Vehicle fuel cell hydrogen heating system and control method

Abstract

The invention discloses a vehicle fuel cell hydrogen heating system and a control method, and belongs to the technical field of fuel cells. The heating system comprises a hydrogen micro-channel heat exchanger, a plurality of heating membranes are fixedly arranged on the surface of a shell of the hydrogen micro-channel heat exchanger, and each heating membrane is provided with a temperature sensor. A heating diaphragm is controlled to be at a safe heating temperature through a fuel cell domain controller FCU, meanwhile, hydrogen is indirectly heated in a hydrogen micro-channel heat exchanger in combination with a PTC heater, and hydrogen heating in a high and cold state is assisted to be improved. Heating modes ('water total heating + membrane total heating ', 'water semi-heating + membrane total heating', 'membrane total heating 'and'stable self-heat production') are intelligently selected according to the environment temperature, and water heating and membrane heating coupling heating is realized, so that the parasitic power of the vehicle fuel cell running in a low-temperature environment is reduced, the hydrogen electricity safety in a fuel cell system is improved, and the service life of the vehicle fuel cell is prolonged. More liquid water is prevented from entering the fuel cell stack, the power generation performance of the fuel cell is improved, and the service life is prolonged.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of fuel cell technology, and more particularly to a hydrogen heating system for vehicle fuel cell and a control method. BACKGROUND

[0002] Fuel cell electric vehicles use high-pressure gaseous hydrogen as an energy carrier, which is stored in a hydrogen storage cylinder with a rated pressure of 35 MPa or 70 MPa, and is reduced to 1.2-1.5 MPa by the vehicle-mounted hydrogen system to enter the fuel cell system for electrochemical reaction. However, hydrogen does work on the outside during the pressure reduction process, and will absorb a large amount of heat from the outside, resulting in the temperature of fresh hydrogen entering the fuel cell being lower than the ambient temperature. Especially in the high-cold application scenario of fuel cell electric vehicles, the temperature of hydrogen in the hydrogen storage cylinder is close to -30℃, or even lower, and the hydrogen entering the proportional valve or hydrogen injection solenoid valve in the fuel cell system after pressure reduction cannot normally work due to the too low temperature of hydrogen, the hydrogen inlet pressure cannot be normally established, resulting in failure of cold start of the fuel cell in high-cold environment.

[0003] The optimal working temperature of the fuel cell system is generally 60-80℃, and the temperature of hydrogen, air and cooling liquid entering the fuel cell stack is required to reach this temperature range. The fuel cell uses excess hydrogen as the main fuel, and the remaining hydrogen after the reaction is separated by a hydrogen water separator. The high-temperature and high-humidity recycled hydrogen is mixed with fresh hydrogen in the ejector pipe, which is easy to produce a large amount of liquid water droplets entering the fuel cell stack, causing local flooding of the fuel cell stack, and easily causing serious faults such as low single-cell voltage. At the same time, the electrochemical reaction of hydrogen with low temperature and air with high temperature on both sides of the proton exchange membrane is easy to cause the rupture of the proton exchange membrane due to the large temperature difference, accelerate the life attenuation of the fuel cell, and even cause irreversible damage.

[0004] A fuel cell hydrogen heating device and a vehicle are disclosed in Chinese patent application CN 118610509A. The fuel cell hydrogen heating device includes a bottom plate, a heat exchange fin group is arranged on the bottom plate, and the heat exchange fin group extends and distributes along the first direction and the second direction of the bottom plate. The heat exchange fin group extending along the second direction is distributed in a layered heating structure, and a placement channel is arranged between the heat exchange fin groups of adjacent two layers. A hydrogen pipeline is used for hydrogen transmission, and the hydrogen pipeline reciprocally penetrates the placement channel in the layered distribution direction. A fixing assembly is arranged on the bottom plate for fixing the hydrogen pipeline. An electricity generating assembly is detachably connected with the bottom plate and is used for generating electricity. The patent can heat the hydrogen pipeline using the heat of the vehicle itself, avoid liquid water in the hydrogen from entering the gas pipeline of the fuel cell to block the gas path, and ensure the normal work of the fuel cell. However, when the fuel cell is started for the first time at low temperature, the heat of the whole vehicle has not been generated or the heat generated by pure electricity is limited, which leads to too low temperature of the hydrogen used by the fuel cell, causing the failure of starting the fuel cell, and the technical problem of low-temperature cold start cannot be solved.

