DE102020130732A1 - Method for determining a value of a parameter of a battery cell, control device and motor vehicle - Google Patents

Abstract

The invention relates to a method for determining a value of at least one parameter (SOC, K) of at least one battery cell of a battery (14) of a motor vehicle (10), the value of the at least one parameter (SOC, K) depending on a characteristic map (18 ) is determined which is assigned to the at least one battery cell and for the at least one battery cell defines a relationship between an open-circuit voltage (U) of the at least one battery cell and a state of charge (SOC) of the at least one battery cell, with the value of the at least one parameter (SOC , K) is determined repeatedly in successive time steps. It is checked whether the value of the at least one parameter (SOC, K) determined at least for one of the time steps meets a predetermined criterion, and the characteristic map (18) is adapted at least under the condition that the predetermined criterion is not met , according to which at least part of the characteristics map (18) is changed.

Description

The invention relates to a method for determining a value of at least one parameter of at least one battery cell of a battery in a motor vehicle, the value of the at least one parameter being determined as a function of a characteristic map that is assigned to the at least one battery cell and a relationship for the at least one battery cell defined between an open-circuit voltage of the at least one battery cell and a state of charge of the battery cell. The value of the at least one parameter is determined repeatedly in successive time steps. The invention also relates to a control device for a motor vehicle and a motor vehicle.

In order to be able to determine the capacity of batteries, such as lithium-ion batteries, and thus the storable, usable or residual energy, the current state of charge (SOC, State of Charge) is determined using an open-circuit voltage comparison. The comparison is carried out using a characteristic curve or characteristics map, which can also take the form of a table, in particular a voltage table or OCV (open circuit voltage) table. Such a table usually assigns a corresponding open-circuit voltage to a respective state of charge. The capacity of the lithium-ion battery is calculated from the difference in the state of charge before and after a charging or discharging process and from the amount of charge that has flowed. This OCV table is the basis for determining the state of charge. This is determined during the development of an energy storage device using various measurement methods for the cell to be used. However, the problem that arises with regard to the OCV table is that it changes during the use of the energy storage device. This is due to various environmental influences, such as temperature, electrical loads, mechanical influences or calendar aging. As a result, the internal resistance of the cells changes and with it the resulting open-circuit voltage. However, since this is the basis for determining the battery capacity, it can no longer be determined accurately over time. However, the open-circuit voltage does not only change due to a change in the internal resistance. Changes in the electrolyte or the cathode or anode can also lead to changes in the open-circuit voltage. This means that no clear conclusions about a change in capacitance can be drawn from the change in internal resistance. There is therefore no possibility of a correlation between these two variables, so that the internal resistance value is not suitable for checking the plausibility of the capacitance value.

the EP 1 702 219 B1 describes a device for estimating a state of charge of a battery using a neural network, which processes current, voltage and temperature as input data, as well as current time data of a battery cell.

Furthermore, the EP 1 873 542 B1 a battery management system for estimating a state of charge of a battery using a measurement model modeling the battery, which includes an internal resistance, a diffusion impedance and an open circuit voltage.

Furthermore, the U.S. 2017/0146608 A1 a method for determining the state of health and state of charge of a cell based on the entropy of the cell.

According to these methods, no OCV table is used to determine, for example, a state of charge or a capacity of a battery.

Furthermore describes the DE 10 2019 108 498 A1 a battery health estimate based on an open circuit voltage and calibrated data. In particular, a state of charge of the battery is determined using a look-up table that links open-circuit voltages with states of charge. This look-up table is calibrated during vehicle construction with a test protocol that controls the aging of one or more other batteries, such as the dynamic stress test protocol. The calibrated data is related to data from batteries aged in the vehicle and is intended to allow accurate capacity and state of charge estimations in the vehicle. However, this is only the case if the battery cells in the vehicle age in the same way as is the case in the previous tests. For this purpose, it would then first have to be possible to determine the aging state in which the battery cell in question is currently located.

The object of the present invention is therefore to provide a method for determining a value of at least one parameter of a battery cell, a control device and a motor vehicle which make it possible to determine the value of this at least one parameter as precisely and yet as simply as possible, even as the battery cell ages way to determine.

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

In a method according to the invention for determining a value of at least one parameter of at least one battery cell of a battery of a motor vehicle, the value of the at least one parameter is determined as a function of a characteristic diagram that is assigned to the at least one battery cell and a relationship between an open-circuit voltage for the at least one battery cell the at least one battery cell and a state of charge of the at least one battery cell, wherein the value of the at least one parameter is repeatedly determined in successive time steps. Furthermore, it is checked whether the value of the at least one parameter determined at least for one of the time steps satisfies a predetermined criterion, and at least under the condition that the predetermined criterion is not met, the characteristic map is adapted according to which at least part of the characteristic map will be changed.

In other words, this advantageously makes it possible to provide a characteristic map that learns along with it, such as an averaging OCV table, for example. To initialize the method, an initial characteristic map can be used, which can then advantageously be gradually adapted over time. In the context of the present invention, the terms characteristic diagram, characteristic curve and table are used synonymously. In other words, in the present case we are talking about a table, so it should also be able to be understood as a general characteristics map, which can also assume a form other than a tabular form. Such an OCV characteristic is one of the basic data for describing a cell. And this changes during the lifetime of a cell, also usually to different extents depending on the cell type used. The self-learning OCV characteristic can now advantageously ensure that the data basis, for example for determining the battery capacity, is always of the same good quality over the service life. This offers the advantage that the respective cells of the battery can always be operated in the correct voltage range. On the one hand, this extends the service life of the battery, provides reproducible and comprehensible capacity values and thus also improves the reproducible electric range of a vehicle that can be experienced.

