Method and system for adjusting a battery module

Abstract

The invention relates to a method for adjusting a battery module (BM), in particular a battery module (BM) of a traction battery, to a predetermined target voltage (Uz), and to an associated system. A control unit (MB) or a charger (MB) charges or discharges the battery module (BM) with a charging current (IL) (101) until a voltage (Ut) falling between the positive and negative terminals (Kp, Kn) of the battery module (BM) reaches a first turn-off voltage (Ua1) (102). When a first turn-off voltage (Ua1) is reached, the charging current (IL) is turned off, and the regulating unit (MB) measures a relaxation curve (103) between the positive and negative terminals (Kp, Kn) of the battery module (BM) for a predetermined duration. From this measured relaxation curve, a model (104) of the battery module (BM) is derived by an evaluation unit (AE), by means of which a whole relaxation curve (105) is determined. A second switching-off voltage (Ua2) (105) is then determined by the evaluation unit (AE) from the entire deduced relaxation curve in such a way that, after switching off the charging current (IL), a predetermined target voltage (Uz) is used as an idle voltage of the battery module (BM) when the second switching-off voltage (Ua2) is reached. The charging or discharging of the battery module (BM) is then continued with a charging current (IL) until the voltage (Ut) falling between the positive and negative terminals (Kp, Kn) of the battery module (BM) reaches a second turn-off voltage (Ua2) (107). The charging current (IL) is then switched off and a predetermined target voltage (Uz) is generated on the battery module (BM) by means of a relaxation curve (108).

Description

Technical Field

[0001] The invention relates to a method for regulating a battery module, in particular a battery module of a traction battery, to a predetermined target voltage. The invention also relates to an associated system for carrying out the method for regulating a battery module. Background Art

[0002] Nowadays, rechargeable batteries or so-called secondary batteries are also used in electric vehicles, as in many electric drive systems (e.g. mobile phones, electronic devices, etc.). Electric vehicles or hybrid vehicles usually have a high-voltage battery in the powertrain in addition to the electric drive or electric motor that drives the vehicle, which serves as a drive battery or traction battery to provide electrical energy for the electric drive of the vehicle. These batteries are usually rechargeable and generally include a plurality of battery modules connected together. Such battery modules are composed, for example, of a few to many battery cells or cell blocks connected in parallel and in series. The drive battery is divided according to the material used for the battery cell. In this way, for example, lead battery systems, nickel-cadmium battery systems, lithium-ion battery systems, etc. can be used as drive batteries in electric vehicles.

[0003] If a defective battery module is found in the drive battery of a hybrid or electric vehicle, it is usually necessary to replace the defective battery module with a new one. Usually, the battery modules are stored in a state suitable for optimal long-term storage - for example, at a charge state of 30%, etc. However, before the new battery module is installed in the electric vehicle, it must be matched to the charge state of the other battery modules of the drive battery, the so-called State of Charge (abbreviation: SoC), so that after the battery module is replaced, the drive battery can be activated and the entire battery system in the vehicle can function properly.

[0004] Therefore, the battery module undergoes a specific charging process (i.e., specific charging or discharging) before installation and actual operation start, which is also called "conditioning". For example, a so-called conditioning unit or module conditioning system can be used for this specific process to prepare for the installation of the battery module. For example, the battery module to be installed is connected to the conditioning unit via a connecting line, and the desired charging state is achieved, for example, by corresponding charging or discharging, so as to adapt to the current charging state of the battery module of the drive battery. Here, a target voltage is predetermined by the conditioning unit, which corresponds to the required charging state of the battery module. Here, for example, a voltage generated as a stable state of the open circuit voltage of the battery module after the end of the conditioning process (i.e., after the charging process or the discharging process) is used as the target voltage. Here, the open circuit voltage refers to a voltage that depends on the corresponding charging state and exists when there is no additional load between the positive terminal and the negative terminal of the battery module. The open circuit voltage that occurs in the stable state is also called the no-load voltage of the battery module.

[0005] Different charging methods can be used to charge rechargeable battery modules. The difference between these charging methods lies in the different control of the current and voltage when charging the battery module. The battery module is usually charged with a constant current or a constant voltage. For example, a so-called IU charging method is used as a charging method for battery modules (such as lithium-ion battery systems). This IU method combines a constant current charging method with a constant voltage charging method and is also called "constant current constant voltage" or abbreviated as CCCV method. With the CCCV method, charging is first carried out with a constant charging current until a predetermined voltage limit, such as a charging end voltage, is achieved between the terminals of the battery module (usually when the charging unit or the regulating unit is connected). Charging is then continued with a constant voltage, wherein the charging current is automatically reduced near the end of charging. If the charging current reaches or falls below a certain current limit, or a predetermined duration has expired, the charging of the battery module is terminated. Although the CCCV method ensures that the maximum permissible voltage and the charging current (usually recommended by the manufacturer) are not exceeded, this charging method can only charge the battery module to the desired charge state or adjust to the no-load voltage specified as the target voltage after a considerable amount of time.

