A fuel cell cold start auxiliary heating system and method

Abstract

This invention discloses a fuel cell cold start auxiliary heating system and method, belonging to the field of fuel cell technology. The system includes a fuel cell stack composed of multiple unit cells connected in series, multiple thin-film resistance thermometers (RTDs) embedded inside the bipolar plates, and a control unit. The RTDs can be switched to preheating, temperature measurement, or off modes, achieving integrated heating and temperature measurement. The control unit executes a phased strategy: during the preheating stage before cold start, differentiated currents are applied to different areas to create a gradient temperature distribution in the stack, with lower power in the middle and higher at both ends, compensating for heat dissipation from the end plates; during preheating, some RTDs are intermittently switched for temperature measurement, dynamically adjusting the power; after reaching the target temperature, heating is turned off, and cold start is initiated. This invention separates heating from the electrochemical reaction, avoiding interference and reducing control complexity; gradient preheating achieves uniform temperature rise; reusing components simplifies the structure, improving reliability and energy efficiency. It is suitable for cold start of automotive fuel cell stacks in extremely cold environments.

Description

Technical Field

[0001] This invention relates to the field of fuel cell technology, and more specifically, to a fuel cell cold start auxiliary heating system and method. Background Technology

[0002] A proton exchange membrane fuel cell is a power generation device that directly converts the chemical energy present in fuel gas into electrical energy through an electrochemical reaction. It has the advantages of low noise, high efficiency and no pollution. With the advancement of technology and the expansion of application fields, there is a need to develop high-power fuel cell stacks with more cells.

[0003] The cold start problem of fuel cells in low-temperature environments, especially below 0°C, has always been a key technical bottleneck restricting their widespread application. When the ambient temperature is below the freezing point, the water generated inside the fuel cell stack will freeze, blocking the pores of the catalyst layer and the channels of the gas diffusion layer, hindering the transport of reactant gases, and in severe cases, causing irreversible damage to the membrane electrode assembly.

[0004] In existing technologies, the main methods for solving the cold start problem of fuel cells include external heating and internal heating. External heating has a long heat conduction path, slow response speed, and high energy consumption; while internal heating has high heating efficiency, it has the risk of local overheating and is difficult to achieve precise temperature control.

[0005] Existing heating schemes generally adopt a strategy of simultaneous heating and start-up, that is, heating and electrochemical reaction are carried out simultaneously during cold start. This strategy has the following problems: First, the heating current and the electrochemical reaction current are superimposed, which increases the complexity of the control system; second, the heating process and the electrochemical reaction process interfere with each other, making it difficult to accurately control the stack temperature; third, the separation of the heating element and the temperature sensor increases the complexity and cost of the stack structure.

[0006] Furthermore, existing heating schemes generally employ a uniform heating strategy, applying the same heating power to all regions of the fuel cell stack. However, in actual fuel cell stacks, due to the heat dissipation effect of the end plates, the heat loss at both ends is significantly greater than that in the middle region. Uniform heating leads to an uneven temperature distribution where the temperature at both ends is lower and the temperature in the middle is higher. This not only fails to effectively improve cold start performance but may also exacerbate uneven thermal stress distribution, affecting the stack's lifespan.

[0007] The existing patent with publication number CN112983460A provides a fuel cell stack with a differentiated cathode flow field configuration. By using a cathode flow field structure with greater flow resistance near the manifold inlet, the flow resistance of the cathode gas flow field is gradually changed to ensure uniform distribution of gas flow. However, it does not involve technical solutions related to cold start of fuel cell stacks.

[0008] Therefore, developing a fuel cell cold start auxiliary heating system and method that can embed heating elements inside the bipolar plate, integrate heating and temperature measurement functions, adopt a phased control strategy of preheating before cold start and then shutting off heating before restarting, and compensate for heat loss at both ends of the stack, has significant technical value. Summary of the Invention

[0009] In view of the problems existing in the prior art, the present invention provides a fuel cell cold start auxiliary heating system and method, which aims to solve the technical problems in the prior art, such as complex control caused by heating and starting at the same time, mutual interference between heating and electrochemical reaction, separation of heating and temperature measuring elements, and the inability of uniform heating strategy to compensate for heat loss at both ends of the stack.

