DE102015201899B4 - Method for protecting a high-voltage electrical system of a motor vehicle with a first and a second energy source, computer program product and motor vehicle - Google Patents

Abstract

A method for protecting a high-voltage on-board network (1) of a motor vehicle with a first energy source (2) and a second energy source (3), the high-voltage on-board network (1) having a first interruption element (4) for interrupting a first electrical connection between the first Energy source (2) and the high-voltage on-board network (1) as well as a second interruption element (5) for interrupting a second electrical connection between the second energy source (3) and the high-voltage on-board network (1), the first interruption element (4) being set up is to interrupt the first electrical connection when a terminal voltage (UBatt, 1) of the first energy source (2) falls below a threshold value of the terminal voltage (Uth) and the first interruption element (4) is further set up to interrupt the first electrical connection, when a current strength (IBatt, 1) emanating from the first energy source (2) has a first threshold value (I1, th) of the current strength exceeds, and wherein the second interruption element (5) is set up to interrupt the second electrical connection when a current strength (IBatt, 2) emanating from the second energy source (3) exceeds a second threshold value (I2, th) of the current strength, with the steps • Determining a maximum value (Rsc, max) of an electrical short-circuit resistance (RSC) of the high-voltage vehicle electrical system (1), • Determining the threshold value of the terminal voltage (Uth) and the first threshold value of the current intensity (I1, th) in such a way that the high-voltage - On-board network (1) is protected against overcurrents occurring due to an electrical short circuit at least for all values of the electrical short-circuit resistance (Rsc) below the maximum value (Rsc, max) of the electrical short-circuit resistance (Rsc), the step of determining the threshold value of the terminal voltage ( Uth) and the first threshold value of the current intensity (I1, th) takes place under the assumption that the second En energy source (3) is separated from the high-voltage electrical system (1), • determining the second threshold value of the current strength (I2, th) in such a way that the high-voltage electrical system (1) against overcurrents occurring due to an electrical short circuit at least for all below the maximum value (Rsc, max) of the electrical short-circuit resistance (Rsc) lying values of the electrical short-circuit resistance (RSC) is secured, the step of determining the second threshold value of the current strength (I2, th) taking place on the assumption that the second energy source (3) with is connected to the high-voltage on-board electrical system (1).

Description

The present invention relates to a method for protecting a high-voltage (HV) electrical system of a motor vehicle with a first and a second energy source.

Conventional vehicle electrical systems usually have an operating voltage of 12 volts (V), which is provided by a vehicle battery. If an electrical short-circuit occurs in such a low-voltage (LV) on-board network, i.e. if an electrical connection with low electrical resistance is inadvertently established in the LV on-board network, a current flow with high amperage could occur in the NV components without protection Vehicle electrical system, e.g. cables, could overheat and damage it. Electrical fuses are therefore used that interrupt the electrical connection when the respective current intensity exceeds a certain value (nominal current). Individual components can be protected against currents of different magnitudes with different fuses. For example, the rated current of the fuse can be selected depending on the size of the cross section of a cable. As a rule, the range of values for the currents that occur during normal operation of the LV on-board network and the range of values for the currents that can occur in the event of a fault, for example in the event of a short circuit, do not overlap. 1 (a) illustrates this fact by showing the value ranges of the current strengths in normal operation and in the event of a malfunction on a current strength scale. To protect the LV on-board network, it is therefore sufficient to provide electrical fuses whose nominal currents are between the highest value during normal operation of the LV on-board network and the smallest value of the current that occurs in the event of a fault in the LV on-board network.

the end DE 199 61 435 A1 Overvoltage protection is known in two-voltage electrical systems that have different voltage levels. For this purpose, a switching element is arranged in at least one branch of the vehicle electrical system at the higher voltage level, which switching element can be switched by a switching element arranged in a branch of the vehicle electrical system at the lower voltage level.

DE 10 2013 214 726 A1 teaches an arrangement for the electrical protection of a potential short circuit or an overload in a direct current network with system-related, variable internal source resistance; This comprises an isolating element, the tripping characteristic of which is insufficiently dimensioned to protect a first and second line section of the potential short-circuit path in a first operating state of the energy store, and a second safety device, which is set up to protect the first and second line section against a load that occurs in the first operating state occurs below the tripping limit of the isolating element.

DE 601 26 843 T2 discloses a method for protecting against short circuits in electrical power distribution architectures with two voltage levels of a first and second battery, both batteries being equipped with automatic cut-off devices.

US 2013/0 106 432 A1 describes a threshold-value-based capacitive residual current detector for use in vehicles.

Vehicles with an electric drive (electric vehicles) have an HV on-board network. This is characterized by an operating voltage of more than 60 V, preferably between 200 V and 400 V. The term electric vehicle is to be understood as meaning all motor vehicles that can be at least partially driven by means of an electric motor. Electric vehicles without an internal combustion engine and electric vehicles with an internal combustion engine are known. The internal combustion engine of an electric vehicle can be used to drive and / or charge an energy store by means of a generator. Electric vehicles with an internal combustion engine at least partially used for propulsion are known as hybrid electric vehicles. A HV on-board network of an electric vehicle has an electric motor and an energy store, in particular an HV battery, which provides energy for operating the electric motor.

In contrast to what was previously described for a LV on-board network, the value ranges of the current strengths of the HV on-board network can overlap during normal operation and in the event of a fault caused, for example, by a short circuit. 1 (b) illustrates this fact by showing the value ranges of the current strengths in normal operation and in the event of a malfunction on a current strength scale. One reason for this effect is the dependence of the internal resistance of the battery cells in the HV battery on the state of charge (SOC) and the ambient temperature. If current intensities occur in the overlap area of the value ranges of normal operation and malfunction, it cannot be concluded that there is a malfunction solely on the basis of the current strength. To protect the HV on-board network against overcurrents, the terminal voltage of the HV battery can therefore also be monitored. The short-circuit resistance, i.e. the electrical resistance formed by components of the HV on-board network such as cables, plugs and intermediate resistors in the case of a Short circuit in the HV vehicle electrical system usually has such a low value that, in the event of a short circuit, the terminal voltage of the HV battery drops significantly, i.e. drops. For values selected as an example, a short-circuit resistance of 10 mOhm and a short-circuit current strength of 5000 amperes (A) results from Ohm's law ( U = R · I) a short-circuit voltage of 50 V. With a further exemplary assumed HV battery voltage in the range of 200 V to 400 V, the short-circuit voltage is significantly below the HV battery voltage in normal operation, which means a Short circuit can be detected. In summary, it is therefore known to protect an HV battery against overcurrents caused by a short circuit by means of current and voltage measurement. A possible embodiment of such a safeguard is explained in more detail below with reference to the figures.

The current-carrying lines of an HV vehicle electrical system can be suitable for different currents. In particular, cables can have different current-carrying capacities due to different cable cross-sections. It should be noted that the term cable cross-section commonly denotes the size of the cross-sectional area of a cable. For example, a cable of an HV vehicle electrical system in the path between the HV battery and the electric motor, where currents in the range of 200 A can occur, for example, can have a cross section in the range of 35 (mm) ² or more. Other cables in the HV on-board network, which are used, for example, to connect components with a lower power requirement (for example 40 A), can have a smaller cross section (for example in the range of 6 (mm) ² ). The double protection of the HV on-board network described above is usually based on the highest current-carrying capacity of the HV on-board network, for example on the cross-section of the cable between the HV battery and the electric motor. Cables with a smaller cross-section are therefore given additional protection. These additional fuses can be conventional fuses which are arranged locally on the line to be protected and which interrupt the electrical connection when a predetermined current intensity is reached. In addition to this safeguarding of the maximum current intensity, it may be necessary, as explained above, to also detect a voltage drop. For this purpose, however, the voltage monitoring of the terminal voltage of the HV battery explained above can be used, so that the voltage does not have to be monitored locally.

By means of the measures mentioned, an HV on-board network with an energy source, in particular an HV battery, can be effectively protected against overcurrents caused by short circuits.

