Method for controlling a hydrogen fuel cell

Abstract

A method for controlling a hydrogen fuel cell includes, with fuel cell control, measuring an anode leakage rate for the fuel cell, modeling, using the measured anode leakage rate, an effective electrolyte membrane opening size, calculating, using the effective electrolyte membrane opening size, an effective runtime anode leakage rate during fuel cell operation, using the effective runtime anode leakage rate as a low-side metric in calculating emissions and dilution requirements, and initiating adjustments to a fuel cell control strategy based on the effective runtime anode leakage rate and the shutdown leakage rate to extend the fuel cell lifetime.

Description

[0001] The present invention relates generally to fuel cells and, in particular, to control systems for fuel cells. In some applications, fuel cells are designed such that the fuel and oxidant supply flows are flow-through systems; however, these systems add a parasitic load to the fuel cell power and thus reduce the net power that can be extracted. In other configurations, the fuel or oxidant flow, or both, are dead ends. This dead-end operation leads to problems such as water removal and the accumulation of impurities. Furthermore, the degradation of the electrolyte membrane, which separates the anode and cathode, negatively affects the fuel cell and is generally an indication of the end of a fuel cell's service life.

[0002] German patent application DE 10 2013 112 460 A1 describes a system and a method for quantifying anode leakage in a fuel cell system. The system and method include determining whether a leak exists in an anode subsystem of a fuel cell stack and estimating a first effective leakage area using a first leakage value and first operating parameters. The system and method further include increasing airflow to the cathode side of the fuel cell stack and estimating a second effective leakage area using a second leakage flow value and second operating parameters. The system and method also include comparing the first effective leakage area with the second effective leakage area and determining an anode outflow leakage location based on this comparison.

[0003] US 2011 / 0138883A1 describes a method for determining the amount of fuel flow from a high-pressure gas tank to the anode side of a fuel cell stack through a pulsed injector. The anode subsystem pressure is measured just before and just after the injector pulse, and the difference between these pressures is determined. The pressure difference, the volume of the anode subsystem, the ideal gas constant, the anode subsystem temperature, the fuel consumed by the reaction in the fuel cell stack during the injection event, and the fuel transfer through membranes in the fuel cells of the fuel cell stack are used to determine the amount of hydrogen gas injected by the injector.

[0004] The task can be considered to be to specify an improved method for controlling a fuel cell, whereby the operating parameters of the fuel cell are modified based on an effective leakage rate of the electrolyte membrane, which allows for an extended lifetime of the fuel cell when there is a leakage at the electrolyte membrane.

[0005] The problem is solved by a method according to claim 1. Furthermore, a fuel cell is described which can be operated, for example, using the method.

[0006] A method according to the invention for controlling a hydrogen fuel cell comprises, with a fuel cell controller, measuring an anode leakage rate for the fuel cell, modeling, using the measured anode leakage rate and an effective electrolyte membrane opening size, calculating, using the effective electrolyte membrane opening size, an effective runtime anode leakage rate during operation of the fuel cell based on the current operating conditions, using the effective runtime anode leakage rate as a low-side metric in calculating emissions and dilution requirements, and initiating adjustments to a fuel cell control strategy based on one of the following elements: the effective runtime anode leakage rate or a shutdown leakage rate. Measuring an anode leakage rate for the fuel cell further comprises measuring an anode shutdown leakage rate for the fuel cell.

[0007] In one embodiment, measuring an anode leakage rate for the fuel cell further comprises monitoring the pressure drop within the anode during low-power operation of the fuel cell; and at least one of the following steps: estimating the anode leakage rate based on the pressure drop within the anode during low-power operation of the fuel cell and calculating the anode leakage rate based on the anode pressure change as well as the cathode pressure change.

[0008] In one embodiment, initiating adjustments to the fuel cell's control strategy based on the effective run-time anode leakage rate or the shutdown leakage rate further comprises, during fuel cell start-up, increasing the duration of enhanced airflow through a fuel cell cathode to dilute the concentration of hydrogen escaping from the anode, wherein the anode-cathode bias pressure, airflow rate, airflow split, and duration of enhanced airflow are calculated and set based on one of the following: the effective run-time anode leakage rate or the shutdown leakage rate.

[0009] In one embodiment, initiating adjustments to the fuel cell's control strategy based on the effective runtime anode leakage rate or the shutdown leakage rate further includes adjusting, during the fuel cell's runtime operation, a bleed request frequency to vent gas from the fuel cell's anode.

[0010] In one embodiment, initiating adjustments to the fuel cell's control strategy based on the effective runtime anode leakage rate or the shutdown leakage rate further includes increasing, during the fuel cell's runtime operation, the airflow through the cathode to compensate for oxygen consumed by hydrogen gas penetrating the electrolyte membrane.

[0011] In one embodiment, initiating adjustments to the fuel cell's control strategy based on the effective runtime anode leakage rate or the shutdown leakage rate further includes limiting transient load rates during the fuel cell's runtime operation in order to control emissions during and after power load fluctuations.

[0012] In one embodiment, initiating adjustments to the fuel cell's control strategy based on the effective runtime anode leakage rate or the shutdown leakage rate further comprises, during the fuel cell's runtime operation, at least one of the following elements: reducing the bleed frequency, increasing the airflow through the cathode to compensate for the oxygen consumed by the hydrogen gas penetrating the electrolyte membrane, and limiting the transient load rates to control emissions during and after power load fluctuations.

[0013] In one embodiment, initiating adjustments to the fuel cell's control strategy based on the effective runtime anode leakage rate or the shutdown leakage rate further includes, during a shutdown operation of the fuel cell, venting hydrogen gas from the anode and cathode directly to the exhaust, and reducing the anode and cathode pressure.

[0014] In one embodiment, initiating adjustments to the fuel cell's control strategy based on the effective runtime anode leakage rate or the shutdown leakage rate further includes, during a freeze-start operation of the fuel cell, reducing the preload pressure between the anode and the cathode.

[0015] In one embodiment, initiating adjustments to the fuel cell's control strategy based on the effective runtime anode leakage rate or the shutdown leakage rate further includes, during standby operation of the fuel cell, the continuous, periodic monitoring of the pressure drop within the anode, and during a longer period of non-use, the initiation of H2-in-park measures to ensure that sufficient hydrogen gas remains in the anode and cathode for a start-up process if the pressure drop in the anode indicates that oxygen has entered the anode.

[0016] In one embodiment, the method further includes updating the measured anode leakage rate when the power output of the fuel cell is zero.

[0017] An exemplary fuel cell is described. The exemplary fuel cell comprises an anode, a cathode, an electrolyte membrane positioned between the anode and the cathode, and a controller designed to measure an anode leakage rate for the fuel cell and to update the measured anode leakage rate whenever the fuel cell's power output is zero, to model an effective electrolyte membrane opening size using the measured anode leakage rate, to calculate an effective runtime anode leakage rate during fuel cell operation using the effective electrolyte membrane opening size, to use the effective runtime anode leakage rate as a low-side metric in calculating emissions and dilution requirements, and to initiate adjustments to a fuel cell control strategy based on either the effective runtime anode leakage rate or a shutdown leakage rate.

