DE102023102654A1 - Detection of faulty components in an insulation monitor - Google Patents

Abstract

The invention relates to a method for detecting faulty components in an insulation monitor (1), wherein during use of the insulation monitor (1) to determine an insulation resistance Riso(2), the measurement signal voltage Vread(5) present at the insulation monitor or at a point on the insulation monitor is measured and compared with a reference signal, wherein a conclusion is drawn depending on the comparison. The invention further relates to a detection circuit for detecting faulty components of an insulation monitor (1).

Description

The invention relates to a method for detecting faulty components in an insulation monitor and a detection circuit for carrying out the method.

To determine insulation resistance, the high-voltage network in the vehicle is stimulated. The insulation resistance can be estimated from the measured system response. The insulation resistance is determined continuously during operation (e.g. at intervals of 30 seconds each).

In order for the insulation resistance estimate to be considered valid, the proper functioning of the insulation monitor must be checked at each measurement.

For this purpose, a so-called self-test is carried out, which checks the individual components of the electronic hardware for errors. Such errors can be, for example, a short circuit or an interruption (open line) in a component.

From the state of the art, such as the EN 10 2014 205 918 A1 A method for testing an insulation device is known in which a measuring voltage is applied to the insulation device, whereby a total current curve is measured over a specified measuring period. The total current curve is then compared with a reference current curve.

It is the object of the present invention to provide an improved method to reduce the disadvantages of the known solutions.

This task is solved in a generic method in that, during use of the insulation monitor, the measuring signal voltage applied to the insulation monitor is measured and compared with a reference signal.

In other words, the invention relates to a method in which the temporal progression of the output voltage of the electronic circuit measured as part of the estimation of the insulation resistance is compared with a reference voltage. This reference voltage can be determined on the basis of prior knowledge (including previous measurement, previous estimated value of the insulation resistance, nominal component values of the electronic hardware, transfer function of the system behavior) and current system conditions, e.g. intermediate circuit voltage. Since the measured output voltage has a different temporal progression for a faulty component of the electronic hardware than for fault-free hardware, this knowledge can be used to detect component errors. If the deviation of the measured output voltage from the reference voltage is more than a defined value (based on absolute and/or relative deviation), the deviation is recognized by a detection algorithm and the status of the insulation monitor is set to "Not OK". This ensures that a measurement of the insulation resistance is only considered valid if there is no faulty behavior of the electronic hardware. The definition of the limit value at which a deviation is recognized as too large takes several influencing factors into account. As an alternative to voltage, other physical quantities such as current or power can also be used to detect the error in the electronics.

There are numerous advantages. By including previous measurements, previous estimates of insulation resistance, nominal component values of the electronic hardware, transfer function of the system behavior, etc., a dynamic and optimized reference value can be determined so that the system response is always tailored to the changing influences.

For this purpose, a method is used to detect faulty components in an insulation monitor, whereby while the insulation monitor is being used to determine an insulation resistance R, the measurement signal voltage applied to the insulation monitor is measured and compared with a reference signal. A conclusion is drawn depending on the comparison.

Advantageous embodiments are claimed in the subclaims and are explained in more detail below.

Advantageously, the reference signal range takes into account different influencing factors such as the influence of hardware tolerances, noise, estimation accuracy, dynamics of the intermediate circuit voltage, etc.

Preferably, the reference signal can be designed as a reference voltage signal, reference current signal or reference power signal. Alternatively, other physical quantities such as frequency can be used to detect the error in the electronics. This allows a large selection to be made so that the functionality of the insulation monitor can be measured and evaluated based on a wide range of quantities and influences.

Advantageously, it is concluded that a faulty component is present if the measurement signal voltage deviates from the reference signal and/or the reference signal range. This means that if the measurement signal voltage exceeds or falls below a threshold value or a threshold value range, this is determined by the system. The estimated insulation resistance determined by the insulation monitor can then preferably be assessed as invalid.

