DE102015016000A1 - Circuit arrangement for a motor vehicle and method for discharging Y capacities in vehicles with high-voltage on-board electrical system - Google Patents

Abstract

The invention relates to a circuit arrangement (20) for a motor vehicle, having a high-voltage on-board electrical system (10) of a coupling device (24) for coupling an energy store (12) via a first and second vehicle electrical connection (10a, 10b) to the high-voltage vehicle electrical system (10) Mass (18), an insulation resistance (R (+); R (-)) between the first electrical system connection (10a, 10b) and the ground 18, a capacitance (C (+); C (-)) between the first vehicle electrical system connection ( 10a, 10b) and the ground (18) and parallel to the first insulation resistance (R (+); R (-)), a measuring device (26) for measuring the insulation resistance (R (+); R (-)) and / or a voltage between the first vehicle electrical system connection (10a, 10b) and the mass (18), and a control device (26a) which is designed to convert the measuring device (26) from an inactive state to an active state, if the energy store (12 ) is disconnected from the high-voltage vehicle electrical system (10), resulting in a Gesamtisolatio n resistance between the first vehicle electrical system connection (10a; 10b) and the mass (18) is reduced.

Description

The invention relates to a circuit arrangement for a motor vehicle and a method for operating a circuit arrangement of a motor vehicle according to the preambles of the independent claims.

The protection against electric shock is the highest goal in the design of motor vehicle electrical systems in motor vehicles with voltage class B ( ISO 6493-3 ). Here is high voltage according to ECE R100 By definition, the voltage for which an electrical component or circuit is designed whose effective value of the operating voltage is greater than 60 volts and less than or equal to 1500 volts at dc or greater than 30 volts and less than or equal to 1000 volts at ac.

In order to protect persons and farm animals from touching such a voltage, several independent protective measures are carried out. These are divided into basic protection and error protection. The basic protection includes, among other things, protective insulation and housing, which prevent access to active parts constructively. Error protection includes devices that issue a warning message when detecting a fault in the HV (high-voltage) system or transfer the system to a defined state.

A high-voltage on-board electrical system has assumed a safe state whenever it has been switched off in a defined manner. Then all voltages (excluding voltages in the energy store itself) in the system are below the 60 volt touch voltage limit. D.C. or 30 volts A.C., and the risk of electric shock is thus reliably excluded. The voltage within energy storage devices, such as HV batteries or fuel cells, in this state is galvanically isolated from the rest of the electrical system via a switching element, since a complete discharge of energy storage to produce the voltage-free state is not possible. The amount of time it takes to allow a voltage less than 60 volts D.C. and 30 volts A.C. in the system depends on the design of the protection concept. For example, the crash rule valid in the USA allows the shutdown of the high-voltage vehicle electrical system as a protective measure. The requirement until the specified voltage limits are exceeded, amounts to a period of 5 seconds after vehicle standstill. These voltage requirements apply in particular to the voltages HV (+) to HV (-), HV (+) to vehicle mass and HV (-) to vehicle mass.

These voltages are in 1 illustrated. 1 shows schematically a high-voltage vehicle electrical system 10 according to the prior art, with an energy storage system comprising an energy store 12 , which acts as a voltage source, an energy conversion system with an energy conversion device 14 and a drive system 16 , The voltage Vb, which represents the voltage HV (+) to HV (-), via the two terminals of the voltage source or the energy storage 12 measured. The voltages V1, the voltage HV (-) to the vehicle ground 18 represents, and V2, the voltage HV (+) to the vehicle mass 18 represents between the voltage source and the electrical ground 18 measured.

Furthermore, the HV batteries and / or one or more other existing energy storage devices, for example a fuel cell, for providing the supply energy are not the only energy storage devices in a high-voltage on-board electrical system. While these mentioned energy storage devices can usually be switched off by means of switching elements, other, usually much smaller energy storage devices in the system have to be discharged after the shutdown. These can not be separated from the electrical system via switching elements, as this would be too time-consuming. These smaller energy stores are, for example, capacitors which are installed directly in the HV components for buffering energy (so-called X capacitances) or for suppressing interference (Y capacitors). The Y capacitors couple the respective components capacitively with the electrical mass of the vehicle. In addition, high-impedance insulation resistors are installed between the high-voltage on-board electrical system and the ground.

