DE102018219973A1 - Method for determining a parameter of an energy store and energy management system for an energy store - Google Patents

Abstract

The invention relates to a method for determining a parameter of an energy store (102) and an energy management (104) for an energy store (102), which is designed to carry out the method. At least one error capacity (K) is calculated as the parameter of the energy store (102) in the present invention. The at least one error capacitance (K) takes into account a current measurement inaccuracy (FI) of a current sensor (108) and a voltage measurement inaccuracy of a voltage sensor (110), which are used to determine a predetermined total capacitance (K) of the energy store (102), so that the at least one error capacitance (K) depicts a deviation of the predetermined total capacitance (K) from its actual value due to the measurement inaccuracies of the current sensor (108) and the voltage sensor (110).

Description

The invention relates to a method for determining a parameter of an energy store and an energy management system for an energy store, with at least one voltage sensor and a current sensor for detecting energy storage parameters, and with a computing device which is designed, taking into account the energy storage parameters, the method for determining the parameter of the Perform energy storage.

Energy stores, in particular electrochemical energy stores, for example batteries or accumulators, which are preferably designed to be rechargeable, are often provided in motor vehicles for supplying energy to a vehicle electrical system. The motor vehicle electrical system, which is preferably designed as a high-voltage electrical system of the motor vehicle, serves to supply motor vehicle components, such as, for example, electronic power steering and / or an electric motor and / or an alternator.

In order to ensure that the energy storage device functions as intended, the energy storage device is usually checked regularly, for example during a workshop visit and / or by an internal inspection device in the motor vehicle. When checking, a parameter of the energy store, such as a capacity of the energy store, is determined. The capacity of an electrochemical energy store deteriorates because of aging, that is to say over time, due to chemical processes that take place inside the energy store. However, since the capacity is used in particular for a range forecast, for determining a charging duration and in driving operation for determining the state of charge of the energy store, the actual capacity of the energy store should be known as precisely as possible. If the determination of the capacity is inaccurate, for example, a wrong range prediction can occur because the state of charge of the energy store could not be calculated precisely enough while driving. In the worst case, the motor vehicle simply remains lying down while driving, since the energy store can no longer provide sufficient energy to supply the motor vehicle electrical system and the motor vehicle components.

The capacity of the energy storage means in particular the nominal capacity, also called the total capacity, that is to say in particular the maximum amount of energy which the energy storage can absorb and release again when required.

wobei K_R der Gesamtkapazität des Energiespeichers entspricht, $\left|{\displaystyle {\int }_{t_1}^{t_2}Idt}\right|$

entspricht einer von dem Energiespeicher umgesetzten Ladung unter Berücksichtigung von einem Stromstärkeverlauf I während einer vorgegebenen Zeitdauer mit einem Startzeitpunkt t₁ und einem Endzeitpunkt t₂, und |SOC_t2 - SOC_t1| entspricht einem Ruheladezustand-Hub mit dem ersten Ruheladezustand SOC_t1 und dem zweiten Ruheladezustand SOC_t2 .According to the applicant's internal prior art, the capacity, that is to say the total capacity of an energy store, is usually determined as follows: First, the energy store is disconnected from the motor vehicle electrical system, so that the energy store is unloaded, and a first idle state of charge is determined. The first idle state of charge is usually determined with at least one voltage sensor, which is assigned to the energy store and is designed to detect a voltage that drops across the energy store. The motor vehicle electrical system is then reconnected to the energy store and the energy store is operated by the motor vehicle electrical system for a predefined period of time, the energy store being thus either charged and / or discharged in the predefined time period. During the operation of the energy store over the period of time, a current intensity curve is recorded which, due to the charging and / or discharging, flows towards the energy store or away from the energy store into the vehicle electrical system. After the predetermined period of time has elapsed, the energy store is again disconnected from the motor vehicle electrical system and a second idle charge state of the energy store is determined. The capacity of the energy storage is then calculated as follows: $$K_R=\frac{\left|{\displaystyle {\int }_{t_1}^{t_{\mathrm{2nd}}}\mathrm{I.}dt}\right|}{\left|SO{\mathrm{C.}}_{t\mathrm{2nd}}-SO{\mathrm{C.}}_{t1}\right|},$$

where K _R corresponds to the total capacity of the energy store, $\left|{\displaystyle {\int }_{t_1}^{t_{\mathrm{2nd}}}\mathrm{I.}dt}\right|$

corresponds to a charge implemented by the energy store, taking into account a current intensity curve I for a predetermined period of time with a start time t ₁ and an end time t ₂ , and | SOC _t2 - SOC _t1 | corresponds to a idle state hub with the first idle state SOC _t1 and the second idle state SOC _t2 .

In order to calculate the total capacity of the energy store as precisely as possible, it is necessary for the idle state stroke, that is to say an amount of a difference between the second idle state and the first idle state, to be as large as possible, in particular greater than 60%. This means that the energy storage device must be unloaded in order to correctly calculate the total capacity in the case of two strongly different idle charge states, that is to say it must be separate from the vehicle electrical system.

In order to achieve such a large idle state stroke, it is necessary to operate the energy store for at least 15 minutes to several hours after the first idle state has been detected, so that the energy store is charged or discharged before the second idle state can be determined. Particularly in the case of electric vehicles or hybrid vehicles with a long range, which use an appropriate energy storage as a drive (BEV, Battery Electric Vehicle), a state of charge charge stroke of 60% is rarely achieved, which means that the total capacity can generally only be determined very inaccurately. Overall, the disadvantage of calculating the total capacity of the energy store, as is known from the internal prior art, is that the total capacity of the energy store can be determined either with a high expenditure of time or only very imprecisely.

Furthermore, is also from the DE 39 20 629 A1 a method for determining the capacity of an electric accumulator and for charging the same is known.

In addition, in the DE 601 32 951 T2 discloses a detection method for detecting an internal state of a rechargeable battery, a detection device for carrying out such a method and an instrument with such a device.

After all, is also from the DE 10 2007 055 255 A1 a method for determining a capacity of an electrical energy storage is known.

These three methods also have the disadvantage that the determination of the capacity, that is to say in particular the total capacity of the energy store, is either inaccurate or an increased amount of time of several hours is necessary to determine the total capacity of the energy store.

The invention is therefore based on the object of preventing a motor vehicle from lying down as reliably as possible.

This object is solved by the subject matter of the independent claims. Advantageous developments of the invention are disclosed by the dependent claims, the following description and the figures.

