Cold start method for fuel cell system and fuel cell system

Abstract

The invention relates to a cold start method for a fuel cell system. The cold start method comprises the following steps: judging whether the fuel cell system is operated in a cold start mode or not; in the cold start mode, enabling a coolant in an electric pile of the fuel cell system to have a first flow speed; estimating the internal temperature of the electric pile, and comparing the internal temperature with a preset first target temperature; when the internal temperature reaches a specific proportion of the first target temperature, calculating a second flow rate according to the heat production rate of the galvanic pile and the heat dissipation rate of the coolant, and enabling the coolant to flow through the galvanic pile at the second flow rate; and when a preset standard is met, ending the cold start mode. The invention also relates to a corresponding fuel cell system. According to the invention, freezing and cold shock can be avoided, and the coolant flow can be adjusted in a targeted and accurate manner, so that the temperature in the stack is uniformly distributed and the overheating risk is reduced as much as possible.

Description

Technical Field

[0001] The present invention relates to the field of fuel cells, and in particular to a cold start method for a fuel cell system. The present invention also relates to a corresponding fuel cell system. Background Art

[0002] In recent years, with the development of society and technology, people are paying more and more attention to issues such as air pollution and energy loss. Fuel cells are highly efficient power generation devices that convert chemical energy in anode gas and cathode gas directly into electrical energy through electrochemical reactions without going through a combustion process. The reaction product is mainly water and basically no harmful gases are emitted. Therefore, fuel cells have the advantages of high energy conversion efficiency and clean and environmentally friendly.

[0003] When the fuel cell is operating normally, the proton exchange membrane of the stack needs to maintain appropriate humidity to ensure that the proton exchange membrane has the desired proton transfer capacity and avoid "membrane dryness" or "flooding" failures, and the stack should be at a specific operating temperature to achieve optimized operating performance. To this end, it is necessary to continuously supply coolant to the stack, which flows through the stack through the coolant flow channel and takes away the heat generated by the reaction.

[0004] However, when the fuel cell system is started, if the ambient temperature is lower than the minimum operating temperature of the fuel cell, the fuel cell system needs to enter a cold start mode. In the cold start mode, water in the stack may freeze in the gas diffusion layer or the proton exchange membrane, especially on the cathode side, which will block the transport channels of the reaction gases and hinder the electrochemical reaction, and may even damage the microstructure inside the stack, thereby adversely affecting the service life of the fuel cell.

[0005] In existing fuel cell systems, the coolant flow rate supplied remains constant during the cold start process, but an excessive coolant flow rate will cause a cold shock to the fuel cell stack, which can cause the water inside the fuel cell stack to freeze on a large scale and cause a drop in voltage or current, thereby causing the fuel cell system to fail to start. An excessively small coolant flow rate may result in a large temperature difference between the inlet and outlet of the coolant, which can cause the fuel cell stack to overheat and damage the stack. Summary of the invention

[0006] Therefore, the object of the present invention is to propose an improved cold start method for a fuel cell system, in which icing and cold shock can be avoided by rapidly increasing the temperature of the fuel cell stack, and the coolant flow rate is adjusted in a targeted and precise manner, thereby making the temperature inside the fuel cell stack evenly distributed and reducing the risk of overheating as much as possible, thereby achieving a rapid and stable cold start process for the fuel cell system.

[0007] According to a first aspect of the present invention, a cold start method for a fuel cell system is provided, wherein the cold start method comprises at least the following steps:

[0008] S1: Determine whether the fuel cell system should be operated in a cold start mode;

[0009] S2: in the cold start mode, making the coolant in the fuel cell stack of the fuel cell system have a first flow rate;

[0010] S3: estimating the internal temperature of the fuel cell stack, and comparing the internal temperature with a preset first target temperature;

[0011] S4: when the internal temperature reaches a specific ratio of the first target temperature, calculating a second flow rate according to a heat generation rate of the fuel cell stack and a heat dissipation rate of the coolant, so that the coolant flows through the fuel cell stack at the second flow rate;

[0012] S5: When the preset standard is met, the cold start mode is terminated.

