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

Abstract

The invention relates to a method for determining the value of at least one parameter (SOC, K) of at least one battery cell of a battery (14) of a motor vehicle (10), wherein the value of the at least one parameter (SOC, K) is determined according to a characteristic curve set (18), which is associated with the at least one battery cell and defines for the at least one battery cell a relationship between a stable voltage (U) of the at least one battery cell and a state of charge (SOC) of the at least one battery cell, wherein 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 in one of the time steps meets a predetermined criterion, and at least if the predetermined criterion is not met, the characteristic curve set (18) is adjusted, at least a part of the characteristic curve set (18) being changed according to the adjustment.

Description

Technical Field

[0001] The invention relates to a method for determining the value of at least one parameter of at least one battery cell of a battery of a motor vehicle, wherein the value of the at least one parameter is determined based on a characteristic curve family associated with the at least one battery cell, which characteristic curve family defines for the at least one battery cell a relationship between a stable 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. Background Art

[0002] In order to determine the capacity and thus the storable, available energy or also the residual energy in a battery, such as a lithium-ion battery, the current state of charge (SOC) is determined based on the stable voltage compensation. This compensation is carried out based on a characteristic curve or a family of characteristic curves, which can also be in the form of a table, in particular a voltage table or an OCV (open circuit voltage) table. Such a table usually associates the corresponding state of charge with the corresponding stable voltage. The capacity of the lithium-ion storage device 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 this time. Here, the basis for determining the state of charge is the OCV table. With the development of energy storage devices, the OCV table is determined for the cells to be used by various different measurement methods. However, the problem with the OCV table is that it changes during the use of the energy storage device. The reason for this is different environmental influences, such as temperature, electrical load, mechanical influence or aging over time. As a result, the internal resistance of the cell changes and 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 change due to changes in the internal resistance. Changes in the electrolyte or the cathode and / or anode can also lead to changes in the stable voltage. Therefore, changes in the internal resistance cannot clearly be inferred from changes in the capacity. Therefore, it is impossible to obtain a correlation between these two parameters, so that the internal resistance value is not suitable for verifying the credibility of the capacity value.

[0003] 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 the current, voltage and temperature of the battery cells and current time data as input data.

[0004] 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 for modeling the battery, the measurement model comprising internal resistance, diffusion impedance and no-load voltage.

[0005] Furthermore, patent application US 2017 / 0146608 A1 describes a method for determining the state of health and state of charge of a cell based on the entropy of the cell.

[0006] According to this method, an OCV table is not used to determine, for example, the state of charge or capacity of the battery.

[0007] In addition, patent application DE 10 2019 108 498 A1 describes a 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 query table, which links the no-load voltage to the state of charge. When designing the vehicle, the query table is calibrated using test records that control the aging of one or more other batteries, such as test records of dynamic stress tests. The calibrated data is associated with the data of the battery aged in the vehicle, and thus allows accurate estimation of the capacity and state of charge in the vehicle. However, this is only the case when the battery cells in the vehicle are aged in the same way as in the previous test. Therefore, for this purpose, it must first be possible to determine: what kind of aging state the relevant battery cells are currently in. Summary of the invention

[0008] The object of the present invention is therefore 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 determine the value of the at least one parameter as accurately as possible and nevertheless in the simplest way possible even in the event of aging of the battery cells.

[0009] This object is achieved by a method, a control device and a motor vehicle having the features of the respective independent claims. Advantageous embodiments of the invention are the subject matter of the dependent claims, the description and the drawings.

[0010] In the method according to the invention for determining the 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 according to a characteristic curve set which is associated with the at least one battery cell and defines for the at least one battery cell a relationship between a stable voltage of 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 determined repeatedly in successive / sequential time steps. Furthermore, it is checked whether the value of the at least one parameter determined at at least one of the time steps meets a predetermined criterion, and at least if the predetermined criterion is not met, the characteristic curve set is adjusted / adapted, at least a part of the characteristic curve set being changed according to the adjustment.

[0011] In other words, a characteristic curve family that can be learned at any time, for example, an OCV table that can be learned at any time, can be advantageously provided. For the initialization of the method, an initial characteristic curve family can be called here, which can then be advantageously gradually adjusted over time. In the scope of the present invention, characteristic curve family, characteristic curve and table are used synonymously. In other words, if a table is mentioned, it should also be understood as a general characteristic curve family, which can also take a form different from the table form. Such an OCV characteristic curve is the basic data for describing a cell. The OCV characteristic curve changes during the service life of the cell, and also mostly changes to different degrees depending on the type of cell used. By means of the self-learning OCV characteristic curve, it is now advantageously possible to ensure that, for example, the data basis for determining the battery capacity always has the same good quality over the service life. This provides the advantage that the corresponding cells of the battery can always be operated in the correct voltage range. This prolongs the service life of the battery, provides reproducible and reasonable capacity values, and thus also improves the perceptible and reproducible electrical effective range of the vehicle.

