Patent Application
20240175935
This application claims priority to EP Application No. 22209399.9, having a filing date of Nov. 24, 2022, the entire contents of which are hereby incorporated by reference.
The following relates to a method for determining the aging of a battery storage device, to an apparatus for carrying out the method and to a computer program product.
Lithium-ion rechargeable batteries, also referred to as lithium-ion batteries below, are used as energy stores in mobile and stationary applications on account of their high power and energy density. In order to be able to operate these electrochemical energy stores safely, reliably and for as long as possible without maintenance, knowledge of critical operating states, in particular with respect to the state of charge (SOC) and with respect to the state of health (SOH), that is as accurate as possible is necessary.
It is known that the aging of a battery, in particular what is known as the cyclic aging, can be negatively affected by high temperatures and rapid charging at low temperatures, depending on the state of charge, the depth of discharge, and the charging power and the discharge power. It is therefore possible that the same type of battery cell can handle a different large number of load cycles depending on the specified parameters.
In order to determine the expected aging process, an aging characteristic of the battery cell used is determined in the prior art by means of measurements during the design phase of a battery system. The real aging rate with real load profiles is often not tested. Rather, the aging rate, or the cycle stability, is determined on compressed load profiles in so-called RAFF tests. These results are used to parameterize empirical aging models which show the aging process in the application. A future aging process determined on the basis of physical and/or chemical measurements depending the load profile, the operating point and the ambient conditions is difficult to carry out due to the non-linearity of the underlying physical and chemical processes and their complex interactions.
Predicting the state of health of a battery is unfavorably complex. The parameterization of a meaningful aging model is therefore often unfavorably very time-consuming. Furthermore, assumptions often have to be made to assess the aging, which disadvantageously render said assessment inaccurate.
This has the detrimental effect that battery storage devices are dimensioned to be larger than the performance and lifetime requirements require, in order to ensure sufficient power and thus to be able to comply with liability and warranty commitments.
In order to reduce the complexity or other problems mentioned above, methods are known in which the aging behavior of an energy storage device can be determined in a short period of time.
This includes the subject matter of the post-published German patent application 10 2022 201 676.9, in which, in order to solve these disadvantages, a method for measuring the aging of a battery storage device by means of high-precision coulometry (HPC) is disclosed, wherein the battery storage device should be understood there as meaning in particular a lithium-ion rechargeable battery or a lithium-ion battery which is exposed in particular to cyclic and calendar aging, which reduces its maximum usable capacity over the lifetime of the battery storage device. In the method, a sequence comprising a plurality of load patterns is provided. Each load pattern comprises a multiplicity of discharge and charging processes, each with defined depths of discharge (DOD), characteristic mean states of charge (SOC), current intensities, pause times and/or temperatures.
According to the method, the sequence of the plurality of load patterns is run through in a first step, wherein capacity losses (ΔKap) caused by the discharge and charging processes are measured. Furthermore, the residual capacity of the battery storage device is determined in a second step of the method.
This means that an approach that is based on the “High Power Cycling” method and is improved compared to the prior art is known. In this method, however, in order to be able to determine aging rates from measurement data, the underlying data must generally meet certain requirements.
In particular, the data must have a high degree of measurement accuracy, for example a high degree of measurement accuracy with regard to the time, voltage, current and temperature, and ideally must have been generated according to a special measurement procedure.
This ideal measurement procedure requires the cycling of battery cells. Cycling means repeated charging and discharging alternately over a relatively long period of time and within two fixed voltage limits. The charging current, discharge current and ambient temperature must be kept constant.
It is therefore also a disadvantage that, depending on the hardware used, for example in battery production, where high-priced laboratory equipment is not used, it is often difficult in practice to comply with the required measurement accuracy and to exclude disturbing environmental influences, with the result that the described requirements for the measurement data are not always met.
In the case of the HPC method, an attempt is therefore made, when recording the measured values, to keep the ambient conditions ideal by means of appropriate hardware and the complex experiment, in order to be able to adhere to a special measurement procedure precisely, so that the data obtained can be evaluated directly with the HPC analysis method.
