METHOD FOR OPERATING A FUEL CELL SYSTEM, CONTROL DEVICE, AND FUEL CELL SYSTEM

Abstract

The invention relates to a method for operating a fuel cell system (100), having a fuel cell stack (20) with a plurality of fuel cells (110) each having at least one cathode portion (K) and at least one anode portion (A), a compressor (10) for conveying air into the cathode portions (K), a pressure-sustaining valve (40), and a control device (50), the at least one cathode portion (K) being arranged downstream of and in fluid communication with the compressor (10) and upstream of and in fluid communication with the pressure-sustaining valve (40), the fuel cell system (100) having a high-pressure region (HDB) between the compressor (10) and the pressure-sustaining valve (40). The invention further relates to a control device (50) and to a fuel cell system (100).

Claims

1. A method for operating a fuel cell system (100), having a fuel cell stack (20) with a multiplicity of fuel cells (110) each having at least one cathode portion (K) and at least one anode portion (A), a compressor (10) for conveying air into the cathode portions (K), a pressure-maintaining valve (40), and a control device (50), wherein the at least one cathode portion (K) is arranged downstream of and in fluid communication with the compressor (10) and upstream of and in fluid communication with the pressure-maintaining valve (40), wherein the fuel cell system (100) has a high-pressure region (HDB) between the compressor (10) and the pressure-maintaining valve (40), wherein the method comprises the following steps: a) receipt of a demand for an increased air mass flow (ms) to the at least one cathode portion (K) by the control device (50), b) reduction of the pressure in the high-pressure region (HDB) by at least partial opening of the pressure-maintaining valve (40) by the control device (50), c) raising of the air mass flow (ms) to the at least one cathode portion (K) by means of an increase in the speed of the compressor (10) by the control device (50), d) increase in the pressure in the high-pressure region (HDB) by at least partial closure of the pressure-maintaining valve (40) at a constant or approximately constant air mass flow (ms) by the control device (50).

2. The method as claimed in claim 1, characterized in that the fuel cell system (100) further comprises an external moistening device (60), for moistening a membrane (22), wherein the external moistening device (60) is arranged upstream and/or downstream of the at least one cathode portion (K), in fluid communication with the cathode portion (K).

3. The method as claimed in claim 2, characterized in that the pressure in the high-pressure region (HDB) is increased by at least partial closure of the pressure-maintaining valve (40) as a function of a moisture content of the membrane (22).

4. The method as claimed in claim 1, characterized in that the pressure in the high-pressure region (HDB) is reduced by at least partial opening of the pressure-maintaining valve (40) as far as, or almost as far as, a choke limit (SG) of a characteristic map of the compressor (10).

5. The method as claimed in claim 1, characterized in that the fuel cell system (100) further comprises a turbine (30), wherein the turbine (30) is arranged downstream of the cathode portion and in fluid communication with the cathode portion (K), and wherein the pressure-maintaining valve (40) is arranged downstream or upstream of the turbine (30).

6. The method as claimed in claim 1, characterized in that the fuel cell system (100) further comprises a charge air cooler (70), wherein the charge air cooler (70) is arranged downstream of the compressor (10) and/or upstream of the cathode portion (K), in fluid communication with the cathode portion (K).

7. The method as claimed in claim 1, characterized in that the fuel cell system (100) has at least one first bypass (80) having at least one first bypass valve (82), wherein the at least one first bypass (80) has direct fluid-communicating flow guidance from the compressor (10) to the cathode portion (K), parallel to the external moistening device (60) and/or the charge air cooler.

8. The method as claimed in claim 1, characterized in that the fuel cell system (100) has at least one second bypass (84) having at least one second bypass valve (86), wherein the at least one second bypass (84) has direct fluid-communicating flow guidance from the cathode portion (K) to the pressure-maintaining valve (40) and/or the turbine (30), parallel to the external moistening device (60).

9. The method as claimed in claim 1, characterized in that the fuel cell system (100) further comprises an air filter (90), wherein the air filter (90) is arranged upstream of the compressor (10), in fluid communication with the compressor (10).

10. A control device (50), comprising a computing unit (52) and a memory unit (54), characterized in that a program is stored in the memory unit (54) which, when at least partially executed in the computing unit (52), carries out a method as claimed in claim 1.

11. A fuel cell system (100), having a compressor (10) for conveying air, a fuel cell stack (20) with a multiplicity of fuel cells (110) each having at least one cathode portion (K) and at least one anode portion (A), a turbine (30), a pressure-maintaining valve (40), and a control device (50), wherein the at least one cathode portion (K) is arranged downstream of and in fluid communication with the compressor (10) and upstream of and in fluid communication with the pressure-maintaining valve (40), wherein the fuel cell system (100) has a high-pressure region (HDB) upstream of the pressure-maintaining valve (40) and downstream of the turbine (30), characterized in that the fuel cell system (100) is designed to carry out the method according to claim 1.