[0012] 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 separately for each battery cell, so that the corresponding values ​​for the total battery can be easily obtained from the values ​​of these battery cells. In particular, for example, in the case of individual battery cells connected in parallel, the capacities of the individual battery cells can be simply added to the total capacity of the total battery, while in the case of series connection, which is usually present in high-voltage batteries, the total capacity of the high-voltage battery is obtained from the smallest single capacity of the cells. Thus, corresponding characteristic curves can be stored for each individual battery cell, or only for the entire battery. As mentioned at the beginning, a family of characteristic curves can be provided in the form of a table. Nevertheless, this family of characteristic curves is occasionally also referred to as a characteristic curve here. Here, the characteristic curve can also associate a limited number of discrete state of charge values ​​with corresponding stable voltage values. For values ​​between them, interpolation can be performed.

[0013] At least a portion of the characteristic curve family can be, for example, a value pair or a value tuple, or also a plurality of value pairs or value tuples, or a portion of a characteristic curve that relates value ranges to one another. In this case, it is also preferred that the adjustment of the characteristic curve family is limited to the at least a portion, that is, the adjustment is not performed globally, but locally, for example, only for a certain stable voltage value and a corresponding state of charge value or for a certain stable voltage range and a corresponding state of charge range.

[0014] Furthermore, in addition to the stable voltage (also called 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 family. In other words, the characteristic curve family can define the relationship between the state of charge of the at least one battery cell and the stable voltage for different temperatures or temperature ranges. In this case, the value of the at least one parameter is obtained in successive time steps. It can then also be checked in the corresponding time step whether the value of the at least one parameter meets a predetermined criterion. The time steps do not have to be determined in advance and have the same intervals with each other, but the time steps can also be event-triggered. In this case, it is particularly advantageous to have moments before and after the charging or discharging process, in particular when the battery or at least one battery cell should be in a completely relaxed state as far as possible at this moment, that is, the predetermined time should be at rest. This has the advantage that the stable voltage can be obtained particularly accurately, so that this can preferably be used in the course of the method, as will be explained in detail below.

[0015] Furthermore, the at least one parameter is preferably the state of charge of at least one battery cell and / or the capacity of at least one battery cell. The state of charge can be obtained from a characteristic curve diagram by detecting the steady-state voltage of the at least one battery cell and, in particular, also detecting the current temperature of the at least one battery cell and then reading the current state of charge of the at least one battery cell from the characteristic curve diagram for the associated values ​​of the steady-state voltage and temperature. The capacity can be obtained by dividing the amount of charge input into or extracted from the at least one battery cell during the charging or discharging process by the change in the state of charge that occurs during the charging or discharging process. The change in the state of charge is the difference between the initial state of charge before the charging or discharging process and the final state after the charging or discharging process (hereinafter also referred to as the final state of charge). Accordingly, it is also advantageous that the change in the state of charge of the at least one battery cell is implemented in the form of charging or discharging of the at least one battery cell between the individual time steps. In this case, the at least one battery cell does not necessarily have to be fully charged or fully discharged. Charging and discharging of the at least one battery cell should also be understood as a partial charging or partial discharging process. Such charging or discharging processes, in particular in combination with a subsequent stabilization phase, can accordingly trigger the execution of the described method and define corresponding time steps. Accordingly, there can also be relatively long time periods between the individual time steps. However, this has no adverse effect on the described method, since the change in the stable voltage-state of charge characteristic of the battery changes only very slowly over the course of time.

[0016] In another advantageous embodiment 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 minimum degree of jump compared to a determined reference value of the at least one parameter, wherein the characteristic curve family is adjusted at least under the condition that there is a predetermined minimum degree of jump.

[0017] In this context, a jump is understood to mean a change. For example, if a characteristic curve family, such as an OCV characteristic curve, changes during the use of the battery in such a way, or more precisely, the stable voltage-state of charge characteristic of the at least one battery cell changes in relation to the stored OCV characteristic curve in such a way that this has an influence on the determination of the state of charge, this manifests itself in the form of a jump in the state of charge and a jump in the capacity after an adaptation phase, that is to say after a stabilization phase of the battery or at least one battery cell. Advantageously, therefore, such a predetermined minimal jump of the at least one parameter value can be inferred that the stable voltage-state of charge characteristic of the at least one battery cell concerned may have changed, which can then be advantageously taken into account by correspondingly adjusting the characteristic curve family. As described above, the current state of charge of the at least one battery cell can be obtained by measuring the current stable voltage via the characteristic curve family. Another feasible solution for obtaining the state of charge is to perform a current integration of the current input 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 is:

[0018] SOC Ende =SOC Anfang +∫I(t)dt / K,

[0019] Among them, SOC Ende Indicates the state of charge of 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 at least one battery cell.

