Method for detecting an insulation fault in a vehicle electrical system

Abstract

A method for detecting insulation faults in a vehicle on-board electrical system having an HV on-board electrical branch (HB) and an LV on-board electrical branch (LB) specifies that the LV on-board electrical branch (LV) has a positive supply potential (L+) and a negative supply potential (L-) corresponding to the ground potential (M) of the vehicle on-board electrical system. The HV on-board electrical branch (HB) has a positive HV potential (+) and a negative HV potential (-), which are electrically isolated from the potentials of the LV on-board electrical branch (LB). An insulation fault (RF) between at least one of the HV potentials (-, +) and the positive LV potentials (L+, G+) is detected by identifying the current (I) flowing through a voltage limiting circuit (SG) connected between the ground potential (M) and the positive LV potentials (L+, G+).

Description

Background Technology

[0001] It is known that vehicles are equipped with electric drives or other electrical components. To achieve high performance, especially for traction, high voltages of, for example, 400 volts or higher are used, which can be dangerous to humans compared to the otherwise typical 12-volt onboard electrical system.

[0002] For this reason, vehicles with high-voltage onboard electrical systems (that is, high-voltage onboard electrical systems, i.e., HV onboard electrical systems) are equipped with insulation that isolates the HV onboard electrical system from the rest of the onboard electrical system and the ground potential, especially the vehicle chassis electrical ground.

[0003] Because faults in the insulation can lead to contact voltage, which, while not fatal, is harmful to humans, additional mechanisms are in place to monitor such insulation. This insulation monitoring detects the two HV potentials of the HV electrical grid relative to ground, in order to determine the insulation resistance relative to ground (chassis). However, if a high-resistance insulation fault exists, a portion of the low-voltage on-board electrical grid may undetectably connect to a dangerous HV potential. Summary of the Invention

[0004] The objective of this invention is to elucidate a feasible solution for detecting insulation faults between HV vehicle electrical grid branches and low-voltage vehicle electrical grid branches (LV vehicle electrical grid branches), especially even if the insulation fault is of high resistance.

[0005] This task is solved by a method for detecting insulation faults in a vehicle's onboard electrical network. The vehicle's onboard electrical network has an HV onboard electrical network branch and an LV onboard electrical network branch, wherein the LV onboard electrical network branch has a positive supply potential and a negative supply potential corresponding to the ground potential of the vehicle's onboard electrical network, and the HV onboard electrical network branch has a positive HV potential and a negative HV potential, the positive and negative HV potentials being electrically isolated from the potential of the LV onboard electrical network branch. An insulation fault between at least one of the positive and negative HV potentials and the positive LV potential is detected by identifying the current flowing through a voltage-limiting circuit connected between the ground potential and the positive LV potential. Further features, embodiments, characteristics, and advantages will become apparent from the accompanying drawings and the description below.

[0006] It is recommended that a voltage limiting circuit be installed in the LV (low-voltage) vehicle electrical network branch (corresponding to the low-voltage vehicle electrical network branch), so that the current flowing through this circuit indicates that the HV potential is connected to the supply potential of the LV vehicle electrical network branch. For example, communication components, control components, or sensor components within the LV vehicle electrical network branch may come into contact with the HV potential due to an insulation failure. However, depending on the component, these components may burn out without noticeable or detectable current flow, so that although the LV potential is not in contact with the remaining LV vehicle electrical network branch due to the burned-out component, the LV vehicle electrical network wiring or other components still guide the HV potential. Therefore, the voltage limiting circuit provides a stable and reliable component that induces a detectable and reliable current flow when the HV potential comes into contact with the potential of the LV vehicle electrical network branch due to an insulation failure. When the wiring of a low-voltage sensor device (or other LV device) connected to an LV vehicle electrical grid branch comes into contact with the HV potential due to an insulation fault, the input stage of the sensor device connected to the sensor wiring (more commonly, the data- or measurement interface) may burn out undetectably, resulting in no current flowing between the HV and LV vehicle electrical grid branches. However, the sensor wiring remains at the HV potential due to the insulation fault, and there is no detectable current flowing through it due to the burnt-out input stage. The HV potential can then reach other components via this sensor wiring, especially since the sensor device and its wiring are not designed for high-voltage applications and therefore lack the corresponding insulation. A similar situation applies to the communication—or controller—of the LV vehicle electrical grid branch and their interfaces.

