Abstract:
A power generation system and method uses a constant frequency generator to generate electrical power in a generate mode. When operating in a start mode, the constant frequency generator is controlled by a motor controller which at least partially controls another component while the system is in a generate mode. The power generation system and method can be implemented in, for example, an aircraft electrical architecture.

Description:
BACKGROUND OF THE INVENTION 
     This application relates to an electrical generation system and method where a constant frequency generator is associated with a gas turbine engine and is capable of operating in both a start mode (as a starter) and a generate mode (as a generator). 
     Aircraft typically utilize gas turbine engines, which include turbine rotors that rotate to provide power. Generators are connected to each turbine engine in order to produce electrical energy, which is then utilized to power onboard electronic systems, as well as for other uses on the aircraft. 
     A system using a variable frequency generator and a constant frequency generator is described in U.S. patent application Ser. No. 12/406,992 to LeGros, and is hereby incorporated by reference. Typical systems constructed with the combined generator types described in the LeGros application utilize the variable frequency generator in a start mode where the generator acts as a motor and provides an initial motive force to rotate (start) the gas turbine engine. The variable frequency generator is also used in a generate mode, once the gas turbine engine has been started, to generate electrical power. The frequency of the generated electrical power varies depending on the speed of a rotor within the gas turbine engine. 
     The system described in the LeGros application also uses a constant frequency generator which functions only in generate mode, and is switched off during start mode. A constant frequency generator generates power having a constant frequency regardless of the rotor speed. One example constant frequency generator can be found in U.S. Pat. No. 6,838,778 to Kandil, et al., which is hereby incorporated by reference. 
     In order for a constant frequency generator, such as the one described in U.S. Pat. No. 6,838,778 to operate in a start mode, a torque converter, pony motor, and a two overrunning (start) clutches are included within the generator. In addition, a pony motor controller is required to power the pony motor which is within the constant frequency generator. The pony motor is used to get the constant frequency generator to synchronous speed, which then is transferred to an AC (main) bus. The torque converter is then allowed to fill with oil which allows the synchronous motor torque to provide a motive force to start the turbine engine. Many practical applications, such as an aircraft power generation system, require the minimization of the size and weight of each component. The addition of a torque converter and a pony motor runs contrary to this concept. 
     SUMMARY OF THE INVENTION 
     A generation system and method utilizes a constant frequency generator to generate electrical power. The generation system has a motor controller which controls the constant frequency generator while operating in a start mode. The motor controller is used to generate various controlled frequencies during generate mode. Also disclosed and claimed is an aircraft electrical architecture incorporating the above electrical generation system and method. 
     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 
         FIG. 1  schematically illustrates an aircraft incorporating the present invention, operating in a generate mode. 
         FIG. 2  schematically illustrates an aircraft incorporating the present invention, operating in a start mode. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     An aircraft  20  operating in a generate mode is schematically illustrated in  FIG. 1 , incorporating a pair of gas turbine engines  22  and  24 . As known, the gas turbine engines  22 ,  24  include a turbine rotor that is driven to rotate by products of combustion. The rotation of the turbine rotor drives a shaft  27  which is connected to a gear box  129 . The gear box  129  translates the rotational movement of the rotor to each of two different shafts which are connected to a variable frequency (and/or constant frequency) generator  28  and a constant frequency generator  26 . 
     The variable frequency generator  28  is connected to two motor controllers  32 ,  34  via a power bus  29 . The motor controllers  32 ,  34  provide control signals and power conversion necessary for the operation of the variable frequency generator  28  through the power bus  29 . The power bus  29  additionally provides variable frequency power to electrical components of the aircraft, which do not need power to be maintained at a set frequency. Techniques for controlling a variable output frequency generator in a generate mode using multiple motor controllers are known in the art. 
     The constant frequency generator  26  is connected to electrical components  36  which require a constant frequency power source via power bus  25 . As is known in the art, no control signals from the motor controllers  32 ,  34  are necessary for constant frequency generator  26  to operate as a generator during a generate mode. 
     When a turbine engine  22 ,  24  is initially starting, it is known to provide a motive force from the connected generators  28 , and  26  (which act as motors during a start mode) to produce the force required to start the engine.  FIG. 2  schematically illustrates an aircraft in a startup mode which utilizes both the variable frequency generator  28  and the constant frequency generator  26  to provide a motive force to the turbine engine  22 ,  24  without the additional inclusion of a torque converter. According to previously known techniques, a constant frequency generator  26  can only operate in a starter mode with the assistance of an additional torque converter acting in conjunction with a pony motor and two start clutches. 
     In order for the example illustrated in  FIG. 2  to operate in the start mode, the constant frequency generator  26  includes a single overrunning (start) clutch  42  which is operable to bypass the constant speed device (CSD), which is used during generation mode. When a line contactor is energized, and electrical power thru the motor controller  34  is provided to the constant frequency generator  26 , the constant frequency generator  26  will operate as a motor and provide a motive force to the shaft. The motor torque will be engaged through the overriding (start) clutch  42  to the input shaft. Once the engine is started, the line contactor  40  will be opened which will reconfigure the aircraft electrical bus to the generation mode as shown in  FIG. 1 . 
     The schematic of  FIG. 2  illustrates one of the motor controllers  34 , which is used to control the output frequency of the variable frequency generator  28  during generate mode, being connected to the constant frequency generator  26  during the start mode. One method of switching the motor controller&#39;s  34  connections, illustrated schematically in  FIGS. 1 and 2 , utilizes a mechanical switch (contactor)  40  to change the electrical bus connections. Other methods and systems for switching a motor controller&#39;s  34  connections are known in the art, and require minimal components. By connecting the already existing motor controller  34  to the constant frequency generator  26 , the motor controller  34  can act in place of the torque converter, pony motor and pony motor controller configuration, which is required in all prior art systems, thereby eliminating components and reducing size and weight. 
     The second motor controller  34  is capable of acting as a start motor controller for item  26  during a start mode since it is otherwise idle during the start mode of the variable frequency generator  28 . This allows for the elimination of the torque converter, one of the two over running (start) clutches, the pony motor and the pony motor controller from the electrical generation system, without requiring the torque converter or the pony motor to be replaced by new components, thereby reducing size and weight and improving efficiency of the overall system. 
     While an example utilizing a second variable frequency generator  28  motor controller  34  which is idle during a start mode has been disclosed above, it is known that alternate motor controllers which are present in the system and idle during a start mode could be used to control the constant frequency generator  26  during a start mode and fall within the above disclosure. 
     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.