Method and controller for operating a fuel cell system, and fuel cell system

Abstract

The invention relates to a method for operating a fuel cell system (100), said fuel cell system (100) having a plurality of fuel cell modules (120) designed as proton-exchange membrane fuel cells. The method has the steps of ascertaining the aging state (153) of the plurality of fuel cell modules (120), adjusting the current target system pressure of the fuel cell system (100) on the basis of the aging state (153) in order to generate an adjusted target system pressure (155), and actuating at least one operating device (130, 140) of the fuel cell system (100) using the adjusted target system pressure (155) in order to operate the fuel cell system (100).

Description

[0001] Description

[0002] title

[0003] Method and control device for operating a fuel cell system and fuel cell system

[0004] State of the art

[0005] The present invention relates to a method, to a corresponding control device and to a corresponding computer program product.

[0006] A PEM fuel cell system (PEM = Proton Exchange Membrane) or proton exchange membrane fuel cell system or polymer electrolyte fuel cell system comprises a fuel cell stack or many individual cells, which may, for example, be stacked and held together by a clamping system. Each individual cell may have a membrane that separates the media on the anode and cathode sides. The majority of individual cells or the stack age over their lifetime, and several aging effects can occur. These aging effects can lead to reduced stack performance or reduced efficiency. In this case, a characteristic curve or pole curve of the stack can deteriorate – at the same electrical current, the cell voltage and thus the efficiency can decrease.

[0007] Disclosure of the invention

[0008] Against this background, the approach presented here presents a method, a control unit which uses this method and finally a corresponding computer program product according to the main claims. Advantageous embodiments arise from the respective subclaims and the following description. According to embodiments, in particular an optimization of the system performance of a fuel cell system over its service life can be achieved. In other words, for example, an operating strategy can be implemented which takes stack aging into account and optimizes the net system performance over the service life. In particular, the target system pressure can be adjusted over the service life in order to take increasing degradation of the stack into account. For this purpose, the estimated or measured stack aging state orStack SOH (stack state of health) can be used to determine the optimal system pressure. This can, for example, increase the overall net system performance over the entire service life. Furthermore, hydrogen consumption can be reduced, the total cost of ownership (TCO) can be lowered over the service life, and performance can be improved.

[0009] A method for operating a fuel cell system is presented, wherein the fuel cell system comprises a plurality of fuel cell modules designed as proton exchange membrane fuel cells, the method comprising the following steps:

[0010] Determining an aging state of the plurality of fuel cell modules;

[0011] Setting a current target system pressure of the fuel cell system depending on the aging condition in order to generate a set target system pressure; and

[0012] Controlling at least one operating device of the fuel cell system using the set target system pressure in order to operate the fuel cell system.

[0013] A plurality of fuel cell modules designed as proton exchange membrane fuel cells can also be referred to as a fuel cell stack or, more precisely, a PEM fuel cell stack (PEM = Proton Exchange Membrane), a proton exchange membrane fuel cell stack, or a polymer electrolyte fuel cell stack. Such fuel cell stacks comprise many individual fuel cell modules or single cells, which can be stacked and held together, for example, by a clamping system. Each individual cell can contain a membrane that separates the media on the anode and cathode sides. So-called bipolar plates can be arranged between the individual cells or fuel cell modules, through which cooling water can flow to dissipate heat loss from the chemical reaction. The aging state can also be referred to as the so-called state of health (SoH).The aging state refers to the majority of fuel cell modules and can also be referred to as the stack SoH. In the determining step, the current aging state can be compared with a reference state. Steps of the method can be repeated and additionally or alternatively performed continuously over the service life of the fuel cell system. The at least one operating device can be at least one actuator of the fuel cell system.

[0014] In the adjustment step, the set target system pressure can be equal to or greater than the target system pressure in the new state of the majority of fuel cell modules under the same load condition of the fuel cell system. The current target pressure can be set higher than in the new state under the same load condition of the system in order to reduce the influence of the aging condition on the usable system performance. Thus, if the aging condition worsens, the target system pressure can be increased in order to maximize system performance even if the fuel cell modules degrade over their service life.