The X capacitors in the components can be actively or passively discharged after their shutdown to relieve the charge within the required time. For Y capacitors, the discharge situation is a bit more difficult because permanently contacted resistors would significantly reduce the insulation resistance of the vehicle, which would be counterproductive to the safety of the vehicle. In contrast, active discharge circuits would further increase the complexity in the component. In addition, with a total energy content of all Y-capacitors in the vehicle of less than 0.2 Joule a discharge is not explicitly specified, since in such symmetrical conditions in the high-voltage vehicle electrical system, the situation is not critical. However, these symmetrical properties of a high-voltage vehicle electrical system are not always given. It may make sense technically to use filter capacities of different sizes. Further asymmetries arise when the insulation resistances in the system are unequal between the high-voltage potentials. Especially the latter leads to the fact that the voltage distribution is different.

Therefore, a measure must be taken to realize a timely discharge even for such a design of the Y capacitors. Only then can a discharge of these components in the required time be achieved. What is aggravating added is that the insulation resistance of the vehicle, which is crucial here for the residual discharge, has no fixed size. This depends on many parameters such as temperature, aging, operating conditions and other influences. A qualitative and, above all, safety-relevant objective is to keep the insulation resistance at a high level over the entire service life of a vehicle.

In addition, it is known that vehicles today monitor this insulation resistance during operation of the vehicle and active high-voltage vehicle electrical system. For this purpose, so-called insulation monitoring devices or insulation monitors are used, which determine the insulation resistance and compare it with a defined limit value. If the insulation resistance falls below this limit value, a vehicle-specific reaction is carried out. This may take the form of a warning message requesting service or, in very serious cases, an activation ban on the high-voltage vehicle electrical system. An embodiment of such insulation monitoring is for example in the EP 0 654 673 B1 described.

The object of the present invention is therefore to provide a circuit arrangement for a motor vehicle and a method for operating a circuit arrangement which provide the fastest possible possible discharge of energy stores of the high-voltage vehicle electrical system, in particular the Y capacitors.

This object is achieved by a circuit arrangement and a method for operating a circuit arrangement with the features according to the independent claims. Advantageous embodiments of the invention can be found in the dependent claims.

The circuit arrangement according to the invention for a motor vehicle has a high-voltage on-board electrical system with a first and a second vehicle electrical system connection, a coupling device which is designed to couple an energy store via the first and second vehicle electrical system connection to the high-voltage vehicle electrical system and to disconnect it electrically from the first and second vehicle electrical system connection of the high-voltage vehicle electrical system , an electrical ground, a first insulation resistance between the first on-board power supply terminal and the ground, a first capacitance between the first on-board power supply terminal and the ground and parallel to the first insulation resistance, and a measuring device, which is designed to measure the first insulation resistance and / or one Measure the voltage between the first vehicle electrical system connection and the earth. In this case, the measuring device has an active and an inactive state and, moreover, has a control device for activating the measuring device, wherein the control device is designed to convert the measuring device from the inactive state into the active state and from the active state into the inactive state and wherein a total insulation resistance between the first onboard power supply terminal and the ground has a first value when the metering device is in the inactive state and the total insulation resistance has a second value that is less than the first value when the metering device is in the active state. Furthermore, the control device is designed to control the measuring device in such a way that the measuring device is transferred from the inactive to the active state when the energy store is disconnected from the electrical system.

The invention is based on the recognition that measuring devices, such as insulation monitors or even voltage taps, in the performance of measurements affect the overall insulation resistance, and reduce this particular. Reduction of the total insulation resistance can now be advantageously used to quickly discharge the first capacitance, that is, in particular the Y capacitances. In accordance with the invention, this is accomplished by transferring the measuring device into the active state when the energy store is disconnected from the electrical system. The active state of the measuring device is to be understood in this case that not necessarily in this active state, a voltage measurement or insulation resistance measurement is performed, but only so that a switching of one or more switchable elements, for example a resistor, the measuring device takes place, whereby the Overall insulation resistance for the duration of the active state is reduced.

For rapid discharge of the first capacitor can thus be used advantageously already existing facilities that provide the measuring device, the high-voltage vehicle electrical system, which in total a very fast and, above all, cost-effective discharge of the Y-capacity can be accomplished.

