Aircraft electrical architecture comprising a multi-stack fuel cell and an electrical power distribution system adapted to power at least one aircraft electric propulsion motor and auxiliary loads

Abstract

This aircraft electrical architecture comprises a fuel cell (PC) with multiple stacks (S1, S2, S3) connected in series and including an electrical power distribution system (1) to at least one aircraft propulsion electric motor (EM) and to at least one auxiliary electrical load (CE1, CE2) required for the operation of the fuel cell (PC). The electrical power distribution system (1) is adapted to supply each electric motor (EM) from all stacks (S1, S2, S3) only during a nominal operating phase of the fuel cell (PC). The electrical power distribution system (1) is also adapted to supply each auxiliary electrical load (CE1, CE2) from only some of the stacks (S1, S2, S3) during a preliminary start-up phase of the fuel cell (PC). Figure 1

Description

Title of the invention: Aircraft electrical architecture comprising a multi-stack fuel cell and an electrical power distribution system adapted to power at least one aircraft electric propulsion motor and auxiliary loads technical field

[0001] The present invention relates to an electrical power distribution system adapted to power at least one electric propulsion motor for an aircraft and accessory loads from a fuel cell. Previous techniques

[0002] Climate change is a major concern for many legislative and regulatory bodies around the world. Various restrictions on carbon emissions have been, are being, or will be adopted by various States.

[0003] Civil aviation has been mobilizing for several years now to contribute to the fight against climate change.

[0004] Technological research efforts have already led to very significant improvements in the environmental performance of aircraft. Consequently, the Applicant is constantly working to reduce its 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.

[0005] This sustained research and development work focuses on new generations of aircraft engines, the weight reduction of aircraft, in particular through the materials used and lighter on-board equipment, the development of the use of electrical technologies to provide propulsion, and finally aviation biofuels.

[0006] In order to provide the required electrical power while minimizing the weight of electrical equipment, it is advantageous to raise the voltage of aeronautical electrical networks, for example above 400V.

[0007] New aircraft with electric or hybrid electric thermal propulsion using, for example, batteries and fuel cells as main power sources generally operate at voltages above 400 Vdc and involve powers exceeding 100 kW.

[0008] Most often, the loads present on these aircraft use high voltage converters to alternating current or direct current respectively called DC / AC converters or DC / DC converters.

[0009] On the one hand, such DC / AC or DC / DC converters have predetermined maximum voltages which should not be exceeded in order to protect the converters, for example 1200 Vdc maximum to protect the MOSFET bridge arms of the converters.

[0010] On the other hand, fuel cells have transient output voltages (typically at startup) that exceed their nominal output voltages. Indeed, the output voltages drop very rapidly as soon as power is distributed to the loads. For example, when the no-load starting voltage is 1000 Vdc, the nominal voltage can drop to between 850 Vdc and 600 Vdc depending on the power demand.

[0011] There is therefore a risk of incompatibility between the high voltage level at the output of the stacks of a fuel cell (especially at the start of the cell) and the acceptable voltage level at the network and electrical loads.

[0012] To mitigate this risk, two methods are commonly used. The first method involves using voltage converters to limit the maximum voltage of the stacks, at least during the power supply start-up phase. The second method involves oversizing the loads powered by the stacks to withstand high voltage levels.

[0013] However, these methods have the major drawback of affecting the mass of the aircraft. Description of the invention

[0014] In this context, the invention aims to provide an electrical power distribution system that does not penalize the mass of aircraft and that allows the transient regime of the fuel cell to pass, without damaging the power conversion electronics and without affecting the permissible voltages of the loads used, which must remain high in order to draw as little current as possible for the same power demand.

[0015] The invention relates to an electrical architecture for an aircraft comprising a fuel cell with several stacks connected in series and an electrical power distribution system to at least one electric propulsion motor of the aircraft and to at least one electrical accessory load of the aircraft necessary for the operation of the fuel cell.

[0016] The electrical power distribution system is adapted to supply the electric motor from all the stacks and only during a nominal operating phase of the fuel cell, the electrical power distribution system being adapted to supply each accessory electrical load from only a part of the stacks during a prior start-up phase of the fuel cell.

[0017] Thanks to the invention, it is possible to supply loads (for example, the aircraft's electric propulsion motor) at a lower voltage than the transient output voltage of the fuel cell (particularly that generated during startup), without increasing the aircraft's mass, since the fuel cell starts autonomously without external interference. Advantageously, it is possible to avoid the need for voltage regulation equipment, particularly at the source (fuel cell stacks), the electrical grid, and the loads.

