Method for charging an electrical energy storage unit

Abstract

A method for charging or discharging an electrical energy storage cell is described, wherein the method comprises the following steps: a) determining at least one self-discharge current variable, in particular a self-discharge current, of the electrical energy storage cell at least one predefined first state-of-charge variable value, in particular a predefined first voltage value of the electrical energy storage cell; b) charging or discharging the electrical energy storage cell with a predefined charging current or discharging current to at least one predefined second state-of-charge variable value, in particular a predefined second voltage value of the electrical energy storage cell, wherein the predefined second state-of-charge variable value is determined as a function of the at least one self-discharge current variable. A corresponding device, a corresponding computer program, a corresponding machine-readable storage medium and a corresponding application of the device are also described.

Description

Technical Field

[0001] The invention proceeds from a method for charging an electrical energy storage cell, a device for charging an electrical energy storage cell, a corresponding computer program, a corresponding machine-readable storage medium and a corresponding use of the device. Background Art

[0002] In the course of increasing electrification, in particular of motor vehicles, electrical energy stores are becoming increasingly important. During the operation of these electrical energy stores, special attention is paid to minimizing aging, i.e., for example, minimizing a decrease in capacitance or minimizing an increase in internal resistance. The corresponding aging can be roughly divided into two categories: so-called cyclic aging and so-called calendar aging. Cyclic aging refers to a decrease in capacitance or an increase in resistance during operation of the electrical energy store, i.e., a decrease in current. Calendar aging refers to aging when aging occurs outside of operation.

[0003] In particular, these two effects have a relevant impact in the case of motor vehicles with electrical energy storage devices. In order to achieve the highest possible range, these vehicles are charged to a very high state of charge. In this case, the vehicle may not be moved immediately after precharging, but rather parked for a certain period of time, for example overnight, or in the case of unused vehicles in the case of car sharing, parked until the next use.

[0004] However, at very high charge states, the aging of the electrical energy storage device is usually significantly higher than at low or reduced charge states. For this reason, the battery pack may not be fully charged, that is, not to the technically or physically highest possible charge state, although this is displayed to the user. The usability of the electrical energy storage device is reduced as a result, for example, the electrical range of the electric vehicle is reduced. This is disadvantageous due to the anyway limited electrical range of the electric vehicle. Ideally, a balance can be found between excessive aging and a correspondingly high charge state.

[0005] The publication JP 5227669 A2 describes how, among other things, knowledge of the self-discharge current of a battery can be used for the charging process of the battery.

[0006] No. 6,137,261 describes how to use the self-discharge current for the diagnosis of a battery. Summary of the invention

[0007] Advantages of the present invention

[0008] Disclosed is a method for charging an electrical energy storage unit.

[0009] In this case, at least one self-discharge current variable of the electrical energy storage unit is determined at least at a predefined first state of charge variable value. The self-discharge current variable can be, for example, a self-discharge current of the electrical energy storage unit. The state of charge variable value can be, for example, a state of charge value, such as 55%, or a voltage value, such as 4 V. Likewise, the self-discharge current variable can be determined at a plurality of different state of charge variable values ​​in order to determine a correlation between the self-discharge current variable and the state of charge variable.

[0010] Subsequently, the electrical energy storage unit is charged or discharged with a predefined charging current or discharging current up to a predefined second state of charge parameter value. In this case, the predefined second state of charge parameter value is determined based on at least one self-discharge current parameter previously determined. For example, the predefined second state of charge parameter value can be determined so that a compromise between the highest possible state of charge and the smallest possible aging is achieved. In this case, an increased self-discharge current parameter is associated with a more severe aging, wherein, for example, it is assumed that the irreversible portion of the self-discharge is either dominant or at least proportional to the total self-discharge. As a result, the greater the self-discharge current parameter, the more severe the aging of the electrical energy storage unit. However, in this case, it is mostly meaningless to use the minimum value of the self-discharge current parameter to determine the second state of charge parameter value. This may mostly only result in determining a very small predefined second state of charge parameter value. Possible aspects for a meaningful determination of the predefined second state-of-charge variable value from the determined self-discharge current variable are, for example, an increased increase or decrease in the self-discharge current variable.

