CN114518537A - Method, control device and motor vehicle for determining the value of a parameter of a battery cell - Google Patents

Abstract

The invention relates to a method for obtaining a value for at least one parameter (SOC, K) of at least one cell of a battery (14) of a motor vehicle (10), wherein at least one parameter (SOC, K) is obtained from a characteristic curve family (18). The values of the parameters (SOC, K), the characteristic curve family is associated with the at least one battery cell and defines for the at least one battery cell the stable voltage (U) of the at least one battery cell and the at least one battery cell The relationship between the state of charge (SOC) of a battery cell, wherein the values of at least one parameter (SOC, K) are repeatedly obtained in successive time steps. Here it is checked whether the value of at least one parameter (SOC, K) obtained at least at one of the time steps fulfills predetermined criteria, and at least if the predetermined criteria are not fulfilled, the adjustment A characteristic curve family (18), at least a part of which is changed according to the adjustment.

Description

Method, control device and motor vehicle for determining the value of a parameter of a battery cell

technical field

The invention relates to a method for determining the value of at least one parameter of at least one cell of a battery of a motor vehicle, wherein the value of the at least one parameter is determined on the basis of a family of characteristic curves associated with the at least one battery cell , the characteristic curve family defines the relationship between the stable voltage of the at least one battery cell and the state of charge of the battery cell for the at least one battery cell. Here, the determination of the value of the at least one parameter is repeated in successive time steps. The invention also relates to a control device for a motor vehicle and to a motor vehicle.

Background technique

In order to be able to determine the capacity and thus the storable, usable or still remaining energy in a battery, for example a lithium-ion battery, the current state of charge (SOC, State of Charge) is determined on the basis of a constant voltage compensation. The compensation is performed on the basis of a characteristic curve or a characteristic curve family, which can also take the form of a table, in particular a voltage table or an OCV (open circuit voltage) table. Such tables typically associate corresponding states of charge with corresponding stable voltages. The capacity of the lithium-ion memory is calculated by the difference in the state of charge before and after the charging or discharging process and by the amount of charge flowing at that time. Here, the basis for determining the state of charge is the OCV table. With the development of accumulators, this OCV table is determined for the monomer to be used by various measurement methods. A problem with the OCV table, however, is that it changes during the use of the accumulator. The reasons for this are various environmental influences, such as, for example, temperature, electrical load, mechanical influences or ageing over time. As a result, the internal resistance of the cell and thus the resulting stable voltage also changes. However, since the stable voltage is the basis for determining the battery capacity, the battery capacity can no longer be accurately determined over time. However, the stable voltage does not only vary due to changes in internal resistance. Changes in the electrolyte or cathode and/or anode can also result in changes in the stable voltage. Therefore, the change in capacity cannot be clearly inferred from the change in internal resistance. Therefore, it is impossible to obtain a correlation between these two parameters, so that the internal resistance value is not suitable for checking the reliability of the capacity value.

Patent document EP 1 702 219 B1 describes a device for estimating the state of charge of a battery by means of a neural network which processes as input data current, voltage and temperature of the battery cells and current time data.

Furthermore, patent document EP 1 873 542 B1 describes a battery management system for estimating the state of charge of a battery using a measurement model that models the battery, the measurement model including internal resistance, diffusion impedance and no-load voltage .

Furthermore, patent application US 2017/0146608 A1 describes a method for determining the state of health and state of charge of a monomer based on its entropy.

According to this method, the OCV table is not used to determine eg the state of charge or capacity of the battery.

Furthermore, patent application DE 10 2019 108 498 A1 describes battery state estimation based on no-load voltage and calibrated data. In particular, the state of charge of the battery is determined here using a look-up table, which relates the no-load voltage to the state of charge. At vehicle design, the look-up table is calibrated with test records that control the aging of one or more additional batteries, eg, test records of dynamic stress tests. The calibrated data is correlated with the data of the battery aged in the vehicle and thereby allows accurate estimation of capacity and state of charge in the vehicle. However, this is only true if the battery cells in the vehicle age in the same way as they did in previous tests. For this purpose, accordingly, it must firstly be possible to determine what state of aging the relevant battery cell is currently in.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a method for determining the value of at least one parameter of a battery, a control device and a motor vehicle, which make it possible to obtain the best possible accuracy even when the battery cells are gradually ageing. And nonetheless the value of the at least one parameter is determined in as simple a manner as possible.

This object is achieved by a method, a control device and a motor vehicle with the features of the corresponding independent claims. Advantageous refinements of the invention are the subject of the dependent claims, the description and the drawings.

In the method according to the invention for obtaining the value of at least one parameter of at least one cell of a battery of a motor vehicle, the value of the at least one parameter is obtained from a characteristic curve set which is associated with the at least one battery cell is associated with the battery and defines for the at least one battery cell a relationship between the stable voltage of the at least one battery cell and the state of charge of the at least one battery cell, wherein in a sequential/sequential The value of the at least one parameter is obtained repeatedly in time steps. Furthermore, it is checked whether the value of the at least one parameter, obtained at least at one of the time steps, satisfies a predetermined criterion, and at least if the predetermined criterion is not met, the characteristic curve family is adjusted/adapted , at least a part of the characteristic curve family is changed according to the adjustment.

