Method for monitoring a high-voltage vehicle electrical system

Abstract

The invention relates to a method for monitoring a high-voltage electrical system (2), in particular of a battery-electric vehicle (1), having a first and a second electrical system line (3a, 3b) with a first and a second electrical potential (P1, P2), during precharging of the high-voltage electrical system (2). According to the method, during precharging of the high-voltage electrical system (2) with electrical energy, a first potential difference (U1) between the first potential (P1) and an electrical ground potential (P0) is compared with a second potential difference (U2) between the second potential (P2) and the electrical ground potential (P0) and is monitored for the presence of an asymmetry.

Description

[0001] The invention relates to a method for monitoring a high-voltage electrical system, in particular of a battery-electric vehicle. The invention further relates to a control unit configured / programmed to implement this method, as well as to a battery-electric vehicle having such a control unit. In one variant, the monitoring circuit and / or the control unit described above can be part of the DC-DC converter described above, i.e., integrated into the DC-DC converter.

[0002] For battery-electric vehicles (BEVs) or hybrids with electric drives operating at voltages above 60 volts, functional safety must be given high priority according to ISO 26262. In particular, safety-critical hazards must be detected as early as possible in order to trigger appropriate fault or system responses.

[0003] With regard to the use of high-voltage electrical systems in battery-electric vehicles, measures to improve operational safety are already known. In conventional vehicles, the high-voltage electrical system is usually designed as a so-called IT network. This means that both the positive potential and the negative potential of the high-voltage electrical system, including the electric drive train and high-voltage battery, are electrically isolated from the vehicle's ground, or that at least only extremely high-resistance electrical connections are provided between the vehicle's ground and the two potentials. To avoid safety-critical conditions, it is therefore important to detect an electrical short circuit or a low-resistance connection between the high-voltage electrical system and the vehicle's ground in a timely manner in order to initiate appropriate countermeasures.

[0004] This is especially true for the so-called electrical pre-charging of the high-voltage electrical system with electrical energy. During pre-charging of the high-voltage electrical system, the electrical voltage level of the high-voltage electrical system is continuously raised to that of the high-voltage battery, or at least brought very close to that voltage level, before the high-voltage battery is electrically connected to the actual high-voltage electrical system. This prevents voltage flashovers and, consequently, the formation of wear-promoting arcs when establishing the electrical connection between the high-voltage battery and the high-voltage electrical system due to the comparatively high electrical voltage difference between the high-voltage battery and the high-voltage electrical system.

[0005] Against this background, WO 2021 / 244899 proposes performing said electrical precharging using a low-voltage battery arranged in a low-voltage electrical system of a motor vehicle, which is connected to the vehicle's high-voltage electrical system via a DC / DC converter. Said DC / DC converter is designed such that, in boost converter mode, it can convert the low-voltage voltage of the low-voltage battery into a higher voltage and feed it to the high-voltage electrical system, thereby enabling the desired precharging of the high-voltage electrical system.

[0006] In light of the above explanations, it is an object of the present invention to provide an improved method for monitoring a high-voltage electrical system of a battery-electric vehicle, which addresses the above-mentioned problem.

[0007] This object is achieved by the subject matter of the independent patent claims. Preferred embodiments are the subject matter of the dependent patent claims.

[0008] The basic idea of ​​the invention is therefore to monitor the respective potential difference between the vehicle ground and the two electrical potentials of the high-voltage electrical system of a battery-electric vehicle with the aid of an electrical monitoring circuit during the above-described electrical pre-charging of the high-voltage electrical system with regard to the occurrence of an asymmetry in these two potential differences. Such an asymmetry is a reliable indicator that the desired electrical insulation of the high-voltage electrical system from the vehicle ground is no longer sufficiently present. Since said monitoring already takes place during the pre-charging of the high-voltage electrical system, appropriate countermeasures can be initiated if such an asymmetry is detected during the pre-charging process, thus preventing safety-critical conditions in the high-voltage electrical system.In particular, as an effective countermeasure, the pre-charging of the high-voltage vehicle electrical system can be aborted prematurely and the electrical connection of the high-voltage battery to the high-voltage vehicle electrical system, which usually follows pre-charging, can be dispensed with.

[0009] The electrical monitoring circuit essential to the invention can comprise electrical components for detecting said asymmetry, with the aid of which the two electrical potential differences between the two on-board power supply lines of the high-voltage on-board power supply and the vehicle ground can be determined. In the solution proposed here, the electrical monitoring circuit is thus particularly useful for comparing a first potential difference between the first potential of said first on-board power supply line and a ground potential of the vehicle with a second potential difference between the second potential and the ground potential.

[0010] In accordance with the inventive concept explained above, the method according to the invention is used to monitor a high-voltage vehicle electrical system during an electrical pre-charging process, wherein the high-voltage vehicle electrical system has a first and a second electrical vehicle electrical system line with a first and a second electrical potential, respectively. As already explained, in the context of the present invention, the term “electrical pre-charging” is to be understood as bringing an electrical voltage or potential difference between the two electrical system lines of the high-voltage vehicle electrical system closer to the electrical output voltage of the high-voltage battery still to be connected to the high-voltage vehicle electrical system. It is assumed here that a certain electrical capacity is present in the high-voltage vehicle electrical system. This capacity can be provided by individual capacities of the electrical consumers connected to the high-voltage vehicle electrical system, but also – alternatively or additionally – by at least one so-calledintermediate circuit capacitor may be formed.

