Method for determining a current state of charge of a battery, battery arrangement and motor vehicle

Abstract

The invention relates to a method for determining a current state of charge (SOCO, SOC1, SOC2) of a battery (14) of a specific battery type, wherein a characteristic curve field (22) is provided which specifies an internal resistance (Ri) for the specific battery type as a function (26) of the state of charge (SOC) for the specific battery type for various predetermined temperature ranges (ΔT), a current temperature (T) of the battery (14) is measured, a current internal resistance value (Ri0, Ri1) of the battery (14) is determined, and the current state of charge (SOCO, SOC1, SOC2) of the battery (14) is determined on the basis of the current temperature (T) and the current internal resistance value (Ri0, Ri1) using the characteristic curve field (22).

Description

[0001] The invention relates to a method for determining a current state of charge value of a battery of a specific battery type, as well as to a battery arrangement comprising a battery of a specific battery type and a control device for determining a current state of charge value of the battery. The invention also includes a motor vehicle comprising such a battery arrangement.

[0002] To ensure reliable and safe operation of a vehicle's electrical system, determining the state of charge (SOC) of on-board or traction batteries plays a crucial role, particularly as part of battery condition monitoring. Several established methods exist for this determination in the automotive sector. For example, given an initial state of charge and a known battery capacity, current integration can be used to determine the change in state of charge under load, such as during charging or discharging. Another method involves 100% recalibration with a fully charged battery. Measuring the battery's resting voltage provides a highly accurate indication of its current state of charge.

[0003] A disadvantage of these known methods is that they are either very inaccurate or only feasible under very specific conditions. For example, the method for determining the state of charge using current integration leads to an error that increases over time, resulting in a significant deviation from the actual state of charge of the battery in the medium term. While known recalibration methods could remedy this, they rely on specific environmental and system conditions, such as a fully charged battery or open-circuit voltage. However, for recalibration by measuring the battery's open-circuit voltage to be possible at all, the characteristic curve between the state of charge and the battery's open-circuit voltage must allow for a clear correlation between the state of charge and the battery's open-circuit voltage for the respective cell chemistry used.This is not the case with some cell chemistries, such as a lithium iron phosphate battery (LiFePO4), which is due to the flat characteristic curve.

[0004] In this context, for example, DE 10 2013 206 189 A1 describes a method for determining the state of charge of an accumulator, in which the state of charge is determined on the basis of a voltage differential, i.e. the derivative of the voltage curve of the accumulator, via a suitable variable.

[0005] Furthermore, DE 11 2013 006 736 T5 describes a method and a device for estimating remaining battery capacity, according to which the battery capacity is determined when switching between charging and discharging the battery. The capacity determination is based on recording the battery's discharge voltage. Here too, the capacity determination can only be performed in a specific situation, namely when switching between charging and discharging the battery.

[0006] DE 199 03 239 A1 describes a method for determining the state of charge of a battery connected to a charger, in which measured values ​​of the battery are used to determine the internal resistance and the respective state of charge is determined by comparing the determined internal resistance with a stored cell-specific internal resistance characteristic curve.

[0007] EP 1 877 812 B1 describes a method for generating a lookup table of cell resistance versus state of charge of a lithium-sulfur battery of a specific type and for determining its capacity.

[0008] DE 100 02 473 A1 describes a method for determining the state of charge using two different methods, whereby the individually obtained results are weighted according to their reliability.

[0009] The object of the present invention is therefore to provide a method for determining the current state of charge of a battery, a battery arrangement and a motor vehicle which allow the simplest and most accurate determination of the state of charge.

[0010] This problem is solved by a method for determining the current state of charge of a battery, by a battery arrangement, and by a motor vehicle with the features according to the respective independent claims. Advantageous embodiments of the invention are the subject of the dependent claims, the description, and the figures.

