A fuel cell shutdown purge method and device

Abstract

The present invention provides a fuel cell shutdown purging method and device. The method includes operating the fuel cell system in the lowest allowable output power state by adopting a constant current output mode, increasing the air flow rate above a first flow rate threshold, and at this time, not humidifying the air, and purging until the output voltage of the fuel cell stack reaches a first critical voltage threshold; operating the fuel cell system in the allowable lowest output power state by adopting a constant current output mode, increasing the air flow rate above a second flow rate threshold, and humidifying the air, and purging until the output voltage of the fuel cell stack reaches a second critical voltage threshold; operating the fuel cell system in a constant voltage state by adopting a constant voltage output mode, and purging until the output current of the fuel cell stack reaches a critical current threshold to complete the purging, and the critical current threshold is determined according to the ambient temperature. The present invention adopts a stepped segmented balanced purging method and uses a multi-mode purging method, effectively improving the purging efficiency and success rate.

Description

Technical Field

[0001] The present invention relates to the technical field of fuel cells, and in particular, to a fuel cell shutdown purge method and device. Background Art

[0002] As a new energy device, a fuel cell system has the characteristics of zero emissions, high power density, outstanding energy conversion efficiency, strong low-temperature startup ability, excellent reliability, etc., and is attracting more and more attention from enterprises and research institutions in various countries. The fuel cell system converts the chemical energy in the hydrogen fuel into electrical energy through the electrochemical reaction of hydrogen and oxygen, releases a certain amount of heat, and at the same time generates a large amount of water inside the fuel cell stack. When working at room temperature, the long-term presence of too much water in it will cause the membrane electrode to delaminate or change the hydrophilicity and hydrophobicity of the diffusion layer, affecting the battery performance and life. And under low-temperature conditions, water will condense into ice, causing irreversible damage to the fuel cell membrane electrode. In order to prevent the above situations from occurring, after the fuel cell system receives a shutdown command, it is usually necessary to purge it to reduce the residual water content in the fuel cell.

[0003] The currently adopted conventional shutdown purge method generally controls the load current in a constant current mode and monitors the impedance or stack characteristic parameters in real time. The stack voltage fluctuates within a wide range, and the stack fluid distribution is uneven, resulting in inconsistent purge degrees and large relative deviations among the individual cells inside the stack, reducing the overall reliability of the stack. In addition, under low-temperature conditions, the purge operation means are single, which also makes the purge process unstable, and extreme situations may occur, reducing the purge success rate. While affecting the use performance, it will also reduce the life of the fuel cell stack.

[0004] In summary, the existing fuel cell purge methods mainly have the following two defects:

[0005] 1. The problems caused by the uneven distribution of the fuel cell stack fluid and the changes in external conditions existing in the actual use process are not considered, so it is difficult to always maintain the same purge effect.

[0006] 2. For a fuel cell system purged in the existing conventional manner, especially in a low-temperature environment, when starting again after shutdown, large differences between individual cells are likely to occur, thereby affecting the reliability. At the same time, the stack voltage of the fuel cell stack fluctuates greatly during the purge process, causing damage to the durability of the fuel cell stack. Summary of the Invention

[0007] In view of the deficiencies of the prior art, the present invention provides a fuel cell shutdown purge method and device, which adopts a stepped segmented balanced purge method and uses monitoring variables such as ambient temperature, coolant temperature, fuel cell stack voltage, and single-cell deviation as judgment bases, reducing the damage to the fuel cell during the purge process and being beneficial to improving the reliability and durability of the fuel cell.

[0008] The technical means adopted by the present invention are as follows:

[0009] The present invention discloses a fuel cell shutdown purge method, including:

[0010] Obtain the ambient temperature and coolant temperature at which the fuel cell operates; operate the fuel cell system in the lowest allowable output power state by adopting a constant current output mode, increase the air flow rate above the first flow rate threshold, and at this time, do not humidify the air, and purge until the output voltage of the fuel cell stack reaches the first critical voltage threshold;

[0011] Operate the fuel cell system in the allowable lowest output power state by adopting a constant current output mode, increase the air flow rate above the second flow rate threshold, and humidify the air, and purge until the output voltage of the fuel cell stack reaches the second critical voltage threshold; the relationship between the first critical voltage threshold and the second critical voltage threshold is determined according to the ambient temperature and coolant temperature;

[0012] Operate the fuel cell system in a constant voltage state by adopting a constant voltage output mode, and purge until the output current of the fuel cell stack reaches the critical current threshold to complete the purge, and the critical current threshold is determined according to the ambient temperature.

