Abstract:
A generation method performed by a generator module of an electricity network of an aircraft, the electricity network including a power supply line powered by the generator module, a DC bus powered from the power supply line via a rectifier, and at least one electrical actuator powered with AC from the DC bus via an inverter. The generation method includes: delivering an AC voltage as a function of a voltage setpoint and of a voltage measured in the on-board network; and determining the voltage setpoint as a function of an operating parameter of the actuator.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The invention relates to electrically powering a network that is dedicated to a piece of equipment of an aircraft. 
         [0002]    It is known to power electricity networks on board an aircraft from an on-board generator. Typically, the generator is a generator connected to a propulsion engine of the aircraft or to an auxiliary power unit (APU) having a gas turbine. 
         [0003]    In conventional manner, such a generator comprises a main electrical machine that forms a main electricity generator operating in synchronous mode after the associated turbine engine has been started and is running. The main electrical machine has an inducer rotor and stator windings that deliver alternating current (AC) power to a three-phase bus of an electricity network of the aircraft. 
         [0004]    The dedicated network also has power supply equipment in which a direct current (DC) bus is powered from the AC voltage of the three-phase bus via a rectifier. The power supply equipment powers three-phase electrical actuators from the DC voltage of the DC bus via inverter type power converters. 
         [0005]    The AC voltage of the three-phase bus or the DC voltage of the DC bus is controlled by means of a generator control unit (GCU) that delivers DC to a stator inducer of an exciter having rotor windings connected to the rotor inducer of the main electrical machine via a rotary rectifier. Typically, the control unit of the generator causes the excitation DC to vary in such a manner as to maintain the AC of the three-phase bus or the DC of the DC bus equal to a constant setpoint value. The electrical power needed for powering the inducer of the exciter may be delivered by an auxiliary electricity generator such as a permanent-magnet synchronous generator, or it may be derived from the on-board electricity network of the aircraft. 
         [0006]    In an electricity network of this type, the inverter type power converters that power the actuators need to be dimensioned so as to accommodate both electrical and thermal stresses associated with the mechanical power that is needed for operating the actuator. Such power converters are generally pieces of equipment that are heavy and bulky. 
       OBJECT AND SUMMARY OF THE INVENTION 
       [0007]    The invention seeks to provide a generation method and a generator module that make it possible to avoid at least some of the drawbacks of the above-mentioned prior art. 
         [0008]    To this end, the invention provides a generation method performed by a generator module of an electricity network of an aircraft, said electricity network comprising a power supply line powered by said generator module, a DC bus powered from said power supply line via a rectifier, and at least one electrical actuator powered with AC from the DC bus via an inverter; 
         [0009]    the generation method comprising a step of delivering an AC voltage as a function of a voltage setpoint and of a voltage measured in said on-board network; 
         [0010]    said generation method being characterized in that it comprises a step of determining said voltage setpoint as a function of an operating parameter of said actuator. 
         [0011]    Thus, by means of these characteristics, the DC voltage of the DC bus depends on the operating parameter of the actuator. This makes it possible to limit the dimensioning of the inverter and/or to reduce the dissipation of the inverter. 
         [0012]    In an implementation, said measured voltage is the voltage of the DC bus. 
         [0013]    The operating parameter may be a speed of rotation of the actuator. 
         [0014]    Correspondingly, the invention provides a generator module for an electricity network of an aircraft, said generator module being suitable for delivering an AC voltage as a function of a voltage setpoint and of a voltage measured in said electricity network, said electricity network comprising a power supply line powered by said generator module, a DC bus powered from said power supply line via a rectifier, and at least one electrical actuator powered with AC from the DC bus via an inverter; 
         [0015]    said generator module being characterized in that it includes a module for determining said voltage setpoint as a function of an operating parameter of said actuator. 
         [0016]    In an embodiment, the generator module comprises a generator and a generator control unit, the generator being suitable for delivering said AC voltage as a function of a control current determined by the generator control unit, the generator control unit being suitable for determining the control current as a function of the voltage setpoint and of the voltage measured in said on-board network. 
         [0017]    The advantages and characteristics mentioned above with reference to the generation method also apply to the generator module. 
