Method for determining at least one current capacitance value of a y capacitance of a high-voltage on-board power system and electronic computing device

Abstract

The invention relates to a method for determining at least one current capacitance value (38) of a Y-capacitance (34, 36) of an on-board power system (12) of a motor vehicle (10), wherein a high-voltage energy store (16) of the on-board power system (12) is electrically connected to an energy store outer portion (30) by means of a switching device (40) of the on-board power system (12), and wherein a first insulation resistance (42) is determined from a capacitance value (48) of the on-board power system (12) by means of a first insulation monitor (20) in an energy store inner portion (18) of the on-board power system (12), wherein a second insulation resistance (44) of the on-board power system (12) is determined by means of at least one central second insulation monitor (28) of the energy store outer portion (30), and the first insulation resistance (42) is compared with the second insulation resistance (44). In order to determine the first insulation resistance (42) of the on-board power system (12) by means of the first insulation monitor (20), the capacitance value (48) is adjusted in accordance with the comparison result in such a way that the first insulation resistance (42) converges on the second insulation resistance (44). The invention also relates to an on-board power system (12).

Description

Technical Field

[0001] This invention relates to a method for determining, by means of an electronic computing device, at least one current capacitance value of a Y-capacitor in a high-voltage on-board electrical network for at least a partially electrically driven motor vehicle. The invention also relates to an on-board electrical network. Background Technology

[0002] It is known from the prior art that in the onboard electrical system of at least partially electrically driven motor vehicles, the total capacitance (technically referred to as Y capacitance) between potentials HV+ and HV- in the high-voltage vehicle system and the corresponding vehicle ground is... Y The limit value of the Y capacitor represents a permissible parameter that must be determined during manufacturing or when the system is defined. This value is limited because the capacitor can discharge to a human body when simultaneously touching an HV-potential and a vehicle, potentially causing a dangerous electric shock. Knowing the actual value of the Y capacitor is crucial because it is incorporated as a component, partly due to parasitic effects and partly to eliminate interference from components within its electronic circuitry, thus affecting insulation compatibility.

[0003] DE 10 2016 006 642 A1 relates to a high-voltage battery for motor vehicles, comprising a conductive battery casing and a stack of cell units connected in series to provide a high-voltage voltage. The cell units are arranged within the battery casing, wherein each cell unit is connected between a high-voltage positive conductor conductively connected to the positive terminal of the cell stack and a high-voltage negative conductor conductively connected to the negative terminal of the cell stack. The high-voltage battery also includes an insulation measuring device designed to determine an insulation fault based on the insulation resistance between the cell stack and the battery casing. A locating device is designed to locate the determined insulation fault within the cell unit based on a first voltage applied between the high-voltage positive conductor and the battery casing and / or a second voltage applied between the high-voltage negative conductor and the battery casing. The invention also relates to a corresponding method.

[0004] According to DE 10 2010 054 413 A1, a method for locating insulation faults within a system is provided. The system includes a DC section with a high-voltage side (HV+) and a low-voltage side (HV-) and an AC section comprising an inverter with at least one series circuit consisting of two power switches connected between the high-voltage side (HS side) and the low-voltage side (LS side). The DC section is supplied with a DC voltage from a DC voltage source. Power switches directly applied to the HS side are switched on corresponding to the HS-on state, and power switches directly applied to the LS side are switched on corresponding to the LS-on state. In each of these two on states, the HS insulation voltage between the HS side and ground and the LS insulation voltage between the LS side and ground are measured, respectively. Finally, based on the measurement results, it is determined whether an insulation fault exists in the DC section or the AC section.

[0005] DE 10 2016 214 458 A1 discloses an apparatus and method for detecting dielectric breakdown in an environmentally friendly vehicle. The apparatus includes a measuring mechanism configured to measure the resistance value of an insulation resistance located on a high-voltage battery. The apparatus also includes a control device configured to measure the voltage applied across the insulation resistance using the measuring mechanism and to analyze the pattern of the measured voltage to detect the portion of the dielectric breakdown.

[0006] DE 10 2018 002 926 A1 relates to an onboard electrical network for a motor vehicle, having at least one first potential line and a second potential line, wherein the onboard electrical network is designed to be subjected to a DC voltage between the potential lines in accordance with a specified operation, wherein the onboard electrical network has at least one Y capacitor electrically connected to one of the potential lines at a first terminal and electrically connected to a reference potential at a second terminal, wherein a switching element is connected in series with respect to the at least one Y capacitor.

