Method for changing a fuel cell system over to a standby mode as well as such a fuel cell system

Patent metadata

Field	Value
Publication number	US-2016204456-A1
Application number	US-201614995018-A
Country	US
Kind code	A1
Filing date	Jan 13, 2016
Priority date	Jan 14, 2015
Publication date	Jul 14, 2016
Grant date	—

Abstract

A method for changing a fuel cell system from a normal mode of operation over to a standby mode comprises the following steps:
a) reducing the load withdrawal—via the electric circuit of the fuel cell stack—down to a load within the range from −1% to +5% around a load with an optimal system efficiency, b) regulating down the anode pressure down via the anode supply system, c) in the meantime, maintaining and controlling the cathode gas feed via the cathode supply system so that the pressure differential between the anode spaces and the cathode spaces does not exceed a prescribed maximum pressure differential, d) switching off the cathode gas feed if the pressure differential between the anode spaces and of the fuel cell stack and the environment has reached the prescribed maximum pressure differential, and e) switching off the load withdrawal via the external electric circuit at the latest when a prescribed minimum limit voltage of the fuel cell stack has been reached.

First claim

What is claimed is:

1 . A method for changing a fuel cell system from a normal mode of operation over to a standby mode, the fuel cell system having a fuel cell stack comprising cathode spaces and anode spaces, an anode supply system, a cathode gas supply system as well as an external electric circuit, the method comprising the following steps:
a) reducing a load withdrawal—via the electric circuit of the fuel cell stack—down to a load within the range from −1% to +5% around a load with an optimal system efficiency at which the fuel cell system exhibits a maximum efficiency, b) regulating down or controlling down the anode pressure down via the anode supply system so that an anode operating pressure is gradually reduced, c) in the meantime, maintaining and controlling the cathode gas feed via the cathode supply system in such a way that a pressure differential that sets in between the anode spaces and the cathode spaces does not exceed a prescribed maximum pressure differential, d) switching off the cathode gas feed if a further pressure differential between the anode spaces and of the fuel cell stack and an environment has reached the prescribed maximum pressure differential, and e) switching off the load withdrawal via the external electric circuit at the latest when a prescribed minimum limit voltage of the fuel cell stack has been reached.

2 . The method as recited in claim 1 wherein an electric energy of the fuel cell stack generated to switch off the power withdrawal from the stack in step (e) is fed to an electric consumer or to a battery connected to the fuel cell stack via the electric circuit.

3 . The method as recited in claim 1 wherein an electric consumer is an auxiliary aggregate of the fuel cell system or an external consumer.

4 . The method as recited in claim 1 wherein the switching off the cathode gas feed includes switching off a conveying device for the cathode operating gas.

5 . The method as recited in claim 1 wherein the conveying device is a compressor.

6 . The method as recited in claim 1 wherein a recirculation of the anode operating gas is maintained while the anode pressure is being controlled down or regulated down in step (b) and while the cathode gas feed is being maintained in step (c).

7 . The method as recited in claim 1 wherein the load set in step (a) is within the range from −0.7% to +3% around a load with an optimal system efficiency (L opt ).

8 . The method as recited in claim 7 wherein the load set in step (a) is within the range from −0.5% to +1%.

9 . The method as recited in claim 1 wherein the prescribed maximum pressure differential is within the range from 0.1 bar to 0.3 bar.

10 . The method as recited in claim 1 wherein the prescribed maximum pressure differential is within the range from 0.15 bar to 0.25 bar.

11 . A fuel cell system with a fuel cell stack comprising:
cathode spaces and anode spaces; an anode supply system; a cathode gas supply system; and an external electric circuit, the fuel cell system performing the method as recited in claim 1 .

Assignees

• Volkswagen Ag

Inventors

• Mueller Johannes
• Arendt Martin

Classifications

• H01M2250/20

  Fuel cells in motive systems, e.g. vehicle, ship, plane · CPC title

• H01M8/04228 Primary

  during shut-down · CPC title

• H01M8/04753

  of fuel cell reactants · CPC title

• H01M8/04104 Primary

  Regulation of differential pressures · CPC title

• Y02E60/50

  Fuel cells · CPC title