[0013] Further, determining the relationship between the first critical voltage threshold and the second critical voltage threshold according to the ambient temperature and coolant temperature includes:

[0014] If the ambient temperature is lower than the first conditional temperature threshold and the coolant temperature is higher than the first operating temperature threshold, the first critical voltage threshold and the second critical threshold are set differently, with a specified constant voltage value difference;

[0015] If the ambient temperature is lower than the first conditional temperature threshold and the coolant temperature is not higher than the first operating temperature threshold, the first critical voltage threshold and the second critical threshold are the same.

[0016] Further, determining the critical current threshold according to the ambient temperature includes:

[0017] If the ambient temperature is lower than the first conditional temperature threshold, the critical current threshold of the fuel cell is not greater than the first specified current threshold;

[0018] If the ambient temperature is not lower than the first conditional temperature threshold, the critical current threshold of the fuel cell is not greater than the second specified current threshold, and the first specified current threshold is less than the second specified current threshold.

[0019] Further, when the fuel cell system is operating in a constant voltage output mode and in a constant voltage state, if the ambient temperature is lower than the first conditional temperature threshold and the coolant temperature is not higher than the second operating temperature threshold, no humidification control is performed on the air.

[0020] Further, when the fuel cell system is operating in a constant current output mode and in the lowest allowable output power state, before purging until the output voltage of the fuel cell stack reaches the first critical voltage threshold, it further includes:

[0021] Judging the voltage deviation of the single cell of the fuel cell stack. If the voltage deviation of the single cell of the fuel cell stack is greater than the first critical voltage deviation threshold, directly operate the fuel cell system in the lowest allowable output power state in the constant current output mode, increase the air flow rate to above the second flow rate threshold, and perform humidification treatment on the air.

[0022] Further, the longest execution time of the purging process is not greater than the preset control duration. If this condition is not met, the purging is completed in advance.

[0023] Further, the first flow rate threshold is more than twice the normal operating demand flow rate of the fuel cell stack.

[0024] Further, during the purging execution, the coolant temperature is controlled within the optimal operating temperature range of the fuel cell stack.

[0025] Further, during the purging execution, the fuel cell system is set to operate in an internal circulation.

[0026] The present invention also discloses a fuel cell shutdown purging device, including:

[0027] A temperature acquisition unit for acquiring the ambient temperature and the coolant temperature at which the fuel cell operates;

[0028] A primary purging control unit for operating the fuel cell system in the lowest allowable output power state in the constant current output mode, increasing the air flow rate to above the first flow rate threshold, without performing humidification treatment on the air at this time, and purging until the output voltage of the fuel cell stack reaches the first critical voltage threshold;

[0029] The secondary purge control unit is used to make the fuel cell system operate in the lowest allowable output power state by adopting the output constant current mode, increase the air flow rate above the second flow rate threshold, and humidify the air, and purge until the output voltage of the fuel cell stack reaches the second critical voltage threshold; the relationship between the first critical voltage threshold and the second critical voltage threshold is determined according to the ambient temperature and the coolant temperature;

[0030] The tertiary purge control unit is used to make the fuel cell system operate in a constant voltage state by adopting the output constant voltage mode, and purge until the output current of the fuel cell stack reaches the critical current threshold to complete the purge, and the critical current threshold is determined according to the ambient temperature.

[0031] Compared with the prior art, the present invention has the following advantages:

[0032] 1. The present invention relies on the sensors for self-detection possessed by a general fuel cell system to obtain data and make corresponding judgments, and has strong universality.