In other words, it is thereby advantageously possible to provide a readily learned characteristic curve family, for example a readily learned OCV table. For the initialization of the method, an initial characteristic curve set can be called up, which can then advantageously be adjusted gradually over time. In the context of the present invention, characteristic curve family, characteristic curve and table are used synonymously. In other words, if a table is mentioned, this should also be understood as a general characteristic curve family, which can also take a form other than the tabular form. This OCV characteristic curve is the basic data used to describe the monomer. The OCV characteristic curve changes over the service life of the monomers and also mostly varies to varying degrees depending on the type of monomers used. By means of the self-learning OCV characteristic curve, it can now advantageously be ensured that the data base for determining the battery capacity, for example, is always of the same good quality over the service life. This gives the advantage that the corresponding cells of the battery can always be operated in the correct voltage range. This on the one hand prolongs the service life of the battery, provides reproducible and plausible capacity values, and thereby also improves the reproducible electric range that can be felt by the vehicle.

The battery of the motor vehicle is preferably a high-voltage battery, which in turn comprises a plurality of battery cells. In this case, the method described can be carried out individually for each battery cell, so that the corresponding value for the total battery can simply be obtained from the values of these battery cells. In particular, for example in the case of parallel connection of the individual cells, the capacities of the individual cells can simply be added to give the total capacity of the total battery, whereas in the case of a series connection, which is usually present in high voltage batteries, from the cells The smallest single capacity of the high-voltage battery gives the total capacity. Corresponding characteristic curves can then be stored accordingly for each individual battery cell, or only for the entire battery. As mentioned at the outset, characteristic curve families can be provided in tabular form. Nevertheless, this family of characteristic curves is occasionally also referred to here as characteristic curves. In this case, the characteristic curve can also relate a limited number of discrete state-of-charge values to corresponding stable voltage values. For values in between, interpolation can be performed.

At least a part of a characteristic curve family can be, for example, a value pair or value tuple, or also a plurality of value pairs or value tuples, or a part of a characteristic curve which associates value ranges with one another. In this case, it is also preferred that the adjustment of the characteristic curve set is limited to the at least one part, that is to say that the adjustment is not carried out globally, but locally, for example only for certain stable voltage values and corresponding charges The state value or adjusted for the determined stable voltage range and the corresponding state of charge range.

Furthermore, in addition to the steady voltage (also referred to as the no-load voltage) and the state of charge, further parameters, in particular the temperature of the at least one battery cell, can also be taken into account in the characteristic curve set. In other words, the characteristic curve family can define the relationship between the state of charge and the steady voltage of the at least one battery cell for different temperatures or temperature ranges. Here, the value of at least one parameter is obtained in successive time steps. It is then likewise possible to check in the corresponding time step whether the value of the at least one parameter satisfies a predetermined criterion. The time steps do not have to be predetermined and have the same interval from each other, but can also be event-triggered. In this case, it is advantageous, in particular, at times before and after the charging or discharging process, in particular when the battery or at least one battery cell should be in a fully relaxed state as far as possible at this time, that is to say, The predetermined time should be at static time. This has the advantage that a stable voltage can thereby be obtained particularly precisely, so that this is preferably used during the method, as will be explained in detail below.

Furthermore, the at least one parameter is preferably the state of charge of the at least one battery cell and/or the capacity of the at least one battery cell. In this case, the state of charge can be obtained from the characteristic curve family by detecting the stable voltage of the at least one battery cell, in particular also the current temperature of the at least one battery cell, and then for the associated stable voltage The current state of charge of the at least one battery cell is read from the characteristic curve set with the value of the temperature and the temperature. Rather, capacity may be obtained by dividing the amount of charge input to or extracted from the at least one battery cell during a charging or discharging process by the change in state of charge that occurs during the charging or discharging process. Here, the state of charge change is the difference between the initial state of charge before the charging or discharging process and the final state (hereinafter also referred to as the final state of charge) after the charging or discharging process. Correspondingly, it is also advantageous that the change in the state of charge of the at least one battery cell is carried out in the form of charging or discharging of the at least one battery cell between the various time steps. Here, the at least one battery cell does not necessarily have to be fully charged or fully discharged. The charging and discharging of the at least one battery cell is also to be understood as a partial charging or partial discharging process. Such a charging or discharging process, in particular in conjunction with a subsequent stabilization phase, can accordingly trigger the execution of the described method and define corresponding time steps. Accordingly, there may also be relatively long periods of time between each time step. However, this has no detrimental effect on the described method, since the change in the steady voltage-state-of-charge characteristic of the battery just changes only very slowly over the course of time.

In another advantageous design solution of the present invention, when checking whether a predetermined criterion is met, it is checked whether the obtained value of the at least one parameter has a predetermined value compared with a certain reference value of the at least one parameter. Minimal jumps, wherein the characteristic curve family is adjusted at least in the presence of predetermined minimum jumps.

A jump is understood here to mean a change. For example, if the characteristic curve family, for example the OCV characteristic curve, changes during battery use in such a way that the stable voltage-state-of-charge characteristic of the at least one battery cell changes relative to the stored OCV characteristic curve in such a way that this Influences on the determination of the state of charge, this then takes the form of a jump in the state of charge and a jump in capacity after the adaptation phase, that is to say after the stabilization phase of the battery or at least one cell. Advantageously, therefore, such a predetermined minimum jump in the value of said at least one parameter may infer that the stable voltage-state-of-charge characteristic of the at least one battery cell involved may have changed, which is then the case This can advantageously be taken into account by adjusting the characteristic curve set accordingly. As described above, the current state of charge of the at least one battery cell can be obtained by measuring the current stable voltage by means of a characteristic curve set. Another possibility for obtaining the state of charge consists in the current integration of the current fed into the at least one battery cell during the charging process or extracted from the at least one battery cell during the discharging process. In other words, for example for the charging process, there are:

SOC _Ende = SOC _Anfang +∫I(t)dt/K,

Among them, SOC _Ende represents the state of charge of the at least one battery cell after the charging process, SOC _Anfang represents the state of charge of the battery cell before the charging process, I represents the charging current, and K represents the capacity of the at least one battery cell.

