DE102018214984A1 - Method for determining an ambient temperature of a first electrical energy storage unit in conjunction with second electrical energy storage units, and corresponding device, computer program and machine-readable storage medium - Google Patents

Abstract

A method for determining the ambient temperature of a first electrical energy storage unit is described, the first electrical energy storage unit being connected to second electrical energy storage units. The following steps are carried out: a) determining a temperature of the first electrical energy storage unit using a temperature sensor; b) determining a temperature difference between the first electrical energy storage unit and the surroundings of the first electrical energy storage unit; c) determining an ambient temperature as a function of the temperature of the first electrical energy storage unit and the temperature difference. Furthermore, a corresponding device, a corresponding computer program and a corresponding machine-readable storage medium are described.

Description

The present disclosure describes a method for determining the ambient temperature of a first electrical energy storage unit, which is in a network with second electrical energy storage units.

State of the art

Electrical energy storage units, in particular battery cells or electrical energy stores constructed from the same, show a strong dependency of their performance, i.e. in particular their ability to deliver or absorb current, their temperature. Typically, the permissible electrical current drops sharply when the current is supplied or in particular when the current is drawn at temperatures of around or below 0 ° C. An amperage that is higher than the permissible level thus often leads to damage to an electrical energy storage unit, for example lithium plating - the unwanted deposition of lithium - which cannot be reversed. Compliance with the permissible current strengths is therefore an important requirement when operating electrical energy storage units. The permissible current strengths can have a dependence on the temperature of the electrical energy storage units in order to take into account the temperature dependence of the performance.

Typically, for reasons of cost, not all electrical energy storage units which are installed in a network, for example in a battery pack, are provided with temperature sensors. It is therefore not possible to determine the temperatures of all electrical energy storage units directly. A temperature sensor is often used, which is located on what is supposed to be the hottest electrical energy storage unit during operation. This means that only the temperature of the supposedly hottest cell is immediately available.

The temperatures of the further electrical energy storage units in the network are optionally determined using mathematical models and methods. Since the mathematical models typically model heat exchange processes, knowledge of an ambient temperature of the corresponding electrical energy storage unit is required for precise mathematical modeling. If there is no knowledge of the ambient temperature, the temperatures of the further electrical energy storage units can only be estimated imprecisely. It is therefore necessary that their respective current limits have a corresponding safety buffer, as a result of which it is not possible to call up the entire performance of the further electrical energy storage units.

As a consequence, the electrical energy storage units are usually oversized. In particular, a larger electrical capacity of the electrical energy storage units or another type of cell, for example with different cell chemistry, may be required.

In the publication US 2007/0024244 describes a method for determining the ambient temperature, a control process being triggered based on the determined temperature.

Disclosure of the invention

Advantages of the invention

A method for determining an ambient temperature of a first electrical energy storage unit is disclosed, the first electrical energy storage unit being connected to second electrical energy storage units. A network can represent a battery pack, for example.

A temperature of the first electrical energy storage unit is determined using a temperature sensor. The temperature sensor can be mounted in or on the first electrical energy storage unit.

Furthermore, a temperature difference between the first electrical energy storage unit and the surroundings of the first electrical energy storage unit is determined. The surroundings can represent, for example, the air surrounding the first electrical energy storage unit or, for example, one Edging made of metal of the first electrical energy storage unit or the first electrical energy storage unit and the second electrical energy storage units.

Furthermore, an ambient temperature of the surroundings of the first electrical energy storage unit is determined as a function of the temperature of the first electrical energy storage unit and the temperature difference.

This is advantageous because it determines the temperature of the surroundings of the first electrical energy storage unit and can therefore also be used to adjust the current limits of the first electrical energy storage unit to suit the temperature. This advantageously enables higher power to be drawn from the first electrical energy storage unit.

Further advantageous embodiments of the present invention are the subject of the dependent claims.

An electrical current strength of an electrical current flowing into or out of the first electrical energy storage unit is expediently determined and compared with a predefined threshold value, with the current strength at least determining and determining the temperature of the first electrical energy storage unit when the predefined threshold value is reached and / or undershot the temperature difference between the first electrical energy storage unit and its environment is carried out. This is advantageous because the ambient temperature can be determined more precisely under these conditions.

