Control device for a fuel cell system

Abstract

The present invention relates to a control device for a fuel cell system, in particular a fuel cell system of a drive system of an aircraft, which has at least one fuel cell, an air supply line with an air supply device for controlling an air mass flow which is supplied to the fuel cell, and an air humidification device for humidifying the air in the air supply line, characterised by an air humidity detection device for detecting or estimating an air humidity, a first control loop for controlling the air mass flow as a function of the detected or estimated air humidity, and a second control loop for controlling a humidification parameter of the air humidification device as a function of the detected or estimated air humidity and / or the air mass flow.

Description

[0001] CONTROL DEVICE FOR A FUEL CELL SYSTEM

[0002] DESCRIPTION

[0003] Technical area

[0004] The present invention relates to a control device for a fuel cell system.

[0005] State of the art

[0006] For example, the relative humidity within a fuel cell system can be relevant for optimizing its performance. System components such as humidifiers can be used to control this humidity. Such a humidification device is installed in an air supply line of the fuel cell.

[0007] Description of the invention

[0008] The present invention is based on the technical problem of providing an advantageous control device for a fuel cell system.

[0009] The control device according to claim 1 is directed to a fuel cell system that, in addition to at least one fuel cell, has an air supply line with an air supply device and an air humidification device. The latter is provided for humidifying the air in the air supply line, i.e., the air supplied to the fuel cell. The control device further comprises a humidity detection device for determining an air humidity, as well as a first and second control loop. The first control loop controls the air mass flow as a function of the determined air humidity, whereas the second control loop controls a humidification parameter of the air humidification device (as a function of the determined air humidity and / or the air mass flow).The control of the air mass flow as a function of the determined air humidity with the first control loop can in particular include or be an adjustment of the air mass flow to adjust the air humidity, which can be determined continuously, for example.

[0010] The humidity detection device can, for example, be arranged in the air supply line.

[0011] The humidity sensing device can detect or estimate the humidity at the outlet of the fuel cell, in the fuel cell and / or in the air supply line.

[0012] In one embodiment, the humidity detection device detects or estimates the humidity at the outlet of the fuel cell as a function of the inlet conditions.

[0013] The second control loop can control or adjust the humidification parameter of the air humidification device depending on the detected or estimated air humidity and / or depending on the air mass flow, in particular in the air supply line.

[0014] The humidification parameter can be controlled in such a way that, by means of a corresponding or required adjustment of the humidification parameter, the air humidity and / or the air mass flow, in particular in the air supply line and / or in front of the fuel cell, (respectively) returns to the respective setpoint value, i.e. the setpoint air humidity or the setpoint air mass flow, maintains this and / or is set to this.

[0015] This combination of first and second control loops can be advantageous, for example, in that the adjustment of the air mass flow, which is the target of the first control loop, can be implemented relatively quickly. To do this, the first control loop can influence the air supply device, e.g., by adjusting a controllable valve and / or by changing the pump output. However, varying the air mass flow or air ratio (air stoichiometry) not only changes the humidity but also leads to a deviation from the actual target air ratio, which is why adjusting the humidity solely via the air mass flow would be disadvantageous with regard to continuous operation. Therefore, a humidification parameter is adjusted using the second control loop.

[0016] Although this setting or its effectiveness takes, for example, longer than the change via the air mass flow, it can, in contrast, be maintained throughout further operation (e.g. until the next control intervention). The humidification parameter can be controlled as a function of the determined air humidity, in particular indirectly via the first control loop, and additionally, simultaneously or alternatively as a function of the air mass flow and / or the deviation in the air mass flow, i.e. for example as a function of the control intervention of the first control loop. In simple terms, by accepting a temporary deviation from the target air ratio with the first control loop, a period is bridged until the adjustment of the humidification parameter with the second control loop takes effect. Overall, this can, for example, be advantageous in spite of a temporarily suboptimal air ratio, in order to expand the process window with regard toThe optimal humidity, for example, can be comparatively small.

