Capacitive function test for varistors in high-voltage protection devices for onboard vehicle electrical systems

Abstract

The present invention relates to a method for testing the proper function of a high-voltage protection device for an onboard vehicle electrical system. The protection device includes a varistor or other voltage limiting element. According to the method, a capacitive component of the AC impedance of the varistor or voltage limiting element is detected. Additionally, the capacitive component is compared with a nominal capacitance value, wherein the nominal capacitance value characterizes the capacitance of the operating varistor or voltage limiting element. If the comparison result determines that the capacitive component deviates from the nominal capacitance value by a predetermined amount, the varistor or voltage limiting element is determined to be in a defective state. Furthermore, the present invention relates to a high-voltage protection circuit for a vehicle and a high-voltage onboard vehicle electrical system.

Description

Background Technology

[0001] It is known that an electric drive unit powered by a battery is mounted in a vehicle. Here, in addition to a DC-DC voltage converter, an inverter is also provided, and a charging circuit connecting the drive unit and the battery is also provided within the onboard vehicle electrical system. On the one hand, since these components are high-voltage components to reach high power, they must operate at a nominal voltage exceeding 60V, for example, 400V or 800V. This requires enhanced safety measures, which are provided, for example, by high-voltage insulators, and specifically by a high-voltage onboard electrical system galvanically isolated from the low-voltage compartment of the onboard electrical system. On the other hand, these high-voltage components, which use low-voltage signals, need to be monitored or controlled. These low-voltage signals are exchanged via a line extending from the high-voltage onboard electrical system branch to the low-voltage compartment.

[0002] This was found to lead to the purpose of providing an option to make these low-voltage lines safe against dangerous high-voltage potentials.

[0003] The objective is achieved by the subject matter of the independent claim. Additional characteristics, features, embodiments, and advantages are revealed from the dependent claims, description, and drawings.

[0004] It is proposed to provide a high-voltage protection device for an onboard vehicle electrical system that is protected from high-voltage potentials through a varistor or other voltage limiting element. This may occur for one reason in that the varistor (or other voltage limiting element) itself discharges a dangerous high-voltage potential to a reference potential and / or provides current flow (which can be safely detected through additional measures, such as an insulation monitor) caused by the dangerous high-voltage potential (in a low-voltage line) through the varistor (or other voltage limiting element). Here, the varistor (or other voltage limiting element) is used for protection in that conduction is initiated when a high-voltage potential appears at a point in the onboard electrical system that would not occur under fault-free conditions.

[0005] Varistors and other voltage limiting elements have the characteristic that, as components, the voltage applied to the relevant component conducts when the voltage exceeds a threshold voltage (or breakdown voltage) and does not conduct otherwise. This threshold voltage exceeds, for example, 20V or 40V. Additionally, these components have the characteristic of having different capacitance characteristics in a defective state (e.g., a state where the rated capacitance value exists) than in a defective state (e.g., after overloading or after exceeding aging limits). These components may be provided by varistors (as mentioned) or by voltage limiting elements such as gas discharge tubes, spark gaps, protection diodes, thyristor circuits, DIACs, Zener diodes, and / or 4-layer diodes. In the following, characteristics, features, and embodiments applicable to both the varistors and other voltage limiting elements mentioned herein are described. In particular, the term "varistor" is used to refer to a varistor (component), gas discharge tube, spark gap, protection diode, thyristor circuit, DIAC, Zener diode and / or 4-layer diode, or other components having the characteristics mentioned in the introduction.

[0006] Since the function of the aforementioned varistors is critical for protection, the function of these varistors is tested as claimed in the subject matter of the claim. This is done by determining the varistors and their capacitances, as it is possible to determine whether the varistors are in a defective or non-defective state based on their capacitances. The known characteristics of the varistors are known, for example, because the capacitance in a non-defective state is known in the varistor's datasheet. If a high voltage is supplied to the varistors to conduct, the varistors may be damaged, for example, by an excessively high current flow (i.e., a current higher than the maximum current specified by the design), and the varistors may no longer operate correctly. If a voltage below the varistor's threshold voltage is used, this cannot be reliably tested because the varistors do not conduct when the voltage is too low (below the threshold), and the resistance is too high (regardless of the applied voltage) when the varistors are in a defective state. Testing with high voltage (exceeding the threshold voltage) hides the danger of dangerous contact voltage.

