DE102022200374A1 - Fuel cell system and method for operating a fuel cell system - Google Patents

Abstract

The invention relates to a fuel cell system with a large number of fuel cell stacks, each fuel cell stack being coupled to at least one inlet air path of the fuel cell system for supplying inlet air and to at least one exhaust air path of the fuel cell system for removing exhaust air. The fuel cell system also comprises at least one connection path, which is arranged between at least one exhaust air path, which is coupled to at least one first fuel cell stack, and at least one air supply path, which is coupled to at least one second fuel cell stack that is different from the at least one first fuel cell stack, and is designed to supply exhaust air from the at least one first fuel cell stack to the intake air of the at least one second fuel cell stack. At least one valve device is arranged in the at least one connection path, which valve device is designed to change a quantity of the exhaust air that is supplied to the intake air of the at least one second fuel cell stack.

Description

The present invention relates to a fuel cell system and a method for operating a fuel cell system.

State of the art

In fuel cell vehicles (FCV), in which, among other things, the drive energy is also supplied by one or more fuel cell systems (FCS), the oxidizing agent oxygen from the ambient air is usually used to Fuel cell to react with hydrogen to form water or water vapor and thus to deliver electrical power through electrochemical conversion.

The ambient air is to be supplied to the fuel cell stack by means of an air conveying system or air compression system. This requires a corresponding variable air mass flow and a corresponding pressure level.

Water management in the membrane and thus also in the cathode path is essential for the operation of a proton exchange membrane (PEM) stack. The membrane must be sufficiently wet to conduct protons. The risk of drying out is particularly high in the cathode entry area.

For this purpose, systems with external humidifiers, e.g. membrane humidifiers or water injection, or with higher system pressures can be operated in order to ensure humidification of the anode and cathode within the stack. At higher pressure, the air absorbs less water.

It is also possible for stacks to become internally humidified via the cathode and anode pathway, i.e. water is conducted from cathode to anode and water is also transported from anode to cathode in different cell areas. This requires a sufficiently high system pressure and a corresponding stack design with thin membranes. Another consequence of this is that the system cannot be operated in some operating ranges or can only be operated with a reduction in performance (derating), for example at high ambient temperatures, when driving uphill or with aged stacks.

Disclosure of Invention

The invention provides a fuel cell system and a method for operating a fuel cell system with the features of the independent patent claims.

Preferred embodiments are the subject of the respective dependent claims.

According to a first aspect, the invention relates to a fuel cell system with a large number of fuel cell stacks, each fuel cell stack being coupled to at least one inlet air path of the fuel cell system for supplying inlet air and to at least one exhaust air path of the fuel cell system for discharging exhaust air. Furthermore, the fuel cell system comprises at least one connection path, which is arranged between at least one exhaust air path, which is coupled to at least one first fuel cell stack, and at least one supply air path, which is coupled to at least one second fuel cell stack that is different from the at least one first fuel cell stack, and is designed for this purpose is to supply exhaust air from the at least one first fuel cell stack to the supply air of the at least one second fuel cell stack. At least one valve device is arranged in the at least one connection path, which valve device is designed to change a quantity of the exhaust air which is supplied to the intake air of the at least one second fuel cell stack.

According to a second aspect, the invention relates to a method for operating a fuel cell system according to the invention, wherein the at least one valve device is activated in order to control an amount of exhaust air from the at least one first fuel cell stack, which is fed to the intake air of the at least one second fuel cell stack.

Advantages of the Invention

The cathode of the at least one second fuel cell stack can be humidified by supplying exhaust air from a first fuel cell stack to the supply air of at least one further second fuel cell stack. The invention thus enables a flexible and variable possibility of humidifying the cathode supply air, which is advantageous for optimizing operation and also for reducing degradation.

Due to the humidification, the necessary stack entry pressure can be further reduced and thus the compressor requirements can be reduced and the system design of the compressor and fuel cell stack can be optimized, resulting in lower system costs.

In addition, the hydrogen consumption is reduced because the cathode entry area is better moistened and this area is then operated with better efficiency and the overall efficiency is thus improved. Furthermore, an external humidifier (e.g. membrane humidifier) can be dispensed with.

Furthermore, the supply air of the at least one second fuel cell stack can be cooled by the exhaust air of the at least one first fuel cell stack. This can increase efficiency and relieve the cooling circuit.

Another advantage is that there is no pressure loss due to external humidifiers, which leads to higher system efficiency and lower parasitic losses and thus improved hydrogen consumption.

The transfer of exhaust air from a first fuel cell stack into the supply air can take place at one or more points in a supply air path of a further fuel cell stack or also of several fuel cell stacks.

According to a further embodiment of the fuel cell system, changing the amount of exhaust air includes sealing or closing off the connection path. This can be done in particular for all operating conditions that do not require the supply of moist exhaust air to the supply air of another fuel cell stack or in which the enabling conditions are not present.