[0010] To solve the above-mentioned technical problems, the technical solution of the present invention is: a fuel cell cold start auxiliary heating system, comprising a fuel cell stack, multiple thin-film thermistors, and a control unit. The fuel cell stack is composed of multiple unit cells connected in series, and each unit cell is formed by stacking bipolar plates and membrane electrode assemblies. The multiple thin-film thermistors are respectively embedded inside the bipolar plates of each unit cell, and each thin-film thermistor is configured to selectively operate in a preheating mode, a temperature measurement mode, or a shutdown mode. The control unit is electrically connected to the multiple thin-film thermistors. During the preheating phase: the control unit applies differentiated heating currents to the thin-film RTDs in each region, causing the internal temperature of the fuel cell stack to exhibit a preset gradient distribution, wherein the power is low in the middle region and high at both ends along the stacking direction; during the preheating process: some thin-film RTDs are intermittently switched to temperature measurement mode to acquire the real-time temperature of each region and dynamically adjust the gradient power distribution; after preheating is completed: all thin-film RTDs are switched to off mode to stop heating; during the cold start process: some thin-film RTDs are switched to temperature measurement mode to monitor changes in the stack temperature.

[0011] Furthermore, multiple thin-film thermal resistors are arranged in an array along the stacking direction of the battery pack, and at least one thin-film thermal resistor is embedded in the bipolar plate of each cell.

[0012] Furthermore, the thin-film thermal resistor is embedded inside the plate body between the cathode gas flow field and the cooling liquid flow field of the bipolar plate, and is isolated from the reaction gas flow channel and the cooling liquid flow channel by the bipolar plate material.

[0013] Furthermore, the material of the thin-film resistance thermometer is platinum resistance thermometer, with a resistance temperature coefficient greater than 0.003 / ℃. The thin-film resistance thermometer is distributed in a serpentine pattern in the active area of ​​the bipolar plate, covering an area of ​​80% of the active area of ​​the bipolar plate.

[0014] On the other hand, the present invention provides a fuel cell cold start auxiliary heating method based on the above-mentioned fuel cell cold start auxiliary heating system, comprising the following steps: Before the fuel cell cold start, the stack is preheated by multiple thin-film thermal resistors embedded in the bipolar plates. During the preheating process, the control unit applies differentiated heating current to the thin-film thermal resistors in each region according to a preset gradient power distribution strategy. The gradient power distribution strategy is that the heating power is low in the middle region and high in the two end regions along the stacking direction. During the preheating process, some thin-film thermal resistors are intermittently switched to temperature measurement mode to obtain the real-time temperature of each area, and the heating power of each area is dynamically adjusted according to the real-time temperature feedback. Once the stack temperature reaches the preset preheating target temperature, all thin-film RTDs are switched to the off mode to stop heating. Start the fuel cell for a cold start; During the cold start process, some thin-film RTDs are switched to temperature measurement mode to monitor the temperature change of the fuel cell stack in real time.

[0015] Furthermore, the gradient power distribution strategy includes: along the stacking direction, the heating power of the cell in the middle region of the stack is lower than that of the cell at both ends of the stack, and the ratio of the power at both ends to the power in the middle region is 1.2:1 to 1.8:1.

[0016] Furthermore, the heating power of the cathode gas inlet region is lower than that of the cathode gas outlet region, and the ratio of the power in the inlet region to the power in the outlet region is 1:1.1 to 1:1.5.

[0017] Furthermore, among the multiple cell units, 20% of the cell units at each end of the battery stack are divided into two end regions, and the remaining 60% of the cell units are divided into a middle region. The heating power density applied to the two end regions is 20% to 50% higher than that of the middle region.

[0018] Furthermore, the switching cycle between the thin-film thermal resistor and the preheating mode is 100ms to 1s, wherein the duty cycle of the preheating mode is 70% to 90%, the heating current density applied in the preheating mode is 0.5 to 5W / cm², and the detection current applied in the temperature measurement mode does not exceed 1mA; the target preheating temperature is 0℃ to 10℃.

[0019] Furthermore, if the stack temperature is detected to be lower than the preset safety threshold during the cold start process, the control unit restarts the preheating mode to supplement heating.

