Fuel cell and associated control method

Abstract

Fuel Cell and Associated Control Method This fuel cell (20) comprises several unit cells, which are stacked along a main axis (A30) to form a stack (30) of cells. The stack is housed in a casing (22) with a jacket (24) closed by a first cover (26B) and a second cover (26A), opposite the first cover along the main axis. When the fuel cell is in its operating configuration, the main axis is substantially horizontal, and the casing has a top and a bottom side.The first cover includes a main ventilation inlet (434), which opens into the housing at the highest point of the first cover, while the second cover includes a first main ventilation outlet (442) which opens into the housing at the highest point of the second cover, and a second main outlet (444), which opens into the housing at the lowest point of the second cover. See Figure 2 for abbreviations.

Description

Title of the invention: Fuel cell and associated control method

[0001] The present invention relates to a fuel cell, as well as a method for controlling such a fuel cell.

[0002] A fuel cell is a device that generates electricity through an electrochemical reaction between a fuel, for example dihydrogen, and an oxidant, for example oxygen from the air. This discussion focuses on proton exchange membrane fuel cells with a solid electrolyte – also known as PEMFCs – which typically comprise a stack of several unit cells, each constituting an electrochemical generator.

[0003] Schematically, each unit cell comprises two separators, also called polar plates, between which a solid electrolyte in the form of a proton exchange membrane is interposed. The membrane is made, for example, of a sulfonated perfluorinated polymer material. Within each cell, each separator, together with the corresponding membrane, delimits a reactive compartment. One of the two reactive compartments, called the cathodic compartment, houses a cathodic element, formed by a cathodic catalytic layer located on the surface of the membrane, while the other reactive compartment, called the anodic compartment, houses an anodic element, formed by an anodic catalytic layer located on the surface of the membrane. The assembly of the membrane and the anodic and cathodic catalytic layers forms a membrane-electrode assembly, generally known by the acronym AME in French, or MEA in English.

[0004] For two adjacent cells, a separator from one of the two cells is placed back-to-back with a separator from the other cell. These two separators together form a bipolar separator, also called a bipolar plate. A cooling compartment, through which a cooling fluid such as glycol water circulates, is generally provided between the two separators of the bipolar separator.

[0005] Dihydrogen, air, and coolant are referred to as "operating fluids," which are supplied to the fuel cell during its operation. Dihydrogen and air are reactants, while the coolant does not participate in the electrochemical reaction. Depending on the operating phases of the fuel cell, the supply of one or more of the operating fluids is continuous, intermittent, or even interrupted.

[0006] The fuel cell provides openings to supply fluids to each of the reactive compartments and to the fluids between two adjacent cells. In a widely used design, each bipolar separator supplies, on one side, the fuel to the cell adjacent to that side and, on the other side, the oxidant to the cell adjacent to that other side, the supplies provided by the bipolar separators being in parallel.

[0007] Generally, in a single cell, the cathode compartment is supplied with an oxidant, for example oxygen, most often in the form of an oxygen-containing air supply, and the anode compartment is supplied with a fuel, for example dihydrogen. When the stack is formed, the cathode compartments of the single cells communicate with each other, step by step, forming a cathode circuit of the stack. Similarly, the anode compartments of the single cells communicate with each other, step by step, forming an anode circuit of the stack.During the operation of the fuel cell, the anodic circuit of the stack is supplied with hydrogen by an anodic supply circuit of the fuel cell, while the cathodic circuit of the stack is supplied with air - and therefore oxygen - by a cathodic supply circuit of the fuel cell, and the stack is supplied with cooling fluid by a cooling circuit.

[0008] Each reactive compartment also generally includes a gas diffusion layer, located between the bipolar separator and the catalytic layer, allowing good circulation of the fuel or oxidizer from the separator to the catalytic layer.

[0009] When the fuel cell is operating, the electrochemical reaction creates an electrical potential difference between the two separators of each unit cell. The fuel cell therefore includes an electrical isolation device, designed to prevent any electrical contact between two adjacent bipolar separators and between each cell and the external environment, as well as a sealing device to prevent leaks of the operating fluids, in particular to prevent the fluid circulating in one reactive compartment from contaminating an adjacent reactive compartment.

[0010] The electrical potential difference between the two separators of each unit cell creates a voltage across the terminals of each unit cell, designated as the "cell voltage". All the cells of the fuel cell are electrically connected together in series, so that the voltage delivered across the terminals of the stack is equal to the sum of the cell voltages of all the unit cells.

[0011] The stack is housed in a casing, which is generally sealed and in which several openings are provided, intended for supplying the stack with operating fluids, for electrical connections, for connections to sensors, etc. During the operation of the fuel cell, hydrogen may leak from the stack and accumulate in the casing around the stack, which leads to a risk of explosion.

[0012] In particular, when the fuel cell is completely shut down and depolarized, the anodic feed circuit is closed, and gases other than hydrogen, notably air containing oxygen, nitrogen, etc., tend to enter the anodic circuit of the stack. When the fuel cell is restarted, the anodic feed circuit is reopened, along with the opening of the anodic purge solenoid valve, so as to purge the anodic circuit until it contains essentially only hydrogen. During this step, the cathodic feed circuit is kept closed, preventing the fuel cell from repolarizing. The hydrogen circulates in the stack without being consumed by an electrochemical reaction, and possible micro-leaks may occur, releasing hydrogen into the casing.

[0013] To prevent the accumulation of hydrogen within the casing, which could lead to a risk of explosion, it is known to ventilate the casing, around the stack, with ventilation air. Furthermore, due to the thermal cycles of the fuel cell, the humidity contained in the air of the casing sometimes condenses, forming liquid water, which can impair the proper functioning of the cell. It is therefore necessary to remove the humidity from the casing.

[0014] US20220190362 describes, for example, a fuel cell comprising an inlet Ventilation and a ventilation outlet are arranged at the top of the case to facilitate the removal of any hydrogen that may be present inside. However, this document remains silent on the issue of moisture removal.

[0015] It is these problems that the invention intends to remedy in particular, by proposing a fuel cell comprising an improved ventilation circuit.