• - eine weitere HV-Batterie;
• - eine Brennstoffzelle;
• - ein elektrischer Generator zur Umwandlung mechanischer Energie in elektrische Energie;
• - eine Ladeschnittstelle zur unmittelbaren oder mittelbaren (mittels eines Ladegeräts) Verbindung einer fahrzeugexternen Energiequelle mit dem HV-Bordnetz;
• - ein Spannungswandler (DC/DC-Wandler), welcher ein NV-Bordnetz des Kraftfahrzeugs mit dem HV-Bordnetz verbindet.

HV electrical systems can, however, have more than one energy source. Examples of further energy sources of an HV on-board network in addition to the HV battery that can feed an electric current into the HV on-board network are

• - another HV battery;
• - a fuel cell;
• - an electrical generator for converting mechanical energy into electrical energy;
• - A charging interface for the direct or indirect (by means of a charger) connection of an energy source external to the vehicle with the HV on-board network;
• - A voltage converter (DC / DC converter), which connects an LV on-board network of the motor vehicle with the HV on-board network.

An electric generator can itself be the electric motor used to drive the electric vehicle. If the moving vehicle is not being driven, the electric motor can act as a generator and convert the kinetic energy of the vehicle into electrical energy, which is fed back into the HV battery via the HV on-board network. In this way, the electric motor can be used to brake. This process is also known as braking force recovery or recuperation. An electric generator can also be another electric motor. This additional electric motor can convert kinetic energy generated by an internal combustion engine into electrical energy. Since this extends the range of the electric vehicle, it is referred to as a range extender.

The safeguarding of the HV vehicle electrical system explained above by means of current and voltage monitoring is based on the case of an energy source. If the HV on-board network has at least one additional energy source, this must also be taken into account when protecting the HV on-board network.

The object of the present invention is therefore to specify a simple and reliable method for protecting a high-voltage electrical system of a motor vehicle with a first and a second energy source. The task also consists in providing a computer program product for executing the method. Furthermore, the object is to provide a motor vehicle with a high-voltage electrical system that is protected against short circuits in a simple and reliable manner, with a first and a second energy source.

The object is achieved in a method with the features of claim 1, according to a computer program product Claim 8 and a motor vehicle with the features of claim 9. Advantageous developments of the invention are the subject matter of the dependent claims.

The present invention can be used for any of the other energy sources listed above. However, the invention is particularly useful in the case of other energy sources with a large energy content, since these can cause high and long-lasting short-circuit currents. The invention is therefore particularly useful and suitable for protecting HV vehicle electrical systems which have a second HV battery or a fuel cell as a second energy source.

The method according to the invention enables a high-voltage electrical system of a motor vehicle to be protected with a first and a second energy source, the high-voltage electrical system having a first interruption element for interrupting a first electrical connection between the first energy source and the high-voltage electrical system and a second interruption element for interruption comprises a second electrical connection between the second energy source and the high-voltage electrical system. The first interruption element is set up to interrupt the first electrical connection when a terminal voltage of the first energy source falls below a threshold value of the terminal voltage and / or when a current intensity emanating from the first energy source exceeds a first threshold value of the current intensity. In other words, the first interruption element can disconnect the first energy source from the HV vehicle electrical system in the event of an overcurrent and / or an undervoltage. The second interruption element is set up to interrupt the second electrical connection if a current intensity emanating from the second energy source exceeds a second threshold value for the current intensity. In other words, the second interruption element can disconnect the second energy source from the HV vehicle electrical system in the event of an overcurrent.

According to the method according to the invention, a maximum value of an electrical short-circuit resistance (denoted by the symbol Rsc, max) of the high-voltage on-board electrical system is determined in a first step. The maximum value of the electrical short-circuit resistance is determined in a manner known per se in the prior art from the properties of the components used in the HV vehicle electrical system. The maximum value of the electrical short-circuit resistance should correspond to at least that value of the electrical short-circuit resistance that can maximally occur in the HV vehicle electrical system. For this purpose, the electrical properties of the components of the HV on-board network, such as cables, plugs and intermediate resistors, known from data sheets, measurements and the like can be used. If an analysis of the HV on-board network shows, for example, that in the event of a short circuit in the HV on-board network, the short-circuit resistance formed by the current-carrying components 10 mOhm, the maximum value of the electrical short-circuit resistance is determined to be at least 10 mOhm, i.e. R _SC , _max ≥ 10 mOhm. The maximum value of the electrical short-circuit resistance is preferably determined in such a way that it significantly exceeds the short-circuit resistance formed by the current-carrying components, that is, for example, Rsc, max = 100 mOhm.

In a second step, the threshold value of the terminal voltage is determined ( U _th ) and the first threshold value of the current intensity ( I _{1, th} ) in such a way that the high-voltage on-board network is protected against overcurrents occurring due to an electrical short circuit at least for all values of the electrical short-circuit resistance that are below the maximum value of the electrical short-circuit resistance. This second step of determining the threshold value of the terminal voltage and the first threshold value of the current intensity takes place on the assumption that the first energy source is connected to the high-voltage on-board network, while the second energy source is disconnected from the high-voltage on-board network.

In the execution of the second step, the first threshold value of the current intensity ( I _{1, th} ), as this can result from the previously known properties of the components of the HV electrical system. For each of these components, a maximum current value is generally known or can be determined for which this component is suitable. For example, depending on their cross-section, cables can carry a certain maximum current without being excessively heated. In this case, the period of time for which a component can conduct a current of a certain strength can preferably also be taken into account. From the first threshold value of the current strength and the maximum value of the electrical short-circuit resistance, the highest possible threshold value of the terminal voltage can be determined using Ohm's law as follows: $$U_{tH}\ge {\mathrm{R.}}_{sc,max}\cdot {\mathrm{I.}}_{\mathrm{1,}tH}$$

In a third step according to the invention, the second threshold value of the current strength is determined ( I _{2, th} ) in such a way that the high-voltage electrical system against overcurrents occurring due to an electrical short circuit at least for all below the maximum value of the electrical Short-circuit resistance lying values of the electrical short-circuit resistance is secured. This third step of determining the second threshold value of the current intensity takes place on the assumption that the first and the second energy source are connected to the high-voltage on-board electrical system. In other words, after the conceptual removal of the second energy source from the high-voltage vehicle electrical system, the second energy source is now added back to the HV vehicle electrical system in the third step. For repetition, it should be pointed out that in the second method step the threshold values were selected in such a way that in any case those short circuits would not be protected whose short-circuit resistance would be above the maximum value of the electrical short-circuit resistance. In other words, the HV on-board network is protected against all short-circuits whose short-circuit resistance is below the maximum value of the electrical short-circuit resistance. In the first process step, however, the maximum value of the electrical short-circuit resistance was selected in such a way that actually possible short-circuits in the HV on-board network have a short-circuit resistance that is below the maximum value of the electrical short-circuit resistance. Since a second energy source can now cause an additional flow of current, the resistance value, below which the HV on-board network is protected against short circuits, drops. This will be explained in detail below with reference to the figures. The second threshold value of the current intensity can therefore be determined in the third step in such a way that the resistance value below which the HV on-board network is protected against short circuits is at most so small that it is still at least as large as the largest in the HV on-board network actually occurring short-circuit resistance. It can happen that in the third step it is determined that adding the second energy source is not possible (ie it will I _{2, th} = 0 A determined) or does not make sense (ie it becomes a value I _{2, th} determined, which is greater than 0 A, but which is smaller than the value of the current that the second energy source should be able to deliver in the normal operation of the HV on-board network). In this case, the process can be terminated and restarted from the beginning, whereby the threshold values determined at the time the process was terminated (i.e. U _th and or I _{1, th} and I _{2, th} ) are adapted (that is, increased or decreased) when the method is carried out again to such an extent that the second energy source can be added.

The method according to the invention can advantageously be expanded to include several energy sources. The HV on-board network can comprise a further energy source and a further interruption element for interrupting a further electrical connection between the further energy source and the HV on-board network. The further interruption element is set up to interrupt the further electrical connection if a current intensity emanating from the further energy source exceeds a further threshold value for the current intensity. In an additional method step, the further threshold value of the current intensity is then determined in such a way that the HV on-board network is protected against overcurrents occurring due to an electrical short circuit at least for all values of the electrical short-circuit resistance that are below the maximum value of the electrical short-circuit resistance, the step of determining the Further threshold value of the current intensity takes place on the assumption that the first, the second and the further energy source are connected to the HV on-board network. The further energy source can be a third energy source of the HV vehicle electrical system. Due to the advantageous embodiment, the HV on-board network can also be secured for more than one further energy source, in that the additional method step is carried out for each further energy source.

