Cathode closed air-cooled fuel cell system and low-temperature starting method thereof

Abstract

The application provides a cathode closed air-cooled fuel cell system and a low-temperature starting method thereof, and can realize reliable low-temperature starting, improve the adaptability of the electric pile to a low-temperature environment and prolong the service life of the electric pile, and comprises the following steps: when it is monitored that the temperature of the electric pile is lower than a low-temperature first threshold value, a cooling path heater and an air path heater are started, the rotating speed of a cooling path fan and the rotating speed of a blower are cooperatively controlled, the difference between the temperature at the outlet of the cooling air and the temperature at the outlet of the air path is maintained in a preset interval; when it is monitored that the temperature of the electric pile reaches the low-temperature first threshold value, a load current is applied, and the load current increases with time at a preset slope; when it is monitored that the temperature of the electric pile reaches a preset second low-temperature threshold value, the load current is continuously increased to a target current, and then the rotating speed of the cooling path fan is cooperatively adjusted according to the deviation between the monitored temperature of the electric pile and a gradient target temperature and the change trend of the temperature of the electric pile until the temperature of the electric pile rises to be close to the optimal operating temperature of the electric pile.

Description

Technical Field

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

[0002] Proton exchange membrane fuel cells (PEMFCs) are crucial devices for directly converting hydrogen energy into electrical energy. Air-cooled PEMFCs, in particular, have broad application prospects in portable power supplies, drones, and backup power due to their simple structure, compact system, and lack of complex liquid hydrothermal management systems. Closed-cathode air-cooled stacks, because their cathodes are not in direct contact with the environment and air supply and heat dissipation are separate, offer advantages in environmental adaptability, durability, and lifespan compared to open-cathode air-cooled stacks. However, their low-temperature startup therefore requires more refined strategies. Currently, the main strategies for low-temperature startup of fuel cell systems include: a. Thermal insulation and heat preservation methods: High-performance thermal insulation materials such as polystyrene are used to insulate and preserve the fuel cell stack or system. The use of thermal insulation and heat preservation measures for the fuel cell stack not only increases the complexity of the system structure, but also puts forward higher requirements for the system's high-temperature heat dissipation. Furthermore, thermal insulation and heat preservation are the main auxiliary means and cannot actively raise the temperature. The heat dissipation medium of the air-cooled fuel cell stack is air, which has limited heat dissipation capacity. This method affects the high-temperature heat dissipation capacity, and the fuel cell stack is sensitive to high temperature, which can easily lead to system overheating, derating, or even shutdown. b. Active heating method: The heating element is in direct contact with the membrane electrode, and the temperature is rapidly increased by directly heating the membrane electrode. The active heating method has high requirements for the assembly of the heating element and the membrane electrode. Poor contact can easily cause uneven heating. Moreover, the membrane electrode is in contact with the high-temperature heating element and cold air at the same time, which creates a huge temperature difference and accelerates the aging of the fuel cell stack. Furthermore, the start and stop of the heating element causes the fuel cell stack to experience drastic temperature and operating condition changes, which is not conducive to its lifespan. c. Self-heating method of fuel cell stack: By controlling the fuel cell stack to operate at a low voltage (single cell voltage < 0.5V), more chemical energy is converted into heat energy, thereby heating the fuel cell stack; however, the self-heating method of fuel cell stack can lead to uneven temperature distribution inside the fuel cell stack. At low temperatures, the water produced by the reaction will freeze, blocking the catalyst pores and gas diffusion layer, hindering the transport of reactant gases, resulting in start-up failure. Moreover, the mechanical damage of ice crystals to the catalyst layer severely accelerates the aging of the fuel cell stack. Summary of the Invention

[0003] The purpose of this invention is to overcome the shortcomings of the prior art and provide a cathode closed-loop air-cooled fuel cell system and its low-temperature start-up method. By performing multi-stage coordinated control of the heaters, fans, blowers and stack loads of the air and cooling circuits, reliable low-temperature start-up is achieved. At the same time, the thermal shock and internal temperature difference during the start-up process are reduced, the low-temperature environmental adaptability of the stack is improved and its service life is extended.