[0011] In a method according to the invention for determining a current state of charge value of a battery of a specific battery type, a characteristic field is provided which indicates an internal resistance for the specific battery type for respective different predetermined temperature ranges as a function of the state of charge for the specific battery type. Furthermore, a current temperature of the battery is measured, and a current internal resistance value of the battery is determined. Based on the current temperature and the current internal resistance value, the current state of charge value of the battery is determined using the characteristic field. If the measured current temperature lies in one of the predetermined temperature ranges in which the dependence of the internal resistance on the state of charge for an internal resistance value of the characteristic field has an extreme value, the state of charge value of the battery is determined using the characteristic field in such a way that it is checked whetherwhether at least two state-of-charge values ​​exist in the characteristic curve field which are assigned according to the dependency to the measured internal resistance value for the predetermined temperature range in which the current temperature lies, and if so, the at least two state-of-charge values ​​are determined from the characteristic curve field, and the current state-of-charge value of the battery is equated with one of the at least two state-of-charge values ​​according to a predetermined selection procedure, wherein, according to the predetermined selection procedure, the state-of-charge value of the battery is equated with one of the at least two state-of-charge values ​​determined from the characteristic curve field depending on an internal resistance value determined in a previous time step, and / or the type of extremum, i.e., depending on whether the extremum represents a minimum or a maximum, and / or a current charging situation of the battery.i.e., depending on whether the battery is currently being charged or discharged.

[0012] Both the current battery temperature and the current internal resistance can be easily determined. In particular, both the battery temperature and internal resistance can be determined using a method independent of the state of charge; that is, a method that allows the temperature and internal resistance to be determined even without knowledge of the battery's current state of charge. The current state of charge can then be determined based on the measured internal resistance and temperature using the characteristic curves. Furthermore, such a determination can be performed in virtually any operating situation of the battery and the vehicle, for example, when the battery is used in a vehicle. This results in significantly fewer situational limitations regarding the determination of a battery's state of charge.In particular, this enables continuous monitoring and determination of the battery's state of charge. Furthermore, there are no restrictions regarding the type of battery or battery type, which in this context refers to the cell chemistry used in the battery. A corresponding set of characteristic curves, that is, a set of characteristic curves for a specific battery type, can be easily generated, for example experimentally, for any battery type and thus easily used for the inventive method for any specific battery type.To determine such a characteristic curve array, a test battery of a specific cell type can be provided, and then the corresponding internal resistance value of the test battery can be determined for various temperatures within predetermined temperature ranges and for different states of charge, for example, when the test battery is successively discharged or charged. A quasi-continuous measurement of the internal resistance can also be performed for a continuously decreasing or increasing state of charge of the test battery, so that ultimately a corresponding continuous characteristic curve can be provided for each predetermined temperature range, describing the relationship between internal resistance and state of charge for the specific battery type. The results or characteristic curves obtained in this way can then be stored in a characteristic curve array for the specific battery type.This can be performed for numerous test batteries of various battery types, i.e., with different cell chemistries. Thus, a suitable characteristic curve field can be provided for each battery type. Furthermore, the relationship between battery temperature, internal resistance, and state of charge can be determined experimentally with exceptional precision, enabling a particularly accurate determination of the battery's current state of charge based on such a characteristic curve field. This allows the inventive method to be used advantageously and without restriction for any cell chemistry, i.e., for any battery type, while simultaneously enabling the state of charge to be determined with exceptional accuracy in almost any situation. For example, the inventive method can also be applied to cell chemistries such as those found in lithium iron phosphate batteries.This makes it advantageous to determine or recalibrate the state of charge using the knowledge of the internal resistance and the temperature in a particularly simple and efficient way.

[0013] In the context of the invention, a battery can generally be understood to mean any energy storage device, in particular an electrochemical energy storage device. The battery is preferably designed as an energy storage device based on lithium-ion technology. The invention is preferably used in motor vehicles. In this context, the battery can be a motor vehicle battery, such as an on-board power supply battery or traction battery. However, the invention can also be used in entirely different fields of application, such as in electronic devices that use a battery or accumulator as their energy supply, or generally an electrochemical energy storage device, in particular a rechargeable energy storage device, as their energy source. Such electronic devices can be, for example, tablets, smartphones, laptops, smartwatches, or the like.