[0016] To this end, the invention relates to a fuel cell, comprising: - several unit cells, which are stacked along a main axis to form a cell stack, - a casing, which provides an internal space for the stack, and which includes: • a sleeve, which has a substantially cylindrical shape extending parallel to the main axis and which includes two end openings, • a first cover and a second cover, different from the first cover, the two covers sealing the two openings in the sleeve and, together with the sleeve, defining the internal compartment of the housing,

[0017] in which: - when the fuel cell is in a usage configuration: • the main axis is approximately horizontal, • The case has a top side and a bottom side, - the first cover includes a main ventilation inlet, by which of the ventilation air is introduced into the internal housing, the main inlet opening, in the internal housing, at the highest point of the first cover, - the second cover includes a first main ventilation outlet, through which the ventilation air introduced into the internal housing is evacuated, the first main outlet opening, in the internal housing, at a highest point of the second cover, so that the ventilation air introduced through the main inlet exits through the first main outlet, sweeping through a high part of the internal housing, carrying away fluids lighter than air, notably hydrogen, - the second cover also includes a second main outlet, which opens, in the internal housing, at a lowest point of the second cover, so that the ventilation air introduced through the main inlet tends to carry away fluids heavier than air, in particular water.

[0018] Thanks to the invention, the second main ventilation outlet is located at the lowest point of the housing, which facilitates the drainage of any liquid water that may be present and which tends to accumulate by gravity in the lower part of the housing's internal compartment. Simultaneously, the first main inlet and the first main outlet are each located in the upper part of the housing, where hydrogen, being lighter than air, tends to accumulate. The overall ventilation efficiency of the housing is thus improved.

[0019] According to advantageous but not mandatory aspects of the invention, such a fuel cell may incorporate one or more of the following features taken individually or in any technically permissible combination: - The fuel cell also includes a switching unit, which is integral to the casing and is configured to open or close a power circuit of the stack, - The switching unit includes an enclosure, which provides an internal volume and includes: • a first side and a second side, which is opposite the first side and which is oriented towards the first lid, • a top side and a bottom side, which are different from the first and second sides, the top side and the top side of the switching unit being respectively located on the same side as the top and bottom sides of the casing when the fuel cell is in operating configuration, The switching unit includes: an auxiliary ventilation inlet, which is located on the first side and through which ventilation air is introduced into an internal volume of the switching unit; a first auxiliary ventilation outlet, which is located on the second side and through which the ventilation air introduced by the auxiliary inlet is discharged; the auxiliary inlet and the first auxiliary outlet each open onto a respective high point of the internal volume and are configured so that when ventilation air is introduced by the auxiliary inlet and exits by the first auxiliary outlet, the ventilation air carries away fluids lighter than air contained in the internal volume, including hydrogen; the first auxiliary outlet is connected to the first main inlet, so that the ventilation air used for the enclosure is first used as ventilation air for the switching unit. The switching unit includes a second auxiliary outlet, which is located on the second side of the switching unit and opens into the internal volume through a lowest point of the internal volume, so that when ventilation air is introduced through the auxiliary inlet, the ventilation air exiting through the second auxiliary outlet tends to carry fluids heavier than air, including water. The first terminal plate includes, besides the main inlet, a second main inlet, which opens into the internal housing through a lowest point. The second auxiliary outlet is connected to the second main inlet.The fuel cell includes an air supply circuit, which is configured to supply air to a cathode circuit of the stack, the supply circuit comprising: a compressor, configured to compress air, an inlet line, which connects the compressor to an inlet of the cathode circuit, and an outlet line, which connects to an outlet of the cathode circuit of the stack, an exhaust, configured to allow air exiting the cathode circuit and passing through the outlet line to escape to the outside environment, a first isolation valve, which is configured to close the inlet line and which is arranged between the compressor and the stack, a second isolation valve, which is configured to close the outlet line and which is arranged between the stack and the exhaust. • a humidifier, which includes a regulating portion, which is traversed by the inlet pipe, which is located between the first isolation valve and the stack and which is configured to regulate a humidity level in the air passing through the inlet pipe, and a recovery portion, which is traversed by the outlet pipe, which is located between the second isolation valve and the stack and which is configured to recover humidity from the air passing through the outlet pipe,

[0020] wherein the fuel cell also comprises: - a bypass circuit, which includes an inlet, through which the bypass circuit is connected to the inlet pipe, and an outlet, through which the bypass circuit is configured to supply the housing with ventilation air, the inlet of the bypass circuit being connected to the inlet pipe between the compressor and the first isolation valve, - a calibrated orifice, which is arranged on the bypass circuit, the calibrated orifice having a reduced passage cross-section compared to the rest of the bypass circuit and being configured to limit an airflow through the bypass circuit. - The fuel cell also includes: • a cooling circuit, configured to supply the stack of unit cells with a cooling fluid, for example glycol water, and • a heat exchanger, configured to exchange thermal energy between the air passing through the inlet pipe and the cooling fluid, the heat exchanger being located, along the inlet pipe, between the compressor and the inlet of the bypass circuit. - The air supply circuit includes: • a pressure sensor, which is arranged between the heat exchanger and the humidifier and which is configured to measure pressure at the inlet of the bypass circuit, • a bypass valve, which is arranged between the inlet of the bypass circuit and the exhaust, the bypass valve being configured to regulate an air pressure at the inlet of the bypass circuit, so as to regulate an airflow through the calibrated orifice.

[0021] According to another aspect, the invention also relates to a method for controlling a fuel cell as defined above, in which: - a compressor power is adjusted, - Next, we measure the pressure in the inlet of the bypass circuit using a pressure sensor, - then, depending on the measured pressure, an opening of the bypass valve is adjusted in order to regulate the pressure in the inlet of the bypass circuit and to regulate the airflow through the calibrated orifice, the adjustment of the bypass valve opening being chosen using a law, previously recorded in a fuel cell computer, which relates the airflow through the calibrated orifice and a pressure differential on either side of the calibrated orifice.

[0022] According to advantageous but not mandatory aspects of the invention, such a piloting method may incorporate one or more of the following features taken individually or in any technically permissible combination: - with the fuel cell initially at rest, the first isolation valve and the second isolation valve are closed, so as to isolate the cathode circuit, - Next, the compressor power is adjusted to a maximum operating value, while the bypass valve is closed, in order to maximize the airflow through the bypass circuit, - then, hydrogen is supplied to an anodic circuit of the stack, so as to purge the anodic circuit of gases other than hydrogen. - Initially, the fuel cell is in a production mode in which: • the compressor operates at a first non-zero power level, • The first isolation valve is fully open, • The bypass valve is completely closed. - then, we increase the compressor power to a second power level, higher than the first level, while the first isolation valve is partially closed, while keeping the bypass valve completely closed.

[0023] This control method induces the same advantages as those mentioned above with regard to the fuel cell of the invention.