[0006] Furthermore, it may be necessary to carry out a targeted discharge process in order to reach a predetermined target voltage at the battery module or a desired depth of discharge (so-called "Depth of Discharge" (abbreviation: DoD)) of the battery module. However, deviations from the predetermined target voltage may also occur here. After the discharge process is completed, for example after the discharge current is switched off, the voltage between the terminals of the battery module rises until the no-load voltage is reached. This voltage change after the discharge is completed also leads to a deviation from the predetermined target voltage. As a result, the no-load voltage occurring at the battery module is usually higher than the desired target voltage.

[0007] For example, document WO 2020 / 227821 A1 discloses a matching charging method for a battery in order to accelerate the charging of the battery. To this end, at least one discharge pulse is applied to the battery during the charging process of the battery, and a first value of the relaxation voltage is measured during the relaxation process after the discharge pulse, and a second value of the relaxation voltage is measured after a predetermined waiting time. Then, the charging parameters of the charging process are adjusted according to the difference between the two measured voltage values. Thus, the charging process of the battery can also be accelerated using the method in document WO 2020 / 227821 A1. However, it is difficult to specify a desired target voltage for the battery that should be reached as a no-load voltage after charging using the method described.

[0008] In addition, document US2018 / 0145527 A1 also discloses a battery charging method for accelerating battery charging, in which the problem of battery aging is additionally taken into account by adjusting a shutdown criterion for terminating the battery charging process after each charging process or after a predetermined number of charging processes. Summary of the invention

[0009] It is therefore an object of the present invention to provide a method and an associated system which enable a time-efficient and highly accurate regulation of a predetermined target voltage at a battery module.

[0010] This object is achieved by a method and a system according to the independent claims. Advantageous embodiments of the invention are described in the dependent claims.

[0011] According to the invention, the object is achieved by a method of the type described at the outset, wherein a battery module is charged or discharged with a charging current until the voltage dropped between the positive and negative terminals of the battery module reaches a first cut-off voltage. When the first cut-off voltage is reached, the charging current is cut off, and a relaxation curve between the positive and negative terminals of the battery module is measured for a predetermined duration. A model of the battery module is derived from the measured relaxation curve, and the entire relaxation curve is determined with the aid of the model. A second cut-off voltage is determined from the determined relaxation curve in such a way that a predetermined target voltage appears as the no-load voltage of the battery module when the second cut-off voltage is reached after the charging current is cut off. Then, the battery module is continued to be charged or discharged with the charging current until the voltage dropped between the positive and negative terminals of the battery module reaches the second cut-off voltage. Preferably, the battery module is charged or discharged with a constant charging current.

[0012] The main aspect of the solution proposed by the present invention is that the battery module can be charged or discharged with a specified predetermined, preferably constant charging current. In this way, the charging or discharging of the battery module to the desired charge state or discharge state is significantly accelerated. In addition, with the help of the method of the present invention, in particular by using a battery module model determined by a measured relaxation curve segment, the entire relaxation curve determined by means of the model and based on the second shutdown voltage derived therefrom, after the charging process or the discharging process is completed, the predetermined target voltage is adjusted with high accuracy on the battery module. After the charging current is turned off, when the second shutdown voltage is reached, the battery module relaxes and a predetermined target voltage is generated relatively accurately on the battery module as a no-load voltage.

[0013] The first cut-off voltage is suitably specified for the charging process in such a way that the no-load voltage that occurs on the battery module after the relaxation curve for the first cut-off voltage is less than a predetermined target voltage. Similarly, the first cut-off voltage can be specified for the discharging process in such a way that the no-load voltage that occurs on the battery module after the relaxation curve for the first cut-off voltage is greater than a predetermined target voltage. Here, it is important to select the first cut-off voltage for the battery module to be charged or discharged accordingly in such a way that the first cut-off voltage is close to the predetermined target voltage so that a relaxation curve / relaxation process between the positive and negative terminals of the battery module is then measured, which relaxation curve roughly corresponds to the relaxation curve to the target voltage as the no-load voltage. For this purpose, the first cut-off voltage can be selected, for example, in such a way that the cut-off voltage is within a predeterminable range that is higher and / or lower than the predetermined 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. In addition, during the use of the method, the first cut-off voltage can also be adjusted for different battery module types and predetermined target voltages based on measured data (such as the terminal voltage during the method, the measured relaxation curve, etc.) so that the battery module to be adjusted can be more accurately charged to the desired charging state or discharged to the desired discharge state.

