Methods for operating a fuel cell system and fuel cell system

Abstract

To improve the operation methods of fuel cell systems. [Solution] The method of operating a fuel cell system includes the step of driving and controlling a proportional valve device to control the amount of recirculating medium supplied from a recirculation circuit to the fuel line of the fuel cell stack, wherein the proportional valve device may be operated continuously or in pulsed mode according to predetermined operating parameters, and as a result, during pulsed operation, at least one pressure pulse is generated within the fuel cell stack.

Description

Technical Field

[0001] The present invention relates to a method for operating a fuel cell system. Further, the present invention relates to a fuel cell system.

Background Art

[0002] Known fuel cell systems require oxygen in air and hydrogen for a chemical reaction. For this purpose, a fuel cell has an anode and a cathode. During operation, hydrogen is supplied to the anode, and an oxidant, that is, oxygen in air, is supplied to the cathode. Many PEM fuel cells have a connection between the stack anode outlet and the stack anode inlet. Inside the PEM fuel cell, the gas present in the anode is recycled. Thus, unconsumed hydrogen should be fed back into the system to improve efficiency. Further, in order to replenish the hydrogen consumed in the fuel cell, a metering valve is incorporated in the anode circuit, and fresh hydrogen is metered and supplied by the metering valve. To maintain the recirculation in the anode circuit, some technical device is required. Typically, this technical device is a pump or a blower. A frequently used pump is, in this case, a jet pump system, but it may also be a positive displacement pump or a blower. Combinations are also often used. A system having only a jet pump, a so-called Jetpump-only-System, is a very low-cost and easily operable variant. However, this type of system has some limitations.

[0003] Typically, the control or metering of hydrogen in the anode circuit is performed via one or more metering valves. This allows a desired pressure to be set. Moisture content and gas concentration can be regulated by purge and drain valves in the anode circuit. Information such as pressure, temperature, flow rate, operating point, humidity, or similar may be used for this regulation. In this case, the supply to the fuel cell is provided by a continuously meterable valve (also called a proportional valve) or by a clock-controlled valve. In the case of a continuous or proportional valve, the cross-section or valve stroke is adjusted. In this case, the flow rate, and thus the pressure, can be regulated very uniformly. In the case of a clock-controlled valve, the average anode pressure, and thus the amount supplied, is regulated by changing the time between the open and closed positions of the valve. This, due to the principle, results in a periodic increase in pressure during the open position phase and a decrease in pressure during the closed position phase. Clock control of the inflow, i.e., temporally, results in a phase with very high inflow (full load volumetric flow rate) and a phase with no inflow at all. During the opening phase, extremely strong flow occurs through the cell, resulting in extremely good water transport and extremely good H2 supply. On average, this inflow is equal to the inflow through a proportionally opening valve. In other words, there exists a system in which the pressure is kept constant or regulated on average by periodic opening and closing.

[0004] For example, Patent Document 1 discloses a method for recirculating the anode gas in the anode circuit of a fuel cell system using at least two jet pumps connected in parallel, in order to compensate for the weakened recirculation output of the jet pump in the partial load or low load region.

[0005] In general, pressure pulses can be a burden that affects the lifespan of fuel cell systems, especially fuel cell stacks, and in some cases, the valves used. Therefore, attention should be paid to the waveform, pulse intensity or amplitude, and the number of pulses over the total operating time. For this reason, it is advisable to avoid using clock-controlled or pulsed operation unnecessarily. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] International Publication No. 2022144183 [Overview of the project] [Problems that the invention aims to solve]

[0007] The present invention provides a method for operating a fuel cell system having the features of claim 1 and a fuel cell system having the features of claim 8. [Means for solving the problem]

[0008] According to a first aspect of the present invention, a method for operating a fuel cell system is provided. This method includes the step of driving and controlling a proportional valve device to control the amount of recirculating medium supplied from a recirculation circuit to the fuel line of a fuel cell stack, wherein the proportional valve device may be operated continuously, or operated in pulsed mode or clock-controlled mode according to predetermined operating parameters, and as a result, during pulsed operation, at least one pressure pulse is generated in the fuel cell stack.