If, for example, the HV on-board network has a total of four energy sources, then all the required threshold values are determined one after the other. First, the step of determining the threshold value of the terminal voltage and the first threshold value of the current intensity takes place on the assumption that the second energy source and all other energy sources (i.e. the third and fourth energy sources) are disconnected from the HV on-board network. The step of determining the second threshold value of the current intensity then takes place on the assumption that the second energy source is connected to the HV vehicle electrical system. The assumption includes that the first energy source is also connected to the HV vehicle electrical system, but that the third and fourth energy sources are separated from the HV vehicle electrical system. This is followed by the step of determining the further, third threshold value for the current intensity, assuming that the third energy source is connected to the HV vehicle electrical system. The assumption includes that the first and second energy sources are also connected to the HV vehicle electrical system, but that the fourth energy source is separated from the HV vehicle electrical system. Finally, the step of determining the further, fourth threshold value of the current intensity takes place on the assumption that the fourth energy source is connected to the HV vehicle electrical system. The assumption includes that all other energy sources, i.e. the first, second and third, are also connected to the HV on-board network.

The steps of determining the second and all further threshold values of the current intensity can thus be carried out one after the other as described. However, all or some of these steps can also be combined in an alternative embodiment. This is supposed to are again explained using the aforementioned example of a HV on-board network with four energy sources. First, as explained above, the step of determining the threshold value of the terminal voltage and the first threshold value of the current intensity takes place on the assumption that the second energy source and all other energy sources (i.e. the third and fourth energy sources) are disconnected from the HV vehicle electrical system. This is followed by a step of determining the second threshold value and all further threshold values of the current intensity in such a way that the HV on-board network is protected against overcurrents occurring due to an electrical short circuit at least for all values of the electrical short-circuit resistance that are below the maximum value of the electrical short-circuit resistance, the step of The second threshold value and all further threshold values of the current intensity are determined on the assumption that the second energy source and all further energy sources are connected to the HV vehicle electrical system. In this embodiment, the second energy source and all further energy sources are assumed to be connected to the HV on-board network, not one after the other, but at the same time.

In any case, the steps of determining the second and all further threshold values of the current intensity must be carried out in such a way that the result is that the HV on-board network is protected against overcurrents of all energy sources due to an electrical short circuit, at least for all values of the electrical short-circuit resistance that are below the maximum value of the electrical short-circuit resistance is. In other words, it must be taken into account that all energy sources together supply a total current that must be taken into account when protecting the HV on-board network. This is achieved in the above-described embodiment of the method, in which the energy sources are successively assumed to be connected to the HV on-board network, in that with each step of adding an energy source, all of the energy sources assumed to be connected to the HV on-board network in the previous steps continue as with connected to the HV on-board network.

It should be pointed out that the method does not necessarily have to take into account all energy sources of the HV vehicle electrical system 1. In particular, it is conceivable that certain energy sources cannot deliver a current at the same time. This applies, for example, to recuperation (braking force recovery) and the charging interface (for connecting an external energy source), which cannot be active at the same time, since the vehicle is stationary during charging. In order to protect the HV on-board network, however, it is necessary in the method according to the invention to take into account all energy sources that can supply a current at the same time.

In a further embodiment, it can be taken into account if the first interruption element only interrupts the first electrical connection when the terminal voltage of the first energy source falls below the threshold value of the terminal voltage for a first period of time and / or when the current intensity from the first energy source exceeds the first threshold value of the current intensity for a second period of time. In this case, the method can be developed with particular advantage in that the step of determining the threshold value of the terminal voltage and the first threshold value of the current intensity includes determining the first time period and / or the second time period. In this way, it can be taken into account that the maximum current carrying capacity of an element, e.g. a cable, can also be linked to a period of time. For a certain amperage (in A), a period of time (in seconds) can be given for which the element, e.g. the cable, can at most conduct the amperage. Such a period of time can be determined by being able to take it from a data sheet of a component. However, it can also be determined by measurements, for example by temperature measurements, and / or by simulations. The advantage of this embodiment is that if a high current level occurs only for an uncritically short time, the energy source is not disconnected from the HV on-board network. There are therefore no unnecessary interruptions in the energy supply to the HV on-board network.

In a further embodiment, it can be taken into account if the second interruption element only interrupts the second electrical connection when the current intensity emanating from the second energy source exceeds the second threshold value of the current intensity for a third period of time. The step of determining the second threshold value of the current intensity can then advantageously include determining the third time period.

In a further refinement, it can be taken into account if the further interruption element only interrupts the further electrical connection when the current intensity emanating from the further energy source exceeds the further threshold value of the current intensity for a further period of time. The step of determining the further threshold value of the current intensity can then advantageously include determining the further time period.

A combination of the above-mentioned embodiments is particularly advantageous. In this embodiment, both the first and the second interruption element (ie also the possibly present further interruption element) set up to interrupt the respective electrical connection after the respective time period has elapsed.

The first time period can be constant or can be selected as a function of the terminal voltage of the first energy source. Likewise, the second time period can be constant or can be selected as a function of the current strength emanating from the first energy source. The third time period can also be constant or can be selected as a function of the current intensity emanating from the second energy source. The further period of time can also be constant or be selected as a function of the current strength emanating from the further energy source. The term function can be understood to mean a mathematical mapping rule. The term function can also be understood to mean a table of values.

By choosing one or more of the time periods as a function, the aforementioned fact can be taken into account that the maximum current carrying capacity of an element of an HV electrical system is often not or not exclusively given by a value in amperes, but by a formula or graphically indicated function that assigns a duration to each value of the current intensity. Such a function, for example specified in a data sheet of the element of the HV on-board network, can therefore be taken for a given value of the current intensity for which the element can carry a current of this current intensity for the longest without being unacceptably heated or otherwise impaired.

In a further embodiment of the invention, the second (and / or, if the further energy source is present, the further) threshold value of the current intensity can be set, the method being carried out when the second and / or further energy source is added to and / or started up in an existing HV on-board network . The method then includes the further step of setting the second and / or further threshold value of the current intensity. The method can thus be used in an advantageous manner to secure an already existing HV on-board network when an additional energy source is added to the HV on-board network or when an already existing but not yet active additional energy source is connected to the HV on-board network. For example, the method can be carried out every time an internal combustion engine with a generator (rank extender) serving to extend the range is put into operation.

The process according to the invention can be used in many ways. One possible use is in the development of on-board networks. The method can be used in particular in automated tools, e.g. software programs, for on-board network development. The invention therefore also comprises a computer program product, in particular a digital storage medium, comprising a set of instructions which, when executed on a computer, cause the computer to carry out the steps of the claimed method. A digital storage medium can be a CD-ROM, a DVD or some other write-once or rewritable data carrier. A digital storage medium can also be formed by a server on which the computer program product is made available for downloading by means of a data connection. The server can be an internet server.

Another possible use of the method according to the invention is the operation of on-board networks, i.e. in the event that an additional energy source is added to an HV on-board network of a motor vehicle or that an already existing, but not yet active, additional energy source is connected to the HV on-board network . The invention therefore also comprises a motor vehicle with the features of claim 9. The motor vehicle has a control device connected to the second interruption element, which is set up to set the second threshold value of the current intensity, the control device being set up to carry out the method according to claim 7.

The control device can be arranged permanently in the motor vehicle and connected to the second (and / or to the further) interruption element. The control unit can be used to carry out the method according to the invention when the second energy source is connected to the HV on-board network.

