DE102016219621A1 - Method for balancing calculation parameters for temperature determination in an energy store - Google Patents

Abstract

In a method for the adjustment of calculation parameters (f (X)) for temperature determination in an energy store having at least one battery module, which comprises at least one battery cell, in particular for an electrically driven vehicle, the following steps will be performed at predetermined times. A state is detected in which a dependence of the internal temperature value (Tint) on an external temperature value (text) which corresponds to a temperature outside the at least one battery cell is known. An actual internal temperature value of the energy store is determined. A current value (X) of an internal physical quantity of the energy store is determined, which varies in a known dependence on the internal temperature (Tint) of the energy store. An internal temperature value (Tint) for the energy storage is calculated from the determined value (X) using a previous set of calculation parameters (f (X)). The actual internal temperature value is compared with the calculated internal temperature value (Tint), and the set of calculation parameters (f (X)) is adjusted when the calculated internal temperature value (Tint) deviates from the actual internal temperature value.

Description

The invention relates to a method for balancing calculation parameters for temperature determination in an energy store, in particular an energy store of an electrically driven vehicle.

Such an energy store is usually composed of several battery modules, each of which comprises a plurality of individual battery cells in which the chemical reaction to generate electricity takes place.

The electrical energy storage should always be kept within a certain temperature range, so that optimum performance can be achieved, safe operation is ensured and aging processes are minimized. Crucial here is obviously the current internal temperature of the individual battery cells of the energy storage.

To reduce the technical complexity and thus the cost, however, the temperatures are usually detected only in a few places in the energy storage and also usually not inside the individual battery modules or even the individual battery cells, but by a temperature sensor in the region of an outer housing, the energy storage against the Environment completes. This external temperature so measured may differ by a relatively large amount from the actual internal temperature in the battery cells and may have a considerable time delay therefrom.

It is also known to derive a temperature from a measured impedance of the energy store, which varies in a known dependence on the temperature. However, the calculation of the internal temperature from the measured values also includes the current aging state of the individual battery cells, which is subject to aging processes or other wear factors and therefore changes over the life of the energy store.

The object of the invention is to increase the accuracy of a method for determining the internal temperature of the energy store in a simple manner.

• a) Erkennen eines thermischen Gleichgewichts zwischen einem internen Temperaturwert innerhalb einer Batteriezelle und einem externen Temperaturwert, der einer Temperatur außerhalb der wenigstens einen Batteriezelle entspricht,
• b) Ermitteln eines tatsächlichen internen Temperaturwerts des Energiespeichers,
• c) Ermitteln eines aktuellen Werts einer internen physikalischen Größe des Energiespeichers, die in einer bekannten Abhängigkeit von der internen Temperatur des Energiespeichers variiert,
• d) Berechnen eines internen Temperaturwerts für den Energiespeicher aus dem ermittelten Wert unter Verwendung eines bisherigen Satzes von Berechnungsparametern,
• e) Vergleichen des tatsächlichen internen Temperaturwerts mit dem berechneten internen Temperaturwert und
• f) Anpassen des Satzes von Berechnungsparametern, wenn der berechnete interne Temperaturwert vom tatsächlichen internen Temperaturwert abweicht.

This is achieved by a method having the steps given in claim 1. For balancing calculation parameters for temperature determination in an energy store with at least one battery module, which comprises at least one battery cell and which is used in particular for an electrically driven vehicle, the following steps are carried out at predetermined times:

• a) detecting a thermal equilibrium between an internal temperature value within a battery cell and an external temperature value which corresponds to a temperature outside the at least one battery cell,
• b) determining an actual internal temperature value of the energy store,
• c) determining a current value of an internal physical quantity of the energy store which varies in a known dependence on the internal temperature of the energy store,
• d) calculating an internal temperature value for the energy store from the determined value using a previous set of calculation parameters,
• e) comparing the actual internal temperature value with the calculated internal temperature value and
• f) adjusting the set of calculation parameters if the calculated internal temperature value deviates from the actual internal temperature value.

