Air-cooled fuel cell system and low-temperature starting control method

Abstract

The invention discloses an air-cooled fuel cell system and a low-temperature start control method, and belongs to the technical field of fuel cells, and the air-cooled fuel cell system comprises a fuel cell stack, a bidirectional cooling fan, a mainboard, a first housing, a second housing, a first temperature sensor and a second temperature sensor. In cooperation with cycle control of low-efficiency reaction and normal reaction, the problem of thermal runaway of the fuel cell stack caused by long-term continuous heating in the same area due to the fact that low-temperature starting temperature regulation cannot be performed in the prior art is avoided, and efficient, safe and quick starting of the air-cooled fuel cell system in a low-temperature environment is realized; and the air-cooled fuel cell system is particularly suitable for wide application in cold regions.

Description

An air-cooled fuel cell system and a cryogenic start-up control method Technical Field

[0001] This invention belongs to the field of fuel cell technology, specifically relating to an air-cooled fuel cell system and a low-temperature start-up control method. Background Technology

[0002] Air-cooled (such as wind-cooled) fuel cells are widely used in drones, portable power supplies, and small mobile devices due to their advantages such as compact structure, no need for external water cooling system, and lightweight design. Their low-temperature start-up performance (especially in environments of -20℃ to 0℃) directly determines the adaptability and reliability of their application equipment in cold regions, which is one of the core technical bottlenecks for the industrial application of air-cooled fuel cells.

[0003] Currently, traditional methods for low-temperature start-up of air-cooled fuel cells mainly fall into two categories: external auxiliary heating and self-heating methods based on low-efficiency reactions (under-air reactions). Specifically:

[0004] 1) External auxiliary heating is currently the most widely used low-temperature start-up solution. Its core principle is to preheat the fuel cell stack, cathode intake air, or anode hydrogen gas using an external heating device (such as an electric heating element, heating wire, or hot air generator). Once the fuel cell temperature rises to the start-up threshold (usually above 0°C), the fuel cell can then be started for normal operation. This method has extremely high energy consumption, high equipment cost, low start-up efficiency, and the layout can easily lead to uneven temperature distribution in the battery. Local overheating may damage core components such as the membrane electrode assembly, affecting the battery's lifespan.

[0005] 2) Self-heating methods for inefficient reactions typically employ unidirectional cooling fans as an alternative to external auxiliary heating. This results in the inefficient reaction continuously occurring at the same location on the bipolar plates, making low-temperature start-up temperature control impossible. The core principle is to utilize the fuel cell's inefficient reaction process to increase mass transfer polarization, generating significant waste heat and allowing the battery to heat up itself. While this method eliminates the need for external heating devices, reducing energy consumption and cost to some extent, it presents serious safety hazards and start-up stability issues. The core problem lies in the fact that during the inefficient reaction, current concentration easily occurs at the air inlet, causing a sharp increase in the local heat generation rate. If the airflow is controlled too low at this time, the air cannot promptly remove the large amount of locally generated waste heat, leading to a rapid rise in local temperature and potentially causing thermal runaway. If the airflow is increased to avoid thermal runaway, a large amount of low-temperature air will rapidly flow through the battery cathode, not only removing waste heat and slowing the battery's temperature rise rate but also easily causing freezing and blockage of the cathode flow channel and gas diffusion layer, ultimately leading to start-up failure.

[0006] Furthermore, in traditional water-cooled fuel cell systems or closed-loop air-cooled fuel cell systems, the reaction air and cooling air chambers are independent and decoupled. However, in open-loop air-cooled fuel cell systems, a fan provides the reaction air, and the reaction air itself also acts as a cooling medium (cooling air) to dissipate heat from the stack. This deep coupling of reaction air and cooling air poses significant challenges to thermal management. Moreover, traditional air-cooled fuel cells cannot flexibly adjust airflow direction and heat exchange efficiency, further exacerbating the risks of uneven temperature distribution, thermal runaway, or freeze-start failure, making this approach difficult to scale up for application.

[0007] In view of the shortcomings of the existing technologies, there is an urgent need for a solution that can address the problems of high energy consumption, high cost, and low efficiency during low-temperature start-up of air-cooled fuel cells, as well as the tendency of inefficient reaction heating methods to cause thermal runaway or start-up failure. Summary of the Invention

[0008] The purpose of this invention is to address the above-mentioned problems by proposing an air-cooled fuel cell system and a low-temperature start-up control method, which helps to avoid thermal runaway of the fuel cell stack and achieve efficient, safe, and rapid start-up of the fuel cell stack in a low-temperature environment.

[0009] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0010] This invention proposes an air-cooled fuel cell system, comprising a fuel cell stack, which includes a plurality of alternately stacked bipolar plates and membrane electrode assemblies. The air-cooled fuel cell system also includes a bidirectional cooling fan, a main board, a first casing, a second casing, a first temperature sensor, and a second temperature sensor, wherein:

[0011] The first cover and the second cover are disposed opposite to each other on both sides of the fuel cell stack, and the arrangement direction of the first cover and the second cover is perpendicular to the stacking direction of the bipolar plates and the membrane electrode.

[0012] A bidirectional cooling fan is connected to the second casing. In forward rotation mode, it drives air to flow sequentially through the first casing, the fuel cell stack, and the second casing. In reverse rotation mode, it drives air to flow sequentially through the second casing, the fuel cell stack, and the first casing. In both forward and reverse rotation modes, the fuel cell stack undergoes low-efficiency and normal reactions sequentially. A first temperature sensor is connected to the first casing and is used to detect the temperature inside the first casing as the inlet or outlet temperature of the fuel cell stack. A second temperature sensor is connected to the second casing and is used to detect the temperature inside the second casing as the outlet or inlet temperature of the fuel cell stack.

[0013] The bidirectional cooling fan, the first temperature sensor, and the second temperature sensor are all electrically connected to the motherboard.

[0014] Preferably, the first housing, the second housing, and the bidirectional cooling fan are arranged coaxially.

[0015] A low-temperature start-up control method for an air-cooled fuel cell system, based on the aforementioned air-cooled fuel cell system, includes the following steps:

[0016] S1. Determine whether the inlet temperature of the fuel cell stack is lower than the low temperature start-up threshold. If yes, proceed to step S2. Otherwise, proceed to the normal start-up process, that is, under sufficient air conditions, heat the fuel cell stack to the normal operating temperature to complete the start-up of the fuel cell stack.

