DE102021110879B3 - Method, device and computer program product for correcting a measured insulation voltage - Google Patents

Abstract

The present invention relates to a method for correcting a measured insulation voltage (118) between a high-voltage potential (106) and a low-voltage potential (108), in particular in a vehicle, using the measured insulation voltage (118) and one between the high-voltage potential (106) and the low-voltage potential (108) built-in capacitance (120) and an insulation resistance (122) determined between the high-voltage potential (106) and the low-voltage potential (108), an error (126) of the measured insulation voltage (118) is determined, using the error ( 126) and the measured insulation voltage (118) a corrected insulation voltage (128) is output.

Description

technical field

The present invention relates to a method for correcting a measured insulation voltage between a high-voltage potential and a low-voltage potential, in particular in a vehicle, and a corresponding device.

State of the art

The present invention will be described in the following mainly in connection with traction batteries for vehicles. However, the invention can be used for any application in which a high-voltage battery voltage is to be measured.

In a vehicle, the traction battery is integrated into the vehicle's high-voltage system. The high-voltage system separates a high-voltage potential of the traction battery from a low-voltage potential of an auxiliary battery in the vehicle.

For example, to detect leakage currents between the high-voltage potential and the low-voltage potential, an electrical voltage can be measured between the high-voltage potential and the low-voltage potential.

the DE 10 2015 101 074 A1 discloses a method and a circuit arrangement for determining an insulation value of a network, a measuring arrangement being temporarily connected to the network and a reference point. The method comprises the steps: measuring a first voltage on the grid when the measuring arrangement is not connected to the grid, connecting the measuring arrangement to the grid, measuring a second voltage on the grid, disconnecting the measuring arrangement from the grid, measuring a third voltage at the grid, determining an isolation quantity based on at least one element of the measurement arrangement, the first voltage, the second voltage and the third voltage.

US 2012/0 221 269 A1 discloses a method and system for determining leakage resistances in a bus system. The bus system has a floating DC bus that is connected to the bus voltage source. The system also includes a pair of known resistors, each connected to the bus through a switch. The method includes measuring a voltage between the bus and ground and measuring a voltage between ground and the second terminal with the first switch closed and the second switch open. The method also includes measuring a voltage between the bus and ground and measuring a voltage between ground and the second terminal with the first switch open and the second switch closed. The first and second leakage resistances are then calculated as a function of the known resistances and the measured voltages.

Description of the invention

One object of the invention is therefore to provide an improved method for correcting a measured insulation voltage between a high-voltage potential and a low-voltage potential in a vehicle and a corresponding improved device using means that are as simple as possible in terms of design.

The object is solved by the subject matter of the independent claims. Advantageous developments of the invention are specified in the dependent claims, the description and the accompanying figures. In particular, the independent claims of a claim category can also be developed analogously to the dependent claims of another claim category.

When accelerating a vehicle using an electric drive of the vehicle, a high-voltage voltage provided by a traction battery of the vehicle drops due to an internal resistance of the traction battery. Conversely, the high-voltage voltage increases when recuperating using the electric drive.

However, the high-voltage voltage is also influenced during acceleration and recuperation by the electrical influences of capacitances and resistances between a high-voltage system and a mass of the vehicle.

With the approach presented here, the high-voltage in the vehicle can be monitored under dynamic conditions and corrected if necessary.

A method for correcting a measured insulation voltage between a high-voltage potential and a low-voltage potential, in particular in a vehicle, is presented, using the measured insulation voltage and a capacitance installed between the high-voltage potential and the low-voltage potential and an insulation resistance determined between the high-voltage potential and the low-voltage potential, an error in the measured isolation voltage is determined, using the error and the measured isolation voltage, a corrected isolation voltage is output.

A high-voltage potential can correspond to a motor vehicle high-voltage. The high voltage can be several hundred volts, for example 400 volts. The high voltage can also be up to 1000 volts. A low-voltage potential can be a ground potential of a vehicle, for example. A body of the vehicle can be at ground potential. However, the low-voltage potential can also be 12 volts, 24 volts or 48 volts.

