High-voltage system for a motor vehicle with passive, detachable discharge circuits for Y-capacitances

Abstract

The invention relates to a high-voltage system (1') for a motor vehicle, comprising: - an electrical high-voltage energy storage device (2) with storage-side HV connections (5a, 5b), - a high-voltage on-board network (3) having on-board network-side HV connections (6a, 6b) and a capacitance arrangement (10) with one X-capacitance (Cx) and two Y-capacitances (Cy1, Cy2), - a switching device (4) connected to the HV connections (5a, 5b, 6a, 6b) for connecting the high-voltage energy storage device (2) and the high-voltage on-board network (3), - a discharge device (11') for discharging the capacitor arrangement (10), which has a discharge resistor (Re) connected to the vehicle electrical system-side HV connections (6a, 6b) and a passive discharge circuit (12a, 12b) for each Y-capacitor (Cy1, Cy2), wherein the discharge circuits (12a, 12b) are designed to discharge the Y-capacitors (Cy1, Cy2) and each have at least one diode (D) for this purpose, wherein the diodes (D) are reverse-biased with respect to a normal polarity of voltages (Uy1, Uy2) dropped across the Y-capacitors (Cy1, Cy2) when the switching device (4) is closed, and wherein the at least one diode (D) of a discharge circuit (12b) is caused by a polarity change of the voltage (Uy2) at the associated Y-capacitor (Cy2) by charging the Y-capacitances (Cy1, Cy2) and by the discharge resistance-related potential coupling of the on-board network-side HV connections (6a, 6b), can be polarized in the forward direction to discharge the Y-capacitances (Cy1, Cy2),wherein the discharge device (11') has a contacting element (14) which, in a first state, electrically connects the discharge circuits (12a, 12b) to the ground potential (M) and, in a second state, separates the discharge circuits (12a, 12b) from the ground potential (M) for a dielectric strength test of the high-voltage system (1) with the switching device (4) closed.

Description

[0001] The invention relates to a high-voltage system for a motor vehicle according to the preamble of claim 1. The invention also relates to a motor vehicle with a high-voltage system according to claim 8 and to a method for testing a motor vehicle with regard to the dielectric strength of the high-voltage system according to claim 9.

[0002] In this case, the focus is on electrified motor vehicles, such as electric vehicles, hybrid vehicles, and fuel cell vehicles, with high-voltage systems. Such high-voltage systems typically include a high-voltage energy storage device designed to supply high-voltage components, such as an electric drive motor, of a high-voltage electrical system of the motor vehicle. HV terminals of the high-voltage energy storage device carrying HV potential are typically connected to HV terminals of the high-voltage electrical system via a switching device, which may include contactors or relays, for example. The high-voltage electrical system can be switched off via this switching device by isolating the high-voltage energy storage device, in particular galvanically, from the high-voltage electrical system.

[0003] The high-voltage electrical system also contains capacitances that are either deliberately introduced, for example in the form of interference suppression capacitors, or parasitically, for example due to the design. When the switching device is closed, the X-capacitance is connected to HV terminals, i.e., a positive pole and a negative pole, of the high-voltage energy storage device. When the switching device is closed, the Y-capacitances are each connected to one of the HV terminals and a ground potential, the so-called vehicle ground, which is provided, for example, by the vehicle body or the vehicle chassis. The HV terminals on the electrical system and storage side have no electrical connection to the ground potential, apart from strictly monitored parasitic insulation resistances.In addition, a discharge resistor is usually required, which is connected in parallel to the X-capacitor and is designed to discharge the X-capacitor, for example, after the switching device is opened. This eliminates any risk to persons posed by the high-voltage energy storage device and the X-capacitors if both HV potentials come into contact.

