Method for monitoring insulation resistances and corresponding computer program and control unit

Abstract

The invention relates to a method for monitoring insulation between two electrical conductors (102, 103), in particular high-voltage electrical conductors, and ground (104) by means of an insulation monitoring circuit, wherein the insulation monitoring circuit has two switches (SWTestP, SWTestM), the method comprising the following steps: (a) changing a switching state (115, 116) of the two switches (SWTestP, SWTestM) at a first time (t1); (b) again changing the switching state (115, 116) of the two switches (SWTestP, SWTestM) at a second time (t2), which is a predetermined time interval (114) after the first time (t1); (c) Receiving a measured value (Pha2, Pha3) that is representative of a voltage (UChsGnd) between a first electrical line (103) of the two electrical lines (102, 103) and ground (104) at a third time (t3) during the specified time interval (114);(d) Receiving a change value (ΔUBat) that is representative of a change in voltage (UBat) between the two electrical conductors (102, 103) before the third time (t3); (e) Correcting the measured value (Pha2, Pha3) based on the change value (ΔUBat); and (f) Determining an insulation resistance (RisoPP, RisoPM, RisoLP, RisoLM) based on the corrected measured value (Pha2, Pha3). The invention further relates to a corresponding control unit and computer program.

Description

TECHNICAL AREA

[0001] The present disclosure relates to methods and control devices for monitoring insulation resistances, in particular for a high-voltage system of a motor vehicle. BACKGROUND OF THE INVENTION

[0002] In high-voltage (HV) battery and drive systems for motor vehicles, insulation resistances between electrical conductors and ground must be determined to ensure safe and reliable operation. It must be ensured that these insulation resistance values ​​do not fall below the threshold values ​​specified by the vehicle manufacturers. Insulation monitoring methods, such as those described in DE 10 2021 203 919 A1 or DE 10 2018 222 123 B4, can be used for this purpose. However, it has been shown that such methods can produce erroneous insulation resistance values ​​under certain conditions. In such cases, safe operation of the battery and drive systems can no longer be guaranteed. Undetected insulation faults can lead to uncontrolled fault currents, which may endanger human lives, cause fires, or result in other property damage.

[0003] From DE 10 2014 204 870 A1, a device for monitoring electrical insulation in a vehicle's electrical system is known, comprising (i) a voltage source for generating DC voltages with a first and a second voltage value, (ii) a current connection point through which a positive power supply line and a negative power supply line of the electrical system are electrically connected, (iii) a first current path between the positive power supply line and the current connection point, (iv) a second current path between the negative power supply line and the current connection point, (v) a third current path between the current connection point and the voltage source, (vi) at least two current measuring units: a first current measuring unit in the first current path, a second current measuring unit in the second current path, and a third current measuring unit in the third current path, and (vii) a detection unit.set up to determine an insulation resistance between the vehicle electrical system and electrical ground from current readings of at least two current measuring units and the first and second voltage readings. SUMMARY AND FORMS OF EXECUTION

[0004] Therefore, one objective of the present disclosure is to provide a method and corresponding control device for insulation monitoring, wherein in situations where conventional methods provide inaccurate or erroneous results, the insulation resistance(s) are corrected accordingly.

[0005] This task is accomplished by a method for insulation monitoring, a computer program, and a control unit according to the independent patent claims. Advantageous embodiments and further developments are described in the dependent claims, the following description, and the drawings.

[0006] According to a first aspect, a method is provided for monitoring insulation between two electrical conductors, in particular high-voltage electrical conductors, and ground by means of an insulation monitoring circuit, wherein the insulation monitoring circuit has two switches.The method comprises the following steps: (a) changing the switching state of the two switches at a first time point; (b) changing the switching state of the two switches again at a second time point, which is a predetermined time interval after the first time point; (c) receiving a measured value that is representative of and / or corresponds to a voltage between a first electrical conductor of the two electrical conductors and ground at a third time point during the predetermined time interval; (d) receiving a change value that is representative of and / or corresponds to a change in a voltage between the two electrical conductors before the third time point; (e) correcting the measured value based on the change value; and (f) determining, in particular calculating, an insulation resistance based on the corrected measured value.

[0007] According to another aspect, a control unit, in particular a battery management system, is provided which is configured to carry out the previously described procedure. According to one embodiment, the control unit includes the insulation monitoring circuit. Alternatively, the insulation monitoring circuit can also be arranged in a battery, in particular in or on a battery housing.

[0008] According to another aspect, a battery system is provided which includes the previously described control unit including insulation monitoring circuitry and a battery, in particular a vehicle battery and / or a high-voltage battery.