[0009] A second aspect of the present invention presents a fuel cell system. The fuel cell system comprises a fuel cell stack having an anode and a cathode, and a recirculation circuit for recirculating a recirculation medium at the anode. The fuel cell system further comprises a fuel pipeline for supplying hydrogen to the fuel cell stack, and a proportional valve device connected to the fuel pipeline and the recirculation circuit. The fuel cell system further comprises a control device connected to the fuel pipeline and / or the recirculation circuit and / or the proportional valve device, configured to carry out the method according to the present invention.

[0010] The fundamental concept of this invention is to provide a hybrid operation consisting of clock-controlled drive control for clock operation or pulse operation, and continuous operation. In this case, a valve or proportional valve device that basically operates continuously is used to realize both operation methods. This means that the operation of the fuel cell system can be divided into an operation method in which it is always pulse-controlled / clock-controlled, and an operation method in which this is not basically performed. This is possible because, by driving it in a clock-controlled manner, even valves originally designed for continuous operation can be operated in clock operation or pulse operation. The drive control of the proportional valve device is carried out by a control device, particularly a fuel cell control unit. The amount of fuel supplied is directly controlled by the proportional valve device, and at this time, the amount of recirculated medium is indirectly affected.

[0011] The pressure pulses or oscillations within the anode circuit during clock operation can be used to periodically generate a large pressure difference between the anode inlet and anode outlet. The pressure at the anode inlet is measured, in particular, between the fuel cell stack and the proportional valve device, i.e., downstream of the proportional valve device and at any point upstream of the fuel cell stack. Furthermore, the pressure at the anode outlet is measured, in particular, downstream of the fuel cell stack. These pressure pulses or oscillations allow for efficient removal of water accumulation in the fuel cell stack, even at low operating loads, and can also increase recirculation or anode lambda.

[0012] One advantage is that fuel cell systems can be operated in an optimized manner, especially when a jet pump-only system is provided. By using pulsed operation with targeted and controlled use as needed, the burden on the fuel cell system can be kept within an acceptable range. In particular, the total number of pulse cycles can be significantly reduced compared to pure clock operation.

[0013] In the sense of the present invention, clock operation or pulse operation refers to switching the valve position between a slightly open position, for example, up to 10% open, and a significantly larger open position, for example, at least 90% open. This means that during clock operation, the proportional valve device alternately opens substantially completely and closes substantially completely, resulting in near maximum flow rate or almost no flow rate.

[0014] Advantageous configurations and variations can be seen from further dependent claims and from the description with reference to the drawings.

[0015] According to one evolution of this method, predetermined operating parameters encompass model variables, measured values, and / or operating loads. The predetermined operating parameters of a fuel cell system may vary depending on the operating mode, and switching between operating modes depends on predetermined limits for these operating parameters. Thus, multiple pressure pulses (including individual pressure pulses) can be generated as needed. For example, a proportional valve device can be pulsed when it detects the passage of a limit value for the cell voltage signal or another measured signal. A single pressure pulse or a series of pressure pulses can be generated depending on the predetermined operating parameters or the associated operating conditions.

[0016] In another development of this method, when the model variables detect the occurrence of water accumulation in the fuel cell stack, the proportional valve device is operated in pulse mode. For example, since the probability of water accumulation is relatively high at low operating loads, the system can switch from continuous operation to pulse mode early when low operating loads are reached, and especially before low operating loads are reached.

[0017] According to another development of this method, when a model variable or measured value reaches a predetermined nitrogen concentration or predetermined filling level, the proportional valve device is pulsed.

[0018] According to another development of this method, a proportional valve gear is variably driven and controlled by a sinusoidal, serrated, trapezoidal, rectangular, pulse-width modulated, or arbitrary control signal to generate at least one pressure pulse. Variably driven means, in particular, that the control signal may have a variable amplitude and / or variable frequency. This type of optimized waveform for the control signal can further reduce the load on the fuel cell stack during operation.

[0019] For example, a proportional valve device may have a metering valve or hydrogen metering valve, abbreviated as "HGI (Hydrogen Gas Injector)," belonging to the pumping device. The hydrogen metering valve can be driven and controlled by variable amplitude and variable frequency. Furthermore, drive control between clock operation and continuous operation is readily applicable. The control signal, in particular the transition of the control signal, has an effect on the short-term effective pressure delta between the anode inlet and anode outlet of the stack. Furthermore, the control signal can affect the supply conditions of the cell within one cycle. In this respect, the drive control can be optimized with respect to the operating point by adapting the operating parameters.

