DE102019202465A1 - Method for operating a battery system in a motor vehicle and a correspondingly operable battery system and motor vehicle - Google Patents

Abstract

The invention relates to a method for operating a battery system (16) in a motor vehicle (10), the battery system (16) having several battery cells (34) for generating a battery voltage (U) and a battery current (I) at battery connections (40) of the battery system (16) and at least one examination device (EIS) for performing a cell test on the battery cells (34). The invention provides that an excitation signal (45) is set and an electrical response signal (46) from the network (N) is received by the at least one examination device (EIS) from the network (N) and depending on the response signal (46) at least one parameter value (25) of the electrical network (N) is determined.

Description

The invention relates to a method for operating a battery system in a motor vehicle, it being assumed that a plurality of battery cells and at least one examination device for carrying out a respective cell test of the battery cells are present in the battery system. The invention also provides a battery system in which the method can be carried out, as well as a motor vehicle in which the battery system according to the invention is provided.

The electric drive of an electric vehicle can consist of a battery system and power electronics connected to it as an electric network for controlling the connected electric machine. The control of the electrical machine (for example its speed) takes place through targeted control of the power electronics by means of a control system. For the regulation, characteristic values or parameter values of the electrical machine, the battery system and the power electronics as well as the mechanical components that are driven by the electrical machine must be known. Typically these parameter values are determined during production. However, these parameter values of the individual components (electrical network with power electronics, electrical machine, mechanical components) can change over time. The parameter values of the components can change due to aging / wear or due to their current operating status (for example temperature). On the other hand, spreading errors (such as faulty contacts or electrical insulation) can affect the parameter values.

However, since the parameter values cannot usually be determined during operation of the motor vehicle, a prediction model that is intended to predict the behavior of the motor vehicle has to fall back on the original parameter values determined during production, which makes the prognosis imprecise. Faults in the electric vehicle can also only be detected on the basis of nominal characteristic values or nominal parameter values which are only representative of a motor vehicle that is new to production.

From the US 2014/0117938 A1 a battery system for an electric vehicle is known which has a measuring device by means of which individual battery cells of the battery system can be subjected to an individual cell test. With this, at least one parameter value of the battery system itself can be determined. A measurement of the power electronics, the electrical machine or the mechanical components of the electric vehicle is not provided, however, so that no updated parameter values can be provided for this.

One form of analysis or a cell test for a battery cell is given by electrochemical impedance spectroscopy (EIS), as it is for example in the WO 2016/012922 A1 is described. It can be implemented on the basis of a control device for a battery. With this, however, only an internal battery analysis of a battery cell, i.e. a cell test, is usually possible.

From the US 2003/0052689 A1 the use of electrochemical impedance spectroscopy for cell tests in a battery system is also known.

The problems described arise not only in an electric vehicle, but generally in a motor vehicle in which a battery system is provided which has one or more battery cells and to which an electrical network with at least one electrical component is connected. Monitoring such a network usually requires additional sensors and possibly actuators, which undesirably increases the circuit complexity.

The invention is based on the object of also making it possible to monitor the electrical network connected to the battery system in a motor vehicle with a battery system.

The object is achieved by the subjects of the independent claims. Advantageous embodiments of the invention are described by the dependent claims, the following description and the figures.

The invention provides a method for operating a battery system in a motor vehicle. The battery system has a plurality of battery cells which are set up to generate a battery voltage and a battery current at battery connections of the battery system. Furthermore, the battery system has at least one examination device for performing a cell test on the battery cells. In particular, at least one examination device for electrochemical impedance spectroscopy (EIS) of individual battery cells of the battery system is provided. The battery cells are each designed to be switchable, i.e. they are switchable battery cells in that at least one switching element is provided in each battery cell for switching a cell current of the battery cell and the battery system has a control device for controlling the at least one switching element of the respective Has battery cell. Each individual battery cell can therefore be switched on and off individually between the battery connections. Switchable battery cells are also referred to here as SmartCells.