[0007] However, using the capacity test proposed in this specification, the function of the varistor can be determined without applying a high test voltage exceeding a threshold value, and accordingly, the conductivity starting (in a defect-free state) can be tested.

[0008] Accordingly, a method for testing the function of a high-voltage protection device (abbreviated as: protection circuit) for an onboard vehicle electrical system is described, wherein the high-voltage protection device comprises a varistor. Here, the capacitance of the varistor is determined, and based on this capacitance, it can be inferred whether the varistor is operating, or whether the varistor is in a defective or non-defective state. Thus, the capacitive component of the varistor's AC impedance is detected. For example, after detecting this through active measurement, the detected capacitance component is evaluated and, in particular, compared with the rated capacitance value. Here, for example, a difference may be formed between the detected capacitance component and the rated capacitance value (a value provided in a non-defective state of the varistor), or the capacitance component is compared with the capacitance interval, which is a characteristic range of the varistor in a non-defective state (e.g., considering manufacturing tolerances). The rated capacitance value is a characteristic of the capacitance of an operating varistor, i.e., a varistor in a non-defective state; The corresponding interval is a characteristic of the capacitance or capacitance range of the operating varistor.

[0009] If the comparison result determines that the capacitive component deviates by a predetermined amount from the rated capacitance value, the varistor is determined to be in a defective state. This rated value may be provided, for example, by the limit of the capacitance gap, which is a characteristic of the capacitance of the operating varistor. In this case, comparing with the limit value corresponds to comparing the detected capacitive component with the gap defined by the limit value. The following describes the comparison with the rated capacitance value in a simplified manner, where this may involve comparing with a single value, comparing with the limit of the gap representing the operating varistor, or comparing with a value within this gap.

[0010] The predetermined size reflects the extent to which a component of the rated capacitance value deviates from the rated capacitance value but achieves a defect-free state, or reproduces the limit where exceeding it is presumed to indicate a defect in the varistor. This size is also used to account for detection or measurement errors and manufacturing tolerances of the varistor to avoid false assumptions that the varistor is defective due to conventional measurement or detection errors, or when the rated capacitance value typically spreads.

[0011] Detection can be performed through an active measurement process in which an AC signal is applied to a varistor and then the AC voltage signal generated in the varistor is detected. Capacitance, or the capacitive component, arises due to the relationship between the AC signal and the AC voltage signal applied in a known manner. Additionally, a complementary measurement is possible in which an AC voltage signal is applied to the varistor and the related AC signal applied to the varistor is detected. When an AC signal is applied, the AC voltage directly applied to the varistor can be determined, or a voltage that varies depending on the voltage applied to the varistor can be determined, and an AC voltage signal can be formed from this voltage. When an AC voltage signal is applied to the varistor, the AC signal can be detected in that the current flowing through the varistor itself is detected, or in that the voltage applied to the shunt (which corresponds to AC) is determined with the help of a shunt resistor for measuring the current. Both AC voltage signals and alternating current signals are directly measured signals, or signals can be derived from them, particularly using amplifiers, voltage dividers, shunt resistors, etc.

[0012] As mentioned, the capacitive component can be actively measured, that is, by applying an excitation signal (applying an AC signal or an AC voltage signal) and detecting an AC voltage signal or an AC signal generated therefrom that reflects the response to the excitation signal. In the case of multiple varistors, each varistor may be provided with its own device for active detection, or a single identical detection device may be used via multiplexing, wherein this common device is connected alternately or sequentially to various varistors to return the capacitive component. Thus, the capacitive component of the varistor may be detected using individual devices (e.g., one per varistor). Each varistor or a subgroup thereof may be provided with its own signal source (a current or voltage source for the applied AC voltage signal or AC signal). Alternatively, or in combination with this, each varistor or a subgroup thereof may be provided with its own measurement device that detects the resulting signal (an AC voltage signal when AC is applied, and an AC signal when AC voltage is applied). Accordingly, there is a separate measurement device for each varistor or its subgroup, and this measurement device detects the resulting signal present in the associated varistor.

