METHOD FOR OPERATING A FUEL CELL SYSTEM, AND CONTROL DEVICE

Abstract

The invention relates to a method for operating a fuel cell system, wherein hydrogen from a tank and recirculated hydrogen are fed as anode gas to at least one fuel cell via an anode circuit (1), and water (6) contained in the anode gas is separated by means of a water separator (2) integrated into the anode circuit (1), is collected in a container (3), and is removed from the system by intermittently opening a drain valve (4). According to the invention, the following steps are carried out to detect whether the container (3) is full: opening a purge valve (5) on the container (3), acquiring the point in time of a sudden change in the opening cross-section of a hydrogen metering valve integrated into the anode circuit (1) to maintain a set pressure in the anode circuit (1), and comparing said point in time with the point in time the purge valve (5) opened.

The invention further relates to a control device for carrying out the method or individual method steps.

Claims

1. A method for operating a fuel cell system, wherein hydrogen from a tank and recirculated hydrogen are fed as anode gas to at least one fuel cell via an anode circuit (1), and water (6) contained in the anode gas is separated by means of a water separator (2) integrated into the anode circuit (1), is collected in a container (3), and is removed from the system by intermittently opening a drain valve (4), wherein the following steps are carried out to detect whether the container (3) is full: opening a purge valve (5) on the container (3), acquiring a point in time (t.sub.2) of a sudden change in the opening cross-section of a hydrogen metering valve integrated into the anode circuit (1) to maintain a set pressure in the anode circuit (1), and comparing said point in time (t.sub.2) with a point in time (t.sub.1) the purge valve (5) opened.

2. The method according to claim 1, wherein, in order to detect the point in time (t.sub.2) of a sudden change in the opening cross-section of the hydrogen metering valve, the actuator current for actuating the hydrogen metering valve is evaluated.

3. The method according to claim 1, wherein, in order to evaluate the actuator current, a control unit of the fuel cell system is used with the aid of which the hydrogen metering valve is actuated.

4. The method according to claim 2, wherein, depending on the evaluation of the actuator current, the drain valve is actuated, preferably with the aid of the control unit.

5. The method according to claim 2, wherein signals that are used as the basis for the evaluation of the actuator current are previously subjected to a filtering and/or averaged over time.

6. The method according to claim 2, wherein a debouncing time of the purge valve (5) is considered in the evaluation of the actuator current.

7. The method according to claim 2, wherein a load change occurring with the purge valve (5) open is considered in the evaluation of the actuator current.

8. A control unit for a fuel cell system, wherein hydrogen from a tank and recirculated hydrogen are fed as anode gas to at least one fuel cell via an anode circuit (1), and water (6) contained in the anode gas is separated by means of a water separator (2) integrated into the anode circuit (1), is collected in a container (3), and is removed from the system by intermittently opening a drain valve (4) wherein the control unit is configured to: control opening a purge valve (5) on the container (3), acquire a point in time (t.sub.2) of a sudden change in the opening cross-section of a hydrogen metering valve integrated into the anode circuit (1) to maintain a set pressure in the anode circuit (1), and compare said point in time (t.sub.2) with a point in time (t.sub.1) the purge valve (5) opened.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The invention and its advantages will be explained in further detail in the following with reference to the accompanying drawings. Shown are:

[0021] FIG. 1 a schematic illustration of a water separator integrated into an anode circuit of a fuel cell system; and

[0022] FIG. 2 a graph illustrating the actuator flow path as a function of the fill level in the tank of the water separator.

DETAILED DESCRIPTION

[0023] FIG. 1 shows, by way of example, a water separator 2 integrated in an anode circuit 1. The water separator 2 comprises a container 3 for collecting water 6, which is separated from the anode gas of the anode circuit 1 by means of the water separator 2. To empty the container 3, a drain valve 4 is provided on the floor-side. This is opened depending on the fill level of the container 3. Furthermore, a purge valve 5 is provided on the side of the container 3. Via this purge valve, anode gas enriched with nitrogen can be removed from the anode circuit 1. However, this presupposes that the fill level in the container 3 is not so high that the purge valve 5 lies below the water level. Otherwise, with the opening of the purge valve 5, water 6 and not gas 7 will escape. The water 6 exits until the fill level H.sub.max is reached. This is dictated by the vertical position of the purge valve 5 on the container 3.

[0024] Gas 7 exiting the container 3 upon opening of the purge valve 5 is replaced with fresh hydrogen. This is metered into the anode circuit using a hydrogen metering valve (not shown). The hydrogen metering valve or an actuator (not shown) of the hydrogen metering valve is actuated accordingly via a control unit (not shown). Accordingly, the opening the purge valve 5 is accompanied by an increase in the actuator current. This relationship is illustrated by way of example in FIG. 2, wherein the middle diagram b) indicates the opening and closing of the purge valve 5 over time t, and the bottom diagram c) shows the associated actuator flow path. Note that the last time the purge valve 5 is opened, the increase in the actuator current is significantly delayed (see arrow 8). This is due to the fact that the container 3 has filled with water over time, so that the fill level at the point in time t.sub.1 of opening of the purge valve 5 was above H.sub.max. That is to say, with the opening of the purge valve 5 at time t.sub.1, only water 6 has initially escaped from the container 3. Only when the fill level has fallen so far that gas is discharged does the actuator current also increase. This is the case at the point in time t.sub.2. The temporal offset between t.sub.1 and t.sub.2 thus indicates that the container 3 is full and should be emptied by opening the drain valve 4.