Advantageously, the calculation parameters contain a relationship with an aging state of the energy store and in particular of the individual battery cells. The state of aging depends not only on the actual age of the energy storage or the individual battery cells, but also from other signs of wear, the previous number of charge cycles or the like.

The method according to the invention makes use of the fact that it is possible to clearly deduce from an external temperature value the actual actual internal temperature value within one or all of the battery cells when the energy store is in thermal equilibrium, for example with its environment. The knowledge of the actual internal temperature, which in this case results without a temperature measurement inside the battery cell, makes it easy to adapt or track the set of calculation parameters used during operation for calculating the internal temperature value, in particular with a current one Aging condition of the energy storage is balanced. The calculation of the internal temperature values can thus always be based on the calculation parameters corresponding to the current aging state of the energy store so that the calculated internal temperature value always deviates only slightly from the actual internal temperature value. In this way, internal energy storage temperature values determined during normal operation can be used to improve the power output, to achieve a higher range and to specify a state prediction of the energy store.

A single set of calculation parameters is part of a set of calculation parameters that includes a plurality of sets of calculation parameters.

In general, the totality of the calculation parameters describes a dependence of at least one cell-internal physical quantity both on the internal temperature and on other influences which change the temperature dependence, in particular over long periods of time.

The totality of the calculation parameters can be represented both by previously determined analytical or empirical equations, or determined as individual data or value pairs with the internal temperature empirically or via a simulation. It can for example be in the form of a characteristic field, a family of curves or a lookup table, from which the respective set of calculation parameters used is taken.

A single set of calculation parameters consists e.g. from a group of data, for example a function of the internal temperature value depending on the physical quantity or a lookup table, or only one or more individual values, e.g. determine the curvature of the function describing the temperature dependence. The set of calculation parameters preferably describes the temperature dependence of the internal physical variable over a temperature range relevant to the operation of the energy store, for a specific aging state of the energy store or one of its battery modules or one of its battery cells.

When adjusting the calculation parameters, a set of calculation parameters is selected from the previously determined and stored set of calculation parameters. The adjustment takes place by replacing the previously used set of calculation parameters with another set of calculation parameters from the stored set of calculation parameters, which better matches the current state of aging of the energy store than the parameter set used hitherto. As a rule, no calculation parameters are newly determined and added to the whole. Of course, if the determined value pair of the actual internal temperature value and the determined physical quantity does not lie on a known value pair of the totality of the calculation parameters, a suitable average of two adjacent known value pairs of the calculation parameters can be formed to represent the adjusted set of calculation parameters.

The totality of the calculation parameters preferably contains a clear relationship between the physical quantity and the internal temperature value for the entire relevant temperature range for different aging states of the energy store. It is therefore sufficient to be able to determine a single value pair from the physical quantity and the current internal temperature in order to be able to select a unique, adjusted set of calculation parameters which allows a correct calculation of the internal temperature for the entire relevant temperature range. Therefore, the method according to the invention is preferably carried out in each case only for a single current internal temperature value.

The adaptation of the set of calculation parameters at predetermined times ensures that during operation, the calculation of the internal temperature value always takes place with calculation parameters, which in particular reflect the current aging state of the energy store.

For example, the given times may follow a predetermined interval, including, for example, a few weeks or months. However, the adjustment of the set of calculation parameters may be e.g. also be carried out in each case as part of a vehicle inspection.

Preferably, the set of calculation parameters is adjusted only if the calculated internal temperature value deviates by more than a predetermined difference from the actual internal temperature value. The difference value may e.g. 1 K amount. It has been found that small deviations have no negative effects, so that the size of the totality of the calculation parameters and thus the effort for their preliminary determination can be reduced.

