BACKGROUND OF THE INVENTION

Electrical systems, such as those found in an aircraft power distribution system, employ electrical bus bars and miles of wiring for delivering power from electrical power sources to electrical loads. In the event of an unexpected electrical condition or electrical fault, currents may be shorted or transmitted through a normally nonconductive medium, such as air, resulting in unexpected operations of the power distribution system.

BRIEF DESCRIPTION OF THE INVENTION

In one embodiment, a method for limiting current in a circuit having a power source electrically coupled with a solid state power controller (SSPC), the SSPC configured to operate in a first conducting state and a second non-conducting state and further coupled with an electrical load via a transmission wire. The method includes a sensing of a current along the transmission wire, comparing the sensing of the current to a current profile, determining a pulse width modulation (PWM) duty cycle for operating the SSPC in the first state and second state based on the comparison, and operating the SSPC according to the duty cycle.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is a schematic circuit diagram of a power distribution system in accordance with one embodiment of the invention.

FIG. 2 is a series of graphs showing the response of the power distribution system, in accordance with the first embodiment of the invention. DESCRIPTION OF EMBODIMENTS OF THE INVENTION

The described embodiments of the present invention are directed to an electrical power distribution system, which may be used, for example, in an aircraft. While this description is primarily directed toward a power distribution system for an aircraft, it is also applicable to any environment using an electrical system for transmitting power from a power source to an electrical load.

FIG. 1 illustrates an exemplary schematic circuit diagram of a power distribution system 10, such as an exemplary power distribution system in an aircraft, comprising a power source, for example, a generator 12, an electrical switch, such as a solid state power switch (SSPC) 14, and an electrical load 16. As shown, the power distribution system 10 further comprises electrical interconnects, cables, cable junctions, or bus bars, illustrated as a first electrical transmission wire 18 electrically coupling the generator 12 with the SSPC 14, and a second electrical transmission wire 20 electrically coupling the SSPC 14 with the electrical load 16. The SSPC 14 may include a controllable switching component 22, and a diode, such as a flywheel diode 24, biased from, for example, electrical ground to the power line, downstream from the switching component 22. As shown, the SSPC 14 may comprise additional electrical components, for example, an inductance 26 downstream from the switching component 22 and a capacitance 48 configured downstream from the switching component 22 and across the second transmission wire 20 output. The SSPC 14 may further include a current sensor 28 positioned upstream from the switching component 22, and capable of sensing and/or measuring the electrical current characteristics of the current flowing through the power distribution system 10 and/or the current demand characteristics of the system 10. While the current sensor 28 is shown positioned upstream from the switching component 22, the sensor 28 is capable of performing the same or similar functionality at other locations in the power distribution system 10, and thus the illustrated location is merely one non-limiting example of sensor 28 placement. Alternatively, the current sensor 28 may be located downstream from the switching component 22, or on either transmission wire 18, 20. Additional current sensor 28 locations are envisioned.

One example of the SSPC 14 may comprise a silicon carbide (SiC) or Gallium Nitride (GaN) based, high bandwidth power switch. SiC or GaN may be selected based on their solid state material construction, their ability to handle large power levels in smaller and lighter form factors, and their high speed switching ability to perform electrical operations very quickly. For example, one non-limiting example of an SSPC may be able to handle 10 Amps and high speed switching such as 1 MHz. Alternative SSPC 14 examples are envisioned. Another example of the SSPC 14 may comprise further silicon- based power switch, also capable of high speed switching. In yet another example, the SSPC 14 may also provide power conversion capabilities for the power distribution system 10. For example, the generator 12 may supply power at 28 VDC, which the SSPC 14 may convert to 270 VDC for powering the electrical load 16.

It is envisioned that the switching component 22 is controllable to operate in an open (non-conducting) state that prevents electrical transmission from the generator 12 to the electrical load, and a closed (conducting) state that allows electrical transmission from the generator 12 to the electrical load 16. The flywheel diode 24, the inductance 26, and the capacitance 48 may each be selected or chosen based on electrical characteristics to provide for transient energy protection, as well as electrical energy storage and filtering means, generated during the toggling between the first and second states of the switching component 22. For example, the components 24, 26, 48 may be selected to account for known or unknown transmission line 20 or load 16 electrical characteristics, and, for instance, limit the rate of increase of current flow during the switching to a conductive state of the switching component 22, and/or maintain the voltage to the load 16 during the switching to a non-conductive state of the switching component 22. These selectable component 24, 26, 48, may further, for example, limit electromagnetic interference generated by the system 10 to predetermined or acceptable levels. The switching component 22 of the SSPC 14 is envisioned to comprise a field-effect transistor (FET); however, alternative switching components 22 are envisioned.

