Method for determining the capacity of an electrical energy storage unit

Abstract

A method for determining the capacity of an electrical energy storage unit within an electrical energy storage system having a plurality of electrical energy storage units is described, wherein the electrical energy storage system has at least one switching device which is set up to electrically disconnect the electrical energy storage unit whose capacity is to be determined from the current flow path of the electrical energy storage system in the charging and / or discharging direction and / or to electrically connect the electrical energy storage unit whose capacity is to be determined to the current flow path in the charging and / or discharging direction. Here, the electrical energy storage unit is disconnected from the current flow path of the electrical energy storage system, a first voltage value of the terminal voltage of the electrical energy storage unit is determined, the electrical energy storage unit is connected to the current flow path, the electrical energy storage unit is charged and / or discharged, the electrical energy storage unit is disconnected again from the current flow path, a second voltage value of the terminal voltage of the electrical energy storage unit is determined, and the capacity of the electrical energy storage unit is determined from the first voltage value and the second voltage value.

Description

TECHNICAL FIELD

[0001] The present disclosure starts from a method for determining the capacity of an electrical energy storage unit. BACKGROUND

[0002] Due to the increasing electrification, in particular in the field of vehicles or cars, mobile electrical energy storage systems are increasingly being employed. In the case of lithium-ion technology, which is increasingly being employed, in particular, predefined limit values, such as voltage and state of charge limit values, need to be adhered to in order to guarantee the safety and service life of the electrical energy storage system. Furthermore, it is important for the user of the electrical energy storage system to have an accurate knowledge of the capacity, that is to say the storage capability, of the electrical energy storage unit of the corresponding electrical energy storage system. For this purpose, by means of a battery management system, corresponding updates of the capacity value of the electrical energy storage unit are carried out at irregular intervals. By means of the capacity value, it is possible, for example, to display to the user the remaining range of the electrically driven vehicle. The more frequently the update can be carried out, the more accurately the range of the vehicle can be displayed to the user. SUMMARY

[0003] Advantages of the invention

[0004] A method for determining the capacity of an electrical energy storage unit is disclosed. Here, the electrical energy storage unit is part of an electrical energy storage system having a plurality of electrical energy storage units, wherein the electrical energy storage system has at least one switching device which is set up to electrically switch out of the current flow path of the electrical energy storage system in the charging and / or discharging direction the electrical energy storage unit whose capacity is to be determined and / or to electrically switch into the current flow path of the electrical energy storage system in the charging and / or discharging direction the electrical energy storage unit whose capacity is to be determined. Here, the capacity is the current charge quantity which can be stored in the electrical energy storage unit at maximum, for example under permissible operating conditions. The current charge quantity can be reduced, for example, as a result of ageing effects. The at least one switching device can be constructed, for example, as a full bridge or as a half bridge. Such embodiments are derived, for example, from the earlier applications DE 10 2010 027 857 and DE 10 2010 027 861.

[0005] Within the method, by means of the switching device, the electrical energy storage unit is switched out of the current flow path of the electrical energy storage system in the charging and / or discharging direction in order to be able to achieve an approach to a steady state or quasi-steady state of the electrical energy storage unit, since the voltage value of the no-load voltage of the electrical energy storage unit can be determined particularly accurately in the present invention.

[0006] Furthermore, a first voltage value of the terminal voltage of the electrical energy storage unit is determined. This is advantageous in the switched-off or decoupled state, since, as mentioned, the voltage value of the no-load voltage of the electrical energy storage unit can be determined simply and accurately in this case.

[0007] Furthermore, by means of the switching device, the electrical energy storage unit is connected in the charging and / or discharging direction into the current flow path of the electrical energy storage system, so that the electrical energy storage unit can be charged or discharged again.

[0008] Furthermore, the electrical energy storage unit is charged and / or discharged with a predefined first charge quantity and / or charged and / or discharged until a predefined first state of charge and / or until a predefined first voltage level. Advantageously, the electrical energy storage unit thereafter has a different state of charge and / or a different voltage level than before.