[0020] Compared with the prior art, the present invention has at least the following beneficial effects: By embedding the thin-film thermal resistor inside the bipolar plate and adopting a staged control strategy to achieve differentiated heating and dynamic temperature adjustment, the problems of low heating efficiency, high risk of local overheating, and uneven temperature distribution in the prior art are solved. It has the advantages of improving heating efficiency, reducing the risk of local overheating, achieving uniform temperature distribution inside the stack, simplifying the control system, and improving cold start performance; by realizing heating and temperature measurement functions in the preheating stage and temperature measurement functions in the start-up stage using the same thin-film element, the function of the element is reused; by embedding the thin-film thermal resistor inside the bipolar plate, it is isolated from the reaction gas flow channel and the coolant flow channel through the bipolar plate material, avoiding the influence of the heating element on the gas flow distribution and electrochemical reaction.

[0021] Furthermore, this invention employs a phased control strategy of preheating-shutdown-start, which completely separates the heating process from the electrochemical reaction process, avoiding mutual interference between the heating current and the electrochemical reaction current, and simplifying the design of the control system. After preheating is completed, the heating function is turned off, and the heat accumulated during the preheating stage is used for cold start, reducing energy consumption during the cold start process.

[0022] Furthermore, by using a gradient power distribution that is low in the middle and high at both ends, the heat loss at both ends of the fuel cell stack is precisely compensated, enabling the entire fuel cell stack to achieve uniform temperature rise during the preheating process, thus avoiding the problems of overheating in the middle area and undercooling at both ends. During the cold start process, the fuel cell stack temperature is continuously monitored, and when the temperature is lower than the safety threshold, the preheating mode can be restarted for supplementary heating, thereby improving the reliability of cold start.

[0023] Applying the technical solution of this invention, a cold-start auxiliary heating system and method for a fuel cell with a thin-film resistance thermometer embedded in a bipolar plate includes: a thin-film resistance thermometer array embedded inside the bipolar plate, a control unit electrically connected to it, and a phased control strategy of preheating-shutdown-start. During the preheating phase, the control unit applies a gradient heating power distribution—low in the middle and high at both ends—to different regions of the fuel cell stack based on real-time temperature feedback; after preheating is completed, the heating function is turned off, and then the fuel cell is started for cold start. Attached Figure Description

[0024] To more intuitively and clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments are briefly introduced below.

[0025] Figure 1 This is a schematic diagram of the structure of the fuel cell cold start auxiliary heating system with a bipolar plate embedded thin-film thermal resistor provided in an embodiment of the present invention; Figure 2 A partial cross-sectional schematic diagram of a bipolar plate embedded thin-film thermal resistor provided in an embodiment of the present invention; In the attached diagram, 1 is an insulating plate; 2 is a current collector; 3 is a bipolar plate; 4 is a membrane electrode; 5 is a cell unit; 6 is a fastening bolt; 7 is an end plate; 8 is a fastening nut; 9 is an anode gas manifold; 10 is a cooling liquid manifold; 11 is a cathode gas manifold; 12 is a thin-film resistance thermometer; and 13 is a control unit. Detailed Implementation

[0026] To make the technical solutions and advantages of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings: Figure 1 This is a schematic diagram of a fuel cell cold start auxiliary heating system with embedded thin-film thermal resistors in bipolar plates, provided by an embodiment of the present invention. The system includes an end plate structure, a fuel cell stack, fastening bolts and nuts, multiple thin-film thermal resistors, and a control unit. The end plate structure includes two insulating plates 1 and two current collectors 2. The fuel cell stack is composed of multiple unit cells 5 connected in series. Each unit cell 5 is formed by stacking bipolar plates 3 and membrane electrode 4. Multiple thin-film thermal resistors 12 are embedded inside the bipolar plates 3 of each unit cell. The control unit 13 is electrically connected to the multiple thin-film thermal resistors 12. The insulating plates 1 and current collectors 2 are combined and encapsulated at opposite ends of the stack body. The end plate structure 7 is sealed by applying pressure to the end plate structure 7 with fastening bolts 6. The end plate structure 7 includes two insulating plates 1 and two current collectors 2, encapsulated on opposite sides of the stack body. The insulating plates 1 and current collectors 2 are stacked to form the end plate structure 7, which is encapsulated at both ends of the fuel cell stack. The current collectors 2 are in close contact with the fuel cell stack body. The fastening bolts 6 press the end plate structure 7 to seal the fuel cell stack. The fastening bolts and nuts are located outside the stack body. The two ends of the fastening bolts 6 are connected to the fastening nuts 8 outside the two end plates through internal and external thread engagement. One of the end plates 7 is connected to the anode gas manifold 9, the cooling liquid manifold 10 and the cathode gas manifold 11. The anode gas manifold 9, the cooling liquid manifold 10 and the cathode gas manifold 11 are all connected to the corresponding flow channels on the unit cell 5.