According to a further embodiment of the fuel cell system, this includes a control device which is designed to activate the at least one valve device in order to change the amount of exhaust air which is supplied to the intake air of the at least one second fuel cell stack. By controlling the valve device, the invention enables the supply air to be humidified as a function of the operating point. This makes it possible to extend the system operation or to maintain the full performance requirement. In the mostly mobile application, the fuel cell system must adequately cover a very large operating range with very different boundary and environmental conditions. Due to the possibility of controlling the amount of exhaust air that is made available to the supply air, the operating range can be expanded (especially in peripheral areas), so that derating can be avoided or the number of deratings can be delayed or reduced. The system design can be improved, which reduces costs.

According to a further embodiment of the fuel cell system, the control device is designed to determine the quantity of exhaust air supplied, taking into account pressures, mass flows and/or temperatures in the at least one exhaust air path, which is coupled to the at least one first fuel cell stack, and in the at least one intake air path, which is coupled to the at least one second fuel cell stack to set. This gives an additional degree of freedom. Pressures, mass flows, fluid composition, in particular humidity or water content and/or temperatures, both from the extraction fuel cell stack and from the target fuel cell stack can be taken into account.

According to a further embodiment of the fuel cell system, the control device is designed to supply exhaust air from the at least one first fuel cell stack to the supply air of the at least one second fuel cell stack only when a pressure in the at least one exhaust air path, which is coupled to the at least one first fuel cell stack, is greater as a print in the at least one supply air path, which is coupled to the at least one second fuel cell stack. This ensures a pressure gradient.

According to a further embodiment of the fuel cell system, the control device is designed to coordinate the individual fuel cell stacks with regard to the pressure level in such a way that a sufficient pressure difference between the extraction point for the exhaust air and the metering point for the supply air is ensured. For this purpose, the control device can control the at least one valve device in such a way that a desired quantity/mass or a desired quantity flow/mass flow is transferred between the fuel cell stacks.

According to a further embodiment of the fuel cell system, the control device is designed to coordinate the operation and the pressure levels by means of a power-sharing operating strategy.

According to a further embodiment of the fuel cell system, waste air from the at least one first fuel cell stack is continuously fed to the supply air of the at least one second fuel cell stack. The humidification and/or cooling thus takes place continuously. For this purpose, the fuel cell stacks can already be arranged according to the pressure conditions during implementation.

According to a further embodiment of the fuel cell system, the control device is designed to supply exhaust air from the at least one first fuel cell stack to the supply air of the at least one second fuel cell stack in intermittent operation (e.g. clocked, adaptive, triggered by parameters and/or triggered by events). Exhaust air is preferably fed to the supply air only at those operating points at which the cathode is not sufficiently moistened, particularly at the inlet. It can thus be provided a needs-based humidification or cooling. Due to the aging of the stack and also system degradation over the lifetime, the variable dosing can enable or improve an adaptive mode of operation.

According to a further embodiment of the fuel cell system, the control device is designed to control the valve devices by means of a learning and adaptive method. This results in a gradual improvement or optimization and an adaptation over the lifetime of the fuel cell system and over different applications.

According to a further embodiment of the fuel cell system, this comprises an exhaust valve and/or a turbine in the exhaust air path, with the exhaust air branching off in the exhaust air path downstream of the first fuel cell stack and upstream of the exhaust valve and/or the turbine. This ensures a sufficient pressure level.

According to a further embodiment of the fuel cell system, this includes a compressor device, wherein the compressor device is arranged in the supply air path, which is coupled to the at least one second fuel cell stack. The exhaust air is introduced into the supply air path preferably downstream after the compression. A cost reduction is possible since, for example, a maximum requirement for a compressor with regard to the pressure ratio can be reduced and/or a design of the fuel cell stack at the full load point can be improved, for example by lowering the pressure requirement and the parasitic power of the air compression system.

According to a further embodiment of the fuel cell system, the compressor device comprises a multiplicity of compressor stages, the at least one connection path being designed to supply exhaust air from the at least one first fuel cell stack to the intake air of the at least one second fuel cell stack at least between two compressor stages of the compressor device.

According to a further embodiment of the fuel cell system, this comprises an air-liquid heat exchanger, wherein the air-liquid heat exchanger is arranged in the supply air path, which is coupled to the at least one second fuel cell stack, and wherein the at least one connection path is designed to transport exhaust air from the supplying at least one first fuel cell stack to the supply air of the at least one second fuel cell stack upstream and/or downstream of the air-liquid heat exchanger.

According to a further embodiment of the fuel cell system, this includes a droplet separator, wherein the droplet separator is arranged in the exhaust air path, which is connected to the at least is coupled to a first fuel cell stack, and wherein the at least one connection path is designed to discharge exhaust air from the at least one first fuel cell stack downstream with respect to the droplet separator and to supply it to the supply air of the at least one second fuel cell system.