The battery of the motor vehicle is preferably a high-voltage battery, which in turn comprises a number of battery cells. The method described can be carried out individually for each battery cell, in which case the corresponding values for the entire battery can be easily determined from those of the battery cells. In particular, in the case of a parallel connection of the individual battery cells, for example, the capacities of the individual battery cells can simply be added to the total capacity of the entire battery and in the case of a series connection, as is usually the case in high-voltage batteries, the total capacity of the high-voltage battery results from the smallest individual capacity of the cells. A corresponding characteristic curve can then be stored accordingly for each individual battery cell or only for the battery as a whole. As mentioned at the outset, the characteristics map can be provided in tabular form. Nevertheless, this map is sometimes also referred to as a characteristic curve. In this case, this characteristic curve can also assign corresponding no-load voltage values to a finite number of discrete state-of-charge values. Interpolation can be performed for values in between.

The at least one part of the characteristics map can represent, for example, a value pair or value tuple or also a number of pairs or tuples or a section of a characteristic curve which assigns value ranges to one another. It is also preferred that the adjustment of the characteristics map is limited to at least one part, i.e. the adjustment does not take place globally but locally, for example only for a specific open-circuit voltage value or open-circuit voltage range and corresponding state of charge value or state of charge range.

Furthermore, a further parameter, in particular the temperature of the at least one battery cell, can be taken into account in the characteristic diagram in addition to the no-load voltage, also known as no-load voltage, and the state of charge. In other words, the characteristics map can define a relationship between the state of charge of the at least one battery cell and the open-circuit voltage for different temperatures or temperature ranges. The value of the at least one parameter is determined in successive time steps. The check as to whether the value of the at least one parameter satisfies a predetermined criterion can then also take place in these corresponding time steps. These time steps do not have to be defined beforehand and then have the same distance from one another, but can also be event-triggered. Points in time before and after a charging or discharging process are particularly advantageous, in particular the battery or the at least one battery cell should be in a completely relaxed state at this point in time, ie it should be at rest for a predetermined time. This has the advantage that the no-load voltage can be determined particularly precisely, so that it is preferable to use this in the course of the method, as will be explained in more detail below.

The at least one parameter also preferably represents a state of charge of the at least one battery cell and/or a capacity of the at least one battery cell. The state of charge can be determined based on the characteristic map by detecting the off-load voltage of the at least one battery cell, in particular also the current temperature the at least one battery cell, and then the current state of charge of the at least one battery cell is read out from the characteristics map for the associated values of the no-load voltage and the temperature. The capacity, on the other hand, can be determined by dividing the amount of charge that was supplied to or removed from the at least one battery cell during a charging or discharging process by the change in the state of charge that took place during this charging or discharging process. The change in state of charge represents the difference between an initial state of charge before the charging or discharging process and an end state, also referred to below as the final state of charge, after the charging or discharging process. Accordingly, it is also advantageous if the state of charge of the at least one battery cell is changed between respective time steps in the form of charging or discharging the at least one battery cell. The at least one battery cell does not necessarily have to be fully charged or fully discharged. Partial charging or partial discharging processes should also be understood as charging and discharging the at least one battery cell. Such charging or discharging processes, in particular in combination with subsequent rest phases, can correspondingly trigger the implementation of the described method and define a corresponding time step. Correspondingly, there can also be relatively long periods of time between the respective time steps. However, this does not have a disadvantageous effect on the method described, since a change in the open-circuit voltage/state of charge characteristic of a battery changes only very slowly over time.

In a further advantageous embodiment of the invention, when checking whether the predetermined criterion is met, it is checked whether the determined value of the at least one parameter has a jump of a predetermined minimum magnitude compared to a certain reference value of the at least one parameter, with at least under the condition that the jump of a predetermined minimum height is present, the map is adapted.

wobei SOC_Ende den Ladezustand der mindestens einen Batteriezelle nach dem Ladevorgang bezeichnet, SOC_Anfang den Ladezustand der Batteriezelle vor dem Ladevorgang, I den Ladestrom und K die Kapazität der mindestens einen Batteriezelle.A jump is understood as a change. If, for example, the characteristic field, such as the OCV characteristic, changes during the service life of the battery, more precisely, the open-circuit voltage-state of charge characteristics of the at least one battery cell should change compared to the stored OCV characteristic in such a way that this has an impact on the Has state of charge determination, this is expressed in the form of state of charge and capacity jumps after an adaptation phase, that is, after a rest phase of the battery or the at least one battery cell. Such a jump in the predetermined minimum level of the at least one parameter value advantageously allows conclusions to be drawn that the open-circuit voltage/state of charge characteristic of the at least one battery cell in question may have changed, which can then advantageously be taken into account by appropriately adjusting the characteristic map. As described above, the current state of charge of the at least one battery cell can be determined via the characteristic map by measuring the current no-load voltages. A further possibility for determining the state of charge consists in the current integration of the current which was supplied to the at least one battery cell during a charging process or was taken from the at least one battery cell during a discharging process. In other words, for a loading process, for example: $${\text{SOC}}_{\text{End}}={\text{SOC}}_{\text{beginning}}+{\displaystyle \int \text{l}\left(\text{t}\right)}\text{German/K},$$

where SOC _End denotes the state of charge of the at least one battery cell after charging, SOC _Start denotes the state of charge of the battery cell before charging, I is the charging current and K is the capacity of the at least one battery cell.