[0017] Preferred embodiments can be found in the dependent claims and the entire disclosure, whereby the presentation of the features does not always distinguish in detail between device and method or use aspects; in any case, the disclosure is implicitly to be read with regard to all claim categories. In particular, all information relating to the "control device for a fuel cell system" is always intended to be disclosed with regard to a "fuel cell system" with such a control device, which thus comprises, in addition to the fuel cell, air supply line (with air supply device), and air humidification device, also the control device with air humidity detection device and first and second control loops.

[0018] In general terms, one approach in the present case is to adjust the humidity during operation of a fuel cell using a first and a second control loop, whereby a short-term or rapid change in the humidity occurs via the first control loop, but over time the long-term adjustment occurs via the second control loop (and thus the intervention of the first control loop can be reduced).

[0019] The "humidity detection device" is designed to determine the humidity. "Determining" can be a measurement and / or an estimate, such as a calculation, e.g., a rough estimate.

[0020] According to a preferred embodiment, the air humidity detection device has an observer (estimator) that is configured to estimate the air humidity. This is preferably done on the basis of mass balances, so for example the amount of water at the outlet of the fuel cell can be estimated as a function of the inlet conditions. The following characteristic values ​​of the fuel cell system can be included in the estimation, for example: an inlet pressure and / or an outlet pressure and / or an air mass flow, in particular an inflowing air mass flow and / or an air mass flow at the outlet of the fuel cell, and / or a temperature, in particular a temperature of the inflowing air and / or a temperature at the outlet of the fuel cell, and / or a temperature at the outlet of a cooling system and / or a current emitted by the fuel cell or the stack and / or an air humidity, e.g. a relative or absolute air humidity, at the inlet.The humidity at the inlet can also be measured; see below for details. In general, the estimator can reduce system complexity, for example, or at least the amount of necessary humidity measurements. For example, the need for complex humidity detection, especially with a sensor, at the fuel cell outlet can be eliminated.

[0021] According to a preferred embodiment, the humidity detection device is designed without a humidity sensor at the outlet of the fuel cell or stack, in other words, no sensor for detecting humidity is arranged at the outlet. This should not generally rule out the use of sensors there; for example, a temperature sensor could be provided. Nevertheless, a completely sensorless design at the outlet is preferred, meaning there is no sensor at that point. Reference is made to the above comments on reduced system complexity, where humidity measurements, in particular, can be comparatively complex.

[0022] According to an alternative preferred variant, the humidity at the fuel cell outlet can also be measured, i.e., a humidity sensor can be installed at the outlet. This variant, combined with the estimator, can, for example, allow for a control of the estimated values. Likewise, the humidity measured at the outlet side can also be used, for example, to estimate the humidity in the air supply line.

[0023] In a preferred embodiment, the humidity detection device has a sensor with which the humidity is measured on the inlet side during operation, preferably in the air supply line. In combination with an outlet-side sensor (see above), the control device can then also be designed without an estimator, for example; however, an estimator can also be provided in combination with humidity sensors on the inlet and outlet sides (e.g., double control). Particularly preferred, for example with regard to system complexity, is a variant in which the inlet-side humidity sensor is combined with the estimator, but the humidity detection device is designed without a humidity sensor on the outlet side.

[0024] The "humidification parameter" to which the second control loop is directed can, in general terms, be, for example, a setting value of the humidification device that influences the degree of humidification by the humidification device. The humidification parameter can be, for example, a humidifier temperature, a water volume, or a pressure in the humidifier, but also, for example, a bypass or mixing ratio and / or the mass flow in the humidification device.

[0025] The air humidification device can, generally also in combination or in particular alternatively, comprise or be a bubble humidifier, a membrane humidifier, an evaporator, a water injection device and / or a device for mixing different air streams with different humidities. In the case of the bubble humidifier, but also in the case of the evaporator and the water injection device, the humidification parameter(s) can be, for example, a water quantity and / or temperature and / or pressure. In the case of the membrane humidifier, however, a bypass ratio and / or mass flows can be adjusted to adjust the air humidity. In the mixing device, the humidity in the incoming air streams can be adjusted (e.g., by appropriately adjusting a humidifier arranged there) or, in particular, the mixing ratio can be adjusted using the second control loop.

