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

Abstract

The invention relates to a method (10a; 10b) for operating a fuel cell device (12), wherein in at least one method step electrical power is provided by at least one fuel cell unit (14, 16, 18) of the fuel cell device (12) and wherein in at least one method step a deviation of the provided electrical power from an electrical power output by the fuel cell device (12) is compensated by means of an electrical energy storage unit (20) of the fuel cell device (12). It is proposed that in at least one process step the supplied electrical power is adjusted depending on the state of charge of the electrical energy storage unit (20).

Description

State of the art

[0001] A method for operating a fuel cell device has already been proposed, wherein in at least one method step electrical power is provided by at least one fuel cell unit of the fuel cell device and wherein in at least one method step a deviation of the provided electrical power from an electrical power output by the fuel cell device is compensated by means of an electrical energy storage unit of the fuel cell device. Disclosure of the invention

[0002] The invention is based on a method for operating a fuel cell device, wherein in at least one method step electrical power is provided by at least one fuel cell unit of the fuel cell device and wherein in at least one method step a deviation of the provided electrical power from an electrical power output by the fuel cell device is compensated by means of an electrical energy storage unit of the fuel cell device.

[0003] It is proposed that in at least one method step of the method, the electrical power provided is adjusted as a function of a state of charge of the electrical energy storage unit. The fuel cell device preferably comprises a grid feed-in unit for feeding the electrical power into a power grid, which can be designed, for example, as an interconnected grid or an isolated grid. The fuel cell device can comprise precisely one or more fuel cell units which are connected jointly, in particular electrically in parallel, to the grid feed-in unit. The grid feed-in unit preferably comprises at least one current converter, in particular inverter, for adapting the electrical power to the grid. The electrical energy storage unit is preferably connected, in particular electrically in parallel, to the at least one fuel cell unit on the grid feed-in unit.

[0004] The output power is preferably a grid-side power of the grid feed-in unit. The output power preferably comprises the power provided by the fuel cell unit and an electrical storage power of the electrical energy storage unit. When the electrical energy storage unit is discharged, the electrical storage power of the energy storage unit increases the output power of the grid feed-in unit relative to the power provided by the fuel cell unit. When the electrical energy storage unit is charged, the electrical storage power of the energy storage unit decreases the internal power of the grid feed-in unit relative to the power provided by the fuel cell unit. Preferably, a fuel cell control unit of the fuel cell unit maintains the at least one fuel cell at an operating point, in particular as a function of a predetermined modulation.Preferably, a control device of the fuel cell device specifies a target modulation of the fuel cell unit depending on the output power. Preferably, the control device adapts the target modulation of the fuel cell unit to a changing output power, in particular so that the provided power is at least substantially equal to the output power. "Substantially equal" is to be understood, in particular, as equal except for an excess amount dependent on a specific configuration of the fuel cell device to compensate for losses, in particular of the power converter, and / or to supply electronics of the fuel cell device or the like.Preferably, the control device sets a target value of the electrical storage power of the electrical storage unit to a minimum value, in particular 0 W, at a stable operating point of the fuel cell unit and a constant output power. For an operating point change dependent on the target modulation, the fuel cell unit typically requires a transition period during which the provided power generally does not correspond to the output power. The electrical energy storage unit is preferably designed to compensate for the deviation between the provided power and the output power during the operating point change of the fuel cell unit.The electrical energy storage unit is preferably designed to compensate for the deviation of the provided power from the output power during a short-term voltage drop of the power grid, for which a grid operator of the power grid prescribes a fault ride-through (FRT) behavior of the fuel cell device, for example according to VDE-AR-N 4105 or VDE-AR-N 4110.

[0005] The electrical state of charge preferably describes or characterizes how much electrical energy is stored by means of the electrical storage unit, in particular in relation to a total capacity of the electrical storage unit. Preferably, the control device determines the target modulation of the fuel cell unit as a function of the electrical state of charge. Preferably, the control device increases the target modulation of the fuel cell unit when the state of charge falls below a minimum charge value. The minimum charge value is preferably greater than 20%, preferably greater than 30%, particularly preferably greater than 40% of the total capacity of the electrical storage unit. The minimum charge value is preferably less than 60%, preferably less than 50%, particularly preferably at most 45% of the total capacity of the electrical storage unit.The control device preferably increases the target modulation of the fuel cell unit when the state of charge rises above a maximum charge value. The maximum charge value is preferably greater than 40%, preferably greater than 50%, particularly preferably at least 55% of the total capacity of the electrical storage unit. The maximum charge value is preferably less than 80%, preferably less than 70%, particularly preferably less than 60% of the total capacity of the electrical storage unit.