In principle, the determination of the value of the internal physical quantity and the calculation of the internal temperature value can be effected therefrom in total for the entire energy store, for one or more of the battery modules or for one or more of the individual battery cells. Preferably, an internal temperature value is always determined for all individual battery cells, since this gives the most accurate image of the current state of aging of the energy storage and thus, for example, excessive aging processes due to excessive temperature of individual battery cells can be avoided.

Determining the value of the internal physical quantity is usually done by directly measuring that size itself or another quantity from which the internal physical quantity is easily derivable.

An especially preferred internal physical quantity is the impedance, since this quantity can be easily detected with the necessary accuracy and both its real part and its imaginary part show a direct, unambiguous temperature dependence. For example, it would also be possible to detect a passage frequency of the measuring circuit used, which is likewise dependent on the internal cell temperature.

In principle, it would be possible to use any other sensibly measurable physical quantity which shows a suitable temperature dependence.

The method for adjusting the calculation parameters is advantageously carried out when there is a thermal equilibrium between the immediate surroundings of the energy store and the interior of the energy store and thus of the individual battery cells. In this case, it can either be assumed that the same temperature prevails inside the energy store as, for example, directly at the outer housing of the energy store, or a known dependency can be used for a dynamic thermal equilibrium. In this case, for example, the temperature of the energy store can be adjusted selectively by heating or cooling, and utilize a known, previously determined heat distribution or heat conduction between the heating / cooling means, the interior of the battery cells and the immediate environment of the energy storage.

In step b), that is to say when determining the actual internal temperature value of the energy store, an external temperature is preferably measured, and the actual internal temperature value is set equal to the measured external temperature value. For this purpose, the energy storage should be in a thermal equilibrium, in which the external temperature coincides with the internal temperature.

In or on the energy store, at least one temperature sensor is preferably arranged, for example in direct contact with an outer housing of the energy store, wherein the temperature sensor can be arranged outside or inside in the outer housing. It has been found that the use of a single temperature sensor is sufficient. In this way, the external temperature value can be easily determined by a temperature measurement on an outer casing of the energy store.

In one possible variant of the method, step a), that is to say the detection of a thermal equilibrium, comprises recognizing that the energy store is in an idle state in which it does not emit heat energy. The idle state is defined in particular by the fact that no energy is released by a power requirement to the energy storage, but also no energy absorption by a charging current. The detected idle state should preferably last longer than a predetermined period of time, for example about 20 minutes, before performing steps b) and c) to ensure that a thermal equilibrium has actually set.

In this case, for example, a phase of the standstill of the vehicle can be exploited, for example, if this is turned off overnight, so after a certain time the particular fully charged energy storage has assumed ambient temperature after completion of the charging process. In this case, it can be assumed that the internal actual temperature of the battery cells coincides with the ambient temperature of the energy storage.

Alternatively, it is also possible to purposefully bring about the thermal equilibrium in step a) by setting the energy store to a predetermined external temperature value, in particular by heating or cooling.

In this case, the heating or cooling preferably takes place only when the energy storage is supplied with charging current.

The detection of the thermal equilibrium in step a) can also include determining a time gradient of the calculated internal temperature value and of the external temperature value and to carry out the further steps only if the gradients lie below a predefined threshold value. This means that the calculated internal temperature value and the external temperature value must not change too much over a predetermined period of time, for example about 20 minutes, before it is assumed that the energy store is in thermal equilibrium. Only after reaching the thermal equilibrium, and thus in particular a match of the external and the actual internal temperature value, the measurement of the external temperature value and the physical quantity and the calculation of the internal temperature and the adjustment of the set of calculation parameters are performed.

Specifically, in the current normal running mode, the internal temperature value is determined simply by determining the value of the internal physical quantity and calculating the internal temperature value from the detected physical quantity value using the current set of calculation parameters adjusted using a method described above.

For the purposes of this application, a "calculation" is understood to mean in principle both a mathematical calculation from an analytically or empirically determined formula and also a look-up in a characteristic field or a look-up table.

