Abstract:
An electrical power supply device for an aircraft on the ground, the device including two electricity generators driven by an auxiliary power unit, wherein the first generator is connected by a selective connection/disconnection mechanism to an aircraft network and to an electrical taxiing network, and is configured to deliver either a first AC voltage to the aircraft network when it is connected to that network, or an AC voltage or a power to the taxiing network when it is connected to that network, and wherein the second generator is connected by the connection/disconnection mechanism to the aircraft network to deliver the first AC voltage to that network solely when the first generator is powering the taxiing network.

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to a device for electrically powering an aircraft on the ground, the device comprising at least two electricity networks: an aircraft electricity network, in particular for powering the cabin and the cockpit of the aircraft; and an electrical taxiing network. 
     DESCRIPTION OF THE RELATED ART 
     Applications FR 10/55457 and FR 10/59612 in the name of the Applicant describe respectively a device for powering the electricity network of an aircraft, and an electrical configuration for processing the energy that is regenerated by electrical actuators during taxiing operations of an aircraft. 
     An aircraft is said to be “taxiing when it is traveling or running on the ground using the wheels of the aircraft landing gear. Taxiing is said to be “electrical” when the wheels of at least one undercarriage of the aircraft (and in general the wheels of the main landing gear) are driven by electric motors, which form part of the taxiing network. 
     The aircraft and taxiing networks are powered by at least one generator driven by an auxiliary power unit (APU). 
     In the prior art, the APU is started by means of an independent starter powered by a battery, and it has an outlet shaft for driving the above-specified generator. 
     Several electrical configurations have been proposed for powering aircraft and taxiing networks by using energy delivered by the APU. 
     A first prior art electrical configuration has two electricity generators driven by the APU. The first generator delivers an AC voltage Vac 1  (230 volts (V)) to the taxiing network, and the second generator delivers an AC current (AC) voltage Vac 2  (115 V) to the aircraft network. The taxiing network includes an electronic motor control unit (MCU) for controlling the electric motors driving the wheels of the aircraft, which unit is connected to the first generator by connection/disconnection means. 
     The advantage of that configuration is that the taxiing and aircraft networks are independent of each other and they are powered by generators that are distinct. As a result, constraints concerning validation for certification of the aircraft network (of the ATA 24 type) have no effect on the taxiing network, which may therefore have a simplified electronic control unit, thereby reducing the weight of that unit (by about 50 kilograms (kg)). 
     Nevertheless, both of the above-mentioned generators have relatively high electrical powers, respectively 120 kilovolt amps (kVA) and 90 kVA, in addition to the electrical power of the starter of the APU. A relatively large amount of electrical power is thus installed on board the aircraft. As a result of their high electrical power levels, the generators are heavy and bulky, and it can be difficult or even impossible to mount them on the outlet shaft of the APU. 
     In a second electrical configuration of the prior art, the aircraft and taxiing networks are powered by a common high-power generator (150 kVA), which is driven by the APU. That generator delivers an AC voltage Vac 2  (115 V) to the aircraft and taxiing networks, which are connected to the generator by connection/disconnection means. The taxiing network and has an electronic power unit connected to the electric motors for driving the wheels of the aircraft. 
     The drawback of that electrical configuration is that the taxiing network must comply with all of the network standards (e.g. of the ATA 24 type) that are applicable to the aircraft, and it is powered by the voltage Vac 2  at 115 V. The electronic power unit of the taxiing network includes an energy conversion function serving to increase the voltage level without polluting the aircraft network. In general, this function is performed by an auto transformer rectifier unit (ATRU), thereby leading to a significant increase in the weight of this unit (by about 50 kg to 100 kg). 
     Proposals have also been made, in another prior art electrical configuration, to power the taxiing network of an aircraft by means of at least one generator driven by an engine of the aircraft, the aircraft electrical network being powered by another generator driven by an APU. Nevertheless, that configuration makes it necessary to run an engine, thereby leading to significantly smaller savings in fuel consumption to be expected from the aircraft having an electrical taxiing function. 
