Method for electrically connecting a first three-conductor DC voltage system of an electrically powered motor vehicle and a second three-conductor DC voltage system, computer program and / or computer-readable medium, control unit and motor vehicle

Abstract

Method (100) for electrically connecting a first three-conductor DC system (221, 222, 400) of an electrically powered motor vehicle (200) and a second three-conductor DC system (301) comprising (321, 322, 400), wherein the method (100) comprises: detecting (110) a first y-voltage (211) of the first DC system (201) between a first conductor (221) of the first DC system (201) and a protective conductor (400) and a first y-voltage (311) of the second DC system (301) between a first conductor (321) of the second DC system (301) and the protective conductor (400); Determine (120) a first voltage difference (411) between the first y-voltage (211) of the first DC voltage system (201) and the first y-voltage (311) of the second DC voltage system (301);and output (130) of a first closing signal (251) for closing a first switching device (231) of the motor vehicle (200) for electrically connecting the first conductor (221) of the first DC voltage system (201) with the first conductor (321) of the second DC voltage system (301) depending on a first threshold condition relating to the first voltage difference (411).

Description

[0001] The present disclosure relates to a method for electrically connecting a first three-conductor DC voltage system of an electrically driven motor vehicle and a second three-conductor DC voltage system, and to a control unit configured to at least partially carry out the method. Furthermore, a motor vehicle having the control unit is provided. Additionally or alternatively, a computer program is provided comprising instructions which, when executed by a computer, cause the computer to at least partially carry out the method. Additionally or alternatively, a computer-readable medium is provided comprising instructions which, when executed by a computer, cause the computer to at least partially carry out the method.

[0002] A particular application of the disclosure may be an electrical connection of an electrically powered motor vehicle and an off-board charging station for a direct current charging process. The off-board charging station is and / or comprises the second direct current system.

[0003] An energy storage device of an electrically powered motor vehicle, also called an electric vehicle or BEV (battery electric vehicle), including a plug-in hybrid electric vehicle, which draws all or part of its energy from the energy storage device or vehicle batteries and can be charged bidirectionally at an external charging station or charging point or charging column.

[0004] The energy storage device can be charged using direct current (DC charging), whereby the energy storage device is supplied with a direct current by the charging station to charge the energy storage device and increase its state of charge and / or to discharge it and decrease its state of charge during so-called bidirectional charging. Direct current charging is often used for charging at higher charging power levels, known as fast charging.

[0005] An electrical connection between the motor vehicle and the charging station is regulated, for example, in the 2020 standard "Electrically propelled road vehicles - Wired power transmission - Safety requirements," DIN EN ISO 17409:2020-10. This standard specifies electrical safety requirements for a wired connection of electrically propelled road vehicles to an external electrical circuit. External electrical circuits include external electrical power supplies and external electrical charges. This includes the charging station.

[0006] The vehicle and the charging station each represent a separate IT system or network. This can lead to a ground offset, for example, in the case of insulation asymmetries.

[0007] During a charging process, a plug connection ultimately establishes mechanical and electrical contact between the vehicle and the charging station. Protective earth, as the reference potential, is typically connected first.

[0008] Since the vehicle and the charging station are connected via three conductors, different y-voltages arise due to the insulation asymmetries. The y-voltages, or common-mode voltages, are defined by a positive potential and a protective conductor or equipotential bonding conductor, as well as by a negative potential and the protective conductor. Different y-voltages can occur on the charging station and vehicle sides.

[0009] Before charging begins, a differential voltage, also called x-voltage, is determined on the vehicle side between the positive and negative potentials on the vehicle side—that is, a voltage between the two high-voltage potentials. The charging station adjusts to the charging station's differential voltage according to the vehicle's differential voltage (so-called pre-charging).

[0010] The motor vehicle includes two contactors as switching devices for electrically connecting the motor vehicle and the charging station. It is known that the connection between the charging station and the motor vehicle is established independently of the applied y-voltages, i.e., solely by the equalization of the x-voltage achieved by closing the contactors or charging contactors.

[0011] The connection thus achieved between the charging station and the vehicle for charging by means of the contactors leads to a significant inrush current in the event of significant y-voltage differences (ground offset), which can cause the contactors to age.

