DE102021203919A1 - Insulation monitor for detecting an insulation fault in an electrical insulation of an electrical system - Google Patents

Abstract

The invention relates to an insulation monitor (1) for detecting an insulation fault in an electrical insulation (2) of an electrical system, the insulation (2) being arranged between a DC voltage with a positive pole (B1+) and a negative pole (B1-) of the electrical system. The insulation monitor (1) has test resistors (3, 5), switches (4, 6) and a control and evaluation device that is configured to set up three circuit phases and, by means of an adjustment calculation or extrapolation of voltage values within a predetermined time interval, to calculate voltage values in the circuit phases and determine a failure of the insulation (2) based on the determined voltage values.

Description

The present invention relates to an insulation monitor for detecting an insulation fault in an electrical insulation of an electrical system, for example an electric vehicle.

Diagnostic methods for insulation resistances in isolated voltage distribution networks (IT networks) have been known for a long time. The method of measuring three voltages with a combined asymmetry measurement for insulation monitoring has been used for a long time. In static operation, i.e. when the high voltage does not change or changes only slightly, this method is very reliable. Problems with the method, however, are that the required settling time of the individual measurement steps and thus the time it takes for an insulation fault to be detected is relatively long, for example several 10 s depending on the time constant of the system the high voltage changes rapidly, as is common when operating an electric vehicle, for example. There is also uncertainty in the on-board self-diagnosis of the insulation monitoring, i.e. there is not always a reliable distinction between "insulation fault" and "fault in the insulation monitoring circuit". The requirements for insulation monitoring are described in IEC 61557-8. The international standard ISO17409 requires insulation monitoring in IT networks.

Conventional insulation monitoring methods are used, for example, in DE 10 2015 213 399 A1 and EP 0 654 673 B1 described.

It is the object of the present invention to provide an insulation monitor that is faster and more reliable. This object is solved by the subject matter of the independent patent claim. The invention is further developed according to the subject matter of the dependent patent claims.

One aspect of the present invention provides an insulation monitor for detecting an insulation fault in an electrical insulation of an electrical system. The insulation is placed between a positive and a negative DC voltage of the electrical system, the insulation monitor comprising: a first test resistor between the positive and a ground, a first switch being placed between the first test resistor and the positive or the ground; a second test resistor between the negative terminal and ground, a second switch being positioned between the second test resistor and the negative terminal or ground; a measurement circuit configured to measure a first voltage across the first test resistor, a second voltage across the second test resistor, and/or a third voltage between the negative pole and the positive pole; and a control and evaluation device configured to establish a first circuit phase in which the first switch is closed and the second switch is open, and after the first circuit phase a second circuit phase in which the second switch is closed and the first switch is open. The control and evaluation device is also configured to use an adjustment calculation or extrapolation of the voltage values of the first, the second or the third voltage within a predetermined time interval at least during one of the first and second switching phases to estimate a presumably steady-state end value of at least one of the voltage values would occur if full settling time were available; and determine a failure of the insulation based on the estimated final value of the voltage value. This means that the full settling time does not have to be waited for, so that the insulation monitor works faster.

In one embodiment, the control and evaluation device is configured to establish a third circuit phase, in which both the first and second switches are closed, between the first and second circuit phases. In one embodiment, the control and evaluation device is configured to estimate a presumably stationary end value of one of the voltage values within a predetermined time interval at least during one of the first to third circuit phases by means of the adjustment calculation or the extrapolation, and the error of the insulation on the basis of the estimated to determine the final value of the voltage value. This allows the insulation monitor to determine the insulation fault more reliably based on the estimated final value.

In one embodiment, the control and evaluation device uses a preferably two-stage neural network that is trained in an external device.

In one embodiment, the control and evaluation device sets up the first and second circuit phases alternately and is configured to determine the following states of the measurement circuit and the insulation: the measurement circuit and the insulation are error-free if the voltage values temporarily both exceed an upper predetermined threshold and fall below a lower predetermined threshold; the insulation has a fault on the positive pole or the first switch is blocked in the closed state if the lower predetermined threshold is not fallen below; the insulation has a fault on the negative pole or the first switch is blocked in the open state if the upper predetermined threshold is not exceeded; the insulation has a fault on the negative pole or the second switch is stuck closed if the upper predetermined threshold is not exceeded; the insulation has a fault on the positive pole or the second switch is blocked in the open state if the lower predetermined threshold value is not fallen below. In this way, not only a fault in the insulation is determined, but also a possible fault in the measurement circuit.

In one embodiment, the DC voltage has a variable maximum value and the control and evaluation device establishes the first and second circuit phases alternately and is configured to determine the following state of the measuring circuit and the insulation: the first or the second switch is defective if a value of the voltage values during the first switching phase does not drop below a predetermined increase threshold value.