[0011] The electrical output voltage of the high-voltage battery can be, in particular, 300V, 400V, 500V, or 800V. Only after such an approximation is the electrical connection established between the high-voltage battery and the two on-board power supply lines of the high-voltage on-board power supply. The electrical on-board power supply voltage of the high-voltage on-board power supply, defined by the potential difference between the two on-board power supply lines, then corresponds exactly to the output voltage of the high-voltage battery. The first on-board power supply line can be an electrical positive line, which is consequently connected to an electrical positive terminal of the high-voltage battery. The second on-board power supply line can accordingly be an electrical negative line, which is electrically separate from the first on-board power supply line and accordingly connected to an electrical negative terminal of the high-voltage battery. At least one electrical high-voltage consumer can be connected to each of the two electrical on-board power supply lines.

[0012] During the electrical pre-charging process, it is particularly conceivable to increase the potential difference between the two vehicle electrical system lines, starting from a zero value, over a suitable charging period to a level approximately equal to 80%, preferably 90%, of the electrical output voltage generated by the high-voltage battery. In the 80% case, with a nominal electrical output voltage of the high-voltage battery of 400 volts between its positive and negative terminals, the voltage level of the high-voltage vehicle electrical system, i.e., the potential difference between the two vehicle electrical system lines, would be increased to a final value of 320 volts over a certain period of time during the electrical pre-charging process.

[0013] In the method according to the invention, during pre-charging of the high-voltage vehicle electrical system, a first potential difference between the first potential and an electrical ground potential is compared with a second potential difference between the second potential and the electrical ground potential and monitored for the presence of an asymmetry. Such an asymmetry is a reliable indicator that the integrity of the high-voltage vehicle electrical system is disrupted, i.e. that the required electrical insulation of the two vehicle electrical system lines from the electrical ground potential or the vehicle ground is no longer provided to the required extent. The term “asymmetry” can be understood in particular to mean that at a specific monitoring time the value of the first potential difference is different from the value of the second potential difference.

[0014] In a preferred embodiment of the method according to the invention, the electrical monitoring circuit already presented can be electrically connected to the two vehicle electrical system lines for monitoring and comparing the two potential differences during precharging, at least temporarily. In this embodiment, said monitoring circuit is designed such that the first vehicle electrical system line is connected to the electrical ground potential with a high resistance via at least one first ohmic resistor, and the second vehicle electrical system line is connected to the electrical ground potential with a high resistance via at least one second ohmic resistor. To determine and monitor the first and second potential differences, the electrical voltages dropped across the first and second ohmic resistors, respectively, can be determined and compared with one another.

[0015] Particularly preferably, an asymmetry can be determined to be present if a deviation between the two determined electrical voltages and thus between the two potential differences exceeds a predetermined threshold. Such a deviation between the two potential differences is a clear indication that the resistance value of at least one of the two originally at least high-resistance electrical connections between the first or second vehicle electrical system line and the electrical ground potential has decreased.

[0016] Particularly preferably, an error signal can be generated upon detection of such an asymmetry. This allows appropriate countermeasures to be initiated before a safety-critical condition is reached in the high-voltage electrical system.

[0017] Alternatively or additionally, if an asymmetry is detected, the electrical pre-charging of the high-voltage vehicle electrical system can be aborted.

[0018] According to an advantageous further development, the high-voltage electrical system is supplied with electrical energy from the high-voltage battery after the electrical pre-charging process is completed. Optionally, the monitoring of the potential differences described above can be terminated after the pre-charging process is completed.

[0019] According to an advantageous development of the method according to the invention, the high-voltage electrical system is electrically connectable or connected to an electrical energy storage device, in particular a rechargeable one, via a DC-DC converter and is also electrically connectable or connected via at least one switch to an electrical high-voltage battery for supplying the high-voltage electrical system with electrical energy. Said switch can be an electromechanical switch, in particular a contactor, or a semiconductor switch, in particular a power transistor. In this development, the electrical precharging takes place with the switch open and with the high-voltage battery disconnected from the high-voltage electrical system. The high-voltage electrical system is thus precharged using electrical energy from the energy storage device, which is supplied to the high-voltage electrical system by means of the DC-DC converter in a boost converter mode.The energy storage device can be an accumulator, a low-voltage battery, or a fuel cell, which can be connected to a low-voltage electrical system of the battery-electric vehicle to supply it with electrical energy. It is understood that the electrical voltage level of the high-voltage electrical system is then higher than that of the low-voltage electrical system.

[0020] According to an alternative advantageous development, the pre-charging can be carried out by electrical energy from the high-voltage battery, which is supplied to the high-voltage vehicle electrical system when the switch is open via an electrical bridging circuit arranged parallel to this switch.

