Method for operating a fuel cell device, and fuel cell device

Abstract

The invention relates to a method (10a; 10b) for operating a fuel cell device (12a) which is connected to a power network, wherein in at least one method step, the provision of electric current by the fuel cell device (12a) is adjusted in the event of a temporary drop in voltage of the power network. It is proposed that a fluid supply (14a) of the fuel cell device (12a) during the temporary drop in voltage of the power network is at least partially maintained.

Description

[0001] Description

[0002] Method for operating a fuel cell device and a fuel cell device

[0003] State of the art

[0004] A method for operating a fuel cell device which is connected to a power grid has already been proposed, wherein in at least one method step a provision of electrical current by the fuel cell device is adapted in the event of a brief voltage drop in the power grid.

[0005] Disclosure of the invention

[0006] The invention is based on a method for operating a fuel cell device which is connected to a power grid, wherein in at least one method step a provision of electrical current by the fuel cell device is adapted in the event of a brief voltage drop in the power grid

[0007] It is proposed that a fluid supply to the fuel cell device be at least partially maintained during a short-term voltage drop in the power grid. The fuel cell device is preferably an electrical generating unit or an electrical generating system, in particular as defined by VDE-AR-N 4105. The fuel cell device preferably comprises at least one fuel cell unit. The at least one fuel cell unit comprises at least one fuel cell, preferably a plurality of fuel cells, which are interconnected in particular in at least one fuel cell stack and / or a network of fuel cell stacks and are in particular intended for joint operation.The at least one fuel cell is preferably designed as a solid oxide fuel cell, alternatively as a molten carbonate fuel cell, as a polymer electrolyte fuel cell, as a direct methanol fuel cell, or the like. The fuel cell device preferably comprises at least one inverter, via which the at least one fuel cell unit is electrically connected to the power grid. Preferably, the at least one fuel cell unit and the inverter are part of a primary electrical network, in particular a single primary electrical circuit, of the fuel cell device. The power grid is preferably provided to connect the fuel cell device to at least one load. The power grid can be a public power grid, in particular an interconnected grid, or an island grid. Preferably, the power grid and the at least one inverter are part of a secondary electrical network.

[0008] A “short-term voltage drop” is to be understood as a voltage curve which, in terms of amplitude and duration, lies within a voltage limit curve and, in particular, which never falls below the voltage limit curve in terms of a voltage value. The voltage limit curve is preferably specified by a grid operator of the electricity grid and, for example, defined in a national or regional grid code / transmission code, such as the grid and system rules of the German transmission grid operators. After a voltage drop, the voltage limit curve typically shows a return to a minimum voltage, for example 90% of a nominal voltage, of the electricity grid within a maximum of 5 seconds, preferably within a maximum of 3 seconds, in particular within a maximum of 1.5 seconds or shorter. The voltage limit curve preferably defines whether a generating unit / generating plant is fault-ride-through (FRT) capable, i.e.i.e., the generating unit / generating plant is only disconnected from the power grid when the voltage falls below the limit value, in particular for its own protection. A voltage profile of the power grid can fall below the voltage limit value due to a decreasing voltage amplitude or due to a return to the voltage minimum that is too slow or does not occur at all. The fuel cell device preferably comprises a control unit for adjusting the electrical current of the fuel cell device. The electrical current of the fuel cell device is preferably the electrical current within the primary grid, in particular the electrical current through the at least one fuel cell. An internal voltage limit value is preferably stored in the control unit, which at any time has an amplitude that is equal to or smaller than the corresponding amplitude of the voltage limit value of the grid operator.In particular, the internal voltage limit profile is identical to the voltage limit profile of the grid operator. The internal voltage limit profile can be partially on the voltage limit profile of the grid operator or lower in terms of amplitude, but not intersect the voltage limit profile of the grid operator. Preferably, the control unit and / or the inverter disconnects the primary grid from the secondary grid when a voltage drop in the secondary grid falls below the internal voltage limit profile.

