Method for determining a hydrogen concentration at an anode inlet or outlet of a fuel cell stack

Abstract

The invention relates to a method for determining a hydrogen concentration (H2A) at an anode inlet or outlet (62, 66). The method comprises the steps of measuring (A) a discharge hydrogen concentration (H2Ab), measuring (B) a fuel cell stack current (IB) or stack power (PB), determining (D) a minimum hydrogen concentration (H2min) before opening the discharge valve (42) using the discharge hydrogen concentration (H2Ab) and at least one stored curve, and calculating (E) a hydrogen concentration (H2A) during a discharge phase using the minimum hydrogen concentration (H2min) and the fuel cell stack current (IB) or the stack power (PB) and a stored curve for a rate of change in hydrogen concentration over time. The method additionally comprises the steps of closing (G) the discharge valve (42) when a predefined upper limit value of the hydrogen concentration (H2A) is reached, calculating (H) a hydrogen concentration (H2A) during a closing phase of the discharge valve (42) using the hydrogen concentration (H2A) when the discharge valve (42) is closed and the fuel cell stack current (IB) or the stack power (PB) and a stored curve for a rate of change in hydrogen concentration over time, and opening (J) the discharge valve (42) when a predefined lower limit value for the hydrogen concentration (H2A) is reached during the closing phase.

Description

[0001] R.415114

[0002] - 1 -

[0003] Description

[0004] Title:

[0005] Method for determining the hydrogen concentration at an anode inlet or outlet of a fuel cell stack

[0006] The present invention relates to a method for determining the hydrogen concentration at an anode inlet or outlet of a fuel cell stack during a draining phase and a closing phase of a drain valve. Furthermore, the invention relates to a device for determining the hydrogen concentration.

[0007] State of the art

[0008] Fuel cell systems are becoming increasingly popular as a power source for light and heavy-duty trucks. In fuel cell systems, oxygen (from the air) and hydrogen react to produce water, waste heat, and electricity (which can be used, for example, to power an electric motor) in a process known as "cold combustion." The air path (or cathode path) of the fuel cell and the hydrogen path (or anode path) within the fuel cell stack are separated by a very thin membrane (e.g., 100 pm thick). This membrane allows the protons of the hydrogen atoms to "flow" from the anode path to the cathode, where they react with oxygen atoms. The electrons of the hydrogen atoms travel via electrodes to the cathode, generating an electric current that can be used to charge a battery or power an electric motor.Due to the presence of water as a reactant, it is important that a drying process is initiated when a fuel cell system is shut down to remove excess water or water vapor from the system. R.415114.

[0009] - 2 -

[0010] In fuel cell operation, hydrogen is injected into the anode, i.e., the anode path of a fuel cell, via the HGI (Hydrogen Injection Valve). To ensure that there is always enough hydrogen available for the chemical reaction of hydrogen and air, the injected mass of hydrogen always exceeds the required mass. This is referred to as H₂ excess, similar to the air excess in combustion engine operation. Another side effect of the reaction of hydrogen and air to produce electricity and waste heat in a PEM fuel cell stack is that nitrogen (from the air) passes from the cathode side (air side) of the fuel cell through the membrane between the cathode and anode into the anode, meaning that a gas mixture of hydrogen and nitrogen is present at the anode outlet.

[0011] During operation, the gas mixture at the anode outlet changes significantly. Hydrogen is consumed, while nitrogen flows from the cathode to the anode, leading to a continuous decrease in the hydrogen concentration. Depending on the fuel cell's characteristics, the hydrogen concentration must not fall below a certain threshold. Furthermore, an excessively low hydrogen concentration in the anode leads to a drop in overall efficiency. To prevent low overall efficiency and a low hydrogen concentration (corresponding to an excessively high nitrogen concentration), a purge valve is installed. This valve opens periodically to release a small portion of the gas mixture from the anode. When the purge valve is open, the anode loses both nitrogen and the hydrogen it actually requires. At this point, the purge valve's actuation is triggered purely by the stacked flow rate.The higher the stack flow rate, the more frequently the flushing valve is activated.

[0012] The time delays between the opening of the purge valve and the corresponding increase in the exhaust gas hydrogen concentration result from the fact that the sensor measuring the hydrogen concentration in the fuel cell's exhaust gas is located some distance downstream of the purge valve outlet. The same applies to the time delay between the opening of the purge valve and the change in the hydrogen concentration at the anode. The measurement of the hydrogen concentration at the anode is R.415114.

