Method and protection device for protecting a device against a fault current, and motor vehicle

Abstract

The invention relates to a method (7) for protecting an electronic device from a fault current by means of a safety device. The invention also relates to a corresponding protection device and to a motor vehicle equipped therewith. In the method (7), a currently expected normal operation current rising slope (5) when there is no fault and a currently expected fault current rising slope (6) when there is a fault are determined. In addition, an actual given current measurement current rise slope is determined. The measured current (I) flowing through the fuse is identified as a fault current (2) if the fault current rise slope (6) is greater than the normal operating current rise slope (5) by more than a predetermined threshold value and the difference between the fault current rise slope (6) and the measured current rise slope is less than a predetermined difference threshold value. In this case, the safety device is then automatically triggered.

Description

Technical Field

[0001] The invention relates to a method and a protection device for protecting electrical and / or electronic equipment from fault currents. The invention also relates to a motor vehicle equipped with the protection device. Background Art

[0002] Nowadays, electrical and electronic systems are used very extensively. In order to avoid damage or safety risks, fuses can be used. However, this can also cause problems depending on the application. Thus, for example, conventional fuses can have a triggering time of several milliseconds and therefore react relatively slowly. Although electronic fuses can in principle switch faster, this can also be potentially dangerous, especially with relatively large inductances.

[0003] As a solution, a method for protecting an electronic system from overcurrent and short circuit is described in DE102011121604A1. In this method, the determined actual value of the current rise slope of the operating current is compared with a set value, which is dynamically set by a control unit to the maximum allowable current rise slope of the operating current according to the design of the system and / or the current current requirement. If the actual value of the current rise slope exceeds the first set value, the protection switch is triggered by the control unit to interrupt the operating current. This should achieve improved safety in order to identify and subsequently prevent potential short circuit risks early. However, it may be difficult to reliably distinguish the operating current from the fault current based solely on the current rise slope, so that high energy may still occur in the event of a fault and must be handled.

[0004] As another solution, DE102009007969A1 describes a short-circuit protection device for limiting short-circuit currents in high-energy DC power grids. In it, a first switch for bridging a resistor when there is no short circuit is connected in parallel with a resistor for conducting and limiting the short-circuit current. In addition, a monitoring and control device is provided for monitoring the current flowing through the switch and disconnecting the switch when the current flowing through the switch exceeds a predetermined limit value. In this way, the short-circuit current occurring in the event of a short circuit should be reliably controlled. Summary of the invention

[0005] The object of the present invention is to realize a particularly reliable and safe fault current protection.

[0006] This object is solved by the technical solution of the independent claim. Other possible designs of the present invention are disclosed in the dependent claims, the description and the drawings. The features, advantages and possible designs set forth in the description of one of the technical solutions of the independent claims are at least similarly regarded as the features, advantages and possible designs of the corresponding technical solutions of the other independent claims and each possible combination of the technical solutions of the independent claims, if necessary in combination with one or more of the dependent claims.

[0007] The method according to the invention can be used to protect electrical and / or electronic equipment from fault currents by means of a fuse. Such a fuse can be automatically disconnected or triggered in order to avoid or reduce damage to the equipment caused by a fault current (e.g. an overcurrent or a short-circuit current) or the disruptive effects that such a fault current may cause. The method according to the invention comprises a plurality of method steps, which can be applied accordingly in the operation of the equipment.

[0008] In a method step of the method according to the invention, the normal operating current currently expected at a predetermined position of the device when there is no fault (i.e. when the device is in normal operation without fault) is determined. The position can be a fuse in particular, so that in other words, it can be determined what normal operating current should flow through the fuse at present. However, other positions can also be predetermined or predefined for determining the normal operating current, such as directly before or after the fuse or the like along the line including the fuse. This enables the corresponding flexible application of the method. In addition, the corresponding current normal operating current rising slope expected when there is no fault is determined according to the expected normal operating current or the time variation curve of the expected normal operating current. In other words, the normal operating current gradient expected when there is no fault is determined, for example in amperes / seconds (A / s). Depending on the design of the device, the normal operating current rising slope can also be different or change even when there is no fault. For example, in the case of a capacitive load protected or supplied by a fuse, the normal operating current is the corresponding expected capacitive charging current, and the normal operating current rising slope can depend on the capacitance of the load in this case.