[0012] Other applications are also conceivable. For example, both DC voltage systems can be integrated into the motor vehicle. One application for this is connecting the motor vehicle to an AC power source, such as an AC charging station. For this purpose, the motor vehicle has a voltage converter (AC / DC voltage converter) that is supplied with an AC voltage and can output a DC current on the output side as a second DC voltage system.

[0013] Against the background of this prior art, the object of the present disclosure is to provide an improved method suitable for enriching the prior art. A specific embodiment of the disclosure can solve the problem of providing an intelligent electrical connection strategy with which less wear on the switching device can be achieved.

[0014] The problem is solved by the features of the independent claim. The subclaims contain optional developments of the disclosure.

[0015] The object is then achieved by a method for electrically connecting a first three-conductor DC voltage system of an electrically driven motor vehicle and a second three-conductor DC voltage system.The method comprises: detecting a first y-voltage of the first DC voltage system between a first conductor of the first DC voltage system and a protective conductor and a first y-voltage of the second DC voltage system between a first conductor of the second DC voltage system and the protective conductor; determining a first voltage difference between the first y-voltage of the first DC voltage system and the first y-voltage of the second DC voltage system; and outputting a first closing signal for closing a first switching device of the motor vehicle for electrically connecting the first conductor of the first DC voltage system to the first conductor of the second DC voltage system as a function of a first threshold condition relating to the first voltage difference.

[0016] It was recognized that inrush currents can be significantly reduced if a different criterion than that known in the prior art is used to close the switching devices or contactors. In this case, a y-voltage-based closing criterion can be used instead of the purely x-voltage-based closing criterion. Accordingly, the y-voltages can be considered. It was recognized that high inrush currents can result from asymmetrical y-voltages. During the course of increasing the voltage in the charging station, the so-called pre-charging, a point in time can always be reached in which the voltage across one of the two switching devices satisfies the threshold condition, for example, is below a voltage threshold. If the first switching device is closed at this point in time, low-load or completely load-free switching can take place, thus reducing wear.

[0017] The first closing signal can be output when the first voltage difference is less than or equal to 20 V. This ensures that the first switching device is closed in a low-load state. This can result in a particularly effective reduction of wear.

[0018] The method may comprise: detecting a second y-voltage of the first DC voltage system between a second conductor of the first DC voltage system and a protective conductor and a second y-voltage of the second DC voltage system between a second conductor of the second DC voltage system and the protective conductor; determining a second voltage difference between the second y-voltage of the first DC voltage system and the second y-voltage of the second DC voltage system; and outputting a second closing signal for closing a second switching device of the motor vehicle for electrically connecting the second vehicle-side conductor to the second charging station-side conductor depending on a second threshold condition relating to the second voltage difference.

[0019] It was discovered that the second switching device, which is necessary to close the DC charging circuit, can be closed even at a lower voltage in the x and y directions than with the purely x-voltage-based criterion. When a switching device or contactor is closed, the voltage across the second switching device or contactor is always equal to the difference between the x voltages and, at the same time, the difference between the y voltages. Due to the lower y voltage adjustment when closing the second switching device, the second switching device also experiences significantly less aging due to the greatly reduced inrush current.

[0020] The second closing signal can be output when the second voltage difference is less than or equal to 20 V. This ensures that the second switching device is closed in a low-load state. This allows for a particularly effective reduction in wear.

[0021] The second closing signal can be output such that the first switching device connects the first conductor of the first DC voltage system to the first conductor of the second DC voltage system at a first point in time, and the second switching device connects the second conductor of the first DC voltage system to the second conductor of the second DC voltage system at a second point in time independent of the first point in time. The method can thus be effectively implemented in the case of asymmetric potentials in the motor vehicle or charging station, i.e., a ground offset. In the case of a ground offset, first one of the voltage differences becomes zero, and later the other of the voltage differences becomes zero. Accordingly, the first point in time and the second point in time are separated.

