Circuit arrangement for a motor vehicle to provide a redundant power supply for a safety consumer

Abstract

A circuit arrangement for a motor vehicle to provide a redundant power supply for a safety load (SHV) comprises a switching network, a first battery cell sub-string (BT1) with several first battery cells (BZ1), and a second battery cell sub-string (BT2) with at least one second battery cell (BZ2). The first and second battery cell sub-strings (BT1, BT2) are connected in series, with the at least one second battery cell (BZ2) having a higher capacity than one or more of the first battery cells (BZ1). The switching network is configured to electrically connect the first and / or second battery cell sub-string (BT1, BT2) to an on-board electrical system (BDN) depending on operating conditions, thus providing an operating voltage to the on-board electrical system (BDN).In a safe operating state, the switching network provides the operating voltage via the second battery cell substring (BT2), so that at least the safety load (SHV) is operated.

Description

[0001] The following description relates to a circuit arrangement for a motor vehicle for providing a redundant power supply for a safety load. Furthermore, an on-board electrical system for a motor vehicle and a vehicle with such a circuit arrangement are described. State of the art

[0002] Motor vehicles are increasingly equipped with so-called safety loads, such as electric steering systems (drive-by-wire) or brakes (brake-by-wire), the failure of which poses a significant safety risk. It is therefore necessary to ensure that such safety loads remain functional for at least a certain period of time even in the event of a fault, e.g., in the event of a power grid failure supplying these safety loads, in order to bring the vehicle into a safe state during this time, e.g., to a stop, park on the side of the road, or in the nearest parking space. Therefore, a redundant power grid for such safety-relevant loads is required, particularly in autonomous driving.

[0003] To provide a safety reserve, the energy network has to be designed in multiple and decoupled configurations. For example, in conventional energy supply networks (or on-board power systems), two batteries are provided, each designed to provide a voltage of 12 V. Safety loads can then be connected to both of these batteries, so that these safety loads can be supplied with energy from one or the other of these batteries depending on the operating situation. Furthermore, there are motor vehicles that have a 48 V on-board power system in addition to a 12 V on-board power system. Such an on-board power system could then require three batteries: one to provide the 48 V voltage and two further batteries for redundant power supply to the 12 V on-board power system or at least the safety loads.

[0004] Such solutions are typically complex and laborious. In particular, the multiple batteries required lead to high complexity and, above all, very high costs and space requirements when providing a redundant on-board power supply for the safety loads.

[0005] Another problem is often that battery types are used whose state-of-charge (SoC) is difficult to determine. With precise knowledge of the state-of-charge, a faulty or dangerous operating situation can be detected early and the vehicle electrical system can be switched to a safety mode. Especially for battery types such as lithium iron phosphate (LFP) batteries, which are increasingly being used as traction batteries in electric vehicles, determining the state of charge is only possible using complex measuring devices and algorithms.

[0006] One object is to provide a circuit arrangement, an on-board power supply system and a motor vehicle which make it possible to provide a redundant power supply for at least one safety consumer with less effort.

[0007] This object is achieved by a circuit arrangement, an on-board power supply system, and a motor vehicle according to the independent and subordinate claims. Advantageous embodiments and further developments are set forth in the dependent claims. Summary

[0008] It is understood below that each feature described for any embodiment may be used alone or in combination with other features described herein, and may be used in combination with one or more features of any other embodiment, or in any combination of any other embodiment, unless expressly described as an alternative. Furthermore, equivalents and modifications not described below may be used without departing from the scope of the claimed subject matter.

[0009] The term "battery cell" is used synonymously for all terms commonly used in the art for galvanic elements and electrochemical storage cells. In particular, battery cells can be implemented as "lithium-ion batteries," such as lithium batteries, lithium cells, lithium-ion cells, lithium-polymer cells, lithium-ion battery cells, and lithium-ion accumulators. This particularly includes rechargeable batteries, so-called secondary batteries. The terms "battery" and "electrochemical storage cell" can also be used synonymously with the terms "lithium-ion battery" and "lithium-ion cell."

