Hybrid propulsion system for a multi-engine aircraft

CA 02964672 2017-04-13 WO 2016/062945 1 PCT/FR2015/052770 Hybrid propulsion system of a multi-engine aircraft Technical field The invention falls within the field of free-turbine turbomachines, such as are commonly found on the helicopters.

For the record, a free-turbine turbomachine (sometimes referred to by the acronym TAG as an acronym for gas turbine) comprises a power turbine or free turbine which, in a helicopter, drives the helicopter's rotors via a free wheel and a main transmission box (also designated by the acronym BTP), and also a gas generator consisting mainly of a compressor, a combustion chamber and a high pressure turbine.

A mechanical reduction gear or accessory box is used to connect the shaft of the gas generator to an electrical machine (abbreviated as MEL) consisting of a stator and a rotor, which can operate either as a motor (starter) or as a generator.

In motor mode, the electric machine is powered by a source of electrical energy and develops a motor torque so as to drive the gas generator of the turbomachine in rotation, in particular for the purpose of ensuring its start-up and the mode of standby, thereby performing assistance to the gas generator.

In generator mode, the electrical machine is driven in rotation by the gas generator so as to draw mechanical power from the latter, which is then converted into electrical power to supply a low-voltage DC on-board network of the aircraft in flight ( still referred to by the acronym RDB).

The RDB is generally connected to a low voltage electricity storage device, for example a 28 volt storage battery.

The invention relates more particularly to a hybrid propulsion system of a multi-engine aircraft, in particular twin-engine or tri-engine, that is to say a system comprising at least one turbomachine that can be set to CA 02964672 2017-04- 13 WO 2016/062945 2 PCT/FR2015/052770 standby during a flight phase referred to as the economic flight phase, while one or more other turbomachines are kept active.

STATE OF THE ART When an aircraft equipped with two turbomachines is in a cruising flight situation, it has been proposed in documents FR2967132 and FR2967133 to put one of the two turbomachines in a standby mode so as to desynchronize its free turbine from the gearbox. transmission while increasing the speed of the other turbomachine, which makes it possible to reduce the overall fuel consumption of the system.

The invention thus lies in particular in the context of a reduction in the consumption of an at least twin-engine helicopter, in which, in economical cruising flight, that is to say in a flight phase characterized by a power demand each engine is quite weak resulting in a very high specific consumption (abbreviated as CS), one of the turbines is put on standby so that the other engine operates at high speed and therefore benefits from a much lower specific consumption.

Several variants of this standby regime have been proposed.

In a standby regime, called customary idle, the combustion chamber is ignited and the gas generator shaft rotates at a speed between 60 and 80% of the rated speed.

In a first variant, called super idle, the gas generator of the desynchronized gas turbine can be regulated at a low idle speed, where the shaft of the gas generator rotates at a speed between 20 and 60% of the speed nominal.

In a second variant, called assisted super idle, the MGB's desynchronized gas turbine gas generator can also be regulated to a low idle speed, and simultaneously an assist motor torque is applied to the gas generator by the between the electric machine and the accessory box.

CA 02964672 2017-04-13 WO 2016/062945 3 PCT / FR2015/052770 In a third variant, the combustion chamber of the turbomachine can be completely switched off, and it is then proposed to keep the gas generator rotating at a speed to facilitate relighting at the end of the cruise flight phase.

The range of suitable speeds can be qualified as a preferential ignition window.

This mode of operation, called turning mode, is an extended assistance of the gas generator. The shaft of the gas generator rotates, mechanically assisted, at a speed between 5 and 20% of the nominal speed.

In these operating modes, which are likely to be maintained throughout the cruise flight, the power transmitted to the MGB by the turbomachine on standby is generally zero, and it is generally not possible to take power on his gas generator.

In the variants which have just been mentioned, it is necessary to be able to quickly reactivate the desynchronized turbomachine, in particular in an emergency situation, for example in the event of failure of another turbomachine, if there are three turbomachines or more in total, ¨ or of the other turbomachine if there are two turbomachines. This is in particular the reason for maintaining the gas generator rotating at a speed facilitating re-ignition in the system where the combustion chamber is extinguished.