[0013] Compared with the prior art, in the cold start method for a fuel cell system according to the present invention, when it is determined that the system should operate in a cold start mode, the coolant is first allowed to flow through the fuel cell stack of the fuel cell system at a relatively low first flow rate, so that the heat energy generated by the stack is retained inside the stack as much as possible, thereby rapidly increasing the internal temperature of the stack to avoid icing and cold shock. When the estimated internal temperature of the stack reaches a specific proportion of the first target temperature, the flow rate of the coolant is increased to a second flow rate, which is calculated based on the heat generation rate of the stack and the heat dissipation rate of the coolant. In this way, the coolant flow rate can be specifically and accurately adjusted in combination with the actual operating conditions of the stack, so that the temperature inside the stack is evenly distributed and overheating of the stack is prevented, thereby ensuring a rapid and stable cold start process for the fuel cell system and enabling the fuel cell system to reliably achieve the desired performance as quickly as possible.

[0014] Exemplarily, in step S4, the heat generation rate of the fuel cell stack is made equal to the heat dissipation rate of the coolant.

[0015] Exemplarily, the heat dissipation rate is derived from the temperature difference between the coolant inside the fuel cell stack and the bipolar plate wall, the heat loss area of ​​the fuel cell stack, and the heat dissipation coefficient of the coolant; and / or, the heat dissipation rate is derived from the inlet and outlet temperature difference, density, specific heat capacity and flow rate of the coolant.

[0016] Exemplarily, in step S3, the internal temperature is calculated from the initial temperature of the coolant, the heat generated by the fuel cell stack and the thermal capacity of the fuel cell stack; and / or, in step S3, the internal temperature is estimated based on the outlet air temperature of the fuel cell stack.

[0017] Exemplarily, the cold start method additionally includes step S6 performed after step S4: when the outlet temperature exceeds a preset second target temperature, increasing the flow rate of the coolant to a third flow rate.

[0018] Exemplarily, the second target temperature is greater than or equal to the first target temperature; and / or, in step S6, when the inlet temperature of the coolant is less than the third target temperature, the third flow rate is the maximum allowable flow rate of the coolant and / or the rated flow rate during normal operation of the fuel cell system; and / or, in step S6, the third flow rate is set so that the inlet and outlet temperature difference of the coolant is less than a temperature difference threshold.

[0019] Exemplarily, in step S1, when the ambient temperature and / or the initial temperature of the coolant is less than 0°C, it is determined that the fuel cell system should operate in cold start mode; and / or, the first flow velocity is 0 m / s; and / or, the first target temperature is greater than 0°C; and / or, the specific ratio is less than or equal to 1.

[0020] Exemplarily, the preset standard includes at least one of the following groups: the output power of the fuel cell stack reaches a preset power; the inlet temperature and / or outlet temperature of the coolant reaches a fourth target temperature.

[0021] According to a second aspect of the present invention, there is provided a fuel cell system, wherein the fuel cell system at least comprises:

[0022] - a stack having bipolar plates and a membrane electrode assembly and provided with a coolant inlet and a coolant outlet for a coolant;

[0023] - a coolant circuit configured to redirect coolant discharged from a coolant outlet to the coolant inlet;

[0024] a coolant circulation pump, which is arranged in the coolant circuit and is configured to drive the coolant to flow in the coolant circuit;

[0025] - a first temperature sensor arranged at the coolant outlet to sense the outlet temperature of the coolant;

[0026] - a second temperature sensor arranged at the coolant inlet to sense the inlet temperature of the coolant; and

[0027] - A controller configured and adapted to implement the cold start method according to the invention.

[0028] Exemplarily, the fuel cell system further includes a third temperature sensor disposed at the coolant outlet, wherein the third temperature sensor is configured to sense an outlet air temperature at the coolant outlet. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The present invention will be described in more detail below with reference to the accompanying drawings, so that the principles, features and advantages of the present invention can be better understood. The accompanying drawings include:

[0030] Figure 1 A schematic block diagram of a fuel cell system according to an exemplary embodiment of the present invention is shown;

[0031] Figure 2 A schematic flow chart of a cold start method for a fuel cell system according to an exemplary embodiment of the present invention is shown. DETAILED DESCRIPTION

[0032] In order to make the technical problems, technical solutions and beneficial technical effects to be solved by the present invention more clearly understood, the present invention will be further described in detail below with reference to the accompanying drawings and multiple exemplary embodiments.

