Method for determining the state of a battery cell

Abstract

Method for determining a respective state of a plurality of cells (1, 2, 3, 4) of a battery (5), the method comprising at least the following steps: a) performing a charging process (6) or a discharging process (7) of the cells (1, 2, 3, 4); b) determining a discharge voltage (8) of each cell (1, 2, 3, 4) and a charge voltage (9) of each cell (1, 2, 3, 4); c) determining at least one state parameter (10, 11) for each cell (1, 2, 3, 4), wherein the state parameter is derived from the discharge voltage (8) and the charge voltage (9), wherein the discharge voltage (8) and the charge voltage (9) of at least one other cell (4, 3, 2, 1) are taken into account for the state parameter.

Description

Technical Field

[0001] This invention relates to a method for determining the state of batteries in a battery pack, particularly a high-voltage battery pack. Specifically, the method focuses on determining the state of a battery while taking into account the state of other batteries within the same battery pack. Background Technology

[0002] These high-voltage battery packs are particularly used in motor vehicles to store electrical energy for driving traction drive systems. The battery pack typically consists of multiple cells, each with a terminal voltage of 1.5 to 4 volts. These cells are at least partially connected in series, thus providing a traction voltage of 60 to 1500 volts DC.

[0003] Under current and future legislation, it is necessary to detect the condition of the battery pack or battery while the vehicle is in operation. In particular, by determining the battery's condition, early fault identification and early maintenance can be performed, thereby preventing battery or battery pack failures during operation and enabling timely replacement of the battery or battery pack.

[0004] Known methods for determining the state of a battery or battery pack typically only provide a snapshot, without detecting the development of the battery or battery pack's state (e.g., SOH - state of health).

[0005] A method for determining the aging state of a battery pack is known from DE 10 2009 000 337 A1. This method involves recording the impedance spectrum of the battery pack cells.

[0006] A method for monitoring the cells in a lithium-ion battery pack is known from DE 10 2011 117 249 A1. In this case, the charging capacity varies depending on the voltage of the corresponding battery pack.

[0007] A method for operating a secondary battery pack is known from DE 10 2014 214 314 A1. This method involves detecting the state parameters of each battery and deriving an operating strategy from them. Summary of the Invention

[0008] The object of this invention is to at least partially solve the problems identified with reference to the prior art. In particular, a method for determining the state of cells in a battery pack should be considered. Specifically, this method should also enable a discussion of the evolution of the state over the course of its service life.

[0009] The method having the features according to claim 1 helps to solve these tasks. Advantageous extensions are the subject of the dependent patent claims. Features listed separately in the patent claims can be combined with each other in a technically meaningful way and can be supplemented by explanatory facts in the specification and / or details in the drawings, which illustrate further embodiments of the invention.

[0010] A method for determining the corresponding states of multiple cells in a battery pack is proposed. In particular, this method should be able to determine the state of at least one cell in the battery pack, preferably the state of each cell in the battery pack.

[0011] The method includes at least the following steps:

[0012] a) Perform the charging or discharging process of the battery;

[0013] b) Determine the discharge voltage and the charging voltage of each of the batteries;

[0014] c) Determine at least one state parameter for each battery, wherein the state parameter is derived from the discharge voltage and the charge voltage, wherein the discharge voltage and the charge voltage of at least one other battery are taken into account for the state parameter.

[0015] The division of method steps into a) through c) as described above (not exhaustively) should primarily be intended for differentiation only, and does not impose any order or dependency. For example, the frequency of method steps may vary during system setup and / or operation. It is also possible for method steps to overlap at least partially in time. Particularly preferably, method steps b) and c) are performed during or immediately after step a). Specifically, steps a) through c) are performed in the listed order.

[0016] The charging and discharging processes refer to processes in which current is supplied to the battery (charging process) or discharged from the battery (discharging process), respectively. In particular, this method can be used to evaluate each charging process regardless of the amount of current supplied or discharged.

[0017] Within the scope of step b), the discharge voltage and charge voltage are determined or measured for each of the batteries under consideration. The discharge voltage represents the voltage of the battery after the discharge process. The charge voltage represents the voltage of the battery after the charge process. The voltages of multiple batteries are determined, in particular, at the same time point, i.e., all discharge voltages are determined at a common time point and all charge voltages are determined at another common time point.

