Abstract:
An apparatus, and a method of controlling a solid state power controller (“SSPC”) selectively allows a current through a solid state power control switch in response to the current in a plurality of SSPCS exceeding at least one threshold. A microprocessor module collects power surge data from a plurality of groups of SSPCs, and determines if the amount of power surge data within a group of SSPCs is sufficient to constitute a lightning threat. If the microprocessor module determines a lightning threat is present, the microprocessor module sends a command to certain SSPCs in the afflicted group to lockout an instantaneous trip protection for the duration of the lightning threat, allowing the power surge to pass from the SSPCs to a load or plurality of loads, leaving the SSPCs undamaged.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates generally to vehicle power systems and, more particularly, to solid state power controls. 
     Vehicles, such as aircraft, typically utilize one or more power distribution units or power modules to distribute power from a primary power source to various vehicle systems. The solid state power controls in a power distribution unit typically include an electronic switch, such as a FET, and electronic circuitry that provides wiring protection. The FET and circuitry are often referred to as a solid state power controller (“SSPC”). The SSPC has found widespread use because of its desirable status capability, reliability, and packaging density. A typical power distribution unit may include hundreds or thousands of SSPCs. 
     SSPCs also must operate in the presence of lightning, which can adversely impact electronic devices by causing power surges. Traditionally, aircraft had an aluminum skin that attenuated the lightning current induced on the wires. Some aircraft now use composite materials instead of aluminum for weight and strength benefits. However, composite materials do not provide the same level of attenuation to lightning as aluminum. When lightning hits an aircraft chassis, hundreds of volts may surge between a load in the vehicle system and the aircraft chassis. As such, the lightning requirements of SSPCs have increased. 
     U.S. patent application Ser. No. 11/491,803 entitled “Method to Increase the Lightning Capability In a Solid-State Power Controller”, now U.S. Pat. No. 7,626,797, describes a method of operating SSPCs in a high-energy lightning environment. This method enables the SSPC to survive a lightning threat and return a load to its defined state once the threat has passed. The method described in this application is suitable for most single-stroke lightning applications and may be suitable for many multiple-stroke lightning applications. However, additional enhancements can be made to prevent repeated potential cycling off and on under an auto-recover mechanism that is part of this prior system during a multiple-stroke lightning application. The discussion with regard to how this occurs from U.S. patent application Ser. No. 11/491,803 is incorporated herein by reference. 
     There is a need for a simple, relatively inexpensive SSPC with improved lightning protection, that is suitable for exposure to multiple-stroke lightning, that can operate within a lightning environment with minimal system disruption, and that can protect loads from multiple power cycling. 
     SUMMARY OF THE INVENTION 
     SSPC software communicates to a main microprocessor module that a lightning pulse has occurred. The microprocessor module collects and processes this information. If a sufficient number of lightning indications are collected, the microprocessor module notifies other associated SSPCs in the system to lockout an instantaneous trip protection. When their instantaneous trip lockout is engaged, the SSPCs will not trip on lightning current pulses even if the current exceeds an instantaneous trip threshold. This prevents nuisance trips and ensures that current will pass to a load or plurality of loads, leaving the SSPCs undamaged. 
     These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The various features and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the currently preferred embodiment. The drawings that accompany the detailed description can be briefly described as follows. 
         FIG. 1  illustrates selected portions of an example solid state power controller with lightning protection. 
         FIG. 2  illustrates a microprocessor module and a plurality of SSPCs that communicate through a serial hardware interface. 
         FIG. 3  illustrates a plurality of power distribution units and an associated microprocessor module in an example environment of an aircraft. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       FIG. 1  illustrates selected portions of an example solid state power controller (SSPC)  18  for use in a vehicle, such as an aircraft. For the purposes of this discussion a single FET is shown, while in practice it is common to have multiple FETs in parallel. In this example, the SSPC  18  includes a logic section  32  and a power section  34 . The logic section  32  includes an isolated power supply  20 , which channels power from a power source  22  to a microcontroller  38  and a gate drive  40 . The microcontroller  38  controls gate drive  40 , which opens and closes a switch  42 . When the gate drive  40  is turned on, the switch  42  is closed and the SSPC  18  turns ON. When the gate drive  40  is turned off, the switch  42  is opened and the SSPC  18  turns OFF. Although only one switch  42  is shown in this example, multiple switches may be used in the same manner as described. An instantaneous trip module  44  and a lightning module  46  sense the electrical current flow through the SSPC  18 . Instantaneous trip module  44  acts as a comparator, and determines when current meets or exceeds an instantaneous trip threshold. Lightning module  46  also acts as a comparator, and determines when current meets or exceeds a higher lightning threshold. Microcontroller  38  transmits power surge data to an SSPC communications interface  66  via communications line  48 . The SSPC communications interface  66  transmits power surge data back to the microcontroller  38  via communications line  50 . The SSPC communications interface  66  also communicates with other SSPCs  18 . 