[0017] S2. The bidirectional cooling fan is activated to perform an inefficient response in forward rotation mode;

[0018] S3. After a first preset time, determine whether the outlet temperature of the fuel cell stack detected by the second temperature sensor is higher than the over-temperature threshold temperature. If yes, the bidirectional cooling fan performs a normal response in forward rotation mode. If no, repeat step S3.

[0019] S4. After a second preset time, determine whether the outlet temperature of the fuel cell stack detected by the second temperature sensor is lower than the first low temperature threshold. If yes, the bidirectional cooling fan performs a low-efficiency response in reverse mode. If no, repeat step S4.

[0020] S5. After a third preset time, determine whether the outlet temperature of the fuel cell stack detected by the first temperature sensor is higher than the over-temperature threshold temperature. If yes, the bidirectional cooling fan performs a normal response in reverse mode. If no, repeat step S5.

[0021] S6. After a fourth preset time, determine whether the outlet temperature of the fuel cell stack detected by the first temperature sensor is lower than the second low temperature threshold. If not, repeat step S6. If yes, return to step S2 until the outlet temperature of the fuel cell stack reaches the third low temperature threshold. Then, perform the normal startup process to complete the startup of the fuel cell stack.

[0022] Preferably, the target airflow rate required during normal reaction is between the overheating boundary of the airflow rate corresponding to the highest voltage cell and the undercooling boundary of the airflow rate corresponding to the lowest voltage cell in the fuel cell stack during low-efficiency reaction.

[0023] Preferably, the airflow overheating boundary is calculated as follows:

[0024] Different average current densities were set for the fuel cell stack, and the in-plane current density distribution of the membrane electrode under low efficiency reaction was obtained by using the current density partitioning characterization method.

[0025] The in-plane current density distribution is input into the fluid simulation software to obtain the highest operating temperature in all zones of the membrane electrode under different air flow rates, forming a table of the relationship between air flow rate and highest operating temperature.

[0026] Based on the maximum withstand temperature of the membrane electrode, the air flow rate under the current average current density is found in the relationship table between air flow rate and maximum operating temperature as the corresponding target air flow rate. The target air flow rate under different average current densities is fitted to form the air flow rate overheating boundary.

[0027] Airflow undercooled boundary The calculation is as follows:

[0028] ;

[0029] in, This represents the heat output of a single cell in a fuel cell stack. This refers to the inlet temperature of the fuel cell stack. This represents the outlet temperature threshold of the fuel cell stack. Specific heat capacity.

[0030] Preferably, the heat generation power of a single cell in the fuel cell stack The calculation is as follows:

[0031] ;

[0032] in, This represents the average voltage of a single cell in the fuel cell stack. This represents the current in the fuel cell stack.

[0033] Preferably, the airflow required for the fuel cell stack during low-efficiency reactions The calculation is as follows:

[0034] ;

[0035] In the formula, The stoichiometric ratio of air on the cathode side. For the current of the fuel cell stack, This represents the number of electrons transferred per mol of reactants. is Faraday's constant.

[0036] Preferably, the low-efficiency reaction is to reduce the cathode-side air stoichiometry of the fuel cell stack to less than or equal to 1, and the PWM duty cycle of the bidirectional cooling fan under the low-efficiency reaction is P1; the normal reaction is that the cathode-side air stoichiometry of the fuel cell stack is equal to the cathode-side air stoichiometry when the outlet temperature of the fuel cell stack is the normal operating temperature, and the PWM duty cycle of the bidirectional cooling fan under the normal reaction is P2, satisfying P2 > P1.

[0037] The low-temperature start-up threshold, the first low-temperature threshold, the second low-temperature threshold, the third low-temperature threshold, and the normal operating temperature increase sequentially, with the low-temperature start-up threshold... The operating temperature is -5℃ to 0℃, the normal operating temperature is 60℃ to 80℃, and the over-temperature threshold temperature is... , This is the highest temperature that the membrane electrode can withstand.

[0038] Preferably, the target airflow required for normal reaction is the midpoint value of the line connecting the points taken on the airflow overheat boundary and the airflow undercool boundary at the corresponding average current density.

[0039] Preferably, the PWM duty cycle of the bidirectional cooling fan is obtained as follows:

[0040] The outlet temperature of the fuel cell stack is obtained at the target airflow rate. The flow resistance of the bidirectional cooling fan is obtained based on the air pressure-airflow curve of the bidirectional cooling fan and the outlet temperature of the fuel cell stack, and is equivalent to the flow resistance of the fuel cell stack. The PWM duty cycle of the bidirectional cooling fan is obtained based on the target airflow rate and the flow resistance of the fuel cell stack.

[0041] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0042] This invention overcomes the problems of high energy consumption, high cost, and low start-up efficiency of external auxiliary heating methods in existing air-cooled fuel cell systems at low temperatures, as well as the risk of thermal runaway or freezing failure due to improper airflow control in heating low-efficiency reactions. Specifically, by combining the adjustable direction of a bidirectional cooling fan with cyclical control of low-efficiency and normal reactions, this invention avoids the problem of thermal runaway of the fuel cell stack caused by long-term continuous heating in the same area due to the inability of existing technologies to control the temperature during low-temperature start-up. This invention achieves efficient, safe, and rapid start-up of air-cooled fuel cell systems in low-temperature environments, while also taking into account the requirements of control flexibility and lightweight design. It is particularly suitable for the widespread application of air-cooled fuel cell systems in cold regions, avoiding the risk of start-up failure due to poor low-temperature performance of air-cooled fuel cell systems. Attached Figure Description

[0043] Figure 1 is a schematic diagram of the air-cooled fuel cell system of Embodiment 1 of the present invention;

[0044] Figure 2 is a schematic diagram of the internal structure of the air-cooled fuel cell system of Embodiment 1 of the present invention;

[0045] Figure 3 is a flowchart of the low-temperature start-up control method of the air-cooled fuel cell system in Embodiment 2 of the present invention;

[0046] Figure 4 shows the changes in current and average single-cell battery voltage under the forward and reverse rotation modes of the bidirectional cooling fan in Embodiment 2 of the present invention.