[0006] "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.

[0007] Thanks to the configuration according to the invention, the state of charge of the energy storage unit can advantageously be maintained within a medium range. In particular, the risk that the energy storage unit will not be able to absorb or release energy in the event of a sudden change in load, for example, due to a (grid) failure, can be advantageously kept low. The fuel cell device can be operated maintenance-free, in particular without interruption, for an advantageously long period of time. In particular, the risk of deep discharge and / or premature aging of the energy storage unit can advantageously be kept low.

[0008] It is further proposed that in at least one method step of the method, the state of charge of the electrical energy storage unit is regulated to a target state of charge. Preferably, the control device comprises at least one state of charge controller. The state of charge controller comprises, for example, at least one proportional element (P element), at least one integral element (I element), and / or a differential element (D element). The state of charge controller preferably comprises a PI controller or a PID controller. Alternatively or additionally, the state of charge controller comprises a deadband controller. The state of charge controller preferably outputs a signal that correlates with a control difference between the target state of charge and an actual value of the state of charge. The control device determines the actual value of the state of charge, for example, by temporally integrating the storage power. Preferably, the state of charge controller outputs a target value of the storage power as a signal.The control device preferably sets the target modulation of the fuel cell unit depending on the target storage power. The target charge level is preferably between 30% and 70%, preferably between 40% and 60%, particularly preferably between 45% and 55%, in particular 50%, of the total capacity of the electrical energy storage unit. The design according to the invention advantageously allows the charge level to be reliably maintained.

[0009] It is further proposed that in at least one method step of the method the state of charge of the electrical energy storage unit is adjusted by means of a multi-stage control system. Preferably, the control system comprises at least a first control stage and at least one further control stage, in particular at least two further control stages. Each control stage preferably comprises at least one controller. The control stages preferably build on one another in a cascading manner. Preferably, a control difference of the further control stages is dependent on an output of the first control stage. Preferably, a control difference of an additional control stage is dependent on an output of the further control stage. The first control stage preferably comprises the state of charge controller. The further stage comprises, for example, a storage power controller for regulating the storage power.The additional control stage comprises, for example, an output power controller for regulating the output power. Preferably, the final control stage of the control system outputs the target modulation. The inventive design advantageously allows the charge level to be maintained within a range of the target charge level, the grid connection conditions of the power grid to be met, and a predetermined target output power of the fuel cell device to be maintained. In particular, the risk that either the target charge level, the grid connection conditions, and / or the target output power are not met can be advantageously minimized.

[0010] It is further proposed that, in at least one method step of the method for adjusting the state of charge, an electrical storage power at the energy storage unit is controlled as a function of the state of charge. The storage power is preferably controlled by the storage power controller of the further control stage. The storage power controller preferably comprises a PI controller or a PID controller. The storage power controller preferably outputs a signal that correlates with a control difference between the setpoint value of the storage power and an actual value of the storage power. The storage power controller preferably obtains the setpoint value of the storage power from the state of charge controller.The control device determines the actual value of the stored power, for example, as the difference between the provided power, which is detected in particular by the fuel cell control unit, and the output power, which is detected in particular by the grid feed-in unit. Alternatively or additionally, the energy storage unit comprises a power meter that detects the stored power. Preferably, the storage power controller outputs a power control value as a signal to the grid feed-in unit in order to determine the output power. Particularly preferably, the control device or a higher-level control system of the fuel cell system modifies the power control value before transferring it to the grid feed-in unit in order to keep the output power grid-compliant, in particular according to VDE-AR-N 4105 or VDE-AR-N 4110.For example, the control device increases or decreases the power control value if a grid frequency of the power grid lies outside a tolerance band around a grid frequency setpoint. For example, the control device limits a maximum value and / or a maximum rate of change of the power control value. Due to the inventive design, charging and discharging of the energy storage unit is subject to advantageously extensive control. In particular, charging and discharging of the energy storage unit can advantageously be limited to a few situations, such as in the event of a (grid) fault and / or an excessively rapid change in the externally tapped power and / or excessively rapid predetermined operating point changes. This can advantageously further slow down aging of the energy storage unit.