[0022] In other words, the above description can be summarized as follows, with reference to a specific embodiment that is described as non-limiting to the present disclosure: The disclosure relates to an intelligent, low-wear contactor closing strategy for the DC charging of electric vehicles. The basic idea is an intelligent contactor closing strategy that uses two y-voltage-based (common mode) closing criteria instead of the purely x-voltage-based (differential mode). As the voltage in the charging station ramps up, a point in time is always reached at which the voltage across one of the two contactors experiences a zero crossing (or is below a threshold value). If a first contactor is closed at this point in time (completely load-free and wear-free switching), a load-free y-voltage equalization takes place between the vehicle and the charging station.A second contactor (necessary to close the DC charging circuit) thus closes at a lower voltage in the x- and y-direction than with the purely x-voltage-based criterion (a maximum of 20V according to the aforementioned DIN EN ISO 17409). Due to the lower y-voltage adjustment when closing the second contactor, it also experiences significantly less aging due to an inrush current determined by simulations.

[0023] Furthermore, a computer program is provided, comprising instructions which, when the program is executed by a computer, cause the computer to at least partially carry out or implement the method described above.

[0024] A program code of the computer program may be in any code, in particular in a code suitable for motor vehicle controls.

[0025] What has been described above with reference to the method also applies analogously to the computer program and vice versa.

[0026] Furthermore, a control unit for a motor vehicle is provided, wherein the control unit is configured to at least partially execute or perform the method described above. Thus, the method is a computer-implemented method.

[0027] The control unit can, for example, be comprised of a battery management unit (BMU). The control unit can be an electronic control unit (ECU). The control unit can be an intelligent processor-controlled unit that can communicate with other modules, for example, via a central gateway (CGW), and that can, if necessary, form the vehicle's on-board network via fieldbuses such as the CAN bus, LIN bus, MOST bus, and FlexRay, or via automotive Ethernet, for example, together with telematics control units. It is conceivable that the control unit controls functions relevant to the driving behavior of the motor vehicle, such as engine management, power transmission, and / or regulates a charging process.

[0028] What has been described above with reference to the method and the computer program also applies analogously to the control unit and vice versa.

[0029] Furthermore, a motor vehicle comprising the control device described above is provided.

[0030] The motor vehicle may be a passenger car, in particular an automobile. The optionally automated motor vehicle may be an electrically powered motor vehicle. The motor vehicle may include an electric drive that can be powered by electrical energy provided by the energy storage device to drive the motor vehicle.

[0031] What has been described above with reference to the method, the control unit, the battery control unit and the computer program also applies analogously to the motor vehicle and vice versa.

[0032] Furthermore, a computer-readable medium, in particular a computer-readable storage medium, is provided. The computer-readable medium comprises instructions that, when the program is executed by a computer, cause the computer to at least partially execute the method described above.

[0033] This means that a computer-readable medium can be provided that contains a computer program as defined above. The computer-readable medium can be any digital data storage device, such as a USB stick, a hard drive, a CD-ROM, an SD card, or an SSD card. The computer program does not necessarily have to be stored on such a computer-readable storage medium to be provided to the motor vehicle; it can also be obtained externally via the Internet or otherwise.

[0034] What has been described above with reference to the method, the control unit, the computer program and the automated motor vehicle also applies analogously to the computer-readable medium and vice versa.

[0035] An embodiment is described below with reference to the figures. Fig. 1 schematically shows a motor vehicle according to one aspect of the disclosure; Fig. 2 schematically shows voltages and a current as a function of time when electrically connecting an electrically driven motor vehicle and an external vehicle charging station for a direct current charging process according to the prior art; Fig. 3 schematically shows voltages and a current, each as a function of time, during an electrical connection of an electrically driven motor vehicle and an off-board charging station for a direct current charging process according to an example of a method according to one aspect of the disclosure; Fig. 4 schematically shows voltages and a current, each as a function of time, during an electrical connection of an electrically driven motor vehicle and a vehicle-external charging station for a direct current charging process according to an example of a method according to one aspect of the disclosure; and Fig. 5 is a flowchart of a method according to one aspect of the disclosure.

[0036] Fig. 1 schematically shows a motor vehicle 200 according to one aspect of the disclosure.

[0037] The motor vehicle 200 is an electrically driven motor vehicle 200. For this purpose, the motor vehicle 200 has an electric drive (not shown) and an energy storage device 205. The electric drive can be supplied with electrical energy by the energy storage device 205, which the electric drive can convert into mechanical energy and vice versa. In the process, the charge level of the energy storage device 205 decreases. The motor vehicle 201 has a first DC voltage system 201 comprising three conductors 221, 222, 400.