The invention will now be described in more detail with reference to several embodiments with reference to the accompanying drawings. In the drawings show:

1 a schematic representation of an energy storage device with which the inventive method can be performed;

2 a method of calculating an internal temperature value of the energy store from an internal physical quantity during normal operation;

3 a schematic representation of the detection of the internal physical quantity in the energy storage;

4 and 5 schematic representations of the temperature dependence of the real part and the imaginary part of the impedance of a battery cell, which can be used as an internal physical quantity, for different old battery cells;

6 a variant of a method according to the invention, wherein an adaptation of the set of calculation parameters takes place when the energy storage is passive in thermal equilibrium with its environment;

7 a variant of the method according to the invention, in which an adaptation of the set of calculation parameters takes place when the gradients of the internal and the external temperature are below a certain threshold value; and

8th a variant of the method according to the invention, in which a temperature of the energy storage device is actively set to produce a thermal equilibrium.

In 1 is an energy storage 10 for example, shown for an electrically powered vehicle. Under electrically powered vehicles are understood here vehicles that relate their drive energy completely, partially or only in certain driving situations from an electrical energy storage.

In an outer housing 12 of the energy store 10 are several battery modules 14 each of which receives a certain number of individual battery cells 16 includes.

The energy storage 10 is with a control unit 18 Among other things, the load delivery to consumers such as electric motors that power the vehicle and a supply of charging current for charging the battery cells 16 controls.

In this example is on the inside of the outer case 12 a single temperature sensor 20 arranged, which can detect an external temperature _value T _ext , which also to the control unit 18 is passed on. The control unit 18 may be in communication with other controls, not shown, for example, of the vehicle.

In normal operation of the energy storage 10 , For example, in the normal driving operation of the electrically driven vehicle, the temperature of the energy storage 10 supervised. In this case, an internal temperature T _{int is} crucial, which, due to the heat development at power output, is very different from that at the outer housing 12 measured external temperature T _{ext may} differ.

To determine the internal temperature T _int in the current driving operation, a current value X of a suitable internal physical quantity of the energy store is measured, which is in a known dependence on the internal temperature T _{int of} the energy store 10 varied. In this example, the value X is always unambiguously derivable from an impedance Z, so that the value X and the impedance Z will be equivalently used hereinafter. The internal temperature T _int is calculated from the value X and sent to the control unit 18 output. A set of calculation parameters f (X) is used for the calculation, which exists, for example, as a function or as a value set in a lookup table. This general process is in 2 clarified.

In the example shown here, the temperature T _int at the level of the battery cells 16 recorded, ie it is for each individual battery cell 16 performed an impedance measurement and determines its own internal temperature T _int .

The temperature _values T _{int of} all battery cells 16 are averaged, for example, to obtain a single, energy storage relevant temperature value. It is also possible to check for deviations at this point, for example, on individual, overheated battery cells 16 ,

Instead of a measurement at the level of the battery cells 16 could also be an impedance measurement for one or all of the battery modules 14 be performed or even a single impedance measurement, with which the impedance of the entire energy storage 10 is detected. The most accurate measurement of the temperature distribution within the energy store 10 Obtained, of course, if the impedance of all individual battery cells 16 is measured.

3 shows an example of the measurement of the impedance Z of the battery cells 16 ,

The battery cells 16 are connected here serially (indicated by the battery string on the left edge of the 3 ). Every single battery cell 16 is with its own measuring electronics 22 provided for measuring the impedance Z of the respective battery cell 16 (or any other suitable internal physical quantity).

The measuring electronics 22 is with a communication electronics 24 connected, in turn, each battery cell 16 own communication electronics 24 assigned. The individual communication electronics 24 the battery cells 16 are linear in a daisy chain with each other and with the control unit 18 connected.