[0015] In the determination step, the aging state can also be estimated using an estimation method or measured using a determination method. An example of such a determination method is the so-called GCM (Galvanostatic Charging Method). This allows the aging state to be determined in a suitable manner with the specific accuracy required, depending on the circumstances.

[0016] According to one embodiment, an anode-side operating device can be controlled in the control step to regulate an anode-side pressure depending on the set target system pressure. The anode-side pressure can be an anode inlet pressure. The anode-side operating device can include a hydrogen metering valve. In this way, the anode-side degradation effects of the stack can be minimized, thereby optimizing the system's performance over its lifetime. Such anode-side pressure adjustment is easily implemented for most fuel cell systems.

[0017] In the control step, a cathode-side operating device can also be controlled to regulate a cathode-side pressure depending on the set target system pressure. The cathode-side pressure can be a cathode inlet pressure. The cathode-side operating device can have at least one compressor. This allows, above all, the cathode-side degradation effects of the stack to be minimized in order to optimize the system's performance over its lifetime. Such a cathode-side pressure adjustment is readily feasible if at least one air compressor is present.

[0018] Furthermore, in the determining step, at least one contribution variable can be determined that contributes to a change in the aging state. In the adjusting step, the set target system pressure can be generated depending on whether the at least one contribution variable can be influenced by adjusting the target system pressure, an anode-side pressure, and additionally or alternatively a cathode-side pressure. In this way, a particularly targeted and precise pressure adjustment can be made to effectively counteract degradation.

[0019] The at least one contribution can include an anode-side mass transport resistance, a cathode-side mass transport resistance, an anode-side loss of electrochemically active surface area, a cathode-side loss of electrochemically active surface area, and additionally or alternatively, a proton conductivity. The mass transport resistance can also be referred to as mass transfer resistance. Thus, relevant contributions can be considered in each case.

[0020] The approach presented here further provides a control unit configured to perform or implement the steps of a variant of a method presented here in corresponding devices. This embodiment of the invention in the form of a control unit also allows the problem underlying the invention to be solved quickly and efficiently.

[0021] In this context, a control unit can be understood as an electrical device that processes sensor signals and outputs control and / or data signals depending on them. The control unit can have an interface that can be implemented in hardware and / or software. In a hardware implementation, the interfaces can, for example, be part of a so-called system ASIC, which contains a wide variety of functions of the control unit. However, it is also possible for the interfaces to be separate integrated circuits or to consist at least partially of discrete components. In a software implementation, the interfaces can be software modules that are present, for example, on a microcontroller alongside other software modules.

[0022] A fuel cell system is also presented, comprising the following features: a plurality of fuel cell modules configured as proton exchange membrane fuel cells; at least one operating device; and an embodiment of a control unit mentioned herein, wherein the control unit is connected to the plurality of fuel cell modules and the at least one operating device in a signal-transmitting manner.

[0023] Also advantageous is a computer program product with program code that can be stored on a machine-readable medium such as a semiconductor memory, a hard disk memory or an optical memory and is used to carry out the method according to one of the embodiments described above when the program product is executed on a computer or a device.

[0024] The approach presented here is explained in more detail below using the accompanying drawings. Figure 1 shows a schematic representation of an exemplary embodiment of a fuel cell system;

[0025] Fig. 2 shows a flow chart regarding the generation of a set target system pressure by an embodiment of a control unit of a fuel cell system;

[0026] Fig. 3 shows a flow chart with regard to the generation of a set target system pressure taking into account cathode-side contribution variables by an embodiment of a control unit of a fuel cell system;

[0027] Fig. 4 shows a flow diagram for generating a set target system pressure taking into account anode-side contribution variables by an embodiment of a control unit of a fuel cell system; and

[0028] Fig. 5 is a flowchart of an embodiment of a method for operating a fuel cell system.