[0018] Discharge voltage, especially the lowest voltage during the charging process. Charging voltage, especially the highest voltage during the charging process.

[0019] In particular, the charging process can be used to execute the method multiple times. For example, the corresponding voltage of the battery can be determined at a specific point in time during a further charging process, and the method can be executed with these voltages in mind.

[0020] Within the scope of step c), at least one state parameter is determined for each battery under consideration. This state parameter is derived from the battery's discharge and charge voltages. However, the corresponding voltages of at least one other battery, and in particular, the corresponding voltages of all other batteries under consideration, may also be considered.

[0021] Specifically, the state parameters are determined through normalization. This normalization allows the states of different batteries to be compared with each other.

[0022] Specifically, at least one state parameter is determined for at least a plurality of charging or loading processes, wherein the evolution of the state parameter determined in this manner is taken into account.

[0023] Because this method can be performed at any time for any type of charging process or regardless of the amount of current extracted or delivered, the reasonableness of previous results can be easily checked. Here, previously determined state parameters can be checked or verified by frequently repeating the method. Furthermore, the evolution of state parameters and thus the state of the battery can be tracked with high time resolution.

[0024] Specifically, one of the state parameters is at least a capacity parameter or a balance parameter. This capacity parameter describes the ratio of the battery's discharge voltage to its charge voltage, taking into account the ratio of other batteries. In particular, the capacity parameter thus describes the difference between the discharge voltage and the charge voltage during the battery charging process. A larger difference corresponds to a smaller battery capacity because a small amount of current can lead to a larger difference in battery voltage. Conversely, a smaller difference corresponds to a larger battery capacity.

[0025] The balance parameters describe the battery's discharge voltage level and charge voltage level compared to the corresponding voltage levels of other batteries. Specifically, the balance parameters describe the difference between the battery's first charge voltage level (i.e., value) compared to the corresponding first charge voltage level of other batteries and the battery's second discharge voltage level compared to the corresponding second discharge voltage level of other batteries.

[0026] Negative balance means, for example, that the battery with the lowest discharge rate compared to other batteries, that is, the battery with the lowest discharge voltage among all batteries, is charged the least during the charging process, that is, it has the lowest charging voltage among all batteries.

[0027] Positive balance means, for example, that the battery that discharges the least compared to other batteries, i.e., the battery with the highest discharge voltage among all batteries, is charged at the maximum intensity during charging, i.e., the battery with the highest charging voltage among all batteries.

[0028] Compensated balance means, for example, that the battery with the third lowest discharge voltage (i.e., the battery with the third lowest discharge voltage among all batteries) is charged with the third highest charging intensity (i.e., the battery with the third highest charging voltage among all batteries).

[0029] Specifically, the determined discharge and charge voltages of each battery are normalized to determine the state parameters. The normalized charge voltage x for battery i is... i Applicable to: Among them, the normalized discharge voltage y for battery i i Applicable to: y i = .

[0030] Here:

[0031] U xi The charging voltage of the battery i under consideration;

[0032] U xmax The maximum charging voltage of all considered batteries i = 1 to n;

[0033] U xmin The minimum charging voltage for all considered batteries i = 1 to n;

[0034] U yi The discharge voltage of the battery i under consideration;

[0035] U ymax The maximum discharge voltage of all considered batteries i = 1 to n;

[0036] U ymin The minimum discharge voltage for all considered batteries i = 1 to n.

[0037] The number of batteries is n, where i or n are natural numbers, i.e., n = 2, 3, 4, ...

[0038] The normalization of the charging voltage is therefore performed by the difference between the maximum charging voltage and the minimum charging voltage of all batteries during this charging process.

[0039] The normalization of the discharge voltage is therefore performed by the difference between the maximum discharge voltage and the minimum discharge voltage of all batteries during this charging process.

[0040] The normalization enables the comparison of one cell in the battery pack with the other cells.

[0041] In particular, the at least one state parameter is the capacity parameter C of battery i. i Applicable to: .

[0042] In particular, the at least one state parameter is the balance parameter B of battery i. i Applicable to: .

[0043] In particular, the reciprocal of the state parameter is considered in determining the battery state. Specifically, C i The reciprocal is In particular, B i The reciprocal is .