The invention provides a method for determining a parameter of an energy store. In a step a), the method comprises detecting a first idle charge state of the energy store with at least one voltage sensor. The energy store is then operated in a step b) for a predetermined period of time by connecting a motor vehicle electrical system to the energy store. In a step c), a current intensity profile of the energy store is then recorded with a current sensor during operation of the energy store over the predetermined period of time in accordance with step b). After the specified period of time has elapsed, in step d) the energy store is first put into an idle state by disconnecting the energy store from the vehicle electrical system. This is followed by a determination of an overall charge that has flowed through the current sensor over the predetermined period of time, from the current intensity curve recorded in step c). Finally, a charge actually converted by the energy store is determined from the current intensity curve recorded in step c), and a second idle charge state of the energy store is detected with the at least one voltage sensor. In a step e), at least one charge determination error is next determined, taking into account the charge actually converted by the energy store, which has flowed through the current sensor over the predetermined period of time, and a predetermined current measurement inaccuracy of the current sensor. In a step f), there is then also a determination of at least one state of charge determination error, taking into account a rest state of charge stroke of the energy store and a rest state of charge stroke error, the rest state of charge stroke being formed taking into account the first and the second rest state of charge and the rest state of charge stroke error from the Resting state of charge stroke is formed taking into account a predetermined voltage measurement inaccuracy of the voltage sensor. Finally, in step g), at least one error capacity is determined as a parameter of the energy store, taking into account the at least one charge determination error and the at least one charge state determination error.

The invention is based on the knowledge that the total capacity of an energy store can be determined with good accuracy even with a low idle state stroke if the current measurement inaccuracy of the current sensor and the voltage measurement inaccuracy of the voltage sensor are taken into account. For this purpose, a charge determination error, that is to say an error in the detection of the current intensity curve due to the current measurement inaccuracy of the current sensor, is determined, and a charge state determination error, that is to say an error in the detection of the first and second idle charge states due to the voltage measurement inaccuracy of the voltage sensor, is determined. A so-called error capacity can then be determined, in particular calculated, with the aid of the charge determination error and the charge state determination error. Due to the error capacity, a new total capacity of the energy store is determined, so to speak Measurement inaccuracies of the current sensor and the voltage sensor are taken into account.

By determining the error capacity, there is the advantage that an overall capacity of the energy store can be determined in a less time-consuming manner and nevertheless as precisely as possible. In particular, by comparing the at least one error capacity with a predefined total capacity of the energy store, a smaller charge state lift can also be used to calculate a new total capacity of the energy store. The time for charging and / or discharging the energy store is thus reduced, so that the new total capacity can be determined with sufficient accuracy even when the motor vehicle is at rest. As a result, the new total capacity can also be redetermined more frequently, which means that the range forecast and the state of charge can be determined with greater precision. A possible stopping of the motor vehicle due to an inaccurately determined total capacity and a resulting incorrectly displayed state of charge of the energy store can therefore be reliably identified by taking into account the voltage measurement inaccuracy and the current measurement inaccuracy, and the energy store can be charged to enable further travel.

The first or second idle state of charge detected in step a) or in step d) can be determined, for example, by detecting an idle voltage (OCV, Open Circuit Voltage) of the energy store with the aid of the at least one voltage sensor. In addition to the at least one voltage sensor, it is also particularly preferred to use a temperature sensor which is associated with the energy store and is designed to determine a current temperature of the energy store. On the basis of the measured no-load voltage and the current temperature, it is then possible to draw more precise conclusions about the particular state of charge of the energy storage device.

The motor vehicle electrical system, which can be coupled to the energy store, can be designed, for example, as an electrical circuit which comprises both electrical consumers and electrical suppliers for the energy store. Electrical consumers can be, for example, light-emitting diodes, resistors, capacitors or the like. In contrast, a recuperation device, in particular a generator and / or a further electrical energy store, such as a battery or a capacitor, can serve as the electrical provider. Depending on the operation of the electrical circuit, that is to say the motor vehicle electrical system, when the energy storage device is connected to the motor vehicle electrical system, the energy storage device can be charged, that is to say supplied with electrical energy, or discharged, that is to say that energy is withdrawn from the electrical energy storage device. Within the specified period of time, either charging and discharging alternately, or it can only be charged, or the energy store can only be discharged. The motor vehicle electrical system can represent, for example, a real motor vehicle electrical system that is installed in a motor vehicle, or can be designed as a test circuit that is used, for example, by a customer service during a routine check of the energy store.

The current inaccuracy of the current sensor according to step e) and the voltage measurement inaccuracy of the voltage sensor according to step f) can preferably be specified by a manufacturer of the current sensor or of the voltage sensor. A typical value range for a voltage measurement inaccuracy of a voltage sensor can be, for example, 3 mV and a typical value for a current measurement inaccuracy of a current sensor can be, for example, 1%. Current inaccuracy means that when the current intensity curve is detected, the current intensity detected by the current sensor can deviate from its actual value by up to 1%. Analogously, voltage measurement inaccuracy means that when the open-circuit voltage is detected in order to determine the closed-charge state of the energy store, the detected open-circuit voltage can deviate from its actual value by up to 3 mV.

The invention also includes further embodiments which result in additional advantages.

One embodiment provides that a first and a second charge determination error are determined in accordance with step e), the first charge determination error resulting if the charge actually converted by the energy store is underestimated due to the predetermined current measurement inaccuracy of the current sensor and the second charge determination error results, if the charge actually converted by the energy store is overestimated due to the predetermined current inaccuracy of the current sensor.

That is, if a current measurement inaccuracy of 1% is specified by a manufacturer of the current sensor, for example, two charge determination errors are calculated. The first charge determination error results when it is assumed that the current intensity curve recorded in step c) deviates from its actual value by a negative value, that is to say here by -1%. Accordingly, in this case, that of the Energy storage is actually underestimated charge, hereinafter also referred to as net charge. In contrast to this, the second charge determination error results if it is assumed that the current intensity curve recorded according to step c) deviates from its actual value by a positive value, that is to say here by +1%. In this case, the net load is overestimated.

A further embodiment provides that a first and a second state of charge determination error are determined in accordance with step f), the first state of charge determination error resulting if the idle state of charge lift error is underestimated due to the predetermined voltage measurement inaccuracy of the voltage sensor, and the second state of charge determination error results if the Idle state-of-charge error is overestimated due to the specified voltage measurement inaccuracy of the voltage sensor.

