Aircraft electric propulsion system
The electric propulsion system for aircraft uses a synchronous generator and dual motor configuration with a differential train to decouple rotational speeds, enhancing power density and efficiency by minimizing converter weight and simplifying starting and synchronization.
Patent Information
- Authority / Receiving Office
- FR · FR
- Patent Type
- Patents
- Current Assignee / Owner
- Filing Date
- 2021-12-23
- Publication Date
- 2026-03-27
AI Technical Summary
Existing electric propulsion systems for aircraft suffer from reduced power density and efficiency due to the use of power converters, which increase weight and complicate actuator starting and synchronization.
An electric propulsion system comprising a rotating electrical energy source with a synchronous generator, a first synchronous motor connected via an alternating current circuit, a direct current circuit with converters, and a second motor connected via a differential train, allowing decoupling of rotational speeds and facilitating synchronization and starting.
The system achieves improved power density and efficiency by reducing converter weight and simplifying starting and synchronization, enabling efficient operation with reduced power requirements.
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Abstract
Description
Title of the invention: Electric propulsion system for an aircraft technical field
[0001] The present invention relates to the electrification of aircraft propulsion. This electrification aims to replace all or part of the current propulsion based on thermal sources with electrical sources and effectors for environmental reasons (pollution, noise, etc.).
[0002] The invention relates more particularly to an electric propulsion chain. Prior art
[0003] A propulsion chain schematically comprises at least one energy source, at least one actuator, or propellant, and one or more energy distribution circuits to connect the energy source and the actuator. The energy source comprises, for example, a gas turbine and a synchronous generator.
[0004] The main criteria for evaluating the performance of a propulsion chain are power density and efficiency.
[0005] Electric propulsion systems comprising a direct current electrical distribution circuit are known. These systems incorporate power converters to convert the alternating operating voltages of the energy sources and actuators into direct current voltages.
[0006] Each power converter has control features, which notably allow for complete decoupling between the rotational speed of the power source and the rotational speed of the actuator. Furthermore, it is easy to connect a battery (DC source) to a DC power distribution circuit.
[0007] One disadvantage of these electric propulsion chains is that the power converters reduce the efficiency of the electric propulsion chain and increase its weight, which reduces its power density.
[0008] Electric propulsion systems comprising an alternating current electrical distribution circuit are also known. In this case, the connection between the energy source and the actuator is direct, i.e., without a power converter.
[0009] This improves power density and efficiency compared to a propulsion system incorporating power converters. However, the functionality of the propulsion system is also more limited. In particular, the rotational speed of the actuators is coupled to the rotational speed of the energy source.
[0010] Another disadvantage of these electric propulsion chains is that starting the actuators is more complex because their synchronization with the energy source must This can be achieved by adding power converters. These converters can also connect a battery to the electric propulsion system. However, adding these converters also increases the weight of the propulsion system, thus reducing its power density and efficiency. Description of the invention
[0011] The invention aims to solve the problems of the prior art by providing an electric propulsion system for an aircraft, comprising
[0012] - A rotating electrical energy source comprising a synchronous generator powered by an internal combustion engine,
[0013] - A first synchronous electric motor whose input is connected to an output from the synchronous generator by an alternating current electrical circuit,
[0014] - A rotating propulsion element,
[0015] Characterized in that it comprises
[0016] - A direct current electrical circuit comprising in series from an input connected to the alternating current electrical circuit: a first alternating current / direct current converter, a direct current electrical connection and a second direct current / alternating current converter,
[0017] - A second electric motor, one input of which is connected to an output of the DC / AC converter,
[0018] - A differential train comprising a first input shaft connected to the first motor synchronous electric, a second input shaft connected to the second electric motor and an output shaft connected to the rotating propulsion unit.
[0019] Thanks to the invention, the rotational speed of an actuator is decoupled from the rotational speed of the energy source.
[0020] The starting of the propulsion chain and the synchronization between the energy source and the actuator are facilitated.
[0021] According to a preferred feature, the electric propulsion chain of an aircraft further comprises a DC voltage source connected to the DC electrical circuit.
[0022] According to a preferred characteristic, the second motor has a lower power than the first motor.