The amount of the predefined threshold value is advantageously between 0 A and 10 A, preferably between 0 A and 5 A, particularly preferably between 0 A and 1 A. This advantageously ensures that the first electrical energy storage unit does not become too strong due to ohmic losses inside ”is heated, which increases the accuracy of the determination of the ambient temperature. The step of determining the ambient temperature can also be carried out if the predefined threshold value is exceeded, as long as it is ensured that the temperature of the first electrical energy storage unit and the temperature difference are determined when the current intensity reaches and / or falls below the predefined threshold value.

A temperature of another of the second electrical energy storage units is expediently determined as a function of the determined ambient temperature of the first electrical energy storage unit. In order to maintain current limits of the further electrical energy storage unit, power electronics are activated, the current limits being set as a function of the determined temperature of the further electrical energy storage unit. Such power electronics can be an inverter, for example. This is advantageous since the current limits can be set more precisely, that is to say less conservatively - with less safety reserve - as a function of the determined ambient temperature, as a result of which a higher power output or power consumption is possible. This is particularly relevant for applications of electrical energy storage units in which they have to consume a lot of power in a short time, for example in so-called boost recuperation systems based on 48V.

The temperature sensor is expediently mounted in or on the first electrical energy storage unit. This is advantageous since the temperature of the first electrical energy storage unit can thus be determined directly.

The temperature difference between the first electrical energy storage unit and the surroundings of the first electrical energy storage unit is expediently determined as a function of a rate of change in the temperature of the first electrical energy storage unit over time. This is advantageous since the rate of change in the temperature of the first electrical energy storage unit can be determined in a simple manner using the temperature sensor, which enables the method to be implemented quickly and easily and the ambient temperature to be determined precisely.

The temperature difference between the first electrical energy storage unit and the surroundings of the first electrical energy storage unit is expediently determined as a function of a constant, the constant representing the ratio of a heat capacity of the first electrical energy storage unit to a thermal resistance of the first electrical energy storage unit. This is advantageous since the constant can be determined in a simple manner by laboratory tests, that is to say in advance of the execution of the method, which enables the method to be implemented easily.

The execution sequence of the individual method steps is advantageously adapted in accordance with the requirements of a specific application. For example, the temperature of the first electrical energy storage unit can be determined before the current intensity of the electrical current flowing into or out of the first electrical energy storage unit can be determined. There is also a reverse execution of the process steps.

The disclosure furthermore relates to a device for determining the ambient temperature of a first electrical energy storage unit, comprising a temperature sensor which is in particular mounted in or on the first electrical energy storage unit, and at least one means which are set up to carry out the steps of the disclosed method.

This is advantageous because it enables the advantages of the disclosed method to be realized.

The at least one means can comprise, for example, a battery management control device and corresponding power electronics, for example 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 control device, can also be such a means. An electronic control unit, in particular an electronic control unit, which for example includes a microcontroller and / or an application-specific hardware module, e.g. an ASIC, can be understood, but may also include a personal computer or a programmable logic controller.

The disclosure furthermore relates to a computer program which comprises instructions which cause the disclosed device to carry out the disclosed method steps. This is advantageous because the advantages of the disclosed method can be realized by the computer program.

The disclosure furthermore relates to a machine-readable storage medium on which the disclosed computer program is stored. In addition to the above-mentioned advantages of the disclosed method, there is the further advantage that the disclosed computer program can be easily distributed on the machine-readable storage medium.

An electrical energy storage unit can in particular be understood to mean an electrochemical battery cell and / or a battery module with at least one electrochemical battery cell and / or a battery pack with 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 of the type lithium polymer accumulator, nickel-metal hydride accumulator, lead-acid accumulator, lithium-air accumulator or lithium-sulfur accumulator or very generally an accumulator of any electrochemical composition. A capacitor is also possible as an electrical energy storage unit.

Figure list

Advantageous embodiments of the invention are shown in the figures and detailed in the following description.

• 1 ein Flussdiagramm des offenbarten Verfahrens gemäß einer ersten Ausführungsform;
• 2 ein Flussdiagramm des offenbarten Verfahrens gemäß einer zweiten Ausführungsform;
• 3 ein Flussdiagramm des offenbarten Verfahrens gemäß einer dritten Ausführungsform; und
• 4 eine schematische Darstellung der offenbarten Vorrichtung gemäß einer Ausführungsform.

Show it:

• 1 a flowchart of the disclosed method according to a first embodiment;
• 2 a flowchart of the disclosed method according to a second embodiment;
• 3 a flowchart of the disclosed method according to a third embodiment; and
• 4 is a schematic representation of the disclosed device according to an embodiment.