[0044] Specifically, an intervention limit is defined for each state parameter. When the intervention limit is exceeded, the relevant battery is determined to be in a repair state.

[0045] Specifically, the intervention limit is determined based on the state parameters defined for multiple batteries.

[0046] Specifically, an arithmetic mean of the state parameters of the battery under consideration is formed for the corresponding state parameters, wherein the intervention limit is, for example, at least 130%, preferably at least 150% or even 200% of the average value.

[0047] Specifically, the intervention limits are redefined for either the last charging or discharging cycle. In particular, the arithmetic mean can be recalculated for each charging cycle. In this way, the continuous degradation of the battery throughout its lifespan can be taken into account.

[0048] In particular, the method can be implemented in a control device that is at least configured for the diagnosis of the battery pack and, if necessary, for operation.

[0049] Battery packs can be used in motor vehicles to store energy, wherein the battery pack supplies electrical power to at least one traction drive unit of the motor vehicle.

[0050] In particular, a motor vehicle with a traction drive device and the described battery pack device is proposed.

[0051] A control device or data processing system is also proposed, which is equipped, configured, or programmed to perform the described methods.

[0052] In addition, the method can also be executed by a computer or by a processor of a control unit or data processing system.

[0053] Therefore, a system for data processing is also proposed, comprising a processor adapted / configured to perform the method or portions thereof. Specifically, the system for data processing includes at least one voltage detector for determining or measuring voltages (e.g., charging and discharging voltages) and means suitable for performing the steps of the method in order to determine the state of multiple cells in a battery pack.

[0054] A computer-readable storage medium is provided, comprising instructions that, when executed by a computer / processor, cause the computer / processor to perform at least some steps of the method or the proposed method.

[0055] Statements of method are particularly applicable to methods implemented in battery pack devices, motor vehicles, and / or computers (i.e., computers or processors, systems for data processing, computer-readable storage media), and vice versa.

[0056] In particular, the use of the indefinite article (“a”) in the description of patent claims and restates thereof should be understood as being for itself rather than as a numeral. The correspondingly introduced terms or elements should therefore be understood as the existence of at least one, and in particular, multiple.

[0057] It should be noted beforehand that the numerals used herein (“first,” “second,” ...) are primarily (only) used to distinguish multiple similar objects, sizes, or processes; that is, there is no mandatory pre-given order and / or interdependence of these objects, sizes, or processes. If dependencies and / or order are necessary, they are explicitly stated herein or will be apparent to those skilled in the art when examining the specifically described design. If a component may appear multiple times (“at least one”), the description of one component may equally apply to all or part of the multiple components, but this is not mandatory. Attached Figure Description

[0058] The invention and its technical field will now be explained in more detail with reference to the accompanying drawings. It should be noted that the invention should not be limited to the embodiments mentioned. In particular, unless explicitly stated otherwise, certain aspects of the facts explained in the drawings may be extracted and combined with other components and understandings of this specification. It should be particularly noted that these figures, and especially the scale shown, are merely illustrative. Wherein:

[0059] Figure 1 Two diagrams are shown, illustrating the charging process of the battery pack;

[0060] Figure 2 Three diagrams are shown, illustrating the intermediate discharge process;

[0061] Figure 3 A diagram showing a battery with low capacity is provided.

[0062] Figure 4 A diagram showing a battery with a large capacity is provided.

[0063] Figure 5 A diagram of a battery with a negative balance is shown;

[0064] Figure 6 A diagram of a battery with positive equilibrium is shown;

[0065] Figure 7 A diagram of a battery with a compensated balance is shown;

[0066] Figure 8 Two graphs are shown, illustrating the charging process of multiple batteries and their normalized voltages;

[0067] Figure 9 It shows according to Figure 8 A graph showing the capacity parameters of multiple batteries;

[0068] Figure 10 It shows according to Figure 8 A graph showing the balance parameters of multiple batteries;

[0069] Figure 11 It shows according to Figure 9 A graph of the reciprocal of the capacity parameter;

[0070] Figure 12 It shows according to Figure 10 A graph of the reciprocals of the equilibrium parameters;

[0071] Figure 13 Three graphs are shown, illustrating the normalized voltage, reciprocal of the capacity parameter, and reciprocal of the balance parameter for all batteries during the charging process; and