An aspect therefore relates to specify a technical solution that solves the disadvantages of the prior art, in particular to realize a simple and reliable method for determining states of health of a rechargeable battery.
The method according to embodiments of the invention for determining the aging of a battery storage device comprises a plurality of steps:
With the method according to embodiments of the invention, manipulated signals are generated from signals for measurement data from a cycling process and can be used by the high-precision coulometry, HPC, method, even if these signals originate from measurement data from a cycling process which were not generated according to the HPC method or its framework conditions for a cycling process.
The apparatus according to embodiments of the invention comprises means for carrying out the method according to embodiments of the invention or one of the preferred configurations and developments of the method, in particular at least one module for carrying out the method.
The computer program product (non-transitory computer readable storage medium having instructions, which when executed by a processor, perform actions) according to embodiments of the invention is able to be loaded directly into a memory of a programmable computing unit, containing program code means for carrying out the method according to embodiments of the invention or one of the preferred configurations and developments of the method when the computer program product is executed in the computing unit.
Thus, methods and their measurements, which were not originally generated for this purpose and thus initially do not have the required accuracy at the beginning of the method according to embodiments of the invention, can also be used within the scope of the method according to embodiments of the invention to determine the aging rate of batteries using the HPC method.
In one development of the method according to embodiments of the invention, the part of the measurement data is branched from the measurement data formed by the parameters measured over the cycles in such a way that a part of the measurement data formed by the parameters measured over the cycles, which precedes the part in terms of time, in particular fluctuates greatly in terms of its values due to a transient condition with respect to at least one of the parameters, is excluded.
This assists embodiments of the invention in being able to form the usable voltage window to be as large as possible, because the temporally preceding part of the recorded measurement data from the cycling process, for example the first half or the first two thirds, can usually be discarded. In the first part of the measurement data, which is cut off here, the cell of a battery storage device is usually in a transient response, with the result that the last part of the measurement provides the actually meaningful data. This uses embodiments of the invention in an advantageous manner and contributes to increasing the precision of the result of determining the aging rate.
It is possible to determine the values manually if the method according to embodiments of the invention is developed in such a way that the first value and the second value are determined by capturing a user input.
However, these values will be generated automatically. This is achieved according to one development of the method according to embodiments of the invention, in which the first value and the second value are generated by a module performing the manipulation.
In such a module, the manipulation according to embodiments of the invention, in particular the determination of the voltage limits, can be achieved using circuitry. Circuitry solutions, which can form the module at least partially, are, for example, so-called field programmable gate arrays, as an example of an integrated circuit (IC) of digital technology, into which a logical circuit can be loaded; non-programmable gates are also conceivable. However, the module will at least partially resort to or integrate a central control device, so that at least one part of embodiments of the invention can use a computer unit. This allows a maximum degree of freedom in terms of optimizations, but also in terms of the possibilities of signal transmission and/or processing.
In a further development of the method according to embodiments of the invention, the first value and the second value are determined in such a way that they are generated, in particular individually for each cycle, depending on the measured temperature of at least one of the cells of the battery storage device.
As a result, the method according to embodiments of the invention can also be used to compensate for adverse temperature influences, because the voltage limit for each cycle can be set individually and coupled to the measured cell temperature by means of this development. Temperature-related changes in the overvoltage can thus be compensated.
The method according to embodiments of the invention can also be developed in such a way that the determination depending on the temperature takes place at least on the basis of a dependence of the DC internal resistance of the cell on the current direction, on the SOC and/or the temperature, in particular by reading out a table reflecting this assignment.
This makes it possible to use advantageous possibilities for coupling between the voltage limit and temperature. This can be achieved in a particularly simple and advantageous manner if it is possible to generate signals by reading out measurement data stored in a structured manner, for example measurement data available by reading out a table.