Preferably, the value of the reference signal or the reference signal range is predefined, measured in advance or estimated in advance. This allows the previously explained influencing factors to be included, particularly in the estimation, so that precise functioning of the method for detecting faulty components is ensured. Depending on the selected operating modes, however, it is necessary that the intermediate circuit voltage is included in the measurement or estimation of the reference signal or the reference signal range.

Preferably, the reference signal is defined by a value corridor for a reference range. This ensures that even if the measuring resistance deviates atypically, a faulty component is still detected.

The method is particularly preferably carried out when the DC switch is open or closed. The way in which the reference signal and in particular the limit value for error detection are determined depends on the switch positions for the high-voltage intermediate circuit and for a reference impedance. The method can thus be carried out with two operating modes. In a first operating mode, the DC switch is open during the self-test and only during the self-test and the reference switch is closed. In this operating mode, the measured output voltage is independent of the value of an insulation impedance arranged in the high-voltage network circuit. Furthermore, the output voltage, i.e. the measurement signal voltage, is independent of the value of an intermediate circuit voltage in the high-voltage network. This means that the reference signal is also independent of the value of the insulation impedance and the intermediate circuit voltage. The reference signal or reference voltage can thus be determined in advance and does not have to be adjusted during operation. The reference limit value set in the first operating mode is therefore only dependent on component values and the component tolerances of the resistors and capacitors installed in the electronic circuit. The second operating mode is characterized by the fact that the DC switch and the reference switch are open (reference components are only designed for low voltage, reference impedance and insulation impedance are connected in parallel when the switch is closed). This means that the measurement signal voltage depends on both the insulation impedances and the intermediate circuit voltage. The reference signal or reference voltage is also dependent on the value of the insulation impedance and the dynamics of the intermediate circuit voltage. The reference voltage must therefore be adjusted during operation. The reference voltage can be determined on the basis of prior knowledge (e.g. previous measurement, previous estimate of the insulation resistance, nominal component values of the electronic hardware, transfer function of the system behavior). This means that the reference limit value is also dependent on the component tolerances of the resistors and capacitors installed in the electronic circuit, on the value of the insulation impedance and its estimation accuracy, and on the dynamics of the intermediate circuit voltage. Alternatively, the following combinations of switch positions can lead to different operating modes. A total of four operating modes exist, including the first operating mode: DC switch open, reference impedance open, second operating mode: DC switch open, reference impedance closed, third operating mode: DC switch closed, reference impedance open, fourth operating mode: DC switch closed, reference impedance closed. Certain faulty components can only be detected with certain combinations of switch positions. In order to be able to detect all faulty components, it is advantageous if all switch positions and operating modes are taken into account during the process. Nevertheless, it is of course important that the invention is not restricted to this.

The invention also relates to a detection circuit for detecting faulty components of an insulation monitor, which is designed to carry out the method for detecting component faults in the insulation monitor circuit. It should be understood that the detection circuit can be used, but does not have to be used. A combination of switch positions is preferred/necessary in order to be able to make a statement for all components of the circuit as to whether a component is faulty or not. It is therefore important that the combination of switch positions is taken into account in order to be able to make a statement for all components of the circuit as to whether the component is faulty or not.

The invention is explained in more detail below with the help of a drawing.

• 1 ein Ersatzschaltbild eines erfindungsgemäßen Isolationswächters;
• 2 ein Diagramm des Anregungsspannungssignals V_s und der Messsignalspannung V_read;
• 3 Ausgangsspannungsdiagramme eines Widerstands R_iso für einen geöffneten DC-Schalter im Hochspannungsnetzteil;
• 4 eine grafische Darstellung eines Detektionsalgorithmus; und
• 5 Referenzausgangsspannungsdiagramme mit und ohne Toleranzeinflüsse sowie der sich daraus ergebende Toleranzbereich der Referenzspannung.