[0011] It is further proposed that, in at least one method step of the method, the electrical power output by the fuel cell device is regulated as a function of the state of charge of the electrical energy storage unit. The output electrical power is preferably regulated by the output power controller. The additional control stage preferably comprises the output power controller. The output power controller preferably comprises a PI controller or a PID controller. The output power controller preferably outputs a signal that correlates with a control difference between a target power to be output and an actual value of the output power. The target power to be output is preferably specified by an operator of the fuel cell device. The target power to be output can be a constant value or a temporal profile.The output power is preferably detected by the grid feed-in unit, which is adjusted depending on the state of charge, in particular via the state of charge controller and the storage power controller. The output power controller preferably outputs the target modulation of the fuel cell unit as a signal. In an embodiment with multiple fuel cell units, the output power controller preferably outputs a total target modulation of an entire unit of all fuel cell units as a signal, wherein the control device determines individual target modulations for the different fuel cell units in a subsequent power distribution step of the method and transmits them to the respective fuel cell unit. Due to the embodiment according to the invention, the target power to be output can advantageously be reliably covered, in particular despite control of the state of charge.

[0012] It is further proposed that in at least one method step of the method, a target electrical power to be output by the fuel cell device, in particular the aforementioned one, is set as a function of the state of charge. Preferably, the control device reduces the target power to be output, in particular compared to a value predetermined, for example, by an operator, if the state of charge falls below a charging limit. The charging limit is, for example, identical to the minimum charging value. Alternatively or additionally, the charging limit is less than or equal to half the target state of charge, in particular less than or equal to 25% of the total capacity of the energy storage unit. The charging limit is preferably greater than a quarter of the target state of charge, in particular greater than 10% of the total capacity of the energy storage unit.Preferably, a reduction in the target power to be output depends on, in particular proportional to, the target value of the storage power. The design according to the invention can advantageously further reduce the risk of deep discharge of the energy storage unit.

[0013] It is further proposed that in at least one method step of the method, the state of charge of the electrical energy storage unit is only actively adjusted if a deviation of the state of charge and / or the storage power from a target state of charge, in particular the one already mentioned, is outside a tolerance band around the target state of charge. The tolerance band preferably has a bandwidth of more than 2%, preferably more than 6%, particularly preferably at least 8%, of the total capacity of the energy storage unit. The tolerance band preferably has a bandwidth of less than 20%, preferably less than 15%, particularly preferably at most 12%, of the total capacity of the energy storage unit. The tolerance band is preferably arranged symmetrically around the target state of charge. Alternatively, an upper limit of the tolerance band is further or closer to the target state of charge than a lower limit of the tolerance band.As long as the state of charge is within the tolerance band, the control device preferably sets the control difference of the state of charge controller to zero and / or switches off the state of charge controller, in particular an enable signal of the state of charge controller. If the state of charge is outside the tolerance band, the control device preferably determines the control difference as the difference between the actual state of charge value and the target state of charge or the limit of the tolerance band closest to the actual state of charge value, in particular the upper or lower limit, and / or switches on the state of charge controller, in particular an enable signal of the state of charge controller. The design according to the invention advantageously allows the risk of oscillating behavior of the control to be kept low. In particular, an operating point of the fuel cell unit can advantageously be kept stable.In particular, the risk of excessive dominance of the state of charge controller, especially relative to the influence of the output power controller, on the target modulation can be advantageously kept low.

[0014] It is further proposed that in at least one method step of the method, an electrical storage power applied to the electrical energy storage unit, in particular the one already mentioned, is only actively adjusted if a deviation of the storage power from a target storage power is outside a power tolerance band by a target storage power. The power tolerance band preferably has a bandwidth of more than 2%, preferably more than 6%, particularly preferably at least 8%, of the total capacity of the energy storage unit. The power tolerance band preferably has a bandwidth of less than 20%, preferably less than 15%, particularly preferably at most 12%, of the total capacity of the energy storage unit. The power tolerance band is preferably arranged symmetrically around the target value of the storage power.Alternatively, an upper limit of the power tolerance band is further or closer to the target value of the storage power than a lower limit of the power tolerance band. As long as the storage power is within the power tolerance band, the control device preferably sets the control difference of the storage power controller to zero and / or switches off the storage power controller, in particular an enable signal of the storage power controller. If the storage power is outside the power tolerance band, the control device preferably determines the control difference as the difference between the actual value of the storage power and the target value of the storage power or the limit of the power tolerance band closest to the actual value of the storage power, in particular the upper or lower limit, and / or switches on the storage power controller, in particular an enable signal of the storage power controller.The inventive design advantageously minimizes the risk of oscillating control behavior. In particular, an operating point of the fuel cell unit can be advantageously kept stable. In particular, the risk of excessive dominance of the storage power controller, particularly relative to the influence of the output power controller, on the target modulation can be advantageously minimized.

