Method for detecting and locating defective battery cells in a battery cell arrangement, and energy storage system designed for this purpose

Abstract

The invention relates to a method for detecting and locating defective battery cells (22d) in a battery cell arrangement (20) of an electrical energy storage system (10), wherein the battery cell arrangement (20) is formed from a plurality of electrically interconnected battery cells (22), and wherein the method comprises the following steps: time-resolved measurement of temperatures (T1(t), T2(t), ...) at several temperature measuring points distributed over the battery cell arrangement (20); detection of a fault event in the battery cell arrangement (20) if the measurement of the temperatures (T1(t), T2(t), ...) shows that at least one of the measured temperatures (T1(t), T2(t), ...) rises excessively; after detection of a fault event, evaluation of the measured temperatures (T1(t), T2(t), ...) based on a thermal model of the battery cell arrangement (20) taking into account the arrangement of the temperature measuring points, in order to identify at least one of the battery cells (22) as a defective battery cell (22d).

Description

[0001] The present invention relates to a method for detecting and locating defective battery cells in a battery cell arrangement of an electrical energy storage system. Furthermore, the invention relates to a correspondingly designed energy storage system.

[0002] The field of the invention relates to energy storage, for example, in connection with the generation of electrical energy from intermittent energy sources such as photovoltaics, etc., in order to enable the energy to be provided on demand regardless of the time of its generation. Furthermore, energy storage plays a central role, for example, in the automotive sector for supplying energy to an electric drive system of a vehicle such as a battery electric vehicle (BEV) or a hybrid electric vehicle (HEV).

[0003] In particular, in the aforementioned applications, electrical energy storage devices are used in which the energy is stored in a plurality of parallel and / or serially connected rechargeable battery cells (e.g. electrochemical battery cells), which form the battery cell arrangement of the electrical energy storage system.

[0004] It is known from the prior art to equip such energy storage systems with a battery management system (BMS for short) in order to control the operation (charging and discharging) of individual battery cells and / or subunits of the battery cell arrangement formed therefrom, such as, in particular, battery cell modules that can be individually switched on and off within the battery cell arrangement. Furthermore, the BMS enables the aforementioned components of the battery cell arrangement or the battery cell arrangement as a whole to be monitored (e.g., recording cell voltages, charge states, temperatures, etc.) and thus, if necessary, also to protect against overload (e.g., deep discharge protection, overcharge protection, overheating protection, etc.).

[0005] Thermal management of such an energy storage system ("traction battery") is particularly necessary in modern electrified vehicles. In cold ambient temperatures, for example, the battery cell arrangement may first need to be preheated to ensure its performance, for example with regard to high discharge power (e.g., during acceleration) and / or high charging power (e.g., at a charging station or, for example, as recuperation power during braking), and also to protect the battery cells from damage (e.g., lithium plating in Li-ion batteries) and premature aging. In contrast, in other situations, cooling of the battery cell arrangement is necessary for the same reasons as part of the thermal management performed by the battery management system.

[0006] Various fault events can occur in the battery cell array. These include, for example, defects in individual battery cells, whether due to aging phenomena, e.g., after dendrite formation in electrochemical cells, and / or due to thermal or mechanical influences. Such defects can lead to internal short circuits and, consequently, to excessive and often rapid heating of the affected battery cells. Excessive heating of a defective battery cell can cause safety-critical problems in the battery cell array.

[0007] Previous temperature control systems for heating and cooling electrical energy storage systems are usually connected externally to the battery cell array or the individual battery cells. The heat generated in the battery cells can be dissipated, for example, via a so-called TIM ("thermal interface material") to a heat sink through which a cooling medium (such as water) flows. Cooling of a plate-shaped battery cell array can be implemented, for example, as a base cooling system with a cooling plate on the underside of the battery cell array. Alternatively, cooling can also occur from above or from the side.

[0008] Temperature sensors can be installed in the battery cell array to monitor the temperature. However, for cost reasons, the temperature of each individual battery cell is not usually determined with a dedicated temperature sensor; instead, only a reduced number of temperature sensors are installed in the battery cell array.

[0009] In the event of a critical temperature development in a battery cell without dedicated measurement sensors on all battery cells, timely detection of a potentially critical condition is disadvantageously delayed. A further disadvantage of this state of the art, without direct temperature measurement on each battery cell, is that it only allows for a rough localization of a faulty battery cell.

[0010] It is therefore an object of the present invention to enable, in a simple manner, detection and improved localization of defective battery cells in a battery cell arrangement of an electrical energy storage system.

[0011] According to a first aspect of the invention, this object is achieved by a method according to claim 1. Advantageous embodiments and further developments of the invention emerge from the further claims and the following description.

[0012] The method according to the invention for detecting and locating defective battery cells in a battery cell arrangement of an electrical energy storage system comprises the following steps: a) time-resolved measurement of temperatures at several temperature measuring points distributed over the battery cell arrangement, b) Determining a fault event in the battery cell assembly if the measurement of the temperatures shows that at least one of the measured temperatures increases excessively, c) after detecting a fault event, evaluating the measured temperatures based on a thermal model of the battery cell arrangement taking into account the arrangement of the temperature measuring points in order to identify at least one of the battery cells as a defective battery cell.

[0013] The invention advantageously makes it possible, after a fault event has been detected in the battery cell arrangement, to locate a defective battery cell that caused the fault event. Furthermore, the invention can advantageously also be used, for example, to implement efficient fault plausibility testing. In a further development of the invention, the evaluation carried out in step c) is further designed to estimate a temperature of the battery cell identified as defective. Fault detection and localization of defective battery cells with impermissibly high heat development as well as temperature estimation of cell temperatures enable, in particular, early detection of safety-critical conditions (e.g., "thermal runaway").

[0014] The temperature measurement provided in step a) can be carried out by means of a temperature measuring device which comprises a plurality of temperature sensors arranged distributed over the battery cell arrangement, wherein the positions of the individual temperature sensors correspond to the individual temperature measuring points.

[0015] The time-resolved measurement of the temperatures is preferably provided as a periodic recording of measured values ​​of the individual temperatures, e.g. with a period in the range of 10 ms to 1 s, in particular 50 ms to 200 ms.

