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) connected to an electrical power network, wherein in at least one method step an adjustment of the provision of electrical current by the fuel cell device (12a) is made in the event of a short-term voltage drop in the electrical power network. It is proposed that the fluid supply (14a) to the fuel cell device (12a) is maintained at least partially during the short-term voltage drop in the electrical power network.

Description

Background Technology

[0001] A method has been proposed for operating a fuel single-cell device connected to a power grid, wherein in at least one method step, the current supplied through the fuel single-cell device is adjusted in the event of a short-term voltage drop in the power grid. Summary of the Invention

[0002] The present invention relates to a method for operating a fuel single-pool device connected to a power grid, wherein in at least one method step, the supply of current through the fuel single-pool device is adjusted in the event of a short-term voltage drop in the power grid.

[0003] It is proposed that the fluid supply to the fuel cell unit be maintained at least partially during short-term voltage drops in the power grid. The fuel cell unit is preferably an electricity generating unit or device, particularly in the sense of VDE-AR-N 4105. The fuel cell unit preferably comprises at least one fuel cell unit. At least one fuel cell unit comprises at least one fuel cell, preferably multiple fuel cells, which are interconnected, particularly in a composite structure of at least one fuel cell stack and / or fuel cell stack, and are particularly configured for common operation. At least one fuel cell is preferably constructed as a solid oxide fuel cell, alternatively as a molten carbonate fuel cell, polymer electrolyte fuel cell, direct methanol fuel cell, etc. The fuel cell unit preferably includes at least one inverter, through which at least one fuel cell unit is electrically connected to the power grid. Preferably, at least one fuel cell unit and the inverter are part of the primary grid of the fuel cell unit, particularly a single primary current loop. The power grid is preferably configured to connect the fuel cell unit to at least one load. The power grid can be a public power grid, especially an interconnected grid or an independent power grid. Preferably, the power grid and at least one inverter are part of a secondary power grid.

[0004] "Short-term voltage drop" should refer to a voltage curve that is within the voltage limit curve in both amplitude and duration, and whose magnitude, in particular, does not fall below the voltage limit curve at any time. The voltage limit curve is preferably pre-defined by the power grid operator and specified, for example, in national or regional grid codes / transmission codes, such as the grid and system rules of the German transmission grid operator. The voltage limit curve typically has a return path to the minimum voltage of the power grid, such as 90% of the rated voltage, within at most 5 seconds, preferably at most 3 seconds, and especially at most 1.5 seconds or less, after the voltage drop. The voltage limit curve is preferably defined to indicate whether the generating unit / equipment has fault ride-through capability, that is, the generating unit / equipment, especially for its own protection, only disconnects from the power grid when it falls below the voltage limit curve. The voltage curve of the power grid may fall below the voltage limit curve due to reduced voltage amplitude or due to a too-slow or incomplete return path to the minimum voltage.

[0005] The single-fuel-pool unit preferably includes a regulating unit for regulating the current of the single-fuel-pool unit. The current of the single-fuel-pool unit is preferably the current within the primary grid, particularly the current through at least one single fuel-pool. Preferably, the regulating unit stores an internal voltage limit curve, which at any given time has an amplitude equal to or less than the corresponding amplitude of the grid operator's voltage limit curve. In particular, the internal voltage limit curve is identical to the grid operator's voltage limit curve. The internal voltage limit curve can be segmentally on or below the grid operator's voltage limit curve in terms of amplitude, but does not intersect with the grid operator's voltage limit curve. When the voltage of the secondary grid drops below the internal voltage limit curve, the regulating unit and / or inverter preferably separate the primary grid from the secondary grid.

[0006] In at least one adjusted operating mode of a single-fuel-cell device, the regulating unit adjusts the current within the primary grid according to the voltage of the secondary grid during a short-term voltage drop. Optional single-fuel-cell devices include at least one additional operating mode in which the current, voltage, and / or power of the primary circuit are regulated to constant values ​​during a short-term voltage drop in the secondary grid, for example, by using at least a portion of the power in the primary circuit to charge the energy storage device's accumulators, particularly batteries, supercapacitors, etc., or to operate the equivalent load of the single-fuel-cell device, such as a heating resistor. When not only the energy storage device but also the equivalent load is unavailable, for example because the single-fuel-cell device does not include either an energy storage device or an equivalent load, or because the energy storage device and / or the equivalent load cannot or should not receive additional power, the regulating unit preferably executes the adjusted operating mode.

