Patent Application
20060141299
The invention generally relates to detecting and handling a fault condition in a fuel cell system.
A fuel cell is an electrochemical device that converts chemical energy produced by a reaction directly into electrical energy. For example, one type of fuel cell includes a polymer electrolyte membrane (PEM), often called a proton exchange membrane, that permits only protons to pass between an anode and a cathode of the fuel cell. At the anode, diatomic hydrogen (a fuel) is reacted to produce hydrogen protons that pass through the PEM. The electrons produced by this reaction travel through circuitry that is external to the fuel cell to form an electrical current. At the cathode, oxygen is reduced and reacts with the hydrogen protons to form water. The anodic and cathodic reactions are described by the following equations:
H2→2H++2e− at the anode of the cell, and Equation 1
O2+4H++4e−→2H2O at the cathode of the cell. Equation 2
A typical fuel cell has a terminal voltage near one volt DC. For purposes of producing much larger voltages, several fuel cells may be assembled together to form an arrangement called a fuel cell stack, an arrangement in which the fuel cells are electrically coupled together in series to form a larger DC voltage (a voltage near 100 volts DC, for example) and to provide more power.
The fuel cell stack may include flow plates (graphite composite or metal plates, as examples) that are stacked one on top of the other, and each plate may be associated with more than one fuel cell of the stack. The plates may include various surface flow channels and orifices to, as examples, route the reactants and products through the fuel cell stack. Several PEMs (each one being associated with a particular fuel cell) may be dispersed throughout the stack between the anodes and cathodes of the different fuel cells. Electrically conductive gas diffusion layers (GDLs) may be located on each side of each PEM to form the anode and cathodes of each fuel cell. In this manner, reactant gases from each side of the PEM may leave the flow channels and diffuse through the GDLs to reach the PEM.
The fuel cell stack is one out of many components of a typical fuel cell system, as the fuel cell system includes various other components and subsystems, such as a cooling subsystem, a cell voltage monitoring subsystem, a control subsystem, a power conditioning subsystem, etc. The particular design of each of these subsystems is a function of the application that the fuel cell system serves.
During the lifetime of the fuel cell system, there is a likelihood that at least one component of the fuel cell system may fail and cause a fault condition (a low cell voltage or a low cell signal-to-noise ratio, for example) in the system. Although the fault condition may be relatively easy to detect, it may be relatively more difficult to identify which component of the fuel cell system caused the fault condition. Shutting down the fuel cell system for purposes of determining which component caused the fault condition may not be an economically efficient solution.
Thus, there is a continuing need for better ways to diagnose and handle a fault condition in a fuel cell system.
In an embodiment of the invention, a technique that is usable with a fuel cell system includes comparing at least one parameter of the fuel cell system to a predetermined signature to identify an entity of the fuel cell system, which possibly caused a fault condition in the fuel cell system. The technique includes operating the fuel cell system to change the parameter(s); and in response to this operation, the technique includes determining whether the identified entity caused the fault condition.
Advantages and other features of the invention will become apparent from the following drawing, description and claims.
Referring to
A fault condition signifies that one of the monitored critical parameters of the fuel cell system is outside of its specified range. This quite often means, a particular process (a CO process, for example) is not working properly in the fuel cell system due to the failure of a particular “entity,” such as a component, subsystem, or subassembly (containing one or more individual components that may have failed) of that process. Herein the phrase “serviceable subassembly” is used to refer to a subassembly or subsystem of the fuel cell system, which can be replaced as a unit.
As a more specific example, a CO process in the fuel cell system may fail and thus, produce an unacceptably high level of CO that causes a fault condition. The CO process may include, for example, a CO oxidizer, an air valve and an air valve controller, each of which may fail or work improperly to cause overall failure of the CO process.
However, the CO process may not be the only cause of the critical CO parameter being out of bounds. For example, the high CO level may also be attributable to a defective shift reactor process.
As a result of the high CO level, fuel cells of the fuel cell stack may have low signal-to-noise ratios and may have low terminal voltages. Thus, these parameters may be recognized (pursuant to block 3 of
Still referring to
To further illustrate an application of the technique 2, due to a detected high CO level (as an example), the fuel cell system may initially assume that the CO oxidation process is defective. With this assumption, the fuel cell system is operated to increase the air flow to the CO oxidizer of the fuel cell system. In less than a minute, if the entity that controls the CO oxidization process has failed, then the cell voltages and signal-to-noise ratio (i.e., the observed “parameters”) change. For this example, this means that if the entity that controls the CO oxidation process has failed, then the cell voltages increase and the signal-to-noise ratios of the fuel cells of the fuel cell stack improve in response to the flow of air to the CO oxidizer being increased.
If, however, the observed parameter(s) do not change, then another entity (component/subsystem/subassembly) may be the source of the fault condition. Continuing the example above, if the increase in air flow to the CO oxidizer does not produce the expected increases in the cell voltages and signal-to-noise ratios, then the fuel cell system may target another entity as possibly causing the fault condition. For example, if increasing the air flow to the CO oxidizer does not raise the cell voltages and signal-to-noise ratios as expected, then the fuel cell system operates to target the shift reactor (another potential cause of the high CO level) of the system.
