Method and apparatus for handling fault current in high-voltage batteries

Abstract

This invention relates to a method for handling fault current in a high-voltage battery (2) connected to a charging station (3) via a charging circuit (13), wherein an electrical protection conductor connection (9) is established between a protection conductor (4a) on the charging station side and a protection conductor (4b) on the battery side, which is electrically insulated relative to a first high-voltage potential (HV+) and a second high-voltage potential (HV-) on the battery side in a fault-free state, so as to connect the protection conductor (4b) on the battery side to the ground potential (PE) on the charging station side via the protection conductor (4a) on the charging station side, so as to apply a charging voltage to the high-voltage battery (2) in an optional charging step, the charging voltage being higher than the nominal charging voltage of the charging station (3) and having been boosted by a boost converter (14) belonging to the charging circuit (13), so as to transfer electrical energy from the charging station (3) to the high-voltage battery (2). The invention further relates to a related charging circuit.

Description

Technical Field

[0001] The present invention relates to a method for handling fault current in a high-voltage battery, the high-voltage battery being electrically connected to a charging station via a charging circuit and related devices. Background Technology

[0002] Electric vehicles (EVs), such as hybrid electric vehicles (HEVs) or battery electric vehicles (BEVs), typically have high-voltage batteries (e.g., traction batteries) as energy storage units, with nominal voltages of, for example, 400V or 800V. In the present context, as is customary in the automotive industry, DC voltages greater than 60V, particularly greater than 200V, such as 400V or 800V to approximately 1500V, are understood as high voltage or high voltage potentials (also referred to herein as HV potentials). Voltages equal to or less than 60V, such as 12V, 24V, 48V, or 60V, are understood as low voltage or low voltage potentials. In connection with the invention disclosed herein, the terms “high voltage” or “low voltage” are used synonymously with the terms “high voltage potential” or “low voltage potential”, having the voltage level or range specified above.

[0003] When electric vehicles with high-voltage batteries, such as those with a nominal battery voltage of 800V, are charged at an external charging station, a lower nominal charging voltage than the nominal battery voltage is provided, i.e., less than 800V in a given example, such as 400V. A charging circuit with a boost converter, in this case a DC / DC converter, is typically used to convert the charging voltage provided by the charging station to correspond to or higher than the nominal battery voltage of the electric vehicle's high-voltage battery. For example, such a DC converter can be provided in the electric vehicle. When charging via cable, and when the high-voltage battery is electrically connected to the charging station via a charging cable without charging current, arrangements and measures for fault current protection are required according to DIN EN IEC 61851-1. Among other things, this includes establishing a conductive protective conductor connection between the protective conductor on the charging station side and the protective conductor on the battery side, which is conductively connected to the ground potential on the charging station side, so that the protective conductor on the battery side is electrically insulated from the high-voltage potential on the battery side of the high-voltage battery in a non-faulty state, and electrically insulated from the ground potential on the charging station side via the protective conductor on the charging station side. Typically, the protective conductor on the battery side is conductively connected to the vehicle body; this is known as vehicle grounding. In the event of a fault, one of the high-voltage potentials (HV+ or HV-) on the battery side is connected to the protective conductor terminal on the battery side with low resistance. This is understood as a fault condition, generating a fault current circuit through the charging connection, the charging station, and one of the common protective conductors, where the associated fault current is supplied by the high-voltage battery. Typically, this fault current causes the protective element located in the fault current circuit and positioned on the charging station side to "go out of control," resulting in the charging connection on the charging station side applying the fault current separately, and the protective conductor connection being connected with low resistance, thus short-circuiting. This causes the fault current amperes to increase, thereby exceeding the current carrying capacity of the protective conductor connection. However, in the event of contact, the application of protective conductor connections with a voltage exceeding 60 volts relative to ground can pose a considerable risk to the life and limbs of those in contact and must be avoided at all costs. Furthermore, since the wiring on the charging station side, which forms the protective conductor in a DC charging station with a lower nominal charging voltage, is not designed for this intensity of fault current, the continuous fault current causes overheating and eventually melts the protective conductor on the charging station side. This causes irreversible damage to the charging station and deprives the protective conductor of its function, resulting in a high voltage potential (HV+ or HV-) that is electrically connected to the protective conductor on the battery side. In the event of contact, this poses a danger to the life and limbs of the person in contact.Although it is known to use insulation monitoring devices, or so-called "ISO monitors," in high-voltage power grids to measure the insulation resistance between the PE (protective earth) and the high-voltage-carrying lines to ensure the safe operation of the high-voltage charging grid, where safety mechanisms interrupt current transmission, including fault current transmission, if the measured insulation resistance is too low, such as by disconnecting switches or relays, ISO monitors have a certain hysteresis due to the delay between current transmission detection and disconnection. Therefore, this measure is insufficient to ensure the required safety under the aforementioned fault conditions. Summary of the Invention