[0009] According to another aspect, a computer program is provided that includes instructions which, when executed by a computer, cause it to perform the procedure described above. In the context of this disclosure, a computer is defined, for example, as a device that processes data using programmable computational instructions. Computers can be embedded in everyday devices, such as the control units of motor vehicles.

[0010] According to another aspect, a storage medium is provided with a computer program, wherein the computer program includes instructions which, when the computer program is executed by a computer, cause it to carry out the procedure described above.

[0011] In the context of this disclosure, an electrical conductor is defined, for example, as a means for transmitting electrical energy and / or electrical signals. The electrical conductor may be a high-voltage conductor. The electrical conductor may connect a terminal of a battery, in particular a positive terminal or a negative terminal of the battery, to a terminal to which one or more loads may be connected. The terminal may be a link terminal. The two electrical conductors may connect a positive terminal of the battery to a positive terminal and a negative terminal of the battery to a negative terminal.

[0012] In the context of this disclosure, high voltage is defined, for example, as an alternating voltage greater than 30 V, in particular less than 1 kV, and / or a direct voltage greater than 60 V, in particular less than 1.5 kV. An electrical conductor can be a high-voltage conductor if corresponding voltages occur between the electrical conductor and ground.

[0013] In the context of this disclosure, insulation resistance is defined, for example, as the resistance between electrical conductors and / or between an electrical conductor and ground. According to one embodiment, the insulation resistance indicates the degree or state of insulation. Predefined threshold values ​​for the insulation resistance can correlate with various protection classes.

[0014] In the context of this disclosure, an insulation monitoring circuit is defined, for example, as an electrical circuit by means of which one or more insulation resistances can be determined. The insulation monitoring circuit comprises at least two switches. Each switch can be configured to connect one of the two electrical conductors to ground and / or to disconnect it from ground. The switches can be connected in series with a respective test resistor. The switches and / or test resistors can be connected in parallel with corresponding insulation resistances.

[0015] In the context of the present disclosure, a switching state is defined, for example, in relation to the switching position of one or more switches, in particular the at least two switches. The beginning of the switching state can be defined by the switching of at least one of the switches. The end of the switching state can also be defined by the switching of at least one of the switches. The switching state can be defined such that none of the switches are switched during the switching state. In other words, a switching state can be defined over the period between two directly successive switch changes. A switching sequence can be defined as a succession of several switching states, in particular several directly successive switching states.

[0016] Changing the switching state of the two switches may require switching at least one of them. Between the change and the subsequent change, i.e., during the specified time interval, the switching state of both switches may remain unchanged. The specified time interval then refers to the duration of the switching state between the change and the subsequent change. The specified time interval may, but does not necessarily, include the first and second points in time.

[0017] In the context of this disclosure, the expression "based on" can mean that the specified quantity is taken into account, for example, for correcting, determining, or calculating, but other quantities besides the one specified may also be considered. "Based on" is therefore not exclusive.

[0018] The previously described method and / or control unit can be advantageous to ensure reliable operation of the insulation monitoring circuit and thus enable safe operation of the battery system.

[0019] Methods for determining insulation resistance can produce inaccurate or even erroneous results if a change in battery voltage occurs during a switching state before the third measurement point. This change could be caused, for example, by a load change in an electric motor connected to the battery system or by recuperation. The insulation monitoring circuit has one or more RC elements characterized by measuring resistors, insulation resistances, and parasitic capacitances. Due to such an RC element, the voltage between the first electrical conductor and ground stabilizes only slowly after a change in battery voltage, for example, only after several seconds. Therefore, it can happen that the voltage between the first electrical conductor and ground has not stabilized sufficiently by the third measurement point.Because this voltage is needed for calculating the insulation resistance, an inaccurate or faulty insulation resistance value can result, with corresponding uncertainties for touch protection in the case of an undetected one-sided insulation fault, up to and including the risk of a vehicle fire in the case of an undetected two-sided insulation fault.

[0020] By correcting the measured value based on any voltage changes in the battery voltage, a correct insulation resistance, or at least an insulation resistance within specified error tolerances, can be calculated.

[0021] According to one embodiment, two insulation resistances are determined, wherein one of the insulation resistances is between one of the two electrical conductors and ground, and the other insulation resistance is between the other of the two electrical conductors and ground.

[0022] According to one embodiment, the voltage between the two electrical conductors is a battery voltage, measured particularly in or at a battery, for example within a battery housing, and / or a load-side voltage, for example a link voltage. An associated measuring device can be part of the insulation monitoring circuit.