[0015] Furthermore, a control device for a fuel cell device for carrying out a method according to the invention is proposed. A "control device" or 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. Components of the control device are preferably arranged on a common circuit board and / or advantageously arranged in a common housing. The control device preferably comprises at least the charge state controller and the storage power controller. The output power controller can be part of the control device or the higher-level control system of the fuel cell system.The control device preferably comprises a grid output port for outputting the power control value to the grid feed-in unit, in particular via a grid security module of the higher-level control system of the fuel cell system. The control device preferably comprises a fuel cell output port for outputting the target modulation to the fuel cell unit. The control device preferably comprises at least one storage power input port for receiving the actual value of the storage power. The control device preferably comprises at least one state of charge input port for receiving the actual value of the state of charge. The control device preferably comprises at least one output power input port for receiving the actual value of the output power.The configuration according to the invention advantageously makes it possible to provide a control device by means of which the state of charge can be maintained in a range around the target state of charge, grid connection conditions of the power grid can be maintained and a predetermined target output power of the fuel cell device can be maintained.

[0016] Furthermore, a fuel cell device is proposed, comprising at least one fuel cell unit for providing electrical power, at least one electrical energy storage unit connected to the fuel cell unit, and at least one control device according to the invention. The fuel cell device is preferably a generating plant within the meaning of VDE-AR-N 4105 or VDE-AR-N 4110. The fuel cell device preferably comprises the grid feed-in unit connected to the fuel cell unit. The electrical storage unit comprises, for example, at least one battery, a power capacitor, a supercapacitor, or the like, in order to store the energy required to compensate for the deviation between the provided power and the output power.The fuel cell unit preferably comprises at least one fuel cell, in particular a plurality of fuel cells, which are intended for joint operation. The at least one fuel cell device is preferably designed as a solid oxide fuel cell, alternatively as a molten carbonate fuel cell, as a polymer electrolyte fuel cell, or the like. The fuel cell device preferably comprises the control system to which the regulating device is connected. The design according to the invention makes it possible to provide an advantageously reliable, grid-compatible, and low-maintenance fuel cell device.

[0017] The method according to the invention, the control device according to the invention, and / or the fuel cell device according to the invention are not intended to be limited to the application and embodiment described above. In particular, the method according to the invention, the control device according to the invention, and / or the fuel cell device according to the invention may, in order to fulfill a function described herein, have a number of individual elements, components, units, and method steps that differs from the number stated 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. Drawings

[0018] 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.

[0019] They show: Fig. 1 a schematic representation of a fuel cell device according to the invention, Fig. 2 a schematic flow diagram of a method according to the invention and Fig. 3 a schematic flow diagram of a further embodiment of a method according to the invention. Description of the embodiments

[0020] Fig. 1 shows a fuel cell device 12. The fuel cell device 12 comprises at least one fuel cell unit 14 and, here by way of example, several further fuel cell units 16, 18 for providing electrical power. The fuel cell units 14, 16, 18 preferably each comprise a plurality of fuel cells, in particular solid oxide fuel cells, as well as peripheral devices for operating the respective fuel cells. The fuel cells of each of the fuel cell units 14, 16, 18, together with the associated peripheral devices, are preferably arranged in a common housing of the fuel cell units 14, 16, 18. The fuel cell units 14, 16, 18 can preferably be operated independently of one another and, in particular, can be individually controlled. The fuel cell device 12 preferably comprises a grid feed-in unit 30.The fuel cell units 14, 16, 18 are preferably electrically connected in parallel to the grid feed-in unit 30. The grid feed-in unit 30 is preferably provided to feed the power provided by the fuel cell units 14, 16, 18 into an external power grid 32. The grid feed-in unit 30 preferably comprises at least one current converter, in particular an inverter, for converting the power provided by the fuel cell units 14, 16, 18 into a form compatible with the power grid. The fuel cell units 14, 16, 18 are shown here as direct current sources, which are connected to the grid feed-in unit 30, in particular, via a direct voltage bus. Alternatively, the fuel cell units 14, 16, 18 are designed as alternating voltage sources.