[0023] Thus, the direct current electrical circuit is used to transmit a limited power. The same applies to the converters, which limits their weight and ensures good power density for the propulsion system.
[0024] According to a preferred feature, the electric propulsion system of an aircraft further comprises a contactor located at the output of the rotating electrical power source. The contactor allows the rotating electrical power source to be disconnected, particularly during the start-up of the propulsion system.
[0025] The invention also relates to a method for starting the electric propulsion system of an aircraft as previously described, characterized in that it comprises the following steps:
[0026] - control for opening the contactor,
[0027] - control of the DC electrical connection power supply by the battery,
[0028] - command of the first converter so that it drives the first motor for increase its rotational speed until the first motor reaches the speed of the generator and the voltage of the first motor reaches the voltage of the generator,
[0029] - command of the second converter to supply and control the second motor to reduce the speed of the rotating propulsion unit,
[0030] - control of the contactor closing when the first motor has reached the generator speed and that the voltage of the first motor has reached the generator voltage.
[0031] The invention also relates to a method of varying the speed of the rotating propulsion element of the electric propulsion chain of an aircraft as previously presented, after the start of the propulsion chain, characterized in that it includes the step of controlling the second DC / AC converter so that it drives the second motor in speed to control the speed of the rotating propulsion element.
[0032] The invention also relates to an aircraft comprising an electric propulsion chain as previously described.
[0033] The methods and the aircraft have similar advantages to those previously stated. Brief description of the drawings
[0034] Other features and advantages will become apparent from the following description of preferred embodiments, given by way of non-limiting examples, described with reference to the figures in which:
[0035] [Fig-1] illustrates an electric propulsion chain according to an embodiment of the invention,
[0036] [Fig.2] illustrates the start-up of the electric propulsion chain of the [Fig.1],
[0037] [Fig.3] illustrates a method for starting the electric propulsion chain, according to an embodiment of the invention,
[0038] [Fig.4] illustrates simulation results of the operation of the chain of electric propulsion,
[0039] [Fig.5] illustrates an electric propulsion chain according to another embodiment of the invention,
[0040] [Fig.6] illustrates an electric propulsion chain according to another embodiment of the invention,
[0041] [Fig.7] illustrates an electric propulsion chain according to another embodiment of the invention, and
[0042] [Fig.8] illustrates an electric propulsion chain according to another embodiment of the invention.
[0043] Identical, similar or equivalent parts of the different figures bear the same numerical references so as to facilitate the transition from one figure to another.
[0044] The different parts represented in the figures are not necessarily shown on a uniform scale, in order to make the figures more legible.
[0045] The different possibilities (variants and embodiments) should be understood as not being mutually exclusive and can be combined. Description of embodiments
[0046] According to a preferred embodiment, shown in [Fig. 1], an electric propulsion chain is intended to equip an aircraft.
[0047] The electric propulsion system comprises a rotating electrical power source 1 including a synchronous generator 11 driven by a heat engine 12. The heat engine 12 is, for example, a gas turbine or a piston engine. The synchronous generator 11 is, for example, of the permanent magnet or wound rotor type.
[0048] The electric propulsion system also includes an alternating current electrical circuit 2 connected to an output of the synchronous generator 11. The connected alternating current electrical circuit 2 is also connected to an input of a first synchronous motor 3, referred to as the main motor. The first synchronous motor 3 is, for example, of the permanent magnet or wound rotor type.
[0049] The alternating current electrical circuit 2 includes a contactor 21 capable of disconnecting the rotating electrical energy source 1 from the components located downstream or, on the contrary, of connecting them electrically.
[0050] The electric propulsion chain also includes a DC electrical circuit 4. The DC electrical circuit 4 includes a first AC / DC converter 41 connected to the AC electrical circuit 2, downstream of the contactor 21. The AC / DC converter 41 is connected to a DC electrical link 42, which is itself connected to a second DC / AC converter 43. It should be noted that the two converters are bidirectional and can be controlled in AC / DC and DC / AC.
[0051] A battery 8 is connected to the DC electrical circuit 4.
[0052] The electric propulsion system also includes a second motor 5, called motor auxiliary, one of whose inputs is connected to an output of the DC / AC converter 43. The second synchronous motor 5 is for example of the permanent magnet or wound rotor type.
