Fuel cell durability optimization

Abstract

A method of controlling a hydrogen fuel cell includes, with a controller of the fuel cell: measuring an anode leakage rate of the fuel cell; modeling an effective electrolyte membrane orifice size using the measured anode leakage rate; calculating an effective runtime anode leak rate during operation of the fuel cell using the effective electrolyte membrane orifice size; using the active runtime anode leak rate as a low side metric when calculating emission and dilution requirements; and starting adjustment of a control strategy of the fuel cell based on the effective anode leakage rate during operation and the shutdown leakage rate so as to prolong the service life of the fuel cell.

Description

Technical Field

[0001] This invention relates generally to fuel cells, and more particularly to control systems for fuel cells. Background Technology

[0002] In some applications, fuel cells are designed as flow-through systems for both fuel and oxidant supply streams. However, these systems add parasitic loads to the fuel cell output, thereby reducing the net power that can be extracted. In other configurations, either the fuel or oxidant stream, or both, are "dead-ended." This dead-end operation causes problems such as water removal and impurity buildup. Furthermore, degradation of the electrolyte membrane separating the anode and cathode negatively impacts the fuel cell and typically indicates the end of its lifespan.

[0003] Therefore, there is a need for an improved fuel cell, fuel cell propulsion system, and method for controlling the fuel cell, wherein the operating parameters of the fuel cell are modified based on the effective leakage rate of the electrolyte membrane, thereby allowing for an extended fuel cell lifespan in the presence of leakage across the electrolyte membrane. Summary of the Invention

[0004] According to several aspects of this disclosure, a method for controlling a hydrogen fuel cell includes: using a controller of the fuel cell, measuring the anode leakage rate of the fuel cell, modeling the effective electrolyte membrane orifice size using the measured anode leakage rate, calculating the effective operating anode leakage rate during operation of the fuel cell using the effective electrolyte membrane orifice size based on current operating conditions, using the effective operating anode leakage rate as a low-side metric when calculating emission and dilution requirements, and initiating adjustments to the control strategy of the fuel cell based on the effective operating anode leakage rate or the shutdown leakage rate.

[0005] On the other hand, measuring the anode leakage rate of a fuel cell also includes measuring the anode shutdown leakage rate of the fuel cell.

[0006] According to another aspect, measuring the anode leakage rate of a fuel cell also includes: monitoring pressure decay within the anode during low-power operation of the fuel cell; and at least one of the following: estimating the anode leakage rate based on pressure decay within the anode during low-power operation of the fuel cell; and calculating the anode leakage rate based on both anode pressure changes and cathode pressure changes.

[0007] According to another aspect, the adjustment of the control strategy for starting the fuel cell based on the effective operating anode leakage rate or shutdown leakage rate also includes increasing the duration of the increased airflow through the cathode of the fuel cell during the start-up period of the fuel cell to dilute the concentration of hydrogen leaking from the anode, wherein the anode-to-cathode bias, airflow rate, airflow splitting and the duration of the increased airflow are calculated and adjusted based on the effective operating anode leakage rate or shutdown leakage rate.

[0008] According to another aspect, adjusting the control strategy for the fuel cell based on the effective operating anode leakage rate or shutdown leakage rate also includes adjusting the venting request frequency to discharge gas from the anode of the fuel cell during the operation of the fuel cell.

[0009] According to another perspective, adjustments to the control strategy for fuel cells based on the effective operating anode leakage rate or shutdown leakage rate also include increasing the gas flow through the cathode during fuel cell operation to compensate for the oxygen consumed by hydrogen permeating through the electrolyte membrane.

[0010] According to another perspective, adjustments to the control strategy for fuel cells based on the effective operating anode leakage rate or shutdown leakage rate also include limiting transient load rates during fuel cell operation to control emissions during and after power load fluctuations.

[0011] According to another aspect, adjustments to the control strategy for the fuel cell based on the effective operating anode leakage rate or shutdown leakage rate also include: during the operation of the fuel cell, performing at least one of the following: reducing the venting frequency; increasing the gas flow through the cathode to compensate for the oxygen consumed by hydrogen permeating through the electrolyte membrane; and limiting the transient load rate to control emissions during and after power load fluctuations.

[0012] According to another aspect, adjustments to the control strategy for fuel cells based on the effective operating anode leakage rate or shutdown leakage rate also include: during fuel cell shutdown operations, directly venting hydrogen from the anode and cathode to the exhaust device; and reducing the anode and cathode pressures.

[0013] According to another perspective, adjusting the control strategy for fuel cells based on the effective operating anode leakage rate or shutdown leakage rate also includes reducing the bias voltage between the anode and cathode during the freeze-start operation of the fuel cell.

[0014] According to another aspect, adjustments to the control strategy for fuel cells based on the effective operating anode leakage rate or shutdown leakage rate also include: continuously and periodically monitoring the pressure decay within the anode during the standby operation of the fuel cell, and initializing H2 retention measures during long periods of non-use to ensure that when the pressure decay within the anode indicates that oxygen has leaked into the anode, there is still sufficient hydrogen in the anode and cathode for start-up operation.

[0015] According to another aspect, the method also includes updating the measured anode leakage rate when the power output of the fuel cell is zero.

[0016] According to several aspects of this disclosure, a fuel cell includes an anode, a cathode, an electrolyte membrane located between the anode and the cathode, and a controller adapted to: measure the anode leakage rate of the fuel cell and update the measured anode leakage rate when the power output of the fuel cell is zero; model the effective electrolyte membrane orifice size using the measured anode leakage rate; calculate the effective operating anode leakage rate during operation of the fuel cell using the effective electrolyte membrane orifice size; use the effective operating anode leakage rate as a low-side metric when calculating emission and dilution requests; and initiate adjustments to the control strategy of the fuel cell based on the effective operating anode leakage rate or the shutdown leakage rate.

[0017] On the other hand, when measuring the anode leakage rate of a fuel cell, the controller is also adapted to measure the anode shutdown leakage rate of the fuel cell.

[0018] According to another aspect, when measuring the anode leakage rate of a fuel cell, the controller is also adapted to monitor the pressure decay within the anode during low-power operation of the fuel cell, and to estimate the anode leakage rate based on the pressure decay within the anode during low-power operation of the fuel cell.

[0019] According to another aspect, when adjusting the control strategy for the fuel cell based on the effective operating anode leakage rate or shutdown leakage rate, the controller is further adapted to: increase the duration of the increased airflow through the cathode of the fuel cell during the start-up period of the fuel cell to dilute the concentration of hydrogen leaking from the anode, wherein the anode-to-cathode bias, airflow rate, airflow split, and duration of the increased airflow are calculated and adjusted based on one of the following: the effective operating anode leakage rate or shutdown leakage rate.

[0020] According to another aspect, when adjusting the control strategy for the fuel cell based on the effective operating anode leakage rate or shutdown leakage rate, the controller is also adapted to perform at least one of the following during the operation of the fuel cell: reducing the venting frequency; increasing the gas flow through the cathode to compensate for the oxygen consumed by the hydrogen permeating through the electrolyte membrane; and limiting the transient load rate to control emissions during and after power load fluctuations.

[0021] According to another aspect, when adjusting the control strategy of the fuel cell based on the effective operating anode leakage rate or shutdown leakage rate, the controller is also adapted to directly discharge hydrogen from the anode and cathode to the exhaust device during the shutdown operation of the fuel cell; and to reduce the anode and cathode pressure.

[0022] According to another aspect, when adjusting the control strategy for the fuel cell based on the effective operating anode leakage rate or shutdown leakage rate, the controller is also adapted to: reduce the bias voltage between the anode and cathode during the freeze-start operation of the fuel cell, and continuously and periodically monitor the pressure decay in the anode during long periods of non-use of the fuel cell, and initialize H2 retention measures to ensure that when the pressure decay in the anode indicates that oxygen has leaked into the anode, there is still enough hydrogen in the anode and cathode for the start-up operation.

