Charging energy stores of vehicles at weak energy supply networks

Abstract

The invention relates to a sub-onboard network (1) for a vehicle (30), wherein the sub-onboard network (1) has at least one energy store (2) and a regulating device (9) for charging the energy store (2) of the vehicle (30). In order to improve the charging of the energy store, it is proposed that the sub-onboard network further has an onboard network interface (3) for connection to electrical components (31) of the vehicle (30), a direct voltage interface (4) for connection to a land-side charging station (20) and an energy subgrid (5), wherein a switching device (6) is arranged between the onboard network interface (3) and the energy subgrid (5), wherein a charging device (7) is arranged between the energy store (2) and the energy subgrid (5), wherein the direct voltage interface (4) is conductively connected to the energy subgrid (5), wherein the sub-onboard network (1) has at least one power converter (8) which is connected to the energy subgrid (5) on the alternating voltage side and can be operated as an AC / DC converter and as a DC / DC converter, wherein the power converter (8) is designed by means of the regulating device (9) to operate the energy subgrid (5) as a direct voltage grid during the charging process and as an alternating voltage grid during the independent operation of the vehicle (20). The invention also relates to a vehicle having such a sub-onboard network, to a land-side charging station and to a charging system. The invention also relates to a method for operating such a sub-onboard network (1) or such a vehicle (20) or such a charging system (40), wherein the power converter (8) is operated as a DC / DC converter during the charging process and as an AC / DC converter during the independent operation.

Description

Technical Field

[0001] The present invention relates to an onboard subsystem for a vehicle, in particular a water vehicle, wherein the onboard subsystem comprises at least one energy storage device and a regulating device for charging the vehicle's energy storage device from a land-based charging station. The present invention also relates to a vehicle, in particular a water vehicle, comprising at least one such onboard subsystem. The present invention also relates to a land-based charging station comprising a land-based energy storage device and a land-based power converter. The present invention also relates to a charging system comprising such an onboard subsystem or such a vehicle and such a land-based charging station. The present invention also relates to a method for operating such an onboard subsystem or such a vehicle. Background Art

[0002] In the vehicle sector, particularly in ferries and other ships, diesel engines are increasingly being replaced for short and medium distances by electric drive systems with energy storage, such as batteries. Because charging stations on land, such as at ship moorings, often have only a weak network that limits the available electrical power, these energy storage systems are also installed on land in addition to vehicle-side energy storage (batteries). In this arrangement, the energy grid operator provides continuous power via the energy supply network, but this power is insufficient to charge the energy storage of a vehicle that only makes a short stop, such as a watercraft, within a reasonable timeframe. For this reason, the land-side energy storage is continuously charged and, when the ship is docked, energy from the land-side energy storage is transferred from the land-side energy storage to the vehicle-side energy storage.

[0003] The land-side energy storage is charged by converting the AC voltage from the energy supply network into a DC voltage. To charge the vehicle-side energy storage, the DC voltage of the land-side energy storage is converted back into an AC voltage. The vehicle-side energy storage is then charged with an AC current, which is then converted back into a DC current in the vehicle.

[0004] For this purpose, a plurality of components of the same type are provided on the land side and the vehicle side in order to ensure the energy flow. Summary of the Invention

[0005] The object of the present invention is to improve the charging of a vehicle-side energy storage device.

[0006] The object is achieved by an onboard subsystem for a vehicle, in particular for a water vehicle, wherein the onboard subsystem comprises: at least one energy storage device, a control device for charging the energy storage device of the vehicle, an onboard network interface for connecting to electrical components of the vehicle, a DC voltage interface for connecting to a charging station on land, and an energy subsystem, wherein a switching device is provided between the onboard network interface and the energy subsystem, wherein a charging device is provided between the energy storage device and the energy subsystem, wherein the DC voltage interface is electrically conductively connected to the energy subsystem, wherein the onboard subsystem comprises at least one power converter, which is connected to the energy subsystem on the AC voltage side and can be operated as an AC / DC (alternating current / direct current) regulator and as a DC / DC (direct current / direct current) regulator, wherein the power converter is designed by means of the control device to operate the energy subsystem as a DC voltage network during a charging process and as an AC voltage network during independent vehicle operation. Furthermore, the object is achieved by a vehicle, in particular for a water vehicle, comprising at least one such onboard subsystem. The object is also achieved by a land-side charging station having a land-side energy storage and a land-side power converter, wherein a land-side DC voltage connection for connection to a DC voltage connection of such an onboard subsystem or to such a vehicle is provided in the electrical connection between the land-side energy storage and the land-side power converter, wherein the power transferable via the land-side power converter is less than the continuous power transferable via the land-side DC voltage connection. Furthermore, the object is achieved by a charging system having such an onboard subsystem or such a vehicle and such a land-side charging station, wherein the land-side DC voltage connection of the land-side charging station is electrically connected to the DC voltage connection of the onboard subsystem. The object is also achieved by a method for operating such an onboard subsystem or such a vehicle or such a charging system, wherein the power converter is operated as a DC / DC converter during the charging process and as an AC / DC converter during stand-alone operation.