[0021] According to an advantageous development of the method according to the invention, the bridging circuit can have at least one further electrical switch and an ohmic resistor arranged electrically in series with this further electrical switch. Said further switch can be an electromechanical switch, in particular a contactor, or a semiconductor switch, in particular a power transistor. In this development, this further switch is closed during precharging of the high-voltage vehicle electrical system, so that electrical energy is transferred from the high-voltage battery to the high-voltage vehicle electrical system. Said bridging circuit enables precharging of the high-voltage vehicle electrical system using the high-voltage battery.The bridging circuit allows the high-voltage vehicle electrical system to be proposed in a similar way to the variant explained above, which uses a DC-DC converter. However, in this case, electrical energy is not used from the electrical energy source, but from the high-voltage battery. The aforementioned ohmic resistance acts as an electrical current limiter and thus prevents the undesirable occurrence of arcs when the additional switch is closed. The additional switch can also be an electromechanical switch, in particular in the form of a so-called "contactor", or a semiconductor switch. Two such additional switches can expediently be provided, with a first electrical switch connecting a positive terminal of the high-voltage battery to the first vehicle electrical system line when closed, and interrupting these connections when open.Accordingly, a second electrical switch connects a negative terminal of the high-voltage battery to the second vehicle electrical system line when closed and interrupts these connections when open.

[0022] The invention further relates to a control unit for a battery-electric vehicle with an electric drive train for driving the vehicle. The control unit according to the invention is configured or programmed to implement the method according to the invention presented above. The advantages of the method according to the invention explained above are therefore transferred to the control unit according to the invention.

[0023] The invention also relates to a battery-electric vehicle having an electric drive train for driving the vehicle. The battery-electric vehicle can be an electric vehicle with a purely electric drive or a hybrid vehicle with a hybrid drive. The battery-electric vehicle according to the invention also has a high-voltage electrical system, which has a first electrical system line with a first electrical potential and a second electrical system line with a second electrical potential. The electric drive train of the battery-electric vehicle is connected to the high-voltage electrical system as an electrical high-voltage consumer, but other electrical high-voltage consumers can also be connected to the high-voltage electrical system. Furthermore, the high-voltage electrical system is electrically connected to an electrical energy storage device via an electrical DC-DC converter.This electrical energy storage device can be a low-voltage battery, an accumulator, or a fuel cell, which in turn can be connected to a low-voltage electrical system of the battery-electric vehicle in order to supply it with electrical energy. Furthermore, the vehicle also comprises a high-voltage battery, which, in order to supply the high-voltage electrical system with electrical energy, can be or is electrically connected to the high-voltage electrical system via at least one switch, preferably via at least one electromechanical switch or via at least one semiconductor switch. The at least one switch can be switched between a closed state, in which the electrical connection between the high-voltage battery and the high-voltage electrical system is present, and an open state, in which this electrical connection is interrupted. Two such switches are preferably provided.The positive terminal of the high-voltage battery can then be connected or connected to the first on-board power supply line of the high-voltage on-board power supply via a first switch. Similarly, the negative terminal of the high-voltage battery can be connected or connected to the second on-board power supply line of the high-voltage on-board power supply via a second switch.

[0024] According to the invention, the vehicle further comprises an electrical monitoring circuit for comparing a first potential difference between the first potential of the first vehicle electrical system line and an electrical ground potential of the vehicle with a second potential difference between the second potential and the electrical ground potential. Finally, the vehicle according to the invention can comprise a control unit according to the invention as presented above. The advantages of the method according to the invention explained above are therefore transferred to the battery-electric vehicle according to the invention.

[0025] In a preferred embodiment of the vehicle according to the invention, the monitoring circuit comprises an electrical monitoring line which connects the first electrical on-board power supply line to the ground potential via at least one first ohmic resistor, in particular a high-ohmic resistor, and also connects the second electrical on-board power supply line to the ground potential via at least one second ohmic resistor, in particular a high-ohmic resistor. In this embodiment, the ground potential is arranged between the two ohmic resistors or, alternatively, is electrically connected to an electrical branch arranged between the two ohmic resistors in the monitoring line. Furthermore, the monitoring circuit comprises a first electrical voltage measuring device electrically connected to the ground potential for determining a (first) electrical voltage drop across the first ohmic resistor.Accordingly, the monitoring circuit comprises a second electrical voltage measuring device electrically connected to the ground potential for determining a (second) electrical voltage drop across the second ohmic resistor. By comparing the two electrical voltages, the high-voltage vehicle electrical system can be monitored for the presence of an asymmetry in the course of the method according to the invention.

[0026] In a preferred embodiment of the vehicle according to the invention, the monitoring circuit comprises two electrical switches. These two switches can be used to selectively electrically connect or disconnect the electrical monitoring line from the two vehicle electrical system lines. The monitoring line can be conveniently connected to the first vehicle electrical system line via a first of the two switches and to the second vehicle electrical system line via a second of the two switches.

[0027] In a particularly advantageous manner, the two ohmic resistors in the monitoring line can be part of an electrical resistor chain with several ohmic resistors arranged in series with each other in the monitoring line. Such a resistor chain is technically particularly easy to implement using conventional ohmic resistors and is therefore also cost-effective.

[0028] Particularly usefully, the DC-DC converter can have a high-voltage side connected to the high-voltage electrical system and a low-voltage side connected to the electrical energy storage device. The high-voltage side can be galvanically isolated from the low-voltage side and coupled to it inductively or as a transformer.