[0023] According to one embodiment, the voltage between the first electrical conductor and ground is a voltage between an electrical conductor that is connected or connectable to a negative terminal of a battery and ground, for example a so-called KL31 voltage, or a voltage between a conductor that is connected or connectable to a positive terminal of the battery and ground.

[0024] According to one embodiment, the method further comprises: determining a time interval between a point in time of the voltage change, in particular a beginning and / or an end of the voltage change, and a third point in time, wherein the measured value is corrected based on this time interval. The voltage change can occur instantaneously or over a period of time. The voltage change can be caused by a load change of a consumer connected to the battery, for example, by a load demand for accelerating a vehicle and / or by recuperation during braking of the vehicle. In the first case, the battery voltage can decrease; in the second case, the battery voltage can increase. With such load changes, the gradient of the voltage change in the battery voltage can be steep, for example, so steep that the voltage change occurs almost instantaneously.Such an embodiment can be advantageous because the time span can have a significant influence on the extent to which the voltage change affects the measured value, i.e., the extent to which the measured value needs to be corrected.

[0025] According to one embodiment, the voltage change occurs over a period of time, and the measured value is corrected based on this period and / or the shape of the voltage change. For example, the start and / or end times of the period can be taken into account. Such an embodiment can be advantageous because the period and / or the shape of the voltage change can influence whether the voltage between the first electrical conductor and ground stabilizes sufficiently by the third time point, or how large any necessary correction of the measured value should be.

[0026] According to one embodiment, the voltage change occurs instantaneously. Such an embodiment can be advantageous because, with an instantaneous change, the required correction can be determined particularly easily.

[0027] According to one embodiment, the measured value is only corrected if the change value exceeds a predetermined voltage threshold and / or the time interval exceeds a predetermined time threshold. The predetermined voltage threshold can be, for example, 20 V, in particular 10 V, and in particular 5 V. Such an embodiment can be advantageous because, in the case of small voltage changes and / or voltage changes shortly before the third point in time, i.e., the measurement time, the corresponding corrections can be negligibly small. However, in the case of voltage changes shortly before the third point in time, the battery voltage before the voltage change would have to be used to calculate the insulation resistance.

[0028] According to one embodiment, the measured value is only corrected if the time interval falls below a predetermined further time threshold. This further time threshold can, for example, be determined by a period during which the voltage between the first electrical conductor and ground approximately stabilizes. It can also be defined in relation to the predetermined time interval, for example, as a specific fraction of the time interval, such as two-thirds or four-fifths. Such an embodiment can be advantageous because, if the voltage signal is sufficiently stabilized at the third time point, a correction may not be necessary. To calculate the insulation resistance, the battery voltage after the voltage change would have to be used.

[0029] According to one embodiment, several measured values ​​are determined for different switching states of a switching sequence. These measured values ​​are optionally corrected according to the described method, and the insulation resistance is determined based on the multiple, optionally corrected, measured values. In particular, the ratio of the optionally corrected measured value to the voltage between the two conductors, for example, the battery voltage, can be relevant for determining the insulation resistance.

[0030] According to one embodiment, the correction of the measured value takes into account a calibratable characteristic map. Multiple calibratable characteristic maps can also be considered. The characteristic map can be stored, for example, in the form of a lookup table and / or in the form of functional dependencies. Such an embodiment can be advantageous if there is no simple relationship between the change value and / or time interval and the correction of the measured value.

[0031] According to one embodiment, calibratable characteristic maps are taken into account for different switching states of a switching sequence.

[0032] According to one embodiment, the characteristic map has at least one of the following parameters as an input parameter: the time interval; the change value. In particular, both parameters can be used as input parameters, whereby a common characteristic map or separate characteristic maps for the parameters can be used. Further input parameters can be: the period of the voltage change, the curve of the voltage change. Such an embodiment can be advantageous because the correction of the measured value by the aforementioned parameters can be determined with sufficient accuracy.

[0033] According to one embodiment, the characteristic map has a correction offset and / or a correction factor as output parameters, and the correction of the measured value takes the correction offset and / or the correction factor into account. For example, the measured value can first be multiplied by the correction factor and then the correction offset added, or vice versa. Such an embodiment can be advantageous because the correction is performed using simple means that require little computing power and time, while simultaneously achieving a sufficiently accurate correction so that the corrected measured value lies within the relevant tolerance limits.

[0034] According to one embodiment, the characteristic map is calibrated on a test bench.