[0013] An option for detecting the capacitive components of multiple varistors by signal multiplexing is described below. Here, the capacitive components of multiple or all varistors are detected continuously using the same device, particularly using signal multiplexing. It may be provided that the same signal source applies an AC signal to all varistors or a subgroup thereof. This may occur continuously through a multiplexing device, or the AC signal (or AC voltage signal) may be applied simultaneously to all varistors or a subgroup thereof. Alternatively, or in combination with this, the same measurement device may detect the resulting signal particularly continuously from all varistors or a subgroup thereof. When detecting the resulting signal of the varistors continuously, it is desirable to also use signal multiplexing during the measurement. Furthermore, since it is possible to determine that at least one of the varistors is defective by detecting a rapid increase in the capacitive component even in the case of multiple varistors, the same device may detect the resulting signal simultaneously (without signal multiplexing) from all varistors or a subgroup thereof. As a result, signal multiplexing may not be necessary. In particular, using signal multiplexing during measurement has the advantage of not only being able to detect whether at least one of the varistors is defective, but also which varistor is defective. Therefore, detection can be performed on a per-varistor basis and is not limited to subgroups or all varistors.

[0014] Preferably, the method is performed for a varistor that connects the potential of a low-voltage line to the onboard vehicle electrical system ground. This low-voltage line originates from a high-voltage zone and, if there is a defect in the insulator within the high-voltage zone (relative to ground), can deliver a voltage too high to trigger the varistor (i.e., the varistor may become partially or completely conductive). This relates particularly to a varistor or all varistors in which a capacitive component is detected. In particular, this relates to a varistor in which the detected capacitive component is compared to a rated capacitance value. In other words, the varistor in which the state is determined is preferably connected to a reference potential, such as the onboard vehicle electrical system ground. This connection is preferably indirect, that is, routed through at least one impedance having an inductive and / or ohmic resistance component. Thus, the method can be performed for a varistor connected to a reference potential (e.g., onboard vehicle electrical system ground) through an inductance and / or resistor. In particular, when the varistor on which the present method is performed is connected through a circuit or impedance having an inductive component, a low-pass filter is created in the direction of the onboard vehicle electrical system ground when viewed from the varistor. Accordingly, the embodiment provides connecting the varistor(s) to a reference potential through a low-pass filter or through a filter having attenuation that increases with frequency, or through a high-pass blocking filter. As a result, by isolating the reference potential from this detection, (active) detection of the capacitive component of the varistor's AC impedance can be performed in such a way that the inductance blocks the AC component of the reference potential generated by the active detection. In other words, the capacitive component of the varistor's AC impedance is preferably (actively) detected by a circuit connected in series with the onboard vehicle electrical system ground, and an impedance exists between this circuit and the onboard vehicle electrical system ground, and this circuit attenuates the AC voltage or AC signal directed toward the onboard vehicle electrical system ground.When detecting a capacitive component, preferably an AC signal is used, and the frequency is configured such that the aforementioned impedance produces a frequency-dependent attenuation of at least 10, 30, or 50 dB at this frequency. The impedance is also designed accordingly (in relation to the frequency of the AC signal used). The frequency may be 1 kHz, greater than 10 kHz, preferably at least 100 kHz, 1 MHz, or 5 MHz.

[0015] Below, a vehicle high-voltage protection circuit suitable for carrying out the method described herein is described in particular. The vehicle high-voltage protection circuit (abbreviated as: protection circuit) includes at least one protection connector configured to be connected to a low-voltage line coming from a high-voltage zone. The protection circuit further includes at least one varistor. The protection connector is connected to the ground connector of the vehicle high-voltage protection circuit through this varistor. Here, the reference potential assigned to the vehicle chassis is generally referred to as the ground connector. This also applies to the ground of the onboard vehicle electrical system. The ground connector referred to herein is specifically the ground of the onboard vehicle electrical system or is generally a reference potential specified for the onboard electrical system.

