Voltage converter system and method for operating same

Abstract

The invention relates to a voltage converter system (500) for a vehicle having a high-voltage on-board power system and a low-voltage on-board power system, wherein the voltage converter system has one or more DC-DC converters, connected in parallel, having one or more DC-DC converter phases (11, 12), connected in parallel, and has a charging device (20), wherein the voltage converter system has at least one first connection (101) for connecting to the high-voltage on-board power system, wherein the one or more DC-DC converters (11, 12) and the charging device (20) are electrically connected to the at least one first connection (101), wherein the voltage converter system has at least one second connection (102) for connecting to the low-voltage on-board power system, wherein the one or more DC-DC converters (11, 12) are electrically connected to the at least one second connection (102), wherein the voltage converter system has at least one third connection (103) for connecting to an external voltage source (4), wherein the charging device (20) is or can be electrically connected to the at least one second connection (102).

Description

[0001] Description

[0002] title

[0003] Voltage converter system and method for operating such a system

[0004] The present invention relates to a voltage converter system for a vehicle having a high-voltage electrical system and a low-voltage electrical system, as well as a method for operating such a voltage converter system.

[0005] Background of the invention

[0006] Electric vehicles are trending in the automotive industry because they use cleaner energy and can deliver better performance than fossil-fuel-powered vehicles. On-board charging devices can be used to charge energy storage devices in electric vehicles.

[0007] Disclosure of the invention

[0008] According to the invention, a voltage converter system and a method for operating such a system are proposed, having the features of the independent patent claims. Advantageous embodiments are the subject of the subclaims and the following description.

[0009] The invention relates to vehicles with a high-voltage electrical system and a low-voltage electrical system, in particular electric vehicles. In electric vehicles, so-called CharCon devices (onboard chargers including DC-DC converters, i.e., "converters") can be used to supply the 12V electrical system (or generally a low-voltage electrical system). Such a CharCon device is therefore a voltage converter system with a charging device (onboard charger) and one or possibly several DC-DC converters. One or each of the several DC-DC converters, then connected in parallel, can in turn have one or more DC-DC converter phases.

[0010] The charging device can be used, for example, to charge an energy storage device in the high-voltage vehicle electrical system, e.g., from an external AC power source. The high-voltage vehicle electrical system and the low-voltage vehicle electrical system can be connected to each other via one or more DC-DC converters. While the low-voltage vehicle electrical system, as mentioned above, can have a DC voltage of 12V, the high-voltage vehicle electrical system can have a DC voltage of 48V or 60V or more. In general, however, the high-voltage vehicle electrical system should have a higher DC voltage than the low-voltage vehicle electrical system.

[0011] The DC-DC converter(s) do not traditionally have particularly high or safety-relevant requirements regarding their availability or failure rates (so-called FIT rates). However, there is a desire for increased availability requirements. Particularly for vehicles with a higher degree of automation, e.g. from approximately SAE Level 3 (for HAD, i.e. "highly automated driving"), the requirement for the availability of the 12V or low-voltage or low-voltage electrical system (LV-BN) increases due to the necessary safety-relevant X-by-wire systems (e.g. for steering and braking). For safe operation, ASIL D or approximately 10 FIT is generally required at the vehicle level. Accordingly, the availability requirements for the DC-DC converter derived by automobile manufacturers increase to approximately ASIL B(D) or approximately 100 FIT, e.g. by distributing the safety load between an LV-BN battery and the DC-DC converter.

[0012] To meet this requirement, it may be necessary to provide the total DC-DC power via several independent or redundant DC-DC converters or DC-DC converter phases. To ensure that sufficient power is still available even in the event of a so-called single fault ("single fault"), the total DC-DC converter power installed in the device must be higher than (or at least equal to) the power required in the event of a fault. If no or only a slight power reduction compared to the rated power is permitted in the event of a fault, this leads to additional expenditures in the device (cost, installation space) and the associated "overdesign."