[0053] The electric propulsion chain also includes a differential train 6, or epi-cycloidal train, which includes a first input shaft 61 connected to the first synchronous motor 3, a second input shaft 62 connected to the second motor 5 and an output shaft 63 connected to a rotating propulsion element 7.
[0054] The rotating propulsion element 7 is, for example, a propeller.
[0055] The differential gear 6 is a mechanical transmission that connects the two input shafts and the output shaft, these three shafts having different rotational speeds, with a single mathematical relationship: the speeds of two of the shafts determine that of the third. More precisely, the differential gear 6 performs a weighted summation of the rotational speeds of the input shafts 61 and 62 and thus determines the rotational speed of the output shaft 63. Consequently, the rotational speed of the propeller 7 is a weighted summation of the rotational speeds of the motors 3 and 5.
[0056] The differential train 6 includes gears connected to the input and output shafts. The gears of a differential train are often called "sun", "ring" and "satellite".
[0057] Let Nsoi, Ncou, and Nsat be the number of teeth of the "sun", "ring", and "satellite" gears, respectively, and Wsoi, Wcou, and Wsat be the rotational speeds of the "sun", "ring", and "satellite" gears, respectively. The speed equation is:
[0058] Nsol.Wsol+Ncou.Wcou = (Nsol+Ncou).Wsat
[0059] Thus the rotational speed of the output shaft 63 of the differential train depends on the rotational speed of the two input shafts 61 and 62.
[0060] The electric propulsion chain also includes a control module 9 configured to control the operation of the various elements of the electric propulsion chain.
[0061] Furthermore, considering the alternating current electrical circuit 2 connected between the source 1 and the first synchronous motor 3, the connection between the source and the load is direct, i.e., without a power converter. This implies that the electrical frequencies of the source 1 and the first motor 3 are equal. In the absence of operation of the direct current circuit 4 and the second motor 5, the rotational speed of the first motor 3, and therefore that of the propeller 7, is coupled to the rotational speed of the rotating electrical energy source 1.
[0062] Considering the DC electrical circuit 4 connected between the source 1 and the second synchronous motor 5, the first AC / DC converter 41 allows the conversion of alternating current into direct current and the second DC / DC converter AC converter 43 allows the conversion of direct current to alternating current. Converters 41 and 43 also have a control function that allows the rotational speed of the rotating electrical power source 1 to be decoupled from the rotational speed of the second motor 5.
[0063] More specifically, the speed control of the second motor 5 is ensured by the second converter 43. The first converter 41 allows either the regulation of the voltage of the direct current electrical link 42 or the transfer of power to the alternating current electrical circuit 2.
[0064] Thus, the architecture comprising the alternating current electrical circuit 2 and the first synchronous motor 3 in parallel with the direct current electrical circuit 4 and the second synchronous motor 5, the two motors being connected to the differential train 6, makes it possible to decouple the rotational speed of the propeller from the rotational speed of the rotating electrical energy source 1. In other words, this architecture makes it possible to vary the rotational speed of the propeller, at a constant rotational speed of the energy source 1.
[0065] The power ratings of the electric motors 3 and 5 are chosen such that the power of the second (auxiliary) motor 5 is less than the power of the first (main) motor 3. Preferably, the power of the second motor 5 is equal to a fraction of the power of the second motor 3.
[0066] It should be noted that the power ratio of motors 3 and 5 also approximately defines the ratio of the motor rotation speeds.
[0067] For example, the first motor 3 provides between 80 and 95%, preferably 90%, of the propeller's rotational speed, and the second motor provides a maximum of between 5 and 20%, preferably 10%, of the propeller's rotational speed. The ratio of the motor power outputs determines a range of possible variations in the propeller's rotational speed, while keeping the rotational speed of the power source 1 constant. Thus, the DC electrical circuit 4 is used to transmit a limited amount of power. The same applies to the converters 41 and 43, which limits their weight and ensures good power density for the propulsion system.
[0068] Figures 2 and 3 represent the case of the start-up of the electric propulsion chain. Figure 3 is a flowchart showing steps E1 to E3 implemented in the control module 9.
[0069] Considering the alternating current electrical circuit 2 connected between the source 1 and the first synchronous motor 3, it is recalled that the rotational speeds of the energy source 1 and the motor 3 are coupled.
