Method and system for conditioning a battery module

Abstract

The invention relates to a method for conditioning a battery module (BM), in particular a battery module (BM) of a traction battery, to a predetermined target voltage (Uz). The invention also relates to an associated system. The battery module (BM) is charged or discharged (101) with a charging current (IL) by a conditioning unit (MB) or a charging apparatus (MB) until a first switch-off voltage (Ua1) is reached (102) by a voltage (Ut) which drops between a positive and a negative terminal (Kp, Kn) of the battery module (BM). When the first switch-off voltage (Ua1) is reached, the charging current (Il) is switched off and a relaxation curve between the positive and negative terminals (Kp, Kn) of the battery module (BM) is measured (103) by the conditioning unit (MB) for a predetermined period of time. A model of the battery module (BM) is derived (104) from this measured relaxation curve by an analysis unit (AE), by means of which model the entire relaxation curve is determined (105). A second switch-off voltage (Ua2) is then identified (105) from the entire determined relaxation curve by the analysis unit (AE) such that, after the charging current (IL) has been switched off when the second switch-off voltage (Ua2) has been reached, the predetermined target voltage (Uz) is adopted as the open-circuit voltage of the battery module (BM). The battery module (BM) is then charged or discharged further with the charging current (IL) until the second switch-off voltage (Ua2) is reached (107) by the voltage (Ut) which drops between the positive and negative terminal (Kp, Kn) of the battery module (BM). The charging current (IL) is then switched off and the predetermined target voltage (Uz) is obtained (108) at the battery module (BM) as a result of the relaxation curve.

Description

[0001] Method and system for conditioning a battery module

[0002] Technical area

[0003] The present invention relates to a method for conditioning a battery module, in particular a battery module of a traction battery, to a predetermined target voltage. Furthermore, the present invention relates to an associated system for carrying out the method for conditioning the battery module.

[0004] State of the art

[0005] Today, as in many electrically powered systems (e.g., mobile phones, electronic devices, etc.), rechargeable batteries, or so-called secondary batteries, are also used in electrically powered vehicles. Electric vehicles or hybrid vehicles typically have a high-voltage battery in the drivetrain, in addition to an electric drive unit or motor for propelling the vehicle. This high-voltage battery acts as a drive or traction battery and supplies electrical energy to the vehicle's electric drive unit. These batteries are typically rechargeable and usually comprise several interconnected battery modules.

[0006] Such battery modules consist, for example, of anything from a few to a large number of parallel and serially connected accumulator cells or cell blocks. Traction batteries are differentiated according to the materials used for the accumulator cells. For example, lead-acid accumulator systems, nickel-cadmium accumulator systems, lithium-ion accumulator systems, etc., can be used as traction batteries in electrically powered vehicles.

[0007] If a defective battery module is detected in the drive battery of a hybrid or electric vehicle, it is usually necessary to replace the defective battery module with a new one. Battery modules are typically stored in a state designed for optimal, long-term storage—e.g., at a state of charge of 30%, etc. Before installation in an electrically powered vehicle, however, a new battery module must be adjusted to the state of charge—the so-called state of charge (SoC)—of the other battery modules in the drive battery so that the drive battery can be activated after the battery module is replaced, and the entire battery system in the vehicle functions properly.

[0008] Before installation and commissioning in practical operation, the battery module is therefore subjected to a special charging process (i.e. a special charging or discharging), which is also referred to as "conditioning". For this special process, which prepares the battery module for installation, a so-called conditioning unit or a module conditioning system can be used, for example. The battery module to be installed is connected to the conditioning unit, for example via connecting cables, and is brought to a desired charge level, e.g. by appropriate charging or discharging, and thus adjusted to the current charge level of the battery modules of the drive battery. The conditioning unit specifies a target voltage which corresponds to the charge level desired for the battery module. The target voltage is, for example, a voltage which, after the end of the conditioning process - i.e.after the charging or discharging process - results in the steady-state open-circuit voltage of the battery module. Open-circuit voltage is defined as a voltage that depends on the respective state of charge and is present between a positive and a negative terminal of the battery module without a connected load. The open-circuit voltage that occurs in the steady-state is also referred to as the resting voltage of the battery module.

[0009] Different charging methods can be used to charge rechargeable battery modules. The charging methods differ in that they control the current and voltage when charging the battery module. Battery modules are usually charged using a constant current or a constant voltage. For battery modules such as lithium-ion accumulator systems, a so-called IU charging method is used. The IU method combines the constant current charging method with the constant voltage charging method and is also referred to as the “constant current constant voltage” or CCCV method for short. With the CCCV method, charging is first carried out with a constant charging current until a predetermined voltage limit, e.g. a final charging voltage, is reached between the terminals of the battery module - usually with a charging unit or charger connected.