[0033] 2. The present invention solves the problem of unbalanced water distribution in the electrodes during the purge process of the fuel cell through timely humidification control means. By using the water temperature and the deviation of the battery monomers as the judgment basis to determine the humidification entry moment, while improving the purge efficiency of the fuel cell system, it prolongs the service life of the fuel cell and reduces the damage to the fuel cell system caused by dry gas purge.

[0034] 3. The present invention adopts multi-mode purge, but introduces the constant voltage mode purge in a specific stage of the purge process, which improves the uniformity of the monomer voltage during the purge process. In addition, taking the voltage as the judgment basis, when the conditions are met, entering the constant voltage purge reduces the water production of the stack, greatly shortens the purge time, and thus makes the purge effect more ideal.

[0035] In summary, the present invention improves the air supply of the fuel cell, can humidify the air according to requirements, adopts the stepped segmented balanced purge method, online monitors the state of the fuel cell, timely cuts in the humidification function through logical judgment, and uses the multi-mode purge method, effectively improving the purge efficiency and success rate. At the same time, implementing the fuel cell shutdown purge method is beneficial to the restart of the fuel cell system, reduces the damage to the fuel cell during the purge process, and is conducive to improving the reliability and durability of the fuel cell system. It is suitable for wide promotion in the field of fuel cells. Description of the Drawings

[0036] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0037] Figure 1 It is a flowchart of a fuel cell shutdown purge method in an embodiment.

[0038] Figure 2 It is a structural diagram of a fuel cell shutdown purge system in an embodiment.

[0039] In the figure: 1. Air flow meter; 2. Air compressor; 3. Three-way valve; 4. Humidifying device; 5. Fuel cell stack; 6. FCU controller; 7. Ambient temperature sensor; 8. Coolant temperature sensor. Specific embodiments

[0040] In order to enable those skilled in the art to better understand the solution of the present invention, the following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the drawings in the embodiments of the present invention. Obviously, the described embodiments are only some of the embodiments of the present invention, rather than all of them. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention. The terms "first", "second", etc. in the specification and claims of the present invention and the above drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged under appropriate circumstances so that the embodiments of the present invention described here can be implemented in an order different from those illustrated or described here. In addition, the terms "comprising" and "having" and any variations thereof are intended to cover non-exclusive inclusion. For example, a process, method, system, product or device comprising a series of steps or units does not necessarily have to be limited to those steps or units clearly listed, but may include other steps or units not clearly listed or inherent to these processes, methods, products or devices.

[0041] The present invention discloses a fuel cell shutdown purge method, including:

[0042] S1. Obtain the ambient temperature and coolant temperature at which the fuel cell operates, and make the fuel cell system operate at the lowest allowable output power state by adopting the output constant current mode, increase the air flow to above the first flow threshold, and at this time, do not humidify the air, and purge until the output voltage of the fuel cell stack reaches the first critical voltage threshold. The first flow threshold is more than twice the normal working demand flow of the fuel cell stack.

[0043] Further, S1 also includes judging the voltage deviation of each single cell of the fuel cell stack. Once the voltage deviation of each single cell of the fuel cell stack is greater than the first critical voltage deviation threshold, S2 is directly executed.

[0044] S2. Make the fuel cell system operate in the allowable minimum output power state by adopting the output constant current mode, increase the air flow rate to above the second flow rate threshold, and perform humidification treatment on the air, and purge until the output voltage of the fuel cell stack reaches the second critical voltage threshold; the relationship between the first critical voltage threshold and the second critical voltage threshold is determined according to the ambient temperature and the coolant temperature.

[0045] Specifically, if the ambient temperature is lower than the first conditional temperature threshold and the coolant temperature is higher than the first operating temperature threshold, the first critical voltage threshold and the second critical threshold are set differently, with a specified constant voltage difference. If the ambient temperature is lower than the first conditional temperature threshold and the coolant temperature is not higher than the first operating temperature threshold, the first critical voltage threshold and the second critical threshold are the same.

