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

Abstract

The invention relates to a method for operating a fuel cell system (100) having at least one fuel cell stack (101) and at least one air system (10), wherein in the at least one air system (10) a exhaust gas recirculation path (EGR) is provided between an intake path (11) to the at least one fuel cell stack (101) and an exhaust path (12) of the at least one fuel cell stack (101), wherein a mixing site (MS) between the exhaust gas recirculation path (EGR) to the intake path (11) is arranged downstream of an air filter (AF) and upstream of an air compression device (Comp), in particular a second air compression device, the method having: - determining a current content and a predicted content of liquid water in the mixing fluid at an inlet into the air compression device and / or upstream of the air compression device (Comp), - performing at least one measure (M1, M2, M3, M4) for reducing the content of liquid water in the mixing fluid at an inlet into the air compression device (Comp) in dependence on the determination.

Description

Technical Field

[0001] This invention relates to a method for operating a fuel cell system. The invention also relates to a computer program product, a control unit, and a fuel cell system. Background Technology

[0002] For vehicles (FCVs) whose driving energy is also provided by one or more fuel cell systems (FCS), oxidant oxygen from ambient air is typically used to react with hydrogen in the fuel cell to produce water (or water vapor) and thus provide electrical power through electrochemical conversion.

[0003] A key aspect of PEM stack operation is water management within the membrane and therefore in the cathode path. The membrane must be sufficiently wetted to conduct protons. The risk of drying out is significantly higher, especially in the cathode entry region. Therefore, different humidification schemes exist, including: - External humidification via membrane humidifier - Humidification via an internal fuel cell stack with anode-cathode synergy If necessary, combine with other options (as described below): - Water is sprayed through a water storage device. - Exhaust Gas Recirculation (EGR).

[0004] In exhaust gas recirculation, or EGR, a portion of the humidified fuel cell stack exhaust gas is diverted from the exhaust path to the intake path (usually for the same fuel cell stack).

[0005] Exhaust gas recirculation, or EGR, can be achieved in the following ways: 1. Utilizing the pressure drop between the extraction section in the exhaust gas path and the inflow section in the intake gas path; 2. Alternatively, an additional fluid compression device can be used to increase the pressure of the exhaust gas to a higher level.

[0006] The inflow section in the intake path where fresh air and exhaust gas flow mix can be called the mixing section.

[0007] In differential pressure driven exhaust gas recirculation, or EGR (Solution 1), an EGR valve (preferably adjustable and preferably sealed closed) is used to regulate and / or suppress the EGR fluid flow rate according to existing technology. Summary of the Invention

[0008] This invention provides a method for operating a fuel cell system having the features of the independent method claims. Furthermore, this invention also provides a corresponding computer program product, a corresponding control unit, and a corresponding fuel cell system having the features of the parallel claims. Here, the features and details described in conjunction with different embodiments and / or aspects of the invention are of course also applicable to other embodiments and / or aspects, and vice versa, so that the disclosures regarding various embodiments and / or aspects are always mutually referenced or may be mutually referenced.

[0009] According to a first aspect, the present invention provides a method for operating a fuel cell system having at least one fuel cell stack and at least one air system.

[0010] In at least one air system, an exhaust gas recirculation path is provided between an intake path leading to at least one fuel cell stack and an exhaust path from at least one fuel cell stack (or another fuel cell stack).

[0011] The mixing area between the exhaust gas recirculation path and the intake path is located downstream of the air filter and upstream of the air compressor, especially the second air compressor.

[0012] This method has the following steps: - Determine the current and predicted content of liquid water in the mixed fluid at the inlet of the air compressor or upstream of the air compressor; - Implement at least one measure, Used to reduce the content of liquid water in the mixed fluid at the inlet of the air compressor or upstream of the air compressor, based on the determination.

[0013] The steps of the method can be performed in a pre-given or altered order. The steps of the method can be performed simultaneously, at least partially simultaneously, and / or sequentially.

[0014] Fuel cell systems (or simply systems) are preferably used in mobile applications, such as in vehicles, particularly fuel-powered vehicles, and especially in commercial vehicles where long service life is required. Fuel cell systems can be used as the primary energy supply unit for vehicles. Furthermore, in the context of this invention, fuel cell systems can be used as an energy supply for auxiliary and / or power drives in vehicles, such as hybrid vehicles. However, fuel cell systems can also be used in stationary applications, such as in generators.