[0007] DE 10 2020 003 878 A1 also illustrates a high-voltage on-board electrical network for at least partially electrically driven motor vehicles, having at least one high-voltage accumulator and an external portion thereof. The high-voltage accumulator has a protection mechanism designed to electrically connect the high-voltage accumulator to the external portion thereof, and the high-voltage accumulator also has a first insulation monitor. Additionally, the high-voltage on-board electrical network has a central second insulation monitor, at least for the external portion thereof.

[0008] DE 10 2013 216 801 A1 discloses a system and method for simultaneously calculating the insulation resistance value and Y capacitance value of an energy storage system. In this case, a first signal is injected into the energy storage system, wherein the output signal of the energy storage system is then acquired as a response to the first signal. Thus, in one method, the value of the Y capacitance and the value of the insulation resistance are determined from the first signal and the output signal. Summary of the Invention

[0009] The objective of this invention is to provide a method and an onboard electrical network that enables more accurate determination of the Y capacitor within the onboard electrical network.

[0010] This task is accomplished by the method according to the independent claim and by an onboard electrical system. Advantageous embodiments are described in the dependent claims.

[0011] One aspect of the invention relates to a method for determining at least one current capacitance value of a Y capacitor in a high-voltage on-board electrical network for at least a partially electrically driven motor vehicle using an electronic computing device, wherein a high-voltage accumulator of the high-voltage on-board electrical network is electrically connected to an external portion of the accumulator using a switching device of the high-voltage on-board electrical network, and wherein a first insulation resistance is determined based on the capacitance value of the on-board electrical network using a first insulation monitor located within the accumulator of the high-voltage on-board electrical network.

[0012] It is stipulated that the second insulation resistance of the vehicle electrical network, especially the high-voltage vehicle electrical network, is determined by means of at least one central second insulation monitor, and the first insulation resistance is compared with the second insulation resistance by means of the electronic computing device of the vehicle electrical network, and the capacitance value is adjusted / adapted according to the comparison result so that the first insulation resistance of the vehicle electrical network is determined by means of the first insulation monitor: that is, the first insulation resistance is made to converge with / adapt to the second insulation resistance.

[0013] Therefore, it is feasible that even when the current capacitance value of the entire vehicle-mounted power grid is unknown, the first insulation resistance can still be determined by the first insulation monitor. Thus, the first insulation monitor inside the energy storage unit of the high-voltage vehicle-mounted power grid can be used to accurately determine the insulation resistance of the entire vehicle-mounted power grid.

[0014] It should be noted that the second insulation monitor does not need to know the current capacitance value of the vehicle electrical network in order to determine the insulation resistance within the entire vehicle electrical network and can perform the determination independently of this.

[0015] The first insulation monitor inside the accumulator of the high-voltage vehicle-mounted electrical network was originally designed to determine the insulation resistance of the accumulator within the high-voltage vehicle-mounted electrical network. This required the current capacitance value of the vehicle-mounted electrical network under test, which was known to the accumulator and stored in the computing device. Therefore, the first insulation monitor inside the accumulator of the high-voltage vehicle-mounted electrical network could accurately determine the insulation resistance of the accumulator based on the capacitance value. However, to determine the insulation resistance of the entire vehicle-mounted electrical network, the capacitance value of the entire network, which is usually unknown, was required in principle.

[0016] The method now uses the electronic computing device of the vehicle's electrical network to compare the first insulation resistance with the second insulation resistance by changing and continuously adjusting the capacitance value associated with the first insulation resistance until the first insulation resistance matches the second insulation resistance. Since the insulation resistances of the first and second insulation monitors are now similar, and in particular identical, it can be assumed that the capacitance value considered when determining the first insulation resistance now corresponds to the current capacitance value of the vehicle's electrical network.

[0017] By comparing the insulation resistance of the first and second insulation monitors, the current capacitance value of the vehicle electrical network can be indirectly inferred and determined. This current capacitance value can then be written to and stored in a computing device or other data storage, and in particular, used as an initial capacitance value for determining the insulation resistance of the entire vehicle electrical network. Other functions related to capacitance, especially Y-capacitors, can then retrieve and use the currently determined capacitance value.

