Fuel cell system having an energy source backup

• US 6,761,987 B2
• Filed: 03/30/2001
• Issued: 07/13/2004
• Est. Priority Date: 03/31/2000
• Status: Expired due to Fees

• Current Assignee: Plug Power Inc.
• Original Assignee: Plug Power Inc.
• Inventors: McElroy, James F., Marvin, Russel H.
• Primary Examiner(s): Bell, Bruce F.
• Assistant Examiner(s): WILLS, MONIQUE M
• Application Number:
  US09/823,263
• Publication Number:
  US 20020021109A1
• Time in Patent Office: 1,201 Days
• Field of Search: 429/12, 429/13, 429/22, 429/23, 429/7, 429/9, 429/20, 320/134, 320/101, 361/62, 361/111, 307/64, 307/31, 307/29, 307/66
• US Class Current: 429/423
• CPC Class Codes: H01M 16/006 of fuel cells with rechargeable batteries
• CPC Class Codes: H01M 8/04089 of gaseous reactants
• 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 8/04776 at auxiliary devices, e.g. reformer, compressor, burner
• CPC Class Codes: H01M 8/0488 of fuel cell stacks
• CPC Class Codes: H01M 8/0491 of fuel cell stacks
• CPC Class Codes: H01M 8/04947 of auxiliary devices, e.g. batteries, capacitors
• CPC Class Codes: H01M 8/04955 Shut-off or shut-down of fuel cells
• CPC Class Codes: H01M 8/0612 from carbon-containing material
• CPC Class Codes: H02J 7/34 Parallel operation in networks using both storage and other dc sources, e.g. providing buffering H02J7/14 takes precedence
• CPC Class Codes: Y02E 60/10 Energy storage using batteries
• CPC Class Codes: Y02E 60/50 Fuel cells

Abstract

A fuel cell includes a fuel cell subsystem, a battery and a circuit. The fuel cell subsystem is adapted to furnish power to a load. The circuit is adapted to connect the battery to the load when the fuel cell subsystem substantially delays in responding to a change in the power.

Claims

1. A fuel cell system comprising:

a fuel cell subsystem comprising a fuel cell stack adapted to furnish power to a load;

a battery;

a first circuit adapted to selectively connect the battery to the load and isolate the battery from the load based on a response of the fuel cell subsystem to a change in the power;

a current sensor to indicate a current through the fuel cell stack; and

a second circuit coupled to the current sensor to monitor cell voltages of the fuel cell stack, determine the minimum of the cell voltages and prevent the current from exceeding a maximum threshold current based on the minimum cell voltage.

2. The fuel cell system of claim 1, wherein the fuel cell subsystem comprises:

a fuel cell stack adapted to receive a hydrogen flow; and

a fuel processor to produce the hydrogen flow.

3. The fuel cell system of claim 2, wherein the fuel cell subsystem further comprises:

a controller adapted to monitor the power and regulate a rate at which the fuel processor produces the hydrogen flow based on the monitored power.

4. The fuel cell system of claim 1, wherein the first circuit is further adapted to connect the battery to the load based on a fuel cell stack voltage of the fuel cell subsystem.

5. The fuel cell system of claim 1, wherein the first circuit comprises:

a first diode to couple the battery to the fuel cell subsystem when a stack voltage of the fuel cell subsystem is near a predefined threshold voltage.

6. The fuel cell system of claim 1, wherein the second circuit comprises:

a voltage regulator adapted to regulate a stack voltage of the fuel cell stack and limit the current through the stack.

7. A method comprising:

using a fuel cell stack to furnish power to a load;

selectively connecting a battery to the load and isolating the battery from the load based on a response of the fuel cell stack to a change in the power;

monitoring a current through the fuel cell stack;

monitoring cell voltages of the fuel cell stack;

determining the minimum of the cell voltages; and

preventing the current from exceeding a maximum threshold current based on the minimum cell voltage.

8. The method of claim 7, further comprising:

monitoring the power;

producing hydrogen;

regulating a rate of the production in response to the monitoring; and

providing the hydrogen to a fuel cell stack of the system.

9. A The method of claim 7, further comprising:

connecting the battery to the load based on a fuel cell stack voltage of the fuel cell subsystem.

10. The method of claim 7, further comprising:

connecting the battery to the load when a stack voltage of the fuel cell subsystem is near a predefined threshold voltage.

11. The method of claim 7, further comprising:

using a voltage regulator to regulate a stack voltage of the fuel cell stack and limit the current through the stack.

12. A fuel cell system comprising:

a fuel cell subsystem adapted to measure a lowest cell voltage and further adapted to furnish power to a load, wherein the fuel cell subsystem is connected to the load through a diode;

a fuel processor subsystem adapted to furnish reformate to the fuel cell subsystem; and

a supplemental power subsystem adapted to furnish power to the load when the lowest cell voltage drops below a predefined threshold voltage, wherein the supplemental power subsystem is connected to the load through a diode a current sensor to indicate a current through a fuel cell stack of the fuel cell subsystem; and

a circuit coupled to the current sensor to monitor cell voltages of said fuel cell stack, determine the minimum of the cell voltages and prevent the current from exceeding a maximum threshold current based on the minimum cell voltage.

13. A fuel cell system comprising:

a fuel cell subsystem adapted to measure a lowest cell voltage and further adapted to furnish power to a load, wherein the fuel cell subsystem is connected to the load through a diode;

a fuel processor subsystem adapted to furnish reformate to the fuel cell subsystem;

a supplemental power subsystem adapted to furnish power to the load when the lowest cell voltage drops below a predefined threshold voltage, wherein the supplemental power subsystem is connected to the load through a diode; and

a controller adapted to monitor the power and regulate a rate at which the fuel processor produces the hydrogen flow based on the monitored power a current sensor to indicate a current through a fuel cell stack of the fuel cell subsystem; and

a circuit coupled to the current sensor to monitor cell voltages of said fuel cell stack, determine the minimum of the cell voltages and prevent the current from exceeding a maximum threshold current based on the minimum cell voltage.

14. The fuel cell system of claim 13, further comprising:

a predefined threshold voltage of −

0.35 volts.

15. The fuel cell system of claim 13, further comprising:

a predefined threshold voltage of more than −

0.4 volts.

16. The fuel cell system of claim 13, further comprising:

a predefined threshold voltage of more than −

0.5 volts.