Patent Application
20130062885
Gas turbine engines, also known as combustion turbine engines, are rotary engines that extract energy from a flow of combusted gases passing through the engine onto a multitude of turbine blades. Gas turbine engines have been used for land and nautical locomotion and power generation, but are most commonly used for aeronautical applications such as for airplanes and helicopters. In airplanes, gas turbine engines are used for propulsion of the aircraft.
Gas turbine engines also usually power a number of different accessories such as generators, starter/generators, permanent magnet alternators (PMA), fuel pumps, and hydraulic pumps, e.g., equipment for functions needed on an aircraft other than propulsion. For example, contemporary aircraft need electrical power for avionics and motors. A generator coupled with a gas turbine engine will convert the mechanical power of the engine into electrical energy needed to power accessories.
Gas turbine engines can have two or more spools, including a low pressure (LP) spool that provides a significant fraction of the overall propulsion system thrust, and a high pressure (HP) spool that drives one or more compressors and produces additional thrust by directing exhaust products in an aft direction. A triple spool gas turbine engine includes a third, intermediate pressure (IP) spool.
It is known to couple an AC generator with the HP spool of gas turbine engine to produce electrical power in the form of alternating current (AC power). Efforts have also been made to extract AC power from the LP spool in addition to the HP spool. U.S. patent application Ser. No. 12/981,044, filed Dec. 29, 2010 discloses a system in which variable frequency AC power is drawn from the HP spool and constant frequency AC power is drawn from the LP spool. It is also known to rectify AC power generated from a gas turbine engine to produce DC power used by accessories in an aircraft.
In one embodiment, a gas turbine includes a high pressure (HP) spool, a low pressure (LP) spool, an AC generator, an LP drive assembly having an input mechanically coupled to the LP spool and an output mechanically coupled to the AC generator, a DC generator, and an HP drive assembly having an input mechanically coupled to the HP spool and an output mechanically coupled to the DC generator.
In another embodiment, a method for powering an aircraft system includes extracting AC power from a low pressure (LP) spool of a gas turbine engine, extracting DC power from a high pressure (HP) spool of the gas turbine engine, supplying the AC power extracted by the AC generator to a load, and supplying the DC power extracted by the DC generator to a load.
In the drawings:
The subject matter disclosed herein relates to power extraction from an aircraft engine, and more particularly to an electrical power system architecture which enables production of electrical power from a multiple spool turbine engine. However, it is also contemplated that the subject matter disclosed herein has general application to electrical power system architectures in non-aircraft applications, such as industrial, commercial, and residential applications.
In the illustrated embodiment, the system architecture 40 includes a DC generator 42, shown herein as a starter-generator 42, configured to produce an direct current (DC) power from mechanical power supplied by the HP spool 26 and an AC generator (or alternator) 44 configured to produce alternating current (AC) power from mechanical power supplied by the LP spool 28.
The HP spool 26 can be operably coupled with the DC starter-generator 42 by an HP drive assembly having an input mechanically coupled to the HP spool 26 and an output mechanically coupled to the DC starter-generator 42. One embodiment of the HP drive assembly is an accessory gearbox 46, where the DC starter-generator 42 can be mounted and coupled to the accessory gearbox 46. Within the accessory gearbox 46, power may also be transferred to other engine accessories. The DC starter-generator 42 converts mechanical power supplied by the HP spool 26 into electrical power and produces a DC power output 48. The DC starter-generator 42 also provides a starting function to the engine of the aircraft. Alternatively, the DC generator 42 on the HP side of the system architecture 40 may comprise a generator that does not provide a starting function to the engine of the aircraft. In this case, a separate starter motor connected to the accessory gearbox 46 can be provided to perform the starting function for the aircraft. Furthermore, the system architecture 40 can include multiple generators drawing mechanical power from the HP spool 26 to produce DC power in order to provide a measure of redundancy.