[0007] Further advantageous embodiments of the present invention are described in the exemplary embodiments.

[0008] The present invention is based, in particular, on the recognition that charging efficiency can be improved if energy is transferred using a DC voltage. This allows for the elimination of lossy conversion processes. At the same time, existing components of the onboard subsystem or vehicle can be used in different operating modes. The power converter can function as a DC / DC converter during the charging process and, outside of charging, as an AC / DC converter when no electrical connection to a land-based charging station is present. Operation without a charging station is also referred to as stand-alone operation, as it is independent of the land-based energy supply.

[0009] Here, a distinction is made between components provided in the onboard subsystem or vehicle, such as power converters, DC converters, and step-down converters, and the functions that these components can perform, such as DC / DC converters or AC / DC converters. For example, a power converter can operate both as a DC / DC converter and as an AC / DC converter.

[0010] To switch between the AC / DC converter and DC / DC converter operating modes, the power converter can be designed as a single-phase or three-phase converter. Furthermore, in order to select a suitable switching frequency, it may prove advantageous to provide an inductance at at least one AC voltage-side interface. Furthermore, for reasons of symmetry and uniform load distribution, it is advantageous to provide the same inductance at all AC voltage-side interfaces, at least with regard to their electrical characteristics. The inductance can be formed, for example, by a choke or a transformer. Alternatively or additionally, it may be possible to use the line inductance of the power supply line, i.e., the connecting cables of the power subnetwork, as the inductance. In other words, the inductance is then formed by the lines, in particular the cables, of the power subnetwork.

[0011] For charging, energy is drawn from the land-side energy storage and transmitted to the energy storage of the onboard component network using DC voltage and DC current. Therefore, at the land-side charging station, the land-side power converter only needs to be designed for transmitting energy from the energy supply network to charge the land-side energy storage. The power required for this is significantly lower than the charging power used to charge the vehicle. Since the land-side DC voltage interface for transmitting electrical energy to the onboard component network is located between the land-side power converter and the land-side energy storage, no current flows through the land-side power converter during charging. On the one hand, this saves electrical losses, and on the other hand, the land-side power converter can be designed to be significantly less powerful and more cost-effective, since it is used for the weak network at the land-side charging station, where high power is not available.

[0012] The land-side power converter therefore only needs to be designed for a small charging circuit for a weak land network and does not need to be designed for high discharge currents for rapid charging of vehicle batteries, as in previously known applications.

[0013] When a DC voltage is applied, a DC current is transmitted from the DC voltage interface on the land side to the DC voltage interface of the onboard subsystem. This DC voltage interface is connected to the energy network of the onboard subsystem. This energy network can be operated as a DC voltage network or an AC voltage network using a power converter. To this end, the power converter operates as a DC / DC converter during the charging process in the first case and as an AC / DC converter during stand-alone operation in the second case. Depending on the vehicle's operating type, i.e., charging or stand-alone operation, the power converter components can be operated and used differently. This dual use of existing and expensive components allows the onboard subsystem for charging to be designed particularly cost-effectively.

[0014] If the energy network is designed as a three-phase network, i.e., has three conductors, it can be operated as a three-phase AC network when it is operated as an AC network. During the charging process, if it is operated as a DC network, the DC voltage is applied between two of the three conductors.

[0015] The power converter is connected to the energy storage device on the DC voltage side, i.e., with its intermediate circuit. This can be done directly if the power converter is located in the charging device. Alternatively, the power converter can also be connected to the energy storage device on the DC voltage side, for example, via a DC voltage regulator, i.e., a step-down converter, or via the charging device (if the power converter is located outside the charging device).

