DE102018206353B3 - Method for determining charge states of cells in a battery - Google Patents

Abstract

The invention relates to a method for determining charge states of a plurality of cells (132, 152) in a battery (130, 150), wherein the cells (132, 152) are arranged on a single strand (134, 154) or at least two in parallel connected strands (134, 154) are distributed in the battery (130, 150), wherein the cells (132, 152) are arranged in series within the strand (134, 154). The method comprises the steps:
a) providing an internal resistance value of each cell (132, 152);
b) metrological detection of a voltage applied to each cell (132, 152) voltage;
c) determining a value for a current through each string (134, 154) using a difference between the metrologically detected voltage applied to each cell (132, 152) and an estimated voltage resulting from an estimate of the state of charge of each cell ( 132, 152), taking into account the value of the internal resistance of each cell (132, 152); and
d) adjusting the estimate of the charge state of each cell (132, 152) using the determined value for the current through each leg (134, 154).
The method makes it possible to determine the charge states of the plurality of cells (132, 152) in the battery (130, 150) in real time, whereby the number of required current sensors can be reduced compared to the prior art.

Description

Field of the invention

The invention relates to a method for determining charge states of a plurality of cells in a battery, wherein the cells are distributed on a single strand or on at least two parallel connected strands in the battery, wherein the cells are arranged within a string in series or series connection are a computer program adapted to perform the steps of the method and a battery management system appropriately equipped to perform the method.

State of the art

To determine a state of charge of each individual battery cell or cell within a battery or a battery system, at least one current sensor is required for each individual strand, which can preferably each be operated and read out by means of a battery management system. These current sensors make it possible to determine the partial current to be determined by the respective string in order to be able to determine the state of charge (SOC) of each individual cell in the battery in this way. At the same time, however, a power dissipation drops across each of the current sensors used, which can assume a considerable order of magnitude, in particular for larger batteries, which may have 10 to 100 strings, which is disadvantageous in particular with regard to cost and energy efficiency of the battery management system. It would therefore be desirable to be able to reduce the number of required current sensors while the accuracy of the determination of the charge states remains as constant as possible.

vorgenommen, wobei der Term SOC_k (0) einen Startpunkt, d.h. den elektrischen Ladungszustand zur Zeit t=0, angibt und wobei Q_n eine in einem Datenblatt angegebene oder anderweitig bestimmte Nennladungskapazität der betreffenden Zelle in der Batterie bezeichnet. Hierbei ist mindestens ein Stromsensor pro Strang erforderlich ist, um alle Teilströme durch alle Stränge messtechnisch erfassen zu können.Various methods for determining charge states of a plurality of cells in a battery are known from the prior art. In this case, in order to determine an electrical charge state SOC _k (t) in a string k of the cells arranged cells, an integration of the current i _k (t) through the strand k over the time t according to equation (1) is usually $$SO{C}_k\left(t\right)={\displaystyle {\int }_0^t{i}_k\left(\tau \right)d\tau \text{/}{Q}_n}+SO{C}_k\left(0\right)$$

wherein the term SOC _k (0) indicates a starting point, ie the electric charge state at the time t = 0, and wherein Q _n denotes a rated charge capacity of the respective cell in the battery indicated in a data sheet or otherwise determined. In this case, at least one current sensor per strand is required in order to detect all partial flows through all strands metrologically.

Alternatively or additionally, complicated control technology filter algorithms can usually be used, with usually only individual cells being considered or only the partial flows being considered as pure input variables by a single strand. Again, at least one current sensor per strand is still needed so as to allow a metrological detection of the partial flows through each strand and thus a knowledge of all partial flows through all strands.

J. Kim, J. Shin, C. Jeon, and B. Cho, "High accuracy state-of-charge estimation of li-ion battery pack based on screening process," in Applied Power Electronics Conference and Exposure (APEC), 2011 , Twenty-Sixth Annual IEEE. IEEE, 2011, pp. 1984-1991 , describe such a method in which the cells of a battery are described by means of a unit cell model. However, it is not possible to determine deviations in the charge states between individual cells because the unit cell model only considers a medium charge state.

H. Dai, X. Wei, Z. Sun, J. Wang, and W.Gu., "Online cell socmentation of li-ion battery packs using dual-time-scale Kalman filtering for ev applications," Applied Energy 95, p 227-237, 2012 , propose a two-stage algorithm in which first a mean charge state of all cells in a string is determined and then a difference of the actual charge state of each individual cell to the average charge state is determined, using a double time scale to reduce the computational effort.

F. Sun and R. Xiong, "A novel dual-scale cell state-of-charge estimation approach for series-connected battery packs used in electric vehicles," Journal of Power Sources 274, pp. 582-594, 2015 , fit under In addition, considering the average state of charge, the electrical resistance and the capacitance of each individual cell using bias correction.

S. Sepasi, R. Ghorbani, and BY Liaw, "Extended Extended Calman Filter for State of charge estimation of battery packs," Journal of Power Sources 255, pp. 368-376, 2014 , for this purpose, present a method not only for estimating the state of charge, but also a state of health (SOH) in one strand.

M.-S. Wu, C.-Y. Lin, Y.-Y. Wang, C.-C. Wan, and C. Yang, "Numerical simulation for the discharge of batteries in series and / or parallel-connected battery packs," Electrochimica Acta 52, pp. 1349-1357, 2006 , propose an iterative algorithm for simulating the current distribution in a serial and / or parallel battery system. However, the proposed algorithm requires a considerable amount of computation and is therefore not suitable for real-time application.

CJ Chun, J. Back, GS Seo, B. Cho, J. Kim, IK Chang, and S. Lee, "Current sensorless state-of-charge estimation algorithm for lithium-ion batteries using filtered terminal voltage," Journal of Power Sources 273, pp. 255-263, 2015 , use a filtered output voltage to determine the state of charge of the cells in a battery, waiving simultaneous measurement of the partial currents. However, this method requires long waiting times for a sufficient accuracy of the determination of the state of charge. Moreover, the inverse of the relationship between the state of charge and the open circuit voltage (SOC-OCV) is used here, which, however, can not be used for all types of lithium-ion batteries.

In the DE 10 2012 014 436 A1 the cell current is determined by a cell current function using the internal resistance, the cell voltage and the cell temperature.

The DE 10 2009 038 663 A1 shows battery groups connected in parallel, where the battery groups consist of series-connected batteries.

Object of the invention

Based on this, the object of the present invention is to provide a method for determining charge states of a plurality of cells in a battery, a computer program and a battery management system, which at least partially overcome the disadvantages and limitations of the prior art.

In particular, the proposed method should make it possible to be able to determine charge states of the individual cells in the battery in real time, whereby the number of required current sensors can be reduced compared to the prior art.

