Method and device for determining the concentration of hydrogen in fuel cells

Abstract

A method for determining the hydrogen concentration (CH2) in an anode (6) of at least one fuel cell (4) comprises: (A) repeatedly measuring the electric current (i) output by the at least one fuel cell (4) and providing a plurality of current measurement values (i(t)); (B) repeatedly measuring the hydrogen concentration (kH2) in a gas mixture (26, 28) which flows out of a purge valve (20) which is arranged at an outlet (9) of the at least one fuel cell (20), and providing a plurality of hydrogen concentration measurement values (kH2(t)); (C) calculating relative current measurement values (irel(t)) from the measured current measurement values (i(t)) and calculating relative hydrogen concentration measurement values (krel(t)) from the measured hydrogen concentration measurement values (kH2(t)); (D) determining scaled current measurement values (iscal(t)) by multiplying the relative current measurement values (irel(t)) by a current scaling factor (gi) and determining scaled hydrogen concentration measurement values (kscal(t)) by multiplying the relative hydrogen concentration measurement values (krel(t)) by a hydrogen concentration scaling factor (gH2); (E) forming difference values (diff(t)) from the scaled current measurement values (iscal(t)) and the scaled hydrogen concentration measurement values (kscal(t)); (F) integrating or summing the difference values (diff(t)) over time (t); and (G) adding a bias value (GH2) to the integral D(T) or to the sum D(T) of the difference values (diff(t)).

Description

[0001] Description

[0002] title

[0003] Method and apparatus for determining the concentration of hydrogen in

[0004] Fuel cells

[0005] The invention relates to a method and a device for determining the concentration of hydrogen in the anode of fuel cells. The invention also relates to a fuel cell system with such a device and to a motor vehicle equipped with a fuel cell system according to the invention.

[0006] State of the art

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

[0008] To increase efficiency, fuel cells are often operated in a so-called anode recirculation mode. In this mode, the hydrogen-containing gases exiting the anode of the fuel cell are returned to the anode inlet via an anode recirculation circuit, in order to utilize the hydrogen still contained in the exiting gases for energy generation.

[0009] Since nitrogen accumulates in the anode recirculation circuit during operation in anode recirculation mode and displaces hydrogen, thus reducing the hydrogen concentration in the anode recirculation circuit, the anode recirculation circuit is regularly purged with hydrogen by opening a purge valve to ensure efficient operation of the fuel cell system. Purging the anode recirculation circuit can be performed particularly efficiently if the hydrogen concentration in the fuel cell anode is known, as the purging process can then be adjusted to the current hydrogen concentration in the anode.

[0010] The methods and devices known so far for measuring the hydrogen concentration in the anode of a fuel cell are complex and expensive. They are therefore not suitable for mass production, for example in motor vehicles.

[0011] It is therefore an object of the invention to provide a method and a device that make it possible to determine the hydrogen concentration in the anode of a fuel cell more easily and cost-effectively.

[0012] Disclosure of the invention

[0013] A method according to the invention for determining the hydrogen concentration in an anode of at least one fuel cell during the operation of the at least one fuel cell comprises the following steps: repeatedly measuring the electric current delivered by the at least one fuel cell and providing several current measurements; repeatedly measuring the hydrogen concentration in a gas mixture flowing from a purge valve arranged at an outlet of an anode of the at least one fuel cell and providing several hydrogen concentration measurements; calculating relative current measurements from the measured current measurements and calculating relative hydrogen concentration measurements from the measured hydrogen concentration measurements;Determining scaled current measurements by multiplying the relative current measurements by a current scaling factor and determining scaled hydrogen concentration measurements by multiplying the relative hydrogen concentration measurements by a hydrogen concentration scaling factor; calculating difference values ​​from the scaled current measurements and the scaled hydrogen concentration measurements;

[0014] Integrating or summing the difference values ​​over time; and adding a bias value to the integral or difference values. The current and hydrogen concentration measurements are taken continuously or repeatedly, for example, periodically at constant time intervals. These time intervals can be, for example, 50 ms to 150 ms, and in particular 100 ms.