[0007] The method proposed herein allows for the targeted generation of a current through a voltage-limiting circuit. This current is unrelated to the burnout behavior of interfaces such as those of sensor devices, communication devices, or controllers, or to other components of the LV on-board electrical network branch when the HV potential reaches them. The voltage-limiting circuit can detect and reliably identify the current, indicating that the HV potential is being applied to components of the LV on-board electrical network branch.

[0008] Voltage limiting circuits are particularly well-suited to the voltage of HV on-board electrical networks, unlike LV components. This suitability is exemplified by an implementation where a limited current is directed through the voltage limiting circuit when an HV voltage (between HV+ and HV-, or between ground and HV+ or HV-) is applied. Even if no detectable current flows due to an insulation fault, the processing described herein can particularly identify when an HV potential is applied to a component (e.g., a control, communication, or sensor component) of an LV on-board electrical network branch. For example, active measurement of insulation resistance cannot reliably detect such sensor faults, especially when a component in the LV component is burned out, preventing a connection from being provided between the line (low voltage) connected to that component and the remaining LV on-board electrical network branches. The terms "LV component" and "LV device" (e.g., in control, communication, or sensor devices) are synonymous herein.

[0009] Therefore, a method for detecting insulation faults in a vehicle's onboard electrical system is described. The vehicle's onboard electrical system here has HV onboard electrical system branches and LV onboard electrical system branches. HV onboard electrical system branches can also be referred to as high-voltage onboard electrical system branches. LV onboard electrical system branches can also be referred to as low-voltage onboard electrical system branches. The prefix "high voltage" or "HV" defines a component or onboard electrical system branch or section thereof operating at an operating voltage greater than 60 volts, particularly at least 200, 400, 600, 800, or 100 volts. Contact with the operating voltage is dangerous for a person. The prefixes "LV" and "low voltage" are synonymous and mean operating voltages less than 60 volts, particularly, for example, 12 to 14 volts, essentially 24 volts, or essentially 48 volts. No special measures are required to avoid contact with these operating voltages.

[0010] The LV (Low Voltage) on-board electrical grid branch has a positive supply potential and a negative supply potential. The negative supply potential corresponds to the ground potential of the vehicle's on-board electrical grid, particularly the chassis potential. The HV (High Voltage) on-board electrical grid branch has a positive and a negative HV potential. These two HV potentials are electrically isolated from the potentials of the LV on-board electrical grid branch. This electrical isolation is primarily based on (electrical) insulation, whereby it is explained how faults in this insulation can be detected. The HV potentials do not have a reference ground potential, so as to avoid dangerous currents upon contact.

[0011] Detect insulation faults between at least the HV potential and the positive LV potential. The positive LV potential here refers to the LV potential that is positive relative to ground as a supply potential, as well as potentials that are not ground, such as signal potentials like control, data, or measurement signals, because they are typically positive relative to ground. However, these potentials can also be negative relative to ground, at least temporarily, depending on the specific design of the vehicle electrical system and the signals transmitted.

[0012] The HV potential is the supply potential. The LV potential can be the positive LV supply potential as mentioned, but it can also be the potential of a conductor, such as a sensor, communication, or control conductor, or other component. Insulation faults are detected by identifying the current flowing through a voltage-limiting circuit. This voltage-limiting circuit is connected between the ground potential and the positive LV potential (that is, the potential to be monitored). The voltage-limiting circuit is configured to not conduct below the breakdown voltage and conduct above this voltage. Thus, the current indicates an excessively high voltage, that is, a voltage above the breakdown voltage of the voltage-limiting circuit.