[0014] Furthermore, it is advantageous if an equivalent circuit diagram of the battery module is used as the model of the battery module, which equivalent circuit diagram is parameterized by an adaptive calculation method based on the measured relaxation curve. This makes it possible in a simple manner to approach and simulate the properties and behavior of the battery module as accurately as possible and thus to adjust the predetermined target voltage on the battery module as accurately as possible.

[0015] It is advantageous here if the least square method (or in German: least square method) is used as the adaptive calculation method for parameterizing the equivalent circuit diagram of the battery module. With this method, real data, such as a segment of a measured relaxation curve, can be detected. Assuming that the measured data are close to the essentially "correct" data and that there is a certain relationship between the measured data, the method can be used to find a function that describes this relationship as well as possible, that is, an equivalent circuit diagram or a function that describes the characteristics of the battery module as accurately as possible.

[0016] An advantageous embodiment of the invention provides that, for parameterizing the equivalent circuit diagram of the battery module, upper and lower limit values ​​are respectively predetermined for the corresponding parameters of the equivalent circuit diagram of the battery module. The predetermined limit values ​​prevent the equivalent circuit diagram parameters from assuming unrealistic values ​​in a simple manner. In this way, for example, it is prevented that the voltage and / or the time constant assume values ​​less than zero.

[0017] Another aspect of the invention also relates to a system for regulating a battery module to a predetermined target voltage, the system having at least one regulating unit and an analyzing unit, wherein the battery module can be charged or discharged to the predetermined target voltage in an efficient and time-saving manner using the system.

[0018] For this purpose, the regulating unit can be connected to the positive and negative terminals of the battery module via connecting lines. In addition, the regulating unit is further configured to: measure the voltage dropped 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; cut off the charging current when the first and second cut-off voltages are reached respectively and measure the relaxation curve between the positive and negative terminals of the battery module within a predetermined time period.

[0019] The analysis unit is configured to derive a model of the battery module from a relaxation curve measured by the control unit over a predetermined duration, with which the entire relaxation curve can be determined, and from which the second shutdown voltage is determined. The analysis unit can be designed as an independent unit and has a communication connection with the control unit. The analysis unit can therefore be used very easily with different control units or can be replaced very easily.

[0020] As an alternative, the analysis unit can also be integrated in the regulating unit. Thus, the regulating unit and the analysis unit can form a common unit which is, for example, convenient for handling or transportation.

[0021] Ideally, the upper and lower limit values ​​for parameterizing the battery module model in the method according to the invention can be stored in the analysis unit. To this end, the analysis unit can have, for example, a storage unit or a storage area. It is also conceivable that the limit values ​​for parameterization are input, for example, via an input / output unit and then stored in the analysis unit. In addition, measurement data (e.g., voltage curves, relaxation curves, etc.) and target voltages for, for example, different battery module types can be stored in a storage unit or in a storage area, which can then be used, for example, for analysis purposes and / or for adjusting the first shutdown voltage. As an alternative, these data can also be stored directly in the regulation unit.

[0022] An advantageous embodiment variant of the invention provides that the control unit has a temperature sensor, with which the current battery temperature can be determined. Thus, for example, temperature-dependent properties of the battery module (such as different relaxation curves at different temperatures, etc.) can also be taken into account when controlling the battery module. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Refer to the following Figures 1 to 4 The invention is explained in detail, and the drawings show advantageous structural designs of the invention by way of example, schematically and non-limitingly. The drawings show:

[0024] Figure 1 is a process of the method of the present invention for regulating a battery module;

[0025] Figure 2 is a simplified equivalent circuit diagram of a battery module;

[0026] Figure 3 is a curve of current and voltage changes of the battery module during the charging process according to the method of the present invention;

[0027] Figure 4 A system is provided for carrying out the method of the invention for regulating a battery module. DETAILED DESCRIPTION

[0028] Figure 1 FIG. 1 shows an exemplary process of a method for regulating a battery module BM. For this purpose, for example, the terminals Kp and Kn of the battery module BM (i.e., the positive terminal KP and the negative terminal Kn of the battery module BM) are connected to a regulating unit MB or a charger MB via a connecting line L. The regulating unit MB or the charger MB provides a charging current I L , and then the battery module BM is charged to a predetermined target voltage Uz using the charging current, so that it can be charged to a desired state of charge or discharged to a desired depth of discharge.

[0029] To start the method, a charging current I is switched on for a first charging step 101. L The charging current I L is predetermined, for example in the form of a current magnitude or a time curve, and may be, for example, a constant charging current I L Here, for example, a maximum permissible charging current I for the corresponding battery module BM is selected. L , which can be predetermined by the manufacturer and / or the type of battery used, which accelerates the charging or discharging. During the first charging step 101, the battery module BM is charged with a charging current I L In addition, the voltage Ut dropped between the positive and negative terminals Kp, Kn of the battery module BM is continuously measured during the first charging step 101 and the further sequence.