[0016] A larger number of temperature sensors or temperature measuring points results in correspondingly higher costs for the energy storage system, but on the other hand, it advantageously increases the speed and accuracy achievable with the invention for detecting fault events and subsequently locating defective battery cells. As an advantageous compromise, the number of temperature measuring points can be in the range of 1% to 20%, in particular 5% to 10%, of the number of battery cells (monitored with them).

[0017] In general, a substantially uniform distribution of the temperature measuring points over the battery cell arrangement is preferred, ie for example in the case of a planar battery cell arrangement over the area occupied by the battery cell arrangement.

[0018] In one embodiment of the invention, it is provided that the temperatures measured in step a) are temporarily stored at least until the identification of at least one of the battery cells as a defective battery cell in step c) is completed.

[0019] Thus, in the evaluation of the measured temperatures performed in step c), it is advantageous to also take into account, in particular, measured values ​​whose measurement (measured value recording) already took place at a time before the error event was detected. In a generally advantageous embodiment, in the evaluation performed in step c), the temperature measured values ​​already recorded at at least three temperature measuring points before the error event was detected can be taken into account.

[0020] Alternatively or additionally, such "early" recorded measured values ​​can advantageously also be used in step b) to assess whether an excessive temperature increase has occurred (which causes the detection of a fault event). According to one embodiment, this assessment performed in step b) can, in particular, take into account, for example, the temperature measured values ​​recorded at at least two temperature measuring points before the detection of the fault event.

[0021] In one embodiment, in step b), the presence of an “excessive temperature increase” is assumed if the temperature in question exceeds a predetermined first threshold value.

[0022] In one embodiment, in step b), the presence of an excessive temperature increase is assumed if a time derivative of the temperature in question exceeds a predetermined second threshold value.

[0023] In one embodiment, in step b), the presence of an excessive temperature increase is assumed if a temporal second derivative of the temperature in question exceeds a predetermined third threshold value.

[0024] It should be noted that normally (apart from random exceptions), each of the temperatures measured at the temperature measuring points does not directly, i.e., simultaneously and to the same extent, reflect the temperature increase of the defective battery cell in the battery cell array. Nevertheless, there is at least a tendency towards a correlation between these temperatures, so that, to a certain extent, the criterion of exceeding the first threshold detects an increased temperature of the defective cell, the criterion of exceeding the second threshold detects an increased thermal output of the defective cell, and the criterion of exceeding the third threshold detects a temporal increase in the thermal output of the defective cell.

[0025] In this respect, all of the aforementioned criteria are suitable for assessing the presence of an "excessive temperature rise" and, if necessary, for determining the fault event based on this. In principle, these criteria can therefore be used individually or in any combination in step b), i.e., one, two, or all three of these criteria.

[0026] For each of the aforementioned criteria, it can advantageously be provided that the relevant (first, second or third) threshold value is specified as a function of at least one operating parameter of the energy storage system.

[0027] In one embodiment, the first threshold value is specified as a function of at least one such operating parameter. In one embodiment, the second threshold value is specified as a function of at least one such operating parameter. In one embodiment, the third threshold value is specified as a function of at least one such operating parameter.

[0028] In this case, operating parameters of the energy storage system can be parameters measured on the battery cell array or determined by other means, such as a temperature and / or a state of charge of the battery cell array. Furthermore, a charging or discharging current determined for the battery cell array can be considered. For example, such operating parameters can also be parameters derived (calculated) from several measured variables.

[0029] In the case of the aforementioned dependence of a threshold value on at least one such operating parameter, for example, an instantaneous value of the operating parameter and / or often advantageously also a temporal progression of the operating parameter preceding the instantaneous value can be used.

[0030] In one embodiment, at least one threshold value is specified as a function of a “temperature of the battery cell arrangement,” wherein this temperature can be determined, in particular, for example, as an average value of the temperatures measured at certain (or all) of the temperature measuring points of the battery cell arrangement.

[0031] Particularly when using the invention for battery cell arrays above a certain power density and / or in mobile situations with varying ambient temperatures, such as in the automotive sector, it may even be necessary in practice, apart from exceptional cases, to specify at least the first threshold value as a function of the operating parameter "temperature of the battery cell array." This advantageously takes into account the fact that the temperatures of the individual battery cells, even in a completely fault-free state, can vary greatly depending on the current (or immediately preceding) charging or discharging power. It is therefore expedient to "track" the "threshold temperature" of the fault event detection accordingly.

[0032] In one embodiment, in addition to the criterion of an excessive temperature increase, at least one further criterion is also provided, the fulfillment of which results in the detection of a fault event. Such a further criterion could, for example, be fulfilled if a measurement of the cell voltages of the battery cells shows that at least one of these voltages drops excessively (e.g., compared to an average value of the cell voltages of the battery cells). Another such criterion could, for example, consist of an excessive increase in pressure and / or an excessive increase in the concentration of a specific gas (e.g., H2) in the battery cell arrangement.

[0033] There are many possibilities for the concrete (mathematical) design of the evaluation of the measured temperatures carried out in step c) based on a thermal model of the battery cell arrangement.

[0034] In one embodiment, for example, the thermal model models each battery cell as a heat source with a predetermined heat output and a predetermined heat capacity. Heat transfers between adjacent battery cells and between battery cells and the environment of the battery cell arrangement can be taken into account by predetermined thermal resistances between the adjacent battery cells or between the battery cells and the environment modeled as a heat sink.

[0035] In this embodiment, the evaluation effort is advantageously reduced in that the battery cell arrangement is not divided into a very large number of very small elements (e.g., according to a so-called finite element method), and the thermal interactions between these elements are modeled. Rather, in this embodiment, the battery cells themselves are considered as "elements," and their respective interactions with other battery cells and / or at least one element of the environment are modeled using a limited number of thermal resistances (or equivalently, thermal conductances).Therefore, a thermal model provided within the scope of the invention, which is used in the evaluation in the above-mentioned step c) and / or forms the basis of the design (algorithm) of this evaluation, can also be imagined as a "resistance network", in which network nodes are formed by the battery cells and one or more components of an environment (e.g. TIM, heat sink, etc.) in order to model heat flows or to draw conclusions about the location and extent of the causative (excessive heat generating) fault event from temperature increases at certain (known) locations.