[0020] Thus, the state of charge of at least one battery cell can be obtained on the one hand by a stable voltage measurement based on a characteristic curve family and on the other hand by current integration. The corresponding values ​​can be compared with each other to check whether a jump in the state of charge occurs between two time steps. That is, the state of charge value can be compared with a reference value, which represents the value of the state of charge obtained by current integration. As a result, the reference value for the state of charge can change over the time step, because the reference value is always obtained again for each time step. As can be seen from the above equation, the capacity of at least one battery cell can also be obtained based on the state of charge before and after the charging process and based on the charging current. The capacity obtained in this way can be compared with a reference value, for example, a capacity value initially given for a new battery or at least one battery cell. Similarly, it can be checked whether the newly obtained capacity has a jump, that is, a change, relative to the reference value. Of course, this also applies to the discharge process in a similar way. If necessary, the capacity value can also be adjusted in 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 the subsequent time step. Accordingly, the reference values ​​for capacity and state of charge are varied over time if necessary.

[0021] However, the problem that arises when optimally adjusting the characteristic diagram is that in addition to the characteristic diagram, the capacity of at least one battery cell also changes over time. If, in the calculation, both the characteristic diagram and the capacity are unknown (because they change), then approximately an equation with two unknowns (as given above) is obtained. In this case, it is not possible to relate this change to the capacity or the OCV table or, in general, the characteristic diagram without further considerations. In this case, the invention is further based on the recognition that an evaluation of the extent of the respective jump described above and the direction of the jump leads to conclusions, based on which measures can be defined, which specify whether and in which direction the OCV characteristic diagram must be adjusted in order to minimize or completely 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, the measures to be taken can advantageously be specified in detail.

[0022] Therefore, another advantageous design 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 for the corresponding value whether it has a predetermined minimum corresponding jump compared to the corresponding reference value determined for the corresponding time step. At this time, the minimum degree that such a jump must have can be defined for each of the two parameters, namely the state of charge and the capacity. In addition, each of the parameters can also be assigned its own reference value, as already described and defined above. Therefore, the reference value for the state of charge can be provided by the current integral in terms of the corresponding charging or discharging process, and the reference value for the capacity can be, for example, the value for the capacity in the previous time step or initially provided. As a result, the reference value can be re-provided for the corresponding time step. Now, the conclusions that can now be drawn from the possible jumps of the values ​​obtained are discussed below.

[0023] Here, according to another advantageous embodiment of the present invention, for the first case, i.e., in a certain time step in the time steps, neither the value of the acquired capacity nor the value of the acquired state of charge has a predetermined minimum corresponding jump compared to the corresponding reference value for the certain time step, then the characteristic curve is not adjusted at least before the next time step immediately following. That is, if neither the state of charge nor the capacity has a jump, it can be assumed that these values ​​are normal and the characteristic curve does not need to be adjusted.

[0024] According to another advantageous embodiment of the present invention, for the second case, i.e., only the value of the capacity has a jump in a certain time step in the time step, the characteristic curve family is adjusted according to the jump direction of the jump and according to the direction of the change in the state of charge before the time step. In this case, the jump direction defines the direction of deviation of the current value from the reference value. That is, if the value of the capacity provided at the certain time step is greater than the reference value, it is referred to as an upward jump below. If the value of the capacity is less than the reference value, it is referred to as a downward jump below. Accordingly, up and down represent the respective jump directions of the jump. In addition, the direction of the change in the state of charge defines whether charge is input to the at least one battery cell between the certain time step and the time step directly before the certain time step (for example, within the scope of a charging process) or whether charge is extracted from the at least one battery cell, for example, during operation of the motor vehicle, for example, by discharging the at least one battery cell. For example, if at least one battery cell is charged, the capacity is defined by dividing the charge amount input to the at least one battery cell during the charging process by the change in the state of charge, that is, by dividing by the difference between the state of charge of the at least one battery cell after the charging process and the state of charge of the at least one battery cell before the charging process. After the charging process, and in particular after waiting for a certain relaxation time, the state of charge can be obtained by the characteristic curve family based on the measurement of the stable voltage and on the other hand by the current integration starting from the initial state of charge before the charging process. Accordingly, if there is no jump in the state of charge after charging, it can be assumed that this final state of charge value is normal. Since the capacity has a jump and the state of charge difference enters the capacity, it can be concluded that there is a problem in the initial state of charge, that is, there is a problem in the state of charge of the at least one battery cell before charging. Therefore, taking the above-mentioned charging process as an example, it can be concluded that if the capacity jumps downward, the low voltage, that is, the stable voltage of the initial state of charge is actually lower than the value given in the characteristic curve family. Conversely, in the case of an upward jump in capacity, it can be concluded that the low voltage is actually higher. This can advantageously enable the family of characteristic curves to be corrected accordingly. In the case of a downward jump in capacity, for the case of the above-described charging process, the stabilization voltage for the initial state of charge is correspondingly corrected downward, in particular so that this leads to a new value for the initial state of charge, which in turn leads to a new state of charge difference and also to a new capacity value that no longer has a jump. This can be done accordingly when there is an upward jump in capacity. In this case, the stabilization voltage for the initial state of charge is corrected upward, thereby correcting the capacity value, so that the corrected capacity value no longer has a jump relative to the reference value. In the above-described discharge process, the "high" stabilization 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, during the regulation, a direct proportionality between the stabilization voltage and the state of charge is always assumed and used as a premise, ie the greater the stabilization voltage, the higher the state of charge.