[0004] In this context, the object of the present invention is to provide a method and related charging apparatus for handling fault currents, which limits the impact of fault currents caused by the low-resistance electrical connection between the high-voltage terminals on the battery side and the protective conductor, thereby improving fault current protection, particularly when the charging station is connected to a high-voltage battery whose nominal battery voltage exceeds the nominal voltage of the charging station (especially 400V), thus improving protection for people and protection against damage to the charging station. Furthermore, the charging method and charging apparatus should be technically simple, cost-effective, and have a compact and lightweight construction.

[0005] This objective is achieved by a method and apparatus for handling fault currents in high-voltage batteries. Other particularly advantageous embodiments of the invention are disclosed in the corresponding dependent claims. It should be noted that features individually referenced in the claims can be combined with each other in any technically meaningful manner (and may cross class boundaries, such as methods and apparatus), and represent other embodiments of the invention. The invention is additionally characterized and defined in the specification, particularly in conjunction with the accompanying drawings.

[0006] It should also be noted that the conjunction “and / or” used below, which sits between two features and links them to each other, should always be interpreted as meaning that in a first embodiment of the subject matter of the invention, only the first feature may be provided, in a second embodiment, only the second feature may be provided, and in a third embodiment, both the first and second features may be provided.

[0007] Furthermore, the term "approximately" as used herein should specify a tolerance range that is considered common by those skilled in the art. In particular, the term "approximately" should be understood as a tolerance range of up to + / -20%, preferably up to + / -10%.

[0008] Relative terms related to features, such as "larger," "smaller," "higher," "lower," etc., should be interpreted within the framework of this invention as dimensional deviations of the relevant feature caused by production and / or realization, within the production / realization tolerances defined for the corresponding production or realization of the relevant feature, and are not considered relative terms. In other words, the size of a feature is considered "larger," "smaller," "higher," "lower," etc., than the size of the feature being compared, only when the two dimensions being compared differ so significantly in quantity that this dimensional difference is certainly not within the tolerances caused by the production / realization of the relevant feature, and is thus the result of targeted action.

[0009] The method according to the invention relates to the handling of fault current in a high-voltage battery connected to a charging station via a charging circuit, particularly in a motor vehicle. In the steps provided according to the invention, a high-voltage battery, for example, having a nominal battery voltage of approximately 900 volts, and an associated charging circuit are provided. For example, the high-voltage battery is not necessarily a traction battery of a motor-driven motor vehicle. Furthermore, a charging circuit is provided having at least one boost converter and is preferably located on the battery side, particularly the motor vehicle side. "Battery side" refers to the arrangement associated with the high-voltage battery, such as mechanical fixing and electrical connection.

[0010] In another step according to the invention, a charging station, preferably a DC charging station, is provided, having a nominal charging voltage lower than the nominal battery voltage, for example, about 450 volts. For example, the charging station is connected to the power grid.

[0011] According to the present invention, a connection step is provided, wherein an electrical protective conductor connection is established between a protective conductor on the charging station side and a protective conductor on the battery side, so as to connect the protective conductor on the battery side to the ground potential (also referred to as "PE" or "protective ground") on the charging station side via the protective conductor on the charging station side. The protective conductor on the charging station side and the protective conductor on the battery side form a common protective conductor connected to the ground potential on the charging station side via the protective conductor connection. In a non-fault state, the protective conductor on the battery side and the common protective conductor are electrically insulated relative to a first high voltage potential and a second high voltage potential on the battery side.