[0016] The protection circuit additionally includes a detection device. This detection device is connected to the varistor via a signal transmission method. A direct line-by-line connection or a connection through a filter, capacitive coupling and / or a voltage divider or amplifier may be considered a signal transmission connection. The detection device is configured to detect the capacitive component of the varistor's AC impedance, particularly based on the signal transmission connection with the varistor. Additionally, the protection circuit includes an evaluation device. This evaluation device is connected downstream of the detection device. The evaluation device is configured to compare the capacitive component detected by the detection device with the varistor's rated capacitance value. Furthermore, this evaluation device is configured to output a fault signal at the signal output of the evaluation device if the deviation exceeds a predetermined magnitude. This identifies that the varistor is defective. Thus, the detection device is designed to perform the step of detecting the capacitive component described herein. Generally, the evaluation device is configured to compare the capacitive component detected by the detection device as described.

[0017] Here, the evaluation device does not necessarily need to be connected downstream of the detection device, but rather may be part of the detection device, and may be connected downstream of an entity (e.g., a measurement device) configured to detect the capacitive component of the AC impedance of a varistor, for example. According to one embodiment, the detection device includes at least one measurement device, an alternating signal source, and additionally a comparator, and the comparator may perform a comparison step and output a signal characteristic of a fault state accordingly.

[0018] In addition, in the case of a protection circuit, an AC source or an AC voltage source may be used as previously described in relation to the method. If the protection circuit includes an AC source, this source is connected to at least one varistor (in a signal transmission manner) and is configured to apply AC to the varistor. Thus, AC is used for excitation. A detection device or its measuring device is connected to the varistor in a signal transmission manner and is configured to detect the voltage generated (in response) due to the AC applied to the varistor. Here, the AC source may be part of the detection device, or the AC source may be outside the detection device (having the measuring device and possibly the comparison device).

[0019] Alternatively, an AC voltage source may be used for excitation, that is, for active measurement. This source is connected to at least one varistor via a signal transmission method. Additionally, the AC voltage source is configured to apply an AC voltage to a varistor connected directly or indirectly to the source through capacitive coupling, a resistor network, and / or an amplifier. A detection device is likewise connected to the varistor (via a signal transmission method). The detection device is configured to detect the current generated by the AC voltage applied to the varistor. The AC voltage source may be part of the detection device (which may additionally include a measurement device and / or a comparison device such as a comparator). Alternatively, the AC voltage source is provided externally from the detection device.

[0020] In a specific embodiment, when the capacitive component of the varistor is (actively) detected, the capacitive component is excited by an AC signal generated from a communication unit connected to a low-voltage line to which the varistor is also connected. Here, a communication signal (sensor signal, control signal, etc.) is used, for example, to excite the varistor, and the communication signal is transmitted while performing a sensor evaluation method, an open-loop or closed-loop control method, or a method of supplying low voltage to a low-voltage component. The signal source for the AC signal (i.e., AC source or AC voltage source) is not, in this case, a dedicated signal source, but rather a control unit, a sensor unit, etc., that performs an additional function and is connected to the low-voltage line to which the varistor is also connected. Accordingly, the terms dedicated AC source and AC source refer to both a dedicated AC signal source and an AC signal source that have an additional function and, in the context of this function, generate an AC signal, e.g., a data signal, a communication signal, a control signal, a sensor signal, etc. In addition, a low-voltage power circuit through which power is transmitted via a low-voltage line can provide such an AC signal to detect capacitive components, for example, when an AC signal is used in a high-voltage region to supply power to a low-voltage component.

[0021] Therefore, to implement a protection circuit or to perform the method described herein, in this case, it is sufficient to simply add a passive detection device, that is, a detection device that has no signal source of its own but has a measurement unit and / or an evaluation unit, to an existing device.

[0022] The protection circuit may include multiple varistors. Here, a detection device may be provided for each varistor or a subgroup thereof. This detection device is connected to each varistor via a signal transmission method. This detection device may be provided to only one measurement device of the detection device, or to only the measurement device assigned to the detection device. In this case, there is a fixed association between the varistor and the detection device. Alternatively, a selection switch may be provided to connect the detection device (or the measurement device) to all varistors or subgroups thereof. Here, the selection switch is configured to connect the detection device to the selected varistor or the selected varistor subgroup. Thus, the selection switch is configured to select one element (varistor or subgroup) from among multiple elements among the varistors or subgroups to connect this element to the detection device. Then, the detection device can sequentially determine the capacitive components of each of the various varistors or various subgroups of varistors. Signal multiplexing is performed through the selection switch. In particular, the select switch is configured to sequentially connect an alternating current or AC voltage signal source to another varistor or another subgroup. A common signal source that applies an alternating current signal (alternating current or AC voltage) to all varistors or all subgroups may also be provided, while only the detection device can select individual varistors or subgroups through the select switch.