[0014] The term "state of charge" generally refers to the numerical value indicating the battery's state of charge. Similarly, the term "internal resistance" refers to the numerical value indicating the battery's internal resistance.

[0015] The ultimately determined current state of charge of the battery can be provided as a corresponding signal, which triggers a function. Such a function can be a control function for controlling at least one component, for example, the battery assembly or the vehicle, or a further calculation step, a recalibration of the state of charge, or the display of the current state of charge or corresponding information, such as a predicted range or a charging prompt, on a display, or even the storage of the currently determined state of charge values ​​in memory.

[0016] Furthermore, any number of different predetermined temperature ranges can be defined. For example, a respective temperature range of 1°C can be measured at least over a maximum single-digit Celsius range. The total of the respective different temperature ranges covers a total temperature range that can be defined for each application. For automotive applications, this total temperature range can extend from -30°C to 75°C, for example. For other applications, such as mobile communications devices, the total temperature range can be measured differently and preferably covers all possible operating temperatures of the battery.

[0017] In an advantageous embodiment of the invention, if the measured current temperature of the battery lies in one of the predetermined temperature ranges in which the dependence of the internal resistance on the state of charge rises or falls strictly monotonically, the state of charge value of the battery is determined by means of the characteristic curve field in such a way that the state of charge value of the battery is set equal to a state of charge value of the characteristic curve field which, for the predetermined temperature range in which the currently measured temperature of the battery lies, is assigned to the currently measured internal resistance value according to the dependence.Therefore, if for a specific temperature range there is a clear way to assign the internal resistance value to the state of charge for the specific battery type, which is the case if the characteristic curve describing the relationship between internal resistance and state of charge rises or falls strictly monotonically, then the corresponding state of charge value of the battery can be read from the characteristic curve field in a particularly simple way for a determined current temperature and the current internal resistance value.

[0018] In practice, it has been shown that, depending on the cell chemistry, a clear correlation between internal resistance and state of charge is not always possible. For example, there are cases where the characteristic curve for a specific temperature range, or even several or all specific temperature ranges, exhibits a maximum or minimum, or even several such extremes. Accordingly, it may also happen that more than one state of charge value can be assigned to a given internal resistance value for a specific temperature range.Therefore, it is provided according to the invention that, if the measured current temperature lies in one of the predetermined temperature ranges in which the dependence of the internal resistance on the state of charge for an internal resistance value of the characteristic field has an extremum, the state of charge value of the battery is determined by means of the characteristic field in such a way that it is checked whether at least two state of charge values ​​exist in the characteristic field which are assigned according to the dependence to the measured internal resistance value for the predetermined temperature range in which the current temperature lies, and if so, the at least two state of charge values ​​are determined from the characteristic field and the current state of charge value of the battery is equated with one of the at least two state of charge values ​​according to a predetermined selection method.It is now advantageous to check whether there is more than one possible assignment of the internal resistance value to the corresponding state of charge value. If this is not the case, the procedure described above can be followed, and the corresponding state of charge value can simply be read from the characteristic curve field for the measured temperature and the determined internal resistance value. However, if there is more than one assignable state of charge value for a measured or determined internal resistance value, there are further advantageous methods to determine which of these at least two possible state of charge values ​​represents the current state of charge of the battery.

[0019] According to the invention, it is provided that, according to the predetermined selection method, the state of charge of the battery is equated with one of the at least two state of charge values ​​determined from the characteristic curve field, depending on an internal resistance value determined in a previous time step and / or depending on the type of extremum, i.e., depending on whether the extremum represents a minimum or a maximum and / or depending on a current charging situation of the battery, i.e., depending on whether the battery is currently being charged or discharged.

