Method for operating a fuel cell system

Abstract

The invention relates to a method for operating a fuel cell system (100) comprising: at least one fuel cell stack (11) in which a plurality of stacked fuel cells are arranged; an anode system (200); and a cathode system (200), wherein a value of an operating characteristic of the fuel cell system (100) is determined, and, if the value of the operating characteristic of the fuel cell system (100) exceeds or falls below a threshold value, a first load point of the fuel cell system (100) is adapted to a second load point of the fuel cell system (100), wherein the current flow of the fuel cell stack (11) is higher at the second load point than at the first load point.

Description

[0001] Description

[0002] title

[0003] Method for operating a fuel cell system;

[0004] The invention relates to a method for operating a fuel cell system having the features of the preamble of independent claim 1.

[0005] State of the art

[0006] It is known from the prior art that fuel cell systems exist that have an anode system and a cathode system. The anode system consists of an anode supply line that supplies fuel to a fuel cell stack, and an anode recirculation line that recirculates anode exhaust gas to the anode supply line via a feed unit.

[0007] The cathode system consists of a cathode supply line, which can house a compressor and supply air to the fuel cell stack. Furthermore, the cathode system consists of a cathode outlet line through which cathode exhaust gas is transported from the cathode system into the exhaust system.

[0008] Disclosure of the invention

[0009] The method according to the invention for operating a fuel cell system with the features according to independent claim 1 has the advantage that aging of fuel cell components, in particular of an anode recirculation conveying unit and / or a jet nozzle with a metering valve and / or a purge valve and / or drain valve, can be slowed down.

[0010] The aging of the fuel cell components is slowed down by determining a value of an operating characteristic of the fuel cell system and, if the value of the operating characteristic of the fuel cell system exceeds or falls below a limit value, an adjustment of a first load point of the fuel cell system to a second load point of the fuel cell system takes place, wherein the current flow of the fuel cell stack is higher at the second load point than at the first load point.

[0011] It is advantageous if the operating characteristic represents a temperature at a fuel cell component, in particular an anode recirculation conveying unit and / or a jet nozzle with a metering valve and / or a purge valve and / or drain valve, in the anode system. The fuel cell components in the anode system have an increased temperature when a reduced flow of reactant or anode exhaust gas flows through the anode system. With a reduced flow, the fuel cell components in the anode system can no longer be cooled in a targeted manner. This is particularly the case when the fuel cell system is operated at a partial load point of, for example, 35% of the maximum load of the fuel cell system. The method according to the invention increases the load point so that the anode system has an increased flow of reactant.

[0012] It is advantageous if the temperature of a fuel cell component is determined using a characteristic map, particularly using the parameters of the fuel cell system's voltage and current. This eliminates the need for additional sensors in the fuel cell system and ensures a compact and cost-effective design.

[0013] It is advantageous if the operating characteristic represents a voltage difference between a first fuel cell and a second fuel cell in the fuel cell stack. The voltage difference between a first fuel cell and a second fuel cell decreases when water accumulates within the fuel cell, thereby reducing the supply of reactants. This is particularly the case with a reduced flow of reactant or anode exhaust gas in the anode system.

[0014] It is advantageous if the voltage difference is calculated using a first voltage measurement and a second voltage measurement, which are determined by a voltage monitoring unit (Cell Voltage Monitoring). The voltage monitoring unit is an integral part of the fuel cell system. This eliminates the need for additional components such as sensors in the fuel cell system and ensures a compact design. It is advantageous if the operating characteristic is a differential pressure between a first pressure in the anode inlet line and a second pressure in the recirculation line. At a low differential pressure, there is a reduced flow of reactant or cathode exhaust gas, so that sufficient cooling of the fuel cell components in the anode system is no longer guaranteed.

[0015] It is advantageous that if the second amount of energy provided at the second load point is higher than the first amount of energy provided at the first load point, the difference between the second amount of energy and the first amount of energy is stored in an external battery. This allows the energy to be made available to the fuel cell system or a vehicle component at a later time.