[0013] - 3 - a very difficult matter: Currently, there is no physical sensor that can be used in a series application.

[0014] Document WO 2024 / 165309 A1 describes a method for controlling a fuel cell system, specifically a PEM fuel cell system comprising a fuel cell stack, an exhaust line, and a fuel line with a recirculation loop. It describes steps for measuring H₂ and H₂O concentrations in a measuring line, followed by the application of a trained machine learning method to determine further concentrations and to adjust purge and drain intervals. The method aims to optimize the efficiency and performance of the fuel cell system.

[0015] The object of the invention is to provide a method for more accurately estimating the hydrogen concentration at the anode output of the fuel cell, thus enabling more efficient operation of the fuel cell. Furthermore, a device for determining the hydrogen concentration at the anode output of the fuel cell is to be provided.

[0016] The problem is solved by a method for determining a hydrogen concentration at an anode outlet of a fuel cell stack according to claim 1. Furthermore, a device for determining a hydrogen concentration according to claim 6 is specified. Preferred embodiments are described in the dependent claims.

[0017] Disclosure of the invention

[0018] The invention discloses a method for determining a hydrogen concentration at an anode inlet or outlet of a fuel cell stack during a draining phase and a closing phase of a drain valve. The method comprises the steps of measuring a drain hydrogen concentration in the flow direction downstream of the drain valve during the draining phase, measuring a fuel cell stack current or fuel cell stack power, and determining a minimum hydrogen concentration at the R.415114

[0019] - 4 -

[0020] anode inlet or outlet before opening the drain valve, using the drain hydrogen concentration measured in the drain stream during the drain phase and at least one stored curve, and calculating a hydrogen concentration at the anode inlet or outlet during a drain phase, using the minimum hydrogen concentration and the fuel cell stack current or stack power and a stored curve during the drain phase for a temporal hydrogen concentration slope.

[0021] Furthermore, the procedure includes the steps of closing the drain valve upon reaching a predefined upper limit of the hydrogen concentration at the anode inlet or outlet during the drain phase, calculating a hydrogen concentration at the anode inlet or outlet during a closing phase of the drain valve, using the hydrogen concentration at the anode inlet or outlet at the time of closing the drain valve and the fuel cell stack current or stack power and a stored curve during the closing phase for a temporal hydrogen concentration slope, and opening the drain valve upon reaching a predefined lower limit for the hydrogen concentration at the anode inlet or outlet during the closing phase.

[0022] The anode inlet or outlet is the position on the anode where the gas mixture enters or exits. Accordingly, such measurements should not be taken far from the anode. The drain phase is the phase in which the gas mixture is discharged from the anode via the drain valve. During the drain phase, the drain valve is open. The closing phase describes the operation of the device with the drain valve closed. The discharge hydrogen concentration indicates the hydrogen concentration of the gas mixture that has exited the drain valve. This value is measured downstream of the drain valve in the direction of flow.

[0023] The invention utilizes a relationship between a minimum hydrogen concentration at the anode inlet or outlet and a hydrogen concentration measured in a subsequent draining phase. R.415114 is relevant here.

[0024] - 5 - at least one curve is provided, which allows the minimum hydrogen concentration before opening the drain valve to be determined based on the hydrogen concentration during the draining phase. This allows the hydrogen concentration at the anode inlet or outlet to be easily determined before opening the drain valve.

[0025] Similarly, there is a correlation between the hydrogen concentration at the anode inlet or outlet during the draining phase and the fuel cell stack current or stack power. Accordingly, a curve for the hydrogen concentration gradient during the draining phase can be generated from experiments. Starting from the minimum hydrogen concentration, the hydrogen concentration at the anode inlet or outlet can be determined based on the hydrogen concentration gradient and the opening time of the drain valve. This makes it possible to close the drain valve at a desired hydrogen concentration value, thus preventing unnecessary hydrogen discharge. This allows for hydrogen conservation, enabling more efficient operation of the fuel cell stack.