[0030] In the first detection step 102, it is detected whether the measured voltage Ut reaches the first cut-off voltage Ua1. If it is determined in the first detection step 102 that the voltage Ut measured between the positive and negative terminals Kp, Kn of the battery module BM reaches the first cut-off voltage Ua1, the charging current I LThe battery module BM is switched off. A relaxation process is thereby triggered in the battery module BM. In a measuring step 103, the variation of the relaxation process or the relaxation curve is measured over a predetermined duration, for example by the regulating unit MB or the charger MB. For this purpose, for example, the variation of the voltage Ut dropped between the positive and negative terminals Kp, Kn of the battery module BM is recorded over a predetermined duration. As a result of the measuring step 103, a segment of the relaxation curve of the battery module BM is obtained.

[0031] In this case, for example, a first cut-off voltage Ua1 is selected for the charging process such that the charging current I L ), so that after the entire relaxation process is completed, a no-load voltage less than the predetermined target voltage will be generated on the battery module BM. For example, for the discharge process, the first shutdown voltage Ua1 is similarly selected in the following manner, so that after the entire relaxation process is completed, a no-load voltage greater than the target voltage will be generated on the battery module BM. For example, the first shutdown voltage Ua1 can be selected for the battery modules BM to be adjusted separately based on empirical values. In this way, for example, a voltage value can be selected for the first shutdown voltage Ua1, which is within a predeterminable range that is higher than and / or lower than the predetermined target voltage Uz, or the voltage value deviates from the predetermined target voltage Uz by a predeterminable percentage. When selecting the first shutdown voltage Ua1, it is important that the shutdown voltage is close to the predetermined target voltage Uz, so that the battery modules have approximately the same relaxation characteristics.

[0032] In addition, the first cut-off voltage Ua1 can be adjusted over time for various different battery module types and predetermined target voltages Uz or charge or discharge states. For this purpose, for example, the first cut-off voltage Ua1 can be specified for the process of initial charging or discharging of the battery module type to the predetermined target voltage Uz - as described in detail above. During each execution of the adjustment method for the corresponding battery module type, data (such as the voltage curve between the terminals Kp, Kn, the relaxation curve, etc.) can be collected and then analyzed and evaluated. The first cut-off voltage Ua1 can then be adjusted based on these measured data in order to more accurately adjust to the predetermined target voltage Uz on the battery module BM.

[0033] As the duration of measuring the relaxation curve or the curve of the voltage Ut between the positive and negative terminals Kp, Kn of the battery module BM in the measuring step 103, for example, several minutes, for example, ideally two minutes, can be specified. Since extremely drastic changes in the relaxation curve (such as instantaneous voltage drop during charging, instantaneous voltage increase during discharging, etc.) are usually cut off when the charging current I L It occurs immediately thereafter, so that the predetermined duration is selected such that these changes are detected during the measured relaxation process.

[0034] A model of the battery module BM can then be derived from the measured relaxation curve in a modeling step 104, which model is a good approximation of the behavior of the battery module BM. For example, an equivalent circuit diagram is used as a starting point for the model of the battery module BM, by means of which the characteristics and behavior of the battery module BM can be approximated as accurately as possible.

[0035] Figure 2 By way of example, such a simplified equivalent circuit diagram is shown, which is used, for example, in the modeling step 104 to derive a model of the battery module BM.

[0036] This equivalent circuit diagram has, for example, an ideal voltage source Uoc, which constitutes the open circuit voltage Uoc of the battery module BM. The open circuit voltage Uoc depends on the current charge state of the battery module BM, and the more the battery module BM is charged, the greater the open circuit voltage. A resistor Ro is connected in series with the voltage source Uoc, which constitutes the internal resistance Ro of the battery module. The resistance Ro also depends on the corresponding charge state of the battery module BM. The value of the internal resistance Ro can be measured, for example, from the relaxation process measurement in the measurement step 103 (for example, from the voltage jump when the measurement is started). As an alternative, the value of the internal resistance Ro can also be obtained, for example, from the data table of the corresponding battery module BM. The current I L Refers to the charging current I of the battery module BM L According to the current I L The battery module BM is charged or discharged according to the sign of . A time-dependent voltage Ut is dropped between the positive terminal Kp and the negative terminal Kn of the equivalent circuit diagram. When the battery module is completely relaxed, that is, in a stable state, and there is no load connected between the terminals Kp and Kn, the voltage Ut is equivalent to the open circuit voltage Uoc.

