High-voltage system for motor vehicle having passive discharge circuit for Y-capacitor

Abstract

The invention relates to a high-voltage system (1) for a motor vehicle, comprising:-an electrical high-voltage energy store (2), which has a store-side HV connection (5a, 5b),-a high-voltage on-board electrical system (3), which has an on-board electrical system-side HV connection (6a, 6b) and a capacitance arrangement (10), which comprises an X capacitance (Cx) and two Y capacitances (Cy1, Cy2), a switching device (4) connected to the HV connection (5a, 5b, 6a, 6b) for connecting the high-voltage energy store (2) to the high-voltage on-board electrical system (3), a discharge device (11) for discharging the capacitance arrangement (10), which discharge device has a discharge resistor (Re) connected to the on-board electrical system-side HV connection (6a, 6b) and a passive discharge circuit (12a, 12b) for each Y capacitance (Cy1, Cy2), the discharge circuits (12a, 12b) are designed to discharge the Y capacitance (Cy1, Cy2) and each have at least one diode (D) for this purpose, said diode (D) being polarized in the cut-off direction with respect to the normal polarity of the voltage (Uy1, Uy2) falling across the Y capacitance (Cy1, Cy2) when the switching device (4) is closed. The at least one diode (D) of a discharge circuit (12b) can be polarized in the conduction direction by changing the polarity of the voltage (Uy2) at the associated Y capacitance (Cy2) for discharging the Y capacitance (Cy1, Cy2), said polarity changing being caused by charging the Y capacitance (Cy1, Cy2) and by a potential coupling of the on-board network-side HV connection (6a, 6b) determined by the discharge resistance.

Description

Technical Field

[0001] The present invention relates to a high-voltage system for a motor vehicle. The high-voltage system has an electrical high-voltage energy storage and a high-voltage on-board power system, wherein the high-voltage energy storage includes an HV connection terminal on the storage side, and the high-voltage on-board power system includes an HV connection terminal on the on-board power system side and a capacitor arrangement structure. The capacitor arrangement structure has an X capacitor and two Y capacitors, wherein the X capacitor is connected to the HV connection terminal on the on-board power system side, and the Y capacitors are respectively connected to one of the HV connection terminals on the on-board power system side and the ground potential of the high-voltage system. In addition, the high-voltage system has a switching device and a discharge device for discharging the capacitor arrangement structure, wherein the switching device is connected to the HV connection terminals on the storage side and the on-board power system side in order to connect the high-voltage energy storage to the high-voltage on-board power system. In addition, the present invention relates to a motor vehicle having a high-voltage system. Background Art

[0002] At present, interest is focused on high-voltage systems for electrified motor vehicles, that is, electric vehicles, hybrid vehicles and fuel cell vehicles. Such high-voltage systems usually have a high-voltage energy storage device, which is designed to supply power to high-voltage components of the motor vehicle, such as an electric drive machine, a high-voltage onboard power supply. A charging connection can also belong to the high-voltage onboard power supply, through which the high-voltage energy storage device can be connected to a charging station outside the vehicle for charging. The HV connection of the high-voltage energy storage device, which conducts the HV potential, is usually connected to the HV connection of the high-voltage onboard power supply via a switching device, which can have a current contactor, for example. The high-voltage onboard power supply can be disconnected by the switching device, in which the high-voltage energy storage device is disconnected from the high-voltage onboard power supply, in particular in terms of current.

[0003] In addition, the high-voltage onboard power supply system has a capacitor, which is introduced into the high-voltage onboard power supply system either intentionally, for example in the form of an interference suppression capacitor, or parasitically, for example due to the structure. Here, the X capacitor is connected to the HV connection (i.e. the positive and negative poles) of the high-voltage energy storage device in the closed state of the switching device. The Y capacitor is connected to one of the HV connection terminals and the ground potential (so-called vehicle ground) in the closed state of the switching device. The HV connection terminals on the onboard power supply side and the storage side do not have an electrical connection to the ground potential except for the strictly monitored parasitic insulation resistance. In addition, a discharge resistor is usually specified, which is connected in parallel with the X capacitor and is designed to discharge the X capacitor, for example, after the switching device is opened. Therefore, when the two HV potentials are contacted, the harm to personnel from the high-voltage energy storage device and the X capacitor can be eliminated.