[0013] This breakdown voltage is greater than the maximum operating voltage or rated voltage of the LV on-line electrical branch, so current only flows when there is an excessively high voltage at the positive LV potential relative to ground. Excessive voltage here refers to a voltage exceeding the breakdown voltage, particularly exceeding a predetermined value or exceeding the maximum operating voltage of the LV on-line electrical branch. Because the voltage limiting circuit is equipped with a special characteristic—a current flowing above a specific breakdown voltage—that components or devices such as sensor evaluation circuits, communication circuits, control circuits, and the like do not necessarily need to have, excessively high voltages at the positive LV potential can be reliably identified by means of the voltage limiting circuit, even if otherwise no current flows from the HV on-line electrical branch to ground; that is, the fault cannot be definitively identified even by active insulation resistance measurement. In particular, the associated interfaces (through which the wiring connects to the associated components) do not perform reliably under overvoltage, especially since these interfaces are designed for low voltage (<60 V).

[0014] One implementation specifies that the current is identified by the offset of one HV potential relative to the ground potential. This is determined by a passive voltage measurement of the HV potential relative to the ground potential. Alternatively, only the HV potential relative to the ground potential can be measured. The HV potential can be determined, in particular, by detecting the voltage between HV potentials and by subtracting the voltage between other HV potentials and the ground potential.

[0015] When an insulation fault exists between the HV potential and the positive LV potential, the voltage limiting circuit selectively generates a shift of at least one HV potential relative to the ground potential through the current flowing through it. Without the voltage limiting circuit, this is related to the characteristics of the LV component with a positive LV potential at that location, particularly whether these components generate a reliable current flowing through them when overvoltage occurs at the LV potential, or whether they do not generate a corresponding current flowing through them when the voltage is too high at the LV potential due to the burnout of a component (the LV component's interface or the LV component itself) or a fuse.

[0016] Furthermore, the current flowing through the voltage-limiting circuit can be identified by means of a potential change rate exceeding a predetermined value. The potential change rate indicates the extent to which the Cy capacitor (parasitic or dedicated filter capacitor) is recharged when a current is present. The predetermined value (used to identify the current) specifically exceeds a value that represents the maximum potential change rate observed during active insulation measurements. The potential change rate is specifically the rate at which the voltage between an HV potential and the ground potential changes over time. Here, the predetermined value can be at least 100 volts / ms, 500 volts / ms, 100 volts / ms, or at least 100 volts / μs. When the potential change rate is below the predetermined value, no current is identified according to the method specified herein.

[0017] Alternatively or in combination, the current can be identified by the magnitude of the potential difference, which is generated by a change, that is, the potential difference generated after the change. This corresponds to the static case of potential change, that is, the potential difference after the potential change. Therefore, the current can be identified by the change in the potential difference between the HV potential and the ground potential. When the generated potential difference is lower than a predetermined value, the current can be detected. It is preferable that this potential difference can be detected when the voltage between the HV potentials is within a standard range. The standard range here corresponds, for example, to the standard operating voltage. The predetermined value here can be, for example, a maximum of 60 volts, 50 volts, 30 volts, or 20 volts, especially a maximum of 20 volts or 16 volts. In an exemplary embodiment, the predetermined value is approximately 60 volts, 50 volts, or 40 volts, or 20 V or 16 V. Preferably, the predetermined value is lower than the minimum value that occurs during active insulation measurement.

[0018] One implementation specifies that the offset is identified by means of an insulation monitor or by means of at least one voltmeter, which is part of or connected to the insulation monitor.