[0011] This has the advantage that aging of the electrical energy storage unit is reduced, wherein at the same time a sufficient state of charge of the electrical energy storage unit is achieved. Further advantageous embodiments of the invention are the subject of the following description.

[0012] Suitably, the step of determining the self-discharge current parameter comprises: determining at least one free-wheeling voltage parameter of the electrical energy storage unit at at least two different points in time Here, the current flowing into or out of the electrical energy storage cell must be equal to or lower than a predefined current value in terms of value, and must be, for example, not greater than 1C, or not greater than 0.1C, or not greater than 0.05C, or not greater than 0.01C in terms of value. Here, 1C means, for example, that in the case of an electrical energy storage cell with a capacitance of 2Ah, a current of 2A flows. The idling voltage variable can be, for example, the idling voltage of the electrical energy storage cell, as it can be measured without a current flowing through the poles of the electrical energy storage cell or without a current flowing between different electrodes of the electrical energy storage cell. It is also possible to determine the idling voltage variable with the aid of a mathematical model, for example with the aid of an electrical equivalent circuit diagram model. The two different time points are preferably separated by a plurality of minutes, in particular more than ten minutes or more than one hour, preferably a plurality of hours, so that typically only a voltage difference in the range of a few millivolts occurs. Thus, for example, the parking situation of a vehicle having the electrical energy storage unit is advantageously adapted.

[0013] Furthermore, at least one self-discharge current variable is determined as a function of the determined no-load voltage variable. This has the advantage that the self-discharge current can be determined without current measurements during a change in the no-load voltage variable, for which, for example, a typically available voltage measuring device is used. For example, the corresponding charge quantity is advantageously determined using a known no-load voltage curve, also called an OCV curve, and the difference in the no-load voltage of the electrical energy storage cell at two different points in time, whereby the self-discharge current can then be determined, for example, taking into account the capacitance of the electrical energy storage cell.

[0014] The electrical energy storage cell is preferably charged with a predefined voltage at at least one predefined first state of charge variable value. In particular, the predefined voltage can be a constant voltage. After a sufficiently long waiting period, a constant current appears at the electrical energy storage cell, which reflects the self-discharge of the electrical energy storage cell and thus the self-discharge current of the electrical energy storage cell. This allows at least one self-discharge current variable to be determined based on the current that appears in or at the electrical energy storage cell after a predefined period of time. This has the advantage that the disclosed method can be integrated into a charging process of the electrical energy storage cell without significantly prolonging the charging time of the electrical energy storage cell.

[0015] Advantageously, at least one self-discharge current variable determined in the case of at least one predefined first state of charge variable value is stored in a data memory. This has the advantage that the method does not have to be carried out in each charging process, since the correlation between the self-discharge current variable and the state of charge variable stored in the data memory can be traced. In addition, it is possible to track changes in the correlation and thus, for example, determine the aging of the electrical energy storage unit. For example, in the case of excessive aging over time, this information can be incorporated into the charging process by, for example, correspondingly adapting the predefined second state of charge variable value, for example reducing the state of charge.

[0016] Advantageously, the temperature of the electrical energy storage unit is determined, wherein the predefined charging current or discharging current for charging and / or discharging the electrical energy storage unit is specified as a function of the determined temperature of the electrical energy storage unit. This is advantageous because, in general, the electrical energy storage unit can be charged with a greater current at a higher temperature without excessive aging or even damage occurring. At the same time, it is taken into account that, in general, higher temperatures occur with increased self-discharge. Typically, the temperature is determined by means of a temperature sensor, such as a thermocouple, mounted on, at or in the electrical energy storage unit.

[0017] The subject matter of the present disclosure is also a device for charging an electrical energy storage unit, wherein the device comprises at least one device which is configured to carry out the steps of the disclosed method. In this case, the at least one device can in particular comprise an electronic battery management controller which communicates, if necessary, with corresponding power electronics in order to control the charging and / or discharging. The advantages mentioned apply accordingly.