[0016] In one advantageous embodiment of the present invention, the power converter is provided in the charging device. The power converter, which switches between operating as a DC / DC converter and an AC / DC converter, can be formed by the power converter in the charging device. The charging device is then connected directly to the DC voltage interface of the onboard power supply subsystem via the energy grid. If the voltage of the land-side energy storage is lower than that of the onboard power supply subsystem, the power converter in the charging device can control or regulate the charging process.

[0017] In another advantageous embodiment of the present invention, a buck converter is arranged in the intermediate circuit of the power converter in the charging device, so that the buck converter converts the voltage applied to the intermediate circuit to a lower voltage at the energy storage. In this embodiment, energy flow between the land-side energy storage and the energy storage of the onboard component network can be performed independently of the voltage level of the respective energy storage. This means that the voltage of the land-side energy storage can be lower, equal to, or higher than the voltage of the energy storage of the onboard component network. This arrangement provides the greatest possible flexibility and allows charging of the energy storage at all charging stations with DC voltage transmission using the onboard component network, independent of the voltage level of the land-side energy storage.

[0018] In another advantageous embodiment of the present invention, the onboard subsystem includes an inverter for feeding the drive motor, wherein the power converter is formed by the inverter. Since the drive motor is typically not running during charging, the inverter serves as a power converter for charging and is used to control the charging. The inverter can also be used to control the energy flow, thereby effectively utilizing components already present in the vehicle. The electrical connection between the inverter and the drive motor is advantageously disconnected, for example, by means of a motor switch, which can be designed, for example, as a mechanical switch, contactor, or disconnector.

[0019] In another advantageous embodiment of the present invention, the charging device includes a DC converter. Using a DC converter also allows, in this embodiment, the energy flow between the land-side energy storage and the energy storage of the onboard component network to be independent of the voltage level of the respective energy storage. This means that the voltage of the land-side energy storage can be lower, equal to, or higher than the voltage of the energy storage of the onboard component network. This embodiment also provides the greatest possible flexibility and allows the energy storage to be charged at all charging stations with DC voltage transmission via the onboard component network, independent of the voltage level of the land-side energy storage.

[0020] In this case, the energy flow for charging the energy storage device can be regulated or controlled by an inverter as a power converter or by a DC converter of the charging device.

[0021] In this case, the DC converter can be designed as a step-up regulator, a step-down converter, or a combination of a step-up and step-down converter.

[0022] In another advantageous embodiment of the present invention, the onboard power subsystem includes a power rectifier, which together with the inverter forms a frequency converter for feeding the drive motor, wherein the power rectifier forms a switching device. If the power rectifier is equipped with switchable semiconductors, a separate switch as a switching device can be dispensed with. This embodiment also eliminates the need for additional components for implementing the switching device by using already existing components of the onboard power subsystem for charging. This allows the onboard power subsystem to operate particularly efficiently and be manufactured cost-effectively.

[0023] In this case, the power rectifier can separate the onboard network interface and the energy subsystem from one another and connect them to one another via the function of the AC / DC converter and exchange current between the energy subsystem and the onboard network interface.

[0024] In another advantageous embodiment of the present invention, an onboard network power converter is provided between the energy subnetwork and the onboard network interface. During the charging process, the vehicle's electrical components are supplied with electrical energy from the energy subnetwork using the onboard network power converter. To ensure that the onboard network is also supplied with electrical energy during the charging process even when the switching device is disconnected, the onboard network power converter can be integrated into the onboard network subnetwork. This allows the electrical components to be supplied with energy via a land-based charging station. Additional energy sources or energy storage devices, such as additional batteries or diesel generators, can be omitted for supplying the vehicle's electrical components.

[0025] In another advantageous embodiment of the present invention, the vehicle has at least two onboard sub-networks, wherein the onboard sub-networks are electrically connected to each other at the onboard network interface and at the DC voltage interface. Precisely for vehicles, especially for water vehicles, redundant energy supply from energy storage and charging of the energy storage are very important in order to ensure high availability and high reliability of the vehicle. Precisely for water vehicles, this is particularly advantageous for safe operation. Two or more onboard sub-networks can be provided in a simple manner to redundantly supply power to the electrical components of the vehicle and charge the energy storage. In this case, the individual components of the corresponding onboard sub-networks, such as power converters and energy storages, can then also be designed smaller. In the example of two onboard sub-networks, the power converters and energy storages can, for example, be configured at half the power. If the first of the two onboard sub-networks fails, the energy storage of the second onboard sub-network can still be charged and the operation of the vehicle can be ensured by supplying power to the electrical components. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The present invention will be described and explained in more detail below based on the embodiments shown in the accompanying drawings.