[0038] Motor vehicle 200 is configured to be charged at an off-board charging station 300 using a direct current (DC). This means that, through an electrical connection between motor vehicle 200 and charging station 300, energy storage device 205 can be supplied with electrical energy to increase or decrease the state of charge of energy storage device 205 during bidirectional charging. Charging station 300 has a second DC voltage system 301 comprising three conductors 321, 322, 400.

[0039] To connect the motor vehicle 200 to the charging station 300, the motor vehicle 200 and the charging station 300 are configured to establish a plug connection 500 between the motor vehicle 200 and the charging station 300. In this case, the first DC voltage system 201 and the second DC voltage system 301 are electrically connected to one another. For this purpose, the motor vehicle 200 has, for example, a charging socket or charging receptacle, and the charging station 300 has a plug (not shown).

[0040] The charging station 300 is shown schematically and comprises three electrical conductors 321, 322, 400: a protective conductor 400 and a potential equalization conductor, respectively, and, each shown with a dot-dashed line, a first conductor 321 of the second DC voltage system 301 and a second charging station-side conductor 322 of the second DC voltage system 301. In addition, the charging station 300 can comprise electrical resistors and / or capacitances or capacitors, not shown, arranged between the first conductor 321 of the second DC voltage system 301 and the second conductor 322 of the second DC voltage system 301, between the first conductor 321 of the second DC voltage system 301 and the protective conductor 400 and / or between the second conductor 322 of the second DC voltage system 301 and the protective conductor 400.

[0041] An x-voltage 340 of the second DC voltage system 301 is present between the first conductor 321 of the second DC voltage system 301 and the second conductor 322 of the second DC voltage system 301. A first y-voltage 311 of the second DC voltage system 301 is present between the first conductor 321 of the second DC voltage system 301 and the protective conductor 400. A second y-voltage 312 of the second DC voltage system 301 is present between the second conductor 322 of the second DC voltage system 301 and the protective conductor 400. For example, the first conductor 321 of the second DC voltage system 301 carries a positive potential (DC+ conductor) and the second conductor 322 of the second DC voltage system 301 carries a negative potential (DC- conductor).

[0042] The motor vehicle 200 is also shown schematically and comprises three electrical conductors 221, 222, 400: the protective conductor 400, and a first conductor 221 of the first DC voltage system 201 and a second conductor 222 of the first DC voltage system 201. In addition, the motor vehicle 200 can comprise electrical resistors and / or capacitances or capacitors, not shown, arranged between the first conductor 221 of the first DC voltage system 201 and the second conductor 222 of the first DC voltage system 201, between the first conductor 221 of the first DC voltage system 201 and the protective conductor 400 and / or between the second conductor 222 of the first DC voltage system 201 and the protective conductor 400.

[0043] An x-voltage 240 of the first DC voltage system 201 is present between the first conductor 221 of the first DC voltage system 201 and the second conductor 222 of the first DC voltage system 201. A first y-voltage 211 of the first DC voltage system 201 is present between the first conductor 221 of the first DC voltage system 201 and the protective conductor 400. A second y-voltage 212 of the first DC voltage system 201 is present between the second conductor 322 of the first DC voltage system 201 and the protective conductor 400. For example, the first conductor 221 of the first DC voltage system 201 carries a positive potential (DC+ conductor) and the second conductor 222 of the first DC voltage system 201 carries a negative potential (DC- conductor).

[0044] The motor vehicle 200 has a control unit 250. The control unit 250 or the motor vehicle 200 is configured to control the Fig. 5. For this purpose, the motor vehicle 200 has Fig. 1 has a first switching device 231 and a second switching device 232.

[0045] When the plug connection 500 is established, the first switching device 231 and the second switching device 232 are each open, i.e., there is no electrical connection between the charging station 300 and the energy storage device 205. The protective conductor 400 can connect the motor vehicle 200 and the charging station 300 to one another.

[0046] The control unit 250 is configured to apply a first closing signal 251 to the first switching device 231 in order to close the first switching device 231 and thus establish an electrical connection between the first conductor 321 of the second DC voltage system 301 and the first conductor 221 of the first DC voltage system 201 and thus electrically connect the charging station 300 and the energy storage device 205 via the first conductor 321 of the second DC voltage system 301 and the first conductor 221 of the first DC voltage system 201.