Consequently, the state of charge of the at least one battery cell can be determined on the one hand based on the characteristic map and via an open-circuit voltage measurement, and on the other hand via current integration. These respective values can be compared with one another in order to check whether there has been a jump in the state of charge between two time steps. The state of charge value can therefore be compared with a reference value which represents the state of charge value determined on the basis of current integration. As a result, this reference value for the state of charge may change from time step to time step, since this is always determined anew for each time step. Like an obi As can be seen from the equation, the capacity of the at least one battery cell can also be determined as a function of the states of charge before and after a charging process and as a function of the charging current. The capacity determined in this way can be compared with a reference value, such as a capacity value initially specified for the new battery or the at least one battery cell. Analogously, it can be checked in this way whether the newly determined capacitance has a jump, ie a change compared to this reference value. Of course, this also applies analogously to a discharging process. If necessary, the capacitance value can also be adjusted in the course of the method, as is described in more detail below. This means that a newly determined capacitance value can also be set as a new reference value for subsequent time steps. Accordingly, these reference values for the capacity and the state of charge may change from time step to time step.

However, one problem that arises when the characteristic map is optimally adapted is that, over time, the capacity of the at least one battery cell changes in addition to the characteristic map. If both the map and the capacity are unknown in the calculation because they have changed, the result is an equation like the one given above with two unknowns. In this case, without further consideration, it is not possible to assign the change to the capacity or the OCV table or, in general, to the map. The invention is also based on the finding that the evaluation of the height of the respective jumps described above and their directions allows conclusions, on the basis of which measures can be defined that specify whether and in which direction the OCV map must be adjusted to to minimize or even eliminate future jumps in the state of charge and capacity. Precisely when both the state of charge and the capacity are considered as the at least one parameter, statements about measures to be taken can advantageously be specified.

It is therefore a further advantageous embodiment of the invention if, in each of the time steps, the value of the state of charge and the value of the capacitance are determined as the at least one parameter and it is checked for the respective values whether they have a respective jump of a predetermined minimum level compared to have a respective reference value determined for the respective time step. The minimum level that such a jump must have can be specifically defined for each of the two parameters state of charge and capacity. In addition, each of these parameters is also assigned its own reference value, as has already been described and defined above. The reference value for the state of charge can therefore be provided via a current integration with regard to a corresponding charging or discharging process; the reference value for the capacity can represent a value for the capacity provided in a time step previously or initially. Thus, these reference values can be newly provided for a respective time step. The conclusions that can now be derived from any jumps in these determined values are now discussed below.

According to a further advantageous embodiment of the invention, it is provided that for the first case that at a specific time step of the time steps neither the determined value of the capacitance nor the determined value of the state of charge shows a respective jump of a predetermined minimum level compared to respective reference values for this specific one Have time step, no adjustments to the map are performed at least before a subsequent next time step. So if neither the state of charge nor the capacity show a jump, it can be assumed that these values are correct and no adjustment of the characteristic map is necessary.

According to a further advantageous embodiment of the invention, for the second case that at a specific time step of the time steps only the value of the capacitance has the jump, the characteristics map is adapted as a function of a jump direction of the jump and as a function of a direction of the time step preceding it State of charge change carried out. The jump direction defines the direction in which the current value deviates from the reference value. If the value of the capacitance provided at the specific time step is greater than the reference value, then this is referred to below as a jump upwards. If the value of the capacitance is less than the reference value, this is referred to below as a downward jump. The top and bottom represent the jump directions of the jump. The direction of the change in state of charge also defines whether the at least one battery cell between the specific time step and the time step immediately before was charged, for example as part of a charging process, or charge was removed, for For example, by discharging the at least one battery cell, for example when the motor vehicle is in operation. For example, if the at least one battery cell is charged, the capacity is defined by the amount of charge that was supplied to the at least one battery cell during this charging process, divided by the change in state of charge, i.e. the difference between the State of charge of the at least one battery cell after charging and the state of charge of the at least one battery cell before charging. After the charging process and in particular after waiting for a certain relaxation time, the state of charge can be determined based on the measurement of the no-load voltage via the characteristic map, and on the other hand also via the current integration starting from the initial state of charge before the charging process. If the state of charge does not show a jump after charging, it can be assumed that this final state of charge value is correct. Since the capacity has a jump and the difference in the state of charge is included in the capacity, it can accordingly be concluded that the problem lies with the initial state of charge, ie with the state of charge of the at least one battery cell before charging. Using the example of a previous charging process, it can be concluded that when the capacity jump has occurred, the lower voltage, i.e. the open-circuit voltage of the initial state of charge, is actually lower than specified in the characteristic diagram. Conversely, if there is a jump in capacity, it can be concluded that this lower voltage is actually higher. This now advantageously enables a corresponding correction of the characteristics map. When the capacity jumps down, the open-circuit voltage for the initial state of charge is corrected downwards for the case of the previous charging process, in particular in such a way that this leads to a new value for the initial state of charge, this to a correspondingly new state of charge difference and this to a new one Capacitance value leads, which just no longer has a jump. The same procedure can be followed if there is a jump in capacity. In this case, the off-load voltage for the initial state of charge is corrected upwards, resulting in a correction for the capacitance value, which then no longer shows a jump to the reference value. In the case of a previous discharging process, the "upper" open-circuit voltage values that are assigned to the initial states of charge are adjusted analogously, since in this case the initial states of charge are higher than the final states of charge. In addition, a direct proportionality between open-circuit voltage and state of charge is always presupposed and assumed during the adjustments, ie the higher the state of charge, the greater the open-circuit voltage.