[0013] The required nominal power and power in the event of a fault from the DC-DC converter could, for example, be 3 kW each. In a fault-tolerant redundant system, this could, for example, be implemented with three DC-DC converter phases of 1.5 kW each. These can, for example, be connected via individual or a shared EMC filter with a first connection (alternatively several redundant connections) to the HV battery or generally to the high-voltage vehicle electrical system and via a second connection (alternatively several redundant connections) to the low-voltage vehicle electrical system. If one phase fails, two phases with 1.5 kW each are still available, i.e. a total of 3 kW.

[0014] A total of 4.5 kW of DC-DC converter power must be installed, meaning the high availability requirement in this case leads to a significant overdesign in terms of DC-DC power: 4.5 kW instead of 3 kW total power. Without increased availability requirements, the system could also be implemented with just one or two phases with a total power of 3 kW.

[0015] It is therefore desirable to present a redundant, highly available DC-DC converter system without overdesign or with significantly reduced overdesign of the DC-DC converter performance compared to conventional systems.

[0016] For this purpose, a voltage converter system for a vehicle with a high-voltage on-board electrical system and a low-voltage on-board electrical system is proposed. The voltage converter system has one or more DC-DC converters connected in parallel with one or more DC-DC converter phases connected in parallel, and a charging device, as already mentioned above. The voltage converter system has a first connection (or possibly a plurality of first connections) for connection to the high-voltage on-board electrical system, wherein the one or more DC-DC converters and the charging device are electrically connected to the first connection. In addition, the voltage converter system has a second connection (or possibly a plurality of second connections) for connection to the low-voltage on-board electrical system, wherein the one or more DC-DC converters are electrically connected to the second connection. Furthermore, the voltage converter system has a third connection (or possibly a third connection) for connection to the high-voltage on-board electrical system.(also several third connections) to an external voltage source, e.g., an alternating voltage from a power grid. The charging device preferably comprises an isolating stage (e.g., a transformer) and an AC-DC converter, wherein a DC side of the AC-DC converter is electrically connected to the isolating stage, and wherein the isolating stage is electrically connected to the first connection.

[0017] The charging device is now electrically connected or connectable to the second terminal. In this way, the charging device can be used, at least temporarily, as a DC-DC converter to compensate for the power lost due to the failure of a DC-DC converter phase (or of a DC-DC converter) in the event of a fault. In one embodiment, the voltage converter system is configured to connect the first terminal to the third terminal in the event of a fault in one or more parallel-connected DC-DC converters and to convert DC voltage between the high-voltage vehicle electrical system and the low-voltage vehicle electrical system by means of the charging device.

[0018] When operating a voltage converter system, DC voltage is converted between the high-voltage vehicle electrical system and the low-voltage vehicle electrical system by means of one or more parallel-connected DC-DC converters. In the event of a fault in one or more of the parallel-connected DC-DC converters, DC voltage is converted between the high-voltage vehicle electrical system and the low-voltage vehicle electrical system by means of the charging device. This is possible because the function of the charging device (or charger) is never safety-relevant in terms of its availability or absolutely necessary for safety. Furthermore, critical driving situations that require a high level of availability of low-voltage vehicle electrical system DC-DC converters only occur while driving, during which the vehicle cannot be charged anyway. The possible use of a so-called V2L function (e.g.A power outlet in the vehicle, if present, would have to be disabled in such a fault situation, for example, interrupting the charging of the laptop via the AC outlet in the vehicle. However, given the rarity of this situation, this represents a reasonable and manageable limitation.

[0019] In one embodiment, the voltage converter system has a switching device and is configured to selectively electrically connect the charging device to the second terminal by means of the switching device. In particular, the voltage converter system can be configured to selectively electrically connect an AC side of the AC-DC converter to the second terminal or to the third terminal by means of the switching device. The switching device can, for example, comprise one or more switches, as will be explained later by way of example.

