Method for determining at least one battery parameter of a battery, correspondingly operable battery and motor vehicle

Abstract

Method for determining at least one battery parameter of a battery (10) of an at least partially electrically powered motor vehicle (KFZ), comprising a plurality of electrically interconnected, switchable battery cells (12), wherein at least one switching element (24, 26) for switching a current in the respective battery cell is integrated in each of the switchable battery cells (12), wherein the battery has a control device (28) which is configured to control the switching elements (24, 26) of the battery cells (12), and wherein each of the switchable battery cells (12) has a measuring device (30) which is configured to detect at least one cell parameter of the respective battery cell (12), and the cell parameter of each battery cell (12) depends on the cell parameter of a respective other of the battery cells (12) of the battery (10), characterized in that - the control device (28) interrupts and establishes a current flow in at least one of the battery cells (12) by controlling the switching elements (24, 26) of the battery cells (12), whereby the at least one cell parameter of the at least one battery cell (12) is changed, wherein - the change in the at least one cell parameter of the at least one battery cell (12) excited in this way is an excitation signal (34) which changes the respective at least one cell parameter and / or a second parameter correlated with the cell parameter of at least some of the remaining battery cells (12) of the battery (10), - the change in the at least one cell parameter and / or the second parameter correlated with the cell parameter in the excited battery cell (12) and a) in each of the remaining battery cells (12) of the battery or b) in a predetermined subgroup of battery cells (12) of the battery (10) is detected by the respective measuring device (30) of the respective battery cell (12) as a respective response signal (40), and - the at least one battery parameter of the battery (10) is determined on the basis of the response signals (40) according to a predetermined determination rule.

Description

[0001] The invention relates to a method for determining at least one battery parameter of a battery of an at least partially electrically powered motor vehicle, for example an electric or hybrid vehicle, wherein the battery comprises a plurality of switchable battery cells electrically interconnected with one another.

[0002] A switchable battery cell within the meaning of the invention is a battery cell in which at least one switching element for switching a current is integrated. In the battery according to the invention, a plurality of such switchable battery cells are electrically interconnected to form a battery pack. Such an arrangement of interconnected switchable battery cells can be designed such that several of the switchable battery cells are interconnected in parallel and form a cell level. Several such cell levels can be interconnected in series to form a cell string. In the battery pack, one string or several such strings can be electrically interconnected in parallel. Mechanically, the battery cells can be arranged or organized in battery modules, each of which can already contain several battery cells connected in parallel and in series.For example, a 4p3s battery module provides a series connection (s) of three cell levels, each of which comprises a parallel connection (p) of four battery cells. A battery according to the invention can consist of any number of battery modules, resulting in a system or circuit of electrically interconnected, switchable battery cells.

[0003] Batteries constructed from battery modules containing switchable battery cells are well known. The advantage of such a battery is that by controlling the switching elements of the switchable battery cells, each of the switchable battery cells can be switched on or off as needed. This allows, for example, defective battery cells to be selectively removed from the battery circuit.

[0004] US 5 656 915 A discloses a battery composed of several switchable battery cells with individual cell monitoring and individual cell control.

[0005] US 9 172 254 B2 also discloses a battery system consisting of several switchable battery cells for use in an electrically powered motor vehicle.

[0006] US 2012 / 0064378 A1 describes a protective device for a battery with a plurality of battery cells, comprising an electrical switching element.

[0007] Conventional batteries typically include a battery management system that can predict battery behavior for an upcoming load profile or load case based on predetermined battery parameters. The prediction is usually performed using a simulation model in which the battery parameters are stored.

[0008] To provide such battery parameters for monitoring or predicting battery behavior, the individual cell parameters in the individual battery cells are typically first determined in prototypes. Methods for determining cell parameters include, for example, cyclical discharging and charging processes (cycling) or electrochemical impedance spectroscopy (EIS) measurements. The individual battery cells are typically assembled into prototype structures. The prototypes correspond to batteries as installed in at least partially electrically powered vehicles.Based on the prototype setups and measurements, the cell parameters of the battery cells and / or system parameters of the battery, such as electrical, thermal, and / or mechanical properties, can then be determined under realistic conditions, and the behavior of the individual battery cells in the connected state can be investigated. The determined cell parameters and / or system parameters of the battery are transmitted to the battery management system, where they are stored as the battery parameters.

