Method and apparatus for charging or discharging a battery system

Abstract

The invention relates to a method for charging or discharging a battery system (20), the battery system (20) having at least two battery cells (21-x) which are connected in parallel and / or in series and which can only be charged or discharged together, a voltage (U) being set as a setting variable by means of a current (I) or power (P) as a setting variable, the current (I) or the power (P) is specified taking into account the first state-of-charge-dependent characteristic curve (3-1) and the second state-of-charge-dependent characteristic curve (3-2), and wherein the first state-of-charge-dependent characteristic curve (3-1) and the second state-of-charge-dependent characteristic curve (3-2) have opposite slopes at least in sections. The invention further relates to a device (1) for charging or discharging a battery system (20).

Description

Technical Field

[0001] The invention relates to a method and a device for charging or discharging a battery system. Background Art

[0002] Depending on the temperature, duration of power-on and state of charge, lithium-ion cells can only absorb a limited charging current without being damaged. This maximum current also varies with the state of aging (SOH) of the lithium-ion cell. In addition, there is the difficulty that in a battery system, multiple cells can be connected in series or in parallel and the cells can have different temperatures and / or states of aging and / or states of charge. Therefore, it is currently necessary to know the state of charge and aging of all cells in the system as well as the coldest and hottest points at each point in time. This also means that the temperature gradient within the cell must be known in order to actually know the coldest and hottest points in the entire battery system. These two points, together with the state of charge and aging of each cell, determine the maximum possible charging current at each point in time. Since a relaxed battery can absorb a higher current than the maximum possible continuous current for a short period of time, the reaction of the cell to the charging current over time must also be known. In addition, the maximum permissible charging current also depends on the mechanical pressure or force acting on the battery cell. In addition, a state of charge distribution, i.e. different states of charge, can occur between individual battery cells within a battery system. In addition, a state of charge distribution can also occur within a battery cell. This state of charge distribution must be taken into account when selecting (regulating) the charging current, since the charging current generally depends on the state of charge. However, determining the state of charge of each individual battery cell connected in parallel and the state of charge distribution within a battery cell cannot be realized in a technically meaningful manner in practical operation.

[0003] DE 10 2021 108 085 A1 discloses a method for determining at least one control parameter of a charging device for supplying charge to a lithium-based electrical energy storage device, for which purpose a charging current is applied to the electrical energy storage device as a function of at least one state parameter of the electrical energy storage device. To determine the at least one control parameter, a limiting function is determined by which the supplied charge quantity is linked to a limit voltage in such a way that the anode potential is greater than a predefined anode potential value when the connection voltage is less than the limit voltage, wherein the predefined anode potential value is greater than zero volts relative to a Li / Li+ reference electrode. Summary of the invention

[0004] The technical problem to be solved by the present invention is to improve a method and a device for charging or discharging a battery system.

[0005] According to the invention, this object is achieved by a method having the features of the invention and a device having the features of the invention. Advantageous embodiments of the invention are apparent from the exemplary embodiments.

[0006] In particular, a method for charging or discharging a battery system is provided, wherein the battery system has at least two battery cells connected in parallel and / or in series, which can only be charged or discharged together, wherein a voltage is regulated as a control variable using a current or a power as a setting variable, wherein the current or the power is predetermined taking into account a first charge state-dependent characteristic curve and a second charge state-dependent characteristic curve, and wherein the first charge state-dependent characteristic curve and the second charge state-dependent characteristic curve have opposite slopes at least in sections.

[0007] Furthermore, in particular, a device for charging or discharging a battery system is proposed, wherein the battery system has at least two battery cells connected in parallel and / or in series, which can only be charged or discharged together, and the device comprises a regulator, wherein the regulator is arranged to regulate a voltage as a control variable by means of a current or a power as a setting variable, wherein the current or the power is predetermined taking into account a first charge state-dependent characteristic curve and a second charge state-dependent characteristic curve, and wherein the first charge state-dependent characteristic curve and the second charge state-dependent characteristic curve have opposite slopes at least in sections.

[0008] Furthermore, in particular, a method for charging or discharging a battery system is provided, wherein the battery system has a battery cell, wherein a voltage is regulated as a controlled variable using a current or a power as a set variable, wherein the current or the power is predetermined taking into account a first charge state-dependent characteristic curve and a second charge state-dependent characteristic curve, and wherein the first charge state-dependent characteristic curve and the second charge state-dependent characteristic curve have opposite slopes at least in sections.

