DE102021005534B3 - Method for determining at least one current capacitance value of a Y capacitance of an on-board electrical system and on-board electrical system - Google Patents

Abstract

The invention relates to a method for determining at least one current capacitance value (28) of a Y capacitance of an on-board electrical system (12) for an at least partially electrically operated motor vehicle (10) using an electronic computing device (24) in the on-board electrical system (12), in which of an insulation monitor (26) of the vehicle electrical system (12), the current capacitance value (28) is determined, with an iteration process being used to approximate a value of a current insulation resistance (20, 22) using the insulation monitor (26) and, depending on a speed, a Convergence of the insulation resistance value (30) used in the iteration process determines the current capacitance value (28). The invention also relates to an on-board electrical system (12).

Description

The invention relates to a method for determining at least one current capacitance value of a Y capacitance of a high-voltage vehicle electrical system for an at least partially electrically operated motor vehicle using an electronic computing device. Furthermore, the invention relates to an electronic computing device.

It is already known from the prior art that the limit value of all capacitances in an on-board electrical system of an at least partially electrically operated motor vehicle between the electrical potentials HV+ and HV- and a respective vehicle mass in an HV vehicle system, known as C _Y in technical usage, represents an approval-relevant variable that must be produced when manufacturing or when determining the system. This value is limited because this capacity is discharged through the body if an HV potential and the vehicle are touched at the same time and could therefore lead to a dangerous electrical current flowing through the body. Since these capacitances are caused by parasitic effects on the one hand and are built into the electronic circuits of components in the form of components to suppress interference on the other hand, and also have an influence on the insulation coordination, it is important to know the actual value of this Y capacitance as well as possible.

The DE 10 2016 006 642 A1 relates to a high-voltage battery for a motor vehicle, comprising an electrically conductive battery housing, a battery cell stack which is formed from a large number of battery cells electrically connected in series to provide a high-voltage voltage and which are arranged inside the battery housing, the battery cell stack between a high voltage - A positive line, which is electrically conductively connected to the positive pole of the battery cell stack, and a high-voltage negative line, which is electrically conductively connected to the negative pole of the battery cell stack, and an insulation measuring device, which is designed to, depending on an insulation resistance between the Battery cell stack and the battery case to determine an insulation fault. A localization device is designed to localize the determined insulation fault in the battery cell stack as a function of a first voltage present between the high-voltage positive line and the battery housing and/or a second voltage present between the high-voltage negative line and the battery housing. The invention also relates to a corresponding method.

According to the DE 10 2010 054 413 A1 a method is provided for locating an insulation fault in a system that has a DC section with a high side (HV+) and a low side (HV-) and an AC section including an inverter with at least one series connection of two power switches connected between the high side (HS side) and the low side (LS side) is connected. The DC section is supplied with a DC voltage from a DC voltage source. The circuit breaker directly on the HV side is switched through according to an HV switch-on state, the circuit breaker directly on the LS side is switched through according to a LS switch-on state, a HV insulation voltage is measured between the HV side and a Ground and an LS insulation voltage between the LS side and the ground in each of the two switching states and finally determining on the basis of the measurement results whether there is an insulation fault in the DC section or AC section.

In the DE 10 2016 214 458 A1 an apparatus and method for detecting dielectric breakdown in an environmentally friendly vehicle is presented. The device includes a measuring device configured to measure resistance values of insulation resistors arranged across a high-voltage battery, and a controller configured to measure a voltage applied to the insulation resistor using the measuring device and analyze a pattern of the measured voltage. to detect a portion of the dielectric breakdown.

The DE 10 2018 002 926 A1 relates to an electrical system for a motor vehicle, with at least one first and one second electrical potential line, the vehicle electrical system being designed so that an electrical DC voltage is applied between the potential lines during normal operation, the vehicle electrical system having at least one Y capacitor which is electrically coupled with a first connection to one of the potential lines and to a second connection with an electrical reference potential, wherein a switching element is connected in series with the at least one Y-capacitor.

From the DE 10 2020 003 222 A1 a method for monitoring a Y-capacitance of an electrically operated vehicle is known. In this case, a test voltage is mutually impressed between a potential of the electrically operated vehicle and an electrical reference potential of the electrically operated vehicle and as a function of the mutual impression the test voltage discharges and/or charges the Y-capacitance. If the capacitance value of the Y capacitance exceeds a specified limit value, this is recognized as an error.

In addition, the also shows the DE 10 2020 102 658 A1 a method for monitoring y-capacitances in an electrically operated motor vehicle.

The DE 10 2019 109 720 A1 discloses a method for determining capacitances of bypass capacitors in a charging cable during a charging process of an energy store. A first output of the energy source is electrically connected to a ground potential via a first bypass capacitor and a second output of the energy source is electrically connected to a ground potential via a second bypass capacitor. A first test resistor and a first switching means are connected in parallel with the first bypass capacitor and a second test resistor and a second switching means are connected in parallel with the second bypass capacitor.