[0029] Before advantageous embodiments of the present invention are described below, the background and principles of embodiments will first be briefly explained.

[0030] A proton exchange membrane fuel cell system or PEM fuel cell system or PEMFCS (PEM = Proton Exchange Membrane, proton exchange membrane; FCS = Fuel Cell System) or polymer electrolyte fuel cell system comprises a plurality of individual cells arranged in a so-called stack. Such a stack ages over its lifetime, and several aging effects can occur. These aging effects can lead to reduced stack performance, i.e. the characteristic curve or pole curve of the stack can deteriorate. In other words, for the same electrical current the cell voltage can drop and thus the efficiency can be reduced. When a certain age-related power loss is reached, e.g. 10% or 20% of the start or beginning of life (BoL), the service life limit (End of Life, EoL) of the stack or system is reached. A distinction can be made between lifetime stack andDegradation of stack power and lifetime PEMFCS or degradation of net system power. The net system power P_SysNet is defined as the stack power P_Stack minus the auxiliary power of the PEMFCS, such as compressors, pumps, fans, heaters, etc. Due to the dominant power demand of the compressor (EAC = Electrical Air Compressor) in the air system, P_SysNet is often simplified to PSysNet's P_Stack-P_EAC.

[0031] When designing the fuel cell system and defining the trajectory of the control targets, P_SysNet must be optimized during system development. The optimum at BoL is systematically at lower operating pressures than at EoL. The reason for this is that the sensitivity of the stack pole curve to pressure changes changes with pressure degradation. This means that a pressure increase above, for example, 2.5 bar at BoL leads to a comparatively small increase in stack power AP_Stack,BoL = P_Stack,BoL(2.5 bar + Ap) - P_Stack,BoL(2.5 bar). At the same time, the power requirement for compression also increases, usually by AP_EAC. This means that there is no advantage to a further pressure increase, which results in: APSysNet (p>2.5 bar) < 0 at BoL. At EoL, the improvement in the pole curve is much more pronounced for the same pressure increase.If the mass transport resistances increase from the flow field to the catalyst layer, the stack's mass transport losses can be reduced or compensated by increasing the pressure in the flow field. Thus, despite a degraded stack, a condition similar to that at BoL can be achieved again, resulting in: APSysNet (p>2.5 bar) > 0 at EoL. With a pressure increase of, for example, 0.5 bar, the EoL stack can deliver performance comparable to BoL. Even an increase of 0.3 bar has a significant positive effect.

[0032] Such a pressure increase is possible in many fuel cell systems, for example during regular operation at partial load, which should be possible in all systems, or in the case of two-stage charging, for example with two compressors, especially EACs, with a two-stage EAC or with a combination of EAC and TAC (Turbine Driven Air Compressor). Pressure increase is possible on the anode side in many fuel cell systems because the mean pressure upstream of the hydrogen metering valve is usually above 5 bar. Pressure increase is also possible on the cathode side in many fuel cell systems, although the pressure is actively built up: In air systems with two-stage charging, where the advantages in terms of consumption and performance can be realized, with two EACs in series, with a two-stage EAC or EAC with two compressor wheels without recuperation or turbine, with EAC and TAC, usuallygenerally at loads below the rated load, where the advantage of consumption arises in real ferry operation, and often during operation at sea level when the air system still has a reserve for altitude operation, where the advantage of consumption in the cycle arises.

[0033] In the following description of advantageous embodiments of the present invention, the same or similar reference numerals are used for the elements shown in the various figures and having a similar effect, whereby a repeated description of these elements is omitted.

[0034] Fig. 1 shows a schematic representation of an embodiment of a fuel cell system 100. The fuel cell system 100 comprises a plurality of fuel cell modules 120 designed as proton exchange membrane fuel cells. The fuel cell modules 120 are arranged in a so-called stack 110. The fuel cell system 100 further comprises at least one operating device 130, 140, which is an actuator, a control element, or the like. Furthermore, the fuel cell system 100 comprises a control unit 150. The control unit 150 is connected to the plurality of fuel cell modules 120 and the at least one operating device 130, 140 in a signal-transmitting manner.