[0020] In this way, power is fed directly into the low-voltage vehicle electrical system via the AC-side output of the charging device (or charger). In the event of a fault in the DC-DC converter, the PFC stage (AC-DC converter) is connected, for example, to the 12V system. When power is fed from the HV battery or high-voltage vehicle electrical system via the charging device into the low-voltage vehicle electrical system, the output voltage of the charging device should also be regulated to the voltage in the low-voltage vehicle electrical system so that the required power flow from the HV battery or high-voltage vehicle electrical system to the low-voltage vehicle electrical system is achieved. In addition to the voltage in the low-voltage vehicle electrical system, the current flow and the power flow via the charging device into the low-voltage vehicle electrical system are particularly suitable as controlled variables.It should be noted that the charging device is often designed for a significantly higher voltage (effective values ​​typically in the range of 220 V to 240 V) than the voltage of the low-voltage vehicle electrical system (approx. 12 V). The power that can be fed into the low-voltage vehicle electrical system is therefore limited to approximately 5% of the charging device's power without modification of the charging device, i.e., approximately 550 watts for 11 kW charging devices and approximately 1100 watts for 22 kW charging devices. Especially with 11 kW charging devices, the power could be very limited - depending on the specific power requirements of the DC-DC converter in the event of a fault. In this respect, it may be advisable to design the charging device for a sufficiently high power.

[0021] In one embodiment, the isolation stage of the charging device is or can be electrically connected to the second terminal. For this purpose, the isolation stage can have an intermediate tap, wherein the isolation stage is or can be electrically connected to the second terminal via the intermediate tap. In particular, the voltage converter system can have an additional rectifier stage via which the intermediate tap is or can be electrically connected to the second terminal. In one embodiment, the voltage converter system also has a switching device via which the intermediate tap can be electrically connected to the additional rectifier stage.

[0022] This allows for dual use of selected components of the charging device (or charger) or the use of a modified charging device. The intermediate tap can, for example, be provided as a third port of the isolation transformer by applying a third winding with an additional output with an adjusted voltage for the DC-DC converter function.

[0023] Here, the isolation stage of a conventional charging device is modified. Via an additional output, an optional switch and a rectifier stage can be used to feed power into the second connection for the low-voltage vehicle electrical system, for example in the event of a fault in the DC-DC converter. The modified isolation stage and the additional rectifier stage are particularly characterized by the fact that they can generate a voltage with sufficient power that is adapted to the low-voltage vehicle electrical system. In order to feed power into the low-voltage vehicle electrical system via the modified charging device in the event of a fault in the DC-DC converter system, a closed-loop control system may also be required. The power, the output voltage and the output current are particularly suitable as controlled variables.

[0024] In addition to the hardware topology of the voltage converter system, i.e. the highly available DC-DC converter, another technical aspect can be an independent control or computer concept as well as a concept for an independent supply voltage, with which redundancy or resilience against the occurrence of individual faults can be achieved.

[0025] In one embodiment, the voltage converter system therefore comprises a plurality of separate control and / or regulation and / or voltage supply devices, each configured to control and / or regulate and / or supply voltage to one or more of the parallel-connected DC-DC converters and the charging device. In concrete terms, for example, individual redundant DC-DC converter phases or DC-DC converters can be supplied with independent computers and / or supply voltages, which may result in additional costs.

[0026] To reduce development costs, it may be sensible to construct a modular CharCon comprising an independent charger and an independent DC-DC converter. Independent here means in particular that both the charger and the DC-DC converter have their own "infrastructure," such as the computer structure (microcontroller and system base chip) and supply voltage, which are implemented independently of each other. Another reason to use independent microcontrollers for the charger and DC-DC converter may be that a single microcontroller reaches its limits in terms of performance or resources for certain CharCon versions. Due to the intrinsic independence inherent in the described system due to the modularity, the independence of the various supply paths of the low-voltage vehicle electrical system via the DC-DC converter and the charger is also ensured, i.e.Here, the implementation of a redundant system can be achieved cost-effectively due to the independent infrastructure that already exists.

[0027] Further advantages and embodiments of the invention will become apparent from the description and the accompanying drawings.

[0028] The invention is illustrated schematically in the drawing using exemplary embodiments and is described below with reference to the drawing.