[0046] S3. Make the fuel cell system operate in a constant voltage state by adopting the output constant voltage mode, and purge until the output current of the fuel cell stack reaches the critical current threshold to complete the purge. The critical current threshold is determined according to the ambient temperature. Specifically, if the ambient temperature is lower than the first conditional temperature threshold, the critical current threshold of the fuel cell is not greater than the first specified current threshold; if the ambient temperature is not lower than the first conditional temperature threshold, the critical current threshold of the fuel cell is not greater than the second specified current threshold, and the first specified current threshold is less than the second specified current threshold.

[0047] Further, in S3, when the ambient temperature is lower than the first conditional temperature threshold and the coolant temperature is not higher than the second operating temperature threshold, no humidification control is performed on the air.

[0048] Further, the longest execution time of the purge process is not greater than the preset control duration. If this condition is not met, the purge is completed in advance. Further, during the purge execution, the coolant temperature is controlled within the optimal operating temperature range of the fuel cell stack. And the fuel cell system is set to operate in an internal circulation. The following further illustrates the solution and effect of the present invention through specific application examples.

[0049] According to Figure 1 As shown, a fuel cell shutdown purge method disclosed in this embodiment is a shutdown purge method that performs logical judgment according to the ambient temperature and the coolant temperature. After receiving the shutdown instruction, the fuel cell system executes the following process:

[0050] First step: Operate the fuel cell system in the lowest allowable output power state with a constant current output mode, increase the air flow rate above the first flow rate threshold and do not perform humidification control on the air, and purge until the output voltage of the fuel cell stack reaches the first critical voltage threshold.

[0051] Second step: Operate the fuel cell system in the lowest allowable output power state with a constant current output mode, change the air flow path and degree of flow to humidify it, maintain the air flow rate above the second flow rate threshold, and purge until the output voltage of the fuel cell stack reaches the second critical voltage threshold.

[0052] Third step: Operate the fuel cell system in a constant voltage state with a constant voltage output mode, and purge until the output current of the fuel cell stack reaches the critical current threshold to complete the purge.

[0053] During the execution of each step, judge the longest purge execution time. If it is greater than or equal to the preset control duration, the purge is completed in advance. The fuel cell shutdown purge method adopted in this embodiment is based on the fuel cell system as shown in Figure 2 and mainly includes an air flow meter 1, an air compressor 2, a three-way valve 3, a humidifying device 4, a fuel cell stack 5, an FCU controller 6, an ambient temperature sensor 7, and a coolant temperature sensor 8. The FCU controller 6 communicates with components such as the air flow meter 1, the air compressor 2, the three-way valve 3, the ambient temperature sensor 7, and the coolant temperature sensor 8 through hard wires and CAN lines.

[0054] The fuel cell system generates electricity through the electrochemical reaction of hydrogen and air and outputs it to the corresponding load. The air is provided by the air compressor according to the instructions of the FCU controller, and the required flow rate is counted by the air flow meter. During the operation of the fuel cell system, the fuel cell stack requires appropriately humidified air, which is achieved by the three-way valve and the humidifying device. The application scenarios of the fuel cell system are numerous, such as vehicle applications, ship applications, aviation applications, stationary power stations, backup power supplies, mobile power supplies, etc. Among them, the environmental conditions are different. When operating at normal temperature (temperature above zero degrees), the fuel cell stack generates water. Excessive water staying in it for a long time will cause the membrane electrode to delaminate or change the hydrophilicity and hydrophobicity of the diffusion layer, affecting the battery performance and life. In most scenarios when using the fuel cell system, it faces low temperature conditions (below zero degrees), and the water will condense into ice, causing irreversible damage to the fuel cell membrane electrode. To prevent the above situations from occurring, after the fuel cell system receives a shutdown instruction, it usually needs to be purged to reduce the residual water content in the fuel cell. The ambient temperature sensor and the coolant temperature sensor can directly characterize the condition of the fuel cell stack. Therefore, the FCU controller selects the corresponding parameter values to complete the purge activity according to the purge method.

[0055] In practical applications, after the fuel cell system FCU controller 6 receives a shutdown instruction, purging begins. First, the fuel cell system operates at the lowest allowable output power state in a constant current mode, and at the same time, a temperature judgment for determining the critical voltage threshold is performed.

