Operation mode of fuel cell and fuel cell system for executing the same

Abstract

The application discloses a kind of fuel cell operation mode and the fuel cell system for executing it in the technical field of fuel cell, it contains the following start-up step and / or shutdown step: step S, start-up step: step S1, start-up starts, first inject hydrogen flow to the anode of fuel cell, temporarily inject air flow to cathode;Step S2, in the case where air flow has not been injected to the cathode of fuel cell, load is pulled from fuel cell, set gradually increasing to a certain current of pull load current;Step S3, inject air flow to the cathode of fuel cell, air flow gradually increases to a certain value;Step S4, after step S3 is completed, fuel cell enters idle state;Step s, shutdown step: step s1, reduce the set pull load current of fuel cell and cathode air flow;Step s2, close the air flow of cathode, wait for average single cell voltage to drop to close to 0V;Step s3, cut off pull load current;Step s4, close the hydrogen flow of anode.

Description

Technical Field

[0001] This invention relates to the technical field of fuel cells, and in particular to an operating mode of a fuel cell and a fuel cell system for performing the same. Background Technology

[0002] Fuel cells use hydrogen as an energy source to generate electricity, and the reaction product is water. They have high energy conversion efficiency and are an environmentally friendly and efficient new energy source.

[0003] The durability, or lifespan, of a fuel cell is a crucial indicator. Since the cost per kilowatt of a fuel cell remains relatively high, only good durability can minimize the hourly depreciation cost and ensure its economic viability.

[0004] Most industrial products exhibit significantly better durability under no-load / light-load operation than under full-load operation. Fuel cells, however, are an exception. Under no-load / very light-load operation, the high voltage of a single cell not only accelerates the oxidation / agglomeration of the catalyst but also generates oxygen free radicals (free oxygen atoms), accelerating the degradation of the proton exchange membrane material. While adding precious metals such as iridium to the catalyst and adding free radical quenchers to the proton exchange membrane can significantly alleviate these problems, these measures significantly increase cost rather than being an economical choice.

[0005] Current fuel cell operation typically involves establishing a single-cell voltage (e.g., 0.95V) under no-load conditions upon startup. The load current is then increased to a sufficiently low level (e.g., no more than 0.82V) for idling. The load current is then further increased based on load requirements, for example, to reach the rated single-cell voltage of 0.65V. When the load current significantly decreases or even returns to zero, the load is reduced to idling to recharge the battery. Once the battery is fully charged and there is still no load demand, the load is reduced back to the no-load voltage, and the system is shut down while simultaneously discharging any remaining no-load voltage using a bleed resistor.

[0006] The above operating mode significantly reduces the time when the single-cell voltage exceeds 0.82V, effectively ensuring the lifespan of the fuel cell. However, during the startup and transition from load to idle, the transition from idle to no-load and shutdown, and the discharge of residual no-load voltage after shutdown, there are still brief periods when the single-cell voltage exceeds 0.82V, even reaching 0.95V. With fuel cells undergoing numerous startup and shutdown cycles, especially in applications requiring frequent startup and shutdown, the performance degradation should not be underestimated. Summary of the Invention

[0007] The purpose of this section is to outline some aspects of embodiments of the present invention and to briefly describe some preferred embodiments. Simplifications or omissions may be made in this section, as well as in the abstract and title of the invention, to avoid obscuring the purpose of these documents; however, such simplifications or omissions should not be construed as limiting the scope of the invention.

[0008] Therefore, the purpose of this invention is to provide an operating mode of a fuel cell and a fuel cell system that implements it, which can further improve the durability of the fuel cell.

[0009] After conducting an in-depth and detailed analysis of existing technologies and the division of labor within existing industries, the inventors believe that:

[0010] Only voltage drops caused by insufficient hydrogen supply to the anode are dangerous and harmful. Voltage drops caused by insufficient air supply to the cathode, while temporarily reducing or even eliminating output power, are not only harmless to the fuel cell itself, but can even generate concentration current at near-0V low voltages, delivering a small amount of anode hydrogen to the cathode to maintain the catalyst and purge impurities. Furthermore, only an increased deviation from the average voltage of a single cell under heavy / full load conditions indicates poor quality; an increased deviation under light load conditions is insignificant unless caused by insufficient hydrogen supply to the anode.

[0011] To address the aforementioned technical problems, this invention provides an operating mode for a fuel cell and a fuel cell system for executing it, employing the following technical solution: it includes the following start-up and / or shutdown steps:

[0012] Step S, Power-on procedure:

[0013] Step S1: When starting up the fuel cell, first inject hydrogen gas into the anode and temporarily suspend the injection of air into the cathode.