[0036] In one embodiment, the battery cell arrangement comprises at least one planar arrangement of battery cells, ie, a "battery cell layer," in which, mathematically speaking, the battery cells can be arranged, for example, at the points of a grid, e.g., on a square grid or, for example, on a hexagonal grid. Such a battery cell layer can, for example, have an approximately rectangular contour. Several such battery cell layers can also be stacked together to form the battery cell arrangement.

[0037] When the battery cells are arranged in a battery cell layer, e.g. on a square grid (cf. e.g. in Fig. 1) For example, it can be provided that in the thermal model, with regard to heat transfer between adjacent battery cells, the four nearest neighboring cells (with minimal spacing) are taken into account for cells located "inside" the battery cell arrangement, and the model therefore provides four thermal resistances to neighboring cells for these cells. For battery cells "at the edge" of the battery cell arrangement, there are then three such nearest neighboring cells, and for battery cells "in a corner" of the battery cell arrangement, there are two such nearest neighboring cells, and accordingly three or two such thermal resistances. To increase the level of detail of the model, it can be considered on a square grid to additionally consider thermal resistances for each battery cell to the cells located slightly further away (diagonally adjacent), for exampleFor "internal" cells, four additional thermal resistors are required, for "edge" cells, two additional thermal resistors are required, and for "corner" cells, one additional thermal resistor is required. If the battery cell layer is cooled by a flat, extended heat sink (e.g., "floor cooling"), the model can include an additional thermal resistor for each battery cell facing this environment to account for the heat transfer between the cells and this environment, which is modeled as a heat sink.

[0038] If the battery cells are arranged in a battery cell layer on a different grid, such as a hexagonal grid, the thermal model can be designed analogously, with only minor adjustments. The model can then be designed with relatively few thermal resistors and possibly only a few or even a single heat sink. With a hexagonal grid, with regard to heat transfer between adjacent battery cells, the six nearest neighboring cells (with minimal spacing) would have to be considered for the "inner" cells, for example.

[0039] When (quantitatively) specifying each thermal resistance between two adjacent battery cells on the grid in question, it is advantageous to consider whether the two cells in question are directly connected to each other via their electrical contacts. In the case of such electrical contact, a lower thermal resistance value should be provided than in the case without such electrical contact. Thus, the portions of heat transfer between adjacent battery cells that occur via the electrical contacts can also be taken into account.

[0040] In this respect, with regard to the thermal resistances to be provided between neighboring cells in the thermal model, it is generally advisable to focus primarily on their "thermal neighborhood" (and less on their geometric neighborhood), i.e. to provide thermal resistances in the model that, starting from a specific battery cell, only run to the neighboring cells that are actually coupled to it with the "minimal thermal resistances".

[0041] If a battery cell layer of the battery cell arrangement is cooled “from the side”, this can be taken into account in the model, for example for each battery cell located at the edge of the battery cell layer, by a thermal resistance to this environment (modeled as a heat sink).

[0042] A modeling of a component or environment of the battery cell arrangement as a heat sink can be provided, for example, as a boundary condition, according to which the heat sink is assigned a fixed predetermined temperature, which can, for example, correspond to the temperature of a cooling medium used.

[0043] The evaluation provided for in the invention “taking into account the arrangement of the temperature measuring points” means that one or more battery cells are identified (located) during the evaluation in which, according to the thermal model, excessive heating caused by a defect causes respective temperature increases (or temporal temperature profiles) at the temperature measuring points that “match” the temperatures actually observed (measured in time-resolved fashion) at the temperature measuring points. Furthermore, such an evaluation can be used to estimate the temperature of the defective cell(s). Put simply, the location of a fault event (defective cell(s)) that generates excessive heat within the battery cell arrangement determines the “relationships” between the temperature profile parameters of the temperature profiles measured at the various temperature measuring points, whereas the heat output orTemperature of the fault event determines the “extent” (e.g. maximum temperatures reached, temperature rise rates, etc.) of the temperature increases.

[0044] There are many different options for the specific design of such an evaluation.

[0045] For this purpose, the evaluation can, according to one embodiment, comprise, for example, a correlation analysis in order to calculate a correlation between, on the one hand, modeled temperature profiles and, on the other hand, measured temperature profiles for a large number of fundamentally possible fault events, in order to then, for example, identify one of the battery cells as defective for whose defect-related overheating a maximum correlation results. Optionally, the evaluation in this case can, for example, provide for increasing the correlation even further by tentatively assuming one or more defects in neighboring cells of the said battery cell in order to possibly identify one or more additional cells as defective. According to one embodiment, an appropriate compensation calculation (e.g. "parameter fit") can be used not only to locate the fault event but also to estimate the heat output and / or temperature of the fault event.

[0046] According to an advantageous embodiment, for such a correlation calculation, for example, at least one "temperature profile parameter" can first be determined (calculated) for each measured temperature profile, which is then compared, in a sense, with a corresponding temperature profile parameter, i.e., one predicted by the thermal model, during the correlation calculation. In this case, the identification of (at least) one defective cell can be based on a particularly large or maximum correlation between the temperature profile parameter(s) determined from the measurement and the temperature profile parameter(s) predicted by the model.

[0047] A further embodiment of the evaluation provides that a "distance parameter" is calculated for each temperature measuring point from the temperatures measured at the temperature measuring points in a time-resolved manner, taking into account the thermal model. This "distance parameter" is representative of a (geometric) distance of the fault event (defective battery cell) from the respective temperature measuring point, in order to subsequently determine the position of a defective battery cell (i.e., to identify it as defective) from preferably three (or more) such distance parameters with the aid of a geometric calculation. In this case, the identification of a defective cell can be based on its position in a two-dimensional arrangement ("battery cell layer") being determined, for example, as an "intersection of several lines", or its position in a three-dimensional arrangement (e.g., stacked battery cell layers), being determined, for example, as an "intersection of several surfaces" (e.g.,spherical surfaces, ellipsoidal surfaces, etc.). This method using geometric calculations is comparable to geographical positioning using a satellite-based positioning system (such as GPS, etc.), whereby the temperature measuring points correspond to the positions of the satellites and the position of the defective cell corresponds to the position of the object to be located.

[0048] According to an advantageous embodiment, for a calculation of distance parameters, for example, for each measured temperature profile, at least one "temperature profile parameter" can first be determined (calculated), from which a suitable distance parameter can then be determined (calculated), for example with the aid of the thermal model (or its mathematical implications), which in turn is used as an input variable for the aforementioned geometric calculation of the position of a defective battery cell.