Maintaining the gas generator rotating in the preferential ignition window (steering mode) and prolonged assistance to the gas generator regulated at idle (assisted super idle mode) require relatively low power, the interest of the system residing in its use for a long duration of flight.

It has been proposed in documents FR2967132 and FR2967133, among other solutions, to use an electric starter powered by a starter/generator connected to the gas generator of the other turbomachine, or a generator driven directly or indirectly by the free turbine of the other turbomachine.

CA 02964672 2017-04-13 WO 2016/062945 4 PCT / FR2015/052770 As for the emergency restart from a situation of low speed or combustion chamber off, it requires applying to the shaft of the generator gas a high power due to the high inertia of the rotating assemblies and the resistant torque of the turbomachine compressor.

This power must be delivered for a short period, of the order of a few seconds, in order to guarantee rapid start-up of the turbomachine.

It has been suggested in the document FR2967133 to use, among other solutions, a source of electrical energy, in particular a supercapacitor, in order to power an electric machine which provides occasional assistance to the gas generator.

In document EP2581586, it has also been proposed to use two supercapacitors (which are electric storage devices), which are each charged respectively by an electric generator driven by the gas generator of one of the two turbomachines, and which serve each, punctually, to start the other turbomachine from an off state of the latter.

The object of the present invention is in particular, in this context, to provide a practical technical means of carrying out, on an aircraft which is at least twin-engine, the function of rapid reactivation from an economical mode of the turbine, by using instead of the conventional electric starter an electro-technical system powered by the on-board network or by a specific electrical power supply network and ensuring different operating modes which are:

- The ground start of the gas turbine, - The economy mode, where a turbomachine is put in standby mode, which is an energy saving mode and which does not deliver mechanical power to the rotor of the aircraft, - The normal in-flight reactivation of the turbine, which was previously in economy mode, which constitutes a reliable start-up from standby mode, without significant time constraints, and CA 02964672 2017-04-13 WO 2016/062945 5 PCT/FR2015/052770 - The rapid in-flight reactivation of the turbine, which was previously in economy mode, which constitutes an emergency start allowing, over a minimum time, the powering up of the turbomachine from standby mode, that is to say its rapid exit from standby mode to reach a speed, called nominal speed, in which the turbomachine supplies mechanical power to the power transmission box .

An emergency standby output regime is one in which the combustion chamber is ignited and the gas generator shaft is driven to a speed of between 80 and 105%, within a period of less than 10s after a command from wake up.

A normal standby exit regime is a regime in which the combustion chamber is ignited and the shaft of the gas generator is driven towards a speed of between 80 and 105%, within a period of between 10 s and 1 min after a wake-up command.

A turbomachine capable of operating in a standby mode is referred to as a hybrid turbomachine.

The hybridization of propulsion systems makes it possible to increase their efficiency.

On the other hand, the mass of current electrotechnical components makes them difficult to use for on-board applications on aircraft.

It is therefore necessary to design and develop an architecture dimensioned as accurately as possible to propose a propulsion system capable of flying in economical cruise, where the power necessary for flight is delivered by a minimum of turbomachines, the others being put in standby mode, while allowing a turbomachine to effectively exit its sleep mode, by a normal reactivation or a rapid reactivation.

CA 02964672 2017-04-13 WO 2016/062945 6 PCT / FR2015/052770 It is also necessary, for questions of reliability, to be able to carry out regular tests of the reactivation system and to meet all the operating safety requirements and certification of propulsion systems.