[0014] Step S2: Before air flow is injected into the cathode of the fuel cell, load is applied from the fuel cell, and the load current is gradually increased to a certain level.

[0015] Step S3: Inject air flow into the cathode of the fuel cell, and gradually increase the air flow rate to a certain value;

[0016] After step S3 is completed, the fuel cell enters an idling state;

[0017] Step s, power-off steps:

[0018] Step s1: Reduce the set load current and cathode airflow of the fuel cell;

[0019] Step s2: Turn off the air flow to the cathode and wait for the average single cell voltage to drop to near 0V;

[0020] Step s3: Disconnect the load current;

[0021] Step s4: Shut off the hydrogen flow at the anode.

[0022] Optionally, the power-on and / or power-off steps specifically include:

[0023] Step A, Power-on procedure:

[0024] Step A1: When starting up the fuel cell, first inject hydrogen gas into the anode and then temporarily suspend the injection of air into the cathode.

[0025] Step A2 involves applying a load to the fuel cell before airflow is injected into the cathode. The load current is gradually increased until the average single-cell voltage during normal operation is just below the set safe voltage at the idle current. At this point, the average single-cell voltage is typically less than 0.1V, which is harmless. Meanwhile, because the concentration current driven by the concentration voltage is relatively small, the actual load current may not reach the set load current, but this does not affect the parameter settings for the load application device.

[0026] Step A3: Inject airflow into the cathode of the fuel cell, gradually increasing the airflow rate to a set value; the set airflow rate can be a value from existing technology. After this step is completed, the fuel cell enters an idling state.

[0027] Step B, Power off procedure:

[0028] Step B1: Reduce the set load current and cathode air flow of the fuel cell to reduce the load until the average single cell voltage is just below the set safe voltage, which is the state when step A3 is completed.

[0029] Step B2: Turn off the air flow to the cathode, wait for the average single cell voltage to drop to near 0V, and further wait for the set load current to be unable to be maintained, that is, the actual load current is less than the set load current.

[0030] Step B3: Disconnect the load current;

[0031] Step B4: Turn off the hydrogen flow at the anode.

[0032] Optionally, the set safety voltage is less than or equal to 0.85V; the set safety voltage is less than or equal to 0.82V. According to current technology, the idle current density corresponding to the set safety voltage less than or equal to 0.82V is 0.3-0.6A / cm². 2 .

[0033] Optionally, due to the need for storage and cold start in cold regions in some applications, the fuel cell is typically dried before shutdown to avoid damage from freeze-thaw cycles. This results in a high proton impedance of the proton exchange membrane during startup. To prevent the driest cell in the series circuit from experiencing negative voltage damage due to its high proton impedance caused by excessively rapid startup, the process time of step A2 is preferably greater than 3 seconds, and more preferably greater than 6 seconds; similarly, the process time of step A3 is preferably greater than 3 seconds, and more preferably greater than 6 seconds.

[0034] The above solution can effectively prevent the fuel cell from being subjected to voltages exceeding the set safe voltage, thus mitigating the damage to durability caused by switching on and off, and is especially suitable for applications that require frequent start-stop.

[0035] In some applications, low-power idling is required. If the average single-cell voltage at idle is set to less than 0.82V, and the idling current density is set to 0.5A / cm², then... 2 Therefore, the idle power is still too high. Thus, the inventors have provided an alternative solution, which includes the following power-on and / or power-off steps:

[0036] Optionally, the power-on steps specifically include:

[0037] Step C, Power-on procedure:

[0038] Step C1: When starting up the fuel cell, first inject hydrogen gas into the anode and temporarily suspend the injection of air into the cathode;

[0039] Step C2: Before air flow is injected into the cathode of the fuel cell, load is applied from the fuel cell by gradually increasing the load current to the starting current (e.g., the current corresponding to a current density of 0.3 A / cm2).

[0040] In step C3, airflow is injected into the cathode of the fuel cell, with the flow rate gradually increased while monitoring the average single-cell voltage. When the average single-cell voltage just reaches or slightly falls below the set safe voltage, the airflow is stopped. At this point, the deviation of the individual cell voltages from the average will increase, but this is harmless.

[0041] Optionally, the power-on steps specifically include:

[0042] Step C4: If the application scenario does not require a larger current load, then maintain the operation of the starting current in step C2.

[0043] Step C5: If the application requires a larger load current, gradually increase the set load current while simultaneously increasing the airflow rate. This ensures the average single-cell voltage is maintained at or slightly below the set safe voltage. Completing this step may, but not necessarily, achieve the idle state seen at the end of step A3. During this step, the air metering ratio is likely to increase accordingly. Simultaneously, the load current also increases, and the increase in airflow rate may be even greater.