[0026] Similarly, a relationship exists between the hydrogen concentration at the anode inlet or outlet during the closing phase and the fuel cell stack current or stack power. A curve can thus be defined for the rate of change of hydrogen concentration. Based on the hydrogen concentration at the anode inlet or outlet when the drain valve closes, as well as the rate of change of hydrogen concentration and the time, the hydrogen concentration at the anode inlet or outlet can be determined. This makes it possible to open the drain valve later, thus preventing unnecessary hydrogen consumption. At the same time, it prevents the anode from being permanently damaged by an excessively low hydrogen concentration.

[0027] This method allows for hydrogen savings without impairing the fuel cell's function. The fuel cell can therefore be operated more efficiently and safely. R.415114

[0028] - 6 -

[0029] In a preferred embodiment of the invention, the maximum value measured during the draining phase for the drain hydrogen concentration is used. Towards the end of the draining phase, the drain hydrogen concentration increases. By using a maximum value for the drain hydrogen concentration, it is ensured that one of the last measured values ​​is used. This value most closely corresponds to the actual hydrogen concentration present in the system. Therefore, by using a maximum value, the drain hydrogen concentration can be determined easily.

[0030] In a further preferred embodiment of the invention, an average value at the end of the draining phase is used for the drain hydrogen concentration. Determining the hydrogen concentration at the end of the draining phase has the advantage that, due to the increasing hydrogen concentration towards the end of the draining phase, a more accurate value for the calculation during the closing phase can be determined. Additionally, calculating an average value can compensate for sensor noise or measurement errors. This also improves the accuracy of determining the hydrogen concentration at the anode inlet or outlet during the closing phase.

[0031] Preferably, several curves for the discharge hydrogen concentration and a minimum hydrogen concentration are stored, with the appropriate curve being selected according to the fuel cell stacking current or stacking power. Although the minimum hydrogen concentration can also be determined from a single curve, this curve only approximates the actual situation. By using several curves generated for specific fuel cell stacking currents or stacking power, the actual minimum hydrogen concentration can be better approximated. Accordingly, more accurate values ​​for the minimum hydrogen concentration can be obtained with multiple curves. This allows for more precise control of the opening and closing times of the discharge valve, resulting in further hydrogen savings.The efficiency of such a fuel cell stack can be further improved by this method. R.415114.

[0032] - 7 -

[0033] In an advantageous further development, the drain valve is closed or opened a certain time factor before reaching the upper and lower limits, respectively. This time factor is determined from a stored curve as a function of the fuel cell stack current or stack power. The time factor is a calculated time that is taken into account when determining the upper and lower limits. It represents the time by which the actual hydrogen concentration at the anode inlet or outlet differs from the hydrogen concentration calculated based on a hydrogen concentration measurement at the drain valve. In other words, a measurement at the drain valve determines a value that has already passed at the anode inlet or outlet.

[0034] By correcting the measured value using the time factor, the actual hydrogen concentration at the anode inlet or outlet can be determined. This time factor correction allows for a more accurate determination of the actual hydrogen concentration at the anode inlet or outlet. Consequently, hydrogen can be saved, and damage to the fuel cell due to an excessively low hydrogen concentration can be avoided.

[0035] The invention further discloses a device for determining a hydrogen concentration. The device comprises a hydrogen sensor for measuring a hydrogen concentration, wherein the hydrogen sensor is arranged downstream of a drain valve in the direction of flow, a current sensor or sensor for measuring a fuel cell stack current or stack power, and a control unit that performs a method according to one of the preceding claims. Such a device has the properties and advantages described above.

[0036] The method described above can, in particular, be implemented by a computer and thus embodied in software. The invention therefore also relates to a computer program with machine-readable instructions which, when executed on one or more control units, R.415114

[0037] - 8 - cause the control unit(s) to execute the described procedure.

[0038] The invention also relates to a machine-readable data carrier and / or a downloadable product containing the computer program. A downloadable product is a digital product that can be transmitted over a data network, i.e., downloaded by a user of the data network, and which can, for example, be offered for immediate download in an online shop.

[0039] Furthermore, the invention relates to a control unit which includes such a computer program and / or the machine-readable data carrier and / or download product.

[0040] Exemplary embodiments of the invention are shown in the drawing and explained in more detail in the following description. It shows:

[0041] Figure 1 Fuel cell system with an embodiment of a

[0042] Device for determining a hydrogen concentration for carrying out a method according to the invention, and

[0043] Figure 2 shows a method for determining a hydrogen concentration at an anode inlet or outlet of a fuel cell stack according to an embodiment of the invention.

