Fuel cell system having decreased deterioration during initiation

• US 8,715,872 B2
• Filed: 12/26/2006
• Issued: 05/06/2014
• Est. Priority Date: 12/27/2005
• Status: Active Grant

• Current Assignee: Nissan Motor Co., Ltd.
• Original Assignee: Nissan Motor Co., Ltd.
• Inventors: Shimoi, Ryoichi, Iimori, Takashi, Goto, Kenichi, Kamihara, Tetsuya
• Primary Examiner(s): Ruddock, Ula C
• Assistant Examiner(s): CHUO, TONY SHENG HSIANG
• Application Number:
  US12/096,414
• Publication Number:
  US 20090197129A1
• Time in Patent Office: 2,688 Days
• Field of Search: None
• US Class Current: 429/429
• CPC Class Codes: H01M 2008/1095 Fuel cells with polymeric electrolytes
• CPC Class Codes: H01M 2250/20 Fuel cells in motive systems, e.g. vehicle, ship, plane
• CPC Class Codes: H01M 8/04089 of gaseous reactants
• CPC Class Codes: H01M 8/04097 with recycling of the reactants H01M8/04119, H01M8/04104 take precedence
• CPC Class Codes: H01M 8/04104 Regulation of differential pressures
• CPC Class Codes: H01M 8/04201 Reactant storage and supply, e.g. means for feeding, pipes
• CPC Class Codes: H01M 8/04223 during start-up or shut-down; Depolarisation or activation, e.g. purging; Means for short-circuiting defective fuel cells
• CPC Class Codes: H01M 8/04238 Depolarisation
• CPC Class Codes: H01M 8/04388 of anode reactants at the inlet or inside the fuel cell
• CPC Class Codes: H01M 8/04395 of cathode reactants at the inlet or inside the fuel cell
• CPC Class Codes: H01M 8/04402 of anode exhausts
• CPC Class Codes: H01M 8/04462 of anode exhausts
• CPC Class Codes: H01M 8/04559 of fuel cell stacks
• CPC Class Codes: H01M 8/04567 of auxiliary devices, e.g. batteries, capacitors
• CPC Class Codes: H01M 8/04597 of auxiliary devices, e.g. batteries, capacitors
• CPC Class Codes: H01M 8/04619 of fuel cell stacks
• CPC Class Codes: H01M 8/04753 of fuel cell reactants
• CPC Class Codes: H01M 8/04761 of fuel cell exhausts
• 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 8/241 : with solid or matrix-supported electrolytes
• CPC Class Codes: H01M 8/2457 : with both reactants being gaseous or vaporised
• CPC Class Codes: H01M 8/2475 : Enclosures, casings or containers of fuel cell stacks
• CPC Class Codes: Y02E 60/50 : Fuel cells
• CPC Class Codes: Y02T 90/40 : Application of hydrogen technology to transportation, e.g. using fuel cells

Abstract

A fuel cell system can be initiated in shorter time while minimizing the deterioration of a fuel cell. The fuel cell system includes a fuel cell stack having a fuel electrode, an oxidizer electrode and an electrolyte membrane disposed there between, the fuel cell producing electricity by an electrochemical reaction of a fuel gas and an oxidizer gas, which are supplied to the fuel electrode and the oxidizer electrode, respectively; a fuel gas supplying device for supplying the fuel gas to the fuel cell stack; an oxidizer gas supplying device for supplying the oxidizer gas to the fuel cell stack; a current controlling device for extracting a current from the fuel cell stack; and a voltage sensor disposed in at least two of the fuel cell stacks. A controller controls the current controlling device such that a minimum voltage, which is obtained from the voltage sensor after a fuel gas is supplied to the fuel electrode without supplying the oxidizer gas to the oxidizer electrode at the time of initiating, becomes zero volts or more. Then, the oxidizer gas is supplied to the oxidizer to start producing electricity.

Claims

1. A fuel cell system including a fuel cell stack, a fuel gas supplying unit for supplying fuel gas to the fuel cell stack, and an oxidizer gas supplying unit for supplying oxidizer gas to the fuel cell stack, wherein the fuel cell stack includes a plurality of stacked cells each formed by interposing an electrolyte membrane between a fuel electrode supplied with the fuel gas and an oxidizer electrode supplied with the oxidizer gas, the fuel cell system comprising:

a current control device that extracts a current from the fuel cell stack;

a voltage sensor that measures voltages from a plurality of different cells of the fuel cell stack; and

a controller electrically coupled to the fuel gas supplying unit, the oxidizer gas supplying unit, current control device, and the voltage sensor;

wherein the controller is programmed to cause the fuel gas to be supplied to the fuel electrode without supplying the oxidizer gas to the oxidizer electrode at a time of initiating operation of the fuel cell stack,

wherein the controller is programmed to extract through the current control device a current sufficient to inhibit deterioration of the electrolyte membrane after a minimum value detected by the voltage sensor becomes zero volts or more,

wherein the controller is programmed to determine weather to finish the current extraction based on variations of the current amount extracted by the current control device, and

wherein the controller is programmed to cause the oxidizer gas to be supplied to the oxidizer electrode to start producing electricity in the fuel cell stack once the current extraction has finished.

