Method for heating a fuel cell system

Abstract

Method for heating a fuel cell system (100) comprising at least one fuel cell stack (11), a cooling circuit (400) in which a coolant circulates and in which a heating element (47) and a delivery unit (43) are arranged, wherein during an operational standstill the heating element (47) is activated to heat the coolant.

Description

[0001] R. 415980

[0002] - 1 -

[0003] Description

[0004] title

[0005] Method for heating a fuel cell system

[0006] The invention relates to a method for heating a fuel cell system with the features of the preamble of independent claim 1.

[0007] State of the art

[0008] 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.

[0009] During operation of the fuel cell system, the reactants fuel and air flow into the fuel cell stack to obtain electrical energy in a cold combustion reaction.

[0010] The waste heat from the fuel cell stack is dissipated via a cooling circuit and can be released into the environment through a vehicle radiator. A coolant circulates within this cooling circuit.

[0011] If the fuel cell system is started at sub-zero temperatures, local icing can occur in the fuel cell stack. This ice formation hinders the reaction within the fuel cell stack, thus slowing down or preventing the system from starting. Simultaneously, the fuel cell stack should be warmed up as quickly as possible during startup.

[0012] In the patent application DE 10 2021 207 908 A1, a method for operating a fuel cell system, in particular during a cold start and / or freeze start of the fuel cell system, is disclosed in order to achieve a R. 415980

[0013] - 2 -

[0014] to bring the coolant temperature at the inlet to the fuel cell stack to a desired stagnation temperature.

[0015] Disclosure of the invention

[0016] The inventive method for heating a fuel cell system with the features according to independent claim 1 has the advantage that the coolant can be heated to a temperature higher than the ambient temperature during a standstill, if no waste heat is available for heating from the fuel cell system itself, particularly during ambient temperatures in the range of 0°C. This allows the fuel cell stack to be kept warm during a standstill and ensures that it already has a suitable fuel cell stack temperature when the fuel cell system is restarted.

[0017] It is advantageous to compare the fuel cell stack temperature with a fuel cell stack limit temperature and activate the heating element when the fuel cell stack temperature falls below the fuel cell stack limit temperature. This allows the fuel cell stack to be reliably set to a temperature above the fuel cell stack limit temperature.

[0018] The fuel cell stack temperature can advantageously be determined using a model based on the ambient temperature and / or the coolant temperature and / or the shutdown duration. This eliminates the need for an additional sensor within the fuel cell stack and allows for a more compact design.

[0019] The fuel cell stack temperature can advantageously be determined using impedance spectroscopy, in particular of a high-frequency resistor, and / or an infrared radiation signal. This allows for an accurate determination of the fuel cell stack temperature using reliable measurement methods.

[0020] The fuel cell stack temperature can advantageously be determined by measuring the coolant temperature of coolant R. 415980 with the pump unit activated.

[0021] - 3 - is measured. This allows the fuel cell stack temperature to be measured indirectly using existing sensors, without the need for additional components.

[0022] Advantageously, the coolant temperature is compared to a coolant threshold, and the heating element is activated when the coolant temperature falls below this threshold. This allows for efficient temperature control of the fuel cell stack, as the fuel cell stack temperature cools down more slowly than the coolant temperature during a shutdown, thus enabling an approximate determination of whether the heating element should be activated.

[0023] It is advantageous to compare the ambient temperature with a first ambient temperature threshold and activate the heating element when the ambient temperature falls below this threshold. This allows for efficient use of the heating element, as the fuel cell stack does not cool below ambient temperature during the fuel cell system's shutdown, thus ensuring that the heating element is only activated when the temperature falls below the first ambient temperature threshold.

[0024] Advantageously, the heating element can only be activated within a certain downtime period following a shutdown of the fuel cell system. This efficiently prevents the inventive method from being carried out unnecessarily in a fuel cell system that is permanently shut down. This can be the case, for example, with a fuel cell system installed in a vehicle that is permanently parked.

[0025] It is advantageous if the heating element can only be activated when the ambient temperature exceeds a second ambient temperature threshold. This efficiently prevents energy-intensive heating of the coolant at very low ambient temperatures, for example, below -25°C.

[0026] Advantageously, the heating element can only be activated after a predetermined period of time during the fuel cell system's shutdown. This results in R. 415980

[0027] - 4 - ensured that the method according to the invention is only carried out when a cooling of the fuel cell stack is to be expected.

[0028] A fuel cell system and the method according to the invention are explained in more detail below with reference to drawings with preferred embodiments.

[0029] They show:

[0030] Fig. 1 shows a schematic topology of a fuel cell system;

[0031] Fig. 2 shows a flowchart of the method according to the invention in a first embodiment;

[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 400.

[0033] The at least one fuel cell stack 11 has a fuel cell stack temperature, which represents the current temperature of the at least one fuel cell stack 11. The fuel cell stack temperature can change; for example, the fuel cell stack temperature can decrease if the at least one fuel cell stack 11 is in a low ambient temperature environment, such as 0 °C, and the fuel cell system 100 is inactive, so that no waste heat is generated in the fuel cell system 100.