[0025] In another advantageous embodiment of the present invention, for the third case, i.e., in a certain time step of the time steps, both the value of the capacity and the value of the state of charge have a corresponding jump, and the corresponding jumps have the same jump direction, the characteristic curve family is adjusted according to the jump direction of the jump and according to the direction of the change of the state of charge before the time step. Thus, for example, if the state of charge and the capacity have a jump with the same jump direction, this is initially unreliable, because the state of charge difference and the capacity are inversely proportional to each other / indirectly proportional. From this, it can be concluded that there must be two superimposed effects at this time. This is explained again below using the charging process as an example, but similarly, this can also be applied to the discharge process: that is, if the final state of charge of at least one battery cell jumps upward, then the initial state of charge must actually be associated with a higher stable voltage, that is, so that the state of charge difference is effectively reduced for the charging or discharging process under consideration. Now, accordingly, the stable voltage of the low state of charge, that is, the initial state of charge, can be corrected upward. This is particularly applicable to the case where both the capacity value and the state of charge value jump upward. If, however, a downward jump in both the state of charge and the capacity is determined, the stable voltage of the low state of charge is correspondingly corrected downward. If, instead of a charging process, a discharge process is examined, the stable voltage of the low state of charge is correspondingly not corrected, but the stable voltage of the high state of charge corresponding to the corresponding initial state of charge during the discharge process is corrected. Thus, in this case, suitable measures can advantageously also be taken to take into account the change in the characteristic curve family.

[0026] In another advantageous design of the present invention, for the fourth case, that is, in a certain time step of the time step, not only the value of the capacity but also the value of the state of charge have a corresponding jump, and the corresponding jump has an opposite jump direction at this time, then at least before the next time step immediately following, the characteristic curve family is not adjusted. In addition, 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 change of the state of charge before this time step, and the rationality is checked in particular in the next time step. If it is determined that the jump of the state of charge value is opposite to the jump of the capacity value, there are many possible conclusions. For example, both new values ​​may be correct and the capacity may not have been learned, or both values ​​are wrong. Therefore, it is advantageous not to adjust the characteristic curve family first, but only the capacity. In other words, the capacity newly obtained in this time step is set to a new reference value. This is particularly applicable to the charging process described above, and also to the discharge process. Subsequently, the rationality of the measure is advantageously checked in a subsequent time step. If the measure is correct, that is, the capacity is adjusted in the correct way, then in the subsequent time step, no jump is recorded in the state of charge value and the capacity value, that is, everything is normal, that is, the first situation described above occurs. Otherwise, one of the other situations discussed here is obtained, and then the corresponding measures explained here can be taken again.

[0027] In the fourth case described above, it is advantageous that the newly adjusted capacity value is not initially 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 that implement functions based on the current capacity of at least one battery cell and / or the current state of charge of at least one battery cell can, for example, continue to use the previous and verified values ​​of these parameters until the new values ​​have also been verified and plausibility checked. In other words, multiple charging and discharging cycles (which also require different measures) are often required to obtain a plausible result. The basis for this is that, as described at the beginning, equations with two unknowns cannot be solved in one step. However, since the change process in the battery is very slow when the cells are intact, continuous learning is possible at any time. Since unreliable results or results that cannot be directly verified for plausibility may occur in a single step, it is also possible to perform the calculation in the background. Therefore, the changes have no effect on the values ​​used by the control unit for actual calculations and are 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 may 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.

[0028] In addition, there is a fifth case, which occurs when only the value of the state of charge has a jump and the value of the capacity has no jump in a certain time step in the time step. In this case, according to another advantageous design of the present invention, at least before the next time step immediately following, the characteristic curve group is not adjusted, and before the next time step, the value of the capacity is adjusted according to the jump direction of the jump and according to the direction of the change of the state of charge before the time step, and if this situation occurs again in the next time step, the characteristic curve group is adjusted in the next time step. That is, if it is determined in a time step that only the state of charge has a jump and the capacity has no jump, then in this case a two-stage measure is set. In this case, the knowledge based on the assumption that the capacity is too small or the stable voltage of the final state of charge is incorrect. Therefore, it is particularly advantageous to first correct the capacity in the first step, that is, if a downward state of charge jump is determined after the above-mentioned charging process, the capacity is corrected upward, and vice versa, that is, if an upward state of charge jump is determined after the above-mentioned charging process, the capacity is corrected downward. In this case, the amount of correction corresponds to the capacity difference resulting from the jump in the state of charge. This can then correct the situation mentioned first, namely that the capacity was assumed to be too small. If this is true, then the correction measure leads to the first situation described above, that is, everything is normal. Otherwise, that is, if the problem occurs again in a subsequent time step, then as a further measure, the characteristic curve family is corrected, more precisely, depending on the direction of the jump in the final state of charge, the stabilization voltage is corrected upward or downward, which is associated with the final state of charge in the case of the charging process. In other words, if a downward jump in the state of charge has been determined, the stabilization voltage is also corrected downward, and in the case of an upward jump in the state of charge, the stabilization voltage is also corrected upward. In the case of the discharge process, the correction direction of the stabilization voltage is exactly the opposite.

