Operating procedures for a fuel cell system

Abstract

The presented invention relates to an operating method (100) for operating a fuel cell system (200) comprising a jet pump hydrogen metering valve (209) and a bypass hydrogen metering valve (211), wherein the operating method (209) comprises: - Determining (101) a hydrogen concentration in an anode subsystem (205) of the fuel cell system (200), - Determining (103) an actual lambda value based on the determined hydrogen concentration, - Determining (105) setpoints for movement of the jet pump hydrogen metering valve (209) and the bypass hydrogen metering valve (211) based on a deviation between the actual lambda value and a specified setpoint lambda value, - Setting (107) the setpoints at the jet pump hydrogen metering valve (209) and the bypass hydrogen metering valve (211), whereby the setpoints are adjusted when a hydrogen concentration in the anode subsystem (205) and / or a load demand on the fuel cell system (200) changes.

Description

[0001] The presented invention relates to an operating method and a fuel cell system according to the appended claims. State of the art

[0002] Polymer electrolyte membrane (PEM) fuel cell systems convert hydrogen using oxygen to electrical energy, generating waste heat and water.

[0003] Converting hydrogen means that hydrogen molecules are consumed or removed on the anode side.

[0004] A PEM fuel cell consists of an anode supplied with hydrogen, a cathode supplied with air, and the polymer electrolyte membrane placed in between.

[0005] In practical applications, several such fuel cells are stacked to increase the generated electrical voltage. Within this fuel cell stack, called a "stack," are supply channels that supply the individual cells with hydrogen and air and transport depleted moist air and depleted anode exhaust gas.

[0006] The depleted anode exhaust gas still contains large amounts of hydrogen and is therefore returned to the inlet of the fuel cell stack or anode subsystem, a process known as recirculation. This occurs within a recirculation path.

[0007] Recirculation can be achieved actively by means of a recirculation fan and / or passively by means of a jet pump.

[0008] Special water separators are used to separate liquid water from the gaseous part of the anode exhaust gas. In addition to their separation function, the separator also stores the separated water. When the storage tank is full, the water is drained by opening a so-called drain valve.

[0009] Through diffusion processes, nitrogen enters the anode compartment or an anode subsystem.

[0010] The supply of fresh hydrogen is provided by hydrogen dosing valves, which can be designed as proportional valves or switching valves. Known control strategies involve using one or more hydrogen dosing valves to regulate the gas pressure within the anode subsystem, measured by a pressure sensor at a defined position, to a defined target pressure depending on the system operating point.

[0011] The recirculation performance of a jet pump depends, among other things, on the anode gas composition and the supplied propellant mass flow, which in turn is proportional to the electrical current provided by a respective fuel cell system and thus depends on an operating point of the fuel cell system.

[0012] Depending on the gas concentration, the jet pump then supplies the fuel cell stack with more or less anode gas. In some combinations, this can lead to operation in damaging ranges. Disclosure of the invention

[0013] Within the scope of the invention presented, a fuel cell system and an operating method for operating the fuel cell system are presented. Further features and details of the invention emerge from the respective subclaims, the description, and the drawings. Features and details described in connection with the operating method according to the invention naturally also apply in connection with the fuel cell system according to the invention, and vice versa, so that with regard to the disclosure of the individual aspects of the invention, reference is always made to each other.

[0014] The invention presented serves in particular to provide a robust fuel cell system.

[0015] Thus, according to a first aspect of the invention presented, an operating method for operating a fuel cell system comprising a jet pump hydrogen metering valve and a bypass hydrogen metering valve is presented.

[0016] The presented operating method comprises determining a hydrogen concentration in an anode subsystem of the fuel cell system, determining an actual lambda value based on the determined hydrogen concentration and the operating point of a jet pump of the fuel cell system, determining setpoints for a movement of the jet pump hydrogen dosing valve and the bypass hydrogen dosing valve based on a deviation between the actual lambda value and a predetermined setpoint lambda value, and adjusting the setpoints on the jet pump hydrogen dosing valve and the bypass hydrogen dosing valve, wherein the setpoints are adjusted when a hydrogen concentration in the anode subsystem and / or a load demand on the fuel cell system changes.