[0005] Chinese patent application CN 111322898A discloses a hydrogen fuel cell hydrogen heat exchanger and a use method thereof. The heat exchanger includes a heat exchange core, the heat exchange core includes a plurality of spaced compression air flow channels and cooling liquid flow channels, the two ends of the compression air flow channel are connected with a compression air inlet cavity and a compression air outlet cavity respectively, the compression air inlet cavity and the compression air outlet cavity are connected with a compression air inlet and a compression air outlet respectively, the heat exchange core is located at the two ends of the cooling liquid flow channel and is connected with a cooling liquid inlet cavity and a cooling liquid outlet cavity respectively, the cooling liquid inlet cavity and the cooling liquid outlet cavity are connected with a cooling liquid inlet and a cooling liquid outlet respectively, a hydrogen pipeline is installed in the cooling liquid outlet cavity, and the gas inlet and the gas outlet of the hydrogen pipeline extend to the outside through the cooling liquid outlet cavity. The patent heats the cooling liquid by compressed air, and then heats the hydrogen to a suitable temperature by the cooling liquid for use by the hydrogen fuel cell. The hydrogen heat exchange area of this hydrogen heat exchanger is small, and the heat exchange effect is poor, which can meet the use in a lower environment temperature. However, there are still great technical barriers in high-cold application scenarios, such as the increase in the volume of the heat exchanger, the increase in the power of the PTC water heater, the increase in the system integration volume, and the small environmental applicability range. SUMMARY

[0006] The present application provides a vehicle fuel cell hydrogen heating system and a control method, which aims to solve the above problems existing in the prior art fuel cell hydrogen heating system.

[0007] The present application adopts the following technical solutions: The application discloses a hydrogen heating system for a fuel cell vehicle, which comprises a hydrogen micro-channel heat exchanger, wherein the hydrogen micro-channel heat exchanger is provided with a cooling medium inlet and a cooling medium outlet at two ends of a heat medium channel, and is provided with a hydrogen inlet and a hydrogen outlet at two ends of a cooling medium channel; the cooling medium inlet is connected with a rear end of a thermostat of a stack cooling subsystem, and the cooling medium outlet is connected with an inlet of a water pump of the stack cooling subsystem; the hydrogen inlet is connected with a pipeline of an on-board hydrogen system, and the hydrogen outlet is connected with a hydrogen proportional valve or a hydrogen injection electromagnetic valve; a plurality of heating film pieces are fixedly arranged on the surface of the shell of the hydrogen micro-channel heat exchanger, and each heating film piece is provided with a temperature sensor; and the heating film pieces and the temperature sensors are electrically connected with a fuel cell area controller FCU.

[0008] In a preferred embodiment, the internal medium of the heat medium channel and the hydrogen in the cooling medium channel of the hydrogen micro-channel heat exchanger are opposite to each other, the cooling medium inlet corresponds to the hydrogen outlet, and the cooling medium outlet corresponds to the hydrogen inlet.

[0009] In a preferred embodiment, the shell of the hydrogen micro-channel heat exchanger has four surfaces, and one heating film piece is attached to each surface.

[0010] In a preferred embodiment, the heating film piece is a flexible heating film piece, the back surface of the heating film piece is provided with high-temperature glue, and the heating film piece is highly attached to the surface of the shell of the hydrogen micro-channel heat exchanger.

[0011] In a preferred embodiment, deionized medium is used as the cooling medium of the heat medium channel of the hydrogen micro-channel heat exchanger, and the upper layer and the lower layer of the heating film piece are both isolated by an insulating layer.