[0018] For example, the control system for measuring the anode leakage rate for the fuel cell is also designed to measure an anode shutdown leakage rate for the fuel cell.

[0019] For example, the control system for measuring the anode leakage rate of the fuel cell is further designed to monitor the pressure drop within the anode during low-power operation of the fuel cell and to estimate the anode leakage rate based on the pressure drop within the anode during low-power operation of the fuel cell.

[0020] For example, when initiating adjustments to the fuel cell's control strategy based on the effective run-time anode leakage rate or the shutdown leakage rate, the control is further designed to increase the duration of the increased airflow through a fuel cell cathode during fuel cell start-up in order to dilute the concentration of hydrogen leaked from the anode, whereby the anode-cathode bias pressure, airflow rate, airflow split, and duration of the increased airflow are calculated based on the effective run-time anode leakage rate or the shutdown leakage rate.

[0021] For example, while initiating adjustments to the fuel cell's control strategy based on the effective runtime anode leakage rate or the shutdown leakage rate, the control system is further designed to perform at least one of the following actions during the fuel cell's runtime operation: reducing the bleed frequency, increasing the airflow through the cathode to compensate for the oxygen consumed by the hydrogen gas penetrating the electrolyte membrane, and limiting transient load rates to control emissions during and after power fluctuations.

[0022] For example, while initiating adjustments to the fuel cell's control strategy based on the effective runtime anode leakage rate or the shutdown leakage rate, the control system is further designed to vent hydrogen gas from the anode and cathode directly into the exhaust during a fuel cell shutdown operation, thereby reducing the anode and cathode pressure.

[0023] For example, while initiating adjustments to the fuel cell's control strategy based on the effective runtime anode leakage rate or the shutdown leakage rate, the control system is further designed to reduce the bias pressure between the anode and cathode during a freeze-start operation of the fuel cell, and, during a longer period of fuel cell non-use, to continuously monitor the pressure drop within the anode on a periodic basis and to initiate H2-in-park measures to ensure that sufficient hydrogen gas remains within the anode for a start operation if the pressure drop within the anode indicates that oxygen has entered the anode. Fig. Figure 1 is a schematic view of a vehicle with a fuel cell propulsion system, which includes a fuel cell; Fig. Figure 2 is a schematic side view of a fuel cell; Fig. 3 is a schematic block diagram of the in Fig. 2 fuel cell shown; Fig. 4A is a schematic side view of the in Fig. 2 shown fuel cell, illustrating how hydrogen migrates from the anode to the cathode through permeation within the electrolyte membrane; Fig. 4B is the schematic side view of the in Fig. 4A fuel cell shown, wherein the airflow device increases the airflow through the cathode; Fig. 4C is the schematic side view of the in Fig. 4A fuel cell shown, wherein the airflow device increases the airflow through both the cathode and a cathode bypass valve; Fig. 4D is the schematic side view of the in Fig. 4A fuel cell shown, wherein the cathode bypass valve is closed and the airflow device maintains an increased airflow through the cathode to force the remaining hydrogen out of the cathode; Fig. 5 is the schematic side view of the in Fig. 4A fuel cell shown, wherein, during a shutdown operation, a shut-off valve is open so that hydrogen gas can be vented from the anode via an anode purge valve through the cathode to an exhaust pipe or directly to the exhaust pipe of the vehicle; Fig. Figure 6 is a schematic flowchart illustrating a process.

[0024] Exemplary embodiments are now described in more detail with reference to the accompanying drawings. In accordance with one exemplary embodiment, it shows Fig. 1 A vehicle 10 with an associated fuel cell 50. The vehicle 10 generally comprises a chassis 12, a body 14, front wheels 16, and rear wheels 18. The body 14 is mounted on the chassis 12 and essentially encloses components of the vehicle 10. The body 14 and the chassis 12 can together form a frame. The front wheels 16 and the rear wheels 18 are each rotatably connected to the chassis 12 near a corner of the body 14.

[0025] In various embodiments, the vehicle 10 is an autonomous vehicle. For example, an autonomous vehicle 10 is one that is automatically controlled to transport passengers from one place to another. In the embodiment shown, the vehicle 10 is depicted as a passenger car, but it should be noted that any other vehicle, including motorcycles, trucks, sport utility vehicles (SUVs), motorhomes (RVs), etc., can also be used. In one exemplary embodiment, the vehicle 10 is equipped with a so-called Level Four or Level Five automation system. A Level Four system signifies a "high degree of automation," meaning that an automated drive system takes over all aspects of the dynamic driving task, depending on the driving mode, even if a human driver does not respond appropriately to a request for intervention.A Level 5 system means "full automation" and refers to the complete execution of all aspects of the dynamic driving task by an automated drive system under all road and environmental conditions that can be handled by a human driver. The new aspects of this description are also applicable to non-autonomous vehicles.

[0026] As shown, the vehicle 10 generally comprises a fuel cell drive system 20, a transmission system 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 control unit 34, and a wireless communication module 36. In an embodiment in which the vehicle 10 is an electric vehicle powered by the fuel cell 50 or a stack of multiple fuel cells 50, the transmission system 22 may be omitted. The transmission system 22 is configured to transmit the power of the fuel cell drive system 20 to the front wheels 16 and the rear wheels 18 of the vehicle according to selectable gear ratios. In various embodiments, the transmission system 22 may comprise a continuously variable automatic transmission, a continuously variable transmission, or another suitable transmission.The braking system 26 is configured to exert a braking torque on the front wheels 16 and the rear wheels 18 of the vehicle. The braking system 26 may, in various embodiments, comprise friction brakes, a wire brake, a regenerative braking system such as an electric motor, and / or other suitable braking systems. The steering system 24 influences the position of the front wheels 16 and the rear wheels 18. While it is shown for illustrative purposes that it includes a steering wheel, the steering system 24 may, in some embodiments considered within the scope of this description, such as a fully autonomous vehicle, not include a steering wheel.

[0027] The sensor system 28 comprises one or more sensing devices 40a-40n that detect observable conditions of the external environment and / or the internal environment of the autonomous vehicle 10. The sensor devices 40a-40n may include, but are not limited to, radars, lidars, global positioning systems, optical cameras, thermal cameras, ultrasonic sensors, and / or other sensors. In an exemplary embodiment, the plurality of sensing devices 40a-40n comprises at least an engine speed sensor, an engine torque sensor, an electric 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 plurality of sensing devices 40a-40n further comprises sensors for determining information about the environment of the vehicle 10, for example, an ambient air temperature sensor, an air pressure sensor, and / or a photo and / or video camera positioned to view the environment in front of the vehicle 10. The actuator system 30 comprises one or more actuator devices 42a-42n that control one or more features of the vehicle 10, such as, but not limited to, the drive system 20, the transmission system 22, the steering system 24, and the braking system 26.