[0009] A device for charging or discharging a battery system is also proposed, wherein the battery system has a battery cell, the device comprising a regulator, wherein the regulator is configured to regulate a voltage as a controlled variable using a current or a power as a set variable, wherein the current or the power is predetermined taking into account a first charge state-dependent characteristic curve and a second charge state-dependent characteristic curve, and wherein the first charge state-dependent characteristic curve and the second charge state-dependent characteristic curve have opposite slopes at least in sections.

[0010] The method and the device make it possible to regulate the charging or discharging based on the state of charge of the battery system as an entire system, in particular without having to know the state of the individual battery cells for this purpose. One of the basic ideas here is to use two state-of-charge-dependent characteristic curves for regulation, wherein the two characteristic curves have opposite slopes at least in sections. This makes it possible to maintain limit values ​​of electrical variables during charging and discharging, in particular in the event of an erroneous estimate of the state of charge.

[0011] The voltage, current, internal resistance and power during charging and discharging, in particular the total voltage, total current, total internal resistance and total power of the battery system. In particular, the parameters of the individual battery cells are not detected and / or used.

[0012] In particular, it is provided that the voltage at the battery system is detected, wherein this voltage is used as a control variable during the control.

[0013] In particular, it is provided that the characteristic curve predetermines a maximum value (limit value) for a suitable electrical variable which must not be exceeded. By using two characteristic curves, two such variables can be taken into account and / or used for regulation according to the method. It can be provided that during regulation, compliance with the first characteristic curve is first checked and then with the second characteristic curve. However, it can also be provided that during regulation, compliance with the second characteristic curve is first checked and then with the first characteristic curve. Furthermore, compliance with both characteristic curves can also be checked simultaneously.

[0014] The first state-of-charge-dependent characteristic curve and the second state-of-charge-dependent characteristic curve are determined in particular under laboratory conditions, in particular in empirical tests and / or with the aid of simulations. It is thereby possible, for example, to determine a characteristic curve for a maximum voltage that is dependent on the state of charge. For this purpose, measurements can be performed, for example, on a 3-electrode laboratory cell. In addition, pressure, thickness or high-precision coulomb measurements can also be performed. In addition, a predetermined current characteristic field (in particular taking into account the safety margin) can also be applied to the cell and in this way a state-of-charge-dependent characteristic curve for the maximum voltage can be determined. For example, a simulation can be performed based on a half-cell model.

[0015] The components of the device, in particular the regulator, can be designed individually or in combination as a combination of hardware and software, for example as a program code executed on a microcontroller or microprocessor. However, it can also be provided that the components are designed individually or in combination as an application specific integrated circuit (ASIC) and / or a field programmable gate array (FPGA).

[0016] In one specific embodiment, it is provided that the characteristic curve has opposite slopes in all charge states. This makes it possible to provide a particularly simple implementation of the method and the device and ensure that the limit values ​​are adhered to at all times.

[0017] In one embodiment, it is provided that the first state of charge-dependent characteristic curve predetermines a maximum voltage that increases with the state of charge during charging or discharging. This makes it possible to limit the voltage during charging and discharging. This is based on the idea that when the maximum charging or discharging current is determined for each state of charge and it is assumed that the anode potential is the limiting factor, a temperature-independent, state of charge-dependent full-cell voltage trajectory is obtained. In particular, this full-cell voltage trajectory then forms the first state of charge-dependent characteristic curve. As the state of charge increases, the full-cell voltage trajectory increases.

[0018] In one specific embodiment, it is provided that the first state-of-charge-dependent characteristic curve specifies a maximum internal resistance which increases with the state of charge during charging or discharging. In this case, the internal resistance can be calculated from the current and the overvoltage (external voltage, ie, the voltage under load minus the open-circuit voltage). In this case, the overvoltage can be estimated in a manner known per se from a model.

[0019] In one specific embodiment, it is provided that the second charge state-dependent characteristic curve specifies a maximum current which decreases with the charge state during charging or discharging. As a result, the current during charging and discharging can be limited.

[0020] In one embodiment, it is provided that the second charge state-dependent characteristic curve predetermines a maximum power which decreases with the charge state during charging or discharging. This makes it possible to limit the power during charging or discharging. In this case, the power can be a power calculated from the current and the voltage (i.e. P = U*I; where P is the power, U is the voltage, and I is the current). In principle, the power can also be a power loss, which is calculated, for example, from the internal resistance and the current (i.e. P = R*I 2 ) or by overvoltage and current (i.e. P = U Ü *I) calculated.