[0010] Conditioning unit - is reached. Charging then continues at a constant voltage, with the charging current automatically decreasing towards the end of the charging process. If the charging current reaches or falls below a defined current limit, or if a predefined time period has elapsed, charging of the battery module is terminated. While the CCCV process ensures that a maximum permissible voltage and a charging current - usually recommended by the manufacturer - are not exceeded, this charging process requires a great deal of time to charge a battery module to a desired charge level or to set a resting voltage specified as the target voltage.

[0011] Furthermore, it may be necessary to perform a targeted discharge process in order to achieve a specified target voltage on the battery module or a desired depth of discharge (DoD) of the battery module. However, deviations from the specified target voltage can also occur during this process. After the discharge process has ended, for example, after a discharge current has been switched off, the voltage between the terminals of the battery module increases until the open-circuit voltage is reached. This voltage change after the discharge has ended also causes a deviation from the specified target voltage. The open-circuit voltage that occurs on the battery module is then usually higher than the desired target voltage.

[0012] For example, WO 2020 / 227821 A1 discloses an adapted charging method for a battery to accelerate charging. For this purpose, at least one discharge pulse is applied to the battery during a charging process, and a first relaxation voltage value is measured during a relaxation process following the discharge pulse, followed by a second relaxation voltage value after a predetermined waiting time. Charging parameters for the charging process are then adjusted based on the difference between the two measured voltage values. This can be used to accelerate the battery's charging process using the method described in WO 2020 / 227821 A1. However, it is hardly possible to specify a desired target voltage for the battery, which should be reached as the resting voltage after charging.

[0013] From the document US 2018 / 0145527 A1, a charging method for a battery is also known in order to accelerate the charging of a battery, in which battery aging is additionally taken into account by adapting a switch-off criterion for ending a charging process of the battery after each charging process or after a predetermined number of charging processes.

[0014] Description of the invention

[0015] The invention is therefore based on the object of specifying a method and an associated system which make it possible to set a predetermined target voltage on a battery module in a time-efficient manner and with relatively high accuracy.

[0016] This object is achieved by a method and a system according to the independent claims. Advantageous embodiments of the present invention are described in the dependent claims.

[0017] According to the invention, the object is achieved by a method of the type mentioned at the outset, in which a battery module is charged or discharged with a charging current until a first cut-off voltage is reached from a voltage drop between a positive and a negative terminal of the battery module. After the first cut-off voltage is reached, the charging current is switched off and a relaxation curve between the positive and negative terminals of the battery module is measured over a predetermined period of time. A model of the battery module is derived from the measured relaxation curve and the entire relaxation curve is determined using this model. A second cut-off voltage is determined from the determined relaxation curve in such a way that after the charging current is switched off, the predetermined target voltage is established as the rest voltage of the battery module at the second cut-off voltage.The battery module is then charged or discharged with the charging current until the voltage drop between the positive and negative terminals of the battery module reaches the second cutoff voltage. Preferably, the battery module is charged or discharged with a constant charging current.

[0018] The main aspect of the solution proposed according to the invention is that the battery module can be charged or discharged with a certain predetermined, preferably constant, charging current. This significantly accelerates the charging or discharging of the battery module to a desired charge or discharge state. Furthermore, with the aid of the method according to the invention - especially by using the model of the battery module determined from a measured section of the relaxation curve, the entire relaxation curve determined using the model, and on the basis of the second cut-off voltage derived therefrom - the predetermined target voltage can be set on the battery module with relatively high accuracy after completion of the charging or discharging process. After the charging current is switched off upon reaching the second cut-off voltage, the battery module relaxes, and the predetermined target voltage is established relatively precisely as the resting voltage on the battery module.

[0019] For a charging process, the first cut-off voltage is expediently specified in such a way that a resting voltage, which arises after the relaxation curve for the first cut-off voltage at the battery module, is lower than the specified target voltage. Analogously, for a discharging process, the first cut-off voltage can be specified in such a way that a resting voltage, which arises after the relaxation curve for the first cut-off voltage at the battery module, is higher than the specified target voltage. It is important that the first cut-off voltage for the battery module to be charged or discharged is selected such that the first cut-off voltage is close to the specified target voltage, so that a relaxation curve is subsequently measured between the positive and negative terminals of the battery module that approximately corresponds to the relaxation curve to the target voltage as the resting voltage.For this purpose, the first cut-off voltage can be selected, for example, so that it lies within a predeterminable range above and / or below the predeterminable target voltage or, for example, deviates from the target voltage by a predeterminable percentage. The predeterminable range or the predeterminable percentage can be determined, for example, based on empirical values. Furthermore, the first cut-off voltage can be adjusted during the use of the method based on measured data (e.g., terminal voltage during the method, measured relaxation curves, etc.) for different battery module types and predeterminable target voltages in order to charge or discharge the battery module to be conditioned even more precisely to the desired charge or discharge state.