[0049] “Temperature profile parameters” that can be used advantageously in the invention, for example for use in correlation calculations or geometric calculations of the aforementioned type, are, for example: - a time of onset of the temperature increase in question, - a point in time during the temperature rise in question at which this temperature rise has reached a certain percentage (e.g. 50%) of a maximum temperature rise for the temperature in question, and - a maximum temperature rise achieved.

[0050] In one embodiment of the method, for example, it is provided that in step c), a time at which the temperature rise begins is determined for at least one of the measured temperatures. This time is also referred to below as the "onset time." A particular relevance of this parameter is that it is generally greater the further away the heat source (defective battery cell) is from the relevant temperature measuring point.

[0051] In one embodiment of the method, it is provided that in step c) a parameter is determined for at least one of the measured temperatures which is representative of a temperature rise rate. In particular, such a parameter can be determined, for example, a point in time during the temperature rise at which the temperature rise has reached a certain percentage of a maximum temperature rise for this temperature. Such a percentage can in particular be set, for example, in the range from 20% to 80% (e.g., 50%). If set to, for example, 50%, this point in time can also be referred to as the “half-life point”. A particular relevance of this parameter is that it is generally smaller the further away the heat source (defective battery cell) is from the temperature measuring point in question.

[0052] In one embodiment of the method, in step c), a maximum temperature rise achieved is determined for at least one of the measured temperatures. The temperature reached in this process is also referred to below as the "maximum temperature." A particular relevance of this parameter is that it is generally smaller the further away the heat source (defective battery cell) is from the relevant temperature measuring point.

[0053] In one embodiment, the identification of at least one of the battery cells as a defective battery cell in step c) is based on determining the position of the defective battery cell, taking into account distances from this position between several of the temperature measuring points determined during the evaluation. As already explained, for this purpose, for example, at least one temperature profile parameter can first be calculated for each measured temperature profile in order to calculate the aforementioned distances from these temperature profile parameters.

[0054] Alternatively or in addition to the above-explained embodiments of the evaluation carried out in step c), a method of artificial intelligence is also contemplated within the scope of the invention, such as, in particular, so-called "supervised machine learning." For example, an algorithm that has been previously trained using training data (so-called "labeled data") can be used for the evaluation in step c), wherein temperature profile data relating to the temperature profiles at the temperature measuring points, each together with associated error event data containing the position (and possibly temperature) of at least one defective battery cell, are to be used as training data. An algorithm trained in this way can then be used in step c) to identify at least one of the battery cells as a defective battery cell (output) based on the temperature profiles measured at the temperature measuring points in step a) (input).Training data suitable for this method can be determined empirically (e.g., by simulating various fault events and measuring temperature profiles) or calculated from the aforementioned thermal model of the battery cell arrangement. Even when using such an artificial intelligence method, one or more of the aforementioned "temperature profile parameters" can be determined during the evaluation in step c), which can then, for example, form components of the input data to be fed to the trained algorithm.

[0055] According to a further aspect of the invention, the object set out at the outset is achieved by an electrical energy storage system (cf. claim 9) which comprises: - a battery cell arrangement formed from a plurality of electrically interconnected battery cells, - a temperature measuring device for the time-resolved measurement of temperatures at several temperature measuring points distributed over the battery cell arrangement, and - a detection device configured to detect a fault event in the battery cell arrangement when the measurement of the temperatures shows that at least one of the measured temperatures increases excessively, and to evaluate the measured temperatures based on a thermal model of the battery cell arrangement, taking into account the arrangement of the temperature measuring points, in order to identify at least one of the battery cells as a defective battery cell.

[0056] The embodiments and special configurations described here for the detection and localization method according to the invention can, individually or in any combination, also be provided in an analogous manner as embodiments or special configurations of the energy storage system according to the invention, and vice versa.

[0057] Advantageous embodiments of the energy storage system also emerge from the following description of possible designs of the individual components. Battery cell arrangement

[0058] The battery cell arrangement can, for example, be formed from more than 50, in particular more than 100 battery cells electrically connected to one another in parallel and / or series and, as such, form the energy storage device of the energy storage system. Alternatively, however, the battery cell arrangement represents only one of a plurality of “battery cell modules” (each having, for example, a smaller number of battery cells), which as a whole form the energy storage device of the energy storage system. Often, a plurality of such, for example identically designed, battery cell modules are electrically connected to one another in parallel and / or series in a controllable manner (e.g. by means of a battery management system) in such a way that they can be individually switched on and off in the system. In one embodiment, a plurality of (e.g. 2 to 20) battery cell modules are provided, each containing at least 10 (e.g. 10 to 100) battery cells.If the energy storage system comprises several battery cell modules between which there is no significant thermal interaction (e.g. due to interposed heat sinks, etc.), the detection and localization method according to the invention can be provided separately for each of these modules. Battery cells

[0059] The battery cells can, in particular, be electrochemical battery cells. Examples include lithium-ion cells based on mixed transition metal oxides of lithium, which can be based on materials such as lithium nickel cobalt manganese oxide (NCM), lithium titanate (LTO), lithium ferrophosphate (LFP), or lithium nickel manganese oxide (LNMO). Ultracapacitors, for example, can also be considered as battery cells. Temperature measuring device

[0060] The temperature measuring device is used for the time-resolved measurement of temperatures at several temperature measuring points distributed throughout the battery cell array. For this purpose, it can, for example, comprise a number of temperature sensors distributed throughout the battery cell array, with "at least one temperature sensor per 20 battery cells" whose individual positions correspond to the individual temperature measuring points. The corresponding temperature measured values ​​can be transmitted to the recording device for evaluation there, for example, via a wired or wireless method.Battery cell arrangements are known from the prior art in which a plurality of cell monitoring units are provided to monitor the individual cell voltages of the battery cells. These monitoring units are distributed over the battery cell arrangement and each electrically connected to an associated battery cell, and which detect the cell voltages of the associated battery cells and provide corresponding measured values. Within the scope of the present invention, such cell monitoring units can have the necessary temperature sensors (or be electrically connected thereto) and thus define the temperature measuring points. If the temperature sensors or such cell monitoring units are each equipped with a radio device, the measured values ​​generated by the temperature sensors or cell monitoring units (e.g. also containing temperature measurement data) can be transmitted wirelessly to the detection device via a radio connection (if necessary).together with measurement data concerning the aforementioned cell voltages). Recording device