[0028] The vehicle control unit 34 comprises 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-designed or commercially available processor, a central processing unit (CPU), a graphics processing unit (GPU), an auxiliary processor among several processors connected to the vehicle control unit 34, a semiconductor-based microprocessor (in the form of a microchip or chipset), a macroprocessor, any combination thereof, or generally any device for executing instructions. The computer-readable storage device or medium 46 can comprise volatile and non-volatile memory, e.g., read-only memory (ROM), random-access memory (RAM), and keep-alive memory (RAM).(keep-alive memory, KAM). KAM is a persistent or non-volatile memory that can be used to store various operating variables while at least one processor 44 is switched off. The computer-readable memory device or computer-readable storage medium 46 can be implemented using any number of known memory devices such as PROMs (programmable read-only memory), EPROMs (electrical PROMs), EEPROMs (electrically erasable PROMs), flash memory, or other electrical, magnetic, optical, or combined memory devices capable of storing data, some of which represent executable instructions used by the controller 34 in controlling the vehicle 10.

[0029] The instructions can comprise one or more separate programs, each containing an ordered list of executable instructions for implementing logical functions. When executed by the at least one processor 44, the instructions receive and process signals from the sensor system 28, perform logic, calculations, procedures, and / or algorithms to automatically control the components of the vehicle 10, and generate control signals for the actuator system 30 to automatically control the components of the vehicle 10 based on the logic, calculations, procedures, and / or algorithms. Although in Fig. 1 where only one controller 34 is shown, embodiments of the vehicle 10 may include any number of controllers 34 which communicate via any suitable communication medium or combination of communication media and which cooperate to process the sensor signals, perform logic, calculations, methods and / or algorithms and generate control signals to automatically control features of the autonomous vehicle 10.

[0030] The wireless communication module 36 is configured to wirelessly transmit information to and from other remote units 48, such as other vehicles (“V2V” communication), infrastructure (“V2I” communication), remote systems, remote servers, cloud computers, and / or personal devices. In one exemplary embodiment, the communication system 36 is a wireless communication system configured to communicate over a wireless local area network (WLAN) using IEEE 802.11 standards or using cellular data communication. However, additional or alternative communication methods, such as a dedicated short-range communication channel (DSRC channel), are also considered within the scope of this description.DSRC channels refer to one- or two-way short- to medium-range wireless communication channels specifically designed for use in motor vehicles, as well as a range of protocols and standards.

[0031] The vehicle control unit 34 is a non-general electronic control unit comprising a pre-programmed digital computer or processor, memory or non-transient computer-readable medium used to store data such as control logic, software applications, instructions, computer code, data, lookup tables, etc., and a transceiver [or input / output connectors]. Computer-readable media includes all types of media accessible to a computer, such as read-only memory (ROM), random-access memory (RAM), a hard disk drive, a compact disc (CD), a digital video disc (DVD), or any other type of storage. A "non-transient" computer-readable medium excludes wired, wireless, optical, or other communication links carrying transient electrical or other signals.A non-transitory computer-readable medium includes media on which data can be permanently stored and media on which data can be stored and later overwritten, such as a rewritable optical disc or an erasable storage device.

[0032] Computer code encompasses all types of program code, including source code, object code, and executable code.

[0033] With reference to the Fig. 2, the fuel cell propulsion system 20 comprises a stack 52 with 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 free energy change resulting from an oxidation reaction is converted into electrical energy. A fuel cell 50 comprises an anode 54 (fuel electrode) and a cathode 56 (oxidation electrode) separated by an interposed ion-conducting electrolyte 58. 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 (H2). +) 64 and electrons 66. Gaseous hydrogen 60 has high reactivity and high energy density in the presence of a suitable catalyst 62. Similarly, an oxidizing agent 68 (usually air, O2) is supplied to the cathode 56 of the fuel cell, which reacts with a suitable catalyst 70 at the cathode 56. Gaseous oxygen 68 is readily and inexpensively available in air for use in fuel cells. The anode 54 receives hydrogen gas 60, and the cathode 56 receives oxygen 68 or air.

[0034] The hydrogen gas 60 is dissociated in the anode 54 to generate free hydrogen protons 64 and electrons 66. The anode 54 and the cathode 56 are electrically connected to a load 72 (e.g., an electronic circuit) via an external circuit conductor. The hydrogen protons 64 pass through the electrolyte 58 to the cathode 56, as indicated by arrow 74. The electrons 66 from the anode 54 cannot pass through the electrolyte 58 and are therefore conducted through the load 72, as indicated by arrow 76, to perform work before being sent to the cathode 56, as indicated by arrow 78. Proton exchange membrane fuel cells (PEMFCs) are a popular type of fuel cell for vehicles and generally include a proton-conducting membrane made of solid polymer electrolyte for an electrolyte 58, such as hydrogen. B. a perfluorosulfonic acid membrane.The catalysts 62, 70 of the anode 54 and the cathode 56 typically consist of finely dispersed catalytic particles, usually platinum (Pt), applied to carbon particles and mixed with an ionomer, with the catalytic mixture being deposited on opposite sides of the electrolyte membrane 58. The combination of the anode catalyst mixture (anode catalyst 62), the cathode catalyst mixture (cathode catalyst 70), the gas diffusion layers 134, 136, and the membrane (electrolyte 58) forms a membrane electrode assembly (MEA). The membranes block the transport of gases between the anode side 54 and the cathode side 56 of the fuel cell 50, while allowing the transport of protons 64 to carry out the anodic and cathodic reactions at the respective electrodes 54, 56.At the cathode 56, the oxygen gas 68 reacts with the hydrogen protons 64 migrating through the electrolyte 58 and the incoming electrons 66 from the external circuit, producing water 80 as a byproduct. This byproduct, water 80, is typically removed as steam. The overall reaction occurring in the fuel cell 50 is the sum of the reactions at the anode 54 and the cathode 56, with some of the free reaction energy being released directly as electrical energy (used by the load 72). The difference between this available free energy and the heat of reaction is generated as heat, as indicated by arrow 82.

[0035] In an exemplary embodiment, several fuel cells 50 are combined in a fuel cell stack 52 to generate the desired power output. A fuel cell stack 52 typically comprises a series of flow-field or bipolar plates arranged between the various MEAs in the stack 52, with the bipolar plates and the MEAs positioned between two end plates. The bipolar plates include an anode side and a cathode side for adjacent fuel cells 50 in the stack 52. Anode gas flow channels are provided on the anode side of the bipolar plates, through which the anode reactant gas 60 can flow to the respective MEA. Cathode gas flow channels are provided on the cathode side of the bipolar plates, through which the cathode reactant gas 68 can flow to the respective MEA. One end plate contains anode gas flow channels, and the other end plate contains cathode gas flow channels.The bipolar plates and end plates are made of a conductive material, such as stainless steel or a conductive composite. The end plates conduct the current generated by the fuel cells out of the stack 52. The bipolar plates also contain flow channels through which a coolant flows. The fuel (hydrogen) 60 and the oxidizer (air) 68 are directed to their respective sides 54 and 56 via distributors. In some applications, the fuel 60 and oxidizer 68 supply flows are designed as flow-through systems, which, however, add a parasitic load to the power of the fuel cell 50 and thus reduce the net extractable power. In other configurations, the fuel flow or the oxidizer flow, or both, are dead ends. This dead-end operation leads to problems such as water loss and impurity buildup.Therefore, in an exemplary embodiment of the present description, the flow capacity of the fuel 60 into and through the anode side 54 of the fuel cell 50 is controlled by an anode valve 84 or anode valves that allow a selective flow of the converted fuel gas 90 from the anode 54 to the atmosphere surrounding the fuel cell 50.