[0009] In at least one adaptation operating mode of the fuel cell device, the control unit adjusts the current within the primary network depending on the voltage of the secondary network during a brief voltage drop. Optionally, the fuel cell device comprises at least one further operating mode in which the current, the voltage, and / or an electrical power of the primary circuit is regulated to a constant value during a brief voltage drop in the secondary network, for example by using at least part of the electrical power of the primary circuit to charge an energy storage device of the fuel cell device, in particular a battery, a supercapacitor, or the like, or to operate a substitute load of the fuel cell device, for example a heating resistor.The control unit preferably executes the adaptation operating mode when neither energy storage nor substitute load is available, for example because the fuel cell device comprises neither energy storage nor substitute load, for example because the energy storage and / or the substitute load cannot or should not absorb any further electrical power.

[0010] In the at least one adaptation operating mode, the current within the primary network correlates, in particular positively, preferably with a voltage curve in the secondary network, preferably also in the case of a brief voltage drop. The at least one fuel cell is provided for the electrochemical conversion of a fuel. A conversion rate of the fuel through the at least one fuel cell preferably correlates with the current within the primary network. The fuel cell unit preferably comprises at least one fuel feed unit for adjusting a flow rate of the fuel through the at least one fuel cell, in particular for adjusting a supply rate of fresh fuel.The fuel cell unit preferably comprises at least one recirculation conveying unit for adjusting a flow rate of the fuel through the at least one fuel cell, in particular for adjusting a feed-back rate of exhaust gas from the at least one fuel cell into the fuel. The fuel conveying unit, the recirculation conveying unit, and / or the oxygen conveying unit are preferably designed as a pump, compressor, or blower, or alternatively as a continuous valve. The fuel cell unit preferably comprises at least one oxygen conveying unit for adjusting a flow rate of oxygen, in particular in the form of air, through the at least one fuel cell.Preferably, in at least one method step of the method, the control unit adjusts the fuel delivery unit, the recirculation delivery unit, and / or the oxygen delivery unit, preferably during the control of at least one electrochemical parameter that describes the electrochemical conversion by the at least one fuel cell. The at least one electrochemical parameter is configured, for example, as the current or electrical power through the at least one fuel cell, as the fuel utilization of the at least one fuel cell, as the temperature of the exhaust gas and / or the at least one fuel cell, as the combustion-air ratio of the exhaust gas, or the like.

[0011] Preferably, in the event of a brief voltage drop, the fuel delivery unit, the recirculation delivery unit, and / or the oxygen delivery unit continue to operate, in particular continue to operate at an unchanged delivery rate, continue to operate at a reduced delivery rate relative to a maximum delivery rate, or continue to be set to a value determined within the scope of the control of the at least one electrochemical parameter. Preferably, at least one minimum, control-compliant, or unchanged flow rate of the fuel and / or oxygen is maintained, in particular one that is different from zero.Preferably, the fuel feed unit, the recirculation feed unit and / or the oxygen feed unit is only switched off or set to a feed rate of zero and / or a fuel shut-off valve of the fuel cell device is closed if the voltage curve of the secondary network falls below the internal voltage limit curve.

[0012] The inventive design advantageously allows a dead time of the fuel cell device after the brief voltage drop to be kept short. In particular, the fuel cell device is immediately operational with respect to the fluid dynamics of fuel, oxygen, and exhaust gas. In particular, a time period for pressure buildup and / or refilling of the fuel cell unit with fuel can advantageously be kept short, in particular avoided. Furthermore, the provision of electrical power by the at least one fuel cell unit can be kept in line with the power grid, in particular in line with the voltage limit profile of the grid operator, so that the fuel cell device is considered FRT-capable, in particular regardless of the presence of an energy storage device and / or a substitute load.

