Method and device for determining hydrogen consumption during operation of a fuel cell system

Abstract

A method for the instantaneous determination of the current hydrogen consumption (ṁH2PEMSys) during operation of a fuel cell system (2), comprising: measuring the electrical current (iStck) currently provided by the fuel cell system (2); calculating the current hydrogen consumption (ṁH2Farady) of the chemical reaction of the fuel cell system (2) from the measured electrical current (iStck); calculating the hydrogen consumption (ṁH2Purge) for purging the anode circuit of the fuel cell system (2); calculating the consumption of hydrogen molecules (ṁH2An) that diffuse through at least one membrane (10) of the fuel cell system (2) without participating in the chemical reaction; and adding the hydrogen consumptions thus calculated to determine the total current hydrogen consumption (ṁH2PEMSys) of the fuel cell system (2).

Description

The invention relates to a method and a device for the delay-free determination of the current hydrogen consumption during the operation of a fuel cell system.The device also relates to a motor vehicle which is equipped with a fuel cell system and with a device for the delay-free determination of the current hydrogen consumption during the operation of a fuel cell system.Prior ArtIn order to reduce the environmental emissions of motor vehicles, electric motors are increasingly used in motor vehicles instead of internal combustion engines. In order to supply the electric motors in motor vehicles with electrical energy, fuel cell systems which are operated with hydrogen can be used instead of batteries.In order to be able to determine the range of a motor vehicle equipped with such a fuel cell system, it is desirable to be able to determine the current consumption of hydrogen during the operation of a fuel cell system without delay.Disclosure of the InventionA method according to the invention for the delay-free determination of the current hydrogen consumption during the operation of a fuel cell system comprises the following steps: (A) measuring the electrical current provided by the fuel cell system; (B) calculating the current hydrogen consumption of the chemical reaction of the fuel cell system from the measured electrical current; (C) calculating the hydrogen consumption for the flushing of the anode circuit of the fuel cell system; (D) calculating the consumption of hydrogen molecules which diffuse through at least one membrane of the fuel cell system without participating in the chemical reaction; and (E) adding the hydrogen consumption calculated in this way in order to determine the total current hydrogen consumption of the fuel cell system.The invention also comprises a device for the delay-free determination of the current hydrogen consumption during operation of a fuel cell system, wherein the device comprises: a current sensor which is provided and designed for measuring the electrical current output by the fuel cell; and a calculation device which is designed to execute a method according to the invention for measuring the current hydrogen consumption of the fuel cell system on the basis of the electrical current measured by the current sensor.The invention furthermore comprises a motor vehicle having at least one electric motor and having a fuel cell system which is provided and designed to supply the at least one electric motor with electrical energy. The motor vehicle additionally has a device according to the invention for the delay-free determination of the current hydrogen consumption during operation of the fuel cell system.A method according to the invention and a device according to the invention make it possible to determine the current consumption of hydrogen during operation of a fuel cell system without delay and with good accuracy. The range of a motor vehicle equipped with a fuel cell system can be reliably determined in this way. It can thus be avoided that the motor vehicle remains lying before reaching its destination or before reaching the next hydrogen filling station due to hydrogen deficiency.The operational safety of motor vehicles which are driven by fuel cell systems can be improved considerably in this way.In one embodiment, the method includes calculating the current hydrogen consumption of the chemical reaction occurring in the fuel cell system based on Faraday's law.According to Faraday's law, the actual hydrogen consumption of the chemical reaction taking place in the fuel cell system can be determined reliably and with sufficient accuracy based on the current supplied from the fuel cell.In one embodiment, the measured hydrogen consumption determined using Faraday's law based on the measured current delivered from the fuel cell is filtered by a low pass filter to remove noise that may be superimposed on the measured current. The low-pass filter can have a cut-off frequency in the range from 0.1 Hz to 10 Hz, for example.In one embodiment, calculating the hydrogen consumption resulting from purging the anode circuit of the fuel cell system includes determining the hydrogen pressure upstream of a purge valve located in the anode circuit and calculating the hydrogen consumption for purging based on the hydrogen pressure determined upstream of the purge