[0016] It is advantageous that, if the second amount of energy provided at the second load point is higher than the first amount of energy provided at the first load point, and the difference between the second amount of energy and the first amount of energy is consumed by at least one fuel cell component, in particular by a cathode feed unit and / or an anode recirculation feed unit and / or a coolant feed unit, the amount of energy required by the fuel cell component is increased. The additional energy provided is thus made available to and consumed by the fuel cell components.

[0017] It is advantageous if, when operating the fuel cell system at the second load point, a defined amount of nitrogen (N2) is enriched in the anode system so that the second amount of energy provided corresponds to the amount of energy provided at the first load point. This reduces the efficiency of the fuel cell system and prevents more energy being provided than can be consumed by the fuel cell system or vehicle components.

[0018] It is advantageous if, when operating the fuel cell system at the second load point, the air supply to the cathode system is reduced so that the second amount of energy provided corresponds to the amount of energy provided at the first load point. This reduces the efficiency of the fuel cell system and prevents more energy being provided than can be consumed by the fuel cell system or vehicle components.

[0019] Description of the drawings

[0020] The fuel cell system and the method according to the invention are explained in more detail below with reference to drawings with preferred embodiments.

[0021] They show:

[0022] Fig. 1 shows a schematic topology of a fuel cell system and

[0023] Fig. 2 is a flow chart of the method according to the invention.

[0024] 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).

[0025] 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, oxygen is made available to the system as a reactant.

[0026] A cathode supply line 31 is arranged in the cathode system 300 and leads into the fuel cell stack 11. Oxygen is supplied to the fuel cell stack 11 via the cathode supply line 31.

[0027] A cathode compressor 33 is located within the cathode supply line 31. The cathode compressor 33 conveys air into the fuel cell stack 11. A cathode outlet line 32 is arranged in the cathode system 300. Gases, such as cathode exhaust gas and / or fluids, such as product water, are discharged from the cathode system 300 via the cathode outlet line 32.

[0028] 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 the anode compartment A, the fuel is made available to the fuel cell system 100 as a reactant.

[0029] An anode supply line 22, a recirculation line 21 and an anode outlet line 23 are arranged in the anode system.

[0030] The anode supply line leads into the fuel cell stack 11. Fuel is supplied to the fuel cell stack 11 via the anode supply line 22.

[0031] The recirculation line 21 is connected to the anode chamber A and the anode supply line 22.

[0032] The fuel supply to the fuel cell stack 11 can be superstoichiometric, 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, the anode exhaust gas is recirculated from the recirculation line 21 into the anode supply line 22.

[0033] A recirculation conveying unit 25 is optionally arranged within the recirculation line 21. The recirculation conveying unit 25 supports the recirculation of the anode exhaust gas from the recirculation line 21 into the anode supply line 22.

[0034] A jet pump with a metering valve 26 is arranged in the anode supply line 22. The jet pump with a metering valve 26 is arranged between the anode supply line 22 and the recirculation line 21 and connects them.

[0035] The anode outlet line 23 is connected to the recirculation line 21. Gases, such as anode exhaust gas and / or fluids, such as water, are discharged from the anode system 200 via the anode outlet line 23.

[0036] A drain valve 24 is arranged in the anode outlet line 23. When the drain valve 24 is opened, water is drained from the anode system 200. The jet pump with metering valve 26 doses fuel into the anode system 200 accordingly to maintain a continuous flow rate. In an alternative embodiment, the drain valve 24 can be designed as a combined purge-drain valve 24, so that anode exhaust gas and / or water can be drained from the anode system 200 via the combined purge-drain valve 24.

[0037] The waste heat from the fuel cell stack 11 is dissipated via a cooling circuit and can be released into the environment via a vehicle radiator. A coolant is recirculated within the cooling circuit. The coolant is pumped through the fuel cell stack 11 by a coolant delivery unit. A 3-way valve ensures that the vehicle radiator can be partially or completely bypassed.