[0010] The term "vehicle electrical system" refers to the entirety of all electrical components in a vehicle, such as a motor vehicle. The vehicle electrical system is designed for the power supply (vehicle power system) and / or the information flow between components and control units (vehicle communication system). Furthermore, a distinction is made below between circuitry and vehicle electrical system. It is possible to provide one or more circuitry for one vehicle electrical system. It is also possible to provide one or more circuitry for one or more vehicle electrical systems. In this sense, the circuitry can also be considered part of a vehicle electrical system.

[0011] According to one embodiment, a circuit arrangement for a motor vehicle for providing a redundant power supply for a safety load comprises a switching network, a first battery cell sub-string with a plurality of first battery cells, and a second battery cell sub-string with at least one second battery cell. The first and second battery cell sub-strings are connected in series, wherein the at least one second battery cell has a higher capacity than one or more of the first battery cells.

[0012] The switching network is configured to electrically connect the first and / or second battery cell substring to an on-board electrical system depending on operating conditions, thereby providing an operating voltage to the on-board electrical system. In a safety operating state, the switching network provides the operating voltage via the second battery cell substring, ensuring that at least the safety load is operated.

[0013] During normal operation, the vehicle electrical system can be supplied by the first and / or second battery cell sub-string. The operating voltage is provided. For this purpose, the switching network sets a suitable switching state that electrically connects the vehicle electrical system to the first and second battery cell sub-string. The battery cells of the first and second battery cell sub-string are discharged during operation, with the second battery cells having a higher capacity. For example, it is provided that in a charging operating state, the battery cells of the first and second battery cell sub-string are charged such that the second battery cells have a higher charge in accordance with their higher capacity. This higher charge serves as a safety reserve for the safety operating state.

[0014] In the safety operating state, the switching network switches the circuitry to a safety switching state. In this state, the operating voltage across the second battery cell sub-string drops and is supplied to the vehicle electrical system. Due to the higher capacity and higher charge of the battery cells, a safety load can be operated at least for a critical period.

[0015] The safety operating state can be activated, for example, as a result of fault events. Fault events can be indicated in the vehicle by electronic components, such as one or more control units, or by sensors and / or measuring devices.

[0016] The description is based in particular on the considerations outlined below. One aspect focuses on the use of a cell type with increased capacity and a more favorable OCV curve as part of an LFP traction battery. The cell type with increased capacity allows for emergency operation and improved determination of the state-of-charge (SoC) of the traction battery, for example, for a 12 V emergency supply. In one possible implementation, for example, NMC cells are integrated in series with LFP cells. However, the NMC cells are also larger (higher capacity) so that the amount of energy required for an emergency supply is available (even when the remaining traction battery is discharged). This results in a number of advantages, such as synergies in monitoring electronics and cooling. An accurate SoC determination of the NMC cells also allows an indirect and more precise determination (or calculation) of the LFP component.If necessary (e.g., in the event of a drive-by-wire power supply failure), an emergency supply can be provided for safety consumers in an on-board network. A further advantage is that the electrical connection can largely be designed to match the rest of the high-voltage storage system. The high-voltage storage system, consisting of two battery sub-strings, can be charged after use through cell balancing.

[0017] According to one embodiment, the switching network is configured to provide the operating voltage to the vehicle electrical system via the first and second battery cell sub-strings in a regular operating state. For example, the first and second battery cell sub-strings are part of a traction battery. Alternatively, it is possible to provide the operating voltage to the vehicle electrical system via the first battery cell sub-string.

[0018] According to one embodiment, the plurality of first battery cells of the first battery cell sub-string are connected in series. Alternatively or additionally, the first battery cells are of the same type. The first battery cells are connected in series, so that the operating voltage results from the sum of the individual nominal voltages. The operating voltage can also result from a voltage conversion, for example by a DC-DC converter, before it is made available to the vehicle electrical system. Alternatively, the first and / or second battery cells can be connected in parallel, even partially or in a combination of series / parallel connection, for example in the first battery cell sub-string. This allows greater capacity to be achieved. Using the same type simplifies the operation, in particular the charging, of the circuit arrangement.