[0015] In a method according to the invention, the differences between the scaled current measurements and the scaled hydrogen concentration measurements are calculated when the underlying current and hydrogen concentration measurements are taken at the same time. Each difference value is thus uniquely assigned to the time at which the underlying measurements were taken.

[0016] The invention also includes a device for determining the hydrogen concentration in an anode of at least one fuel cell during the operation of the at least one fuel cell.Such a device according to the invention comprises: a current sensor configured and provided to measure an electric current delivered by the at least one fuel cell during operation and to provide corresponding current measurements; a hydrogen concentration sensor configured and provided to measure hydrogen concentrations in a gas mixture flowing from a purge valve arranged at an outlet of an anode of the at least one fuel cell and to provide corresponding hydrogen concentration measurements; and an evaluation device configured and provided to receive the measurements provided by the current sensor and the hydrogen concentration sensor and to evaluate them using a method according to the invention as previously described, in order to determine the hydrogen concentration in the anode of the at least one fuel cell.

[0017] The current and hydrogen concentration measurements are taken continuously or repeatedly, for example periodically at constant time intervals. These time intervals can be, for example, 50 ms to 150 ms, and in particular 100 ms.

[0018] Using a method and a device according to the invention, the hydrogen concentration in the anode of at least one fuel cell can be determined with good accuracy during the fuel cell's operation using commercially available and inexpensive sensors. In particular, the hydrogen concentration in the anode can be determined with sufficient accuracy to control the purge valve in an anode recirculation circuit of a fuel cell system, enabling the fuel cell system to be operated very efficiently.

[0019] The invention also includes a method for operating at least one fuel cell with an anode, wherein a purge valve is provided at an outlet of the anode, and wherein the method comprises determining the hydrogen concentration in the anode of the at least one fuel cell during the operation of the at least one fuel cell using a method according to the invention as previously described, and controlling the purge valve on the basis of the hydrogen concentration in the anode of the at least one fuel cell thus determined.

[0020] The invention also comprises a fuel cell system with at least one fuel cell having an anode; a purge valve arranged at an outlet of the anode of the at least one fuel cell; a device according to the invention for determining the hydrogen concentration in the anode of the at least one fuel cell; and a control device configured to actuate the purge valve based on the hydrogen concentration determined by the device for determining the hydrogen concentration. The control device is particularly configured to open the purge valve when the hydrogen concentration determined by the device for determining the hydrogen concentration falls below a predetermined limit value.

[0021] At least one fuel cell in such a fuel cell system can be operated very efficiently because the purging of the anode recirculation circuit of the at least one fuel cell can be adjusted to the current hydrogen concentration in the anode of the at least one fuel cell. This prevents the purge valve from being opened too infrequently or too frequently.

[0022] In one embodiment, the fuel cell system comprises multiple fuel cells. The fuel cell system can, in particular, include a fuel cell stack comprising multiple fuel cells. By combining multiple fuel cells in a fuel cell system, especially in a fuel cell stack, the electrical power provided by the fuel cell system can be increased.

[0023] The invention also includes a motor vehicle with at least one electric motor and with a fuel cell system according to the invention, which is designed and configured to provide electric current for operating the at least one electric motor.

[0024] In one embodiment, calculating the relative current measurements involves determining a maximum current value among the measured current measurements, which is not exceeded by any of the measured current measurements, and dividing the measured current measurements by this maximum current value. This results in relative current measurements that are dimensionless quantities in the range between zero and one.

[0025] In one embodiment, calculating the relative hydrogen concentration measurements involves determining a maximum hydrogen concentration value from the measured hydrogen concentration measurements, which is not exceeded by any of the measured hydrogen concentration measurements, and dividing the measured hydrogen concentration measurements by the maximum hydrogen concentration value. This results in relative hydrogen concentration measurements that are dimensionless quantities in the range between zero and one.

[0026] Scaling the measured hydrogen concentration and current to dimensionless quantities that lie in an identical range of values ​​between zero and one makes it possible to simplify the determination of the hydrogen concentration in the anode recirculation circuit.

