Method for operating an electrical energy storage device

Abstract

The invention presented relates to a method for operating an electric energy storage device, the aging characteristics of which are estimated on the basis of an expected aging profile, wherein a rapid charging characteristic profile of the electric energy storage device to be used is determined based on a comparison between a detected aging state of the electric energy storage device and a target aging state of the electric energy storage device determined on the basis of the expected aging profile.

Description

Background Art

[0001] Electrical energy storage devices, such as batteries used in electric or hybrid vehicles, experience a certain degree of aging. This aging can generally be described in two parts: a calendar component and a periodic component. The periodic aging is caused by the amount of charge passed through, that is, by the use of the electrical energy storage device. In the case of lithium-ion batteries, the charging process is a decisive factor in aging. Specifically, the following relationship applies: the faster the charging process is carried out, the greater the aging of the lithium-ion battery during this period.

[0002] When operating lithium-ion batteries, such as those currently used in electric vehicles, a so-called rapid charging characteristic curve is maintained, which allows rapid charging within a defined time with defined aging. This rapid charging characteristic curve is compiled using a series of laboratory tests. Batteries are generally designed so that only a predetermined number of charging cycles, planned over their entire service life, allow for rapid charging. Thus, for example, a battery might be designed for 200 rapid charging cycles out of a total of 1,000 charging cycles. If this number is exceeded, the battery ages faster than specified. Similarly, additional influences, such as aggressive discharge processes or high temperatures, can accelerate aging. If a battery ages faster than specified, it may need to be replaced before reaching the end of its planned service life.

[0003] Related prior art is known from US 2016 / 0172886 and US 2016 / 0006286. Summary of the Invention

[0004] In contrast, the method according to the invention for operating an electrical energy storage device, the aging characteristics of which are estimated using an expected aging profile, has the advantage that the rapid charging characteristic profile to be used for the electrical energy storage device is determined based on a comparison of the detected aging state of the electrical energy storage device with a target aging state of the electrical energy storage device determined using the expected aging profile. The electrical energy storage device can be, in particular, a battery, in particular a lithium-ion battery.

[0005] Advantageously, the rapid charging characteristic curve to be used is determined by selecting the rapid charging characteristic curve to be used from a plurality of stored rapid charging characteristic curves that differ from one another with respect to their influence on the aging behavior of the electrical energy storage device. This allows the method to be implemented in a particularly simple manner.

[0006] Advantageously, the rapid charging characteristic curve to be used is determined such that a future deviation between the detected aging state of the electrical energy storage device and the target aging state of the electrical energy storage device determined based on the expected aging profile is smaller than the associated deviation between the detected aging state of the electrical energy storage device and the target aging state of the electrical energy storage device determined based on the expected aging profile, which is expected when using a standard rapid charging characteristic curve. The standard rapid charging characteristic curve can, in particular, be a rapid charging characteristic curve that allows for the fastest possible charging of an electrical energy storage device, such as a battery. The "associated deviation" here refers, in particular, to a deviation at the time of the predicted future deviation.

[0007] Advantageously, the rapid charging characteristic curve to be used is determined such that the aging state of the electric energy storage device detected at a future horizontal point in time coincides with the associated aging state determined by the expected aging profile. In other words, the rapid charging characteristic curve to be used is selected such that, after one or more rapid charging processes performed using the rapid charging characteristic curve to be used, the aging state of the electric energy storage device again coincides with the expected aging state. If the electric energy storage device ages faster than planned, this advantageously allows for corrective intervention in the aging profile of the electric energy storage device and thus restores the target aging characteristic of the electric energy storage device. A "horizontal point in time" can be any future point in time that is in the future for at least the duration of the rapid charging process. Advantageously, the horizontal point in time is far enough in the future that multiple rapid charging processes can be performed using the rapid charging characteristic curve to reach the horizontal point in time.

[0008] Advantageously, a user of the electrical energy storage device, particularly a user of an electric vehicle in which a battery is installed, can select the fast-charging characteristic curve to be used by selecting from among the available fast-charging characteristic curves. This advantageously allows the user to personally determine how far in the future the leveling time should lie. In other words, the user of the electrical energy storage device can personally determine how many fast-charging cycles must be performed using the fast-charging characteristic curve to be used until the detected aging state of the electrical energy storage device is consistent with the aging state ascertained from the expected aging curve. By selecting the number of fast-charging cycles to be used, the user of the electrical energy storage device can directly select how long the fast-charging process should last in the future using the fast-charging characteristic curve, as there is a direct correlation between the duration of the fast-charging process and the positive impact on the aging state of the electrical energy storage device. In an advantageous embodiment, the available fast-charging characteristic curve can be identical to a plurality of stored fast-charging characteristic curves.