[0019] According to one embodiment, the second battery cell or the second battery cells of the second battery cell substring each have a higher capacity than each of the first battery cells, or each have a higher capacity than the first battery cells combined. The capacity and requirements of the individual battery cells result from the desired application, for example, from the necessary reserves to operate the backup load(s) for a desired period of time.

[0020] According to one embodiment, the first battery cells are or comprise lithium iron phosphate batteries. The one or more second battery cells are or comprise lithium-ion batteries based on lithium nickel manganese cobalt oxide. Such cells are particularly suitable as "second battery cells" that have a defined open-circuit voltage (VOC), or OCV curve for short, with a comparatively steep gradient. This is met, among other things, by lithium nickel cobalt manganese (NMC) and lithium titanium oxide spinel (LTO) battery cells.

[0021] According to one embodiment, the second battery cells are or include cells with a defined open-circuit voltage and a steep gradient. In particular, the gradient is greater than 45°, for example, higher than a corresponding reference voltage of the first battery cells. Cell types with increased capacity and a more favorable OCV curve for determining SoC (for example, for 12V emergency power) can be used as a possible guideline.

[0022] According to one embodiment, the one or more second battery cells have a capacity greater than the first battery cells by a predetermined capacity, for example, by at least 20 Ah. The predetermined capacity available as a buffer can be estimated from the power for the safety loads multiplied by the time until a vehicle is in a safe state. For example, 2 kW * 120 seconds = 5.5 Ah (at 12 V). The power can be increased by a buffer factor. The predetermined capacity, or the power, should also be available at extreme operating temperatures, for example, -20 °C.

[0023] According to one embodiment, the switching network comprises switches controllable by a control unit of the vehicle electrical system. The switches can be electromechanical switches. Semiconductor switches are also common in vehicle electrical system applications.

[0024] Furthermore, an on-board electrical system for a motor vehicle is proposed, comprising a circuit arrangement for a motor vehicle for providing a redundant power supply for a safety load. In one embodiment, the system comprises at least one safety load and a circuit arrangement according to one of the preceding aspects. Furthermore, a control unit is provided and configured to control the switching network and thus place the circuit arrangement into the safety operating state.

[0025] The control unit is coupled to the switching network and configured to control the switching network. The switching network subsequently sets the operating states of the circuit arrangement through defined switching states, such as the safety operating state. The control unit comprises, for example, a microcontroller or logic, which is configured through programming or hardware to effect the defined switching states of the switching network.

[0026] According to one embodiment, the vehicle electrical system further comprises a sensor and / or measuring device. The sensor and / or measuring device comprises at least one temperature sensor, a pressure sensor, a gas sensor, an acceleration sensor, a voltage meter, and / or a current meter. The control unit is configured to detect measurement signals from the sensor and / or measuring device and to switch the circuit arrangement to the safety operating state depending on the detected measurement signals. Further events that can lead to the safety operating state include fault events in the vehicle that require the safety consumers to be supplied by emergency mode (for example, a short circuit in a (12V) consumer, failure of a DC / DC converter, cooling failure, etc.). These faults can be indicated by suitable sensors and / or measuring devices or by the control unit.

[0027] Before the safety operating state is initiated by the control unit, measurement signals from the sensors and / or measuring devices are evaluated. This can be achieved, for example, using suitable threshold values. Examples include temperature sensors, gas sensors, acceleration sensors, voltage and / or current measuring devices. For example, a safety-relevant condition is detected when a critical temperature (temperature sensor) is reached or a gas is detected (pressure sensor or gas sensor). The measurement signals then indicate a critical condition or defect in one of the battery cell sub-strings. A measurement signal from an acceleration sensor can indicate an unusual braking event or an impact. If the acceleration sensor detects a critical braking event or impact, the safety operating state can be activated as a precaution. For the 12V emergency operation of the safety consumers, the failure of the high-voltage system may be irrelevant (e.g.Drive loss). In accordance with legal requirements, the safety loads (e.g., brakes, steering, HAF) are designed redundantly (e.g., two brake diagonals, two windings in EPS, etc.), which are also powered by two 12V / 48V supplies. If one supply fails, the safety operating mode (or emergency operation) can be initiated.