[0024] The invention will be better understood, and other advantages thereof will become more apparent from the following description of several embodiments of a fuel cell and a control method, in accordance with its principle, given solely by way of example and with reference to the accompanying drawings, in which:

[0025] - [Fig. 1] [Fig. 1] schematically represents, on an inset a), a vehicle, in accordance with a first embodiment of the invention, the vehicle comprising a fuel cell, also according to the invention, on an insert b), a housing for the fuel cell of the insert a), and on an insert c), a stack of the fuel cell fuel of the insert a), the stack being received in the housing of the insert b);

[0026] - [Fig.2] [Fig.2] is a schematic representation of the fuel cell of the [Fig. 1], and

[0027] - [Fig.3] [Fig.3] is a figure analogous to [Fig.2], representing a stack with fuel according to a second embodiment of the invention.

[0028] A vehicle 10 is shown in [Fig. 1]. Vehicle 10 is here a road vehicle, such as a car, truck, or forklift. Alternatively, vehicle 10 is a railway vehicle such as a train or subway, or even an aircraft or ship.

[0029] The vehicle 10 here comprises wheels 12, through which the vehicle 10 rests on a ground 14. The ground 14 is assumed to be substantially horizontal, the following description being given in relation to the orientation of the various elements of the vehicle 10 as represented in the figures, knowing that it may be otherwise in reality.

[0030] The vehicle 10 includes a fuel cell 20. The fuel cell 20, also referred to simply as fuel cell 20 in this description, moves with the vehicle 10 and is a fuel cell mounted on the vehicle's chassis, referred to as an "on-board" fuel cell, as opposed to stationary fuel cells, which are fixed, placed on the ground or in a building. The fuel cell 20 is powered by fuel, in this case hydrogen, which reacts with oxygen from the air to generate electricity for the operation of the vehicle 10, with some of the fuel's energy being dissipated as heat. In particular, the vehicle 10 includes, for its movement, an electric motor, which is powered by the electrical energy generated by the fuel cell 20. The electric motor is not shown.

[0031] With reference to [Fig. 1 a), the fuel cell 20 comprises a casing 22, also called a housing, the casing 22 comprising a sleeve 24. The sleeve 24 has the shape of a hollow cylinder, extending along a principal axis A20 and having a substantially rectangular cross-section. The sleeve 24 provides an internal compartment V24 with two opposing end openings, the end openings being sealed respectively by two covers 26A and 26B. The two covers 26A and 26B and the sleeve 24 thus define the internal compartment V24, which is also, by extension, an internal compartment of the casing 22. The covers 26A and 26B each extend along planes orthogonal to the principal axis A20. The sleeve 24 and the covers 26A and 26B are preferably made of electrically insulating material, such as a polymer material, possibly fiber-reinforced.Alternatively, covers 26A and 26B are coated, at least on one inner face, with an electrically insulating material.

[0032] Fluidic conduits 28 are provided through the housing 22 to allow the Passage of operating fluids for the fuel cell 20. The operating fluids here comprise three fluids: two gaseous fluids, in this case air (containing oxygen) and hydrogen, and a dielectric heat transfer fluid, for example, a liquid (in this case, glycol water). The fluid passages are formed by fluid connections, which are located here on cover 26A, situated on the right of [Fig. 1] b). Alternatively, all or part of the fluid connections are located on cover 26B. Alternatively, all or part of the fluid connections are located on the casing 24.

[0033] In the illustrated example, the stack 20 comprises three pairs of fluid connections 28, each pair being intended for the circulation of a specific operating fluid. The three pairs of fluid connections 28 include a first pair of connections 28A, a second pair of connections 28B, and a third pair of connections 28C. For each pair of connections, one of the connections, referred to as the "inlet connection," is intended for the intake of the corresponding operating fluid, while the other connection, referred to as the "outlet connection," is intended for the extraction of the corresponding operating fluid. In the figures, the direction of flow of the operating fluids is schematically represented by arbitrarily oriented arrows, although this may be different in reality. The size and arrangement of the fluid connections 28 are not limiting.

[0034] The stack 30 of the fuel cell 20 is shown schematically in partially exploded perspective in inset c) of [Fig.1].

[0035] The stack 30 is held between two end plates 31A and 31B, which are schematically represented in Figure 1a) and Figures 2 and 3. The end plates 31A and 31B make it possible in particular to hold the stack 30 in the housing 22, and to supply the stack 30 with fuel, in the example of dihydrogen in gaseous form, and with oxidizer, in the example of air in gaseous form, and, where applicable, the circulation of a heat transfer fluid for a cooling circuit.

[0036] The invention will be described more particularly in the context of a common construction in which the stack 30 is formed of several unit cells 32, each comprising a membrane-electrode assembly 34 and two bipolar plates 36, arranged on either side of the membrane-electrode assembly 34. The membrane-electrode assembly 36 is also referred to as MEA 36 in the context of this description. However, the invention is also applicable in the context of fuel cells of another type, in particular of the solid electrolyte ion-exchange membrane type. The membrane-electrode assemblies 34 and the bipolar plates 36 are each substantially planar and are stacked along a stacking axis A30, which is considered to coincide with the main axis A20 when The stack of 30 is received in the case of 24.

[0037] When the fuel cell 20 is mounted in the vehicle 10, in a normal operating configuration, the cell 20 is stationary relative to the vehicle 10. Thus, the main axis A20 is considered to be substantially horizontal, while the casing 22 has an upper side 21A and a lower side 21B, which is opposite the upper side 21A and which is located between the upper side 21A and the ground 14. In the illustrated example, the covers 26A and 26B are considered to extend along substantially vertical planes.

[0038] It is assumed that, for a given fuel cell 20, all the unit cells 32, also simply called cells 32, are identical to each other, and therefore have identical characteristics. In practice, each bipolar plate 36 is positioned between two consecutive cells 32 and is common to both of these consecutive cells 32. Each bipolar plate 36 comprises a first face 16A, called the anode face, which supplies one of the two cells 32 with dihydrogen, and a second face 16B, which is opposite the first face 16A and is called the cathode face, which supplies the other of the two cells 32 with air. In other words, a cell 32 is supplied with dihydrogen by a first bipolar plate 36 and with air by a second bipolar plate. Since air contains oxygen, the cell 32 is thus supplied with oxygen.

[0039] In the following description, the terms oxygen and dioxygen, as well as hydrogen and dihydrogen, are used interchangeably.