[0027] Figure 1 A first embodiment of a charging system is shown,

[0028] Figure 2 A second embodiment of a charging system is shown,

[0029] Figure 3 A charging device having a power converter and a buck converter is shown, and

[0030] Figure 4 A vessel is shown with redundant sub-onboard networks. DETAILED DESCRIPTION

[0031] Figure 1A first embodiment of a charging system 40 is shown. The charging system 40 includes an onboard power subsystem 1 and a land-side charging station 20. The land-side charging station 20 has a land-side power converter 22 and a land-side energy storage 21. Since the land-side energy storage 21 has a DC voltage at its interface, the network voltage of the energy supply network 23 used to charge the land-side energy storage 21 is converted to a DC voltage by means of the land-side energy storage 22. The land-side energy storage 21 is used to reduce the load on the energy supply network 23 when charging a vehicle 30 (not shown here). To avoid having to draw the entire charging power from the energy supply network 23, energy is temporarily stored in the land-side energy storage 21. A branch to the land-side DC voltage interface 24 is provided in the DC voltage connection between the land-side power converter 22 and the land-side energy storage 21. This branch is configured to connect to the DC voltage interface 4 of the onboard power subsystem of the vehicle 30. During charging, all or at least a large portion of the energy is drawn from the land-side energy storage 21 to keep the current in the energy supply network 23 low, i.e., within a predefined limit value. This is advantageous particularly in the case of weak grids, as is common near the coast or at other ship mooring locations, since feedback effects on the energy supply grid 23, such as voltage dips, can thereby be avoided.

[0032] The onboard subnetwork 1 has an energy storage 2, which can be charged by a charging station 20 on the land side. For this purpose, the onboard subnetwork 1 is connected at its DC voltage interface 4 to a DC voltage interface 24 on the land side. The DC voltage interface 4 is connected to an energy subnetwork 5. In this case, the energy subnetwork 5 can be designed as a bus, for example. A power converter 8 is arranged between the energy subnetwork 5 and the energy storage 2. The power converter 8 is connected to the energy subnetwork 5 on the AC voltage side and to the energy storage 2 on the DC voltage side. During the charging process, the energy subnetwork 5 is operated as a DC voltage network and the power converter 8 controls or regulates the charging process of the energy storage 2. In the embodiment described, the power converter 8 is part of the charging device 7. In this case, the energy storage 2 can be connected directly to the intermediate circuit of the power converter 8. Alternatively, it is also possible to arrange other components, such as a step-down converter, between the intermediate circuit of the power converter 8 and the energy storage 2. This arrangement is described below. Figure 3 Described and explained in more detail in .

[0033] In order to operate the energy subnetwork 5 as a DC voltage network, a switching device 6 is provided between the onboard network interface 3 and the energy subnetwork 5. The switching device electrically separates the onboard network interface 3 and the energy subnetwork 5 from each other, for example, by means of a switch. Since the AC voltage for supplying the electrical components 31 of the vehicle 30 is applied to the onboard network interface 3, it is also possible for the switching device 6 to be designed as a further power converter that can establish an energy exchange between the onboard network interface 3 with AC current and the energy subnetwork 5 with DC current by operating the further power converter as an AC / DC converter.

[0034] The power converter 8 is controlled or regulated by means of a regulating device 9. The regulating device 9 can be, for example, part of the charging device 7 or, as shown, can also be arranged outside the charging device 7.

[0035] If the switchgear 6 is designed as a switch and isolates the onboard network interface 3 from the energy subnetwork 5 during the charging process, it has proven advantageous to provide an onboard network power converter 17 between the energy subnetwork 5 and the onboard network interface 3, which supplies electrical energy to the electrical components 31 of the vehicle 30 during the charging process. This makes it possible to dispense with an energy source, such as a diesel generator in a ship, or other energy storage devices, since the energy supply can then be provided from a land-based charging station via the energy subnetwork 5.

[0036] During the charging process, the energy subsystem 5 operates as a DC voltage network. In stand-alone operation, i.e., outside the charging process, the energy subsystem 5 operates as an AC voltage network, which supplies electrical energy from the energy storage 2 via the power converter 8 to the electrical components 31 of the vehicle 30.