[0018] In other words, this method can be used to approximately or very precisely determine what is also called C in the high-pressure system within a motor vehicle. Y The value of the Y capacitance. The sum of the Y capacitances is related to the permit, and is especially useful for checking the compliance of the entire system when using vehicle structures connected to high-voltage systems. Furthermore, a simple insulation measuring device provides accurate values ​​knowing the corresponding Y capacitance. If, for example, the second insulation monitor in the high-voltage system fails, the battery-mounted insulation measuring device, in other words, the first insulation monitor, can serve as an alternative, allowing the high-voltage system to continue operating. This prevents a complete breakdown / total failure of the vehicle. Because C has been identified and stored... Y The value is thus more accurate when the insulation paper is determined by the alternative equipment, thereby preventing false alarms about insulation faults with greater security and meeting the corresponding legal trigger thresholds in the event of a fault.

[0019] If the determined capacitance value or the insulation resistance determined by the first insulation monitor differs from that of the second insulation monitor, then the changed C stored in the internal insulation monitor can be repeatedly used recursively. Y The values ​​are calculated until the two measured results are consistent.

[0020] Furthermore, it also enables improved identification of unbalanced loads. To reliably identify unbalanced loads and respond accordingly, the required C can be known at any time. Y Value and the C Y The value also dynamically adapts to the aging and temperature processes. This is because C can be determined. Y Therefore, it is possible to forgo setting or storing corresponding parameters for each vehicle configuration. Vehicle modifications and the accompanying changes within the high-voltage system are also directly compensated for.

[0021] Therefore, improved availability in the event of a breakdown saves vehicle users time and costs, as they can continue driving their vehicles to at least the nearest factory without having to wait for them to be towed away.

[0022] Specifically, it is stipulated that the first insulation monitor, located inside the high-voltage accumulator, can determine the insulation resistance of the high-voltage accumulator before it is switched on. Simultaneously, a second insulation monitor, located in other components, measures the insulation resistance of the rest of the high-voltage on-board electrical network to prevent the accumulator, or, for example, a fuel cell, from being connected to the high-voltage on-board electrical network with potential insulation problems. If the external central second insulation monitor fails, the insulation value of the rest of the high-voltage on-board electrical network is unknown, and it should be assumed that a fault exists due to the permissible correlation of this value, potentially prohibiting vehicle operation and causing a breakdown. It is also stipulated that, in the event of a second insulation monitor failure, the first insulation monitor, designed to have a weakened function compared to the second insulation monitor, takes over the determination of the insulation value. However, for this purpose, the first insulation monitor requires the capacitance value of the on-board electrical network region whose insulation resistance needs to be determined. But since the capacitance value is determined and stored for current use while the second insulation monitor is still active by bringing the first insulation resistance to converge with the second insulation resistance, the first insulation monitor can now take over the determination of the insulation resistance for the on-board electrical network, especially the entire on-board electrical network, by means of the stored capacitance value. Therefore, emergency operation of the vehicle can be achieved when the second insulation monitor fails. The probability of failure can be further reduced by determining the Y capacitance value.

[0023] Because different configurations with various capacitance values ​​can be achieved depending on the connection status of each part of the vehicle electrical network, multiple capacitance values ​​can be determined and stored. Thus, for each possible vehicle electrical network configuration, depending on the connection status of a local area of ​​the vehicle electrical network, its own capacitance value can be stored, and it can also be retrieved in the working state of its respective configuration and used to determine the first insulation resistance with the help of the first insulation monitor.

[0024] This invention therefore takes particular advantage of the fact that the more accurately the Y capacitance at each high-voltage potential is known, the better the first insulation monitor functions. If the second insulation monitor malfunctions, reliable further operation can be achieved by prior determination of the Y capacitance using the first insulation monitor.

[0025] According to an advantageous embodiment, an initial capacitance value for the capacitance value is preset as a stored capacitance value in the storage device of an electronic computing device. For example, this initial capacitance value may be determined and stored in the storage device when the vehicle electrical system is manufactured. Now, corresponding aging within the vehicle electrical system may cause deviations in the initial capacitance value. This deviation may in turn lead to different determinations of the insulation resistance. According to the present invention, the initial capacitance value is replaced or supplemented using the current capacitance value. It may be advantageous to retain the original initial capacitance value in memory so that the current capacitance value can be compared with it. As already stated, the currently determined capacitance value may also correspond to other configurations of the vehicle electrical system and therefore be other capacitance values. Advantageously, a history of the determined and stored capacitance values ​​can also be created, by which changes and perhaps also the aging of the vehicle electrical system or vehicle electrical system areas can be identified.

