20);
(ii) means (200) for measuring the time-of-flight of an acoustic wave in gas present in the enclosure (100); and
(iii) processing means (300) configured to receive the time-of-flight measurements and compare the measured time-of-flight with at least one reference value for the time- of-flight corresponding to a normal operating condition of the battery assembly (20), wherein the processing means (300) is further configured to generate a signal indicating malfunction of the battery assembly (20) if the measured time-of-flight deviates from the at least one reference value for the time-of-flight.
2. The sensor arrangement (10) according to claim 1, wherein the processing means (300) is configured to use a predetermined time-of-flight interval corresponding to a normal operating condition of the battery assembly (20) as the at least one reference value for the time-of-flight, and wherein the processing means (300) is further configured to generate the signal indicating malfunction of the battery assembly (20) if the measured time-of-flight falls outside the predetermined interval.
3. The sensor arrangement (10) according to claim 2, further comprising a temperature sensor (400) arranged to measure the temperature within the enclosure (100), wherein the processing means (300) is further configured to adjust the predetermined time- of-flight interval based on the measured temperature to compensate for changes in temperature.
4. The sensor arrangement (10) according to any one of the preceding claims, wherein the processing means (300) is further configured to low-pass filter the measured time-of-flight at a first cut-off to establish a baseline value (A) corresponding to a normal operating condition of the battery assembly (20), and to low-pass filter the measured time- of-flight at a second cut-off higher than the first cut-off to establish a filtered measurement value (B) and wherein the processing means (300) is further configured to generate the signal indicating malfunction of the battery assembly (20) if the filtered measurement value (B) exceeds or falls below the baseline value (A) by more than a first predetermined threshold (C).
5. The sensor arrangement (10) according to any one of the preceding claims, wherein the processing means (300) is further configured to calculate the derivative of the measured time-of-flight, and wherein the processing means (300) is further configured to generate the signal indicating malfunction of the battery assembly (20) if the calculated derivative of the measured time-of-flight exceeds or falls below a second predetermined threshold.
6. The sensor arrangement (10) according to any one of the preceding claims, wherein the means (200) for measuring the time-of-flight of the acoustic wave comprises an ultrasonic transducer (200) arranged in the enclosure (100) and configured to transmit and receive an ultrasonic wave along an acoustic path within the enclosure (100).
7. The sensor arrangement (10) according to claim 6, wherein the ultrasonic transducer (200) comprises a piezoelectric element or a capacitive micromachined ultrasonic transducer, CMUT.
8. The sensor arrangement (10) according to claim 6 or 7, wherein the enclosure (100) comprises a casing arranged to be mounted on or near the battery assembly (20), wherein the ultrasonic transducer (200) is arranged in the casing such that the acoustic path of the ultrasonic wave is disposed between two opposing surfaces separated by a predetermined distance.
9. The sensor arrangement (10) according to claim 8, wherein a fixed surface of the battery assembly (20) is used as one of the opposing surfaces.
10. The sensor arrangement (10) according to any one of the preceding claims, further comprising a structure (130) arranged to be positioned on or near the battery assembly (20) in order to direct gas released from the battery assembly (20) towards the enclosure (100).
11. The sensor arrangement (10) according to any one of the preceding claims, further comprising a temperature sensor (400) arranged to measure the temperature within the enclosure (100), wherein the processing means (300) is further configured to determine whether the measured temperature lies within a predetermined temperature range corresponding to a normal operating condition of the battery assembly (20), and to generate a signal indicating malfunction of the battery assembly (20) if the measured temperature falls outside the predetermined temperature range.
12. A battery management system, BMS, (30) comprising at least one battery assembly (20) connected thereto, and at least one sensor arrangement (10) for detecting malfunction in a battery assembly (20) according to any one of the preceding claims arranged in the vicinity of the respective at least one battery assembly (20) in such a way that gas released from the at least one battery assembly (20) enters into the enclosure (100) of the at least one sensor arrangement (10).
13. The BMS of claim 12, wherein the BMS is configured to shut down the at least one connected battery assembly (20) in response to receiving a signal indicating malfunction of the at least one battery assembly (20).
14. A method of detecting malfunction in a battery assembly (20), the method comprising the steps of:
(i) providing an enclosure (100) delimiting a space and arranging the enclosure (100) in the vicinity of the battery assembly (20) in such a way that gas released from the battery assembly (20) enters into the enclosure (100);
(ii) measuring the time-of-flight of an acoustic wave in gas present within the enclosure (100) by means of an acoustic velocity meter;
(iii) comparing the measured time-of-flight with at least one reference value for the time- of-flight corresponding to a normal operating condition of the battery assembly (20); and
(iv) generating a signal indicating malfunction of the battery assembly (20) if the measured time-of-flight deviates from the at least one reference value for the time- of-flight.
15. The method according to claim 14, wherein a predetermined interval corresponding to a normal operating condition of the battery assembly (20) is used as the at least one reference value for the time-of-flight, and wherein the signal indicating malfunction of the battery assembly (20) is generated if the measured time-of-flight falls outside the predetermined interval.
16. The method according to claim 15, further comprising measuring the temperature within the enclosure (100) and adjusting the predetermined time-of-flight interval based on the measured temperature to compensate for changes in temperature.
17. The method according to claim 15 or 16, further comprising low-pass filtering the measured time-of-flight to establish a baseline value (A) corresponding to a normal operating condition of the battery assembly (20), and wherein the signal indicating malfunction of the battery assembly (20) is generated if the measured time-of-flight exceeds or falls below the baseline value (A) by more than a first predetermined threshold (C).
18. The method according to any one of claims 15-17, further comprising calculating the derivative of the measured time-of-flight, and wherein the signal indicating malfunction of the battery assembly (20) is generated if the calculated derivative of the measured time-of-flight exceeds or falls below a second predetermined threshold.
19. The method according to any one of claims 15-18, further comprising measuring the temperature in the enclosure (100), determining whether the measured temperature lies within a predetermined temperature range corresponding to a normal operating condition of the battery assembly (20), and generating a signal indicating malfunction of the battery assembly (20) if the measured temperature falls outside the predetermined temperature range.
20. The method according to any one of claims 15-19, further comprising shutting down the battery assembly (20) in response to generation of the signal indicating malfunction of the battery assembly (20).
21. The method according to any one of claims 15-20, wherein the time-of-flight is measured continuously or intermittently.
PCT/EP2020/081137 2019-11-08 2020-11-05 Arrangement and method for detecting malfunction in a battery WO2021089700A1 (en)

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