Fuel cell system and water state control method thereof

Abstract

The application discloses a fuel cell system and a water state control method thereof, and relates to the technical field of fuel cells.The system comprises a fuel cell stack, a magnetic heat conversion device, a cooling liquid circulation subsystem and a water state control subsystem.The bipolar plate of the fuel cell stack is provided with a cooling liquid flow channel for the cooling liquid at a set temperature.The magnetic heat conversion device is arranged outside the cooling liquid flow channel.The cooling liquid circulation subsystem is communicated with the cooling liquid flow channel in the fuel cell stack through a pipeline.The water state control subsystem can monitor the temperature of the cooling liquid in and out of the fuel cell stack and the spatial distribution of different forms of water in the fuel cell stack, and can control the working state of the cooling liquid circulation subsystem and the working state of the magnetic heat conversion device according to the temperature and the water state distribution information.The fuel cell system and the water state control method thereof can realize low-temperature rapid cold start and uniform distribution of the water state between single cells and in the single cells in the normal operation process, avoid the occurrence of local water flooding or membrane dry failure, and further improve the output performance and service life of the fuel cell system.

Description

Technical Field

[0001] This invention relates to the field of fuel cell technology, and in particular to a fuel cell system and a method for controlling the water state therein. Background Technology

[0002] Proton exchange membrane fuel cells (PEMFCs) have become one of the core energy devices in distributed power generation, transportation, and other fields due to their significant advantages such as high energy density, high energy conversion efficiency, low operating noise, and zero pollutant emissions. The proton exchange membrane, its core functional component, plays a crucial role in isolating reactants at the electrodes and conducting protons. Currently, commercially used PEMFCs are mainly perfluorosulfonic acid type. The proton conduction performance of this type of membrane is highly sensitive to membrane water content. Deviating from an optimal water content range can directly lead to water management failures: when the membrane water content is too low, the conductivity of the PEMFC drops significantly, resulting in membrane dryness; when the membrane water content is too high, excess liquid water can block the reactant gas transport channels, increasing mass transfer resistance and simultaneously reducing membrane conductivity, resulting in flooding. Both types of failures severely affect the output performance and operational stability of the fuel cell.

[0003] To meet the high-power demands of practical applications, fuel cell stacks typically consist of hundreds of large-area cells connected in series. The increased size of the fuel cell stack leads to a significant non-uniform distribution of water, air, and thermal states within it. Due to the "weakest link" effect, localized water state anomalies in the fuel cell stack can rapidly conduct and affect the healthy operation of the entire stack. Therefore, achieving precise control of the water state within the fuel cell stack and maintaining a uniform distribution of water between and within cells is crucial for improving the output performance and extending the lifespan of the fuel cell stack.

[0004] Currently, the mainstream methods for controlling the water state of fuel cells are humidification control and liquid cooling temperature control. Humidification control indirectly regulates the membrane water content by adjusting the relative humidity when the reactant gases enter the fuel cell stack. Liquid cooling control, on the other hand, uses a water pump to drive the coolant to circulate within the bipolar plate channels of the fuel cell stack, combined with an external heat exchanger and PTC heater to achieve overall heat dissipation or heating of the fuel cell stack. By changing the saturated vapor pressure of the membrane, it promotes the evaporation or condensation of water within the membrane. However, both of these control methods are based on adjusting the external input conditions of the fuel cell stack, which cannot overcome the limitations imposed by the spatial size of the fuel cell stack. They are difficult to achieve precise and independent control of the local water state of the fuel cell stack, which can easily lead to a continuous increase in the differences in water state between and within individual cells. Therefore, they still cannot fundamentally prevent the occurrence of local membrane dryness and flooding failures.

[0005] While existing technologies have attempted to optimize fuel cell thermal management and water state monitoring, significant limitations remain. Some technologies propose fuel cell thermal management systems based on the magnetocaloric effect, utilizing a magnetic heat storage device in conjunction with a permanent magnet to achieve magnetization heat release. This heat is then transferred through the coolant to preheat the fuel cell stack at low temperatures, accelerating cold start-up. However, this technology treats the fuel cell stack as a whole, only achieving overall heating and failing to provide independent temperature control for localized areas. Furthermore, it does not address the management of the internal water state of the fuel cell stack, thus failing to mitigate localized water management failures.