[0035] According to one embodiment, the voltage profile between the first electrical conductor and ground during the time interval is extrapolated to correct the measured value. For this purpose, the previous profile from the first time point up to the beginning of the time interval can be fully or partially considered. Extrapolation can be linear or, for example, using a second-order function. Such an embodiment can be advantageous because no complex calibration is required, and sufficient accuracy may still be achieved.

[0036] According to one embodiment, the method further comprises: determining a time offset between the change in voltage between the two electrical conductors, in particular the onset of the voltage change, and a corresponding change in voltage between the first electrical conductor and ground, taking the time offset into account when correcting the measured value. Such an embodiment can be advantageous if the time relationship between the voltage between the two electrical conductors and the voltage between the first conductor and ground is unclear and / or cannot be neglected for calculating the insulation resistance. For example, the voltages mentioned can be measured by different measuring systems, such as a battery-powered measuring system and a measuring system of the insulation monitoring circuit.

[0037] According to one embodiment, the time offset is determined on a test bench. According to another embodiment, it can be assumed that the time offset, once determined, does not change, for example, over the lifetime of the associated motor vehicle.

[0038] According to one embodiment, the third point in time lies in the last quarter of the specified time interval, particularly in the last fifth. Such an embodiment can be advantageous if the voltage signal has sufficiently stabilized by these time periods.

[0039] According to one embodiment, the third time point is chosen such that the voltage between the first electrical conductor and ground approximately stabilizes by the third time point, particularly if no voltage change is detected or the detected voltage change is below a predetermined threshold. Such a condition may be necessary for a correct determination of the insulation resistance.

[0040] According to one embodiment, the voltage between the first electrical conductor and ground stabilizes approximately by the third time point if at least one of the following conditions is met: the slope of the voltage curve before or at the third time point is less than a predetermined slope threshold; the voltage change between the first electrical conductor and ground in an end segment of the predetermined time interval is less than five percent, in particular less than two percent, of the voltage change during the entire predetermined time interval, with the third time point falling within that end segment. The duration of the end segment can, for example, be at most one-quarter of the predetermined time interval, in particular at most one-fifth. The end segment can encompass a portion of the switching state that extends to the end of the switching state.The voltage changes can be determined by minimum and maximum values ​​within the corresponding time period or interval, in particular by the difference between the maximum and minimum values. Such criteria can be particularly easy to implement, requiring little computing and storage capacity. It can be ensured that a voltage value measured in the final section, especially at the end of the corresponding switching state, deviates from the final voltage only by a predefined voltage threshold.

[0041] According to one embodiment, one of the two switches is configured to disconnect an electrical connection between one of the electrical conductors and ground, and / or the other of the two switches is configured to disconnect an electrical connection between the other of the electrical conductors and ground. The two electrical conductors can be connected to a positive terminal or a negative terminal of a battery, in particular a vehicle battery, or can be connected by means of a switch, in particular a contactor. The switches can be connected in series with a respective test resistor. The switches and / or test resistors can be connected in parallel with the corresponding insulation resistances.

[0042] According to one embodiment, ground is assigned to the chassis of a motor vehicle. In particular, one terminal of each switch can be electrically connected to the chassis. An opposite terminal can be connected to the corresponding electrical line. Such a configuration can be particularly advantageous in high-voltage systems because, for safety reasons, none of the battery terminals may be connected to ground. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Further advantages and beneficial designs and further developments of the method and the control unit result from the following exemplary embodiments shown in connection with the figures.

[0044] They show: Fig. 1 a battery system with an insulation monitoring circuit for use in an insulation monitoring method according to an embodiment of the present disclosure; Fig. 2 a switching sequence for determining insulation resistances and a corresponding voltage waveform between an electrical conductor and ground for use in a method for insulation monitoring according to an embodiment of the present disclosure; Fig. 3 and Fig. 4 changes in a battery voltage that affect the voltage profile between an electrical conductor and ground, such that a measured value must be corrected using a method according to an embodiment of the present disclosure; Fig. 5 a schematic representation of a characteristic map for correcting the measured value using a method according to an embodiment of the present disclosure.