[0040] In the example, each bipolar plate 36 is formed by the assembly of two half-plates, which form channels for the circulation of the heat transfer fluid. The circulation of this heat transfer fluid plays no role in the electrochemical reactions of the fuel cell 10, but it does allow for the control of the temperature of the cells 32. In normal operation of the fuel cell 20, the fuel cell 20 generates electricity while releasing heat, which is dissipated by circulating the heat transfer fluid. The heat transfer fluid then acts as a coolant. In certain specific phases, particularly during a cold start of the fuel cell, the heat transfer fluid is used to heat the fuel cell.However, through common usage, the heat transfer fluid is generally called "cooling fluid", and the circuit in which the heat transfer fluid circulates is called the "cooling circuit", the term "cooling" not implying any particular function.

[0041] In each cell 32, a distinction is made between an anodic compartment, formed between the bipolar plate 36 supplying the cell with dihydrogen and the membrane 34, and a cathodic compartment, formed between the bipolar plate 36 supplying the cell with air and the membrane. Generally, in each unit cell 32, the cathodic compartment is supplied with an oxidant, for example oxygen, here in the form of The stack 30 is supplied with oxygen-containing air, and the anodic compartment is supplied with fuel, for example, dihydrogen. When the stack 30 is formed, the cathodic compartments of the unit cells 32 communicate with each other, step by step, forming a cathodic circuit 38A of the stack. Similarly, the anodic compartments of the unit cells communicate with each other, step by step, forming an anodic circuit 38B of the stack. Likewise, the cooling compartments of the unit cells 32 communicate with each other, step by step, forming a cooling circuit 38C of the stack 30.

[0042] During the operation of the fuel cell, the cathode circuit 38A of the stack 30 is supplied with air—and therefore with oxygen—by a cathode supply circuit 40 of the stack 20, while the anode circuit 38B of the stack 30 is supplied with hydrogen by an anode supply circuit 50 of the stack 20, and the cooling circuit 38C of the stack 30 is supplied with cooling fluid by a cooling supply circuit 60 of the stack. The cathode supply circuit 40, the anode supply circuit 50, and the cooling circuit 60 are partially shown in [Fig. 2].

[0043] The cathode 38A, anodic 38B, and cooling 38C circuits are located within the stack 30, which is housed in the casing 24, and are collectively referred to as the internal circuits 38 of the fuel cell 20. In contrast, the cathodic feed 40, anodic 50, and cooling 60 circuits are external circuits of the fuel cell 20. Each internal circuit 38 is associated with one of the pairs of fluid connections 28A, 28B, or 28C, through which this internal circuit 30 is connected to the corresponding external circuit. The cathodic feed 40 is also called the "air supply circuit," or simply the "air circuit."Similarly, the anodic supply circuit 50 is also called the "hydrogen supply circuit" 50, or simply the "hydrogen circuit" 50, while the cooling supply circuit 60 is also called the "external cooling circuit" 60, as opposed to the cooling circuit 38C which is internal to the stack 30.

[0044] The cathode ray feed circuit 40 is now described.

[0045] The cathode supply circuit 40, also called the air supply circuit or simply the air circuit, is configured to supply air to the cathode circuit 38A of the stack 30 of unit cells 32. The air supply circuit 40 includes an air inlet 402, through which fresh air is supplied.

[0046] The air circuit 40 also includes a compressor 404, which is configured to compress the air supplied by the air inlet 402. The air circuit 40 also includes an inlet line 406, which connects the compressor 404 to an inlet of the cathode ray circuit 38A of the stack 30. The air circuit 40 also includes a line outlet 408, which connects to an outlet of the cathode circuit 38A of the stack 30. The air circuit 40 also includes an exhaust 410, configured to allow air to escape to the outside environment, the air exiting the cathode circuit 38A and passing through the outlet duct 408. In normal operation of the fuel cell 20, fresh air enters the cathode circuit 38A through the inlet duct 406, the oxygen contained in this fresh air is combined with protons during the electrochemical reaction occurring in each of the unit cells 32, producing water, and the oxygen-depleted and water-enriched air exits the cathode circuit 38A through the exhaust 410.

[0047] The air circuit 40 also includes a first isolation valve 412, which is configured to close off the inlet line 406 and is arranged between the compressor 404 and the stack, more precisely between the compressor 404 and the inlet of the cathode circuit 38A. Preferably, the first isolation valve 412 is a proportional valve, which allows the inlet line 406 to be completely or partially closed. Generally, a valve that is "closed" does not allow any fluid to pass through. A valve that is not closed is an open valve, that is, one that allows fluid to pass through it, whether the valve is "partially open" or "fully open." By extension, a "partially open" valve is therefore also "partially closed."

[0048] The air circuit 40 also includes a second isolation valve 414, which is configured to close off the outlet line 410 and which is arranged between the stack 30 and the exhaust 410, more precisely between the outlet of the cathode circuit 38A and the exhaust 410. Preferably, the second isolation valve 414 is a proportional valve, which allows the outlet line 408 to be completely or partially closed.

[0049] The air circuit includes a first pressure sensor 415, which is arranged here at the inlet of the cathode circuit 38A, between the first isolation valve 412 and the stack 30. The first pressure sensor 415 is configured to measure an air pressure at the inlet of the cathode circuit 38A.

[0050] The air circuit 40 advantageously includes a humidifier 420, which comprises: - a regulating portion 422, which is traversed by the inlet pipe 408, which is located between the first isolation valve 412 and the stack 30, more precisely between the first isolation valve 412 and the inlet of the cathode circuit 38A, and which is configured to regulate a humidity level in the air passing through the inlet pipe 408, and - a recovery section 424, which is crossed by the outlet pipe 410, which is located between the second isolation valve 414 and the stack 30, more precisely between the second isolation valve 414 and the outlet of the cathode circuit 38A, and which is configured to recover moisture from the air passing through the outlet pipe 410.

[0051] In simplified terms, the humidifier recovers all or part of the moisture transported by the air exiting the cathode duct 38A, and regulates the humidity of the air entering the cathode circuit 3 8A.

[0052] The air circuit 40 advantageously includes a bypass circuit 416, which connects the outlet of the cathode circuit 38A to the outlet line 410, without passing through the recovery portion 424. The bypass circuit 416 allows bypassing the humidifier 420, for example, when it is not necessary to recover moisture from the air exiting the cathode circuit 38A. The bypass circuit 416 is connected to the outlet line 410 by a junction point 417, which is located between the second isolation valve 414 and the exhaust 410, downstream of the second isolation valve 414. Throughout this description, the terms "upstream" and "downstream" are used in relation to the normal flow direction of the fluids, liquid or gaseous, during the normal operation of the fuel cell. The air circuit 40 also includes a third isolation valve 418, which is located on the bypass circuit 416.Preferably, the third isolation valve 418 is a proportional valve, which allows the bypass circuit 416 to be completely or partially closed. It is understood that the coordinated control of the second and third isolation valves 414 and 418 allows all or part of the airflow exiting the cathode circuit 38A to pass through the bypass circuit 416 or through the recovery portion 424, according to the needs for recovering the humidity contained in the air exiting the cathode circuit 38A.

