Method for monitoring insulation resistances and corresponding 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) switching the two switches (SWTestP, SWTestM) according to a switching sequence (111) consisting of a sequence of several switching states (112) of the two switches (SWTestP, SWTestM); (b) determining a profile of a predetermined quantity (118, 119) during a predetermined switching state of the several switching states (112); (c) extrapolating at least a part of the profile to obtain a saturation value of the predetermined quantity (118, 119) for the predetermined switching state; and (d) Determine at least one insulation resistance (RisoPP, RisoPM, RisoLP, RisoLM) based on the saturation value.Furthermore, the invention 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. SUMMARY AND FORMS OF EXECUTION

[0003] 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.

[0004] 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.

[0005] Thus, 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 comprises two switches. The method comprises the following steps: (a) switching the two switches according to a switching sequence consisting of a succession of several switching states of the two switches; (b) determining a waveform of a given quantity during a given switching state of the several switching states; (c) extrapolating at least a portion of the waveform to obtain a saturation value of the given quantity for the given switching state; and (d) determining at least one insulation resistance, in particular two insulation resistances, based on the saturation value.

[0006] 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.

[0007] 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.

[0008] 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.

[0009] 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.

[0010] 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.

[0011] 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.

[0012] 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.

[0013] 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.

[0014] In the context of the present disclosure, a switching state is defined, for example, in terms of the switching position of one or more switches, in particular the 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.

[0015] In the context of the present disclosure, a predetermined quantity is defined, for example, as a quantity that changes in response to the switching of the two switches during the switching sequence. For example, the predetermined quantity may be representative of a voltage between one of the two electrical conductors and ground, and / or representative of a ratio of the voltage between one of the two electrical conductors and ground to a voltage between the two electrical conductors, in particular a battery voltage or a link voltage.

[0016] In the context of this disclosure, a saturation value is defined, for example, as a value obtained by extrapolating at least part of the curve. The saturation value can correlate with a value that, as time progresses during the given switching state, is approached or reached by the curve of the given quantity, but not exceeded. The saturation value can approximate such a value. Such a value can be a limit that would be reached in the limiting case of an infinitely long waiting 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 unfavorable changes in the operating conditions occur during a switching state, such as a change in battery voltage. This change can 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 specified value, for example, if it is based on the voltage between one of the two electrical conductors and ground, does not stabilize sufficiently or reach a saturation value by the end of the specified switching state. Because such a saturation value is required for calculating the insulation resistance, an inaccurate or erroneous value for the insulation resistance can result, with corresponding uncertainties regarding contact protection and even the risk of a vehicle fire.

[0020] By extrapolating the curve during the specified switching state and determining a saturation value, relevant changes in the framework conditions, such as the battery voltage, can be taken into account, and a correct insulation resistance or at least an insulation resistance within specified error tolerances can be calculated.

[0021] Furthermore, the method and the corresponding control unit can be advantageous for determining a saturation value even if the duration of the specified switching state is chosen so short that such a saturation value is not even approximately reached. This may be necessary with certain hardware configurations, for example, when large test resistors are selected for the insulation monitoring circuit. Such large test resistors can be a suitable choice for further test sequences to reduce or prevent leakage currents, for example, between the two electrical conductors. Therefore, the method and the control unit can enable particularly short diagnostic times.

[0022] 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.

[0023] According to one embodiment, the curve is stored in a memory, in particular a buffer memory, for example in the form of measured values ​​at intervals of at most 5 ms, and in particular at most 1 ms. According to one embodiment, the extrapolation is based on these measured values. For example, the extrapolation, such as a linear extrapolation, can be based on at least 70% of the initial values ​​in the memory. The saturation value can be determined based on the extrapolation at the end of the duration of the specified switching state.

[0024] According to one embodiment, the method further comprises: determining whether a discontinuity exists in the curve, whereby the extrapolation considers only the curve before the discontinuity, specifically not the curve after and during the discontinuity. A discontinuity can be defined, for example, by a deviation from a predefined function curve, particularly an exponential function. Alternatively or additionally, a discontinuity can be defined by a change exceeding a predetermined threshold within a predetermined time period. Alternatively or additionally, a discontinuity can be defined by the fact that the magnitude of a slope in the curve exceeds a predetermined limit. Alternatively or additionally, a discontinuity can be defined by the fact that a slope in the curve is negative and / or a positive slope increases during the course of the curve.Such an embodiment can be advantageous because, due to such discontinuities, it can happen that a saturation value is neither reached nor even approximated during the specified switching state.

[0025] According to one embodiment, the curve up to the end of the predetermined switching state is considered for extrapolation if no discontinuity is detected in the curve. Such an embodiment can be advantageous for enabling short switching state durations and thus short diagnostic times, during which a saturation value is neither reached nor approached, even without discontinuity.