In a further advantageous embodiment of the invention, for the third case that at a specific time step of the time steps both the value of the capacity and the value of the state of charge have the respective jump and the respective jumps have the same jump direction, an adaptation of the characteristic diagram in Carried out as a function of a jump direction of the jump and as a function of a direction of the state of charge change preceding the time step. If, for example, the state of charge and the capacity have a jump with the same jump direction, this is initially implausible since the difference in state of charge and the capacity are indirectly proportional to one another. From this, in turn, the conclusion can be drawn that there must be two superimposed effects here. This is explained below again using the example of a charging process, but can also be used analogously for a discharging process: If the final state of charge of at least one battery cell jumps up, the initial state of charge must also be assigned to a higher open-circuit voltage in real terms , in such a way that the difference in state of charge is effectively reduced for the charging or discharging process under consideration. Accordingly, the open-circuit voltage of the lower state of charge, ie the initial state of charge, can now advantageously be corrected upwards. This is especially true when both the capacitance value and the state of charge value jump upwards. If, on the other hand, a jump in the state of charge and jump in capacity has been determined, the open-circuit voltage of the lower state of charge must be corrected downwards accordingly. If a charging process is not considered, but rather a discharging process, the open-circuit voltage of the lower state of charge is corrected instead of that of the upper state of charge, which corresponds to the corresponding initial states of charge during a discharging process. In this way, suitable measures can advantageously also be taken in these cases in order to take account of the changes in the characteristics map.

In a further advantageous embodiment of the invention, for the fourth case that at a specific time step of the time steps both the value of the capacity and the value of the state of charge have the respective jump and the respective jumps have an opposite jump direction, the characteristic map is at least not adapted performed before a subsequent next time step. In this case, the value of the capacitance is also adjusted as a function of a jump direction of the jump and as a function of a direction of the change in state of charge preceding the time step, and a plausibility check is carried out in particular in a next time step. If opposite jumps in the state of charge value and the capacitance value are detected, then there are several possible conclusions. For example, both new values can be correct and the capacity can be even may not have been taught in yet or both values are wrong. It is therefore advantageous not to adjust the map at first and only to adjust the capacity. In other words, the capacitance newly determined in this time step is then set as the new reference value. This applies in particular to a previous charging process as well as a discharging process. A plausibility check of this measure can then advantageously take place in the subsequent time steps. If this measure was correct, i.e. if the capacity was adjusted correctly, the following time steps will result in the case that there is neither a jump in the state of charge value nor in the capacity value, i.e. everything is in order, i.e. the above occurs first case one. Otherwise, one of the other cases discussed here will arise and the corresponding measures set out here can then be taken.

Especially in the last-mentioned fourth case, it can be advantageous that the newly adapted capacitance value is initially not used as a basis for any further calculation method or other functions in the motor vehicle until a plausibility check has been carried out. Other function modules of the motor vehicle, which perform functions depending on the current capacity of the at least one battery cell and/or the current state of charge of the at least one battery cell, can, for example, access previous and verified values of these parameters until the new values are also verified and were checked for plausibility. In other words, several charging and discharging cycles are sometimes necessary, which also require different measures in order to arrive at a plausible result. This follows from the fact that, as described above, an equation with two unknowns cannot be solved in one step. Since the change processes within the battery are very slow with intact cells, continuous learning is possible. Since implausible or not immediately plausible results can occur in individual steps, it is also possible to let these calculations run in the background. In this way, the changes have no effect on the values that the control unit actually calculates with and are also not visible to the driver. For example, it can be provided that the results are only used for the real calculation when they have a high level of trustworthiness. A high degree of reliability can be defined, for example, by the fact that the jumps in the state of charge and the capacity are below a predetermined value, which is preferably between 2 and 4 percent of the relevant values.

There is also a fifth case, which occurs when at a specific time step of the time steps only the value of the state of charge shows the jump and not the value of the capacity. In this case, according to a further advantageous embodiment of the invention, it is provided that the characteristics map is not adapted at least before a subsequent next time step and before the next time step that the value of the capacitance is adapted as a function of a jump direction of the jump and as a function of a direction of the carry out the change in state of charge preceding the time step, and if this case occurs again in the next time step, carry out an adjustment of the characteristics map in a time step after the next. If only a jump in capacity is detected in a time step, but not in the state of charge, two-stage measures are provided in this case. The insight underlying this case is that the capacity was assumed to be too small or the open circuit voltage of the final state of charge is incorrect. It is therefore particularly advantageous to first correct the capacity in a first step, namely upwards if a jump in the state of charge was detected after a previous charging process and vice versa, i.e. the capacity is corrected downwards if there was a jump in the state of charge after a previous charging process was found upwards. The amount of the correction corresponds to the difference in capacitance that results from the jump in the state of charge. This would then correct the former case, namely that the capacitance was assumed to be too small. If this is indeed the case, the corrective action will lead to the first case described above, in which everything is fine. Otherwise, i.e. if this problem occurs again in a subsequent time step, the map is corrected as a further measure, namely the open-circuit voltage, which in the case of a charging process is assigned to the final state of charge, is corrected upwards or downwards, depending on the jump direction of the final state of charge. In other words, if a drop in the state of charge was detected, the open-circuit voltage is also corrected downwards, and in the case of a leap in the state of charge, the open-circuit voltage is also corrected upwards. In the case of a discharge process, the correction direction of the open-circuit voltage is exactly the opposite.

In this case, too, it is advantageous that the relevant results, i.e. in particular the adjusted capacities, are only used as a basis for further calculations if they have a high level of trustworthiness and, for example, these assumptions or measures have been verified in subsequent time steps. Although now the If the specific examples above relate primarily to charging processes, then these measures can also be used in a corresponding manner for discharging processes of the at least one battery cell. Furthermore, the measures described apply both to complete loading and unloading processes as well as to partial strokes in the loading and unloading direction.