An insulation monitor of the vehicle can have at least one measuring resistor that can be switched between the high-voltage potential and the low-voltage potential and a measuring device for detecting the insulation voltage across the resistor, i.e. an electrical voltage dropping across the resistor.

The measuring resistor can be a high-impedance resistor, so that no significant electrical current flows between the high and the low-voltage potential across the resistor. The measuring resistor can be connected to the high-voltage potential and/or the low-voltage potential using a switch and can be separated from the high-voltage potential and/or the low-voltage potential after the insulation voltage has been detected.

The insulation voltage depends on an electrical voltage between the high-voltage potential and the low-voltage potential and the electrical resistance of the measuring resistor.

The course of the insulation voltage over time depends on a capacitance installed between the high-voltage potential and the low-voltage potential and on an insulation resistance present between the high-voltage potential and the low-voltage potential. The insulation voltage at the measuring resistor can therefore deviate from a battery voltage of the traction battery.

The capacitance can result from at least one electrical component of the vehicle that is connected between the high-voltage potential and the low-voltage potential. The capacitance can be designed as a capacitor, in particular as a Y-capacitor. The capacity of the component is known. In the case of several components, the capacities interact or add up to lead to an overall capacity.

Since the insulation voltage at the measuring resistor is influenced by the insulation resistance and the capacitance, the course of the insulation voltage is time-dependent. Since the capacitance and the insulation resistance are known, an error in the measured insulation voltage compared to the battery voltage can be determined and the actual insulation voltage can thus be deduced. Using the corrected insulation voltage, the insulation resistance can be determined for the next calculation.

The error can also be determined using an error determined at a previous point in time. The error can be determined iteratively or numerically. By using the error determined at the previous point in time, the error can be approximated or estimated.

A time profile of the fault can be determined using a time profile of the measured insulation voltage and the capacitance as well as the determined insulation resistance. A time profile of the corrected insulation voltage can be output using the time profile of the error and the time profile of the measured insulation voltage. That featured here The method provided can be carried out continuously or at time intervals, ie, for example periodically.

A first error in the measured first insulation voltage can be determined using a first insulation voltage measured between high-voltage plus and ground and a first capacitance installed between high-voltage plus and ground and a first insulation resistance determined between high-voltage plus and ground. A corrected first isolation voltage can be output using the first error and the measured first isolation voltage. A second error in the measured second insulation voltage can be determined using a second insulation voltage measured between high-voltage minus and ground and a second capacitance installed between high-voltage minus and ground and a second insulation resistance determined between high-voltage minus and ground. A corrected second isolation voltage can be output using the second error and the measured second isolation voltage. The isolation voltages can be asymmetrical. The insulation voltages can be divided according to a capacitance ratio between the first capacitance and the second capacitance. Likewise, the insulation voltages can be divided according to a resistance ratio between the first insulation resistance and the second insulation resistance. The breakdown of the insulation voltages can be influenced at different points in time by the capacitances and the insulation resistances.

At the beginning of the determination of the error, an estimate of the insulation resistance can be used as the insulation resistance. The insulation resistance can be iteratively optimized based on the estimated value. By optimizing, the error can be determined with increasing accuracy.

At the beginning of the determination of the error, an estimate of the capacitance can be used as the capacitance. The capacity can be iteratively optimized based on the estimated value. By optimizing, the error can be determined with increasing accuracy.

At the beginning of the determination of the fault, the capacitance can be considered more than the insulation resistance. In the course of determining the fault, the insulation resistance can be considered more than the capacitance. At the beginning of the determination, the error is more dependent on the capacitance than on the insulation resistance. In the course of the determination, the error depends more on the insulation resistance than on the capacity. In particular, the error at the beginning of the determination is more dependent on a ratio of the capacitances than on a ratio of the insulation resistances. In the course of the determination, the error is more dependent on the insulation resistance ratio than on the capacitance ratio.