     BRIEF SUMMARY OF THE INVENTION 
     A particular object of the invention is to reduce or eliminate in a manner that is simple, effective, and inexpensive, at least some of the above-mentioned drawbacks of the prior art by means of a novel electrical configuration for electrically taxiing an aircraft. 
     To this end, the invention provides an electrical power supply device for an aircraft on the ground, the device comprising two electricity generators driven by an auxiliary power unit, the first generator being for powering an electrical taxiing network including electric motors for driving wheels of the aircraft, and the second generator being for powering an aircraft electricity network, the power supply device being characterized in that the first generator is connected by selective connection/disconnection means to the aircraft and taxiing networks, for delivering a first AC voltage Vac 2  to the aircraft network when it is connected to that network, or a higher AC voltage Vac 1  or a power P to the taxiing network when it is connected to that network, and in that the second generator is connected by connection/disconnection means to the aircraft network in order to deliver said AC voltage Vac 2  to that network solely when the first generator is powering the electrical taxiing network. 
     In the device of the invention, the first generator driven by the auxiliary power unit is used to power the taxiing network when the aircraft needs to taxi on the ground, and to power the aircraft network when the taxiing network is not being powered. This first generator is said to be “hybrid”, and it is capable of delivering selectively a voltage Vac 1  for powering the taxiing network or a voltage Vac 2  for powering the aircraft network. In a variant, the first generator may be capable of delivering selectively a power P for powering the taxiing network, or a voltage Vac 2  for powering the aircraft network. The second generator is used for powering the aircraft network while the first generator is powering the electrical taxiing network. The second generator is advantageously dimensioned to be capable of supplying only the needs of the aircraft on the ground, thus making it possible to reduce the on-board electrical power and thus the volume that is installed in the aircraft. The connection/disconnection means are controlled, during taxiing, to connect the first generator to the taxiing network (in order to power it with a voltage Vac 1  or with a power P) and the second generator to the aircraft network (in order to power it with a voltage Vac 2 ), and during other stages of the operation of the aircraft, to connect the first generator to the aircraft network in order to power it with a voltage Vac 2 , the second generator then being stopped. 
     The invention thus makes it possible both to design the taxiing network without complying with the constraints imposed by the standards (of the ATA 24 type) applicable to the network specific to the aircraft, and also to reduce the harmonic pollution constraints associated with the taxiing function. 
     According to another characteristic of the invention, one of the two generators is a starter/generator suitable for starting the auxiliary power unit, and it can thus replace the independent starter used in the prior art, thereby constituting a significant saving in weight. Furthermore, this starter/generator is mounted on the APU in the place of the starter (i.e. on the group gearwheel generally dedicated to the starter in the prior art) and it therefore does not impede mounting the other generator on the outlet shaft of the APU. 
     The device of the invention also includes an electronic power unit that is connected to the starter/generator for controlling the starting of the auxiliary power unit. This unit may comprise control means of the generator control unit (GCU) type for regulating the current or the voltage delivered by the starter/generator and for protecting it in the event of electrical overload. 
     The first generator is preferably a three-stage synchronous generator with wound rotor excitation. Varying rotor excitation makes it possible either to vary the output voltage from the generator between the values Vac 1  and Vac 2 , or else to switch between a voltage generator (delivering an AC voltage Vac 2  that is substantially constant) and a current or power generator delivering a substantially constant current or power as a function of the needs for taxiing, e.g. a power of 150 kilowatts (kW). 
     The first generator may deliver a voltage of 115 Vac (Vac 2 ) at a power of 90 kVA when it is connected to the aircraft network or a voltage of 230 Vac (Vac 1 ) and a power of 150 kW (for a generator that is regulated in voltage or in power) when it is connected to the taxiing network. 