[0020] Furthermore, it is advantageous to use an electrical equivalent circuit diagram of the battery module for the model, which is parameterized using an adaptive calculation method based on the measured relaxation curve. This makes it easy to approximate and simulate the properties and behavior of the battery module as accurately as possible, thus allowing the specified target voltage on the battery module to be set as precisely as possible.

[0021] It is advantageous to use a least-squares method as an adaptive calculation method for parameterizing the battery module's electrical equivalent circuit. This method can be used to examine real data—such as the measured section of the relaxation curve. Assuming that the measured data are close to the underlying "correct" data and that a certain relationship exists between the measured data, this method can be used to find a function that describes this relationship as accurately as possible. This means an equivalent circuit or a function that describes the properties of the battery module as accurately as possible.

[0022] A practical embodiment of the invention provides that, for parameterizing the electrical equivalent circuit of the battery module, upper and lower limit values ​​are specified for each of the parameters of the equivalent circuit of the battery module. Specifying limit values ​​simply prevents the parameters of the equivalent circuit from assuming unrealistic values. For example, this prevents voltages and / or time constants from being assumed to be values ​​less than zero.

[0023] In a further aspect, the invention also relates to a system for conditioning a battery module to a predetermined target voltage, which system has at least one conditioning unit and one analysis unit, wherein the system can be used to charge or discharge a battery module to a predetermined target voltage efficiently and in a time-saving manner.

[0024] For this purpose, the conditioning unit can be connected to the positive and negative terminals of the battery module via connecting cables. Furthermore, the conditioning unit is configured to measure a voltage drop between the positive and negative terminals of the battery module and compare it with a first cut-off voltage and a second cut-off voltage; to switch off a charging current when the first and second cut-off voltages are reached, and to measure a relaxation curve between the positive and negative terminals of the battery module for a predetermined period of time.

[0025] The analysis unit is configured to derive a model of the battery module from the relaxation curve measured by the conditioning unit for the specified period of time, which model can be used to determine the entire relaxation curve, and to determine a second cutoff voltage from the entire relaxation curve. The analysis unit can be implemented as a standalone unit and have a communication connection with the conditioning unit. This allows the analysis unit to be easily used with different conditioning units or to be easily exchanged.

[0026] Alternatively, the analysis unit can also be integrated into the conditioning unit. This would form a single unit, which would be easy to handle or transport, for example.

[0027] Ideally, upper and lower limit values, which are used for parameterizing the model of the battery module in the course of the method according to the invention, can be stored in the analysis unit. For this purpose, the analysis unit can have, for example, a memory unit or a memory area. It would also be conceivable for the limit values ​​for parameterization to be entered, for example, via an input / output unit and then stored in the analysis unit. Furthermore, measurement data (e.g. voltage curves, relaxation curves, etc.) for, for example, different battery module types and target voltages can be stored in the memory unit or in the memory area, which data can then be used, for example, for analysis purposes and / or for adapting the first cut-off voltage. Alternatively, this data could also be stored directly in the conditioning unit.

[0028] A suitable embodiment of the invention provides that the conditioning unit has a temperature sensor with which the current battery temperature can be determined. This allows, for example, temperature-dependent behavior of the battery module—e.g., different relaxation curves at different temperatures, etc.—to be taken into account when conditioning the battery module.

[0029] Brief description of the figures. The present invention is explained in more detail below with reference to Figures 1 to 4, which show exemplary, schematic, and non-limiting advantageous embodiments of the invention. Herein:

[0030] Fig. 1 shows a sequence of the method according to the invention for conditioning a battery module

[0031] Fig. 2 a simplified electrical equivalent circuit diagram of the battery module

[0032] Fig. 3 shows a curve of current and voltage during a charging process of the battery module according to the method according to the invention

[0033] Fig. 4 a system for carrying out the method according to the invention for conditioning a battery module

[0034] Implementation of the invention

[0035] Figure 1 shows an example of the process for conditioning a battery module BM. For this purpose, for example, terminals Kp, Kn of the battery module BM—i.e., a positive terminal Kp and a negative terminal Kn of the battery module BM—are connected via connecting lines L to a conditioning unit MB or a charger MB. The conditioning unit MB or the charger MB provides a charging current II, with which the battery module BM can then be charged to a predetermined target voltage Uz and thus to a desired state of charge or discharged to a desired depth of discharge.

[0036] To start the method, a charging current l is switched on for a first charging step 101. The charging current l is predetermined, for example in terms of magnitude or as a temporal profile of a current, and can be, for example, a constant charging current l . In this case, for example, a maximum permissible charging current l is selected for the respective battery module BM, which can be predetermined, for example, by the manufacturer and / or a battery type used, which can accelerate charging or discharging. During the first charging step 101, the battery module BM is charged accordingly with the charging current l during a charging process or discharged accordingly during a discharging process.