The battery system is operated by means of the method according to the invention in such a way that at least one parameter value is also determined by means of the battery system which does not describe a component in the battery system itself, but at least one component outside the battery system. At least one parameter value external to the battery system is thus determined. For this purpose, an excitation signal is emitted into an electrical network connected to the battery connections. This can be an unchangeable, constant excitation signal or a time-varying excitation signal. Due to the electrical connection between the battery connections on the one hand and the network on the other hand, the excitation signal from the battery connections continues into the electrical network. The at least one examination device, which is actually provided for the internal cell tests within the battery system, is now also used to measure via the battery connections how the electrical network beyond the battery connections reacts to the excitation signal. For this purpose, the at least one examination device receives an electrical response signal from the network from the network via the battery connections. Depending on the response signal, the at least one examination device determines at least one parameter value of the electrical network itself and / or at least one mechanical component coupled to the electrical network via an electromechanical transducer by means of a predetermined analysis rule. The electromechanical converter is, in particular, an electrical machine that is provided as a travel drive. A mechanical component can, for example, be part of a mechanical travel drive which is coupled to the electrical network via the electrical machine.

The invention therefore advantageously uses at least one examination device, which is provided for a battery-internal cell test of the battery cells, to determine at least one parameter value of a battery-external electrical network and / or a battery-external mechanical component.

The at least one examination device and / or the control device for controlling the switching elements of the battery cells can each be provided, for example, at the battery cell level, i.e. by individual components in each battery cell, and / or at the system level as separate, battery-cell-external units of the battery system. The respective examination device can be implemented on the basis of at least one integrated circuit (IC) and / or at least one microprocessor and / or at least one microcontroller. The control device can be provided on the basis of at least one integrated circuit and / or at least one microprocessor and / or at least one microcontroller. In the event that a processor device (microprocessor and / or microcontroller) is provided, the method steps can be provided as a program code that has program instructions that, when executed by the at least one examination device or control device, carry out the respective method steps that are performed by the at least one The examination device or the control device are to be carried out according to the method.

The invention also comprises embodiments which result in additional advantages.

So far it has not been specified how the excitation arises. In principle, several variants are conceivable here, which can also be combined.

In one embodiment, by setting a switching constellation of the at least one switching element of the battery cells at the battery connections, the control device sets the battery voltage and / or the battery current with a predetermined time signal curve as the excitation signal. In other words, by setting a switching constellation of the at least one switching element of the battery cells at the battery connections, the control device of the battery system sets the battery voltage and / or the battery current to a predetermined temporal signal profile that propagates in the electrical network connected to the battery connections. This signal curve then represents an excitation signal.

In one embodiment, the said switching constellation in the battery cells is set iteratively or step-wise by the control device by minimizing a deviation of the actually generated excitation signal at the battery connections from a target excitation signal by means of signal control. In other words, the excitation signal is enforced in its temporal course by means of a signal control. In this way, for example, a current value of a battery current that is to be used as an excitation signal can be adjusted to a desired curve. The battery system can thus act as a current and / or voltage source.

In addition or as an alternative to the switching configuration in the battery cells, the at least one examination device has its own current and / or voltage source, by means of which it generates the excitation signal. In this second variant, the at least one examination device contains its own current and / or voltage source (and in particular the circuit / switch required for this). The energy for this can then come from the battery cell itself or from an auxiliary voltage network (eg 12 volt on-board network).

In addition or as an alternative to this, an excitation signal generated by driving is used. In this additional variant, the system does not actively stimulate / intervene, but rather uses the stimulus from operation (called passive EIS). The switching elements are still important because they organize which cells are measured / operated here as well.

In one embodiment, the at least one examination device processes the received response signal by means of electrochemical impedance spectroscopy in order to determine the at least one parameter value. In other words, a program code or a program module is used which is actually intended for the battery-internal cell test. Since impedance spectroscopy provides for a spectral analysis, this can also be used to determine the at least one parameter value of a component external to the battery. No separate analysis software is therefore necessary. In this case, the analysis specification mentioned thus includes the EIS.

Additionally or alternatively, the at least one examination device calculates a transmission behavior of the network from a ratio of the battery voltage and the battery current, from which the at least one parameter value can be derived. For example, an impulse response or the frequency response of the network can be determined by the analysis rule. If it is known which electrical components are connected in the network and / or which mechanical components are coupled to the network via the electromechanical converter, at least one parameter value can be derived for these components on the basis of an electrical model of the network from the determined transmission behavior. A system identification method can be used as a basis for this. For example, an iterative fitting process can be used.

