Patent Abstract:
A method for interrupting a current of an electrical power supply line includes integrating a supply line signal of the electrical power supply line over a predetermined time period to obtain an integrated signal, determining whether the integrated signal meets a predetermined condition, and using a current interrupting element to interrupt the current if the integrated signal meets the predetermined condition.

Full Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based upon and claims the benefit of prior German Application No. 10 2014 005 524.8, filed on Apr. 15, 2014, the entire contents of which are incorporated herein by reference. 
     TECHNICAL FIELD 
     The disclosure relates to a method for interrupting a current and, more particularly, a method, safety device, and associated device for interruption a current in an electrical arc. 
     BACKGROUND OF THE DISCLOSURE 
     In an electrical system of a vehicle with an operating voltage of 48V, for example, parallel electrical arcs may be created, which on the one hand limit the current in such a fashion that a melting fuse is not triggered, but on the other hand may cause a fire in the vehicle. 
     Furthermore, a cable break in the 48V electrical system may result in a serial electrical arc that cannot be protected by a melting fuse because the resulting current is less than the load current. This type of serial electrical arc can also cause a fire. 
     SUMMARY 
     One object of the present disclosure is to provide a solution for recognizing undesired states of an electrical system, in particular an electrical system of a vehicle. 
     This object is achieved according to the characteristics of the appended claims. 
     In accordance with the disclosure, there is provided a method for interrupting a current, wherein a signal of a supply line is integrated at least over a predetermined time period, and the current in the supply line is interrupted by means of a separating element if the signal that is integrated over at least the predetermined time period meets a predetermined condition. 
     In particular, a plurality of time periods, which may be different, can be integrated and evaluated in the scope of the predetermined condition. 
     The supply line signal can be a signal in the supply line or a signal that is determinable by means of the supply line. For example, it can be a current through a component that is connected to the supply line. It can also be a voltage drop at the component that is connected to the supply line. 
     In this context, it is an advantage that a precise signal determination (such as current determination) is possible per at least one time period, with the time period being designed flexibly. In particular, the at least one time period may be short compared to a time period in which a conventional (such as melting, for example) fuse would trigger. Another advantage is that a plurality of time periods can be determined and coupled with each other, for example to take into account a load characteristic of an electrical fault, such as an electrical arc, as precisely as possible. As a result, a conventional fuse with a predetermined triggering curve can therefore be upgraded with an active triggering curve that in particular takes into account time periods during which the energy detected in the fuse would not have been sufficient to trigger the fuse. 
     It is a development of the present disclosure that the current in the supply line is not interrupted, if the signal integrated over the at least one predetermined time period does not meet the predetermined condition, or if the signal integrated over the at least one predetermined time period meets another predetermined condition. 
     It is a further development of the present disclosure that the signal integrated over the at least one predetermined time period meets a predetermined condition if it reaches and/or exceeds a predetermined threshold value. 
     In particular, a plurality of threshold values may be provided, such as, for example, one each threshold value for each signal that is integrated over a predetermined time period. 
     In particular, it is a development of the present disclosure that the signal integrated over a predetermined time period is determined by averaging. 
     It is also a development of the present disclosure that the averaging is a squared averaging. 
     Furthermore, it is a development of the present disclosure that the signal is or comprises a current or a voltage. 
     In the scope of an additional development, the signal is a current through a fuse or a voltage drop at the fuse. 
     A further development is that the signal is a voltage drop at a fuse, with a resistance value of the fuse being determined at a temperature, and the resistance value and the voltage determining the current through the fuse. 
     In one embodiment, the signal is integrated by means of at least two integrators, with each of the integrators having its own integration time constant (meaning its own time period). 
     An alternate embodiment is that the predetermined condition is realized by means of a logical interconnection based on the results of the at least two integrators. 