The architectures of hybrid aircraft propulsion systems proposed so far are complex and involve significant on-board masses, or do not allow testing of equipment ensuring rapid reactivation or do not meet the necessary reliability and availability requirements. Disclosure of the Invention In order to remedy the aforementioned drawbacks, in accordance with the invention, there is proposed a hybrid propulsion system for a multi-engine aircraft, comprising a plurality of free-turbine turbomachines each equipped with a gas generator, among which at least a first turbomachine, referred to as a hybrid turbomachine, is capable of operating in at least one standby regime during stabilized flight of the aircraft, while other turbomachines of said plurality of turbomachines operate alone during this stabilized flight, the hybrid turbomachine being associated with at least a first electrotechnical chain comprising a first electric machine able to operate as a starter and as a generator, itself connected to a first power electronics module, itself selectively connected to a specific network of electrical energy supply, such as an on-board network, and to at least one first electrical energy storage device, said hybrid turbomachine being further associated with a second electrotechnical chain identical to said first electrotechnical chain and comprising a second electric machine able to operate as a starter and as a generator, itself connected to a second power electronics module, itself selectively connected to said specific electrical energy supply network and to at least one second CA 02964672 2017-04-13 WO 2016/062945 7 PCT/FR2015/052770 electrical energy storage device, characterized in that each of the first and second electrotechnical chains is adapted to deliver a maximum power at least equal to half of the total power (Prr) necessary for a rapid reactivation of the said hybrid turbomachine and in that each of the first and second chains electrical engineering is adapted so as to be able to selectively deliver to the hybrid turbomachine either a starting power or a normal reactivation power (Pdem), either standby power (Pv), or half standby power (Pv/2), or half rapid reactivation power (Prr/2).

Preferably, the starting power or normal reactivation power is of the order of 20% of the total rapid reactivation power (Prr).

Preferably, the standby power is of the order of 3 to 5010 of the total rapid reactivation power (Prr).

According to one aspect of the invention, each of the first and second power electronics modules is adapted so as to be able to receive power respectively from the first or from the second electrical energy storage device to supply power respectively in an isolated manner and in alternation with the other of said first and second power electronics modules, each of the first and second electric machines with normal starting power or reactivation power (Pdem).

According to another aspect of the invention, each of the first and second power electronics modules is adapted so as to be able to receive power respectively from the first or from the second electrical energy storage device to supply power respectively and simultaneously with the the other of said first and second power electronics modules, each of the first and second electrical machines with a rapid reactivation half power (Prr/2).

CA 02964672 2017-04-13 WO 2016/062945 8 PCT / FR2015/052770 According to yet another aspect of the invention, each of the first and second power electronics modules is adapted so as to be able to receive power from said network specific electric power supply for supplying respectively, and simultaneously with the other of said first and second power electronics modules, the first and the second electric machine, either with half start-up power or half normal reactivation power (Pdem/2), or with half standby power (Pv/2).

As a variant, each of the first and second power electronics modules is adapted so as to be able to receive power respectively from the first or from the second electrical energy storage device to supply power respectively, and simultaneously with the other of said first and second power electronics modules, the first and the second electrical machine, either with half start-up power or half normal reactivation power (Pdem/2), or with half standby power (Pv/2).

According to yet another aspect of the invention, each of the first and second power electronics modules is adapted so as to be able to receive power from said specific electrical power supply network to supply power respectively in isolation and alternately with the other of said first and second power electronics modules, the first and the second electric machine, either with normal starting power or reactivation power (Pdem), or with standby power (Pv).

According to yet another aspect of the invention, each of the first and second power electronics modules is adapted so as to be able to receive power from said specific electrical energy supply network or respectively from the first or from the second electrical energy storage device to supply power respectively in an isolated manner and in CA 02964672 2017-04-13 WO 2016/062945 9 PCT/FR2015/052770 alternation with the other of said first and second power electronics modules, or simultaneously the first and the second electric machine, with a variable power (Pvar), less than or equal to half of the total power (Prr) necessary for rapid reactivation of said hybrid turbomachine, in order to be able to perform power periodically.

According to a particular embodiment, the first and second electrical energy storage devices comprise two physically separate storage devices.

According to another possible embodiment, the first and second electrical energy storage devices comprise two separate but physically grouped storage devices.

The invention also relates to a multi-engine aircraft, comprising a hybrid propulsion system as mentioned above.

The aircraft may be a helicopter.

Brief description of the figures Other characteristics and advantages of the invention will emerge from the detailed description of particular embodiments of the invention, with reference to the appended drawings, in which:

