DE102008010711A1 - Fuel cell system operating method for vehicle, involves designing control such that gas pressure of fuel and oxidant are coupled with each other by coupling control, and modifying gas flow rate without influence of gas pressure - Google Patents

Abstract

The method involves detecting and determining mass flow rate of gas, and controlling the gas mass flow rate in gas mass flow rate-control path to a reference variable according to control algorithm. A fuel control path, an oxidant control path and the gas mass flow rate-control path are provided with respective control algorithms in a control circuit. A control is designed in the control circuit such that gas pressure of fuel e.g. hydrogen, and oxidant e.g. air, are coupled with each other by a coupling control. The gas flow rate is modified without influence of the corresponding gas pressure. An independent claim is also included for a fuel cell system with a control arrangement for controlling a gas pressure value of gaseous fuel and gaseous oxidant in respective guide paths of a fuel cell.

Description

The The invention relates to a method for operating a fuel cell system with the features mentioned in the preamble of claim 1 and a Fuel cell system with a controller arrangement with the in the preamble of claim 13 mentioned features.

The Fuel cells are known to be a promising, forward-looking Form of energy conversion. In different areas could in the not too distant future completely new products establish. The basic principle of the fuel cell is based on the Oxidation of the fuel by electrochemical means in a galvanic Cell. This chemical energy is directly into electrical energy converted, which can be used in many ways. For example, it is possible to drive a vehicle using an electric motor or the on-board power supply already in a pre-production license.

The achievable efficiencies of a fuel cell are well above those of conventional energy conversion technologies. The Demand for reduction of energy consumption by more efficient Energy conversion technologies can be fulfilled.

For The use of sub-megawatts of hydrogen has made more sense Energy carrier exposed. This is with oxygen, for example, from the air to water oxidized. The hydrogen can be provided in different ways. He can for Example stored in pure form or by reforming of hydrocarbons be generated.

The both reactants are usually spatially separated separated, wherein the separation is designed so that they are not electrical is conductive. The released electrons in the reaction are thus forced to move through an electrical circuit from the anode to the cathode, causing them to do work can.

at The fuel cell reaction produces pure water, which is primarily accumulates at the cathode and removed with the exhaust gas becomes. Depending on the operating temperature, the water can be in liquid or gaseous form or in a mixture of both available.

to technical implementation of high-performance fuel cells On the basis of polymer membranes, there are currently two promising ones Technologies.

To the it is the well-known low-temperature fuel cell, whose Functionality through a sulfonated fluoropolymer (Nafion, etc.). The proton line is dependent on the water content of the polymer material. As a result, the operating temperature is at atmospheric pressure limited to below 100 ° C. For this guy is therefore a corresponding water management necessary. Most need The reaction gases are even moistened to dry out the To avoid membrane. Too much water in liquid However, shape can interfere with the supply of reaction gases.

Of the second type is the so-called high-temperature polymer membrane fuel cell. This is basically a phosphoric acid fuel cell with an operating temperature of approx. 160 ° C. As the proton conduction mechanism Here is independent of the water, no minimum moisture the membrane needed. Critical, however, is in this type the fuel cell the appearance of water in liquid Shape. In this case, there is a risk of discharging phosphoric acid from the polymer membrane and thus damage to the fuel cell. This can be the case in particular with cold starts.

The Separation of the two reactants in the fuel cell takes place often due to a very thin electrolyte membrane due to of pressure differences between the gas pressures of air and hydrogen can be destroyed very easily. The liquid operated Fuel cells do not have such significant pressure differential sensitivity but have other disadvantages.

The regulation of the gas pressures (of hydrogen and air) and of the air mass flow is therefore of particular importance in the fuel cell system, since these variables influence the achievable dynamics of the overall system and at the same time prescribe a maximum pressure difference between the gases for the fuel cell. The requirement for the coupling of the non-coupled by the physical system variables hydrogen and air pressure and their decoupling from the air mass flow make the application of a coupling control sense, for example, in Konigorski U .: Output variable coupling for linear multivariable systems. at Automatisierungstechnik 47 (1999) 4 pp. 165-170 is presented.