This means that if a voltage measurement inaccuracy of 3 mV is specified by a manufacturer of the voltage sensor, two state of charge determination errors are calculated. The first state of charge determination error arises if it is assumed that the first idle state is overestimated and the second idle state is underestimated. Thus, the idle state stroke is largely underestimated. In the case of an overestimated first idle state of charge, it is assumed that the first idle voltage, which is detected by the voltage sensor for determining the first idle state of charge, is measured higher than its actual value due to the voltage measurement inaccuracy of the voltage sensor. The first quiescent voltage therefore deviates from its actual value by, for example, +3 mV. Similarly, in the case of an underestimated second idle state of charge, it is assumed that the second idle voltage is measured lower than its actual value due to the voltage measurement inaccuracy of the voltage sensor. The second quiescent voltage therefore deviates from its actual value by, for example, -3 mV.

In contrast, the second state of charge determination error results when the first idle state is underestimated and the second idle state is overestimated. As a result, the idle state stroke is largely overestimated. In the case of the underestimated first idle state of charge, it is assumed that the first idle voltage is measured lower than its actual value due to the voltage measurement inaccuracy of the voltage sensor. The first quiescent voltage therefore deviates from its actual value by, for example, -3 mV. Accordingly, in the overestimated second idle state of charge, it is assumed that the second idle voltage is measured higher than its actual value due to the voltage measurement inaccuracy of the voltage sensor, for example deviates from its actual value by +3 mV.

A further embodiment provides that a first and a second fault capacity are determined in accordance with step g), the first fault capacity taking into account the first charge determination error and the second state of charge determination error and the second fault capacity taking into account the second charge determination error and the first state of charge determination error results.

In other words, the first fault capacity is when the net charge is underestimated and the idle state stroke is overestimated, and the second fault capacity is when the net charge is overestimated and the idle state stroke is underestimated. The first and second error capacities limit a range of values for the total capacity of the energy store in which the total capacity of the energy store can fluctuate.

This has the advantage that the error capacity is determined as a so-called worst case error capacity (WCF, worst case error capacity). This means that the fault capacity is calculated in such a way that a maximum deviation of the two fault capacities from the specified total capacity is taken into account due to the current measurement inaccuracy and the voltage measurement inaccuracy.

A further embodiment sees in a step h) a determination of a capacity range of the energy store, taking into account a deviation of the first and second error capacities from a predetermined total capacity of the energy store.

For this purpose, for example, as mentioned in relation to the internal state of the art, the capacity of the energy store can be determined and adopted as the predetermined total capacity, or a capacity specified by the manufacturer of the energy store can serve as the predetermined total capacity. A deviation of the predetermined total capacity by the two fault capacities can then be calculated, so that the capacity range results. In other words, the capacity range is a value range in which the value of the predetermined total capacity can fluctuate, the upper and lower limit value of the capacity range being specified in particular by both fault capacities.

A further embodiment comprises, in step i), outputting the capacity range to an output device.

The output device can be, for example, a display, ie a screen, for example in the interior of a motor vehicle. Alternatively, the output device can also be a screen of an energy storage test device that is used, for example, in a workshop during maintenance of the motor vehicle in order to check the capacity of the energy store. In this way, a user and / or an employee of the workshop can determine as easily as possible whether the idle state stroke has been chosen to be large enough to determine the total capacity of the energy store with sufficient accuracy.

A further embodiment comprises, in a step j), checking whether the capacity range is within a predetermined value range, the capacity range being validated only if the check is positive.

This means that a range of values is defined within which the predefined total capacity may lie and a check is carried out to determine whether the capacity range, which is limited by the first and second error capacities, lies within this range of values. If the check is positive, the capacity range is within the specified value range, the capacity range is validated, that is, it is assumed to be valid and can be released for further calculations, for example. The capacity range can be stored, for example, in a memory which is assigned to the motor vehicle and can be used, for example, to calculate a range of the motor vehicle or a charging duration, or a state of charge when the motor vehicle is in operation.

der wenigstens eine Ladezustandsbestimmungsfehler SOC_E gegeben ist durch $SO{C}_E=\left|SO{C}_{t2}-SO{C}_{t1}\right|\pm \Delta SO{C}_E,$

und der wenigstens eine Kapazitätsmessfehler K_E gegeben ist durch $K_E=\frac{Q_E}{SO{C}_E},$

wobei $\left|{\displaystyle {\int }_{t_1}^{t_2}Idt}\right|$

die von dem Energiespeicher tatsächlich umgesetzte Ladung, basierend auf dem Stromstärkeverlauf I und einem Startzeitpunkt t₁ und einem Endzeitpunkt t₂ der Zeitdauer, darstellt, FI_E die Strommessungenauigkeit des Stromsensors darstellt, ${\displaystyle {\int }_{t_1}^{t_2}\left|I\right|}$

dt die Gesamtladung, die über die vorgegebene Zeitdauer durch den Stromsensor geflossen ist, darstellt, |SOC_t2 - SOC_t1| den Ruheladezustand-Hub mit dem ersten Ruheladezustand SOC_t1 und dem zweiten Ruheladezustand SOC_t2 darstellt, und ΔSOC_E den Ruheladezustand-Hubfehler darstellt.Another embodiment provides that the at least one charge determination error Q _E is given by $Q_E=\left|{\displaystyle {\int }_{t_1}^{t_{\mathrm{2nd}}}\mathrm{I.}dt}\right|\pm F{\mathrm{I.}}_E\cdot {\displaystyle {\int }_{t_1}^{t_{\mathrm{2nd}}}\left|\mathrm{I.}\right|dt,}$

the at least one state of charge determination error SOC _E is given by $SO{\mathrm{C.}}_E=\left|SO{\mathrm{C.}}_{t\mathrm{2nd}}-SO{\mathrm{C.}}_{t1}\right|\pm \Delta SO{\mathrm{C.}}_E,$

and the at least one capacitance measurement error K _E is given by $K_E=\frac{Q_E}{SO{\mathrm{C.}}_E},$

in which $\left|{\displaystyle {\int }_{t_1}^{t_{\mathrm{2nd}}}\mathrm{I.}dt}\right|$

represents the charge actually converted by the energy store, based on the current intensity curve I and a start time t ₁ and an end time t _{2 of} the time period, FI _E represents the current inaccuracy of the current sensor, ${\displaystyle {\int }_{t_1}^{t_{\mathrm{2nd}}}\left|\mathrm{I.}\right|}$

dt represents the total charge that has flowed through the current sensor over the predetermined time period, | SOC _t2 - SOC _t1 | the idle state hub with the first idle state SOC _t1 and the second idle state SOC _t2 represents, and ΔSOC _E represents the idle state lift error.