[0018] For example, the electrical power distribution system includes a main bus adapted to supply at least one electric motor and at least one secondary bus adapted to supply all or part of the accessory electrical loads.

[0019] Advantageously, the electrical power distribution system includes a two-pole main contactor associated with all the stacks and the main bus, the two poles of the main contactor being connected each to one of the extreme potential terminals of the fuel cell, so as to be able to supply the main bus with a total voltage corresponding to the sum of the individual voltages of all the stacks.

[0020] According to a first embodiment, the electrical power distribution system comprises at least one two-pole secondary contactor, each secondary contactor being associated with a secondary bus and only a portion of the stacks, with at least one pole of each secondary contactor being connected to an intermediate potential terminal of the fuel cell. This configuration allows the auxiliary loads to be powered from only a portion of the fuel cell stacks.

[0021] According to a second embodiment, the electrical power distribution system comprises at least one triplet of single-pole secondary contactors, each triplet being associated with a secondary bus, the first secondary contactor of each triplet being connected to an intermediate potential terminal of the fuel cell, and the second and third secondary contactors of each triplet being connected to one of the extreme potential terminals of the fuel cell. This configuration allows for better stack balancing and improved aging.

[0022] Preferably, the electrical power distribution system includes at least one electrical pre-charge device equipped with at least one resistor and mounted in parallel with an associated contactor.

[0023] According to another aspect, the method relates to a power supply method implemented by an electrical architecture as defined above. The method comprises the steps of: - during a preliminary start-up phase of the fuel cell, auxiliary electrical loads are supplied from only a portion of the stacks, - during a nominal operating phase of the fuel cell, each electric motor is powered from all the stacks.

[0024] According to one embodiment, the method is implemented by an electrical architecture as defined above according to the second embodiment, the power supply of the accessory electrical loads by the secondary bus(es) being achieved by closing the first secondary contactor of each triplet connected to the intermediate potential terminal and one of the second or third secondary contactors of the triplet connected to a terminal of opposite sign to the intermediate potential terminal, and the power supply of the electric motor by the main bus being achieved by closing the main contactor.

[0025] Preferably, the method includes an additional step of opening the secondary contactors of each triplet carried out during the electric motor supply step and an additional step of closing the second and third secondary contactors so as to supply the accessory electrical loads from the stack.

[0026] According to another embodiment, the power supply method is implemented by an electrical architecture as defined above according to the first embodiment, the supply of the accessory electrical loads by the secondary bus(es) being carried out by closing all the secondary contactors, and the supply of the electric motor by the main bus being carried out by closing the main contactor.

[0027] According to another aspect, the invention relates to an aircraft comprising an electrical architecture as defined above. Brief description of the drawings

[0028] Other objects, features and advantages of the invention will become apparent from the following description, given solely by way of non-limiting example, and made with reference to the accompanying drawings in which:

[0029] [Fig-1] and [Fig.2] are schematic representations of an electrical architecture comprising a fuel cell with three and five stacks respectively, according to a first embodiment of the invention; and

[0030] [Fig.3] and [Fig.4] are schematic representations of an electrical architecture comprising a fuel cell with three and five stacks respectively according to a second embodiment of the invention. Detailed description of at least one embodiment

[0031] With reference to [Fig.1], an electrical architecture for an aircraft is shown according to an embodiment of the invention.

[0032] The electrical architecture comprises a PC fuel cell and an electrical power distribution system 1 to a primary consumer of the aircraft, for example an aircraft propulsion electric motor ME, and to at least one IEC accessory electrical load, CE2, necessary for the operation of the PC fuel cell, for example an oil pump and / or an air compressor. In the example illustrated in [Fig. 1], there are two IEC accessory electrical loads, CE2, corresponding for example to an oil pump and an air compressor.

[0033] The PC fuel cell comprises several stacks SI, S2, S3, here three in number, which are connected in series with each other. The number of series-connected stacks of the fuel cell can take any integer value greater than or equal to two without affecting the generality of the invention.

[0034] The number of stacks connected in series is chosen to achieve a desired voltage level. For example, for applications related to the electric propulsion of aircraft, the total voltage can range from 400 Vdc to 3000 Vdc. In the example of [Fig. 1], each stack SI, S2, S3 provides a voltage between its positive and negative terminals, respectively denoted Ul, U2, and U3. The series connection of the stacks SI, S2, S3 means that the fuel cell PC provides a total voltage UT equal to the sum of the voltages of each stack, namely UT = Ul + U2 + U3.

