DE102023203228A1 - Method for determining a state of a battery and a data processing system - Google Patents

Abstract

The invention is directed to a method for determining a state of a battery (1), wherein the battery (1) has a plurality of cells (2, 3, 4) which are connected at least in series with one another; wherein the method comprises at least the following steps:
a) applying an alternating current (5) to the plurality of cells (2, 3, 4);
b) measuring the alternating voltage (6) generated thereby at the battery (1);
c) determining the impedance from the impressed and measured alternating current (5) and the measured alternating voltage (6) for the plurality of cells (2, 3, 4), so that an average value for at least one temperature of the cells (2, 3, 4) is determined for the plurality of cells (2, 3, 4).

Description

The invention relates to a method for determining a state of a battery, in particular a high-voltage battery. The invention further relates to a data processing system which is suitably designed to carry out the method.

Such high-voltage batteries are used in particular in motor vehicles to store electrical energy for driving traction drives. A battery is usually made up of a number of cells, each cell having a terminal voltage of 1.5 to 4 volts. The cells are at least partially connected in series so that a traction voltage of 60 to 1,500 volts DC is provided.

The temperature of a high-voltage battery, or more precisely the temperature of the battery cells, is now measured indirectly by temperature sensors attached to the outside of the cells. This results in a local difference between the temperature measurement point and the inside of the cell, which results in a temperature difference. In addition, temperatures change due to temperature capacities and thermal conductivity, so that a difference in temperatures also occurs over time. For the rapid charging of high-voltage batteries, precise knowledge of the cell temperature is important, since the current is reduced if a critical temperature is exceeded. The more accurately the temperature can be measured, the smaller the safety margin can be from the true critical temperature of the cells. Therefore, charging time can be reduced by measuring the cell temperature precisely.

The internal cell temperature can be determined using the well-known impedance spectroscopy. In impedance spectroscopy, a phase relationship between current and voltage is evaluated and the real or imaginary part of a cell resistance is determined. This is done by running through the frequency response of an impressed current from very low frequencies (0.1 Hz) to high frequencies (10 kHz). This process takes a lot of time and a lot of energy is taken from the cell to impress the current. In addition, interference generated by the vehicle's consumers has a strong effect and distorts the measurement signal. The measurement results of voltage and current are evaluated using complex algorithms. This then allows a conclusion to be drawn, for example, about the absolute value of the internal cell temperature. This method is very sensitive to interference and is currently only used under laboratory conditions. Since this impedance spectroscopy is known to measure every cell, the system costs are higher than without impedance spectroscopy and the system is relatively complex. The technology may not be used.

From the DE 10 2013 103 921 A1 A temperature measuring system for cells in a battery pack, which includes several cells connected in series and in parallel, is known. An alternating voltage signal is applied to the battery pack and a voltage sensor detects a voltage signal from one cell or several cells connected in parallel. A current sensor also detects a current signal for the battery pack. The temperature of the cell group - i.e. the cells connected in parallel if necessary - is determined from the impedance and frequency determined in this way.

From the DE 10 2017 218 715 A1 A method for determining the temperature and charge state of a single lithium-ion cell using impedance values is known.

From the DE 10 2020 110 466 A1 A method for determining a state of at least one cell of a battery is known, wherein a plurality of cells connected in series are subjected to an alternating current and the alternating voltage generated is measured on at least two cells. A difference in the states of the cells is determined based on the phase position of the alternating voltages.

The object of the present invention is to at least partially solve the problems mentioned with reference to the prior art. In particular, a method for determining the status of a battery is to be proposed. In particular, this is intended to detect damage to a cell or the battery during operation of a motor vehicle at an early stage and to reduce or prevent any danger to a user of the motor vehicle.

A method with the features according to claim 1 contributes to the solution of these tasks. Advantageous further developments are the subject of the dependent claims. The features listed individually in the claims can be combined with one another in a technologically meaningful way and can be supplemented by explanatory facts from the description and/or details from the figures, whereby further embodiments of the invention are shown.

