Abstract:
The present disclosure broadly relates to apparatuses and methods for generating electric power. More particularly, the present disclosure relates to a self-excited electric generator. The self-excited electric generator may include auxiliary windings to provide a source of electricity to an associated generator control unit (GCU). The apparatuses and methods of the present invention may provide added benefits of reducing excitation requirements from the GCU. Thereby, the apparatuses and methods may reduce cost, weight, and size of an electric generator, and may increase reliability of associated systems.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    Brushless, self-excited generators, for aircraft electric power generation, are typically three-stage machines. The three stages include: 1) a permanent magnet generator (PMG), 2) an exciter generator, and 3) a main generator. 
         [0002]    In addition to providing electric power to auxiliary equipment in an aircraft, the main generator may be used to start main engines of the aircraft and/or to start an auxiliary power unit (APU) engine. 
         [0003]    Elimination of the separate PMG is desirable. Providing an auxiliary source of electric power to an associated generator control unit (GCU) is also desirable. 
       SUMMARY OF THE INVENTION 
       [0004]    In one aspect of the present invention, a self-exciting electrical generator includes a main generating including a rotor and a stator, wherein the rotor includes a plurality of main stator windings and a plurality of auxiliary windings, wherein the main stator windings include a first gauge wire and the auxiliary windings include a second gauge wire, wherein a second diameter of the second gauge wire is less than a first diameter of the first gauge wire, wherein the main stator windings are configured to supply electrical power to an electrical load bus, wherein the auxiliary windings are configured to supply electrical power to a generator control unit, and wherein the rotor includes a plurality of field windings configured to receive electrical power from an exciter. 
         [0005]    In another aspect of the present invention, a self-exciting electrical generator assembly includes an exciter generator; and a main generating including a rotor and a stator, wherein the rotor includes a plurality of main stator windings and a plurality of auxiliary stator windings electrically isolated from the main stator windings, and wherein the rotor includes a plurality of field windings configured to receive electrical power from the exciter generator. 
         [0006]    In a further aspect of the present invention, an electrical generator system includes a generator control unit; an exciter generator; and a main generator including a rotor and a stator, wherein the stator includes a plurality of main stator windings to supply electrical power to an electrical load bus and a plurality of auxiliary windings to supply electrical power to the generator control unit. 
         [0007]    These and other features, aspects and advantages of the present invention will become better understood with reference to the following drawings, description and claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  depicts a block diagram of an electrical power generation system according to an exemplary embodiment of the present invention; 
           [0009]      FIG. 2  depicts an electrical schematic for an electrical power generation system according to an exemplary embodiment of the present invention; 
           [0010]      FIG. 3  depicts a cross-section view of a main generator stator according to an exemplary embodiment of the present invention; and 
           [0011]      FIG. 4  depicts a cross-section view of an exciter generator according to an exemplary embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0012]    The following detailed description is of the best currently contemplated modes of carrying out exemplary embodiments of the invention. The description is not to be taken in a limiting sense, but is made merely for the purpose of illustrating the general principles of the invention, since the scope of the invention is best defined by the appended claims. 
         [0013]    Various inventive features are described below that can each be used independently of one another or in combination with other features. However, any single inventive feature may not address any of the problems discussed above or may only address one of the problems discussed above. Further, one or more of the problems discussed above may not be fully addressed by any of the features described below. 
         [0014]    Generally, embodiments of the present invention may provide self-excitation of a main electric generator while satisfying short circuit operation requirements of an associated generator control unit (GCU). For example, a stator of an exciter generator may include permanent magnets to provide excitation of the main generator. A stator of the main generator may include auxiliary windings to provide electric power to the GCU. 
         [0015]    Turning to  FIG. 1 , a block diagram of an electrical generation system  100  may include a generator/exciter  105 , a generator control unit (GCU)  110 , a generator line controller (GLC)  115 , and a generator load bus  120 . The GCU  110  may receive an electric power input  111  from an auxiliary winding of the generator/exciter  105 . The GCU  110  may also receive a current input  112  from a current sensor  125  and/or a voltage input  113  from a voltage sensor  130  from an output of the generator/exciter  105 . The GCU  110  may determine an excitation output signal  106  and/or a GLC output signal  116  based on, for example, the electric power input  111 , the current input  112  and/or the voltage input  113 . In turn, a generator/exciter electric power output  117  may be based, for example, on the excitation output signal  106 . Furthermore, a state (e.g., an open state or a closed state) of the GLC  115  may be based, for example, on the GLC output signal  116 . 