Embodiments of the invention

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

1 shows a flow diagram of the disclosed method according to a first embodiment. In a first step S11 a temperature of a first electrical energy storage unit is determined by means of a temperature sensor mounted in or on the first electrical energy storage unit. The first electrical energy storage unit is in a network with second electrical energy storage units.

nach ΔT_cell2env umgestellt: $$\mathrm{\Delta }{T}_{cell2env}=\frac{m\ast c_p\ast \frac{dT}{dt}-A_{cell2cell}\ast {\alpha }_{cell2cell}\ast \mathrm{\Delta }{T}_{cell2cell}-\dot{Q}}{A_{cell2env}\ast {\alpha }_{cell2env}}$$

In a second step S12 a temperature difference between the first electrical energy storage unit and the surroundings of the first electrical energy storage unit is determined. This is the formula $$m\ast c_p\ast \frac{dT}{dt}=\dot{Q}+A_{cell2env}\ast {\alpha }_{cell2env}\ast \mathrm{\Delta }{T}_{cell2env}+A_{cell2cell}\ast {\alpha }_{cell2cell}\ast \mathrm{\Delta }{T}_{cell2cell}$$

converted to ΔT _cell2env : $$\mathrm{\Delta }{T}_{cell2env}=\frac{m\ast c_p\ast \frac{dT}{dt}-A_{cell2cell}\ast {\alpha }_{cell2cell}\ast \mathrm{\Delta }{T}_{cell2cell}-\dot{Q}}{A_{cell2env}\ast {\alpha }_{cell2env}}$$

die zeitliche Änderungsrate der Temperatur der ersten elektrischen Energiespeichereinheit, A_cell2cell die Fläche, über die Wärme mit benachbarten elektrischen Energiespeichereinheiten ausgetauscht wird, α_cell2cell den Wärmeübertragungskoeffizienten zu benachbarten elektrischen Energiespeichereinheiten, ΔT_cell2cell die Temperaturdifferenz zwischen der ersten elektrischen Energiespeichereinheit und einer benachbarten Zelle, Q einen Wärmestrom, welcher sich aus ohmschen Verlusten und Wärme aufgrund chemischer Rekationen zusammensetzt, A_cell2env die Fläche, über die Wärme mit der Umgebung ausgetauscht wird und α_cell2env den Wärmeübertragungskoeffizienten zu der Umgebung, beispielsweise Luft, der ersten elektrischen Energiespeicherungseinheit.M represents the mass of the electrical energy storage unit, c _p the specific heat capacity of the electrical energy storage unit, $\frac{dT}{dt}$

the rate of change of the temperature of the first electrical energy storage unit over time, A _cell2cell the area over which heat is exchanged with neighboring electrical energy storage _units , α _cell2cell the heat transfer coefficient to neighboring electrical energy storage _units , ΔT _cell2cell the temperature difference between the first electrical energy storage unit and an adjacent cell, Q one Heat flow, which is made up of ohmic losses and heat due to chemical recations, A _cell2env the area over which heat is exchanged with the environment and α _cell2env the heat transfer coefficient to the environment, for example air, of the first electrical energy storage unit.

wobei der Term Q zu Q̇ = R ∗ I² gesetzt wird, da die durch ohmsche Verluste in der Zelle erzeugte Verlustleistung typischerweise stark dominierend ist im Wärmestrom Q. Somit stellt R einen Innenwiderstand der ersten elektrischen Energiespeichereinheit dar und I den durch sie fließenden elektrischen Strom bzw. dessen Stromstärke. Der Strom beziehungsweise die Stromstärke kann mit einem Stromsensor ermittelt werden. Somit wird unter Berücksichtigung der Systemkenngrößen m, c_p, A_cell2env, α_cell2env und R und der für die erste elektrische Energiespeichereinheit gemessenen Größen I und $\frac{dT}{dt}$

die Temperaturdifferenz zwischen der ersten elektrischen Energiespeichereinheit und der Umgebung der ersten elektrischen Energiespeichereinheit ermittelt.Since there is usually only minimal heat exchange between adjacent electrical energy storage units, the corresponding term is neglected and it results $$\mathrm{\Delta }{T}_{cell2env}=\frac{m\ast c_p\ast \frac{dT}{dt}-R\ast I^2}{A_{cell2env}\ast {\alpha }_{cell2env}}$$