[0015] A fuel cell system may have multiple fuel cell stacks (or simply stacks), each fuel cell stack having multiple stacked fuel cells and associated functional systems, including: a dielectric system (air system or cathode system, fuel system or anode system, cooling system) and an electrical system. Preferably, the fuel cell system may include multiple modules, which are in the form of a single stack of multiple stacked fuel cells.

[0016] Exhaust air can also be referred to as waste gas or exhaust flow. The waste gas recirculation path can also be referred to as a waste gas recirculation line or exhaust air recirculation line. The air compressor can also be referred to as an air compressor or compressor.

[0017] The present invention recognizes that the exhaust gas flow is humid and may contain liquid water (water droplets). Furthermore, condensation may occur in the exhaust gas recirculation line, which could also generate water droplets there.

[0018] At the mixing section, water droplets can enter the air intake path. Downstream of the mixing section, water droplets can also be carried into the air compressor. If water droplets impact the compressor impeller, significant degradation can occur here. Furthermore, the gas bearings of the rotor-shaft system may be damaged. Other components, such as sensors, may also be damaged by liquid water or experience functional limitations.

[0019] The method is used to ensure component protection of the air compressor unit after the mixing section when using exhaust gas recirculation, or to extend the service life of the air compressor unit. Furthermore, the method also enables component protection for other components and reduces functional limitations caused by liquid water.

[0020] The method can be advantageously applied to two-stage compression compressor systems. It can also be applied to single-stage compressor systems.

[0021] Advantageously, the method may include measures to reduce the content of liquid water in the mixed fluid at the inlet of the air compressor or upstream of the air compressor, based on the determination: M1: Limits the EGR rate or the opening section of the EGR valve so that the humidity at the compressor inlet (downstream of the mixing section) drops below 100% (i.e., no more liquid water is present).

[0022] This measure can be supported (and / or at least partially replaced) by other measures for better complete mixing: for example, installing a mixer to vaporize any possible droplets, and / or other methodological measures M2 and / or M3 and / or M4 as described below.

[0023] M2: Load distribution (so-called balancing) between two air compressors (see...) Figure 4 This causes the humidity of the air supplied to the compressor (the mixed air after the mixing section) to decrease significantly, or even drop below 100%.

[0024] To reduce humidity at the compressor inlet, the first compressor can be operated at a high load and the second compressor at a low load.

[0025] The higher temperature level of the fresh air after the first compression stage allows for better absorption (evaporation / vaporization) of potential liquid water from the EGR fluid.

[0026] If conditions (not only the fuel cell stack operating conditions but also the surrounding environmental conditions) change, the load distribution can also be adjusted accordingly.

[0027] For example, if the risk of excessive humidity at the inlet of the second compressor is reduced, the first compressor can operate at a lower load.

[0028] For example, if the risk of excessive humidity at the inlet of the second compressor increases, the first compressor can operate at a higher load.

[0029] M3: It can reduce the cooling of fresh air, for example, through the intercooler, so that fresh air at a higher temperature can be used at the mixing section.

[0030] M4: Increases the fluid flow rate through the stack bypass path, thereby mixing the stack exhaust gas fluid with stack bypass air with low moisture content. The EGR fluid drawn downstream contains low liquid water content and has reduced humidity.

[0031] The advantage of this method is that it protects components of the air compression unit downstream of the mixing section, especially the compressor impeller and gas bearing, and improves their service life.

[0032] Advantageously, the at least one of the measures may have a first measure, according to which a limitation is imposed on the exhaust gas recirculation fluid, preferably on the cross-section of the exhaust gas recirculation path, particularly adaptively.

[0033] According to another advantage, the at least one measure may have a second measure, according to which a balance is performed between the first air compressor and the second air compressor, particularly adaptively, and the balance is preferably used for power distribution.

[0034] According to another advantage, the at least one measure may have a third measure, according to which the supply of air before the air compressor is reduced, particularly adaptively reduced.

