Method for determining a fuel utilization factor of a fuel cell unit in a fuel cell device, in particular SOFC fuel cell device

Abstract

The invention is based on a method for determining a fuel utilization factor of a fuel cell unit in a fuel cell device (10a; 10b; 10c), in particular an SOFC fuel cell device, which has at least one fuel cell unit (12a; 12b; 12c), in particular a fuel cell stack, at least one blower unit (14a; 14b; 14c), and at least one control and regulating unit (16a; 16b; 16c), with an operating step (18a; 18b; 18c) in which the fuel cell unit (12a; 12b; 12c) obtains electrical energy from a gaseous medium, wherein the blower unit (14a; 14b; 14c) regulates and drives a recirculation circuit (20a; 20b; 20c) in the operating step (18a; 18b; 18c) and wherein an operation of the fuel cell device (10a; 10b; 10c) is regulated by means of the control and regulating unit (16a; 16b; 16c) in the operating step (18a; 18b; 18c). It is proposed that in at least one comparison step (24a; 24b; 24c) a fuel utilization factor of the fuel cell unit (12a; 12b; 12c) is estimated by means of an empirical estimation.

Description

Prior ArtA method for determining a fuel utilization level of a fuel cell unit in a fuel cell device, in particular an SOFC fuel cell device, which has at least one fuel cell unit, in particular a fuel cell stack, at least one blower unit, and at least one open-loop and closed-loop control unit, having an operating step in which the fuel cell unit acquires electrical energy from a gaseous medium, wherein the blower unit regulates and drives a recirculation circuit in the operating step and wherein an operation of the fuel cell device is regulated by means of the open-loop and closed-loop control unit in the operating step, has already been proposed.Disclosure of the InventionThe invention is based on a method for determining a fuel utilization level of a fuel cell unit in a fuel cell device, in particular an SOFC fuel cell device, which has at least one fuel cell unit, in particular a fuel cell stack, at least one blower unit, and at least one open-loop and closed-loop control unit, having an operating step in which the fuel cell unit acquires electrical energy from a gaseous medium, wherein the blower unit regulates and drives a recirculation circuit in the operating step, and wherein an operation of the fuel cell device is regulated by means of the open-loop and closed-loop control unit in the operating step.It is proposed that in at least one comparison step, a fuel utilization factor of the fuel cell unit is estimated by means of empirical estimation.In this context, a "fuel cell device" is to be understood to mean, in particular, a device which is configured to generate an electrical energy in an operating step. The fuel cell device is preferably configured to provide a power system. The fuel cell device is preferably designed as an SOFC fuel cell device, in particular a solid oxide fuel cell. The fuel cell device preferably has a feed element which feeds an energy carrier, for example natural gas, and / or electrical energy into the fuel cell device. The fuel cell system preferably has a discharge element which discharges exhaust gases and / or electrical energy from a fuel cell system. In particular, it is conceivable for the fuel cell device to be supplied with oxygen from the ambient air by the supply element. It is also conceivable that the fuel cell device is supplied with pure oxygen via the supply element in order to supply the efficiency of the fuel cell device. Preferably, the supply element and the discharge element are designed as a pipeline. Particularly preferably, the supply element and the discharge element are designed for guiding a gaseous medium. In particular, it is conceivable for the fuel cell device to have a heat exchanger which is configured to utilize a thermal energy arising in the fuel cell unit. In particular, it is conceivable for the fuel cell device to have a cooling unit in a recirculation circuit, which cooling unit is configured to cool a gaseous medium heated by a blower unit. "Established" is to be understood in particular as specially programmed, designed and / or equipped. The fact that an object is set up for a specific function is to be understood in particular to mean that the object fulfills and / or executes this specific function in at least one application state and / or operating state.Preferably, the fuel cell device has a fuel utilization ratio. In this context, a "fuel utilization level" is to be understood to mean, in particular, a percentage or a ratio of the actually used fuel in relation to the total amount of the fuel used. Preferably, in an operating step, a fuel utilization factor of the fuel cell device is adapted.In this context, a "fuel cell unit" is to be understood to mean, in particular, a unit which is configured to obtain electrical energy from a gaseous medium in an operating step. The fuel cell unit is preferably designed as a fuel cell stack. The fuel cell unit is preferably configured to obtain electrical energy and heat electrochemically from the chemical energy of an energy carrier. The fuel cell unit is preferably configured to obtain electrical energy from a gaseous medium. The fuel cell unit is preferably configured to convert chemical reaction energy of a continuously supplied fuel and an oxidizing agent into electrical energy. Particular preference is given, for example, to using natural gas as fuel and oxygen as oxidizing agent. Alternatively, other fuels that appear expedient to a person skilled in the art, for example methanol, butane, ammonia and / or hydrogen, are also conceivable. Preferably, in an operating step, electrical energy is generated in the fuel cell unit between an anode and a cathode. Preferably, the anode cleaves the electrons of the fuel. Preferably, the electrons are conducted into the cathode via a connecting element. The fuel cell unit preferably has at least one fuel cell. Particularly preferably, the fuel cell unit has a plurality of fuel cells. Preferably, all fuel cells in a fuel cell unit are identical. Alternatively, it is conceivable for the fuel cell units to be of different design. Preferably, each fuel cell has an anode and a cathode. Preferably, all fuel cells of a fuel cell unit are configured to be electrically connected to one another. Preferably, the fuel cells are electrically connected in series or in parallel to achieve the desired output voltage and power. Preferably, the fuel cell unit has a fuel utilization ratio. Preferably, in an operating step, a fuel utilization level of the fuel cell unit is kept constant.In this context, a "blower unit" is to be understood to mean, in particular, an element which accelerates a gaseous medium. Preferably, a gaseous medium is accelerated by the blower unit to a medium flow. Preferably, the blower unit generates an air flow of the gaseous medium. The blower unit preferably has at least one moving blade element, by means of which a rotational movement is converted into a linear movement of the gaseous medium. The heat transfer device preferably has a drive unit which drives the at least one moving blade element in a rotational manner. A "moving blade element" is to be understood in particular as an element which converts a converted enthalpy at least substantially completely or partially into flow energy of a gaseous medium. Preferably, the blower unit is arranged in a recirculation circuit. Preferably, the blower unit is arranged at least substantially partially, preferably at least to a large extent and particularly preferably completely in a recirculation circuit. The expression "at least a major part" is to be understood here in particular as meaning at least 