According to a further embodiment of the fuel cell system, this comprises at least one passive heat exchanger, wherein the at least one passive heat exchanger is designed to cool the air supply to the at least one first fuel cell stack using the exhaust air from the at least one first fuel cell stack, and the at least one connection path is designed for this purpose , discharge exhaust air from the at least one first fuel cell stack upstream of the passive heat exchanger and supply it to the supply air of the at least one second fuel cell system downstream of the passive heat exchanger. Passive heat exchangers relieve the liquid cooling circuit, since waste heat is disposed of with exhaust air. Furthermore, a turbine output can be increased by a higher turbine inlet temperature and no water separator is necessary. In these cases, the air-to-liquid heat exchanger can be small or even eliminated entirely by this measure, since the cooling can be accomplished by the moist air transferred in the connection path. In this case, extraction preferably takes place upstream of the passive heat exchanger, so that the exhaust air to be transferred is not too hot.

According to a further embodiment of the method for operating the fuel cell system, the fuel cell stacks are matched to one another or to one another in such a way that operating conditions for controlling the at least one valve device are present. In particular, the required pressure differences between the fuel cell stacks can be adjusted. The fuel cell stacks can be tuned by adjusting a power split between the fuel cell stacks and one or more energy storage devices coupled to the fuel cell stacks. Alternatively or additionally, the tuning of the fuel cell stacks can take place by setting a power distribution between the fuel cell stacks. Alternatively or additionally, the fuel cell stack can be tuned by adjusting the tuned operating parameters of a water management system in the fuel cell stack.

Within the scope of this invention, the water management can relate to all relevant operating conditions and operating parameters that are relevant for the fuel cell stack and the moisture management of the membrane. The target values determined from this are converted into operational management by a water management control system. The operating parameters of the respective fuel cell stack include the relevant stack-specific parameters such as pressure levels, mass flows, temperatures, excess stoichiometry, fluid compositions, such as moisture content or water content, activities of the media flows involved, air, hydrogen and coolant and the electrical variables, e.g. voltage, current density, current and impedance.

According to a further embodiment of the method for operating a fuel cell system, the fuel cell stacks are coordinated with regard to the operating parameters of the respective water management, in particular pressure levels, air mass flows, temperatures and fluid composition or moisture or water content.

According to a further embodiment of the method for operating a fuel cell system, performing water management in the fuel cell stack includes matching a pressure level and over-stoichiometry in a cathode path of the respective fuel cell stack, setting a stack temperature, setting a coolant temperature, setting an inlet humidity at the Cathode and/or adjustment of an exit activity at the cathode of the respective fuel cell stack.

According to a further embodiment of the method for operating a fuel cell system, operating parameters of the fuel cell system are also set taking into account at least one optimization goal, the at least one optimization goal comprising minimizing consumption and/or minimizing aging of the fuel cell stack.

According to a further embodiment of the method for operating a fuel cell system, at least one of pilot control, prediction, detection, plausibility checking and regulation is carried out as part of an operating strategy of the fuel cell system, taking into account the activation of the at least one valve device.

character list

• 1 ein Brennstoffzellensystem gemäß einer ersten Ausführungsform der Erfindung;
• 2 ein Brennstoffzellensystem gemäß einer zweiten Ausführungsform der Erfindung;
• 3 ein Brennstoffzellensystem gemäß einer dritten Ausführungsform der Erfindung;
• 4 ein Brennstoffzellensystem gemäß einer vierten Ausführungsform der Erfindung;
• 5 ein Brennstoffzellensystem gemäß einer fünften Ausführungsform der Erfindung;
• 6 ein Brennstoffzellensystem gemäß einer sechsten Ausführungsform der Erfindung;
• 7 eine Steuereinrichtung zur Verwendung in einem erfindungsgemäßen Brennstoffzellensystem; und
• 8 ein Flussdiagramm eines Verfahrens zum Betreiben eines Brennstoffzellensystems gemäß einer Ausführungsform der Erfindung.

Show it:

• 1 a fuel cell system according to a first embodiment of the invention;
• 2 a fuel cell system according to a second embodiment of the invention;
• 3 a fuel cell system according to a third embodiment of the invention;
• 4 a fuel cell system according to a fourth embodiment of the invention;
• 5 a fuel cell system according to a fifth embodiment of the invention;
• 6 a fuel cell system according to a sixth embodiment of the invention;
• 7 a control device for use in a fuel cell system according to the invention; and
• 8th a flowchart of a method for operating a fuel cell system according to an embodiment of the invention.

Elements and devices that are the same or have the same function are provided with the same reference symbols in all figures. The numbering of method steps is for the sake of clarity and is generally not intended to imply a specific chronological order. In particular, several method steps can also be carried out simultaneously.

Description of the exemplary embodiments

Further advantages, features and details of the invention result from the following description, in which various exemplary embodiments are described in detail with reference to the drawing.