[0021] It can also be provided that the first charge state-dependent characteristic curve and / or the second charge state-dependent characteristic curve depicts a combination of electrical variables and / or predetermines limit values ​​for such a combination of electrical variables.

[0022] In one specific embodiment, it is provided that the temperature of the battery system is detected and / or estimated, wherein the first state-of-charge-dependent characteristic curve and / or the second state-of-charge-dependent characteristic curve are temperature-dependent, wherein the detected and / or estimated temperature is taken into account. As a result, temperature influences can be taken into account, so that the control during charging or discharging can be further improved.

[0023] In one embodiment, it is provided that the state of charge of the battery system is estimated based on the time integral of the current during charging or discharging. To this end, the state of charge estimator integrates the current flowing during charging or discharging. This provides a balanced amount of charge flowing into and / or out of the battery system. Based on the starting value and the total amount of charge that can be stored in the battery system, the current state of charge can be determined in this way. For example, the state of charge (SOC) can be indicated as a percentage or an absolute value in ampere hours (Ah) with reference to the maximum amount of charge that can be stored.

[0024] In one embodiment, it is provided that the charge state of the battery system is estimated based on an open circuit voltage state of charge (OCV / SOC) characteristic curve and / or with the aid of an electrical battery model. The open circuit voltage state of charge (OCV / SOC) characteristic curve enables the charge state to be estimated based on the measurement of the open circuit voltage of the battery system in the unloaded state. The electrical battery model allows the charge state to be estimated in a manner known per se based on measurable electrical variables (open circuit voltage, voltage, current, internal resistance, etc.). The open circuit voltage state of charge (OCV / SOC) characteristic curve and / or the electrical battery model are determined, for example, by means of measurements under laboratory conditions, i.e. by means of empirical tests and / or by means of simulations.

[0025] Further features of the embodiment of the device are derived from the description of the embodiment of the method. The advantages of the device are respectively the same as the advantages of the embodiment of the method. The embodiments of the method and device for charging and discharging a battery system having only one battery cell are in particular the same as the embodiments of the method and device for charging and discharging a battery system having a plurality of battery cells. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The present invention will be described in more detail below according to preferred embodiments with reference to the accompanying drawings. In the accompanying drawings:

[0027] FIG1 shows a schematic diagram of an embodiment of a device for charging or discharging a battery system;

[0028] 2a, 2b, 2c show schematic diagrams for explaining the mode of operation of embodiments of the method and the device;

[0029] FIG. 3 shows the results of a simulated charging process for a battery system having two battery cells connected in parallel and regulation according to the method. DETAILED DESCRIPTION

[0030] FIG. 1 shows a schematic diagram of an embodiment of a device 1 for charging or discharging a battery system 20. The battery system 20 comprises two battery cells 21 - x which are connected in parallel (alternatively also in another way), but which can only be charged and discharged together. The battery cells 21 - x are in particular lithium-ion battery cells. The device for charging and discharging a battery system having only one battery cell is designed essentially in the same way as the embodiment shown in FIG. 1 and is therefore not discussed separately.

[0031] The device 1 comprises a regulator 2. The regulator 2 is configured to regulate a (total) voltage U as a control variable, which is composed of voltages U1, U2 at the battery cells 3-x, by means of a current I or power P as a setting variable. The current I or power P is divided into currents I1, I2 or powers P1, P2 at the individual battery cells 21-x. The voltage U and the current I or power P are related to the battery system 20 as a whole system, that is, the corresponding values ​​of the individual battery cells 21-x are unknown and not detected. The voltage U at the battery system 20 is detected by means of a sensor device (not shown) provided for this purpose.

[0032] It is provided that during the control, a current I or a power P is predefined taking into account the first charge state-dependent characteristic curve 3-1 and the second charge state-dependent characteristic curve 3-2. The first charge state-dependent characteristic curve 3-1 and the second charge state-dependent characteristic curve 3-2 have opposite slopes at least in sections. The control is carried out in particular in such a way that a maximum value (limit value) predefined by the characteristic curve 3-x is not exceeded.

