Abstract:
An example solid state contactor assembly includes a switching element having a field-effect transistor and a diode in parallel. The switching element is configured to communicate electric current along a current flow path extending from a first bus bar to a second bus bar. A control device is configured to selectively communicate current along a portion of the current flow path through the field-effect transistor or the diode of the switching element.

Description:
BACKGROUND 
     This disclosure relates to power distribution systems and, more specifically, to solid state contactors between busses. 
     In a typical electrical power distribution system, such as an aircraft electrical power distribution system, a power center includes at least one essential bus for distributing power to various components. A plurality of power sources may communicate power to the essential bus, including any number of AC and DC busses. The power sources are typically coupled to the essential bus using a DC contactor and a diode in series, which undesirably adds size and weight to the system. There is also a significant power loss when standard power diodes are used to conduct current. 
     SUMMARY 
     An example chip on bus bar solid state contactor assembly includes a switching element having a field-effect transistor and a diode in parallel. The switching element is configured to communicate electric current along a current flow path extending from a first bus bar to a second bus bar such that the switching element determines a direction of the electrical current. A control device is configured to selectively communicate current along a portion of the current flow path through the field-effect transistor or the diode of the switching element. 
     An example power distribution system for an aircraft includes a first DC bus having a first bus bar. The first DC bus is electrically isolated from a second DC bus having a second bus bar. An aircraft component is electrically connected to the first bus bar. A solid state contactor assembly electrically connects the first bus bar and the second bus bar. The contactor assembly includes a control device and a plurality of switching elements. Each switching element includes a field-effect transistor and diode in parallel. The control device is configured to drive the switching elements to control an electrical current between the first and second bus bars such that the switching elements determine a direction of the electrical current. 
     An example method of electrically connecting a first bus bar and second bus bar includes electrically connecting the first bus bar to the second bus bar using a solid state contactor assembly. The solid state contactor assembly has multiple switching elements each having a field-effect transistor and diode in parallel. The direction of current flow between the first bus bar and the second bus bar is controlled using the plurality of switching elements. 
     These and other features of the present disclosure can be best understood from the following specification and drawings, the following of which is a brief description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic view of an aircraft power distribution system including solid state contactor (“SSC”) assemblies. 
         FIG. 2A  is a schematic view of the SSC assembly shown in  FIG. 1  in an OFF state. 
         FIG. 2B  is a schematic view of the SSC assembly shown in  FIG. 1  in the ON state. 
         FIG. 2C  is a schematic view of the SSC assembly shown in  FIG. 1  in another ON state. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIG. 1 , an aircraft  10  includes a power distribution system  12  having a first generator  14 , a second generator  16 , and a ram air turbine  18  electrically coupled to an AC bus  20 . The AC bus  20  is electrically coupled to a transformer rectifier unit  22  (“TRU”), which converts AC into DC. The TRU  22  is electrically coupled to an essential DC bus  24  and provides DC to the essential DC bus  24 . 
     Essential DC bus  24  includes a bus bar  28 . In addition to being supplied current from the TRU  22 , the essential DC bus  24  can be supplied current by a plurality of secondary DC busses  34 . Each secondary bus  34  is electrically isolated from essential DC bus  24 . Each secondary bus  34  includes a bus bar  36 . A power source  42 , such as a battery, is electrically coupled to each secondary bus  34  and provides power to each secondary bus  34 . Busses  34 , being powered by a battery  42 , are generally a lower voltage than the output of TRU  22 . In one example, SSC assembly  40  is configured so that current from bus  34  will instantaneously power essential DC bus  24  when TRU  22  fails. Additionally, current from TRU  22  is blocked from flowing to battery  42  unless battery charging is needed. The bus bar  36  of each secondary bus  34  is electrically coupled to the bus bar  28  of the essential DC bus  24  through a solid state contactor (“SSC”) assembly  40 . In this example, the SSC assembly is a chip on bus bar SSC assembly  40  such that the components of the SSC assembly  40  are disposed directly on an internal bus bar  87  (shown in  FIG. 2A-2C ). However, other SSC assemblies  40  may be used. The essential DC bus  24  is connected to components  44  such that the essential DC bus  24  provides power to the external components  44 . 