In this case, the first insulation resistance can be provided by one or more electrical resistance components in a series and / or parallel connection. For example, individual loads coupled to the high-voltage vehicle electrical system can have respective individual insulation resistances each contribute to the resulting first insulation resistance. Similarly, the first capacitance may be provided by one or more capacitors in a series and / or parallel connection. Such capacitors can also be installed in the respective consumer components.

In an advantageous embodiment of the invention, the measuring device comprises an insulation monitoring device and / or an insulation monitor and / or a voltage divider. In this way, monitoring of the insulation resistance can advantageously be simultaneously provided, or in other words, the structural components provided for monitoring the insulation resistance can simultaneously be used for the rapid discharge of the Y capacitances.

It represents a particularly advantageous embodiment of the invention, when the measuring device comprises a detuning resistor and is set up so that the detuning connected in a transfer from the inactive state to the active state of the measuring device in the case of separation of the energy storage from the high-voltage electrical system parallel to the first insulation resistance becomes. As a result, a particularly rapid discharge of the Y capacitances can advantageously take place via the detuning resistor connected in parallel in the event of a fault. However, the measuring device may also comprise a different type of insulation monitoring device, which does not introduce comparative resistance directly, because even such insulation monitoring devices affect the total insulation resistance in the active state and set this particular down.

In a further advantageous embodiment of the invention, the circuit arrangement has a second capacitance between the second electrical system connection and the ground, in particular wherein the second capacitance is different from the first capacitance. The second capacity can in turn be formed by a plurality of individual capacities, in particular of the individual electrical consumers. The invention shows just its advantages in combination with such a single-ended system in which therefore a high-voltage potential is coupled to the ground via a different capacity, as the other high-voltage potential with the mass, because it is precisely in this situation, it is not possible that at a decoupling of the energy storage, the charges of the capacities, in particular the first and the second, each completely compensate each other. There then remain residual charges, which can still be discharged very quickly by the activation of the measuring device.

Furthermore, the invention relates to a method for operating a circuit arrangement of a motor vehicle, wherein the circuit arrangement is designed as the circuit arrangement according to the invention or one of its embodiments. According to the inventive method, the measuring device is transferred from the inactive to the active state when the energy storage is disconnected from the electrical system.

The features described for the circuit arrangement according to the invention and its embodiments, feature combinations and their advantages apply in the same way for the inventive method. In addition, the physical features mentioned in connection with the circuit arrangement according to the invention allow the development of the method according to the invention by further method steps.

Furthermore, the invention also relates to a motor vehicle with a circuit arrangement according to the invention.

Further advantages, features and details of the invention will become apparent from the following description of a preferred embodiment and from the drawing. The features and feature combinations mentioned above in the description as well as the features and feature combinations mentioned below in the description of the figures and / or shown alone in the figures can be used not only in the respectively specified combination but also in other combinations or in isolation, without the scope of To leave invention.

Showing:

1 a schematic representation of a high-voltage vehicle electrical system according to the prior art;

2 a schematic representation of a circuit arrangement with a high-voltage vehicle electrical system;

3a a schematic representation of a portion of the circuit arrangement with an active discharge device for the X-capacitors;

3b a schematic representation of a portion of the circuit arrangement with a passive discharge device for the X-capacitors;

4 a schematic representation of the circuit arrangement 2 as an equivalent circuit diagram; and

5 a schematic representation of the circuit arrangement with an insulation monitoring device.

2 shows a schematic representation of a circuit arrangement 20 with a high-voltage on-board network 10 , The representation is to be understood as a circuit diagram or equivalent circuit diagram with which the high-voltage vehicle electrical system 10 including the component-related capacities is shown in simplified form. The circuit arrangement 10 has a power source unit 22 with an energy storage 12 on. The energy storage 12 may represent, for example, a HV battery and / or a fuel cell. Furthermore, the high-voltage electrical system 10 a plurality of components, for example consumers, in particular a first component K1, a second component K2 up to an n-th component Kn. Depending on the version, capacitors Cx, Cy (+), Cy (-) are installed in the components K1, K2, Kn, which carry voltage during operation. The X capacitors Cx are used for smoothing the voltage and as an energy buffer and can assume high values (value range microfarads) up to millifarads. The Y capacitors Cy (-), Cy (+) are used for suppression and usually have lower capacitance values (value range picofarads) up to Nanofarad. Furthermore, the respective components K1, K2, Kn insulation resistances Riso (+), Riso (-), which are in the range of several megohms. The load resistances R _load depicted in the equivalent circuit symbolically represent the actual component load and are not effective when the component K1, K2, Kn is switched off. Therefore, they can not be used for discharging the component-near capacitors without additional measures (suitable control).