[0033] The state of charge SOC is estimated by means of a state of charge estimator 4 of the device 1. It can be provided that the state of charge SOC of the battery system 20 is estimated based on the time integral of the current I during charging or discharging. Alternatively or additionally, it can be provided that the state of charge SOC of the battery system 20 is estimated based on an open circuit voltage state of charge (OCV / SOC) characteristic curve and / or by means of an electrical battery model.

[0034] In the example shown, it is provided in particular that the first state-of-charge-dependent characteristic curve 3 - 1 specifies a maximum voltage Ulim which increases with the state of charge SOC during charging or discharging.

[0035] Furthermore, in the example shown, it is provided in particular that the second state-of-charge-dependent characteristic curve 3 - 2 predetermines a maximum current Ilim which decreases with the state of charge SOC during charging or discharging.

[0036] In the example shown, it is provided in particular that the characteristic curves 3 - 1 , 3 - 2 have opposite slopes at all states of charge SOC.

[0037] Alternatively, it may be provided that the first state-of-charge-dependent characteristic curve 3 - 1 specifies a maximum internal resistance which increases with the state of charge SOC during charging or discharging.

[0038] Alternatively, it may be provided that the second state-of-charge-dependent characteristic curve 3 - 2 specifies a maximum power which decreases with the state of charge SOC during charging or discharging.

[0039] It may be provided that a temperature T of the battery system 20 is detected and / or estimated, wherein the first state-of-charge-dependent characteristic curve 3 - 1 and / or the second state-of-charge-dependent characteristic curve 3 - 2 are temperature-dependent, and wherein the detected and / or estimated temperature T is taken into account. For example, it may be provided that the characteristic curve 3 - x is selected or parameterized based on the detected and / or estimated temperature T.

[0040] 2a, 2b and 2c show schematic diagrams for explaining the mode of operation of an embodiment of the method and device. Each of the three figures shows the details of the charge state at a single point in time.

[0041] In FIG. 2 a , the state of charge estimator 4 estimates a state of charge SOC which corresponds to the average value of the states of charge SOC1, SOC2 of the two battery cells 21 - x ( FIG. 1 ). For example, due to the higher temperature in the battery cell 21 - 2 compared to the battery cell 21 - 1 , the battery cell 21 - 2 has a lower internal resistance. Therefore, the (total) charging current I is divided into two partial currents I1 and I2 of unequal magnitude. The charging current I2 is greater than the charging current I2. As a result, the state of charge SOC2 of the battery cell 21 - 2 increases faster than the state of charge SOC1 of the battery cell 21 - 1 . Since the state of charge estimator 4 ( FIG. 1 ) can only detect the (total) current I or the (total) voltage U of the battery cells 21 - x connected in parallel, only the average value of the state of charge SOC obtained from the states of charge SOC1, SOC2 of the battery cells 21 - x is detected. The charge regulation by the charge regulator 2, which releases the maximum permissible voltage Ulim as a function of the state of charge SOC based on the first state-of-charge-dependent characteristic curve 3-1, will release a voltage (here Ulim) which is too great in the case of the battery cell 21-1. However, according to the method described in the present disclosure, the current I will be limited to a current Ilim which is less than Ilim1 according to the second state-of-charge-dependent characteristic curve 3-2. Since both limits are taken into account in the regulation, the result is that neither the current limit nor the voltage limit is violated. In contrast, regulation with a single characteristic curve (e.g. only with the first state-of-charge-dependent characteristic curve 3-1) will lead to an excess of the maximum voltage in the battery cell 21-1. In the case of the battery cell 21-2, an excessive current limit value (Ilim instead of Ilim2) will initially be assumed, but the voltage limit value Ulim is less than Ulim2, whereby the resulting current I is also limited. Since both limits are taken into account in the regulation, the result is that neither the current limit nor the voltage limit is violated. In contrast, control using a single characteristic curve (for example using only the second charge-state-dependent characteristic curve 3 - 2 ) would lead to an exceeding of the maximum current in the battery cell 21 - 2 .

[0042] In FIG. 2 b , the state of charge estimator 4 ( FIG. 1 ) estimates a state of charge SOC greater than the average value SOC of the states of charge SOC1 , SOC2 of the two battery cells 3 - x due to an error. A charging regulation that releases the maximum voltage U according to the state of charge SOC would release an excessively high voltage Ulim in the case of the battery cell 3 - 1 and the battery cell 3 - 2 . However, according to this method, the current is limited to Ilim by the second state of charge-dependent characteristic curve 3 - 2 , so that this value is less than Ilim1 and Ilim2 . Since both limitations are taken into account in the regulation, the result is that neither the current limit nor the voltage limit is violated. In contrast, regulation using a single characteristic curve (e.g. only using the first state of charge-dependent characteristic curve 3 - 1 ) would lead to an excess of the maximum voltage in the two battery cells 21 - 1 , 21 - 2 .