     The second generator may deliver electrical power lying in the range 30 kVA to 40 kVA, and a voltage Vac 1  of 115 V at 400 hertz (Hz). The electrical power on-board the aircraft for operation on the ground is thus much less than that used in the prior art as described above (120 kVA 130 kVA, as compared with 210 kVA in the prior art). Furthermore, because of its low electrical power, the second generator is compact and can be driven together with the first generator by the outlet shaft of the APU. 
     The present invention also relates to a method of electrically powering an aircraft on the ground by means of a device as described above, the method being characterized in that it comprises a step consisting in powering the taxiing network by the first generator and the aircraft network by means of the second generator, and a step consisting in powering the aircraft network by means of the first generator when the taxiing function is not in use, the second generator then not being used. 
     Advantageously, the first generator is a three-stage synchronous generator with wound rotor excitation, and the excitation of this generator is controlled by an electronic power unit for switching between a generator of the voltage Vac 1  to a generator of the voltage Vac 2  or from a generator of a power P to a generator of the voltage Vac 2 . 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       The invention can be better understood and other characteristics, details and advantages thereof appear more clearly on reading the following description made by way of nonlimiting example and with reference to the accompanying drawings, in which: 
         FIGS. 1 and 2  are both diagrammatic views of respective prior art electrical power supply devices for aircraft; 
         FIG. 3  is a diagrammatic view of an electrical power supply device of the present invention for an aircraft; 
         FIG. 4  is a diagrammatic view of a three-stage synchronous generator with wound rotor excitation of the invention; and 
         FIGS. 5 and 6  are diagrammatic views of embodiment variants of the power supply device of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Reference is made initially to  FIG. 1 , which shows an aircraft having a prior art device  10  for feeding electricity both to an aircraft network  12 , in particular for powering equipment in the cockpit and the passenger cabin of the aircraft, and also for powering an electrical taxiing network  14 . 
     Each network  12 ,  14  is powered by a respective electricity generator  16 ,  18  driven by an auxiliary power unit  20 , referred to below by the acronym APU. 
     The APU  20  is situated at the rear of the aircraft fuselage and has an outlet shaft (not shown) for driving the rotors of the generators  16 ,  18 . The APU  20  is fitted with an independent starter (not shown), which is connected to a battery and to means for controlling the starting of the APU. 
     The generator  16  has electrical power of 90 kVA and it delivers an AC voltage Vac 2  at 115 V to the network  12 , which network is shown diagrammatically in  FIG. 1  as a primary distribution unit  22  connected by an electrical harness  24  to the generator  16 . 
     The generator  18  has electrical power of 120 kVA and delivers an AC voltage Vac 1  of 230 V to the taxiing network  14 , which is represented diagrammatically by four motors (M)  26 , connected to an electronic motor control unit (MCU)  28 , which is itself connected by a rectifier  30  to the generator  18 . The output from the generator  18  is connected to the taxiing network  14  by connection/disconnection means  32  that serve to isolate the generator from the taxiing network  14  when the taxiing function is not desired, e.g. while the aircraft is in flight. 
     This electrical configuration presents the drawbacks described above, which are due mainly to the relatively high electrical powers of the generators  16 ,  18  (respectively 90 kVA and 120 kVA), to their weight, and to the space that they occupy. 
       FIG. 2  shows an aircraft fitted with another prior art device  110  for electrically powering the aircraft network  112  and the taxiing network  114 . 
     The networks  112 ,  114  are powered by a common electricity generator  116  that is driven by an APU  120 . 
     The output from the generator  116  is connected to the networks  112 ,  114  by connection/disconnection means  132  and it delivers an AC voltage Vac 2  at 115 V to these networks. 
     The electronic power unit (MCU)  128  of the taxiing network  114  includes an auto transformer rectifier unit (ATRU) module for converting energy, which module serves to increase the voltage level delivered by the generator  116 . 
     This other electrical configuration also presents drawbacks, which are due mainly to the fact that the ATRU module gives rise to a significant increase in the weight of the electronic power unit (MCU)  128 , and that the taxiing network  114  needs to comply with all of the certification standards applicable to the network  112  of the aircraft  12  (of the ATA 24 type). 
