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

Abstract

A method for delay-free determination of the current hydrogen consumption (ṁH2PEMSys) during operation of a fuel cell system (2) comprises: measuring the electrical current (iStck) provided currently by the fuel cell system (2); from the electrical current (iStck) measured, calculating the current hydrogen consumption (ṁH2Farady) of the chemical reaction of the fuel cell system (2); calculating the hydrogen consumption (ṁH2Purge) for purging the anode circuit of the fuel cell system (2); calculating the consumption of hydrogen molecules (ṁH2An) which diffuse through at least one membrane (10) of the fuel cell system (2) without taking part in the chemical reaction; and summing the hydrogen consumptions thus calculated so as to determine the overall current hydrogen consumption (ṁH2PEMSys) of the fuel cell system (2).

Description

[0001] Description

[0002] title

[0003] Method and device for determining hydrogen consumption during operation of a fuel cell system

[0004] The invention relates to a method and a device for determining the current hydrogen consumption during operation of a fuel cell system without delay.

[0005] The device also relates to a motor vehicle equipped with a fuel cell system and with a device for determining the current hydrogen consumption during operation of a fuel cell system without delay.

[0006] State of the art

[0007] To reduce environmentally harmful emissions from motor vehicles, electric motors are increasingly being used in vehicles instead of combustion engines. To supply electric motors in motor vehicles with electrical energy, hydrogen-powered fuel cell systems can be used instead of batteries.

[0008] 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 operation of a fuel cell system without delay.

[0009] Disclosure of the invention

[0010] A method according to the invention for determining the current hydrogen consumption during operation of a fuel cell system without delay comprises the following steps: (A) measuring the electrical current provided by the fuel cell system;

[0011] (B) to calculate the current hydrogen consumption of the chemical reaction of the fuel cell system from the measured electric current;

[0012] (C) calculate the hydrogen consumption for purging the anode circuit of the fuel cell system;

[0013] (D) calculate the consumption of hydrogen molecules diffusing through at least one membrane of the fuel cell system without participating in the chemical reaction; and

[0014] (E) add the hydrogen consumptions calculated in this way to determine the total current hydrogen consumption of the fuel cell system.

[0015] The invention also includes a device for determining the current hydrogen consumption during operation of a fuel cell system without delay, the device comprising: a current sensor provided and configured to measure the electrical current output by the fuel cell; and a calculation device configured to carry out a method according to the invention to measure the current hydrogen consumption of the fuel cell system based on the electrical current measured by the current sensor.

[0016] The invention further comprises a motor vehicle with at least one electric motor and a fuel cell system designed and configured to supply the at least one electric motor with electrical energy. The motor vehicle additionally comprises a device according to the invention for instantaneously determining the current hydrogen consumption during operation of the fuel cell system.

[0017] A method and device according to the invention make it possible to determine the current hydrogen consumption during operation of a fuel cell system without delay and with high accuracy. The range of a motor vehicle equipped with a fuel cell system can be reliably determined in this way. This prevents the vehicle from breaking down due to a lack of hydrogen before reaching its destination or before reaching the next hydrogen refueling station.

[0018] The operational safety of motor vehicles powered by fuel cell systems can be significantly improved in this way.

[0019] In one embodiment, the method includes calculating the actual hydrogen consumption of the chemical reaction taking place in the fuel cell system based on Faraday's law.

[0020] Using 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 delivered by the fuel cell.

[0021] In one embodiment, the measured hydrogen consumption, determined using Faraday's law based on the measured current output by the fuel cell, is filtered through a low-pass filter to remove any noise that may be superimposed on the measured current. The low-pass filter may, for example, have a cutoff frequency in the range of 0.1 Hz to 10 Hz.

[0022] In one embodiment, calculating the hydrogen consumption resulting from purging the anode circuit of the fuel cell system comprises determining or measuring 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 or measured upstream of the purge valve.