[0053] The hydrogen supply circuit 50 is shown in part. The hydrogen circuit 50 includes an anodic inlet line 52, which is connected to the inlet of the anodic circuit 38B and through which a flow of hydrogen is introduced into the stack 30. The hydrogen circuit 50 includes an anodic outlet line 54, which connects an outlet of the anodic circuit 38B to the exhaust 410. The unconsumed hydrogen in the stack 30 is thus diluted, in the exhaust 410, with the air exiting the outlet line 408, before being discharged into the external environment.

[0054] When the fuel cell 20 is supplied with both hydrogen and air to produce electricity, the fuel cell 20 is in a so-called "production" mode of operation, or simply "in production." In the illustrated example, when the fuel cell 20 is in production mode, the amount of electricity generated by the fuel cell 20 is regulated by the impedance applied to its terminals. The amount of hydrogen injected by the hydrogen circuit 50 into the anode circuit 38B is directly induced by the consumption of the molecules In the stack at iso-anodic pressure, the oxygen from the air injected by the air circuit 40 is injected in a superstoichiometric manner with active control, i.e., in excess, so as never to run out. For example, the amount of oxygen injected into the cathodic circuit 38A is approximately double the amount required for the electrochemical reaction with the hydrogen injected into the anodic circuit 38B.

[0055] According to examples of fuel cell control 20, in production mode, the compressor 404 power is adjusted to a nominal production value so as to inject fresh air into the inlet line 406 at a nominal production flow rate, while the first isolation valve 412 is left open, preferably fully open, and the second and third isolation valves 414 and 418 are controlled in a coordinated manner so as to control the air pressure within the cathode circuit 38A. The air pressure within the cathode circuit 38A is measured by means of the first pressure sensor 415. The second and third isolation valves 414 and 418, taken together, are outlet valves 414 and 418 of the cathode circuit 38A, which allow the air pressure in the cathode circuit 38A to be regulated.

[0056] The external cooling circuit 60 is configured to supply the stack 30 of cells 32 with a cooling fluid, for example, glycol water. The external cooling circuit 60 generally includes a pump, intended to circulate the cooling fluid in the cooling circuit, and at least one radiator, intended to dissipate into the external environment the heat absorbed by the cooling fluid as it passes through the cooling circuit 38C. The pump and radiator of the external cooling circuit 60 are not shown. Depending on the case, the pump and radiator are not exclusively part of the cooling circuit, but are common components of the vehicle 10. This aspect is not described in further detail.

[0057] In the illustrated example, the air circuit 40 advantageously includes a heat exchanger 428, also simply called exchanger 428, which is configured to exchange thermal energy between the air passing through the inlet pipe 406 and the cooling fluid, the heat exchanger 428 being located, along the inlet pipe 406, between the compressor 404 and the first isolation valve 412.

[0058] According to one aspect of the invention, the air from the supply circuit 40 is used to ventilate the interior of the casing 22. The fuel cell 20 thus includes a bypass circuit 430, which comprises an inlet 432, through which the bypass circuit 430 is connected to the inlet line 406, and an outlet 434, through which the bypass circuit 430 is configured to supply the casing 22 with ventilation air. The inlet 432 of the bypass circuit 430 is located between the compressor 404 and the first isolation valve 412. In the illustrated example, the inlet 432 of the bypass circuit 430 is connected to the air circuit 40 between the heat exchanger 428 and the first isolation valve 412.

[0059] The fuel cell 20 also includes a calibrated orifice 436, which is arranged on the bypass circuit 430, the calibrated orifice 436 having a reduced passage area compared to the rest of the bypass circuit 430 and being configured to limit an airflow through the bypass circuit 430.

[0060] The fuel cell 20 also includes a second pressure sensor 438, which is configured to measure an air pressure at the inlet of the bypass circuit 430. The second pressure sensor 438 is arranged here on the inlet line 406, between the first isolation valve 412 and the heat exchanger 428.

[0061] According to another aspect of the invention, a first cover among the two covers 26A and 26B, here cover 26B, comprises a main ventilation inlet 440 102, through which ventilation air is introduced into the internal housing V24, the main inlet 440 opening, in the internal housing V24, at a highest point of the first cover 26B. With reference to [Fig. 2], the outlet 434 of the bypass duct 430 is connected to the main ventilation inlet 440, the outlet 434 of the bypass duct 430 being coincident with the main ventilation inlet 440.

[0062] A second cover, one of the two covers 26A and 26B, here cover 26A, includes a first main ventilation outlet 442, through which the ventilation air introduced into the internal housing V24 by the main inlet 440 is discharged. The first main outlet 442 is connected to the exhaust 410 via a first discharge pipe 443. The first main outlet 442 is thus located on a cover opposite the cover on which the main inlet 440 is provided.

[0063] The first main outlet 442 opens into the internal housing V24 at the highest point of the second cover 26A, so that the ventilation air introduced through the first main inlet 440 exits through the first main outlet 442, sweeping across the upper part of the internal housing V24 and carrying away any fluids lighter than air that may be present in the internal housing V24. In particular, any hydrogen leaks tend to accumulate in the upper part of the internal housing V24 and are thus carried away by the ventilation air.

[0064] The second cover 26A also includes a second main outlet 444, which opens into the internal housing V24 at the lowest point of the second cover 26A, so that the ventilation air introduced through the first main inlet 440 tends to carry away any fluids heavier than air that may be present in the internal housing V24, particularly water. The second main outlet 444 is connected to the exhaust 410 via a second conduit. evacuation 445.

[0065] The particular arrangement of the first main ventilation inlet 440, the first main ventilation outlet 442 and the second main ventilation outlet 444 allows efficient ventilation of the internal housing V24, contributing to the proper functioning and longevity of the fuel cell 20.

[0066] When ventilation air is introduced into the internal housing V24 through the first main inlet 440, all of this ventilation air eventually reaches the exhaust 410, passing, on the one hand, through the first main outlet 442 and then the first exhaust pipe 443 and, on the other hand, through the second main outlet 444 and then the second exhaust pipe 445.