Example current characteristics measurable by the current sensor 28 may include, but are not limited to, instantaneous current, average current, rate of change in current, or the current demand of the electrical load 16. While the current sensor 28 is illustrated measuring the current characteristics at the SSPC 14, other measurement locations are envisioned. While the current sensors 28 is described as "sensing" and/or "measuring" the electrical current of the power distribution system 10, it is envisioned that sensing and/or measuring may include the determination of a value indicative or related to the electrical current characteristics, and not the actual current values.

The SSPC 14 may further include a controller 30 having an input to receive the sensed current measurement from the current sensor 28, and capable of generating and providing a control signal 32 output to the switching component 22. It is envisioned that the control signal 32 is capable of controlling the switching component 22, and thus, controlling the operation of the SSPC 14. The controller 30 is envisioned to include any components capable of receiving the sensed current measurement and capable of generating and providing a control signal 32, and may include any number of digital processors or analogue circuits capable of functioning and/or controlling as described herein. As shown, the controller 30 may further include memory 34 and a current profile 36. The memory 34 may include random access memory (RAM), read-only memory (ROM), flash memory, or one or more different types of portable electronic memory, such as discs, DVDs, CD-ROMs, etc., or any suitable combination of these types of memory. The controller 30 may be operably coupled with the memory 34 such that one of the controller 30 and the memory 34 may include all or a portion of a computer program having an executable instruction set for controlling the operation of the SSPC 14 and/or switching component. The program may include a computer program product that may include machine-readable media for carrying or having machine-executable instructions or data structures stored thereon. Such machine-readable media may be any available media, which can be accessed by a general purpose or special purpose computer or other machine with a processor. Generally, such a computer program may include routines, programs, objects, components, data structures, algorithms, etc. that have the technical effect of performing particular tasks or implement particular abstract data types. Machine-executable instructions, associated data structures, and programs represent examples of program code for executing the exchange of information as disclosed herein. Machine-executable instructions may include, for example, instructions and data, which cause a general purpose computer, special purpose computer, controller 30, or special purpose processing machine to perform a certain function or group of functions. Additionally, the current profile 36, may comprise a series of one or more sub-profiles, for example a maximum current profile and/or a transitory current profile, wherein each profile is individually defined by a set of predetermined or dynamic electrical characteristics, electrical limits, and/or algorithms. In one example, the maximum current profile may define a predetermined maximum current value the power distribution system 10 can transmit without electrical failure. In another example, the maximum current profile may define a current value that is indicative of an electrical fault or over-current condition in the system 10. In yet another example, the maximum current profile may define a current value slightly above a predetermined maximum current value the power distribution system 10 can transmit without electrical failure. In another example of a sub-profile, a transitory current profile may define an allowable or maximum change in current for the power distribution system 10, for instance, over a temporal factor, such as a moving period of time or time window of the most recent two seconds. In one non- limiting example, a transitory current profile may provide for limiting the current to ten times the normal expected value for a period of 1 millisecond, then limiting the current to five times the normal expected value for a period of 9 milliseconds. Alternative temporal factors or periods or limitations are envisioned.

Additionally, the exemplified current profiles 36 defined above are a non- exhaustive list of possible profiles 36, and additional profiles 36 are envisioned defining particular electrical characteristics. For instance, a plurality of current profiles 36 are envisioned for different modes of operation that take into account the expected electrical characteristics of a various load operations, such as an electric motor starting, or an initial power up/on phase of a load, or even to take into account known transient electrical characteristics to which the system 10 may be subjected to, such as a lightning strike. Each of these pluralities of current profiles 36 may define a maximum current sub- profile and/or a transient current sub- profile, with each profile 36 or sub-profile only being applicable as needed, according to the present operation of the system 10. In another example, at least one current profile 36 may be based on a predetermined or estimated thermal profile of the SSPC 14 and/or the switching component 22 such that the profile 36 describes possible component 14, 22 failures. In yet another example, at least one current profile 36 may be based on a desire to minimize the generation of electromagnetic interference in the system 10, or a desire to minimize excessive transitory demand on the system 10. While the controller 30 is illustrated as a subcomponent of the SSPC 14, alternative configurations are contemplated wherein the controller 30 may provide control of the SSPC 14 from a remote location. For example, one controller 30, provided away from the SSPC 14, may be configured to provide control for one or more SSPCs 14 or sets of SSPCs 14. Furthermore, embodiments are envisioned wherein the memory 34 may be may be separate from the controller 30, but may be in communication with the controller 30 such that it may be accessed by the controller 30. For example, it is contemplated that the suitable controller programs stored in the memory 34 may be updated through the wireless communication link, or from a common memory storage system. Furthermore, while the current profile 36 is shown as a subcomponent of the controller 30, alternative non-limiting configurations are envisioned, for example, wherein the current profile 36 is stored in the memory 34, or remotely from the controller 30.