Furthermore, the invention also relates to a control device for a motor vehicle, which is designed to carry out a method according to the invention or one of its embodiments. The control device can have a data processing device or a processor device that is set up to carry out an embodiment of the method according to the invention. For this purpose, the processor device can have at least one microprocessor and/or at least one microcontroller and/or at least one FPGA (Field Programmable Gate Array) and/or at least one DSP (Digital Signal Processor). Furthermore, the processor device can have program code which is set up to carry out the embodiment of the method according to the invention when executed by the processor device. The program code can be stored in a data memory of the processor device.

The invention also includes a motor vehicle with such a control device. The motor vehicle according to the invention is preferably designed as a motor vehicle, in particular as a passenger car or truck, or as a passenger bus or motorcycle.

The advantages described for the method according to the invention and its embodiments apply in the same way to the control device according to the invention and the motor vehicle according to the invention.

The invention also includes developments of the control device according to the invention and of the motor vehicle according to the invention, which have features as have already been described in connection with the developments of the method according to the invention. For this reason, the corresponding developments of the control device according to the invention and the motor vehicle according to the invention are not described again here.

The invention also includes the combinations of features of the described embodiments. The invention also includes implementations that each have a combination of the features of several of the described embodiments, unless the embodiments were described as mutually exclusive.

• 1 eine schematische Darstellung eines Kraftfahrzeugs mit einer Batterie und einer Steuereinrichtung zum Ermitteln eines Werts zumindest eines Batterieparameters gemäß einem Ausführungsbeispiel der Erfindung; und
• 2 ein Ablaufdiagramm zur Veranschaulichung eines Verfahrens zum Ermitteln eines Werts mindestens eines Batterieparameters gemäß einem Ausführungsbeispiel der Erfindung.

Exemplary embodiments of the invention are described below. show:

• 1 a schematic representation of a motor vehicle with a battery and a control device for determining a value of at least one battery parameter according to an embodiment of the invention; and
• 2 a flowchart to illustrate a method for determining a value of at least one battery parameter according to an embodiment of the invention.

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

In the figures, the same reference symbols designate elements with the same function.

1 shows a schematic representation of a motor vehicle 10, which has a control device 12 and a battery 14 such as a high-voltage battery. The control device 12 also has a memory 16 in which a characteristic map 18, in particular an OCV table, is stored. This OCV table assigns respective open circuit voltage values of the battery 14 to corresponding state of charge values for respective temperature ranges. The state of charge SOC is in 1 illustrated schematically for the battery 14 shown there, in particular pictorially in the form of loading bars. The state of charge SOC is typically given as a percentage from 0 percent to 100 percent. The maximum amount of charge that can be accommodated in a battery 14 defines the capacity K of a battery 14. If a partial amount ΔQ of charge is supplied to the battery 14, this results in a change in the state of charge ΔSOC. The capacitance K can be determined from this as follows: K = ΔQ/ΔSOC. The charging quantity ΔQ can in turn be determined from the charging current I, in particular according to ΔQ=jldt. If, for example, the battery 14 is charged for one hour with a current of 30 amperes, this corresponds to a charge being supplied to the battery 14 quantity ΔQ of 30 ampere hours. If the state of charge was increased from 0 percent to 100 percent in the course of such a charging process, these 30 ampere hours correspond to the capacity K of the battery 14.

Starting from an initial state of charge, the final state of charge of the battery 14 can be determined via current integration, for example. On the other hand, the current state of charge SOC of the battery 14 can also be determined via the characteristics map 18, which is stored in the memory 16 of the control device 12. To do this, only the off-load voltage U of the battery 14 must be determined. This typically takes place after the battery 14 has been idle, since the open-circuit voltage U can then be determined particularly precisely. These measured values, namely the no-load voltage U and the battery current I during charging and/or discharging processes of the battery 14, can also be made available to the control device 12. Knowing these variables and with the help of characteristics map 18, control device 12 can, for example, always determine current values for the state of charge SOC and make them available to other systems, or display them to a driver, for example.

In conventional methods for determining the state of charge, which use an open-circuit voltage table or OCV table, there is the problem that such an OCV table for the battery in question is only valid for the battery when it is new. The open-circuit voltage state of charge characteristic changes with the use of the energy store, which is due to various environmental influences such as temperature, electrical loads, mechanical influences and calendar aging. As a result, the internal resistance of the cells, for example, changes and with it the resulting open-circuit voltage for the corresponding charge states. However, the open-circuit voltage does not only change due to a change in the internal resistance. Changes in the electrolyte or the cathode or anode can also lead to changes in the open-circuit voltage. If this is not taken into account in the OCV table, there will be increasing inaccuracies in determining the battery capacity and the state of charge over time.

According to the invention, this can now advantageously be avoided by adapting the OCV table 18 initially taken as a basis over time, in particular to the current state of the battery 14 is optimally adapted to the battery characteristics. This procedure will now be described in detail below.

For this shows 2 a flowchart to illustrate a method for determining at least one value of a battery parameter according to an embodiment of the invention. This battery parameter represents in particular both the state of charge SOC and the capacity K of the battery 14. Based on these values, which are determined repeatedly in particular in successive time steps, the OCV table 18 is adjusted, or more precisely, a decision is made about a possible adjustment of this Characteristic field 18 and the capacity K. However, such an adjustment initially requires some considerations, because in addition to the OCV characteristic, the capacity K of the cells or the battery 14 also changes. If now in the calculation both the OCV characteristic 18 and the capacity K are unknown because they may have changed, this results in an equation with two unknowns. In this case it is then no longer possible, at least not without further considerations, to assign the change to the capacitance K or the OCV table 18 . To solve this problem, the method described below can be used. Should an OCV characteristic curve 18 change during the period of use in such a way that this affects the determination of the state of charge SOC, which would result in the form of jumps in the state of charge value and capacity value after an adaptation phase, the height of the respective jumps and their direction i.e. greater than, equal to, less than the state of charge value or capacity value before the adaptation phase, evaluated and, based on this, corresponding conclusions and measures are defined in which direction the OCV characteristic curve 18 must be adapted, if necessary, to future jumps in the state of charge and the capacity minimize or even eliminate K.