[0033] It should be understood that, in this document, the expressions "first", "second", etc. are used for descriptive purposes only and should not be understood as indicating or implying relative importance, nor should they be understood as implicitly indicating the number of technical features indicated. Features defined as "first" or "second" may explicitly or implicitly indicate that at least one of the features is included.

[0034] Figure 1 A schematic block diagram of a fuel cell system 100 according to an exemplary embodiment of the present invention is shown.

[0035] like Figure 1As shown, the fuel cell system 100 includes a stack 10, which is the place where electrochemical reactions occur and serves as the core of the entire fuel cell system 100, wherein the stack 10 is formed by stacking a plurality of fuel cell monomers in series, each fuel cell monomer having a membrane electrode assembly and bipolar plates located on both sides of the membrane electrode assembly, and the membrane electrode assembly is composed of a proton exchange membrane located in the middle and catalyst layers and gas diffusion layers located on both sides. When the fuel cell system 100 is operating normally, the anode gas, usually hydrogen, is supplied to the anode of the membrane electrode assembly, reaches the catalyst layer through the gas diffusion layer, and decomposes into hydrogen ions and releases two electrons under the catalytic action of the anode catalyst, such as platinum, and then the hydrogen ions pass through the proton exchange membrane to reach the cathode, and react with the cathode gas, such as oxygen in the air, that reaches the catalyst layer through the gas diffusion layer on the other side under the action of the cathode catalyst to generate water, and the released electrons form an electric current in the external circuit, wherein the reaction gas supplied to the stack 10 through the gas circuit of the fuel cell system 100 reaches the bipolar plates of each fuel cell monomer through the gas manifold respectively, and is distributed to the active area of ​​the membrane electrode assembly through the gas flow channel of the bipolar plate. For the sake of overview, the internal structure of the stack 10 and the reaction gas circuit of the fuel cell system 100 are not shown. In addition, in order to ensure that the stack 10 operates at the operating temperature and avoid the problem of overheating and burning, the coolant is supplied to each fuel cell monomer through the coolant manifold, and the coolant flows through the stack 10 through the coolant flow channel of the bipolar plate, thereby taking away the heat generated by the stack 10. Here, the fuel cell stack 10 is provided with a coolant inlet 11 and a coolant outlet 12 for coolant, wherein the coolant inlet 11 is connected to a coolant supply manifold portion to supply the coolant to the coolant flow channels of each fuel cell monomer, and the coolant outlet 12 is connected to a coolant discharge manifold portion to discharge the heated coolant flowing through the active area of ​​the fuel cell monomer from the fuel cell stack 10.

[0036] like Figure 1 As shown, the fuel cell system 100 includes a coolant circuit 20, which is configured to redirect the coolant discharged from the coolant outlet 12 to the coolant inlet 11, thereby realizing the circulation of the coolant. Here, the coolant should have characteristics such as good thermal conductivity, low viscosity, high boiling point and low freezing point, such as up to -45°C. The coolant can be an ethylene glycol type coolant, a propylene glycol type coolant or another coolant type that is considered meaningful by those skilled in the art.

[0037] like Figure 1As shown, the fuel cell system 100 includes a coolant circulation pump 30, which is arranged in the coolant circuit 20 and is configured to drive the coolant to circulate in the coolant circuit 20. The flow rate of the coolant in the coolant circuit 20 can be adjusted by controlling the impeller speed of the coolant circulation pump 30.

[0038] like Figure 1 As shown, the fuel cell system 100 includes a first temperature sensor 41 arranged at the coolant outlet 12 of the stack 10 and a second temperature sensor 42 arranged at the coolant inlet 11 to sense the outlet temperature and the inlet temperature of the coolant, respectively. The internal temperature distribution of the stack 10 can be determined and the operation of the stack 10 can be evaluated by the outlet temperature and the inlet temperature of the coolant. In addition, it is also possible that a third temperature sensor 43 is also arranged at the coolant outlet 12 of the stack 10, and the third temperature sensor is configured to sense the outlet air temperature at the coolant outlet 12, and the outlet air temperature is related to the coolant temperature and can reflect the internal temperature of the stack 10 to a certain extent.

