DE102020110066A1 - Method for determining a current state of aging of an electrical energy store and electrical energy store - Google Patents

Abstract

The invention relates to a method for determining a current state of aging of an electrical energy store of a motor vehicle by means of an electronic computing device (10), in which a maximum cell growth force is determined by means of the electronic computing device (10) by means of a first mathematical model (12), the cell growth force being a Force describes which a battery cell of the electrical energy store is allowed to generate due to the aging of the battery cell within a housing of the electrical energy store, the maximum cell growth force being described in the first mathematical model (12) as a function of a maximum state of aging, with a current charge throughput (∑Q ) is determined within the battery cell by means of the electronic computing device (10), with the aid of a second mathematical model (14) which shows the relationship between the charge throughput (∑Q) and the state of aging and describes how the current aging condition is determined as a function of the current charge throughput (∑Q) and the current aging condition is compared with the maximum aging condition by means of the electronic computing device (10). The invention also relates to an electrical energy store (10).

Description

The invention relates to a method for determining a current state of aging of an electrical energy store of an at least partially electrically operated motor vehicle by means of an electronic computing device of the electrical energy store according to the preamble of claim 1. The invention also relates to an electrical energy store.

Lithium-ion battery cells increase in thickness over the course of their life cycle. Only when a battery cell can no longer be used, the so-called End of Life (EOL), does growth stop. For this reason, a corresponding installation space must be kept in the prior art in order to allow the growth of the battery cell. By pre-tensioning the battery cells, growth can be slowed down, but not stopped. In a battery module with tensioned battery cells, the reserved buffer zone can be reduced if the state of the deformation or the pressure build-up is tracked using a model-based estimate.

Sufficient installation space is usually reserved in electrical energy storage devices for cell growth until the end of growth with zero percent residual capacity. Often, however, the area of up to 70 percent of the remaining capacity is sufficient for the life cycle of an electrical energy storage system. This increases the price and installation space without generating additional customer benefits. In the case of complex prismatic cell geometries, a mechanism with a predetermined breaking point can stop the growth in thickness by prematurely disconnecting the electrical connection. However, this makes the structure of the battery cell more complex, more expensive and the volumetric energy density lower.

The WO 2017/087807 A1 discloses an electrical device having a battery and a battery management system. The battery management system includes a controller in electrical communication with a pressure sensor to monitor the health of the battery. The controller applies a health status method that uses a non-electrical signal from force measurements in combination with an incremental capacity analysis to estimate battery depletion and other health indicators with better accuracy than the existing methods. The pressure sensor can provide the force measurement signal to the controller, which can then determine which incremental capacity curve to use based on the force for the particular battery. The controller then runs a program that uses the data from the pressure sensor and the stored incremental capacity curves based on the force to estimate the capacity depletion and signal the percentage of health to the user.

The object of the present invention is to create a method and an electrical energy store by means of which a state of aging or a state of health of the electrical energy store can be reliably determined.

This object is achieved by a method and by an electrical energy store according to the independent claims. Advantageous embodiments are specified in the subclaims.

One aspect of the invention relates to a method for determining a current state of aging of an electrical energy store of an at least partially electrically operated motor vehicle by means of an electronic computing device of the electrical energy store, in which a maximum cell growth force is determined by means of the electronic computing device by means of a first mathematical model, the cell growth force being a Force describes which a battery cell of the electrical energy store is allowed to generate due to aging of the battery cell within a housing of the electrical energy store, the maximum cell growth force being described in the mathematical model as a function of a maximum state of aging.

It is provided that a current charge throughput within the battery cell is determined by means of the electronic computing device, with the current aging state being determined as a function of the current charge throughput and the current one using a second mathematical model that describes the relationship between the charge throughput and the state of aging Aging condition is compared with the maximum aging condition by means of the electronic computing device.

This makes it possible for the state of aging of the electrical energy store to be estimated using the two mathematical models. In particular, this is sensor-independent, whereby a reliable and robust estimate of the state of aging or the state of health (State oh Health - SOH) can be realized. This estimation-based shutdown saves costs compared to a dedicated sensor and is more robust, since no force sensor can fail because it does not exist. Corresponding limits or threshold values are stored in a software-based manner and can be adjusted accordingly on the basis of new findings.

In other words, at the end of the mechanical design of the electrical energy store, the relationship between the average remaining capacity, which may correspond to the state of aging or the state of health (SOH), of the battery cells and the force build-up in the mechanical cell block assembly is determined in several tests becomes. The maximum permitted force, defined by the mechanical stability of the block and the cells themselves, is converted into a maximum permitted average remaining cell capacity. During operation, the battery control device, in other words the electronic computing device, tracks the remaining capacity and when the critical limit is reached, the connection of the battery cell is prevented.