[0023] At least one varistor is preferably connected to the ground connector through a high-pass filter. This prevents the alternating current signal (alternating current or AC voltage) provided for active measurement from discharging toward the ground connector or penetrating into additional components of the onboard vehicle electrical system through the ground connector. In one embodiment, at least one varistor is connected to the ground connector through an inductance and / or a resistor. Additionally, the use of a resistor can attenuate the alternating current or AC voltage component while it is being transmitted to the ground connector.

[0024] As mentioned, the method and the device described herein are used to protect at least one low-voltage line emerging from a high-voltage zone. Here, the high-voltage zone is provided in a closed housing. For example, a low-voltage line emerges from this housing to control, inspect, or power a (low-voltage) component inside the high-voltage zone. In particular, at least one low-voltage line passes through a housing wall that spatially closes the high-voltage zone. In other words, at least one low-voltage line passes through a boundary, thereby spatially separating the high-voltage zone, particularly from the low-voltage zone or the periphery of the high-voltage zone. In one embodiment, at least one low-voltage line passes through an insulator that separates the high-voltage zone from the low-voltage zone.

[0025] In the following, this is explained in more detail with reference, for example, to high-voltage onboard vehicle electrical systems.

[0026] A high-voltage onboard vehicle electrical system having a spatially separated high-voltage zone is provided, and at least one low-voltage line extends from the high-voltage zone. At least one low-voltage line passes through the spatial boundary of the high-voltage zone. This boundary separates the high-voltage zone from the surroundings, particularly the low-voltage zone. Here, the low-voltage line may lead from the high-voltage zone to the low-voltage zone. If a high-voltage protection circuit as described herein is provided, at least one protection connector of the protection circuit is connected to at least one low-voltage line. If multiple low-voltage lines are provided, the protection circuit preferably has at least the same number of protection connectors so that one individual protection connector is provided for each low-voltage line.

[0027] The high-voltage zone is separated from the low-voltage zone by insulation. That is, at least one low-voltage line exits from the high-voltage zone through this insulation. Insulation may be provided by the spatial boundary of the high-voltage zone, by a housing, or by an enclosure of the high-voltage zone. The aforementioned protection circuit is located in the low-voltage zone. The low-voltage zone has a ground potential, for example, the potential of the chassis, and the ground connector of the protection circuit is preferably connected to this potential. The ground potential is provided specifically separately from the high-voltage zone. The protection connector or low-voltage line is galvanically connected to the ground potential. For this reason, using a varistor allows for the detection of insulation faults or galvanic insulation faults between the high-voltage zone and the low-voltage zone on one side, and between the low-voltage zone, ground potential, or ground connector on the other.

[0028] Low-voltage lines can serve as sensor lines. Specifically, low-voltage lines can lead to sensors within the high-voltage zone. These types of components are designed, for example, as temperature sensors, voltage sensors, current sensors, pressure sensors, etc. Low-voltage lines can also serve as data lines, specifically for communicating with components within the high-voltage zone. For example, a data line can be a control line for controlling a component within the high-voltage zone from the low-voltage zone. Conversely, a data line can be used for a component within the high-voltage zone to control a component within the low-voltage zone or to communicate with it, for example, to transmit sensor data. An example of this is communication between a battery management system within the high-voltage zone and a component in the low-voltage zone.

[0029] Finally, the low-voltage line may be a low-voltage supply line extending from a component in a high-voltage zone to a low-voltage zone to receive low voltage from the low-voltage zone. An example of this is a low-voltage source connected to a sensor or communication component within a high-voltage zone via a low-voltage line in the form of a low-voltage supply line and configured to supply to such a component within the high-voltage zone. For fault-free operation, that is, fault-free isolation or galvanic isolation with respect to ground potential or ground connector, the voltage of such lines is typically less than 60V (specifically less than 24V). For example, a data line may carry a voltage varying from 0V to 5V or from 0V to 12V. This also applies to the supply line. An embodiment provides a plurality of low-voltage lines, wherein at least one of these low-voltage lines is a sensor line, at least one is a data line, and / or at least one is a low-voltage supply line. Brief explanation of the drawing