[0004] However, the electrical connection of the HV terminals to the vehicle body via the Y capacitors is problematic. To prevent danger to persons from contacting even a single HV potential, the deliberately incorporated Y capacitors can be designed in such a way, for example, that their capacitance is reduced to such an extent that the total energy content of the Y capacitors does not exceed a predetermined threshold. However, in the case of interference suppression capacitors, this has a negative impact on the EMC behavior of the high-voltage vehicle electrical system. Furthermore, the design of the Y capacitors must take into account the voltage applied to the Y capacitors, which influences their energy content.However, this voltage is influenced by the parasitic insulation resistances, in particular an age-related changing ratio of the insulation resistances and a possibly associated unbalanced load in the high-voltage system, so that the total energy content of the Y-capacitances can exceed the predetermined threshold value, depending on the nature of the unbalanced load.

[0005] For this purpose, DE 10 2020 006 919 A1 proposes determining information about such an unbalanced load and determining a parameter characterizing the energy quantity of the Y-capacitors. The parameter can be, for example, a voltage, a voltage ratio, a ratio of insulation resistances, or the like. If an unbalanced load is detected, measures can be initiated. Such a measure could be, for example, disconnecting the high-voltage vehicle electrical system or reducing the voltage at the Y-capacitors, for example, via a discharge device. The method described in DE 10 2020 006 919 A1 is complex in that the unbalanced load must first be determined in order to initiate an appropriate measure.Disconnecting the high-voltage electrical system by opening the switching device can also be ineffective if the Y-capacitors continue to be charged via high-resistance, parasitic connections between the high-voltage energy storage device and the high-voltage electrical system. Such a high-resistance connection can occur, among other things, via aging-related particle deposits in a contactor housing or via a monitoring device for monitoring contactor switching operations, such as a contactor adhesive detection device.

[0006] In order to discharge the Y-capacitances even when they are charged via the high-impedance, parasitic connections when the switching device is open, the generic document DE 10 2022 123 754 B3 proposes connecting a passive discharge circuit in parallel with each Y-capacitance. The discharge circuits each have at least one diode. These diodes are reverse-biased with respect to a normal polarity of the voltages dropped across the Y-capacitances when the switching device is closed. To discharge the Y-capacitances, the at least one diode of a discharge circuit is forward-biased by a polarity change of the voltage at the associated Y-capacitance, which is caused by the charging of the Y-capacitances and by the potential coupling of the on-board electrical system-side HV connections.

[0007] However, these discharge circuits connected to the vehicle chassis can lead to a faulty dielectric strength test of the high-voltage system, which is performed, for example, as an end-of-line test at the end of the vehicle assembly and manufacturing process and is used to test for faulty insulation resistance and insulation strength. During the dielectric strength test, a test voltage is applied between an HV connection and the vehicle chassis with the switching device closed and thus with the high-voltage energy storage unit and the high-voltage electrical system connected. A leakage path created by the discharge circuit between the respective HV connection and the vehicle chassis can lead to an insulation resistance measurement that is too low, making the dielectric strength test inconclusive and therefore not feasible.

[0008] It is an object of the present invention to provide a discharge device for reducing an amount of energy in Y-capacitances of a high-voltage system of a motor vehicle, which also enables a reliable and correct dielectric strength test of the high-voltage system.

[0009] This object is achieved according to the invention by a high-voltage system, a motor vehicle, and a method having the features according to the respective independent patent claims. Advantageous embodiments of the invention are the subject of the dependent patent claims, the description, and the figures.

[0010] A high-voltage system according to the invention for a motor vehicle comprises an electrical high-voltage energy storage device with storage-side HV connections and a high-voltage electrical system with electrical system-side HV connections and a capacitor arrangement. The capacitor arrangement comprises an X-capacitor connected to the electrical system-side HV connections and two Y-capacitors, each connected to one of the electrical system-side HV connections and a ground potential of the high-voltage system. Furthermore, the high-voltage system comprises a switching device connected to the storage-side and electrical system-side HV connections for connecting the high-voltage energy storage device to the high-voltage electrical system, as well as a discharge device for discharging the capacitor arrangement.