[0035] According to another advantage, the at least one measure may include a fourth measure, according to which the fluid flow rate via the stack bypass path (13) is increased. In other words, the at least one measure may have a fourth measure, according to which the liquid water content in the EGR fluid is reduced by mixing dried fluid from the stack bypass path into the stack exhaust gas upstream of the EGR fluid extraction from the exhaust gas path, and thus reducing the humidity and water content in the exhaust gas path.

[0036] According to one implementation, it is conceivable that the first measure can be used as the primary measure, since control of exhaust gas recirculation can be set through exhaust gas recirculation.

[0037] It is conceivable that if the first measure has been activated, and the content of liquid water in the mixed fluid at the inlet of the air compressor is too high and / or the first measure is too restrictive, then the second and / or third and / or fourth measures shall be activated to support and / or replace the first measure.

[0038] According to one implementation, it is conceivable that the third measure may be used as available, and / or the third measure may initiate support for and / or replacement of the second measure.

[0039] According to one implementation, it is conceivable that the fourth measure can be used in relation to the operating point and / or the fourth measure can be activated in support of and / or in lieu of the second measure or another measure.

[0040] In principle, it is conceivable that the at least one measure may include multiple measures, which are performed sequentially, at least partially overlapping, and / or simultaneously.

[0041] Advantageously, when determining the current and predicted content of liquid water in the mixed fluid at the inlet of the air compressor, at least one of the following parameters during fuel cell system operation can be considered, particularly adaptively: - Operating parameters in the cathode path through at least one fuel cell stack include: -pressure, -temperature, -mass flow rate -Moore's flow - Humidity, and / or - Liquid water content, -Environmental parameters, including: -pressure, -temperature, - Humidity, and / or - Liquid water content, - System parameters in the intake path, exhaust path, and / or fuel cell bypass path, including: -pressure, -temperature, -mass flow rate -Moore's flow - Humidity, and / or - The content of liquid water.

[0042] In this way, it becomes possible to reliably determine the current and predicted content of liquid water in the mixed fluid at the inlet of the air compressor.

[0043] In principle, it can be conceivable that the steps of the method are performed sequentially, at least partially overlapping, and / or simultaneously.

[0044] Furthermore, it is conceivable that the method can be repeated.

[0045] Furthermore, it is conceivable that the method can be performed when exhaust gas recirculation is required.

[0046] According to another aspect, the present invention provides a computer program product comprising instructions that, when implemented by a computer, such as a computing unit of a control unit, cause the computer to perform a method that can be operated as described above. The same advantages as those described above in conjunction with the method according to the invention can be achieved by means of the computer program product. These advantages are hereby fully invoked.

[0047] The corresponding control unit provides another aspect of the invention. In the storage unit of the control unit, a computer program can be stored in the form of code, which, when implemented by the computing unit of the control unit, executes a method that can run as described above. The same advantages as those described above in conjunction with the method according to the invention can be achieved by means of the control unit. These advantages are fully referenced hereafter.

[0048] A corresponding fuel cell system with a corresponding control unit provides another aspect of the invention. The same advantages as those described above in combination with the method according to the invention can be achieved by means of a fuel cell system. These advantages are hereby fully described. Attached Figure Description

[0049] The invention, its further extensions, and its advantages are explained in more detail below with reference to the accompanying drawings. The drawings schematically illustrate: Figure 1 : An exemplary system topology Figure 2 Another exemplary system topology, Figure 3 Another exemplary system topology, Figure 4Another exemplary system topology, and Figure 5 An exemplary process of the proposed method. Detailed Implementation

[0050] In different drawings, the same parts of the invention are always given the same reference numerals, so these same parts are usually described only once.

[0051] Figures 1 to 5 This is used to explain the method developed for operating a fuel cell system 100 having at least one fuel cell stack 101 and at least one air system 10.

[0052] In at least one air system 10, an exhaust gas recirculation path (EGR) is provided between an intake path 11 leading to at least one fuel cell stack 101 and an exhaust path 12 from at least one fuel cell stack 101 (or another fuel cell stack).

[0053] The mixing section MS between the exhaust gas recirculation path EGR and the intake path 11 is located downstream of the air filter AF and upstream of the air compressor Comp, especially the second air compressor.