[0044] Optionally, the shutdown step specifically includes:

[0045] Step D, Power off procedure:

[0046] Step D1: If the load current before shutdown is greater than the idle state after step C5 above, then reduce the set load current and cathode airflow of the fuel cell to reduce the load until the average single cell voltage is just below the set safe voltage; otherwise, proceed directly to the next step.

[0047] Step D2: Gradually reduce the load current until it reaches the starting current described in step C2. During this process, the air flow rate is reduced simultaneously until it reaches the flow rate at the end of step C3. In this step, the air metering ratio will decrease accordingly, and the load current will also decrease, with a larger reduction in the air flow rate.

[0048] Step D3: Turn off the airflow to the cathode and wait for the average single-cell voltage to drop to near 0V;

[0049] Step D4: After waiting for an appropriate amount of time (in order to deplete the oxygen molecules remaining in the cathode), cut off the load current.

[0050] Step D5: Shut off the hydrogen flow at the anode.

[0051] The above-mentioned workaround can achieve a current density of only 0.3 A / cm². 2 It can operate at low power even in smaller scenarios to avoid damage from high voltage, thus meeting the needs of more application scenarios.

[0052] A fuel cell system that performs the operation mode of a fuel cell as described above is characterized by comprising: a fuel cell, a component for regulating load current, a component for regulating anode hydrogen flow, a component for regulating cathode air flow, and a controller for controlling the component for regulating load current, the component for regulating anode hydrogen flow, and the component for regulating cathode air flow.

[0053] Optionally, the component for regulating the load current adopts a Boost DC-DC converter, which can keep the input current (i.e., the output current of the fuel cell) constant at a set value when other power sources (such as batteries) provide a small amount of driving power, and withstand the condition where the input voltage drops to close to 0V; the component for regulating the anode hydrogen flow adopts a hydrogen inlet solenoid valve; and the component for regulating the cathode air flow adopts a centrifugal blower.

[0054] In summary, the present invention has at least one of the following beneficial effects:

[0055] This invention can better avoid the high voltage during the start-up and shutdown of fuel cells, thereby improving the durability of fuel cells, especially in applications that require frequent start-up and shutdown. Attached Figure Description

[0056] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0057] Figure 1 This is a schematic block diagram of the fuel cell system structure of the present invention. Detailed Implementation

[0058] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0059] In the description of this invention, it should be noted that the terms "upper," "lower," "inner," "outer," "top / bottom," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0060] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installed," "equipped with," "sleeved / connected," "connected," etc., should be interpreted broadly. For example, "connection" can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium; it can be a connection within two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0061] Example 1

[0062] In such Figure 1 In the system shown, the fuel cell is a cathode-closed, air-cooled stack of 18 small cells, with each individual cell having an active area of ​​28 cm². 2 Its design concept differs slightly from traditional water-cooled fuel cells in that its air metering ratio under full-load rated conditions is 4 times, which is about twice that of the traditional method. The cooling fan and its shroud structure, as well as the temperature control method, related to air cooling are well-known to existing automation professionals and are omitted from the diagram, so they will not be elaborated further. The hydrogen venting solenoid valve and its pulse hydrogen venting method, as well as the start-up purging method, are also well-known to existing automation professionals and are omitted from the diagram, so they will not be elaborated further.

[0063] Step A, upon power-on, the controller performs the following steps:

[0064] Step A1: Open the hydrogen inlet solenoid valve to inject hydrogen gas into the anode of the fuel cell. At this point, an average single-cell voltage of approximately 0.6V is observed; existing electrochemical professionals should know that this is caused by a small amount of oxygen molecules remaining at the cathode.

[0065] Step A2: Starting from 0, the input load current setting of the Boost DC-DC converter is linearly increased to 16.8A (corresponding to 0.6A / cm²) over a period of 6 seconds. 2 (Current density). During this process, it was observed that the average single-cell voltage dropped below 10mV, but the actual concentration current generated did not reach 16.8A, but only 2-3A.

[0066] In step A3, the centrifugal blower is started, and the air flow injected into the cathode starts from 0 and linearly increases to 22SL / min (corresponding to 4 times the air metering ratio of 16.8A current) over 6 seconds. During this process, it was observed that the load current first increased to 16.8A and then remained constant, followed by an increase in the average single-cell voltage to approximately 0.81V. The fuel cell then enters an idling state.

[0067] Step B, during shutdown, the controller performs the following steps:

[0068] In step B1, the input load current setting of the Boost DC-DC converter was reduced to 16.8A, and the airflow injected into the cathode by the centrifugal blower was also reduced accordingly to 22 SL / min. After this process, the average single-cell voltage was observed to be approximately 0.805V.