[0009] The battery parameters of a battery determined on the basis of a prototype structure for use in a simulation model of the battery for the purpose of predicting the battery behavior in a specific load profile or load case are usually disadvantageously assumed to be unchangeable for the entire life cycle of the battery and are not updated for a respective ageing state of the battery cells that make up the battery.

[0010] Furthermore, determining battery parameters based on prototype setups with new battery cells does not allow for the localization and quantification of electrical, thermal, and / or mechanical couplings between individual battery cells. Furthermore, the battery parameters determined based on prototype setups are only partially transferable to the batteries actually used, since the battery-specific cell parameters of the battery cells and / or system parameters of an actually used battery may differ from the battery parameters determined based on a respective prototype setup, for example, due to manufacturing reasons.

[0011] Using the battery parameters determined as described above, the simulation model is created, which is used to predict the behavior of a battery, i.e., the behavior of a system of interconnected battery cells. Since, as described above, the battery parameters determined using a prototype setup are neither battery-specific nor adapted to the aging of individual battery cells, the simulation model inevitably loses accuracy over time. Battery management systems based on such simulation models are also inevitably flawed.

[0012] The battery parameters determined as described above can also be used for real-time battery health estimation or other methods.

[0013] The invention is based on the object of providing battery-specific battery parameters adapted to the aging state of a battery, which can be entered into a simulation model of the battery in order to eliminate the above-mentioned disadvantages in predicting the battery behavior.

[0014] The object is achieved by the subject matter of the independent patent claims. Advantageous developments of the invention are described by the dependent patent claims, the following description, and the figures.

[0015] The invention provides a method for determining at least one battery parameter of a battery of an at least partially electrically powered motor vehicle. The battery comprises a plurality of electrically interconnected, switchable battery cells, wherein at least one switching element for switching a current in the respective battery cell is integrated into each of the switchable battery cells. Furthermore, the battery has a control device configured to control the switching elements of the battery cells. Each of the switchable battery cells has a measuring device configured to detect at least one cell parameter of the respective battery cell. A cell parameter can be a mechanical and / or a thermal and / or an electrical cell parameter. The respective cell parameter of each battery cell depends on the cell parameter of a respective other of the battery cells.In other words, a change in a respective cell parameter in one of the battery cells influences the value of the respective cell parameter in other battery cells, for example a neighboring battery cell.

[0016] The method according to the invention is characterized in that the control device interrupts and / or establishes a current flow in at least one of the battery cells by controlling the switching elements of the battery cells, thereby changing the at least one cell parameter of the at least one battery cell. In other words, by selectively connecting and / or disconnecting one of the battery cells of the battery, a cell parameter in the respective battery cell is changed.

[0017] The change in the at least one cell parameter of the at least one battery cell excited in this way is an excitation signal. One cell parameter can be, for example, the temperature of the excited battery cell. In this case, a change in temperature, for example, an increase in temperature, is the excitation signal. The excitation signal changes the respective at least one cell parameter and / or a secondary parameter correlated with the cell parameter of at least some of the remaining battery cells of the battery in the manner described.

[0018] One cell parameter can, for example, also be the internal cell pressure of the excited battery cell. In this case, a change in the internal cell pressure, for example, an increase in pressure, is the excitation signal. The excitation signal changes, in the manner described, the respective at least one cell parameter and / or a secondary parameter correlated with the cell parameter of at least some of the remaining battery cells of the battery. In this case, the temperature of at least some of the remaining battery cells of the battery could be considered as a secondary parameter.

[0019] Changing a particular cell parameter in one of the battery cells may change the value of any other cell parameter (but in particular also the respective one) in another battery cell.

[0020] In the example case of a temperature increase in the excited battery cell, the temperature of at least some of the remaining battery cells also increases. In this case, the heat transfer may depend, for example, on the heat transfer coefficient of the respective battery cell.

[0021] According to the invention, it is provided that the change in the at least one cell parameter and / or the second parameter correlated with the cell parameter in the excited battery cell and a) in each of the remaining battery cells of the battery or b) is detected in a predetermined subgroup of battery cells of the battery by the respective measuring device of the respective battery cell as a respective response signal. The measuring device can, for example, be a respective temperature sensor that detects the temperature increase in one of the remaining battery cells of the battery or in a predetermined subgroup of battery cells of the battery. The predetermined subgroup can also comprise an individual battery cell. The temperature increase in a respective battery cell can depend on whether, for example, a heat transfer coefficient is subject to age-related changes.