2. The fuel cell system of claim 1, wherein the controller is programmed to extract through the current control device the current from the fuel cell stack after supplying the fuel gas to the fuel electrode and after the minimum voltage detected by the voltage sensor becomes a predetermined value or more.

3. The fuel cell system of claim 2, wherein the controller is programmed to extract through the current control device the current from the fuel cell stack after the minimum value detected by the voltage sensor becomes 12 millivolts or more per one cell.

4. The fuel cell system of claim 2, wherein the controller through the current control device is programmed to extract sufficient current to maintain a target fuel utilization rate relative to the supplied fuel gas.

5. The fuel cell system of claim 4, wherein the sufficient current extracted from the fuel cell stack by the controller through the current control device corresponds to the target fuel utilization rate or below.

6. The fuel cell system of claim 2, wherein, the controller is programmed to control the current extracted from the fuel cell stack through the current control device so that all voltages detected by the voltage sensor at the time of initiating becomes zero volts or more.

7. The fuel cell system of claim 6, wherein, the controller is programmed to control the current extracted from the fuel cell stack through the current control device so that a maximum current is extracted when all voltages detected by the voltage sensor at the time of initiating becomes zero volts or more.

8. The fuel cell system of claim 7, wherein the current control device is electrically coupled to auxiliary machinery and to a battery that provides an auxiliary power source, and a maximum current extracted from the fuel cell stack through the current control device is determined from a sum of a charging amount of the battery and a consumed power amount of the auxiliary machinery.

9. The fuel cell system of claim 2, wherein the controller is programmed to control the current extracted from the fuel cell stack through the current control device in response to a total voltage of the fuel cell stack based on voltages detected by the voltage sensor.

10. The fuel cell system of claim 9, wherein the current extracted from the fuel cell stack through the current control device increases in response to an increase in the total voltage of the fuel cell stack that is detected by the voltage sensor.

11. The fuel cell system of claim 9, wherein the controller is programmed to control the current extracted from the fuel cell stack through the current control device such that variations of all voltages detected by the voltage sensor become a predetermined value or below.

12. The fuel cell system of claim 2, wherein the current control device is electrically coupled to auxiliary machinery and to a battery that provides an auxiliary power source, and the controller is programmed to output to the current control device a target command current that is a maximum amount or below equal to a sum of a charging amount of the battery and a consumed power amount of the auxiliary machinery.

13. The fuel cell system of claim 12, wherein the current extracted from the fuel cell stack through the current control device is less than the maximum amount or below equal to the sum of the charging amount of the battery and the consumed power amount of the auxiliary machinery.

14. The fuel cell system of claim 1, wherein the voltage sensor comprises a separate voltage sensor disposed in each cell of the plurality of stacked cells in the fuel cell stack.

15. The fuel cell system of claim 1, wherein the voltage sensor comprises a separate voltage sensor disposed in each of a group of cells of the plurality of stacked cells in the fuel cell stack.

16. The fuel cell system of claim 1, wherein the voltage sensor comprises pairs of voltage sensors, and each pair of voltage sensors is disposed in at least one of:

each cell of the plurality of stacked cells in the fuel cell stack, and each of a group of cells of the plurality of stacked cells in the fuel cell stack.

17. The fuel cell system of claim 16, wherein each of the pairs of voltage sensors comprise a first voltage sensor measuring voltage at a fuel gas supply side and a second voltage sensor measuring voltage at a fuel gas exhaust side.

18. The fuel cell system of claim 2, wherein the controller is programmed to compare a target command current relative to a real current extracted from the fuel cell stack through the current control device, and the controller is programmed to terminate current extraction through the current control device if the real current is lower than the target command current.

19. The fuel cell system of claim 1, Wherein the controller is programmed to terminate current extraction through the current control device in response to both voltage and current.