[0027] In one embodiment, the current scaling factor, the hydrogen concentration scaling factor, and the bias value are determined based on experiments and measurements. These experiments and measurements can be performed using complex, large, and expensive experimental setups and measuring instruments that are not suitable for mass production applications, for example, in motor vehicles. With such setups and instruments, the current scaling factor, the hydrogen concentration scaling factor, and the bias value can be determined with good accuracy.

[0028] When determining the current gain factor, the hydrogen concentration gain factor and the bias value from the values ​​measured by the sensors, methods of linear regression and / or methods of artificial intelligence, such as neural networks, can be used to determine the current gain factor, the hydrogen concentration gain factor and the bias value efficiently and with high accuracy.

[0029] In one embodiment, a method according to the invention for operating at least one fuel cell comprises opening the purge valve when the hydrogen concentration in the anode of the at least one fuel cell, as determined according to the invention, falls below a predetermined limit value, in order to increase the hydrogen concentration in the anode by purging the anode recirculation circuit.

[0030] The procedure may include keeping the flushing valve open for a fixed period of time.

[0031] Alternatively, the procedure can involve keeping the purge valve open until the hydrogen concentration in the anode of at least one fuel cell exceeds a predetermined second limit. This allows the opening time of the purge valve to be flexibly adapted to the current operating conditions of the fuel cell.

[0032] An embodiment of the invention is described below with reference to the accompanying figures.

[0033] Brief description of the characters

[0034] Figure 1 shows a schematic view of a fuel cell system according to the invention.

[0035] Figure 2 shows a diagram in which an experimentally determined hydrogen concentration and a hydrogen concentration determined with a device according to the invention are plotted. Figure 3 shows a schematic view of a motor vehicle with a fuel cell system according to the invention.

[0036] Character description

[0037] Figure 1 shows a schematic view of a fuel cell system 2 according to an embodiment of the invention.

[0038] The fuel cell system 2 comprises at least one fuel cell 4 or a fuel cell stack containing several fuel cells 4, with an anode 6 and a cathode 8. A membrane 10, in particular a polymer electrolyte membrane 10, is arranged between the anode 6 and the cathode 8.

[0039] The cathode 8 is supplied with gaseous oxygen (O2), in particular oxygen-containing air 30 from the environment, via an oxygen supply system which is not shown in detail.

[0040] Gaseous hydrogen 26 (H2) is supplied to the anode 6 via a hydrogen supply system 12, 14.

[0041] The hydrogen 26 and the oxygen react at or in the membrane 10 to form water (H2O). An electrical voltage U is generated between electrodes 6a, 8a, which are arranged in the anode 6 and in the cathode 8, so that an electric current i can be drawn from the at least one fuel cell 4 to operate electrical loads, for example electric motors.

[0042] The hydrogen supply system 12, 14 comprises a hydrogen source 14 that provides gaseous hydrogen 26, and a hydrogen metering valve 15 that makes it possible to regulate the supply of hydrogen to the anode 6.

[0043] Since the hydrogen 26 does not completely react to form water when flowing through the anode 6 once, the hydrogen-containing gas mixture 26, 28 flowing out of the anode 6 is returned to the anode 6 via an anode recirculation circuit 12 in order to utilize this hydrogen for the generation of electrical energy. During operation of the at least one fuel cell 4, nitrogen from the air 30, which is supplied to the cathode 8 of the at least one fuel cell 4, also enters the anode 6 and accumulates in the anode recirculation circuit 12 over time. As a result, the proportion of nitrogen 28 in the anode recirculation circuit 12 increases during operation of the at least one fuel cell 4 at the expense of the proportion of hydrogen 26.

[0044] In order to enable the most efficient operation of at least one fuel cell 4, the anode recirculation circuit 12 must be regularly purged to reduce the proportion of nitrogen 28 in the gas mixture circulating in the anode recirculation circuit 12 and to increase the hydrogen content in the gas mixture again.