In one embodiment, the analysis rule accordingly provides that the respective parameter value is determined by means of a predetermined fitting method or adaptation method for adapting model parameters of a model of the electrical network to the response signal. Using the fitting method, at least one model parameter of the electrical network is iteratively set or adapted so that a model response that the model generates as a function of the excitation signal corresponds to the response signal to such an extent that a predetermined fitting criterion is met, for example a difference is less than a threshold. The difference can be calculated as the sum of the squares of the differences between the model response and the response signal for several sample points or sample values. The fitting method or the fitting method has the advantage that a complex model can also be configured with a plurality of model parameters if a response signal is present.

In one embodiment, at least one parameter value of the at least one switching element is determined and / or the excitation signal is emitted into the electrical network of an electric travel drive of the motor vehicle. At least one cell-internal parameter value can therefore be determined for, for example, the at least one switching element (for example the volume resistance Rdson). Additionally or alternatively, it is assumed that a drive with power electronics and an electrical machine is connected to the battery system at the battery connections. The at least one parameter is then determined accordingly in the travel drive. As a result, a model can be configured for the drive, on the basis of which a control or a control system can be configured for the driving operation of the motor vehicle.

In one embodiment, an intermediate circuit capacitor can be connected between the battery connections in the network. In this embodiment, at least one switching element or a plurality of switching elements connected downstream of the intermediate circuit capacitor from the point of view of the battery connections is electrically blocked and at least one parameter value of the intermediate circuit capacitor is determined. Since the switching elements connected downstream of the intermediate circuit capacitor are switched to be electrically blocking, only the intermediate circuit capacitor is effective in the network from the point of view of the battery connections and at least one parameter value can be determined for this. Said switching elements can, for example, be part of the power electronics of the one travel drive, that is to say for example switching elements of a converter.

In one embodiment, a short circuit is switched between the battery connections in the network by means of power electronics (for example by means of a converter) and at least one parameter value is determined by switching elements of the power electronics. Such a parameter value can for example be the volume resistance Rdson and / or a voltage drop across diodes and / or at least a parasitic effect. The power electronics can therefore also be measured from the battery system with regard to the at least one parameter.

In one embodiment, at least one parameter value of strings of an electrical machine is determined in the network. In other words, the excitation signal is sent in electrical coils (strands) of the electrical machine. This can be done, for example, through power electronics, in that their switching elements are switched appropriately or accordingly. An electrical machine, that is to say the aforementioned electromechanical converter, can thus also be measured.

As already stated, the intermediate circuit capacitor, a converter and an electrical machine can be connected in series in the network from the point of view of the battery connections. In order to measure these electrical components individually, one embodiment provides that the control device changes at least one switching setting in the network after receiving the response signal and then at least one further parameter value is determined by means of the analysis rule using at least one further excitation signal. It can therefore be provided, for example, that the intermediate circuit capacitor is first measured with the downstream converter switched to be electrically blocking and then switching elements of the converter are then switched to be electrically conductive, for example in order to measure the switching elements of the converter in the manner described. Thus, starting from the battery connections, at least one parameter value can be determined one after the other for an electrical component and then, after changing the switch setting, the next electrical component, which is connected downstream from the point of view of the battery system, can be measured with regard to its at least one parameter value.

Here, the influence of a signal contribution from an electrical component that has already been measured can be determined and removed from the received mixed signal. In one embodiment, the response signal is received by the at least one examination device with a signal contribution from the battery cells superimposed on the response signal (ie a battery-internal signal contribution) and / or a signal contribution from a further component contained in the network. This further component of the network can, for example, be a component that has already been measured, for which at least one parameter value has already been determined, but which cannot be switched off in the network for a further measurement and therefore continues to generate a signal when an excitation signal is passed into the network becomes. The response signal and the signal contribution are received by the at least one examination device as a mixed signal, the signal contribution that is superimposed on the response signal being already specified or known in the at least one examination device, i.e. it is specified or stored from a previous measurement, how the superimposed signal contribution (with a given excitation signal) has to look like or run. The at least one examination device accordingly removes the signal contribution from the mixed signal on the basis of the known signal profile in order to reconstruct or obtain the response signal. Information relating to the at least one parameter value can thus also be extracted from a superimposed mixed signal by removing a known signal contribution from at least one other component. The removal can be carried out, for example, by subtracting or on the basis of an inverse transfer function by means of a convolution or in the spectral range, wherein the inverse transfer function can be formed on the basis of a model of the other component that has already been measured (whose parameter value is therefore already known).