[0026] According to one embodiment, a discontinuity exists if the slope of the curve is negative or if a positive slope increases during the curve. Such a criterion for identifying discontinuities can be implemented particularly easily and with low computing power and memory requirements.

[0027] According to one embodiment, only discontinuities within a predetermined range of the duration of the specified switching state are considered, for example, in the last two-thirds, and in particular the second half, of the duration of the specified switching state. Such an embodiment can be advantageous because otherwise a saturation value might still be reached or approximated.

[0028] According to one embodiment, the discontinuity correlates with a change in the voltage between the two electrical conductors. Such an embodiment can be advantageous because, in practice, inaccurate or erroneous insulation resistances are frequently determined due to such voltage changes. These voltage changes, for example, changes in battery voltage, can be caused by load demands for accelerating a vehicle and / or by recuperation during deceleration.

[0029] According to one embodiment, extrapolation only occurs if the specified value increases or decreases by a specified threshold during the discontinuity. The specified value can be representative of the ratio between a voltage between one of the electrical conductors and ground to a voltage between the two electrical conductors. The specified threshold can be determined by stipulating that the measured insulation resistance may only deviate from the actual insulation resistance to a specified extent, for example, it may not be lower than a specified value or a specified proportion or percentage than the actual insulation resistance. Furthermore, it may be necessary, for example due to safety considerations, that the measured insulation resistance is not greater than the actual insulation resistance.Extrapolating only under certain conditions can save computing power and enable faster diagnoses.

[0030] According to one embodiment, the specified value is representative of the ratio of a voltage between one of the electrical conductors and ground to a voltage between the two electrical conductors. Such an embodiment can be advantageous because only such ratios are required for calculating the insulation resistance(s); therefore, the absolute voltages do not need to be known. Even if discontinuities can occur in the individual voltages, these may cancel each other out, and the ratio may still be continuous.

[0031] According to one embodiment, the voltage between the two electrical conductors is a battery voltage, measured 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. An advantage of using the battery voltage is that insulation monitoring can also be performed when the vehicle is stationary or parked, in which case one or more load-side connections are typically disconnected from the battery.

[0032] 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.

[0033] According to one embodiment, the specified quantity is representative of a voltage between one of the electrical lines and ground and / or the specified quantity is based on the voltage between one of the electrical lines and ground.

[0034] According to one embodiment, extrapolation is performed based on an exponential function. The exponential function can be fitted based on its behavior, in particular based on its behavior during the switching state up to a discontinuity, if one exists. For this purpose, the respective behavior can be considered fully or partially. Alternatively, a linear fit or, for example, a second-order function can be used. Such an embodiment can be advantageous because the exponential behavior can be determined by an RC element of the insulation monitoring circuit. A time constant of the exponential function can, for example, be determined by the product R*C, where R can be determined by the relevant resistances, in particular the test resistance and insulation resistance, and C by the relevant capacitances, in particular parasitic capacitances.Extrapolation can be advantageous because it eliminates the need for complex calibration, for example for a characteristic map, and may still achieve sufficient accuracy.

[0035] According to one embodiment, in the predetermined switching state, one of the two switches is closed and the other is open. Determining one or both insulation resistances may require the respective saturation values ​​of the two switching states, in which one switch is closed and the other open. These two saturation values, in particular corresponding saturation ratios of a voltage between one of the electrical conductors and ground to a voltage between the two electrical conductors, may be sufficient for determining the insulation resistances, especially in combination with the values ​​of test resistors and / or measuring resistors.

[0036] According to one embodiment, the method further comprises: determining a final value of the curve during the predetermined switching state, wherein the at least one insulation resistance is calculated based on the saturation value obtained by extrapolation only if the final value deviates from a previous final value of an earlier execution, in particular the immediately preceding execution, of the switching sequence by more than a predetermined final value threshold; otherwise, the at least one insulation resistance is calculated based on the final value. Such an embodiment can be advantageous for excluding relevant voltage fluctuations, for example, of the battery voltage. Comparing corresponding values ​​of different switching sequences can be a particularly simple method for detecting relevant changes that might require extrapolation of the curve.According to one embodiment, a predetermined part of the curve is used for the extrapolation, in particular at least 50 percent, in particular at least 70 percent, of the values ​​from the beginning of the predetermined switching state.

[0037] According to one embodiment, the final value lies in the last quarter of the duration of the predetermined switching state, particularly in the last fifth. Such an embodiment can be advantageous if the predetermined value has sufficiently stabilized by these time periods.

[0038] According to one embodiment, the final value is chosen such that the voltage between one of the electrical conductors and ground has already approximately stabilized. According to another embodiment, the voltage between one of the electrical conductors and ground approximately stabilizes if the slope of the voltage curve is less than a predetermined slope threshold.