The method begins in step S10, in which initially a capacity value for the capacity K of the battery 14 and also a current state of charge value for the state of charge SOC of the battery 14 are specified or assumed. In the case of the capacity K, for example when the battery 14 is new, it can be assumed that this initially corresponds to the initial value specified by the supplier of the battery 14 . The OCV table 18 initially used should also be correct when the battery 14 is new, the battery characteristics in terms of the assignment of open-circuit voltage values to the respective state of charge values of the state of charge SOC, in particular for the respective temperature ranges. This initial value for the state of charge SOC can be provided on the basis of this table 18 in step S10, for example.

Then, in this example, a charging process is performed in step S12 to charge the battery 14 . The battery can be fully or only partially charged. The following examples accordingly refer to the case according to which such a loading process has preceded it. However, the method can also be carried out analogously with appropriate adjustments for a previous discharging process of the battery.

From the charging current I during this charging process, the value of which is supplied to the control device 12, the control device 12 can determine the final state after this charging process in step S12, knowing the initial state of charge provided in step S10. This determination can, for example, follow the charging process and can also be carried out in step S12. Furthermore, in step S14 the current state of charge SOC of the battery 14 is determined on the basis of the characteristics map 18 . This is preferably done after the battery 14 has been at rest, since this determination is based on the measurement of the open-circuit voltage U. The capacity K can be determined in step S16 from the current state of charge value obtained in this way, which so to speak represents the value for the final state of charge of the battery 14 after the charging process. This results from the integral current and the state of charge difference between the final state of charge and the initial state of charge, as shown in 1 already described. These two values, newly obtained in steps S14 and S16, for the capacity K and the current state of charge SOC can then be compared with a respective reference value. For the capacity K, this reference value represents the capacity value K initially provided in step S10. The reference value for the current state of charge SOC represents the final state of charge value determined at the end of the charging method in step S12, which was calculated on the basis of the current integration.

In this case, it is checked in particular whether the relevant newly determined values have a jump Δ1, Δ2 with respect to the respective reference values. For this purpose, for example, on the one hand it can be checked in step S18 whether there is a jump in the state of charge Δ1. If this is not the case, it can also be checked in step S20 whether there is a jump in capacity Δ2. Even if it is determined in step S18 that there is a jump in the state of charge Δ1, it can also be checked in step S22 whether there is a jump in capacity Δ2. In other words, both are checked in any case, namely whether there is a jump in capacity Δ2 and whether there is a jump in the state of charge Δ1, with the chronological sequence of this check being irrelevant. In particular, these two checks could also take place simultaneously. If, for example, it is determined in step S18 that there is no jump in the state of charge Δ1, and it is also determined in step S20 that there is also no jump in capacity Δ2, the system proceeds to step S24, in which it is determined that everything is OK, i.e. that the determined values are correct and the OCV table 18 is still up-to-date, as well as the value of the capacitance K. The process then goes back to step S10 and the method starts again, with the battery then not necessarily being charged again in the subsequent step S12 14 must take place, but for example a discharging process can also take place.

If it is determined in step S18 that there is no jump in the state of charge Δ1, but it is determined in step S20 that there is a jump in capacity Δ2, the OCV table 18 can be adjusted in step S26. This is based on the finding that the rest voltage value, which according to Table 18 is associated with the initial state of charge value that was specified in step S10, is no longer up-to-date and is actually higher or lower, depending on the jump direction of the capacity jump Δ2. In particular, an adjustment can be made as explained in the following example: According to this example, an initial state of charge of the battery 14 is first determined. This is done by measuring the no-load voltage U, which is 3400 mV, for example. The state of charge value corresponding to this no-load voltage U can be determined using OCV table 18. A corresponding section of Table 18 can look like this, for example: State of charge SOC open circuit voltage U 34% 3500mV 22% 3450mV 20% 3400mV 18% 3350mV

In this example, the initial state of charge value is 20%. Furthermore, the currently assumed capacity K of the battery 14 is 49 Ah. The battery 14 is then charged to a final state of charge of 85%, which can be determined on the basis of the current integration of the charging current I. After the idle phase of the battery 14, a state of charge value of 85% is determined based on the determination of the no-load voltage U and using the characteristics map 18, ie the state of charge SOC is not subject to any jump Δ1. After the idle phase, however, the capacity K jumps to 50 Ah and thus shows a jump Δ2 upwards. Since the final state of charge value does not show any jump Δ1, it can be assumed that it is correct. Accordingly, it can be concluded that an incorrect initial state of charge value den caused a jump in capacity. The capacity is therefore actually 2% less, ie the initial state of charge SOC is actually 2% lower at 18% and not at 20%. The open-circuit voltage U 3400 mV measured initially, ie before charging, is not assigned to the state of charge value of 20% but to 18%. In other words, the no-load voltage U real to be assigned to the state of charge value 20% is higher than 3400 mV. Thus, the OCV table 18 can be corrected accordingly, specifically by correcting the open circuit voltage value for 20% up to 3450 mV.

If the capacity K jumps down, the no-load voltage U is also corrected downwards, and if the capacity K jumps up, the no-load voltage, which corresponds to the initial state of charge, is corrected upwards. The process then starts again from the beginning.