[0004] To achieve the above objectives, the technical solution adopted by the present invention is: a cathode closed-loop air-cooled fuel cell system, comprising a fuel cell stack, characterized in that it further comprises: The cooling unit includes a cooling path heater and a cooling path fan located on both sides of the fuel cell stack. The cooling path fan draws air so that the air in the cooling path passes sequentially through the cooling path heater, the fuel cell stack, and the cooling path fan. A heating unit, comprising a blower and an air path heater sequentially connected to the air path of the fuel cell stack, wherein the blower draws air so that the air for heating the fuel cell stack passes sequentially through the air path heater, the blower, and the fuel cell stack; The monitoring unit includes temperature sensors, which are respectively disposed on the fuel cell stack, the cooling unit, and the heating unit.

[0005] Furthermore, the monitoring unit includes; The first temperature sensor is installed at the air inlet of the blower to monitor the temperature at the air inlet of the blower. The second temperature sensor is installed at the air outlet of the blower to monitor the temperature at the air outlet of the blower. The third temperature sensor is installed at the air outlet of the fuel cell stack to monitor the temperature at the air outlet of the fuel cell stack. A fourth temperature sensor is installed on the fuel cell stack to monitor the stack temperature. The fifth temperature sensor is located at the cooling air outlet of the fuel cell stack and is used to monitor the temperature at the cooling air outlet of the fuel cell stack.

[0006] A method for low-temperature start-up of a cathode closed-loop air-cooled fuel cell system, characterized by comprising the following steps: Monitor the fuel cell stack temperature. When the fuel cell stack temperature is detected to be lower than the first low temperature threshold, start the cooling circuit heater and the air circuit heater, and coordinately control the speed of the cooling circuit fan and the blower to keep the temperature difference between the cooling air outlet and the air circuit outlet within a preset range. Once the temperature of the fuel cell stack reaches the first low-temperature threshold, a load current is applied to the fuel cell stack via a DC / DC controller. The load current increases over time at a preset slope, wherein the slope is dynamically adjusted according to the current temperature of the fuel cell stack. Once the stack temperature is detected to have reached the preset second low temperature threshold, the load current is increased to the target current. Then, the speed of the cooling fan is adjusted in coordination with the deviation between the monitored stack temperature and the gradient target temperature, as well as the trend of stack temperature change, to control the stack temperature rise rate until the stack temperature rises to near the optimal operating temperature of the stack.

[0007] Furthermore, the coordinated control of the cooling circuit fan speed and blower speed is specifically performed as follows: Adjust the speed of the cooling circuit fan to stabilize the outlet temperature of the cooling circuit within the first preset temperature range; The blower initially runs at its minimum speed. Once the temperature at the blower's air inlet reaches the threshold, the blower's speed is adjusted. Under the premise of ensuring that the temperature at the blower's air outlet does not exceed its safety threshold, the temperature difference between the air outlet and the cooling air outlet is maintained within a preset temperature difference range.

[0008] Furthermore, the dynamic adjustment method for the slope of the load current is as follows: the lower the current temperature of the fuel cell stack, the smaller the slope of the load current.

[0009] Furthermore, when the stack temperature is detected to reach the first low temperature threshold, hydrogen is supplied with periodic pulses to promote membrane electrode activation. When the open circuit voltage of the stack reaches the preset voltage threshold, the load current is applied. If the voltage drop rate of the fuel cell stack exceeds a preset rate threshold during the application of load current, the increase of load current is reduced or paused; when the fuel cell stack voltage reaches a preset target value, the increase of load current is stopped.