[0054] Exhaust gas recirculation, or EGR, can be achieved in the following ways: 1. Utilizing the pressure drop between the extraction section in the exhaust gas path and the inflow section in the intake gas path (see...) Figure 1 , 3 and 4); 2. Alternatively, an additional fluid compression device can be used to increase the pressure of the exhaust gas to a higher level (see...). Figure 2 ).

[0055] In differential pressure driven exhaust gas recirculation, or EGR (Scheme 1), an EGR valve EGRV (preferably adjustable and preferably sealed closed) is used to regulate and / or suppress the EGR fluid flow rate.

[0056] This method has the following steps: - Determine the current and predicted content of liquid water in the mixed fluid at the inlet of the air compressor, or upstream of the air compressor Comp. - Implement at least one of the following measures: M1, M2, M3, or M4. Used to reduce the content of liquid water in the mixed fluid at the inlet of the air compressor Comp, according to the determination.

[0057] The steps of the method can be performed in a pre-given or altered order. The steps of the method can be performed simultaneously, at least partially simultaneously, and / or sequentially.

[0058] The exhaust air is mostly humid and may contain liquid water (water droplets). In addition, condensation may occur in the exhaust gas recirculation (EGR) line, which can generate water droplets there.

[0059] At the mixing section MS, the water droplets can enter the intake path 11. Furthermore, downstream of the mixing section MS, the water droplets can be carried into the air compressor Comp. If the water droplets impact the compressor impeller, significant degradation may occur here. If liquid water enters the gas bearing path of the air compressor Comp, bearing damage and / or significant degradation may occur here.

[0060] The method is used to protect components of the air compressor unit after the mixing section MS when using exhaust gas recirculation (EGR) and to extend the service life of the air compressor unit Comp. Additionally, other components can be protected from liquid water and their functionality ensured (e.g., in the case of sensors).

[0061] This method can be advantageously applied to two-stage compression compressor systems (see [link]). Figure 4 This method can also be applied to single-stage compressor systems (see [link]). Figure 3 ).

[0062] Advantageously, the method may include measures (M1 and / or M2 and / or M3 and / or M4) for reducing the liquid water content in the mixed fluid at the inlet of the air compressor Comp, according to the determination: M1: Limits the EGR rate or the opening section of the EGR valve so that the humidity at the compressor inlet (downstream of the mixing section) drops below 100% (i.e., no more liquid water is present).

[0063] This measure M1 can be supported (and / or at least partially replaced) by other measures for better complete mixing: for example, installing a mixer to vaporize any possible droplets, and / or other methodological measures M2 and / or M3 and / or M4 as described below.

[0064] M2: Load distribution (so-called balancing) between two air compressors (see...) Figure 4 This causes the humidity of the air supplied to the compressor (the mixed air after the mixing section) to decrease significantly, or even drop below 100%.

[0065] To reduce humidity at the compressor inlet, the first air compressor Comp can be operated at a high load and the second air compressor Comp can be operated at a low load.

[0066] The higher temperature level of the fresh air following the first air compressor Comp allows for better absorption (evaporation / vaporization) of any possible liquid water from the EGR fluid.

[0067] If conditions (not only the fuel cell stack operating conditions but also the surrounding environmental conditions) change, the load distribution can also be adjusted accordingly.

[0068] For example, if the risk of excessive humidity at the inlet to the second air compressor Comp is reduced, the first air compressor Comp can operate at a lower load.

[0069] For example, if the risk of excessive humidity increases at the inlet to the second air compressor Comp, the first air compressor Comp can operate at a higher load.

[0070] M3: It can reduce the cooling of fresh air, for example, through an intercooler (if present), so that fresh air at a higher temperature is available at the mixing section MS.

[0071] M4: Increases the fluid flow rate through the stack bypass path, thereby mixing the stack exhaust gas fluid with the stack bypass air with a low moisture content, and the EGR fluid drawn downstream contains a low content of liquid water and has reduced humidity.

[0072] Figure 5 This illustrates one possible process of the method in the sense of the present invention.

[0073] The method relates to the operation of a system 100 with exhaust gas recirculation, or EGR, such that if exhaust gas recirculation, or EGR, is released by the system controller, the method can be initiated (step 105).

[0074] In step 110, the system can be run by EGR release.

[0075] In step 120, the current and future / predicted content of liquid water in the mixed fluid at the inlet of the air compressor Comp (downstream of the mixing section MS) is determined.

