Method for operating a fuel cell system, fuel cell system, and control device

Abstract

The invention relates to a method for operating a fuel cell system (100) having at least one fuel cell stack (11) and an anode system (200), wherein a drain valve (24) is arranged in the anode system (200), wherein the following steps are carried out: i. switching the drain valve (24), wherein the switching describes a transition of the drain valve (24) from an open switch position into a closed switch position and vice versa ii. determining a switching feature from a current characteristic curve of the drain valve (24) iii. determining whether fuel flows through the drain valve (24) during the switching of the drain valve (24).

Description

[0001] R. 401277

[0002] - 1 -

[0003] Description

[0004] Method for operating a fuel cell system, fuel cell system, control unit

[0005] The invention relates to a method for operating a fuel cell system with the features of the preamble of independent claim 1. Furthermore, the invention relates to a fuel cell system and a control unit.

[0006] State of the art

[0007] It is known from the prior art that fuel cell systems include a fuel cell stack, an anode system, a cathode system and a cooling circuit.

[0008] During operation of the fuel cell system, the reactants hydrogen and air flow into the fuel cell stack to obtain electrical energy in a cold combustion reaction.

[0009] Water separators are used to separate liquid water from the gaseous component of the anode exhaust gas. In addition to its separation function, the water separator also stores the separated water. Once the storage tank is full, the water is discharged by opening a drain valve.

[0010] In the patent application DE 10 2021 205 569 A1, a method for detecting the fill level of a water tank in the anode system using a metering valve is described.

[0011] R. 401277

[0012] - 2 -

[0013] Disclosure of the invention

[0014] The fuel cell system according to the invention with the features according to independent claim 1 has the advantage that, by switching the drain valve, conclusions can be drawn about the water level in the anode system, in particular in the water separator, and thus additional sensors can be dispensed with.

[0015] It is advantageous if a switching characteristic is the difference between a local maximum and a local minimum of the current on the current characteristic curve during the switching of the drain valve. Since the difference between the local maximum and the local minimum of the current on the current characteristic curve during the switching of the drain valve depends on the viscosity of the substance or mixture present, it is possible to precisely determine whether fuel is present at the drain valve.

[0016] Advantageously, the switching characteristic is the time duration during switching between the local maximum and the local minimum of the current on the drain valve's current characteristic curve. Since this time duration depends on the viscosity of the substance or mixture present, it allows for a precise determination of whether fuel is present at the drain valve.

[0017] It is advantageous if the switching characteristic is a gradient of the current characteristic during the switching of the drain valve between the local maximum and the local minimum of the current. Since the gradient of the current characteristic during the switching of the drain valve between the local maximum and the local minimum of the current depends on the viscosity of the substance or mixture present, it is possible to precisely determine whether fuel is present at the drain valve.

[0018] Advantageously, exceeding a limit value of the switching characteristic serves to determine whether fuel is flowing through the drain valve. This limit value allows the process to be carried out effectively and reliably. R. 401277

[0019] - 3 -

[0020] It is advantageous if the switching action involves the drain valve transitioning from a closed to an open position, and if the switching characteristic exceeds the limit value, the drain valve closes. This reduces fuel discharge from the drain valve, thereby increasing operational reliability and optimizing the efficiency of the fuel cell system.

[0021] Advantageously, switching involves the drain valve transitioning from an open to a closed position. If the switching characteristic exceeds the threshold, the next opening of the drain valve is delayed by a defined period. This reduces the probability of fuel being discharged from the drain valve during the next switching operation, thereby increasing operational reliability and optimizing the efficiency of the fuel cell system.

[0022] It is advantageous if a fuel cell system is suitable for carrying out the method according to the invention. This makes it possible to implement the method according to the invention in a fuel cell system.

[0023] Advantageously, a control unit is suitable for carrying out the method according to the invention. This makes it possible to implement the method according to the invention in the control unit of the fuel cell system.

[0024] Description of the drawings

[0025] The method according to the invention is explained in more detail below with reference to drawings and a preferred embodiment.

[0026] They show:

[0027] Fig. 1 schematic topology of a fuel cell system;

[0028] Fig. 2 shows a current characteristic curve of a drain valve;

[0029] Fig. 3 shows the switching behavior of a drain valve; R . 401277

[0030] - 4 -

[0031] Fig. 4 shows an embodiment of the method according to the invention;

[0032] Figure 1 shows a schematic topology of a fuel cell system 100 with at least one fuel cell stack 11, an anode system 200, a cathode system 300 and a cooling circuit not shown.

[0033] The anode system 200 supplies an anode compartment A of the fuel cell stack 11 with a fuel or anode fluid, in particular hydrogen (H2) as a reactant. By supplying fuel to anode compartment A, the fuel is made available to the fuel cell system 100 as a reactant.

