DE102019202461A1 - Method and battery state detection device for determining a usable energy content of an energy store of a motor vehicle - Google Patents

Abstract

The invention relates to a method for determining a usable energy content (EE, EL) of an energy store (10), the usable energy content (EE, EL) representing energy (EL) which can be supplied to the energy store (10) when the energy store (10) is being charged represents an energy (EE) that can be drawn from the energy store (10) when the energy store (10) is discharged. The usable energy content (EE, EL) is determined as a function of an energy loss (EV) that occurs during charging or discharging and as a function of an energy (E0) stored or storable in the energy store (10), which in turn depends on a stored characteristic curve (14), which indicates a dependency of an open circuit voltage of the energy store (10) on a state of charge (SOC) of the energy store (10), is determined.

Description

The invention relates to a method for determining a usable energy content of an energy store, wherein the usable energy content represents energy that can be supplied to the energy store when the energy store is charged and represents energy that can be drawn from the energy store when the energy store is discharged. The invention also includes a battery state detection device for a motor vehicle.

In order to be able to ensure error-free and safe operation in the energy network of a motor vehicle, the determination of the currently usable battery energy, i.e. the charging or discharging energy of the on-board network or traction batteries, plays an important role as part of the battery status detection. In the automotive environment, there are already known methods for realizing this determination. These calculation methods work with the aid of the current battery voltage or the nominal battery voltage. However, these variables are highly dependent on the current battery load, that is to say the current battery current, and are only valid for a load by a battery current corresponding to a C-rate, for which the nominal battery voltage is also defined. A 1C battery current represents the battery current corresponding to a C rate of 1C, and is in particular defined in such a way that this 1C battery current leads to a complete discharge of a fully charged energy store in one hour. However, since completely different battery currents can also occur during normal operation of an energy storage device, a robust statement about the currently usable battery energy over different operating loads, in particular for different C-rates, is difficult.

The determination of the currently usable charging energy or discharging energy of on-board network and traction batteries is basically a predictive method. This means that before, at the beginning or also during a charging or discharging process, the energy that can ultimately be used up to the end of this process should be predicted, that is to say it should be predicted before the end of this process. For example, as is also the case or the objective within the scope of the invention, it should be determined predictively during a discharge process how much energy can be drawn from the energy store until it is completely discharged. During a charging process, it should be determined in an analogue predictive manner how much energy can still be supplied to the energy store until it is fully charged.

The energy calculation is based on current values, such as the current or nominal battery voltage. Correspondingly, previous methods have the major disadvantage that they do not allow the charging or discharging energy to be determined particularly precisely, since the battery voltage that is actually set at the battery terminals during the subsequent load during charging or discharging can deviate significantly from this previously assumed battery voltage. Consequently, especially with varying battery voltages, i.e. battery voltages that are different from the previously assumed battery voltage, great inaccuracies can arise in determining the charging or discharging energy that can ultimately be used in the corresponding charging or discharging process.

The DE 10 2012 010 486 A1 describes a method for evaluating an aging condition of a battery using a family of characteristics in normal operation, whereby at the beginning of a discharge process the initial voltage of the battery, the discharge current and the temperature of the battery are determined, based on these variables, a characteristic is selected from the family of characteristics and a The initial state of the battery can be determined. At the end of the charging process, the final voltage of the battery is measured and compared with the voltage expected at the end of the discharge based on the selected characteristic curve, and the aging status of the battery is evaluated from this. In addition, in the event that the final voltage is less than the expected voltage at the end of the discharge process, it can be concluded that the actual capacity of the battery is less than the capacity assumed at the beginning of the discharge process. A prognosis, in particular with regard to a usable energy content of an energy store, cannot be provided on the basis of this method, however, since knowledge of the final voltage is required to carry out this method, which can only be determined at the end of a discharge process.

Furthermore describes the DE 10 2005 023 365 A1 a method for determining a battery size using a mathematical battery model that describes the thermal and / or electrical behavior of a battery. The future electrical load on the battery can be estimated and the battery model can calculate the future development of the battery size on the basis of the estimated electrical load. The battery size determined by the battery model can be, for example, the battery temperature, the state of charge, the performance, the internal resistance of a voltage dropping inside the battery. A determination of the usable energy content is also based on this procedure Energy storage, especially in a predictive manner, not possible.

Furthermore describes the DE 10 2016 207 571 A1 a diagnostic method for a battery arrangement with a plurality of battery cells, wherein the load voltage of a respective battery cell is measured and compared with a reference value and a diagnostic signal is generated on the basis of the comparison. The accuracy of the diagnostic method is to be increased further by initially measuring the open circuit voltages of the battery cells in the no-load state and holding them ready as a correction value. The diagnostic method is intended to monitor the temperature budget and / or the resistance ratios with regard to internal resistance and / or contact resistance of the individual battery cells. However, this method also does not determine any usable energy content of an energy store.

The object of the present invention is therefore to provide a method and a battery state detection device which enable a usable energy content of an energy store to be determined in the simplest and most precise way possible.

This object is achieved by a method and a battery state detection device with the features according to the respective independent patent claims. Advantageous configurations of the invention are the subject matter of the dependent claims, the description and the figures.