[0035] The control unit 150 is configured to operate the fuel cell system 100 or to control its operation. For this purpose, the control unit 150 comprises a determination device 152, a setting device 154, and a control device 156. Furthermore, the control unit 150 comprises an interface 151, which can also be referred to as a data interface or signal interface.

[0036] The determination device 152 of the control unit 150 is designed to determine an aging state 153 of the plurality of fuel cell modules 120 or of the stack 110 of fuel cell modules 120. In particular, the determination device 152 is designed to determine the aging state 153 using system data 115. The determination device 152 is designed to read in and receive the system data 115 from the fuel cell modules 120 or from the stack 110 via the interface 151. The determination device 152 is also designed to provide the aging state 153 in the form of a state signal and, optionally, additionally the system data 115 to the setting device 154. According to one embodiment, the determination device 152 is designed to estimate the aging state 153 using an estimation method or, alternatively, to measure it using a determination method.

[0037] The setting device 154 is configured to set a current target system pressure of the fuel cell system 100 depending on the aging state 153 in order to generate a set target system pressure 155. The setting device 154 is also configured to transmit the set target system pressure 155 to the control device 156. According to one exemplary embodiment, the setting device 154 is configured to generate the set target system pressure 155 such that, for the same load state of the fuel cell system 100, it is equal to or greater than the target system pressure in the new state of the plurality of fuel cell modules 120.

[0038] The control device 156 is configured to control the at least one operating device 130 and / or 140 of the fuel cell system 100 using the set target system pressure 155 in order to operate the fuel cell system 100. The control device 156 is configured to control the at least one operating device 130 and / or 140 using a control signal 157. The control signal 157 includes parameters or commands for operating the fuel cell system 100 at the set target system pressure 155.

[0039] According to one embodiment, the control device 156 is designed to control an anode-side operating device 130 in order to regulate an anode-side pressure depending on the set target system pressure 155. The anode-side operating device 130 comprises, for example, a hydrogen metering valve. Additionally or alternatively, according to one embodiment, the control device 156 is designed to control a cathode-side operating device 140 in order to regulate a cathode-side pressure depending on the set target system pressure 155. The cathode-side operating device 140 comprises, for example, at least one compressor or the like.

[0040] Fig. 2 shows a flowchart for generating a set target system pressure 155 by an embodiment of a control unit of a fuel cell system. The flowchart represents a process that is applied by the control unit from one of the figures described herein or a similar control unit and / or by the method from one of the figures described herein or a similar method. In addition to the system data 115, the aging state 153 of the plurality of fuel cells is also taken into account to generate the set target system pressure 155.

[0041] In other words, the flow diagram refers to a process in which, in addition to the usual relationships in a so-called top-level coordinator, such as current density / load, temperature, etc., i.e., in addition to the system data 115, the current stack SoH or aging state 153 is taken into account when determining the set target system pressure 155. This allows the net system performance of the fuel cell system to be optimized over its lifetime. The top-level coordinator is also designed, for example, for activity-based water management.

[0042] Fig. 3 shows a flowchart relating to the generation of a set target system pressure 155 taking into account cathode-side contribution variables by an embodiment of a control unit of a fuel cell system. The flowchart represents a process that is applied by the control unit from one of the figures described herein or a similar control unit and / or by the method from one of the figures described herein or a similar method. In particular, the cathode-side degradation effects of the stack are minimized in order to optimize the performance of the fuel cell system over its lifetime. In particular, a cathode pressure is adjusted over its lifetime. The flowchart is similar to the flowchart from Fig. 2, except that the aging state 153 is divided in more detail into contribution variables that contribute to a change in the aging state 153.The system data 115 also includes, for example, a table of operating points or the like.

