DE102019200506A1 - Measuring arrangement, motor vehicle and method for determining a complex impedance - Google Patents

Abstract

The invention relates to a measuring arrangement for determining a complex impedance (Z1, Z2) of at least one first electrical component (12), the measuring arrangement (10) having the electrical component (12) and a measuring device (16) which is connected to the first electrical component (12) is coupled and which is designed, for example by means of impedance spectroscopy, to determine the complex impedance (Z1, Z2) of the first electrical component (12). The measuring arrangement (10) has at least one second electrical component (12) which is arranged in a parallel circuit (14) with the first electrical component (12), a current sensor (18) being assigned to at least the first electrical component (12) which is connected in series with the first electrical component (12), the measuring device (16) being designed to measure the complex impedance (Z1, Z2) of the first electrical component (12) as a function of one of the current sensors (18) determined current (Iac1, lac2, lacn) flowing through the first component (12).

Description

The invention relates to a measuring arrangement for determining a complex impedance of at least one electrical component, such as a battery cell, the measuring arrangement comprising the electrical component and a measuring device which is coupled to the electrical component and which is designed to determine the complex impedance of the electrical component Component. The invention also includes a motor vehicle and a method for determining a complex impedance of at least one electrical component.

A battery cell is not an ideal voltage source, but rather an electrochemical system that can provide limited energy and power through internal resistances or dynamic processes. The resistance, in particular the complex resistance, which is referred to in the present case as complex impedance, can be calculated from current and voltage values. For example, to measure the AC resistance as a complex function of frequency, the battery can be selectively excited via the poles. As a result, an entire impedance spectrum can be recorded, which, as a transfer function, reflects the electrical behavior of the battery cell and is often approximated by an electrical equivalent circuit diagram. With such an impedance spectroscopy, however, impedances for different excitation frequencies do not necessarily have to be determined, but it is also possible to determine only one impedance value for a specific frequency. By applying an impedance measuring device, it is possible to carry out such an electrochemical impedance spectroscopy, which is also referred to as EIS, or in general to determine impedance on battery cells. From the determined impedance, further statements can then be made about the battery cell, for example about its state of aging.

Furthermore shows the DE 10 2013 103 921 A1 also a possibility of how a temperature of the cell pack can also be determined from a determined impedance of a cell pack from battery cells by means of a look-up table.

Furthermore describe the US 2015/0145520 A1 and the EP 2 551 689 A2 Method by means of which the individual impedances of battery cells which are arranged in a series circuit can be determined.

With the increasing electrification of motor vehicles, more and more high-voltage batteries are being used. With regard to high-voltage batteries, on the one hand, the determination or prognosis of the aging condition of the high-voltage battery and the determination of electrical properties of this high-voltage battery are particularly relevant for safety reasons. Accordingly, it is advantageous to be able to determine such properties of such a battery as simply, detailed and comprehensively as possible.

It is therefore an object of the present invention to provide a measuring arrangement, a motor vehicle and a method which, by means of impedance determination or impedance spectroscopy, enable the most detailed and simple determination of electrical properties of a component assembly with a plurality of electrical components.

This object is achieved by a measuring arrangement, by a motor vehicle and by a method with the features according to the respective independent patent claims. Advantageous embodiments of the invention are the subject of the dependent claims, the description and the figures.

A measuring arrangement according to the invention for determining a complex impedance of at least one first electrical component has the first electrical component and a measuring device which is coupled to the first electrical component and which is designed to determine the complex impedance of the first electrical component, for example using impedance spectroscopy. The measuring arrangement has at least one second electrical component which is arranged in parallel with the first electrical component, with at least the first electrical component being assigned a current sensor which is connected in series with the first electrical component, the measuring device being designed for this to determine the complex impedance of the first electrical component as a function of a current detected by the current sensor and flowing through the first component.

As mentioned at the beginning, the first electrical component and the at least one second electrical component are preferably battery cells, in particular a high-voltage battery; nevertheless, the invention and its configurations can advantageously also generally be used to determine the complex impedance of any electrical component Apply component or any electrical components in a completely analogous manner. Such electrical components can also be double-layer capacitors and / or fuel cells, for example.

The invention is based on the finding that battery cells in battery systems are increasingly also connected in parallel in order to to achieve the required performance and capacity requirements. However, in the case of cells connected in parallel in particular, it is not readily possible to determine individual characteristics, such as quiescent voltage and impedance, since in cells connected in parallel the current is distributed to the cells and with a single current sensor for measuring the total current, as is shown in the prior art Technology is common, according to the individual impedance of battery cells can not be determined in a parallel network. In particular, no attention is currently paid to the configuration of a parallel connection of cells. In contrast, cells connected in parallel are usually treated like a single larger battery cell. This means, for example, that a parallel connection of several individual cells is often synonymously referred to as "cell". Known measuring arrangements are accordingly not able to extract the electrical behavior of individual cells from cells in a parallel connection. This results in a significant difference for the technical possibilities that result from the invention if each individual cell can be identified and characterized in an electrical parallel network of cells. If, on the other hand, only the (super) cell from a plurality of interconnected individual cells can be characterized as an overall cell without any reference to the individual cells in a parallel network, this represents a significant restriction of the functionality. The invention, on the other hand, opens up new dimensions, namely that of electrical differentiation from parallel-connected Cells.

This is also made possible according to the invention in a particularly simple manner in that a current sensor is connected in series with the cell, or in general with the first electrical component, which now advantageously makes it possible to specifically detect the current flowing through this electrical component, and not just one Total current through the entire parallel connection, which does not contain individual cell characteristics. This detected individual current flowing through the first component can now advantageously be used for impedance spectroscopy or impedance determination, which advantageously makes it possible to determine the complex impedance of this first electrical component, although this can also be achieved in a parallel connection with other electrical components such as the at least one is a second electrical component.