[0045] Identical, similar, or similarly effective elements are marked with the same reference symbols in the figures. In some figures, individual reference symbols have been omitted for clarity. The figures and the relative sizes of the elements depicted within them are not to be considered to scale. Rather, individual elements may be exaggerated for better representation and / or comprehensibility. DETAILED DESCRIPTION OF EXAMPLES OF EXECUTION

[0046] Fig. Figure 1 shows a battery system 100 of a motor vehicle with a high-voltage battery 101 and an insulation monitoring circuit. The battery system 100 has a first electrical conductor 102, which connects a positive terminal B1+ of the battery 101 to a left-side or load-side positive terminal A1+ / P1+ of the battery system 101, and a second electrical conductor 103, which connects a negative terminal B1- of the battery 101 to a left-side or load-side negative terminal A1- / P1-. Both electrical conductors 102 and 103 are insulated from ground 104 by a battery-side insulation 105 with corresponding insulation resistances RisoPP and RisoPM, and a left-side insulation 106 with corresponding insulation resistances RisoLP and RisoLM. Ground 104 is connected to the vehicle chassis.The positive-side electrical conductor 102 is insulated from ground 104 by the insulation resistance RisoPP on the battery side and by the insulation resistance RisoLP on the left side. The negative-side electrical conductor 103 is insulated from ground 104 by the insulation resistance RisoPM on the battery side and by the insulation resistance RisoLM on the left side. A positive-side parasitic capacitance Cy1 exists between the positive-side electrical conductor 102 and ground 104. A negative-side parasitic capacitance Cy2 exists between the negative-side electrical conductor 103 and ground 104. Here, too, a distinction can be made between left-side and battery-side parasitic capacitances, if necessary.

[0047] The insulation monitoring circuit, or insulation monitor, has a positive-side electrical connection between the positive-side electrical line 102 and ground 104. This positive-side electrical connection includes a positive-side test switch SWTestP and a positive-side test resistor RTestP connected in series with it. Both the positive-side test switch SWTestP and the positive-side test resistor RTestP are connected in parallel with the positive-side insulation resistances RisoPP and RisoLP.

[0048] Similarly, the insulation monitoring circuit or insulation monitor has a negative-side electrical connection between the negative-side electrical line 103 and ground 104. This negative-side electrical connection comprises a negative-side test switch SWTestM and a negative-side test resistor RTestM connected in series with it. Both the negative-side test switch SWTestM and the negative-side test resistor RTestM are connected in parallel with the negative-side insulation resistors RisoPM and RisoLM.

[0049] The insulation monitoring circuit also includes a voltage measurement circuit by means of which a voltage UMEAS_KL31 between the negative-side electrical conductor 103 and ground 104, the so-called KL31 voltage, can be measured, in particular arranged between the electrical connection with the negative-side test switch SWTestM and the negative link terminal A1- / P1-. The voltage measurement device includes measuring resistors RMeasU, RMeasL and, for example, an analog-to-digital converter. Using this and / or another measurement circuit, the ground voltage or chassis voltage UChsGnd between ground 104 and the negative-side electrical conductor 103 can be determined.

[0050] The battery system 100 also features one or more measuring circuits for the battery voltage UBat or the link voltage ULink, which may include corresponding measuring resistors RRlink, RLink and / or analog-to-digital converters. Furthermore, contactors SWK1 and SWK3, respectively, are arranged in the positive-side electrical line 102 and the negative-side electrical line 103, respectively, which can be used to disconnect the connection between the battery and the respective link terminal or corresponding loads connected to the link terminals. A pre-charge switch SWK2, connected in parallel to the negative-side contactor SWK3, with a pre-charge resistor RK2 connected in series with it, can be used, among other things, for contactor weld detection, i.e., for detecting a malfunctioning contactor, for example, one that has been welded shut.

[0051] A high-voltage (HV) line 102, 103 to be monitored has an insulation resistance (RisoPP, RisoPM, RisoLP, RisoLM) of several hundred megaohms to several gigahertz as a parasitic component in a fault-free state. Additionally, the lines 102, 103 exhibit parasitic capacitances (Cy1, Cy2) as a physical property. This analysis considers the parasitic capacitances (Cy1, Cy2) located between the HV plus (HV+) line 102 and chassis ground (ChsGnd) 104, as well as between chassis ground 104 and the HV minus (HV-) line 103. These capacitances can range from a few nanofarads to several microfarads.

[0052] In the referenced insulation monitoring system, a measuring circuit is connected in parallel to the insulation resistance RisoPM, RisoLM. This circuit is characterized by the fact that the measuring resistors RTestP, RTestM, connected in parallel to the insulation resistances RisoPP, RisoPM, RisoLP, RisoLM, generate different voltage levels on a measurement signal through alternating switching. The insulation resistances between HV+ and ChsGnd, and ChsGnd and HV-, are determined from the ratio of the resulting measuring voltages UChsGnd and the battery voltage UBat. The typical measuring resistors RTestP, RTestM for such a system range from several hundred kΩ to several MΩ.