Disclosure of the invention

This object is achieved by a method for determining charge states of a plurality of cells in a battery, by a computer program and a battery management system according to the features of the independent patent claims. Advantageous developments, which can be implemented individually or in any combination, are shown in the dependent claims.

Hereinafter, the terms "having", "having", "including" or "including" or any grammatical variations thereof are used in a non-exclusive manner. Accordingly, these terms may refer to situations in which, in addition to the features introduced by these terms, there are no other features or to situations in which one or more other features are present. For example, the expression "A has B", "A has B", "A includes B" or "A includes B" can both refer to the situation in which, apart from B, there is no further element in A. (ie a situation in which A consists exclusively of B), as well as the situation in which, in addition to B, one or more further elements in A are present, for example element C, elements C and D or even further elements ,

It is further to be understood that the terms "at least one" and "one or more" and grammatical variations of these terms, when used and expressed in connection with one or more elements or features, are intended to make the element or feature simple or may be provided more than once, as a rule be used only once, for example, at the first introduction of the feature or element. In a subsequent renewed mention of the feature or element of the corresponding term "at least one" or "one or more" is usually no longer used, without limiting the possibility that the feature or element may be provided simply or repeatedly.

Furthermore, the terms "preferably", "in particular", "for example" or similar terms are used below in connection with optional features, without restricting alternative embodiments thereof. Thus, features introduced by these terms are optional features, and it is not intended by these features to limit the scope of the claims and, in particular, the independent claims. Thus, as those skilled in the art will recognize, the invention may be practiced using other embodiments. Similarly, features introduced by "in one embodiment of the invention" or by "in one embodiment of the invention" are to be understood as optional features without, however, being construed as limiting alternative embodiments or the scope of the independent claims. Furthermore, these introductory expressions are intended to leave untouchable all possibilities of combining the features introduced thereby with other features, be they optional or non-optional features.

In a first aspect, the present invention relates to a method for determining charge states of a plurality of cells in a battery. The term "battery" here refers to an electrical interconnection of at least two electrochemical cells, which are also referred to as "galvanic cells" or "battery cells", which are preferably used for storage of chemical energy and for the delivery of electrical energy. Each cell in the battery at all times occupies a so-called "state of charge" (SOC), which is typically expressed as a percentage of an actual electrical charge stored in the cell in question with respect to the total charge capacity Q _{n of} the cell can be specified. As a "cell" usually a device is named, which has two spatially separated electrodes, each having a different polarity and therefore can also be referred to as a "cathode" or as an "anode". In the cell, the two electrodes are in contact with one another via at least one ion-conducting electrolyte, while a separator permeable to the ions electrically insulates the two electrodes from one another in order to avoid a short circuit. In addition to so-called "primary batteries", which can be used only once during their life cycle, there are a large number of so-called "secondary batteries" which can be charged and discharged over a large number of cycles with electrical energy. For this purpose, a use of suitable active materials is required, which can be reversibly convert between at least two electronic states, in order to be able to convert chemical energy into electrical energy or vice versa in this way. In the case of lithium-ion batteries, these may typically be LiNi _x Mn _y Co _z O ₂ (NMC), LiFePO ₄ (LFP), LiCoO ₂ (LCO) or LiMn ₂ O ₄ (LMO). However, other types of batteries, cells and / or materials are also possible.

The plurality of cells is arranged in the context of the present invention as an "array" in the form of a series-parallel configuration. For this purpose, the cells are arranged in a single strand or distributed on at least two, in parallel connected strands, wherein each of the strands has exactly one single cell or at least two arranged in series cells. The arrangement of the cells in the battery, i. a first number of strands in the battery and a second number of cells in each strand are each fixed and known. The term "connected" refers to an electrically conductive connection. The term "series connection" or "series connection" here refers to a successive attachment of at least two cells within a strand in such a way that thereby a single current path is formed by the at least two cells. Consequently, two cells connected in series are traversed by a current of the same height. In contrast thereto, the term "parallel connection" designates an arrangement of at least two cells in separate strands, with a total current flowing through the battery being divided as partial currents onto the strands which are electrically connected to one another. According to the present invention, the configuration of the array, i. the number of strands and the number of cells located in each strand, in principle arbitrary, for safety reasons a maximum, voltage applied to the battery voltage should not be exceeded.

1. a) Bereitstellen eines Wertes für einen Innenwiderstand einer jeden Zelle;
2. b) messtechnische Erfassung einer an jeder Zelle anliegenden Spannung;
3. c) Bestimmen eines Wertes für einen Strom durch jeden Strang unter Verwendung einer Differenz zwischen der an jeder Zelle anliegenden messtechnisch erfassten Spannung und einer geschätzten Spannung, welche aus einem Schätzwert für den Ladungszustand einer jeden Zelle ermittelt wird, wobei der Wert für den Innenwiderstand einer jeden Zelle berücksichtigt wird; und
4. d) Anpassen des Schätzwertes für den Ladungszustand einer jeden Zelle unter Verwendung des bestimmten Wertes für den Strom durch jeden Strang.

The present process comprises at least the following steps a) to d), wherein steps a) to d) in the order given can preferably be carried out successively, starting with step a) and ending with step d), wherein it may be particularly advantageous to repeat steps b) to d) several times. The method according to the invention comprises the following steps:

1. a) providing a value for an internal resistance of each cell;
2. b) metrological detection of a voltage applied to each cell voltage;
3. c) determining a value for a current through each string using a difference between the metrologically detected voltage applied to each cell and an estimated voltage determined from an estimate of the state of charge of each cell, wherein the value of the internal resistance of each Cell is taken into account; and
4. d) adjusting the estimate of the charge state of each cell using the determined value for the current through each leg.

According to step a), a value for an internal resistance of each cell is provided. The value thus provided for the internal resistance of each cell can be determined simultaneously or, preferably, beforehand by metrological detection of a voltage applied to each cell and stored, in particular for later provision according to step a). To determine the value for the internal resistance of each cell, a metrological detection of a voltage applied to the cell in question can be made and from this the internal resistance of the relevant cell can be determined. Here, the term "metrological detection" denotes a method step for the determination of raw data, which serves as a starting point for the determination of further data, possibly in cooperation with further metrologically recorded raw data or data derived therefrom.

According to a cell model described in more detail below, a voltage applied to each cell from an open circuit voltage (OCV), which can adjust due to the sought charge state of the cell in question, from a diffusion voltage due to diffusion processes and / or charge transfer within the cell as well as from a further voltage which flows due to the ohmic internal resistance of the relevant cell through which a current flows. The term "internal resistance" here refers to an electrical resistance which describes a direct response in the form of a voltage to an exposure of the cell to an external current according to Ohm's law. However, the internal resistance, without affecting the present method, may depend on the state of charge of the cell or other quantities, in particular a temperature prevailing in the cell, and may assume a higher value, in particular at low charge states.

