Fuel cell health management system

• US 20030211372A1
• Filed: 05/16/2003
• Published: 11/13/2003
• Est. Priority Date: 03/29/2002
• Status: Active Grant

• Current Assignee: Estco Battery Management Incorporated
• Original Assignee: Estco Battery Management Incorporated
• Inventors: Adams, William A., Gardner, Christopher L., Vered, Ron, Dunn, James H.
• Granted Patent: US 7,038,424 B2
• Time in Patent Office: Days
• US Class Current: 429/23
• CPC Class Codes: H01M 8/04238 Depolarisation
• CPC Class Codes: H01M 8/04559 of fuel cell stacks
• CPC Class Codes: H01M 8/04589 of fuel cell stacks
• CPC Class Codes: H01M 8/04619 of fuel cell stacks
• CPC Class Codes: H01M 8/04951 of the individual fuel cell
• CPC Class Codes: Y02E 60/50 Fuel cells

Abstract

Methods and devices for rejuvenating, supplementing, or bypassing an individual fuel cell or a group of fuel cells, in a fuel cell stack, is disclosed. The methods and devices provide for a mechanism for removing catalyst poisons on both the anode portion and the cathode portion of the fuel cell and providing an improvement in the operation of the electrolytes. A controller that controls a variable resistor or a variable power supply in parallel with an individual fuel cell or a group of fuel cells in a stack is utilized. Adjusting the resistive value of the variable resistor, or the voltage level of the variable power supply, directly controls the current in the fuel cell. In accordance with Kirchoff s Current Law, decreasing the fuel cell voltage increases the current through the fuel cell, while the fuel cell stack is operational, and poisons deposited on the anode and cathode electrocatalysts are removed, thereby rejuvenating the fuel cell. Typically, the removal of cell poisons only requires short, periodic pulsing of the fuel cell potential. Methods and devices for determining the limiting processes within a fuel cell thus enabling the optimization of the fuel cell stack performance to diagnose the fuel cell stack are also disclosed.

Claims

1. A device for performing an operation on an individual fuel cell while the fuel cell is operational, the device comprising:

a variable resistive means coupled to the fuel cell; and

a controller for adjusting the variable resistive means, the controller having measuring means for determining a voltage level and a current level of the fuel cell, the controller adjusting the variable resistive means based on the voltage level and the current level of the fuel cell.

5. A device as defined in claim 1, 2, 3, or 4, wherein the operation is a rejuvenating operation.

7. A device as defined in claim 1, 2, 3, or 4, wherein the operation is a bypass operation.

2. A device for performing an operation on an individual fuel cell while the fuel cell is operational, the device comprising:

a variable power supply coupled to the fuel cell; and

a controller for adjusting the variable power supply applied across the fuel cell, the controller having measuring means for determining a voltage level and a current level of the fuel cell, the controller adjusting the variable power supply based on the voltage level and the current level of the fuel cell.

6. A device as defined in claim 2 or 4, wherein the operation is a supplementing operation.

3. A device for performing an operation on an individual fuel cell in a fuel cell stack, the fuel cell stack having a plurality of fuel cells coupled to each other in series, the device comprising:

a controller having measuring means for determining a voltage level across each fuel cell and a current level across the fuel cell stack;

a plurality of variable resistive means for providing a variable resistive value, each variable resistive means coupled to one of the plurality of fuel cells, and each variable resistive means connected to the controller; and

a power supply coupled to the controller;

wherein the controller adjusts the variable resistive value to change the voltage level across a particular fuel cell.

4. A device as defined in claim 3, wherein the power supply derives power from the fuel cell stack.

8. A device for performing an operation on an individual fuel cell in a fuel cell stack, the fuel cell stack having a plurality of fuel cells coupled to each other in series, the device comprising:

a controller having measuring means for determining a voltage level across each fuel cell a current level across the fuel cell stack;

a plurality of variable power supplies for providing a variable voltage source, each variable power supply coupled to one of the plurality of fuel cells, and each variable power supply connected to the controller; and

a power supply coupled to the controller;

wherein the controller adjusts the voltage level of the each variable power supply to change the voltage level across a particular fuel cell.