[0076] Here, the following parameters can be considered, especially adaptively, during the operation of the fuel cell system: - Operating parameters BP in the cathode path through at least one fuel cell stack 101 include: -pressure, -temperature, -mass flow rate -Moore's flow - Humidity, and / or - Liquid water content, -Environmental parameters UP, including: -pressure, -temperature, - Humidity, and / or - Liquid water content, - The system parameters SP in the intake path 11, exhaust path 12 and / or fuel cell bypass path 13 include: -pressure, -temperature, -mass flow rate -Moore's flow - Humidity, and / or - The content of liquid water.

[0077] In step 130, a first measure M1 may be initiated, which, in particular, adaptively restricts the cross-section of the exhaust gas recirculation fluid, preferably the exhaust gas recirculation path (EGR).

[0078] The maximum cross-sectional area of ​​the EGR path (or the maximum mass flow rate or molar flow rate of the EGR fluid) can be determined from the current or predicted parameters so that the mixed fluid supplied to the compressor is not too wet or there is no risk of droplets forming.

[0079] This variable limit can be continuously reset and adjusted in the system controller.

[0080] The first measure M1 can limit the maximum possible mass flow rate or molar flow rate of the EGR fluid.

[0081] If the first measure M1 is too limiting / restrictive, the second measure M2 can be applied as an additional or alternative measure in the case of a two-stage air compression system.

[0082] In step 140, the risk of exceeding a threshold determined for, for example, humidity / activity / water content, in the mixed fluid downstream of the mixing section MS at the inlet to the compression unit Comp can be assessed.

[0083] The following can be obtained from the steps and / or parameters listed above: - Is / when is there a risk of droplets impacting the compressor, or... - Whether / when the current limit derived from measure M1 is reached.

[0084] If the above situation occurs, a trigger signal can be set in step 141 to trigger the second measure M2 and / or the third measure M3 and / or the fourth measure M4.

[0085] In step 150, a second measure M2 may be initiated, according to which a balance preferably used for power distribution is adaptively performed between the first air compressor Comp and the second air compressor Comp.

[0086] Therefore, measure M2 can be configured to change the load distribution ("balance") between the first air compressor Comp and the second air compressor Comp, thereby reducing the humidity in the inflow to the second air compressor Comp, or suppressing the risk of droplet impact.

[0087] Here, the first air compressor Comp can be operated at a high load and the second air compressor Comp can be operated at a low load, so that the same fuel cell stack operating point can be exhibited, but the conditions before the second air compressor Comp are changed, which is particularly beneficial for component protection.

[0088] Therefore, it is possible to set and then adjust the restrictions on the EGR path accordingly (measure M1 can be adjusted) to achieve a higher EGR rate.

[0089] In step 160, a third measure M3 and / or a fourth measure M4 may be activated, wherein the cooling of the supply air L1 before the air compressor Comp is adaptively reduced, so that fresh air at a higher temperature is available at the mixing section MS.

[0090] The third measure M3 has a smaller dynamic response than the second measure M2, allowing it to be implemented in a cascaded manner, i.e., more slowly. The third measure can also be applied only when the second measure M2 cannot be implemented or reaches its limit.

[0091] The fourth measure M4 can be implemented as a measure with a higher dynamic response, so that the fourth measure can also be executed before measure M3.

[0092] Examples of the second measure M2 and / or the third measure M3 and / or the fourth measure M4 (especially as a response to changes in surrounding environmental conditions) can be described as follows: For example, if the ambient temperature decreases (at the same EGR rate, the humidity at the inlet of the second air compressor Comp will increase), the load on the first air compressor Comp can be increased and the load on the second air compressor Comp can be decreased, and / or the cooling of fresh air by the intercooler IC can be reduced, and / or the amount of fluid bypassed via the stack can be increased.

[0093] For example, if the ambient humidity decreases (e.g., when driving through a tunnel), more freedom is created (at the same EGR rate, the humidity at the inlet of the second air compressor Comp will be reduced), which can reduce the load on the first air compressor Comp.