In one embodiment, the earth leakage monitor is installed in an electric vehicle, which is the electrical system.

character list

• 1 shows an equivalent circuit diagram of an insulation monitor according to an embodiment;
• 2 shows an extrapolation of a voltage profile according to an embodiment;
• 3 shows voltage curves during a three-phase switching operation according to an embodiment;
• 4 shows voltage curves for detecting error states according to an embodiment; and
• 5 shows voltage curves for detecting error states according to an embodiment.

Description of exemplary embodiments

1 shows an equivalent circuit diagram of an insulation monitor 1 according to an embodiment. The insulation monitor 1 detects an insulation fault in an electrical insulation 2 of an electrical system, with the insulation 2 being arranged between a DC voltage with a positive pole B1+ and a negative pole B1- of the electrical system. The insulation monitor 1 has a first test resistor 3 between the positive pole B1+ and a ground M, a first switch 4 being arranged between the first test resistor 3 and the positive pole B1+ or the ground M; and a second test resistor 5 between the negative pole B1- and the ground M, a second switch 6 being arranged between the second test resistor 5 and the negative pole B1- or the ground M. The insulation monitor 1 also has a measuring circuit 7 which is configured to measure a first voltage between ground M and B1- and a second voltage between the negative pole B1- and the positive pole B1+. The measuring circuit 7 has measuring points 8 at which the measured voltages can be tapped.

• - eine erste Spannung zwischen Masse und B1- und eine zweite Spannung zwischen Masse und B1+;
• - eine erste Spannung zwischen Masse und B1+ und eine zweite Spannung zwischen B1- und B1+.

There are alternative options:

• - a first voltage between ground and B1- and a second voltage between ground and B1+;
• - a first voltage between ground and B1+ and a second voltage between B1- and B1+.

The insulation monitor 1 also has a control and evaluation device that is configured to set up a first switching phase in which the first switch 4 is closed and the second switch 6 is open, and after the first switching phase a second switching phase in which the second Switch 6 is closed and the first switch 4 is open.

The voltages are measured in the following order:

First, a voltage is measured between the positive pole B1+ and the negative pole B1-, then a voltage is measured between the positive pole B1+ and the ground M, and then a voltage is measured between the negative pole B1- and the ground M. Usually, however, only two of the voltages are recorded by a voltmeter, since the third voltage results automatically from the mesh set from the first two voltages.

The timing is as follows: First, the first circuit phase is set up, ie the first test resistor 3 is switched on by means of the first switch 4, the settling time is awaited and the voltages are measured again. Then the second switching phase is set up, ie the first switch 4 is opened and the first test resistor 3 is switched off. The second test resistor 5 is then switched on, the settling time is awaited and the voltages are measured again, and then the second test resistor 5 is switched off again and the first test resistor 3 is switched on again, so that the first circuit phase is set up again. The test resistors 3, 5 are switched on and off alternately as long as the insulation monitor 1 is active.

The settling or reaction time results from the capacitances CY present in the system, i.e. the capacitances between the positive pole B1+ and the ground M, and the resistances involved. During the settling time, the voltage at the capacitances CY on the positive side and the negative side changes, resulting in the so-called recharging curve.

Switching the two test resistors 3, 5 on or off results in a new circuit with new network equations. Since there are two unknown variables in the system, i.e. the two insulation resistances, one needs two modifications of the network equations, which is known from mathematics, especially the Gaussian algorithm.

Depending on the time constant, it can take a relatively long time for the maximum response time to reach its stable final value. This directly affects the accuracy of the calculation results. The maximum response time is currently normatively limited to 30 s, although car manufacturers usually require shorter response times (e.g. 15 s). In the next revision of ISO17409, a maximum response time of 10 s is required.

2 shows the extrapolation of a voltage profile according to an embodiment. The control and evaluation device is also configured to determine probable steady-state end values of the voltage values that would occur within a predetermined time interval at least during one of the first and second switching phases by means of an adjustment calculation or extrapolation of the voltage values of the first, the second or the third voltage , if one had the full settling time available; and determine an insulation 2 failure based on the estimated extrapolated final values of the voltage values. In this way, the insulation resistance can be determined more quickly. The underlying problem so far has been that sometimes there was less time available than would be necessary for a complete settling. The voltage profile is therefore now extrapolated to the probable steady-state end value of the voltage within the time available. The extrapolation of the curve progression is also known as curve fitting. Instead of only evaluating the voltage value of the recharging curve that is reached within the available reaction time, intermediate values, ie the small circles in the 2 , extrapolated to the stationary final value. The value ΔV in the 2 denotes a difference from the stationary final value at the end of an available time interval. The vertical line in the 2 represents the response time available. Depending on the time constant in the system, the stationary final value may not be reached. The probable steady-state final value can be estimated from the curve profile measured within the available range.