[0045] A purge valve 20 is provided downstream of the outlet 9 of the anode 6 for purging the anode recirculation circuit 12. Opening the purge valve 20 allows nitrogen 28 to be released from the anode recirculation circuit 12. Since not only nitrogen but also hydrogen 26 exits the anode recirculation circuit 12 through the open purge valve 20, the purge valve 20 must not be opened too frequently or for too long in order to ensure efficient operation of the fuel cell system 2.

[0046] In order to operate the fuel cell system 2 as efficiently as possible, it is advantageous to know the hydrogen concentration CH2 in the anode 6 of at least the fuel cell 4 and to adjust the opening of the purge valve 20 to the current hydrogen concentration CH2 in the anode 6.

[0047] Measuring the hydrogen concentration CH2 in anode 6 using conventional methods and sensors is complex and expensive.

[0048] The invention therefore provides a new method and a new device 25 which make it possible to determine the hydrogen concentration CH2 in the anode 6 of at least one fuel cell 4 with commercially available, cost-effective sensors 16, 18 with sufficiently good accuracy.

[0049] A device 25 according to the invention comprises a current sensor 16, which is designed and provided to measure the electric current i taken from the at least one fuel cell 4 and to provide corresponding current measurement values ​​i(t).

[0050] The device 25 according to the invention further comprises a hydrogen concentration sensor 18, which is arranged downstream of the anode 6 at the outlet of the purge valve 20. The hydrogen concentration sensor 18 is designed and configured to measure the hydrogen concentration in the gas mixture flowing out of the anode 6 and to provide corresponding hydrogen concentration measurements kH2(t).

[0051] The device 25 according to the invention also includes an evaluation device 22, which is designed and provided to receive and evaluate the measured values ​​i(t), kH2(t) provided by the current sensor 16 and the hydrogen concentration sensor 18 in order to determine the hydrogen concentration CH2 in the anode 6 of the at least one fuel cell 4.

[0052] The current measurements i(t) and the hydrogen concentration measurements kH2(t) are measured continuously or repeatedly, in particular regularly, and made available to the evaluation device 22.

[0053] The evaluation device 22 determines the largest of the measured current values ​​i(t) as the maximum current value i. max (imax > i(t)) and the largest of the measured hydrogen concentration values ​​kH2(t) as the maximum hydrogen concentration value k max (k max > kH2(t)).

[0054] The evaluation device 22 then determines relative current measurements lrel(t) = i(t) / imax and relative hydrogen concentration measurements krel(t) = k H 2(t) / k max f by subtracting the measured current values ​​i(t) and the measured hydrogen concentration values ​​kH2(t) from the maximum current value i max or by the maximum hydrogen concentration value k max to be divided. The relative current measurements calculated in this way i re i(t) and relative hydrogen concentration measurements k re i(t) are dimensionless and have values ​​between zero (0%) and one (100%).

[0055] In a subsequent step, current measurements i are scaled by multiplication with a current scaling factor gi or with a hydrogen concentration scaling factor gH2. sca i(t) and scaled hydrogen concentration measurements k S cai(t) calculates:

[0056] In a subsequent step, the difference diff(t) between the relative current value i is calculated for each time t. sc ia(t) and the relative hydrogen concentration measurement c S da(t) determines: diff(t) — kscal(t) " lscal(t).

[0057] The differences diff(t) determined in this way are integrated over time t up to the current time T or, in the case of a discrete measurement and calculation, summed:

[0058] To the integral or sum D(T) that has been determined in this way, a so-called bias value GH2 is added in order to arrive at the calculated value CH2(T) for the current hydrogen concentration CH2(T) in the anode 6:

[0059] C H2 (T) = G H2 + D(T).

[0060] The current scaling factor gi, the hydrogen concentration scaling factor g cThe bias value GH2 and the current scaling factor gt, and the hydrogen concentration scaling factor g, are constants that are characteristic parameters of the respective fuel cell system 2. c and the bias-bias value GH2 can be determined on the basis of experiments and measurements with elaborate measuring setups or measuring devices, which make it possible to determine the hydrogen concentration CH2 in the anode 6 of at least one fuel cell 4 with high accuracy, but which are not suitable for series production.