[0047] The control unit 250 is configured to apply a second closing signal 252 to the second switching device 232 in order to close the second switching device 232 and thus establish an electrical connection between the second conductor 322 of the second DC voltage system 301 and the second conductor 222 of the first DC voltage system 201 and thus electrically connect the charging station 300 and the energy storage device 205 via the second conductor 322 of the second DC voltage system 301 and the second conductor 222 of the first DC voltage system 201.

[0048] When both switching devices 231, 232 are closed, the energy storage device 205 can be charged or discharged by means of the charging station 300. The closing of the switching devices 231, 232 takes place after a pre-charging process (“pre-charging”), in which from a pre-charging time tp (see Fig. 2 to 4) the charging station-side voltage, i.e. the x-voltage 340 of the second DC voltage system 301, the first y-voltage 311 of the second DC voltage system 301 and / or the second y-voltage 312 of the second DC voltage system 301, are increased.

[0049] The times at which the switching devices 231, 232 are closed to electrically connect the charging station-side conductors 321, 322 to the vehicle-side conductors 221, 222 are relevant for the durability of the switching devices 231, 232. The closing of the switching devices 231, 232 according to the prior art is described with reference to Fig. 2. The closing of the switching devices 231, 232 according to the disclosure is described with reference to Fig. 3 and Fig. 4 described.

[0050] Fig. 2 schematically shows voltages 211, 311, 212, 312, 600 and a current 601, each as a function of time t, during an electrical connection of an electrically driven motor vehicle 200 and a vehicle-external charging station 300 for a direct current charging process according to the prior art. Fig. 2 is made with reference to Fig. 1 described.

[0051] Fig. 2 (A) shows the first y-voltage 211 of the first DC voltage system 201 and the first y-voltage 311 of the second DC voltage system 301, for example, each a positive potential. Fig. 2 (B) shows the second y-voltage 212 of the first DC voltage system 201 and the second voltage 312 of the second DC voltage system 301, for example a negative and a positive potential.

[0052] The first switching device 231 is closed at a first time t1, and the second switching device 232 is closed at a second time t2, at the same time t. The first time t1 is thus equal to the second time t2. The switching devices 231, 232 are closed when the x-voltage 340 of the second DC voltage system 301 is equal to the x-voltage 240 of the first DC voltage system 201.

[0053] By referring to Fig. 1 described resistive and / or capacitive connections between the conductors 221, 222, 321, 322, however, peaks in a voltage 600, for example related to conductors 221, 321 around the first switching device 231, may occur as in Fig. 2 (C). This causes inrush currents, which result in a peak of a current 601 through the or one of the switching devices 231, 232, see Fig. 2 (D). The reason for this is the high differences in the common-mode voltages, i.e., the y-voltages 211, 212, 311, 312 at the switching devices 231, 232, or a ground offset when closing the electrical connection.

[0054] Fig. 3 schematically shows voltages 211, 311, 212, 312 and a current 601, each as a function of time t, during an electrical connection of an electrically driven motor vehicle 200 and a vehicle-external charging station 300 for a direct current charging process according to an example of a method according to one aspect of the disclosure. Fig. 3 is made with reference to Fig. 1 described.

[0055] Fig. 3 (A) shows the first y-voltage 211 of the first DC voltage system 201 and the first y-voltage 311 of the second DC voltage system 301, for example, each a positive potential. Fig. 3 (B) shows the second y-voltage 212 of the first DC voltage system 201 and the second y-voltage 312 of the second DC voltage system 301, for example, each a negative potential.

[0056] According to Fig. 3, the switching devices 231, 232 are closed according to one of Fig. 2 different criteria. The closing of the switching devices 231, 232 and thus the connection of the vehicle-side conductors 221, 222 with the charging station-side conductors 321, 322 takes place with regard to the y-voltages 211, 212, 311, 212; thus not with regard to the x-voltages 240, 340.

[0057] Thus, the first y-voltage 211 of the first DC voltage system 201 between the first conductor 221 of the first DC voltage system 201 and the protective conductor 400 and the first y-voltage 311 between the first conductor 321 of the second DC voltage system 301 and the protective conductor 400 are detected. From this, the first voltage difference 411 between the first y-voltage 211 of the first DC voltage system 201 and the first y-voltage 311 of the second DC voltage system 301 is determined. The second y-voltage 212 of the first DC voltage system 201 between the second conductor 222 of the first DC voltage system 201 and the protective conductor 400 and the second y-voltage 312 of the second DC voltage system 301 between the second conductor 322 of the second DC voltage system 301 and the protective conductor 400 are recorded.From this, the second voltage difference 412 between the second y-voltage 212 of the first DC voltage system 201 and the second y-voltage 312 of the second DC voltage system 301 is determined.

