METHOD FOR DETECTING AN INSULATION FAULT IN A VEHICLE ON-BOARD ELECTRICAL SYSTEM

Abstract

A method for detecting an insulation fault in a vehicle on-board electrical system having an HV on-board electrical system branch and an LV on-board electrical system branch provides for the LV on-board electrical system branch to have a positive supply potential and a negative supply potential that corresponds to a ground potential of the vehicle on-board electrical system. The HV on-board electrical system branch has a positive HV potential and a negative HV potential which are DC-isolated from the potentials of the LV on-board electrical system branch. An insulation fault between at least one of the HV potentials and a positive LV potential is detected by identifying a current flow through a voltage limiting circuit connected between the ground potential and the positive LV potential.

Claims

1. A method for detecting an insulation fault in a vehicle on-board electrical system having an HV on-board electrical system branch and an LV on-board electrical system branch, wherein the LV on-board electrical system branch has a positive supply potential and a negative supply potential that corresponds to a ground potential of the vehicle on-board electrical system, and the HV on-board electrical system branch has a positive HV potential and a negative HV potential which are DC-isolated from the potentials of the LV on-board electrical system branch, wherein an insulation fault between at least one of the HV potentials and a positive LV potential is detected by identifying a current flow through a voltage limiting circuit connected between the ground potential and the positive LV potential.

2. The method as claimed in claim 1, wherein the current flow is identified on the basis of a shift of one of the HV potentials with respect to the ground potential.

3. The method as claimed in claim 2, wherein the current flow is identified on the basis of a potential change rate that is above a predetermined value.

4. The method as claimed in claim 2, wherein the current flow is identified on the basis of a change to a potential difference between the HV potential and the ground potential that is below a predetermined value, wherein this potential difference occurs while the voltage between the HV potentials is within a normal range.

5. The method as claimed in claim 2, wherein the shift is identified by an insulation monitor.

6. The method as claimed in claim 5, wherein the insulation monitor also carries out an active insulation test of the HV on-board electrical system branch by actively reversing the charge of Cy capacitances between the ground potential on the one hand and the HV potentials on the other hand and detecting a potential shift caused by the charge reversal, wherein the active charge reversal is interrupted when a current flow through the voltage limiting circuit is identified.

7. The method as claimed in claim 6, wherein, during the active charge reversal, a potential difference between one of the HV potentials and the ground potential does not drop below a minimum voltage and the current flow through the voltage limiting circuit is identified on the basis of a change to a potential difference between the HV potential and the ground potential that is below a predetermined value, wherein this value is smaller than the minimum voltage.

8. The method as claimed in claim 5, wherein the current flow through the voltage limiting circuit is identified by measuring at least one voltage between at least one of the HV potentials on the one hand and the ground potential on the other hand by at least one voltmeter which is connected to the insulation monitor or by at least one voltmeter which is evaluated by its own evaluation circuit and has no direct signal-transmitting connection to the insulation monitor.

9. The method as claimed in claim 1, wherein at least one of the following measures is carried out if the insulation fault is identified by identifying a current flow through the voltage limiting circuit: disconnecting a high-voltage storage battery of the HV on-board electrical system branch from the remaining HV on-board electrical system branch by circuit breakers; disconnecting at least one Cy filter capacitor of the HV on-board electrical system; disconnecting a charging post connected to the HV on-board electrical system; discharging the HV on-board electrical system branch; and disconnecting an HV on-board electrical system sub-branch from an inverter HV on-board electrical system sub-branch which has a traction inverter.

10. The method as claimed in claim 1, wherein the voltage limiting circuit, whose current flow is identified, is connected between the ground potential and a positive LV potential which is a positive supply potential of the LV on-board electrical system branch.

11. The method as claimed in claim 1, wherein the voltage limiting circuit, whose current flow is identified, is connected between the ground potential and a positive LV potential which is a positive line potential of the LV on-board electrical system branch.

12. The method as claimed in claim 11, wherein an LV device is connected to the ground potential and to a positive supply potential of the LV on-board electrical system branch, and wherein lines are connected to the LV device, wherein at least one of the lines has a positive LV potential.

13. The method as claimed in claim 12, wherein the LV device is an LV communication apparatus or an LV sensor apparatus or an LV control device.

14. The method as claimed in claim 1, wherein the voltage limiting circuit, whose current flow is measured, comprises a varistor, a gas discharge tube, a spark gap, a protective diode, a thyristor circuit, a DIAC, a Zener diode and/or a four-layer diode.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0035] The FIGURE serves to explain the method described here in more detail and shows an on-board electrical system circuit provided for carrying out the method.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0036] The FIGURE shows a vehicle on-board electrical system FB having a low-voltage storage battery NA which is connected to an HV on-board electrical system branch HB via a low-voltage converter. The HV on-board electrical system branch LB is connected via the converter NW to the LV on-board electrical system branch LB which also contains the low-voltage storage battery NA. A high-voltage storage battery HA is provided in the high-voltage on-board electrical system branch HB and is connected via an isolating apparatus TS and via a storage battery connection BA. The storage battery connection BA is located between the high-voltage storage battery HA and the circuit breakers TS. The circuit breakers are designed with two poles.