[0072] Figure 14 Three graphs are shown, which illustrate the reciprocals of the capacity parameters for all batteries for three different charging processes. Detailed Implementation

[0073] Figure 1 Two graphs are shown, illustrating the charging process 6 of battery pack 5. Voltage 12 is plotted on the vertical axis of the graph. Time 13 is plotted on the horizontal axis of the graph. Battery pack 5 comprises multiple batteries 1, 2, 3, 4. At the beginning of the charging process 6, the discharge voltage 8 of each battery 1, 2, 3, 4, ... n is measured, where n = 88. At the end of the charging process, the charging voltage 9 of each of the batteries 1, 2, 3, 4, ... n is measured.

[0074] Figure 2 Three diagrams are shown, one of which illustrates the intermediate discharge process 7. This occurs according to... Figure 1 During the charging process 6, voltage 12 is plotted on the vertical axis of the graph, and current 14 (the discharge current in this case) is plotted on the upper right side. Time 13 is plotted on the horizontal axis of the graph. It can be seen that when battery pack 5 discharges with current 14, batteries 1, 2, 3, and 4 exhibit different voltage change processes 12. (Reference...) Figure 1 Related statements.

[0075] Figures 3 through 7 below illustrate the voltage 12 changes of each battery, where the battery pack 5 under examination contains a total of 88 batteries, from battery 0 to battery 87. The voltage changes described below are always illustrated illustratively for each battery individually, referred to here as battery 1.

[0076] Figure 3 A diagram of a battery 1 with low capacity is shown. Figure 4 A diagram of a battery 1 with a large capacity is shown. The following will describe it together. Figure 3 and Figure 4 .

[0077] Voltage 12 is plotted on the vertical axis of the graph. Time 13 is plotted on the horizontal axis of the graph. The time interval between the discharge voltage 8 and the charging voltage 9 of the first battery 1 is also shown. Figure 3 The significant difference observed corresponds to the low capacity of battery 1, because a smaller current 14 causes a large difference in the voltage 12 of battery 1. Conversely, a small difference corresponds to the high capacity of battery 1. This state is... Figure 4 As shown in the image.

[0078] Figure 5 A diagram of battery 1 with a negative balance is shown. Figure 6 A diagram of battery 1 with positive equilibrium is shown. Figure 7 A diagram of battery 1 with compensated balance is shown. The following will describe the process together. Figures 5 to 7 .

[0079] Voltage 12 is plotted on the vertical axis of the graph. Time 13 is plotted on the horizontal axis of the graph.

[0080] As shown in Figure 5, negative balance means that the first battery 1, which has the lowest discharge voltage among all batteries 1, 2, 3, and 4 compared to the other batteries 2, 3, and 4, is charged the least during the charging process 6, that is, the charging voltage 9 is the lowest among all batteries 1, 2, 3, and 4.

[0081] As shown in Figure 6, positive balance means that the first battery 1, which discharges the least compared to other batteries 2, 3, and 4, is the battery with the highest discharge voltage among all batteries 1, 2, 3, and 4. It is charged with the highest intensity during the charging process 6, meaning that the charging voltage 9 is the highest among all batteries 1, 2, 3, and 4.

[0082] As shown in Figure 7, the compensated balance means that, compared with other batteries 1, 2, 3, and 4, the first battery 1, which has the third lowest discharge voltage 8 among all batteries 1, 2, 3, and 4, is charged with the third highest intensity in a charging process 6, which means that the charging voltage 9 is the third highest among all batteries 1, 2, 3, and 4.

[0083] Figure 8 Two figures are shown illustrating the charging process 6 of multiple batteries 1, 2, 3, and 4, and their normalized voltages 15 and 16. In the left figure, voltage 12 is plotted on the vertical axis, and time 13 is plotted on the horizontal axis. The battery pack 5 comprises multiple batteries 1, 2, 3, and 4. At the start of the charging process 6, the discharge voltage 8 of each battery 1, 2, 3, and 4 is measured. The first battery 1 has a discharge voltage 8 of, for example, 3.002 volts. At the end of the charging process 6, the charging voltage 9 of each of the batteries 1, 2, 3, and 4 is measured. Here, the first battery 1 has a charging voltage 9 of, for example, 4.131 volts.