[0023] Further applicability will become apparent from the description provided herein. It should be understood that the specification and specific examples are for illustrative purposes only and are not intended to limit the scope of this disclosure. Attached Figure Description

[0024] The accompanying drawings described herein are for illustrative purposes only and are not intended to limit the scope of this disclosure in any way.

[0025] Figure 1 This is a schematic diagram of a vehicle having a fuel cell propulsion system including a fuel cell according to an exemplary embodiment of the present disclosure;

[0026] Figure 2 This is a side view schematic diagram of a fuel cell according to an exemplary embodiment;

[0027] Figure 3 yes Figure 2 A schematic block diagram of a fuel cell is shown.

[0028] Figure 4A yes Figure 2 The schematic side view of the fuel cell shown illustrates how hydrogen migrates from the anode to the cathode through permeation within the electrolyte membrane;

[0029] Figure 4B yes Figure 4A The diagram shows a side view of a fuel cell, in which an airflow device increases the airflow through the cathode;

[0030] Figure 4C yes Figure 4A The schematic diagram of the side view of the fuel cell shown illustrates that an airflow device increases the airflow through the cathode and through the cathode bypass valve.

[0031] Figure 4D yes Figure 4AThe diagram shows a side view of a fuel cell, in which the cathode bypass valve is closed and the gas flow device maintains an increased gas flow through the cathode to push the remaining hydrogen out of the cathode.

[0032] Figure 5 yes Figure 4A The side view schematic diagram of the fuel cell shown illustrates that, during shutdown operation, the isolation valve opens, allowing hydrogen to be discharged from the anode through the anode purging valve, through the cathode to the tailpipe, or directly to the vehicle's tailpipe; and

[0033] Figure 6 This is a schematic flowchart illustrating a method according to an exemplary embodiment of the present disclosure.

[0034] The accompanying drawings are not necessarily drawn to scale, and some features may be enlarged or minimized, such as to show details of specific components. In some cases, known components, systems, materials, or methods have not been described in detail to avoid obscuring this disclosure. Therefore, the specific structural and functional details disclosed herein should not be construed as limiting, but only as the basis for the claims and as a representative basis for teaching those skilled in the art to apply this disclosure in different ways. Detailed Implementation

[0035] The following description is merely exemplary in nature and is not intended to limit this disclosure, its application, or its uses. Furthermore, it is not intended to be bound by any express or implied theory presented in the foregoing technical fields, background art, summary of the invention, or the following detailed description. It should be understood that throughout the drawings, corresponding reference numerals denote similar or corresponding parts and features. As used herein, the term "module" means any hardware, software, firmware, electronic control components, processing logic, and / or processor device, individually or in any combination, including but not limited to: application-specific integrated circuits (ASICs), electronic circuits, processors (shared, dedicated, or grouped) and memories executing one or more software or firmware programs, combinational logic circuits, and / or other suitable components providing the described functionality. Although the drawings shown herein depict examples with certain element arrangements, additional intermediate elements, devices, features, or components may be present in actual embodiments. It should also be understood that the drawings are merely illustrative and may not be drawn to scale.

[0036] As used herein, the term "vehicle" is not limited to automobiles. While this article primarily describes the technology in the context of automobiles, the technology is not limited to automobiles. These concepts can be used in a variety of applications, such as those relating to aircraft, ships, other vehicles, stationary applications, and consumer electronics components.

[0037] The provision of exemplary embodiments makes this disclosure comprehensive and fully conveys the scope to those skilled in the art. Numerous specific details, such as examples of specific compositions, components, apparatuses, and methods, are set forth to provide a thorough understanding of embodiments of this disclosure. It will be apparent to those skilled in the art that specific details are not required, exemplary embodiments may be embodied in many different forms, and none should be construed as limiting the scope of this disclosure. In some exemplary embodiments, known processes, known apparatus structures, and known technologies are not described in detail.

[0038] The terminology used herein is for the purpose of describing particular exemplary embodiments only and is not intended to be limiting. As used herein, the singular forms “a / an” and “the” may also be intended to include the plural forms unless the context clearly indicates otherwise. The terms “comprising,” “including,” “containing,” and “having” are inclusive and thus specify the presence of the stated features, elements, compositions, steps, integrals, operations, and / or components, but do not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components, and / or groups thereof. While the open-ended term “comprising” should be understood as a non-limiting term used to describe and claim the various embodiments presented herein, in some respects it may be understood alternatively as a more restrictive and limiting term, such as “consisting of” or “substantially consisting of.” Therefore, for any given embodiment recounting compositions, materials, components, elements, features, integrals, operations, and / or process steps, this disclosure also specifically includes embodiments consisting of compositions, materials, components, elements, features, integrals, operations, and / or process steps described below, or substantially consisting of such compositions, materials, components, elements, features, integrals, operations, and / or process steps. In the case of “consisting of…”, the alternative embodiments exclude any additional compositions, materials, components, elements, features, integrals, operations and / or process steps, while in the case of “consisting substantially of…”, any additional compositions, materials, components, elements, features, integrals, operations and / or process steps that substantially affect the basic and novel characteristics are excluded from such embodiments, but any compositions, materials, components, elements, features, integrals, operations and / or process steps that do not substantially affect the basic and novel characteristics may be included in the embodiments.

[0039] Any methods, steps, procedures, and operations described herein should not be construed as requiring them to be performed in the specific order discussed or shown, unless specifically identified as such. It should also be understood that additional or alternative steps may be employed unless otherwise stated.

[0040] When a component, element, or layer is referred to as being “on,” “joined to,” “connected to,” or “attached to” another component or layer, it may be directly on, directly joined to, directly connected to, or directly attached to the other component, element, or layer, or there may be intermediate elements or layers present. Conversely, when an element is referred to as being “directly on,” “directly joined to,” “directly connected to,” or “directly attached to” another component or layer, there may be no intermediate elements or layers present. Other terms used to describe relationships between elements should be interpreted in a similar manner (e.g., “between” vs. “directly between,” “adjacent” vs. “directly adjacent,” etc.). As used herein, the term “and / or” includes any and all combinations of one or more of the related listed items.

[0041] Although the terms first, second, third, etc., may be used herein to describe various steps, elements, components, regions, layers, and / or portions, these steps, elements, components, regions, layers, and / or portions should not be limited by these terms unless otherwise stated. These terms may be used only to distinguish one step, element, component, region, layer, or portion from another. Terms such as “first,” “second,” and other numerical terms, when used herein, do not imply sequence or order unless the context clearly indicates otherwise. Therefore, the first step, element, component, region, layer, or portion discussed below may be referred to as the second step, element, component, region, layer, or portion without departing from the teachings of the exemplary embodiments.

[0042] For ease of description, this document uses spatial or temporal relative terms such as “before,” “after,” “inside,” “outside,” “below,” “below,” “lower,” “above,” “upper,” etc., to describe the relationship of one element or feature to another element or feature shown in the figure. In addition to the orientation depicted in the figure, spatial or temporal relative terms may be intended to cover different orientations of the device or system during use or operation.

