Granted Patent B2

US 7,887,960 · App. 11/466,832 · Granted Feb 15, 2011

Abstract

Claims (57)

1. A method of operating an electrochemical conversion assembly comprising a plurality of electrochemical conversion cells arranged in a conductively coupled fuel cell stack, wherein respective ones of said cells comprise membrane electrode assemblies positioned between first and second reactant flowfields and said membrane electrode assemblies comprise a proton exchange membrane, said method comprising:

initiating operation of said fuel cell stack according to an initial set of operating parameters comprising hydration, wherein said operation of said fuel cell stack runs through a plurality of operational cycles characterized by changes in humidification, of said membrane electrode assemblies;

extracting cyclic stress data representative of said plurality of operational cycles;

determining a life spent value L X representing stack life expended over said plurality of operational cycles, wherein said life spent value L X is a function of fatigue life data of the fuel cell stack and a stress histogram that is derived from said cyclic stress data arising from said cyclic stress imparted upon said membrane electrode assembly over said plurality of operational cycles;

determining an actual usage value L U representing a number of said operational cycles executed from initiation of said fuel cell stack operation, wherein said actual usage value L U is substantially independent of stress imparted upon said membrane electrode assembly over said plurality of operational cycles;

comparing said life spent value L X to said actual usage value L U ; and

controlling at least one operating parameter comprising hydration of said electrochemical conversion assembly as a function of said comparison of said life spent value L X to said actual usage value L U .

2. A method as claimed in claim 1 wherein said data representative of said plurality of operational cycles is extracted from measurements taken from said fuel cell stack.

3. A method as claimed in claim 1 wherein said life spent value L X is determined by generating cyclic stress data representing the operation of said fuel cell stack.

4. A method as claimed in claim 3 wherein said cyclic stress data comprises a simplified representation of the operation of said fuel cell stack created though rainflow analysis or another technique for determining the impact of a plurality of stress cycles.

5. A method as claimed in claim 3 wherein said life spent value L X is further determined from maximum membrane stress determinations for respective stress cycles within said cyclic stress data.

6. A method as claimed in claim 5 wherein:

said stress cycles are characterized by a membrane hydration history; and

said maximum membrane stress determinations are made using a look-up table correlating membrane stress with said membrane hydration history.

7. A method as claimed in claim 1 wherein:

said life spent value L X is determined by generating cyclic stress data representing the operation of said fuel cell stack;

said life spent value L X is further determined from membrane stress determinations for respective stress cycles within said cyclic stress data; and

said life spent value L X is further determined using said membrane stress determinations and data representing one or more fatigue life curves of said fuel cell stack.

8. A method as claimed in claim 1 wherein:

said life spent value L X is determined by generating cyclic stress data representing the operation of said fuel cell stack;

said cyclic stress data comprises a simplified representation of the operation of said fuel cell stack created though rainflow analysis or another technique for determining the impact of a plurality of stress cycles;

said life spent value L X is further determined by generating a stress histogram from said cyclic stress data; and

said life spent value L X is further determined using said stress histogram and data representing one or more fatigue life curves of said fuel cell stack.

9. A method as claimed in claim 1 wherein said actual usage value L U is determined from a count of operational cycles executed from initiation of said fuel cell stack operation, a measurement of time elapsed from initiation of said fuel cell stack operation, or some other representation that is not a function of stress imparted upon said membrane electrode assembly over said plurality of operational cycles.

10. A method as claimed in claim 1 wherein said method comprises:

maintaining said operating parameter when there is no significant difference between said life spent value L X and said actual usage value L U ; and

modifying said operating parameter when there is a significant difference between said life spent value L X and said actual usage value L U .

11. A method as claimed in claim 10 wherein said method comprises modifying said operating parameter to a less aggressive value when said life spent value L X exceeds said actual usage value L U by a substantial margin.

12. A method as claimed in claim 10 wherein said method comprises modifying said operating parameter to a more aggressive value when said life spent value L X is exceeded by said actual usage value L U by a substantial margin.