55%, advantageously at least 65%, preferably at least 75%, particularly preferably at least 85% and particularly advantageously at least 95%. "At least substantially" is to be understood in this context in particular as meaning that a deviation from a predefined value deviates in particular by less than 25%, preferably by less than 10% and particularly preferably by less than 5% of the predefined value. Particularly preferably, the guide blade element is arranged completely in a recirculation circuit.In this context, an "operating step" is to be understood to mean, in particular, a method step in which the fuel cell device is operated, in particular in a regular and / or permanent manner. Preferably, in the operating step, an electrical energy is generated in a fuel cell unit. In the operating step, an operation of a fuel cell device is preferably regulated and / or monitored by means of a control and regulating unit. Preferably, in an operating step, a fuel, in particular natural gas, is supplied to the fuel cell device. Preferably, in the operating step, a fuel utilization factor of the fuel cell device is varied by means of a control and regulating unit. Preferably, in the operating step, a fuel utilization factor of the fuel cell device is varied stepwise by means of a control and regulating unit. Preferably, a comparison step is carried out in one operating step. A "comparison step" is to be understood in this context in particular as a method step in which the fuel utilization factor of the fuel cell unit is determined empirically. Preferably, in the comparison step, the fuel utilization factor of the fuel cell unit is determined empirically depending on at least one further parameter of the fuel cell device. In the comparison step, the fuel utilization factor of the fuel cell unit is preferably determined empirically via the influence of the further parameters of the fuel cell device on a cell voltage.In this context, a "recirculation circuit" is to be understood to mean, in particular, a circuit which is configured to provide a return flow of waste products and / or unused fuel, in particular natural gas. Preferably, in an operating step, a fuel, in particular natural gas, is supplied to the recirculation circuit by means of the feed element. Preferably, the recirculation circuit connects a blower unit and a fuel cell unit by means of a circuit. Preferably, a fuel, in particular natural gas, is supplied between the blower unit and the fuel cell unit by means of the supply element. Preferably, the recirculation circuit directs a volume flow of the discharge element at least partially, preferably to a large extent, from the discharge element to the blower unit. In particular, it is conceivable for the open-loop and closed-loop control unit to continuously regulate the proportion of the volume flow derived from the derivative element via the rotational speed of the blower unit. The recirculation circuit is preferably configured to regulate and ensure a supply of the fuel cell unit in an operating step. The recirculation circuit is preferably configured to regulate and maintain a pressure and flow regulation of the volume flow in a fuel cell unit in an operating step. In particular, it is conceivable for the recirculation circuit to have a cooling element, by means of which the operating temperature of the fuel is regulated in an operating step.An "open-loop and closed-loop control unit" is to be understood in particular as a unit having at least one electronic control unit. A "control electronics" is to be understood in particular as a unit having a processor unit and having a memory unit and having an operating program stored in the memory unit. The open-loop and closed-loop control unit is preferably configured to adapt an operation of the fuel cell device in an operating step. The control and regulating unit is preferably configured to regulate the blower unit in an operating step. The control and regulating unit is preferably configured to adapt an operation of the fuel cell device in an operating step and to regulate the blower unit in parallel. The control and regulating unit preferably has a user interface via which a user can monitor and control an operating step and / or a comparison step. In particular, it is conceivable for the open-loop and closed-loop control unit to automatically carry out an operating step in a cyclical sequence.By the configuration according to the invention of the method for determining a fuel utilization level of a fuel cell unit in a fuel cell device, in particular an SOFC fuel cell device, advantageous properties with regard to a simplified determination of the fuel utilization level of a fuel cell unit can be provided. In particular, advantageous properties with regard to monitoring and regulating a fuel cell device can be provided. In particular, advantageous properties with regard to a lower complexity of the fuel cell device can be provided. In particular, a method can be provided without using a sensor for measuring a fuel utilization level of a fuel cell unit. In this way, in particular advantageous properties with regard to cost saving can be provided.Furthermore, it is proposed that in at least one comparison step, the fuel utilization rate of the fuel cell unit is empirically estimated via a gradient of the cell voltage when a fuel utilization rate of the fuel cell device changes. In the comparison step, the influence of a variation of the fuel utilization factor of the fuel cell device (FU_Sy) on the fuel utilization factor of the fuel cell unit (FU_Stk) is preferably determined empirically. In the comparison step, an influence of different fuel utilization levels of the fuel cell device on a cell voltage (u_cell) is preferably presented. Preferably, in the comparison step, a fuel utilization rate of the fuel cell device is estimated via a function of the gradient of the cell voltage from the fuel utilization rate of the fuel cell device. Preferably, in the comparison step, a diagram is created by means of the function of the gradient of the cell voltage as a function of the fuel utilization factor of the fuel cell device. Preferably, in the comparison step, the function shown in the diagram is empirically evaluated. In the comparison step, a fuel utilization rate of the fuel cell unit is preferably determined empirically via the gradient of the function of the gradient of the cell voltage as a function of the fuel utilization rate of the fuel cell device. Particularly preferably, in the comparison step, the fuel utilization rate of the fuel cell unit is calculated via the formula. In this way, in particular advantageous properties with regard to a simplified determination of the fuel utilization level of a fuel cell unit can be provided.It is furthermore proposed that the fuel utilization factor of the fuel cell device and the current cell voltage be determined in at least one determination step. In this context, a "determination step" is to be understood to mean, in particular, a method step in which the required parameters of the fuel cell device for an empirical determination of the fuel utilization level of the fuel cell unit are determined. Preferably, in the determination step, the fuel utilization rate of the fuel cell device and the current cell voltage are determined. In the determination step, the fuel utilization factor of the fuel cell device (FU_Sy_ 1) is preferably determined via an energy balancing at the fuel cell unit. Alternatively and / or additionally, the fuel utilization factor of the fuel cell device is determined in the determination step via the energy balancing at the hot box. Alternatively and / or additionally, in the determination step, the fuel utilization factor of the