[0035] As previously stated, the PC fuel cell exhibits two distinct operating regimes, namely a transient regime and a nominal regime, with voltage levels in the transient regime being higher than those reached in the nominal regime. The nominal regime corresponds to a nominal operating phase of the PC fuel cell reached when power is distributed to the consumers, here the electric motor ME and the IEC, CE2 accessory electrical loads. The transient regime corresponds, for example, to a preliminary start-up phase of the PC fuel cell.

[0036] The electrical power distribution system 1 is adapted to supply the main consumer(s), here the electric motor ME, from all stacks SI, S2, S3 and only during the nominal operating phase of the fuel cell PC and is adapted to supply each accessory electrical load IEC, CE2 from only part of the stacks during the pre-start-up phase of the fuel cell PC.

[0037] As illustrated in the example in [Fig. 1], the distribution system 1 includes, for example, a main bus BUS 1 adapted to supply only the main consumer(s), here the electric motor ME. The distribution system 1 also includes at least one secondary bus BUS 2 adapted to supply only all or part of the accessory electrical loads IEC, CE2.

[0038] The electric motor ME here comprises two electric stars which are each supplied by a specific DC / AC converter from the main bus BUS 1. Alternatively, the electric motor ME may comprise a different number of electric stars and / or the electric stars may be supplied by a single DC / AC converter.

[0039] In the example illustrated in [Fig.1], each IEC accessory electrical load, CE2 is powered by a specific DC / AC converter from the secondary bus BUS 2. In variants illustrated in [Fig.2] and [Fig.4], each IEC accessory electrical load, CE2 is powered from a specific secondary bus.

[0040] The electrical power distribution system 1 comprises a two-pole main contactor KP, KPA, KPB, associated with all the stacks SI, S2, S3, etc., and the main bus BUS 1. The two poles KPA, KPB of the main contactor KP are each connected to one of the extreme potential terminals of the fuel cell PC, so as to supply the main bus BUS 1 with a total voltage UT corresponding to the sum of the individual voltages of all the stacks SI, S2, S3, etc. Thus, when the main contactor KP is closed, the main bus BUS 1 is supplied with the total voltage UT of the fuel cell PC. In other words, all the stacks SI, S2, and S3 are between the two extreme potential terminals.

[0041] According to a first embodiment illustrated in [Fig. 1] and [Fig. 2], the electrical power distribution system 1 comprises at least one secondary contactor, here two secondary contactors KS2, KS3, each having two poles KS2A, KS2B, KS3A, KS3B. Each secondary contactor KS2, KS3, etc., is associated with a secondary bus BUS 2, BUS 3, etc., and with only a portion of the stacks SI, S2, S3, etc. At least one of the poles of each secondary contactor KS2, KS3, etc., is connected to an intermediate potential terminal of the fuel cell PC. An intermediate potential terminal is a terminal located between the two extreme potential terminals. Thus, when a secondary contactor is closed, the associated secondary bus is supplied with only a portion of the total voltage of the fuel cell PC.

[0042] It is possible to provide that the two poles of a secondary contactor are connected to intermediate potential terminals. This configuration is relevant when the number of two-pole secondary contactors is at least three.

[0043] It should be noted that identical or similar elements bear the same references from one figure to another.

[0044] The electrical architecture illustrated in [Fig. 2] comprises a PC fuel cell with five stacks SI, S2, S3, S4, and S5 and two secondary buses, BUS 2 and BUS 3, each associated with an IEC accessory electrical load, CE2. When the secondary contactor KS2 is closed, BUS 2 is powered only by stacks S4 and S5. When the secondary contactor KS3 is closed, BUS 3 is powered only by stacks S1, S2, and S3.

[0045] In the example illustrated in [Fig.1], the secondary bus BUS 2 is supplied only by the stacks SI and S2, when the secondary contactor KS2 is closed.

[0046] According to a second embodiment illustrated in [Fig. 3] and [Fig. 4], the electrical power distribution system 1 comprises at least one triplet of single-pole secondary contactors KS'2a, KS'2b, KS'2c, KS'3a, KS'3b, KS'3c. Each triplet is associated with a secondary bus BUS 2, BUS 3. A first secondary contactor KS'2b, KS'3b of each triplet is connected to an intermediate potential terminal of the fuel cell PC, a second secondary contactor KS'2a, KS'3a and a third secondary contactor KS'2c, KS'3c of each triplet being connected each to one of the extreme potential terminals of the fuel cell PC.

[0047] It is therefore possible to choose to supply the secondary buses either from only some of the stacks, or from all of the stacks.

[0048] In the example of [Fig. 3], when contactors KS'2b and KS'2c are closed and contactor KS'2a is open, BUS 2 is supplied only by stacks SI and S2, at a voltage corresponding to the sum of the voltages of these two stacks. By opening contactor KS'2b and closing contactor KS'2a, BUS 2 is supplied by all stacks SI, S2, and S3, at a voltage corresponding to the total voltage UT supplied by the fuel cell PC.