The invention thus advantageously enables individual cell characterization of battery cells connected in parallel by means of sensors and intelligent detection of the current distribution. This enables a highly precise determination of the condition of all individual cells in the battery system. The measuring arrangement thus enables an exact determination of the condition of an individual cell with the aid of the current distribution and provides knowledge about the impedance of each individual cell, for example in the battery system, and not just the impedance of the entire battery or an entire parallel line. Another advantage is that the method mentioned, which is carried out by the measuring arrangement, can also be used during operation, as will be described in more detail later. The individual impedances of individual battery cells can thus also be determined during operation of the battery cell and without the need to isolate individual cells.

If the electrical components, as is preferably the case, are battery cells, the measuring device is preferably designed for electrochemical impedance spectroscopy or impedance determination. The measuring device can in particular be designed to carry out galvanostatic impedance spectroscopy or impedance determination and / or potentiostatic impedance spectroscopy or impedance determination. In galvanostatic impedance spectroscopy, the electrical components are excited by a current excitation signal and the voltage response is measured, while in potentiostatic impedance spectroscopy or impedance determination, the electrical components are excited by a voltage excitation signal, and the current response is measured accordingly. The excitation signal can be provided by the measuring device, but this does not necessarily have to be the case. For example, the load current of a load coupled to the electrical components can also be used as the current excitation signal, as will also be explained in more detail later. A load, as is often referred to below in the following, should generally be understood to mean both an energy sink and an energy source or combinations thereof. Such a load can thus represent, for example, an electrical consumer of the motor vehicle, and also, for example, a charger of the motor vehicle that can be coupled to an external energy source, an inductive charging unit, the motor of the motor vehicle in generator operation, or the like, via which one or more of the battery cells supply energy is feedable. Accordingly, a load current should generally also be understood to mean a charge current.

Furthermore, the electrical components are excited at least with one frequency, in particular with a voltage excitation signal with at least one frequency or a current excitation signal with at least one frequency. A suggestion can also be made with a signal which has several different frequencies.

In the same way as the complex impedance of the first electrical component is determined, the complex impedance of each further electrical component that is in the parallel connection can also be determined quite analogously.

Accordingly, it is a further advantageous embodiment of the invention if the measuring arrangement has a plurality of electrical components comprising the first and the at least one second electrical component in the parallel connection, with each of the electrical components being assigned a current sensor which is connected in series with the associated electrical component and is designed to measure the electrical current through the associated electrical component, the measuring device being designed to separately determine the complex impedance of a respective component as a function of the respective currents detected by the current sensors. In general, two or more such electrical components can be connected to one another in parallel, that is to say they are located in parallel, and the current flowing through this component can be determined for each electrical component by the assigned current sensor, which is then advantageously used for determination the respective complex impedance of the individual components can be used.

In a further advantageous embodiment of the invention, the measuring arrangement has a plurality of electrical components comprising the first and the at least one second electrical component in the parallel connection, each of which, apart from a single specific one of the components, being assigned a current sensor which is connected in series with the assigned electrical component is and is designed for measuring the electrical current through the associated electrical component, in particular with the measuring arrangement having a total current sensor which is connected in series for parallel connection and which is designed for measuring a total current flowing through the parallel connection, the measuring device being designed for this purpose to determine a current through the only specific component as a function of the respective currents detected by means of the current sensors assigned to the electrical components and the total current detected by means of the total current sensor.

In other words, a total current sensor can also be provided, which detects the total current through the parallel connection, so a current sensor does not necessarily have to be provided for each individual component in the parallel connection, but one can also be dispensed with, since the individual current through it affects individual component can then be determined from the difference between the total current and the remaining individual currents. The use of an overall current sensor is particularly advantageous, since the relevant impedances of the respective electrical components can then also be determined in this way, even if the current excitation signal is unknown, since this can then be detected accordingly by the overall current sensor. If, as described above, the measuring device is designed, for example, for active impedance spectroscopy or impedance determination and can impress a known total current as an excitation signal, in particular as an alternating current, the electrical components can optionally also dispense with the total current sensor since this total current is then known.

In a further advantageous embodiment of the invention, the first electrical component and the at least one second electrical component represent a respective electrochemical memory, in particular a battery cell, for example a lithium-ion cell, for a high-voltage battery of a motor vehicle.

As already mentioned at the beginning, however, the invention can be used in a completely analog manner on any type of electrical component or electrical components which are arranged in a parallel connection. However, especially in connection with electrochemical energy stores such as battery cells, the invention has particularly great advantages. This is due to the fact that today's motor vehicles are increasingly electrified and have corresponding high-voltage batteries. Monitoring such a high-voltage battery and in particular also its individual cells is particularly relevant on the one hand from a safety perspective, and on the other hand also with regard to the determination and / or prognosis of an aging state or the remaining service life of such a high-voltage battery. The most detailed possible analysis options for the electrical properties of individual battery cells are therefore particularly advantageous for users of such electric vehicles. In the same way, it has also proven to be advantageous to use parallel connections of individual battery cells within such a network to provide a high-voltage battery, since this makes it easier to achieve the required performance and capacity requirements. Thus, especially in connection with the determination of the individual complex impedances of battery cells within a parallel connection, the invention offers particular added value for electromobility.