[0043] The contributions shown here include a proton conductivity 353A, a mass transport resistance 353B or mass transfer resistance of the cathode, a mass transport resistance 353C or mass transfer resistance of the anode, an ECSA loss 353D of the cathode (ECSA = electrochemically active surface area), an ECSA loss 353E of the anode, a double layer conductivity 353F and an electrical conductivity 353G. The proton conductivity 353A is a generally pressure-sensitive loss contribution, the mass transport resistance 353B of the cathode and the ECSA loss 353D of the cathode are pressure-sensitive loss contributions on the cathode side, the mass transport resistance 353C of the anode and the ECSA loss 353E of the anode are pressure-sensitive loss contributions on the anode side, and the double-layer conductivity 353F and the electrical conductivity 353G are loss contributions independent of pressure changes.

[0044] To generate the set target system pressure 155, the proton conductivity 353A, the mass transport resistance 353B of the cathode, and the ECSA loss 353D of the cathode are taken into account with respect to the aging state 153. The set target system pressure 155 is primarily or exclusively to be understood as a cathode inlet pressure.

[0045] Fig. 4 shows a flowchart for generating a set target system pressure 155 taking into account anode-side contribution variables by an embodiment of a control unit of a fuel cell system. The flowchart represents a process that is applied by the control unit from one of the figures described herein or a similar control unit and / or by the method from one of the figures described herein or a similar method. The flowchart corresponds to the flowchart from Fig. 3 with the exception that, to generate the set target system pressure 155 with regard to the aging state 153, the proton conductivity 353A, the mass transport resistance 353C of the anode, and the ECSA loss 353E of the anode are taken into account here. The set target system pressure 155 is to be understood primarily or exclusively as an anode inlet pressure.This primarily involves minimizing the anode-side degradation effects of the stack to optimize the performance of the fuel cell system over its lifetime. In particular, the anode pressure is adjusted over the lifetime.

[0046] With reference to Fig. 3 and Fig. 4, it should be noted that at least one of the mentioned contribution variables 353A, 353B, 353C, 353D, 353E is determined by the control unit from one of the figures described herein or a similar control unit and / or by the method from one of the figures described herein or a similar method, which contributes to a change in the aging state 153, wherein the set target system pressure 155 is generated depending on whether the at least one of the mentioned contribution variables 353A, 353B, 353C, 353D, 353E can be influenced by setting the target system pressure, an anode-side pressure and / or a cathode-side pressure.

[0047] The stack SoH (State of Health) or aging state 153 is broken down into various loss / degradation contributions or contribution sizes 353A, 353B, 353C, 353D, 353E, 353F, and 353G. A distinction can be made between pressure-sensitive contributions, i.e., those influenced by changes in system pressure, and those that are not. A further distinction is possible within the pressure-sensitive loss contributions:

[0048] - Generally pressure sensitive, e.g. membrane humidity, which depends on anode and cathode operation.

[0049] - Pressure sensitive to anode pressure, e.g. anode transport losses.

[0050] - Pressure sensitive to cathode pressure, e.g. cathode transport losses.

[0051] With advanced SoH estimators and / or SoH determination methods, e.g., GCM (Galvanostatic Charging Method), it is possible to identify the loss contributions or contribution sizes individually. The procedure for pressure adjustment can be detailed accordingly with detailed information about the current loss / degradation contributions or contribution sizes of the stack SoH or aging state 153, as shown in Fig. 3 and Fig. 4. A combination of the approaches from Fig. 3 and Fig. 4 is also possible. In general, it is ensured that the resulting actual pressures of the various fluid systems remain within the permissible pressure differences, e.g., the pressure difference between anode and cathode across the membrane. This means that it is possible that a target pressure increase of the cathode also implies a target pressure increase of the anode, and vice versa.

[0052] Fig. 5 shows a flowchart of an embodiment of a method 550 for operating a fuel cell system. The method 550 for operating can be executed to operate a fuel cell system or to control the operation of a fuel cell system. The method 550 for operating can be carried out in conjunction with the fuel cell system from one of the figures described herein or a similar fuel cell system. The steps of the method 550 for operating can be executed using a control unit from one of the figures described herein or a similar control unit.