[0036] The MEAs in the fuel cells 50 are permeable and therefore allow nitrogen in the air to pass from the cathode side 56 of the stack through the anode side 54 of the stack 52 and accumulate there, a phenomenon often referred to as nitrogen crossover. Although the pressure on the anode side 54 may be somewhat higher than the pressure on the cathode side 56, the partial pressures on the cathode side 56 cause air to pass through the electrolyte membrane 58. Nitrogen on the anode side 54 of the fuel cell 50 dilutes the hydrogen 60, so that the fuel cells 50 in the stack 52 can become depleted of hydrogen 60 if the nitrogen concentration rises above a certain percentage, e.g., 50%. If a fuel cell 50 becomes depleted of hydrogen, the fuel cell stack 52 cannot generate sufficient electrical power and the catalyst 62 in the anode 54 and the catalyst 70 in the cathode 56 in the fuel cell stack 52 may be damaged.Furthermore, under high load, the evaporation of the byproduct water 80 at the cathode 56 occurs more slowly than its formation, and the water 80 tends to migrate back through the polymer electrolyte 58 to the anode side 54. Some areas of the fuel cell 50 are cooler than others, and the 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, which can poison the reaction sites of the anode. Inert impurities also lead to performance losses because they lower the fuel partial pressure. 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 stack 52.This allows for the controlled venting of a portion (perhaps from 0.1 to 10%) of the gaseous fuel (reactive fuel gas) through a throttled opening, thereby removing accumulated impurities, water, and fine particles from the anode side and restoring the fuel cell's performance. For clarity and to avoid confusion, the accumulated gases that are vented are referred to here as "reactive fuel gas." It should be clear to experts that the reacted fuel gas is primarily hydrogen with traces of water and possibly nitrogen, carbon dioxide, and carbon monoxide. Depending on the fuel cell's design, other gases may also be present in the reactive fuel gas.

[0037] A fuel cell propulsion system control system comprises control algorithms that determine a desirable minimum concentration of hydrogen gas 60 in the anode 54 and cause the anode valve 84 to open when the gas concentration falls below this threshold. It also controls the duration and intervals between successive purging cycles and monitors the fuel cell's power output to ensure that the output is approximately proportional to the amount of hydrogen 60 consumed by the fuel cell 50. The fuel cell propulsion system control system can be the vehicle control unit 34 or a separate control unit that communicates with the vehicle control unit 34 and is responsible for controlling the fuel cell propulsion system 20. However, the release of hydrogen 60 into the atmosphere can pose a safety risk if the hydrogen 60 concentration exceeds a target value.By increasing the airflow 68 into the cathode side 56 of the fuel cell 50, the hydrogen 60 contained in the purged gas is diluted so that the hydrogen concentration in the exhaust pipe 101 is low enough to be safely discharged into the atmosphere when the purged gas reaches the atmosphere surrounding the fuel cell 50.

[0038] It is known in engineering to estimate the molar fraction of gases in the anode side 54 of a fuel cell stack 52 using a sensor or model to determine when to bleed the anode side 54 or the anode subsystem. For example, gas concentration estimation (GCE) models are known to estimate hydrogen, nitrogen, oxygen, water vapor, etc., in various volumes of a fuel cell system, such as in the anode flow field, anode lines, cathode flow field, cathode head, and other lines. This allows the controller 34 to determine when to initiate the opening of the anode valve 84 for purging.

[0039] Furthermore, it is known in engineering to monitor and measure gas leaks at the anode 54 in a fuel cell 50. Gas leaks from the anode 54 subsystem in a fuel cell 50 pose a significant problem, as the hydrogen gases present in the mixture can impair the overall efficiency of the system and product safety. For example, cracks in the bipolar plate and / or the seal can present significant safety risks, which can have catastrophic consequences for an otherwise repairable fuel cell stack and potentially create a hazardous environment for the vehicle operator. Moreover, due to emission requirements, the detection of hydrogen gas leaks must be accurate to ensure regulatory compliance and enable reactive measures to be taken if gas escapes from the anode 54.

[0040] There are known methods for determining the total amount of molecular gas in the anode volume 54 of the fuel cell stack 52 at the beginning of a leak detection period during the leak detection condition. Such methods also determine a crossover loss of hydrogen gas 60 from the anode volume 54 of the fuel cell stack 52 during the leak detection period as a result of permeation through membranes (electrolyte membrane 58) in the fuel cell stack 52; determine an overboard loss of hydrogen gas 60 from the anode volume 54 of the fuel cell stack 52 during the leak detection period as a result of permeation through other components, such as O-rings, valves, and seals, in the fuel cell stack 52; and determine a reaction loss of hydrogen gas 60 from the anode volume 54 of the fuel cell stack 52 during the leak detection period as a result of an electrochemical reaction in the stack 52.These procedures also determine the total amount of molecular gas in the anode volume 54 of the fuel cell stack 52 at the end of the leak detection period and subtract it from the hydrogen gas 60 present in the anode volume 54 at the beginning of the leak detection condition, yielding the total gas loss. The crossover, overboard, and reaction losses are added to obtain an additional loss, which is subtracted from the total gas loss to determine the anode volume 54 leakage loss. This anode leakage loss is compared to a predefined threshold to determine whether the gas leak is large enough to trigger the end of life of the fuel cell 50.

[0041] Further details on measuring the shutdown leakage rate of the anode 54 of a fuel cell 50 are contained in US patent US 8 524 405 B2 Salvador et al., granted on September 3, 2013, and US patent US 11 043 682 B2 Gagliardo et al., granted on June 22, 2021, both of which are assigned to GM Global Technology Operations LLC.

[0042] In an exemplary embodiment of the present description, the controller 34 of the fuel cell 50 is able to measure an anode leakage rate for the fuel cell 50 and to update the measured anode leakage rate whenever the power output of the fuel cell 50 is zero, either by measuring an anode shutdown leakage rate for the fuel cell according to known methods as described above, or by monitoring the pressure drop within the anode 54 during low-power operation of the fuel cell 50 and by estimating the anode leakage rate based on the pressure drop observed within the anode 54 during low-power operation of the fuel cell 50. The measured anode leakage rate can be updated whenever the fuel cell 50 is operated at zero power consumption.Each time current flows through fuel cell 50, errors occur during leak testing. Therefore, the measured anode leak rate is updated when fuel cell 50 is not drawing current, for example, when vehicle 10 is stationary in traffic. The estimated low-power leak rate is used as a substitute for the fuel cell 50 power-out leak rate (shutdown leak rate) for calculating the effective leak opening size in situations where the shutdown leak rate cannot be successfully performed or cannot be performed regularly due to long operating times. Cathode pressure also affects the rate of change of anode pressure. This becomes even more pronounced when the fuel cell membrane degrades. Therefore, the patented method for measuring the anode shutdown leak rate can be updated to account for both the change in anode pressure and the change in cathode pressure when measuring the anode leak rate.