[0007] In at least one adjusted operating mode, the current within the primary grid is preferably positively correlated with the voltage curve in the secondary grid, especially under short-term voltage drops. At least one fuel cell is provided for the electrochemical conversion of fuel. The fuel conversion rate through the at least one fuel cell is preferably correlated with the current within the primary grid. The fuel cell unit preferably includes at least one fuel delivery unit for regulating the flow rate of fuel through the at least one fuel cell, particularly for regulating the supply rate of fresh fuel. The fuel cell unit preferably includes at least one recirculation delivery unit for regulating the flow rate of fuel through the at least one fuel cell, particularly for regulating the feedback rate of exhaust gas from the at least one fuel cell to the fuel. The fuel delivery unit, recirculation delivery unit, and / or oxygen delivery unit are preferably configured as pumps, compressors, or blowers, or alternatively as continuous valves. The fuel cell unit preferably includes at least one oxygen delivery unit for regulating the flow rate of oxygen, particularly in the form of air, through the at least one fuel cell. Preferably, in at least one method step of the method, the regulating unit regulates the fuel delivery unit, the recirculation delivery unit, and / or the oxygen delivery unit while regulating at least one electrochemical parameter, said at least one electrochemical parameter describing the electrochemical conversion carried out through at least one fuel cell. The at least one electrochemical parameter may be configured as, for example, the current or electrical power passing through the at least one fuel cell, the fuel utilization of the at least one fuel cell, the temperature of the exhaust gas and / or the at least one fuel cell, the combustion air ratio of the exhaust gas, etc.

[0008] Preferably, even with a short-term voltage drop, the fuel delivery unit, recirculation delivery unit, and / or oxygen delivery unit should continue operating, particularly at a constant delivery power, or limited to a delivery power reduced relative to the maximum delivery power, or further adjusted to a value identified within the range of adjustment for at least one electrochemical parameter. Preferably, at least one, particularly non-zero, minimum, consistent with adjustment, or constant flow rate of fuel and / or oxygen should be maintained. If the voltage curve of the secondary grid is below the internal voltage limit curve, it is preferable to simply disconnect the fuel delivery unit, recirculation delivery unit, and / or oxygen delivery unit or adjust them to zero delivery power and / or close the fuel shut-off valve of the fuel cell unit.

[0009] The design according to the invention allows for a short dead time of the fuel cell unit after a short voltage drop. In particular, the fluid dynamics of the fuel cell unit with respect to fuel, oxygen, and exhaust gas are immediately operable. The duration of pressure formation and / or refilling for the fuel cell unit can be advantageously shortened, and in particular avoided. Furthermore, current can be supplied through at least one fuel cell unit in accordance with the power grid, particularly with the voltage limit curve of the grid operator, making the fuel cell unit capable of FRT, especially regardless of the presence of an accumulator and / or equivalent load.