[0047] Figure 5 is a schematic diagram of the operating boundary of the target airflow under normal reaction conditions in Embodiment 2 of the present invention;

[0048] Figure 6 shows the relationship between the outlet temperature and flow resistance of the fuel cell stack under different airflow rates in Embodiment 2 of the present invention.

[0049] Figure 7 is a diagram of the air pressure-air volume curve of the bidirectional cooling fan in Embodiment 2 of the present invention;

[0050] Figure 8 is a schematic diagram of the voltage inconsistency of each cell in the fuel cell stack under low-efficiency reaction in Embodiment 2 of the present invention;

[0051] Figure 9 is a graph showing the relationship between average current density and air flow rate in Embodiment 2 of the present invention;

[0052] Figure 10 shows the relationship between the average current density and peak current density of the fuel cell stack under low-efficiency reaction in Example 2 of the present invention.

[0053] Explanation of reference numerals in the attached diagram: 1. Hydrogen inlet; 2. Hydrogen outlet; 3. Second temperature sensor; 4. Reaction zone; 5. Bidirectional cooling fan; 6. Main board; 7. Second casing; 8. Bipolar plate; 9. First temperature sensor; 10. First casing; 11. Fuel cell stack. Detailed Implementation

[0054] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0055] It should be noted that when a component is referred to as being "connected" to another component, it can be directly connected to the other component or there may be an intervening component. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of the application.

[0056] Example 1:

[0057] As shown in Figures 1-2, an air-cooled fuel cell system includes a fuel cell stack 11, which comprises several alternately stacked bipolar plates and membrane electrode assemblies. The air-cooled fuel cell system also includes a bidirectional cooling fan 5, a main board 6, a first casing 10, a second casing 7, a first temperature sensor 9, and a second temperature sensor 3, wherein:

[0058] The first cover 10 and the second cover 7 are disposed opposite to each other on both sides of the fuel cell stack 11, and the arrangement direction of the first cover 10 and the second cover 7 is perpendicular to the stacking direction of the bipolar plates and the membrane electrode.

[0059] A bidirectional cooling fan 5 is connected to the second housing 7. In forward rotation mode, it drives air to flow sequentially through the first housing 10, the fuel cell stack 11, and the second housing 7. In reverse rotation mode, it drives air to flow sequentially through the second housing 7, the fuel cell stack 11, and the first housing 10. In both forward and reverse rotation modes, the fuel cell stack undergoes low-efficiency and normal reactions sequentially. A first temperature sensor 9 is connected to the first housing 10 and is used to detect the temperature inside the first housing 10 as the inlet or outlet temperature of the fuel cell stack 11. A second temperature sensor 3 is connected to the second housing 7 and is used to detect the temperature inside the second housing 7 as the outlet or inlet temperature of the fuel cell stack 11.

[0060] The bidirectional cooling fan 5, the first temperature sensor 9, and the second temperature sensor 3 are all electrically connected to the motherboard 6.

[0061] In one embodiment, the first housing 10, the second housing 7, and the bidirectional cooling fan 5 are coaxially arranged.

[0062] In this embodiment, the air-cooled fuel cell system is an open-type air-cooled fuel cell system. The bidirectional cooling fan 5 serves both as reaction air for the reaction and as cooling air for the fuel cell stack 11, with deep coupling between the reaction air and the cooling air. As shown in Figures 1 and 2, the air-cooled fuel cell system of this embodiment consists of a fuel cell stack 11, a bidirectional cooling fan 5, a main board 6, a first housing 10, a second housing 7, a first temperature sensor 9, and a second temperature sensor 3. The fuel cell stack 11 includes several alternately stacked bipolar plates 8 and membrane electrode assemblies (not shown in Figures 1 and 2). The fuel cell stack 11 is a prior art structure well known to those skilled in the art. The bipolar plates 8 are provided with a hydrogen inlet 1, a hydrogen outlet 2, and a reaction zone 4, which are prior art structures well known to those skilled in the art. The first temperature sensor 9 is located on the first housing 10, and the second temperature sensor 3 is located on the second housing 7. The first temperature sensor 9, the second temperature sensor 3, the bidirectional cooling fan 5, and the main board 6 are electrically connected and can perform electrical, signal, and communication interactions.

[0063] In forward rotation mode, the second temperature sensor 3 detects the outlet temperature (referred to as outlet temperature) of the fuel cell stack 11, and the first temperature sensor 9 detects the inlet temperature (referred to as inlet temperature) of the fuel cell stack 11. In reverse rotation mode, the second temperature sensor 3 detects the inlet temperature of the fuel cell stack 11, and the first temperature sensor 9 detects the outlet temperature of the fuel cell stack 11. In Figure 2, the arrow at Z indicates the airflow direction in forward rotation mode, and the arrow at F indicates the airflow direction in reverse rotation mode. As shown in Figure 2, during the low-efficiency reaction stage, when the bidirectional cooling fan 5 is in forward rotation mode, the inlet area of ​​the reaction zone 4 of the bipolar plate 8 (corresponding to the thermal runaway area A in forward rotation mode in Figure 2, such as thermal runaway area A occupying 1 / 20 to 1 / 4 of the area of ​​the reaction zone 4 of the bipolar plate 8 and being close to the air inlet side in forward rotation mode) has a serious risk of thermal runaway; when the bidirectional cooling fan 5 is in reverse rotation mode, the inlet area of ​​the reaction zone 4 of the bipolar plate 8 (corresponding to the thermal runaway area B in reverse rotation mode in Figure 2, such as thermal runaway area B occupying 1 / 20 to 1 / 4 of the area of ​​the reaction zone 4 of the bipolar plate 8 and being close to the air inlet side in reverse rotation mode) has a serious risk of thermal runaway.