[0009] Advantageously, the leveling time or the selection information associated with the leveling time of the available rapid-charging characteristic curves is displayed to the user of the electrical energy storage device before selecting the rapid-charging characteristic curve to be used. The leveling time of the available rapid-charging characteristic curves is the time at which the detected aging state of the electrical energy storage device, through the use of the rapid-charging characteristic curve to be used, can correspond to the target aging state of the electrical energy storage device determined based on the expected aging curve. The associated selection information can be the individual influence of each variable associated with the leveling time, such as the rapid-charging characteristic curve, on the aging state of the electrical energy storage device, or, since physical relationships are defined here, the associated selection information can be the duration of a complete rapid-charging process using the corresponding rapid-charging characteristic curve.

[0010] The electrical energy storage device advantageously comprises a battery of an electric vehicle, since the described method is particularly suitable for operating lithium-ion batteries of electric vehicles.

[0011] A device that is designed to carry out each step of the method according to the present invention is advantageous. Furthermore, a computer program that is designed to carry out each step of the method according to the present invention when the computer program is executed on a computing unit is advantageous. The computing unit can be, for example, a control unit of the electrical energy storage device, such as a battery management system (BMS) of a battery.

[0012] Within the scope of the method presented, a fast charging characteristic curve previously determined in the laboratory is advantageously used.

[0013] As an alternative to observing the aging state of the electrical energy storage device, it is also possible to observe the aging gradient of the electrical energy storage device, that is, the change in the aging state of the electrical energy storage device per unit of time, and use this as the basis for the presented method. It is also conceivable to perform the presented method not using defined times, such as horizontal times, but rather using the total charge flowing through the electrical energy storage device as a reference system. Similarly, the total number of charging operations of the electrical energy storage device can be used as a reference system.

[0014] In particular, if the electrical energy storage device is a battery, the aging state of the electrical energy storage device can be, for example, in particular a state of health (SOH). C ). Used to determine SOH C The methods are sufficiently known from the prior art.

[0015] The described method is advantageously carried out using an aging controller, which can be a software module, for example. Using the aging controller, a degradation factor (DegFac) can be determined, which is used to reduce the aging of the electrical energy storage device. The degradation factor is as follows:

[0016]

[0017] to be calculated.

[0018] SOH here denotes the state of health, ie a measure for the aging of the electrical energy storage device. HOR represents the charge throughput, which is constant over the entire service life of the electrical energy storage device. HOR The product of the aging gradient and the aging margin (Alteringshorizont). The aging margin is the difference between two health state values ​​at different times. The subscript mess is used to denote a measured variable. The subscript est is used to denote an estimated variable. Soll Describes the expected aging gradient for an electric energy storage device, where:

[0019]

[0020] This relationship.

[0021] Qmax is the charge flow during the service life of an electrical energy storage device, for example a battery, from the expected start of service life (BOL) to the expected end of service life (EOL). estAs the quotient t consisting of the measured charge throughput and the measured capacity loss according to:

[0022]

[0023] to confirm. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] An embodiment of the present invention is described in detail below.

[0025] Figure 1 shows a schematic diagram of an electric vehicle;

[0026] Figure 2 A schematic diagram showing the respective effects of different rapid charging characteristics on the aging behavior of an electrical energy storage device;

[0027] Figure 3 A schematic diagram shows the effect of the use of a fast charging characteristic curve to be used on the aging state of an electrical energy storage device;

[0028] Figure 4 A schematic flow chart of an embodiment of the method according to the present invention is shown. DETAILED DESCRIPTION

[0029] Figure 1 A schematic diagram of an electric vehicle (10) is shown, which comprises an electric motor (17) and an electric energy storage device (12). The electric energy storage device (12) comprises a storage unit (14) and a control unit (16). The electric energy storage device can be a lithium-ion battery in particular. The method described is particularly suitable for operating a battery of an electric vehicle.