[0029] Short description of the drawings

[0030] Figure 1 shows schematically a vehicle to explain the invention.

[0031] Figure 2 shows schematically a DC-DC converter system to explain a background of the invention

[0032] Figures 3, 4 schematically show a voltage converter system to explain a background of the invention.

[0033] Figures 5 to 9 show schematically voltage converter systems in various embodiments.

[0034] Embodiment(s) of the invention

[0035] Figure 1 schematically shows a vehicle 105 for explaining the invention. The vehicle 100 has, by way of example, a high-voltage electrical system 1 and a low-voltage electrical system 2, as well as a voltage converter system 100, via which the high-voltage electrical system 1 is electrically connected to the low-voltage electrical system 2. Also shown, by way of example, is an external voltage source 4, to which the voltage converter system 100 can be electrically connected, e.g., via a charging interface 3 on the vehicle 105.

[0036] In the following, the same elements or components will be designated by the same reference numerals in order to simplify the description and to be able to build on one another for different figures.

[0037] Figure 2 schematically illustrates a DC-DC converter system 200. The DC-DC converter system 200 comprises, for example, three parallel-connected DC-DC converter phases 11, 12, 13. Furthermore, the DC-DC converter system 200 comprises a first terminal 101 for connection to the high-voltage vehicle electrical system, wherein the plurality of DC-DC converter phases 11, 12, 13 are electrically connected to the first terminal 101. Furthermore, the DC-DC converter system 200 comprises a second terminal 102 for connection to the low-voltage vehicle electrical system, wherein the plurality of DC-DC converter phases 11, 12, 13 are electrically connected to the second terminal 102.

[0038] This is an example of a redundant DC-DC converter system 200. A required nominal power and power in the event of a fault in the DC-DC converter system are, for example, 3 kW each. In a fault-tolerant redundant system, this could, for example, be implemented with three DC-DC converter phases 11, 12, 13, each with 1.5 kW, as shown. These can, for example, be connected via individual or a common EMC filter 31, 32 to the first connection (alternatively several redundant connections) 101 to the high-voltage vehicle electrical system or an HV battery, and via a second connection 102 to the low-voltage vehicle electrical system. If one phase fails (e.g. 13), two phases 11, 12, each with 1.5 kW, i.e. a total of 3 kW, are still available.

[0039] A total of 4.5 kW of DC-DC converter power must be installed, meaning the high availability requirement in this case leads to a significant overdesign in terms of DC-DC power: 4.5 kW instead of 3 kW total power. Without increased availability requirements, the system could also be implemented with just one or two phases with a total power of 3 kW.

[0040] Figure 3 schematically illustrates a voltage converter system 300, a so-called CharCon with a high-availability DC-DC converter system. The voltage converter system 300 comprises, for example, two parallel-connected DC-DC converter phases 11, 12 (these can, for example, belong to one or two separate DC converters).

[0041] In addition, the voltage converter system 300 has a first connection 101 for connection to the high-voltage vehicle electrical system, wherein the plurality of DC-DC converter phases 11, 12 are electrically connected to the first connection 101, for example via EMC filters 31. The DC-DC converter phases are thus electrically supplied via this connection. In addition, the voltage converter system 200 has a second connection 102 for connection to the low-voltage vehicle electrical system, wherein the plurality of DC-DC converter phases 11, 12 are electrically connected to the second connection 102, for example via EMC filters 32.

[0042] It may also be possible to feed energy from the low-voltage vehicle electrical system back into the high-voltage vehicle electrical system, e.g. to pre-charge capacitors before the battery contactor is switched on or to feed energy from solar cells mounted on the vehicle into the high-voltage vehicle electrical system.

[0043] In addition, the voltage converter system 300 has a charging device 20 (the charger), which in turn typically has an isolating stage 21 and an AC-DC converter 22 (a so-called PFC stage, where PFC stands for "power factor control"). This allows power to be transferred between the high-voltage vehicle electrical system via the first connection 101 and the EMC filter 31 and an external voltage source via, for example, an EMC filter 33 including a relay matrix and the connection point 103, as also explained by way of example with reference to Figure 1 and the voltage converter system 100. Depending on the configuration, the power flow can occur in both directions (charging operation or discharging operation, V2x) or only in one direction (charging operation only or discharging operation only). Figure 4 shows a schematic representation of a voltage converter system 400. This can be, for example, the voltage converter system 300 according to Figure 3 or a variant thereof, but with a more detailed representation.

