FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
& The Patent Rules, 2003
COMPLETE SPECIFICATION
1.TITLE OF THE INVENTION:
HYBRID PROPULSION SYSTEM FOR MULTI-ROTOR ROTARY WING AIRCRAFT,
COMPRISING IMPROVED DC/AC CONVERSION MEANS
2. APPLICANT:
Name: SAFRAN HELICOPTER ENGINES
Nationality: France
Address: 64510 BORDES, France.
3. PREAMBLE TO THE DESCRIPTION:
The following specification particularly describes the invention and the manner in which it
is to be performed:
2
DESCRIPTION
Technical field
The present invention relates to a hybrid propulsion system for multi-rotor
rotary wing aircrafts, as well as a method for manufacturing such a hybrid propulsion
system.
State of prior art
5 From the state of the art, it is known a hybrid propulsion system for a multirotor rotary wing aircraft comprising:
- an internal combustion engine, and an electric generator coupled to the
internal combustion engine such that in use, the internal combustion engine drives the
electric generator,
10 - a rectifier connected to the electric generator to convert an alternating
current delivered by the electric generator into a direct current, means for converting
the direct current into alternating current, and an electric network connecting the
rectifier to the conversion means,
- electric motors connected to the conversion means such that in use, the
15 conversion means supply the first electric motors with alternating current, and
- propellers coupled to the electric motors such that in use, the electric motors
drive the propellers.
In particular, the conversion means comprise inverters respectively connected
to the electric motors so as to supply the latter with alternating current.
20 However, these propulsion systems have the drawback to be relatively heavy.
Disclosure of the invention
In particular, the invention has the purpose to provide a simple, economic and
efficient solution to this problem.
3
To that end, it provides a hybrid propulsion system for a rotary wing aircraft,
comprising:
- an internal combustion engine and an electric generator coupled to the
internal combustion engine such that in use, the internal combustion engine drives the
5 electric generator,
- a rectifier connected to the electric generator to convert an alternating
current delivered by the electric generator into a direct current, conversion means
configured to convert the direct current into alternating current, and an electric
network connecting the rectifier to the conversion means,
10 - at least one first group of at least two first electric motors connected to the
conversion means such that in use, the conversion means supply the first electric
motors with alternating current, and
- propellers respectively coupled to the first electric motors such that in use,
the first electric motors drive the propellers.
15 According to the invention, the conversion means comprise a first inverter
configured to supply the first electric motors in parallel.
The main principle of the invention thus consists in joining together the power
supply of several electric motors of a hybrid propulsion system of a rotary wing aircraft
by means of a same inverter.
20 Thus, the invention allows a weight reduction with respect to the known hybrid
propulsion systems, on the one hand, by reducing the number of inverters, and also by
reducing the number and weight of the CEM filters.
Furthermore, the power supply of several electric motors by a same inverter
enables the synchronisation of these electric motors to be optimised. That enables the
25 lift of the hybrid propulsion system to be improved.
Preferably, the first electric motors supplied by the first inverter are two in
number.
In some embodiments of the invention, the propellers coupled to the first
electric motors are two coaxial contra-rotating propellers.
30 In a preferred embodiment of the invention, the hybrid propulsion system
comprises at least one other group of at least two other electric motors, and other
4
propellers respectively coupled to these other electric motors, and the conversion
means comprise, for the or each other group of other electric motors, another
corresponding inverter configured to supply the other corresponding electric motors in
parallel.
5 In this case, the first electric motors and the other motors have advantageously
an intrinsic characteristic the variance of which, calculated for the motors of any of the
first group and the other or each other group, is lower than the variance of said
intrinsic characteristic calculated for all the first electric motors and the other electrical
motors.
10 The intrinsic characteristic(s) considered are preferably electric or
electromagnetic characteristics such as stator resistances, synchronous inductances,
and rotor fluxes.
Preferably, the hybrid propulsion system further comprises an energy storage
unit connected to the electric network in parallel with the electric generator.
15 The invention also relates to a multi-rotor rotary wing aircraft, comprising a
hybrid propulsion system of the type described above.