During operation, in an aircraft embodiment for example, an operating gas turbine engine may provide mechanical energy to provide a driving force for the generator 12, which outputs electricity in response. The generator 12, in turn, provides the generated power to the SSPC 14 via the first transmission wire 18, which in turn, is controllable by the controller 30 to deliver the power to the electrical loads 16, via the second transmission wire 20. Additional power sources for providing power to the electrical loads 16, such as emergency power sources, ram air turbine systems, starter/generators, or batteries, are envisioned. It will be understood that while one embodiment of the invention is described in an aircraft environment, the invention is not so limited and has general application to electrical power systems in non-aircraft applications, such as other mobile applications and non-mobile industrial, commercial, and residential applications. During operation of the power distribution system 10, unexpectedly high currents travelling through at least one of the transmission wires 18, 20, SSPC 14, and/or switching component 22 may cause system 10 failure or an over-temperature condition in the system 10. One non-limiting example of unexpectedly high currents may be defined by current exceeding a designed operating range by a predetermined factor, such as by ten times the operating range. One non-limiting example of an unexpectedly high current, maximum transmissible current, or "over-current" condition, may be fifteen times the maximum expected current for the system 10. Higher over-current conditions and/or limits are envisioned. While embodiments of the invention envision whole system 10 failures, one non- limiting example may expect that a common point of failure due to an over-current condition may occur in or at the FET or switching component 22.

Over-current conditions may occur due to electrical arcing or electrical shorts in an environment where, for example, physical defects in an electrical connection cause a permanent or temporary loss in transmission capabilities, or a sudden transmission of high levels of current. While electrical arcing and/or electrical shorts are described, additional causes of over-current conditions are envisioned, such as lightning strikes, current rush during starting conditions, etc.

It is envisioned the controller 30 operates to protect the power distribution system 10 from over-current or over-temperature conditions by using the current profile 36 and applying said profile 36 to control operating characteristics of the power distribution system 10. A method for operating the power distribution system 10 to limit the transmission of current through the system 10 is described herein. First, the current sensor 28 provides a sensing of current along at least one transmission wire 18, 20 of the system 10 under normal operation (i.e. the switching component 22 in a closed state), and this sensing of current is provided to the controller 30. It is envisioned that the current sensor 28 may, for example, provide the sensing of current at timed increments, continuously, or when polled by the controller 30.

The controller 30 then compares the sensing of the current against at least one of the current profiles 36. This comparison may, for example, determine if the sensed current is greater than a maximum current profile for the system 10. Alternatively, the comparison may determine if the sensed current in a particular operating condition of the system 10 (e.g. electric motor starting, initial power up/on phase of a load, lightning strikes, etc.) is greater than the corresponding maximum current profile for that operating condition. In the example of a transitory current profile, the comparison may determine if the change in current, which may be sensed over a time period, exceeds or is greater than at least one transitory current profile. In implementation, the one or more current profiles and/or the characteristics of the current sensor 28 may be converted to an algorithm, which may be converted to a computer program comprising a set of executable instructions, which may be executed by the controller 30.

The controller 30 then determines how to control the operation of the SSPC 14 based on the aforementioned comparison. For example, the controller 30 may generate a pulse width modulation (PWM) signal, having a duty cycle, such that the controller 30 may control the amount of current transmission through the SSPC 14 according to said duty cycle. As used herein, a "duty cycle" is defined as the percentage of one period in which a signal is active, which, for example, may correspond to operating the SSPC 14 in a first conducting state. Alternative definitions of a "duty cycle" defining operations of the SSPC 14 and/or the switching component 22 are envisioned. If the controller 30 generates this PWM signal as the control signal 32, it is envisioned the SSPC 14 will operating by toggling the switching component from the first conducting state to the second non-conducting state repeatedly, according to the duty cycle, such that the average current flow and/or the power transmission of the SSPC 14 along the transmission wires 18, 20 may be proportional to the control signal 32 (i.e. the PWM duty cycle signal). One non-limiting example of a proportional duty cycle response may include wherein average current flow of ninety percent of the previous current flow or current demanded by the electrical load 16 in response to a ninety percent duty cycle signal. Alternative proportional responses are envisioned, and embodiments of the invention are not limited to a one-to-one proportional response between the average current and duty cycle signal.