Conversely, the invention and in particular the formula described above can also be used to determine the second idle state of charge as a parameter of the energy store from a predefined first idle state and a predefined error capacity. This method is therefore based on the same inventive concept as the previously described method and is explained in more detail below.

In this method, in step k) a first idle charge state of the energy store is determined by detecting at least one first idle voltage with at least one voltage sensor. In a subsequent step I), a capacity range for a predetermined total capacity of the energy store is determined. This is followed in a step m) by determining a second idle state of charge as a parameter of the energy store, which is assigned to the capacity area. The second quiescent charge state is determined taking into account a second quiescent voltage as a function of the first quiescent voltage and a predefined error capacity. The specified error capacity is in the specified capacity range. In addition, at least an error capacity is determined as a function of a predetermined charge determination error and a predetermined state of charge determination error. The charge determination error arises taking into account a predetermined charge that is dependent on a time period and is implemented by the energy store taking into account a current measurement inaccuracy of a current sensor for determining the charge. The state of charge determination error, on the other hand, is given as a function of an idle state of charge stroke dependent on the predetermined total charge of the energy store, taking into account a voltage measurement inaccuracy of the voltage sensor. Finally, in step n), the energy store is operated by connecting a test circuit to the energy store, by means of which the energy store converts the predetermined charge until the second idle charge state is reached.

In this way, for example, at least one map, in particular at least one table, can be stored in a memory that is assigned to the motor vehicle. The individual values of the at least one map represent the represents at least one capacitance measurement error as a function of the first and the second open-circuit voltage. A second open-circuit voltage can therefore be read from the characteristic diagram for a predetermined first open-circuit voltage and a predetermined error capacitance.

The characteristic diagram for the at least one fault capacity, also referred to below as the fault capacity characteristic diagram, can preferably be determined as follows: First, a given state of charge of the energy store can be determined from the predetermined total capacity of the energy store at different temperatures for a series of first rest voltages. A first state of charge map of the energy store can be stored in the storage device, so to speak. Then, based on the predetermined voltage measurement inaccuracy of the voltage sensor, at least one first state of charge error map can be determined. The entries of the first state of charge error map can in particular represent a respective state of charge of the energy store, which results if the series of first rest voltages are underestimated or overestimated due to the voltage measurement inaccuracy.

From the first state of charge map and the first state of charge error map, a state of charge-stroke map and a state of charge-stroke error map can now be determined. For this purpose, in particular a second state of charge map and a second state of charge error map can be taken into account, which are formed on the basis of a row of second open-circuit voltages identical to the series of first open-circuit voltages.

The individual entries of the state of charge-stroke characteristic map each represent in particular a state of idle state of charge depending on one of the first idle voltages from the series of first idle voltages and one of the second idle voltages from the series of second idle voltages a difference between each of the first idle states of charge of the first state of charge map and each of the second idle states of charge of the second state of charge map can thus be understood.

The individual entries in the state of charge-stroke error map can preferably represent a rest-charge state-stroke error. The idle state-of-charge error preferably results if, due to the voltage measurement inaccuracy of the voltage sensor, the entries of the state of charge-stroke map, that is to say the respective idle state-of-charge strokes, deviate from their actual value. In particular, the idle state stroke errors represent a percentage deviation of the respective idle state stroke.

The state of charge determination error can now be determined from the entries in the state of charge-stroke map and the corresponding entries in the state of charge-stroke error map.

The predetermined charge determination error is still missing to determine the error capacity map. For this purpose, in particular the test circuit is provided, which is designed such that a defined amount of charge is withdrawn and / or supplied from the energy store when the energy store is connected to the test circuit. The test circuit therefore in particular knows the amperage which is supplied and / or removed from the energy store at any time during charging and / or discharging by the test circuit. If, for example, the energy store is discharged for a predetermined period of time, both the charge actually converted by the energy store and the total charge flowing through the current sensor provided for detecting the current strength are known. If the current measurement inaccuracy of the current sensor is also taken into account, the charge determination errors can be specified from the charge actually implemented by the energy store, the total charge and the current measurement inaccuracy.

Due to the design of the test circuit described above, it is now also possible to assign a defined charge determination error to each entry in the state of charge-stroke map and correspondingly also to each entry in the state of charge-stroke error map.

Finally, the entries of the error capacity map can be determined taking into account the defined charge determination error and the predetermined charge state determination error.

The method has the advantage that, particularly during maintenance of the motor vehicle in a workshop, the capacity of the energy store can be determined quickly and nevertheless with sufficient accuracy. An employee in the workshop can measure the first open circuit voltage and define any capacity range. The employee can then be given the second open-circuit voltage to which the energy storage device of the motor vehicle must be charged or discharged so that the resulting capacity of the energy storage device lies within the predetermined capacity range. The capacity range is preferably limited by the at least one error capacity and possibly the predetermined total capacity of the energy store.

The invention also provides an energy management system for an energy store. The energy management system comprises at least one voltage sensor and at least one current sensor for detecting energy storage parameters, as well as a computing device which is designed to carry out the method according to the invention, taking into account the energy storage parameters.

This means that the energy management system comprises at least one voltage sensor which is assigned to the energy store and can detect a voltage which drops across the energy store, and a current sensor which is also assigned to the energy store and can detect a current intensity curve from or to the energy store. In this case, the energy storage parameters are to be understood as the voltage of the energy store and the current profile of the energy store. In addition, a temperature sensor can also be provided, which is assigned to the energy store and is designed to detect a temperature of the energy store. This temperature can then also represent one of the energy storage parameters. Furthermore, the energy management system also includes the computing device, the energy storage parameters being transmitted in particular to the computing device, so that the computing device can determine the at least one error capacity as a parameter of the energy storage device.

The invention also includes combinations of the features of the described embodiments. The embodiments and advantages described for the method according to the invention also apply analogously to the energy management system according to the invention and vice versa.

• 1 eine schematische Darstellung eines Kraftfahrzeugs mit einem Energiemanagementsystem für einen Energiespeicher;
• 2 eine schematische Darstellung von einzelnen Verfahrensschritten einer Ausführungsform des erfindungsgemäßen Verfahrens;
• 3 ein schematisches Diagramm von Ruheladezustands-Hüben, falls der erste bzw. zweite Ruheladezustand aufgrund einer Spannungsmessungenauigkeit eines Spannungssensors über- bzw. unterschätzt wird;
• 4a eine schematische Tabelle eines Ruheladezustand-Hubfehlers in Abhängigkeit von einer ersten und zweiten Ruhespannung bei einer Temperatur von 20°C, für den Fall, dass der Ruheladezustand-Hub überschätzt wird; und
• 4b eine schematische Tabelle des Ruheladezustand-Hubfehlers abhängig von der ersten und zweiten Ruhespannung bei einer Temperatur von 20°C, für den Fall, dass der Ruheladezustand-Hub unterschätzt wird.