         [0016]    With reference to  FIG. 2 , an electrical schematic diagram of an electric power generation system  200  may include a main stator  205 , a main rotor  215 , rotating rectifiers  217 , an exciter rotor  220 , and an exciter stator  224 . The electrical power generation system  200  may be similar to, for example, the exciter/generator  105  of  FIG. 1 . The main stator  205  and the main rotor  215  may be included within, for example, a main generator (e.g., a main generator of generator/exciter  105  of  FIG. 1 ). The exciter rotor  220  and the exciter stator  224  may be included within, for example, an exciter generator (e.g., an exciter of generator/exciter  105  of  FIG. 1 ). 
         [0017]    As illustrated in  FIG. 2 , the main stator may include a first main winding  206 , a second main winding  207 , and a third main winding  208 . The first main winding  206 , the second main winding  207 , and the third main winding  208  may provide electric power to, for example, an electrical system (e.g., electric bus  120  of  FIG. 1 ) of an aircraft. 
         [0018]    The main stator  205  may further include a first auxiliary winding  210 , a second auxiliary winding  211 , and a third auxiliary winding  212 . The first auxiliary winding  210 , the second auxiliary winding  211 , and the third auxiliary winding  212  may provide electric power to, for example, a GCU (e.g., GCU  110  of  FIG. 1 ). By providing the auxiliary windings  210 ,  211 ,  212  separate from the main windings  206 ,  207 ,  208 , a short circuit on the main windings (or electric load bus) will not impose a short circuit on the electric power to the GCU. As further illustrated in  FIG. 2 , the main rotor  215  may include a rotor coil  216  and rotating rectifiers  217 . 
         [0019]    The exciter rotor  220  may include a first exciter rotor winding  221 , a second exciter rotor winding  222 , and a third exciter rotor winding  223 . The exciter stator  224  may include an exciter stator winding  225  and an exciter permanent magnet having a South magnetic pole  226  and a North magnetic pole  227 . While the exciter stator  224  is depicted in  FIG. 2  as only including a single exciter stator winding  225  and a single exciter permanent magnet  226 ,  227 , it should be understood that the exciter stator  224  may include any number of exciter stator windings  225  and/or any number of exciter permanent magnets  226 ,  227  (e.g., exciter stator windings and exciter stator permanent magnets as depicted in the exciter generator cross section of  FIG. 4 ). 
         [0020]    Generally, a main generator may have phase windings in a stator, and field windings on a rotor. The main generator may further include an auxiliary winding. An exciter generator may have a three-phase winding on a rotor and a field winding on a stator. The exciter stator may include permanent magnets. 
         [0021]    Turning to  FIG. 3 , a main generator stator  300  may include a plurality of main generator poles  305 , a plurality of main generator main stator windings  310 , and a plurality of main generator stator auxiliary windings  315 . The main generator stator  300  may form part of a generator/exciter (e.g., generator/exciter  105  of  FIG. 1 ) and/or a main generator stator (e.g., main stator  205  of  FIG. 2 ). The plurality of main generator main stator windings  310  may be arranged in a three-phase configuration (e.g., main generator stator main windings  206 ,  207 ,  208  of  FIG. 2 ). The plurality of a main generator auxiliary stator windings  315  may be arranged in a three-phase configuration (e.g., main generator stator auxiliary windings  210 ,  211 ,  212  of  FIG. 2 ). As illustrated in  FIG. 3 , the main windings, which generate power to the load, are located next to respective slot openings. The auxiliary windings, which power the GCU, are located at a bottom of the respective slot, next to a yoke. Positions of these main windings and auxiliary windings may be switched. Pole numbers are included in  FIG. 3  for illustrating an example slot sequence. The specific pole numbers as shown in  FIG. 3  are not intended to limit the apparatus in any way. 
         [0022]    With reference to  FIG. 4 , an exciter generator  400  may include an exciter stator  405 , an exciter rotor  412 , and an air gap  410  between the exciter stator  405  and the exciter rotor  412 . The exciter generator  400  may form part of a generator/exciter (e.g., generator/exciter  105  of  FIG. 1 ) and/or an exciter stator (e.g., exciter stator  224  of  FIG. 2 ). The exciter stator  405  may include a plurality of exciter stator poles  415 ,  420 ,  425 ,  430 ,  435 ,  440 ; a plurality of exciter stator permanent magnets  416 ,  421 ,  426 ,  431 ,  436 ,  441 ; and a plurality of exciter stator windings  417 ,  418 ,  422 ,  423 ,  427 ,  428 ,  432 ,  433 ,  437 ,  438 ,  442 ,  443 . 