[0070] This implies that, in the absence of operation of the DC circuit 4 and the second motor 5, the propeller must be driven at a relatively high speed in order to drive the first motor 3 at the speed corresponding to that of the energy source. 1. This therefore requires significant power.
[0071] Thanks to the invention, starting the electric propulsion system is made easier. Indeed, to start the electric propulsion system, the generator 11 and the first motor 3 must be synchronized before they are connected.
[0072] The start-up of the electric propulsion chain is carried out in the following manner.
[0073] At step El, the control module 9 commands the opening of the contactor 21. When contactor 21 is open, generator 11 and first motor 3 are not connected.
[0074] In the next step E2, the control module 9 commands the actual start-up of the electric propulsion system. Under the effect of this command:
[0075] - the battery powers the DC electrical connection 42 and therefore the converters weavers 41 and 43;
[0076] - the first converter 41 is controlled as an inverter (DC / AC) allowing power to be supplied the first motor 3. The converter 41 controls the motor 3 in speed and voltage. It also measures the speed (electrical frequency) and voltage (amplitude and phase) of the generator 11. The converter 41 controls the motor 3 to increase its rotational speed until the motor 3 reaches the speed of the generator 11 (synchronous speed) and also until the voltage of the motor 3 reaches the voltage of the generator 11. The speed control is done in such a way as to obtain the voltages of the generator and the motor perfectly synchronized (in phase);
[0077] - the motor 5 is powered and controlled by the second converter 43 to limit (or even cancel) the speed of propeller 7. To achieve this, the second motor 5 is driven in the opposite direction to the first motor 3. The differential gear performs the weighted summation of the speeds, which remains low, or even zero. Thus, the power required for starting is greatly reduced. The speed of propeller 7 is measured, and motor 5 is regulated to limit the speed of propeller 7.
[0078] When the motor 3 has reached the speed of the generator 11 (synchronous speed) and the voltage of the motor 3 has reached the voltage of the generator 11 in phase and amplitude, step E2 is followed by step E3 in which the control module 9 commands the closing of the contactor 21. The energy source 1 then supplies the first motor 3.
[0079] Next, the rotational speed of the second motor is brought down to around zero. The propeller speed then corresponds to the speed of the first motor.
[0080] The invention makes it possible to reduce the starting power of the electric propulsion system by limiting or eliminating the speed of the propeller 7. This feature is particularly advantageous in the case of a fixed-pitch propeller, for which it is not possible to limit the torque by pitch control. The invention can also be applied to a variable-pitch propeller.
[0081] During operation of the electric propulsion chain after its start-up, the rotating electrical power source 1 is connected to the first motor 3 via the alternating current electrical circuit 2.
[0082] The first AC / DC converter 41 can be controlled to supply the DC electrical circuit 4, and therefore the second motor 5, from the energy source 1 or, on the contrary, to transmit power to the main motor 3.
[0083] It is recalled that the rotation speed of the propeller 7 is a weighted sum of the rotation speeds of the motors 3 and 5.
[0084] The second DC / AC converter 43 is controlled to drive the second motor 5 in speed to control the rotational speed of the propeller 7. For example, if the second motor 5 is controlled at zero speed, the rotational speed of the propeller 7 is that of the first motor 3 with the weighting coefficient defined by the differential gear up to.
[0085] If the second motor 5 is controlled in positive speed, respectively negative, the rotational speed of the propeller 7, which is a weighted sum of the rotational speeds of the motors 3 and 5, is greater, respectively less, than that of the first motor 3 up to the weighting coefficient defined by the differential gear.
[0086] It should be noted that the power ratio of motors 3 and 5 also approximately defines the ratio of the motors' rotational speeds. Thus, if the power of the second motor 5 is equal to 10% of the power of the first motor, it will be possible to obtain approximately a 10% speed variation.
[0087] When the propeller is driven by aerodynamic forces of the wind (in English: windmilling), it is possible to transfer to the battery 8 some of the energy generated by the rotation of the propeller 7 under the effect of the wind by passing through the first motor and / or the second motor.