[0006] In terms of water state detection and assessment, existing technologies mostly rely on external or overall parameters such as fuel cell internal resistance, reactant gas inlet / outlet temperature / pressure, and ohmic impedance to identify water state. However, these methods have significant drawbacks: fuel cell internal resistance is highly sensitive to membrane dryness faults but struggles to accurately characterize flooding faults; while gas inlet / outlet parameters and ohmic impedance are overall parameters of the fuel cell stack and cannot reflect the differences in water state distribution between or within individual cells, making it difficult to accurately diagnose localized water management faults and provide effective guidance for localized water state control. Furthermore, control methods based on these external parameters can only achieve coarse control by adjusting reactant gas humidity and overall coolant temperature, failing to provide targeted mitigation for existing localized membrane dryness or flooding faults. The accuracy and effectiveness of these controls cannot meet the operational requirements of high-power fuel cell stacks.

[0007] In summary, existing fuel cell water state control technologies have significant shortcomings in terms of precise local detection, local temperature regulation, and targeted fault mitigation. There is an urgent need to design a technical solution that can achieve uniform distribution of water state between and within cells during rapid cold start at low temperatures and normal operation, avoid local flooding or membrane dryness faults, and thus improve the output performance and service life of fuel cell systems. Summary of the Invention

[0008] The purpose of this invention is to provide a fuel cell system and its water state control method to solve the problems existing in the prior art. It can achieve uniform distribution of water state between and within cells during low-temperature rapid cold start and normal operation, avoid local flooding or membrane dryness failure, and thus improve the output performance and service life of the fuel cell system.

[0009] To achieve the above objectives, the present invention provides the following solution: This invention provides a fuel cell system, comprising: A fuel cell stack includes multiple bipolar plates and multiple membrane electrode assemblies arranged alternately. The bipolar plates are provided with coolant channels to allow coolant at a set temperature to flow through them. Multiple magnetocaloric device mounting slots are uniformly arranged on the outside of the coolant channels, and magnetocaloric conversion devices are installed in the magnetocaloric device mounting slots. A coolant circulation subsystem, connected to the coolant flow channels within the fuel cell stack via piping, is capable of introducing coolant at a set temperature into the coolant flow channels and circulating the coolant between the coolant circulation subsystem and the coolant flow channels at a set rate; and The water state control subsystem can monitor the temperature of the coolant entering and exiting the fuel cell stack and the spatial distribution of water in different states inside the fuel cell stack. Based on the temperature and water state distribution information, it controls the working state of the coolant circulation subsystem and the working state of the magnetocaloric conversion device to achieve local temperature regulation inside the fuel cell stack.

[0010] In one embodiment, the fuel cell stack further includes a current collector, an insulating plate, and an end plate. A plurality of bipolar plates and a plurality of membrane electrodes are alternately stacked to form an electrode group. The current collector is provided at both ends of the electrode group. The end plate is provided outside the current collector. The insulating plate is provided between the end plate and the current collector.

[0011] In one embodiment, reactive gas channels are provided on both sides of the bipolar plate, and a coolant channel is provided in the middle of the bipolar plate.

[0012] In one embodiment, the mounting groove of the magnetocaloric device is filled with a thermally and electrically conductive adhesive to fix the magnetocaloric conversion device and realize the thermoelectric conduction between the magnetocaloric conversion device and the bipolar plate.

[0013] In one embodiment, the end plate includes an air inlet end plate, which has a reaction gas collection and discharge port and a coolant collection and discharge port. Multiple magnetic field generator mounting slots are evenly distributed around the interior of the air inlet end plate, and a magnetic field generator is fixedly installed in each slot. A battery is connected to each magnetic field generator. A low-field nuclear magnetic resonance main magnetic field system mounting slot is also provided inside the air inlet end plate, and a low-field nuclear magnetic resonance main magnetic field system is installed in each slot.

[0014] In one embodiment, the end plate includes a blind end plate, and a plurality of magnetic field generator mounting slots are evenly formed around the inside of the blind end plate. A magnetic field generator is fixedly installed in the magnetic field generator mounting slot. A battery is connected to the outside of the magnetic field generator. A low-field nuclear magnetic resonance radio frequency system mounting slot is formed inside the blind end plate, and a low-field nuclear magnetic resonance radio frequency system is installed in the low-field nuclear magnetic resonance radio frequency system mounting slot.