[0012] According to the present invention, another connection step is provided, which is performed almost simultaneously with the above-described connection step, to establish a charging connection, a charging connection from a first high voltage potential on the charging station side to a first high voltage potential on the battery side, and a charging connection from a second high voltage potential on the charging station side to a second high voltage potential on the battery side, so as to apply a charging voltage to the high voltage battery in an optional charging step, which is higher than the nominal charging voltage of the charging station and has been boosted by a boost converter (e.g., a DC / DC converter), so as to transfer electrical energy from the charging station to the high voltage battery.

[0013] Preferably, an electrical protection conductor connection and multiple charging connections are established via a charging cable. The charging cable can be connected to a high-voltage battery on one hand, and to a charging station on the other hand via one or more plug-in connections. In this case, the initial setup is the same as described above.

[0014] In the event of a fault condition, where a fault current circuit is formed via a low-resistance connection between a first high-voltage potential on the battery side or a second high-voltage potential on the battery side and a protective conductor terminal on the battery side, utilizing the fault current supplied from the high-voltage battery, the method provides a step in which a fault current controller, such as a fault current limiter, reduces the fault current to a reduced fault current and / or limits the fault current to a reduced fault current during the fault condition. Optionally, the limiting or reduction may be performed immediately or with a delay after a positive detection of the fault condition by the detection device, and optionally only after the fault current controller is activated, for example, by connecting the fault current controller to the fault current circuit. For example, the delay may be a result of signal processing and / or delayed activation of the fault current controller, which may be necessary.

[0015] By reducing or limiting the fault current according to the present invention, at least one of the above-mentioned fault states can be avoided, such as short circuit of the protection element on the charging station side, melting and interruption of the protection conductor connection, and at least applying a potential corresponding to the high voltage potential to the protection conductor terminal on the battery side.

[0016] Preferably, the fault current is limited by a fault current controller such that the contact potential on the protective conductor terminal on the battery side is no greater than 350 volts, and preferably no greater than 60 volts, relative to the grounding potential on the charging station side. Therefore, danger to people, such as in the event of manual contact with the protective conductor terminal on the battery side, can be avoided.

[0017] Preferably, the minimum cross-section of the protective conductor on the charging station side, for example as part of the internal wiring of the charging station, is 0.75 mm. 2 Or even less. For example, the fault current is regulated by a fault current controller so that the current-carrying capacity of the protective conductor on the charging station side is not compromised.

[0018] Preferably, the charging station has a protective element, such as a variable resistor, to which a fault voltage (more preferably more than 50% of the nominal battery voltage) drops across the variable resistor in a fault condition. For example, the fault current is regulated by a fault current controller so that the current-carrying capacity of the protective element is not compromised.

[0019] According to one embodiment, the fault current controller is integrated into a common protective conductor, such as in the charging cable. Preferably, the fault current controller is integrated into the protective conductor on the battery side, making activation (e.g., electrical connection) of the fault current controller optional. Preferably, the fault current controller is part of the charging circuit and is activated, for example, by a charging circuit element.

[0020] According to a preferred embodiment, a fault current controller is disposed in a charging connection, which consists of a first charging connection and a second charging connection, and a fault current is applied to this charging connection. Preferably, all charging connections are provided with a fault current controller.

[0021] Preferably, after a confirmed fault condition is detected, the fault current circuit is interrupted within a time frame of up to 20 ms, more preferably up to 15 ms, and most preferably up to 10 ms.

[0022] In one embodiment, definitive detection is the result of voltage monitoring of the protective conductor connection, particularly the voltage monitoring of the protective conductor on the battery side. For example, if a measured voltage present on the protective conductor on the battery side is found to converge to one of the high-voltage potentials on the battery side to a predetermined extent, a fault condition is definitively detected.

[0023] According to a preferred embodiment, a fault state is determined by an insulation monitoring device used to determine and monitor the insulation resistance between a first high voltage potential (HVP) on the battery side and a protective conductor on the battery side and / or the insulation resistance between a second high voltage potential (HVP) on the battery side and a protective conductor on the battery side, and to detect the fault state definitively, for example, based on the corresponding insulation resistance dropping below a corresponding predetermined value.

[0024] Preferably, the charging connection carrying the fault current, consisting of at least a first charging connection and a second charging connection, is interrupted by a battery-side protection device (e.g., a switching relay) after a minimum duration. This protection device is preferably located outside the charging station. Preferably, the protection device includes a smoke and fire separation component and / or a reversibly separable semiconductor element.