[0064] Working principle:

[0065] When the air-cooled fuel cell system is operating, the inlet temperature of the fuel cell stack 11 is detected by a corresponding temperature sensor. The bidirectional cooling fan 5 alternates between forward and reverse rotation based on the detected temperature values ​​and a preset temperature threshold. The PWM duty cycle of the bidirectional cooling fan 5 can also be adjusted to achieve low-temperature start-up. Specifically, the ambient temperature (inlet temperature of the fuel cell stack 11) is obtained through the first temperature sensor 9 or the second temperature sensor 3. When the ambient temperature is greater than or equal to the low-temperature start-up threshold... Time (e.g., the low-temperature start-up threshold can be used) (Set to 0℃), execute the normal startup process. The normal startup process is the process of applying load and heating the fuel cell stack 11 to the normal operating temperature (60℃~80℃). This is generally achieved by applying load current to the fuel cell stack 11 and maintaining a sufficient supply of reactant gas. This is a routine operation well known to those skilled in the art. When the ambient temperature is below the low-temperature startup threshold... The following process is executed: a low-efficiency reaction phase under forward rotation of the bidirectional cooling fan 5, a normal reaction phase under forward rotation of the bidirectional cooling fan 5, a low-efficiency reaction phase under reverse rotation of the bidirectional cooling fan 5, and a normal reaction phase under reverse rotation of the bidirectional cooling fan 5. Specifically, the bidirectional cooling fan 5 is first started to execute the low-efficiency reaction in forward rotation mode; it is then determined whether the outlet temperature of the fuel cell stack 11 detected by the second temperature sensor 3 is higher than the over-temperature threshold temperature. If so, the bidirectional cooling fan 5 executes the normal reaction in forward rotation mode; it is then determined whether the outlet temperature of the fuel cell stack 11 detected by the second temperature sensor 3 is lower than the first low-temperature threshold temperature. If so, the bidirectional cooling fan 5 executes the low-efficiency reaction in reverse rotation mode; it is then determined whether the outlet temperature of the fuel cell stack 11 detected by the first temperature sensor 9 is higher than the over-temperature threshold temperature. If so, the bidirectional cooling fan 5 executes the normal reaction in reverse rotation mode; it is then determined whether the outlet temperature of the fuel cell stack 11 detected by the first temperature sensor 9 is lower than the second low-temperature threshold temperature. If so, the forward and reverse rotation of the bidirectional cooling fan 5 is repeated until the outlet temperature of the fuel cell stack 11 reaches the third low-temperature threshold temperature, at which point the normal start-up process is executed, completing the low-temperature start-up of the fuel cell stack 11. Among them, the low-temperature start-up threshold, the first low-temperature threshold, the second low-temperature threshold, the third low-temperature threshold, and the normal operating temperature increase sequentially, and the low-temperature start-up threshold... The operating temperature is -5℃ to 0℃, the normal operating temperature is 60℃ to 80℃, and the over-temperature threshold temperature is... , The maximum withstand temperature of the membrane electrode, such as the over-temperature threshold temperature. =30℃.

[0066] This air-cooled fuel cell system combines the adjustable direction of a bidirectional cooling fan with cyclical control of low-efficiency and normal reactions. This avoids the problem of thermal runaway of the fuel cell stack caused by long-term continuous heating in the same area due to the inability of existing technologies to control the low-temperature start-up temperature. It achieves efficient, safe, and rapid start-up of the air-cooled fuel cell system in low-temperature environments, while also taking into account the requirements of control flexibility and integration. It is especially suitable for the widespread application of air-cooled fuel cell systems in cold regions, avoiding the risk of start-up failure due to poor low-temperature performance of air-cooled fuel cell systems.

[0067] Example 2:

[0068] As shown in Figures 3-10, a low-temperature start-up control method for an air-cooled fuel cell system, based on the air-cooled fuel cell system of Example 1, includes the following steps:

[0069] S1. Determine whether the inlet temperature of the fuel cell stack 11 is lower than the low temperature start-up threshold. If yes, proceed to step S2. Otherwise, proceed to the normal start-up process, that is, under sufficient air conditions, heat the fuel cell stack 11 to the normal operating temperature to complete the start-up of the fuel cell stack.

[0070] S2. Start the bidirectional cooling fan 5 to perform an inefficient response in forward rotation mode;

[0071] S3. After a first preset time, determine whether the outlet temperature of the fuel cell stack 11 detected by the second temperature sensor 3 is higher than the over-temperature threshold temperature. If yes, the bidirectional cooling fan 5 performs a normal response in forward rotation mode. If no, repeat step S3.

[0072] S4. After a second preset time, determine whether the outlet temperature of the fuel cell stack 11 detected by the second temperature sensor 3 is lower than the first low temperature threshold. If yes, the bidirectional cooling fan 5 performs a low-efficiency response in reverse mode. If no, repeat step S4.

[0073] S5. After a third preset time, determine whether the outlet temperature of the fuel cell stack 11 detected by the first temperature sensor 9 is higher than the over-temperature threshold temperature. If yes, the bidirectional cooling fan 5 performs the normal response in reverse mode. If no, repeat step S5.

[0074] S6. After a fourth preset time, determine whether the outlet temperature of the fuel cell stack 11 detected by the first temperature sensor 9 is lower than the second low temperature threshold. If not, repeat step S6. If yes, return to step S2 until the outlet temperature of the fuel cell stack 11 reaches the third low temperature threshold. Then, perform the normal startup process and complete the startup of the fuel cell stack 11.

[0075] The ambient temperature (inlet temperature of fuel cell stack 11) is obtained through either the first temperature sensor 9 or the second temperature sensor 3. When the ambient temperature is lower than the low-temperature start-up threshold... Time (e.g., the low-temperature start-up threshold can be used) If the temperature is set to 0℃, proceed to step S2; otherwise, proceed with the normal startup process. The normal startup process involves applying a load to the fuel cell stack 11 and raising its temperature to the normal operating temperature (60℃~80℃). This is generally achieved by applying a load current to the fuel cell stack 11 and maintaining a sufficient supply of reactant gas, a routine operation well-known to those skilled in the art. For ambient temperatures below the low-temperature startup threshold... The process is as follows: a low-efficiency reaction stage when the bidirectional cooling fan 5 rotates forward, a normal reaction stage when the bidirectional cooling fan 5 rotates forward, a low-efficiency reaction stage when the bidirectional cooling fan 5 rotates in reverse, and a normal reaction stage when the bidirectional cooling fan 5 rotates in reverse. During each reaction stage, the temperature detected by the temperature sensor is checked at preset intervals. The preset intervals may be equal or unequal in different reaction stages, or real-time detection can be achieved, and adjustments can be made according to actual needs.