[0028] A predictive approach is possible with voltage and / or current measuring devices. If current and / or voltage measurement signals fall below preset thresholds, this can indicate a developing safety-relevant condition. On the other hand, the measurement signals can show that there is insufficient capacity left in the first battery sub-string for regular operation. Due to the safety reserve of the second battery sub-string, i.e. the higher capacity of the second battery cells, at least one safety load can be operated in the safety operating state. The safety load is, for example, the steering (drive-by-wire) and braking system (brake-by-wire). For such safety loads, it must be ensured that they continue to operate even in the event of a fault, e.g.In the event of a failure of an on-board electrical system supplying these safety consumers, they must remain functional for at least a certain period of time, allowing the vehicle to be brought to a safe state during this time, e.g., to come to a complete stop, park at the side of the road, or park in the nearest parking space. For this purpose, the control unit, for example, informs the on-board electrical system that the safety operating state has been activated. Subsequently, additional control units take over emergency control for the safety consumer(s), for example, the steering and brakes.

[0029] Furthermore, a motor vehicle is proposed. The motor vehicle is, for example, an electric vehicle. The first and second battery cell sub-strings can form a high-voltage storage unit and a traction battery, respectively. The motor vehicle is equipped with an on-board electrical system according to one of the preceding aspects.

[0030] In the following, exemplary embodiments of the invention are described with reference to the accompanying drawings. Further details, preferred embodiments, and further developments emerge from them. Identical or similarly functioning components are provided with the same reference numerals in the figures. The illustrated components and their relative sizes are not to be considered to scale. To the extent that components and parts in the various figures have the same function, their description is not necessarily repeated for each of the following figures. Brief description of the drawings

[0031] In detail: Fig. 1 an embodiment of a circuit arrangement, Fig. 2 shows a further embodiment of a circuit arrangement. Detailed description

[0032] Fig. Figure 1 shows an exemplary embodiment of a circuit arrangement. The drawing shows a schematic circuit for better illustration. The circuit arrangement is designed for a motor vehicle and for providing a redundant power supply for a safety load (SHV).

[0033] The circuit arrangement comprises a first battery cell sub-string BT1 (high-voltage storage) with a plurality of first battery cells BZ1 and a second battery cell sub-string BT2 (high-voltage storage) with a plurality of second battery cells BZ2. The first and second battery cell sub-strings are connected in series. In each sub-string, the cells are of the same type. In this example, the battery cells in the first battery cell sub-string are lithium iron phosphate batteries (LFP). The battery cells in the second battery cell sub-string are, for example, NMC batteries, i.e. a lithium-ion battery that uses lithium nickel manganese cobalt oxide (NMC). The nominal voltage of an individual NMC battery is between 3.6 V and 3.7 V. In this example, four NMC batteries are provided in the second battery cell sub-string and, when connected in series, result in approximately 14.4 V and 14.7 V, respectively, which are dropped across the second battery cell sub-string.This means that the second battery cell sub-string is configured for a 12 V on-board electrical system (BDN) and can provide the operating voltage of 12 V for the on-board electrical system. The on-board electrical system can be, for example, a 12 V on-board electrical system or a 48 V on-board electrical system (low voltage).

[0034] The number of second battery cells BZ2 provided in the second battery cell substring BT2 depends on their nominal voltage and the operating voltage of the vehicle electrical system. In this example, the vehicle electrical system BDN has an operating voltage of 12 V, so four NMC batteries in the second battery cell substring provide the operating voltage. The circuit arrangement can be adapted accordingly for other vehicle electrical systems. For example, the vehicle electrical system can be designed for an operating voltage of 24 V, so eight NMC batteries in the second battery cell substring provide the operating voltage. These considerations can also be applied analogously to other vehicle electrical systems, e.g., a 48 V vehicle electrical system.