Furthermore, it is advantageous if the measuring device has at least one voltage sensor, which is designed to detect a voltage drop across the first electrical component detect, the measuring device being designed to determine the complex impedance of the first electrical component as a function of the detected voltage. As already described, knowledge of the current flowing through the electrical component in question and the voltage drop across this electrical component is required to determine the complex impedance. One of these two variables is impressed on as an excitation variable, which, however, can also be done by a load and does not necessarily have to be actively by the measuring device. If this is nevertheless designed for active impedance spectroscopy or impedance determination, in particular for potentiostatic impedance spectroscopy or impedance determination, according to which an excitation voltage is impressed, then the voltage sensor described can also be omitted, since the voltage drop across the first electrical component, which is in particular identical to it, is then also eliminated the total voltage drop across the parallel circuit and the individual voltage drop across the respective further electrical components connected in parallel is known in advance and does not have to be measured. Nonetheless, great advantages of galvanostatic impedance spectroscopy or impedance determination can be seen in connection with the measurement of battery cells. Regardless of whether this is now carried out actively or passively by the measuring device, a voltage measurement is accordingly advantageous, which can be carried out accordingly by the voltage sensor mentioned.

In principle, this voltage sensor can be arranged at any point with respect to the electrical components, in particular parallel to one, more or all of the electrical components. In principle, however, a plurality of sensors, in particular voltage sensors, can also be connected, for example, in parallel to a respective electrical component in order to measure the respective voltages, which are identical anyway, except for measurement errors or measurement noise, and to use them to determine the respective complex impedances . It is also conceivable to use a plurality of voltage sensors for voltage measurement and to accommodate them separately from or together with one, part or all of the current sensors in one or more housings or devices. For example, the voltage sensor connected in parallel with a respective component and the current sensor connected in series with the relevant electrical component can form a measuring device which is assigned to the relevant electrical component. Such a measuring device can also optionally also include an excitation source, such as a current excitation source. In principle, the measuring device can thus also be implemented with several impedance measuring devices by using one, several or all impedance measuring devices for excitation, the current sensors of the impedance measuring devices are used for the described current measurement and the voltage sensors of the impedance measuring devices are used accordingly for the described voltage measurement.

Numerous possible embodiments of the measuring device are thus provided. In a preferred and particularly inexpensive and simple variant, the measuring device is designed as an impedance measuring unit connected in parallel with the parallel connection. In other words, the measuring device can be designed as a single impedance measuring device which is connected in parallel to connect the plurality of electrical components in parallel. In addition, corresponding current sensors are connected in series with the relevant components, in particular, optionally except for one. The respective current measurement values can, for example, also be transmitted to the impedance measuring device, which can then determine the corresponding individual impedances based thereon and, for example, also the total impedance of the parallel connection.

In a further advantageous embodiment of the invention, the measuring device has at least one excitation source, which is designed to generate an excitation signal and to apply the excitation signal to the parallel connection and / or the first component and / or the at least one second component. The measuring device is thus designed to carry out an active impedance spectroscopy or impedance determination, according to which an excitation signal can now be actively impressed on the individual components by the excitation source of the measuring device. This excitation source can, for example, also be connected in parallel to the parallel connection of the electrical components, but it can also be connected in any other position, for example also in series with the respective electrical components. At the same time, several excitation sources can be used, the excitation signals of which can then be superimposed accordingly. In general, the excitation source or the at least one excitation source can be designed to excite the system, in particular the respective electrical components, galvanostatically or potentiostatically. The determination of the respective individual impedances does not necessarily require the excitation signal to be known, as has already been described, since this can be measured by the sensors described, in particular voltage and / or current sensors, in particular separately for each electrical component of the parallel connection. The type and configuration of the excitation signal can also be of any type. So they are sinusoidal, multi-sinusoidal, or any Possible forms of suggestion. A multi-sinusoidal excitation represents an excitation by means of an excitation signal, which consists of several sinusoidal and superimposed individual excitation signals.

Nonetheless, it is particularly advantageous if the suggestion can be predetermined and can therefore be assumed to be known. Accordingly, the excitation signal does not have to be measured and measurement errors can be reduced. In addition, an excitation with a sinusoidal excitation signal of a single frequency, which can be generated by one or more sources, the excitation sources mentioned, has proven to be particularly advantageous. The great advantage of a sinusoidal excitation, in particular a monofrequency sinusoidal active excitation, is that the frequency of the excitation signal can be specifically tailored to the application and the frequency range of interest. Thus, in the case of impedance spectroscopy or impedance determination, the frequency ranges of interest can be approached and scanned by a suitable choice of the application signal or its frequency. In general, the preferred frequency range is in a range between the millihertz range and the kilohertz range. In addition, a particularly good signal-to-noise ratio can be provided by an excitation signal with a single frequency, which ultimately reduces the measurement errors of the measurement results and increases the measurement accuracy.

In a further advantageous embodiment of the invention, the measuring device is designed to measure the impedance as a function of a current flowing through the first component, which at least partially represents a load current, through an electrical consumer coupled to at least the first electrical component and / or an energy-providing component is effected, and to be determined as a function of the detected voltage drop across the first electrical component.

In particular, the impedance spectroscopy or impedance determination for determining the complex impedance of at least the first electrical component can also be carried out completely passively using such a load current, which is caused by an electrical consumer and / or by an energy supplying component, for example by the electrical components, if they are designed as corresponding battery cells, are supplied with electrical energy or are supplied with energy for charging, can be determined. Accordingly, the measuring device is designed to carry out a passive impedance spectroscopy or impedance determination. Advantageously, however, the measuring device can also combine an active impedance spectroscopy or impedance determination with a passive impedance spectroscopy or impedance determination. In other words, as already described, the measuring device can actively impress an excitation signal on the electrical components. This can also overlap with a load current caused by the named electrical consumer or by the component providing energy. The resulting current flowing through the respective electrical components can then in turn be detected by the relevant current sensors described. Accordingly, the complex impedance of the respective electrical components can advantageously be determined without restriction at any time, in particular also during the operation of the motor vehicle and while the battery cells are under load.