[0076] Specifically, the bidirectional cooling fan 5 is activated to perform a low-efficiency reaction in forward rotation mode. The PWM duty cycle of the bidirectional cooling fan 5 is P1. The outlet temperature of the fuel cell stack 11 is monitored in real time by the second temperature sensor 3. Under low-efficiency reaction conditions, the in-plane current density distribution of the membrane electrode is extremely uneven, and the outlet temperature of the fuel cell stack 11 gradually increases (the normal reaction stage is necessarily a heating process). When the outlet temperature of the fuel cell stack 11 exceeds the over-temperature threshold temperature... When the temperature is set to 30℃, the normal reaction is executed in the forward rotation mode of the bidirectional cooling fan 5. The PWM duty cycle of the bidirectional cooling fan 5 is P2. Because the in-plane current density distribution of the membrane electrode is more uniform under normal reaction conditions, the outlet temperature of the fuel cell stack 11 slowly decreases (the normal reaction stage is always a cooling process) until the outlet temperature of the fuel cell stack 11 is lower than the first low temperature threshold. Time (e.g., set to 5℃).

[0077] Then, the inefficient response of the bidirectional cooling fan 5 in reverse mode is executed. The PWM duty cycle of the bidirectional cooling fan 5 is P1. The outlet temperature of the fuel cell stack 11 is detected in real time by the first temperature sensor 9. When the outlet temperature of the fuel cell stack 11 is higher than the over-temperature threshold temperature... At this time, the bidirectional cooling fan 5 operates normally in reverse mode, with its PWM duty cycle at P2, until the outlet temperature of the fuel cell stack 11 falls below the second low-temperature threshold. If the temperature is set to 10℃, return to step S2 until the third low temperature threshold is reached. The normal startup process was executed, and the low-temperature startup of fuel cell stack 11 was completed.

[0078] In one embodiment, the target airflow required during normal reaction is between the overheating boundary of the airflow corresponding to the highest voltage cell and the undercooling boundary of the airflow corresponding to the lowest voltage cell in the fuel cell stack 11 during low-efficiency reaction.

[0079] Among them, the airflow region between the overheating boundary and the undercooling boundary of airflow during low-efficiency reaction is taken as the reasonable selection region of the target airflow required during normal reaction (normal reaction conditions).

[0080] In one embodiment, the airflow overheating boundary is calculated as follows:

[0081] Different average current densities were set for the fuel cell stack 11, and the in-plane current density distribution of the membrane electrode under low efficiency reaction was obtained by the current density partitioning characterization method.

[0082] The in-plane current density distribution is input into the fluid simulation software to obtain the highest operating temperature in all zones of the membrane electrode under different air flow rates, forming a table of the relationship between air flow rate and highest operating temperature.

[0083] Based on the maximum withstand temperature of the membrane electrode, the air flow rate under the current average current density is found in the relationship table between air flow rate and maximum operating temperature as the corresponding target air flow rate. The target air flow rate under different average current densities is fitted to form the air flow rate overheating boundary.

[0084] Airflow undercooled boundary The calculation is as follows:

[0085] ;

[0086] in, This represents the heat generation power of a single cell in fuel cell stack 11. The inlet temperature of fuel cell stack 11. The outlet temperature threshold of fuel cell stack 11 Specific heat capacity.

[0087] In one embodiment, the heat generation power of a single cell in the fuel cell stack 11 The calculation is as follows:

[0088] ;

[0089] in, This represents the average single-cell voltage of fuel cell stack 11. This represents the current of fuel cell stack 11.

[0090] In obtaining the airflow overheating boundary (hereinafter referred to as the overheating boundary), different average current densities of the fuel cell stack 11 are first set, and the in-plane current density distribution of the membrane electrode under low efficiency reaction is obtained using the current density partitioning characterization method. The in-plane current density distribution of each part is input into fluid simulation software (such as Fluent software) to obtain the highest operating temperature of all partitions of the membrane electrode under different airflow rates, forming a relationship table between airflow rate and highest operating temperature. Based on the highest tolerance temperature of the membrane electrode, the airflow rate under the current average current density is searched in the relationship table between airflow rate and highest operating temperature (e.g., the highest tolerance temperature of the membrane electrode corresponds to the highest operating temperature) as the corresponding target airflow rate. The target airflow rates under different average current densities form the airflow overheating boundary. Figure 10 shows the relationship table between the average current density and peak current density of the fuel cell stack under low efficiency reaction. Generally, the peak current density of the membrane electrode is at least twice the average current density of the fuel cell stack 11. Moreover, as the average current density of the fuel cell stack 11 increases, the peak current density of the membrane electrode also gradually increases. The higher the current density, the more severe the risk of thermal runaway. The airflow overheat boundary is fitted using linear fitting or least squares fitting, or other fitting methods well known to those skilled in the art.

[0091] The airflow undercooling boundary (hereinafter referred to as the undercooling boundary) is based on the heat generation power of a single cell in fuel cell stack 11. Through formula Calculated, where, The outlet temperature threshold of fuel cell stack 11 indicates what happens when the outlet temperature of fuel cell stack 11 is lower than... At this temperature, the membrane electrode will freeze; it can generally be set to 0℃, T in The ambient temperature is the inlet temperature of fuel cell stack 11. Therefore, during the normal reaction phase, it is necessary to cool down the high-temperature region during the low-efficiency reaction. The supercooled and superheated airflow boundaries of the low-efficiency reaction can be used as the target airflow during the normal reaction, which satisfies the normal electrochemical reaction and also cools down the high-temperature region from the previous low-efficiency reaction phase. Ultimately, the target airflow during the normal reaction switches within the shaded areas of the supercooled and superheated airflow boundaries in Figure 5.

[0092] In one embodiment, the airflow required for the fuel cell stack 11 during low-efficiency reactions The calculation is as follows:

[0093] ;

[0094] In the formula, The stoichiometric ratio of air on the cathode side. For the current of fuel cell stack 11, This represents the number of electrons transferred per mol of reactants. is Faraday's constant.

[0095] Figure 5 is a schematic diagram of the operating boundary of the target air flow rate under normal reaction conditions in the low-temperature start-up control method of the air-cooled fuel cell system of the present invention. When the air-cooled fuel cell system enters the low-efficiency reaction stage, the air flow rate required for the low-efficiency reaction of the fuel cell stack 11 follows the broken line formed by the rectangular points in Figure 5 (low-efficiency reaction conditions). The formula for calculating the air flow rate is as follows: ,in, The stoichiometric ratio of air on the cathode side. The current of fuel cell stack 11 is equal to the average current density multiplied by the effective reaction area. This represents the number of electrons transferred per mol of reactants. This is the Faraday constant. The stoichiometric ratio of air on the cathode side in low-efficiency reactions is generally between 0.9 and 1. The air flow rate in this stage can also be calibrated in advance through experiments and stored in the memory of the motherboard 6, as shown in Figure 9.