[0021] The fuel cell device 12 comprises an electrical energy storage unit 20 with at least one or more storage elements, such as, in particular, a battery, a supercapacitor, and / or a power capacitor. The energy storage unit 20 is preferably electrically connected to the grid feed-in unit 30 in parallel with the fuel cell units 14, 16, 18. The energy storage unit 20 preferably comprises a storage current converter 34, via which the storage element is connected to the DC bus.

[0022] The fuel cell device 12 preferably comprises at least one control system 36 for operating the fuel cell device 12. The control system 36 preferably comprises a control device 28 for carrying out methods 10a and 10b, which are explained in more detail in the following figures. The control device 28 is preferably provided for electrical power management of the fuel cell device 12, in particular for determining a target modulation of the fuel cell units 14, 16, 18 and / or a control value of the grid feed-in unit 30 in order to adjust the power output from the fuel cell device 12 to the power grid 32. The control system 36 preferably comprises at least one grid security module 38.The grid security module 38 preferably controls or regulates the grid feed-in unit 30 in order to keep the power output by the fuel cell device 12 to the power grid 32 in compliance with the power grid, in particular according to VDE-AR-N 4105 or VDE-AR-N 4110. The grid security module 38 preferably modifies the control value determined by the control device 28 using predetermined grid functions in order to keep the output power in compliance with the power grid. The control system 36 preferably comprises a power distribution module 40 for determining individual target modulations of the various fuel cell units 14, 16, 18 depending on the target modulation of the entire fuel cell device 12 determined by the control device 28. The grid security module 38 and / or the power distribution module 40 can be designed as a standalone module of the control system 36, in particular as a prefabricated part, or can be integrated into the control device 28.

[0023] The control system 36 may include further components which are not shown here, such as, for example, an air conditioning control for air conditioning a location where the fuel cell device 12 is used, a fluid control for adjusting a supply of fuel and / or fresh air to the fuel cell units 14, 16, 18, a thermal power control for managing operating heat produced by the fuel cell units 14, 16, 18, or the like.

[0024] In the Fig. 2 and Fig. 3 shows different embodiments of the method according to the invention and the control device according to the invention, each of which is connected to the fuel cell system of Fig. 1. 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 generally also be made to the drawings and / or the description of the other exemplary embodiments. To distinguish the exemplary embodiments, the letter a is added to the reference numerals of the exemplary embodiment in the Fig. 2. In the example of the Fig. 3, the letter a is replaced by the letter b.

[0025] Fig. 2 shows a signal flow diagram of the method 10a for operating the fuel cell device 12 from Fig. 1 by means of a control device 28a. In at least one method step of the method 10a, electrical power is provided by at least one of the fuel cell units 14, 16, 18 of the fuel cell device 12. In at least one method step, a deviation between the provided electrical power and the electrical power output by the fuel cell device 12 to the power grid 32 by means of the grid feed-in unit 30 is compensated for by means of the electrical energy storage unit 20 of the fuel cell device 12. In at least one method step, the provided electrical power is adjusted as a function of a state of charge of the electrical energy storage unit 20. Preferably, the control device 28a outputs a target modulation 64a of the entire fuel cell device 12.Preferably, a fuel cell control unit of at least one of the fuel cell units 14, 16, 18 adjusts the power provided by at least one of the fuel cell units 14, 16, 18 as a function of the target modulation 64a. The control device 28a preferably determines the target modulation 64a as a function of the state of charge of the electrical energy storage unit 20.

[0026] The control device 28a preferably comprises a state of charge controller 50a. In at least one method step of the method 10a, the state of charge controller 50a regulates the state of charge of the electrical energy storage unit 20 to a target state of charge 22a. Preferably, the control device determines the target modulation 64a using the state of charge controller 50a as a function of a control difference between an actual value 48a of the state of charge and the target state of charge 22a. The state of charge controller 50a can be configured as a PI controller, a PID controller, or a deadband controller. The control device 28a preferably uses an average state of charge, for example, between 40% and 60%, in particular 50% of a total capacity of the energy storage unit 20, as the target state of charge 22a.