Alternatively or additionally, the method according to embodiments of the invention can also be developed in such a way that, for the determination of the first value and the second value, on the basis of at least one part of the measured parameters of the cycle and/or a directly adjacent cycle, for example the amount of charge, current, time for generating, in particular on the basis of an interpolation, values that are stored as further values of the parameters of the cycle and/or a directly adjacent cycle are used.
This optimizes the signals for the HPC method; in particular, the relationship between amounts of charge and other parameters of the measurements for balancing according to the HPC method is obtained and/or used for this purpose.
A further advantageous development of the method according to embodiments of the invention is provided if the first value and/or the second value is/are determined in such a way that
This provides a simple but effective process for maximizing time windows for usable voltage profiles. In addition to the developments already mentioned for achieving this effect, this development also offers the advantage that hardware-related fluctuations, for example due to an excessively low resolution during the measurement, especially of the voltage values, can be eliminated.
Alternatively or additionally, the method according to embodiments of the invention can be advantageously developed in such a way that, for at least one cycle,
This provides a simple and efficient process for manipulating the measurements or the measured parameters according to embodiments of the invention.
According to a further development of the method according to embodiments of the invention, the method is carried out in a computer-aided manner in a computing unit, thus resulting in maximum degrees of freedom for measurements, signal processing and/or optimization of the method.
The advantages cited with regard to the method according to embodiments of the invention and its preferred configurations and developments can be analogously applied to the apparatus according to embodiments of the invention and also lie in the fact that they allow the method to be carried out by way of their implementation.
The same also applies to the computer program product according to embodiments of the invention.
Some of the embodiments will be described in detail, with reference to the following figures, wherein like designations denote like members, wherein:
The exemplary embodiments explained in
In particular, the exemplary embodiments that follow merely show illustrative realization possibilities, how in particular such realizations of the teaching according to embodiments of the invention could be manifested, since it is impossible and also not helpful or necessary for the understanding of embodiments of the invention to name all these realization possibilities.
In the exemplary embodiments, the described components of the embodiments each represent individual features of embodiments of the invention which are to be considered independently of one another, and which each also refine embodiments of the invention independently of one another and are therefore also to be considered to be a constituent part of embodiments of the invention individually or in a combination other than that shown.
Furthermore, the described embodiments may also be supplemented by further features of embodiments of the invention that have already been described.
Identical reference signs have the same meaning in the various figures.
As an exemplary embodiment of the method according to embodiments of the invention, the sequence for setting an upper voltage limit and corresponding manipulation of measurement data is illustrated in
In a first step S1, the data measured according to the exemplary embodiment are read in. This are at least measurement data from a cycling process having a plurality of cycles.
It does not have to be an HPC apparatus HPCV or a cycling process in the context of an HPC method; rather, all methods mentioned at the outset, which perform a cycling process for determining battery states, are included here as long as they determine the measurement data necessary for embodiments of the invention.
Furthermore, it may be advantageous to develop this exemplary embodiment in such a way that the measurement data from the first cycles are not read in or are not used, since there can be a transient response in the first cycles, which can falsify the results of the method, in particular in the subsequent steps.
If measurement data are involved, the measurement data are divided into charging and discharge cycles according to a second method step S2.
In addition to the division, an upper voltage limit is defined in a third step S3 according to the exemplary embodiment of the method according to embodiments of the invention.
The upper voltage limit is selected in accordance with the exemplary embodiment in such a way that a consistent limit is possible over a definable measurement range that is to be analyzed and at the same time only as few measurement data as possible are above this limit.
In a fourth step S4, the time and index of the respective first measured values of the charging curves, which are above the selected, i.e. determined, upper voltage limit, are determined.
In addition, in a fifth step S5, two new measured values per charging cycle are generated by interpolation.
In this case, according to the exemplary embodiment of the method according to embodiments of the invention, the first of the two new measured values represents the last measured value of the charging cycle (current=charging current). The second new measured value represents the first measured value of the pause (current=0).
In a sixth step S6, an amount of charge ΔQch,i, which has flowed into the battery/battery cell above the defined upper voltage limit, is also determined for each charging cycle.