The DE 10 2006 005 175 discloses an apparatus and corresponding method for controlling the differential pressure between the cathode and anode of a fuel cell. It is proposed a device for controlling the differential pressure between an anode region and a cathode region of a fuel cell, wherein the Vor a differential pressure sensor for measuring the differential pressure between the anode region and the cathode region, a first actuator for controlling the inflow of fuel into the anode region and a control device for controlling and / or controlling the first actuator, wherein the control device for controlling and / or controlling the first actuator is formed on the basis of the signal of the differential pressure sensor. This type of control can not ensure very rapid control of the gas pressures and is particularly subject to a residual deviation, which manifests itself as an inaccuracy of the control, which must be deducted as a precaution of a possible pressure difference, whereby the dynamics and efficiency of a fuel cell can be reduced.

The DE 10 2005 018 070 A1 discloses a fuel cell system using an oxygen sensor for measuring the oxygen concentration in the cathode exhaust gas from the fuel cell stack. A controller provides a signal that drives a compressor that delivers air to a cathode input of the stack so that the compressor provides the desired oxygen to reach the desired cathode lambda. In one embodiment, the fuel cell system also uses an air flow meter that measures the amount of air that is applied to the compressor. The controller compares the oxygen input to the stack with the oxygen output from the stack for diagnostic purposes, such as determining the presence of leaks. A temperature sensor may be used to measure the temperature of the cathode effluent and a pressure sensor may be used to measure the pressure of the cathode effluent to thereby compensate for the water vapor in the cathode effluent.

DE 11 2005 000 587 T5 discloses a fuel cell system having a pressure regulating means for controlling the pressure of the fuel gas.

DE 101 19 377 B4 discloses a method for operating a fuel cell, in which an overpressure relative to the anode space is generated in the cathode space, at least for a short time, in order to force water out of the cathode space into the anode space.

DE 102 97 104 T5 describes a method of operating a fuel cell system having a regulated fuel delivery system and a controlled oxidant delivery system controlled by a controller to control one of the delivery systems in dependence on the dynamics of the other, particularly the mass flows of the fuel and the oxidant in dependence be controlled by the load current of the fuel cell. It also describes the use of differential equations to describe and build simulation models. The proposed solutions, however, are not intended to regulate, balance or maintain a pressure differential between the fuel and the oxidant, whereby a sensitive polymer membrane may be exposed to higher pressure differences that could destroy it. Although the coupled dynamic control of the mass flows of the fuel and the oxidizing agent can exert a certain compensatory effect on the pressure difference, it is not directly equivalent that be excluded by two mutually coupled mass flows of the gases involved large pressure differences in a dynamically changing system , Since the measuring variable used in each case is the other participating gas as the triggering control variable, the system already specifies that the regulation of the mass flow of the gas to be controlled can be carried out only with a delay, whereby a clear pressure difference is always unavoidable.

Of the Invention is therefore based on the object, the fuel pressure and the oxidant pressure of a gaseous operated Fuel cell each coupled so coupled together that They under all operating conditions in a large dynamic Operating range as constant as possible and given have predetermined pressure difference between them. Furthermore belongs It is an object of the invention, the pressure of the air mixture of to decouple the changes in the air mass flow.

zugrunde gelegt, das hier beispielhaft in vektorieller Form beschrieben ist. Zusammengefasst sind die obigen Differenzial-Gleichungen in einer Kurzform dargestellt: x .LW = ALW·xLW + BLW·uLW yLW = CLW·xLW wobei die verwendeten Systemgrößen wie folgt aufzuschlüsseln sind:
A_LW Systemmatrix, B_LW Eingangsmatrix, C_LW Ausgangsmatrix, x_LW n-dimensionaler Zustandsvektor, u_LW = [u_Komp, U_DK, u_RV] der Eingangsvektor und y_LW = [p_L, m . p_W] der Ausgangsvektor.For the controller design according to the invention is a linear, time-invariant system of the air and hydrogen routes of the fuel cell system

which is described here by way of example in vector form. In summary, the above differential equations are shown in a short form: x. LW = A LW .x LW + B LW · u LW y LW = C LW .x LW where the system sizes used are to be broken down as follows:
A _LW system matrix, B _LW input matrix, C _LW output matrix, x _LW n-dimensional state vector, u _LW = [u _comp , U _DK , u _RV ] the input vector and y _LW = [p _L , m. p _W ] the output vector.

The The present invention relates to a method for operating a Fuel cell system with a regulation of the gas pressure values of a gaseous Fuel and a gaseous oxidant in the respective supply lines of a fuel cell, wherein the Gas pressure values of the fuel gas used, preferably hydrogen, and the oxidizing agent used, preferably the air / oxygen, physically not coupled to each other.