The object of the present invention is to create a method and an electronic computing unit, by means of which a more precise determination of a Y capacitance within an on-board electrical system can be implemented.

This object is achieved by a method and by an electronic computing device according to the independent patent claims. Advantageous embodiments are specified in the dependent claims.

One aspect of the invention relates to a method for determining at least one current capacitance value of a Y-capacitance of an electrical system for an at least partially electrically operated motor vehicle using an electronic computing device of the electrical system, in which the current capacitance value is determined using an insulation monitor of the electrical system.

It is provided that an iteration process is used to approximate a value of a current insulation resistance using the insulation monitor, and the current capacitance value is determined as a function of a speed of convergence of the insulation resistance value used in the iteration process.

In particular, it is therefore proposed to determine the capacitance value, which can also be referred to as the C _y value, using the iteration method with only one insulation monitor within the on-board electrical system, which corresponds in particular to a high-voltage network. For this purpose, an assumed C _y value can optionally be determined in a first step by iteration, in particular as an input value, via the insulation monitor, an insulation resistance. In a main process step, the C _y values are then specified for the iteration and the C _y value that has either converged the fastest or whose determined insulation resistance is closest to the value from the optional first step is then specified with sufficient accuracy as C _y value, i.e. as the current capacitance value. In particular, the current capacitance value is measured with one insulation monitor, for example by determining an iteration of the C _y values in an optional first step and in particular in a main step in which the best C _y value is assumed to be the one at where the iteration converges fastest. For this purpose, for example, the convergence can still optionally be based on the insulation value from the first step.

The iteration to a specific insulation resistance is thus replaced by the fastest converging iteration, based on whose initial value of the C _y value is then adopted as the specific C _y value.

According to an advantageous embodiment, a starting capacitance value is specified as a stored capacitance value in a storage device of the electronic computing device, and the current capacitance value for the Y capacitance is adjusted as a function of the comparison.

Furthermore, it can be provided that the starting capacitance value is specified when the motor vehicle is manufactured.

It is also advantageous if the current capacitance value is stored in a memory device of the electronic computing device for future evaluation.

Provision can furthermore be made for the current insulation resistance of the on-board electrical system to be determined by means of the insulation monitor as a function of the determined current capacitance value.

A further aspect of the invention relates to an on-board electrical system for an at least partially electrically operated motor vehicle, with at least one electronic computing device and at least one insulation monitor, the on-board electrical system being designed to carry out a method according to the preceding aspect. In particular, the method is carried out using the on-board electrical system.

Furthermore, the invention also relates to a motor vehicle with an on-board electrical system according to the preceding aspect. The motor vehicle can be operated at least partially electrically or fully electrically.

Advantageous configurations of the method are to be regarded as advantageous configurations of the on-board electrical system. For this purpose, the on-board electrical system has specific features that require the method to be carried out.

For example, the electronic computing device can have processors, circuits, in particular integrated circuits, in order to enable the method to be carried out.

The method presented is in particular a computer-implemented method. A further aspect of the invention therefore also relates to a computer program product with program code means which cause an electronic computing device to carry out a method according to the preceding aspect when the program code means are processed by the electronic computing device. Furthermore, the invention also relates to a computer-readable storage medium with the computer program product according to the preceding aspect.

Further advantages, features and details of the invention result from the following description of a preferred exemplary embodiment and from the drawing. The features and combinations of features mentioned above in the description and the features and combinations of features mentioned below in the description of the figures and/or shown alone in the single figure can be used not only in the combination specified in each case, but also in other combinations or on their own, without the frame to abandon the invention.

The single figure shows a schematic side view of an embodiment of a motor vehicle with an embodiment of an on-board electrical system.

Elements that are the same or have the same function are provided with the same reference symbols in the figures.

The figure shows a schematic side view of an embodiment of a motor vehicle 10 with an embodiment of an electrical system 12 . In particular, a first insulation resistance 20 can be formed, for example, from the HV plus line 14 to a vehicle ground 18 . Furthermore, a second insulation resistance 22 can be formed by the HV minus strand 16 between the vehicle ground 18 .

The vehicle electrical system 12 is designed in particular for the at least partially electrically operated motor vehicle 10. Alternatively, the motor vehicle 10 can also be operated fully electrically. The on-board electrical system 12 also has an electronic computing device 24, which can also be embodied as a battery management system, for example. Furthermore, the vehicle electrical system 12 has, in particular, an insulation monitor 26 .

One aspect of the invention relates to a method for determining at least one current capacitance value 28 of a Y capacitance of the on-board electrical system 12 for the motor vehicle 10 using the electronic computing device 24. It is provided that the current capacitance value is determined indirectly using the insulation monitor 26 via an iteration method 28 is determined.