[0061] When determining the current amplification factor gt, the hydrogen concentration amplification factor g c and the bias-bias value GH2, methods such as linear regression and / or artificial intelligence methods, especially neural networks, can be used.

[0062] Figure 2 shows a diagram in which, by way of example, an experimentally determined or measured hydrogen concentration CH2 in the anode 6 of a fuel cell 4 is shown as a solid line and a hydrogen concentration CH2(T) in the anode 6 determined with a device 25 or with a method according to the invention is shown as a dashed line as a function of time T.

[0063] Using a method and a device according to the invention, the hydrogen concentration CH2(T) in the anode 6 of at least one fuel cell 4 can be determined with good accuracy during operation using commercially available and inexpensive sensors 16, 18.

[0064] Since the hydrogen concentration sensor 18 is located at the outlet of the purge valve 20, the hydrogen concentration kH2(t) in the gas mixture 26, 28 can only be measured when the purge valve 20 is open. When the purge valve 20 is closed, the hydrogen concentration CH2 in the anode 6 decreases according to the current scaling factor gi.

[0065] Using a method and a device according to the invention, the hydrogen concentration CH2(T) in the anode 6 can be determined, in particular with an accuracy sufficient to control the purge valve 20 based on the hydrogen concentration CH2(T) thus determined, so that the fuel cell system 2 can be operated very efficiently. For this purpose, the fuel cell system 2 has, in particular, a control device 24 which is designed and provided to receive the hydrogen concentration CH2(T) determined by the device according to the invention and to control the purge valve 20 based on the hydrogen concentration CH2(T) determined by the device. H2 (T). The activation of the purge valve 20 can, in particular, include opening the purge valve 20 when the currently determined hydrogen concentration CH2(T) falls below a predetermined limit value Cnmit (CH2(T) < Climit).

[0066] The flushing valve 20 can be controlled in such a way that it remains open for a fixed predetermined period of time.

[0067] Alternatively, the purge valve 20 can be controlled so that it remains open until the hydrogen concentration CH2 in the anode 6 of at least one fuel cell 4 reaches a predetermined second limit value Cii m it2 exceeds. This allows the opening time of the purge valve 20 to be flexibly adapted to the current operating conditions of the fuel cell 4.

[0068] Figure 3 shows a schematic view of a motor vehicle 1 which is driven by an electric motor 5 which is supplied with electrical energy by a fuel cell system 2 according to the invention.

[0069] The motor vehicle 1 has four wheels 3 and at least one electric motor 5, which is designed and intended to drive at least two of the four wheels 3 of the motor vehicle 1. The electric motor 5 can also be intended to drive all four wheels 3 of the motor vehicle 1.

[0070] In an alternative 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 for driving the respective wheel 3.

[0071] The electric motor 5 is supplied with electrical energy via a motor control 7, which is provided by the fuel cell system 2.

[0072] A fuel cell system 2 according to the invention can also be used in motor vehicles

[0073] 1 are used, which have more or less than four wheels 3.

Claims

1. Method for determining the hydrogen concentration (CH2) in an anode (6) of at least one fuel cell (4) during the operation of the at least one fuel cell (4), wherein the method comprises: A) multiple measurements of the electric current (i) supplied by the at least one fuel cell (4) and provision of multiple current measurements (i(t)); B) multiple measurements of the hydrogen concentration (kH2) in a gas mixture (26, 28) flowing out of a purge valve (20) arranged at an outlet (9) of the at least one fuel cell (20), and providing multiple hydrogen concentration measurements (kH2(t)); C) Calculating relative current measurements (i re i(t)) from the measured current values ​​(i(t)) and calculation of relative hydrogen concentration values ​​(k re i(t)) from the measured hydrogen concentration values ​​(kn2(t)); D) Determining scaled current measurements (i sca i(t)) by multiplying the relative current measurements (i re i(t)) with a current scaling factor (gi) and determining scaled hydrogen concentration measurements (k S cai(t)) by multiplying the relative hydrogen concentration measurements (krei(t)) with a hydrogen concentration scaling factor (gH2); E) Forming difference values ​​(diff(t)) from the scaled current measurements (iscai(t)) and the scaled hydrogen concentration measurements (k sca i(t)); F) Integrating or summing the difference values ​​(diff(t)) over time (t); G) Adding a bias value (GH2) to the integral (D(T)) or to the sum (D(T)) of the difference values ​​(diff(t)).