- Figure 1 shows a diagram of a hybrid architecture of a propulsion system for a turbomachine with two electrotechnical control chains according to a first embodiment of the invention, - Figure 2 shows a diagram of a hybrid architecture of a propulsion system for a turbomachine with two electrotechnical control chains according to a second embodiment of the invention, CA 02964672 2017-04-13 WO 2016/062945 10 PCT/FR2015/052770 - Figure 3 presents a diagram showing the operation of the hybridized architecture of Figure 1 in standby mode with a single active electrotechnical control chain, - FIG. 4 presents a diagram showing the operation of the hybridized architecture of FIG. 1 in standby mode with two active electrotechnical control chains, - Figure 5 presents a diagram showing the operation of the hybridized architecture of Figure 1 in normal start-up or reactivation mode with a single active electrotechnical control chain powered by an on-board network, - Figure 6 presents a diagram showing the operation of the hybridized architecture of Figure 1 in normal start-up or reactivation mode with a single active electrotechnical control chain powered by an electrical energy storage device, - Figure 7 presents a diagram showing the operation of the hybridized architecture of figure 1 in start-up or normal reactivation mode with two active electrotechnical control chains powered by the on-board network, - Figure 8 presents a diagram showing the operation of the hybridized architecture of FIG. 1 in rapid reactivation mode with two active electrotechnical control chains powered by electrical energy storage devices, and - Figure 9 presents a diagram showing the operation of the hybridized architecture of Figure 1 in variable power test driving mode with two active electrotechnical control chains powered by the on-board network and by storage devices electric energy.

Detailed description CA 02964672 2017-04-13 WO 2016/062945 11 PCT / FR2015/052770 The hybrid propulsion system of a multi-engine aircraft according to the invention comprises a plurality of free turbine turbomachines each equipped with a gas generator , among which at least one first turbomachine, or hybrid turbomachine, is able to operate in at least one standby mode during stabilized flight of the aircraft, while other turbomachines of the plurality of turbomachines operate alone during this stabilized flight.

In FIGS. 1 to 9, this single hybrid turbomachine 1 and the electrotechnical control chains of this hybrid turbomachine have been represented, the other turbomachines used possibly being conventional.

However, it is also possible, on the same aircraft, to implement several hybrid turbomachines similar to the hybrid turbomachine 1 described with reference to the appended drawings. The invention can thus be applied to all of the turbomachines of a multi-engine architecture of an aircraft.

If we refer to FIG. 1, we see that the hybrid turbomachine 1 is associated with first and second identical electrotechnical chains each comprising an electric machine 2 respectively 3 able to operate as a starter and as a generator, itself connected to a power electronics module 4 respectively 5, itself selectively connected to a specific electrical power supply network 8, such as an on-board network, and to at least one electrical energy storage device 6 respectively 7.

Each of the electrotechnical chains is adapted to deliver a maximum power at least equal to half of the total power Prr necessary for rapid reactivation of the hybrid turbomachine 1.

In FIG. 1, first and second electrical energy storage devices 6, 7 have been shown which comprise two storage devices which are physically separated and each make it possible to deliver at least half of the total power and energy. necessary for a rapid reactivation of the CA 02964672 2017-04-13 WO 2016/062945 12 PCT/FR2015/052770 turbomachine 1, or which each make it possible to supply the power necessary for a normal reactivation of the turbomachine 1.

However, as shown in Figure 2, the first and second electrical energy storage devices may comprise two separate storage devices 66, 67 and isolated from each other, but physically grouped together in a single physical entity 60 and each constituting half of this entity.

The storage members 6, 7 or 66, 67, even more simply called storage devices, can be electrochemical or electrostatic in nature.

Each of the first and second electrotechnical chains is adapted so as to be able to deliver to the hybrid turbomachine 1 selectively, either a start-up power or a normal reactivation power Pdem, or a standby power Pv, or a half-standby power Pv/2, i.e. a half power of rapid reactivation Prr/2.

The starting power or normal reactivation power is generally of the order of 20% of the total rapid reactivation power Prr.

Standby power is usually in the order of 3-5% of the total fast wake-up power Prr.

Each dedicated power electronics module 4, 5 is capable in a limited time of supplying the corresponding electrical machine 2, 3 with at least half the power required for rapid reactivation, that is to say Prr/ 2, or the power required for normal reactivation Pdem (which also corresponds to a starting power).

Each dedicated power electronics module 4; 5 is itself supplied with energy either by the corresponding storage device 6, 66; 7, 67, either by the on-board network 8 of the aircraft, or by both at the same time.

It should be noted that the power available from the on-board network 8 is a priori limited since this CA 02964672 2017-04-13 WO 2016/062945 13 PCT/FR2015/052770 on-board network 8 must also provide the electrical power necessary to all embedded systems.

