Generator with hybrid excitation for a hybrid electric propulsion system

Abstract

The invention relates to a hybrid electric propulsion system (200) for a turbojet engine, comprising: - a first permanent magnet synchronous machine (230) connected to an AC-DC converter (231) and intended to be connected to a high-pressure shaft (222) of the turbojet engine; - a hybrid excitation generator (240) comprising a brushless synchronous machine (242), a second permanent magnet synchronous machine (241) connected in series with the brushless synchronous machine, and a bridge rectifier (243) connected to the brushless synchronous machine, the hybrid excitation generator being intended to be connected to a low-pressure shaft (212) of the turbojet engine and the brushless synchronous machine comprising a generator (3421), an exciter (3422), rotating diodes placed between the generator and the exciter, and a DC-DC converter (244) connected to the exciter; - an energy storage system (250); and - a DC power supply network connected to the AC-DC converter and to the bridge rectifier.

Description

[0001] Description

[0002] Title of the invention: Hybrid excitation generator of a hybrid electric propulsion system

[0003] Technical Field

[0004] The present invention relates to the general field of hybrid aircraft propulsion systems and more particularly to a hybrid excitation generator for the electrical power supply of the propulsion system.

[0005] Prior art

[0006] Climate change is a major concern for many legislative and regulatory bodies around the world. Indeed, various carbon emission restrictions have been, are being, or will be adopted by various states. In particular, an ambitious standard applies to both new aircraft types and those already in operation, requiring the implementation of technological solutions to ensure their compliance with current regulations. Civil aviation has been mobilizing for several years now to contribute to the fight against climate change.

[0007] Technological research efforts have already led to very significant improvements in the environmental performance of aircraft. The Applicant takes into consideration the impact factors in all phases of design and development to obtain less energy-intensive, more environmentally friendly aeronautical components and products whose integration and use in civil aviation have moderate environmental consequences with the aim of improving the energy efficiency of aircraft.

[0008] Consequently, the Applicant is constantly working to reduce its negative climate impact by using methods and operating virtuous development and manufacturing processes that minimize greenhouse gas emissions to the minimum possible in order to reduce the environmental footprint of its activity. This sustained research and development work focuses on new generations of aircraft engines, aircraft weight reduction, and the development of the use of electrical technologies to provide propulsion. Thus, certain turbojets are equipped with a hybrid electric propulsion system comprising at least one bidirectional electrical source connected to the high-pressure shaft and another connected to the low-pressure shaft of the turbojet. This electrical system supplies the loads of the aircraft and / or the propulsion engine.

[0009] As illustrated in Figure 1, the hybrid electric propulsion system 100 conventionally comprises from upstream to downstream in the direction of gas flow, a fan 101, a low pressure compressor BPI 10, a high pressure compressor 120, a combustion chamber 130 which receives fuel 102, a high pressure turbine 121, a low pressure turbine 111 and a primary exhaust nozzle 103. The compressor 110 and the turbine 111 are connected by the low pressure shaft 112 and form a low pressure body. The compressor 120 and the turbine 121 are connected by the high pressure shaft 122 and form, with the combustion chamber 130, a high pressure body. The high pressure generator GHP is driven directly or via a transmission shaft by the high pressure shaft 122. The low pressure generator GBP is driven by the low pressure shaft 112.

[0010] Conventionally, this electric propulsion system is powered by wound rotor synchronous machines which have the advantage of being able to control the output voltage by the excitation circuit as well as the short-circuit current in the event of a fault. To reduce the mass and volume of the system and improve its efficiency and voltage quality, these synchronous machines can be replaced by permanent magnet synchronous machines (151, 152) associated with power converters (161, 162). These converters make it possible to rectify and regulate the voltage to supply a DC power network.This solution is particularly suitable for generators connected to the high pressure shaft 122 whose shaft rotation speed range is not very wide (speed ratio between 1.5 and 2.5), because over a large speed range (ratio greater than 5), there is a risk of instability of the voltage control at high speed when a strong defluxing is used to limit the current, and an increase in the mass of the harnesses and the power converter due to the strong currents at low speed.

[0011] One solution is to use a hybrid excitation generator that allows controlling the short-circuit current without using a controlled converter on the power circuit. But this generator requires bidirectional current excitation, as described in US patent 5,397,975, which requires powering the generator rotor with rotating collectors, which have a limited lifespan, or having a more complex machine with excitation at the stator level, as described in the article "Hybrid Excitation Synchronous Alternator Connected to a Diode Rectifier with a Resistive Load" by Y. Amara, AH Ben Ahmed, E. Hoang, L. Vido, M. Gabsi and M. Lécrivain published in EPE Journal 04 / 2006.

