Abstract:
A power distribution system which may be provided in an aircraft for example is described, the power distribution system comprising: a power distribution bus and a plurality of localized voltage converters each supplied by the power distribution bus. By providing a plurality of localized voltage converters, the power distribution system may use fewer, or just a single power distribution bus at a particular voltage and convert to the desired voltage at or near to each of a plurality of pieces of electrical equipment being supplied.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The field of the present invention generally relates to a power distribution system such as a power distribution system for an aircraft for example. 
     2. Description of Related Art 
     One of the primary concerns for aircraft is system weight. Being able to reduce weight reduces an aircraft&#39;s fuel consumption and increases its range. An aircraft&#39;s structure, fuel, equipment and electrical wiring all contribute to its weight. The weight of electrical wiring and associated equipment for a commercial aircraft may be several hundred kilograms or several tonnes. 
     It is an aim of an embodiment of the present invention to reduce the weight of an aircraft&#39;s electrical wiring and/or associated equipment. 
     BRIEF SUMMARY OF THE INVENTION 
     According to a first aspect of the present invention, there is provided a power distribution system for an aircraft for receiving electrical power from one or more aircraft engines, the power distribution system comprising: a power distribution bus and a plurality of localised voltage converters each supplied by the power distribution bus, wherein the localized voltage converters each include a power supply arranged to provide an adjustable output voltage. 
     By providing a plurality of localised voltage converters, the power distribution system may use fewer, or just a single power distribution bus at a particular voltage and convert, to the desired voltage at or near to each of a plurality of pieces of electrical equipment being supplied. This provides a considerable weight saving in electrical wiring and associated equipment such as transformers/power distribution boxes over conventional systems which typically have at least three power distribution buses along the length of an aircraft, each at a different voltage (typically 28 volts, 115 volts and 230 volts) to supply the various types of electrical equipment provided on the aircraft. 
     Furthermore, localised voltage converters, which may be provided for one or a few components, are typically much smaller and lighter than a main voltage converter for a bus supplying an entire aircraft at a particular voltage and so may be accommodated far more easily in an aircraft. 
     According to another aspect there is provided an aircraft comprising a power distribution system comprising: a power distribution bus and a plurality of localised voltage converters each supplied by the power distribution bus. 
     According to another aspect there is provided an aircraft comprising two or more power distribution systems, each power distribution system comprising: one power distribution bus and a plurality of localised voltage converters each supplied by the power distribution bus 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: 
         FIG. 1  illustrates a conventional electrical power distribution system in an aircraft; 
         FIG. 2  illustrates a power distribution system of an embodiment illustrating an embodiment of present invention; 
         FIG. 3  illustrates a more detailed example of a power distribution system of an embodiment of the present invention; and 
         FIG. 4  illustrates a localised power converter. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  illustrates an aircraft  10  provided with a conventional power distribution system. As can be seen, the aircraft is provided with a number of engines  11  which, as well as providing thrust for the aircraft, provide electrical power for various pieces of electrical equipment provided on the aircraft. The aircraft  10  is provided with a Primary Power Distribution Box (PPDB)  13  which receives electrical power from the engines  11  via appropriate electrical connectors  12 . The PPDB  13  contains a number of transformers to provide electrical power to at least three power buses  14 ,  15 ,  16  each at a different voltage, typically 230 volts AC, 115 volt AC and 28 volts DC, Although a single PPDB 13  and corresponding set of buses  14 ,  15 ,  16  is shown in  FIG. 1 , an aircraft may have two or more PPDBs  13  and sets of buses  14 ,  15 ,  16 . For example a set may be provided on each side of the aircraft  10  or for each engine. 
     An aircraft typically has a variety of electrical components with differing power load requirements. For example some hydraulic systems, for example for operating flaps on the wings and/or lifting of landing gear will have a higher power load requirement and will typically receive power from the higher voltage bus  14 . Other electrical components on the aircraft such as ovens for the galley, instruments for the cockpit and in-flight entertainment for passengers will typically require less power and may be connected to one of the other lower voltage buses  15 ,  16 . 
     As can be seen in  FIG. 1  electrical power is remotely converted to appropriate system voltages at the PPDB  13  and then fed to various secondary power distribution boxes (SPDB)  18  for subsequent distribution to the various aircraft components/loads. 