13. A method as claimed in claim 1 wherein said operating parameters comprise membrane hydration, membrane temperature, membrane dehydration rate, membrane heating/cooling rate, flowfield hydration, flowfield temperature, reactant flow rates, or combinations thereof.

14. A method as claimed in claim 1 wherein:

said fuel cell stack is characterized by a design life and said life spent value L X is determined as a percentage of said design life of said fuel cell stack;

said actual usage value L U is determined as a percentage of said design life of said fuel cell stack; and

said life spent value L X and said actual usage value L U are compared as respective percentages of said design life of said fuel cell stack.

15. A method of determining life expended in an electrochemical conversion assembly comprising a plurality of electrochemical conversion cells arranged in a conductively coupled fuel cell stack, wherein respective ones of said cells comprise membrane electrode assemblies positioned between first and second reactant flowfields and said membrane electrode assemblies comprise a proton exchange membrane, said method comprising:

initiating operation of said fuel cell stack according to an initial set of operating parameters comprising hydration, wherein said operation of said fuel cell stack runs through a plurality of operational cycles characterized by changes in humidification, of said membrane electrode assemblies;

extracting cyclic stress data representative of said plurality of operational cycles; and

determining a life spent value L X representing stack life expended over said plurality of operational cycles, wherein said life spent value L X is a function of fatigue life data of the fuel cell stack and a stress histogram that is derived from said cyclic stress data arising from said cyclic stress imparted upon said membrane electrode assembly over said plurality of operational cycles.

16. A method as claimed in claim 15 wherein:

said life spent value L X is determined by generating cyclic stress data representing the operation of said fuel cell stack;

said life spent value L X is further determined from membrane stress determinations for respective stress cycles within said cyclic stress data; and

said life spent value L X is further determined using said membrane stress determinations and data representing one or more fatigue life curves of said fuel cell stack.

17. A method as claimed in claim 15 wherein:

said life spent value L X is determined by generating cyclic stress data representing the operation of said fuel cell stack;

said cyclic stress data comprises a simplified representation of the operation of said fuel cell stack created though rainflow analysis or another technique for determining the impact of a plurality of stress cycles;

said life spent value L X is further determined by generating a stress histogram from maximum membrane stress determinations for respective stress cycles within said cyclic stress data; and

said life spent value L X is further determined using said stress histogram and data representing one or more fatigue life curves of said fuel cell stack.

18. An electrochemical conversion assembly comprising a plurality of electrochemical conversion cells arranged in a conductively coupled fuel cell stack and a programmable controller operatively coupled to said fuel cell stack, wherein:

respective ones of said cells comprise membrane electrode assemblies positioned between first and second reactant flowfields of said stack;

said membrane electrode assemblies comprise a proton exchange membrane;

said programmable controller is configured to control of at least one operating parameter of said electrochemical conversion assembly by

facilitating fuel cell stack operation according to an initial set of operating parameters comprising hydration, wherein said operation of said fuel cell stack runs through a plurality of operational cycles characterized by changes in humidification, of said membrane electrode assemblies;

facilitating the extraction of cyclic stress data representative of said plurality of operational cycles;

facilitating the determination of a life spent value L X representing stack life expended over said plurality of operational cycles, wherein said life spent value L X is a function of fatigue life data of the fuel cell stack and a stress histogram that is derived from said cyclic stress data arising from said cyclic stress imparted upon said membrane electrode assembly over said plurality of operational cycles;

facilitating the determination of an actual usage value L U representing a number of said operational cycles executed from initiation of said fuel cell stack operation, wherein said actual usage value L U is substantially independent of stress imparted upon said membrane electrode assembly over said plurality of operational cycles;

facilitating the comparison of said life spent value L X to said actual usage value L U ; and

controlling at least one operating parameter comprising hydration of said electrochemical conversion assembly as a function of said comparison of said life spent value L X to said actual usage value L U .

Assignments (12)