[0029] In this case, it is also advantageous if the relevant results, i.e. in particular the adjusted capacity, are used as a basis for further calculations only when there is a high degree of confidence and, for example, the assumption or measure is confirmed in a subsequent time step. Although the special examples explained above relate primarily to charging processes, these measures can also be used in a corresponding manner for discharging processes of at least one battery cell. Furthermore, the described measures are applicable not only to complete charging and discharging processes, but also to partial processes in the charging and discharging direction.

[0030] Furthermore, the invention also relates to a control device for a motor vehicle, which is designed to execute 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 execute 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 a program code, which is designed to execute an embodiment of the method according to the invention when it is run by the processor device. The program code can be stored in a data memory of the processor device.

[0031] The invention also includes a motor vehicle having such a control device. The motor vehicle according to the invention is preferably designed as a car, in particular a passenger car or a truck, or a bus or a motorcycle.

[0032] The advantages described with respect to the method according to the invention and its embodiments apply in the same manner to the control device according to the invention and to the motor vehicle according to the invention.

[0033] The present invention also includes improvements of the control device according to the invention and of the motor vehicle according to the invention, which have the features already described in conjunction with the improvements of the method according to the invention. For this reason, the corresponding improvements of the control device according to the invention and of the motor vehicle according to the invention will not be described in detail here.

[0034] The present invention also includes combinations of features of the described embodiments. Therefore, as long as the embodiments are not described in a mutually exclusive manner, the present invention also includes implementations having a combination of features of a plurality of the described embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Next, an embodiment of the present invention is described.

[0036] Figure 1 A schematic diagram of a motor vehicle having a battery and a control device for determining a value of at least one battery parameter according to an exemplary embodiment of the present invention is shown; and

[0037] Figure 2 A flow chart is shown for illustrating a method for obtaining a value of at least one battery parameter according to an exemplary embodiment of the present invention. DETAILED DESCRIPTION

[0038] The embodiments explained below are preferred embodiments of the present invention. The components of the embodiments described in the embodiments are respectively individual features of the present invention that can be viewed independently of each other, and these features also improve the present invention independently of each other. Therefore, the present disclosure should also include combinations that are different from the feature combinations of the embodiments shown. In addition, the described embodiments can also be supplemented by other features of the features of the present invention that have been described.

[0039] In the figures, the same reference numerals respectively denote elements having the same function.

[0040] Figure 1 The schematic diagram of a motor vehicle 10 is shown, which has a control device 12 and a battery 14, for example a high-voltage battery. The control device 12 also has a memory 16 in which a characteristic curve 18, in particular an OCV table, is stored. The OCV table associates corresponding stable voltage values ​​of the battery 14 with corresponding state of charge values ​​for corresponding temperature ranges. Figure 1 , the state of charge SOC is schematically shown for the battery 14 shown there, in particular graphically 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 charge that can be accommodated in the battery 14 defines the capacity K of the battery 14. If a partial charge ΔQ is input into the battery 14, a change in the state of charge ΔSOC is obtained. From this, the capacity K can be obtained as follows: K=ΔQ / ΔSOC. The charge 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 with a current of 30 amperes, this corresponds to a charge ΔQ input to the battery 14 of 30 ampere hours. If during this charging process the state of charge increases from 0% to 100%, then these 30 ampere hours correspond to the capacity K of the battery 14.

[0041] Starting from the initial state of charge, the final state of charge of the battery 14 can be obtained, for example, by 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 curve group 18 stored in the memory 16 of the control device 12. For this purpose, only the stable voltage U of the battery 14 must be obtained. This is typically done after the stabilization phase of the battery 14, because a particularly accurate determination of the stable voltage U can be achieved at this time. These measured values, namely the stable voltage U and the battery current I during the charging and / or discharging process of the battery 14, can also be provided to the control device 12. Knowing these parameters and with the help of the characteristic curve group 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, for example, indicate it to the driver.

[0042] 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 relevant battery are only valid for the new state of the battery. That is, the stable voltage-state of charge characteristic changes with the use of the energy storage device, which is caused by different environmental influences such as temperature, electrical load, mechanical influences and aging over time. As a result, for example, for the corresponding state of charge, the internal resistance of the cell changes and thus also the resulting stable voltage. However, the stable voltage does not only change due to changes in the internal resistance. Changes in the electrolyte or the 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 determining the battery capacity and obtaining the state of charge will increase over time.

