FUEL CELL SYSTEM AND METHOD FOR PURGING A FUEL CELL SYSTEM

Abstract

The present invention relates to a method for adjusting an operating mode of a fuel cell system (1) comprising: at least one fuel cell stack (2) having an anode portion (3) and a cathode portion (4); an anode supply line (5) for conveying fuel from a fuel source (6) to the anode portion (3); a fuel supply device (7) for supplying the fuel in the anode supply line (5) to the anode portion (3); an anode discharge line (8) for discharging anode exhaust gas from the anode portion (3) into the environment; and a purge unit (9) for purging the anode portion (3); said method comprising the steps of: determining a purge start time and/or a purge duration in which the anode portion (3) is intended to be purged by the purge unit (9); and shifting the fuel supply device (7) from a normal operation into a fuel-supply operation specific to the purge operation on the basis of the determined purge start time and/or purge duration, wherein the shifting into the fuel-supply operation specific to the purge operation is carried out temporally before and/or during the determined purge duration. The invention also relates to a fuel cell system (1), a computer program product (16) and a memory means having a computer program product (16) stored thereon for carrying out the method according to the invention.

Claims

1. Method for adjusting an operating mode of a fuel cell system (1), which comprises at least one fuel cell stack (2) having an anode portion (3) and a cathode portion (4), an anode supply line (5) for conveying fuel from a fuel source (6) to the anode portion (3), a fuel supply device (7) for supplying the fuel in the anode supply line (5) to the anode portion (3), an anode discharge line (8) for discharging anode exhaust gas from the anode portion (3) into the environment, and a purge unit (9) for purging the anode portion (3), said method comprising the steps of: determining a purge start time and/or a purge duration in which the anode portion (3) is intended to be purged by the purge unit (9), and shifting the fuel supply device (7) from a normal operation into a fuel-supply operation specific to the purge operation on basis of the determined purge start time and/or purge duration, wherein the shifting into the fuel-supply operation specific to the purge operation is carried out temporally before and/or during the determined purge duration.

2. Method according to claim 1, characterised in that the fuel supply device (7) comprises at least one injector and a duty cycle and/or injection frequency of the injector is adjusted by shifting the fuel supply device (7) from normal operation into the fuel-supply operation specific to the purge operation.

3. Method according to claim 1, characterised in that the fuel cell system (1) comprises a recirculation line (10) for conveying anode exhaust gas from the anode portion (3) to the fuel supply device (7) as well as a recirculation pump (11) for pumping the anode exhaust gas through the recirculation line (10) to the fuel supply device (7), wherein the recirculation pump (11) is shifted from a normal operation into a pump operation specific to the purge operation on the basis of the determined purge start time and/or purge duration, and wherein the shifting into the pump operation specific to the purge operation is carried out temporally before and/or during the determined purge duration.

4. Method according to claim 1, characterised in that a pressure difference between the anode portion (3) and the cathode portion (4) is determined and the fuel-supply operation of the fuel supply device (7) specific to the purge operation and/or the pump operation of the recirculation pump (11) specific to the purge operation are regulated on the basis of the determined pressure difference.

5. Fuel cell system (1), comprising a fuel cell stack (2) having an anode portion (3) and a cathode portion (4), an anode supply line (5) for conveying fuel from a fuel source (6) to the anode portion (3), a fuel supply device (7) for supplying the fuel in the anode supply line (5) to the anode portion (3), an anode discharge line (8) for discharging anode exhaust gas from the anode portion (3) into the environment, and a purge unit (9) for purging the anode portion (3), characterised by a purge time determination unit (14) for determining a purge start time and/or a purge duration in which the anode portion (3) is intended to be purged by the purge unit (9), and a shifting unit (15) for shifting the fuel supply device (7) from a normal operation into a fuel-supply operation specific to the purge operation temporally before and/or during the determined purge duration on the basis of the determined purge start time and/or purge duration.

6. Fuel cell system (1) according to claim 5, characterised in that the fuel supply device (7) comprises at least one injector as well as the shifting unit (15) having at least one setting means (15a, 15b) for shifting the fuel supply device (7) from normal operation into the fuel-supply operation specific to the purge operation by adjusting a duty cycle and/or an injection frequency of the injector.

7. Fuel cell system (1) according to claim 5, characterised by a recirculation line (10) for conveying anode exhaust gas from the anode portion (3) to the fuel supply device (7) and a recirculation pump (11) for pumping the anode exhaust gas through the recirculation line (10) to the fuel supply device (7), wherein the shifting unit (15) comprises a pump module (15c) for shifting the recirculation pump (11), on the basis of the determined purge time, from a normal operation into a pump operation specific to the purge operation temporally before and/or after the determined purge start time.

8. Fuel cell system (1) according to claim 5, characterised in that the fuel cell system (1) comprises a pressure determination unit (13) for determining a pressure difference between the anode portion (3) and the cathode portion (4), wherein the shifting unit (15) comprises a regulation unit (15d) for regulating the fuel-supply operation of the fuel supply device (7) specific to the purge operation and/or the pump operation of the recirculation pump (11) specific to the purge operation on the basis of the determined pressure difference.