valve.The hydrogen pressure upstream of the purge valve is a good indicator of hydrogen consumption resulting from purging the anode circuit of the fuel cell system.In one embodiment, the method includes calculating hydrogen consumption for purging the anode circuit using a polynomial function. The polynomial function may in particular be a function of the hydrogen pressure measured upstream of the purge valve. The polynomial function may include a 2nd order polynomial.The coefficients of the polynomial may have been determined experimentally or with the aid of model calculations / simulations.In one embodiment, calculating the hydrogen consumption resulting from purging the anode circuit of the fuel cell system includes applying a delay function to account for the delay in pressure change in opening and closing the purge valve.An input of the delay function may be a control signal that controls the purge valve.The delay function may be a step function or a continuous function.The delay introduced by the delay function may be up to 1 s. The delay function can represent, in particular, a delay in the range from 0.25 s to 0.75 s.In one embodiment, the consumption of hydrogen molecules that diffuse through at least one membrane of the fuel cell system without participating in the chemical reaction and that are therefore not taken into account when applying Faraday's law is calculated on the basis of the hydrogen partial pressure at the anode.The hydrogen partial pressure at the anode can be calculated in particular from the gas pressure at the anode, i.e. from the pressure difference between the inlet and the outlet of the anode, and the mean hydrogen concentration in the anode gas.The average hydrogen concentration may be determined from the electric current supplied from the fuel cell.In one embodiment, the hydrogen concentration at the anode of the fuel cell system is determined using a table of the electrical current currently being provided by the fuel cell. The entries in the table may have been determined experimentally or with the aid of model calculations / simulations.In another embodiment, the hydrogen concentration at the anode of the fuel cell system is determined with the aid of a polynomial regression from the electrical current provided by the fuel cell. The coefficients of the polynomial may have been determined experimentally or on the basis of model calculations / simulations.The polynomial regression can comprise, for example, a 3rd order polynomial, such that the hydrogen concentration at the anode of the fuel cell system is a 3rd order polynomial of the electrical current provided by the fuel cell.In one embodiment, the method additionally comprises determining an additional hydrogen consumption of the fuel cell system caused by residual effects and adding it to the total consumption. Thereby, the accuracy of the calculated hydrogen consumption can be further improved.The residual effects can be taken into account in particular in the calculation of the hydrogen consumption by the hydrogen molecules which diffuse through at least one membrane of the fuel cell system without participating in the reaction, and the coefficients of the polynomial can be integrated.An embodiment of the invention will be described below with reference to the accompanying figures.Brief Description of the FiguresFIG. 1 shows a schematic view of a motor vehicle which is driven by an electric motor which is fed by a fuel cell system. FIG. 2 is a schematic view of a fuel cell system. FIG. 3 schematically illustrates a method according to the invention for the delay-free determination of the current hydrogen consumption during the operation of a fuel cell system.DESCRIPTION OF THE FIGURESFIG. 1 shows a schematic view of a motor vehicle which is driven by an electric motor 5 which is fed by a fuel cell system 2.The motor vehicle 1 has four wheels 3 and at least one electric motor 5, which is provided for driving at least two wheels 3 of the motor vehicle 1. The electric motor 5 can also be provided for driving all four wheels 3 of the motor vehicle 1. In an alternative exemplary embodiment, which is not explicitly shown in the figures, an electric motor 5 can be provided on at least one of the wheels 3, in particular on each of the wheels 3, of the motor vehicle 1.The electric motor 5 is supplied with electrical energy via a motor controller 7, which is made available by the fuel cell system 2.FIG. 2 is a schematic view of the fuel cell system 2.The fuel cell system 2 comprises at least one fuel cell 4 with an anode 6 and a cathode 8, The fuel cell system 2 can have a plurality of fuel cells 4, which can be arranged in a fuel cell stack ("fuel cell stack").For reasons of simplified illustration, an exemplary embodiment of the invention is described below with reference to a fuel cell system 2 which has a single fuel cell 4. The invention can likewise be used in fuel cell systems 2 which have a plurality of fuel cells 4, in particular a fuel cell stack.The anode 6 and the cathode 8 of the fuel cell 4 are separated from one another by a membrane 10.Oxygen, in particular in the form of oxygen-containing ambient air, is supplied to the cathode 8 of the fuel cell 4 by an oxygen supply system 12.The fuel cell system 2 furthermore comprises a