The ultimately determined impedances of the respective electrical components can then advantageously be used, for example, to determine an aging state of the respective electrical components and / or also to determine the temperature of a current temperature of the respective electrical components, as well as for numerous other evaluation or analysis methods. Since a determination of the respective impedances is also possible during operation, for example an impedance determination of the respective electrical components can be carried out at predetermined times independently of a current operating state of the motor vehicle.

The at least one electrical consumer can be, for example, a typical high-voltage consumer, such as power electronics for an electric motor and / or an electric air conditioning compressor and / or a converter device.

Furthermore, the invention also relates to a high-voltage battery for a motor vehicle, which has a measuring arrangement according to the invention or one of its embodiments. Furthermore, the invention also relates to a motor vehicle with a measuring arrangement according to the invention or one of its configurations.

Accordingly, the advantages described for the measuring arrangement according to the invention and their configurations apply in the same way to the high-voltage battery according to the invention and the motor vehicle according to the invention.

The motor vehicle according to the invention is preferably used as a motor vehicle, in particular as Cars or trucks, or designed as a bus or motorcycle.

Furthermore, the invention also relates to a method for determining a complex impedance of at least one first electrical component by means of a measuring device which is coupled to the first electrical component and which determines the complex impedance of the first electrical component. The measuring arrangement has at least one second electrical component, which is arranged in parallel with the first electrical component, with at least the first electrical component being associated with a current sensor which is connected in series with the first electrical component, the measuring device having the complex impedance of the first electrical component as a function of a current detected by the current sensor and flowing through the first component.

Here, too, the advantages mentioned for the measuring arrangement according to the invention and its configurations apply in the same way to the method according to the invention.

The invention also includes further developments of the method according to the invention which have features as have already been described in connection with the further developments of the measuring arrangement according to the invention. For this reason, the corresponding developments of the method according to the invention are not described again here.

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

• 1 eine schematische Darstellung einer Messanordnung zum Bestimmen einer komplexen Impedanz gemäß einem Ausführungsbeispiel der Erfindung;
• 2 eine schematische Darstellung einer Messanordnung zum Bestimmen einer komplexen Impedanz mit verschiedenen Möglichkeiten zur Anordnung einer oder mehrerer Anregungsquellen gemäß einem Ausführungsbeispiel der Erfindung;
• 3 eine grafische Darstellung des Stromanregungssignals sowie der gemessenen Gesamtspannung und der gemessenen Einzelströme durch die jeweiligen Batteriezellen gemäß einem Ausführungsbeispiel der Erfindung;
• 4 eine grafische Darstellung der Fourier-Transformierten des Stromanregungssignals, der gemessenen Gesamtspannung sowie der gemessenen Einzelströme gemäß einem Ausführungsbeispiel der Erfindung; und
• 5 eine grafische Darstellung der aus den gemessenen jeweiligen Einzelströmen durch die jeweiligen Batteriezellen und der Gesamtspannung ermittelten komplexen Impedanzen für die einzelnen Batteriezellen sowie die Gesamtimpedanz der Parallelschaltung der Batteriezellen gemäß einem Ausführungsbeispiel der Erfindung.

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

• 1 a schematic representation of a measuring arrangement for determining a complex impedance according to an embodiment of the invention;
• 2nd a schematic representation of a measuring arrangement for determining a complex impedance with different possibilities for arranging one or more excitation sources according to an embodiment of the invention;
• 3rd a graphical representation of the current excitation signal and the measured total voltage and the measured individual currents through the respective battery cells according to an embodiment of the invention;
• 4th a graphic representation of the Fourier transform of the current excitation signal, the measured total voltage and the measured individual currents according to an embodiment of the invention; and
• 5 a graphic representation of the complex impedances for the individual battery cells determined from the measured individual currents through the respective battery cells and the total voltage and the total impedance of the parallel connection of the battery cells according to an embodiment of 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 further 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 that have already been described.

In the figures, the same reference numerals designate elements that have the same function.

1 shows a schematic representation of a measuring arrangement 10th to determine a complex impedance of several electrical components, which in this example are battery cells 12th are executed, which are in a parallel connection 14 are arranged according to an embodiment of the invention. The measurement arrangement 10th has one as an impedance measuring device 16 , especially as a galvanostatic impedance measuring device 16 trained measuring device. This impedance meter 16 is parallel to the parallel connection 14 switched and includes a voltage sensor 16a , a current sensor 16b as well as a source of inspiration 16c , in particular a current source for providing a current excitation signal. By means of the voltage sensor 16a can the over the parallel connection 14 falling total voltage Uges can be measured, and with the current sensor 16b can by the parallel connection 14 flowing total current I _A can be measured.

On the basis of the measurement device alone 16 measurable quantities, namely the total current I _A and the total voltage Uges, only the total impedance of the parallel cell network can be determined. The electrical behavior of the cell network, i.e. the parallel connection 14 with the battery cells connected in parallel 12th , is from the outside for the impedance measuring device 16 thus only recognizable as a single cell, the capacity of which is derived from the individual capacities and the impedance is derived from the individual impedances of the cells 12th put together. Only based on that by the measuring device 16 The measurements provided are a distribution of the total impedance of the parallel connection 14 into the impedances of the individual cells 12th so not possible. So the impedances of the individual cells 12th one of the two quantities from voltage or current must be the characteristic of the individual cell 12th contain. In parallel connections, the voltage is Uges of all components, that is the cells in this example 12th , galvanically fixed to a potential. So that is at the single cells 12th falling respective voltages are identical and identical to the total voltage Uges. For this reason, the electrical characteristic of the component, for example the battery cells 12th , in parallel connection 14 only reflect in the stream. Since the total current I _A affects the individual cells 12th in parallel connection 14 distributed, it is initially unknown which current flows through the individual battery cells 12th flows.