[0029] In this variant, the DC-DC converter can at least be switched between normal operation, known as buck converter mode, and boost converter mode. In normal operation, the DC-DC converter converts a high-voltage electrical voltage provided by the high-voltage battery on the high-voltage side into a low-voltage voltage provided on the low-voltage side. In boost converter mode, however, the DC-DC converter converts a low-voltage electrical voltage provided by the electrical energy storage device on the low-voltage side into a high-voltage voltage provided on the high-voltage side.A DC-DC converter equipped with these two operating modes is often already installed as standard in modern battery-electric vehicles and can thus be used in the boost converter mode, which is already available as standard, to electrically precharge the high-voltage electrical system during implementation of the method according to the invention. Thus, in vehicles equipped in this way, the need to provide special electrical and electronic components for precharging the high-voltage electrical system is eliminated.

[0030] According to a further advantageous development of the vehicle according to the invention, the battery-electric vehicle according to the invention comprises an electrical bridging circuit arranged electrically parallel to the at least one switch between the high-voltage battery and the high-voltage electrical system for precharging the high-voltage electrical system with electrical energy from the high-voltage battery. Particularly preferably, the electrical bridging circuit can have at least one further electrical switch and an ohmic resistor arranged electrically in series with this further electrical switch. A bridging circuit configured in this way is technically comparatively simple, particularly compared to the DC-DC converter explained above.This further development therefore proves to be particularly advantageous if the DC-DC converter explained above with the option of boost converter operation for pre-charging the high-voltage vehicle electrical system is not available.

[0031] Further important features and advantages of the invention emerge from the subclaims, from the drawings and from the associated description of the figures based on the drawings.

[0032] It is understood that the features mentioned above and those to be explained below can be used not only in the combination specified in each case, but also in other combinations or on their own, without departing from the scope of the present invention.

[0033] Preferred embodiments of the invention are illustrated in the drawings and are explained in more detail in the following description, wherein the same reference numerals refer to the same or similar or functionally identical components.

[0034] They show, schematically: Fig. 1 shows, by way of example and in a circuit diagram-like representation, the components of a battery-electric vehicle according to the invention that are relevant for the method according to the invention Fig. 2 in a circuit diagram-like detailed representation of the high-voltage electrical system of the Fig. 1 in the area of ​​the monitoring circuit, Fig. 3 is a flowchart illustrating the method according to the invention by way of example.

[0035] The Fig. 1 shows, in a roughly schematic and circuit diagram-like representation, an example of a battery-electric vehicle 1 according to the invention, which can be a vehicle with a purely battery-electric drive or with a hybrid drive. The vehicle 1 has an electric drive train 17, indicated only roughly schematically, for driving the vehicle 1. The vehicle 1 also has a high-voltage electrical system 2, which has a first electrical system line 3a with an associated first electrical potential P1 and a second electrical system line 3b with an associated second electrical potential P2. The electric drive train 17 is connected to the high-voltage electrical system 2 as a high-voltage electrical consumer 4, but other high-voltage electrical consumers 4 can also be connected to the high-voltage electrical system 2.

[0036] Furthermore, the vehicle 1 also includes a high-voltage battery 7, which can be electrically connected to the high-voltage electrical system 2 via two electrical switches 8a, 8b to supply the high-voltage electrical system 2 with electrical energy. The high-voltage battery 7 includes a positive terminal 18a and an electrical negative terminal 18b and, during operation, generates an electrical output voltage V between these two terminals 18a, 18b. A, which can be 400 V, for example. The two switches 8a, 8b can be formed by electromechanical switches, in particular in the form of a respective “contactor,” and can each be adjusted between an open and a closed state. However, the two switches 8a, 8b can also be formed by semiconductor switches, in particular by power transistors. A first 8a of the two switches 8a, 8b, in the closed state, electrically connects an electrical positive terminal 18a of the high-voltage battery 7 to the first on-board power supply line 3a of the high-voltage on-board power supply system 2. When the first switch 8a is open, this electrical connection is interrupted. Accordingly, a second 8b of the two switches 8a, 8b, in the closed state, electrically connects an electrical negative terminal 18b of the high-voltage battery 7 to the second on-board power supply line 3b. When the second switch 8b is open, this electrical connection is interrupted.

[0037] In addition, the high-voltage electrical system 2 is electrically connected to a rechargeable electrical energy storage device 6 via a DC-DC converter 5—also known to those skilled in the art as a "DC-DC converter." The electrical energy storage device 6 can be a low-voltage battery 19, in particular a 24V or 12V battery, which, during normal operation of the DC-DC converter 5, can be supplied with electrical energy from the high-voltage battery 7 and, in particular, charged. However, the electrical energy storage device 6 can also be an accumulator or a fuel cell.

[0038] In the example of Fig. 1, the DC-DC converter 5 has a high-voltage side 21a connected to the high-voltage vehicle electrical system 2 and a low-voltage side 21b connected to the electrical energy storage device 6 or the low-voltage battery 19. The high-voltage side 21a can, for example, be inductively coupled to the low-voltage side 21b. In this case, the high-voltage side 21a is therefore galvanically isolated from the low-voltage side 21b. The DC-DC converter 5 can be switched between normal operation, step-down converter operation, and step-up converter operation. In normal operation, the DC-DC converter 5 converts an electrical high-voltage voltage HV provided by the high-voltage battery 7 on the high-voltage side 21a into a low-voltage voltage NV provided on the low-voltage side 21b. In this way, the electrical energy storage device 6 or the low-voltage battery 19 can be charged with electrical energy from the high-voltage battery 7. By means of the energy storage device 6 orDuring normal operation, a low-voltage electrical system of the vehicle 1 (not shown) can be supplied with electrical energy from the low-voltage battery 19.