[0061] The detection device serves to detect a fault event in the battery cell arrangement and, in this case, to identify at least one of the battery cells as a defective battery cell. The detection device is preferably implemented as a program-controlled computer device or as a functional component (software and / or hardware) of such a program-controlled computer device (e.g., battery management system). The detection device can, for example, have a temperature detection unit in the form of a temperature measurement interface for receiving temperature measurement data provided by the temperature measurement device during the time-resolved measurement of the temperatures at the temperature measurement points. If the temperature sensors orIf the cell monitoring units containing these are each equipped with a radio device, the temperature measurement data can be transmitted wirelessly to a temperature measurement interface designed as a radio interface. The detection device can further comprise, for example, an evaluation device (implemented as software and / or hardware) to carry out the evaluation of the measured temperatures based on the thermal model. The thermal model forms a basis for a localization algorithm, which runs, for example, in a program-controlled manner in the detection device and by means of which, after a fault event is detected, at least one battery cell is identified as defective (and, if necessary, its temperature is also estimated).

[0062] In one embodiment, the electrical energy storage system further comprises a voltage measuring device for measuring cell voltages at the battery cells of the battery cell arrangement in a time-resolved manner and transmitting corresponding cell voltage measured values ​​to the detection device, which can be taken into account, for example, in the detection of fault events and / or evaluation for the purpose of localization (in addition to the temperatures measured at the temperature measuring points). For example, cell voltages measured at the battery cells can lead to a corresponding determination in the assessment of the presence of a fault event carried out in step b) if the voltage measurement shows that at least one of the measured cell voltages drops excessively (which indicates a defect in the cell in question).A detection of a fault event and / or localization of a correspondingly defective battery cell based on the cell voltage measurement can, for example, be advantageously used to verify the plausibility of a corresponding detection and / or localization based on the evaluation of the temperatures measured at the temperature measuring points, or vice versa.

[0063] According to a further aspect of the invention, the use of a method of the type described here and / or an energy storage system of the type described here is proposed for detecting and locating fault events in a battery cell arrangement of an electrical energy storage system for supplying energy to a vehicle. The vehicle can, in particular, be a vehicle equipped with an electric drive system, such as a battery electric vehicle (BEV) or hybrid electric vehicle (HEV), wherein the energy storage system is provided for the electrical supply of this drive system.

[0064] According to a further aspect of the invention, a computer program product comprising program code is proposed which, when executed on a data processing device, carries out a method of the type described here. The data processing device can, in particular, be the detection device of an electrical energy storage system of the type described here.

[0065] The invention will be further described below using exemplary embodiments with reference to the accompanying drawings. They schematically depict: Fig. 1 a block diagram of an electrical energy storage system according to an embodiment, Fig. 2 an exemplary representation to illustrate a location-dependent course of a temperature in a battery cell arrangement after the occurrence of a defect in a battery cell, Fig. 3 an exemplary representation to explain a relationship between time-dependent temperature profiles at several temperature measuring points and the position of a defective battery cell within a battery cell arrangement, and Fig. 4 an exemplary representation of several time-dependent temperature curves at the temperature measuring points of Fig. 3.

[0066] Fig. 1 shows an electrical energy storage system 10 for supplying an electrical system of a vehicle equipped with an electric drive (e.g. BEV, HEV).

[0067] For this purpose, the energy storage system 10 comprises a battery cell arrangement 20, which is formed from a plurality of electrically interconnected battery cells 22, and a battery management system (BMS) 30 for controlling and monitoring the battery cell arrangement 20.

[0068] In the example, the battery cells 22 are each cylindrical and designed as electrochemical battery cells (e.g., lithium-ion cells). For charging and discharging the electrical energy storage device formed by the battery cell arrangement 20, the energy storage system 10 is equipped with an energy storage connection 40.

[0069] In the example shown, the battery cell arrangement 20 comprises a plurality of flat or plate-shaped battery cell layers 24, each with an approximately rectangular contour, for example, which each form part of the energy storage device formed by the energy storage system 10 and can, for example, represent battery cell modules that can be separately switched on and off in the system. In the example, the energy storage device comprises a plurality of such battery cell layers 24 in a stacked arrangement, wherein a cooling layer (not shown) for cooling the battery cells 22 can be interposed between battery cell layers 24 that are adjacent to one another in pairs in the stack.

[0070] For example, the illustrated battery cell arrangement 20 could thus be approximately cuboid-shaped and be formed, for example, from 4 such battery cell layers 24, in each of which 100 battery cells 22 are electrically connected.

[0071] The battery management system 30 implemented as a program-controlled computer device is as in Fig. 1 symbolized at 31 via a data interface with the battery cell arrangement 20 in order to monitor the operation (charging and discharging) of the energy storage device in a program-controlled manner (e.g. charging / discharging current measurement, etc.) and can, in the example, communicate operating parameters such as charge state, charging / discharging current, temperatures, etc. (e.g. also individually for the individual layers or modules 24) recorded in the area of ​​the energy storage system 10 to an external device (e.g. central control unit of the vehicle) via a connection (data interface) symbolized at 32.

[0072] The battery management system 30 protects the components of the battery cell arrangement 20 from overloading, for example, by preventing further charging for overcharge protection or further discharging for deep discharge protection. To accomplish the monitoring tasks of the battery management system 30, the battery cell arrangement 20 is equipped with sensors to detect a series of operating parameters from the area of ​​the battery cell arrangement 20 and deliver corresponding signals or data to the battery management system 30. From a functional perspective, the components provided in the battery cell arrangement 20 and used for this detection could also be considered part of the battery management system 30.

[0073] In the example shown, the sensors in the area of ​​the battery cell arrangement 20 are used to record, in particular, several temperatures at different respective measuring points within the battery cell arrangement 20 as well as respective cell voltages at the battery cells 22.

[0074] As a component of this sensor system, the electrical energy storage system 10 includes, for example, a temperature measuring device formed by several temperature sensors arranged distributed across the battery cell layer 24. The figure shows exemplary temperature sensors 37-1, 37-2, 37-3, and 37-4, which serve for the time-resolved measurement of respective temperatures T1, T2, T3, and T4 at several temperature measuring points arranged distributed across the battery cell layer 24.