[0010] Furthermore, after the fuel cell stack temperature reaches the preset second low-temperature threshold, the speed of the cooling fan is adjusted using the following formula: Where D is the actual opening degree of the cooling fan, Dmax is the maximum opening degree of the cooling fan, Ttag is the target gradient temperature of the fuel cell stack, Tlow2 is the second low temperature threshold, and K is the cooling fan adjustment coefficient.

[0011] Furthermore, when the stack temperature is less than Ttag and the stack temperature shows an upward trend, K remains unchanged; when the stack temperature remains unchanged or shows a downward trend, K is adjusted to decrease until the stack temperature shows an upward trend and K is stopped from being adjusted. When the stack temperature is greater than Ttag and shows an upward trend, adjust K to increase it until the stack temperature remains constant or shows a downward trend, then stop adjusting K; adjust Ttag to approach the optimal operating temperature of the stack.

[0012] Furthermore, after monitoring that the stack temperature has reached the preset second low temperature threshold, the blower speed is increased according to the preset calibration relationship while increasing the load current.

[0013] Furthermore, after monitoring that the stack temperature has reached a preset second low temperature threshold, the air circuit heater is turned off when the load current reaches the target current value.

[0014] Furthermore, when the stack temperature rises to near the optimal operating temperature of the stack, it enters conventional steady-state regulation and control.

[0015] Compared with the prior art, the present invention has the following significant advantages: This invention employs a multi-stage startup strategy. In the low-temperature preheating stage, the cooling path and air path are heated simultaneously. The temperature difference between the outlets of the cooling path and air path is used as the control target. By coordinating the control of the speed of the cooling path fan and the speed of the blower, the internal and external temperature difference of the fuel cell stack is maintained within a reasonable range. This ensures that heat is simultaneously and evenly input from the reaction channel and heat dissipation channel of the fuel cell stack, minimizing the internal temperature difference during the preheating stage and protecting the fuel cell stack structure. During the low-temperature start-up phase, this invention links the slope of the applied load current to the real-time temperature of the fuel cell stack. By coordinating and controlling the heating power of the air path, the heating power of the cooling path, and the load-bearing rate of the fuel cell stack, the heating rate of the fuel cell stack is precisely controlled, achieving self-heating control where the heating is gentler at lower temperatures. This ensures that the heat generation rate is always within a safe range, avoiding damage to the catalyst layer of the fuel cell stack. During the gradient heating stage, this invention employs a composite control strategy that controls the deviation between the stack temperature and the gradient target temperature, as well as the trend of stack temperature change. This strategy enables the stack temperature to rise strictly according to a preset smooth curve, avoiding temperature abrupt changes and overshoot, and achieving a stable transition from low-temperature startup to steady-state operation. This improves the low-temperature adaptability of the cathode closed-circuit air-cooled stack system and extends the stack life. Attached Figure Description

[0016] Figure 1 This is a schematic block diagram of relevant modules of a cathode closed air-cooled fuel cell stack system in one embodiment of the present invention; Figure 2 This is a flowchart of a low-temperature start-up method for a cathode closed-loop air-cooled fuel cell system according to an embodiment of the present invention. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0018] like Figure 1 As shown, the cathode closed-circuit air-cooled fuel cell system on which the implementation in the embodiment depends includes at least the following core modules related to cryogenic start-up control: cathode closed-circuit air-cooled stack, cooling unit, heating unit, and monitoring unit.

[0019] The cooling unit includes cooling path heaters 2 and cooling path fans 3 located on both sides of the fuel cell stack 1. The cooling path fans 3 draw air, causing the air in the cooling path to pass sequentially through the cooling path heaters 2, the fuel cell stack 1, and the cooling path fans 3. In this embodiment, the cooling path fans 3 are arranged downstream of the cooling path using a suction method. The suction of the cooling path fans 3 will create a negative pressure zone in the heat dissipation channel inside the fuel cell stack. The external atmospheric pressure will drive the air to flow in evenly from the entire inlet section, ensuring that the airflow distribution of each heat dissipation channel is uniform, thereby achieving uniform heat dissipation or preheating. This avoids the problem of uneven flow caused by the tendency of gas to take the path of least resistance in traditional blowing type. In this embodiment, the cooling path fans 3 adopt a suction mode, which helps to distribute the cooling air evenly inside the fuel cell stack.