[0019] It can be specified that the insulation monitor also performs active insulation testing on the HV on-board electrical grid branch. This is done by actively recharging or discharging (or charging) the Cy capacitor between the ground wire on one side and the HV potential on the other side. The Cy capacitor can be assembled from parasitic capacitance and a dedicated filter, such as that used in EMV filters. Since the size of the Cy capacitor is essentially known, a potential change rate (between the ground wire on one side and at least one HV potential on the other side) is generated by means of an equally known current for active recharging or discharging, which characterizes the insulation resistance. The active insulation test is therefore a test of the rate of discharge or charging of the Cy capacitor when a test current is applied. The test current is preferably generated or at least controlled by the insulation monitor. The active insulation test also specifies the detection of a potential shift due to recharging. This involves the shift of the HV potential relative to the ground wire. Because the insulation monitor detects the potential shift of the HV potential relative to the ground potential, this insulation monitor can also be used to identify the current flowing through the voltage limiting circuit.

[0020] On the other hand, when an outflow current through the voltage limiting circuit is detected, active recharging or discharging is interrupted by the insulation monitor. The outflow current can be identified in particular by means of the potential shift caused by the outflow current through the voltage limiting circuit. At least one voltmeter can be used, which can also be used for active insulation testing by the insulation monitor, or at least one voltmeter can be used that is not evaluated by the insulation monitor.

[0021] During active recharging, the potential difference between one of the HV potentials and the ground potential preferably does not drop below the minimum voltage. This is especially true for their values. The minimum voltage for an HV on-board electrical branch with a nominal voltage of 800 V is, for example, at least 60 V or 100 V. The minimum voltage caused by active insulation testing is at least 7%, 8%, 10%, or 15% of the rated voltage of the HV on-board electrical system. The current flowing through the voltage limiting circuit is preferably identified by the change in the potential difference between the HV potential and the ground potential, which is below a predetermined value. This value is particularly less than the minimum voltage. In an HV on-board electrical branch with a nominal voltage of 800 V, this value is, for example, at a maximum of 15 volts, 16 volts, 20 volts, or 25 volts, and if necessary, 30 volts, 40 volts, or 50 volts (especially less than 60 volts). The range from which the minimum voltage is selected is higher than the range from which a predetermined value is selected.

[0022] Therefore, in other words, although the insulation monitor is recharged (involving the Cy capacitor) during active insulation resistance measurement and a minimum voltage is generated, no voltage value (=predetermined value) related to the current flowing through the voltage limiting circuit is generated during active insulation measurement. When current flows through the voltage limiting circuit, more precisely, a current flows through which a potential difference is generated that is smaller than the minimum voltage that occurs during common active insulation resistance measurements (simply put, insulation measurements) (e.g., smaller than a predetermined gap). This allows for the differentiation of different measurements and the output of different fault types: a first fault is output when the voltage value is below the predetermined value, and a second fault is output when the insulation resistance measurement results in a resistance value below the resistance limit.

[0023] It can be specified that the current flowing through the voltage limiting circuit is identified by measuring at least one voltage between at least one potential in the HV potential on one side and at least one voltage between the ground potential on the other side. At least one voltmeter is used here, which is connected to or is part of the insulating rectifier. Alternatively, at least one voltmeter that can be evaluated by its own evaluation circuit can be used. This voltmeter does not have a direct signal transmission connection to the insulation monitor. In other words, it can be specified that the voltmeter used here is not evaluated by the insulation monitor.

[0024] When determining the potential difference resulting from the current flowing through the voltage-limiting circuit, this can be accomplished by at least one voltmeter and its own evaluation circuit connected to the voltmeter, which is at least logically separate from the insulation monitor. The associated voltmeter and evaluation circuit thus form a self-contained unit, for example housed within a high-voltage housing, which also contains other components of the high-voltage vehicle power grid branch, such as HV switches and / or HV batteries, and, if necessary, HV transformers and / or HV charging circuits.

