Air system of fuel cell and control method of air in-pile humidity

Abstract

The invention relates to the technical field of fuel cells, and particularly discloses an air system of a fuel cell and a control method of air in-pile humidity, the air system comprises an air filter, an air compressor, a main intercooler and a membrane humidifier which are connected in sequence, and an auxiliary intercooler is arranged at the main intercooler in parallel; a three-way valve is arranged among the main intercooler, the auxiliary intercooler and the humidifier, a first inlet of the three-way valve is connected with the main intercooler, a second inlet of the three-way valve is connected with the auxiliary intercooler, and an outlet of the three-way valve is connected with the humidifier. The moisture transfer amount of the film humidifier is related to the air temperature of the dry side inlet, and meanwhile, the main intercooler and the auxiliary intercooler are different in cooling capacity, so that the air temperature of the dry side inlet is controlled by controlling the opening degrees of the two inlets of the three-way valve, the humidity of air entering a pile is accurately adjusted, and the whole air system is simple and convenient in structure and low in cost. The method for controlling the air humidity is flexible, and the stability of the performance of the fuel cell can be ensured.

Description

Technical Field

[0001] The present invention relates to the technical field of fuel cells, and in particular to an air system of a fuel cell and a method for controlling humidity of air entering the stack. Background Art

[0002] With the rapid development of related technologies of hydrogen fuel cells, its advantages of high efficiency, environmental friendliness, and high reliability are widely known. However, the system performance and R&D cost of fuel cell engines are still problems that hinder their large-scale application. Reasonable fuel cell control strategies are conducive to improving fuel cell output and maintaining stable operation. Fuel cells obtain the required electrical energy through the hydrogen-oxygen reaction inside the stack, and air humidity has an important influence on the electrochemical reaction. Too high or too low humidity will affect the performance of fuel cells. At present, the structure of the air system before entering the stack is generally an air compressor, an intercooler, a three-way valve, and a humidifier. Among them, the intercooler is used for air cooling, and the humidifier is used for air humidification. The humidity of the air entering the stack is affected by the intercooler and the humidifier. However, these two parts are mechanical parts. Although the air temperature can be adjusted by adjusting the water pump speed and the thermostat opening, thereby affecting the air entering the stack humidity, it cannot adaptively adjust the humidity when the ambient temperature, humidity, and flow rate change greatly. Therefore, the reliability is poor, which easily leads to reduced fuel cell performance. Summary of the invention

[0003] In order to overcome the deficiencies of the prior art, the present invention provides an air system for a fuel cell and a method for controlling the humidity of air entering the stack, which can accurately and stably control the humidity of air entering the stack and improve the system performance of the fuel cell.

[0004] The present invention adopts the following technical solutions:

[0005] A fuel cell air system is connected to a fuel cell stack, comprising an air filter, an air compressor, a main intercooler, and a humidifier connected in sequence, the humidifier being connected to the fuel cell stack, a secondary intercooler being arranged in parallel at the main intercooler, a three-way valve being arranged between the main intercooler, the secondary intercooler and the humidifier, a first inlet of the three-way valve being connected to the main intercooler, a second inlet of the three-way valve being connected to the secondary intercooler, and an outlet of the three-way valve being connected to the humidifier.

[0006] Furthermore, the inlet of the main intercooler is connected to the air compressor. The main intercooler has a long cooling pipeline and a strong cooling capacity. In the high-power working mode, it can cool 200°C air to 40 degrees Celsius, but due to its long pipeline, its energy loss is also large.

[0007] Furthermore, the inlet of the secondary intercooler is connected to the air compressor. The cooling pipeline of the secondary intercooler zone is short and the cooling capacity is poor. In the high-power working mode, the air at 200°C can only be cooled to 120°C. Similarly, due to the short pipeline, the energy loss is also small.

[0008] The three-way valve combines the air flowing through the two intercoolers into one pipeline for transporting to the humidifier, and controls the air flow of the two intercoolers by adjusting the opening of the first inlet and the second inlet of the three-way valve, thereby more accurately controlling the air temperature.