1. a) Beaufschlagen der Mehrzahl von Zellen mit einem Wechselstrom;
2. b) Messen der dadurch an der Batterie erzeugten Wechselspannung;
3. c) Ermitteln der Impedanz aus dem aufgeprägtem (beaufschlagten) Wechselstrom und dem gemessenem Wechselstrom und der gemessenen Wechselspannung für die Mehrzahl von Zellen, so dass für die Mehrzahl von Zellen ein Mittelwert für zumindest eine Temperatur der Zellen ermittelt wird.

A method for determining a state of a battery is proposed, wherein the battery has a plurality of cells which are at least partially connected in series with one another The method comprises at least the following steps:

1. a) applying an alternating current to the plurality of cells;
2. b) measuring the alternating voltage generated at the battery;
3. c) determining the impedance from the impressed (charged) alternating current and the measured alternating current and the measured alternating voltage for the plurality of cells, so that an average value for at least one temperature of the cells is determined for the plurality of cells.

The above (non-exhaustive) classification of the process steps into a) to c) is primarily intended to serve as a distinction and does not force a sequence and/or dependency. The frequency of the individual process steps can also vary. It is also possible that process steps overlap one another at least partially. Process steps b) and c) particularly preferably take place during step a). In particular, steps a) and b) take place simultaneously. In particular, step c) takes place at the same time or at a different time to steps a) and b).

In particular, the method involves carrying out impedance spectroscopy for a plurality of cells that are at least partially connected in series. In particular, the method is carried out for all cells of the battery. In particular, the alternating voltages occurring at each cell are not measured, but only the alternating voltage of the plurality of cells is determined. In particular, only one value of the alternating voltage is measured, namely only the value (or curve) of the alternating voltage of the plurality of cells.

Therefore, impedance spectroscopy is not carried out for a single cell or for cells (exclusively) connected in parallel.

In particular, in step c), or after determining the impedance of the majority of cells, the phase relationship between the alternating current and the alternating voltage is evaluated using the basically known method of impedance spectroscopy and the real or imaginary part of a resistance of the majority of cells is thus determined. To do this, in particular in step a), the frequency response of an impressed current is run through from very low frequencies (0.1 Hz) to high frequencies (10 kHz).

According to step a), in particular an alternating current, e.g. with a frequency of more than 1 Hz [Hertz], in particular between 1 Hz and 10 kHz, preferably between 10 Hz and 10 kHz, particularly preferably of 100 Hz, is impressed into the majority of cells of the battery.

In particular, the sum of the alternating voltage applied to each cell results in the so-called system voltage of the battery or of the plurality of cells under consideration. In particular, only this (one) alternating voltage of the plurality of cells is measured. This alternating voltage is measured at the same time as the applied alternating current, so that a phase relationship between the measured values for voltage and current can be determined.

Since all cells of the majority of cells or of a battery behave in almost the same way, the phase relationship of the alternating voltage of the individual cells to the alternating current also behaves analogously to the alternating voltage of the battery or of the majority of cells under consideration to the alternating current.

In particular, the alternating voltage of the majority of cells is analyzed in relation to the applied alternating current using impedance spectroscopy, so that this results in particular in an average value of the real parts and the imaginary parts of the internal resistance of all cells of the majority of cells. This also results in particular in an average value of the phase relationship of the alternating voltage of the individual cells to the alternating current.

In particular, depending on the frequency of the alternating current applied, these values can be used to determine the mean values of SOC (state of charge; state of charge of the battery or the majority of cells), SOH (state of health; state of aging of the battery or the majority of cells) and the temperature of the majority of cells (i.e. an average value for the total number of cells considered).

In particular, SOC refers to the ratio of the remaining capacity of the cells (i.e. the capacity present in the cells under consideration at a current point in time) to the actual capacity of the cells (i.e. the maximum capacity possible at that point in time of the cells under consideration).