[0022] Based on the response signals, at least one battery parameter is determined according to a predetermined determination rule, for example, the heat transfer coefficient between two battery cells. The determination rule can be implemented, for example, according to the generally known methods of system identification, with a respective excitation signal being used as an input signal and a respective response signal as an output signal.

[0023] The invention provides the advantage that, by controlling the switching elements, specific sub-areas of the battery can be specifically stimulated, in extreme cases down to the individual battery cell level. This selective stimulation of individual sub-areas of the battery and / or individual battery cells of the battery makes it possible to minimize overlapping response signals from a large number of battery cells. The determination of at least one battery parameter can therefore be carried out locally in a predetermined sub-area of ​​the battery. Since the method can be carried out after the battery has been produced and at various points in the battery's life cycle, this has the advantage that a respective battery parameter that is up-to-date and tailored to the respective aging state of a battery and / or battery cell can always be provided to the battery management system.

[0024] The invention also includes embodiments which provide additional advantages.

[0025] One embodiment provides that each of the measuring devices is configured to detect a respective electrical and / or mechanical and / or thermal cell parameter of a respective battery cell. In other words, each of the measuring devices comprises a current sensor and / or a voltage sensor and / or a temperature sensor and / or a strain gauge and / or a pressure sensor (mechanical measurement). This results in the advantage that all variables relevant for the system identification described above can be measured in each of the battery cells. A current sensor can, for example, be a transducer with a Hall probe or shunt resistor, or a direct-imaging current sensor with a Hall sensor. A temperature sensor can, for example, be a thermistor and / or a PTC thermistor and / or a semiconductor temperature sensor or a PTC resistor (PTC - Positive Temperature Coefficient).A strain gauge can be, for example, a foil strain gauge and / or a wire strain gauge and / or a semiconductor strain gauge.

[0026] A further embodiment provides that the control device switches the switching elements according to at least one predetermined switching configuration. A switching configuration can contain information about which areas of a battery are to be specifically stimulated. This results in the advantage that a respective cell parameter and / or battery parameter is determined only for a predetermined sub-area of ​​the battery. A predetermined sub-area can, for example, be a sub-area of ​​the battery that is subject to increased stress due to its proximity to heat-radiating components within the motor vehicle.

[0027] According to a further embodiment, the control device repeats the switching of the switching elements for a cyclic measurement according to the at least one predetermined switching configuration according to a predetermined schedule. In other words, it can be provided that certain subregions of the battery are to be stimulated at regular intervals in order to monitor the temporal change of a respective cell parameter and / or battery parameter there as a function of aging processes with high precision. This can be particularly useful, for example, if a subregion of a battery is located near higher-temperature components and must be closely monitored.

[0028] According to a further embodiment, it is provided that a predetermined maintenance measure is triggered depending on the at least one cell parameter and at least one known state parameter of the battery. In other words, a maintenance measure is triggered if the at least one cell parameter lies outside a predetermined value range. The value range is set depending on the at least one cell parameter and a known state parameter of the battery. A known state parameter can, for example, be a known age of a battery. For example, a fixed assignment of a respective cell parameter and a known state parameter of the battery can be stored in a look-up table. If the at least one cell parameter lies outside a predetermined value range, a predetermined maintenance measure can be triggered.A predetermined maintenance measure can, for example, be the permanent bridging of a battery cell or a sub-area of ​​battery cells in which the at least one cell parameter lies outside a predetermined value range.

[0029] A further embodiment provides that the at least one battery parameter is made available to a digital simulation model of the battery, and the digital simulation model digitally maps or simulates an operating state of the battery. In other words, it can be provided to generate a simulation model of the battery. The predetermined model structure of the simulation model corresponds to the interconnection state of the individual battery cells of the battery. The goal of the modeling is to achieve a simulation of the real battery. Such a simulation model can, for example, be a CFD model (CFD - Computational Fluid Dynamics). In such a simulation model, a digital mapping of the individual battery cells of the battery and the system of interconnected battery cells takes place. In other words, a digital twin of the battery is generated.By knowing at least one of the battery's current operating parameters, the digital twin can also constantly map the battery's current operating status and predict its behavior. This offers the advantage of allowing maintenance measures to be initiated at an early stage.

[0030] According to a further embodiment, the predetermined subgroup of battery cells comprises the battery cells immediately adjacent to the excited battery cell. In other words, a battery cell is excited by controlling the switching elements, while the measuring devices of all or some of the immediately adjacent battery cells detect the change in the respective cell parameter. For example, contact resistances, i.e., electrical and / or thermal contact resistances, can be determined for the battery cells adjacent to the excited battery cell.