In one embodiment, a corresponding setpoint parameter value is specified for the at least one parameter value and a fault is signaled to the battery system and / or in the network and / or the at least one mechanical component if the at least one parameter value changes from its corresponding setpoint parameter value deviates by more than a predetermined tolerance value. In this way, automated error detection is advantageously provided.

The invention also includes a battery system by means of which the method according to the invention can be carried out. In the manner described, the battery system has a plurality of battery cells in order to generate a battery voltage and a battery current at battery connections of the battery system, and the battery system has at least one testing device for performing a cell test on the battery cells. The battery cells are designed to be switchable in the manner described. The battery system according to the invention is set up in the manner described to carry out an embodiment of the method according to the invention, for which purpose a control device and the at least one examination device can be configured in the manner described.

Finally, the invention also includes a motor vehicle in which an embodiment of the battery system according to the invention is provided. The motor vehicle according to the invention can be designed as a motor vehicle, in particular as a passenger vehicle or truck, or as a passenger bus or as a motorcycle. It is in particular an electric vehicle or hybrid vehicle, as an electrically drivable motor vehicle. The battery system can be designed as a so-called high-voltage battery or traction battery, for example.

The invention also includes the combinations of the features of the described embodiments.

• 1 eine schematische Darstellung einer Ausführungsform des erfindungsgemäßen Kraftfahrzeugs; und
• 2 ein Flussschaudiagramm zur Veranschaulichung einer Ausführungsform des erfindungsgemäßen Verfahrens.

Exemplary embodiments of the invention are described below. This shows:

• 1 a schematic representation of an embodiment of the motor vehicle according to the invention; and
• 2 a flowchart to illustrate an embodiment of the method according to the invention.

The exemplary embodiments explained below are preferred embodiments of the invention. In the exemplary embodiments, the described components of the embodiments each represent individual features of the invention that are to be considered independently of one another and that also develop the invention independently of one another. Therefore, the disclosure is intended to include combinations of the features of the embodiments other than those shown. Furthermore, the described embodiments can also be supplemented by further features of the invention already described.

In the figures, the same reference symbols denote functionally identical elements.

1 shows a motor vehicle 10 , which, in the manner described, can be a motor vehicle, in particular a passenger car or truck, or a passenger bus or a motorcycle. The car 10 can be driven electrically and can be used as a drive 11 have an electrical part 12 and a mechanical part 13 can provide. The electrical part 12 can with the mechanics part 13 via an electric machine 14th be coupled, which represents an electromechanical converter and thus both to the electrical part 12 as well as the mechanical part 13 can be counted.

In the electrical part 12 can in addition to the electric machine 14th other electrical components 15th be provided, with in 1 as an electrical component 15th a battery system 16 and as a further electrical component 15th a power electronics 17th are shown.

In the mechanics part 13 can in addition to the electric machine 14th as further mechanical components 18th a mechanical clutch 19th , a braking system 20th and at least one bike 21st , which represents a mechanical load, may be provided.

For controlling the electrical components 15th of the electrical part 12 and the mechanical components 18th of the mechanical part 13 can be a control device 22nd be provided, the control signals 23 to control the drive 11 can generate. The control device 22nd a processor device 24 exhibit.

In the motor vehicle 10 can be provided at least one parameter value 25th that drives the traction drive 11 describes or for the drive 11 is characteristic in the motor vehicle 10 to determine after the traction drive 11 already in the motor vehicle 10 is built in. Thus the at least one parameter value can 25th also in the operation of the motor vehicle 10 , for example in a standstill phase 26th , for example during parking, can be determined.

There can also be a mechanical boundary condition, for example by controlling the brake system 20th take place whereby drive shafts 31 of the mechanical part 13 can be blocked what also a rotor 32 the electric machine 14th prevents it from turning even if it is a mechanical torque 33 in the drive shafts 31 generated. A drive voltage U through the battery system, for example, can be used as the excitation signal 16 be generated. The drive voltage U can be provided by the battery system 16 for example on the basis of switchable battery cells 34 generated in the battery system 16 can be connected in parallel in groups and then the groups can be connected in series to generate the battery voltage U. Conversely, a plurality of battery cells can also be provided 34 to connect serially to strings and then to connect these strings in parallel. This can be done for all battery cells 34 or intended for subgroups.