[0011] The discharge device has at least one discharge resistor connected to the vehicle electrical system-side HV terminals and a passive discharge circuit for each Y-capacitance. The discharge circuits are designed to discharge the Y-capacitances, which may be charged due to parasitic high-resistance connections between the vehicle electrical system-side HV terminals and the ground potential with the storage-side HV terminals, even when the switching device is open. For this purpose, the discharge circuits each have at least one diode, wherein the diodes are reverse-biased with respect to a normal polarity of the voltages dropped across the Y-capacitances when the switching device is closed.The at least one diode of a discharge circuit can be polarized in the forward direction by changing the polarity of the voltage at the associated Y-capacitance to discharge the Y-capacitances. The polarity change is caused by the charging of the Y-capacitances and by the potential coupling of the HV connections on the vehicle electrical system side due to the discharge resistance. Furthermore, the discharge device has a contacting element that electrically connects the discharge circuits to ground potential in a first state and disconnects them from ground potential in a second state for a dielectric strength test of the high-voltage system with the switching device closed.

[0012] The invention further relates to a motor vehicle with a high-voltage system according to the invention, wherein a body or chassis of the motor vehicle provides the ground potential. The motor vehicle is an electrified motor vehicle and has the high-voltage energy storage device of the high-voltage system as a traction battery. The high-voltage energy storage device has a plurality of energy storage cells that are interconnected or can be interconnected as needed. The storage-side high-voltage connections, or HV connections for short, or poles of the high-voltage energy storage device carry a high-voltage potential and are connected to the switching device. The switching device can be arranged internally or externally within the storage device, for example in a relay box or contactor box. The switching device can have HV relays or contactors, wherein each contactor is electrically connected to a storage-side HV connection.The switching device can be part of a so-called switching matrix, in which individual storage units of the high-voltage energy storage system can be connected in series or parallel as required.

[0013] The high-voltage system includes, in particular, a monitoring device for monitoring the switching device, which bridges the switching device with high impedance even when open. The monitoring device is designed, in particular, to detect a so-called contactor seal, i.e., an undesirable, low-impedance connection between the high-voltage energy storage device and the high-voltage vehicle electrical system caused by welding of the switching contacts of the switching device. The monitoring device can, for example, include measuring resistors connected in parallel to the contactors. These measuring resistors provide a permanent high-impedance connection between the high-voltage energy storage device and the high-voltage vehicle electrical system, even when the switching device is open.

[0014] The high-voltage electrical system has the HV connections on the electrical system side, which are connected to the HV connections on the storage side via the switching device. When the switching device is closed, the high-voltage potential present at the storage-side HV connections is also present at the HV connections on the electrical system side. The high-voltage electrical system can have a variety of high-voltage components, such as a traction motor and other high-voltage consumers, as well as a charging connection for connecting to an external charging station. Furthermore, the high-voltage electrical system has the capacitance arrangement with the X-capacitance and the two Y-capacitances. The capacitances can be at least partially interference suppression capacitors of a filter device of the high-voltage electrical system. The capacitances can also be at least partially parasitic, design-related capacitances of the high-voltage electrical system.The X-capacitance can encompass all parasitic and non-parasitic capacitances connected between the vehicle electrical system's HV terminals and thus not connected to ground potential. A first Y-capacitance can encompass all parasitic and non-parasitic capacitances connected to a first, for example, positive-side, vehicle electrical system's HV terminal and ground potential. A second Y-capacitance can encompass all parasitic and non-parasitic capacitances connected to a second, for example, negative-side, vehicle electrical system's HV terminal and ground potential.

[0015] The high-voltage system also has parasitic insulation resistors on the storage and on-board network sides, which form high-impedance electrical connections between the HV terminals and the ground potential. These insulation resistors can age unevenly, causing the voltage across the insulation resistors to be distributed asymmetrically, thus creating an unbalanced load. Since the insulation resistors are connected in parallel with the Y-capacitors, a voltage asymmetry caused by an unbalanced load also affects the voltage across the Y-capacitors and thus the energy content of the Y-capacitors. If the energy content of at least one of the Y-capacitors exceeds a predetermined threshold, contact with an HV potential can endanger people.