[0043] Throughout this disclosure, numerical values ​​represent approximate measurements or limitations on ranges to cover minor deviations from given values ​​and embodiments having approximately the mentioned values, as well as embodiments having precisely the mentioned values. Except for the working examples provided at the end of the detailed description, all numerical values ​​of parameters (e.g., quantities or conditions) in this specification (including the appended claims) should be understood to be modified in all cases by the term "approximately," regardless of whether "approximately" actually precedes the numerical value. "Approximately" implies that the stated numerical value allows for some slight imprecision (accuracy achieved by some method; approximately or fairly close to the value; almost). If the imprecision provided by "approximately" is not understood in the art to have that general meaning, then "approximately" as used herein at least indicates a variation that may arise from common methods of measuring and using such parameters. For example, "approximately" with respect to percentages includes a variation of + / - 5%, "approximately" with respect to temperature includes a variation of + / - 5 degrees, and "approximately" with respect to distance includes + / - 10%. Additionally, the disclosure of ranges includes disclosing all values ​​throughout the range and further subdivisions of the range, including endpoints and subranges given for that range.

[0044] In addition, the disclosure of a range includes disclosing all values ​​within the entire range and further subdivisions of the range, including endpoints and subranges given for that range.

[0045] Exemplary embodiments will now be described more fully with reference to the accompanying drawings. According to exemplary embodiments, Figure 1 A vehicle 10 with an associated fuel cell 50 is shown. The vehicle 10 generally includes a chassis 12, a body 14, front wheels 16, and rear wheels 18. The body 14 is mounted on the chassis 12 and generally surrounds the components of the vehicle 10. The body 14 and chassis 12 may together form a frame. The front wheels 16 and rear wheels 18 are each rotatably connected to the chassis 12 near a corresponding corner of the body 14.

[0046] In various embodiments, vehicle 10 is an autonomous vehicle. Autonomous vehicle 10 is, for example, a vehicle 10 automatically controlled to transport passengers from one location to another. Vehicle 10 is depicted as a passenger car in the illustrated embodiment, but it should be understood that any other vehicle may be used, including motorcycles, trucks, sport utility vehicles (SUVs), recreational vehicles (RVs), etc. In exemplary embodiments, vehicle 10 is equipped with a so-called Level 4 or Level 5 automation system. Level 4 system means “high automation,” referring to the performance of the autonomous driving system in specific driving modes across various aspects of a dynamic driving task, even if the human driver does not appropriately respond to intervention requests. Level 5 system means “full automation,” referring to the full-time performance of the autonomous driving system across all road and environmental conditions manageable by a human driver for all aspects of a dynamic driving task. Novel aspects of this disclosure are also applicable to non-autonomous vehicles.

[0047] As shown in the figure, vehicle 10 generally includes a fuel cell propulsion system 20, a drivetrain 22, a steering system 24, a braking system 26, a sensor system 28, an actuator system 30, at least one data storage device 32, a vehicle controller 34, and a wireless communication module 36. In embodiments where vehicle 10 is an electric vehicle powered by a fuel cell 50 or a battery stack including multiple fuel cells 50, the drivetrain 22 may be absent. The drivetrain 22 is configured to transmit power from the fuel cell propulsion system 20 to the front wheels 16 and rear wheels 18 of the vehicle according to a selectable speed ratio. According to various embodiments, the drivetrain 22 may include a stepped automatic transmission, a continuously variable transmission (CVT), or other suitable transmission. The braking system 26 is configured to provide braking torque to the front wheels 16 and rear wheels 18 of the vehicle. In various embodiments, the braking system 26 may include friction brakes, brake-by-wire brakes, regenerative braking systems (such as electric motors), and / or other suitable braking systems. The steering system 24 affects the position of the front wheels 16 and rear wheels 18. Although depicted as including a steering wheel for illustrative purposes, in some embodiments contemplated within the scope of this disclosure, such as for fully automated vehicles, the steering system 24 may not include a steering wheel.

[0048] Sensor system 28 includes one or more sensing devices 40a-40n that sense observable conditions of the external and / or internal environment of the autonomous vehicle 10. Sensing devices 40a-40n may include, but are not limited to, radar, lidar, global positioning system, optical camera, thermal imager, ultrasonic sensor, and / or other sensors. In an exemplary embodiment, the multiple sensing devices 40a-40n include a motor speed sensor, a motor torque sensor, an electric drive motor voltage and / or current sensor, an accelerator pedal position sensor, a coolant temperature sensor, a cooling fan speed sensor, and a transmission oil temperature sensor. In another exemplary embodiment, the multiple sensing devices 40a-40n also include sensors for determining information about the environment surrounding the vehicle 10, such as an ambient air temperature sensor, an atmospheric pressure sensor, and / or a photographic and / or video camera positioned to observe the environment in front of the vehicle 10. Actuator system 30 includes one or more actuator devices 42a-42n that control one or more features of the vehicle 10, such as, but not limited to, the propulsion system 20, the transmission system 22, the steering system 24, and the braking system 26.

[0049] The vehicle controller 34 includes at least one processor 44 and a computer-readable storage device or medium 46. The at least one data processor 44 can be any custom or commercially available processor, central processing unit (CPU), graphics processing unit (GPU), auxiliary processor among a plurality of processors associated with the vehicle controller 34, semiconductor-based microprocessor (in the form of a microchip or chipset), macroprocessor, any combination thereof, or any means generally used for executing instructions. The computer-readable storage device or medium 46 can include, for example, volatile and non-volatile storage devices such as read-only memory (ROM), random access memory (RAM), and keep-alive memory (KAM). KAM is persistent or non-volatile memory that can be used to store various operational variables when at least one data processor 44 is powered off. The computer-readable storage device or medium 46 can be implemented using any of a variety of known storage devices, such as PROM (programmable read-only memory), EPROM (electrical PROM), EEPROM (electrically erasable PROM), flash memory, or any other electrical, magnetic, optical, or combined storage device capable of storing data, some of which represent executable instructions used by the controller 34 when controlling the vehicle 10.

[0050] These instructions may include one or more separate programs, each comprising an ordered list of executable instructions for implementing logical functions. When executed by at least one processor 44, the instructions receive and process signals from the sensor system 28, execute logic, calculations, methods, and / or algorithms for automatically controlling components of the vehicle 10, and generate control signals to the actuator system 30 based on the logic, calculations, methods, and / or algorithms to automatically control the components of the vehicle 10. Although Figure 1 Only one controller 34 is shown in the figure. Embodiments of vehicle 10 may include any number of controllers 34 that communicate via any suitable communication medium or combination of communication media and cooperate to process sensor signals, perform logic, calculations, methods and / or algorithms, and generate control signals to automatically control the features of autonomous vehicle 10.

[0051] The wireless communication module 36 is configured to wirelessly transmit information to and from other remote entities 48, such as, but not limited to, other vehicles (“V2V” communication), infrastructure (“V2I” communication), remote systems, remote servers, cloud computers, and / or personal devices. In an exemplary embodiment, the communication system 36 is a wireless communication system configured to communicate using the IEEE 802.11 standard or via a wireless local area network (WLAN) using cellular data communication. However, additional or alternative communication methods, such as Dedicated Short Range Communication (DSRC) channels, are also considered within the scope of this disclosure. A DSRC channel refers to a one-way or two-way short- to medium-range wireless communication channel designed specifically for automotive use, along with a set of corresponding protocols and standards.

[0052] The vehicle controller 34 is a non-general-purpose electronic control device that includes a pre-programmed digital computer or processor, memory or non-transitory computer-readable medium, and transceivers (or input / output ports) for storing data such as control logic, software applications, instructions, computer code, data, lookup tables, etc. Computer-readable medium includes any type of media that can be accessed by a computer, such as read-only memory (ROM), random access memory (RAM), hard disk drive, optical disc (CD), digital video disc (DVD), or any other type of memory. "Non-transitory" computer-readable medium does not include wired, wireless, optical, or other communication links that transmit transient electrical or other signals. Non-transitory computer-readable medium includes media that can permanently store data and media that can store and subsequently rewrite data, such as rewritable optical discs or erasable storage devices. Computer code includes any type of program code, including source code, object code, and executable code.