The invention further relates to a method for manufacturing a hybrid
propulsion system of the type described above, comprising at least the respective
steps of:
20 - providing a plurality of electric motors, propellers, an internal combustion
engine, an electric generator, a rectifier, an electric network, and a first inverter;
- coupling the electric generator to the internal combustion engine;
- connecting the rectifier to the electric generator;
- connecting the first inverter to the rectifier by means of the electric network;
25 - selecting, among the plurality of electric motors, a first group of at least two
first electric motors;
- connecting the first electric motors in parallel with the first inverter;
- coupling at least part of the propellers to the first electric motors.
In the preferred embodiment of the invention, the method further comprises
30 the respective steps of:
5
- selecting, among the plurality of electric motors, at least one other group of at
least two other electric motors;
- providing, for the or each other group of other electric motors, a
corresponding other inverter;
5 - connecting the other electric motors of the or each other group in parallel
with the corresponding other inverter.
Preferably, the first electric motors and the other electric motors are chosen so
as to have an intrinsic characteristic the variance of which, calculated for the motors of
any of the first group and the other or each other group, is lower than the variance of
10 said intrinsic characteristic calculated for all the first electric motors and the other
electric motors.
Brief description of the drawings
The invention will be better understood, and further details, advantages and
characteristics thereof will appear upon reading the following description made by way
15 of non-limiting example and in reference to the appended drawings in which:
- Fig. 1 is a schematic top view of a multi-rotor rotary wing aircraft according to
a preferred embodiment of the invention;
- Fig. 2 is a partial schematic view of a hybrid propulsion system equipping the
aircraft of Fig. 1;
20 - Fig. 3 is a schematic view of a part of the hybrid propulsion system of Fig. 2,
illustrating in particular an inverter and two electric motors belonging to this system.
Detailed disclosure of preferred embodiments
Fig. 1 illustrates a rotary wing aircraft 10, for example an octorotor aircraft, of
the type comprising four pairs 12, 14, 16, 18 of contra-rotating propellers 12A, 12B,
25 14A, 14B, 16A, 16B, 18A, 18B.
Generally, these propellers are respectively coupled to electric motors (nonvisible in Fig. 1) which therefore rotatably drive the propellers. These electric motors
are themselves supplied with electric energy by an electric generator 20 driven by an
internal combustion engine 22 such as a turbomachine. The connection between the
6
electric generator 20 and the electric motors is operated in direct current, under a
relatively high voltage, for the purpose of improving the power supply stability and
power management. To that end, a rectifier ensures conversion of the alternating
current delivered by the electric generator 20 into direct current, whereas conversion
5 means ensure conversion of this direct current into alternating current for the electric
motors, as will more clearly appear in what follows. The connection between the
electric generator 20 and the direct current electric motors is in particular
advantageous because the electric generator 20 operates at a constant rate and thus
makes it possible to have a stable direct current voltage after conversion.
10 Preferentially, an energy storage unit 26 is also provided to temporarily supply
the electric motors by completing or substituting for the electric generator 20, in a
known manner per se. The energy storage unit 26 is for example of the
electrochemical type but can alternatively be of the electrostatic (capacitive) or
mechanical type.
15 The direct current connection mentioned above has in this case a further
advantage because such a connection provides a simple manner to connect the
electric generator 20 and the energy storage unit 26, on the one hand, to the electric
motors, on the other hand.
Alternatively, the energy storage unit 26 can be connected to the rest of the
20 system through a chopper, also called a direct-direct current converter, making it
possible in particular to ensure a proper recharge of the energy storage unit 26 and
also to ensure a redundancy of the electrical system should the energy storage unit 26
be failing.
All of these elements form a hybrid propulsion system 30, which will now be
25 described in further detail in reference to Fig. 2.
The hybrid propulsion system 30 thus comprises the internal combustion
engine 22 and the electric generator 20. The latter typically includes a rotor coupled to
an output shaft 32, such as a shaft of a free or connected turbine, of the internal
combustion engine 22.
7
An electrical output of the electric generator 20 is connected to an input of the
rectifier 34 to convert the alternating current AC provided by the electric generator 20
into direct current DC.
An output of the rectifier 34 is connected in parallel, by means of an electric
5 network 44, to respective inputs of conversion means, namely a first inverter 36, a
second inverter 38, a third inverter 40 and a fourth inverter 42, provided to reconvert
the direct current DC into alternating current AC for supplying the electric motors.
More precisely, the first inverter 36 has an output connected in parallel to a
first group 46 of two first electric motors 46A, 46B, thus supplied with alternating
10 current AC by the first inverter 36.