[0009] In a further method step of the method according to the invention, the respective currently expected fault current and the respectively corresponding fault current rise slope, ie the respective currently expected fault current gradient, are determined at a predetermined location or at the predetermined location in the event of a fault, in particular an electrical short circuit.

[0010] To determine these variables, for example, corresponding predetermined electrical parameters describing or characterizing the device can be used. Likewise, for example, a voltage can be measured over time in a device or between two predetermined points and used as a basis or input for determining the variables.

[0011] In a further method step of the method according to the invention, the current actually flowing through the predetermined location is measured with respect to time. The actually measured current can also be referred to as the measurement current here. The corresponding, respectively currently actual, i.e. actually given measurement current rise slope, i.e. the corresponding measurement current gradient, is further determined based on the measured time curve of the measurement current.

[0012] When at least two predetermined conditions are met, the measured current is then identified as a fault current and the fuse is automatically triggered. The fuse can be automatically disconnected in this case to interrupt the fault current flowing through the device or the fuse and thus also interrupt the fault current flowing through the device to be protected. If the current expected fault current rise slope is greater than the current expected normal operating current rise slope when there is a fault than the predetermined threshold, the first condition for identifying the measured current as a fault current and not identifying it as a normal operating current is met. For this purpose, the expected fault current rise slope and the expected normal operating current rise slope can be determined permanently or quasi-continuously or at a high frequency (in order to achieve or realize a sufficiently fast protection effect) and compared accordingly. In particular, the absolute values ​​of these current rise slopes can be compared with each other. The corresponding error tolerance or confidence can be adjusted or considered by the predetermined threshold. For example, the threshold can be minimized in the case of the accuracy or reliability given or achievable in the determination of the expected fault current rise slope and the expected normal operating current rise slope in the corresponding application. This can, for example, depend on the accuracy of the available parameters or parameter values ​​used to describe or characterize the device, the resolution of the corresponding model and / or the like.

[0013] The second condition for identifying the measured current as a fault current is that the difference between the current expected fault current rise slope and the current measured current rise slope when a fault occurs, in particular the absolute value of the difference is less than a predetermined difference threshold value. For example, the absolute value of the difference between the measured current rise slope and the expected fault current rise slope can be compared with the absolute value of the fault current rise slope etc. increased by a predetermined confidence value or confidence component.

[0014] In other words, if the expected normal operating current rise slope and the expected fault current rise slope differ from each other sufficiently so that a fault (such as a short circuit) can be distinguished from normal operation with a corresponding degree of confidence or a correspondingly high degree of credibility, and if in this case the expected fault current rise slope and the actual measured current rise slope are close enough to each other so that a fault or a short circuit can actually be determined with a corresponding degree of confidence or a corresponding degree of credibility, the fault current can be identified and the fuse can be automatically triggered accordingly.

[0015] As soon as the corresponding fault current or short circuit or the like is detected or determined, it can be directly isolated by opening the fuse.

[0016] The method proposed in this article can distinguish between the normal maximum operating current and the fault current or short-circuit current particularly early and particularly reliably, which cannot be simply and quickly realized in the traditional overcurrent disconnection mechanism, for example, based on the capacitance of the device or the corresponding load. Compared with the traditional overcurrent disconnection mechanism that only reacts to the measured current exceeding the threshold, the fault current can be detected particularly early through the present invention. This is because not only the absolute value of the current flowing through is monitored or considered here, but also the current rising slope is monitored or considered. Therefore, it is finally possible to react and trigger the fuse device when the absolute fault current is particularly small. Compared with the traditional overcurrent disconnection mechanism (the device and the fuse are designed the same in other aspects), this can reduce the energy that needs to be processed in the corresponding fault situation. This can also reduce the corresponding damage caused by the automatic triggering of the fuse and thus help to improve the safety and robustness of the device and / or the protective device as a whole.