[0026] According to one embodiment, the humidification parameter controlled in the second control loop is:

[0027] - A temperature of the air humidification device, especially in the case of a bubble humidifier as air humidification device,

[0028] - an operating parameter of a membrane humidifier, e.g. bypass ratio, mass flows, especially in the case of a membrane humidifier as an air humidification device,

[0029] - an evaporation parameter, e.g. water quantity, temperature, pressure, especially in the case of an evaporator as an air humidification device,

[0030] - a water injection parameter, such as water quantity, temperature, pressure, particularly in the case of a water injection device as an air humidification device, and / or a mixing ratio, particularly in the case of a device for mixing different air streams with different volatilities as an air humidification device. According to a preferred embodiment, the control device is configured such that, if the determined air humidity, particularly at the outlet of the fuel cell, in the fuel cell, in the air supply line, and / or in the air supply device, lies outside a predetermined range, the air mass flow is controlled in a first step with the first control loop such that the air humidity returns to the predefined range. Due to this control intervention, the air mass flow in the air supply line then temporarily deviates from a target mass flow.However, by adjusting the humidification parameter of the air humidification device after the first step or in parallel, the air mass flow can again approach or reach the target mass flow, whereby the changed humidification parameter does not leave the predetermined air humidity range.

[0031] The application also relates to a fuel cell system comprising at least one fuel cell, an air supply line with an air supply device for regulating the air mass flow supplied to the fuel cell, and an air humidification device. Furthermore, the fuel cell system comprises a control device as discussed above, with a humidity detection device, and with first and second control loops.

[0032] The at least one fuel cell can, in particular, be part of a fuel cell stack (so-called stack) in which several fuel cells are placed side by side. During operation, a reaction gas, usually hydrogen, can be supplied to the fuel cell or stack in addition to the air, or more generally, the oxygen. This gas can be converted into water with the oxygen, and the released energy can be used electrically to generate electricity.

[0033] The application further relates to a propulsion system, in particular for an aircraft, wherein the propulsion system comprises a control device disclosed herein, in particular a fuel cell system with such a control device. The application also relates to an aircraft with such a propulsion system.

[0034] The application further relates to a method for controlling a fuel cell system, wherein, in a first step, it is determined whether the air humidity is within a predetermined range. In a further step, in the event of a deviation, the air mass flow is controlled such that the air humidity returns to the predetermined range. Furthermore, subsequently or simultaneously, a humidification parameter of the air humidification device is adjusted or controlled such that the air mass flow again approaches or can reach the target value, while the air humidity remains within the predefined range.

[0035] With regard to further possible process details, such as the different variants of the humidity detection device (with or without estimator, sensors, etc.), reference is made to the remaining disclosure.

[0036] Short description of the drawings

[0037] In the following, the invention is explained in more detail using an exemplary embodiment, whereby the individual features within the scope of the independent claims can also be essential to the invention in other combinations and no distinction is made in detail between the different claim categories.

[0038] In detail,

[0039] Figure 1 shows a fuel cell system in schematic representation;

[0040] Figure 2 shows a control device for the fuel cell system according to Figure 1 in a schematic diagram;

[0041] Figure 3 shows a schematic representation of an aircraft with a propulsion system using fuel cells. Preferred embodiment of the invention

[0042] Fig. 1 shows a fuel cell system 1 comprising a plurality of fuel cells 2. These are assembled into a stack 3 and held together by end cover plates 4 that are braced against each other (not shown in detail). During operation, the fuel cells 2 are supplied with air 7 from an air supply device 6 via an air supply line 5. In detail, the air supply device 6 comprises an air reservoir 8 and a mass flow controller 9. Furthermore, an air humidification device 10 is arranged in the air supply line 5, for example a bubble humidifier 10.1 and / or a membrane humidifier 10.2. Depending on the design, the air humidification device 10 can, for example, be connected to a water reservoir 11.