The invention and its refinements now advantageously make it possible to detect this single cell characteristic by using current sensors 18th in series with the respective battery cells 12th are switched. In the in 1 The example shown is for each battery cell 12th the parallel connection 14 also a corresponding current sensor 18th connected in series. In other words, the series connections are each of a battery cell 12th and assigned current sensor 18th connected in parallel to each other. However, fewer current sensors can also be used 18th be provided. For example, is that from the excitation source 16c output current signal known, and also flows through the battery cells 12th not even a load current, for example the current sensor 16b of the impedance meter 16 omitted. Furthermore, a single current can flow through one of the battery cells 12th also as the difference between the total current I _A and the measured currents through the other battery cells 12th are calculated, so that in principle also one of the battery cells 12th assigned current sensors 18th can be omitted.

In the example 1 now detects a first current sensor 18th the current through a first battery cell 12th , which is designated I _ac1 , a second current sensor 18th detects the single current through a second battery cell 12th the parallel connection 14 , which is designated I _ac2 , and any number of other current sensors 18th that any number of additional battery cells 12th can also be assigned accordingly also detect the individual currents through this respective battery cell 12th that are labeled I _acn in this example. Ultimately, you can also use a reduced number of current sensors 18th or with the one in here 1 shown arrangement ultimately all cell currents I _ac1 , I _ac2 , lacn are determined for each path. From knowledge of the total voltage Uges and these individual _currents I _ac1 , I _ac2 , lacn, in principle the individual impedances of the respective battery cells can now 12th can be calculated directly. For this purpose, the measurement signals from the sensors 18th also the measuring device 16 can be supplied for evaluation, or a higher-level evaluation device can be provided, which measures the measured values of the sensors 18th as well as corresponding data from the impedance measuring device 16 receives the individual impedances of the respective battery cells 12th to investigate. Thus, in this example, active electrochemical impedance spectroscopy with directional excitation is combined with passive electrochemical impedance spectroscopy using sensor technology and data analysis at the cell level, e.g. filtering, drift compensation, FFT (Fast Fourier Transform).

In principle, in order to measure the total voltage Uges, there is a single voltage measuring device, such as that of the impedance measuring device 16 , sufficient. However, it is also possible to implement a plurality of voltage measurements, in particular by means of respective voltage sensors, and these separately from or together with one, part or all of the current sensors 18th accommodate in one or more housings or devices. It is also possible to use multiple impedance meters 16 to use, then one, several or all of the impedance measuring devices 16 can be used for excitation, the current sensors 16b of impedance measuring devices 16 for measuring the individual currents through the battery cells 12th can be used and the voltage sensors 16a of the respective impedance measuring devices 16 can be used to measure the total voltage Uges. These individual impedance meters 16 are then constructed so that their respective current sensors 16b at the position of in 1 shown current sensors 18th are arranged, and the voltage sensors 16a are arranged so that the above the respective battery cells 12th falling voltage Uges is measurable, for example parallel to the respective battery cells 12th are switched.

Also for the design of the excitation by the excitation source 16c , in particular also by several sources of excitation, as described in more detail below, there are also several possibilities. Any device that can excite the system galvanostatically or potentiostatically is used for the excitation. In principle, the relevant impedances of the cells 12th can also be determined without knowledge of the excitation signal. Any excitation signal can also be used. If the excitation signal is unknown and this also represents current excitation, this can be done with the current sensor, for example 16b , and the individual _currents I _ac1 , I _ac2 , lacn through the battery cells 12th through the assigned current sensors 18th be measured anyway. In the case of potentiostatic stimulation, this can Voltage excitation signal accordingly by the voltage sensor 16a measured and therefore does not have to be assumed to be known. Sinusoidal forms of excitation, multi-sine forms of excitation or any form of excitation are conceivable as forms of excitation.

In a preferred embodiment, the excitation, that is to say that from the excitation source 16c generated excitation signal, predetermined and is thus known. It is generally not necessary to determine the individual impedances, the battery cells 12th to be actively acted upon by an excitation signal. The determination of the individual impedances can also be based, for example, on a purely passive impedance spectroscopy or impedance determination. This can be done, for example, by using the individual cells 12th flowing load current in the operation of the motor vehicle electrical system, in which the measuring arrangement 10th is arranged and used is used. Such a load or one or more electrical consumers and also an energy supplying component can, for example, be parallel to the parallel connection 14 are switched and through the battery cells 12th be powered or the battery cells 12th supply with battery.

However, it is preferred to generate an active excitation signal at least in addition to such a load current. For this purpose, a sinusoidal excitation signal is preferably generated. Active excitation has the advantage that it enables the frequency ranges of interest to be examined in a targeted manner. Excitation with a signal of a single frequency, as is the case for example with a sinusoidal signal, also increases the signal-to-noise ratio. Nevertheless, the excitation signal can also be superimposed by a load current. Accordingly, the individual impedance measurement can advantageously also be carried out with the measuring arrangement during operation of the on-board electrical system 10th be performed. This means that individual impedances of the battery, in particular high-voltage batteries, of which the individual battery cells can also be used 12th constitute a part, can also be determined during operation under load of the battery, without the need for individual cells 12th must be isolated.