[0017] In a possible extension of the present invention, the expected normal operating current or the corresponding normal operating current rising slope and the expected fault current or the corresponding fault current rising slope are calculated by means of two different predetermined models. Such a predetermined model can therefore model the device and its electrical characteristics or current conduction behavior. Here, the first model can model normal operation that complies with regulations and specifications, i.e., without faults. On the contrary, a second model that is different therefrom, in particular different, can model the fault condition or fault operation of the device. It is also possible here that the second model models the corresponding behavior of multiple different types or features of the fault or the device and / or can predetermine multiple different second models in order to model the corresponding operation or behavior of different types or features of the fault or the device. Therefore, it is possible to react to different situations flexibly and accurately, that is, for example, to ensure the corresponding fast and reliable triggering of the fuse even in different fault situations.

[0018] The model-based current rise slope calculation proposed here allows for particularly simple and flexible adaptation to different situations, operating strategies and / or changes in the device and / or, for example, changes in the load connected thereto or the like. Thus, for example, a predetermined calculation model can be adapted accordingly during the operation of the device significantly more simply, faster and more flexibly, especially, for example, also dynamically, compared to a corresponding adaptation of a hardware circuit or the like that describes the corresponding behavior of the device. The predetermined model can in particular be a computer model or include a computer model that can be executed, for example, by means of a corresponding computer device. Such a computer device can be configured, for example, as a controller or a control unit or the like, in particular as a part of a protection device that is provided for applying the method according to the invention.

[0019] In a possible embodiment of the invention, the time profile of the voltage in the device is measured and used as input for the model. For example, the voltage can be measured between two predetermined or predefined points of the device and / or the fuse and / or relative to ground or ground or the like. This can be, in particular, the operating voltage of the device, for which fluctuations or deviations can be expected in the event of a fault relative to the operating voltage value or profile during normal operation without faults. Such a voltage can be measured relatively simply, inexpensively, quickly and accurately and therefore constitutes an effective possibility or basis for being able to ultimately distinguish between normal current rise slopes and fault current rise slopes based thereon.

[0020] In a possible extension of the present invention, at least the equivalent resistance, inductance and component capacitance of the device are used as parameters of the model, and these parameters have parameter values ​​that are predetermined or adapted for the corresponding device individually. The equivalent resistance can be, for example, a combination of the equivalent series resistance (ESR) of the resistance of the line to be protected by means of a fuse and its capacitance, or a corresponding short-circuit resistance. The inductance can be, for example, or include the line inductance of the line to be protected. The component capacitance can be, for example, the capacitance of a capacitive load supplied by a fuse or a line to be protected. Different models can include one or more of these parameters respectively. In particular, the parameters of the model do not have to be consistent with each other. Therefore, for example, a first model for determining an expected normal operating current or a normal operating current rising slope can include all three of the parameters, while a second model for determining an expected fault current or a fault current rising slope can, for example, include only two of the parameters, for example, only equivalent resistance and inductance, or the like. The parameters described here can be particularly simple and low-cost and at the same time accurately and reliably model the current rising slope and ultimately determine them.

[0021] In another possible design of the present invention, an electronic safety device is used as a safety device. The electronic safety device is controlled to trigger to interrupt the current conduction through the safety device. After such triggering, once a predetermined reset or reset standard is met, the safety device is automatically switched to conduction again. Such a reset standard can be or include, for example, a predetermined time interval and / or current or, for example, a voltage applied on one side of the safety device relative to a predetermined measuring point or reference point or reference potential, etc. is lower than a predetermined reset threshold. In this way, not only effective protection of the device can be achieved, but also particularly robust and convenient operation of the device can be achieved. Therefore, for example, when the fault that caused the initial triggering of the safety device is eliminated, the power supply to the device via the safety device can be automatically continued, that is, restored. This can be achieved by using an electronic safety device, because compared with traditional fuses, such a safety device can be reversibly switched, that is, triggered and reset, multiple times. This can also achieve corresponding low-cost protection of the corresponding device, because it is not necessary to replace the safety device after each triggering. In addition, electronic fuses can be switched or triggered significantly faster than conventional fuses, for example, they have switching or triggering times in the range of a few picoseconds compared to switching or triggering times of a few milliseconds. Likewise, the use of electronic fuses enables more precise adaptation to the device or line to be protected and thus, for example, enables correspondingly narrower designs or increases in the utilization of the corresponding device or line.