     There are a plurality of potential logical interconnections. For example, the integrated signals may meet the predetermined condition if each signal is greater or equal to a threshold value (or a plurality of threshold values). For example, a logical AND-operation can be used for this purpose. 
     In some embodiments, the threshold value can take into account or depict a load characteristic of an electrical fault, such as a serial and/or a parallel electrical arc. In this way, the triggering curve of the fuse, which may be relatively slow, can be effectively and efficiently upgraded with a quick acting triggering curve. This results in a safety system that comprises the fuse as well as a detection unit with a separating element to detect electrical arcs, for example, and if an electrical arc is detected, the current relative to a load can be switched off. 
     In addition, it should be noted that the interruption of the current in the supply line can be temporary or permanent. In particular, an additional signalization can be performed, which indicates to a control device, for example, that an electrical arc has been detected. Optionally, the separating element could remain open until the fault can be corrected and/or a control device resets the circuit introduced here. 
     The explanations regarding the method also apply correspondingly to the other claim categories. 
     Also in accordance with the present disclosure, there is provided a device having a separating element, and a detection unit that is used to integrate a signal of a supply line over at least a predetermined time period. The detection unit is set up in such a fashion that a current in the supply line can be interrupted by means of the separating element if the signal integrated over at least a predetermined time period meets a predetermined condition. 
     It is a development of the present disclosure that the device comprises a fuse, with the signal being a current through the fuse, or a voltage drop at the fuse. 
     For example, the fuse may be a melting fuse in the current path of the supply line. 
     In some embodiments, the detection unit includes a differential amplifier, which is used to detect a voltage drop at the fuse, and an evaluation unit that compares the predetermined condition with the voltage drop at the fuse, and correspondingly triggers the separating element. 
     It is an additional development that the separating element is an electronic or a remotely activated switch. 
     Furthermore, a safety device comprising at least one of the devices described here is provided to attain the object of the present disclosure. 
     Said safety device can also be considered a safety system. 
     In the scope of a development of the present disclosure, the safety device can be used in an operating system, in particular a vehicle electrical system such as a 48V electrical system of a vehicle. 
     The solution presented here furthermore comprises a computer program product that can be loaded directly into a memory of a digital computer and comprises parts of program code that are suitable to perform the steps of the method described here. 
     In particular, the aforementioned detection unit and/or evaluation unit can be developed as a processor unit and/or a circuit arrangement that is at least partially firmly wired or logical, and is set up, for example, to execute the aforementioned process. Said detection unit and/or evaluation unit may be or comprise any type of processor or computer with the appropriate necessary peripheral devices (memory, input/output interfaces, input-output devices, etc.). 
     The above explanations relating to the method apply correspondingly to the device. The device may be executed in one component or distributed to a plurality of components. 
     The aforementioned properties, characteristics and advantages of this invention as well as the way in which they are achieved become clearer and more comprehensible in connection with the following schematic description of embodiments, which are explained in more detail in connection with the drawings. For the sake of clarity, the same or equally acting elements may have the same reference symbols. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram for the detection of a parallel electrical arc and for performing an appropriate action after the electrical arc is detected. 
         FIG. 2  shows an example of a timeline of a current in the case of the parallel electrical arc. 
         FIG. 3  is a diagram having a y-axis that shows a duration for a time period t RMS , during which a squared average (RMS) is formed, and the y-axis of said squared average having a current I(t) as a function of said time. 
         FIG. 4  shows a schematic diagram based on  FIG. 1  in the case of a serial electrical arc. 
         FIG. 5  show a diagram with a plurality of time signal runs: a total current through the load, a voltage at the fuse, and a voltage at the load. 
         FIG. 6  shows the example of a circuit for the detection unit shown in  FIG. 1  or  FIG. 4 . 
         FIG. 7  shows an example of the mechanical integration of an analog filter. 
     