hydrogen supply system 14, which is provided and designed to supply hydrogen from a hydrogen reservoir 16 to the anode 6 of the fuel cell 4.The hydrogen and oxygen supplied to the fuel cell 4 react to water (H 2 O) in the fuel cell 4. During this reaction, electrical energy is released, which is made available by the fuel cell 4 as an electrical current i Stck.The hydrogen from the hydrogen reservoir 16 is supplied to the fuel cell 4 through a shut-off valve ("shut-off valve") 18, a metering valve ("closing valve") 20 and a delivery device 22, for example an ejector.The gas flow emerging from the anode 6 of the fuel cell 4 is passed through a water separator 24, in which liquid constituents of the gas flow are separated from gaseous constituents of the gas flow.The gaseous constituents are fed back into the delivery device 22 and from there into the anode 6 of the fuel cell 4.The liquid constituents and nitrogen present in the anode circuit are discharged into the environment through a purge valve ("purge valve").A current sensor 30 is located on the fuel cell 4, which is provided and designed to supply the electric current i Stck, which is provided by the fuel cell 4, in order to supply an electric motor 5 with electric energy via a motor controller 7, as is shown in FIG. 1.At a hydrogen inlet 6 aand at a hydrogen outlet 6 bof the anode 6, there is in each case an anode pressure sensor 32 a, 32 b, which is provided and designed to measure hydrogen pressure p Anln at the hydrogen inlet 6 aand pressure p AnOut at the hydrogen outlet 6 bof the anode 6.At an inlet of the water separator 24, there is a flushing pressure sensor 34, which is provided and designed to measure a gas pressure p purge, which is referred to below as "flushing pressure" p purge.The fuel cell system 2 also comprises a control device 28, which is provided and designed to actuate the delivery device 22 and the valves 18, 20, 26 of the hydrogen supply system 14 such that the fuel cell 4 provides a desired electric current i Stck, in particular an electric current i Stck, which is requested by the motor controller 7.The fuel cell system 2 additionally comprises a calculation device 36, which is provided and designed to determine the current consumption of hydrogen during operation of the fuel cell system 2 and to make it available as a measurement variable.The calculation device 36 can be formed as part of the control device 28, as part of the motor controller 7 or as a separate calculation device 36.An exemplary embodiment of a method according to the invention for the delay-free determination of the current hydrogen consumption during the operation of the fuel cell system 2, which can be carried out by the calculation device 36, is described below with reference to FIG. 3.In a first line 100 of a method according to the invention, the current hydrogen consumption ≅PH2Faraday of the chemical reaction in the fuel cell 4 is calculated.For this purpose, first of all, in a step 110, the electrical current i Stck currently provided by the fuel cell system is measured using the current sensor 30.Using Faraday's law, the current hydrogen consumption H2Faraday of the chemical reaction which takes place in the fuel cell 4 is then calculated in a following step 120.Here, i Stck is the measured electric current currently supplied by the fuel cell system; n Cells is the number of fuel cells in the fuel cell system; M H2 is the molar mass of hydrogen (2.016 g / mol); and F is the Faraday constant (96485.33 C / mol).In a second line 200, hydrogen consumption ≅ purge is calculated, which results from the purging of the anode circuit of the fuel cell system 2.The calculation of the hydrogen consumption purge, which results from the purging of the anode circuit of the fuel cell system 2, is based on the gas pressure p PurgeVlv upstream of the purge valve and the control signal C PurgeVlv, with which the purge valve is activated.C purgeVlv and p purgeVlv can be measured, for example, using corresponding sensors in step 210. p purgeVlv can be measured, in particular, using the scavenging pressure sensor 34.Alternatively, C purgeVlv and p purgeVlv can also be read out in step 210 from a control device of the motor vehicle 1 and / or from a cloud-based database in which field data of vehicles 1 equipped with fuel cells 4 are stored.The hydrogen consumption purge, which results from the purging of the anode circuit of the fuel cell system 2, can then be calculated in a following step 220 using the equation b e.In this equation, flgDelayTonToff(pPurgeVlv ) is a so-called delay function which models the delay of the change in the gas flow or the gas pressure when the purge valve is opened and closed.The delay function flgDelayTonToff(pPurgeVlv) may be a step function or a continuous function.The delay function, in particular the delay time defined by the flgDelayTonToff(pPurgeVlv), can be determined experimentally at the respective fuel cell system 2. Alternatively, the delay time can also be determined by numerical model calculations / simulations.The delay time defined by the delay function may be, for example, a delay time in the range of 0.25 s to 0.75 s. Depending on the respective fuel cell system 2, the delay time can vary significantly and in particular can also assume significantly