[0022] In another possible embodiment of the invention, the predetermined threshold value is designed (as part of the condition for identifying the measured current as a fault current) so that in the event of a fault, in particular in the event of a short circuit, the fuse is already triggered, i.e. disconnected, at a smaller fault current, i.e. at a smaller measured current, than in the case of a purely overcurrent-based triggering mechanism of the fuse (the device or the fuse being designed in the same way in other respects). In this sense, a purely overcurrent-based disconnection mechanism is achieved if, as the only condition for the triggering of the fuse, at least one predetermined value is predetermined or checked to exceed a predefined maximum value (which can still be expected in the fault-free normal operation of the device). Although this value can be minimized here, it must have a certain minimum value, for example, due to tolerances, measurement uncertainties, limited accuracy of predictions of the device behavior in fault-free normal operation, etc. On the contrary, an earlier and more accurate and reliable automatic triggering of the fuse can be achieved by the design proposed herein. As a result, as also described elsewhere, for example, the energy accumulated in the event of a fault or when the fuse is automatically triggered can be reduced and thus ultimately a higher safety can be achieved and / or a correspondingly smaller and more cost-effective triggering of the relevant components can be achieved.

[0023] The invention also relates to a protection device for protecting electrical or electronic equipment from fault currents. The protection device according to the invention comprises an electronically controllable fuse, a measuring device for measuring the current flowing through the fuse during operation, and a control device for controlling the fuse taking into account the measured current. The protection device according to the invention or its control device is hereby configured to carry out or apply the method according to the invention, in particular automatically. The protection device according to the invention can in particular be a protection device described in conjunction with the method according to the invention or corresponding thereto. Therefore, the protection device according to the invention can have some or all of the properties and / or features mentioned in connection therewith.

[0024] In a possible extension of the present invention, the fuse is configured as an electronic fuse that can be reversibly switched, and the electronic fuse includes at least one controllable transistor, especially MOSFET. Thus, the fuse can be particularly simple to control and has a particularly short switching time. In addition, the avalanche effect of the transistor can be used or utilized in this case, so as to allow the generated current to continue flowing after the fuse is triggered and therefore allow it to gradually disappear. This can prevent the formation of destructive voltage spikes, which otherwise may still cause damage to the device and / or other components even after the fuse is triggered. Using the avalanche effect can be a particularly low-cost and less expensive feasible solution for this. This is achieved by the present invention, because the triggering mechanism based on the current gradient of the fuse can reduce the maximum follow-flow energy after the fuse is triggered compared to the traditional overcurrent disconnection mechanism or overcurrent triggering mechanism and therefore the overload risk of the transistor or the avalanche effect can be limited to a practically manageable value.

[0025] In a possible extension of the present invention, the protection device includes a freewheeling diode. This freewheeling diode can allow residual energy to continue to flow or allow the generated current to continue to flow and gradually disappear after the fuse is triggered. Thus, damage caused by, for example, an uncontrolled voltage rise after the fuse is triggered can be avoided. For this reason, the use of the freewheeling diode proposed here can be realized particularly simply, safely and reliably by the present invention, because due to the triggering mechanism based on the current gradient of the fuse, the energy of the freewheeling can be reduced, for example, compared with the traditional purely overcurrent-based triggering mechanism, and therefore even if a simple and low-cost design is adopted, the freewheeling diode can be reliably and without other measures. Overload. Therefore, the use of a freewheeling diode can constitute a particularly simple, low-cost and effective feasible solution for further protection.