[0043] The controller 34 is then able to model an effective electrolyte membrane opening size based on the measured anode leakage rate. The controller 34 thus uses the measured anode leakage rate to model an opening size within the electrolyte membrane 58 that corresponds to the measured anode leakage rate. With the modeled electrolyte membrane opening size, the controller 34 can calculate an effective anode leakage rate for each operating state of the fuel cell 50. Subsequently, the controller 34 calculates an effective runtime anode leakage rate during operation of the fuel cell based on the effective electrolyte membrane opening size.

[0044] As mentioned previously, increasing the airflow 68 to the cathode side 56 or the bypass valve 110 of the fuel cell 50 dilutes the hydrogen 60 present in the purged gas (reactive fuel gas 90) so that the concentration of hydrogen 60, when the purged gas reaches the atmosphere surrounding the fuel cell 50, is low enough to be safely vented into the atmosphere. Once the controller 34 has calculated the effective anode leakage rate during operation, it uses this rate as a low-side parameter when calculating emissions and dilution requirements. Thus, regardless of other operating conditions, the controller 34 uses the calculated effective anode leakage rate during operation as a baseline and calculates the emission values ​​and dilution requirements based on the presumed hydrogen gas values ​​according to the calculated effective anode leakage rate during operation.

[0045] Furthermore, the controller 34 is capable of directly initiating adjustments to the fuel cell 50's control strategy based on the effective runtime anode leakage rate or the shutdown leakage rate. Such adjustments include modifying the fuel cell 50's operating parameters to compensate for the leak. As the electrolyte membrane 58 deteriorates over time, the controller 34 calculates and updates an effective anode leakage rate and, instead of triggering the fuel cell 50's end-of-life, initiates adjustments to the control strategy by modifying the operating parameters to account for and compensate for the anode leak at the electrolyte membrane 58, thus enabling continued safe operation of the fuel cell 50 beyond anode leakage rates that would traditionally trigger the end of its life.

[0046] With further reference to Fig. 2, Fig. 3 and Fig. 4A In an exemplary embodiment of the present description, the control unit 34 is designed to monitor, with a first sensor or model 86 connected to the control unit 34, the concentration of hydrogen gas 60 present at the anode 54 of the fuel cell 50; with a second sensor or model 88 connected to the control unit 34, the accumulated liquid water 80 present at the anode 54 of the fuel cell 50 (which is collected in a liquid reservoir 140); and to initiate a selective purge of reacted fuel gas 90 (via the opening of an anode purge valve 122) when the concentration of hydrogen gas 60 present at the anode 54 is lower than a predetermined concentration, or to drain liquid water 80 from the anode 54 of the fuel cell 50.when the amount of accumulated liquid water 80 present at the anode 54 (within the liquid accumulator 140) is greater than a predetermined threshold, a water drain valve 142 is opened, allowing liquid water 80 to be drained from the liquid accumulator 140 to the cathode inlet 144 or to the exhaust pipe 101.

[0047] The control unit 34, with the aid of the first sensor or model 86, can detect when the concentration of hydrogen gas 60 in the anode drops due to the presence of too much nitrogen or other impurities in the reacted fuel gas 90, and thus cause the control unit 34 to initiate a selective purge of the reacted fuel gas 90 from the anode 54. This reduces the pressure in the anode 54, allowing pure H2 fuel 60 to enter the anode 54 from the injection nozzle, thereby increasing the amount of hydrogen 60 in the anode 54.Likewise, the control unit 34 can detect, using the second sensor or model 88, when the amount of accumulated liquid water 80 inside the anode 54 rises to a level that hinders the catalytic reaction of the hydrogen gas 60 inside the anode 54, causing the control unit 34 to initiate a selective drain of the liquid water from the anode 54 through the water drain valve 142.

[0048] Once the controller 34 initiates a selective purging or emptying of the anode 54, it monitors the air flow rate 68 into the fuel cell 50 using a third sensor or model 92 and estimates the required air flow rate 68 into the fuel cell 50 necessary to dilute the hydrogen 60 concentration in the exhaust pipe 101 below a predetermined value. As mentioned earlier, a safe hydrogen 60 concentration in the discharged reactive fuel gas 90 (exhaust pipe 101) is below a target value. The controller 34 purges the anode 54 with highly concentrated H2 (e.g., 75%) into the cathode inlet 144 or the exhaust pipe 101. Simultaneously, a high airflow is directed through the cathode 56 or the bypass valve 110 to the outlet (exhaust pipe 101). If sufficient additional air is supplied, the H2 concentration in the exhaust gas at exhaust 101 is below a target value. There are two possibilities.The first option is to direct the air into the cathode inlet, the second into the exhaust. The advantage of the first option is that highly concentrated H2 in the cathode 56 mixes with air and reacts to directly produce water. Therefore, the amount of H2 entering the exhaust at the exhaust pipe 101 is significantly reduced.

[0049] The controller 34 increases the air flow rate 68 into the fuel cell 50 by actuating an airflow device 94, which can force air 68 into the fuel cell 50. The airflow from the airflow device 94 can force air through the shut-off valve 102 into the cathode 56, or alternatively, the airflow from the airflow device 94 can force air through the cathode bypass valve 110 directly to the exhaust (end pipe 101). The airflow device 94 can be a blower, a turbine, or a compressor that draws in ambient air from outside and forces the air 68 into the fuel cell 50. The controller 34 increases the force with which the airflow device forces the air 68 into the fuel cell, thus increasing the volume of air 68 forced through the fuel cell.Under normal operating conditions, the airflow device 94 is designed to introduce air 68 into the fuel cell 50 at a normal operating flow rate. When a purge of the reacted fuel gas 90 or a discharge of liquid water is initiated, the controller 34 actuates the airflow device 94 to increase the flow rate of the air 68 entering the fuel cell 50 from the normal operating flow rate to the estimated required flow rate to dilute the concentration of hydrogen 60 present in the reacted fuel gas 90 at the exhaust pipe 101 to a target level.

[0050] In an exemplary embodiment, the controller 34 is able to initiate adjustments to the control strategy of the fuel cell 50 based on the effective runtime anode leakage rate or the shutdown leakage rate. These adjustments include 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 the hydrogen gas 60 escaping from the anode 54. Here, the bias pressure between the anode 54 and cathode 56, the airflow rate, the airflow distribution, and the duration of the increased airflow are calculated based on the effective runtime anode leakage rate.