[0020] The heating unit includes a blower 4 and an air heater 5 connected sequentially to the air path of the fuel cell stack 1. The blower 4 draws air, causing the air for heating the fuel cell stack 1 to pass sequentially through the air heater 5, the blower 4, and the fuel cell stack 1. The air heater 5 is a PTC heater. When cold air flows through the PTC heater, the temperature difference is large, the heat exchange efficiency is high, and the PTC can generate heat at a higher power. At the same time, the temperature of the heated air can be monitored by a temperature sensor located at the inlet of the blower to prevent excessively hot air from being drawn in and damaging the blower.

[0021] The monitoring unit includes temperature sensors, which are respectively installed on the fuel cell stack, the cooling unit, and the heating unit. In this embodiment, the monitoring unit includes: The first temperature sensor T1 is installed at the air inlet of the blower to monitor the temperature at the air inlet of the blower. The second temperature sensor T2 is installed at the air outlet of the blower to monitor the temperature at the air outlet of the blower. The third temperature sensor T3 is located at the air outlet of the fuel cell stack and is used to monitor the temperature at the air outlet of the fuel cell stack. The fourth temperature sensor, T4, is installed on the fuel cell stack and is used to monitor the stack temperature. The fifth temperature sensor, T5, is located at the cooling air outlet of the fuel cell stack and is used to monitor the temperature at the cooling air outlet of the fuel cell stack.

[0022] In addition, the cathode closed-circuit air-cooled fuel cell system also includes a DC / DC controller for controlling the stack output power.

[0023] The embodiment provides a low-temperature start-up method for a cathode closed-loop air-cooled fuel cell system, including the following steps: Low temperature preheating stage: Monitor the stack temperature. When the stack temperature is found to be lower than the first low temperature threshold, start the cooling circuit heater and air circuit heater, and coordinate the control of the cooling circuit fan speed and blower speed to keep the temperature difference between the cooling air outlet and the air circuit outlet within the preset range. Low-temperature startup phase: When the stack temperature is detected to have reached the first low-temperature threshold, a load current is applied to the stack through the DC / DC controller. The load current increases over time at a preset slope. The slope is dynamically adjusted according to the current temperature of the stack. Gradient heating phase: After the stack temperature is detected to have reached the preset second low temperature threshold, the load current is increased to the target current. Then, the speed of the cooling fan is adjusted in coordination with the deviation between the stack temperature and the gradient target temperature and the trend of stack temperature change to control the stack heating rate until the stack temperature rises to close to the optimal operating temperature of the stack.

[0024] In this embodiment, the low-temperature preheating stage is specifically performed as follows: Step S11: When the temperature of the fourth temperature sensor T4 is detected to be lower than the first low temperature threshold, the low temperature preheating stage is entered. Step S12: Start the cooling circuit heater to heat the air, start the cooling circuit fan, and direct the airflow in the cooling circuit as follows. Figure 1 As shown, the cooling fan speed is adjusted so that the temperature at the cooling air outlet of the fifth temperature sensor T5 is within the first preset temperature range. Step S13: Simultaneously start the air circuit heater, and run the blower at the minimum speed. When the temperature at the air inlet of the blower of the first temperature sensor T1 reaches the threshold, adjust the blower speed so that the temperature at the air outlet of the blower of the second temperature sensor T2 does not exceed the safety threshold. Then, ensure that the temperature difference between the air outlet of the fuel cell stack of the third temperature sensor T3 and the cooling air outlet of the fuel cell stack of the fifth temperature sensor T5 is within the preset range, thereby achieving uniform preheating. Step S14: Monitor the stack temperature of the fourth temperature sensor T4 in real time. When the monitored temperature of the fourth temperature sensor T4 reaches the first threshold for low-temperature start-up, it is determined that the preheating is completed and the low-temperature start-up stage begins.