9. A device as defined in claim 8, wherein the power supply derives power from the fuel cell stack.

10. A device as defined in claim 8, wherein the operation is rejuvenating operation.

11. A device as defined in claim 8, wherein the operation is a supplementing operation.

12. A device as defined in claim 8, wherein is a bypass operation.

13. A device for performing an operation on an individual fuel cell in a fuel cell stack, the fuel cell stack having a plurality of fuel cells coupled to each other in series, the device comprising:

a controller having measuring means for determining a voltage level and a current level across the fuel cell stack;

a variable resistive means controlled by the controller; and

a switch means connected across each of the plurality of fuel cells, and connected to both the controller and the variable resistive means;

wherein the controller adjusts a variable resistive value of the variable resistive means to change the voltage level across a particular fuel cell based on the voltage level and the current level, and

wherein the controller enables the switch to increase current through the particular fuel cell.

14. A device as defined in claim 13, wherein the operation is a rejuvenating operation.

15. A device as defined in claim 13, wherein the operation is a bypass operation.

16. A device for performing an operation on an individual fuel cell in a fuel cell stack, the fuel cell stack having a plurality of fuel cells coupled to each other in series, the device comprising:

a controller having measuring means for determining a voltage level and a current level across the fuel cell stack;

a variable power supply controlled by the controller; and

a switch means connected across each of the plurality of fuel cells, and connected to both the controller and the variable resistive means;

wherein the controller adjusts a voltage level of the variable power supply to change the voltage level across a particular fuel cell based on the voltage level and the current level, and

wherein the controller enables the switch to increase current through the particular fuel cell.

17. A device as defined in claim 16, wherein the operation is a rejuvenating operation.

18. A device as defined in claim 16, wherein the operation is a supplementing operation.

19. A device as defined in claim 16, wherein is a bypass operation.

20. A method of rejuvenating an individual fuel cell, including the steps of:

a) coupling a variable resistive means across the fuel cell;

b) providing a voltage source to the variable resistive means;

c) measuring a voltage level across the fuel cell;

d) measuring a current level across the fuel cell; and

d) controlling the variable resistive means based on the voltage level and the current level measured in step c) and d).

21. A method of bypassing an individual fuel cell in a stack of fuel cells, including the steps of:

a) coupling a variable resistive means across the fuel cell;

b) providing a voltage source to the variable resistive means;

c) measuring a voltage level across the fuel cell; and

d) controlling the variable resistive means based on the voltage level measured in step c) to bypass current through the variable resistive means.

22. A method of rejuvenating an individual fuel cell in a fuel cell stack, including the steps of:

a) coupling a variable power supply across the fuel cell;

b) providing a voltage level across the fuel cell;

c) measuring a voltage level across the fuel cell and a current level of the fuel cell stack; and

d) controlling the voltage level based on the voltage level and the current level measured in step c).

23. A method of bypassing an individual fuel cell in a fuel cell stack, including the steps of:

a) coupling a variable power supply across the fuel cell;

b) providing a voltage level across the fuel cell;

c) measuring a voltage level across the fuel cell and a current level of the fuel cell stack; and

d) controlling the voltage level based on the voltage level and the current level measured in step c) to bypass current from the fuel cell.

24. A method of supplementing an individual fuel cell in a stack of fuel cells, including the steps of:

a) coupling a variable power supply across the fuel cell;

b) providing a voltage level across the fuel cell;

c) measuring a voltage level across the fuel cell and a current level of the fuel cell stack; and

d) controlling the voltage level based on the voltage level and the current level measured in step c) to supplement the voltage level across the fuel cell.

25. A method of detecting and rejuvenating a weak fuel cell in a stack of fuel cells by a fuel cell management system, including the steps of:

a) selecting a fuel cell for detection;

b) measuring a voltage level of the selected fuel cell;

c) comparing the voltage level with a predefined voltage level threshold;

d) if the voltage level is less than the predefined voltage level threshold, adjusting a variable resistive value across the fuel cell to increase the current through the fuel cell, and output the voltage level measured in step b) to update the fuel cell management system; and

e) if the voltage level is at least equal to the predefined voltage level threshold, repeating steps a) through e).

26. A method of detecting catalyst poisons in at least two fuel cells in a fuel cell stack and prioritizing the rejuvenation of at least two fuel cells by a fuel cell management system, including the steps of:

a) measuring a voltage level across each of the at least two fuel cells;

b) measuring a voltage level across the fuel cell stack;

c) detecting a level of catalyst poisons in at least two fuel cells based on the voltage level measured in step a) and the voltage level measured in step b);

d) prioritizing each of the at least two fuel cells based on the level of catalyst poisons determined in step c);

e) for a highest priority level, adjusting a variable resistive value across a first fuel cell having the highest priority level, and updating the level of catalyst poisons in the first cell;

f) if the two fuel cells have been prioritized in step d), adjusting a variable resistive value across a second fuel cell; and

g) if at least two fuel cells have been prioritized in step d), repeating step c) through g).

