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DE-102024210775-A1 - Fuel cell system, method for operating a fuel cell system and vehicle with a fuel cell system

DE102024210775A1DE 102024210775 A1DE102024210775 A1DE 102024210775A1DE-102024210775-A1

Abstract

The presented invention relates to a fuel cell system (100) for converting energy, wherein the fuel cell system (100) comprises: - a fuel cell stack (101) comprising an anode compartment (103) and a cathode compartment (105), - an air system (107) for supplying the cathode space (105) with air, wherein the air system (107) comprises a compressor (109) for compressing air, - a cathode exhaust gas recirculation system (111) configured to recirculate exhaust gas flowing out of the cathode chamber (105) at least partially through the cathode chamber (105), wherein the cathode exhaust gas recirculation system (111) comprises a switchable cathode recirculation valve (113), and - a computing unit (115) configured to open the cathode recirculation valve (113) when an airflow to be supplied to the cathode chamber (105) violates a pumping limit of the compressor (109).

Inventors

  • Mark Hellmann
  • Jonas Breitinger

Assignees

  • Robert Bosch Gesellschaft mit beschränkter Haftung

Dates

Publication Date
20260513
Application Date
20241108

Claims (10)

  1. Fuel cell system (100) for converting energy, the fuel cell system (100) comprising: - a fuel cell stack (101) comprising an anode compartment (103) and a cathode compartment (105), - an air system (107) for supplying air to the cathode compartment (105), the air system (107) comprising a compressor (109) for compressing air, - a cathode exhaust recirculation system (111) configured to recirculate exhaust gas flowing out of the cathode compartment (105) at least partially through the cathode compartment (105), the cathode exhaust recirculation system (111) comprising a switchable cathode recirculation valve (113), and - a computing unit (115) configured to open the cathode recirculation valve (113) when a The airflow supplied to the cathode space (105) violates a pumping limit of the compressor (109).
  2. Fuel cell system (100) according to Claim 1 , characterized in that the cathode recirculation valve (113) is arranged in a connecting line (125) which connects an exhaust gas tract (121) of the fuel cell system (100) with an air duct for supplying the cathode chamber (105) with air, wherein the connecting line (125) is part of the cathode exhaust gas recirculation system (111), and wherein the cathode recirculation valve (113) is configured to block, in a first position, the connecting line (125) against the flow of an air stream from the air duct, bypassing the cathode chamber (105) into the exhaust gas tract (121), or, in a second position, to allow the flow of an air stream from the air duct into the exhaust gas tract (121) through the connecting line (125) and, as a result, to unthrottle a fluid path downstream of the compressor (109).
  3. Fuel cell system (100) according to Claim 1 or 2 , characterized in that the cathode recirculation valve (113) is permeable in two directions, wherein in a first direction an airflow from an air duct for supplying the cathode chamber (105) with air flows through the cathode recirculation valve (113) to the exhaust tract when an airflow to be supplied to the cathode chamber (105) violates a pumping limit of the compressor (109), and wherein in a second direction an airflow from the exhaust tract (121) flows through the cathode recirculation valve (113) to the air duct when there is a requirement for cathode recirculation.
  4. Fuel cell system (100) according to one of the preceding claims, characterized in that the computing unit (115) is configured to open the cathode recirculation valve (113) when the airflow to be supplied to the cathode chamber (105) is so low or the pressure ratio between the inlet pressure of the compressor (109) and the outlet pressure of the compressor (109) is so high that the surge limit of the compressor (109) is violated.
  5. Fuel cell system (100) according to one of the preceding claims, characterized in that the computing unit (115) is configured to measure the inlet pressure of the compressor (109) by means of a pressure sensor arranged in the direction of flow in an air duct upstream of the compressor (109) or to determine it on the basis of an ambient pressure.
  6. Fuel cell system (100) according to one of the preceding claims, characterized in that the fuel cell system (100) further comprises at least one sensor (117) for measuring a pressure and/or an air mass flow and/or a temperature in the air system (107) and/or the exhaust tract (121).
  7. Fuel cell system (100) according to one of the preceding claims, characterized in that the fuel cell system (100) does not include a bypass path (123) which, in addition to the cathode exhaust gas recirculation system (111), connects the exhaust gas tract (121) directly to an air line for supplying the cathode space (105) with air.
  8. Fuel cell system (100) according to one of the preceding claims, characterized in that the computing unit (115) is configured to match an airflow supplied to the fuel cell stack (101) with a predetermined operating point in a characteristic map of the compressor (109), which spans a pressure ratio between an inlet and an outlet of the compressor (109) and a flow rate through the compressor (109), and to open the cathode recirculation valve (113) in the event that the airflow violates a surge limit specified by the characteristic map for the predetermined operating point.
  9. Vehicle (300), wherein the vehicle (300) has a fuel cell system (100) according to one of the Claims 1 until 8 includes.
  10. Method (200) for operating a fuel cell system (100), in particular a fuel cell system (100) according to one of the preceding Claims 1 until 8 , wherein the method (200) comprises: - opening (205) a cathode recirculation valve (113) of the fuel cell system (100) when an airflow to be supplied to a cathode space (105) of a fuel cell stack (101) of the fuel cell system (100) violates a pump limit of a compressor (109) for supplying air to the cathode space (105).