[0025] The present invention also relates to a charging circuit, particularly a charging circuit for motor vehicles, configured to cooperate with a high-voltage battery having a nominal battery voltage and a charging station having a nominal charging voltage lower than the nominal battery voltage, to perform a fault current handling method of any of the above embodiments, wherein the charging circuit at least has the aforementioned fault current controller. For this purpose, the charging circuit has, for example, a controller in the form of a digital processing unit, such as a microprocessor, a microcontroller, or a digital signal processor (DSP). To avoid delays caused by digital signal processing, the charging circuit has a largely discrete configuration. Preferably, at least the fault current controller, if provided, activates the required activation circuitry and has a discrete configuration.

[0026] The present invention also relates to an assembly comprising a charging station, a high-voltage battery and a charging circuit as described above.

[0027] Note that the definitions of the apparatus related to the terminology, as well as the effects and advantages of the features of the apparatus, can be fully referenced to the disclosure of the corresponding definitions, effects, and advantages of the method according to the invention, and vice versa. Therefore, for the sake of a more concise description, the repetition of explanations of substantially the same features, their effects, and advantages may be largely omitted herein, without such omission being construed as a limitation on the various subjects of the invention. Attached Figure Description

[0028] Other advantages and features of the invention will become apparent from the following description of exemplary embodiments thereof. These descriptions should be understood as non-limiting and will be explained below with reference to the accompanying drawings. The drawings schematically illustrate: Figure 1 It is a schematic functional diagram for explaining a fault state that will be dealt with by the method according to the invention, wherein the first fault condition can be avoided by the invention; Figure 2 This is a schematic functional diagram used to explain the second type of fault condition, which is caused by a fault state and can be avoided by the present invention; Figure 3 This is a schematic functional diagram used to explain the method sequence according to the present invention; Figure 4 This is a schematic diagram of the fault current curve.

[0029] In various drawings, functionally equivalent parts are always provided with the same reference numerals, so that they are usually described only once. Detailed Implementation

[0030] like Figure 1As shown, when a motor vehicle 1 (in this case, an electric vehicle) with a high-voltage battery 2 (e.g., a battery with a nominal battery voltage of 900V) is charged at an external charging station 3 via cable 7, the charging station 3 provides a nominal charging voltage lower than the nominal battery voltage, i.e., less than 900V in a given embodiment, such as 450V. A charging circuit 13 with a boost converter 14 (in this case, a DC / DC converter) is used to convert the charging voltage provided by the charging station 3 so that it corresponds to or is higher than the nominal battery voltage of the high-voltage battery 2 of the motor vehicle. When charging via cable, and when the high-voltage battery 2 is already electrically connected to the charging station 3 via the charging cable 7 without charging current, arrangements and measures for fault current protection are required according to DIN EN IEC 61851-1. This includes establishing a conductive protective conductor connection 9 for the protective conductor 4a on the charging station side, which is electrically connected to the ground potential PE on the charging station side, and connected to the protective conductor 4b on the battery side, such that the protective conductor 4b on the battery side is electrically insulated from the high-voltage potentials HV+ and HV- on the battery side of the high-voltage battery 2 in a non-faulty state, and electrically insulated from the ground potential PE on the charging station side via the protective conductor 4a on the charging station side. Typically, the protective conductor 4b on the battery side is at least partially formed by the vehicle body and is commonly referred to as vehicle ground. In addition to the protective conductor connection 9 established via cable 7, multiple charging connections 5 and 6 are formed when establishing the plug-in connection. Specifically, on one hand, the first high-voltage potential HVP on the charging station side is connected to the first high-voltage potential HV+ on the battery side via charging circuit 13; and on the other hand, the second high-voltage potential HVN on the charging station side is connected to the second high-voltage potential HV- on the battery side via charging circuit 13. During the charging process, a charging voltage higher than the nominal charging voltage of charging station 3, which has been boosted by the boost converter 14 belonging to charging circuit 13, can be applied to the high-voltage battery 2 to transfer electrical energy from charging station 3 to the high-voltage battery 2.