Each dedicated power electronics module 4, 5 is also capable of continuously supplying the corresponding electric machine 2, 3 for its use in the standby mode of the turbomachine 1 and is also suitable for controlling the corresponding electric machine 2, 3 for the reliable start-up or normal reactivation procedure.

Each of the electric machines 2, 3 is adapted to deliver at least half the power necessary for rapid reactivation and the power necessary for normal reactivation.

Furthermore, each electric machine 2, 3 which drives the gas generator of a hybridized turbomachine 1, is capable of continuously maintaining the latter in standby mode, of starting the turbomachine 1 and of carrying out normal reactivation.

The turbomachine 1 is equipped with a box of accessories making it possible to accommodate the two electric machines 2, 3, in addition to the standard equipment necessary for the correct operation of the turbomachine 1.

A description will now be given with reference to FIGS. 3 to 9 of different modes of operation of the architecture according to the invention.

In these figures, the non-active elements of the architecture are represented in dotted lines, while the active elements of the architecture are represented in the normal way in continuous lines.

Figures 3 and 4 show how the standby mode of the turbomachine 1 can be achieved by the two electrotechnical chains according to two different embodiments, where the energy is in all cases taken from the on-board network 8.

As illustrated in FIG. 3, the power Pv necessary for the standby mode, which represents about 3 to 5/o of the total power Prr available, can be delivered alternately between the two electrotechnical chains and the missions.

CA 02964672 2017-04-13 WO 2016/062945 14 PCT / FR2015/052770 In FIG. 3, the electrotechnical chain is represented as active comprising the first electrical machine 2 and the first power electronics module 4 supplied by the network edge 8, while the second electric machine 3, the second power electronics module 5, and the storage devices 6 and 7 are not used.

In a following mission of the aircraft, the roles would be reversed and it would be the second electric machine 3 and the second power electronics module 5 supplied by the on-board network 8 which would be active, while the first electric machine 2, the first power electronics module 4, and the storage devices 6 and 7 would not be called upon.

FIG. 4 shows an embodiment in which, in standby mode of the turbomachine 1, the two electrotechnical chains are simultaneously active, but each only delivers a power Pv/2 equal to half the power Pv necessary for the mode standby, that is to say of the order of 1 to 3% of the total power Prr.

The first and second electric machines 2, 3 and the first and second power electronics modules 4, 5 are thus simultaneously active from the on-board network 8, while the storage devices 6, 7 are not called upon.

FIGS. 5 to 7 show how the normal start-up or reactivation mode of the turbomachine 1 can be achieved by the two electrotechnical chains according to three different embodiments.

In the first embodiment illustrated in FIG. 5, the energy corresponding to a normal mechanical or reactivation power Pdem, which is typically of the order of 20% of the total power Prr necessary for rapid reactivation, is taken from the on-board network 8 and a single electrotechnical chain is used.

In FIG. 5, the electrotechnical chain comprising the first electrical machine 2 and the first power electronics module 4 supplied by the on-board network 8 has been represented as active, while the second electrical machine 3, the second module of power electronics 5, and the storage devices 6 and 7 are not used.

In a following mission of the aircraft, the roles would be reversed and it would be the second electric machine 3 and the second power electronics module 5 powered by the on-board network 8 which would be active, while the first electric machine 2, the first power electronics module 4, and the storage devices 6 and 7 would not be called upon.

The embodiment of FIG. 6 is similar to that of FIG. 5, insofar as a single electrotechnical chain is used, but the energy corresponding to a mechanical or normal reactivation power Pdem, which is typically of the order of 20% of the total power Prr necessary for rapid reactivation, is taken not from the on-board network 8, but from a storage device.

In FIG. 6, the electrotechnical chain comprising the first electrical machine 2 and the first power electronics module 4 supplied by the storage device 6 has been represented as active, while the second electrical machine 3, the second electronics module of power 5, the storer 7 and the on-board network 8 are not called upon for this operation.

In a following mission of the aircraft, the roles would be reversed and it would be the second electric machine 3 and the second power electronics module 5 powered by the storage device 7 which would be active, while the first electric machine 2, the first power electronics module 4, the storer 6 and the on-board network 8 would not be called upon.