12. The fuel cell system (100) as claimed in claim 9, further having a charge air cooler (70), a first bypass (80) having a first bypass valve (82), a second bypass (84) having a second bypass valve (86) and/or an air filter (90), wherein the at least one first bypass (80) has direct fluid-communicating flow guidance from the compressor (10) to the cathode portion (K), parallel to the external moistening device (60) and/or the charge air cooler, and/or wherein the at least one second bypass (84) has direct fluid-communicating flow guidance from the cathode portion (K) to the pressure-maintaining valve (40) and/or the turbine (30), parallel to the external moistening device (60).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The following figures are each schematic and

[0019] FIG. 1 shows a flow path of the fuel cell system having an air filter, a turbine, a motor and a compressor, a charge air cooler, a moistening device, a cathode portion, a pressure-maintaining valve and a first and a second bypass, each having a first and a second bypass valve, respectively,

[0020] FIG. 2 shows a characteristic map of a compressor, in which the pressure ratio across the compressor is plotted against the air mass flow of the compressor, with an initial state and a target state of the method according to the invention, wherein the characteristic map is bounded by a choke limit and a surge limit and has curves of the same rotational speed,

[0021] FIG. 3 shows a fuel cell system with a fuel cell of a fuel cell stack and a control device.

[0022] In the following figures, identical reference signs are used for the same technical features, even of different exemplary embodiments.

DETAILED DESCRIPTION

[0023] FIG. 1 shows a schematic, planar flow path of the fuel cell system 100. FIG. 1 shows the flow path of the air mass flow ms within the fuel cell system 100. By way of example, the fuel cell system 100 has an air filter 90 upstream of the compressor 10. The compressor 10 is operatively coupled, e.g. by means of a shaft, to a motor and a turbine 30. The fuel cell system 100 further has a charge air cooler 70 downstream of the compressor 10 for cooling the air mass flow ms. The fuel cell system 100 further has a moistening device 60, in particular an external moistening device 60, upstream of the at least one cathode portion K. A first bypass 80 having a first bypass valve 82 provides a parallel flow path to the charge air cooler 70 and the moistening device 60 to permit a direct flow path from the compressor 10 to the cathode portion K. In order to recover fluid, in particular water, the moistening device 60 can be flowed through again downstream of the cathode portion K. A second bypass 84 permits a parallel flow path downstream of the cathode portion K. A high-pressure region HDB according to the invention extends downstream from the compressor 10 as far as a pressure-maintaining valve 40 or a turbine 30 of the fuel cell system 100. With the method according to the invention and the control device 50 according to the invention, a fuel cell system 100 according to the invention which is designed in this way particularly advantageously allows a rapid and efficient response of a fuel cell system 100 to a demand for an increase in load, that is to say a demand for increased energy output by the fuel cell system 100.

[0024] FIG. 2 shows a characteristic map of a compressor 10, in which the pressure ratio across the compressor 10 is plotted against the air mass flow ms of the compressor 10. An initial state P1 and a target state P4 are shown in the characteristic map. The target state P4 represents the demand for increased power output by the fuel cell system 100. For the increased power output of the fuel cell system 100, an increased mass flow ms is required at the inlet of the cathode portion K (not shown). For a particularly efficient increase in the power of the fuel cell system 100, the air mass flow ms is increased from the initial state P1 along a line N with a constant rotational speed of the compressor 10 to a first intermediate state P2. The air mass flow ms is increased by at least partial opening of the pressure-maintaining valve 40 (not shown) at the end of the high-pressure region HDB (not shown). From the first intermediate state P2 to the second intermediate state P3, the air mass flow ms is further increased by increasing the rotational speed of the compressor 10. From the second intermediate state P3 to the target state P4, with a constant air mass flow ms, the pressure ratio across the compressor 10 is increased by further acceleration of the rotational speed of the compressor 10. Such an operating characteristic of the compressor 10 allows a particularly efficient and rapid response of a fuel cell system 100 to a demand for an increase in load, that is to say a demand for increased energy output by the fuel cell system 100.

[0025] A fuel cell system 100 with a fuel cell 110 of a fuel cell stack 20 and a control device 50 is shown in FIG. 3. The control device 50 comprises a computing unit 52 and a memory unit 54, wherein a program is stored in the memory unit 54 which, when at least partially executed in the computing unit 52, carries out a method as per the first aspect.