1 shows a multiple fuel cell system 1000 with three fuel cell subsystems 14 to 16, which are each supplied with air from an environment 1 via an air supply path 201 to 203. FIG. Exhaust air flows from a respective exhaust air path 301 to 303 from the respective fuel cell stacks 11 to 13 into the environment 1. The intake air is filtered via air filters 2 to 4 and then compressed via compressors 5, 7, 9 and made available to the fuel cell stacks 11 to 13.

The exhaust air flows through turbines 6, 8, 10. The fluids from the anode circuits (purge gas, drain fluid or combinations of purge drain fluid) are then pumped into the exhaust air paths by means of valves (purge valve, drain valve or purge drain valves) 20-22 downstream of the turbines 6,8,10. The supply air paths 201 to 203 of the fuel cell stacks 11 to 13 are linked to the exhaust air paths 301 to 303 of the same fuel cell stack 11 to 13 through the fuel cell stack and through the stack bypass paths. The supply air flows through the respective fuel cell stack 11 to 13 and/or through a valve 29 to 31 through the stack bypass connection paths 23, 25, 27 and is supplied to the exhaust air upstream of the turbines 6, 8, 10 and optionally flows through a second Connection path 24, 26, 28 and is fed downstream with respect to the turbines 6, 8, 10 of the exhaust air.

Connection paths 401 to 403 (each with at least one line) are also provided, which connect the exhaust air from the first fuel cell stack 11 to the intake air of the second fuel cell stack 12, the exhaust air from the second fuel cell stack 12 to the intake air of the third fuel cell stack 13 and the exhaust air from the third fuel cell stack 13 to the Supply air of the first fuel cell stack 11 can supply. A valve device 17 to 19 is arranged in each connection path 401 to 403 in order to adjust the quantity of exhaust air supplied. The valve devices 17 to 19 also serve as a shut-off device and can be designed, for example, as a throttle valve with a sealing function.

The fuel cell system 1000 also includes a control device 500, which controls the valve devices 17 to 19 and the other actuators, such as air compressors 5, 7, 9 and e.g. valves 29 to 31 and other valves, in order to regulate the amount of air supplied (supply air or . exhaust air) and to control the pressure levels.

The invention is not limited to the number of fuel cell stacks 11 to 13 shown. Next, not all connection paths 401 to 403 between different fuel cell stacks 11 to 13 be realized. For example, the connection path 403 from the third fuel cell stack 13 to the first fuel cell stack 11 can be optional.

Further, the invention is applicable to various air system topologies. The compressors 5, 7, 9 can be single-stage or multi-stage, single-flow or multi-flow. The turbines 6, 8, 10 can be coupled to an electric compressor in the supply air path or to a turbocharger that is only driven by the respective turbine 6, 8, 10. The turbines 6, 8, 10 can also be optional. Instead of turbines, pressure control valves can also be installed.

2 shows another fuel cell system 2000. This differs from that in FIG 1 Fuel cell system 1000 shown in that the compressors of the second fuel cell subsystem 15 and the third fuel cell subsystem 16 each have two compressor stages 51, 52 and 56, 57, with air-liquid heat exchangers 58 to 60 being formed downstream in front of the fuel cell stacks 11 to 13.

The exhaust air from the first fuel cell stack 11 is supplied via a first connection path 404 with a first valve device 53 between the two compressor stages 51, 52 of the second fuel cell subsystem 15 and via a second connection path 405 with a second valve device 54 between the two compressor stages 56, 57 of the third fuel cell subsystem 16 supplied.

The exhaust air from the second fuel cell stack 12 is introduced via a third connection path 407 with a third valve device 55 between the air-liquid heat exchanger 58 and the fuel cell stack 13 of the third fuel cell subsystem 16 .

The exhaust air from the third fuel cell stack 13 can optionally be introduced via a fourth connection path 403 with a fourth valve device 19 between the compressor 5 and the air-liquid heat exchanger 59 and/or between the air-liquid heat exchanger 59 and the fuel cell stack 11 of the first fuel cell subsystem 14 become. Since the pressure loss across the air-liquid heat exchanger 59 is low, exhaust air can be introduced into the supply air of the first fuel cell subsystem 14 at two points.

In general, a single valve device 19 can in particular serve a number of metering points in the air inlet path of another fuel cell subsystem 14 to 16 or in the air inlet paths of a number of fuel cell subsystems 14 to 16 .

3 shows another fuel cell system 3000. This differs from that in FIG 1 Fuel cell system 1000 shown in that no turbines 6, 8, 10 are present and thus no energy recuperation from the exhaust gas takes place.

To control the pressure, control valves 70 to 72 are provided in the exhaust air path. The branch in the exhaust air path occurs downstream of the fuel cell stack 11 to 13 and upstream of a control valve 70 to 72.