[0013] It is further proposed that during the brief voltage drop in the grid, a thermal efficiency of the fuel cell device is shifted at the expense of an electrical efficiency of the fuel cell device. A thermal or electrical efficiency of the fuel device preferably describes a ratio of a thermal or electrical energy produced by the at least one fuel cell unit in relation to a chemical energy of the fuel. Preferably, the at least one fuel cell converts less fuel during the brief voltage drop than immediately before the brief voltage drop. The conversion rate of the at least one fuel cell can correlate with a voltage curve in the secondary grid during the brief voltage drop or can be actively set to zero by the control unit.During the brief voltage drop, the fuel is thermally converted, preferably at least partially, preferably to a greater extent than immediately before the brief voltage drop, in particular substantially completely, by means of a burner unit of the fuel cell device, in particular the fuel cell unit. The burner unit preferably comprises at least one burner, in particular an afterburner and / or a preheater, which is arranged together with the at least one fuel cell in a common housing of the fuel cell unit. Alternatively or additionally, the burner unit comprises a central burner to which several fuel cell units of the fuel cell device are connected.A thermal conversion of the fuel can be distributed among the different burners of the burner unit during the brief voltage drop or can preferably be carried out by just one of the burners, in particular the afterburner. The burner unit, in particular the afterburner, is provided for at least substantially complete conversion of the fuel, at least for a maximum duration of the brief voltage drop, i.e. for a maximum duration of the internal voltage limit profile. The term "substantially complete conversion of the fuel" should preferably be understood to mean at least a conversion of the fuel or a fuel mixture, so that an exhaust gas from the conversion comprises a residue of at most 5%, preferably at most 1%, particularly preferably at most 0.5% of the fuel based on the volume and / or mass of the exhaust gas.Preferably, the afterburner is designed to convert the fuel at least substantially completely, at least for the maximum duration of the brief voltage drop, in particular during continuous operation, at an intended maximum flow rate of the fuel through the fuel cell unit, particularly preferably independently of a conversion rate of the at least one fuel cell. Alternatively, the afterburner is designed as a function of a minimum conversion rate of the at least one fuel cell, for example when the internal voltage limit profile has a minimum of the voltage profile that is different from zero. Due to the configuration according to the invention, a fuel supply rate to the fuel cell unit can advantageously be kept high during the brief voltage drop without increasing the risk of fuel residues escaping from the fuel cell device.In particular, the fuel cell device can advantageously be operated safely even during a brief voltage drop. It is further proposed that, during the brief voltage drop in the network, a thermal mass of the fuel cell device, in particular of an afterburner of the fuel cell device, be used to at least partially absorb heat produced by the fuel cell device during the brief voltage drop. Preferably, the thermal mass is a heat capacity of the burner unit, in particular of the afterburner, which is designed to absorb heat generated, and in particular not dissipated by the exhaust gas, during at least substantially complete conversion of the fuel by the burner unit, in particular by the afterburner.The thermal mass can be realized by a specific component, which is preferably integrally connected to the burner unit, or by a design of the burner unit itself, such as wall thickness, total volume, material used, or the like. Preferably, the temperature of the burner unit, in particular of the afterburner, is increased by the conversion of the fuel during the brief voltage drop compared to a value immediately before the brief voltage drop. In particular, the temperature of the burner unit correlates negatively with the voltage curve of the secondary network.Alternatively or additionally, the burner unit comprises a cooling or heat distribution system, such as a metallic connecting element to another thermal mass of the fuel cell device, a heat pipe, air cooling, or water cooling, to keep the temperature of the burner unit below a maximum permissible temperature. The inventive design allows the fuel cell device to be advantageously operated independently of external heat removal.

[0014] It is further proposed that the fluid supply be switched off, in particular only when at least one temperature parameter of the fuel cell device, in particular of the afterburner, exceeds a limit value. The temperature parameter preferably indicates the temperature of the burner unit, in particular of the afterburner, by direct measurement at the afterburner or by measuring a temperature of the exhaust gas downstream of the burner unit. Particularly preferably, the thermal mass is designed such that it keeps the temperature parameter below the limit value for at least a voltage drop that is still considered brief, which in particular has exactly the internal voltage limit profile. After a brief voltage drop, the fuel cell device has a thermal equilibration phase in which the temperature parameter drops to a value corresponding to a stable target operating point of the fuel cell device.If a further brief voltage drop occurs within the thermal equalization phase, the temperature parameter may exceed the limit value. Preferably, if the limit value is exceeded, the control unit reduces the supply rate of fresh fuel and oxygen to the at least one fuel cell or shuts off the fluid supply. Preferably, the fluid supply shuts off within the thermal equalization phase after the brief voltage drop only once the further brief voltage drop has ended. Particularly in the latter case, the limit value is preferably lower than the maximum permissible temperature of the burner unit. The inventive design advantageously minimizes the risk of overheating of the fuel cell device while simultaneously remaining FRT-capable.