fuel cell device is determined via a measurement of the gas volume flow and the associated heating value in a current operating state. Furthermore, any other determination of the fuel utilization factor of the fuel cell device that appears expedient to a person skilled in the art is conceivable. Preferably, the current cell voltage (u_ 1) is measured in the determination step. Furthermore, any other determination of the current cell voltage that appears expedient to a person skilled in the art is conceivable. In this way, in particular advantageous properties with regard to a determination of the fuel utilization level of a fuel cell device and the current cell voltage can be provided.Furthermore, it is proposed that in at least one adaptation step, by means of a change in the supplied natural gas volume flow, an active variation, in particular in at least two stages, of the fuel utilization factor of the fuel cell device is carried out. An "adaptation step" is to be understood in this context in particular as a method step in which a parameter of the fuel cell device is adapted. Preferably, in the adjusting step, a fuel utilization rate of the fuel cell device is adjusted. Preferably, the fuel utilization factor of the fuel cell device is adapted by changing the supplied natural gas volume flow. Preferably, in the adjusting step, an active variation of the fuel utilization rate of the fuel cell device is performed. Particularly preferably, in the adaptation step, an active variation is carried out in at least two stages of the fuel utilization factor of the fuel cell device. Furthermore, any other number of stages of the active variation of the fuel utilization level of the fuel cell device that appear expedient to a person skilled in the art is conceivable. Preferably, in the adaptation step, a natural gas volume flow supplied to the fuel cell device is regulated by means of the open-loop and closed-loop control unit. In particular, it is conceivable for the fuel cell device to have a further blower unit, by means of which the supplied natural gas volume flow of the fuel cell device is regulated. In particular, it is conceivable that in the adaptation step the open-loop and closed-loop control unit adjusts a supplied natural gas volume flow of the fuel cell device via the further blower unit. Preferably, in the adaptation step, an supplied natural gas volume flow is increased by means of the open-loop and closed-loop control unit. Alternatively, it is conceivable that in the adaptation step, an supplied natural gas volume flow is reduced by means of the control and regulating unit. Preferably, in the adaptation step, a fuel utilization factor of the fuel cell device is reduced by increasing the supplied natural gas volume flow. In this way, in particular advantageous properties with regard to a regulation of the fuel cell device can be provided. In particular, advantageous properties with regard to a simplified determination of the fuel utilization factor of a fuel cell unit can be provided.It is furthermore proposed that in at least one adaptation step by means of the blower unit, in particular by adaptation of the recirculation volume flow of the recirculation circuit, a fuel utilization factor of the fuel cell unit is kept constant. Preferably, in the adaptation step, a blower unit is automatically regulated via the open-loop and closed-loop control unit. Preferably, in the adaptation step, a recirculation volume flow of the recirculation circuit is regulated via the blower unit. Preferably, in the adaptation step, a recirculation volume flow of the recirculation circuit is regulated by means of the rotational speed of the blower unit. Preferably, in the adaptation step, the rotational speed of the blower unit is regulated via the open-loop and closed-loop control unit as a function of a measured value determined in the fuel cell unit, in order to keep the fuel utilization level of the fuel cell unit constant. In an adjustment step, the fuel utilization rate of the fuel cell unit is preferably kept constant by means of the recirculation volume flow, simultaneously with the adjustment of the fuel utilization rate of the fuel cell device. Preferably, in the adjusting step, a recirculation flow is increased when the fuel utilization ratio of the fuel cell device is reduced. Alternatively, in the adjusting step, a recirculation flow is decreased as the fuel utilization rate of the fuel cell device is increased. In this way, in particular advantageous properties with regard to a regulation of the fuel cell device can be provided. In particular, advantageous properties with regard to a simplified determination of the fuel utilization factor of a fuel cell unit can be provided.Furthermore, it is proposed that in at least one further determination step, the fuel utilization factor of the fuel cell device and the current cell voltage are determined after an adaptation step. Preferably, the further determination step is carried out after an adaptation step. Preferably, the further determination step is carried out identically to the determination step. In the further determination step, the fuel utilization factor of the fuel cell device (FU_Sy_ 2) is preferably determined via an energy balancing at the fuel cell unit. Alternatively and / or additionally, in the further determination step, the fuel utilization factor of the fuel cell device is determined via the energy balancing at the hot box. Alternatively and / or additionally, in the further determination step, the fuel utilization factor of the fuel cell device is determined by measuring the gas volume flow and the associated heating value in a current operating state. Furthermore, any other determination of the fuel utilization factor of the fuel cell device that appears expedient to a person skilled in the art is conceivable. In the further determination step, the current cell voltage (u_ 2) is preferably measured after an adaptation step. Furthermore, any other determination of the current cell voltage that appears expedient to a person skilled in the art is conceivable. In this way, in particular advantageous properties with regard to a determination of the fuel utilization level of a fuel cell device and the current cell voltage after an adaptation step can be provided.It is furthermore proposed that in at least one calculation step, the cell voltage gradient is calculated on the basis of the values determined in the determination step and the further determination step. Preferably, in the calculation step, the cell voltage gradient is calculated on the basis of the fuel utilization levels of the user device (FU_Sy_ 1, FU_Sy_ 2) determined in the determination step and the further determination step and the associated cell voltages (u_ 1, u_ 2). In this context, a "calculation step" is to be understood to mean, in particular, a method step in which the cell voltage gradient (du_cell / dFU_Sy) is determined. Preferably, the cell voltage gradient is calculated in the calculation step. Preferably, in the calculating step, the cell voltage gradient is calculated by the formula. Preferably, a calculation step is performed in the operation step. Preferably, the calculation step is performed after the determination step, the adjustment step, and the further determination step in the operation step. In this way, in particular advantageous properties with regard to a determination of the fuel utilization level of a fuel cell device and the current cell voltage after an adaptation step can be provided.According to a further exemplary embodiment, it is proposed that the settings of the adaptation step are repeated in at least one adaptation step and the fuel utilization factor of the fuel cell device and the