[0051] With renewed reference to Fig. 4A, when the fuel cell is switched off, hydrogen gas 60 can accumulate in the cathode 56 through permeation 96 in the electrolyte membrane 58, as indicated by arrow 98. The emission levels in an exhaust pipe 101 of the vehicle 10 downstream of the fuel cell 50 are acceptable due to the closed state of a shut-off valve 102, located between the airflow device 94 and the cathode 56, and the closed state of a backpressure valve 104, located between the cathode 56 and the exhaust pipe 100. The shut-off valve 102 and the backpressure valve 104 retain hydrogen gas 60, which escapes from the anode 54 into the cathode 56 via the electrolyte membrane 58, within the cathode 56.

[0052] With reference to Fig. 4B, at the start of the fuel cell 50 start-up, the shut-off valve 102 is held closed until the airflow through the airflow device 94 rises to a predetermined level. Thus, when the shut-off valve 102 is opened, the airflow is sufficient to prevent backflow of the hydrogen gas 60 from the cathode 56, and the airflow from the airflow device 94, as indicated by arrow 106, begins to force the hydrogen gas 60 in the cathode 56 out through the counterpressure valve 104, as indicated by arrow 108, thereby reducing the level of hydrogen gas 60 in the cathode 56.

[0053] Referring to Fig. 4C the increased airflow is continued both through a cathode bypass valve 110, which bypasses the cathode 56, as indicated by arrow 112, and through the cathode 56 itself, as indicated by arrow 114, whereby hydrogen gas 60 is purged from the fuel cell 50, as indicated by arrow 116, and finally, with reference to Fig. 4D, after the main amount of H2 has been flushed out of the cathode 56, the cathode bypass valve 110 could be closed, and the increased airflow will continue only directly through the cathode 56, as indicated by arrow 118, to push the remaining hydrogen gas 60 out of the cathode 56, as indicated by arrow 120.

[0054] In another exemplary embodiment, the controller 34 is able to initiate adjustments to the control strategy of the fuel cell 50 based on the effective runtime anode leakage rate or the shutdown leakage rate. During the runtime operation of the fuel cell 50, these adjustments include initiating a bleed function to vent hydrogen gas 60 from the anode 54 of the fuel cell 50. During the runtime operation of the fuel cell 50, the pressures within the anode 54 are higher than the pressures within the cathode 56, thereby promoting the permeation of hydrogen gas 60 through the electrolyte membrane 58. This condition is further enhanced by the degradation of the electrolyte membrane 58 over time, thus increasing the permeation rate through the electrolyte membrane 58. Initiating a bleed function via the anode purge valve 122 to drain the hydrogen gas 60 from the anode 54 increases the concentration of the hydrogen gas 60 in the anode.Such bleeding can be achieved by continuous rinsing through the degraded membrane 58 as described above, whereby the content of hydrogen gas 60 could be increased due to the continuous rinsing through the degraded membrane 58.

[0055] In another exemplary embodiment, the controller 34 is able to initiate adjustments to the control strategy of the fuel cell 50 based on the effective anode leakage rate during operation or the shutdown leakage rate. During the operation of the fuel cell 50, these adjustments involve increasing the airflow through the cathode 56 to compensate for the oxygen 68 consumed by the hydrogen gas 60 entering 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 oxygen content 68 contained therein. The escape of hydrogen gas 60 from the anode 54 to the cathode 56 through a degraded electrolyte membrane 58 displaces the air 68 in the cathode 56, thereby reducing the amount of oxygen 68 available for reaction with hydrogen protons 64 and free electrons 66.By increasing the airflow, the oxygen 68 is fed into the cathode 56 more quickly, resulting in an increased supply of oxygen 68 and preventing a potential voltage loss of the fuel cell 50.

[0056] In another exemplary embodiment, the controller 34 is able to initiate adjustments to the control strategy of the fuel cell 50 based on the effective runtime anode leakage rate or the shutdown leakage rate. During the runtime operation of the fuel cell 50, these adjustments include limiting the transient load rates to control emissions within the fuel cell 50. A high leakage rate at the electrolyte membrane 58 causes pure hydrogen gas 60, which has not yet been decomposed into hydrogen protons 64, to escape from the anode 54 to the cathode 56. During the ramp-up phase (the power increases rapidly), the H2 escaping through the highly degraded membrane 58 to the cathode 56 can be quickly forced into the exhaust stream, and the airflow at the cathode cannot be increased quickly enough to dilute the H2 content.During a downward movement (drastic power reduction), the airflow can decrease too rapidly with the power reduction. This could result in a large amount of H2 entering the exhaust gases without sufficient dilution. As mentioned earlier, emissions from the fuel cell 50 can become a problem if there is insufficient air available. To compensate for this, the controller 34 limits the load change rate at which the fuel cell 50 can be subjected, ensuring that only a load change rate that the fuel cell 50 can handle is permitted, thus avoiding a potential emissions problem. This situation may result in the vehicle 10 operating at reduced power, which may or may not be acceptable to the driver / passenger of the vehicle 10.

[0057] Thus, if such limitations and reduced performance of vehicle 10 occur, the owner can choose to accept the reduced performance and continue operating vehicle 10 to extend the service life of fuel cell 50, or alternatively, they can choose not to accept such reduced performance and consider this condition the end of the fuel cell 50's service life. In this way, the owner / operator of a vehicle can decide whether to extend the service life of fuel cell 50 at the cost of reduced performance or to replace / repair the fuel cell 50 immediately.

[0058] In another exemplary embodiment, the controller 34 is able to initiate adjustments to the control strategy of the fuel cell 50 based on the effective anode leakage rate during operation or the shutdown leakage rate. During shutdown operation of the fuel cell 50, these adjustments include venting hydrogen gas 60 from the anode 54 and the cathode 56 directly into the exhaust (tailpipe 101) and reducing the pressure in the anode 54 and the cathode 56. During shutdown, the pressure inside the anode 54 must be higher than the pressure inside the cathode 56 so that the system can measure / verify the shutdown leakage rate of the anode 54. Detecting shutdown leaks is the final step in shutting down a fuel cell.During this time, hydrogen gas 60, which is not consumed when the fuel cell 50 is switched off, is forced from the anode 54 to the cathode 56 due to the bias pressure of the anode 54 above the cathode 56 and can accumulate in the cathode 56.

[0059] With reference to Fig. 5. During shutdown operation, hydrogen gas 60 is vented from the anode 54 to the cathode inlet 144 and then via the anode purge valve 122 (arrow 124) and the cathode backpressure valve 104 to the exhaust (tailpipe 101) or directly to the exhaust. Simultaneously, hydrogen gas 60 is vented from the cathode 56 directly to the exhaust by opening the backpressure valve 104, as indicated by arrow 130.Thus, immediately after the leak test of the anode 54 at the end of the shutdown operation of the fuel cell 50, the anode purge valve 122, the anode drain valve 142, the cathode bypass valve 110 and the back pressure valve 104 can be opened so that excess hydrogen gas 60 in the fuel cell 50 can escape to the atmosphere via the exhaust pipe 101. This reduces the pressure difference between the anode 54 and the cathode 56 and decreases the amount of hydrogen gas 60 that continues to pass through the electrolyte membrane 58 from the anode 54 to the cathode 56 during the shutdown period.