     Under some conditions, such as a lightning strike, a transient current may surge through the vehicle causing a power surge. The transient current may be, for example, an induced current, other known type of transient current, or a transient current from another source besides lightning. In the disclosed example, the SSPC  18  provides lightning protection to reduce the risk that the SSPC  18  becomes damaged from a power surge caused by the transient current. As described in patent application 11/491,803, the following examples illustrate the operation of the instantaneous trip module  44  and the lightning module  46 . 
     In one example, the SSPC  18  is OFF (switch  42  is open) when a transient current occurs. If the transient current meets or increases above an instantaneous trip threshold, the instantaneous trip module  44  turns on the gate drive  40  which then turns ON the switch  42 . The switch  42  can handle more transient current when ON because the voltage across the switch  42  will be lower, thus reducing the transient energy that the switch  42  must absorb. The transient current flows to the load during this time to thereby protect the SSPC  18  from damage. As the transient current decreases below the instantaneous trip threshold, the instantaneous trip module  44  removes the gate drive  40  command to force the switch  42  OFF. Optionally, a time delay is used before turning off gate drive  40  to allow the SSPC  18  to cool. 
     In another example, the SSPC  18  is ON when the transient current occurs. The transient current increases the current through the switch  42  until the instantaneous trip threshold is met or exceeded. At this point, the microcontroller  38  begins to turn OFF the switch  42  and set an auto-recover function. The process of turning OFF the switch  42  takes some time, typically fractions of a second. During this time, the current may increase, decrease, or remain steady. 
     If the current increases, but not fast enough to meet or exceed the lightning threshold before the switch turns OFF, the switch  42  is turned back ON upon meeting or exceeding the lightning threshold. If the current increases quickly enough to meet or exceed the lightning threshold before the switch  42  turns OFF, the microcontroller  38  cancels the command to turn OFF the switch  42  such that the switch remains ON. In the ON state, the transient current passes to the load to thereby protect the SSPC  18  from damage. 
     If the transient current decreases or remains steady and does not reach the lightning threshold, the switch  42  turns OFF and the auto-recover logic functions to turn the SSPC  18  back ON after a time delay time to allow cooling. 
     After the switch  42  is turned back ON, if the current remains above the instantaneous trip threshold but below the lightning threshold, the switch  42  turns OFF and the auto-recover logic again functions to turn the SSPC  18  back ON after another time delay to allow cooling. It is assumed that current above the instantaneous trip threshold is from a shorted load and not lightning if multiple attempts to auto-recover continue to produce current above the instantaneous trip threshold but below the lightning threshold. In response, a protective trip is set in the microprocessor  38 , and the SSPC  18  turns OFF. 
     Thus, the disclosed examples provide for turning the SSPC  18  ON in response to the transient current meeting or exceeding the instantaneous trip threshold or lightning threshold, depending on the initial ON or OFF state of the SSPC  18 . This provides the benefit of passing the transient current on to the load to protect the SSPC  18  from damage. Furthermore, the lightning module  46  requires little additional hardware in the SSPC  18 , which helps keep costs and packaging density low. Although the SSPC  18  as shown in  FIG. 1  is a direct current type, one of ordinary skill in the art who has the benefit of that disclosure will recognize that the disclosed examples are also applicable to alternating current type SSPCs. 
       FIG. 2  illustrates how a microprocessor module  60  communicates with a plurality of power distribution units  64 , which each contain a plurality of SSPCs. The microprocessor module  60  has a serial communications interface  62 , and each of the plurality of power distribution units  64  has an SSPC communications interface  66 . The power distribution units  64  transmit serial power surge data over communication line  68  to the microprocessor module  60 . The microprocessor module  60  transmits serial power surge over communication line  70  to the plurality of power distribution units  64 . All of the serial power surge data is communicated between the interfaces  62  and  66 . 