[0053] The operating method 550 comprises a determining step 552, a setting step 554, and a controlling step 556. In the determining step 552, an aging state of the plurality of fuel cell modules of the fuel cell system is determined. Subsequently, in the setting step 554, a current target system pressure of the fuel cell system is set depending on the aging state in order to generate a set target system pressure. Subsequently, in the controlling step 556, at least one operating device of the fuel cell system is controlled using the set target system pressure in order to operate the fuel cell system.

[0054] In summary, and in other words, according to exemplary embodiments, the aging state of the majority of fuel cells is taken into account when deriving the target operating pressure. Optionally, detailed information about degradation proportions, e.g., anode versus cathode, is also taken into account when determining the current target pressures of the anode and / or cathode.

[0055] The exemplary embodiments described and shown in the figures are selected only as examples. Different exemplary embodiments can be combined with one another in their entirety or with regard to individual features. One exemplary embodiment can also be supplemented by features of another exemplary embodiment. Furthermore, the method steps presented here can be repeated and performed in a different order than the one described.

[0056] If an embodiment comprises an “and / or” link between a first feature and a second feature, this is to be read as meaning that the embodiment according to one embodiment has both the first feature and the second feature and according to another embodiment has either only the first feature or only the second feature.

Claims

Claims 1. A method (550) for operating a fuel cell system (100), wherein the fuel cell system (100) comprises a plurality of fuel cell modules (120) designed as proton exchange membrane fuel cells, the method (550) comprising the following steps: Determining (552) an aging state (153) of the plurality of fuel cell modules (120); Setting (554) a current target system pressure of the fuel cell system (100) depending on the aging state (153) in order to generate a set target system pressure (155); and Controlling (556) at least one operating device (130, 140) of the fuel cell system (100) using the set target system pressure (155) in order to operate the fuel cell system (100).

2. Method (550) according to claim 1, wherein in step (554) of setting the set target system pressure (155) for the same load state of the fuel cell system (100) is equal to or greater than the target system pressure in the new state of the plurality of fuel cell modules (120).

3. Method (550) according to one of the preceding claims, wherein in the step (552) of determining the aging state (153) is estimated using an estimation method or measured using a determination method.

4. Method (550) according to one of the preceding claims, wherein in the step (556) of controlling an anode-side operating device (130) is controlled in order to regulate an anode-side pressure depending on the set target system pressure (155).

5. Method (550) according to one of the preceding claims, wherein in the step (556) of controlling, a cathode-side operating device (140) is controlled in order to regulate a cathode-side pressure depending on the set target system pressure (155).

6. Method (550) according to one of the preceding claims, wherein in the step (552) of determining, at least one contribution variable is determined which contributes to a change in the aging state (153), wherein in the step (554) of adjusting, the adjusted target system pressure (155) is generated depending on whether the at least one contribution variable can be influenced by adjusting the target system pressure, an anode-side pressure and / or a cathode-side pressure 7. The method (550) according to claim 6, wherein the at least one contribution variable comprises an anode-side mass transport resistance (353C), a cathode-side mass transport resistance (353B), an anode-side loss of electrochemically active surface area (353E), a cathode-side loss of electrochemically active surface area (353D) and / or a proton conductivity (353A).

8. Control device (150) which is designed to carry out the steps of a method (550) according to one of the preceding claims in corresponding devices (152, 154, 156).

9. A fuel cell system (100) comprising: a plurality of fuel cell modules (120) configured as proton exchange membrane fuel cells; at least one operating device (130, 140); and a control unit (150) according to claim 8, wherein the control unit (150) is connected to the plurality of fuel cell modules (120) and the at least one operating device (130, 140) in a signal-transmitting manner.

10. Computer program product with program code for carrying out the method (550) according to one of claims 1 to 7, when the program product is executed on a device.

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