[0025] When an insulation fault is identified by identifying the current flowing through the voltage limiting circuit, at least one of the following measures can be performed. As a measure, it can be specified that the high-voltage battery of the HV vehicle-mounted power grid branch is isolated from the other HV vehicle-mounted power grid branches by means of a disconnect switch. It can also be specified that at least one Cy filter capacitor of the HV vehicle-mounted power grid branch, especially the Cy filter capacitor of the inverter and / or traction motor, is isolated. Alternatively or additionally, it can be specified as a measure that the charging pile connected to the HV vehicle-mounted power grid is isolated. Furthermore, it can be specified as a measure that the HV vehicle-mounted power grid branch is discharged (especially toward ground potential). Finally, it can be specified as a measure that the HV vehicle-mounted power grid sub-branch is isolated from the inverter HV vehicle-mounted power grid sub-branch. Here, the inverter-HV vehicle-mounted power grid sub-branch has a traction inverter. This can be specified in particular by isolating the inverter-HV vehicle-mounted power grid sub-branch. The inverter-HV vehicle-mounted power grid sub-branch has a traction inverter and / or a motor for traction vehicles.

[0026] If, for example, the Cy filter capacitor is isolated upon detection of an insulation fault, then although a worse EMV filtering characteristic is produced, this isolation avoids the generation of excessively high contact voltages.

[0027] It can be specified that the voltage limiting circuit is connected between the ground potential and the positive LV potential (under normal circumstances) that guides the positive supply potential of the LV vehicle electrical network, and the current passing through the voltage limiting circuit is identified.

[0028] Furthermore, it can be specified that the voltage limiting circuit is connected between the ground potential and the (positive) LV potential, which is the line potential of the LV vehicle electrical network, and the current flowing through the voltage limiting circuit can be identified. This line potential can be the potential of the sensor line, communication line, or control line.

[0029] The LV device can be connected to the ground potential and the positive supply potential of the LV vehicle electrical network branch. This connection can be established via a first connection side. Furthermore, at least one line in the circuit can be connected, for example, to another connection side, such as to the interface of the LV device, wherein this line can have a (positive) LV potential (or a potential different from ground). Multiple lines can be connected to this side, wherein at least one of the lines has a generally positive LV potential different from ground. This can be, for example, a signal line. A voltage limiting circuit can be connected between the ground potential and a conductor, such as a conductor of a sensor line or a communication line. According to one embodiment, the line connected to the voltage limiting circuit does not necessarily have to be a positive LV potential in the sense of a positive supply potential, but can be, for example, a signal line.

[0030] An LV device can be an LV communication device, such as a CAN bus circuit, or an LV sensor device, such as a temperature, current, or voltage measurement unit. Alternatively, an LV device can be an LV controller. Here, the LV potential connected to the circuit or voltage limiting circuit can be a control line or a conductor, which is part of the control line.

[0031] Finally, the voltage limiting circuit can incorporate a varistor, a gas discharge protection device, a spark gap, a protection diode, a thyristor circuit, a DIAC, a Zener diode, and / or a four-layer diode to measure the current flowing through the voltage limiting circuit. The voltage limiting circuit is typically configured to conduct above the limiting voltage (= breakdown voltage) and not conduct below the limiting voltage. Therefore, the current flowing through the circuit indicates an excessively high voltage, that is, a voltage exceeding the limiting voltage or breakdown voltage. The aforementioned components can also be incorporated into any combination of voltage limiting circuit components.

[0032] The voltage limiting circuit can be connected between the ground potential and the LV potential and can be connected to a section of the LV vehicle electrical network branch via a fuse, in which the low-voltage battery is located. The fuse may thus burn out in the event of a faulty insulation, while the voltage limiting circuit also provides a current through which the insulation resistance decreases; this current can be detected and faults can be output by means of this current. The fuse then protects the LV equipment and, in particular, the LV equipment interface, which is connected via the fuse.