Thus, the state of charge of the at least one battery cell can be determined on the one hand by a steady voltage measurement on the basis of the characteristic curve family, and on the other hand by a current integration. The corresponding values can be compared with each other to check whether a transition in state of charge occurs between two time steps. That is, the state of charge value may be compared with a reference value representing the value of the state of charge obtained from the current integration. Thus, the reference value for the state of charge may change with time steps, since it is always re-acquired for each time step. As can be seen from the above equation, depending on the state of charge before and after the charging process, and on the charging current, the capacity of at least one battery cell can also be obtained. The capacity thus obtained can be compared with a reference value, eg a capacity value initially given for a new battery or at least one battery cell. Similarly, it can thus be checked whether the newly acquired capacity has a jump, ie a change, with respect to this reference value. Of course, similarly, this also applies to the discharge process. If necessary, the capacity value can also be adjusted during the course of the method, which is described in more detail below. This means that the newly obtained capacity value can also be set as a new reference value for subsequent time steps. Correspondingly, the reference values for the capacity and state of charge are changed over time steps as necessary.

However, the problem that arises when adjusting the characteristic curve set optimally is that, in addition to the characteristic curve set, the capacity of at least one battery cell also changes over the course of time. Now, if in the calculation not only the family of characteristic curves but also the capacity is unknown (because they change), it is approximated to get an equation with two unknowns (as given above). In this case, it is not possible to correlate this change with a capacity or OCV table or, in general, a characteristic curve family without other considerations. In this case, the invention is further based on the knowledge that an evaluation of the magnitude and direction of the transitions described above can lead to a conclusion, from which a measure can be defined, which measures are specified in order to enable future charging Jumps in state and capacity are minimized or eliminated completely, whether and in which direction the OCV characteristic curve family must be adjusted. Exactly when both the state of charge and the capacity are considered as the at least one parameter, the measures to be taken can advantageously be specified in detail.

Therefore, another advantageous design solution of the present invention is to obtain the value of the state of charge and the value of the capacity as the at least one parameter in each time step, and to check the corresponding value, which is the corresponding time step Whether there is a predetermined minimum degree of corresponding jump compared to the determined corresponding reference value. At this point, the minimum degree that such a transition must have can be defined for each of two parameters, state of charge and capacity. Furthermore, each of the parameters can also be assigned its own reference value, as already described and defined above. Thus, the reference value for the state of charge may be provided by the current integration over the corresponding charging or discharging process, the reference value for the capacity may be, for example, the value for the capacity in a previous time step or initially provided . Thereby, the reference value can be provided again for the corresponding time step. Now, the conclusions that can now be deduced from the possible jumps in the obtained values are discussed next.

Here, according to another advantageous design of the invention, for the first case, that is, at a certain time step of the time steps, the value of the obtained capacity and the value of the obtained state of charge are the same as those of the If there is no corresponding jump of a predetermined minimum degree compared to the corresponding reference value for this specific time step, the characteristic curve set is not adjusted at least until the next immediately following time step. That is, if neither the state of charge nor the capacity has a jump, then these values can be considered normal and the characteristic curve family does not need to be adjusted.

According to another advantageous design of the invention, for the second case, ie, in the case of a specific time step in the time step, only the value of the capacity has a jump, then according to the direction of the jump and according to the direction of the jump The direction of the state of charge change before the time step, adjusting the characteristic curve family. At this point, the jump direction defines the direction of the deviation of the current value from the reference value. That is, if the value of the capacity provided at the determined time step is greater than the reference value, it is hereinafter referred to as a jump up. If the value of the capacity is smaller than the reference value, it is hereinafter referred to as a jump down. Accordingly, up and down represent the respective transition directions of the transitions. Furthermore, the direction of the change of the state of charge defines, between the specific time step and the time step immediately preceding the specific time step, an input of charge to the at least one battery cell (for example in the context of the charging process) ) or, for example, during operation of the motor vehicle, charge is extracted from the at least one battery cell, for example by discharging the at least one battery cell. For example, if at least one battery cell is charged, by dividing the amount of charge input to the at least one battery cell during this charging process by the state of charge change, that is to say by the at least one battery cell after the charging process The difference between the state of charge of the battery cell and the state of charge of the at least one battery cell prior to the charging process defines the capacity. After the charging process, and in particular after waiting for a defined relaxation time, the state of charge can be obtained from the characteristic diagram from the measurement of the stable voltage, and on the other hand also by starting from the initial state of charge before the charging process Perform current integration to obtain the state of charge. Accordingly, if the state of charge does not jump after charging, it can be considered that the final state of charge value is normal. Since the capacity has a jump and the difference in the state of charge into the capacity, it can accordingly be concluded that there is a problem in the initial state of charge, that is to say in the state of charge of the at least one battery cell before charging There is a problem in . Thus, taking the above-described charging process as an example, it can be concluded that if the capacity jumps downwards, the low voltage, that is to say the stable voltage of the initial state of charge, is actually lower than the value given in the characteristic curve family. Conversely, it can be concluded that the lower voltage is actually higher when the capacity jumps up. This advantageously allows a corresponding correction of the characteristic curve family. At a downward jump in capacity, for the case of the above-mentioned charging process, the stabilizing voltage for the initial state of charge is corrected downwards accordingly, in particular so that this brings about a new value for the initial state of charge, the new The value accordingly leads to a new state of charge difference and also to a new capacity value that no longer has jumps. When there is an upward capacity jump, it can be done accordingly. In this case, the stabilizing voltage for the initial state of charge is corrected upwards, whereby a correction of the capacity value is carried out, so that the corrected capacity value accordingly no longer has a jump with respect to the reference value. During the discharge process described above, the "high" stable voltage value associated with the initial state of charge is similarly adjusted, since in this case the initial state of charge is higher than the final state of charge. Furthermore, when adjusting, it is always assumed and assumed that the steady voltage is proportional/directly proportional to the state of charge, that is, the higher the steady voltage, the higher the state of charge.