[0015] It is further proposed that the fluid supply be kept at least substantially constant during the brief voltage drop. The fluid supply preferably comprises a subordinate control for adjusting an operating parameter, in particular speed, torque, flow rate, or the like, to a fluid supply setpoint predetermined by the control unit. Keeping the fluid supply constant should preferably be understood to mean that the control unit sets a constant value for the fluid supply setpoint of the fluid supply for the duration of the brief voltage drop. The control unit preferably determines the fluid supply setpoint as a manipulated variable within the framework of the control of the at least one electrochemical parameter.Preferably, the control unit uses as a constant value a last determined value before the voltage drop or an average value of the fluid supply setpoint in a time window up to the voltage drop. Alternatively, the control unit sets the fluid supply setpoint to a predetermined error standard value. Preferably, during the voltage drop, the control unit suspends the control of the electrochemical parameter, at least by means of the fluid supply, preferably completely. Alternatively, the control unit continues the control of the electrochemical parameter unchanged even during the brief voltage drop and adjusts the fluid supply setpoint during the brief voltage drop, in particular depending on the electrical current through the at least one electrochemical cell.The inventive design advantageously minimizes the risk of over-regulation of the electrochemical parameter, particularly due to the relatively rapid changes in the electric current through the at least one fuel cell during the voltage drop. In particular, the risk of a damaging excess of oxygen in the at least one fuel cell upon resumption or ramp-up of the electrochemical conversion can advantageously be minimized.

[0016] It is further proposed that, as already explained above, during the brief voltage drop, the fluid supply be set to a value that is predetermined by an operating point of the fuel cell device, which was determined in a time window before the brief voltage drop. The operating point is preferably a result of the control of the electrochemical parameter. The operating point links, in particular, the fluid supply setpoint with the electrochemical parameter of the fuel cell device. By means of the configuration according to the invention, the fluid dynamics within the fuel cell device can advantageously be kept constant during the brief voltage drop. In particular, parameter fluctuations, in particular pressure and / or density fluctuations, within the fuel cell device can advantageously be kept small during the brief voltage drop.

[0017] It is further proposed that control of the fluid supply be resumed after the brief voltage drop when an electrical current provided by the fuel cell device at least substantially equals a predetermined threshold value. Control of the fluid supply here means determining the fluid supply setpoint as part of the control of the electrochemical parameter. The subordinate control of the operating parameter of the fluid supply as a function of the fluid supply parameter is preferably continuously active during operation of the fluid supply. In the simplest case, control is resumed when the electrical current exceeds the threshold value. Preferably, control is resumed when the electrical current is within a tolerance band around a current setpoint value, which is limited by the threshold value, for a specified period of time.The current setpoint is preferably contained in the operating point, as a function of which the fluid supply setpoint was determined for the duration of the brief voltage drop. The threshold value can be specifically determined by a concrete configuration of the fuel cell device, in particular as a function of a susceptibility to or tolerance of the control of the electrochemical parameter with respect to a deviation of a temperature of the fuel cell device from a specified operating temperature. By means of the configuration according to the invention, the fluid dynamics within the fuel cell device can advantageously be kept constant during the brief voltage drop. In particular, parameter fluctuations, in particular pressure and / or density fluctuations, within the fuel cell device can advantageously be kept small after the brief voltage drop.