• – der Gasdruck des Brennstoffs in einer Brennstoffregelstrecke nach einem ersten Regelalgorithmus auf eine vorgegebene erste Führungsgröße geregelt wird;
• – der Gasdruck des Oxidationsmittels in einer Oxidationsmittelregelstrecke nach einem zweiten Regelalgorithmus auf eine vorgegebene zweite Führungsgröße geregelt wird;
• – der Gasmassenstrom wenigstens eines der beiden Gase direkt oder indirekt erfasst und ermittelt wird, und nach einem dritten Regelalgorithmus auf eine dritte vorgegebene veränderbare Führungsgröße in einer Gasmassenstrom-Regelstrecke geregelt wird;
• – die Brennstoffregelstrecke, die Oxidationsmittelregelstrecke und die Gasmassenstrom-Regelstrecke mit ihren jeweiligen Regelalgorithmen in einen sie alle umfassenden Regelkreis einbezogen werden,

und in diesem umfassenden Regelkreis eine Regelung derart ausgeführt wird, dass der Gasdruck des Brennstoffs und des Oxidationsmittels durch eine Verkopplungsregelung aneinander gekoppelt werden und die Änderungen des Gasmassenstroms (m ._L) wenigstens eines der beiden Gase keinen Einfluss auf den korrespondierenden Gasdruck (p_L) ausüben, sind die Aufgaben der vorliegenden Erfindung gelöst.As a result of that

• - The gas pressure of the fuel in a fuel control path is controlled according to a first control algorithm to a predetermined first reference variable;
• - The gas pressure of the oxidizing agent is controlled in an oxidant control system according to a second control algorithm to a predetermined second reference variable;
• - The gas mass flow of at least one of the two gases is detected directly or indirectly and determined, and is controlled by a third control algorithm to a third predetermined variable command variable in a gas mass flow system;
• - The fuel control line, the oxidant control system and the gas mass flow control system with their respective control algorithms are included in a comprehensive them all control loop,

and in that extensive loop feedback control is carried out such that the gas pressure of the fuel and the oxidizing agent are coupled to one another by a Verkopplungsregelung and the changes of the gas mass flow (m. _L) of at least one of the two gases will not affect the corresponding gas pressure (p _L) exercise, the objects of the present invention are achieved.

According to one further embodiment of the method according to the present invention the control in the comprehensive control loop is fed back as one Regulation of one or more composite types of control executed a multi-variable controller. It Various types of known control loop applications can be used here, cascadable and in any complexity in relation used with each other.

In a preferred embodiment of the method according to the present Invention will be the regulation in the comprehensive control loop as a State control in the state space with a state feedback executed. It is known that the state regulation in is capable of one or more parameter parameters to be controlled to be able to regulate precisely and particularly dynamically. Further is characterized - as mentioned above - a Coupling of physically uncoupled parameter sizes possible. This makes it possible according to the invention the control deviations of the parameter sizes are very high to keep low, creating a maximum pressure difference between Fuel and oxidizer more efficient at a higher permissible value can be regulated without the mechanical To endanger the integrity of an electrolyte membrane.

In a particularly preferred embodiment of the present invention is the state control of the fuel control path and the oxidant control system in the comprehensive control circuit according to the invention a linear, time-invariant system of equations.

The state feedback is controlled in a preferred embodiment of the method of the present invention so that a coupling condition is met, which causes an equality of the gas pressures (p _W = p _L ) of the fuel and the oxidizing agent.

According to still another aspect of the present invention, the state feedback is controlled so as to satisfy a coupling condition that causes a predetermined pressure difference (Δp) of the gas pressures of the fuel (p _W ) and the oxidant (p _L ) and the gas pressure of the fuel therearound predetermined pressure difference is regulated higher than the gas pressure of the oxidizing agent.

Preferably is the predetermined pressure difference between the pressure of the fuel and the oxidizing agent in a range between 0.1 and 0.5 bar, more preferably substantially at 0.2 bar. This pressure difference is preferably for operating a gaseous working Fuel cell required.

According to the invention according to a further embodiment of the present invention Invention the first and second prescribing the respective gas pressure Command variable in a predetermined Relationship coupled together.