[0031] In the event of a fault, the high-voltage potential HV+ or HV- on the battery side (HV- in this case), connected with low resistance to the protective conductor terminal 4b on the battery side, is understood as a fault state and is indicated by lightning bolt 11. This fault current circuit, through one of the charging connections 5 and 6 (5 in this case), generates a fault current circuit between the charging station 3 and the common protective conductor connection 9, where the relevant fault current FI, indicated by the arrow, is supplied by the high-voltage battery 2. Typically, this fault current FI causes the protective element 8, which is affected by the fault current circuit and located on the charging station side, to "go out of control." On the charging station side, this causes charging connection 5 (to which the fault current is applied respectively) and the protective conductor connection 9 to be connected with low resistance and thus short-circuited. This results in an increase in the fault current amperes, leading to a potential on the protective conductor connection 9 greater than 60 volts, making contact dangerous, and applying a load exceeding the current carrying capacity to the protective conductor connection 9. Furthermore, because the wiring on the charging station side, particularly in DC charging stations with lower nominal charging voltages, forming the protective conductor 4a, is not designed for this intensity of fault current, the continuous fault current FI causes overheating and ultimately leads to the melting of the protective conductor 4a on the charging station side. Figure 2 As shown, and marked by reference numeral 17, an interruption indication is present. This constitutes irreversible damage to charging station 3 and deprives the protective conductor connection 9 of its function, resulting in a high voltage potential HV+ or HV- (here, HV-) existing on the protective conductor 4b electrically connected to the battery side. Furthermore, a voltage exceeding 60V relative to ground constitutes a dangerous voltage upon contact and thus poses a danger to the life and limbs of anyone in contact.

[0032] The method according to the invention avoids these failure conditions, and refers to Figure 3 An explanation has been provided. The initial situation is the same as described above. The method according to the invention relates to the handling of fault current in a high-voltage battery 2 in a motor vehicle 1 connected to a charging station 3 via a charging circuit 13. In the steps provided according to the invention, a high-voltage battery 2 having, for example, a nominal battery voltage of approximately 900 volts and an associated charging circuit 13 are provided. The high-voltage battery 2 is not necessarily, for example, a traction battery of a motor vehicle 1 driven by an electric motor. Furthermore, a charging circuit having at least one boost converter is provided, and is preferably located on the battery side, particularly on the motor vehicle side. "Battery side" is understood to refer to the arrangement associated with the high-voltage battery 2, such as mechanical fixing and electrical connection.

[0033] In another step according to the invention, a charging station 3, preferably a DC charging station, is provided with a nominal charging voltage less than the nominal battery voltage, for example, about 450 volts. The charging station 3 is connected to a power grid, for example, not shown.

[0034] According to the present invention, a connection step is provided in which an electrical protective conductor connection 9 is established between a protective conductor on the charging station side and a protective conductor on the battery side, so as to connect the protective conductor 4b on the battery side to the ground potential PE on the charging station side via the protective conductor 4a on the charging station side. The protective conductor 4a on the charging station side and the protective conductor 4b on the battery side form a common protective conductor connected to the ground potential PE on the charging station side through the protective conductor connection 9. In a non-fault state, the protective conductor 4b on the battery side, as well as the common protective conductor, are electrically insulated relative to the first high voltage potential HV+ and the second high voltage potential HV- on the battery side, and are not electrically connected, as... Figure 3 The lightning bolt shown in Figure 11.

[0035] According to the present invention, another connection step is provided, which is performed almost simultaneously with the above-described connection step, so as to establish a charging connection 5, 6 from the first high voltage potential HVP on the charging station side to the first high voltage potential HV+ on the battery side, and on the other hand, to establish a charging connection 5, 6 from the second high voltage potential HVN on the charging station side to the second high voltage potential HV- on the battery side, so as to apply a charging voltage to the high voltage battery 2 in an optional charging step. This charging voltage is higher than the nominal charging voltage of the charging station and has been boosted by a boost converter 14, such as a DC / DC converter, so as to transfer electrical energy from the charging station 3 to the high voltage battery 2. Here, the electrical protection conductor connection 9 and the plurality of charging connections 5, 6 are established through a charging cable 7, which can be connected to the high voltage battery 2 on the one hand, and to the charging station 3 on the other hand through one or more plug-in connections.

