Method and apparatus for operating a battery

Abstract

The invention relates to a method for operating a battery (50), wherein the battery (50) is charged or discharged by means of a charge controller (2), wherein at least one control variable (Y) of the charge controller (2) is kept constant between a predetermined first state of charge (SOC1) and a predetermined second state of charge (SOC2), and wherein, at least during this constant period between the predetermined first state of charge (SOC1) and the predetermined second state of charge (SOC2), a state of charge (SOC) of the battery (50) is estimated by means of a model (4) based on at least one measured variable (Z) acquired at the battery (50). The invention further relates to a device (1) for operating a battery (50).

Description

[0001] The invention relates to a method and a device for operating a battery.

[0002] Lithium-ion cells can only accept a certain charging current without being damaged, depending on temperature, charging duration, and state of charge. This limiting current also changes with the aging of the lithium-ion cell. Furthermore, a battery system can contain multiple cells connected in series or parallel, which may have different states of charge, temperatures, or stages of aging. Therefore, it is currently necessary to know the state of charge and aging of all cells in the system at any given time, as well as the coldest and warmest points. Additionally, a state of charge distribution can occur between individual battery cells within the system.

[0003] Knowing the state of charge of the battery or battery cells is important for optimal battery operation.

[0004] The state of charge is required, for example, for fast charging, as, according to current technology, the maximum permissible current depends, among other things, on the state of charge (aging, temperature, etc.) of the battery cells. Furthermore, care must be taken to ensure that the battery cells are not overcharged (e.g., only with a final charging voltage of 3.7 V, 4.2 V, 4.3 V, 4.5 V, etc.). The state of charge must also be known for range or runtime predictions. Additionally, according to current technology, the battery cell must not fall below a defined voltage (e.g., 2 V, 2.5 V, 3 V) during operation. Finally, the battery cell must not be deeply discharged.

[0005] One problem here is that, due to technically unavoidable errors (especially in cost-optimized systems), the current signal measured during measurement does not mathematically correspond exactly to the charge (state of charge) of the battery cell. Furthermore, aging effects, passive anode effects, self-discharge, and / or balancing of the battery cells using additional electronics lead to further inaccuracies in determining the state of charge, as these effects are not captured by a current sensor according to current technology.

[0006] US 2022 / 0089059A1 describes a method for operating a system to determine the state of charge (State of Charge) of a motor vehicle battery. The method includes providing operating parameters of the battery, providing a calculated State of Charge in the motor vehicle using a State of Charge model that specifies a calculated State of Charge as a function of at least one battery model parameter, and determining a reference State of Charge using a reference State of Charge model as a function of the operating parameters. The reference State of Charge model is trained to indicate the reference State of Charge as a function of operating variables and / or a predefined aging state.The procedure further includes performing a correction of at least one battery model parameter depending on a difference between the reference state of charge and the calculated state of charge, in order to adapt the calculated state of charge to the reference state of charge.

[0007] The invention is based on the objective of improving a method and a device for operating a battery, particularly with regard to estimating the battery's state of charge.

[0008] The problem is solved according to the invention by a method with the features of claim 1 and a device with the features of claim 10. Advantageous embodiments of the invention are set forth in the dependent claims.

[0009] In particular, a method for operating a battery is provided, wherein the battery is charged or discharged by means of a charge control system, wherein at least one control variable of the charge control system is kept constant (or is constant) between a predetermined first state of charge and a predetermined second state of charge, wherein at least during this constant section between the predetermined first state of charge and the predetermined second state of charge, a state of charge of the battery is estimated by means of a model based on at least one measured variable acquired at the battery.

[0010] Furthermore, in particular a device for operating a battery is provided, comprising a charging control unit configured for controlled charging or discharging of the battery, and a data processing unit, wherein the charging control unit is configured to keep at least one controlled variable of the charging control unit constant between a predetermined first state of charge and a predetermined second state of charge, wherein the data processing unit is configured to obtain at least one measured variable detected at the battery and, at least during the constant section between the predetermined first state of charge and the predetermined second state of charge, to estimate a state of charge of the battery using a model based on the at least one measured variable detected at the battery.