In a further advantageous refinement of the invention, for the third case, that is, for a certain time step in the time step, both the value of the capacity and the value of the state of charge have corresponding jumps, and this When the corresponding transitions have the same transition direction, the characteristic curve family is adjusted according to the transition direction of the transition and according to the direction of the state of charge change before this time step. So, for example, if the state of charge as well as the capacity have transitions with the same direction of transition, this is not plausible in the first place, since the difference in state of charge and capacity are inversely/indirectly proportional to each other. The conclusion that can be drawn from the relay is that there must be two superimposed effects at this time. This is explained in the following again using the example of the charging process, but this can also be used again for the discharging process in an analogous manner: that is, if the final state of charge of at least one cell jumps upwards, the initial state of charge is therefore actually must also be associated with a higher stable voltage, so that the difference in state of charge becomes effectively smaller for the charging or discharging process under consideration. Now, the stable voltage of the low state of charge, that is to say the initial state of charge, can advantageously be corrected upwards accordingly. This is especially true when not only the capacity value but also the state of charge value jumps upwards. And if it is determined that both the state of charge and the capacity jump downward, the stable voltage of the low state of charge is revised downward accordingly. If instead of the charging process, the discharge process is examined instead, then correspondingly, instead of correcting the stable voltage of the low state of charge, the stable voltage of the high state of charge corresponding to the corresponding initial state of charge during the discharge process is corrected. Therefore, suitable measures can advantageously also be taken in this case to take into account changes in the characteristic curve family.

In a further advantageous refinement of the invention, for the fourth case, ie for a specific time step of the time steps, both the value of the capacity and the value of the state of charge have corresponding jumps, and this When the corresponding transition has the opposite transition direction, the characteristic curve family is not adjusted at least until the next time step immediately following. Furthermore, in this case, the value of the capacity is adjusted according to the jump direction of the jump and according to the direction of the state of charge change before this time step, and is checked for plausibility in particular in the next time step. If it is determined that the jump in the state of charge value is the opposite of the jump in the capacity value, there are several possible conclusions. For example, both new values may be correct and the capacity may not have been learned, or both values may be wrong. It is therefore advantageous to first not adjust the characteristic curve family, but only the capacity. In other words, the newly acquired capacity in this time step is set as the new reference value. This applies in particular to the above-mentioned charging process, but also to the discharging process. The plausibility of this measure is then advantageously checked in subsequent time steps. If this measure is correct, that is, the capacity is adjusted in the correct way, then in the following time steps it happens that no jumps are recorded in either the state of charge value nor the capacity value, i.e. all Normal, that is to say, the first situation described above occurs. Otherwise, one of the other situations discussed here is obtained, and the measures set forth here accordingly can then be taken again.

Exactly in the last-mentioned fourth case it is advantageous that the newly adjusted capacity value is initially not used as a basis for further calculation processes or other functions in the motor vehicle until a plausibility check has been completed. Other functional modules of the motor vehicle, which function as a function of 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, continue to use the current and verified values of these parameters until The new values are also validated and plausibility checked. In other words, multiple charge and discharge cycles (which also require different measures) are often required to obtain reliable results. The basis for this is that, as described at the beginning, an equation with two unknowns cannot be solved in one step. However, since the process of change within the battery is very slow when the cells are intact, it can be learned continuously and at any time. It is also possible to carry out the calculations in the background, since results that cannot be trusted or that cannot be directly checked for plausibility can occur in a single step. Therefore, the change has no effect on the value actually calculated by the controller and is not visible to the driver. For example, it can be provided that the result is only used for the actual calculation if it has a high degree of confidence. For example, a high confidence level can be defined in that the jump in state of charge and capacity is below a predetermined value, preferably between 2% and 4% of the relevant value.

Furthermore, there is also a fifth case, which occurs when only the value of the state of charge has a jump and the value of the capacity does not have a jump at a certain one of the time steps. In this case, according to a further advantageous refinement of the invention, the characteristic curve family is not adjusted at least until the next time step immediately following, and before this next time step, according to the transition of the transition direction and adjust the value of the capacity according to the direction of the state of charge change before that time step, and if this happens again in the next time step, adjust the characteristic curve family in the next time step. That is, if it is determined in one time step that only the state of charge has a jump and no capacity jump, then a two-stage approach is set in this case. The knowledge based in this case is that the capacity is assumed to be too small or that the stable voltage of the final state of charge is incorrect. It is therefore particularly advantageous to first correct the capacity in a first step, to be precise if a downward transition of the state of charge is determined after the above-described charging process, to correct the capacity upward, and vice versa, that is to say, If an upward state-of-charge transition is determined after the above-described charging process, the capacity is corrected downward. At this time, the amount of correction corresponds to the difference in capacity obtained from the transition of the state of charge. This then corrects the first mentioned situation, ie the capacity assumption is too small. If this is realistic, the corrective action leads to the first situation described above, ie everything is OK. Otherwise, ie if the problem recurs in a subsequent time step, the characteristic curve family is corrected as a further measure, to be precise, depending on the direction of transition of the final state of charge, upward or downward to stabilize voltage, which in the case of the charging process is associated with the final state of charge. In other words, if a downward transition in the state of charge has been determined, the stable voltage is also revised downward, and in the case of an upward transition in the state of charge, the stable voltage is also revised upward. In the case of the discharge process, the correction direction of the stabilized voltage is just the opposite.