The determination of the value for the internal resistance of each cell by metrological detection of a voltage applied to each cell can preferably be carried out by a device designed for this purpose, which is usually referred to as a "battery management system". The battery management system can also be used to store the already determined values for the internal resistance of each cell, in particular for the subsequent provision according to step a). In a particularly preferred embodiment, the values for the internal resistance of each cell can be determined only once in advance, stored in a table and read out from the table as needed. Alternatively or additionally, the battery management system may determine further values for the internal resistance of each cell, for example, after the timeout or after the occurrence of a specified event. Preferably, a voltage applied to a single cell voltage can be determined by means of a voltage measuring device, which can also be referred to as a "voltmeter", wherein the relevant voltage measuring device can be located in the battery management system and / or can be read by the battery management system. In a similar manner, moreover, at least one current sensor, which is also referred to as an "ammeter", may be provided, which may enable the determination of a total current flowing through the battery or the partial currents in individual strings.

According to step b), a metrological detection of a voltage applied to each cell takes place. Preferably, for this purpose, the voltage applied to a single cell voltage can be determined by means of the above-mentioned voltmeter or "voltmeter", wherein the relevant voltage measuring device can be located in the battery management system and / or can be read by the battery management system.

According to step c), this is followed by a determination of a value for a current through each string using a difference between the measured voltage applied to each cell and an estimate of the cell voltage, which is based on an estimate of the charge state of each cell, particularly preferably with reference to FIG Estimate the voltages for the diffusion processes and / or the charge transfer, is determined. Here, the value provided according to step a) for the internal resistance of each cell is taken into account. The term "determination of a difference" or "determination of a difference" here denotes a method step which makes a difference between two determined values. In order to determine the difference, the "Kalman filter" can be used, which is a recursive method, whereby a real-time determination can be made possible by means of this estimation algorithm. To determine a separate current flow estimate, which is determined using the internal resistance of each cell in the string provided in step a), an estimation algorithm can be used which, without knowledge of the current through the cell, passes the current determine the single strand or the partial flow by at least two interconnected strands. The term "estimate" here denotes a value determined by means of an estimation algorithm, which the estimation algorithm assumes as the most probable value. As an estimation algorithm, a "Kalman filter" known from the prior art can be preferably used, wherein the "Kalman filter designates an estimation algorithm in which a multiplicity of measured values, which may have inaccuracies, are used, and from this an estimated value for a more accurate one Variable is generated. Preferably, this estimation algorithm can have a two-stage method, wherein-in a first stage-an estimated value for the variables is generated according to their accuracy and-in a second stage-further measured values are used to increase the measurement accuracy. Accordingly, according to step c), an initially generated estimated value can be used and, according to step d), adapted to the determined values for the current through each strand. However, it is also possible to use other estimation algorithms. Regardless of the estimation algorithm actually used, the internal resistance of each cell in the string can be used to determine the current, particularly the partial current, through the string.

According to step d), the charge state estimate of each cell is adjusted using the determined difference from step c). The term "fitting the estimate" refers to a change in the value which the estimation algorithm takes as the next most probable value after a further step. This finally makes it possible to determine the desired charge states for each individual cell in the string. The term "determining the state of charge" or "determining the states of charge" in this case refers to a determination of the state of charge (SOC) for each individual cell in the strand in question, usually as a percentage of a cell actually stored electrical charge with respect to the total charge capacity Q _{n of} the cell.

In a particularly preferred embodiment of the present method, at least steps b) to d) can be repeated after a first time at at least one further time, preferably at a multiplicity of successive points in time. Here, in a particularly advantageous manner, the charge state estimate of each cell, adapted according to step d) at a previous time, may be used at a subsequent time as the charge state estimate of each cell according to step c). In this way, the present method can be performed as a recursive method at the successive times. Two successive times can be separated from each other by a time interval of 0.001 s to 10 s, preferably from 0.01 s to 1 s, particularly preferably from 0.05 s to 0.5 s, with successive time intervals preferably being able to be equidistant. However, other embodiments are possible, for example, non-equidistant time intervals or the implementation of steps b) to d) after the expiration of time or after the occurrence of a specified event. Regardless of the type of execution, in this way a better estimate of the flow, in particular the partial flow, can be obtained by at least one strand.

The method presented here with the steps a) to d) is particularly suitable for determining the desired charge states for each individual cell in a single strand of the battery, wherein the entire cells of the battery in the strand are connected in series or series. Alternatively, this method can also be used for the determination of the sought charge states for each individual cell, which are distributed on one or on more than a single strand of the battery, as far as the individual strands of the battery are preferably considered independently. Regardless of whether the cells in the battery are distributed over one or more strands, it is possible to make a good estimate of the sought charge states of each individual cell, with their quality increasing as the number of cells in at least one cell increases, as shown in more detail below Strand is also increasing. In a particularly advantageous manner, in contrast to methods known from the prior art, a metrological detection of a current value can be completely omitted.

In a particularly preferred embodiment of the present method, however, the individual strands of the battery are no longer considered independently, but in relation to each other, whereby synergies between some or even all strands of the battery may result in that the estimated values for a strand in Estimates for other strands, especially for adjacent strands. In this particularly preferred embodiment, the battery thus has at least two strands. According to the invention, the charge states of each cell in a string are determined in each case together with the charge states of each cell in an adjacent strand. In accordance with Kirchhoff's 1st law, this implies that the total flow is divided into individual partial flows in the strands. In order to determine the partial flows of each strand according to step c), preferably a total current through the battery, in particular by means of a current sensor, can be detected by measurement and subsequently used in the estimation algorithm, whereby the division of the individual partial currents into the strands can be considered successively or simultaneously , Thus, for determining the estimated value for a partial flow through a selected branch, the estimated values of the individual charge states and / or the estimated value for a partial flow can be included by one or more other strings. In particular, in the cell model already mentioned, differences between the different strands of the battery can be taken into account by using a separate strand resistance for each individual strand and assuming that the voltage drop across each strand is assumed to be equal, according to Kirchhoff's second law.