• Auch hier wird wieder von einer Anfangskapazität von 49 Ah ausgegangen und die Batterie wird auf einen Ladezustandswert von 85 % geladen. Nach der Ruhephase wird ein Sprung der Kapazität auf 50 Ah festgestellt und eine Sprung des End-Ladezustands nach oben auf 88,3%. Eine Korrektur der Kapazität von 49Ah auf 50Ah (102% der ursprünglichen Kapazität) würde eine Korrektur des Ladezustands auf 83,3%, d.h. 98% des ursprünglichen Wertes (Kehrwert von 102%) verursachen. Der Ladezustand SOC spring aber real um 5% auf 90%, d.h. der Gesamtsprung wäre dann 3,3% + 1,7% = 5%. Daraus ergibt sich für den realen Ladezustandssprung Δ1 : $$\mathrm{\Delta }1={\text{SOC}}_{\text{neu}}-\left({\text{K}}_{\text{alt}}{\text{/K}}_{\text{neu}}\right)\times {\text{SOC}}_{\text{alt}})$$
  

On the other hand, if it is determined in step S18 that the state of charge value has a jump Δ1 with respect to its reference value, and if it is also determined in step S22 that the capacity K also has a jump Δ2, then it is checked in step S28 whether capacity K and state of charge SOC have the same jump direction or an opposite jump direction. If these have the same jumping direction, then there is a transition to step S30, in which characteristic map 18 is again corrected. This is based on the knowledge that the open-circuit voltage U, which is assigned to the initial state of charge value, has a lower or higher voltage in real terms than that specified in Table 18, depending on the jump direction. If there is a jump direction downwards, then the open-circuit voltage value for this initial state of charge is corrected downwards, and otherwise upwards. An example calculation can look like this:

• Here, too, an initial capacity of 49 Ah is assumed and the battery is charged to a state of charge value of 85%. After the idle phase, the capacity jumped to 50 Ah and the final state of charge jumped up to 88.3%. A correction of the capacity from 49Ah to 50Ah (102% of the original capacity) would cause a correction of the state of charge to 83.3%, ie 98% of the original value (reciprocal of 102%). However, the SOC state of charge jumps by 5% to 90% in real terms, ie the total jump would then be 3.3% + 1.7% = 5%. This results in the real state of charge jump Δ1: $$\mathrm{\Delta }1={\text{SOC}}_{\text{New}}-\left({\text{K}}_{\text{old}}{\text{/K}}_{\text{New}}\right)\times {\text{SOC}}_{\text{old}})$$
  

SOC _new designates the state of charge 88.3% after the rest phase and SOC _old the state of charge 85%, K _old the originally assumed capacity 49 Ah and K _new the new capacity 50 Ah. Assuming again that the initial state of charge was 20%, e.g. according to the following OCV table: State of charge SOC open circuit voltage U 30% 3500mV 25% 3450mV 20% 3400mV 15% 3350mV

With the calculated jump of 5%, the no-load voltage U for 20% must now be corrected to the value of 25%, i.e. 5% total correction. Accordingly, the voltage 3450 mV is then entered for the state of charge value 20%.

If, on the other hand, it is determined in step 28 that the jumps Δ1, Δ2 of capacity K and state of charge SOC have opposite directions, then a transition is made to step S32. This case can have several causes. In particular, this can mean that both values are OK or the capacitance K has not yet been taught in or both values are incorrect. Accordingly, it is provided that in step S32 the capacitance K is first adjusted, that is to say the capacitance value determined in step S16 is set equal to the new capacitance value when the method is repeated in step S10. This procedure is then checked for plausibility in subsequent time steps. If this assumption was correct, then in the following steps without further changes the case will arise that there are no longer any jumps Δ1, Δ2. Otherwise one of the other cases described or cases to be described will occur and an appropriate measure will be taken.

If it is determined in step S22 that there is no jump in capacity, then in step S34 it is first checked whether this case also existed in the previous time step, ie the case that only the state of charge value has a jump Δ1, but not the capacity value. If this is not the case, the capacitance K is corrected in step S36. The correction direction depends on the jump direction of the state of charge value. If the state of charge jumped down, the capacity K is corrected up and vice versa. In this case, the capacitance K is corrected by the amount that corresponds to a change in capacitance that results from the jump Δ1 in the state of charge value. Then the method starts over with this new capacitance value in step S10. If, on the other hand, this situation occurs again, ie if it is determined in step S34 that this case has already occurred in the previous time step, then there is a transition to step S38 gone, in which the characteristic 18 is corrected. In particular, the no-load voltage value that is assigned to the final state of charge value is again corrected in this case. The open-circuit voltage value is corrected upwards if the state of charge value has also jumped upwards, and corrected downwards if the state of charge value has jumped downwards. The method is then carried out again with a corrected characteristics map 18 in step S10.

The two adjustments described for step S36 and step S38 are in turn based on the knowledge that the case where there is merely a jump in the state of charge value can in turn have a number of causes. On the one hand, it may be that the capacity was assumed to be too small, which can be compensated for by the measures in step S36.

On the other hand, it can also be the case that the idle state value is not correct, which in turn can be corrected by the measures described in step S38.

From this it can be seen in particular that some corrections require several time steps in order to determine which values require a change or not, ie whether the characteristic curve 18 and/or the capacitance K may need to be corrected. Nevertheless, this can advantageously be determined clearly using the method described, if necessary in several time steps, so that ultimately a learning OCV table 18 can be provided which also reflects the correct battery characteristics with regard to open-circuit voltage and state of charge as the battery 14 ages. The capacity can also be adapted in this way to its age-related changes. Since it can also be assumed that the capacity K slowly decreases over the service life of the battery 14, it is also conceivable, for example, that larger jumps above a definable threshold value can be assumed to be implausible. In other words, if, for example, an upward jump in capacitance is determined that is above this threshold value, then this capacitance value can be assumed to be implausible, for example. As a result, it can be defined, for example, that this measurement is discarded and/or must first be checked for plausibility in a further time step in order to take further measures, such as adjusting the capacity and/or table 18 . Above all, for example, an even tighter limit value can also be assumed in the case of upward corrections, because the capacitance K does not increase over the service life. However, smaller corrections in both directions should always remain permissible due to measurement inaccuracies in current and voltage. In addition, the capacity K can be determined not only for the entire battery 14, but also for each cell or cell group, for example. It is then also possible to check the calculated capacitance values against one another for plausibility.