[0039] According to one embodiment, the method further comprises: setting an error variable such that the error variable indicates an insulation problem if the deviation between the final value and the saturation value obtained by extrapolation is less than a predetermined deviation threshold. According to one embodiment, it is concluded that the deviation between the final value and a previous final value is not caused by a voltage change, for example, in the battery voltage, but possibly by an actual insulation problem. According to one embodiment, the insulation problem is indicated, for example, visually, audibly, and / or haptically. According to one embodiment, the battery is disconnected if an insulation problem is present.

[0040] 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.

[0041] 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 of the switch can be electrically 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.

[0042] According to one embodiment, several saturation values ​​and / or final values ​​are determined for different switching states, in particular two switching states, of a switching sequence, and the at least one insulation resistance is determined based on the several saturation values ​​and / or final values. 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 the actual and the calculated behavior of an insulation resistance when the battery voltage changes; Fig. 4 to 8 the course of a voltage between an electrical conductor and ground during a switching sequence for determining insulation resistances, wherein the battery voltage changes to varying degrees during the switching sequence and such changes can be compensated for by extrapolation according to an embodiment of the present disclosure; Fig. 9 and Fig. 10. Compare the course of a normalized and a non-normalized voltage between an electrical conductor and ground under different changes in battery voltage.

[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 or insulation monitor. 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 resistances 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 circuit includes measuring resistors RMeasU, RMeasL and, for example, an analog-to-digital converter. Using this and / or another measurement circuit, the insulation 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. Such measuring circuits may, but do not have to, be part of the insulation monitoring circuit. 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 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 that exist 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 different voltage levels are generated on a measurement signal by alternately switching measuring resistors RTestP, RTestM, which are connected in parallel to the insulation resistances RisoPP, RisoPM, RisoLP, RisoLM. 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 faulty. In general, disturbances affecting the insulation resistance are more dominant the greater the difference between the voltages between one of the electrical lines and ground, for example, the KL31 voltages, during the different phases Pha1, Pha2, and Pha3. In the case of a one-sided insulation fault, where, for example, the positive insulation is approximately 60 kΩ and the negative insulation is in the MΩ range, the voltage levels are close together. A disturbance then has only a minor influence because the transient amplitude that can be overcome is relatively small, e.g., only 30 V.However, even a small deviation can have critical consequences, because the value of the positive resistance is already close to the error case.

[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 RTestP and the state 116 of the negative-side test switch RTestM. An upper line indicates a closed switch, and a lower line indicates an open switch. For example, in the first switching state 112 (phase 1) of the switching sequence 111, the positive-side switch RTestP and the negative-side switch RTestM are closed; in the second switching state 112 (phase 2), the positive-side switch RTestP is closed and the negative-side switch RTestM is open; in the third switching state 112 (phase 3), the positive-side switch RTestP is open and the negative-side switch RTestM is closed. The switching sequence 111 then repeats.

[0060] In the lower part of Fig. Figure 2 shows a corresponding voltage waveform 118 of the insulation 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 continuous calculation of an insulation resistance RisoPP, RisoPM, RisoLP, RisoLM over time t. The calculated value 121 of the insulation resistance is compared with the actual value 120. During critical phases 122, when the battery voltage UBat changes, the calculated value 121 can deviate significantly from the actual value 120. This is particularly problematic if the deviation exceeds or falls below predetermined limits 123. Specifically, for safety reasons, the calculated value 121 should not exceed the actual value 120 and / or should not fall below the actual value 120 by a predetermined percentage, proportion, or absolute value.

[0062] Fig. Figure 4 shows again the voltage curve 118 of the insulation or chassis voltage UChsGnd during a switching sequence 111 for determining insulation resistances according to Fig. 2. At the end of the second and third switching states 112, i.e., phase 2 and phase 3, corresponding measurement windows 130 are provided, during which measured values ​​of the chassis voltage UChsGnd are determined. Based on these measured values, the insulation resistances RisoPP, RisoPM, RisoLP, and RisoLM can be calculated.

[0063] Fig. Figures 5 to 8 then show various examples where a change in the battery voltage UBat before or during a measurement window 130 causes a corresponding change in the chassis voltage UChsGnd, which leads to discontinuities 133 in the chassis voltage UChsGnd and consequently to differing measured values ​​131 in the measurement window 130. If the insulation resistances RisoPP, RisoPM, RisoLP, RisoLM are calculated based on such differing measured values, inaccurate or even erroneous values ​​result, as in Fig. Figure 3 shows that the problem can be at least partially solved by using extrapolated values ​​132 for calculating the insulation resistances RisoPP, RisoPM, RisoLP, and RisoLM instead of the measured values ​​131.