[0020] According to another development of this method, when the proportional valve device is operated in pulsed mode, it generates regular pressure pulses, at least temporarily, particularly for system state determination. Advantageously, the pressure pulses can be effectively utilized for system state determination when they appear regularly.

[0021] According to another development, the method further comprises adapting the magnitude of the pressure pulse in accordance with the water accumulation in the detected fuel cell stack or in accordance with the risk associated with water accumulation in the fuel cell stack, where the risk includes the step of calculating based on operating conditions. The magnitude of the amplitude is, for example, in a correlation relationship with the cross-sectional opening of the proportional valve device and in a corresponding relationship with the flow rate provided by the proportional valve device. The magnitude of the amplitude depends on or is limited by the supply pressure upstream of the proportional valve device, the consumption or operating point of the fuel cell, and / or the configured size of the proportional valve device. By considering the influencing factors and adapting the magnitude of the amplitude to a scale sufficient to eliminate or prevent water accumulation, the burden is further reduced.

[0022] For example, during an emergency water accumulation or under operating conditions where the probability of water accumulation is extremely high, the magnitude of the amplitude may be adapted so that a large amplitude is provided. An average amplitude may be provided in the normal region where there is a normal risk regarding water accumulation. Further, a reduced amplitude with respect to the average amplitude may be provided when the risk associated with water accumulation is reduced.

[0023] The drive control or control may be performed situationally or reactively according to the measured values, that is, without pre-control. Pre-control is also possible. Alternatively or additionally, adjustment or closed-loop control may be provided.

[0024] According to a development of the fuel cell system, the recirculation medium contains hydrogen not consumed by the fuel cell stack and nitrogen not separated, and the proportional valve device has a hydrogen metering valve.

[0025] Furthermore, the proportional valve device may have, in addition to the hydrogen metering valve, a jet pump, for example. The jet pump may have a first inlet, a second inlet, a suction region, a mixing tube, and a diffuser region. The anode gas flows through the jet pump, at least partially in the flow direction, which is parallel to the longitudinal axis of the jet pump. The majority of the flow-through region of the jet pump is, in example, formed at least substantially tubularly and is used to pump and / or guide a fluid, in particular hydrogen containing proportions of water and nitrogen, within the proportional valve device. The jet pump is supplied with a driving medium through the second inlet, which flows into the suction region or mixing tube through the nozzle passage. In addition, the proportional valve device is supplied with a recirculating medium through the first inlet, which is, in particular, unused hydrogen from the anode region of the fuel cell, especially from the fuel cell stack, and the recirculating medium may also contain water and nitrogen. The driving medium in this case can be derived from a tank and can be under high pressure, especially pressures exceeding 5 bar.

[0026] The driving medium is discharged through the nozzle into the suction area and / or mixing tube. The hydrogen flowing through the nozzle and used as the driving medium has a pressure difference and / or velocity difference with respect to the recirculating medium flowing into the jet pump from the first inlet, at which point the driving medium has a particularly higher pressure of at least 5 bar. When the so-called jet pump effect occurs, the lower-pressure recirculating medium is pumped into the central flow area of ​​the jet pump. At this point, the driving medium, having the described pressure difference and particularly a high velocity that may be close to the speed of sound, flows through the nozzle into the suction area and / or mixing tube.

[0027] The nozzle can have, for example, a cavity inside in the form of a flow opening, through which the fluid can flow. At this time, the drive medium collides with the recirculation medium already present in the suction region and / or the mixing pipe. Based on the high speed difference and / or pressure difference between the drive medium and the recirculation medium, internal friction and turbulent flow occur between the media. At this time, shear stress occurs in the boundary layer between the high-speed drive medium and the significantly lower-speed recirculation medium. This stress causes momentum transfer, and at this time, the recirculation medium is accelerated and entrained. Mixing is carried out according to the principle of conservation of momentum. At this time, the recirculation medium is accelerated in the flow direction, and a pressure drop occurs with respect to the recirculation medium, thereby starting the suction action, and as a result, more recirculation medium is additionally pumped from the region of the first inlet. This effect can be referred to as the jet pump effect. By the drive control of the metering supply of the drive medium by the hydrogen metering valve in the proportional valve device, the pumping rate of the recirculation medium can be adjusted to match the demand of the entire fuel cell system at each time according to the operating state and operating requirements. In an exemplary operating state in which the hydrogen metering valve of the proportional valve device is in the closed state, it can be prevented that the drive medium additionally flows into the central flow region of the proportional valve device from the second inlet, and as a result, the drive medium can no longer flow into the suction region and / or the mixing pipe toward the recirculation medium in the flow direction, and thus the jet pump effect stops. After passing through the mixing pipe, the mixed medium to be pumped, particularly the medium composed of the recirculation medium and the drive medium, flows into the diffuser region in the flow direction, and at this time, a decrease in the flow velocity can occur in the diffuser region. From there, the medium flows, for example, further into the anode region of the fuel cell. The hydrogen metering valve can be directly present in the proportional valve device and may particularly form a common component group together with the proportional valve device. In this case, the proportional valve device may have an integrated drive nozzle. In this case, fresh anode gas, particularly the drive medium, is supplied to the proportional valve device through the hydrogen metering valve and / or the integrated drive nozzle.