[0044] The EMC filter 33 including relay matrix is ​​shown here specifically with an AC filter 33' and three switches S1, S2, S3 as the relay matrix. Instead of a general third connection, four third connections 103 are shown here, namely for three AC phases L1, L2, L2 and a neutral conductor N. Accordingly, the AC-DC converter 22 (PFC stage) has half-bridges with individual switches S11 to S19, as well as inductors and capacitors not explicitly named. The isolation stage 21 is shown as an isolation transformer, with a winding 21.1 on the DC side and a winding 21.2 on the AC side. In addition, the isolation stage 21 has switches S21 to S24 on the AC side and switches S41 to S44 on the DC side. An unnamed intermediate circuit capacitor is also provided.

[0045] The DC-DC converter phases 11, 12 are depicted here as conventional rectifiers with switches S31 to S33 and S51 to S53, respectively, as well as unlabeled windings. The DC-DC converter phases 11, 12 are electrically connected to the low-voltage vehicle electrical system via the EMC filters 33 (here with switch S35 and unlabeled capacitors) with, for example, two second terminals 102.

[0046] The EMC filters 31 are specifically shown here with a high-voltage EMC filter 33" and a DC-DC EMC filter 3T (e.g., including the mainboard). Via the EMC filters 31, both the charging device 20 and the DC-DC converter phases 11, 12 are connected to the high-voltage vehicle electrical system via, for example, two first connections 101.

[0047] The topology has been chosen here only as an example; other topologies are also conceivable. Relays or semiconductor switches, for example, can be used as switches or switching elements. Typically, MOSFETs, IGBTs, SiC-FETs or GaN-FETs are used here, and in some places diodes (Si, SiC or GaN) are also used. Figure 5 schematically shows an embodiment of a voltage converter system 500. The voltage converter system 500 basically corresponds to the voltage converter system 300 according to Figure 3, but additionally with a switching device. The voltage converter system 500 is configured to electrically connect the charging device 20 optionally to the second terminal 102 or to the third terminal 103 by means of the switching device. Here, the switching device has, for example, a first part 42 and optionally a second part 41. Furthermore, a special control in the event of a fault in the DC-DC converter system (iehere the DC-DC converter phases 11, 12).

[0048] In the event of a fault, switch 42 is designed to connect the output stage (PFC stage) of charging device 20 (the charger) via EMC filter 32 (alternatively, directly) to second terminal 102 (i.e., an output). This allows charging device 20 to be used to feed power into the low-voltage vehicle electrical system.

[0049] Figure 6 schematically illustrates a further embodiment of a voltage converter system 600. The voltage converter system 600 may correspond to the voltage converter system 500 shown in Figure 5, but is shown in more detail. A large portion of the voltage converter system 600 corresponds to the voltage converter system 400 shown in Figure 4, but the switching device from Figure 5, specifically the first part 42, is shown in detail.

[0050] The first part 42 has, in particular, the switches S101 to S104. The outputs or phases L1 to L3 of the charging device 20, in particular of the AC-DC converter, are fed back to the positive second terminal 102 or output in the low-voltage vehicle electrical system via the three switches (here, for example, relays) S102 to S104. In addition, the negative pole of the intermediate circuit capacitor is fed back to the negative second terminal 102 or output of the low-voltage vehicle electrical system via the further switch S101. Alternatively, it would also be conceivable, in particular, for the switches S102 to S104 to be connected to the negative output of the low-voltage vehicle electrical system and for the switch S101 to connect the positive pole of the intermediate circuit to the positive output of the low-voltage vehicle electrical system.