[0027] Multiple thin-film resistance thermometers 12 are embedded inside the bipolar plates 3 of each cell 5, integrating heating and temperature measurement functions. This simplifies the stack structure, as the thin-film resistance thermometers 12 can both preheat the stack as heaters and monitor the temperature in real time as sensors, eliminating the need for additional temperature sensors and improving space utilization.

[0028] The control unit 13 is the core of the system, responsible for receiving sensor signals, executing preset control strategies, and sending commands to actuators such as thin-film resistors (RTDs) to achieve temperature management and heating control of the fuel cell stack. Multiple thin-film RTDs 12 are embedded within the bipolar plates 3 of each cell. Each RTD is configured to selectively operate in preheating mode, temperature measurement mode, or off mode. The embedding position of the RTDs can be selected according to design requirements, and the materials used for the RTDs can be materials with good temperature coefficients, such as nickel or copper resistors.

[0029] During the preheating phase, the control unit 13 is configured to apply differentiated heating currents to the thin-film resistance thermometers in each region, resulting in a preset temperature gradient distribution within the fuel cell stack. This gradient distribution features lower power in the middle region and higher power at both ends along the stacking direction. The control unit 13 can apply a higher heating current to the thin-film resistance thermometers at both ends of the stack, and a lower heating current to the thin-film resistance thermometers in the middle region, based on a preset fixed power curve.

[0030] During preheating, the control unit 13 intermittently switches some thin-film resistors (RTRs) to temperature measurement mode to acquire real-time temperatures in each area and dynamically adjust the gradient power distribution. For example, the control unit 13 can switch a group of RRTs to temperature measurement mode at set intervals to acquire temperature data for their respective areas. After preheating is complete, the control unit 13 switches all RRTs to shutdown mode to stop heating. The determination of preheating completion can be based on a fixed temperature threshold; the control unit 13 will then cut off the heating current to all RRTs, putting them into a non-operating state. During cold start, the control unit 13 switches some RRTs to temperature measurement mode to monitor stack temperature changes. After the fuel cell begins generating electricity, the control unit 13 can continuously or periodically activate some RRTs for temperature monitoring. The monitored temperature data can be used to record the stack's operating status or to issue alarms when temperatures are abnormal. The stack is fully preheated to the target temperature before startup, then heating is stopped, and the fuel cell is started. Staged control avoids the superposition of heating current and electrochemical reaction current, simplifies the complexity of the control system, and eliminates the mutual interference between the heating process and the electrochemical reaction process, making the stack temperature control more precise.

[0031] The stack body consists of 40 unit cells 5 connected in series, and each unit cell is composed of a bipolar plate 3 and a membrane electrode 4 stacked together.

[0032] like Figure 1As shown, the thin-film resistor 12 is embedded inside the bipolar plate 3, specifically located inside the plate between the cathode gas flow field and the cooling liquid flow field of the bipolar plate 3. Each thin-film resistor 12 is made of platinum resistance Pt100, with a temperature coefficient of resistance of approximately 0.00385 / ℃, and is distributed in a serpentine pattern in the active region of the bipolar plate 3, covering an area of ​​80% of the active area of ​​the bipolar plate 3.

[0033] The control unit 13 is electrically connected to a plurality of thin-film thermistors 12 and is configured to execute different control strategies during the preheating phase, the shutdown phase and the start-up phase.

