Abstract:
An adaptive fusing electrical circuit (circuit) including a power supply and an electrical load drawing an electrical current therethrough. The circuit includes a current detector that measures a current level through the circuit. An interruption switch, which is normally closed, is electrically coupled to the electrical load and the current detector having an open state and a closed state. A controller is coupled to the power supply, the current detector, and the switch, the controller monitors the current level and a first circuit parameter of the electrical circuit. The controller interrupts the electrical current by switching the interruption switch from the closed state to the open state when the current level and the first circuit parameter are outside corresponding guard bands.

Description:
BACKGROUND OF INVENTION 
     The present invention relates generally to automotive electrical power systems, and more particularly, to a method and apparatus of adaptive fusing within an electrical circuit. 
     Various types of multi-voltage level on-board systems have been proposed for automobiles. Typically, the automotive electrical systems use 14 volts. Recently, however, the automotive industry has started to discuss moving to a higher system voltage, such as 42 volts. A higher voltage system is particularly adapted to supply power to high power loads, such as the integrated starter alternator of the vehicle. The use of higher voltages allow the use of lower current for existing electrical loads, and allowing more power to be available for other loads. 
     Higher voltage systems create increased arcing between switch contacts and terminals upon separation. The severity of the arc increases drastically with increase in voltage. Various drawbacks may also be evident. 
     In 42-Volt systems, when electrical contacts are separated or brought close together an electrical arc may occur between the contacts, which has a sparl/arc intensity and temperature much more severe as compared with the present 14-Volt systems. Unfortunately, present passive fusing schemes, such as in-line fuses, only protect against an over-current condition and not against most common series or parallel faults caused by arcing between contacts. For example, in the case of loads such as motors and lamps, the fuse element is usually oversized so as to be capable of withstanding the large inrush currents, which is pre-selected based on the usage profiles of these loads. In-line fuses therefore are incapable of protecting against short circuits of very small duration (slow blow) or resistive shorts that do not significantly exceed usual 350% rated current of the fuse to blow quickly, thereby overstressing circuit wires. 
     Recently, there has been an introduction of an Arc Fault Circuit Interrupter (AFCI), as in U.S. Pat. Nos. 5,835,321 and 5,121,282, based on the detection of a high frequency signal seen during a sustained arc during a showering arc (amplitude varying arc having different frequency components). The frequency detection could be problematic, especially in the case of arcing with inductive or capacitive elements in series, due to filtering of these high frequencies, depending on the location of the arc (after the load). However, for vehicle applications the detection and filtering system is so coarse that the AFCI could falsely trip. A false trip occurs when a fusing technique falsely interrupts current in an electrical circuit when a normal increase in current level occurs for a brief period of time during normal operation. U.S. Pat. No. 5,839,092 looks at rate-of-change of current and polarity in household AC-systems. The system described in patent ″092 does not consider duration of the arcs, which is therefore inapplicable for vehicle environments having various components with various normal operating characteristics. During normal operation insignificant arcs may occur, which would cause the patent ″092 to interrupt the current. For example, in the case of the main battery supply, a false trip of the fuse would cause the vehicle to loose power. 
     Therefore, it is desirable to develop a new technique for electrical current interruption. The new technique should be capable of interrupting a circuit during an arc fault while minimizing false tripping. Additionally, the new technique should be capable of adapting to load conditions that it is being used to protect. 
     SUMMARY OF INVENTION 
     The forgoing and other advantages are provided by a method and apparatus of adaptive fusing for an electrical circuit. An adaptive fusing electrical circuit including a power supply and an electrical load drawing an electrical current therethrough. The circuit includes a current detector that measures a current level through the circuit. An interruption switch, which is normally closed, is electrically coupled to the electrical load and the current detector having an open state and a closed state. A controller is coupled to the power supply, the current detector, and the switch. The controller monitors the current level and a first circuit parameter of the circuit. The controller has a first guard band corresponding to the current level and a second guard band corresponding to the first circuit parameter. The controller compares the current level to the first guard band and the first circuit parameter to the second guard band. The controller interrupts the electrical current by switching the interruption switch from the closed state to the open state when the current level is outside the first guard band and the first circuit parameter is outside the second guard band. 
     The present invention has several advantages over existing fusing techniques. One advantage of the present invention is that it provides an improved and reliable adaptive fusing technique. The present invention also interrupts the circuit during an arc fault while minimizing false tripping. 