[0010] Furthermore, it is proposed that the thermal efficiency of the fuel cell unit be transferred at the expense of its electrical efficiency during a short-term voltage drop in the power grid. The thermal or electrical efficiency of the fuel cell unit preferably describes the ratio of the thermal or electrical energy generated by at least one fuel cell unit to the chemical energy of the fuel. Preferably, at least one fuel cell converts less fuel during the short-term voltage drop than immediately before the voltage drop. The conversion rate of at least one fuel cell can be correlated with the voltage curve in the secondary power grid during the short-term voltage drop or actively set to zero by the regulating unit. Especially by means of the burner unit of the fuel cell unit, particularly the fuel cell unit itself, the fuel thermally converted during the short-term voltage drop is preferably at least partially, preferably more, than immediately before the short-term voltage drop. The burner unit preferably includes at least one burner, particularly an afterburner and / or a preheater, which is arranged together with at least one fuel cell in a common housing of the fuel cell unit. As an alternative or supplementary option, the burner unit includes a central burner to which multiple fuel single-pool units of the fuel single-pool device are connected. The thermal conversion of the fuel can be distributed to different burners of the burner unit during a short voltage drop period, or preferably performed by only one burner, especially an afterburner. The burner unit, especially the afterburner, is configured to at least substantially completely convert the fuel, at least for the maximum duration of the short voltage drop, i.e., the maximum duration of the internal voltage limit curve. "Substantially completely converting the fuel" preferably means at least the conversion of the fuel or fuel mixture, such that the converted exhaust gas includes at most 5%, preferably at most 1%, and particularly preferably at most 0.5% of the fuel relative to the volume and / or mass of the exhaust gas. Preferably, the afterburner is designed to substantially completely convert the fuel at the maximum flow rate of the fuel through the fuel single-pool units, at least for the maximum duration of the short voltage drop, especially during continuous operation, which preferably does not depend on the conversion rate of at least one fuel single-pool. For example, when the internal voltage limit curve has a non-zero minimum value, as an alternative, the afterburner is designed based on the minimum conversion rate of at least one fuel cell. With the design according to the invention, the fuel supply rate of the fuel cell unit can be advantageously maintained at a high level during short voltage drops without increasing the risk of excess fuel leakage from the fuel cell unit. In particular, the fuel cell unit can also be advantageously and safely operated during short voltage drops.

[0011] Furthermore, it is proposed that the heat capacity of a single-fuel unit, particularly the afterburner of a single-fuel unit, be utilized during short-term voltage drops in the power grid to at least partially absorb the heat generated by the single-fuel unit during this period. The preferred heat capacity is that of the burner unit, particularly the afterburner, designed to absorb the heat generated during fuel conversion, especially heat not carried away by exhaust gases, as the fuel is at least substantially completely converted through the burner unit, particularly the afterburner. This heat capacity can be achieved through special components preferably interlocked with the burner unit material or through the design of the burner unit itself, such as, in particular, wall thickness, overall volume, and materials used. During the short-term voltage drop, the temperature of the burner unit, particularly the afterburner, is preferably increased by fuel conversion relative to the value immediately preceding the short-term voltage drop. In particular, the temperature of the burner unit is negatively correlated with the voltage curve of the secondary power grid. As an alternative or supplementary solution, the burner unit includes a cooling device or heat distribution system, connecting elements of metal with other heat capacity relative to the fuel monocell unit, heat pipes, air cooling device or water cooling device, in order to maintain the temperature of the burner unit below the maximum permissible temperature. With the design according to the invention, the fuel monocell unit can be advantageously operated independently of external heat reduction.

[0012] Furthermore, it is proposed that the fluid supply be cut off only when at least one temperature parameter of the fuel cell unit, especially the afterburner, exceeds a limit value. The temperature parameter is preferably indicated by direct measurement at the afterburner or by measurement of the temperature of the exhaust gas downstream of the burner unit. Particularly preferred is that the heat capacity is designed to keep the temperature parameter below the limit value for at least one voltage drop that is considered short-lived, especially one with an internal voltage limit curve. After the short-lived voltage drop, the fuel cell unit has a thermal compensation phase in which the temperature parameter drops to a value corresponding to the stable target-operating point of the fuel cell unit. If a further short-lived voltage drop occurs within the thermal compensation phase, the temperature parameter may exceed the limit value. Preferably, the regulating unit reduces the supply rate of fresh fuel and oxygen to at least one fuel cell or cuts off the fluid supply when the limit value is exceeded. The fluid supply is preferably cut off only, preferably within the thermal compensation phase following the short-lived voltage drop, at the end of the further short-lived voltage drop. Especially during the final treatment, the limit value is preferably below the maximum permissible temperature of the burner unit. The design according to the present invention can advantageously keep the risk of overheating of the fuel single-cell unit low while maintaining FRT capability.