Show it:

• 1 an equivalent circuit diagram of an insulation monitor according to the invention;
• 2 a diagram of the excitation voltage signal V _s and the measurement signal voltage V _read ;
• 3 Output voltage diagrams of a resistor R _iso for an open DC switch in the high voltage power supply;
• 4 a graphical representation of a detection algorithm; and
• 5 Reference output voltage diagrams with and without tolerance influences as well as the resulting tolerance range of the reference voltage.

The figures are merely schematic in nature and serve only to understand the invention. The same elements are provided with the same reference numerals.

1 shows an equivalent circuit diagram of an insulation monitor 1 according to the invention with two insulation impedances coupled to it. These each have an insulation resistance R _iso 2 parallel to an insulation capacitance C _iso 3 . The values of the insulation impedances (R _iso+ , C _iso+ ) and (R _iso- , C _iso- ) are generally different from one another and independent of one another. A voltage source arranged in the insulation monitor 1 outputs the excitation voltage signal Vs 6 , e.g. a square wave signal, which excites the insulation monitor 1 and the insulation impedances. The intermediate circuit voltage V _DCLink 4 is determined at the electrical connection between the insulation monitor 1 and the insulation impedances. The measurement signal voltage V _read 5 is determined between two resistors of the insulation monitor 1.

2 shows a diagram of the excitation voltage signal V _s 6 and the measurement signal voltage V _read 5. The upper diagram 7 shows the excitation voltage signal V _s 6. It can be seen that the excitation voltage signal V _s 6 has a square wave function and is periodic. The lower diagram 8 shows the measurement signal voltage V _read 5, where a nominal reference output voltage without component tolerances 9 and a range of deviation of the reference curve 10 for a variation of the components within the specified tolerances can be seen. All components of the electronic circuit of the insulation monitor 1 have tolerances due to manufacturing.

3 shows output voltage diagrams of a resistor R _iso 2 for an open DC switch in the high-voltage power supply. Diagram 11 shows an output voltage diagram when the resistor R _iso 2 is interrupted with the DC switch open, Diagram 12 shows the relative deviation in percent of the output voltage when the resistor R _iso 2 is interrupted in relation to the reference output voltage where there is no error, for various component tolerances of the insulation monitor hardware, the an output voltage diagram for a short circuit of the resistor R _iso 2 with an open DC switch and the relative deviation in percent of the output voltage in the event of a short circuit of the resistor R _iso 2 in relation to the reference output voltage at which no error is present, with the DC switch f open for various component tolerances of the insulation monitor hardware. Since a defined minimum number of measuring points lie outside the defined tolerance bands for all possible component tolerance combinations, the detection of the fault cases interruption and short circuit of the resistor R _iso 2 is reliably possible in this example. The detection works analogously for faults in other components.

An algorithm is used to output a faulty circuit of the insulation monitor hardware in the software. For example, the median value is formed from a defined number of measuring points, e.g. the relative deviation of the output voltage (the same applies to absolute deviation) and compared with the defined limit curves. If a violation of the limit curves is detected, an internal counter is incremented. This process takes place continuously with each measurement process. If the internal counter reaches a defined value, the state of the insulation monitor is set to "faulty". This process is an example of the 4 which shows the detection algorithm. 4 show the an enlarged section of the detection algorithm. The diagram shows, from top to bottom: error detection of the measurement signal voltage V _read 5 in which an error detection graph of the measurement signal voltage V _read 17, a moving median value graph of the error detection of the measurement signal voltage V _read 17 and a tolerance range 18 are shown. The second diagram from the top shows a counter over time which is incremented by one when a threshold is violated. The counter can only be incremented if the counter in the third diagram from the top is at zero. After a threshold violation is detected, the counter in the third diagram from the top is set to a defined integer value. For subsequent measurement points, the counter is decremented by one until the value zero is reached again. This makes error detection more robust against measurement noise/errors, since the same outlier is only evaluated once and does not lead to a further increase in the counter in the second figure from the top. The evaluation is paused for a defined time. In the last diagram, i.e. the In the bottom diagram, the insulation monitor error is shown over time. It can be seen that in the 5th segment, at time 0.581 seconds, an error was detected and the insulation monitor is therefore set to "Not OK" because more than three limit value violations were detected (counter in the second diagram from the top reaches the value three (value can be freely set)).