The suggestion can, as for example in 1 shown on the common connection terminals 20 of the components connected in parallel, in particular cells 12th , done as by the source of excitation 16c of the measuring device 16 . The excitation can, however, also take place through excitation sources which are serial to one or more components, in particular the cells 12th , are switched. Possible positions for such sources of inspiration 22 are in 2nd shown schematically. 2nd again shows a simplified schematic representation of a measuring arrangement 10th according to an embodiment of the invention, which also like 1 can be described. In addition, here are different possible positions for sources of excitation 22 shown. The one for parallel connection 14 excitation source connected in parallel 22 can for example the power source 16c of the measuring device 16 represent, or also a voltage source for a potentiostatic excitation, as also described or a connection of a combination of several sources. Furthermore, there are now further sources of inspiration 22 shown, each in series with one of the battery cells 12th the parallel connection 14 are switched. One or more of the excitation sources shown can thus be used to excite or to provide the active excitation signal, current signal and / or voltage signal 22 be used. Becomes an excitation signal from several of these excitation sources 22 provided at the same time, the corresponding excitation signals are superimposed.

Now are the individual _currents I _ac1 , I _ac2 , lacn through the respective battery cells 12th known, as well as those on these battery cells 12th falling total voltage Uges, there are now numerous possibilities to use these measured values to determine the individual impedances of the cells 12th to determine. The possibilities for evaluating the measurement signals are varied. In particular, various mathematical methods can be used for evaluating the current and voltage measurement data and for determining the impedances.

The following is an example of a possible implementation of the individual impedance determination of the cells connected in parallel 12th described in more detail.

For simplification, it is assumed that the parallel connection 14 only two battery cells connected in parallel 12th comprises, the individual currents through these relevant battery cells 12th , as in 1 shown with I _ac1 and I _ac2 . The one above the individual battery cells 12th falling individual voltages, which are identical to the total voltage, which is across the parallel connection 14 drops, are still designated with Uges, as well as the total current through the parallel connection 14 with I _A. Furthermore, a known excitation signal is also assumed, which provides the total current I _A. The rest of the structure can also be used 1 be described, that is, an impedance measuring device 16 parallel to parallel connection 14 be switched and generate this excitation signal, in particular the current excitation signal I _A. In principle, with this structure, Ohm's law makes it possible to determine the individual impedances directly without further signal processing. In the application is an immediate one Determination of the individual impedances without further signal processing is difficult, however, because the impedance is a complex value, for the calculation of which the amplitude and frequency and phase position must first be determined from the current and voltage signals before the impedance can be calculated using Ohm's law. In addition, regarding the current measurement at cell level, a relatively small and inexpensive current sensor should be used 18th measuring ranges as large as possible, resolution, accuracy, low measuring noise and offset errors are provided.

The following is an example for calculating the respective impedances of the battery cells 12th described.

3rd shows a graphic representation of the by the excitation source 16c generated current excitation signal I _{A over} time, and also by the voltage sensor 16a detected total voltage Uges, and the two by the current sensors 18th recorded individual currents through the battery cells 12th , which are again _labeled I _ac1 and I _ac2 . In this example, as described, a sinusoidal excitation, in particular with only a single frequency, was selected. This frequency is referred to below as ω ₀ . This frequency is _ges for all excitation signals I _A, U, I _{ac1, ac2} I equal, as it is a linear time invariant system in this case.

$$I_{ac2}=I_2\cdot e^{-i\omega t+{\phi }_{i2}}$$

$$I_A=I\cdot e^{-i\omega t+{\phi }_1}$$

$$U_{ges}=U\cdot e^{-i\omega t+{\phi }_U}$$

$$Z=\frac{U_{ges}}{I_A}$$

The time signals, as in 3rd shown, transform current excitation I _A , total voltage Uges and individual _currents I _ac1 , I _ac2 into frequency range f. As a result of the Fourier transformation, there is a frequency spectrum of the sinusoidal signals contained, which sum up to give the time signal. In the present example, the result of the Fourier transformation is, for example, by the measuring device 16 as an FFT (Fast Fourier Transform) can be performed in 4th shown. Since the excitation signal has only one frequency, namely where, the Fourier transform in the frequency domain now gives the respective amplitudes for the excitation signal I _A , the total voltage Uges and the individual _currents I _ac1 , I _ac2 at the frequency ω _{0 in question} . The signals in the time and frequency domain can thus be used to determine amplitudes, frequencies and phases of the partial signals. Since, as described, only a sinusoidal signal was selected as the excitation signal, there is only one sinusoidal output signal for the total voltage Uges and the partial currents I _ac1 , I _ac2 , which can now be represented in a space vector model as follows due to the same frequency ω ₀ : $${\mathrm{I.}}_{ac1}={\mathrm{I.}}_1\cdot e^{-i\omega t+{\phi }_{i1}}$$

$${\mathrm{I.}}_{ac\mathrm{2nd}}={\mathrm{I.}}_{\mathrm{2nd}}\cdot e^{-i\omega t+{\phi }_{i\mathrm{2nd}}}$$

$${\mathrm{I.}}_A=\mathrm{I.}\cdot e^{-i\omega t+{\phi }_1}$$

$$U_{Ges}=U\cdot e^{-i\omega t+{\phi }_U}$$

$$\mathrm{Z.}=\frac{U_{Ges}}{{\mathrm{I.}}_A}$$

Here I ₁ , I ₂ denote the respective amplitudes of the individual _currents I _ac1 , I _ac2 , and I the amplitude of the excitation _signal I _A , and U the amplitude of the total voltage Uges. In this example, the frequencies ω each correspond to the named individual frequency ω ₀ . Furthermore, φ _I1 , φ _I2 , φ _I and φ _U denote the phases of the respective signals. For example, the phase φ _{I of} the excitation signal I _A can be taken as a reference value for the other phases φ _I1 , φ _I2 , φ _U and, for example, set to zero.

