Electrical architecture for an aircraft comprising a multi-stack fuel cell and an electrical energy distribution system suitable for supplying at least one electric propulsion motor of the aircraft and auxiliary loads

Abstract

The invention relates to electrical architecture for an aircraft comprising a fuel cell (PC) having multiple stacks (S1, S2, S3) which are connected in series and comprising an electrical energy distribution system (1) supplying at least one electric propulsion motor (ME) of the aircraft and at least one auxiliary electrical load (CE1, CE2) required for the fuel cell (PC) to operate. The electrical energy distribution system (1) is suitable for supplying each electric motor (ME) from all of the stacks (S1, S2, S3) only during a nominal operating phase of the fuel cell (PC), the electrical energy distribution system (1) being suitable for supplying each auxiliary electrical load (CE1, CE2) from only some of the stacks (S1, S2, S3) during a preliminary phase of starting the fuel cell (PC).

Description

[0001] DESCRIPTION

[0002] TITLE: 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

[0003] technical field

[0004] The present invention relates to an electrical power distribution system adapted to power at least one electric propulsion motor for an aircraft and auxiliary loads from a fuel cell.

[0005] Previous techniques

[0006] 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.

[0007] Civil aviation has been mobilizing for several years now to contribute to the fight against climate change.

[0008] Technological research efforts have already led to very significant improvements in the environmental performance of aircraft. Consequently, the Applicant is continuously working to reduce its climate impact by employing methods and operating virtuous development and manufacturing processes that minimize greenhouse gas emissions to the absolute minimum, in order to reduce the environmental footprint of its business.

[0009] This sustained research and development work focuses on new generations of aircraft engines, the weight reduction of aircraft, particularly through the materials used and lighter on-board equipment, the development of the use of electrical technologies to provide propulsion, and finally aviation biofuels.

[0010] 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.

[0011] 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 power outputs exceeding 100 kW.

[0012] 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.

[0013] 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.

[0014] On the other hand, fuel cells have transient output voltages (typically at startup) that exceed their nominal output voltages. This is because 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.

[0015] 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 level of the network and electrical loads.

[0016] To mitigate this risk, two methods are typically used. The first method involves using voltage converters to limit the maximum voltage of the stacks, at least during the power supply's initial load phase. The second method involves oversizing the loads powered by the stacks to withstand high voltage levels.

[0017] However, these methods have the major drawback of affecting the mass of the aircraft.

[0018] Description of the invention

[0019] 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 to draw as little current as possible for the same power demand.

[0020] The invention relates to an electrical architecture for an aircraft comprising a fuel cell with several stacks connected in series and a system for distributing electrical energy 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.

[0021] The electrical power distribution system is adapted to supply the electric motor from all 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 some of the stacks during a prior start-up phase of the fuel cell.

[0022] Thanks to this 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 weight, as the fuel cell starts autonomously without external interference. Advantageously, it is possible to avoid the need for voltage regulation equipment, especially at the source (fuel cell stacks), the electrical grid, and the loads.

[0023] 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.

[0024] 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.

[0025] 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.

[0026] 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, with 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.

[0027] Preferably, the electrical power distribution system includes at least one electrical pre-charge device equipped with at least one resistor and connected in parallel with an associated contactor. In 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, supplying the auxiliary electrical loads from only some of the stacks; and during a nominal operating phase of the fuel cell, supplying each electric motor from all the stacks.

[0028] According to one embodiment, the process is implemented by an electrical architecture as defined above according to the second embodiment, the supply of the accessory electrical loads by the secondary bus(es) being carried out 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 supply of the electric motor by the main bus being carried out by closing the main contactor.

[0029] Preferably, the process 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.

[0030] According to another embodiment, the power supply process 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.

[0031] In another aspect, the invention relates to an aircraft comprising an electrical architecture as defined above. Brief description of the drawings

[0032] 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:

[0033] [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

[0034] [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.

[0035] Detailed description of at least one embodiment

[0036] With reference to [Fig 1], an electrical architecture for an aircraft is shown according to one embodiment of the invention.

[0037] The electrical architecture includes a PC fuel cell and an electrical power distribution system 1 to a primary consumer of the aircraft, for example an electric propulsion motor ME, and to at least one auxiliary electrical load CE1, CE2 required for the operation of the PC fuel cell, for example an oil pump and / or an air compressor. In the example shown in [Fig 1], there are two auxiliary electrical loads CE1, CE2, corresponding for example to an oil pump and an air compressor.

[0038] The PC fuel cell comprises several stacks SI, S2, S3, here three in number, which are connected in series. 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.

[0039] The number of stacks connected in series is chosen to achieve a desired voltage level. For example, for applications related to electric aircraft propulsion, the total voltage can range from 400 Vdc to 3000 Vdc. In the example in [Fig 1], each stack S1, S2, S3 provides a voltage between its positive and negative terminals, respectively denoted U1, U2, and U3. The series connection of the stacks S1, S2, S3 means that the PC fuel cell provides a total voltage UT equal to the sum of the voltages of each stack, namely UT = U1 + U2 + U3.

[0040] As previously mentioned, the PC fuel cell exhibits two distinct operating regimes: a transient regime and a nominal regime. Voltage levels in the transient regime are higher than those reached in the nominal regime. The nominal regime corresponds to the nominal operating phase of the PC fuel cell, reached when power is distributed to the loads, in this case the electric motor ME and the accessory electrical loads CE1 and CE2. The transient regime corresponds, for example, to a preliminary start-up phase of the PC fuel cell.