Naturally, when the embodiment of FIG. 2 is implemented, storer 66 and storer 67 play the role of storers 6 and 7 respectively.

FIG. 7 shows an embodiment in which, in start-up or normal reactivation mode of the turbomachine 1, the two electrotechnical chains are simultaneously active, but each only delivers a power Pdem/2 equal to half the power Pdem necessary for standby mode, that is to say typically of the order of 20% of the total power Prr.

The first and second electrical machines 2, 3 and the first and second power electronics modules 4, 5 are thus simultaneously active.

CA 02964672 2017-04-13 WO 2016/062945 16 PCT / FR2015/052770 In FIG. 7, links are shown showing that the energy is taken by the first and second power electronics modules 4, 5 from of the on-board network 8, while the storage devices 6, 7 are not used.

However, as a variant, in the case of the embodiment of FIG. 7, where the two electrotechnical chains are simultaneously active, the first and second power electronics modules 4, 5 could take the energy corresponding to Pdem/ 2 respectively from the storage devices 6 and 7 (or 66 and 67 if the embodiment of FIG. 2 is used) and not from the on-board network 8.

FIG. 8 shows an embodiment in which, in rapid reactivation mode of the turbomachine 1, the two electrotechnical chains are simultaneously active, in simultaneous and coordinated operation, but each only delivers a power Prr/2 equal to the half of the total power Prr required for fast reactivation mode.

The first and second electrical machines 2, 3 and the first and second power electronics modules 4, 5 are thus simultaneously active.

In the case of the embodiment of FIG. 8, the energy is taken by the first and second power electronics modules 4, 5 in the first place from the storage devices 6 and 7 (or 66 and 67 in the case of the mode embodiment of FIG. 2), in equal parts with a power of the order of Prr/2.

However, additional power can, if necessary, be taken, by the first and second power electronics modules 4, 5, from the on-board network 8.

FIG. 9 illustrates a configuration of the architecture of FIG. 1, in which a test is carried out by applying a variable power Pvar, where Pvar can vary between an almost zero power and a power equal to half of the total power Prr , for each complete electrotechnical chain in order to guarantee the proper functioning and performance of the system.

This test is preferably done each time the propulsion system of the aircraft is started on the ground, but can also be done in flight if necessary.

CA 02964672 2017-04-13 wo 2016/062945 17 PCT/FR2015/052770 The energy required for the proper functioning tests can be provided as the case may be by the on-board network 8, or by the energy storage devices 6, 7 or 66, 67.

The tests can be carried out alternately or simultaneously with the two electrotechnical chains.

In FIG. 9, the case has been symbolized by way of example where all the branches of all the electrotechnical chains are the subject of simultaneous tests with a variable power Pvar which is thus delivered by the storage devices 6, 7 and by the network edge 8 to each of the power electronics modules 4, 5.

The present invention provides various advantages over existing solutions and allows in particular:

- A one-time reactivation test every two missions for each electrotechnical chain thanks to the start-up procedure before each mission by alternating the use of the electrotechnical chains;

- A permanent test of the operation of the electrotechnical chain thanks to the standby mode which uses the electrotechnical chain(s) and which makes the electrical machines run permanently when using the economy mode;

- A segregation of the electrotechnical chains is ensured in particular for the energy storage part by the implementation of two identical storers 6, 7 physically dissociated and adapted to each store half of the maximum energy required (Prr/2) or by the implementation of a single storer 60 grouping two identical storers 66, 67 adapted to each store half of the maximum energy required (Prr/2), these two identical storers 66, 67 being in the same physical unit with isolation between them;

- A redundancy of the normal reactivation mode thanks to the two independent electrotechnical chains;

- Redundancy of power sources insofar as normal reactivation can be obtained either from a 6.7 or CA 02964672 2017-04-13 wo 2016/062945 18 PCT/FR2015/052770 66, 67 storer or from the on-board network 8, depending on the availability of these sources;

- A minimized and optimized dimensioning of the two electrotechnical chains which makes it possible to add the powers of the two electrotechnical chains to obtain the power necessary for rapid reactivation (see figure 8).

In general, the invention is not limited to the embodiments presented, but extends to all variants within the scope of the appended claims.