[0051] In this way, a direct feed into the low-voltage vehicle electrical system is achieved via the AC-side output of the charging device 20, for example, by connecting the PFC stage 22 to the low-voltage vehicle electrical system in the event of a DC-DC converter failure. When feeding power from the high-voltage vehicle electrical system into the low-voltage vehicle electrical system via the charging device 20, the output voltage of the charging device should also be regulated to the voltage in the low-voltage vehicle electrical system, ensuring the required power flow from the high-voltage vehicle electrical system to the low-voltage vehicle electrical system.

[0052] As already mentioned, it should be noted that the charging device 20 is often designed for a significantly higher voltage than the voltage of the low-voltage vehicle electrical system. The power that can be fed into the low-voltage vehicle electrical system may therefore be limited without modifying the charging device.

[0053] Figure 7 schematically illustrates one embodiment of a voltage converter system 700. The voltage converter system 700 essentially corresponds to the voltage converter system 300 shown in Figure 3, but with a modified isolation stage 21+.

[0054] In the event of a fault in the DC-DC converter, power is fed into the second terminal 102 or the low-voltage vehicle electrical system via a further output (the intermediate tap) via an optional switch device 51 and a rectifier stage 52. The modified isolating stage 21+ and the rectifier 52 are particularly characterized in that they generate a voltage with sufficient power that is adapted to the low-voltage vehicle electrical system. In the event of a fault in the DC-DC converter system, closed-loop control may also be necessary for feeding power into the low-voltage vehicle electrical system via the modified charger. The power, the output voltage, and the output current are particularly suitable as controlled variables. Figure 8 shows a schematic representation of a further embodiment of a voltage converter system 800. The voltage converter system 800 can correspond to the voltage converter system 700 according to Figure ?, but is shown in more detail.A large part of the voltage converter system 800 corresponds to the voltage converter system 400 shown in Figure 4, but the modified isolation stage 21+, the optional switching device 51 and the additional rectifier stage 52 are shown in more detail.

[0055] The modification of the isolation stage 21+ is carried out by applying an additional winding to the isolation transformer present in the charger, thus creating a three-port isolation transformer 230 from a two-port isolation transformer (as shown in Figure 4). The additional winding is characterized, for example, by its winding number being optimally adapted to the voltage generated by it, to the low-voltage vehicle electrical system into which power is fed in the event of a DC-DC converter failure. The cross-section of the winding can be adapted to the required power.

[0056] The newly created third output of the isolation transformer 230, an intermediate tap 231, is connected to a rectifier or the additional rectifier stage 52 via the optional switching device 51—shown here with switch S201—which is to be closed in the event of a DC-DC converter failure. This can be implemented, for example, as a full bridge with four switches S211 to S214 or diodes, as shown. Other rectifier circuits are also conceivable.

[0057] The output of the additional rectifier stage 52 is connected to the output or second connection 102 so that in the event of a fault in the DC-DC converter, power can be fed directly into the low-voltage vehicle electrical system via the modified charger. As already described, regulation of the power path may also be necessary. In principle, it is possible for the modified charger or the modified charging device 20 to provide the entire power required in the event of a fault in the DC-DC converter. In this way, the DC-DC converter could, for example, also be designed as single-phase or non-redundant or without increased availability performance. However, a combination is also conceivable, e.g. consisting of two redundant DC-DC converter phases and the modified charger, which in the event of a fault in a DC-DC converter phase only compensates for the portion of power lost in the DC-DC converter due to the fault that occurred.

[0058] Figure 9 schematically illustrates one embodiment of a voltage converter system 900. The voltage converter system 900 essentially corresponds to the voltage converter system 300 shown in Figure 3, but with an explicitly modular design with a DC-DC system 19 comprising the DC-DC converter phases 11, 12 and a charging system 29 comprising the charging device 20. The EMC filters 32 and 33 (including relays) are separated again accordingly here; likewise, the EMC filters 31 are explicitly separated into a part 31a and a part 31b.

[0059] In addition, the voltage converter system 900 has a control device 71 and a voltage supply device 61 for the DC-DC system 19 and a control device 72 and a voltage supply device 62 for the charging system 29.