[0043] Now, according to the invention, this situation can be advantageously avoided by adjusting the initially underlying OCV table 18 over time, in particular by adapting it to the current state of the battery 14. That is, an OCV table 18 that is learned over time is advantageously provided, whereby the OCV table is advantageously optimally adapted to the battery characteristics at any time. Now, this approach is described in detail below.

[0044] to this end, Figure 2 A flow chart is shown for illustrating a method for obtaining at least one value of a battery parameter according to an embodiment of the 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. Based on these values, which are obtained repeatedly in successive time steps, an adjustment of the OCV table 18 is performed, or more precisely a possible adjustment of the characteristic curve family 18 and the capacity K is determined. However, this adjustment first requires some considerations, because in addition to the OCV characteristic curve, the capacity K of the cell or battery 14 also changes. Now, if both the OCV characteristic curve 18 and the capacity K are unknown during the calculation (because they may have both changed), an equation with two unknowns is obtained. In this case, it is then no longer possible, at least without further considerations, to associate 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 impact on the determination of the state of charge SOC (which manifests itself in the form of a jump in the state of charge value and the capacity value after the adaptation phase), the extent of the corresponding jump and its direction are evaluated, that is, greater than, equal to, or less than the state of charge value or capacity value before the adaptation phase, and corresponding conclusions and measures are defined on this basis, namely: in which direction the OCV characteristic curve 18 must be adjusted (if necessary) in order to minimize or completely eliminate future jumps in the state of charge and capacity K.

[0045] Here, the method is started in step S10, in which a capacity value for the capacity K of the battery 14 and a current state-of-charge value for the state-of-charge SOC of the battery 14 are first determined or assumed. For the capacity K, it is assumed, for example, in a new state of the battery 14 that the capacity K initially corresponds to an 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 be in accordance with the battery characteristics, which involves associating stable voltage values ​​with corresponding state-of-charge values ​​of the state-of-charge SOC, in particular for corresponding temperature ranges. For example, an initial value for the state-of-charge SOC can be provided in step S10 according to this table 18.

[0046] Next, in this example, a charging process is performed in step S12 to charge the battery 14. At this time, the battery can be fully charged or only partially charged. The following example accordingly relates to the case of such a charging process as described above. However, for the above-mentioned discharge process of the battery, the method can also be implemented similarly by corresponding adjustments.

[0047] During the charging process, from the charging current I, whose value is supplied to the control device 12, the final state after the charging process in step S12 can be obtained, knowing the initial state of charge provided in step S10. This acquisition can, for example, be carried out immediately after the charging process and also in step S12. Furthermore, in step S14, the current state of charge SOC of the battery 14 is obtained based on the characteristic curve family 18. Preferably, this is carried out after a 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 obtained in this way, which is the value of the so-called final state of charge of the battery 14 after the charging process. The capacity is obtained 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 Figure 1 As described. Subsequently, the two values ​​for capacity K and current state of charge SOC newly obtained in steps S14 and S16 can be compared with corresponding reference values. For capacity K, the reference value is the capacity value K initially provided in step S10. The reference value for 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.

[0048] In this case, in particular, it is checked whether the newly obtained value in question has a jump Δ1, Δ2 relative to the corresponding reference value. 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 not, it can 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, wherein the time sequence of such checks is not important. In particular, these two checks can also be carried out simultaneously. Thus, if, for example, it is determined in step S18 that there is no jump in the state of charge Δ1, and in addition it is determined in step S20 that there is no jump in capacity Δ2, then the process moves to step S24, in which it is determined that everything is OK, that is, the obtained values ​​are correct and the values ​​of the OCV table 18 and the capacity K are still up to date. Subsequently, the method is transferred to step S10 again and the method is restarted from the beginning, and then in the following step S12 the battery 14 does not necessarily have to be charged again, but a discharging process can also be carried out, for example.

[0049] If it is determined in step S18 that there is no state of charge jump Δ1, but it is determined in step S20 that there is a capacity jump Δ2, the OCV table 18 can be adjusted in step S26. This is based on the recognition that the stable voltage value associated with the starting state of charge value determined in step S10 according to table 18 is no longer up to date and is actually higher or lower depending on the jump direction of the capacity jump Δ2. In particular, the adjustment can be carried out as explained in the following example: According to this example, the initial state of charge of the battery 14 is first obtained. This is achieved by measuring the stable voltage U (which is, for example, 3400mV). According to the OCV table 18, the state of charge value corresponding to this stable voltage U can be obtained. For example, a corresponding fragment of table 18 can be shown as follows:

[0050]

[0051]

[0052] In this example, the initial state of charge value is accordingly 20%. In addition, the capacity K of the battery 14 currently assumed is 49 Ah. Subsequently, the battery 14 is charged to a final state of charge of 85%, which can be obtained based on the current integral 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 group 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 assumed that the final state of charge value is correct. Accordingly, it can be concluded that the incorrect initial state of charge value causes this capacity jump. That is, the capacity is actually 2% lower, that is, the initial state of charge SOC is actually 2% lower, which is 18% instead of 20%. Therefore, the stabilization voltage U of 3400 mV measured at the beginning, that is, before charging, is not associated with a state of charge value of 20% but with 18%. In other words, the stabilization voltage U associated with the state of charge value 20% is actually higher than 3400 mV. Therefore, the OCV table 18 can be corrected accordingly by correcting the stabilization voltage value for the state of charge value 20% upwards to 3450 mV in particular.