The corrected insulation voltage can be output as the difference between the error and the measured insulation voltage. The corrected isolation voltage can be easily calculated.

The method can be implemented, for example, in software or hardware or in a mixed form of software and hardware, for example in a control unit.

The approach presented here also creates a device that is designed to carry out, control or implement the steps of a variant of the method presented here in corresponding devices.

The device can be an electrical device with at least one computing unit for processing signals or data, at least one memory unit for storing signals or data, and at least one interface and/or one communication interface for reading in or outputting data that are embedded in a communication protocol, be. The computing unit can be, for example, a signal processor, a so-called system ASIC, or a microcontroller for processing sensor signals and outputting data signals as a function of the sensor signals. The storage unit can be, for example, a flash memory, an EPROM or a magnetic storage unit. The interface can be designed as a sensor interface for reading in the sensor signals from a sensor and/or as an actuator interface for outputting the data signals and/or control signals to an actuator. The communication interface can be designed to read in or output the data in a wireless and/or wired manner. The interfaces can also be software modules that are present, for example, on a microcontroller alongside other software modules.

A computer program product or computer program with program code, which can be stored on a machine-readable carrier or storage medium such as a semiconductor memory, a hard disk memory or an optical memory and for carrying out, implementing and/or controlling the steps of the method according to one of the embodiments described above, is also advantageous used, especially when the program product or program is run on a computer or device.

character list

• 1 eine Darstellung eines Isolationswächters mit einer Vorrichtung gemäß einem Ausführungsbeispiel; und
• 2 Darstellungen von Spannungsverläufen gemäß einem Ausführungsbeispiel.

An advantageous exemplary embodiment of the invention is explained below with reference to the accompanying figures. Show it:

• 1 a representation of an insulation monitor with a device according to an embodiment; and
• 2 Representations of voltage curves according to an embodiment.

The figures are only schematic representations and only serve to explain the invention. Elements that are the same or have the same effect are provided with the same reference symbols throughout.

Detailed description

1 10 shows an illustration of an insulation monitor with a device 100 according to an exemplary embodiment. The insulation monitor is part of a vehicle's high-voltage system. The high-voltage system has a traction battery 102 that provides a high-voltage potential 106 via a battery voltage 104 . The insulation monitor is connected between the high-voltage potential 106 and a low-voltage potential 108 of the vehicle. The low-voltage potential 108 is part of a low-voltage system of the vehicle. The low-voltage potential 108 is here at a ground 110 of the vehicle.

The insulation monitor has a measuring resistor 112 that can be switched between the high-voltage potential 106 and the low-voltage potential 108 , a switch 114 for switching the measuring resistor 112 and a measuring device 116 for detecting an insulation voltage 118 at the measuring resistor 112 . The insulation monitor is connected in parallel to a capacitor 120 arranged between the high-voltage potential 106 and the low-voltage potential 108 and in parallel to an insulation resistance 122 of the high-voltage system against the low-voltage potential 108 .

Due to an internal resistance of the traction battery 102, the battery voltage 104 depends on a load condition of the traction battery 102. If the battery voltage 104 changes, the insulation resistance 122 and the capacitance 120 result in a corruption of the insulation voltage 118, which the insulation monitor can detect. Measured isolation voltage 118 is corrected using device 100 .

The device 100 reads the measured isolation voltage 118 and, using a value of the isolation resistance 122 and a value of the capacitance 120, determines an error 126 of the measured isolation voltage 118. Using the error 126 and the measured isolation voltage 118, the device 100 determines a corrected isolation voltage 128 .

In one embodiment, the insulation monitor has two measuring resistors 112 (R_measp, R_measn), two switches 114 (SW_p, SW_n) and two measuring devices 116 . The first measuring resistor 112 (R_measp), the first switch 114 (SW_p) and the first measuring device 116 are arranged between a positive pole 130 of the high-voltage potential 106 and the low-voltage potential 108 . The second measuring resistor 112 (R_measn), the second switch 114 (SW_n) and the second measuring device 116 are arranged between a negative pole 132 of the high-voltage potential 106 and the low-voltage potential 108 . Since the low-voltage potential 108 is at ground 110, between the positive pole 130 and ground 110 and between the negative pole 132 and ground 110 approximately half the high-voltage potential 106 or half the battery voltage 104 (U_Bat) is present.