[0009] By means of the switching device, the electrical energy storage unit is decoupled again in the charging and / or discharging direction from the current flow path of the electrical energy storage system, so that the stable / quasi-stable state is reached again as far as possible.

[0010] A second voltage value of the electrical energy storage unit is determined, by means of which, as described above, the voltage value of the no-load voltage of the electrical energy storage unit can be determined again simply and accurately.

[0011] Finally, the capacity of the electrical energy storage unit is determined at least on the basis of the first voltage value and the second voltage value.

[0012] The method is advantageous in that, by decoupling the electrical energy storage unit, it is possible to determine the capacity of the electrical energy storage unit accurately and flexibly, which enables a safe and reliable operation of the electrical energy storage system.

[0013] The method can be implemented, for example, in a computer-implemented manner.

[0014] Further advantageous embodiments of the application are given.

[0015] Suitably, the first voltage value is determined after a predefined first waiting time and / or when a predefined first rate of change of the terminal voltage is reached. Here, in particular a rate of change by amount is advantageous, since it can be inferred therefrom that the corresponding physical and / or chemical equilibrium processes in the electrical energy storage unit are close to a steady state. This is advantageous, since the value of the terminal voltage can thus be assumed with sufficient accuracy to be the value of the no-load voltage without performing additional calculations. The waiting time can here depend on the type of electrical energy storage unit and thus be selected as a function of the application. In the preparation phase of the application, the predefined rate of change can also be determined, for example experimentally or on the basis of a model, in order to achieve a predefined accuracy of the no-load voltage value determined from the terminal voltage value.

[0016] Suitably, the second voltage value is determined after a predefined second waiting time and / or when a predefined second rate of change of the terminal voltage is reached. Here, in particular a rate of change by amount is advantageous, since it can be inferred therefrom that the corresponding physical and / or chemical equilibrium processes in the electrical energy storage unit are close to a steady state. This is advantageous, since the value of the terminal voltage can thus be assumed with sufficient accuracy to be the value of the no-load voltage without performing additional calculations. The waiting time can here depend on the type of electrical energy storage unit and thus be selected as a function of the application. In the preparation phase of the application, the predefined rate of change can also be determined, for example experimentally or on the basis of a model, in order to achieve a predefined accuracy of the no-load voltage value determined from the terminal voltage value.

[0017] Suitably, the steps of disconnecting, determining the voltage value, connecting, charging and discharging (as described above) are performed repeatedly and two or more voltage values of the terminal voltage are thus determined. This is advantageous in order to determine a plurality of voltage values and thus to increase the accuracy of the capacity determination.

[0018] Suitably, the capacity is determined by adapting a predefined open-circuit voltage curve to the determined voltage values. This is advantageous, since the shape of the open-circuit voltage curve is mostly not changed in shape, but is for example compressed, depending on the type of electrical energy storage unit. This can be extended as follows: different characteristic curves are set for different electrodes or electrode materials, which in superposition result in the open-circuit voltage characteristic curve. For example, in the case of a lithium ion cell, an anode characteristic curve for the anode potential to lithium and a cathode characteristic curve for the cathode potential to lithium can be set, which in superposition or upon differencing result in the open-circuit voltage characteristic curve. These two characteristic curves are then adapted accordingly in order to provide the open-circuit voltage characteristic curve which reflects the determined voltage values as exactly as possible. Thus, in an advantageous manner, the capacity effect can also be determined separately for the anode and the cathode.

[0019] Suitably, the state of charge of the electrical energy storage unit is determined from the determined voltage values. This is advantageous in order to calculate therefrom by differencing and corresponding scaling the charge quantity difference, which can be employed in determining the capacity.

[0020] Furthermore, the subject matter of the present disclosure is a computer program which is set up to carry out all the steps of the disclosed method. Thus, the mentioned advantages can be achieved.