[0013] Furthermore, it is proposed that the fluid supply be kept at least substantially constant during the short voltage drop period. The fluid supply preferably includes a lower-level regulation to adapt operating parameters, particularly speed, torque, delivery power, etc., to a fluid supply target value predetermined by the regulating unit. "Keeping the fluid supply constant" preferably means that the regulating unit specifies a constant value for the fluid supply target value during the short voltage drop duration. The regulating unit preferably determines the fluid supply target value as a regulation amount within the range of regulation of at least one electrochemical parameter. Preferably, the regulating unit uses the last determined value before the voltage drop or the average value of the fluid supply target value over the time window up to the voltage drop as the constant value. Alternatively, the regulating unit adjusts the fluid supply target value to a predetermined fault standard value. Preferably, the regulating unit performs regulation of the electrochemical parameters preferably completely during the voltage drop period, at least by means of the fluid supply. Alternatively, the regulating unit also continues to regulate the electrochemical parameters without change during the short voltage drop period, and adjusts the fluid supply target value, particularly based on the current flowing through at least one electrochemical cell, during the short voltage drop period. With the design according to the invention, it is advantageous to keep the over-adjustment of the current flowing through at least one fuel cell, which regulates the electrochemical parameters, particularly due to the relatively rapid change during the voltage drop period, small. Especially when restarting or resuming electrochemical conversion, it is advantageous to keep the risk of harmful oxygen excess in at least one fuel cell low.

[0014] Furthermore, as explained above, the fluid supply is adjusted to a predetermined value during the short voltage drop period by the following operating point of the fuel cell unit, which has been identified within a time window prior to the short voltage drop. The operating point is preferably the result of adjustments to electrochemical parameters. Specifically, the operating point links the target fluid supply value to the electrochemical parameters of the fuel cell unit. With the design according to the invention, it is advantageous to maintain constant fluid dynamics within the fuel cell unit during the short voltage drop period. In particular, it is advantageous to keep parameter fluctuations, especially pressure and / or density fluctuations, within the fuel cell unit small during the short voltage drop period.

[0015] Furthermore, it is proposed that after a short voltage drop, the fluid supply regulation is restarted when the current supplied through the fuel cell unit is at least substantially equal to a predetermined threshold. Here, within the scope of electrochemical parameter regulation, fluid supply regulation refers to the determination of the target value of the fluid supply. Lower-level regulation of the fluid supply operating parameters, dependent on the fluid supply parameters, preferably operates continuously during fluid supply operation. In the simplest case, regulation restarts when the current exceeds the threshold. Regulation preferably restarts when the current is within a threshold-limited tolerance band surrounding the target current value for a specified duration. The target current value is preferably included in the following operating point, based on which the target fluid supply value for the duration of the short voltage drop is defined. The threshold can here be specifically defined by the specific design of the fuel cell unit, the deviation of the fuel cell unit temperature from a predetermined operating temperature, and especially by the susceptibility to or tolerance of the electrochemical parameter regulation. The design according to the invention allows for the advantageous maintenance of constant fluid dynamics within the fuel cell unit during short voltage drops. In particular, it allows for the advantageous maintenance of minimal parameter fluctuations, especially pressure and / or density fluctuations, within the fuel cell unit after a short voltage drop.

[0016] Furthermore, it is proposed that the inverter of the fuel cell unit, especially the inverter already mentioned, should be pre-defined as to whether the voltage drop should be assessed as short-term. Preferably, the inverter has FRT capability. Preferably, the inverter transmits at least one grid signal, particularly related to the motor, or persistently to the regulating unit, depending on the voltage of the secondary grid. Preferably, the grid signal encodes at least two, especially exactly two, states of the secondary grid. Preferably, the grid signal encodes the normal state of the secondary grid, in which the secondary grid operates at least substantially according to the nominal voltage or at most experiences a short-term voltage drop. Preferably, the grid signal encodes the fault state of the secondary grid, in which the voltage drop exceeds the short-term voltage drop. The encoding can be implemented digitally as TTL-level via grid signal transmission / non-transmission, etc. Optionally, the grid signal can further distinguish between short-term voltage drops and normal operation of the secondary grid based on the nominal voltage. Specifically, the regulating unit preferably assesses fluctuations in the current and / or voltage of the primary grid as short-term voltage drops in the secondary grid only when the grid signal indicates a normal state or no fault state. If fluctuations in the current and / or voltage of the primary grid are outside the permissible range predetermined by adjusting electrochemical parameters, and the inverter's grid signal does not indicate a normal state or, if the grid signal indicates a fault state, the regulating unit preferably disconnects the fuel cell unit. If fluctuations in the current and / or voltage of the primary grid are outside the permissible range predetermined by adjusting electrochemical parameters, then, as long as the grid signal indicates a normal state or no fault state, the regulating unit operates the fuel cell unit, specifically according to the method steps described above. With the design according to the invention, it is advantageous to easily and reliably distinguish between fluctuations in the primary grid consistent with regulation, short-term voltage drops in the secondary grid, and more serious fault states of the fuel cell unit and / or the grid.