[0060] In another exemplary embodiment, the controller 34 is able to initiate adjustments to the control strategy of the fuel cell 50 based on the effective runtime anode leakage rate or the shutdown leakage rate. During a freeze-start operation of the fuel cell 50, these adjustments include reducing the bias pressure between the anode 54 and the cathode 56. During the freeze-start of the fuel cell 50, a high bias pressure between the anode 54 and the cathode 56 is normally desirable so that the anode 54 and the cathode 56 can reach an equilibrium of nitrogen partial pressure to prevent N2 ingress without excessively affecting the hydrogen concentration at the anode; therefore, no purge request is necessary, as ice could block the gas flow.However, constant leakage through a damaged electrolyte membrane 58 makes the high bias pressure unnecessary and allows a change in strategy in which hydrogen gas 60 is directed from the anode 54 to the cathode 56, and then escapes through the damaged membrane 58.

[0061] In a freeze-start operation, the fuel cell 50 is activated when the temperature inside the fuel cell 50, measured by a fourth sensor or model 132, falls below a predetermined value, e.g., the freezing point (0 degrees Celsius). The components of a fuel cell include the electrolyte membrane 58, the catalyst layers 62 and 70, the gas diffusion layers 134 and 136, the microporous layer, and the bipolar plate. Hydrogen and air currents flow through the flow channels of the anode 54 and cathode 56, respectively. Diffusion and convection of the gases occur simultaneously in the porous layers. The catalyst layers 62 and 70 consist of a mixture of catalyst particles, ionomer, and a porous carbon framework. Electrochemical reactions take place at the three-phase coexistence sites (ionomer, gas, and catalyst) in the catalyst layers 62 and 70. During operation, electricity is generated, and water is produced as a reaction product.During a cold start, water transitions from one phase or state to another. It can be absorbed by the ionomer and become membrane water. Some of the membrane water may freeze due to sub-zero temperatures. Water can also evaporate from the ionomer. The resulting water vapor seeps through the porous layers and enters the flow channel. Water vapor can also condense and accumulate as ice within the porous layers. Finally, under certain conditions, water can remain in a supercooled liquid state. During a cold start, the temperature rises due to the exothermic electrochemical reaction. A successful cold start requires that the temperature of the catalyst layers 62, 70 exceeds the melting point of ice before the reaction sites and diffusion pathways become blocked.In this case, the ice melts and liquid water can flow out, so the stoichiometry in the cathode is low to generate enough heat until the fuel cell warms up.

[0062] In another exemplary embodiment, the control unit 34 is designed to initiate adjustments to the control strategy of the fuel cell 50 based on the effective runtime anode leakage rate or shutdown leakage rate, which includes the fuel cell 50 continuously and periodically monitoring the pressure drop in the anode 54 during standby operation, e.g., when the vehicle 10 is idling at a traffic light or during a traffic jam, and updating the shutdown leakage rate when the power output is zero.

[0063] During extended periods of disuse, H2-parking measures are employed to ensure that sufficient hydrogen gas 60 remains in the anode 54 for a start-up process when the pressure drop in the anode 54 indicates that oxygen 68 has entered the anode 54. These H2-parking measures include industrially established methods that prevent the hydrogen gas 60 from completely escaping the anode 54 and cathode 56 during a period of inactivity. This ensures that when the fuel cell 50 actuator is restarted and a start-up process begins, no oxygen is present in the anode 54, enabling an efficient start-up without damaging the fuel cell 50 electrodes. If the pressure in both the anode 54 and cathode 56 is higher than ambient atmospheric pressure, H2-parking measures may be unnecessary.However, if the pressure in the anode 54 or the cathode 56 is lower than the ambient air pressure, air can enter the fuel cell 50. If the pressure drop in the anode 54 indicates that oxygen has entered the fuel cell 50, the controller 34 can initiate H2-in-park measures to compensate for this leak.

[0064] Referring to Fig.Section 6 comprises a method 200 for controlling a hydrogen fuel cell 50 with a fuel cell controller 34, starting at block 202, measuring an anode leakage rate for the fuel cell 50, transitioning to block 204, modeling an effective electrolyte membrane opening size using the measured anode leakage rate, transitioning to block 206, calculating, using the effective electrolyte membrane opening size, an effective runtime anode leakage rate during operation of the fuel cell 50, transitioning to block 208, using the effective runtime anode leakage rate as a low-side metric when calculating emissions and dilution requirements, and, transitioning to block 210, initiating adjustments of a fuel cell 50 control strategy based on one of: the effective runtime anode leakage rate or a shutdown leakage rate.

[0065] In one exemplary embodiment, measuring an anode leakage rate for fuel cell 50 in block 202 further comprises, transitioning to block 212, measuring an anode shutdown leakage rate for fuel cell 50. In another exemplary embodiment, measuring an anode leakage rate for fuel cell 50 in block 202 further comprises monitoring the pressure drop in anode 54 during low-power operation of fuel cell 50 and estimating the anode leakage rate based on the pressure drop in anode 54 during low-power operation of fuel cell 50 when transitioning to block 214.

[0066] In another exemplary embodiment, initiating adjustments to the control strategy of the fuel cell 50 based on one of: the effective run-time anode leakage rate or a shutdown leakage rate in block 210, furthermore, when transitioning to block 218, during the start-up of the fuel cell 50, includes increasing the duration of an increased airflow through a cathode 56 of the fuel cell 50 (which could pass through a cathode or cathode bypass valve) to dilute the concentration of hydrogen 60 escaping from the anode 54, wherein the bias pressure between anode 54 and cathode 56, the airflow rate, the airflow split, and the duration of the increased airflow are calculated based on the effective run-time anode leakage rate.

[0067] In another exemplary embodiment, initiating adjustments to the control strategy of the fuel cell 50 based on the effective anode leakage rate during operation or the shutdown leakage rate in block 210 further includes adjusting a bleed function request frequency during the operating time of the fuel cell 50 to vent hydrogen gas 60 from the anode 54 of the fuel cell 50 by transitioning to block 220.

[0068] In another exemplary embodiment, initiating adjustments to the control strategy of the fuel cell 50 based on the effective anode leakage rate during operation or the shutdown leakage rate in block 210 further includes, when transitioning to block 222, increasing the airflow through the cathode 56 during the operating time of the fuel cell 50 to compensate for the oxygen 68 consumed by the hydrogen gas 60 passing through the electrolyte membrane 58.

[0069] In another exemplary embodiment, initiating adjustments to the control strategy of the fuel cell 50 based on the effective anode leakage rate during operation or the shutdown leakage rate in block 210 further includes, when transitioning to block 224, limiting transition load rates during the operating time of the fuel cell 50 in order to control emissions within the fuel cell 50 during and after power load fluctuations.

[0070] In another exemplary embodiment, initiating adjustments to the control strategy of the fuel cell 50 based on the effective runtime anode leakage rate or the shutdown leakage rate in block 210 further comprises switching to block 226 during a shutdown operation of the fuel cell 50, venting hydrogen gas 60 from the anode 54 and the cathode 56 directly to the exhaust at the exhaust pipe 101, and reducing the bias pressure between the anode 54 and the cathode 56 in block 228.