[0012] In a preferred embodiment, the outermost layer of the heating film piece is covered by a fireproof sponge and covered by an aluminum foil.

[0013] The application further provides a control method for hydrogen heating of a fuel cell vehicle, which adopts the hydrogen heating system for the fuel cell vehicle, and the specific steps are as follows: S1, the fuel cell area controller FCU receives a start-up instruction, checks whether the basic conditions for starting up are met, and if yes, operates the water pump of the battery, and makes the cooling medium pass through the "small circulation" channel by adjusting the thermostat; S2, whether the ambient temperature T0 is lower than-20 DEG C is judged, if yes, the "water full heating + film full heating" mode is started, the PTC heater is operated at the maximum power, and all the heating film pieces are operated at the maximum power; if not, S3 is entered; S3, whether the ambient temperature T0 is lower than-10 DEG C is judged, if yes, the "water half heating + film full heating" mode is started, the PTC heater is operated at half of the heating power, and all the heating film pieces are operated at the maximum power; if not, S4 is entered; S4, judging whether the ambient temperature T0 is lower than 2℃, if yes, starting the "film full heating" mode, the PTC heater is in the closed state, and all the heating film sheets are in the maximum power operation; S5, when the fuel cell stack outlet water temperature T1 exceeds -10℃ and the hydrogen temperature T3 exceeds 10℃, the FCU performs the normal start-up process; S6, judging whether the outlet water temperature T1 exceeds 50℃, if yes, the cooling medium starts the "large circulation" channel; when the outlet water temperature T1 is in the range of 50-55℃, the water temperature increases by 1℃, the thermostat opening degree y increases by 2%; when the outlet water temperature T1 is in the range of 55-58℃, the water temperature increases by 1℃, the thermostat opening degree y increases by 4%; when the outlet water temperature T1 is in the range of 58-60℃, the water temperature increases by 1℃, the thermostat opening degree y increases by 2%; when the outlet water temperature exceeds 60℃, the thermostat no longer changes.

[0014] Specifically, the above-mentioned "small circulation" channel refers to from the water pump to the PTC heater, through the thermostat to the fuel cell stack and the hydrogen micro-channel heat exchanger, and finally back to the water pump inlet; the "large circulation" channel refers to from the water pump to the radiator, through the thermostat to the fuel cell stack and the hydrogen micro-channel heat exchanger, and finally back to the water pump inlet.

[0015] Further, in the above-mentioned step S3, step S4 or step S5, when the temperature of any one of the heating film sheets exceeds 60℃, the power supply relay pulse width PWM of the heating film sheet is adjusted lower by the fuel cell area controller FCU, and the heating film sheet is protected from overheating according to the heating film sheet temperature exceeding 2℃, the power supply pulse width amplitude is reduced by 6% at the rate; if the heating film sheet temperature is detected again to be lower than 60℃, the heating film sheet is ensured to be in a constant temperature state of 60℃ according to the heating film sheet temperature being lower than 2℃, the power supply pulse width amplitude is increased by 4% at the rate; if the hydrogen temperature sensor T3 exceeds 30℃, the PTC heater is in the shutdown state, and the "film full heating" single mode is turned to; if the hydrogen temperature sensor T3 exceeds 45℃, the heating film sheet stops working, and the fuel cell "stable self-heat" mode is turned to.

[0016] Further, in the above-mentioned step S6, if the fuel cell controller FCU detects that the ambient temperature exceeds 30℃, the above-mentioned thermostat increases the opening degree by 2% respectively.

[0017] From the above description of the present application, compared with the prior art, the present application has the following advantages: 1. The present application pastes multiple flexible heating film pieces on the surface of the shell of a hydrogen micro-channel heat exchanger, and controls the heating film at a safe heating temperature by a fuel cell area controller FCU to realize a hydrogen efficient and rapid heating scheme, and indirectly heats hydrogen in the hydrogen micro-channel heat exchanger by combining a PTC water heater to assist in improving hydrogen heating in a high-cold state (environmental temperature <-20℃), avoid long waiting time for heating, poor heat preservation effect, etc., and can also be compatible with the existing industry water heating technology route.

