Fuel cell system and method for operating a fuel cell system

Abstract

The present invention relates to a method (100) for operating a fuel cell system (300). The method (100) comprises: - determining (101) a pressure in an anode subsystem (307) of the fuel cell system (300); - determining (103) an electric current provided by a fuel cell stack (301) of the fuel cell system (300); - comparing (105) the determined pressure and the determined electric current with a characteristic map (200), the characteristic map (200) comprising an allowable range (201) which is delimited by a limit region (203), the limit region (203) being dynamically determined depending on a temperature of the fuel cell stack (301), and wherein, if the pressure present in the anode subsystem (307) and / or the electric current provided by the fuel cell stack (301) lies outside the allowable range (201), the fuel cell system (300) is controlled such that the pressure present in the anode subsystem (307) and / or the electric current provided by the fuel cell stack (301) is returned into the allowable range (201).

Description

[0001] Description

[0002] title and methods for operating a tems

[0003] The presented invention relates to a method for operating a fuel cell system and a fuel cell system according to the attached claims.

[0004] State of the art

[0005] Fuel cell systems convert hydrogen supplied by an anode subsystem and oxygen supplied by a cathode subsystem into water and electrical energy.

[0006] Known fuel cell systems lack a mechanism for adjusting the anode subsystem to ensure an adequate hydrogen supply and the discharge of liquid water from the fuel cell stack. This is because, for example, the control unit lacks information on the true operating state of the fuel cell system due to a lack of sensors.

[0007] One challenge in operating a fuel cell system is the unavoidable coupling of the anode and cathode subsystems via a limited membrane differential pressure. This means that if, for example, a high pressure in the cathode subsystem is required to discharge liquid water from the fuel cell stack or to increase power output, then the pressure in the anode subsystem must also be increased. Due to a lack of knowledge about the actual operating conditions, fuel cell systems are generally designed and operated conservatively. This leads to energy-inefficient operation, for example, through frequent purging of the fuel cell stack.

[0008] Disclosure of the invention

[0009] Within the scope of the presented invention, a fuel cell system and a method for operating the fuel cell system are introduced. Further features and details of the invention will become apparent from the respective dependent claims, the description, and the drawings. Features and details described in connection with the method according to the invention naturally also apply in connection with the fuel cell system according to the invention, and vice versa, so that the disclosure regarding the individual aspects of the invention always refers, or can refer, to each other.

[0010] The invention presented here serves in particular to provide a possibility for fuel-efficient operation of a fuel cell system.

[0011] Thus, according to a first aspect of the presented invention, a method for operating a fuel cell system is presented.

[0012] The presented method comprises determining a pressure in an anode subsystem of the fuel cell system, determining an electric current supplied by a fuel cell stack of the fuel cell system, and comparing the determined pressure and electric current with a characteristic map, wherein the characteristic map includes a permissible range limited by a cutoff range, the cutoff range being dynamically determined as a function of the temperature of the fuel cell stack, and wherein, in the event that the pressure in the anode subsystem and / or the electric current supplied by the fuel cell stack are outside the permissible range, the fuel cell system is adjusted such that the pressure in the anode subsystem and / or the electric current supplied by the fuel cell stack return to the permissible range.

[0013] The presented invention is based on the understanding that the operating parameters anode pressure (i.e., pressure in the anode subsystem) and the electrical current supplied by the fuel cell stack are crucial for fulfilling the operating requirements of the anode subsystem. All other parameters, such as temperature, humidity, etc., play a subordinate role in comparison. Accordingly, it is possible to derive a simple yet sufficient operating strategy for specific operating requirements based on the operating parameters of anode subsystem pressure and the electrical current supplied by the fuel cell stack.

[0014] According to the invention, such an operating strategy is achieved by using a characteristic map that includes a permissible range which is limited by a blocking range.

[0015] The characteristic curve spans the dimensions of pressure in the anode subsystem and electrical current supplied by the fuel cell stack.

[0016] The restricted area prevents the fuel cell system from operating in a range or with settings where the supply of sufficient reactants to the fuel cell stack and the discharge of liquid water from the fuel cell stack are at risk.

[0017] By determining the blocking range based on temperature, the permissible range is always kept as large as possible or dynamically maximized, so that a conservative design for, for example, a purging interval can be omitted and the fuel cell system can be operated in a demand-oriented and correspondingly energy-efficient manner.

[0018] It may be provided that the fuel cell system is adjusted by adjusting at least one operating parameter from the following list of operating parameters: pressure in the anode subsystem, electrical current supplied by the fuel cell stack, temperature of the fuel cell stack, relative humidity in the fuel cell stack.

[0019] By adjusting at least one of the preceding operating parameters, a state of the fuel cell system can be changed so that the pressure in the anode subsystem and / or the electrical current provided by the fuel cell stack returns to the permissible range.