[0027] The control device 28a adjusts the state of charge of the electrical energy storage unit 20 by means of a multi-stage control. The control device 28a adjusts the state of charge in particular by specifying the target modulation 64a. The method 10a comprises, for example, three stages. A first control stage of the method 10a is carried out by the state of charge controller 50a. A further control stage of the method 10a is carried out by a storage power controller 54a of the control device 28a. An additional control stage of the method 10a is carried out by an output power controller 62a of the control device 28a. The stages are cascaded. Preferably, an output of the first control stage is connected to an input of the further control stage. Preferably, an output of the further control stage is connected to an output of the additional control stage.

[0028] The storage power controller 54a can be configured as a PI controller or a PID controller. To adjust the state of charge, the storage power controller 54a regulates an electrical storage power with which the energy storage unit 20 is charged or discharged, depending on the state of charge. Preferably, the control device 28a determines the target modulation 64a using the storage power controller 54a as a function of a control difference between an actual value 52a of the storage power and a target storage power 26a. The target storage power 26a is preferably output by the state of charge controller 50a. The target storage power 26a is preferably zero if the state of charge is within a tolerance band around the target state of charge 22a.The actual value 52a of the storage power results in particular from the difference between the power output by the fuel cell device 12 and the power provided by the at least one fuel cell unit 14, 16, 18.

[0029] The output power controller 62a regulates the electrical power output by the fuel cell device 12 depending on the state of charge of the electrical energy storage unit 20. The storage power controller 54a preferably outputs a control value 66a for the grid feed-in unit 30 to the grid security module 38. The grid security module 38 modifies the control value 66a, if necessary using one or more predetermined grid functions, in order to keep the output electrical power grid-compliant. The grid security module 38 preferably forwards the modified control value 68a to the grid feed-in unit 30. In the event of a change in the control value 66a relative to a previous value of the control value 66a that is irrelevant with regard to grid security, the modified control value 68a is identical to the control value 66a. The grid feed-in unit 30 preferably adjusts the output power depending on the modified control value 68a.The grid feed-in unit 30 preferably reports an actual value 60a of the output power to the output power controller 62a. The output power controller 62a preferably outputs the target modulation 64a as a function of a control difference between the actual value 60a of the output power and a target power 24a to be output by the fuel cell device 12. The target power 24a to be output is specified, for example, by an operator of the fuel cell device 12.

[0030] Due to the design according to the invention, the state of charge can be maintained in a medium range, the energy storage unit 20 can be charged or discharged predominantly only in the event of (mains) disturbances, and the output power can be maintained at the predetermined target output power 24a.

[0031] Fig. 3 shows a signal flow diagram of the method 10b for operating the fuel cell device 12 from Fig. 1 by means of a control device 28b. In at least one method step of the method 10b, an electrical power is provided by at least one of the fuel cell units 14, 16, 18 of the fuel cell device 12. In at least one method step, a deviation between the provided electrical power and the electrical power output by the fuel cell device 12 to the power grid 32 by means of the grid feed-in unit 30 is compensated for by means of the electrical energy storage unit 20 of the fuel cell device 12. In at least one method step, the provided electrical power is adjusted as a function of a state of charge of the electrical energy storage unit 20.

[0032] The control device 28b comprises a correction module 70b, which determines a control value 66b for the grid feed-in unit 30 as a pre-control value of a target modulation 64b of the fuel cell units 14, 16, 18 and sends it to the grid security module 38. The correction module 70b determines the control value 66b preferably by correcting a target power 24b to be output by the fuel cell device 12, in particular by limiting the target power 24b to be output, depending on a maximum power 80b and / or minimum power 82b that can be provided by the fuel cell units 14, 16, 18. The control device 28b preferably requests a modified control value 68b from the grid security module 38.Preferably, the method 10b comprises an addition step 77b in which the control device 28b adds a required power adjustment 86b for charging or discharging the energy storage unit 20, determined by a storage power controller 54b of the control device 28b, to the modified control value 68b in order to determine the target modulation 64b.

[0033] The control device 28b preferably comprises a storage power module 72b, which comprises the storage power controller 54b. The storage power module 72b preferably comprises an amplitude filter 84b. The amplitude filter 84b sets values ​​of a control difference of the storage power controller 54b within a tolerance band around zero, preferably to zero. The electrical storage power applied to the electrical energy storage unit 20 is, in particular, only actively adjusted when a deviation of the storage power from a target storage power 26b is outside the tolerance band around the target storage power 26b. The amplitude filter 84b is preferably connected, as shown here, to a switching input of a switch (as shown here), which connects either the control difference or a standard value to a signal input of the storage power controller 54b, or to an enable input of the storage power controller 54b.