[0018] 2. The present application can intelligently select four heating modes according to the environmental temperature (water full heating + film full heating, water half heating + film full heating, film full heating, and stable self-produced heat), realize a water heating and film heating coupled heating control scheme, thereby reducing the parasitic power of a vehicle fuel cell running in a low temperature environment, and can also self-adaptively adjust the hydrogen heating power according to the temperature of the fuel cell stack, improve the hydrogen safety inside the fuel cell system, prevent the fuel cell stack from entering more liquid water, and improve the fuel cell power generation performance and service life. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 is a schematic diagram of the fuel cell hydrogen heating system of the present application.

[0020] Figure 2 is a structural schematic diagram of the hydrogen micro-channel heat exchanger of the present application.

[0021] Figure 3 is a schematic diagram of the fuel cell hydrogen heating control method of the present application. Figure 2

[0022] Figure 4 is a flowchart of the fuel cell hydrogen heating control method of the present application. DETAILED DESCRIPTION

[0023] The specific embodiments of the present application will be described below with reference to the accompanying drawings. In order to fully understand the present application, many details are described below, but the present application can also be implemented without these details for those skilled in the art. For well-known components, methods and processes, the following will not be described in detail.

[0024] The present embodiment provides a vehicle fuel cell hydrogen heating system, which refers to Figure 1 ​, including a hydrogen micro-channel heat exchanger 10 installed in a fuel cell system. The fuel cell system includes a fuel cell stack, an air path subsystem, a hydrogen path subsystem, and a stack cooling subsystem. Among them, the air path subsystem is a common subsystem in the field of fuel cells, and is not the focus of the present scheme, and will not be described in detail here. The hydrogen path subsystem includes: an on-board hydrogen system 21, a hydrogen proportional valve 22 (or a hydrogen injection electromagnetic valve), an ejector 23, a gas-water separator 24, a drain electromagnetic valve 25, and a tail pipe 26. And the stack cooling subsystem includes: a water pump 31, a radiator 32, a PTC heater 33, and a thermostat 34.

[0025] The hydrogen micro-channel heat exchanger 10 is made of micro-channel technology to maximize the specific surface area per unit volume, obtain the maximum heat exchange area (more than ten times that of a shell-and-tube heat exchanger), and is made by lapping dozens of core plates under vacuum and high temperature and high pressure welding.

[0026] Referring to Figure 2 The hydrogen micro-channel heat exchanger 10 has a cooling medium inlet 11 and a cooling medium outlet 12 at both ends of the heat medium channel, and a hydrogen inlet 13 and a hydrogen outlet 14 at both ends of the coolant channel. The medium flow directions in the heat medium channel and the coolant channel are opposite, the cooling medium inlet 11 of the heat medium channel corresponds to the hydrogen outlet 14, and the cooling medium outlet 12 of the heat medium channel corresponds to the hydrogen inlet 13, which improves the heat exchange efficiency. In order to be more compactly arranged inside the fuel cell system, the cooling medium inlet 11 and the hydrogen inlet 13 are arranged vertically, which facilitates the concentrated arrangement of the pipelines in two directions.

[0027] Referring to Figure 2 and Figure 3 The hydrogen micro-channel heat exchanger 10 has a plurality of heating film pieces 15 fixed on the surface of the shell. Specifically, the shell of the hydrogen micro-channel heat exchanger has four surfaces, and one heating film piece 15 is pasted on each surface. The heating film piece 15 preferably adopts a flexible heating film piece. In addition to the arrangement requirement of the pipeline interface, the area of the heating film piece 15 is as consistent as possible with the surface area of the micro-channel, which effectively improves the heat exchange area, and the back of the heating film has a high-temperature glue, which is highly adhered to the surface of the heat exchanger, improving the heating uniformity.

[0028] Since the cooling medium is deionized medium, and must flow through the inside of the fuel cell stack, there may be a situation that the insulation value of the hydrogen micro-channel heat exchanger is low. Therefore, an insulation layer is used on the upper and lower layers of the heating film piece to avoid the risk of reducing the insulation value of the cooling liquid, while meeting the requirements of high insulation strength and high heat conduction efficiency.

