METHOD FOR DISCHARGING A VEHICLE HIGH-VOLTAGE ELECTRICAL SYSTEM, ON-BOARD VEHICLE ELECTRICAL SYSTEM, AND INSULATION MONITORING DEVICES

Abstract

A method for discharging a vehicle high-voltage electrical system, which is galvanically isolated from a ground potential, in the presence of a residual current makes provision for the following step: determining whether a residual current flows between a first HV potential of the vehicle high-voltage electrical system and the ground potential or a residual current flows between a second HV potential of the vehicle high-voltage electrical system and the ground potential. The method furthermore makes provision to discharge only that Cy capacitance which exists between the ground potential and that HV potential from which or to which the residual current flows. The discharging is triggered by determining the existence of a residual current. Furthermore, an on-board vehicle electrical system and an insulation monitoring device which are designed for performing the method are described. In addition, a corresponding charging-station high-voltage electrical system is described.

Claims

1. A method for discharging a vehicle high-voltage electrical system, which is galvanically isolated from a ground potential, in the presence of a residual current, the method comprising: determining whether a residual current flows between a first HV potential of the vehicle high-voltage electrical system and the ground potential or a residual current flows between a second HV potential of the vehicle high-voltage electrical system and the ground potential; and discharging only that Cy capacitance which exists between the ground potential and that HV potential from which or to which the residual current flows, wherein the discharging is triggered by determining the existence of a residual current.

2. The method as claimed in claim 1, wherein discharging of that Cy capacitance which is connected between the ground potential and that HV potential which has no residual current flow is prevented.

3. The method as claimed in claim 1, wherein, after discharging the Cy capacitance which is connected to the HV potential linked to the residual current flow, the other Cy capacitance is discharged.

4. The method as claimed in claim 1, wherein, after discharging the Cy capacitance which is connected to the HV potential linked to the residual current flow, a high-voltage source of the vehicle high-voltage electrical system is disconnected.

5. The method as claimed in claim 1, wherein a fault signal is emitted if a residual current is determined.

6. The method as claimed in claim 1, wherein, after discharging the Cy capacitance which is connected to the HV potential linked to the residual current flow, a Cx capacitance which exists between the first HV potential and the second HV potential is discharged.

7. The method as claimed in claim 1, wherein the determining of whether a residual current flows between a first HV potential of the vehicle high-voltage electrical system and the ground potential or a residual current flows between a second HV potential of the vehicle high-voltage electrical system and the ground potential comprises: measuring an impedance across which the residual current flows, wherein furthermore the step of discharging the Cy capacitance is carried out only if this impedance lies in an impedance range which characterizes the impedance of a human body, wherein disconnection of a high-voltage source of the vehicle high-voltage electrical system and/or discharging of a Cx capacitance which exists between the first HV potential and the second HV potential is prevented.

8. The method as claimed in claim 1, wherein the determining of whether a residual current flows between a first HV potential of the vehicle high-voltage electrical system and the ground potential or a residual current flows between a second HV potential of the vehicle high-voltage electrical system and the ground potential comprises: measuring a rate of change of a voltage between ground and one of the HV potentials, wherein it is determined that a residual current exists if the absolute value of the rate of change lies above a limit which characterizes the maximum rate of change which occurs during an active insulation measurement.

9. An insulation monitoring device of a vehicle high-voltage electrical system, wherein the insulation monitoring device has a ground potential connection and a first and a second HV potential connection, wherein the insulation monitoring device comprises: a residual current detection means which is designed to detect a first residual current between a first HV potential of the first HV potential connection and the ground potential of the ground potential connection, and a second residual current between a second HV potential of the second HV potential connection and the ground potential of the ground potential connection; and a discharging circuit, wherein the residual current detection means is connected to the discharging circuit such that it can drive the latter, wherein the discharging circuit is configured to connect only the first HV potential connection to the ground potential connection in a controlled manner if the residual current detection means captures the first residual current, and to connect only the second HV potential connection to the ground potential connection if the residual current detection means captures the second residual current.

10. The insulation monitoring device as claimed in claim 9, wherein the discharging circuit has a first discharging switch between the first HV potential connection and the ground potential connection, and has a second discharging switch between the second HV potential connection and the ground potential connection, which discharging switches are configured to be closed only one at a time, and not simultaneously.

11. An on-board vehicle electrical system having an insulation monitoring device as claimed in claim 9 and having a ground potential and a vehicle high-voltage electrical system which is galvanically isolated from said ground potential and has a first HV potential and a second HV potential, wherein the first HV potential connection of the insulation monitoring device is connected to the first HV potential of the vehicle high-voltage electrical system, the second HV potential connection of the insulation monitoring device is connected to the second HV potential of the vehicle high-voltage electrical system, and the ground potential connection of the insulation monitoring device is connected to the ground potential of the on-board vehicle electrical system.

12. An insulation monitoring device of a charging-station high-voltage electrical system, wherein the insulation monitoring device has a ground potential connection and a first and a second HV potential connection, wherein the insulation monitoring device comprises: a residual current detection means which is designed to detect a first residual current between a first HV potential of the first HV potential connection and the ground potential of the ground potential connection, and a second residual current between a second HV potential of the second HV potential connection and the ground potential of the ground potential connection; and a discharging circuit, wherein the residual current detection means is connected to the discharging circuit such that it can drive the latter, wherein the discharging circuit is configured to connect only the first HV potential connection to the ground potential connection in a controlling manner if the residual current detection means measures the first residual current, and to connect only the second HV potential connection to the ground potential connection if the residual current detection means measures the second residual current.