current cell voltage are subsequently determined. Preferably, in the adaptation step, the natural gas volume flow and the recirculation flow are reset to an initial state. An "adaptation step" is to be understood in this context in particular as a method step in which all adaptations of the adaptation step are repeated. Preferably, in the adjusting step, the fuel utilization rate of the fuel cell device and the current cell voltage are determined. Preferably, in the adaptation step, the fuel utilization factor of the fuel cell device is determined via an energy balancing at the fuel cell unit. Alternatively and / or additionally, the fuel utilization factor of the fuel cell device is determined in the adaptation step via the energy balancing at the hot box. Alternatively and / or additionally, in the adaptation step, the fuel utilization factor of the fuel cell device is determined via a measurement of the gas volume flow and the associated heating value in a current operating state. Furthermore, any other determination of the fuel utilization factor of the fuel cell device that appears expedient to a person skilled in the art is conceivable. Preferably, the current cell voltage is measured in the adaptation step. Furthermore, any other determination of the current cell voltage that appears expedient to a person skilled in the art is conceivable. In this way, in particular advantageous properties with regard to monitoring the fuel cell device can be achieved.According to a further exemplary embodiment, it is proposed that in at least one control step, the values determined in an adaptation step are correlated with the values determined in a determination step in order to check the influence of the adaptation step on the fuel utilization level of the fuel cell device and the current cell voltage. In the control step, the values determined in an adaptation step are preferably compared with the values determined in a determination step and evaluated. Preferably, in the control step, a result of the evaluation of the comparison of the fuel utilization factor of the fuel cell device and the cell voltage is determined in a determination step and an adaptation step to the control and regulating unit. In a control step, an adaptation step and a further determination step are preferably restarted if the fuel utilization level of the fuel cell device and the cell voltage in an adaptation step differ from the fuel utilization level of the fuel cell device and the cell voltage in a determination step. Preferably, in a control step, the fuel cell device is regulated on the basis of the empirically determined fuel utilization factor of the fuel cell unit if the fuel utilization factor of the fuel cell device and the cell voltage in an adaptation step is identical to the fuel utilization factor of the fuel cell device and the cell voltage in a determination step. A "control step" is to be understood in this context as meaning, in particular, a method step in which the results are validated. In this way, in particular advantageous properties with regard to monitoring the fuel cell device can be achieved.According to a further exemplary embodiment, it is proposed that in at least one comparison step, the fuel utilization factor of the fuel cell unit is empirically estimated via a change of a natural gas volume flow of the fuel cell device and / or of a recirculation volume flow of the recirculation circuit. Preferably, in the comparison step, the influence of a variation of a natural gas volume flow of the fuel cell device and / or of a recirculation volume flow of the recirculation circuit of the fuel cell device on the fuel utilization level of the fuel cell unit is determined empirically. Preferably, in the comparison step, an influence of different natural gas volume flows of the fuel cell device and / or of a recirculation volume flow of the recirculation circuit on a cell voltage is determined. Preferably, in the comparison step, the fuel utilization rate of the fuel cell device is estimated via a function of the gradient of the cell voltage. In particular, it is conceivable that quantities measured and / or calculated in the comparison step, such as a temperature value or the heating value of the natural gas used, enter into the correlation. In the comparison step, an empirical correlation is preferably derived from measurement and / or simulation campaigns and is stored on the control and regulating unit by means of characteristic curves, characteristic maps, polynomial approaches or other data-based models. In this way, in particular advantageous properties with regard to a simplified determination of the fuel utilization level of a fuel cell unit can be provided.Furthermore, it is proposed that, in at least one operating step, the fuel cell device has a rechargeable battery element which compensates for energy fluctuations by buffering. In the operating step, energy fluctuations which take place by the adaptation step are preferably compensated by means of the battery element. In the operating step, energy fluctuations which arise as a result of the increase in the supplied natural gas volume flow are preferably stored by means of the battery element. In addition, it is conceivable for the fuel cell device to be used in a cluster operating strategy and for a further fuel cell device to take over the buffering at least substantially, preferably at least a major part and particularly preferably completely. Preferably, in an operating step, an electrical constant total energy is provided by means of the cluster operating strategy. The expression "at least a major part" is to be understood here in particular as meaning at least 55%, advantageously at least 65%, preferably at least 75%, particularly preferably at least 85% and particularly advantageously at least 95%. In this way, in particular advantageous properties with regard to an operation of a fuel cell device can be achieved.According to a further exemplary embodiment, it is proposed that in at least one evaluation step, the fuel utilization factor of the fuel cell unit is ascertained by means of the detection of the time of a gradient change. An "evaluation step" is to be understood in this context in particular as a method step in which a gradient is evaluated and evaluated. Preferably, in the evaluation step, the time of a gradient change of the fuel utilization rate of the fuel cell unit is determined via the function. Preferably, in the evaluation step, a fuel utilization factor of the fuel cell unit is detected in the event of a horizontal bending of the function. Preferably, in the evaluation step, an operating step is evaluated cyclically by means of an evaluation step in order to determine the fuel utilization level of the fuel cell unit. Preferably, in the evaluation step, the time of a gradient change is detected at a high fuel utilization level of the fuel cell device. In an evaluation step, a gradient change preferably occurs only at a high fuel utilization level of the fuel cell device. In this way, in particular advantageous properties with regard to an evaluation and evaluation of the fuel utilization level of the fuel cell unit can be provided.According to a further exemplary embodiment, it is proposed that, in at least one monitoring step, the permissible fuel utilization level of the fuel cell unit is detected as being exceeded by detecting the time of a gradient change. In this context, a "monitoring step" is to be understood to mean, in particular, a method step in which operation of a fuel cell device is monitored. Preferably, a cyclical execution of the operating step is monitored in the monitoring step. Preferably, in the monitoring step, a message is transmitted to the control and