[0039] like Figure 1 As shown, the fuel cell system 100 includes a controller 50, which is respectively connected to each temperature sensor to receive signals about the inlet and outlet temperatures, and is connected to the coolant circulation pump 30 to send a control signal to the coolant circulation pump 30, thereby adjusting the coolant flow rate. Here, the controller 50 is configured to implement the cold start method for the fuel cell system 100 according to the present invention.

[0040] Figure 2 A schematic flow chart of a cold start method for a fuel cell system according to an exemplary embodiment of the present invention is shown.

[0041] like Figure 2 As shown, the cold start method according to the present invention comprises at least the following steps:

[0042] S1: judging whether the fuel cell system 100 should be operated in the cold start mode according to the initial conditions, if yes, entering the cold start mode, if no, entering the normal mode;

[0043] S2: In the cold start mode, the coolant in the stack 10 of the fuel cell system 100 has a first flow rate, the first flow rate is, for example, 0 m / s, so that the coolant in the stack 10 first remains stationary and no coolant flows into or flows out of the stack 10, so that the heat generated by the stack 10 is completely used to increase the temperature of the coolant in the stack 10, thereby achieving a rapid increase in the internal temperature of the stack 10 and avoiding ice formation or cold shock, but other coolant flow rates that are considered meaningful by those skilled in the art may also be considered, the coolant flow rate being greater than 0 m / s;

[0044] S3: The controller 50 estimates the internal temperature of the battery stack 10, and compares the internal temperature with a preset first target temperature, wherein the first target temperature should be greater than 0° C., for example, 5° C., and of course, other temperature values ​​that are considered meaningful by those skilled in the art may also be considered, wherein the internal temperature of the battery stack 10 can be continuously monitored in real time, and the internal temperature of the battery stack 10 can also be obtained at a certain frequency interval;

[0045] S4: when the internal temperature calculated in step S3 reaches a specific ratio of the first target temperature, a second flow rate is calculated according to the heat generation rate of the fuel cell stack 10 and the heat dissipation rate of the coolant flowing through the fuel cell stack 10, so that the coolant flows through the fuel cell stack 10 at the second flow rate, and the second flow rate is significantly greater than the first flow rate, wherein the specific ratio is used as a safety factor to further reduce the overheating risk of the fuel cell stack 10 and can be determined according to experimental data and / or empirical data, for example, 0.8;

[0046] S5: When the preset standard is met, the cold start mode is terminated and the normal operation mode is switched.

[0047] Exemplarily, in step S1 , when the ambient temperature and / or the initial temperature of the coolant is less than 0° C., it is determined that the water in the stack 10 of the fuel cell system 100 is at risk of freezing and the fuel cell system 100 should be operated in a cold start mode.

[0048] For example, in step S3, the internal temperature of the stack 10 can be calculated from the initial temperature of the coolant, the heat generated by the stack 10 and the heat capacity of the stack 10, wherein:

[0049] The heat generation of the battery stack 10 is calculated according to the following formula (1):

[0050]

[0051] Wherein, Q is the heat generated by the battery stack 10, I is the current of the battery stack 10, E0 is the reversible voltage of the battery stack 10, U is the output voltage of the battery stack 10, and t is the duration of step S3;

[0052] The heat capacity of the stack 10 is calculated according to the following formula (2):

[0053] C=c BPP *m BPP +c MEA *m MEA +c coolant *m coolant (2)

[0054] Wherein, C is the heat capacity of the stack 10, c BPP is the specific heat capacity of the bipolar plates of the stack 10, m BPP is the mass of the bipolar plates of the stack 10, c MEA is the specific heat capacity of the membrane electrode assembly of the stack 10, m MEA is the mass of the membrane electrode assembly of the stack 10, c coolant is the specific heat capacity of the coolant, m coolant is the mass of the coolant inside the fuel cell stack 10;

[0055] The internal temperature of the battery stack 10 is calculated by the following formula (3):

[0056]

[0057] Wherein, T is the internal temperature of the stack 10, and T0 is the initial temperature of the coolant, wherein the initial temperature T0 of the coolant can be detected by, for example, the first temperature sensor 41 at the coolant outlet 12 and / or the second temperature sensor 42 at the coolant inlet 11. The temperature increase value of the stack 10 can be obtained by the ratio of the heat generation Q of the stack 10 and the heat capacity of the stack 10, thereby accurately evaluating the internal temperature T of the stack 10.