13. The insulation monitoring device as claimed in claim 12, wherein the discharging circuit has a first discharging switch between the first HV potential connection and the ground potential connection, and has a second discharging switch between the second HV potential connection and the ground potential connection, which discharging switches are configured to be closed only one at a time, and not simultaneously.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The FIGURE serves to explain the methods and apparatuses described here.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] The FIGURE shows an on-board vehicle electrical system FB having a vehicle high-voltage electrical system HN. The vehicle high-voltage electrical system has a first, positive HV potential HV+ and a second, negative HV potential HV−. All poles of the disconnecting switches TS, TS′, which separably connect a high-voltage rechargeable battery A of the vehicle high-voltage electrical system HN to the HV potentials HV+, HV−, are connected to rechargeable battery connections 1, 2 of the vehicle high-voltage electrical system HN. The on-board vehicle electrical system FB furthermore has a ground potential M. This potential M can be a negative supply potential of an on-board low-voltage electrical system (not illustrated). The potential M (and in particular the on-board low-voltage electrical system) are galvanically isolated from the vehicle high-voltage electrical system HN. The potential M is in particular the chassis potential of the vehicle in which the on-board vehicle electrical system FB is provided.

[0025] If a person touches the chassis (ground potential M), illustrated by the resistor RF, and there exists an insulation fault of the vehicle high-voltage electrical system HN in such a way that the chassis has a (high) voltage with respect to the ground potential M, a residual current FI flows through this person. In the illustrated case, a residual current FI flows from the first (i.e. positive) HV potential HV+ to the ground potential. The procedure described here makes provision, if the presence of a residual current FI is detected, for the HV potential HV+ to be shifted toward the ground potential by closing a switch S1. Since a Cy capacitance C1 exists between the HV potential HV+ and the ground potential (for instance realized by parasitic capacitances of the vehicle high-voltage electrical system HN or of the HV potential HV+ with respect to the ground potential M and an EMC filter capacitance between these potentials), this Cy capacitance is discharged when shifting the HV potential HV+ toward the ground potential M. This switch S1 is therefore referred to as discharging switch S1. This procedure is also provided for the second HV potential HV− if this second HV potential is connected to the ground potential M via a resistor RF′ (for instance the body resistance of a person), as a result of which a residual current FI′ arises.

[0026] So that only the relevant HV potentials touched by a person are brought to the level of the harmless ground potential M by discharging the relevant Cy capacitance, and no further, time-consuming discharging operations have to be carried out, the non-relevant Cy capacitance is not discharged toward ground potential M. If the residual current FI occurs at the HV potential HV+, the Cy capacitance Cy1 between M and HV+ is discharged by closing the discharging switch S1. The discharging switch S2, which is connected to the non-relevant potential HV−, is not closed in the event of such a fault (cf. RF) with respect to HV+. If the residual current FI′ occurs at the HV potential HV−, the Cy capacitance Cy1 between M and HV− is discharged by closing the discharging switch S2. The discharging switch S1, which is connected to the non-relevant potential HV+, is not closed in the event of such a fault (cf. RF′) with respect to HV−. The Cx capacitor Cx (for instance an intermediate circuit capacitor) between the HV potentials HV+ and HV− is not discharged via the discharging switches S1, S2.

[0027] The presence of a residual current (RF or RF′) is captured by the residual current detection means FE which is connected to the ground potential M and to the HV potentials HV+, HV− via the ground potential connection MA and via a first and a second HV potential connection HA1, 2. These connections and the residual current detection means FE are part of the insulation monitoring device IW. This insulation monitoring device furthermore comprises the discharging switches S1, S2 which are connected via current limiting resistors R1, R2 to ground M and to the HV potentials HV+, −, respectively. The discharging switch S1 is (directly) connected to the ground potential M via the resistor R1 and is connected to the HV potential HV+. The discharging switch S2 is connected to the HV potential HV+ via the resistor R2 and is (directly) connected to the ground potential M. Both switches can however be directly connected to the respective HV potential and via respective resistors R1, R2 to the ground potential. Varistors can be used instead of or in combination with the resistors R1, R2. The resistors and/or varistors can be provided by a plurality of series-connected resistor components or varistor components in order to realize a redundancy. The switches S1, S2 can also each be formed of a series circuit comprising a plurality of switching elements (in particular transistors such as MOSFETs). The result of this is a redundancy and lower maximum voltages, since the voltage across the discharging switches is divided between the switching elements of the series circuits.

[0028] The residual current detection means FE, by measuring the voltage between HV+, HV− on the one hand and on the other hand M, captures whether a potential shift arises due to a residual current RF, RF′. As a result, it can be determined whether a residual current RF, RF′ is present and from which HV potential this residual current emanates (or which faulty HV potential is the cause of the residual current). The residual current generally arises due to an insulation fault of the high-voltage electrical system HN with respect to the ground potential M and can therefore also be called insulation fault current.

[0029] With reference to the FIGURE, the insulation monitoring device IW of a charging-station high-voltage electrical system described here or a corresponding charging station can also be described: The connections 1, 2 are in this case a charging connection of the charging station or connections of the insulation monitoring device which are connected to DC charging connections of the charging station. The potentials HV+, − are the DC high-voltage potentials of the charging station or potentials of the monitoring device that are connected hereto (via connections HA1, HA2). A ground potential M of the charging station is connected to the potentials HV+, − of the charging station via charging-station discharging switches S1, S2. Discharging resistors R1, R2, in series with the switches S1, S2, reduce or limit the discharging current. In the event of an insulation fault being captured, only one of the switches is closed. The manner of operation of the charging-station-related components and embodiments is the same as that of the vehicle-related components and embodiments, for which reason the FIGURE can also be used for explaining the charging-station-related components. With regard to the charging-station-related components, reference is made to the properties, modes of operation and features of the vehicle-related components. On account of the comparable properties and features, the same reference signs are used to illustrate the equivalences between vehicle-related components and charging-station-related components.