[0026] Another advantage is that the initial capacitance value can be preset during the manufacturing of the vehicle. In particular, the corresponding measurements can be performed on the vehicle and the corresponding initial capacitance value, which also corresponds to the Y capacitance value, can be taken into account. These can then be stored, for example, in a storage device and used by an electronic computing device in the future.

[0027] It has also proven advantageous to periodically compare the first insulation resistance with the second insulation resistance and perform adjustments to the current capacitance value. In particular, the corresponding measurements from the first and second insulation monitors are periodically compared, especially during operation of the high-voltage vehicle-mounted power grid. This is particularly advantageous when switching between the first and second insulation monitors. If the value is sufficiently constant after multiple measurements, the value of the first insulation monitor can be compared with the value of the second insulation monitor. If the two insulation resistances are approximately identical, especially exactly identical, then the capacitance value substantially corresponds to the current capacitance value and is applied as the current capacitance value, which in particular approximately corresponds to the actual value of the sum of the corresponding Y capacitances.

[0028] Another advantage is that the first capacitance value is repeatedly adjusted to determine the current capacitance value. In other words, this method is broadly equivalent to balancing an analog measurement bridge, where the unknown value is also determined by comparing it with a known value. This capacitance value is continuously and repeatedly adjusted until the value of the first insulation resistance corresponds to the second insulation resistance measurement value determined using a second insulation monitor without knowing the capacitance. Therefore, a simple yet reliable method can be provided.

[0029] In another advantageous embodiment, the current capacitance value is stored in the storage device of the electronic computing device for future evaluation. In other words, the current capacitance value determined in this method is stored. The currently stored capacitance value can then be taken into account in future measurements. Thus, for example, it can be stipulated that the currently determined capacitance value is taken into account in future checks, wherein a comparison and balancing of the insulation resistances of the first and second insulation monitors is then performed.

[0030] It is also advantageous to determine the current insulation resistance of the vehicle's electrical network using a first insulation monitor based on the determined current capacitance value. For example, it can determine the aging of the insulation within the vehicle. Thus, appropriate warnings can be issued to vehicle users regarding faults in a specific component of the vehicle or its insulation, thereby enabling them to, for example, enter a factory in advance and avoid, for example, breaking down on the road.

[0031] According to another advantageous embodiment, after adjusting the current capacitance value, the current capacitance value is re-determined and compared with the adjusted current capacitance value. This allows verification of the determined Y capacitance value for the first insulation monitor. Therefore, it can be verified whether the currently determined capacitance value also corresponds to the actual capacitance value.

[0032] It can also be stipulated that, since there are generally more than one accumulator installed in a motor vehicle, the remaining first insulation monitors of each accumulator can also determine C using the method of this invention. Y The electronic computing device can then generate an average value for all determined results. This average value can then be stored and used as the current capacitance value. Alternatively, the capacitance determined by the first insulation monitor can be compared first, so that outliers or erroneous values ​​are not considered when calculating the average. Alternatively, if multiple values ​​exist, the median of those values ​​can be stored as the current capacitance value.

[0033] Another aspect of the invention relates to an onboard electrical network for at least partially electrically driven motor vehicles, comprising at least one electronic computing device, a high-voltage energy storage device, a first insulation monitor, and a second insulation monitor, wherein the onboard electrical network is designed to perform the method according to the preceding aspect. In particular, the method is performed by means of the onboard electrical network.

[0034] Another aspect of the invention relates to a motor vehicle having an onboard electrical network according to a prior aspect. The motor vehicle is particularly at least partially electrically driven. The motor vehicle is particularly fully electric.

[0035] Advantageous implementations of this method should be considered advantageous implementations of onboard electrical systems and motor vehicles. Onboard electrical systems and motor vehicles therefore possess the subject matter characteristics that allow the execution of this method. Attached Figure Description

[0036] Other advantages, features, and details of the invention will become apparent from the following description of preferred embodiments and in conjunction with the drawings. The features and combinations of features mentioned above in the specification, as well as those mentioned below in the description of the drawings and / or shown individually in the unique figures, may be used not only in their respective specified combinations, but also in other combinations or individually, without departing from the scope of the invention.

[0037] Figure 1 A schematic circuit block diagram of an embodiment of a motor vehicle having an onboard electrical network is shown.

