DE102022201051A1 - Method for regulating at least one stack temperature of a fuel cell device and fuel cell device - Google Patents

Abstract

The invention relates to a method (56) for regulating at least one stack temperature of a fuel cell device (10), the fuel cell device (10) having a plurality of fuel cell stacks (12), with at least a first stack temperature of a first fuel cell stack (12a) of the plurality of fuel cell stacks (12) is detected. It is proposed that at least the first fuel cell stack (12a) has a first fuel metering device (58a) which is designed to supply the first fuel cell stack (12a) with fuel, and that the first stack temperature is determined by means of a first fuel metering by the first fuel metering device ( 58a) is regulated.

Description

The invention relates to a method for regulating at least one stack temperature of a fuel cell device according to the species of the independent claim. The invention further relates to a fuel cell device.

State of the art

Fuel cell devices are known which have a plurality of fuel cell stacks. Typically, the fuel cell stacks are cooled via a common air supply, with the stack temperature being regulated by adjusting the air flow. Individual fuel cell stacks can have different cooling requirements due to aging, their arrangement and/or production variability. For example, the fuel cell stack with the highest degradation can become too hot. In the controls known from the prior art, the cooling is adapted via the air flow to the hottest fuel cell stack. This has the disadvantage that the remaining fuel cell stacks can be cooled down too much, so that they can no longer be operated under optimal temperature conditions.

Disclosure of Invention

Advantages

The present invention describes a method for regulating at least one stack temperature of a fuel cell device, wherein the fuel cell device has a plurality of fuel cell stacks, wherein at least a first stack temperature is detected by a first fuel cell stack of the plurality of fuel cell stacks. According to the invention, at least the first fuel cell stack has a first fuel metering device, which is designed to supply the first fuel cell stack with fuel, and the first stack temperature is regulated by means of a first fuel metering by the first fuel metering device.

This has the advantage that the first stack temperature of the first fuel cell stack can be set independently of the stack temperatures of the remaining fuel cell stacks from the plurality of fuel cell stacks. In this way, all fuel cell stacks can be operated in an optimized manner, which enables the fuel cell device to be operated safely, with a long service life, and efficiently.

A fuel cell device is to be understood in particular as a device which in particular forms a part, in particular a functional part, in particular a structural and/or functional component, of a fuel cell system or the entire fuel cell system.

In this context, a fuel cell system is to be understood in particular as a system for stationary and/or mobile production, in particular electrical and/or thermal energy, using at least one fuel cell unit.

In this context, a fuel cell stack is to be understood in particular as a unit with a plurality of fuel cells. A fuel cell is provided in particular to convert at least one chemical reaction energy of at least one, in particular continuously supplied, fuel gas, in particular hydrogen, and at least one oxidizing agent, in particular oxygen, in particular into electrical energy. The fuel cell can be designed in particular as a solid oxide fuel cell (SOFC). A plurality of fuel cells is typically electrically connected to one another in series in a fuel cell stack.

A fuel supply means a source for a fuel that is supplied to the fuel cell device. For example, the fuel supply can be a connection for an external fuel supply line, for example from a natural gas network or from a hydrogen bottle. A fuel can be, for example, natural gas, hydrogen or a mixture of natural gas and hydrogen. Other fuels and mixtures of fuels are also conceivable in variants, for example the fuel B can have natural gas, hydrogen, methane, ammonia and/or coal gas or synthesis gas.

A plurality of fuel cell stacks should be understood to mean, in particular, at least two fuel cell stacks.

The fact that a stack temperature is detected is to be understood in particular to mean that a temperature of a fuel cell stack is measured. The temperature of the fuel cell stack can be measured directly on the fuel cell stack. It is also conceivable that the stack temperature is approximated or derived by measuring another temperature, for example an exhaust air or an exhaust gas of the fuel cell stack can be measured and the stack temperature can be determined from this temperature. For example, it is conceivable that, in a first approximation, the temperature of the exhaust air from the fuel cell stack at the fuel cell lenstack is measured and set equal to the stack temperature in a first approximation. Alternatively, it is conceivable that, as an approximation, the temperature of a waste material from the fuel cell stack is measured on the fuel cell stack and, in a first approximation, is set equal to the stack temperature. In advantageous variants, it is conceivable that the temperature is measured at a cathode exhaust gas duct and/or anode exhaust gas duct and is used to determine and/or approximate the stack temperature.

The fact that a stack temperature of a fuel cell device is regulated should be understood to mean in particular that at least one stack temperature of a fuel cell stack is regulated. The fact that a stack temperature of a fuel cell stack is regulated is to be understood in particular as meaning that operating parameters of the fuel cell stack are adapted or set in such a way that the stack temperature lies in a desired, predetermined range. In particular, it is possible for the operating parameters to be varied via a controller, in particular a control circuit, such that the measured stack temperature is within the specified temperature range. In this case, the measured stack temperature is preferably the controlled variable, which is compared with a specified setpoint value. The adjustable operating parameters of the fuel cell stack are the manipulated variables, which are adjusted by the controller in such a way that the deviation of the actual value of the measured stack temperature from the setpoint is minimized. Control, in particular feed-forward control, is also possible, in which, for example, if there is an excessive deviation in the measured stack temperature, the necessary adjustment of the operating parameters is determined on the basis of the value of the deviation, for example from a stored table of values provided for this purpose an analytical model and/or from a simulation model.

The heat balance or energy balance of the fuel cell stack is essential for the stack temperature. On the one hand, chemical energy is supplied to the fuel cell stack in the form of fuel and air. This is at least partially converted into electrical energy, which is taken from the fuel cell via a current or a current tap, the rest of the chemical energy supplied is heat generated during the reaction, which is dissipated via air cooling or cathode gas cooling and/or fuel cooling or anode gas cooling . The value of the current from the current draw is decisive for the amount of fuel that is converted in the fuel cell stack. If more fuel is supplied than can be oxidized according to the current draw, part of the fuel is discharged unprocessed together with the exhaust gases on the anode side of the fuel cell stack. Accordingly, the unreacted amount of fuel can be used for cooling.