[0056] According to the control decision, the judgment result is ① (the first critical voltage threshold is equal to the sum of the second critical voltage threshold and the constant voltage value) or ② (the first critical voltage threshold is equal to the second critical voltage threshold). Since the voltage of the fuel cell stack will continuously decrease after the purging operation.

[0057] When purging reaches the first critical voltage, the second step is entered. According to ① (the first critical voltage threshold is equal to the sum of the second critical voltage threshold and the constant voltage value), the air flow path and the degree of air flow are changed through the action of the three-way valve to humidify the air entering the fuel cell stack. The degree of humidification is determined according to the operating conditions of the fuel cell stack, and it can be low-level humidification or high-level humidification. After the air is humidified, the voltage drop rate of the fuel cell stack caused by the purging action will slow down. When purging reaches the second critical voltage threshold, the second step is completed. During the above process, before the output voltage of the fuel cell stack reaches the first critical voltage threshold, the voltage deviation of the fuel cell stack single cell is greater than the first critical voltage deviation threshold, and the FCU controller 6 forces it to enter the second step and directly perform humidification;

[0058] In addition, when purging reaches the first critical voltage, the second step is entered. According to ② (the first critical voltage threshold is equal to the second critical voltage threshold), therefore, the action change of the three-way valve in the second step is executed, and then the second step is exited and the third step is entered. The longest execution time of the purging process is not greater than the preset control duration. If this condition is not met, the purging is completed in advance.

[0059] Since the fuel cell system is equipped with a DC / DC converter, the fuel cell system can be made to operate in a constant voltage state by controlling the DC / DC converter. This state has the ability to achieve power adaptation output according to the state of the fuel cell stack, which helps to protect the fuel cell stack. When purging reaches the critical current threshold of the fuel cell stack output current, the purging is completed.

[0060] The following are examples for illustration respectively:

[0061] Embodiment 1

[0062] The ambient temperature is 25°C. The ambient temperature sensor is integrated on the air pipeline. At the moment of shutdown, the coolant temperature is between 65°C and 80°C. The coolant temperature sensor is arranged at the coolant inlet of the fuel cell stack 5.

[0063] The minimum allowable output power of the fuel cell system is 6 kW. At this time, the fuel cell stack operates at about 100 mA / cm2, and the required air flow rate is 400 slpm; the first flow threshold is set between 1200 and 3000 slpm; the second flow threshold is set between 1000 and 2400 slpm; the preset control duration is set between 3 and 10 min; the first critical voltage threshold is set between 0.78 and 0.82 times the number of fuel cell stack sections, where the number of fuel cell stack sections refers to the number of fuel cell monomers (the same below); the second critical voltage threshold is equal to the first critical voltage threshold; the first critical voltage deviation threshold is the difference between the voltage of a single fuel cell stack cell and the minimum voltage of a single cell (the same below), and is set between 100 and 200 mV; the critical current threshold is set to the second specified current threshold, and the value range is 5 to 20 A.

[0064] First step, operate the fuel cell system in the minimum allowable output power state using the constant current output mode, increase the air flow rate above the first flow threshold and do not perform humidification control on the air, and purge until the output voltage of the fuel cell stack reaches the first critical voltage threshold. When the voltage deviation of a single fuel cell stack cell is greater than the first critical voltage deviation threshold, the FCU controller 6 forces to jump out of the first step and enter the second step.

[0065] Second step, change the air flow path and degree of flow to humidify it, keep the air flow rate above the second flow threshold. Since the second critical voltage threshold is equal to the first critical voltage threshold, then the second step is completed.

[0066] Third step, operate the fuel cell system in the constant voltage state using the constant voltage output mode, and purge until the output current of the fuel cell stack reaches the critical current threshold to complete the purge.

[0067] The longest execution time of the purge process is not greater than the preset control duration. If this condition is not met, the purge is completed in advance.