[0034] The anode system 200 includes an anode supply line 22, a recirculation line 21 and an anode outlet line 23.

[0035] The anode supply line 22 leads into the fuel cell stack 11. Fuel is supplied to the fuel cell stack 11 via the anode supply line 22.

[0036] The recirculation line 21 is connected to the anode compartment A. The anode exhaust gas flowing from the anode compartment A is transported via the recirculation line 21 into the anode outlet line 23.

[0037] Fuel can be supplied to the fuel cell stack 11 at a superstoichiometric rate, so that the anode exhaust gas still contains fuel. To make the fuel contained in the anode exhaust gas available to the anode system 200, anode exhaust gas is recirculated from the recirculation line 21 into the anode supply line 22.

[0038] A jet pump 26 is arranged in the anode supply line 22. The jet pump connects the anode supply line 22 and the recirculation line 21.

[0039] The jet pump 26 can, in an alternative embodiment, be configured as a combined valve jet pump assembly 26. A combined valve jet pump assembly typically includes a metering valve and a jet pump. The metering valve is, for example, rigidly connected to the jet pump 26 by means of a screw connection. R. 401277

[0040] - 5 -

[0041] The ratio of fuel to anode exhaust gas in the anode supply line 22 downstream of the jet pump 26 is varied with the aid of the jet pump 26.

[0042] A recirculation pumping unit 25 is optionally arranged within the recirculation line 21. The recirculation pumping unit 25 can be a compressor designed as a blower, pump and / or compressor.

[0043] The recirculation pump unit 25 supports a recirculation of the anode exhaust gas from the recirculation line 21 into the anode supply line 22.

[0044] A water separator 30 is arranged within the recirculation line 21. The water separator 30 is positioned upstream of the recirculation pumping unit 25 in the direction of flow. Water is extracted from the anode exhaust gas by means of the water separator 30. The water separator 30 can be configured in various ways: as an automatic water separator 30 or as a manual water separator 30 and / or with an additional filter and / or with additional active cooling.

[0045] The anode outlet line 23 is connected to the recirculation line 21 via the water separator 30. Gases, such as anode exhaust gas and / or fluids, such as product water, are discharged from the anode system 200 via the anode outlet line 23.

[0046] A drain valve 24 is arranged in the anode outlet line 23. When the drain valve 24 opens, product water is discharged from the anode system 200. The combined valve jet pump arrangement 26 meters fuel into the anode system 200 accordingly to maintain a continuous flow rate.

[0047] In an alternative embodiment, the drain valve 24 can also be configured as a combined purge and drain valve 24. R. 401277

[0048] - 6 -

[0049] The cathode system 300 supplies a cathode chamber K of the fuel cell stack 11 with oxygen (O2) as a reactant. Oxygen is a component of air. By supplying air to the fuel cell system 100, the oxygen is made available to it as a reactant.

[0050] In the cathode system 300, a cathode supply line 31 is arranged, through which air is supplied to the cathode system 300 and which opens into the cathode chamber K of the fuel cell stack 11. In the cathode system 300, a cathode outlet line 32 is arranged, through which cathode exhaust gas is discharged from the fuel cell stack 11.

[0051] A control unit 500 is provided to regulate and control processes in the fuel cell system 100. This also includes the processing of at least one measurement signal for the execution of the method according to the invention.

[0052] In an alternative embodiment, more than one fuel cell stack 11 can also be arranged in the fuel cell system 100 without restricting the implementation of the method according to the invention.

[0053] The method according to the invention can be carried out in a fuel cell system 100 with several fuel cell stacks 11 in parallel or sequentially.

[0054] Figure 2 shows a current characteristic curve of the drain valve 24 during the opening switching process. The current characteristic curve is shown as an example and is not to scale.

[0055] The yi-axis represents current in amperes. The xi-axis represents time in seconds.

[0056] The y2-axis represents the voltage in volts. The x2-axis represents the time in seconds.

[0057] The current characteristic of the drain valve 24 depends on the viscosity of the substance or mixture of substances that is discharged via the drain valve 24. R. 401277

[0058] - 7 -

[0059] The diagram shows a first curve 1, a second curve 2, and a third curve 3.

[0060] The first curve 1 shows the current profile of the drain valve 24 over time when fuel is present in the drain valve 24 during opening, with a first point P1 and a second point P2. The first point P1 represents a local maximum of the current during the opening switching process. The second point P2 represents a local minimum of the current during the opening switching process.

[0061] The second curve 2 shows the current profile of the drain valve 24 over time when water is present in the drain valve 24 during opening, with a third point P3 and a fourth point P4. The third point P3 represents a local maximum of the current during the opening switching process. The fourth point P4 represents a local minimum of the current during the opening switching process.

[0062] The third curve 3 shows a voltage applied to the drain valve 24 over time.