[0004] However, the electrical connection of the HV connection to the vehicle ground via the Y capacitor is problematic. In order to prevent harm to personnel when only one HV potential is already in contact, the intentionally introduced Y capacitor can be designed in such a way that, for example, its capacitance is reduced so that the total energy storage of the Y capacitor does not exceed a predetermined threshold value. However, this has a negative impact on the EMC characteristics in the high-voltage onboard power system when using interference suppression capacitors. In addition, the voltage applied to the Y capacitor and affecting the energy storage must be taken into account when designing the Y capacitor. However, this voltage is affected by parasitic insulation resistance, in particular the proportion of insulation resistance that changes due to aging (Verhältnis) and unbalanced loads that may be associated with this in the high-voltage system, so that the total energy storage of the Y capacitor may exceed a predetermined threshold value due to the influence of the unbalanced load.

[0005] DE102020006919A1 proposes to find out information about such unbalanced load and determine the characteristic parameter of the amount of energy of the Y capacitor for this purpose. This characteristic parameter can be, for example, voltage, voltage ratio, ratio of insulation resistance or the like. Measures can be introduced when an unbalanced load is identified. Such measures can be, for example, the disconnection of the high-voltage onboard power supply or the reduction of the voltage on the Y capacitor, for example, the reduction by the discharge device. The method shown in the prior art is therefore expended, and the unbalanced load must first be found out so that suitable measures can be introduced. In addition, the disconnection of the high-voltage onboard power supply by opening the switching device may be invalid, if the Y capacitor is also further charged by the high-ohmic parasitic connection between the high-voltage energy storage and the high-voltage onboard power supply. Such a high-ohmic connection can also be carried out by the particle deposition determined by aging in the housing of the contactor or by a monitoring device for monitoring the switching process of the contactor, for example, the so-called contactor bonding identification. Summary of the invention

[0006] The object of the present invention is to provide a simple, cost-effective and reliable solution for reducing the amount of energy in a Y capacitor of a high-voltage onboard power supply system of a motor vehicle.

[0007] According to the invention, this object is achieved by a high-voltage system and a motor vehicle having the features according to the respective independent claims. Advantageous embodiments of the invention are the subject of the dependent claims, the description and the drawings.

[0008] The high-voltage system for a motor vehicle according to the present invention comprises an electrical high-voltage energy storage device including an HV connection terminal on the storage side and a high-voltage on-board power system including an HV connection terminal on the on-board power system side and a capacitor arrangement structure. The capacitor arrangement structure comprises an X capacitor and two Y capacitors, the X capacitor being connected to the HV connection terminal on the on-board power system side, and the Y capacitors being respectively connected to one of the HV connections on the on-board power system side and the ground potential of the high-voltage system. In addition, the high-voltage system comprises a switching device and a discharge device for discharging the capacitor arrangement structure, the switching device being connected to the HV connection terminals on the storage side and on the on-board power system side in order to connect the high-voltage energy storage device to the high-voltage on-board power system.

[0009] The discharge device has at least one discharge resistor connected to the HV connection on the vehicle power supply side and a passive discharge circuit for each Y capacitor. The discharge circuit is designed to discharge the Y capacitor even when the switch device is open due to the parasitic high-ohmic connection between the HV connection on the vehicle power supply side and the ground potential and the HV connection on the storage side. For this purpose, the discharge circuits each have at least one diode, wherein the diode is polarized in the cut-off direction with respect to the normal polarity of the voltage dropped on the Y capacitor when the switch device is closed. The at least one diode of a discharge circuit can be polarized in the conduction direction for discharging the Y capacitor by changing the polarity of the voltage on the associated Y capacitor, wherein the polarity change is caused by charging the Y capacitor and by coupling the potential of the HV connection on the vehicle power supply side determined by the discharge resistor.