27. A method of detecting and rejuvenating a weak fuel cell in a stack of fuel cells by a fuel cell management system, including the steps of:

a) selecting a fuel cell for detection;

b) measuring a voltage level of the selected fuel cell;

c) comparing the voltage level with a predefined voltage level threshold;

d) if the voltage level is less than the predefined voltage level threshold, applying a voltage level value across the fuel cell to increase the current through the fuel cell, and output the voltage level measured in step b) to update the fuel cell management system; and

e) if the voltage level is at least equal to the predefined voltage level threshold, repeating steps a) through e).

28. A method of detecting catalyst poisons in at least two fuel cells in a fuel cell stack and prioritizing the rejuvenation of at least two fuel cells by a fuel cell management system, including the steps of:

a) measuring a voltage level across each of the at least two fuel cells;

b) measuring a voltage level across the fuel cell stack;

c) detecting a level of catalyst poisons in at least two fuel cells based on the voltage level measured in step a) and the voltage level measured in step b);

d) prioritizing each of the at least two fuel cells based on the level of catalyst poisons determined in step c);

e) for a highest priority level, applying a voltage level across a first fuel cell having the highest priority level, and updating the level of catalyst poisons in the first cell;

f) if the two fuel cells have been prioritized in step d), applying a voltage level value across a second fuel cell; and

g) if at least two fuel cells have been prioritized in step d), repeating step c) through g).

29. A method of detecting catalyst poisons and rejuvenating a weak fuel cell in a stack of fuel cells by a fuel cell management system, including the steps of:

a) measuring a stack voltage level;

b) comparing the stack voltage level with a predefined stack voltage level;

c) if the stack voltage level is less than the predefined stack voltage level, executing the steps of;

c1) selecting a fuel cell for detection;

c2) measuring a cell voltage level of the fuel cell;

c3) comparing the cell voltage level with a predefined cell voltage level threshold;

c4) if the voltage level is less than the predefined cell voltage level threshold, adjusting a variable resistive value across the fuel cell, and outputting cell voltage level measured in step to update the fuel cell management system;

c5) if the voltage level is at least equal to the predefined voltage level threshold, repeating steps a) through c); and

d) if the stack voltage level is at least equal to the predefined voltage, repeating steps a) through d).

30. A method of detecting catalyst poisons and rejuvenating a weak fuel cell in a stack of fuel cells by a fuel cell management system, including the steps of:

a) measuring a stack voltage level;

b) comparing the stack voltage level with a predefined stack voltage level;

c) if the stack voltage level is less than the predefined stack voltage level, executing the steps of;

c1) selecting a fuel cell for detection;

c2) measuring a cell voltage level of the fuel cell;

c3) comparing the cell voltage level with a predefined cell voltage level threshold;

c4) if the voltage level is less than the predefined cell voltage level threshold, applying a voltage level across the fuel cell, and outputting cell voltage level measured in step to update the fuel cell management system;

c5) if the voltage level is at least equal to the predefined voltage level threshold, repeating steps a) through c); and

d) if the stack voltage level is at least equal to the predefined voltage, repeating steps a) through d).

31. A method of bypassing a weak fuel cell in a stack of fuel cells detected by a fuel cell management system, including the steps of:

a) selecting a fuel cell for detection,

b) measuring a voltage level of the selected fuel cell and a current level of the stack of fuel cells;

c) comparing the voltage level with a predefined voltage level threshold; and

d) if the voltage level is less than the predefined voltage level threshold, applying a variable power supply for increasing the voltage level across the selected fuel cell to bypass current flowing through the fuel cell to the power supply and output the voltage level measured in step (b) to update the fuel cell management system.

32. A method of bypassing a weak fuel cell in a stack of fuel cells detected by a fuel cell management system, including the steps of:

a) selecting a fuel cell for detection,

b) measuring a voltage level of the selected fuel cell and a current level of the stack of fuel cells;

c) comparing the voltage level with a predefined voltage level threshold; and

d) if the voltage level is less than the predefined voltage level threshold, applying a variable power supply for increasing the voltage level across the selected fuel cell to bypass current flowing through the fuel cell to the power supply.