In a further preferred embodiment of the present invention become the air mass flow and the gas pressure of the oxidizing agent each regulated so that the gas pressure of the oxidant independently from the mass air flow.

beschrieben, das ohne ein D-Glied auskommt.The linear, time-invariant system of equations is in a preferred further embodiment of the present invention as a vectorial system of equations

described, which manages without a D-member.

In The comprehensive control circuit according to the invention is the guidance accuracy of the at least one reference variable according to a further embodiment of the present invention Invention predetermined by at least one state parameter of a Filters set.

There the detection of the state parameters of a state control often very may be complicated, is in a preferred embodiment of Method of the present invention in parallel with the comprehensive Control circuit operated an observer system, the outputs of the comprehensive control loop and the observer control path and the result of the comparison to the entrance of the observer route is supplied. The execution of the Observer Rig can be designed in a known manner.

To Another aspect of the present invention is the present Invention of a fuel cell system with a regulator assembly for Control of the gas pressure values of a gaseous fuel and a gaseous oxidizing agent in the respective ones Supply lines of a fuel cell, wherein the gas pressure values the fuel used, preferably hydrogen, and the one used Oxidizing agent, preferably the air / oxygen, physically not coupled to each other.

Thereby, that the fuel cell system according to the invention so regulated by means of a state feedback is that a coupling condition is met, in which the respective pressure or the partial pressure of the oxidizing agent and the fuel are equal to each other, and the pressure of the oxidant no dependence on the oxidant mass flow has, the objects of the present invention are achieved.

According to one further embodiment of the present invention the pressure difference between the pressure or the partial pressure of the Oxidant and the fuel 0.1 to 0.5 bar and more preferably essentially 0.2 bar. This value is due to the mechanical load limit specified the electrolyte membrane used, that is from both the polymer material used and the geometric ones Dimensions, in particular the membrane thickness dependent.

The has fuel cell system according to the invention further in a preferred embodiment of the present invention Means on the operation of the procedure according to one of the above allow described method features.

Further preferred embodiments of the invention will become apparent from the others, in the subclaims mentioned features.

The Coupling control of the gas pressures according to the invention of the fuel and the oxidizing agent allows one very fast and accurate, coupled pressure control of the two gases, such that a pressure difference required between the gas pressures can be met very accurately. As a result, on the one hand, the electrolyte-polymer membrane against mechanical destruction due to excessive Pressure difference efficiently protected and on the other hand a fuel cell by enabling a larger one Pressure difference can be operated more efficiently, for example, a to achieve better efficiency in energy conversion.

The Invention will be described below in embodiments the accompanying drawings explained. Show it:

1 a schematic representation of an embodiment of the invention control loop for the coupled control of the gas pressures of the fuel and the oxidizing agent and decoupled rules of the mass flow of the oxidizing agent with a state feedback;

2A a simulated waveform of the coupled gas pressures and the decoupled from the two gas mass flow of one of the gases when changing a coupled gas pressure;

2 B a simulated signal curve of the gas pressures coupled to one another and the mass flow of one of the gases decoupled from the two gas pressures when the decoupled mass flow changes, and

3A . 3B . 3C and 3D a non-linear total simulation with a PI coupling control.

1 shows a schematic representation of an inventive embodiment of the control loop for the coupled control of the gas pressures of the fuel and the oxidant and decoupled control of the mass flow of the oxidation by means of a state feedback.

The scheme shows a state _{controller system} with state feedback with a _{routing vector} w _LW = [p _LWsoll m. _LSoll ], a regulator matrix R and a prefilter matrix F.

The coupling of the gas pressures is defined as T ₂ = [1 0 -1]. The transformed output matrix is consequently C ~ LW = [C 1LW T 2 C LW ] T = [C 1LW C ~ 2EV ] T ,

By choosing the eigenvalues λ _Ri to determine the dynamics of the closed loop and by evaluating the equations C ~ 2EV (λ Ri I - A) -1 B LW p i = 0, i = 1, ..., m and V Ri = (λ Ri I - A LW ) -1 B LW p i one obtains m linear independent property vectors V _Ri , and parameter vectors p _i . The review of the necessary and sufficient condition for the existence of a coupling state control Rank [V R1 N C1 ] = n with N _C1 as the solution of the equation C _1LW N _C1 = 0 further ensures that the first two output variables air pressure and air mass flow can be controlled by their respective _{reference variables} .