[0043] In FIG. 2 c , the state of charge estimator 4 ( FIG. 1 ) estimates a state of charge SOC that is less than the average of the states of charge SOC1 , SOC2 of the two battery cells 3 - x. The charging control would initially assume an excessively large current limit value (Ilim instead of Ilim1 and Ilim2). However, according to this method, the voltage limit value Ulim is less than Ulim1 and Ulim2, thereby also limiting the current I generated during charging. Since both limits are taken into account in the control, the result is that neither the current limit nor the voltage limit is violated. In contrast, a control using a single characteristic curve (e.g. only using the second state of charge-related characteristic curve 3 - 2 ) would result in an excess of the maximum current in the two battery cells 21 - 1 , 21 - 2.

[0044] The illustrated scenario is merely exemplary in nature and serves to illustrate the method and device described in the present disclosure. In principle, the characteristic curve 3 - x can also map other variables and / or have a different course.

[0045] FIG3 shows the results of a simulated charging process for a battery system schematically shown in FIG1 with two battery cells connected in parallel and regulation according to the method. In this case, the temperature of the battery cell is 10° C. and the temperature of the other battery cell is 50° C. The simulation parameters used are as follows:

[0046] - Cell chemistry (Zellchemie): NMC (nickel cobalt manganese)

[0047] - Battery capacity: 100 Ah

[0048] - Battery cell heat capacity: 2000 J / K

[0049] - Isothermal boundary conditions

[0050] - Heat exchange coefficient between cells connected in parallel: 0 W / K

[0051] - Initial state of charge at the start of the simulation: 5% (of maximum charge)

[0052] - Resistance of the connecting elements of cells connected in parallel: 0 Ohm

[0053] - Contact resistance: 0 Ohm

[0054] - Cell internal resistance at 10°C: 1 mOhm to 3 mOhm

[0055] - Cell internal resistance at 50°C: 0.5 mOhm to 1.5 mOhm

[0056] - The first charge state-dependent characteristic curve specifies the maximum voltage Ulim (limit voltage)

[0057] - The second charge state-dependent characteristic curve specifies the maximum current Ilim (limiting current)

[0058] In the upper left of FIG. 3 , the (total) current I, the respective maximum currents Ilim1, Ilim2, and the currents I1, I2 of the battery cells are shown in A, respectively; in the upper right, the (total) state of charge SOC and the states of charge SOC1 and SOC2 of the battery cells are shown in %; in the lower left, the (total) voltage U, the respective voltages U1, U2 at the battery cells, and the maximum voltage Ulim (limit voltage) and the maximum voltages Ulim1 and Ulim2 resulting from SOC1 and SOC2 are shown in V, respectively; in the lower right, the temperatures T1, T2 of the two battery cells are shown in ° C. The variables are shown above the time axis in seconds.

[0059] It should be noted that in particular only Ulim, I and SOC and temperature are used for regulation. In particular, I1, I2, Ulim1, Ulim2, SOC1 and SOC2 are not known in practice and are only used to illustrate the method described in the present disclosure within the scope of simulations.

[0060] It can be clearly seen that, by means of the regulation according to the method, the currents I1 , I2 always remain below the respectively associated maximum currents Ilim1 , Ilim2 . The voltages U1 , U2 also always remain below the maximum voltage Ulim.

[0061] Reference numerals list

[0062] 1 Equipment

[0063] 2 Regulator

[0064] 3-1 First charging state related characteristic curve

[0065] 3-2 Second charging state related characteristic curve

[0066] 4 Charge State Estimator

[0067] 20 battery system

[0068] 21-x battery cells

[0069] I Current

[0070] I1 current (first battery cell)

[0071] I2 current (second battery cell)

[0072] Ilim maximum current

[0073] Ilim1 maximum current (based on SOC1)

[0074] Ilim2 maximum current (based on SOC2)

[0075] P Power

[0076] P1 power (first battery cell)

[0077] P2 power (second battery cell)