     Another advantage of the present invention is that it is capable of adapting to the load conditions that it is being used to protect. In other words, the present invention adapts to aging effect of loads by monitoring current decay rates during normal operating conditions. 
     The present invention itself, together with further objects and attendant advantages, will be best understood by reference to the following detailed description, taken in conjunction with the accompanying drawing. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     For a more complete understanding of this invention reference should now be had to the embodiments illustrated in greater detail in the accompanying figures and described below by way of example: FIG. 1 is a block diagrammatic view of a vehicle using an adaptive fusing electrical circuit in accordance with an embodiment of the present invention. 
     FIG. 2 is a schematic view of an adaptive fusing apparatus applied in a series arc according to an embodiment of the present invention. 
     FIG. 3 is a graph of current versus time showing a typical MAKE arc and a typical BREAK arc for a 42V system. 
     FIG. 4 is an enlarged view of a portion of the MAKE arc of FIG.  3 . 
     FIG. 5 is a schematic view of an adaptive fusing apparatus applied in a parallel arc according to an embodiment of the present invention. 
     FIG. 6 is a schematic view of a dual adaptive fusing apparatus applied in a parallel circuit according to an embodiment of the present invention. 
     FIG. 7 is flow chart illustrating an adaptive fusing technique according to an embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION 
     In the following figures the same reference numerals are used to refer to the same components. Also in the following description, various operating parameters and components are described for one constructed embodiment. These specific parameters and components are included as examples and are not meant to be limiting. 
     While the present invention is described with respect to a method and apparatus of adaptive fusing for a 42V electrical circuit within a vehicle, the following method is capable of being adapted for various purposes and is not limited to the following applications and electrical systems: vehicle circuits, residential systems, commercial systems, communication systems, or other electrical circuits and systems that need adaptive fusing. 
     Referring now to FIG. 1, a block diagrammatic view of a vehicle  10  using an adaptive fusing electrical circuit  12  in accordance with an embodiment of the present invention is shown. The circuit  12  is a series circuit, which includes a 42V power supply  14 . Supply  14  although described as a 42V power supply may be of various voltage levels. The supply  14  may be, but is not limited to one of the following: a motor, a generator, a vehicle voltage bus, or other resistive or inductive power supplying source. Supply  14  transfers electrical current to the adaptive fusing apparatus  16 . The adaptive fusing apparatus  16  monitors the current transfer through the circuit  12 . The current transferred through the apparatus  16  is drawn by the load  18 . The load  18  may be any vehicle component that uses electrical power. 
     Referring now to FIG. 2, a schematic view of an adaptive fusing apparatus  16  applied in a series circuit  12  according to an embodiment of the present invention is shown. Electrical current represented by arrow  21  is transferred from supply  14  through the adaptive fusing apparatus  16  and electrical contacts  17  to the load  18 . One skilled in the art would recognize that load  18  may be either a resistive or inductive load. 
     The apparatus  16  has a controller  22  in series with an interrupt switch  24 . The switch  24  has a closed state and an open state. The controller  22  opens switch  24  when predetermined conditions are met. The switch  24  is used to selectively allow current to be drawn from load  18 . Although, the present invention is described with regards to a switch  24 , one skilled in the art would realize that the present invention might be applied to any electrical component that may produce arcing, such as a motor or resistive load. The switch  24  is also in series with a current sensor  26 . The current sensor  26  measures current transferred through circuit  20 . 
     The controller  22  may be of various style and type and is not limited to one of the following: microprocessor or signal processor, and a series of logic devices. The switch (breaker)  14  is an electromechanical relay, an active device such as a MOSFET, or other electronic control device. The controller  22  of the present invention has RAM, EEPROM, or flash memory for storing values associated with guard bands. In general, a guard band is a determined range with an upper boundary and a lower boundary. The upper and lower boundaries may be a single constant or continuous value or may be a varying set of values that are measured over time. A determined range is related to a circuit parameter selected from the following list: current, duration of current, voltage, temperature, resistance, frequency, amplitude, inductance, impedance, or other electrical or mechanical parameter. The determined range may be predetermined or may be adaptively created or changed during vehicle  10  operation. Each electrical device in circuit  12  has its own characteristics which are related to the above mentioned parameters. Controller  22  is capable of learning the duration of short arcs during switch closure or opening, and any brush-arcs during the operation of dc-motors, so as to protect against a false trip. The usual current decay rates when turning-off an inductive load via a switch are also learned. Since the current pass through the circuit  12  is being monitored, any over-current condition is easily detectable. 