[0020] This approach is particularly advantageous when the relevant characteristic curve, which describes the relationship between internal resistance and state of charge for a specific temperature range, exhibits only a single extremum, i.e., either a minimum or a maximum. Knowing whether this extremum is a maximum or a minimum is also beneficial. This information can be easily obtained from the corresponding characteristic curves in the characteristic curve field. In such a situation, it is especially advantageous to consider and compare the battery's internal resistance values, determined successively over time, to determine the correct state of charge value from the two possible values ​​in the characteristic curve field.If, for example, the internal resistance decreases with increasing state of charge of the battery according to the corresponding characteristic curve for a certain temperature range, initially falling to a minimum and then rising again with further increasing state of charge, it is possible to easily determine whether one is currently on the falling branch of the characteristic curve or on the rising branch on the other side of the minimum by determining the internal resistance in two successive time steps during the charging of the battery.If two possible state-of-charge values ​​from the characteristic curve are relevant for the current state of charge, and these two state-of-charge values ​​lie on opposite sides of the curve's minimum, this ambiguity can be resolved using the selection procedure described above, according to which specific internal resistance values ​​are compared sequentially over time. Knowledge of the battery's current charging status is particularly advantageous for this. If, for example, the internal resistance decreases over time as the battery's state of charge increases, as is the case when the battery is charging, then, conversely, the internal resistance would increase over time when the battery is discharging.By taking into account these three pieces of information – namely, the additional consideration of an internal resistance value determined in a previous time step, the information about the type of extremum of the characteristic curve, and the information about the current state of charge of the battery – it is advantageously possible to easily determine the correct current state of charge value even for cell chemistries, i.e., for battery types, that do not always allow a clear correlation between the internal resistance and the state of charge of the battery.

[0021] The current charge status of the battery can be easily determined, for example, by measuring the battery current. Batteries typically contain various sensors, such as temperature sensors to determine the current temperature and current sensors to measure the total battery current, which can therefore be advantageously used to determine the state of charge. The battery current represents the total current flowing into or out of the battery. Based on the sign of this current, i.e., its direction, it can be easily determined whether current is being drawn from the battery, as is the case during discharge, or whether current is being supplied to the battery, as is the case during charging.

[0022] In a further advantageous embodiment of the invention, according to the predetermined selection method, a second state of charge value of the battery is determined by means of a temporal current integration of a battery current of the battery and compared with the at least two state of charge values ​​determined from the characteristic curve field, wherein the one of the at least two state of charge values ​​from the characteristic curve field is equated with the current state of charge value of the battery which has a smaller difference from the second state of charge value. In other words, to resolve the ambiguity described above in the case of an ambiguous assignment between the internal resistance value and the state of charge for one or more predetermined temperature ranges, methods known from the prior art for determining the state of charge can also be used.This is particularly advantageous when a characteristic curve of the characteristic curve field for a specific battery type has several maxima or minima, or generally more than one extremum.

[0023] While this is rather rare in practice, according to this advantageous embodiment of the invention, the state of charge can be determined as a second state of charge value, for example, via the current integral, and used as a plausibility condition. However, to provide this second state of charge value, i.e., to determine the current state of charge of the battery using a further method, not only current integration is suitable, but also other methods for determining the state of charge of a battery, as described above and known from the prior art. In this way, the state of charge of a battery for a specific battery type can advantageously always be reliably determined for all eventualities.

[0024] In a further advantageous embodiment of the invention, the current internal resistance value is determined as the quotient of the voltage change in the battery voltage resulting from a change in the battery current and the change in the battery current. Here again, the battery current represents the total current flowing into or out of the battery. In particular, this is a common method for determining the internal resistance of a battery. Thus, the internal resistance can be determined via the current and voltage profile under a current load and the resulting voltage response, especially as the quotient of these quantities.The internal resistance can thus be described by the formula Ri = ΔU / ΔI, where Ri denotes the internal resistance, ΔI the current load or the change in battery current (current and current intensity are used synonymously here), and ΔU the voltage response resulting from the change in battery current, i.e., the change in battery voltage. Again, other methods known from the prior art for determining the internal resistance can be used, which do not require knowledge of the battery's state of charge.