Exemplary embodiments of the invention are described below. This shows:

• 1 a schematic representation of a motor vehicle with an energy management system for an energy store;
• 2nd a schematic representation of individual method steps of an embodiment of the method according to the invention;
• 3rd a schematic diagram of idle state strokes if the first or second idle state is over or underestimated due to a voltage measurement inaccuracy of a voltage sensor;
• 4a a schematic table of an idle state stroke error depending on a first and second idle voltage at a temperature of 20 ° C, in the event that the idle state stroke is overestimated; and
• 4b a schematic table of the idle state stroke error depending on the first and second idle voltage at a temperature of 20 ° C, in the event that the idle state stroke is underestimated.

The exemplary embodiments explained below are preferred embodiments of the invention. In the exemplary embodiment, the described components of the embodiments each represent individual features of the invention that are to be considered independently of one another, which also further develop the invention independently of one another and are therefore also to be regarded individually or in another combination than the one shown as part of the invention. Furthermore, the described embodiments can also be supplemented by further features of the invention that have already been described.

In the figures, the same reference numerals designate elements that have the same function.

1 shows a motor vehicle 100 with an energy management system 104 and an electrical energy storage 102 . The energy storage 102 can be designed, for example, as a battery, in particular as a rechargeable battery, that is to say, for example, as an accumulator and for operating the motor vehicle 100 , or to operate a vehicle electrical system 120 serve.

The energy storage 102 is with the energy management system 104 coupled, the energy management system 104 is designed to record and process energy storage parameters. The energy management system points to this 104 a computing device 106 and a variety of sensors, such as a current sensor 108 , a voltage sensor 110 and a temperature sensor 112 on. The large number of sensors are preferred to the energy store 102 connected and can thereby record the energy storage parameters of the energy storage.

It can by the current sensor 108 For example, a current can be measured by the vehicle electrical system 120 to the energy storage 102 flows or from the energy storage 102 to the vehicle electrical system 120 flows. At the same time, the voltage sensor 110 a voltage, in particular an open circuit voltage, is measured with which the energy store 102 through the vehicle electrical system 120 is applied, or with the energy storage 102 the vehicle electrical system 120 acted upon. The temperature sensor can accordingly 112 trained a current temperature of the energy storage 102 capture. In the embodiment in 1 are the amperage, the voltage and the Temperature is shown as an energy storage parameter of the energy storage.

The recorded energy storage parameters can then be carried out by a respective transmission 114 , 116 and 118 to the computing device 106 be transmitted. The computing device can use the transmitted energy storage parameters 106 then at least one parameter of the energy store, such as determining at least one error capacity.

The computing device can calculate the at least one error capacity 106 also be designed by a control command 122 for example to control a switching element in order to store the energy 102 from the vehicle electrical system 120 to disconnect or the energy storage 102 with the vehicle electrical system 120 connect to.

The individual method steps, such as how the at least one error capacity can be calculated on the basis of the energy storage parameters, are shown in 2nd shown. The in 2nd illustrated embodiment of the method according to the invention with a starting step 200 started. Then in one step 202 a first state of charge SOCt ₁ of the energy storage 102 determined, the first idle state SOCt ₁ in particular from a first rest voltage U ₁ by the voltage sensor 110 can be detected, and a first temperature of the energy storage, which is based on the temperature sensor 112 can be measured, is determined. Usually the first state of charge can be idle SOCt ₁ based on the measured temperature and the measured no-load voltage U ₁ can be read out in a simple manner from a characteristic diagram or a table which is stored, for example, by a manufacturer of the motor vehicle in a memory which is assigned to the motor vehicle.

In a subsequent step 204 can the computing device 106 the control command 122 send so that the vehicle electrical system 120 with the energy storage 102 is connected so that the energy storage through the vehicle electrical system 120 can be operated. In a subsequent step 206 a period of time can now be predefined by which it can be determined how long the energy store is kept by the vehicle electrical system 120 to be operated.

Then takes place in one step 208 the detection of a current of the energy store 102 through the current sensor 108 . After detecting the current, there is a query as to whether the specified time period has expired J or not N. If the specified time has not yet expired N, the step is 208 continue until the query shows that the specified period of time has elapsed J. By repeatedly recording the current strength according to step 208 A current intensity curve thus results over the predetermined period of time, that is to say one through the current sensor 108 recorded current over time.

After the specified period of time has elapsed in one step 210 a move of the energy storage 102 into an idle state by by the control signal 122 the computing device 106 the vehicle electrical system 120 from the energy storage 102 is separated. Subsequently, as in 2nd represented by the computing device 106 the steps 212 , 214 and 216 for example, run in parallel. Doing so in the step 212 a total charge determined by the current sensor over the predetermined period of time 108 has flowed, taking into account the step 208 recorded current intensity curve. At the same time, the step 208 Current intensity curve also recorded by the energy store 102 actually converted cargo can be calculated. Finally, a second idle state of charge SOC _t2 of the energy storage can be determined by the voltage sensor 110 a second resting voltage U ₂ and through the temperature sensor 112 a second temperature is measured and sent to the computing device 106 be transmitted. Analogous to the first idle state SOC _t1 can also be the second idle state SOC _t2 based on the measured second open circuit voltage U ₂ and the measured second temperature can be read out from a map or a table which is stored in the memory assigned to the motor vehicle.

Subsequently, in one step 218 a charge determination error Q _E based on the determined total charge according to step 212 and that according to step 214 certain charge actually converted by the energy store. Furthermore, to calculate the charge determination error Q _E also a current measurement inaccuracy 217 of the current sensor 108 considered.

In one step 220 can then be a state of charge determination error SOC _E based on the step 202 certain first idle state of charge SOCt ₁ , according to step 216 certain second idle state SOC _t2 and a predetermined voltage measurement inaccuracy 219 of the voltage sensor 110 certainly. Both the current measurement inaccuracy 217 of the current sensor 108 as well as the voltage measurement inaccuracy 219 of the voltage sensor 110 from a manufacturer of the current sensor 108 or the voltage sensor 110 be specified and stored, for example, in the memory assigned to the motor vehicle.