     In one example, the AC bus  20  and essential DC bus  24  are disposed within electrical power center  26 . In this example, the electrical power center  26  is an emergency electrical power center  26  such that the TRU  22  is conducting about 200 A, and the output of the essential DC bus  24  is about 28V. However, it is within the contemplation of this disclosure to use other electrical power centers having additional components, and different power distribution. 
     In operation, the first generator  14 , second generator  16 , or ram air turbine  18  supply power to the AC bus  20 . The AC bus  20  distributes current to the TRU  22 , which converts the AC to DC. TRU  22  provides DC through a switch  46  to the essential DC bus  24 . Essential DC bus  24  can receive alternate DC from the secondary busses  34  through SSC assembly  40 . Essential DC bus  24  distributes power to external components  44 , such as electronics, controls, or other external devices. A power panel control unit  41  selects the power sources  14 ,  16 ,  18  and controls the logic of the SSC assembly  40 . 
     Although only one SSC assembly  40  or  40 ′ is shown, connecting one of the bus bar  36  to the associated one of the bus bar  28 , multiple SSC assemblies  40 ,  40 ′ could be used. SSC assemblies  40 ,  40 ′ may be located on the bus bars  28 ,  36  of any of the essential DC bus  24  or secondary busses  34 . Additionally, any number of secondary busses  34  may be used, depending on system requirements. 
     Referring to  FIG. 2A-2C , the SCC  40  is disposed on internal bus bar  87  and includes a switching element  60   a  and a switching element  60   b . The features of the SSC  40 ′ would be similar to the SSC  40 . Switching elements  60   a ,  60   b  are in series and each include a diode  64  in parallel with a FET  66 . The diode  64   a  of switching element  60   a  is directed in an opposite direction from the diode  64   b  of switching element  60   b . Switching element  60   a  is electrically coupled to the bus bar  36  of the secondary bus  34  while switching element  60   b  is electrically coupled to bus bar  28  of essential DC bus  24 . 
     Each switching element  60   a ,  60   b  is electrically coupled to a control device  70   a ,  70   b . Control device  70   a  includes a comparator  72   a , a gate drive  74   a , and an OR gate  50   a  connected to the comparator  72   a  and having a control input  52   a  controlled by the power panel control unit  41 . Control device  70   b  includes a comparator  72   b , a gate drive  74   b , and an OR gate  50   b  connected to the comparator  72   b  and having a control input  52   b  controlled by the power panel control unit  41 . Each comparator  72   a ,  72   b  has inputs  78   a ,  78   b  connected on either side of each switching element  60   a ,  60   b . The comparator  72   a ,  72   b  is thus able to read a voltage drop across the connected switching element  60   a ,  60   b.    
     The comparator  72   a ,  72   b  uses inputs  78   a  and  78   b  to compare the voltage drop across connected switching element  60   a ,  60   b . When there is a voltage drop from first position  80   b  to second position  82   b  of switching element  60   b , the gate drive  74   b  communicates with the connected gate  76   b  of the attached FET  66   b  to instruct the FET  66   b  to close the gate  76   b  and allow flow through the FET  66   b . However, if the comparator  72   b  reads a voltage drop from second position  82   b  to first position  80   b , there is electric current flowing towards the secondary bus  34  as opposed to the essential DC bus  24 . The comparator  72   b  then communicates with the gate drive  74   b , which in turn communicates to open the gate  76   b  of the FET  66   b  and prevent current flow through the FET  66   b . When the gate  76   b  is open, the diode  64   b  of the switching element  60   b  will block flow towards the secondary bus  34 . After the voltage drop direction is reversed back in the direction of the essential DC bus  24 , the comparator  72   b  will again communicate with the gate drive  74   b  to order the FET  66   b  to close its gate  76   b  and allow current to flow through the FET  66   b  again. The gate drive  74   a , comparator  72   a , diode  64   a , FET  66   a , and gate  76   a  of switching element  60   a  operate in substantially the same manner for electrical current that is intended to flow from the essential DC bus  24  towards secondary bus  34 . 