[0010] In addition, the present invention relates to a motor vehicle having a high-voltage system according to the present invention. However, the high-voltage system can also be used for other applications that are not specific to motor vehicles. The motor vehicle is an electrified motor vehicle and has a high-voltage energy storage of the high-voltage system as a traction battery. The high-voltage energy storage has a plurality of energy storage units that are connected to each other or can be connected as required. The high-voltage connection end on the storage side, referred to as the HV connection end for short, or the poles of the high-voltage energy storage leads the high-voltage potential and is connected to the switching device. The switching device can be arranged inside the storage device or outside the storage device, for example in a relay box. The switching device can have an HV relay or a current contactor, wherein each current contactor is electrically connected to the HV connection end on the storage side. The switching device can be part of a so-called switching matrix, in which individual storage units of the high-voltage energy storage can be connected in series or in parallel as required.

[0011] The high-voltage system has, in particular, a monitoring device for monitoring a switching device, by which the switching device is bridged with high resistance even in the open state. The monitoring device is designed, in particular, to detect so-called contactor sticking, i.e. an undesired low-resistance connection between the high-voltage energy storage device and the high-voltage onboard power supply due to welding of the switching contacts of the switching device. The monitoring device can, for example, have a measuring resistor connected in parallel with the current contactor. By means of the measuring resistor, a continuous high-resistance connection is provided between the high-voltage energy storage device and the high-voltage onboard power supply even when the switching device is open.

[0012] The high-voltage on-board power grid has an HV connection on the on-board power grid side, which is connected to the HV connection on the storage side through a switching device. In the closed state of the switching device, the high-voltage potential applied to the HV connection on the storage side is also applied to the HV connection on the on-board power grid side. The high-voltage on-board power grid can have a plurality of high-voltage components, such as traction machines and other high-voltage consumers, and the high-voltage on-board power grid can have a charging connection for connecting to a charging station outside the vehicle. In addition, the high-voltage on-board power grid has a capacitor arrangement structure including the X capacitor and the two Y capacitors. The capacitor can be at least partially an anti-interference capacitor of a filter device of the high-voltage on-board power grid. The capacitor can also be a capacitor of the high-voltage on-board power grid that is at least partially parasitic and determined by the structure. The X capacitor can summarize all parasitic and non-parasitic capacitors here, which are connected between the HV connections on the on-board power grid side and therefore have no connection to the ground potential. The first Y capacitor may include all parasitic and non-parasitic capacitances, which are connected to the HV connection on the first (eg, positive) onboard power supply side and the ground potential. The second Y capacitor may include all parasitic and non-parasitic capacitances, which are connected to the HV connection on the second (eg, negative) onboard power supply side and the ground potential.

[0013] In addition, the high-voltage system has parasitic insulation resistances on the energy storage side and the onboard power supply side, which form a high-ohmic, electrical connection between the HV connection and the ground potential. The insulation resistance may age unevenly here, so that the voltage is distributed asymmetrically on the insulation resistance and the insulation resistance thus forms an unbalanced load. Since the insulation resistance is connected in parallel with the Y capacitor, the voltage asymmetry caused by the unbalanced load also acts on the voltage on the Y capacitor and thus on the energy storage of the Y capacitor. If the energy storage of at least one of the Y capacitors exceeds a predetermined threshold value, a hazard to personnel occurs when the HV potential is touched.

[0014] In order to discharge the capacitor, the high voltage system has a discharge device. In order to discharge the X capacitor, at least one discharge resistor is provided, which is connected between the HV connection terminals on the vehicle power supply side and is therefore connected in parallel with the X capacitor. After the switching device is opened, the at least one discharge resistor discharges the X capacitor and thus reduces the voltage applied to the X capacitor and the energy storage of the X capacitor. Because the at least one discharge resistor is continuously connected to the HV connection terminal on the vehicle power supply side and because the resistance value of the discharge resistor is significantly smaller than the resistance value of the insulation resistor and is, for example, in the kilo-ohm range, there is a low-ohmic coupling between the high voltage potentials. This low-ohmic coupling causes the voltage applied to the Y capacitor, i.e., the voltage dropped between the corresponding HV connection terminal and the ground potential, to have the same polarity when the switching device is closed in the normal operation of the high voltage system. This polarity of the voltage on the Y capacitor in the normal operation of the high voltage system is referred to as the normal polarity here. However, as soon as the Y capacitor is charged due to a parasitic high-resistance connection between the HV terminal on the storage side and the HV terminal on the vehicle electrical system side, for example a bridging contactor, and due to a parasitic high-resistance connection between the HV terminal and the ground potential due to the insulation resistance, the polarity of one of the voltages at the Y capacitor is reversed due to the potential coupling due to the discharge resistor. This polarity reversal of the voltage at one of the Y capacitors is used by the discharge circuit of the discharge device.

