Abstract:
A power management and distribution system includes a source block having a power distribution line, wherein the power distribution line includes a distribution switch. At least one load block is in operable communication with the power distribution line and having a plurality of load block power output lines, wherein each of the plurality of load block power output lines includes a load switch. Further included is a plurality of loads each carried power by at least one of the plurality of load block power output lines. Yet further included is a protection logic unit comprising at least one algorithm for comparing a power characteristic to a power characteristic threshold at a plurality of locations, wherein the protection logic unit selectively determines which of the source block switches, distribution switches and the load switches of the plurality of load block power output lines are opened based on at least one comparison.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to power management and distribution systems, and more particularly to such systems having fault detection and isolation assemblies, as well as methods directed toward fault detection and isolation for such systems. 
     In typical electrical power generation and distribution systems, the measurement of currents on power wiring and protection of the wiring, as well as connected equipment, is needed in the event of failure. An aircraft is one illustrative example of an application for such systems. For aircraft systems, electrical energy is essential for continued flight when relying on electrical flight controls, and is also flight critical for electrically driven hydraulic pumps. Aircraft power systems may use a variety of power characteristics including AC (Alternating Current) or DC (Direct current) systems. Further typical variations of power types may include power sources, loads and distribution of nominal voltages including, but not limited to 28 Vdc, 270 Vdc, or 540 Vdc and 26 Vac, 115 Vac, and 230 Vac. The AC system types may also include Constant Frequency (CF), or Variable Frequency (VF) systems with a wide variation in output current and power ratings. Severe wiring or internal faults within these systems and within power distribution equipment panels or wiring may cause loss of power to these flight critical systems. Protective functions and assemblies within the power distribution systems improve flight safety by preventing or minimizing the effect of system or wiring faults. Rapid detection and isolation, as well as segregation, of short circuit faults are desirable due to the localized heating and damage that high current or arcs may cause. 
     Arcing type faults can be difficult to distinguish from normal non-linear or pulsed type load effects. Typical power systems have relied on current sensors at multiple locations on each wire segment and dedicated controllers and protection functions for each wire. These methods are large, heavy and expensive, have high power losses, or have other undesirable features. 
     BRIEF DESCRIPTION OF THE INVENTION 
     According to one embodiment, an AC or DC power management and distribution system having a fault detection and isolation assembly includes at least one source block having a power distribution line, wherein the power distribution line includes a distribution switch. For applications using AC power, each of the switches, buses and sources, etc., may represent either single phase or 3 phase circuits. Also included is at least one load block in operable communication with the power distribution line and having a plurality of load block power output lines, wherein each of the plurality of load block power output lines includes a load switch. Further included is a plurality of loads each carried power by at least one of the plurality of load block power output lines. Yet further included is a protection logic unit comprising at least one algorithm for comparing a power characteristic to a power characteristic threshold at a plurality of locations, wherein the protection logic unit selectively determines which of the distribution switch and the load switches of the plurality of load block power output lines are opened based on at least one comparison. 
     According to another embodiment, a power management and distribution system having a fault detection and isolation assembly includes at least one source block having a plurality of power distribution lines, wherein each of the plurality of power distribution lines includes a distribution switch and a source switch. Also included is a plurality of load blocks, each of the plurality of load blocks in operable communication with at least one of the plurality of power distribution lines and having a plurality of load block power output lines, wherein each of the plurality of load block power output lines includes a load switch. Further included is a plurality of loads carried power by at least one of the plurality of load block power output lines. Yet further included is a protection logic unit comprising at least one algorithm for comparing a power characteristic to a power characteristic threshold at a plurality of locations, wherein the protection logic unit selectively determines which of the distribution switches and the load switches are opened. 