[0094] If the fuel cell stack operating point changes, causing an increase in the water content of the exhaust gas fluid and therefore the EGR fluid, then as a component protection measure, the load on the first air compressor Comp can be increased, and / or the cooling of fresh air through the intercooler IC can be reduced, and / or the amount of fluid bypassed through the fuel cell stack can be increased.

[0095] The corresponding computer program product, the corresponding control unit ECU, and the corresponding fuel cell system 100 having the corresponding control unit ECU are other aspects of the present invention.

[0096] The above explanation of the embodiments is merely illustrative within the framework of examples. Of course, the various features of the embodiments can be freely combined with each other without departing from the scope of the invention, as long as it is technically meaningful.

Claims

1. A method for operating a fuel cell system (100), the fuel cell system having at least one fuel cell stack (101) and at least one air system (10). in, In the at least one air system (10), an exhaust gas recirculation (EGR) path is provided between the intake path (11) leading to the at least one fuel cell stack (101) and the exhaust path (12) from the at least one fuel cell stack (101). The mixing section (MS) between the exhaust gas recirculation path (EGR) and the intake path (11) is located downstream of the air filter (AF) and upstream of the air compressor (Comp), particularly the second air compressor. The method has the following characteristics: - Determine the current and predicted content of liquid water in the mixed fluid at the inlet of the air compressor (Comp) and / or upstream of the air compressor. - Implement at least one measure (M1, M2, M3, M4). Used to reduce the content of liquid water in the mixed fluid at the inlet of the air compressor (Comp) according to the determination.

2. The method according to claim 1, in, The at least one of the measures (M1, M2, M3, M4) includes a first measure (M1) according to which a restriction is imposed on the cross-section of the exhaust gas recirculation fluid, preferably the exhaust gas recirculation path (EGR), and is carried out adaptively.

3. The method according to claim 1 or 2, in, The at least one measure (M1, M2, M3, M4) includes a second measure (M2) according to which a balance is performed between the first air compressor (Comp) and the second air compressor (Comp), particularly adaptively, and the balance is preferably used for power distribution.

4. The method according to any one of the preceding claims, in, The at least one of the measures (M1, M2, M3, M4) includes a third measure (M3) according to which the cooling of the supply air (L1) before the air compressor (Comp) is reduced, particularly adaptively reduced.

5. The method according to any one of the preceding claims, in, The at least one of the measures (M1, M2, M3, M4) includes a fourth measure (M4) according to which the fluid flow rate via the stack bypass path (13) is increased.

6. The method according to any one of the preceding claims, in, If the first measure (M1) has been activated, and the content of liquid water in the mixed fluid at the inlet of the air compressor (Comp) is too high and / or the first measure (M1) is too restrictive, then the second measure (M2) and / or the third measure (M3) and / or the fourth measure (M4) are activated to support and / or replace the first measure (M1).

7. The method according to any one of the preceding claims, in, The at least one measure (M1, M2, M3, M4) includes multiple measures, which are performed sequentially, at least partially overlapping, and / or simultaneously.

8. The method according to any one of the preceding claims, in, When determining the current and predicted content of liquid water in the mixed fluid at the inlet of the air compressor (Comp), at least one of the following parameters during the operation of the fuel cell system (100) is considered, particularly adaptively: - Operating parameters (BP) in the cathode path through the at least one fuel cell stack (101) include: -pressure, -temperature, -mass flow rate -Moore's flow rate - Humidity, and / or - Liquid water content, - Environmental parameters (UP), including: -pressure, -temperature, - Humidity, and / or - Liquid water content, -System parameters (SP) in the intake path (11), exhaust path (12) and / or fuel cell bypass path (13) include: -pressure, -temperature, -mass flow rate -Moore's flow rate - Humidity, and / or - The content of liquid water.

9. The method according to any one of the preceding claims, in, The method steps are performed sequentially, at least partially overlapping, and / or simultaneously. And / or, the method is performed repeatedly. And / or, the method is performed when exhaust gas recirculation is required.

10. A computer program product, comprising instructions that, when implemented by a computer, cause the computer to perform the method according to any one of the preceding claims.

11. A control unit (ECU) having a computing unit and a storage unit, wherein code is stored in the storage unit, the code executing the method according to any one of the preceding claims when at least partially implemented by the computing unit.

12. A fuel cell system (100) having a control unit (ECU) according to the preceding claim.

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