[0096] As shown in Figure 8, when the air-cooled fuel cell system is in the low-efficiency reaction stage, the voltage consistency of each cell in the fuel cell stack 11 is poor. The fuel cell stack 11 consists of several cells, a technique well-known to those skilled in the art. Among the cells in the fuel cell stack 11, there are cells in normal reaction and cells in low-efficiency reaction. m represents the number of cells in the fuel cell stack 11; in this embodiment, the number of cells m = 13. Cells in normal reaction have a high cathode-side air stoichiometry, typically greater than 1, resulting in a higher voltage. Cells in low-efficiency reaction have a low cathode-side air stoichiometry, typically less than 1, resulting in a lower voltage. For cells in low-efficiency reaction, due to the concentrated current in the cathode-side air inlet region, there is a risk of thermal runaway. It is necessary to maintain the temperature of the cathode-side air inlet region below the required temperature to prevent the membrane electrode assembly from overheating. Therefore, the airflow provided by the bidirectional cooling fan 5 cannot be too low. Among all cells in low-efficiency reaction, the cell with the lowest voltage (i.e., the lowest voltage cell) exhibits the broken line (airflow overheating boundary) formed by the dots shown in Figure 5. For batteries with normal reactions, due to the relatively uniform current density distribution, it is necessary to maintain the temperature above the required level to prevent water freezing inside the membrane electrode, which would hinder gas mass transfer. Among all normally reacting batteries, the battery with the highest voltage (i.e., the highest voltage battery) exhibits a broken line (air flow supercooling boundary) formed by the triangular points shown in Figure 5. In the low-efficiency reaction, the reactant is oxygen, satisfying… .

[0097] In one embodiment, the low-efficiency reaction is to reduce the cathode-side air stoichiometry of the fuel cell stack 11 to less than or equal to 1, and the PWM duty cycle of the bidirectional cooling fan 5 under the low-efficiency reaction is P1; the normal reaction is that the cathode-side air stoichiometry of the fuel cell stack 11 is equal to the cathode-side air stoichiometry when the outlet temperature of the fuel cell stack 11 is the normal operating temperature, and the PWM duty cycle of the bidirectional cooling fan 5 under the normal reaction is P2, satisfying P2 > P1.

[0098] The low-temperature start-up threshold, the first low-temperature threshold, the second low-temperature threshold, the third low-temperature threshold, and the normal operating temperature increase sequentially, with the low-temperature start-up threshold... The operating temperature is -5℃ to 0℃, the normal operating temperature is 60℃ to 80℃, and the over-temperature threshold temperature is... , This is the highest temperature that the membrane electrode can withstand.

[0099] Specifically, the inefficient reaction (air deficiency reaction) involves reducing the air stoichiometry on the cathode side of the fuel cell stack 11 to less than or equal to 1. This air deficiency increases mass transfer polarization and raises the waste heat of the fuel cell stack 11. In the inefficient reaction, the average single-cell voltage of the fuel cell stack 11 is typically controlled at 0.2 V, and the current density in the cathode-side air inlet region of the fuel cell stack 11 usually increases significantly, while the current density in the cathode-side air outlet region decreases to 0. For example, in low-efficiency reactions, the active surface area is 200. ~400 The average current density of fuel cell stack 11 is 0.6. At that time, the peak current density in the air inlet region on the cathode side can reach 5.6. The heat generation power of a single cell in fuel cell stack 11 is calculated. The higher the current density in the air inlet region on the cathode side, the greater the heat generation power, thus posing a serious risk of thermal runaway in the corresponding region. As shown in Figure 2, during the low-efficiency reaction stage, when the bidirectional cooling fan 5 is in forward rotation mode, the inlet region of the reaction zone 4 of the bipolar plate 8 (corresponding to the thermal runaway-prone region A in forward rotation mode in Figure 2, such as region A occupying 1 / 20 to 1 / 4 of the area of ​​the reaction zone 4 of the bipolar plate 8 and being close to the air inlet side in forward rotation mode) poses a serious risk of thermal runaway. When the bidirectional cooling fan 5 is in reverse rotation mode, the inlet region of the reaction zone 4 of the bipolar plate 8 (corresponding to the thermal runaway-prone region B in reverse rotation mode in Figure 2, such as region B occupying 1 / 20 to 1 / 4 of the area of ​​the reaction zone 4 of the bipolar plate 8 and being close to the air inlet side in reverse rotation mode) also poses a serious risk of thermal runaway. Normal reaction refers to the air stoichiometry ratio on the cathode side of fuel cell stack 11 being equal to the air stoichiometry ratio when the temperature of fuel cell stack 11 is at its normal operating temperature (e.g., 60℃), such as 2.5. Air stoichiometry ratio refers to the ratio of the actual air supply to the theoretically available air volume in fuel cell stack 11 to the amount of air participating in the reaction.