[0025] In this embodiment, the temperature difference between the cooling air outlet and the air path outlet is taken as the core control target. By simultaneously preheating the air path and cooling heat dissipation path of the fuel cell reactor and actively controlling the temperature difference between them, the problem of excessive internal temperature difference of the fuel cell reactor caused by traditional heating methods is avoided from the source, and the fuel cell reactor structure is effectively protected.

[0026] In this embodiment, during the low-temperature startup phase, the following steps are performed: Step S21: Supply hydrogen gas with periodic pulses to promote membrane electrode activation; Step S22: When the open-circuit voltage of the fuel cell stack reaches the threshold, the DC controller applies a load current that gradually increases from small to large. The initial current is very small, and the slope is adjusted according to the temperature of the fuel cell stack temperature sensor T4. The dynamic adjustment method of the load current slope is: the lower the current temperature of the fuel cell stack, the smaller the slope of the load current. As the output current of the fuel cell stack increases, the voltage of the fuel cell stack decreases. When the voltage of the fuel cell stack reaches the preset target value, the current increase is stopped. If the voltage drops too quickly and the voltage drop rate of the fuel cell stack exceeds the preset rate threshold, the increase of the load current is immediately reduced or suspended. Step S23: Monitor the fourth temperature sensor T4 in real time. When the temperature of the fourth temperature sensor T4 reaches the second threshold for low-temperature start-up, it is determined that the low-temperature start-up is complete and enters the gradient temperature rise stage.

[0027] The root cause of the failure of existing self-heating technologies lies in the fact that the heat generation rate exceeds the heat transfer rate, leading to localized water accumulation and freezing. In this embodiment, the load current rise slope is dynamically adjusted according to the current temperature of the fuel cell stack, achieving adaptive self-heating control. This ensures that the heat generation rate matches the fuel cell stack's capacity. When the fuel cell stack temperature is low, its internal heat transfer capacity is poor. At this time, the system applies a very small slope, making the heat generation rate extremely gentle. This ensures that the generated water has enough time to be carried away by the airflow or evaporated by the slowly conducted heat, thereby avoiding freezing. As the temperature rises, the heat transfer capacity increases, and the fuel cell stack correspondingly increases the loading rate. This solves the freezing problem of the fuel cell stack during the self-heating process and avoids fatal mechanical damage to the fuel cell stack's catalyst layer.

[0028] In this embodiment, the gradient heating stage is specifically executed as follows: Step S31: Continue to increase the load current in a smooth ramp manner until the target current is reached. While increasing the fuel cell load current, increase the blower speed. The relationship between the fuel cell load current and the blower speed can be obtained from calibration. Step S32: After the load reaches the target current, turn off the air circuit heater. At this time, the temperature rise of the compressed air from the blower can ensure that the feed temperature is within the normal range. Step S33: After the fuel cell stack temperature reaches the preset second low temperature threshold, the speed of the cooling fan is adjusted using the following formula: Where D is the actual opening degree of the cooling fan, Dmax is the maximum opening degree of the cooling fan, Ttag is the target gradient temperature of the fuel cell stack, Tlow2 is the second low temperature threshold, and K is the cooling fan adjustment coefficient. The actual opening degree D of the cooling fan, calculated by the formula, can be converted into a PWM duty cycle signal, which can be used to adjust the speed of the cooling fan. When the stack temperature is lower than the stack's gradient target temperature Ttag and the stack temperature shows an upward trend, K remains unchanged; when the fourth temperature sensor T4 detects that the stack temperature is unchanged or shows a downward trend, K is adjusted to decrease until the stack temperature shows an upward trend and K is stopped being adjusted. When the stack temperature is greater than Ttag and shows an upward trend, adjust K to increase K until the stack temperature remains unchanged or shows a downward trend, then stop adjusting K; adjust the stack gradient target temperature Ttag to approach the stack's optimal operating temperature. The execution of step S33 ensures that the stack temperature detected by T4 rises smoothly along the preset ideal gradient curve, avoiding temperature shocks.