[0017] The presented operating method is based on a control of a mass flow of fuel provided by a jet pump hydrogen metering valve and a bypass hydrogen metering valve as a function of a load point of the fuel cell system and a hydrogen concentration in an anode subsystem of the fuel cell system, so that the fuel cell system is operated in an optimal lifetime.

[0018] It can be provided that the hydrogen concentration in the anode subsystem is determined as a function of a nitrogen concentration in the fresh fuel, a crossover rate of a cathode subsystem of the fuel cell system as a function of an electrical current provided by the fuel cell system, taking into account an opening geometry of respective valves used to provide the fuel.

[0019] The hydrogen concentration in the anode subsystem can be determined as the minimum hydrogen concentration for a worst-case scenario by balancing the nitrogen concentration in the fresh hydrogen and the crossover rate from the cathode side as a function of the stack current and knowledge of the valve opening durations and their geometrically determined outflow curves. For this purpose, an outflow curve specific to a particular fuel cell system and a correspondingly specific crossover rate are specified or determined.

[0020] Furthermore, the inert gas flow contained in the fuel is taken into account in the balance to determine the hydrogen concentration.

[0021] It may further be provided that the hydrogen concentration in the anode subsystem is determined by determining a hydrogen concentration in the anode gas by means of a hydrogen concentration sensor in an inlet region or an outlet region of the anode subsystem.

[0022] By determining the hydrogen concentration based on a nitrogen concentration in the fresh hydrogen and the crossover rate from the cathode side as a function of the stack current and the knowledge of the valve opening times and their geometrically determined outflow curves, a cost-intensive hydrogen concentration sensor in the anode subsystem can be dispensed with.

[0023] In case a hydrogen concentration sensor is present, complex computational operations for calculating or estimating a hydrogen concentration based on dependent parameters and their application in each new system configuration can be dispensed with.

[0024] It may further be provided that the hydrogen concentration in the anode subsystem is determined by modeling a gas composition in the anode subsystem using a mathematical data model or physical model.

[0025] By using a mathematical model to model the hydrogen concentration, a costly hydrogen concentration sensor in the anode subsystem can be omitted.

[0026] For this purpose, the mathematical model can mathematically map or simulate the behavior of the fuel cell system for different load requirements.

[0027] It may further be provided that the hydrogen concentration in the anode subsystem is determined by comparing a pressure loss of a component in the anode subsystem with an electrical current provided by the fuel cell system.

[0028] By evaluating a pressure loss at a component in the anode subsystem, such as a water separator or a jet pump, the current hydrogen concentration in the anode subsystem can be reliably determined using an allocation scheme. To maximize accuracy, a temperature in the anode subsystem can be included in the allocation scheme. The allocation scheme is specifically determined in advance for a particular fuel cell system, for example, based on a test bench run.

[0029] It can further be provided that the hydrogen concentration in the anode subsystem is determined based on a humidity and a nitrogen concentration in the anode gas, wherein the nitrogen concentration is determined by means of a nitrogen concentration sensor in an inlet region or an outlet region of the anode subsystem.

[0030] By measuring the nitrogen concentration in the anode gas using a nitrogen concentration sensor at the anode inlet or anode outlet, the hydrogen concentration in the anode subsystem can be determined, particularly taking into account humidity in the anode subsystem.

[0031] It can further be provided that an electrical current provided by the fuel cell system is determined on the basis of the determined hydrogen concentration in the anode subsystem, and the actual lambda is determined on the basis of a predetermined characteristic map that assigns a lambda value to a respective value of the electrical current provided by the fuel cell system.

[0032] From a respective determined hydrogen concentration in the anode subsystem, an actual lambda, ie a lambda value currently present in the anode subsystem, can be deduced.

[0033] Using a map representing the anode gas lambda versus current, the actual lambda can be assigned to a setpoint or target lambda for a given electrical current, i.e., a current point. The anode gas lambda versus current map must first be created specifically for a given anode subsystem or fuel cell system, e.g., calculated using a simulation.

[0034] It can further be provided that, based on the drive current of the jet pump hydrogen metering valve measurable in the fuel cell system of approximately 0-5 A, a known hydrogen mass flow can be determined depending on the pre-pressure and temperature of the hydrogen at the inlet of the jet pump hydrogen metering valve. Using the hydrogen mass flow, a known recirculation mass flow can also be determined from a measurement / calculation of the jet pump at a known pressure difference via the jet pump.