In this example, it is envisioned the switching component 22 is capable of switching operations faster than the PWM duty cycle of the control signal 32, such that the speed switching component 22 is not a limiting factor. However, alternative embodiments are envisioned wherein the control signal 32, duty cycle signal, or operation of the SSPC 14 is limited by the switching speed of the switching component 22.

As described, the controller 30 may determine a PWM duty cycle for operating the SSPC 14 in the first conducting state and the second non-conducting state based on the comparison of the sensed current with the current profile. The controller 30 then generates the PWM duty cycle signal as the control signal 32, which is provided to control the switching component 22 of the SSPC 14. Thus, the SSPC 14 is operated according to the PWM duty cycle signal.

Thus, according to the aforementioned method, in an electrical circumstance wherein the sensed current satisfies a comparison with a current profile 36 or sub-profile, the controller 30 may control the SSPC 14 to, for example, reduce the duty cycle signal in order to reduce the current transmission along the transmission wires 18, 20 to a value less than, for instance, the maximum current profile. Likewise, the controller 30 may determine a reduced duty cycle is warranted when a comparison of the sensed current with a transitory current profile indicates the current demand is changing too rapidly, for instance, according to the previously described thermal profile, or according to a desire to minimize the generation of electromagnetic interference or minimizing excessive transitory demand. In this example, the controller 30 may determine a reduced duty cycle, such that the average power along the transmission wires 18, 20 is reduced to less than the transitory current profile.

Additionally, in instances where the sensed current is indicative of an electrical fault, the controller 30 may operate the SSPC 14 with a duty cycle of zero percent, which correspondingly holds the switching component 22 in the second non-conducting state, and thus permanently or temporarily disables the power distribution system 10 until the failure can be addressed, for example, by maintenance personnel. Likewise, where the comparison of the sensed current does not satisfy any current profile (which may be indicative of no unexpected electrical characteristics), the SSPC 14 may be operated with a duty cycle signal of one hundred percent, holding the switching component 22 in the first conducting state.

It is envisioned that the above-mentioned steps may occur continuously or intermittently, and may be repeated indefinitely, or cease after a predetermined number of repetitions, for example.

While only a single generator 12, SSPC 14, first transmission wire 18, second transmission wire 20, electrical load 16, and controller 30 are illustrated for ease of understanding, alternate power distribution systems 10 are envisioned having one or more of the aforementioned components 12, 14, 16, 18, 30 configured to define a robust power distribution system 10, or network of systems 10. For example, alternative configurations are envisioned having more than one electrical load 16 coupled to each SSPC 14, more than one set of transmission wires 18, 20 configured in series or parallel, or more than one SSPC 14 configured to selectively couple multiple sets of transmission wires 18 to additional portions of the power distribution system 10. Additionally, embodiments are envisioned wherein, for example, one controller 30 remotely controls operation of a plurality of SSPCs 14.

One embodiment of the power distribution system 10 operation may be further understood with reference to the time-aligned graphs presented in FIG. 2. As illustrated, a first graph 50 shows an example current demand signal (shown as a dotted line 52) and a corresponding system current signal 54, for example, as measured by the current sensor 28. The first graph 50 further indicates a maximum current profile 55 current value, which may indicate an electrical fault. Also illustrated, a second graph 56 shows a duty cycle signal 58, wherein the first and second graphs 50, 56 are time-aligned. In an example first transient demand 60, such as turning on a small light bulb, the current demand signal 52 rises slightly while the system current 54 is operating at one hundred percent duty cycle. It is envisioned that the comparison of the sensed current with the current profile 36 will determine that no change is needed to account for the small first transient demand 60, and thus the system 10 is capable of keeping the duty cycle signal at one hundred percent and provides sufficient system current 54 to account for the current demand 52.

In an example second transient demand 62, such as starting an electric motor, the current demand signal 52 rises sharply, but levels off. In this second transient demand 62, a comparison of the sensed current with the current profile 36 may determine the sensed current exceeds a transitory current profile, indicating the change in current is too great. In this example, the duty cycle signal 58 may be reduced, for example, in a step down sequence, to limit the amount of power transmitted on the transmission wires 18, 20 to prevent an over-current condition in the system 10. Once the second transient demand 62 has passed, a further comparison of the sensed current may no longer exceed the transitory current profile, and the controller 30 may determine an increase in the duty cycle signal 58 can be achieved.