[0015] The individual discharge circuits each have a diode. In particular, each discharge circuit has a cascade circuit including at least two diodes. For voltage symmetry, each diode can have a resistor connected in parallel. The first discharge circuit is connected to the first HV connection terminal and the ground potential on the vehicle power supply side. The second discharge circuit is connected to the second HV connection terminal and the ground potential on the vehicle power supply side. The discharge circuit is therefore connected in parallel with each Y capacitor. For each discharge circuit, at least one diode is provided so that the at least one diode is polarized in the cut-off direction when the normal polarity of the voltage on the Y capacitor to which it belongs is. Once the Y capacitor is charged and the voltage on one of the Y capacitors undergoes a potential reversal based on the potential coupling determined by the discharge resistor, the at least one diode of the discharge circuit connected in parallel is polarized in the conduction direction and discharges the Y capacitor. The diode therefore reduces the voltage on the Y capacitor and the amount of energy stored in the Y capacitor. Because the amount of energy rises quadratically with the voltage, in order to reduce the amount of energy of the Y capacitor, the reduction of the voltage is obviously more efficient than the reduction of the capacitance of the Y capacitor. Since the discharge circuit is designed passively and always reacts when the Y capacitor is charged, there is no need to detect the charging, ie, to intentionally control the discharge circuit. As a result, the discharge device is designed to be particularly simple and cost-effective.

[0016] It has proven to be advantageous if each discharge circuit has at least one protection diode, for example a Z diode or a suppressor diode, which is polarized in the forward direction with respect to the normal polarity of the corresponding voltage and which forms a reverse polarity protection against a polarity reversal provided by an insulation monitor to ground of a charging station external to the vehicle. By means of the at least one protection diode, to which a series resistor is preferably connected upstream for protection, the discharge circuit tolerates a polarity reversal of the voltage applied by the insulation monitor to ground (for example due to a shift in the ground potential).

[0017] The embodiments described with regard to the high-voltage system according to the invention and their advantages apply correspondingly to the motor vehicle according to the invention.

[0018] Further features of the invention are apparent from the claims, the drawings and the description of the drawings. The features and feature combinations mentioned above in the description and the features and feature combinations mentioned below in the description of the drawings and / or shown only in the drawings can be used not only in the respectively indicated combination but also in other combinations or alone. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The invention will now be explained in more detail with reference to a preferred embodiment and with reference to the accompanying drawings.

[0020] Figure 1 An exemplary diagram showing a circuit diagram of a high-voltage system of a motor vehicle during normal operation;

[0021] Figure 2 Shown in accordance with Figure 1 The high-voltage system is in the discharge operation of the Y capacitor of the high-voltage system. DETAILED DESCRIPTION

[0022] In the figures, identical elements or elements having the same function are provided with the same reference symbols.

[0023] Figure 1 and Figure 2 A high-voltage system 1 for an electrically driven motor vehicle is shown. The high-voltage system 1 has an electrical high-voltage energy storage device 2 and a high-voltage onboard power supply system 3. The high-voltage energy storage device 2 and the high-voltage onboard power supply system 3 can be connected via a switching device 4. For this purpose, HV connections 5a, 5b on the storage side and HV connections 6a, 6b on the onboard power supply side are connected to contactors 7a, 7b of the switching device 4. Figure 1 The medium current contactors 7a, 7b are closed, so that the high-voltage energy storage device 2 and the high-voltage onboard power supply system 3 are electrically connected. Figure 2, the contactors 7a, 7b are opened, so that the high-voltage energy storage 2 and the high-voltage onboard power supply 3 are disconnected. Both the high-voltage energy storage 2 and the high-voltage onboard power supply 3 have parasitic insulation resistors 8a, 8b, 9a, 9b, which are connected to the HV terminals 5a, 5b, 6a, 6b and the ground potential M of the motor vehicle. The insulation resistors 8a, 8b on the storage side are connected to the corresponding HV terminals 5a, 5b on the storage side and the ground potential M, and the insulation resistors 9a, 9b on the onboard power supply side are connected to the corresponding HV terminals 6a, 6b on the onboard power supply side and the ground potential M.