[0035] Together with the determined hydrogen concentration in the anode subsystem, an actual lambda can be determined based on a given characteristic map.

[0036] A more precise determination of the actual lambda can be carried out by means of a temperature correction of the freshly supplied hydrogen using formula (1). M_H2=raw*c*A

[0037] The speed of sound is c_X = root (kappa * R_H2* T_H2 / m_mol)

[0038] It can further be provided that, in order to determine the target values ​​for a movement of the jet pump hydrogen dosing valve and the bypass hydrogen dosing valve, a target recirculation volume flow is concluded on the basis of the deviation between the actual lambda value and the specified target lambda value and the hydrogen concentration in the anode subsystem as well as a pressure in the inlet area of ​​the hydrogen dosing valve, and a driving mass flow for the jet pump is calculated on the basis of the target recirculation volume flow and a characteristic curve of a steel pump of the anode subsystem.

[0039] If a given actual lambda deviates from a given target lambda, a correction / adjustment must be made in the control of the jet pump hydrogen dosing valve. To do this, a target recirculation volume flow can first be calculated using the given target lambda, a given hydrogen concentration at the anode subsystem, and optionally using a temperature in the anode subsystem and a pressure at the inlet area of ​​the anode subsystem. A target propellant mass flow for the jet pump can then be calculated using the target recirculation volume flow and a jet pump characteristic curve. The control of the jet pump hydrogen dosing valve and / or the bypass hydrogen dosing valve can then be defined using information about the hydrogen dosing valve.

[0040] Accordingly, it can be provided that a pressure in the anode subsystem is adjusted as a function of a predetermined operating strategy by means of the jet pump hydrogen dosing valve and / or the bypass hydrogen dosing valve.

[0041] Different operating strategies can be set. For example, if recirculation is not desired, a fresh hydrogen flow rate is set using the bypass hydrogen metering valve. Anode pressure is regulated by adjusting the bypass hydrogen metering valve.

[0042] In the case of throttled recirculation, a fresh hydrogen mass flow is divided between the jet pump hydrogen dosing valve and the bypass hydrogen dosing valve, so that the jet pump hydrogen dosing valve and the bypass hydrogen dosing valve jointly regulate the recirculation and the fresh hydrogen mass flow also regulates the anode pressure via the bypass hydrogen dosing valve.

[0043] In the case of non-throttled recirculation, a fresh hydrogen mass flow is fed into the jet pump hydrogen dosing valve so that it regulates the recirculation and the anode pressure.

[0044] According to a second aspect, the presented invention relates to a fuel cell system for converting energy.

[0045] The presented fuel cell system comprises a fuel cell stack, a cathode subsystem, an anode subsystem and a computing unit, wherein the anode subsystem comprises a jet pump hydrogen dosing valve and a bypass hydrogen dosing valve, and wherein the computing unit is configured to carry out a possible embodiment of the presented operating method.

[0046] In the context of the invention presented, a computing unit is understood to mean a computer, a processor, a control unit or any other programmable circuit.

[0047] Advantages that are described in detail with respect to the operating method for operating a fuel cell system according to the first aspect of the invention equally apply to the fuel cell system for converting energy according to the second aspect of the invention.

[0048] Further advantages, features, and details of the invention will become apparent from the following description, which describes exemplary embodiments of the invention in detail with reference to the drawings. The features mentioned in the claims and in the description may be essential to the invention individually or in any combination.

[0049] They show: Fig. 1 a schematic representation of a possible design of the presented operating procedure, Fig. 2 a schematic representation of a possible design of the presented fuel cell system.

[0050] In Fig. 1 illustrates an operating method 100 for operating a fuel cell system including a jet pump hydrogen metering valve and a bypass hydrogen metering valve.

[0051] The operating method 100 comprises a first determination step 101 in which a hydrogen concentration in an anode subsystem of the fuel cell system is determined, a second determination step 103 in which an actual lambda value is determined based on the determined hydrogen concentration, a determination step 105 in which target values ​​for a movement of the jet pump hydrogen metering valve and the bypass hydrogen metering valve are determined based on a deviation between the actual lambda value and a predetermined target lambda value, and an adjustment step 107 in which target values ​​are adjusted on the jet pump hydrogen metering valve and the bypass hydrogen metering valve, the target values ​​being adjusted when a hydrogen concentration in the anode subsystem and / or a load requirement on the fuel cell system changes.