From the charge determination error Q _E according to step 218 and the state of charge determination error SOC _E according to step 220 can eventually in one step 222 at least one error capacity K _E can be calculated as a parameter of the energy store. The process can conclude with a final step 224 be ended.

wobei Q_E den wenigstens einen Ladungsbestimmungsfehler darstellt, SOC_E den wenigstens einen Ladezustandsbestimmungsfehler darstellt, $\left|{\displaystyle {\int }_{t_1}^{t_2}Idt}\right|$

die von dem Energiespeicher tatsächlich umgesetzte Ladung mit dem Stromstärkeverlauf I und einem Startzeitpunkt t₁ und einem Endzeitpunkt t₂ der vorgegebenen Zeitdauer darstellt, FI_E die Strommessungenauigkeit des Stromsensors darstellt, ${\displaystyle {\int }_{t_1}^{t_2}\left|I\right|dt}$

die Gesamtladung, die über die vorgegebene Zeitdauer durch den Stromsensor geflossen ist, darstellt, |SOC_t2 - SOC_t1| den Ruheladezustand-Hub mit dem ersten Ruheladezustand SOC_t1 und dem zweite Ruheladezustand SOC_t2 darstellt, und ΔSOC_E den Ruheladezustand-Hubfehler darstellt.The at least one error capacity can be particularly preferred K _E can be calculated using the following formula: $$K_E=\frac{Q_E}{SO{\mathrm{C.}}_E}=\frac{\left|{\displaystyle {\int }_{t_1}^{t_{\mathrm{2nd}}}\mathrm{I.}dt}\right|\pm F{\mathrm{I.}}_E\cdot {\displaystyle {\int }_{t_1}^{t_{\mathrm{2nd}}}\left|\mathrm{I.}\right|dt}}{\left|SO{\mathrm{C.}}_{t\mathrm{2nd}}-SO{\mathrm{C.}}_{t1}\right|\pm \Delta SO{\mathrm{C.}}_E},$$

in which Q _E which represents at least one charge determination error, SOC _E which represents at least one state of charge determination error, $\left|{\displaystyle {\int }_{t_1}^{t_{\mathrm{2nd}}}\mathrm{I.}dt}\right|$

represents the charge actually implemented by the energy store with the current intensity curve I and a start time t ₁ and an end time t _{2 of} the predetermined time period, FI _E represents the current inaccuracy of the current sensor, ${\displaystyle {\int }_{t_1}^{t_{\mathrm{2nd}}}\left|\mathrm{I.}\right|dt}$

represents the total charge that has flowed through the current sensor over the predetermined period of time, | SOC _t2 - SOC _t1 | the idle state hub with the first idle state SOC _t1 and the second idle state SOC _t2 represents, and ΔSOC _E represents the idle state lift error.

As shown in formula (2), there are therefore two different charge determination errors Q _E . The first charge determination error Q _E1 results when the charge actually converted by the energy store, hereinafter also called the net charge, results from the current measurement accuracy FI _E of the current sensor 108 is underestimated. This happens when the current measurement inaccuracy FI _E is less than zero in formula (2) as a negative sign of the current measurement inaccuracy FI _E shown. The second charge determination error Q _E2 arises if the charge actually converted by the energy store is due to the current measurement inaccuracy FI _E of the current sensor 108 is overestimated. In this case the current measurement is inaccurate FI _E stated as greater than zero, which in formula (2) is a positive sign of the current measurement inaccuracy FI _E is shown.

Analogously, there are also two state of charge determination errors SOC _E , namely a first state of charge determination error SOC _E1 and a second state of charge determination error SOC _E2 . This results in the first state of charge determination error SOC _E1 , in case the idle state hub ΔSOC _R due to the voltage measurement inaccuracy of the voltage sensor 110 is underestimated. In this case, namely the idle state lift error ΔSOC _E less than zero, as represented by a negative sign in formula (2). In contrast, the second state of charge determination error results SOC _E2 if the idle state hub ΔSOC _R due to the voltage measurement inaccuracy of the voltage sensor 110 is overestimated. Thus, as also represented in formula (2) by a positive sign, there is an idle state lift error ΔSOC _E greater than zero.

The idle state lift error ΔSOC _E can take into account, for example, the idle state stroke ΔSOC _R and the voltage measurement inaccuracy of the voltage sensor 110 be formed. The shows 3rd 1 shows a schematic illustration of a respective idle state stroke ΔSOC +, ΔSOC _R and ΔSOC-, in the event that the first idle state of charge SOC _t1 and the second idle state SOC _t2 due to the voltage measurement inaccuracy of the voltage sensor 110 are overestimated or underestimated. In the 3rd the abscissa shows a respective state Z, namely the first fault state E ₁ (SOC _R ) , the real idle state of charge SOC _R and the second fault condition E ₂ (SOC _R ) . The ordinate shows the state of charge SOC in percent. As from the diagram in 3rd results in an overestimated idle state-of-charge stroke ΔSOC + in the event that, due to the voltage measurement inaccuracy of the voltage sensor 110 an overestimated first idle state of charge SOC _{t1 +} and an underestimated second idle state of charge SOC _{t2- are} measured. Correspondingly, there is an underestimated idle state of charge stroke ΔSOC-, in the event that due to the voltage measurement inaccuracy of the voltage sensor 110 an underestimated first idle state of charge SOCt ₁ - and an overestimated second idle state of charge SOC _{t2 + is} measured. The idle state hub SOC _R accordingly arises in the event that the first idle state of charge SOCt ₁ and the second idle state SOC _t2 through the voltage sensor 110 were measured correctly. The resulting idle state lift error ΔSOC _E can then compare the idle state hub ΔSOC _R can be calculated with the overestimated idle state stroke ΔSOC + or by comparison with the underestimated idle state state stroke ΔSOC-.

Examples of calculated values for the resulting idle state lift error ΔSOC _E in percent are in the tables 4a and 4b shown. As the basis for the calculation of the respective idle state-of-lift error ΔSOC _E became a starter battery as an energy store 102 a motor vehicle 100 with a given Total capacity K _r of 60 Ah used. At the same time, a voltage measurement inaccuracy of the voltage sensor 110 of +/- 3 mV assumed. In the case of the starter battery mentioned, a quiescent voltage of 3400 mV corresponds approximately to a quiescent charge state of 0% and a quiescent voltage of 4150 mV corresponds to a quiescent state of charge of 100%.