[0075] Individual ones of the temperature sensors 37-1, 37-2, 37-3 and 37-4 or the entirety of these temperature sensors are also referred to below by the reference number “37”, and individual ones of the temperatures T1, T2, T3 and T4 or the entirety of these temperatures are also referred to below by the reference symbol “T”.

[0076] The temperatures T measured by the temperature sensors 37 as well as the cell voltages measured by the cell voltage sensors (not shown) are communicated via the connection 31 (wired or wireless) to a detection device 33 of the BMS 30.

[0077] For this purpose, the detection device 33 has a voltage detection unit 34 and a temperature detection unit 36, into which, in the example, the measurement data supplied by the sensors is input and forwarded from there to an evaluation device 35 for evaluation of this data within the framework of battery management. With regard to the implementation of the BMS 30 as a program-controlled computing device or functional component thereof, it should be noted that the components 34, 35, 36 also ultimately represent components of the computing device (e.g., comprising a microcontroller) implemented by software and / or hardware.

[0078] The detection device 33 is configured to detect, by means of the evaluation device 35, a fault event in the battery cell arrangement 20 if the measurement of the temperatures T shows that at least one of the measured temperatures T is increasing excessively. Such a temperature increase is an indicator of a defect in one or more battery cells 22 in the battery cell layer 24 in which the excessive temperature increase was measured.

[0079] The detection device 33 is further designed to evaluate, by means of the evaluation device 35, the temperatures T measured in the relevant battery cell layer 24 based on a respective “thermal model” of this battery cell layer 24, taking into account the arrangement of the temperature measuring points (ie positions of the temperature sensors 37-1, 37-2, 37-3 and 37-4), after detection of such a fault event, in order to identify at least one of the battery cells 22 of the relevant battery cell layer 24 as a defective battery cell 22.

[0080] Since in the present example the plurality of stacked battery cell layers 24 are thermally "decoupled" from one another by the respective intermediate cooling layers, which can be designed, for example, as plate-shaped heat sinks through which a cooling medium (e.g. water) flows, i.e. the excessive heat generated by a defective battery cell 22 in a specific battery cell layer 24 can only spread within this battery cell layer 24, it is sufficient to base the evaluation on the thermal model of this battery cell layer 24 when identifying the defective battery cell 22.

[0081] The method implemented by the battery management system 30 for detecting and locating defective battery cells 22 is explained in more detail below using a few examples.

[0082] Fig. Figure 2 is an exemplary representation illustrating heat propagation in an arrangement of a row of battery cells 22, initially assumed to be simplified as one-dimensional, along a direction with a spatial coordinate x. The figure shows a location-dependent profile of a temperature T(x) in the illustrated battery cell arrangement at a specific time after the occurrence of an excessively heat-generating defect in a battery cell 22d (indicated in the figure by a lightning symbol).

[0083] Immediately after the occurrence of the defect, there is an increase in temperature T(x) only in the area of ​​the defective cell 22d, corresponding to a relatively sharply defined "peak" around a position "xd" of the cell 22d in the course of the temperature T(x). As time progresses, the heat propagation in both directions away from the position x=xd leads to a broadening of the peak (as in Fig. 2).

[0084] It is assumed that, as in Fig. 2, a time-resolved measurement of the respective temperature T1 or T2 is carried out at several (here: two) temperature measuring points arranged at positions x1 and x2 distributed across the battery cell arrangement. On the basis of a suitable "thermal model" of the battery cell arrangement shown, i.e. one based on the physical laws of heat propagation, the position xd at which the defective cell 22d is located can be calculated by evaluating the measured temporal temperature profiles T1(t) and T2(t), where t denotes time, taking into account the arrangement positions x1 and x2 of the temperature measuring points, i.e. this defective cell 22d can be localized.

[0085] For example, the thermal model can model the battery cells 22 as a heat source with a specified heat output and a specified heat capacity. The heat output of each battery cell 22 can be specified, for example, as a function of a current operating state of the battery cells 22 (e.g., determined from a measurement of operating parameters). In contrast, the heat capacity of each battery cell 22 can be specified, for example, as essentially dependent only on the cell design, i.e., in particular, the materials used for the cell or the spatial distribution of these materials.

[0086] Since the battery cells 22 are arranged spatially close to one another, direct heat transfers occur between adjacent battery cells 22. The thermal model can account for such heat transfers between adjacent battery cells 22 by specifying thermal resistances between pairs of adjacent cells 22. When specifying these thermal resistances, those portions of these heat transfers that occur via the electrical contacts of adjacent and electrically contacted battery cells 22 can also be considered.

[0087] Further heat transfers, such as those between battery cells 22 and the environment of the battery cell arrangement acting as a heat sink, can be taken into account by the thermal model by appropriately predefined thermal resistances between the battery cells 22 and the environment modeled as a heat sink.

[0088] When evaluating the measured temperature profiles T1(t) and T2(t), it is possible to determine, for example, for each of the temperature measuring points x1, x2, at which point in time the respective temperature rise begins (“onset” time). In the example of Fig. 2, a temperature increase will, for example, first be detectable at x1 and only later at x2, because the defect position xd and thus “heat source” is closer to x1 than to x2.

[0089] Furthermore, during the evaluation, for example, for each of the temperature measuring points x1, x2, a point in time (related to the respective onset time) in the course of the temperature increase can be determined at which the temperature increase has reached a certain percentage (e.g. 50%) of a maximum temperature increase for this temperature measuring point x1 or x2. In the example of Fig. 2, this time point (or time span from the onset time point) will be smaller at x1 than at x2, because the smaller distance from x1 to xd (compared to the distance from x2 to xd) not only causes an earlier onset of the temperature rise at x1, but also a subsequent faster reaching of the maximum temperature at x1, which represents an equilibrium state.

[0090] Furthermore, during the evaluation, for example, a maximum temperature rise can be determined for each of the temperature measuring points x1, x2, which is the difference between the mentioned maximum temperature and an initial temperature (e.g. at the onset time, or already before). In the example of Fig. 2, the maximum temperature rise reached at x1 will be larger than that at x2, which is also a consequence of the smaller distance from x1 to xd (compared to the distance from x2 to xd).