[0067] In simplified terms, by application of Bernoulli's theorem, an airflow Q passing through the calibrated orifice 436 is proportional to the square root of a pressure differential AP across this calibrated orifice 436. In other words: Q = √(AP), where k is a constant depending on the geometry of the calibrated orifice, this constant taking into account pressure losses. Since the exhaust 410 is connected to the external environment, the pressure downstream of the calibrated orifice is close to atmospheric pressure and therefore relatively constant. As a result, to a first approximation, the flow rate through the calibrated orifice 436 is proportional to the square root of the pressure measured by the second sensor 438. Thus, the calibrated orifice 436 allows a portion of the airflow circulating in the air supply circuit 40 to be taken, and this taken air to be used for the ventilation of the housing 24.This avoids the need to install a complete ventilation circuit, including a second air intake, a second compressor in addition to compressor 404, etc. As a corollary, adjusting the inlet pressure of the bypass circuit 430 allows adjustment of the ventilation air flow circulating through the calibrated orifice 436.

[0068] One way to adjust the inlet pressure of the bypass circuit 430 is to adjust the power of the compressor 404 and the opening of the first isolation valve 412. Advantageously, the fuel cell also includes a bypass valve 450, which is arranged between the inlet 432 of the bypass circuit 430 and the exhaust 410, the bypass valve 450 being configured to regulate an air pressure at the inlet of the bypass circuit 430, so as to regulate an air flow through the calibrated orifice 436. The bypass valve 450 is preferably a propositional valve.

[0069] It is understood that when the bypass valve 450 is fully open, most of the air injected by the compressor 404 into the inlet line 406 tends to pass directly to the exhaust 410. When the bypass valve is fully closed, the air injected by the compressor 404 is shared between the bypass circuit and the cathode circuit 38A - if of course the first isolation valve 412 is not closed, and if the second and third isolation valves 414 and 418 are not both closed When the bypass valve 450 is partially open - or partially closed, which is equivalent -, the airflow injected into the air circuit 406 by the compressor 404 is divided between a first portion which passes directly through the bypass valve 450 to the exhaust 410, a second portion which passes through the calibrated orifice 436 and serves as ventilation air for the housing 22, and a possible third portion, depending on the opening of the first, second and third isolation valves 412, 414 and 418.

[0070] The fuel cell 20 includes a computer, which is configured to receive measurements from the first and second pressure sensors 415 and 138, to adjust the power of the compressor 404, and to adjust a total or partial closing or opening of each of the isolation valves 412, 414 and 418 and the bypass valve 450. The computer is not shown.

[0071] The invention also relates to a method for controlling the fuel cell 20. In general, the fuel cell control process 20 comprises the following steps: - we adjust the compressor power to 404, - Next, a pressure is measured in the inlet 432 of the bypass circuit 430, here using the second pressure sensor 438, - then, depending on the pressure measured in the inlet 432 of the bypass circuit 430, an opening of the bypass valve 450 is adjusted, so as to regulate the pressure in the inlet 432 of the bypass circuit 430 and to regulate the airflow through the calibrated orifice 436.

[0072] The opening of the bypass valve 450 is adjusted using a pre-programmed law that relates the airflow through the calibrated orifice 436 to a pressure differential AP across the calibrated orifice 436. A first example of a pre-programmed law is the law derived from Bernoulli's theorem, described previously. According to another alternative example, a multidimensional chart is pre-programmed into the computer, the chart relating, in particular, the pressures measured by the first and second pressure sensors 415 and 438 to the opening positions of the isolation valves and the bypass valve 450.

[0073] According to a first specific example of a control method, the fuel cell 20 is considered to be initially in production mode, in a stabilized regime. Thus, the compressor 404 operates at a given, non-zero power level, called the first level; the first isolation valve 412 is fully open, while the second and third isolation valves 414 and 418 are each open to an appropriate level, in order to ensure sufficient air pressure in the cathode circuit 38A, and, on the other hand, to ensure the recovery of humidity at the desired level in the humidifier 420. The bypass valve 450 is in a closed position. If, for any reason, it becomes necessary to urgently increase the ventilation flow rate in the housing 22—for example, if a hydrogen sensor detects an increase in the hydrogen concentration in the housing 22—then the power of the compressor 404 is adjusted to a second level, higher than the first level, while the first isolation valve 412 is partially closed to prevent an increase in the airflow in the cathode circuit 38A, while keeping the bypass valve 450 fully closed. This forces an increase in pressure at the inlet of the bypass circuit 430, which in turn increases the airflow through the bypass circuit 430.

[0074] As an alternative to this first particular example, when it is necessary to increase the ventilation flow rate in the housing 22, then the power of the compressor 404 is adjusted to a power higher than the first level, preferably to a maximum power, while the first isolation valve 412 is partially closed so as to prevent an increase in the air flow rate in the cathode circuit 38A, and the bypass valve 450 is partially opened, so as to regulate the air pressure at the inlet of the bypass circuit 430. The air flow rate through the calibrated orifice 436 is thus regulated.

[0075] According to another specific example of a control method, the fuel cell 20 is initially stopped, the first isolation valve 412 and the second isolation valve 414 are closed, so as to isolate the cathode circuit 38A. When the bypass circuit 416 is present, the third isolation valve 418 is also closed. The hydrogen supply circuit 50 is also closed. The bypass valve 450 is normally open at rest. Next, the power of the compressor 404 is adjusted to a maximum operating value, maximizing exhaust ventilation, while the three isolation valves 412, 414 and 418 are kept closed, and the bypass valve 450 is closed, so as to maximize the airflow injected into the bypass circuit 430. Then, hydrogen is supplied to the anodic circuit 38B of the stack 30, so as to purge the anodic circuit 38B of gases other than hydrogen.The ventilation airflow through the housing 22 is thus maximized, reducing the risks associated with potential hydrogen leaks. If the amount of air injected into the bypass circuit 430 is too high, simply open the bypass valve 450 to the desired level to lower the pressure at the inlet of the bypass circuit 430. Alternatively, or in addition, it is also possible to reduce the power of the compressor 404.

[0076] A 20' fuel cell, according to a second embodiment of the invention, is shown in [Fig. 3]. In the second embodiment, The elements analogous to those of the first embodiment bear the same reference numerals and function in the same way. The following primarily describes the differences between the first and second embodiments of the invention.

[0077] One of the main differences between the second embodiment and the first is that the fuel cell 20' of the second embodiment includes a switching unit 80. The switching unit 80, also called an HVSU (High Voltage Switch Unit), is electrically connected to the stack 30 through the housing 22, for example through the first cover 26B, and is electrically arranged in series between the stack 30 and the rest of the fuel cell 20'. The electrical connections are not shown. In particular, the switching unit 80 is generally electrically arranged in series between the stack 30 and a DC / DC converter. The converter is not shown.