The heat flow dQ/dt removed from the fuel cell stack by the air or cathode gas corresponds to the product of the mass flow of the air or the cathode gas dm/dt, the specific heat capacity of the air or the cathode gas and the temperature difference of the air or the cathode gas between the Input and output from the fuel cell stack ΔT. Conceivable operating parameters of the fuel cell stack, which are suitable for regulating or controlling the stack temperature, are the mass flow of the air or the cathode gas, for example via a speed or power of a compressor, a blower and/or a fan for the air supply; and/or a temperature of the air supplied to the fuel cell stack, for example the output of a preheater for the air or a connection or activation of a corresponding heat exchanger. In order to cool the fuel cell stack, in particular more air can be supplied to the fuel cell stack or the air flow can be increased

The heat flow dQ/dt removed from the fuel cell stack by the fuel or exhaust gases or anode gas corresponds to the product of the mass flow of the fuel or exhaust gases or the anode gas dm/dt and the specific heat capacity of the fuel or exhaust gases or the anode gas and the temperature difference of the fuel or the exhaust gases or the anode gas between the input and the output of the fuel cell stack ΔT. Conceivable operating parameters of the fuel cell stack that are suitable for regulating or controlling the stack temperature are the mass flow of the fuel or the anode gas, for example via a speed or power of a compressor, a blower and/or a fan for the fuel supply or for the anode recirculation or an anode recirculation circuit; and/or a temperature of the air supplied to the fuel cell stack, for example the output of a preheater for the air or a connection or activation of a corresponding heat exchanger. In order to cool the fuel cell stack, in particular more fuel or anode gas can be supplied to the fuel cell stack or the fuel flow or anode gas flow can be increased.

In this context, a recirculation circuit or an anode recirculation circuit should be understood to mean, in particular, a fluid connection or a fluid path, which cher is intended to supply an anode waste gas containing fuel or hydrogen and water from at least one fuel cell stack to a mixing point, at which the anode waste gas is mixed with the at least substantially pure fuel or hydrogen. In particular, the recirculation circuit is provided to feed fuel or hydrogen that has not been converted back to the fuel cell stack on the anode side. In particular, the mixture of the anode waste gas and the fuel or hydrogen is intended to be fed to the fuel cell stack on the anode side. A compressor can be designed as a blower, for example.

Another conceivable operating parameter of the fuel cell stack, which is suitable for regulating or controlling the stack temperature, is the current drawn from the fuel cell stack or the current draw. In this way, the current consumption or the electrical power dissipated can be reduced in order to cool the fuel cell stack. In this way, on the one hand, the heat generated during the oxidation reaction is reduced, and on the other hand, less of the fuel supplied to the fuel cell stack is oxidized, so that this unreacted amount of fuel contributes to the cooling.

The preferred temperature range of the stack temperature to which control is applied, or a target temperature or a target temperature range for the control, depends on the structural details of the fuel cell stack or the fuel cell device and is typically between 580 °C and 640 °C for SOFCs, preferably between 600°C and 630°C, more preferably between 610°C and 620°C. In the case of electrolyte-supported cells (Electrolyte Supported Cells—ESC), the preferred temperature range for the stack temperature is typically between 750° C. and 950° C., preferably between 800° C. and 900° C., particularly preferably between 850° C. and 875° C.

In fuel cell devices, all fuel cell stacks are typically supplied with a common air supply line. Based on the assumption that all fuel cell stacks should have the same setpoint temperature, the state of the art often provides coarse regulation of the stack temperatures by adjusting the air supply. Typically, the stack temperature of the fuel cell stack that deviates the most, preferably the most upwards, from the setpoint value is used and this stack temperature is regulated to the setpoint temperature or within the setpoint temperature range via the air supply. This has the disadvantage that all fuel cell stacks are cooled using the same air flow, so that there is the possibility that fuel cell stacks that have a lower cooling requirement than the fuel cell stack used for regulation are cooled too much and are not operated in an optimal temperature range. The present invention therefore offers the advantage that the fuel cell stacks can be individually temperature-controlled using a further independent control parameter or operating parameter. For example, the first fuel cell stack, which has a higher cooling requirement due to increased aging, can be cooled by increasing the first fuel metering by the first fuel metering device, without the air flow to all the fuel cell stacks having to be reduced, so that the rest of the plurality of fuel cell stacks continue to flow can be supplied with an air flow optimized for their temperature control.

A fuel metering device is to be understood in particular as meaning a device which is provided for metering the amount of fuel supplied to the associated fuel cell stack. For example, the fuel metering device can have an adjustable nozzle or a valve which adjusts the amount of fuel supplied to the fuel cell stack from a fuel supply line. It is also conceivable that the number of fuel cell stacks has a common fuel supply line, which supplies all fuel cell stacks with largely the same amount of fuel, and the first fuel metering device represents an additional fuel supply for the first fuel cell stack, which supplies a further, individually adjustable amount of fuel.

Further stack temperatures of further fuel cell stacks of the plurality of fuel cell stacks are advantageously recorded and the respective stack temperature is regulated by means of an adjustment of a fuel metering by a fuel metering device of the respective fuel cell stack. In particular, it is possible for the stack temperature to be regulated by the fuel cell stacks which are susceptible to a deviation in the stack temperature, for example due to their arrangement in the fuel cell device, for example in a particularly cool or particularly warm area. For example, it is conceivable that the majority of the fuel cell stacks are arranged directly adjacent to one another. The centrally arranged fuel cell stacks have more adjacent fuel cell stacks than the fuel cell stacks arranged on the outside, so that the fuel cell stacks arranged on the outside can cool down faster than the fuel cell stacks arranged on the inside. The stack temperature of each of the fuel cell stacks of the plurality of is particularly advantageous Fuel cell stacks are detected and the respective stack temperature is regulated by adjusting a fuel metering of the respective fuel cell stack. This enables a particularly precise and optimal operation of all fuel cell stacks, which enables a particularly safe, long-lasting and efficient operation of the fuel cell device.