[0037] Furthermore, during the first charging step 101 and the further process, a voltage Ut dropping between the positive and the negative terminal Kp, Kn of the battery module BM is continuously measured.

[0038] In a first test step 102, a check is carried out to determine whether the measured voltage Ut reaches a first cut-off voltage Ua1. If it is determined in the first test step 102 that the voltage Ut measured between the positive and negative terminals Kn, Kp of the battery module BM reaches the first cut-off voltage Ua1, the charging current I is switched off. This triggers a relaxation process in the battery module BM. In a measuring step 103, a profile of the relaxation process or a relaxation profile for a predetermined period of time is measured, for example by the conditioning unit MB or by the charger MB. For this purpose, for example, a profile of the voltage lit dropping between the positive and negative terminals Kp, Kn of the battery module BM is recorded during the predetermined period of time. A section of the relaxation profile of the battery module BM is obtained as the result of the measuring step 103.

[0039] The first cut-off voltage Ua1, at which the charging current l is switched off, is selected, for example, for a charging process such that, after an entire relaxation process, an open-circuit voltage would arise at the battery module BM which is lower than the specified target voltage. Analogously, for a discharging process, for example, a first cut-off voltage Ua1 is selected such that, after an entire relaxation process, an open-circuit voltage would arise at the battery module BM which is higher than the target voltage. The first cut-off voltage Ua1 can be selected, for example, based on empirical values ​​for the battery module BM to be conditioned. For example, a voltage value can be selected for the first cut-off voltage Ua1 which lies within a specifiable range above and / or below the specified target voltage Uz or which deviates from the specified target voltage Uz by a specifiable percentage.When selecting the first cut-off voltage Ua1, it is important that it is close to the specified target voltage Uz so that the battery module has approximately the same relaxation behavior.

[0040] The first cut-off voltage Ua1 can also be adapted over time for different battery module types and specified target voltages Uz or charge or discharge states. For example, the first cut-off voltage Ua1 can be specified as listed above for the first charging or discharging process of a battery module type to a specified target voltage Uz. Each time the conditioning process is carried out for the respective battery module type, data (e.g. voltage curve between the terminals Kp, Kn, relaxation curve, etc.) can be collected and subsequently evaluated. The first cut-off voltage Ua1 can then be adjusted based on this measured data in order to set the specified target voltage Uz on the battery module BM even more precisely.

[0041] The time period during which the relaxation curve or the voltage Ut curve between the positive and negative terminals Kp, Kn of the battery module BM is measured in measurement step 103 can be specified as a few minutes, e.g., ideally two minutes. Since the most significant changes in the relaxation curve (e.g., transient voltage drop during charging, transient voltage increase during discharging, etc.) usually occur immediately after the charging current I is switched off, the specified time period is selected such that these changes are captured in the measured relaxation curve.

[0042] From the measured relaxation curve, a model for the battery module BM can then be derived in a modeling step 104, which represents a good approximation of the behavior of the battery module BM. As a starting point for the model of the battery module BM, for example, an electrical equivalent circuit is used, which allows the properties and behavior of the battery module BM to be approximated as accurately as possible.

[0043] Figure 2 shows, for example, such a simplified electrical equivalent circuit diagram, which is used, for example, in modeling step 104 to derive the model of the battery module BM.

[0044] This equivalent circuit diagram shows, for example, an ideal voltage source lloc, which describes an open circuit voltage lloc of the battery module BM. The open circuit voltage Uoc depends on the current state of charge of the battery module BM and is higher the more the battery module BM is charged. A resistor Ro, which describes an internal resistance Ro of the battery module, is arranged in series with the voltage source Uoc. The resistance Ro also depends on the current state of charge of the battery module BM. A value for the internal resistance Ro can, for example, be determined from the measurement of the relaxation curve in measurement step 103 - e.g. from a voltage jump at the start of the measurement. Alternatively, the value of the internal resistance Ro can, for example, also be taken from data sheets for the respective battery module BM. A current l describes the charging current l of the battery module BM.Depending on the sign of the current l, the battery module BM is either charged or discharged. A time-dependent voltage Ut drops between a positive terminal Kp and a negative terminal Kn of the equivalent circuit. This voltage Ut corresponds to the open-circuit voltage Uoc when the battery module is fully relaxed—i.e., in a steady state and no load is connected between the terminals Kp and Kn.