In a method according to the invention for determining a usable energy content of an energy store, the usable energy content represents an energy that can be supplied to the energy store when the energy store is being charged and an energy that can be drawn from the energy store when the energy store is discharged. The usable energy content is dependent on a loading or unloading occurring energy loss and determined as a function of an energy stored or storable in the energy store, which in turn is determined as a function of a stored characteristic curve that indicates a dependency of an open circuit voltage of the energy store on a state of charge of the energy store.

The invention is based on the knowledge that the usable energy content of an energy store, i.e. the maximum amount of energy that can be drawn from the energy store when it is discharged until it is completely discharged, does not match the energy stored in the energy store before it was discharged, and also when the battery or battery is charged. of the energy store the usable energy content, ie the maximum energy that can be fed to the energy store until the energy store is fully charged does not match the energy ultimately stored in the energy store by this charging process after charging, since energy losses inevitably occur, in particular at the internal resistance of such an energy store. If, for example, a certain amount of energy is stored in a battery cell and the battery cell is then discharged and the energy used to operate a consumer, the energy supplied to the consumer is less than the energy originally stored in the battery cell, since a certain proportion of this amount of energy is, for example, Heat loss was implemented by the internal resistance. The same applies to charging a battery cell. In order to fully charge a battery cell, for example, a greater amount of energy is required that must be supplied to this battery cell than the total energy that is ultimately stored in the battery cell after the charging process, since a certain proportion of the energy supplied is also lost during the charging process the internal resistance of the battery cell is converted.

The actually usable energy content of the energy store can thus be determined in a particularly precise and simple manner by initially dividing this usable energy content into two parts, namely the loss part, which represents the energy loss occurring during charging or discharging, and the stored or storable energy content, which for example, is actually stored in the energy store before a discharge process or can actually still be stored in the energy store before a charging process. Another particularly great advantage of the invention, however, is primarily that a characteristic curve is used to determine the stored or storable energy content which indicates the dependency of the open circuit voltage of the energy store at least on the state of charge of the energy store. The state of charge of the energy store can be determined particularly easily using known methods and is therefore available in any case within the scope of the battery state detection. This advantageously enables a particularly precise determination of the energy content stored or storable in the energy store, without having to make any imprecise assumptions about a nominal voltage or the like. In addition, the energy content that can be stored in the energy store or the energy content stored in the energy store is independent of a current battery load and can therefore be determined in a particularly simple manner using the characteristic curve without having to take any other battery variables into account. The current battery load is only included in the amount of energy used during charging or Unloading represents loss of energy. This can advantageously be taken into account by taking into account a current battery current when determining this energy loss, as will be explained in more detail later. By logically subdividing the usable energy content into a portion that is independent of the current battery load and a portion that is dependent on the battery load, a particularly precise determination of the usable energy content can be provided in a particularly simple manner.

The energy store can generally represent an individual battery cell of a battery or also an overall battery with several battery cells.

The determination of the usable energy content is preferably a predictive determination, in particular an expected or maximum possible usable energy content of the energy store. In other words, the determination of the usable energy content of the energy store should take place before a charging process of the energy store or a discharging process of the energy store has ended and accordingly before the energy store is completely discharged or is completely charged. The knowledge of the usable energy content can then advantageously be used by an energy management device of the motor vehicle for an adapted control of charging or discharging processes of the energy store, for example for suitable control of a recuperation operation or the like.

It is particularly advantageous if the stored or storable energy is determined as a function of the characteristic curve of a stored family of characteristics, which indicates the dependence of the open-circuit voltage of the energy store on the state of charge of the energy store and on a temperature of the energy store. By additionally taking into account the temperature of the energy store, the accuracy in determining the energy content stored in the energy store or the energy content that can still be stored can be determined much more precisely. Such a family of characteristics, which describes the relationship between the state of charge of the energy store, the temperature and the open-circuit voltage, accordingly specifies the associated open-circuit voltage of the energy store for a given state of charge value of the energy store and a given temperature of the energy store. This can then advantageously be used to determine the stored or storable energy of the energy store. In other words, for a given temperature of the energy store, a characteristic curve which describes the corresponding relationship between the state of charge of the energy store and the open circuit voltage of the energy store can be selected and then the open circuit voltage of the energy store can then be determined based on the given state of charge of the energy store. Conversely, the current state of charge of the energy store can first be specified, a corresponding characteristic curve, which describes the relationship between the temperature of the energy store and its open-circuit voltage, can be selected and the open-circuit voltage of the energy store at the current point in time can then be determined using the current given temperature. In all cases the rest voltage is the same.

Furthermore, it is advantageous if the usable energy content is determined as the energy content that can actually be extracted from the energy store when the energy store is discharged as the difference between the energy stored in the energy store and the energy loss occurring during discharge. If a discharging process of the energy store is considered first, the energy content that can actually be extracted from the energy store represents the difference between the energy currently stored in the energy store and the energy loss that occurs when the energy store is discharged. When the energy store is discharged, the usable energy content can thus be determined in a simple manner as the difference described. This also applies analogously if the energy storage device is not fully discharged, but only partially discharged, for example. In this case, the usable energy content, i.e. the partial energy content that can actually be extracted from the energy store when discharging or partially discharging the energy store, can be determined in the case of such a partial discharge as the difference between the change in the energy stored in the energy store and the energy loss occurring during partial discharge. Because of the energy losses, the energy that can ultimately be drawn from the energy store during discharging is also less than the energy stored in the energy store.