It is also advantageous in this case that the relevant result, ie, in particular the adjusted capacity, is used as a basis for further calculations when there is a high degree of confidence and the assumption or measure is confirmed, for example, in a subsequent time step. Although the specific example explained above mainly concerns the charging process, these measures can also be used in a corresponding manner for the discharging process of at least one battery cell. Furthermore, the described measures apply not only to the complete charging and discharging process, but also to partial processes in the charging and discharging direction.

Furthermore, the invention also relates to a control device for a motor vehicle which is designed to carry out the method according to the invention or one of its embodiments. The control device can have a data processing device or a processor device which is designed 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 Logic Gate Array) and/or at least one DSP (Digital Signal Processor). Furthermore, the processor device may have program code which is configured to carry out, when run by the processor device, an embodiment of the method according to the invention. The program code may be stored in the data memory of the processor device.

The invention also includes a motor vehicle having such a control device. The motor vehicle according to the invention is preferably designed as a motor vehicle, in particular a passenger car or a lorry, or a bus or a 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 improvements of the control device according to the invention and the motor vehicle according to the invention, which have the features already described in connection with the improvements of the method according to the invention. For this reason, the control device according to the invention and corresponding refinements of the motor vehicle according to the invention will not be described in detail here.

The invention also includes combinations of features of the described embodiments. Accordingly, the invention also includes implementations having a combination of features of several of the described embodiments, as long as the embodiments are not described in a mutually exclusive manner.

Description of drawings

Next, embodiments of the present invention are described. in:

FIG. 1 shows a schematic diagram of a motor vehicle having a battery and a control device for obtaining a value of at least one battery parameter according to an embodiment of the present invention; and

FIG. 2 shows a flowchart for illustrating a method for obtaining a value of at least one battery parameter according to an embodiment of the present invention.

Detailed ways

The examples explained below are preferred embodiments of the present invention. The components of the embodiments described in the examples are each individual features of the invention, which can be regarded independently of each other, which also improve the invention independently of each other. Therefore, the present disclosure shall also include combinations of features other than those of the illustrated embodiments. Furthermore, the described embodiments may also be supplemented by other features of the invention already described.

In the figures, the same reference numerals respectively denote elements having the same function.

FIG. 1 shows a schematic diagram of a motor vehicle 10 with a control device 12 and a battery 14 , for example a high-voltage battery. Furthermore, the control device 12 has a memory 16 in which a characteristic curve map 18 , in particular an OCV table, is stored. The OCV table correlates corresponding stable voltage values of the battery 14 to corresponding state of charge values for corresponding temperature ranges. In FIG. 1 , the state of charge SOC is shown schematically for the battery 14 shown there, in particular in the form of a charging progress bar. Typically, the state of charge SOC is given as a percentage from 0% to 100%. Here, the maximum amount of charge that can be contained in the battery 14 defines the capacity K of the battery 14 . If the partial charge amount ΔQ is input to the battery 14 , the change in the state of charge ΔSOC is thereby obtained. Thus, the capacity K can be obtained as follows: K=ΔQ/ΔSOC. The charge quantity ΔQ can in turn be obtained from the charging current I, in particular according to ΔQ=∫Idt. For example, if the battery 14 is charged for one hour at a current of 30 amps, this corresponds to the amount of charge ΔQ input to the battery 14 at 30 amps. If during this charging process the state of charge increases from 0% to 100%, this 30 ampere hour corresponds to the capacity K of the battery 14 .

Starting from the initial state of charge, the final state of charge of the battery 14 can be obtained, for example, by means of current integration. On the other hand, the current state of charge SOC of the battery 14 can also be determined by means of a characteristic map 18 stored in the memory 16 of the control device 12 . For this it is only necessary to obtain the stable voltage U of the battery 14 . This is typically carried out after the stabilization phase of the battery 14 , since a particularly accurate acquisition of the stabilization voltage U can be achieved here. These measured values, ie the steady voltage U and the battery current I during charging and/or discharging of the battery 14 , can likewise be provided to the control device 12 . Knowing these parameters and using the characteristic diagram 18 , the control device 12 can always determine the current value of the state of charge SOC, for example, and provide it to other systems or indicate it to the driver, for example.

A problem with conventional methods for determining the state of charge using stable voltage tables or OCV tables is that such OCV tables for the associated battery are only applicable to the new state of the battery. That is, the stable voltage-state-of-charge characteristics vary with the use of the accumulator, which results from different environmental influences, such as temperature, electrical load, mechanical influence, and aging over time. As a result, for example, for the corresponding state of charge, the internal resistance of the cell and thus the resulting stable voltage also changes. However, the stable voltage does not only vary due to changes in internal resistance. Changes in the electrolyte or cathode and/or anode can also lead to changes in the stable voltage. If these are not taken into account in the OCV table, the inaccuracy in the determination of the battery capacity and in the state of charge acquisition increases over time.

Now, according to the present invention, this situation can be advantageously avoided by adjusting the OCV table 18 initially as a basis over time, in particular to match the current state of the battery 14 . That is, an OCV table 18 that is learned at any time is advantageously provided, whereby the OCV table is advantageously optimally matched to the battery characteristics at all times. Now, this practice is described in detail below.