[0015] In one embodiment, the coolant circulation subsystem includes a three-way valve, a cooling fan assembly, a water pump, and a heater; two ports of the three-way valve are respectively connected to the inlet of the cooling fan assembly and the inlet of the heater via pipelines, and the third port of the three-way valve is connected to the drain outlet of the fuel cell stack; the outlet of the cooling fan assembly and the outlet of the heater are connected to the inlet of the fuel cell stack via pipelines equipped with the water pump; the three-way valve, cooling fan assembly, water pump, and heater are respectively communicatively connected to the water state control subsystem via low-voltage signal lines.

[0016] In one embodiment, the water state control subsystem includes a water state controller, a battery, a low-field nuclear magnetic resonance (NMR) device, and coolant inlet and outlet temperature sensors. The coolant inlet and outlet temperature sensors are located at both the inlet and outlet of the fuel cell stack. The low-field NMR device is located on one side of the fuel cell stack and connected to it via a low-voltage signal line. The battery is connected to a magnetocaloric conversion device within the fuel cell stack via a current transmission line. The three-way valve, cooling fan assembly, water pump, heater, battery, low-field NMR device, and coolant inlet and outlet temperature sensors are communicatively connected to the water state controller via the low-voltage signal line.

[0017] The present invention also provides a water state control method for a fuel cell system as described above, including a rapid and uniform temperature rise control process for the fuel cell stack during cold start, wherein the rapid and uniform temperature rise control process for the fuel cell stack during cold start includes the following steps: The low-field nuclear magnetic resonance device is in operation; The spatial distribution of liquid water and solid ice inside the fuel cell stack was determined through scanning analysis. Based on the distribution of solid ice, the magnetocaloric conversion device is activated, and the heating rate of different regions of the fuel cell stack is controlled by the field synergy superposition of magnetic field generators in different directions. The coolant circulation system works in coordination to achieve rapid and uniform heating inside the fuel cell stack during cold start-up; A low-field nuclear magnetic resonance device periodically scans the spatial distribution of water ice inside a fuel cell stack, and the changes in solid ice distribution are obtained after calculation. The rate of solid ice melting in the region is less than the specified value. V set Or the volume content of solid ice is greater than the specified value. Then, by adjusting the working state of the magnetocaloric conversion device, the heating power of the corresponding area can be increased; the melting rate of solid ice in the area should not be less than the specified value. V set Or the volume content of solid ice does not exceed the specified value. Then the heating state of the original magnetocaloric conversion device will be maintained until the fuel cell stack reaches the target temperature.

[0018] In one embodiment, the method further includes a process for controlling the uniform distribution of water state inside the fuel cell stack under normal operation, which includes the following steps: The low-field nuclear magnetic resonance device operates periodically; The spatial distribution of liquid water and membrane water inside the fuel cell stack is obtained through scanning analysis, and it is determined whether the fuel cell stack has experienced flooding or membrane drying failure. If a flooding fault occurs, the faulty individual cell and its in-plane fault region can be further located based on the nuclear magnetic resonance results. When the magnetocaloric conversion device is in operation, the temperature of the membrane electrode in the fault area increases, which accelerates the evaporation of excess liquid water and keeps the temperature in other areas constant. Once the flooding fault is completely eliminated, the magnetocaloric conversion device gradually stops working with the help of the coolant circulation system, ensuring uniform temperature distribution of the fuel cell stack during this process. If membrane dryness failure occurs, the faulty monomer and its in-plane fault region can be located based on the nuclear magnetic resonance results. With the cooperation of the coolant circulation system, the magnetocaloric conversion device works and reaches the preset stable state; The magnetocaloric conversion device is controlled to stop working. During this process, the heat absorption effect of the magnetocaloric conversion device is used to reduce the temperature of the membrane electrode in the fault area, accelerate the condensation of water vapor, while the temperature in other areas remains unchanged, and finally eliminate the membrane dryness fault.

[0019] The present invention achieves the following technical effects compared to the prior art: This invention integrates multiple magnetocaloric conversion devices uniformly within bipolar plates to improve the uniformity of water state distribution during fuel cell stack operation. Specifically, when a flooding fault is detected in a certain area of ​​the fuel cell stack due to excessive liquid water accumulation, the temperature of the fault area can be rapidly increased by rationally controlling the operating status of each magnetocaloric conversion device, accelerating the evaporation and discharge of liquid water. Similarly, when a membrane dryness fault is detected in a certain area of ​​the fuel cell stack due to insufficient liquid water, the temperature of the fault area can be rapidly reduced by rationally controlling the shutdown process after the magnetocaloric conversion devices are turned on, promoting more liquid water condensation, restoring the membrane electrode to a wet state, and ultimately achieving and maintaining a uniform distribution of water state between and within individual fuel cell stack cells.