[0028] The present invention will be described below with reference to the drawings of the drawings.

Brief Description of the Drawings

[0029] [Figure 1] This is a schematic diagram of a fuel cell system according to one embodiment of the present invention. [Figure 2] This is a block diagram of the method steps for operating a fuel cell system according to one embodiment of the present invention. [Modes for carrying out the invention]

[0030] In the diagrams, the same symbols refer to the same or functionally identical components unless otherwise stated. The numbers assigned to the method steps are for clarity and generally do not imply a specific chronological order. In particular, multiple method steps may be performed simultaneously.

[0031] Further advantages, features, and details of the present invention can be found in the following description. Different embodiments are described in detail below with reference to the drawings.

[0032] Figure 1 shows a schematic diagram of a fuel cell system 1 according to one embodiment of the present invention.

[0033] The fuel cell system 1 hereby comprises, as an example, one fuel cell stack 101. The fuel cell stack 101 has a cathode 105 and an anode 103. Hydrogen is supplied to the anode 103 via a fuel line 20. A high-pressure tank 21 and a pressure regulating valve 22 are present at the inlet of the fuel line 20. Further components may be arranged within the fuel line 20 to supply fuel to the anode 103 of the fuel cell stack 101 as needed. Excess fuel, along with a certain amount of water and nitrogen that diffuses to the anode 103 through the cell membrane, is guided back into a recirculation circuit 50 and mixed with fuel metered and replenished from the fuel line 20.

[0034] Various components, such as a pump or blower 52, may be arranged to drive the flow within the recirculation circuit 50. A hydrogen metering valve 51 is located at the transition between the fuel line 20 and the recirculation circuit 50.

[0035] The hydrogen metering valve 51 ensures that fresh hydrogen is supplied to the recirculation circuit 50. The hydrogen metering valve 51 can be configured as a proportional valve, that is, a valve that acts proportionally. The adjustment strategy within the fuel cell system is such that the hydrogen metering valve 51 adjusts the gas pressure in the recirculation circuit 50 to a specified target pressure according to the system operating point.

[0036] The recirculation circuit 50 may also include a water separator 2 to separate water from the anode gas present within the recirculation circuit 50. The water separator has, for example, a container 3 for collecting the separated water. To empty this container 3, it is connected to a drain line 40 via a drain valve 41. The drain line 40 typically directs excess water into an off-gas pipeline connected to the surrounding area.

[0037] A pressure sensor 25 is located within the fuel pipeline 20. The pressure sensor 25 is positioned upstream of the hydrogen metering valve 51 and measures the pressure between the pressure regulating valve 22 and the hydrogen metering valve 51 within the fuel pipeline 20.

[0038] Furthermore, the fuel cell system 1 includes a control device, particularly a fuel cell control unit (not shown), which is configured to perform a method of operating the fuel cell system 1, as described in the embodiment shown in Figure 2, for example.

[0039] Figure 2 shows a block diagram of the method steps for operating a fuel cell system 1 according to one embodiment of the present invention.

[0040] This method comprises step S1, which involves identifying or measuring predetermined operating parameters. These predetermined operating parameters may include model variables, measured values, operating loads, and / or equivalent parameters.