An alternative solution for measuring and communicating the measured impedance values would be, for example, from the control unit 18 a separate measuring and / or data line to each of the battery cells 16 lead while the measuring electronics 22 and the communication electronics 24 in the control unit 18 is integrated. As a middle ground, it would be conceivable, every battery module 14 a measuring electronics 22 and a communication electronics 24 assign and each battery cell 16 of the respective battery module 14 with this measuring electronics 22 to connect via a measuring line, in which case the individual communication electronics 24 with the control unit 18 communicate.

The use of measuring electronics 22 at the level of the battery cells 16 has the advantage that only short analogue cable routes are necessary, which facilitates the impedance measurement. Since the evaluation of the measurement, so the determination of the value X from the impedance Z and possibly already the calculation of the internal temperature T _int at the level of the battery cells 16 takes place, reduces the communication effort with the control unit 18 compared to a solution where the measurement is central to the control unit 18 is carried out.

The internal temperature _value T _int for the single battery cell 16 , the battery module 14 and / or the entire energy storage 10 is calculated from the value X using a predetermined set of calculation parameters f (X). The set of calculation parameters f (X) is in the form of, for example, a function of the impedance from the internal temperature T _int .

Like in the 4 and 5 9, both the real part Re (Z) of the impedance Z and the imaginary part Im (Z) of the impedance show an appropriate temperature dependence so as to be able to determine the internal temperature T _int from the measured values.

However, the temperature dependence of the impedance Z also includes other variables, including the degree of aging of the battery cell 16 , As the 4 and 5 show, the curve changes depending on an aging state of the battery cell 16 , In this way, over time, a deviation of the calculated internal temperature T _int from the actual internal temperature would result, if always the same set of calculation parameters f (X), which corresponds to a specific aging state of the energy store 10 during which it would correspond to its lifetime.

For the compilation of a set of calculation parameters, the temperature dependence of the impedance Z (or any other suitable internal physical quantity) for the entire life of the energy storage 10 depict, in particular depending on an aging of the battery cells 16 , eg empirically or analytically determined functions like those in 4 and 5 shown used. Such curves can also be based on the creation of a map which, for example, a family of curves for different aging states of the battery cells 16 represents, or a lookup table, in which the associated value T _int to the determined value X of the internal physical quantity for different aging states are stored, in this case, for example, the real part Re (Z) or imaginary part Im (Z) of the impedance Z.

Thus, the set of calculation parameters allows a correct calculation of the internal temperature T _int as a function of the value X when using the respective appropriate set of calculation parameters f (X) describing the current aging state of the energy storage.

To the set of calculation parameters f (X) used to the actual current aging state of the energy storage 10 is adjusted at predetermined times independently of the normal method of determining the internal temperature T _int during operation Adjustment of the set of calculation parameters f (X) performed. In this case, the set of calculation parameters f (X) is adjusted so that, in the calculation of the internal temperature _value T _int, the current state of aging of the energy store, which depends on age, wear or the like, is taken into account.

6 shows a first variant of a method for adjusting the set of calculation parameters f (X) for the temperature determination of the internal temperature T _{int of} the energy storage 10 ,

First, it checks and detects whether the energy storage 10 is in a thermal equilibrium, for example, the internal temperature value T _{int of} the battery cells 16 is equal to the ambient temperature. It would also be possible to work here with a dynamic equilibrium, if the connection for example between a heat absorption of the energy storage 10 and the self-adjusting temperature T _{ext is known} on the outer housing.

Only when the energy storage 10 is in a known thermal equilibrium, the adjustment of the set of calculation parameters f (X) is performed.

The detection of the thermal equilibrium is, for example, as in 6 shown empirically performed so that it checks if the energy storage 10 is in an idle state, so neither outputs nor absorbs power, so no external consumers are operated and the energy storage 10 also not loaded. If the time at rest is more than a predetermined time t _rest , which may be greater than 20 minutes, for example, it is assumed that a thermal equilibrium.