In a particular embodiment of the present method, in which the cells are distributed in at least three parallel connected strands in the battery, an inclusion of the estimated value for a partial flow through an adjacent strand can be carried out successively for the strands arranged in parallel. In this case, the estimated values determined for one strand can be successively transferred to the estimation algorithm for the respectively adjacent strand. In a particularly preferred embodiment of the method, a mesh with one of the two adjacent strands can be formed for each strand and in each case the estimated value for the partial flow through the mesh can be determined. The term "mesh" also goes back to the second Kirchhoff's law, which states that partial stresses within a closed electrical current path, which can also be called "circulation", in the absence of temporally changing magnetic fluxes, of which in the present Case can be assumed to add to zero, so that the current within the mesh can be assumed to be constant. Now, if two adjacent strands are considered as a single mesh, their current can be related to each other. In other words. From an already determined estimated value for the current through a selected path, it is thus possible in each case to determine an estimated value for the current through a selected adjacent path.

In addition, in a particular embodiment of the present method, non-adjacent strands can also be correlated with one another.

Regardless of the chosen embodiment, by means of which individual strands of the battery are related to each other, it is sufficient in this case to detect only the total current through the battery and to use in the estimation algorithm. This can save up to one current sensor per string, which significantly reduces both the expense of the battery and the battery management system.

For further details with regard to the method according to the invention, in particular with regard to carrying out the individual method steps, reference is made to the embodiments below.

In a further embodiment, however, alternatively or in addition to the metrological detection of the total current, at least one partial flow can be detected by one of the strands of the battery, wherein according to the invention at least one strand of the battery remains, in which no metrological detection of the partial flow takes place. In this way, metrologically additionally detected values can be included in the determination of the charge states of the individual cells, but at the expense of a higher number of current sensors.

In another aspect, the present invention relates to a computer program configured to perform the steps of the method of determining charge states of a plurality of cells in a battery as described herein. In this way, the desired parameters and variables can be calculated, preferably in real time, whereby specific parameters can be predetermined, metrologically recorded, calculated and stored. In this case, the computer program can be stored in particular in an electronic memory, which can be located in a battery management system described in more detail below. Alternatively or additionally, the computer program and the parameters and variables used therein can be stored externally, in particular on external memories, a server or within a cloud, and made available online as needed.

In a further aspect, the present invention relates to a battery management system that is equipped to carry out the method according to the invention. The term "battery management system" here refers to a one-part or multi-part device, which is set up to operate and monitor the battery by setting parameters and variables, preferably in real time, predetermined, metrologically recorded, calculated and stored. For this purpose, the battery management system can preferably have a plurality of components which can be arranged inside and / or outside a housing. In particular, discrete or integrated circuits or a combination thereof may be provided for this purpose, for example application-specific integrated circuits (ASICs), universal circuits, in particular FPGAs (field programmable gate arrays) or FPAAs (Field Programmable Analog Arrays), microcomputers or Computer. However, other types of embodiment of the battery management system are possible.

• - mindestens ein Spannungsmessgerät, welches zur messtechnischen Erfassung einer an jeder Zelle anliegenden Spannung eingerichtet ist; und
• - mindestens eine Auswerteeinrichtung, welche zur Ermittlung der Ladungszustände einer jeden Zelle unter Verwendung eines Computerprogramms, welches dazu ausgestattet ist, um die Schritte des hierin beschriebenen Verfahrens zur Ermittlung von Ladungszuständen einer Vielzahl von Zellen in einer Batterie durchzuführen.

The battery management system for determining charge states of a plurality of cells in a battery, wherein the cells are distributed on a single strand or on at least two parallel connected strands in the battery, wherein the cells are arranged in a string in series, in this case comprises at least

• - At least one voltage measuring device, which is set up for the metrological detection of a voltage applied to each cell voltage; and
• at least one evaluation device, which is used to determine the charge states of each cell using a computer program which is equipped to perform the steps of the method described herein for determining charge states of a plurality of cells in a battery.

• - mindestens eine Einrichtung zur Auslesung eines Stromsensors, welcher zur messtechnischen Erfassung eines Gesamtstroms durch die Batterie oder eines Teilstroms durch einen einzelnen Strang der Batterie eingerichtet ist.

In a particular embodiment, the battery management system may further comprise

• - At least one means for reading a current sensor, which is adapted for metrological detection of a total current through the battery or a partial flow through a single strand of the battery.

For further details with respect to the battery management system, reference is made to the description of the method according to the invention.

Advantages of the invention

The present method is suitable for the determination of charge states of a plurality of cells in a battery, wholly or partially dispensing with very accurate and therefore expensive as well as expensive current sensors. Since any power sensor used in the battery necessarily dissipates a power loss when carrying out a current measurement, thereby power losses of the battery in determining the charge states of the cells can be significantly reduced. This significantly reduces costs and costs in the form of current sensors and energy for their operation. A prior art bias adjustment of the various current sensors may be completely or partially eliminated. The proposed distributed estimation method can also advantageously reduce the required computation time and memory requirements of the system.

list of figures

Further details and features of the present invention will become apparent from the following description of preferred embodiments, in particular in conjunction with the dependent claims. In this case, the respective features can be implemented on their own or in combination with one another. However, the invention is not limited to the embodiments. The embodiments are shown schematically in the following figures. Here, like reference numerals in the figures designate the same or functionally identical elements or with respect to their functions corresponding elements.

• 1 ein Blockschaltbild einer Batterie und eines zugehörigen Batteriemanagementsystems zur Durchführung eines aus dem Stand der Technik bekannten Verfahrens zur Ermittlung von Ladungszuständen einer Vielzahl von Zellen in der Batterie;
• 2 eine schematische Darstellung eines in Verfahren zur Ermittlung des Ladungszustands einer einzigen Zelle eingesetzten Kalman-Filters;
• 3 ein Blockschaltbild für ein Zellmodell der Zelle einer Batterie;
• 4 ein Blockschaltbild eines bevorzugten Ausführungsbeispiels zur Ermittlung von Ladungszuständen einer Vielzahl von Zellen, welche in einem einzigen Strang angeordnet sind;
• 5 ein Blockschaltbild eines weiteren bevorzugten Ausführungsbeispiels zur Ermittlung von Ladungszuständen einer Vielzahl von Zellen, welche in mindestens zwei benachbarten Strängen angeordnet sind;
• 6 ein Blockschaltbild eines weiteren bevorzugten Ausführungsbeispiels zur Ermittlung von Ladungszuständen einer Vielzahl von Zellen, welche in mindestens zwei benachbarten Strängen angeordnet sind;
• 7A-7C: eine schematische Darstellung von verschiedenen bevorzugten Ausführungsbeispielen zur Ermittlung von Ladungszuständen einer Vielzahl von Zellen in mindestens zwei benachbarten Strängen;
• 8A-8C: eine Darstellung eines Vergleichs von direkten Messungen mit Ergebnissen aus der Durchführung des erfindungsgemäßen Verfahrens zur Ermittlung eines Ladungszustands einer Einzelzelle;
• 9A-9C: eine Darstellung eines Vergleichs von direkten Messungen mit Ergebnissen aus der Durchführung des erfindungsgemäßen Verfahrens zur Ermittlung der Ladungszustände von jeweils 3 Zellen in 2 Strängen; und
• 10A-10D: eine Darstellung eines Vergleichs von direkten Messungen mit Ergebnissen aus der Durchführung des erfindungsgemäßen Verfahrens zur Ermittlung der Ladungszustände von jeweils 3 Zellen in 3 Strängen.