where the term Q is set to Q̇ = R ∗ I ² , since the power loss generated by ohmic losses in the cell is typically very dominant in the heat flow Q. Thus, R represents an internal resistance of the first electrical energy storage unit and I the electrical current flowing through it or its amperage. The current or the current strength can be determined with a current sensor. Taking into account the system parameters m, c _p , A _cell2env , α _cell2env and R and the variables I and. Measured for the first electrical energy storage unit $\frac{dT}{dt}$

the temperature difference between the first electrical energy storage unit and the surroundings of the first electrical energy storage unit is determined.

In a third step S13 is then determined by means of T _env = T _sens + ΔT _cell2env , where T _sens represents the temperature of the first electrical energy storage unit determined in the first step, the ambient temperature of the first electrical energy storage unit.

2 shows a flow diagram of the disclosed method according to a second embodiment. In a first step S21 a current intensity of an electrical current flowing from a first electrical energy storage unit is determined. So this happens when the first electrical energy storage unit is discharged. Alternatively, the first step S11 can also be carried out during a charging process of the first electrical energy storage unit. The first electrical energy storage unit is in a network with second electrical energy storage units.

Then in a second step S22 the in the first step S21 Compare the determined current strength with a predefined threshold value, for example 1 A here. If the determined current strength is above the predefined threshold value, the first step becomes again S21 carried out. If the ascertained current is below the ascertained threshold value or if the ascertained amperage is equal to the ascertained threshold value, the third step is followed S23 continued. The term R ∗ I ² can be neglected due to the low current. Typically, the predefined threshold value is therefore chosen such that the influence of the heating of the first electrical energy storage unit due to a current flow is small or negligible.

In the third step S23 the temperature of the first electrical energy storage unit is determined using a temperature sensor attached to the electrical energy storage unit. At least the temperature of the first electrical energy storage unit at the measuring point is thus known.

Hierbei bezeichnet k eine Konstante, wobei die Konstante das Verhältnis von einer Wärmekapazität der ersten elektrischen Energiespeichereinheit zu einem Wärmewiderstand der ersten elektrischen Energiespeichereinheit repräsentiert. Diese Konstante k kann beispielsweise im Vorfeld der Verfahrensausführung mittels eines Experiments im Labor einfach ermittelt werden.In a fourth step S24 a temperature difference is determined between the first electrical energy storage unit and the surroundings of the first electrical energy storage unit, the following formula being used for this purpose: $$\mathrm{\Delta }{T}_{cell2env}=\frac{m\ast c_p}{\underset{k}{\underbrace{A_{cell2env}\ast {\alpha }_{cell2env}}}}\frac{dT}{dt}$$

Here, k denotes a constant, the constant representing the ratio of a heat capacity of the first electrical energy storage unit to a thermal resistance of the first electrical energy storage unit. This constant k can easily be determined, for example, in the run-up to the execution of the method by means of an experiment in the laboratory.

In a fifth step S25 is then determined by means of T _env = T _sens + ΔT _cell2env , where T _sens represents the temperature of the first electrical energy storage unit determined in the first step, the ambient temperature of the first electrical energy storage unit.

3 shows a flow diagram of the disclosed method according to a third embodiment. The first step S31 corresponds to the first step S11 , the second step S32 corresponds to the second step S12 and the third step S33 corresponds to the third step S13 , The first electrical energy storage unit is in a network with second electrical energy storage units.

wobei gegebenenfalls Terme vernachlässigt werden können, da beispielsweise der Wärmeaustausch mit benachbarten elektrischen Energiespeichereinheiten oder die Wärmeerzeugung aufgrund ohmscher Verluste in der Zelle relativ gering sind. Gegebenenfalls kann das mathematische Modell Teil eines Kalmanfilters oder eines Luenberger-Beobachters oder einer anderen geeigneten regelungstechnischen Struktur sein.In a fourth step S34 the temperature of a further electrical energy storage unit is determined, the further electrical energy storage unit being one of the second electrical energy storage units. A mathematical model for the temperature of the further electrical energy storage unit is used, so that a temperature sensor on the further electrical energy storage unit is not required. For example, the mathematical model can contain a differential equation for the temperature estimation of the further electrical energy storage unit, such as the following: $$m\ast c_p\ast \frac{dT}{dt}=\dot{Q}+A_{cell2env}\ast {\alpha }_{cell2env}\ast \mathrm{\Delta }{T}_{cell2env}+A_{cell2cell}\ast {\alpha }_{cell2cell}\ast \mathrm{\Delta }{T}_{cell2cell}$$

where appropriate, terms may be neglected, since, for example, the heat exchange with neighboring electrical energy storage units or the generation of heat due to ohmic losses in the cell are relatively low. If necessary, the mathematical model can be part of a Kalman filter or a Luenberger observer or another suitable control structure.