Accordingly, it is advantageous if the usable energy content during charging, namely the maximum energy content that can be supplied when charging the energy store, is determined as the sum of the energy that can still be stored in the energy store and the energy loss occurring during charging. The energy that can be fed to an energy store during charging is greater than the energy that can still be stored in the energy store, since the energy store also has to be supplied with an amount of energy that is ultimately lost as heat loss, for example through the internal resistance of the energy store. Accordingly, one can advantageously, the usable energy content when charging the energy store as the sum of the energy losses occurring during charging and the energy that can still be stored in the energy store, for example with a certain initial state of charge. Thus, for example, it is possible to determine the maximum amount of energy that can still be supplied to an energy store until it is fully charged. In the same way, the usable energy content in the case of a partial charge of the energy store can be determined, i.e. how much energy can still be supplied to an energy store until it reaches a predetermined state of charge that differs from a full charge of the energy store. Accordingly, in such a situation, the usable energy content can be determined as the sum of the change in the energy stored in the energy store and the energy loss that occurs during partial charging. The change in the energy stored in the energy store can also be understood as a future change in the energy stored in the energy store. So, for example, is the current state of charge of the energy store 50 Percent and if the energy storage device is to be charged up to a final state of charge of 80 percent, this represents a change in the state of charge of 30 percent. This makes it easy to determine how much energy must or can be fed to an energy storage device before it starting from the current state of charge has reached a certain discharge state.

The determination of the usable energy content in the case of a partial discharge or partial charge is, however, of less interest in most cases, although this can be determined just as easily in the same way. In the context of the present invention, the usable energy content is therefore preferably the energy content during charging that can still be supplied to the energy store, starting from a current state of charge, at most up to a full charge corresponding to a state of charge of 100%, and during unloading it is the energy content that the Energy storage, starting from a current state of charge, can still be removed at most up to full discharge, corresponding to a state of charge of 0%.

It is also advantageous if the energy loss that occurs is determined as a function of a battery current and a specific internal resistance of the energy store. This applies both when charging the energy store and when discharging the energy store. This embodiment of the invention is particularly advantageous because it is precisely the internal resistance of the energy store and also the current battery current that are the decisive influencing variables of the energy loss that occurs during charging or discharging. For example, the greater the internal resistance of the energy store, the greater the energy losses. At the same time, the higher the battery current, the greater the energy losses. These two variables can also be provided in a simple manner, in particular by measurement and / or by methods known from the prior art, in particular for determining the internal resistance of the energy store. Both the battery current and the internal battery resistance represent parameters that are typically determined or measured in any case as part of the battery status detection using independent methods. It is therefore easy to fall back on these variables in order to be able to advantageously determine the energy loss that occurs during charging and discharging particularly precisely. For example, the current battery current can simply be determined at the beginning of a charging or discharging process and the energy loss to be expected over the entire charging or discharging process can be determined as a function of this current battery current or the current strength and the specific internal resistance of the energy store. Since the energy loss can also be determined particularly precisely in this way, the above-mentioned variables, namely the energy that can still be supplied to the energy store when it is charged and the energy that can be drawn from the energy store when it is discharged, can be determined particularly precisely. In one case, only the energy loss that occurs during discharging, which can be calculated or estimated as described, must simply be subtracted from the energy stored in the energy store, and this energy loss simply added to the energy that can still be stored in the energy store when charging the energy store.

The energy loss can also be repeatedly prognostically determined several times during a charging or discharging process, so that, for example, changes in the battery current can be taken into account in this forecast and the forecast for the remaining charging or discharging process can be corrected or adapted based on this.

In a further advantageous embodiment of the invention, the total energy loss occurring during charging or discharging is determined as the product of the battery current, the capacity of the energy store, the change in the state of charge of the energy store and a certain loss resistance, which at least depends on the internal resistance of the energy store. The loss resistance can not only take into account the internal resistance of the energy store, but also, for example, other resistances, such as interconnection resistances or similar. Energy losses also occur in such resistors, which can thus advantageously be taken into account. To determine the energy loss at such resistors, the only input variables required are the current battery current, the capacity of the energy store, the internal resistance, the initial state of charge and the expected final state of charge of the energy store, which, as described above, is preferably 0% when discharging and 100% when charging. amounts. In other words, the power loss and thus also the total usable energy can be determined in a simple way that can still be supplied to the energy store when charging the energy store up to a certain discharge state or up to full charge, or up to this in the case of the energy store being discharged can be removed from a certain discharge state or until it is fully discharged.