[0053] Switching a measuring resistor RTestP, RTestM initiates a charging process whose charging time is determined by the RC circuit consisting of the insulation resistance RisoPP, RisoPM, RisoLP, RisoLM and the measuring resistor RTestP, RTestM, and the parasitic capacitance Cy1, Cy2. Similarly, with any other fluctuation in the battery voltage UBat, such as those caused by dynamic processes during acceleration or recuperation of the HV battery 101, the measuring voltage is subject to a delay by the RC circuit compared to the battery voltage UBat.

[0054] The charging process via the RC circuit can typically take several seconds with fault-free insulation. In the referenced circuit, the insulation resistances RisoPP, RisoPM, RisoLP, and RisoLM are always determined after switching operations by waiting until a saturated measurement voltage (5-τ value) can be assumed, even with very high-resistance insulation; this typically takes several seconds.

[0055] During dynamic driving, situations arise where high load demands for vehicle acceleration cause the battery voltage UBat to drop sharply, or high recuperation during braking can cause the battery voltage UBat to rise sharply. The gradients of these voltage changes ΔUBat can be very steep. The timing of a battery voltage change ΔUBat is random. The effect of the battery voltage change ΔUBat on the partial voltage UChsGnd is delayed by the RC circuit.

[0056] Typically, to determine the insulation resistance RisoPP, RisoPM, RisoLP, RisoLM, the voltages UBat and UChsGnd are measured at fixed measurement times Pha2 and Pha3. These measurement times Pha2 and Pha3 are chosen so that UChsGnd has sufficient time to stabilize after switching the measuring circuit, assuming a fixed battery voltage UBat. The two voltages are therefore proportional to the resistance ratio of the measuring circuit and the insulation resistance.

[0057] If a battery voltage change ΔUBat occurs due to driving dynamics shortly before a measurement point Pha2 or Pha3, the long charging time of the RC circuit prevents a directly proportional relationship between UBat and UChsGnd from being established. The calculation of the insulation resistance becomes inaccurate or erroneous.

[0058] Fig. Figure 2 illustrates a method which uses the circuit made of Fig. 1 enables monitoring of one or more insulation resistances RisoPP, RisoPM, RisoLP, RisoLM, depending, among other things, on the switch positions of the contactors SWK1, SWK3 and the pre-charge switch SWK2.The procedure comprises the following steps: (i) switching at least two switches SWTestP, SWTestM of the insulation monitoring circuit according to a switching sequence 111 consisting of a sequence of several switching states 112 with a respective duration 114 of, for example, 7 seconds for each of the switching states 112; (ii) receiving measured values ​​Pha2, Pha3 of a voltage UChsGnd between the negative-side electrical conductor 103 and ground 104 at times at the end of an associated switching state 112; (iii) receiving measured values ​​of a voltage UBat between the two electrical conductors 103, 104 at the same times; and (iv) determining one or more insulation resistances RisoPP, RisoPM, RisoLP, RisoLM based on the measured values ​​received in the two previous steps, in particular the ratio of the voltages UChsGnd to UBat at the two times mentioned above at which the measured values ​​Pha2 and Pha3 are measured.The monitoring sequence can be performed once or several times in a system activation or driving cycle.

[0059] The various switching states 112 are determined by the state 115 of the positive-side test switch SWTestP and the state 116 of the negative-side test switch SWTestM. An upper line indicates a closed switch and a lower line an open switch. For example, in the first switching state 112, the positive-side switch SWTestP is closed and the negative-side switch SWTestM is open; in the second switching state 112, the positive-side switch SWTestP is open and the negative-side switch SWTestM is closed; in the third switching state 112, both the positive-side switch SWTestP and the negative-side switch SWTestM are closed. The switching sequence 111 then repeats.

[0060] In the lower part of Fig. Figure 2 shows a corresponding voltage profile 118 of the ground or chassis voltage UChsGnd, determined, for example, based on the KL31 voltage UMEAS_KL31. During the duration 114 of the switching states 112 of the switching sequence 110, sufficient saturation of the voltage signal is achieved so that the insulation resistances RisoPP, RisoPM, RisoLP, and RisoLM can be correctly determined. It has been shown that the ratios of the chassis voltage UChsGnd to the battery voltage UBat at measuring points Pha2 and Pha3 are relevant for determining the insulation resistances RisoPP, RisoPM, RisoLP, and RisoLM. These voltage values, or the resulting voltage ratios, can be sufficient for the calculation.

