Abstract:
An aircraft electric power supply system ( 10 ) for supplying electric power to onboard electric devices ( 20 ) during flight. To reduce the devices&#39; power draw, the electric power is supplied via modulation at an increment-percentage that is determined by present conditions. An optimum portfolio can be established for the electrical devices ( 20 ) collectively, this portfolio being selected in accordance with an energy-management criterion or other aircraft objectives.

Description:
RELATED APPLICATION 
       [0001]    This application claims priority under 35 U.S.C. §119(e) to U.S. Provisional Patent Application No. 61/151,202 filed on Feb. 10, 2009. The entire disclosure of this application is hereby incorporated by reference. To the extent that inconsistencies exist between the present application and any incorporated applications, the present application governs interpretation to the extent necessary to avoid indefiniteness and/or clarity issues. 
     
    
     BACKGROUND 
       [0002]    An aircraft will typically contain an electrical power system for providing electrical power to its onboard electric devices during flight. For example, an aircraft can have an electrical generator that is rotated by its engine to produce electrical power. Onboard electrical devices (e.g., electrothermal ice protection units) are accordingly adapted to operate when supplied with electric power from this power source during flight. 
       SUMMARY 
       [0003]    An aircraft&#39;s electrical devices are each supplied electrical power in a modulated manner such that, for each increment, electrical power is either supplied to the respective electric device or it is not. An equivalent “average” power is created by such modulation, without having to directly reduce voltage to the electrical device (which is often not practical). It has been found that many electrical devices (e.g., ice protection units) can adequately perform in most flight conditions with well under their conventional 100% power draws. 
         [0004]    Such a modulated electric power supply not only reduces overall power consumption, but also enhances energy management. For each electrical device and its given on-off increment percentage, many different increment distribution patterns will be suitable. The different (suitable) patterns for all of the devices can be arrayed into a multitude of unique combinations, from which an optimum pattern portfolio can be selected to meet a particular objective. For example, the optimum pattern portfolio can minimize the devices&#39; collective power draw during each increment and/or it can minimize increment-to-increment variation. 
     
    
     
       DRAWINGS 
         [0005]      FIG. 1  is a diagram of an aircraft and its electric power system. 
           [0006]      FIG. 2  is a diagram of the electric power system. 
           [0007]      FIGS. 3A-3E  are diagrams relating to electric-supply increments and the distribution patterns corresponding thereto. 
           [0008]      FIGS. 4A-4D  show possible increment-distribution patterns and portfolios that can be created thereby. 
           [0009]      FIGS. 5A-5D  are tables comparing different modulation portfolios. 
           [0010]      FIGS. 6A-6M  are tables schematically showing a power-management algorithm. 
       
    
    