     Referring now to FIG. 3, a graph of current versus time showing a typical MAKE arc  50  and a typical BREAK arc  52  for a 42V system is shown. Curve  54  represents voltage across load  18  and curve  56  represents current passing through load  18 . As electrical contacts  17  are brought together an arc occurs referred to as the MAKE arc  50  as shown as part of curves  54  and curve  56 . A close-up view of the MAKE arc  50  is best seen in FIG.  4 . As the contacts  17  are separated another arc may occur, which is referred to as the BREAK arc  52  as shown as part of curves  54  and curve  56 . 
     The controller  22  monitors current level, duration of the current level, and frequency information. The current level duration caused by an arc depends on the opening speed of switch  24 , the contact surface area present on switch  24 , the number of contacts present in switch  24 , and arc suppression similar to magnetic blow out. The controller  22  opens switch  24  when the current level and the duration of the current level caused by an arc are outside a first guard band and a second guard band respectively. The present invention also compares a signature of the current information with that of a determined signature, which corresponds to load  18  during normal operation. When the current profile is outside the first guard band and the signature measured is outside an adaptable signature guard band having an upper boundary and a lower boundary the controller opens switch  24  to interrupt the current transfer. A controller  22  also analyzes the frequency spectrum of the signal together with the sudden current bursts and current decay characteristics, and compares its signature to a set of determined arc parameters. Frequency domain analysis detects sudden drops or increases in current and the on set of a showering arc. The aforementioned allows the controller  22  to determine severity of the arc. Depending on the severity and repetition rate, the controller  22  trips switch  24  to the open state, isolating the power to the fault and loads downstream. The controller  22  may also send a signal via a Controller Area Network (CAN) message to a vehicle main computer (not shown) identifying the location of the arc or tripped switch. Identifying the location of the increase in current aids in troubleshooting circuit  12  and may provide information on the severity of the arc. 
     The controller  22  also includes the fuse-curve characteristics, based on a predetermined percentage increase of the current through the circuit. These characteristics will be actively varied to compensate for both cold and warm temperatures. 
     In operation, controller  22  learns normal current and arc duration from operating load  18 . The controller  22  then establishes a guard band around normal operating parameter levels to prevent any possible nuisance tripping. Controller  22  measures and saves the normal current levels and the normal allowable arc durations for load  18 , thereby, allowing it to evaluate whether the arc durations are greater than a maximum allowable arc duration for a particular current level. When this determination proves positive, the controller  22  will interrupt the current  21  by tripping switch  24  to the open state. 
     The present invention is capable of detecting resistive short circuits which are intermittent, and has the capability of being remotely tripped, for example, by an airbag in the event of a crash, through CAN messaging or via a vehicle voltage bus. A resistive short could happen at various locations in circuit  12 . A resistive short may occur in any vehicle component as between contacts on a switch or between unshielded wire or between an unshielded wire and a vehicle&#39;s metallic body or a vehicle ground. Another example of when a resistive short may occur is when electrical contacts are pulled apart, sometimes referred to as a “hot swap”, in which the current drops suddenly followed by a slow decay rate. The present invention will ensure fast over-current protection, especially when shorts to ground occur, greatly reducing the potential for a hazardous condition. Apparatus  16  is adaptable to any fusing characteristic including; duration of current, fusing amperage, fusing power, or other fusing characteristics, which depends on the load. Normal operational current levels, and normal arc durations due to resistive and inductive load operation are included within the apparatus  16  for circuit  12 . Each of these parameters have a designated guard band so as to prevent nuisance trips, while at the same time prevent extended arcs that could potentially cause an undesirable or hazardous condition. 