[0043] In some embodiments of the invention, no air reservoir 8 is provided, but the air is taken directly from the environment.

[0044] In some embodiments of the invention, the mass flow controller 9 comprises or consists of a compressor.

[0045] Air, and thus oxygen, is supplied to the fuel cells 2 during operation via the air supply line 5. Furthermore, a process gas supply line 15 is provided, via which fuel, e.g., hydrogen, is supplied to the fuel cells 2. In addition, there may be, for example, a cooling circuit 16 (shown only schematically here), through which a cooling fluid can flow through the fuel cell stack 3 during operation. At an outlet 17, the portion of unreacted air can be discharged via an air discharge line 18, for example, together with water as a chemical reaction product of power generation.

[0046] Fig. 2 shows a control device 20 with which the air humidity RH in a fuel cell system 1 according to Figure 1 can be controlled. The air humidity RH can be specified, for example, as relative air humidity or absolute air humidity and is not limited to a specific humidity level in the present disclosure. For this purpose, the control device 20 first has a air humidity detection device 21 with which the air humidity RH can be determined. In the present case, the air humidity detection device 21 is equipped with an observer 22 or estimator and a sensor 23. The sensor 23 detects the air humidity RHi. n in the air supply line 5.

[0047] Based on the humidity RHin, the estimator in this example uses mass balances to estimate a humidity RH out at the outlet 17 of the fuel cell 2 or determines it. This could be measured alternatively to the estimation or in combination therewith with a sensor 24, which is optionally shown accordingly. In addition to RHin, the estimator can use further variables 25 when determining RHout, for example, an inlet pressure and / or an outlet pressure and / or an inflowing air mass flow and / or a temperature of the inflowing air and / or a temperature at the outlet of the cooling system 16 and / or a current output by the fuel cell 2 or the stack 3.

[0048] Depending on the measured humidity, the humidity is set or adjusted using the control device 20. For this purpose, the control device 20 comprises a first control loop 31, which, via a controller 32, e.g., a PI controller, regulates the air mass flow controller 9 (see also Figure 1) and thus the air mass flow 35 in the air supply line 5 in such a way that the humidity returns to a predefined range. However, this causes the air mass flow 35 to deviate from a setpoint.

[0049] A second control loop 41 detects the deviation of the air mass flow 35 from the setpoint. A controller 42 of the second control loop 41, e.g., a PI controller, then initiates a change in an operating parameter 45 of the air humidification device 10 (see also Figure 1). The operating parameter 45 is adjusted by the second control loop 41 so that the air humidity remains within the predefined range, even if the air mass flow 35 is reset, e.g., stepwise or continuously, to its setpoint. The operating parameter 45 can, for example, be the temperature 45.1 in the case of a bubble humidifier, or a bypass ratio 45.2 or mass flow 45.3 in the case of a membrane humidifier. A value to which the operating parameter 45 is to be set can, for example, be read from a table 46.

[0050] Fig. 3 shows a schematic representation of an aircraft 60 having a propulsion system 61. This system includes an electric motor 62, a propeller 63, and a fuel cell system 1 with a control device 20, which supplies the electric motor 62 with electrical power.