[0029] In this embodiment, the K coefficient is adjusted based on the temperature change trend to achieve feedforward control. When T4 <Ttag And when the temperature rises in a good direction, K remains unchanged; when T4 <Ttag However, if the temperature stagnates or drops, it indicates excessive cooling. In this case, reduce K to decrease the fan speed and reduce heat dissipation; when T4 >Ttag If the temperature is still rising, it indicates a risk of overshoot. Therefore, K is increased to raise the fan speed and enhance heat dissipation. By adjusting the K coefficient, the fuel cell stack can actively manage the temperature rise rate, ensuring the stack temperature monitored by T4 is maintained. It precisely approaches the optimal operating temperature along an ideal, smooth curve.

[0030] Step S34: When the fourth temperature sensor T4 detects that the stack temperature has risen to near the optimal operating temperature of the stack, it enters steady-state regulation control, which is implemented based on existing regulation methods.

[0031] The key parameters involved in the low-temperature start-up method in this embodiment can be set as follows: First threshold for low temperature: 0℃~3℃; Second low temperature threshold: 20℃~30℃; The first preset temperature range for the cooling circuit outlet temperature is 20℃~70℃; Temperature threshold at the blower inlet: 20℃~50℃; The safe temperature threshold at the blower outlet is 30℃~70℃; Target temperature gradient (Ttag) for fuel cell stack: 50℃~70℃ Preset threshold for open-circuit voltage of fuel cell stack: 0.85 V ~ 0.9 V (single cell voltage); Preset threshold for the rate of voltage drop of the fuel cell stack: 0.55 V ~ 0.65 V (single cell voltage); Preset target voltage for fuel cell stack: 0.6 V ~ 0.72 V (single cell voltage); The preset temperature difference range between the cooling air outlet and the air path outlet is 0℃~10℃; In a specific embodiment of the present invention, the key parameter settings involved in the low-temperature start-up method are as follows: The first threshold for low temperature is 0°C; The second threshold for low temperature is 20°C; The final target temperature for the gradient is 70°C. The temperature threshold at the blower inlet is 10°C; The safety threshold at the blower outlet is 65°C; The first preset temperature range for the cooling path outlet is 25°C ~ 35°C; The preset temperature difference range between the air path and the cooling path outlet is ±5°C; It should be noted that the above values ​​are merely examples, and those skilled in the art can adapt and adjust the above parameters through limited conventional experiments based on the specific fuel cell stack model, power rating, and application environment.

[0032] Existing control strategies are crude and cannot accurately track the ideal temperature rise curve. In this embodiment, during the gradient temperature rise stage, while controlling the speed of the cooling fan, the deviation between the current temperature and the target, as well as the temperature change trend, are monitored. When the system predicts that the temperature is about to deviate from the target, it will intervene in advance by adjusting the K value, so that the stack temperature can be guided to the target operating point in an extremely smooth and stable manner, avoiding drastic temperature fluctuations and overshoot, as well as temperature shock damage.

[0033] In this embodiment, by designing targeted and synergistic control strategies for different stages of preheating, startup, and temperature rise, the startup problem of cathode closed air-cooled fuel cell stacks in low-temperature environments is effectively solved, achieving a fast and safe startup process. While ensuring startup performance, the reliability and durability of the fuel cell stack are greatly improved, and the application range of the fuel cell stack in extremely cold environments is broadened.

[0034] In an embodiment of the present invention, a computer-readable storage medium is also provided, on which a program is stored, which, when executed by a processor, implements the low-temperature start-up method of the cathode closed air-cooled fuel cell system as described above.