[0030] Figure 2 A schematic diagram shows the respective effects of different fast charging characteristic curves on the aging behavior of an electrical energy accumulator (12). Reference numeral 20 designates an aging state axis or a health state axis, wherein low values ​​on the aging state axis correspond to a high degree of aging. Reference numeral 22 designates a time axis. Alternatively, axis 22 can also be a charge axis, on which the accumulated total charge flowing through the electrical energy accumulator (12) during its service life is plotted. Alternatively, axis 22 can be a charge cycle axis, on which the sum of the charging cycles performed or to be performed of the electrical energy accumulator (12) is plotted.

[0031] The first rapid charging characteristic curve (24) has a first influence on the aging behavior of the electrical energy storage device (12). Figure 2As shown in , the state of health decreases over time. The second fast-charging characteristic curve (25) has a second influence on the aging characteristics of the energy storage device (12). The third fast-charging characteristic curve (26) has a third influence on the aging characteristics of the energy storage device (12). The fourth fast-charging characteristic curve, which corresponds to the standard-fast-charging characteristic curve, has a fourth influence on the aging characteristics of the energy storage device (12). As can be seen in Figure 2 As can be seen in the figure, the influence of the standard-rapid charging characteristic curve (27) is designed so that when using the standard-rapid charging characteristic curve for the rapid charging process of the electrical energy storage device (12), a low state of health (SOH) is reached at a relatively early time, while when using, for example, the first rapid charging characteristic curve (24), the same state of health (SOH) is reached at a later time.

[0032] Figure 3 A schematic diagram shows the effect of the use of a fast charging characteristic curve to be used on the aging state of the electrical energy storage device (12). Reference numeral 30 again denotes the aging state axis or health state axis. Reference numeral 32 again denotes the time axis or charge axis or charging cycle axis. Function 34 represents the expected aging curve, i.e., the decrease in the health state of the electrical energy storage device (12) over time. Figure 3 In the example shown, the actual aging state of the energy storage device (12) is detected at a first moment (38). The health state corresponding to the starting points of the arrows with reference numerals 35 and 36 is determined. The health state of the energy storage device (12) determined at the first moment (38) is lower than the target aging state of the energy storage device (12) determined with the aid of the expected aging curve (34), which corresponds to the value of the expected aging curve (34) at the first moment (38).

[0033] Continued operation of the energy storage device using the standard-fast charging characteristic curve (27) results in a detected aging state of the energy storage device (12) at the horizontal time (39) corresponding to the end point of the arrow indicated by reference numeral 35. In other words, continued operation of the energy storage device (12) using the standard-fast charging characteristic curve (27) results in a deviation between the detected aging state and the target aging state corresponding to the value of the aging profile (34) expected at the horizontal time (39). The fast charging characteristic curve to be used can be, for example, the first fast charging characteristic curve (24), and using the fast charging characteristic curve to be used can ensure that the detected aging state of the energy storage device (12) at the horizontal time (39) again corresponds to the aging profile (34) expected at the horizontal time (39). This is possible because the rapid charging characteristic curve to be used, for example the first rapid charging characteristic curve (24), has a smaller influence on the aging behavior of the electrical energy storage device (12) than the standard rapid charging characteristic curve (27).

[0034] Figure 4 A schematic flow chart of an embodiment of the method according to the present invention is shown. The embodiment begins with step 100, in which a rapid charging process is started. The electrical energy storage device (12) can be a lithium-ion battery of an electric vehicle (10), and the rapid charging process of the electrical energy storage device (12) can be started, for example, by connecting the electrical energy storage device (12) to a rapid charging station or by actuating a corresponding operating element. Step 110 is performed immediately after step 100.

[0035] In step 110, a check is performed to determine whether the fast-charging characteristic curve to be used has been recently modified. A recent modification could, for example, be a modification carried out within a few predeterminable fast-charging cycles. For example, a check could be performed to determine whether the currently stored fast-charging characteristic curve has been used ten times for a fast-charging process. If the check within step 110 indicates that the fast-charging characteristic curve has been recently modified, step 150 follows step 110. If the check within step 110 indicates that the fast-charging characteristic curve has not been recently modified, i.e., for example, the stored fast-charging characteristic curve has been used for ten fast-charging cycles, step 120 follows.