4a now shows a table with exemplary values of the idle state lift error ΔSOC _E in percent depending on the first resting voltage U ₁ and the second open circuit voltage U ₂ said starter battery at a temperature measured by the temperature sensor of 20 ° C, in the event that the idle state stroke ΔSOC _R as in 3rd shown, due to the voltage measurement inaccuracy of the voltage sensor 110 was overestimated. Accordingly shows 4b a table with exemplary values for the idle state lift error ΔSOC _E in percent depending on the first resting voltage U ₁ and the second open circuit voltage U ₂ at one by the temperature sensor 112 measured temperature of 20 ° C, in the event that the idle state stroke ΔSOC _R as in 3rd shown, due to the voltage measurement inaccuracy of the voltage sensor 110 was underestimated. Due to the voltage measurement inaccuracy of +/- 3 mV of the voltage sensor 110 this results in two different idle state lift errors ΔSOC _E and correspondingly, as mentioned above, two state of charge determination errors, namely the first state of charge determination error SOC _E1 and the second state of charge determination error SOC _E2 .

Overall, there are therefore two charge determination errors Q _E1 and Q _E2 due to the current measurement inaccuracy FI _E of the current sensor 108 and there are two state of charge determination errors SOC _E1 and SOC _E2 due to the voltage measurement inaccuracy of the voltage sensor 110 . In the worst case, this also results in two error capacities K _E , namely the so-called first worst case error capacity K _E1 (first worst case error capacity) and the so-called second worst case error capacity K _E2 (second worst case error capacity). The first worst case error capacity K _E1 is the first charge determination error Q _E1 and the second state of charge determination error SOC _E2 educated. Accordingly, the second charge determination error form Q _E2 and the first state of charge determination error SOC _E1 the second worst case error capacity K _E2 .

An example calculation of the first worst case error capacity K _E1 and the second worst case error capacity K _E2 is now given below. The calculation uses the previously mentioned starter battery as an energy store 102 with a total capacity K _R of 60 Ah. Furthermore, there is a current measurement inaccuracy in this exemplary calculation FI _E of +/- 1% and a voltage measurement inaccuracy of +/- 3 mV. As the first resting tension U ₁ can by the voltage sensor 110 For example, a voltage of 3600 mV can be detected at a temperature of 20 ° C, which in the starter battery mentioned is about a first idle state SOC _t1 of 31% would correspond. As a second resting tension U2 For example, a voltage of 3750 mV could be measured, which in the starter battery is approximately a second idle state SOC _t2 would correspond to 58%. This results in a idle state stroke ΔSOC _R of 27%.

At the same time, the current sensor could use this example calculation 108 a gross charge, i.e. a total charge, that is generated by the current sensor over the specified period of time 108 flowed from 19 Ah, with a net charge, that is from the energy storage 102 So the starter battery actually converted charge could correspond to 16 Ah, for example.

In the event that the idle state hub ΔSOC _R due to the measurement inaccuracy of the voltage sensor 110 would be overestimated for the idle state stroke error ΔSOC _R according to the table in 4a based on the predetermined first open circuit voltage U ₁ and the predetermined second open circuit voltage U ₂ give a value of 1.05%. Would, however, the idle state hub ΔSOC _R due to the measurement inaccuracy of the voltage sensor 110 would be underestimated, according to 4b based on the predetermined first open circuit voltage U ₁ and the predetermined second open circuit voltage U ₂ a idle state lift error ΔSOC _E of -1.22%.

wobei sich in Bezug auf die vorgegebene Gesamtkapazität der Starterbatterie von 60 Ah eine prozentuale erste Worst-Case- Fehlerkapazität K_E1 [%] von: $$K_{E1}\left[\%\right]=\frac{1}{60Ah}\ast \mathrm{56,4}Ah-1=-\mathrm{6,0}\%$$

If the specified values of the exemplary calculation are now inserted into the formula (2), the result for the first worst case error capacity KEI is: $$K_{E1}=\frac{16AH-1\%\ast \mathrm{19th}AH}{\mathrm{27th}\%+1.05\%}=56.4AH$$

with respect to the given total capacity of the starter battery of 60 Ah, a percentage of the first worst case error capacity K _E1 [%] of: $$K_{E1}\left[\%\right]=\frac{1}{60AH}\ast 56.4AH-1=-6.0\%$$

wobei sich in Bezug auf die Gesamtkapazität der Starterbatterie eine prozentuale zweite Worst-Case-Fehlerkapazität K_E2 [%] ergibt zu: $$K_{E2}\left[\%\right]=\frac{1}{60Ah}\ast \mathrm{62,8}Ah-1=\mathrm{4,8}\%$$

Analogously, the second worst case error capacity K _E2 results in the example calculation: $$K_{E\mathrm{2nd}}=\frac{16AH+1\%\ast \mathrm{19th}AH}{\mathrm{27th}\%-1.22\%}=62.8AH,$$

in relation to the total capacity of the starter battery, a second worst case error capacity K _E2 [%] results in: $$K_{E\mathrm{2nd}}\left[\%\right]=\frac{1}{60AH}\ast 62.8AH-1=4.8\%$$

Overall, the total capacity K _{R of} the starter battery in this exemplary calculation can deviate from its original value, namely 60 Ah, in the worst case by + 4.8% or -6%. Due to the voltage measurement inaccuracy of the voltage sensor 110 and the current measurement inaccuracy of the current sensor 108 the capacity of the energy storage device can therefore be in a capacity range from 56.4 Ah to 62.9 Ah.

If, for example, a maximum deviation of the total capacity is set to <5%, so that a maximum value range of 57 Ah to 63 Ah is specified for the capacity range, it can be determined for the exemplary calculation that the capacity range or at least the lower limit of the capacity range is outside the specified value range. In this case, the idle state stroke of 27% is not enough to cover the total capacity of the energy store 102 To be determined with sufficient accuracy even with a low idle state stroke.

Overall, the invention thus provides a possibility for calculating at least one worst case error capacity in motor vehicles with electrochemical energy stores.