[0058] The first closing signal 251 is output when the first voltage difference 411 is less than or equal to 20 V. The second closing signal 252 is output when the second voltage difference 412 is less than or equal to 20 V.

[0059] In Fig. 3, accordingly, first the second voltage difference 412 is less than or equal to 20 V and initially at a second time t2 the second switching device 232 is closed. Subsequently, the first voltage difference 411 is less than or equal to 20 V and at a first time t1 the first switching device 231 is closed. The second time t2 is before the first time t1. The first closing signal 251 and the second closing signal 252 are output such that the first switching device 231 connects the first conductor 221 of the first DC voltage system 201 to the first conductor 321 of the second DC voltage system 301 at a first time t1 and the second switching device 232 connects the second conductor 222 of the first DC voltage system 201 to the second conductor 322 of the second DC voltage system 301 at a second time t2 different from the time t1.

[0060] There are hardly any inrush currents when the second switching device 232 is closed, see Fig. 3 (C), since the common mode voltage of the charging station 300 and the common mode voltage of the motor vehicle 200 overlap.

[0061] Fig. 4 schematically shows voltages 211, 311, 212, 312 and a current 601, each as a function of time t, during an electrical connection of an electrically driven motor vehicle 200 and a vehicle-external charging station 300 for a direct current charging process according to an example of a method according to one aspect of the disclosure. Fig. 4 is made with reference to Fig. 3. The differences between the Fig. 3 and Fig. 4 described.

[0062] In Fig. 4, there is symmetry on the vehicle and charging station sides. Therefore, the first voltage difference 411 and the second voltage difference 412 become zero simultaneously. Thus, the first switching signal 251 and the second switching signal 252 are output simultaneously, and the switching devices 231, 232 are closed simultaneously. The first time t1 is therefore equal to the second time t2. This results in an inrush current, which, however, only leads to low currents 601, see Fig. 4 (C).

[0063] Fig. 5 shows a flow diagram of a method 100 according to one aspect of the disclosure. The method 100 is a method 100 for electrically connecting a first DC voltage system 201 comprising three conductors 221, 222, 400 of an electrically driven motor vehicle 200 and a second DC voltage system 301 comprising three conductors 321, 322, 400. Such a motor vehicle is described with reference to Fig. 1 described. Fig. 5 is made with reference to Fig. 1 to 4 described.

[0064] A first y-voltage 211 of the first DC voltage system 201 between a first conductor 221 of the first DC voltage system 201 and a protective conductor 400 and a first y-voltage 311 of the second DC voltage system 301 between a first conductor 321 of the second DC voltage system 301 and the protective conductor 400 are detected 110.

[0065] A first voltage difference 411 between the first y-voltage 211 of the first DC voltage system 201 and the first y-voltage 311 of the second DC voltage system 301 is determined 120.

[0066] A first closing signal 251 is output 130 to close a first switching device 231 of the motor vehicle 200 for electrically connecting the first conductor 221 of the first DC voltage system 201 to the first conductor 321 of the second DC voltage system 301 as a function of a first threshold condition relating to the first voltage difference 411.

[0067] The first closing signal 251 is output when the first voltage difference 411 is less than or equal to 20 V.

[0068] A second y-voltage 212 of the first DC voltage system 201 between a second conductor 222 of the first DC voltage system 201 and a protective conductor 400 and a second y-voltage 312 of the second DC voltage system 301 between a second conductor 322 of the second DC voltage system 301 and the protective conductor 400 are detected 140.

[0069] A second voltage difference 412 between the second y-voltage 212 of the first DC voltage system 201 and the second y-voltage 312 of the second DC voltage system 301 is determined 150.

[0070] A second closing signal 252 is output 160 to close a second switching device 232 of the motor vehicle 200 for electrically connecting the second vehicle-side conductor 222 to the second charging station-side conductor 322 as a function of a second threshold condition relating to the second voltage difference 412.