The first measuring resistor 112 (R_measp) and the first measuring device 116 can be connected in parallel with a first capacitance (C_yp) 120 and a first insulation resistance (R_isop) 122 to measure a first isolation voltage 118 by the first switch 114 (SW_p). The second measuring resistor 112 (R_measn) and the second measuring device 116 can be used to measure a second isolation voltage 118 are switched by the second switch 114 (SW_n) in parallel with a second capacitance 120 (C_yn) and a second isolation resistance 122 (R_ison).

The device reads the first measured isolation voltage 118 and the second measured isolation voltage 118 . The device 100 determines a first error 126 of the first measured isolation voltage 118 using one of the first measured isolation voltage 118, the first capacitance 120 and the first isolation resistance 122. Using the first error 126 and the first measured isolation voltage 118, the device 100 determines a first corrected isolation voltage 128. The device 100 determines a second error 126 of the second measured isolation voltage 118 using the second measured isolation voltage 118, the second capacitance 120 and the second isolation resistance 122. Using the second error 126 and the second measured isolation voltage 118 the device determines 100 a second corrected isolation voltage 128.

2 shows representations of three voltage curves according to an embodiment. The voltage curves are shown in two time-correlated diagrams, which have the time t in seconds on the abscissa and a voltage U in volts on the ordinate.

The first diagram shows a course of a battery voltage 104 of a traction battery of a vehicle during a sequence of acceleration processes of the vehicle.

A first longer acceleration process is followed by two shorter acceleration processes and then another longer acceleration process. When not under load, the traction battery has a battery voltage of 400 volts. The battery voltage 104 drops due to an internal resistance of the traction battery during the acceleration processes. In this case, there is also an electrical influence of the capacitance arranged between the high-voltage potential and the low-voltage potential and of the insulation resistance. Due to the capacity, the battery voltage 104 first drops sharply during an acceleration process and then approaches a minimum value approximately asymptotically. The lowest value can be up to approx. 60 volts below an initial value. After the acceleration process, the battery voltage 104 rises sharply again and approaches 400 volts approximately asymptotically.

The course of a measured insulation voltage 118 during the acceleration processes is shown in the second diagram. The measured insulation voltage 118 theoretically corresponds to half the battery voltage 104 in the first diagram. Here, too, the influence of the capacitance is clearly recognizable. The measured insulation voltage also drops during the acceleration process. In contrast to the battery voltage 104, the measured insulation voltage 118 only increases to a lower value after the longer acceleration processes than before the respective acceleration process. After the shorter acceleration processes, the measured insulation voltage 118 increases to a higher value than before the respective acceleration process. As a result, the measured insulation voltage 118 reaches a higher value than half the battery voltage 104 after the second short acceleration process.

In addition, the course of an insulation voltage 128 corrected according to the approach presented here is shown in the second diagram. The corrected insulation voltage 128 is corrected by an instantaneous error 126 in relation to the respectively measured insulation voltage 118 due to the electrical influence of the capacitance and the insulation resistance.

The corrected isolation voltage 128 does not show any dips during the acceleration processes and only follows a trend of the measured isolation voltage 118.

In other words, an optimized insulation measurement through error estimation to correct for voltage fluctuations is presented.

Strong acceleration and recuperation processes in the vehicle can cause fluctuations in the high-voltage battery voltage. These fluctuations have a negative effect on the insulation measurement of the internal insulation monitor (so-called IsoMonitor). To determine the insulation resistances in the vehicle, this measures the insulation voltages between high-voltage plus and ground as well as high-voltage minus and ground and assumes a stable voltage. The voltage fluctuations can lead to severe measurement inaccuracies and even to the measurement being aborted. With a passive isolation measurement method, known resistances are connected in parallel with the insulation resistances and the charge-reversal curve of the insulation voltages during the switching process is analyzed.