[0011] The method and device enable improved estimation of a battery's state of charge. For this purpose, the battery is charged or discharged under controlled conditions within a constant-state interval between a predefined first and second state of charge. During this constant-state interval, at least one control variable of the charging system is kept constant. This results in other parameters describing the battery's state exhibiting a defined state-of-charge-dependent profile. Such a profile can be described, in particular, by means of a model, for example, in the form of characteristic curves (or maps). At least during the constant-state interval between the predefined first and second states of charge, the battery's state of charge is estimated using a model based on at least one measured parameter acquired from the battery.In particular, the model can estimate the state of charge based on the known profile of at least one measured variable. The advantage is that the at least one constant controlled variable is known, and therefore fewer parameters need to be measured and / or estimated at the battery. Because the profile of the at least one measured variable is defined in relation to the state of charge, the model can use this profile to estimate the state of charge. This improves the estimation of the state of charge. The state of charge estimated from the measured at least one variable is taken into account, especially in charge control.

[0012] The constant section comprises, in particular, a range of at least 50%, preferably at least 60%, and most preferably at least 70% of the total charge that can be stored in the battery. Accordingly, the first and second states of charge are predetermined. These states of charge must be selected in advance (i.e., in particular before charging begins and, if necessary, before charging ends) such that battery damage exceeding a normally expected level (for example, 0.0001% to 1% damage per charge cycle) is avoided. The normally expected level of battery damage per charge cycle is determined in advance, for example, by means of battery aging tests. The controlled variable, which is kept constant in this constant section, may, in particular, be selected to be smaller than physically possible.

[0013] It is specifically intended that the constant section, i.e., the values ​​for the first state of charge and the second state of charge, and a value of at least one controlled variable are chosen in such a way that technically specified operating parameters of the battery or battery cells (e.g. a maximum voltage, etc.) are maintained.

[0014] It is specifically intended that the model is or has been parameterized using suitable data. In particular, it is intended that, for parameterizing the model, a multitude of charging and / or discharging processes are or have been carried out under various boundary conditions, with the state of charge being determined separately in each case. "Separately" here means, in particular, by means of a method that is independent of the method described in this disclosure or that determines the state of charge in a different way. Such a method can, for example, operate using current integration via battery measuring devices and / or open-circuit voltage-state-of-charge curves, etc. The boundary conditions or the data include different initial states of charge, a constant value of at least one controlled variable, and various values ​​of the measured variable and / or, in the case of multiple measured variables, combinations of at least one measured variable.Based on this data, the model is parameterized in such a way that the model can reproduce the data as accurately as possible when the model is applied, meaning that a deviation between a state of charge estimated by the model and the separately determined state of charge is minimized.

[0015] It may be possible for the device to be integrated into a battery management system.

[0016] Parts of the device, in particular the charging control and / or the data processing unit, can be designed individually or collectively as a combination of hardware and software, for example as program code that runs on a microcontroller or microprocessor. However, it is also possible for parts to be designed individually or collectively as an application-specific integrated circuit (ASIC) and / or a field-programmable gate array (FPGA).

[0017] In one embodiment, the at least one controlled variable comprises a cell voltage. The cell voltage is then kept constant during the constant-voltage section. This results in a defined current profile. In particular, the current is measured as a measured variable in this embodiment. Due to the known at least one controlled variable and the defined current profile in relation to the state of charge, the model can better estimate the battery's state of charge.

[0018] It is specifically intended that the method be applied to each (individual) battery cell. According to the prior art, a voltage is measured for each individual battery cell in a battery system, although in the case of parallel-connected battery cells, usually only one voltage is measured. In this case, a state of charge is also determined for each individual battery cell in the battery system and is also required for charge control (battery operation).

[0019] In one embodiment, the at least one measured quantity comprises a current or a charging power. This enables simple measurement using a current sensor.

[0020] In one embodiment, the at least one measured variable includes temperature. This allows for a more accurate estimation of the state of charge, as temperature has a significant influence on this estimation. The temperature is measured, for example, using a temperature sensor.

[0021] In one embodiment, the model is provided to be, or includes, a trained machine learning model. This allows a model to be provided that can estimate a state of charge for each value of the at least one measured quantity. The machine learning model can, for example, be, or include, an artificial neural network. The machine learning model is trained, for example, using suitable training data. The training data is generated, in particular, from the data described above. For example, for supervised learning of the machine learning model, data pairs can be generated in which each measured quantity is paired with the (separately determined) state of charge (as the underlying truth). The machine learning model is trained with these data pairs in a manner known per se by means of supervised learning.After training, the trained machine learning model can estimate a charge level based on similar input data, i.e., the recorded at least one measured quantity.