In particular, SOH refers to the ratio of the actual capacity of the cells to the nominal capacity of the cells (i.e. the nominal capacity of the cells, which is specified, for example, by the manufacturer of the cells or the battery).

The frequency of the alternating current applied for SOC determination is in particular at a few Hertz, the frequency for determining the temperature is about 100 to 300 Hertz.

In particular, the plurality of cells comprises at least 50 cells, preferably at least 100 cells, particularly preferably at least 200 cells, which are connected in series with one another. In particular, the plurality of cells comprises all cells of a battery cell that are connected in series with one another.

In particular, in addition to each cell connected in series, the battery has at least one further cell connected in parallel to the respective cell. In particular, in step a), these cells, preferably all cells of the battery, are also subjected to the alternating current. In particular, the resulting alternating voltage is measured for these cells, i.e. in particular all cells of the battery.

In particular, the alternating current and the alternating voltage are measured simultaneously by a single integrated circuit (also called a chip).

An integrated circuit is also known as an application-specific integrated circuit (ASIC). Its function cannot be changed after it has been manufactured.

In particular, the determination of the impedance according to step c) is also carried out in the integrated circuit. In particular, the accuracy of the measurement can be increased by the simultaneous measurement via a single integrated circuit, because the measurements of alternating voltages and alternating current are then carried out as synchronously as possible.

In particular, the measured values of the alternating current and the alternating voltage are transmitted to a circuit arranged at a spatial distance from the integrated circuit. In particular, the determination of the impedance according to step c) is carried out there.

In particular, the alternating current and the alternating voltage are measured by circuits arranged at a distance from one another. In particular, synchronicity of the measured alternating voltage and the measured alternating current must be ensured. In particular, the phase shift resulting from the spatial separation should be significantly smaller than the phase shift caused by the plurality of cells.

In particular, a state of charge and a state of health of the battery or the majority of cells are additionally determined from the impedance determined in step c).

In particular, if the imaginary part of the determined impedance changes, it can be concluded, if necessary by comparison with reference values stored in a controller, that a cell resistance of at least one cell of the plurality of cells changes, e.g. as a result of a temperature increase at the start of thermal propagation.

A data processing system (control unit) is also proposed which is equipped, configured or programmed to carry out the described method. The data processing system can measure an alternating current impressed on a plurality of cells of a battery connected in series with one another and a resulting alternating voltage and can determine an impedance of the plurality of cells from this. Furthermore, the data processing system can determine an average value for at least one temperature of the cells from the impedance for the plurality of cells. In particular, the data processing system can also determine an SOC or an SOH for the plurality of cells under consideration and/or for the battery or a respective average value of these parameters for the respective cell from the impedance for the plurality of cells.

Furthermore, the method can also be carried out by a computer or with a processor of a control unit.

The method can in particular be implemented in a control unit, wherein the control unit is provided at least for the diagnosis, and possibly also for the operation, of the battery.

The battery can be used in a motor vehicle to store energy, whereby at least one traction drive of the motor vehicle is supplied with electrical energy via the battery.

In particular, a motor vehicle with a traction drive and a battery arrangement comprising the described battery and the data processing system is proposed.

A computer-readable storage medium may be provided which comprises instructions which, when executed by a computer/processor, cause the computer/processor to carry out the method or at least some of the steps of the proposed method.

The statements on the method are particularly transferable to the motor vehicle, the battery and/or the computer-implemented method (i.e. the computer or the processor, the data processing system, the computer-readable storage medium) and vice versa.

A consumer already present in the vehicle, e.g. an HV heater, a pulse inverter or a heating mat control, can be used to impose the alternating current. The changing current of the electric drive can also serve as a signal source.