[0064] Fig. Figure 5 shows the chassis voltage UChsGnd for a negative voltage change of the battery voltage UBat during measurement in phase 2. Fig. 6 for a positive voltage change of the battery voltage UBat during measurement in phase 2. Fig. Figure 7 shows the chassis voltage UChsGnd for a negative voltage change of the battery voltage UBat during measurement in phase 3. Fig. 8 for a positive voltage change of the battery voltage UBat during measurement in phase 3.

[0065] Fig. 9 and Fig. Figure 10 shows in the lower section the voltage curve 118 of the insulation or chassis voltage UChsGnd during a switching sequence 111 for determining insulation resistances according to Fig. 2. A voltage change of 50V in the battery voltage UBat during switching sequence 111 results in a discontinuity 133. The voltage change in Fig. 9 is negative, in Fig. 10 positive.

[0066] The upper section shows the corresponding normalized voltage curve 119, i.e., the ratio of chassis voltage UChsGnd to battery voltage UBat. For clarity, a middle range of values ​​is omitted (indicated by a solid horizontal line), so that only the respective peaks of the normalized voltage curve 119 are shown. Corresponding discontinuities 133, caused by the aforementioned voltage changes, are also visible in the normalized voltage curve 119. 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 119 Ratio of chassis voltage to battery voltage 120 actual insulation resistance 121 calculated insulation resistance 122 critical phase 123 Limit value 130 measuring windows 131 measured value 132 extrapolated value 133 Discontinuity 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 TestM negative-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 BatBattery voltage DU Bat Battery voltage change R RLink , R Link Link measuring resistors t time QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] DE 10 2021 203 919 A1

[0002] DE 10 2018 222 123 B4

[0002]

Claims

[1] 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: - Switching the two switches (SWTestP, SWTestM) according to a switching sequence (111) consisting of a sequence of several switching states (112) of the two switches (SWTestP, SWTestM); - Determining a course of a given quantity (118, 119) during a given switching state of several switching states (112); - Extrapolating at least part of the curve to obtain a saturation value of the given quantity (118, 119) for the given switching state; and - Determine at least one insulation resistance (RisoPP, RisoPM, RisoLP, RisoLM) based on the saturation value. [2] Method according to the preceding claim, further comprising: Determine whether there is a discontinuity (133) in the graph, whereby the extrapolation only considers the graph before the discontinuity (133). [3] Method according to the preceding claim, wherein a discontinuity (133) exists when a slope of the course is negative or a positive slope increases during the course. [4] Method according to claim 2 or 3, wherein the discontinuity (133) correlates with a change in a voltage (UBat, ULink) between the two electrical lines (102, 103). [5] Method according to any one of claims 2 to 4, wherein extrapolation is only performed if the predetermined quantity (118, 119) increases or decreases by a predetermined threshold value at the discontinuity (133). [6] Method according to one of the preceding claims, wherein the specified quantity (119) is representative of a ratio of a voltage (UChsGnd) between one of the electrical lines (102, 103) and ground (104) to a voltage (UBat, ULink) between the two electrical lines (102, 103). [7] Method according to one of the preceding claims, wherein extrapolation is performed based on an exponential function. [8] Method according to one of the preceding claims, wherein in the predetermined switching state one of the two switches (SWTestP, SWTestM) is closed and the other is open. [9] Method according to one of the preceding claims, further comprising: determining a final value of the curve during the predetermined switching state, wherein the at least one insulation resistance (RisoPP, RisoPM, RisoLP, RisoLM) is calculated based on the saturation value obtained by extrapolation only if the final value deviates from a previous final value of a previous execution of the switching sequence (111) by more than a predetermined final value threshold, and otherwise the at least one insulation resistance (RisoPP, RisoPM, RisoLP, RisoLM) is calculated based on the final value. [10] Method according to the preceding claim, further comprising: Setting an error variable such that the error variable indicates an isolation problem if a deviation between the final value and the saturation value obtained by extrapolation is less than a specified deviation threshold. [11] Method according to one of the preceding claims, wherein one of the two switches (SWTestP, SWTestM) is configured to disconnect an electrical connection between one of the electrical lines (102, 103) and ground (104), and / or the other of the two switches (SWTestP, SWTestM) is configured to disconnect an electrical connection between the other of the electrical lines (102, 103) and ground (104). [12] Method according to one of the preceding claims, wherein mass (104) is assigned to the chassis of a motor vehicle. [13] Computer program comprising instructions which, when executed by a computer, cause the computer to carry out the method according to any one of claims 1 to 12. [14] Control unit, in particular battery management system, which is configured to carry out a method according to any one of claims 1 to 12.

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