       FIG. 2  illustrates a power distribution system in accordance with an embodiment of the present invention. In this example, the power distribution system has a power distribution bus  110  and a plurality of localised voltage converters  120 . As the localised voltage converters  120  convert the voltage on the bus  110  to the appropriate voltage required by any loads  130  close to the converters  120 , a bus  110  operating at only a single voltage is required. This significantly reduces the weight of electrical wiring compared to the arrangement shown in  FIG. 1  which requires separate buses  14 ,  15 ,  16  each operating at a different voltage. It is preferable that the highest system voltage is employed in the power distribution bus  110  as the size and weight of the wiring to provide the bus  110  may be reduced. When a lower voltage is required for given equipment, (which for the same power will demand a higher current and thus thicker wiring), this will be locally converted by the localised voltage converter  120  and supplied by wiring  131  over a shorter distance. Thus, the lower voltage, higher current, thicker wiring  131  will only be required for the relatively short distances between the localised voltage converters  120  and the appropriate lower voltage load  130 , further reducing the weight of the wiring in the power distribution system. 
     The localised voltage converters  120  may be arranged to supply power at one or two other voltages (e.g. 28 V DC, 115 V AC) as well as at the voltage of the power distribution bus (e.g. 230 V AC). 
       FIG. 3  shows a more detailed example of the embodiment of the present invention shown in  FIG. 2 . As shown schematically in this example, the Primary Power Distribution Box (PPDB)  100  can be much smaller than in the conventional power distribution shown  FIG. 1  as it is only required to supply one voltage as opposed to the multiple voltages provided by the PPDB  13  illustrated in  FIG. 1 . The simplified PPDB  100  of an embodiment of the present invention will consequently be significantly smaller, lighter and less expensive than the conventional PPDB  13  thus further saving weight and costs. 
     The localised voltage converters  120  illustrated in  FIG. 2  may be integrated with the Secondary Power Distribution Boxes (SPDB)  140  illustrated in  FIG. 3 , Whilst the SPDB  140  may be slightly increased in size due to the requirement for a localised voltage converter  120 , this is more than made up for the simplification provided by only having to receive one supply voltage from the power distribution bus  110 , Thus overall, the SPDBs  140  in embodiments of the present invention are smaller and lighter than conventional examples which receive power from several buses each at a different voltage. 
     For electrical equipment which requires the voltage provided by the bus  110 , a localised voltage converter will not be required at that point and so an even more simplified SPDB  150  may be used which will be arranged to receive only a single voltage from the power distribution bus  110  and which will not require a localised voltage converter. For example, with the power distribution bus  110  arranged to provide the highest available voltage for equipment on the aircraft (in this example 230 V) such as for retracting the landing gear, the SPDB  150  supplying the landing gear retractor will not require any localised voltage conversion. 
     Consequently, by providing a plurality of localised voltage converters  120  such that the power distribution bus  110  may provide fewer voltages, typically only a single voltage, this provides significant reduction in the weight of electrical wiring for the power distribution bus  110  as well as simplification and thus reductions in weight, size and cost of the PPDB  100  and SPDB  140 . 
       FIG. 4  illustrates an example of a localised voltage converter  120 . In this example the localised voltage converter  120  receives electrical power from the bus  110  at the highest voltage of loads supplied by the power distribution system, which in this example is 230 volts AC. The localised voltage converter  120  provides an output at a lower voltage, which for many aircraft may be, for example, 115 volts AC or 28 volts DC, but in this example is 28 volts DC. 
     The localised voltage converter  120  of this example includes a Switch Mode Power Supply (SMPS) transformer arrangement  200 . The SMPS transformer arranged of this example is provided with the appropriate windings to be able to step up and step down to provide the desired output voltage, in this example 28 volts. In this example, the localised voltage converter  120  also includes a capacitor  210 /diode arrangement  220  to provide AC/DC conversion and a Power Factor Correction Stage  230  to reduce phase shift. The SNIPS arrangement  200  is provided with a unity power factor by the high voltage intermediate rail  240 . 
     As explained above, the power distribution bus  110  preferably operates at only a single voltage and that this single voltage is preferably at the highest voltage of loads/electrical equipment supplied by the power distribution system, in this example 230 volts AC. As the bus operates at just the higher voltage, consequently, the electrical wiring of the bus  110  may be thinner than that of buses supplying a lower voltage which consequently would have a higher current. The power distribution bus  110  preferably also provides AC power. By operating at a relatively high switching frequency, preferably 10 kHz or above, more preferably higher than 50 kHz, a physically smaller, lighter and efficient localised voltage converter  120  may be provided. Providing a smaller and lighter localised voltage converter  120  enables it to be integrated into the aircraft structure more easily without requiring the provision of dedicated supports etc. realising further weight reduction and simplification. 
     Although embodiments of the present invention have been described above with reference to the accompanying drawings, many variations may be made to the examples provided without departing from the present invention. For example, an aircraft may be provided with only one two or more power distribution systems. Furthermore, each power distribution system may receive power from one or more engines.