[0030] FIG. 1 illustrates a high-voltage onboard vehicle electrical system having a protection circuit according to the present invention for a more detailed explanation of an embodiment of the subject matter described in this specification. Specific details for implementing the invention

[0031] The high-voltage onboard vehicle electrical system (FB) of FIG. 1 has a spatially separated high-voltage zone (HV) adjacent to a low-voltage zone through an insulator (IN). A low-voltage line (NL) exists within the low-voltage zone (NV), and this low-voltage line exits the high-voltage zone, passes through the insulator (IN), and specifically also passes through a housing where the high-voltage zone (HV) is located and which leads to the low-voltage zone (NV). Components connected to each other by the low-voltage line (NL) are not shown for clarity. However, generally, the depicted low-voltage line can be assumed to mean that at least one component of the low-voltage zone (NV) is connected to at least one component of the high-voltage zone (HV).

[0032] Low voltage lines (NL) are exemplified by signal lines (SL), data lines (DL), and supply lines (VL), and the lowest line among the lines (NL) may be a communication line.

[0033] The high-voltage onboard vehicle electrical system (FB) of FIG. 1 is additionally equipped with a vehicle high-voltage protection circuit (briefly, protection circuit). This high-voltage protection circuit has multiple protection connectors (SA, SA') for connecting to low-voltage lines (NL). The protection connectors are used to connect to individual low-voltage lines and also to connect the varistors (V) of the protection circuit. The varistors of FIG. 1 are assigned to a specific low-voltage line (NL) or a specific protection connector (SA) in each case. On the opposite side of the protection connectors, the varistor (V) is connected to the ground connector (MA) of the protection circuit through the inductance (L) specifically illustrated. This prevents the AC voltage or alternating current component used for measurement from reaching the ground connector (MA) or the ground potential (M) of the low-voltage zone during active measurement. The ground connector (MA) of the protection circuit is connected to the ground or ground potential (M) of the low-voltage zone (NV) as illustrated. Inductance generally forms a low-pass filter, preventing AC components from transitioning from the protection circuit to other potentials in the low-voltage region (NV).

[0034] The protection circuit may be designed to have a detection device (EE') having an AC source (Q) on one side and a shunt resistor or measuring resistor (Rs) on the other. The AC source is connected to a varistor, specifically to the side of the varistor (V) opposite the protection connector, through the measuring resistor (Rs). A measuring device (ME) is provided in parallel with the measuring resistor (Rs). In the illustrated example, this may be provided as a voltage measuring device. It measures the voltage generated when the AC source (Q) applies an AC signal to the varistor (V) through the measuring resistor (Rs). The measuring device (ME) outputs a signal indicating the magnitude of the capacitive component of the selected (measured) varistor (V). This magnitude is transmitted to a comparator (K) connected downstream of the measuring device (ME). This comparator compares the value corresponding to the capacitive component with a predetermined value to determine whether the capacitive component of the relevant varistor or the measured capacitance is within the rated range or does not deviate from the rated value by a predetermined amount. The result is output to the output (A) of the comparator, and the signal of the output (A) reflects whether the associated varistor (V) is identified as defective based on the capacitive component that deviates too abruptly.

[0035] A selector switch (MX) is provided to select the varistor (V) to be measured, and this switch is connected to a current source (Q) (via resistor (RI)) and optionally connected to one of the protection connectors (SA') along with the source (Q). To better explain the function, the protection connector (SA') is shown separately from the protection connector (SA). Here, the protection connector (SA) is used to connect the varistor to the low-voltage line (NL), and the protection connector (SA') is used to connect the detection device (EE') (or its AC source (Q)) to the individual line (NL). Furthermore, the protection connector (SA') is used to connect the measurement unit (ME) or the associated measurement resistor (Rs) to the low-voltage line (NL) (via the selector switch (MX)). Thus, the protection connector (SA') is used to actively detect or measure the capacitive component of the varistor (V), and the varistor, in turn, is used to discharge current in the event of an excessive voltage (relative to ground) on the low-voltage line (NL). It can be seen that the protection connectors (SA' and SA) are connected to the same potential, and in the actual embodiment, the protection connectors (SA' and SA) are connected to each other within the protection circuit to form a common protection connector for the low-voltage line (NL). As a result, each low-voltage line (NL) needs to be connected only once.