[0031] A preferred embodiment of the invention provides that by controlling the switching elements of the respectively excited battery cell, the cell is heated up and the at least one cell parameter is a temperature. The change in the temperature of the at least one battery cell excited in this way is then an excitation signal which changes the temperature of another battery cell of the battery and / or at least some of the remaining battery cells of the battery. According to this embodiment, it is provided that the change in the respective temperature in the excited battery cell and a) in each of the remaining battery cells of the battery or b) in a predetermined subgroup of battery cells of the battery is detected by the respective measuring device of the respective battery cell as a respective response signal. In this case, a measuring device can be a temperature sensor according to the embodiment described above.Based on the response signals, according to the embodiment described here, a heat transfer resistance within the battery is determined as at least one battery parameter of the battery according to a predetermined determination rule.

[0032] According to a further preferred embodiment of the method described here, it is provided that by controlling the switching elements of the respectively excited battery cell, this cell is mechanically deformed, and the at least one cell parameter is an external shape. The mechanical deformation can be caused by the current flow in the battery cell: A known effect that can occur here is so-called swelling. The mechanical deformation of the at least one battery cell excited (deformed) in this way is then an excitation signal that mechanically deforms another battery cell of the battery and / or at least some of the remaining battery cells of the battery.The respective mechanical deformation of the excited battery cell and a) each of the remaining battery cells of the battery or b) a predetermined subgroup of battery cells of the battery is detected by the respective measuring device of the respective battery cell as a respective response signal. In this case, such a measuring device can be a strain gauge according to the above description. Based on the response signals thus detected, according to the embodiment described here, a deformation resistance or a stiffness within the battery is determined as at least one battery parameter of the battery according to a predetermined determination rule.

[0033] According to a further advantageous embodiment, it is provided that by controlling the switching elements of the respectively excited battery cell, its respective cell voltage is changed, and the at least one cell parameter is a cell voltage. The change in the cell voltage of the at least one battery cell excited in this way is then an excitation signal that changes the cell voltage of at least some of the remaining battery cells of the battery. The respective change in the cell voltage of the excited battery cell and a) each of the remaining battery cells of the battery or b) a predetermined subgroup of battery cells of the battery is then detected by the respective measuring device of the respective battery cell as a respective response signal. In this case, a measuring device can be a voltage sensor according to the above description.Based on the response signals thus acquired, according to the embodiment described here, a contact resistance within the battery is determined as at least one battery parameter according to a predetermined determination rule. This offers the advantage that, for example, corrosion at the voltage taps of the individual battery cells and / or damaged insulation between two adjacent battery cells can be detected particularly early.

[0034] The invention also relates to the battery of an at least partially electrically driven motor vehicle, which is designed to undergo a method for determining at least one battery parameter according to one of the previously described embodiments.

[0035] Furthermore, the invention relates to a motor vehicle with a battery as described above. The motor vehicle according to the invention is preferably designed as a motor vehicle, in particular as a passenger car or truck, or as a passenger bus or motorcycle.

[0036] The invention also includes combinations of the features of the described embodiments.

[0037] Exemplary embodiments of the invention are described below. Shown are: Fig. 1 a schematic representation of a partial region of a battery according to the invention comprising a plurality of switchable battery cells; Fig. 2 a schematic representation of a portion of a conventional battery comprising non-switchable battery cells; Fig. 3 a schematic representation of a partial region of a battery according to the invention, comprising a plurality of switchable battery cells, according to one of the described embodiments; Fig. 4 a schematic representation of two different switching states of a switchable battery cell; Fig. 5 is a schematic representation of various system variables upon excitation of a switchable battery cell according to an embodiment described here; Fig. 6 is a schematic representation of a battery comprising a plurality of switchable battery cells in a switching configuration; and Fig. 7 a schematic representation of a battery comprising a plurality of switchable battery cells in a further switching configuration.

[0038] The exemplary embodiments explained below are preferred embodiments of the invention. In the exemplary embodiments, the described components of the embodiments each represent individual, independently considered features of the invention, which also further develop the invention independently of one another and are thus also to be considered as components of the invention, either individually or in a combination other than that shown. Furthermore, the described embodiments can also be supplemented by further features of the invention already described.