Another mechanical boundary condition can be caused by opening the clutch 19th adjusted, making the rotor 32 can run at idle with no load.

The drive 11 can have an examination device EIS, by means of which at least one electrical variable in the drive 11 detected or measured and the at least one parameter value 25th can be determined. The examination facility EIS can also be used for a Cell test of individual battery cells 34 be provided, for example, on the basis of an electrochemical impedance spectroscopy.

Every battery cell 34 can be made switchable by adding cell connections 35 both over a branch of cells 36 with the electrochemical battery cell 37 as well as a bypass branch 38 , which on the electrochemical battery cell 37 past or these are bridged, interconnected. In the branch of cells 36 and the bypass branch 38 a switching element SA, SB can be provided, through which the respective circuit branch (cell branch 36 and bypass branch 38 ) in a circuit 39 of the electrical part 12 can be switched. The battery cells 34 can by means of contactor switches S +, S- with battery connections 40 of the battery system 16 are connected, whereby the battery voltage U to the power electronics 17th can be provided.

The power electronics 17th can for example be a power converter 41 have from a direct current of the battery system 16 an alternating current in electrical phase lines 42 the electric machine 14th can generate. The converter can do this 41 switching elements in a manner known per se T1 , T2 , T3 , T4 , T5 , T6 which can be provided on the basis of at least one transistor. The power electronics 17th can also use an intermediate circuit capacitor 43 have in a known manner. On due to the battery voltage U and the converter 41 in the phase lines 42 Generated alternating current can be in electrical coils 44 the electric machine 14th generate in a known manner a rotating magnetic field through which the rotor 32 with the torque 33 is acted upon, which is the rotor 32 to the drive shaft 31 can deliver.

The power electronics 17th with the intermediate circuit capacitor 43 and the converter 41 represents together with the phase lines 42 and the coils 44 one to the battery terminals 40 connected electrical network N.

By the control device 22nd and the examination device EIS can determine the at least one parameter value 25th a method can be carried out which is described below using 1 and 2 is described.

The method can provide at least one measurement run in which for at least one parameter value 25th a corresponding predetermined measurement can be provided.

In one step S10 can the control device 22nd by setting a switching constellation of the at least one switching element SA, SB of the battery cells 34 at the battery connections 40 the battery voltage U and / or a battery current I with a predetermined signal curve over time as an excitation signal 45 can be adjusted, whereby the excitation signal 45 into one that the battery connections 40 connected electrical network N is output. A respective switching constellation is therefore the combination of the specific switching states of the switching elements SA, SB of the battery cells 34 .

In one step S11 can by the examination device EIS from the network N via the battery connections 40 an electrical response signal 46 of the network N can be received. Provision can be made for the response signal to be transmitted by the examination device EIS 46 only together with one of the response signal 46 superimposed signal contribution of the battery cells 34 and / or a further component contained in the network N is received as a mixed signal, with the signal profile of the excitation signal 45 the respective signal contribution of the at least one further component is predetermined or stored in the examination device EIS, and the examination device EIS removes the signal contribution from the mixed signal in order to produce the response signal 46 to reconstruct.

In one step S12 can be performed by the examination device EIS as a function of the response signal 46 by means of a predetermined analysis specification 47 the at least one parameter value 25th of the electrical network N and / or at least one with the network N via an electromechanical converter, ie the electrical machine 14th , coupled mechanical component 18th be determined.

This is because an undetected change in the at least one parameter value 25th the drive components of the travel drive 11 can have an adverse effect on the drive control and thus the vehicle behavior of the motor vehicle 10 to have. Creeping errors such as an increase in the resistance of individual switching elements T1 to T6 of power electronics 17th showing a change in their parameter values 25th effect, but can now be recognized during operation.

The battery system 16 preferably comprises switchable battery cells for this purpose 34 , whereby each battery cell can be bridged, switched active and high-resistance by means of the switching elements SA, SB. The battery system also has 16 by means of the examination device EIS, preferably via the possibility of carrying out an electrochemical impedance spectroscopy. With this impedance measurement, the resistance is determined as the ratio of voltage curve and current curve and thus characterizes the electrical transmission behavior. This can be implemented both at the battery cell level or at the system level.