[0037] Figure 2 Another embodiment of the charging system 40 is shown. To avoid repetition, reference is made to Figure 1The description and reference numerals used therein are omitted. In the exemplary embodiment described, the power converter 8 is not formed by the charging device 7, but rather by the drive system of the vehicle 30. The drive system includes a power rectifier 15 and an inverter 12 for feeding the drive motor 13. The power rectifier 15 and the inverter 12 form a frequency converter 16. The power converter 8 is formed by the inverter 12. To avoid current flow and the resulting losses in the drive motor 13, the drive motor 13 is disconnected from the energy subgrid 5 by means of a motor switch 18 during the charging process. However, since the vehicle 30 is not driven during the charging process, this is not a disadvantage but an advantage, as the inverter 12 can advantageously be used to charge the vehicle 30 during charging. In the exemplary embodiment described, the energy storage 2 is provided via the charging device 7 with the intermediate circuit of the frequency converter 16, that is, at the connection between the inverter 12 and the power rectifier 15. The charging process can be controlled or regulated by either the power converter 8 or the charging device 7.

[0038] In this embodiment, the switching device 6 is formed by a power rectifier 15. This power rectifier can disconnect the onboard network interface 3 from the energy subnetwork 5 or, if the power rectifier 15 has switchable semiconductors, connect the AC voltage of the onboard network interface 3 to the DC voltage of the energy subnetwork 5 and ensure energy transmission between these points. In this embodiment, the energy subnetwork 5 also operates as a DC voltage network during the charging process and as an AC voltage network in stand-alone operation. By using the power rectifier 15 as a switching device, the onboard network converter 17 is not required if the power rectifier 15 has switchable semiconductors, so it is not shown in this embodiment. Optionally, in this embodiment, the onboard network converter 17 can also be inserted between the energy subnetwork 5 and the onboard network interface 3 to supply energy to the electrical components 31 from the energy subnetwork 5 during the charging process.

[0039] Figure 3 An embodiment of a charging device 7 is shown, which has a power converter 8 and a step-down converter 10 connected thereto on the DC voltage side. The charging device 7 is capable of Figure 1 In order to be able to charge the energy store 2 independently of the voltage level at the DC voltage connection 4 .

[0040] Figure 4 A vehicle 30 is shown, which in this exemplary embodiment is designed as a water vehicle. For redundancy reasons, vehicle 30 has two onboard power subsystems 1, whose DC voltage interfaces 4 are connected to a charging interface 32. Likewise, electrical components 31 of the vehicle can be supplied with power, for example, from both onboard power subsystems 1, since onboard power interface 3 is arranged in parallel and thus connected to one another.

[0041] In summary, the present invention relates to an onboard subsystem for a vehicle, in particular a water vehicle, wherein the onboard subsystem comprises at least one energy storage device and a control device for charging the vehicle's energy storage device. To improve the charging of the energy storage device, it is proposed that the onboard subsystem further comprises an onboard network interface for connecting to electrical components of the vehicle, a DC voltage interface for connecting to a land-based charging station, and an energy subnetwork, wherein a switching device is provided between the onboard network interface and the energy subnetwork, wherein a charging device is provided between the energy storage device and the energy subnetwork, wherein the DC voltage interface is electrically conductively connected to the energy subnetwork, wherein the onboard subsystem comprises at least one power converter, which is connected to the energy subnetwork on the AC voltage side and can be operated as an AC / DC converter and as a DC / DC converter, wherein the power converter is designed, by means of the control device, to operate the energy subnetwork as a DC voltage network during the charging process and as an AC voltage network during independent vehicle operation. The present invention also relates to a vehicle having such an onboard subsystem, a land-based charging station, and a charging system. The invention also relates to a method for operating such an onboard partial network or such a vehicle or such a charging system, wherein the power converter is operated as a DC / DC converter during the charging process and as an AC / DC converter during stand-alone operation.