[0053] refer to Figure 2 The fuel cell propulsion system 20 includes a stack 52 comprising a plurality of fuel cells 50. In an exemplary embodiment, each fuel cell 50 is a hydrogen fuel cell, which is an electrochemical device in which a change in free energy resulting from an oxidation reaction is converted into electrical energy. Each fuel cell 50 includes an anode 54 (fuel cell) and a cathode 56 (oxidant electrode), separated by an ion-conducting electrolyte 58 located therebetween. A chemically oxidizable fuel 60 (typically hydrogen, H2) is supplied to the anode 54 and ionized on a suitable catalyst 62 to produce hydrogen protons (H2O). + 64 and 66. Gaseous hydrogen 60 exhibits high reactivity and high energy density in the presence of a suitable catalyst 62. Similarly, an oxidant 68 (typically air, O2) is supplied to the fuel cell cathode 56 and reacts with a suitable catalyst 70 at the cathode 56. Gaseous oxygen 68 can be readily and economically obtained from air for use in the fuel cell. The anode 54 receives hydrogen 60 and the cathode 56 receives oxygen 68 or air.

[0054] Hydrogen 60 dissociates in anode 54 to produce free hydrogen protons 64 and electrons 66. Anode 54 and cathode 56 are electrically connected to load 72 (such as electronic circuitry) via external circuit conductors. Hydrogen protons 64 pass through electrolyte 58 to cathode 56, as indicated by arrow 74. Electrons 66 from anode 54 cannot pass through electrolyte 58 and are therefore directed through load 72, as indicated by arrow 76, to do work before being sent to cathode 56, as indicated by arrow 78. Proton exchange membrane fuel cells (PEMFCs) are a popular type of fuel cell used in vehicles and generally consist of a solid polymer electrolyte proton-conducting membrane, such as a perfluorosulfonic acid membrane, for electrolyte 58. Catalysts 62, 70 of anode 54 and cathode 56 generally consist of finely granulated catalytic particles, typically platinum (Pt), supported on carbon particles and mixed with an ionomer, wherein the catalytic mixture is deposited on opposite sides of electrolyte membrane 58. The combination of the anode catalytic mixture (anode catalyst 62), the cathode catalytic mixture (cathode catalyst 70), gas diffusion layers 134, 136, and the membrane (electrolyte 58) defines the membrane electrode assembly (MEA). The membrane blocks gas transport between the anode side 54 and the cathode side 56 of the fuel cell 50, while allowing the transport of protons 64 to complete the anodic and cathode reactions on their respective electrodes 54, 56. At the cathode 56, oxygen 68 reacts with hydrogen protons 64 migrating through the electrolyte 58 and electrons 66 entering from the external circuitry to produce water 80 as a byproduct. The byproduct water 80 is typically extracted as steam. The total reaction occurring in the fuel cell 50 is the sum of the reactions at the anode 54 and the cathode 56, where a portion of the reaction free energy is released directly as electrical energy (used by the load 72). This difference between the available free energy and the heat of reaction is generated as heat, as indicated by arrow 82.

[0055] In an exemplary embodiment, multiple fuel cells 50 are combined in a fuel cell stack 52 to generate the required electricity. The fuel cell stack 52 generally includes a series of flow fields or bipolar plates located between multiple MEAs within the fuel cell stack 52, wherein the bipolar plates and MEAs are situated between two end plates. Each bipolar plate includes an anode side and a cathode side for adjacent fuel cells 50 in the fuel cell stack 52. An anode gas flow channel is provided on the anode side of the bipolar plate, allowing anode reactant gas 60 to flow to the corresponding MEA. A cathode gas flow channel is provided on the cathode side of the bipolar plate, allowing cathode reactant gas 68 to flow to the corresponding MEA. One end plate includes an anode gas flow channel, while the other end plate includes a cathode gas flow channel. The bipolar plates and end plates are made of conductive materials, such as stainless steel or conductive composite materials. The end plates discharge the electricity generated by the fuel cells into the fuel cell stack 52. The bipolar plates also include flow channels through which cooling fluid flows. Fuel (hydrogen) 60 and oxidant (air) 68 are introduced to their respective sides 54, 56 via manifolds. In some applications, the fuel 60 and oxidant 68 supply streams are designed as flow systems; however, these systems increase the parasitic load on the output of the fuel cell 50 and thus reduce the net extractable power. In other configurations, the fuel stream or the oxidant stream, or both, are “dead-end.” Such dead-end operation can cause problems such as water removal and impurity buildup. Therefore, in exemplary embodiments of this disclosure, the flow capacity of fuel 60 into and through the anode side 54 of the fuel cell 50 is controlled by an anode valve 84 or multiple anode valves, thereby allowing the post-reaction fuel gas 90 to selectively flow from the anode 54 into the atmosphere surrounding the fuel cell 50.

[0056] The MEA in fuel cell 50 is permeable, thus allowing nitrogen from the air on the cathode side 56 of the fuel cell stack to permeate and be collected in the anode side 54 of the fuel cell stack 52, commonly referred to as nitrogen bridging. Although the pressure on the anode side 54 may be slightly higher than that on the cathode side 56, the partial pressure on the cathode side 56 will cause air to permeate through the electrolyte membrane 58. The nitrogen in the anode side 54 of fuel cell 50 dilutes the hydrogen 60, so that if the nitrogen concentration increases above a certain percentage, such as 50%, fuel cell 50 in fuel cell stack 52 may lack hydrogen 60. If fuel cell 50 becomes hydrogen-deficient, fuel cell stack 52 will not be able to generate sufficient power and may damage the catalyst 62 in the anode 54 and the catalyst 70 in the cathode 56 of fuel cell stack 52. Furthermore, under heavy loads, the evaporation of byproduct water 80 at the cathode 56 occurs more slowly than its formation, and water 80 tends to migrate back to the anode side 54 through the polymer electrolyte 58. Some points on the fuel cell 50 are colder than others, and moisture condenses into liquid water 80 at these locations, flooding the anode 54 and hindering the reaction at the anode 54. Additionally, other impurities accumulate at the anode 54 and may poison the anode reaction sites. Inert contaminants can also reduce fuel partial pressure, leading to performance loss. Therefore, it is known in the art to provide an anode valve 84 in the anode exhaust line of the fuel cell stack 52 to remove nitrogen and water 80 from the anode side 54 of the fuel cell stack 52. This allows for the control of the emission of a certain proportion (possibly from 0.1% to 10%) of gaseous fuel (post-reaction fuel gas) through a throttling opening, removing accumulated impurities, water 80, and fine particles from the anode side 54 and restoring the performance of the fuel cell 50. For clarity and to avoid confusion, the accumulated gas being emitted is referred to herein as "post-reaction fuel gas." Those skilled in the art will understand that post-reaction fuel gas is primarily hydrogen 60 with trace amounts of water 80 and possibly nitrogen, carbon dioxide, and carbon monoxide. Depending on the construction of the fuel cell 50, other gases may also be present in the post-reaction fuel gas.

[0057] The fuel cell propulsion system controller includes a control algorithm that identifies the minimum required hydrogen 60 concentration in the anode 54 and causes the anode valve 84 to open when the gas concentration falls below this threshold. This controls the length of continuous purging and the intervals between continuous purgings, and monitors the fuel cell power output to provide exhaust gas that is approximately proportional to the amount of hydrogen 60 consumed by the fuel cell 50. The fuel cell propulsion system controller may be the vehicle controller 34, or a separate controller that communicates with the vehicle controller 34 and is dedicated to controlling the fuel cell propulsion system 20. However, releasing hydrogen 60 into the open air if the concentration is higher than the target value could pose a safety hazard. Increasing the flow rate of air 68 entering the cathode side 56 of the fuel cell 50 dilutes the hydrogen 60 present in the purging gas, so that when the purging gas reaches the atmosphere surrounding the fuel cell 50, the hydrogen concentration in the tailpipe 101 is low enough to be safely released into the atmosphere.