In detail show:

• 1 a block diagram of a battery and an associated battery management system for performing a method known in the prior art for detecting charge states of a plurality of cells in the battery;
• 2 a schematic representation of a Kalman filter used in methods for determining the charge state of a single cell;
• 3 a block diagram for a cell model of the cell of a battery;
• 4 a block diagram of a preferred embodiment for determining charge states of a plurality of cells, which are arranged in a single strand;
• 5 a block diagram of another preferred embodiment for determining charge states of a plurality of cells, which are arranged in at least two adjacent strands;
• 6 a block diagram of another preferred embodiment for determining charge states of a plurality of cells, which are arranged in at least two adjacent strands;
• 7A-7C : A schematic representation of various preferred embodiments for determining charge states of a plurality of cells in at least two adjacent strands;
• 8A-8C : a representation of a comparison of direct measurements with results from carrying out the method according to the invention for determining a charge state of a single cell;
• 9A-9C : a representation of a comparison of direct measurements with results from carrying out the method according to the invention for determining the charge states of 3 cells each in 2 strands; and
• 10A-10D : A representation of a comparison of direct measurements with results from carrying out the method according to the invention for determining the charge states of 3 cells in 3 strands.

Description of the embodiments

1 shows a block diagram of a battery 110 which have a variety of cells 112 has, where the cells 112 here on several strings connected in parallel 114 in the battery 110 are distributed, with the cells 112 within each strand 114 are arranged in the form of a series or series circuit. Exemplary are in 1 three parallel strands 114 shown; the points ... indicate, however, that in addition a basically arbitrary number of strands 114 in the relevant battery 110 can be present.

For determining charge states of each individual cell 112 in the battery 110 According to a method known from the prior art is one with the battery 110 cooperative battery management system 116 provided, which is set up, on the one hand one on each cell 112 voltage applied V and on the other hand, a partial current i _k , k = 1 ... M, separated by each one of the M strands 114 the battery 110 metrologically to capture. This is indicated by the battery management system 116 one voltmeter each 118 (Voltmeter) for metrological detection of each cell 112 applied voltage V on. Furthermore, each individual strand has 114 the battery 110 via at least one separate current sensor 120 (Ammeter), each by the battery management system 116 can be read out.

können üblicherweise die elektrischen Ladungszustände SOC_k(t) der in einem einzelnen Strang k 114 in der Batterie 110 angeordneten Zellen 112 zur Zeit t ermittelt werden, wofür mindestens ein Stromsensor 120 pro Strang 114 erforderlich ist, um alle Teilströme i_k(t), k = 1 ... M, durch alle M vorhandenen Stränge 114 messtechnisch erfassen zu können. Der Term SOC_k (0) gibt hierbei einen Startpunkt, d.h. den elektrischen Ladungszustand zur Zeit t=0, an. Weiterhin bezeichnet Q_n eine Nennladungskapazität der betreffenden Zelle 112 in der Batterie 110, welche aus einem Datenblatt entnommen oder anderweitig bestimmt werden kann. Mit Kenntnis der durch das jeweilige Spannungsmessgerät 118 ermittelten Spannung jeder einzelnen Zelle 112 in der Batterie 110 lassen sich verbesserte Werte für die ermittelten Ladungszustände SOC_k(t) jeder Zelle 112 des Strangs k 114 angeben.Using current integration i _k (t) over time t according to equation (1) $$SO{C}_k\left(t\right)={\displaystyle {\int }_0^t{i}_k\left(\tau \right)d\tau \text{/}{Q}_n+}SO{C}_k\left(0\right)$$

For example, the electric charge states SOC _k (t) that are present in a single strand k can usually be determined 114 in the battery 110 arranged cells 112 be determined at the time t, for which at least one current sensor 120 per strand 114 is required to divide all sub-streams i _k (t), k = 1 ... M, through all M existing strands 114 to be able to record metrologically. The term SOC _k (0) indicates a starting point, ie the electric charge state at time t = 0. Furthermore, Q _n denotes a nominal charge capacity of the cell in question 112 in the battery 110 , which can be taken from a data sheet or otherwise determined. With knowledge of the respective voltage measuring device 118 determined voltage of each individual cell 112 in the battery 110 can be improved values for the determined charge states SOC _k (t) of each cell 112 of the strand k 114 specify.

As already mentioned, state-of-the-art control algorithms for estimating the state of charge of each individual cell usually continue to be complex 112 in the battery 110 known. In this case, the partial flows are usually through a single strand 114 and the voltages of the individual cells 112 considered as input to the selected filter algorithm. 2 shows a schematic representation of a Kalman filter already used in the prior art 122 , in which the voltage u _{k of} the individual cell 112 and the current i _k through the associated strand 114 form the input variables that make up, inter alia, the output variables charge state SOC (state of charge, short SOC) and covariance P of the state of charge can be determined by estimation. Here, the state of charge SOC usually denotes a percentage of the charge of the cell 112 with respect to the total charge capacity Q _{n of} the cell 112 , The Kalman filter 122 serves to reduce errors in metrologically acquired measured values and estimates for the non-directly measurable system size state of charge SOC every single cell 112 to determine. Again, to determine the state of charge SOC per strand 114 at least one current sensor 120 needed.

3 shows, also for the Kalman filter 122 usable, a single cell 112 descriptive cell model 124 commonly referred to as a "1 RC model". Alternatively, however, more sophisticated cell and battery models are known in the art. In the present cell model 124 it settles on every cell 112 applied voltage u _k from three separate terms which can be given according to equation (2) as follows: $$u_k=OCV\left(SO{C}_k\right)+u_{RC.k}+R_0{i}_k,$$

• - ein erster Term OCV(SOC_k) eine Leerlaufspannung (engl. open circuit voltage, kurz OCV), welche sich aufgrund des gesuchten Ladungszustands SOC der betreffenden Zelle 112 einstellen kann,
• - ein zweiter Term u_RC,k eine Diffusionsspannung aufgrund von Diffusionsprozessen und/oder Ladungstransfer in der Zelle 112, welche sich schematisch mittels eines parallelen Widerstands R_p und einer parallelen Kapazität C_p ausdrücken lassen, sowie
• - ein dritter Term R₀i_k eine weitere Spannung, welche sich aufgrund des ohmschen Innenwiderstands R₀ der betreffenden Zelle 112, durch welche der Strom i_k fließt, ergibt.