[0069] Step B2: Turn off the centrifugal blower and wait. During this wait, it was observed that after approximately 7 seconds (including the time it takes for the airflow to gradually decrease as the centrifugal blower goes from rotating to stopping), the average single-cell voltage dropped below 10mV. Then, after approximately 2 seconds, the actual load current dropped to 5-6A. (Note: At this time, the input load current setting of the Boost DC-DC converter remained unchanged at 16.8A.)

[0070] Step B3: Turn off Boost DC-DC converter, which cuts off the load current; the actual load current quickly becomes 0A; the average single-cell voltage does not show a significant rebound.

[0071] Step B4: Close the hydrogen inlet solenoid valve, which means cutting off the hydrogen flow from the anode.

[0072] Example 2:

[0073] The system principle block diagram is the same as that of Embodiment 1.

[0074] Step C, upon power-on, the controller performs the following steps:

[0075] In step C1, the hydrogen inlet solenoid valve is opened to inject a stream of hydrogen into the anode of the fuel cell. At this point, a single-cell voltage of approximately 0.6V on average is observed. Electrochemical professionals should know that this is caused by a small amount of oxygen molecules remaining at the cathode.

[0076] Step C2: The input load current setting of the Boost DC-DC converter is linearly increased from 0 to 8.4A (corresponding to 0.3A / cm²) over a period of 3 seconds. 2 (Current density). During this process, it was observed that the average single-cell voltage dropped below 10mV, and the actual concentration current generated was 2.4A, which was less than the set value.

[0077] Step C3: Start the centrifugal blower and gradually increase the air flow rate injected into the cathode from 0 at a rate of 1.0 SL / min. When the flow rate reaches approximately 5.0 SL / min (corresponding to an air metering ratio of 1.8 times for an 8.4A current), the average single-cell voltage rises to approximately 0.810V, at which point the increase in air flow rate automatically stops. At this point, the observed deviation of the single-cell voltage from the mean is approximately 60mV, which is harmless.

[0078] Step C4: Since the application scenario requires operation at approximately 14A, proceed to the next step.

[0079] In step C5, the input load current setting of the Boost DC-DC converter is linearly increased from 8.4A to 14A over a period of 2 seconds. Simultaneously, the airflow rate of the centrifugal blower is increased at a rate of 3.0 SL / min, reaching 18.35 SL / min after approximately 4.5 seconds (corresponding to a 4-fold airflow rate to the 14A current). The average single-cell voltage is observed to initially decrease slightly before recovering to approximately 0.802V, at which point the voltage deviation from the average is observed to be approximately 10mV.

[0080] Step D, when shutting down, the controller performs the following steps:

[0081] Step D1: Due to the small load current before shutdown (only 14A, corresponding to a current density of 0.5A / cm³), 2 Therefore, proceed directly to the next step.

[0082] In step D2, over 5 seconds, the input load current setting of the Boost DC-DC converter is linearly reduced to 8.4A, and simultaneously the airflow of the centrifugal blower is linearly reduced to 5.0SL / min, returning to the state at the completion of C3. At this point, the average single-cell voltage is observed to be approximately 0.805V.

[0083] Step D3: Turn off the centrifugal blower. The average single-cell voltage drops below 10mV after approximately 6 seconds (including the time it takes for the airflow to gradually decrease as the centrifugal blower goes from rotating to stopping).

[0084] In step D4, after waiting for another 2 seconds (to deplete any remaining oxygen molecules on the cathode), the Boost DC-DC converter is then turned off, effectively cutting off the load current. The actual load current immediately drops to 0A. The average single-cell voltage does not show a significant rebound.

[0085] Step D5: Close the hydrogen inlet solenoid valve, which means cutting off the hydrogen flow from the anode.

[0086] The above are all preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Therefore, all equivalent changes made in accordance with the structure, shape and principle of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A mode of operation for a fuel cell, characterized in that: It includes the following power-on and / or power-off steps: Step S, Power-on procedure: Step S1: When starting up the fuel cell, first inject hydrogen gas into the anode and temporarily suspend the injection of air into the cathode. Step S2: Before air flow is injected into the cathode of the fuel cell, load is applied from the fuel cell, and the load current is gradually increased to a certain level. Step S3: Inject air flow into the cathode of the fuel cell, and gradually increase the air flow rate to a certain value; After step S3 is completed, the fuel cell enters an idling state; Step s, power-off steps: Step s1: Reduce the set load current and cathode airflow of the fuel cell; Step s2: Turn off the air flow to the cathode and wait for the average single cell voltage to drop to near 0V; Step s3: Disconnect the load current; Step s4: Shut off the hydrogen flow at the anode.