[0039] In the figures, the same reference symbols denote elements with the same function.

[0040] Fig. Figure 1 shows a schematic representation of a portion of a battery 10 according to the invention in a motor vehicle. In the embodiment shown here, the battery 10 comprises a plurality of electrically interconnected, switchable battery cells 12. For the sake of clarity, however, only one battery cell 12 is provided with a reference numeral. In the embodiment shown here, the battery cells 12 are electrically interconnected in parallel within cell levels 14. The cell levels 14 shown themselves are interconnected in series. Furthermore, Fig. 1 a power source 16. Each of the switchable battery cells 12 has a cell branch 18 with a galvanic cell 20 and a bypass branch 22. The cell branch 18 comprises a switching element 24 for opening and closing the cell branch 18. The bypass branch 22 comprises a further switching element 26 for opening and closing the bypass branch 22. By controlling the switching elements 24, 26, the control device of the battery 10 (not shown) can specifically switch individual battery cells 12 on or off. In addition, each of the battery cells 12 comprises a measuring device 30, which can detect a thermal and / or electrical and / or mechanical cell parameter in the manner described above.

[0041] Fig. 2 shows, in contrast to the battery 10 according to the invention, a conventional battery consisting of a plurality of non-switchable battery cells.

[0042] Fig. 3 shows a portion of a battery 10 according to the invention comprising a plurality of electrically interconnected switchable battery cells 12, as described above. Fig. The switching configuration 32 shown in Figure 3 provides that the switchable battery cells of cell level A and the switchable battery cells of cell level C are bridged. This means that in all switchable battery cells 12 of both cell level A and cell level C, the respective bypass switches 26 are closed and the respective cell branch switches 24 are open. In the Fig. In the switching configuration shown in Figure 3, the switching elements 24, 26 of the switchable battery cells 12 of cell level B are connected such that all but one of the switchable battery cells 12 are bridged. This means that for all but one of the battery cells 12 of cell level B, the respective switching element 24 of the cell branch is open and the respective further switching element 26 of the bypass branch is closed. The one remaining battery cell 12 of cell level B (see dashed border) or the switching elements 24, 26 of this battery cell 12 are controlled such that a passive state is established. In the passive state (= "idle mode"), both switching elements 24, 26 of the battery cell 12 are open. In the Fig. In the switching configuration 32 shown in Figure 3, the battery cell 12 of cell level B marked by the dashed border carries no current.

[0043] Not in Fig. Figure 3 shows a further switching configuration in which the switching elements 24, 26 of the battery cell 12 marked by the dashed border are controlled such that the battery cell 12 is in an active state (switching element 24 of the cell branch closed and switching element 26 of the bypass branch opened). If the battery cell 12 of cell level B marked by the dashed border is switched to the active state, the remaining battery cells 12 of cell level B are switched to the passive state (= "idle mode") (both switching elements 24, 26 open).

[0044] It can now be provided that an active state and a passive state are alternately created for the battery cell of cell level B marked by the dashed border, i.e. that the two described switching configurations are alternated. This ensures that the battery cell 12 of cell level B marked by the dashed border alternately carries the total current (active state) and no current (passive state or "idle mode"). The remaining switchable battery cells 12 (those of cell levels A and C, as well as all except the battery cell 12 of cell level B marked by the dashed border) carry no current, since they are either, as in Fig. 3, are bridged (when the marked battery cell 12 is in “idle mode”), or are passively switched (when the marked battery cell 12 is actively switched).

[0045] To avoid a short circuit in the charging unit or an interruption in power during load operation, battery cells 12 that are further away and have little or no influence on the measurement can, for example, be switched to active during the phases in which the battery cell 12 marked by the dashed border is in the passive state (= "idle mode"). Alternatively, it is also conceivable that the battery 10 is specifically subjected to a suitable charging profile (current = 0 during idle phases) during charging. If the battery 10 is synthetically subjected to a load (e.g., for system identification) that does not correspond to regular operation in the vehicle, the interruption in power is irrelevant.

[0046] Fig. 4 shows schematic enlarged representations of switchable battery cells 12, wherein the representation on the left side shows a battery cell 12 in the passive state (= “idle mode”) and the representation of the battery cell 12 on the right side shows the battery cell 12 in the active state.

[0047] In the Fig. 3 and Fig. 4, a temperature change in one of the switchable battery cells 12 of cell level B is caused by alternately establishing an active and a passive state of one of the switchable battery cells of cell level B as excitation signal 34.