[0039] In boost converter mode, the DC-DC converter 5 converts the low-voltage electrical voltage NV provided by the electrical energy storage device 6 on the low-voltage side 21b into a high-voltage voltage HV provided on the high-voltage side 21a. In boost converter mode, the DC-DC converter 5 can electrically precharge the high-voltage vehicle electrical system 2 in the course of the method according to the invention, which will be explained in more detail below. In the high-voltage electrical system 2 there is a certain electrical capacity C, which is Fig. 1 is shown in dashed lines. The high-voltage electrical system 2 therefore has a specific capacitance C. This capacitance C can be formed by individual capacitances (not shown) of the electrical consumers connected to the high-voltage electrical system 2, but also—alternatively or additionally—by at least one so-called intermediate circuit capacitor (not shown), in particular as part of the DC-DC converter 5.

[0040] How Fig. 1, the vehicle 1 according to the invention or the high-voltage electrical system 2 further comprises an electrical monitoring circuit 9 arranged between the first electrical system line 3a and the second electrical system line 3b and connecting the two electrical system lines 3a, 3b with high resistance. To clarify the structure of the monitoring circuit 9, the Fig. 2 shows a circuit diagram-like representation of the high-voltage vehicle electrical system 2 in the area of ​​this monitoring circuit 9. The monitoring circuit 9 enables a comparison, to be carried out in the course of the method according to the invention, of a first potential difference U1 between the first potential P1 of the first vehicle electrical system line and a ground potential P0 of the vehicle 1 with a second potential difference U2 between the second potential P2 of the second vehicle electrical system line 3b and the ground potential P0. In a nominal state of the vehicle 1 - with the exception of the aforementioned high-resistance connection via the monitoring circuit 9 - the electrical ground potential P0 is galvanically isolated from the high-voltage vehicle electrical system 2, including the high-voltage battery 7.

[0041] The monitoring circuit 9 comprises for determining the two potential differences according to Fig. 2 an electrical monitoring line 10 which electrically connects the two on-board power supply lines 3a, 3b to one another. The electrical monitoring line 10 also connects the first electrical on-board power supply line 3a with a high resistance to the electrical ground potential P0 of the vehicle 1 via a first ohmic resistor R1 and a further first ohmic resistor R1*, which are arranged electrically connected in series with one another in the monitoring line 10. In an analogous manner, the electrical monitoring line 10 connects the second electrical on-board power supply line 3b with a high resistance to the electrical ground potential P0 of the vehicle 1 via a second ohmic resistor R2 and a further second ohmic resistor R2*, which are arranged electrically connected in series with one another in the monitoring line 10.The ground potential P0 is electrically connected to an electrical branch 11 arranged between the two ohmic resistors R1, R2 in the monitoring line 10. The ohmic resistors R1, R1*, R2, R2* are electrically connected in series in the monitoring line 10 and form an electrical resistance chain 22 with a total electrical resistance R-Ges = R1 + R1* + R2 + R2*.

[0042] How Fig. 2, the monitoring circuit 9 further comprises a first electrical voltage measuring device 12a, which is electrically connected to the ground potential P0, for determining an electrical voltage V1 dropped across the first ohmic resistor R1. Correspondingly, the monitoring circuit 9 comprises a second electrical voltage measuring device 12b, which is electrically connected to the ground potential P0, for determining an electrical voltage V2 dropped across the second ohmic resistor R2. If the values ​​of the four ohmic resistors R1, R1*, R2, R2* are known, the two electrical potentials P1, P2 can be calculated from the measured voltages V1, V2 using Kirchhoff's laws in a simple manner known to those skilled in the art.

[0043] According to Fig. 2, the monitoring circuit 9 comprises two electrical switches 13a, 13b. By means of these two switches 13a, 13b, the electrical monitoring line 10 can be selectively electrically connected to or disconnected from the vehicle electrical system lines 3a, 3b. The four electrical resistors R1, R1*, R2, R2* are electrically connected in series with one another and arranged between these two switches 13a, 13b. The two switches 13a, 13b can be electromechanical switches, but also semiconductor switches, in particular transistors. By means of a first 13a of the two switches 13a, 13b, the monitoring line 10 can be selectively electrically connected to or disconnected from the first vehicle electrical system line 3a. Correspondingly, by means of a second 13b of the two switches 13a, 13b, the monitoring line 10 can be selectively electrically connected to or disconnected from the second vehicle electrical system line 3b.