The control device can also only temporarily be connectable to the motor vehicle and in particular only temporarily connectable to the second (and / or further) interruption element. In this case, the control device can be used when a previously non-existent second (or further) energy source is added to a high-voltage electrical system of a motor vehicle. This could be the case, for example, if a motor vehicle is retrofitted with an additional HV battery, a range extender or a fuel cell. The motor vehicle is particularly advantageously set up to establish a data connection between the control unit and the second interruption element by means of a data bus connection of the motor vehicle. from It is particularly advantageous if the motor vehicle comprises a diagnostic interface, the diagnostic interface being set up to connect the control device to the data bus of the motor vehicle. The control device can be a device used in vehicle workshops that are qualified to work on HV on-board networks. If the HV on-board network is expanded by an energy source in such a workshop, the second and / or further threshold value for the current intensity can be set by means of the control device. The HV on-board network, which has been expanded to include the additional energy source, is then secured. In an advantageous development, the threshold values of further or all interruption elements of the HV on-board network can be set by means of the control device. When adding a second or further energy source, the entire method can then advantageously be carried out, for example also determining and setting the threshold values of the first interruption element.

• 1 (a) eine schematische Darstellung der Wertebereiche der Stromstärken in einem beispielhaften NV-Bordnetz,
• 1 (b) eine schematische Darstellung der Wertebereiche der Stromstärken in einem beispielhaften HV-Bordnetz,
• 2 eine schematische Darstellung der Elemente eines beispielhaften HV-Bordnetzes,
• 3 eine schematische Darstellung eines beispielhaften Unterbrechungselements,
• 4 ein erstes Prinzip-Schaltbild eines HV-Bordnetzes mit einem ersten Energiespeicher im Kurzschlussfall,
• 5 ein zweites Prinzip-Schaltbild eines HV-Bordnetzes mit einem ersten Energiespeicher im Kurzschlussfall,
• 6 eine Darstellung der in einem HV-Bordnetz mit einem ersten Energiespeicher abgesicherten beispielhaften Wertebereiche,
• 7 ein erstes Prinzip-Schaltbild eines HV-Bordnetzes mit einem ersten und einem zweiten Energiespeicher im Kurzschlussfall,
• 8 ein zweites Prinzip-Schaltbild eines HV-Bordnetzes mit einem ersten und einem zweiten Energiespeicher im Kurzschlussfall,
• 9 eine Darstellung der in einem HV-Bordnetz mit einem ersten und einem zweiten Energiespeicher abgesicherten beispielhaften Wertebereiche,
• 10 eine beispielhafte Darstellung des größten noch abgesicherten Wertes des Kurzschlusswiderstands als Funktion der Stromstärke eines zweiten Energiespeichers,
• 11 eine beispielhafte Darstellung der Zeitdauer der Stromtragfähigkeit beispielhafter Elemente eines HV-Bordnetzes sowie der Zeitdauer beispielhafter Unterbrechungselemente als Funktion der Stromstärke.

Further details, features and advantages of the invention emerge from the following description and the figures. Show it

• 1 (a) a schematic representation of the value ranges of the current strengths in an exemplary LV on-board network,
• 1 (b) a schematic representation of the value ranges of the current strengths in an exemplary HV vehicle electrical system,
• 2 a schematic representation of the elements of an exemplary HV on-board network,
• 3 a schematic representation of an exemplary interruption element,
• 4th a first principle circuit diagram of a HV on-board network with a first energy store in the event of a short circuit,
• 5 a second principle circuit diagram of an HV on-board network with a first energy store in the event of a short circuit,
• 6th a representation of the exemplary value ranges secured in a HV on-board network with a first energy store,
• 7th a first principle circuit diagram of a HV on-board network with a first and a second energy store in the event of a short circuit,
• 8th a second principle circuit diagram of a HV on-board network with a first and a second energy store in the event of a short circuit,
• 9 a representation of the exemplary value ranges secured in a HV on-board network with a first and a second energy store,
• 10 an exemplary representation of the greatest value of the short-circuit resistance that is still secured as a function of the current strength of a second energy store,
• 11 an exemplary representation of the duration of the current carrying capacity of exemplary elements of an HV vehicle electrical system and the duration of exemplary interruption elements as a function of the current strength.

In the figures, the same reference symbols denote the same features of the illustrated embodiments of the invention. It should be noted that the figures shown and the associated description are merely exemplary embodiments of the invention. In particular, representations of combinations of features in the figures and / or the description of the figures are not to be interpreted in such a way that the invention necessarily requires the implementation of all of the features mentioned. Other embodiments of the invention may include fewer, more, and / or different features. The scope of protection and the disclosure of the invention result from the accompanying patent claims and the complete description.

1 (a) illustrates, as already mentioned, the value ranges of the current strengths in an LV on-board network in normal operation and in the event of a malfunction on a current strength scale. It turns out that the two areas are separated from each other. The LV on-board network can therefore be secured in a relatively simple manner against electrical short circuits by using electrical fuses, the nominal currents of which are between the highest value during normal operation of the LV on-board network and the lowest value of the current that occurs in the event of a fault in the LV on-board network.

Using the for HV on-board networks in 1 (b) The ranges of values shown make it clear that HV on-board electrical systems cannot usually be protected using simple electrical fuses. The value ranges overlap. Current strengths in this overlap area may have been caused by an electrical short circuit. However, it is also possible that the currents occur in the overlapping area when the HV on-board network is operating properly. One reason for this effect is that the internal resistance of the battery cells of the HV battery is not constant, but increases as the state of charge (SOC) and / or the ambient temperature falls.

2 shows a schematic representation of the elements of an exemplary HV vehicle electrical system 1 of a motor vehicle. The HV on-board network 1 includes an HV battery 2 as the first energy store. Individual components of the power electronics of the HV on-board network 1 are in the present example in one Power electronics module 16 arranged. Power lines within the power electronics module 16 could be designed as busbars, while the outside of the power electronics module 16 arranged components by means of cable connections with this 16 can be connected. The cable connections can include cables, plugs, screw connections and other connecting elements. It should be noted that the illustrated arrangement of the HV vehicle electrical system is only to be understood as an example and in no way restrictive. The HV battery 2 is via a two-pin direct current (DC) cable connection 14th electrically with the power electronics module 16 and thus connected to the other DC components of the HV on-board network. The electrical connection of the HV battery 2 with the further HV on-board network can by means of the first interruption element 4th to be interrupted. This 4th is related to 3 explained in more detail below. A second energy source is also shown 3 and a second interruption element 5 . The second source of energy 3 and the second interruption element 5 are shown in dashed lines. This is to illustrate that this second source of energy 3 in the course of the method according to the invention, conceptually from the HV on-board network 1 Will get removed. The second source of energy 3 could be another HV battery or a fuel cell in the example shown. An electric motor 6th , which can be used to drive the motor vehicle, is again driven by alternating current (AC). He 6th is therefore via a three-pin AC cable connection 15th with one in the power electronics module 16 arranged inverter 9 which in turn is connected to the DC cable connection on the DC side 14th connected is. An NV battery 7th , which can have a voltage of 12 V, 14 V or 48 V, for example, is by means of a direct current converter (DC / DC converter) 8th with the HV on-board network 1 tied together. Of course, the LV on-board network can include further components, not shown. Via an AC charging interface 10 , which by means of a charger 11 with the HV on-board network 1 connected, the HV battery can 1 Loading. The shown cable connection between the AC charging interface 10 and the charger arranged in the power electronics module 11 is two-pole, so enables single-phase charging. It could also be a three-phase AC charging interface. Various HV components are also shown 12th of the HV on-board network 1 . Here 12th it could be an electric heater, an air conditioning compressor, a range extender and / or a DC charging interface. According to the power requirement of a respective HV component 12th and the cable cross-section that is used to connect the respective HV component 12th to the HV on-board network 1 is used, a backup 13th be provided in the respective current path, each locally protecting the element of the HV on-board network (eg the cable) to which it is connected from overcurrents. Not all DC cable connections 14th of the HV on-board network 1 necessarily have the same cable cross-section. For example, the DC cable connections 14th , in which high currents occur, have a cross section in the range of 35 (mm) ² or more. Examples of this could be: the DC cable connection 14th in the path between the HV battery 1 and inverter 9 who have favourited DC cable connection 14th in the path between the HV battery 3 and inverter 9 who have favourited AC cable connection 15th between electric motor 6th and inverter 9 . Other DC cable connections such as the DC cable connection to a HV component 12th with a lower power requirement can have a smaller cross section, for example in the range of 6 (mm) ² .