[0053] If the capacity K changes suddenly downward, the stabilization voltage U is also corrected downward, and if the capacity K changes suddenly upward, the stabilization voltage corresponding to the initial state of charge is corrected upward. The method then starts again from the beginning.

[0054] On the other hand, if it is determined in step S18 that the state of charge value has a jump Δ1 relative to its reference value, and if it is further determined in step S22 that the capacity K also has a jump Δ2, then it is also checked in step S28 whether the capacity K and the state of charge SOC have the same jump direction or opposite jump directions. If both have the same jump direction, then transfer to step S30, in which the characteristic curve family 18 is corrected again. This is based on the recognition that, depending on the jump direction, the stable voltage U associated with the initial state of charge value actually has a lower or higher voltage than given in table 18. If the jump direction is downward, the stable voltage value for the initial state of charge is correspondingly corrected downward, otherwise it is corrected upward. A calculation example can be shown as follows:

[0055] Here again, an initial capacity of 49 Ah is assumed and the battery is charged to a state of charge value of 85%. After the stabilization phase, a capacity jump to 50 Ah is determined and the state of charge eventually jumps upward to 88.3%. Correcting the capacity from 49 Ah to 50 Ah (102% of the original capacity) results in a correction of the state of charge to 83.3%, that is, 98% of the original value (the inverse 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 jump Δ1 we obtain:

[0056] Δ1=SOC neu -(K alt / K neu )×SOC alt ,

[0057] Here, SOC neu Indicates 88.3% state of charge after steady state, SOC alt Indicates 85% state of charge, K alt The original assumed capacity is 49Ah, K neu The new capacity is 50Ah. If we assume again that the initial state of charge is 20%, for example according to the following OCV table:

[0058]

[0059] Therefore, the stabilization voltage U for 20% must now be corrected to the value at 25% by the calculated 5% step, ie, a total correction of 5%. Accordingly, a voltage of 3450 mV is then entered for the state of charge value 20%.

[0060] 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, then transfer to step S32. This situation can have various reasons. In particular, this may mean that both values ​​are normal, or the capacity K has not yet been learned, or both values ​​are wrong. Accordingly, it can be provided that in step S32, the capacity K is first adjusted, that is, the capacity value obtained in step S16 is equal to the new capacity value when the method is repeated in step S10. The rationality of this approach is then checked in subsequent time steps. If this assumption is correct, then in subsequent steps, in the absence of other changes, jumps Δ1, Δ2 no longer occur. Otherwise, the other situations described or one of the situations to be described occurs, and corresponding measures are taken.

[0061] If it is determined in step S22 that no capacity jump occurs, then in step S34 it is first checked whether this situation has also occurred in the previous time step, that is, only the state of charge value has a jump Δ1 and the capacity value has not changed. If this is not the case, the capacity K is corrected in step S36. In this case, the direction of the correction depends on the direction of the jump in the state of charge value. If the state of charge jumps downward, the capacity K is corrected upward, and vice versa. In this case, the capacity K is corrected by a value corresponding to the change in capacity resulting from the jump Δ1 in the state of charge value. Then, in step S10, the method starts from the beginning with this new capacity value. If, on the other hand, this situation reappears, that is, it is determined in step S34 that this situation has already occurred in the previous time step, then the method is transferred 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. In this case, when the state of charge value jumps upward, the stable voltage value is also corrected upward, and when the state of charge value jumps downward, the stable voltage value is also corrected downward. The method is then carried out again in step S10 with the corrected characteristic map 18 .

[0062] Here, the two adjustment options described for step S36 and step S38 are again based on the recognition that a single jump in the state of charge value can have multiple causes. On the one hand, it may be that the assumed capacity is too small, which can be compensated by the measures in step S36. On the other hand, however, it may also be that the steady-state value is not normal, which in turn can be corrected by the measures described for step S38.

[0063] In particular, it can be seen that some corrections require multiple time steps to determine which values ​​need to be changed, that is, whether the characteristic curve 18 and / or the capacity K must be corrected. However, this can nevertheless be determined explicitly by the described method, if necessary in multiple time steps, so that an OCV table 18 that is learned at any time can ultimately be provided, which also reflects the correct battery characteristics in terms of steady-state voltage and state of charge during the aging process of the battery 14. The capacity can also be matched to its changes caused by aging 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 considered unreliable. In other words, if, for example, an upward capacity jump higher than the threshold value is determined, then, for example, the capacity value can be considered unreliable. Therefore, it can be defined, for example, that the measurement result is discarded and / or that in order to take further measures, such as adjusting the capacity and / or the table 18, the credibility must first be checked in another time step. In particular, narrower limit values ​​can be assumed, for example, in the case of upward corrections, because the capacity K does not increase during the service life. However, due to the measurement accuracy in the current and voltage, smaller corrections should also be allowed in both directions. Furthermore, the capacity K can be determined independently not only for the entire battery 14, but also, for example, for each cell or cell group. It is then also possible to check the plausibility of the calculated capacity values ​​against each other.