[0036] In step 120, the aging state of the electrical energy storage device (12) is detected. For this purpose, the health state of the electrical energy storage device (12) can be determined, for example, using methods known from the prior art. Furthermore, within the scope of step 120, the target aging state of the electrical energy storage device (12) at the current moment is determined. For this purpose, the expected aging curve (34) of the electrical energy storage device (12) at the current moment is analyzed. Step 120 is followed by step 130.

[0037] In step 130, the aging state of the electrical energy storage device (12) detected in step 120 is compared with the target aging state of the electrical energy storage device (12) determined in step 120. If this comparison results in a deviation greater than a predefinable tolerance, step 130 is followed by step 140. If the comparison does not result in a deviation greater than a predefinable tolerance, step 130 is followed by step 100.

[0038] The electric energy storage device (12) can in particular be a lithium-ion battery of an electric vehicle (10), and in step 140 different fast-charging characteristic curves and selection information for the different fast-charging characteristic curves associated with the horizontal time can be displayed to the user of the electric energy storage device (12). The selection information associated with the horizontal time can in particular be a certain number of fast-charging processes that must be performed with the corresponding fast-charging characteristic curve in order to reconcile the detected aging state of the electric energy storage device (12) with the target aging state of the electric energy storage device (12). The selection information associated with the horizontal time (39) can also be, for example, the duration of the fast-charging process that is required to charge the electric energy storage device (12) when using each fast-charging characteristic curve. The user of the electric energy storage device (12) then selects the fast-charging characteristic curve displayed to him. In an alternative embodiment, the fast-charging characteristic curve is selected within the scope of step 140 not by the user but by a computing unit that implements an embodiment of the method according to the present invention. Step 140 is followed by step 150.

[0039] In step 150, the fast charge characteristic curve selected in step 140 is stored in a memory, and a fast charge process is subsequently performed using the newly stored fast charge characteristic curve. If the fast charge characteristic curve is not newly stored within the scope of step 150, the fast charge process is performed using the already stored fast charge characteristic curve.

[0040] The described embodiment of the method according to the invention makes it possible to increase the service life of the electrical energy storage device (12), which can in particular be a lithium-ion battery. Overloading of the electrical energy storage device (12) due to too frequent rapid charging is detected by means of the described embodiment of the method according to the invention and compensated by using a suitable rapid charging characteristic curve. As a result, a specified expected service life of the electrical energy storage device (12) is maintained. It is particularly advantageous that the described embodiment of the method according to the invention does not require additional hardware but can be implemented solely by using suitable software.

Claims

1. A method for operating an electrical energy storage device (12), the aging behavior of which is estimated using an expected aging curve (34), characterized in that: A fast charging characteristic curve to be used for the electric energy storage device (12) is determined based on a comparison between the detected aging state of the electric energy storage device and a target aging state of the electric energy storage device determined by means of an expected aging profile, wherein the fast charging characteristic curve allows fast charging at a defined aging within a defined time, wherein the fast charging characteristic curve to be used is determined in such a way that the aging state detected at a future horizontal point in time (39) of the electric energy storage device corresponds to the associated aging state determined by the expected aging profile (34), wherein a user of the electric energy storage device (12) can select the fast charging characteristic curve to be used by selecting available fast charging characteristic curves, and wherein the horizontal point in time (39) or selection information of the available fast charging characteristic curves associated with the horizontal point in time (39) is displayed to the user of the electric energy storage device (12) before selecting the fast charging characteristic curve to be used.

2. The method according to claim 1, characterized in that The rapid charging characteristic curve to be used is determined in such a way that a future deviation between the detected aging state of the electric energy accumulator (12) and a target aging state of the electric energy accumulator (12) determined with the aid of an expected aging profile (34) is smaller than the associated deviation between the detected aging state of the electric energy accumulator (12) and the target aging state of the electric energy accumulator (12) determined with the aid of the expected aging profile (34) when using a standard rapid charging characteristic curve (27).

3. The method according to claim 1, characterized in that A fast charging characteristic curve to be used is determined by selecting the fast charging characteristic curve to be used from a plurality of stored fast charging characteristic curves that differ from one another with respect to their influence on the aging behavior of the electrical energy storage device.

4. The method according to any one of claims 1 to 3, characterized in that The electrical energy storage device (12) comprises a battery of an electric vehicle (10).

5. Apparatus configured to carry out each step of the method according to claim 1. 6 . A computer program product comprising a computer program configured to execute each step of the method according to claim 1 , when the computer program is run on a computer.

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