[0035] The battery cells BZ1, BZ2 of the first and second battery substrings BT1, BT2 together form a high-voltage storage unit HVS for the vehicle in which they are installed, for example, an electric vehicle. The battery cells are, for example, part of the vehicle's traction battery. To create further redundancies, the circuit arrangement presented here can be provided multiple times, for example, twice, so that a possible failure of the first and second battery cell substrings can also be compensated. The additional circuit arrangements are generally designed to supply the same on-board electrical system BDN. Alternatively, or in addition, further, even redundant, circuit arrangements can be provided for other on-board electrical systems.

[0036] In this exemplary embodiment with LFP and NMC batteries, the second battery cells BZ2 (NMC) from the second battery cell sub-string BT2 have a higher capacity than the first battery cells BZ1 (LFP). Other battery types can be installed. One aspect of the proposed circuit arrangement is that the batteries of the second sub-string have a higher capacity than the batteries of the first sub-string. The higher capacity serves for safety operation of the vehicle electrical system with one or more safety loads (in this example, the 12 V vehicle electrical system).

[0037] The circuit arrangement also includes a switching network. The switching network comprises a number of controllable switches. The switches can be electromechanical switches. Semiconductor switches are also common in on-board electrical system applications. The switching network can be controlled by a dedicated control unit (STG) or by a control unit already provided in the on-board electrical system (BDN), which additionally controls the switching network. For example, the control unit comprises a microcontroller or a suitable logic device.

[0038] The switching network comprises switches S1 to S3. The first and second battery cell sub-strings are connected in series via a first node N1. The first switch S1 couples the first node N1 to the first battery cell sub-string. The second and third switches S2, S3 are connected in parallel, with the second switch S2 being coupled via the first node N1 and the third switch S3 to the second battery cell sub-string. The second and third switches S2, S3 thus make it possible to tap the voltage drop across the second battery cell sub-string BT2 and, depending on the switching state of the two switches, to make it available to the vehicle electrical system as operating voltage. The vehicle electrical system can be electrically coupled to the circuit arrangement via the two switches S2, S3.

[0039] The switching network can implement different switching states of switches S1 to S3. This electrically connects the first and / or second battery cell sub-string BT1, BT2 to the on-board electrical system BDN depending on the operating states. During operation, the operating voltage required for the operation of the on-board electrical system is then supplied to the on-board electrical system in different ways defined by the switching states. In particular, the switching network can set a safety operating state. In this example, switches S2 and S3 are both closed. Switch S1 can be open or closed. In this way, the second battery cell sub-string BT2 is electrically connected to the on-board electrical system, and the operating voltage is supplied to the on-board electrical system via the second battery cell sub-string BT2.The second battery cells BZ2 of the second battery cell sub-string are dimensioned so that their capacity is sufficient to operate at least the safety consumer SHV.

[0040] During normal operation of the circuit arrangement, switches S2 and S3 are open. Switch S1 is closed. The operating voltage for the on-board electrical system BDN is provided by the two battery sub-strings BT1, BT2, and a corresponding operating current is fed into the on-board electrical system BDN. Regular operation can be replaced by the safety operating state under various events. For example, the circuit arrangement or the on-board electrical system is supplemented with sensors and / or measuring devices that monitor the regular operation of the circuit arrangement. Examples include temperature sensors, gas sensors, acceleration sensors, voltage and / or current measuring devices. Measurement signals from the sensors and / or measuring devices are recorded by the control unit STG and compared with predetermined threshold values.For example, a safety-relevant condition is detected when a critical temperature (temperature sensor) is reached or a gas is detected (gas sensor). The measurement signals then indicate a critical condition or defect in one of the battery cell sub-strings BT1, BT2. A signal from an acceleration sensor can indicate an unusual braking event or an impact. If the acceleration sensor detects a critical braking event or impact, the safety operating state can be activated as a precaution. Other events that can lead to a safety operating state include fault events in the vehicle that require the safety consumers to be supplied by emergency mode (e.g., short circuit in a (12V) consumer, failure of a DC / DC converter, cooling failure, etc.). These faults can be indicated by suitable sensors and / or measuring devices or by the control unit.