[0023] The hydrogen pressure upstream of the purge valve is a good indicator of the hydrogen consumption resulting from purging the anode circuit of the fuel cell system.

[0024] In one embodiment, the method comprises calculating the 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 second-order polynomial.

[0025] The coefficients of the polynomial can be determined experimentally or by model calculations / simulations.

[0026] 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 when opening and closing the purge valve.

[0027] An input variable of the delay function can be a control signal that controls the flush valve.

[0028] The delay function can be a step function or a continuous function.

[0029] The delay introduced by the delay function can be up to 1 s. In particular, the delay function can represent a delay in the range of 0.25 s to 0.75 s.

[0030] 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 are therefore not taken into account in the application of Faraday's law is calculated based on the hydrogen partial pressure at the anode.

[0031] The hydrogen partial pressure at the anode can be calculated in particular from the gas pressure at the anode, ie from the pressure difference between the inlet and the outlet of the anode, and the average hydrogen concentration in the anode gas.

[0032] The average hydrogen concentration can be determined from the electrical current provided by the fuel cell.

[0033] In one embodiment, the hydrogen concentration at the anode of the fuel cell system is determined using a table based on the electrical current currently supplied by the fuel cell. The entries in the table may have been determined experimentally or using model calculations / simulations.

[0034] In another embodiment, the hydrogen concentration at the anode of the fuel cell system is determined using a polynomial regression from the electrical current provided by the fuel cell. The coefficients of the polynomial can be determined experimentally or based on model calculations / simulations.

[0035] For example, the polynomial regression may include a 3rd order polynomial such that the hydrogen concentration at the anode of the fuel cell system is a 3rd order polynomial of the electric current provided by the fuel cell.

[0036] 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. This can further improve the accuracy of the calculated hydrogen consumption.

[0037] The residual effects can be taken into account, in particular, when calculating the hydrogen consumption by the hydrogen molecules that 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.

[0038] An embodiment of the invention is described below with reference to the accompanying figures.

[0039] Short description of the characters

[0040] Figure 1 shows a schematic view of a motor vehicle powered by an electric motor fed by a fuel cell system.

[0041] Figure 2 shows a schematic view of a fuel cell system. Figure 3 schematically illustrates a method according to the invention for instantaneously determining the current hydrogen consumption during operation of a fuel cell system.

[0042] Character description

[0043] Figure 1 shows a schematic view of a motor vehicle driven by an electric motor 5 which is fed by a fuel cell system 2.

[0044] 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 embodiment, 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.

[0045] The electric motor 5 is supplied with electrical energy via a motor control 7, which is provided by the fuel cell system 2.

[0046] Figure 2 shows a schematic view of the fuel cell system 2.

[0047] 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").

[0048] For the sake of simplicity, an exemplary embodiment of the invention is described below with reference to a fuel cell system 2 having a single fuel cell 4. The invention can also be used in fuel cell systems 2 having multiple fuel cells 4, in particular a fuel cell stack.

[0049] The anode 6 and the cathode 8 of the fuel cell 4 are separated from each other by a membrane 10. Oxygen, particularly 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.

[0050] The fuel cell system 2 further 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.

[0051] The hydrogen and oxygen supplied to the fuel cell 4 react within the fuel cell 4 to form water (H2O). This reaction releases electrical energy, which is then made available by the fuel cell 4 as electrical current.

[0052] The hydrogen from the hydrogen reservoir 16 is supplied to the fuel cell 4 through a shut-off valve 18, a dosing valve 20 and a conveying device 22, for example an ejector.

[0053] The gas flow emerging from the anode 6 of the fuel cell 4 is passed through a water separator 24 in which liquid components of the gas flow are separated from gaseous components of the gas flow.

[0054] The gaseous components are returned to the conveying device 22 and from there to the anode 6 of the fuel cell 4.

[0055] The liquid components and nitrogen in the anode circuit are released into the environment through a purge valve.