• • Eine Impedanzspektroskopie für die gesamte Batterie (bzw. die Mehrzahl von Zellen) ist mit geringerem apparativem Aufwand durchführbar;
• • Die durchgeführten Messungen sind robust bzw. aussagekräftig, weil nur kurze Messleitungen (also Verbindungen zwischen dem zur Messung bzw. Auswertung verwendeten Schaltkreis und der Batterie bzw. der Mehrzahl von Zellen) benötigt werden und weil keine Messleitungen zu den einzelnen Zellen bereitgestellt werden müssen;
• • Es ist kein Zusatzaufwand erforderlich, weil die Wechselspannung und der Wechselstrom der Batterie bzw. der Mehrzahl von Zellen (und nicht der einzelnen Zelle) im Betrieb und für den Betrieb der Batterie sowieso gemessen werden müssen;
• • Die Auswertung der Messwerte bzw. die Bestimmung der Impedanz und die daraus abgeleiteten Werte für die Temperatur, den SOC und/ oder den SOH kann durch einfache Software bzw. Programme erfolgen.

The proposed method has certain advantages over classical (known) measurement methods:

• • Impedance spectroscopy for the entire battery (or the majority of cells) can be carried out with less equipment;
• • The measurements carried out are robust and meaningful because only short measuring lines (i.e. connections between the circuit used for measurement or evaluation and the battery or the majority of cells) are required and because no measuring lines have to be provided to the individual cells;
• • No additional effort is required because the AC voltage and AC current of the battery or the majority of cells (and not the individual cell) must be measured during operation and for the operation of the battery anyway;
• • The evaluation of the measured values or the determination of the impedance and the derived values for the temperature, the SOC and/or the SOH can be carried out using simple software or programs.

However, defects in individual cells or deviations in certain parameters (voltage, current, phase shift) occurring in individual cells cannot be detected or assigned to the individual cell.

The use of indefinite articles ("a", "an", "an" and "another"), particularly in the patent claims and the description reflecting them, is to be understood as such and not as a number. Terms or components introduced accordingly are therefore to be understood as being present at least once and, in particular, can also be present multiple times.

As a precaution, it should be noted that the numerals used here ("first", "second", ...) primarily serve (only) to distinguish between several similar objects, sizes or processes, and in particular do not necessarily specify a dependency and/or sequence of these objects, sizes or processes. If a dependency and/or sequence is required, this is explicitly stated here or it is obvious to the person skilled in the art when studying the specifically described design. If a component can occur multiple times ("at least one"), the description of one of these components can apply equally to all or part of the majority of these components, but this is not mandatory.

• 1: eine Batterieanordnung; und
• 2: ein Diagramm.

The invention and the technical environment are explained in more detail below with reference to the accompanying figures. It should be noted that the invention is not intended to be limited by the exemplary embodiments given. In particular, unless explicitly stated otherwise, it is also possible to extract partial aspects of the facts explained in the figures and combine them with other components and findings from the present description. In particular, it should be noted that the figures and in particular the size relationships shown are only schematic. They show:

• 1 : a battery arrangement; and
• 2 : a diagram.

1 shows a battery arrangement 14 which comprises a battery 1 and a data processing system 9. The battery 1 comprises a plurality of cells 2, 3, 4 which are connected to one another in series and in parallel. As part of the method, in step a), the plurality of cells 2, 3, 4 are supplied with an alternating current 5. According to step b), the alternating voltage 6 thereby generated on the battery 1 is measured. According to step c), the impedance is determined from the impressed and measured alternating current 5 and the measured alternating voltage 6 for the plurality of cells 2, 3, 4, so that an average value for at least one temperature of the cells 2, 3, 4 is determined for the plurality of cells 2, 3, 4.

The alternating current 5 and the alternating voltage 6 are measured simultaneously by a single integrated circuit 7 (also referred to as a chip). In particular, the determination of the impedance according to step c) is also carried out in the integrated circuit 7. In particular, the accuracy of the measurement can be increased by the simultaneous measurement via a single integrated circuit 7, because the measurements of the alternating voltage 6 and the alternating current 5 are then carried out as synchronously as possible.