In a fifth step S35 power electronics, for example an inverter, are then actuated in order to comply with at least one current limit value of the further electrical energy storage unit. The current limit value becomes dependent on that in the fourth step S34 determined temperature of the further electrical energy storage unit set. This makes it possible to call up a higher output from the further electrical energy storage unit, since the current limit value can be set less conservatively on the basis of the known temperature.

The disclosed method is advantageously used in particular for the current limit value in the charging direction, since electrical energy storage units, in particular those based on lithium-ion, have lower ones Temperatures, especially below 5 ° C, should only be charged with reduced currents in order to avoid damage. By means of the disclosed method, this current limit value in the charging direction can be set less conservatively, that is to say higher, since the temperature of the further electrical energy storage unit is determined and is therefore known.

Zusätzlich zu den bereits oben eingeführten Größen werden in der vorstehenden Gleichung die Größe A_cell2cool, welche eine Fläche der ersten elektrischen Energiespeichereinheit zu einem Kühlelement, beispielsweise eine Kühlplatte repräsentiert, die Größe α_cell2cool, welche einen Wärmeübertragungskoeffizienten zu dem Kühlelement repräsentiert, und ΔT_cell2cool, welche eine Temperaturdifferenz zwischen der ersten elektrischen Energiespeichereinheit und dem Kühlelement repräsentiert, eingeführt.If the first electrical energy storage unit is exposed to active cooling, the formula for determining the temperature difference between the first electrical energy storage unit and the surroundings of the first electrical energy storage unit is: $$\begin{array}{c}m\ast c_p\ast \frac{dT}{dt}=\dot{Q}+A_{cell2env}\ast {\alpha }_{cell2env}\ast \mathrm{\Delta }{T}_{cell2env}+A_{cell2cell}\ast {\alpha }_{cell2cell}\ast \mathrm{\Delta }{T}_{cell2cell}\\ +A_{cell2cOOl}\ast {\alpha }_{cell2cOOl}\mathrm{\Delta }{T}_{cell2cOOl}\end{array}$$

In addition to the quantities already introduced above, in the above equation the size A _cell2cool , which represents an area of the first electrical energy storage unit to form a cooling element, for example a cooling plate, the size α _cell2cool , which represents a heat transfer coefficient to the cooling element, and ΔT _cell2cool , which represents a temperature difference between the first electrical energy storage unit and the cooling element.

Depending on the application, individual terms may be neglected without significantly influencing the end result. For example, the heat transport between the electrical energy storage units can be neglected. This means that the term A _cell2cell ∗ α _cell2cell ∗ ΔT _{cell2cell is not taken} into _account in the determination of the temperature difference without the final result noticeably deviating. Likewise, the term Q can be disregarded for low or no electrical currents.

welche nach ΔT_cell2env umgestellt werden kann: $$\mathrm{\Delta }{T}_{cell2env}=\frac{m\ast c_p\ast \frac{dT}{dt}-A_{cell2cool}\ast {\alpha }_{cell2cool}\ast \mathrm{\Delta }{T}_{cell2cool}}{A_{cell2env}\ast {\alpha }_{cell2env}}$$

$$\mathrm{\Delta }{T}_{cell2env}=\frac{m\ast c_p}{\underset{k1}{\underbrace{A_{cell2env}\ast {\alpha }_{cell2env}}}}\ast \frac{dT}{dt}-\frac{A_{cell2cool}\ast {\alpha }_{cell2cool}}{\underset{k2}{\underbrace{A_{cell2env}\ast {\alpha }_{cell2env}}}}\ast \mathrm{\Delta }{T}_{cell2cool}$$