Now the external temperature value T _{ext is} measured, for example via the temperature sensor 20 of the energy store 10 , This value T _ext is equated to an actual internal temperature, since the energy storage 10 is in thermal equilibrium with the environment and thus has assumed a total ambient temperature.

In addition, the value X of the internal physical quantity, in this case the impedance Z, is measured, in this example for each battery cell 16 ,

With the previous set of calculation parameters f (X), an internal temperature value T _{int is} calculated from the value X.

By forming a difference, it is checked whether there is a deviation .DELTA.T between the actual internal temperature, ie the external temperature value T _ext , and the calculated internal temperature value T _int . If the difference ΔT is greater than a predefined threshold value S _T , which can amount to 1 K, for example, the set of calculation parameters f (X) is adapted to a set of the totality of the calculation parameters, which corresponds to the current aging state of the energy store 10 better corresponds.

Depending on the structure of the energy storage 10 (see above) becomes a common set of calculation parameters f (X) for the entire energy store 10 , each a separate set of calculation parameters f (X) for each battery module 14 of the energy store 10 or a separate set of calculation parameters f (X) for each battery cell 16 of the energy store 10 used, which is adjusted if necessary.

The following temperature measurements of the temperature T _int during operation are then carried out with the new adapted set of calculation parameters f (X), so that the internal temperature T _{int of} the battery cells calculated from the impedance Z 16 is correct again.

In contrast to the time-controlled adjustment just described, a temperature-controlled adjustment can also be carried out. This is in 7 shown.

In this case, for example, first checked whether a heat input in the energy storage 10 is small, so no large load delivered or a strong charging current is recorded. If this is the case, a time gradient dT _int / dt of the internal temperature T _{int is} checked. If this is below a predetermined threshold value S _G , the external temperature value T _{ext is} measured and the time gradient dT _ext / dt is also checked here. If this too is below a predetermined threshold value S _G , then the value X is determined by a measurement of the impedance Z and from this the internal temperature value T _{int is} calculated with the previous set of calculation parameters f (X).

From the difference ΔT of the calculated temperature value T _int and the actual internal temperature, which corresponds to the external temperature value T _ext , it is decided whether the set of calculation parameters f (X) is adjusted or whether the previous sentence is retained. An adaptation takes place, as in the example just described, when the difference ΔT from the calculated internal temperature value T _int and the actual internal temperature, ie T _ext , is greater than a threshold value S _T , for example 1 K.

Instead of waiting until a thermal equilibrium with an ambient temperature has been established, it is also possible to actively use the entire energy store 10 set to a predetermined target temperature T _target , by deliberately heating or cooling. In this case too, when the thermal equilibrium is reached, the external temperature value T _{ext is then} equal to the current internal temperature value.

In the in 8th variant shown, this method is only performed when the energy storage 10 is idle and is loading.

The energy storage 10 is brought to a target temperature T _target , wherein an external heating / cooling device used or can be exploited in particular for heating the charging current.

To check whether a thermal equilibrium has been reached, the external temperature value T _{ext is} measured and compared with the target temperature T _target , as long as these two temperatures coincide.

Now the value X is measured and from this with the previous set of calculation parameters f (X) the internal temperature value T _{int is} calculated.

The state of thermal equilibrium is assumed reached when a time gradient dT _int / dt of the internal temperature T _int becomes smaller than a predetermined threshold value S _G.

If this condition is fulfilled, the temperature difference ΔT is formed from the internal temperature _value T _int and the external temperature _value T _ext . If this difference is greater than a predefined threshold value S _T , the set of calculation parameters f (X) is adapted, otherwise the previous sentence is retained.