[0048] Fig. 5 shows, with reference to the descriptions of the Fig. 2, Fig. 3 and Fig. 4 the involved cell parameters in detail. The left column shows the excitation of a conventional battery system (i.e. a conventional battery) according to Fig. 2 and the right column shows the excitation of the battery 10 according to the invention according to Fig. 3 and Fig. 4. Fig. 5 shows the excitation of the two systems using a constant current 36 as an example. In the case of the conventional system (i.e. the conventional battery according to Fig. 2) the constant current is distributed among the individual parallel-connected battery cells based on the internal resistance of the connected battery cells. Thus, the same cell current 38 is established in all battery cells. A temperature measurement of the conventional battery cells produces a response signal 40' for each of the battery cells, which is superimposed and thus smoothed by the response signals of all other battery cells in the battery (see Fig. 5 bottom left).

[0049] The cell-individual excitation according to the invention is shown in the right column in Fig. 5. The excitation is also carried out via a constant current 36. As can be seen from the Fig. 3 and Fig. 4, the switchable battery cells 12 of cell levels A and C are bridged. In cell level B, all but one of the switchable battery cells 12 are bridged. This one of the switchable battery cells 12 in cell level B, however, is alternately switched to an active and a passive state. If one battery cell 12 in cell level B is switched to the active state, the remaining battery cells 12 of cell level B are switched to a passive state (= "idle mode").

[0050] In the active state, a current flow occurs in one battery cell 12, and a cell current 38 is measured. In the passive state, the current flow in the one switchable battery cell 12 is interrupted, and a cell current 38' is measured. This relationship is shown in the middle graph of the right column in Fig. 5. By alternating active and passive switching of the switchable battery cell 12 of cell level B, it alternately carries the total current (constant current 36) and no current. This allows this battery cell 12 to be operated as a controlled heat source, with which the system (i.e., the battery 10) is thermally excited. The thermal signal of the thus excited battery cell 12 is shown in the lower graph of the right-hand column of the Fig. 5 as excitation signal 34. In the exemplary embodiment shown here, the respective temperature changes in the battery cells 12 adjacent to the excited battery cell 12 are shown as response signals 40. The response signals 40 are not superimposed by any response signals from battery cells other than the battery cells 12 of the excited sub-area and are therefore advantageously not smoothed. From the response signals 40 thus acquired, the thermal parameters of the individual switchable battery cells 12 can be determined in the manner described above using the known methods of system identification. Knowledge of the thermal cell parameters of the individual battery cells 12 of the battery 10 allows the heat transfer resistance within the battery 10 to be determined.

[0051] The figures described above are used to demonstrate, by way of example, the cell-individual excitation of the battery 10 for determining thermal parameters.

[0052] The Fig. 6 and Fig. 7 show two different applications of the method according to the invention. According to the Fig. 6, exactly one battery cell 12 of the battery 10 is excited. This changes the at least one cell parameter of the excited battery cell 12. The change in the at least one cell parameter of the excited battery cell 12 changes, as an excitation signal 34, the respective at least one cell parameter and / or a second parameter correlated with the cell parameter of at least some of the remaining battery cells 12 of the battery 10. The change in the at least one cell parameter and / or the second parameter correlated with the cell parameter in the excited battery cell 12 and a) in each of the remaining battery cells 12 of the battery 10 or b) in a predetermined subgroup of battery cells 12 of the battery 10 is measured by the respective measuring device 30 (not shown). Fig. 6) of the respective battery cell 12 as a respective response signal 40 (not shown in Fig. 6 shown).

[0053] According to the Fig. In the application shown in Figure 7, four battery cells 12 of the battery 10 are excited. As a result, the at least one cell parameter of each of the four excited battery cells 12 changes. The respective change in the at least one cell parameter of the excited battery cells 12 changes, as an excitation signal 34, the respective at least one cell parameter and / or a second parameter correlated with the cell parameter of at least a portion of the remaining battery cells 12 of the battery 10. The respective change in the at least one cell parameter and / or the second parameter correlated with the cell parameter in the excited battery cells 12 and a) in each of the remaining battery cells 12 of the battery 10 or b) in a predetermined subgroup of battery cells 12 of the battery 10 is measured by the respective measuring device 30 (not shown). Fig. 7) of the respective battery cell 12 as a respective response signal 40 (not shown in Fig. 7 shown).