     In  FIG. 2A , the bus bars  28 ,  36  are shown in an OFF state. Therefore, no current is moving through the SSC  40  and there is no flow through either switching element  60   a ,  60   b.    
     In this example, the FET  66   a ,  66   b  is a power MOSFET; however, other FETs  66   a ,  66   b  may be used. 
     In  FIG. 2B , the bus bar  36  of the secondary bus  34  is in an ON state such the power panel control unit  41  signals electrical current to be available through the SSC assembly  40  to the bus bar  28  of the essential DC bus  24 . Control input  52   a  signals OR gate  50   a  to close the gate  76   a  of the FET  66   a . Control input  52   b  is inactive such that the comparator  72   b  signals the gate  76   b  of FET  66   b  to open or close. In this example, during system power up, current moves through the FET  66   a  of switching element  60   a  and through the diode  64   b  of switching element  60   b  to establish the direction of the electrical current. In this example, the direction of the electrical current is from secondary bus  34  to essential DC bus  24 . When the essential DC bus  24  is powered by TRU  22 , diode  64   b  prevents electrical current from flowing from essential DC bus  24  to secondary bus  34 . 
     In  FIG. 2C , once the direction of the electrical current is established the bus bar  36  of the secondary bus  34  remains in an ON state and continues to distribute current through the SSC assembly  40  to the bus bar  28  of the essential DC bus  24 . In this example, after the direction is established, switching element  60   b  moves current through the FET  66   b  instead of the diode  64   b , generating power savings. 
     While the current moves through the FET  66   a  of switching element  60   a  and through the FET  66   b  of switching element  60   b  to the bus bar  28  of the essential DC bus  24 , the comparator  72   a  reads a voltage drop from first position  80   a  to second position  82   a  for switching element  60   a  and the comparator  72   b  reads a voltage drop from first position  80   b  to second position  82   b  for switching element  60   b.    
     When the comparator  72   b  detects a voltage drop across switching element  60   b  from second position  82   b  to first position  80   b , the gate drive  74   b  is instructed to communicate with the FET  66   b  to open the gate  76   b  of the FET  66   b . (This position is shown in  FIG. 2B .) If current is moving from essential DC bus  24  to secondary bus  34 , the control device  70   a  connected to switching element  60   a  would work in a similar manner as the control device  70   b  connected to switching element  60   b.    
     As a result of gate  76   b  of switching element  60   b  being open, current cannot move through the FET  66   b  and instead moves through diode  64   b  of switching element  60   b . Because the diode  64   b  forces current in a singular direction, the voltage drop direction is reversed. When the comparator  72   b  detects a voltage drop from first position  80   b  to second position  82   b , it will communicate to the gate drive  74   b  to order the gate  76   b  closed and current will flow through FET  66   b  of switching element  60   b.    
     Although the example electric current in  FIGS. 2A-2C  is shown flowing through the SSC  40  from secondary bus  34  to essential DC bus  24 , flow may move through the SSC  40  in the opposite direction in a the same manner as described above. When power panel control unit  41  signals electric current to flow from essential DC bus  24  to secondary bus  34 , control input  52   a  and control input  52   b  are reversed such that control input  52   a  is inactive and control input  52   b  signals OR gate  50   b  to close the gate  76   b  of the FET  66   b.    
     By using SSC assembly  40 , a single assembly  40  is able to implement flow pathways of numerous traditional combinations, such as a contactor, a contactor and diode in parallel, and contactor in series with a diode. By using a FET  66   a ,  66   b  in parallel with a diode  64   a ,  64   b  within the assembly  40 , the losses due to voltage drop through diodes are reduced as diodes are only used to determine flow direction. Additionally, by using a single component, the SSC assembly  40 , the size and weight of the electrical power center  26  is minimized. 
     Although example embodiments have been disclosed, a worker of ordinary skill in the art would recognize that certain modifications would come within the scope of the claims. For that reason, the following claims should be studied to determine the true scope and content.