Since in general the temperature dependence of the internal physical quantity, in this case the impedance Z, is known and stored in the entirety of the calculation parameters, for example in the control unit 18 or in the individual measuring units 22 , it is sufficient to carry out a calibration measurement at a single temperature _value T _ext . As a result, it is possible to find the associated curve of the family of curves, which is then used as an adapted set of calculation parameters f (X) until the next adjustment. For this purpose, a typical ambient temperature value between -20 and + 30 ° C is normally suitable. By actively setting the temperature, it is possible to specify a desired temperature value T _target which is independent of the ambient temperature currently prevailing.

In the control unit 18 For example, one or all of the three methods described may be stored, wherein, depending on the ambient temperature, the appropriate method may be selected to perform the adjustment of the set of calculation parameters f (X).

In general, a comparison of the set of calculation parameters f (X) only takes place when the energy store 10 is in a thermal equilibrium, since in this case the actual internal temperature value corresponds in particular to the measured external temperature value T _ext and is therefore exactly known or determinable.

The thresholds used can be chosen differently for different measurements as needed.

Claims (11)

Method for adjusting calculation parameters (f (X)) for temperature determination in an energy store ( 10 ) with at least one battery module ( 14 ), the at least one battery cell ( 16 ), in particular for an electrically driven vehicle, wherein the following steps are carried out at predetermined times: a) detection of a thermal equilibrium between an internal temperature value (T _int ) of at least one battery cell ( 16 ) and an external temperature _value (T _ext ) _{corresponding to} a temperature outside the at least one battery cell ( 16 ), b) determining an actual internal temperature value of the energy store ( 10 c) determining a current value (X) of an internal physical quantity of the energy store ( 10 ) in a known dependence on the internal temperature (T _int ) of the energy store ( 10 d) calculating an internal temperature value (T _int ) for the energy store ( 10 ) from the determined value (X) using a previous set of calculation parameters (f (X)), e) comparing the actual internal temperature value with the calculated internal temperature value (T _int ), and f) fitting the set of calculation parameters (f (f) X)) when the calculated internal temperature value (T _int ) deviates from the actual internal temperature value. Method according to Claim 1, characterized in that the calculation parameters (f (X)) are related to an aging state of the energy store ( 10 ) contain. Method according to one of the preceding claims, characterized in that the set of calculation parameters (f (X)) only then is adjusted when the calculated internal temperature value (T _int ) deviates by more than a predetermined difference (S _T ) from the actual internal temperature value. Method according to one of the preceding claims, characterized in that to determine the value (X) of the internal physical quantity, an impedance (Z) of the energy store ( 10 ) is measured. Method according to one of the preceding claims, characterized in that in step b) for determining the actual internal temperature value, the external temperature (T _ext ) is measured and the actual internal temperature value is set equal to the measured external temperature value (T _ext ). Method according to one of the preceding claims, characterized in that the external temperature _value (T _ext ) by a temperature measurement on an outer housing ( 12 ) of the energy store ( 10 ) is determined. Method according to one of the preceding claims, characterized in that it is detected in step a) that the energy store ( 10 ) is in a dormant state in which it does not give off heat energy. Method according to one of claims 1 to 6, characterized in that in step a) the thermal equilibrium is brought about by the energy storage ( 10 ) is set to a predetermined external temperature value (T _target ) by the energy storage ( 10 ) is heated or cooled. A method according to claim 8, characterized in that the setting of the predetermined external temperature value (T _target ) only takes place when the energy storage ( 10 ) is supplied with charging current. Method according to one of the preceding claims, characterized in that step a) comprises determining a time gradient of the calculated internal temperature value (T _int ) and the external temperature value (T _ext ) and steps b) and c) are performed only when the gradient is below a predetermined threshold (S _G ). Method for determining temperature in an energy store ( 10 ) with at least one battery module ( 14 ), the at least one battery cell ( 16 ), in particular for an electrically driven vehicle, comprising the steps of: determining a value (X) of the internal physical size of the energy store ( 10 ), - calculating the internal temperature value (T _int ) for the energy store ( 10 ) from the determined value (X) using calculation parameters (f (X)) determined according to a method according to one of the preceding claims.

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