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

• DE 3920629 A1 [0008]
• DE 60132951 T2 [0009]
• DE 102007055255 A1 [0010]

Claims (10)

Method for determining a parameter of an energy store (102), comprising the following steps: a) detecting a first idle state of charge (SOC _t1 ) of the energy store (102) with at least one voltage sensor (110), b) operating the energy store (102) over a predetermined period of time by connecting a motor vehicle electrical system (120) to the energy store (102), c) detecting a current profile of the energy store (102) with a current sensor (108) during operation of the energy store (102) over the predetermined time period in accordance with step b), and d) after the specified period of time has elapsed: - putting the energy store (102) into an idle state by disconnecting the energy store (102) from the motor vehicle electrical system (120), - determining a total charge that has flowed through the current sensor (108) over the specified period of time the current intensity curve recorded in step c), - determining a charge actually converted by the energy store (102) the current intensity curve recorded in step c), and - detecting a second idle state of charge (SOC _t2 ) of the energy store (102) with the at least one voltage sensor (110), e) determining at least one charge determination error (Q _E ) taking into account that of the energy store (102 ) actually implemented charge, the total charge that has flowed through the current sensor over the predetermined period of time, and a predetermined current measurement inaccuracy (FI _E ) of the current sensor (108), f) determining at least one state of charge determination error (SOC _E ) taking into account a state of charge state of charge ( ΔSOC _R ) of the energy store (102) and a rest state of charge stroke error (ΔSOC _E ), the rest state of charge stroke (ΔSOC _R ) taking into account the first and second rest state of charge (SOC _t1 , SOC _t2 ), and the rest state of charge- Stroke error (ΔSOC _E ) from the idle state stroke (ΔSOC _R ) taking into account a specified voltage measurement inaccuracy of the voltage sensor (110), and g) determining at least one error capacity (K _E ) as a parameter of the energy store (102), taking into account the at least one charge determination error (Q _E ) and the at least one charge state determination error (SOC _E ). Procedure according to Claim 1 , characterized in that a first and a second charge determination error (Q _E , Q _E1 , Q _E2 ) are determined in accordance with step e), the first charge determination error (Q _E1 ) resulting when the charge actually converted by the energy store (102) is underestimated on the basis of the predefined current measurement inaccuracy (FI _E ) of the current sensor (108) and the second charge determination error (Q _E2 ) results if the charge actually converted by the energy store (102) is based on the predefined current measurement inaccuracy (FI _E ) of the current sensor (108 ) is overestimated. Method according to one of the preceding claims, characterized in that a first and a second state of charge determination error (SOC _E , SOC _E1 , SOC _E2 ) are determined in accordance with step f), the first state of charge determination error (SOC _E1 ) resulting when the idle state of charge stroke (ΔSOC _R ) is underestimated due to the predetermined voltage measurement inaccuracy of the voltage sensor (110) and the second state of charge determination error (SOC _E2 ) results when the idle state of charge stroke (ΔSOC _R ) is overestimated due to the predetermined voltage measurement inaccuracy of the voltage sensor (110). Procedure according to Claim 2 and 3rd , characterized in that according to step g) a first and a second error capacity (K _E , K _E1 , K _E2 ) are determined, the first error capacity (K _E1 ) taking into account the first charge determination error (Q _E1 ) and the second state of charge determination error (SOC _E2 ), and wherein the second error capacity (K _E2 ) takes into account the second charge determination error (Q _E2 ) and the first state of charge determination error (SOC _E1 ). Procedure according to Claim 4 , characterized by a step h) determining a capacity range of the energy store (102) taking into account a deviation of the first and second error capacitance (K _E1 , K _E2 ) from a predetermined total capacity (K _R ) of the energy store (102). Procedure according to Claim 5 , characterized by a step i) outputting the capacity range as a function of the predetermined total capacity (K _R ) on an output device. Procedure according to Claim 6 , characterized by a step j) checking whether the capacity range is within a predetermined value range, the at least one error capacity (K _E , K _E1 , K _E2 ) being validated only if the checking is positive. Method according to one of the preceding claims, characterized in that - the at least one charge determination error Q _{E is} given by $$Q_E=\left|{\displaystyle {\int }_{t_1}^{t_{\mathrm{2nd}}}\mathrm{I.}dt}\right|\pm F{\mathrm{I.}}_E\cdot {\displaystyle {\int }_{t_1}^{t_{\mathrm{2nd}}}\left|\mathrm{I.}\right|dt},$$

- The at least one state of charge determination error SOC _{E is} given by SOC _E = | SOC _t2 - SOC _t1 | ± ΔSOC _E , and - the at least one error capacity K _{E is} given by $K_E=\frac{Q_E}{SO{\mathrm{C.}}_E},$

in which - $\left|{\displaystyle {\int }_{t_1}^{t_{\mathrm{2nd}}}\mathrm{I.}dt}\right|$

represents the charge actually implemented by the energy store with the current intensity curve I and a start time t ₁ and an end time t _{2 of} the time period, FI _{E represents} the current measurement inaccuracy of the current sensor, ${\displaystyle {\int }_{t_1}^{t_{\mathrm{2nd}}}\left|\mathrm{I.}\right|dt}$

dt represents the total charge that has flowed through the current sensor over the specified period of time, - | SOC _t2 - SOC _t1 | represents the idle state stroke ΔSOC _R with the first idle state SOC _t1 and the second idle state SOC _t2 , and - ΔSOC _{E represents} the idle state stroke error. Method for determining a parameter of an energy store (102), comprising the following steps: k) determining a first idle state of charge (SOC _t1 ) of the energy store (102) by detecting at least one first open circuit voltage (U ₁ ) with at least one voltage sensor (110), I) Determining a capacity range for a predetermined total capacity (K _R ) of the energy store (102), m) determining a second idle state of charge (SOC _t2 ) as a parameter of the energy store (102) which is assigned to the capacity area, taking into account a second idle voltage (U ₂ ) as a function of the first open-circuit voltage (U ₁ ) and a predetermined error capacity (K _E ), the predetermined error capacity (K _E ) - being within the defined capacity range, - as a function of a predetermined charge determination error (Q _E ) and a predetermined state of charge determination error (SOC _E ) is determined, the charge determination error (Q _E ) being determined taking into account a v on a time-dependent, predetermined charge, which is implemented by the energy store (102) taking into account a current measurement inaccuracy (FI _E ) of a current sensor (108) for determining the charge, and the state of charge determination error (SOC _E ) as a function of one of the predetermined total charge (K _R ) of the energy store (102) dependent state of charge (ΔSOC _R ) taking into account a voltage measurement inaccuracy of the voltage sensor (110), n) operating the energy store (102) by connecting a test circuit to the energy store (102), by the the energy store (102) implements the predetermined charge until the second idle charge state (SOC _t2 ) is reached. Energy management system (104) for an energy store (102), with at least one voltage sensor (110) and a current sensor (108) for detecting energy storage parameters and with a computing device (106) which is designed, taking into account the energy storage parameters, a method according to Claim 1 perform.

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