regulating unit as soon as the fuel utilization level of the fuel cell unit exceeds and / or reaches a maximum fuel utilization level of the fuel cell unit. Preferably, in the operating step, a fuel utilization factor of the fuel cell unit is regulated on the basis of the message transmitted in a monitoring step. In this way, in particular advantageous properties with regard to monitoring the operation of a fuel cell device can be provided.The invention furthermore proposes a fuel cell device, in particular an SOFC fuel cell device, for carrying out a method according to the invention. Preferably, the fuel cell device is configured to perform an operation step. The fuel cell device is preferably configured to generate electrical energy. The fuel cell device preferably has a feed element which feeds an energy carrier, for example natural gas, and / or electrical energy into the fuel cell device. The fuel cell system preferably has a discharge element which discharges exhaust gases and / or electrical energy from a fuel cell system. The fuel cell device is preferably designed as an SOFC fuel cell device. Particularly preferably, the fuel cell device is operated with natural gas. The fuel cell device is preferably embodied in multiple parts. The fuel cell device preferably has at least one fuel cell unit. The fuel cell device preferably has at least one blower unit. The fuel cell device preferably has at least one recirculation circuit. In particular, it is conceivable for the fuel cell device to have a cooling unit in a recirculation circuit, which cooling unit is configured to cool a gaseous medium heated by a blower unit. In this way, in particular advantageous properties with regard to a method according to the invention for operating a fuel cell device can be provided.The method according to the invention for operating a fuel cell device is not intended to be limited to the application and embodiment described above. In particular, the method according to the invention for operating a fuel cell device in order to fulfil a mode of operation described herein can have a number which differs from a number of individual elements, components and units and method steps mentioned herein. In addition, in the value ranges specified in this disclosure, values lying within the stated limits should also be considered as disclosed and usable as desired.DRAWINGFurther advantages are evident from the following description of the drawings. Three exemplary embodiments of the invention are shown in the drawing. The drawings, specification and claims contain numerous features in combination. The skilled person will expediently also consider the features individually and summarize them to form meaningful further combinations.The following are shown: FIG. 1 shows a fuel cell device according to the invention in a schematic illustration, FIG. 2 shows a schematic flow diagram of a method for a method ofFIG. 3 shows a schematic flow diagram of an exemplary embodiment of a method for operating a fuel cell device according to the invention, and FIG. 4 shows a schematic flow diagram of an exemplary embodiment of a method for operating a fuel cell device according to the invention.DESCRIPTION OF THE EMBODIMENTSFIG. 1 shows a fuel cell device 10 a, in particular an SOFC fuel cell device, for carrying out a method according to the invention. The fuel cell device 10 ais configured to execute an operation step 18. The fuel cell device 10 ais configured to generate electric power. The fuel cell device 10 aincludes a supply element 28 athat supplies a power carrier, for example hydrogen, and / or electrical power into the fuel cell device 10 a. The fuel cell device 10 aincludes a discharge element 26 awhich discharges exhaust gases and / or electrical energy from a fuel cell device. The fuel cell device 10 ais configured as an SOFC fuel cell device. The fuel cell device 10 ais operated with natural gas. The fuel cell device 10 ais embodied in multiple parts. The fuel cell device 10 aincludes at least one fuel cell unit 12 a. The fuel cell device 10 aincludes at least one blower unit 14 a. The fuel cell device 10 acomprises at least one recirculation circuit 20 a. In particular, it is conceivable for the fuel cell device 10 ato be supplied with oxygen from the ambient air by the supply element 28 a. It is also conceivable that the fuel cell device 10 ais supplied with pure oxygen via the supply element 28 ato increase the efficiency of the fuel cell device 10 a. The supply element 28 aand the discharge element 26 aare configured as a pipeline. The supply element 28 aand the discharge element 26 aare designed for guiding a gaseous medium. In particular, it is conceivable for the fuel cell device 10 ato have a heat exchanger which is configured to utilize a thermal energy arising in the fuel cell unit 12 a. In particular, it is conceivable for the fuel cell device 10 ato have a cooling unit in a recirculation circuit 20 a, which cooling unit is configured to cool a gaseous medium heated by a blower unit 14 a.The fuel cell unit 12 ais designed as a fuel cell stack. The fuel cell unit 12 ais configured to obtain electrical energy and heat electrochemically from the chemical energy of an energy carrier. The fuel cell unit 12 ais configured to obtain electrical energy from a gaseous medium. The fuel cell unit 12 ais configured to convert chemical reaction energy of a continuously supplied fuel and an oxidizing agent into electrical energy. For example, natural gas is used as the fuel and oxygen as the oxidizing agent. Alternatively, other fuels that appear expedient to a person skilled in the art, for example methanol, butane, ammonia and / or hydrogen, are also conceivable. In an operating step 18 a, electrical energy is generated between an anode and a cathode in the fuel cell unit 12 a. The anode cleaves the electrons of the fuel. The electrons are conducted into the cathode via a connecting element. The fuel cell unit 12 aincludes at least one fuel cell. The fuel cell unit 12 aincludes a plurality of fuel cells. All fuel cells are formed identically in one fuel cell unit 12 a. Alternatively, it is conceivable for the fuel cells to be of different design. Each fuel cell has an anode and a cathode. All fuel cells of a fuel cell unit 12 aare configured to be electrically connected to one another. The fuel cells are electrically connected in series or in parallel to achieve the desired output voltage and power. The fuel cell unit 12a has a fuel utilization ratio.The blower unit 14 agenerates an air flow of the gaseous medium. The blower unit 14 acomprises at least one moving blade element, by means of which a rotational movement is converted into a linear movement of the gaseous medium. The blower unit 14 aincludes a drive unit which rotationally drives the at least one moving blade element. The blower unit 14 ais arranged in a recirculation circuit 20 a. The blower unit 14 ais arranged at least substantially partially, preferably at least to a large extent and particularly preferably completely in a recirculation circuit 20 a.In an operating step 14 a, a fuel, in particular natural gas, is supplied to the recirculation circuit 20 aby means of the supply element 28 a. The recirculation circuit 20 aconnects a blower unit 14 aand a fuel cell unit 12 aby means of a circuit. A fuel, in particular natural gas, is supplied between the blower unit 14 aand the fuel cell unit 12 aby means of the supply element 28 a. The recirculation circuit 20 aroutes a volume flow of the discharge element 26 a, at least partially, preferably to a large extent, from the discharge element 26 ato the blower unit 14 a. In particular, it is conceivable for a control and regulating unit 16 ato continuously regulate the