Conventionally, it is assumed that a voltage drop in the high-voltage battery voltage has a symmetrical effect on the insulation voltages. For example, if the high-voltage battery voltage drops by 50V, then each isolation voltage is assumed to drop by 25V. In fact, the voltage dip is initially divided with the ratio of the Y capacitances and later with the ratio of the insulation resistances. This is taken into account in the approach presented here, which means that a voltage drop can be corrected very precisely.

In the approach presented here, an error estimator determines the current error in the battery voltage and then uses the previously determined error, the insulation voltages and the previously determined insulation resistances and Y capacitances to calculate the current error in the insulation voltages. With the first calculation, assumptions are made for the starting values of the insulation resistance and the Y-capacitance. It is also taken into account that the error in the insulation voltages is initially distributed with the ratio of the Y capacitances and only later with the ratio of the insulation resistances.

With the approach presented here, improved measurement accuracy can be achieved with the same measurement duration and increased availability.

1 shows an example of a high-voltage system of an electric vehicle and contains the high-voltage battery voltage, known, switchable measuring resistors between the high-voltage system and low-voltage ground, unknown insulation resistances to be determined between the high-voltage system and low-voltage ground and known Y-capacitors between the high-voltage system and low-voltage ground.

The following diagrams in 2 show an exemplary driving profile based on fluctuations in the battery voltage U_ _Bat and the effect of the driving profile on the measurable insulation voltages, which serve as the basis for determining the insulation resistances. This determination is possible in various variants. From the diagrams it can be seen that the ideal insulation voltage has an "exponential" course due to the charging/discharging of the Y-capacitors. This is an important criterion for the precise determination of the insulation resistances in a sufficiently short time. Furthermore, it can be seen that the disturbed insulation voltage deviates significantly from the ideal curve. The RC behavior is only partially recognizable.

For the correction approach presented here, differential equations of the high-voltage system shown above are set up for the two insulation voltages. These describe the dynamic behavior of the insulation voltages as a function of the system parameters insulation resistance (R _iso ), measuring resistance (R _meas ), capacity C _y ) and internal resistance of the battery (R _bat ). R _p and R _n here represent the resistance value of the parallel connection of measuring resistor and insulation resistance (eg R _p =R _isop || R _measp ) as long as the measuring circuit is connected to the high-voltage system. Otherwise R _p = R _isop . $${\text{u}}_{{\text{isop}}^{\left(\text{t}\right)}}=\frac{1}{{\text{C}}_{\text{p}}}{\displaystyle \int \left(\frac{{\text{u}}_{{\text{asked}}^{\left(\text{t}\right)}}-{\text{u}}_{{\text{isop}}^{\left(\text{t}\right)}}-{\text{u}}_{{\text{ison}}^{\left(\text{t}\right)}}}{{\text{R}}_{\text{asked}}}-\frac{{\text{u}}_{\text{isop}}}{{\text{R}}_{\text{p}}}\right)}{\text{German U}}_{{\text{ison}}^{\left(\text{t}\right)}}=\frac{1}{{\text{C}}_{\text{n}}}\cdot {\displaystyle \int \left(\frac{{\text{u}}_{{\text{asked}}^{\left(\text{t}\right)}}-{\text{u}}_{{\text{isop}}^{\left(\text{t}\right)}}-{\text{u}}_{{\text{ison}}^{\left(\text{t}\right)}}}{{\text{R}}_{\text{asked}}}-\frac{{\text{u}}_{{\text{ison}}^{\left(\text{t}\right)}}}{{\text{R}}_{\text{n}}}\right)}\text{German}$$