The impedance Z of the overall system results from the division of the total voltage Uges by the current excitation signal I _A.

$$Z_2=\frac{U_2}{I_{act2}}=\frac{U_{ges}-U_{OCV2}}{I_A-I_{ac1}}=Z\cdot \frac{1-\frac{U_{OCV2}}{U_{ges}}}{1-\frac{I_{ac1}}{I_A}}$$

The impedances Z ₁ , Z _{2 of} the individual cells can now be determined via Ohm's law 12th determine among other things as follows: $${\mathrm{Z.}}_1=\frac{U_1}{{\mathrm{I.}}_{act1}}=\frac{U_{Ges}-U_{O\mathrm{C.}V1}}{{\mathrm{I.}}_A-{\mathrm{I.}}_{ac\mathrm{2nd}}}=\mathrm{Z.}\cdot \frac{1-\frac{U_{O\mathrm{C.}V1}}{U_{Ges}}}{1-\frac{{\mathrm{I.}}_{ac\mathrm{2nd}}}{{\mathrm{I.}}_A}}$$

$${\mathrm{Z.}}_{\mathrm{2nd}}=\frac{U_{\mathrm{2nd}}}{{\mathrm{I.}}_{act\mathrm{2nd}}}=\frac{U_{Ges}-U_{O\mathrm{C.}V\mathrm{2nd}}}{{\mathrm{I.}}_A-{\mathrm{I.}}_{ac1}}=\mathrm{Z.}\cdot \frac{1-\frac{U_{O\mathrm{C.}V\mathrm{2nd}}}{U_{Ges}}}{1-\frac{{\mathrm{I.}}_{ac1}}{{\mathrm{I.}}_A}}$$

Here U _{OCV1 denote} the open circuit voltage of the first battery cell 12th and U _OCV2 the open circuit voltage of the corresponding second battery cell 12th . The individual impedances Z ₁ , Z ₂ were expressed in accordance with the above formulas as a function of the total impedance Z. The total impedance Z of the parallel connection 14 can, for example, by the impedance measuring device 16 be given directly. In order to determine the relevant no-load voltages U _OCV1 , U _OCV2 , it is possible, for example, to use the characteristic SOC-OCV relationship and the specified one State of charge of the battery cell concerned 12th to determine. In other words, the quiescent voltage Uocvx of a corresponding battery cell 12th can be determined according to the following formula: $$U_{O\mathrm{C.}Vx}=f^{-1}\left(SO{\mathrm{C.}}_x\right)$$

Here, f ^-1 (SOC _x ) denotes the SOC-OCV relationship, which shows the dependency of the rest voltage Uocvx, for example as a formula, look-up table or the like, on the state of charge SOC _{x of} a battery cell in question 12th pretends.

Hierbei bezeichnet „mean(U_ges(t))“ den Mittelwert des zeitlichen Verlaufs der Gesamtspannung U_ges(t), das heißt insbesondere den zeitlichen Mittelwert. Somit lassen sich also für eine bestimmte Frequenz ω₀ die Impedanzen Z₁, Z₂ der Batterieeinzelzellen 12 ermitteln. Das beschriebene Verfahren kann ganz analog für mehrere Frequenzen wiederholt werden, um die Impedanzen Z₁, Z₂ für verschiedene Frequenzen aufzunehmen. Die Ergebnisse der beschriebenen Messungen beziehungsweise Berechnungen sind in 5 grafisch in einem Nyquist-Diagramm aufgetragen, wobei auf der Abszisse der Realteil Re der jeweiligen Impedanzen in Ohm Ω, das heißt der Einzelimpedanzen Z₁, Z₂ und der Gesamtimpedanz Z, aufgetragen ist, und auf der Ordinate der Imaginärteil -Im der jeweiligen Impedanzen ebenfalls in Ohm Ω. Hierbei ist zu erkennen, dass eine der beiden Zellen 12, welcher die Impedanz Z₂ zugeordnet ist, einen höheren ohmschen Widerstand als die andere Zelle 12 aufweist, was beispielsweise ein Indiz für eine stärkere Alterung sein kann.In an advantageous implementation, in this special case, the selected excitation can be used to easily identify the open circuit voltage using the following formula: $$U_{O\mathrm{C.}Vx}=mean\left(U_{Ges\left(t\right)}\right)$$

Here, “mean (U _{tot (t)} )” denotes the mean value of the time profile of the total voltage U _{tot (t)} , that is to say in particular the mean time value. Thus, for a certain frequency ω _0, the impedances Z ₁ , Z _{2 of} the individual battery cells can be 12th determine. The described method can be repeated quite analogously for several frequencies in order to record the impedances Z ₁ , Z ₂ for different frequencies. The results of the measurements and calculations described are in 5 plotted graphically in a Nyquist diagram, the real part Re of the respective impedances in ohm Ω, that is to say the individual impedances Z ₁ , Z ₂ and the total impedance Z, being plotted on the abscissa, and the imaginary part -Im of the respective impedances on the ordinate also in ohms Ω. It can be seen that one of the two cells 12th , which is assigned the impedance Z ₂ , a higher ohmic resistance than the other cell 12th shows what can be an indication of a stronger aging, for example.

The mathematical methods of network theory can also be used to determine the total impedance Z from the two impedance curves Z ₁ , Z ₂ , which is indicated by the calculated impedance ZB as a corresponding curve in FIG 5 is also illustrated. The result of the calculation ZB shows that the total impedance Z can be composed of the individual impedances Z ₁ , Z ₂ , since the calculated values represented by the curve ZB are almost congruent with the total impedance curve Z, which is based on measurements of the total voltage Uges and the total current I _A is based. However, it is not possible to calculate back from the total impedance Z to the individual impedance values Z ₁ , Z ₂ , which is why the measuring arrangement according to the invention and its embodiments represent the optimal possibility of determining such cell impedances Z ₁ , Z ₂ .