Since implausible results can occur in individual steps, it is also possible to run these calculations in the background. The changes thus have no influence on the values with which the control unit 12 actually calculates and are not visible to the customer. Only when the results have a high level of reliability and, for example, the jumps in the state of charge and the capacity are below a certain value, such as between 2 and 4 percent of the relevant values, are the values also used for the real calculation.

Overall, the examples show how the invention can be used to provide a learning OCV characteristic curve for determining the state of charge of an electrical energy store, which can take account of the changes during the service life of a battery cell or battery. Such a self-learning OCV characteristic ensures that the data basis for determining the battery capacity over the service life is always of the same good quality. This offers the advantage that the cell can always be operated in the correct voltage range. On the one hand, this extends the service life of the storage system, provides reproducible and traceable capacity values and thus also improves the reproducible electric range of the vehicle that can be experienced.

QUOTES INCLUDED IN DESCRIPTION

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

Patent Literature Cited

• EP 1702219 B1 [0003]
• EP 1873542 B1 [0004]
• US 2017/0146608 A1 [0005]
• DE 102019108498 A1 [0007]

Claims (10)

Method for determining a value of at least one parameter (SOC, K) of at least one battery cell of a battery (14) of a motor vehicle (10), the value of the at least one parameter (SOC, K) being determined as a function of a characteristic diagram (18), which is assigned to the at least one battery cell and for the at least one battery cell defines a relationship between an open-circuit voltage (U) of the at least one battery cell and a state of charge (SOC) of the at least one battery cell, the value of the at least one parameter (SOC, K) in is repeatedly determined in successive time steps, characterized in that it is checked whether the value of the at least one parameter (SOC, K) determined at least in one of the time steps fulfills a predetermined criterion, and at least under the condition that the predetermined criterion is not fulfilled, an adjustment of the characteristics map (18) is carried out, according to which at least part of the K ennfeldes (18) is changed. procedure after claim 1 , characterized in that the at least one parameter (SOC, K) represents a state of charge (SOC) of the at least one battery cell and/or a capacity (K) of the at least one battery cell. Method according to one of the preceding claims, characterized in that between respective time steps a change in the state of charge of the at least one battery cell is carried out in the form of charging or discharging the at least one battery cell. Method according to one of the preceding claims, characterized in that when checking whether the predetermined criterion is met, it is checked whether the determined value of the at least one parameter (SOC, K) has a jump (Δ1, Δ2) of a predetermined minimum level compared to a has a specific reference value of the at least one parameter (SOC, K), wherein the characteristic map (18) is adapted at least under the condition that the jump (Δ1, Δ2) is of a predetermined minimum magnitude. Method according to one of the preceding claims, characterized in that in each of the time steps the value of the state of charge (SOC) and the value of the capacity (K) are determined as the at least one parameter (SOC, K) and the respective values are checked, whether these have a respective jump (Δ1, Δ2) of a predetermined minimum height compared to a respective reference value determined for the respective time step. procedure after claim 5 , characterized in that - for the first case that at a specific time step of the time steps neither the determined value of the capacity (K) nor the determined value of the state of charge (SOC) shows a respective jump (Δ1, Δ2) of a predetermined minimum level compared to have respective reference values for this specific time step, the characteristics map (18) is not adapted at least before a subsequent next time step, and/or - for the second case that at a specific time step of the time steps only the value of the capacitance (K) makes the jump (Δ2), an adaptation of the characteristics map (18) is carried out as a function of a jump direction of the jump (Δ2) and as a function of a direction of the state of charge change preceding the time step. Method according to any of the preceding Claims 5 or 6 , characterized in that for the third case that at a specific time step of the time steps both the value of the capacity (K) and the value of the state of charge (SOC) have the respective jump (Δ1, Δ2), and the respective jumps ( Δ1, Δ2) have the same jump direction, the characteristics map (18) is adapted as a function of a jump direction of the jump (Δ1, Δ2) and as a function of a direction of the state of charge change preceding the time step. Method according to any of the preceding Claims 5 until 7 , characterized in that - for the fourth case that at a specific time step of the time steps both the value of the capacity (K) and the value of the state of charge (SOC) have the respective jump (Δ1, Δ2), and the respective jumps (Δ1, Δ2) have an opposite jump direction, no adjustment of the characteristic map (18) is carried out at least before a subsequent next time step, and an adjustment of the value of the capacitance (K) depending on a jump direction of the jump (Δ1, Δ2) and in is carried out as a function of a direction of the change in state of charge preceding the time step, and a plausibility check is carried out in a next time step; and/or - for the fifth case that at a specific time step of the time steps only the value of the state of charge (SOC) shows the jump (Δ1), no adjustment of the characteristics map (18) is carried out at least before a subsequent next time step, and before the next time step an adjustment of the value of the capacitance (K) is carried out as a function of a jump direction of the jump (Δ1) and as a function of a direction of the state of charge change preceding the time step, and if this case in the next time step occurs again, in a time step after next an adaptation of the characteristics map (18) is carried out. Control device (12) for a motor vehicle, which is designed to carry out a method according to one of the preceding claims. Motor vehicle (10) with a control device claim 9 .

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