$${\text{U}}_{{\text{n}}_{\text{k}}}=\frac{{\text{R}}_{\text{p}}\cdot {\text{U}}_{{\text{bat}}_{\text{k}}}\cdot \Delta \text{t}-{\text{C}}_{\text{n}}\cdot {\text{R}}_{\text{n}}\cdot {\text{U}}_{{\text{n}}_{\text{k}-1}}+{\text{C}}_{\text{p}}\cdot {\text{R}}_{\text{n}}\cdot {\text{R}}_{\text{p}}\cdot {\text{U}}_{{\text{p}}_{\text{k}-1}}+{\text{C}}_{\text{n}}\cdot {\text{R}}_{\text{n}}\cdot {\text{R}}_{\text{p}}\cdot {\text{U}}_{{\text{bat}}_{\text{k}}}}{{\text{R}}_{\text{n}}\cdot \Delta \text{t}+{\text{R}}_{\text{p}}\cdot \Delta \text{t}+{\text{C}}_{\text{n}}\cdot {\text{R}}_{\text{n}}\cdot {\text{R}}_{\text{p}}+{\text{C}}_{\text{p}}\cdot {\text{R}}_{\text{n}}\cdot {\text{R}}_{\text{p}}}$$

The differential equation system consisting of the differential equations mentioned above is solved. There are various approaches for this, just as there are for determining the insulation resistance from the voltage profile. The implicit Euler method, which represents a numerical solution method, is used here as an example. The equations result after some transformations and the assumption that the internal battery resistance is = 0 Ω. $${\text{u}}_{{\text{n}}_{\text{k}}}=\frac{{\text{R}}_{\text{n}}\cdot {\text{u}}_{{\text{asked}}_{\text{k}}}\cdot \Delta \text{t}+{\text{C}}_{\text{n}}\cdot {\text{R}}_{\text{n}}\cdot {\text{u}}_{{\text{n}}_{\text{k}-1}}-{\text{C}}_{\text{p}}\cdot {\text{R}}_{\text{n}}\cdot {\text{R}}_{\text{p}}\cdot {\text{u}}_{{\text{p}}_{\text{k}-1}}+{\text{C}}_{\text{p}}\cdot {\text{R}}_{\text{n}}\cdot {\text{R}}_{\text{p}}\cdot {\text{u}}_{{\text{asked}}_{\text{k}}}}{{\text{R}}_{\text{n}}\cdot \Delta \text{t}+{\text{R}}_{\text{p}}\cdot \Delta \text{t}+{\text{C}}_{\text{n}}\cdot {\text{R}}_{\text{n}}\cdot {\text{R}}_{\text{p}}+{\text{C}}_{\text{p}}\cdot {\text{R}}_{\text{n}}\cdot {\text{R}}_{\text{p}}}$$

$${\text{u}}_{{\text{n}}_{\text{k}}}=\frac{{\text{R}}_{\text{p}}\cdot {\text{u}}_{{\text{asked}}_{\text{k}}}\cdot \Delta \text{t}-{\text{C}}_{\text{n}}\cdot {\text{R}}_{\text{n}}\cdot {\text{u}}_{{\text{n}}_{\text{k}-1}}+{\text{C}}_{\text{p}}\cdot {\text{R}}_{\text{n}}\cdot {\text{R}}_{\text{p}}\cdot {\text{u}}_{{\text{p}}_{\text{k}-1}}+{\text{C}}_{\text{n}}\cdot {\text{R}}_{\text{n}}\cdot {\text{R}}_{\text{p}}\cdot {\text{u}}_{{\text{asked}}_{\text{k}}}}{{\text{R}}_{\text{n}}\cdot \Delta \text{t}+{\text{R}}_{\text{p}}\cdot \Delta \text{t}+{\text{C}}_{\text{n}}\cdot {\text{R}}_{\text{n}}\cdot {\text{R}}_{\text{p}}+{\text{C}}_{\text{p}}\cdot {\text{R}}_{\text{n}}\cdot {\text{R}}_{\text{p}}}$$

The two equations now describe the behavior of the insulation voltages in discrete-time form. Δt is the time between two evaluations of the equations (eg sampling time of the voltage = 1 ms). x _k is the value of the variable "x" at time "k", i.e. at the current time. x _k-1 is the value of the variable "x" at the time "k-1", i.e. in the previous evaluation step.