[0061] Fig. Figure 3 shows a repeated execution of the switching sequence 111 from Fig. 2 with switching states 112 and a state duration of 114. However, the voltage profile of the chassis voltage UChsGnd is now influenced by fluctuations in the battery voltage UBat. As can be seen from the comparison of the profiles of chassis voltage UChsGnd and battery voltage UBat along the common time axis t, the change in battery voltage UBat only fully affects the chassis voltage UChsGnd after a certain period of time. As already explained several times, this can lead to an inaccurate or incorrect determination of the insulation resistances RisoPP, RisoPM, RisoLP, and RisoLM.

[0062] Accordingly, a method is required that takes into account the influence of such fluctuations when monitoring the insulation between two electrical conductors 102, 103 and ground 104. The method also uses the insulation monitoring circuit from [reference missing]. Fig. 1, which in particular includes the positive-side test switch SWTestP and the negative-side test switch SWTestM. Aspects of such a method are described in the Fig. 4 and Fig. Figure 5 illustrates the procedure. The procedure comprises the following steps: (a) changing the switching state 115, 116 of the two switches SWTestP, SWTestM at a first time t1; (b) changing the switching state 115, 116 of the two switches SWTestP, SWTestM again at a second time t2, which is a predetermined time interval 114 after the first time t1; (c) receiving a measured value Pha2, Pha3, corresponding to a voltage UChsGnd between a first electrical line 102, 103 of the two electrical lines and ground 104 at a third time t3 during the predetermined time interval 114; (d) receiving a change value ΔU Bat,which corresponds to a voltage change between the two electrical conductors 102, 103 before the third time t3; (e) correcting the measured value Pha2, Pha3 based on the change value ΔUBat; and (f) calculating an insulation resistance RisoPP, RisoPM, RisoLP, RisoLM based on the corrected measured value Pha2, Pha3. Furthermore, a time interval Δt between the voltage change ΔUBat, in particular the start of the voltage change, and the third time t3 can also be taken into account for correcting the measured value Pha2, Pha3.

[0063] A related method comprises the following steps: 1. Determination of the magnitude of the voltage change based on the battery voltage UBat or an equivalent signal corresponding to the change in load or recuperation (ΔUBat); 2. Determination of the time of the change relative to the measurement time (Δt); 3. Possibility of computationally correcting the measurement signal Pha2, Pha3 by a factor of 122 and / or offset 121; 4. Determination of the factor 122 / offset 121 using a freely calibratable characteristic map 125 with input parameter magnitude of change ΔU; 5. Determination of the factor 122 / offset 121 using a freely calibratable characteristic map 125 with input parameter change interval Δt; 6. Combination of the corrections from ΔU and Δt; 7. Determination of the parameters to be calibrated for factor 122 / offset 121 to correct the measurement signal Pha2, Pha3 determined at measurement time t3 by simulation and measurement at the test station.

[0064] Fig. Figure 4 shows an excerpt of switching sequence 111 from the Fig. 2 and Fig. 3. The time t3, at which the measured value Pha2, Pha3 is determined, and the time t2, at which the switching state of the two switches SWTestP, SWTestM is changed again, approximately coincide. This means that the measured value Pha2, Pha3 is determined shortly before the corresponding change in switching state.

[0065] Fig.Figure 5 illustrates a characteristic map 125, which can be used to correct the measured value Pha2, Pha3. Input parameters are the change ΔU of the change in battery voltage UBat and the time interval Δt between the change in battery voltage UBat and the measurement time t3 of the measured value Pha2, Pha3 of the chassis voltage UChsGnd. Depending on these input parameters ΔU, Δt, a correction 120 is determined, which, for example, includes a factor 122 and an offset 121 as output parameters of the characteristic map 125. For the correction, the measured value Pha2, Pha3 is first multiplied by the factor 122 and then the offset 121 is added. REFERENCE MARK 100 battery system 101 Battery 102 positive-side electrical line 103 negative-side electrical conduction 104 Mass / Chassis 105 battery-side insulation 106 left-side insulation 111 Switching sequence 112 Switching state 114 Duration of condition 115 Positive-side test switch status 116 Negative-side test switch status 118 Chassis voltage 120 correction 121 Offset 122 factor 125 map B1+ positive battery terminal B1 negative battery terminal A1+ / P1+ positive link A1 / P1 negative link connection R isoPP Battery-side positive insulation resistance R isoPM Battery-side negative insulation resistance R isoLP left-side positive insulation resistance R isoLM left-side negative insulation resistance C y1 positive-side capacity C y2 negative-side capacity SW TestP positive-side test switch R TestP positive-side test resistor SW TestMnegative-side test switch R TestM negative-side test resistor SW K1 positive-side protector SW K3 negative-side contactor SW K2 Pre-charge switch R PreChg Pre-charge resistor U MEAS_KL31 KL31 voltage U ChsGnd Chassis voltage Phase 2, first measurement of the chassis voltage Pha3 second measurement of the chassis voltage R MeasU , R MeasL Chassis measuring resistors U Link Link voltage U Bat Battery voltage DU Bat Battery voltage change R RLink , R Link Link measuring resistors t time t1 first time point t2 second time point t3 third time point t4 Time of battery voltage change Δt Time interval between t4 and t3