[0038] A control unit 500 is provided to regulate and control all control-related processes in the fuel cell system 100. This also includes the processing of information for executing the method according to the invention.

[0039] The control unit 500 can communicate with the sensors in the fuel cell system 100 to monitor sensor values. The control unit 500 can control the actuators in the fuel cell system 100 to carry out the method according to the invention accordingly.

[0040] In addition, the control unit 500 can be in a communication connection with an external computing unit in order to outsource process steps and / or calculations in whole or in part to the external computing unit.

[0041] Figure 2 shows an embodiment of the method according to the invention.

[0042] The fuel cell components in the anode system exhibit an elevated temperature when a reduced flow of reactant or anode exhaust gas flows through the anode system. With a reduced flow, the fuel cell components in the anode system can no longer be cooled in a targeted manner, and the high temperatures cause accelerated aging of the fuel cell components. This is particularly the case when the fuel cell system is operated at a partial load point of, for example, 35% of the maximum load of the fuel cell system. The method according to the invention increases the load point, so that the anode system exhibits an increased flow of reactant.

[0043] The method is initiated in step S100. The method according to the invention is initiated or executed during operation of the fuel cell system 100.

[0044] In step S200, a value of an operating characteristic of the fuel cell system 100 is determined.

[0045] In a first embodiment, the operating feature may represent a temperature at a fuel cell component, in particular an anode recirculation conveying unit (25) and / or the jet nozzle with metering valve (26) and / or a purge valve and / or the drain valve (24), in the anode system (200).

[0046] The temperature at the fuel cell component can be determined using a temperature sensor located on or near the fuel cell component.

[0047] The temperature of the fuel cell component can be determined using a characteristic map, in particular using the parameters of a voltage of the fuel cell system 100 and a current of the fuel cell system 100.

[0048] In a second embodiment, the operating characteristic may represent a voltage difference between a first fuel cell and a second fuel cell in the fuel cell stack 11.

[0049] The voltage difference can be formed via a first voltage measurement and a second voltage measurement, each of which is determined via a voltage monitoring unit.

[0050] In a third embodiment, the operating characteristic may be a differential pressure from a first pressure in the anode inlet line 22 to a second pressure in the recirculation line 21.

[0051] The first pressure and the second pressure can each be measured using a pressure sensor. In step S300, the value of the operating characteristic is compared with a limit value, and a check is made to determine whether the value of the operating characteristic exceeds or falls below the limit value.

[0052] In the first embodiment, if the operating characteristic has exceeded the limit value, a step S400 is executed

[0053] In the second embodiment, if the operating characteristic has fallen below the limit value, step S400 is executed

[0054] In the third embodiment, if the operating characteristic has fallen below the limit value, step S400 is executed

[0055] In step S400, an adjustment of a first load point of the fuel cell system 100 to a second load point of the fuel cell system 100 takes place, wherein at the second load point the current flow of the fuel cell stack 11 is higher than at the first load point.

[0056] Subsequently, a step S500 is executed. In step S500, the method according to the invention is terminated.

[0057] If the second amount of energy provided at the second load point is higher than the first amount of energy provided at the first load point, the difference between the second amount of energy and the first amount of energy can be stored in an external battery.

[0058] If the second amount of energy provided at the second load point is higher than the first amount of energy provided at the first load point, the difference between the second amount of energy and the first amount of energy can be consumed by at least one fuel cell component, in particular the anode recirculation feed unit 25 and / or a coolant feed unit, by increasing the amount of energy required by at least one fuel cell component.

[0059] When operating the fuel cell system 100 at the second load point, a defined amount of nitrogen (N2) can be enriched in the anode system 200 so that the second amount of energy provided corresponds to the amount of energy provided at the first load point.

[0060] When operating the fuel cell system (100) at the second load point, the air supply to the cathode system (300) can be reduced so that the second amount of energy provided corresponds to the amount of energy provided at the first load point.

[0061] In an alternative embodiment, it is also possible to carry out the method according to the invention with more than one fuel cell stack 11.