Advantageous developments of the method are possible due to the features listed in the subclaims.

It is advantageous if at least one second stack temperature is detected by a second fuel cell stack of the plurality of fuel cell stacks and at least the second fuel cell stack has a second fuel metering device and the second stack temperature is regulated by means of a second fuel metering by the second fuel metering device. This enables a particularly precise and optimal operation of all fuel cell stacks, which enables a particularly safe, long-lasting and efficient operation of the fuel cell device.

The method is further improved if the first fuel metering or the first fuel metering device and the second fuel metering or the second fuel metering device are set during the regulation such that the total deviation of the first stack temperature and the second stack temperature from a target temperature is minimized. This enables particularly efficient regulation. In this way, the fuel cell stacks can in particular balance each other out during regulation.

The fact that the total deviation of the first stack temperature and the second stack temperature and, if applicable, a third stack temperature from a target temperature is minimized should be understood in particular to mean that during regulation, each stack temperature is no longer regulated to a target value, but rather the total deviation of the first stack temperature and the second stack temperature and possibly the third stack temperature is minimized. In other words, the value of the total deviation is minimized, regulated to zero if possible, with the total deviation being a scalar value which depends on the first stack temperature and the second stack temperature and possibly the third stack temperature. For example, the total deviation could be the sum of the amounts of the respective differences from the stack temperatures under consideration to the setpoint temperature. It is also conceivable that the total deviation is the sum of the mean square deviation of the stack temperatures considered from the target temperature. In principle, different approaches for the total deviation are conceivable, in particular it is possible that temperature deviations of different fuel cell stacks are evaluated to different degrees, for example the deviation of the first stack temperature from the target temperature can be weighted more heavily in the total deviation than the deviation of the second stack temperature from the target temperature.

A further improvement is possible if the first stack temperature is regulated by means of a first current draw from the first fuel cell stack. In particular, the first stack temperature is regulated by means of the first current draw and the first fuel metering device or first fuel metering. In other words, the fuel metering and the current draw are two operating parameters of the first fuel cell stack, which are adjusted as manipulated variables in order to regulate the stack temperature. In this way, finer regulation of the stack temperature is possible. In particular, the control can be optimized with regard to further target parameters. For example, regulation based on fuel metering alone could lead to an excessive drop in performance of the first fuel cell stack, which can be reduced by additional adjustment of the first current draw.

A particularly reliable regulation of the first current draw is possible if the first fuel cell stack is electrically connected in series with a second fuel cell stack of the plurality of fuel cell stacks and the first current draw is adjusted by a controllable first resistor which is electrically connected in parallel with the first fuel cell stack. This enables the current through the first fuel cell stack to be lowered in a particularly simple manner, so that the first current draw is lowered without the current through the second fuel cell stack being lowered. The second fuel cell stack advantageously has a controllable second resistor which is electrically connected in parallel with the second fuel cell stack. In this way, it is possible to set a second current draw of the second fuel cell stack, in particular to regulate a second stack temperature of the fuel cell stack. It is possible that further fuel cell stacks of the plurality of fuel cell stacks are each connected in parallel with an assigned controllable resistor, so that the respective current draw can be adjusted. It is conceivable that all fuel cell stacks are electrically connected in series. It is also conceivable that a group of fuel cell stacks are electrically connected in series. It is particularly conceivable that several groups of fuel cell stacks are present, the fuel cell stacks of a group are electrically connected in series with one another and the groups are electrically connected in parallel with one another.

In further variants, it is possible for the first fuel cell stack to be electrically connected in parallel with a third fuel cell stack of the plurality of fuel cell stacks and for the first current draw to be adjusted by a controllable first DC/DC converter or DC voltage converter, which is electrically connected in series with the first fuel cell stack is. In particular, this has the additional advantage that it is possible to simultaneously control or adjust the current draw from further fuel cell stacks connected in series with the first fuel cell stack, without changing the current draw from the third fuel cell stack and possibly further fuel cell stacks connected in series with the third fuel cell stack. It is conceivable for a group of several fuel cell stacks to be electrically connected in parallel and for each of the fuel cell stacks in the group of several fuel cell stacks to be assigned a DC/DC converter connected in series with the respective fuel cell stack. It is also conceivable for several groups of fuel cell stacks to be present, with the fuel cell stacks of a group being electrically connected in series with one another and the groups being electrically connected in parallel with one another, with a DC/DC converter being electrically connected in series in each group.

A power requirement for the majority of the fuel cell stacks is advantageously taken into account in the regulation. It is typically provided that the fuel cell device serves a power requirement which is provided by the plurality of fuel cell stacks. If, for example, the power consumption of one of the fuel cell stacks is reduced to regulate the stack temperature, then the electrical power provided by this fuel cell stack is also reduced. According to this advantageous variant of the method, one or more fuel cell stacks, advantageously all of the remaining fuel cell stacks, can now be regulated to a slightly higher current draw, so that the required power can be supplied overall. The slightly higher power consumption is associated with an increase in the respective stack temperatures, which can be adjusted in the control system by changing another operating parameter of the fuel cell stack, for example by increasing or adjusting a total air supply to all fuel cell stacks.