    
    
     DETAILED DESCRIPTION 
     The solution described here can be used for electrical systems, for example for electrical systems for vehicles, in particular for 48V electrical systems. 
       FIG. 1  shows a schematic diagram comprising a battery  101 , which in this example provides a voltage of about 48V relative to ground  102 . The positive pole of the battery  101  is coupled to the positive pole of a load  105  via a separating element  103 , a fuse  104 , and a supply line  110 . The negative pole of the battery  101  is coupled to the negative pole of the load  105  via a ground line  111 . 
     The load  105  may be any consumer circuit or any switching circuit, such as an operating device in a vehicle, for example. 
     A voltage drop at the fuse  104  is determined by a detection unit  107  in that one each terminal of the fuse  104  is connected to an input of a differential amplifier  108 . The output of the differential amplifier  108  is connected to an evaluation unit  109 , which, according to the output signal of the differential amplifier  108 , triggers the separating element  103 , e.g., opens or closes the separating element  103 . 
     The evaluation unit  109  and the differential amplifier  108  are examples of components of the detection unit  107 . 
     The detection unit  107  is therefore used to determine a voltage drop at the fuse  104 , and with said voltage drop an estimation is made as to a current through the fuse  104 , in particular a change of the current (dl/dt). 
     The evaluation unit  109  can be developed as a (micro) controller, a processor, or the like. Also, the evaluation unit  109  can be realized in form of an at least partially analog circuit (comprising an analog filter, for example). 
     The separating element  103  is a switch that can be electronically triggered, for example. For this purpose, a semiconductor switch, such as a transistor, MOSFET, JFET, IGBT, etc., and/or any other remotely activated switch (such as a relay) can be used. 
       FIG. 1  also shows the case of a fault in form of a parallel electrical arc  106  that forms between the supply line  110  and ground  102  (as a parallel short circuit). This type of intermittent electrical arc  106  limits the current through the fuse  104  in such a fashion that the energetic average is not sufficient for triggering the fuse  104 . Therefore, the electrical arc  106  remains unrecognized and may represent cause for a fire. 
     To prevent this, the voltage drop at the fuse  104  is supplied to the evaluation unit  109 , for example to an analog input of a microcontroller, via the differential amplifier  108 . In this way, the voltage drop at the fuse  104  can be measured and recorded continuously or at specific predetermined times, for example, by the evaluation unit  109 . For example, to that end, the evaluation unit  109  comprises an analogue-digital-converter that converts the signal provided by the differential amplifier  108  into digital values (samples) and then processes said digital values. In particular, a timeline of the digital values obtained in this manner, for example over a predetermined time period, can be taken into account to draw conclusions about a change in the voltage drop at the fuse  104 . 
     The temperature of the fuse  104  can be determined with a model of the fuse  104  or with a temperature sensor. The temperature is coupled to a resistance value of the fuse  104 , which, for example, can be determined by the evaluation unit  109  by means of stored data (for example in the form of a look-up table). With the (temperature-dependent) resistance value obtained in this manner, the current through the fuse can be determined using the known voltage drop at the fuse according to Ohm&#39;s Law (voltage drop divided by the resistance value). 
     The determined current can be averaged for at least one predetermined time period, for example. For example, time windows with durations of 0.1 ms, 1 ms, 10 ms can be used. In particular, averaging can be done by forming the squared average (also called RMS or QMW). In squared averaging, larger values have a greater influence than smaller values. 
     If multiple time periods are taken into account, the results of the averages determined for each time period can be coupled and the interconnection provides a signal that can be used to open the separating element  103 . The interconnection may be an AND-operation, for example. A comparison to a predetermined threshold value can also be made and used to determine an active triggering curve, e.g., a measurement for the opening of the separating element  103 . 
       FIG. 2  shows the example of a timeline of a current in the case of the parallel electrical arc. The parallel electrical arc causes irregular current peaks with high currents, some over 700 A. In the present case, said current peaks are too short for the energy they transmit to trigger the fuse  104 . 
       FIG. 3  shows a diagram where the y-axis shows a duration for a time period t RMS , during which a squared average (RMS) is formed, and where the x-axis shows a current I(t) as a function of said time. 
     A curve  303  represents a triggering curve of the fuse  104 . For example, the fuse  104  can trigger when a current of 100 A is permanently applied. However, if the current is applied for only a few milliseconds or a few tens of milliseconds, the fuse  104  will not trigger. 
     A curve  302  shows a load characteristic of the parallel electrical arc  106 , for example corresponding to the timeline shown in  FIG. 2 . Because the time-dependent current I(t) of the electrical arc  106  does not reach the triggering curve of the fuse  104  (e.g. the curve  302  is positioned left of the curve  303 ), the electrical arc  106  does not lead to an activation and an interruption of the circuit by the fuse  104 . 
     By means of the detection unit  107 , the solution shown here facilitates that the triggering characteristic of the fuse  104  (curve  303 ) is upgraded with an active triggering characteristic according to a curve  304 , which in particular takes into account such time periods as are typical for an electrical arc, but are too short to trigger the fuse  104 . By means of the active triggering characteristic, the separating element  103  can already be opened and therefore the electrical arc  106  can be interrupted when the curve  304  is reached and/or exceeded (from left to right in  FIG. 3 ). Because the curve  304  is near the curve  302 , i.e., near the load characteristic of the electrical arc  106 , the number of faulty triggers can be reduced and/or in particular minimized. 