[0045] Furthermore, several RC elements R1C1, ..., RiCi are arranged in series between the internal resistance Ro and the positive terminal Kp of the battery module BM. The RC elements R1C1, ..., RiCi each have a parallel connection consisting of a resistor R1, ..., Ri and a capacitor C1, ..., Ci. The respective capacitors C1, ..., Ci represent a capacitive behavior inside the battery module BM. The resistances R1, ..., Ri result from charge transport inside the battery module BM. The RC elements R1C1, ..., RiCi are used in the equivalent circuit to be able to model a dynamic or time-dependent behavior of the battery module BM, such as a relaxation behavior of the battery module BM, with corresponding time constants. For a good approximation of the relaxation behavior, at least two RC elements R1C1, R2C2 are provided in the equivalent circuit.In order to achieve good accuracy with the lowest possible computational effort, three RC elements R1C1, ... , R3C3 are provided in the equivalent circuit diagram.

[0046] In modeling step 104, for example, a model of the battery module BM is determined based on a simplified, electrical equivalent circuit diagram—as shown in Figure 2. For this purpose, the equivalent circuit diagram of the battery module BM is parameterized using the relaxation curve measured in measurement step 103. This means that suitable parameter values ​​for the open-circuit voltage Uoc, the internal resistance Ro, and for the RC elements R1C1, ..., RiCi used for the equivalent circuit diagram are derived from the measured section of the relaxation curve.

[0047] For example, a so-called least-squares method is used to calculate the appropriate parameter values. The least-squares method derives its optimality criterion directly from the known data, such as the section of the relaxation curve measured in measurement step 103. This criterion describes a deterministic error function, which consists of the sum of the squared deviations of the given function, which is why the method is also called the method of least error squares in German. The calculation of appropriate parameter values ​​from the measured section of the relaxation curve using the least-squares method can be carried out using calculation software such as GNU Octave. GNU Octave is free software for numerically solving mathematical problems (e.g., matrix calculations, (differential) systems of equations, integration, etc.).

[0048] In order to be able to determine the parameter values ​​for the electrical equivalent circuit of the battery module BM and thus the model of the battery module BM from the measured section of the relaxation curve, the relaxation curve after a charging process for the electrical equivalent circuit with, for example, three RC elements R1C1, ... , R3C3 is described with the following formula:

[0049] Here, the following are used:

[0050] Ut is a time-dependent voltage between the terminals Kp, Kn of the battery module BM;

[0051] Uoc and Uo are the open-circuit voltage and rest voltage, respectively, to which the relaxation curve drops after a long time; ILO is the charging current l with which the battery module BM was charged until the first cut-off voltage Ua1 was reached;

[0052] R1, R2, R3 resistance values ​​of the RC elements in the equivalent circuit;

[0053] - C1, C2, C3 capacitance values ​​of the RC elements in the equivalent circuit;

[0054] - t is a time variable; and

[0055] - e is Euler's number.

[0056] This formula can be simplified by summarizing the respective resistance values ​​R1, R2, R3 and capacitance values ​​C1, C2, C3 to form time constants T1, T2, T3. Based on the time constants T1, T2, T3, it can be estimated how long the respective RC element R1, C1, ..., R3, C3 needs until the voltage drop ILO*R1, ILO*R2, ILO*R3 across the respective RC element R1, C1, ..., R3, C3 has discharged. The products of the current ILO and the respective resistance value R1, R2, R3 can be summarised to form voltage drops U1, U2, U3 across the respective RC element R1, C1, ..., R3, C3. This results in a simplified formula for the time-dependent voltage lit between the terminals Kp, Kn, which describes the relaxation curve of the battery module BM after a charging process:

[0057] Using this simplified formula and the section of the relaxation curve measured in measurement step 103, parameter values ​​for the voltages Uo, U1, U2, U3 and for the time constants T1, T2, T3 can then be determined. To ensure that these parameter values ​​cannot assume unrealistic values ​​(e.g. negative values, etc.), upper and lower limit values ​​are defined for the individual parameter values ​​of the voltages Uo, U1, U2, U3 and time constants T1, T2, T3. By specifying upper and lower limit values, additional roles for the individual parameters can be defined. For example, the parameter value of the voltage Uo specifies a voltage value to which the voltage Ut drops after a long time. This voltage value Uo therefore corresponds to the open-circuit voltage of the battery module BM.An upper limit and a lower limit of the voltage Uo are determined, for example, as a percentage of a first measured value of the voltage Ut after a transient voltage drop after switching off the charging current I. In other words, for the limit values ​​of the voltage Uo, the first measured value of the relaxation curve measured in measurement step 103 after the transient voltage drop is used.

[0058] The parameter values ​​of the voltages U1, U2, U3 and the corresponding time constants T1, T2, T3 largely determine the respective exponential voltage drops, whereby, for example, a first voltage U1 and a first time constant T1 describe a first, fast range of the voltage drop, a second voltage U2 and a second time constant T2 describe a second, medium range of the voltage drop and a third voltage U3 and a third time constant T3 describe a third, slow range of the voltage drop in the relaxation curve after the charging process of the battery module Bm. The lower limit for the parameter values ​​of the voltages U1, U2, U3 is, for example, a value of zero in order to avoid negative voltage values. A value of 1 volt can be selected as the upper limit for the voltage parameters U1, U2, U3, for example.Depending on the battery module BM to be conditioned and its properties, other voltage values ​​can also be used for the upper limit of the respective voltage parameter U1, U2, U3. The upper and lower limits of the time constants T1, T2, T3 can, for example, be specified in such a way that the respective range of the voltage drop (i.e., fast, medium, or slow) is taken into account accordingly.