The X capacitors Cx in the components K1, K2, Kn can be actively or passively discharged after switching off the components K1, K2, Kn, in order to reduce the charge within the required time. This is realized with smaller X capacitors Cx by means of a passive resistance discharge, as in 3b is shown. In this case, a resistor R is connected in parallel to an X capacitor Cx, which thus permanently bridges the X capacitor Cx.

At higher discharge rates this makes no sense for reasons of permanent power loss. Therefore, in this case, so-called active discharge circuits are preferable as shown in FIG 3a is illustrated schematically. The discharge circuit in this case has a controller ECU, which switches the resistor R to the X-capacitor Cx in parallel, as soon as the main energy storage 12 by means of switching elements 24 (see 2 ) was separated. These switching elements 24 can be designed, for example, as a shooter, via which the energy storage 12 with the high voltage on-board network 10 can be coupled. The corresponding connection points of the high-voltage on-board electrical system 10 are used here as the first and second vehicle electrical system connection 10a . 10b designated. The potential at the first vehicle electrical system connection 10a is referred to below as HV (+) potential and is in 4 and 5 represented as HV +, while the potential at the second electrical system connection 10b hereinafter referred to as HV (-) - potential and in 4 and 5 shown as HV.

However, for the Y capacitors Cy (+), Cy (-), the discharge situation is somewhat more difficult since permanently contacted resistors would significantly reduce the insulation resistance of the vehicle, which would be counterproductive to the safety of the vehicle. Active discharging circuits would further increase the expense in the component. In addition, with a total energy content of all Y capacitors Cy (-), Cy (+) in the vehicle of less than 0.2 Joule a discharge is not explicitly specified. As will be shown below, the situation is also uncritical, as long as there are symmetrical conditions in the high-voltage vehicle electrical system.

A symmetric high-voltage system in this context is also symmetric with respect to insulation resistance and leakage capacitances Cy (+), Cy (-), that is, for example, that the sum of the sum of all Y capacitances Cy (+) having the HV (+) potential with the crowd 18 couple, that is between the positive electrical system connection 10a and the crowd 18 are equal to the sum of the sum of all Y capacitances Cy (-) that are between the HV (-) potential and the ground 18 are arranged, that is, between the negative electrical system connection 10b and the crowd 18 , In order to describe the discharge behavior of the Y-capacitances Cy (+) and Cy (-), the in 2 illustrated circuit arrangement 10 in 4 once again simplified. The energy storage 12 , such as a HV battery, can by means of two contactors 24 from the remaining high-voltage on-board electrical system 10 be separated. All insulation resistances Riso (+) from HV (+) potential to ground 18 are represented by the equivalent resistance R (+). Insulation resistance Riso (-) from HV (-) potential to ground 18 are summarized in the resistor R (-). Analogous to the insulation resistances, all Y capacitances Cy (-), Cy (+) of the various components K1, K2, Kn are in the capacitances C (+) (Y capacitance between HV (+) potential and ground 18 ) and C (-) (Y capacitance between HV (-) potential and ground 18 ) summarized. The sum of the DC link capacities is represented by a capacitance Cx. R _L describes the sum of all discharging resistors R, which are provided for the discharge of the DC link capacitances Cx.

Will the two switches 24 (Main contactors) open, discharges the DC link capacitance, that is, the X-capacitance Cx, via the designated discharge resistor R _L. At, as in 4 through the "+" And "-" symbols on the Y capacitances C (+), C (-) illustratively shown, symmetrically charged Y capacitances C (+), C (-), the charges can also through the low-resistance discharge resistors Unload or equalize R _L. The discharge branch via the parallel insulation resistors R (+), R (-) plays a negligible role in this case, since these resistors are very high-impedance. The charge equalization of the Y capacitances C (+), C (-) is completed very quickly in this process. As soon as the voltage Vb (cf. 1 ) between the high-voltage potentials has fallen below the limit of 60 volts, are also the partial voltages to ground 18 safely below the limit, since these each have the amount 1/2 of the intermediate circuit voltage.

The discharge of the Y-capacitances C (+), C (-) takes place in this case as fast as the Y-capacitances C (-), C (+) are charged with the different polarity and a closed via the discharge resistor R _L Form circuit.