Claims

[1] Method for monitoring insulation between two electrical conductors (102, 103) and ground (104) by means of an insulation monitoring circuit, wherein the insulation monitoring circuit has two switches (SWTestP, SWTestM), the method comprising the following steps: - Changing a switching state (115, 116) of the two switches (SWTestP, SWTestM) at a first time point (t1); - changing the switching state (115, 116) of the two switches (SWTestP, SWTestM) again at a second time (t2), which is a predetermined time interval (114) after the first time (t1); - Receiving a measured value (Pha2, Pha3) that is representative of a voltage (UChsGnd) between a first electrical line (103) of the two electrical lines (102, 103) and ground (104) at a third time (t3) during the specified time interval (114); - Receiving a change value (ΔUBat) that is representative of a change in voltage (UBat) between the two electrical lines (102, 103) before the third time (t3); - Correcting the measured value (Pha2, Pha3) based on the change value (ΔUBat); and - Determining an insulation resistance (RisoPP, RisoPM, RisoLP, RisoLM) based on the corrected measured value (Pha2, Pha3). [2] Method according to the preceding claim, wherein the method further comprises: determining a time interval (Δt) between a time point (t4) of the voltage change and the third time point (t3), wherein the correction of the measured value (Pha2, Pha3) is based on the time interval (Δt). [3] Method according to the preceding claim, wherein the voltage change takes place over a period of time and the measured value (Pha2, Pha3) is corrected based on the period of time and / or a course of the voltage change. [4] Method according to claim 2 or 3, wherein the measured value (Pha2, Pha3) is only corrected if the change value (ΔUBat) exceeds a predetermined voltage threshold and / or the time interval (Δt) exceeds a predetermined time threshold. [5] Method according to one of the preceding claims, wherein the measured value (Pha2, Pha3) is only corrected if the time interval (Δt) falls below a predetermined further time threshold. [6] Method according to any one of claims 2 to 5, wherein the correction of the measured value (Pha2, Pha3) takes into account a calibratable characteristic map (125). [7] Method according to the preceding claim, wherein the characteristic map (125) has as input parameters at least one of the following parameters: the change value (ΔUBat), the time interval (Δt). [8] Method according to claim 6 or 7, wherein the characteristic map (125) has a correction offset (121) and / or a correction factor (122) as an output parameter and the correction of the measured value (Pha2, Pha3) takes into account the correction offset (121) and / or the correction factor (122). [9] Method according to any one of claims 2 to 6, wherein for correcting the measured value (Pha2, Pha3) a voltage profile of the voltage (UChsGnd) between the first electrical line (103) and ground (104) during the time interval (Δt) is extrapolated. [10] Method according to one of the preceding claims, further comprising: determining a time offset between the change in voltage (UBat) between the two electrical conductors (102, 103) and a corresponding change in voltage (UChsGnd) between the first electrical conductor (103) and ground (104), wherein the time offset is taken into account when correcting the measured value (Pha2, Pha3). [11] Method according to one of the preceding claims, wherein the third time point (t3) is in the last quarter of the specified time interval (114). [12] Method according to one of the preceding claims, wherein the third time (t3) is selected such that the voltage (UChsGnd) between the first electrical line (103) and ground (104) approximately stabilizes up to the third time (t3) if no change in the voltage (UBat) between the two electrical lines (102, 103) is detected or the detected change in voltage is below a predetermined change threshold. [13] Method according to the preceding claim, wherein the voltage (UChsGnd) between the first electrical conductor (103) and ground (104) approximately stabilizes up to the third time (t3) if at least one of the following conditions is met: a slope of the voltage profile before or at the third time (t3) is less than a predetermined slope threshold; a voltage change of the voltage (UChsGnd) between the first electrical conductor (103) and ground (104) in an end section of the predetermined time interval (114) is less than five percent of a voltage change during the entire predetermined time interval (114), wherein the third time (t3) lies in the end section. [14] Computer program comprising instructions which, when executed by a computer, cause it to perform a method according to any one of claims 1 to 13. [15] Control unit which is configured to carry out a method according to any one of claims 1 to 13.

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