[0056] On the fuel cell 4 there is a current sensor 30 which is provided and designed to measure the electrical current istck provided by the fuel cell 4 in order to supply an electric motor 5 with electrical energy via a motor controller 7, as shown in Figure 1.

[0057] At a hydrogen inlet 6a and at a hydrogen outlet 6b of the anode 6 there is an anode pressure sensor 32a, 32b, which is provided and designed to measure hydrogen pressure pAnin at the hydrogen inlet 6a and pressure pAnout at the hydrogen outlet 6b of the anode 6. At an inlet of the water separator 24 there is a purge pressure sensor 34, which is provided and designed to measure a gas pressure p P ur ge , which is referred to below as "flushing pressure" p P ur ge to measure.

[0058] The fuel cell system 2 also comprises a control device 28, which is provided and designed to control the conveying device 22 and the valves 18, 20, 26 of the hydrogen supply system 14 such that the fuel cell 4 provides a desired electrical current istck, in particular an electrical current istck that is requested by the engine control 7.

[0059] The fuel cell system 2 further 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 measured variable.

[0060] The calculation device 36 can be designed as part of the control device 28, as part of the engine control 7 or as a separate calculation device 36.

[0061] An embodiment of a method according to the invention for determining the current hydrogen consumption during operation of the fuel cell system 2 without delay, which can be carried out by the calculation device 36, is described below with reference to Figure 3.

[0062] In a first strand 100 of a method according to the invention, the current hydrogen consumption rhpH2Faraday of the chemical reaction in the fuel cell 4 is calculated.

[0063] For this purpose, in a step 110, the electrical current istck currently provided by the fuel cell system is first measured with the current sensor 30.

[0064] Applying Faraday’s law, a following

[0065] Step 120 the current hydrogen consumption rhH2Faraday of the chemical

[0066] Reaction that takes place in fuel cell 4, calculated:

[0067] Where: istck is the measured electrical current currently provided by the fuel cell system; nceiis is the number of fuel cells in the fuel cell system;

[0068] MH2 is the molar mass of hydrogen (2.016 g / mol); and

[0069] F is the Faraday constant (96485.33 C / mol).

[0070] In a second line 200, hydrogen consumption rh pU r g e, which results from the purging of the anode circuit of the fuel cell system 2.

[0071] The calculation of the hydrogen consumption rhpurge resulting from purging the anode circuit of the fuel cell system 2 is based on the gas pressure ppur ge viv upstream of the flush valve and the control signal cp U r ge viv, which controls the flush valve. c P ur g eviv and p pU r g eviv can be measured, for example, in step 210 using appropriate sensors. p pU r g eviv can be measured in particular with the flushing pressure sensor 34.

[0072] Alternatively, c pU r ge viv and p pU r g eviv can also be read out in step 210 from a control unit of the motor vehicle 1 and / or from a cloud-based database in which field data from vehicles 1 equipped with fuel cells 4 are stored.

[0073] The hydrogen consumption rh pU rg e, 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 In this equation, flgDelayTonToff(pPurgeVlv) is a so-called delay function that models the delay in the change in gas flow or gas pressure when opening and closing the purge valve.

[0074] The delay function flgDelayTonToff(pPurgeVlv) can be a step function or a continuous function.

[0075] The delay function, in particular the delay time defined by flgDelayTonToff(pPurgeVlv), can be determined experimentally on the respective fuel cell system 2. Alternatively, the delay time can also be determined by numerical model calculations / simulations.

[0076] The delay time defined by the delay function can, for example, be 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 considerably and, in particular, can assume significantly larger values, in particular values ​​of more than 1 s.

[0077] The second factor in the equation for determining the hydrogen consumption itipurge resulting from purging the anode circuit of the fuel cell system 2 is a polynomial, in particular a second-order polynomial, of the gas pressure pPurgeVIv prevailing upstream of the purge valve.

[0078] The coefficients aO, a1, a2 of the polynomial can be determined experimentally on the respective fuel cell system 2. Alternatively, the coefficients can also be determined by numerical model calculations / simulations of the fuel cell system 2.