Analogously, the other inverters 38, 40, 42 have respective outputs which are
respectively connected in parallel to other groups 48, 50, 52 each comprising two
other corresponding electric motors 48A, 48B, 50A, 50B, 52A, 52B.
The hybrid propulsion system 30 thus includes several groups each having two
15 electric motors, and is configured such that the motors of a same group are supplied
with electric energy by a same corresponding inverter.
Both electric motors 46A-52B of each group are respectively coupled to both
propellers of a corresponding pair 12-18 of contra-rotating propellers.
Supplying the electric motors by a same inverter enables the weight of the
20 hybrid propulsion system to be reduced.
In addition, such a configuration enables these motors, and thus the propellers
driven by the same to be properly synchronised. That enables the lift of the hybrid
propulsion system to be improved, particularly in the case of a contra-rotating
propeller system such as the system illustrated in the figures.
25 On the other hand, the energy storage unit 26 is also connected in parallel to
each of the inverters 36-42.
The electric motors 46A-52B are all of the same type. However, to optimise the
joint control and the synchronisation of both motors of each group, the electric
motors 46A-52B are distributed in the different groups 46-52 so as to have at least one
30 intrinsic characteristic the variance of which, calculated for the electric motors of any
of the groups 46-52, is lower than the variance of said intrinsic characteristic calculated
8
for all the electric motors 46A-52B. In other words, the electric motors are gathered
according to the value of the abovementioned intrinsic characteristic to minimise the
value deviation in this characteristic within each group.
The intrinsic characteristic(s) considered are preferably electric or
5 electromagnetic characteristics such as stator resistances, synchronous inductances,
and rotor fluxes.
In the preferred embodiment of the invention, the electric motors 46A-52B are
multiphase asynchronous motors. These motors can be of different types such as
induction motors or variable reluctance motors.
10 Preferentially, both electric motors of each group are of the multirotor monostator type, which enables weight and volume of the electric motors to be reduced
while aiding in minimising the variance of the stator starting resistors of the electric
motors within each group. That in particular enables the equality of the respective
electric currents within both electric motors of a same group to be favoured.
15 Fig. 3 illustrates an exemplary configuration of the first inverter 36 as well as
the first two electric motors 46A, 46B. The other inverters 38-42 have an analogous
configuration.
As shown in Fig. 3, the first inverter 36 is a bridge inverter comprising three
inverter arms 60, 62, 64 respectively delivering the three alternating current
20 phases 66, 68, 70 to each of both first electric motors 46A, 46B. The first inverter 36
includes a backup inverter arm 72 which is initially inoperative and which is provided
to replace one of the three arms 60, 62, 64 should it fails. The first inverter 36 further
includes conventionally a module 74 for controlling the inverter arms 60, 62, 64 and a
CEM filtering module 76.
25 The hybrid propulsion system 30 can be manufactured by means of a method
comprising the steps of:
- providing the electric motors 46A-52B, the propellers 12A-18B, the internal
combustion engine 22, the electric generator 20, the rectifier 34, the electric
network 44, and the conversion means consisting of the first inverter 36, the second
30 inverter 38, the third inverter 40 and the fourth inverter 42;
- coupling the electric generator 20 to the internal combustion engine 22;
9
- connecting the rectifier 34 to the electric generator 20;
- connecting each of the inverters 36-42 to the rectifier 34 by means of the
electric network 44;
- distributing the electric motors 46A-52B into groups of two motors, such that
5 the variance of at least one intrinsic characteristic of the electric motors calculated for
the motors of any of the groups 46-52, is lower than the variance of said intrinsic
characteristic calculated for all the electric motors 46A-52B;
- connecting the electric motors of each group to a corresponding inverter 36-
42 in parallel;
10 - coupling the propellers to the electric motors 46A-52B respectively.
As explained above, the general principle of the invention consists in joining
together the power supply of electric motors of a hybrid propulsion system of a multirotor rotary wing aircraft by means of inverters.
This general principle can be applied to various configurations of hybrid
15 propulsion systems, without departing from the scope of the present invention.
Thus, the number of propellers can be higher than or lower than 8. It can for
example be equal to four in the case of a quadrirotor type aircraft, sometimes called a
quadricopter. In addition, the propellers driven by the electric motors of a same group
may not assume a configuration of coaxial contra-rotating propellers.