[0021] Furthermore, the subject matter of the present disclosure is a machine-readable storage medium on which a computer program is stored. Thus, the computer program can be easily distributed and implemented.

[0022] Furthermore, the subject matter of the present disclosure is a device for determining the capacity of an electrical energy storage unit within an electrical energy storage system having a plurality of electrical energy storage units, wherein the electrical energy storage system has at least one switching device which is set up to electrically decouple at least one electrical energy storage unit whose capacity is to be determined from the current flow path of the electrical energy storage system in the charging and / or discharging direction and / or to electrically couple at least one electrical energy storage unit whose capacity is to be determined into the current flow path in the charging and / or discharging direction, the device comprising at least one device, in particular an electronic control unit, which is set up to carry out all the steps of the present method. This is advantageous, since it enables the present method to be easily employed. The at least one device can for example comprise a battery management control device or an electronic control unit. The electronic control unit can in particular be understood as an electronic control device which for example comprises a microcontroller and / or special hardware components, for example an ASIC, but a personal computer or a programmable logic controller can likewise belong thereto.

[0023] Furthermore, the subject matter of the present disclosure is an electrical energy storage system comprising a plurality of electrical energy storage units and the disclosed device. Here, the electrical energy storage system has at least one switching device which is set up to electrically disconnect at least one electrical energy storage unit whose capacity is determined from a current flow path of the electrical energy storage system in the charging and / or discharging direction and / or to electrically connect at least one electrical energy storage unit whose capacity is determined into the current flow path in the charging and / or discharging direction.

[0024] The electrical energy storage unit can in particular be understood as an electrochemical battery cell and / or as a battery module having at least one electrochemical battery cell and / or as a battery pack having at least one battery module. For example, the electrical energy storage unit can 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 can be a lithium-ion battery cell or a lithium-ion battery module or a lithium-ion battery pack. Furthermore, the battery cell can be a lithium polymer accumulator type, a nickel metal hydride accumulator type, a lead-acid accumulator type, a lithium-air accumulator type or a lithium-sulfur accumulator type or, more generally, an accumulator of any electrochemical compound. BRIEF DESCRIPTION OF DRAWINGS

[0025] Advantageous embodiments of the application are shown in the drawings and are explained in more detail in the following description.

[0026] Figure 1 An electrical energy storage system having a plurality of electrical energy storage units is shown according to an embodiment, the electrical energy storage system having corresponding switching devices;

[0027] Figure 2 A flowchart of the disclosed method is shown according to an embodiment; and

[0028] Figure 3 A schematic voltage profile of an electrical energy storage unit whose capacity is determined according to the disclosed method is shown.

[0029] In all figures, identical reference signs designate identical device components or identical method steps. DETAILED DESCRIPTION

[0030] Figure 1 An electrical energy storage system 1 is shown, the electrical energy storage system 1 having a plurality of electrical energy storage units 2 and having assigned switching devices 3, respectively, which are set up to electrically disconnect electrical energy storage units 2 whose capacity is determined from a current flow path 5 of the electrical energy storage system 1 in the charging and / or discharging direction and / or to electrically connect electrical energy storage units 2 whose capacity is determined into the current flow path 5 in the charging and / or discharging direction.

[0031] Furthermore, the electrical energy storage system 1 has a device 4 for determining the capacity of the electrical energy storage unit 2, as already disclosed above. Here, the device 4 comprises an electronic control unit, which is not explicitly shown in the present application. The electronic control unit is here set up to carry out the method described above.

[0032] Here, the device 4 is set up to determine the corresponding voltage values by means of suitable connections. These connections are not explicitly shown in the present application, but can be wired or wireless, for example. The corresponding voltage sensors are here arranged on the electrical energy storage unit 2.