[0033] Furthermore, an on-board electrical network can be configured to implement the method, particularly by designing the on-board electrical network for detecting insulation faults in the vehicle's on-board electrical network. This on-board electrical network has an HV on-board electrical network branch and an LV on-board electrical network branch. The LV on-board electrical network branch has a positive supply potential and a negative supply potential, wherein the negative supply potential corresponds to the ground potential (M) of the vehicle's on-board electrical network. The HV on-board electrical network branch has a positive HV potential and a negative HV potential, electrically isolated from the potential of the LV on-board electrical network branch. The on-board electrical network is also designed to detect insulation faults between at least one HV potential and the positive LV potential by identifying the current flowing through a voltage-limiting circuit, wherein the on-board electrical network has such a voltage-limiting circuit connected between the ground potential and the positive LV potential. Furthermore, the on-board electrical network can have the device features mentioned within the scope of the method described herein, and the on-board electrical network can be configured to implement the features of the method described herein. Attached Figure Description

[0034] Figure 1 This is used to explain the methods described herein in more detail and to illustrate an onboard electrical grid circuit for implementing the methods. Detailed Implementation

[0035] Figure 1 A vehicle on-board electrical network FB with a low-voltage battery NA is shown. This low-voltage battery is connected to the HV (High Voltage) on-board electrical network branch HB via a low-voltage converter. The HV on-board electrical network branch LB is connected to the LV (Low Voltage) on-board electrical network branch LB via a converter NW, and the low-voltage battery NA is also located in this LV branch. A high-voltage battery HA is located in the high-voltage on-board electrical network branch HB, and this high-voltage battery is connected via a disconnector TS and a battery connector BA. The battery connector BA is located between the high-voltage battery HA and the disconnector TS. The disconnector is designed to be two-pole.

[0036] Furthermore, Cy capacitors Cy1 and Cy2 are located in the high-voltage vehicle electrical network HB. These Cy capacitors are positioned between the ground potential M and the negative HV potential HV-, or between the ground potential M and the positive HV potential HV+. In the low-voltage vehicle electrical network branch LB, a negative LV potential L- corresponding to the ground potential M is provided. The ground potential M preferably corresponds to the vehicle's chassis potential. Similarly, a positive LV potential L corresponding to the supply potential is provided.

[0037] The HV vehicle electrical grid branch supplies two supply potentials, L- and L+, to low-voltage devices NG, such as sensor evaluation circuits. The sensor evaluation circuit also includes a line L with a positive LV potential G+ and a negative LV potential G-. Potential G- can correspond to potential L- or M. The positive potential G+ is a positive line potential, but can typically be a line potential, such as the potential of a signal conductor. The low-voltage device NG can also be referred to as an LV device.

[0038] As shown, line L can continue and lead to other components, such as other sensors. The low-voltage device NG can be, for example, a communication device, such as a CAN bus circuit, to which multiple other components are connected. The line can be led from the housing of the HV component and, in particular, to the area containing the LV component or a conductor with a ground potential. This is critical if the line is directed to the HV potential, as this line may come into contact with ground or the LV component, especially since the line is designed for LV applications and therefore does not have the insulation found in the HV component.

[0039] To prevent insulation faults from propagating to potential G+, which typically extends to the signal potential of the LV on-board electrical branch LB, a voltage limiting circuit SG is provided. If an insulation fault exists in the form of a related resistor RF (see the dotted line connection), then this faulty insulation resistor connects the positive HV potential + to potential G+ and thus to the conductor or line L, which belongs to the LV on-board electrical branch and can lead to other components. This can also load other components of the LV on-board electrical system with the HV potential +, resulting in potentially dangerous contact voltages at other LV components.