The LP spool 28 can be operably coupled with the AC generator 44 by an LP drive assembly having an input mechanically coupled to the LP spool 28 and an output mechanically coupled to the AC generator 44. One embodiment of the LP drive assembly is a constant speed drive (CSD) 50 which converts the variable speed input from the LP spool 28 to constant speed. The CSD 50 can be mechanically coupled to the AC generator 44 and drives the AC generator 44 at a constant speed. The AC generator 44 can be configured to produce alternating current (AC) power from mechanical power supplied by the LP spool 28, and can be a brushless AC generator. Although the embodiment shown herein is described as using one AC generator 44 on the LP side of the system architecture 40, another embodiment of the invention may use multiple AC generators 44 drawing mechanical power from the LP spool 28 to produce AC power in order to provide a measure of redundancy. Furthermore, while a separate AC generator 44 and CSD 50 are discussed herein, an integrated drive generator which combines the CSD 50 and generator 44 into a common unit can alternatively be used.
The AC generator 44 can have a main stator with dual windings 52, 54, with each winding configured to provide a different output. The first winding 52 is configured to provide a constant frequency AC power output 56 for driving motor loads without the need for a motor controller. The AC generator 44 has a generator control unit 58 that is configured to regulate the voltage of the constant frequency AC power output 56. For example, some common avionics use 26, 28, or 115 V AC.
The second winding 54 can be configured to convert a portion of the AC power produced by the AC generator 44 to a DC power output 60.
In operation, with the gas turbine engine 10 stared, HPT 22 rotates the HP spool 26 and the LPT 24 rotates the LP spool. The accessory gearbox 46 is driven by the rotating HP spool 26, and transmits mechanical power from the HP spool 26 to the DC starter-generator 42. The DC starter-generator 42 converts mechanical power supplied by the HP spool 26 into electrical power and produces the DC power output 48. The CSD 50 is driven by the rotating LP spool 28, and transmits mechanical power from the LP spool 28 to the AC generator 44. The AC generator 44 converts the mechanical power supplied by the LP spool 28 into electrical power, a portion of which can be produced as the AC power output 56 by the first winding 52 and a portion of which can be produced as the DC power output 60 by the second winding 54. The AC power output 56 can be provided to an electrical bus 64 configured to supply AC power to one or more loads 66 that require an AC power supply. The DC power output 60 of the AC generator 44 driven by the LP spool 28 is paralleled with the DC output 48 of the DC starter-generator 42 driven by the HP spool 26 to create a combined DC power output 68. The combined DC power output 68 can then be provided to an electrical bus 70 configured to supply DC power to one or more loads 72 that require a DC power supply. Depending on the type of load drawing power, the DC and/or AC power extracted by the system architecture 40 may undergo further processing before being used by the loads 66, 72.
The paralleling of the DC power output 60 generated by the LP spool 28 with the DC power output 48 generated by the HP spool 26 enables the DC loads 72 of the aircraft to be shared by the HP spool 26 and the LP spool 28. The DC load sharing between the HP and LP spools 26, 28 can be accomplished seamlessly by regulating the excitation of the DC starter-generator 42. For example, during an aircraft descend mode, load on the DC starter-generator 42 driven by the HP spool 26 can be minimized at the expense of the DC power output 60 from the AC generator 44 driven by the LP spool 28. Such a load sharing scheme can have the effect of avoiding a potential stall issue within the gas turbine engine 10 of
The system architecture disclosed herein provides a hybrid electrical power system to an aircraft. One advantage that may be realized in the practice of some embodiments of the described systems and methods is that both AC and DC power can be extracted from the gas turbine engine 10. The operating efficiency of the gas turbine engine 10 is also increased by seamlessly controlling the power drawn from HP and LP spools 26, 28. Furthermore, in cases where the loads includes induction motors, the need for a motor controller or motor control electronics can be eliminated since a constant frequency AC power output 56 is produced by the first winding 52.
Another advantage that may be realized in the practice of some embodiments of the described systems and methods is that the system architecture 40 can offer a level of redundant DC power generation, since DC power can be extracted from the LP spool 28 as well as the HP spool 26 of the gas turbine engine 10. Drawing power from both spools 26, 28 offers increased redundancy for DC power, such that in the event of a failure of one of the spools 26, 28 or generators 42, 44, DC power may still be extracted from the remaining operational spool 26, 28 and generator 42, 44.
Still another advantage that may be realized in the practice of some embodiments of the described systems and methods is the avoidance of engine stall issues that are typically encountered during a descend mode of the aircraft by sharing the DC load between the HP and LP spools 26, 28. Being able to draw power from the LP spool as well as the HP spool permits allows the aircraft to run at lower rpms during descent without risk of stall, thereby preserving fuel efficiency of the aircraft.
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.