     DESCRIPTION 
       [0011]    Referring now to the drawings, and initially to  FIG. 1 , an electric power system  10  is schematically shown installed on an aircraft  12 . In the illustrated aircraft  12 , engines  14  provide propulsive thrust and also electric power to a controller  16 . The controller  16  is operably coupled to a modulator  18  which supplies electric power to a plurality of electrical devices  20   a - 20   j.  The electrical power can (but need not) be provided at a relatively constant voltage (e.g., 115 VAC, 230 VAC, etc.). As is seen by referring additionally to  FIG. 2 , the controller  16  comprises a determiner  22  and an optimizer  24 . 
         [0012]    The power system  10  and/or the aircraft  12  can include at least two electrical devices  20 , at least three electrical devices  20 , at least four electrical devices  20 , at least five electrical devices  20 , at least six electrical devices  20 , at least eight electrical devices  20 , at least ten electrical devices  20 , and/or at least twenty electrical devices  20 . At least some (and/or all) of the electrical devices  20  can comprise ice-protection devices mounted for, example, on leading edges, wings, engine nacelles, and/or windshield surfaces. The devices  20  can be located relatively adjacent to, and/or relatively remote from, each other on the aircraft  12 . 
         [0013]    The modulator  18  supplies electric power to each electric device  20  in a modulated manner for a plurality of increments summing into a time period. The increments can be, for example, less than 1 second, less than 0.5 second, less than 0.25 second, between 0.10 second and 0.20 second, and/or about 0.15 second. The time periods represent substantially longer windows than the increments, and they can be, for example, at least 5 seconds, and/or at least 10 seconds. Each time period can have at least four increments, at least ten increments, at least 15 increments, and/or at least nineteen increments. 
         [0014]    As shown schematically in  FIG. 3A , for example, the time period can include twenty increments, and electric power can be supplied to the device  20  during ten of the twenty increments (i.e., 50% of the increments). The distribution of these ten increments creates the distribution pattern shown in  FIG. 3B . And as is shown in  FIG. 3C , there are numerous other distribution patterns that also correspond to the same increment percentage (e.g., 50%). A pattern of power modulation within a time period such as depicted in  FIG. 3  may be temporally repeated as necessary to fulfill the purpose of the power application. 
         [0015]    The controller&#39;s determiner  22  determines, for each electric device  20 , an increment percentage representing the number increments during which the device  20  must receive electrical power to adequately perform in a present condition. The present condition can be detected, sensed, measured, input (e.g., by the pilot), and/or pre-programmed to trigger upon another event. 
         [0016]    If the electric device  20  is a deicer or other ice protection unit, the relevant present condition can comprise a measured temperature. For example, at a relatively warm outside air temperature (OAT), a 25% increment percentage may be sufficient. At a moderately colder OAT, a 50% increment percentage may be sufficient. At still colder OAT&#39;s, a 75% increment percentage could suffice. Only in worst case situations (e.g., the lowest OAT an aircraft could ever possibly encounter) would a 100% increment percentage probably be necessary. The present condition could additionally or alternatively relate to other temperature conditions such as the surface temperature of a specific region of the relevant aircraft surface. 
         [0017]    In the example shown in  FIG. 3A  and discussed in the preceding paragraphs, certain increment percentages (e.g., 25%, 50%, 75%, 100% etc.) are employed. But such parameters need not be limited to these or other preset percentages. In fact, the number of increment percentages is confined only by the number of increments available. If twenty increments are used, for example, percentages in 5% intervals (e.g., 5%, 10%, 15%, 20% . . . 95%, 100%) is possible and perhaps preferred. 
         [0018]    The present condition can comprise non-temperature flight conditions. For example, an aircraft&#39;s icing vulnerability is affected by factors such as altitude, aircraft speed, angle of attack, flight phase (e.g., takeoff, climb, cruise, approach, landing, etc.), position of movable parts (e.g., ailerons, flaps, slats, spoilers, elevators, rudders, etc.), cloud characteristics, and/or liquid water content. The determiner can take these and other flight conditions into account when appraising deicer power requirements. 
         [0019]    The present condition could also or instead comprise parameters stemming from details of the electrical device itself. For example, with resistance-heating elements (deicers or not), the power density achieved by a given voltage depends upon the elements&#39; resistance. The determiner can take realtime resistance readings into consideration when ascertaining the increment percentage that each electrical device must receive in order for it to perform adequately its duties. 
         [0020]    Resistance can vary among originally-installed electrical devices because of manufacturing tolerances. And this variance can be further complimented as original devices are removed and replacement devices installed. Damage during flight (e.g., a bird strike) can further introduce resistance-adjustments into the equation. Moreover, resistance changes with temperature, so even with the most precisely manufactured devices, resistance characteristics can change during the course of a flight. On this latter point, the ability to adjust for resistance changes may allow the use of more economic resistance materials (e.g., copper) as a constant resistance is no longer essential to accurately estimate heating capacity. 
         [0021]    The present condition could further include the voltage from the power source so as to compensate for unanticipated voltage fluctuations from the source. 
         [0022]    Upon determination of the increment percentage for each electrical device  20 , each device  20   a - 20   j  will have a plurality of suitable increment distribution patterns. These distributions patterns can be arrayed into a multitude of unique portfolios, all of which will meet the increment-percentage requirements of each individual device  20 . 