       FIG. 3  illustrates a microprocessor module  60  and a plurality of power distribution units  64  in an example environment of an aircraft. Serial power surge data is transmitted between the microprocessor module  60  and the plurality of power distribution units  64  via communications interfaces  62  and  66  and serial data communication lines  68  and  70 . 
     If certain conditions are met, the SSPC software will notify the microprocessor module  60  that a lightning pulse has occurred. In one example, there are two conditions the microprocessor module  60  will use to determine if lightning has occurred: in a first case if current meets or exceeds an instantaneous trip threshold, and in a second case if current exceeds the instantaneous trip threshold and meets or exceeds a lightning threshold. 
     In the first case, the current in an SSPC meets or exceeds the instantaneous trip threshold. The microcontroller  38  of the SSPC would then add lightning indication to the power surge data transmitted to the microprocessor module  60  along communication line  68 . This case accommodates AC SSPCs that do not have a lightning module. 
     In the second case, when the lightning threshold has been reached, transient current meets or exceeds the higher lightning threshold of an SSPC. The microcontroller  38  of the SSPC would then add a lightning indication to the power surge data transmitted to the microprocessor module  60  along communication line  68 . This case, however, only applies to DC SSPCs, as AC SSPCs do not contain a lightning module to measure the lightning threshold. 
     When a sufficient number of conditions have been reached within one of the plurality of power distribution units  64 , the microprocessor module  60  will command all SSPCs within the power distribution unit that have been commanded ON to lockout their instantaneous trip protection until 1.5 seconds has transpired. The instantaneous trip lockout command is transmitted along with other data to the power distribution unit  64  along communication line  70 . An example sufficient number of SSPCs is greater than two, which accommodates the possibility that up to two SSPCs may exceed their instantaneous trip threshold due to a pin-to-pin short circuit, and not due to lightning. The ARP5412A industry standard defines lightning as extending up to 1.5 seconds and including up to 14 pulses randomly spaced between 10 and 200 milliseconds. To accommodate this industry standard, other SSPC functions, such as arc fault protection, can also be inhibited for 1.5 seconds if desired. It would be obvious to one skilled in the art to alter the present invention to meet different industry standards of greater than or less than the 1.5 second lightning duration, or to alter the instantaneous trip 1.5 second lockout time accordingly for this, or other reasons. 
     An SSPC whose instantaneous trip protection is locked out will allow current to pass from the SSPC to the load, even if that current meets or exceeds the instantaneous trip threshold. By preventing the instantaneous trip and allowing the current to pass to the load, the SSPC is left undamaged. In addition, these locked out SSPCs will not have to repeatedly turn off and back on to check if the lightning threat is still present. By locking out the instantaneous trip protection for the entire 1.5 second duration of the lightning threat, nuisance trips and power cycling is avoided. SSPCs will still follow normal control ON/OFF commands as recited in patent application Ser. No. 11/491,803 during this time. In addition, SSPCs will also maintain wiring protection via the normal SSPC overcurrent trip curve protection during this time. The SSPC overcurrent trip curve protection enables the SSPC to set a circuit breaker protective trip in response to a sufficiently high current. 
     When the 1.5 second timer of the microprocessor module  60  expires, the instantaneous trip lockout will be reset. Once the lockout is removed, the SSPCs restore their instantaneous trip protection. 
     In another embodiment of the present invention, the microprocessor module  60  can use other conditions to determine a lightning threat. In one example, when an SSPC experiences multiple instantaneous trips within a predetermined time, it will turn off its SSPC output and set a circuit breaker protective trip by opening a switch  42 . In this example, microprocessor module  60  monitors each SSPC for a circuit breaker protective trip. If a sufficient number of circuit breaker protective trips have been activated within a preset defined period, the microprocessor module  60  may reset the tripped SSPCs so that current may pass to a load or plurality of loads, leaving the SSPCs undamaged and reducing the impact to the vehicle from multiple instances of tripped SSPCs from a common cause event such as lightning. 
     In either of the disclosed embodiments, there is a finite amount of time needed for the microprocessor module  60  to collect power surge data, process that data, and command ON SSPCs to lockout instantaneous trip protection. Depending on timing and the lightning detection method selected, it may also be necessary to reset SSPC circuit breaker protective trips. 
     Although a preferred embodiment of this invention has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.