[0017] Furthermore, a single-cell fuel cell device is proposed having at least one, particularly as mentioned above, regulating unit for implementing the method according to the invention. "Regulating unit" should particularly refer to a unit having at least one control electronics device. "Control electronics device" should particularly refer to a unit having a processor unit and a storage unit, and having an operating program stored in the storage unit. The single-cell fuel cell device preferably includes an inverter. The single-cell fuel cell device preferably includes at least one single-cell fuel cell unit. Optionally, the single-cell fuel cell device includes multiple, particularly structurally identical, single-cell fuel cell units. In a design having multiple single-cell fuel cell units, the single-cell fuel cell device can have at least one central inverter, to which multiple, particularly all, single-cell fuel cell units are connected in parallel. Alternatively, at least one of the single-cell fuel cell units, particularly each single-cell fuel cell unit, includes a dedicated inverter, which is arranged, particularly together with at least one single-cell fuel cell of the single-cell fuel cell unit, inside the housing of the single-cell fuel cell unit. At least one single-cell fuel cell unit preferably includes at least a fuel delivery unit and / or an oxygen delivery unit as part of the fluid supply mechanism of the single-cell fuel cell device. At least one fuel cell unit preferably includes a burner unit, particularly an afterburner, which is fluidically connected to at least one fuel cell. The fuel cell unit preferably includes additional components for fluid manipulation and / or thermal management, such as, in particular, waste heat transfer devices, shut-off valves, metering valves, fuel reforming units, steam feed units, etc.

[0018] "Set up" should in particular refer to something specifically programmed, designed, and / or equipped. "An object is set up for a specific function" should in particular refer to the object performing and / or executing that specific function in at least one application state and / or runtime state.

[0019] The design according to the invention provides a single-cell fuel unit that can advantageously operate without an energy storage device and / or equivalent load during short-term voltage drops in the power grid. In particular, it provides an advantageously low-cost, compact, and FRT-capable single-cell fuel unit.

[0020] The method and / or the fuel single-pool device according to the invention should not be limited to the applications and embodiments described above. In particular, the method and / or the fuel single-pool device according to the invention can have a different number of individual elements, components, units, and method steps than those mentioned here, in order to fulfill the operating principle described here. Furthermore, values ​​within the limits mentioned for the numerical ranges described in this disclosure should be considered disclosed and freely usable. Attached Figure Description

[0021] Further advantages will become apparent from the following description of the accompanying drawings. Two embodiments of the invention are illustrated in the drawings. The drawings, description, and claims contain a large number of features in combination. Those skilled in the art will also be able to observe the stated features individually and generalize them into other meaningful combinations.

[0022] Figure 1 A schematic diagram of a single fuel tank device according to the present invention is shown; Figure 2 A schematic flowchart of the method according to the invention is shown; and Figure 3 A schematic flowchart illustrating an alternative design scheme to the method according to the present invention is shown. Detailed Implementation