Unfortunately, these symmetrical properties of the high-voltage vehicle electrical system are not always given. It may make sense technically to use filter capacities of different sizes. Further asymmetry arises when the insulation resistance in the system between the high-voltage potentials are unequal. Especially the latter leads to the fact that the voltage distribution is different. If this happens, the discharge will not behave as explained above.

In the following, an asymmetrical HV system will now be explained in more detail, in which therefore the sum of the Y capacitances Cy (+) between the HV (+) potential and the ground 18 unlike the sum of the Y-capacitances Cy (-) between the HV (-) potential and the ground 18 is. In such an asymmetrical system, in which, for example, a high-voltage potential to ground 18 For example, the total capacitance C (+) is between the HV (+) potential and ground 18 twice the total capacity C (-) between the HV (-) potential and ground 18 On the former, the double charge is stored according to Q = C · U. In such a case, now the switches 24 for separating primary energy storage 12 opened, the DC link capacitance Cx is again discharged quickly via the low-resistance discharge resistor R _L. At the same time, charge equalization takes place in parallel between the Y capacitances C (+) and C (-). This process is again very fast, as this takes place via the relatively low-resistance discharge resistor R _L. This charge equalization occurs until ultimately both Y capacitances C (+) and C (-) are charged approximately the same, which prevents them from further discharging each other across the discharge resistor R _L. A further discharge of the Y capacitances C (+), C (-) is in this case only possible via the very high-impedance insulation resistors R (+), R (-). This process of discharging the Y capacitances C (-), C (+) may take a long time, depending on the value of the insulation resistances R (+), R (-). With correspondingly high insulation resistances R (+), R (-), as is generally desired, this circumstance leads to the partial voltages V1, V2 (cf. 1 ) against vehicle mass 18 can not reach the threshold voltage of 60 volts in the given time. In such a case, it may happen, for example, that the discharge time is maintained with respect to the voltage Vb between the HV (+) and HV (-) potential, the discharge time with respect to the voltage between the positive high-voltage potential and ground 18 however, it is exceeded.

Precisely for this asymmetrical vehicle electrical system structure, therefore, a measure must be taken to realize a timely discharge for this design of the Y capacitors C (+), C (-). Only then can a discharge of these components in the required time be achieved. In addition, it is desirable to keep the insulation resistance R (+), R (-) as high as possible throughout the life of a vehicle. For this purpose, the insulation resistance R (-), R (+) during operation of the vehicle and active high-voltage vehicle electrical system 10 be monitored. For this purpose, so-called insulation monitoring devices or insulation monitors can be used, which determine the insulation resistance and compare it with a defined limit value. If the insulation resistance falls below this limit, a vehicle-specific reaction is carried out. Among other things, the processes for insulation monitoring can be carried out automatically in control units.

In order to monitor the insulation resistance R (-), R (+), for example, comparative resistances can be introduced for a defined measuring time. Over this measurement time, the voltage in the high-voltage vehicle electrical system 10 as well as the voltages between the high-voltage potentials and ground 18 and from this the insulation resistance R (+), R (-) is calculated. In the calculation, for example, the comparison resistance, which is temporarily brought between a high-voltage potential, be eliminated in the calculation. So then the respective vehicle insulation resistances R (-), R (+) can be calculated. During the measurement time, when the comparison resistances are switched on, these influence the total vehicle insulation resistance. In particular, this is significantly reduced for the period of the measurement.

The measurement of voltages between the high-voltage potentials and the vehicle chassis also influence the insulation resistance. For this purpose, a defined voltage tap is introduced between the measuring points. This can be carried out for example in the form of a voltage divider, which is turned on for the time of measurement. The relevant for the evaluation measurement signal is then detected via a dedicated circuit and provided to a control device for calculation available.

The invention now advantageously uses this change in the total insulation resistance by, for example, the insulation monitor itself or by voltage measurements in the system. This should now be based on 5 be illustrated.

5 shows a schematic representation of the circuit arrangement 20 as already too 4 described. The circuit arrangement 20 now also has a measuring device 26 on, which may be formed in this example as insulation monitoring. This includes the measuring device 26 a control device 26a and a resistor R26. Again, this resistor R26 is representative. This can represent a single resistor or even a complex circuit with a plurality of resistors and / or other components, for example, a switchable voltage divider, a comparison resistor or detuning resistor.