The method is further improved if, during regulation, the first current draw and a first fuel metering of the first fuel metering device are adjusted in such a way that the deviation of the first stack temperature from a target temperature, the deviation of the first current draw from the current target value, and the deviation of the metered by the first fuel metering device first amount of fuel to be minimized from a fuel setpoint. In this way, the regulation of the stack temperature can be further refined, in particular deviations in fuel metering and current consumption can also be minimized.

The fact that the deviation of the first stack temperature from a target temperature, the deviation of the first current draw from the current target value and the deviation of the first fuel quantity metered by the first fuel metering device from a fuel target value are minimized is to be understood in particular that not only the stack temperature is is regulated to a target value, but the deviation of the stack temperature, the fuel quantity and the current consumption from their respective target values are minimized. To this end, a scalar total operating value is advantageously minimized, which depends on the respective deviations of the stack temperature, the fuel quantity and the power consumption from their respective desired value. To this end, the stack temperature, fuel quantity and power consumption or their respective deviations from the respective desired values are advantageously converted into dimensionless values which can be offset against one another. In this case, in particular the deviations in the stack temperature, the fuel quantity and the power consumption can be weighted differently, depending on the technical requirements of the present fuel cell device. For example, a deviation in the amount of fuel can be weighted more heavily if a change in the amount of fuel is particularly unfavorable, or a deviation in the power consumption can be weighted less if such a deviation can be easily compensated for by the other fuel cell stacks.

In further variants, the regulation also takes into account the deviations in the stack temperature, the fuel quantity and the current draw from their respective desired values from at least one further fuel cell stack, advantageously from all fuel cell stacks. For this purpose, for example, a scalar overall operating value can be minimized, which depends on the respective deviations of the stack temperature, the fuel quantity and the power consumption from their respective desired value of all fuel cell stacks under consideration.

It is also advantageous if at least the first fuel cell stack has a first air metering has direction, which is adapted to supply the first fuel cell stack with air, and wherein the first stack temperature is regulated by means of the first air metering device. The fact that the stack temperature is regulated by means of the first air metering device is to be understood in particular to mean that the stack temperature is regulated by adjusting a first air metering, with the air metering being provided by the air metering device. In particular, the first stack temperature is regulated by means of the first fuel metering or the first fuel metering device and the first air metering or the first air metering device. In other words, the air metering and the current draw are two operating parameters of the first fuel cell stack, which are adjusted as manipulated variables in order to regulate the stack temperature. In this way, finer regulation of the stack temperature is possible. In particular, the control can be optimized with regard to further target parameters. For example, regulation based on the fuel metering alone could lead to an excessive drop in performance of the first fuel cell stack, which can be reduced by additional adjustment of the air metering. Advantageously, this variant can also be improved with a regulation of the current draw, which enables the current draw as a further control variable for the regulation.

An air metering device is to be understood in particular as a device which is provided for metering the amount of air supplied to the associated fuel cell stack. For example, the air metering device can have an adjustable nozzle or a valve which adjusts the amount of air supplied to the fuel cell stack from an air supply line. It is also conceivable that the number of fuel cell stacks has a common air supply line, which supplies all fuel cell stacks with largely the same amount of air, and the first fuel metering device represents an additional air supply for the first fuel cell stack, which supplies a further, individually adjustable amount of air.

Finer control is possible if the first fuel metering and a first air metering of the first air metering device are adjusted during the regulation in such a way that the deviation of the first stack temperature from a target temperature, the deviation of the first current draw from the current target value and the deviation of the metered by the first air metering device first air volume can be minimized by an air target value. For this purpose, a scalar total operating value is advantageously minimized, which depends on the respective deviations of the stack temperature, the air volume and the power consumption from their respective desired value. The regulation can be further refined if the deviation of the first amount of fuel from a desired fuel value is also minimized. For this purpose, a scalar overall operating value can be minimized, which depends on the respective deviations of the stack temperature, the amount of air, the amount of fuel and the power consumption from their respective setpoint.

A fuel cell device with a plurality of fuel cell stacks is also advantageous, with at least one first fuel cell stack having a first temperature sensor for detecting a first stack temperature, with the fuel cell device having at least one first fuel metering device, which is designed to supply the first fuel cell stack with fuel, and wherein the fuel cell device has a control unit which is designed to receive the first stack temperature and wherein the control unit is set up to set a first fuel metering for the first fuel cell stack and wherein the control unit is designed to carry out a method according to the present invention and the first stack temperature by means of regulate the first fuel metering by the first fuel metering device. Such a fuel cell device works particularly reliably and requires little maintenance.

The control unit is advantageously designed to set a first current draw from the first fuel cell stack and/or to control the at least one air metering device if an air metering device is present. At least the control device is designed in particular to control a common fuel supply for the plurality of fuel cell stacks.

Furthermore, the control unit is designed in particular to control a common air supply for the plurality of fuel cell stacks.

It has turned out to be particularly advantageous if the first temperature sensor is arranged on a cathode exhaust gas duct on the first fuel cell stack. This enables a particularly reliable estimation of the first stack temperature. The first temperature sensor is advantageously arranged directly on the cathode exhaust gas outlet of the first fuel cell stack.

The fuel cell device is further improved when the plurality of fuel cell stacks have a common fuel supply. In this way, the structure of the Simplify fuel cell device. A common fuel supply is to be understood in particular as meaning that the plurality of fuel cell stacks are fluidly connected to a fuel source and the same fuel quantity or largely the same fuel flow is supplied to each fuel cell stack. In the context of the present invention, the common fuel supply is designed to deliver a largely equal basic amount of fuel to the plurality of fuel cell stacks, while at least one first fuel metering device is provided for precisely setting the first fuel metering. In particular, it is therefore possible for the common fuel supply to provide a basic proportion of fuel metering to all fuel cell stacks that is largely the same for all fuel cell stacks, while the respective fuel metering devices enable an exact adjustment of the respective fuel metering of the associated, respective fuel cell stack.