To target the shift reactor, the fuel cell system operates in the following manner: the fuel cell system increases the air to the shift reactor to increase the oxygen to carbon ratio, and the fuel cell system increases the fuel to the shift reactor used for purposes of humidification.
In response to this operation of the fuel cell stack, the fuel cell system observes the same pattern (cell voltages and signal-to-noise ratios). If the cell voltages increase and the signal-to-noise ratios increase over a particular time interval (less than one minute, for example) then the shift reactor is identified as the defective component.
Therefore, referring to
In this loop, the technique 10 includes operating (block 16) the fuel cell system to initiate a change in one or more parameters consistent with the identified entity having caused the fault condition. The change is observed (block 18), and if the observed change is conclusive (diamond 20), then the loop ends, as the failure code is updated (block 22) to identify the defective entity. Otherwise, if blocks 16 and 18 do not produce conclusive results, the loop continues and control transitions back to block 14.
It is noted that in some embodiments of the invention, the fuel cell system uses the techniques that are disclosed herein to narrow down the number of potentially defective entities (components/subsystems/subassemblies). Thus, sometimes, the techniques that are disclosed herein may be used to narrow the potentially defective entities down to a number greater than one (such as two, for example). Even though the specific defective component/subassembly may not be identified, fewer components or subsystems need to be evaluated in a service call, for example. Thus, in the context of this application, the identified “entity” may include multiple potentially-defective components, subsystems or subassemblies.
The detection of a fault condition in the fuel cell system may transition the fuel cell system from a normal mode of operation (the mode of operation when no fault conditions exist) into a fault tolerant mode of operation, in some embodiments of the invention. Thus, in these embodiments of the invention, the techniques 2 and 10 described herein may be performed by the fuel cell system in the fault tolerant mode of operation and may last until the fault condition is corrected. Therefore, in accordance with some embodiments of the invention, the fault mode of operation of the fuel cell system continues until the defective component is repaired through operation of the fuel cell system or the shutting down and repair of the fuel cell system via a service call.
For certain circumstances (described below), the fault condition may be reversible without requiring the shutting down the fuel cell system. For such a reversible fault condition, the fuel cell system is operated to effectively reverse the fault condition and take the fuel cell system out of the fault tolerant mode. If, however, the fault is not reversible, then the fuel cell system makes a determination regarding the timing for a service call to service or replace the defective entity that caused the fault condition.
More specifically, referring to
Some faults, however, cannot be reversed, and thus, the defective entity cannot be repaired. For example, a fault condition may arise when an insufficient level of oxygen is being provided to the fuel cells. For this fault condition, either the air blower to the fuel cell stack or a membrane in the fuel cell stack may have failed. However, either a failure in the air blower or a failure in the membrane is not reversible via operation of the fuel cell system, in some embodiments of the invention.
If the fault is not reversible, then the fuel cell system takes into account several considerations to plan the timing of the repair and/or replacement of the defective entity via a service call. For example, in some embodiments of the invention, the fuel cell system determines (block 54) the damage to other components of the fuel cell system due to operation of the fuel cell system in the fault tolerant mode.
Therefore, for example, if by operating in the fault tolerant mode, significant damage may have occurred to other fuel cell system components, then a relatively sooner service call is scheduled. However, if by operating in the fault tolerant mode, significant damage has not occurred to any other component of the fuel cell system, then a relatively later service call may be scheduled.
As another example of a consideration for planning the service call, the fuel cell system may determine (block 58) customer input regarding cost optimization and system availability. Thus, for example, the customer of the fuel cell system may suffer more economic damage, for example, due to shutdown of the fuel cell system than the cost incurred to the system due to the continued running of the fuel cell system with the defective component. Furthermore, the customer may specify a certain fuel cell system cost level that triggers a service call; may specify that the fuel cell system, if possible, should only be shut down during certain days or hours; etc. Therefore, all or some of these factors may influence when the fuel cell system schedules a service call.
As yet another example of the considerations that are taken by the fuel cell system, in some embodiments of the invention, the fuel cell system may determine (block 60) the maintenance cost of replacing the defective entity versus the cost that is attributable to continuing to run the system in the fault tolerant mode. Therefore, for example, if no further damage occurs to other components of the fuel cell system, then the fuel cell system may schedule a service call solely based on other factors, as the timing does not affect future operation of the fuel cell system. Furthermore, the fuel cell system may determine (block 62) the cost of planned and unplanned service calls when making the determination of when to schedule service.
Therefore, in accordance with the technique 50, in some embodiments of the invention, the fuel cell system determines (block 64) how long the fuel cell system should continue to run (and thus, when the service call should occur) in response to blocks 54, 58, 60 and 72 of the technique 50. Subsequently, the fuel cell system updates (block 70) control data that indicates when the service call should occur and which component(s) need to be repaired/replaced in the service call.