[0059] Analogous to the modeling of the relaxation curve of the battery module BM after a charging process, a relaxation curve for the battery module after a discharging process can also be modeled in modeling step 104. For this purpose, a section of the relaxation curve measured in measurement step 103 for the specified period of time (e.g., 2 minutes) – this time after switching off the charging current l during the discharging process – as well as the simplified electrical equivalent circuit of the battery module BM described above are also used. The corresponding parameter values ​​are then determined, for example, again using the least squares method. For this purpose, the following formula for the time-dependent voltage Ut at the terminals Kp, Kn of the battery module BM can be used, for example:

[0060] The voltage Uo indicates a voltage value that largely corresponds to the open-circuit voltage of the battery module BM or to which the time-dependent voltage Ut rises after a long period of time. The voltage parameters U1, U2, U3 and the time constants T1, T2, T3 each determine exponential voltage increases, distinguishing between a fast, medium, and slow range of the voltage increase. To determine the model of the battery module BM during the discharge process, appropriately adapted upper and lower limit values ​​can also be specified for the parameter values ​​of the voltages U1, U2, U3 and the time constants T1, T2, T3.After the parameter values ​​for the voltages 11o, U1, U2, U3 and time constants T1, T2, T3 have been determined in modeling step 104, for example by means of the least square method from the section of the relaxation curve measured in measurement step 103, the entire relaxation curve for the respective charging process or for the respective discharging process of the battery module BM can be determined in a simulation step 105. This means that the curve of the time-dependent voltage lit from the switching off of the charging current l until the reaching of the open-circuit voltage Uo between the terminals Kp, Kn of the battery module BM is simulated. From this determined, entire relaxation curve, an overall difference can be determined between the voltage when the charging current l is switched off at the terminals Kp, Kn of the battery module BM - ie the first switch-off voltage Ua1 - and a voltage that has developed at the battery module BM after a long period of time (e.g.at least one hour up to several hours). From this, a second cut-off voltage Ua2 can then be determined in simulation step 105 such that after the charging current I is switched off at the second cut-off voltage Ua2, the predetermined target voltage Uz is assumed to be the resting voltage of the battery module.

[0061] In a second charging step 106, the battery module BM is further charged or discharged with the charging current l , which corresponds, for example, to the maximum permissible charging current l for the battery module BM. In a second test step 107, it is checked whether the voltage Ut, which drops between the positive and negative terminals Kp, Kn of the battery module BM and is continuously measured, reaches the second cutoff voltage Ua2 determined in simulation step 105.

[0062] If it is determined in the second test step 107 that the second cut-off voltage Ua2 is reached by the voltage Ut dropping between the positive and negative terminals Kp, Kn, the charging current l is switched off again or permanently in a switch-off step 108. After the charging current l is switched off, a relaxation process begins again in the battery module BM. In the process, the voltage Ut at the battery module BM drops in the switch-off step 108 after the charging process to a rest voltage which corresponds to the specified target voltage Uz. After a discharging process, the voltage Ut at the battery module BM rises to a rest voltage which corresponds to the specified target voltage Uz after the charging current l is switched off in the switch-off step 108.

[0063] Figure 3 shows, by way of example, a time profile of the voltage Ut between the positive terminal Kp and the negative terminal Kn of the battery module, as well as a time profile of the charging current l, which is constant here, during a charging process of the battery module BM. The conditioning method according to the invention is used to charge the battery module BM to a desired charge level or to set the predefined target voltage Uz. Time t is plotted on a horizontal axis. Voltage U and current I are plotted on a vertical axis. Furthermore, the predefined target voltage Uz, which is to be established as the resting voltage at the battery module BM after completion of the exemplary charging process, as well as the first cut-off voltage Ua1 and the second cut-off voltage Ua2 are plotted on the vertical axis. Furthermore, a maximum charging current value l permissible for the battery module BM is plotted on the vertical axis. max is drawn.