[0023] Figure 1 A single-cell fuel unit 12a is shown. The single-cell fuel unit 12a preferably includes at least one single-cell fuel cell unit 22. The single-cell fuel cell unit 22a preferably includes a single-cell fuel cell composite structure 24a, the single-cell fuel cells being particularly preferably electrically connected in series for common operation. The single-cell fuel cell composite structure 24a is here functionally represented by a single single-cell fuel cell having a fuel electrode 26a and an oxygen electrode 28a. The single-cell fuel cell composite structure 24a is preferably configured for electrochemical conversion of the fuel while supplying oxygen, particularly oxygen from the air. The single-cell fuel cell unit 22a preferably includes a fluid supply mechanism 14a for supplying fuel, such as methane, hydrogen, and / or ammonia as pure substances or as mixtures, particularly natural gas or biogas, to the single-cell fuel cell composite structure 24a and for supplying oxygen, particularly air. The single-cell fuel unit 12a includes at least one regulating unit 20a. The regulating unit 20a is particularly preferably configured for regulating the flow rate of the fluid supply mechanism 14a, particularly the flow rate of fuel and / or oxygen. Adjustment unit 20a is configured to implement method 10a or 10b, the method being... Figure 2 Alternatively, this can be explained in detail in section 3. The fuel cell unit 22a preferably includes an inverter 18a for feeding the electrical power provided by the fuel cell composite structure 24a into the power grid.

[0024] The fluid supply mechanism 14a preferably includes at least one fuel delivery unit 30a for delivering fuel to the fuel electrode 26a. The fuel delivery unit 30a is preferably configured as a blower. The fuel pool unit 22a preferably includes at least one fuel line 44a leading from the fluid supply mechanism 14a to the fuel electrode 26a. Along the fuel line 44a, the fuel pool unit 22a includes, for example, a recirculation delivery unit 36a for regulating the feedback rate of exhaust gas into the fuel line 44a, a fuel recovery unit 38a for transferring heat from the feedback exhaust gas to the fuel in the fuel line 44a, a fuel preheater 40a for transferring heat from the afterburner exhaust gas leaving the fuel pool unit 22a to the fuel in the fuel line 44a, and / or a reforming unit 42a for reforming the fuel, particularly in this order with respect to the direction of fuel flow.

[0025] The fluid supply mechanism 14a preferably includes a fuel shut-off valve 32a for coupling or decoupling the fuel delivery unit 30a to or from the fuel line 44a. Alternatively, the fluid supply mechanism 14a includes another fuel branch 34a for feeding a different fuel, particularly starter fuel such as pure hydrogen used to start the fuel pool unit 22a, into the fuel line 44a. This other fuel branch 34a preferably includes another fuel shut-off valve 35a for coupling or decoupling a source of the other fuel to or from the fuel line 44a.

[0026] The fuel cell unit 22a preferably includes at least one afterburner 16a for converting residual fuel in the exhaust gas flowing from the fuel electrode 26a. The afterburner 16a is preferably connected downstream of the fuel cell composite structure 24a to the fuel electrode 26a and the oxygen electrode 28a. The afterburner outlet of the afterburner 16a is preferably connected to the fuel preheater 40a.

[0027] The fuel cell unit 22a preferably includes a feedback line 48a for feeding back a portion of the exhaust gas flowing from the fuel electrode 26a. The feedback line 48a is preferably connected to the fuel electrode 26a parallel to the afterburner 16a. The feedback line 48a preferably includes a fuel recovery unit 38a. The feedback line 48a preferably includes a feedback-oxygen preheater 50a for transferring heat from the fed-back exhaust gas to oxygen. The confluence of the feedback line 48a into the fuel line 44a is preferably positioned upstream of the recirculation delivery unit 36a and, in particular, downstream of the fuel delivery unit 30a.

[0028] The fluid supply mechanism 14a preferably includes an oxygen delivery unit 52a for delivering oxygen, particularly air, to the oxygen electrode 28a. The oxygen delivery unit 52a is preferably configured as a blower. The fuel cell unit 22a preferably includes a main oxygen pipeline 54a connecting the fluid supply mechanism 14a to the oxygen electrode 28a. The main oxygen pipeline 54a preferably includes an exhaust gas-oxygen preheater 56a for transferring heat from the exhaust gas of the afterburner 16a to the oxygen. The fuel cell unit 22a preferably includes a bypass pipeline 58a, which includes the oxygen preheater 56a. The bypass pipeline 58a includes, for example, an electric heating element for heating the oxygen. The fuel cell unit 22a preferably includes a preheating pipeline 60a in which the feedback-oxygen preheater 50a is arranged. The preheating pipeline 60a preferably enters the main oxygen pipeline 54a upstream of the exhaust gas-oxygen preheater 56a. The fluid supply mechanism 14a preferably includes an oxygen regulating unit 62a for coupling or decoupling the oxygen delivery unit 52a from the main oxygen line 54a, the bypass line 58a, and / or the preheating line 60a. The oxygen regulating unit 62a is represented herein by three single valves and can also be a multi-way valve or be configured as a multi-way valve.