[0033] Figure 2 A flowchart of the disclosed method according to one implementation form is shown. Here, at least the electrical energy storage unit whose capacity is determined is arranged within an electrical energy storage system having a plurality of electrical energy storage units, as for example in Figure 1 is shown. Here, the electrical energy storage system has at least one switching device, which is set up to electrically disconnect at least one electrical energy storage unit whose capacity is determined from the current flow path of the electrical energy storage system in the charging and / or discharging direction and / or to electrically connect at least one electrical energy storage unit whose capacity is determined into the current flow path in the charging and / or discharging direction.

[0034] In a first step S21, the electrical energy storage unit whose capacity is determined is connected into the current flow path of the electrical energy storage system in the charging direction by means of the switching device. As a result, the electrical energy storage unit can be charged, but not discharged.

[0035] In a second step S22, the electrical energy storage unit is charged until a predefined first voltage level. The first voltage level is preferably above 3.6 volts.

[0036] In a third step S23, the electrical energy storage unit is disconnected from the current flow path of the electrical energy storage system in the charging direction by means of the switching device. Since the electrical energy storage unit has only been connected in the charging direction before, the electrical energy storage unit is thus separated from the current flow path of the electrical energy storage system.

[0037] In a fourth step S24, a first voltage value of the end voltage of the electrical energy storage unit is determined. This is preferably carried out after a predefined first waiting time.

[0038] In a fifth step S25, the electrical energy storage unit is connected into the current flow path of the electrical energy storage system in the discharging direction by means of the switching device, so that discharging is possible.

[0039] In a sixth step S26, the electrical energy storage unit is discharged until a predefined second voltage level, so that there is a predefined voltage difference between the two voltage levels.

[0040] In a seventh step S27, the electrical energy storage unit is disconnected again, this time from the current flow path in the discharging direction. Thus, the electrical energy storage unit is separated from the current flow path of the electrical energy storage system.

[0041] In an eighth step S28, a second voltage value of the terminal voltage of the electrical energy storage unit is determined. Preferably, this is performed after a predefined second waiting time.

[0042] Finally, in a ninth step S29, the capacity of the electrical energy storage unit is determined from the first voltage value and the second voltage value.

[0043] Figure 3 A schematic voltage curve of an electrical energy storage unit is shown, the capacity of which is determined according to the disclosed method. Here, the upper diagram shows the switching position S1 of the switching device, as described for example in Figure 1 , that is to say, whether the electrical energy storage unit is switched into the current flow path of the electrical energy storage system in the charging or discharging direction or is disconnected.

[0044] From the time t0 until the time t1, the electrical energy storage unit is connected in the charging direction by means of the switching device to the current flow path of the electrical energy storage system and is charged according to the lower diagram, which illustrates the terminal voltage U1 of the electrical energy storage unit. Charging is performed until the time t1, at which the predefined first voltage level is reached.

[0045] At the time t1, the electrical energy storage unit is disconnected from the current flow of the electrical energy storage system, so that it cannot be charged or discharged. As can be seen from the lower diagram, the terminal voltage asymptotically approaches the resting value, that is to say the no-load voltage value. Preferably, the first voltage value is determined at the time t2 shortly before the electrical energy storage unit is connected in the discharging direction to the current flow path of the electrical energy storage system, which makes it possible to perform discharging.

[0046] From the time t2 until the time t3, the electrical energy storage unit is connected in the discharging direction by means of the switching device to the current flow path of the electrical energy storage system and is discharged according to the lower diagram, which illustrates the terminal voltage U1 of the electrical energy storage unit. Discharging is performed until the time t3, at which the predefined first voltage level is reached.

[0047] At time t3, the current flow from the electrical energy storage system is switched off from the electrical energy storage unit, so that the electrical energy storage unit cannot be charged nor discharged. As can be seen from the lower graph, the terminal voltage asymptotically approaches a stationary value, i.e. the no-load voltage value. Preferably, shortly before the electrical energy storage unit is again switched into the current flow path of the electrical energy storage system in the discharging direction, a second voltage value is determined at time t4. From the determined voltage values, the capacity of the electrical energy storage unit can then be determined.

