Fuel cell system and method for operating such a system

1. A method for operating a fuel cell system including: a fuel cell having a cathode input and a cathode output; a cathode supply path situated upstream from the cathode input and connected thereto; a cathode exhaust gas path situated downstream from the cathode output and connected thereto; a conveyor situated in the cathode supply path for conveying a cathode gas flow into the cathode input or an adjustable exhaust gas throttle situated in the cathode exhaust gas path for influencing a flow resistance of the cathode exhaust gas path; and a regulator configured to regulate the cathode gas flow or a cathode pressure, the method comprising the following steps at least in a stationary or upward-transient operation of the fuel cell:

regulating the cathode gas flow by varying a position of the exhaust gas throttle; and

regulating a cathode pressure by varying a rotational speed of the conveyor;

wherein an increase in the cathode gas flow takes place during the upward-transient operation of the fuel cell, the method further comprising a step of at least temporarily reducing a flow resistance of the cathode exhaust gas path for increasing the cathode gas flow by varying the position of the exhaust gas throttle; and

wherein during the upward-transient operation of the fuel cell, an increase in the cathode pressure takes place, and the method further comprising a step of increasing the rotational speed of the conveyor for increasing the cathode pressure,

the temporarily reducing the flow resistance of the cathode exhaust gas path occurring before or at a same time as the increasing of the rotational speed.

2. The method as recited in claim 1 wherein the temporarily reducing the flow resistance of the cathode exhaust gas path takes place before the increasing the rotational speed of the conveyor for increasing the cathode pressure.

3. The method as recited in claim 1 wherein an increase in the cathode gas flow takes place during the upward-transient operation of the fuel cell, the step of at least temporarily reducing the flow resistance of the cathode exhaust gas path taking place at the beginning of a time period of the step of increasing the rotational speed of the conveyor.

4. The method as recited in claim 1 wherein further comprising the following steps during a downward-transient operation:

regulating the cathode gas flow by varying the rotational speed of the conveyor; or

regulating the cathode pressure by varying the position of the exhaust gas throttle.

5. The method as recited in claim 4 wherein during the downward-transient operation of the fuel cell:

a reduction of the cathode gas flow takes place, and the method further includes a step of reducing the rotational speed of the conveyor for reducing the cathode gas flow; or

a reduction of the cathode pressure takes place, and the method further includes a step of at least temporarily reducing the flow resistance of the cathode exhaust gas path by varying the position of the exhaust gas throttle.

6. The method as recited in claim 5 wherein the step of at least temporarily reducing the flow resistance of the cathode exhaust path occurs at the beginning of a time period of the step of reducing the rotational speed of the conveyor.

7. The method as recited in claim 1 wherein the fuel cell system:

has a waste path connecting the cathode supply path downstream from the conveyor to the cathode exhaust gas path downstream from the exhaust gas throttle and includes an adjustable waste throttle for influencing a flow resistance of the waste path, and the method further comprises a step of regulating the cathode gas flow by varying a position of the waste throttle; or

has a bypass path connecting the cathode supply path downstream from the conveyor to the cathode supply path upstream from the conveyor and includes an adjustable bypass throttle for influencing a flow resistance of the bypass path, and the method further comprises a step of regulating the cathode gas flow by varying a position of the bypass throttle.

8. The method as recited in claim 1 further comprising sensing a cathode supply path pressure downstream from the conveyor and upstream from or at the cathode input.

9. The method as recited in claim 8 further comprising regulating the cathode gas flow as a function of the sensing of the cathode supply path pressure.

10. A method for operating a fuel cell system including: a fuel cell having a cathode input and a cathode output; a cathode supply path situated upstream from the cathode input and connected thereto; a cathode exhaust gas path situated downstream from the cathode output and connected thereto; a conveyor situated in the cathode supply path for conveying a cathode gas flow into the cathode input or an adjustable exhaust gas throttle situated in the cathode exhaust gas path for influencing a flow resistance of the cathode exhaust gas path; and a regulator configured to regulate the cathode gas flow or a cathode pressure, the method comprising the following steps:

during an upward-transient operation of the fuel cell, temporarily reducing a flow resistance of the cathode exhaust gas path by varying the position of the exhaust gas throttle; and

during a downward-transient operation of the fuel cell, also temporarily reducing the flow resistance of the cathode exhaust gas path by varying the position of the exhaust gas throttle.

11. The method as recited in claim 10 wherein during the upward-transient operation of the fuel cell, an increase in the cathode pressure takes place, and the method further comprising a step of increasing the rotational speed of the conveyor for increasing the cathode pressure,

the temporarily reducing the flow resistance of the cathode exhaust gas path during the upward-transient operation occurring before or at a same time as the increasing of the rotational speed.

12. The method as recited in claim 11 wherein during the downward-transient operation of the fuel cell, the method further includes a step of reducing the rotational speed of the conveyor for reducing the cathode gas flow.

13. A method for operating a fuel cell system including: a fuel cell having a cathode input and a cathode output; a cathode supply path situated upstream from the cathode input and connected thereto; a cathode exhaust gas path situated downstream from the cathode output and connected thereto; a conveyor situated in the cathode supply path for conveying a cathode gas flow into the cathode input or an adjustable exhaust gas throttle situated in the cathode exhaust gas path for influencing a flow resistance of the cathode exhaust gas path; and a regulator configured to regulate the cathode gas flow or a cathode pressure, the method comprising the following steps at least in a stationary or upward-transient operation of the fuel cell:

regulating the cathode gas flow by varying a position of the exhaust gas throttle; or

regulating a cathode pressure by varying a rotational speed of the conveyor; and

further comprising sensing a cathode supply path pressure downstream from the conveyor and upstream from or at the cathode input, and regulating the cathode gas flow or the cathode pressure as a function of the sensing of the cathode supply path pressure.

14. The method as recited in claim 13 further comprising metering an air mass upstream of the conveyor.

15. The method as recited in claim 13 wherein both the cathode gas flow and the cathode pressure are regulated.

16. The method as recited in claim 13 wherein both the cathode gas flow and the cathode pressure are regulated during the upward-transient operation of the fuel cell.

17. The method as recited in claim 13 wherein during the upward-transient operation of the fuel cell, an increase in the cathode pressure takes place, and the method further comprising a step of increasing the rotational speed of the conveyor for increasing the cathode pressure,

a temporarily reducing the flow resistance of the cathode exhaust gas path occurring before or at a same time as the increasing of the rotational speed.