[0020] This invention integrates multiple magnetocaloric conversion devices uniformly within bipolar plates. When the fuel cell stack requires a low-temperature cold start, the magnetocaloric conversion devices are activated appropriately based on the internal solid ice and liquid water distribution identified by nuclear magnetic resonance (NMR). Simultaneously, the cooling fluid circulation system provides heating, enabling the fuel cell stack to quickly reach the target temperature. This also improves the consistency and uniformity of water distribution between and within individual cells during the process, preventing shortened fuel cell stack lifespan due to localized solid ice anomalies. Furthermore, this control method is also applicable to normal heating of the fuel cell stack, increasing the heating rate. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 This is a schematic diagram of a fuel cell system in one or more embodiments of the present invention; Figure 2 This is a diagram of a bipolar plate structure in one or more embodiments of the present invention; Figure 3 A structural diagram of the stack inlet end plate in one or more embodiments of the present invention; Figure 4 This is a structural diagram of a blind end plate in one or more embodiments of the present invention; Figure 5 This is a flowchart illustrating the water state control process during the cold start of a fuel cell system in one or more embodiments of the present invention. Figure 6 This is a flowchart illustrating the water state control process of a fuel cell system during normal operation in one or more embodiments of the present invention. Figure 7 for Figure 2 AA sectional view.

[0023] In the diagram: 1-Fuel cell stack, 2-Three-way valve, 3-Cooling fan assembly, 4-Water pump, 5-Heater, 6-Coolant inlet / outlet temperature sensor, 7-Pipeline, 8-Low-voltage signal line, 9-Water status controller, 10-Low-field nuclear magnetic resonance device, 11-Battery, 12-Current transmission line, 13-Bipolar plate, 14-Coolant flow channel, 15-Magnetic-thermal device mounting slot, 16-Magnetic-thermal conversion device, 17-Reaction gas flow channel, 18-Inlet end plate, 19-Reaction gas collection and exhaust port, 20-Coolant collection and exhaust port, 21-Magnetic field generator mounting slot, 22-Magnetic field generator, 23-Low-field nuclear magnetic resonance main magnetic field system mounting slot, 24-Low-field nuclear magnetic resonance main magnetic field system, 25-Way trough, 26-Blind end plate, 27-Low-field nuclear magnetic resonance radio frequency system mounting slot, 28-Low-field nuclear magnetic resonance radio frequency system. Detailed Implementation

[0024] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] The purpose of this invention is to provide a fuel cell system and its water state control method to solve the problems existing in the prior art. It can achieve uniform distribution of water state between and within cells during low-temperature rapid cold start and normal operation, avoid local flooding or membrane dryness failure, and thus improve the output performance and service life of the fuel cell system.

[0026] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0027] refer to Figure 1 , Figure 2 , Figure 3 , Figure 4 and Figure 7This invention provides a fuel cell system, including a fuel cell stack 1, a coolant circulation subsystem, and a water state control subsystem. The fuel cell stack 1 includes multiple bipolar plates 13 and multiple membrane electrode assemblies (MEAs) arranged alternately. Each bipolar plate 13 is welded from two single-stage plates, with reactant gas channels 17 on both sides and a coolant channel 14 in the middle. Multiple magnetocaloric device mounting slots 15 are uniformly arranged on the outer side of the coolant channel 14, located at the bottom or sides of the coolant channel 14, allowing magnetocaloric conversion devices 16 to fit tightly against the adjacent outer wall of the coolant channel 14. A magnetocaloric conversion device 16 is installed within the mounting slot 15. This device is made of a special material, primarily gadolinium, gadolinium-silicon-germanium alloy, lanthanum-iron-silicon, etc. When an external magnetic field is applied, the temperature of this special material rises, and... The material releases heat, but when the external magnetic field is removed, the material temperature decreases, thus absorbing heat. At the same time, the magnetocaloric device mounting groove 15 is also filled with a highly thermally and electrically conductive adhesive to fix the magnetocaloric conversion device 16 and realize its rapid thermoelectric conduction with the bipolar plate 13. The coolant circulation subsystem is connected to the coolant flow channel 14 in the fuel cell stack 1 through a pipeline, and can introduce coolant at a set temperature into the coolant flow channel 14, and make the coolant circulate between the coolant circulation subsystem and the coolant flow channel 14 at a set rate. The water state control subsystem can monitor the temperature of the coolant entering and leaving the fuel cell stack 1 and the spatial distribution of water in different forms inside the fuel cell stack 1, and control the working state of the coolant circulation subsystem and the working state of the magnetocaloric conversion device 16 respectively according to the temperature and water state distribution information, so as to realize the regulation of the local temperature inside the fuel cell stack 1.