In a further advantageous embodiment of the invention, depending on the, in particular expected or maximum possible, change in the state of charge of the energy store during charging or discharging and depending on the at least one characteristic curve, a mean open-circuit voltage during charging or discharging is determined and the stored or storable Energy determined as a function of the mean rest voltage. As already described at the beginning, the open circuit voltage of the energy store depends on the current state of charge of the energy store. This dependency, in particular also the additional temperature dependency, can be stored in the form of the family of characteristics and accordingly also taken into account when calculating the usable energy content. However, since the state of charge also changes during charging and discharging of an energy store, the open circuit voltage of the energy store accordingly usually does not remain constant during such a charging process or discharging process, but rather changes as well. This change can now advantageously be taken into account by the averaging described. In this way, the energy stored or still storable in the energy store can be determined particularly precisely. The mean value can be formed in accordance with any predetermined formation rule, for example as an arithmetic mean, geometric mean, quadratic mean, etc. Arithmetic averaging is preferred because it provides particularly accurate results.

In a further advantageous embodiment of the invention, the stored or storable energy is determined as the product of the mean open-circuit voltage and the, in particular expected or maximum possible, change in the amount of charge stored in the energy store, the change in the amount of charge being the product of the capacity of the energy store and the change in the state of charge of the energy store, which is in particular to be expected or, in turn, maximally possible, is determined. If an energy store is charged or discharged, the amount of charge stored in it also changes, which is the product of its capacity and the change in the state of charge. The change in this amount of charge multiplied by the mean open-circuit voltage thus advantageously provides the energy stored in the energy store before the discharge process or the energy that can still be stored in the energy store before a charging process.

Overall, the usable energy content, both during a charging process and during a discharging process, as defined at the beginning, can be determined as a function of a few input variables, namely the current state of charge of the energy store, the current battery current, which represents the current charging current during charging and represents the current discharge current when discharging, for example when the charging or discharging process begins or a forecast current, if known or specified in certain situations, continues to depend on the current internal resistance of the energy store and optionally other connection resistances, a current temperature of the energy store and the Energy storage capacity. The capacity of the energy storage device can also vary over the course of its service life. Accordingly, it is advantageous if the current capacity of the energy store is repeatedly determined, so that the calculation of the usable energy content can also be adapted to the state of aging of the energy store.

Only a few input variables are therefore required to determine the usable energy content, which are typically measured or determined anyway in the course of the battery status detection and are already available to the system. With the aid of the described family of characteristics, the usable energy content can be determined or forecast at any time, adapted to the situation, precisely and in a particularly simple and inexpensive manner.

Furthermore, the invention also relates to a battery status detection device for a motor vehicle, the battery status detection device being designed to determine a usable energy content of an energy store of the motor vehicle, the usable energy content representing an energy that can be fed to the energy store when charging the energy store and one that can be fed to the energy store when the energy store is discharged Energy storage represents removable energy. The battery state detection device is designed to determine the usable energy content as a function of an energy loss that occurs during charging or discharging and as a function of energy stored or storable in the energy storage device, and this as a function of a stored characteristic curve which depends on an open circuit voltage of the energy storage device to determine a state of charge of the energy storage device.

The advantages described for the method according to the invention and its configurations apply in the same way to the battery state detection device according to the invention. In addition, the method steps described in connection with the method according to the invention and its configurations make it possible to develop the battery state detection device according to the invention by means of further corresponding object features.

In addition, a battery with a battery state detection device according to the invention or one of its configurations should also be regarded as belonging to the invention, as well as a motor vehicle with such a battery.

The motor vehicle according to the invention is preferably designed as a motor vehicle, in particular as a passenger vehicle or truck, or as a passenger bus or motorcycle.

The invention also includes the combinations of the features of the described embodiments.

Exemplary embodiments of the invention are described below.

• 1 eine schematische Darstellung eines Energiespeichers und einer Batteriezustandserkennungseinrichtung zum Bestimmen eines nutzbaren Energieinhalts des Energiespeichers gemäß einem Ausführungsbeispiel der Erfindung;
• 2 eine schematische Darstellung des Energiespeichers, welcher als Ersatzschaltbild veranschaulicht ist, und der Batteriezustandserkennungseinrichtung zum Bestimmen des nutzbaren Energieinhalts des Energiespeichers gemäß einem Ausführungsbeispiel der Erfindung;
• 3 ein Kennlinienfeld, welches den Zusammenhang zwischen der Ruhespannung, der Temperatur und dem Ladezustand des Energiespeichers angibt, zur Bestimmung des nutzbaren Energieinhalts des Energiespeichers gemäß einem Ausführungsbeispiel der Erfindung;
• 4 eine schematische Darstellung des Zusammenhangs zwischen dem im Energiespeicher gespeicherten Energieinhalt, dem nutzbaren Energieinhalt und der Verlustenergie beim Entladen des Energiespeichers gemäß einem Ausführungsbeispiel der Erfindung; und
• 5 eine schematische Darstellung des Zusammenhangs der in den Energiespeicher speicherbaren Energie, der Energieverluste und des nutzbaren Energieinhalts des Energiespeichers beim Laden des Energiespeichers gemäß einem Ausführungsbeispiel der Erfindung.

Show:

• 1 a schematic representation of an energy store and a battery state detection device for determining a usable energy content of the energy store according to an embodiment of the invention;
• 2 a schematic representation of the energy store, which is illustrated as an equivalent circuit diagram, and the battery state detection device for determining the usable energy content of the energy store according to an embodiment of the invention;
• 3 a family of characteristics indicating the relationship between the open-circuit voltage, the temperature and the state of charge of the energy store for determining the usable energy content of the energy store according to an embodiment of the invention;
• 4th a schematic representation of the relationship between the energy content stored in the energy store, the usable energy content and the energy loss when discharging the energy store according to an embodiment of the invention; and
• 5 a schematic representation of the relationship between the energy that can be stored in the energy store, the energy losses and the usable energy content of the energy store when charging the energy store according to an exemplary embodiment of the invention.