[0049] In the example of [Fig. 4], when contactors KS'2b and KS'2a are closed and contactor KS'2c is open, BUS 2 is supplied only by stacks S3, S4, and S5, at a voltage corresponding to the sum of the voltages of these three stacks. In the same example, when contactors KS'3b and KS'3c are closed and contactor KS'3a is open, BUS 3 is supplied only by stacks S1, S2, and S3, at a voltage corresponding to the sum of the voltages of these three stacks. By opening the KS'2b contactor and closing the KS'2c contactor, on the one hand, and by opening the KS'3b contactor and closing the KS'3a contactor, on the other hand, BUS 2 and BUS 3 are each supplied by the entirety of the stacks SI, S2, S3, S4 and S5, at a voltage corresponding to the total voltage UT supplied by the PC fuel cell.

[0050] Preferably, the electrical power distribution system 1 includes at least one electrical pre-charge device DP equipped with at least one resistor and connected in parallel with an associated contactor. The electrical pre-charge device DP limits the inrush current and thus protects the electronic equipment located downstream. In addition, the DP electrical pre-charge device prevents the triggering of nuisance protection due to a current spike.

[0051] In the embodiments given above, the electrical architecture comprises a fuel cell with several stacks connected in series, thus constituting an electrical power line. Alternatively, it is possible to provide an electrical architecture comprising several electrical power lines connected in parallel. In this case, the electrical distribution system comprises several elementary electrical distribution subsystems, each elementary subsystem being associated with a power line.

[0052] An example of the implementation of a method for supplying a main current consumer of the aircraft (here an electric propulsion motor ME) implemented by an electrical architecture as described above is presented below.

[0053] The process begins during a preliminary start-up phase of the PC fuel cell, with a step of supplying the IEC, CE2 accessory electrical loads from only a part of the stacks.

[0054] The process continues during a nominal operating phase of the PC fuel cell, by a step of supplying the ME electric motor from all the stacks.

[0055] An example of an embodiment of a method for supplying a main current consumer of the aircraft (here an electric propulsion motor ME) implemented by an electrical architecture according to the first embodiment described previously ([Fig.1] and [Fig.2]).

[0056] The process begins during a preliminary start-up phase of the fuel cell PC, with a step of supplying the accessory electrical loads IEC, CE2, achieved by closing all the secondary contactors KS2, KS3, etc. During the preliminary start-up phase of the fuel cell PC, the main contactor KP is left open, which prevents any supply of power to the electric motor ME.

[0057] The process continues during a nominal operating phase of the fuel cell PC, by a step of supplying the electric motor ME via the main bus BUS 1, achieved by closing the main contactor KP. During the nominal operating phase of the fuel cell PC, the accessory electrical loads IEC, CE2 are supplied via the secondary bus(es) BUS 2, BUS 3, etc., by keeping all the secondary contactors KS2, KS3, etc., closed.

[0058] The method may include an optional step of detecting the nominal operating phase performed before the electric motor ME power supply step. The detection of the nominal phase may, for example, be performed when the level the total voltage supplied by the PC fuel cell is below a predetermined threshold.

[0059] An example of the implementation of a power supply process implemented by an electrical architecture according to the second embodiment described previously is presented below ([Fig.3] and [Fig.4]).

[0060] The process begins during a preliminary start-up phase of the fuel cell PC, with a step of supplying the accessory electrical loads IEC, CE2 via the secondary bus(es) BUS 2, BUS 3, etc. This is achieved by closing the first secondary contactor KS'2b, KS'3b, etc. of each triplet connected to the intermediate potential terminal and one of the second KS'2a, KS'3a or third KS'2c, KS'3c secondary contactors of the triplet connected to a terminal of opposite sign to the intermediate potential terminal. During the preliminary start-up phase of the fuel cell PC, the power supply to the electric motor ME is cut off by opening the main contactor KP.

[0061] The process continues during a nominal operating phase of the fuel cell PC, by a step of supplying the electric motor ME by the main bus BUS 1 carried out by closing the main contactor KP.

[0062] Alternatively, the method may include an additional step of opening the secondary contactors of each triplet carried out during the electric motor ME supply step and an additional step of closing the second KS'2a, KS'3a and third KS'2c, KS'3c secondary contactors so as to supply the accessory electrical loads from all the stacks.

[0063] The method may include an optional step for detecting the nominal operating phase, performed before the electric motor ME power supply step. Nominal phase detection may, for example, be performed when the total voltage level supplied by the fuel cell PC is below a predetermined threshold.