[0100] Figure 3 illustrates the low-temperature start-up control method for the air-cooled fuel cell system of the present invention, and Figure 4 shows the changes in current and average single-cell voltage under the forward and reverse rotation modes of the bidirectional cooling fan 5. In this embodiment, the low-temperature start-up threshold... The temperature is 0℃, the normal operating temperature is 80℃, and the temperature exceeds the threshold. First low temperature threshold The second low temperature threshold is 5℃. The third low temperature threshold is 10℃. The initial temperature is 40℃, but can be adjusted according to actual needs. When the low-temperature start-up mode is executed, the air-cooled fuel cell system first enters the low-efficiency reaction stage. At this time, the average single-cell voltage of the fuel cell stack 11 is generally low, such as 0.2V, and the bidirectional cooling fan 5 is in forward rotation mode (the arrow at Z in Figure 2 indicates the airflow direction in forward rotation mode). Due to the current concentration phenomenon in the cathode side air inlet area of ​​the fuel cell stack 11 during the low-efficiency reaction, the temperature of the membrane electrode and bipolar plate 8 in the thermal runaway region A gradually rises. The air (cooling air) also rises in temperature after exchanging heat with the membrane electrode and bipolar plate 8, and the outlet temperature of the fuel cell stack 11 is monitored at the second temperature sensor 3. When the outlet temperature of the fuel cell stack 11 rises to the over-temperature threshold temperature... ( When the maximum tolerance temperature of the membrane electrode assembly (MEA) is set to -15℃ (e.g., 30℃), the air-cooled fuel cell system enters the normal reaction phase. The average single-cell voltage of the fuel cell stack 11 is relatively high, such as 0.7 V, and the bidirectional cooling fan 5 is in forward rotation mode. Because the current density distribution is relatively uniform during the normal reaction phase, and the PWM duty cycle of the bidirectional cooling fan 5 is large, resulting in a large airflow, the temperature of the MEA and bipolar plates 8 in the cathode-side air inlet region of the fuel cell stack 11 decreases accordingly, and the outlet temperature of the fuel cell stack 11 also decreases. When the second temperature sensor 3 detects that the outlet temperature of the fuel cell stack 11 has dropped to the first low-temperature threshold... ( When the temperature is set to 5℃, the air-cooled fuel cell system enters a low-efficiency reaction stage, but the bidirectional cooling fan 5 is in reverse mode (the arrow at F in Figure 2 indicates the direction of airflow in reverse mode). At this time, the average single-cell voltage of the fuel cell stack 11 is generally low, such as 0.2 V, and the temperature of the membrane electrode assembly (MEA) and bipolar plate 8 in the thermal runaway region B gradually rises. The air temperature also rises after exchanging heat with the MEA and bipolar plate 8, reaching the outlet temperature of the fuel cell stack 11 monitored by the first temperature sensor 9. As the temperature of the MEA and bipolar plate 8 gradually increases, when it rises to the over-temperature threshold temperature... At this time, the air-cooled fuel cell system enters the normal reaction phase, the average single-cell voltage of the fuel cell stack 11 increases, for example, to 0.7V, and the bidirectional cooling fan 5 is in reverse mode. It is then determined whether the outlet temperature of the fuel cell stack 11 detected by the first temperature sensor is lower than the second low-temperature threshold. ( (This can be set to 10℃). If so, the above process is repeated until the outlet temperature of the fuel cell stack 11 reaches the third low-temperature threshold. ( When the temperature is set to 40℃, the normal startup process is executed, the low-temperature startup of fuel cell stack 11 is completed, and the low-temperature startup process of the air-cooled fuel cell system ends.

[0101] In one embodiment, the target airflow required for normal reaction is the midpoint value of the line connecting the points taken on the airflow overheat boundary and the airflow undercool boundary at the corresponding average current density.

[0102] The target airflow rate required for normal operation is determined by the midpoint of the line connecting the points on the current average current density airflow overheat boundary and the airflow undercool boundary. It is easy to understand that the target airflow rate required for normal operation is sufficient as long as it falls within the range of the airflow overheat boundary and the airflow undercool boundary; the specific value can be adjusted according to actual needs.

[0103] In one embodiment, the PWM duty cycle of the bidirectional cooling fan 5 is obtained as follows:

[0104] The outlet temperature of the fuel cell stack 11 under the target airflow is obtained. The flow resistance of the bidirectional cooling fan 5 is obtained based on the air pressure-airflow curve of the bidirectional cooling fan 5 and the outlet temperature of the fuel cell stack 11, and is equivalent to the flow resistance of the fuel cell stack 11. The PWM duty cycle of the bidirectional cooling fan 5 is obtained based on the target airflow and the flow resistance of the fuel cell stack 11.

[0105] The bidirectional cooling fan 5 can rotate in both directions according to the temperature sensor's monitoring value and compare it with a preset temperature threshold, while also controlling the PWM duty cycle of the bidirectional cooling fan 5.

[0106] Figure 6 shows the relationship between the outlet temperature and flow resistance of the fuel cell stack under different airflow rates. This relationship can be obtained in advance through experimental testing on a test bench or calculated using fluid simulation software (such as Fluent software), and is well-known to those skilled in the art. After obtaining the target airflow rate, the flow resistance of the air flowing through the fuel cell stack 11 can be obtained based on the outlet temperature of the corresponding temperature sensor.

[0107] Figure 7 shows the air pressure-airflow curve of the bidirectional cooling fan. The air pressure-airflow curve of the bidirectional cooling fan 5 represents its own parameters. The mainstream control method is PWM (Pulse Width Modulation) control. By adjusting the duty cycle (0%~100%) of a fixed-frequency square wave pulse, the average supply voltage of the motor of the bidirectional cooling fan 5 is controlled, thereby precisely adjusting the speed of the motor of the bidirectional cooling fan 5. The higher the duty cycle, the higher the average supply voltage, and the faster the speed of the bidirectional cooling fan 5; conversely, the lower the duty cycle, the slower the speed. The PWM duty cycle of the bidirectional cooling fan 5 can be uniquely determined based on the target airflow and flow resistance.

[0108] It should be noted that the method of the present invention can be used not only for low-temperature start-up processes where the ambient temperature (inlet temperature of fuel cell stack 11) is below zero degrees Celsius, but also for any scenario where the fuel cell stack 11 needs to be heated.

[0109] This low-temperature start-up control method for air-cooled fuel cell systems combines the adjustable direction of bidirectional cooling fans with cyclical control of low-efficiency and normal reactions. It avoids the problem of thermal runaway of fuel cell stacks caused by long-term continuous heating in the same area due to the inability of existing technologies to regulate low-temperature start-up temperature. This method enables efficient, safe, and rapid start-up of air-cooled fuel cell systems in low-temperature environments, while also taking into account the requirements for control flexibility and integration. It is especially suitable for the widespread application of air-cooled fuel cell systems in cold regions, avoiding the risk of start-up failure due to poor low-temperature performance of air-cooled fuel cell systems.

[0110] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0111] The embodiments described above are merely specific and detailed examples of the embodiments described in this application, and should not be construed as limiting the scope of the application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these modifications and improvements all fall within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the appended claims.