[0044] In the example scenario, the vehicle 1 further comprises an electrical bridging circuit 14 arranged electrically in parallel with the two electrical switches 8a, 8b between the high-voltage battery 7 and the high-voltage vehicle electrical system 2. The bridging circuit 14 comprises - in addition to the first switch 8a - a further first electrical switch 15a and a first ohmic resistor 16a arranged electrically in series with this further electrical switch 15a, which together electrically connect the positive terminal 18a of the high-voltage battery 7 electrically in parallel with the first vehicle electrical system line 3a of the high-voltage vehicle electrical system when the further first electrical switch 15a is in a closed state.Accordingly, the bridging circuit 14 comprises—in addition to the second switch 8b—a further second electrical switch 15b and a second ohmic resistor 16b arranged electrically in series with this further second electrical switch 15b, which together electrically connect the negative terminal 18b of the high-voltage battery 7 in parallel with the second switch 8b and the second on-board power supply line 3b of the high-voltage on-board power supply when the further second electrical switch 15b is in a closed state. The bridging circuit 14 can thus be used as an alternative to the DC-DC converter 5 for pre-charging the capacitance C of the high-voltage on-board power supply 2 with electrical energy from the high-voltage battery 7 if this is not available or only available without boost converter operation.The two ohmic resistors 16a, 16b act as electrical current limiters when an electrical pre-charging current flows from the high-voltage battery 7 via the bridging circuit 14 into the high-voltage vehicle electrical system 2 in order to pre-charge the capacity C of the high-voltage vehicle electrical system 2.

[0045] The following is a flow chart of the Fig. 3 illustrates the method according to the invention by way of example. In the example explained below, the capacitance C of the high-voltage electrical system 2 is precharged using the DC-DC converter 5.

[0046] At the beginning of the method according to the invention, the two switches 8a, 8b are each open, so that the high-voltage battery 7 is electrically disconnected from the high-voltage vehicle electrical system 2. Likewise, the two electrical switches 13a, 13b of the monitoring circuit 9 are open, so that the monitoring line 10 is electrically disconnected from the two vehicle electrical system lines 3a, 3b. Finally, the two electrical switches 15a, 15b of the bridging circuit 14 are also open, since the electrical pre-charging takes place using the DC-DC converter 5. This means that the bridging circuit 14 can be dispensed with to carry out the method according to the invention according to the present example. In the example scenario, an electrical output voltage of V A , which the high-voltage battery 7 provides between the electrical positive terminal 18a and the electrical negative terminal 18b, 400 volts.

[0047] According to a first measure a) of the method, the DC-DC converter 5 is switched into boost converter mode by the control unit 20 if this has not been done before the start of the implementation of the method.

[0048] In a second measure b) following measure a), the above-described electrical precharging of the capacitance C of the high-voltage vehicle electrical system 2 is initiated in boost converter mode of the DC-DC converter 5. For this purpose, the DC-DC converter 5 is controlled accordingly by the control unit 20. The potential difference DIFF between the two potentials P1 and P2, i.e., DIFF = P1 - P2, initially at a zero value, continuously increases during the precharging of the high-voltage vehicle electrical system 2.

[0049] In a third measure c), the two electrical switches 13a, 13b of the monitoring circuit 9 are switched to the closed state by appropriate control by the control unit 20, thereby activating the monitoring circuit 9. Activation preferably occurs at the start of the electrical precharging or immediately before or after the start of the precharging.

[0050] In the course of a fourth measure d), during the pre-charging of the high-voltage electrical system 2, it is monitored whether an asymmetry occurs with regard to the values ​​of the two electrical potentials P1, P2 compared to the ground potential P0.

[0051] For this purpose, in the course of measure d) during pre-charging, the two voltage measuring devices 12a, 12b determine the electrical voltages V1 and V2 dropped across the first ohmic resistor R1 and the second ohmic resistor R2, respectively. From the voltage value V1, given knowledge of the values ​​of the four ohmic resistors R1, R1*, R2, R2*, the instantaneous (first) electrical potential difference U1 between the first electrical potential P1 of the first vehicle electrical system line 3a and the electrical ground potential P0, i.e. U1 = P1 - P0, can be determined in a manner known to those skilled in the art. From the second voltage value V2, the instantaneous (second) electrical potential difference U2 between the second electrical potential P2 and the ground potential P0, i.e. U2 = P2 - P0, can be determined accordingly.

[0052] In the course of measure d), the two determined potential differences U1, U2 are continuously compared during precharging and continuously checked for the presence of an asymmetry. In the example scenario, such an asymmetry exists when a deviation DELTA between the two monitored potential differences U1, U2 exceeds a predetermined threshold S0, i.e., as soon as DELTA = |U1 + U2| > S0 is met. In variants of the example, other criteria for the presence of an asymmetry can also be specified.

[0053] If such an asymmetry is detected in measure d) during precharging, an error signal can be generated by the control unit 20 in a further measure x).

[0054] Alternatively or in addition to measure x), the electrical precharging of the high-voltage electrical system 2 can be aborted in another further measure y). In this way, a safety-critical state of the high-voltage electrical system 2 described above is avoided. After execution of measure(s) x) or y), the execution of the method according to the invention is completed.