2. The operating mode of a fuel cell according to claim 1, characterized in that: The power-on and / or power-off steps specifically include: Step A, Power-on procedure: Step A1: When starting up the fuel cell, first inject hydrogen gas into the anode and then temporarily suspend the injection of air into the cathode. Step A2: Before air flow is injected into the cathode of the fuel cell, load is applied from the fuel cell, and the load current is gradually increased to the idle current such that the average single cell voltage during normal operation is just less than the set safe voltage. Step A3: Inject airflow into the cathode of the fuel cell, gradually increasing the airflow rate to a set value; After step A4 and step A3 are completed, the fuel cell enters an idling state. Step B, Power off procedure: Step B1: Reduce the set load current and cathode air flow of the fuel cell to reduce the load until the average single cell voltage is just below the set safe voltage, which is the state when step A3 is completed. Step B2: Turn off the air flow to the cathode, wait for the average single cell voltage to drop to near 0V, and further wait for the set load current to be unable to be maintained, that is, the actual load current is less than the set load current. Step B3: Disconnect the load current; Step B4: Turn off the hydrogen flow at the anode.

3. The operating mode of a fuel cell according to claim 2, characterized in that: The set safety voltage is less than or equal to 0.85V; the process time of step A2 is greater than 3 seconds; the process time of step A3 is greater than 3 seconds.

4. The operation mode of a fuel cell according to claim 3, characterized in that: The set safety voltage is less than or equal to 0.82V, and the corresponding idle current density is 0.3-0.6A / cm². 2； The process time of step A2 is greater than 6 seconds; the process time of step A3 is greater than 6 seconds.

5. The operating mode of a fuel cell according to claim 1, characterized in that: The power-on process specifically includes: Step C, Power-on procedure: Step C1: When starting up the fuel cell, first inject hydrogen gas into the anode and temporarily suspend the injection of air into the cathode; Step C2: Before air flow is injected into the cathode of the fuel cell, load is applied from the fuel cell, and the load current is gradually increased to the starting current. In step C3, airflow is injected into the cathode of the fuel cell, the flow rate is gradually increased, and the average single cell voltage is monitored. When the average single cell voltage is less than or equal to the set safe voltage, the increase in airflow is stopped. After step C3 is completed, the fuel cell enters the idling state.

6. The operation mode of a fuel cell according to claim 5, characterized in that: The starting current is less than or equal to a current density of 0.3 A / cm². 2 The corresponding current.

7. The operating mode of a fuel cell and the fuel cell system executing it according to claim 5, characterized in that: The power-on process specifically includes: Step C4: If the application scenario does not require a larger current load, then maintain the operation of the starting current in step C2. In step C5, if the application scenario requires a larger load current, the set load current is gradually increased while the air flow is gradually increased, so that the average single cell voltage is maintained at less than or equal to the set safe voltage. After step C5 is completed, the fuel cell enters the idling state.

8. The operating mode of a fuel cell and the fuel cell system executing it according to claim 7, characterized in that: The shutdown procedure specifically includes: Step D, Power off procedure: Step D1: If the load current before shutdown is greater than the idle state after step C5 above, then reduce the set load current and cathode airflow of the fuel cell to reduce the load until the average single cell voltage is just below the set safe voltage; otherwise, proceed directly to the next step. Step D2: Gradually reduce the load current until it is reduced to the starting current described in step C2, while simultaneously reducing the air flow rate until it is reduced to the flow rate at the time when step C3 is completed. Step D3: Turn off the airflow to the cathode and wait for the average single-cell voltage to drop to near 0V; Step D4: After waiting for an appropriate amount of time, disconnect the load current. Step D5: Turn off the hydrogen flow at the anode.

9. A fuel cell system that performs the operation mode of a fuel cell as described in any one of claims 1-8, characterized in that: It includes a fuel cell, a component for regulating load current, a component for regulating anode hydrogen flow, a component for regulating cathode air flow, and a controller for controlling the component for regulating load current, the component for regulating anode hydrogen flow, and the component for regulating cathode air flow.

10. The fuel cell system according to claim 9, characterized in that: The component for regulating the load current adopts a Boost DCDC, which is used to keep the output current of the fuel cell constant at a set value when there is a small amount of driving power provided by other power sources, and to withstand the condition that the input voltage drops to close to 0V. The component for regulating the hydrogen flow at the anode is a hydrogen inlet solenoid valve; The component for regulating the cathode airflow is a centrifugal blower.

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