[0009] Furthermore, the humidifier is configured as a membrane humidifier, which is provided with a dry side and a wet side, with a membrane arranged in the middle, the dry side includes a dry side inlet and a dry side outlet, the wet side includes a wet side inlet and a wet side outlet, the dry side inlet is connected to the outlet of the three-way valve, the dry side outlet is connected to the air inlet of the fuel cell stack, the wet side inlet is connected to the air outlet of the fuel cell stack, a throttle is arranged at the wet side outlet, and the air humidified by the humidifier flows out from the dry side outlet into the fuel cell stack to participate in the reaction.

[0010] Furthermore, a temperature sensor is provided at the dry side inlet of the humidifier, and a humidity sensor is provided at the dry side outlet of the humidifier. After being humidified by the humidifier, the air enters the fuel cell stack from the dry side outlet and its humidity is measured.

[0011] The present invention also provides another technical solution:

[0012] A method for controlling the humidity of air entering the stack is implemented in the air system of the fuel cell described above, and the specific steps are as follows:

[0013] S1: Start the air system and let air in;

[0014] S2: Read the values ​​of the temperature sensor and the humidity sensor to determine whether the air temperature at the dry side inlet reaches the expected temperature;

[0015] S3: When the air temperature at the dry side inlet is lower than the desired temperature, the opening W of the three-way valve is adjusted according to the air temperature at the dry side inlet to increase it to the desired temperature and then the humidity of the air entering the pile is adjusted; when the air temperature at the dry side inlet is higher than the desired temperature, the opening W of the three-way valve is adjusted according to the humidity value of the air entering the pile at the dry side outlet;

[0016] S4: Read the temperature sensor value at this time to determine whether the air temperature at the dry side inlet is lower than a specific temperature;

[0017] S5: If the air temperature at the dry side inlet is not lower than the specific temperature, enter step S3 to adjust the opening W of the three-way valve according to the air inlet humidity until the desired humidity is reached;

[0018] If the air temperature at the dry side inlet is lower than a specific temperature, determine whether the air inlet humidity is greater than the expected humidity;

[0019] S6: When the air temperature at the dry side inlet is lower than a specific temperature and the air inlet humidity is greater than the desired humidity, proceed to step S3 to adjust the opening W of the three-way valve according to the air inlet humidity until the desired humidity is reached;

[0020] When the air temperature at the dry side inlet is lower than a specific temperature and the air inlet humidity is lower than the desired humidity, the process proceeds to step S3 to adjust the opening W of the three-way valve according to the air temperature at the dry side inlet until the desired humidity is reached.

[0021] Furthermore, the PI algorithm is used for calculation, and the opening W of the three-way valve adjusted according to the humidity of the air entering the stack is specifically calculated as: W = K p *ΔR+K i *∫ΔR,

[0022] The K p is the P factor, the K i is the I factor, the K p , K i The ΔR is confirmed by bench calibration and is the difference between the actual air inlet humidity and the expected humidity.

[0023] Furthermore, the specific calculation formula for adjusting the opening W of the three-way valve according to the air temperature at the dry side inlet is: W = K p *ΔT+K i *∫ΔT, where ΔT is the difference between the actual dry side inlet air temperature and the expected temperature.

[0024] Furthermore, the desired temperature of the air at the dry side inlet is the air temperature corresponding to when the moisture transfer of the membrane humidifier reaches a maximum value.

[0025] For membrane humidifiers, the water transfer is expressed by Fick's law: Where M v is the molar mass of water; A is the membrane area; c1 and c2 are the water concentrations in the wet and dry boundary membranes, respectively; δ m is the thickness of the film; D w is the diffusion coefficient of water, which is related to the membrane water content and membrane temperature. The water transfer amount first increases and then decreases with the increase of the dry side inlet temperature. It is calculated that the water transfer amount reaches the maximum value when the dry side inlet air temperature reaches the expected temperature.

[0026] In the present invention, the selected humidifier calculates that the air temperature at the dry side inlet is 43°C when the moisture transfer reaches the maximum value. Therefore, when adjusting the air inlet humidity, the air temperature at the dry side inlet can be set to 43 degrees Celsius so that the inlet humidity can reach the maximum value.