[0058] It is known in the art to use sensors or models to estimate the mole fraction of gas in the anode side 54 of the fuel cell stack 52 to determine when to perform purging of the anode side 54 or the anode subsystem. For example, gas concentration estimation (GCE) models are known to be used to estimate hydrogen, nitrogen, oxygen, water vapor, etc., in various volumes of the fuel cell system (such as anode flow fields, anode conduits, cathode flow fields, cathode headers, and conduits). Therefore, the controller 34 can determine when to initiate the opening of the anode valve 84 for purging.

[0059] Furthermore, monitoring and measuring gas leakage from the anode 54 within the fuel cell 50 is known in the art. Gas leakage from the anode 54 subsystem within the fuel cell 50 is a major concern because the type of hydrogen present in the mixture can affect overall system efficiency and product safety. For example, bipolar plate and / or seal rupture can lead to serious safety issues, potentially catastrophic for repairable fuel cell stacks and creating a hazardous environment for vehicle operators. Moreover, hydrogen leak detection must be accurate due to emission requirements to ensure compliance and enable reactive action should gas be lost from the anode 54.

[0060] Known methods exist for determining the total amount of molecular gas in the anode 54 volume of the fuel cell stack 52 at the start of the leak detection period during leak detection conditions. These methods also determine cross-loss of hydrogen 60 from the anode 54 volume of the fuel cell stack 52 due to permeation through the membrane (electrolyte membrane 58) in the fuel cell stack 52 during the leak detection period; excessive loss of hydrogen 60 from the anode 54 volume of the fuel cell stack 52 due to permeation through other components in the fuel cell stack 52, such as gaskets, valves, and seals, during the leak detection period; and reaction loss of hydrogen 60 from the anode 54 volume of the fuel cell stack 52 due to electrochemical reactions in the fuel cell stack 52 during the leak detection period. These methods also determine the total amount of molecular gas in the anode 54 volume of the fuel cell stack 52 at the end of the leak detection period and subtract it from the hydrogen 60 present in the anode 54 volume at the start of the leak detection conditions to give the total gas loss. Adding the cross-loss, excessive loss, and reaction loss yields the additional loss, which is subtracted from the total gas loss to obtain the leakage loss from the anode 54 volume. This anode leakage loss is compared with a predetermined threshold to determine whether there is a significant gas leak sufficient to trigger the end of the life of fuel cell 50.

[0061] Further details of measuring the shutdown leakage rate of the anode 54 of the fuel cell 50 are contained in U.S. Patent No. 8,524,405, issued September 3, 2013, to Salvador et al., and U.S. Patent No. 11,043,682, issued June 22, 2021, to Gagliardo et al., both of which are assigned to GM Global Technology Operations LLC and are hereby incorporated by reference.

[0062] In an exemplary embodiment of this disclosure, the controller 34 of the fuel cell 50 is adapted to measure the anode leakage rate of the fuel cell 50 and to measure the anode shutdown leakage rate of the fuel cell by a known method (e.g., the method described above), or by monitoring the pressure decay within the anode 54 during low-power operation of the fuel cell 50 and estimating the anode leakage rate based on the pressure decay observed within the anode 54 during low-power operation of the fuel cell 50, updating the measured anode leakage rate when the power output of the fuel cell 50 is zero. The measured anode leakage rate can be updated at any time when the fuel cell 50 operates at zero power consumption. When the power output of the fuel cell 50 is zero (shutdown leakage rate), the estimated leakage rate obtained during the low-power period is used as a substitute for the leakage rate (shutdown leakage rate) to allow for effective leakage orifice size calculation in cases where shutdown leakage rates cannot be successfully or regularly performed due to extended long operating times. Cathode pressure also affects the anode pressure change rate. This becomes more important when the fuel cell membrane degrades. Therefore, the patented anode shutdown leakage rate measurement method can be updated to simultaneously consider anode pressure changes and cathode pressure changes when measuring the anode leakage rate.

[0063] The controller 34 is then adapted to model the effective electrolyte membrane orifice size using the measured anode leakage rate. Therefore, the controller 34 uses the measured anode leakage rate to model the orifice size within the electrolyte membrane 58, which will correspond to the measured anode leakage rate. Using the modeled electrolyte membrane orifice size, the controller 34 can calculate the effective anode leakage rate under any operating conditions of the fuel cell 50. The controller 34 then uses the effective electrolyte membrane orifice size to calculate the effective operating anode leakage rate during fuel cell operation.

[0064] As described above, increasing the flow rate of air 68 entering the cathode side 56 or bypass valve 110 of fuel cell 50 dilutes the hydrogen 60 present in the purge gas (reacted fuel gas 90), so that when the purge gas reaches the atmosphere surrounding fuel cell 50, the concentration of hydrogen 60 is sufficiently low to be safely released into the atmosphere. Once the controller 34 calculates the effective operating anode leakage rate, it uses the effective operating anode leakage rate as a low-side metric when calculating emission and dilution requests. Therefore, regardless of other operating conditions, the controller 34 uses the calculated effective operating anode leakage rate as a baseline and calculates emission levels and dilution requests based on the assumed hydrogen 60 level according to the calculated effective operating anode leakage rate.

[0065] Furthermore, the controller 34 is adapted to initiate adjustments to the control strategy of the fuel cell 50 directly based on the effective operating anode leakage rate or shutdown leakage rate. This adjustment includes modifying the operating parameters of the fuel cell 50 to compensate for leakage. Therefore, as the electrolyte membrane 58 degrades over time, the controller 34 will calculate and continuously update the effective anode leakage rate without triggering the end-of-life of the fuel cell 50. This will initiate adjustments to the control strategy of the fuel cell 50, modifying the operating parameters to account for and compensate for anode leakage through the electrolyte membrane 58, and allowing the fuel cell 50 to operate safely and continuously beyond the anode leakage rate that would conventionally trigger the end-of-life.

[0066] Refer again Figure 2 , Figure 3 and Figure 4A In an exemplary embodiment of this disclosure, the controller 34 is adapted to monitor the concentration of hydrogen 60 present at the anode 54 of the fuel cell 50 using a first sensor or model 86 communicating with the controller 34, and to monitor the accumulated water 80 liquid (captured in the liquid collector 140) present at the anode 54 of the fuel cell 50 using a second sensor or model 88 communicating with the controller 34. When the concentration of hydrogen 60 present at the anode 54 is less than a predetermined concentration, selective removal of the reacted fuel gas 90 is initiated (by opening the anode removal valve 122), or by opening the drain valve 142. When the amount of accumulated liquid water 80 present at the anode 54 (in the liquid collector 140) is greater than a predetermined threshold, liquid water 80 is discharged from the anode 54 of the fuel cell 50, allowing liquid water 80 to be discharged from the liquid collector 140 to the cathode inlet 144 or the tailpipe 101.

[0067] The system controller 34, using a first sensor or model 86, can detect when the concentration of hydrogen 60 within the anode decreases due to excessive nitrogen or other impurities in the post-reaction fuel gas 90, thereby prompting the controller 34 to selectively remove the post-reaction fuel gas 90 from the anode 54. This reduces the pressure within the anode 54 and allows pure H2 fuel 60 to enter the anode 54 from the injector, thus increasing the amount of hydrogen 60 within the anode 54. Similarly, the system controller 34, using a second sensor or model 88, can detect when the amount of liquid water 80 accumulated within the anode 54 reaches a level that hinders the catalytic reaction of hydrogen 60 within the anode 54, thereby prompting the controller 34 to selectively drain liquid water from the anode 54 through the drain valve 142.