[0051] LIST OF REFERENCE SYMBOLS

[0052] Fuel cell system 1

[0053] Fuel cell 2

[0054] Fuel cell stack 3

[0055] Cover plates 4

[0056] Air supply line 5

[0057] Air supply device 6

[0058] Air 7

[0059] Air reservoir 8

[0060] Air mass flow controller 9

[0061] Humidification device 10

[0062] Bubble humidifier 10.1

[0063] Membrane humidifier 10.2

[0064] Water reservoir 11

[0065] Cooling circuit 16

[0066] Exit 17

[0067] Air discharge line 18

[0068] Control device 20

[0069] Humidity detection device 21

[0070] Sensor 23

[0071] Sensor 24

[0072] First control loop 31

[0073] Controller 32

[0074] Air mass flow 35

[0075] Second rule loop 41

[0076] Controller 42

[0077] Humidification parameters 45

[0078] Temperature 45.1

[0079] Bypass ratio 45.2

[0080] Mixing ratio and / or mass flows 45.3 Table 46

[0081] Aircraft 60

[0082] Drive system 61

[0083] Electric motor 62 Propeller 63

Claims

CLAIMS 1. Control device (20) for a fuel cell system (1), in particular a fuel cell system (1) of a propulsion system of an aircraft, which has at least one fuel cell (2), an air supply line (5) with an air supply device (6) for controlling an air mass flow (35) which is supplied to the fuel cell (2), and an air humidification device (10) for humidifying the air (7) in the air supply line (5), characterized by an air humidity detection device (21) for detecting or estimating an air humidity, a first control loop (31) for controlling the air mass flow (35) as a function of the detected or estimated air humidity, and a second control loop (41) for controlling a humidification parameter (45) of the air humidification device (10) as a function of the detected or estimated air humidity and / or the air mass flow (35).

2. Control device (20) according to claim 1, wherein the air humidity detection device (21) has an observer (22) which is designed to estimate air humidity, in particular at the outlet of the fuel cell, in the fuel cell, in the air supply line (5) and / or in the air supply device (6), by means of mass balances.

3. Control device (20) according to claim 1 or 2, wherein the air humidity detection device (21) is designed to be sensorless at least at the outlet (17) of the fuel cell (2).

4. Control device (20) according to claim 1 or 2, wherein the humidity detection device (21) has a sensor (24) for detecting the humidity at the outlet (17) of the fuel cell (2).

5. Control device (20) according to one of the preceding claims, wherein the air humidity detection device (21) has a sensor (23) for detecting the air humidity in the air supply line (5).

6. Control device (20) according to one of the preceding claims, wherein the humidification parameter (45) controlled in the second control loop (31) relates to a temperature (45.1), a water quantity, a pressure, a bypass ratio (45.2), a mixing ratio and / or mass flows (45.3).

7. Control device (20) according to one of the preceding claims, wherein the air humidification device (10) comprises a bubble humidifier (10.1), a membrane humidifier (10.2), an evaporator, a water injection device and / or a device for mixing different air streams with different humidities.

8. Control device (20) according to one of the preceding claims, wherein the control device (20) is configured such that, upon detection of an air humidity outside a predetermined range, it first controls the air mass flow (35) by means of the first control loop (31) such that the air humidity returns to the predetermined range, wherein a target mass flow in the air supply line (5) is briefly deviated from and subsequently or in parallel the humidification parameter (45) of the air humidification device (10) is controlled such that the air mass flow (35) can return to the target mass flow or returns without leaving the predetermined air humidity range.

9. Fuel cell system (1), with at least one fuel cell (2), an air supply line (5) with an air supply device (6) for regulating an air mass flow (35) which is supplied to the fuel cell (2), and an air humidification device (10) for humidifying the air in the air supply line (5), wherein the fuel cell system (1) further comprises a control device (20) according to one of the preceding claims.

10. Drive system (61), in particular for an aircraft (60), wherein the drive system (61) comprises a control device (20) according to one of claims 1 to 8 or a fuel cell system (1) according to claim 9.

11. An aircraft (60) having a propulsion system (61) according to claim 10.

12. A method for controlling a fuel cell system (1) comprising at least one fuel cell (2), an air supply line (5) with an air supply device (6) for the controllable supply of air (7) to the fuel cell (2) and an air humidification device (10) for humidifying the air (7) in the air supply line (5), comprising the steps: Detecting whether air humidity, in particular at the outlet of the fuel cell, in the fuel cell, in the air supply line (5) and / or in the air supply device (6), is within or outside a predetermined range, Regulating the air mass flow (35) in the air supply line (5) so that the humidity returns to the predetermined range if it is outside it, Controlling a humidification parameter (45) of the air humidification device (10) so that the air mass flow (35) can return to a target mass flow or returns without leaving the predetermined air humidity range.

13. Method according to claim 12 for controlling a fuel cell system (1) according to claim 9 or drive system (61) according to claim 10.

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