When determining the parameter vectors, the remaining degrees of freedom for decoupling the air pressure from the air mass flow can be used here. The choice of the remaining n-m parameter vectors must then be made in accordance with the invention such that all rights vector vectors are linearly independent of one another, that is to say that rank V _R = n holds. From the right-eigenvectors and the parameter vectors, the controller matrix can then be calculated to: R = [p, ..., p n ] [V R1 , ..., V rn ]

The pre-filter F according to the invention by evaluation of the equation [B LW , V R1 ] [F ~, M] T = 0 certainly. In order to adjust the guiding _accuracy , the filter is additionally modified by a relationship F = F ~ · Q with Q = [C _1LW (B _LW R - A _LW ) ^-1 B _LW F ~] ^-1 . A preferred guide transfer function G _wLW (s) = C _LW (sI-A _LW + B _LW R) ^-1 B _LW F can be calculated with what has been said.

This in 1 illustrated integration element 20 is part of the controlled system. This reflects the behavior of the gas pressures and the mass air flow.

2A shows a simulated waveform of the coupled gas pressures and a decoupled from the two gas mass flow of one of the gases when changing a coupled gas pressure with the reference variable w1 = P _LWSoll .

If the setpoint of at least one of the two gas pressures leaps and bounds is changed, follow the respective gas pressures the Sollweitsprung with almost the same dynamics. At the same time remains the mass flow of the air is constant.

2 B shows a simulated waveform of the coupled gas pressures and decoupled from the two gas mass flow of one of the gases, preferably the air, when changing the decoupled mass flow with the reference variable w1 = m. _LSoll .

In these three arranged one above the other corresponding Diagrams shows that a change in mass flow the air does not affect the gas pressures of hydrogen and the air exerts.

3A . 3B . 3C and 3D shows a non-linear total simulation of a preferred embodiment according to the invention with a PI-Verkoppelungsregelung.

For the integration of the controller in a non-linear simulation of the entire fuel cell system, the coupling controller has been extended by an integral component in order to compensate for disturbances and nonlinearities. 3A to 3D show the result of such a simulation.

It can be seen that the gas pressures of the hydrogen p _W and the air p _L the respective corresponding setpoint jumps in 3A follow almost synchronously. In the present preferred embodiment of the present invention, the gas pressures of the air and the hydrogen are preferably between 2 and 3 bar.

The pressure difference Δp in 3B shows in case of faults or setpoint jumps only very small deviations from the predetermined setpoint, which in this case is preferably 0.2 bar in the present embodiment and corresponds to the mechanical strength of the electrolyte-polymer membrane used.

The main disturbances to the respective pressure control are on the air side by air mass flow changes and on the hydrogen side by cyclically opening the drain valve u _PV (often called engl. Purge valve) caused. At the time course of in 3C shown air mass flow m. _L is its intended decoupling of the in 3A Correspondingly represented air pressure p _L clearly visible.

In 3D the manipulated variables of the important actuators are shown relative in% values corresponding to the signal diagrams arranged above them. Here, the solid line shows the relative course of the control valve manipulated variable u _RV , the dashed line shows the relative course of a throttle control variable u _DK , the dotted line shows the relative course of the discharge valve manipulated variable u _PV and the dashed line shows the relative course of the Compressor control variable u _Comp .

The previous embodiments of the present invention are by way of example only, and not to be construed as limiting the present invention. The present invention can easily be applied to other applications become. The description of the embodiment is by way of illustration provided and not to the scope of the claims limit. Many alternatives, modifications and Variants are obvious to one of ordinary skill in the art without that he is the scope of the present invention would have to leave the, in the following claims is defined.

10

State feedback controller

12

controlled system

20

Integrator, integral component

A

matrix

B

input matrix

C

output matrix

m.