[0016] The high-voltage system includes a discharge device for discharging the capacitances. The discharge device can, for example, be arranged in a common housing with the switching device, so that the discharge device is integrated into the contactor box. To discharge the X-capacitance, at least one discharge resistor is provided, which is connected between the HV terminals on the vehicle electrical system and thus connected in parallel with the X-capacitance. This at least one discharge resistor discharges the X-capacitance after the switching device is opened, thus reducing the voltage across the X-capacitance and thus the energy content of the X-capacitance.Since at least one discharge resistor is permanently connected to the HV connections on the vehicle electrical system and since a resistance value of the discharge resistor is significantly smaller than a resistance value of the insulation resistors and is, for example, in the kiloohm range, a low-resistance coupling exists between the high-voltage potentials.

[0017] This low-impedance coupling results in the voltages applied to the Y-capacitors, i.e., the voltage drop between the respective HV terminal and ground potential, being of the same polarity during normal operation of the high-voltage system with the switching device closed. This polarity of the voltages across the Y-capacitors during normal operation of the high-voltage system is referred to here as normal polarity. However, as soon as the Y-capacitors charge due to the parasitic, e.g., contactor-bridging, high-impedance connection between the storage-side HV terminals and the vehicle electrical system-side HV terminals, as well as due to the parasitic, insulation-resistance-related high-impedance connection between the HV terminals and ground potential, the polarity of one of the voltages across the Y-capacitors reverses due to the potential coupling caused by the discharge resistance.This polarity reversal of the voltage at one of the Y-capacitors is utilized by the discharge circuits of the discharge devices.

[0018] The discharge circuits each have a diode. In particular, each discharge circuit has a cascade of at least two diodes. For voltage balancing, each diode can have a resistor connected in parallel. A first discharge circuit is connected to the first HV terminal on the vehicle electrical system side and to ground potential. The second discharge circuit is connected to the second HV terminal on the vehicle electrical system side and to ground potential. The discharge circuits are thus each connected in parallel to a Y-capacitor. For example, first terminals of the discharge circuits can be connected to the respective HV terminal on the vehicle electrical system side, and second terminals of the discharge circuits can be connected at a node that is electrically connected to ground potential.

[0019] In each discharge circuit, at least one diode is arranged such that it is reverse-biased when the voltage across the associated Y-capacitor is of normal polarity. As soon as the Y-capacitors charge and the voltage across one of the Y-capacitors undergoes a potential reversal due to the potential coupling caused by the discharge resistance, at least one diode in the parallel-connected discharge circuit is forward-biased and discharges the Y-capacitors. The diodes thus reduce the voltages across the Y-capacitors and thus the energy stored in the Y-capacitors. Since the energy quantity increases quadratically with the voltage, reducing the voltage to reduce the energy quantity of the Y-capacitors is significantly more efficient than reducing the capacitances of the Y-capacitors.Because the discharge circuits are passive and a discharge circuit always reacts when the Y capacitors charge, no detection of the charging process is required, nor is any conscious activation of the discharge circuits necessary. This makes the discharge device particularly simple and cost-effective.

[0020] In order to be able to subject motor vehicles whose high-voltage systems are equipped with such discharge circuits to a dielectric strength test at the end of assembly or production, in which the insulation resistance of the high-voltage system against the vehicle body is measured and monitored when the switching device is closed, the discharge circuits for this dielectric strength test can be separated from ground potential and thus from the vehicle body. This prevents a leakage path from forming via the associated discharge circuit to the vehicle body when the test voltage is applied between one of the high-voltage connections and the vehicle body. This leakage path is detected as an insulation resistance that falls below a predetermined limit and, as a result, an insulation fault that does not actually exist is detected during the dielectric strength test.