[0027] Further, the desired temperature of the air at the dry side inlet is 43° C., the specific temperature of the air at the dry side inlet is 45° C., and the desired humidity of the air entering the stack depends on the situation.

[0028] The present invention has at least the following beneficial effects:

[0029] 1. The air system of a fuel cell provided by the present invention is provided with two main intercoolers and a sub-intercooler with different cooling capacities, and the opening of two inlet valves of a three-way valve is controlled to realize accurate and rapid control of the air temperature;

[0030] 2. The air system of a fuel cell provided by the present invention uses a membrane humidifier to perform air humidification treatment, and uses the water transfer amount of the membrane humidifier to control and adjust the humidity of the air entering the stack by utilizing the relationship between the air temperature at the dry side inlet and the water transfer amount of the membrane humidifier, so as to ensure the stability of the performance of the fuel cell, and the structure of the entire air system is simple and easy to operate; 3. The method for controlling the humidity of the air entering the stack provided by the present invention adjusts the opening of the three-way valve through the PT algorithm to adjust the humidity of the air entering the stack, and sets the air temperature limit as the control amount to adjust the opening of the three-way valve. The entire control process is flexible and accurate, and avoids the air temperature, humidity and flow affecting the performance of the fuel cell. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 A schematic structural diagram of an air system of a fuel cell provided by the present invention;

[0032] Figure 2 The present invention provides a flow chart of a method for controlling the humidity of air entering a pile.

[0033] Explanation of reference numbers: 1. Air filter; 2. Air compressor; 3. Main intercooler; 4. Auxiliary intercooler; 5. Three-way valve; 6. Temperature sensor; 7. Membrane humidifier; 8. Humidity sensor; 9. Fuel cell stack; 10. Throttle valve; 11. First inlet of three-way valve; 12. Second inlet of three-way valve; 13. Outlet of three-way valve. DETAILED DESCRIPTION

[0034] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0035] Embodiment 1

[0036] Combination Figure 1As shown, the present invention discloses an air system of a fuel cell, which is connected to a fuel cell stack 9, and includes an air filter 1, an air compressor 2, a main intercooler 3, a three-way valve 5 and a membrane humidifier 7 which are connected in sequence. The membrane humidifier 7 is connected to the fuel cell stack 9, and a secondary intercooler 4 is arranged in parallel at the main intercooler 3. The main intercooler 3, the secondary intercooler 4 and the membrane humidifier 7 are connected through the three-way valve 5, a first inlet 11 of the three-way valve is connected to the main intercooler 3, a second inlet 12 of the three-way valve is connected to the secondary intercooler 4, and an outlet 13 of the three-way valve is connected to the membrane humidifier 7.

[0037] The membrane humidifier 7 is provided with a dry side and a wet side, with a membrane in the middle. The dry side includes a dry side inlet and a dry side outlet, and the wet side includes a wet side inlet and a wet side outlet. The dry side inlet is connected to the three-way valve outlet 13, the dry side outlet is connected to the air inlet of the stack, and the wet side inlet is connected to the air outlet of the stack. A throttle 10 is provided at the wet side outlet. The air humidified by the humidifier flows out from the dry side outlet and enters the stack to participate in the reaction.

[0038] The membrane humidifier selected in this embodiment has been calculated. When the moisture transfer of the humidifier reaches the maximum value, the dry side inlet temperature is about 43°C.

[0039] A temperature sensor 6 is provided at the dry side inlet for measuring the temperature of the air at the dry side inlet, and a humidity sensor 8 is provided at the dry side outlet for measuring the humidity of the air at the dry side outlet.

[0040] In actual operation, the air passes through the air filter and air compressor and enters the main intercooler and the auxiliary intercooler. Due to the different cooling capacities of the main intercooler and the auxiliary intercooler, the temperature of the air entering the humidifier can be controlled by adjusting the opening W of the first inlet and the second inlet of the three-way valve. The air entering the humidifier enters the fuel cell stack from the dry side outlet after humidification to participate in the reaction.