[0029] Each heating film 15 is provided with a temperature sensor for real-time detection of the temperature of the heating film surface and for over-temperature protection. The heating power supply wire harness of the heating film 15 and the temperature sensor sampling wire harness are led out by welding + gluing fixation mode, connected to the fuel cell area controller FCU for collection, and the heating temperature is controlled in real time by software. In order to prevent heat loss, after the hydrogen micro-channel heat exchanger 10 is pasted with the heating film 15, the outermost layer is wrapped with a 20mm-thick fireproof sponge (not shown in the figure), covered with aluminum foil, and fixed on the fuel cell system sheet metal shell by bolts.

[0030] Referring to Figure 1 and Figure 2 , the hydrogen inlet 13 is connected to the pipeline of the vehicle-mounted hydrogen system 21, the hydrogen pressure is 13±2bar, the hydrogen temperature is close to the ambient temperature, and even for a long time under reduced pressure and heat absorption, the hydrogen temperature may be lower than the ambient temperature. The hydrogen outlet 14 is connected to the hydrogen proportional valve 22 (or hydrogen injection electromagnetic valve), and the hydrogen is reduced in pressure through the hydrogen proportional valve 22 or the hydrogen injection electromagnetic valve, and a hydrogen temperature sensor T3 is arranged in the middle.

[0031] Referring to Figure 1 and Figure 2 , the hydrogen at the hydrogen outlet of the fuel cell stack is mixed with the hydrogen heated by the hydrogen micro-channel heat exchanger 10 after passing through the gas-water separator 24 inside the ejector 23, and is injected into the hydrogen inlet of the fuel cell stack. The lower end of the gas-water separator 24 is provided with a drain electromagnetic valve 25 for pulse discharge of water in the hydrogen to prevent liquid water from being generated by mixing cold hydrogen with hydrogen heated by the hydrogen micro-channel heat exchanger 10, thereby blocking the gas cavities inside the ejector and the fuel cell stack.

[0032] Referring to Figure 1 and Figure 2 , the cooling medium inlet 11 is connected to the rear end of the thermostat 34 of the stack cooling subsystem, and is connected in parallel with the cooling medium pipeline of the fuel cell stack. The cooling medium outlet 12 is connected to the inlet of the water pump 31 of the stack cooling subsystem. When the cooling medium temperature is detected to be relatively low, the cooling medium passes through the "small circulation" channel: from the water pump 31 to the PTC heater 33, through the thermostat 34 to the fuel cell stack and the hydrogen micro-channel heat exchanger 10, and finally back to the inlet of the water pump 31; when the cooling medium temperature is relatively high, the cooling medium passes through the "large circulation" channel: from the water pump 31 to the radiator 32, through the thermostat 34 to the fuel cell stack and the hydrogen micro-channel heat exchanger 10, and finally back to the inlet of the water pump 31.

[0033] The control method of the above vehicle fuel cell hydrogen heating system, referring to Figure 4 , specifically includes the following steps: S1, the fuel cell area controller FCU receives the start-up instruction, checks whether the basic conditions for start-up are met, if yes, the cell water pump is operated, the cooling medium passes through the "small circulation" channel by adjusting the thermostat.