[0026] The invention also relates to a motor vehicle having an onboard electrical system and a protective device according to the invention integrated in the onboard electrical system. Since today's motor vehicles often use relatively high operating voltages and can transmit relatively large amounts of electrical energy in their onboard electrical systems and can also have an increasing number of electronic components and systems that react sensitively to fault currents, short circuits, voltage spikes and the like, the method according to the invention or the protective device according to the invention has particularly useful application cases. In addition, the invention can also ensure or improve occupant protection particularly simply, effectively and efficiently by limiting the energy of the subsequent flow of the fuse triggering, i.e., for example, without taking additional measures that increase costs or weight.

[0027] Other features of the invention can be derived from the claims, the drawings and the description of the drawings. The features and feature combinations mentioned above in the description and the features and feature combinations shown below in the description of the drawings and / or in the drawings alone can be used not only in the respectively given combination but also in other combinations or alone without departing from the scope of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The attached pictures are as follows:

[0029] Figure 1 An exemplary schematic diagram showing time curves of operating current and short-circuit current in different designs of an electronic device for illustrating an overcurrent protection disconnection mechanism;

[0030] Figure 2 An exemplary schematic diagram showing time variation curves of a current rise slope of an operating current and a current rise slope of a short-circuit current in different designs of an electronic device, for illustrating a protective disconnection mechanism based on a current gradient; and

[0031] Figure 3 An exemplary schematic diagram for explaining the implementation of a current gradient-based protection disconnection mechanism is shown. DETAILED DESCRIPTION

[0032] In the figures, identical and functionally identical parts are provided with the same reference symbols.

[0033] In order to avoid component damage and to increase functional safety, electrical or electronic devices can be protected with the aid of electronic fuses. However, it can be challenging to trigger such fuses as early as possible in the event of a fault, but not to trigger them unnecessarily in normal, fault-free operation. For illustration, Figure 1An exemplary schematic diagram is shown, in which the time t is plotted on the x-axis and the current I is plotted on the y-axis, which current can flow through the fuse during operation, for example. The figure plots different changes in the normal operating current 1 for different capacitances of the supplied load. In addition, the change curve of the short-circuit current 2 that occurs in the event of a fault is also plotted. It can be seen here that below the maximum operating current 3 that normally occurs in fault-free normal operation, the normal operating current 1 cannot be reliably distinguished from the short-circuit current 2. For example, in this example, when the load capacitance is 10 mF, the maximum operating current 3 is about 580 A. Even if the maximum operating current 3 may be lower at a lower load capacitance, the current can still rise similarly accordingly until the corresponding maximum operating current 3 is reached, regardless of whether a fault exists.

[0034] If a conventional overcurrent disconnection mechanism is used here, disconnection, i.e. triggering of the fuse, can therefore be provided when the threshold value 4 is above the maximum normally occurring maximum operating current 3. The threshold value 4 can be, for example, approximately 600 A. In the present example, the threshold value 4 will occur at a triggering time ts of approximately 130 μs.

[0035] Such relatively large currents can be particularly critical when the inductance L of the line to be protected is also relatively large, since in this case a correspondingly large amount of energy E can be stored according to the following formula:

[0036] ,

[0037] And in order to avoid overvoltage after the fuse is triggered, this energy must be dissipated. This may be accompanied by the risk of overloading components, such as transistors and / or freewheeling diodes of the fuse. In principle, in order to reduce this problem, the inductance L can be reduced, for example by using shorter lines. However, this is not easy to achieve in many applications, such as in motor vehicles, because the line length is basically fixed, for example, by the given size of the motor vehicle or the given geometry of the cable harness.

[0038] Therefore, as another solution, we can strive to or determine the earliest possible triggering time t s .