To this end, FIG. 2 shows a flowchart for illustrating a method for obtaining at least one value of a battery parameter according to an embodiment of the present invention. In this case, the battery parameter is in particular not only the state of charge SOC but also the capacity K of the battery 14 . On the basis of these values, in particular obtained repeatedly in successive time steps, an adjustment of the OCV table 18 is carried out, more precisely a possible adjustment of the characteristic curve 18 and the capacity K is determined. However, this adjustment requires some consideration first, because in addition to the OCV characteristic curve, the capacity K of the cell or battery 14 also varies. Now, if at the time of calculation not only the OCV characteristic curve 18 but also the capacity K are unknown (since they may have both changed), an equation with two unknowns is obtained. Thus, in this case it is no longer possible, at least without other considerations, to correlate this change with the capacity K or the OCV table 18 . To solve this problem, the method described below can be used. Now, if the OCV characteristic curve 18 changes during use in such a way that it has an influence on the determination of the state of charge SOC (this manifests itself in the form of jumps in the state of charge value and the capacity value after the adaptation phase), evaluate the corresponding The degree and direction of the jump in the OCV characteristic curve 18 (if required) in order to minimize or completely eliminate future jumps in state of charge and capacity K.

Here, the method starts in step S10 in which the capacity value of the capacity K of the battery 14 and the current state of charge value of the state of charge SOC of the battery 14 are first determined or assumed. For the capacity K, it is assumed, for example, in the new state of the battery 14 that the capacity K initially corresponds to the initial value provided by the supplier of the battery 14 . In the new state of the battery 14, the initially used OCV table 18 should also conform to the battery characteristics, which involves associating the steady voltage value with the corresponding state of charge value of the state of charge SOC, especially for the corresponding temperature range. For example, the initial value of the state of charge SOC may be provided according to the table 18 in step S10.

Next, in this example, a charging process is performed to charge the battery 14 in step S12. At this point, the battery can be fully charged or only partially charged. The following examples accordingly relate to the case of such a charging process as previously described. However, for the aforementioned discharge process of the battery, the method can also be carried out analogously with corresponding adjustments.

During the charging process, from the charging current I, the value of which is supplied to the control device 12, the final state of charge after the charging process in step S12 can be obtained, knowing the initial state of charge provided in step S10 state. This acquisition can, for example, follow the charging process and also take place in step S12. Furthermore, in step S14 the current state of charge SOC of the battery 14 is obtained from the characteristic curve family 18 . Preferably, this is done after the stabilization phase of the battery 14, since the determination is based on the measurement of the stabilization voltage U. In step S16, the capacity K can be obtained from the current state of charge value thus obtained, which is the value of the so-called final state of charge of the battery 14 after the charging process. This capacity is derived from the current integral and the state of charge difference between the final state of charge and the initial state of charge, as already described with reference to FIG. 1 . These two values for the capacity K and the current state of charge SOC, newly obtained in steps S14 and S16, can then be compared with corresponding reference values. For the capacity K, the reference value is the capacity value K initially provided in step S10. The reference value of the current state of charge SOC is the final state of charge value calculated from the current integration obtained at the end of the charging process in step S12.

Here, in particular, it is checked whether the newly acquired value in question has a jump Δ1, Δ2 with respect to the corresponding reference value. For this purpose, on the one hand, for example, it can be checked in step S18 whether there is a state-of-charge transition Δ1. If not, it can additionally be checked in step S20 whether there is a capacity jump Δ2. Even if it is determined in step S18 that there is a jump in the state of charge Δ1, it can likewise be checked in step S22 whether there is a jump in capacity Δ2. In other words, both are checked anyway, ie whether there is a jump in capacity Δ2 and whether a jump in state of charge Δ1 is present, wherein the temporal order of such checks is not important. In particular, it is also possible to carry out both checks at the same time. Thus, if, for example, it is determined in step S18 that there is no state of charge jump Δ1, and further it is determined in step S20 that there is also no capacity jump Δ2, then move to step S24, where it is determined that everything is OK , that is, the obtained value is correct and the OCV table 18 and the value of the capacity K are still up to date. Subsequently, step S10 is transferred again, and the method is started from the beginning, then, in the following step S12 , the charging of the battery 14 does not necessarily have to be carried out again, but, for example, a discharging process can also be carried out.

If it is determined in step S18 that there is no state of charge jump Δ1, whereas it is determined in step S20 that there is a capacity jump Δ2, then the OCV table 18 may be adjusted in step S26. This is based on the knowledge that the stable voltage value associated with the initial state-of-charge value determined in step S10 according to table 18 is no longer up-to-date and, depending on the jump direction of the capacity jump Δ2, is actually more up-to-date. higher or lower. In particular, the adjustment can be made here as explained in the following example: According to this example, first the initial state of charge of the battery 14 is obtained. This is achieved by the measurement of the stable voltage U, which is, for example, 3400 mV. According to the OCV table 18, the state of charge value corresponding to the stable voltage U can be obtained. For example, a corresponding fragment of Table 18 might look like this:

In this example, the initial state of charge value is correspondingly 20%. In addition, the capacity K of the battery 14 currently assumed is 49 Ah. Next, the battery 14 is charged to a final state of charge of 85%, which can be obtained from the current integration of the charging current I. After the stabilization phase of the battery 14 , a state-of-charge value of 85% is obtained again based on the acquisition of the stabilization voltage U and using the characteristic curve 18 , that is, the state of charge SOC has no jump Δ1 . However, after the stabilization phase, the capacity K jumps to 50 Ah and thus has an upward jump Δ2. Since the final state of charge value has no jump Δ1, it can be considered that the final state of charge value is correct. Correspondingly, it can be concluded that an incorrect initial state of charge value caused the jump in capacity. That is, the capacity is actually 2% lower, that is, the initial state of charge SOC is actually 2% lower, 18% instead of 20%. Therefore, the steady voltage U of 3400 mV measured at the beginning, that is to say before charging, is not associated with a state of charge value of 20% but with 18%. In other words, the stable voltage U associated with 20% of the state of charge value is actually higher than 3400 mV. Therefore, the OCV table 18 can be corrected accordingly by correcting the stable voltage value for 20% of the state-of-charge value up to 3450 mV, in particular.

If the capacity K jumps downwards, the stable voltage U is also revised downwards, while if the capacity K jumps upwards, the stable voltage corresponding to the initial state of charge is revised upwards. Next, start the method from scratch again.

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 it is furthermore determined in step S22 that the capacity K also has a jump Δ2, then it is also checked in step S28 that the capacity Whether K and state of charge SOC have the same transition direction or opposite transition directions. If the two have the same transition direction, the process goes to step S30, where the characteristic curve family 18 is corrected again. This is based on the knowledge that, depending on the transition direction, the stable voltage U associated with the initial state of charge value actually has a lower or higher voltage than that given in Table 18. If the transition direction is downwards, the stable voltage value for the initial state of charge is corrected downwards accordingly, otherwise it is corrected upwards. An example calculation could look like this:

Here again an initial capacity of 49 Ah is assumed, and the battery is charged to 85% of the state of charge value. After the stabilization phase, it was determined that the capacity jumped to 50 Ah and the final state of charge jumped up to 88.3%. Correcting the capacity from 49Ah to 50Ah (102% of the original capacity) results in a state of charge correction of 83.3%, that is, 98% of the original value (the reciprocal of 102%). However, the state of charge SOC actually jumps by 5% to 90%, that is, the total jump is then 3.3%+1.7%=5%. Thus, for the actual state-of-charge transition Δ1, we obtain:

Δ1=SOC _neu -(K _alt /K _neu )×SOC _alt ,

Here, SOC _neu represents the state of charge of 88.3% after the steady state, SOC _alt represents the state of charge of 85%, K _alt is the originally assumed capacity of 49 Ah, and K _neu is the new capacity of 50 Ah. If assumed again, the initial state of charge is 20%, e.g. according to the following OCV table:

Therefore, the settling voltage U for 20% must now be corrected to the value at 25% with a calculated jump of 5%, that is, a total correction of 5%. Then, a voltage of 3450 mV is entered correspondingly for the state of charge value of 20%.

On the other hand, if it is determined in step S28 that the jumps Δ1, Δ2 of the capacity K and the state of charge SOC have opposite directions, the process proceeds to step S32. This situation can have a number of reasons. In particular, this could mean that both values are OK, or that the capacity K has not yet been learned, or that both values are wrong. Accordingly, it can be provided that in step S32 the capacity K is first adjusted, ie the capacity value obtained in step S16 is made equal to the new capacity value when the method is repeated in step S10. Then, the plausibility of this approach is tested in subsequent time steps. If this assumption is correct, then in the subsequent steps, in the absence of other changes, the transitions Δ1, Δ2 no longer occur. Otherwise, one of the other situations described or to be described occurs and corresponding action is taken.

If it is determined in step S22 that no capacity jump has occurred, then in step S34 it is first checked whether this has also occurred in the previous time step, ie only the state of charge value has a jump Δ1 and the capacity The value does not jump. If this is not the case, the capacity K is corrected in step S36. At this time, the correction direction is related to the transition direction of the state of charge value. If the state of charge jumps downwards, the capacity K is corrected upwards, and vice versa. Here, the capacity K is corrected by a value corresponding to the change in capacity obtained from the jump Δ1 of the state of charge value. Then, in step S10, the method is started from the beginning with this new capacity value. Conversely, if this situation recurs, that is to say it is determined in step S34 that this situation has already occurred in the previous time step, then a transition is made to step S38 in which the characteristic curve 18 is corrected. In particular, the stable voltage value associated with the final state of charge value is corrected again at this time. Here, when the state of charge value jumps upward, the stable voltage value is also revised upward, and when the state of charge value jumps downward, the stable voltage value is also revised downward. The method is then repeated in step S10 with the corrected characteristic curve set 18 .

Here, the two adjustment schemes described for steps S36 and S38 are again based on the knowledge that only one jump in the state of charge value has multiple causes. On the one hand it may be that the assumed capacity is too small, which can be compensated for by the measures in step S36. On the other hand, however, it is also possible that the steady-state value is abnormal, which in turn can be corrected by the measures described for step S38.

In particular, it can be seen that some corrections require several time steps to determine which values need to be changed, ie whether the characteristic curve 18 and/or the capacity K must be corrected. Nevertheless, this can advantageously be determined unambiguously by the method described, if necessary in a number of time steps, so that an OCV table 18 that can be learned over time can finally be provided, which is also reflected in the aging process of the battery 14 . Correct battery characteristics in terms of stable voltage and state of charge. The capacity can also be matched to its aging-induced changes in this way. Since it can also be assumed that the capacity K decreases slowly during the service life of the battery 14 , it is also conceivable, for example, that larger jumps above a definable threshold value can be regarded as implausible. In other words, if, for example, an upward capacity jump higher than the threshold value is determined, the capacity value may be considered implausible, for example. Thus, it can be defined, for example, that the measurement result is discarded and/or that in order to take further action, such as adjusting the capacity and/or the table 18, the plausibility must first be checked in another time step. In particular, narrower limits can be assumed, for example, when correcting upwards, since the capacity K does not increase during the service life. However, depending on the accuracy of the measurements in current and voltage, minor corrections in both directions should also be allowed to remain. Furthermore, the capacity K can be determined independently not only for the entire battery 14 , but also for example additionally for each cell or group of cells. It is then also possible to mutually check the plausibility of the calculated capacity values.