In particular, it is provided that an iteration method is used to approximate a value of a current insulation resistance 20, 22 using the insulation monitor 26 and that the current capacitance value 28 is determined as a function of a speed of convergence of the insulation resistance value 30 used in the iteration method.

In particular, only the insulation monitor 26 is therefore required. This has a special functionality or property, so that the correct capacitance value 28, which can also be referred to as the C _y value, is always output over time, the time required for this being the shorter the more precisely the parameter entered in the software reflects reality . To solve the problem, and thus to determine the capacitance value 28, there are in particular two options described below.

A first possibility corresponds to a two-stage solution. In particular, this has an iterative number search or iterative approximation step to the actually correct value of the on-board electrical system 12 . For this purpose, either an arbitrary value or no value at all for the capacitance value 28 is initially specified. This is followed by an indefinite period of time until the result of the insulation resistance measurement converges. Seen over time, the initial value, or the value after the first iteration, is getting closer and closer to the actual kor correct value of the on-board electrical system 12 . The result now corresponds to the correct insulation resistance 20, 22. In the second step, a simple approximation is carried out. For this purpose, the method is carried out several times with different capacitance values 28 and it is checked how much time is required to obtain the result of the first step. The value that comes closest to the result of the first step corresponds with sufficient accuracy to the current capacitance value 28.

Alternatively, for example, only one method step can be carried out, which consists of a simple approximation. In this case, several values for the capacitance value 28 are specified. A check is then carried out to determine how long it takes for the insulation resistance 20, 22 to converge for the respective values. That predetermined value at which the measurement takes the least time corresponds with sufficient accuracy to the current capacitance value 28 of the on-board electrical system 12 new measurement cycle or next run. It is then checked whether the convergence occurs faster or slower than in the previous measurement. If there are time deviations in this case, it is necessary to check the C _y capacitance determined. If this is not the case, the minimum corresponds to the current capacitance value 28 of the on-board electrical system 12 with sufficient accuracy.

The use of the last saved value is particularly advantageous for measurements that are carried out in close succession, for example several ignition cycles during the vehicle usage day, for example as occurs in distribution traffic, since the time until convergence is significantly reduced and thus the starting process of the motor vehicle 10 can be accelerated.

In both variants, a certain deviation from the exact value for the current capacitance value 28 of the overall system is tolerable, since the on-board electrical system 12 is designed taking into account inaccuracies in a certain value range.

In particular, a sufficiently precise determination of the current capacitance value 28 within the on-board electrical system 12, which can in particular also be referred to as a high-voltage on-board electrical system, is thus made possible. Since the sum of these capacities is relevant for approval, the conformity of the entire system can be checked, in particular when using vehicle bodies with a connection to the on-board electrical system 12 . In particular, the invention thus offers the advantage that the instantaneous capacitance value 28 can be determined using only a single insulation monitor 26 . This in turn can lead to cost savings for the on-board electrical system 12 .

Reference List

10

motor vehicle

12

On-board electrical system

14

High-voltage plus line

16

High-voltage negative strand

18

vehicle mass

20

First insulation resistance

22

Second insulation resistance

24

electronic computing device

26

isolation guard

28

Current capacity value

30

insulation resistance value

Claims (6)

Method for determining at least one current capacitance value (28) of a Y capacitance of an on-board electrical system (12) for an at least partially electrically operated motor vehicle (10) by means of an electronic computing device (24) of the on-board electrical system (12), in which by means of an insulation monitor ( 26) of the vehicle electrical system (12), the current capacitance value (28) is determined, characterized in that an iteration process is used to approximate a value of a current insulation resistance (20, 22) using the insulation monitor (26) and, depending on a speed, a Convergence of the insulation resistance value (30) used in the iteration process determines the current capacitance value (28). procedure after claim 1 , characterized in that a starting capacitance value is specified as a stored capacitance value in a storage device of the electronic computing device (24) and the current capacitance value (28) for the Y capacitance is adjusted as a function of the comparison. procedure after claim 2 , characterized in that the starting capacitance value is specified when the motor vehicle (10) is manufactured. Method according to one of the preceding claims, characterized in that the current capacitance value (28) is stored in a memory device of the electronic computing device (24) for future evaluation. Method according to one of the preceding claims, characterized in that the current insulation resistance (20, 22) of the vehicle electrical system (12) is determined by means of the insulation monitor (26) as a function of the determined current capacitance value (28). On-board electrical system (12) for an at least partially electrically operated motor vehicle (10), with at least one electronic computing device (24) and with an insulation monitor (26), the on-board electrical system (12) for carrying out a method according to one of the Claims 1 until 5 is trained.

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