The parameter values of each individual battery cell 34 and the battery system 16 can by switching individual battery cells on and off 34 be identified. In addition, however, you can now switch the battery cells appropriately 34 and control of the power electronics 17th individual components of power electronics 17th up to strands or coils 44 the electric machine 14th be measured, i.e. generally the network N.

Parameter changes can thus be measured during operation. This allows the control to be adapted, which increases the control quality. In addition, existing and impending errors can be recognized. By applying the EIS to the entire drive system 11 errors in the entire functional chain, such as contact errors in the high-voltage cabling (high-voltage - electrical voltage greater than 60 volts), can be detected.

1 shows the traction drive as an example 11 of a battery electric vehicle, consisting of a battery system 16 , Power electronics 17th and electric machine 14th . The battery system 16 is through a switchable battery cell 34 - Consists of the electrochemical battery cell 37 , the active switch as switching element SA and the bypass switch as switching element SB - as well as an EIS investigation device implemented here as an example at battery cell level and the contactors S +, S-.

The implementation of the method described is independent of the number of battery cells 34 , their interconnection and the specific implementation of the switching elements SA, SB, as long as they allow individual battery cells to be activated, bridged and switched to high resistance. The EIS examination device can be used once per battery system 16 or per battery cell 34 will be realized. Is the EIS per battery cell 34 realized, it can be combined to obtain an EIS at the system level. Synchronizing the individual EIS components results in a combined stimulation for the overall system.

The battery system can be measured as follows: By connecting individual battery cells to be measured 34 The battery-internal parameter values of the individual battery cells can be connected to the EIS system 34 be identified. If the EIS examination device is implemented at system level, identification is carried out by activating the battery cells to be tested 34 . If the EIS examination device is implemented at battery cell level, the battery cell can 34 isolated by high-resistance switching and examined separately. For this purpose, the EIS examination device can be directly connected to the cell 37 be connected (i.e. in front of the switching element SA or with a connection point between the cell 37 and the switching element SA).

The connection of several battery cells 34 among each other can accordingly by connecting several battery cells 34 take place simultaneously. By closing the contactors S +, S- and disconnecting the battery cells 34 the EIS examination device can control the remaining drive 11 measured.

The power electronics can be measured as follows: There are no switching elements T1 to T6 the power electronics closed, the intermediate circuit capacitor can be targeted 43 to be examined. By closing the switch T1 and T2 or alternatively T3 and T4 or alternatively T5 and T6 can continue the switches T1 to T6 be examined one after the other. However, you are not limited to three-phase induction machines, as shown in 1 is shown, but it can generally be m phases, thus also 2 phases or more than 3 phases (m is equal to or greater than 1). In addition, one is not restricted to induction machines, but any type of electrical machine can be used in a similar or known manner (for example direct current machine, reluctance machine).

The measurement of the electrical machine 14th can be done as follows: By closing the switch T1 and T4 , or alternatively T3 and T6 or alternatively T5 and T2 can be the strands or coils 44 the electric machine 14th examined and their parameter values identified.

Faulty connections can be determined as follows: Because the EIS investigation device from the battery system 16 from the entire remaining traction drive 11 up to the electric machine 14th and even a reaction from the electric machine 14th also mechanical components 18th can investigate, faults along the entire functional chain, such as faulty connections or insulation, can be detected.

As a parameter value 25th For example, an impedance, in particular a frequency profile of the impedance, can be determined in each case.

Overall, the examples show how the invention can provide a system diagnosis in a travel drive using EIS.