     According to yet another embodiment, a method of fault detection and isolation for a power management and distribution system is provided. The method includes carrying power from a power source through at least one source switch to at least one source block. Also included is carrying power from the at least one source block directly to a load block. Further included is carrying power from the at least one load block through at least one load switch to a load. Yet further included is measuring a power characteristic at a plurality of locations along a power path and calculating a power characteristic difference between at least two of the plurality of locations. Also included is comparing the power characteristic difference to a power characteristic threshold. Further included is opening at least one of the at least one source switch, the at least one distribution switch and the at least one load switch if the power characteristic difference exceeds the power characteristic threshold. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The subject matter which is regarded as the invention is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which: 
         FIG. 1  is a schematic illustration of a power management and distribution system having at least one source block and at least one load block according to a first embodiment; 
         FIG. 2  is a schematic illustration of a power management and distribution system having at least one source block and a plurality of load blocks according to a second embodiment; 
         FIG. 3  is a schematic illustration of a power management and distribution system having at least one source block and a plurality of load blocks according to a third embodiment; and 
         FIG. 4  is a flow diagram according to a method of fault detection and isolation for the power management and distribution system. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to  FIG. 1 , a first embodiment of a power management and distribution (“PMAD”) system is schematically illustrated and identified with the reference numeral  10 . In one embodiment, the PMAD system  10  is configured to detect and isolate faults. The PMAD system  10  may be incorporated into a variety of applications, including vehicles, with one example of such a vehicle being an aircraft. The PMAD system  10  includes a power block  12 . The term “power block” conceptually refers to hardware structure that functionally monitors and protects at least one load, but typically a plurality of load circuits. Nominally, this may include solid state power controllers (SSPCs), control logic, processing logic, internal communications busses, and power supplies to power various control elements. It may also include the devices necessary to convert the power from what is available at the input to the power block  12  to what the various loads require (e.g. AC to DC conversion). The power block  12  also includes at least one protection logic unit  14  that comprises algorithms used to provide for identification and isolation of failures, such that a minimum of user equipment is affected. 
     As shown in the illustrated embodiment, the power block  12  includes at least one, but typically a plurality of, power source supplies  16  that provide at least one source block input line  18  to at least one source block  20 , beginning what will be referred to as a power path  21 . AC system types may include Constant Frequency (CF), or Variable Frequency (VF) systems with a wide variation in output current and power ratings. At least one source switch  22  is disposed in operable communication with each source block input line  18 . The power path  21  continues to at least one, but typically a plurality of, distribution switches  24  that each are in operable communication with a source block power output line  26  that carries power to at least one load block  28 , with the power path  21  splitting in the event a plurality of load blocks  28  are provided power through distribution switch  24 . A load block input line  30  continues the power path  21  to at least one, but typically a plurality of, load switches  32  that are each in operable connection with load zone  34  that is ultimately powered by the load path  21 . The loads  34  may take on a variety of forms, and in an application related to an aircraft, the loads  34  may include, but is not limited to, flight control systems. A typical load block  28 , for example, load block A per  FIG. 1  provides for separate and unique load utilization equipment L 1 -L 8 , with each corresponding L 1 -L 8  switch being separately controllable. Similarly, load block B may have separately controllable switch elements L 1 -L 8  providing power to other unique load utilization equipment L 1 -L 8 . 
     The aforementioned protection logic unit  14  is configured to receive a variety of data from numerous components of the PMAD system  10 , with one example of such components relating to power characteristics at a plurality of locations throughout the PMAD system  10 , and more particularly within the power block  12 . The power characteristics include common characteristics, such as current and voltage, for example, but it is to be appreciated that numerous other characteristics may be monitored and communicated to the protection logic unit  14 , either explicitly or inherently. The plurality of locations referenced above may include several locations along the power path  21 , such as the source block input line  18 , between the source switch  22  and the distribution switch  24 , between the distribution switch  24  and the load block input line  30  and the at least one load switch  32 , and between the at least one load switch  32  and the loads  34 . These locations are merely illustrative and it is to be understood that numerous other locations within the PMAD system  10  may be monitored, depending on the application configuration. 
     Monitoring a power characteristic, such as current, at the plurality of locations provides the protection logic unit  14  to determine a plurality of current differences along the power path  21 , which may be used to determine if a significant current loss is occurring at critical locations. The calculated current differences may be compared to a power characteristic threshold that is predetermined to account for typical errors in the monitoring devices, such as current sensors. This reduces the likelihood that a false fault detection and isolation occurs (i.e., one or more of the load switches  32  is opened) in the PMAD system  10 . Additionally, the current difference may be monitored over a specified time period to ensure that non-ideal behaviors such as sensor saturation, current sub-transient effects, sensor signal sampling or communications time skewing induced errors do not cause improper fault detection and isolation. Such a time period is typically less than or equal to about 20 milliseconds (ms). An algorithm representing the fault detection scheme described above is generally as follows:
 
Fault={(Current  A −Current  B )&gt;(1+0.08)*Normal Rated Current}
 
     The preceding algorithm is merely exemplary and may be modified with respect to the allowable error of 8% that is shown above. Current A and Current B are illustrative currents measured at the plurality of locations described above. In the case where the current difference exceeds the power characteristic threshold, at least one switch is opened, thereby cutting off the supply of power to one or more components or loads. 
     The PMAD system  10  is configured to calculate a plurality of current differences and the provision of such data to one or more logic units, including the protection logic unit  14 , allows the sensing of a fault at a variety of locations. Such monitoring and employment of algorithms identifies a fault at the “lowest level” in the PMAD system  10 , with the lowest level referring to a location closest to the loads  34 , thereby alleviating the need to trip, or open, a switch excessively far “upstream” in the system, which would unnecessarily result in the loss of power to numerous components that should otherwise be functioning. 
