Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
  • F02N—STARTING OF COMBUSTION ENGINES; STARTING AIDS FOR SUCH ENGINES, NOT OTHERWISE PROVIDED FOR
  • F02N11/00—Starting of engines by means of electric motors
  • F02N11/04—Starting of engines by means of electric motors the motors being associated with current generators
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F05—INDEXING SCHEMES RELATING TO ENGINES OR PUMPS IN VARIOUS SUBCLASSES OF CLASSES F01-F04
  • F05B—INDEXING SCHEME RELATING TO WIND, SPRING, WEIGHT, INERTIA OR LIKE MOTORS, TO MACHINES OR ENGINES FOR LIQUIDS COVERED BY SUBCLASSES F03B, F03D AND F03G
  • F05B2220/00—Application
  • F05B2220/50—Application for auxiliary power units (APU's)

Definitions

• This invention relates to a starting system for turbine engines such as those employed in aircraft, and more specifically, a starting system which makes substantial use of existing components of a generating system associated with the turbine engine.
• Turbine engines utilized in, for example, aircraft have been started in any of a variety of ways.
• One typical starting scheme may utilize an air turbine connected in driving relation to the turbine engine.
• the air turbine is provided with air under pressure from an auxiliary power unit (APU) and driven until it in turn brings the turbine engine up to a self sustaining speed.
• APU auxiliary power unit
• VSCF variable speed, constant frequency inverter system
• An exemplary embodiment of the invention achieves the foregoing object in a generating system including a brush ⁇ less generator coupled to the turbine and having at least one plural phase output winding in which electrical power may be induced by a magnetic field produced in a main field powered by an exciter.
• a full wave rectifier including two diodes for each phase and interconnected in a bridge which is connected to the winding and is adapted to provide a DC output for use in the system is also included.
• the generator is utilized as an A.C. synchro ⁇ founded motor for the turbine through the use of a plurality of semiconductors, one for each diode, each having a conduction path connected in shunt relation to the corres ⁇ ponding diode within the bridge.
• An inverter controller is connected to the control electrode of the semiconductors for selectively operating the semiconductors so that the semi ⁇ conductors in the diodes operate as an inverter.
• the system is completed by the provision of means for selectively applying a D.C. signal to the bridge oppositely of the winding.
• the semiconductors are transistors and the conduction path is the emitter-collector conduction path and the control electrode is the base.
• the invention contemplates that the foregoing com ⁇ ponents be utilized in a system further including a variable speed, constant frequency inverter for providing an A.C. signal and connected to the bridge oppositely of the winding, that is, on the same side as the means for selec ⁇ tively applying a D.C. signal.
• Fig. 1 is a schematic view of an existent generating system for operation by a turbine engine such as an aircraft turbine engine utilizing a variable speed, constant fre ⁇ quency inverter;
• Fig. 2 is a schematic similar to Fig. 1 but illus ⁇ trating the additional components added according to the invention to convert a rectifier bridge found in the prior art into an inverter so as to allow the system to be util ⁇ ized for starting in addition to power generation.
• FIG. 1 A typical prior art power generating system of the type employing a variable speed, constant frequency inverter is illustrated in Fig. 1. The same will be described in that the invention is specifically directed to providing such a system with an engine start capability.
• the system illustrated in Fig. 1 includes a wound field, wild frequency brushless generator of conventional construction, which, as is well known, includes one or more generator output windings 10. As illustrated in Fig. 1, two such windings are provided and each is a star connected, three-phase winding. Electrical power is induced in the windings 10 as a result of a rotating field, frequently termed the "main field" carried " by the generator, rotor and designated 12. The main field creates the rotating magnetic field and the magnetic field is in turn generated by elec ⁇ trical power provided by an exciter 14 which in turn is conventionally powered by a permanent magnet generator 16. All of these components form a part of the brushless gen ⁇ erator and may be driven, when operated in a generating mode, by a turbine engine 18 connected to the generator rotor.