[0037] In addition, a plurality of RC elements R1C1, ..., RiCi are connected 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 circuit consisting of a resistor R1, ..., Ri and a capacitor C1, ..., Ci. The corresponding capacitors C1, ..., Ci represent the capacitive characteristics inside the battery module BM. The resistors R1, ..., Ri are generated due to charge migration inside the battery module BM. The RC elements R1C1, ..., RiCi are used in the equivalent circuit diagram to be able to model the dynamic or time-related characteristics of the battery module BM, such as the relaxation characteristics of the battery module BM, using corresponding time constants. In order to closely approximate the relaxation characteristics, at least two RC elements R1C1, R2C2 are provided in the equivalent circuit diagram, for example. In order to obtain good accuracy with as little computational effort as possible, three RC elements R1C1, ..., R3C3 are provided in the equivalent circuit diagram, for example.

[0038] In the modeling step 104, for example, based on a simplified equivalent circuit diagram (such as Figure 2 The model of the battery module BM is determined by measuring the relaxation curve measured in the measurement step 103. For this purpose, the equivalent circuit diagram of the battery module BM is parameterized with the aid of the relaxation curve measured in the measurement step 103. That is, parameter values ​​suitable for the open circuit voltage Uoc, the internal resistance Ro and the RC elements R1C1, ..., RiCi used in the equivalent circuit diagram are derived from the segments of the measured relaxation curve.

[0039] In order to calculate suitable parameter values, for example, the so-called least square method is used. The least square method obtains its optimization criterion directly from the corresponding known data, such as from the fragment of the relaxation process measured in the measurement step 103. This criterion describes a deterministic error function, which is composed of the sum of square differences of a predetermined function, so the least square method is also called the minimum error square method in German. For example, suitable parameter values ​​can be calculated from the measured relaxation curve fragment using the least square method with the help of computing software (such as GNU Octave). GNU Octave is a free software for digitally solving mathematical problems (such as matrix calculations, (differential) equations, integration, etc.).

[0040] In order to be able to determine parameter values ​​of an equivalent circuit diagram of the battery module BM from a measured segment of the relaxation process and thus determine a model of the battery module BM, the relaxation process after the charging process is described using the following formula for an equivalent circuit diagram having, for example, three RC elements R1C1, ..., R3C3:

[0041]

[0042] in:

[0043] - Ut is the time-dependent voltage between the terminals Kp, Kn of the battery module BM;

[0044] -Uoc or Uo is the open circuit voltage or no-load voltage, to which the relaxation curve drops after a long time;

[0045] -I L0 is the charging current I L , using the charging current to charge the battery module BM until the first cut-off voltage Ua1 is reached;

[0046] - R1, R2, R3 are the resistance values ​​of the RC components in the equivalent circuit;

[0047] -C1, C2, C3 are the capacitance values ​​of the RC components in the equivalent circuit;

[0048] -t is the time variable; and

[0049] -e is Euler's number.

[0050] This formula can be simplified in the following way, that is, the corresponding resistance values ​​R1, R2, R3 and capacitance values ​​C1, C2, C3 are combined into time constants τ1, τ2, τ3. Based on the time constants τ1, τ2, τ3, the voltage I dropped across the corresponding RC elements R1C1, ..., R3C3 until the corresponding RC elements R1C1, ..., R3C3 can be estimated. L0 *R1, I L0 *R2, I L0 *The time required until R3 has been discharged. Here, the current I L0 The product of the corresponding resistance values ​​R1, R2, R3 can be combined into the voltage drops U1, U2, U3 across the corresponding RC elements R1C1, ..., R3C3. This results in a simplified formula for the time-dependent voltage Ut between the terminals Kp, Kn, which describes the relaxation process of the battery module BM after the charging process:

[0051]

[0052] Then, using this simplified formula and the relaxation curve segment measured in the measurement step 103, parameter values ​​for the voltages U0, U1, U2, U3 and for the time constants τ1, τ2, τ3 can be determined. In order to avoid unrealistic values ​​(such as negative values, etc.) for these parameter values, upper and lower limit values ​​are specified for the parameter values ​​of the voltages U0, U1, U2, U3 and the time constants τ1, τ2, τ3. By determining the upper and lower limit values ​​in advance, the effects of the parameters can be additionally specified. Here, for example, the parameter value of the voltage U0 represents a voltage value to which the voltage Ut drops after a long time. Therefore, this voltage value U0 corresponds to the no-load voltage of the battery module BM. The upper and lower limit values ​​of the voltage U0 are determined, for example, by the shutdown of the charging current I L This means that the first measured value of the relaxation curve measured in the measuring step 103 after the transient voltage drop is used as the limiting value for the voltage U0.