[0022] In one embodiment, the model is designed or includes at least one characteristic curve and / or a lookup table. The characteristic curve and / or the lookup table link the at least one measured variable to a value for the state of charge. This allows the model to be provided with minimal computational effort. The characteristic curve and the lookup table can, in particular, be multidimensional with more than one input dimension. For example, the measured variables current, temperature, and state of health (SOH) can be provided as input dimensions. The characteristic curve can also be stored as a function, for example, as a multidimensional polynomial function.

[0023] In one embodiment, it is provided that a SOH value of the battery is estimated and additionally supplied to the model as an input variable.

[0024] In one embodiment, it is provided that a large number of charging and / or discharging processes are or have been carried out under different boundary conditions to parameterize the model. This has already been described above.

[0025] In one embodiment, it is provided that the attainment of the predetermined second state of charge is verified by comparison with the estimated state of charge, whereby charging or discharging with the at least one constant controlled variable is terminated when the comparison result shows that the predetermined second state of charge has been reached. In particular, after reaching the second state of charge, especially above the second state of charge, a different value of the controlled variable can be set, for example, to increase the state of charge by charging up to a predetermined maximum state of charge.

[0026] Further features for the design of the device result from the description of embodiments of the method. The advantages of the device are the same in each case as in the embodiments of the method.

[0027] The invention is explained in more detail below with reference to preferred embodiments and the figures. These show: Fig. 1 a schematic representation of an embodiment of the device for operating a battery; Fig. 2 a schematic representation of a curve showing the controlled variable versus the state of charge, to illustrate the invention; Fig. 3a to 3d schematic representations of the trends of the controlled variable and of measured variables over time, to illustrate an embodiment; Fig. 4 a schematic representation of current curves versus state of charge for different boundary conditions (starting state of charge); Fig. 5 a schematic representation to illustrate the method and the device; Fig. 6 a schematic flowchart of an embodiment of the method.

[0028] The Fig. Figure 1 shows a schematic representation of an embodiment of the device 1 for operating a battery 50. The device 1 comprises a charging control unit 2 and a data processing unit 3. The device 1 is particularly designed to carry out the method described in this disclosure.

[0029] The charging control system 2 is configured to keep at least one controlled variable Y of the charging control system 2 constant between a predefined first state of charge (SOC1) and a predefined second state of charge (SOC2). The charging control system 2 is otherwise designed in a manner known per se. In particular, the charging control system 2 determines a manipulated variable U based on a control deviation between a setpoint value of the at least one controlled variable Y and a measured actual value of the at least one controlled variable Y, which is then set.

[0030] The data processing unit 3, for example, comprises a computing unit 3-1 and a memory 3-2. The computing unit 3-1 is configured to perform the necessary arithmetic operations for carrying out the procedure and can access data stored in the memory 3-2 for this purpose.

[0031] The data processing device 3 is configured to obtain at least one measured quantity Z recorded at the battery 50 and to estimate a state of charge SOC of the battery 50 at least during the constant section between the specified first state of charge SOC1 and the specified second state of charge SOC2 using a model 4 based on the at least one measured quantity Z recorded at the battery 50.

[0032] A sensor 5 can be provided to detect at least one measured quantity Z at the battery 50. The sensor 5 can be part of the device 1.

[0033] It is specifically intended that the recorded at least one measurement variable Z is transmitted to the charging control 2 and taken into account by it when regulating.

[0034] The Fig. Figure 2 shows a schematic representation of a characteristic curve to illustrate the method and the device. The constant section lies between the predetermined first charge state SOC1 and the predetermined second charge state SOC2, in which the charge control 2 ( Fig. 1) which keeps at least one controlled variable Y constant. For a state of charge (SOC) that is less than SOC1 or greater than SOC2, the controlled variable Y can have different values.

[0035] It can be stipulated that at least one controlled variable Y comprises a cell voltage V. The manipulated variable U is then, for example, a current I.

[0036] It may be provided that at least one measured quantity Z includes a current I or a charging power P.

[0037] It may be provided that at least one of the measured variables Z includes a temperature T. This is measured, for example, by means of a temperature sensor (not shown) on the battery cells of the battery.