[0021] To provide this separation between the discharge circuits and the ground connection, the discharge circuits are connected to ground potential via the non-destructively removable contacting element. For example, the contacting element can be arranged in the electrical connection between the node and ground potential. The contacting element thus provides a switchable electrical connection between the discharge circuits and ground potential. For example, the contacting element can be a controllable switch. In the first state, the contacting element establishes the electrical connection. This state of the contacting element is provided, for example, after the dielectric strength test and remains there for the service life of the motor vehicle. In other words, the first state is permanently provided as soon as the dielectric strength test is successfully completed.The second state is used for the dielectric strength test. In the second state, the contact element is not yet installed on the vehicle, for example, so the electrical connection between the discharge circuits and the ground potential is broken. Only after the dielectric strength test is the contact element installed in the vehicle and thus transferred to the first state.

[0022] It can be provided that the node at which the discharge circuits are interconnected is electrically connected to an electrical connecting element. The connecting element is connected by means of the detachable contact element to a carrier for holding a component of the high-voltage system, which in turn is electrically connected to the body of the motor vehicle, which carries the ground potential. The carrier can, for example, be a cast metal plate, which can be part of the high-voltage energy storage device and which can be mechanically and electrically connected to the vehicle body. The discharge circuits are thus indirectly electrically connected to the vehicle body and thus to the ground potential via the carrier.

[0023] Particularly preferably, the connecting element is a metallic screw tab, and the contacting element is a metallic screw, via which the metallic screw tab is screwed to the carrier and which thereby electrically connects the node to the ground potential. For example, the screw tab can be led out of the contactor box, in which the discharge circuits are arranged and electrically connected to the screw tab in the node point. The screw can be guided through this screw tab and screwed into the carrier on which the contactor box is arranged and held. This can provide the electrical connection between the discharge circuits and the ground potential. In addition, the screw can fix the contactor box to the carrier and thus establish a mechanical connection between the contactor box and the carrier.

[0024] Since the electrical connection between the discharge circuits and the ground potential only needs to be broken for the end-of-line dielectric strength test, but can remain in place during continuous operation of the vehicle, the provision of a screw, which is only inserted once after the end of the dielectric strength test, represents a cost-effective and simple solution for providing the two states of the contacting element.

[0025] The embodiments presented with reference to the high-voltage system according to the invention and their advantages apply accordingly to the motor vehicle according to the invention and to the method according to the invention.

[0026] Further features of the invention emerge from the claims, the figures, and the description of the figures. The features and combinations of features mentioned above in the description, as well as the features and combinations of features mentioned below in the description of the figures and / or shown alone in the figures, can be used not only in the respective specified combination, but also in other combinations or on their own.

[0027] The invention will now be explained in more detail using a preferred embodiment and with reference to the drawings. They show: Fig. 1 shows a circuit diagram of a high-voltage system of a motor vehicle according to the prior art; Fig. 2 the high-voltage system according to Fig. 1 during a dielectric strength test; Fig. 3. a representation of a circuit diagram of a high-voltage system according to the invention; and Fig. 4 a schematic representation of a contactor box of the high-voltage system, which is connected to a carrier of the high-voltage system.

[0028] In the figures, identical and functionally identical elements are provided with the same reference numerals.

[0029] Fig. Figure 1 shows a high-voltage system 1 for an electrically powered motor vehicle according to the prior art. The high-voltage system 1 comprises an electrical high-voltage energy storage device 2 and a high-voltage on-board electrical system 3. The high-voltage energy storage device 2 and the high-voltage on-board electrical system 3 can be interconnected via a switching device 4. For this purpose, the storage-side HV connections 5a, 5b and the on-board electrical system-side HV connections 6a, 6b are connected to contactors 7a, 7b of the switching device 4. Fig. In Figure 1, the contactors 7a, 7b are shown closed, so that the high-voltage energy storage unit 2 and the high-voltage electrical system 3 are electrically connected. Both the high-voltage energy storage unit 2 and the high-voltage electrical system 3 have parasitic insulation resistors 8a, 8b, 9a, 9b, which are connected to the HV terminals 5a, 5b, 6a, 6b and a ground potential M of the motor vehicle. The storage-side insulation resistors 8a, 8b are connected to the respective storage-side HV terminals 5a, 5b and the ground potential M, and the electrical system-side insulation resistors 9a, 9b are connected to the respective electrical system-side HV terminals 6a, 6b and the ground potential M.