[0068] Once controller 34 initiates selective purging or venting of anode 54, controller 34 uses a third sensor or model 92 to monitor the flow rate of air 68 entering fuel cell 50 and estimates the required flow rate of air 68 entering fuel cell 50, which is necessary to dilute the concentration of hydrogen 60 present in tailpipe 101 below a predetermined level. As described above, the safe concentration of hydrogen 60 in the vented post-reaction fuel gas 90 (tailpipe 101) is below the target level. Controller 34 purges the high concentration of H2 (e.g., 75%) from anode 54 into cathode inlet 144 or tailpipe 101. Simultaneously, a high airflow is also propelled through cathode 56 or bypass valve 110 to the exhaust device (tailpipe 101). By providing sufficient additional air, the H2 concentration in the exhaust device at tailpipe 101 will be below the target level. There are two options: the first is purging to cathode inlet, and the second is purging to exhaust device. The advantage of the first option is that the high concentration of H2 will mix with air in cathode 56 and react directly to generate water. Therefore, the amount of H2 entering the exhaust system at tailpipe 101 will be greatly reduced.

[0069] The controller 34 increases the flow rate of air 68 entering the fuel cell 50 by actuating an airflow device 94 adapted to push air 68 into the fuel cell 50. The airflow from the airflow device 94 can push air through the isolation valve 102 into the cathode 56, or the airflow from the airflow device 94 can push air directly to the exhaust device (tailpipe 101) through the cathode bypass valve 110. The airflow device 94 can be a blower, turbine, or compressor adapted to draw in ambient air and push the air 68 into the fuel cell 50. The controller 34 increases the force by which the airflow device pushes the air 68, thereby increasing the volume of air 68 pushed through the fuel cell. During normal operating conditions, the airflow device 94 is adapted to deliver air 68 to the fuel cell 50 at a normal operating flow rate. When the reaction-induced fuel gas 90 is purged or liquid water is discharged, the controller 34 actuates the airflow device 94 to increase the flow rate of air 68 entering the fuel cell 50 from the normal operating flow rate to the estimated required flow rate, so as to dilute the concentration of hydrogen 60 present in the reaction-induced fuel gas 90 at the tailpipe 101 to the target level.

[0070] In an exemplary embodiment, the controller 34 is adapted to adjust the control strategy of the fuel cell 50 based on the effective operating anode leakage rate or the shutdown leakage rate, including increasing the duration of the increased airflow through the cathode bypass valve 110 of the fuel cell 50 during startup to dilute the concentration of hydrogen 60 leaking from the anode 54. Here, the bias voltage from the anode 54 to the cathode 56, the airflow rate, the airflow split, and the duration of the increased airflow are calculated based on the effective operating time anode leakage rate.

[0071] Refer again Figure 4A When the fuel cell is shut down, hydrogen 60 can accumulate in the cathode 56 through permeation 96 within the electrolyte membrane 58, as indicated by arrow 98. Due to the closed state of the isolation valve 102 located between the gas flow device 94 and the cathode 56, and the closed state of the back pressure valve 104 located between the cathode 56 and the tailpipe 100, the emission level in the tailpipe 101 of the vehicle 10 downstream of the fuel cell 50 is acceptable. The isolation valve 102 and back pressure valve 104 retain hydrogen 60 leaking from the anode 54 through the electrolyte membrane 58 into the cathode 56 within the cathode 56.

[0072] refer to Figure 4B At the start-up of fuel cell 50, isolation valve 102 remains closed until the airflow through airflow device 94 increases to a predetermined level. Therefore, when isolation valve 102 opens, the airflow is sufficient to prevent hydrogen 60 from flowing back from cathode 56, and the airflow from airflow device 94, as indicated by arrow 106, begins to push the hydrogen 60 within cathode 56 out through back pressure valve 104, as indicated by arrow 108, thereby reducing the level of hydrogen 60 within cathode 56.

[0073] refer to Figure 4C The increased airflow continues through the cathode bypass valve 110 (as shown by arrow 112) bypassing the cathode 56 and through the cathode 56 itself (as shown by arrow 114), where hydrogen 60 is purged from the fuel cell 50, as shown by arrow 116, and finally referenced Figure 4D After most of the H2 has been removed from the cathode 56, the cathode bypass valve 110 can be closed, and the increased airflow continues directly through the cathode 56 as indicated by arrow 118, to expel the remaining hydrogen 60 from the cathode 56 as indicated by arrow 120.

[0074] In another exemplary embodiment, the controller 34 is adapted to adjust the control strategy of the fuel cell 50 based on the effective operating anode leakage rate or the shutdown leakage rate, including activating a venting function during the operation of the fuel cell 50 to discharge hydrogen 60 from the anode 54 of the fuel cell 50. During the operation of the fuel cell 50, the pressure within the anode 54 is higher than the pressure within the cathode 56, thus promoting the permeation of hydrogen 60 through the electrolyte membrane 58. This situation is further amplified by the degradation of the electrolyte membrane 58 over time, thereby allowing an increased permeation rate through the electrolyte membrane 58, and activating the venting function via the anode purge valve 122 to discharge hydrogen 60 from the anode 54 increases the concentration of hydrogen 60 therein. This venting can be achieved by continuous purging through the degradation membrane 58 as described above, wherein the level of hydrogen 60 can be increased due to the continuous purging through the degradation membrane 58.

[0075] In another exemplary embodiment, the controller 34 is adapted to initiate adjustments to the control strategy of the fuel cell 50 based on the effective operating anode leakage rate or the shutdown leakage rate, including increasing the airflow through the cathode 56 during the operation of the fuel cell 50 to compensate for the oxygen 68 consumed by the hydrogen 60 permeating through the electrolyte membrane 58. As described above, the controller 34 actuates the airflow device 94 to increase the airflow forced into the cathode 56, thereby increasing the level of oxygen 68 therein. Hydrogen 60 leaks from the anode 54 to the cathode 56 through the degraded electrolyte membrane 58, displacing the air 68 within the cathode 56 and reducing the amount of oxygen 68 available to react with hydrogen protons 64 and free electrons 66. By increasing the airflow, oxygen 68 is supplied to the cathode 56 more rapidly, thereby providing an increased supply of oxygen 68 and avoiding potential voltage losses generated by the fuel cell 50.

[0076] In another exemplary embodiment, controller 34 is adapted to initiate adjustments to the control strategy of fuel cell 50 based on the effective operating anode leakage rate or shutdown leakage rate, including limiting transient load rates during the operation of fuel cell 50 to control emissions within fuel cell 50. High leakage through electrolyte membrane 58 will allow pure hydrogen 60, which has not been decomposed into hydrogen protons 64, to leak from anode 54 to cathode 56. During rising transients (rapid power increase), H2 leaking to cathode 56 through highly degraded membrane 58 may be rapidly pushed into the exhaust system, and the cathode airflow may not increase quickly enough to dilute the H2 level therein. During falling transients (sharp power decrease), the airflow may decrease too quickly as the current decreases. Therefore, a large amount of H2 may also enter the exhaust system without sufficient dilution. As mentioned above, emissions from fuel cell 50 can become problematic when available air is insufficient. To compensate for this, controller 34 limits the rate of load change that can be placed on fuel cell 50, thereby allowing fuel cell 50 to adapt only to the rate of load change and avoiding potential emission problems. This situation may force vehicle 10 to operate at a reduced performance level, which may or may not be acceptable to the driver / passengers of vehicle 10. Therefore, the owner of vehicle 10 may choose to accept the performance reduction and continue operating vehicle 10, thereby extending the life of fuel cell 50, when such limitations and performance reduction occur. Alternatively, the owner may not accept this performance degradation and may choose to consider this situation as a life-end event for fuel cell 50. Thus, the vehicle owner / operator can choose to extend the life of fuel cell 50 at the cost of reduced performance, or choose to immediately replace / repair fuel cell 50.