[0060] The possibility of electrically connecting the charging device 20 to the second connection 102, or of connecting it thereto, is not explicitly shown here. However, this can be done as explained, for example, with reference to Figures 5 to 8.

[0061] As mentioned, in addition to the hardware topology of the voltage converter system, another technical aspect can be an independent control or computer concept as well as a concept for an independent supply voltage, as shown in Figure 9, which can in particular achieve redundancy or resilience against the occurrence of individual faults.

Claims

Claims 1. A voltage converter system (500, 600, 700, 800, 900) for a vehicle with (105) a high-voltage vehicle electrical system (1) and a low-voltage vehicle electrical system (2), wherein the voltage converter system has one or more parallel-connected DC-DC converters with one or more parallel-connected DC-DC converter phases (11, 12) and a charging device (20), wherein the voltage converter system has at least one first connection (101) for connection to the high-voltage vehicle electrical system, wherein the one or more DC-DC converters (11, 12) and the charging device (20) are electrically connected to the at least one first connection (101), wherein the voltage converter system has at least one second connection (102) for connection to the low-voltage vehicle electrical system, wherein the one or more DC-DC converters (11, 12) are electrically connected to the at least one second connection (102) are connected,wherein the voltage converter system has at least one third terminal (103) for connection to an external voltage source (4), wherein the charging device (20) is electrically connected or connectable to the at least one second terminal (102).

2. Voltage converter system according to claim 1, wherein the charging device (20) comprises an isolating stage (21, 21+) and an AC-DC converter (22), wherein a DC side of the AC-DC converter is electrically connected to the isolating stage, wherein the isolating stage is electrically connected to the at least one first terminal (101).

3. Voltage converter system (500, 600) according to claim 1 or 2, wherein the voltage converter system comprises a switching device (42) and is arranged to selectively electrically connect the charging device (20) to the at least one second terminal by means of the switching device.

4. Voltage converter system (500, 600) according to claim 2 and 3, wherein the voltage converter system is configured to electrically connect an AC side of the AC-DC converter selectively to the at least one second terminal (102) or to the at least one third terminal (103) by means of the switching device (42).

5. Voltage converter system (700, 800) according to claim 2, wherein the isolating stage (21+) of the charging device is electrically connected or connectable to the at least one second terminal (102).

6. The voltage converter system (700, 800) according to claim 5, wherein the isolating stage has an intermediate tap (231), and wherein the isolating stage is or can be electrically connected to the second terminal via the intermediate tap.

7. Voltage converter system (700, 800) according to claim 6, which has an additional rectifier stage (52) via which the intermediate tap is or can be electrically connected to the second terminal.

8. Voltage converter system (700, 800) according to claim 7, which has a switching device via which the intermediate tap can be electrically connected to the additional rectifier stage.

9. Voltage converter system (500, 600, 700, 800, 900) according to one of the preceding claims, wherein the charging device is electrically connected or connectable to the at least one third terminal (103).

10. Voltage converter system (500, 600, 700, 800, 900) according to one of the preceding claims, with several separate control and / or regulation and / or voltage supply devices (61, 62, 71, 72) which are used to control and / or regulate and / or supply voltage to the one or more DC-DC converters connected in parallel and the charging device.

11. Voltage converter system (500, 600, 700, 800, 900) according to one of the preceding claims, which is configured, in the event of a fault in the one or more parallel-connected DC-DC converters, to connect the first terminal to the third terminal and to convert DC voltage between the high-voltage vehicle electrical system and the low-voltage vehicle electrical system by means of the charging device.

12. A method for operating a voltage converter system (500, 600, 700, 800, 900) according to one of the preceding claims, wherein direct voltage is converted between the high-voltage vehicle electrical system and the low-voltage vehicle electrical system by means of the one or more DC-DC converters connected in parallel, wherein in the event of a fault in the one or more DC-DC converters connected in parallel, direct voltage is converted between the high-voltage vehicle electrical system and the low-voltage vehicle electrical system by means of the charging device.

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