[0063] To open drain valve 24, a voltage is applied to the drain valve 24. When a voltage is applied to the drain valve 24, current begins to flow. When the current reaches its local maximum at the first point P1 or the third point P3, the drain valve 24 begins to open. When the current reaches its local minimum at the second point P2 or the fourth point P4, the drain valve 24 is fully open.

[0064] The flow characteristic of the drain valve 24 depends on the viscosity of the substance or mixture being discharged via the drain valve 24. The lower the viscosity, the steeper the slope between the local minimum and the local maximum of the flow characteristic. The viscosity of hydrogen is lower than the viscosity of water.

[0065] With increasing viscosity of the substance or mixture, the current characteristic of the drain valve 24 shows a curve between the local maximum and the local R. 401277

[0066] - 8 -

[0067] The minimum exhibits a larger gradient. Furthermore, the time difference between the local maximum and the local minimum on the Xi-axis decreases with increasing viscosity of the substance or mixture. The difference in current values ​​between the local maximum and the local minimum on the yr-axis decreases with increasing viscosity of the substance or mixture.

[0068] The current difference of the yr coordinates from the second point P2 and the first point P1 is greater than the current difference of the yr coordinates from the fourth point P4 and the third point P3. Therefore, it is possible to determine from the current difference of the yr coordinates from the second point P2 and the first point P1 whether fuel is flowing through the drain valve 24, since the current difference is greater for a substance with low viscosity, especially fuel, than for a substance, especially water, with higher viscosity than fuel.

[0069] The time required for the drain valve 24 to travel from the first point P1 to the second point P2 is longer than the time required for the drain valve 24 to travel from the third point P3 to the fourth point P4. Therefore, it is possible to determine whether fuel is flowing through the drain valve 24 based on the Xi coordinates of the local maximum and local minimum, since the time between the local maximum and the local minimum of the flow characteristic of the drain valve 24 is longer for fuel than for water.

[0070] The gradient between the first point P1 and the second point P2 is steeper than the gradient between the third point P3 and the fourth point P4. This allows the determination of whether fuel is flowing through the drain valve 24 via the gradient, since the gradient between the local maximum and the local minimum of the flow characteristic of the drain valve 24 is less steep for fuel than for water.

[0071] Figure 3 shows the switching behavior of a drain valve 24 depending on whether fuel and water are discharged from the drain valve 24. R. 401277

[0072] - 9 -

[0073] The fill level of water separator 30 is shown on the yi axis. The time in seconds is shown on the xi axis.

[0074] The switching of drain valve 24 is shown on the y2-axis. The time in seconds is shown on the X2-axis.

[0075] In section 1a, the water separator 30 is full. In section 1b, the water separator 30's fill level drops from full to empty.

[0076] In section 2a, the drain valve 24 is switched and opens. Water is present at the drain valve 24. In section 2b, the drain valve 24 is open and water flows out of the drain valve 24. In section 2c, the drain valve 24 is switched and closes. During section 2c, fuel flows out of the drain valve 24.

[0077] The graph of section 2a, where water is discharged through drain valve 24, rises more steeply than the graph of section 2c, where hydrogen is discharged. The different switching behavior of drain valve 24 depending on the substance or mixture of substances allows us to determine whether fuel flows through drain valve 24 during its switching operation.

[0078] Figure 4 shows an embodiment of the method according to the invention.

[0079] Using the method according to the invention, it is possible to determine whether fuel is being discharged from the drain valve 24 or the combined purge-drain valve 24 without requiring an additional sensor. Thus, it can be detected when the water discharge has ceased and when fuel begins to flow from the anode circuit.

[0080] The process is initiated in step S100. The process according to the invention is carried out during the operation of the fuel cell system 100. R. 401277

[0081] - 10 -

[0082] In step S200 the drain valve 24 is then switched, whereby the switching is a transition of the drain valve 24 from a closed switching position to an open switching position.

[0083] In step S300, a switching characteristic is then determined from a current characteristic curve of the drain valve 24.

[0084] In a first embodiment, the switching feature is a current difference between a local maximum and a local minimum of the current characteristic during the switching of the drain valve 24.

[0085] In a second embodiment, the switching characteristic is a time duration during switching between the local maximum and the local minimum of the current characteristic of the drain valve 24.

[0086] In a third embodiment, the switching feature is a gradient of the current characteristic curve during the switching of the drain valve 24 between the local maximum and the local minimum.

[0087] In step S400, it is then determined whether fuel flows through the drain valve 24 during the transition from a closed switching position to an open switching position by determining whether the switching characteristic exceeds a limit value.

[0088] If the switching characteristic exceeds the limit value, i.e., fuel is discharged from the drain valve 24, a step S500 is subsequently executed. In step S500, the drain valve 24 is closed so that no more fuel is discharged through it. If it is already detected when the drain valve 24 is opened that fuel is being discharged, the discharge of hydrogen can be reduced by subsequently closing the drain valve 24, as this prematurely terminates the draining process.