[0077] In another exemplary embodiment, controller 34 is adapted to initiate adjustments to the control strategy of fuel cell 50 based on the effective operating anode leakage rate or shutdown leakage rate, including directly venting hydrogen 60 from anode 54 and cathode 56 to an exhaust device (tailpipe 101) during shutdown operation of fuel cell 50 and reducing the pressure of anode 54 and cathode 56. During shutdown, the pressure within anode 54 must be higher than the pressure within cathode 56 to enable the system to measure / test the anode 54 shutdown leakage rate. Shutdown leakage detection is the final step in fuel cell shutdown operation. During this period, unconsumed hydrogen 60 when fuel cell 50 shuts down is pushed from anode 54 to cathode 56 due to the bias voltage of anode 54 on cathode 56 and may accumulate within cathode 56.

[0078] refer to Figure 5 During shutdown operations, hydrogen 60 from anode 54 is discharged to cathode inlet 144, and then discharged to the exhaust device (tailpipe 101) via anode purge valve 122 (as indicated by arrow 124) and cathode back pressure valve 104, or directly to the exhaust device. Simultaneously, hydrogen 60 from cathode 56 is discharged directly to the exhaust device via the opening of back pressure valve 104, as indicated by arrow 130. Therefore, immediately following the shutdown leak test of anode 54, at the end of the shutdown operation of fuel cell 50, anode purge valve 122, anode drain valve 142, cathode bypass valve 110, and back pressure valve 104 can all be fully opened to allow excess hydrogen 60 within fuel cell 50 to be discharged to the exhaust device at tailpipe 101, thereby reducing the pressure difference between anode 54 and cathode 56 and reducing the continued permeation from anode 54 through electrolyte membrane 58 to cathode 56 during the shutdown period.

[0079] In another exemplary embodiment, controller 34 is adapted to initiate adjustments to the control strategy of fuel cell 50 based on the effective operating anode leakage rate or the shutdown leakage rate, including reducing the bias between anode 54 and cathode 56 during a freeze-start operation of fuel cell 50. During a freeze-start of fuel cell 50, a high bias between anode 54 and cathode 56 is typically required to achieve nitrogen partial pressure equilibrium between anode 54 and cathode 56 to prevent N2 permeation without unduly affecting the anode hydrogen concentration; therefore, a purging request is not necessary, considering that ice may block the gas flow. However, continuous leakage through the degraded electrolyte membrane 58 renders the high bias unnecessary, enabling strategy modifications including venting hydrogen 60 from anode 54 to cathode 56 and then through the degraded membrane 58.

[0080] Freeze-start refers to the activation of fuel cell 50 when the temperature measured by the fourth sensor or model 132 within fuel cell 50 falls below a predetermined level (e.g., freezing (0 degrees Celsius)). The fuel cell components include an electrolyte membrane 58, catalyst layers 62 and 70, gas diffusion layers 134 and 136, a microporous layer, and bipolar plates. Hydrogen and air flows through flow channels in anode 54 and cathode 56, respectively. Gas diffusion and convection coexist in the porous layer. Catalyst layers 62 and 70 consist of a mixture of catalyst particles, ionomers, and porous carbon backbones. Electrochemical reactions occur at the three-phase coexistence sites (ionomers, gas, and catalyst) in catalyst layers 62 and 70. Electricity is generated during operation, and water is produced as a reaction product. During cold start, water changes from one phase or state to another. It can be absorbed by the ionomer and become membrane water. Due to temperatures below freezing, some membrane water transforms into frozen membrane water. Water can also evaporate from the ionomer. The resulting vapor permeates through the porous layer and enters the flow channels. Water vapor can also deposit as ice and accumulate in the porous layers. Finally, water can remain in a supercooled liquid state under certain conditions. During cold start, the temperature rises due to exothermic electrochemical reactions. A successful cold start requires the temperature of the catalyst layer 62, 70 to exceed the melting point of ice before the reaction sites and diffusion paths are blocked. In this case, the ice melts and liquid water can be drained, resulting in a low stoichiometry within the cathode, which cannot generate enough heat until the fuel cell warms up.

[0081] In another exemplary embodiment, the controller 34 is adapted to initiate adjustments to the control strategy of the fuel cell 50 based on the effective operating anode leakage rate or the shutdown leakage rate, including during standby operation, such as when the vehicle 10 is idling at a traffic light or during traffic congestion, the fuel cell 50 continuously and periodically monitors the pressure decay within the anode 54, and updates the shutdown leakage rate when the power output is zero.

[0082] During prolonged periods of inactivity, when a pressure drop within anode 54 indicates that oxygen 68 has leaked into anode 54, H2 confinement measures are used to ensure sufficient hydrogen 60 remains within anode 54 for startup operation. H2 confinement measures incorporate methods known in the industry suitable for ensuring that hydrogen 60 is not completely eliminated from anode 54 and cathode 56 during shutdown, thereby ensuring that when fuel cell 50 is restarted and startup operation begins, there is no oxygen in anode 54 for effective startup without damaging the electrodes of fuel cell 50. H2 confinement measures may be unnecessary when the pressures within both anode 54 and cathode 56 are higher than ambient air pressure. However, if the pressure within anode 54 or cathode 56 is lower than ambient air pressure, air may leak into fuel cell 50. If a pressure drop within anode 54 indicates that oxygen leakage into fuel cell 50 has occurred, controller 34 can initialize H2 confinement measures to compensate for this leakage.

[0083] refer to Figure 6 The method 200 for controlling the hydrogen fuel cell 50 includes, starting from block 202, using the fuel cell controller 34, measuring the anode leakage rate of the fuel cell 50, moving to block 204, modeling the effective electrolyte membrane orifice size using the measured anode leakage rate, moving to block 206, calculating the effective operating anode leakage rate during operation of the fuel cell 50 using the effective electrolyte membrane orifice size, moving to block 208, using the effective operating anode leakage rate as a low-side metric when calculating emission and dilution requests, and moving to block 210, initiating an adjustment of the control strategy for the fuel cell 50 based on the effective operating anode leakage rate or the shutdown leakage rate.

[0084] In an exemplary embodiment, measuring the anode leakage rate of the fuel cell 50 at block 202 further includes moving to block 212 to measure the anode shutdown leakage rate of the fuel cell 50. In another exemplary embodiment, measuring the anode leakage rate of the fuel cell 50 at block 202 further includes moving to block 214 to monitor pressure decay within the anode 54 during low-power operation of the fuel cell 50, and moving to block 216 to estimate the anode leakage rate based on the pressure decay within the anode 54 during low-power operation of the fuel cell 50.

[0085] In another exemplary embodiment, the adjustment of the control strategy for the fuel cell 50 based on the effective operating anode leakage rate or shutdown leakage rate further includes: moving to block 218 to increase the duration of an increased airflow through the cathode 56 of the fuel cell 50 during startup (which may be achieved through a cathode or cathode bypass valve) to dilute the concentration of hydrogen 60 leaking from the anode 54, wherein the bias voltage from the anode 54 to the cathode 56, the airflow rate, the airflow split, and the duration of the increased airflow are calculated based on the effective operating anode leakage rate.

[0086] In another exemplary embodiment, initiating an adjustment of the control strategy for the fuel cell 50 at block 210 based on the effective operating anode leakage rate or shutdown leakage rate further includes: moving to block 220 to adjust the venting function request frequency to vent hydrogen 60 from the anode 54 of the fuel cell 50 during operating operation of the fuel cell 50.