[0025] In a particularly advantageous embodiment of the invention, the current internal resistance value is continuously determined based on the continuous detection of current fluctuations in the measured battery current and the voltage changes in the battery voltage associated with these current fluctuations, particularly as the quotient of these quantities. This embodiment of the invention is based on the understanding that small current fluctuations, usually caused by unwanted fluctuations or disturbances in the vehicle electrical system, can advantageously be used to determine the internal resistance. Such disturbances or fluctuations in the vehicle electrical system lead to current ripple on the battery current, meaning that the battery's direct current is superimposed with an alternating current.By continuously measuring the battery current and voltage, the battery's internal resistance can advantageously be determined from the corresponding current fluctuations and the resulting voltage responses. This has the significant advantage that no special situation needs to be initiated for the internal resistance measurement, such as deliberately inducing a specific current load, which would disrupt the battery's normal operation and could only be performed when the vehicle is stationary or similar conditions. This advantageous embodiment of the invention allows the battery's internal resistance to be continuously determined and monitored, ultimately providing a permanent and continuous monitoring capability for the battery's state of charge.This continuous monitoring and calculation of the internal resistance also enables the embodiment described above to resolve ambiguities in assigning an internal resistance value to a state-of-charge value, particularly advantageously, if the corresponding characteristic curve exhibits one or more extrema. In such a situation, these ambiguities can be easily resolved by considering the time course of the internal resistance. This is now possible in a simple and reliable manner thanks to this advantageous embodiment of the invention, as it allows for a continuous or quasi-continuous determination of the internal resistance in any situation.

[0026] Furthermore, the invention relates to a battery arrangement comprising a battery of a specific battery type and a control unit for determining the current state of charge of the battery. The control unit includes a memory in which a characteristic curve array is stored, specifying the internal resistance for the specific battery type as a function of its state of charge for various predetermined temperature ranges. The battery arrangement includes a sensor device designed to detect the current temperature of the battery and determine its current internal resistance value. The control unit is designed to determine the current state of charge of the battery based on the current temperature and internal resistance value using the characteristic curve array. The control unit is designed to...if the measured current temperature lies in one of the predetermined temperature ranges in which the dependence of the internal resistance on the state of charge for an internal resistance value of the characteristic field has an extremum, to determine the state of charge value of the battery using the characteristic field in such a way that the control device checks whether at least two state of charge values ​​exist in the characteristic field which, according to the dependence, are assigned to the measured internal resistance value for the predetermined temperature range in which the current temperature lies, and if so, to determine the at least two state of charge values ​​from the characteristic field and to equate the current state of charge value of the battery with one of the at least two state of charge values ​​according to a predetermined selection method,wherein, according to the predetermined selection procedure, the state of charge of the battery is equated with one of the at least two state of charge values ​​determined from the characteristic curve field, depending on an internal resistance value determined in a previous time step, and / or the type of extremum, i.e., depending on whether the extremum represents a minimum or a maximum, and / or a current charging situation of the battery, i.e., depending on whether the battery is currently being charged or discharged.

[0027] The sensor device can, for example, include a temperature sensor integrated into the battery to detect the current temperature. Furthermore, the sensor arrangement can include at least one current sensor and one voltage sensor to detect the battery current and voltage, enabling the determination of the battery's current internal resistance.

[0028] Furthermore, the invention also relates to a motor vehicle with a battery arrangement according to the invention or one of its embodiments.

[0029] Furthermore, the advantages described in connection with the inventive method and its embodiments apply equally to the inventive battery arrangement and the inventive motor vehicle. Moreover, the process steps described in connection with the inventive method and its embodiments enable the further development of the inventive battery arrangement and the inventive motor vehicle by means of further corresponding material features.

[0030] Furthermore, the invention also includes combinations of the described embodiments.

[0031] Exemplary embodiments of the invention are described below. Shown are: Fig. 1 a schematic representation of a motor vehicle with a battery arrangement according to an embodiment of the invention; and Fig. 2 a schematic representation of a characteristic curve which describes the relationship between the internal resistance and the state of charge for a specific battery type and a specific temperature range, on the basis of which the state of charge of the battery is determined according to an embodiment of the invention.