[0012] It is therefore desirable to have an electric propulsion system with reduced mass and volume that can support a wide speed range.

[0013] Statement of the invention

[0014] The invention relates to a hybrid electric propulsion system for a turbojet engine comprising:

[0015] - a first permanent magnet synchronous machine connected to a direct voltage to alternating voltage converter, intended to be connected to a high pressure shaft of the turbojet, and configured to operate in motor mode or in generator mode;

[0016] - a hybrid excitation generator comprising a brushless synchronous machine, a second permanent magnet synchronous machine connected in series to the brushless synchronous machine, and a rectifier bridge connected to the brushless synchronous machine, the hybrid excitation generator being intended to be connected to a low pressure shaft of the turbojet engine and the brushless synchronous machine comprising a generator, an exciter, rotating diodes placed between the generator and the exciter and a DC voltage to DC voltage converter connected to the exciter,

[0017] - an energy storage system; and

[0018] - a continuous power supply network connected to the direct voltage to alternating voltage converter and to the rectifier bridge.

[0019] Thus, thanks to the invention, the different operating modes make it possible to optimize the sizing and mass of the hybrid excitation generator system:

[0020] - at high speed and high power, the brushless synchronous machine can compensate for the reactive energy of the second permanent magnet machine;

[0021] - at low speed and high power, the brushless synchronous machine operates in “boost” mode; and

[0022] - at high speed and low power, the brushless synchronous machine operates in “brake” mode.

[0023] The operation of the constant current and voltage hybrid excitation generator is also independent of the speed of the low pressure shaft.

[0024] Furthermore, the fact that the synchronous machine is brushless means that the stator does not need to be complicated, as is usually the case in three-stage machines traditionally used as generators. Furthermore, being brushless, the synchronous machine in the hybrid excitation generator has an extended service life, as there is no longer any need to regularly change the brushes. Since there is no rotating contact, the excitation current is unidirectional.

[0025] Thus, the voltage of the DC power supply network can be controlled at constant power over a wide speed range with a unidirectional excitation current by current and voltage loops, unlike the prior art where this is controlled by the speed measurement. In addition, thanks to the hybrid excitation generator, the short-circuit current of the DC power supply network can be controlled in order to ensure conventional protection by load selectivity. Thus, the hybrid excitation generator is protected against the risks of overheating thanks to the limitation of the short-circuit current.

[0026] Voltage control is compatible with conventional control electronics such as the “Generator Control Unit” or GCU. It limits the short-circuit current in the event of an internal fault and controls the network short-circuit current to ensure selectivity of the protections.

[0027] According to a particular characteristic of the invention, the energy storage system comprises a DC voltage to DC voltage converter and a battery, the battery being connected to the DC voltage to DC voltage converter which is connected to the DC power supply network.

[0028] According to one embodiment of the invention, the DC voltage to DC voltage converter of the hybrid excitation generator of the brushless synchronous machine is connected to a DC voltage generator.

[0029] This generator provides the excitation current to the exciter of the brushless synchronous machine when the turbojet engine is started.

[0030] According to another embodiment of the invention, the DC voltage to DC voltage converter of the hybrid excitation generator of the brushless synchronous machine is connected to an output of the rectifier bridge and to the DC power supply network.

[0031] This allows for autonomous excitation of the brushless synchronous machine and eliminates the need for a direct voltage generator (or the permanent magnet generator conventionally connected to aircraft generators) to power the exciter of the brushless synchronous machine when starting the turbojet.

[0032] Another subject of the invention relates to an aircraft comprising at least one turbojet engine equipped with a hybrid electric propulsion system according to the invention, the hybrid electric propulsion system supplying loads of the aircraft. Yet another subject of the invention is a method for controlling a hybrid electric propulsion system according to the invention comprising:

[0033] - compensation of reactive energy from the second permanent magnet synchronous machine by the high-speed, high-power brushless synchronous machine;

[0034] - operation in “boost” mode of the brushless synchronous machine at low speed and high power; and

[0035] - operation in "brake" mode of the brushless synchronous machine at high speed and low power; the hybrid excitation generator operating at constant current and voltage independently of a low pressure shaft speed

[0036] Brief description of the drawings

[0037] Other characteristics and advantages of the present invention will emerge from the description given below, with reference to the appended drawings which illustrate exemplary embodiments thereof which are not limiting in nature.