Regardless of the localization of such a switchable voltage divider or comparison resistor in the high-voltage vehicle electrical system 10 , this can be used for the procedure. For example, are several such switchable elements between the high-voltage potentials and ground 18 available, these can also be used simultaneously. For the time range in which the elements are switched on, they simulate the function of an "active" discharge. Since today's motor vehicles are extensively networked, the function of the connection of the voltage divider or the detuning resistors in the insulation monitoring 26 to be controlled. For this purpose, a suitable control device after switching off the power source, that is, when the energy storage 12 about the shooter 24 from the electrical system 10 disconnecting the corresponding high-voltage components to close their switching elements for a limited time. Is the high-voltage electrical system 10 For example, equipped with an active discharge of the X capacitors Cx, a control of the switching elements can also be coupled to this control. While the active discharge of the X-capacitors Cx requires no time limit, it makes sense to limit the switching elements, which reduce the total insulation resistance, in time. An external, possibly carried out by the service manual measurement of the insulation resistance, otherwise might be misinterpreted.

By a circuit arrangement 20 , as in 5 represented, now the total insulation resistance of the vehicle can be advantageously influenced. In particular, the total insulation resistance can now be reduced by applying the existing measuring resistors or low-impedance detuning resistors, such as resistor R26, to a suitable insulation monitor 26 specifically after opening the battery contactors 24 temporarily switched on, whereby the residual discharge can be positively influenced.

If, for example, the detuning resistance R26 of the insulation monitoring 26 temporarily after disconnecting the energy storage 12 is switched on, due to the low value of this resistance, only a one-sided connection necessary, which additionally reduces the effort.

In order to reduce the structural complexity to a minimum and at the same time to achieve the highest possible efficiency, an already existing resistor R26 in the insulation monitoring is for the acceleration of this discharging process 26 most suitable, which is cyclically switched during operation between the high-voltage potentials and vehicle ground to calculate the vehicle insulation resistance.

If one has the situation that Y-capacities Cy (+), Cy (-) in the vehicle, which are primarily used as a filter component, are constructed asymmetrically, or in the component value are too large that a discharge is generally required, can by a controlled connection of the detuning resistor R26 after disconnecting the power source or the energy storage 12 this capacity will be unloaded on time. This is advantageously achieved by a coordinated time control, which of the isolation monitor 26 can be carried out independently, if he, for example, in the source or the energy storage 12 is installed. Then the source, such as an HV battery, can be opened immediately after opening the battery contactors 24 the isolation guard 26 control accordingly.

Additionally or alternatively, an insulation monitor can also be used 26 can be used, which does not work with detuning resistors. In this case, at least one voltage tap to be measured partial voltages is present. This can be used in the same way to deliberately lower the total insulation resistance, thus discharging the Y-capacity as quickly as possible.

Overall, such a circuit arrangement and a method for operating a circuit arrangement are provided, which enable in a particularly cost-effective manner, a rapid discharge of the Y-capacitances.

LIST OF REFERENCE NUMBERS

10

HV-board network

10a, 10b

Board power connector

12

energy storage

14

Power conversion device

16

drive system

18

Electrical mass

20

circuitry

22

Power source unit

24

switching element

26

measuring device

26a

control device

K1, K2, Kn

component

cx

X-capacity

Cy (-), Cy (+), C (-), C (+)

Y capacity

Riso (-), Riso (+), R (-), R (+)

insulation resistance

R _load

load resistance

R, R _L

discharge

R26

Verstimmwiderstand

ECU

controller

HV +

Positive high-voltage potential

HV

Negative high-voltage potential

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• EP 0654673 B1 [0009]

Cited non-patent literature

• ISO 6493-3 [0002]
• ECE R100 [0002]

Claims (6)