[0032] The exemplary embodiments explained below are preferred embodiments of the invention. In the exemplary embodiments, the described components of the embodiments each represent individual, independently considered features of the invention, which also further develop the invention independently of one another and are thus also to be considered as components of the invention, either individually or in a combination other than that shown. Furthermore, the described embodiments can also be supplemented by further features of the invention already described.

[0033] In the figures, functionally identical elements are each provided with the same reference symbols.

[0034] Fig. Figure 1 shows a schematic representation of a motor vehicle 10 with a battery arrangement 12 according to an embodiment of the invention. The battery arrangement 12 comprises a battery 14, which has several battery cells 16, such as lithium-ion cells. The battery arrangement 12 also includes a control unit 18, which has a memory 20 in which a characteristic curve array 22 is stored. This characteristic curve array 22 corresponds to the battery type or cell chemistry of the battery 14. In other words, the characteristic curve array 22 was created using a test battery of the same battery type as the present battery 14 and thus has the same cell chemistry. This characteristic curve array 22 therefore describes, for the battery type of the battery 14, the relationship between the internal resistance and the state of charge for the specific battery type for various predetermined temperature ranges.To determine the current state of charge of battery 14, the control unit 18 can determine the current state of charge of battery 14 based on a currently measured temperature T and a currently measured internal resistance value, using this characteristic curve field 22. A suitable temperature sensor 23 can be used to measure the current battery temperature T, preferably located near battery 14, particularly near the battery cells 16. Multiple temperature sensors 23 can also be used and provided to measure the current temperature T of battery 14. Furthermore, the current internal resistance value can be determined based on a current and voltage profile under a current load and the resulting voltage response. For this purpose, the battery arrangement 12 can also include a current sensor 19 and a voltage sensor 21.The current sensor 19 can detect the battery current I, which is drawn from or supplied to the battery, depending on the situation. Furthermore, the voltage sensor 21 can detect the total voltage U available at the battery 14. The measured quantities T, I, and U, acquired by these sensors—that is, the current sensor 19, the voltage sensor 21, and the temperature sensor 23—can be continuously fed to the control unit 18, which determines the corresponding current state of charge of the battery 14 based on these quantities and the characteristic curve field 22. The control unit 18 can be integrated into a battery housing 24, which also contains the battery 14. The control unit 18 can also be part of a battery management system for the battery assembly 12.

[0035] Fig. 2 shows a graphical representation of a characteristic curve 26 for a predetermined temperature range ΔT, which describes the relationship between the internal resistance Ri and the state of charge SOC. If, for example, the control device 18 detects a current temperature T which lies within this predetermined temperature range ΔT, the control device 18 can now determine the state of charge SOC of the battery 14 assigned to the currently determined internal resistance Ri according to the characteristic curve field 26 on the basis of the characteristic curve field 22, in particular the characteristic curve 26 present for this predetermined temperature range ΔT. In this Fig. 2, the relationship between the internal resistance Ri and the state of charge SOC is not clear across the entire range. In this example, the characteristic curve 26 therefore has a minimum M. If, for example, as shown here as an example, a first internal resistance value Ri0 is determined for which a clear assignment to the state of charge SOC is possible, the corresponding state of charge value SOC0 is assigned to the determined internal resistance value Ri0 according to this clear assignment. However, if an internal resistance value Ri1 is determined for which the assignment is not clear but, as shown here, ambiguous, the assigned state of charge value can be determined as follows: If the characteristic curve 26 has only a single minimum M, then in this situation at most two potential candidates for the state of charge value are possible, which are designated here as an example SOC1 and SOC2.Furthermore, the internal resistance value determined in a previous time step, which is designated here as Ri2 by way of example, can advantageously be taken into account. In addition, it is also determined whether the battery 14 is currently in a state in which the battery 14 is being charged or in which the battery 14 is being discharged. This can be determined in a simple manner based on the measurement of the current I by the current sensor 19. If, for example, it is determined that the battery 14 is currently being charged, i.e. the state of charge SOC is increasing over time and the internal resistance Ri2 of the battery 14 determined in the previous time step is greater than the currently determined internal resistance value Ri1, it follows that the internal resistance Ri decreases as the state of charge SOC increases. This in turn means that the currently determined internal resistance value Ri1 as well as the previously determined internal resistance value Ri2 change with respect to the representation in . Fig.2 must be located to the left of the minimum M. This means that the state of charge value corresponding to the currently measured internal resistance Ri1 must also be located to the left of the minimum M and accordingly represents the state of charge value designated SOC1. If, instead, one were to consider a situation in which the battery 14 is currently being discharged, exactly the opposite would occur and the state of charge value corresponding to the currently measured internal resistance value Ri1 would be to the right of the minimum M and thus represents the state of charge value designated SOC2. By observing the temporal progression of the internal resistance Ri, it is advantageously possible to determine at which point on the characteristic curve 26 one is currently located, even if the assignments between the internal resistance Ri and the state of charge SOC are not clear.Furthermore, should cases arise in which such a characteristic curve 26 has several maxima or minima, which is rather unusual in practice, the state of charge determined via a current integral can, for example, be used as a plausibility condition.