[0071] In another exemplary embodiment, initiating adjustments to the control strategy of the fuel cell 50 based on the effective runtime anode leakage rate or the shutdown leakage rate in block 210 further includes reducing the bias pressure between the anode 54 and the cathode 56 during a freeze-start operation of the fuel cell 50 in block 230.

[0072] In another exemplary embodiment, initiating adjustments to the control strategy of the fuel cell 50 based on the effective runtime anode leakage rate or the shutdown leakage rate in block 210 further includes continuously switching to block 232 on a periodic basis during standby operation of the fuel cell 50, monitoring the pressure drop within the anode 54 when the power output is zero, and, during a longer period of non-use, switching to block 234, initiating H2-in-park measures to ensure that sufficient hydrogen gas 60 remains within the anode 54 for a start-up operation when the pressure drop within the anode 54 indicates that oxygen 68 has entered the anode 54.

[0073] In another exemplary embodiment, the method 200 further includes updating the measured anode leakage rate when the power output of the fuel cell 50 is zero, with the method returning to block 204 and continuing with the updated measured anode leakage rate.

[0074] A fuel cell 50, a fuel cell propulsion system 20, and a method 200 of the present description offer several advantages. These include determining how much airflow is required to dilute escaping reactive fuel gas 90 within the anode 54 such that the concentration of hydrogen gas 60 therein is low enough to be safely vented to the atmosphere, and using an effective anode shutdown leak or a low-power leak rate during operation to implement adjustments that allow the fuel cell 50 to continue operation after substantial degradation of the electrolyte membrane 58.In this way, concerns regarding emissions due to the degradation of the electrolyte membrane 58 and the balance of system leakage that escapes directly into the exhaust gases are eliminated, since the controller 34 actively monitors such degradation / leakage and automatically makes adjustments to the operating parameters (airflow, transition load, opening / closing of the anode purge or drain valve, cathode bypass valve, isolating valve and back pressure valve) to compensate for the degradation of the electrolyte membrane 58 and the leakage of the system balance and to ensure that the emissions of the fuel cell 50 are within the acceptable range.

[0075] Furthermore, aspects of the fuel cell 50, the fuel cell drive system 20 and the method 200 of the present description enable a fuel cell 50 to be operated beyond the specified end-of-life parameters, which are based on the degradation of the anode and the equilibrium of the system or the leak (which exits directly into the exhaust), by actively monitoring and automatically detecting when degradation of the electrolyte membrane 58 and a leak of the equilibrium of the system (which exits directly into the exhaust) occur, and by automatically making adjustments to the operating parameters of the fuel cell 50 so that the fuel cell 50 can continue to be operated with acceptable emission values.

[0076] To the extent that such adjustments entail the cost of reduced fuel cell 50 performance (lower power output), an owner / operator of a vehicle with a fuel cell 50 or a fuel cell propulsion system 20 as described herein has the advantage of being able to selectively decide either to accept the reduced performance aspects of the adjustments made by the controller 34 and thus extend the life cycle of the fuel cell 50, or, after such adjustments have been made by the controller 34, to decide that the fuel cell 50 should be repaired / replaced immediately. This improves the overall customer experience, as the owner / operator can make the decision.

Claims

[1] Method (200) for controlling a hydrogen fuel cell (50) comprising the following: with a control unit (34) of the fuel cell (50): Measuring an anode leak rate for the fuel cell (50); Modeling, using the measured anode leakage rate, an effective electrolyte membrane opening size; Calculate, using the effective electrolyte membrane opening size, an effective runtime anode leakage rate during operation of the fuel cell (50) based on the current operating conditions; Using the effective runtime anode leakage rate as a low-side metric when calculating emissions and dilution requirements; and Initiating adjustments to a fuel cell control strategy (50) based on one of the following elements: the effective runtime anode leakage rate; or a shutdown leakage rate; wherein measuring an anode leak rate for the fuel cell (50) further includes measuring an anode shutdown leak rate for the fuel cell (50). [2] Method (200) according to claim 1, wherein measuring an anode leak rate for the fuel cell (50) further comprises: Monitoring a pressure drop within the anode (54) during low-power operation of the fuel cell (50); and at least one of the following steps: Estimating the anode leakage rate based on the pressure drop within the anode (54) during low-power operation of the fuel cell (50); and Calculating the anode leakage rate based on both the anode pressure change and the cathode pressure change. [3] Method (200) according to claim 1, wherein initiating adjustments of the control strategy of the fuel cell (50) based on the effective runtime anode leakage rate or the shutdown leakage rate further comprises: when starting up the fuel cell (50), increasing the duration of increased airflow through a cathode (56) of the fuel cell (50) to dilute the concentration of hydrogen (60) exiting the anode (54); wherein the preload pressure between anode (54) and cathode (56), the airflow rate, the airflow split and the duration of the increased airflow are calculated and set based on one of the following quantities: the effective runtime anode leakage rate; or the shutdown leakage rate. [4] Method (200) according to claim 3, wherein initiating adjustments of the control strategy of the fuel cell (50) based on the effective run-time anode leakage rate or the shutdown leakage rate further comprises adjusting, during the run-time operation of the fuel cell (50), a bleed request frequency to vent gas from the anode (54) of the fuel cell (50). [5] Method (200) according to claim 4, wherein initiating adjustments of the control strategy of the fuel cell (50) based on the effective run-time anode leak rate or the shutdown leak rate further comprises increasing, during the run-time operation of the fuel cell (50), the airflow through the cathode (56) to compensate for oxygen consumed by hydrogen gas (60) penetrating the electrolyte membrane. [6] Method (200) according to claim 5, wherein initiating adjustments of the control strategy of the fuel cell (50) based on the effective run-time anode leakage rate or the shutdown leakage rate further comprises limiting, during the run-time operation of the fuel cell (50), transient load rates in order to control emissions during and after power load fluctuations. [7] Method (200) according to claim 3, wherein initiating adjustments of the control strategy of the fuel cell (50) based on the effective run-time anode leakage rate or the shutdown leakage rate further comprises at least one of the following steps during the run-time operation of the fuel cell (50): Reducing the bleed frequency; Increasing the airflow through the cathode (56) to compensate for the oxygen consumed by the hydrogen gas (60) penetrating the electrolyte membrane; and Limiting transient load rates to control emissions during and after power load fluctuations. [8] Method (200) according to claim 7, wherein initiating adjustments of the control strategy of the fuel cell (50) based on the effective runtime anode leakage rate or the shutdown venting of hydrogen gas (60) from the anode (54) and the cathode (56) directly to the exhaust; and Reducing the anode and cathode pressure. [9] Method (200) according to claim 8, wherein initiating adjustments of the control strategy of the fuel cell (50) based on the effective run-time anode leakage rate or the shutdown leakage rate further comprises, during a freeze-start operation of the fuel cell (50), reducing the bias pressure between the anode (54) and the cathode (56).

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