[0044] Figure 1 shows a fuel cell system 10 with an embodiment of a device 14 for determining a hydrogen concentration for carrying out a method according to the invention. The fuel cell system 10 comprises a fuel cell stack 18, which includes an anode 22 and a cathode 26. The anode 22 is supplied with hydrogen from a hydrogen tank 30 by means of a valve 34 and a pump 38. A drain valve 42 is arranged downstream of the anode 22 in the flow direction, through which a portion of the gas mixture can be drained from the anode 22. R.415114

[0045] - 9 -

[0046] The fuel cell system 10 additionally includes the device 14 for determining the hydrogen concentration. The device 14 comprises a hydrogen sensor 46 located downstream of the drain valve 42, which measures the hydrogen concentration of the gas mixture after the drain valve 42. A portion of the gas mixture is transported back to the anode 22 via a recirculating air blower 50. The device 14 also includes a sensor 54 with which a fuel cell stack current or fuel cell stack power can be determined. Additionally, a control unit 58 of the device 14 is provided, which receives the measured values ​​from the hydrogen sensor 46 and the sensor 54 and controls the drain valve 42 to open or close. The control unit 58 is intended to determine the hydrogen concentration directly at an anode inlet 62 or an anode outlet 66.

[0047] Figure 2 shows a representation of a method for determining a hydrogen concentration H₂A at an anode inlet or outlet 62, 66 of a fuel cell stack 18 according to an embodiment of the invention. In a first step A of the method, a discharge hydrogen concentration H₂Ab is measured by means of the hydrogen sensor 46 during a discharge phase of the discharge valve 42. In such a phase, the discharge valve 42 is open, so that the gas mixture flows past the hydrogen sensor 46 downstream of the discharge valve 42. The maximum value occurring during this phase is used as the discharge hydrogen concentration H₂Ab. In a next step B, the fuel cell stack current IB or the fuel cell stack power PB is continuously measured.

[0048] In a subsequent step C, based on the fuel cell current IB or the fuel cell stack power PB, a corresponding curve is selected from several stored curves for the discharge hydrogen concentration H2Ab and a minimum hydrogen concentration H2min. This curve corresponds to the magnitude of the fuel cell stack current IB or the stack power PB. These curves were previously determined experimentally and computationally and are stored in the control unit 58. In a subsequent step D, a minimum hydrogen concentration H2min at the anode inlet or outlet 62, 66 is determined before the discharge valve 42 is opened, based on the selected curve and the discharge hydrogen concentration H2Ab. R.415114

[0049] - 10 -

[0050] In the next process step E, a hydrogen concentration H2A at the anode inlet or outlet 62, 66 is determined during a discharge phase. This value H2A is calculated using the previously determined minimum hydrogen concentration H2min at the anode inlet or outlet 62, 66, the fuel cell stack current IB, the stack power PB, and a stored curve for the hydrogen concentration gradient during the discharge phase. In a subsequent step F, a time factor TF is determined, which is calculated from another stored curve based on the fuel cell stack current IB or the stack power PB. This time factor TF indicates the time delay between the value H2Ab measured at the hydrogen sensor 46 and the actual value H2A present at the anode inlet or outlet.

[0051] In a subsequent step G, during the draining phase, the drain valve 42 is closed when a predefined upper limit of the hydrogen concentration H2A at the anode inlet or outlet 62, 66 is reached. This is carried out taking into account the time factor TF, so that the drain valve 42 is closed by the time factor TF before the theoretical upper limit determined via the drain hydrogen concentration H2Ab.

[0052] In a further step H, the hydrogen concentration at the anode inlet or outlet H2A is determined during a closing phase of the drain valve 42. For this purpose, the current hydrogen concentration gradient is determined using the hydrogen concentration H2s at the anode inlet or outlet 62, 66 at the time the drain valve 42 closes and the fuel cell stack current IB or stack power PB, based on a stored curve for the hydrogen concentration gradient. Starting from the hydrogen concentration H2s at the anode inlet or outlet 62, 66 at the time the drain valve 42 closes, the current hydrogen concentration H2A at the anode inlet or outlet 62, 66 can thus be determined using the hydrogen concentration gradient and the time elapsed since the drain valve 42 closed.