9. Computer program product (16), comprising commands that prompt a computer to carry out the method according to claim 1 when said computer program product (16) is executed by said computer.

10. Memory means having stored thereon a computer program product (16) according to claim 9.

11. Method according to claim 2, characterised in that the fuel cell system (1) comprises a recirculation line (10) for conveying anode exhaust gas from the anode portion (3) to the fuel supply device (7) as well as a recirculation pump (11) for pumping the anode exhaust gas through the recirculation line (10) to the fuel supply device (7), wherein the recirculation pump (11) is shifted from a normal operation into a pump operation specific to the purge operation on the basis of the determined purge start time and/or purge duration, and wherein the shifting into the pump operation specific to the purge operation is carried out temporally before and/or during the determined purge duration.

12. Method according to claim 2, characterised in that a pressure difference between the anode portion (3) and the cathode portion (4) is determined and the fuel-supply operation of the fuel supply device (7) specific to the purge operation and/or the pump operation of the recirculation pump (11) specific to the purge operation are regulated on the basis of the determined pressure difference.

13. Method according to claim 3, characterised in that a pressure difference between the anode portion (3) and the cathode portion (4) is determined and the fuel-supply operation of the fuel supply device (7) specific to the purge operation and/or the pump operation of the recirculation pump (11) specific to the purge operation are regulated on the basis of the determined pressure difference.

14. Fuel cell system (1) according to claim 6, characterised by a recirculation line (10) for conveying anode exhaust gas from the anode portion (3) to the fuel supply device (7) and a recirculation pump (11) for pumping the anode exhaust gas through the recirculation line (10) to the fuel supply device (7), wherein the shifting unit (15) comprises a pump module (15c) for shifting the recirculation pump (11), on the basis of the determined purge time, from a normal operation into a pump operation specific to the purge operation temporally before and/or after the determined purge start time.

15. Fuel cell system (1) according to claim 6, characterised in that the fuel cell system (1) comprises a pressure determination unit (13) for determining a pressure difference between the anode portion (3) and the cathode portion (4), wherein the shifting unit (15) comprises a regulation unit (15d) for regulating the fuel-supply operation of the fuel supply device (7) specific to the purge operation and/or the pump operation of the recirculation pump (11) specific to the purge operation on the basis of the determined pressure difference.

16. Fuel cell system (1) according to claim 7, characterised in that the fuel cell system (1) comprises a pressure determination unit (13) for determining a pressure difference between the anode portion (3) and the cathode portion (4), wherein the shifting unit (15) comprises a regulation unit (15d) for regulating the fuel-supply operation of the fuel supply device (7) specific to the purge operation and/or the pump operation of the recirculation pump (11) specific to the purge operation on the basis of the determined pressure difference.

17. Computer program product (16), comprising commands that prompt a computer to carry out the method according to claim 2 when said computer program product (16) is executed by said computer.

18. Computer program product (16), comprising commands that prompt a computer to carry out the method according to claim 3 when said computer program product (16) is executed by said computer.

19. Computer program product (16), comprising commands that prompt a computer to carry out the method according to claim 4 when said computer program product (16) is executed by said computer.

Description

[0028] Other measures that improve the invention can be deduced from the following description of various exemplary embodiments of the invention, which are represented schematically in the figures, in which:

[0029] FIG. 1 is a block diagram for describing a fuel cell system according to a preferred embodiment of the present invention.

[0030] FIG. 2 is a flow diagram for explaining a method according to a first embodiment of the present invention, and

[0031] FIG. 3 is a flow diagram for explaining a method according to a second embodiment of the present invention.

[0032] FIG. 1 is a schematic block diagram for describing a fuel cell system 1 according to a preferred embodiment. The fuel cell system 1 comprises a fuel cell stack 2 having an anode portion 3 and a cathode portion 4. Moreover, the fuel cell system 1 comprises an anode supply line 5 for conveying fuel from a fuel source 6 to the anode portion 3, a fuel supply device 7 for supplying the fuel through the anode supply line 5 to the anode portion 3, an anode discharge line 8 for discharging anode exhaust gas from the anode portion 3 into the environment surrounding the fuel cell system 1, and a purge unit 9 for purging the anode portion 3. Furthermore, the fuel cell system 1 comprises a cathode supply line 18 for conveying cathode gas, in particular in the form of air, to the cathode portion 4 as well as a cathode discharge line 19 for conveying cathode exhaust gas or cathode exhaust air away from the cathode portion 4 into the environment surrounding the fuel cell system 1. A pressure reduction unit 12 in the form of a shut-off valve is arranged upstream of the fuel supply device 7 and downstream of the fuel source 6 for reducing the pressure in the anode supply line 5 and, accordingly, in the anode portion 3.