4 shows another fuel cell system 4000. Only two fuel cell subsystems 14, 15 are provided here. The exhaust air from the first fuel cell stack 11 is introduced via a valve device 17 and a first connection path 408 between the compressor 7 and the air-liquid heat exchanger 60 of the second fuel cell subsystem 15 and optionally via the valve device 17 and a second connection path 409 between the air-liquid heat exchanger 60 and Fuel cell stack 12 of the second fuel cell subsystem 15 introduced.

The introduction point or feed point can thus be downstream or upstream with respect to the liquid heat exchanger 60 . Introducing it upstream has the advantage that the exhaust air can also contain liquid water droplets. If the dosing takes place before the liquid heat exchanger 60, i.e. in warm air, then these droplets can vaporize or evaporate better and the flow is also homogenized in the liquid heat exchanger 60. A further advantage is that the supply air is already cooled by metering in the moist air and the liquid heat exchanger 60 therefore has to dissipate less heat.

According to further embodiments, metering in just before the fuel cell stack 11 to 13 is also possible, provided the exhaust air does not contain a significant amount of liquid water or droplets.

5 shows another fuel cell system 5000, which differs from that in 4 fuel cell system 4000 shown differs in that in the exhaust air path 301 of the first fuel cell subsystem 14 a turbine 6 and furthermore a water separator 90 arranged between the fuel cell stack 11 and the turbine 6 are formed. The water separator 90 protects the turbine 6 from droplets, since the exhaust air from the fuel cell stack 11 can also contain liquid water in the form of droplets. The exhaust air is removed between the water separator 90 and the turbine 6 and fed to the air intake path 302 of the second fuel cell subsystem 15 via a connection path 410 with a valve device 17 . The branching downstream of the droplet separator 90 avoids the entry of liquid water into the fuel cell stack 12.

According to a further embodiment, a heat exchanger as in 4 provided, wherein the sampling point can also be upstream of the water separator 90 .

6 shows another fuel cell system 6000, which differs from that in 4 shown fuel cell system 4000 differs in that further passive heat exchanger (gas-gas heat exchanger) 100, 103 are provided, which cool the hot air in the supply air path through cooler exhaust air. The exhaust air is branched off in the exhaust gas path between the fuel cell stack 11 and the passive heat exchanger 100 of the first fuel cell subsystem 14 and introduced via a connection path 411 with a valve device 17 between the air-liquid heat exchanger 60 and the passive heat exchanger 101 of the second fuel cell subsystem 15. Since the gas-gas heat exchanger 100, 103 already significantly cools the compressed supply air, the supply air for the fuel cell stack 12 can be cooled by metering via the connection path 411 to such an extent that the gas-liquid heat exchanger 60 can be saved with an optimized design.

7 shows a control device 600 for use in a fuel cell system according to the invention, in particular one of the fuel cell systems 1000 to 6000 described above.

The controller 600 includes a first control unit 110, a second control unit 111, and first through n-th stack control units 112-1 through 112-n, where n denotes the number of fuel cell stacks 11-13. These components are each coupled to the valve devices 113 and can each be implemented as a separate computing device or by the same computing device.

The first control unit 110 enables a power split between an energy store (e.g. a high-voltage battery) and the fuel cell system 1000-6000. A requirement for a total electrical output is determined by the overall vehicle control system or by the drive train, which is necessary for implementing the travel trajectory and possibly other consumers in the vehicle. This power can be supplied by either energy storage or energy converters, or both, depending on the operating conditions and the level of power demand. The energy stores are preferably used for boosting when accelerating and for energy recuperation.

The second control unit 111 is used for power splitting between fuel cell subsystems (FCS energy converters). For this purpose, the required total power is divided among the fuel cell subsystems as a partial requirement. The division can be symmetrical or asymmetrical. For reasons of optimization, for example depending on aging, consumption, running time, etc., an asymmetrical division can be advantageous. For example, individual fuel cell stacks can be switched off at part load.

According to a further embodiment, the first control unit 110 and the second control unit 111 are combined in a coordinator.

The first to nth stack control units 112-1 to 112-n serve to control or regulate the individual fuel cell stacks 11 to 13. Different operating conditions for the individual fuel cell stacks 11 to 13 can result from different power requirements Pell, Pel2, Pel3. Furthermore, each fuel cell stack 11 to 13 can also have a different aging condition and therefore also requires different operating parameters.

The stack control units 112-1 to 112-n take over the water management of the fuel cell stack 11 to 13 and the moisture management of the membrane. Different parameters or operating conditions can be taken into account, which influence the membrane humidity or the membrane water content and other states in the fuel cell stack 11 to 13 . The most important parameters here are the pressure pCath at the cathode inlet, the excess air lambdaCath, the mass flow mfCath am cathode inlet, the associated current intensity iStack, the temperature TCool of the coolant, the temperature difference dTCool of the coolant across the fuel cell stack 11 to 13, the humidity fiCath at the cathode inlet and the impedance response of the fuel cell stack 11 to 13.