[0038] [Fig. 1] Figure 1 represents, schematically and partially, a hybrid electric propulsion system according to the prior art.

[0039] [Fig. 2] Figure 2 represents, schematically and partially, a hybrid electric propulsion system according to one embodiment of the invention.

[0040] [Fig. 3] Figure 3 shows, schematically and partially, the brushless synchronous machine included in the hybrid electric propulsion system of the invention.

[0041] [Fig. 4] Figure 4 represents, schematically and partially, a hybrid electric propulsion system according to another embodiment of the invention.

[0042] Description of the embodiments Figure 2 shows, schematically and partially, a hybrid electric propulsion system 200 of a turbojet according to a first embodiment of the invention. This system 200 makes it possible to supply electrical power to loads 270. The loads 270 represent loads of an aircraft, such as the engine loads and the aircraft loads. The engine loads can be pumps for fuel and / or oil, de-icing and / or the various actuators. The aircraft loads can be loads of all the electrical systems, such as those of the flight controls and / or the landing gear controls and / or the pumps and / or the air conditioning and / or the wing de-icing and / or the taxiing and / or the cabin electrical network and / or the converter for the low voltage network, etc.

[0043] The system 200 comprises a first permanent magnet synchronous machine 230 connected to a direct voltage to alternating voltage converter 231. This first permanent magnet synchronous machine 230 is intended to be connected to the high pressure shaft 222 of the turbojet.

[0044] The system 200 also comprises a hybrid excitation generator 240 intended to be connected to the low pressure shaft 212 of the turbojet engine. This generator 240 comprises a rectifier bridge 243 connected to a brushless synchronous machine 242 shown in more detail in FIG. 3. The brushless synchronous machine 242 is itself connected in series to a second permanent magnet synchronous machine 241.

[0045] The brushless synchronous machine 242 comprises a generator 3421, an exciter 3422 and rotating diodes 3423 connected between the generator 3421 and the exciter 3422. This machine 242 does not include any rotating contacts, which extends the service life of the machine 242 because it is no longer necessary to regularly change the brushes. The excitation current coming from a direct current source via the DC voltage to DC voltage converter 244 is supplied to the exciter 3422, and more particularly to its stator. The rotor of the exciter 3422 is induced with an alternating voltage, the signal of which is rectified by the rotating diodes 3423. This makes it possible to supply the rotor of the generator 3421 with direct current which will thus generate a rotating magnetic field in the stator of the generator 3421. The stator of the generator 3421 thus generates a three-phase current which will be rectified by the rectifier bridge 243.

[0046] In order to supply the exciter 3422 with direct current, a direct voltage to direct voltage converter 244 is connected to the exciter 3422.

[0047] In this first embodiment, the DC voltage to DC voltage converter 244 which supplies the excitation current to the exciter 3422 is connected to a DC voltage generator 245. This DC voltage generator 245 can be replaced by a permanent magnet generator connected to the low pressure shaft.

[0048] Finally, the system 200 may comprise an energy storage system 250 which may be a battery connected to a DC voltage to DC voltage converter, itself connected to the DC power supply network. In the case of high speed, this energy storage system 250 makes it possible to consume the minimum energy necessary for voltage control if the power consumed by the loads 270 of the turbojet engine is insufficient.

[0049] Figure 4 represents, schematically and partially, a hybrid electric propulsion system 400 of a turbojet according to a second embodiment of the invention.

[0050] The system 400 comprises a first permanent magnet synchronous machine 430 connected to a direct voltage to alternating voltage converter 431. This first permanent magnet synchronous machine 430 is intended to be connected to the high pressure shaft 422 of the turbojet.

[0051] The system 400 also comprises a hybrid excitation generator 440 intended to be connected to the low pressure shaft 412 of the turbojet engine. This generator 440 comprises a rectifier bridge 443 connected to a brushless synchronous machine 442, the operation of which has been described previously with reference to FIGS. 2 and 3. The brushless synchronous machine 442 is itself connected in series to a second permanent magnet synchronous machine 441.

[0052] In this second embodiment, the DC voltage to DC voltage converter 444 which supplies the excitation current to the exciter 3422 is connected to the output of the rectifier bridge 443 and to the DC power supply network. Thus the converter 444 is powered directly by the output of the rectifier bridge 443, this allows for completely autonomous control of the generator 4421, and to do without the permanent magnet generator which is conventionally connected to the same motor shaft, i.e. to the low pressure shaft 412, to start the generator 4421 when the engine starts. Thus, at start-up, as soon as the low pressure shaft 412 starts to rotate, the permanent magnet machine 441 generates sufficient voltage to power the converter 444 to control the DC voltage and the excitation current of the exciter 4422.