The structure of the fuel cell device can also be simplified if the plurality of fuel cell stacks have a common air supply. A common air supply is to be understood in particular as meaning that the plurality of fuel cell stacks are fluidly connected to an air source and the same air quantity or largely the same air flow is supplied to each fuel cell stack.

character list

• 1 ein schematisches Schaltbild eines Ausführungsbeispiels einer Brennstoffzellenvorrichtung,
• 2 ein schematisches elektrisches Schaltbild des Ausführungsbeispiels,
• 3 ein schematisches elektrisches Schaltbild einer Variante der Brennstoffzellenvorrichtung,
• 4 das Verfahren gemäß der vorliegenden Erfindung und
• 5 einen Ausschnitt von einem Schaltbild einer weiteren Varianten der Brennstoffzellenvorrichtung.

Exemplary embodiments of the fuel cell device and the method are shown in the drawings and explained in more detail in the following description. Show it

• 1 a schematic circuit diagram of an embodiment of a fuel cell device,
• 2 a schematic electrical circuit diagram of the embodiment,
• 3 a schematic electrical circuit diagram of a variant of the fuel cell device,
• 4 the method according to the present invention and
• 5 a section of a circuit diagram of a further variant of the fuel cell device.

Description

The same parts are given the same reference numbers in the different design variants.

In 1 a schematic circuit diagram of an exemplary embodiment of a fuel cell device 10 is shown. The fuel cell device 10 includes, for example, two fuel cell units 12, a first fuel cell unit 12a and a second fuel cell unit 12b. In the exemplary embodiment shown, the fuel cell units 12 are designed as fuel cell stacks 12 which have a multiplicity of fuel cells, in the present case solid oxide fuel cells (SOFC). The first fuel cell unit 12a is in the in 1 shown embodiment, a first fuel cell stack 12a. The second fuel cell unit 12b is in the in 1 shown embodiment, a second fuel cell stack 12b.

Furthermore, the fuel cell device 10 comprises a multiplicity of processor units 14. Within the scope of this invention, a processor unit 14 is to be understood in particular as a unit or component of the fuel cell device 10 which is not a fuel cell unit 12. In the present case, the processor units 14 are units for the chemical and/or thermal preparation and/or post-processing of at least one medium to be converted and/or converted in a fuel cell unit 12, such as a fuel gas, air and/or an exhaust gas .

One of the processor units 14 is a heat exchanger 18 arranged in an air supply 16 for heating an oxygen-containing air L supplied to the fuel cell units 12. In the present case, the air L is supplied to a cathode space 20 of the fuel cell units 12, for example in normal operation , while in each case an anode space 22 reformed fuel RB, in the present hydrogen, is supplied. In the fuel cell units 12, the reformed fuel RB is electrochemically converted by the participation of oxygen from the air L, with the generation of electricity and heat.

The reformed fuel RB is produced by the fuel cell device 10 being supplied with fuel B, in the present case for example natural gas, via a fuel feed 24 , which fuel B is reformed in a further processor unit 14 , in the present case a reformer 26 .

Furthermore, the fuel cell units 12 are connected on the exhaust gas side to a further processor unit 14 , in the present case to an afterburner 28 . Exhaust gas from the fuel cell units 12 is supplied to the afterburner 28, in the present case cathode exhaust gas KA via a cathode Exhaust gas guide 30 and part of the anode exhaust gas AA via an anode exhaust gas guide 32. The cathode exhaust gas KA contains unused air L or unused oxygen, while the anode exhaust gas AA may contain unreacted, reformed fuel RB and/or possibly non-reformed fuel B . By means of the afterburner 28, the anode exhaust gas AA, or possibly contained therein unreacted, reformed fuel RB and / or possibly contained therein unreformed fuel B, with the admixture of the cathode exhaust gas KA, or the oxygen contained therein Air L, combusted, allowing additional heat to be generated.

The hot exhaust gas A produced during the combustion in the afterburner 28 is discharged from the afterburner 28 via an exhaust gas duct 34 via a further processor unit 14, in the present case via a heat exchanger 36. The heat exchanger 36 is in turn fluidically connected to the reformer 26 so that heat is transferred from the hot exhaust gas A to the fuel B supplied to the reformer 26 . Accordingly, the heat of the hot exhaust gas A can be used for reforming the fuel B supplied in the reformer 26 .

A further processor unit 14 , in the present case the heat exchanger 18 , is located downstream of the heat exchanger 36 in the exhaust duct 34 , so that the remaining heat of the hot exhaust gas A can be transferred to the air L supplied in the air duct 16 . Correspondingly, the remaining heat of the hot exhaust gas can be used for preheating the supplied air L in the air duct 16 .

In addition, the fuel cell device 10 has a return 38 by means of which part of the anode exhaust gas AA can be branched off from the anode exhaust gas line 32 and fed to an anode recirculation circuit 40 . The anode waste gas AA that is branched off passes through a further processor unit 14, in the present case a further heat exchanger 39.

By means of the anode recirculation circuit 40, the branched-off portion of the anode waste gas AA can be returned or fed back to the respective anode space 22 of the fuel cell units 12 and/or the reformer 26, so that the unreacted, reformed fuel possibly contained in the branched-off anode waste gas AA RB can subsequently be converted in the fuel cell unit 12 and/or the non-reformed fuel B contained in the branched-off anode waste gas AA can subsequently be reformed in the reformer 26 . As a result, the efficiency of the fuel cell device 10 can be further increased. In addition, fresh fuel B can be admixed via the fuel feed line 24 to the anode exhaust gas AA that has been branched off and recirculated in the anode recirculation circuit 40 . By means of the further heat exchanger 39, heat can then be transferred from the branched off anode waste gas AA from the return line 38 to the fuel mixture produced by the admixture of the fresh fuel B in the anode recirculation circuit 40 for thermal processing.