[0024] In addition, the high-voltage onboard power supply system 3 has a capacitor arrangement structure 10, which has an X capacitor Cx and two Y capacitors Cy1, Cy2. The capacitors Cx, Cy1, Cy2 can be formed, for example, by intentionally introduced capacitors and / or parasitic capacitances. The X capacitor Cx is connected to the HV terminals 6a, 6b on the onboard power supply side. The first Y capacitor Cy1 is connected to the positive first HV terminal 6a on the onboard power supply side and to the ground potential M. The second Y capacitor Cy2 is connected to the negative second HV terminal 6b on the onboard power supply side and to the ground potential M. Therefore, the HV terminals 5a, 5b, 6a, 6b have an electrical connection to the ground potential M through the insulation resistors 8a, 8b, 9a, 9b and the Y capacitors Cy1, Cy2.

[0025] In order to discharge the capacitors Cx, Cy1, and Cy2 when the switch device 4 is opened, the high-voltage system 1 has a discharge device 11. The discharge device 11 includes a discharge resistor Re, which is connected in parallel with the X capacitor Cx. In addition, the discharge resistor Re is low-ohmically coupled to the potential of the HV connection terminals 6a, 6b on the onboard power supply side. In order to discharge the Y capacitors Cy1 and Cy2, the discharge device 11 has two passive discharge circuits 12a and 12b, wherein the first discharge circuit 12a is connected in parallel with the first Y capacitor Cy1 and is therefore connected to the first HV connection terminal 6a on the onboard power supply side and the ground potential M. The second discharge circuit 12b is connected in parallel with the second Y capacitor Cy2 and is connected to the second connection terminal 6b on the onboard power supply side and the ground potential M.

[0026] In addition, Figure 1, the voltages Ux, Uy1, Uy2 applied to the capacitors Cx, Cy1, Cy2 in the closed state of the switching device 4 are shown. Due to the coupling of the HV connections 6a, 6b on the vehicle power supply side provided by 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 circuit including diodes D, which are polarized in the blocking direction with respect to the voltages Uy1, Uy2, so that the discharge circuits 12a, 12b are inactive in normal operation of the high-voltage system 1 when the switching device 4 is closed and therefore at the normal polarity of the voltages Uy1, Uy2.

[0027] If the switching device 4 is now Figure 2 , there is nevertheless a high-ohmic connection 13 between the HV connections 5a, 5b, 6a, 6b (here via the contactors 7a, 7b of the switching device). The high-ohmic connection may exist, for example, due to aging-related particle deposits on the contactors 7a, 7b, which shorten the air gap and creepage distance between the switching contacts of the contactors 7a, 7b. The high-ohmic connection 13 can also be provided by a monitoring device (not shown here), which monitors the switching process of the contactors 7a, 7b and is configured, for example, to detect undesired contact welding of the switching contacts of the contactors 7a, 7b. In addition, there is a high-ohmic connection 14 between the HV connections 5a, 5b, 6a, 6b and the ground potential M due to the insulation resistances 8a, 8b, 9a, 9b. The high-ohmic connections 13, 14 may also lead to charging of the Y capacitors Cy1, Cy2 even in the open state of the switching device 4.

[0028] The coupling provided by the discharge resistor Re of the HV connection terminals 5a, 5b is responsible for charging the Y capacitor, and one of the voltages Uy1, Uy2, here the voltage Uy2, undergoes a potential reversal. Which voltage of the voltages Uy1, Uy2 undergoes a potential reversal depends on the ratio of the insulation resistors 8a, 8b, 9a, 9b and the resistance of the high-ohmic connection 13. This potential reversal is responsible for: the diode D of one of the discharge circuits 12a, 12b, here the diode D of the discharge circuit 12b connected in parallel with the second Y capacitor Cy2 is polarized in the conduction direction and thus the voltage Uy1, Uy2 on the Y capacitors Cy1, Cy2 is dissipated. The Y capacitors Cy1, Cy2 are therefore discharged through the side that undergoes the potential reversal. In order to symmetrize the voltage of the voltage dropped on the diodes D, each diode D is connected in parallel with a resistor Rs. Furthermore, each discharge circuit 12a, 12b has a Z diode Z, for example a 60V-Z diode, upstream of which a respective series resistor Rv is connected and which is designed to provide protection against polarity reversal of the high-voltage system 1 via an insulation-to-ground monitor of a charging station external to the vehicle (not shown here).