         [0023]    Typically, a generator may be required to provide 2.5 to 3 pu short circuit current, to a GCU, for 5 seconds for fault clearing. By definition, a point of regulation (POR) voltage of a main generator output will be close to zero during a short circuit. Therefore, if a GCU was supplied from the same main generator output, the GCU will have no power and the main generator will go off-line. There are multiple ways to keep power to the GCU for the duration of the short circuit. One possibility is to use a separate main stator winding in a permanent magnet generator (PMG) (e.g., auxiliary windings  210 ,  211 ,  212  of  FIG. 2 ). These separate (or auxiliary) windings may be designed with wires having a diameter less than wires used in the main stator windings, given the low power rating and short duration required for the auxiliary windings. The associated wires may be distributed, for example, over entire stator slots, and may be designed to be magnetically decoupled from the main generator main stator windings. 
         [0024]    As illustrated in  FIG. 4 , permanent magnets  416 ,  421 ,  426 ,  431 ,  436 ,  441  may be added to the exciter generator stator  400  in any of the locations as depicted with either solid or dashed lines. These permanent magnets  416 ,  421 ,  426 ,  431 ,  436 ,  441  may be used to self-excite the exciter generator  400  and, thereby, eliminate a separate PMG. For example, the permanent magnets  416 ,  421 ,  426 ,  431 ,  436 ,  441  in the exciter stator  400  may create flux to generate initial voltage across generator main terminals, or from a dedicated winding  221 ,  222 ,  223 , once the exciter generator is rotating. This initial voltage may be fed to a generator control unit (GCU)  110 , and when the voltage reaches a predetermined level, the GCU  110  may begin to provide electric current to exciter stator windings, which adds to the associated field flux. At this point, the exciter stator winding  221 ,  22 ,  223  and permanent magnets  416 ,  421 ,  426 ,  431 ,  436 ,  441  may both create flux to generate an ever larger voltage at the terminals of the exciter generator, until rated voltage is achieved. This approach may also reduce excitation requirements from the GCU  110 . 
         [0025]    A separate PMG may be eliminated since the permanent magnets  416 ,  421 ,  426 ,  431 ,  436 ,  441  in the exciter stator may provide an initial self-excitation, which in turn can be used to provide excitation for the exciter generator via the generator control unit (GCU)  110 . Windings  206 ,  207 ,  208  in a main generator  205 ,  215  may be used to supply electric power to the GCU  110 , thereby, eliminating dedicated PMG feeders. Alternatively, auxiliary windings  210 ,  211 ,  212  may be included in a stator  205 ,  300  of a main generator to supply the GCU  110 . The auxiliary windings  210 ,  211 ,  212  may continue to provide power to the GCU  110  in the event that the main generator outputs  206 ,  207 ,  208  are short circuited. Since the exciter output may be rectified to the main generator rotor field  216 , and a main generator waveform and power quality, may not be compromised by adding the permanent magnets  416 ,  421 ,  426 ,  431 ,  436 ,  441  in the exciter stator  400 . The permanent magnets  416 ,  421 ,  426 ,  431 ,  436 ,  441  may be chosen such that a normal regulation performance of the generator  205 ,  215 , via the GCU  110  and exciter generator  220 ,  224 , may be unaffected (including load-off transient performance). 
         [0026]    Permanent magnets  416 ,  421 ,  426 ,  431 ,  436 ,  441  may be inserted within an exciter generator stator  400 , or may be adhered to a surface of the stator core pole shoes, in a fashion that the majority of the generated flux will travel across an associated air gap, enter into an exciter rotor, and induce voltage in a main generator rotor winding  216  to provide initial excitation to start the self-excitation process. Alternatively, the permanent magnets  416 ,  421 ,  426 ,  431 ,  436 ,  441  may supply additional flux to boost generator flux during normal generator or starter operations. Several configurations for the permanent magnets  416 ,  421 ,  426 ,  431 ,  436 ,  441  can provide necessary flux pattern. For example, an alternative arrangement for the permanent magnets  416 ,  421 ,  426 ,  431 ,  436 ,  441  is to insert a permanent magnet section axially between exciter stator laminations with two non-magnetic barriers (e.g., one permanent magnet  416 ,  421 ,  426 ,  431 ,  436 ,  441  on each side, or put a magnet section at the end of the exciter stator lamination with one non-magnetic barrier. 
         [0027]    It should be understood, of course, that the foregoing relates to exemplary embodiments of the invention and that modifications may be made without departing from the spirit and scope of the invention as set forth in the following claims.