[0068] During the execution of the purge, the coolant temperature can be stabilized between 60 and 70 °C through control means. One is to operate the fuel cell system in the internal circulation, and the other is to control the rotational speed or stop the radiator fan of the fuel cell system.

[0069] Embodiment 2

[0070] The ambient temperature is -20 °C, integrated inside the air filter, and the coolant temperature at the shutdown moment is between 50 and 65 °C. The coolant temperature sensor is arranged at the coolant outlet of the fuel cell stack.

[0071] The minimum allowable output power of the fuel cell system is 9 kW. At this time, the fuel cell stack operates at about 100 mA / cm2, and the required air flow rate is 600 slpm; the first flow threshold is set to be between 1500 and 3500 slpm; the second flow threshold is set to be between 1200 and 3000 slpm; the preset control duration is set to be between 3 and 10 min; the first critical voltage threshold is set to be between 0.8 and 0.83 times the number of cells of the fuel cell stack; the second critical voltage threshold is between 0.76 and 0.8 times the number of cells of the fuel cell stack and maintains a specified constant voltage difference from the first critical voltage threshold; the first critical voltage deviation threshold is set to be between 100 and 300 mV; the critical current threshold is set as the first specified current threshold, and the value range is 1 to 15 A.

[0072] In the first step, the fuel cell system is operated in a constant current output mode at the minimum allowable output power state, the air flow rate is increased above the first flow threshold and no humidification control is performed on the air, and purging is carried out until the output voltage of the fuel cell stack reaches the first critical voltage threshold, and the first step is completed.

[0073] In the second step, the fuel cell system is operated in a constant current output mode at the minimum allowable output power state, the air flow path and the flow degree are changed to humidify it, the air flow rate is maintained above the second flow threshold, and purging is carried out until the output voltage of the fuel cell stack reaches the second critical voltage threshold, and the second step is completed.

[0074] In the third step, the fuel cell system is operated in a constant voltage output mode at a constant voltage state, and purging is carried out until the output current of the fuel cell stack reaches the critical current threshold, and the purging is completed.

[0075] The longest execution time of the purging process is not greater than the preset control duration. If this condition is not met, the purging is completed in advance.

[0076] During the purging execution, the coolant temperature can be stabilized between 55 and 70 °C by control means. One is to make the fuel cell system operate in an internal circulation, and the other is to control the rotation speed of the radiator fan of the fuel cell system.

[0077] Embodiment 3

[0078] The ambient temperature is -30 °C, and the coolant temperature at the shutdown moment is 35 to 50 °C.

[0079] The minimum allowable output power of the fuel cell system is 5 kW. At this time, the fuel cell stack operates at about 80 mA / cm2, and the required air flow rate is 320 slpm; the first flow threshold is set between 1000 and 2400 slpm; the second flow threshold is set between 800 and 2200 slpm; the preset control duration is set between 3 and 10 min; the first critical voltage threshold is set between 0.75 and 0.82 times the number of cells of the fuel cell stack; the second critical voltage threshold is equal to the first critical voltage threshold; the first critical voltage deviation threshold is set between 100 and 300 mV; the critical current threshold is set as the first specified current threshold, and the value range is 1 to 10 A.

[0080] First step, operate the fuel cell system in the minimum allowable output power state by adopting the output constant current mode, increase the air flow rate above the first flow threshold and do not perform humidification control on the air, and purge until the output voltage of the fuel cell stack reaches the first critical voltage threshold, and the first step is completed;

[0081] Second step, change the air flow path and degree of flow to humidify it, keep the air flow rate above the second flow threshold, and since it is equal to the first critical voltage threshold, then the second step is completed;

[0082] Third step, operate the fuel cell system in the constant voltage state by adopting the output constant voltage mode, and purge until the output current of the fuel cell stack reaches the critical current threshold, and the purge is completed;

[0083] The longest execution time of the purge process is not greater than the preset control duration. If this condition is not met, the purge is completed in advance.

[0084] During the execution of the purge, the coolant temperature can be stabilized between 45 and 50 °C by control means. One is to operate the fuel cell system in the internal circulation, and the other is to control the rotation speed or stop of the radiator fan of the fuel cell system.