The supply of air L in the air supply 16, the supply of fuel B in the fuel supply 24 and the recirculation rate of the anode waste gas AA in the anode recirculation circuit 40 can be regulated and/or coordinated via compressors 42 in the respective lines.

Furthermore, the fuel cell device 10 has a heating element 44 for, in the present case additional, heating of the air L supplied to the fuel cell units 12 in a bypass line 46, as a result of which the operating efficiency of the fuel cell device 10 is increased.

For example, the first fuel cell stack 12a has a first temperature sensor 48a, which is arranged on a cathode exhaust gas outlet of the cathode exhaust gas duct 30 on the first fuel cell stack 12a. The first temperature sensor 48a thus detects in particular a temperature of the cathode exhaust gas KA on the first fuel cell stack 12a, which is a good approximation of the first stack temperature.

For example, the second fuel cell stack 12b has a second temperature sensor 48b, which is arranged on a cathode exhaust gas outlet of the cathode exhaust gas duct 30 on the second fuel cell stack 12b. The second temperature sensor 48b thus detects in particular a temperature of the cathode exhaust gas KA on the second fuel cell stack 12b, which is a good approximation of the second stack temperature.

As can be seen clearly, both fuel cell stacks 12 are supplied with air L via the air supply 16 and a compressor 42 in the exemplary embodiment. Fluidically, the two fuel cell stacks 12 are connected in parallel via the air supply 16 . The two fuel cell stacks 12 thus have a common air supply 16 , 42 . The two fuel cell stacks 12 thus have a common air supply, with air L conveyed by a compressor 42 being guided to the respective fuel cell stack 12 via two air supply lines 16 fluidically connected in parallel with one another. The common air supply 16 is in particular the same air flow L is largely supplied to both fuel cell stacks 12 .

in 1 In the exemplary embodiment shown, both fuel cell stacks 12 are supplied with fuel B or reformed fuel RB via the fuel supply and, for example, a reformer 26 . The fuel B and the reformed fuel RB are each transported by a compressor 42 on the fuel feed 24 and by a compressor 42 in the anode recirculation circuit 40 . In the exemplary embodiment, the fuel cell stacks 12 are fluidically connected in parallel to the reformer 26 . The two fuel cell stacks 12 thus have a common fuel supply 24 , 26 , 42 . In the exemplary embodiment shown, this common fuel supply 24, 26, 42 provides the two fuel cell stacks 12 with a largely identical basic quantity of fuel.

In other words, the two fuel cell stacks 12 have a common fuel supply, with fuel B delivered by the compressor 42 or reformed fuel RB being fed to the respective fuel cell stack 12 via two fuel feeds 24 fluidically connected in parallel with one another. The common fuel feed 24 means that the same fuel flow B or flow of reformed fuel RB is supplied to both fuel cell stacks 12 in particular.

in the in 1 shown embodiment, the first fuel cell stack 12a an additional first fuel metering device 58a. The first fuel metering device 58a is fluidically connected to the fuel feed 24, the first fuel metering device 58a being fluidically connected to the first fuel cell stack 12a just before the fuel feed 24 is connected. In this way, the first fuel metering device 58a is designed to introduce fuel B and/or reformed fuel RB into the fuel feed line 24 in the flow direction just before the first fuel cell stack 12a, so that in particular the fuel B or reformed fuel RB introduced through the fuel metering device 58a in the first fuel cell stack 12a is initiated. It is also conceivable that the first fuel metering device 58a is connected directly to the fuel cell stack 12a. The first fuel metering device 58a is provided to supply an individually metered amount of fuel B to the first fuel cell stack 12a. In this way, the amount of fuel that is routed jointly to all fuel cell stacks 12 via the fuel supply 24 can be adjusted by an additional amount of fuel.

In 1 For the sake of clarity, FIG. 1 does not show how the first fuel metering device 58a is supplied with fuel B or reformed fuel RB. It is conceivable that the first fuel metering device 58a is connected to the reformer 26 like the common fuel feed 24 . The first fuel metering device 58a can have its own compressor 42 . It is also conceivable that the first fuel metering device 58a has its own reformer 26 . It is also conceivable that the first fuel metering device 58a has its own fuel source, which is different from the fuel source of the common fuel supply 24. In alternative variants, it is possible for the first fuel metering device 58a to function as an adjustable metering valve or an adjustable throttle in the fuel supply 24 is formed in front of the first fuel cell stack 12a, so that the quantity of fuel B transported through the common fuel supply 24 to the first fuel cell stack 12a can be adjusted by this metering valve or this throttle without changing the quantity of fuel B transported to the second fuel cell stack 12b.

For example, the second fuel cell stack 12b in 1 shown embodiment, an additional second fuel metering device 58b, which is intended to supply the second fuel cell stack 12b with an individually meterable amount of fuel B or amount of reformed fuel RB. The second fuel metering device 58b is fluidically connected to the fuel feed 24, the second fuel metering device 58b being fluidically connected to the second fuel cell stack 12b just before the fuel feed 24 is connected.

2 illustrates the electrical interconnection of the two fuel cell units 12 or fuel cell stacks 12. In the exemplary embodiment shown, the first fuel cell stack 12a is connected in series with the second fuel cell stack 12b. For example, a DC/AC converter 50 is connected to the two fuel cell stacks 12 . This is provided in particular to convert the DC voltage generated by the fuel cell stack 12 into an AC voltage.

The first fuel cell stack 12a has a controllable first resistor 52a which is connected electrically in parallel with the first fuel cell stack 12a. The second fuel cell stack 12b also has a controllable second resistor 52b which is connected electrically in parallel with the second fuel cell stack 12b. In this way, the first stack temperature can also be set by setting the first Regulate the current draw via the first resistor 52a. Furthermore, a second stack temperature of the second fuel cell stack 12b can also be regulated by setting a second current draw from the second fuel cell stack 12b via the second resistor 52b.