     The invention makes it possible to remedy at least some of the drawbacks of the prior art by powering the taxiing network and the network specific to the aircraft by means of two generators, one of which is “hybrid” and is capable of powering either network in selective manner. 
       FIG. 3  shows a preferred embodiment of the device  210  of the invention, in which an APU  220  situated at the rear of the fuselage of an aircraft drives the rotors of two independent electricity generators  216 ,  218 . 
     The output from the generator  216  is connected by connection/disconnection means  232  to the input of a primary distribution unit  222  of the aircraft network, with the output(s) of the unit  222  being connected for example to equipment in the cockpit and to various compartments of the aircraft fuselage. The electrical connections between the unit  222 , the means  232 , and the generator  216  are established by electrical harnesses  224 . 
     The generator  216  has electrical power lying in the range 30 kVA to 40 kVA and it delivers an AC voltage Vac 2  to the aircraft network  212 , e.g. at 115 V and 400 Hz. 
     The output from the generator  218  is connected by connection/disconnection means  232  to the input of a rectifier  230  of the taxiing network, the output from the rectifier  230  being connected to the input of an electronic power unit (MCU)  228  which powers the motors  226  for driving the wheels of the main landing gear of the aircraft. There may be four of these motors  226 . 
     In the example shown, the means  232  for connecting/disconnecting the generators  216 ,  218  to the networks  212 ,  214  are formed by a common green taxiing power control unit (GNTPCU) having contactors or the like that are suitable for establishing electrical connections between the generator  218  and the taxiing network  214 , between the generator  218  and the aircraft network  212 , and between the generator  216  and the aircraft network  212 . The GNTPCU serves to manage the electrical configurations of the aircraft by means of contactors and it further includes at least one generator control unit (GCU) type card for controlling the excitation of the generator  218 , as described below. 
     The generator  218  has electrical power of about 90 kVA, for example, and it is suitable for powering the taxiing network  214  and the aircraft network  212 . 
     When the taxiing function is not in use, the output from the generator  218  is connected by the means  232  to the aircraft network  212  and it delivers an AC voltage Vac 2  to this network, e.g. 115 V at 400 Hz. The output from the generator  218  is disconnected from the taxiing network  214  by the means  232 . The output from the generator  216  may also be disconnected from the network  212  by the means  232 . The contactors of the GNTPCU are then in the positions as shown in  FIG. 3 . 
     When the taxiing function needs to be used, the output from the generator  216  is connected by the means  232  to the aircraft network  212  and it delivers an AC voltage Vac 2  to this network, e.g. 115 V at 400 Hz. The output from the generator  218  is connected by the means  232  to the taxiing network  214  and it delivers an AC voltage Vac 1  to this network, e.g. 230 V at 400 Hz, or a power P, which may for example be 150 kW at 230 V. The contactors of the GNTPCU are then in the positions as shown in  FIG. 3   a.    
     The rectifier  230  is of the AC/DC type and it serves to convert the AC voltage Vac 1  into a DC voltage Vdc 1 . The MCU  228  may have contactors or at least one energy converter, each including one or more inverters. Advantageously, the inverters operate merely in electricity-switching mode when the generator  218  is delivering electricity or power to the taxiing network  214 . 
     The generator  216  is preferably a starter/generator (S/G), which is capable of being used in “motor” mode when energy is applied thereto for the purpose of starting the APU  220 . This makes it possible to omit the starter that used to be dedicated to starting the APU in the prior art. The low-power generator  216  is mounted on the APU  220  instead of the original starter, which makes it possible to avoid hindering installing the generator  218  on the outlet shaft of the APU  220 . 
     In a variant, it is a generator  218  that is used for starting the APU  220 . The generator  218 , which is suitable for selectively delivering two voltages Vac 1  and Vac 2 , or a voltage Vac 2  and a power P, is advantageously a three-stage synchronous generator with wound rotor excitation, and its principle of operation is shown diagrammatically in  FIG. 4 . 