[0018] It is further proposed that an inverter of the fuel cell device, in particular the one already mentioned, specifies whether a voltage drop is to be assessed as short-term. The inverter is preferably FRT-capable. The inverter preferably sends at least one grid signal, in particular on an ad hoc or permanent basis, to the control unit, which depends on a voltage of the secondary grid. The grid signal preferably encodes at least two, in particular exactly two, states of the secondary grid. The grid signal preferably encodes a normal state of the secondary grid, in which the secondary grid operates at least substantially at nominal voltage or at most a short-term voltage drop in the secondary grid occurs. The grid signal preferably encodes a fault state of the secondary grid, in which a voltage drop exceeds a short-term voltage drop.Coding can be implemented digitally, as a TTL level, by transmitting / not transmitting the grid signal, or the like. Optionally, the grid signal also distinguishes between a brief voltage drop and normal operation of the secondary grid at nominal voltage. Preferably, the control unit evaluates a fluctuation in the electrical current and / or voltage of the primary grid as a brief voltage drop in the secondary grid, in particular only if the grid signal indicates the normal state or does not indicate the fault state. If the fluctuation in the electrical current and / or voltage of the primary grid lies outside a permissible range specified by the control of the electrochemical variable, without the grid signal of the inverter indicating the normal state, or if the grid signal indicates the fault state, the control unit preferably switches off the fuel cell device.If the fluctuation in the electrical current and / or voltage of the primary grid lies outside a permissible range specified by the control of the electrochemical variable, the control unit allows the fuel cell device to operate, in particular according to the method steps described above, as long as the grid signal indicates the normal state or does not indicate the fault state. The inventive design advantageously allows a simple and reliable distinction to be made between control-compliant fluctuations in the primary grid, a brief voltage drop in the secondary grid, and a more serious fault state of the fuel cell device and / or the grid.

[0019] Furthermore, a fuel cell device with at least one control unit, in particular the one already mentioned, for carrying out a method according to the invention is proposed. A "control unit" is to be understood in particular as a unit with at least one control electronics unit. "Control electronics" is to be understood in particular as a unit with a processor unit and with a memory unit as well as with an operating program stored in the memory unit. The fuel cell device preferably comprises the inverter. The fuel cell device preferably comprises the at least one fuel cell unit. Optionally, the fuel cell device comprises a plurality of, in particular identical, fuel cell units.In a configuration with multiple fuel cell units, the fuel cell device can have at least one central inverter to which multiple, in particular all, fuel cell units are connected in parallel. Alternatively, at least one, in particular each, of the fuel cell units comprises a specific inverter, which is arranged, in particular, together with at least one fuel cell of the fuel cell unit within a housing of the fuel cell unit. The at least one fuel cell unit preferably comprises at least the fuel feed unit and / or the oxygen feed unit as part of the fluid supply of the fuel cell device. The at least one fuel cell unit preferably comprises the burner unit, in particular the afterburner, which is fluidically connected to the at least one fuel cell.The fuel cell unit preferably comprises further components for fluid handling and / or heat management, such as in particular exhaust gas heat exchangers, shut-off valves, metering valves, a fuel reformer, a steam feed unit or the like.

[0020] "Intended" should be understood in particular to mean specifically programmed, designed, and / or equipped. The fact that an object is intended for a specific function should be understood in particular to mean that the object fulfills and / or performs this specific function in at least one application and / or operating state.

[0021] The inventive design makes it possible to provide a fuel cell device that can advantageously be operated even without an electrical energy storage device and / or a backup load during a brief voltage drop in the grid. In particular, an advantageously cost-effective, low-component, compact, and FRT-capable fuel cell device can be provided.

[0022] The method according to the invention and / or the fuel cell device according to the invention should not be limited to the application and embodiment described above. In particular, the method according to the invention and / or the fuel cell device according to the invention can have a number of individual elements, components, units, and method steps that differs from the number stated herein to fulfill a function described herein. Furthermore, in the value ranges specified in this disclosure, values ​​within the stated limits are also to be considered disclosed and can be used arbitrarily.

[0023] Drawings Further advantages will become apparent from the following description of the drawings. The drawings illustrate two exemplary embodiments of the invention. The drawings, the description, and the claims contain numerous features in combination. Those skilled in the art will also expediently consider the features individually and combine them into useful further combinations.

[0024] They show:

[0025] Fig. 1 is a schematic representation of a fuel cell device according to the invention,

[0026] Fig. 2 is a schematic flow diagram of a method according to the invention and

[0027] Fig. 3 is a schematic flow diagram of an alternative embodiment of a method according to the invention.