[0064] Since unreliable results may occur in individual steps, it is also possible to perform the calculation in the background. The change thus has no effect on the values ​​used for the actual calculation by the controller 12 and is not visible to the driver. Only when the result has a high degree of confidence and, for example, the jump in the state of charge and capacity is below a certain value (for example, between 2% and 4% of the value in question) is this value also used for the actual calculation.

[0065] In summary, the example shows how the invention provides a constantly learning OCV characteristic curve for determining the state of charge of an electrical energy storage device, by means of which changes during the service life of a battery cell or battery can be taken into account. This self-learning OCV characteristic curve ensures that the data basis for determining the battery capacity is always of the same good quality over the service life. This provides the advantage that the cells can always be operated in the correct voltage range. This prolongs the service life of the storage device, provides reproducible and sensible capacity values, and thereby also improves the perceptible and reproducible electrical range of the vehicle.

Claims

1. A method for determining the value of at least one parameter (SOC, K) of at least one battery cell of a battery (14) of a motor vehicle (10), wherein: The value of the at least one parameter (SOC, K) is obtained according to a characteristic curve family (18), which is associated with the at least one battery cell and defines for the at least one battery cell a relationship between a stable voltage (U) of the at least one battery cell and a state of charge (SOC) of the at least one battery cell, wherein the value of the at least one parameter (SOC, K) is repeatedly obtained in successive time steps, It is characterized in that checking whether the value of the at least one parameter (SOC, K) obtained at least in one of the time steps satisfies a predetermined criterion, and at least if the predetermined criterion is not met, implementing an adjustment of the characteristic curve family (18), changing at least a part of the characteristic curve family (18) according to the adjustment, wherein in each of the time steps, a value of the state of charge (SOC) and a value of the capacity (K) are obtained as the at least one parameter (SOC, K), and for the respective value it is checked whether it has a respective jump (Δ1, Δ2) of a predetermined minimum degree compared to the respective reference value determined for the respective time step, wherein For the first case, i.e., in a specific one of the time steps, neither the value of the capacity (K) nor the value of the state of charge (SOC) obtained has a corresponding jump (Δ1, Δ2) of a predetermined minimum degree compared to the corresponding reference value for the specific time step, the characteristic curve group (18) is not adjusted at least until the next subsequent time step, and / or For the second case, i.e., if only the value of the capacity (K) has a jump (Δ2) in a certain one of the time steps, the characteristic curve group (18) is adjusted according to the jump direction of the jump (Δ2) and according to the direction of the change in the state of charge before this time step.

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

3. The method according to claim 1 or 2, characterized in that: Between the individual time steps, a 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.

4. The method according to claim 1 or 2, characterized in that: When checking whether a predetermined criterion is met, it is checked whether the obtained value of the at least one parameter (SOC, K) has a predetermined minimum jump (Δ1, Δ2) compared to a determined reference value of the at least one parameter (SOC, K), wherein, at least under the condition that the predetermined minimum jump (Δ1, Δ2) exists, the characteristic curve group (18) is adjusted.

5. The method according to claim 1 or 2, characterized in that: For the third case, i.e., in a certain time step among the time steps, both the value of the capacity (K) and the value of the state of charge (SOC) have corresponding jumps (Δ1, Δ2), and the corresponding jumps (Δ1, Δ2) have the same jump direction, then the characteristic curve group (18) is adjusted according to the jump direction of the jump (Δ1, Δ2) and according to the direction of the change in the state of charge before the time step.

6. The method according to claim 1 or 2, characterized in that: For the fourth case, that is, in a certain time step among the time steps, both the value of the capacity (K) and the value of the state of charge (SOC) have corresponding jumps (Δ1, Δ2), and the corresponding jumps (Δ1, Δ2) have opposite jump directions, then the characteristic curve family (18) is not adjusted at least before the next subsequent time step, and the value of the capacity (K) is adjusted according to the jump direction of the jump (Δ1, Δ2) and according to the direction of the change of the state of charge before the time step, and a credibility check is performed in the next time step; and / or For the fifth case, that is, in a certain time step among the time steps, only the value of the state of charge (SOC) has a jump (Δ1), then the characteristic curve group (18) is not adjusted at least before the next time step, and before the next time step, the value of the capacity (K) is adjusted according to the jump direction of the jump (Δ1) and according to the direction of the change in the state of charge before the time step, and if this situation occurs again in the next time step, the characteristic curve group (18) is adjusted in the next time step.

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

8. A motor vehicle (10) having a control device according to claim 7.

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