[0030] The high-voltage electrical system 3 also has a capacitance arrangement 10, which has an X-capacitance Cx and two Y-capacitances Cy1, Cy2. The capacitances Cx, Cy1, Cy2 can be formed, for example, by deliberately introduced capacitors and / or parasitic capacitances. The X-capacitance Cx is connected to the electrical system-side HV terminals 6a, 6b. The first Y-capacitance Cy1 is connected to the first positive HV terminal 6a on the electrical system side and to ground potential M. The second Y-capacitance Cy2 is connected to the second negative HV terminal 6b on the electrical system side and to ground potential M. Thus, the HV terminals 5a, 5b, 6a, 6b have an electrical connection to the ground potential M via the insulation resistors 8a, 8b, 9a, 9b and the Y-capacitors Cy1, Cy2.

[0031] To discharge the capacitances Cx, Cy1, Cy2 when the switching device 4 is open, the high-voltage system 1 has a discharge device 11. The discharge device 11 comprises a discharge resistor Re, which is connected in parallel to the X-capacitance Cx. This discharge resistor Re also couples the potentials of the vehicle electrical system-side HV connections 6a, 6b with low resistance. To discharge the Y-capacitances Cy1, Cy2, the discharge device 11 has two passive discharge circuits 12a, 12b, wherein a first discharge circuit 12a is connected in parallel to the first Y-capacitance Cy1 and is thus connected to the first vehicle electrical system-side HV connection 6a and the ground potential M. A second discharge circuit 12b is connected in parallel to the second Y-capacitance Cy2 and is connected to the second vehicle electrical system-side connection 6b and the ground potential M.The discharge circuits 12a, 12b can, for example, be connected at a node K which is electrically connected to the ground potential M.

[0032] In addition, Fig. 1 shows the voltages Ux, Uy1, Uy2 applied to the capacitors Cx, Cy1, Cy2 when the switching device 4 is closed. Due to the coupling of the vehicle electrical system-side HV terminals 6a, 6b provided via the discharge resistor Re, the voltages Uy1, Uy2 applied to the Y capacitors Cy1, Cy2 have the same polarity. The discharge circuits 12a, 12b each have a cascade of diodes D that are reverse-biased with respect to the voltages Uy1, Uy2, so that the discharge circuits 12a, 12b are inactive during normal operation of the high-voltage system 1 when the switching device 4 is closed and thus when the voltages Uy1, Uy2 have normal polarity.

[0033] If the switching device 4 is now opened (in Fig. 1 is shown by the dashed lines), a high-resistance connection 13 can still exist between the HV terminals 5a, 5b, 6a, 6b, here via the contactors 7a, 7b of the switching device. This can arise, for example, due to age-related particle deposits on the contactors 7a, 7b, which shorten the air and creepage distances between the switching contacts of the contactors 7a, 7b. This high-resistance connection 13 can also be provided by a monitoring device (not shown here), which monitors the switching operations of the contactors 7a, 7b and is designed, for example, to detect undesired contact welding of the switching contacts of the contactors 7a, 7b. In addition, high-resistance connections 14 exist between the HV terminals 5a, 5b, 6a, 6b and the ground potential M due to the insulation resistances 8a, 8b, 9a, 9b.These high-resistance connections 13, 14 can lead to a charging of the Y-capacitances Cy1, Cy2 even when the switching device 4 is open.