[0035] Those skilled in the art will understand that embodiments of the present invention can be provided as methods, computer-readable storage media, or computer program products. Therefore, embodiments of the present invention can take the form of entirely hardware embodiments, entirely software embodiments, or embodiments combining software and hardware aspects. Furthermore, embodiments of the present invention can take the form of computer program products implemented on one or more computer-readable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-readable program code.

[0036] The embodiments of the present invention are described with reference to flowchart illustrations and / or block diagrams of methods, computer apparatuses, or computer program products according to embodiments of the invention. These computer program instructions may be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing terminal device to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing terminal device, create means for implementing the functions specified in the flowchart illustrations and / or block diagrams.

[0037] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing terminal device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means that implement the functions specified in the flowchart.

[0038] In an embodiment of the present invention, a computer program product is also provided, including a computer program / instructions that, when executed by a processor, implement the steps of the above-described method.

[0039] In practical applications, the aforementioned computer program products include, but are not limited to: fuel cell systems, fuel cell stack systems, smartphones, desktop computers, laptops, tablets, host computers, and server platforms, etc., without specific limitations.

[0040] The foregoing has provided a detailed description of the cathode closed-loop air-cooled fuel cell system, the low-temperature start-up method for the cathode closed-loop air-cooled fuel cell system, the computer-readable storage medium, and the application of the computer program product provided by this invention. Specific examples have been used to illustrate the principles and implementation methods of this invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of this invention. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of this invention. Therefore, the content of this specification should not be construed as a limitation of this invention.

Claims

1. A low-temperature start-up method for a cathode-closed air-cooled fuel cell system, characterized in that, This is based on a cathode-closed air-cooled fuel cell system, which includes a fuel cell stack and also includes: The cooling unit includes cooling path heaters and cooling path fans located on both sides of the fuel cell stack. The cooling path fan draws air so that the air in the cooling path passes sequentially through the cooling path heater, the fuel cell stack, and the cooling path fan; A heating unit, comprising a blower and an air path heater sequentially connected to the air path of the fuel cell stack, wherein the blower draws air so that the air for heating the fuel cell stack passes sequentially through the air path heater, the blower, and the fuel cell stack; A monitoring unit, comprising a plurality of temperature sensors, wherein the temperature sensors are respectively disposed on the fuel cell stack, the cooling unit and the heating unit; The method includes the following steps: Low-temperature preheating stage: Monitor the stack temperature. When the stack temperature is found to be lower than the first low-temperature threshold, start the cooling circuit heater and the air circuit heater, and coordinately control the speed of the cooling circuit fan and the blower to keep the temperature difference between the cooling air outlet and the air circuit outlet within a preset range. Low-temperature startup phase: When the temperature of the fuel cell stack reaches the first low-temperature threshold, a load current is applied to the fuel cell stack through the DC / DC controller. The load current increases with time at a preset slope. The slope is dynamically adjusted according to the current temperature of the fuel cell stack. Gradient heating stage: When the stack temperature is detected to have reached the preset second low temperature threshold, the load current is increased to the target current. Then, the speed of the cooling fan is adjusted in coordination with the deviation between the stack temperature and the gradient target temperature and the trend of stack temperature change to control the heating rate of the stack until the stack temperature is close to the optimal operating temperature of the stack. After the fuel cell stack temperature reaches the preset second low temperature threshold, the speed of the cooling fan is adjusted using the following formula: D = K *(T4-Tlow2)*Dmax / (Ttag-Tlow2) Where D is the actual opening degree of the cooling fan, Dmax is the maximum opening degree of the cooling fan, Ttag is the target gradient temperature of the fuel cell stack, Tlow2 is the second low temperature threshold, K is the cooling fan adjustment coefficient, and T4 is the fuel cell stack temperature detected by the sensor. The actual opening degree D of the cooling fan is converted into a PWM duty cycle signal, which is used to adjust the speed of the cooling fan.