[0039] to this end, Figure 2 An exemplary schematic diagram is shown for illustrating the disconnection or triggering mechanism of a fuse based on a current gradient. Here, too, the time t is plotted on the x-axis. And the current rise rate IA is plotted on the y-axis. Figure 1, a plurality of different normal operating current rise slopes 5 are plotted here as an example, such as can occur under different load capacitances in fault-free normal operation. In addition, a short-circuit current rise slope 6 is plotted here to illustrate the fault situation. Compared with the conventional overcurrent disconnection mechanism based on the value of the current I, monitoring the current rise rate IA of the current I flowing through the fuse makes it possible to detect a fault current or a short circuit earlier. Therefore, depending on the load capacitance, the corresponding fault current or short circuit can be detected earlier with a predetermined confidence level. For example, here again in the case of a load capacitance of 10 mF, a short circuit can be distinguished from normal operation with a feasible confidence level after approximately 45 μs. In other words, short circuit detection and thus the corresponding automatic triggering of the fuse can then already be possible at the triggering time t S = 45 μs and is therefore significantly earlier than Figure 1 The triggering time t of the corresponding overcurrent disconnection mechanism shown in S =130 μs.

[0040] At the earlier triggering time t achieved here S = 45 μs, the current I is only about 200 A and is therefore significantly lower than Figure 1 At time t S = 130 μs gives about 600 A, even though the devices represented and the fuses are otherwise designed identically. Therefore, in the corresponding example, Figure 1 In the overcurrent disconnection mechanism shown in FIG. 1 , the energy flowing after the fuse is triggered is approximately 360 mJ and Figure 2 In the case of the current gradient-based disconnection mechanism shown in , it is approximately 40 mJ. Thus, by taking into account the current rise rate IA in the condition or criterion for the automatic triggering of the fuse, it is possible to achieve, by way of example, a reduction of the subsequent energy by approximately 89%.

[0041] Thus, increased device protection, increased overcurrent time protection, undervoltage protection and thermal overload protection can be achieved or improved. Thus, for example, increased functional safety of ASIL-classified components can be achieved in a relatively simple manner.

[0042] To further illustrate, Figure 3 An exemplary schematic diagram 7 of a method for protecting electrical or electronic equipment by means of a fuse that can be triggered automatically according to the current rise rate IA is shown. The method starts in method step S1. There, for example, the corresponding protection device or the electrical or electronic equipment protected thereby can be put into operation, for example by presetting or loading parameter values, models, threshold values, and / or the like. In method step S2, the time curve of the current I(t) flowing through the fuse is measured. In method step S3, the corresponding current rise slope or gradient m of the measured current I(t) is determined therefrom.iMess .

[0043] In parallel, the time profile of the current I(t) can be calculated in step S4. Two corresponding current rise slopes or gradients can be calculated here with the aid of two predetermined models. On the one hand, the current rise slope m that can be expected in normal operation without faults can be calculated in method step S5. iLoad For this purpose, a corresponding predetermined normal operating model 8 can be used or evaluated in method step S6:

[0044]

[0045] Among them, u(t) is the time variation curve of the voltage, R is the predetermined equivalent resistance, L is the predetermined inductance and C is the predetermined capacitance in the corresponding device or the supplied load.

[0046] On the other hand, in parallel therewith, in method step S7 the current rise slope m which can be expected in each case at the present time in the event of a fault or a short circuit can be calculated. iSC For this purpose, a corresponding predetermined short-circuit model 9 can be used or evaluated in method step S8. This short-circuit model can be predetermined, for example, as follows:

[0047]

[0048] Then, in method step S9, the current rise slope m to be expected in normal operation without faults can be checked. iLoad The expected current rise slope m during a fault iSC Whether the predetermined deviation conditions are met:

[0049]

[0050] Here, δ is a predetermined, desired confidence level, for example, about 10%, for distinguishing a short circuit or fault situation from normal operation. If this first condition is not met, the method can be continued as described above in the next cycle. For example, the current rise slope m can then be calculated. iMess With m iSC The corresponding next expected value of .