[0071] The second closing signal 252 is output when the second voltage difference 412 is less than or equal to 20 V.

[0072] The second closing signal 252 is output such that the first switching device 231 connects the first conductor 221 of the first DC voltage system 201 to the first conductor 321 of the second DC voltage system 301 at a first time t1, and the second switching device 232 connects the second conductor 222 of the first DC voltage system 201 to the second conductor 322 of the second DC voltage system 301 at a second time t2 independent of the first time t1. The second time t2 may be before the first time t1. List of reference symbols 100 procedures 110 Capture 120 Investigate 130 Issues 140 Capture 150 Investigate 160 Issues 200 motor vehicles 201 first direct current system 205 Energy storage device 211 first vehicle-side asymmetric voltage 212 second vehicle-side asymmetric voltage 221 first vehicle-side conductor 222 second vehicle-side conductor 231 first switching device 232 second switching device 240 x voltage of the first DC voltage system 250 control unit 251 first closing signal 252 second closing signal 300 charging stations 301 second DC voltage system 311 first y-voltage of the second DC voltage system 312 second y-voltage of the second DC voltage system 321 first conductor of the second DC voltage system 322 second conductor of the second DC voltage system 340 x voltage of the second DC voltage system 400 protective conductors 411 first voltage difference 412 second voltage difference 500 connectors 600 voltage 601 Electricity t time t1 first time point t2 second time point tp precharge time QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited non-patent literature

[0000] DIN EN ISO 17409:2020-10

[0005]

Claims

[1] Method (100) for electrically connecting a first three-conductor (221, 222, 400) DC voltage system (201) of an electrically driven motor vehicle (200) and a second three-conductor (321, 322, 400) DC voltage system (301), the method (100) comprising: - detecting (110) a first y-voltage (211) of the first DC voltage system (201) between a first conductor (221) of the first DC voltage system (201) and a protective conductor (400) and a first y-voltage (311) of the second DC voltage system (301) between a first conductor (321) of the second DC voltage system (301) and the protective conductor (400); - determining (120) a first voltage difference (411) between the first y-voltage (211) of the first DC voltage system (201) and the first y-voltage (311) of the second DC voltage system (301); and - Outputting (130) a first closing signal (251) for closing a first switching device (231) of the motor vehicle (200) for electrically connecting the first conductor (221) of the first DC voltage system (201) to the first conductor (321) of the second DC voltage system (301) as a function of a first threshold condition relating to the first voltage difference (411). [2] The method of claim 1, wherein the first closing signal (251) is output when the first voltage difference (411) is less than or equal to 20 V. [3] The method of claim 1 or 2, wherein the method (100) comprises: - detecting (140) a second y-voltage (212) of the first DC voltage system (201) between a second conductor (222) of the first DC voltage system (201) and a protective conductor (400) and a second y-voltage (312) of the second DC voltage system (301) between a second conductor (322) of the second DC voltage system (301) and the protective conductor (400); - determining (150) a second voltage difference (412) between the second y-voltage (212) of the first DC voltage system (201) and the second y-voltage (312) of the second DC voltage system (301); and - Outputting (160) a second closing signal (252) for closing a second switching device (232) of the motor vehicle (200) for electrically connecting the second vehicle-side conductor (222) to the second charging station-side conductor (322) as a function of a second threshold condition relating to the second voltage difference (412). [4] The method of claim 3, wherein the second closing signal (252) is output when the second voltage difference (412) is less than or equal to 20 V. [5] Method according to claim 3 or 4, wherein the second closing signal (252) is output such that the first switching device (231) connects the first conductor (221) of the first DC voltage system (201) to the first conductor (321) of the second DC voltage system (301) at a first time (t1) and the second switching device (232) connects the second conductor (222) of the first DC voltage system (201) to the second conductor (322) of the second DC voltage system (301) at a second time (t2) independent of the first time (t1). [6] Computer program and / or computer-readable medium comprising instructions which, when the program or instructions are executed by a computer, cause the computer to carry out the method (100) and / or the steps of the method (100) according to one of claims 1 to 5. [7] Control unit (250) for a motor vehicle (200), wherein the control unit (250) is configured to carry out the method (100) according to one of claims 1 to 5. [8] Motor vehicle (200) comprising the control device (250) according to claim 7.

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