[0053] As previously, the hybrid electric propulsion system 400 may comprise an energy storage system 450 which may be a battery connected to a DC voltage to DC voltage converter itself connected to the DC electrical power supply network. In the case of high speed, this energy storage system 450 makes it possible to consume the minimum energy necessary for voltage control if the power consumed by the loads 470 of the turbojet engine is insufficient, and if it is not possible to adjust the control of the voltage of the DC electrical power supply network by the DC voltage to AC voltage converter 431, for example in the case of a torque or power limitation imposed by the turbomachine.

[0054] In both embodiments described, the voltage control of the hybrid excitation generator can be achieved from current and voltage regulation loops as is already the case for three-stage generators. For example, a first PI (Proportional Integral) corrector generates a DC current setpoint from a measurement error of the DC voltage at the output of the rectifier bridge. This setpoint is limited by the network short-circuit current setpoint. This setpoint is in turn compared to the measurement of the network current, passes through a corrector, for example of the PI type, to generate the excitation current setpoint which is naturally limited to 0 by the rotating diodes.

[0055] In addition, the hybrid excitation generator can be designed to prioritize certain factors to optimize its sizing according to the application. We can use: - the hybridization ratio which compares the flux of the permanent magnet machine to the total flux of the hybrid excitation generator; or

[0056] - the power ratio between the permanent magnet machine and the brushless synchronous machine as a function of the hybridization ratio and thus optimize the mass or efficiency of the generator; or

[0057] - the short-circuit current with zero excitation by the no-load electromotive force of the permanent magnet machine and by the inductance of the brushless synchronous machine; or

[0058] - the operating curve at minimum power depending on the application.

[0059] Regardless of the embodiment, the brushless synchronous machine and the second permanent magnet synchronous machine of the hybrid excitation generator are integrated together in the rotor and share the same stator. In other words, they are placed in series on the rotor of the hybrid excitation generator and they share the same stator which forms the stator of the hybrid excitation generator.

[0060] The invention also relates to an aircraft comprising a hybrid electric propulsion system as described above. This hybrid electric propulsion system makes it possible to provide electrical power to the loads of the aircraft by controlling the voltage of the direct current electrical network.

Claims

Claims

1. Method for controlling a hybrid electric propulsion system (200, 400) of a turbojet comprising: - a first permanent magnet synchronous machine (230, 430) connected to a direct voltage to alternating voltage converter (231, 431), intended to be connected to a high pressure shaft (222, 422) of the turbojet, and configured to operate in motor mode or in generator mode; - a hybrid excitation generator (240, 440) comprising a brushless synchronous machine (242, 442), a second permanent magnet synchronous machine (241, 441) connected in series to the brushless synchronous machine (242, 442), and a rectifier bridge (243, 443) connected to the brushless synchronous machine (242, 442), the hybrid excitation generator being intended to be connected to a low pressure shaft (212, 412) of the turbojet engine and the brushless synchronous machine (242, 442) comprising a generator (3421), an exciter (3422), rotating diodes (3423) placed between the generator and the exciter and a DC voltage to DC voltage converter (244, 444) connected to the exciter; - an energy storage system (250); and - a direct current power supply network connected to the first direct current to alternating current converter (231, 431) and to the rectifier bridge (243, 443); the method comprising: - compensation of reactive energy from the second permanent magnet synchronous machine by the high-speed, high-power brushless synchronous machine; - operation in “boost” mode of the brushless synchronous machine at low speed and high power; and - the operation in "brake" mode of the brushless synchronous machine at high speed and low power; the hybrid excitation generator operating at constant current and voltage independently of a speed of the low pressure shaft.

2. A control method according to claim 1, wherein the energy storage system comprises a DC voltage to DC voltage converter and a battery, the battery being connected to the DC voltage to DC voltage converter which is connected to the DC power supply network.

3. A control method according to any one of claims 1 or 2, wherein the DC voltage to DC voltage converter (244) of the hybrid excitation generator (240) of the brushless synchronous machine (242) is connected to a DC voltage generator (245).

4. A control method according to any one of claims 1 or 2, wherein the DC to DC voltage converter (444) of the hybrid excitation generator (440) of the brushless synchronous machine (442) is connected to an output of the rectifier bridge (443) and to the DC power supply network.

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