For online monitoring of the remaining capacity, a voltage relaxation (Open Circuit Voltage, OCV) in a high state of charge is first waited for and the associated cell voltages are saved. It then waits for an OCV state in the low state of charge range. The remaining capacity of each cell can be determined using a stored open-circuit voltage curve, which is particularly valid for the SOH target state, and the discharged net amount of charge between the two relaxation points. In this way, the remaining capacity of each individual cell can be determined selectively at least at certain time intervals. Between two valid determinations of the remaining capacity, this is estimated using a conservative aging model. For example, the worst-case relationship between loss of capacity and energy throughput can be used here.

According to an advantageous embodiment, if the current aging condition corresponds to the maximum aging condition, a warning signal for a user is generated by means of the electronic computing device.

It is also advantageous if the first mathematical model and / or the second mathematical model are specified experimentally.

In a further advantageous embodiment, the maximum aging condition is specified with a safety buffer.

Another aspect of the invention relates to an electrical energy store for an at least partially electrically operated motor vehicle, with at least one battery cell and with at least one electronic computing device, the electrical energy store being designed to carry out a method according to the preceding aspect. In particular, the method is carried out by means of the electrical energy store.

Yet another aspect of the invention relates to a motor vehicle with an electrical energy store. The motor vehicle is at least partially operated electrically, in particular operated fully electrically.

Advantageous embodiments of the method are to be regarded as advantageous embodiments of the electrical energy store and of the motor vehicle. For this purpose, the electrical energy store and the motor vehicle have objective features which enable the method or an advantageous embodiment thereof to be carried out.

Further advantages, features and details of the invention emerge from the following description of preferred exemplary embodiments and with reference to the drawings. The features and combinations of features mentioned above in the description as well as the features and combinations of features mentioned below in the description of the figures and / or shown alone in the figures can be used not only in the respectively specified combination, but also in other combinations or on their own, without the scope of the Invention to leave.

• 1 ein schematisches Ablaufdiagramm einer Ausführungsform des Verfahrenes; und
• 2 ein schematisches elektrische Arbeit-Kapazitätsdiagramm.

Show:

• 1 a schematic flow diagram of an embodiment of the method; and
• 2 a schematic electrical work capacity diagram.

Identical or functionally identical elements are provided with the same reference symbols in the figures.

1 shows a schematic view of a flow chart according to an embodiment of the invention. In particular, the method takes place in an electronic computing device 10 an electrical energy store, not shown, with at least one battery cell instead. This in 1 The method shown has the particular aim of preventing the electrical energy store of a motor vehicle, not shown, from being mechanically damaged as a result of excessive cell growth, that is to say before a battery cell module bursts or can be blown open.

In a first step S1 in particular, an empirical or an experimental determination of the relationship takes place between a state of aging, which can also be referred to as state-of-health (SOH), and a force, in particular a cell growth force, which acts on a module frame of the electrical energy store as a result of an increase in cell thickness. A first mathematical model is used for this purpose 12th generated. In a second step S2 the determination of a maximum force induced by cell thickness growth at which the module frame breaks is also carried out empirically or experimentally. This force corresponds based on the first mathematical model 12th a maximum SOH. Now the SOH would actually only have to be continuously determined or monitored while the motor vehicle is in operation. Appropriate precautionary measures could then be initiated in good time before the SOH reaches the maximum SOH value. The disadvantage here, however, is the measurement of the open circuit voltage (OCV) for the determination of SOH, for which the battery cells of the electrical energy store have to be in a relaxed state.

However, this is usually only achieved after a long waiting period, which can be in the range of one or even several hours. Direct, continuous determination of the SOH during operation is therefore not possible. According to the invention, a substitute variable is therefore used that can be continuously determined and with the help of which one can infer the SOH. Thus, the SOH is determined indirectly continuously with the help of the substitute measured variable. The substitute measured variable is as in a third step S3 described, the charge throughput (ΣQ). The relationship between the charge throughput ∑Q and SOH is also determined empirically / experimentally. Thus, a direct relationship between the charge throughput ∑Q and the SOH is known.

In a fourth step S4 the charge throughput ∑Q is thus continuously measured during operation and with the aid of a second mathematical model 14th the SOH is determined and using the first mathematical model 12th monitors the approach to the maximum allowable cell thickness growth.