In accordance with a seventh step S7, the measured values above the upper voltage limit are deleted.
A further, eighth method step S8 involves determining the time and index of the last measured values of the discharge curves. This takes place as a ninth step S9 in the form of a repetition until the amount of charge ΔQch,i has been removed from the battery/battery cell.
In a tenth method step S10, two new measured values per discharge cycle are generated by interpolation. According to the exemplary embodiment of the method according to embodiments of the invention, the first of the two new measured values represents the last measured value of the discharge cycle (current=discharge current). The second new measured value represents the first measured value of the pause (current=0).
As a further, eleventh method step S11, provision is made, according to the exemplary embodiment of the method according to embodiments of the invention, for the measured values until ΔQch,i was discharged to be deleted.
In a twelfth step S12, the charge balance is then recalculated.
A lower voltage limit is set mutatis mutandis according to this exemplary embodiment of the method according to embodiments of the invention, i.e. in steps which are analogous for the inventor when considering the procedure explained above and are carried out in an interchanged or analogous manner, possibly individually adapted to the aim of determining the lower voltage limit, in particular with regard to the charging/discharge cycle and direction.
An illustration of the insertion of the upper voltage limit according to the described exemplary embodiment of the method according to embodiments of the invention is shown in
In this case, the original measurement data are represented as a solid line, the upper voltage limit defined in accordance with the exemplary embodiment is represented as a dotted line and the data modified in accordance with the exemplary embodiment of the method are represented as a dot-dashed line.
The insertion is illustrated in somewhat more detail in
Three graphs can be seen, wherein the measured values newly inserted in accordance with the method according to embodiments of the invention from the point of intersection of the charging curve with the upper voltage limit can be seen in the uppermost, first graph, the middle, second graph shows the profile of the amount of charge ΔQch,i, as is shown when using the exemplary embodiment of the method according to embodiments of the invention, and finally the measured values newly inserted according to the exemplary embodiment of the method according to embodiments of the invention when the amount of charge ΔQch,i is undershot in the discharge curve can be seen in the lower, third graph.
The image in
The lower, second graph illustrates, with the modified voltage values (solid line) inserted according to embodiments of the invention into these original data in accordance with the exemplary embodiment of the method according to embodiments of the invention, values which are provided for the HPC method and ensure by the method according to embodiments of the invention that the defined upper voltage limit (dot-dashed line) which is also depicted is not exceeded.
A lower voltage limit is set mutatis mutandis, i.e. in an analogous and reversed manner.
Embodiments of the invention described allow a more accurate and more robust determination of battery aging rates determined by the HPC method.
The algorithm used is able to positively influence the quality of the data used. This means that data which were not originally generated for this purpose and initially do not have the required accuracy can also be used to determine the aging rate of batteries using the HPC method.
In addition, there are extensive data collections from measurement series for determining the battery aging, wherein the battery aging was determined according to the conventional method. With the conventional method, battery cells are cycled at different operating points and checkup measurements are carried out at certain intervals.
In contrast to the HPC method, the aging rates are determined from the checkup measurements and not from the cycling processes themselves. The measurement data from the cycling processes are not usually evaluated, although a lot of information about the battery aging is hidden in these data. The cycling data obtained from the conventional determination of aging rates generally do not meet the requirements of the HPC method and therefore cannot be used directly for HPC evaluations.
The aging rates are usually determined according to the conventional method (cycling and checkup alternately).
In other words, some advantages of embodiments of the invention can be listed as follows:
Although the present invention has been disclosed in the form of preferred embodiments and variations thereon, it will be understood that numerous additional modifications and variations could be made thereto without departing from the scope of the invention.
For the sake of clarity, it is to be understood that the use of “a” or “an” throughout this application does not exclude a plurality, and “comprising” does not exclude other steps or elements.
| Number | Date | Country | Kind |
|---|---|---|---|
| 22209399.9 | Nov 2022 | EP | regional |
