System stack contingency and efficiency switching

• US 20040202901A1
• Filed: 04/14/2003
• Published: 10/14/2004
• Est. Priority Date: 04/14/2003
• Status: Active Grant

• Current Assignee: GM Global Technology Operations LLC (General Motors Company)
• Original Assignee: GM Global Technology Operations Incorporated (General Motors Company)
• Inventors: Logan, Victor W., Dandalides, James W.
• Granted Patent: US 7,247,398 B2
• Time in Patent Office: Days
• US Class Current: 429/13
• CPC Class Codes: H01M 8/04246 Short circuiting means for defective fuel cells detection of defective fuel cells H01M8/04664, methods for shunting fuel cells H01M8/04955
• CPC Class Codes: H01M 8/04589 of fuel cell stacks
• CPC Class Codes: H01M 8/04597 of auxiliary devices, e.g. batteries, capacitors
• CPC Class Codes: H01M 8/04679 of fuel cell stacks
• CPC Class Codes: H01M 8/04902 of the individual fuel cell
• CPC Class Codes: H01M 8/04932 of the individual fuel cell
• CPC Class Codes: H01M 8/249 comprising two or more groupings of fuel cells, e.g. modular assemblies
• CPC Class Codes: Y02E 60/50 Fuel cells

Abstract

A switching system and control method therefor are provided and implemented with a fuel cell stack system. The switching system enables fuel cell stacks to be connected in series for providing power to a power user while removing the particular disadvantages of a series circuit. In the event of a stack fault, the faulty stack may be bypassed, whereby the remaining stacks provide power to the power user at reduced capacity. The stack is continuously monitored and is reintroduced to the series circuit if the fault clears. If the fault reoccurs a predetermined number of times after the stack has been reintroduced, a “reduced capacity” mode is initiated. Additionally, in the event of a reduced or an increased current demand, stacks are selectively switched in and out of the series connection, for limiting the overall operation voltage range of the fuel cell stack system.

Claims

1. A method of operating a fuel cell stack system having a plurality of fuel cell stacks in series connection, comprising the steps of:

monitoring each of the plurality of fuel cell stacks for a particular condition; and

bypassing at least one fuel cell stack of the plurality of fuel cell stacks if said condition is detected.

2. The method of claim 1, further comprising the step of reconnecting said at least one fuel cell stack if said condition is cleared.

3. The method of claim 1, wherein said condition is a fault condition.

4. The method of claim 3, further comprising the steps of:

counting a number of times a particular fuel cell stack recurrently achieves said fault condition; and

initiating a reduced capacity mode if said number of times is equal to a predetermined value.

5. The method of claim 1, wherein said condition is one of a reduced current demand and an increased current demand.

6. The method of claim 5, further comprising the steps of:

determining a number of fuel cell stacks to bypass, as a function of said reduced current demand; and

selecting one or more fuel cell stacks to bypass.

7. The method of claim 6, wherein said step of selecting comprises determining an average operating time for said plurality of fuel cell stacks, and selecting stacks having an above average operating time.

8. The method of claim 5, further comprising the steps of:

determining a number of fuel cell stacks to reconnect, as a function of said increased current demand; and

selecting one or more fuel cell stacks to reconnect.

9. The method of claim 8, wherein said step of selecting comprises determining an average operating time for said plurality of fuel cell stacks, and selecting stacks having a below average operating time.

10. The method of claim 1, wherein said step of bypassing at least one fuel cell stack of the plurality of fuel cell stacks comprises the steps of:

operating a switch to prohibit a current flow through said at least one fuel cell stack; and

redirecting said current flow through remaining fuel cell stacks in the fuel cell stacks system.

11. The method of claim 2, wherein said step of reconnecting said at least one fuel cell stack comprises the steps of:

operating a switch to enable a current flow through said at least one fuel cell stack; and

redirecting said current flow back through said at least one fuel cell stack.

12. A fuel cell system having a, plurality of fuel cell stacks connected in a series circuit, comprising:

an operation monitor associated with each of the fuel cell stacks for monitoring an operational characteristic of the fuel cell stacks; and

a switching circuit associated with each of the fuel cell stacks and in respective electrical communication with said operation monitor for selectively bypassing a particular fuel cell stack from the circuit in response to a signal from said operation monitor.

13. The fuel cell system of claim 12, wherein said operation monitor is a voltage monitor for monitoring the voltage over a particular fuel cell stack.

14. The fuel cell system of claim 12, wherein said operation monitor is a current load monitor for monitoring the current demand.

15. The fuel cell system of claim 12, wherein said switching circuit comprises one of an electromechanical switch and a solid-state switch operable by said operation monitor for selectively bypassing an associated fuel cell stack.

16. The fuel cell system of claim 15, wherein said switching circuit further comprises a diode which is reverse biased when said electromechanical switch is closed and forward biased when said electromechanical switch is open for enabling continuous current flow through the series circuit.

17. A method of operating a fuel cell stack system having a plurality of fuel cell stacks in series connection, comprising the steps of:

monitoring each of the plurality of fuel cell stacks for one of a fault condition and a change in load demand;

bypassing at least one fuel cell stack of the plurality of fuel cell stacks if a fault condition thereof is detected;

reconnecting said at least one fuel cell stack if said fault condition clears;

bypassing at least one fuel cell stack of the plurality of fuel cell stacks if a reduced load demand is detected; and

reconnecting said at least one fuel cell stack if an increased load demand is detected.

18. The method of claim 17, further comprising the steps of:

counting a number of times a particular fuel cell stack recurrently achieves said fault condition; and

initializing a reduced capacity mode if said number of times is equal to a predetermined value.

19. The method of claim 17, further comprising the steps of:

determining a number of fuel cell stacks to bypass, as a function of said reduced load demand; and

selecting one or more fuel cell stacks to bypass.

20. The method of claim 19, wherein said step of selecting comprises determining an average operating time for said plurality of fuel cell stacks, and selecting stacks having an above average operating time.

21. The method of claim 17, further comprising the steps of:

determining a number of fuel cell stacks to reconnect, as a function of said increased load demand; and

selecting one or more fuel cell stacks to reconnect.

22. The method of claim 21, wherein said step of selecting comprises determining an average operating time for said plurality of fuel cell stacks, and selecting stacks having a below average operating time.

23. The method of claim 17, wherein said steps of bypassing at least one fuel cell stack of the plurality of fuel cell stacks comprises the steps of:

operating a switch to prohibit a current flow through said at least one fuel cell stack; and

redirecting said current flow through remaining fuel cell stacks in the fuel cell stacks system.

24. The method of claim 17, wherein said steps of reconnecting said at least one fuel cell stack comprises the steps of:

operating a switch to enable a current flow through said at least one fuel cell stack; and

redirecting said current flow back through said at least one fuel cell stack.

25. A method of operating a fuel cell system having a plurality of fuel cell stacks supplying electrical power to an external load comprising:

monitoring the external load and adjusting a number of stacks powering the external load as the external load varies.

26. A method of operating a fuel cell system having a plurality of fuel cell stacks connected in series to collectively provide a system voltage to an external load, comprising:

varying the system voltage by adjusting a number of stacks powering the external load.

27. A method of operating a fuel cell system having a plurality of fuel cell stacks supplying electrical power to an external load, comprising:

monitoring a service time of individual stacks and minimizing a variance in service time among the individual stacks by powering the external load with one or more stacks having relatively low service time and bypassing one or more stacks having relatively high service time.