[0079] In a third strand 300, the consumption of hydrogen molecules that diffuse through the at least one membrane 10 of the fuel cell 4 without participating in the chemical reaction in the fuel cell 4 is calculated. These hydrogen molecules do not contribute to the power generation in the fuel cell 4. Additionally, this third strand 300 also takes into account the hydrogen consumption of the fuel cell system 2, which is caused by other, small effects, so-called "residual effects." Such residual effects can include, for example, leaks in the fuel cell system 2 and other hydrogen drain effects.

[0080] In a first step 310, the gas pressure pAn at the anode 6 of the fuel cell 4 is first determined. The gas pressure pAn at the anode 6 of the fuel cell 4 can be calculated, in particular, as the arithmetic mean of the gas pressure pAnin at the inlet of the anode 6 and the gas pressure pAOut at the outlet of the anode 6:

[0081] 15

[0082] In a following step 320, the average hydrogen concentration XH2An in the anode gas flow supplied to the anode 6 of the fuel cell 4 is determined.

[0083] The average hydrogen concentration XH2An in the anode gas flow can be taken, for example, from a table 320a, which links the electrical current istck currently provided by the fuel cell system 2 with an average hydrogen concentration XH2An in the anode gas flow.

[0084] The entries in Table 320a can be determined experimentally or by numerical model calculations / simulations.

[0085] Alternatively, the average hydrogen concentration XH2An in the anode gas flow can be calculated by a polyom regression 320b from the electrical current istck currently provided by the fuel cell 4:

[0086] The use of a third-order polynomial has proven to be effective. The coefficients cO, d, c2, and c3 of the polynomial can be determined experimentally on the respective fuel cell system 2. Alternatively, the coefficients can also be determined by numerical model calculations / simulations.

[0087] If both the gas pressure pAn at the anode 6 and the hydrogen concentration XH2An in the anode gas flow are known, the hydrogen partial pressure pH2An at the anode 6 can be calculated in a subsequent step 330 as follows:

[0088] PH2 An = %H2 An * PAn

[0089] 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 istck currently provided by the fuel cell 4 and the previously calculated hydrogen partial pressure pH2An at the anode 6 of the fuel cell 4:

[0090] Where: nceiis is the number of fuel cells in the fuel cell system; and riiH2Crossover is the crossover flow rate for each fuel cell of the fuel cell system

[0091] The crossover flow rate rhH2Crossover is a specific value of each fuel cell 4. A typical value for the crossover flow rate rhH2Crossover is, for example, 1 .0495*10-5 g / (s * bar).

[0092] The coefficients b1, b2, b3, b4, and b5 can be determined experimentally on 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 rhH2Farady, itiH2Purge, and iiiH2An, which contribute to the current hydrogen consumption of the fuel cell system 2, are added to obtain the current total hydrogen consumption rhH2PEMSys of the fuel cell system 2: / '2 PEM Sys = / 2 Faraday + / 2 Purge + ™H2 Crossover Rest

[0093] The previously described calculation of the current total hydrogen consumption rhH2PEMSys of the fuel cell system 2, in particular the described approximation of the individual contributions rhH2Farady, riiH2Purge and riiH2An, is generally only valid within a limited range istckMin < istck < istckMax of the electrical current istck provided by the fuel cell 4.

[0094] In order to prevent the described method for calculating the current total hydrogen consumption rhH2PEMSys of the fuel cell system 2 from providing erroneous results, the method can be deactivated in an optional step 500 if the electrical current istck currently provided by the fuel cell 4 of the fuel cell system 2 lies outside the predetermined range [istckMin; istckMax] in which the previously described approximations and calculations are valid.

[0095] A method and a device according to the invention make it possible to continuously determine with high accuracy the current hydrogen consumption during operation of a fuel cell system 2 comprising at least one fuel cell 4. The expected operating time and the resulting expected range of a motor vehicle 1 powered by electrical power provided by the fuel cell system 2 can thus be continuously and reliably determined.