[0036] Optionally, the age of the battery 14 can be taken into account in this procedure, i.e., in the characteristic curve-based determination of the state of charge (SOC), for example, by multiplying the determined internal resistance Ri by a corresponding factor that depends on the age of the battery 14. The factor is greater than 1 and increases the older the battery 14 is. This factor can also be determined experimentally specifically for each battery type, i.e., for each cell chemistry.

[0037] Overall, the invention and its embodiments provide a particularly simple and effective method for determining the state of charge or for recalibrating the state of charge, which can be used at any time and, above all, is independent of chemicals.

Claims

[1] Method for determining a current state of charge value (SOCO, SOC1, SOC2) of a battery (14) of a specific battery type, comprising the steps: a) providing a characteristic field (22) which indicates an internal resistance (Ri) for the specific battery type for respective different predetermined temperature ranges (ΔT) as a function (26) of the state of charge (SOC) for the specific battery type, b) measuring a current temperature (T) of the battery (14); c) determining a current internal resistance value (Ri0, Ri1) of the battery (14); d) On the basis of the current temperature (T) and the current internal resistance value (Ri0, Ri1), determining the current state of charge value (SOCO, SOC1, SOC2) of the battery (14) by means of the characteristic field (22); characterized bythat, if the measured current temperature (T) lies in one of the predetermined temperature ranges (ΔT) in which the dependency (26) of the internal resistance (Ri) on the state of charge (SOC) for an internal resistance value (Ri0, Ri1) of the characteristic field (22) has an extremum (M), the state of charge value (SOC1, SOC2) of the battery (14) is determined by means of the characteristic field (22) in such a way that it is checked whether at least two state of charge values ​​(SOC1, SOC2) exist in the characteristic field (22) which, according to the dependency (26), are assigned to the measured internal resistance value (Ri0, Ri1) for the predetermined temperature range (ΔT) in which the current temperature (T) lies, and if so, the at least two state of charge values ​​(SOC1, SOC2) are determined from the characteristic field (22), and the current state of charge value (SOC1, SOC2) of the battery (14) is determined according to a predetermined selection procedure is equated with one of at least two state of charge values ​​(SOC1, SOC2),wherein, according to the predetermined selection method, the state of charge value (SOC1, SOC2) of the battery (14) is set equal to one of the at least two state of charge values ​​(SOC1, SOC2) determined from the characteristic field (22) as a function of: - an internal resistance value (Ri2) determined in a previous time step; and / or - the type of extremum (M), ie depending on whether the extremum represents a minimum (M) or a maximum; and / or - a current charging situation of the battery (14), ie depending on whether the battery (14) is currently being charged or discharged. [2] Method according to claim 1, characterized bythat if the measured current temperature (T) lies in one of the predetermined temperature ranges (ΔT) in which the dependency (26) of the internal resistance (Ri) on the state of charge (SOC) increases or decreases strictly monotonically, the state of charge value (SOCO, SOC1, SOC2) of the battery (14) is determined by means of the characteristic curve field (22) in such a way that the state of charge value (SOCO, SOC1, SOC2) of the battery (14) is set equal to a state of charge value (SOCO, SOC1, SOC2) of the characteristic curve field (22) which, for the predetermined temperature range (ΔT) in which the currently measured temperature (T) of the battery (14) lies, is assigned to the currently measured internal resistance value (Ri0, Ri1) according to the dependency. [3] Method according to claim 1 or 2, characterized by that the current charging situation is determined by