[0028] Description of the embodiments

[0029] Figure 1 shows a fuel cell device 12a. The fuel cell device 12a preferably comprises at least one fuel cell unit 22. The fuel cell unit 22a preferably comprises a fuel cell assembly 24a of fuel cells, which are particularly preferably electrically connected in series for joint operation. The fuel cell assembly 24a is functionally represented here by a single fuel cell with a fuel electrode 26a and an oxygen electrode 28a. The fuel cell assembly 24a is preferably intended for the electrochemical conversion of a fuel with the addition of oxygen, in particular atmospheric oxygen.The fuel cell unit 22a preferably comprises a fluid supply 14a for supplying the fuel cell assembly 24a with the fuel, for example methane, hydrogen and / or ammonia as a pure substance or as a mixture, in particular natural gas or biogas, and with the oxygen, in particular air. The fuel cell device 12a comprises at least one control unit 20a. The control unit 20a is particularly preferably provided for adjusting the fluid supply 14a, in particular a flow rate of the fuel and / or the oxygen. The control unit 20a is provided for carrying out a method 10a or 10b, which is explained in more detail in Figures 2 and 3, respectively. The fuel cell unit 22a preferably comprises an inverter 18a for feeding electrical power provided by the fuel cell assembly 24a into a power grid.

[0030] The fluid supply 14a preferably comprises at least one fuel delivery unit 30a for delivering the fuel to the fuel electrode 26a. The fuel delivery unit 30a is preferably designed as a fan. The fuel cell unit 22a preferably comprises at least one fuel line 44a, which leads from the fluid supply 14a to the fuel electrode 26a.The fuel cell unit 22a comprises, along the fuel line 44a, for example, a recirculation conveying unit 36a for adjusting a feed-back rate of exhaust gas into the fuel line 44a, a fuel recuperator 38a for transferring heat from the fed-back exhaust gas to the fuel in the fuel line 44a, a fuel preheater 40a for transferring heat from an afterburner exhaust gas leaving the fuel cell unit 22a to the fuel in the fuel line 44a and / or a reformer 42a for reforming the fuel, in particular in this order with respect to a flow direction of the fuel.

[0031] The fluid supply 14a preferably comprises a fuel shutoff valve 32a for coupling or decoupling the fuel feed unit 30a to the fuel line 44a. Optionally, the fluid supply 14a comprises a further fuel branch 34a for feeding a further fuel into the fuel line 44a, in particular a starter fuel such as pure hydrogen for starting up the fuel cell unit 22a. The further fuel branch 34a preferably comprises a further fuel shutoff valve 35a for coupling or decoupling a source of the further fuel to the fuel line 44a.

[0032] The fuel cell unit 22a preferably comprises at least one afterburner 16a for converting fuel residues in the exhaust gas exiting the fuel electrode 26a. The afterburner 16a is preferably connected downstream of the fuel cell assembly 24a to the fuel electrode 26a and the oxygen electrode 28a. An afterburner outlet of the afterburner 16a is preferably connected to the fuel preheater 40a.

[0033] The fuel cell unit 22a preferably comprises a return line 48a for feeding back a portion of the exhaust gas exiting the fuel electrode 26a. The return line 48a is preferably connected to the fuel electrode 26a in parallel with the afterburner 16a. The return line 48a preferably comprises the fuel recuperator 38a. The return line 48a preferably comprises a return oxygen preheater 50a for transferring heat from the returned exhaust gas to the oxygen. A point where the return line 48a opens into the fuel line 44a is preferably arranged upstream of the recirculation feed unit 36a with respect to the fuel, and in particular downstream of the fuel feed unit 30a.

[0034] The fluid supply 14a preferably comprises an oxygen delivery unit 52a for delivering oxygen, in particular air, to the oxygen electrode 28a. The oxygen delivery unit 52a is preferably designed as a blower. The fuel cell unit 22a preferably comprises a main oxygen line 54a, which connects the fluid supply 14a to the oxygen electrode 28a. The main oxygen line 54a preferably comprises an exhaust gas oxygen preheater 56a for transferring heat from the afterburner exhaust gas of the afterburner 16a to the oxygen. The fuel cell unit 22a preferably comprises a bypass line 58a, which comprises the exhaust gas oxygen preheater 56a. The bypass line 58a comprises, for example, an electrical heating element for heating the oxygen. The fuel cell unit 22a preferably comprises a preheating line 60a, in which the return oxygen preheater 50a is arranged.The preheating line 60a preferably opens into the main oxygen line 54a upstream of the exhaust gas oxygen preheater 56a. The fluid supply 14a preferably comprises an oxygen control unit 62a for coupling or decoupling the oxygen supply unit 52a to the main oxygen line 54a, to the bypass line 58a, and / or to the preheating line 60a.