[0034] Cooling circuit 400 represents a closed fluid circuit. Cooling circuit 400 serves to temperature-control the at least one fuel cell stack 11 by flowing a coolant through a coolant path KM of the at least one fuel cell stack 11.

[0035] Cooling circuit 400 has a cooling circuit line 45, which forms a closed circuit in which a coolant circulates. In cooling circuit line 45 R. 415980

[0036] - 5 - a valve 41, a vehicle radiator 42, a conveying unit 43 and a temperature sensor 44 are arranged

[0037] The temperature sensor 44 is located between the coolant path KM and the valve 41. The temperature sensor 44 allows the coolant temperature of the coolant to be measured at the outlet of the at least one fuel cell stack 11.

[0038] The vehicle cooler 42 is arranged downstream of the valve 41 in the direction of flow. The waste heat from the at least one fuel cell stack 11 can be dissipated to the environment via the vehicle cooler 42.

[0039] The pumping unit 43 is arranged between the vehicle radiator 42 and the at least one fuel cell stack 11. The pumping unit 43 supports the circulation of the coolant in the cooling circuit 400.

[0040] A bypass line 46 runs parallel to the vehicle radiator 42. The bypass line 46 is connected to the valve 41 and opens downstream of the vehicle radiator 42 in the direction of flow. A heating element 47 is arranged in the bypass line 46. The heating element 47 can heat the coolant.

[0041] With the help of valve 41, the coolant can be directed at least partially or completely into the bypass line 46 by placing valve 41 in a switching position that allows the coolant to flow through the bypass line 46.

[0042] In an alternative embodiment, the valve 41 can also be arranged in the bypass line 46.

[0043] The cathode system 300 supplies a cathode chamber K 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.

[0044] In the cathode system 300, a cathode inlet 31 and a cathode outlet 32 ​​are arranged. R. 415980

[0045] - 6 -

[0046] The cathode supply line 31 leads into the at least one fuel cell stack 11 and supplies air to the at least one fuel cell stack 11. Optionally, a pumping unit is arranged in the cathode supply line 31.

[0047] The cathode outlet 32 ​​is connected to at least one fuel cell stack 11. Air and / or fluids, such as product water, are discharged from the cathode system 300 via the cathode outlet 32.

[0048] The anode system 200 supplies an anode compartment A of the at least one fuel cell stack 11 with a fuel or anode gas, in particular hydrogen (H2), as a reactant.

[0049] The anode system 200 includes an anode supply line 22, a recirculation line 21, an anode outlet 23 and a jet pump 26.

[0050] The anode supply line 22 is connected to a fuel tank (not shown) and leads into the anode compartment K of the at least one fuel cell stack 11. Fuel is supplied from the fuel tank (not shown) to the anode compartment A via the anode supply line 22 and made available as reactant.

[0051] The recirculation line 21 is connected to the anode chamber A and leads into the jet pump 26. Fuel can be supplied to the at least one fuel cell stack 11 at a superstoichiometric rate, so that the anode exhaust gas still contains fuel. To make the fuel available to the anode system, anode exhaust gas is recirculated from the recirculation line 21 into the anode supply line 22.

[0052] A jet pump 26 is arranged in the anode supply line 22. The jet pump is arranged between the anode supply line 22 and the recirculation line 21 and connects them.

[0053] An anode outlet 23 is arranged in the anode system 200. The anode outlet 23 is connected to the recirculation line 21. Gases, such as anode exhaust gas and / or fluids, such as product water, are discharged from the anode system 200 via the anode outlet 23. R. 415980

[0054] - 7 -

[0055] 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.

[0056] Figure 2 shows an embodiment of the method according to the invention.

[0057] Using the method according to the invention, the at least one fuel cell stack 11 can be heated when the fuel cell system 100 cannot provide waste heat for heating during a standstill, particularly during ambient temperatures below 0°C, by heating the coolant of the cooling circuit 400. This allows the fuel cell stack 11 to be kept warm during a standstill and to already have a suitable fuel cell stack temperature when the fuel cell system 100 is started up.

[0058] In step S100, the process is initiated, so that step S100 represents the start. The process according to the invention is executed after the fuel cell system 100 has been shut down, so that the fuel cell system 100 is in an operational stop or standstill. The process can be started after a predetermined period of time during the operational stop of the fuel cell system 100.

[0059] In step S200, the ambient temperature is compared with a first ambient temperature limit value. The first ambient temperature limit value can be, for example, 0°C.

[0060] If the ambient temperature exceeds the first ambient temperature limit, step S201 is executed. In step S201, an initial time period is determined that must elapse before step S200 is executed again. This initial time period can be stored in a table based on the ambient temperature.