[0091] Through a suitable (based on a thermal model) evaluation of such "temperature profile parameters" determined from the measured temperatures T1(t) and T2(t), one or more of the battery cells 22 can be identified as defective. Furthermore, within the scope of this evaluation, it is even advantageous to estimate the temperature of the fault event or, in the example of Fig. 2 of the temperature of the defective cell 22d is possible. In particular, considering a position of one or more defective cells known through localization, the maximum temperature rise achieved at each of the temperature measuring points is, in a sense, a measure of the temperature of the defective cell(s), so that the position of the defective cell(s) in conjunction with the "absolute values" of the maximum temperature rises enables the aforementioned estimation. Analogous considerations also apply to the other temperature profile parameters discussed here, so that the evaluation of their measured values ​​(especially "absolute values") also provides a basis for the estimation.

[0092] The method thus implemented for detecting and locating defective battery cells is described below with reference to the Fig. 3 and Fig. 4 is explained again for a two-dimensional arrangement of battery cells.

[0093] Fig. 3 is an exemplary representation of a two-dimensional arrangement of battery cells 22 on a square grid, which is, for example, one of the battery cell layers 24 of the Fig. 1 can be the energy storage system 10 shown.

[0094] In the following description of the example of Fig. 3 essentially only refers to the differences to the one with reference to Fig. 2 already described example and hereby expressly refers to the description of this previous embodiment ( Fig. 2).

[0095] The battery cell layer 24 in Fig. 3 formed battery cell arrangement extends over a large area, so that the position of each of the battery cells 22 is given by respective location coordinates x and y.

[0096] Again, assume that an excessive heat-generating defect of a battery cell 22d (indicated by a lightning symbol in the figure) occurs.

[0097] By means of several (here: four) temperature measuring sensors 37-1 to 37-4 arranged at respective positions (x1,y1) to (x4,y4) distributed over the battery cell layer 24, a time-resolved measurement of respective temperatures T1(t) to T4(t) is carried out.

[0098] Fig. 4 shows an example of these measured temporal temperature profiles T1(t) to T4(t) at the positions (x1,y1) to (x4,y4) in the example of Fig. 3

[0099] Based on a suitable thermal model of the battery cell arrangement, by evaluating the temporal temperature profiles T1(t) to T4(t) taking into account the arrangement positions or temperature measuring points (x1,y1) to (x4,y4), a position (xd,yd) can be calculated at which the defective cell 22d is located in the example shown, ie this defective cell 22d can be localized.

[0100] When evaluating the temperature curves T1(t) to T4(t), for example, one or more of the temperature curve parameters already explained can be determined for each of the temperature measuring points at the positions (x1,y1) to (x4,y4).

[0101] In Fig. 4, for example, the temperature curves T1(t) to T4(t) have different "onset" times to1 to to4. First, a temperature rise begins at time to2 at position (x2,y2), then at time to3 at position (x3,y3), then at time to4 at position (x4,y4), and finally at time to1 at position (x1,y1).

[0102] In addition, different maximum temperatures T1max to T4max can be seen from the temperature curves T1(t) to T4(t), from which in turn different maximum temperature increases T1max - T0, T2max - T0, T3max - T0 and T4max - T0 result, where T0 denotes an initial temperature at the respective position, which is assumed to be identical for all positions (x1,y1) to (x4,y4) in the example and was previously measured (e.g. at the respective onset time).

[0103] Finally, the temperature profiles T1(t) to T4(t) show different time periods which the temperature increases each require in order to reach a certain proportion (e.g. 50%) of the respective maximum temperature increase T1max - T0, T2max - T0, T3max - T0 or T4max - T0, starting from the respective onset time t01, t02, t0 or t04. This definition of a temperature profile parameter representative of a temperature increase rate is to be understood as an example and can be modified in many ways within the scope of the invention. An example of a modified parameter would be the time period which the respective temperature increase requires to increase from a certain first proportion (e.g. 10%) of the maximum temperature increase to a certain second proportion (greater than the first proportion, e.g. 90%) of the maximum temperature increase.

[0104] The determination of such temperature profile parameters, which can be determined in a simple manner from the temperature profiles T1(t) to T4(t), allows, in particular, for example, conclusions to be drawn as part of the evaluation regarding the respective distances between, on the one hand, the temperature measuring point in question and, on the other hand, the defective cell 22d, in order to calculate the position (xd,yd) of the defective cell 22d based thereon.

[0105] Regarding a suitable thermal model to describe the Fig. 3 shown two-dimensional arrangement of the battery cells 22 is, in contrast to the example of Fig. 2 it should be noted that, for example, for battery cells 22 located inside the arrangement, four thermal resistors are required to the four nearest neighbouring cells (in Fig. 3 left, right, above and below the cell 22 in question).

[0106] For one of the battery cell layers 24 (in Fig. 3) through which a cooling medium of a specific temperature flows, the model of the cooling plate can, for example, assign a fixed temperature (as a boundary condition) corresponding to that of the cooling medium. A calculation of the position (xd,yd) of the defective battery cell 22d can, for example, be carried out with the aid of a geometric calculation, in which the position (xd,yd) in the two-dimensional arrangement (battery cell layer 24) is determined as an intersection point of respective circles around the positions (x1,y1) to (x4,y4), the radii of which were determined based on an evaluation of the temperature profiles T1(t) to T4(t) or, in particular, for example, one or more of the above-mentioned temperature profile parameters. Such circular lines are expedient in the case of heat propagation in the respective battery cell layer 24 that can be described as isotropic (in the xy plane) essentially or on a larger length scale.

[0107] In the case of an anisotropic heat propagation in the xy-plane of the battery cell layer 24, such a geometric calculation can also be carried out, although for the determination of the intersection points, different lines must be provided instead of circular lines. Here is an example: Assume in the example of Fig. 3 are each in the horizontal direction (in Fig. 3) battery cells 22 which are immediately adjacent to one another are electrically connected to one another via their electrical contacts (e.g. “connected in series”), but not in the vertical direction (in Fig. 3). Then, in the thermal model, thermal resistances are calculated differently depending on whether heat flows are to be directed horizontally or vertically (in Fig. 3) are taken into account, and anisotropic heat propagation, in which, for example, the excessive heat emanating from the defective cell 22d spreads more rapidly and strongly in the horizontal direction than in the vertical direction. In this case, ellipses, for example, can be used to determine the intersection point instead of circular lines.