[0034] This application provides a fuel cell cold start auxiliary heating method based on the above system, including the following steps: S1, before the fuel cell cold start, the stack is preheated by multiple thin-film thermal resistors 12 embedded in the bipolar plate 3; S2, During the preheating process, the control unit 13 applies differentiated heating current to the thin film thermal resistor 12 in each region according to a preset gradient power distribution strategy. The gradient power distribution strategy is that the heating power is low in the middle region and high in the two end regions along the stacking direction of the fuel cell. S3, during the preheating process, some thin-film thermal resistors 12 are intermittently switched to temperature measurement mode to obtain the real-time temperature of each area, and the heating power of each area is dynamically adjusted according to the real-time temperature feedback. S4. When the stack temperature reaches the preset preheating target temperature, switch all thin-film thermal resistors 12 to the off mode and stop heating. S5, start the fuel cell for a cold start; S6, during the cold start process, some thin-film thermal resistors 12 are switched to temperature measurement mode to monitor the temperature change of the fuel cell stack in real time.

[0035] As an optional embodiment, in the 40 cell units, cells 1-8 and 33-40 are divided into two end regions, totaling 16 cells, and cells 9-32 are divided into the middle region, totaling 24 cells.

[0036] The gradient power distribution strategy in step S2 includes: along the stacking direction of the fuel cell, the heating power of the cell in the middle region of the fuel cell is lower than that of the cell at both ends of the fuel cell, and the ratio of the power at both ends to the power in the middle region is 1.2:1 to 1.8:1; the gradient power distribution strategy in S2 also includes a gradient along the gas flow direction: the heating power of the cathode gas inlet region is lower than that of the cathode gas outlet region, and the ratio of the power in the inlet region to the power in the outlet region is 1:1.1 to 1:1.5.

[0037] The specific power settings are as follows: the preheating power density of the two end regions is set to 1.2 W / cm², and the preheating power density of the middle region is set to 0.9 W / cm², with a power ratio of 1.33:1 between the two end regions and the middle region. During the preheating stage, the control unit 13 applies differentiated heating currents to the thin-film thermal resistors 12 in each region according to a preset gradient power distribution strategy. Since the heat dissipation loss is greater in the two end regions of the fuel cell stack at low temperatures, the control unit 13 applies relatively higher heating currents to the thin-film thermal resistors 12 in these regions to generate more heat. For the middle region of the fuel cell stack, where heat dissipation loss is relatively small, the control unit 13 applies relatively lower heating currents. The internal temperature of the fuel cell stack exhibits a gradient distribution along the stacking direction, with lower power in the middle region and higher power in the two end regions, compensating for heat dissipation losses in the two end regions and avoiding the temperature unevenness problem caused by traditional uniform heating. By clearly defining the cell range of different regions in the fuel cell stack, precise and efficient gradient power preheating is achieved.

[0038] Cells 1-8 and 33-40 are designated as the two-end regions, requiring higher heating power to ensure rapid attainment of the target temperature. Cells 9-32 are designated as the middle region, which may have relatively good heat preservation or lower heat dissipation requirements during preheating, thus requiring relatively lower heating power. The heating power density applied to the two-end regions is 20%-50% higher than that of the middle region. During preheating, the control unit 13 provides a larger current or higher voltage to the thin-film thermal resistors 12 in the two-end regions to achieve higher heat output. By applying differentiated heating currents to the thin-film thermal resistors 12 in each region through the control unit 13, a preset gradient temperature distribution is achieved within the stack. This gradient distribution results in lower power in the middle region and higher power in the two-end regions along the stack stack direction. By applying higher heating power to the two-end regions, the heat dissipation effect of the end plates is effectively compensated, solving the problem of uneven temperature distribution caused by traditional uniform heating, where the temperature at the two ends of the stack is lower and the temperature in the middle is higher. A more uniform temperature distribution inside the fuel cell stack reduces thermal stress, which helps extend the stack's lifespan and improves the success rate and efficiency of cold starts.

[0039] This application arranges multiple thin-film thermal resistors 12 in an array along the stacking direction of the battery pack, with at least one thin-film thermal resistor embedded in the bipolar plate 3 of each cell 5. This ensures that each cell 5 has independent heating and temperature measurement capabilities throughout the entire stacking direction. This allows the control unit 13 to perform fine-grained management of various regions of the battery pack along the stacking direction. When the control unit 13 applies differentiated heating currents to the thin-film thermal resistors 12 in each region according to a preset gradient power distribution strategy, such as low power in the middle region and high power at both ends, the array distribution can accurately respond to control commands, and the heating power of each cell 5 or each region can be independently adjusted. Simultaneously, with at least one thin-film thermal resistor 12 embedded in the bipolar plate 3 of each cell 5, when the control unit 13 intermittently switches some of the thin-film thermal resistors 12 to temperature measurement mode during preheating, it can acquire real-time temperature data for each cell 5 or each region along the stacking direction. This provides accurate feedback for dynamically adjusting the gradient power distribution, enabling more accurate perception and control of the temperature field inside the battery pack, effectively avoiding problems such as local overheating or insufficient preheating. In addition to implementing gradient power distribution along the stacking direction of the fuel cell, a gradient power distribution strategy is also implemented along the gas flow direction.