[0041] 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 CE I, CE2 from only part of the stacks during the pre-start-up phase of the fuel cell PC.

[0042] 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 CE I, CE2.

[0043] The ME electric motor here comprises two electric stars, each powered by a specific DC / AC converter from the main bus BUS 1. Alternatively, the ME electric motor may comprise a different number of electric stars and / or the electric stars may be powered by a single DC / AC converter.

[0044] In the example shown in [Fig 1], each accessory electrical load CE I, CE2 is powered by a specific DC / AC converter from the secondary bus BUS 2. In variants shown in [Fig 2] and [Fig 4], each accessory electrical load CE I, CE2 is powered from a specific secondary bus.

[0045] 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 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 that the main bus 1 can be supplied 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 1 is supplied with the total voltage UT of the fuel cell PC. In other words, all the stacks SI, S2, and S3 are connected between the two extreme potential terminals.

[0046] 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.

[0047] It is possible to connect the two poles of a secondary contactor to intermediate potential terminals. This configuration is relevant when there are at least three two-pole secondary contactors.

[0048] It should be noted that identical or similar elements bear the same references from one figure to another.

[0049] 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 secondary contactor KS2 is closed, BUS 2 is powered only by stacks S4 and S5. When secondary contactor KS3 is closed, BUS 3 is powered only by stacks SI, S2, and S3.

[0050] In the example illustrated in [Fig 1], the secondary bus BUS 2 is powered only by stacks SI and S2, when the secondary contactor KS2 is closed.

[0051] 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 are each connected to one of the extreme potential terminals of the fuel cell PC.

[0052] It is therefore possible to choose to power the secondary buses either from only some of the stacks, or from all of the stacks.

[0053] In the example in [Fig 3], when contactors KS'2b and KS'2c are closed and contactor KS'2a is open, BUS 2 is powered 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 powered by all stacks SI, S2, and S3, at a voltage corresponding to the total voltage UT supplied by the PC fuel cell.

[0054] In the example in [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.

[0055] 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 downstream electronic equipment. Furthermore, the electrical pre-charge device DP prevents nuisance protection from being triggered by a current surge.

[0056] In the previously given examples, the electrical architecture includes a fuel cell with multiple stacks connected in series, thus forming a single power line. Alternatively, an electrical architecture can be designed with multiple power lines connected in parallel. In this case, the electrical distribution system comprises several elementary power distribution subsystems, each subsystem being associated with a power line.

[0057] The following presents 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 previously.

[0058] The process begins during a preliminary start-up phase of the PC fuel cell, with a step of supplying the accessory electrical loads CE I, CE2 from only a part of the stacks.

[0059] The process continues during a nominal operating phase of the PC fuel cell, with a step of supplying the ME electric motor from all the stacks. An example of an implementation of a method for supplying a main current consumer of the aircraft (here an ME propulsion electric motor) implemented by an electrical architecture according to the first embodiment described previously is presented below ([Fig 1] and [Fig 2]).

[0060] The process begins during a preliminary start-up phase of the fuel cell PC, with a step of supplying the accessory electrical loads CE1, 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.

[0061] The process continues during a nominal operating phase of the PC fuel cell, with 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 PC fuel cell, the accessory electrical loads CE1, CE2 are supplied via the secondary bus(es) BUS 2, BUS 3, etc., by keeping all secondary contactors KS2, KS3, etc., closed.

[0062] 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.

[0063] We present below an example of the realization of a power supply process implemented by an electrical architecture according to the second embodiment described previously ([Fig 3 ] and [Fig 4]).

[0064] The process begins during a preliminary start-up phase of the fuel cell PC, with a step of supplying the accessory electrical loads CE1, CE2 via the secondary bus(es) BUS2, BUS3, 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.

[0065] The process continues during a nominal operating phase of the PC fuel cell, by a step of supplying the electric motor ME by the main bus BUS 1 carried out by closing the main contactor KP.

[0066] Alternatively, the process 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.

[0067] 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 (CE1, CE2) of the 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 (CE1, 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 (CE I, 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 to a secondary bus (BUS 2, BUS 3) and to only part of the stacks (SI , 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) comprises at least one electrical pre-charge device (DP) provided 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 for providing a power supply implemented by an electrical architecture according to claim 1, comprising the steps of: - during a preliminary start-up phase of the fuel cell (PC), supply of accessory electrical loads (CE I , CE2) from only part of the stacks (SI , S2, S3), - during a nominal operating phase of the fuel cell (PC), power supply to each electric motor (ME) from all the stacks (SI, S2, S3) 8. A method for supplying power according to claim 7 implemented by an electrical architecture according to claim 4 comprising the steps of: during a preliminary start-up phase of the fuel cell (PC), supplying the electrical loads accessories (CE I , CE2) by the secondary bus(es) (BUS 2, BUS 3 , etc) carried out by closing all the secondary contactors (KS2, KS3), and during a nominal operating phase of the fuel cell (PC), supply of all or part of the electric motors (ME) by at least one main bus (BUS 1) carried out by closing the main contactor (KP).

9. 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 (CE1, 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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