[0041] A predictive approach is possible with voltage and / or current measuring devices. If current and / or voltage measurement signals fall below preset thresholds, this can indicate a developing safety-relevant condition. On the other hand, the measurement signals can show that there is insufficient capacity left in the first battery sub-string BT1 for regular operation. Due to the safety reserve of the second battery sub-string BT2, i.e. the higher capacity of the second battery cells BZ2, at least one safety load SHV can be operated in the safety operating state. The safety load is, for example, the steering (drive-by-wire) and braking system (brake-by-wire). For such safety loads, it must be ensured that they also function in the event of a fault, e.g.If an on-board power supply (BDN) fails to supply these safety consumers, the BDN must remain functional for at least a certain period of time to transfer the vehicle to a safe state during this time, e.g., to a stop, park at the side of the road, or park in the nearest parking space. For this purpose, the STG control unit, for example, informs the BDN on-board power supply that the safety operating state has been activated. Subsequently, additional control units for the safety consumer(s) take over emergency control, for example, the steering and brakes.

[0042] The safety operating state is initiated, for example, by the control unit, by the switching network closing switches S2 and S3. In this switching state, the operating voltage across the second battery sub-string BT2 drops and is supplied to the on-board electrical system BDN and one or more safety loads SVH. Due to the higher capacity of the battery cells BZ2 of the second battery sub-string, sufficient operating current is available for the safety loads to transfer the vehicle to a safe state.

[0043] Switch S1 is closed or open. If there is still residual current in the first battery sub-string BT1, this can be made available to the on-board electrical system BDN. The first battery sub-string BT1 primarily supplies the drive with energy (high-voltage storage). Normally, however, the 12V on-board electrical system can also be supplied via the DC-DC converter GSW. In the event of a fault, switch S1 can be opened, meaning the DC-DC converter can no longer supply the 12V on-board electrical system and the drive is also no longer supplied. It may also be necessary, and appropriate measurement signals from the sensors and / or measuring devices will indicate to the STG control unit, to separate the first battery sub-string BT1 from the second battery sub-string BT2 by opening switch S1.

[0044] Fig. 2 shows a further embodiment of the circuit arrangement. The circuit arrangement is based on the Fig.1 and described above. The circuit arrangement is supplemented by a DC-DC converter GSW and two further switches S4 and S5. The DC-DC converter, together with the third and fourth switches S3, S4, is connected in parallel to the series circuit comprising the first and second battery sub-strings BT1, BT2. Furthermore, the DC-DC converter is coupled to node N1 via the fifth and second switches and is also connected to the second battery sub-string. The on-board electrical system BDN or the safety load SHV is represented in the drawing by a resistor that is connected via a second circuit node N2 to the fifth and second switches and to the third switch S3.

[0045] In this embodiment, during normal operation, the first, fourth, and fifth switches S1, S4, S5 are closed, and the second and third switches S2, S3 are open. The on-board electrical system BDN with the safety load SHV is supplied by the shared battery string consisting of the first and second battery substrings BT1, BT2. The DC-DC converter GSW provides the operating voltage for the on-board electrical system.

[0046] In the safety operating state, the fourth and fifth switches S4, S5 are open, and the second and third switches S2, S3 are closed. The DC-DC converter GSW no longer provides the operating voltage for the on-board network BDN. Instead, the operating voltage is tapped via the second battery sub-string BT2. In this exemplary embodiment, the second battery sub-string does not require a DC-DC converter because the number of battery cells provided (here, four cells) is selected for the required operating voltage. As discussed above, the first switch S1 can be open or closed.

[0047] The STG control unit can have an additional function beyond initiating the safety operating state. In the exemplary embodiments shown above, LFP batteries were used as the first battery cells BZ1 and NMC batteries as the second battery cells BZ2. LFP batteries have the well-known disadvantage of having an unfavorable OCV (open-circuit voltage) curve, which only allows an inaccurate determination of the state of charge (SoC). NMC batteries, on the other hand, have a more favorable OCV curve and allow a more precise SoC determination. The control unit is configured, for example, to perform the SoC determination for battery cells BZ2 of the second battery substring.