The tables 80A and 80B have a column 86 that identifies a signature that is associated with a possible fault condition. As an example, in both rows 97, the same signature exists in column 86. Thus, analyzing a signature alone for purposes of identifying a defective component that caused a fault condition is not by itself determinative. Therefore, the above-described operation of the fuel cell system is used for purposes of identifying the defective entity.
In this regard, the tables 80A and 80B include a column 88 of test procedures that are used to discriminate between potentially defective entities. For example, for the rows 97a (
The tables 80A and 80B also each includes a column 90 that identifies a detectable signature change that is associated with the test procedure that is set forth in column 88. Furthermore, the tables 80A and 80B include a column 92 that depicts a time to observe the pattern change. Therefore, for example, the time that is associated with detecting the defective component for a high CO level is less than about one minute. In contrast, referring to column 92 of row 97e (
The tables 80A and 80B also each includes a column 94 that identifies an action to be taken in the fault tolerant mode once the associated entity has been confirmed to be defective. For example, for the rows 97a that are associated with a high CO level, the column 94 identifies increasing the baseline air flow device to the CO oxidation process, when the CO oxidation process is confirmed as failing; and the column 94 identifies increasing the air-to-fuel ratio of the shift reactor when the shift reactor is confirmed as being defective.
It is noted that operation of the fuel cell system in the fault tolerant mode does not necessarily reverse the fault, but rather, the operation at least attempts to preserve the ability of the fuel cell system to operate until a service call is performed to address the fault condition. For example, the row 97e (
Lastly, the tables 80A and 80B include a column 96 that identifies whether the fault condition is reversible. Therefore, for example, for the rows 97a that are associated with the high CO level fault condition, if the defect is attributed to either the CO oxidization process or the shift reactor, then the defect is reversible. This is to be contrasted with, for example, a fault condition that is caused by a membrane rupture (row 97e of
Referring to
As depicted in
The action to take does not have to be determined solely by the controller. Fault alerts to the customer, service provider, or manufacturer could enable case-by-case decision making. Decisions may be executed locally or remotely. Service manuals/service software diagnostic procedures could also enable control parameters to be tuned to the new set of conditions, depending on the particular embodiment of the invention.
As a more specific example,
In some embodiments of the invention, the fuel cell system 150 includes a fuel cell stack 170 that receives a fuel flow at an anode inlet port 172 and an oxidant flow at a cathode inlet port 174. In response to these flows, the fuel cell stack 170 produces a stack voltage (called “VSTACK”) that appears on a stack output line 172. A power conditioning subsystem 180 of the fuel cell system 150 converts the VSTACK voltage into an AC voltage (for the exemplary fuel cell system depicted in
The fuel cell system 150 may include various other subsystems and components, such as, for example, a stack monitoring circuit 200 that is coupled to the fuel cell stack 170 for purposes of monitoring the cell voltages of the fuel cell stack 170 and generally monitoring the health of the fuel cell stack 170. The stack monitoring circuit 200 may be in communication with one or more electrical communication lines 204 that communicate signals to direct the monitoring of the fuel cell stack 170 by the circuit 200. Furthermore, the stack monitoring circuit 200 may be in electrical communication with one or more electrical communication lines 202 for purposes of providing data to a controller 260 of the fuel cell system 150 regarding the monitored condition and cell voltages of the fuel cell stack 170.
In some embodiments of the invention, the controller 260 may include a processor 262 (one or more microcontrollers or microprocessors, for example) that is coupled to a memory 264 of the controller 260. The memory 264, in turn, may store instructions 268 that cause the processor 262, when executed, to perform one or more of the techniques 2, 10 and 50 that are described herein. Thus, the controller 260 may, for example, receive status information (via electrical communication lines 270) from various sensors and circuits (such as the stack monitoring circuit 200, for example) of the fuel cell system 150 and produce electrical control signals that propagate on electrical communication lines 272 to control the various components of the fuel cell system 150.
Thus, the controller 260 may, depending on the particular embodiment of the invention, recognize signatures that identify fault conditions, control the operation of the fuel cell system 150 to effect a change in a pattern to identify a defective entity, may analyze changes in observed parameters to identify failed entities, may control operation of the fuel cell system 150 after a particular defective entity is identified, may plan a shut down and/or service call to service a defective entity, etc.
In some embodiments of the invention, the fuel cell system 150 may include, for example, a coolant subsystem 230 that circulates a coolant through the fuel cell stack 170. Furthermore, in some embodiments of the invention, the fuel cell system 150 may include an anode humidifier 240 and a cathode humidifier 244 that provide respective humidified fuel and oxidant flows to the fuel cell stack 170. The anode humidifier 270 may receive its fuel flow, for example, from a fuel processor 242. The fuel processor 242 may include, for example, a CO oxidizer and a shift reactor, in some embodiments of the invention. Furthermore, the cathode humidifier 244 may receive its air flow from a cathode blower 248 of the fuel cell system 150. As also depicted in
The components and subsystems that are depicted in
While the invention has been disclosed with respect to a limited number of embodiments, those skilled in the art, having the benefit of this disclosure, will appreciate numerous modifications and variations therefrom. It is intended that the appended claims cover all such modifications and variations as fall within the true spirit and scope of the invention.