[0087] In another exemplary embodiment, initiating an adjustment of the control strategy for the fuel cell 50 at block 210 based on the effective operating anode leakage rate or shutdown leakage rate further includes: moving to block 222 to increase the airflow through the cathode 56 during the operation of the fuel cell 50 to compensate for the oxygen 68 consumed by the hydrogen 60 permeating through the electrolyte membrane 58.

[0088] In another exemplary embodiment, initiating an adjustment of the control strategy for the fuel cell 50 at block 210 based on the effective operating anode leakage rate or shutdown leakage rate further includes moving to block 224 to limit transient load rates during the operation of the fuel cell 50 to control emissions within the fuel cell 50 during and after power load fluctuations.

[0089] In another exemplary embodiment, the adjustment of the control strategy for the fuel cell 50 at block 210 based on the effective operating anode leakage rate or shutdown leakage rate further includes: during the shutdown operation of the fuel cell 50, moving to block 226 to directly discharge hydrogen 60 from the anode 54 and cathode 56 to the exhaust device at the tailpipe 101, and moving to block 228 to reduce the bias voltage between the anode 54 and cathode 56.

[0090] In another exemplary embodiment, initiating an adjustment of the control strategy for the fuel cell 50 at block 210 based on the effective operating anode leakage rate or shutdown leakage rate further includes: during a freeze-start operation of the fuel cell 50, moving to block 230 to reduce the bias voltage between the anode 54 and the cathode 56.

[0091] In another exemplary embodiment, the adjustment of the control strategy for the fuel cell 50 at block 210 based on the effective operating anode leakage rate or shutdown leakage rate further includes: during standby operation of the fuel cell 50, moving to block 232 to continuously and periodically monitor the pressure decay within the anode 54 when the power output is zero, and during long periods of non-use, moving to block 234 to initialize H2 residence measures to ensure that sufficient hydrogen 60 is maintained within the anode 54 for start-up operation when the pressure decay within the anode 54 indicates that oxygen 68 has leaked into the anode 54.

[0092] In yet another exemplary embodiment, method 200 further includes: moving to block 238 to update the measured anode leakage rate as long as the power output of fuel cell 50 is zero, wherein the method returns to block 204 and continues using the updated measured anode leakage rate.

[0093] The fuel cell 50, fuel cell propulsion system 20, and method 200 disclosed herein offer several advantages. These include determining how much airflow is needed to dilute the post-reaction fuel gas 90 leaving the anode 54 such that the concentration of hydrogen 60 therein is sufficiently low to be safely released into the atmosphere, and using an effective anode shutdown leakage rate or low-power operation leakage rate to achieve adjustments that allow the fuel cell 50 to continue operating after significant degradation of the electrolyte membrane 58. This eliminates concerns about emissions related to the balance between degradation of the electrolyte membrane 58 and equipment leakage directly into the exhaust system, as the controller 34 actively monitors this degradation / leakage and automatically balances operating parameters (airflow, transient load, opening / closing of anode purge or drain valves, cathode bypass valves, isolation valves, and back pressure valves) to compensate for the degradation of the electrolyte membrane 58 and equipment leakage, ensuring that emissions from the fuel cell 50 are within acceptable limits.

[0094] Furthermore, various aspects of the fuel cell 50, fuel cell propulsion system 20, and method 200 disclosed herein allow the fuel cell 50 to automatically adjust its operating parameters to allow it to operate at acceptable emission levels based on the balance between anode and equipment degradation / leakage (direct leakage to the exhaust device) by actively monitoring and automatically detecting when degradation of the electrolyte membrane 58 and equipment leakage (direct leakage to the exhaust device) occur.

[0095] Finally, in this context, regarding the cost of such an adjustment leading to a reduction in the performance of the fuel cell 50 (lower power output), the owner / operator of a vehicle equipped with a fuel cell 50 or fuel cell propulsion system 20 according to the teachings of this disclosure will have the ability to selectively decide to accept the performance reduction benefits implemented by the controller 34, thereby extending the lifespan of the fuel cell 50, or to determine that the fuel cell 50 should be repaired / replaced immediately upon such an adjustment being implemented by the controller 34. This allows the owner / operator to make decisions that improve the overall customer experience.

[0096] The description in this disclosure is merely exemplary in nature, and variations thereof without departing from the spirit and scope of this disclosure are intended to fall within its scope. Such variations should not be considered as departing from the spirit and scope of this disclosure.

Claims

1. A method for controlling a hydrogen fuel cell, comprising: Using the controller of the fuel cell: Measure the anode leakage rate of the fuel cell; The effective electrolyte membrane orifice size was modeled using the measured anode leakage rate; Based on the current operating conditions, the effective operating anode leakage rate during the operation of the fuel cell is calculated using the effective electrolyte membrane orifice size. When calculating emissions and dilution requirements, the effective operating anode leakage rate is used as a low-side metric. as well as The control strategy for the fuel cell is adjusted based on the effective operating anode leakage rate or shutdown leakage rate.

2. The method according to claim 1, wherein, The measurement of the anode leakage rate of the fuel cell also includes measuring the anode shutdown leakage rate of the fuel cell.

3. The method according to claim 1, wherein, The measurement of the anode leakage rate of the fuel cell also includes: During low-power operation of the fuel cell, the pressure decay within the anode is monitored; and At least one of the following: The anode leakage rate is estimated based on the pressure decay within the anode during low-power operation of the fuel cell; and The anode leakage rate is calculated based on both anode pressure changes and cathode pressure changes.

4. The method according to claim 1, wherein, The adjustment of the control strategy for the fuel cell based on the effective operating anode leakage rate or shutdown leakage rate also includes: During the startup of the fuel cell, the duration of the increased airflow through the cathode of the fuel cell is increased to dilute the concentration of hydrogen leaking from the anode. The anode-to-cathode bias, airflow rate, airflow split, and duration of the increased airflow are calculated and adjusted based on one of the following: The effective operating anode leakage rate; or The downtime leakage rate.

5. The method according to claim 4, wherein, The adjustment of the control strategy for the fuel cell based on the effective operating anode leakage rate or shutdown leakage rate further includes: adjusting the venting request frequency during the operation of the fuel cell to vent gas from the anode of the fuel cell.

6. The method according to claim 5, wherein, The adjustment of the control strategy for the fuel cell based on the effective operating anode leakage rate or shutdown leakage rate further includes: increasing the airflow through the cathode during the operation of the fuel cell to compensate for the oxygen consumed by the hydrogen permeating through the electrolyte membrane.

7. The method according to claim 6, wherein, The adjustment of the control strategy for the fuel cell based on the effective operating anode leakage rate or shutdown leakage rate further includes: limiting the transient load rate during the operation of the fuel cell to control emissions during and after power load fluctuations.

8. The method according to claim 4, wherein, The adjustment of the control strategy for the fuel cell based on the effective operating anode leakage rate or shutdown leakage rate further includes: performing at least one of the following during the operation of the fuel cell: Reduce the frequency of venting; Increase the gas flow through the cathode to compensate for the oxygen consumed by the hydrogen permeating through the electrolyte membrane; and Limit transient load rates to control emissions during and after power load fluctuations.

9. The method according to claim 8, wherein, The adjustment of the control strategy for the fuel cell based on the effective operating anode leakage rate or shutdown leakage rate also includes during the shutdown operation of the fuel cell: Hydrogen gas is directly discharged from the anode and the cathode to an exhaust device; and Reduce the pressure of the anode and cathode.

10. The method according to claim 9, wherein, The adjustment of the control strategy for the fuel cell based on the effective operating anode leakage rate or shutdown leakage rate further includes: reducing the bias voltage between the anode and the cathode during the freeze-start operation of the fuel cell.

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