proportion of the volume flow derived from the derivative element 26 avia the rotational speed of the blower unit 14 a. The recirculation circuit 20 ais configured to regulate and ensure a supply of the fuel cell unit 12 ain an operating step 18. The recirculation circuit 20 ais configured to regulate and maintain a pressure and flow regulation of the volume flow in a fuel cell unit 12 ain an operating step 18 a. In particular, it is conceivable for the recirculation circuit 20 ato have a cooling element, by means of which the operating temperature of the fuel is regulated in an operating step 18 a.The open-loop and closed-loop control unit 16 ais configured to adapt an operation of the fuel cell device 10 ain an operating step 18 a. The control and regulating unit 16 ais configured to regulate the blower unit 14 ain an operating step 18 a. The control and regulating unit 16 ais configured to adapt an operation of the fuel cell device 10 aand to regulate the blower unit 14 ain parallel in an operating step 18 a. The control and regulating unit 16 ahas a user interface via which a user can monitor and control an operating step 18 aand / or a comparison step 24 a. In particular, it is conceivable for the open-loop and closed-loop control unit 16 ato automatically carry out an operating step 18 ain a cyclical sequence.FIG. 2 shows a method for determining a fuel utilization level of a fuel cell unit 12 ain a fuel cell device 10 a, in particular an SOFC fuel cell device, which has at least one fuel cell unit 12 a, in particular a fuel cell stack, at least one blower unit 14 a, and at least one open-loop and closed-loop control unit 16 a. The method for operating a fuel cell device 10 acomprises an operating step 18 ain which the fuel cell unit 12 aacquires electrical energy from a gaseous medium, wherein the blower unit 14 acontrols and drives a recirculation circuit 20 ain the operating step 18 a, and wherein an operation of the fuel cell device 10 ais controlled by means of the control and regulating unit 16 ain the operating step 18 a. In at least one comparison step 24 a, a fuel utilization factor of the fuel cell unit 12 ais estimated by means of empirical estimation. In operation 18 a, an electrical energy is generated in a fuel cell unit 12 a. In the operating step 18 a, an operation of a fuel cell device 10 ais regulated and / or monitored by means of a control and regulating unit 16 a. In operating step 18 a, a fuel, in particular natural gas, is supplied to fuel cell device 10 a. In operating step 18 a, a fuel utilization factor of fuel cell device 10 ais varied by means of a control and regulating unit 16 a. In the operating step 18 a, a fuel utilization rate of the fuel cell device 10 ais varied in stages by means of a control and regulating unit 16 a. In the operating step 18 a, a comparison step 24 ais carried out. In the comparison step 24 a, the fuel utilization factor of the fuel cell unit 12 ais determined empirically as a function of at least one further parameter of the fuel cell device 10 a. In the comparison step 24 a, the fuel utilization factor of the fuel cell unit 12 ais empirically determined via the influence of the further parameters of the fuel cell device 10 aon a cell voltage.In at least one comparison step 24 a, the fuel utilization rate of the fuel cell unit 12 ais empirically estimated via a gradient of the cell voltage when a fuel utilization rate of the fuel cell device 10 ais changed. In the comparison step 24 a, the influence of a variation of the fuel utilization rate of the fuel cell device 10 a(FU_Sy) on the fuel utilization rate of the fuel cell unit 12 a(FU_Stk) is determined empirically. In the comparison step 24 a, an influence of different fuel utilization levels of the fuel cell device 10 aon a cell voltage (u_cell) is determined. In the comparison step 24 a, a fuel utilization rate of the fuel cell unit 12 ais empirically estimated via a function of the gradient of the cell voltage from the fuel utilization rate of the fuel cell device 10 a. In the comparison step 24 a, a diagram is created by means of the function of the gradient of the cell voltage as a function of the fuel utilization level of the fuel cell device 10 a. In the comparison step 24 a, the function represented in the diagram is empirically evaluated. In the comparison step 24 a, a fuel utilization rate of the fuel cell unit 12 ais empirically determined via the gradient of the function of the gradient of the cell voltage as a function of the fuel utilization rate of the fuel cell device 10 a. In the comparison step 24 a, the fuel utilization rate of the fuel cell unit 12 ais calculated via the formula.In at least one determination step 22 a, the fuel utilization factor of the fuel cell device 10 aand the current cell voltage are determined. In the determination step 22 a, the fuel utilization factor of the fuel cell device 10 a(FU_Sy_ 1) is determined via an energy balancing at the fuel cell unit 12 a. Alternatively and / or additionally, in the determination step 22 a, the fuel utilization factor of the fuel cell device 10 ais determined via the energy balancing at the hot box. Alternatively and / or additionally, in the determination step 22 a, the fuel utilization factor of the fuel cell device 10 ais determined via a measurement of the gas volume flow and the associated heating value in a current operating state. Furthermore, any other determination of the fuel utilization factor of the fuel cell device 10 a, which appears expedient to a person skilled in the art, is conceivable. In the determination step 22 a, the current cell voltage (u_ 1) is measured. Furthermore, any other determination of the current cell voltage that appears expedient to a person skilled in the art is conceivable.In at least one adaptation step 30 a, an active variation, in particular in at least two stages, of the fuel utilization factor of the fuel cell device 10 ais carried out by means of a change in the supplied natural gas volume flow. In the adjustment step 30 a, a fuel utilization rate of the fuel cell device 10 ais adjusted. In the adaptation step 30 a, the fuel utilization factor of the fuel cell device 10 ais adapted by changing the supplied natural gas volume flow. In the adjustment step 30 a, an active variation of the fuel utilization rate of the fuel cell device 10 ais performed. In the adjustment step 30 a, active variation is performed in at least two stages of the fuel utilization rate of the fuel cell device 10 a. Furthermore, any other number of stages of the active variation of the fuel utilization rate of the fuel cell device 10 aappearing appropriate to a person skilled in the art is conceivable. In the adaptation step 30 a, a natural gas volume flow supplied to the fuel cell device 10 ais regulated by means of the open-loop and closed-loop control unit 16 a. In particular, it is conceivable for the fuel cell device 10 ato have a further blower unit, by means of which the supplied natural gas volume flow of the fuel cell device 10 ais regulated. In particular, it is conceivable that in the adaptation step 30 a, the open-loop and closed-loop control unit 16 acontrols a supplied natural gas volume flow of the fuel cell device 10 avia the further blower unit. In the adaptation step 30 a, an supplied natural gas volume flow is increased by means of the control and regulating unit 16 a. Alternatively, it is conceivable that in the adaptation step 30 a, an supplied natural gas volume flow is reduced by means of the control and regulating unit 16 a. In the adaptation step 30 a, a fuel utilization factor of the fuel cell device 10 ais reduced by increasing the supplied natural gas volume flow.In at least one adaptation step 30 a, a fuel utilization