[0108] If the battery cell layer 24 of Fig. 3 If one or more additional (stacked) battery cell layers are arranged vertically adjacent (orthogonal to the xy plane), the thermal model must be provided accordingly in three dimensions. In this case, thermal resistors that thermally couple adjacent battery cells 22 within each of the battery cell layers must be considered, on the one hand, in or parallel to the xy plane, and thermal resistors that thermally couple adjacent battery cells 22 within each of the battery cell layers, orthogonal to the xy plane, must be considered.

[0109] Based on such a three-dimensional model, the evaluation can also be carried out, for example, with the help of a geometric calculation, whereby suitable surfaces (e.g. spherical surfaces, ellipsoidal surfaces, etc.) must be provided for the corresponding determination of intersection points instead of lines (e.g. circles, ellipses, etc.).

[0110] Information about the result of the evaluation performed can be stored, for example, in an error memory of the energy storage system 10 and / or communicated to a control device of the relevant vehicle via the data interface 32 for such storage (and possibly also display). After the error event has been detected and evaluated, an affected battery cell module within the energy storage system 10 can also be shut down, for example.

[0111] In summary, the invention and the described embodiments advantageously enable detection and improved localization of a defective battery cell in a battery cell arrangement of an electrical energy storage system. In addition to estimating the position of the defective cell, an estimation of the temperature of the defective cell can also be realized. In the fault-free state of the battery cell arrangement, the temperature measuring points show at least approximately identical temperatures. Due to the more or less simultaneous temperature increase at the various temperature measuring points, a fault event can be detected and / or well verified. A more precise evaluation of the temporal temperature profiles or of certain profile parameters (such as rise height, rise time, etc.) allows the spatial localization of the defective cell and, in addition, an estimate of its temperature.By taking particular account of the temperature profile at the temperature measuring point closest to the defective cell, a possible critical condition can be detected and a potentially impending so-called “thermal runaway” can be avoided, for example, by taking suitable countermeasures (e.g. limiting the electrical power of the energy storage system, switching off the energy storage system or at least one battery cell module, etc.). List of reference symbols 10 Energy storage system 20 battery cell arrangement 22 battery cells 22d defective battery cell 24 Battery cell layer (e.g. battery cell module) 30 Battery management system 31 Connection (data interface) 32 Connection (data interface) 33 Recording device 34 Voltage detection unit 35 Evaluation device 36 Temperature recording unit 37 temperature sensors 40 Energy storage connection T Temperature t time

Claims

[1] Method for detecting and locating defective battery cells (22d) in a battery cell arrangement (20) of an electrical energy storage system (10), wherein the battery cell arrangement (20) is formed from a plurality of electrically interconnected battery cells (22), and wherein the method comprises the following steps: a) time-resolved measurement of temperatures (T1(t), T2(t), ...) at several temperature measuring points distributed over the battery cell arrangement (20), b) detecting a fault event in the battery cell arrangement (20) if the measurement of the temperatures (T1(t), T2(t), ...) shows that at least one of the measured temperatures (T1(t), T2(t), ...) increases excessively, c) after detecting a fault event, evaluating the measured temperatures (T1(t), T2(t), ...) based on a thermal model of the battery cell arrangement (20) taking into account the arrangement of the temperature measuring points in order to identify at least one of the battery cells (22) as a defective battery cell (22d). [2] Method according to claim 1, wherein the temperatures (T1(t), T2(t), ...) measured in step a) are temporarily stored at least until the identification of at least one of the battery cells (22) as a defective battery cell (22d) in step c) is completed. [3] Method according to claim 1 or 2, wherein in step b) the presence of an excessive temperature rise is assumed if the temperature in question (T1(t), T2(t), ...) exceeds a predetermined first threshold value and / or a time derivative of the temperature in question (T1(t), T2(t), ...) exceeds a predetermined second threshold value. [4] Method according to one of the preceding claims, wherein the thermal model models the battery cells (22) each as a heat source with a predetermined heat output and a predetermined heat capacity and takes into account heat transfers between adjacent battery cells (22) and between battery cells (22) and an environment of the battery cell arrangement (20) through predetermined thermal resistances between the adjacent battery cells (22) or between the battery cells (22) and the environment modeled as a heat sink. [5] Method according to one of the preceding claims, wherein in step c) a time (to1, to2, ...) of the onset of the temperature rise is determined for at least one of the measured temperatures (T1(t), T2(t), ...). [6] Method according to one of the preceding claims, wherein in step c) for at least one of the measured temperatures (T1(t), T2(t), ...) a point in time in the course of the temperature rise is determined at which the temperature rise has reached a certain percentage of a maximum temperature rise (T1max - T0, T2max - T0, ...) for this temperature. [7] Method according to one of the preceding claims, wherein in step c) a maximum achieved temperature rise (T1max - T0, T2max - T0, ...) is determined for at least one of the measured temperatures (T1(t), T2(t), ...). [8] Method according to one of the preceding claims, wherein in step c) the identification of the at least one of the battery cells (22) as a defective battery cell (22d) is based on a determination of a position (xd; (xd,yd)) of the defective battery cell (22d) taking into account distances of several of the temperature measuring points from this position (xd; (xd,yd)) determined during the evaluation. [9] Electrical energy storage system (10), comprising: - a battery cell arrangement (20) formed from a plurality of electrically interconnected battery cells (22), - a temperature measuring device (36, 37) for the time-resolved measurement of temperatures (T1(t), T2(t), ...) at a plurality of temperature measuring points distributed over the battery cell arrangement (20), and - a detection device (33) which is designed to detect a fault event in the battery cell arrangement (20) if the measurement of the temperatures (T1(t), T2(t), ...) shows that at least one of the measured temperatures (T1(t), T2(t), ...) increases excessively, and to evaluate the measured temperatures (T1(t), T2(t), ...) based on a thermal model of the battery cell arrangement (20) taking into account the arrangement of the temperature measuring points in order to identify at least one of the battery cells (22) as a defective battery cell (22d). [10] Computer program product comprising a program code which, when executed on a data processing device, carries out a method according to one of claims 1 to 8.

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