[0053] The parameter values ​​of the voltages U1, U2, U3 and the corresponding time constants τ1, τ2, τ3 essentially determine the corresponding exponential voltage drop, wherein, for example, the first voltage U1 and the first time constant τ1 describe a first rapid range of the voltage drop in the relaxation curve after the charging process of the battery module BM, the second voltage U2 and the second time constant τ2 describe a second medium range of the voltage drop, and the third voltage U3 and the third time constant τ3 describe a third slow range of the voltage drop. Here, the lower limit value of the parameter values ​​of the voltages U1, U2, U3 is, for example, a "zero" value in order to avoid negative voltage values. For example, a value of 1 volt can be selected as the upper limit value of the voltage parameters U1, U2, U3. However, depending on the battery module BM to be adjusted and its characteristics, other voltage values ​​can also be used for the upper limit values ​​of the corresponding voltage parameters U1, U2, U3. For example, the upper and lower limit values ​​of the time constants τ1, τ2, τ3 can be predetermined in such a way that the corresponding range of the voltage drop (i.e., rapid, medium or slow) is taken into account accordingly.

[0054] Similar to the modeling of the relaxation curve of the battery module BM after the charging process, the relaxation curve of the battery module after the discharging process can also be modeled in the modeling step 104. For this purpose, the relaxation curve segment measured in the measuring step 103 within a predetermined time period (for example, 2 minutes) is also used - this time during the discharging process, the charging current I is turned off. L Afterwards - and the above-mentioned simplified equivalent circuit diagram of the battery module BM. Then, for example, the corresponding parameter values ​​are determined again by the least square method. For this purpose, for example, the following formula for the time-dependent voltage Ut at the terminals Kp, Kn of the battery module BM can be derived:

[0055]

[0056] The voltage U0 represents a voltage value which corresponds essentially to the no-load voltage of the battery module BM or to which the time-dependent voltage Ut rises after a long time. The voltage parameters U1, U2, U3 and the time constants τ1, τ2, τ3 determine the exponential voltage rise, respectively, wherein a division is made between a fast, medium and slow range of the voltage rise. In order to determine the model of the battery module BM during the discharge process, upper and lower limit values ​​(corresponding, adapted) can also be predetermined for the parameter values ​​of the voltages U1, U2, U3 and the time constants τ1, τ2, τ3.

[0057] In the modeling step 104, after the parameter values ​​for the voltages U0, U1, U2, U3 and the time constants τ1, τ2, τ3 have been determined from the relaxation curve segments measured in the measuring step 103, for example by the method of least squares, the entire relaxation curve of the corresponding charging process or the corresponding discharging process of the battery module BM can be determined in the simulation step 105. That is, the time-dependent voltage Ut is simulated from the charging current I L The process from shutdown until the no-load voltage U0 is reached between the terminals Kp, Kn of the battery module BM. From this determined overall relaxation curve, it can be determined that the charging current I L The total difference between the voltage at the terminals Kp, Kn of the battery module BM during shutdown, i.e., the first shutdown voltage Ua1, and the no-load voltage U0 that appears at the battery module BM after a long duration (e.g., at least one hour to several hours). Thus, in the simulation step 105, the second shutdown voltage Ua2 can be determined so that the charging current I L The predetermined target voltage Uz is then adopted as the no-load voltage of the battery module.

[0058] In the second charging step 106, the battery module BM is charged with a maximum allowable charging current I L The charging current I L The battery module BM is further charged or discharged. In this case, in a second detection step 107 , it is detected whether the voltage Ut dropped between the positive and negative terminals Kp, Kn of the battery module BM and continuously measured has reached the second cut-off voltage Ua2 determined in the simulation step 105 .

[0059] If it is determined in the second detection step 107 that the voltage Ut dropped between the positive and negative terminals Kp, Kn reaches the second cut-off voltage Ua2, the charging current I is restarted or finally switched off in the cut-off step 108. L Shutdown. At the charging current I LAfter the shutdown, a relaxation process is restarted in the battery module BM. At the same time, the voltage Ut on the battery module BM drops to a no-load voltage corresponding to a predetermined target voltage Uz in the shutdown step 108 after the charging process is completed. After the discharge process is completed, the voltage Ut on the battery module BM is turned off in the shutdown step 108. L It then rises to a no-load voltage corresponding to a predetermined target voltage Uz.

[0060] exist Figure 3 FIG. 1 shows by way of example the time course of the voltage Ut between the positive terminal Kp and the negative terminal Kn of the battery module and the (here constant) charging current I during the charging process of the battery module BM. L The time variation curve of the battery module BM is shown in FIG. 1 . The control method of the present invention is used to charge the battery module BM to a desired charge state or to adjust to a predetermined target voltage Uz. The time t is shown on the horizontal axis. The voltage U and the current I are shown on the vertical axis. In addition, the predetermined target voltage Uz that should appear as a no-load voltage on the battery module BM after the exemplary charging process is completed, as well as the first shutdown voltage Ua1 and the second shutdown voltage Ua2 are also written on the vertical axis. In addition, the maximum charging current value I allowed for the battery module BM is also marked on the vertical axis. max .