[0040] The voltage limiting circuit SG is used to selectively and predictably generate a through current I when the HV potential (+) enters the LV vehicle electrical network LB due to an insulation fault RF. The through current I is shown by a dashed line. On the one hand, it can detect the potential shift generated between the ground potential M and one of the HV potentials (+ or -). On the other hand, the through current I can also be detected by an ammeter. Preferably, the shift is detected by observing the rate of change due to the sudden appearance of the insulation resistance RF. This rate of change is significantly faster than the rate of change of the + or - potential relative to M caused by the test current during active insulation resistance measurement. Furthermore, due to the voltage limiting circuit and its breakdown voltage (from which the voltage limiting circuit conducts), another potential shift of the HV potential (+ or -) relative to the ground potential M is generated. This shift is particularly large than that occurring during recharging or discharging during active insulation resistance measurement, and it also occurs faster (i.e., with a higher rate of voltage change). Here, the voltage obtained corresponding to the breakdown voltage of the voltage limiting circuit can be clearly separated from the minimum voltage generated to the minimum extent during active insulation resistance measurement.

[0041] The breakdown voltage of the voltage limiting circuit is slightly less than the minimum voltage observed during active insulation resistance measurement. This allows for the detection of faults separately, especially as shown in the diagram (connection between the HV+ and LV signal lines).

[0042] An insulation monitor IM can be configured. This insulation monitor can be connected to voltmeters V1 and V2, which detect the voltage between HV potential + and ground potential M or HV potential - and ground potential M. The insulation monitor IM can actively measure the insulation resistance using these voltmeters. Furthermore, these voltmeters V1 and V2 can also be specified to implement the methods described herein, for example, by measuring the rate of change of potential or the observed potential shift. However, it is preferable to use voltmeters independent of the insulation monitoring circuit IM, wherein an evaluation circuit is connected to these voltmeters, and the voltmeters and evaluation circuit are configured to implement the methods described herein for active insulation resistance measurement independent of the insulation monitoring circuit IM.

[0043] Finally, the charging device LG is shown, which connects to the charging connector LA via a three-phase cable. The charging station LS can be connected to the charging connector LA.

[0044] If current is detected as described, it can be specified that the disconnect switch TS is opened, thereby disconnecting the HV battery HA. As an alternative or additional option, it can be specified that the charging circuit LG suppresses or interrupts the charging process. Furthermore, it can be specified that active insulation resistance measurement is prohibited by applying a test current for detecting insulation resistance through the insulation monitoring circuit IM.

[0045] Finally, it should be noted that the insulation monitoring circuit IM monitors the insulation resistance between potential M on one side and potentials + and - on the other side, specifically by actively applying a test current and determining the corresponding expected potential shift. This active insulation resistance measurement differs from detecting the current I passing through the voltage limiting circuit SG, because the latter identifies an insulation fault in the high-voltage vehicle-mounted grid branch HB relative to the low-voltage vehicle-mounted grid branch LB or line L even when the connection between potentials G+ and L+ is broken (e.g., a burnt-out transistor in the low-voltage equipment NG).

[0046] An insulation fault (RF) can be considered as a state and the resistor that triggers this state.

Claims

1. A method for detecting insulation faults in a vehicle's onboard electrical network, the vehicle's onboard electrical network having an HV onboard electrical network branch (HB) and an LV onboard electrical network branch (LB), wherein, The LV on-board electrical grid branch (LB) has a positive supply potential (L+) and a negative supply potential (L-) corresponding to the ground potential (M) of the vehicle on-board electrical grid, and the HV on-board electrical grid branch (HB) has a positive HV potential (+) and a negative HV potential (-), the positive and negative HV potentials (+, -) being electrically isolated from the potential of the LV on-board electrical grid branch (LB), wherein an insulation fault (RF) between at least one of the positive and negative HV potentials (+, -) and the positive LV potential (L+, G+) is detected by identifying the current (I) flowing through a voltage limiting circuit (SG), the voltage limiting circuit being connected between the ground potential (M) and the positive LV potential (L+, G+), wherein the voltage limiting circuit is configured to not conduct below the breakdown voltage and conduct above the voltage.