For the estimation algorithm, the control and evaluation device uses a (preferably two-stage) neural network that was trained in an external device. The neural network is trained using test vectors from simulations and real measured values on the computer, i.e. the computing effort on the control and evaluation device is advantageously limited to the basic arithmetic operations.

3 shows voltage curves during a three-phase switching operation according to an embodiment. Viso denotes the measured voltage and Vb denotes the DC or system voltage in the electrical system. The control and evaluation device is also configured to set up a third switching phase, in which both the first and the second switch 4, 6 are closed, between the first and the second switching phase. Here, the operation described above with two switching phases is supplemented by a third switching phase. In the additional, third switching phase, both switches 4, 6 are closed simultaneously. The changed switching sequence of the switches 4, 6 provides a changed recharging curve with three voltage levels instead of two.

Preferably, not only the first and the second switching phase are taken into account in the extrapolation, but also the third switching phase, i.e. the control and evaluation device is configured to, by means of the adjustment calculation or the extrapolation of voltage values within a predetermined time interval at least during one of the first to third circuit phase to estimate estimated steady-state end values of the voltage values, and to determine the insulation 2 error based on the estimated end values.

The procedure of 2 can therefore be used both in operation with the first and second circuit phase and in operation with the first to third Circuit phase are carried out. It should be noted that in the 3 the first circuit phase is labeled "Phase 1", the second circuit phase is labeled "Phase 3", and the third circuit phase is labeled "Phase 2".

4 shows voltage curves for detecting error states according to an embodiment. A reliable diagnosis of the switches 4, 6 can thus be carried out with a distinction between "insulation fault" and "fault in the measuring circuit". The underlying problem is that even with defective switches 4, 6, which can be blocked in the open or closed state, a recharging curve can be measured. Based on a deviation of the recharging curves from the normal case, it can be concluded that there is a "fault in the measuring circuit", in particular switches 4, 6. If there is a fault in the switches 4, 6, the amplitude of the charge-reversal curve is reduced or the mean value is shifted. However, insulation faults also have this effect on the charge-reversal curves. An insulation fault on the positive side results in a mean shift towards higher voltages and at the same time a smaller amplitude (ie same symptoms as a switch stuck closed). An insulation fault on the negative side results in a mean shift towards lower voltages and at the same time a smaller amplitude (ie same symptoms as a switch stuck open). the fog 4 shows the curves in two-phase circuit operation as an example for the first switch 4 on the positive side. Numeral 41 denotes the voltage waveform of the first voltage in the normal case, numeral 42 denotes the voltage waveform of the first voltage when the first switch 4 is blocked in the open state, and numeral 43 denotes the voltage waveform of the first voltage when the first switch 4 is in the closed state is blocked.

• 1) Die Messchaltung 7 und die Isolierung 2 sind fehlerfrei, wenn die Spannungswerte zeitweise sowohl einen oberen vorbestimmten Schwellwert überschreiten als auch einen unteren vorbestimmten Schwellwert unterschreiten.
• 2) Die Isolierung 2 hat einen Fehler an dem Pluspol B1+ oder der erste Schalter 4 ist im geschlossenen Zustand blockiert, wenn der untere vorbestimmte Schwellwert nicht unterschritten wird.
• 3) die Isolierung 2 hat einen Fehler an dem Minuspol B1- oder der erste Schalter 4 ist im geöffneten Zustand blockiert, wenn der obere vorbestimmte Schwellwert nicht überschritten wird.
• 4) Die Isolierung 2 hat einen Fehler an dem Minuspol B1 - oder der zweite Schalter 6 ist im geschlossenen Zustand blockiert, wenn der obere vorbestimmte Schwellwert nicht überschritten wird.
• 5) Die Isolierung 2 hat einen Fehler an dem Pluspol B1+ oder der zweite Schalter 6 ist im geöffneten Zustand blockiert, wenn der untere vorbestimmte Schwellwert nicht unterschritten wird.

The control and evaluation device sets up the first and the second circuit phase alternately and is configured to determine the following states of the measurement circuit 7 and the insulation 2:

• 1) The measuring circuit 7 and the insulation 2 are error-free if the voltage values temporarily both exceed an upper predetermined threshold value and fall below a lower predetermined threshold value.
• 2) The insulation 2 has a fault at the positive pole B1+ or the first switch 4 is blocked in the closed state if the lower predetermined threshold value is not fallen below.
• 3) the insulation 2 has a fault on the negative pole B1 or the first switch 4 is blocked in the open state if the upper predetermined threshold value is not exceeded.
• 4) The insulation 2 has a fault on the negative pole B1 - or the second switch 6 is blocked in the closed state if the upper predetermined threshold is not exceeded.
• 5) The insulation 2 has a fault at the positive pole B1+ or the second switch 6 is blocked in the open state if the lower predetermined threshold value is not fallen below.