In a fifth step S5 As already mentioned, precautionary measures are taken in good time before the maximum SOH is reached, i.e. a warning message is displayed to the driver at a certain SOH value, which prompts him, for example, to drive to the nearest workshop and have the electrical energy storage checked . In connection with the present invention, timely therefore means that a SOH value is set which in any case still allows driving to the next workshop before the SOH maximum value is reached at which the electrical energy store is mechanically due to bursting of the module cells is harmed. Through this safety buffer (see line 18th in 2 ) the safety shutdown of the electrical energy storage device during operation or a safety non-activation of commissioning are not required, but the said warning message to the driver is sufficient.

In a sixth step S6 takes place after the warning message is issued to the driver that he can, for example, drive to a workshop. There the battery or the electrical energy storage device is checked. A detailed capacity determination is carried out for this purpose. If it turns out that the SOH is still sufficiently far from the maximum SOH, the electrical energy storage device can continue to be used and, for example, further kilometers are enabled for the user to use. The method according to the invention then starts from the beginning. If it turns out that the SOH corresponds to the maximum SOH or comes impermissibly close to it, the electrical energy storage device has had its day and may have to be replaced by a new electrical energy storage device.

2 shows a schematic electrical work capacity diagram. The electrical work in megawatt hours is plotted on the abscissa and the capacity in percent is plotted on the ordinate. In particular, the end-of-life capacity of the electrical energy store is indicated by the designation EOL. This is particularly indicated by the dashed line 16 shown. By the dotted line 18th in particular, a safety buffer based on a measurement tolerance capacity is shown. Through the line 20th the course of the capacity of an average customer is shown. Through the line 22nd a so-called worst-case scenario for the use of the energy storage system is shown. Furthermore, the 2 so-called recalibration values 24 and 26th . There is also an initial limit value 28 as well as recalibrated limit values 30th , 32 shown.

The 2 thus shows that in operation by the electronic computing device 10 the remaining capacity can be tracked. In particular, it is shown how the capacity gradually decreases through normal use, which is indicated by the line 20th is shown. As a precaution, however, one must always keep an eye on the case that the electrical energy storage device is used in such a way that it is maximally stressed and maximally degraded, which is shown in particular by the worst-case scenario. Such maximum stressful use can take place after every normal use, so this is due to the recalibration values 24 , 26th is shown. Furthermore, a buffer is kept in reserve for the sake of security, the measurement tolerances for the Determination of the capacity taken into account. The EOL capacity, that is to say the capacity of the electrical energy storage device at the end of its usefulness in the motor vehicle, corresponds to the maximum state of aging or the maximum SOH.

The limit value of the EOL capacity and thus also the maximum SOH must and can therefore be recalibrated, in particular recalibrated, on the basis of usage behavior. This can in particular also be referred to as tracking. This is particularly due to the recalibration values 24 and 26th shown.

Overall, the invention shows a shutdown of a high-voltage battery due to cell thickness growth on the basis of an estimate of the remaining capacity.

List of reference symbols

10

electrical energy storage

12

first mathematical model

14th

second mathematical model

16

End-of-life line

18th

Safety buffer line

20th

Average line

22nd

Worst case line

24

Recalibration value

26th

Recalibration value

28

initial limit value

30th

recalibrated limit value

32

recalibrated limit value

S1

first step

S2

second step

S3

Third step

S4

fourth step

S5

fifth step

S6

sixth step

QUOTES INCLUDED IN THE DESCRIPTION

This list of the documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent literature cited

• WO 2017/087807 A1 [0004]

Claims (5)

A method for determining a current state of aging of an electrical energy store of an at least partially electrically operated motor vehicle by means of an electronic computing device (10) of the electrical energy store, in which a maximum cell growth force is determined by means of the electronic computing device (10) by means of a first mathematical model (12), wherein the cell growth force describes a force which a battery cell of the electrical energy store is allowed to generate due to the aging of the battery cell within a housing of the electrical energy store, the maximum cell growth force being described in the first mathematical model (12) as a function of a maximum state of aging, characterized in that a current charge throughput (∑Q) within the battery cell is determined by means of the electronic computing device (10), which by means of a second mathematical model (14) describes the relationship between the charge throughput (∑Q) and the aging condition, the current aging condition is determined as a function of the current charge throughput (∑Q) and the current aging condition is compared with the maximum aging condition using the electronic computing device (10). Procedure according to Claim 1 , characterized in that if the current aging condition matches the maximum aging condition, a warning signal for a user is generated by means of the electronic computing device (10). Procedure according to Claim 1 or 2 , characterized in that the first mathematical model (12) and / or the second mathematical model (14) are predetermined experimentally. Method according to one of the preceding claims, characterized in that the maximum aging condition is specified with a safety buffer (18). An electrical energy store for an at least partially electrically operated motor vehicle, with at least one battery cell and with at least one electronic computing device (10), the electrical energy store for performing a method according to one of the Claims 1 to 4th is trained.

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