[0052] In Fig. 2 shows a fuel cell system 200 for converting energy.

[0053] The fuel cell system 200 comprises a fuel cell stack 201, a cathode subsystem 203, an anode subsystem 205 and a computing unit 207, wherein the anode subsystem 205 comprises a jet pump hydrogen metering valve 209 and a bypass hydrogen metering valve 211, and the computing unit 207 is configured to carry out the operating method 100 according to Fig. 1 to be carried out.

Claims

[1] Operating method (100) for operating a fuel cell system (200) comprising a jet pump hydrogen metering valve (209) and a bypass hydrogen metering valve (211), wherein the operating method (209) comprises: - determining (101) a hydrogen concentration in an anode subsystem (205) of the fuel cell system (200), - determining (103) an actual lambda value based on the determined hydrogen concentration, - determining (105) target values ​​for a movement of the jet pump hydrogen metering valve (209) and the bypass hydrogen metering valve (211) based on a deviation between the actual lambda value and a predetermined target lambda value, - Setting (107) the setpoints on the jet pump hydrogen dosing valve (209) and the bypass hydrogen dosing valve (211), wherein the setpoints are adjusted when a hydrogen concentration in the anode subsystem (205) and / or a load requirement on the fuel cell system (200) changes. [2] Operating method (100) according to claim 1, characterized by that the hydrogen concentration in the anode subsystem (205) is determined as a function of a nitrogen concentration in the fresh fuel at the anode inlet, a crossover rate of a cathode subsystem (203) of the fuel cell system (200) as a function of an electrical current provided by the fuel cell system (200), taking into account an opening geometry of respective valves used to provide the fuel. [3] Operating method (100) according to claim 1, characterized bythat the hydrogen concentration in the anode subsystem (205) is determined by determining a hydrogen concentration in the anode gas by means of a hydrogen concentration sensor in an inlet region or an outlet region of the anode subsystem (205). [4] Operating method (100) according to claim 1, characterized by that the hydrogen concentration in the anode subsystem (205) is determined by modeling a gas composition in the anode subsystem (205) using a mathematical model and / or physical data. [5] Operating method (100) according to claim 1, characterized by that the hydrogen concentration in the anode subsystem (205) is determined by comparing a pressure loss of a component in the anode subsystem (205) with an electrical current provided by the fuel cell system (200). [6] Operating method (100) according to claim 1, characterized bythat the hydrogen concentration in the anode subsystem (205) is determined based on a humidity and a nitrogen concentration in the anode gas, wherein the nitrogen concentration is determined by means of a nitrogen concentration sensor in an inlet region or an outlet region of the anode subsystem (205). [7] Operating method (100) according to one of the preceding claims, characterized by , that an electric current provided by the fuel cell system (200) is determined based on the determined hydrogen concentration in the anode subsystem (205), and the actual lambda is determined based on a predetermined characteristic map which assigns a lambda value to a respective value of the electrical current provided by the fuel cell system (200). [8] Operating method (100) according to one of the preceding claims, characterized by , that in order to determine the target values ​​for a movement of the jet pump hydrogen metering valve (209) and the bypass hydrogen metering valve (211), a target recirculation volume flow is determined based on the deviation between the actual lambda value and the predetermined target lambda value and the hydrogen concentration in the anode subsystem (205) as well as a pressure in the inlet area of ​​the anode subsystem (205), and a driving mass flow for the jet pump is calculated based on the desired recirculation volume flow and a characteristic curve of a jet pump of the anode subsystem (205). [9] Operating method (100) according to one of the preceding claims, characterized by that a pressure in the anode subsystem (205) is adjusted as a function of a predetermined operating strategy by means of the jet pump hydrogen metering valve (209) and / or the bypass hydrogen metering valve (211). [10] Fuel cell system (200) for converting energy, wherein the fuel cell system (200) comprises: - a fuel cell stack (201), - a cathode subsystem (203), - an anode subsystem (205), - a computing unit (207), wherein the anode subsystem (205) comprises a jet pump hydrogen metering valve (209) and a bypass hydrogen metering valve (211), and wherein the computing unit (207) is configured to carry out an operating method (100) according to one of claims 1 to 9.

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