[0040] When applying differentiated heating currents to the thin-film resistors 12 in different regions, the control unit 13 considers not only the power differences between the two ends and the middle region of the fuel cell stack, but also the path of the cathode gas flow, ensuring that the heating power in the cathode gas inlet region is lower than that in the cathode gas outlet region. This synergistic dual-gradient power distribution allows for more precise control of the temperature field inside the fuel cell stack. Because the cathode gas is at a lower temperature upon entering the stack, and water vapor condenses more readily in the outlet region as the reaction proceeds, ice blockage is more likely to form there. By applying a relatively lower heating power in the inlet region and a relatively higher heating power in the outlet region, heat losses due to gas flow and phase change can be compensated for, resulting in a more uniform temperature distribution throughout the fuel cell stack, including along the gas flow direction, thus preventing localized overcooling or overheating.

[0041] As an optional embodiment, during the preheating process, the control unit 13 applies differentiated heating currents to the thin-film resistors 12 in each region according to a preset gradient power distribution strategy, and intermittently switches some of the thin-film resistors 12 to temperature measurement mode to obtain the real-time temperature of each region. Based on the real-time temperature feedback, the heating power of each region is dynamically adjusted. When the stack temperature reaches the preset preheating target temperature of 0℃~10℃, all thin-film resistors 12 are switched to the off mode to stop heating. The fuel cell is then started for cold start, and the stack temperature change is continuously monitored during the cold start process. This application, by setting a preheating target temperature of 0℃~10℃, enables the fuel cell stack to reach an ideal temperature state before cold start that effectively prevents internal icing while avoiding overheating. During the preheating process, the control unit 13 continuously receives real-time temperature data measured by multiple thin-film resistors 12. Real-time temperature data indicates that the overall or critical area temperature of the fuel cell stack has reached the target temperature. Control unit 13 executes step S4 to switch all thin-film thermal resistors 12 to the off mode, thereby stopping heating. This ensures the optimization of the preheating process, so that the fuel cell stack is in the best working condition at startup, avoiding performance degradation or damage due to excessively low temperature, and also avoiding energy waste due to excessively high temperature.

[0042] During the preheating process, the control unit 13 intermittently switches some of the thin-film resistors 12 to temperature measurement mode. The switching operation occurs on a cycle of 100ms to 1s, with the duty cycle of the preheating mode controlled at 70% to 90%, and the applied detection current in temperature measurement mode not exceeding 1mA. Through periodic switching, the system can acquire real-time temperature data for each region and dynamically adjust the gradient power distribution based on feedback information. For example, when the temperature rise rate of a certain region deviates from the preset curve, the control unit 13 will adjust the heating current density of the thin-film resistors 12 in that region accordingly, maintaining it within the effective operating range of 0.5 to 5 W / cm², thereby avoiding the risk of localized overheating.

[0043] As an optional embodiment, the mode switching sequence of the thin-film RTDs during the preheating and startup phases is as follows: During the preheating phase, each thin-film RTD periodically switches between preheating mode and temperature measurement mode. A complete control cycle T = 500 ms, where the preheating mode duty cycle is 80% (400 ms preheating time) and the temperature measurement mode duty cycle is 20% (100 ms temperature measurement time). The heating current density applied in preheating mode is 1.2 W / cm² at both ends and 0.9 W / cm² in the middle region; the detection current applied in temperature measurement mode is 0.5 mA. After preheating is complete, all thin-film RTDs switch to the off mode. After the startup phase begins, only some thin-film RTDs are switched to temperature measurement mode, while the rest remain off. A polling temperature measurement strategy is used, with only 1 / 5 of the thin-film RTDs in temperature measurement mode at any given time, and the measurement cycle is 1 second.