20 The number of inverters can also vary, as well as the type of these inverters.
In addition, the number of electric motors supplied by a same inverter can be
higher than two. However, it is desirable that this number remains relatively low to
preserve a sufficient redundancy of the propulsion members, such a redundancy being
desirable to ensure aircraft safety.
25 In its most general aspect, the hybrid propulsion system according to the
invention thus includes at least one inverter and at least two electric motors supplied
by this inverter.
10
WE CLAIM:
1. A hybrid propulsion system (30) for a multi-rotor rotary wing aircraft (10),
comprising:
5 - an internal combustion engine (22) and an electric generator (20) coupled to
the internal combustion engine such that in use, the internal combustion engine drives
the electric generator,
- a rectifier (34) connected to the electric generator to convert an alternating
current delivered by the electric generator into a direct current, conversion means
10 configured to convert the direct current into alternating current, and an electric
network (44) connecting the rectifier to the conversion means,
- at least one first group (46) of at least two first electric motors (46A, 46B)
connected to the conversion means such that in use, the conversion means supply the
first electric motors with alternating current,
15 - propellers (12A, 12B) respectively coupled to the first electric motors such
that in use, the first electric motors drive the propellers, characterised in that the
conversion means comprise a first inverter (36) configured to supply the first electric
motors in parallel.
20 2. The hybrid propulsion system according to claim 1, wherein the first electric
motors (46A, 46B) supplied by the first inverter (36) are two in number.
3. The hybrid propulsion system according to claim 2, wherein the
propellers (12A, 12B) coupled to the first electric motors (46A, 46B) are two coaxial
25 contra-rotating propellers.
4. The hybrid propulsion system according to any of claims 1 to 3, comprising at
least one other group (48, 50, 52) of at least two other electric motors (48A, 48B, 50A,
50B, 52A, 52B), and other propellers (14A, 14B, 16A, 16B, 18A, 18B) respectively
30 coupled to these other electric motors, and wherein the conversion means comprise,
for the or each other group of other electric motors, another corresponding
11
inverter (38, 40, 42) configured to supply the other corresponding electric motors in
parallel.
5. The hybrid propulsion system according to claim 4, wherein the first electric
5 motors (46A, 46B) and the other electric motors (48A, 48B, 50A, 50B, 52A, 52B) have
an intrinsic characteristic the variance of which, calculated for the motors of any of the
first group (46) and the other or each other group (48, 50, 52), is lower than the
variance of said intrinsic characteristic calculated for all the first electric motors and
the other electric motors.
10
6. The hybrid propulsion system according to any of claims 1 to 5, further
comprising an energy storage unit (26) connected to the electric network (44) in
parallel with the electric generator (20).
15 7. A multi-rotor rotary wing aircraft (10), comprising a hybrid propulsion
system (30) according to any of claims 1 to 6.
8. A method for manufacturing a hybrid propulsion system (30) according to
any of claims 1 to 6, comprising at least the respective steps of:
20 - providing a plurality of electric motors, propellers, an internal combustion
engine (22), an electric generator (20), a rectifier (34), an electric network (44), and a
first inverter (36);
- coupling the electric generator (20) to the internal combustion engine (22);
- connecting the rectifier (34) to the electric generator (20);
25 - connecting the first inverter (36) to the rectifier (34) by means of the electric
network (44);
- selecting, among the plurality of electric motors, a first group (46) of at least
two first electric motors (46A, 46B);
- connecting the first electric motors (46A, 46B) in parallel with the first
30 inverter (36);
12
- coupling at least part of the propellers (12A, 12B) to the first electric
motors (46A, 46B).
9. The method according to claim 8 for manufacturing a hybrid propulsion
5 system (30) according to claim 5, further comprising the respective steps of:
- selecting, among the plurality of electric motors, at least one other group (48,
50, 52) of at least two other electric motors (48A, 48B, 50A, 50B, 52A, 52B);
- providing, for the or each other group of other electric motors, another
corresponding inverter (38, 40, 42);
10 - connecting the other electric motors of the or each other group in parallel
with the corresponding other inverter.
10. The method according to claim 9, wherein the first electric motors (46A,
46B) and the other electric motors (48A, 48B, 50A, 50B, 52A, 52B) are chosen so as to
15 have an intrinsic characteristic the variance of which, calculated for the motors of any
of the first group (46) and the other or each other group (48, 50, 52), is lower than the
variance of said intrinsic characteristic calculated for all the first electric motors and
the other electric motors.