[0053] Subsequently, in step I, a time factor TF is determined, which is calculated from a stored curve based on the fuel cell stack current IB and the stack power PB. This value TF also indicates the time by which the water-R.415114

[0054] - 11 - The measured value H2Ab by substance sensor 46 is delayed compared to the actual value H2A present at the anode inlet 62 or anode outlet 66. In a further step, J opens the drain valve when a predefined lower limit for the hydrogen concentration at the anode inlet or outlet 62, 66 is reached. This is also carried out taking into account the time factor TF, so that the drain valve 42 opens by the time factor TF before the theoretical lower limit.

[0055] For another cycle, the process starts again from scratch, so that during each phase the hydrogen concentration H2A at the anode input or

[0056] Outlet 62, 66 can be determined.

Claims

R.415114 - 12 - Claims 1. Method for determining a hydrogen concentration (H2A) at an anode inlet or outlet (62, 66) of a fuel cell stack (18), during a draining phase and a closing phase of a drain valve (42), comprising the steps: Measuring (A) a discharge hydrogen concentration (H2Ab) in the direction of flow downstream of the discharge valve (42) during the discharge phase, Measuring (B) a fuel cell stack current (IB) or a fuel cell stack power (PB), Determining (D) a minimum hydrogen concentration (H2min) at the anode inlet or outlet (62, 66) before opening the drain valve (42), using the drain hydrogen concentration (H2Ab) measured in the drain stream during the drain phase and at least one stored curve, Calculating (E) a hydrogen concentration (H2A) at the anode inlet or outlet (62, 66) during a draining phase, using the minimum hydrogen concentration (H2min) and the fuel cell stacking current (IB) or stacking power (PB) and a stored curve during the draining phase for a temporal hydrogen concentration slope, closing (G) the draining valve (42) when a predefined upper limit of the hydrogen concentration (H2A) at the anode inlet or outlet (62, 66) is reached during the draining phase, Calculate (H) a hydrogen concentration (H2A) at the anode inlet or outlet (62, 66) during a closing phase of the drain valve (42), using the hydrogen concentration (H2A) at the anode inlet or outlet (62, 66) when closing the drain valve (42) and the fuel cell stack current (IB) or stack power (PB) and a stored curve during the closing phase for a temporal hydrogen concentration slope, and R.415114 - 13 - Opening (J) of the drain valve (42) upon reaching a predefined lower limit for the hydrogen concentration (H2A) at the anode inlet or outlet (62, 66) during the closing phase.

2. Method according to claim 1, characterized in that the maximum value for the drain hydrogen concentration (H2Ab) measured during the draining phase is used as the drain hydrogen concentration (H2Ab).

3. Method according to claim 1, characterized in that an average value at the end of the draining phase is used as the drain hydrogen concentration (H2Ab).

4. Method according to one of the preceding claims, characterized in that several curves for discharge hydrogen concentration (H2Ab) and a minimum hydrogen concentration (H2min) are stored, wherein the corresponding curve is selected according to a level of the fuel cell stack current (IB) or the stack power (PB) (C).

5. Method according to one of the preceding claims, characterized in that the drain valve (42) is closed or opened by a time factor (TF) before reaching the upper and before reaching the lower limit, wherein the time factor (TF) is determined from a stored curve as a function of the fuel cell stack current (IB) or the stack power (PB).

6. Device (14) for determining a hydrogen concentration (H2A) at an anode inlet or outlet (62, 66) of a fuel cell stack (18), comprising: a hydrogen sensor (46) for measuring a hydrogen concentration (H2Ab), wherein the hydrogen sensor (46) is arranged downstream of a drain valve (42), a current sensor or sensor (54) for measuring a fuel cell stack current (IB) or stack power (PB), and a control unit (58) which performs a method according to one of the preceding claims. R.415114 - 14 - 7. Computer program containing machine-readable instructions which, when executed on one or more control units (58), cause the device (14) to execute a method according to any one of claims 1 to 5.

8. Machine-readable data carrier and / or download product containing the computer program according to claim 7.

9. Control unit (58) equipped with the computer program according to claim 7, and / or with the machine-readable data carrier and / or download product according to claim 8.

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