[0085] Embodiment 4

[0086] The ambient temperature is -20 °C, integrated inside the air filter, and the coolant temperature at the shutdown moment is between 50 and 65 °C, arranged at the coolant outlet of the fuel cell stack.

[0087] The minimum allowable output power of the fuel cell system is 6 kW. At this time, the fuel cell stack operates at about 100 mA / cm2, and the required air flow rate is 400 slpm; the first flow threshold is set between 1000 and 2400 slpm; the second flow threshold is set between 800 and 2200 slpm; the preset control duration is set between 3 and 10 min; the first critical voltage threshold is set between 0.75 and 0.82 times the number of cells of the fuel cell stack; the first critical voltage deviation threshold is set between 100 and 300 mV; the critical current threshold is set as the first specified current threshold, and the value range is 1 to 10 A.

[0088] In the first step, the fuel cell system is operated in a constant current output mode at the minimum allowable output power state, the air flow rate is increased above the first flow threshold and no humidification control is performed on the air, but the output voltage of the fuel cell stack does not reach the first critical voltage threshold, and the first step is completed.

[0089] In the second step, the fuel cell system is operated in a constant current output mode at the allowable minimum output power state, the air flow path and the flow degree are changed to humidify it, the air flow rate is maintained above the second flow threshold, and it is purged until the output voltage of the fuel cell stack reaches the second critical voltage threshold, and the second step is completed.

[0090] In the third step, the fuel cell system is operated in a constant voltage output mode at a constant voltage state, and it is purged until the output current of the fuel cell stack reaches the critical current threshold, and the purging is completed.

[0091] The longest execution time of the purging process is not greater than the preset control duration. If this condition is not met, the purging is completed in advance.

[0092] During the purging execution, the coolant temperature can be stabilized at 55 - 70 °C through control means. One is to make the fuel cell system operate in an internal circulation, and the other is to control the rotation speed of the radiator fan of the fuel cell system.

[0093] Corresponding to a fuel cell shutdown purging method proposed by the present invention, the present invention also discloses a fuel cell shutdown purging device, including:

[0094] A temperature acquisition unit, which is used to obtain the ambient temperature and the coolant temperature of the fuel cell operation;

[0095] A primary purging control unit, which is used to operate the fuel cell system in a constant current output mode at the minimum allowable output power state, increase the air flow rate above the first flow threshold, and at this time, no humidification treatment is performed on the air, and it is purged until the output voltage of the fuel cell stack reaches the first critical voltage threshold;

[0096] The secondary purge control unit is used to make the fuel cell system operate in the lowest allowable output power state by adopting the output constant current mode, increase the air flow rate above the second flow rate threshold, and humidify the air, and purge until the output voltage of the fuel cell stack reaches the second critical voltage threshold; the relationship between the first critical voltage threshold and the second critical voltage threshold is determined according to the ambient temperature and the coolant temperature;

[0097] The tertiary purge control unit is used to make the fuel cell system operate in a constant voltage state by adopting the output constant voltage mode, and purge until the output current of the fuel cell stack reaches the critical current threshold to complete the purge, and the critical current threshold is determined according to the ambient temperature.

[0098] For the embodiments of the present invention, since they correspond to the above embodiments, the description is relatively simple. For the relevant similarities, please refer to the description in the above embodiments, and details are not described herein again.

[0099] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A fuel cell shutdown purging method, characterized in that, Including: Obtain the ambient temperature and coolant temperature at which the fuel cell operates; operate the fuel cell system in the minimum allowable output power state by adopting a constant current output mode, increase the air flow rate above a first flow rate threshold, and at this time, do not perform humidification treatment on the air, and purge until the output voltage of the fuel cell stack reaches a first critical voltage threshold; Operate the fuel cell system in the allowable minimum output power state by adopting a constant current output mode, increase the air flow rate above a second flow rate threshold, and perform humidification treatment on the air, and purge until the output voltage of the fuel cell stack reaches a second critical voltage threshold; the relationship between the first critical voltage threshold and the second critical voltage threshold is determined according to the ambient temperature and the coolant temperature: if the ambient temperature is lower than a first conditional temperature threshold and the coolant temperature is higher than a first operating temperature threshold, then the first critical voltage threshold and the second critical threshold are set differently, with a specified constant voltage value difference; if the ambient temperature is lower than the first conditional temperature threshold and the coolant temperature is not higher than the first operating temperature threshold, then the first critical voltage threshold and the second critical threshold are the same; Operate the fuel cell system in a constant voltage state by adopting a constant voltage output mode, and purge until the output current of the fuel cell stack reaches a critical current threshold to complete the purge, and the critical current threshold is determined according to the ambient temperature.