The exemplary embodiments explained below are preferred embodiments of the invention. In the exemplary embodiments, the described components of the embodiments each represent individual features of the invention that are to be considered independently of one another and that also develop the invention independently of one another. Therefore, the disclosure is intended to include combinations of the features of the embodiments other than those shown. Furthermore, the described embodiments can also be supplemented by further features of the invention already described.

In the figures, the same reference symbols denote functionally identical elements.

1 shows a schematic representation of an energy store 10 and a battery condition detection device 12 to determine a usable energy content EE, EL of the energy store 10 according to an embodiment of the invention. Also 2 shows a schematic representation of the energy store 10 , but as an equivalent circuit diagram, and again the battery condition detection device 12 to determine the usable energy content EE, EL of the energy store 10 .

Becomes the energy store 10 discharged, the usable energy content EE, in particular the final charging energy EE, actually represents the energy store 10 removable energy, while the energy storage device is charging 10 the usable energy EL, i.e. the charging energy that the energy store 10 represents energy actually supplied or energy that can still be supplied up to full charge. These energy contents EE, EL differ from that in the energy store 10 stored or storable energy E0 (compare 4th and 5 ), as explained in more detail later. Before the determination of this usable energy content EE, EL is discussed in more detail, first of all, using 1 and 2 the relevant battery sizes are explained and illustrated.

The energy storage 10 can generally represent a battery. This can be a single battery cell, for example for a high-voltage battery of the motor vehicle, or it can also be such a high-voltage battery itself, which in turn has several individual battery cells. In the following, a single battery cell is used as an energy store 10 To illustrate the determination of the usable energy content EE, EL, the method described can, however, also be transferred quite analogously to an interconnection of several battery cells, since the relevant battery sizes of a high-voltage battery or in general a battery with several individual battery cells are based on known physical relationships from the individual Have cell sizes determined easily by calculation. For example, a respective battery cell, such as the energy store 10 , have a current state of charge SOC.

The energy storage 10 thus has a current state of charge SOC in the present example, which is shown in 1 through the hatched area of the energy store 10 is illustrated. This current state of charge SOC can be determined by measurement using known methods and the battery state detection device 12 provide. The current temperature is also displayed T of the energy storage 10 detected and as an input variable of the battery state detection device 12 provided. During a charging or discharging process of the energy storage device 10 can also use the battery power I. measured and also the battery condition detection device 12 to be provided. Furthermore, in 1 nor those on the poles 10a , 10b of the energy storage 10 falling battery voltage U illustrates. However, this battery voltage U is not relevant in the present case for calculating the usable energy content EE, EL. On the other hand, however, the open-circuit voltage OCV of the energy store 10 like this in 2 is illustrated. In the load-free state of the energy store 10 especially if there is no battery power for a long time I. has flowed, the open-circuit voltage OCV of the energy store is correct 10 with the one at the poles 10a , 10b otherwise, i.e. under load, in the case of a discharge it is smaller in magnitude than the rest voltage OCV and in the case of charging is larger in magnitude than the rest voltage OCV, since there is a voltage drop at an internal resistance in the load case RI of the energy storage 10 comes. Like the equivalent circuit diagram of the energy store 10 in 2 illustrated, the energy storage 10 as a series circuit of a first resistor R1 at which a first voltage drop U1 occurs in the load case, and a parallel connection from a capacitance C. who have the capacity C. of the energy storage 10 illustrated, and a second resistor R2 can be understood at which a second voltage drop in the load case U2 occurs. The total resistance of this series connection represents the internal resistance RI of the energy storage 10 represent.

Also for determining this internal resistance RI numerous methods are known from the prior art. This internal resistance too RI is determined repeatedly, as well as the capacity C. of the energy storage 10 and the battery condition detection device 12 provided. 2 also illustrates the state of the energy store 10 when discharging, but the same applies when charging the energy store 10 , only that then, for example, the charging current I. reverses its flow direction.

The battery condition detection device 12 consequently uses the input variables current state of charge SOC, current battery current I. , especially the information about whether the energy storage 10 is currently being charged or discharged, as well as the current internal resistance RI , the current temperature T and the current capacity C. of the energy storage 10 in order to determine the usable energy content EE, EL. In addition, there is a discharge state of the energy store 10 Assumed 100% when charging and 0% when discharging. When discharging the energy store 10 this means that the current state of charge SOC also corresponds to the maximum possible change in state of charge.

Some of these input variables are recorded continuously, such as the battery current I. , the current state of charge SOC and the current temperature T of the energy storage 10 as well as the internal resistance RI , while for example the current capacity C. of the energy storage 10 can be determined much less often, as this changes over the course of the service life of the energy store 10 changes slowly.