Description

The presented invention relates to a fuel cell system for converting energy, a method for operating a fuel cell system and a vehicle with a fuel cell system according to the attached claims. State of the art In a typical air system of a fuel cell system, valves are used to control the airflow through the air system. The printed matter DE 10 2022 210 075 A1 Robert Bosch GmbH describes a fuel cell system with a compressor, a cathode exhaust recirculation system, and a bypass path. The bypass path serves to directly divert air from an air duct to supply a cathode chamber of a fuel cell stack within the fuel cell system, in addition to the cathode exhaust recirculation system. Disclosure of the invention Within the scope of the presented invention, a fuel cell system, a method for operating a fuel cell system, and a vehicle 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 fuel cell system according to the invention naturally also apply in connection with the method and the vehicle according to the invention, and vice versa, so that the disclosure of the individual aspects of the invention is always, or can always be, mutually interdependent. The presented invention serves in particular to provide a possibility for the robust operation of a fuel cell system. Thus, according to a first aspect of the presented invention, a fuel cell system for converting energy is presented. The presented fuel cell system comprises a fuel cell stack comprising an anode compartment and a cathode compartment, an air system for supplying air to the cathode compartment, wherein the air system includes a compressor for compressing air, a cathode exhaust recirculation system configured to recirculate exhaust gas flowing out of the cathode compartment at least partially through the cathode compartment, wherein the cathode recirculation system includes a switchable cathode recirculation valve, and a computing unit configured to open the cathode recirculation valve when an airflow to be supplied to the cathode compartment violates a compressor's pumping limit. The presented invention is based on the use of a cathode recirculation valve to reduce the flow rate of a fluid path downstream of a compressor in a fuel cell system. Accordingly, the cathode recirculation valve is used for two purposes: firstly, to set a recirculation rate for recirculated cathode exhaust gas, and secondly, to divert air from an air system of the fuel cell system past a fuel cell stack, thereby protecting the compressor of the air system from damaging pumping operation and ensuring an airflow through the air system that always maintains the compressor's pumping limit. Due to the use of the cathode recirculation valve to discharge air from the air system into the exhaust tract of the presented fuel cell system, an additional air duct path to the recirculation system, such as an additional bypass path connecting an air supply line to the fuel cell stack or its cathode chamber to the exhaust tract, can be omitted. Accordingly, the number of openings in the air system and the exhaust tract is minimized. Therefore, the presented invention minimizes the probability of leakage from the air system or the exhaust tract and enables robust operation of the fuel cell system. It can be provided that the cathode recirculation valve is arranged in a connecting line that connects the exhaust tract to an air line for supplying the cathode chamber with air, wherein the connecting line is part of the cathode exhaust recirculation system, and wherein the cathode recirculation valve is configured to block the connecting line in a first position against the flow of an air stream from the air line into the exhaust tract, or in a second position to allow the connecting line to flow, in particular bypassing the cathode chamber, with an air stream from the air line into the exhaust tract and, as a result, to reduce the flow rate of a fluid path downstream of the compressor. A cathode recirculation valve, movable between at least two positions, allows the fluid path to be recirculated in the direction of flow. The compressor can be controlled so that, if necessary, i.e., in the event that an airflow to be supplied to the cathode chamber violates a pumping limit of the compressor, in particular bypassing or at least partially bypassing the cathode chamber, i.e., by means of a bypass path, it can be fluidly coupled to the exhaust tract and, as a result, de-throttled. For example, in its second position, the cathode recirculation valve can allow recirculation of cathode exhaust gas into the air system or air duct to supply the cathode chamber with air, if an airflow to be supplied to the cathode chamber complies with the compressor's pumping limit. Accordingly, it can further be provided that the cathode recirculation valve is permeable