In an example third transient demand 64, such as an electrical fault or short in the transmission wire 20, the current demand raises very sharply, raising the current demand signal 52 beyond the maximum current profile 55. As shown, at first the system current signal 54 attempts to match the rise in current demand signal 52, along with a corresponding reduction in duty cycle signal 58, however, when the system current signal 54 reaches the maximum current profile 55 limit. It is envisioned that the comparison of the sensed current with the maximum current profile indicates an electrical fault, and thus, the controller 30 determines the duty cycle signal 58 should be set to zero percent, and correspondingly the switching component 22 is held in the second non-conducting state, dropping the system current signal to zero.

The first and second graphs 50, 56 are intended to be simplistic illustrations of an operation of one embodiment of the invention, and are not intended to accurately represent exact electrical responses in a system 10. Alternative system 10 responses are envisioned wherein, for example, the duty cycle signal 58 response may be linear.

Many other possible embodiments and configurations in addition to that shown in the above figures are contemplated by the present disclosure. For example, it is envisioned the flywheel diode 24 may be replaced by a second switching component, which may be controllable by the controller 30 or another device, to reduce power losses during operation. Furthermore, while the SSPC 14 is illustrated as connected directly between the generator 12 and load 16, embodiments of the invention are envisioned wherein the SSPC 14 is one of hundreds or thousands of SSPCsl4 which may be directly connected to one or more generators 12, or which may be connected in a hierarchical chain of 'primary' controls coupled with the one or more generators 12, and providing power through a network of chained SSPCs 14, relays, contactors, circuit breakers, etc., such that the SSPC 14 may drive one or more loads 16, directly or indirectly. Additionally, the design and placement of the various components may be rearranged such that a number of different in-line configurations could be realized.

The embodiments disclosed herein provide a method for limiting or interrupting current in a circuit. The technical effect is that the above described embodiments enable the limiting of current in the circuit to prevent or reduce over-current and/or over- temperature conditions. One advantage that may be realized in the above embodiments is that the above described embodiments provide for reducing system current in response to an over-current condition, which may limit the over-current condition to a limited time. Over-current conditions may be indicative of a parallel or arcing fault in the system, which may generate intense localized heat from resistive losses at the fault, which could further lead to an electrical fire, smoke, melting of or damage to components, or catastrophic failures of the electrical system or greater structure, such as an aircraft. Thus, by limiting the current in the system, and correspondingly, limiting the time the system operating in an over-current condition, the likelihood of thermal runaway due to a fault is reduced.

Another advantage of the above-described embodiments is the method allows for detection and prevention of an over-temperature condition at the switching component of the SSPC, which is likely to be a point of thermal failure during an over-current or over- temperature condition. The method thus allows for increased protection of the switching component and SSPC due to the current limiting technique described above. Furthermore, the above-described method may be applied to a plurality of SSPCs to ensure thermal failure protection across each of the SSPCs, or if failure occurs, further protection from thermal damage, electrical fire, smoke, etc. due to the disabling of the SSPC. Yet another advantage of the above-described embodiments is that the method allows for temporal transitory currents in excess of normal operating conditions to reduce and/or eliminate "nuisance tripping" events, such as starting an electric motor or lightning strike, which may otherwise trigger system disabling. Thus the method improves power quality by continuing to operate through nuisance tripping events. The method may also employ filtering techniques to further reduce erroneous false-positive fault indications.

Even yet another advantage of the above-described embodiments is that the method allows for the control of current in the system while limiting the electromagnetic interference and/or excessive transitory demands, each of which may affect coupled or adjacent electrical systems. Furthermore, by instituting the above-described methodology, the SSPC may be capable of controlling the current flow with a much lower average power dissipation (for example, via lower, predictable thermal losses), such that SSPC components may be designed and/or selected with more accurate tolerances and less robust heat and/or stress dissipation characteristics. Additionally, the above-described system provides for controllable operation of a switch with minimal voltage drop when in the conducting state and current demand is below the maximum level.

The above-described embodiments, thus, provide for increased safety for an aircraft electrical power distribution system and hence improve the overall safety of the aircraft and air travel. Furthermore, by disabling the electrical circuits in the event of over- current and/or over-temperature conditions reduces or eliminates any additional maintenance time and/or costs associated with having to replace electrical components damaged or destroyed due to the over- current and/or over-temperature fault, as well as reduces or eliminates additional maintenance time and/or costs associated with diagnosis of nuisance tripping events.

This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.