     The generator  218  comprises a wound main rotor  250  driven by the outlet shaft  248  of the APU inside a wound main stator  252 . The generator  218  is of the three-stage type (3 rotor/stator assemblies) and in addition to the assembly comprising the main rotor  250  and the main stator  252 , it further comprises a permanent-magnet rotor  254  and stator  256 , and a rotor  258  and a stator  260  of an exciter, the permanent-magnet rotors  254 ,  258  and the exciter being secured to the outlet shaft  248  of the APU. 
     The output from the rotor  258  of the exciter is connected to the input of a diode rectifier  262 , which is secured to the shaft  248 , and which has its output connected to the input of the main rotor  250 . 
     The input of the stator  260  of the exciter and the output of the permanent magnet rotor two and  256  are connected to regulation and control means  264  including at least one GCU card that regulates the current or the voltage of the generator  218  and that protects it in the event of electrical overload. These means  264  are also connected to the output of the main stator  252  and they include means for detecting the voltage or the current delivered to the networks  212 ,  214  of the aircraft. The means  264  may be housed in the GNTPCU. 
     The generator  218  can thus operate as follows. 
     The outlet shaft  248  from the APU  220  drives the main rotor  250  of the generator  218  at a predetermined speed. The regulation and control means  264  regulate the power supply to the stator  260  of the exciter so as to generate a magnetic field that induces current in the rotor  258  of the exciter, this current leaving the rotor  258  and being rectified by the rectifier  262  prior to powering the main rotor  250  in order to induce a given voltage or current in the main stator  252  of the third stage of the generator. The permanent-magnet rotor  254  and stator  256  serve in particular to inform the means  264  about the speed of rotation of the shaft  248 . 
     The main rotor  250  induces a current or a voltage in the main stator  252  of the purpose of powering one or the other of the above-mentioned networks  212 ,  214 . The means  264  control the excitation of the generator  218  as a function of the voltage or the current detected at the output from the generator, in such a manner that the generator delivers a defined voltage (Vac 1  or Vac 2 ) that is substantially constant, or possibly varying, in order to power in particular the taxiing network, and that can be thought of as a voltage generator, or delivers a substantially constant current or power, and that can be thought of as a current/power generator in particular for powering the taxiing network. 
     The variation in the excitation of the generator  218  makes it possible to change from a mode of regulating the voltage Vac 2  (for powering the network  212  with Vac 2 , e.g. 115 V) to a mode of regulating power P (for powering the network  214  with power P, for example 150 kW), or from a mode of regulating voltage Vac 2  (for powering the network  212  with Vac 2 , e.g. 115 V) to a mode of regulating the voltage Vac 1  (for powering the network  214  with the voltage Vac 1 , e.g. at 230 V). 
     The generator  218  preferably delivers a voltage of 115 Vac and a power of 90 kVA when it is connected to the aircraft network, and a power of 150 kW when it is connected to the taxiing network. 
     In the variant embodiment of  FIG. 5 , and electronic power unit  270  of the starter box unit (SBU) type is connected to the harness  224 , in parallel with the unit  222 . This unit  270  is used for controlling starting of the APU  220  via the starter/generator  216  or  218 . Under such circumstances, the way in which the contactors of the GNTPCU (means  232 ) are controlled may be adapted accordingly. 
     The variant embodiment of  FIG. 6  differs from that of  FIG. 4  in that the MCU is a replaced by a motor starter control unit (MSCU) or a motor starter unit (MSU)  272 . The MSU  272  incorporates some of the power electronics of the GNTPCU in order to control starting of the APU  220  by means of the starter/generator  216  or  218 . 
     The electrical system for starting the APU that is used in the present invention may be of the type described in application WO-A2-2010/079308 in the name of the Applicant. 
     In yet another variant (not shown), the taxiing network has a number of motors (M)  226  that is not equal to four, and that is equal to two, for example.