The stack control units 112 - 1 to 112 -n can also use these variables to calculate an outlet activity actCathout at the cathode outlet of the fuel cell stack 11 to 13 . The stack control units 112-1 to 112-n can achieve by regulation that these values are in a predetermined and variable, adjustable and/or operating mode dependent range. The moisture fiCath at the cathode inlet can be adjusted by controlling the valve devices 17-19, 53-55. This results in several degrees of freedom, with one degree of freedom also being able to be used with high dynamics.

wobei mAirStack die Luftmasse im jeweiligen Brennstoffzellenstapel 11 bis 13 und mAirStackStöchiometrisch das stöchiometrische Verhältnis der Luftmasse im jeweiligen Brennstoffzellenstapel 11 bis 13 bezeichnet.The following applies to the excess air at the cathode: $$\text{IambdaCath}=\text{mAirStack}/\text{mAirStackSt}\ddot{\text{O}}\text{chiometric},$$

where mAirStack denotes the air mass in the respective fuel cell stack 11 to 13 and mAirStackStöchiometric denotes the stoichiometric ratio of the air mass in the respective fuel cell stack 11 to 13.

In normal operation, lambdaCath is greater than 1 so that sufficient oxygen partial pressure is still available in the output area of the fuel cell stack 11 to 13 and the entire surface of the fuel cell stack 11 to 13 can be used to generate power, which is also necessary for the high degree of efficiency.

To get the same exit activity actCathout, the cathode pressure pCath can be increased and the excess air lambdaCath at the cathode decreased, or the cathode pressure pCath decreased and the excess air lambdaCath at the cathode increased.

Even with this degree of freedom, the stack control units 112-1 to 112-n can adapt the pressure level and coordinate it in such a way that the supply air can be humidified by using the connection paths with the valves 17-19, 53-55. A change in the temperature level Tcool also represents a degree of freedom, but with significantly less dynamics. This also affects the pressure level pCathSoll.

According to one specific embodiment, the stack control units 112-1 to 112-n are designed to control the valve devices 17-19, 53-55 in order to humidify and/or cool cathode supply air. This control represents an additional degree of freedom. In this case, coordination or optimization takes place between the stack control units 112-1 to 112-n.

According to a further embodiment, the second control unit 111 can also be designed to carry out or change the power distribution in such a way that the valve devices 17-19, 53-55 can be used due to the resulting pressure level to humidify and/or cool the cathode supply air.

Furthermore, the first control unit 110 can also be designed to carry out or change the power distribution in such a way that the valve devices 17-19, 53-55 can be used due to the resulting pressure level to humidify and/or cool the cathode supply air.

The control can be carried out situationally or reactively depending on measured values, i.e. without pre-control. Pre-control is also possible. Furthermore, the control can be optimized and carried out with advance trajectory planning, with the benefit and quality increasing significantly. A predictive optimization can take place within one level (first control unit 110, second control unit 111 or stack control units 112-1 to 112-n), cascaded or coupled across all levels.

The method, with the release or triggering of the transfer of a certain amount of media, duration, monitoring, diagnosis and control of the valve devices 17-19, 53-55, can be carried out based on signals from sensors as well as model-based (with real-time capable models).

8th shows a flowchart of a method for operating a fuel cell system, in particular one of the fuel cell systems 1000 to 6000 described above.

In this case, in a first method step S1, sensor data are generated which depend on the current operating conditions of the fuel cell system 1000 to 6000.

In a further method step S2, the at least one valve device 17-19; 53-55 are controlled by a control device 500, 600 in order to change and adjust the amount of exhaust air supplied. This can be a control method that regulates certain parameters, which can be determined using the sensor data, to specified values.

A release condition for a possible dosing can be checked during activation. Accordingly, it is required that the pressure pExhAusnahme at the point of consumption in the first fuel cell subsystem 14 to 16 is higher than the sum of the pressure pInDosierstelle at the dosing point in the second fuel cell subsystem 14 to 16 and the additional pressure losses dpLosses in the connection path 401-409 and the valve device 17- 19; 53-55, ie there must be a potential gradient: $$\text{pExhExtraction}\left(\text{FCS\_i}\right)>\text{pin dosing point}\left(\text{FCS\_k}\right)+\text{dpLosses}$$

Other release conditions can be taken into account, such as dilution conditions with regard to purge, drain or purge-drain processes through the anode path.

A possible dosing requirement is requested by the second fuel cell subsystem 14 to 16, i.e. humidification of the supply air, which is required in the second fuel cell subsystem 14 to 16.

The required dosing quantity or the necessary dosing quantity flow is determined from the conditions of the supply air at the dosing point in the second fuel cell subsystem 14 to 16 (in terms of temperature, pressure and/or mass flow) and the conditions of the exhaust air at the removal point in the first fuel cell subsystem 14 to 16 (in terms of humidity , water content, etc.) and the required stack entry conditions (required pressure, mass flow and/or humidity) are determined.