3 shows a schematic representation of an exemplary interruption element 4th the HV battery 2 . The break element 4th is between the battery cells 20th the HV battery 2 and the external connections (not shown) of the HV battery 2 arranged so that there is 4 if necessary the HV battery 2 from the rest of the HV on-board network 1 can detach. The interruption element shown has three different interruption mechanisms. This can be useful for comprehensive protection, since each of the interruption mechanisms can be effective in a different range of values for the current intensity. This will be discussed below with reference to 11 explained. However, interrupt elements need by no means have all three interrupt mechanisms. Rather, they can also have only one of the interruption mechanisms or any combination of two interruption mechanisms. The first illustrated interruption mechanism consists of a safety element 41 that interrupts the electrical connection when a certain current level is exceeded. It should be noted that also for each of the two lines 14th a separate fuse could be provided. It can be with the fuse element 41 for example a fuse. The security element 41 can, for example, protect the area of very high currents (e.g. greater than 1000 A). The two other interruption mechanisms shown are set up to interrupt the electrical connection as a function of a measured voltage and / or a measured current. A voltage sensor is used for this 42 and a current sensor 43 intended. Both sensors 42 , 43 are with an evaluation circuit 44 tied together. These 44 evaluates the from the sensors 42 , 43 transmitted measured values and compares the measured values with stored threshold values. If one of the measured values exceeds or falls below the associated threshold value, the evaluation circuit controls a controllable switch 45 at what this 45 interrupts the electrical connection. The evaluation circuit 44 is set up for the execution of the present invention in such a way that it interrupts the connection when the measured current intensity exceeds a threshold value of the current intensity and / or when the measured voltage falls below a threshold value of the voltage. In other words, there is a second interruption mechanism in the described current monitoring and a third interruption mechanism in the described voltage monitoring. The second interruption mechanism (current monitoring) can protect the range of medium currents (eg greater than 400 A), for example. The third interruption mechanism (voltage monitoring) can protect the range of low currents (eg less than 400 A), for example. The voltage monitoring is the essential interruption mechanism in overcoming the related to 1 (b) described problem. In the in 1 (b) In the overlap area shown, a current-based interrupt mechanism cannot be used effectively. On the other hand, voltage monitoring can be used effectively in this area to detect a short circuit, since in the event of a short circuit the voltage drops significantly due to the low short circuit resistance. Voltage monitoring is therefore an important part of safeguarding an HV on-board network 1 . As will be explained in more detail below, the present invention can be understood to include the effectiveness of voltage monitoring in the presence of a second energy source 3 in the HV on-board network 1 ensures.

The second interruption element 5 can be structured in the same way as the one in 3 shown interruption element 4th . However, this is not necessary to carry out the invention. In particular, the second interruption element must 5 according to the invention do not have a voltage-based interruption mechanism, but only a current-based interruption mechanism. The second interruption element 5 so can only be a backup 41 and / or current monitoring 43 , 44 , 45 include.

4th shows a first principle circuit diagram of a HV on-board network 1 with a first energy store 2 in the event of a short circuit. The short circuit is caused by elements of the HV on-board network 1 formed, which are inadvertently connected to each other in an electrically conductive manner. The connection does not necessarily have to be galvanic. A short circuit can also be caused by arcing. The short-circuit connection has an overall electrical resistance value Rsc (unit ohm). It should be noted that the in 4th The resistance shown does not represent a component, but rather symbolizes the entire resistance of the short-circuit connection. The HV battery 2 , their interruption element 4th in 4th is not shown, provides a terminal voltage U _{Batt, 1} and a current flowing through the short-circuit connection I _{Batt, 1} .

5 shows a second principle circuit diagram of a HV on-board network 1 with a first energy store 2 in the event of a short circuit. the 5 shows the same fact as that 4th . The battery cells connected in series are also shown 20th the HV battery 2 . The battery cells are shown as ideal voltage sources that each provide a voltage U _i, i = 1, ..., n. In addition, the internal resistance is in each case R _i , i = 1, ..., n, of each battery cell. Its value does not have to be constant, but can depend on the ambient temperature, the state of charge of the battery cell and / or other parameters. For the sake of clarity, it is assumed here that the HV battery 2 only the identical battery cells shown connected in series 20th having. It should be noted that this is for explanatory purposes and is not to be understood as restrictive. As a rule, HV batteries can comprise battery cells connected to one another in series and / or in parallel. These battery cells can be different and in particular deliver a different voltage.

It should now be based on the 5 shows how the first two method steps according to the invention can be carried out.

In the first step, the maximum value Rsc, max of the electrical short-circuit resistance Rsc is determined. For this purpose, precise knowledge of the structure of the HV on-board network, i.e. the elements and their arrangement and interconnection, is necessary. From this knowledge as well as from empirical values and, if necessary, measurements and tests, the respective short-circuit resistance Rsc can be determined for different conceivable short-circuit cases. The maximum value Rsc, max of the electrical short-circuit resistance is then to be selected such that it exceeds each of the short-circuit resistances Rsc determined in this way. In other words, the maximum value Rsc, max should be determined in such a way that it is greater than any short-circuit resistance that could actually occur in the HV vehicle electrical system. In the present example it should be assumed that the maximum value of the electrical short-circuit resistance Rsc, max = 150 mOhm.

The second step is the threshold U _th the terminal voltage U _{Batt, 1} and the first threshold I _{1, th} the amperage I _{Batt, 1} determined in such a way that the high-voltage electrical system 1 against overcurrents occurring due to an electrical short circuit at least for all below the Maximum value Rsc, max of the electrical short-circuit resistance lying values of the electrical short-circuit resistance is secured. For this it is assumed that the second energy source 3 from the HV on-board network 1 is separated.

und der Wert der Klemmenspannung U_{Batt, 1} im Kurzschlussfall zu $$U_{Batt\mathrm{,1}}=n\cdot U_i\frac{R_{sc}}{n\cdot R_i+R_{sc}}.$$

The battery current is calculated according to Kirchhoff's laws I _{Batt, 1} in the event of a short circuit $${\mathrm{I.}}_{\mathrm{B.}att\mathrm{,1}}=\frac{n\cdot U_i}{n\cdot {\mathrm{R.}}_i+{\mathrm{R.}}_{sc}}$$

and the value of the terminal voltage U _{Batt, 1} in the event of a short circuit $$U_{\mathrm{B.}att\mathrm{,1}}=n\cdot U_i\frac{{\mathrm{R.}}_{sc}}{n\cdot {\mathrm{R.}}_i+{\mathrm{R.}}_{sc}}.$$

The value I _{Batt, 1} can be the first threshold I _{1, th} Do not exceed the current strength, as the first interruption element 4th is set up, in this case the electrical connection between the HV battery 2 and the rest of the HV on-board network 1 to interrupt. So it applies $${\mathrm{I.}}_{\mathrm{B.}att\mathrm{,1}}\le {\mathrm{I.}}_{\mathrm{1,}tH}.$$

Furthermore, the value U _{Batt, 1} the threshold U _th Do not fall below the terminal voltage, as the first interruption element 4th is set up, in this case the electrical connection between the HV battery 2 and the rest of the HV on-board network 1 to interrupt. So it applies $$U_{\mathrm{B.}att\mathrm{,1}}\ge U_{tH}.$$

When performing the second step, it is advantageous to first set the first threshold value I _{1, th} to determine the current strength, as this can result from the previously known properties of the components of the HV on-board network. For each of these components, a maximum current value is generally known or can be determined for which this component is suitable. For example, depending on their cross-section, cables can carry a certain maximum current without being excessively heated. In the present example it is assumed that a threshold value of I _{1, th} = 500 A is determined from the known properties of the components of the HV vehicle electrical system. The first and second time periods can advantageously also be determined. It should be noted, however, that the first interruption element due to its technical properties (hardware properties, for example reaction times or switching times of the components 41 , 45 , as well as software properties, e.g. arithmetic processes in the evaluation circuit 44 ) anyway a certain period of time until the first electrical connection is interrupted 14th needed. This period of time is known to the person skilled in the art or can be determined by the person skilled in the art. If this period has a value suitable for protecting the HV on-board network, the first and second periods do not have to be determined and set separately.