Denote this

• a first term OCV (SOC _k ) an open circuit voltage (OCV for short), which depends on the required state of charge SOC the cell in question 112 can adjust
• - a second term u _{RC, k} a diffusion voltage due to diffusion processes and / or charge transfer in the cell 112 , which is schematically by means of a parallel resistor R _p and a parallel capacity C _p express as well
• - a third term R ₀ i _k another voltage, which is due to the ohmic internal resistance R ₀ the cell in question 112 through which the stream i _k flows, results.

The required state of charge SOC (in%) of the relevant cell 112 settles in the battery model 124 according to 3 for discrete times k, k + 1, ... according to the following equation (3): $$\left(\begin{array}{c}SO{C}_{k+1}\\ u_{RC.k+1}\end{array}\right)=\left(\begin{array}{c}SO{C}_k\\ -\frac{T}{R_p{C}_p}{u}_{RC.k}\end{array}\right)+\left(\begin{array}{c}\frac{100\eta T}{Q_n}{i}_k\\ \frac{T}{c_p}{i}_k\end{array}\right),$$

Denote this Q _n the charge capacity of the cell 112 . T a sampling rate resulting from a distance between two adjacent times k, k + 1 to which the desired state of charge SOC is calculated in each case, and η is a coefficient for the overall consideration in the cell 112 occurring losses. However, the coefficient η in lithium-ion batteries can typically have a value of η≈0.99 when the cell is charged 112 and from η≈1 when unloading the cell 112 Therefore, it usually does not play any special role in determining the charge state of the cell 112 ,

4 shows a schematic representation of a battery 130 in which the state of charge SOC the plurality of cells located therein 132 can be determined by a first, preferred embodiment of the method according to the invention. In the embodiment according to 4 are all cells 132 as an example in the battery model 124 shown and connected in series in a single strand 134 the battery 130 arranged. Exemplary are in 4 two cells 132 shown; the dots ... indicate, however, that in addition a basically arbitrary number of cells 132 in the relevant strand 134 can be present.

ist aus einer Differenz zwischen den einzelnen messtechnisch erfassten, an jeder Zelle 132 anliegenden Spannung u_k somit - im Unterschied zum Stand der Technik - bereits ein Rückschluss auf den Strom i_k = i in dem Strang 134 und damit durch jede einzelne Zelle 132 möglich. Aus diesem Grunde ist die im Stand der Technik übliche messtechnische Erfassung des Stroms i durch den Strang 134, etwa mittels des in 1 schematisch dargestellten Stromsensors 120, überflüssig und es kann darauf verzichtet werden.In contrast to the prior art, in this embodiment of the method according to the invention is not a current sensor 120 provided with which the current through the strand 134 metrologically recorded could be. However, the charge state can still be achieved by means of the method according to the invention SOC each one of the plurality of cells in it 132 be determined. This is possible because of a determination of the third term R ₀ i _k , ie the voltage which is due to the ohmic internal resistance R ₀ the cell in question 132 , The current i _k , which through the respective cell 132 flows, lets determine. This determination is based on a fact known from electrical engineering that the cells 132 in the series connection present here within the string 134 which does not have a branch, form a single current path and therefore all N cells 132 in the strand 134 from the same electric current i = i _k , k = 1, ..., N are traversed. Because here too a battery management system 136 is provided, which in each case a voltage measuring device 138 (Voltmeter) for metrological detection of each cell 132 applied voltage u _k for which according to equation (2) holds that $$u_k=OCV\left(SO{C}_k\right)+u_{RC.k}+R_0{i}_k.$$

is from a difference between the individual metrologically recorded, at each cell 132 applied voltage u _k thus - in contrast to the prior art - already a conclusion on the current i _k = i in the strand 134 and with every single cell 132 possible. For this reason, the usual in the prior art metrological detection of the current i through the strand 134 , about by means of in 1 schematically illustrated current sensor 120 , superfluous and it can be dispensed with.

The sought charge state SOC (in%) of each of the cells 132 in the strand 134 can be adjusted according to the battery model used here 124 according to 4 for the discrete points in time k, k + 1, ... so that also equation (3) can be determined: $$\left(\begin{array}{c}SO{C}_{k+1}\\ u_{RC.k+1}\end{array}\right)=\left(\begin{array}{c}SO{C}_k\\ -\frac{T}{R_p{C}_p}{u}_{RC.k}\end{array}\right)+\left(\begin{array}{c}\frac{100\eta T}{Q_n}{i}_k\\ \frac{T}{c_p}{i}_k\end{array}\right),$$

For more details on the presentation in accordance with 4 will be on the description for 3 directed.

For the present embodiment of the method according to the invention thus the current i _k = i is used in the strand 134 as an unknown input variable, which can be estimated at the same time as part of the measured quantity and the state equations. For making the estimation, in particular, the Kalman filter known from the prior art described above can be used. Other ways of making the estimate are possible. In a preferred embodiment, the current i _k = i in the strand 134 determined using a least squares method known from the literature. Particularly preferably, this method can be combined with the Kalman filter and the estimates thus determined. The advantage of this is that with an increasing number of cells 132 in the strand 134 the estimate made becomes more accurate because only a single value for the current i _k = i in the string 134 must be determined, however, more measurements due to each cell 132 applied voltage u _k available. The present embodiment of the method according to the invention can thus also for a plurality of strands arranged in parallel 134 be used as long as each individual strand 134 is considered separately from each other. As will be explained in more detail below, however, particular advantages may result from a common consideration of two or more strands. This results in further advantages of this embodiment of the method according to the invention, which are in a modular structure and which therefore express themselves in particular in an expandable configuration, in a low required computing power and in a suitability as a backup solution and / or emergency solution.

5 shows a schematic representation of another battery 150 in which the state of charge SOC of the plurality of cells therein 152 can also be determined by a further preferred embodiment of the method according to the invention. In the embodiment according to 5 each are three cells 152 in series in each case one of the p strands 154 the battery 150 arranged. Exemplary are in 5 three cells each 152 in three separate strands 154 shown; the respective points ... indicate, however, that in addition a basically arbitrary, but equal number of cells 152 in a huge number of strands 154 can be present.