[0041] Embodiment 2

[0042] Combination Figure 2 As shown, the present invention discloses a method for controlling the humidity of air entering the stack. The method is performed in the air system of the fuel cell disclosed in the first embodiment. The specific operation steps are as follows:

[0043] S1: Start the air system and let air in;

[0044] S2: Read the values ​​of the temperature sensor and humidity sensor to determine whether the air temperature at the dry side inlet reaches 43°C;

[0045] S3: When the air temperature at the dry side inlet is lower than 43°C, adjust the opening of the three-way valve W according to the air temperature at the dry side inlet to increase it to the desired temperature and then adjust the humidity of the air entering the pile, W = K p *ΔT+K i *∫ΔT,Kp is the P factor, K i is the I factor, K p , K i Confirmed by bench calibration, ΔT is the difference between the actual dry side inlet air temperature and the expected temperature;

[0046] When the air temperature at the dry side inlet is greater than 43°C, adjust the opening W of the three-way valve according to the air humidity value at the dry side outlet, W = k p *ΔR+K i *∫ΔR, ΔR is the difference between the actual air humidity entering the pile and the expected humidity;

[0047] S4: Read the temperature sensor value at this time to determine whether the air temperature at the dry side inlet is lower than 45°C;

[0048] S5: If the air temperature at the dry side inlet is not lower than 45°C, proceed to step S3 to adjust the opening W of the three-way valve according to the air inlet humidity until the desired humidity is reached;

[0049] If the air temperature at the dry side inlet is lower than 45°C, determine whether the air inlet humidity is greater than the expected humidity;

[0050] S6: When the air temperature at the dry side inlet is lower than 45°C and the air inlet humidity is greater than the desired humidity, proceed to step S3 to adjust the opening W of the three-way valve according to the air inlet humidity until the desired humidity is reached;

[0051] When the air temperature at the dry side inlet is lower than 45° C. and the air inlet humidity is lower than the desired humidity, the process proceeds to step S3 to adjust the opening W of the three-way valve according to the air temperature at the dry side inlet until the desired humidity is reached.

[0052] Since the desired temperature of the air at the dry side inlet is the air temperature corresponding to the maximum water transfer of the membrane humidifier,

[0053] For membrane humidifiers, the water transfer is expressed by Fick's law: Where M v is the molar mass of water; A is the membrane area; c1 and c2 are the water concentrations in the wet and dry boundary membranes, respectively; δ m is the thickness of the film; D w is the diffusion coefficient of water, which is related to the water content and temperature of the membrane. Under ideal conditions, the wet side temperature is set to 353K and the water transfer amount m is observed. v,mem As the dry side inlet temperature T 2,inThe change trend of the dry side inlet temperature shows that the water transfer of the membrane humidifier selected in this embodiment increases first and then decreases with the increase of the dry side inlet temperature. It is calculated that the water transfer reaches the maximum value when the dry side inlet temperature is about 43°C. Therefore, when adjusting the air inlet humidity, the air temperature at the dry side inlet can be set to 43 degrees Celsius, and the water transfer of the membrane humidifier is the maximum when the humidification effect is the best.

[0054] Therefore, in a method for controlling the humidity of air entering the stack disclosed in the present invention, the opening of the three-way valve is adjusted corresponding to the numerical value of the air temperature at the dry side inlet, and the three-way valve is adjusted according to the air temperature difference or the air humidity difference in real time according to the air temperature at the dry side inlet. The humidity of the air entering the stack can be accurately and quickly controlled to ensure that the performance of the fuel cell will not be damaged.

[0055] The above descriptions are merely embodiments of the present invention and are not intended to limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made using the contents of the present invention specification and drawings, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A fuel cell air system connected to a fuel cell stack, characterized in that: It includes an air filter, an air compressor, a main intercooler, and a humidifier which are connected in sequence. The humidifier is connected to the battery stack. A secondary intercooler is arranged in parallel with the main intercooler. A three-way valve is arranged between the main intercooler, the secondary intercooler and the humidifier. The first inlet of the three-way valve is connected to the main intercooler, the second inlet of the three-way valve is connected to the secondary intercooler, and the outlet of the three-way valve is connected to the humidifier.