20. The fuel cell system of claim 2, wherein the controller is programmed to terminate current extraction through the current control device in response to a ratio of fuel gas concentration to oxidizer gas concentration at the fuel electrode that is greater than a predetermined value that is based on at least one of current and voltage of the fuel cell stack.

21. The fuel cell system of claim 20, wherein the controller is programmed to terminate current extraction through the current control device in response to the ratio of the fuel gas concentration to oxidizer gas concentration at the fuel electrode being greater than a predetermined value based on at least one of the current and the voltage of the fuel cell stack while the oxidizer gas concentration at the oxidizer electrode begins to decrease.

22. The fuel cell system of claim 1, wherein the controller is programmed to terminate current extraction through the current control device in response to a decrease of at least one of current and voltage of the fuel cell stack.

23. The fuel cell system of claim 22, wherein the controller is programmed to record a maximum value of at least one of current and voltage of the fuel cell stack, and the controller is programmed to terminate current extraction through the current control device in response to a decrease in at least one of the current and the voltage by at least one of a predetermined value and a predetermined ratio with respect to the maximum value.

24. The fuel cell system of claim 1, wherein the fuel cell stack comprises a fuel cell stack case protecting the fuel cell stack, and the controller is programmed to terminate current extraction through the current control device in response to a fuel gas concentration in the fuel cell stack case that is greater than a predetermined concentration.

25. The fuel cell system of claim 24, wherein the fuel cell stack comprises a fuel gas concentration sensor disposed in the fuel cell stack case, and the controller is programmed to compare an output of the fuel gas concentration sensor to an estimated fuel gas concentration in the fuel cell stack case, the estimated fuel gas concentration being calculated by the controller based on fuel gas pressure at the fuel electrode and a period of current extraction through the current control device.

26. The fuel cell system of claim 24, wherein an outlet of the fuel cell stack case comprises a fuel gas concentration sensor, and the controller is programmed to supply the oxidizer gas to the fuel cell stack case and the current extraction through the current control device is performed during at least a predetermined period, and wherein the controller is programmed to correct the fuel gas concentration value measured by the fuel gas concentration sensor to a higher value if a value measured by the fuel gas concentration sensor is greater than a predetermined concentration, and wherein the controller is programmed to correct the fuel gas concentration value measured by the fuel gas concentration sensor to a lower value if a value measured by the fuel gas concentration sensor is the predetermined concentration or below.

27. The fuel cell system of claim 1, wherein the controller is programmed to terminate current extraction through the current control device in response to fuel gas concentration at the oxidizer electrode that is greater than a predetermined concentration.

28. The fuel cell system of claim 27, wherein the fuel cell stack comprises a fuel cell stack case protecting the fuel cell stack, and wherein the fuel cell stack comprises a first fuel gas concentration sensor disposed at the oxidizer electrode, and the controller is programmed to compare an output of the fuel gas concentration sensor to an estimated fuel gas concentration in the fuel cell stack case, the estimated fuel gas concentration being calculated by the controller based on fuel gas pressure at the fuel electrode and a period of current extraction through the current control device.

29. The fuel cell system of claim 28, wherein the controller is programmed to correct the fuel gas concentration value measured by the first fuel gas concentration sensor at the oxidizer electrode in response to humidity of the electrolyte membrane.

30. The fuel cell system of claim 29, wherein an idle time measuring unit measures an interval from a previous operation stoppage of the fuel cell stack to an initiation of the fuel cell stack, and the controller is programmed to estimate the humidity of the electrolyte membrane based on the interval measured by the idle time measuring unit.

31. The fuel cell system of claim 28, wherein an outlet of the fuel cell stack case comprises a second fuel gas concentration sensor, and the controller is programmed to supply oxidizer gas to the fuel cell stack case and the current extraction through the current control device is performed during at least a predetermined period, and wherein the controller is programmed to correct the fuel gas concentration value measured by the second fuel gas concentration sensor to a higher value if a value measured by the second fuel gas concentration sensor is greater than a predetermined concentration, and wherein the controller is programmed to correct the fuel gas concentration value measured by the second fuel gas concentration sensor to a lower value if a value measured by the second fuel gas concentration sensor is the predetermined concentration or below.

32. The fuel cell system of claim 1, wherein the an oxidizer flow amount detector outputs to the controller a signal corresponding to an amount of oxidizer gas flowing to the oxidizer electrode, and the controller is programmed to terminate current extraction through the current control device in response to an absence of oxidizer gas flowing to the oxidizer electrode.

33. The fuel cell system of claim 1, wherein a fuel gas circulation system recirculates the fuel gas remaining in the fuel cell stack.