[0035] The oxygen control unit 62a is shown here functionally represented by three individual valves and can be designed in the same way or as a multi-way valve. Figure 2 shows the method 10a for operating the fuel cell device 12a, which is connected to the power grid. The method 10a preferably comprises a regular operation 64a of the fuel cell device 12a. In the regular operation 64a, the control unit 20a preferably carries out a control, in particular known per se, of an electrochemical parameter, for example a fuel utilization, the electrochemical conversion of the fuel in the fuel cell assembly. In the regular operation 64a, a power setpoint of the provided electrical power, in particular of an electrical current linked to the provided electrical power, is preferably specified.The control unit 20a preferably attempts to maintain the fuel cell device 12a at an operating point dependent on the power setpoint by adjusting a setting of the fluid supply 14a. In particular, the control unit 20a determines at least one fluid supply setpoint, for example a fuel supply setpoint, a recirculation rate setpoint, and / or an oxygen supply setpoint, depending on a control difference defined by the operating point. Preferably, the control unit 20a outputs the at least one fluid supply setpoint to a control or regulating unit of the component of the fluid supply 14a to be adjusted. The component to be adjusted can in particular be the fuel feed unit 30a, the recirculation feed unit 36a, the oxygen feed unit 52a, the fuel shutoff valve 32a, the further fuel shutoff valve 35a, and / or the oxygen control unit 62a.

[0036] The method 10a preferably includes voltage monitoring 66a of the power grid. Preferably, the inverter 18a checks a voltage of the power grid in the voltage monitoring 66a. Preferably, the inverter 18a outputs a grid signal to the control unit 20a, which encodes a state of the power grid. The grid signal can be configured as an enable signal or as an error signal, depending on which the control unit 20a continues to operate the fuel cell unit 22a or whether the control unit 20a initiates a shutdown process 70a of the fuel cell unit 22a.Preferably, the grid signal indicates whether the voltage of the power grid is within a tolerance band around a nominal voltage of the power grid, except for any short-term voltage drops, or whether a voltage curve of the power grid goes beyond a short-term voltage drop, in particular falls below a predetermined voltage limit curve. The inverter 18a specifies whether a voltage drop is to be assessed as short-term.

[0037] The method 10a preferably comprises an error evaluation 68a, which is preferably carried out when the control unit 20a receives the network signal as an enable signal oras long as it does not receive the grid signal as an error signal In the error evaluation 68a, the control unit 20a preferably checks whether a fluctuation in the electrical current through the fuel cell assembly 24a is within a permissible fluctuation range for the control of the electrochemical parameter If a fluctuation in the electrical current through the fuel cell assembly 24a is within a permissible fluctuation range for the control of the electrochemical parameter, the control unit 20a preferably continues the regular operation 64a If a fluctuation in the electrical current through the fuel cell assembly 24a is outside a permissible fluctuation range for the control of the electrochemical parameter, the control unit 20a preferably carries out an error operation 72a of the method 10a. The control unit 20a preferably carries out the error operation 72a as long as the control unit 20a receives the grid signal as an enable signal oras long as it does not receive the grid signal as an error signal and the deviation of the electrical current from the setpoint power value through the fuel cell assembly 24a is outside the permissible fluctuation range. The error mode 72a is preferably executed when there is a brief voltage drop in the power grid.

[0038] During fault operation 72a, control unit 20a preferably suspends control of the electrochemical parameter. In particular, this correlates the electrical current through fuel cell device 12a with the short-term voltage drop in the power grid during a short-term voltage drop. Control unit 20a at least partially maintains the fluid supply 14a of fuel cell device 12a during the short-term voltage drop in the power grid. During the short-term voltage drop, control unit 20a maintains the fluid supply 14a at least substantially constant by specifying at least one constant fluid supply setpoint for the duration of fault operation 72a.During the brief voltage drop, the control unit 20a determines, as the fluid supply setpoint, a value of the fluid supply setpoint that is predetermined by an operating point of the fuel cell device 12a, which was determined in a time window before the brief voltage drop. In particular, the control unit 20a sets the fluid supply setpoint during the fault mode 72a to the most recently determined fluid supply setpoint of the regular mode 64a. The control unit 20a reduces the fluid supply setpoint in the fault mode 72a compared to the regular mode 64a, in particular only if at least one temperature parameter of the fuel cell device 12a, in particular of the afterburner 16a, exceeds a limit value.