For determining the charge states SOC of each individual cell 152 in the battery 150 is also one with the battery 150 cooperative battery management system 156 provided, which to it is set up, on the one hand one at each individual cell 152 voltage applied u _k and - in the present embodiment according to 5 - a total flow i _g through the entire battery 150 metrologically to capture. This is indicated by the battery management system 156 one voltmeter each 158 (Voltmeter) for metrological detection of each cell 152 applied voltage u _k on. To simplify the illustration in 5 are the connections between the voltage measuring devices 158 and the individual cells 152 only for the first strand S _I shown; however, corresponding compounds also exist for each of the cells 152 in the further strands S _b , b = 2, ... p. Furthermore, here is a single current sensor 160 (Ammeter) for metrological detection of the total current i _g provided by the battery management system 156 can be read out.

In this embodiment of the method according to the invention, apart from each individual cell 152 applied voltage u _k , thus only the total current i _g metrologically recorded, taking in a battery model used here 162 in every strand S _b , b = 1, ... p an additional resistor R _{c, b} , b = 1, ... p is provided. According to the invention, a division of the metrologically detected total current takes place i _g through the entire battery 150 on the current i _{p, b} for each strand S _b , b = 1, ... p, for which according to equation (4): $$i_{p.b}=i_G\frac{R_{i.G}}{R_{i.b}}+\frac{R_{i.G}}{R_{i.b}}\left({\displaystyle {\Sigma }_{a=1}^p\frac{{\displaystyle {\Sigma }_{r=1}^s\left(OC{V}_{r.a}+u_{RC.r.a}-OC{V}_{r.b}-u_{RC.r.b}\right)}}{R_{i.a}}}\right),$$

Here, R _{i, g} denote the total resistance of the battery 150 , which preferably by means of the metrologically detected total flow i _g can be determined, and R _{i, b} the respective resistance of each strand S _b , b = 1, ... p, which is due to the distribution of the total current i _g on every single strand S _b , b = 1, ... p. Further denote OCV _{r, b} and OCV _{r, a} the open circuit voltages for a consider strand b and the open circuit voltages for the others in the battery 150 existing strands a. In an analogous way u _{RC, r, b} and u _{RC, r, a} the diffusion voltage for a consider strand b and the diffusion voltage for the others in the battery 150 existing strands a.

6 shows the schematic representation of the other battery 150 in which the state of charge SOC of the plurality of cells therein 152 can be determined by a further, particularly preferred embodiment of the method according to the invention. The representation according to 6 corresponds largely to the illustration according to 5 , wherein the illustrated meshes i _{m, b,} b = 1, ... p, schematically indicate that in each case the current through adjacent strands arranged 154 is considered in the form of a mesh. According to the 2nd Kirchhoff's law, which is also referred to as "set of stitches" or "stitch rule", all partial stresses of a mesh, ie a closed circulation, which in the representation according to 6 from each adjacent to each other arranged strands 154 can result in the absence of time-varying magnetic fluxes, which can be assumed in the present case, however, to zero. This results in a division of the metrologically detected total flow i _g through the entire battery 150 on the stream i _{p, b} for every single strand S _b , b = 1, ... p according to equation (5) as $$i_{p.b}=-\frac{{\displaystyle {\Sigma }_{r=1}^s\left(OC{V}_{r.b}-OC{V}_{r.b-1}\right)+}{\displaystyle {\Sigma }_{r=1}^s\left(u_{RC.r.b}-u_{RC.r.b-1}\right)-}\left({\displaystyle {\Sigma }_{r=1}^s{R}_{i.r.b-1}+R_{c.b-1}}\right)\left(i_{m.b-1}-i_{m.b}\right)}{{\displaystyle {\Sigma }_{r=1}^s{R}_{i.r.b}+R_{c.b}}}$$

For strands 154 that are on the edge of the battery 150 can be located and therefore only over a single adjacent strand 154 Instead of equation (5) above, a correspondingly adapted equation applies, which can be easily determined by the person skilled in the art.

As a result, the strands adjacent to each other can be made 154 not as in the embodiment according to 4 only be considered independently, but be put in relation to each other. While in the embodiment according to 5 basically all existing strands 154 be related to each other to the total current to the individual partial currents for the strands 154 to split, in the embodiment according to 6 taking into account the 2nd Kirchhoff law, each successive or simultaneous, the individual partial currents for the strands 154 divided up.

Different types, like those in the battery 130 . 150 existing strands 134 . 154 are related to each other, are schematically in the 7A to 7C shown. While in the execution after 7A , which embodiment according to 4 corresponds, the strands 134 the battery 130 only be considered independently, is carried out in the execution 7B a unidirectional communication of the strands 154 the battery 150 according to which for a first strand 154 determined partial flow for the determination of the partial flow for this purpose adjacent second strand 154 ' can be used. Successively can for a second strand 154 ' determined partial flow for the determination of the partial flow for this purpose further adjacent arranged third strand 154 ' be used etc. In the execution after 7C finally, a multilateral communication of the strands takes place 154 the battery 150 according to which for a single strand 154 Determined partial flow of all other strands 154 is transmitted. In addition, a combination of the in the 7A to 7C schematically illustrated communication of the strands 134 . 154 in the battery 130 . 150 possible, for example, by first a unidirectional communication between a first group of adjacent strands takes place and a value determined in this case is exchanged bidirectionally with a value determined for another group of adjacent strands.

Regardless of the type of communication between the individual strands 134 . 154 the battery 130 . 150 can the metrological detection of the total current i _g completely eliminated ( 7A) or suffice ( 7B or 7C) , wherein the metrological detection of the total current i _g generally in an increase in the accuracy of determining the charge states SOC of the individual cells 132 . 152 can affect. Even with metrological detection of the total current i _g requires the inventive method by a reduced number of required current sensors a significantly lower cost compared to known from the prior art method, which is mainly positive in reduced power losses of the battery 130 . 150 can express.

In a further embodiment (not shown here) may alternatively or additionally to the metrological detection of the total current i _g at least one partial flow i _b , b = 1 ... p, separated by one or more of p strands 154 the battery 150 be detected by measurement, wherein according to the invention at least one strand 154 the battery 150 remains in which no metrological detection of the partial flow i _b he follows. In this way, metrologically additionally detected values can be used to determine the charge states SOC of the individual cells 152 but at the expense of a higher number of current sensors 120 . 160 in the battery 150 , which is both the expense of the battery 150 as well as for the battery management system 156 increases, so that the object of the present invention can be achieved only partially.

In the 8A to 8C a representation of a comparison of direct current measurements and a current integration based thereon according to the above equation (1) with results from the implementation of the inventive method for determining a charge state SOC of a single cell. 8A this shows a temporal course 170 (Time in s) of an experimental determination of the charge state SOC in% of a single cell and - for comparison - a time course 172 the determination of the state of charge SOC the single cell according to the present method. How out 8B shows, there is a difference 174 in the determination of the state of charge SOC between the two temporal processes 170 . 172 at most about 2%. Depending on the accuracy of the measuring instruments and the determined internal resistance of the cell, however, the deviation may assume other values.