Circuit arrangement ( 20 ) for a motor vehicle, comprising - a high-voltage on-board electrical system ( 10 ) with a first and a second vehicle electrical system connection ( 10a . 10b ); A coupling device ( 24 ), which is designed to store an energy store ( 12 ) via the first and second vehicle electrical system connection ( 10a . 10b ) with the high-voltage on-board electrical system ( 10 ) and from the first and second vehicle electrical system connection ( 10a . 10b ) of the high-voltage vehicle electrical system ( 10 ) to be electrically separated; An electrical mass ( 18 ); A first insulation resistance (R (+); R (-)) between the first electrical system connection ( 10a ; 10b ) and the mass 18 ; A first capacity (C (+), C (-)) between the first on-board power supply ( 10a ; 10b ) and the mass ( 18 ) and parallel to the first insulation resistance (R (+); R (-)); A measuring device ( 26 ), which is designed to measure the first insulation resistance (R (+); R (-)) and / or a voltage between the first electrical system connection ( 10a ; 10b ) and the mass ( 18 ), the measuring device ( 26 ) has an active and an inactive state; and a control device ( 26a ) for driving the measuring device ( 26 ), wherein the control device ( 26a ) is designed to allow the measuring device ( 26 ) from the inactive state to the active state and from the active state to the inactive state, wherein a total insulation resistance between the first vehicle electrical system connection ( 10a ; 10b ) and the mass ( 18 ) has a first value when the measuring device ( 26 ) is in the inactive state and the total insulation resistance has a second value which is smaller than the first value, when the measuring device ( 26 ) is in the active state; characterized in that the control device ( 26a ) is designed to allow the measuring device ( 26 ) such that the measuring device ( 26 ) is transferred from the inactive to the active state when the energy storage ( 12 ) from the high-voltage on-board electrical system ( 10 ) is separated. Circuit arrangement ( 20 ) according to claim 1, characterized in that - the first insulation resistance (R (+); R (-)) is provided by one or more electrical resistance components (Riso (+); Riso (-)) in a series and / or parallel connection is; and - the first capacitance (C (+); C (-)) is provided by one or more capacitors (Cy (+); Cy (-)) in series and / or parallel connection. Circuit arrangement ( 20 ) according to one of the preceding claims, characterized in that the measuring device ( 26 ) comprises an insulation monitoring device and / or an insulation monitor and / or a voltage divider. Circuit arrangement ( 20 ) according to one of the preceding claims, characterized in that the measuring device ( 26 ) comprises a detuning resistor (R26) and the measuring device ( 26 ) is set up in such a way that the detuning resistor (R26) in the event of a transfer from the inactive state to the active state in the case of a separation of the energy store ( 12 ) from the high-voltage on-board electrical system ( 10 ) is connected in parallel to the first insulation resistance (R (+); R (-)). Circuit arrangement ( 20 ) according to one of the preceding claims, characterized in that the circuit arrangement ( 20 ) a second capacitance (C (-); C (+)) between the second vehicle electrical system connection ( 10b ; 10a ) and the mass ( 18 in particular, wherein the second capacitance (C (-); C (+)) is different from the first capacitance (C (+); C (-)). Method for operating a circuit arrangement of a motor vehicle, comprising the circuit arrangement - a high-voltage on-board electrical system ( 10 ) with a first and a second vehicle electrical system connection ( 10a . 10b ); A coupling device ( 24 ), which is designed to store an energy store ( 12 ) via the first and second vehicle electrical system connection ( 10a . 10b ) with the high-voltage on-board electrical system ( 10 ) and from the first and second vehicle electrical system connection ( 10a . 10b ) of the high-voltage vehicle electrical system ( 10 ) to be electrically separated; An electrical mass ( 18 ); A first insulation resistance (R (+); R (-)) between the first electrical system connection ( 10a ; 10b ) and the mass 18 ; A first capacity (C (+), C (-)) between the first on-board power supply ( 10a ; 10b ) and the mass ( 18 ) and parallel to the first insulation resistance (R (+); R (-)); A measuring device ( 26 ), which is designed to measure the first insulation resistance (R (+); R (-)) and / or a voltage between the first electrical system connection ( 10a ; 10b ) and the mass ( 18 ), the measuring device ( 26 ) has an active and an inactive state; and a control device ( 26a ) for driving the measuring device ( 26 ), wherein the control device ( 26a ) is designed to allow the measuring device ( 26 ) from the inactive state to the active state and from the active state to the inactive state, wherein a total insulation resistance between the first vehicle electrical system connection ( 10a ; 10b ) and the mass ( 18 ) a first value when the measuring device ( 26 ) is in the inactive state and the total insulation resistance has a second value which is smaller than the first value, when the measuring device ( 26 ) is in the active state; characterized in that the measuring device ( 26 ) is transferred from the inactive to the active state when the energy storage ( 12 ) from the high-voltage on-board electrical system ( 10 ) is separated.

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