In addition to these input variables, the battery status detection device uses 12 to determine the usable energy content EE, EL also advantageously a family of characteristics 14th , which for example in a memory 16 the battery condition detection device 12 can be stored. This family of characteristics is in 3 schematically illustrates and gives the relationship between the open-circuit voltage OCV of the energy store 10 , the current temperature T of the energy storage 10 and the current state of charge SOC of the energy store 10 on. The current temperature T and the current state of charge SOC also the current open-circuit voltage OCV of the energy store 10 determine. In this way, the Open-circuit voltage OCV of the energy storage 10 into the calculation of the usable energy content EE, EL of the energy store 10 without having to measure this open-circuit voltage OCV directly, which in any case only occurs when the energy storage device is at rest 10 would be possible and not under load.

Depending on the input variables mentioned and using the family of characteristics 14th the usable energy content EE, EL of the energy store can now 10 can be determined in a simple manner, as will now be described below.

First, the usable energy content EE, EL is divided into two energy components, in particular also arithmetically, as will be explained in more detail later, namely into a first component, the energy losses that occur EV describes, and a second component, which represents the energy content in the energy store 10 is stored (in the case of unloading) or can still be stored (in the case of loading) and which is subsequently included with E0 is designated. This structure is in 4th and 5 illustrated schematically.

4th shows schematically the relationship between that in the energy store 10 stored energy content E0 , the energy losses EV and the usable energy content EE in the event of the energy storage device being discharged 10 . Before this discharge process, the energy store can 10 for example have an initial state of charge SOC, which is the initial energy content E0 of the energy storage 10 certainly. Now the energy storage 10 , in particular completely, discharged, but not all of it in the energy store 10 stored energy content E0 as usable energy EE the energy storage 10 be removed, because when discharging the energy storage 10 energy losses are inevitable EV whereby part of the original energy storage 10 stored energy E0 get lost. Correspondingly, the usable energy content EE in the case of a discharge process can now advantageously be calculated as the difference from that in the energy store 10 initially stored energy E0 and the loss of energy when discharging EV determine.

E0 kann dabei die vor dem Entladevorgang anfangs im Energiespeicher 10 gespeicherte Energie darstellen, insbesondere wenn der nutzbare Energieinhalt EE bei einem Entladevorgang bestimmt werden soll, bei welchem der Energiespeicher 10 vollständig entladen werden soll.Accordingly, the usable energy content EE can be expressed as follows: $$\text{EE}=\text{E0}-\text{EV}\text{.}$$

E0 can be stored in the energy store before the discharge process 10 represent stored energy, especially if the usable energy content EE is to be determined during a discharge process in which the energy store 10 should be completely discharged.

Should the energy storage 10 are not completely discharged, but only partially, so the usable energy content EE can be completely analogous when discharging the energy store 10 , especially during partial discharge, as the difference from the change in the energy store 10 stored energy E0 and the loss of energy during partial discharge EV determine. In the event of partial discharge, can E0 in the above equation also only the change in the energy store 10 Designate stored energy, i.e. the difference between the energy stored in the energy store at the beginning before the discharge process 10 stored energy and that in the energy storage 10 remaining energy after the charging process, resulting in a predefined future state of charge SOC of the energy store 10 corresponds.

In this way, it is possible to advantageously predict how much usable energy will be in the energy store 10 the maximum that can be withdrawn during one discharge.

Even during a charging process, the usable energy EL can be determined by the two components of the energy losses EV and that in the energy store 10 still storable energy E0 express. This is in 5 illustrates which schematically shows the relationship between the usable energy EL in the energy store 10 storable energy E0 and the energy losses EV in the event of the energy storage device being charged 10 illustrated. There is also energy loss when charging EV must ultimately occur in the energy store 10 more energy can be supplied in the form of the usable energy EL than after the charging process, ultimately through this charging in the energy store 10 is stored. During this charging process in the energy store 10 energy that can still be stored is included E0 designated. Is the energy storage before the charging process 10 already partially loaded, so provides E0 the energy that can still be stored during the charging process E0 represents, in particular again until the energy store is fully charged 10 or up to a desired discharge state SOC. Accordingly, the usable energy content EL for a charging process can be expressed as follows: $$\text{Tbsp}=\text{E0}+\text{EV}\text{.}$$

Through the breakdown of the usable energy content EE, EL in both cases, that is, both when charging and discharging the energy store 10 , the usable energy content EE, EL can advantageously be divided into one component, namely that of the energy store 10 storable energy E0 or stored energy E0 , which depends on the charging or discharging current I. and is therefore also independent of a current battery load, and one component, namely the lost energy EV , which from the charging current I. or discharge current I. and thus depends on the current battery load.