However, it is also conceivable that only the first fuel cell stack 12a has the first resistor 52a and not the second fuel cell stack 12b. The stack temperatures could be regulated here, for example, by first setting the second stack temperature by setting the common air supply 16, 42 and then setting the first stack temperature by setting the first current draw via the first resistor 52a.

3 shows an alternative embodiment in which the fuel cell device 10 has four fuel cell stacks 12 . For example, the first fuel cell stack 12a and the second fuel cell stack 12b are electrically connected in series with one another, and a third fuel cell stack 12c and a fourth fuel cell stack 12d are electrically connected in series with one another. A controllable first electrical resistor 52a, which is provided for controlling the first stack temperature, is connected in series with the first fuel cell stack 12a. A controllable second electrical resistor 52b is connected in series with the second fuel cell stack 12b and is provided for controlling the second stack temperature. A controllable third electrical resistor 52c is connected in series with the third fuel cell stack 12c and is provided for controlling a third stack temperature of the third fuel cell stack 12c. A controllable fourth electrical resistor 52d is connected in series with the fourth fuel cell stack 12d and is provided for controlling a fourth stack temperature of the fourth fuel cell stack 12d.

Furthermore, a first DC/DC converter 54a is electrically connected in series with the first fuel cell stack 12a—and, for example, with the second fuel cell stack 12b. For example, a second DC/DC converter 54b is electrically connected in series with the third fuel cell stack 12c and the fourth fuel cell stack 12d. The first fuel cell stack 12a, the second fuel cell stack 12b and the first DC/DC converter 54a are electrically connected in parallel with the third fuel cell stack 12c, fourth fuel cell stack 12d and the second DC/DC converter 54b. In this case, the DC/DC converters 54 are provided for regulating or adjusting the current through or the current draw from the fuel cell stacks 12 connected in series that are assigned to them. In particular, the first DC/DC converter 54a is provided to set the first current draw from the first fuel cell stack 12a.

The power lines are then combined after the two DC/DC converters 54 and these are connected to the DC/AC converter 50 . In this way, it is possible in particular that, for example by changing the first current draw on the first fuel cell stack 12a via the first DC/DC converter 54a, without the third current draw on the third fuel cell stack 12c - which is electrically parallel to the first fuel cell stack 12a and the first DC / DC converter 54a is connected - to change. This enables individual regulation of the stack temperature of fuel cell stacks 12 electrically connected in parallel by adapting the current draw via the respective DC/DC converter 54.

The DC/DC converters 54 allow, in particular, a change in the current or current tap on all fuel cell stacks 12 electrically connected in series with the DC/DC converter 54 3 The variant shown with adjustable resistors 52a also makes it possible to selectively change the individual current draw on individual fuel cell stacks 12 within a group of fuel cell stacks 12 electrically connected in series. For example, it is conceivable that in 3 In the variant shown, the second stack temperature of the second fuel cell stack 12b is first regulated by adjusting the second current tap by the first DC/DC converter 54a and then the first stack temperature of the first fuel cell stack 12a is regulated by adjusting the first current tap by the first resistor 52a.

Further variants are conceivable in which groups of, for example, two, three or more fuel cell stacks 12 are connected electrically in series with a DC/DC converter 54 each and several such groups are connected electrically in parallel with one another. The fuel cell stacks 12 of such a group can advantageously each have a controllable resistor 52 electrically connected in parallel.

4 12 illustrates a method 56 for regulating the first stack temperature of the first fuel cell stack 12a of FIG 1 and 2 shown fuel cell device 10. For this purpose, the first stack temperature is determined in a first step S1. For this purpose, for example, the temperature is received by the first temperature sensor 48a and used as the first stack temperature. Then, in a second step, the first stack temperature temperature compared with a target value. For example, the setpoint is 615 °C. If the first stack temperature does not deviate from the desired value by more than a tolerance value, method 56 is continued via path A again with step S1. For example, the tolerance value is 5°C. If the stack temperature deviates from the setpoint by more than the tolerance value, method 56 continues via path B with step S3.

In step S3, the first fuel metering is changed via the first fuel metering device 58a. If the first stack temperature ascertained in step S1 is less than the target value, then the first fuel metering is lowered. If the first stack temperature ascertained in step S1 is greater than the target value, then the first fuel metering is increased. In this case, the increase or decrease in the first fuel metering can take place either by a predefined absolute or relative value. It is also conceivable that the increase or decrease in the first fuel metering depends on the extent of the deviation of the first stack temperature from the target value, for example it is conceivable that the first fuel metering increases or decreases more with a larger deviation. The method then continues again with step S1.

It is conceivable that, for example, an error counter is used to count the number of consecutive determinations of an excessive deviation in the determined first stack temperature in step S2 and, if there is a specified critical number of errors, for example ten, an error reaction takes place, for example the first fuel cell stack 12a is switched off . It is also conceivable that in step S2 or another step following step S1 it is checked whether the ascertained stack temperature falls below a critical lower value or exceeds a critical upper value and, if so, an error reaction takes place.

In a variant of method 56, it is conceivable that in step S2 the first fuel metering is increased if the first stack temperature determined in step S1 is greater than the setpoint, in particular by increasing the first fuel quantity metered by the first fuel metering device 58a of the first fuel cell stack 12a becomes. If the first stack temperature determined in step S1 is lower than the target value, a further operating parameter of the first fuel cell stack 12a is changed, for example an air supply 16, 42 common to all fuel cell stacks 12 is set in such a way that the air flow is lowered - for example by lowering a fan speed ; and/or in that a first current draw from the first fuel cell stack is increased; and/or in that a first quantity of air metered by a first air metering device 60a of the first fuel cell stack 12a is reduced (see 5 ). It is also conceivable that a first DC/DC converter 54a is electrically connected in series with the first fuel cell stack 12a and that the first current draw is increased in step S2 if the first stack temperature determined in step S1 is less than the setpoint value by the current is increased by the first fuel cell stack 12a by the first DC/DC converter 54a.