[0034] S2, whether the ambient temperature T0 is lower than -20℃, if yes, the "water full heating + film full heating" mode is started, the PTC heater is operated at maximum power, and all the heating films are operated at maximum power; if not, S3 is entered; S3, whether the ambient temperature T0 is lower than -10℃, if yes, the "water half heating + film full heating" mode is started, the PTC heater is operated at half heating power, and all the heating films are operated at maximum power; if not, S4 is entered; S4, whether the ambient temperature T0 is lower than 2℃, if yes, the "film full heating" mode is started, the PTC heater is in the off state, and all the heating films are operated at maximum power; S5, when the fuel cell stack outlet water temperature T1 exceeds -10℃ and the hydrogen temperature T3 exceeds 10℃, the FCU executes the normal start-up process; S6, whether the outlet water temperature T1 exceeds 50℃, if yes, the cooling medium passes through the "large circulation" channel; when the outlet water temperature T1 is in the range of 50-55℃, the water temperature increases by 1℃, the thermostat opening degree y increases by 2%; when the outlet water temperature T1 is in the range of 55-58℃, the water temperature increases by 1℃, the thermostat opening degree y increases by 4%; when the outlet water temperature T1 is in the range of 58-60℃, the water temperature increases by 1℃, the thermostat opening degree y increases by 2%; when the outlet water temperature exceeds 60℃, the thermostat no longer changes.

[0035] In the above steps S2, S3 or S4, when the temperature of any one of the heating films exceeds 60℃, the fuel cell area controller FCU adjusts the heating film power supply relay pulse width PWM, according to the heating film temperature exceeding 2℃, the power supply pulse width amplitude is reduced by 6% at the rate of protecting the heating film from overheating, if the heating film temperature is detected to be lower than 60℃ again, according to the heating film temperature being lower than 2℃, the power supply pulse width amplitude is increased by 4% at the rate of ensuring the heating film to be in a constant temperature state of 60℃; if the hydrogen temperature sensor T3 exceeds 30℃, the PTC heater is in the off state, and the "film full heating" single mode is entered; if the hydrogen temperature sensor T3 exceeds 45℃, the heating film stops working, and the fuel cell "stable self-heat" mode is entered.

[0036] In the above step S6, if the fuel cell controller FCU detects that the ambient temperature exceeds 30℃, the above electronic thermostats are increased by 2% opening degree respectively, to improve the self-adaptive ability of the ambient temperature to the fuel cell heat dissipation.

[0037] Since the liquid hydrogen storage temperature reaches-253 DEG C, after gaseous evaporation in the liquid hydrogen storage and supply system, the hydrogen is in low-temperature gaseous state, at this time, the hydrogen still needs to be heated further in the fuel cell system, therefore, the hydrogen heating scheme provided by the application is also applicable to the vehicle-mounted liquid hydrogen storage and supply system.

[0038] The above merely describes the specific embodiments of the present application, but the design concept of the present application is not limited thereto, and any non-essential modification of the present application by using the concept shall be deemed as an infringement of the protection scope of the present application.

Claims

1. A hydrogen heating system for a vehicle fuel cell, characterized by: It includes a hydrogen microchannel heat exchanger, wherein a cooling medium inlet and a cooling medium outlet are respectively provided at both ends of the heat medium channel of the hydrogen microchannel heat exchanger, and a hydrogen inlet and a hydrogen outlet are respectively provided at both ends of the refrigerant channel; the cooling medium inlet is connected to the rear end of the thermostat of the fuel cell cooling subsystem, and the cooling medium outlet is connected to the water pump inlet of the fuel cell cooling subsystem; the hydrogen inlet is connected to the on-board hydrogen system pipeline, and the hydrogen outlet is connected to the hydrogen proportional valve or the hydrogen injection solenoid valve; a plurality of heating diaphragms are fixedly provided on the outer surface of the hydrogen microchannel heat exchanger, each heating diaphragm is provided with a temperature sensor, and the heating diaphragm and the temperature sensor are respectively electrically connected to the fuel cell domain controller FCU.

2. A vehicle fuel cell hydrogen heating system according to claim 1, characterized in that: The medium inside the heat medium channel and the hydrogen inside the coolant channel of the hydrogen microchannel heat exchanger flow in opposite directions, the cooling medium inlet corresponds to the hydrogen outlet, and the cooling medium outlet corresponds to the hydrogen inlet.

3. The vehicle fuel cell hydrogen heating system according to claim 1, characterized in that: The shell of the hydrogen microchannel heat exchanger has four surfaces, and each surface is adhered with a heating film.