[0078] The switching unit 80 is configured to open or close a power circuit of the stack 30, so as to electrically isolate the stack 30 from the rest of the fuel cell 20'. The switching unit 80 is integral with the housing 22, generally attached to the first cover 26B. In the illustrated example, the switching unit 80 is also connected to the external cooling circuit 60, so as to regulate the temperature of the switching unit 80.

[0079] The switching unit 80 comprises an enclosure 82, which provides an internal volume V82 and which includes a first side 84A and a second side 84B, which is opposite the first side 84A and which is oriented towards the first cover 26B. The enclosure 82 also includes an upper side 86A and a lower side 86B, which are different from the first and second sides 84A and 84B, the upper side 86A and the lower side 86B of the switching unit 80 being respectively located on the same side as the upper sides 21A and lower sides 21B of the housing 22. When the switching unit 80 is attached to the first cover 26B, the internal volume V82 communicates with the internal housing V24, and hydrogen, resulting from leaks from the stack 30 and located in the internal housing V24, may also end up in the internal volume V82. The internal volume V82 must therefore be ventilated to remove this hydrogen.

[0080] For this purpose, the switching unit 80 comprises: - a first auxiliary ventilation inlet 88, which is located on the first side 84A of the enclosure 82 and through which ventilation air is introduced into the internal volume V82 of the switching unit 80, - a first auxiliary ventilation outlet 90, which is located on the second side 84B of the envelope 82 and through which the ventilation air introduced by the first auxiliary inlet 88 is evacuated.

[0081] The first auxiliary output 90 is connected to the first main input 434, so that the ventilation air used for the housing 22 is previously used as ventilation air for the switching unit 80. In other words, the switching unit 80 is interposed, on the branch circuit 430, between the calibrated orifice 436 and the first main inlet 434 of the housing 22.

[0082] Advantageously, the first auxiliary inlet 88 and the first auxiliary outlet 90 each open onto a highest point of the internal volume V82 and are arranged so that, when ventilation air is introduced through the first auxiliary inlet 88 and exits through the first auxiliary outlet 90, the ventilation air carries away fluids lighter than air contained in the internal volume V82, in particular hydrogen.

[0083] It also happens that the humidity contained in the air condenses in the internal volume V82. This humidity and liquid water must also be removed. Advantageously, the switching unit 80 also includes a second auxiliary outlet 92, which is located on the same side as the first auxiliary outlet 90 and which opens into the internal volume V82 at its lowest point, so that the ventilation air introduced through the first auxiliary inlet 88 tends to carry away fluids heavier than air, particularly water. The first terminal plate 26B includes a second main inlet 446, which opens into the internal housing V24 at its lowest point, the second auxiliary outlet 92 being connected to the second main inlet 446.

[0084] Advantageously, when the vehicle 10 is located on a horizontal ground 14, the second auxiliary outlet 92 is located at least as high as the second main inlet 446, so as to promote the gravity flow of liquid water.

[0085] According to an alternative aspect of the invention, the method for controlling the fuel cell 20 / 20' can be implemented even if the air circuit does not open into the upper part of the internal housing V24 of the casing 24 or into the upper part of the internal volume V82 of the switching unit 80. In particular, the control method can be implemented as soon as the bypass circuit 430 includes a calibrated orifice 436 and, where applicable, the bypass valve 450 is installed between the inlet 406 and outlet 408 lines, allowing the air pressure in the inlet of the bypass circuit 430 to be regulated.The control method can be implemented independently of the fuel cell's orientation in the operating configuration, in particular when the main axis A30 is not horizontal, and / or the top or bottom sides of the casing are not fixed, and / or the ventilation inlets or outlets do not open at the highest or lowest points of the enclosures concerned.

[0086] Thus, according to an example of an alternative control method, the control method includes the following steps, during which: - a compressor power 404 is adjusted, - a pressure is measured in the inlet 432 of the bypass circuit 430 with the help of pressure sensor 438, - then, depending on the measured pressure, an opening of the bypass valve 450 is adjusted so as to regulate the pressure in the inlet of the bypass circuit 430 and to regulate the airflow through the calibrated orifice 436, the adjustment of the opening of the bypass valve 450 being chosen using a law, which is previously recorded in a computer of the fuel cell and which relates the airflow through the calibrated orifice and a pressure differential on either side of the calibrated orifice.

[0087] Advantageously: - with the fuel cell initially at rest, the first isolation valve 412 and the second isolation valve 414 are closed, so as to isolate the cathode circuit 3 8A, - next, the power of the compressor 404 is adjusted to a maximum operating value, while the bypass valve 450 is closed, in order to maximize the airflow through the bypass circuit 430, - then, hydrogen is supplied to an anodic circuit (38B) of the stack 30, so as to purge the anodic circuit (38B) of gases other than hydrogen.

[0088] Advantageously: - Initially, the fuel cell is in a production mode in which: • Compressor 404 operates at a first non-zero power level, • the first isolation valve 412 is fully open, and • The 450 bypass valve is completely closed, - then, the power of the compressor 404 is increased to a second power level, higher than the first level, while the first isolation valve 412 is partially closed, while keeping the bypass valve 450 completely closed.

[0089] The embodiments and variants mentioned above can be combined with each other to generate new embodiments of the invention.

Claims

Demands

1. Fuel cell (20; 20'), comprising: • several unit cells (32), which are stacked along a principal axis (A30) so as to form a stack (30) of cells, • a housing (22), which provides an internal compartment (V24) for receiving the stack (30), and which includes: • a sleeve (24), which has a substantially cylindrical shape extending parallel to the main axis (A30) and which includes two end openings, • a first cover (26B) and a second cover (26A), different from the first cover (26B), the two covers sealing the two openings of the sleeve (24) and delimiting, with the sleeve (24), the internal housing (V24) of the casing (22), in which: • when the fuel cell (20; 20') is in a usage configuration: • the main axis (A30) is approximately horizontal, • The case (22) has a top side and a bottom side, • the first cover (26B) includes a main ventilation inlet (434), through which ventilation air is introduced into the internal housing (V24), the main inlet (434) opening, in the internal housing (V24), at a highest point of the first cover (26B), • The second cover (26A) includes a first main ventilation outlet (442), through which the ventilation air introduced into the internal housing (V24) is discharged. The first main outlet (442) opens, within the internal housing (V24), at the highest point of the second cover (26A), so that the ventilation air introduced through the main inlet (434) exits through the first main outlet (442), sweeping across a high portion of the internal housing (V24). dragging fluids lighter than air, notably hydrogen, the second cover (26A) also includes a second main outlet (444), which opens, in the internal housing (V24), at a lowest point of the second cover (26A), so that the ventilation air introduced by the main inlet (434) tends to carry away fluids heavier than air, in particular water.