Claims

1. A high-voltage system (1) for a motor vehicle, comprising: an electrical high-voltage energy store (2) having store-side HV connections (5a, 5b), - a high-voltage on-board power system (3), the high-voltage on-board power system having an HV connection terminal (6a, 6b) on the on-board power system side and a capacitor arrangement structure (10), the capacitor arrangement structure comprising an X capacitor (Cx) and two Y capacitors (Cy1, Cy2), the X capacitor being connected to the HV connection terminal (6a, 6b) on the on-board power system side, and the Y capacitor being connected to one of the HV connection terminals (6a, 6b) on the on-board power system side and a ground potential (M) of the high-voltage system (1), a switching device (4) connected to the HV connections (5a, 5b, 6a, 6b) on the storage side and on the onboard power supply side for connecting the high-voltage energy storage device (2) to the high-voltage onboard power supply (3), - a discharge device (11) for discharging the capacitive arrangement (10), It is characterized in that The discharge device (11) comprises a discharge resistor (Re) connected to the HV connection (6a, 6b) on the vehicle power supply side and a passive discharge circuit (12a, 12b) for each Y capacitor (Cy1, Cy2), wherein the discharge circuits (12a, 12b) are designed to discharge the charged Y capacitors (Cy1, Cy2) due to the parasitic high-resistance connection (13, 14) between the HV connection (6a, 6b) on the vehicle power supply side and the ground potential (M) and the HV connection (5a, 5b) on the storage side even when the switching device (4) is open, and for this purpose the discharge circuits each have at least one A diode (D) is provided, wherein the diode (D) is polarized in a blocking direction with respect to the normal polarity of a voltage (Uy1, Uy2) dropped across a Y capacitor (Cy1, Cy2) when a switching device (4) is closed, and the at least one diode (D) of a discharge circuit (12b) is polarized in a conducting direction by a polarity change of a voltage (Uy2) across an associated Y capacitor (Cy2) for discharging the Y capacitor (Cy1, Cy2), the polarity change being caused by charging the Y capacitor (Cy1, Cy2) and by a potential coupling of an HV connection (6a, 6b) on the vehicle power supply side determined by a discharge resistor.

2. The high-voltage system (1) according to claim 1, characterized in that The high-voltage system (1) has a monitoring device for monitoring a switching device (4), by which the switching device (4) is bridged with high resistance even in the open state.

3. The high-voltage system (1) according to claim 1 or 2, characterized in that The capacitance (Cx, Cy1, Cy2) is formed at least partially by interference suppression capacitors of a filter device of the high-voltage onboard power supply system (3).

4. The high-voltage system (1) according to one of the preceding claims, characterized in that The capacitances (Cx, Cy1, Cy2) are formed at least partially by parasitic capacitances of the high-voltage onboard electrical system (3).

5. The high-voltage system (1) according to any one of the preceding claims, characterized in that Each discharge circuit (12a, 12b) has a cascade circuit including at least two diodes (D).

6. The high-voltage system (1) according to claim 4, characterized in that Each diode (D) has a resistor (Rs) connected in parallel in order to symmetrize the diode (D) voltage of the corresponding cascade circuit.

7. The high-voltage system (1) according to any one of the preceding claims, characterized in that Each discharge circuit (12a, 12b) has at least one protection diode (Z) which is polarized in a forward direction with respect to the normal polarity of the voltage (Uy1, Uy2) and which forms a reverse polarity protection against a reverse polarity provided by an insulation-to-ground monitor of a charging station external to the vehicle. 8 . A motor vehicle comprising a high-voltage onboard electrical system ( 1 ) according to one of the preceding claims.

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