[0064] For example, at a starting time tO, the charging process of the battery module BM is started. For this purpose, the charging current l is switched on at the starting time tO in order to charge the battery module BM, for example, with the maximum permissible value l max for the charging current l. As a result, the time-dependent voltage Ut between the positive and negative terminals Kp, Kn of the battery module BM begins to rise. If the time-dependent voltage Ut reaches the first cut-off voltage Ua1 at a first time t1, the charging current l is switched off. The time period from the start time t0 to the first time t1 thus corresponds to the first charging step 101. The cut-off voltage Ua1, in order to end the first charging step 101 at the first time t1, is selected such that for the first cut-off voltage Ua1, after an entire relaxation process, an open-circuit voltage is set which is below the target voltage Uz. When selecting the first cut-off voltage Ua1, it is also important that it is close to the specified target voltage Uz so that the battery module BM has approximately the same relaxation behavior as with the target voltage Uz.In Figure 3, for example, a voltage value was selected for the first cut-off voltage Ua1 that is a few millivolts above the target voltage Uz, for example, within a predefined range. It would also be conceivable to select a voltage value for the first cut-off voltage Ua1 that is a few millivolts below the target voltage Uz, for example, within a predefined range.

[0065] By switching off the charging current I at the first time t1, a relaxation process is generated in the battery module BM and the voltage Ut begins to fall as a result of the relaxation process. The relaxation curve or the curve of the voltage Ut is measured in measuring step 103 for a predetermined period of time (e.g. two minutes). The measuring step 103 is started, for example, at the first time t1 and ended after the predetermined period of time at a second time t2. From the section of the relaxation curve measured between the first time t1 and the second time t2, the model of the battery module BM is then determined in modeling step 104, with which the entire relaxation curve of the battery module for a desired state of charge as well as the second switch-off voltage Ua2 can be determined in simulation step 105.

[0066] At the second time t2, the charging current l is switched on again in order to continue charging the battery module with the maximum permissible value lmax of the charging current l. This means that at the second time t2, the second charging step 106 begins. The battery module BM continues to be charged until the voltage lt reaches the second cut-off voltage Ua2 at a third time t3. At the third time t3, the charging current l is then finally switched off. From the third time t3, or after the charging current l is switched off, the voltage Ut drops - in accordance with the relaxation curve - towards the rest voltage, which corresponds to the specified target voltage Uz. The charging process can - as shown in Figure 3 - be continued with the maximum permissible charging current l max can be carried out in a time-efficient manner, with the voltage Ut dropping to the specified target voltage Uz with relatively high accuracy after the charging process is completed. However, during the charging process, it must be ensured that the second cut-off voltage Ua2 remains within a permissible voltage range for the battery module BM, since the battery module is overcharged up to this voltage value Ua2.

[0067] Figure 4 shows, by way of example and schematically, a system which is set up to carry out the conditioning method shown by way of example in Figure 1 for a battery module BM, in particular a battery module BM for a traction or drive battery. The battery module BM can be connected to a conditioning unit MB or a charging device MB via connecting lines L for a conditioning process - i.e. for charging or discharging to a desired state of charge or to a desired depth of discharge. For this purpose, for example, a positive connection Kp and a negative connection Kn of the battery module BM are each connected to the conditioning unit MB via a connecting line L in order to set the predetermined target voltage Uz on the battery module BM by appropriately charging or discharging the battery module BM. The target voltage Uz should be reached after the corresponding charging or discharging process has ended.During the discharge process in the steady state of the battery module BM, the open-circuit voltage drops between the positive terminal Kp and the negative terminal Kn.

[0068] To carry out the method, the conditioning unit MB is configured - in addition to charging or discharging the battery module BM with the charging current l - to measure the voltage Ut which changes over time as a result of the respective charging or discharging process, wherein the voltage Ut drops between the positive terminal Kp and the negative terminal Kn of the battery module BM. Furthermore, the conditioning unit MB compares the measured voltage Ut, e.g. in the first test step 102, with the first cut-off voltage Ua1 and in the second test step 107 with the second cut-off voltage Ua2, in order to switch off the charging current l when the first and second cut-off voltages Ua1 and Ua2 are reached, respectively. Furthermore, the conditioning unit MB is configured to determine a relaxation curve after switching off the charging current l when the first cut-off voltage Ua1 is reached - i.e.to measure the voltage lit between the positive and negative terminals Kp, Kn of the battery module BM - for a specified period of time.

[0069] Furthermore, the conditioning unit MB can be equipped with a temperature sensor (e.g., an infrared temperature sensor). This temperature sensor can be used, for example, to determine and monitor the current battery temperature. The determined temperature of the battery module BM can then be incorporated into the conditioning process, for example, to achieve the specified target voltage Uz even more precisely.

[0070] The system also has an analysis unit AE, which can be designed as a standalone unit, for example, and is connected to the conditioning unit MB via a communication link KV. Alternatively, the analysis unit AE can also be integrated into the conditioning unit MB. The analysis unit AE is designed to derive a model of the battery module BM from a section of the relaxation curve measured by the conditioning unit MB for the specified period of time. To do this, the analysis unit AE can, for example, use a simplified, electrical equivalent circuit diagram of the battery module BM, which is shown, for example, in Figure 2, and determine parameter values ​​for this using an adaptive calculation method, such as the least squares method.For the parameterization of the equivalent circuit diagram, upper and lower limit values ​​for the respective parameters can be stored in the analysis unit AE, for example, in a storage unit SE, which are adapted, for example, to common, desired states of charge (e.g., SoC 60%) or depths of discharge (e.g., DoD 30%) of the battery module BM. The storage unit SE can, for example, be integrated into the analysis unit AE or be designed as an external storage unit SE that is connected to the analysis unit AE.