         [0018]    The invention also provides an aircraft having an electricity network including a generator module of the invention, a power supply line powered by said generator module, a DC bus powered from said power supply line via a rectifier, and at least one electrical actuator powered with AC from the DC bus via an inverter. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         [0019]    The invention can be better understood on reading the following description made by way of non-limiting indication and with reference to the accompanying drawing, in which: 
           [0020]      FIG. 1  is a diagram of an electricity network dedicated to powering power supply equipment on board an aircraft; 
           [0021]      FIG. 2  is a graph showing an operating curve of an electrical actuator; 
           [0022]      FIG. 3  is a graph showing electrical losses in a converter powering an actuator having the operating curve as shown in  FIG. 2 ; and 
           [0023]      FIGS. 4 and 5  are similar to  FIGS. 2 and 3  respectively, and relate to another type of electrical actuator. 
       
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
       [0024]      FIG. 1  shows the electricity network of an aircraft, in its environment. The electricity network  1  is a network dedicated to powering power supply equipment  30  and it comprises a generator module  20 , the power supply equipment  30 , and a three-phase power supply line  3  connecting the generator module  20  to the power supply equipment  30 . 
         [0025]    The generator module  20  delivers a three-phase voltage V AC . In the example shown, the generator module  20  comprises a generator  2  and a generator control unit  6 . 
         [0026]    The generator  2  is mechanically connected to an engine  7  that may for example be an engine for providing propulsion or else an auxiliary power unit of the aircraft. The generator  2  may be a starter/generator suitable for operating as an electric motor when starting the engine  7 . 
         [0027]    When the generator  2  is driven in rotation by the engine  7 , it delivers a three-phase voltage V AC  that depends on a control current I e  delivered by the generator control unit  6 . By way of example, the generator  2  is a three-stage generator of the type described in the introduction. 
         [0028]    The power supply line  3  is powered with the three-phase voltage  AC  delivered by the generator  2 . 
         [0029]    The power supply equipment  30  has a DC bus  4 , a rectifier  5 , and inverters  8 . The DC bus  4  is powered by a DC voltage V DC  from the three-phase voltage V AC  of the power supply line  3  via the rectifier  5 . 
         [0030]    Electrical actuators  9  are electrically powered by the power supply equipment  30 . More precisely, each electrical actuator  9  is powered with a three-phase voltage from the DC bus  4  via an inverter  8 . Each electrical actuator  9  is typically an electric motor of operation that may be characterized by a speed of rotation, written v 9 , and by a torque, written C 9 . 
         [0031]    The generator control unit  6  receives measurement signals representative of the DC voltage V DC  of the DC bus  4  and of the speed of rotation v 9 , and it delivers the control current I e  to the generator  2 . 
         [0032]    For this purpose, the generator control unit  6  uses a control loop in which the control current I e  is determined as a function of the DC voltage  VDC  of the DC bus  4  and of a DC voltage setpoint V DC     —     set . 
         [0033]    The setpoint V DC     —     set  is determined by the generator control unit  6  as a function of the speed of rotation v 9 . Thus, in the electricity network  1 , the DC voltage V DC  of the DC bus  4  depends on the speed of rotation v 9 , thereby making it possible to limit dissipation and to limit the dimensioning of the inverters  8 , as explained below with reference to  FIGS. 2 to 5 . 
         [0034]    It is known that the mechanical power P m  of an electrical actuator  9  may be expressed as follows: P m =v 9 ×C 9 . It is also known that the torque C 9  increases with the phase current I of the electrical actuator  9 . 
         [0035]    This mechanical power P m  corresponds to an absorbed electrical power P e  that is proportional to the product U 9 ×I, where U 9  is the voltage delivered to the actuator  9  by the inverter  8 . 
         [0036]    At a low speed of rotation v 9 , and regardless of the torque C 9 , the mechanical power P m , and thus the absorbed electrical power P e , are low. The voltage U 9  delivered to the actuator  9  by the inverter  8  can therefore be low. 
         [0037]      FIG. 2  is a graph showing an operating curve for a first type of electrical actuator  9 , plotting the torque C 9  as a function of the speed of rotation v 9 . As shown in  FIG. 2 , the torque C 9  is practically at a maximum over the entire range of speeds up to a speed Ω 1 . 
         [0038]      FIG. 3  is a graph showing variation in the power P 8  that is dissipated in an inverter  8  connected to an electrical actuator  9 , plotted as a function of the speed v 9 , for an electrical actuator  9  of the type shown in  FIG. 2 . The curve  11  corresponds to a DC voltage V DC  that varies with the speed v 9  in accordance with the present invention. The curve  10  corresponds to a DC voltage VDC that is kept constant, as in the prior art mentioned in the introduction, and it is given for comparison purposes. 