From the first threshold I _{1, th} the current intensity and the maximum value Rsc, max of the electrical short-circuit resistance can be the minimum threshold value U _th calculate the terminal voltage using Ohm's law: $$U_{tH}\ge {\mathrm{R.}}_{sc,max}\cdot {\mathrm{I.}}_{\mathrm{1,}tH}.$$

In the present numerical example, the result would be $$U_{tH}\ge {\mathrm{R.}}_{sc,max}\cdot {\mathrm{I.}}_{\mathrm{1,}tH}=150\text{m}\mathrm{\Omega }\cdot 500\text{A.}=75\text{V}.$$

The minimum value calculated in this way (U _th = 75 V) represents the lowest value that the threshold value of the terminal voltage may assume. It should, however, with regard to the later on the HV on-board network 1 Second energy source to be added 3 a higher value can be selected so that the electrical connection is interrupted by the interruption element 4th even with a correspondingly smaller drop in the terminal voltage U _{Batt, 1} he follows. The resulting additional safety area can be used for adding the second energy source 3 be used. This will be discussed below with reference to the third method step according to the invention. _{A value U th} = 137.5 V is determined for the present example.

Alternatively, the second method step according to the invention could also be carried out by first setting the threshold value U _th the terminal voltage is determined and then the first threshold value by means of Ohm's law I _{1, th} the amperage is calculated.

It should be noted that the threshold U _th the terminal voltage and the first threshold value I _{1, th} the current intensity can also be determined in other ways than described above. In particular, any possibility known to those skilled in the art of protecting HV on-board networks is suitable for determining these threshold values for a HV on-board network with a single energy source.

• • Anzahl der Batteriezellen n = 96,
• • Spannung jeder der Batteriezellen U_i = 4 V.

The value ranges in which the exemplary HV on-board network 1 is secured. These value ranges are in the 6th shown. In addition to the above-mentioned exemplary numerical values, the following additional exemplary numerical values are used as a basis:

• • Number of battery cells n = 96,
• • Voltage of each of the battery cells U _i = 4 V.

On the abscissa of the coordinate system shown are values R _i the internal resistance of each battery cell is plotted. Values Rsc of the electrical short-circuit resistance are plotted on the ordinate of the coordinate system shown.

There are three locus curves of the terminal voltage in the coordinate system U _{Batt, 1} plotted, with the three locus curves _{corresponding to the values U Batt, 1} = 96 V, U _{Batt, 1} = 137.5 V and U _{Batt, 1} = 192 V. The middle of the named locus curves of the terminal voltage U _Batt is thus at the same time the locus curve 61 of the threshold U _th the terminal voltage.

There are also eight locus curves of the battery current in the coordinate system I _{Batt, 1} plotted, the eight locus curves having the values I _{Batt, 1} = 1000 A, I _{Batt, 1} = 900 A, I _{Batt, 1} = 800 A, I _{Batt, 1} = 700 A, I _{Batt, 1} = 600 A, I _{Batt , 1} = 500 A, I _{Batt, 1} = 400 A and I _{Batt, 1} = 300 A. The locus of the battery current determined by I _{Batt, 1 = 400 A} I _{Batt, 1} is thus the locus at the same time 62 of the first threshold I _{1, th} the amperage.

The first interruption element is as described above 4th set up to interrupt the electrical connection when the first threshold value of the current strength is exceeded and when the voltage drops below the threshold value of the terminal voltage. So everyone is in 6th shown value ranges on the left of the locus 62 and to the right of the locus 61 secured. An unsecured value range remains 60 whose lowest ordinate value is Rsc = 275 mOhm.

So it is made using the representation of the 6th it can be seen that the underlying HV on-board network 1 with a single source of energy 2 is adequately secured.

The following is intended to be the case of a HV on-board network 1 with two energy sources 2 , 3 to be viewed as. 7th shows a first principle circuit diagram of such an HV vehicle electrical system 1 with a first 2 and a second energy store 3 in the event of a short circuit. This in 7th HV on-board network shown 1 thus corresponds to the in 4th illustrated HV on-board network, which is a second energy source 3 was expanded. The second source of energy 3 creates a stream I _{Batt, 2} which together with that of the first energy source 2 generated electricity I _{Batt, 1} flows over the short-circuit connection. That to interrupt the electrical connection of the second energy source 3 with the rest of the HV on-board network 1 established second interruption element 5 is in the 7th not shown.

8th shows a second principle circuit diagram of a HV on-board network 1 with a first 2 and a second energy store 3 in the event of a short circuit. The representation again corresponds to that of 5 , expanded to include an additional energy source 3 , which in the 8th as an ideal power source 3 is shown.

Compared to the above-discussed case of an HV on-board network 1 with only one first energy source 2 An additional current now flows I _{Batt, 2} via the short-circuit connection. This has an impact on the hedging explained above. First, however, it can be determined that the current-based protection (namely that the first interruption element 4th is configured to interrupt the first electrical connection when one of the first energy source 2 outgoing amperage I _{Batt, 1} a first threshold I _{1, th} the current strength) by expanding the HV on-board network 1 a second energy source is not impaired. In contrast, the voltage-based protection (namely that the first interruption element 4th is set up to interrupt the first electrical connection when a terminal voltage U _{Batt, 1} the first source of energy 2 a threshold U _th the terminal voltage) due to the additional current I _{Batt, 2} impaired. The process on which voltage-based protection is based is that in the event of a short circuit, the battery voltage U _{Batt, 1} collapses due to the low short-circuit resistance Rsc. This break-in can be detected and a short circuit can be established. By adding the second source of energy 3 and by the electricity it supplies 3 I _{Batt, 2} becomes that of the voltage sensor 42 of the first interruption element 4th Detected voltage dip is reduced. If the terminal voltage falls below U _{Batt, 1} the first source of energy 2 then not the threshold U _th the terminal voltage, there is no interruption of the electrical connection. Because of this, it can do so in the case of a single source of energy 2 properly secured HV on-board network 1 not a second source of energy without further safeguarding measures 3 to be added.

$$U_{Batt\mathrm{,1}}=R_{sc}\cdot \left(\frac{n\cdot U_i}{n\cdot R_i+R_{sc}}+I_{Batt\mathrm{,2}}\right),$$

$$U_{th}\ge R_{sc,max}\cdot \left(I_{\mathrm{1,}th}+I_{Batt\mathrm{,2}}\right).$$

To further explain the effect of adding the second energy source 3 below are the formulas derived above for the case of one around the one current I _{Batt, 2} supplying second energy source 3 supplemented HV on-board network 1 specified: $${\mathrm{I.}}_{\mathrm{B.}att\mathrm{,1}}=\frac{n\cdot U_i}{n\cdot {\mathrm{R.}}_i+{\mathrm{R.}}_{sc}},$$

$$U_{\mathrm{B.}att\mathrm{,1}}={\mathrm{R.}}_{sc}\cdot \left(\frac{n\cdot U_i}{n\cdot {\mathrm{R.}}_i+{\mathrm{R.}}_{sc}}+{\mathrm{I.}}_{\mathrm{B.}att\mathrm{,\; 2}}\right),$$

$$U_{tH}\ge {\mathrm{R.}}_{sc,max}\cdot \left({\mathrm{I.}}_{\mathrm{1,}tH}+{\mathrm{I.}}_{\mathrm{B.}att\mathrm{,\; 2}}\right).$$

9 shows an illustration of the in a HV vehicle electrical system 1 with a first 2 and a second energy store 3 secured exemplary value ranges. The 9 the 6th . The only difference is that in the 7th and 8th illustrated additional second energy source 3 . For the 9 became an amperage I _{Batt, 2} = 400 A assumed. In comparison of the 6th and 9 can be seen that by adding the second energy source 3 the unsecured value range 60 , as described above with reference to 6th described by the two loci 61 , 62 is limited, significantly enlarged. The lowest ordinate value of the unsecured value range 60 is now Rsc = 153 mOhm.