[0044] During cold start, the control unit 13 continuously monitors the stack temperature. When any area's temperature is detected to be below the preset safety threshold of -5°C, the control unit 13 restarts the preheating mode to supplement heating of that area until the temperature rises above 0°C. By continuously monitoring the stack temperature during the fuel cell cold start, the control unit 13 immediately triggers the thin-film resistor 12 to re-enter the preheating mode to supplement heating of the stack when the stack temperature falls below the preset safety threshold. During the fuel cell cold start phase, the control unit 13 periodically switches some of the thin-film resistors 12 to temperature measurement mode according to step S6 described above to obtain real-time temperature information inside the stack. When the real-time temperature data is analyzed by the control unit 13 and it is confirmed that the temperature of any area is below the preset safety threshold, the heating function of the thin-film resistor 12 is reactivated. The thin-film resistor 12 will apply heating current again to supplement heat to the stack, thereby raising the stack temperature back to the safe operating range. This mechanism ensures that even if an unexpected temperature drop occurs during the cold start process, the stack can receive timely heat supplementation, avoiding performance degradation or damage caused by low temperatures.

[0045] Simulation results verify the effectiveness of the technical solution of this invention: by employing a phased control strategy of preheating-shutdown-start and a gradient preheating strategy with low temperature in the middle and high temperature at both ends, uniform preheating inside the fuel cell stack is achieved, such as... Figure 2 As shown, the output voltage of the battery end cells of the fuel cell stack heated by a gradient power of 90-60W is about 5% higher than that of the battery end cells of the fuel cell stack heated by a uniform power of 75-75W.

[0046] The fuel cell cold start auxiliary heating system and method with embedded thin-film thermal resistors in bipolar plates provided by this invention can be widely applied to low-temperature cold start scenarios for proton exchange membrane fuel cells, and is particularly suitable for cold start of automotive fuel cell stacks in extremely cold environments. The technical solution of this invention is based on mature MEMS thin-film fabrication technology, and the thin-film thermal resistors can be embedded in bipolar plates in batches, exhibiting good manufacturability and economy.

[0047] In summary, this invention provides a fuel cell cold start auxiliary heating system and method with bipolar plates embedded thin-film thermal resistors. Each thin-film thermal resistor is configured to selectively operate in preheating mode, temperature measurement mode, or off mode, achieving integrated heating and temperature measurement functions. The control unit executes a phased control strategy: during the preheating stage before cold start, differentiated heating currents are applied to the thin-film thermal resistors in each region, resulting in a gradient temperature distribution within the fuel cell stack with lower power in the middle region and higher power at both ends along the stacking direction, to compensate for heat loss from the end plates; during preheating, some thermal resistors are intermittently switched to temperature measurement mode, with real-time feedback and dynamic adjustment of power distribution; after preheating reaches the target temperature, all thermal resistors are switched to off mode to stop heating, and the fuel cell is then started for cold start; during cold start, some thermal resistors are switched to temperature measurement mode to continuously monitor the stack temperature, and preheating is restarted for supplementary heating when the temperature falls below a safe threshold. By employing a phased control system of preheating-shutdown-start, the heating process is completely separated from the electrochemical reaction, avoiding current interference and reducing control complexity. A gradient preheating strategy with lower temperatures in the middle and higher temperatures at both ends ensures uniform temperature rise of the fuel cell stack. By reusing heating and temperature measurement functions on the same thin-film element, the stack structure is simplified, improving cold-start reliability and energy efficiency. This system is particularly suitable for cold-starting automotive fuel cell stacks in extremely cold environments.

[0048] The specific embodiments described above further illustrate the technical problems solved by the present invention, the technical solutions, and the beneficial effects. It should be understood that the above descriptions are merely embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention can have various modifications and variations. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A fuel cell cold start auxiliary heating system, characterized in that, The system includes a fuel cell stack, multiple thin-film resistors (12), and a control unit (13). The fuel cell stack is composed of multiple cell units (5) connected in series. Each cell unit (5) is formed by stacking bipolar plates (3) and membrane electrodes (4). Multiple thin-film resistors (12) are embedded inside the bipolar plates (3) of each cell unit. Each thin-film resistor is configured to selectively operate in a preheating mode, a temperature measurement mode, or a shutdown mode. The control unit (13) is electrically connected to the multiple thin-film resistors (12). During the preheating stage: the control unit (13) applies differentiated heating currents to the thin-film thermal resistors in each region, so that the internal temperature of the stack is distributed in a preset gradient, wherein the power is low in the middle region and high in the two end regions along the stacking direction; during the preheating process: some thin-film thermal resistors are intermittently switched to temperature measurement mode to obtain the real-time temperature of each region and dynamically adjust the gradient power distribution; after the preheating is completed: all thin-film thermal resistors are switched to the off mode to stop heating; during the cold start process: some thin-film thermal resistors are switched to temperature measurement mode to monitor the temperature change of the stack.