In addition to the methods presented here via the Fourier transformation and the complex AC calculation, other methods such as, for example, special filter techniques from control engineering can also be implemented with the described method in signal processing. For example, model-based methods such as the Kalman filter or methods from artificial intelligence are conceivable here.

In addition, the impedance determination method is not limited to two cells, but can be expanded to any number of cells. It is primarily intended for use in a vehicle and in particular for use in the electrochemical impedance spectroscopy of traction batteries installed in the vehicle in online diagnostics, but is generally applicable for the impedance determination of any electrical component using any evaluation method.

Overall, the examples show how the invention can provide an impedance measurement of cells connected in parallel, by means of which, using additional current sensors, it is possible to determine the state of all individual cells in the battery system with high precision. It enables an exact determination of the condition of an individual cell with the aid of the current distribution and provides knowledge about the impedance of each individual cell in the battery system and not just the entire battery or an entire parallel line. Another advantage is that the method mentioned can also be used during operation. It therefore delivers the individual cell impedances of the battery even during operation and without the need to isolate individual cells.

QUOTES INCLUDE IN THE DESCRIPTION

This list of documents listed by the applicant has been generated automatically and is only included 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

• DE 102013103921 A1 [0003]
• US 2015/0145520 A1 [0004]
• EP 2551689 A2 [0004]

Claims (10)

Measuring arrangement for determining a complex impedance (Z1, Z2) of at least one first electrical component (12), the measuring arrangement (10) having the first electrical component (12) and a measuring device (16) which is connected to the first electrical component (12) is coupled, and which is designed to determine the complex impedance (Z1, Z2) of the first electrical component (12), characterized in that the measuring arrangement (10) has at least one second electrical component (12) which is connected to the first electrical component (12) is arranged in a parallel circuit (14), with at least the first electrical component (12) being assigned a current sensor (18) which is connected in series with the first electrical component (12), the measuring device (16) is designed to measure the complex impedance (Z1, Z2) of the first electrical component (12) as a function of a current (I _ac1 , I _ac2 , I _a. flowing through the first component (12) detected by the current sensor (18) _cn ) to be determined. Measuring arrangement (10) after Claim 1 characterized in that the measuring arrangement (10) has a plurality of electrical components (12) comprising the first and the at least one second electrical component (12) in the parallel circuit (14), each of the electrical components (12) having a current sensor (18) is assigned, which is connected in series with the assigned electrical component (12) and is designed for measuring the electrical current (I _ac1 , I _ac2 , I _acn ) through the assigned electrical component (12), the measuring device (16) being designed for this purpose is to separately determine the complex impedance (Z1, Z2) of a respective electrical component (12) as a function of the respective currents (I _ac1 , I _ac2 , I _acn ) detected by the current sensors (18). Measuring arrangement (10) after Claim 1 , characterized in that the measuring arrangement (10) has a plurality of electrical components (12) comprising the first and the at least one second electrical component (12) in the parallel circuit (14), each one except for one specific component (12) Current sensor (18) is assigned, which is connected in series with the assigned electrical component (12) and is designed for measuring the electrical current (I _ac1 , I _ac2 , I _acn ) through the assigned electrical component (12), the measuring arrangement ( 10) has a total current sensor (16b) which is connected in series with the parallel connection (14) and which is designed to measure a total current (I _A ) flowing through the parallel connection (14), the measuring device (16) being designed to a current (I _ac1 , I _ac2 , I _acn ) through the only specific component (12) as a function of the respective currents (I _ac1 , detected by means of the current sensors (18) assigned to the electrical components (12), I _ac2 , I _acn ) and the total current (I _A ) detected by means of the total current _sensor (16a). Measuring arrangement (10) according to one of the preceding claims, characterized in that the first electrical component (12) and the at least one second electrical component (12) represent a respective electrochemical memory, in particular a battery cell (12) for a high-voltage battery. Measuring arrangement (10) according to one of the preceding claims, characterized in that the measuring device (16) has at least one voltage sensor (16a) which is designed to detect a voltage (U _tot ) dropping at the first electrical component (12), wherein the measuring device (16) is designed to determine the complex impedance (Z1, Z2) of the first electrical component (12) as a function of the detected voltage (Uges). Measuring arrangement (10) according to one of the preceding claims, characterized in that the measuring device (16) is designed as an impedance measuring unit (16) connected in parallel with the parallel connection (14). Measuring arrangement (10) according to one of the preceding claims, characterized in that the measuring device (16) has at least one excitation source (16c, 22) which is designed to generate an excitation signal and the parallel connection (14) and / or the first component (12) and / or to apply the excitation signal to the at least one second component (12). Measuring arrangement (10) according to one of the preceding claims, characterized in that the measuring device (16) is designed to _measure the impedance (Z1, Z2) as a function of a current (I _ac1 , I _ac2 , through the first component (12)) I _acn ), which at least partially represents a load current, which is brought about by an electrical consumer coupled to at least the first electrical component (12) and / or by a component providing energy, and as a function of the detected electrical component on the first ( 12) determining the falling voltage (U _tot ). Motor vehicle with a measuring arrangement (10) according to one of the preceding claims. Method for determining a complex impedance (Z1, Z2) of at least a first electrical component (12) by means of a measuring device (16), which is coupled to the first electrical component (12), and the complex impedance (Z1, Z2) of the first electrical component (12), characterized in that the measuring arrangement (10) has at least one second electrical component (12), which is arranged with the first electrical component (12) in a parallel circuit (14), with at least the first electrical component (12) being assigned a current sensor (18) which is shown in Series is connected to the first electrical component (12), the measuring device (16) the complex impedance (Z1, Z2) of the first electrical component (12) as a function of one detected by the current sensor (18) by the first component (12) flowing current (I _ac1 , I _ac2 , I _acn ) determined.

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