10 shows an exemplary representation of the largest value Rsc of the short-circuit resistance that is still valid as a function 100 the amperage I _{Batt, 2} of the second energy store 3 . The calculation rule for the function follows from Ohm's law 100 : $${\mathrm{R.}}_{sc}=\frac{U_{tH}}{{\mathrm{I.}}_{\mathrm{1,}tH}+{\mathrm{I.}}_{\mathrm{B.}att\mathrm{,\; 2}}}.$$

The other numerical values are the same as those mentioned above. How related to 9 explained, for a current intensity I _{Batt, 2} = 400 A, the greatest value of the short-circuit resistance that is still secured is Rsc = 153 mOhm. Using the function curve 100 it becomes clear that the largest value Rsc of the short-circuit resistance that is still secured with increasing current intensity I _{Batt, 2} decreases rapidly. From a certain value onwards, this is the one for the effective protection of the HV on-board network 1 Required condition that the maximum value of the electrical short-circuit resistance corresponds at least to that value of the electrical short-circuit resistance that can maximally occur in the HV vehicle electrical system is no longer met.

In the third method step according to the invention, the second threshold value I _{2, th of} the current intensity is therefore determined in such a way that the high-voltage vehicle electrical system 1 is protected against overcurrents occurring due to an electrical short circuit at least for all values of the electrical short circuit resistance Rsc which are below the maximum value Rsc, max of the electrical short circuit resistance. This can be done by rewriting the formula above as follows: $${\mathrm{I.}}_{\mathrm{2,}tH}=\frac{U_{tH}}{{\mathrm{R.}}_{sc,max}}-{\mathrm{I.}}_{\mathrm{1,}tH}=\frac{137.5\text{V}}{150\text{m}\mathrm{\Omega }}-500\text{A.}\approx \text{400 A}.$$

The value actually resulting from this calculation I _{2, th} = 416.7 A was rounded off slightly to 400 A above. This is advantageous in order to protect the HV on-board network 1 to add a safety margin resulting from the rounding off. However, the result of the above formula must not be rounded up, as the above calculation rule is the highest threshold value I _{2, th} the amperage at which the HV on-board network 1 for all values of the electrical short-circuit resistance Rsc lying below the maximum value Rsc, max of the electrical short-circuit resistance Rsc.

The second threshold I _{2, th} the amperage can also be graphed using the representation of the 10 can be determined by plotting the maximum value Rsc, max of the electrical short-circuit resistance on the ordinate and corresponding to the functional characteristic 100 associated abscissa value is read off. In the present example, Rsc, max = 150 mOhm. So one reads out 10 the value I _{2, th} = 400 A. So if the second threshold I _{2, th} exceeds a value of 400 A, the second energy source by means of the second interruption element 5 from the HV on-board network 1 severed. The HV on-board network 1 is therefore also in the presence of two energy sources 2 , 3 Protected against overcurrents caused by short circuits.

It should be noted that these numerical examples contain roundings. An exact determination of the numerical values is possible by using the calculation rules listed above.

It is related to 10 it should also be noted that the distance of the threshold value selected in the second method step U _th the terminal voltage U _{Batt, 1} from its lowest possible value (in the numerical example above U _th = 75 V) to the second threshold value I _{2, th} the current strength. If in the extreme case U _th = 75 V had been chosen, a value of I _{2, th} = 0 A would have had to be determined in the third process step. An addition of the second energy source 3 to the HV on-board network 1 would therefore not have been possible. In this case, the process can be terminated and started again from the beginning, using the threshold values determined at the time the process was terminated When the method is carried out again, they are adapted (that is, increased or decreased) to such an extent that the second or, if applicable, all further energy sources can be added.

$$U_{Batt\mathrm{,1}}=R_{sc}\left(\frac{n\cdot U_i}{n\cdot R_i+R_{sc}}+I_{\mathrm{2,}th}+I_{Batt\mathrm{,3}}\right),$$

$$U_{th}\ge R_{sc,max}\cdot \left(I_{\mathrm{1,}th}+I_{\mathrm{2,}th}+I_{Batt\mathrm{,3}}\right).$$

If the HV on-board network were to include a further (third) energy source, its battery power would be I _{Batt, 3} are taken into account in the following step of determining the further threshold value of the current strength as follows: $${\mathrm{I.}}_{\mathrm{B.}att\mathrm{,1}}=\frac{n\cdot U_i}{n\cdot {\mathrm{R.}}_i+{\mathrm{R.}}_{sc}},$$

$$U_{\mathrm{B.}att\mathrm{,1}}={\mathrm{R.}}_{sc}\left(\frac{n\cdot U_i}{n\cdot {\mathrm{R.}}_i+{\mathrm{R.}}_{sc}}+{\mathrm{I.}}_{\mathrm{2,}tH}+{\mathrm{I.}}_{\mathrm{B.}att\mathrm{,\; 3}}\right),$$

$$U_{tH}\ge {\mathrm{R.}}_{sc,max}\cdot \left({\mathrm{I.}}_{\mathrm{1,}tH}+{\mathrm{I.}}_{\mathrm{2,}tH}+{\mathrm{I.}}_{\mathrm{B.}att\mathrm{,\; 3}}\right).$$

The function 100 Corresponding function of the greatest value Rsc of the short-circuit resistance that is still secured as a function of the current strength I _{Batt, 3} of the further energy storage would be as follows: $${\mathrm{R.}}_{sc}=\frac{U_{tH}}{{\mathrm{I.}}_{\mathrm{1,}tH}+{\mathrm{I.}}_{\mathrm{2,}tH}+{\mathrm{I.}}_{\mathrm{B.}att\mathrm{,\; 3}}}.$$

It should be noted that the 9 and 10 each from a HV on-board network 1 with exactly two energy sources 2 , 3 go out. When adding a further (third) energy source, these figures could be adapted or newly created in accordance with the above calculation rules.

11 shows an exemplary representation of the duration T (in seconds) the current carrying capacity of exemplary elements of a HV on-board network 1 with a single source of energy 2 as well as the duration of exemplary interruption elements 41 , 42 , 43 , 44 as a function of the current strength I. (in amps). The value curve 113 gives the current carrying capacity of an exemplary cable connection 14th , 15th with a large cable cross-section, for example in the current path between the HV battery 2 and electric motor 6th could be used. For a certain current value I. on the abscissa can be determined by means of the curve 113 read off the ordinate for what maximum period of time T (in seconds) the cable connection can carry the current without being unduly stressed. In the same way there is the value curve 114 the current-carrying capacity of an exemplary cable connection with a small cable cross-section, such as that used for connecting one of the HV components 12th to the power electronics module 16 could be used. If the periods of time are to be taken into account when carrying out the invention, the respective interruption elements, depending on the current intensity, must establish the electrical connection within a period of time that is at most as long as that indicated by the curves 113 , 114 interrupt specified. Preferred can be those related to 3 interruption mechanisms shown in different value ranges of the current intensity I. works. The value curve 115 gives for an exemplary fuse element 13th the time in seconds until the electrical connection is interrupted. From the course of the curves 115 , 114 it results that the securing element 13th especially in the value areas 111 , 112 the current is effective. in these areas 111 , 112 lies the curve 115 below the curve 114 . The curve 116 gives an exemplary value curve for a through the fuse elements 41 , 42 , 43 , 44 , 45 formed interruption element again. The security element 41 determines the course of the curve 116 in the range of values 112 , i.e. at very high currents. The electricity-based protection 43 , 44 , 45 can be in a medium range of values 111 the amperage be particularly effective. The voltage-based protection 42 , 44 , 45 can be particularly effective in a lower value range 110 of the current intensity. You can tell that the curve 116 overall below the curve 113 that lies through the action of the securing elements 41 , 42 , 43 , 44 , 45 the cable connection 14th , 15th (with large cable cross-section) of the HV on-board network 1 is protected against overcurrents. Since at the same time the lower sections of the curves 115 , 116 below the curve 114 the connections with a small cable cross-section are also secured, so that in the present example the entire HV on-board network is covered by the entirety of the safeguarding measures 1 is protected against overcurrents. In the 11 periods shown T the securing elements 41 , 42 , 43 , 44 , 45 can be adjustable. But you can also check the technical properties of the fuse elements 41 , 42 , 43 , 44 , 45 be given. For example, the illustrated periods of time can be determined by hardware properties and software properties of the security elements 41 , 42 , 43 , 44 , 45 until the electrical connection is interrupted. Are these periods of time for securing the HV on-board network 1 suitable, as in the in 11 If the example shown is the case, the time periods do not have to be set separately.