[0037] Cy capacitors Cy1, Cy2 are also located in the high-voltage on-board electrical system HB. These are located between the ground potential M and the negative HV potential HV−, or between the ground potential M and the positive HV potential HV+. A negative LV potential L−, which corresponds to the ground potential M, is provided in the low-voltage on-board electrical system branch LB. The ground potential M preferably in turn corresponds to the chassis potential of the vehicle. A positive LV potential L, which corresponds to a supply potential, is also provided.

[0038] The two supply potentials L−, L+ of the HV on-board electrical system branch supply a low-voltage device NG, for example a sensor evaluation circuit. The sensor evaluation circuit also comprises a line L with a positive LV potential G+ and a negative LV potential G−. The potential G− can correspond to the potential L− or M. The positive potential G+ is a positive line potential, but may generally be a line potential, for example as the potential of a signal conductor. The low-voltage device NG can also be referred to as an LV device.

[0039] As shown, the line L can be continued and lead to other components, for example to other sensors. For example, the low-voltage device NG can be a communication apparatus, for example a CAN bus circuit, to which a plurality of further components are connected. In particular, the line can lead out of a housing in which HV components are located and can in particular be routed out into an area in which LV components or conductors with ground potential are located. It would be critical if the line carried HV potential since this can come into contact with ground or LV components, especially since the line is equipped for LV applications and thus does not have the insulation used for HV components.

[0040] A voltage limiting circuit SG is provided in order to prevent an insulation fault from propagating into the potential G+, that is to say generally into a signal potential of the LV on-board electrical system branch LB. If there is an insulation fault in the form of an associated resistance RF, compare dot-dashed connection, the positive HV potential + is connected to the potential G+ via this faulty insulation resistance and thus to a conductor or line L which belongs to the LV on-board electrical system branch and can lead to other components. As a result, other components of the LV on-board electrical system can also be loaded with the HV potential +, which leads to possibly dangerous contact voltages on other LV components.

[0041] The voltage limiting circuit SG is used to generate a current flow I in a targeted and predictable manner when an HV potential (+) crosses over into the LV on-board electrical system LB via the insulation fault RF. The current flow I is shown with a dashed line. On the one hand, the resulting potential shift between ground potential M and one of the HV potentials+, − can be detected. On the other hand, the current flow I can also be detected by an ammeter. Preferably, the shift is detected by considering a change rate resulting from the sudden occurrence of the insulation resistance RF. This change rate is significantly faster than the change rate of the potential +, − with respect to M, which occurs due to the test current during an active insulation measurement. In addition, due to the voltage limiting circuit and its breakdown voltage, from which it conducts, there is a different potential offset of the HV potentials+, − with respect to the ground potential M. In particular, this offset is greater than with the charge reversal or discharging that occurs during the active insulation resistance measurement and the offset is also established more quickly (i.e. has a higher voltage change rate). In this way, the resulting voltage, which corresponds to the breakdown voltage of the voltage limiting circuit, can be clearly separated from the minimum voltage which minimally results during the active insulation resistance measurement.

[0042] The breakdown voltage of the voltage limiting circuit is smaller by a minimum margin than the minimum voltage that occurs during the active insulation resistance measurement. As a result, the faults can be detected separately from one another; in particular, a fault can be detected as shown (connection between HV+ and an LV signal line).

[0043] An insulation monitor IM can be provided. This can be connected to voltmeters V1, V2 which capture the voltage between the HV potential + and ground M or between the HV potential − and ground M. With these, the insulation monitoring IM can actively measure the insulation resistance. Furthermore, provision may be made for these voltmeters V1, V2 to also be used to carry out the method described here, for example by measuring the potential change rate or the resulting potential shift. However, voltmeters that are independent of the insulation monitoring circuit IM are preferably used, wherein an evaluation circuit is also connected to these voltmeters, wherein the voltmeters and the evaluation circuit are configured to carry out the method described here, independently of the active insulation resistance measurement of the insulation monitoring circuit IM.

[0044] Finally, a charging device LG is shown, which is connected to a charging connection LA via a three-phase line. A charging post LS can be connected to the charging connection LA.

[0045] If a current flow is identified according to the method, provision may be made for the circuit breakers TS to be opened in order to thus disconnect the HV storage battery HA. Alternatively or additionally, provision may be made for the charging circuit LG to suppress or interrupt a charging process. In addition, provision may be made for an active insulation resistance measurement to be prevented by the insulation monitoring circuit IM, in particular the injection of a test current for detecting the insulation resistance.

[0046] Finally, it should be noted that the insulation monitoring circuit IM monitors the insulation resistance between the potential M on the one hand and the potentials +, − on the other hand, in particular by actively injecting a test current and determining the corresponding expected potential shift. This active insulation resistance measurement differs from the detection of a current flow I through the voltage limiting circuit SG, since the latter identifies an insulation fault in the high-voltage on-board electrical system branch HB with respect to the low-voltage on-board electrical system branch LB or the line L, even if the connection between the potentials G+ and L+ is broken (e.g. a burnt-out transistor in the low-voltage device NG).

[0047] The insulation fault RF can be considered to be a state and the resistance that triggers it.