[0038] In the figure, identical or functionally identical parts are labeled with the same reference numerals. Detailed Implementation

[0039] Figure 1 An embodiment of a motor vehicle 10 having an onboard electrical network 12 is schematically shown. The onboard electrical network 12 is designed for at least partially electrically driven motor vehicles 10, especially fully electric motor vehicles 10. The onboard electrical network 12 is, in particular, a so-called high-voltage onboard electrical network. The onboard electrical network 12 has at least one electronic computing device 14. In addition, the onboard electrical network 12 has at least one high-voltage energy storage device 16. It can be specified that the onboard electrical network 12 also has a number of other high-voltage energy storage devices 16. The onboard electrical network 12 also has a first insulation monitor 20 in the internal portion 18 of the energy storage device, which is connected to the ground 22 of the motor vehicle 10. The first insulation monitor 20 is connected to the high-voltage potentials 24 and 26 of the high-voltage energy storage device 16. In particular, the first insulation monitor is connected to the high-voltage positive potential 24 and the high-voltage negative potential 26.

[0040] The vehicle-mounted electrical network 12 also has a second insulation monitor 28, which may also be referred to as a central insulation monitor. The second insulation monitor 28 is formed in the energy storage external portion 30 of the vehicle-mounted electrical network 12. It may also be specified that the vehicle-mounted electrical network 12 includes a pre-charging device 32 for pre-charging the energy storage external portion 30.

[0041] The first insulation monitor 20 is designed to have significantly reduced functionality compared to the second insulation monitor 28.

[0042] A first Y capacitor 34 can be formed in the high-voltage positive path 24, and a second Y capacitor 36 can be formed in the high-voltage negative path 26. The first Y capacitor 34 is therefore a Y capacitor formed between the high-voltage positive path 24 and the ground 22, while the second Y capacitor 36 is a Y capacitor formed between the high-voltage negative path 26 and the ground 22.

[0043] In a method for determining at least one current capacitance value 38 of the Y capacitors 34, 36 of the high-voltage on-board electrical network 12 of at least partially electrically driven motor vehicle 10 by means of an electronic computing device 14, the high-voltage accumulator 16 of the high-voltage on-board electrical network is electrically connected to the external portion 30 of the accumulator by means of a switching device 40 of the high-voltage on-board electrical network 12, and a first insulation resistance 42 is determined based on the capacitance value 48 of the on-board electrical network 12 by means of a first insulation monitor 20 in the internal portion 18 of the accumulator of the on-board electrical network 12.

[0044] It is stipulated that the second insulation resistance 44 of the vehicle electrical network 12 is determined at least by means of the second insulation monitor 28 of the external part 30 of the energy storage device, and the first insulation resistance 42 is compared with the second insulation resistance 44 by means of the electronic computing device 14 of the vehicle electrical network 12, and the capacitance value 48 is adjusted according to the comparison result in order to determine the first insulation resistance 42 of the vehicle electrical network 12 by means of the first insulation monitor 20, that is, so that the first insulation resistance 42 is similar to the second insulation resistance 44.

[0045] Specifically, it can be stipulated that the initial capacitance value used to determine the first insulation resistance 42 is preset as a capacitance value stored in the storage device 46 of the electronic computing device 14. By comparing the first insulation resistance 42 with the second insulation resistance 44, the capacitance value 48 can be determined and adopted as the current capacitance value 38 of the Y capacitors 34 and 36. The initial capacitance value can be preset, in particular, during the manufacturing of the motor vehicle.

[0046] Therefore, it is specifically proposed that, in order to determine the first insulation resistance 42, a first insulation monitor 20 within the accumulator can be used, which should have full knowledge of the Y capacitors 34 and 36. That is, only when the stored C values ​​of the Y capacitors 34 and 36 are known... Y The measured value of the first insulation resistance 42 is only matched when the values, especially the sum of Y capacitors 34 and 36, are considered. It is now proposed that the result of the second insulation monitor 28 be taken into account as a reference, and that the value be periodically switched between the central insulation monitor and the battery-internal insulation monitors 20 and 28 during the operation of the vehicle electrical network 12. If the value remains sufficiently constant after multiple measurements, the value of the first insulation monitor 20 can be compared with the value of the second insulation monitor 28. If they match, then the value of capacitor 48 stored in the first insulation monitor 20 for calibration is approximately equal to the actual value of the sum of Y capacitors 34 and 36.