These two simplifications lead to the equation $$m\ast c_p\ast \frac{dT}{dt}=A_{cell2env}\ast {\alpha }_{cell2env}\ast \mathrm{\Delta }{T}_{cell2env}+A_{cell2cOOl}\ast {\alpha }_{cell2cOOl}\ast \mathrm{\Delta }{T}_{cell2cOOl}.$$

which can be converted according to ΔT _cell2env : $$\mathrm{\Delta }{T}_{cell2env}=\frac{m\ast c_p\ast \frac{dT}{dt}-A_{cell2cOOl}\ast {\alpha }_{cell2cOOl}\ast \mathrm{\Delta }{T}_{cell2cOOl}}{A_{cell2env}\ast {\alpha }_{cell2env}}$$

$$\mathrm{\Delta }{T}_{cell2env}=\frac{m\ast c_p}{\underset{k1}{\underbrace{A_{cell2env}\ast {\alpha }_{cell2env}}}}\ast \frac{dT}{dt}-\frac{A_{cell2cOOl}\ast {\alpha }_{cell2cOOl}}{\underset{k2}{\underbrace{A_{cell2env}\ast {\alpha }_{cell2env}}}}\ast \mathrm{\Delta }{T}_{cell2cOOl}$$

The two constants k1 and k2 can be determined, for example, in a simple manner before the method is carried out in the laboratory by means of a laboratory experiment.

3 shows a schematic representation of the disclosed device 40 according to one embodiment. Here is the device 40 in connection with battery cells 42 arranged in a series connection and via cell connectors 47 electrically connected to each other. A temperature sensor 41 is on the middle battery cell 46 of the compound consisting of seven battery cells attached to the temperature of the middle battery cell 46 to investigate. An environment 43 the middle battery cell 46 is formed by the surrounding air.

The temperature sensor 41 transmits a temperature variable to the electronic control unit 44 , This transmission can take place, for example, wirelessly or by wire. On the electronic control unit 44 there is a computer program which comprises instructions for executing the disclosed method. The electronic control unit controls these commands 44 a power electronics 45 , for example an inverter, in order to set a predefined current limit value for a further one in the battery cells located in the network 42 to be observed, the predefined current limit depending on the temperature of the middle battery cell determined in the disclosed method 46 is set.

QUOTES INCLUDE IN THE DESCRIPTION

This list of documents listed by the applicant has been generated automatically and is only included 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

• US 2007/0024244 [0006]

Claims (10)

Method for determining the ambient temperature of a first electrical energy storage unit (46), the first electrical energy storage unit (46) being connected to second electrical energy storage units (42), comprising the steps: a) determining a temperature of the first electrical energy storage unit (46) using a temperature sensor (41); b) determining a temperature difference between the first electrical energy storage unit (46) and the surroundings (43) of the first electrical energy storage unit (46); c) determining an ambient temperature as a function of the temperature of the first electrical energy storage unit (46) and the temperature difference. Procedure according to Claim 1 , further comprising the steps: d) determining a current strength of an electrical current flowing into or out of the first electrical energy storage unit (46); e) comparing the current strength with a predefined threshold value, at least steps a) and b) being carried out when the current strength reaches and / or falls below the predefined threshold value. Method according to one of the preceding claims, further comprising the steps: f) determining a temperature of another of the second electrical energy storage units (42) as a function of the ambient temperature determined in step c); g) controlling power electronics (45) to maintain at least one current limit value of the further electrical energy storage unit (42), the current limit value being set as a function of the temperature of the further electrical energy storage unit (42) determined in step f); Procedure according to Claim 3 The temperature of the further electrical energy storage unit (42) is determined in step f) using a mathematical model. Method according to one of the preceding claims, wherein the temperature sensor (41) in step a) is mounted in or on the first electrical energy storage unit (46). Method according to one of the preceding claims, wherein the temperature difference in step b) is determined as a function of a rate of change in the temperature of the first electrical energy storage unit (46) over time. Method according to one of the preceding claims, wherein the temperature difference in step b) is determined as a function of a constant, the constant representing the ratio of a heat capacity of the first electrical energy storage unit (46) to a thermal resistance of the first electrical energy storage unit (46). Device (40) for determining the ambient temperature of a first electrical energy storage unit (46), comprising a temperature sensor (41) and at least one means, in particular an electronic control unit (44), which are set up, the steps of the method according to one of the Claims 1 to 7 to execute. A computer program comprising instructions that cause the device (40) to Claim 8 the process steps according to one of the Claims 1 to 7 executes. Machine-readable storage medium on which the computer program according Claim 9 is saved.

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