[0018] The at least one device may, for example, include a battery management controller and corresponding power electronics, such as an inverter and current sensors and / or voltage sensors and / or temperature sensors. An electronic control unit, in particular in the form of a battery management controller, may also be such a device. An electronic control unit may be understood in particular as an electronic controller, which may, for example, include a microcontroller and / or an application-specific hardware module, such as an ASIC, but may also include a personal computer or a programmable control device with a memory.

[0019] An electrical energy storage unit may be understood in particular as an electrochemical battery cell and / or a battery module having at least one electrochemical battery cell and / or a battery pack having at least one battery module. For example, the electrical energy storage unit may be a lithium-based battery cell or a lithium-based battery module or a lithium-based battery pack. In particular, the electrical energy storage unit may be a lithium-ion battery cell or a lithium-ion battery module or a lithium-ion battery pack. Furthermore, the battery cell may be of the type of a lithium-polymer battery, a nickel-metal hydride battery, a lead-acid battery, a lithium-air battery or a lithium-sulfur battery or, in general, a battery of any electrochemical composition. Capacitors are also possible as electrical energy storage units.

[0020] Furthermore, the subject matter of the present disclosure is a computer program comprising instructions which cause the disclosed device to carry out the method steps of the disclosed method. The advantages mentioned apply accordingly.

[0021] Furthermore, the subject matter of the disclosure is a machine-readable storage medium on which the disclosed computer program is stored. The advantages mentioned apply correspondingly.

[0022] The subject matter of the present disclosure is also the use of the disclosed device, wherein the disclosed device is used in electrically driven vehicles, including hybrid vehicles, in stationary electrical energy storage facilities, in electrically operated hand tools, in portable devices for telecommunications or data processing, and in household appliances. In particular, the use of the device is also advantageous in the case of household appliances, since the device usually remains unused for a longer period of time after a shorter use. If the household appliance is now supplied with electrical energy from an electrical energy storage unit, the aging of the electrical energy storage unit can be reduced by the disclosed device. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Advantageous embodiments of the present invention are shown in the drawings and are described in more detail in the following description.

[0024] Figure 1 A flow chart showing a disclosed method according to a first embodiment;

[0025] Figure 2 A flow chart showing a disclosed method according to a second embodiment;

[0026] Figure 3 A flow chart showing a disclosed method according to a third embodiment;

[0027] Figure 4A flow chart showing a disclosed method according to a fourth embodiment;

[0028] Figure 5 a schematic diagram showing the disclosed apparatus according to one embodiment; and

[0029] Figure 6 Schematic diagram showing the dependence of the self-discharge current of an electrical energy storage cell on the state of charge of the electrical energy storage cell. DETAILED DESCRIPTION

[0030] The same reference numerals denote the same device components or the same method steps in all the figures.

[0031] Figure 1 A flow chart of the disclosed method according to a first embodiment is shown. In this case, in a first step S11, the self-discharge current of the electrical energy storage unit is determined at least in a predefined first charge state of the electrical energy storage unit. In a second step S12, the electrical energy storage unit is subsequently charged with a predefined charging current to a predefined second charge state. In this case, the predefined second charge state is determined as a function of the self-discharge current determined in the first step S11.

[0032] Figure 2 A flow chart of the disclosed method according to a second specific embodiment is shown. In this case, in a first step S21, the no-load voltage of the electrical energy storage unit is determined at at least two different points in time, wherein the current flowing into or out of the electrical energy storage unit does not exceed a predefined current value in terms of value. For this purpose, a sufficiently long wait is made after the current loading of the electrical energy storage unit, for example, a plurality of minutes, in particular more than 10 minutes, so that no normal relaxation of the battery voltage is detected. The two different points in time are, for example, a plurality of hours apart.

[0033] In a second step S22, the charge is determined from the difference in the idling voltage at two different points in time with the aid of an idling voltage curve stored in a memory and the capacitance of the electrical energy storage unit, and the average self-discharge current is determined with the aid of the charge calculated in this way and the time difference between the two different points in time, wherein the idling voltage curve reproduces the dependency of the idling voltage on the state of charge of the electrical energy storage unit.