[0047] If the determined value of the first insulation resistance 42 is different from the value of the second insulation resistance 44 determined by the second insulation monitor 28, then the changes in capacitance 48, especially C, can be repeated recursively. YThe value is determined until the two insulation resistance measurements are consistent. A remeasurement can then be performed for confirmation. This method is broadly equivalent to balancing an analog measurement bridge, where the unknown value is also determined by comparison with known values. The value of capacitor 48 used for the first insulation monitor 20 is continuously adjusted until the value of the first insulation resistance 42 measured by it corresponds to the value of the second insulation resistance 44, wherein the second insulation resistance 44 is determined based on the second insulation monitor 28, particularly with respect to C. Y The value is determined regardless of other factors.

[0048] Since there are usually more than one high-voltage accumulator 16 installed in the vehicle 10, this method can also be used to determine C through the other insulation monitors of the high-voltage accumulator 16. Y The value can be used to calculate the average of all given results.

[0049] List of reference numerals

[0050] 10 Motor vehicles

[0051] 12 Vehicle-mounted power grid

[0052] 14 Electronic computing devices

[0053] 16 High-voltage accumulators

[0054] 18. Internal components of the accumulator

[0055] 20 First Insulation Monitor

[0056] 22 Grounding

[0057] 24 High-voltage positive path

[0058] 26 High-voltage negative path

[0059] 28 Second Insulation Monitor

[0060] 30. External part of the accumulator

[0061] 32 Pre-charging device

[0062] 34 First Y capacitor

[0063] 36 Second Y capacitor

[0064] 38 Current capacitance value

[0065] 40 Switching device

[0066] 42 First insulation resistance

[0067] 44 Second insulation resistance

[0068] 46 Storage devices

[0069] 48 Capacitance value

Claims

1. Method for determining at least one current capacitance value (38) of a vehicle electrical system Y-capacitance (34, 36) by means of an electronic computing device (14), the Y-capacitance being used in a vehicle electrical system (12) of an at least partially electrically driven motor vehicle (10), wherein - the high-voltage energy store (16) of the vehicle electrical system (12) is electrically connected to the energy store outer portion (30) by means of a switching device (40) of the vehicle electrical system (12), wherein a first insulation resistance (42) is determined from a capacitance value (48) of the vehicle electrical system (12) by means of a first insulation monitor (20) in an energy store inner portion (18) of the vehicle electrical system (12), wherein an initial capacitance value for the capacitance value (48) is predefined as a stored capacitance value in a memory device (46) of the electronic computing device (14), characterized in that - a second insulation resistance (44) of the vehicle electrical system (12) is determined by means of at least one central second insulation monitor (28) of the energy store outer portion (30), wherein the second insulation resistance (44) is determined independently of a capacitance value of the vehicle electrical system Y capacitor (34, 36) by means of the second insulation monitor (28), - the first insulation resistance (42) is compared with the second insulation resistance (44) by means of the electronic computing device (14) of the vehicle electrical system (12), and the capacitance value (48) is adjusted in accordance with the comparison for determining the first insulation resistance (42) of the vehicle electrical system (12) by means of the first insulation monitor (20) in such a way that the first insulation resistance (42) converges toward the second insulation resistance (44), wherein the capacitance value (48) in the case where the first insulation resistance (42) is closest to the second insulation resistance (44) is adopted as the current capacitance value (38).

2. The method of claim 1, wherein, The initial capacitance value is predefined when the motor vehicle (10) is manufactured.

3. The method according to claim 1 or 2, characterized in that, The first insulation resistance (42) is compared with the second insulation resistance (44) at regular intervals and the adaptation of the capacitance value (48) is carried out.

4. The method of claim 3, wherein, The adjustment of the capacitance value (48) is repeated for determining the current capacitance value (38).

5. The method of claim 3 wherein, The current capacitance value (38) is stored as an initial capacitance value in the memory device (46) of the electronic computing device (14) for future evaluations.

6. The method of claim 5, wherein the step of After the current capacitance value (38) has been adjusted and stored as an initial capacitance value, a further redetermination of the current capacitance value (38) is carried out and the redetermined value is compared with the stored initial capacitance value.

7. The method of claim 1 or 2, wherein, The current first insulation resistance (42) of the vehicle electrical system (12) is determined by means of the first insulation monitor (20) in accordance with the determined current capacitance value (38).

8. An on-board electrical system (12) for an at least partially electrically driven motor vehicle (10) having at least one electronic computing device (14), a high-voltage energy accumulator (16), a first insulation monitor (20) and a second insulation monitor (28), wherein The vehicle electrical system (12) is designed to carry out the method according to one of claims 1 to 7. The vehicle electrical system (12) is designed to carry out the method according to one of claims 1 to 7.

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