[0028] In one embodiment, the fuel cell stack 1 further includes a current collector, an insulating plate, and an end plate. Multiple bipolar plates 13 and multiple membrane electrode assemblies are alternately stacked to form an electrode assembly. Current collectors are provided at both ends of the electrode assembly. An end plate is provided outside the current collector, and an insulating plate is provided between the end plate and the current collector. Reactant gas channels 17 are provided on both sides of the bipolar plates 13, and a coolant channel 14 is provided in the middle of the bipolar plates 13.

[0029] In one embodiment, the end plate includes an inlet end plate 18 and a blind end plate 26 disposed at both ends of the electrode assembly. To achieve active control of the magnetocaloric conversion device 16, taking a U-shaped fuel cell stack as an example, the inlet end plate 18 is provided with a reaction gas collection and discharge port 19 and a coolant collection and discharge port 20. Multiple magnetic field generator mounting slots 21 are evenly distributed around the inside of the inlet end plate 18. Magnetic field generators 22 are fixedly installed in the magnetic field generator mounting slots 21, and each magnetic field generator 22 can work independently. A battery 11 is connected to the outside of the magnetic field generator 22. Multiple magnetic field generator mounting slots are evenly distributed around the inside of the blind end plate 26. 21. A magnetic field generator 22 is fixedly installed in the magnetic field generator mounting slot 21. A storage battery 11 is connected to the magnetic field generator 22. These magnetic field generators 22 can adjust the direction and intensity of the magnetic field in each region of the fuel cell stack 1 by adjusting the input current, thereby controlling the working state of the magnetocaloric conversion device 16 in different regions. The magnetic field generator 22 and the storage battery 11 are connected by a wiring harness through a pre-embedded wiring trough 25. In addition, in order to obtain the spatial distribution of the water state inside the fuel cell stack 1, the end plate also integrates key components of the low-field nuclear magnetic resonance device 10 to support the normal operation of the low-field nuclear magnetic resonance device 10. Specifically, the air inlet end plate 18 has a low-field nuclear magnetic resonance main magnetic field system mounting slot 23 inside, and a low-field nuclear magnetic resonance main magnetic field system 24 is installed in the slot, which can provide a uniform and stable static magnetic field for water state distribution detection; the blind end plate 26 has a low-field nuclear magnetic resonance radio frequency system mounting slot 27 inside, and a low-field nuclear magnetic resonance radio frequency system 28 is installed in the slot, which is used to excite nuclear spins and receive the resonance signals they release. The water state distribution can be obtained through signal analysis. It should be noted that the low-field nuclear magnetic resonance device 10 operates at a low frequency and is synchronized with the magnetic field generator 22 during operation, so there is no interference between the two.

[0030] In one embodiment, the coolant circulation subsystem includes a three-way valve 2, a cooling fan assembly 3, a water pump 4, and a heater 5. Two ports of the three-way valve 2 are connected to the inlet of the cooling fan assembly 3 and the inlet of the heater 5 respectively via pipes 7. The third port of the three-way valve 2 is connected to the drain outlet of the fuel cell stack 1. The outlets of the cooling fan assembly 3 and the heater 5 are connected to the inlet of the fuel cell stack 1 via pipes 7 equipped with the water pump 4. The three-way valve 2, cooling fan assembly 3, water pump 4, and heater 5 are each communicatively connected to the water state control subsystem via their respective low-voltage signal lines 8. In this embodiment, the cooling fan assembly 3 is used to achieve rapid heat exchange between the coolant and the surrounding environment, reducing the temperature of the coolant flowing into the fuel cell stack 1. The heater 5 is a PTC heater, used to increase the temperature of the coolant flowing into the fuel cell stack 1. The water pump 4 is used to control the circulation rate of the coolant in pipes 7. The three-way valve 2 is used to switch between the large and small circulation paths of the coolant. The large circulation path is the coolant outlet, the three-way valve 2, the cooling fan assembly 3, the water pump 4, the coolant inlet, and the fuel cell stack 1 to achieve heat dissipation of the fuel cell stack 1. The small circulation path is the coolant outlet, the three-way valve 2, the PTC heater, the water pump 4, the coolant inlet, and the fuel cell stack 1 to achieve heating of the fuel cell stack 1.