[0051] However, if, on the other hand, the first condition is met in method step S9, the method can be continued in method step S10. There, the second predetermined condition can be checked:

[0052]

[0053] This allows the previously determined measured current rise slope m to be verified. iMess The current rise slope m currently expected in the event of a fault according to the corresponding regulations iSCAre they close enough to each other so that a fault or a short circuit can actually be determined with a predetermined confidence level δ. δ can have the same value as the first condition checked in method step S9, for example. However, another predetermined value can also be used for δ here. If this second condition is not met, the method can also be continued as described above in the next cycle.

[0054] If, on the other hand, it is determined in method step S10 that the second condition is also met, this can be evaluated as a detected fault situation or fault current or short circuit. Accordingly, the fuse can then be automatically triggered in method step S11, ie, opened.

[0055] Overall, the described examples show how a current gradient-based triggering or disconnection of an electronic fuse can be achieved in order to protect electrical and / or electronic devices particularly reliably, safely and early.

[0056] Reference numerals list

[0057] 1 Normal operating current

[0058] 2 Short circuit current

[0059] 3Maximum operating current

[0060] 4Threshold

[0061] 5 Normal operating current rising slope

[0062] 6 Short-circuit current rising slope

[0063] 7 Charts

[0064] 8 Normal Operation Model

[0065] 9 Short Circuit Model

[0066] S1-S11 Method Steps

[0067] I Current

[0068] IA current rise rate

[0069] t time

[0070] t S Trigger moment

Claims

1. Method for protecting electrical and / or electronic equipment from fault currents by means of a fuse (7), in, During device operation: Determine a corresponding currently expected normal operating current (1) and a corresponding currently normal operating current rising slope (5) at a predetermined position of the device when there is no fault; Determining a corresponding current expected fault current (2) and a corresponding fault current rising slope (6) at the predetermined position when a fault occurs; measuring a current (I) actually flowing through the predetermined location with respect to time (t) and determining a corresponding corresponding current measured current rising slope; If the current expected fault current rise slope (6) is greater than the current expected normal operating current rise slope (5) by more than a predetermined threshold value and at the same time the difference between the current expected fault current rise slope (6) and the current measured current rise slope is less than a predetermined difference threshold value, the measured current is identified as a fault current (2) and the fuse is automatically triggered.

2. The method (7) according to claim 1, It is characterized in that The expected normal operating current rise slope (5) and the expected fault current rise slope (6) are calculated with the aid of two different predetermined models.

3. The method (7) according to claim 2, It is characterized in that The time profile of the voltage of the system is measured and used as input for the model.

4. The method (7) according to claim 2 or 3, It is characterized in that As parameters of the model, the equivalent resistance, inductance and component capacitance of the device are used, which have parameter values ​​which are predetermined individually for the respective device.

5. The method (7) according to any one of the preceding claims, It is characterized in that An electronic fuse is used as the fuse, which is controlled to be triggered to interrupt the current conduction and, after such triggering, automatically switches back to conduction as soon as a predetermined reset criterion is met.

6. The method (7) according to any one of the preceding claims, It is characterized in that The predetermined threshold value is designed such that in the event of a fault, in particular a short circuit, the fuse trips already at a lower value of the fault current (2) than in the case of a purely overcurrent-based tripping mechanism of the fuse in an otherwise identical installation.

7. A protective device for protecting an electrical or electronic device against a fault current (2), comprising an electronically controllable fuse, a measuring device for measuring the current (I) flowing through the fuse during operation, and a control device for controlling the fuse taking into account the measured current (I), in, The protective device is provided for carrying out a method (7) according to any one of the preceding claims.

8. The protection device according to claim 7, It is characterized in that The fuse is designed as a reversibly switchable electronic fuse which comprises at least one controllable transistor, in particular a MOSFET.

9. The protection device according to claim 7 or 8, It is characterized in that The protection device comprises a freewheeling diode. 10 . A motor vehicle comprising an onboard electrical system and a protection device according to claim 7 integrated in the onboard electrical system.

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