In addition, the insulation monitor can only be set to "defective" if a "not OK" is detected in a certain number of consecutive measurement series or if a "not OK" is detected in several measurement series from a defined number of measurement series (e.g. 3 out of 5). This would lead to a delayed indication of the defect, but would also prevent the insulation monitor from being incorrectly classified as defective, for example due to a strong change in the intermediate circuit voltage.

The formation of the median value and the use of a counter serve to make the fault detection more robust against measurement noise/errors. This prevents the state of the insulation monitor from being falsely set to "faulty" even though no fault is present.

5 shows reference output voltage diagrams with and without tolerance influences. It is assumed that the insulation resistances and capacitances are known (e.g. from previous measurements/estimation algorithms). The reference voltage is thus determined depending on the insulation impedance. The upper diagram 19 is divided into two graphs. The upper graph shows reference output voltages with and without component tolerances for different resistance and capacitance values 20. The lower diagram shows a percentage deviation of the output voltages with component tolerances related to a reference output voltage with component tolerances 21. A tolerance range can then be determined based on the tolerance influences as in diagram 22.

List of reference symbols

1

Insulation monitor

2

Insulation resistance R _iso

3

Insulation capacity C _iso

4

Intermediate circuit voltage V _DCLink

5

Measuring signal voltage V _read

6

Excitation voltage signal V _s

7

Input voltage diagram

8th

Output voltage diagram

9

nominal reference output voltage

10

Deviation of the reference curve

11

Output voltage diagram for open DC switch

12

Output voltage diagram with an open circuit fault with DC switch open

13

second output voltage diagram for open DC switch

14

Output voltage diagram with a short circuit with DC switch open

15

Detection algorithm

16

Error detection of the measuring signal voltage V _read

17

moving median value of the error detection of the measuring signal voltage V _read

18

Tolerance range

19

Output voltage diagram reference impedance

20

Nominal reference output voltage without component tolerances

21

Nominal reference output voltage with component tolerances

22

resulting tolerance range

QUOTES INCLUDED IN THE DESCRIPTION

This list of documents listed 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 accepts no liability for any errors or omissions.

Cited patent literature

• DE 102014205918 A1 [0005]

Claims (9)

Method for detecting faulty components in an insulation monitor (1), wherein during use of the insulation monitor (1) to determine an insulation resistance R _iso (2), the measurement signal voltage V _read (5) applied to the insulation monitor is measured and compared with a reference signal, wherein a conclusion is drawn depending on the comparison. Procedure according to Claim 1 , characterized in that the reference signal range takes into account different influencing factors. Procedure according to Claim 1 or 2 , characterized in that the reference signal is a reference voltage signal, a reference current signal or a reference power signal. Procedure according to one of the Claims 1 until 3 , characterized in that it is concluded that a faulty component is present if the measuring signal voltage V _read (5) deviates from the reference signal to a defined extent for a defined number of measuring points. Method according to one of the Claims 1 until 4 , characterized in that if the measuring signal voltage V _read (5) deviates from the reference signal, the determined insulation resistance R _iso (2) is evaluated as invalid. Method according to one of the Claims 1 until 5 , characterized in that the reference signal is defined by a value corridor for a reference range. Method according to one of the Claims 1 until 6 , characterized in that the reference range takes into account different influencing factors. Procedure according to one of the Claims 1 until 7 , characterized in that the method can be carried out while the DC switch is open or closed. Detection circuit for determining faulty components of an insulation monitor (1), arranged to carry out the method according to one of the preceding claims.

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