2. The fuel cell shutdown purge method according to claim 1, wherein Determining the critical current threshold according to the ambient temperature includes: If the ambient temperature is lower than the first conditional temperature threshold, the critical current threshold of the fuel cell is not greater than a first specified current threshold; If the ambient temperature is not lower than the first conditional temperature threshold, the critical current threshold of the fuel cell is not greater than a second specified current threshold, and the first specified current threshold is less than the second specified current threshold.

3. A fuel cell shutdown purge method according to claim 1, characterized in that, When operating the fuel cell system in a constant voltage state by adopting a constant voltage output mode, if the ambient temperature is lower than the first conditional temperature threshold and the coolant temperature is not higher than a second operating temperature threshold, no humidification control is performed on the air.

4. A fuel cell shutdown purge method according to claim 1, characterized in that, When operating the fuel cell system in the minimum allowable output power state by adopting a constant current output mode, before purging until the output voltage of the fuel cell stack reaches the first critical voltage threshold, it further includes: Judge the voltage deviation of each single cell of the fuel cell stack. If the voltage deviation of each single cell of the fuel cell stack is greater than a first critical voltage deviation threshold, directly operate the fuel cell system in the allowable minimum output power state by adopting a constant current output mode, increase the air flow rate above the second flow rate threshold, and perform humidification treatment on the air.

5. A fuel cell shutdown purge method according to claim 1, characterized in that, The longest execution time of the purge process is not greater than a preset control duration. If this condition is not met, the purge is completed in advance.

6. A fuel cell shutdown purge method according to claim 1, characterized in that, The first flow rate threshold is more than twice the normal working demand flow rate of the fuel cell stack.

7. A fuel cell shutdown purge method according to claim 1, characterized in that, During the execution of the purge, control the coolant temperature within the optimal working temperature range of the fuel cell stack.

8. A fuel cell shutdown purge method according to claim 1, characterized in that, During the execution of the purge, set the fuel cell system to operate in an internal circulation.

9. A fuel cell shutdown purge device, characterized in that, Including: A temperature acquisition unit for obtaining the ambient temperature and coolant temperature at which the fuel cell operates; The primary purge control unit is used to make the fuel cell system operate at the lowest allowable output power state by adopting the output constant current mode, increase the air flow rate above the first flow rate threshold, and at this time, no humidification treatment is performed on the air, and purge until the output voltage of the fuel cell stack reaches the first critical voltage threshold; The secondary purge control unit is used to make the fuel cell system operate at the allowable lowest output power state by adopting the output constant current mode, increase the air flow rate above the second flow rate threshold, and perform humidification treatment on the air, and purge until the output voltage of the fuel cell stack reaches the second critical voltage threshold; The relationship between the first critical voltage threshold and the second critical voltage threshold is determined according to the ambient temperature and the coolant temperature: If the ambient temperature is lower than the first conditional temperature threshold and the coolant temperature is higher than the first operating temperature threshold, the first critical voltage threshold and the second critical threshold are set differently, with a specified constant voltage value difference. If the ambient temperature is lower than the first conditional temperature threshold and the coolant temperature is not higher than the first operating temperature threshold, the first critical voltage threshold and the second critical threshold are the same; The tertiary purge control unit is used to make the fuel cell system operate at a constant voltage state by adopting the output constant voltage mode, and purge until the output current of the fuel cell stack reaches the critical current threshold to complete the purge, and the critical current threshold is determined according to the ambient temperature.

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