Mass flow change

R

knob matrix

Ap

pressure difference

p _L

Air pressure, Oxidant pressure

p _W

Hydrogen pressure, fuel pressure

p _LSoll

setpoint the air pressure, the oxidant pressure

p _WSoll

setpoint the hydrogen pressure, the fuel pressure

u _RV

Regulator valve control variable

u _DK

Throttle manipulated variable

u _PV

Drain valve manipulated variable

u _comp

Compressor control value

w

command variable

x

state variable

y

output

indices

L

air

W

hydrogen

LW

air and hydrogen

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• - DE 102006005175 [0012]
• DE 102005018070 A1 [0013]
• - DE 112005000587 T5 [0014]
• - DE 10119377 B4 [0015]
• - DE 10297104 T5 [0016]

Cited non-patent literature

• - Konigorski U .: Output variable coupling in linear multivariable systems. at Automatisierungstechnik 47 (1999) 4 pp. 165-170 [0011]

Claims (15)

A method for operating a fuel cell system with a regulation of the gas pressure values of a gaseous fuel and a gaseous oxidant in the respective supply lines of a fuel cell, wherein the gas pressure values of the fuel gas used, preferably hydrogen, and the oxidant used, preferably the / the air / oxygen, physically not together are coupled, characterized in that - the gas pressure of the fuel is controlled in a fuel control line according to a first control algorithm to a predetermined first reference variable; - The gas pressure of the oxidizing agent is controlled in an oxidant control system according to a second control algorithm to a predetermined second reference variable; - The gas mass flow of at least one of the two gases is detected directly or indirectly and determined, and is controlled by a third control algorithm in a gas mass flow system controlled to a third predetermined variable command variable; - The fuel control line, the oxidant control system and a gas mass flow control system with their respective control algorithms are included in a comprehensive them all loop, and in this comprehensive control loop, a control is performed such that the gas pressure of the fuel and the oxidant are coupled by a coupling control together and the changes of the gas mass flow (m. _L) of at least one of the two gases do not exert any influence on the corresponding gas pressure (p _L). Method according to claim 1, characterized in that that the regulation in the comprehensive control loop as a feedback Regulation of one or more composite types of control a multi-variable controller is executed. Method according to one of the preceding claims, characterized in that the control in the comprehensive control loop as a state control in the state space with a state feedback (R) is executed. Method according to claim 3, characterized that the state control of the fuel control path and the oxidant control system in the comprehensive control loop a linear, time-invariant system is based on equations. Method according to one of the preceding claims, characterized in that the state feedback is controlled so that a coupling condition is met, which causes an equality of the gas pressures (p _W = p _L ) of the fuel and the oxidizing agent. Method according to one of the preceding claims, characterized in that the state feedback is controlled so that a coupling condition is met, which causes a predetermined pressure difference (Δp) of the gas pressures of the fuel (p _W ) and the oxidant (p _L ) and the gas pressure of Fuel is regulated by this predetermined pressure difference higher than the gas pressure of the oxidant. Method according to Claim 6, characterized that the predetermined pressure difference preferably in a range between 0.1 and 0.5 bar, more preferably at 0.2 bar. Method according to one of the preceding claims, characterized in that the respective gas pressure predetermining first and second reference variable in one predetermined ratio are coupled together. Method according to one of the preceding claims, characterized in that the air mass flow and the gas pressure of the oxidizing agent are each controlled so that the gas pressure of Oxidizing agent is independent of the air mass flow. Method according to one of the preceding claims 4 to 9, characterized in that the linear, time-invariant system of equations as a vectorial system of equations

is described. Method according to one of the preceding claims 4 to 10, characterized in that in the comprehensive control loop the guidance accuracy of the at least one reference variable can be predetermined and by at least one state parameter a filter (F) is set. Method according to one of the preceding claims 4 to 11, characterized in that parallel to the comprehensive Control circuit is operated by a observer, wherein the Outputs of the comprehensive control circuit and the observer control system be compared and the result of the comparison the receipt of the Observer control line is supplied. Fuel cell system with a regulator arrangement for controlling the gas pressure values of a gaseous fuel and a gaseous oxidant in the respective supply lines of a fuel cell, wherein the gas pressure values of the fuel used, preferably hydrogen, and the oxidant used, preferably the / the air / oxygen, are not physically coupled to each other characterized in that the fuel cell system is controlled by state feedback (R) so as to satisfy a coupling condition in which the respective pressure or partial pressure of the oxidant (p _L ) and the fuel (p _W ) are equal to each other, and Pressure of the oxidizing agent has no dependence on the oxidant mass flow ( _m.L ). Fuel cell system according to claim 13, characterized characterized in that the pressure difference between the pressure or the partial pressure of the air-gas mixture and the hydrogen gas between 0.1 to 0.5 bar, more preferably substantially 0.2 bar is. Fuel cell system according to one of the claims 13 to 14, characterized in that the fuel cell system Having means for operating the method according to one of Claims 1 to 12 allow.