Claims

1 . A method for the instantaneous determination of the current hydrogen consumption (rhH2PEMSys) during operation of a fuel cell system (2), the method comprising: (A) to measure the electrical current (istck) currently provided by the fuel cell system (2); (B) to calculate the current hydrogen consumption (rhH2Faraday) of the chemical reaction of the fuel cell system (2) from the measured electric current (istck); (C) to calculate the hydrogen consumption (rhH2Faraday) for purging the anode circuit of the fuel cell system (2); (D) to calculate the consumption (rhH2An) of hydrogen molecules diffusing through at least one membrane (10) of the fuel cell system (2) without participating in the chemical reaction; and (E) to add the hydrogen consumptions (rhH2Faraday, riiH2Faraday, rhH2An) calculated in this way to determine the total current hydrogen consumption (rhH2PEMSys) of the fuel cell system (2).

2. The 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 (rhH2PEMSys).

3. The method according to claim 1 or 2, wherein the method comprises calculating the current hydrogen consumption (rhH2Faraday) of the chemical reaction of the fuel cell system (2) based on Faraday's law.

4. The method according to claim 3, wherein the method additionally comprises filtering the current hydrogen consumption (rhH2Faraday) of the chemical reaction, calculated on the basis of Faraday's law, through a low-pass filter.

5. The method according to any one of the preceding claims, wherein calculating the hydrogen consumption (rhH2Purge) for purging the anode circuit of the fuel cell system (2) comprises calculating the hydrogen consumption (rhH2Purge) for purging on the basis of the hydrogen pressure (pp U r g e) upstream of a purge valve (26); the method comprising in particular calculating the hydrogen consumption (rhH2Purge) for purging using a polynomial which is a second-order polynomial of the hydrogen pressure (pp U r g e) upstream of the flushing valve (26).

6. The method according to any one of the preceding claims, wherein calculating the hydrogen consumption (rhH2Purge) for purging the anode circuit of the fuel cell system (2) comprises applying a delay function to account for the opening and closing of the purge valve (26).

7. Method according to one of the preceding claims, wherein the method comprises determining the hydrogen concentration (XH2AP) at the anode (6) of the fuel cell system (2) with the aid of a table (320b) from the electrical current (istck) provided by the fuel cell (4).

8. The method according to any one of claims 1 to 6, wherein the method comprises determining the hydrogen concentration (XH2AP) at the anode (6) of the fuel cell system (2) by means of a polynomial regression from the electrical current (istck) provided by the fuel cell (4).

9. The method according to claim 8, wherein the polynomial regression comprises a 3rd order polynomial, and / or wherein the coefficients of the polynomial are determined experimentally or on the basis of simulation calculations.

10. Device for instantaneous determination of the current Hydrogen consumption (rhH2PEMSys) during operation of a fuel cell system (2), the device comprising: a current sensor (30) for measuring the electrical current (istck) 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 claims in order to measure the current hydrogen consumption (rhH2PEMSys) of the fuel cell system (2) on the basis of the electrical current (istck) measured by the current sensor (30).

11. Device according to claim 10, wherein the device additionally comprises at least one pressure sensor (32a, 32b) configured to measure a hydrogen pressure (pAn) at an anode (6) of the fuel cell system (2); and wherein the calculation device (7) is configured to take into account the pressure (pAn) measured by the at least one pressure sensor (32a, 32b) when determining the current hydrogen consumption of the fuel cell system (2).

12. A motor vehicle (1) comprising at least one electric motor (5) and a fuel cell system (2) configured to supply the at least one electric motor (5) with electrical energy; wherein the motor vehicle (1) additionally comprises a device according to claim 10 or 11, which is provided and configured for the instantaneous determination of the current hydrogen consumption (rhH2PEMSys) during operation of the fuel cell system (2).

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