[0036] In the event of a fault condition indicated by lightning 11, a fault current circuit is formed by connecting the first high-voltage potential HV+ on the battery side or the second high-voltage potential HV- on the battery side (the latter in this case) with a low resistance to the protective conductor terminal 4b on the battery side, through the charging station 3 and the protective conductor terminal 9. The fault current is provided by the high-voltage battery 2. The method provides the following steps: During the fault condition, at least for a predetermined minimum duration, the fault current FI is reduced to a reduced fault current FI' by the fault current controller 15 (e.g., a fault current limiter) and / or the fault current FI is limited to a reduced fault current FI' within a predetermined time range. Optionally, the limitation or reduction occurs immediately upon the occurrence of the fault condition, or is delayed after a positive detection of the fault condition by a detection device not shown.

[0037] By reducing or limiting the fault current according to the present invention, at least one of the above-mentioned fault states can be avoided, such as a short circuit of the protection element 8 on the charging station side, for example... Figure 1As shown, the melting and interruption of a protective conductor, particularly the melting and interruption of the protective conductor 4a on the charging station side, and the application of at least one of the high voltage potentials HV+ or HV- to the protective conductor terminal 4b on the battery side.

[0038] In the embodiment shown here, the minimum cross-sectional area of ​​the protective conductor 4a on the charging station side, for example as part of the internal wiring of the charging station 3, is 0.75 mm. 2 Or even less. For example, the fault current FI is regulated by the fault current controller 15 so that the current carrying capacity of the common protection conductor, especially the protection conductor 4a on the charging station side, is not compromised within a predetermined time range.

[0039] Here, the charging station 3 has a protective element 8, such as a variable resistor, to which a fault voltage of 550V (which constitutes at least a portion of the nominal battery voltage) drops in the event of a fault. For example, the fault current FI is regulated by a fault current controller 15 so that the current-carrying capacity of the protective element 8 is not compromised, at least for a predetermined time.

[0040] like Figure 3 As shown, the fault current controller 15 is integrated into the protection conductor 4b on the battery side and is part of the charging circuit 13.

[0041] Here, the fault current FI is limited by the fault current controller 15 such that the contact potential on the protective conductor 4b on the battery side is no greater than 350 volts relative to the ground potential on the charging station side. Therefore, danger to humans, such as in the event of manual contact with the protective conductor 4b on the battery side, can be avoided. In the illustrated embodiment, the minimum duration is at least 15 ms, during which the fault current controller 15, starting from the fault state and including a response time if necessary, reduces the fault current FI to a reduced fault current FI', as... Figure 4 As shown. In this case, the dashed line represents the curve of the fault current FI, because without the measures according to the invention, the fault current FI will develop, setting an interruption before it is finally established (in Figure 4 (not shown in the image), as in combination Figure 2 The interruption of the fault current FI' starting from time point t1 is at least due to the charging connections 5 and 6 carrying the fault current being interrupted after the shortest duration. Figure 3 The result of the interruption of the protective device 16 (such as the smoke and fire separation component) on the battery side shown.

Claims

1. A method for handling fault current in a high-voltage battery (2) connected to a charging station (3) via a charging circuit (13), the method comprising the steps of: - Provide the nominal battery voltage to the high-voltage battery (2), the nominal battery voltage being located between a first high-voltage potential (HV+) on the battery side and a second high-voltage potential (HV-) on the battery side; - Provide the charging circuit (13); - Provide a nominal charging voltage to the charging station (3), the nominal charging voltage being less than the nominal battery voltage, the nominal charging voltage existing between a first high voltage potential (HVP) on the charging station side and a second high voltage potential (HVN) on the charging station side; - An electrical protection conductor connection (9) is established between the protection conductor (4a) on the charging station side and the protection conductor (4b) on the battery side. The electrical protection conductor connection (9) is electrically insulated relative to the first high voltage potential (HV+) and the second high voltage potential (HV-) on the battery side in a fault-free state, so as to connect the protection conductor (4b) on the battery side to the ground potential (PE) on the charging station side via the protection conductor (4a) on the charging station side. - The charging circuit (13) establishes charging connections (5, 6) between the first high voltage potential (HVP) on the charging station side and the first high voltage potential (HV+) on the battery side, and between the second high voltage potential (HVN) on the charging station side and the second high voltage potential (HV-) on the battery side, so as to apply a charging voltage to the high voltage battery (2) in an optional charging step. This charging voltage is higher than the nominal charging voltage of the charging station (3) and has been boosted by the boost converter (14) belonging to the charging circuit (13) so as to transfer electrical energy from the charging station (3) to the high voltage battery (2). - The occurrence of a fault condition, wherein a fault current circuit is formed via the charging station (3) and the protection conductor (9) by a low-resistance connection (11) between the first high voltage potential (HVP) on the battery side or the second high voltage potential (HVN) on the battery side and the protection conductor (4b) on the battery side, wherein the fault current (FI) is provided by the high voltage battery (2). - During a fault condition, the fault current (FI) is reduced and / or limited to a reduced fault current (FI') by a fault current controller (15) belonging to the charging circuit (13), which is greater than zero and less than the fault current (FI).