larger values, in particular values of more than 1 s.The second factor in the equation for determining the hydrogen consumption ≅ Purge, which results from the purging of the anode circuit of the fuel cell system 2, is a polynomial, in particular a 2nd order polynomial, of the gas pressure pPurgeVl prevailing upstream of the purge valve.The coefficients a0, a1, a2of the polynomial can be determined experimentally at the respective fuel cell system 2. Alternatively, the coefficients can also be determined by numerical model calculations / simulations of the fuel cell system 2.In a third strand 300, the consumption of hydrogen molecules is calculated, which diffuse through the at least one membrane 10 of the fuel cell 4 without participating in the chemical reaction in the fuel cell 4. These hydrogen molecules do not contribute to power generation in the fuel cell 4.In addition, this third branch 300 also takes into account the hydrogen consumption of the fuel cell system 2, which is caused by further, small effects, so-called "residual effects". Such residual effects can comprise, for example, leaks in the fuel cell system 2 and other drains ("drain effects") of hydrogen.In a first step 310, first the gas pressure p An at the anode 6 of the fuel cell 4 is determined. The gas pressure p An at the anode 6 of the fuel cell 4 can be calculated in particular as an arithmetic mean value from the gas pressure p Anln at the inlet of the anode 6 and the gas pressure p AOut at the outlet of the anode 6:In a following step 320, the average hydrogen concentration x H2An in the anode gas flow which is supplied to the anode 6 of the fuel cell 4 is determined.The average hydrogen concentration x H2An in the anode gas flow can be taken, for example, from a table 320 a, which links the electrical current i Stck currently provided by the fuel cell system 2 to an average hydrogen concentration x H2An in the anode gas flow.The entries in the table 320a may be determined experimentally or by numerical model calculations / simulations.Alternatively, the mean hydrogen concentration x H2An in the anode gas flow can be calculated by a polyom regression 320 bfrom the electrical current i Stck currently provided by the fuel cell 4:The use of a 3rd order polynomial has proven successful in this case.The coefficients c0, c1, c2, c3of the polynomial can be determined experimentally at the respective fuel cell system 2. Alternatively, the coefficients can also be determined by numerical model calculations / simulations.If both the gas pressure p An at the anode 6 and the hydrogen concentration x H2An in the anode gas flow are known, the hydrogen partial pressure p H2An at the anode 6 can be calculated as follows in a following step 330.The consumption resulting from hydrogen molecules diffusing through at least one membrane 10 of the fuel cell 4 without participating in the chemical reaction in the fuel cell 4 and from additional "residual effects" is then modeled in a step 340 as a function of the electric current i Stck, which is currently provided by the fuel cell 4, and the previously calculated hydrogen partial pressure p H2An at the anode 6 of the fuel cell 4: ei is: n Cells the number of fuel cells in the fuel cell system; and H2Crossover the crossover flow rate for each fuel cell of the fuel cell systemThe crossover flow rate ≅ H2Crossover is a specific value of each fuel cell 4. a typical value for the crossover flow rate ≅ H2Crossover is, for example, 1.0495*10-5 g / (s*bar).The coefficients b1, b2, b3, b4and b5may be determined experimentally at the respective fuel cell system 2. Alternatively, the coefficients can also be determined by numerical model calculations / simulations.In a final step 400, the previously calculated contributions H2Farady, H2Purge and diagrammatically H2An, which contribute to the current hydrogen consumption of the fuel cell system 2, are added in order to thus obtain the current total hydrogen consumption diagrammatically H2PEMSys of the fuel cell system 2:The previously described calculation of the current total hydrogen consumption H2PEMSys of the fuel cell system 2, in particular the described approximation of the individual contributions H2Farady, H2Purge and H2An, is generally valid only within a limited range i StckMin< i Stck< i StckMax of the electric current i Stck provided by the fuel cell 4.In order to prevent erroneous results from being provided by the described method for calculating the current total hydrogen consumption ≅ H2PEMSys of the fuel cell system 2, the method can be deactivated in an optional step 500 if the electric current i Stck, which is currently provided by the fuel cell 4 of the fuel cell system 2, is outside the predefined range [i StckMin; i StckMax] in which the above-described approximations and calculations are valid.A method according to the invention and a device according to the invention make it possible to determine the current hydrogen consumption continuously with high accuracy during the operation of a fuel cell system 2 which comprises at least one fuel cell 4. The expected operating duration and the resultant expected range of a motor vehicle 1, which is driven with electric current provided by the fuel cell system 2, can thus be determined continuously and reliably.