und für einen Ladevorgang durch: $$\text{Q}=\Delta \text{SOC*C}.$$

First the calculation of the energy storage 10 stored or still storable energy E0 described. This energy E0 changes during the battery load, i.e. permanently when charging or discharging, since both the charge Q of the energy storage device changes in these phases 10 as well as the current open-circuit voltage OCV changed. The change in the current battery charge Q can be tracked via the state of charge SOC, whereas the change in the open-circuit voltage OCV with the aid of the family of characteristics 14th is determined and taken into account. The ones in the energy store 10 stored or still storable charge Q depends on the state of charge SOC of the energy store 10 from, as well as from the capacity C. of the energy storage 10 . Correspondingly, this charge Q for a discharge process can be expressed as follows: $$\text{Q}=\text{SOC * C}$$

and for a charging process by: $$\text{Q}=\Delta \text{SOC * C}.$$

So, for example, the energy store 10 a current state of charge SOC before a discharge process, and the energy store has 10 also a capacity C. , the current is calculated in the energy storage 10 stored charge Q as the product of this current state of charge SOC and the capacity C. . On the other hand, it should be determined how much charge Q is still in the energy store during a charging process 10 fits, this can also be put into the energy storage 10 Determine storable charge Q as the product of the still available state of charge ΔSOC, which therefore represents the difference between the 100 percent state of charge and the current state of charge SOC, and the capacity C. . In other words, the change in charge Q results both when charging and when discharging the energy store 10 out of capacity C. multiplied by the change in the state of charge ΔSOC, which corresponds to the current state of charge SOC for the case of discharging, since the discharge state is 0%. The ones in the energy store 10 stored or still storable energy E0 can then be expressed as follows: $$\text{EO}=\overline{O\mathrm{C.}V}\text{* Q}\text{.}$$

Basically, the energy can be expressed as the product of voltage and charge. However, the open-circuit voltage OCV does not remain the same during a charging and discharging process, as is the case with the characteristic curve field 14th It can be seen that SOC usually assumes different values for different states of charge and the state of charge SOC changes during charging and discharging. Accordingly, it is advantageous if to determine the in the energy store 10 stored energy content E0 or energy content that can still be stored E0 the mean value of this open-circuit voltage OCV is taken into account, which is given in the above formula OCV is designated. Since the initial state of charge SOC of the energy storage device is used for both charging and discharging 10 is known or can be determined and the usable energy content EE, EL is usually based on a maximum charge or discharge of the energy store 10 is related, which corresponds to a state of charge SOC of 0 percent or 100 percent, so using the family of characteristics 14th , especially for a currently determined temperature T of the energy storage 10 , also the mean rest voltage in a simple way OCV as the mean of all OCV values during the charging or discharging process, starting from the initial state of charge SOC to the final state of charge SOC. Knowledge of the change in the open-circuit voltage OCV over time during full charging or discharging of the battery or, in general, of the energy store 10 , based on the current state of charge SOC, is therefore in the form of the aforementioned characteristic curve or the characteristic curve field 14th known. In order to make the determination even more robust, the time-dependent change in the open-circuit voltage OCV due to the later charging or discharging can be taken into account in the form of a mean value formation.

The lost energy EV can now be calculated as follows: Assuming a fully charged energy store 10 would with a so-called C-rate of 1 C. are discharged, this would mean that the energy store 10 with its capacity C. fully discharged within an hour. This corresponds to a discharge current, which can also be referred to as 1 C discharge current, which is precisely dimensioned so that the complete discharge of an energy store with a capacity C. this 1C current takes one hour. The same applies in a corresponding manner to a charging process. In such a case, the energy loss EV calculate as follows: $$\text{EV}=\text{PV * 1h}=1{\text{C.}}^2*\text{RI}\text{.}$$

PV denotes the power loss. 1C ² denotes the 1C current multiplied by the capacitance C. of the energy storage 10 . RI refers to the internal resistance of the Energy storage 10 , with additional resistances such as interconnection resistances in the designation RI can be regarded as taken into account. However, the above formula only applies if, for example, a fully charged energy store 10 is completely discharged or a completely discharged energy storage device 10 is fully loaded. Is the change in the state of charge of the energy storage device 10 However, not 100 percent, but is different from it, so the energy loss EV determine as follows: $$\text{EV}=1{\text{C.}}^2*\text{RI * SOC}\text{.}$$

SOC in turn describes the change in the state of charge during the charging or discharging process, in particular the change in the state of charge to be expected. So, for example, should the energy store 10 are discharged, in particular are completely discharged from an initial state of charge, so SOC in this case designates the initial state of charge of the energy store 10 .

However, the energy storage 10 not always charged with a 1 C discharge current or 1 C charge current, but can also be charged or discharged with other currents. This C-rate adjustment for the current battery current I. can be taken into account accordingly as follows: $$\text{EV}=1{\text{C.}}^2*\text{RI * SOC *}\left(\text{I.}/1\text{C.}\right)\text{.}$$

I. refers to the current battery current, for example at the beginning of a charging or discharging process and I / 1C is the ratio of the current charging or discharging current and the charging or discharging current corresponding to a C rate of 1, i.e. the 1C current. This clearly means that a charging current is used I. charged, which represents a multiple of the charging current, which corresponds to a C rate of 1, the energy losses are multiplied accordingly EV . The energy loss can then also be correspondingly EV express as follows: $$\text{EV}=\text{I.}*\text{C * SOC}*\text{RI}\text{.}$$

C. here again denotes the capacity C. of the energy storage 10 . The lost energy EV over the internal resistance RI of the energy storage 10 , in which connection resistances can also be included, results from the integration of the power loss PV. The definition of the 1 C current is used here, which is the current for the complete discharge of the energy store 10 is defined within an hour, making the connection 1 C ² * RI at the same time describes the energy loss that is required for precisely this complete discharge of the energy store 10 would arise. The actually resulting energy loss that occurs during the full charge or discharge of the energy storage device 10 can be determined taking into account the current state of charge SOC and the current level of current (I / C). The usable charging or discharging energy EL, EE at the battery terminals results at any point in time using the above equations.