         [0039]    The power P 8  that is dissipated in an inverter  8  may be resolved into conduction losses and switching losses. Switching losses depend on the product V DC ×I. Given the curve in  FIG. 2 , the current I must be high in order to deliver a high torque C 9 , regardless of the speed of rotation v 9 . Thus, if V DC  is kept constant, the power P 8  is high even at a small speed of rotation v 9 , as shown by curve  10 . 
         [0040]    Nevertheless, as explained above, the voltage U 9  may be small at a small speed of rotation v 9 . However, the voltage U 9  depends on the DC voltage V DC . If it is possible for the voltage U 9  to be low, then the DC voltage V DC  can also be low. Thus, by reducing the DC voltage V DC  at small speeds of rotation v 9 , the power P 8  that is dissipated in an inverter  8  can be reduced in comparison with the curve  10 , as shown by the curve  11 . 
         [0041]    In  FIG. 3 , the curves  10  and  11  meet at a point P at the speed Ω 1 . 
         [0042]    In other words, for an electrical actuator  9  that presents an operating curve of the type shown in  FIG. 2 , it is possible to determine a setpoint voltage V DC     —     set , on which the speed of rotation v 9  of the electrical actuators  9  depends, that makes it possible for the power P 8  that is dissipated in the inverter  8  to be reduced. Thus, the thermal dimensioning of the inverter  8  can be limited. Nevertheless, the electrical dimensioning of the inverter  8  must still make it possible to operate at the above-mentioned point P. 
         [0043]      FIGS. 4 and 5  are graphs similar to the graphs of  FIGS. 2 and 3  respectively, and they relate to a second type of electrical actuator  9  that presents an operating curve having a shape that is different, as shown in  FIG. 4 .  FIGS. 4 and 5  use the same references, without risk of confusion. 
         [0044]    In this embodiment, the torque C 9  is at a maximum at low speeds up to a speed Ω 1 , and then decreases progressively over the remainder of the speed range. 
         [0045]    As in the embodiment of  FIGS. 2 and 3 , the DC voltage V DC  may be small at low speeds of rotation.  FIG. 5  shows that under such circumstances, the power P 8  that is dissipated in the inverter is reduced, as it is in  FIG. 3  (cf. curve  11  situated below curve  10 ). 
         [0046]    Furthermore, in this embodiment, the operating point P 2 , where the power P 8  given by the curve  11  is at a maximum, corresponds to a power that is less than the operating point P 1 , where the power P 8  given by the curve  10  is at a maximum. 
         [0047]    In other words, with an electrical actuator  9  that presents an operating curve of the type shown in  FIG. 4 , it is possible to determine a setpoint V DC     —     set , on which the speed of rotation v 9  of the electrical actuators  9  depends, that enables the power P 8  that is dissipated in the inverter  8  to be reduced, and also to reduce the maximum dissipated power P 8 . It is thus possible for the dimensioning of the inverter  8  to be limited, both thermally and electrically. 
         [0048]    The generator control unit  6  has a determination module that converts the speed of rotation v 9  into a setpoint V DC     —     set . By way of example, the determination module uses a correspondence table or a conversion relationship. The person skilled in the art is capable of designing a determination module that is appropriate for a given operating curve, e.g. of the type shown in  FIG. 2  or of the type shown in  FIG. 4 . 
         [0049]    In a variant, instead of using the speed of rotation v 9 , the generator control unit  6  makes use of some other operating parameter of the electrical actuator  9  in order to determine the setpoint V DC     —     set . 
         [0050]    Also in a variant, the regulation performed by the generator control unit  6  applies to the three-phase voltage V AC  of the power supply line  3 . Under such circumstances, the generator control unit  6  determines a three-phase voltage setpoint V AC     —     set  that is a function of the speed v 9  or of some other operating parameter of the electrical actuator  9 . 
         [0051]    A generator module  20  is described above in which the three-phase voltage delivered by the generator  2  depends on the control current as determined by the control unit  6 . Nevertheless, the invention is not limited to that type of generator module. Thus, the generator module may comprise a self-excited asynchronous generator associated with switched capacitors in order to provide a plurality of voltage levels. In a variant, the generator module may comprise a self-excited asynchronous generator associated with an inverter delivering magnetization current for DC regulation. Also in a variant, the generator module may comprise a multi-winding permanent-magnet synchronous generator for operating at a plurality of levels. 
         [0052]    An example application for the electricity network  1  lies in green taxiing of an aircraft. In this example, the actuators  9  are electric motors suitable for enabling the aircraft to taxi and the engine  7  is an auxiliary power unit. The propulsion engines of the aircraft then do not need to be running, thus achieving significant fuel savings.