2. Method according to claim 1, wherein the calculation of the relative current measurements (i re i(t)) includes a maximum current value (i max) to determine the measured current values ​​(i(t)) and to divide the measured current values ​​(i(t)) by the maximum current value (imax); and / or wherein calculating the relative hydrogen concentration values ​​(krei(t)) includes determining a maximum hydrogen concentration value (k max ) to determine the measured hydrogen concentration values ​​(kH2(t)) and to subtract the measured hydrogen concentration values ​​(kH2(t)) from the maximum hydrogen concentration value (k max to divide.

3. Method according to claim 1 or 2, wherein the current scaling factor (gi), the hydrogen concentration scaling factor (gH2) and the bias value (GH2) are determined on the basis of experiments and / or measurements.

4. Method according to claim 3, wherein the current scaling factor (gi), the hydrogen concentration scaling factor (gH2) and the bias value (GH2) are determined from the experiments and / or measurements using linear regression and / or neural networks.

5. Method for operating at least one fuel cell (4) with an anode (6), wherein the method comprises determining the hydrogen concentration (CH2) in the anode (6) of the at least one fuel cell (4) during the operation of the at least one fuel cell (4) using a method according to one of claims 1 to 4 and controlling the purge valve (20) on the basis of the hydrogen concentration (CH2) in the anode (6) of the at least one fuel cell (4) thus determined.

6. Method according to claim 5, wherein the method in particular comprises opening the purge valve (20) when the determined hydrogen concentration (CH2) in the anode (6) of the at least one fuel cell (4) falls below a predetermined limit value (Citmit).

7. Device (25) for determining the hydrogen concentration (CH2) in an anode (6) of at least one fuel cell (4) during the operation of the at least one fuel cell (4), the device (25) comprising: a current sensor (16) configured and provided to measure an electric current (i) delivered by the at least one fuel cell (4) during operation and to provide corresponding current measurements (i(t)); a hydrogen concentration sensor (18) configured and provided to measure hydrogen concentrations (kH2) in a gas mixture (26, 28) flowing from a purge valve (20) arranged at an outlet (9) of the at least one fuel cell (20), and to provide corresponding hydrogen concentration measurements (kh2(t));and an evaluation device (22) which is designed and provided to receive the measured values ​​(i(t), kh2(t)) provided by the current sensor (16) and the hydrogen concentration sensor (18) and to evaluate them using a method according to one of claims 1 to 4 in order to determine the hydrogen concentration (CH2) in the anode (6) of the at least one fuel cell (4).

8. Fuel cell system (2) comprising: at least one fuel cell (4) having an anode (6); a purge valve (20) arranged at an outlet (9) of the at least one fuel cell (4); a device (25) for determining the hydrogen concentration (CH2) in the anode (6) of the at least one fuel cell (4) according to claim 7; and a control device (24) configured to control the flushing valve (20) on the basis of the hydrogen concentration (CH2) determined by the device (25) for determining the hydrogen concentration (CH2); wherein the control device (24) is in particular configured to open the flushing valve (20) when the hydrogen concentration (CH2) determined by the device (25) for determining the hydrogen concentration (CH2) falls below a predetermined limit value (Citmid).

9. Fuel cell system (2) according to claim 8, wherein the fuel cell system (2) comprises several fuel cells (4), wherein the fuel cell system (2) in particular comprises a fuel cell stack comprising several fuel cells (4).

10. Motor vehicle (1) with at least one electric motor (5) and a fuel cell system (2) according to claim 8 or 9, which is designed and configured to provide electric current (i) for operating the at least one electric motor (5).

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