Claims

1. An air-cooled fuel cell system, comprising a fuel cell stack, said fuel cell stack including a plurality of alternately stacked bipolar plates and membrane electrode assemblies, characterized in that: The air-cooled fuel cell system further includes a bidirectional cooling fan, a main board, a first casing, a second casing, a first temperature sensor, and a second temperature sensor. The first and second casings are positioned opposite each other on either side of the fuel cell stack, and their arrangement is perpendicular to the stacking direction of the bipolar plates and membrane electrode assembly. The bidirectional cooling fan is connected to the second casing and, in forward rotation mode, drives air to flow sequentially through the first casing, the fuel cell stack, and the second casing; in reverse rotation mode, it drives air to flow sequentially through the second casing, the fuel cell stack, and the first casing. In both forward and reverse rotation modes, the fuel cell stack undergoes low-efficiency and normal reactions sequentially. The first temperature sensor is connected to the first casing and is used to detect the temperature inside the first casing as the inlet or outlet temperature of the fuel cell stack. The second temperature sensor is connected to the second casing and is used to detect the temperature inside the second casing as the outlet or inlet temperature of the fuel cell stack. The bidirectional cooling fan, the first temperature sensor, and the second temperature sensor are all electrically connected to the main board.

2. The air-cooled fuel cell system as described in claim 1, characterized in that: The first cover, the second cover, and the bidirectional cooling fan are arranged coaxially.

3. A low-temperature start-up control method for an air-cooled fuel cell system, based on the air-cooled fuel cell system of claim 1 or 2, characterized in that: The process includes the following steps: S1. Determine if the inlet temperature of the fuel cell stack is lower than the low-temperature start-up threshold. If yes, proceed to step S2; otherwise, proceed with the normal start-up process, i.e., maintain sufficient air supply and heat the fuel cell stack to the normal operating temperature to complete the start-up of the fuel cell stack; S2. Start the bidirectional cooling fan to perform the low-efficiency response in forward rotation mode; S3. After a first preset time, determine if the outlet temperature of the fuel cell stack detected by the second temperature sensor is higher than the over-temperature threshold. If yes, the bidirectional cooling fan performs the normal response in forward rotation mode; otherwise, repeat step S3; S4. After a second preset time, determine if the outlet temperature of the fuel cell stack detected by the second temperature sensor is higher than the low-temperature threshold. If the temperature is below the first low temperature threshold, the bidirectional cooling fan performs an inefficient response in reverse mode; otherwise, step S4 is repeated. S5: After a third preset time, it is determined whether the outlet temperature of the fuel cell stack detected by the first temperature sensor is higher than the over-temperature threshold. If so, the bidirectional cooling fan performs a normal response in reverse mode; otherwise, step S5 is repeated. S6: After a fourth preset time, it is determined whether the outlet temperature of the fuel cell stack detected by the first temperature sensor is lower than the second low temperature threshold. If not, step S6 is repeated; if so, step S2 is returned until the outlet temperature of the fuel cell stack reaches the third low temperature threshold, at which point the normal startup process is executed, completing the startup of the fuel cell stack.

4. The low-temperature start-up control method for an air-cooled fuel cell system as described in claim 3, characterized in that: The target airflow rate required for the normal reaction is between the overheating boundary of the airflow rate corresponding to the highest voltage cell and the undercooling boundary of the airflow rate corresponding to the lowest voltage cell in the fuel cell stack during the low-efficiency reaction.

5. The low-temperature start-up control method for an air-cooled fuel cell system as described in claim 4, characterized in that: The airflow overheating boundary is calculated as follows: different average current densities of the fuel cell stack are set, and the in-plane current density distribution of the membrane electrode under low efficiency reaction is obtained by using the current density partitioning characterization method; the in-plane current density distribution of each part is input into the fluid simulation software to obtain the highest operating temperature in all partitions of the membrane electrode under different airflow rates, forming a relationship table between airflow rate and highest operating temperature. Based on the highest withstand temperature of the membrane electrode, the airflow rate at the current average current density is found in the relationship table between airflow rate and maximum operating temperature as the corresponding target airflow rate. The target airflow rates at different average current densities are fitted to form the airflow overheat boundary; the airflow undercool boundary... The calculation is as follows: ;in, This represents the heat output of a single cell in a fuel cell stack. This refers to the inlet temperature of the fuel cell stack. This represents the outlet temperature threshold of the fuel cell stack. Specific heat capacity.

6. The low-temperature start-up control method for an air-cooled fuel cell system as described in claim 5, characterized in that: The heat generation power of a single cell in the fuel cell stack The calculation is as follows: ;in, This represents the average voltage of a single cell in the fuel cell stack. This represents the current in the fuel cell stack.

7. The low-temperature start-up control method for an air-cooled fuel cell system as described in claim 3, characterized in that: The airflow required by the fuel cell stack during low-efficiency reactions The calculation is as follows: In the formula, The stoichiometric ratio of air on the cathode side. The current of the fuel cell stack, This represents the number of electrons transferred per mol of reactants. is Faraday's constant.

8. The low-temperature start-up control method for an air-cooled fuel cell system as described in claim 3, characterized in that: The inefficient response is defined as reducing the cathode-side air stoichiometry of the fuel cell stack to less than or equal to 1, and the PWM duty cycle of the bidirectional cooling fan under the inefficient response is P1; the normal response is defined as the cathode-side air stoichiometry of the fuel cell stack being equal to the cathode-side air stoichiometry when the fuel cell stack outlet temperature is at the normal operating temperature, and the PWM duty cycle of the bidirectional cooling fan under the normal response is P2, satisfying P2 > P1; the low-temperature start-up threshold, the first low-temperature threshold, the second low-temperature threshold, the third low-temperature threshold, and the normal operating temperature increase sequentially, and the low-temperature start-up threshold... The normal operating temperature is -5℃ to 0℃, and the over-temperature threshold temperature is 60℃ to 80℃. ， This is the highest temperature that the membrane electrode can withstand.

9. The low-temperature start-up control method for an air-cooled fuel cell system as described in claim 4, characterized in that: The target airflow required for the normal reaction is the midpoint value of the line connecting the points taken on the airflow overheat boundary and the airflow undercool boundary at the corresponding average current density.

10. The low-temperature start-up control method for an air-cooled fuel cell system as described in claim 9, characterized in that: The PWM duty cycle of the bidirectional cooling fan is obtained as follows: the outlet temperature of the fuel cell stack is obtained at the target airflow rate; the flow resistance of the bidirectional cooling fan is obtained based on the air pressure-airflow curve of the bidirectional cooling fan and the outlet temperature of the fuel cell stack, which is equivalent to the flow resistance of the fuel cell stack; and the PWM duty cycle of the bidirectional cooling fan is obtained based on the target airflow rate and the flow resistance of the fuel cell stack.

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