QUOTES INCLUDED IN THE DESCRIPTION

This list of the documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent literature cited

• US 2014/0117938 A1 [0004]
• WO 2016/012922 A1 [0005]
• US 2003/0052689 A1 [0006]

Claims (14)

A method for operating a battery system (16) in a motor vehicle (10), the battery system (16) having multiple battery cells (34) for generating a battery voltage (U) and a battery current (I) at battery connections (40) of the battery system (16) and has at least one examination device (EIS) for carrying out a cell test of the battery cells (34), the battery cells (34) each being designed to be switchable by having at least one switching element (SA, SB) in each battery cell (34) for switching a cell current of the battery cell ( 34) is provided and the battery system (16) has a control device (22) for controlling the at least one switching element (SA, SB) of the respective battery cell (34), characterized in that an excitation signal (45) is transmitted to the battery terminals (40 ) connected electrical network (N) is output and through the at least one examination device (EIS) from the network (N) via the battery connections (40 ) an electrical response signal (46) of the network (N) is received and, depending on the response signal (46) by means of a predetermined analysis rule (47), at least one parameter value (25) of the electrical network (N) and / or at least one with the network (N) is determined via a mechanical component (18) coupled to an electromechanical transducer. Procedure according to Claim 1 , wherein the control device (22) by setting a switching constellation of the at least one switching element (SA, SB) of the battery cells (34) at the battery connections (40) the battery voltage (U) and / or the battery current (I) with a predetermined time signal curve as sets the excitation signal (45), and / or wherein the examination device (EIS) has its own current and / or voltage source, by means of which it generates the excitation signal (45), and / or wherein an excitation signal (45) resulting from driving is used becomes. Procedure according to Claim 2 , the switching constellation being iteratively set by the control device (22) in that a deviation of the generated excitation signal from a setpoint excitation signal is minimized by means of a signal control. Method according to one of the preceding claims, wherein the at least one examination device (EIS) for determining the at least one parameter value (25) processes the response signal (46) by means of electrochemical impedance spectroscopy as an analysis specification (47) and / or wherein the at least one examination device (EIS) by means of an analysis rule (47) which provides for the calculation of a ratio of the battery voltage (U) and the battery current (I), calculates a transmission behavior of the network (N) and determines the at least one parameter value (25) therefrom. Method according to one of the preceding claims, wherein the analysis rule (47) provides that the respective parameter value (25) is determined by means of a predetermined fitting method for adapting model parameters of a model of the electrical network (N) to the response signal (46). Method according to one of the preceding claims, wherein at least one parameter value (25) of the at least one switching element (SA, SB) is determined and / or the excitation signal (45) in the electrical network (N) of an electric drive (11) of the motor vehicle (10) ) is output and at least one parameter value (25) of the travel drive (11) is determined. Method according to one of the preceding claims, wherein an intermediate circuit capacitor (43) is connected between the battery connections (40) in the network (N) and at least one switching element (T1-T6) connected downstream of the intermediate circuit capacitor (43) from the point of view of the battery connections (40) is electrical is switched off and at least one parameter value (25) of the intermediate circuit capacitor (43) is determined. Method according to one of the preceding claims, in the network (N) by means of power electronics (17) a short circuit is switched between the battery connections (40) and at least one parameter value (25) is determined by switching elements (T1-T6) of the power electronics (17) . Method according to one of the preceding claims, wherein at least one parameter value (25) of strands (44) of an electrical machine (14) is determined in the network (N). Method according to one of the preceding claims, wherein the control device (22) changes at least one switching setting in the network (N) after receiving the response signal (46) and then at least one further parameter value (25) by means of at least one further excitation signal (45) is determined by means of the analysis specification (47). Method according to one of the preceding claims, wherein the at least one examination device (EIS) uses the response signal (46) with a signal contribution of the battery cells (34) superimposed on the response signal (46) and / or a further component contained in the network (N) as a Mixed signal is received, the respective signal contribution of the at least one further to the signal profile of the excitation signal (45) Component in the at least one examination device (EIS) is specified, and the at least one examination device (EIS) removes the signal contribution from the mixed signal in order to reconstruct the response signal (46). Method according to one of the preceding claims, wherein a corresponding setpoint parameter value is specified for the at least one parameter value (25) and a fault is specified in the battery system (16) and / or in the network (N) and / or the at least one mechanical component (18 ) is signaled if the at least one parameter value (25) deviates from its corresponding setpoint parameter value by more than a predetermined tolerance value. Battery system (16) with several battery cells (34) for generating a battery voltage (U) and a battery current (I) at battery connections (40) of the battery system (16) and with at least one examination device (EIS) for carrying out a cell test of the battery cells (34) , wherein the battery cells (34) are each designed to be switchable, characterized in that the battery system (16) is set up to carry out a method according to one of the preceding claims. Motor vehicle (10) with a battery system (16) Claim 13 .

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