2. Fuel cell (20') according to claim 1, wherein: • The fuel cell also includes a switching unit (80), which is integral with the housing (22) and which is configured to open or close a power circuit of the stack (30), • The switching unit (80) includes an enclosure (82), which provides an internal volume (V82) and which includes: • a first side (84A) and a second side (84B), which is opposite the first side and which is oriented towards the first cover (26B), • an upper side (86A) and a lower side (86B), which are different from the first and second sides, the upper side (86A) and the upper side (86B) of the switching unit (80) being respectively located on the same side as the upper (21A) and lower (21B) sides of the housing (22) when the fuel cell (20') is in operating configuration, • The switching unit (80) comprises: • an auxiliary ventilation inlet (88), which is located on the first side (84A) and through which ventilation air is introduced into an internal volume (V82) of the switching unit, • a first auxiliary ventilation outlet (90), which is located on the second side (84B) and through which the ventilation air introduced by the auxiliary inlet (88) is discharged, • The auxiliary input (88) and the first auxiliary output (90) each terminate at a respective point at the top of the volume internal (V82) and are configured so that when ventilation air is introduced through the auxiliary inlet (88) and exits through the first auxiliary outlet (90), the ventilation air carries away fluids lighter than air contained in the internal volume (V88), including hydrogen, • the first auxiliary outlet (90) is connected to the first main inlet (434), so that the ventilation air used for the housing (22) is first used as ventilation air for the switching unit (80).

3. Fuel cell (20') according to claim 2, wherein: • the switching unit (80) includes a second auxiliary outlet (92), which is located on the second side (84B) of the switching unit (80) and which opens into the internal volume (C82) through a lowest point of the internal volume (V82), such that when ventilation air is introduced through the auxiliary inlet (88), the ventilation air exiting through the second auxiliary outlet (92) tends to carry away fluids heavier than air, in particular water, • the first terminal plate (26B) includes, in addition to the main inlet (434), a second main inlet (446), which opens into the internal housing (V24) through a lowest point, • the second auxiliary outlet (92) is connected to the second main inlet (446).

4. Fuel cell (20; 20') according to any one of claims 1 to 3, wherein the fuel cell comprises an air supply circuit (40), which is configured to supply air to a cathode circuit (38A) of the stack (30), the supply circuit comprising: • a compressor (404), configured to compress air, • an inlet line (406), which connects the compressor (404) to an inlet of the cathode circuit (38A), and an outlet line (408), which connects an outlet of the cathode circuit (38A) of the stack (30), • an exhaust (410), configured to allow air exiting the cathode circuit (38A) and passing through the outlet duct (408) to escape to the external environment, • a first isolation valve (412), which is configured to close off the inlet pipe (406) and which is arranged between the compressor (404) and the stack (30), • a second isolation valve (414), which is configured to close off the outlet pipe (408) and which is arranged between the stack (30) and the exhaust (410), • a humidifier (420), which includes: • a regulating portion (422) which is traversed by the inlet pipe (406), which is located between the first isolation valve (412) and the stack (30) and which is configured to regulate a humidity level in the air passing through the inlet pipe (406), • a recovery portion (422), which is traversed by the outlet pipe (408), which is located between the second isolation valve (414) and the stack (30) and which is configured to recover moisture from the air passing through the outlet pipe (408), and in which the fuel cell (20; 20') also includes: • a bypass circuit (430), which includes an inlet (432), through which the bypass circuit (430) is connected to the inlet line (406), and an outlet (440), through which the bypass circuit (430) is configured to supply the housing (22) with ventilation air, the inlet of the bypass circuit (430) being connected to the inlet line (406) between the compressor (404) and the first isolation valve (412), • a calibrated orifice (436), which is arranged on the bypass circuit (430), the calibrated orifice (436) having a reduced passage cross-section compared to the rest of the bypass circuit (430) and being configured to limit an airflow through the bypass circuit (430).

5. Fuel cell (20; 20') according to claim 4, wherein the fuel cell also comprises: • a cooling circuit (60), configured to supply the stack (30) of unit cells (32) with a cooling fluid, for example glycol water, • a heat exchanger (428), configured to exchange thermal energy between the air passing through the inlet pipe (406) and the cooling fluid, the heat exchanger (428) being located, along the inlet pipe (406), between the compressor (404) and the inlet (432) of the bypass circuit (430).

6. Fuel cell (20; 20') according to any one of claims 4 or 5, wherein: • the air supply circuit (40) comprises: • a pressure sensor (438), which is arranged between the heat exchanger and the humidifier (420) and which is configured to measure a pressure at the inlet of the bypass circuit (430), • a bypass valve (450), which is arranged between the inlet (432) of the bypass circuit (430) and the exhaust (410), the bypass valve (450) being configured to regulate an air pressure at the inlet of the bypass circuit (430), so as to regulate an airflow through the calibrated orifice (436).

7. A method for controlling a fuel cell (20; 20'), the fuel cell conforming to claim 6, wherein: • a compressor power (404) is adjusted, • then, a pressure is measured in the inlet (432) of the bypass circuit (430) using a pressure sensor (438), • then, depending on the measured pressure, an opening of the bypass valve (450) is adjusted so as to regulate the pressure in the inlet of the bypass circuit (430) and to regulate the airflow through the calibrated orifice (436), the adjustment of the opening of the bypass valve (450) being chosen using a law, previously recorded in a fuel cell computer, which relates the airflow through the calibrated orifice and a pressure differential on either side of the calibrated orifice.

8. A piloting method according to claim 7, wherein: • the fuel cell (20; 20') being initially stopped, the first isolation valve (412) and the second isolation valve (414) are closed, so as to isolate the cathode circuit (38A), • then, a compressor power (404) is adjusted to a maximum operating value, while the bypass valve (450) is closed, so as to maximize an airflow through the bypass circuit (430), • then, an anodic circuit (38B) of the stack (30) is supplied with hydrogen, so as to purge the anodic circuit (38B) of gases other than hydrogen.

9. A control method according to claim 7, wherein: • initially, the fuel cell (20; 20') is in a production mode, in which: • the compressor (404) operates at a first non-zero power level, • the first isolation valve (412) is fully open, • the bypass valve (450) is fully closed, • then, the power of the compressor (404) is increased to a second power level, higher than the first level, while the first isolation valve (412) is partially closed, while keeping the bypass valve (450) fully closed.

Images