[0031] In one embodiment, the water state control subsystem includes a water state controller 9, a battery 11, a low-field nuclear magnetic resonance (NMR) device 10, and coolant inlet / outlet temperature sensors 6. A coolant inlet / outlet temperature sensor 6 is provided at both the inlet and outlet of the fuel cell stack 1. The low-field NMR device 10 is located on one side of the fuel cell stack 1 and connected to it via a low-voltage signal line 8. The battery 11 is connected to a magnetocaloric conversion device 16 within the fuel cell stack 1 via a current transmission line 12. The three-way valve 2, cooling fan assembly 3, water pump 4, heater 5, battery 11, low-field NMR device 10, and coolant inlet / outlet temperature sensors 6 are communicatively connected to the water state controller 9 via the low-voltage signal line 8. In this embodiment, the coolant inlet / outlet temperature sensor 6 is used to monitor the temperature of the coolant entering and exiting the fuel cell stack 1 and transmits the measured temperature information to the water state controller 9 via the low-voltage signal line 8. The low-field nuclear magnetic resonance device 10 utilizes the nuclear magnetic resonance phenomenon to observe the spatial distribution of different forms of water, such as liquid water and film water, inside the fuel cell stack 1 in situ. This water state distribution information is also transmitted to the water state controller 9 via the low-voltage signal line 8. Based on the obtained temperature and water state distribution information, the water state controller 9 rationally controls the operating state of key actuators in the coolant circulation subsystem. Simultaneously, it controls the current output from the battery 11 to the magnetocaloric conversion device 16 via the current transmission line 12, thereby adjusting the operating state of the magnetocaloric conversion device 16. The two work together to achieve precise local temperature control inside the fuel cell stack 1, thereby improving the uniformity of the water state distribution.

[0032] This invention integrates multiple magnetocaloric conversion devices 16 uniformly within bipolar plates 13, and then connects these bipolar plates 13 in series with key components such as membrane electrodes and end plates to form a fuel cell stack 1. Due to the small size of the magnetocaloric conversion devices 16, there is virtually no loss in the volumetric power density of the fuel cell stack 1. At the same time, thanks to the additional temperature control capability of the magnetocaloric conversion devices 16, the power of cooling water circuit components such as water pumps 4 and cooling fans can be reduced, thus reducing the space occupied by the fuel cell system. This invention integrates a low-field nuclear magnetic resonance device 10 into the end plates at both ends of the fuel cell stack 1 and powers it through an external battery 11. This overcomes the current limitations of relying solely on external parameters such as voltage, gas inlet and outlet pressure, flow rate, and temperature for analysis, enabling in-situ observation of different forms of water, such as liquid water and modal water, inside the fuel cell stack 1, as well as identification of differences in water state distribution between and within individual cells. Furthermore, this integrated design avoids a significant increase in the volume of the fuel cell system and ensures stable operation under all weather and operating conditions.

[0033] This invention also provides a water state control method for the above-mentioned fuel cell system, including a rapid and uniform temperature rise control process for the fuel cell stack 1 during cold start, such as... Figure 5 As shown, the rapid and uniform temperature rise control process of fuel cell stack 1 under cold start includes the following steps: Based on the number of magnetocaloric conversion devices 16, the fuel cell stack 1 is divided into several equal-volume spatial regions, with the same number of magnetocaloric conversion devices 16 in each region. When the fuel cell system enters the low-temperature cold start process, the low-field nuclear magnetic resonance device 10 first operates, scanning and analyzing to determine the spatial distribution of liquid water and solid ice inside the fuel cell stack 1. Then, based on the distribution of solid ice, the distributed magnetocaloric conversion devices 16 are activated. Based on the synergistic superposition of the fields of the magnetic field generators 22 in different orientations, the heating rate of different regions of the fuel cell stack 1 is controlled. At the same time, the coolant circulation system works in coordination to achieve rapid and uniform heating inside the fuel cell stack 1 during the cold start process, while maintaining better consistency and uniformity of the water state. Specifically, in this process, the low-field nuclear magnetic resonance device 10 periodically scans the spatial distribution of water ice inside the fuel cell stack 1, and after calculation, determines the changes in the distribution of solid ice. It then targets areas where solid ice melts slowly and areas where a significant amount remains, i.e., areas where the solid ice melting rate is less than a specified value. V set Or the volume content of solid ice is greater than the specified value. Then, by adjusting the working state of the magnetocaloric conversion device 16, the heating power of the corresponding area is increased, and the de-icing is accelerated; the melting rate of solid ice in the area is not less than the specified value. V set Or the volume content of solid ice does not exceed the specified value. If the heating state of the original magnetocaloric conversion device 16 is maintained, the fuel cell stack 1 will reach the target temperature.