     For example, the curve  304  can be realized in such a fashion that, for example, an associated current value  305  is predetermined for the time period t RMS =1 ms. Said current value  305  can be used for a first comparison of the output signal of the differential amplifier  108 . Optionally, a second comparison can be performed by specifying a second current value  306  based on the time period t RMS =0.1 ms. The first and the second comparison can be coupled in various ways to determine whether the separating element  103  should be opened. An example of the implemented interconnection is shown, for example, in  FIG. 6  below. 
     Upgrading the triggering characteristic of the fuse  104  with the active triggering characteristic results in a maximum utilization range, as is shown by example left of a curve  301 . 
       FIG. 4  shows a schematic diagram similar to  FIG. 1 . In this respect, reference is made to the explanations above.  FIG. 4  differs to  FIG. 1  in that it shows a serial electrical arc  401  in the supply line  110 . In addition, a capacity  402  is arranged parallel to the load  105 . Said capacity  402  can also be developed as part of the load  105  (for example, if the load  105  comprises a circuit with a capacitor that is arranged in parallel to said circuit). Preferably, the capacity  402  comprises at least one capacitor, with a capacitor value in the one-digit millifarad range and with a resistance of, for example, less than 20 mOhm being provided parallel to the load  105 . In particular, it is possible to customize the dimension of the capacity  402  for the specific user. 
     To ensure protection against this type of serial electrical arc  401  and the fire risk related thereto, the current through the fuse  104  is detected with the voltage drop at the fuse  104 , as described above in the case of the parallel electrical arc  106 . 
     The serial, intermittent electrical arc  401  briefly interrupts the connection to the load  105 , and the connection resumes after the interruption. Because the load  105  is supplied from the capacity  402  from the moment the load  105  is interrupted, the capacity  402  is discharged at least partially (or completely). As soon as the electrical arc resumes a conductive connection, large current peaks result to load the capacity  402 . Such current peaks can be used to detect the serial electrical arc  401 , as in the case of the parallel electrical arc  106 . 
       FIG. 5  shows a diagram with several time signal curves. A signal curve  501  shows a total current through the load  105  (and the fuse  104 ), a signal curve  502  shows a voltage at the fuse  104 , and a signal curve  503  shows a voltage at the load  105 . 
     In the example shown in  FIG. 5 , the supply line  110  is interrupted at a point in time t 1 . The total current  501  and the voltage at the fuse  104  drop to 0; the voltage at the load  105  gradually drops to 0 because the load  105  is first supplied with the energy stored in the capacity  402 . From the point in time t 1  to a point in time t 2 , the intermittent serial electrical arc  401  interrupts the electric circuit. From the point in time t 2  on, the connection to the supply line  110  is temporarily restored; because of the previously discharged capacity  402  there will be high current peaks of the total current  501 , which are above the total current  501  in steady-state (in the present example, the current peaks are above 100 A and below −100 A, whereas in normal operation, the total current  501  is nearly constant at approximately 50 A). Correspondingly, the signal curve  502  results as voltage drop at the fuse. Said signal curve  502  can be evaluated so that the evaluation unit  109  can detect the serial electrical arc  401  and open the separating element  103 . 
       FIG. 6  shows an example of a circuit for the detection unit  107 . The voltage at the fuse  104  is determined by means of a differential amplifier  601  (which can correspond to the differential amplifier  108  mentioned above). 
     As explained above, current peaks during a parallel short circuit (caused by the parallel electrical arc  106 ) lead to a proportional voltage drop at the fuse  104  and/or current peaks result at the fuse  104  due to the charge of the capacity  402  parallel to the load  105  in the case of the serial electrical arc. 
     The output of the differential amplifier  601  is connected to the non-inverting input of an operational amplifier  602  and to the non-inverting input of an operational amplifier  603 . A capacitor C 1  is arranged between the inverting input of the operational amplifier  602  and its output, and a resistor R 1  is switched in parallel to said capacitor. The inverting input of the operational amplifier  602  is connected to ground via a resistor R 3 . A capacitor C 2  is arranged between the inverting input of the operational amplifier  603  and its output, and a resistor R 2  is switched in parallel to said capacitor. The inverting input of the operational amplifier  603  is connected to ground via a resistor R 4 . 
     The output of the operational amplifier  602  is connected to the first input of a comparator  604 . The output of the operational amplifier  603  is connected to the first input of a comparator  605 . The second input of the comparator  604  is connected to the second input of the comparator  605 , and is supplied with a reference voltage Uref via a node. The reference voltage Uref corresponds by example to the voltage that displaces the active triggering characteristic in the direction of the curve  304 . 
     The output of the comparator  604  is connected to the first input of an AND gate  606  and the output of the comparator  605  is connected to the second input of the AND gate  606 . The output of the AND gate  606  provides a signal  607  that indicates an electrical arc fault and with which the separating element  103  can be opened. 
     In the present example, according to  FIG. 6 , the operational amplifiers  602  and  603  with respective wiring represent integrators that determine different time periods for the integration (integration time constants) as a function of the dimensioning of the wiring. The wiring of the operational amplifier  602  determines a time period T 1  according to
 