[0055] If no asymmetry is detected during pre-charging in the course of measure d), the Fig. 3 in a fifth measure e) it is checked whether the potential difference DIFF between the first potential P1 of the first vehicle electrical system line 3a and the second potential P2 of the second vehicle electrical system line 3b has reached a value which is X % of the electrical output voltage V nominally provided by the high-voltage battery 7 Ahas been reached, whereby preferably X > 80, particularly preferably X > 90 applies. The potential difference DIFF can be determined, for example, by means of a voltage measuring device integrated into the DC-DC converter 5 on the high-voltage side (not shown), but it is also conceivable to arrange a separate voltage measuring device directly between the two vehicle electrical system lines 3a, 3b (not shown), as well as a determination by the monitoring circuit 9 itself, since DIFF = P1 - P2 = U1 - U2. In one variant, both the monitoring circuit 9 and the control unit 20 can be part of the DC-DC converter 5, i.e., integrated into the DC-DC converter 5. If the value X% has not yet been reached, the precharging is continued and the process is repeated according to measure d) (see flow chart of the Fig.3). If, however, it is determined in step e) that the said value X% has been reached, then in a sixth step f) the precharging of the high-voltage electrical system 2 is terminated by the control unit 20 controlling the DC-DC converter 5 accordingly.

[0056] Following measure f), in a seventh measure g), by closing the two switches 8a, 8b, the positive terminal 18a of the high-voltage battery 7 can be electrically connected to the first high-voltage line 3a of the high-voltage vehicle electrical system 2, and the negative terminal 18b of the high-voltage battery 7 can be electrically coupled to the second vehicle electrical system line 3b of the high-voltage vehicle electrical system 2. As a result, the high-voltage vehicle electrical system 2 with its electrical high-voltage consumers 4, including the electric drive train 17, is supplied with electrical energy from the high-voltage battery 7 during nominal operation. The vehicle electrical system voltage of the high-voltage vehicle electrical system 2, which is determined by the potential difference P1 - P2, corresponds exactly to the output voltage V A the high-voltage battery 7.

[0057] Even during nominal operation of the high-voltage vehicle electrical system 2, i.e., after the method according to the invention has been terminated following implementation of measure g), monitoring of the two electrical potentials P1, P2 for asymmetry can be continued. In this case, the two switches 13a, 13b of the monitoring circuit 9 each remain in the closed state. However, it is also conceivable that after completion of the pre-charging or the method according to the invention, such monitoring of the two electrical potentials P1, P2 should no longer take place. In this case, the two switches 13a, 13b of the monitoring circuit 9 can each be switched to the open state either after completion of the pre-charging according to measure e) or after closing the two electrical switches 8a, 8b for electrically coupling the high-voltage battery 7 to the high-voltage vehicle electrical system 2 according to measure g), whereby the monitoring circuit 9 is deactivated.

[0058] In a variant of the example described above for implementing the method according to the invention, the precharging according to measure d) can be carried out not using the DC-DC converter 5 as described above, but using the bridging circuit 14. Accordingly, in this variant, in measure b), the two further switches 15a, 15b of the bridging circuit 14 are closed, so that the two vehicle electrical system lines 3a, 3b are precharged by the high-voltage battery 7 in a manner analogous to the electrical precharging by means of the DC-DC converter 5. In this variant, the provision of the DC-DC converter 5 can be dispensed with and measure f) is omitted. In this variant, the precharging in measure g) is ended by the two further switches 15a, 15b of the bridging circuit 14 being switched back to the open state. 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] WO 2021 / 244899

[0005]