[0034] The determination of the self-discharge current in the first step S21 and the second step S22 is carried out at different charge states of the electrical energy storage unit in order to determine the dependence of the self-discharge current on the charge state of the electrical energy storage unit. In the third step S23, it is therefore checked whether the self-discharge current has been determined at a sufficiently large number of different charge states of the electrical energy storage unit. If not, the first step S21 is carried out again, for example in a new parking situation. If the criterion for a sufficiently large number of different charge states is met, the process is continued with the fourth step S24. In this case, several days can pass in order to completely go through the first three steps S21 to S23.

[0035] In a fourth step S24 , the electrical energy storage unit is subsequently charged with a predefined charging current to a predefined state of charge, wherein the predefined state of charge is determined as a function of the determined self-discharge current or as a function of the determined correlation between the self-discharge current and the state of charge.

[0036] Figure 3 A flow chart of the disclosed method according to a third embodiment is shown. In a first step S31 , a predefined constant voltage is applied to the electrical energy storage unit.

[0037] In a second step S32, the self-discharge current is determined from the current occurring at the energy storage area unit after a number of hours. This is possible because the energy storage unit is charged after a number of hours in accordance with the applied predefined constant voltage and the current that continues to flow therefore corresponds to the self-discharge current of the energy storage unit. The current that continues to flow can be measured, for example, by means of a current sensor. The second step S32 can be carried out in a targeted manner at different charge states by applying a voltage corresponding to the determined charge state, preferably a constant voltage, to the energy storage unit. Thus, the correlation of the self-discharge current with the charge state of the energy storage unit is determined.

[0038] In a third step S33, it is determined whether the state of charge of the electrical energy storage unit is higher than a predefined target state of charge. If so, the electrical energy storage unit is discharged with a predefined discharge current to a predefined target state of charge in a fourth step S34. If not, the electrical energy storage unit is charged with a predefined charge current to a predefined target state of charge in a fifth step S35. In this case, the target state of charge is determined in each case as a function of the self-discharge current determined in the second step S32 or as a function of the correlation between the self-discharge current and the state of charge of the electrical energy storage unit.

[0039] Figure 4 A flow chart of the method according to the invention according to a fourth embodiment is shown. In this case, in a first step S41, the free-wheeling voltage of the electrical energy storage unit is determined at at least two different points in time under a predefined first state of charge, wherein the current flowing into or out of the electrical energy storage unit does not exceed a predefined current value in a numerical manner. For this purpose, before the first point in time is measured, a sufficiently long wait is made after the current loading (Strombelastung) of the electrical energy storage unit, for example, for several minutes, in particular for more than 10 minutes, so that a normal relaxation (Relaxation) of the battery voltage is not detected. The two different points in time are separated by several hours, for example. If necessary, the predefined first state of charge is changed by the flowing current, but the flowing current is lower than the predefined current value in a numerical manner. Then, for example, the average value of the state of charge at the two different points in time can be regarded as the predefined first state of charge.

[0040] In a second step S42, the charge quantity is determined from the difference in the idling voltage at two different points in time with the aid of an idling voltage curve stored in a memory and the capacitance of the electrical energy storage unit, and the average self-discharge current is determined with the aid of the charge quantity calculated in this way and the time difference between the two different points in time, wherein the idling voltage curve reproduces the dependency of the idling voltage on the charge state of the electrical energy storage unit.

[0041] In a third step S43 , the self-discharge current determined in the second step at the predefined first charge state is subsequently stored in a data memory in order not to lose sight of the self-discharge current already determined in the case of multiple executions of the method.

[0042] In a fourth step S44 , the temperature of the electrical energy storage cell is determined in order to take into account possible effects of the temperature of the electrical energy storage cell on the self-discharge current and to adapt the charging current of the electrical energy storage cell accordingly.

[0043] In a fifth step S45 , the electrical energy storage cell is subsequently charged with a predefined charging current to a predefined second state of charge, wherein the predefined charging current is specified as a function of the determined temperature of the electrical energy storage cell and the predefined second state of charge is specified as a function of the determined self-discharge current.