T1=2πR1C1,
 
     and the wiring of the operational amplifier  603  determines a time period T 2  according to
 
T2=2πR2C2.
 
     For example, the circuit can be designed for T 1 −1 ms and T 2 −10 ms. 
     At the output of each operational amplifier  602  and  603 , and for the time periods T 1  and/or T 2 , the voltage is proportional to an energy that was taken up by the fuse during that time period. The example lists two time periods T 1  and T 2 . A comparison to the reference voltage Uref is performed for each time period, with the signal  607  opening the separating element  103  only if the energy integrated in both of the two time periods T 1  and T 2  is already larger than a threshold value determined by a the reference voltage Uref. 
     As shown in  FIG. 6 , the logical interconnection  608  of the output signals of the operational amplifiers  602  and  603 , resulting in the signal  607 , is one of many possible implementations. For example, other logical interconnections (such as different gates, for example) and/or multiple reference voltages may be provided. It is furthermore possible that only one single integrator or more than two integrators are provided. 
     One advantage of the solution presented here is that it is possible to determine a precise current value per at least one time period, with said time period optionally being designed flexibly. In particular, the at least one time period may be short compared to a time period in which a conventional fuse (such as a melting fuse, for example), would trigger. Another advantage is that multiple time periods can be predetermined and coupled, for example to take a load characteristic of a fault, such as an electrical arc into account as precisely as possible. As a result, a conventional fuse with a predetermined triggering curve can therefore be upgraded with an active triggering characteristic that in particular takes into account time periods during which the energy detected in the fuse is not sufficient for triggering the fuse. 
       FIG. 7  shows by way of example a mechanical integration of an analog filter  704 , such as according to the circuit shown in  FIG. 6 , for example, for the detection of an electrical arc.  FIG. 7  shows a fuse limiter  701  (such as 48V, for example) in a plan view  707  as well as a lateral view  702 , with the fuse limiter  701  being connected to the analog filter  704  via spacers  703 . Furthermore,  FIG. 7  shows screw connections  705 . 
     By means of a connection line  706 , a plurality of the fuses with analog filter, as shown in  FIG. 7 , can be connected in parallel. 
     Alternately, the analog filter  704  can also be inserted and/or fastened above the fuse limiter  701 . 
     Although the invention was illustrated and described in detail by the at least one embodiment, the invention is not limited to said embodiment and one skilled in the art may derive other variations within the protective scope of the invention. 
     LIST OF REFERENCE SYMBOLS 
     
         
           101  Battery 
           102  Ground 
           103  Separating element (such as an electronic switch or relay, for example) 
           104  Fuse (such as a melting fuse, for example) 
           105  Load 
           106  Parallel electrical arc 
           107  Detection unit 
           108  Differential amplifier 
           109  Evaluation unit 
           110  Supply line 
           111  Ground line 
           301  Curve (limit of the maximum usage range) 
           302  Curve (load characteristic of the electrical arc) 
           303  Triggering curve of the fuse  104   
           304  Active triggering curve 
           305  Current value 
           306  Current value 
           401  Serial electrical arc 
           402  Capacity (comprising at least one capacitor, for example) 
           501  Total current through the load  105  (and the fuse  104 ) 
           502  Voltage at the fuse  104   
           503  Voltage at the load  105   
           601  Differential amplifier 
           602 ,  603  Operational amplifier 
           604 ,  605  Comparator 
           606  AND gate 
           607  Signal (Electrical arc fault) 
           608  Logical interconnection 
         R 1 , . . . , R 4  Resistance 
         C 1 , C 2  Capacitor 
           701  Fuse limiter 
           702  Lateral view 
           703  Spacer 
           704  Analog filter 
           705  Screw connection 
           706  Connecting line 
           707  Plan view

Technology Classification (CPC): 7