[0020] It may also be provided that it is continuously and repeatedly determined whether the measured pressure and electrical current are within the permissible range.

[0021] By continuously determining whether the measured pressure and current are within the permissible range, or by continuously comparing the pressure values ​​in the anode subsystem and the current applied to the fuel cell stack, as measured by appropriate sensors, within the permissible range, the fuel cell system can be continuously regulated or adjusted. In particular, this determination can be performed at a predetermined rate.

[0022] It may also be provided that the fuel cell system is only shut down if the pressure in the anode subsystem and / or the electrical current supplied by the fuel cell stack are outside the permissible range for a duration longer than a specified threshold.

[0023] By setting a threshold for the duration during which the measured values ​​must remain outside the permissible range before a fuel cell system setting is changed, energy-intensive frequent cycling (i.e., changing fuel cell system settings) is prevented, and the time the fuel cell system operates within an energy-optimal range is maximized. In particular, the threshold can be selected based on at least one operating parameter of the fuel cell system.

[0024] For example, the threshold value can be selected depending on at least one operating parameter from the following list of operating parameters, e.g. using a predefined assignment scheme: currently requested load, state of the fuel cell stack, e.g. expressed by estimated amount of water in the anode subsystem and / or cathode subsystem, high-frequency resistance or frequency-dependent internal resistance, or an operating parameter determined by a virtual sensor.

[0025] It may also be provided that the permissible range is additionally limited by a specified additional exclusion zone, which indicates an operating limit of a jet pump of the fuel cell system.

[0026] An additional locking range can prevent the fuel cell system from being set to a state in which an operating limit of the jet pump is exceeded.

[0027] The additional blocking range can either cover a first range in which the operating limit of the jet pump is violated, or a second range that is larger than the first range, so that as soon as the pressure in the anode subsystem approaches the first range, the fuel cell system is adjusted to counteract this approach, for example by increasing the speed of an anode recirculation blower in order to shift the operating limit of the jet pump and, consequently, the additional blocking range.

[0028] Accordingly, it can also be provided that, in the event that the pressure in the anode subsystem lies within the additional blocking range or within a predetermined range around the additional blocking range, an anode recirculation blower of the fuel cell system is set to a predetermined compensation speed. The compensation speed extends an operating limit defined by the jet pump by supplying the jet pump with an increased volume flow via the anode recirculation blower.

[0029] For example, the compensation speed can be a preset speed stored in a memory or a maximum speed of the anode recirculation fan.

[0030] In particular, it may be provided that the fuel cell system is only adjusted if, despite operation of the anode recirculation blower at the compensation speed, the pressure in the anode subsystem and / or the electrical current supplied by the fuel cell stack are outside the permissible range.

[0031] By prioritizing increasing the speed of the anode recirculation blower over adjusting other settings or operating parameters of the fuel cell system, the fuel cell system is operated in an energy-efficient manner for as long as possible.

[0032] According to a second aspect, the presented invention relates to a fuel cell system for converting energy.

[0033] The presented fuel cell system comprises a fuel cell stack, a computing unit and a storage unit, wherein a characteristic map is stored in the storage unit, and wherein the computing unit is configured to execute a possible embodiment of the presented method using the characteristic map stored in the storage unit.

[0034] Advantages described in detail for the method of operating a fuel cell system according to the first aspect of the invention apply equally to the fuel cell system for converting energy according to the second aspect of the invention.

[0035] Further advantages, features, and details of the invention will become apparent from the following description, in which exemplary embodiments of the invention are described in detail with reference to the drawings. The features mentioned in the claims and in the description can each be essential to the invention individually or in any combination.

[0036] They each show schematically:

[0037] Figure 1 shows a possible embodiment of the presented method,

[0038] Figure 2 shows a possible configuration of a characteristic map for use in the method according to Figure 1, and

[0039] Figure 3 shows a possible embodiment of the presented fuel cell system.

[0040] Figure 1 shows a method 100 for operating a fuel cell system.

[0041] The method 100 comprises a first determination step 101 in which a pressure in an anode subsystem of the fuel cell system is determined, e.g. by a pressure sensor at an anode inlet of a fuel cell stack of the fuel cell system.

[0042] Furthermore, the procedure 100 includes a second determination step 103, in which an electric current provided by the fuel cell stack of the fuel cell system is determined, e.g. by means of a current sensor or a voltage sensor.

[0043] Furthermore, the method 100 includes a calibration step 105 in which the determined pressure and the determined electrical current are calibrated with a characteristic map 200 shown, for example, in Fig. 2.

[0044] The characteristic map 200 includes a permissible range 201, which is limited by a blocking range 203, wherein the blocking range 203 is dynamically determined depending on the temperature of the fuel cell stack, as indicated by different blocking range limits 205, for a fuel cell stack temperature of 95°C and 207 for a fuel cell stack temperature of 60°C.