[0034] The coupling of the HV terminals 5a, 5b provided by the discharge resistor Re ensures that one of the voltages Uy1, Uy2, for example the voltage Uy2, undergoes a potential reversal -Uy2 during the charging of the Y-capacitances. Which of the voltages Uy1, Uy2 undergoes a potential reversal depends on the ratio of the insulation resistances 8a, 8b, 9a, 9b and a resistance of the high-impedance connection 13. This potential reversal ensures that the diodes D of one of the discharge circuits 12a, 12b, here the diodes D of the discharge circuit 12b connected in parallel with the second Y-capacitance Cy2, are forward-biased, thus reducing the voltages Uy1, Uy2 at the Y-capacitances Cy1, Cy2. The Y-capacitances Cy1 and Cy2 are thus discharged through the side experiencing the potential reversal. To balance the voltage drop across the diodes D, a resistor Rs is connected in parallel with each diode D.In addition, each discharge circuit 12a, 12b has a Zener diode Z, for example a 60 VZ diode, which is preceded by a series resistor Rv and which is designed to provide protection against reverse polarity of the high-voltage system 1 by an insulation monitor of a vehicle-external charging station (not shown here).

[0035] Due to the electrical connection between the discharge circuits 12a, 12b and the ground potential M, a reliable, meaningful dielectric strength test, which serves to check the insulation resistances 8a, 8b, 9a, 9b, cannot be carried out at the end of the production process of the motor vehicle. During the dielectric strength test, as in Fig. 2, with the switching device 4 closed, a test voltage Up is applied between one of the HV terminals 6a6b, here the HV terminal 6a, and the vehicle body, i.e., the ground potential M. A leakage path 13 is formed between the HV terminal 6a via the high-voltage energy storage device 2 and one of the discharge circuits 12a, 12b, here the discharge circuit 12b, to the ground potential M, which the dielectric strength test detects as faulty insulation between the high-voltage system 1 and the vehicle body.

[0036] To prevent this leakage path 13, a high-voltage system 1' is provided, as shown in Fig. 3. The high-voltage system 1' differs from the high-voltage system 1 according to the prior art in the design of the discharge device 11'. For this purpose, the discharge device 11' also has a contacting element 14, which is arranged here between the node K and the ground potential M. In Fig. 3, the contacting element 14 is shown in a released state, in which the electrical connection between the node K and the ground potential M, and thus between the discharge circuits 12a, 12b and the vehicle body, is severed. This released state of the contacting element 14 is prepared for the dielectric strength test. Once the test is successfully completed, the contacting element 14 is transferred to a contacting state, in which it establishes the electrical connection between the node K and the ground potential M, thus enabling the discharge circuits 12a, 12b to discharge the Y capacitances Cy1, Cy2.

[0037] In Fig.4 schematically shows that the discharge circuits 12a, 12b are arranged in a contactor box 15. The contactors 7a, 7b, for example, can also be arranged in the contactor box 15. The contactor box 15 is mounted on a carrier 16, for example a metal plate, which in turn is connected to the vehicle body via an electrically conductive connection. A metallic screw tab 17 extends from the contactor box 15 and is electrically connected within the contactor box 15 to the node K, in which the discharge circuits 12a, 12b are interconnected. The screw tab 17 is fastened with a screw 18 to the carrier 16, which is at least partially electrically conductive. The screw 18 forms the contacting element 14. The screw 18 is screwed in, in particular, only after the dielectric strength test has been completed. The unscrewed state of the screw 18 corresponds to the loosened state of the contact element 14.The screwed state of the screw 18 corresponds to the contacted state of the contacting element 14. QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] DE 10 2020 006 919 A1

[0005] DE 10 2022 123 754 B3

[0006]