[0038] The Fig. Figures 3a to 3d show schematic representations of the curves for the cell voltage V, the current I, the temperature T, and the state of charge (SOC), each plotted against time t. These curves contain only exemplary values ​​and serve solely to illustrate the method and the device. Depending on a starting state of charge, the curves have defined profiles, knowledge of which is utilized by the method described in this disclosure.

[0039] The Model 4 ( Fig. 1) is parameterized using suitable empirical and / or simulated data. For this purpose, it is specifically planned that a large number of charging cycles will be carried out on battery 50 (or a similar battery model) under various boundary conditions, particularly with regard to a starting state of charge, a final state of charge, and / or temperature. The same procedure can be followed for discharging. However, at least one controlled variable will be kept constant.

[0040] The Fig. Figure 4 shows exemplary schematic representations of three curves where charging occurred at different initial charge levels. The current I or charging power P is shown as a function of the (separately determined) state of charge (SOC). Model 4 is parameterized based on these curves. The goal is for Model 4 to represent the curves as accurately as possible. In other words, starting with a known initial charge level and its corresponding curve shape, the state of charge (SOC) can be estimated using the current I or the charging power P.

[0041] It may be possible to estimate the state of health (SOH) value of battery 50 and feed it into model 4 as an additional input. Accordingly, the SOH value is considered as further input data when parameterizing model 4. An SOH value can be determined, for example, by calculating the amount of energy transferred during charging, based on a charging power P and a time duration, which is then related to a change in the state of charge (SOC). For example, if 50 kWh are charged into the battery and the state of charge (SOC) changes from 25% to 75%, this corresponds to a change of 50%. If battery 50 has a total capacity of, for example, 100 kWh, then the SOH value is 100% (50 kWh / 50% = 100 kWh).However, if, for example, only 40 kWh are charged into battery 50 and the state of charge (SOC) also changes from 25% to 75%, then, with the same total capacity, the resulting SOH value is only 80% (40 kWh / 50% = 80 kWh) of the total capacity.

[0042] It may be envisaged that model 4 is a trained machine learning model 6 ( Fig. 1) is or comprises such a system. The machine learning model 6 can, in particular, be or comprise an artificial neural network. Starting from the curves described above, the machine learning model 6 can be trained. For this purpose, training data is generated from the curves, comprising pairs that each include a starting state of charge and a current or charging power P paired with a value for the state of charge (SOC). The machine learning model 6 is then trained using this training data in a manner known per se, in particular by means of supervised learning.

[0043] Model 4 may be designed or include at least one characteristic curve and / or a lookup table. The at least one characteristic curve and / or the lookup table then specifically depicts the curves which are found in the Fig. Figure 4 shows that, for example, a characteristic curve with the independent variables current I or charging power P, temperature T and SOH, and the dependent variable state of charge (SOC) may be used. Alternatively, a lookup table with the independent variables current I or charging power P, temperature T and SOH, and their respective assigned variables state of charge (SOC) may be used.

[0044] It may be provided that reaching the specified second state of charge SOC2 ( Fig. 1) is checked by comparison with the estimated state of charge (SOC), whereby charging or discharging with the at least one constant control variable Y is terminated when the comparison result shows that the predetermined second state of charge (SOC2) has been reached.

[0045] The Fig. Figure 5 shows a schematic representation illustrating the method and the device. The y-axis represents the measured state of charge (solid curve) and the state of charge (SOC) estimated by the model (dashed curve), both in percent. The x-axis represents the measurement point i (sample point) and the time t. The model used is a trained machine learning model that receives the current I, the temperature T, and the charge quantity Q / 60 as input data. The charge quantity Q is, in particular, the integral of the current and is used here in the unit ampere-seconds (As). Normalization (scaling) to ampere-minutes (= 60 seconds) showed a favorable estimation quality (hence the designation Q / 60). It can be seen that the machine learning model's estimate for all curves during the constant-temperature section agrees very well with the respective measured value.

[0046] It can generally be advantageous to scale the measured quantities before processing them in the model, as demonstrated above using the example of the amount of charge.

[0047] The Fig. Figure 6 shows a schematic flowchart to illustrate one embodiment of the method for operating a battery. The method is carried out, for example, by means of a device according to the one described in the Fig. 1. This embodiment is carried out as shown.