Alternatively, the measured values of the alternating current 5 and the alternating voltage 6 are transmitted to a circuit 8 arranged at a distance from the integrated circuit 7. In particular, the determination of the impedance according to step c) is carried out there.

In the circuit, the SOC, the SOH and the temperature are determined for the majority of cells 2, 3, 4. It is not possible to assign these parameters to the individual cells 2, 3, 4, so that an average value can be determined for each cell 2, 3, 4.

The 2 shows a diagram. The alternating current 5 and the alternating voltage 6 are plotted on the vertical axis. The time 10 is plotted on the horizontal axis. The curves of the alternating current 5 and the alternating voltage 6 are shown. The alternating voltage 6 comprises an imaginary part 11 and a real part 12. The imaginary part 11 has a phase shift 13 compared to the real part 12.

One method for directly measuring the internal cell temperature is so-called impedance spectroscopy. In impedance spectroscopy, a phase relationship between alternating current 5 and alternating voltage 6 is evaluated and the real part 12 or imaginary part 11 of a resistance of the majority of cells 2, 3, 4 is determined. This is done by running through the frequency response of an impressed alternating current 5 from very low frequencies (0.1 Hz) to high frequencies (10 kHz).

list of reference symbols

1

battery

2

first cell

3

second cell

4

third cell

5

alternating current

6

alternating current

7

integrated circuit

8

circuit

9

data processing system

10

Time

11

imaginary part

12

real part

13

phase shift

14

battery arrangement

QUOTES INCLUDED IN THE DESCRIPTION

This list of 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.

Cited patent literature

• DE 102013103921 A1 [0005]
• DE 102017218715 A1 [0006]
• DE 102020110466 A1 [0007]

Claims (9)

Method for determining a state of a battery (1), wherein the battery (1) has a plurality of cells (2, 3, 4) which are at least partially connected in series with one another; wherein the method comprises at least the following steps: a) applying an alternating current (5) to the plurality of cells (2, 3, 4); b) measuring the alternating voltage (6) generated thereby at the battery (1); c) determining the impedance from the impressed and measured alternating current (5) and the measured alternating voltage (6) for the plurality of cells (2, 3, 4), so that an average value for at least one temperature of the cells (2, 3, 4) is determined for the plurality of cells (2, 3, 4). procedure according to patent claim 1 , wherein the plurality of cells (2, 3, 4) comprises at least 50 cells (2, 3, 4) connected in series with one another. Method according to one of the preceding claims, wherein the battery (1) has, in addition to each cell (2, 3, 4) connected in series, at least one further cell (2, 3, 4) connected in parallel to the respective cell (2, 3, 4); wherein in step a) all cells (2, 3, 4) of the battery (1) are supplied with the alternating current (5). Method according to one of the preceding claims, wherein the alternating current (5) and the alternating voltage (6) are measured simultaneously by an integrated circuit (7). procedure according to patent claim 4 , wherein the determination of the impedance according to step c) is also carried out in the integrated circuit (7). procedure according to patent claim 4 , wherein the measured values of the alternating current (5) and the alternating voltage (6) are transmitted to a circuit (8) arranged spatially spaced from the integrated circuit (7) and the determination of the impedance is carried out there according to step c). Method according to one of the preceding patent claims 1 until 3 , wherein the alternating current (5) and the alternating voltage (6) are measured by circuits (7,8) arranged spatially spaced from one another. Method according to one of the preceding claims, wherein a state of charge and a state of health of the battery (1) are additionally determined from the impedance determined in step c). Data processing system (9) which is equipped, configured or programmed to carry out a method according to one of the preceding claims, wherein an alternating current (5) impressed on a plurality of cells (2, 3, 4) of a battery (1) connected in series with one another and a resulting alternating voltage (6) can be measured by the data processing system (9) and an impedance of the plurality of cells (2, 3, 4) can be determined therefrom, wherein an average value for at least one temperature of the cells (2, 3, 4) can be determined by the data processing system (9) from the impedance for the plurality of cells (2, 3, 4).

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