[0061] If the ambient temperature falls below the first ambient temperature limit, step S300 is then executed. R. 415980

[0062] - 8 -

[0063] In an alternative embodiment, it can also be checked whether the ambient temperature falls below a second ambient temperature limit. This second ambient temperature limit could, for example, be -25°C. If the ambient temperature falls below this second limit, step S201 is also executed. Otherwise, step S300 is executed.

[0064] In step S300, the coolant temperature is compared to a coolant limit value. If the coolant temperature exceeds the limit value, step S301 is then executed. In step S301, a second time period is determined that must elapse before step S300 is executed again. This second time period can be stored in a separate table, depending on the coolant temperature.

[0065] If the coolant temperature falls below the coolant limit, step S400 is then executed. In step S400, the fuel cell stack temperature is determined.

[0066] In a first embodiment, the fuel cell stack temperature is determined using a model based on the ambient temperature and / or the coolant temperature and / or a shutdown duration.

[0067] In a second embodiment, the fuel cell stack temperature is determined by means of impedance spectroscopy, in particular of a high-frequency resistor.

[0068] In a third embodiment, the fuel cell stack temperature is determined using an infrared radiation signal.

[0069] In a fourth embodiment, the fuel cell stack temperature is determined by measuring the coolant temperature when the pump unit 43 is activated. In particular, the coolant temperature is measured using the temperature sensor 44. R. 415980

[0070] - 9 -

[0071] Subsequently, step S500 is executed. In step S500, the fuel cell stack temperature is compared with a fuel cell stack limit temperature.

[0072] If the fuel cell stack temperature exceeds the fuel cell stack limit temperature, step S301 is then executed.

[0073] If the fuel cell stack temperature falls below the fuel cell stack limit temperature, a step S600 is then executed.

[0074] In step S600, a keep-warm mode for the fuel cell stack 11 is activated, and the heating element 47 is activated to heat the coolant. In keep-warm mode, the at least one fuel cell stack 11 is maintained within a temperature range, such that the fuel cell stack temperature is neither above nor below this range. The temperature range can, for example, be from 3°C to 8°C. Step S600 is executed for a third time interval. After this third time interval has elapsed, step S700 is executed.

[0075] Step S700 checks whether a process-ending event has occurred. A process-ending event could be that the ambient temperature falls below a second ambient temperature limit, meaning that heating element 47 can only be activated when the ambient temperature exceeds a second ambient temperature limit.

[0076] A process-termination triggering event can be that an operating stop duration has expired, so that the heating element 47 can only be activated within an operating stop duration after an operating stop of the fuel cell system 100.

[0077] A process-termination triggering event could be that the operation of the fuel cell system 100 has been activated and thus sufficient waste heat is available to heat the coolant.

[0078] If no process-termination event has occurred, step S600 is executed again. R. 415980

[0079] - 10 -

[0080] If a process-termination triggering event has occurred, the process according to the invention is subsequently terminated in step S800.

[0081] The process can still 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.

[0082] The control unit 500 can be in communication with the sensors of the fuel cell system 100 in order to monitor the sensor values.

[0083] The control unit 500 can control the actuators in the fuel cell system 100 in order to carry out the procedure accordingly.

[0084] 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.

[0085] 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. 415980 - 11 - Claims 1. Method for heating a fuel cell system (100) with at least one fuel cell stack (11), a cooling circuit (400) in which a coolant circulates and in which a heating element (47) and a conveying unit (43) are arranged, characterized in that the heating element (47) is activated during a standstill to heat the coolant.

2. Method according to claim 1, characterized in that a fuel cell stack temperature is compared with a fuel cell stack limit temperature and the heating element (47) is activated when the fuel cell stack temperature falls below the fuel cell stack limit temperature.

3. Method according to claim 2, characterized in that the fuel cell stack temperature is determined model-based as a function of the ambient temperature and / or a coolant temperature and / or a shutdown duration.

4. Method according to claim 2, characterized in that the fuel cell stack temperature is determined by means of impedance spectroscopy, in particular of a high-frequency resistor, and / or an infrared radiation signal.

5. Method according to claim 2, characterized in that the fuel cell stack temperature is determined by measuring the coolant temperature of the coolant when the pumping unit (43) is activated.

6. Method according to one of the above claims, characterized in that the coolant temperature is compared with a coolant limit value and the heating element (47) is activated when the coolant temperature falls below the coolant limit value. R. 415980 - 12 - 7. Method according to one of the above claims, characterized in that the ambient temperature is compared with a first ambient temperature limit value and the heating element (47) is activated when the ambient temperature falls below a first ambient temperature limit value.

8. Method according to one of the above claims, characterized in that the heating element (47) can only be activated within an operating stop time after an operating stop of the fuel cell system (100).

9. Method according to one of the above claims, characterized in that the heating element (47) can only be activated if the ambient temperature exceeds a second ambient temperature limit value.

10. Method according to one of the above claims, characterized in that the heating element (47) can be activated after a predetermined period of time during the operational stop of the fuel cell system (100).

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