2. The fuel cell cold start auxiliary heating system according to claim 1, characterized in that, Multiple thin-film thermal resistors (12) are arranged in an array along the stacking direction of the battery pack, and at least one thin-film thermal resistor is embedded in the bipolar plate (3) of each cell (5).

3. The fuel cell cold start auxiliary heating system according to claim 1, characterized in that, The thin-film thermal resistor (12) is embedded in the plate body between the cathode gas flow field and the cooling liquid flow field of the bipolar plate (3), and is isolated from the reaction gas flow channel and the cooling liquid flow channel by the bipolar plate material.

4. The fuel cell cold start auxiliary heating system according to claim 1, characterized in that, The thin film resistance thermometer (12) is made of platinum resistance thermometer with a resistance temperature coefficient greater than 0.003 / ℃. The thin film resistance thermometer (12) is distributed in a serpentine pattern in the active area of ​​the bipolar plate (3), covering an area of ​​80% of the active area of ​​the bipolar plate (3).

5. A method for auxiliary heating of a fuel cell during cold start based on the system according to any one of claims 1-4, characterized in that, Includes the following steps: Before the fuel cell is cold-started, the stack is preheated by multiple thin-film thermal resistors (12) embedded in the bipolar plate (3). During the preheating process, the control unit (13) applies differentiated heating current to the thin-film thermal resistors (12) in each region according to a preset gradient power distribution strategy. The gradient power distribution strategy is that the heating power in the middle region is low and the heating power in the two end regions is high along the stacking direction of the fuel cell. During the preheating process, some thin-film thermal resistors (12) are intermittently switched to temperature measurement mode to obtain the real-time temperature of each area, and the heating power of each area is dynamically adjusted according to the real-time temperature feedback. Once the stack temperature reaches the preset preheating target temperature, all thin-film thermal resistors (12) are switched to the off mode to stop heating; Start the fuel cell for a cold start; During the cold start process, some thin-film thermal resistors (12) are switched to temperature measurement mode to monitor the temperature change of the fuel cell stack in real time.

6. The fuel cell cold start auxiliary heating method according to claim 5, characterized in that, The gradient power distribution strategy includes: along the stacking direction, the heating power of the cell in the middle region of the stack is lower than that of the cell at both ends of the stack, and the ratio of power at both ends to power in the middle region is 1.2:1 to 1.8:

1.

7. The fuel cell cold start auxiliary heating method according to claim 5, characterized in that, The heating power of the cathode gas inlet region is lower than that of the cathode gas outlet region, and the ratio of the power in the inlet region to the power in the outlet region is 1:1.1 to 1:1.

5.

8. The fuel cell cold start auxiliary heating method according to claim 5, characterized in that, In the multiple cell units, 20% of the cell units at each end of the cell stack are divided into two end regions, and the remaining 60% of the cell units are divided into a middle region. The heating power density applied to the two end regions is 20% to 50% higher than that of the middle region.

9. The fuel cell cold start auxiliary heating method according to claim 5, characterized in that, The switching cycle of the thin film thermal resistor (12) between the preheating mode and the temperature measurement mode is 100ms~1s, wherein the duty cycle of the preheating mode is 70%~90%, the heating current density applied in the preheating mode is 0.5~5W / cm², and the detection current applied in the temperature measurement mode does not exceed 1mA. The target preheating temperature is 0℃~10℃.

10. The fuel cell cold start auxiliary heating method according to claim 5, characterized in that, When the temperature of the fuel cell stack is detected to be lower than the preset safety threshold during the cold start process, the control unit (13) restarts the preheating mode to supplement the heating.

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