[0034] In one embodiment, the process also includes a process for controlling the uniform distribution of water state inside the fuel cell stack 1 under normal operation, such as... Figure 6 This method addresses the susceptibility of water management failures during actual fuel cell operation by regulating the internal water state of the fuel cell within a reasonable range and maintaining uniform distribution between and within cells to prevent flooding or membrane dryness failures. First, based on the number of magnetocaloric conversion devices 16, the fuel cell stack 1 is divided into several equal-volume spatial regions, with the same number of magnetocaloric conversion devices 16 in each region. Then, a low-field nuclear magnetic resonance (NMR) device 10 operates periodically, scanning and analyzing the spatial distribution of liquid water and membrane water inside the fuel cell stack 1 to determine whether flooding or membrane dryness failure has occurred. If a flooding failure occurs, the NMR results are used to further locate the faulty cell and its specific fault area within its surface. Subsequently, the distributed magnetocaloric conversion devices 16 operate, causing a significant and rapid increase in the membrane electrode temperature within the faulty area, accelerating the evaporation of excess liquid water, and maintaining a relatively constant temperature in other areas. Once the flooding fault is completely eliminated, the distributed magnetocaloric conversion device 16 gradually stops working in cooperation with the coolant circulation system, ensuring uniform temperature distribution in the fuel cell stack 1 during this process. If a membrane dryness fault occurs, the faulty cell and its specific fault area within the plane are first located based on the nuclear magnetic resonance results. Then, the distributed magnetocaloric conversion device 16 operates in cooperation with the coolant circulation system, reaching a preset stable state without significantly affecting the original temperature distribution of the fuel cell stack 1. Then, the distributed magnetocaloric conversion device 16 is controlled to stop working. Utilizing the heat absorption effect of the magnetocaloric conversion device 16 during this process, the membrane electrode temperature in the fault area is significantly reduced, accelerating water vapor condensation, while the temperature in other areas remains basically unchanged, ultimately eliminating the membrane dryness fault.

[0035] 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. Furthermore, those skilled in the art will recognize that, based on the ideas of this invention, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of this invention.

Claims

1. A fuel cell system, characterized in that: include: A fuel cell stack includes multiple bipolar plates and multiple membrane electrode assemblies arranged alternately. The bipolar plates are provided with coolant channels to allow coolant at a set temperature to flow through them. Multiple magnetocaloric device mounting slots are uniformly arranged on the outside of the coolant channels, and magnetocaloric conversion devices are installed in the magnetocaloric device mounting slots. The coolant circulation subsystem is connected to the coolant flow channel in the fuel cell stack through a pipeline, and can introduce coolant at a set temperature into the coolant flow channel and make the coolant circulate between the coolant circulation subsystem and the coolant flow channel at a set rate. as well as The water state control subsystem can monitor the temperature of the coolant entering and exiting the fuel cell stack and the spatial distribution of water in different states inside the fuel cell stack. Based on the temperature and water state distribution information, it controls the working state of the coolant circulation subsystem and the working state of the magnetocaloric conversion device to achieve local temperature regulation inside the fuel cell stack. The fuel cell stack further includes a current collector, an insulating plate, and an end plate. Multiple bipolar plates and multiple membrane electrode assemblies are alternately stacked to form an electrode assembly. Current collectors are located at both ends of the electrode assembly. An end plate is located outside the current collector, and an insulating plate is located between the end plate and the current collector. The end plate includes an inlet end plate with reactant gas collection / discharge ports and coolant collection / discharge ports. Multiple magnetic field generator mounting slots are evenly distributed around the inside of the inlet end plate, and magnetic field generators are fixedly installed within these slots. The magnetic field generators are externally connected to… The system includes a battery; the intake end plate has an internal slot for a low-field nuclear magnetic resonance (NMR) main magnetic field system, and the low-field NMR main magnetic field system is installed in the slot; the end plate includes a blind end plate, and multiple magnetic field generator mounting slots are evenly distributed around the perimeter of the blind end plate, with magnetic field generators fixedly installed in the slots; the magnetic field generators are externally connected to a battery; the blind end plate also has an internal slot for a low-field NMR radio frequency (RF) system, and the low-field NMR RF system is installed in the slot.