[0036] A selection switch (MX) is used to select one of the varistors (V). In the illustrated example, the varistor (V) connected to the signal line (SL) is selected. As a result, an alternating current is applied to this varistor by the selection switch (MX), and similarly, the voltage generated in the associated varistor (V) is detected by the measurement unit (ME) by the same selection switch (MX) in the same manner. The drawing is the same when the source (Q) is an AC voltage source: the voltage is applied to the associated varistor connected to the signal line (SL) on one side through the measurement resistor (Rs) and on the other side through the selection switch (MX). Using the measurement resistor (Rs), the associated current is detected by detecting the voltage drop across this resistor (Rs). Thus, the measurement unit is also used here to detect the current across the resistor (Rs). Alternatively, the measurement unit may directly detect the voltage drop across the varistor (V) (as illustrated by the detection device (EE)). However, regardless of the actual configuration and connection of the measuring unit (ME), this measuring unit can detect the current flowing through the varistor by the measuring resistor (Rs) used as a shunt resistor, measure the voltage, and derive the voltage drop across the varistor (V) from this.

[0037] Instead of using a detection device (EE') for all varistors (V), a selection switch may be used to provide a detection device indicated by reference numeral E. The dashed line on the right indicates a first detection device (EE) connected in parallel to the varistor (V) shown on the far right. Additional detection devices (EE) indicated by dashed lines are connected to other low-voltage lines (NL), i.e., line (VL). In other words, the various detection devices (EE) shown are connected to various varistors to measure the voltage drop across the varistors. Each detection device (EE) has a measurement unit (ME') that detects the voltage drop across the varistor (V). Additionally, each detection device (EE) has a source (Q'), through which an AC voltage signal can be applied to the connected varistor (V). If the source (Q) is an AC source, the measurement unit (ME') detects the voltage drop across the connected varistor (V). If the source (Q') is an AC voltage source, the measuring device (ME') detects the current flowing between the source and the varistor connected thereto. Each detecting device (EE) is configured to calculate the capacitive component of the connected varistor by determining the relationship between the measured or applied current and the drop voltage or applied voltage. The result is transmitted to each comparator (K') as illustrated, and each output (A') outputs a signal identifying whether the measured capacitive component deviates from the rated component by a predetermined magnitude. If the deviation exceeds a predetermined magnitude, the varistor is considered defective. The outputs (A') can be combined, for example, by a logic OR circuit. This detects whether at least one output (A') outputs a signal characterizing a defective varistor. The OR operation can generally have a total output indicating whether at least one of the individual outputs (A') is characteristic of a defective varistor in order to identify or output a defect in a protection circuit or a defect in a group of varistors.