[0061] For example, the charging process of the battery module BM starts at the starting time t0. To this end, the charging current I L , so that for example the charging current I L The maximum permissible value I max The battery module BM is charged. Therefore, the time-dependent voltage Ut between the positive and negative terminals Kp, Kn of the battery module BM begins to increase. If the time-dependent voltage Ut reaches the first cut-off voltage Ua1 at a first time point t1, the charging current I L Therefore, the duration from the start time t0 to the first time point t1 corresponds to the first charging step 101. Here, the shutdown voltage Ua1 for ending the first charging step 101 at the first time point t1 is selected so that a no-load voltage lower than the target voltage Uz is set for the first shutdown voltage Ua1 after the entire relaxation process. In addition, it is important for selecting the first shutdown voltage Ua1 that this shutdown voltage is close to the predetermined target voltage Uz so that the battery module BM has approximately the same relaxation characteristics as at the target voltage Uz. Figure 3 For example, a voltage value is selected for the first cut-off voltage Ua1, which is, for example, a few millivolts higher than the target voltage Uz within a predeterminable range. It is also conceivable to select a voltage value for the first cut-off voltage Ua1, which is, for example, a few millivolts lower than the target voltage Uz within a predeterminable range.

[0062] Since the charging current I is turned off at the first time point t1 L , so a relaxation process is generated in the battery module BM, and the voltage Ut begins to drop through this relaxation process. Here, in the measurement step 103, the relaxation curve or the change curve of the voltage Ut is measured in a predetermined duration (for example, two minutes). For example, the measurement step 103 starts at a first time point t1 and ends at a second time point t2 after the predetermined duration. Then in the modeling step 104, the model of the battery module BM is determined from the relaxation curve segment measured between the first time point t1 and the second time point t2. In the simulation step 105, the model can be used to determine the entire relaxation process of the battery module for the desired charge state and the second shutdown voltage Ua2.

[0063] At the second time point t2, the charging current I L , so that the charging current I L The maximum permissible value I max The battery module continues to be charged. That is, the second charging step 106 is started at the second time point t2. The battery module BM continues to be charged until the voltage Ut reaches the second cut-off voltage Ua2 at the third time point t3. Then, the charging current I is finally cut off at the third time point t3. L From the third time point t3 or after the charging current I is turned off L Afterwards, the voltage Ut (according to the relaxation curve) decreases toward the no-load voltage corresponding to the predetermined target voltage Uz. Figure 3 As shown in the figure, the maximum permissible charging current I max The charging process is time-efficient, wherein the voltage Ut drops to a predetermined target voltage Uz with high accuracy after the charging process is completed. However, during the charging process, it must be ensured that the second cut-off voltage Ua2 is within the permissible voltage range of the battery module BM, since the battery module is overcharged up to this voltage value Ua2.

[0064] Figure 4 A system is shown exemplarily and schematically, the system being configured to perform Figure 1A control method for a battery module BM, in particular a battery module BM for a traction battery or a drive battery, is shown by way of example. For the control process, i.e. for charging to a desired state of charge or discharging to a desired depth of discharge, the battery module BM can be connected to a control unit MB or charger MB via a connecting line L. For this purpose, for example, the positive terminal Kp and the negative terminal Kn of the battery module BM are connected to the control unit MB via a connecting line L in each case, so that a predetermined target voltage Uz is generated at the battery module BM by corresponding charging or discharging of the battery module BM. After the end of the corresponding charging process or discharging process, the target voltage Uz should drop between the positive terminal Kp and the negative terminal Kn in the stable state of the battery module BM as a no-load voltage.

[0065] In order to carry out the method, the control unit MB- is used in addition to the charging current I L In addition to charging or discharging the battery module BM, a voltage Ut which changes over time due to the corresponding charging process or discharging process is also provided, wherein the voltage Ut is dropped between the positive terminal Kp and the negative terminal Kn of the battery module BM. In addition, the regulating unit MB compares the measured voltage Ut, for example, with a first cut-off voltage Ua1 in a first detection step 102 and with a second cut-off voltage Ua2 in a second detection step 107, so as to cut off the charging current I when the first or second cut-off voltage Ua1, Ua2 is reached, respectively. L In addition, the regulating unit MB is further configured to cut off the charging current I when the first cut-off voltage Ua1 is reached. L The relaxation curve (ie the variation curve of the voltage Ut between the positive and negative terminals Kp, Kn of the battery module BM) is then measured within a predetermined time period.

[0066] Furthermore, the control unit MB may also have a temperature sensor (eg an infrared temperature sensor). Using this temperature sensor, for example, the current battery temperature can be determined and monitored. The determined temperature of the battery module BM can then be used, for example, in the control method in order to more accurately reach a predetermined target voltage Uz.