2. The method according to claim 1, wherein, The through current (I) is detected by means of the offset of one of the positive and negative HV potentials (+, -) relative to the ground potential (M).

3. The method according to claim 2, wherein, The current (I) passing through is identified by means of a potential change rate higher than a predetermined value.

4. The method according to claim 2 or 3, wherein, The through current (I) is identified by the change in the potential difference between one of the positive and negative HV potentials (+, -) and the ground potential, which is below a predetermined value, wherein such a potential difference occurs when the voltage between the positive and negative HV potentials (+, -) is within a standard range.

5. The method according to claim 2 or 3, wherein, The offset is identified using an insulation monitor (IM).

6. The method according to claim 5, wherein, The insulation monitor further performs active insulation testing on the HV vehicle electrical grid branch (HB) by actively recharging the Cy capacitors (Cy1, Cy2) between the ground potential (M) on one side and the positive and negative HV potentials (+, -) on the other side and detecting the potential shift caused by the recharging, wherein the active recharging is interrupted when an through current flowing through the voltage limiting circuit (SG) is detected.

7. The method according to claim 6, wherein, During active recharging, the potential difference between one of the positive and negative HV potentials (+, -) and the ground potential does not drop below the minimum voltage caused by active insulation testing, and the through current (I) flowing through the voltage limiting circuit (SG) is identified by the change in the potential difference between one of the positive or negative HV potentials (+) and the ground potential, which is below a predetermined value, wherein the predetermined value is less than the minimum voltage.

8. The method according to claim 5, wherein, The current (I) flowing through the voltage limiting circuit (SG) is identified by measuring at least one voltage between at least one of the positive and negative HV potentials (+, -) on one hand and the ground potential (M) on the other hand, using at least one voltmeter (V1, V2) connected to the insulation monitor (IM) or by means of at least one voltmeter evaluated by the evaluation circuit and not directly connected to the insulation monitor (IM), wherein the evaluation circuit is at least logically separate from the insulation monitor.

9. The method according to any one of claims 1 to 3, wherein, When the insulation fault is identified by identifying the current (I) flowing through the voltage limiting circuit (SG), at least one of the following measures shall be performed: The high-voltage battery (HA) of the HV vehicle electrical grid branch (HB) is isolated from the other HV vehicle electrical grid branches (HB) by means of a disconnect switch (TS); At least one Cy filter capacitor is used to separate the HV vehicle electrical network branch (HB); The charging pile is isolated from the HV vehicle-mounted electrical grid branch (HB); Discharge the HV vehicle-mounted electrical grid branch (HB); The HV vehicle-mounted power grid sub-branch is separated from the inverter HV vehicle-mounted power grid sub-branch with traction inverter.

10. The method according to any one of claims 1 to 3, wherein, The voltage limiting circuit (SG) is connected between the ground potential (M) and the positive LV potential (L+), which is the positive supply potential of the LV vehicle electrical grid branch (LB), and identifies the current (I) passing through the voltage limiting circuit.

11. The method according to any one of claims 1 to 3, wherein, The voltage limiting circuit (SG) is connected between the ground potential (M) and the positive LV potential (G+), which is the positive line potential of the LV vehicle-mounted power grid branch (LB), and identifies the current (I) passing through the voltage limiting circuit.

12. The method according to claim 11, wherein, The LV device (NG) is connected to the ground potential and to the positive supply potential (L+) of the LV vehicle electrical grid branch (LB), and wherein a line (L) is connected to the LV device, wherein at least one of the lines has a positive LV potential (G+).

13. The method according to claim 12, wherein, The LV device (NG) is an LV communication device, an LV sensor device, or an LV controller.

14. The method according to any one of claims 1 to 3, wherein, The voltage limiting circuit (SG) includes a varistor, a gas discharge protection device, a spark gap, a protection diode, a thyristor circuit, a DIAC, a Zener diode, and / or a four-layer diode. The current (I) passing through the voltage limiting circuit is measured.

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