[0084] In the right figure, the value of the normalized charging voltage is 15 x i The normalized discharge voltage value y is plotted on the vertical axis above the horizontal axis. i 16 is plotted on the vertical axis below the horizontal axis. Batteries 1, 2, 3, and 4, i.e., n, are plotted on the horizontal axis.

[0085] according to The normalized charging voltage 15 of the first battery 1 is 1.0 here; wherein the value of the charging voltage 9 of the first battery 1 under consideration is 4.131, the value of the maximum charging voltage 9 of all batteries 1, 2, 3, and 4 under consideration is 4.131, and the value of the minimum charging voltage 9 of all batteries 1, 2, 3, and 4 under consideration is 4.121.

[0086] according to The normalized discharge voltage 16 of the first battery 1 is -0.875; the discharge voltage 8 of the first battery 1 under consideration is 3.002, the maximum discharge voltage 8 of all batteries 1, 2, 3, and 4 under consideration is 3.009, and the minimum discharge voltage 8 of all batteries 1, 2, 3, and 4 under consideration is 3.001.

[0087] Figure 9 It is shown that, according to Figure 8 A graph showing the capacity parameter 10 for multiple batteries 1, 2, 3, and 4. The capacity parameter 10 is plotted on the vertical axis. Batteries 1, 2, 3, and 4, i.e., n, are plotted on the horizontal axis.

[0088] For the capacity parameter C of battery i i 10 Applicable to: For the first battery 1, the capacity parameter 10 is therefore 0.125.

[0089] Figure 10 It is shown that, according to Figure 8 A graph showing the balance parameter 11 for multiple batteries 1, 2, 3, and 4. The balance parameter 11 is plotted on the vertical axis. Batteries 1, 2, 3, and 4, i.e., n, are plotted on the horizontal axis.

[0090] For the balance parameter B of battery i i 11 Applicable to: For the first battery 1, the balance parameter 11 is therefore 0.85.

[0091] Figure 11 It is shown that, according to Figure 9 A graph showing the reciprocal of the capacity parameter 10. The reciprocal of the capacity parameter 10 is plotted on the vertical axis. Batteries 1, 2, 3, 4, and n are plotted on the horizontal axis. For the first battery 1, the reciprocal of the capacity parameter 10 is therefore 8.0.

[0092] Figure 12 It is shown that, according to Figure 10 A graph of the reciprocal of the balance parameter 11. The reciprocal of the balance parameter 11 is plotted on the vertical axis. Batteries 1, 2, 3, 4, i.e., n, are plotted on the horizontal axis. For the first battery 1, the reciprocal of the balance parameter 11 is 1.14 here.

[0093] Figure 13 Three graphs are shown, with the normalized voltages 15 and 16, the reciprocal of capacity parameter 10, and the reciprocal of balance parameter 11 for all batteries 1, 2, 3, 4, ... n, respectively, for charging process 6, where n = 88. In the top graph, the normalized charging voltage 15 x i The values ​​are plotted on the vertical axis above the horizontal axis, representing the normalized discharge voltage y. i The value of 16 is plotted on the vertical axis below the horizontal axis.

[0094] In the middle graph, the reciprocal of the capacity parameter 10 is plotted on the vertical axis.

[0095] The intervention limit 17, which is the reciprocal of the capacity parameter 10, is defined as 2.0.

[0096] In the graph below, the reciprocal of the balance parameter 11 is plotted on the vertical axis.

[0097] The intervention limit 17, which is the reciprocal of the equilibrium parameter 11, is defined as 3.0.

[0098] Batteries exceeding the intervention limit of 17 defined for the corresponding parameters (batteries 7, 8, and 21 in the middle diagram and batteries 11, 33, 50, 52, 61 to 64, and 66 in the lower diagram) can be identified. If these batteries exhibit corresponding anomalies or further deterioration in subsequent stages of the method, they can be selectively replaced if necessary. Maintenance dates can be set based on the detected changes in state parameters to prevent battery failure during operation and to avoid premature battery replacement.

[0099] Figure 14 Three graphs are shown, in which the reciprocal of the capacity parameter 10 for all batteries 1, 2, 3, 4, ... n is shown for three different charging processes, where n = 88. See the date description in the upper right corner of each graph, which is September 7, September 10 and September 11 of the same year.