Thus, ultimately, the usable energy EE, EL as well as when charging and discharging the energy store 10 in a simple manner based on the input variables of the internal battery resistance RI , current state of charge SOC of the energy storage 10 , Battery power I. and the OCV characteristic, which is determined by the map 14th is provided, are determined, in particular with knowledge of the current battery temperature T as well as the current total capacity C. of the energy storage 10 .

Overall, the examples show how the invention provides a determination of the usable energy content of the vehicle electrical system and traction battery in motor vehicles with the help of the OCV characteristics and the internal battery resistance, which with the help of the definition of a counting energy or energy storage energy, an OCV-based determination of the usable charging or discharging energy for traction and electrical system batteries. Since the OCV characteristics are the same for all C rates, this method allows a robust statement to be made about the currently usable charging or discharging energy, even with different battery loads, i.e. with different C rates. In this way, an additional, robust method for determining the usable charging or discharging energy via various C rates can advantageously be provided with the aid of the OCV characteristic.

QUOTES INCLUDED IN THE DESCRIPTION

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

Patent literature cited

• DE 102012010486 A1 [0005]
• DE 102005023365 A1 [0006]
• DE 102016207571 A1 [0007]

Claims (10)

Method for determining a usable energy content (EE, EL) of an energy store (10), the usable energy content (EE, EL) representing an energy (EL) that can be supplied to the energy store (10) when the energy store (10) is charged and when the energy store is discharged (10) represents an energy (EE) that can be drawn from the energy store (10), characterized in that the usable energy content (EE, EL) is dependent on an energy loss (EV) occurring during charging or discharging and depending on an energy loss in the energy store (10 ) stored or storable energy (E0) is determined, which in turn is determined as a function of a stored characteristic curve (14) which indicates a dependency of an open-circuit voltage of the energy store (10) on a state of charge (SOC) of the energy store (10). Procedure according to Claim 1 , characterized in that the stored or storable energy (E0) is determined as a function of the characteristic curve (14) of a stored characteristic curve field (14) which shows the dependence of the open-circuit voltage (OCV) of the energy store (10) on the state of charge (SOC) of the energy store (10) and a temperature (T) of the energy store (10) indicates. Method according to one of the preceding claims, characterized in that the usable energy content (EE, EL) as the energy content (EE) that can actually be extracted from the energy store (10) when discharging the energy store (10) as the difference between the energy stored in the energy store (10) (E0) and the energy loss (EV) resulting from discharging. Method according to one of the preceding claims, characterized in that the usable energy content (EE, EL) as the energy content (EL) which can be supplied when charging the energy store (10) as the sum of the energy (E0) that can still be stored in the energy store (10) and the Energy loss (EV) occurring during charging is determined. Method according to one of the Claims 3 or 4th , characterized in that the occurring energy loss (EV) is determined as a function of a battery current (I) and a specific internal resistance (RI) of the energy store (10). Procedure according to Claim 5 , characterized in that the total energy loss (EV) occurring during charging or discharging is the product of the battery current (I), the capacity (C) of the energy store (10), the change in the state of charge (SOC) of the energy store (10) and a certain loss resistance , which at least depends on the internal resistance (RI) of the energy store (10) is determined. Method according to one of the preceding claims, characterized in that, depending on the change in the state of charge (SOC) of the energy store (10) during charging or discharging and depending on the at least one characteristic curve (14), a mean open-circuit voltage (OCV) during charging or Discharge is determined, and the stored or storable energy (E0) is determined as a function of the mean open-circuit voltage (OCV). Procedure according to Claim 7 , characterized in that the stored or storable energy (E0) is determined as the product of the mean open-circuit voltage (OCV) and the change in the amount of charge stored in the energy store (10), the change in the amount of charge being the product of the capacity (C) of the energy store (10) and the change in state of charge (SOC) of the energy store (10) is determined. Method according to one of the preceding claims, characterized in that the usable energy content (EE, EL) is determined as a function of the following input variables: - current state of charge (SOC) of the energy store (10); - Current battery current (I), which represents the current charging current (I) when charging and the current discharging current (I) when discharging; - Current internal resistance (RI) of the energy store (10); - Current temperature (T) of the energy store (10); and - capacity (C) of the energy store (10). Battery status detection device (12) for a motor vehicle, the battery status detection device (12) is designed to determine a usable energy content (EE, EL) of an energy store (10) of the motor vehicle, the usable energy content (EE, EL) being a value when charging the energy store ( 10) represents energy (EL) which can be fed to the energy store (10) and represents energy (EE) that can be drawn from the energy store (10) when the energy store (10) is discharged, characterized in that the battery state detection device (12) is designed to detect the usable energy content (EE, EL) as a function of an energy loss (EV) occurring during charging or discharging and as a function of an energy (E0) stored or storable in the energy store (10), and this as a function of a stored characteristic curve (14), a dependency of an open-circuit voltage (OCV) of the Energy store (10) from a state of charge (SOC) of the energy store (10) to determine.

Images