Claims

Demands

1. Electrical architecture for an aircraft comprising a fuel cell (PC) with several stacks (SI, S2, S3) connected in series and comprising an electrical power distribution system (1) to at least one electric motor (ME) of aircraft propulsion and to at least one auxiliary electrical load (IEC, CE2) of aircraft required for the operation of the fuel cell (PC), characterized in that the electrical power distribution system (1) is adapted to supply each electric motor (ME) from all the stacks (SI, S2, S3) and only during a nominal phase of operation of the fuel cell (PC), the electrical power distribution system (1) being adapted to supply each auxiliary electrical load (IEC, CE2) from only some of the stacks (SI, S2, S3) during a prior start-up phase of the fuel cell (PC).

2. Electrical architecture according to claim 1, wherein the electrical power distribution system (1) comprises a main bus (BUS 1) adapted to supply at least one electric motor (ME) and at least one secondary bus (BUS 2, BUS 3) adapted to supply all or part of the accessory electrical loads (IEC, CE2).

3. Electrical architecture according to claim 2, wherein the electrical power distribution system (1) comprises a two-pole (KPA, KPB) main contactor (KP) associated with the stacks (SI, S2, S3) and the main bus (BUS 1), the two poles (KPA, KPB) of the main contactor (KP) being connected each to one of the extreme potential terminals of the fuel cell (PC), so as to be able to supply the main bus (BUS 1) with a total voltage (UT) corresponding to the sum of the individual voltages of all the stacks (SI, S2, S3).

4. Electrical architecture according to claim 3, wherein the electrical power distribution system (1) comprises at least one two-pole secondary contactor (KS2, KS3) (KS2A, KS2B, KS3A, KS3B), each secondary contactor (KS2, KS3) being associated with a secondary bus (BUS 2, BUS 3) and only some of the stacks (S1, S2, S3), at least one of the poles of each secondary contactor (KS2, KS3) being connected to an intermediate potential terminal of the fuel cell (PC).

5. Electrical architecture according to claim 3, wherein the electrical power distribution system (1) comprises at least one triplet of single-pole secondary contactors (KS'2a, KS'2b, KS'2c, KS'3a, KS'3b, KS'3c), each triplet being associated with a secondary bus (BUS 2, BUS 3), a first secondary contactor (KS'2b, KS'3b) of each triplet being connected to an intermediate potential terminal of the fuel cell (PC), a second secondary contactor (KS'2a, KS'3a) and a third secondary contactor (KS'2c, KS'3c) of each triplet being connected each to one of the extreme potential terminals of the fuel cell (PC).

6. Electrical architecture according to claim 4 or 5, wherein the electrical power distribution system (1) includes at least one electrical pre-charge device (DP) equipped with at least one resistor and mounted in parallel with an associated contactor (KP, KS2, KS3, KS'2b, KS'2c, KS'3c).

7. A method of power supply implemented by an electrical architecture according to claim 1 comprising steps of: - during a preliminary start-up phase of the fuel cell (PC), supplying the accessory electrical loads (IEC, CE2) from only some of the stacks (SI, S2, S3), - during a nominal operating phase of the fuel cell (PC), supplying each electric motor (ME) from all the stacks (SI, S2, S3)

8. Power supply method according to claim 7 implemented by an electrical architecture according to claim 4 comprising steps of: - during a preliminary start-up phase of the fuel cell (PC), supplying the accessory electrical loads (IEC, CE2) by the secondary bus(es) (BUS 2, BUS 3, etc.) achieved by closing all the secondary contactors (KS2, KS3), and - during a nominal operating phase of the fuel cell (PC), supplying all or part of the electric motors (ME) by at least one main bus (BUS 1) achieved by closing the main contactor (KP).

9. A power supply method according to claim 7 implemented by an electrical architecture according to claim 5 comprising steps of: - during a preliminary start-up phase of the fuel cell (PC), supplying the accessory electrical loads (IEC, CE2) by the secondary bus(es) (BUS 2, BUS 3) achieved by closing the first secondary contactor (KS'2b, KS'3b) of each triplet connected to the intermediate potential terminal and one of the second (KS'2a, KS'3a) or third (KS'2c, KS'3c) secondary contactors of the triplet connected to a terminal of opposite sign to the intermediate potential terminal, and - during a nominal operating phase of the fuel cell (PC), supplying at least one electric motor (ME) by the main bus (BUS 1) achieved by closing the main contactor (KP).

10. Aircraft comprising an electrical architecture according to any one of claims 1 to 6.

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