[0058] In addition, other methods for estimating the internal temperature T of the fuel cell stack 10 can also be considered, such as estimating based on the outlet air temperature of the fuel cell stack 10 detected by the third temperature sensor 43, wherein the outlet air temperature is positively correlated with the internal temperature of the fuel cell stack 10, wherein the proportional relationship between the internal temperature of the fuel cell stack 10 and the outlet air temperature can be derived from empirical data.

[0059] Exemplarily, a preset first target temperature is stored in the controller 50, and the first target temperature is greater than 0°C. When the estimated internal temperature of the battery stack 10 reaches a specific ratio of the first target temperature, it indicates that the internal temperature of the battery stack 10 also exceeds 0°C, which can effectively avoid the problem of icing inside the battery stack 10. Here, the specific ratio acts as a safety factor and can be less than 1, for example, 0.8. When the internal temperature of the battery stack 10 reaches the first target temperature, such as 0.8 of 5°C, that is, when it reaches 4°C, the flow rate of the coolant is increased to the second flow rate, thereby more reliably reducing the risk of overheating. However, it can also be considered that the specific ratio is 1, that is, the flow rate of the coolant is increased when the internal temperature of the battery stack 10 reaches the first target temperature.

[0060] Exemplarily, in step S4, when the internal temperature of the battery stack 10 reaches a specific ratio of the first target temperature, in order to avoid cold shock, the heat dissipation rate of the coolant flowing through the battery stack 10 should not be greater than the heat generation rate of the battery stack 10, and in order to achieve the increase and uniform distribution of the internal temperature of the battery stack 10, the heat dissipation rate of the coolant is equal to the heat generation rate of the battery stack 10. In this way, the problems of icing and cold shock of the battery stack 10 can be effectively prevented, overheating inside the battery stack 10 can be reliably avoided, and the uniform distribution of the internal temperature of the battery stack 10 can be promoted.

[0061] Exemplarily, in step S4, the heat generation rate of the fuel cell stack 10 is calculated according to the following formula (4):

[0062] P generation =I*(E0-U) (4)

[0063] Among them, P generation is the heat generation rate of the battery stack 10, I is the current of the battery stack 10, E0 is the reversible voltage of the battery stack 10, and U is the output voltage of the battery stack 10;

[0064] The heat dissipation rate of the coolant flowing through the fuel cell stack 10 can be calculated according to the following formula (5):

[0065] P dissipation =h*A*ΔT1=h*A*(T coolant -T BPP ) (5)

[0066] Among them, P dissipation is the heat dissipation rate of the coolant, h is the heat dissipation coefficient of the coolant, A is the heat dissipation area of ​​the stack 10, ΔT1 is the temperature difference between the coolant inside the stack and the wall of the bipolar plate, T coolant is the temperature of the coolant inside the stack, T BPP is the temperature of the bipolar plate wall, where the temperature of the coolant inside the stack is T coolant and the temperature of the bipolar plate wall T BPPIt cannot be directly measured, but is calculated in real time through a pre-designed one-dimensional simulation model, wherein the heat dissipation area A of the battery stack 10 is the sum of the inner surface areas of the coolant flow channels of the battery stack 10 and can be provided by the designer or manufacturer of the battery stack 10, and the heat dissipation coefficient h of the coolant is related to the flow rate v of the coolant. The function formula between the heat dissipation coefficient h and the coolant flow rate v can be obtained by fitting, for example, based on experimental data and / or empirical data and / or simulation data.