2. The method according to claim 1, characterized in that, The charging circuit (13) is in the motor vehicle (1).

3. The method according to claim 1, characterized in that, Only after a positive detection of the fault condition, the fault current (FI) is reduced and / or limited to a reduced fault current (FI') by the fault current controller (15) belonging to the charging circuit (13).

4. The method according to claim 1, characterized in that, The reduced fault current (FI') is adjusted by the fault current controller (15) so that the contact potential on the protective conductor (4b) on the battery side is no more than 350 volts relative to the grounding potential on the charging station side.

5. The method according to claim 4, characterized in that, This ensures that the contact potential on the protective conductor (4b) on the battery side is no greater than 60 volts relative to the grounding potential on the charging station side.

6. The method according to claim 1, characterized in that, The minimum cross-sectional area of ​​the protective conductor (4a) on the charging station side is ≤0.75 mm. 2 .

7. The method according to claim 1, characterized in that, The charging station (3) has a protection element (8) disposed in the charging connection (5, 6), to which a fault current (FI) is applied in the fault state.

8. The method according to claim 7, characterized in that, The protective element (8) is a rheostat.

9. The method according to claim 7, characterized in that, A fault voltage exceeding 50% of the nominal battery voltage drops across the charging connection during a fault condition.

10. The method according to claim 7, characterized in that, The fault current (FI) is reduced and / or limited by the fault current controller (15) so that the current carrying capacity of the protection conductor (4a) and / or protection element (8) on the charging station side is not exceeded by the fault current.

11. The method according to claim 1, characterized in that, The fault current controller (15) is integrated into the protective conductor (4b) on the battery side.

12. The method according to claim 1, characterized in that, A fault current controller (15) is set in the charging connection (5, 6) to which the fault current (FI) is applied.

13. The method according to claim 1, characterized in that, The fault current circuit is interrupted within a maximum time frame of 20ms, which occurs after the fault condition is confirmed.

14. The method according to claim 13, characterized in that, The fault current circuit is interrupted within a maximum time frame of 15ms.

15. The method according to claim 14, characterized in that, The fault current circuit is interrupted within a maximum time frame of 10ms.

16. The method according to any one of claims 1-15, characterized in that, The fault condition is determined by an insulation monitoring device, which is used to determine and monitor the insulation resistance between the first high voltage potential (HV+) on the battery side and the protective conductor on the battery side and / or the second high voltage potential (HV-) on the battery side and the protective conductor (4b) on the battery side, and to confirm the fault condition based on the corresponding insulation resistance dropping below the corresponding predetermined value.

17. The method according to any one of claims 1-15, characterized in that, The charging connection (5, 6) carrying at least the reduced fault current (FI') is interrupted by the protection device (16) of the charging circuit (13).

18. The method according to claim 17, characterized in that, The protection device (16) is located outside the charging station (3).

19. The method according to claim 17, characterized in that, The protection device is located on the battery side.

20. The method according to claim 17, characterized in that, The protective device (16) has a fire separation component and / or a reversibly separable semiconductor element.

21. A charging circuit (13) configured to cooperate with a high-voltage battery (2) having a nominal battery voltage and a charging station (3) having a nominal charging voltage lower than the nominal battery voltage to perform the method according to any one of claims 1-20, and having at least a fault current controller (15).

22. The charging circuit (13) according to claim 21, characterized in that, The charging circuit (13) is the charging circuit of the motor vehicle (1).

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