[0067] The system further comprises an analysis unit AE which can be designed, for example, as an independent unit and which is connected to the control unit MB via a communication connection KV. As an alternative, the analysis unit AE can also be integrated into the control unit MB. The analysis unit AE is configured to derive a model of the battery module BM from a relaxation curve segment measured by the control unit MB over a predetermined duration. For this purpose, the analysis unit AE can use, for example, Figure 2, and parameter values ​​are determined for the equivalent circuit diagram by an adaptive calculation method (such as using the least square method). In order to parameterize the equivalent circuit diagram, upper and lower limit values ​​of the corresponding parameters can be stored in the analysis unit AE, for example in a storage unit SE, which limit values ​​are adapted to the respective commonly used desired states of charge (such as SoC 60%) or depths of discharge (such as DoD 30%) of the battery module BM. The storage unit SE can be integrated into the analysis unit AE, for example, or can be configured as an external storage unit SE connected to the analysis unit AE.

[0068] Furthermore, the evaluation unit AE is further configured to determine or simulate the entire relaxation curve (i.e. the voltage Ut between the positive and negative terminals Kp, Kn at the first shutdown voltage Ua1 and the initial shutdown of the charging current I L The analysis unit AE then determines a second shutdown voltage Ua2 from the determined or simulated entire relaxation curve and can transmit this second shutdown voltage, for example, to the control unit MB, which can then continue the control process until the second shutdown voltage Ua2 is reached.

Claims

1. A method for regulating a battery module (BM), in particular a battery module (BM) of a traction battery, to a predetermined target voltage (Uz), characterized in that: Using the charging current (I L ) charges or discharges the battery module (BM) (101) until a voltage (Ut) dropped between the positive and negative terminals (Kp, Kn) of the battery module (BM) reaches a first cutoff voltage (Ua1) (102), and the charging current (I L ) is turned off and a relaxation curve (103) is measured between the positive and negative terminals (Kp, Kn) of the battery module (BM) for a predetermined duration, a model (104) of the battery module (BM) is derived from the measured relaxation curve, the entire relaxation curve is determined by means of the model of the battery module (BM), and a second turn-off voltage (Ua2) (105) is determined from the entire relaxation curve in the following manner, namely, when the charging current (I L ) after which, when the second cut-off voltage (Ua2) is reached, a predetermined target voltage (Uz) is adopted as the no-load voltage of the battery module (BM), and a charging current (I L ) continues to charge or discharge the battery module (BM) (106) until the voltage (Ut) dropped between the positive and negative terminals (Kp, Kn) of the battery module (BM) reaches a second shutdown voltage (Ua2) (107).

2. The method according to claim 1, characterized in that: Using a constant charging current (I L ) charges or discharges the battery module (BM).

3. The method according to claim 1, characterized in that For the charging process, the first cut-off voltage (Ua1) is predetermined such that the no-load voltage occurring after the relaxation curve for the first cut-off voltage (Ua1) is less than a predetermined target voltage (102).

4. The method according to claim 1, characterized in that: For the discharge process, the first cut-off voltage (Ua1) is predetermined such that the no-load voltage occurring after the relaxation curve for the first cut-off voltage (Ua1) is greater than a predetermined target voltage (Uz). (102) 5. The method according to any one of the preceding claims, characterized in that An equivalent circuit diagram of the battery module (BM) is used for the model of the battery module (BM), which equivalent circuit diagram is parameterized by means of an adaptive calculation method based on a measured relaxation curve (104).

6. The method according to claim 5, characterized in that The least square method (104) is used as the adaptive calculation method.

7. The method according to claim 5 or 6, characterized in that: In order to parameterize an equivalent circuit diagram of a battery module (BM), upper and lower limit values ​​are respectively predetermined for corresponding parameters of the equivalent circuit diagram of the battery module (BM).

8. System for regulating 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: a regulating unit (MB), which can be connected to the positive terminal (Kp) and the negative terminal (Kn) of the battery module (BM) via a connecting line (L), and the regulating unit is at least configured to: measure the voltage (Ut) dropped between the positive and negative terminals (Kp, Kn) of the battery module (BM), and compare it with a first cut-off voltage (Ua1) and a second cut-off voltage (Ua2); cut off the charging current (IL) when the first and second cut-off voltages (Ua1, Ua2) are reached, respectively, and measure the relaxation curve between the positive and negative terminals (Kp, Kn) of the battery module (BM) within a predetermined duration; and An analysis unit (AE) is configured at least to derive a model of the battery module (BM) from a relaxation curve measured by a control unit (MB) within the predetermined time period, by means of which the entire relaxation curve can be determined, and to determine a second shutdown voltage (Ua2) from the entire relaxation curve.

9. The system according to claim 8, characterized in that The evaluation unit (AE) is designed as an independent unit and has a communication connection (KV) to the control unit (MB).

10. The system according to claim 8, characterized in that The evaluation unit (AE) is integrated in the control unit (MB).

11. The system according to any one of claims 8 to 10, characterized in that Upper and lower limit values ​​for parameterization of a model of a battery module are stored in the evaluation unit (AE).

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

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