33. A method of supplementing a weak fuel cell in a stack of fuel cells detected by a fuel cell management system, including the steps of:

a) selecting a fuel cell for detection,

b) measuring a voltage level of the selected fuel cell and a current level of the stack of fuel cells;

c) comparing the voltage level with a predefined voltage level threshold;

d) if the voltage level is less than the predefined voltage level threshold, applying a variable power supply for increasing the voltage level across the selected fuel cell to increase the voltage level across the selected fuel cell to at least a voltage level equal to the predefined voltage level threshold.

34. A method of supplementing a weak fuel cell in a stack of fuel cells detected by a fuel cell management system, including the steps of:

a) selecting a fuel cell for detection,

b) measuring a voltage level of the selected fuel cell and a current level of the stack of fuel cells;

c) comparing the voltage level with a predefined voltage level threshold;

d) if the voltage level is less than the predefined voltage level threshold, applying a variable power supply for increasing the voltage level across the selected fuel cell to increase the voltage level across the selected fuel cell to at least a voltage level equal to the predefined voltage level threshold and output the voltage level measured in step (b) to update the fuel cell management system, and

e) if the voltage is at least equal to the predefined voltage level threshold, repeating steps (a) through (c).

35. A method of replacing a weak fuel cell in a stack of fuel cells detected by a fuel cell management system, including the steps of:

a) selecting a fuel cell for detection,

b) measuring a voltage level of the selected fuel cell and a current level of the stack of fuel cells;

c) comparing the voltage level with a predefined voltage level threshold; and

d) if the voltage level is less than the predefined voltage level threshold, adjusting a variable resistive value across the fuel cell to bypass current around the fuel cell.

36. A method of replacing a weak fuel cell in a stack of fuel cells detected by a fuel cell management system, including the steps of:

a) selecting a fuel cell for detection,

b) measuring a voltage level of the selected fuel cell;

c) comparing the voltage level with a predefined voltage level threshold;

d) if the voltage level is less than the predefined voltage level threshold, adjusting a variable resistive value across the fuel cell to bypass current around the fuel cell, and output the voltage level measured in step (b) to update the fuel cell management system, and

e) if the voltage is at least equal to the predefined voltage level threshold, repeating steps (a) through (c).

37. A device for performing an operation on an individual fuel cell in a fuel cell stack, the fuel cell stack having a plurality of fuel cells coupled to each other in series, the plurality of fuel cells including a subset of at least one fuel cell within the plurality of fuel cells, the device comprising:

a controller having measuring means for determining a voltage level and a current level across the subset of at least one fuel cell;

a variable resistive means controlled by the controller; and

a switch means connected across the subset of at least one fuel cell, and connected to both the controller and the variable resistive means;

whereby the controller adjusts the variable resistive value to change the voltage level across the subset of at least one fuel cell based on the voltage level and the current level, and the controller enables the switch to increase current through a particular fuel cell of the subset of at least one fuel cell.

41. A device as in claim 37, 38, 39 or 40, wherein the operation is a rejuvenating operation.

42. A device as in claim 37, 38, 39 or 40, wherein the operation is a bypass operation.

38. A device for performing an operation on at least one individual fuel cell in a fuel cell stack, the fuel cell stack having a plurality of fuel cells coupled to each other in series, the plurality of fuel cells including a subset of at least one fuel cell within the plurality of fuel cells, the device comprising:

a controller having measuring means for determining a voltage level and a current level across the subset of at least one fuel cell;

a variable resistive means controlled by the controller; and

a switch means connected across the subset of at least one fuel cell, and connected to both the controller and the variable resistive means;

whereby the controller adjusts the variable resistive value to adjust the voltage level across the subset of at least one fuel cell based on the voltage level and the current level, and the controller enables the switch to increase current through at least two fuel cells of the subset of at least one fuel cell.

39. A device for performing an operation on at least two fuel cells in a fuel cell stack, the fuel cell stack having a plurality of fuel cells coupled to each other in series, the device comprising:

a controller having measuring means for determining a voltage level and a current level across the fuel cell stack;

a variable resistive means controlled by the controller; and

a switch means connected across each of the plurality of fuel cells, and connected to both the controller and the variable resistive means;

whereby the controller adjusts a variable resistive value of the variable resistive means to change a fuel cell voltage level across each of the at least two fuel cells based on the voltage level and the current level, and the controller simultaneously enables the switch increase current through each of the at least two fuel cells.