[0071] Furthermore, the analysis unit AE is configured to use the derived model of the battery module BM to determine or simulate the entire relaxation curve—i.e., the entire curve of the voltage Ut between the positive and negative terminals Kp, Kn from the first disconnection of the charging current l at the first disconnection voltage Ua1 until the open-circuit voltage is reached at the battery module BM. From the determined or simulated entire relaxation curve, the analysis unit AE then determines the second disconnection voltage Ua2 and can forward this, for example, to the conditioning unit MB, which can then continue the conditioning process up to the second disconnection voltage Ua2.

Claims

Patent claims 1. Method for conditioning a battery module (BM), in particular a battery module (BM) of a traction battery, to a predetermined target voltage (Uz), characterized in that the battery module (BM) is charged or discharged with a charging current (l) (101) until a first cut-off voltage (Ua1) is reached from a voltage (Ut) which drops between a positive and a negative terminal (Kp, Kn) of the battery module (BM) (102), that the charging current (l) is switched off and a relaxation profile is measured between the positive and negative terminals (Kp, Kn) of the battery module (BM) for a predetermined period of time (103), that a model of the battery module (BM) is derived from the measured relaxation profile (104), that the entire relaxation profile is determined using the model of the battery module (BM) and a second cut-off voltage (Ua2) is determined from the entire relaxation profile (105),that after switching off the charging current (l ) upon reaching the second cut-off voltage (Ua2), the specified target voltage (Uz) is assumed to be the resting voltage of the battery module (BM), and that the battery module (BM) continues to be charged or discharged with the charging current (l ) (106) until the voltage (Ut) dropping between the positive and negative terminals (Kp, Kn) of the battery module (BM) reaches the second cut-off voltage (Ua2) (107).

2. Method according to claim 1, characterized in that the battery module (BM) is charged or discharged with a constant charging current (l ).

3. The method of claim 1, characterized in that, for a charging process, the first cut-off voltage (Ua1) is specified such that the resting voltage established for the first cut-off voltage (Ua1) according to the relaxation curve is lower than the specified target voltage. (102) 4. The method of claim 1, characterized in that, for a discharge process, the first cut-off voltage (Ua1) is predetermined such that the open-circuit voltage resulting from the relaxation process for the first cut-off voltage (Ua1) is greater than the predetermined target voltage (Uz). (102) 5. Method according to one of the preceding claims, characterized in that for the model of the battery module (BM) an electrical equivalent circuit of the battery module (BM) is used, which is parameterized by means of an adaptive calculation method on the basis of the measured relaxation curve (104).

6. Method according to claim 5, characterized in that a least-squares method is used as the adaptive computation method (104).

7. Method according to claim 5 or 6, characterized in that upper limits and lower limits are specified for each parameter of the equivalent circuit of the battery module (BM) for parameterizing the electrical equivalent circuit (104).

8. System for conditioning a battery module (BM), in particular a battery module (BM) of a traction battery, to a predetermined target voltage (Uz), characterized in that, at least, the following are provided: - a conditioning unit (MB) which can be connected via connecting leads (L) to a positive terminal (Kp) and a negative terminal (Kp) of the battery module (BM), and which is configured at least to measure a voltage drop (Ut) between the positive and negative terminals (Kp, Kn) of the battery module (BM) and to compare it with a first cut-off voltage (Ua1) and a second cut-off voltage (Ua2); to switch off a charging current (l) when the first and second cut-off voltages (Ua1, Ua2) are reached and to measure a relaxation curve between the positive and negative terminals (Kp, Kn) of the battery module (BM) for a predetermined period of time; and - an analysis unit (AE) which is at least equipped to derive a model of the battery module (BM) from the relaxation profile measured by the conditioning unit (MB) for the specified time period, with which the entire relaxation profile can be determined, and to determine a second cut-off voltage (Ua2) from the entire relaxation profile.

9. System according to claim 8, characterized in that the analysis unit (AE) is designed as an independent unit, wherein the analysis unit (AE) has a communication link (CT) with the conditioning unit (CB).

10. System according to claim 8, characterized in that the analysis unit (AE) is integrated into the conditioning unit (MB).

11. System according to one of claims 8 to 10, characterized in that upper and lower limits for parameterizing the battery module model are stored in the analysis unit (AE).

12. System according to one of claims 8 to 11, characterized in that the conditioning unit (MB) has a temperature sensor for determining a current battery temperature.

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