4. A vehicle fuel cell hydrogen heating system according to claim 3, characterized in that: The heating diaphragm is a flexible heating diaphragm. The back of the heating diaphragm is provided with high-temperature glue, which is highly fitted with the outer shell surface of the hydrogen microchannel heat exchanger.

5. The vehicle fuel cell hydrogen heating system according to claim 1, characterized in that: The heat medium pipeline of the hydrogen microchannel heat exchanger uses deionized medium as the cooling medium, and the upper layer and the lower layer of the heating membrane are both isolated by an insulating layer.

6. The vehicle fuel cell hydrogen heating system according to claim 1, characterized in that: The outermost layer of the heating film is wrapped with flame retardant sponge and covered with aluminum foil.

7. A method for controlling hydrogen heating in a vehicle fuel cell, characterized in that: The vehicle fuel cell hydrogen heating system according to claim 1 is used, and the specific steps are as follows: S1: The fuel cell domain controller (FCU) receives a stack start command and self-checks whether the basic start conditions are met. If so, it starts the battery water pump and adjusts the thermostat to allow the cooling medium to flow through the "small circulation" channel. S2. Determine whether the ambient temperature T0 is lower than -20°C. If so, turn on the "water full heating + membrane full heating" mode, with the PTC heater and all heating membranes operating at maximum power. If not, proceed to S3. S3: Determine whether the ambient temperature T0 is lower than -10°C. If so, turn on the "water half heating + membrane full heating" mode, with the PTC heater operating at half heating power and all heating membranes operating at maximum power. If not, proceed to S4. S4. Determine whether the ambient temperature T0 is lower than 2°C. If so, turn on the "full membrane heating" mode, the PTC heater is turned off, and all heating membranes are running at maximum power; S5. When the fuel cell stack outlet water temperature T1 exceeds -10°C and the hydrogen temperature T3 exceeds 10°C, the FCU executes the normal stack start-up process; S6. Determine whether the outlet water temperature T1 exceeds 50°C. If so, the cooling medium starts to flow through the "large circulation" channel; when the outlet water temperature T1 is within the range of 50-55°C, the thermostat opening y increases by 2% for every 1°C increase in water temperature; when the outlet water temperature T1 is within the range of 55-58°C, the thermostat opening y increases by 4% for every 1°C increase in water temperature; when the outlet water temperature T1 is within the range of 58-60°C, the thermostat opening y increases by 2% for every 1°C increase in water temperature; when the outlet water temperature exceeds 60°C, the thermostat no longer changes.

8. The method for controlling hydrogen heating of a vehicle fuel cell according to claim 7, wherein: The "small circulation" channel refers to the channel from the water pump to the PTC heater, through the thermostat to the fuel cell stack and the hydrogen microchannel heat exchanger, and finally returns to the water pump inlet; the "large circulation" channel refers to the channel from the water pump to the radiator, through the thermostat to the fuel cell stack and the hydrogen microchannel heat exchanger, and finally returns to the water pump inlet.

9. The method for controlling hydrogen heating of a vehicle fuel cell according to claim 7, wherein: In step S2, step S3 or step S4, when the temperature of any heating diaphragm exceeds 60°C, the power relay pulse width PWM of the heating diaphragm is lowered through the fuel cell domain controller FCU, and the power pulse width is reduced at a rate of 6% when the heating diaphragm temperature exceeds 2°C to protect the heating diaphragm from overheating. If the heating diaphragm temperature is detected to be lower than 60°C again, the power pulse width is increased at a rate of 4% when the heating diaphragm temperature is lower than 2°C to ensure that the heating diaphragm is in a constant temperature state of 60°C; if the hydrogen temperature sensor T3 exceeds 30°C, the PTC heater is in the off state and switches to the "full membrane heating" single mode; if the hydrogen temperature sensor T3 exceeds 45°C, the heating diaphragm stops working and switches to the fuel cell "stable self-heating" mode.

10. The method for controlling hydrogen heating of a vehicle fuel cell according to claim 7, wherein: In step S6, if the fuel cell controller FCU detects that the ambient temperature exceeds 30°C, the above thermostats are opened by 2% respectively.

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