Claims

[1] High-voltage system (1') for a motor vehicle, comprising: - an electrical high-voltage energy storage device (2) with storage-side HV connections (5a, 5b), - a high-voltage on-board network (3) comprising on-board HV connections (6a, 6b) and a capacitance arrangement (10) with an X-capacitance (Cx) which is connected to the on-board HV connections (6a, 6b) and two Y-capacitances (Cy1, Cy2) which are each connected to one of the on-board HV connections (6a, 6b) and a ground potential (M) of the high-voltage system (1), - a switching device (4) connected to the storage-side and the on-board network-side HV connections (5a, 5b, 6a, 6b) for connecting the high-voltage energy storage device (2) and the high-voltage on-board network (3), - a discharge device (11') for discharging the capacitance arrangement (10), which has a discharge resistor (Re) connected to the vehicle electrical system HV terminals (6a, 6b) for discharging the X-capacitance and passive discharge circuits (12a, 12b) for discharging the Y-capacitances, which are charged even when the switching device (4) is open due to parasitic high-resistance connections (13, 14) between the vehicle electrical system HV terminals (6a, 6b) and the ground potential (M) with the storage-side HV terminals (5a, 5b), wherein the discharge circuits (12a, 12b) are connected to the respective vehicle electrical system HV terminal of the associated Y-capacitance and the ground potential and each has at least one diode (D), wherein the diodes (D) are connected with respect to a normal polarity of when the switching device is closed (4) voltages (Uy1, Cy2) dropping across the Y capacitancesUy2) are reverse-biased and wherein at least one diode (D) of a discharge circuit (12b) can be polarized to discharge the Y-capacitances (Cy1, Cy2) in the forward direction by a polarity reversal of the voltage (Uy2) at the associated Y-capacitance (Cy2), caused by the charging of the Y-capacitances (Cy1, Cy2) and by the discharge resistor-induced potential coupling of the on-board HV connections (6a, 6b), , characterized by , that the discharge device (11') has a contacting element (14) which in a first state electrically connects the discharge circuits (12a, 12b) to the ground potential (M) and in a second state for a dielectric strength test of the high voltage system (1) with the switching device (4) closed disconnects the discharge circuits (12a, 12b) from the ground potential (M). [2] High-voltage system (1') according to claim 1, characterized by, that the high-voltage system (1') has a monitoring device for monitoring the switching device (4), by which the switching device (4) is also bridged with high resistance in the open state. [3] High-voltage system (1') according to claim 1 or 2, characterized by , that each discharge circuit (12a, 12b) has a cascade of at least two diodes (D) and a parallel resistor (Rs) for each diode (D) to balance the voltage of the diodes (D) of the associated cascade. [4] High-voltage system (1') according to any one of the preceding claims, characterized by , that first connections of the discharge circuits (12a, 12b) are connected to the respective HV connection (6a, 6b) on the vehicle electrical system and second connections of the discharge circuits (12a, 12b) are connected to each other in a node (K) and to the ground potential (M) via the contacting element (14). [5] High-voltage system (1') according to claim 4, characterized by, that the node (K) is electrically connected to an electrical connecting element and wherein the connecting element is connected by means of the detachable contacting element (14) to a carrier (16) for holding a component of the high-voltage system (1), which is electrically connected to a body of the motor vehicle which carries the ground potential (M). [6] High-voltage system (1') according to claim 5, characterized by , that the connecting element is a metallic screw tab (17) and the contacting element (14) is a metallic screw (18) via which the metallic screw tab (17) is detachably screwed to the carrier (16) and which thereby electrically connects the node (K) to the ground potential (M). [7] High-voltage system (1') according to claim 6, characterized by, that the discharge circuits (12a, 12b) and the switching device (4) are arranged in a common housing forming a contactor box (15), wherein the metallic screw tab (17) is led out of the contactor box (15) and wherein the contactor box (15) is held by the support (16). [8] Motor vehicle with a high-voltage electrical system (1') according to one of the preceding claims, wherein a body of the motor vehicle forms the ground potential. [9] Method for testing the dielectric strength of a high-voltage system (1') of a motor vehicle according to claim 8 comprising the steps: - Providing the second state of the contact element (14), - Closing the switching device (4) to connect the high-voltage energy storage device (2) to the high-voltage electrical system (3), - Applying a test voltage (Up) between one of the vehicle electrical system HV connections (6a) and the vehicle body, - Measuring insulation resistances (8a, 8b, 9a, 9b) of the high-voltage system (1') with test voltage (Up) applied, - Verification of the dielectric strength based on the measured insulation resistances (8a, 8b, 9a, 9b), - Providing the first state of the contacting element (14).

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