[0033] The fuel cell system further 1 comprises a controller 17 having a purge time determination unit 14 for determining a purge start time and/or a purge duration in which the anode portion 3 is intended to be or is purged by the purge unit 9, and a shifting unit 15 for shifting the fuel supply device 7 from a normal operation into a fuel-supply operation specific to the purge operation temporally before and/or during the determined purge duration on the basis of the determined purge start time.

[0034] The fuel supply device 7 is designed in the form of at least one injector-ejector. In principle, multiple injectors and/or ejectors and/or combinations thereof may also be provided. The shifting unit 15 comprises two setting means in the form of a duty cycle module 15a and a frequency module 15b for shifting the fuel supply device 7 from normal operation into the fuel-supply operation specific to the purge operation by adjusting a duty cycle and/or an injection frequency of the injector. That is to say, in order to increase the mass flow rate of the fuel to the anode portion 3 and thus to counteract the pressure drop during purging, the duty cycle can be increased by means of the duty cycle module 15a and the injection frequency can be increased by means of the frequency module 15b.

[0035] Furthermore, in the fuel cell system 1, a recirculation line 10 is designed to convey anode exhaust gas from the anode portion 3 to the fuel supply device 7 and a recirculation pump 11 is designed to pump the anode exhaust gas through the recirculation line 10 to the fuel supply device 7, wherein the shifting unit 15 comprises a pump module 15c for shifting the recirculation pump 11, on the basis of the determined purge start time and/or purge duration, from a normal operation into a pump operation specific to the purge operation temporally before the determined purge start time.

[0036] According to the invention, it may also be advantageous for either at least one injector-ejector or a recirculation pump 11 to be provided. It is not necessary for these to be combined as in FIG. 1. If the recirculation line 10 is designed without an injector-ejector, a pressure regulator and/or the recirculation pump 11 is provided instead of the injector-ejector.

[0037] Furthermore, the controller 17 comprises a pressure determination unit 13 for determining a pressure difference between the anode portion 3 and the cathode portion 4, wherein the shifting unit 15 comprises a regulation unit 15d for regulating the fuel-supply operation of the fuel supply device 7 specific to the purge operation on the basis of the determined pressure difference.

[0038] A computer program product 16 is also installed on the controller 17 and comprises commands that prompt a computer, in the present case in the form of the controller 17, to carry out a method described below with reference to FIG. 2 when said computer program product 16 is executed by said computer/controller.

[0039] According to the flow diagram shown in FIG. 2, an imminent purge duration in which the anode portion is intended to be purged by the purge unit 9 is initially determined in a first step S1. In a subsequent step S2, the fuel supply device 7 is shifted or adjusted from a normal operation into a fuel-supply operation specific to the purge operation on the basis of the determined purge duration, wherein the shifting into the fuel-supply operation specific to the purge operation is carried out temporally before and/or during the determined purge duration. With reference to the fuel cell system 1 shown in the FIG. 1 and the fuel supply device 7 integrated in said system in the form of an injector-ejector, a duty cycle and an injection frequency of the injector-ejector is adjusted when the fuel supply device 7 is shifted from normal operation into the fuel-supply operation specific to the purge operation.

[0040] FIG. 3 is a flow diagram for explaining a method for adjusting the fuel cell system 1 according to a second embodiment. The steps S10 and S20 correspond to the steps S1 and S2 of the method explained with reference to FIG. 2. In addition to step S20, another step S30 is performed, in which the recirculation pump 11 is shifted from a normal operation into a pump operation specific to the purge operation on the basis of the determined purge duration, wherein the shifting into the pump operation specific to the purge operation is also carried out temporally before and/or during the determined purge duration. Subsequently, in a step S40, a pressure difference between the anode portion 3 and the cathode portion 4 is continuously determined. In a subsequent step S50, the fuel-supply operation of the fuel supply device 7 specific to the purge operation and/or the pump operation of the recirculation pump 11 specific to the purge operation are regulated on the basis of the determined pressure difference.

[0041] The invention allows other design principles in addition to the embodiments set out above. In other words, the invention should not be considered limited to the exemplary embodiments explained with reference to the figures.

LIST OF REFERENCE SIGNS

[0042] 1 Fuel cell system [0043] 2 Fuel cell stack [0044] 3 Anode portion [0045] 4 Cathode portion [0046] 5 Anode supply line [0047] 6 Fuel source [0048] 7 Fuel supply device [0049] 8 Anode discharge line [0050] 9 Purge unit [0051] 10 Recirculation line [0052] 11 Recirculation pump [0053] 12 Pressure reduction unit [0054] 13 Pressure determination unit [0055] 14 Purge time determination unit [0056] 15 Shifting unit [0057] 15a Duty cycle module (setting means) [0058] 15b Frequency module (setting means) [0059] 15c Pump module [0060] 15d Regulation unit [0061] 16 Computer program product [0062] 17 Controller [0063] 18 Cathode supply line [0064] 19 Cathode discharge line