[0039] In the fault mode 72a, the control unit 20a shifts a thermal efficiency of the fuel cell device 12a at the expense of an electrical efficiency of the fuel cell device 12a. In the fault mode 72a, a thermal mass of the fuel cell device 12a, in particular of an afterburner 16a of the fuel cell device 12a, is used to at least partially absorb heat produced by the fuel cell device 12a during the brief voltage drop.

[0040] The regular operation 64a is resumed after the brief voltage drop if, in the error evaluation 68a, the electrical current provided by the fuel cell device 12a is at least substantially equal to a predetermined threshold value.

[0041] Figure 3 shows a further exemplary embodiment of the invention. The following descriptions and the drawings are essentially limited to the differences between the exemplary embodiments, whereby with regard to components with the same designation, in particular with regard to components with the same reference numerals, reference can in principle also be made to the drawings and / or the description of the other exemplary embodiments, in particular Figures 1 to 2. To distinguish the exemplary embodiments, the letter a is placed after the reference numerals of the exemplary embodiment in Figures 1 to 2. In the exemplary embodiment in Figure 3, the letter a is replaced by the letter b. Figure 3 shows an alternative method 10b for operating a fuel cell device which is connected to a power grid.In at least one fault mode 72b of method 10b, a supply of electrical current by the fuel cell device is adjusted in the event of a brief voltage drop in the power grid. A fluid supply to the fuel cell device is at least partially maintained during the brief voltage drop in the power grid. In fault mode 72b, a control of an electrochemical parameter of a regular mode 64b of method 10b is maintained, in particular unchanged. Preferably, a control unit of the fuel cell device adjusts at least one fluid supply setpoint during fault mode 72b depending on an electrical current through the fuel cell device.

[0042] For further features of method 10b, reference is made to Figure 2 and its description.

Claims

Claims 1 . Method (10a; 10b) for operating a fuel cell device (12a) which is connected to a power grid, wherein in at least one method step a provision of electrical current by the fuel cell device (12a) is adapted in the event of a brief voltage drop in the power grid, characterized in that a fluid supply (14a) of the fuel cell device (12a) is at least partially maintained during the brief voltage drop in the power grid.

2. Method (10a; 10b) according to claim 1, characterized in that during the short-term voltage drop of the network, a thermal efficiency of the fuel cell device (12a) is shifted at the expense of an electrical efficiency of the fuel cell device (12a).

3. Method (10a; 10b) according to claim 1 or 2, characterized in that during the brief voltage drop of the network, a thermal mass of the fuel cell device (12a), in particular of an afterburner (16a) of the fuel cell device (12a), is used to at least partially absorb heat produced by the fuel cell device (12a) during the brief voltage drop.

4. Method (10a; 10b) according to claim 3, characterized in that the fluid supply (14a) is reduced, in particular only when at least one temperature parameter of the fuel cell device (12a), in particular of the afterburner (16a), exceeds a limit value.

5. Method (10a) according to one of the preceding claims, characterized in that during the short-term voltage drop, the fluid supply (14a) is kept at least substantially constant.

6. Method (10a) according to one of the preceding claims, characterized in that during the brief voltage drop, the fluid supply (14a) is set to a value which is predetermined by an operating point of the fuel cell device (12a) which was determined in a time window before the brief voltage drop.

7. Method (10a) according to one of the preceding claims, characterized in that a control of the fluid supply (14a) is resumed after the brief voltage drop when an electrical current provided by the fuel cell device (12a) is at least substantially equal to a predetermined threshold value.

8. Method (10a; 10b) according to one of the preceding claims, characterized in that an inverter (18a) of the fuel cell device (12a) specifies whether a voltage drop is to be assessed as short-term.

9. Fuel cell device (12a) with at least one control unit (20a) for carrying out a method (10a; 10b) according to one of the preceding claims.

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