[0067] The function formula between the heat dissipation coefficient h of the coolant and the flow velocity v is, for example, the following formula (6):

[0068] h=f(v) (6)

[0069] In this case, the heat generation rate P of the fuel cell stack 10 can be generation The heat dissipation coefficient h of the coolant is calculated in combination with the temperature difference ΔT1 between the coolant inside the stack and the wall surface of the bipolar plate and the heat loss area A of the stack 10, and the second flow rate of the coolant is obtained by combining the heat dissipation coefficient with the function formula between the heat dissipation coefficient and the flow rate of the coolant, as shown in the following formula (7):

[0070]

[0071] In addition, it can also be considered that the heat dissipation rate of the coolant flowing through the fuel cell stack 10 can be calculated according to the following formula (8):

[0072] P dissipation =ρ*c*ΔT2*v=ρ*c*(T out -T in )*v (8)

[0073] Where ρ is the density of the coolant, c is the specific heat capacity of the coolant, ΔT2 is the inlet and outlet temperature difference of the coolant, v is the flow rate of the coolant, T out is the outlet temperature of the coolant, T in is the inlet temperature of the coolant. In this case, when the heat dissipation rate of the coolant P dissipation Equal to the heat generation rate P of the stack 10 generation When , the second flow rate of the coolant can be calculated according to the following formula (9):

[0074]

[0075] This enables the coolant flow to be specifically and accurately adjusted in combination with the actual operation of the fuel cell stack 10 , thereby reliably avoiding icing and cold shock problems of the fuel cell stack 10 and promoting uniform temperature distribution inside the fuel cell stack.

[0076] For example, Figure 2As shown, the cold start method according to the present invention additionally comprises a step S6 implemented after step S4: when the outlet temperature T detected by the first temperature sensor 41 is out When the preset second target temperature is exceeded, the flow rate of the coolant is increased to a third flow rate. Here, the second target temperature is greater than or equal to the first target temperature and is stored in the controller 50. This can reduce the risk of overheating inside the fuel cell stack 10 as much as possible.

[0077] For example, in step S6, when the inlet temperature of the coolant T in When the temperature is less than the third target temperature, the third flow rate is the maximum allowable flow rate of the coolant and / or the rated flow rate when the fuel cell system 100 is operating normally, wherein the third target temperature is greater than the second target temperature and is stored in the controller 50. This can promote the temperature inside the fuel cell stack 10 to be evenly distributed as quickly as possible and reliably avoid excessive temperature inside the stack.

[0078] Exemplarily, in step S6, the third flow rate of the coolant is set so that the outlet temperature T out and inlet temperature T in The inlet and outlet temperature difference ΔT2 is less than the temperature difference threshold, which is, for example, 10°C. This can effectively avoid excessive inlet and outlet temperature difference of the coolant, thereby ensuring uniform temperature distribution inside the fuel cell stack 10, maintaining uniform reaction efficiency within the stack and preventing performance degradation.

[0079] Exemplarily, in step S5, when a preset standard is met, the cold start mode is terminated and switched to the normal operation mode, wherein the preset standard includes at least one of the following groups: the output power of the stack 10 or the fuel cell system 100 reaches a preset power, which is, for example, 50% of the rated power of the fuel cell system 100 during normal operation; the inlet temperature T of the coolant is in and / or outlet temperature T out The fourth target temperature is reached, and the fourth target temperature is, for example, 30° C. This ensures a fast and stable cold start process of the fuel cell system 100 .

[0080] In addition, when describing representative embodiments, the specification may have presented the method and / or process as a specific sequence of steps. However, to the extent that the method or process does not rely on the specific order of the steps described herein, the method or process should not be limited to the steps of the specific order described. As will be understood by those of ordinary skill in the art, other sequences of steps are also possible. Therefore, the specific sequence of the steps set forth in the specification should not be interpreted as a limitation to the claims. In addition, the claims for the method and / or process should not be limited to the steps of performing them in the order written, and those skilled in the art can easily understand that these sequences can be changed and still remain within the spirit and scope of the embodiments of the present application.

[0081] The above explanation of the embodiments only describes the invention within the framework of the examples. Of course, the individual features of the embodiments can be freely combined with one another as long as it makes technical sense, without departing from the framework of the invention.