[0045] In the event that the pressure in the anode subsystem and / or the electrical current supplied by the fuel cell stack are outside the permissible range 201, the fuel cell system will be adjusted so that the pressure in the anode subsystem and / or the electrical current supplied by the fuel cell stack return to the permissible range 201.

[0046] Furthermore, in the characteristic map 200 an optional additional blocking area 209 is shown, which indicates an operating limit of a jet pump of the fuel cell system.

[0047] Optionally, a limit line 211 is shown in the characteristic curve 200, so that if the limit line 211 is exceeded by the pressure in the anode subsystem and / or the electrical current provided by the fuel cell stack, the fuel cell system can be prepared to leave the operating limit of a jet pump, for example by gradually increasing the speed of an anode recirculation blower of the fuel cell system.

[0048] Figure 3 shows a fuel cell system 300 for converting energy.

[0049] The fuel cell system 300 comprises a fuel cell stack 301, a computing unit 303 and a storage unit 305, wherein, for example, the characteristic map 200 according to Fig. 2 is stored in the storage unit 305.

[0050] The processing unit 303 is configured, for example, to execute the procedure 100 according to Fig. 1 using the characteristic map 200 stored in the memory 305. An optional anode recirculation blower 308 is arranged in an anode subsystem 307, which leads to a purge / drain valve 309. By increasing the rotational speed of the anode recirculation blower 308, a jet pump 311 receives an increased flow, so that it delivers more of the hydrogen supplied from a tank 315 by a hydrogen metering valve 313, and thus shifts the operating limit of the jet pump 311.

[0051] Hydrogen can be additionally introduced via a bypass valve 317, bypassing the jet pump 311.

Claims

Claims 1. Method (100) for operating a fuel cell system (300), wherein the method (100) comprises: Determining (101) a pressure in an anode subsystem (307) of the fuel cell system (300), Determining (103) an electric current supplied by a fuel cell stack (301) of the fuel cell system (300), comparing (105) the determined pressure and the determined electric current with a characteristic map (200), wherein the characteristic map (200) includes a permissible range (201) which is limited by a blocking range (203), wherein the blocking range (203) is determined dynamically as a function of a temperature of the fuel cell stack (301), and wherein in the event that the pressure in the anode subsystem (307) and / or the electric current supplied by the fuel cell stack (301) are outside the permissible range (201), the fuel cell system (300) is adjusted such that the pressure in the anode subsystem (307) and / or the electric current supplied by the fuel cell stack (301) return to the permissible range (201).

2. Method (100) according to claim 1 , characterized in that the restricted area (203) is selected such that the permissible area (201) ensures a supply of the fuel cell stack (301) with reactants sufficient for operation and a discharge of liquid water from the fuel cell stack (101).

3. Method (100) according to claim 1 or 2, characterized in that, that the fuel cell system (300) is adjusted by adjusting at least one operating parameter from the following list of operating parameters: pressure in the anode subsystem (307), electrical current supplied by the fuel cell stack (301), temperature of the fuel cell stack (301), relative humidity in the fuel cell stack (301).

4. Method (100) according to one of the preceding claims, characterized in that it is continuously and repeatedly determined whether the determined pressure and the determined electric current are within the permissible range (201).

5. Method (100) according to one of the preceding claims, characterized in that the adjustment of the fuel cell system (300) only takes place if the pressure applied in the anode subsystem (307) and / or the electrical current provided by the fuel cell stack (301) are outside the permissible range (201) for a duration that is longer than a predetermined threshold value.

6. Method (100) according to claim 5, characterized in that the threshold value is selected depending on at least one operating parameter of the fuel cell system (300).

7. Method (100) according to one of the preceding claims, characterized in that the permissible range (201) is additionally limited by a predetermined additional blocking range (203) which specifies an operating limit of a jet pump of the fuel cell system (300).

8. Method (100) according to claim 7, characterized in that, that in the event that the pressure in the anode subsystem (307) is in the additional blocking area (209) or in a predetermined area around the additional blocking area (209), an anode recirculation blower (308) of the fuel cell system (300) is set to a predetermined compensation speed.

9. Method (100) according to claim 8, characterized in that the adjustment of the fuel cell system (300) only takes place when, despite operation of the anode recirculation blower (308) at the compensation speed, the pressure in the anode subsystem (307) and / or the electrical current provided by the fuel cell stack (301) are outside the permissible range (201).

10. Fuel cell system (300) for converting energy, wherein the fuel cell system (300) comprises: a fuel cell stack (301), a computing unit (303), a storage unit (305), wherein a characteristic map (200) is stored in the storage unit (305), and wherein the computing unit (303) is configured to execute a method (100) according to any one of claims 1 to 9 using the characteristic map (200) stored in the storage unit (305).

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