[0034] The control device 28b preferably comprises a state of charge module 74b, which comprises a state of charge controller 50b. The state of charge module 74b preferably comprises a further amplitude filter 88b. The further amplitude filter 88b sets values ​​of a control difference of the state of charge controller 50b within a tolerance band around zero, preferably to zero. In particular, the state of charge controller 50b thereby actively adjusts the state of charge of the electrical energy storage unit 20 only when a deviation of an actual value 48b of the state of charge from a target state of charge 22b is outside a tolerance band around the target state of charge 22b. The further amplitude filter 84b is connected here, for example, to an enable input of the storage power controller 54b. The charge state module 74b comprises, for example, an additional or alternative charge state controller 50b', wherein a switch can be used to switch between the charge state controllers 50b, 50b' as required.The state of charge controller 50b is preferably designed as a PI controller or a PID controller. The additional or alternative state of charge controller 50b' is preferably designed as a deadband controller.

[0035] The control device 28b preferably comprises a deep discharge protection module 76b for protecting the energy storage unit 20 from deep discharge during the control of the state of charge. The deep discharge protection module 76b feeds, in particular, an output of the state of charge controller 50b, 50b' into the correction module 70b in order to additionally limit the target power 24b to be output as a function of when deep discharge of the energy storage device 20 is imminent. The output of the state of charge controller 50b, 50b' is preferably used to limit the target power 24b to be output when the state of charge lies outside the tolerance range and / or when a fault detection 78b detects a power fault, and additionally when the control difference of the state of charge controller 50b, 50b' lies within a permissible charge value interval 94b.Otherwise, the deep discharge protection module 76b specifies a default value, in particular zero, to limit the target power 24b to be output. A power fault occurs, for example, if the control deviation of the storage power controller 54b is greater than a threshold value 90b and outside a permissible power value interval 92b.

[0036] Regarding further features of procedure 10b, reference is made to the Fig. 2 and its description. The structure of the individual modules of the control device 28b can also be used to implement the method 10a from Fig. 2 can be used.

Claims

[1] Method (10a; 10b) for operating a fuel cell device (12), wherein in at least one method step, electrical power is provided by at least one fuel cell unit (14, 16, 18) of the fuel cell device (12), and wherein in at least one method step, a deviation of the provided electrical power from an electrical power output by the fuel cell device (12) is compensated by means of an electrical energy storage unit (20) of the fuel cell device (12), characterized by that in at least one method step the electrical power provided is adjusted as a function of a charge state of the electrical energy storage unit (20). [2] Method (10a; 10b) according to claim 1, characterized by that in at least one method step the charge state of the electrical energy storage unit (20) is regulated to a target charge state (22a; 22b). [3] Method (10a; 10b) according to claim 2, characterized by that in at least one method step the charge state of the electrical energy storage unit (20) is adjusted by means of a multi-stage control. [4] Method (10a; 10b) according to one of the preceding claims, characterized by that in at least one method step for adjusting the state of charge, an electrical storage power at the energy storage unit (20) is regulated as a function of the state of charge. [5] Method (10a; 10b) according to one of the preceding claims, characterized by that in at least one method step the electrical power output by the fuel cell device (12) is regulated as a function of the state of charge of the electrical energy storage unit (20). [6] Method (10a; 10b) according to one of the preceding claims, characterized bythat in at least one method step, a desired electrical power (24a; 24b) to be output by the fuel cell device (12) is set as a function of the charge state. [7] Method (10a; 10b) according to one of the preceding claims, characterized by in that in at least one method step the state of charge of the electrical energy storage unit (20) is only actively adjusted if a deviation of the state of charge from a target state of charge (22a; 22b) is outside a tolerance band around the target state of charge (22a; 22b). [8] Method (10a; 10b) according to one of the preceding claims, characterized by in that, in at least one method step, an electrical storage power applied to the electrical energy storage unit (20) is only actively adjusted if a deviation of the storage power from a target storage power (26a; 26b) is outside a tolerance band around a target storage power (26a; 26b). [9] Control device (28; 28a; 28b) for a fuel cell device (12) for carrying out a method (10a; 10b) according to one of the preceding claims. [10] Fuel cell device (12) with at least one fuel cell unit (14, 16, 18) for providing electrical power, with at least one electrical energy storage unit (20) connected to the fuel cell unit (14, 16, 18) and with at least one control device (28; 28a; 28b) according to claim 9.

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