2. The low-temperature start-up method for a cathode closed-loop air-cooled fuel cell system according to claim 1, characterized in that, The monitoring unit includes: The first temperature sensor is installed at the air inlet of the blower to monitor the temperature at the air inlet of the blower. The second temperature sensor is installed at the air outlet of the blower to monitor the temperature at the air outlet of the blower. The third temperature sensor is installed at the air outlet of the fuel cell stack to monitor the temperature at the air outlet of the fuel cell stack. A fourth temperature sensor is installed on the fuel cell stack to monitor the stack temperature. The fifth temperature sensor is located at the cooling air outlet of the fuel cell stack and is used to monitor the temperature at the cooling air outlet of the fuel cell stack.

3. The low-temperature start-up method for a cathode closed-loop air-cooled fuel cell system according to claim 1, characterized in that: The coordinated control of the cooling circuit fan speed and blower speed is specifically executed as follows: Adjust the speed of the cooling circuit fan to stabilize the outlet temperature of the cooling circuit within the first preset temperature range; The blower initially runs at its minimum speed. Once the temperature at the blower's air inlet reaches the threshold, the blower's speed is adjusted. Under the premise of ensuring that the temperature at the blower's air outlet does not exceed its safety threshold, the temperature difference between the air outlet and the cooling air outlet is maintained within a preset temperature difference range.

4. The low-temperature start-up method for a cathode closed-loop air-cooled fuel cell system according to claim 1, characterized in that: The dynamic adjustment method for the slope of the load current is as follows: the lower the current temperature of the fuel cell stack, the smaller the slope of the load current.

5. The low-temperature start-up method for a cathode closed-loop air-cooled fuel cell system according to claim 1, characterized in that: Once the stack temperature is detected to have reached the first low-temperature threshold, hydrogen is supplied periodically in pulses to promote membrane electrode activation. When the open-circuit voltage of the stack reaches the preset voltage threshold, the load current is applied.

6. The low-temperature start-up method for a cathode closed-loop air-cooled fuel cell system according to claim 1, characterized in that: If the voltage drop rate of the fuel cell stack exceeds a preset rate threshold during the application of load current, the increase of load current is reduced or paused; when the fuel cell stack voltage reaches a preset target value, the increase of load current is stopped.

7. The low-temperature start-up method for a cathode closed-loop air-cooled fuel cell system according to claim 1, characterized in that: When the fuel cell stack temperature is less than Ttag and the fuel cell stack temperature shows an upward trend, the cooling fan adjustment coefficient K remains unchanged; when the fuel cell stack temperature remains unchanged or shows a downward trend, K is adjusted to decrease until the fuel cell stack temperature shows an upward trend and K is stopped from being adjusted. When the stack temperature is greater than Ttag and shows an upward trend, adjust K to increase it until the stack temperature remains constant or shows a downward trend, then stop adjusting K; adjust Ttag to approach the optimal operating temperature of the stack.

8. The low-temperature start-up method for a cathode closed-loop air-cooled fuel cell system according to claim 1, characterized in that: After the stack temperature is detected to have reached the preset second low temperature threshold, the blower speed is increased according to the preset calibration relationship while the load current is increased.

9. The low-temperature start-up method for a cathode closed-loop air-cooled fuel cell system according to claim 1, characterized in that: After the stack temperature is detected to have reached the preset second low temperature threshold, the air circuit heater is turned off when the load current reaches the target current value.

10. A low-temperature start-up method for a cathode-closed air-cooled fuel cell system according to claim 1, characterized in that: When the fuel cell stack temperature rises to near the optimal operating temperature of the fuel cell stack, it enters steady-state regulation and control.

11. A computer-readable storage medium having a program stored thereon, characterized in that: When the program is executed by the processor, it implements the low-temperature start-up method for the cathode closed-loop air-cooled fuel cell system as described in claim 1.

12. A computer program product comprising a computer program / instructions, characterized in that, When the computer program / instructions are executed by the processor, they implement the steps of the method of claim 1.

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