5 shows a further variant in which the first fuel cell stack 12a has a first air metering device 60a. The first air metering device 60a is fluidically connected to the air supply 16, the first air metering device 60a being fluidically connected to the first fuel cell stack 12a just before the air supply 16 is connected. In this way, the first air metering device 58a is designed to introduce air L into the air supply 16 in the flow direction just before the first fuel cell stack 12a, so that in particular the air L introduced through the first air metering device 60a is introduced into the first fuel cell stack 12a. It is also conceivable that the first air metering device 60a is connected directly to the fuel cell stack 12a. The first air metering device 60a is provided for supplying an individually metered quantity of air L to the first fuel cell stack 12a. In this way, the air quantity L that is routed jointly to all fuel cell stacks 12 via the air supply 16 can be adjusted by an additional air quantity L. FIG. The first air metering device 60a can have its own compressor 42 . In alternative variants, it is possible for the first air metering device 60a to be designed as a controllable metering valve or as a controllable throttle in the air supply 16 upstream of the first fuel cell stack 12a, so that this metering valve or this throttle causes the air that passes through the common air supply 16 to the first Fuel cell stack 12a transported amount of air L can be adjusted without changing the amount of air L transported to the second fuel cell stack 12b.

For example, the second fuel cell stack 12b in FIG 5 The variant shown has an additional second air metering device 60b, which is provided for supplying an individually metered quantity of air L to the second fuel cell stack 12b. The second air metering device 60b is fluidically connected to the air supply 16, the second air metering device 60b being fluidically connected to the second fuel cell stack 12b just before the air supply 16 is connected.

Claims (13)

Method (56) for regulating at least one stack temperature of a fuel cell device (10), the fuel cell device (10) having a plurality of fuel cell stacks (12), wherein at least one first stack temperature of a first fuel cell stack (12a) of the plurality of fuel cell stacks (12) is detected characterized in that at least the first fuel cell stack (12a) has a first fuel metering device (58a) which is designed to supply the first fuel cell stack (12a) with fuel, and that the first stack temperature is controlled by means of a first fuel metering by the first fuel metering device (58a) is regulated. Method (56) according to claim 1 , characterized in that at least a second stack temperature of a second fuel cell stack (12b) of the plurality of fuel cell stacks (12) is detected and at least the second fuel cell stack (12b) has a second fuel metering device (58b) and the second stack temperature by means of a second fuel metering by the second fuel metering device (58b) is regulated. Method (56) according to claim 2 , characterized in that during the regulation, the first fuel metering or the first fuel metering device (58a) and the second fuel metering or the second fuel metering device (58b) are set such that the overall deviation of the first stack temperature and the second stack temperature from a target temperature is minimized . Method (56) according to one of the preceding claims, characterized in that the first stack temperature is regulated by means of a first current draw from the first fuel cell stack (12a). Method (56) according to claim 4 , characterized in that the first fuel cell stack (12a) is electrically connected in series with a second fuel cell stack (12b) of the plurality of fuel cell stacks (12) and the first current draw is adjusted by a controllable first resistor (52a) which is electrically parallel to the first Fuel cell stack (12a) is connected. Method (56) according to any one of Claims 4 until 5 , characterized in that the first fuel cell stack (12a) is electrically connected in parallel with a third fuel cell stack (12c) of the plurality of fuel cell stacks (12) and the first current draw is adjusted by a controllable first DC/DC converter (54a) which is electrically is connected in series to the first fuel cell stack (12a). Method (56) according to any one of Claims 4 until 6 , characterized in that during the regulation the first current draw and the first fuel metering of the first fuel metering device (58a) are adjusted in such a way that the deviation of the first stack temperature from a setpoint temperature, the deviation of the first current draw from the current setpoint and the deviation of the first fuel metering device (58a) metered first amount of fuel can be minimized from a fuel setpoint. Method (56) according to one of the preceding claims, characterized in that at least the first fuel cell stack (12a) has a first air metering device (60a), which is designed to supply the first fuel cell stack with air, and wherein the first stack temperature is adjusted by means of the first Air metering device (60a) is regulated. Method (56) according to claim 8 , characterized in that during regulation the first fuel metering and a first air metering of the first air metering device (60a) are adjusted in such a way that the deviation of the first stack temperature from a target temperature, the deviation of the first fuel metering from the fuel target value and the deviation of the first air metering device (60a) metered first amount of air can be minimized by an air target value. Fuel cell device (10) with a plurality of fuel cell stacks (12), wherein at least one first fuel cell stack (12a) has a first temperature sensor (48a) for detecting a first stack temperature, wherein the fuel cell device (10) has at least one first fuel metering device (58a) which is designed to supply the first fuel cell stack (12a) with fuel, and wherein the fuel cell device (10) has a control device, which is designed to receive the first stack temperature and wherein the control device for setting a first fuel metering for the first fuel cell stack (12a) is set up and wherein the control device is designed to carry out a method (56) according to one of the preceding claims and to regulate the first stack temperature by means of the first fuel metering by the first fuel metering device (58a). Fuel cell device (10) after claim 10 , characterized in that the first temperature sensor (48a) is arranged on a cathode exhaust gas duct (30) on the first fuel cell stack (12a). Fuel cell device (10) according to one of Claims 10 until 11 , characterized in that the plurality of fuel cell stacks (12) has a common fuel supply (24, 26, 42). Fuel cell device (10) according to one of Claims 10 until 12 , characterized in that the plurality of fuel cell stacks (12) has a common air supply (16, 42).

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