40. A device for performing an operation on at least two fuel cells in a fuel cell stack, the fuel cell stack having a plurality of fuel cells coupled to each other in series, the device comprising:

a controller having measuring means for determining a voltage level and a current level across the fuel cell stack;

a plurality of variable resistive means controlled by the controller; and

a switch means connected across each of the plurality of fuel cells, and connected to both the controller and the plurality of variable resistive means;

whereby the controller adjusts at least two variable resistive values corresponding to at least two variable resistive means, of the plurality of variable resistive means, to change the voltage level across at least two fuel cells respectively, based on the voltage level and the current level, and the controller simultaneously enables the switch to increase current through each of the at least two fuel cells.

43. A device for performing an operation on an individual fuel cell in a fuel cell stack, the fuel cell stack having a plurality of fuel cells coupled to each other in series, the plurality of fuel cells including a subset of at least one fuel cell within the plurality of fuel cells, the device comprising:

a controller having measuring means for determining a fuel cell voltage level and a current level across the subset of at least one fuel cell;

a variable power supply controlled by the controller; and

a switch means connected across the subset of at least one fuel cell, and connected to both the controller and the variable power supply;

whereby the controller adjusts a power supply voltage level of the variable power supply to change the voltage level across the subset of at least one fuel cell based on the fuel cell voltage level and the current level, and the controller enables the switch to increase current through a particular fuel cell of the subset of at least one fuel cell.

47. A device as in claim 43, 44, 45 or 46, wherein the operation is a supplementing operation.

48. A device as in claim 43, 44, 45 or 46, wherein the operation is a bypass operation.

49. A device as in claim 43, 44, 45 or 46, wherein the operation is a rejuvenating operation.

44. A device for performing an operation on at least one individual fuel cell in a fuel cell stack, the fuel cell stack having a plurality of fuel cells coupled to each other in series, the plurality of fuel cells including a subset of at least one fuel cell within the plurality of fuel cells, the device comprising:

a controller having measuring means for determining a fuel cell voltage level and a current level across the subset of at least one fuel cell;

a variable power supply controlled by the controller; and

a switch means connected across the subset of at least one fuel cell, and connected to both the controller and the variable power supply;

whereby the controller adjusts a power supply voltage level of the variable power supply to change the voltage level across the subset of at least one fuel cell based on the voltage level and the current level, and the controller enables the switch to increase current through at least two fuel cells of the subset of at least one fuel cell.

45. A device for performing an operation on at least two fuel cells in a fuel cell stack, the fuel cell stack having a plurality of fuel cells coupled to each other in series, the device comprising:

a controller having measuring means for determining a fuel cell voltage level and a current level across the fuel cell stack;

a variable power supply controlled by the controller; and

a switch means connected across each of the plurality of fuel cells, and connected to both the controller and the variable resistive means;

whereby the controller adjusts a power supply voltage level of the variable power supply to change a fuel cell voltage level across each of the at least two fuel cells based on the voltage level and the current level, and the controller simultaneously enables the switch increase current through each of the at least two fuel cells.

46. A device for performing an operation on at least two fuel cells in a fuel cell stack, the fuel cell stack having a plurality of fuel cells coupled to each other in series, the device comprising:

a controller having measuring means for determining a fuel voltage level of the at least two fuel cells and a current level across the fuel cell stack;

a plurality of variable power supplies controlled by the controller; and

a switch means connected across each of the plurality of fuel cells, and connected to both the controller and the plurality of variable power supplies;

whereby the controller adjusts at least two variable power supply voltage levels corresponding to at least two variable power supplies, of the plurality of variable power supplies, to change the voltage level across the at least two fuel cells respectively, based on the fuel cell voltage level and the current level, and the controller simultaneously enables the switch to increase current through each of the at least two fuel cells.

50. A method of detecting catalyst poisons in at least two fuel cells in a fuel cell stack and prioritizing the rejuvenation of at least two fuel cells by a fuel cell management system, including the steps of:

a) measuring a fuel cell voltage level across each of the at least two fuel cells;

b) measuring a stack voltage level and a current level across the fuel cell stack;

c) detecting a level of catalyst poisons in at least two fuel cells based on the fuel cell voltage level measured in step a) and the stack voltage level measured in step b);

d) prioritizing each of the at least two fuel cells based on the level of catalyst poisons determined in step c); and

e) for a given priority level, adjusting the fuel cell voltage level across at least one fuel cell of the at least two fuel cells, by applying a pulse across the at least one fuel cell, the pulse being defined by at least one parameter, the at least one parameter being determined based on the level of catalyst poisons.