These curves of 4 were created with constant high voltage, with dynamically changing high voltage there is an additional difficulty in the diagnosis.

5 shows voltage curves for detecting error states with dynamically changing high voltage according to an embodiment. Here the DC voltage has a variable maximum value and the control and evaluation device sets up the first and the second circuit phase alternately and is configured to determine that the first or the second switch 4, 6 is defective if a value of the voltage values during of the first switching phase does not fall below a predetermined slope threshold value. Reference numeral 51 designates the voltage waveform of the first voltage in the normal case, reference numeral 52 designates the voltage waveform of the first voltage when the first switch 4 is blocked in the closed state, and reference numeral 53 designates the voltage waveform of the first voltage when the first switch 4 is in the open state is blocked.

Even with dynamic high voltage, the curves for the normal case and the error case with blocked switches 4, 6 in the open or closed state can be distinguished from one another, and can also be distinguished from the actual insulation error. If there is a fault in the switches 4, 6, the significant plateau in the middle between the minimum and maximum value is missing, i.e. the increase in the voltage values during the first switching phase does not fall below a predetermined increase threshold value.

The insulation monitor 1 is advantageously installed in an electric vehicle, which is the electrical system.

QUOTES INCLUDED IN DESCRIPTION

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

Patent Literature Cited

• DE 102015213399 A1 [0003]
• EP 0654673 B1 [0003]

Claims (7)

Insulation monitor (1) for detecting an insulation fault in an electrical insulation (2) of an electrical system, the insulation (2) being arranged between a direct voltage with a positive pole (B1+) and a negative pole (B1-) of the electrical system, the insulation monitor ( 1) has: a first test resistor (3) between the positive pole (B1+) and a ground (M), a first switch (4) between the first test resistor (3) and the positive pole (B1+) or the ground (M) is arranged; a second test resistor (5) between the negative pole (B1-) and the ground (M), a second switch (6) being arranged between the second test resistor (5) and the negative pole (B1-) or the ground (M); a measuring circuit (7) configured to measure a first voltage across the first test resistor (3), a second voltage across the second test resistor (5) and/or a third voltage between the negative pole (B1-) and the positive pole (B1+ ) to eat; and a control and evaluation device configured to set up a first switching phase in which the first switch (4) is closed and the second switch (6) is open, and after the first switching phase a second switching phase in which the second switch (6) is closed and the first switch (4) is open, characterized in that the control and evaluation device is further configured to calculate the voltage values of the first, the second or the third voltage within a predetermined time interval by means of an adjustment calculation or extrapolation estimating, at least during one of the first and second switching phases, a probable steady-state final value of at least one of the voltage values that would occur if a full settling time were available; and determine a failure of the insulation (2) based on the estimated final value of the voltage value. Insulation monitor (1) according to the preceding claim, wherein the control and evaluation device is configured to set up a third circuit phase, in which both the first and the second switch (4, 6) are closed, between the first and the second circuit phase. Insulation monitor (1) according to one of the preceding claims, wherein the control and evaluation device is configured to estimate a probable steady-state final value of one of the voltage values within a predetermined time interval at least during one of the first to third switching phases by means of the adjustment calculation or the extrapolation of voltage values, and determine the failure of the insulation (2) based on the estimated final value of the voltage value. Insulation monitor (1) according to one of the preceding claims, wherein the control and evaluation device uses a preferably two-stage neural network which is trained in an external device. Insulation monitor (1) according to one of the preceding claims, wherein the control and evaluation device sets up the first and the second circuit phase alternately and is configured to determine the following states of the measuring circuit (7) and the insulation (2): the measuring circuit (7) and the insulation (2) are error-free if the voltage values temporarily both exceed an upper predetermined threshold value and fall below a lower predetermined threshold value; the insulation (2) has a fault on the positive pole (B1+) or the first switch (4) is blocked in the closed state if the lower predetermined threshold value is not fallen below; the insulation (2) has a fault on the negative pole (B1-) or the first switch (4) is blocked in the open state if the upper predetermined threshold is not exceeded; the insulation (2) has a fault on the negative pole (B1-) or the second switch (6) is blocked in the closed state if the upper predetermined threshold is not exceeded; the insulation (2) has a fault on the positive pole (B1+) or the second switch (6) is blocked in the open state if the lower predetermined threshold value is not fallen below. Insulation monitor (1) according to one of the preceding claims, in which the direct voltage has a variable maximum value, and in which the control and evaluation device establishes the first and the second circuit phase alternately and is configured to determine the following state of the measuring circuit (7) and the insulation (2 ) to determine: the first or the second switch (4, 6) is defective if a value of the voltage values does not fall below a predetermined increase threshold value during the first switching phase. Insulation monitor (1) according to any one of the preceding claims, wherein the insulation monitor (1) in installed in an electric vehicle, which is the electrical system.

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