     Referring to  FIG. 2 , a second embodiment of the PMAD system  100  is illustrated. PMAD system  100  is similar in construction to PMAD system  10 , but as is shown, a plurality of load blocks  102  each include distinct source block power output lines  104 ,  106 ,  108  that operably carry power to each of the load blocks  102 . Additionally, each of the load blocks  102  communicates power characteristic data to a distribution switch logic unit  110 ,  112 ,  114 . Each of the distribution switch logic units  110 ,  112 ,  114  is in operable communication with the distribution switches  24 . The illustrated embodiment of the PMAD system  100  provides for more discrete control in the event a fault is detected. Specifically, based on the individualized source block power output lines  104 ,  106 ,  108 , a fault detected between the distribution switch  24  and one of the load blocks only requires opening the distribution switch  24  associated with the faulty load block, rather than cutting off power to a plurality of load blocks carried power by the same source block power output line. 
     Referring to  FIG. 3 , a third embodiment of the PMAD system  200  is illustrated. The PMAD system  200  is similar in construction to PMAD systems  10  and  100 , but as is shown, a plurality of load blocks  202  each include combined source block power output lines  204 ,  206 ,  208  that operably carry power to each of the load blocks  202 . Additionally, each of the load blocks  202  communicates power characteristic data to a source switch logic unit  210 . The source switch logic unit  210  is in operable communication with the source switches  22 . The illustrated embodiment of the PMAD system  200  provides for more discrete control in the event a fault is detected. Specifically, based on the individualized source block power output lines  204 ,  206 ,  208 , a fault detected between the source switch  22  and one of the load blocks requires opening each of the source switches  22  that may be providing power to the combined power present on the source bus bar  201  to a plurality of load blocks carried power by the same source block power output line. This architecture provides greater power density by using all of the distribution block outputs to power external loads rather than internal loads, such as the load block card power inputs shown on  FIGS. 1 and 2 . 
     Referring now to  FIG. 4 , a method of fault detection and isolation  300  of the PMAD system  10  is also provided, and the following description is applicable to the second embodiment of the PMAD system  100 . The PMAD system  10 , and more particularly the fault detection and isolation system of the power block  12  have been previously described and specific structural components need not be described in further detail. The method  300  includes carrying power  302  from one or more power supplies  16 , or sources, to the at least one source block  20  through one or more source switches  22  in operable communication with the source block input line  18 . The power is then carried further along the power path  21  into what are referred to as “branches,” which comprise various levels of components of the PMAD system  10 . Power is then carried  304  from the at least one source block  20  through one or more distribution switches  24  to one or more load blocks  28 . The power path(s)  21  to the load blocks  28  may take the form of a single path that splits into a plurality of branches from a single distribution switch to a plurality of load blocks, as in the case of the first embodiment shown in  FIG. 1 . Alternatively, the power paths  21  may be individual lines that distribute power to distinct load blocks  28 , as in the case of the second embodiment shown in  FIG. 2 . Upon reaching the load block, power is distributed  306  through a load switch to a load. 
     As described above, monitoring of one or more power characteristic  308 , such as measurement of current, is conducted at a plurality of locations along the power path. Using the monitored data, one or more current differences may be calculated  310  and compared  312  to a power characteristic threshold, such as a predetermined current threshold. In the event that the current difference exceeds the predetermined current threshold, a fault is identified and corrective action is initiated  314 . Based on the location of the identified fault, an appropriate switch is opened in the location determined by one or more protective logic units, which may be located at various locations within the power block, or alternatively at a remote location of the PMAD system. Opening of a switch cuts off power to all branches below that switch. The logic unit(s) employ algorithms that function to open a switch at the lowest appropriate level (i.e., closest to the load), thereby minimally disrupting power operation of other components or branches of the PMAD system. 
     The resulting effect of the above-described method is that a fault below any load switch results only in removal of the associated load. Faults above any load switch, but below the load block power input line results in a trip of the distribution switch powering the appropriate load block per  FIGS. 1 and 2 . Similarly, a fault above the distribution switch results in opening of the appropriate source switch per  FIGS. 1 and 2 . Similarly, for  FIG. 3 , faults within the assembly above the load block sensor results in opening of the appropriate source switches. Therefore, a layered and segregated protection functionality provides overall failure mode selectivity, isolation and full protection for each segment of the PMAD system, including protection between power blocks, as well as within power blocks. 
     While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.