means of a current measurement of a battery current (I) of the battery (14). [4] Method according to one of the preceding claims, characterized bythat according to the predetermined selection method, a second state of charge value of the battery (14) is determined by means of a temporal current integration of a battery current (I) of the battery (14) and is compared with the at least two state of charge values ​​(SOC1, SOC2) determined from the characteristic curve field (22), and that of the at least two state of charge values ​​(SOC1, SOC2) from the characteristic curve field (22) which has a smaller difference to the second state of charge value is equated with the current state of charge value (SOC1, SOC2) of the battery (14). [5] Method according to one of the preceding claims, characterized by that the current internal resistance value (Ri0, Ri1) is determined as a quotient of a voltage change of a battery voltage (U), which results from a change of a battery current (I) of the battery (14), and the change of the battery current (I). [6] Method according to one of the preceding claims, characterized bythat the current internal resistance value (Ri0, Ri1) is continuously and repeatedly determined based on a continuous detection of current fluctuations of a measured battery current (I) of the battery (14) and on voltage changes in the battery voltage (U) associated with these current fluctuations. [7] Battery arrangement (12) with a battery (14) of a specific battery type and a control device (18) for determining a current state of charge value (S0CO, SOC1, SOC2) of the battery (14), wherein the control device (18) has a memory (20) in which a characteristic field (22) is stored which indicates an internal resistance (Ri) for the specific battery type as a function of the state of charge (SOC) for the specific battery type for respective different predetermined temperature ranges (ΔT), wherein the battery arrangement (12) has a sensor device (19, 21, 23) which is designed to detect a current temperature (T) of the battery (14) and to determine a current internal resistance value (Ri0, Ri1) of the battery (14), wherein the control device (18) is designed to determine the current state of charge value (S0CO, SOC1,SOC2) of the battery (14) by means of the characteristic field (22), characterized bythat the control device (18) is designed, if the measured current temperature (T) lies in one of the predetermined temperature ranges (ΔT) in which the dependency (26) of the internal resistance (Ri) on the state of charge (SOC) for an internal resistance value (Ri0, Ri1) of the characteristic field (22) has an extremum (M), to determine the state of charge value (SOC1, SOC2) of the battery (14) by means of the characteristic field (22) in such a way that the control device (18) checks whether at least two state of charge values ​​(SOC1, SOC2) exist in the characteristic field (22) which, according to the dependency (26), are assigned to the measured internal resistance value (Ri0, Ri1) for the predetermined temperature range (ΔT) in which the current temperature (T) lies, and if so, to determine the at least two state of charge values ​​(SOC1, SOC2) from the characteristic field (22), and the current state of charge value (SOC1,SOC2) of the battery (14) according to a predetermined selection method with one of the at least two state of charge values ​​(SOC1, SOC2), wherein according to the predetermined selection method the state of charge value (SOC1, SOC2) of the battery (14) is equated with one of the at least two state of charge values ​​(SOC1, SOC2) determined from the characteristic field (22) depending on:, - an internal resistance value (Ri2) determined in a previous time step; and / or - the type of extremum (M), ie depending on whether the extremum represents a minimum (M) or a maximum; and / or - a current charging situation of the battery (14), ie depending on whether the battery (14) is currently being charged or discharged. [8] Motor vehicle (10) with a battery arrangement (12) according to claim 7.

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