factor of the fuel cell unit 12 ais kept constant by means of the blower unit 14 a, in particular by adapting the recirculation volume flow of the recirculation circuit 20 a. In the adaptation step 30 a, a blower unit 14 ais automatically regulated via the control and regulating unit 16 a. In the adaptation step 30 a, a recirculation volume flow of the recirculation circuit 20 ais regulated via the blower unit 14 a. In the adaptation step 30 a, a recirculation volume flow of the recirculation circuit 20 ais regulated by means of the rotational speed of the blower unit 14 a. In the adaptation step 30 a, the rotational speed of the blower unit 14 ais regulated via the control and regulating unit 16 adepending on a measured value determined in the fuel cell unit 12 ato keep the fuel utilization level of the fuel cell unit 12 a constant. In the adjustment step 30 a, the fuel utilization rate of the fuel cell unit 12 ais kept constant by means of the recirculation volume flow, simultaneously with the adjustment of the fuel utilization rate of the fuel cell device 10 a. In the adjustment step 30 a, a recirculation flow is increased as the fuel utilization rate of the fuel cell device 10 ais reduced. Alternatively, in the adjustment step 30 a, a recirculation flow is decreased as the fuel utilization rate of the fuel cell device 10 ais increased.In at least one further determination step 32 a, the fuel utilization factor of the fuel cell device 10 aand the current cell voltage are determined after an adaptation step 30 a. The further determination step 32 ais carried out after an adaptation step 30 a. The further determination step 32 ais carried out identically to the determination step 30 a. In the further determination step 30 a, the fuel utilization factor of the fuel cell device 10 a(FU_Sy_ 2) is determined via an energy balancing at the fuel cell unit 12 a. Alternatively and / or additionally, in the further determination step 32 a, the fuel utilization factor of the fuel cell device 10 ais determined via the energy balancing at the hot box. Alternatively and / or additionally, in the further determination step 32 a, the fuel utilization factor of the fuel cell device 10 ais determined via a measurement of the gas volume flow and the associated heating value in a current operating state. Furthermore, any other determination of the fuel utilization factor of the fuel cell device 10 a, which appears expedient to a person skilled in the art, is conceivable. In the further determination step 30 a, the current cell voltage (u_ 2) is measured after an adaptation step 30 a. Furthermore, any other determination of the current cell voltage that appears expedient to a person skilled in the art is conceivable.In at least one calculation step 34 a, the cell voltage gradient is calculated on the basis of the values determined in the determination step 22 aand the further determination step 32 a. In the calculation step 34 a, the cell voltage gradient is calculated on the basis of the fuel utilization levels of the user device 10 a(FU_Sy_ 1, FU_Sy_ 2) determined in the determination step 22 aand the further determination step 32 a, and the associated cell voltages (u_ 1, u_ 2). In the calculation step 34a, the cell voltage gradient is calculated. In the calculation step 34 a, the cell voltage gradient is calculated using the formula. A calculation step 34a is performed in the operation step 18a. The calculation step 34 ais carried out after the determination step 22 a, the adaptation step 30 aand the further determination step 32 ain the operating step 18 a.In at least one operating step 18 a, fuel cell device 10 aincludes a battery element 42 awhich compensates for energy fluctuations due to buffering. In calculation step 34 a, energy fluctuations which take place by adaptation step 30 aare compensated for by means of battery element 42 a. In the calculation step 34 a, energy fluctuations, which arise as a result of the increase in the supplied natural gas volume flow, are stored by means of the battery element 42 a. In addition, it is conceivable for the fuel cell device 10 ato be used in a cluster operating strategy and for a further fuel cell device 10 ato take over the buffering at least substantially, preferably at least a large part and particularly preferably completely. In the calculation step 34 a, an electrical constant total energy is provided by means of the cluster operating strategy.FIGS. 3 and 4 show two further exemplary embodiments of the invention. The following descriptions and the drawings are limited substantially to the differences between the exemplary embodiments, wherein with regard to identically denoted components, 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 of FIGS. 1 to 2. To distinguish between the exemplary embodiments, the letter a is appended to the reference numerals of the exemplary embodiment in FIGS. 1 to 2. In the exemplary embodiments of FIGS. 3 and 4, the letter a is replaced by the letters b and c.FIG. 3 shows a schematic flow diagram of an exemplary embodiment of a method for operating a fuel cell device 10 bin accordance with the invention. In an operating step 18 b, an adaptation step 30 bis carried out. In at least one adaptation step 36 b, the settings of the adaptation step 30 bare repeated and the fuel utilization factor of the fuel cell device 10 band the current cell voltage are then determined. In the adaptation step 36 b, the natural gas volume flow and the recirculation flow are reset to an initial state. In the adaptation step 36 b, the fuel utilization factor of the fuel cell device 10 band the current cell voltage are determined. In the adaptation step 36 b, the fuel utilization factor of the fuel cell device 10 bis determined via an energy balancing at a fuel unit 12 b. Alternatively and / or additionally, in the adaptation step 36 b, the fuel utilization factor of the fuel cell device 10 bis determined via the energy balancing at the hot box. Alternatively and / or additionally, in the adaptation step 36 b, the fuel utilization factor of the fuel cell device 10 bis determined by measuring the gas volume flow and the associated heating value in a current operating state. Furthermore, any other determination of the fuel utilization factor of the fuel cell device 10 b, which appears expedient to a person skilled in the art, is conceivable. In the adaptation step 36 b, the current cell voltage is measured. Furthermore, any other determination of the current cell voltage that appears expedient to a person skilled in the art is conceivable.In at least one control step 38 b, the values determined in an adaptation step 36 bare correlated with the values determined in a determination step 22 bto check the influence of the adaptation step 30 bon the fuel utilization level of the fuel cell device 10 band the current cell voltage. In the control step 38 b, the values determined in an adaptation step 36 bare compared with the values determined in a determination step 22 band evaluated. In the control step 38 b, a result of the evaluation of the comparison of the fuel utilization factor of the fuel cell device 10 band the cell voltage is determined in a determination step 22 band an adaptation step 36 bto the open-loop and closed-loop control unit 16 b. In the monitoring step 38 b, an adaptation step 22 band a further determination step 32 bare restarted if the fuel utilization level of the fuel cell device 10 band the cell voltage in an adaptation step 26 bdiffer from the fuel utilization level of the fuel cell device 10 band the cell voltage in a determination step 22 b. In the control step 38 b, the fuel cell device 10 bis regulated on the basis of the empirically determined fuel utilization factor of the fuel