2. The fuel cell system according to claim 1, characterized in that: The bipolar plate has reaction gas channels on both sides and a coolant channel in the middle.

3. The fuel cell system according to claim 2, characterized in that: The mounting groove of the magnetocaloric device is filled with a thermally and electrically conductive adhesive to fix the magnetocaloric conversion device and realize the thermoelectric conduction between the magnetocaloric conversion device and the bipolar plate.

4. The fuel cell system according to claim 3, characterized in that: The coolant circulation subsystem includes a three-way valve, a cooling fan assembly, a water pump, and a heater. The two ports of the three-way valve are respectively connected to the inlet of the cooling fan assembly and the inlet of the heater via pipelines. The third port of the three-way valve is connected to the drain outlet of the fuel cell stack. The outlet of the cooling fan assembly and the outlet of the heater are connected to the water inlet of the fuel cell stack via pipelines equipped with the water pump. The three-way valve, cooling fan assembly, water pump, and heater are respectively connected to the water state control subsystem via low-voltage signal lines.

5. The fuel cell system according to claim 4, characterized in that: The water state control subsystem includes a water state controller, a battery, a low-field nuclear magnetic resonance (NMR) device, and coolant inlet and outlet temperature sensors. The coolant inlet and outlet temperature sensors are located at both the inlet and outlet of the fuel cell stack. The low-field NMR device is situated on one side of the fuel cell stack and connected to it via a low-voltage signal line. The battery is connected to a magnetocaloric conversion device within the fuel cell stack via a current transmission line. The three-way valve, cooling fan assembly, water pump, heater, battery, low-field NMR device, and coolant inlet and outlet temperature sensors are communicatively connected to the water state controller via the low-voltage signal line.

6. A water state control method for a fuel cell system as described in claim 5, characterized in that: This includes a rapid and uniform temperature rise control process for the fuel cell stack during cold start, which comprises the following steps: The low-field nuclear magnetic resonance device is in operation; The spatial distribution of liquid water and solid ice inside the fuel cell stack was determined through scanning analysis. Based on the distribution of solid ice, the magnetocaloric conversion device is activated, and the heating rate of different regions of the fuel cell stack is controlled by the field synergy superposition of magnetic field generators in different directions. The coolant circulation system works in coordination to achieve rapid and uniform heating inside the fuel cell stack during cold start-up; A low-field nuclear magnetic resonance device periodically scans the spatial distribution of water ice inside a fuel cell stack, and the changes in solid ice distribution are obtained after calculation. The rate of solid ice melting in the region is less than the specified value. V set Or the volume content of solid ice is greater than the specified value. Then, by adjusting the working state of the magnetocaloric conversion device, the heating power of the corresponding area can be increased; the melting rate of solid ice in the area should not be less than the specified value. V set Or the volume content of solid ice does not exceed the specified value. Then the heating state of the original magnetocaloric conversion device will be maintained until the fuel cell stack reaches the target temperature.

7. The water state control method for a fuel cell system according to claim 6, characterized in that: It also includes a process for controlling the uniform distribution of water state inside the fuel cell stack under normal operation, which includes the following steps: The low-field nuclear magnetic resonance device operates periodically; The spatial distribution of liquid water and membrane water inside the fuel cell stack is obtained through scanning analysis, and it is determined whether the fuel cell stack has experienced flooding or membrane drying failure. If a flooding fault occurs, the faulty individual cell and its in-plane fault region can be further located based on the nuclear magnetic resonance results. When the magnetocaloric conversion device is in operation, the temperature of the membrane electrode in the fault area increases, which accelerates the evaporation of excess liquid water and keeps the temperature in other areas constant. Once the flooding fault is completely eliminated, the magnetocaloric conversion device gradually stops working with the help of the coolant circulation system, ensuring uniform temperature distribution of the fuel cell stack during this process. If membrane drying failure occurs, the faulty monomer and its in-plane fault region can be located based on nuclear magnetic resonance results. With the cooperation of the coolant circulation system, the magnetocaloric conversion device works and reaches the preset stable state; The magnetocaloric conversion device is controlled to stop working. During this process, the heat absorption effect of the magnetocaloric conversion device is used to reduce the temperature of the membrane electrode in the fault area, accelerate the condensation of water vapor, while the temperature in other areas remains unchanged, and finally eliminate the membrane dryness fault.

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