The dosing requirements can already be taken into account in the trajectory planning and the pre-control of the systems.

If the release condition is present and dosing is requested, a specific amount/mass or a specific volume flow/mass flow can be added.

The corresponding valve device 17-19; 53-55 is controlled in such a way that the required quantity or mass is removed or added. The valve means 17-19; 53-55 can be clocked here, for example in the case of an open/close valve, or regulated, for example in the case of a continuously operable valve.

The valve actuation is determined from the prevailing conditions, in particular from the pressure drop $$\text{dp}=\text{pExhaust}\left(\text{FCS\_i}\right)-\text{psupply air}\left(\text{FCS\_k}\right).$$

The steps can be executed continuously by the programs of the control device 500, 600, i.e. if conditions or releases or operating modes change, a reaction can be made immediately within a computing cycle (of around 10 ms).

In a multiple fuel cell system 1000-6000, an energy management system (such as the first control unit 110 in 6 ) Make the power split between the fuel cell subsystems 14-16.

An operating point for the air system is determined from a requested power Pel and the boundary conditions and the operating strategy. For example, a requested electrical power Pel requires an operating point
pAir, mAir = f(Pel, pamb, Tamb, fiamb, Tcool, dTcool, lambdaCath, vVeh, actCathout),
where pAir, mAir are air pressure and mass, pamb, Tamb are ambient pressure and mass, fiamb are ambient humidity, Tcool are cooling system temperatures, dTcool are temperature differences from inlet to outlet, lambdaCath are excess air, vVeh are vehicle speeds and actCathout are activity at the cathode outlet. Other dependencies are also possible.

$$\text{FCS}2\to \text{Pe}12\to \text{pAir}\mathrm{2,}\text{mAir}2\to \text{pAirDos}\mathrm{2,}\text{pAirEntn}\mathrm{2,}$$

$$\text{FCS}3\to \text{Pe}13\to \text{pAir}\mathrm{3,}\text{mAir}3\to \text{pAirDos}\mathrm{3,}\text{pAirEntn}\mathrm{3,}$$

wobei pAirDosl-3, pAirEntn1-3 den Druck bei der Dosierstelle bzw. Entnahmestelle bezeichnen.This follows for the case of three fuel cell subsystems FCS1-FCS3 $$\text{FCS}1\to \text{pe}11\to \text{pAir}\mathrm{1,}\text{mAir}1\to \text{pAirDos}\mathrm{1,}\text{pAirEntn}\mathrm{1,}$$

$$\text{FCS}2\to \text{pe}12\to \text{pAir}\mathrm{2,}\text{mAir}2\to \text{pAirDos}\mathrm{2,}\text{pAirEntn}\mathrm{2,}$$

$$\text{FCS}3\to \text{pe}13\to \text{pAir}\mathrm{3,}\text{mAir}3\to \text{pAirDos}\mathrm{3,}\text{pAirEntn}\mathrm{3,}$$

where pAirDosl-3, pAirEntn1-3 designate the pressure at the metering point or extraction point.

From this, the pressure differences between the extraction points and the dosing points can be determined or, conversely, also adjusted. This means that the humidification options can be ensured and coordinated using the energy management system. Real-time optimization algorithms can be used to determine and coordinate the operating conditions.

If the fuel cell stacks 11-13 age differently, this can also be taken into account in the control or regulation, i.e. the adaptive operating strategy takes the aging into account and the humidification options are also ensured over the service life via the power split.

Claims (15)