[0100] In these graphs, the reciprocal of the capacity parameter 10 is plotted on the vertical axis. Batteries 1, 2, 3, 4, ... n are plotted on the horizontal axis, where n = 88.

[0101] Here, in the top image, batteries 7, 8, and 21 are marked as potentially defective; in the middle image, batteries 7 and 65 are marked as potentially defective; and in the bottom image, batteries 7 and 26 are marked as potentially defective.

[0102] As can be seen, a plausibility check can also be performed through repeated measurements. Here it appears that perhaps only the seventh battery is actually defective.

[0103] List of reference numerals

[0104] 1 First Battery

[0105] 2 Second Battery

[0106] 3 Third Battery

[0107] 4. Fourth battery

[0108] 5 battery packs

[0109] 6. Charging process

[0110] 7. Discharge process

[0111] 8 Discharge voltage

[0112] 9. Charging voltage

[0113] 10. Capacity Parameters

[0114] 11. Equilibrium Parameters

[0115] 12 Voltage

[0116] 13 Time

[0117] 14 Current

[0118] 15 Normalized charging voltage x i

[0119] 16 Normalized discharge voltage y i

[0120] 17. Limits to intervention.

Claims

1. A method for determining the corresponding states of a plurality of batteries (1, 2, 3, 4) in a battery pack (5), the method comprising at least the following steps: a) Perform the charging process (6) or discharging process (7) of the batteries (1, 2, 3, 4); b) Determine the discharge voltage (8) and the charging voltage (9) of each of the batteries (1, 2, 3, 4); c) Determine at least one state parameter (10, 11) for each battery (1, 2, 3, 4), wherein the state parameter is derived from the discharge voltage (8) and the charging voltage (9), wherein the discharge voltage (8) and charging voltage (9) of at least one other battery (4, 3, 2, 1) are taken into account for the state parameter, wherein one of the state parameters is at least a capacity parameter (10) or a balance parameter (11); wherein the capacity parameter (10) describes the ratio of the discharge voltage (8) and charging voltage (9) of the battery (1, 2, 3, 4) taking into account the ratio of the other batteries (4, 3, 2, 1); wherein the balance parameter (11) describes the discharge voltage (8) level and charging voltage (9) level of the battery (1, 2, 3, 4) compared with the corresponding voltage (8, 9) levels of the other batteries (1, 2, 3, 4).

2. The method according to claim 1, wherein the at least one state parameter is determined for at least a plurality of charging processes (6) or discharging processes (7), wherein the development of the state parameter thus determined is taken into account.

3. The method according to any one of the preceding claims, wherein the determined discharge voltage (8) and the charging voltage (9) of each battery (1, 2, 3, 4) are normalized to determine the state parameters; wherein the normalized charging voltage x for battery i i (15) Applicable to: ; where the normalized discharge voltage y for battery i is... i (16) Applicable to: y i = ;in U xi : The charging voltage of the battery i under consideration (9); U xmax : The maximum charging voltage of all considered batteries i = 1 to n (9); U xmin : Minimum charging voltage for all considered batteries i = 1 to n (9); U yi : The discharge voltage of the battery i under consideration (8); U ymax : The maximum discharge voltage of all considered batteries i = 1 to n (8); U ymin Minimum discharge voltage for all considered batteries i = 1 to n (8).

4. The method according to claim 3, wherein, The at least one state parameter is the capacity parameter (10)C of battery i. i Applicable to: .

5. The method according to any one of claims 3 and 4, wherein, The at least one state parameter is the balance parameter (11) B of battery i. i Applicable to: .

6. The method according to any one of claims 4 and 5, wherein the reciprocal of the state parameter is taken into account to determine the state of the battery (1, 2, 3, 4).

7. The method according to claim 6, wherein an intervention limit (17) is defined for each state parameter, and when the intervention limit is exceeded, the relevant battery (1, 2, 3, 4) is determined to be in a repair state.

8. The method according to claim 7, wherein, The intervention limit (17) is determined based on the state parameters determined for the plurality of batteries (1, 2, 3, 4).

9. The method according to claim 8, wherein, The intervention limit (17) is redefined for the last charging process (6) or discharging process (7).

10. A control device configured to perform the method according to any one of claims 1 to 9.

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