Since unreliable results can occur in a single step, it is also possible to perform calculations in the background. Therefore, the change has no effect on the value actually calculated by the controller 12 and is not visible to the driver. This value is also used in practice only when the results have high confidence and eg jumps in state of charge and capacity are below a certain value (eg between 2% and 4% of the value in question) calculate.

In general, the example shows how the present invention provides an OCV characteristic curve for determining the state of charge of an electrical energy store, which is learned over time, by means of which the changes over the service life of a cell or battery can be taken into account. . This self-learning OCV characteristic ensures that the data basis for determining the battery capacity is always of the same good quality over the service life. This gives the advantage that the cell can always be operated in the correct voltage range. This on the one hand extends the service life of the memory, provides reproducible and plausible capacity values, and thereby also improves the reproducible electrical range that can be felt by the vehicle.

Claims (10)

1. Method for obtaining a value of at least one parameter (SOC, K) of at least one cell of a battery (14) of a motor vehicle (10), wherein the value of the at least one parameter (SOC, K) is obtained from a family of characteristics (18) which are associated with the at least one cell and which define for the at least one cell a relationship between a steady voltage (U) of the at least one cell and a state of charge (SOC) of the at least one cell, wherein the value of the at least one parameter (SOC, K) is repeatedly obtained in successive time steps,

it is characterized in that the preparation method is characterized in that,

checking whether the value of the at least one parameter (SOC, K), which is obtained at least at one of the time steps, meets a predetermined criterion, and carrying out an adjustment of the characteristic map (18) at least if the predetermined criterion is not met, at least a part of the characteristic map (18) being changed as a function of the adjustment.

2. Method according to claim 1, characterized in that said at least one parameter (SOC, K) is the state of charge (SOC) of said at least one cell and/or the capacity (K) of said at least one cell.

3. The method according to any of the preceding claims, characterized in that the change in the state of charge of the at least one battery cell is carried out in the form of a charging or discharging of the at least one battery cell between the respective time steps.

4. Method according to one of the preceding claims, characterized in that, in checking whether a predetermined criterion is fulfilled, it is checked whether the obtained value of the at least one parameter (SOC, K) has a predetermined minimum degree of transition (Δ 1, Δ 2) compared to a determined reference value of the at least one parameter (SOC, K), wherein the adjustment of the family of characteristics (18) is carried out at least if a predetermined minimum degree of transition (Δ 1, Δ 2) is present.

5. Method according to any of the preceding claims, characterized in that in each of said time steps, a value of the state of charge (SOC) and a value of the capacity (K) are obtained as said at least one parameter (SOC, K) and it is checked for the respective value whether it has a respective transition (Δ 1, Δ 2) of a predetermined minimum extent compared to the respective reference value determined for the respective time step.

6. The method of claim 5,

for the first case, namely: if, at a specific one of the time steps, neither the value of the obtained capacity (K) nor the value of the obtained state of charge (SOC) has a respective transition (Δ 1, Δ 2) to a predetermined minimum extent compared to the respective reference value for the specific time step, the characteristic map (18) is not adjusted at least until the next subsequent time step, and/or

For the second case, namely: at a specific one of the time steps, only the value of the capacity (K) has a jump (Δ 2), the characteristic map (18) is adjusted as a function of the direction of the jump (Δ 2) and as a function of the direction of the change in the state of charge preceding the time step.

7. Method according to claim 5 or 6, characterized in that for the third case: at a specific one of the time steps, both the value of the capacity (K) and the value of the state of charge (SOC) have a respective transition (Δ 1, Δ 2), and the respective transitions (Δ 1, Δ 2) have the same transition direction, the characteristic map (18) is adjusted according to the transition direction of the transitions (Δ 1, Δ 2) and according to the direction of the change in the state of charge prior to the time step.

8. The method according to any of the preceding claims 5 to 7,

for the fourth case, namely: at a specific one of the time steps, both the value of the capacity (K) and the value of the state of charge (SOC) have a respective transition (Δ 1, Δ 2), and the respective transition (Δ 1, Δ 2) has the opposite transition direction, the characteristic map (18) is not adjusted at least until the next subsequent time step, and the value of the capacity (K) is adjusted as a function of the transition direction of the transition (Δ 1, Δ 2) and as a function of the direction of the change in the state of charge prior to the time step, and a plausibility check is carried out at the next time step; and/or

For the fifth case, namely: if, at a specific one of the time steps, only the value of the state of charge (SOC) has a transition (Δ 1), the characteristic map (18) is not adjusted at least until the next subsequent time step, and the value of the capacity (K) is adjusted at least until the next time step according to the transition direction of the transition (Δ 1) and according to the direction of the change in the state of charge before the time step, and if this occurs again at the next time step, the characteristic map (18) is adjusted at the next subsequent time step.

9. A control device (12) for a motor vehicle, which control device is designed to carry out the method according to one of the preceding claims.

10. A motor vehicle (10) having a control device according to claim 9.

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