Fuel cell system (1000-6000), with: a plurality of fuel cell stacks (11-13), each fuel cell stack (11-13) having at least one air supply path (201-203) of the fuel cell system (1000-6000) for supplying air supply and having at least one exhaust air path (301-303) of the fuel cell system (1000-6000) coupled to discharge exhaust air; and at least one connection path (401-411) which is connected between at least one exhaust air path (301-303) which is coupled to at least one first fuel cell stack (11-13) and at least one supply air path (201-203) which is connected to at least one of the at least one first fuel cell stack (11-13) is coupled to a different second fuel cell stack (11-13), and is designed to separate exhaust air from the at least one first fuel cell stack (11-13) from the incoming air from the at least one second fuel cell stack (11-13 ) to supply wherein at least one valve device (17-19; 53-55) is arranged in the at least one connection path (401-411) and is designed to change a quantity of the exhaust air which is added to the intake air of the at least one second fuel cell stack (11-13 ) is supplied. Fuel cell system (1000-6000) according to claim 1 , having a control device (500; 600) which is designed to activate the at least one valve device (17-19; 53-55) in order to change the quantity of exhaust air which is added to the intake air of the at least one second fuel cell stack (11-13 ) is supplied. Fuel cell system (1000-6000) according to claim 2 , wherein the control device (500; 600) is designed to determine the quantity of exhaust air supplied, taking into account pressures, mass flows and/or temperatures in the at least one exhaust air path (301-303) which is connected to the at least one first fuel cell stack (11-13 ) is coupled, and in the at least one supply air path (201-203), which is coupled to the at least one second fuel cell stack (11-13), to set. Fuel cell system (1000-6000) according to claim 3 , wherein the control device (500; 600) is designed to supply exhaust air from the at least one first fuel cell stack (11-13) to the supply air of the at least one second fuel cell stack (11-13) only when a pressure in the at least one exhaust air path (301 -303) which is coupled to the at least one first fuel cell stack (11-13) is greater than a pressure in the at least one supply air path (201-203) which is coupled to the at least one second fuel cell stack (11-13). Fuel cell system (1000-6000) according to one of claims 2 until 4 , wherein the control device (500; 600) is designed to supply exhaust air from the at least one first fuel cell stack (11-13) to the supply air of the at least one second fuel cell stack (11-13) in intermittent operation. Fuel cell system (2000) according to one of the preceding claims, with a compressor device, wherein the compressor device is arranged in the supply air path (201-203) which is coupled to the at least one second fuel cell stack (11-13), the compressor device having a plurality of compressor stages (51, 52), and wherein the at least one connection path (401-411) is designed to supply exhaust air from the at least one first fuel cell stack (11-13) to the supply air of the at least one second fuel cell stack (11-13) at least between two compressor stages (51, 52) of the compressor device. Fuel cell system (2000; 4000) according to any one of the preceding claims, with an air-liquid heat exchanger (58-60), wherein the air-liquid heat exchanger (58-60) in the supply air path (201-203) is arranged, which with is coupled to the at least one second fuel cell stack (11-13), and wherein the at least one connection path (401-411) is designed to take exhaust air from the at least one first fuel cell stack (11-13) and the incoming air from the at least one second fuel cell stack (11-13 ) upstream and/or downstream of the air-liquid heat exchanger (58-60). Fuel cell system (5000) according to one of the preceding claims, with a drop separator (90), wherein the drop separator (90) is arranged in the exhaust air path (301-303) which is coupled to the at least one first fuel cell stack (11-13), and wherein the at least one connection path (401-411) is designed to discharge exhaust air from the at least one first fuel cell stack (11-13) downstream with respect to the droplet separator (90) and to feed it to the supply air of the at least one second fuel cell system (1000-6000). Fuel cell system (6000) according to one of the preceding claims, with at least one passive heat exchanger (100, 103), wherein the at least one passive heat exchanger (100, 103) is designed to transport the air supply to the at least one first fuel cell stack (11-13) through the To cool exhaust air from the at least one first fuel cell stack (11-13), and wherein the at least one connection path (401-411) is designed to exhaust air from the at least one first fuel cell stack (11-13) upstream of the passive heat exchanger (100, 103) discharged and fed to the supply air of the at least one second fuel cell system downstream of the passive heat exchanger (1000-6000). Method for operating a fuel cell system (1000-6000) according to one of the preceding claims, with the step: Activation (S2) of the at least one valve device (17-19; 53-55) in order to control an amount of exhaust air from the at least one first fuel cell stack (11-13) which is fed to the intake air of the at least one second fuel cell stack (11-13). becomes. procedure after claim 10 , wherein the fuel cell stacks (11-13) - by setting a power distribution between the fuel cell stacks (11-13) and at least one energy store coupled to the fuel cell stacks (11-13), and/or - by setting a power distribution between the fuel cell stacks (11- 13) and/or - by setting operating parameters of a water management system in the fuel cell stack (11-13) in such a way that operating conditions for controlling (S2) the at least one valve device (17-19; 53-55) are present. procedure after claim 11 , wherein the fuel cell stack (11-13) are coordinated with one another with regard to the operating parameters of the respective water management, the operating parameters comprising at least one of pressure levels, air mass flows, temperatures, fluid composition, humidity and water content. procedure after claim 11 or 12 , wherein the implementation of a water management of the fuel cell stack (11-13) a vote between a pressure level and an over-stoichiometry in a cathode path of the respective fuel cell stack (11-13), a setting of a stack temperature, a setting of a coolant temperature, a setting of an inlet humidity a cathode and/or setting an exit activity at the cathode of the respective fuel cell stack (11-13). Procedure according to one of Claims 11 until 13 , wherein operating parameters of the fuel cell system (1000-6000) are further adjusted taking into account at least one optimization goal, wherein the at least one optimization goal comprises minimizing consumption and/or minimizing aging of the fuel cell stack (11-13). Procedure according to one of Claims 11 until 14 , wherein at least one of a pilot control, a prediction, a detection, a plausibility check and a regulation is carried out as part of an operating strategy of the fuel cell system (1000-6000), taking into account the activation (S2) of the at least one valve device (17-19; 53-55).

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