[0062] The method according to the invention can be carried out in a fuel cell system 100 in several fuel cell stacks 11 in parallel or sequentially.

[0063] The method may further be carried out at least in part by the control unit 500 of the

[0064] 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 the code is executed by a computing unit of the control unit 500, the program performs a method that can proceed as described above. With the aid of the control unit 500, the same advantages can be achieved that were described above in connection with the method according to the invention. These advantages are incorporated herein by reference in their entirety.

[0065] The control unit 500 may be in communication with the sensors of the fuel cell system 100 to monitor the sensor values.

[0066] The control unit 500 can control the actuators in the fuel cell system 100 in order to carry out the method accordingly.

[0067] Furthermore, the control unit 500 can be in communication with an external computing unit in order to outsource some method steps and / or calculations entirely or partially to the external computing unit. According to a further aspect, the invention provides a computer program product comprising instructions which, when the computer program product is executed by a computer, such as the computing unit of the control unit 500, cause the computer to perform the method, which can proceed as described above. With the aid of the computer program product, the same advantages can be achieved that were described above in connection with the method according to the invention and / or the control unit 500 according to the invention. These advantages are fully incorporated herein by reference.

Claims

Claims 1.) Method for operating a fuel cell system (100) with at least one fuel cell stack (11) in which a plurality of stacked fuel cells are arranged, an anode system (200) and a cathode system (200), characterized in that a value of an operating characteristic of the fuel cell system (100) is determined and if the value of the operating characteristic of the fuel cell system (100) exceeds or falls below a limit value, an adjustment of a first load point of the fuel cell system (100) to a second load point of the fuel cell system (100) takes place, wherein the current flow of the fuel cell stack (11) is higher at the second load point than at the first load point. 2.) Method according to claim 1, characterized in that the operating characteristic represents a temperature at a fuel cell component, in particular an anode recirculation conveyor unit (25) and / or a jet nozzle with metering valve (26) and / or a purge valve and / or a drain valve (24), in the anode system (200) and an adaptation of a first load point of the fuel cell system (100) to a second load point of the fuel cell system (100) takes place when the operating characteristic exceeds the limit value. 3.) Method according to claim 2, characterized in that the temperature is formed via a characteristic map, in particular with the parameters voltage of the fuel cell system (100) and current of the fuel cell system (100). 4.) Method according to claim 1, characterized in that the operating characteristic represents a voltage difference between a first fuel cell and a second fuel cell in the fuel cell stack (11) and an adaptation of a first load point of the fuel cell system (100) to a second load point of the fuel cell system (100) takes place when the operating characteristic falls below the limit value. Method according to claim 4, characterized in that the voltage difference is formed via a first voltage measurement and a second voltage measurement, which are determined via a voltage monitoring unit. Method according to claim 1, characterized in that the operating characteristic represents a differential pressure between a first pressure in the anode inlet line (22) and a second pressure in the recirculation line (21), and an adjustment of a first load point of the fuel cell system (100) to a second load point of the fuel cell system (100) takes place when the operating characteristic falls below the limit value.Method according to claim 1, characterized in that the second amount of energy of the fuel cell system (100) provided at the second load point is higher than the first amount of energy provided at the first load point and the difference between the second amount of energy and the first amount of energy is stored in an external battery. Method according to claim 1, characterized in that the second amount of energy provided at the second load point is higher than the first amount of energy provided at the first load point and the difference between the second amount of energy and the first amount of energy is consumed by at least one fuel cell component, in particular an anode recirculation conveying unit (25) and / or a coolant conveying unit, by increasing the amount of energy required by the fuel cell component. Fuel cell system (100) at the second load point, a defined amount of nitrogen (N2) is enriched in the anode system (200), so that the second amount of energy provided corresponds to the amount of energy provided at the first load point. Method according to claim 1, characterized in that during operation of the Fuel cell system (100) at the second load point, a reduction in the air supply to the cathode system (300) takes place, so that the second amount of energy provided corresponds to the amount of energy provided at the first load point.

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