[0054] The parameters of battery cells are determined through cycling and methods such as electrochemical impedance spectroscopy before they are interconnected to form a large battery pack. Such systems (i.e., batteries consisting of a large number of electrically interconnected battery cells) are primarily used in electric and hybrid vehicles. Prototypical setups can be used to determine the electrical, thermal, and mechanical properties of the battery pack, and to investigate the behavior of the individual cells (i.e., the battery cells) within the interconnected overall system (i.e., the battery). The determined parameters are then adopted for battery management.

[0055] Due to manufacturing fluctuations during the assembly of large battery packs, the determined parameters of the prototype can be subject to considerable variation. Furthermore, the parameters change with increasing age of the system (i.e., the battery). Battery system-specific parameters and those adapted to aging are unknown. In the case of significant outliers, simulation models become inaccurate, and battery management may fail.

[0056] To characterize the battery pack (i.e., to determine at least one of the battery's operating parameters), it can be excited by a current. However, this results in the superimposed response of an extremely complex overall system. Localizing and quantifying electrical, thermal, and mechanical couplings is therefore only possible to a limited extent.

[0057] In a specific embodiment of the invention, each battery cell is equipped with switches (i.e., switching elements, e.g., active and bypass switches) and sensors (i.e., a measuring device). The sensors are capable of measuring all electrical, thermal, and / or mechanical variables relevant for system identification. They therefore include, for example, current and / or voltage sensors, temperature sensors, and / or strain gauges. By specifying switching configurations, selected areas of the battery system are stimulated, allowing the entire system (i.e., the battery) to be selectively characterized.

[0058] The battery pack can be advantageously characterized after production and throughout its life cycle. This ensures that the battery management system always has up-to-date parameters tailored to the battery system. Battery management tailored to the system ensures safe operation, even for aging battery packs. Furthermore, more efficient battery management is possible, allowing greater amounts of power and energy to be extracted from the battery pack. This increases the range of electric and hybrid vehicles.

[0059] By knowing the parameters, it is possible to create a digital image of the battery through simulation. This digital twin makes it possible to predict the behavior of the battery pack.

[0060] By specifically controlling the switches, electrical (e.g., contact resistance), thermal (e.g., heat transfer resistance), and mechanical (e.g., deformation upon excitation) variables (i.e., battery parameters) can be identified. This allows their interactions with all components of the battery pack to be investigated.

[0061] The excitation of the system with a constant current is in Fig. 5 is shown in the left column for the conventional system (i.e., for the conventional battery) and in the right column for the switching system (i.e., for the battery according to the invention with switchable battery cells). In the case of the conventional system, the cell currents of the battery cells connected in parallel are divided based on their internal resistances (cf. Fig. 5 left center). It is not possible to control the current flow through the individual battery cells. Measuring the temperatures of the battery cells yields the combined response of all cells (see Fig. 5 bottom left).

[0062] In the case of the switchable system, the battery cells of cell levels A and C are bridged (active switch open, bypass switch closed) and one of the battery cells of cell level B (see the battery cell of cell level B surrounded by the dashed line in Fig. 3) is alternately switched active (active switch closed, bypass switch open) and high-impedance (both switches open) (cf. Fig. 5 right center). This allows it to be operated as a controlled heat source, with which the system (i.e. the battery) is thermally stimulated. With the built-in sensor technology of the battery cell (see the battery cell outlined by the dashed line of cell level B in Fig. 3) and the neighboring battery cells, the temperature is measured (cf. Fig. 5 bottom right). The thermal parameters of the system (i.e., battery parameters) can be determined from the measured values ​​using established system identification methods.

[0063] Overall, the examples show how the invention can provide selective system identification of a battery and / or individual sub-areas of a battery by means of switchable battery cells.