List of reference symbols

U (V)

Voltage (volts)

R (ohms)

Electrical resistance (ohms)

I (A)

Current (ampere)

T (s)

Duration (seconds)

Rsc, max

Maximum value of the electrical short-circuit resistance

Rsc

Value of the electrical short-circuit resistance

Uth

Terminal voltage threshold

I1, th

First threshold value of the current intensity

I2, th

Second threshold value of the current intensity

UBatt, 1

Terminal voltage

IBatt, 1

Battery power from the first energy source

IBatt, 2

Battery power of the second energy source

IBatt, 3

Battery power of the third energy source

Ui

Voltage of the i-th battery cell

Ri

Internal resistance of the i-th battery cell

n

Number of battery cells

List of reference symbols

1

HV on-board network

2

First source of energy

3

Second source of energy

4th

First interruption element

5

Second interruption element

6th

Electric motor

7th

NV battery

8th

DC / DC converter

9

Inverter

10

Charging interface

11

Charging electronics

12th

High-voltage components

13th

Electrical fuses

14th

DC cable connection

15th

AC cable connection

16

Power electronics

20th

Battery cells of the HV battery

41

Fuse element

42

Voltage sensor

43

Current sensor

44

Evaluation circuit

45

Controllable switch

60

Unsecured value range

61

Locus of the threshold value of the terminal voltage

62

Locus of the first threshold value of the current intensity

100

Function curve

110-112

Ranges of amperage

113-116

Value curves

Claims (12)

A method for protecting a high-voltage electrical system (1) of a motor vehicle with a first energy source (2) and a second energy source (3), the high-voltage electrical system (1) having a first interruption element (4) for interrupting a first electrical connection between the first Energy source (2) and the high-voltage on-board network (1) as well as a second interruption element (5) for interrupting a second electrical connection between the second energy source (3) and the high-voltage on-board network (1), the first interruption element (4) being set up is to interrupt the first electrical connection when a terminal voltage (U _{Batt, 1} ) of the first energy source (2) _falls below a threshold value of the terminal voltage (U th) and the first interruption element (4) is further set up to close the first electrical connection _{interrupt when a current strength (I Batt, 1} ) emanating from the first energy source (2) has a first threshold value (I _{1, th} ) de r current strength exceeds, and wherein the second interruption element (5) is set up to interrupt the second electrical connection when a current strength (I _{Batt, 2} ) emanating from the second energy source (3) exceeds a second threshold value (I _{2, th} ) of the current strength exceeds, with the following steps • Determination of a maximum value (Rsc, max) of an electrical short-circuit resistance (R _SC ) of the high-voltage vehicle electrical system (1), • Determination of the threshold value of the terminal voltage (U _th ) and the first threshold value of the current strength (I _{1, th} ) such that the high-voltage electrical system (1) against due to an electrical short circuit occurring overcurrents at least _{(sc R, max)} for all below the maximum value of the electrical short circuit resistance (R _SC) lying values of the electrical short circuit resistance (R _SC) is secured, wherein the step of determining the threshold value of the terminal voltage (U _th) and the first threshold value , the current intensity (I _{1, th)} made on the assumption that the second power source (3) is separated from the high-voltage electrical system (1), • determining the second threshold value of the current intensity (I _{2, th)} such that the high-voltage On-board network (1) is secured against overcurrents occurring due to an electrical short circuit at least for all values of the electrical short-circuit resistance (R _SC ) below the maximum value (Rsc, max) of the electrical short-circuit resistance (Rsc), the step of determining the second threshold value of the current intensity (I _{2, th} ) takes place on the assumption that the second energy source (3) is connected to the high-voltage on-board electrical system (1) is. Procedure according to Claim 1 , the first interruption element (4) only interrupting the first electrical connection when the terminal voltage (U _{Batt, 1} ) of the first energy source (2) _{falls below the threshold value of the terminal voltage (U th} ) for a first period of time and / or when that of _{the current intensity (I Batt, 1} ) emanating from the first energy source (2) exceeds the first threshold value of the current intensity (I _{1, th} ) for a second period of time, the step of determining the threshold value of the terminal voltage (U _th ) and the first threshold value of the current intensity (I _{1, th} ) comprises determining the first time period and / or the second time period. Procedure according to Claim 2 , wherein the first time period is a function of the terminal voltage (U _{Batt, 1} ) of the first energy source (2) and / or wherein the second time period is a function of the current strength (I _{Batt, 1} ) emanating from the first energy source (2). Method according to one of the preceding claims, wherein the second interruption element (5) only interrupts the second electrical connection when the current intensity (I _{Batt, 2} ) emanating from the second energy source (3) exceeds the second threshold value of the current intensity (I _{2, th} ) for a third period of time, wherein the step of determining the second threshold value of the current intensity (I _{2, th} ) comprises determining the third period of time. Procedure according to Claim 4 , the third period of time being a function of the current strength (I _{Batt, 2} ) emanating from the second energy source (3). Method according to one of the preceding claims, wherein the second (I _{2, th} ) threshold value of the current intensity is adjustable, the method being carried out when adding and / or starting up the second energy source (3) to an existing high-voltage vehicle electrical system (1), with the next step • Setting the second threshold value (I _{2, th} ) of the current intensity. Method according to one of the preceding claims, wherein the high-voltage on-board network (1) comprises a further energy source and a further interruption element for interrupting a further electrical connection between the further energy source and the high-voltage on-board network (1), wherein the further interruption element is set up which interrupt further electrical connection if a current from the further energy source exceeds a further threshold value of the current intensity, with the additional step • Determining the further threshold value of the current intensity in such a way that the high-voltage vehicle electrical system (1) against due to an electrical short circuit (R _{SC ) occurring overcurrents are secured at least for all values of the electrical short-circuit resistance (R SC} ) below the maximum value (Rsc, max) of the electrical short-circuit resistance (Rsc), the step of determining the further threshold value of the current strength assuming e This ensures that the other energy source is connected to the high-voltage on-board electrical system (1). Procedure according to Claim 7 , the further interruption element only interrupting the further electrical connection when the current intensity emanating from the further energy source exceeds the further threshold value of the current intensity for a further period of time, the step of determining the further threshold value of the current intensity in each case comprising determining the further time period. Procedure according to Claim 8 , the further period of time being a function of the current strength emanating from the further energy source. Method according to one of the Claims 7 until 9 , the further threshold value of the current intensity being adjustable, the method being carried out when adding and / or starting up the further energy source to an existing high-voltage electrical system (1), with the further step of setting the further threshold value of the current intensity. Computer program product, in particular digital storage medium, comprising a set of instructions which, when executed on a computer, cause the computer to carry out the steps of the method according to one of the Claims 1 until 10 performs. Motor vehicle with a high-voltage on-board network (1) with a first energy source (2) and a second energy source (3), a first interruption element (4) for interrupting a first electrical connection between the first energy source (2) and the high-voltage on-board network (1 ) and a second interruption element (5) for interrupting a second electrical connection between the second energy source (3) and the high-voltage on-board electrical system (1), the first interruption element (4) being set up to close the first electrical connection interrupt when a terminal voltage (U _{Batt, 1} ) of the first energy source (2) _falls below a threshold value of the terminal voltage (U th) and wherein the first interruption element (4) is further set up to interrupt the first electrical connection when one of the first Energy source (2) outgoing current strength (I _{Batt, 1} ) exceeds a first threshold value of the current strength (I _{1, th} ), and wherein the second interruption element (5) is set up to interrupt the second electrical connection when one of the second energy source ( 3) outgoing current strength (I _{Batt, 2} ) exceeds a second threshold value of the current strength (I _{2, th} ), the second threshold value of the current strength (I _{2, th} ) being adjustable, the high-voltage on-board electrical system (1) further comprising a with the control device connected to the second interruption element (5), which control device is set up to set the second threshold value of the current intensity (I _{2, th} ), the control device for implementation of the procedure Claim 6 is set up.

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