[0029] Figure 2 A method 10a for operating a fuel monocell unit 12a connected to a power grid is shown. Method 10a preferably includes normal operation 64a of the fuel monocell unit 12a. In normal operation 64a, the regulating unit 20a preferably performs adjustments, particularly those known per se, to electrochemical parameters such as fuel utilization and the electrochemical conversion of fuel in the fuel monocell complex. In normal operation 64a, a power target value for the supplied electrical power is preferably predetermined, particularly a power target value for the current associated with the supplied electrical power. The regulating unit 20a attempts to maintain the fuel monocell unit 12a preferably at an operating point dependent on the power target value by adjusting the settings of the fluid supply mechanism 14a. In particular, the regulating unit 20a determines at least one fluid supply target value, such as a fuel supply target value, a recirculation rate target value, and / or an oxygen supply target value, based on the adjustment difference defined by the operating point. Preferably, the regulating unit 20a sends at least one fluid supply target value to the control or regulating unit of the component to be regulated in the fluid supply mechanism 14a. The components to be adjusted may in particular be the fuel delivery unit 30a, the recirculation delivery unit 36a, the oxygen delivery unit 52a, the fuel shut-off valve 32a, another fuel shut-off valve 35a and / or the oxygen regulating unit 62a.

[0030] Method 10a preferably includes voltage monitoring 66a of the power grid. Preferably, inverter 18a checks the voltage of the power grid in voltage monitoring 66a. Preferably, inverter 18a outputs a grid signal to regulation unit 20a, which encodes the state of the power grid. The grid signal can be configured as an enable signal or a fault signal, and regulation unit 20a further operates fuel cell unit 22a or initiates a disconnection process 70a of fuel cell unit 22a based on the enable signal or fault signal. Preferably, the grid signal indicates whether the voltage of the power grid, except for possible short-term voltage drops, is within the tolerance band surrounding the nominal voltage of the power grid, or whether the voltage curve of the power grid exceeds the short-term voltage drop, especially below a predetermined voltage limit curve. Inverter 18a predetermines whether the voltage drop should be assessed as short-term.

[0031] Method 10a preferably includes a fault assessment 68a, which is preferably performed when the regulating unit 20a receives a grid signal as an enable signal or whenever the regulating unit does not receive a grid signal as a fault signal. In the fault assessment 68a, the regulating unit 20a preferably checks whether the fluctuation of the current flowing through the fuel cell composite structure 24a is within the allowable fluctuation range of the electrochemical parameter adjustment. If the fluctuation of the current flowing through the fuel cell composite structure 24a is within the allowable fluctuation range of the electrochemical parameter adjustment, the regulating unit 20a preferably continues normal operation 64a. If the fluctuation of the current flowing through the fuel cell composite structure 24a is outside the allowable fluctuation range of the electrochemical parameter adjustment, the regulating unit 20a preferably performs fault operation 72a of method 10a. The regulating unit 20a preferably performs fault operation 72a whenever the regulating unit 20a receives a grid signal as an enable signal or whenever the regulating unit does not receive a grid signal as a fault signal and the deviation of the current from the target power value flowing through the fuel cell composite structure 24a is outside the allowable fluctuation range. When there is a short-term voltage drop in the power grid, it is preferable to perform fault operation 72a.

[0032] During fault operation 72a, regulating unit 20a preferably performs regulation of electrochemical parameters. Specifically, the current flowing through fuel cell unit 12a is associated with a short-term voltage drop in the power grid. Regulating unit 20a at least partially maintains the fluid supply 14a to fuel cell unit 12a during the short-term voltage drop in the power grid. During the short-term voltage drop, regulating unit 20a maintains the fluid supply 14a at least substantially constant by pre-setting at least one constant fluid supply target value for the duration of fault operation 72a. During the short-term voltage drop, regulating unit 20a determines a value for the fluid supply target value as the fluid supply target value, which is pre-set by the following operating point of fuel cell unit 12a, which has been determined within a time window prior to the short-term voltage drop. Specifically, regulating unit 20a adjusts the fluid supply target value during fault operation 72a to the fluid supply target value last determined during normal operation 64a. During fault operation 72a, the regulating unit 20a reduces the fluid supply target value relative to normal operation 64a only when at least one temperature parameter of the fuel single-pool unit 12a, especially the afterburner 16a, exceeds the limit value.