Claims

1. A method for determining the capacity of an electrical energy storage unit (2) within an electrical energy storage system (1) having a plurality of electrical energy storage units (2), wherein the electrical energy storage system (1) has at least one switching device (3), the switching device (3) being configured to electrically disconnect the electrical energy storage unit (2) of the determined capacity from a current flow path (5) of the electrical energy storage system (1) in the charging and / or discharging direction, and / or to electrically connect the electrical energy storage unit (2) of the determined capacity into the current flow path (5) in the charging and / or discharging direction, the method comprising the steps of: a) disconnecting the electrical energy storage unit (2) from the current flow path (5) of the electrical energy storage system (1) in the charging and / or discharging direction by means of the switching device (3); b) determining a first voltage value of the terminal voltage of the electrical energy storage unit (2), wherein the first voltage value is determined when a first rate of change of the terminal voltage is below an amount; c) connecting the electrical energy storage unit (2) to the current flow path (5) of the electrical energy storage system (1) in the charging and / or discharging direction by means of the switching device (3); d) charging the electrical energy storage unit (2) with a predefined first charge amount and / or discharging the electrical energy storage unit (2) and / or charging the electrical energy storage unit (2) and / or discharging the electrical energy storage unit (2) to a predefined first state of charge and / or to a predefined first voltage level; e) disconnecting the electrical energy storage unit (2) from the current flow path (5) of the electrical energy storage system (1) again in the charging and / or discharging direction by means of the switching device (3); f) determining a second voltage value of the terminal voltage of the electrical energy storage unit (2), wherein the second voltage value is determined when the terminal voltage is below a second rate of change according to the amount; g) determining the capacity of the electric energy storage unit (2) according to the first voltage value and the second voltage value.

2. The method of claim 1, wherein, The determination of the first voltage value in step b) is performed after a predefined first waiting time.

3. The method according to any of the preceding claims 1-2, wherein, After a predefined second waiting time, the determination of the second voltage value in step f) is performed.

4. The method according to any of the preceding claims 1-2, wherein, Repeat steps a) to f) to determine two or more voltage values ​​of the terminal voltage.

5. The method according to any of the preceding claims 1-2, wherein, The capacity is determined in step g) by adjusting a predetermined no-load voltage curve as a function of the determined voltage value.

6. The method according to any of the preceding claims 1-2, wherein, The state of charge of the electrical energy storage unit (2) is determined from the determined voltage values. 7 . A computer program product comprising a computer program which is configured to carry out all the steps of the method according to claim 1 when run on a computer. 8 . A machine-readable storage medium having a computer program stored thereon, the computer program being configured to carry out all the steps of the method according to claim 1 when executed on a computer.

9. A device (4) for determining the capacity of an electrical energy storage unit (2) within an electrical energy storage system (1) having a plurality of electrical energy storage units (2), wherein the electrical energy storage system (1) has at least one switching device (3) which is set up to electrically decouple the electrical energy storage unit (2) whose capacity is to be determined from an electrical current flow path (5) of the electrical energy storage system (1) in the charging and / or discharging direction and / or to electrically couple the electrical energy storage unit (2) whose capacity is to be determined into the electrical current flow path (5) in the charging and / or discharging direction, the device (4) having at least one electronic control unit which is set up to carry out all the steps of the method according to any one of claims 1 to 6.

10. An electrical energy storage system (1) having a plurality of electrical energy storage units (2) and at least one switching device (3) which is set up to electrically decouple at least one electrical energy storage unit (2) whose capacity is to be determined from an electrical current flow path (5) of the electrical energy storage system (1) in the charging and / or discharging direction and / or to electrically couple at least one electrical energy storage unit (2) whose capacity is to be determined into the electrical current flow path (5) in the charging and / or discharging direction, and furthermore having a device (4) according to claim 9.

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