[0088] In this case, the rotation of the propeller 7 drives the rotation of the first and second motors. These then act as generators. The generated energy is returned to the battery 8, via the converters 41 and 43.
[0089] Figure 4 represents simulation results of the operation of the electric propulsion system. More specifically, it represents, from top to bottom, the time-domain diagrams:
[0090] From the rotational speed of the second motor Vsm,
[0091] Of the propeller rotation speed Vh, and
[0092] Of the rotation speed of the first motor Vpm.
[0093] Speeds are expressed in rad / s.
[0094] From time t0 = 0s to time tl = 5s, the electric propulsion system is starting up. Contactor 21 is open. The first motor 3 is gradually driven to synchronous speed with generator 11 via a ramp of speed between the values 0 and 600 rad / s. During this time the second motor 5 is driven according to a speed ramp between 0 and -2000 rad / s in order to limit the speed Vh of the propeller 7. This has the effect of greatly limiting the power during start-up.
[0095] At time t2 = 5.5s, the first motor 3 is synchronized with the generator 11. The contactor 21 is closed to connect the first motor 3 and the generator 11.
[0096] From time t3 = 6s to time t4 = 10s, the speed of the second motor Vsm is gradually reduced to zero, which has the effect of increasing the speed of the propeller Vh and therefore its power.
[0097] From time t5 = 12s to time t6 = 16s, speed variations on the second motor 5 are carried out which allows the speed of the propeller 7 to be varied.
[0098] The invention has been described in the case of an electrical power source and a propeller. It also applies to architectures illustrated in Figures 5 to 8 and comprising:
[0099] - Several sources of electrical energy 1 in parallel, each powering a chain as previously described ([Fig.5]), - Several sources of electrical energy 1 in parallel, each powering a chain as previously described, with a common direct current electrical connection 42 ([Fig.6]), - An electrical power source 1, supplying several chains as previously described via a common alternating current circuit ([Fig.7]), - An electrical power source, supplying several chains as previously described via a common alternating current circuit, the chains having a common direct current electrical connection 42 ([Fig.8]).
Claims
Demands
1. An electric propulsion system for an aircraft, comprising: - a rotating electrical power source (1) including a synchronous generator (11) driven by a heat engine (12), - a first synchronous electric motor (3) one input of which is connected to an output of the synchronous generator by an alternating current electrical circuit (2), - a rotating propulsion unit (7), characterized in that it comprises: - a direct current electrical circuit (4) comprising in series from an input connected to the alternating current electrical circuit: a first alternating / direct current converter (41), a direct current electrical link (42) and a second direct / alternating current converter (43), - a second electric motor (5), one input of which is connected to an output of the direct / alternating current converter,- a differential train (6) comprising a first input shaft (61) connected to the first synchronous electric motor, a second input shaft (62) connected to the second electric motor and an output shaft (63) connected to the rotating propulsion element.
2. An electric propulsion system for an aircraft according to claim 1, further comprising a DC voltage source (8) connected to the DC electrical circuit.
3. An electric propulsion system of an aircraft according to claim 1 or 2, wherein the second motor (5) has a lower power than the power of the first motor (3).
4. An electric propulsion chain for an aircraft according to any one of claims 1 to 3, further comprising a contactor (21) located at the output of the rotating electrical power source (1).
5. A method for starting the electric propulsion system of an aircraft according to claim 4, characterized in that it comprises the steps of: - controlling (El) the opening of the contactor, - control (E2) of the supply of the DC electrical connection by the battery, - control (E2) of the first converter so that it drives the first motor to increase its rotational speed until the first motor reaches the speed of the generator and the voltage of the first motor reaches the voltage of the generator, - control (E2) of the second converter so that it supplies and controls the second motor to decrease the speed of the rotating propulsion element, - control (E3) of the closing of the contactor when the first motor has reached the speed of the generator and the voltage of the first motor has reached the voltage of the generator.
6. Method of varying the speed of the rotating propulsion element of the electric propulsion chain of an aircraft according to any one of claims 1 to 4, after the start of the propulsion chain, characterized in that it comprises the step of controlling the second DC / AC converter (43) so that it drives the second motor (5) in speed to control the speed of the rotating propulsion element.
7. Aircraft comprising an electric propulsion system according to any one of claims 1 to 4.