cell unit 12 bwhen the fuel utilization factor of the fuel cell device 10 band the cell voltage in an adaptation step 36 bare identical to the fuel utilization factor of the fuel cell device 10 band the cell voltage in a determination step 22 b.In at least one comparison step 24 b, the fuel utilization factor of the fuel cell unit 12 bis empirically estimated via a change of a natural gas volume flow of the fuel cell device 10 band / or of a recirculation volume flow of the recirculation circuit 20 b. In the comparison step 24 b, the influence of a variation of a natural gas volume flow of the fuel cell device 10 band / or of a recirculation volume flow of the recirculation circuit 20 bof the fuel cell device 10 bon the fuel utilization level of the fuel cell unit 12 bis determined empirically. In the comparison step 24 b, an influence of different natural gas volume flows of the fuel cell device 10 band / or of a recirculation volume flow of the recirculation circuit 20 bon a cell voltage is determined. In the comparison step 24 b, the gradient of the cell voltage from the fuel utilization rate of the fuel cell device 10 bis estimated via a function. In particular, it is conceivable that quantities measured and / or calculated in the comparison step 24 b, such as a temperature value or the heating value of the natural gas used, enter into the correlation. In the comparison step 24 b, an empirical correlation is derived from measurement and / or simulation maps and stored on the control and regulating unit 16 bby means of characteristic curves, characteristic maps, polynomial approaches or other data-based models.FIG. 4 shows a schematic flow diagram of an exemplary embodiment of a method for operating a fuel cell device 10 caccording to the invention. In at least one evaluation step 40 c, the fuel utilization factor of a fuel cell unit 12 cis determined by means of the detection of the time of a gradient change. In the evaluation step 40 c, the fuel utilization factor of the fuel cell unit 12 cis determined via the function of the time of a gradient change. In the evaluation step 40 c, a fuel utilization factor of the fuel cell unit 12 cis detected in the event of a horizontal bending of the function. In the evaluation step 40 c, an operating step 18 cis evaluated cyclically by means of an evaluation step 40 cin order to determine the fuel utilization level of the fuel cell unit 12 c. In the evaluation step 40 c, the time of a gradient change at a high fuel utilization level of the fuel cell device 10 cis detected. In the evaluation step 40 c, a gradient change occurs only at a high fuel utilization rate of the fuel cell device 10 c.In at least one monitoring step 44 c, the allowable fuel utilization level of the fuel cell unit 12 cis detected to be exceeded by detecting the time of a gradient change. In monitoring step 44 c, a cyclical execution of operating step 18 cis monitored. In monitoring step 44 c, a message is transmitted to a control and regulating unit 16 cas soon as the fuel utilization level of the fuel cell unit 12 cexceeds and / or reaches a maximum fuel utilization level of the fuel cell unit 12 c. In operation 18 c, a fuel utilization factor of the fuel cell unit 12 cis regulated on the basis of the message transmitted in a monitoring step 44 c.

Claims

Method for determining a fuel utilization level of a fuel cell unit (12a; 12b; 12c) in a fuel cell device (10a; 10b; 10c), in particular an SOFC fuel cell device, which has at least one fuel cell unit (12a; 12b; 12c), in particular a fuel cell stack, at least one blower unit (14a; 14b; 14c) and at least one open-loop and closed-loop control unit (16a; 16b; 16c), having an operating step (18a; 18b; 18c) in which the fuel cell unit (12a; 12b; 12c) acquires electrical energy from a gaseous medium, wherein the blower unit (14a; 14b; 14c) acquires a recirculation circuit (20a; 20b; in the operating step (18a; 18b; 18c); 20c) and wherein an operation of the fuel cell device (10a; 10b; 10c) is regulated and driven by means of the control and regulating unit (16a; 16b; 16c) in the operating step (18a; 18b; 18c), characterized in that a fuel utilization factor of the fuel cell unit (12a; 12b; 12c) is estimated by means of empirical estimation in at least one comparison step (24a; 24b; 24c).Method according to Claim 1, characterized in that, in at least one comparison step (24a), the fuel utilization level of the fuel cell unit (12a) is empirically estimated via a gradient of the cell voltage when a fuel utilization level of the fuel cell device (10a) changes.Method according to Claim 1 or 2, characterized in that, in at least one determination step (22a), the fuel utilization factor of the fuel cell device (10a) and the current cell voltage are determined.Method according to one of the preceding claims, characterized in that, in at least one adaptation step (30a), an active variation, in particular in at least two stages, of the fuel utilization level of the fuel cell device (10a) is carried out by means of a change in the supplied natural gas volume flow.Method according to one of the preceding claims, characterized in that, in at least one adaptation step (30a), a fuel utilization factor of the fuel cell unit (12a) is kept constant by means of the blower unit (14a), in particular by adapting the recirculation volume flow of the recirculation circuit (20a).Method according to one of the preceding claims, characterized in that in at least one further determination step (32a), the fuel utilization factor of the fuel cell device (10a) and the current cell voltage are determined after an adaptation step (30a).Method according to one of the preceding claims, characterized in that in at least one calculation step (34a) the cell voltage gradient is calculated on the basis of the values determined in the determination step (22a) and the further determination step (32a).Method according to one of the preceding claims, characterized in that, in at least one adaptation step (36b), the settings of the adaptation step (30b) are repeated and the fuel utilization level of the fuel cell device (10b) and the current cell voltage are subsequently determined.Method according to one of the preceding claims, characterized in that in at least one control step (38b), the values determined in an adaptation step (36b) are correlated with the values determined in a determination step (22b) in order to check the influence of the adaptation step (30b) on the fuel utilization level of the fuel cell device (10b) and the current cell voltage.Method according to Claim 1, characterized in that, in at least one comparison step (24b), the degree of fuel utilization of the fuel cell unit (12b) is empirically estimated via a change in a natural gas volume flow of the fuel cell device (10b) and / or a recirculation volume flow of the recirculation circuit (20b).Method according to one of the preceding claims, characterized in that, in at least one operating step (18a), the fuel cell device (10a) has a rechargeable battery element (42a), which compensates for energy fluctuations by buffering.Method according to Claim 1, characterized in that, in at least one evaluation step (40c), the degree of fuel utilization of the fuel cell unit (12c) is determined by means of the detection of the time of a gradient change.Method according to Claim 12, characterized in that, in at least one monitoring step (44c), the permissible fuel utilization level of the fuel cell unit (12c) is detected as being exceeded by detecting the time of a gradient change.Fuel cell device (10a; 10b; 10c), in particular an SOFC fuel cell device, for carrying out a method according to one of the preceding claims.

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