51. A method as defined in claim 50, wherein the at least one parameter is a voltage level.

52. A method as defined in claim 50, wherein the at least one parameter is a given period in time for each pulse.

53. A method as defined in claim 51, wherein the at least one parameter is a given period in time for the pulse.

54. A method as defined in claim 51, wherein the at least one parameter is a given period in time for the pulse.

55. A method as defined in claim 50, wherein the pulse is periodically applied.

56. A method as defined in claim 51, wherein the pulse is periodically applied.

57. A method as defined in claim 52, wherein the pulse is periodically applied.

58. A method of detecting catalyst poisons in a group of at least two fuel cells in a fuel cell stack and prioritizing the rejuvenation of the group of at least two fuel cells by a fuel cell management system, including the steps of:

a) measuring a fuel cell voltage level across the group of at least two fuel cells;

b) measuring a stack voltage level and a current level across the fuel cell stack;

c) detecting a level of catalyst poisons in the group of at least two fuel cells based on the fuel cell voltage level and the current level measured in step a) and the stack voltage level and the current level measured in step b); and

d) adjusting a variable resistive value of the resistive means connected across the group of at least two fuel cells.

59. A method of detecting catalyst poisons in a group of at least two fuel cells in a fuel cell stack and prioritizing the rejuvenation of the group of at least two fuel cells by a fuel cell management system, including the steps of:

a) measuring a fuel cell voltage level across the group of at least two fuel cells;

b) measuring a stack voltage level and a current level across the fuel cell stack;

c) detecting a level of catalyst poisons in the group of at least two fuel cells based on the fuel cell voltage level measured in step a) and the stack voltage level and the current level measured in step b); and

d) adjusting a variable resistive value of the resistive means connected across the group of at least two fuel cells to bypass current through the resistive means.

60. A method of detecting catalyst poisons in a group of at least two fuel cells in a fuel cell stack and prioritizing the rejuvenation of the group of at least two fuel cells by a fuel cell management system, including the steps of:

a) measuring a fuel cell voltage level across the group of at least two fuel cells;

b) measuring a stack voltage level and a current level across the fuel cell stack;

c) detecting a level of catalyst poisons in the group of at least two fuel cells based on the fuel cell voltage level measured in step a) and the stack voltage level and current level measured in step b); and

d) adjusting a voltage level applied across the group of at least two fuel cells by applying a pulse across the group at least two fuel cells, the pulse being defined by at least one parameter, the at least one parameter being determined based on the level of catalyst poisons.

61. A method as defined in claim 60, wherein the at least one parameter is a voltage level.

62. A method as defined in claim 60, wherein the at least one parameter is a voltage level range.

63. A method as defined in claim 60, wherein the at least one parameter is a given period in time for the pulse.

64. A method as defined in claim 60, wherein the pulse is periodically applied.

65. A device for rejuvenating at least two fuel cells while the fuel cell is operational, the device comprising:

a variable resistive means coupled to the at least two fuel cells; and

a controller for adjusting the variable resistive means, the controller having measuring means for determining a voltage level and a current level of the at least two fuel cells, the controller adjusting the variable resistive means based on the voltage level and the current level of the at least two fuel cells, and the controller deriving power from a power supply.

66. A device for rejuvenating an individual fuel cell while the fuel cell is operational, the device comprising:

a variable power supply coupled to at least two fuel cells; and

a controller for adjusting the variable power supply applied across the at least two fuel cells, the controller having measuring means for determining a voltage level and a current level of the fuel cell, the controller adjusting the variable power supply based on the voltage level and the current level of the at least two fuel cells, and the controller deriving power from the variable power supply.

67. A device for performing an operation on an individual fuel cell while the fuel cell is operational in a fuel cell stack, the device comprising:

a variable resistive means coupled to the fuel cell; and

a controller for adjusting the variable resistive means, the controller having measuring means for determining a fuel cell voltage level and a current level of the fuel cell stack, the controller adjusting the variable resistive means based on the voltage level and the current level of the fuel cell; and

means for determining a limiting process within a fuel cell thus enabling an optimization of a performance level of the fuel cell stack.

68. A device for performing an operation on an individual fuel cell while the fuel cell is operational in a fuel cell stack, the device comprising:

a variable power supply coupled across the fuel cell; and

a controller for adjusting the variable resistive means, the controller having measuring means for determining a fuel cell voltage level and a current level of the fuel cell stack, the controller adjusting a power supply voltage level of the variable power supply to change the voltage level based on the fuel cell voltage level and the current level of the fuel cell; and

means for determining a limiting process within a fuel cell thus enabling an optimization of a performance level of the fuel cell stack.