• each branch of. each winding 10 is connected to a junction 20 between two diodes 22.
• the diodes 22 are arranged with the polarities illustrated and form a bridge of three branches 24, 26, and 28, one for each phase.
• the -branches 24, 26 and 28 are connected in parallel to form the bridge and the sides of each of the diodes 22 remote from the connection points 20 are connected to lines 30 and 32, respectively, which are provided to a conventional variable speed, constant frequency inverter 34.
• the brushless generator includes more than one of the windings 10 such as illustrated in Fig.
• an additional bridge 36 made up in the same form as mentioned previously is provided for each windingand the same is connected to the inverter via the line 30 as well as the line 38.
• Capacitors 40 employed for conventional purposes interconnect the lines 30 and 32, and 30 and 38, respectively.
• the brushless generator upon operation of the turbine, the brushless generator will be operated and the same will have a frequency output that varies according to the speed of the turbine 18.
• the output power of varying frequency is rectified to direct current by the bridge circuits thus described and provided as an input to the inverter 34.
• the inverter is controlled and operated in the conventional fashion, and, when employed in an aircraft, will typically provide a three-phase, 115 volts A.C, 400 hertz output on output lines shown at 42, 44 and 46.
• FIG. 1 An exemplary embodiment of a generating system such as shown in Fig. 1 and provided with engine start capability according to the invention is illustrated in Fig. 2. Where like components are utilized, like reference numerals are given. Moreover, in the interest of brevity, components common to the prior art system already described will not be redescribed.
• a semiconductor such as a transistor 48
• a transistor 48 is placed in shunt relation with each of the diodes 22 in each of the branches 24, 26 and 28 of each bridge. That is to say, a transistor 48 is connected in parallel with each *diode, there being a number of trans ⁇ istors 48 equal to the number of diodes 22 in each bridge.
• the arrangement is such that the collector-emitter conduc ⁇ tion path of each transistor 48 is in parallel with the corresponding diode 22.
• the control electrode or base of each transistor 48 is connected to a corresponding control line 50.
• the control lines 50 are taken to a conventional electronic inverter controller, shown generally at 52. Through conventional operation of the controller 52, the transistors 48 may be caused to operate generally as in the inverter 34 with the diodes 22 acting as flywheel diode to dissipate stored energy when their corresponding transistors 48 are turned off.
• the brushless generator When it is desired to start the turbine 18, the brushless generator is operated as an A.C, synchronous motor with the alternating current being provided to the windings 10 from the bridges when operating as inverters.
• D.C. power to the bridges is provided on the lines 30, ' 32 and 38 from any suitable source, generally designated 60, connected appropriately to the lines via a selectively operable switch 62.
• Optional filters 64 may be employed in the connection if desired.
• the source 60 may be an auxiliary power unit or it may be the output found on the lines 30, 32 and 38 of a gener ⁇ ating system associated with another turbine 18 in a multi-engine aircraft, which turbine is already running.
• the inverter circuit formed utilizing the transistors 48 and the diode 22 will not provide particularly "clean" A.C. power. However, it will be more than adequate for powering the windings 10 so that the brushless generator may operate as an A.C motor. More importantly, an engine start capability is added to the system with only minimal weight addition, requiring only_ the addition of the transistors 48 and the controller 52.
• start system bypasses entirely the A.C. components of the electri ⁇ cal and generating system so that start system operation does not cause degredation of A.C. power available from the generating system.

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• Engineering & Computer Science (AREA)
• Chemical & Material Sciences (AREA)
• Combustion & Propulsion (AREA)
• Mechanical Engineering (AREA)
• General Engineering & Computer Science (AREA)
• Control Of Eletrric Generators (AREA)

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• 1987
  • 1987-07-15 EP EP19870905496 patent/EP0276295A4/de not_active Withdrawn
  • 1987-07-15 WO PCT/US1987/001687 patent/WO1988000653A1/en not_active Application Discontinuation

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