To correct the measured insulation voltage, the two equations are loaded with the voltage change of the measured battery voltage. The result of the evaluation of the equations in each evaluation step k is the error in the insulation voltages U _{iso_err} caused by the fluctuating battery voltage. These are then subtracted from the measured insulation voltages U _{iso_meas} , resulting in the corrected insulation voltages U _{iso_korr} . $${\text{u}}_{{\text{iso\_corr}}_{\text{k}}}={\text{u}}_{{\text{iso\_meas}}_{\text{k}}}-{\text{u}}_{{\text{iso\_err}}_{\text{k}}}$$

Since the devices and methods described in detail above are exemplary embodiments, they can be modified to a large extent in the usual way by a person skilled in the art without departing from the scope of the invention. In particular, the mechanical arrangements and the size ratios of the individual elements to one another are only chosen as examples.

reference list

100

contraption

102

traction battery

104

battery voltage

106

high-voltage potential

108

low-voltage potential

110

Dimensions

112

measuring resistor

114

Switch

116

gauge

118

measured insulation voltage

120

capacity

122

insulation resistance

126

mistake

128

corrected insulation voltage

130

positive pole

132

negative pole

Claims (10)

Method for correcting a measured insulation voltage (118) between a high-voltage potential (106) and a low-voltage potential (108), using the measured insulation voltage (118) and a capacitance (120) installed between the high-voltage potential (106) and the low-voltage potential (108) and an insulation resistance (122) determined between the high-voltage potential (106) and the low-voltage potential (108), an error (126) in the measured insulation voltage (118) is determined, using the error (126) and the measured insulation voltage (118) to correct a corrected Insulation voltage (128) is output. procedure according to claim 1 wherein the error (126) is further determined using an error (126) determined at a past time. Method according to one of the preceding claims, in which using a time profile of the measured insulation voltage (118) and the capacitance (120) and the determined Isola tion resistor (122) a time profile of the error (126) is determined, using the time profile of the error (126) and the time profile of the measured insulation voltage (118) a time profile of the corrected insulation voltage (128) is output. Method according to one of the preceding claims, in which using a first insulation voltage (118) measured between high-voltage plus (139) and ground (110) and a first capacitance (120) installed between high-voltage plus (130) and ground (110) and one between high-voltage plus (130) and ground (110) determined first insulation resistance (122), a first error (126) of the measured first insulation voltage (118) is determined, using the first error (126) and the measured first insulation voltage (118) a corrected first Insulation voltage (128) is output, further using a second insulation voltage (118) measured between high-voltage minus (132) and ground (110) and a second capacitance (120) installed between high-voltage minus (132) and ground (110) and one between high-voltage minus (132) and ground (110) determined second insulation resistance (122), a second error (126) of the measured second insulation voltage (118 ) is determined, wherein a corrected second isolation voltage (128) is output using the second error (126) and the measured second isolation voltage (118). A method according to any one of the preceding claims, wherein an estimate of the insulation resistance (122) is used as the insulation resistance (122) at the beginning of the determination of the fault (126). Method according to one of the preceding claims, in which an estimate of the capacitance (120) is used as the capacitance (120) at the beginning of the determination of the error (126). Method according to one of the preceding claims, in which at the beginning of the determination of the error (126) the capacitance (120) is taken into account more than the insulation resistance (122), with the insulation resistance (122) being taken into account more during the course of the determination of the error (126). is called the capacity (120). Method according to one of the preceding claims, in which the corrected insulation voltage (128) is output as the difference between the error (126) and the measured insulation voltage (118). Device (100), wherein the device (100) is designed to carry out, implement and/or control the method according to one of the preceding claims in corresponding devices. Computer program product that is set up to guide a processor when executing the computer program product to perform the method according to one of Claims 1 until 8th to execute, implement and/or control.

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