[0089] In step S600, the drain valve 24 is then held in a closed switching position for a defined period of time, so that the next opening of the drain valve 24 is delayed compared to the intended opening time R. 401277

[0090] - 11 - takes place. This is intended to encourage sufficient water to accumulate so that when the drain valve is next opened, 24% water is discharged instead of hydrogen.

[0091] Subsequently, in step S1100, it is checked whether a process-termination event, in particular an operational stop, has occurred. If no process-termination event has occurred, step S200 can then be executed again. If a process-termination event, in particular an operational stop, has occurred, step S1200 is then executed, in which the process according to the invention is terminated.

[0092] If the switching characteristic does not exceed the limit value in step S400, step S700 is then executed. In step S700, a draining process takes place so that the water can be removed from the anode system.

[0093] Then, in step S800, the drain valve 24 is switched, whereby the switching is a transition of the drain valve 24 from an open switching position to a closed switching position of the drain valve 24 in order to complete the draining process.

[0094] Subsequently, in step S900, the switching characteristic is determined from a current characteristic curve of the drain valve 24.

[0095] In step S1000, it is then determined whether fuel flows through the drain valve 24 during the closing of the drain valve 24 at the end of the draining process by determining whether the switching characteristic exceeds a limit value.

[0096] If the switching feature exceeds the limit value, step S600 is then executed, since no more water has been discharged at the end of the draining process, as also shown in Fig. 3 section 2c.

[0097] If the switching characteristic does not exceed the limit value, step S1100 is then executed, in which it is checked whether a process-ending trigger R . 401277 .

[0098] - 12 -

[0099] An event, in particular an operational stoppage, has occurred. If no process-terminating event has occurred, step S200 can then be executed again. If a process-terminating event, in particular an operational stoppage, has occurred, step S1200 is then executed, in which the process according to the invention is terminated.

[0100] The process can be carried out, at least in part, by the control unit 500 of the fuel cell system 100. A computer program in the form of code can be stored in a memory unit of the control unit 500. When executed by a processing unit of the control unit 500, this code performs a process that can proceed as described above. The same advantages described above in connection with the process according to the invention can be achieved using the control unit 500. These advantages are fully referenced herein.

[0101] The control unit 500 can be in communication with the sensors of the fuel cell system 100 in order to monitor the sensor values.

[0102] The control unit 500 can control the actuators in the fuel cell system 100 in order to carry out the procedure accordingly.

[0103] Furthermore, the control unit 500 can be in a communication link with an external computing unit in order to outsource some process steps and / or calculations completely or partially to the external computing unit.

[0104] According to another aspect, the invention provides a computer program product comprising instructions which, when executed by a computer, such as the processing unit of the control unit 500, cause the computer to carry out the method, which can proceed as described above. The computer program product offers the same advantages described above in connection with the method and / or the control unit 500 according to the invention. These advantages are fully referenced herein.

Claims

R. 401277 - 13 - Claims 1. A method for operating a fuel cell system (100) with at least one fuel cell stack (11) and an anode system (200), wherein a drain valve (24) is arranged in the anode system (200), characterized in that the following steps are performed: i. Switching the drain valve (24), wherein the switching describes a transition of the drain valve (24) from an open switching position to a closed switching position and vice versa; ii. Determining a switching characteristic from a current characteristic of the drain valve (24); iii. Determining whether fuel flows through the drain valve (24) during the switching of the drain valve (24).

2. Method according to claim 1, characterized in that the switching feature is a current difference between a local maximum and a local minimum of the current characteristic during the switching of the drain valve (24).

3. Method according to claim 1, characterized in that the switching feature is a time period between the local maximum and the local minimum of the current characteristic during the switching of the drain valve (24).

4. Method according to claim 1, characterized in that the switching feature is a gradient of the current characteristic curve between the local maximum and the local minimum during the switching of the drain valve (24).

5. Method according to claim 1, characterized in that it is determined that fuel flows through the drain valve (24) when the switching feature exceeds a limit value.

6. Method according to claim 5, characterized in that the switching is a transition of the drain valve (24) from a closed switching position of the drain valve (24) to an open switching position of the drain valve (24) and when the switching characteristic exceeds the limit value, the drain valve (24) is closed. R. 401277 - 14 - 7. Method according to claim 6, characterized in that the next opening of the drain valve (24) is delayed by a defined period of time.

8. Method according to claim 5, characterized in that the switching is a transition of the drain valve (24) from an open switching position to a closed switching position of the drain valve (24), and if the switching characteristic exceeds the limit value, the next opening of the drain valve (24) is delayed by a defined time period.

9. Fuel cell system (100) for carrying out the method according to one of the above Claims.

10. Control unit (500), suitable for carrying out the method according to one of the above claims.

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