         [0023]    This portfolio concept is shown schematically in  FIGS. 4A-4D , with only three devices  20   a - 20   c  and four increments, for ease of explanation. In this example, device  20   a  has a determined increment percentage of 50% (and six possible patterns i-vi), device  20   b  has a determined increment percentage of 25% (and four possible patterns i-iv), and device  20   c  has a determined incremental percentage of 75% (and four possible patterns i-iv). These different increment patterns can be used to create over ninety unique pattern portfolios, some of which are shown in  FIGS. 4B-4D . 
         [0024]    The controller&#39;s optimizer  24  selects, from the pattern portfolios, an optimum portfolio based on energy-management objectives. For example, if it is desirable for some reason that devices  20   a  and  20   b  not be provided power at the same time, only those portfolios satisfying this criteria could be considered. If the goal is to minimize electric power collectively supplied to the plurality of electric devices at each increment, the pattern portfolios could also be used for this purpose, with added information regarding their relative power consumptions. The optimum pattern portfolio could also or instead be established to minimize the variation in electric power collectively supplied between adjacent increments. Depending upon the circumstances and management objectives, several of the pattern portfolios could be appropriate or only a few (or one) would be sufficient. 
         [0025]    In  FIGS. 5A-5D , four of the electrical devices  20   a - 20   d  are shown. In  FIG. 5A , the devices  20   a - 20   d  are each continuously supplied with electric power, resulting in a steady load of 38 kW. This is representative of a conventional system wherein an electrical device  20  continuously receives electric power when in an active state. For example, in an electric deicer that is cycled through active states (wherein the relevant surface is heated just enough to break the ice&#39;s boundary layer) and inactive states (wherein ice is allowed to accumulate on the relevant surface), electric power is continuously supplied to the deicer when in the active state. 
         [0026]      FIGS. 5B-5D  are representative of the present system  10  wherein an increment-percentage determination is made for each electrical device  20 . In this example, a 75% increment-percentage was determined for electric device  20   a,  a 50% increment-percentage was determined for electric device  20   b,  a 25% increment-percentage was determined for electric device  20   c,  and a 75% increment percentage was determined for electric device  20   d.    
         [0027]    In each of the portfolios shown in  FIGS. 5B-5D , the average load is 22 kW, which is a significant power savings compared to the 38 kW power draw of  FIG. 5A . In  FIG. 5B , however, the variation between maximum load (38 kW) and minimum load (0 kW) is 38 kW. And the load drops from 38 kW to 30 kW (an 8 kW step), drops from 30 kW to 20 kW (a 10 kW step), and from 20 kW to 0 kW (a 20 kW step). Such a drastic variance in max-min load, and/or such big steps along the way, may not be desirable if large swings in power draw are discouraged during flight. 
         [0028]    In  FIGS. 5C-5D , the variation between the maximum load (26 kW) and the minimum load (20 kW) is 6 kW, a substantial reduction from that shown in  FIG. 5B . In  FIG. 5C , the largest step is 6 kW (when load jumps from 20 kW to 26 kW), a definite improvement over the 8 kW, 10 kW, and 20 kW steps that occur in the portfolio shown in  FIG. 5B . In  FIG. 5D , the “step” criteria is improved even further by a more refined portfolio wherein the largest step is 4 kW (when the load jumps/drops between 22 kW and 26 kW). 
         [0029]    The optimum increment profile for each electrical device  20  can involve an in-flight analysis of each possible increment profile combination. Alternatively, this profile can be derived for stored data gathered during a pre-flight analysis of each possible increment combination. This analysis (in-flight and/or pre-flight) may comprises an algorithm, such as a software algorithm executed by, for example, a central processing unit. 
         [0030]    As shown schematically in  FIG. 6A-6M , a suitable algorithm can be developed to provide each electrical device  20  with the required power while minimizing the total power draw at any instance and allowing for a gradual rise/fall of the power draw. 
         [0031]    The algorithm can be developed in the context of rows and columns in a theoretical table (and adapted to the appropriate programming language). In this table, the rows representing the electrical devices  20  and the columns represent the number of intervals in a time period. An additional row is provided on the table to store the totals of the respective columns. Initially, all of the rows contain a zero value. ( FIG. 6A .) 
         [0032]    The electrical devices  20  are initially arranged in an order of descending power draw. In the example of  FIG. 5 , this arrangement results in a sequence of device  20   a  (12 kW), device  20   b  (10 kW), device  20   c  (8 kW), and device  20   d  (8 kW). The a-b-c-d order of the electrical devices  20  is a coincidence in this situation, other more random orders could and would occur. 
         [0033]    For the first electrical device  20   a,  the 75% increment-percentage is transferred to the table by filling in the 75% of the leftmost cells with the corresponding power draw (12 kW) and the total power draw from each column is computed. ( FIG. 6B .) The columns are then sorted in ascending values from left to right. ( FIG. 6C .) 
         [0034]    For the second electrical device  20   b,  the 50% increment-percentage and corresponding draw (10 kW) are added ( FIG. 6D ) and then the columns sorted in ascending order ( FIG. 6E ). This process is repeated for the third electrical device  20   c  (25% increment-percentage and 8 kW power draw) and the fourth electrical device  20   d  (75% increment-percentage and 8 kW power draw), as shown in  FIGS. 6F-6I . 
         [0035]    The table is then decimated in two tables with the first table ( FIG. 6J ) containing the odd columns ( 1 ,  3 ,  5 , . . .  19 ) and the second table ( FIG. 6K ) containing the even columns ( 2 ,  4 ,  6 , . . .  20 ). The column are reversed in the second table so that they are now arranged in a descending order ( FIG. 6L ). The two tables are then concatenated into the final table by inserting the reversed second table to the right of the first table ( FIG. 6M ). 
         [0036]    One may now appreciate that the electrical power system  10  not only reduces overall power consumption of the devices  20 , but also enhances energy management of the aircraft  12 . Although the system  10 , the aircraft  12 , associated methods and/or related elements/steps have been shown and described with respect to certain embodiments, equivalent and obvious alterations and modifications, including applications not related to aircraft, will occur to others skilled in the art upon reading and understanding of this specification.