Further shows 8C a comparison between a time course 176 (Time in s) of an experimental determination of the current I in A by the single cell and - for comparison - a time course 178 the determination of the current I of the single cell according to the present method. Apart from the absolute determination of the current value in A, both times are shown 176 . 178 already in the estimation of the current I for the single cell a very high agreement, which can be improved even when connecting several cells in a string in series.

The 9A to 9C show a representation of a further comparison of direct measurements with results from the implementation of the method according to the invention for determining a state of charge SOC each of 3 serially arranged cells in 2 parallel strands. While 9A respective temporal courses 180 . 181 . 182 . 183 in s of the state of charge SOC in%, are in 9B and 9C respective temporal courses 184 . 185 . 186 . 187 of the current I in A represented by the 2 strands, where the gradients 180 . 181 . 184 . 185 metrologically recorded values, the gradients 182 . 183 . 186 . 187 on values determined according to the present method, the courses 180 . 182 . 184 . 186 on strand 1 and the courses 181 . 183 . 185 . 187 on strand 2 Respectively.

Since in practice the charge state of a cell at the time t = 0 is not known exactly, were in the embodiment according to 9 initializes all start charge states of the cells for estimation with a difference of about 5%. For example, instead of a correct charge state of a cell of 80%, the Kalman filter used here can be given an estimated value of 75%. This deviating initialization can be found in the 9A be recognized in it that the estimated gradients 182 . 183 show a steep upward trend at the beginning of the present method, since the Kalman filter used recognizes and compensates the deviating initialization already in the first few seconds.

The 10A to 10D show a representation of a further comparison of direct measurements with results from the implementation of the method according to the invention for determining a state of charge SOC each of 3 serially arranged cells in 3 parallel strands. 10A shows an example of the temporal courses 188 . 189 . 190 . 191 . 192 . 193 in s of the state of charge SOC in% in the third strand, since the time profiles of the states of charge in the first two strands differ only insignificantly from this. Here, the dashed curves relate 188 . 189 . 190 metrologically recorded values and the continuous gradients 191 . 192 . 193 on values determined according to the present method.

10B to 10D show the respective temporal courses 194 . 195 . 196 . 197 . 198 . 199 of the 3 partial flows i _{p, b} in A through the 3 strands. Here are the progressions 194 . 195 . 196 on values determined according to the present method, the courses 197 . 198 . 199 on the other hand, metrologically recorded values. The courses 194 . 197 refer to strand 1 , the gradients 195 . 198 on strand 2 and the courses 196 . 199 on strand 3 , From a comparison between the time courses can be seen in particular that the time course of the 3 partial flows i _{p, b} which, in the present battery, presumably takes an unusual course due to aging effects, nevertheless is reproduced very well by the present method.

LIST OF REFERENCE NUMBERS

110

battery

112

cell

114

strand

116

Battery Management System

118

Voltage meter (voltmeter)

120

Current sensor (ammeter)

122

Kalman filter

124

cell model

130

battery

132

cell

134

strand

136

Battery Management System

138

Voltage meter (voltmeter)

150

battery

152

cell

154, 154 ', 154 "

strand

156

Battery Management System

158

Voltage meter (voltmeter)

160

Current sensor (ammeter)

162

battery model

170 to 199

Time course

Claims (12)

A method of detecting charge states of a plurality of cells (132, 152) in a battery (130, 150), the cells (132, 152) being coupled to a single string (134, 154) or to at least two strings (134, 154) connected in parallel , 154) are distributed in the battery (130, 150), wherein the cells (132, 152) are arranged in series within the strand (134, 154), comprising the steps: a) providing a value for an internal resistance of each cell (132, 152); b) metrological detection of a voltage applied to each cell (132, 152) voltage; c) determining a value for a current through each string (134, 154) using a difference between the metrologically detected voltage applied to each cell (132, 152) and an estimated voltage resulting from an estimate of the state of charge of each cell ( 132, 152), taking into account the value of the internal resistance of each cell (132, 152); and d) adjusting the estimate of the charge state of each cell (132, 152) using the determined value for the current through each leg (134, 154). Method according to the preceding claim, wherein at least steps b) to d) are repeated after a first time at at least one further time, the estimate of the charge state of a cell (132, 152) adapted to a previous time according to step d) a subsequent time as the estimate of the charge state of a cell (132, 152) according to step c) is used. The method of any one of the preceding claims, wherein the battery (130, 150) has at least two strands (134, 154), wherein the charge states of each cell (132, 152) in a string (134, 154) each in common with the charge states each cell (132, 152) in an adjacent strand (134, 154) are determined, wherein a partial currents in the strands (134, 154) divided total current is detected by measurement, wherein the metrologically detected total current through the battery (130, 150 ) is used to determine the partial flows through each strand (134, 154). A method according to the preceding claim, wherein a separate strand resistance is used for each strand (134, 154) and a voltage drop across each strand (134, 154) is assumed to be equal. Method according to one of the two preceding claims, wherein for determining the estimated value for a partial flow through a strand (134, 154) the estimated value for a partial flow through at least one adjacent strand (134, 154) is included. A method according to any one of the preceding claims, wherein the cells (132, 152) are distributed in at least three parallel connected strands (134, 154) in the battery (130, 150). Method according to the preceding claim, wherein an inclusion of the partial flow estimate by an adjacent strand (134, 154) is performed successively for the parallel strands (134, 154). Method according to one of the two preceding claims, wherein for each strand (134, 154) a mesh with one of the two adjacent strands (134, 154) is formed and the estimated value for the partial flow through the mesh is determined. Method according to one of the preceding claims, wherein the value provided according to step a) for the internal resistance of each cell (132, 152) is determined by metrological detection of a voltage applied to each cell (132, 152) and for a subsequent provision according to step a) is stored. Computer program adapted to perform the steps of the method of any one of the preceding claims. A battery management system (126, 156) for determining charge states of a plurality of cells (132, 152) in a battery (130, 150), wherein the cells (132, 152) are arranged on a single strand (134, 154) or at least two in Parallel connected strings (134, 154) are distributed in the battery (130, 150), wherein the cells (132, 154) within a string (132, 154) are arranged in series, comprising - at least one voltage measuring device (138, 158) , which is set up for the metrological detection of a voltage applied to each cell (132, 152) voltage; and - at least one evaluation device, which is set up to determine the charge states of each cell (132, 152) using a computer program according to the preceding claim. A battery management system according to the preceding claim, further comprising - At least one means for reading a current sensor (160), which for the metrological detection of a total current through the battery (130, 150) or a partial flow through a single strand (134, 154) of the battery (130, 150) is set up.

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