2. The air system of a fuel cell according to claim 1, characterized in that: The inlet of the main intercooler is connected to the air compressor, and the cooling pipeline of the main intercooler is long. The inlet of the auxiliary intercooler is connected to the air compressor, and the cooling pipeline of the auxiliary intercooler is short.

3. The air system of a fuel cell according to claim 2, characterized in that: The humidifier is configured as a membrane humidifier, provided with a dry side and a wet side, the dry side including a dry side inlet and a dry side outlet, the wet side including a wet side inlet and a wet side outlet, the dry side inlet is connected to the outlet of a three-way valve, the dry side outlet is connected to the air inlet of the fuel cell stack, the wet side inlet is connected to the air outlet of the fuel cell stack, and a throttle is provided at the wet side outlet.

4. The air system of a fuel cell according to claim 3, characterized in that: A temperature sensor is provided at the dry side inlet of the humidifier, and a humidity sensor is provided at the dry side outlet of the humidifier. After being humidified by the humidifier, the air enters the fuel cell stack from the dry side outlet and its humidity is measured.

5. A method for controlling the humidity of air entering a pile, characterized in that: The control method is performed in an air system of a fuel cell according to claim 4, and the specific steps are: S1: Start the air system and let air in; S2: Read the values ​​of the temperature sensor and the humidity sensor to determine whether the air temperature at the dry side inlet reaches the expected temperature; S3: When the air temperature at the dry side inlet is lower than the desired temperature, the opening W of the three-way valve is adjusted according to the air temperature at the dry side inlet to increase it to the desired temperature and then the humidity of the air entering the pile is adjusted; when the air temperature at the dry side inlet is higher than the desired temperature, the opening W of the three-way valve is adjusted according to the humidity value of the air entering the pile at the dry side outlet; S4: Read the temperature sensor value at this time to determine whether the air temperature at the dry side inlet is lower than a specific temperature; S5: If the air temperature at the dry side inlet is not lower than the specific temperature, enter step S3 to adjust the opening W of the three-way valve according to the air inlet humidity until the desired humidity is reached; If the air temperature at the dry side inlet is lower than a specific temperature, determine whether the air inlet humidity is greater than the expected humidity; S6: When the air temperature at the dry side inlet is lower than a specific temperature and the air inlet humidity is greater than the desired humidity, proceed to step S3 to adjust the opening W of the three-way valve according to the air inlet humidity until the desired humidity is reached; When the air temperature at the dry side inlet is lower than a specific temperature and the air inlet humidity is lower than the desired humidity, the process proceeds to step S3 to adjust the opening W of the three-way valve according to the air temperature at the dry side inlet until the desired humidity is reached.

6. A method for controlling humidity of air entering a pile according to claim 5, characterized in that: The specific calculation of the opening W of the three-way valve adjusted according to the humidity of the air entering the pile is: W = K p *ΔR+K i *∫ΔR, The K p is the P factor, the K i is the I factor, the K p , K i It is confirmed by bench calibration, and ΔR is the difference between the actual air inlet humidity and the expected humidity.

7. A method for controlling humidity of air entering a pile according to claim 6, characterized in that: The specific calculation formula for adjusting the opening W of the three-way valve according to the air temperature at the dry side inlet is: W = K p *ΔT+K i *∫ΔT, where ΔT is the difference between the actual dry side inlet air temperature and the expected temperature.

8. A method for controlling humidity of air entering a pile according to any one of claims 5 to 7, characterized in that: The desired temperature of the air at the dry side inlet is the air temperature corresponding to when the moisture transfer amount of the membrane humidifier reaches a maximum value.

9. A method for controlling humidity of air entering a pile according to claim 8, characterized in that: The desired temperature of the air at the dry side inlet is 43°C, and the specific temperature of the air at the dry side inlet is 45°C.

Images