[0078] SOC (total) state of charge

[0079] SOC1 State of charge (first battery cell)

[0080] SOC2 State of charge (second battery cell)

[0081] T Temperature

[0082] U (total) voltage

[0083] U1 voltage (first battery cell)

[0084] U2 voltage (second battery cell)

[0085] Ulim Maximum Voltage

[0086] Ulim1 maximum voltage (based on SOC1)

[0087] Ulim2 maximum voltage (based on SOC2)

Claims

1. A method for charging or discharging a battery system (20), in, The battery system (20) comprises at least two battery cells (21-x) connected in parallel and / or in series, wherein the battery cells can only be charged or discharged together. wherein a voltage (U) as a controlled variable is regulated by means of a current (I) or a power (P) as a set variable, wherein the current (I) or the power (P) is predetermined taking into account a first charge state-dependent characteristic curve (3-1) and a second charge state-dependent characteristic curve (3-2), and The first charge state-dependent characteristic curve (3-1) and the second charge state-dependent characteristic curve (3-2) have opposite slopes at least in sections.

2. The method according to claim 1, characterized in that The characteristic curve (3-x) has opposite slopes at all states of charge (SOC).

3. The method according to claim 1 or 2, characterized in that: The first state-of-charge-dependent characteristic curve (3-1) specifies a maximum voltage (Ulim) which increases with the state of charge (SOC) during charging or discharging.

4. The method according to claim 1 or 2, characterized in that: The first state-of-charge-dependent characteristic curve (3-1) specifies a maximum internal resistance which increases with the state of charge (SOC) during charging or discharging.

5. The method according to any one of the preceding claims, characterized in that The second state-of-charge-dependent characteristic curve (3-2) specifies a maximum current (Ilim) which decreases with the state of charge (SOC) during charging or discharging.

6. The method according to any one of claims 1 to 4, characterized in that The second state-of-charge-dependent characteristic curve (3-2) specifies a maximum power which decreases with the state of charge (SOC) during charging or discharging.

7. The method according to any one of the preceding claims, characterized in that The temperature (T) of the battery system is detected and / or estimated, wherein the first charge state-dependent characteristic curve (3-1) and / or the second charge state-dependent characteristic curve (3-2) are temperature-dependent, and wherein the detected and / or estimated temperature (T) is taken into account.

8. The method according to any one of the preceding claims, characterized in that The state of charge (SOC) of the battery system (20) is estimated based on the time integral of the current (I) during charging or discharging.

9. The method according to any one of the preceding claims, characterized in that The state of charge (SOC) of the battery system (20) is estimated based on an open circuit voltage state of charge (OCV / SOC) characteristic curve and / or with the aid of an electrical battery model.

10. A device (1) for charging or discharging a battery system (20), in, The battery system (20) comprises at least two battery cells (21-x) connected in parallel and / or in series, wherein the battery cells can only be charged or discharged together, and the device comprises: A regulator (2), wherein the regulator (2) is configured to regulate a voltage (U) as a controlled variable by means of a current (I) or a power (P) as a set variable, wherein the current (I) or the power (P) is predetermined taking into account a first charge state-dependent characteristic curve (3-1) and a second charge state-dependent characteristic curve (3-2), and The first charge state-dependent characteristic curve (3-1) and the second charge state-dependent characteristic curve (3-2) have opposite slopes at least in sections.

11. A method for charging or discharging a battery system (20), in, The battery system (20) comprises a battery cell (21-x), wherein a voltage (U) as a controlled variable is regulated by means of a current (I) or a power (P) as a set variable, wherein the current (I) or the power (P) is predetermined taking into account a first charge state-dependent characteristic curve (3-1) and a second charge state-dependent characteristic curve (3-2), and The first charge state-dependent characteristic curve (3-1) and the second charge state-dependent characteristic curve (3-2) have opposite slopes at least in sections.

12. A device (1) for charging or discharging a battery system (20), in, The battery system (20) has a battery cell (21-x), and the device comprises: A regulator (2), wherein the regulator (2) is configured to regulate a voltage (U) as a controlled variable by means of a current (I) or a power (P) as a set variable, wherein the current (I) or the power (P) is predetermined taking into account a first charge state-dependent characteristic curve (3-1) and a second charge state-dependent characteristic curve (3-2), and The first charge state-dependent characteristic curve (3-1) and the second charge state-dependent characteristic curve (3-2) have opposite slopes at least in sections.

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