[0048] It is possible, for example, using preset characteristic curves, to determine the state of charge (SoC) of the battery cells BZ2 of the second battery sub-string BT2, and to determine the state of charge of the first battery cells BZ1. This means that the STG control unit can also indirectly measure the state of charge of the first battery cells. As discussed above, the state of charge determined in this way can be used to predict the remaining energy for the operation of the on-board network BDN, and the safety operating state can be activated when predetermined thresholds are reached.

[0049] Although the invention has been illustrated and described in detail using exemplary embodiments, the invention is not limited by the exemplary embodiments. Rather, other variations of the invention may be derived therefrom by those skilled in the art without departing from the scope of the invention as defined by the claims. List of reference symbols BDN on-board network BT1 first battery cell sub-string BT2 second battery cell sub-string BZ1 first battery cells BZ2 second battery cells GSW DC-DC converter N1 Node / Circuit Node N2 node / circuit node SHV safety consumer STG control unit S1 to S5 switches

Claims

[1] A circuit arrangement for a motor vehicle for providing a redundant energy supply for a safety consumer (SHV), comprising a switching network, a first battery cell sub-string (BT1) with a plurality of first battery cells (BZ1) and a second battery cell sub-string (BT2) with at least one second battery cell (BZ2), wherein: - the first and second battery cell sub-strings (BT1, BT2) are connected in series and the at least one second battery cell (BZ2) has a higher capacity than one or more of the first battery cells (BZ1), and - the switching network is configured to electrically connect the first and / or second battery cell sub-string (BT1, BT2) to an on-board network (BDN) depending on operating conditions, so that an operating voltage is provided to the on-board network (BDN), and - the switching network provides the operating voltage via the second battery cell sub-string (BT2) in a safety operating state, so that at least the safety consumer (SHV) is operated. [2] The circuit arrangement according to claim 1, wherein the switching network is configured to provide the operating voltage to the vehicle electrical system (BDN) via the first and second battery cell sub-strings (BT1, BT2) in a regular operating state. [3] The circuit arrangement according to one of the preceding claims, wherein the plurality of first batteries (BZ1) of the first battery cell sub-string (BT1) are connected in series and are of the same type. [4] The circuit arrangement according to one of the preceding claims, wherein the second battery cell (BZ2) or the second battery cells (BZ2) of the second battery cell sub-string (BZ2) each have a higher capacity than each of the first battery cells (BZ1) or each have a higher capacity than the first battery cells (BZ1) together. [5] The circuit arrangement according to one of the preceding claims, wherein: - the first battery cells (BZ1) are or comprise lithium iron phosphate accumulators, and / or - the one or more second battery cells (BZ2) are or comprise lithium-ion accumulators based on lithium nickel manganese cobalt oxide, and / or - the one or more second battery cells (BZ2) are or comprise cells which have a defined open-circuit voltage and which have a steep gradient. [6] The circuit arrangement according to one of the preceding claims, wherein the one or more second battery cells (BZ2) have a capacity greater than the first battery cells (BZ1) by a predetermined capacity, for example at least 20 Ah. [7] The circuit arrangement according to one of the preceding claims, wherein the switching network comprises switches (S1, S2, S3, S4, S5, S6) controllable by a control unit (STG) of the vehicle electrical system (BDN). [8] An on-board power system for a motor vehicle with a circuit arrangement for a motor vehicle for providing a redundant power supply for a safety consumer, comprising: - at least one safety consumer (SHV), - a circuit arrangement according to one of the preceding claims, - a control unit (STG) which is designed to control the switching network and thus put the circuit arrangement into the safety operating state. [9] The on-board network according to claim 8, further comprising a sensor and / or measuring device with at least one temperature sensor, a gas sensor, an acceleration sensor, a voltage and / or current meter, wherein the control unit (STG) is configured to detect measurement signals from the sensor and / or measuring device and to put the circuit arrangement into the safety operating state depending on the detected measurement signals. [10] A motor vehicle with an on-board network according to one of the preceding claims.

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