[0041] This method further includes step S2 of driving and controlling a proportional valve device 51 to control the amount of recirculating medium supplied from the recirculation circuit 50 to the fuel line 20 of the fuel cell stack 101, in which case the proportional valve device 51 may be operated continuously or in pulsed mode according to predetermined operating parameters, and as a result, during pulsed operation, at least one pressure pulse encloses the step in which water accumulation occurs in the fuel cell stack 101. For example, when a model variable detects the occurrence of water accumulation in the fuel cell stack 101, the proportional valve device 51 is operated in pulsed mode. Alternatively or additionally, when a measured value reaches a predetermined nitrogen concentration or a predetermined filling level, the proportional valve device 51 is operated in pulsed mode.

[0042] Optionally, the proportional valve device 51 may be variably driven and controlled by a sinusoidal, sawtooth, trapezoidal, rectangular, or pulse-width modulated control signal to generate at least one pressure pulse. In this case, when the proportional valve device 51 is operated in pulse mode, it can generate at least temporarily regular pressure pulses for system state determination.

[0043] Furthermore, this method includes, for example, step S3 of adjusting the amplitude of the pressure pulse to match the detected water accumulation in the fuel cell stack 101, or to match the risk related to water accumulation in the fuel cell stack 101, where the risk is calculated based on the operating conditions.

[0044] Although the present invention has been described illustratively based on the examples so far, the present invention is not limited to the examples and can be modified in various ways. In particular, combinations of the above examples are also possible. [Explanation of symbols]

[0045] 1. Fuel cell system 2 Water separator 3 containers 20 Fuel line 21 High-pressure tank 22 Pressure regulating valves, pressure regulators 25 Pressure Sensor 40 Drain pipe 41 Drain valve 50 Recirculation circuit 51. Proportional valve device, hydrogen metering valve 52 Blower 101 Fuel Cell Stack 103 Anode 105 Cathode S1 Step of identifying or measuring predetermined operating parameters S2 Steps for driving and controlling the proportional valve device S3 A step to adjust the amplitude of the pressure pulse to match the detected water accumulation in the fuel cell stack, or to match the risk of water accumulation in the fuel cell stack.

Claims

1. A method for operating a fuel cell system (1), Step (S2) of driving and controlling a proportional valve device (51) to control the amount of recirculating medium supplied from a recirculation circuit (50) to the fuel line (20) of the fuel cell stack (101), wherein the proportional valve device (51) may be operated continuously or in pulsed mode according to predetermined operating parameters, and during the pulsed operation, at least one pressure pulse is generated within the fuel cell stack (101), A method for operating a fuel cell system (1).

2. The method according to claim 1, wherein the predetermined operating parameter includes at least one of a model variable, a measured value, and an operating load.

3. The method according to claim 2, wherein when the model variable detects the occurrence of water accumulation in the fuel cell stack (101), the proportional valve device (51) is operated in pulse mode.

4. The method according to claim 2 or 3, wherein the proportional valve device (51) is pulsed when the model variable or the measured value reaches a predetermined nitrogen concentration or a predetermined filling level.

5. The method according to any one of claims 1 to 4, wherein the proportional valve device (51) is driven and controlled by a sinusoidal, sawtooth, trapezoidal, rectangular, or pulse-width modulated control signal to generate at least one of the pressure pulses.

6. The method according to any one of claims 1 to 5, wherein when the proportional valve device (51) is operated in pulse mode, it generates regular pressure pulses at least temporarily, particularly for the purpose of identifying the system state.

7. Furthermore, the method according to any one of claims 1 to 6, comprising the step (S3) of adjusting the magnitude of the amplitude of the pressure pulse to match the detected accumulation of water in the fuel cell stack (101) or to match the risk related to the accumulation of water in the fuel cell stack (101), wherein the risk is determined based on operating conditions.

8. Fuel cell system (1), A fuel cell stack (101) having an anode (103) and a cathode (105), A recirculation circuit (50) that recirculates the recirculating medium at the anode (103), A fuel pipeline (20) that supplies fuel, particularly hydrogen, to the fuel cell stack (101), A proportional valve device (51) connected to the fuel line (20) and the recirculation circuit (50), A control device connected to the fuel line (20) and / or the recirculation circuit (50) and / or the proportional valve device (51), configured to carry out the method according to any one of claims 1 to 7, Equipped with, Fuel cell system (1).

9. The recirculating medium includes hydrogen that was not consumed by the fuel cell stack and nitrogen that was not separated. The proportional valve device (51) has a hydrogen metering valve, The fuel cell system (1) according to claim 8.

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