Claims

[1] A method for determining at least one battery parameter of a battery (10) of an at least partially electrically powered motor vehicle (KFZ), comprising a plurality of electrically interconnected, switchable battery cells (12), wherein at least one switching element (24, 26) for switching a current in the respective battery cell is integrated in each of the switchable battery cells (12), wherein the battery has a control device (28) which is configured to control the switching elements (24, 26) of the battery cells (12), and wherein each of the switchable battery cells (12) has a measuring device (30) which is configured to detect at least one cell parameter of the respective battery cell (12), and the cell parameter of each battery cell (12) depends on the cell parameter of a respective other of the battery cells (12) of the battery (10), characterized by , that - the control device (28) interrupts and establishes a current flow in at least one of the battery cells (12) by controlling the switching elements (24, 26) of the battery cells (12), whereby the at least one cell parameter of the at least one battery cell (12) is changed, wherein - the change in the at least one cell parameter of the at least one battery cell (12) excited in this way is an excitation signal (34) which changes the respective at least one cell parameter and / or a second parameter correlated with the cell parameter of at least some of the remaining battery cells (12) of the battery (10), - the change in the at least one cell parameter and / or the second parameter correlated with the cell parameter in the excited battery cell (12) and a) in each of the remaining battery cells (12) of the battery or b) in a predetermined subgroup of battery cells (12) of the battery (10) is detected by the respective measuring device (30) of the respective battery cell (12) as a respective response signal (40), and - the at least one battery parameter of the battery (10) is determined on the basis of the response signals (40) according to a predetermined determination rule. [2] Method according to claim 1, wherein each of the measuring devices (30) is configured to detect a respective electrical and / or mechanical and / or thermal cell parameter of a respective battery cell (12). [3] Method according to one of the preceding claims, wherein the control device (25) switches the switching elements (24, 26) according to at least one predetermined switching configuration (32, 32'). [4] Method according to claim 3, wherein the control device (25) repeats the switching of the switching elements (24, 26) for a cyclic measurement according to the at least one predetermined switching configuration (32, 32') according to a predetermined schedule. [5] Method according to one of the preceding claims, wherein a predetermined maintenance measure is triggered as a function of the at least one cell parameter and at least one known state parameter of the battery (10). [6] Method according to one of the preceding claims, wherein the at least one battery parameter is made available to a digital simulation model of the battery (10) and the digital simulation model digitally maps an operating state of the battery. [7] Method according to one of the preceding claims, wherein the predetermined subgroup of battery cells (12) comprises the battery cells (12) immediately adjacent to the excited battery cell (12). [8] Method according to one of the preceding claims, wherein - by controlling the switching elements (24, 26) of the respectively excited battery cell (12), the latter is heated and the at least one cell parameter is a temperature, wherein - the change in the temperature of the at least one battery cell (12) excited in this way is an excitation signal (34) which changes the temperature of at least some of the remaining battery cells (12) of the battery (10), - the change in the respective temperature in the excited battery cell (12) and a) in each of the remaining battery cells (12) of the battery (10) or b) in a predetermined subgroup of battery cells (12) of the battery (10) is detected by the respective measuring device (30) of the respective battery cell (12) as a respective response signal (40), and - a heat transfer resistance within the battery (10) is determined on the basis of the response signals (40) according to a predetermined determination rule as a battery parameter of the battery (10). [9] Method according to one of the preceding claims, wherein - by controlling the switching elements (24, 26) of the respectively excited battery cell (12), the latter is mechanically deformed and the at least one cell parameter is an external shape, wherein - the mechanical deformation of the at least one battery cell (12) excited in this way is an excitation signal (34) which mechanically deforms at least a part of the remaining battery cells (12) of the battery (10), - the respective mechanical deformation of the excited battery cell (12) and a) each of the remaining battery cells (12) of the battery (10) or b) a predetermined subgroup of battery cells (12) of the battery (10) is detected by the respective measuring device (30) of the respective battery cell (12) as a respective response signal (40), and - a deformation resistance within the battery (10) is determined on the basis of the response signals (40) according to a predetermined determination rule as a battery parameter of the battery (10). [10] Method according to one of the preceding claims, wherein - by controlling the switching elements (24, 26) of the respectively excited battery cell (12), the respective cell voltage is changed and the at least one cell parameter is a cell voltage, wherein - the change in the cell voltage of the at least one battery cell (12) excited in this way is an excitation signal (34) which changes the cell voltage of at least some of the remaining battery cells (12) of the battery (10), - the respective change in the cell voltage of the excited battery cell (12) and a) each of the remaining battery cells (12) of the battery (10) or b) a predetermined subgroup of battery cells (12) of the battery (10) is detected by the respective measuring device (30) of the respective battery cell (10) as a respective response signal (40), and - a contact resistance within the battery (10) is determined on the basis of the response signals (40) according to a predetermined determination rule as a battery parameter of the battery (10). [11] Battery (10) of an at least partially electrically driven motor vehicle (KFZ), which is designed to carry out a method for determining at least one battery parameter according to one of the preceding claims. [12] Motor vehicle (KFZ) with a battery (10) according to claim 11.

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