Claims

Method for the delay-free determination of the current hydrogen consumption (≅ H2PEMSys) during the operation of a fuel cell system (2), wherein the method comprises: (A) measuring the electrical current (i Stck) currently provided by the fuel cell system (2); (B) calculating the current hydrogen consumption (≅ H2Faraday) of the chemical reaction of the fuel cell system (2) from the measured electrical current (i Stck) (C) calculating the hydrogen consumption (≅ H2Faraday) for the flushing of the anode circuit of the fuel cell system (2); (D) calculating the consumption (H2An) of hydrogen molecules that diffuse through at least one membrane (10) of the fuel cell system (2) without participating in the chemical reaction; and (E) adding the hydrogen consumptions ( H2Faraday, H2Faraday, H2An) calculated in this way to determine the total current hydrogen consumption ( H2PEMSys) of the fuel cell system (2).Method according to claim 1, wherein the method additionally comprises determining an additional hydrogen consumption of the fuel cell system (2) caused by residual effects and adding it to the total current hydrogen consumption (≅ H2PEMSys).Method according to claim 1 or 2, wherein the method comprises calculating the current hydrogen consumption (≅ H2Faraday) of the chemical reaction of the fuel cell system (2) on the basis of Faraday's law.Method according to claim 3, wherein the method additionally comprises filtering the current hydrogen consumption (≅ H2Faraday) of the chemical reaction calculated on the basis of Faraday's law by means of a low-pass filter.Method according to any of the preceding claims, wherein calculating the hydrogen consumption ( diagrammatically H2Purge) for purging the anode circuit of the fuel cell system (2) comprises calculating the hydrogen consumption (diagrammatically H2Purge) for purging based on the hydrogen pressure (p Purge) upstream of a purge valve (26); the method in particular comprising calculating the hydrogen consumption ( diagram H2Purge) for purging using a polynomial which is a 2nd order polynomial of the hydrogen pressure (p Purge) upstream of the purge valve (26).Method according to any of the preceding claims, wherein the calculation of the hydrogen consumption (≅ H2Purge) for the purging of the anode circuit of the fuel cell system (2) comprises applying a delay function to take account of the opening and closing of the purge valve (26).Method according to one of the preceding claims, wherein the method comprises determining the hydrogen concentration (x H2An) at the anode (6) of the fuel cell system (2) with the aid of a table (320b) from the electrical current (i Stck), which is provided by the fuel cell (4).Method according to one of Patent Claims 1 to 6, wherein the method comprises determining the hydrogen concentration (x H2An) at the anode (6) of the fuel cell system (2) with the aid of a polynomial regression from the electrical current (i Stck), which is provided by the fuel cell (4).The method of claim 8, wherein the polynomial regression comprises a 3rd order polynomial, and / or wherein the coefficients of the polynomial are determined experimentally or based on simulation calculations.Device for the delay-free determination of the current hydrogen consumption (≅ H2PEMSys) during the operation of a fuel cell system (2), wherein the device comprises: a current sensor (30) for measuring the electrical current (i Stck); currently output by the fuel cell (4) and a calculation device (7) which is designed to carry out a method according to one of the preceding patent claims in order to measure the current hydrogen consumption (≅ H2PEMSys) of the fuel cell system (2) on the basis of the electrical current (i Stck) measured by the current sensor (30).The device according to claim 10, wherein the device additionally comprises at least one pressure sensor (32a, 32b) configured to measure a hydrogen pressure (p An) at an anode (6) of the fuel cell system (2); and wherein the calculation device (7) is configured to take into account the pressure (p An) measured by the at least one pressure sensor (32a, 32b) when determining the current hydrogen consumption of the fuel cell system (2).Motor vehicle (1) having at least one electric motor (5) and a fuel cell system (2) which is designed to supply the at least one electric motor (5) with electrical energy; wherein the motor vehicle (1) additionally has a device according to Claim 10 or 11 which is provided and designed for the delay-free determination of the current hydrogen consumption (≅ H2PEMSys) during operation of the fuel cell system (2).

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