[0048] In process step 100, it is checked whether the battery's state of charge (SOC) is lower than a predetermined first state of charge (SOC1). Initially, the state of charge (SOC) can be estimated, for example, using an open-circuit voltage-state-of-charge (OCV-SOC) curve in a known manner. If this is the case, process step 101 is continued, at which point the process is terminated. It is specifically intended that below the first state of charge (SOC1), charging or discharging is carried out using a different method.

[0049] If the state of charge (SOC) is greater than the predefined first state of charge (SOC1), the process continues with step 102. In step 102, it is checked whether the state of charge (SOC) is greater than a predefined second state of charge (SOC2). If this is the case, the process continues with step 101, at which point the process is terminated. It is specifically intended that charging or discharging above the second state of charge (SOC2) is carried out using a different method.

[0050] If the state of charge (SOC) is not greater than the predefined second state of charge (SOC2), the process continues with step 103. In step 103, the battery is charged (or discharged) using the charge control system with at least one constant control variable. This at least one constant control variable can, in particular, be a cell voltage.

[0051] In process step 104, at least one measured variable is acquired at the battery. This at least one measured variable is acquired using suitable sensors on the battery cells and / or on the battery itself. The at least one measured variable includes, for example, current and / or temperature. In particular, at least one controlled variable is also acquired and used to determine a control deviation.

[0052] In process step 105, the state of charge (SOC) of the battery is estimated using a model based on at least one measured variable recorded at the battery.

[0053] Subsequently, that is, in a later time step, the process returns to step 100, whereby the state of charge (SOC) estimated by the model is used in steps 100 and 102 when checking. Reference symbol list 1 Device 2. Charging control 3 Data processing equipment 3-1 Computing Equipment 3-2 storage 4 Model 5 Sensors 6 Machine learning model 50 battery 100-105 process steps SOC charge level SOC1 predefined first state of charge SOC2 predefined second state of charge SOH health status (state of health) i measuring point (sample) t time I Current intensity Temperature P Charging power U Control variable V (cell) voltage Y (at least one) controlled variable Z (at least one) measured quantity QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] US 2022 / 0 089 059 A1

[0006]

Claims

[1] Method for operating a battery (50), wherein the battery (50) is charged or discharged by means of a charge controller (2), wherein at least one control variable (Y) of the charge controller (2) is kept constant between a predetermined first state of charge (SOC1) and a predetermined second state of charge (SOC2), wherein at least during this constant section between the specified first state of charge (SOC1) and the specified second state of charge (SOC2) a state of charge (SOC) of the battery (50) is estimated by means of a model (4) starting from at least one measured quantity (Z) recorded at the battery (50). [2] Method according to claim 1, characterized by , that at least one controlled variable (Y) includes a cell voltage (V). [3] Method according to claim 1 or 2, characterized by that at least one measured quantity (Z) includes a current (I) or a charging power (P). [4] Method according to any of the preceding claims, characterized by , that at least one measured quantity (Z) includes a temperature (T). [5] Method according to any of the preceding claims, characterized by that the model (4) is or includes a trained machine learning model (6). [6] Method according to any of the preceding claims, characterized by , that the model (4) is designed or includes at least one characteristic curve and / or a lookup table. [7] Method according to any of the preceding claims, characterized by , that a SOH value (SOH) of the battery (50) is estimated and additionally supplied to the model (4) as an input variable. [8] Method according to any of the preceding claims, characterized by , that to parameterize the model (4) a large number of charging and / or discharging operations are or have been carried out under different boundary conditions. [9] Method according to any of the preceding claims, characterized by , that the attainment of the predetermined second state of charge (SOC2) is verified by comparison with the estimated state of charge (SOC), whereby the charging or discharging with the at least one constant control variable (Y) is terminated when the comparison result shows that the predetermined second state of charge (SOC2) has been reached. [10] Device (1) for operating a battery (50), comprising: a charging control unit (2) configured for controlled charging or discharging of the battery (50), and a data processing unit (3), wherein the charging control (2) is configured to keep at least one control variable (Y) of the charging control (2) constant between a predetermined first state of charge (SOC1) and a predetermined second state of charge (SOC2), wherein the data processing device (3) is configured to obtain at least one measured quantity (Z) recorded at the battery (50) and to estimate a state of charge (SOC) of the battery (50) at least during the constant section between the specified first state of charge (SOC1) and the specified second state of charge (SOC2) using a model (4) starting from the at least one measured quantity (Z) recorded at the battery (50).

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