     An inductive load has a smooth or extended decay rate rather than a sudden increase in current level as with resistive loads, which signify a problem in operation. The controller  22  may have an algorithm, which depends primarily on the current and the current duration of an arc as to detect problems in inductive load operation. The algorithm would perform a time domain analysis to determine the onset and duration of the sustained arc. Frequency domain analysis may also be performed to determine the onset of a showering arc. A sustained arc may occur during the time when load  18  is not drawing power as in the case of a parallel arc. The sustained arc does not show a change in frequency from any normal operation. So if the short occurs in a controlled fashion, there is a possibility that the sustained arc could be present for a relatively long period without any high frequency component. For this reason, the time-domain analysis with detection of the rate of decay of current will be sufficient to detect the sustained arc. A sustained arc may also occur when load  18  is drawing power as in the case of a series arc. When load  18  is drawing power the current  21  may have varying amplitude and frequency even though the current is decaying over time, therefore the frequency domain analysis would be used. 
     Referring now to FIG. 5, a schematic view of an adaptive fusing apparatus  16  applied in a parallel arc  12 ″ according to an embodiment of the present invention is shown. The apparatus  16  transfers current  21  to a first parallel path  70  having a first load  72  and to a second parallel path  74  having a second load  76 . Although, the contacts  17  are shown as part of the second parallel path  74  they may be located anywhere in circuit  12 ″. The controller  22  opens switch  24  when current is outside guard bands determined for the first parallel path  70  and the second parallel path  74 . 
     Referring now to FIG. 6, a schematic view of a dual adaptive fusing apparatus  80  applied in a parallel circuit  12 ″″ according to an embodiment of the present invention is shown. The apparatus  80  may have multiple interrupt switches  82  and current sensors  84  providing the ability to interrupt current from being transferred to either the first load  72  or the second load  76 . Although, circuit  12 ″″ is illustrated as having two interrupt switches  82  and two current level sensors  84  any number of switches or current level sensors may be used in conjunction with additional loads. A message may be sent to a vehicle main computer (not shown) identifying a path where the increase in current level occurred. 
     Referring now to FIGS. 2 and 7, a flow chart illustrating an adaptive fusing technique according to an embodiment of the present invention is shown. 
     In step  100 , electrical current  21  is measured using sensor  26  and normal operating characteristics are determined. The normal operating characteristics include: load profile, current levels, duration of current levels, voltage levels, power consumption, frequency information, and other measurable operating characteristics of the circuit  12 . All the measured values are transferred via measured signals to the controller  22 . 
     In step  102 , the measured signals are filtered using a low pass filter. The filter may be a noise filter, an anti-aliasing, or other filter know in the art. 
     In step  104 , the current change is compared with a predetermined value. The predetermined value represents a value at which a short to ground has occurred. When the current level is greater than the predetermined value step  118  is performed otherwise step  106  is performed. 
     In step  106 , the current level is compared to a determined guard band. When the current level is outside the determined guard band step  108  is performed otherwise either step  110  or  112  is performed. When the current level is similar to a resistive normal operation level step  112  is performed. When the current level is similar to an inductive normal operation level step  110  is performed. 
     In step  110  and  112 , the controller  22  determines that circuit  12  is operating in normal mode and returns back to step  100 . The severity of the arc may be considered in conjunction with other parameters. When the controller  22  determined the severity of the arc and the parameters considered are outside determined guard bands step  118  is performed. 
     In step  108 , the duration of the arc is compared with a determined guard band. When the duration of the current level is outside the determined guard band steps  114  and  116  are executed. 
     In step  114 , the decay rate of the current is compared to a preset or determined value. When the decay rate is less than the preset value step  118  is performed after passing through the logic “OR” gate  117  otherwise the controller  22  returns to step  100 . 
     In step  116 , when change in current level is greater than a predetermined percentage and number of occurrences exceeds a preset count step  118  is performed after passing through the logic “OR” gate  117  otherwise the controller  22  returns to step  100 . 
     In step  118 , an arc has been detected. The controller  22  interrupts the current  21  in circuit  12  to prevent degradation of electrical components and potential hazardous conditions from occurring. 
     The present invention thus achieves an improved and reliable adaptive fusing system by learning the duration of changes in current in combination with other parameters as compared with those in normal operation. In this way, the present invention is capable of interrupting a circuit during an arc while minimizing false tripping. Additionally, the present invention is capable of adapting to the load conditions of which it is protecting. 
     The above-described method, to one skilled in the art, is capable of being adapted for various purposes and is not limited to the following applications: vehicle circuits, residential systems, commercial systems, communication systems, or other electrical circuits and systems that need adaptive fusing. The above-described invention may also be varied without deviating from the true scope of the invention.