[0082] Other advantages and alternative embodiments of the present invention are obvious to those skilled in the art. Therefore, the present invention in its broader sense is not limited to the specific details, representative structures and exemplary embodiments shown and described. On the contrary, those skilled in the art can make various modifications and substitutions without departing from the basic spirit and scope of the present invention.

Claims

1. A cold start method for a fuel cell system (100), characterized in that: The cold start method comprises at least the following steps: S1: determining whether the fuel cell system (100) should be operated in a cold start mode; S2: in the cold start mode, causing the coolant in the fuel cell stack (10) of the fuel cell system (100) to have a first flow rate; S3: estimating the internal temperature of the fuel cell stack (10), and comparing the internal temperature with a preset first target temperature; S4: when the internal temperature reaches a specific proportion of the first target temperature, a second flow rate is calculated according to the heat generation rate of the fuel cell stack (10) and the heat dissipation rate of the coolant, so that the coolant flows through the fuel cell stack (10) at the second flow rate; S5: When the preset standard is met, the cold start mode is terminated.

2. The cold start method according to claim 1, characterized in that: In step S4, the heat generation rate of the fuel cell stack (10) is made equal to the heat dissipation rate of the coolant.

3. The cold start method according to claim 1 or 2, characterized in that: The heat dissipation rate is obtained by the temperature difference between the coolant inside the battery stack and the wall surface of the bipolar plate, the heat loss area of ​​the battery stack (10) and the heat dissipation coefficient of the coolant; and / or The heat dissipation rate is derived from the inlet and outlet temperature difference, density, specific heat capacity and flow rate of the coolant.

4. The cold start method according to any one of the preceding claims, characterized in that In step S3, the internal temperature is calculated from the initial temperature of the coolant, the heat generation of the fuel cell stack (10) and the heat capacity of the fuel cell stack (10); and / or In step S3, the internal temperature is estimated based on the outlet air temperature of the fuel cell stack (10).

5. The cold start method according to any one of the preceding claims, characterized in that The cold start method additionally includes a step S6 performed after the step S4: when the outlet temperature exceeds a preset second target temperature, increasing the flow rate of the coolant to a third flow rate.

6. The cold start method according to claim 5, characterized in that: The second target temperature is greater than or equal to the first target temperature; and / or In step S6, when the inlet temperature of the coolant is less than a third target temperature, the third flow rate is the maximum allowable flow rate of the coolant and / or the rated flow rate when the fuel cell system (100) is operating normally; and / or In step S6, the third flow rate is set so that the inlet and outlet temperature difference of the coolant is smaller than a temperature difference threshold.

7. The cold start method according to any one of the preceding claims, characterized in that In step S1, when the ambient temperature and / or the initial temperature of the coolant is less than 0° C., it is determined that the fuel cell system (100) should be operated in a cold start mode; and / or The first flow velocity is 0 m / s; and / or The first target temperature is greater than 0°C; and / or The specific ratio is less than or equal to 1.

8. The cold start method according to any one of the preceding claims, characterized in that The preset standard includes at least one of the following groups: the output power of the fuel cell stack (10) reaches a preset power; the inlet temperature and / or outlet temperature of the coolant reaches a fourth target temperature.

9. A fuel cell system (100), characterized in that: The fuel cell system (100) comprises at least: - a cell stack (10), the cell stack (10) having bipolar plates and a membrane electrode assembly and provided with a coolant inlet (11) and a coolant outlet (12) for a coolant; - a coolant circuit (20) configured to redirect the coolant discharged from the coolant outlet (12) to the coolant inlet (11); a coolant circulation pump (30), which is arranged in the coolant circuit (20) and is configured to drive the coolant to flow in the coolant circuit (20); - a first temperature sensor (41) arranged at the coolant outlet (12) to sense the outlet temperature of the coolant; - a second temperature sensor (42) arranged at the coolant inlet (11) to sense the inlet temperature of the coolant; and - A controller (50) configured and adapted to implement a cold start method according to any one of claims 1 to 8.

10. The fuel cell system (100) according to claim 9, characterized in that: The fuel cell system (100) further includes a third temperature sensor (43) disposed at the coolant outlet (12), the third temperature sensor (43) being configured to sense an outlet air temperature at the coolant outlet (12).

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