Claims

Claim 1 A method for testing the function of a high-voltage protection device for an onboard vehicle electrical system, wherein the high-voltage protection device has a varistor or other voltage limiting element, and comprises: a step of detecting a capacitive component of the AC impedance of the varistor or the voltage limiting element; a step of comparing the capacitive component with a rated capacitance value, wherein the rated capacitance value is a characteristic of the capacitance of the operating varistor or the operating voltage limiting element; and a step of determining that the varistor or the voltage limiting element is in a defective state if, as a result of the comparison, the capacitive component is determined to deviate from the rated capacitance value by a predetermined amount, wherein the detecting step is performed by (a) applying an AC signal to the varistor or the voltage limiting element and detecting a related AC voltage signal applied to the varistor (V) or the voltage limiting element, or (b) applying an AC voltage signal to the varistor (V) or the voltage limiting element and detecting a related AC signal applied to the varistor or the voltage limiting element. Claim 2 delete Claim 3 A method according to claim 1, wherein each capacitive component of an AC impedance is detected for a plurality of varistors (V) or voltage limiting elements, wherein the capacitive component of the varistor (V) or the voltage limiting element is detected using an individual device (EE), and for each varistor (V) or each voltage limiting element or a subgroup thereof, a self-signal source (Q') applies an AC signal and / or, for each varistor (V) or voltage limiting element or a subgroup thereof, a self-measurement device (ME') detects a resulting signal in the relevant varistor (V) or voltage limiting element, or, wherein the capacitive component of the plurality of varistors (V) or voltage limiting elements is detected by signal multiplexing (SA') using the same device (EE'), and the same signal source (Q) applies an AC signal to all varistors (V) or voltage limiting elements or a subgroup thereof, and / or, the same measurement device (ME) detects a resulting signal in the varistor (V) or the voltage limiting element for all varistors (V) or voltage limiting elements or a subgroup thereof. Claim 4 The method of claim 1, wherein the method is performed on a varistor (V) or a voltage limiting element, and the potential of a low voltage line (NV) coming from a high voltage zone (HV) is connected to an onboard vehicle electrical system ground (MA) through an inductance (L) or a resistor via the varistor or voltage limiting element. Claim 5 A high-voltage protection circuit for a vehicle, comprising: at least one protection connector (SA) configured to be connected to a low-voltage line (NL) coming from a high-voltage zone (HV); at least one varistor (V) or voltage limiting element connecting the protection connector (SA) to a ground connector (MA) of the high-voltage protection circuit for the vehicle; and a detection device (EE; GE) connected to the varistor (V) or the voltage limiting element in a signal transmission manner and configured to detect the capacitive component of the AC impedance of the varistor (V) or the voltage limiting element. and an evaluation device (K), wherein the evaluation device (K) is configured to compare a capacitive component detected by the detection device (EE; GE) with the rated capacitive value of the varistor (V), and output a defect signal to the signal output of the evaluation device (K) when a deviation exceeding a predetermined size occurs, and the defect signal identifies the varistor (V) or the voltage limiting element as a defect, and (a) an AC source (Q) connected to at least one varistor (V) or the voltage limiting element and configured to apply AC to the varistor (V) or the voltage limiting element, wherein the detection device (EE; GE) is connected to the varistor (V) or the voltage limiting element and configured to detect a voltage generated by the AC applied to the varistor (V) or the voltage limiting element, or (b) an AC voltage source connected to at least one varistor (V) or the voltage limiting element and configured to apply AC voltage to the varistor (V) or the voltage limiting element, wherein the detection device (EE; A high-voltage protection circuit for a vehicle comprising an AC voltage source connected to the varistor (V) or the voltage limiting element and configured to detect a current generated by an AC voltage applied to the varistor (V) or the voltage limiting element. Claim 6 delete Claim 7 A high-voltage protection circuit for a vehicle according to claim 5, comprising a plurality of varistors or voltage limiting elements, wherein one detection device (EE') is provided for each varistor (V) or each voltage limiting element, or a subgroup thereof connected to each varistor (V) or voltage limiting element in a signal transmission manner, or a selection switch (MX) is provided, wherein the detection device (EE') is connected to all varistors (V) or voltage limiting elements or a subgroup thereof by the selection switch, and the selection switch (MX) is configured to connect the detection device (EE') to a selected varistor (V) or voltage limiting element or a selected subgroup thereof. Claim 8 A high-voltage protection circuit for a vehicle according to claim 5, wherein the at least one varistor (V) or the at least one voltage limiting element is connected to a ground connector (MA) through an inductance (L) or a resistor. Claim 9 A high-voltage onboard vehicle electrical system comprising a spatially separated high-voltage zone (HV), at least one low-voltage line (NL) extending from the high-voltage zone, and the high-voltage onboard vehicle electrical system comprising a vehicle high-voltage protection circuit according to claim 5, wherein a protection connector (SA) of the vehicle high-voltage protection circuit is connected to the at least one low-voltage line (NL), the high-voltage zone (HV) is insulated from a low-voltage zone (NV) in which the vehicle high-voltage protection circuit is located through an insulator (IN), and a ground connector (MA) of the vehicle high-voltage protection circuit is connected to a ground potential (M) of the low-voltage zone (NV), and the ground potential (M) is galvanically insulated from the high-voltage zone (HV). Claim 10 In claim 9, the at least one low-voltage line (NL) is designed as a sensor line (SL), a data line (DL), or a low-voltage supply line (VL), in a high-voltage onboard vehicle electrical system.

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