[0044] Figure 5A device 70 for charging an electrical energy storage cell is shown, wherein the device 70 comprises an electronic control unit 73. The electronic control unit 73 is configured to receive the voltage of the electrical energy storage cell detected via a voltage sensor 71 and can thereby determine, for example, the charge state and the self-discharge current of the electrical energy storage cell. In addition, the electronic control unit 73 is configured to charge and / or discharge the electrical energy storage cell by sending corresponding commands to a power electronics device 72, such as an inverter, which then regulates the corresponding through-current.

[0045] Figure 6 Schematic diagram 60 shows the dependence of the self-discharge current of an electrical energy storage cell on the state of charge of the electrical energy storage cell. In the diagram 60, the self-discharge current I_sd is plotted on the ordinate axis and the state of charge SOC of the electrical energy storage cell is plotted as a percentage on the abscissa axis. The individual points 61 indicate discrete self-discharge current values ​​at discrete state of charge values, as they can be determined, for example, by means of the disclosed method. It can be seen from the diagram 60, for example, that the self-discharge current increases strongly from a state of charge of 70%. In the disclosed method, a state of charge of 70% can therefore be set as a state of charge variable value, to which the electrical energy storage cell is charged.

Claims

1. A method for charging or discharging an electrical energy storage unit, the method comprising the following steps: a) determining (S11) at least one self-discharge current variable of the electrical energy storage unit at least one predefined first state of charge variable value; b) charging (S12, S24, S35, S45) or discharging (S34) the electrical energy storage unit with a predefined charging current or discharging current up to at least one predefined second state of charge parameter value, wherein the predefined second state of charge parameter value is determined as a function of the at least one self-discharge current parameter, Wherein the step a) of determining comprises: c) determining (S21, S41) at least one free-wheeling voltage variable of the electrical energy storage cell at at least two different points in time, wherein the current flowing into or out of the electrical energy storage cell does not exceed a predefined current value in terms of value; d) Determining ( S22 , S42 ) the at least one self-discharge current variable as a function of the at least one free-wheeling voltage variable determined in step c). 2 . The method according to claim 1 , wherein the predefined first state of charge parameter value is a predefined first voltage value of the electrical energy storage unit. The method according to claim 1 , wherein the self-discharge current parameter is a self-discharge current. 4 . The method according to claim 1 , wherein the predefined second state-of-charge parameter value is a predefined second voltage value of the electrical energy storage unit. The method according to claim 1 , wherein the idling voltage parameter is an idling voltage.

6. The method according to any one of claims 1 to 5, wherein the step a) of determining comprises: e) charging ( S31 ) the electrical energy storage unit with a predefined voltage at the at least one predefined first state of charge variable value; f) Determining ( S32 ) the at least one self-discharge current variable as a function of the current occurring after the predefined period of time in step e). The method according to claim 6 , wherein the predefined voltage is a constant voltage.

8. The method according to any one of claims 1 to 5, further comprising: g) Storing ( S43 ) the at least one self-discharge current variable determined in the case of the at least one predefined first state of charge variable in a data memory.

9. The method according to any one of claims 1 to 5, further comprising: h) determining (S44) the temperature of the electrical energy storage unit, wherein the predefined charging current or discharging current for the charging and / or the discharging of the electrical energy storage unit in step b) is prescribed as a function of the determined temperature of the electrical energy storage unit.

10. A device (70) for charging or discharging an electrical energy storage unit, wherein the device comprises at least one device which is set up to carry out the steps of the method according to any one of claims 1 to 9.

11. The apparatus (70) of claim 10, wherein the device is an electronic battery management controller.

12. A computer program product comprising a computer program, the computer program comprising instructions causing the device (70) according to claim 10 or 11 to implement the method steps according to any one of claims 1 to 9.

13. A machine-readable storage medium having a computer program stored thereon, the computer program comprising instructions causing the apparatus (70) according to claim 10 or 11 to implement the method steps according to any one of claims 1 to 9.

14. Application of the device (70) according to claim 10 or 11, wherein the device is used in electrically driven vehicles, in stationary electrical energy storage facilities, in electrically operated hand tools, in portable devices for telecommunications or data processing, and in household appliances.

15. The use of claim 14, wherein the electrically driven vehicle comprises a hybrid vehicle.

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