[0033] In fault operation 72a, the regulating unit 20a transfers the thermal efficiency of the fuel cell unit 12a at the expense of its electrical efficiency. In fault operation 72a, the heat capacity of the fuel cell unit 12a, especially its afterburner 16a, is utilized to at least partially absorb the heat generated by the fuel cell unit 12a during the short-term voltage drop.

[0034] After a short voltage drop, normal operation resumes 64a when the current supplied by the fuel single-pool unit 12a in the fault assessment 68a is at least substantially equal to a pre-given threshold.

[0035] exist Figure 3 Another embodiment of the invention is shown below. The following description and drawings are essentially limited to the differences between the embodiments, wherein reference can be made in principle to other embodiments, especially to components that are represented the same, particularly those having the same reference numerals. Figures 1 to 2 The accompanying drawings and / or descriptions are provided. To distinguish the embodiments, in... Figures 1 to 2 The letter 'a' is added after the reference numerals in the embodiments shown in the figures. Figure 3 In one embodiment, the letter 'a' is replaced by the letter 'b'.

[0036] Figure 3A method 10b for operating a fuel cell unit connected to a power grid is shown as an alternative. In at least one fault operation 72b of method 10b, adjustments are made to the current supplied to the fuel cell unit in the event of a short-term voltage drop in the power grid. During the short-term voltage drop in the power grid, the fluid supply to the fuel cell unit is maintained at least partially. In fault operation 72b, the regulation of the electrochemical parameters of normal operation 64b of method 10b is maintained, in particular, without change. Preferably, the regulating unit of the fuel cell unit adjusts at least one target value of the fluid supply based on the current flowing through the fuel cell unit during fault operation 72b.

[0037] For other features of method 10b, refer to... Figure 2 And its explanation.

Claims

1. A method (10a; 10b) for operating a fuel cell unit (12a) connected to a power grid, wherein, in at least one method step, the supply of current through the fuel cell unit (12a) is adjusted in the event of a short-term voltage drop in the power grid, characterized in that, The fluid supply (14a) to the fuel cell unit (12a) is maintained at least partially during short-term voltage drops in the power grid.

2. The method according to claim 1 (10a; 10b), characterized in that, During a short period of voltage drop in the power grid, the thermal efficiency of the fuel cell unit (12a) is transferred at the expense of its electrical efficiency.

3. The method according to claim 1 or 2 (10a; 10b), characterized in that, During a short-term voltage drop in the power grid, the heat capacity of the fuel cell unit (12a), especially the afterburner (16a) of the fuel cell unit (12a), is utilized to absorb at least part of the heat generated by the fuel cell unit (12a) during the short-term voltage drop.

4. The method according to claim 3 (10a; 10b), characterized in that, The fluid supply (14a) is cut off only when at least one temperature parameter of the fuel cell unit (12a), especially the afterburner (16a), exceeds a limit value.

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

6. The method (10a) according to any one of the preceding claims, characterized in that, During the short voltage drop period, the fluid supply (14a) is adjusted to a predetermined value by means of the following operating point of the fuel single-pool device (12a), which has been identified in the time window prior to the short voltage drop.

7. The method (10a) according to any one of the preceding claims, characterized in that, After a short voltage drop, the regulation of the fluid supply (14a) resumes when the current supplied through the fuel cell unit (12a) is at least substantially equal to a predetermined threshold.

8. The method according to any one of the preceding claims (10a; 10b), characterized in that, The inverter (18a) of the fuel cell unit (12a) is given in advance whether the voltage drop should be assessed as short-term.

9. A fuel single-pool device (12a) having at least one regulating unit (20a) for implementing the method (10a; 10b) according to any one of the preceding claims.

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