Claims

1. A sub-onboard network (1) for a vehicle (30), wherein: The sub-onboard network (1) has - at least one energy storage device (2), a regulating device (9) for charging the energy storage device (2) of the vehicle (30), - an onboard network interface (3) for connecting to electrical components (31) of the vehicle (30), - a DC voltage interface (4) for connection to a charging station (20) on the land side and -Energy subnet (5), A switching device (6) is arranged between the onboard network interface (3) and the energy subnetwork (5), a charging device (7) is arranged between the energy storage device (2) and the energy subnetwork (5), the DC voltage interface (4) is electrically conductively connected to the energy subnetwork (5), the onboard subnetwork (1) has at least one power converter, which is connected to the energy subnetwork (5) on the AC voltage side and can be operated as an AC / DC converter and as a DC / DC converter, the power converter being designed with the aid of the regulating device (9) to operate the energy subnetwork (5) as a DC voltage network during the charging process and as an AC voltage network during the independent operation of the vehicle (30).

2. The sub-onboard network (1) according to claim 1, wherein: The vehicle is a water vehicle.

3. The sub-onboard network (1) according to claim 1, wherein: An AC voltage for supplying the electrical components (31) of the vehicle (30) is provided at the onboard network interface (3).

4. The onboard sub-network (1) according to any one of claims 1 to 3, wherein: The power converter is arranged in the charging device (7).

5. The sub-onboard network (1) according to claim 4, wherein: In the charging device (7), a buck converter (10) is arranged at the intermediate circuit (11) of the power converter, so that the buck converter (10) converts the voltage applied to the intermediate circuit (11) into a lower voltage at the energy storage (2).

6. The onboard sub-network (1) according to any one of claims 1 to 3, wherein: The onboard subsystem (1) has an inverter (12) for feeding a drive motor (13), wherein the power converter is formed by the inverter (12).

7. The sub-onboard network (1) according to claim 6, wherein: The charging device (7) has a DC converter (14).

8. The sub-onboard network (1) according to claim 6, wherein: The onboard subsystem (1) has a power rectifier (15), which together with the inverter (12) forms a frequency converter (16) for feeding the drive motor (13), wherein the power rectifier (15) forms the switching device (6).

9. The onboard sub-network (1) according to any one of claims 1 to 3, wherein: An onboard network power converter (17) is arranged between the energy subnetwork (5) and the onboard network interface (3).

10. A vehicle (30) having at least one onboard component network (1) according to any one of claims 1 to 9.

11. The vehicle (30) according to claim 10, wherein The vehicle is a water vehicle.

12. A vehicle (30) according to claim 10 or 11, wherein The vehicle (30) has at least two onboard power subsystems (1), wherein the onboard power subsystems (1) are electrically connected to one another at the onboard power supply interface (3) and at the DC voltage interface (4).

13. A land-side charging station (20) having - Energy storage on the land side (21) and - Power converter on the land side, in, A land-side DC voltage interface (24) for connection to a DC voltage interface (4) of a sub-onboard network (1) according to any one of claims 1 to 9 or a vehicle (30) according to any one of claims 10 to 12 is arranged in the electrical connection between the land-side energy storage (21) and the land-side power converter, wherein the power that can be transmitted via the land-side power converter is less than the continuous power that can be transmitted via the land-side DC voltage interface (24).

14. A charging system (40) having - a sub-onboard network (1) according to any one of claims 1 to 9 or a vehicle (30) according to any one of claims 10 to 12, and - a land-side charging station (20) according to claim 13, in, The DC voltage interface (24) on the land side of the charging station (20) is electrically connected to the DC voltage interface (4) of the sub-onboard network (1).

15. A method for operating an onboard subnetwork (1) according to any one of claims 1 to 9, a vehicle (30) according to any one of claims 10 to 12, or a charging system (40) according to claim 14, wherein: The power converter operates as a DC / DC converter during the charging process and as an AC / DC converter during standalone operation.

16. The method according to claim 15, wherein The power transmitted by the land-side charging station (20) is regulated by means of the power converter and the step-down converter (10) or by means of the power converter and the DC converter (14), wherein the step-down converter (10) is arranged in the charging device (7) at the intermediate circuit (11) of the power converter so that the step-down converter (10) converts the voltage applied to the intermediate circuit (11) into a lower voltage at the energy storage (2), and wherein the charging device (7) has the DC converter (14).

17. The method according to claim 15 or 16, wherein The switching device (6) is opened during the charging process.

18. The method according to claim 15 or 16, wherein During the charging process, electrical components (31) of the vehicle (30) are supplied with electrical energy from an energy subnetwork (5) by means of an onboard network power converter (17), wherein the onboard network power converter (17) is arranged between the energy subnetwork (5) and the onboard network interface (3).

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