Claims

[1] Method for monitoring a high-voltage vehicle electrical system (2), in particular of a battery-electric vehicle (1), having a first and a second electrical vehicle electrical system line (3a, 3b) with a first and a second electrical potential (P1, P2), during pre-charging of the high-voltage vehicle electrical system (2), - according to which, during an electrical pre-charging of the high-voltage vehicle electrical system (2) with electrical energy, a first potential difference (U1) between the first potential (P1) and an electrical ground potential (P0) is compared with a second potential difference (U2) between the second potential (P2) and the electrical ground potential (P0), and the two potential differences (U1, U2) are monitored for the presence of an asymmetry using this comparison. [2] Method according to claim 1, characterized by , that - for comparing and monitoring the two potential differences (U1, U2) during pre-charging, an electrical monitoring circuit (9) is at least temporarily electrically connected to the two vehicle electrical system lines (3a, 3b), so that the first electrical vehicle electrical system line (3a) is connected to the ground potential (P0) via at least one first ohmic resistor (R1), in particular a high-resistance resistor, and the second electrical vehicle electrical system line (3b) is connected to the ground potential (P0) via at least one second ohmic resistor (R2), in particular a high-resistance resistor; and that - to determine and monitor the first and second potential difference (P1, P2), the electrical voltages (V1, V2) dropping across the first and second ohmic resistors (R1, R2) are determined and compared with each other. [3] Method according to claim 1 or 2, characterized bythat the presence of an asymmetry is detected when a deviation (DELTA) of the two determined electrical voltages (V1, V2) and thus of the two potential differences (U1, U2) from each other exceeds a predetermined threshold value (S0). [4] Method according to one of claims 1 to 3, characterized by , that - an error signal is generated when an asymmetry is detected; and / or - that if an asymmetry is detected, the electrical pre-charging of the high-voltage electrical system (2) is aborted. [5] Method according to one of the preceding claims, characterized by that after completion of the electrical pre-charging, the high-voltage vehicle electrical system (2) is supplied with electrical energy from the high-voltage battery (7). [6] Method according to one of the preceding claims, characterized by , that - for electrical pre-charging, the high-voltage vehicle electrical system (2) is electrically connected to an electrical energy store (6) via a DC-DC converter (5), so that pre-charging is carried out by means of electrical energy from the energy store (6), which is supplied to the high-voltage vehicle electrical system (2) by means of the DC-DC converter (5) in a boost converter operation thereof, and that - the electrical pre-charging takes place with the high-voltage battery (7) disconnected from the high-voltage vehicle electrical system (2). [7] Method according to one of claims 1 to 5, characterized by that the pre-charging is carried out by electrical energy from the high-voltage battery (7), which is supplied to the high-voltage vehicle electrical system (2) when the switch (8a, 8b) is open via an electrical bridging circuit (14), in particular with electrical current limitation, arranged parallel to this switch (8a, 8b). [8] Method according to claim 7, characterized by , that - the bridging circuit (14) comprises at least one further electrical switch (15a, 15b) and, for electrical current limitation, an ohmic resistor (16a, 16b) arranged electrically in series with this further electrical switch (15a, 15b); and that - the further switch (15a, 15b) is closed during pre-charging, so that electrical energy is transferred from the high-voltage battery (7) to the high-voltage vehicle electrical system (2). [9] Control unit (20) for a vehicle with an electric drive train, characterized by that the control device (20) is set up / programmed to carry out the method according to one of the preceding claims. [10] Battery electric vehicle (1), - with an electric drive train to drive the vehicle, - with a high-voltage on-board network (2) having a first and a second electrical on-board network line (3a, 3b) with a first and second electrical potential (P1, P2), respectively, to which the electric drive train is connected as at least one electrical high-voltage consumer (4) of the high-voltage on-board network (2), wherein the high-voltage on-board network (2) can be or is electrically connected to an electrical energy store (6) via a DC-DC converter (5) for electrical pre-charging thereof, - with a high-voltage battery (7) which can be electrically connected to the high-voltage vehicle electrical system (2) via at least one switch (8a, 8b), preferably via at least one electromechanical switch, in order to supply the high-voltage vehicle electrical system (2) with electrical energy, - with an electrical monitoring circuit (9) for comparing a first potential difference (U1) between the first potential (P1) of the first vehicle electrical system line (3a) and a ground potential (P0) of the vehicle (1) with a second potential difference (U2) between the second potential (P2) of the second vehicle electrical system line (3b) and the ground potential (P0), - with a control device (20) according to claim 9. [11] Vehicle (1) according to claim 10, characterized by , that - the monitoring circuit (9) comprises an electrical monitoring line (10) which connects the first electrical on-board power supply line (3a) to the ground potential (P0) via at least one first ohmic resistor (R1) with high resistance and also connects the second electrical on-board power supply line (3b) to the ground potential (P0) via at least one second ohmic resistor (R2) with high resistance, - wherein the ground potential (P0) is arranged between the two ohmic resistors (R1, R2) or is electrically connected to an electrical branch (11) arranged between the two ohmic resistors (R1, R2) in the monitoring line (10). - wherein the monitoring circuit (9) comprises a first electrical voltage measuring device (12a) electrically connected to the ground potential (P0) for determining a (first) electrical voltage (V1) dropping across the first ohmic resistor (R1) and a second electrical voltage measuring device (12b) electrically connected to the ground potential (P0) for determining a (second) electrical voltage (V2) dropping across the second ohmic resistor (R2). [12] Vehicle according to claim 11, characterized bythat the monitoring circuit (9) comprises at least two electrical switches (13a, 13b) by means of which the electrical monitoring line (10) can be selectively electrically connected to or separated from the on-board power supply lines (3a, 3b). [13] Vehicle according to claim 11 or 12, characterized by that the two ohmic resistors (R1, R2) are part of an electrical resistance chain (22) with several ohmic resistors (R1, R2, R1*, R2*) arranged electrically in series with one another in the monitoring line. [14] Vehicle according to one of claims 10 to 13, characterized by , that - the DC-DC converter (5) has a high-voltage side (21a) connected to the high-voltage vehicle electrical system (2) and a low-voltage side (21b) connected to the electrical energy storage device (6); and that - the DC-DC converter (5) is designed to be switchable at least between a normal operation and a boost converter operation, wherein the DC-DC converter (5) in normal operation converts an electrical high-voltage voltage (HV) provided on the high-voltage side by the high-voltage battery (7) into a low-voltage voltage (NV) provided on the low-voltage side (21b) and, in particular for pre-charging the high-voltage vehicle electrical system (2), in boost converter operation converts an electrical low-voltage voltage (NV) provided on the low-voltage side by the electrical energy store (6) into a high-voltage voltage (HV) provided on the high-voltage side (21a). [15] Vehicle according to one of claims 10 to 14, characterized by , that - for pre-charging the high-voltage vehicle electrical system (2) with electrical energy from the high-voltage battery, an electrical bridging circuit (14), in particular with electrical current limitation, is provided, which is arranged electrically parallel to at least one switch (8a, 8b) between the high-voltage battery (7) and the high-voltage vehicle electrical system (2), - preferably the bridging circuit (14) comprises at least one further electrical switch (15a, 15b) and an ohmic resistor (16a, 16b) arranged electrically in series with this further electrical switch (15a, 15b).

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